Analysis and Control of Three Phase PWM Rectifier for Power Factor Improvement of IM Drive

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1 htt://dx.doi.org/0.272/ijiet.02.9 Analysis and Control of Three Phase PWM Rectifier for Power Factor Imrovement of IM Drive Ajesh P S, Jisha Kuruvila P 2, Dr. Anasraj R 3 PG Scholar, Deartment of Electrical and Electronics Engineering,Mar Athanasius College of Engineering, Kothamangalamam, Kerala, India 2 Assistant Professor, Deartment of Electrical and Electronics Engineering,Mar Athanasius College of Engineering, Kothamangalamam, Kerala, India 3 Associate Professor, Deartment of Electrical and Electronics Engineering, Govt. Engineering College Thrissur, Thrissur, Kerala, India Abstract- Conventional way of obtaining DC ower from AC is by using diode bridge rectifier. In case of diode rectifier, they inject unwanted current harmonics of relatively high amlitude into the grid and also reduces inut ower factor. Reduction in current harmonic injection into the grid and also ower factor can be controlled by using effective control strategies like vector control techniques on ulse width modulated rectifiers. It imroves the ower factor in a great extent. While using PWM rectifier outut voltage can be control. In this aer VOC based three hase PWM rectifier is imlemented for Voltage Source Inverter(VSI) based induction motor drive. At no load induction motor has very low ower factor. It imroves at increasing load from no load to full load. In the VSI based induction motor drives, ower factor and thereby efficiency can be increases by controlled in the rectifier. In vector control method voltage error is a direct inut control variable to realize the fast resonse of the rectifier. The outut voltage of rectifier varies under large disturbance of load, but the good control resulted a more accurate voltage stability and have better dynamics resonse. Simulation of vector controlled PWM rectifier is done in MATLAB/Simulink. It uses a three hase suly with 00 V and obtained a constant outut voltage of 337 V in DC link. Keywords VOC, Three Phase PWM Rectifier, IMC, IM Drive, Power Factor Imrovement, Harmonic Elimination. I. INTRODUCTION Conversion of DC ower from AC ower using an AC to DC converter finds its alication in a wide range of area like electric drives, UPS. etc. Conventionally for obtaining DC ower from AC grid, diode bridge or thyristor bridge rectifiers are used. The use of these toologies is mainly motivated due to their advantages in size, control, reliability, structural simlicity and mainly economics. The usage of such bridge circuits is quite disadvantageous as they inject unwanted current harmonics of relatively high amlitude into the grid. A reduction in current harmonic injection into the grid can be achieved by using effective control strategies like vector control or direct ower control techniques on Pulse Width Modulated rectifiers. In this aer vector controlled PWM rectifier is done, with Vector control or Voltage Oriented control(voc) method. In which, voltage error is a direct inut control variable to realize the fast resonse of the rectifier. The outut voltage of rectifier varies under large disturbance of load, but the good control effect resulted a more accurate voltage stability. have better dynamics resonse comared to conventional control strategies. In vector control method active comonent and reactive comonent of current can be control indeendently. By using this inut ower factor can be controlled in a redefined range. Nearly unity ower factor can be attained by making reactive comonent equals zero. Low ower factor affect the efficiency of whole system. While using inductive load ower factor became very low. In case of induction motor drives, ower factor reduces because induction motor is highly inductive. Induction motors are the most widely used electrical motors. At no load induction motor has very low ower factor. It imroves at increasing load from no load to full load. In this aer VSI based induction motor drive is used as rectifier load. The air-ga between the stator and rotor of an induction motor increase the reluctance of the magnetic circuit develoed in motor. So it draws a large magnetizing current to roduce the required flux in the air-ga. At no-load condition motor draws a large magnetizing comonent and low active comonent to meet the losses. So the ower factor became very low. When load on motor increases active comonent of current increases and ower factor imroves. In the Voltage Source Inverter(VSI) based induction motor drives, ower factor can be controlled in the rectifier. This rectifier controller is turned using Internal Model Control (IMC) method. This is a PID controller turning method. Volume 0 Issue 2 May ISSN:

