System for controlling a PWM inverter having delay time compensation

摘要

A system is provided for controlling a PWM inverter having three main circuit arms in which free-wheel diodes are connected in parallel to positive and negative side switching elements. The inverter takes three phase alternating current from an intermediate portion of the arms on the basis of a voltage supply of a direct current and an ON and OFF operation of the switching elements. The control system includes a circuit for detecting a zero-crossing point of the three phase alternating current. A wave generating circuit generates a PWM wave at every main circuit arm, which changes the level thereof corresponding to ON and OFF operation of the switching elements and is inverted to each other in the positive and negative sides. An on-delay circuit delays a level change timing from ON to OFF of the PWM wave for a short circuit preventing duration. A compensation circuit compensates the PWM wave width of one phase in which a current opposite to other phases flows by expanding and contracting the width at the rate of two times as the short-circuit preventing duration. The expanded and contracted pulse width is added to the on-delay circuit, thereby controlling the switching elements of the inverter main circuit.