FOUR-LEG SHUNT ACTIVE POWER FILTER FOR POWER QUALITY IMPROVEMENT USING PI AND FUZZY CONTROLLERS

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1 FOUR-LEG SHUNT ACTIVE POWER FILTER FOR POWER QUALITY IMPROVEMENT USING PI AND FUZZY CONTROLLERS V.Parimala, Dr.D.GaneshKumar, V.Renugadevi Abstract This paper presents reduction of line current harmonics using Four-leg shunt active power filter with balanced and unbalanced load condition for three phase four wire shunt active power filter. The synchronous reference frame (SRF) method is used to extracting reference current for four-leg shunt active filter. The Hysteresis current controller (HCC) is used to generate gate pulses and applied VSI based four leg shunt active power filter. Two control methods were used for four-leg shunt active power filter one is PI and other one is Fuzzy logic controller. The PI and Fuzzy logic controller to control, four leg shunt active power filter to compensate line current harmonics and neutral current compensation to improve power quality for three-phase four wire system. The main aim of this paper is to reduce the total harmonic distortion (THD) in the line current and neutral current compensation. The MATLAB/Simulink environment is used to model for above four leg topology of shunt active power filter. Index Terms Shunt active power filter, SRF method, Hysteresis current controller, PI and Fuzzy logic controller 1. INTRODUCTION Modern days, three phase four wire distribution power system has been broadly employed in residential and office buildings, manufacturing facilities, schools, etc., to supply low level voltage. The typical loads connected to the three phase four wire power system may be reasonable three phase non-linear loads such as motor drives, power electronics loads, large Uninterruptible power supplies or single phase non-linear loads such as switch-mode power supplies in computer equipment, inverter air conditioners and other power electronic related facilities. The common of these loads have a nonlinear input or unbalanced characteristic, which may cause two problems such as high input current harmonics and extreme neutral current. The survival of current harmonics in power systems increases losses in the lines, decreases the power factor and causes timing errors in sensitive electronic equipment. The harmonic currents produced by balanced three phase non-linear loads are positive-sequence harmonics and negative-sequence Harmonics. Nevertheless harmonic currents produced by single phase non-linear loads which are connected phase to neutral in three phase four wire system are third order zero-sequence harmonics. Two primary approaches for humanizing power quality are passive filter and active filter. Passive filters are broadly worn to eliminate harmonics in power system for its simplicity and low cost still, passive filters have a number of drawbacks such as large size, tuning and risk of resonance problems. Now, the 4-leg active filters have confirmed to be very effective to solve the troubles of current harmonics, reactive power, unbalanced load current and excessive neutral current simultaneously in 3-phase 4-wire system, and can be a much improved solution than conventional passive filters. The Synchronous Reference Frame (SRF) theory [7] was generally applied to calculate the compensating currents assume ideal mains voltages. But, mains voltage may be unbalanced and/or distorted in industrial systems [1]. So, the Four leg APF using the p-q theory does not provide good performance.for humanizing the APF performance under non-ideal mains voltage conditions, various improved methods based on Instantaneous reactive power theory have been future even though superior results have been achieved. However, Instantaneous reactive power methods for harmonic detection in the three phase four wire systems need phase-locked-loop (PLL), low-pass filter and the multiple coordinate transformation[4].nevertheless, the conventional PI controller was used for the generation of a reference current template. The PI controller requires exact linear mathematical models, which are not easy to attain and fails to perform satisfactorily under parameter variations, nonlinearity, load disturbance, etc. Recently, Fuzzy logic controllers (FLC) have generate a good deal of interest in certain applications[7] The benefit of Fuzzy logic controller over conventional controllers are that they do not need accurate mathematical model can work with imprecise inputs, can hold non-linearity, and are more strong than conventional controller. In this work two control methods are used, one is PI and another one is Fuzzy logic controller (FLC) of shunt active power filter for the line current harmonics and neutral current compensation of a nonlinear load. The synchronous reference frame theory is used for generate reference current in four legs shunt active filter and hysteresis controller is used to obtaining a gate pulse for shunt active power filter. A design criterion is described in the selection of power circuit components. Both the control schemed is compared and performance of both the controllers the fuzzy controller has a less line current harmonics THD values compared to PI controller A detailed simulation program of the schemes is developed to predict the performance for different conditions and Simulink models also has been developed for the same for different parameters and operating conditions. Parimala.V Assistant Professor (SG), Department of PG-ES, P.A College of Engineering and Technology, Pollachi. Dr.GaneshKumar.D, Professor, Department of EEE, P.A College of Engineering and Technology, Pollachi. Renugadevi.V,Department of PG-ES, P.A College Of Engineering and Technology, Pollachi Fig.1.1.Four-leg shunt APF with non-linear loads 417

