12-10-2012, 12:57 PM
A New Switching Strategy for Pulse Width Modulation (PWM) Power Converters
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Abstract
This paper presents a new switching strategy for pulse
width modulation (PWM) power converters. Since the proposed
strategy uses independent on/off switching action of the upper or
lower arm according to the polarity of the current, the dead time
is not needed except instant of current polarity change. Therefore,
it is not necessary to compensate the dead time effect and
the possibility of arm short is strongly eliminated. The current
control of PWM power converters can easily adopt the proposed
switching strategy by using the polarity information of the reference
current instead of the real current, thus eliminating the problems
that commonly arise from real current detection. In order to
confirm the usefulness of the proposed switching strategy, experimental
tests were done using a single-phase inverter with passive
loads, a three-phase inverter for induction motor drives, a threephase
ac/dc PWM converter, a three-phase active power filter, and
a class-D amplifier, the results of which are presented in this paper.
INTRODUCTION
POWER conversion technology has recently been undergoing
technological advances, greatly improving the efficiency
of power semiconductor devices that utilize such technology.
Thus, enhancing energy usage efficiency is also causing
an increase in the demands of variable drive system of motors
that use inverters, affecting the area of consumer electronics and
other related industries. The usage of the three-phase ac/dc pulse
width modulation (PWM) converter and the three-phase active
power filter has also increased to maintain the high quality of
the power source line.
Generally, dead time is applied within switching signals to
prevent shorting the circuit of the dc voltage source in using the
bridge-type PWM power converter. This causes output voltage
differences and phase deviations between reference and real
values. To avoid causing detrimental effects to the control performance,
it is necessary to compensate the dead time effects
for the high performance, such as the vector control of the ac
motor.
A NEW SWITCHING STRATEGY
Conventional Switching Method
Fig. 1 shows one arm of the bridge-type power converter.
Typically, dead time is applied between switching signal of
switching device and switching signal of to prevent
shorting the circuit of the converter arm, as shown in Fig. 2.
In case current is negative, however, is not activated although
switching signal is applied because flows through
the freewheeling diode , if the current is continuous. Thus,
switching signal is useless. In case the current is positive,
switching signal is also insignificant for the same reason. If
the polarity information of the current were known, therefore,
the useless switching signal and the dead time would be cancelled.
Dead Time Suppression Method
Fig. 3 shows the switching pattern of the dead time suppression
method. Dead time is applied within arm selection signal
and from the instant that real current reaches the predetermined
threshold level. This methodworks in the sameway as the
bank selection method for noncirculating-current-type cycloconverter
does. Normally, the noncirculating-current-type cycloconverter
is composed of positive bank converter that works
in the positive current mode and negative bank converter that
works in the negative current mode. Since we have to apply sufficient
dead time to prevent the bank short in every instant of current
polarity change, the current intermittence is occurred. Thus,
the circulating-current-type cycloconverter is used to eliminate
the current intermittence. As the same reason, the dead time
suppression method still has as well as problem in the polarity
changing instant detection of the real current and drawback of
current intermittence.
EXPERIMENT RESULTS
Experiments were performed to verify the validity of the proposed
switching strategy. The results of the experiment on the
proposed switching strategy for the current control of a singlephase
inverter with a passive load, a three-phase inverter for the
induction motor drive, a three-phase ac/dc PWM converter, a
three-phase active power filter, and a class-D amplifier are presented
below.
CONCLUSION
In this paper, a new switching strategy for the PWM power
converters is proposed. It is not necessary to compensate the
dead time effect and the possibility of arm short is strongly eliminated.
From the results of an experiment for the current control
of a single-phase inverter with a passive load, a three-phase
inverter for induction motor drives, a three-phase ac/dc PWM
converter, a three-phase active power filter, and a class-D amplifier,
the validity and viability of the proposed strategy were confirmed.
The proposed switching strategy is especially efficient
in fields of current control system in which the polarity information
of the reference current can be used without the problems
entailed by real current detection. Moreover, even in cases of
extra-high-frequency switching operation, good switching performance
is still possible, underlining the viability of the proposed
switching strategy for practical applications.