International Journal of Electrical Engineering & Technology (IJEET) Volume 7, Issue 5, Sep Oct, 2016, pp.79 88, Article ID: IJEET_07_05_008 Available online at http://www.iaeme.com/ijeet/issues.asp?jtype=ijeet&vtype=7&itype=5 ISSN Print: 0976-6545 and ISSN Online: 0976-6553 Journal Impact Factor (2016): 8.1891 (Calculated by GISI) www.jifactor.com IAEME Publication REDUCTION OF HARMONIC DISTORTION IN BLDC DRIVE USING BL-BUCK BOOST CONVERTER BLDC DRIVE Rajesh A V, Bindu S J. and Rekha T. Electrical and Electronics Engineering, College of Engineering Perumon/CUSAT, India. ABSTRACT Conventional dc motors have many attractive properties such as high efficiency and linear torque speed characteristics. The main drawback of the dc motor is the need of periodic maintenance. The brushes of the mechanical commutator eventually wear out and cause undesirable effects such as sparks and acoustic noise. Brushless dc motors (BLDC) in many cases replace conventional dc motors. This paper presents the simulation of a PFC bridgeless (BL) buck-boost convertor fed brushless direct current motor drive and compares its performance with a conventional boost converter drive. The speed control the BLDC motor is done by controlling the dc link voltage of the voltage source inverter (VSI). A BLDC motor when fed by a diode bridge rectifier (DBR)with a high value of DC link capacitor draws peaky current which causes total harmonic distortion (THD) of the supply current in the order of 65% and power factor as low as 0.8. A BL configuration of the buck-boost converter offers the elimination of DBR reducing the conduction losses. The performance of the proposed model is simulated in MATLAB/Simulink environment. Key words: Bridgeless (BL,) diode bride rectifier (DBR), power factor corrected (PFC), total harmonic distortion (THD), discontinuous inductor current mode (DICM). Cite this Article: Rajesh A V, Bindu S J.and Rekha T., Reduction of Harmonic Distortion in BLDC Drive using Bl-Buck Boost Converter BLDC Drive. International Journal of Electrical Engineering & Technology, 7(5), 2016, pp. 79 88. http://www.iaeme.com/ijeet/issues.asp?jtype=ijeet&vtype=7&itype=5 1. INTRODUCTION BLDC Motors are actually a type of permanent magnet synchronous motors. It has a rotor with permanent magnets and stators with windings.they are driven by dc voltage but current commutation is done by solid state switches. The commutation instants are determined by the rotor position and the position of the rotor is detected either by position sensors or by sensor less techniques. BLDC motors have many advantages over conventional DC motors. Few of the advantages are long operating life, high dynamic response, high efficiency better speed v/s torque characteristics noiseless operation higher speed range and higher torqueweight ratio. These BLDC motors are not limited to household applications but are also used in automotive, aerospace, consumer, medical, industrial automation equipments and instrumentation. Power quality problems have become important issues to be considered due to recommended limit of harmonics http://www.iaeme.com/ijeet/index.asp 79 editor@iaeme.com
Rajesh A V, Bindu S J.and Rekha T. in the supply current by various international power quality standards such as the International Electrotechnical Commission (IEC). A BLDC motor when fed by a DBR with high value of dc link capacitor draws peaky current which leads to a THD of supply current of the order of 65% and power factor as low as 0.8.So as to avoid the disadvantages a DBR followed by a power factor corrected converter is utilized for improving the power quality at ac mains. This paper attempts to study and compare the improved BL-buck boost converter fed BLDC motor drive with the conventional boost converter drive. The comparative analysis is done using a MATLAB / SIMULINK environment. 2. BL-BUCK BOOST CONVERTER FED BLDC MOTOR DRIVE The parameters of the BL buck-boost converter are designed such that it operates in discontinuous inductor mode (DCIM) to achieve an inherent power factor correction at ac mains. The speed control of BLDC motor is achieved by the dc link voltage control of VSI using a BL buck-boost converter.this reduces the switching losses in VSI due to the low frequency operation of VSI for the electronic commutation of the BLDC motor. The proposed converter is shown in figure 1 Figure 1 Proposed BL Buck Boost Converter 2.1. Operating Principle of PFC Buck-Boost Converter In the proposed drive of BL BUCK BOOST converter, switches Sw1 and Sw2 operate for the positive and negative half cycles of the supply voltage respectively. During positive half cycle of the supply voltage, switch Sw1, inductor Li1, diodes D1 and Dp are operated to transfer energy to dc link capacitor Cd. Similarly, for the negative half cycle of the supply voltage, switch Sw2, inductor Li2, and diodes D2 and Dn conducts to transfer energy to the dc link voltage. Working of the proposed converter is shown in figure 2. http://www.iaeme.com/ijeet/index.asp 80 editor@iaeme.com
