| 摘要 |
PURPOSE:To prevent abrupt variation of phase reference upon switching and to stabilize bearing of load by providing a phase lock loop employing a standby power source or an inner oscillator as phase reference, a phase reference switcher, means for detecting the phase difference between outputs from the standby power source and an inverter, and a phase reference switching control means. CONSTITUTION:A phase difference monitor 20 is connected with the parallel connection bus at the output stages of inverters No.1-No.n and the output bus of a standby power source 1, then the output from the phase difference monitor 20 is fed to a circuit 20 for switching the phase difference of a PLL circuit 8. If the phase reference of the PLL circuit 8 is switched when the standby power source 1 is abnormal, the phase of bus output is synchronized with the inner oscillator 7 and the phase difference is reduced naturally, between the inner oscillator 7 and the standby power source 1, upon elapse of several cycles after release of the standby power source and oscillation takes place synchronously with the standby power source 1. By such arrangement, abrupt variation of phase reference can be prevented upon switching and bearing of load between the inverters No.1-No.n can be stabilized. |
