Development of a high bandwidth multi-phase multilevel power supply for electricity supply network emulation

The increasing number of distributed power generation systems, and more specifically wind farms, has led to electricity network companies laying down specifications as to how these power sources interact with the grid. The system described here is intended to act as a controllable grid to aid in the testing of these and other systems. The system is based on a voltage source inverter followed by a low pass filter. In order to achieve accurate output voltage control, high bandwidth closed loop control is required. A multi-level inverter was used to exploit the higher switching speeds available with low voltage rating devices. Also the lower switching harmonics in multi-level inverter allows the filter cut-off frequency to be increased in order to achieve a higher bandwidth response. A unit was constructed with a nominal continuous rating of 7.5 kW and experimental results are presented