A resonant DC link inverter for an electric vehicle.
Thesis DisciplineElectrical Engineering
Degree GrantorUniversity of Canterbury
Degree NameMaster of Engineering
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.