| 摘要 |
PURPOSE: To return the neutral terminal voltage back to an optimal level upon occurrence of DC fluctuation by determining the ratio of voltage output time of intermediate phase based on the neutral voltage value and the output current of intermediate phase. CONSTITUTION: A maximum/minimum intermediate voltage command operating unit 29 receives the required output voltage command value for each phase every micro sample time Ts and outputs the maximum, minimum and the remaining intermediate value Vmax , Vmin and Vmid of the output voltage command value for each phase. When the neutral voltage Vo is higher than the intermediate voltage of DC power supply, the charges flowing out from the neutral during micro sample time have a positive value and the neutral voltage Vo decreases otherwise the charges have a negative value and the voltage Vo increases. Since charges proportional to the difference between the voltage Vo and the intermediate voltage of DC power supply flow out from the neutral, the voltage Vo is controlled to approach the intermediate voltage of DC power supply. With such arrangement, DC fluctuation of neutral terminal voltage can be suppressed. |
