Download Harmonic Analysis of 230 V AC Power Supply

Transactions on Engineering and Sciences
Vol.2, Issue 8, August 2014
ISSN: 2347-1964 (Online) 2347-1875 (Print)
Harmonic Analysis of 230 V AC Power Supply
Using LPC2138 Microcontroller
Jeena Joy1
AmalrajP.M.2
Aswin Raghunath3
Nidheesh M.N.4
Vinu Joseph5
1Asst.Prof,
2,3,4,5UG
Dept. of EEE, Mar Athanasius College of Engineering, Kothamangalam.
Student, Dept. of EEE, Mar Athanasius College of Engineering, Kothamangalam.
Abstract: The presence of harmonics in power system is a major concern to power engineers for many
years. With the increasing usage of nonlinear loads in power systems, the harmonic pollution becomes
more serious. One of the widely used computation algorithm for harmonic analysis is Fast Fourier
Transform (FFT). In this project, a harmonic analyzer using FFT is being implemented on ARM7 core
processor LPC2138 [1]. The supply voltage of 230V, 50 Hz is stepped down to 6V using a voltage divider
in order to match the power rating of the processor input. The output from the processor is displayed on
a graphic LCD, which is interfaced to the output ports of the processor.
Keywords: Harmonic Analysis, FFT
I.INTRODUCTION
In recent years, the electrical harmonic pollution is getting more and more serious with the far-ranging
use of nonlinear components in electric and electronic devices. The presence of harmonics in power system
is a major concern to power engineers for many years. Harmonic Pollution increases industrial plant
downtimes and power losses. Harmonic of an electrical signal is the content of the signal whose frequency is
an integer multiple of the fundamental system frequency. The cause of harmonic in a power system is from
highly nonlinear devices. In power system, harmonic analysis is use to determine the impact of harmonic
producing load on a power system.[1] This technique is widely used for system planning, equipment
design, troubleshooting, etc. The effect of harmonics on power system can be in the form of power efficiency
reduction, overheating in wire, ageing of electrical insulation, etc [2].
Several algorithms have been proposed on harmonic analysis and Fast Fourier transform (FFT) is the
most widely used computation algorithm. FFT is an efficient algorithm used to compute Discrete Fourier
transform (DFT). DFT uses a finite set of discrete-time sample of an analogue signal and produces a finite set
of discrete-frequency magnitude spectrum values [3]. This paper focuses on implementation of 240V, 50Hz
power supply harmonic analysis on LPC2138 using FFT technique.
II. HARMONIC CALCULATION USING FFT ALGORITHM
Basically, the computational problem for the DFT is to compute the sequence {X (k)} of N complexvalued numbers given another sequence of data {x(n)} of length N, according to the formula
= , 0 ≤ ≤ − 1
= ⁄
To compute all N values of the DFT requires N 2 complex multiplications and N 2-N complex additions.
Direct computation of the DFT is basically inefficient primarily because it does not exploit the symmetry
and periodicity properties of the phase factor WN. In particular, these two properties are:
⁄
!"!#"! ∶ %
= −
&!'#(')' "!#"! ∶ %
= FFT algorithms, exploit these two basic properties of the phase factor and is another method for
calculating the DFT [4]. While it produces the same result as the other approaches, it is incredibly more
efficient, often reducing the computation time by hundreds. The computation of the N-point DFT via the
decimation-in-time FFT requires only (N/2)log2N complex multiplications and Nlog2N complex
additions.Let us consider the computation of the N = 2v point DFT by the divide-and conquer approach.
Wesplit the N-point data sequence into two N/2-point data sequences f1(n) and f2(n), corresponding to the
even-numbered and odd-numbered samples of x(n), respectively, that is,
* = 2
* = 2 + 1, = 0,1,2, … . , /2 − 1
Thus f1(n) and f2(n) are obtained by decimating x(n) by a factor of 2, and hence the resulting FFT
algorithm is called a decimation-in-time algorithm [5].The computation of N = 8 point DFT is performed in
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Transactions on Engineering and Sciences
Vol.2, Issue 8, August 2014
ISSN: 2347-1964 (Online) 2347-1875 (Print)
three stages, beginning with the computations of four two-point DFTs, then two four-point DFTs, and
finally, one eight-point DFT. The combination for the smaller DFTs to form the larger DFT is illustrated in
Figure 1.
Figure 1: Three stages in the computation of an N = 8-point DFT
Figure 2: Conventional butterfly diagram
Similar to this case in this project 10 stage butterfly analysis is required for a total input of 1024 samples.
A conventional 3 stage butterfly diagram is shown as in figure 2 [6]. 10 stage butterfly analysis is chosen
according to the sampling theory wherein ‘sampling frequency must be twice the maximum frequency
component’. Maximum frequency that is displayed is 500Hz for digital implementation 512Hz is used
[7][8][9][10].
III.LPC2138 MICROCONTROLLER
The LPC2138 microcontroller is based on a 16/32 bit ARM7TDMI-S™ CPU with real-time emulation
and embedded trace support, that combines the microcontroller with 32 kB, 64 kB, 128 kB, 256 kB and 512
kB of embedded high speed Flash memory [11]. A 128-bit wide memory interface and a unique accelerator
architecture enable 32-bit code execution at maximum clock rate. For critical code size applications, the
alternative 16-bit Thumb® Mode reduces code by more than 30 % with minimal performance penalty.
Due to their tiny size and low power consumption, these microcontrollers are ideal for applications
where miniaturization is a key requirement, such as access control and point-of-sale. With a wide range of
serial communications interfaces and on-chip SRAM options of 8/16/32 kB, they are very well suited for
communication gateways and protocol converters, soft modems, voice recognition and low end imaging,
providing both large buffer size and high processing power. Various 32-bit timers, single or dual 10-bit 8
channel ADC(s), 10-bit DAC, PWM channels and 47 GPIO lines with up to nine edge or level sensitive
external interrupt pins make these microcontrollers particularly suitable for industrial control and medical
systems [12].
