A novel approach for voltage sag mitigation using facts device interline dynamic voltage restorer

Voltage sag is one of the most severe power quality disturbances to be dealt with by the industrial sector, as it can cause severe process disruptions and results in substantial economic loss. Voltage sag mitigation can be done using dynamic voltage restorer (DVR) and inter-line dynamic voltage restorer (IDVR). One of the main factors which limit capabilities of DVR in compensating long-duration voltage sags is the amount of stored energy within the restorer. In order to overcome this limitation, IDVR has been proposed where two DVRs each compensating a transmission line by series voltage injection, connected with common dc-link. When one DVR compensates voltage sag, the other DVR of the IDVR replenish the dc-link energy storage. The control strategy adopted for generating reference signal plays a key role in deciding the dynamic behavior of a system. In the existing IDVR system, the amount of real power that a line can transfer to dc-link energy storage depends on the load PF. Due to approximation in the process of the control design the existing control schemes have some tracking error. This work proposes a novel control algorithm for simultaneous sag compensation and replenishing dc bus energy. The simplest pre-sag supply voltage boosting technique is considered for developing a new two neuron control algorithm. Besides, a self-charging technique is developed which maintains the dc capacitor voltage at the desired level. The salient advantages of the proposed method are compensating long duration deeper voltage sags, reduction in size of dc-link capacitor and simplicity of algorithm for digital implementation. Simulation results presented for a simple system under three-phase voltage sag of 40% and -20° phase angle jump demonstrates the efficiency of the proposed system.