Abstract: To provide an electric motor control system capable of reducing torque pulsation resulting from an intermittent control and assuring a smooth acceleration/deceleration. In a speed reference signal converter 9, a deviation between a last time value .omega..sub.r-1 and a this time value .omega..sub.r of the speed reference signal .omega..sub.r of a master control system 1 is computed, the speed reference signal .omega..sub.r from the master control system is converted into a speed reference signal .omega..sub.r * conforming to the computing cycle of the motor control system according to a ratio between the updating cycle of the speed reference signal from the master control system and a computing cycle in a motor control system and said deviation, a motor driving signal is produced according to this converted speed reference signal .omega..sub.r * and a motor 6 is driven.

Abstract: A power conversion apparatus capable of eliminating inexpedient higher harmonic components from its output, without lowering the conversion efficiency. The apparatus includes a first power converter for converting an input power from a power supply into an output power; a detector for detecting an output current and an output voltage of the first power converter; a high harmonic detector for detecting a higher harmonic component on a basis of the output current and the output voltage, and for producing current reference signal corresponding to the detected higher harmonic component; and a second power converter for producing an inverse of the detected higher harmonic component according to the current reference signal, and combining the produced inverse of the higher harmonic component with the output current of the first power converter such that the higher harmonic component in the output current of the first power converter are cancelled by the inverse of the higher harmonic component.