Implementation of single phase watt hour meter using LPC2148 Parmanand Nayak

Implementation of single phase watt hour meter using LPC2148 Parmanand Nayak
Implementation of single phase
watt hour meter using LPC2148
Parmanand Nayak
Department of Electronics and Communication Engineering
National Institute of Technology Rourkela
Rourkela – 769 008, India
Implementation of single phase
watt hour meter using LPC2148
Dissertation submitted in
May 2013
to the department of
Electronics and Communication Engineering
of
National Institute of Technology Rourkela
in partial fulfillment of the requirements
for the degree of
Master of Technology
by
Parmanand Nayak
(Roll 211EC3316)
under the supervision of
Prof. KamalaKanta Mahapatra
Department of Electronics and Communication Engineering
National Institute of Technology Rourkela
Rourkela – 769 008, India
Electronics and Communication Engineering
National Institute of Technology Rourkela
Rourkela-769 008, India.
www.nitrkl.ac.in
Prof. KamalaKanta Mahapatra
Professor
May 30, 2013
Certificate
This is to certify that the work in the thesis entitled Implementation of single
phase watt hour meter using LPC2148 by Parmanand Nayak, bearing roll number
211EC3316, is a record of an original research work carried out by him under my
supervision and guidance in partial fulfillment of the requirements for the award of
the degree of Master of Technology in Electronics and Communication Engineering.
Neither this thesis nor any part of it has been submitted for any degree or academic
award elsewhere.
Prof. Kamala Kanta Mahapatra
Acknowledgment
This dissertation, though an individual work, has benefited in various ways from
several people. Whilst it would be simple to name them all, it would not be easy
to thank them enough.
The enthusiastic guidance and support of Prof.
KamalaKanta Mahapatra
inspired me to stretch beyond my limits. His profound insight has guided my
thinking to improve the final product. My solemnest gratefulness to him.
My sincere thanks to Prof. Ayas Kanta Swain for their continuous encouragement
and invaluable advice.
Many thanks to my comrades and fellow research colleagues.
It gives me a
sense of happiness to be with you all.
Finally, my heartfelt thanks to my family for their unconditional love and
support.
Words fail me to express my gratitude to my beloved parents, who
sacrificed their comfort for my betterment.
Parmanand Nayak
Abstract
The LP C2148 device is the latest system-on-chip (SOC), which belongs to the
ARM generation of devices. This generation of devices belongs to the powerful
32-bit ARM platform bringing in a lot of new features and flexibility to support
robust single, two and 3-phase metrology solutions. This thesis however, discusses
the implementation of 1-phase solution only. These devices find their application in
energy calculation and have the necessary architecture to support them.
Furthermore, for large scale manufacturing, the costs can become lower than
those of the electromechanical meters currently in production. This device presents
a totally electronic single phase energy meter for residential use, based on ARM
processor. A four digit display is used to show the consumed power. A prototype
has been implemented to adequate measurement up to 5A load current from a 230V
(phase to neutral) voltage. Higher current capacity can be easily obtained by simply
replacing the shunt resistor. And, by changing the transformer tap and the voltage
divider ratio, it can be easily manipulated for use in a 220 V supply.
The LPC2148 has a powerful 60 MHz CPU with ARM architecture. The
analog front end consists of up to two channel of 10-bit analog-to-digital converters
(ADC) based on a successive approximation architecture that supports differential
inputs, with conversion time 2.44 micro second per channel. The ADCs operate
independently and are capable to output 10-bit result. They can be grouped together
for simultaneous sampling of voltage and currents on the same trigger. A 32-bit
x 32-bit hardware on this chip can be used to further accelerate math intensive
operations during energy calculation. The software supports calculation of various
parameters for single phase energy calculation. The key parameters measured during
energy measurements are: RMS current and voltage, energies. Alternatively, the
design is ease to fits more computerized applications with features such as remote
reading , demand recording, multiple tariffs, checking, and other.
Keywords: LPC2148 processor, step down transformer, Variable load,current
transducer, operational amplifier, 16X2 LCD.
Contents
Certificate
ii
Acknowledgement
iii
Abstract
iv
List of Figures
viii
List of Tables
x
1 Introduction
1
1.1
Objective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2
1.2
Scope of Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2
1.3
Purpose and Description of Project . . . . . . . . . . . . . . . . . . .
2
1.4
Literature Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
1.5
Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5
2 MEASUREMENT OF ENERGY RELATED QUANTITIES
2.1
6
General Theory and Principles . . . . . . . . . . . . . . . . . . . . . .
6
2.1.1
Real Power . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6
2.1.2
Apparent Power . . . . . . . . . . . . . . . . . . . . . . . . . .
7
2.1.3
Power Factor . . . . . . . . . . . . . . . . . . . . . . . . . . .
7
2.1.4
Reactive Power . . . . . . . . . . . . . . . . . . . . . . . . . .
8
2.1.5
Power and Impedance triangle . . . . . . . . . . . . . . . . . . 14
v
2.2
Operational Considerations
. . . . . . . . . . . . . . . . . . . . . . . 14
2.2.1
Current Sensing . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.2.2
Hall Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.2.3
Hall Effect Sensor . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.2.4
Current Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.2.5
Voltage Sensing . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.2.6
Voltage Division . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.2.7
Voltage Transformer . . . . . . . . . . . . . . . . . . . . . . . 20
2.2.8
Voltage Inputs
2.2.9
Data Analysis and Display . . . . . . . . . . . . . . . . . . . . 22
. . . . . . . . . . . . . . . . . . . . . . . . . . 21
3 DESIGN OF MEASUREMENT SYSTEM AND DATA DISPLAY 24
3.1
General Design Procedure . . . . . . . . . . . . . . . . . . . . . . . . 24
3.2
Hardware Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.3
3.2.1
ARM processor (LPC2148) . . . . . . . . . . . . . . . . . . . . 26
3.2.2
Hall Effect Sensor . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.2.3
TL081 Op Amp . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.2.4
LCD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Software Development . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.3.1
Peripherals Set Up . . . . . . . . . . . . . . . . . . . . . . . . 33
3.3.2
The Foreground Process . . . . . . . . . . . . . . . . . . . . . 35
3.3.3
The Formulae . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.3.4
The Background Process . . . . . . . . . . . . . . . . . . . . . 38
4 EXPERIMENTAL RESULTS
40
4.1
Testing Voltage and Current sensing Circuit . . . . . . . . . . . . . . 40
4.2
Testing for samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
4.3
Tests for sag of signal . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.4
Tests on Current measurement . . . . . . . . . . . . . . . . . . . . . . 43
4.5
Tests on Voltage measurement . . . . . . . . . . . . . . . . . . . . . . 44
vi
4.6
Tests on Consumed Energy measurement . . . . . . . . . . . . . . . . 45
5 Conclusion
47
Bibliography
49
vii
List of Figures
2.1
The instantaneous power p(t) entering a circuit. . . . . . . . . . . . .
7
2.2
Real power dissipated in Resistive circuit . . . . . . . . . . . . . . . .
