A Novel Fuzzy Variable-Band Hysteresis Current Controller For Shunt Active Power Filters
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A Novel Fuzzy Variable-Band Hysteresis Current Controller For Shunt Active Power Filters

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This paper presents a novel fuzzy control scheme ...

This paper presents a novel fuzzy control scheme
applied to shunt active power filters for harmonic and reactive
power compensation. A TSK type fuzzy logic controller is
proposed for APF reference current generation. To control
the maximum switching frequency of the converter within
limit a novel fuzzy hysteresis band current controller is used.
The band height, based on fuzzy control principle is changed
with the value of supply voltage and slope of reference current

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A Novel Fuzzy Variable-Band Hysteresis Current Controller For Shunt Active Power Filters A Novel Fuzzy Variable-Band Hysteresis Current Controller For Shunt Active Power Filters Document Transcript

  • ACEEE Int. J. on Control System and Instrumentation, Vol. 02, No. 02, June 2011 A Novel Fuzzy Variable-Band Hysteresis Current Controller For Shunt Active Power Filters D. A. Gadanayak, Dr. P. C. Panda, Senior Member IEEE, Electrical Engineering Department, Electrical Engineering Department, National Institute of Technology, National Institute of Technology, Rourkela, India Rourkela, India e-mail: godofsilicon@gmail.com e-mail: pcpanda@nitrkl.ac.inAbstract—This paper presents a novel fuzzy control scheme On the other hand, the intelligent control that is based onapplied to shunt active power filters for harmonic and reactive artificial intelligence can emulate the human thinking process.power compensation. A TSK type fuzzy logic controller is In the knowledge of expert that expressed in rules, fuzzy logicproposed for APF reference current generation. To control presents a slightly superior dynamic performance whenthe maximum switching frequency of the converter within compared with a more conventional scheme [11]. Thelimit a novel fuzzy hysteresis band current controller is used.The band height, based on fuzzy control principle is changed advantages of fuzzy logic controllers over conventionalwith the value of supply voltage and slope of reference current. controllers are that they do not require an accurate mathematical model, they can work with imprecise inputs, canKeywords—active power filter, nonlinear load, TSK type fuzzy handle non-linearity and they are more robust thancontroller, harmonics, indirect current control scheme conventional nonlinear controllers [8]. Among various PWM techniques, hysteresis fixed band current control is popularly I. INTRODUCTION used because of its simplicity of implementation. But this Power electronics based non-linear loads such as power technique has the disadvantage of uncontrolled frequency whichconverters in industrial applications, home appliances such as results in increased switching losses and excessive ripples inTV sets, personal computers etc. are increasing in a never before source current. However, an adaptive hysteresis band currentrapid rate. These loads are known as generators of current control technique can be programmed as a function of activeharmonics and tend to distort the supply current. They are also filter and supply parameters to minimize the influence of currentresponsible for low system efficiency, poor power factor, distortions on modulated waveform [10].disturbance to other consumers and interference in nearbycommunication networks. The concept of using active power II .PROPOSED CONTROL SCHEMEfilters in order to compensate harmonic currents and reactive Fig.1 shows the active power filter compensation systempower of locally connected non-linear loads has been so far and Fig.2 shows the schematic diagram of fuzzy control scheme.investigated and shown to be viable solution for power quality To implement the control algorithm in closed loop, the DC sideimprovement [1,2]. APFs, may be classified into pure active filters capacitor voltage is sensed and compared with a reference value.and hybrid active filters [4,5]. Hybrid APFs are primarily used for The error and integration of error are the inputs to the controller.harmonic mitigation. With fast switching, low power loss power A TSK type fuzzy controller is used for this purpose as it iselectronic devices and fast digital signal processing devices shown in [9] that a TSK type fuzzy controller not only reducesavailable at an affordable cost, it is feasible to embed a variety of the total harmonic distortion but also the settling time of DCfunctions into a pure APF to make it a power quality conditioner capacitor is significantly decreased. The