Dynamic Power Quality Compensator with an Adaptive Shunt Hybrid Filter

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1 Interntionl Journl of Electronics nd Drive System (IJPEDS) Vol. 4, No. 4, December 2014, pp. 508~516 ISSN: Dynmic Qulity Compenstor with n dptive Shunt Hybrid Filter Sindhu M R, Mnjul G Nir, T N P Nmbir Deprtment of Electricl nd Electronics Engineering, MRIT VISHW VIDYPEETHM rticle Info rticle history: Received My 24, 2014 Revised Oct 7, 2014 ccepted Oct 20, 2014 Keyword: Hrmonic Distortion Hrmonic Filter Qulity Rective power compenstion ctive Filter BSTRCT Mjor portion of nonliner lods in industries re contributed by vrible speed drives becuse of their desirble fetures such s energy sving, smooth control, flexible opertion nd fst response. These electric drives introduce lrge mount of current nd voltge distortions t the point of common coupling. These distortions re propgted throughout the system nd ffect ll other lods connected in the system. Hence these distortions re to be mitigted with suitble filters instlled ner to the respective lod terminls. This pper presents n effective NN bsed digitl controller for shunt hybrid filter to provide instntneous nd rective compenstion. The performnce of the dptive shunt hybrid filter is verified by simultion nd experimentl studies under stedy stte nd dynmic conditions. The results show tht it is n effective, flexible nd low rted hybrid filter configurtion. Copyright 2014 Institute of dvnced Engineering nd Science. ll rights reserved. Corresponding uthor: Sindhu M R, Deprtment of Electricl nd Electronics Engineering, mrit Vishw Vidy Peethm, mrit ngr, Coimbtore Emil: 1. INTRODUCTION Utilities tke efforts to mintin good power qulity t the point of common coupling (PCC). Mjority of industril lods re induction motor drives [1, 2]. They re preferred becuse of sving in energy, rugged nture, esiness in control nd chepness [1, 2]. Vrious PWM techniques such s Spce Vector pulse width modultion, sinusoidl PWM etc. re implemented [3]-[5]. These re implemented with digitl controllers nd it improved performnce of induction motor drives. These equipment resulted in genertion of lrge mounts of current nd voltge s, reduction in source power, voltge sg, voltge swell etc. [6]. The propgtion of these power qulity issues re prevented by instlling filter of suitble configurtion t point of common coupling. Different power qulity improvement schemes such s pssive filters [6] nd ctive filters [7] re developed by vrious reserchers. Pssive filters hve drwbcks such s bulky in size, high no lod losses, resonnce, fixed compenstion etc [6]. ctive filters provide effective nd dynmic compenstion with the help of efficient controllers [7]. But this scheme is expensive. Hence s n economicl solution, hybrid filters were developed. Here, shunt pssive filter contributes mjor prt of rective power compenstion nd remining s re compensted by shunt ctive filter. Vrious reserch ppers on intelligent digitl controller bsed filters re published [8-12]. This pper describes n NN bsed dptive shunt hybrid filter for mitigtion nd rective power compenstion of djustble speed drives.nn controller helps to provide instntneous nd rective power compenstion under stedy stte nd dynmic conditions. Journl homepge:

2 IJPEDS ISSN: TEST SYSTEM n industril system is selected for performnce study of the dptive shunt hybrid filter. scled down lbortory model of industril drive, three phse 3 HP, 4 pole, induction motor drive is used in this work. It is operted s n djustble speed drive using three phse voltge source inverter. The specifictions of the induction motor drive re shown in Tble 1. Tble 1. Induction Motor Drive Specifictions rting 3 HP Switching frequency 10kHz Rotor resistnce 1.24 Sttor resistnce Vdc 300V Bse frequency 100Hz Sttor Lekge Rectnce 5.12 Rotor Lekge Rectnce 120 No. of poles 4 Moment of Inerti 0.2 kgm 2 The experimentl set up is mde s shown in the block digrm in Figure 1. Figure 1. Schemtic Digrm of Three Test System The VSI is controlled using spce vector PWM. The spce vector PWM bsed speed control is implemented through the following steps: () Mesure the motor quntities (speed nd phse currents) (b) Trnsform them to two phse system (,β) using Clrke trnsformtion (c) Clculte rotor flux spce vector mgnitude nd ngle (d) The sttor current torque nd flux components re seprtely controlled (i sd, i sq ) (e) The output sttor voltge spce vector is clculted using decoupling block (v sd, v sq ) (f) The sttor voltge spce vector is trnsformed by n inverse prk trnsformtion bck from d q reference frme into two phse system fixed with the sttor (v s, v sβ ) (g) Using spce vector modultion, output three phse voltges is generted. The whole process of the speed controller, implemented in the dspic30f4011, is explined using flow chrt in Figure 2. Three phse source currents, nd source voltges t the point of common coupling re sensed nd nlysis is performed with the help of power qulity nlyser. The power system quntities mgnitudes nd wveforms of source currents nd source voltges for different speed settings re shown in Figure 3. Dynmic Qulity Compenstor with n dptive Shunt Hybrid Filter (Sindhu M R)

3 510 ISSN: Figure 3. Source voltge nd source current t the point of common coupling for vrible speed induction motor drive with speed of ()135 rd/sec (Cse I) (b)320 rd/sec (Cse II) Figure 2. Flow chrt of the speed controller Tble 2 shows lrge mount of s in currents t the point of common coupling under stedy stte conditions. When the lod is chnged suddenly from 75% rted lod to 25% rted lod, the source current, rective power demnd nd components re lso chnged correspondingly. The fundmentl component of source current, THD in source current, current components, displcement power, distortion power, source power, rel power, rective power, pprent power nd distortion power in ech cycle is shown in Tble 3. Tble 2(). Fundmentl component of source current nd THD in source current t the point of common coupling with vrible speed induction motor drive under stedy stte conditions Cse Fundmentl component of source current (p.u.) THD in Source Current (%) 5 th 7 th 11 th b c I II th Cse Tble 2(b). Estimtion of system prmeters for the specified lod conditions under stedy stte Displcement power Distortion power Source power Rel Rective I pprent Distortion II IJPEDS Vol. 4, No. 4, December 2014 :

4 IJPEDS ISSN: Tble 3(). Fundmentl component of source current nd THD in source current in ech cycle t the point of common coupling with vrible speed induction motor drive under dynmic conditions Cycle Fundmentl component of source current (p.u.) THD in Source current (%) b c 5 th 7 th I II III IV V VI th th Tble 3(b). Estimtion of system prmeters in ech cycle with vrible speed induction motor drive - under dynmic lod conditions Cycle Displcement power Distortion power Source power Rel Rective I II III IV V VI pprent Distortion Results show n effective filter is necessry to provide vrible rective power nd compenstion to meet IEEE stndrds of good power qulity. ctive filters re commonly used for dynmic power qulity compenstion. But these ctive filters re highly expensive. Hence s n economicl solution, hybrid filters were introduced. Here, shunt pssive filter contributes mjor prt of rective compenstion nd selected compenstion. Only remining compenstion is to be met by the shunt ctive filter. 3. PROPOSED DPTIVE SHUNT HYBRID FILTER FOR POWER QULITY COMPENSTION IN INDUCTION MOTOR DRIVES The dptive shunt hybrid filter consists of three phse dptive shunt pssive filters nd dptive shunt ctive filter. dptive shunt pssive filters re developed by series combintion of thyristor switched series combintion of inductor nd cpcitor. Their vlues re designed such s to provide bypss pth for fifth nd seventh s. It lso provides fundmentl frequency rective power to the system. The cpcitor vlues re selected s 210F nd inductor vlues re 15mH nd 7mH respectively. Remining mounts of s nd rective compenstion currents re provided by the dptive shunt ctive filter. The shunt ctive filter is controlled to inject remining mount of s nd rective compenstion currents such tht source need to supply only rel prt of fundmentl component of current. The schemtic digrm of the filtering system is shown in Figure 4. The hybrid filter elements re controlled by NN bsed intelligent digitl controller. The responsiveness of filter is improved by hysteresis controller bsed closed loop control. PI controller is lso used to compenste for inverter losses nd regultion of dc link voltge. Dynmic Qulity Compenstor with n dptive Shunt Hybrid Filter (Sindhu M R)

5 512 ISSN: Figure 4. Three phse system feeding vrible speed induction motor drive with dptive Shunt Hybrid Filter 3.1. Methodology The lod current in induction motor drive is represented by: i ( t) i sin( t ) i sin( ht ) = Rel prt of fundmentl component L L 1 1 L Lh h3,5, of lod current +Rective prt of fundmentl component of lod current + Hrmonic components of lod current Lh (1) dptive shunt pssive filter compenstes for mjor prt of fundmentl frequency rective power nd s. dptive shunt ctive filter injects remining smll mount of s nd helps to obtin unity power sinusoidl current t the point of common coupling. Three phse instntneous source voltges, fundmentl lod currents nd filter compenstion currents re selected s input quntities for trining dptive NN. The reference compenstion currents re developed by nlog controller circuit. The ctul compenstion currents re compred with reference compenstion currents to generte switching pulses to IGBTs of three phse voltge source inverter. The current trnsducers nd voltge trnsducers smple instntneous lod currents, compenstion currents nd source voltges. Smpled vlue of instntneous lod current is expressed s: N [ 1n 2 n t n1,2,3,... i.e. i L [k] = W sin( nk t) W cos( nk )] [ N n 2n t n2,3,... = W cos( nk t) W sin( nk t)] [ W sin( nk t) W cos( nk )] = i L1, re [k] + i L1, im [k] + h ih [k] (2) where W 1n nd W 2n re mplitudes of sine nd cosine components of the mesured lod current. The eqution is represented in vectoril form s: i L [k] = [W 11 W W 1N W 2N ] sin( kt) cos( kt) sin(2kt) cos(2kt) sin( Nkt) cos( Nkt) The dptive NN network is implemented using Widrow-Hoff weights updting lgorithm [6], [7]. The weights of the connection links re updted using error in the estimted fundmentl component nd IJPEDS Vol. 4, No. 4, December 2014 :

6 IJPEDS ISSN: ctul rel prt of fundmentl component of lod current. The bck propgtion neurl network ws trined with MTLB using 1500 trining ptterns for 2500 epochs with gol of Trining method used is Levenberg Mrqurdt lgorithm. Trined rtificil neurl network consists of two lyers: input lyer (6 neurons), output lyer (7 neurons) nd hidden lyer (6 neurons). The NN network is shown in Figure 5. The performnce chrcteristics of neurl network trining is shown in Figure 6. The NN is progrmmed nd implemented using dspic30f4011 microcontroller. Two bipolr DCs re used for conversion of nlog quntities to digitl quntities. Smpling frequency of 3kHz is selected considering time for sensing input smples, digitl conversion, progrm execution nd genertion of switching signls. The switching pulses re mplified nd given to IGBTs in shunt ctive filter. The isoltion between power circuit nd controller circuit is done using n optocoupler 6N136. The shunt ctive power filter circuit includes power inverter (SKM50GB12B) with three phse IGBT bridge nd two cpcitors of 2200F. The compensting currents injected by three phse inverter through coupling inductors to the point of common coupling. For di F 10 / s, 400V 5 10mH coupling inductor is used. The experimentl results with the dt mx insertion of NN Controller bsed shunt hybrid filter re discussed in following section. Figure 5. rtificil Neurl Network for controlling dptive shunt hybrid filter Figure 6. Performnce plot of trining neurl network for controlling the dptive shunt hybrid filter 4. PERFORMNCE OF NN CONTROLLED SHUNT CTIVE FILTER UNDER DYNMIC CONDITIONS RESULTS ND DISCUSSION The operting performnce of the dptive shunt hybrid filter is studied under dynmic conditions with the ppliction of 25% lod nd 75% lod t t = 0.5s. Fundmentl component of source current, THD in source current nd power system prmeters t the point of common coupling with the instlltion of dptive shunt hybrid filter is shown in Tble 4 nd 5. Figure 7, nd 8 show wveforms of source voltge, lod current, filter current nd source current with the instlltion of dptive shunt hybrid filter under Dynmic Qulity Compenstor with n dptive Shunt Hybrid Filter (Sindhu M R)

7 514 ISSN: dynmic conditions. The performnce of dptive shunt hybrid filter is verified with reduction in source current s nd sinusoidl source currents in phse with source voltges. Wveforms lso confirm the performnce of the filter under dynmic conditions. Tble 4(). Fundmentl component of source current nd THD in source current t the point of common coupling with vrible speed induction motor drive with dptive Shunt Hybrid Filter Stedy stte conditions Cse Fundmentl component of source current (p.u.) THD in Source Current (%) 5 th 7 th 11 th b c I II th Tble 4(b). Estimte of system prmeters for the specified lod conditions with dptive Shunt Hybrid Filter Stedy stte conditions Delivered by Source Displcement Distortion power Source power Cse Rective pprent power Rel Distortion I II Figure 7. Source voltge, Lod current, Filter current, Source current wveforms for induction motor drive lod t 25% rted lod under blnced system with dptive shunt hybrid filter dynmic conditions Figure 8 Experimentl results - Source current wveforms for the induction motor drive lod under blnced system with dptive shunt hybrid filter dynmic conditions; () Without filter, (b) With dptive shunt hybrid filter IJPEDS Vol. 4, No. 4, December 2014 :

8 IJPEDS ISSN: Tble 5(). Fundmentl component of source current nd THD in source current t the point of common coupling with vrible speed induction motor drive fter the instlltion of dptive Shunt Hybrid Filter Dynmic conditions Cycle Fundmentl component of source current (p.u.) THD in Source Current (%) b c 5 th I II III IV V VI th th th Cycle Tble 5(b). Estimte of system prmeters in ech cycle under dynmic lod conditions with the instlltion of dptive Shunt Hybrid Filter Displcement power Distortion power Source power Delivered by Source Rel Rective pprent I II III IV V VI Distortion The simultion nd experimentl results relted to the dptive shunt hybrid filter illustrted: ) single controller is used for controlling both dptive shunt pssive filter nd dptive shunt ctive filter b) The digitl NN bsed controller is flexible nd esy to implement in lrge quntities. c) In the cse of dptive shunt hybrid filter, the kv delivered by source for the lod is much less compred with shunt dptive pssive filter or NN controller bsed shunt ctive filter. d) The fundmentl rective power drwn from source is much reduced nd hence source power is improved. e) The performnce of the NN controller is stisy with blnced/ unblnced source nd blnced/unblnced nonliner lod under stedy stte nd dynmic conditions. 5. CONCLUSION djustble speed induction motor drives cuse lrge mounts of current nd voltge distortions nd rective power bsorption t the point of common coupling. The propgtion of distortions throughout the power system ffects lifetime of ll other power system equipment. Vrious power qulity improvement schemes were suggested by different uthors. This pper shows n NN bsed dptive shunt hybrid filter for power qulity enhncement in vrible speed drive system. The simultion nd experimentl results show effective performnce of dptive shunt hybrid filter under stedy stte nd trnsient conditions. CKNOWLEDGEMENT The uthors wish to thnk mrit Vishw Vidypeethm, Coimbtore nd Deprtment of Science nd Technology, New Delhi for their finncil support for crrying out this work. Dynmic Qulity Compenstor with n dptive Shunt Hybrid Filter (Sindhu M R)

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