9
2.3
Inductive circuit and Reactive Power . . . . . . . . . . . . . . . . . . 10
2.4
Capacitive circuit and Reactive Power
2.5
Single phase active and reactive power . . . . . . . . . . . . . . . . . 13
2.6
Power Triangle, Impedance Triangle. . . . . . . . . . . . . . . . . . . 14
2.7
Power triangle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.8
Typical Connections Inside Electronic Meters . . . . . . . . . . . . . 16
2.9
General Sensor depend on the Hall Effect
. . . . . . . . . . . . . . . . . 12
. . . . . . . . . . . . . . . 18
2.10 Analog Front End for Current Inputs . . . . . . . . . . . . . . . . . . 18
2.11 Current sensing hardware circuit
. . . . . . . . . . . . . . . . . . . . 19
2.12 Voltage Division Circuit . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.13 Ideal transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.14 Analog Front End for Voltage Inputs . . . . . . . . . . . . . . . . . . 21
2.15 Voltage sensing hardware circuit. . . . . . . . . . . . . . . . . . . . . 22
2.16 Input and output waveform . . . . . . . . . . . . . . . . . . . . . . . 22
3.1
1-Phase 2-Wire Star Connection detailed Block Diagram . . . . . . . 25
3.2
Photo of realized digital energy meter . . . . . . . . . . . . . . . . . . 26
3.3
Pinout LPC2148 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.4
LA 55P Current Transducer . . . . . . . . . . . . . . . . . . . . . . . 30
3.5
Connection Diagram of TL081 . . . . . . . . . . . . . . . . . . . . . . 31
3.6
16x2 LCD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
viii
4.1
Input Current signal and Output Current Signal with offset
4.2
Input Voltage signal and Output Voltage Signal with offset . . . . . . 41
4.3
Input Voltage signal and Output Voltage sampled Signal. . . . . . . . 42
4.4
Measurement setup for testing the sag and swell . . . . . . . . . . . . 42
4.5
Measured RMS voltage before and after saging the voltage signal . . 43
4.6
Voltage wave form along with sag . . . . . . . . . . . . . . . . . . . . 43
ix
. . . . . 41
List of Tables
3.1
LCD command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
4.1
Result of Current measurement in the laboratory with standard
multimeter meter & prototype energy meter . . . . . . . . . . . . . . 44
4.2
Result of Voltage measurement in the laboratory with standard
multimeter meter & prototype energy meter . . . . . . . . . . . . . . 45
4.3
Result of Energy measurement in the laboratory with standard
calculation & prototype energy meter . . . . . . . . . . . . . . . . . . 46
x
Chapter 1
Introduction
This application note describes a single-phase power/energy meter. The design
measures active power/energy, potential, and current in a single-phase distribution
environment. The heart of the meter is an ARM processor. All measurements are
took in the digital domain and measurement results are available in LCD.
Power meters are sometimes mention to as energy meters and vise versa.
According to terminology, (active) power is a measure of what is required (or
consumed) in order to perform particular useful work. For example, a bulb with
a 100W rating consumes 100 watts of real power in order to create light (and heat).
Energy, per definition, is the measure of how much work has been required over a
known period of time. In the light bulb example, enlighten the bulb on for an hour
it will consume 100W × 3600s = 360000Ws (watt seconds) = 100Wh (watt hours) =
0.1kWh (kilowatt hours) of energy. The energy meter described in this application
note can be referred to as a energy meter or a watt-hour meter.All measurement
results can be calibrated in the digital domain, eliminate the need for any trimming
components. The calibration event can be self alter, and eliminate the time-spending
manual trimming required in traditional type electromechanical energy meters. The
Digital calibration is fast and efficient, minimize the overall calculation time and
cost. The brain of the meter is the software firmware code, which is provided open
source. In spite of it includes all the functionality required for a single-phase meter,
1
Introduction
Chapter 1
it can be alter and updated at any time,even in the working mode. The software
code is entirely written in C, which makes alteration easy.
1.1
Objective
The main aim of this intended project is to implement and construct a digital energy
meter for domestic appliances. This energy meter will measure the electrical energy
digitally, so user can easily identify how much energy they used at one time.
1.2
Scope of Project
Since the energy meter can calculate or determine the energy consumption of
household appliances, the data can be used for the following studies:
• Calculate the average electrical energy consumption of selected appliances used
in residential sector.
• Examine of the impact of energy efficiency labelling of domestic appliance.
• Forecast of future energy desire in residential sector based on end-use modelling
techniques.
• Implementation of special website/programmers that can teach and promote
efficient and wise use of energy.
1.3
Purpose and Description of Project
The LP C2148 device is the latest system-on-chip (SOC), which belongs to the
ARM generation of devices. This generation of devices belongs to the powerful
32-bit ARM platform bringing in a lot of new features and flexibility to support
robust single, two and 3-phase metrology solutions. This thesis however, discusses
2
Introduction
Chapter 1
the implementation of 1-phase solution only. These devices find their application in
energy calculation and have the necessary architecture to support them.
Furthermore, for large scale manufacturing, the costs can become lower than
those of the electromechanical meters currently in production. This device presents
a totally electronic single phase energy meter for residential use, based on ARM
processor. A four digit display is used to show the consumed power. A prototype
has been implemented to adequate measurement up to 5A load current from a 230V
(phase to neutral) voltage. Higher current capacity can be easily obtained by simply
replacing the shunt resistor. And, by changing the transformer tap & voltage divider
ratio, and it can be easily manipulated for use in a 220 V supply.
The LPC2148 has a powerful 60 MHz CPU with ARM architecture.
The
analog front end consists of up to two channel of 10-bit analog-to-digital converters
(ADC) based on a successive approximation architecture that supports differential
inputs, with conversion time 2.44 micro second per channel. The ADCs operate
independently and are capable to output 10-bit result. They can be grouped together
for simultaneous sampling of voltage and currents on the same trigger. A 32-bit
x 32-bit hardware on this chip can be used to further accelerate math intensive
operations during energy calculation. The software supports calculation of various
parameters for single phase energy calculation. The key parameters measured during
energy measurements are: RMS current and voltage, energies. Alternatively, the
design is ease to fits more computerized applications with features such as remote
reading , demand recording, multiple tariffs, checking, and other.
1.4
Literature Review
In [1], the development of an Energy Meter (EM) this paper help to visualize the
setup .It presents a single phase electrical energymeter based on a microcontroller
from Microchip TechnologyInc.
PIC family.This paper has demonstrated the
possibility of calculating the electrical energy consumption with a microcontroller
3
Introduction
Chapter 1
based electronic meter, as an alternative to the conventional electromechanical
meters.
The developed platform consists of two notable components to measure different
kinds of the power consumption, voltage and current [2]. The power quantities are
sensed and transformed in low level signals using the step down transformer and
current transducer.
Voltage and current sensing circuit uses TL-081 [3] op-amp and LA-55P [4]
component to make both the voltage and current signal measurable.
The TL-081 JFET-input operational amplifier family is designed to offer a wider
selection than any previously developed operational amplifier family.This devices
feature high slew rates, ,low input offset-voltage temperature coefficient and low
input bias and offset input currents.
The Current Transducer LA-55P is used for the electronic measurement of
currents: DC, AC, pulsed, with galvanic isolation between the primary circuit (high
power) and the secondary circuit (electronic circuit).
In [5], an AC Meter development for AC Energy Monitors is described which has
four main sections: signal filtering,Energy Metering and processing, power supply.
In [6] an electronic system is described to measure the real, imaginary and
apparent energies delivered to a load of an AC circuits. The proposed system is
directly connected to a Personal Computer for monitoring the power consumption.
In [7], Explained the design and implementation of Energy Meter, and the
interface between a processor,sensing circuitand display can be categorized into
two main distinctive portions. The first portion consists of the interface between
processor and current/voltage sensing circuit . The second portion comprises the
interface between the 16 x 2LCD and the processor;the interfaces in the first portion
and second portion are both using the standard cables.
4
Introduction
Chapter 1
1.5
Contributions
In most of the reviewed related literatures for sensing the voltage and current signal,
Energy Meter Sensors are employing. Accordingly in order to control the measured
data, calculating and then display, aprocessor should be operated. Data transmission
will be possible through a specific device with unique properties.
