| 摘要 |
PURPOSE:To diagnose simply the deterioration of a smoothing capacitor by a method wherein an input of the capacitor is interrupted, an inverter is made to conduct a PWM operation, a discharge current is let to flow through a load and the electrostatic capacity of the capacitor is determined from a DC voltage and a current value. CONSTITUTION:In the state wherein an AC motor 7, a load, is stopped, an instruction is given to a breaker instructing circuit 8 to break an AC breaker 1. Next, an instruction is given to an inverter control circuit 10 to make an inverter 6 conduct a single- phase PWM switching operation. Thereby a current matched with the motor 7 is let to flow onto the load side, so as to discharge an electric charge of a smoothing capacitor 3. During the period of this discharge, detection outputs of a voltage detector 4 and a current detector 5 are taken in a voltage-current measuring circuit 9 at every prescribed time and the measured data on a voltage of the capacitor 3 and a discharge current are collected. After the end of the discharge, the circuit 10 is stopped, the measured data are sent to a lifetime determining circuit 11, and the electrostatic capacity (time constant of discharge) of the capacitor 3 is calculated to determine the lifetime. The detectors 4 and 5 can be used also as detectors for protection circuit of the inverter 6. |
