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Topology choices for ACIM motor controller...

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I'm building an ACIM motor controller for a pellet stove combustion blower. It's basically just an h-bridge inverter with a boost PFC front stage all controlled by one of the dsPic33 Motor Control MCUs. It runs directly off mains, with the control circuitry fully isolated from the HV stuff. (something I'm debating pulling out since it's only protecting the MCU.)

One of the decisions that I made, which I'm not sure on, is the choice of using only a boost converter with the h-bridge. The motor needs to be fully variable in speed, from 0rpm to max RPM, so this would require a completely variable voltage and frequency.

My choice was to have the PFC regulate a 172v output into the h-bridge, then use the h-bridge like a buck converter to reduce the voltage back down to what is needed for the specific RPM. Does anyone know of any flaws in this design? Would it be better to do all my voltage regulation in the PFC? Insert another stage in between to handle voltage regulation? Or can I use the h-bridge in a buck fashion without troubles?
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Well-Known Member
you can not regulate with the PFC, it will always have ripple on it as the current is following the input voltage.

Technically, you do not need anything beyond an H bridge since the motor is an inductor and the motor constant (K*RPM=V) is a "capacitor". In the real world you need a snubber and high frequency filtering.

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