ABSTRACT
Many DC-AC inverters employ transformers in their overall design, thus eliminating the DC bias that can be injected into the grid. Distributed photovoltaic grid transformers (DPV-GTs) play an important role in performing this basic function. However, many commercial inverters are designed without transformers for higher efficiency, lower cost, and size limitations. In such cases a better approach is to design a filter to remove the DC bias. Possible sources of even harmonics are three-phase half-wave controlled bridges, AC arc furnaces, converters like three-phase rectifiers supplying DC/DC converters, six-pulse cycloconverters, and half-wave rectifiers. Pulse-width modulators in inverter designs produce DC bias when even-power harmonics are contained in the basic voltage waveform and in general with a positive-negative imbalance in the reference voltage. This distortion of the reference voltage is especially predominant when the synchronization of the inverter with the network voltage is achieved by using the zero-crossings of the reference voltage waveform.