In this thesis, all related calculation and transmission of the measured data via
ADC port to a serial adaptor is done with only ARM Processor.
The objective of this intended project is to implement a digital Energy Meter
using ARM processor(LPC2148), measure rms voltage, rms current, consumed
energy and display to LCD. LPC2148 is the processor used in this thesis which
can measured data through ADC.
The desired Energy Meter (EM) is successfully implemented based on ARM
processor(LPC2148).
5
Chapter 2
MEASUREMENT OF ENERGY
RELATED QUANTITIES
2.1
2.1.1
General Theory and Principles
Real Power
For time varying voltages and currents, the power transfer to a load is also time
varying. This time varying power is referred to as instantaneous consumed power.
The real power is the average value of the instantaneous consumed power.The Mean
Power rely on the rms value of load voltage and load current and the phase angle
between them
1
P = Vm Im cos (θv − θi ) = Vrms Irms cos (θv − θi )
2
(2.1)
The real power (P), in watts, dissipated in an AC R-L, R-C, R-L-C circuit is
dissipated in the resistance onlyfor AC sinusoidal current and voltage,
P = I 2R
6
(2.2)
MEASUREMENT OF ENERGY RELATED QUANTITIES
Chapter 2
Figure 2.1: The instantaneous power p(t) entering a circuit.
2.1.2
Apparent Power
Apparent power is the combination of reactive power and true power, and it is the
multiplication of a circuit’s voltage and current, without regards to phase angle.
Apparent power is calculated in the unit of Volt-Amps (VA) and is symbolized by
the capital letter S.
The Apparent Power (S), in volt amperes (VA), is the product of the rms value
of voltage and current.
1
S = Vm Im = Vrms Irms
2
2.1.3
(2.3)
Power Factor
The Power Factor (pf) is the cosine of the phase difference between voltage and
current. Power factor can also be found by dividing real power (P) by apparent
power (S); so we have:
P.F =
P
= cos(θv − θi )
S
P = ApparentP ower × P owerF actor = S × P.F
7
(2.4)
(2.5)
Chapter 2
2.1.4
MEASUREMENT OF ENERGY RELATED QUANTITIES
Reactive Power
Explanation for reactive power says that, In an Alternative Current circuit voltage
and current go rise and fall at the same period, only Active power is transmitted
in circuit and when there is a time shift between voltage and current both active
and reactive power are transmitted. But, when calculated the average in time, the
average real power be found causing a net flow of energy from one section to another
section, whereas average reactive power is null, regardless of the network or state
of the system. In the instance of reactive power(imaginary power), the amount of
energy passing in one direction is been equal to the amount of energy passing in
the opposite direction (or different parts -capacitors, inductors, etc- of a network,
exchange the reactive power). It producing a result that reactive power is neither
produced nor consumed.
But, in reality we calculated reactive power losses, introduce so many equipment’s
for imaginary power compensation to reduce electricity consumption and cost.
The Reactive Power (Q), in volt amperes reactive (VAR), is the power which
toggle between the supply and the reactance of the load and can be calculated from
following equation;
Q = Vrms Irms sin(θv − θi )
(2.6)
It show that the Reactive Power is imaginary part of the Complex Power S.
S = P + j Q = Re {S} + j Im {S}
(2.7)
2
2
S = Irms
Z = Irms
(R + j X) = P + j Q
(2.8)
2
P = Vrms Irms cos(θv − θi ) = Re {S} = Irms
R
(2.9)
2
Q = Vrms Irms sin(θv − θi ) = Im {S} = Irms
X
(2.10)
where
8
Chapter 2
MEASUREMENT OF ENERGY RELATED QUANTITIES
Figure 2.2: Real power dissipated in Resistive circuit
Therefore the equations below can be written as:
V (t) = Vm sin(wt − θ)
(2.11)
I(t) = Im sin(wt)
(2.12)
The instantaneous power is given by
P (t) = Vm Im sin(wt) sin(wt − θ) =
1
× Vm Im × 2 × sin(wt) sin(wt − θ)
2
1
P (t) = Vm Im [{cos(wt) − cos(wt − θ) + sin(wt) − sin(wt − θ)}
2
(2.13)
(2.14)
− {cos(wt) − cos(wt − θ) − sin(wt) − sin(wt − θ)}]
1
P (t) = Vm Im [cos {wt − (wt − θ)} − cos {wt + (wt − θ)}]
2
1
P (t) = Vm Im [cos θ − cos(2wt − θ)]
2
pR (t) = V (t) × I(t) = Vrms Irms cos(2wt)
9
(2.15)
(2.16)
(2.17)
MEASUREMENT OF ENERGY RELATED QUANTITIES
Chapter 2
Since the phase angle between resistive current and voltage is null, the circuit has
neither a lagging nor a leading power factor; therefore the load is Resistive and draws
only active power.
From the above equation 2.17 it is clear that whatever may be the value of cos2wt
can not be greater than one hence the value of P can not be negative value. The
value of P is always positive regardless of the instantaneous direction of voltage v
and current i, that define the energy is flowing in its conventional direction it means
from source to load and P is given the rate of energy consumption by the load and
this is called active power. As this power is absorbed due to resistive effect of an
electrical circuit hence it is also called resistive power.
For a purely inductive circuit, v leads i by 900 as shown in Figure
θ = 900(inductive)
Figure 2.3: Inductive circuit and Reactive Power
The power absorbed or deliver by the inductor can be found as below:
1
PL (t) = Vm Im [cos θ − cos(2wt − θ)]
2
10
(2.18)
Chapter 2
MEASUREMENT OF ENERGY RELATED QUANTITIES
Put θ = + 90o (inductive)
1
PL (t) = Vm Im [0 − cos(2wt − 90o)]
2
1
PL (t) = Vm Im sin(2wt)
2
PL (t) = Vrms Irms sin(2wt)
(2.19)
(2.20)
(2.21)
The net flow of power to the pure (ideal) inductor is zero over a full cycle, and
no energy loss is observed in the transaction.
In the above expression, it is found that the power is flowing in alternative
directions. From 0o to 90o it will have positive half cycle, from 90o to 180o it
will have negative half cycle, from 180o to 270o it will have again positive half
cycle and from 270o to 360o , it will have again negative half cycle. Therefore this
power is alternating in nature with a frequency, twice of supply frequency. As the
power is flowing in alternating direction i.e.from load to source in one half cycle and
from source to load in next half cycle the average value of this power is vanished.
Therefore this power does not do any efficient work. This power is known as reactive
power. As the above illustrate reactive power expression is related to fully inductive
circuit, this reactive power is also called inductive power.
For a purely capacitive circuit, i leads v by 90o as illustrated in figure.
θ = −900 (capacitive)
The power absorbed or delivered by the capaciter can be found as below:
1
PC (t) = Vm Im [cos θ − cos(2wt − θ)]
2
Putθ = −900
11
(2.22)
Chapter 2
MEASUREMENT OF ENERGY RELATED QUANTITIES
Figure 2.4: Capacitive circuit and Reactive Power
1
PC (t) = Vm Im [0 − cos(2wt − 90o )]
2
1
PC (t) = − Vm Im sin(2wt)
2
PC (t) = −Vrms Irms sin(2wt)
(2.23)
(2.24)
(2.25)
Resemble to the previous case, it is apparent that the net flow of power to the
pure(ideal) capacitor is zero over a total cycle, and null energy loss is observed in
the transaction as well.