2 2. SHUNT ACTIVE FILTER 2.1. Introduction: In this case the shunt active power filter operates as a current source injecting the harmonic components generate by the load but phase-shifted by 180. The main idea of the 4-leg APF is to compensate harmonics, reactive power, and neutral current and unbalanced loads.in 3-phase 4-wire systems, two kinds of VSI topologies since 4-leg inverter and three leg inverter (split capacitor) are used. The 4-leg inverter employed 1-leg specially to compensate neutral current. Fig 1 shows the basic compensation principle of the shunt APF. A shunt APF is designed to be connected in parallel with the load, to detect its harmonic current and to inject into the system a compensating current, equal with the load harmonic current. Therefore, the current strained from the power system at the coupling point of the filter will result in sinusoidal Basic compensation principles: The active power filter is controlled to deliver the compensating current if from/to the load to nullify the current harmonics on the AC side and reactive power flow from/to the source there by making the source current in phase with source voltage. Figure 3.2 shows the basic compensation principle of the active power filter and it serve as an energy storage element to bring the real power difference between load and source during the transient period. When the load condition change the real power balance between the mains and the load will be concerned. This real power distinction is to be compensated by the DC capacitor. These adjust the DC capacitor voltage away from the reference voltage. In categorize to keep suitable operation or the active filter, the peak value of the orientation, source current must be familiar to proportionally alter the real power drawn from the source. These real powers charged/discharged by the capacitor compensate the real power dissimilarity between the consumed by the load and that of supplied by the source. If the DC capacitor voltage is improved and attains the reference voltage, the real power absolute from the source is imaginary to be equivalent to that consumed by the load again. = = - (1) - (2) The currents and along with are utilized to make reference filter currents and in d-q coordinates, followed by inverse Park transformation giving away the compensation currents, in the four wires as describe in (2) and (3). - + abc to dqo transform ation (rotating reference frame) LPF LPF PI /FUZZY Fig.3.1Reference current generation dqo to abc transf orma tion = - (3) Fig.2.1.Basic configuration of shunt active filter. 3. CONTROL STATERGIES 3.1. SYNCHRONOUS REFERENCE FRAME (d-q) THEORY In Fig.3.1, the whole reference current generation scheme has been illustrated. The load currents nd are track upon which Park s transformation is performed to obtain corresponding d-q axes currents and as given in (3.1), where ɷ is the rotational speed of synchronously rotating d-q frame. According to - control strategy, only the average value of d-axis component of load current should be strained from supply. Here and indicate the fundamental frequency component of and. The oscillate components and, i.e and are filtered out using low-pass filter. = (4) The reference signals thus obtained are compared with the actual compensating filter currents in a hysteresis comparator, where the real current is forced to follow the reference and provides instantaneous compensation by the APF on account of its easy implementation and quick overcome over fast current transitions. Accordingly provides switching signals to trigger the IGBTs inside the inverter. Ultimately, the filter provides needed compensation for harmonics in the source current and reactive power unbalance in the system [11]. One of the compensation of this method is that angle θ is calculated straight from main voltages and thus makes this method frequency independent by avoiding the PLL in the control circuit. Accordingly synchronizing problem. With balanced and unbalanced conditions of main voltages are also evaded. Thus d-q achieves large frequency operating limit essentially by the cut-off frequency of voltage source inverter HYSTERESIS CURRENT CONTROLLER Hysteresis current controller derives the switching signals of the inverter power switches (IGBTs).The current controllers of the three phases are considered to operate separately [7]. Each current 418