Reduction of Harmonic Distortion in BLDC Drive using Bl-Buck Boost Converter BLDC Drive Figure 2 (a) Figure 2 (b) Figure 2 Shows the working of BL buck- boost converter during positive and negative half cycles 2.2. Design of Proposed BL Buck Boost Converter = 2 2 = 2 2 220 198 The voltage conversion ratio for a buck boost converter is given as = + Here the proposed converter is designed for dc link voltage from 50V (Vdc min) to 200V (Vdc max).hence the minimum and maximum duty ratio as dmin= 0.2016,dmax=0.5025. 2.2.1. Design of Input Inductors (Li1 and Li2) For the buck-boost converter, the value of Lic1 required to operate in critical conduction mode is given as, = (). When R is the equivalent load resistance, d is the duty ratio and fs is the switching frequency. Since the converter operates even at low duty ratio in DICM, the value of Lic1 is calculated at the worst duty ratio of dmin = (1 ) = 50 (1 0.2016) =442.67(). 2! " 90 2 2000 The value of inductances Li1 and Li2 are taken less than 1/10th of the minimum critical value of inductances to ensure deep DICM condition; hence the value of inductance is approximately taken as 35μH. 2.2.2. Design of DC link Capacitance (Cd) The value of the dc link capacitor is calculated for the designed value of Vdc des,, = - 1 3. = 2" 350 100 = 2/ 2/ 2 314 0.03 100 =1857.7(6 Nearest possible value of dc link capacitance is selected as 2200μF http://www.iaeme.com/ijeet/index.asp 81 editor@iaeme.com
Rajesh A V, Bindu S J.and Rekha T. 2.2.3. Design of Input Filter (Lf and Cf), 89 = - :28; / < :28; tan(@)= 350 220 ( 1 314 220 2 )tan(1 ) =401.98(6 Approximately the value of Cf is taken as 330Nf 1 = B2C + 4,! B2C = 1 1 4 2000 0.04F 330 10E 314 GH200 350 I=1.57J). Finally, a low pass filter with inductor and capacitor of 1.6 mh and 330 nf is selected for this particular application 3. SIMULATED PERFORMANCE OF THE PROPOSED BLDC MOTOR DRIVE The proposed model is shown in figure 4. The parameters associated with the BLDC motor such as speed (N), electro-magnetic torque (Te), and stator current (ia) are analyzed for the proper functioning of the BLDC motor. Parameters such as supply voltage (Vs), supply current (is), dc link voltage (Vdc), inductor s currents (ili1, ili2), switch voltages (Vsw1, Vsw2), and switch currents (isw1, isw2) of the PFC BL buck boost converter are evaluated to demonstrate its proper functioning. Figure 3 Block diagram of PFC BL buck boost converter fed BLDC motor drive 4. RESULT ANALYSIS The simulation of the proposed BL buck boost converter is performed in MATLAB 2014/simulink. http://www.iaeme.com/ijeet/index.asp 82 editor@iaeme.com
Reduction of Harmonic Distortion in BLDC Drive using Bl-Buck Boost Converter BLDC Drive 4.1. Steady State Performance of Proposed Drive The performance of the proposed converter BLDC motor drive at speed control by varying dc link voltage from 50 to 200 V is tabulated in Table I. The harmonic spectra of the supply current at rated and light load conditions, i.e., dc link voltages of 200Vand 50 V, are also shown in figure 4. Table 1 Variation of PF & THD with varying dc link voltage V dc N THD of PF (v) (rpm) I s (%) 50 372 4.65 0.9776 100 850 4.32 0.9794 150 1425 3.85 0.9803 200 1528 3.99 0.9813 Figure 4 (a) Figure 4 (b) Figure 4 Harmonic spectra of supply current at rated supply voltage and rated loading on proposed BLDC motor drive for a dc link voltage of (a) 200v and (b) 50v http://www.iaeme.com/ijeet/index.asp 83 editor@iaeme.com
Rajesh A V, Bindu S J.and Rekha T. 4.2. Performance of Proposed Drive under Supply Voltage Variation The performance of the proposed drive is evaluated under different supply voltage (90 & 270). Figure 5 ( a) and (b) shows the harmonic spectra of supply current at ac mains at rated conditions of dc link voltage and load on the BLDC motor with supply voltage as 90 and 270 V, respectively. It is obtained that for 90v supply THD is 3.98 and for 270V it is 4.00. Figure 5 (a) Figure 5 (b) Figure 5 Harmonic spectra of supply current at rated loading on proposed BLDC motor drive with dc link voltages as 200V and supply voltages as (a) 90v and (b) 270v Figure 6 waveform showing current in switches (Q1&Q), diodes (d1&d2), inductor (L1&L2) http://www.iaeme.com/ijeet/index.asp 84 editor@iaeme.com
