ABSTRACT
A power system should ensure good quality of electric power supply, which means the voltage and current waveforms should be balanced and sinusoidal. Furthermore, the voltage and frequency of an electrical system should be within reasonable limits of their rated value. If the voltage and frequency are more or less than their pre-specified value, the performance of the equipment is compromised. Voltage related disturbances and variations are more common in power distribution network, which arise due to various reasons such as voltage drops in the power network, different types of faults in the network, energization of large loads and capacitor banks, switching of heavy loads, loose connections in wiring, switching transients, etc. These voltage related problems are addressed using various voltage compensating passive and active devices. A series active power filter, denoted as Dynamic Voltage Restorer (DVR) is commonly used to compensate for voltage sags, swells and interruptions in a power distribution network. The chapter describes the concept, operation and analysis of single-phase and three-phase DVR compensated systems. A mathematical and graphical representation of DVR is interpreted to find the series voltage injected by the DVR. In the case of a non-feasible solution, the maximum compensation capacity of the DVR voltage is computed (without active power support). Transient operation of DVR and switching control are discussed to realize a practical DVR. There are many other methods which can be used to control DVR with active power support in case of deep sag with phase jumps. A number of examples are given to illustrate the concept, which can be further extended to other methods of DVR control.
