Regen on DC motor with PWM Sweep from -1 to +1

In this simulation, a 24V brush DC motor is powered by an H-Bridge using bipolar PWMs.  The motor shaft is connected to a dyno which drives the motor shaft at a constant speed so that the motor generates a -24V back-EMF.  The PWM is then swept slowly between -1 and +1 to observe the effect it has on the DC bus current, and thus the regenerated energy.