25-05-2012, 12:31 PM
A Voltage Controlled Adjustable Speed PMBLDCM
Drive using A Single-Stage PFC Half-Bridge Converter
A Voltage Controlled Adjustable Speed.pdf (Size: 533.21 KB / Downloads: 75)
Abstract
In this paper, a buck half-bridge DC-DC converter is
used as a single-stage power factor correction (PFC) converter
for feeding a voltage source inverter (VSI) based permanent
magnet brushless DC motor (PMBLDCM) drive. The front end
of this PFC converter is a diode bridge rectifier (DBR) fed from
single-phase AC mains. The PMBLDCM is used to drive a
compressor load of an air conditioner through a three-phase
VSI fed from a controlled DC link voltage. The speed of the
compressor is controlled to achieve energy conservation using a
concept of the voltage control at DC link proportional to the
desired speed of the PMBLDCM. Therefore the VSI is operated
only as an electronic commutator of the PMBLDCM. The stator
current of the PMBLDCM during step change of reference
speed is controlled by a rate limiter for the reference voltage at
DC link. The proposed PMBLDCM drive with voltage control
based PFC converter is designed, modeled and its performance
is simulated in Matlab-Simulink environment for an air
conditioner compressor driven through a 1.5 kW.
INTRODUCTION
ERMANENT magnet brushless DC motors
(PMBLDCMs) are preferred motors for a compressor of
an air-conditioning (Air-Con) system due to its features
like high efficiency, wide speed range and low maintenance
requirements [1-4]. The operation of the compressor with the
speed control results in an improved efficiency of the system
while maintaining the temperature in the air-conditioned zone
at the set reference consistently. Whereas, the existing air
conditioners mostly have a single-phase induction motor to
drive the compressor in ‘on/off’ control mode.
PROPOSED SPEED CONTROL SCHEME OF PMBLDC
MOTOR FOR AIR CONDITIONER
The proposed speed control scheme (as shown in Fig. 1)
controls reference voltage at DC link as an equivalent
reference speed, thereby replaces the conventional control of
the motor speed and a stator current involving various sensors
for voltage and current signals. Moreover, the rotor position
signals are used to generate the switching sequence for the
VSI as an electronic commutator of the PMBLDC motor.
Therefore, rotor-position information is required only at the
commutation points, e.g., every 60°electrical in the threephase
[1-4]. The rotor position of PMBLDCM is sensed using
Hall effect position sensors and used to generate switching
sequence for the VSI as shown in Table-I.
PERFORMANCE EVALUATION OF PROPOSED PFC DRIVE
The proposed PMBLDCM drive is modeled in Matlab-
Simulink environment and evaluated for an air conditioning
compressor load. The compressor load is considered as a
constant torque load equal to rated torque with the speed
control required by air conditioning system. A 1.5 kW rating
PMBLDCM is used to drive the air conditioner compressor,
speed of which is controlled effectively by controlling the DC
link voltage. The detailed data of the motor and simulation
parameters are given in Appendix. The performance of the
proposed PFC drive is evaluated on the basis of various
parameters such as total harmonic distortion (THDi) and the
crest factor (CF) of the current at input AC mains,
displacement power factor (DPF).
CONCLUSION
A new speed control strategy of a PMBLDCM drive is
validated for a compressor load of an air conditioner which
uses the reference speed as an equivalent reference voltage at
DC link. The speed control is directly proportional to the
voltage control at DC link. The rate limiter introduced in the
reference voltage at DC link effectively limits the motor
current within the desired value during the transient condition
(starting and speed control). The additional PFC feature to the
proposed drive ensures nearly unity PF in wide range of speed
and input AC voltage. Moreover, power quality parameters of
the proposed PMBLDCM drive are in conformity to an
International standard IEC 61000-3-2 [5]. The proposed drive
has demonstrated good speed control with energy efficient
operation of the drive system in the wide range of speed and
input AC voltage. The proposed drive has been found as a
promising candidate for a PMBLDCM driving Air-Con load
in 1-2 kW power range.