Voltage Sag, Swell, and Interruption Compensation Using DVR Based on Energy Storage Device

Though we have many power quality issues, voltage sag, interruption and swell are considered to be very important ones as it occurs very frequently and affects the sensitive loads adversely. Though many topologies of DVR are presented in the literature, all the topologies have used P or PI or PID or fuzzy or neural network controllers to mitigate power quality issues. But in this paper, it is proved that it is possible to mitigate the voltage sag, swell and outages using Dynamic Voltage Restorer (DVR), without using any controllers like P, PI, PID, fuzzy or neural networks. The proposed DVR consists of a battery bank as an energy storage device, a Voltage Source Inverter (VSI), control circuitry to generate switching pulses, LC filter and a series transformer. The proposed DVR is connected immediately after the distribution transformer in order to protect the load from supply voltage deviations. The three phase supply voltages are always measured and converted into Direct-Quadrature-Zero (DQ0) quantities and compared with the reference value to generate error signals. When the supply voltage is at rated value, the error signal is zero. So, PWM will not be generated by the control circuitry and the VSI won’t generate any compensating voltage. At this condition, the secondary winding of the series transformer will also be short circuited using a breaker. So, the voltage injected into the line by the DVR is zero. Thus, the load voltage is equal to supply voltage and maintained at rated value. Whenever a sag or swell or interruptions occurs at the supply side, the three phase voltages are not at rated value and also unbalanced. So, error signals will be generated in the DQ0 frame. These error signals in the DQ0 frame are again converted into three phase voltages using inverse DQ0 transformation. Using these three phase error signals, switching pulses are generated for the VSI. The generated compensating voltage is injected along with the supply voltage using the series transformer, in order to maintain the load voltage at rated value. MATLAB Simulink software is used for simulation and the presented results validate that the proposed DVR can effectively mitigate balanced and unbalanced voltage sag of 100%, balanced and unbalanced voltage swell of 100%, single phase outage and three outages.