An approach to regulating the DC-Link voltage of a voltage-source BTB system during power line faults

A voltage-source BTB(Back-To-Back) system for the purpose of achieving power flow control and/or line-frequency change in transmission systems has attractive features of reliable and continuous operation even during power line faults. However, an overvoltage appearing across the dc link during the faults should be limited to as low as possible because it does affect the power device ratings. This paper proposes a dc-link voltage controller for effectively suppressing the overvoltage during power line faults. This controller is characterized by compensating for a time delay inherent in each current controller, and for a power flow imbalance occurring during power line faults. The validity of the proposed controller is confirmed by theory and computer simulation.