By getting the direction function from the output AC current, the applied time of voltage vectors in one PWM period was chosen, the direction of central current was controlled for DC voltage balance.
The cathode polarization: dc through electrode, the cathode potential deviating from the balance to the negative potential moves in the direction of the phenomenon.
阴极极化：直流电通过电极时，阴极电位偏离平衡电位向负的方向移动的现象。
3
The cause that transition current of DC-load in rectifier unit without balance reactor exceeds the range of permission is discussed.