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- 1. International Journal of Electrical and Electronics Engineering Research (IJEEER) ISSN 2250-155X Vol. 3, Issue 2, Jun 2013, 107-114 © TJPRC Pvt. Ltd. A HYBRID ACTIVE POWER FILTER WITH CONTROL SCHEME FOR THE EFFECTIVE COMPENSATION OF INDUSTRIAL POWER SUPPLY KALPANA. K1, MADHUMATHI. M. A2 & MADHUMITHA M3 1 Assistant Professor/EEE, Periyar Maniammai University, Vallam, Tanjore, Tamil Nadu, India 2 Student/IV Year-EEE, Periyar Maniammai University, Vallam, Tanjore, Tamil Nadu, India 3 Final Year – ECE, Easwari Engineering College, Chennai, Tamil Nadu, India ABSTRACT Harmonic currents on the power system can distort the line voltage and lead to several adverse effects including equipment overheating, the malfunction of solid-state equipment and interference with communication systems. In this project I have developed a simple control scheme for hybrid active power filter which is formed by connecting the passive inductance and capacitance filter with the active power filter for compensating the non-linear load. This hybrid active power filter contains the compensation characteristics of both resonant passive and active filters. This system has the ability to compensate both displacement power factor and harmonic current simultaneously. The hybrid active power provides better performances in the high voltage non linear load compensation. KEYWORDS: Non Linear Load, Hybrid, Filter, Compensation, Control INTRODUCTION The extensive application of non linear loads in domestic, commercial, industrial sector causes power quality problems such as harmonic current, poor power factor, unbalance, voltage sag and swell, reactive power burden etc. Some of the examples of nonlinear loads are uncontrolled and controlled rectifiers; variable speed drives both Alternating Current and Direct Current, uninterrupted power supplies, arc furnaces, electronic ballast, programmable logic controllers etc. All these devices are economical, flexible and energy efficient, they may deteriorate power quality by injecting harmonic current into the power system and consuming excessive reactive power, as they are drawing non-sinusoidal current from utilities. These phenomena can cause many problems such as resonance, excessive neutral currents, low power factor etc. In a modern power system, increasing of loads and non-linear equipments have been demanding the compensation of the disturbances caused for them. These nonlinear loads may cause poor power factor and high degree of harmonics. Active power filter technology is the most efficient way to compensate for reactive power and cancel lower harmonics generated by nonlinear loads. The passive tuned filter can be used to provide a low impedance path to ground for harmonic signal. Thus, for eliminating multiple harmonic components, individual filters are installed. This makes the design and coordination of passive filters complicated. Also the possibility of series harmonics, large size etc. makes the passive filter less attractive. Hence we go for hybrid active power filter which has combined characteristics of both active and passive power filters. NEED FOR POWER COMPENSATION The major harmonic sources include PC, television, and computer power supplies to the power converters used in industries. All these products use some type of power conversion, such as ac to ac, ac to dc, dc to dc, or dc to ac,
- 2. 108 Kalpana. K, Madhumathi. M. A & Madhumitha M interestingly these new generation equipments are more sensitive to power quality problems such as harmonics. Secondly these harmonics creates various adverse effects in the power system. More over the customers are becoming more and more aware about the financial impacts of the power quality problems such as harmonics, reactive power, transients etc. Hence it becomes essential for the customers as well as the utilities to limit the harmonic distortion and reactive power consumption to minimum. One of the solutions to limit the harmonic distortion and power factor correction is the use of filters. HYBRID ACTIVE POWER FILTER The hybrid active power filter is nothing but the series combination of active power filter and the passive elements. The harmonics in the power system can be removed in the following ways. By providing a low impedance path to ground for harmonic signal. By injecting compensating signals which are in phase opposition with the harmonic signal present in the system. o For the first one we can use passive tuned filter and for the latter active filter can be used. o Active filter is connected in series with the passive filter through a coupling transformer. Figure 1: PWM VSI Unit Figure 2: Hybrid Active Power Filter ACTIVE POWER FILTER The basic concept of active power filter is that, a harmonic current or voltage can be eliminated by injecting the same harmonic component of current or voltage with equal magnitude and opposite phase. This concept can be implemented using power electronics switches such as IGBT’s, & MOSFET’s and advanced microcontrollers. Apart from compensating the harmonics, the active power filters can supply the reactive power required for the load. Thus, an active power filter can compensate for a wide range of harmonic components and at the same time improve the power factor of the current. The basic functions of an active power filter can be summarized as, Harmonic compensation, harmonic isolation, harmonic damping and harmonic Termination.
