| 摘要 |
A VSC-converter for converting alternating voltage into direct voltage and conversely is controlled so that semiconductor devices of turn-off type connected in anti-parallel with diodes are controlled to be turned on and turned off so that an alternating voltage phase line is alternatively connected to a midpoint (23) of a direct voltage side of the apparatus, the plus pole (7) mad the minus pole (8) of the direct voltage side for generating a train of pulses with determined amplitudes according to a pulse width modulation pattern on the phase output of the apparatus. The midpoint of the direct voltage side is connectable to the phase output through two different so called zero states. The semiconductor devices (13-16, 10, 11) are controlled so that both zero states are each assumed at least once during a half period during which the fundamental frequency component of a voltage set value of the phase output is positive or negative. |