Hence in the expression of capacitive power, it is also indicate that the power
is flowing in alternative directions. From 0o to 90o it will have negative half cycle,
from 90o to 180o it will have positive half cycle, from 180o to 270o it will have again
negative half cycle and from 270o to 360o it will have again positive half cycle. So
this capacitive power is also alternating in nature with a frequency, twice of supply
frequency. Therefore, as inductive power and the capacitive power does not do
any efficient work. This power is also a reactive power.
The consumed power equation can be re-written as:
1
P (t) = Vm Im [cos θ − cos(2wt − θ)]
2
1
P (t) = Vm Im [cos θ − cos 2wt cos θ − sin 2wt sin θ]
2
12
(2.26)
(2.27)
MEASUREMENT OF ENERGY RELATED QUANTITIES
Chapter 2
This above expression has two part of consonant; first one is
1
V I
2 m m
cos θ(1 −
cos 2wt) which never goes negative as because value of (1 − cos 2wt) always greater
or equal to zero but can not equal to negative value.
This portion of the single phase consumed power equation represents the
expression of reactive power which is also known as true power or real power.
The mean of this power will recognize have some non zero value means the power
physically does some efficient work and that is why this power is also called real
power or sometimes it is denoted as true power.
Figure 2.5: Single phase active and reactive power
Second term is
1
2
sin θ sin 2wt which will have negative and positive cycles.
Hence average of this component is vanished. This consonant is known as reactive
component as it travels forth and back on the line without doing any efficient work.
13
Chapter 2
MEASUREMENT OF ENERGY RELATED QUANTITIES
Both active power and reactive power have equalamount of watts but to
emphasize the fact that reactive component represents a non-active power,and it is
calculated in terms of volt-amperes reactive or in short VAR.
2.1.5
Power and Impedance triangle
It is possible to show the relation between S, P and Q in the form of a triangle,and
known as the power triangle as shown in Figure (a). A similar relation between Z,X
and R can be given by the Impedance triangle as shown in Figure (b).
Figure 2.6: Power Triangle, Impedance Triangle.
If S exist in the first quadrant; the reactive power is positive; which means that
the circuit has a lagging power factor and the load is inductive, and if S is in the
fourth quadrant the power is reactive; which means that the load is capacitive and
the circuit has a leading power factor , as illustrated in Figure.
2.2
Operational Considerations
As per the general theory and principles of the Power calculation; voltage and current
is the capital part of the operation therefore measurement of the current and voltage
is the prime requirement.
14
Chapter 2
MEASUREMENT OF ENERGY RELATED QUANTITIES
Figure 2.7: Power triangle
After calculating the values of the current and voltage; calculation of the all other
energy related quantities is possible.
LPC2148, with two analog to digital (A/D) inputs, which is used for computing
the current and voltage values; is preferred due to the ease in programming and the
convenience of display data.
The general block diagram of Typical Connections inside Electronic Meters is
illustrated in Figure 2.8.
In general, all the sensors used for energy meter; work based on two types of signal
processing, namely analog and digital. This signal processing uses multiplication and
averaging for the finding of the information required by an energy meter.
In preceding portions in this chapter all the methods used in this thesis are
explained and in chapter 3 all used components regarding described methods are
clarified.
This section explain various part that constitute the hardware for the design of
a working 1-phase energy meter using the LPC2148. The LPC2148 analog front end
that consists of the ADC is differential and requires that the input voltages at the
pins do not exceed 3.3 volt . In order to meet this requirement, the current and
15
Chapter 2
MEASUREMENT OF ENERGY RELATED QUANTITIES
Figure 2.8: Typical Connections Inside Electronic Meters
voltage inputs need to be step up and step down respectively. And addition, the
ADC not allows a negative voltage , therefore, AC signals from mains can not be
directly interfaced and need level shifters. This subsection describes the analog front
end used for current and voltage channels.
2.2.1
Current Sensing
Current Sensing however [1][16], poses much more difficult problems due to the
rich harmonic content in the current waveform. Current transducer sensor not only
requires a much wider measurement dynamic range, but also necessary to handling
of a much wider frequency range.
Considering merits and demerits, selection of which type of methods to be used
for sensing the current is challenging, so the chosen appropriate possible solution is
to employ the Hall Effect Sensor.
16
Chapter 2
2.2.2
MEASUREMENT OF ENERGY RELATED QUANTITIES
Hall Effect
Hall Effect is a phenomenon through which a conductor carrying an electric
current(I) perpendicular to an applied magnetic field(B) develops a voltage gradient
which make 90 angles to both the current and the magnetic field.
2.2.3
Hall Effect Sensor
The Hall Effect [2] is an ideal sensing technology; in terms of measurement especially
at high frequency. The Hall element is build from a thin sheet of conductive material
along with output connections perpendicular to the direction of current flow in
conductive material. When influence to a magnetic field, it generate an output
voltage proportional to the magnetic field strength applied. The voltage output is
minor (µV) and needs additional electronics to achieve useful voltage levels to do
proper calculation. When the Hall element is merge with the associated electronics,
it create a Hall Effect sensor.
General Sensor depend on the Hall Effect is shown in the Figure 2.9.
2.2.4
Current Inputs
Figure 2.10 shows the analog front end for the current inputs, which is flow through
load. The current through load is measure by current transducer LA 55P. The
current transducer is connected in series with load, it wounded with same wire which
is connected to series. The transducer senses the current which is flow through the
wounded wire and generates the current which is flow through the resistance R. And
we are getting the voltage corresponding to the current which is flow through load.
The sensing voltage is low in amplitude and difficult to measure then it is passes
through amplifier. The amplification factor is depend upon values of R1 and R2,
and step up the voltage below 1 volt peak to peak. Output consist both positive
and negative cycle but processor ADC respond or measure only positive values, it
require level shifter to add a DC offset and pass to precision rectifier, It prevents
17
Chapter 2
MEASUREMENT OF ENERGY RELATED QUANTITIES
Figure 2.9: General Sensor depend on the Hall Effect
Figure 2.10: Analog Front End for Current Inputs
18
MEASUREMENT OF ENERGY RELATED QUANTITIES
Chapter 2
any excursion of negative voltage.
Figure 2.11: Current sensing hardware circuit
2.2.5
Voltage Sensing
Voltage sensing [2][16] is usually obtained by using either the voltage division method
or a step down voltage transformer. Decision making about which method should
be used, is related to the work necessities. Above two mentioned approaches are
used in this project.
2.2.6
Voltage Division
Voltage Division is the most prefer way to divide down the line voltage based on
Ohm’s law. Relationship between input voltage Vin and Output voltage Vout is as
below.
Vout = Vin ×
19
R1
R1 + R2
(2.28)
Chapter 2
MEASUREMENT OF ENERGY RELATED QUANTITIES
Figure 2.12: Voltage Division Circuit
2.2.7
Voltage Transformer
Voltage transformer are used to step down is an electromagnetic device which
consists of two or more coils wound on a magnetic core and changes the voltage
level in a circuit, under fixed frequency.
Consider an ideal transformer as shown in Figure 2.13.
Figure 2.13: Ideal transformer
The ratio of secondary and primary voltage can be obtained from equation as:
V1
N1
I2
=
=
V2
N2
I1
20
(2.29)
Chapter 2
MEASUREMENT OF ENERGY RELATED QUANTITIES
As it is mentioned, ARM processor [LPC2148] is the device, which is been used in
this achievement and the maximum voltage can be sensed by microcontroller is 3.3
V DC.
2.2.8
Voltage Inputs
The analog front-end for voltage inputs is a little different from the analog front end
for the current inputs. The voltage from the mains is usually 230 V and needs to be
brought down to a measurable range.
