Common-mode conduction in matrix-converter-fed motor drive system

The characteristics of common-mode conduction in frequency-converter (FC)-fed motor drive system are summarized and analyzed, including rectifier-inverter (RI) and AC-AC matrix converter (MC) then the effects of power-filter and reactor on the common-mode conduction are outlined when they are appended directly to the FC. It is found that the cause for common-mode conduction is the same for the two kinds of FCs, and so are the expressions and some suppression methods. The fast variation of common-mode voltage is the external cause for common-mode current, and the distributed capacitance inside the motor and that between frame and ground is the internal cause. In an MC-fed motor drive system, the average value of the common-mode voltage is nearly half of that in an RI-fed motor drive system, and the amplitude of the common-mode current is much lower, meaning that the common-mode conduction in the former drive system is not so serious. In addition, the conventional passive power filter also can't eliminate the common-mode conduction in MC-fed motor system, except that some special measures are taken.