Interharmonic Mitigation Using Boost Converter In Variable Speed Drives

Transcription

1 Interharmonc Mtgaton Usg Boost Converter In Varable Speed Drves A.Vjayakumar and Dr.TK.Mahendra 2 Asso.Professor, Electrcal and Electroncs Engeerg, AAM Engeerg College, Kovlvenn, Inda 2 Senor member-ieee, Electroncs and Communcaton Engeerg. Retred Professor- KLN College of engeerg, Madura, Inda Abstract Voltage source verter (VSI) fed ducton motors are wdely used dustres. It jects sgnfcant amount of harmoncs and terharmoncs to the supply system. Interharmoncs are components whose frequences are not an teger multple of the fundamental frequency. Interharmoncs are jected to the supply when two dfferent frequency systems are terlked or due to load unbalance. In ths work motor load unbalance s consdered and a boost converter s desgned to mtgate terharmoncs. Smulaton s carred out PSIM and the superorty of the proposed method s dscussed. Keywords Interharmonc mtgaton, boost converter, Varable Frequency Drve, load unbalance I. INTRODUCTION A varable frequency drve s consdered as a frequency converter whch converts put voltage at the utlty frequency to a voltage at the drve operatg frequency. Among the commonly recognzed sources of Interharmoncs, pulse-wdth-modulated voltage source verter fed ducton motors are popular [2]. VSI fed ducton motor has a front end rectfer whch converts put ac to unregulated dc. In general dode brdge rectfers are used whch are smple and hghly relable [6]. In the dc lk a large capactor s connected to reduce rpples the dc voltage. After the rectfer, a PWM verter converts dc voltage to ac voltage of varable magntude and frequency [4]. As the put and the drve operatg frequences are dfferent, terharmoncs are troduced the utlty current. These terharmoncs have undesrable effects such as overheatg, overstressg of capactor banks, abnormal operaton of electronc relays, telephone terference, lght flcker even though ts magntude s less [3], [5]. Also the terharmonc frequency s not constant and t s varyg wth the load operatg frequency. Therefore t s dffcult to elmate usg passve flters that are tuned at harmonc frequences. Ths work consders load current unbalance by connectg an ductance seres wth the phase wdg []. The effect of load mbalance s analyzed and a boost converter s desgned to mtgate the terharmoncs. The proposed method s smulated PSIM and the results are dscussed. II. INTERHORMONICS DUE TO LOAD UNBALANCE An ductor of 0.25mH s connected seres wth one of the phase wdgs to analyse motor current unbalance. Due to ths motor current unbalance harmonc s transferred from the motor to the dc lk whch s transferred to the rectfer put sde and appears as harmonc and terharmonc the supply sde. Harmonc Transfer to the DC lk from the Inverter The verter put current s gven by S S S (2) nv u u v v w All Rghts Reserved 22

2 I 2 I cos2 (3) nv dc nv out n Internatonal Journal of Recent Trends Engeerg & Research (IJRTER) Volume 02, Issue 04; Aprl [ISSN: ] 3 Where I dc m 2 I p cos p (4) 4 and Su, Sv, Sw are verter swtchg functons. Idc component results actve power transfer. The component Ivs responsble for the change of the verter dc lk current wth two tmes the output frequency. Harmonc Transfer to the Rectfer sde DC lk The dsturbance the verter sde dc lk s transferred to the dc lk of rectfer. The dsturbed current at the dc lk of the rectfer s gven by rect Idc sqrt.2 Ir ect cos 2 out t (5) Where I rect k dcl nk I nv (6) Where k dclks the dc lk current magnfcaton factor. Ths magnfcaton occurs at the dc lk due to parallel resonance []. As the motor output frequency s vared from 0 to f out the rectfer sde dc lk current fluctuates wth the frequency rangg from 0 to 2 f out. Harmonc Transfer through the rectfer For ths analyss, the rectfer swtchg functons are consdered. The rectfer s assumed to conduct contuously. The put currents of the rectfer consderg the swtchg functon are gven by ar br cr S S ar rect br rect S cr rect (7) The swtchg functons of the rectfer are approxmated to ther fundamental components as follows S S ar br A cos t 2 A cos t 3 2 Scr A cos t (8) 3 Where A s the ampltude of the fundamental harmonc component and t s gven by 2sqrt.3 A (9) Thus the derved put current of the rectfer for phase A s 2I cos t ar 2I H 2I cos H Where 2 2 cos t out t t t out All Rghts Reserved 222

3 I A I dc () Internatonal Journal of Recent Trends Engeerg & Research (IJRTER) Volume 02, Issue 04; Aprl [ISSN: ] IH A Irect (2) 2 Thus the unbalance the motor current s propagated to the supply wth two components whch are symmetrcal at 2fout ± f. III. SIMULATION varable frequency choke wth ac dreve Varable frequency drve s smulated PSIM consderg load unbalance wth ac choke the rectfer put sde. The ductor value s chosen by tral and error method and s equal to 200μH. The range of the ductance s between 200μH to mh. Increasg ductance value beyond ths value results voltage dstortons. The dagram of VFD s shown Fg.2 and s smulated for the drve operatg frequency of 40Hz. Smulaton s carred out usg the parameters lsted Table I. Table I AC source Inducton Motor Voltage 400V Rated Power 20kW Frequency 50Hz Rated Voltage 400V Resstance 8mΩ Stator Resstance 0.494Ω Inductance 0.5mH Stator Leakage Inductance H DC Lk Rotor Resstance 0.356Ω Resstance 3.5mΩ Rotor Leakage Inductance H Inductance 0.H Pars of Poles 3 Capactance F Motor Operatg Frequency 40Hz to 50Hz Fg.2 The rectfer put current and ts spectrum analysed usg FFT are shown All Rghts Reserved 223

4 Internatonal Journal of Recent Trends Engeerg & Research (IJRTER) Volume 02, Issue 04; Aprl [ISSN: ] (a) Rectfer put current (b)rectfer put current spectrum The rectfer put current spectrum s analyzed for Interharmoncs. From equaton (0), the rectfer put current has Interharmoncs at frequences of 2fout± f (f supply frequency, fout drve operatg frequency). When the drve operatg frequency s 40Hz, Interharmoncs occur at frequences of 30Hz and 30Hz. The magntude of the terharmonc components are measured and tabulated table II. Interharmonc frequency Table II 30Hz.8 30Hz Interharmonc magntude as % of fundamental Varable frequency drve wth boost converter The ma objectve of the boost converter[7] the dc lk s to elmate Interharmoncs the rectfer put sde. The general block dagram of the proposed system s shown Fg.3. All Rghts Reserved 224

5 Internatonal Journal of Recent Trends Engeerg & Research (IJRTER) Volume 02, Issue 04; Aprl [ISSN: ] The sgle swtch boost converter topology s employed whch has an LC put flter. The boost swtch s turned on at a constant frequency. The dc lk current s subtracted from the reference dc current and the error sgnal after the PI controller s compared wth the hgh frequency carrer sgnal to obta the gate pulse for the boost swtch. The proposed system s smulated PSIM. The rectfer put current and ts spectrum are shown Fg.4 for the drve operatg frequency of 40Hz. (a) Rectfer put current (b) Rectfer put current spectrum Fg.4 When the drve operatg frequency s 40Hz, the terharmonc frequences are at30hz and 30Hz accordg to the relaton 2f out ± f. The magntude of the terharmonc components s measure and tabulated Table III. Table III Interharmonc frequency Interharmonc magntude as % of fundamental 30Hz Hz 0.2 The terharmonc magntudes are greatly reduced by the proposed method. The magntude of the terharmonc components obtaed usg both the methods are compared and s shown Fg.5 whch clearly shows the superorty of the proposed All Rghts Reserved 225

6 Internatonal Journal of Recent Trends Engeerg & Research (IJRTER) Volume 02, Issue 04; Aprl [ISSN: ] 2.00%.50%.00% VFD wth ac choke 0.50% 0.00% 30Hz 30Hz VFD wth boost converter Fg.5 IV.CONCLUSION In ths work, terharmonc the supply sde of VSI fed ducton motor due to motor current unbalance s analyzed. Frst VFD wth ac choke the put sde of the rectfer s smulated usg PSIM. Then VFD wth a sgle swtch boost converter the dc lk s smulated usg PSIM. The magntude of the terharmonc obtaed these two methods are compared whch shows the superorty of the proposed method. REFERENCES. Duro Basc, Input Current Interharmoncs of Varable-Speed Drves due to Motor Current Imbalance, IEEE Trans. Power Del. Vol.25, no. 4, Oct F. De Rosa, R. Langella, A. Sollazzo, and A. Testa, On the Interharmonc Components Generated by Adjustable Speed Drves, IEEE Transactonson Power Delvery, Vol. 20.No.4, pp , Oct S.R. Hadan Amre*, D.G. Xu** Senor Member, IEEE and Y.Q. Lang, Harmoncs and Interharmoncs General VSI/CSI Inverters: Analyss, Modelg and Smulaton, IEEE Gary W. Chang, Fellow, IEEE, Sh-Kuan Chen, Member, IEEE, Hua-Jhe Su, Student Member, IEEE, and Pg-Kue Wang, Accurate Assessment of Harmonc and Interharmonc Currents Generated by VSI-Fed Drves Under Unbalanced Supply Voltages, IEEE Transactons on Power Delvery, vol. 26, No. 2, Aprl IEEE Interharmonc Task Force, Interharmoncs: theory and modelg, IEEE Trans.Power Del.,vol. 22, no. 4, pp , Oct Y. Jang and A. Ekstrom, General analyss of harmonc transfer through converters, IEEE Trans. Power Electron., vol. 2, no. 2, pp , Mar S.M. Bash, N. Marun, S.B. Noor and H.S. Athab, Three-phase Sgle Swtch Power Factor Correcton Crcut wth Harmonc ReductonJournal of Appled All Rghts Reserved 226