The output voltage error compensation for a pulse-width modulated (PWM) voltage source inverter (VSI) is essential for a wide range of semiconductor power conversion applications in order to suppress detrimental output voltage and current distortions. A conventional software-based compensation method added the error voltage to the output voltage reference in a feed-forward manner, and was executed every PWM carrier period. However, the compensation value was the average output voltage error in the carrier period, thus the time delay of the pulse modulated output voltage caused by each switching was not compensated, which also reduced the performance of the synchronous sampling. This paper proposes output voltage compensation for every half of the carrier period, which enables the compensation for the error at each of the switching. In addition, the instantaneous current prediction method has been proposed, which is necessary for the proposed compensation method. The proposed compensation method is more effective than conventional ones based on the average error voltage, especially when the current ripple is large and the current is around 0 A. The proposed method has been confirmed through the experimental setups and it was proved that the low-order current distortions were clearly reduced compared with the conventional compensation method.

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An application of doubly-fed induction generator (DFIG), which is one of adjustable speed generators, to a gas engine cogeneration system has been investigated. . To operate during a blackout as an emergency power supply is one of important roles for the gas engine cogeneration system. However, the DFIG requires initial excitation for startup during a blackout because the DFIG has no excitation source. In this paper, we propose the "blackout start" as a new excitation method to generate a rated voltage at the primary side during a blackout. In addition, a stand-alone operation following a blackout has been investigated by using experimental setup with a real gas engine. Power flows in the generating set with the DFIG at the stand-alone operation have been investigated experimentally. Experimental investigation of the power flow suggests that the generating set with DFIG has optimal speed in minimizing whole system losses.

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