Harmonic Det
Content
ISSN 2249-6343 International Journal of Computer Technology and Electronics Engineering (IJCTEE) Volume 2, Issue 3, June 2012
Harmonic Detection using Microcontroller
Jaipreet Kaur Bhatti, Deepak Asati
Abstract--- Harmonic distortion meter is an instruments that measure harmonic distortion or phase position or simply has been designed for measuring the quality of AC supply. Harmonic distortion is a common problem in power systems, data processing equipment and adjustable speed drives. In communications applications, harmonic distortion meters are used to determine when the original frequency transmitted is split into multiple frequencies due to irregularities in the line. Harmonic distortion meters are important for analyzing the quality of power coming into a system and for determining what is causing the problem. Keywords--- DFT, microcontroller (ATMEGA16), Harmonic detection.
This paper is organized as follows: Section 1- Introduction and need of harmonics detection. Section 2- Explains Solution based on phase lock loop and its drawbacks. Section 3- Detection of harmonics using DFT and its advantages. Section 4- Hardware and circuit required for its working. Section 5- Gives the conclusions of the present work. II. PHASE LOCK LOOP & ITS DRAWBACKS The various harmonics in a power system are typically measured with a heterodyne receiver if we are using analog methods or by a FFT (Fast Fourier Transform) when digital methods are being used. The harmonics can be analyzed over a wide range of frequencies by means of these methods. However, since the circuit configurations that are needed can become very complicated, the equipment tends to be too expensive for practical use. This paper presents a novel harmonic meter using a PLL (Phase Locked Loop) circuit. By means of the phase feedback loop, a reference sinusoidal wave is locked on to the input signal along with the harmonics that we wish to measure, and hence the corresponding harmonic component in the input signal is easily detected. The effectiveness of the proposed harmonic meter is confirmed by experiment. Disadvantage comes to play in case of wrong manual tuning for detection of sinusoidal signal for desired frequency. Multiple frequencies just in case of 2 nd order and 3rd order require use of separate phase detectors which makes it complex and needs fine adjustments. In total harmonics distortion computation a separate logic is required hence hardwired circuit here in inapplicable in case of reading manipulations and processing. In this idea we are using a microcontroller which enrich the above condition by making soft coding approach and hence can be used in performing discrete Fourier transform results. An 8 bit RISC microcontroller ATMEGA16 can provide us 16MIPS of processing power using 16Mhz of clock crystal, along with that it contains a 8 channel 10 bit ADC which suits our application. III. DETECTION OF HARMONICS USING DFT Proposed methodology: In the proposed method a harmonic meter using a microcontroller is designed . The meter is built with a microcontroller and the full wave rectifier front-end circuit. The input signal to the 10-bit ADC is full wave rectified.
I. INTRODUCTION This thesis basically employs a device which shows a method for finding the amplitude of the fundamental frequency and the 3rd harmonic of AC voltage signals. The technique is consummate for identifying the distortions in the AC voltages .For example electronic devices having nonlinear characteristics being used at home and office are mostly computer based equipment with a low power factor switch mode power supply. These power supply sections include charging capacitors which draw current at peak voltages. Thus for a given feeder having finite impedance there can be a voltage drop near the peak voltage resulting in flattened top distortion of AC voltage. To identify these distortions we analyze the output signal in the frequency domain by utilizing efficient digital processing techniques. In this thesis a feature based method is developed to efficiently perform the frequency synthesis and further perform correlation between the output signal and a varying sinusoid signal
Fig. 1: Flattened top AC voltage caused by a low power factor switch mode power supply.
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ISSN 2249-6343 International Journal of Computer Technology and Electronics Engineering (IJCTEE) Volume 2, Issue 3, June 2012 The software performs DFT calculation finding the amplitude of the fundamental frequency and the 3rd harmonic. The distortion is computed by the ratio of the amplitude of the 3rd harmonic to the fundamental frequency. The effectiveness of the proposed harmonic meter is confirmed by experiment. A. Total Harmonic Distortion, THD To measure the wave shape distortion, we use the quantity of the Total Harmonic Distortion, THD (equation 1). THD is the ratio of the power of harmonic components to the power of fundamental frequency. Our concern is the voltage distortion we can just find the sum of the RMS of the harmonic components, Vn and the RMS of the fundamental frequency, V1.
