Output voltage error compensation device for PWM inverter - discriminates polarity of output currents for control of modulator and timer of short-circuit current protection

摘要

A current transformer (24) in each AC output line from the main inverter circuit (20) to an induction motor (23) is wired to the polarity discriminator stage (26) of a microprocessor (25). This delivers an output to a voltage compensator (27) which also receives a DC input from the smoothing capacitor (22) of the input rectifier (21). The pulse width modulator (28) and the short-circuit prevention timer (29) are combined in a gate array. ADVANTAGE - Correct compensation of voltage error arising from short-circuit prevention period is guaranteed by exact polarity discrimination of main circuit output current.