CONTROLLER OF AC MOTOR

PURPOSE:To prevent an abnormal voltage from generating without providing a power factor regulator by regulating the input reactive power of an AC/DC converter in response to a detection signal on the basis of the abnormal rise or fall of the voltage of an AC power source system. CONSTITUTION:Since the reactive current command output from a calculator 23 has a 90 deg. phase difference for a system voltage, the component of 90 deg. phase, i.e., the reactive current can be controlled in proportion to it. Since the amplitude of the command is proportional to the output signal of a folding line circuit 22 and obtained when the system voltage becomes the prescribed value or higher, a reactive current is supplied to the system by a converter 5 if the system voltage abnormally rises to prevent the voltage from abnormally rising. Accordingly, it can prevent the abnormal voltage produced when the AC power source system is switched to an emergency AC generator 2 from generating.