- 3. A Hybrid Active Power Filter with Control Scheme for the Effective Compensation of Industrial Power Supply Reactive power compensation. 109 Negative sequence current/voltage compensation. The passive filter is the combination of resistance, inductance, and capacitance element and tuned to control the particular harmonic frequencies. PROPOSED SYSTEM Figure 3: Block Diagram of the Proposed Filter Unit In this paper we deal with the reactive power compensation using PWMVSI active filter with the shunt passive filter to eliminate the harmonics. Voltage Source Inverter IRF840 MOSFETS are used here (figure.4). Inverter Used here is a voltage source inverter, which is used to switch the supply from the capacitor to the distribution line. It also consists of a diode connected anti parallel to the MOSFET inside will charge the capacitor with the supply voltage. Switching speed depends on the pulse produced by the dsPIC microcontroller based on the values obtained for the compensation current. Its turn off time is 90ns. The voltage that is stored in the capacitor is discharged to the supply line through this inverter circuit. The capacitor will in turn get charged via the diode connected anti parallel to the MOSFET inside the chip. Due to non linear load the current wave form will got distorted by harmonics, so to eliminate the harmonic current we are injecting the same value of current with the help of an inverter and the dc storage capacitor. The switching pulses to the MOSFET gate is provided by the dsPIC30F2010 on calculating the compensator current. Then it is fed to the gate as pulses through gate driver circuit. Each diagonal pair conducts only for one half cycles. That is MOSFET S1 and S2 for positive half cycle and S3 and S4 for negative half cycle.
- 4. 110 Kalpana. K, Madhumathi. M. A & Madhumitha M Figure 4: Voltage Source Inverter When the MOSFET is on there is line current injecting to the source and vice versa. We need to know the load current, line current to determine the injecting current so that it is compensated. This current can be derived from the following equations.
- 5. A Hybrid Active Power Filter with Control Scheme for the Effective Compensation of Industrial Power Supply 111 The voltage equation before non linear load (ac load) is, Vt(t) = vm1 sin (t) The voltage and current equation after adding dc load is, Vt(t)= vdc + vm1sin(t+φv1)+ vm2sin(2t+φv2)+ vm3sin(3t+φv3)+ iL(t)= idc +im1sin(t+φi1)+im2sin(2t+φi2)+ im3sin(3t+φi3)+ …+vmnsin(nt+φvn) …imnsin (nt+φin) The source power can be calculated as, Ps = [vm1imscosφs] / 2 With that the average power can be calculated as the product of vt(t) and iL(t), Plavg= vdcidc+ [vm1im1cosφ1] / 2+ vm2im2cosφ2] / 2+ [vm3im3cosφ3] / 2 +… [vmnimncosφn] / 2 Due to the VSI circuit the dc link capacitor acts as a load. Hence some of the power will be lost in the capacitor. It is obtained by providing PI control loop. Ploss= kp . ev + ki evdt where, kp = gain of proportional controller; ki = gain of integral controller; error voltage, ev = vref - vact The maximum value of source current can be calculated as, ims = 2[Plavg+Ploss] / (vm1cosφs) The above equation can be reduced as, is(t) = imssin(t-φs) With the load current and the fundamental current, the injecting current can be found out as, ic*(t) = iL(t) – is(t) Hence by injecting this compensator current into the line, the affected voltage regulation due to harmonic distortion can be eliminated. Filtering is the most common signal conditioning function, as usually mot all the signal frequency spectrum contains valid data. The common example is 50 Hz AC power line, present in most environments, which will produce noise if amplified. As we are using non linear loads that is both ac and dc loads the load current will be distorted. This in turn affects the supply voltage. This will end by providing multiple zero crossings at the voltage waveforms. So in order to find the accurate amount of magnitude of filter current and its phase angle, we need to know whether the current is lagging or leading. For that we go for synchronous circuit. It does consist of two low pass filter circuits; all pass filters and a z ero crossing circuit. The microcontroller dsPIC30F2010 is used for the computation of filter current and control of the active power filter. The processor has 40MHz clock frequency with an inbuilt analog to digital converter. The ADC is of 10 bit with an input voltage level 0-3V.
