Dynamic Voltage Restorer–A Custom Power Device for Power Quality Improvement in Electrical Distribution Systems

Power quality (PQ) is an important issue in power systems that reflects a measure of quality of energy supply to the consumers. Power electronics-based equipment is increasing in power systems that cause voltage distortions which may damage a sensitive appliance in the distribution grid. Besides, many electrical and electronic equipment is susceptible to power supply disturbances in modern industrial establishments. The most vital power quality issues affecting large commercial and industrial customers are momentary power interruptions and voltage sags. Usually, these PQ issues are associated with the faults that occur in the supplying power systems. Voltage sags are very common since they can be associated with the faults that happen remotely to the customer. Further, these PQ problems with about 4–5 cycles may cause an extensive malfunction to the sensitive equipment. Therefore, an appropriate solution is necessary to handle this problem. A Dynamic voltage restorer (DVR) is a custom power device (CPD) that can protect sensitive equipment against voltage disturbances and improve power quality in electrical distribution systems. In recent years, many CPDs have been developed to meet the need of the industries and their critical load establishment. The DVR is one of the most promising CPDs used to improve the power quality before feeding it to the sensitive load to protect electric appliances from damage. DVR is the combination of a voltage source inverter (VSI), which can impose the voltage in series through a series injection transformer (SIT) with the power distribution system during voltage sag. The required voltage compensation can be achieved by adopting the pulse width modulation (PWM) technique for VSI. The DVR's performance mainly depends upon the control system that includes voltage disturbance detection, reference generation, voltage & current control and PWM switching strategy. The main objective of the control system is to compensate for the disturbance at the earliest using a fast detection technique, optimum control variables for the control circuit and a suitable PWM switching methodology. Many such compensation methods and control techniques are proposed in the literature along with various DVR topologies which are analysed and studied in this chapter.