Cascaded　H-bridges　(CHB)　converter　equipped　with　pulse　width　modulated　(PWM)　rectifiers　has　been　widely　adopted　in　medium-voltage　motor　drive　applications　for　the　ability　of　power　regeneration.　But　capacitor　in　each　submodule　suffers　severe　issue　of　voltage　fluctuation　at　twice　the　inverter　frequency,　which　can　be　worse　when　motor　works　at　low　speed　and　heavy　load.　The　causes　of　voltage　fluctuation　are　studied　in　this　paper,　including　low　running　speed　and　fluctuating　instantaneous　power　of　inductors　in　front-end　rectifiers.　The　fluctuating　power　of　inductors　will　cause　large　voltage　fluctuation　on　capacitors,　and　this　issue　is　ignored　in　previous　studies.　This　paper　also　proposes　an　improved　power　feedforward　method　to　tackle　the　issue　of　fluctuating　power　of　inductors,　in　which　the　input　power　and　output　power　of　submodules　are　totally　counteracted.　By　counteracting　power　of　input　and　output　totally,　voltage　fluctuation　decreases　dramatically　and　capacitance　can　be　minimized.　Therefore,　electrolytic　capacitors　can　be　replaced　by　film　capacitors　with　small　size　and　long　lifetime.　Simulation　results　based　on　6kV,　710kW　motor　verify　the　effectiveness　and　validity　of　the　proposed　method.　©　2020　IEEE.