output of the controller[6]. APF eliminates system harmonics by injecting a current to after a limit is the peak reference source current. This peak valuethe system that is equal to the load harmonics. Since the load is multiplied by unit vectors in phase with the source voltagesharmonics to be compensated may be very complex and to obtain the reference source currents. These reference currentschanging rapidly and randomly, APF has to respond quickly and actual source currents are given to a hysteresis-basedand work with very high control accuracy in current tracking carrierless PWM converter. The difference to the reference current[3].Two types of current control techniques, namely direct template and the actual current decides the operation ofand indirect current control have been discussed in [7]. It switches. Unlike conventional fixed band hysteresis controller,has been found that the indirect current control technique an adaptive hysteresis band current control technique is usedwhich is based on sensing line current only is simpler, requires where the band height, based on fuzzy control principle isless hardware and offers better performance. The scheme changed with the value of supply voltage and slope of referenceuses a conventional PI controller to obtain reference current current.template. However, the design of PI controller requires preciselinear mathematical model of the system which is difficult toobtain and may not give satisfactory performance underparameter variations. 24© 2011 ACEEEDOI: 01.IJCSI.02.02.83
  • ACEEE Int. J. on Control System and Instrumentation, Vol. 02, No. 02, June 2011 A. DC voltage control A TSK type fuzzy controller has been chosen for closed loop control of DC voltage. The error x1(k)=Vdcref-Vdc and integration of error x2(k)=”e(k) are used as input for fuzzy processing. The TSK type fuzzy controller scheme structure is given in Fig.3. The error and integration of error are partitioned into two trapezoidal fuzzy sets P(positive) and N(negative) as given in Fig.4. The values of L1 and L2 depend upon maximum value of error and its integration. The TSK fuzzy controller uses following four simplified rules. R1) If x1(k) is P and x2(k) is P, then u1(k) =a1.x1(k)+a2.x2(k) R2) If x1(k) is P and x2(k) is N, then u2(k) =K2u1(k) R3) If x1(k) is N and x2(k) is P, then u3(k) =K3u1(k) R4) If x1(k) is N and x2(k) is N, then u4(k) =K4u1(k) In the above rules, u1, u2, u3, u4 represent the consequent of TS fuzzy controller. Using Zadeh’s rules for AND operation and the general defuzzifier, the output of the TS fuzzy controller is Fig.1 Basic control Scheme … (1) Fig.2 Block diagram of proposed Scheme (a) (b) Fig.4 Membership functions for (a) x1 and (b) x2 However, for ã=1, we get the centroid defuzzifier with u(k) given by u(k)=a.x1(k)+b.x2(k) … (2) where a=a1K and b=a2K … (3) and Fig3. TSK Fuzzy control scheme with error and its integration … (4) The above TS fuzzy controller is a highly non-linear variable gain controller and the coefficients a1, a2 produce wide variations of controller gain. The values of G1, a1, a2, K2, K3, K4, L1, L2 are given in the Appendix. 25© 2011 ACEEEDOI: 01.IJCSI.02.02.83
  • ACEEE Int. J. on Control System and Instrumentation, Vol. 02, No. 02, June 2011B. Fuzzy hysteresis band current control in Fig.5. The rule is expressed in the form of IF (antecedent) The most commonly used current control strategy is the THEN (consequence) form. Control rule table is given in Table.1.fixed band hysteresis method. But it has the disadvantage of The centre-of-mass method is used for defuzzification.uncontrollable high switching frequency. This high switchingfrequency produces a great stress for the power transistors and III. SIMULATION RESULTSinduces important switching losses. To improve this control, an The system parameters selected for simulation studies areadaptive hysteresis band current control technique can be Vm=100V, Rs=0.1&!, Ls=0.15mH, Rf=0.1&!, Lf=0.66mH, Vdcref=220V.programmed as a function of the active filter and supply A three phase diode rectifier with R-L load is considered as aparameters to minimize the influence of current distortions on non-linear load. Initially load parameters are taken as Ll=20mHmodulated waveform [10]. The hysteresis band is given by and Rl=6.7&!. The switch on response of the system is given in Fig.6. … (5)j= 1, 2, 3; fm is the modulating frequency, is* is the referencesource current and dis* /dt represents its slope. (Fig.6 Performance of the system for load of 6.7ohm &20mH) Fig.5 Membership functions for input variables di s*/dt, vs(t) and output variable HB TABLE.1 CONTROL RULE TABLETo improve active filter performance equation (5) is implementedin our case with fuzzy logic. The supply voltage vs(t) and slopeof reference source current dis*/dt are taken as inputs for fuzzyprocessing and output is HB. To construct a rule base, the inputs Fig.6(e) Source currentare partitioned into five primary fuzzy sets labeled as {NL, NM, Fig.6 Performance of the system for load of 6.7ohm &20mHEZ, PM, PL}. Similarly the output variable HB is divided into fivefuzzy sets labeled as {PVS, PS, PM, PL, PVL}. A triangularmembership function has the advantages of simplicity and easyto implement, hence therefore chosen for this application. Thenormalized membership functions used for fuzzification are given 26© 2011 ACEEEDOI: 01.IJCSI.02.02.83
