This simulation models the effect of bipolar 4-quadrant PWM switching. It is shown that bipolar 4q patterns can regenerate when the back-EMF voltage is higher in amplitude and of the same polarity as the applied voltage. The inverter puts an 80% 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 80% 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, the back-EMF is higher than the applied motor voltage from the inverter, and the inverter regenerates back into the dc bus, creating negative bus power.
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 "04 Bipolar PWMs.asc".