A BRIDGELESS CUK CONVERTER BASED INDUCTION MOTOR DRIVE FOR PFC APPLICATIONS

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1 INTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING & TECHNOLOGY (IJEET) Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM14) ISSN (Print) ISSN (Online) Volume 5, Issue 12, December (2014), pp IAEME: Journal Impact Factor (2014): (Calculated by GISI) IJEET I A E M E A BRIDGELESS CUK CONVERTER BASED INDUCTION MOTOR DRIVE FOR PFC APPLICATIONS RAICHEL MATHEW 1, ASWATHY MOHANDAS P 2 1 PG Scholar, Electrical and Electronics Department, Sree Narayana Gurukulam College of Engineering, Kolenchery, India 2 Assistant Professor, Electrical and Electronics Department, Sree Narayana Gurukulam College of Engineering, Kolenchery, India ABSTRACT A new bridgeless topology for power factor correction is proposed here. Induction motor drives are widely employed in industrial sectors because of their high efficiency, reliability, output etc. They are considered as the major prime movers and consume about 70% to 80% of the total electricity. As a result these drives face many problems related to power quality and power factor. The main reason is the input rectifier bridge. Unity power factor is the main goal of all company. If it is less than unity, then more current has to be supplied. For the power factor improvement a new bridgeless topology is introduced here were input bridge section is absent. Cuk converter is used as the PFC converter which operates in its (DCM) discontinuous conduction mode which offers zero current ON for switches. Proposed model is simulated in Simulink model with suitable control strategies. Comparisons based on performances of conventional and proposed circuits are included. Keywords: Bridgeless Topology, CUK Converter, Discontinuous Conduction Mode DCM, Induction Motor, Zero Current Switching ZCS 1. INTRODUCTION Induction motors are the most suitable electric motors in industrial sector. They are well known for their performance characteristics. Generally they are supplied from an input rectifier section with proper filtering methods [1]. When current flows through the diodes, conduction losses occur due to the voltage drop across it. This will in turn degrades its efficiency especially at low voltages. So the input bridge section is completely eliminated for power factor correction. Thus a new bridgeless topology is introduced. The number of semiconductor devices in the current path is thus reduced. This will in turn reduce losses and improves power factor. PFC also leads to cost savings as well as energy savings. It is inevitable for every converter in order to satisfy the regulatory standards IEC For good power quality and power factor active power factor correction circuits are necessary. In conventional methods single phase rectifiers are used. They operate by rectifying the input voltage and then filter it with large capacitors. Capacitors always maintain a constant voltage approximately as its peak. Currents are drawn in narrow pulses by the capacitors which results in major harmonic issues. It will also leads to severe power quality problems. Harmonics not only destroys its line but also disrupts other devices connected to it [2]. Since pulsated currents are drawn. PFC converters are employed to provide a constant DC source. Many topologies are proposed to sort out the problem of power factor and also for harmonics. In most of PFC circuits, the converter used is boost converter. Boost converter has a 191

2 step up conversion ratio [3]. It can be used in both CCM (continuous conduction mode) and DCM (discontinuous conduction mode). But the disadvantage is that it can be applied for boost operations only. Apart from this it is suffered from high inrush current and isolation problems. As an advance in technology in this paper Cuk converter is used as a PFC converter [4]. The topology based on Cuk converter offers many advantages when compared to other converter topologies. It includes automatic current shaping, both input and output continuous currents, less ripple content in input current, easy implementation, protection from inrush currents etc. Proposed Cuk converter is subjected to be operated in discontinuous conduction mode (DCM) which aids to achieve near unity power factor and reduced total harmonic distortion (THD). Also zero current switching (ZCS) turn ON and turn OFF are possible. Moreover the selected topology still has a problem those three semiconductors in current path. Compared with SEPIC converter [8], Cuk converter has continuous input and output currents even at low ripple. So Cuk converter acts as a common selector in major basic topologies. 2. CONVENTIONAL CUK PFC CONVERTER A conventional PFC Cuk rectifier is drawn in Fig 1. From the circuit, when switch Q is ON current flows through three power semiconductor devices. That is two bridge diodes and one switch. Likewise when the switch is OFF, current will flow through three diodes. So in every switching period current flow through three semiconductor devices, this will result in conduction losses and poor efficiency. Fig 1: Conventional PFC Cuk converter 3. PROPOSED TOPOLOGY In order to reduce the conduction losses and to improve the power supply efficiency, a Cuk converter bridgeless topology is employed. The Cuk converter in DCM offers improved current shaping properties as compared with other fly back converters.apart from all of this the major advantage is concerned with losses in switches and diodes. The performance of new topology is compared with that of the conventional type [9]. The proposed circuit is shown below in Fig 2. Along with it block diagram regarding the proposed system is also shown. Fig 3: Bridgeless Cuk Rectifier 192

