Patent ID: 7202628

Claim:
A frequency converter for outputting an a.c. power to drive a motor, comprising: an inverter unit for inverting a d.c. power to an a.c. power; a control unit for controlling said inverter unit; and a housing for supporting at least said inverter unit and said control unit, wherein a rise time change unit is provided in said housing, said rise time change unit changes a rise time of a waveform of a voltage of the a.c. power output from said inverter unit, and said rise time change unit comprises a core-less reactor coil whose inductance value L is defined by the following equation: L=k*p*T *( a*a )*( N*N )/ b wherein L (henry) is equal to or larger than 0.0003 mH and equal to or smaller than 0.2 mH, k is Nagaoka coefficient, μ equals 4*π*10 −7 , π is circular constant, a is coil diameter (meter), b is coil length (meter), and N is the number of coil turns.