This simulation models the effect of unipolar 4-quadrant PWM switching. When the back-EMF voltage has greater amplitude and the same polarity when compared to the applied voltage, it is shown that unipolar 4q patterns CAN regenerate energy back into the DC bus. The inverter puts a 50% duty-cycle (0 to +24V waveform) 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 while the bus power and bus current are plotted under different speed conditions.
TRANSIENTS: At t=0, the motor is connected to a 24V 50% duty PWM. The dyno speed is set to -200 radians/sec. At 15ms, the dyno speed changes to 100 radians/sec speed. At 30ms, the speed changes again to 300 radians/sec. This last speed change results in a back-EMF which is higher than the applied voltage. By monitoring the bus power, it is evident that this results in regeneration back into the bus.
PLOTS: Bus Power, Motor Torque, Motor Speed, Applied Voltage, Back-EMF Voltage
REQUIREMENTS: Spice Executable, Support Pack
Unzip these simulation files into the same folder as the files extracted from the Support Pack. Then run "05 Unipolar PWMs (4Q operation).asc".