| 摘要 |
PURPOSE: To effectively utilize the total area of variable range of the modulation rate by eliminating potential variation at the neutral point. CONSTITUTION: A neutral point clamping type inverter is controlled by a triangular wave comparing PWM signal including a voltage instruction which is obtained by adding 11 the superimposed amount from a DC-even number order harmonic wave superimposing amount calculating section 2 for stabilizing the neutral point potential the DC power supply formed by a voltage dividing capacitors to the basic wave voltage instruction from a voltage instruction value calculating section 1. A variable limber 7 which provides a smaller limit value when the basic wave voltage instruction value becomes larger is provided between an amplifier 5 for amplifying a varied voltage of the neutral point ▵VN and a multiplier 8 outputting a superimposed amount depending on ▵VN by multiplying such output signal and an output signal of the DC-even number order harmonic wave superimposing amount calculating section 4. Thereby, since the superimposed amount is changed inversely even when the basic wave voltage instruction is changed and thereby the output current is changed, the neutral point potential control capability is kept constant, not resulting in change of the neutral point potential due to the change of output current. |
