SYNCHRONIZATION SWITCHING SYSTEM FOR INVERTER

PURPOSE:To eliminate the switching between a load and an inverter in a relationship of reverse phase to one another by providing a discriminator which discriminates the polarity of the phase difference between the output current of the inverter and the current of a motor. CONSTITUTION:A motor current S1 which is detected through a current transformer 13 and an output S2 from a pulse distributor 11, i.e., an output current of an inverter are applied to an adder 173 of a polarity discriminator 17, which produces a pulse corresponding to the phase difference therebetween. This output pulse is converted via a filter 174 to an average value. The output of the filter 174 is proportional to the phase difference, and becomes maximum at an electric angle of 180 deg.. Therefore, whether the phase difference is 0 deg. or 180 deg. of an electric angle can be discriminated by comparing by a comparator 175 with the output of the filter 174. A power supply system can be controlled in switching on the basis of the output of the discriminator 17.