3 controller determines the switching signals to the inverter bridge.the switching logic for phase A is formulated as follows If ON. If OFF - HB upper switch is OFF and lower switch is upper switch is ON and lower switch is In an identical manner, the switching logic for devices in phase B and C are derived. The switches are restricted asynchronously to ramp the current through the inductor up and down so that it follows the reference. The current ramping up and down linking the two limits is illustrated in fig.3.3.when the current during the inductor surpasses the upper hysteresis limit a negative voltage is applied by the inverter to the inductor. The beginning the current in the inductor to reduce. Once the current reaches the lower hysteresis limit a positive voltage is applied by the inverter to the inductor and this causes the current to boost and the cycle repeats. experience or knowledge database. Firstly, input voltage Vdc and the input reference voltage Vdc-ref have been placed of the angular velocity to be the input variables of the fuzzy logic controller. Then the output variable of the fuzzy logic controller is presented by the control Current Imax. To change these numerical variables into linguistic variables, the subsequent seven fuzzy levels or sets are chosen as: NB (negative big), NM (negative medium), NS (negative small), ZE (zero), PS (positive small), PM (positive medium), and PB (positive big) as shown in 3.4(a). The fuzzy controller is characterized as follows: 1) Seven fuzzy sets for each input and output; 2) Fuzzification using continuous universe of discourse; 3) Implication using Mamdani's min operator; 4) De-fuzzification using the centroid method. ( a) Figure.3.2.Hysteresis current waveform (b) 3.3. PI controller: The control scheme consists of a PI controller, a limiter, and a three phase sine wave generator for the reference current and switching signal generation. The real value of the reference currents is estimated by regulating the DC link voltage. The real capacitor voltage is compared with a set reference value[7] The error signal is then processed through a PI controller, which supply to the zero steady error in tracking the reference current signal. The output of the PI controller is measured as the peak value of the supply current (Imax), which is composed of two components: (a) the fundamental active power component of the load current, and (b) the loss component of the APF; to maintain the average capacitor voltage at a constant value. The peak value of the current (I max ) so attained, is multiplied by the unit sine vectors in phase with the respective source voltages to obtain the reference compensating currents. These estimated reference currents (I sa *, I sb *, and I sc *,I sn, I sn *) and the sensed actual currents ( I sa, I sb, and I sc, I sn ) are compared to a hysteresis controller, which gives the error signal for the modulation technique. This error signal decides the operation of the inverter switches. (c) Fig.3.3.(a) Input Vdc normalized membership function; (b) Input Vdc-ref Normalized Membership Function; (c) Output Imax Normalized Membership Function. 4. SIMULATION RESULTS: The simulation is carried out with three phase four wire system with non-linear load. Here the diode rectifier is used as non-linear load. The Fig-4 shows the circuit diagram without any filter or controller circuit. From this simulation, source current, voltages are taken as the output. The THD value of source current under balanced and unbalanced source condition. The THD value is high because we won t use any controller in this circuit. 3.4 Fuzzy controller: The control scheme consists of Fuzzy controller, limiter and three phase sine wave generator for the reference current generation and generation of switching signals. The crest value of reference currents is estimated by regulating the DC link voltage. The real capacitor voltage is compared with a set reference value. The error signal is then processed during a Fuzzy controller, which supply to zero steady error in tracking the reference current signal [10]. A fuzzy controller converts a linguistic control strategy into an automatic control strategy, and fuzzy rules are constructed by expert Fig 4.1.Simulation for open loop system 419

capacitance(cdc) link Single phase Diode Rectifier(RLC load) Values 315Vrms 50Hz 10mΩ,50µH 12Ω,20mH 1500 µf 15Ω,1mH,470µF AC filter(rc,lc),(rf,lf) side (0.

1(b)waveforms of source current in open loopsystem The simulation results of source current, source voltage and load current are shown in Fig-10 to Fig-11

Waveforms of neutral current in open loop system. Fig.4.2.Simulation for PI controller Figure.4.1(d).

3 shows the closed loop system with PI controller and fuzzy controller along with the SRF (Synchronous Reference Frame) theory.