IV.CIRCUIT CONFIGURATION
The power supply section is to supply Vcc for the controller and graphic LCD. A 230V supply from
the mains if fed to a step down transformer, 12-0-12, the signal will get downsized. This is then rectified
using a full wave rectifier and smoothened using a capacitor. The output thus obtained is regulated using
LM7805 IC to get a 5V DC supply .The LPC2138 has a header of its own to convert the input to 3.3V which is
its working voltage. In the voltage section of the circuitry provides the input for voltage harmonic analysis.
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Techscripts
Transactions on Engineering and Sciences
Vol.2, Issue 8, August 2014
ISSN: 2347-1964 (Online) 2347-1875 (Print)
The signal to be analysed is fed to the voltage transformer, 6-0-6. The output of transformer will be 12V
peak-to-peak. This has to be converted into 3.3V for matching the requirements of the controller. For safe
working, signal is made to 2V peak-to peak using voltage divider. Capacitor is used to prevent the
disruptions on AC side by the DC bias given. Signal is then clamped to a reference of 1.7V using a voltage
bias and identical clamping resistors. Output so obtained can then be given to the ADC channel of LPC2138
for harmonic analysis.
Figure 3: Circuit of power harmonic analyser.
Current section aims at providing input for current harmonic analysis. A 20:5A Current Transformer
(CT) is used. Wire carrying the input current forms the primary whereas the secondary is a wire of many
turns wound around a silicon former. A current which is reduced but proportional to the input current is
produced at the output of the CT. The voltage drop by the current across the resistor which is very small is
amplified using a differential amplifier. Input to the inverting terminal is the small voltage drop and that to
the non-inverting terminal is 1.75V. Microcontroller LPC2138 is the brain of this project. The voltage and
current signals to be analyzed are fed to the two channels of ADC which are pin 27 and 28 respectively.
Reset operation is achieved by using a reset button connected to the pin 25 of the controller. Channels of
ADC can be switched by using the ISP (pin 15). When pin 15 is grounded graphic LCD displays current
harmonics and voltage harmonics otherwise. Graphic LCD is having a resolution of 128*64. The output is
displayed on a graphic LCD which is interfaced to the controller through pin 35 to 48 as shown in figure 3.
V.RESULT
The power harmonic analyzer was used to test the harmonics present in the normal electric supply and
in the output of the ups. Results obtained are as shown in the figure 4. Output of the analyzer is being
displayed on the graphic LCD. It is a plot between FFT magnitude and frequency. For each of the frequency
samples the corresponding FFT magnitude is found out using implemented FFT algorithm.
Figure 4: Harmonics in normal supply and in UPS
Using the harmonic analyser THD at the college hostel at different time during three days were taken,
table 1 shows the reading and a graph is plotted with the variation of THD with time. Figure 5 shows the
THD VS Time curve graph. By analysing the graph it can be seen that THD rises during the time interval
7.00 pm to 9.00 pm as the usage of non-linear loads like fan, lamps and computers is higher.
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Techscripts
Transactions on Engineering and Sciences
Vol.2, Issue 8, August 2014
ISSN: 2347-1964 (Online) 2347-1875 (Print)
Table.1 THD during different days
DAYS
TUESDAY
WEDNESDAY
THURSDAY
8:00 AM
15
13
14
12:00 PM
13
13
14
4:00 PM
16
15
14
8:00 PM
25
27
28
Figure 5: THD VS Time Curve
VI.CONCLUSION
With the proliferation of non-linear loads, the issues of power harmonics are more apparent than ever.
Controlling and monitoring industrial system designs and their effects on utility distribution systems are a
potential problem for the industrial consumer, who is responsible for complying with the IEEE 519-1992
recommended practices and procedures. Industrial facilities should include a system evaluation, including a
harmonic distortion analysis, while planning facility construction or expansion. Vendors of non-linear loads,
such as variable frequency drives, can provide services and recommend equipment that will reduce
harmonics in order to comply with the revised IEEE 519-1992 guidelines.
Hence a power harmonic analyzer is presented using LPC2138 ARM7 core processor. This harmonic
analyzer is capable of analyzing harmonics in a single phase supply and represents the harmonics as a
frequency spectrum. The proposed system provides a harmonic analyzer at much lower cost.
REFERENCES
[1] Dody Ismoyo, Mohammad Awan, NorashikinYahya International Conference on Signal Processing
Systems Harmonic Analysis of 240V AC Power Supply using TMS320C6713 DSK May 15-May 17, 2009
[2] E. Acha and M. Madrigal, Power Systems Harmonics.West Sussex: John Wiley& Sons, Ltd, 2001
[3] Fast Fourier Transform Algorithms with applications August 2008 Todd Mateer Swiss Federal Institute
of Technology Zurich
[4] Fast Fourier Transform Numerical Analysis Seminar Stefan Worner
[5] A.A. Girgis, The Fast Fourier Transform and Its Applications. Upper Saddle River, NJ: Prentice-Hall,
1990
[6] Digital Signal Processing 5th Edition by P. Rameh Babu
[7] H. Xue and R. Yang, “A novel algorithm for harmonic measurement in power system,” in Proc. Int.
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[8] M. Meunier and F. Brouaye, “Fourier transform, wavelets, Pronyanalysis: tools for harmonics and
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[11] ARMv7-M Architecture Reference Manual
[12] THE 8051 Microcontroller and Embedded Systems: using Assembly and C 2nd Editio by Muhammad Ali
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