Voltage Sag Mitigation Using Direct Converter Based DVR without Error Signal

Dynamic voltage restorer is considered to be one of the best device to compensate voltage sag and swell. Recently the DVRs based on direct converters are very popular and works are getting published for various topologies and modulating techniques to explore the efficiency and worth of the same. In this paper, the direct converter is realized using only two bidirectional switches, in order to mitigate voltage sag. The voltage required to compensate the voltage sag is taken from the same phase where the voltage sag has occurred. The direct converter is connected between the line in which the voltage sag has occurred and the series transformer. In the conventional PWM generation technique, the supply voltage is measured and compared with the reference voltage in order to find out the voltage sag and the error voltage signal. This error signal will be compared with the carrier to generate the PWM pulses. Though already papers have been published to mitigate voltage sag using direct converter, in this paper, as one of the efforts to show the flexibility of the direct converter based DVR, the voltage sag is mitigated without measuring the supply voltage and without generating the error signals, since the power required to mitigate the sag is taken from the phase where it occurred. Ordinary PWM technique is used to control the bidirectional switches. In this proposed methodology the DVR is able to compensate 22% of voltage sag. The simulation is carried out in Matlab Simulink and the results are presented for verification.