4 Table-1 System Parameter Figure.4.1(a)waveforms of source voltage in open loop system System Parameter Source voltage(vs) Source frequency(fs) Source impedance (Zs) Three phase Load (RL load) DC capacitance(cdc) link Single phase Diode Rectifier(RLC load) Values 315Vrms 50Hz 10mΩ,50µH 12Ω,20mH 1500 µf 15Ω,1mH,470µF AC filter(rc,lc),(rf,lf) side (0.1Ω,1mH),(2Ω,20µF) Figure.4.1(b)waveforms of source current in open loopsystem The simulation results of source current, source voltage and load current are shown in Fig-10 to Fig-11 respectively. Similar to open loop, the THD vlue of source current is shown under balanced and unbalanced conditions. Fig. 4.1(c).Waveforms of neutral current in open loop system. Fig.4.2.Simulation for PI controller Figure.4.1(d).FFT analysis of line current harmonics in open loop system The Fig-4.2 and 4.3 shows the closed loop system with PI controller and fuzzy controller along with the SRF (Synchronous Reference Frame) theory. Using this SRF theory three phase system is converted into two phases, and the reference current is generated from this. This reference current is given as reference value and the actual current is taken from the filter; these two are compared in the PI and fuzzy controller and the error signal is generated. This again gave as reference to the hysteresis controller to generate the gate signal to the filter switch. Hence, by turning on and off the devices the curren waveform has been improved. The system parameters are shown in Table-1 Figure.4.2 (a).waveforms of source voltage and source current under balance load using PI controller 420

Figure 4.3. Simulation diagram for fuzzy controller Fig.4.3(a).

5 Fig.4.2(b).Waveforms of DC link voltage and neutral current under balanced load using PI controller Figure.4.2 (c).fft analysis of line current harmonics under balanced load using PI controller Figure 4.3. Simulation diagram for fuzzy controller Fig.4.3(a).waveforms of source voltage and source current under balanced load using Fuzzy logic controller. Figure.4.2.(d).waveforms of source voltage and source current under unbalanced load using PI controller Fig.4.3(b).Waveforms of dc link voltage and neutral current under balanced load using Fuzzy logic controller Fig.4.2.(e).Waveforms of DC link voltage and neutral current under balanced load using PI controller Figure.4.2.(f).FFT analysis of line current under unbalanced load using PI controller Fig.4.3(c).FFT analysis of line current under balanced load using Fuzzy logic controller. 421

Even though both of the presented controllers are capable of compensating line current harmonics in 3 phase 4-wire systems, it can be seen that the Fuzzy logic controller has a better dynamic

