12-10-2012, 05:45 PM
Single Phase Induction Motor Drives - A Literature Survey
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Abstract
various existing converter topologies, which have been proposed
for adjustable speed single phase induction motor drives
(SPIMD). Included in the paper are several newly proposed
converter topologies. A study of the merit and demerit of
different converter topologies have been carried out. Various
converter topologies have been compared in this paper. Among
these converter topologies, the adjustable frequency PWM
inverter is the best choice for single-phase induction motor
drives. However, adjustable-frequency drives have not been
widely used with single-phase induction motors. The open-loop
constant V/f control law cannot be used with the single-phase
induction motor drives as it is used with three phase motors. The
variation of the operating frequency at lower speed range with
constant load torque causes variation in the motor’s slip. A
constant V/f control is suitable only over the upper speed range.
However, improvements in the low frequency performance
require the use of constant power dissipation in the motor.
Simulation studies for some of the existing topologies as well as
for the proposed ones have been carried out.
INTRODUCTION
In home appliances, single-phase induction motors
(SPIMs) are commonly used. These motors include
permanent split capacitor (PSC) motors, split phase motors,
permanent magnet synchronous motors, and shaded pole
motors. They are single speed motors and are used in
dishwashers, clothes washers, clothes dryers, hermetic
compressors, fans, pumps, draft inducers, etc. A truly variable
speed operation from this motor with a wide range of speed
and load would help application designers to incorporate
many new features in their products. It would also mean
operation with higher efficiency and better motor utilization.
In industrial applications three phase induction motors have
been used. However, in residential appliances, SPIMs are
preferred due to the greater availability of single-phase
power.
VARIOUS CONVERTER TOPOLOGIES
Single-phase ac/ac chopper:
Variable speed operation of a single phase induction
motor has been obtained through voltage control using triacs
or back to back thyristors, however these suffer from large
harmonic injection into the supply and low power factor, in
addition to a limited speed range. To minimize the harmonic
injection, topologies presented in Figs. 1 and 2 have been
proposed [1,2]. This solution uses only four IGBTs to control
the PSC motor. However, PWM controlled ac controllers are
plagued with difficulties to commutate inductive load current
from one bi-directional switch to another due to finite switch
on/off times. Therefore, the four switches need to operate
properly such as “four-step switching strategy” in order to
prevent voltage spikes. In this circuit there is no need for
costly dc bus capacitors. A small ac capacitor across the ac
source might be needed in special cases to suppress the spikes
on the utility line. Also, snubbers for the devices might be
needed too. The motor performance as well as input power
factor can be improved by implementing various PWM
strategies. However, the speed variation will be over a
limited range.
Single-phase ac/ac cycloconverter [3-6]
The configuration presented in Fig. 3 is an extension of
the previous topology. Again, ac signal is directly converted
to a controlled voltage and frequency ac signal. There is no
need for a dc bus capacitor. In this case, the motor torque and
current can be controlled in a much better manner than the
previous case and a wide range of speed variation can be
obtained. However, 12 more diodes are used with respect to
the previous solution. Also the efficiency suffers in the lower
speed ranges. At lower speeds, the THD is quite significant
and the motor current has a significant discontinuity [5]. The
motor cannot operate above the rated speed. A DC chopper
fed drive has been reported in [6] and is shown in Fig.4.
SIMULATION RESULTS
The simulation results of the motor terminal voltages for
ac/ac converter shown in Fig. 1 is shown in Fig. 14. The
simulation results for Fig. 12 are shown in Figs. 16 & 17. For
the circuit in Fig. 13 [30], the winding currents and the supply
current (in phase with the supply voltage) are shown in Fig.
18 (using current control). For this circuit, a PI regulator was
used. Back emfs were not considered. It is seen that the
output currents closely follow the reference currents.
CONCLUSIONS
The single-phase induction motor can successfully be
driven from a variable frequency power supply. Hence, the
motor speed can be easily adjusted. Other methods for speed
control, such as voltage amplitude control do not allow for the
range of speed, which is possible with the use of a variable
frequency supply. The torque performance of the capacitorconnected
motors can be enhanced at low frequency range by
altering the V/f control law such that the internal power
dissipation in the motor is held constant [19]. High
performance control strategies can be used for adjustable
speed single-phase induction motor drives in combination
with high performance converter topologies. Also, low-cost
high-performance converter topologies have been proposed.
Advantages and disadvantages of different converter
topologies have been discussed. Simulation results for a few
of the existing topologies and the proposed topologies have
been carried out. For the figure of Fig. 12, in order to have
maximum converter utilization, special PWM techniques have
to be used. These include the current hysteresis and Space
Vector PWM technique in which the basis vectors are
unequal.