International Journal of Electrical and Electronics
Engineering Research (IJEEER)
ISSN 2250-155X
Vol. 3, Issue 3, Aug 2013, 59-70
© TJPRC Pvt. Ltd.
A NEW C-DUMP CONVERTER WITH POWER FACTOR CORRECTION FEATURE FOR
BLDC DRIVE
M. BALA KRISHNA1 & M. KIRAN KUMAR
2
1M-Tech Scholar, Department of Electrical And Electronics Engineering, K L University, Guntur, Andhra Pradesh, India
2Assistant 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 single-
switch 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.
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 D1,D2,D3,Dr; 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 C1,C2 ). U1stands 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
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
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), es is the back-electromotive force (back-EMF) of the motor,
Rs is the motor phase resistance, Ls is the motor phase inductance, is is the motor phase current, is the capacitor Co
voltage, Vin is the source input voltage (voltage of the capacitor C1), is the energy recovery circuit inductance, is the
current of the energy recovery inductance , and is the buck factor.
(1)
(2)
(3)
(4)
(5)
( > 0) (6)
(7)
(8)
3)
(9)
(10)
(11)
(12)
4)
(13)
( > 0) (14)
(15)
(16)
Design of the Main Parameter
The main parameters of the proposed converter are derived as follows.
Energy Extracted from the Turnoff Phase
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. isMax 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 Co
The energy extracted from the turnoff phase is delivered to the energy recovery capacitor.
Therefore
= (19)
(20)
where ΔVco is the voltage variation of the capacitor Co. The voltage should be higher than Vdc + es.
Energy Recovery Inductance Lr
According to energy conservation, the energy recovered to source can be described as
= (21)
Where irMax(irMin) 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 irMIN = 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.
64 M. Bala Krishna & M. Kiran Kumar
Figure 6: Control Structure of the Converter in the Charging Mode
SIMULATION & RESULTS
Case 1
Figure 7: Simulation Model of the BLDC Motor Controlled by the C-Dump Converter
Figure 8(a): Recovery Current of the Inductor Lr
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
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
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
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
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. 465–471, Apr. 1999.
2. M. M. Flynn, P. Mcmullen, and O. Solis, “Saving energy using flywheels,” IEEE Ind. Appl. Mag., vol. 14, no. 6,
pp. 69–76, Nov./Dec. 2008.
3. C. W. Lu, “Torque controller for brushless DC motors,” IEEE Trans. Ind. Electron., vol. 46, no. 2, pp. 471–473,
Apr. 1999.
4. R. Krishnan and S. Lee, “PM Brushless dc motor drive with a new power converter topology,” IEEE Trans. Ind.
Appl., vol. 33, pp. 973–982, July/Aug. 1997.
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 2011. 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.
