Analysis of a three-phase AC chopper with high power factor for the use in “PV-to-Heat” applications

The decreasing cost of photovoltaic (PV) systems allows the production of cheap renewable electricity. This has led to an increasing number of installed systems during the past years. Since the storage of electrical energy is still rather expensive, the optimization of the self-consumption coverage gains importance. One solution to higher self-consumption is a method called “PV-to-Heat”, where excess PV energy is not fed into the grid but stored in the form of hot water in the domestic boiler. This article describes a simplified hardware approach for a three-phase PWM chopper for AC/AC conversion. It is suited for low inductive loads like electric heaters. Compared to existing systems, the proposed converter design offers equal or better performance at very low cost and small size. The circuit allows full control of the power flow and provides sinusoidal and symmetrical load currents. The average electrical efficiency is 94.7% for a 6 kW test system. Unlike certain commercial products, there is no need to use a custom heater or access the star point of the load resistor.