Patent ID: 8378599

Claim:
A power transducer which outputs alternating current (AC) power having a variable voltage and a variable frequency, the power transducer comprising: a converter for rectifying an AC voltage of an AC power supply to convert it to a direct current (DC) voltage; a DC intermediate circuit having a smoothing capacitor for smoothing the DC voltage of the converter; a detecting circuit for detecting a voltage of the DC intermediate circuit; a regenerative braking circuit disposed in the DC intermediate circuit; a drive circuit for driving the regenerative braking circuit when the detecting circuit detects a specified voltage; a timer for accumulating an operating time of the regenerative braking circuit to obtain a cumulative operating time; an inverter for converting the DC voltage of the converter to an AC voltage; and a display unit for displaying a permissible duty factor of a power semiconductor calculated or read from a nonvolatile memory, wherein a permissible duty factor and a resistance value of a regenerative braking resistor connected to the regenerative braking circuit of the DC intermediate circuit are individually set, wherein the power transducer performs the steps of: calculating a value of current which flows in the power semiconductor, which is a switching element, in the regenerative braking circuit from the resistance value set for the regenerative braking resistor; obtaining a generation loss of the power semiconductor from the calculated current value, and calculating a permissible duty factor of the power semiconductor; and determining that the regenerative braking circuit can continuously operate when both the set permissible duty factor of a regenerative braking resistor and the calculated permissible duty factor of the power semiconductor are 100% or more.