Abstract
Back-to-back PWM inverter based bidirectional dynamic voltage restorers (DVR) may have worse efficiency than mechanical or SCR based solutions, but they are able to provide a continuously variable voltage in series with the grid. As the injected waveform does not need to be sinusoidal, additional features may also be implemented in software. In this paper it is shown that the compensation of voltage harmonics, flicker, and even voltage transients are all possible to some extent. The power required for the series voltage injection does not need to originate from the same phase where it is injected. Drawing power from the less problematic phases can also be used to increase the voltage symmetry on the unregulated side of the device. It is shown in the paper, that at partial load the complete deactivation of one phase in the active rectifier stage can not only help with asymmetry, but can also increase the efficiency of the system. A method is proposed for the seamless transfer in the active rectifier stage from 3-phase to 2-phase operation and back. It is also shown in the paper, that phase deactivation and electronic bypass of the injection transformer is possible in the output stage as well. The three level half bridge circuit configuration enables this without additional components.
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