SRF Control Algorithm Based DVR for Mitigation Balanced and Unbalanced Voltage Disturbances

The power quality problems occur due to voltage disturbances in the system, caused by electrical system faults, switching of large loads or energization of transformers etc. Such voltage disturbances cause short term rapid changes in amplitude of voltage. These voltage changes such as temporary voltage rise (swell) or voltage reduction (sag) are more frequent and have severe impact on the power system. Among the various custom power devices, the DVR is the most suitable one due to its low cost and simplicity in operation. In this paper, SRF (Synchronous Reference Frame Theory) based DVR (Dynamic Voltage Restorer), is considered and analysed for its performance. There are two types of voltage sag and swell which can occur on any distribution lines; balanced and unbalanced voltage sag and swell which are also known as symmetrical and asymmetrical voltage sag and swell respectively. The control strategy for extracting the compensation voltage in DVR is based on synchronous reference frame theory (SRF) along with a PI controller for generating gate pulses for the VSC. The performance of Synchronous Reference Frame (SRF) theory based DVR for the mitigation of balanced and unbalanced voltage sag, swell, sag and swell in different phase voltages is tested and simulation results carried out by MATLABSIMULINK are presented.