6 5. CONCLUSION: Fig. 4.3(d).waveforms of source voltage and source current under unbalanced load using Fuzzy logic controller In the present paper two controllers are developed and verified for three phase four wire systems. Even though both of the presented controllers are capable of compensating line current harmonics in 3 phase 4-wire systems, it can be seen that the Fuzzy logic controller has a better dynamic performance than the conventional PI controller. Hysteresis current control is used for quick response for generating gate pulses. Additionally, in contrast to the different control strategies; the d-q method is used for obtaining the reference currents in the system. This is due to the verity that the angle θ is considered directly from the main voltage which enables an operation which is frequency independent. As a result, this technique avoids large number of synchronization problems. It can also be seen that the DC voltage regulation system is a stable and steady-state error free system. Thus with fuzzy logic and the (d-q) approach, a shunt active filter can be developed. Simulation results are presented to validate the performance of the shunt active filter. REFERENCES Fig.4.2.(e).Waveforms of dc link voltage and neutral current under unbalanced load using Fuzzy logic controller Fig.4.3(f).FFT analysis of line current in un balanced load under Fuzzy logic controller Table.2.Comparision of PI and Fuzzy Controller with balanced Controller and unbalanced load Source current Balanced condition Source current Unbalanced condition PI 2.70% 4.59% Fuzzy 1.34% 2.70% Table.3.Bar Chart For Shunt Active Power Filter 40 open loop Balanced 0 load Unbalanced load [1]. H.Akagi New trends in active filters for power conditioning, IEEE Trans. Ind. Appl.,Vol. 32, No. 6, pp , Nov./Dec [2]. F. Z. Peng, G. W. Ott Jr., D. J. Adams, Harmonic and reactive power compensation based on the generalized instantaneous reactive power theory for three-phase four-wire systems IEEE Trans. Power Electron.,Vol. 13, No. 5, Nov [3]. V. Soares, P. Verdelho, and G. Marques, Active power filter control circuit based on the instantaneous active and reactive current id iq method, IEEE Power Electronics Specialists Conference, Vol. 2, pp [4]. M Suresh, A. K. Panda, S. S. Patnaik, and S. Yellasiri, Comparison of two compensation control strategies for shunt active power filter in three-phase four-wire system, in Proc. IEEE PES Innovative Smart Grid Technologies, pp. 1-6, [5]. Fang Zheng Peng and Akagi, (1990), A New Approach to harmonic Compensation in Power Systems A combined System of Shunt Passive and Series Active Filters, IEEE Transactions on Industrial Applications, Vol. 26, pp [6]. Karuppanan P and Kamala kanta Mahapatra (2011), PI with Fuzzy Logic Controller based Active Power Line Condtioners - Asian Power Electronics, Vol. 5, pp [7]. Suresh Mikkili and Panda A.K. (2011), PI and fuzzy logic controller based 3-phase 4-wire shunt active filter for mitigation of current harmonics with Id Iq control strategy, Power Electronics (JPE), Vol.11, pp [8]. Suresh Mikkili, Panda A.K. (2012), Real-time Implementation of PI and Fuzzy logic controllers based shunt active filter control strategies for power quality improvement, ELSEVEIR:Electrical Power and Energy System, Vol.43, pp [9]. Saad S and Zellouma L. (2009), Fuzzy logic controller for three-level shunt active filter compensating harmonics and reactive power, Electronics Power System Research, Vol.79, pp [10]. S. K. Jain, P. Agrawal, and H. O. Gupta, Fuzzy logic controlled shunt active power Filter for power quality improvement, Proceedings of Institute of Electrical Engineers, Electrical Power Applications,vol. 149, no. 5, [11]. Rodriguez P, Candela J.I, Luna A and Asiminoaei L. (2009), Current harmonics cancellation in three-phase four-wire systems by using a four-branch star filtering Topology, IEEE Transactions on Power Electronics, Vol. 24,pp

7 [12]. Kirawanich P and O, Connell R.M. (2004), Fuzzy Logic Control of an Active Power Line Condioner, (2004), IEEE Transactions on Power Electronics, Vol. 19, pp Bibliography: V.Parimala has obtained her Bachelor of Engineering Degree in Electrical and Electronics Engineering from Madras University. Master s Degree in Power Electronics and Drives from Anna University. Currently working as Senior Assistant Professor. Her area of interests includes Power Quality, Power Electronics, Soft Computing Techniques and Virtual Instrumentation. Dr.D.Ganeshkumar has obtained his Bachelor of Engineering Degree in Electronics and Instrumentation and Master in Applied Electronics. He has received his PhD in Vibration Analysis using Virtual Instrumentation. Principle investigator for DST, Government of India funded project or Sound and Vibration Analysis in Electrical Machines using Virtual Instrumentation Techniques. His area of interest includes Process Monitoring and Control in Virtual Instrumentation Systems. V.RENUGADEVI has obtained her Bachelor s degree in Electrical and Electronics Engineering from Sri Eshwar College of engineering and currently pursuing her Master s degree in Power Electronics and Drives from P.A. College of Engineering and Technology. Her area of interest includes Power Quality and Drives. 423

REDUCED COMMON MODE NOISE AND LOWER ORDER HARMONIC IN PUSH PULL CONVERTER BY ACTIVE FILTER

REDUCED COMMON MODE NOISE AND LOWER ORDER HARMONIC IN PUSH PULL CONVERTER BY ACTIVE FILTER 1 Yogaprasad R, 2 Thangarasu.S ABSTRACT Power quality problems are major concern in the power systems. Harmonic