Figure 2.14: Analog Front End for Voltage Inputs
Figure 2.14 shows the analog front end for the voltage inputs for a mains voltage
of 220 V. The voltage is brought down to approximately below 2.33 V RMS, which
is 3.33V peak and fed to the input, adhering to the LPC2148 analog limitation. A
common ground voltage can be connected to the GROUND input of the ADC.
In that figure 2.14, 220 volt is step down to 24 volt peak to peak through
step down transformer. The output of transformer is not measurable; to make
it measurable it passes through attenuator to step down the voltage below 1 volt
peak to peak. Output consist both positive and negative cycle but processor ADC
respond or measure only positive values, it require level shifter to add a DC offset
21
Chapter 2
MEASUREMENT OF ENERGY RELATED QUANTITIES
and pass to precision rectifier, It prevents any excursion of negative voltage.
Figure 2.15: Voltage sensing hardware circuit.
Figure shows the input and output waveform of the analog front end for voltage
inputs. Input waveform has higher amplitude as compare to output waveform and
also the output waveform has a DC offset which make all the waveform values
positive as compare to input waveform.
Figure 2.16: Input and output waveform
2.2.9
Data Analysis and Display
After voltage and current measurement procedure [3], next step is data analysis
and display. Samples are taken from ADC peripherals and passed through following
22
Chapter 2
MEASUREMENT OF ENERGY RELATED QUANTITIES
steps :
• Offset Removal
Both voltage and current sample has a offset DC value, to measure the accurate
value of rms voltage and rms current offset removal is necessary.
• Gathering samples
After eliminating offset, accumulate 1000 sample in one second and calculate
rms voltage, rms current, and consumed power on the basis of 1000 samples.
• Display
16x2 LCD display for showing the calculated data or rms voltage, current and
energy, it is necessary.
Microsoft Visual Studio C is a programming language that is designed for
building an application that run on the .NET Framework. C is simple, efficient,
type-safe, and object-oriented.
23
Chapter 3
DESIGN OF MEASUREMENT
SYSTEM AND DATA DISPLAY
3.1
General Design Procedure
As it is mentioned in 2.2.3 and 2.2.5 sections; [2][4][1] Current Transducer or Hall
Effect Sensor are the elements that can be used for current sensing whereas Resistive
Voltage Divider circuit and Voltage Transformer are utilized for voltage sensing. Two
voltages are obtained as the current and voltage signals which is used for energy
calculation.
The detailed Block Diagram of the desired digital energy meter is shown in figure
3.1 . The block diagram that shows the high-level interface used for a single-phase
energy meter application using the LPC2148. Current sensors are connected to the
current channels and a potential transformer is used for corresponding voltages. L
and N show the line and neutral voltages.
This system is designed based on an ARM processor [LPC2148] which acts as
a data acquisition processing and display system. A current and a voltage signal
are connected to its analog inputs and converted into digital form. The LPC2148
can therefore calculate the rms values of measured signals together with the energy
24
Chapter 3
DESIGN OF MEASUREMENT SYSTEM AND DATA DISPLAY
consumed at the measurement terminals.
Figure 3.1: 1-Phase 2-Wire Star Connection detailed Block Diagram
In the last stage Data display is conducted using 16x2 LCD driver. It showing
the calculated data or rms voltage, rms current and consumed energy by load.
3.2
Hardware Design
After explaining the common principles of the design procedure [4][6], the next step
is to simulate the hardware using the multisim software; since not everything can be
simulated through software, some results need to acquired by relying on experiments.
The desired Energy Meter (EM) is successfully implemented based on ARM
processor, which is shown in Figure.
The details for the main parts of Energy Meter are presented in the following
sections.
25
Chapter 3
DESIGN OF MEASUREMENT SYSTEM AND DATA DISPLAY
Figure 3.2: Photo of realized digital energy meter
3.2.1
ARM processor (LPC2148)
The ARM (Advanced RISC Machine) is a 32-bit microcontroller created by a
consortium of companies and manufactured in many different kind of versions. And
it is widely used in modems, cell phones, cameras, personal audio, pagers, and many
more embedded high end applications.
The LPC2148 is a low-power Complementary metal-oxide-semiconductor
(CMOS) 32-bit microcontroller used the enhanced RISC architecture which is used
as the main part of this project.Through executing powerful instructions in a single
clock cycle, the LPC2148 achieves throughputs approaching 17 MIPS sustained 25
MHz permit the system designer, to optimize power consumption versus processing
speed, operating Voltage range for this microcontroller is - 4.5V - 5.5V.
Generic RISC features:
26
Chapter 3
DESIGN OF MEASUREMENT SYSTEM AND DATA DISPLAY
• A huge number of general purpose registers along with the compiler technology
to optimize register usage.
• A limited and ease instruction set.
• An emphasis on modify the instruction pipeline.
• Load and store architecture with ease addressing modes.
Features of LPC2148
• 16/32-bit ARM7TDMI-S microcontroller with in a tiny LQFP64 package.
• 32 kiloByte of on-chip SRAM and 512 kiloByte of on-chip Flash program
memory. 128 bit wide interface/accelerator to enables high speed 60 MHz
operation.
• In-System/In-Application
boot-loader software.
Programming
(ISP/IAP)
through
on-chip
Single Flash sector or full chip erase with in 400
millisecond and programming of 256 bytes in 1 millisecond.
• Embedded ICE and Embedded Trace user interfaces offer real-time debugging
with the on-chip Real time Monitor software and high speed tracing of the
instruction execution.
• Two eight input channel 10-bit Analog to Digital converters provide a total of
up to 16 analog inputs channel, with conversion times as 2.44 µs per channel.
• Single 10-bit Digital to Analog converter provides variable analog output.
• Two 32-bit counters/timers (with four compare and four capture channels
each), Pulse Width Modulator unit (six outputs) and watchdog.
• Real-time clock equipped with an independent power and internal clock supply
permitting extremely low value of power consumption in power save modes.
27
Chapter 3
• Multiple
DESIGN OF MEASUREMENT SYSTEM AND DATA DISPLAY
serial
interfaces
including
two
Universal
asynchronous
receiver/transmitter (16C550), two Fast Inter-IC(I2C) (400 kbit/s), SPI
and SSP with storing and variable data length capabilities.
• Vectored interrupt controller with superable priorities and vector addresses.
• Up to 47 of 5 V tolerant general purpose input/output pins in tiny LQFP64
package.
• level sensitive external interrupt(Up to nine edge) input pins available.
• 60 MHz maximum CPU clock is available from programmable on-chip
Phase-Locked Loop (PLL) with a settling time of 100 microseconds.
• On-chip crystal oscillator with different operating range of 1 MHz to 30 MHz
or with external oscillator vary from 1 MHz to 50MHz.
• Power saving modes include both Idle and Power-down.
• Individual enable/disable of the peripheral functions as well as the peripheral
clock scaling down for procure power optimization.
• Processor wake-up from Power-down mode through external interrupt.
• Single power supply(5 volt) chip with Brown-Out Detection (BOD) and
Power-On Reset (POR) circuits:
• CPU operating voltage range varies from 3.0 V to 3.6 V (3.3 V 10 %) with 5
V tolerant Input/Output pads.
Figure3.3 is shown the Pin out of LPC2148:
As it is illustrated in Port 0.28 and Port 0.30 is merge with AD0.1 and AD0.3
respectively serves as the analog inputs to the A/D converter so Pins 13 and 15 are
used as inputs for the voltage and current values.
28
Chapter 3
DESIGN OF MEASUREMENT SYSTEM AND DATA DISPLAY
Figure 3.3: Pinout LPC2148
This ability of LPC2148 allows to use Port 0 pins as A/D converter and lets the
users read the values which are required therefore these two inputs should be in the
permissible range of at most 3.3 V for microcontroller.
29
Chapter 3
3.2.2
DESIGN OF MEASUREMENT SYSTEM AND DATA DISPLAY
Hall Effect Sensor
The Hall Effect Sensor; empoly in this project is the LA-55P [1] is the element which
senses the required current with the methods that were subjected in the previous
chapter and helps to get accurate results. The Hall Effect Sensor is also called the
Current Transducer since it converts the current into voltage which can be applied
directly to the LPC2148 analog input after amplification. LA-55P is the device
used for the electronic measurement of current: Direct current,pulsed, Alternating
Current, mixed with the galvanic isolation in between the primary circuit (high
power) and the secondary circuit (electronic circuit).
Figure 3.4: LA 55P Current Transducer
Features of this device are as below:
This Hall Effect Sensor with a galvanic isolation between primary and secondary
circuit can be empoly for measurement purposes as this sensor has isolation voltage
up to 2500V and consumes very low power. This LA 55P sensor may be used in
AC variable speed drives, Uninterruptible Power Supplies (UPS), DC motor drives,
Switched Mode Power Supplies (SMPS).
Advantages:
• Excellent accuracy
• Very good linearity
• Low temperature drift
30
Chapter 3
DESIGN OF MEASUREMENT SYSTEM AND DATA DISPLAY
• Optimized response time
• Wide frequency bandwidth
• No insertion losses
• Highly immunity to external interference
• Current overload capability.
3.2.3
TL081 Op Amp
The TL081 [5] series are general purpose operational amplifiers whose performance is
improved according to requirements of industrial standards. The TL081 amplifiers
offer many characteristic which make their application nearly foolproof: overload
protection on the input and output side, no latch-up when the common mode range
is exceeded, and the oscillations are prevented. Their performance is Best over a 00 C
to +700 C temperature range. This amplifier is the most important part which is
used as a attenuator, level shifter and precision rectifier, and the output of which is
applied to the processor to enable the calculation of the different parameter related
to current, voltage and energy meter.
Connection diagram of TL081 is as shown below:
Figure 3.5: Connection Diagram of TL081
31
Chapter 3
3.2.4
DESIGN OF MEASUREMENT SYSTEM AND DATA DISPLAY
LCD
Liquid crystal display [6] or LCD as shown in Figure is one of the most used
devices for alphanumeric output in processor-based circuits.
Their advantages
are their cost,reduced size and convenience of mounting the LCD directly on the
circuit board.LCD is classified according to their interface into Parallel and serial.
The Serial LCD requires less I/O resources but execute slower than their parallel
counterparts and are considerably more costly. In this project, parallel-driven LCD
devices based on the Hitachi HD44780 character-based controller, and which is by
far the most popular controller for microcontroller-driven LCD.
Figure 3.6: 16x2 LCD
The HD44780 is a dot-matrix liquid crystal display controller and driver. The
device displays ASCII alphanumeric characters like as Japanese kana characters,
and some symbols like in Figure 2.10. A single HD44780 can display up to two
28-character lines. An available extension diver makes possible addressing up to 80
characters. The HD44780U contains a 9,920 bit character-generator Read Only
Memory that generate a total of 240 characters: 208 characters with a 58 dot
resolution and 32 characters at a 510 dot resolution. The HD44780U device is
capable of storing 64x8-bit character data in its character generator Read access
Memory. This correlate to eight custom characters in 5x8-dot resolution or four
characters in 5x10-dot resolution. The HD44780U controller is programmable to
three different duty cycles: 1/8 for one line of 58 dots with cursor & 1/11 for one
32
Chapter 3
DESIGN OF MEASUREMENT SYSTEM AND DATA DISPLAY
line of 510 dots with cursor, & 1/16 for two lines of 58 dots with cursor.
The in built commands include homing the cursor,setting display characters to
blink,clearing the display,turning the cursor on and off,turning the display on and
off,reading and writing data to the character generator,shifting the cursor and the
display right-to-left or left-to-right,and to display data ROM.
3.3
Software Development
After testing and simulation of every single part, the operational program for
processor is written under ARM-IDE in conformance with the designed circuit.
The implementation of software for the single-phase metrology is discussed in
this section. The first subsection discusses the set up of various peripherals of the
energy meter. Subsequently, the entire metrology software is described as two major
processes: background process and foreground process.
3.3.1
Peripherals Set Up
The major peripherals are the ADC of LPC2148, clock system, timer, LCD, and so
forth. The LPC2148 has two on-board analog-to-digital converters each of which
provides 10-bits of accuracy with a conversion time of about 2.44 µ sec. Each
converter has an 8-channel analog front end so that there are 16-channels of A/D
available.
For a single phase system at least two ADC are necessary to independently
measure one voltage and current. ADC 0.1 is used to measure the voltage samples
and ADC 0.3 is used to measure the current sample. The sampling of voltage and
current is completed by timer operation. Timer which has the clock frequency 1 MHz
is used to make the sample frequency 1 KHz by generate a delay of 1 millisecond.
The input signal frequency of voltage or current both have 50 Hz frequency and time
period 20 millisecond. In one cycle through ADC processor is getting a 20 sample
and in one seconds it getting a 1000 samples. On basis of one second or 1000 samples
33
Chapter 3
DESIGN OF MEASUREMENT SYSTEM AND DATA DISPLAY
Code(hex)
Table 3.1: LCD command
Command to LCD Instructin register
1
Clear display screen
2
Return home
4
Decrement cursor (shift cursor to left)
6
Increment cursor (shift cursor to right)
5
Shift display right
7
Shift display left
8
Display off, cursor off
A
Display off, cursor on
C
Display on, cursor off
E
Display on, cursor blinking
F
Display on, cursor blinking
10
Shift cursor position to left
14
Shift cursor position to right
18
Shift the complete display to the left
1C
Shift the complete display to the right
38
2 lines and 5x7 matrix
C0
Force cursor to beginning to second line
80
Force cursor to beginning to first line
34
Chapter 3
DESIGN OF MEASUREMENT SYSTEM AND DATA DISPLAY
LPC2148 measure the RMS voltage, RMS current and ENERGY consumed in one
second by load.
After calculating the RMS voltage and current, energy it will display to LCD.
This process is running continuously and update the value of RMS voltage ,RMS
current and energy, and display in LCD.
3.3.2
The Foreground Process
The foreground process [7][9][10][11] includes the initial set up of the LPC2148
hardware and software immediately after a device RESET. Figure shows the
flowchart for this process.
The initialization routines process involves the set up of the analog to digital
converter, clock system, general purpose input/output (GPIO) port pins, timer,
LCD. During normal operation, the background process informs the foreground
process every time a frame of data is available for processing. This data frame
composed of accumulation of energy for 1 second.
This is equal in value to
accumulation of 50 or 60 cycles of measured data samples synchronized to the
incoming voltage signal. In parallel, a data sample counter keeps track of how
many samples have been accumulated over the frame period. This count value can
vary as the software synchronizes with the incoming mains frequency. The data
samples value set consist of processed current, voltage, active energy. All values are
accumulated and further process to obtain the RMS and mean values.
35
Chapter 3
DESIGN OF MEASUREMENT SYSTEM AND DATA DISPLAY
Flow Chart diagram for Foreground process
Reset
Hardware setup;
Clock,ADC,
Timer,port pins,LCD
No
one second
of energy
accumulated
? Wait for
Background
Process
Yes
Calculate RMS values for
current voltage and Active
power
Display RMS value for voltage
current and Active power
3.3.3
The Formulae
This section briefly explain the formulae used for the rms load current & rms load
voltage and energy calculations.
Voltage and Current
As discussed in the above sections simultaneous voltage and current samples are
obtained from two channel of A/D converters at a sampling rate of 1000 Hz. Track
the number of data samples that are present in 1 second is kept and used to obtain
36
Chapter 3
DESIGN OF MEASUREMENT SYSTEM AND DATA DISPLAY
the Root Mean Square values for voltage and current for each phase.
s
Psample count 2
Vi (t)
i=1
Vrms = Kv ×
sample count
Irms = KI ×
s
Where
Psample count
Ii2 (t)
sample count
i=1
(3.1)
(3.2)
Vrms = RMS value of voltage
Irms = RMS value of current
V(i) = Voltage sample at a sample instant ’i’
I(i) = Current sample at a sample instant ’i’
Sample count= Number of data samples in 1 second
Kv = Scaling factor for voltage
Ki = Scaling factor for current
Power and Energy: Consumer power and energy [8][13][14] are calculated
for a frames worth of active energy samples. These samples are phase rectified
and passed on to the foreground process which accumulate the number of samples
(sample count) and use the formulae shown below to calculate total active powers.
Pact = KP ×
Where
Psample count
i=1
Vi (t) × Ii (t)
sample count
(3.3)
Pact = Actual power consumed by load
Kp = Scaling factor for power
V(i) = Voltage sample at a sample instant ’i’
I(i) = Current sample at a sample instant ’i’
Sample count= Number of data samples in 1 second
The consumed energy is then measured based on the active power value for each
frame:
Pact1 =
37
Pact
3600
(3.4)
Chapter 3
DESIGN OF MEASUREMENT SYSTEM AND DATA DISPLAY
Where
Pact1 = Actual power consumed by load in 1 second.
3.3.4
The Background Process
The background process uses the timer as a trigger to collect voltage and current
samples (two values in total). These samples values are further processed and
accumulated in dedicated 32-bit registers. The background function deals mainly
with timing critical events in software. Once sufficient samples (1 second worth) has
been accumulated after then the foreground function is triggered to calculate the
final values of rms voltage, rms current, power and energy. The background process
is also completely responsible for energy calculation for each phase. Below the flow
chart diagram of the background process is shown.
In background process analog to digital converter took the 1000 samples in one
second of voltage and current. First eliminate the offset of both the voltage and
current sample and then calculated the RMS value of voltage, RMS value of current,
and Power consumed by load in one second. After processed calculation notify the
foreground process.
The determined instantaneous voltage and current samples are used to generate
the following information:
• Accumulated squared values of voltage and current for VRM S and IRM S
calculations.
• Accumulated energy samples to measure Active Energy.
38
DESIGN OF MEASUREMENT SYSTEM AND DATA DISPLAY
Chapter 3
Flow Chart diagram for Background process
ADC sample @
1000sec
Read Voltage V
Read Current I
a.Removal residual DC
b.Accumulated samples for
instantaneous Power
c.Accumulate forIrms andVrms
No
one second
of energy
calculated
AndVrms , Irms
calculated
Yes
Accumulated reading Notify
Foreground process
Return to
ADC
39
Chapter 4
EXPERIMENTAL RESULTS
Some measurements with the implemented Energy Meter are conducted regarding
the accuracy of the system for evaluation process. The required performance of the
prototype meter has been evaluated in the laboratory.
4.1
Testing Voltage and Current sensing Circuit
In order to see that voltage and current sensing circuit are correctly doing their
duties, input signal and its related output is controlled by a digital real time
oscilloscope.
Results are shown in the Figure 4.1 Input Current signal and Output Current
Signal with offset Figure 4.2 Input Voltage signal and Output Voltage Signal with
offset.
It is clearly observed on Figure 4.1,4.2 that the sinusoidal input signals is
amplified for current sensing and attenuated for voltage sensing circuit, then both
signals levels are shifted. The output of voltage and current sensing circuit has
positive value in both cycle faithfully with almost no phase shift.
40
EXPERIMENTAL RESULTS
Chapter 4
Figure 4.1: Input Current signal and Output Current Signal with offset
Figure 4.2: Input Voltage signal and Output Voltage Signal with offset
4.2
Testing for samples
In order to see that ADC of LPC2148 are correctly doing their duties, input signal
and its related output is controlled by a digital real time oscilloscope.
Results are shown in the Figure 4.3 Input Voltage signal and Output Voltage
sampled Signal.
It is clearly observed on figure 4.3 that the sinusoidal input signals are correctly
sampled through ADC of LPC2148. Input is applied to the input port of ADC
channel and then ADC digital output is passed to Digital to Analog converter.
Analog output is traced, which is display in CRO as shown above.
41
EXPERIMENTAL RESULTS
Chapter 4
Figure 4.3: Input Voltage signal and Output Voltage sampled Signal.
4.3
Tests for sag of signal
The performance of the prototype meter is evaluated that it can measure the swell
and sag in a time limitation. In common electric circuit it is occur frequently, by
following test it showing the measuring ability.
Figure 4.4: Measurement setup for testing the sag and swell
Figure 4.4 shows the measurement setup for creating a swell and sag signal along
42
EXPERIMENTAL RESULTS
Chapter 4
with energy meter to measure the change.
Figure 4.5: Measured RMS voltage before and after saging the voltage signal
Figure 4.6: Voltage wave form along with sag
4.4
Tests on Current measurement
The performance of the prototype is evaluated by comparing the prototype reading
with the standard meter. Table 4.1 shows true RMS current as measured by standard
meter and proposed meter and relative (%) error.
43
EXPERIMENTAL RESULTS
Chapter 4
Table 4.1:
Result of Current measurement in the laboratory with standard
multimeter meter & prototype energy meter
Number
of Measured
rms
value
of Measured
rms
value
of Relative
measurement current (amp) (Standard current (amp) (Prototype
Error (%)
meter)
meter)
1
0.2793
0.2799
-0.214823
2
0.2903
0.291
-0.24113
3
0.3016
0.302
-0.132626
4
0.3118
0.3125
-0.224503
5
0.3231
0.324
-0.278552
6
0.3324
0.3315
0.2707581
7
0.3427
0.3426
0.02918
8
0.3522
0.353
-0.227144
9
0.3619
0.361
0.2486875
10
0.3714
0.372
-0.161551
11
0.381
0.38
0.2624672
12
0.3906
0.3904
0.0512033
The measured values of current obtained from the readings of the sub standard
meter are considered as standard and compared with proposed method values to
check the accuracy of the metering system.
4.5
Tests on Voltage measurement
The performance of the prototype is evaluated by comparing the prototype reading
with the standard meter. Table 4.2 shows true RMS voltage as measured by standard
meter and proposed meter and relative (%) error.
The measured values of voltage obtained from the readings of the sub standard
44
EXPERIMENTAL RESULTS
Chapter 4
Table 4.2:
Result of Voltage measurement in the laboratory with standard
multimeter meter & prototype energy meter
Number
of Measured
measurement voltage
rms
(volt)
value
of Measured
rms
value
of Relative
(Standard voltage (volt) (Prototype
Error (%)
meter)
meter)
1
130.45
130.56
-0.084323
2
140.1
140.35
-0.178444
3
150.4
150.14
0.1728723
4
160
159.93
0.04375
5
170.9
170.81
0.0526624
6
180.24
180.6
-0.199734
7
190.49
190.4
0.0472466
8
200.2
200.19
0.004995
9
210.1
209.98
0.0571157
10
220.17
219.77
0.1816778
11
230.1
229.8
0.1303781
12
240
239.6
0.1666667
meter are considered as standard and compared with proposed method values to
check the accuracy of the metering system.