- 6. 112 Kalpana. K, Madhumathi. M. A & Madhumitha M The analogue to digital converter of the dsPIC30F2010 accepts only the signal in the range of 0-3V. Hence, the bipolar ±5V output of the sensors is processed to the required voltage level using the signal conditioning circuit. The circuit consists of three stages, those are Attenuator Summer Precision rectifier An attenuator has an attenuation ration of 0.3. Therefore, output of first amplifier is within the range of ±1.5 V. A level shifter is used to shift the signal such that the output is always a uni-polar signal. In the second stage, the bipolar signal of ±1.5 V is shifted by +1.5 V. Thus, the output of second stage amplifier is 0-3 V. The reference of -1.5 V is generated using an adjustable negative voltage regulator (LM337) the input to this regulator is -15 V, which is drawn from the supply of OPAMPs (±15 V). The final stage uses a precision rectifier and a zener diode. The precision rectifier block any negative voltage and zener is used to clip any voltage higher than 3.3V. Hence the output signal obtained after the signal conditioning circuit is always a uni-polar signal of value 0-3V which is compatible with the ADC of dsPIC30F2010. The output from the signal conditioning circuit is fed to the dsPIC micro controller with which the controller will calculate the compensator current. Thus the injecting current is calculated and the VSI is triggered in such a way to compensate the harmonic current. EXPERIMENTAL RESULTS Input Current The input current is sinusoidal waveforms with much less distortion. Figure 5: Input Current Output Current (Uncompensated) The output current will be sinusoidal with more harmonics.
- 7. A Hybrid Active Power Filter with Control Scheme for the Effective Compensation of Industrial Power Supply 113 Figure 6: Uncompensated Output Current Input Voltage The input voltage as shown below is a sinusoidal waveform. Figure 7: Input Voltage Compensated Current From Passive Filter The passive filter give the output with much limited harmonics.but it is not a pure sine waveform. Figure 8: Compensated Current Output from the Passive Filter Compensated Current From Hybrid Active Power Filter The combination of passive filter with the shunt active power filter will produce the compensated current (shown in light shade figure.) and the dark shade shows the output from the HAPF.
- 8. 114 Kalpana. K, Madhumathi. M. A & Madhumitha M Figure 9: Compensated Current Output from the HAPF CONCLUSIONS The HAPF is considered effectual means for harmonics restraint and reactive power compensation in the high capacity power filter. In this paper, based on the filtering principle and parameters, the simulation model is established by MATLAB/Simulink. The simulation conclusion can prove the better performance of the HAPF topology and the control method. REFERENCES 1. “A New Hybrid Active Power Filter for Harmonic Suppression and Reactive Power Compensation”, ZHAO Wei, LUO An, PENG Jianchun, DENG Xia, PENG ke, CICED2008. 2. “An Analysis And Simulation of Shunt Hybrid Active Power Filter”, MA Yue, ZHU Ling in Proceeding of International Conference on Electrical Machines and Systems 2007. 3. “A Single-Phase Hybrid Active Power Filter using Extension p-q Theorem for Photovoltaic Application”, P. C. Tan and Z. Salam and A. Jusoh, IEEE PEDS 2005. 4. “Design and Implementation of A Shunt Active Power Filter with Reduced Dc Link Voltage”, O. Ucak, I. Kocabas, A. Terciyanli, 2007. 5. “Design and Implementation of Hybrid Active Power Filter”, G.Nageswara Rao, Dr.K.Chandra Sekhar, Dr. P.Sangameswara Raju, International Journal of Computer Applications (0975 – 8887) Volume 8– No.10, October 2010. 6. “Enhancement of Power quality using active power filter”, G.Ravindra, P.Ramesh, Dr.T.Devaraju, International Journal of Scientific and Research Publications, Volume 2, Issue 5, May 2012. 7. “Enhancement of Power Quality using active power filter in a Medium-Voltage Distribution Network switching loads”, M. Chandra Sekhar, B. Kiran Babu, International Journal of Modern Engineering Research , Vol.2, Issue.2, Mar-Apr 2012. 8. “New Control Strategy To Improve Power Quality Using A Hybrid Power Filter”, S. P. Litrán, P. Salmerón, R. S. Herrera, and J. R. Vázquez, 2008. 9. “Research on Power Factor Correction Boost Inductor Design Optimization – Efficiency vs. Power Density”, Qingnan Li, Michael A. E. Andersen, and Ole C. Thomsen, 2011.

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