Ramp based control of DVR to mitigate voltage sags/swells

The Dynamic Voltage Restorer (DVR) is a custom power device connected in series with the load, which can control the voltage applied to the load by injecting a voltage of arbitrary amplitude, phase and harmonic component into the line. The conventional hysteresis voltage controller of DVR is simple to implement and has a fast dynamic response etc. However, it suffers from the demerit of variable switching frequency, which may be prohibitively high, increasing the stress levels on the switches and also switching losses. In this paper, a ramp based control of DVR is used to achieve a simple closed loop control and constant switching frequency. The method is also extended to a ramp controller with hysteresis to achieve a reduced constant value of the switching frequency. Detailed simulation has been carried out using PSCAD software.