This simulation models the effect of unipolar 2-quadrant PWM switching. As long as the amplitude of the back-emf voltage in the motor does not exceed the bus voltage, it is shown that unipolar 2q patterns can not regenerate, even when the back-EMF voltage is higher than the applied voltage. The inverter puts a 50% duty-cycle on the motor windings. The motor is then placed on a dyno which controls the motor's speed regardless of the applied PWM. The dyno speed is changed to different values to illustrate the bus power and bus current under different speed conditions.
TRANSIENTS: At t=0, the motor is connected to a 24V 50% duty PWM. The dyno speed is set to -1900 RPM. At 15ms, the dyno speed changes to approximately 900 RPM. At 30ms, the speed is set to about 2800 RPMs. In the latter case, it is shown that the inverter cannot regenerate, even though the resulting back-EMF is higher than the applied voltage from the inverter.
PLOTS: Bus Power, Bus Current, Motor Torque, Applied Voltage, Back-EMF
REQUIREMENTS: Spice Executable, Support Pack
Unzip these simulation files into the same folder as the files extracted from the Support Pack. Then run "03 Unipolar PWMs (2Q operation).asc".