| Summary: | Voltage source PWM inverters have been the mam choice in electric vehicles,
because of circuit simplicity and rugged control schemes. The inverters, however,
suffer from high switching losses, high switching stresses, and EMI problems.
Resonant DC link inverters have been actively considered by many manufacturers for
industrial applications, in order to achieve better performance, higher efficiency, and
higher power density.
This thesis presents the design, implementation, and test results of a resonant DC link
inverter for an electric vehicle application. The resonant DC link inverter operates off
a 240V DC supply, and drives a 2.2kW induction motor. The link frequency is
approximately 70kHz. The resonant inverter uses 600V IGBT devices with an active
clamping circuit limiting the bus voltage below SOOV. A synchronized PWM scheme,
in which, the conventional PWM switching signals are synchronized to zero crossings
of the resonant bus voltage, is used to modulate the resonant inverter.
Operating principles, detailed analyses, and simulations are presented, followed by
power loss calculations and a design optimization to find the optimal values of the
resonant components. The construction of the resonant inverter with the emphasis on
minimizing stray inductance is described. A resonant link control circuit for
maintaining resonant operation and limiting the bus voltage is developed.
Experimental tests demonstrate the successful operation of the resonant inverter with
the induction motor under a rated load, and the capability of bidirectional power flow
is confirmed. Loss measurement shows that under the identical load conditions and
for the same IGBT devices, the resonant inverter has a 78% reduction of the switching
losses in the main devices and a 20% reduction of the total losses in comparison to the
conventional voltage source PWM inverter operating at a PWM switching frequency
of 14kHz.
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