PURPOSE: To obtain an appropriate PWM pulse by adding a zero-phase voltage command to a voltage command so that a PWM pulse of the minimum on-time or longer which is enough to discharge the electric charge of a capacitor may be supplied to a switching element.
CONSTITUTION: A zero-phase voltage command arithmetic device 5 generates a zero phase voltage command Vn* so that it may change its polarity from positive to negative when a voltage command value of each phase of a three-phase ac voltage commands Vu*, Vv* and Vw* changes from positive to negative, and from negative to positive when negative to positive. Then, the zero-phase voltage command Vn* is added to the three-phase ac voltage commands Vu*, Vv* and Vw* and the obtained output voltage commands Vu**, Vv** and Vw** are compared with a carrier wave signal at a PWM pulse arithmetic device 3 and then a PWM pulse is generated. By this method, the output voltage command can skip over a region where a width of the carrier wave signal is small and a PWM pulse width of the minimum on-time of a switching element or longer cannot be obtained. The voltage across an output terminal of a series multiple inverter 1 is not influenced by the addition of the zero- phase voltage command Vn*.
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MATSUI TAKAYUKI
HORIE SATORU
SAITO HIDEJI
TOYODA EIICHI
SAKATA KAZUHIRO
NAKADA KIYOSHI