Advantage of DFT:- Since the AC signal has symmetry between positive cycle and negative cycle. We can find the harmonic component by capturing only half cycle. This reduces computing time by half.
THD =
*100, n=2, 3….N
Most of the harmonic problem is caused by the 3rd component. Since the 3rd harmonic is the 2nd highest energy from the fundamental component. So we interest to find only the 3rd harmonic distortion using equation 2. HD =
*100
Discrete Fourier Transform, DFT We may decompose the periodic waveform, f(t) into the summation of a number of sinusoids waveform easily using the Discrete Fourier Transform (equation 3). A0 is the amplitude of DC components. For AC voltage waveform, A0 is zero.
Fig. 2: The 32-point sample half period AC input signal
IV. BLOCK DIAGRAM OF PROPOSED DESIGN
Bridge Rectifier Amplitude of each harmonics-
Xin [32] Capture 32 samples. Determining Bv & Cv for 1st &3rd Harmonics.
The amplitude for each harmonic can be computed from equation 4.
The coefficients Bv and Cv for each harmonic are easily calculated by multiplying the corresponding sine wave and cosine wave to the input signal respectively (equation 5 and 6). Where delta t is time between sample, T is period, Vy is input signal. 107
Coefficien 3rd order Result t Bv & Cv THD= on for 1st&3rd (V3/V1)* LCD order will be 100 harmonics shown. . Fig.3. Block diagram of proposed design.
ISSN 2249-6343 International Journal of Computer Technology and Electronics Engineering (IJCTEE) Volume 2, Issue 3, June 2012 High quality power supply has a perfect sinusoidal signal with constant frequency and amplitude. On the other hand, the use of nonlinear devices and the time-varying loads in the electric power system is widespread and is growing with even bigger pace. Such devices and loads are consuming distorted current from the power system grid.To preserve high power quality, the most important indices, such as harmonics, sags, swells, short interruptions, imbalances, and flickers, ideally have to be eliminated. Inrecent years, researchers have been developing tools for accurate power quality analysis, as well as devices for mitigation of power supply imperfections. If an electrical quantity is made to vary directly in proportion to this value (temperature etc) then what we have is Analogue signal. Now we have we have brought a physical quantity into electrical domain. The electrical quantity in most case is voltage. To bring this quantity into digital domain we have to convert this into digital form. For this a ADC or analog to digital converter is needed. Most modern MCU including AVRs has an ADC on chip. An ADC converts an input voltage into a number. An ADC has a resolution. A 10 Bit ADC has a range of 0-1023. (2^10=1024) The ADC also has a Reference voltage (ARef). When input voltage is GND the output is 0 and when input voltage is equal to ARef the output is 1023. So the input range is 0-ARef and digital output is 0-1023.
V. HARDWARE AND CIRCUIT DESIGN OF PROPOSED METER
Fig.4 Harmonic detection meter using microcontroller
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ISSN 2249-6343 International Journal of Computer Technology and Electronics Engineering (IJCTEE) Volume 2, Issue 3, June 2012 VI. CIRCUIT DESCRIPTION From the above design, first of all input signal is applied to the circuit which is 220Vac. The bridge rectifier rectifies the ac input to the pulsating dc, which would further made constant 5V with the help of filter-capacitor arrangement and voltage stabilizer so that any change in ac would not proportionally change dc. The dc output is given to the variable resistor which is used to select the voltage which in case of PLL cannot be done because it needs a separate phase detector for different frequencies (voltages) this is then applied to the digital oscilloscope which shows the total coverage of half cycle by capturing 32 samples. The output from this is given to the microcontroller where the software performs the DFT calculations and the final results are displayed on the LCD i.e. the fundamental frequency, the third order harmonic component and the harmonic distortion in percentage. Block diagram of fig.3 shows the step by step procedure of operation. TOOL USED FOR SIMULATION -Professional 7 VII. RESULTS & CONCLUSION Fundamental frequency 3rd order harmonics harmonic distortion 234V 20V 8.7% Proteus
