II. REQUIREMENTS OF SRM CONVERTER
A main problem in certain application is the
selection of converter topology. The SRM Converter
has some essential requirements [6], they are:
• Minimum one switch is capable to conduct
freely in each phase of the motor.
• The converter would be capable to excite the
phase before it enters the generating or
demagnetizing region.
The converter needs to satisfy several other necessities
in order to increase the converter performance; such as
fast Demagnetization time, faster excitation time, high
power, higher efficiency, and fault acceptance. They
are[4], [7]-[9]:
• The converter must be able to allow phase
overlap control because the converter energy
can be provided to one phase whereas at the
same time it is removed from the other phase.
• The phase voltage should be modulated using
Pulse Width Modulation (PWM) technique at
low speeds for the controlling of phase current.
• On each operating point, to inject the sufficient
current into the winding at high speed,
necessary high driving voltage is essential.
This necessary control system can be single
pulse or hysteresis current control. Using this
device; the demagnetization time can be
reduced for avoiding negative torque and / or
allowing an addition of commutation period
(i.e.; dwell angle).
• The demagnetization energy from the leaving
phase must be provided back to the dc source
or should use it in the incoming phase.
• The hysteresis losses and switching losses can
be reduced by the converter, because in order
to decrease the switching frequency it is
capable of freewheeling during the chopping
period.
• In order to decrease the voltage stress through
the semiconductor switches, the converter
takes to be single rail of power source.
• Upon the construction of motor, the converter
would have to be single rail of power source.
• The resonant circuit is needed for the
converter to apply zero-voltage or zero-current
switching for reduction of switching loss.
• Less number of semiconductor switches is
suitable.
• Power factor correction circuit should be
applied for improve the power factor.
• Little complexity of converter is required.
Application and efficiency of this converter is defined
by choosing the appropriate dwell angle, switching
strategy, and control technique (usually hysteresis
current control).