| 摘要 |
PURPOSE:To avoid the impossibility of the operation of a PWM control converter due to the saturation of an AC transformer by calculating the output current of the converter in accordance with the signal obtained by integrating a PWM signal at the time of operating a low frequency and controlling it with the signal. CONSTITUTION:When an output frequency is low and a current transformer 7 saturates, a selecting circuit 13 outputs the signal of an integrator 10 in accordance with the signal of a discriminator 12 and applies it to a comparator 8. The output signal of the comparator 8 is a signal which decides the turning ON or turning OFF of GTO 1, 2 and has a relation of the same waveform as the output voltage of the U phase of the converter. An integrator 10 is an integrator havong primary delay characteristic with time constant equal to that of the coil of a motor 6, and when the output signal of the comparator 8 is inputted, a signal proportional to the motor current can be produced at its output. |
