Power transducer

Abstract

The performance of a power transducer is improved while efficiently using a power semiconductor also by managing the permissible duty factor of the power semiconductor in the regenerative braking circuit provided in the power transducer. The user is allowed to set, through an operation panel provided on the power transducer, the resistance value of the regenerative braking resistor for thermally consuming the rotational energy generated during motor deceleration. The power transducer performs the steps of: calculating the current which flows in the regenerative braking circuit from the resistance value setting; obtaining the generation loss of the power semiconductor in the regenerative braking circuit with the calculated current value; and determining the permissible duty factor of the power semiconductor from the obtained generation loss.

What is claimed is: 
     
         1 . A power transistor 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 regenerative braking circuit which has a resistor and a power semiconductor; and   an inverter for converting the DC voltage of the converter to an AC voltage,   wherein a resistance value of the resistor and a first permissible duty factor of the resistor are able to be set, and   wherein a second permissible duty factor of the power semiconductor is determined based on a relation between the resistance value and the first permissible duty factor.   
     
     
         2 . The power transducer according to  claim 1 ,
 wherein the relation between the resistance value and the first permissible duty factor is predetermined.   
     
     
         3 . The power transducer according to  claim 1 ,
 wherein the relation between the resistance value and the first permissible duty factor is stored in a nonvolatile memory.   
     
     
         4 . The power transducer according to  claim 1 ,
 wherein the relation between the resistance value and the first permissible duty factor is an approximated to a primary curve.   
     
     
         5 . The power transducer according to  claim 1 ,
 wherein the second permissible duty factor of the power semiconductor is determined based on a generation loss of the power semiconductor.   
     
     
         6 . The power transducer according to  claim 1 ,
 wherein the second permissible duty factor of the power semiconductor is determined based on the resistance value.   
     
     
         7 . The power transducer according to  claim 1 , further comprising:
 an intermediate circuit which includes the regenerative braking circuit,   wherein the generation loss of the power semiconductor is determined based on a voltage value of the intermediate circuit.   
     
     
         8 . The power transducer according to  claim 1 ,
 when a cumulative operating time percentage of the regenerative braking circuit reaches one of the first permissible duty factor of the resistor and the second permissible duty factor of the power semiconductor, whichever is smaller, the power semiconductor is deactivated.   
     
     
         9 . The power transducer according to  claim 1 ,
 when the first permissible duty factor of the resistor and the second permissible duty factor of the power semiconductor are over 100%, the regenerative braking circuit can continuously operate.