  • ACEEE Int. J. on Control System and Instrumentation, Vol. 02, No. 02, June 2011 Fig.7 (a) Harmonics distribution spectrum of Load current Fig.8 (d) Harmonic distribution spectrum of source current at t=0.5s Fig.8 Dynamic Response of the system System performance is analysed under dynamic conditions also. At initial stage the load on rectifier is Rl=6.7ohm and Ll=20mH. At time t=0.4s the resistance is increased from 6.7ohm to 10 ohm. Again at time t=0.7s it is decreased to 6.7ohm. The system responses are shown in Fig.8. It can been seen that the settling time of DC capacitor is about one and half cycles. Also the THD is only 1.50%.Fig.7 (b) Harmonics distribution spectrum of Source current at t=0.3s IV. CONCLUSION The total harmonic distortion (THD) of load current is28.26%. After compensation THD of source current is reduced From the simulation responses, it is evident that the referenceto 1.59%. Waveforms in Fig.6 clearly indicate that the harmonic current generator and the adaptive hysteresis band currentcomponent of load current is supplied by APF and the source controller are performing satisfactorily. In all the cases studiedcurrent is in phase with supply voltage. Also it has been observed the total harmonic distortion is well below 5%, the harmonic limitthat the settling time of DC link capacitor voltage is about 1 imposed by IEEE-519 standard. Also the dynamic performancecycle only. of the system is impressive as the settling time of dc-link capacitor voltage is within two cycles. This is quite important in the context that at this condition, the real power balance between the source and the load is realized. V. APPENDIX Parameters used in TSK fuzzy control scheme are G1=1/ Fig.8 (a) Load Current 4000; a1=1.1; a2=0.35; K2=-0.5; K3=1.8; K4=-0.08; L1=30; L2=10 Fig.8 (b) DC link Capacitor voltage Fig.8 (c) Source current 27© 2011 ACEEEDOI: 01.IJCSI.02.02.83
  • ACEEE Int. J. on Control System and Instrumentation, Vol. 02, No. 02, June 2011 REFERENCES [6] Jog, A.N.; Apte, N.G.; , “An Adaptive Hysteresis Band Current Controlled Shunt Active Power Filter,” Compatibility in Power Electronics, 2007. CPE ‘07 , vol., no., pp.1-5, May 29 2007-[1] Akagi, H.; , “Trends in active power line conditioners,” Power June 1 2007 Electronics, IEEE Transactions on , vol.9, no.3, pp.263-268, [7] Singh, B.N.; Chandra, A.; Al-Haddad, K.; , “Performance May 1994 comparison of two current control techniques applied to an[2] Singh, B.; Al-Haddad, K.; Chandra, A.; , “A review of active active filter,” Harmonics And Quality of Power, 1998. filters for power quality improvement,” Industrial Electronics, Proceedings. 8th International Conference on , vol.1, no., IEEE Transactions on , vol.46, no.5, pp.960-971, Oct 1999 pp.133-138 vol.1, 14-18 Oct 1998[3] Zeng, J.; Ni, Y.; Diao, Q.; Yuan, B.; Chen, S.; Zhang, B.; , [8] Jain, S.K.; Agrawal, P.; Gupta, H.O.; , “Fuzzy logic controlled “Current controller for active power filter based on optimal shunt active power filter for power quality improvement,” voltage space vector,” Generation, Transmission and Electric Power Applications, IEE Proceedings - , vol.149, no.5, Distribution, IEE Proceedings- , vol.148, no.2, pp.111-116, pp. 317- 328, Sep 2002 Mar 2001 [9] C.N. Bhende; S. Mishra; S.K. Jain; , “TS-fuzzy-controlled[4] Akagi, H.; , “Active Harmonic Filters,” Proceedings of the active power filter for load compensation,” Power Delivery, IEEE , vol.93, no.12, pp.2128-2141, Dec. 2005 IEEE Transactions on , vol.21, no.3, pp.1459-1465, July 2006[5] Akagi, H.; , “New trends in active filters for power [10] Mekri, F.; Mazari, B.; Machmoum, M.; , “Control and conditioning,” Industry Applications, IEEE Transactions on , optimization of shunt active power filter parameters by fuzzy vol.32, no.6, pp.1312-1322, Nov/Dec 1996 logic,” Electrical and Computer Engineering, Canadian Journal of , vol.31, no.3, pp.127-134, Summer 2006 [11] Arrofiq, M.; Saad, N.; , “PLC-based fuzzy logic controller for induction-motor drive with constant V/Hz ratio,” Intelligent and Advanced Systems, 2007. ICIAS 2007. International Conference on , vol., no., pp.93-98, 25-28 Nov. 2007 28© 2011 ACEEEDOI: 01.IJCSI.02.02. 83