Reduction of Harmonic Distortion in BLDC Drive using Bl-Buck Boost Converter BLDC Drive Figure 7 Waveform showing THD analysis of BLDC drive under rated condition using BL Buck Boost Converter Table 2 Comparison between conventional and proposed system S L NO: TOPOLOGIES POWER FACTOR THD (%) 1. Bridged Boost Converter Drive 0.74 90.85 Bridged Buck Boost Converter Drive 2. 0.83 64.81 Bridgeless Boost Converter Drive 3. BL-Buck Boost Converter Drive 0.92 43.59 4. 0.98 3.86 4.3. Obtained Simulated Result From the simulation of the proposed BL-Buck boost converter, it is obtained that the power factor and THD shows a great improvement than conventional BLDC drives. The corresponding waveforms of the proposed drive are shown in figure 6. The THD analysis of the proposed drive is shown in figure 7. 5. HARDWARE VALIDATION OF PROPOSED BLDC MOTOR DRIVE The control section for the proposed drive is developed by using an ATMEGA 16 microcontroller. The necessary circuitry for isolation between controller and gate drivers of solid-state switches is developed using the TLP 250 IC s. A pre-filtering and isolation circuit for the Hall-Effect sensor is also developed for sensing the Hall-effect position signals. Test results are discussed in the following sections. 5.1. Steady State Performance The performance of the proposed drive is evaluated with the experimental setup developed as shown in figure 8.The output waveforms from different sections such as drivers, controllers, synchronizers and inverters where taken. These are shown under figure http://www.iaeme.com/ijeet/index.asp 85 editor@iaeme.com
Rajesh A V, Bindu S J.and Rekha T. Figure 8 Experimental setup Figure 9 Pulses to inverter complimentary switches 180 phase shift (A-A ) Figure 10 Pulses to adjacent inverter switches 60 Phase shift (A, B) http://www.iaeme.com/ijeet/index.asp 86 editor@iaeme.com
Reduction of Harmonic Distortion in BLDC Drive using Bl-Buck Boost Converter BLDC Drive Figure 11 Output of inverter Figure 12 (a) Figure 12 (b) Figure 12 Waveforms showing pulses to converter switches (Sw1 & Sw2) http://www.iaeme.com/ijeet/index.asp 87 editor@iaeme.com
Rajesh A V, Bindu S J.and Rekha T. 6. CONCLUSION The performance of the PFC BL buck boost converter has been evaluated both simulation and hardware wise. The proposed drive is evaluated under variation of different motor load, dc link voltages and supply voltage variations. The proposed drive is compared with the conventional BLDC drive using boost converter. The results show that the PFC BL buck boost converter BLDC drive has a greater efficiency than the conventional drive. There is a greater improvement in supply current and hence PF compared to conventional drive. It is a recommended solution applicable to low power BLDC motor drives. REFERENCE [1] BIST And Singh, Adjustable Speed PFC Bridgeless Buck Boost Converter Fed BLDC Motor Drive, IEEE Transactions On Industrial Electronics, Vol. 61, No. 6, June 2014 [2] L. Huber, Y. Jang, and M. Jovanovic, Performance evaluation of bridgeless PFC boost rectifiers, IEEE Trans. Power Electron., vol. 23, no. 3, pp. 1381 1390, May 2008 [3] M. R. Sahid, A. H. M. Yatim, Taufik A New AC-DC Converter Using Bridgeless SEPIC IEEE Transactions on Power Electronics, 2010. [4] R.Devasaran, Dr. Pankaj Roy and Dr. Arvind Kumar Singh, Performance and Analysis of PMBLDC Motor Using Fuzzy Logic Controllers. International Journal of Electrical Engineering & Technology (IJEET), 4(6), 2014, pp. 94 109. [5] Yungtaek Jang, Milan M Jovanovich Bridgeless High power factor Buck converter, IEEE Trans. Power Electron., vol. 26, no. 2, pp. 291 297, Feb. 2011. [6] S. Singh and B. Singh, A voltage-controlled PFC Cuk converter based PMBLDCM drive for airconditioners, IEEE Trans. Ind. Appl., vol. 48, no. 2, pp. 832 838, Mar./Apr. 2012. [7] B. Singh, B. N. Singh, A. Chandra, K. Al-Haddad, A. Pandey, and D. P. Kothari, A review of singlephase improved power quality ac-dc converters, IEEE Trans. Ind. Electron., vol. 50, no. 5, pp. 962 981, Oct. 2003. [8] Ansia Assis and Saritha Sathyan, High Step up Boost Converter Based Micro Inverter with MPPT and Current Control. International Journal of Electrical Engineering & Technology (IJEET), 5(12), 2014, pp. 123 130. [9] B. Singh, S. Singh, A. Chandra, and K. Al-Haddad, Comprehen-sive study of single-phase ac-dc power factor corrected converters with high-frequency isolation, IEEE Trans. Ind. Informat., vol. 7, no. 4, pp. 540 556, Nov. 2011. http://www.iaeme.com/ijeet/index.asp 88 editor@iaeme.com