| 摘要 |
PURPOSE: A power factor improvement and pulse amplitude modulation circuit in an inverter system according to a supply voltage frequency is provided to simply embody a circuit by judging whether an input supply voltage is 50Hz or 60Hz and reading a switching frequency stored in a storage element. CONSTITUTION: A rectifier(61) rectifies an input AC power supply to obtain a DC voltage. A choke coil(62) and a smoothing capacitor(63) remove an AC component included in the DC voltage from the rectifier(61). An inverter(64) converts the DC voltage outputted from the smoothing capacitor(63) into a three-phase AC power supply and supplies the three-phase AC power supply to a motor(M). A switching element(Q1) is connected to a front terminal of the smoothing capacitor(63) in parallel and controls charge and discharge operations of the smoothing capacitor(63) according to a switching signal. A zero voltage detector(65) detects a zero point of an input AC power supply. A supply voltage frequency judgment section(70) measures a time between zero points detected by the zero voltage detector(65) and judges whether an input supply voltage is 50Hz or 60Hz. A voltage level detector(67) detects a voltage across the smoothing capacitor(63). A ROM(66) stores data with respect to a sine wave. A controller(68) reads a sine wave data from ROM(66) and control a period of the pulse according to a frequency judged by supply voltage frequency judgment section(70). A driver(69) controls an on/off operation of the switching element(Q1) according to the period of the pulse from the controller(68). |
