I think I am missing something about how the motor controller charges a battery when the generator EMF is below the battery voltage (when voltage boost is required, using flyback EMF).
Looking at the Odrive v3.5 controller schematic, a pretty standard driver circuit is used; the circuit contains diodes allowing reverse/recirculating current flow when switched accordingly. As I understand it, this circuit can be operated in at least two charging modes, depending on how the PWMs are used - either using flyback to boost voltage to charge the battery (when battery voltage is higher than generator EMF), or only using the generator EMF to charge the battery (no flyback voltage boost).
Also as I understand it - in boost mode and PWM state 1, current is recirculating through diodes and two of the motor phases, and no current is flowing in the battery; current builds until the PWM switches to state 2, where the current can then flow into the battery. 0% duty cycle would be if it is always in PWM state 1 (recirculating/building), and never state 2 (flowing back into battery). 100% duty cycle would be always state 2, never 1.
Hence my confusion - if my understanding is correct (it must not be?), when generating in boost mode the current magnitude goes up at lower duty cycle, and down at higher duty cycle (the opposite of what occurs when in motoring mode and the battery is driving the motor). This is because in generating mode with flyback boost, the windings are effectively shorted in state 1 and current is increasing, whereas in state 2 current is decreasing as it dissipates into the battery (going to zero when flyback voltage + gen EMF drops below battery voltage). Avg current increases with time spent in PWM state1, whereas avg current decreases with time spent in PWM state 2.
Is this accurate?
If it operated this way, would it also complicate the story wrt controlling negative torque when voltage boost is NOT required - since current would be flowing regardless of PWM state (but at different rates)?