I’d like to implement regenerative braking in my own brushless ESC I’m designing. I’m stuck however on the part regarding voltage step-up. As I understand it, ESCs during braking usually use the motor as a boost converter to increase back EMF voltage to battery voltage in order to charge it. However, I have no idea how the output voltage is measured for feedback as it would be connected to the bridge supply lines and hence we would actually be measuring supply voltage. How is this feedback achieved in a commercial ESC?
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2\$\begingroup\$ You measure the current flowing into the battery to control the PWM of the ESC. \$\endgroup\$– Kevin WhiteCommented Feb 4, 2021 at 0:21
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\$\begingroup\$ I think for acceleration the ESC PWM controls to duty cycle of current until losses limit speed using a Buck-controlled half bridge. Voltage controls no load RPM but power determines max speed with load., In braking , another half bridge uses the motor as a generator but in PWM Boost-mode to control the current. But as speed decreases so does maximum braking rate, although at a small constant braking rate, the duty cycle would increase as it slows down. \$\endgroup\$– Tony Stewart EE75Commented Feb 4, 2021 at 0:49
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A boost converter isn't really the best way to think about what is happening during regeneration. It's true that inductance boosts the voltage in both cases, but the topology is different. There is no voltage feedback because you aren't controlling the voltage; it's fixed by the supply voltage. You can control the current however.
To get the motor to brake, you apply reverse torque by reversing the current in the motor phases. Exactly how to accomplish this depends on the switching scheme. For example, if you are alternating upper and lower switches in all active half-bridges, you don't need to do anything special. In this case simply reducing the duty cycle to lower the average applied voltage below the back emf reverses the phase current, and power will flow from the motor back to the supply. Be sure to have a supply voltage monitoring circuit that can shut off the bridge if the voltage gets too high because the supply can't absorb all the power.