2 htt://dx.doi.org/0.272/ijiet.02.9 II. THREE PHASE PWM RECTIFIER The ower circuit of the three-hase PWM rectifier is shown in Figure.. In PWM rectifiers, by controlling the width of switching ulse the outut voltage can be controlled in a desired value. In vector controlled PWM rectifiers [2] all quantities are transformed into synchronous(dq) reference frame [3]. In abc reference frame control, all control values are varying with time. so control became more comlicated. In case of dq these values are time indeendent and these values are dc in nature, so a ste change can be alied as a erturbation. Figure. Three Phase PWM Rectifier Figure 2. Single Phase Equivalent of Rectifier The dq model of three hase rectifier is shown below, did L Rid Liq Vsd Vrd dt diq L Riq Lid Vsq Vrq dt () Where, V sd = d comonent of source side voltage. V rd = d comonent of rectifier side voltage. i d = d comonent of current. and others are corresonding q comonents. By making i q = 0, reactive ower become zero and ower factor can be made unity. 2. Control strategy The Figure. 3 shows the controller for PWM rectifier, consists of an inner current controller and an outer dc voltage regulator. The inner current controller controls the inut line currents to track the reference current; the unity ower factor oeration can be achieved if the reference current vector is in hase with the mains voltage. The voltage controller regulates the outut voltage of the rectifier. The current controller oututs the reference voltage, which is used to generate PWM ulses for the rectifier switches [4]. Figure 3. Vector control of PWM rectifier Volume 0 Issue 2 May ISSN:

3 htt://dx.doi.org/0.272/ijiet.02.9 The outer dc voltage regulator PI controller regulates the current indirectly to maintain a constant dc voltage. The seed of outer DC voltage regulator will be low and that of inner current controller will be high. The current controllers are cross couled by a term ωl. 2.2 Internal Model Control Based PI controller Figure 4. Internal Model Control In control alications, model based control are always using to track set oint and reject disturbances. The distinguishing characteristic of IMC [6] structure is the incororation of the rocess model which is in arallel with the actual the lant. To imrove the robustness of the system the effect of model mismatch should be minimized. Since mismatch between the actual rocess and the model usually occur at high frequency end of the systems frequency resonse, a low ass filter f(s) is usually added to attenuate the effects of rocess model mismatch. This contains a lant with Transfer function(tf) g and a controller with TF g c, model of the lant ḡ and a disturbance d. This lant model and actual lant oututs are cancels and d feed to the inut. The controller used in the IMC control is an inverse of lant transfer function series with a low ass filter. Low ass filter is used for make the system imroer, or at high frequency actual lant and lant model outut may mismatch, to avoid it a low ass filter is used. g c (s) = g - (s)*f(s) (2) where f(s)= s Transfer function of low ass filter. The IMC closed loo TF is, gc( s) g ( s) * gc( s) (3) 2.3 Current Controller Design The transfer function can be formed as follows, di Vs Ri jli L Vr 0 dt Lalace transform and TF are, R jl sl i V V s r i g( s) Vs R sl jl (5) Transfer function contains the term jωl this is the cross couling comonent to cancel out the cross couling comonent, V V V jli r s i g ( s) V R sl Rearranging this TF of g - (s) became, g ( s) k T s Where T = L, Time constant R Then IMC closed loo TF, K T ( s) s (4) (6) (7) (8) Volume 0 Issue 2 May ISSN:

4 htt://dx.doi.org/0.272/ijiet.02.9 Rearranging and comaring with transfer function of PI controller. The roortional gain and integral gain can be obtained as, L K i K ii i i R Where, 2f s i controller seed term Voltage Controller Design For voltage controller, 3Eg g( s) sc (0) Closed loo TF of IMC based voltage controller, C 3Egs () Rearranging and comaring with transfer function of PI controller. The roortional gain and integral gain can be obtained as, C K v 3Eg C Kiv (2) 2 3E Here g 0*i 2.5 Soft Startu In case of PWM rectifiers, there will be a voltage error controller which controls the outut voltage in a defined value. When we start this circuit the outut voltage is zero. So the error of voltage controller will be very high, due to this high error there will be a large sike in outut voltage and also in current. (9) Figure 5. Soft start To limit this starting voltage and current sike. Reference voltage needs to control, to control error in limit. For this we control the reference voltage to vary in such a way that a ram. So reference start from an initial value and then increases gradually and reaches its final value after a number of ower cycle. Tyical value of time delay will be 0 ower cycle. 2.6 Design of Comonent Value of suly side inductance is calculated as, Ts L 2V sa i 2 V 3 a max dc Value of DC link caacitance is calculated using, C V W dcv max (3) (4) Volume 0 Issue 2 May ISSN:

5 htt://dx.doi.org/0.272/ijiet.02.9 III. SIMULATION STUDIES Simulation Parameters are shown in Table I. Table - Simulation arameters Parameters Values Source side inductance 9mH Source side resistance 5Ω DC link caacitor 470μF Outut Voltage 337V K i K ii K v e-4 K iv Switching frequency 2kHz The simulation model of Three hase rectifier is shown in Fig. 6. In which suly voltage and currents are transformed into its corresonding α-β and then its dq values, and this feed to the controllers. Current and voltage transformations are done using resective subsystem. The VSI feed induction motor drive is driven by an inverter at a frequency of 30Hz. While running induction motor rated at 45V,50Hz in 30Hz voltage required is only 240V, according to V/F control. This voltage reduction is done because of hardware limitations. The vector control subsystem is used in MATLAB is shown in Figure. 7. Figure 6. Simulation Model of three hase PWM rectifier Figure 7. Simulation of vector control subsystem The vector controlled PWM three hase rectifier outut voltage wave form is shown in Figure. 8. There is a change in torque in motor is alied in 3 Sec, it draws a high current and make a reduction in DC link voltage. This voltage change is comensated by the controller in 0.4sec. Volume 0 Issue 2 May ISSN:

6 htt://dx.doi.org/0.272/ijiet.02.9 Figure 8. Outut Voltage wave form without soft start This shows the voltage regulation wave form. For an induction machine load of HP as load. By imlementing soft start-u voltage sike in start can be eliminate. Figure. 9 shows the outut voltage for soft start-u. Due to the alication of soft startu current sike in the start is also reduced. Figure 9. Outut Voltage wave form with soft start Per hase voltage and current that ensure unity ower factor is shown in Figure. 0. In this figure voltage and current are in hase that ensure unity ower factor oeration. Figure 0. Per hase Voltage and current Fig. shows the FFT analysis of hase current. This shows that THD of suly side current is only 3.79 ercentage. This shows that current harmonics that injected by this three hase PWM rectifier is low. This current harmonic can be further reduces by using large inductor. Figure. FFT analysis of inut current Volume 0 Issue 2 May ISSN:

7 htt://dx.doi.org/0.272/ijiet.02.9 IV.CONCLUSION A vector controlled three hase rectifier is imlemented for a voltage source inverter (VSI) based induction motor drives. Induction motor at its variable load conditions changes it ower factor in wide range. Ranging from 0. to 0.9 but this makes large ower loss. By using PWM rectifier, the ower factor can be make nearly unity. By using vector control, ower factor, outut voltage and current harmonics develoed in the suly currents reduces to a very low value. It hels to imrove ower quality. V. REFERENCE [] F. Fleming and M. Krishnamurthy, Influence of DC-Link Fluctuations on ThreePhase Induction Motor Drives, IEEE Conference on Vehicle Power and Proulsion, 2009, [2] Wang Xu, Huang Kaizheng, Simulation of Three-hase Voltage Source PWM Rectifier Based on Direct Current Control", IEEE conference Congress on Image and Signal Processing, 2008, Vol. 5, [3] Viraj Selarka, Prem Shah, Close Loo Control of Three Phase Active Front End Converter using SVPWM Technique", IEEE International Conference on Electrical Power and Energy Systems, 206 [4] Z. Zhou P.J. Unsworth, Design and analysis of a feedforward control scheme for a three-hase voltage source ulse width modulation rectifier using sensorless load current signal", IET Power Electronics,2009. [5] Srikanthan Sridharan and Phili T. Krein, Minimization of System-Level Losses in VSI-Based Induction Motor Drives: Offline Strategies", IEEE Transactions on Industry Alications, Vol. 53, NO. 2, 207, [6] Sylvain LECHAT SANJUAN, Voltage Oriented Control of ThreePhase Boost PWM Converters", CHALMERS UNIVERSITY OF TECHNOLOGY Gteborg, Sweden,200. [7] Praveen Joseh, Jaison Mathew et.al, Review of current control strategies for a vector Controlled ThreePhase UPF Rectifier", IEEE International Conference on Power, Instrumentation, Control and Comuting (PICC),205 [8] Haoran Shi, Wei Xu, Chenghua Fu and Yao Yang et.al, Research on Three-hase Voltage Tye PWM Rectifier System Based on SVPWM Control", Research Journal of Alied Sciences, Engineering and Technology, 5(2) , 203 [9] Xiao-Qiang, Wei-Yang, He-Rong, Phase locked loo and synchronization methods for grid interfaced converters A Review", Przegld Elektrotechniczny, ISSN , R.87,4/20 [0] L. G. B. Rolim, D. Rodrigues da Costa, M. Aredes, "Analysis and software imlementation of a robust synchronizing PLL based on the q theory", IEEE Transactions on Industrial Electronics,Vol. 53, No. 6, December 2006 [] IEEE Standard IEEE Recommended Practices and Requirements for Harmonic Control In Electrical Power Systems. Volume 0 Issue 2 May ISSN: