Distribution bus voltage control using DVR under the supply frequency variations

This paper discusses a frequency estimation strategy that, when used in conjunction with dynamic voltage restorer (DVR), can hold the magnitude of any distribution bus voltage constant as the supply frequency varies. First the impact of supply frequency variation on the performance of a DVR is illustrated. It has been shown that if a DC battery supplies the DVR, the battery ends up supplying the real power demand of the load. Moreover, the injected voltage in this case can be very high. An alternative mode of operation is discussed which uses the rectifier and DVR in cascade to supply the load. In this mode, a large amount of voltage is injected by the DVR, which is completely undesirable. To avoid this problem, the frequency of the load voltage that has to be regulated by the DVR must be synchronized with the system frequency. In this paper, frequency estimation method is used that can accurately estimate two frequencies even when they are very close to each other. The DVR can then be made to operate at the estimated source frequency. PSCAD/EMTDC and MATLAB results are presented to illustrate the above statements.