4.6
Tests on Consumed Energy measurement
The performance of the prototype is evaluated by comparing the prototype reading
with the standard calculation. Table 4.3 shows the Energy measurement in the
laboratory with standard calculation & prototype energy meter and relative (%)
error.
The measured values of current obtained from the standard calculation and
45
EXPERIMENTAL RESULTS
Chapter 4
Table 4.3: Result of Energy measurement in the laboratory with standard calculation
& prototype energy meter
Number
of Load
measurement
Actual
power
Measured
power
Relative
consumed in ONE
consumed in ONE
Error
Hour(WaatHour)
Hour(WaatHour)
(%)
1
15 watt, 250 volt
13.2
13.1
0.757576
2
11 watt, 240 volt
10.1
10.2
-0.9901
3
100 watt, 230 volt
93.28
93
0.300172
4
100 watt, 250 volt
79.8
79.3
0.626566
compared with proposed method values to check the accuracy of the metering
system.
46
Chapter 5
Conclusion
In this thesis design and implementation of reliable digital Energy Meter based
on ARM microcontroller is described.
With the designed new energy meter;
measurement and LCD display of the desired data are possible. Each system section
is carefully designed to meet the desired accuracy and bandwidth. C language
code is firmware compact and the entire energy calculation algorithm is executed in
minimum number of CPU cycle.
In this achievement, different methods for sensing the current and voltage
are proposed and implemented.
This system is designed based on an ARM
microcontroller which acts as a data acquisition processing and display system. A
current and a voltage signals are connected to their analog inputs and converted
into digital form. The sampled signals of the current and voltage are manipulated
by microcontroller to measure energy meter parameter. The microcontroller can
therefore evaluate the rms values of measured signals together with the consumed
energy at the measurement terminals which enable the calculation of all other energy
related quantities. In this case study we proposed a simple and versatile display
method where the measured data can be easily monitored and display for user.
The new measurement system will certainly help to decrease efficient usage of
time as compared to conventional method of getting the same results. All the table
gives comparison between the standard and prototype. It can be concluded that the
47
Conclusion
accuracy up to 0.1% to 0.2% can be obtained for voltage and current measurement
and less then 1% accuracy can be obtained for energy calculation.
Future work may include monitoring system. In monitoring system we can easily
acquire all the voltage and current sample in every second. Then time to time we
can monitor the signal, if any swell and sag is occur it is display in monitor to inform
user.
48
Bibliography
[1] Current transducer la 55-p/sp1. LEM, page 3, 2002.
[2] Vincent G.and S. Sasitharan. M.K.Mishra, K. Karthikeyan. A dsp-based integrated hardware
set-up for a dstatcom: Design, development, and implementation issues. IETE JOURNAL
OF RESEARCH, 56(1):11–21, 2010.
[3] P. A. V. Loss, M. M. Lamego, G. C. D. Sousa, and J. L. F. Vieira. Single phase microcontroller
based energy meter.
In Conference Record - IEEE Instrumentation and Measurement
Technology Conference, volume 2, pages 797–800, 1998. Cited By (since 1996):9.
[4] Avr465: Single-phase power/energy meter with tamper detection. Atmel, page 40, july 2004.
[5] Tl081 jfet-input operational amplifires. TEXAS INSTRUMENTATION INCORPORATED,
page 45, SEPTEMBER 2004.
[6] Shi-Wei Lee, Cheng-Shong Wu, Meng-Shi Chiou, and Kou-Tan Wu. Design of an automatic
meter reading system. In IECON Proceedings (Industrial Electronics Conference), volume 1,
pages 631–636, 1996. Cited By (since 1996):3.
[7] Implementation of a single-phase electronic watt-hour meter using the msp430f6736. TEXAS
INSTRUMENTATION INCORPORATED, page 27, May 2012.
[8] L. Saranovac, P. Pejovic, and M. Popovic. Digital method for power frequency measurement
using synchronous sampling. IEE Proceedings: Electric Power Applications, 148(2):225–226,
2001. Cited By (since 1996):2.
[9] R. G. Jones. A review of precision ac voltage and current measurements. IEE Colloquium
(Digest), (161):1/1–1/4, 1997.
[10] H. Serra, J. Correia, A. J. Gano, A. M. De Campos, and I. Teixeira.
Domestic
power consumption measurement and automatic home appliance detection. In 2005 IEEE
International Workshop on Intelligent Signal Processing - Proceedings, pages 128–132, 2005.
Cited By (since 1996):9.
49
Bibliography
[11] C. . Young and M. J. Devaney. Digital power metering manifold. IEEE Transactions on
Instrumentation and Measurement, 47(1):224–228, 1998. Cited By (since 1996):6.
[12] U. B. Mujumdar and J. S. Joshi.
Microcontroller based true rms current measurement
under harmonic conditions. In 2010 IEEE International Conference on Sustainable Energy
Technologies, ICSET 2010, 2010.
[13] J. Xi and J. F. Chicharo. A new algorithm for improving the accuracy of periodic signal
analysis. IEEE Transactions on Instrumentation and Measurement, 45(4):827–831, 1996.
Cited By (since 1996):58.
[14] P. Petrovic. New digital multimeter for accurate measurement of synchronously sampled ac
signals. IEEE Transactions on Instrumentation and Measurement, 53(3):716–725, 2004. Cited
By (since 1996):20.
[15] H. Hindersah, A. Purwadi, Farianza Yahya Ali, and N. Heryana. Prototype development
of single phase prepaid kwh meter. In Proceedings of the 2011 International Conference on
Electrical Engineering and Informatics, ICEEI 2011, 2011.
[16] T. Dake and E. zalevli. A precision high-voltage current sensing circuit. IEEE Transactions
on Circuits and Systems I: Regular Papers, 55(5):1197–1202, 2008. Cited By (since 1996):6.
[17] Gerard N. Stenbakken and Amos Dolev.
High-accuracy sampling wattmeter.
IEEE
Transactions on Instrumentation and Measurement, 41(6):974–978, 1992. Cited By (since
1996):15.
[18] Mohamed H. Shwehdi and Chris Jacobsen. Microprocessor-based digital wattmeter system
design.
In Proceedings of the Intersociety Energy Conversion Engineering Conference,
volume 3, pages 1840–1845, 1996. Cited By (since 1996):3.
[19] P. Oksa, M. Soini, L. Sydnheimo, and M. Kivikoski. Considerations of using power line
communication in the amr system. In 2006 IEEE International Symposium on Power Line
Communications and Its Applications, ISPLC’06, pages 208–211, 2006. Cited By (since
1996):9.
[20] L. Li, H. Xiaoguang, H. Jian, and H. Ketai. Research on the architecture of automatic
meter reading in next generation network. In IEEE International Conference on Industrial
Informatics (INDIN), pages 92–97, 2008. Cited By (since 1996):3.
[21] Elham B. Makram, Clarence L. Wright, and Adly A. Girgis.
A harmonic analysis of
the induction watthour meter’s registration error. IEEE Transactions on Power Delivery,
7(3):1080–1088, 1992. Cited By (since 1996):13.
50
Bibliography
[22] Saul Goldberg and William F. Horton. Induction watthour meter accuracy with non-sinusoidal
currents. IEEE Transactions on Power Delivery, PWRD-2(3):683–690, 1987. Cited By (since
1996):2.
51
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertisement