Performance Enhancement of Permanent magnet Brushless Dc Motor Using Multilevel Inverter

Transcription

1 2017 IEEE 7th International Advance Computing Conference Performance Enhancement of Permanent magnet Brushless Dc Motor Using Multilevel Inverter Bonula Sowjanya Kalyani [1] Venu Madhav Mukkavilli [2] Dr. Gopichand naik [3] [1][2] EEE Department, MVGR College of Engineering, Vizianagaram, Andhra Pradesh, India [3] Andhra University College of Engineering,Visakhapatnam, Andhra Pradesh, India [1] [2] Abstract -This report furnishes the brushless DC motor (BLDC) performance when fed by multi level inverter is compared with voltage source inverter (VSI) fed BLDC motor. Total harmonic distortion (THD) of stator currents and back EMF s of BLDC Motor for these two inverter topologies are compared. Over past years for high power and medium voltage control applications multi level inverters are employed. To obtain higher levels of voltage different types of multilevel inverters are used. Among them, Cascaded H-bridge multi level inverters are mostly used due to its advantages over other. Here experimental results of a voltage source inverter fed BLDC motor performance are compared with cascaded H-bridge multilevel inverter driven BLDC motor performance. Index terms- Brushless DC motor; voltage source inverter (VSI); Multi level inverter; Cascaded H -bridge multilevel inverter (CHB); Total harmonic distortion (THD); Torque ripple; I.INTRODUCTION Multi phase Permanent magnet brushless DC motors are wide spread in high power systems due to its advantages like high efficiency, high reliability, and less maintenance [1].In [2], T.M.Jahns and W.L.Soong given that torque pulsations are results from any deviation of source from ideal conditions of motor or from converter side. Using Fourier series coefficients a new current control algorithm is posited by Tae-Sung Kim[3]. This posited algorithm can reduce ripple content in torque due to the phase current commutation of BLDC motor. A method of optimizing the reference phase current waveforms [4] which include the case of three-phase unbalanced conditions is proposed by Sung Jun Park, Han Woong Park, Man Hyung Lee, F.Harashima. Hanselman [5], Carlson et al. [6], Pillay and Krishnan [7], and Ying and Ertugrul [8] implemented the Equation for electromagnetic torque and stated that under trapezoidal back EMF, for the production of constant electromagnetic torque, rectangular excitation currents are required. The power converters must be able to provide smoother voltage level. This can be achieved by using multilevel inverters. naba et.l stated that the term multilevel has introduced by three level inverter. A staircase voltage waveform is achieved with the multi level inverter concept by using chain of power semiconductor switching devices with number of lower level dc voltage sources. Solar cells batteries, thermocouples, Capacitors, power supplies can be applied as sources. The commutation of the switching devices sum these dc sources which are connected to same phase, in order to accomplish high level voltage as output; Nevertheless, the rating of semiconductor switching devices influenced wholly by the rating of the source voltages to which they have connected. This enhances the levels of voltages which prompts to staircase or smooth voltage level. Refer to typical two level inverters multilevel inverters are more advantageous. These can operate at fundamental and higher frequencies. Electromagnetic compatibility problems are less because it can reduces dv/dt stress. Common mode voltage (CM) produced by multilevel inverters is less; therefore bearing stresses are reduced to great extent. The generated output voltages are staircase form, which gives low distortion on output voltages compared to two level inverters [9]-[11]. The basic multilevel inverters are flying capacitor clamped, cascaded H-bridge, neutral point clamped multi level inverters [12]. Lesser Total harmonic distortions and refined output response can be attained by multilevel inverters. Here voltage source inverter fed BLDC motor and level shifted SPWM for Cascaded 5-level H-bridge multilevel inverter driven BLDC motors are simulated using MATLAB and results are presented /17 $ IEEE DOI /IACC

2 I. BRUSHLESS DC MOTOR DRIVEN BY VOLTAGE SOURCE INVERTER The conventional Permanent Magnet BLDC motor controls by rotor position feedback. This rotor position is sensed at every switching instant of 60⁰, by hall sensors to control logic circuit or to the controllers. The gates pulses generated from the logic circuit and are given to the voltage source inverter or current source inverter to switch the stator windings according to the rotor position. Traditional Brushless DC motors use voltage source inverters for switching. The figures shown below are the performance of BLDC motor when driven by a voltage source inverter. For ideal conditions the shape of stator current motor can be sinusoidal or trapezoidal based on shape of Back- EMF. But in practice at every switching instant of 60⁰, there is a deviation from ideal case due it s to phase inductance. Fig.1 to Fig.5 shows simulink model of VSI fed BLDC motor and performance of a permanent magnet BLDC motor supplied by a voltage source inverter. Fig.2. Three phase stator currents of VSI fed BLDC Back EMF s and stator phase currents must be in phase, if any mismatch between these back EMF s and stator phase currents also causes torque ripples. Fig.3.shows electromagnetic torque of voltage source inverter fed Brush less DC motor.it is evident that it takes more transient time of 4.4msec and the ripples occurs at every 60⁰ commutation instant. Fig.4 shows the speed of rotor of a BLDC motor. Fig.3.Back-EMF waveforms of VSI fed BLDC Fig.1.Simulink model of voltage source inverter fed BLDC motor

3 decided by number of voltage levels needed. Each cell consists of separate DC source. For M voltage level it comprises of ½(M-1) series connected single phase H-bridge cells per phase, for which each H-bridge comprises an individual DC source. A matlab simulink model of a BLDC motor driven by a three phase 5-level cascaded h-bridge with level shifted PWM is shown below and the results are enclosed. Both the electromagnetic generated torque and the speed of the motor are important considerations when used for different applications. Fig.4.Electroagnetic torque of VSI fed BLDC Fig.5.Output speed of a BLDC fed by VSI II.5-LEVEL CASCADED H-BRIDGE MULTILEVEL INVERTER WITH LEVEL SHIFTED SPWM FED BRUSHLESS DC MOTOR When the voltage level of voltage increases, the synthesized output waveform becomes smoother and desired, which reduces harmonic content in the waveform. For this purpose, Multi level inverters are being used in motor drive industries because limitations of two level inverters like voltage stresses, harmonics and low power ratings. In cascaded H-bridge multi level inverters, single phase H-bridge cells are connected in series with different or same dc sources. The number of H-bridge cells required for each phase is Fig.6. Simulink model of cascaded H-bridge5-level inverter fed BLDC motor Fig.6.exhibits simulation model of 5-level cascaded H-bridge multi level inverter with level shifted SPWM fed brushless DC motor. And the performance wave forms of 3-phase stator currents, back EMF s, electromagnetic torque, speed of the rotor are shown from Fig.7 to Fig.9. For the same rating of BLDC Machine, Compared to stator currents of VSI driven BLDC motor, the stator currents of CHB driven BLDC

4 motor are almost equal or larger in amplitude and shape of the waveforms varies slightly. Due to continuous switching of multilevel inverter the shape of the back-emf waves were changed. At 90⁰ instant there is a dip or ripple in wave. Because at 90⁰, the input voltage suddenly changes from +Vdc/2 to +Vdc. And this sudden dip also can appear at 270⁰ instant. But it can be negligible due to its lesser magnitude. Fig.9.Electromagnetic torque wave of a CHB driven BLDC motor Fig.10.Rotor speed of a BLDC motor fed by CHB Fig.7. Three phase stator currents of CHB fed BLDC From fig.9.it can be observed that though the ripples are occurring in a frequent manner the time it lasts are very less. IV. ANALYSIS OF TORQUE RIPPLES Fig.8.Three phase Back-EMF wave forms of CHB fed BLDC By using the below relationship the %torque ripple can be deliberated. % = 100 In Fig.4, the average torque is8.525n m, maximum torque is 10.2N m, and minimum torque is 6.85 N m so that from the above relationship the %torque ripple is 39.29%. Whereas In Fig.9, the average torque is N m, maximum torque is 11.85N m, and minimum torque is 9.85 N m so that from the above relationship the %torque ripple is 18.43%. With the suggested topology the %torque ripple is minimized by 20.86%

5 TABLE V.I COMPARISION OF PERFORMANCE ANALYSIS Two level inverter(vsi) Multi level inverter(cascaded H-bridge) %Torque ripple 39.29% 18.43% REFERENCES [1] Byung-geuk cho,young-doo yoon,seungkisul,y.k.kong,j.g.bin,s.j.park,m.l.lee,"a Separate Double-winding 12-phase Brushless DC Motor Drive Fed from Individual H-Bridge Inverters",IEEE pp ,2010. [2] T.M.Jahns and W.L.Soong, "Pulsating torque minimization techniques for permenant AC motor drives-a review", IEEE Trans. on industrial Electronics, vol.43pp , 1996 Transient response time 4.4msec 1.25msec [3] Tae-Sung Kim, Sung-Chan Ahn, Dong-Seok Hyun, A New Current Control Algorithm for Torque Ripple Reduction of BLDC Motors, Proceedings of Industrial Electronics Society Conference IECON 2001,vol. 2, 2001, pp Power factor THD for stator currents 37.67% 8.30% [4] Sung Jun Park, Han Woong Park, Man Hyung Lee, F. Harashima, A New Approach for Minimum-Torque-Ripple Maximum-EfficiencyControl of BLDC Motor, IEEE Transactions on Industrial Electronics, vol. 47, Issue 1, 2000, pp [5] Hanselman D.C."Minimum Torque Ripple, Maximum Efficiency Excitation of Brushless Permanent Magnet Motors", IEEE Trans. Ind. Applicat., vol. 41, pp , June1994. THD for Back- EMF s 29.67% 23.76% [6] Carlson R., Lajoie-Mazenc M., and dos S. Fagundes J. C., "Analysis of Torque Ripple Due to Phase Commutation in Brushless dc Machines, IEEE Trans. Industry Applications, vol. 28,no. 3, May/June1992. Efficiency 89.25% 70.16% TABLE.V.II.BLDC MOTOR PARAMETERS [7] Pillay P. and Krishnan R.,"Modelling, Simulation, and Analysis of Permanent-Magnet Motor Drives", IEEE Trans. Industry Applications, vol. 25, no. 2, March/April [8] Ying L. and Ertugrul N.,"The Dynamic Simulation of the Three-Phase Brushless Permanent Magnet AC Motor Drives with Lab VIEW", AUPEC/EECON Darwin, Australia Sept parameters values [9]A.P.C.rao,y.p.obulesh,ch.saibabu,"analysis and effect of switching frequency and vltage level on Total harmonic distortion in multilevel inverters fed bldc drive".in proc.isco2013,pp Dc link voltage 48v Phase resistance of stator(ω) 650e-3 Phase inductance Stator (mh) 75 Flux linkage established by magnets Number of pole pairs 8 [10] T.A.Lipo,D.G.Holmes,"pulse width modulation for power converter:principles and practice".n.j:john wiley 2003, [11] K.A.corzie, S.D.Sudhoff, and C.A.Whitcomb, "performance characteristics of a cascaded two-level converter", IEEE trans. on Energy Conversion, 14(3), September [12] Ruhina R. Shaikh,prof.J.R. Rana,"Single phase Seven level inverter", International conference on energy efficient Technologies for sustainability, 2016,pp VI.CONCLUSION The performance of BLDC motor when driven by a voltage source inverter is compared with BLDC motor when driven by five level Cascaded H- bridge with level shifted SPWM multilevel inverter for same motor parameters. As the levels of the voltage increases THD gets reduced. When this multi level voltage applied to BLDC motor, the production of torque ripples reduced and the performance of BLDC motor enhanced to great extent. The future work can be extended by using high frequency switching of semiconductor devices