Frequency ,Phase, and Amplitude Tracking in Aircraft Electrical Systems,” [3] M. Karimi-Ghartemani and A.K. Ziarani, “A nonlinear timefrequency analysis method,” IEEE Trans. Signal Process., vol. 52, no. 6, Jun. 2004, pp. 1585–1595 [4] Jovan M. KNEŽEVIĆ1, Vladimir A. KATIĆ2 , “The Hybrid Method for On-line Harmonic Analysis,” 1Brose Fahrzeugteile GmbH & CO. Kommanditgesellschaft, Hallstadt, D-96103, Germany 2University of Novi Sad, Faculty of Technical Sciences, Novi Sad,21000, Serbia. [5] Aboul-Seoud, A.K.; El-Badawy, E.-S.A.; Mokhtar, A.; El-Masry, W.; El-Barbry, M.; Hafez, A.E.-D.S.;, “A simple 8-bit digital microcontroller implementation for chaotic sequence generation ,” National Radio Science Conference (NRSC), 2011 28th Digital Object Identifier: 10.1109/NRSC.2011.5873617 Publication Year: 2011 , Page(s): 1 – 9
As a matter of fact, the frequency analysis of discrete time signals is conveniently performed on a digital signal processor which in our case is designed and programmed in an embedded microcontroller. The project approach applies a computational convenient representation of discrete time signals known as Discrete Fourier transform to estimate the fundamental and third harmonic frequency of the signal. The computation of this ratio can identify the distortion in ac voltage while being drawn through different nonlinear devices so that after detecting the harmonic component we can improve the quality of an ac waveform. REFERENCES
[1] Isamu Yamamoto, Keiju Matsui, Kazuo Tsuboi , “A Harmonic meter using a phase- lock- loop ,” Chubu University, Dep. Electrical Eng. Kasugai ,487-8501, Japan(2001). E-Mail:[email protected]. [2] Francesco Cupertino, Member, IEEE, Elisabetta Lavopa, Pericle Zanchetta, Member, IEEE, Mark Sumner, Senior Member, IEEE, and Luigi Salvatore, “Running DFT-Based PLL Algorithm for
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Harmonic Detection using Microcontroller
Jaipreet Kaur Bhatti, Deepak Asati
Abstract--- Harmonic distortion meter is an instruments that measure harmonic distortion or phase position or simply has been designed for measuring the quality of AC supply. Harmonic distortion is a common problem in power systems, data processing equipment and adjustable speed drives. In communications applications, harmonic distortion meters are used to determine when the original frequency transmitted is split into multiple frequencies due to irregularities in the line. Harmonic distortion meters are important for analyzing the quality of power coming into a system and for determining what is causing the problem. Keywords--- DFT, microcontroller (ATMEGA16), Harmonic detection.
This paper is organized as follows: Section 1- Introduction and need of harmonics detection. Section 2- Explains Solution based on phase lock loop and its drawbacks. Section 3- Detection of harmonics using DFT and its advantages. Section 4- Hardware and circuit required for its working. Section 5- Gives the conclusions of the present work. II. PHASE LOCK LOOP & ITS DRAWBACKS The various harmonics in a power system are typically measured with a heterodyne receiver if we are using analog methods or by a FFT (Fast Fourier Transform) when digital methods are being used. The harmonics can be analyzed over a wide range of frequencies by means of these methods. However, since the circuit configurations that are needed can become very complicated, the equipment tends to be too expensive for practical use. This paper presents a novel harmonic meter using a PLL (Phase Locked Loop) circuit. By means of the phase feedback loop, a reference sinusoidal wave is locked on to the input signal along with the harmonics that we wish to measure, and hence the corresponding harmonic component in the input signal is easily detected. The effectiveness of the proposed harmonic meter is confirmed by experiment. Disadvantage comes to play in case of wrong manual tuning for detection of sinusoidal signal for desired frequency. Multiple frequencies just in case of 2 nd order and 3rd order require use of separate phase detectors which makes it complex and needs fine adjustments. In total harmonics distortion computation a separate logic is required hence hardwired circuit here in inapplicable in case of reading manipulations and processing. In this idea we are using a microcontroller which enrich the above condition by making soft coding approach and hence can be used in performing discrete Fourier transform results. An 8 bit RISC microcontroller ATMEGA16 can provide us 16MIPS of processing power using 16Mhz of clock crystal, along with that it contains a 8 channel 10 bit ADC which suits our application. III. DETECTION OF HARMONICS USING DFT Proposed methodology: In the proposed method a harmonic meter using a microcontroller is designed . The meter is built with a microcontroller and the full wave rectifier front-end circuit. The input signal to the 10-bit ADC is full wave rectified.
I. INTRODUCTION This thesis basically employs a device which shows a method for finding the amplitude of the fundamental frequency and the 3rd harmonic of AC voltage signals. The technique is consummate for identifying the distortions in the AC voltages .For example electronic devices having nonlinear characteristics being used at home and office are mostly computer based equipment with a low power factor switch mode power supply. These power supply sections include charging capacitors which draw current at peak voltages. Thus for a given feeder having finite impedance there can be a voltage drop near the peak voltage resulting in flattened top distortion of AC voltage. To identify these distortions we analyze the output signal in the frequency domain by utilizing efficient digital processing techniques. In this thesis a feature based method is developed to efficiently perform the frequency synthesis and further perform correlation between the output signal and a varying sinusoid signal
Fig. 1: Flattened top AC voltage caused by a low power factor switch mode power supply.
106
ISSN 2249-6343 International Journal of Computer Technology and Electronics Engineering (IJCTEE) Volume 2, Issue 3, June 2012 The software performs DFT calculation finding the amplitude of the fundamental frequency and the 3rd harmonic. The distortion is computed by the ratio of the amplitude of the 3rd harmonic to the fundamental frequency. The effectiveness of the proposed harmonic meter is confirmed by experiment. A. Total Harmonic Distortion, THD To measure the wave shape distortion, we use the quantity of the Total Harmonic Distortion, THD (equation 1). THD is the ratio of the power of harmonic components to the power of fundamental frequency. Our concern is the voltage distortion we can just find the sum of the RMS of the harmonic components, Vn and the RMS of the fundamental frequency, V1.
Advantage of DFT:- Since the AC signal has symmetry between positive cycle and negative cycle. We can find the harmonic component by capturing only half cycle. This reduces computing time by half.
THD =
*100, n=2, 3….N
Most of the harmonic problem is caused by the 3rd component. Since the 3rd harmonic is the 2nd highest energy from the fundamental component. So we interest to find only the 3rd harmonic distortion using equation 2. HD =
*100
Discrete Fourier Transform, DFT We may decompose the periodic waveform, f(t) into the summation of a number of sinusoids waveform easily using the Discrete Fourier Transform (equation 3). A0 is the amplitude of DC components. For AC voltage waveform, A0 is zero.
Fig. 2: The 32-point sample half period AC input signal
IV. BLOCK DIAGRAM OF PROPOSED DESIGN
Bridge Rectifier Amplitude of each harmonics-
Xin [32] Capture 32 samples. Determining Bv & Cv for 1st &3rd Harmonics.
The amplitude for each harmonic can be computed from equation 4.
The coefficients Bv and Cv for each harmonic are easily calculated by multiplying the corresponding sine wave and cosine wave to the input signal respectively (equation 5 and 6). Where delta t is time between sample, T is period, Vy is input signal. 107
Coefficien 3rd order Result t Bv & Cv THD= on for 1st&3rd (V3/V1)* LCD order will be 100 harmonics shown. . Fig.3. Block diagram of proposed design.
