Voltage sag compensation using direct converter based DVR by modulating the error signal

Abstract

The aim of this paper is to present a modulation technique to achieve highest voltage sag compensation using direct converter based dynamic voltage restorer (DVR). The DVR topology proposed in this paper, has a direct converter and a series transformer. The direct converter is fabricated using only two bi-directional switches. The DVR is designed to compensate the sag in a phase by taking power from the same phase. The direct converter is connected between the series transformer and the line in which sag compensation is to be achieved. Conventionally, the PWM pulses for the direct converters are produced by comparing the error signal with the carrier signal. The error signal is obtained by comparing the amplitude of voltage in the line with the amplitude of the reference voltage. If the amplitude of the carrier signal is kept constant and the actual amplitude of error signal is used for PWM generation, it is possible to achieve only 22% of voltage sag compensation. But if the error signal amplitude is modulated according to the amplitude of existing voltage sag in the line, 52% of the voltage sag can be compensated with the THD less than 5%. Simulation results are presented for validating the analysis.