I would like to ask about an estimate for inverter DC link capacitors, where this inverter will supply 48V 20A 3phase Brushless DC motor and it's driven using a 5 kHz PWM.
put on hold as unclear what you're asking by Hearth, RoyC, Warren Hill, Elliot Alderson, Dmitry Grigoryev yesterday
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The bus link capacitance will be primarily determined by the requirement to supply reactive current to the load. That will presumably be not very large for a PM synchronous or brushless DC motor. However you have a range of load conditions and speeds to consider and there is no magnetic excitation adjustment. The un-filtered three-phase rectifier does not have much ripple, but it may be desirable to provide some degree of capacitive filtering. There are probably some text books that cover this. A simulation would also provide an answer. Someone else here may be able to provide a better answer, but there is one vote to close by someone that doesn't understand the question.