ISSN 2249-6343 International Journal of Computer Technology and Electronics Engineering (IJCTEE) Volume 2, Issue 3, June 2012 High quality power supply has a perfect sinusoidal signal with constant frequency and amplitude. On the other hand, the use of nonlinear devices and the time-varying loads in the electric power system is widespread and is growing with even bigger pace. Such devices and loads are consuming distorted current from the power system grid.To preserve high power quality, the most important indices, such as harmonics, sags, swells, short interruptions, imbalances, and flickers, ideally have to be eliminated. Inrecent years, researchers have been developing tools for accurate power quality analysis, as well as devices for mitigation of power supply imperfections. If an electrical quantity is made to vary directly in proportion to this value (temperature etc) then what we have is Analogue signal. Now we have we have brought a physical quantity into electrical domain. The electrical quantity in most case is voltage. To bring this quantity into digital domain we have to convert this into digital form. For this a ADC or analog to digital converter is needed. Most modern MCU including AVRs has an ADC on chip. An ADC converts an input voltage into a number. An ADC has a resolution. A 10 Bit ADC has a range of 0-1023. (2^10=1024) The ADC also has a Reference voltage (ARef). When input voltage is GND the output is 0 and when input voltage is equal to ARef the output is 1023. So the input range is 0-ARef and digital output is 0-1023.
V. HARDWARE AND CIRCUIT DESIGN OF PROPOSED METER
Fig.4 Harmonic detection meter using microcontroller
108
ISSN 2249-6343 International Journal of Computer Technology and Electronics Engineering (IJCTEE) Volume 2, Issue 3, June 2012 VI. CIRCUIT DESCRIPTION From the above design, first of all input signal is applied to the circuit which is 220Vac. The bridge rectifier rectifies the ac input to the pulsating dc, which would further made constant 5V with the help of filter-capacitor arrangement and voltage stabilizer so that any change in ac would not proportionally change dc. The dc output is given to the variable resistor which is used to select the voltage which in case of PLL cannot be done because it needs a separate phase detector for different frequencies (voltages) this is then applied to the digital oscilloscope which shows the total coverage of half cycle by capturing 32 samples. The output from this is given to the microcontroller where the software performs the DFT calculations and the final results are displayed on the LCD i.e. the fundamental frequency, the third order harmonic component and the harmonic distortion in percentage. Block diagram of fig.3 shows the step by step procedure of operation. TOOL USED FOR SIMULATION -Professional 7 VII. RESULTS & CONCLUSION Fundamental frequency 3rd order harmonics harmonic distortion 234V 20V 8.7% Proteus
Frequency ,Phase, and Amplitude Tracking in Aircraft Electrical Systems,” [3] M. Karimi-Ghartemani and A.K. Ziarani, “A nonlinear timefrequency analysis method,” IEEE Trans. Signal Process., vol. 52, no. 6, Jun. 2004, pp. 1585–1595 [4] Jovan M. KNEŽEVIĆ1, Vladimir A. KATIĆ2 , “The Hybrid Method for On-line Harmonic Analysis,” 1Brose Fahrzeugteile GmbH & CO. Kommanditgesellschaft, Hallstadt, D-96103, Germany 2University of Novi Sad, Faculty of Technical Sciences, Novi Sad,21000, Serbia. [5] Aboul-Seoud, A.K.; El-Badawy, E.-S.A.; Mokhtar, A.; El-Masry, W.; El-Barbry, M.; Hafez, A.E.-D.S.;, “A simple 8-bit digital microcontroller implementation for chaotic sequence generation ,” National Radio Science Conference (NRSC), 2011 28th Digital Object Identifier: 10.1109/NRSC.2011.5873617 Publication Year: 2011 , Page(s): 1 – 9
As a matter of fact, the frequency analysis of discrete time signals is conveniently performed on a digital signal processor which in our case is designed and programmed in an embedded microcontroller. The project approach applies a computational convenient representation of discrete time signals known as Discrete Fourier transform to estimate the fundamental and third harmonic frequency of the signal. The computation of this ratio can identify the distortion in ac voltage while being drawn through different nonlinear devices so that after detecting the harmonic component we can improve the quality of an ac waveform. REFERENCES
[1] Isamu Yamamoto, Keiju Matsui, Kazuo Tsuboi , “A Harmonic meter using a phase- lock- loop ,” Chubu University, Dep. Electrical Eng. Kasugai ,487-8501, Japan(2001). E-Mail:[email protected]. [2] Francesco Cupertino, Member, IEEE, Elisabetta Lavopa, Pericle Zanchetta, Member, IEEE, Mark Sumner, Senior Member, IEEE, and Luigi Salvatore, “Running DFT-Based PLL Algorithm for
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