3 The bridgeless Cuk rectifier is formed by connecting two DC-DC converters together. For every switching cycle each converter operates for time (T/2) of the total time. From figure, when switch is ON, the current Iac flows through L 1, Q 1 and Dp. Likewise when switch is OFF, current flows through diode D 01.So in each case, current flows through one or more semiconductor device. As a result the conduction losses in active and passive switches are reduced and circuit efficiency is considerably reduced. Here the slow recovery diodes Dp and Dn always connect the output voltage to input ac line voltage in order to prevent the common mode noise problems. Thus the circuit is free from noise and EMI problems [8]. Also by the reduction of conduction losses, energy savings as well as cost savings can be achieved. In fig (3), there are two recovery diodes along with the two switches. The switches are operated with same control circuitry. That is switch Q 1 is turned ON for positive cycle and Q 2 vice versa. As a result the complexity of the circuit can be reduced [10]. 4. MODE OF OPERATION Before the explanation some assumptions has to be made. The converter should be operated in steady state condition. The components should be ideal and lossless. The value of output capacitor should be large enough to withstand the voltage stresses. Due to symmetry only positive half cycle is to be analyzed. During the positive half cycle, the first half of the circuit involves in the operation. That is the path L 1 -Q 1 -C 1 -L 01 -D 01 is active through diode Dp which connects input source and output. Likewise during the negative half cycle, the path L 2 -Q 2 -C 2 -L 02 -D 02 is active which connects input and output. The Cuk converter is operating in its discontinuous conduction mode which offers additional advantages like natural near unity power factor, zero current switching etc [10]. 5. CONVERTER DESIGN For DCM operation the following condition should be satisfied. Ke<Ke-crict=1/2(M+sin(ωt)) 2 (1) Where Ke is the dimension parameter and is given by, Ke=2L e /R L.T S (2) Let the other parameters be: Input voltage = 100Vrms, output voltage = 48V, power = 150W. From this, output current I 0 = 3.12A. the load resistance is given by V = I R and obtained as 15.3Ω. Assume the output voltage is less than 1% and the switching frequency be 50KHZ. i L1 < 10% I L1 (3) I L2 = (1-D)/F.L 2 (4) V C1 = D.V d.i d /V 0.C.F (5) I L1 = D.Vin/ L.F 1 (6) From the above equations the values of inductor and capacitor are obtained as: L 1 = L 2 =1mH L 01 =L 02 =22µH C 1 =C 2 =1µF C out =12000Μf 193

4 6. SIMULATION AND MODELLING Fig 4: Simulation diagram of conventional Cuk converter Fig 5: Output voltage and current Fig 6: THD of conventional Cuk 194

5 Fig 7: Bridgeless Cuk Converter Fig 8: Output voltage and current TABLE I: SIMULATION DETAILS Input voltage 180V Switching Frequency 20 khz Input inductors L 1 and L 2 1Mh Output inductors L o1 and L o2 22µH Energy transfer capacitors C 1 and C 2 1µF Filter capacitors C o µf Active Switches Q 1 and Q 2 R ds-on =29mΏ Output diodes D o, D o1 and D o2 V f =0.9V Input diodes D p and D n V f =0.7V Filter L & C L=1e -4 & C=39e -2 In fig 4, simulation diagram of conventional Cuk converter is shown. And in fig 5 & 6 the corresponding waveforms of voltages and THD are shown. The power factor is measured in terms of THD. Apart from this in figures 7,8,9 the proposed topology is shown. When compared the THD is reduced from 14.17% to 5.26%, which shows that the proposed system has reduced losses.bas a result the efficiency is higher than that of conventional system. 195

6 Fig 9: THD of bridgeless converter 7. CONCLUSION A new topology based on Cuk converter is proposed and simulated. The proposed topology is simulated with induction motor load. By this the power factor of an IM is increased and considerable efficiency can be achieved. By considering all other converter topologies, Cuk converter becomes the best solution. Apart from conventional systems, bridgeless topologies yield more efficiency and energy savings. As IM are the most commonly used electric motors, the increase in pf and efficiency had lead to tremendous changes in industrial sector REFERENCES [1] J.F.Gieras and M.Wing, Permanent Magnet Motor Technology Design and Application. New York: Marcel Dekker, 2002 [2] N. Mohan, M. Undeland, and W. P. Robbins, Power Electronics: Converters, Applications And Design. Hoboken, Nj: Wiley, 1995 [3] W. Choi, J.Kwon, E. Kim, J. Lee, and B.Kwon, Bridgeless Boost Rectifier with Low Conduction Losses and Reduced Diode Reverse-Recovery Problems IEEE Trans. Ind. Electron., Vol. 54, No. 2, Pp , Apr [4] W. Wei, L. Hongpeng, J. Shigong, And X. Dianguo, A Novel Bridgeless Buck-Boost PFC Converter, In Proc. IEEE Power Electron. Spec. Conf., 2008, Pp [5] Yungtaek Jang, Milan M Jovanovic Bridgeless High Power Factor Buck Converter, IEEE Trans. Power Electron., Vol. 26, No. 2, Pp , Feb [6] M. Mahdavi and H. Farzanehfard, Bridgeless Sepic PFC Rectifier With reduced Components and Conduction Losses, IEEE Trans. Ind. Electron., Vol. 58, No. 9, Pp , Sep [7] Sebastian, J., Cobos, J.A., Lopera, J.M., and Uceda, J.: The Determination of Boundaries Between Continuous And Discontinuous Conduction Mode In PWM Dc-To-Dc Converters Used As Power Factor Regulators, IEEE Trans. Power Electronics, 1995, 10, (5) [8] Cnnda. Sabzali, E. H. Ismail, M. Al-Saffar, and A Fardoun, New Bridgeless DCM Sepic and CukPFC Rectifiers With Low Conduction And Switching losses, IEEE Trans. Ind. Appl., Vol. 47, No. 2, Pp , Mar./Apr [9] Huai Wei, Comparison of Basic Converter Topologies for Power Factor Correction University Of Central Florida, -Orlando, 1998 [10] E.H.Ismailabbas.A.Fardoun,Ahmad.J.Sabazali mustafa.a.al-saffar New Efficient Bridgeless Cuk Rectifiers For PFC Applications, IEEE Trans. Power Electronics Vol. 27, No. 7, July [11] Herawati Yusuf, The Influence Of Air Gaps At 0.4 Duty Cycle On Magnetic Core Type E To Increase The Efficiency of Cuk Converter International Journal of Electrical Engineering & Technology (IJEET), Volume 4, Issue 2, 2013, pp , ISSN Print : , ISSN Online: