A NEW C-DUMP CONVERTER WITH POWER FACTOR CORRECTION FEATURE FOR BLDC DRIVE

Transcription

1 International Journal of Electrical and Electronics Engineering Research (IJEEER) ISSN X Vol. 3, Issue 3, Aug 2013, TJPRC Pvt. Ltd. A NEW C-DUMP CONVERTER WITH POWER FACTOR CORRECTION FEATURE FOR BLDC DRIVE M. BALA KRISHNA 1 & M. KIRAN KUMAR 2 1 M-Tech Scholar, Department of Electrical And Electronics Engineering, K L University, Guntur, Andhra Pradesh, India 2 Assistant Professor, Department of Electrical & Electronics Engineering, K L University, Guntur, Andhra Pradesh, India ABSTRACT Permanent magnet brushless DC motor (PMBLDCM) drives are being employed in many variable speed applications due to their high efficiency, silent operation, compact size, high reliability, ease of control, and low maintenance requirements. These drives have power quality problems and poor power factor at input AC mains as they are mostly fed through diode bridge rectifier based voltage source inverters. To overcome such problems a single-phase singleswitch power factor correction AC-DC converter topology based on a Cuk converter is proposed to feed voltage source inverters based PMBLDCM. A modified C-dump converter for brushless DC (BLDC) machine used, the converter can realize the energy bidirectional flowing and has the capability to recover the energy extracted from the turnoff phase of the BLDC machine. Simulation and experimental results of the proposed system are presented. KEYWORDS: Brushless DC (BLDC) Machine, C-Dump Converter, Power Factor Correction, Speed Control INTRODUCTION Variable speed inverter-fed ac motor drives are being used in a wide variety of industrial applications and consumer products. Cost minimization is a key factor in specially fractional horse power BLDC motor drive for HVAC and other applications. This cost minimization can be achieved by minimization of the inverter configuration, employing an appropriate control and optimal motor design. Up to now, the minimized converters have been designed and applied to induction motor drives [l]. Recently, BLDC motors are being used in various applications, which have attracted the attention of several researchers. BLDC motors are synchronous motors with permanent magnets on the rotor and armature winding on the stator. From the construction point of view, they are the inside-out version of DC motors. The most important advantage of BLDC motors is the removal of the brushes, which eliminates brush maintenance and the sparking associated with them. In comparison with induction motors at fractional horsepower, BLDC motors have a better efficiency and better power factor. Therefore, they produce more output power for the same frame size. These advantages of the BLDC motor come at the expense of increased complexity of the controller and the need for shaft positioning sensors. The permanent magnet brushless DC machine (BLDCM) is one of the suitable motors for the FESS [3]. The common half-bridge topology for high-speed BLDCM is shown in Figure 1. It includes a buck chopper and a half-bridge converter. Compared with the full-bridge converter, the half bridge converter has half the number of switches and avoids the short circuit across the phase leg in the full-bridge converter. However, this half-bridge topology has two disadvantages for the FESS: 1) the energy unidirectional flow, and 2) the energy of the turnoff phase is consumed on the resistance which means the waste of energy.

2 60 M. Bala Krishna & M. Kiran Kumar In order to overcome these drawbacks, a modified C-dump converter for high-speed BLDCM used in the FESS is presented in this paper. The principle of operation and the analysis of the proposed converter are developed. Figure 1: Common Half-Bridge Topology for High-Speed BLDCM STRUCTURE AND PRINCIPLE Figure 2 shows the modified C-dump converter for BLDCM used in the FESS. The proposed converter includes a half-bridge converter (switches Ta, Tb, Tc), an energy recovery chopper (switch Tr; diodes D 1,D 2,D 3,D r ; inductance Lr and capacitor Co), a bidirectional DC DC converter (switches T1, T2 ; inductance L2 and capacitor C3 ), and a DC filter (inductance L1 and capacitors C 1,C 2 ). U 1 stands for the source and R1 stands for the load. The modified converter has two working modes: the FESS charging mode and the FESS discharging mode. In the FESS charging mode, the source supplies energy to the flywheel, therefore S1 is on and S2 is off. In this mode, the half-bridge converter works in the motor operation., Ta, Tb and Tc are operated with the duration of 120 electrical degrees. Tr works in the pulse width modulation (PWM) operation mode and recovers the energy of the turnoff phase to the source [4]. The bidirectional DC DC converter works in buck operation mode (T1 works in PWM operation mode and T2 is off.) to control the motor speed. Figure 3 illustrates the modified converter for the FESS working in the charging mode. Figure 2: Modified C-Dump Converter for the FESS

3 A New C-Dump Converter with Power Factor Correction Feature for BLDC Drive 61 Figure 3: Modified Converter Working in the Charging Mode In the FESS discharging mode, the BLDCM (with flywheel) acts as a generator to discharge the kinetic energy of the flywheel into the load, therefore S1 is off and S2 is on. In this mode, the half-bridge converter acts as a diode rectifier to convert the high-frequency AC to the DC. Ta, Tb, Tc, Tr are Da, Db, Dc all off and form a diode rectifier. With the speed of flywheel decreasing, the output voltage drops. In order to keep the output voltage stable, the bidirectional DC DC converter works in boost operation mode ( T2 works in PWM operation mode and T1 is off). Figure 4 illustrates the modified converter for the FESS working in the discharging mode. Figure 4: Modified Converter Working in the Discharging Mode Figure 5: The Equivalent Circuits of the Converter in its Switching Operation (a) Ts on, Tr on; (b) Ts on, Tr off; (c) Ts off, Tr on; (d) Ts off, Tr off

4 62 M. Bala Krishna & M. Kiran Kumar MODELING AND CONTROL STRATEGY The modeling and analysis of the proposed converter are presented in this part. Dynamic Model Four distinct modes of operation can be identified for the proposed converter in the charging mode. The equivalent circuits of the converter in its switching operation are shown in Figure 5. The voltage drop of the switch and the diode, the resistance of the inductance, and the mutual inductance of the motor phases are ignored. Ts considers as Ta, or Tb, or Tc.Vdc is the bus voltage (voltage of the capacitor C3), e s is the back-electromotive force (back-emf) of the motor, Rs is the motor phase resistance, Ls is the motor phase inductance, i s is the motor phase current, is the capacitor Co voltage, Vin is the source input voltage (voltage of the capacitor C 1 ), is the energy recovery circuit inductance, is the current of the energy recovery inductance, and is the buck factor. (1) (2) (3) (4) ( > 0) (6) (5) 3) (7) (8) (9) (10) (11) 4) (12) ( > 0) (14) (13) (15) Design of the Main Parameter (16) The main parameters of the proposed converter are derived as follows. Energy Extracted from the Turnoff Phase

5 A New C-Dump Converter with Power Factor Correction Feature for BLDC Drive 63 The system works in steady state and the switching loss is ignored. The energy extracted from the turnoff phase can be described as (17) where is the energy extracted from the turnoff phase. i smax is the motor phase current in commutation moment; it can be obtained from (1). The power extracted from the turnoff phase is Where n is the speed of the motor and p is the pairs of poles. Energy Recovery Capacitor C o The energy extracted from the turnoff phase is delivered to the energy recovery capacitor. Therefore = (19) (20) where ΔV co is the voltage variation of the capacitor Co. The voltage should be higher than V dc + e s. Energy Recovery Inductance L r According to energy conservation, the energy recovered to source can be described as = (21) Where i rmax (i rmin ) is the maximum (minimum) current of the inductance Lr. In order to keep the energy recovery fast, the should not be too large. Therefore, it is better for the to Lr work in discontinuous conduction mode i rmin = 0 (23) Control Strategy The control structure of the modified converter working in the charging mode is shown in Figure 6. It includes the motor speed control and the recovery capacitor voltage control. The motor speed control includes double loops: the inner current loop and the outer speed loop. The commutation of phases is decided based on the output of three Hall effect sensors. The motor phases are protected against over current. The proportional integral (PI) control combined with the hysteresis control is used in capacitor voltage control. It is recommended for the converter due to its small voltage fluctuation of the energy recovery capacitor and current ripple of the motor.

6 64 M. Bala Krishna & M. Kiran Kumar SIMULATION & RESULTS Case 1 Figure 6: Control Structure of the Converter in the Charging Mode Figure 7: Simulation Model of the BLDC Motor Controlled by the C-Dump Converter Figure 8(a): Recovery Current of the Inductor Lr

7 A New C-Dump Converter with Power Factor Correction Feature for BLDC Drive 65 Figure 8(b): Voltage across the Capacitor Co Figure 8(c): Voltage across the Switch MOSFET Figure 8(d): Current Flowing in the Phase A Figure 9(a): Discharging Current of the Inductor Lr

8 66 M. Bala Krishna & M. Kiran Kumar Figure 9(b): Output Voltage of the Converter which is Having the Magnitude 100V Figure 9(c): Voltage across the BLDC Rectified by the Diode Rectifier Figure 10: Simulation Model of the BLDC Driven Circuit with the PFC Converter Figure 11(a): Recovery Current of the Inductor Lr

9 A New C-Dump Converter with Power Factor Correction Feature for BLDC Drive 67 Figure 11(b): Voltage across the Capacitor Co Figure 11(c): Voltage across the Switch MOSFET Figure 11(d): Current Flowing in the Phase A Figure 12(a): Discharging Current of the Inductor Lr

10 68 M. Bala Krishna & M. Kiran Kumar Figure 12(b): Output Voltage of the Converter which is Having the Magnitude 100V Figure 12(c): Voltage across the BLDC Rectified by the Diode Rectifier Figure 13: Unity Power Factor of the Source at the Diode Bridge Rectifier Figure 14: Stator Current and the Back EMF of the BLDC Motor

11 A New C-Dump Converter with Power Factor Correction Feature for BLDC Drive 69 Figure 15: Speed Curve of the BLDC Motor, it is Running at a Speed of 2000 r.p.m Figure 16: Electromagnetic Torque Characteristics of the BLDC Motor CONCLUSIONS This paper has presented a modified C-dump converter for BLDCM used in the FESS. The proposed converter can realize the bidirectional energy flowing and has the capability to recover the energy extracted from the turnoff phase which is useful for the motor driver system especially for the FESS. In addition to that power factor improvement is also given an important factor. The principle of operation, modeling, and control strategy of the system has been presented. Simulation and experiment validate the theoretical results and demonstrate the good performance of the converter. From the simulation results the source side power factor is improved though the rectifier output voltage is maintained constant. REFERENCES 1. R. S. Weissbach, G. G. Karady, and R. G. Farmer, Dynamic voltage compensation on distribution feeders using flywheel energy storage, IEEE Trans. Power Delivery, vol. 14, no. 2, pp , Apr M. M. Flynn, P. Mcmullen, and O. Solis, Saving energy using flywheels, IEEE Ind. Appl. Mag., vol. 14, no. 6, pp , Nov./Dec C. W. Lu, Torque controller for brushless DC motors, IEEE Trans. Ind. Electron., vol. 46, no. 2, pp , Apr R. Krishnan and S. Lee, PM Brushless dc motor drive with a new power converter topology, IEEE Trans. Ind. Appl., vol. 33, pp , July/Aug

12 70 M. Bala Krishna & M. Kiran Kumar AUTHOR S DETAILS M. BALAKRISHNA received B. Tech degree in Electrical and Electronics Engineering form Aurora s Engineering college, JNTU, Hyderabad, India, in Currently, he is pursuing M.Tech in Power Electronics and Drives in Electrical Engineering at K L University, Guntur, India. His areas of interest involves Power electronics, Control systems and Electrical machines. M. KIRAN KUMAR received B.Tech Degree in Electrical and Electronics Engineering from Gokula Krishna College of Engineering and Technology, JNTU, Hyderabad, India, in 2007, M.E. Degree in Power Electronics and Drives from Sree Sastha Institute of Engineering and Technology, Anna University, Chennai, India, in 2010 and Pursuing Ph.D in Electrical Engineering at K L University, Guntur, India. Currently he is working as Asst. Professor in Electrical and Electronics Engineering at K L University, Guntur, India. His research interest includes Switched Reluctance Machines, Power Electronics and Control Systems.