Patent ID: 8259426

Claim:
A variable frequency drive for powering a load, comprising: a rectifier comprising an AC input having a plurality of AC input nodes to receive AC electrical input power, a DC output with first and second DC output nodes, and a rectifier network coupled between the AC input nodes and the DC output nodes and providing rectified DC electrical power at the DC output nodes; an intermediate DC circuit comprising first and second DC current paths and at least one electrical storage component; an inverter comprising an AC output with a plurality of AC output nodes for supplying power to a load, and an inverter switching network comprising a plurality of inverter switching devices individually coupled between one of the DC current paths of the intermediate DC circuit and one of the AC output nodes, the inverter switching devices individually operable to selectively electrically couple the corresponding DC current path with the corresponding AC output node according to a corresponding inverter switching control signal to provide variable frequency AC electrical power to the load; at least one filter circuit comprising a plurality of filter capacitors coupled to a neutral node; a feedback circuit providing at least one neutral feedback signal or value based on a sensed condition of the neutral node; a control system, with an inverter control component operative to provide the inverter switching control signals to cause the inverter to selectively convert DC current from the intermediate DC circuit to provide AC electrical power to the AC output according to at least one setpoint signal or value; and a capacitor fault detection circuit receiving the at least one neutral feedback signal or value from the feedback circuit and operative to extract a measured fundamental frequency component from the at least one neutral feedback signal or value at a fundamental frequency of the AC electrical input power, and to determine whether a fault condition is suspected in at least one of the filter capacitors based at least partially on the measured fundamental frequency component.