A new wind turbine generator / battery energy storage utility interface converter topology with medium-frequency transformer

In this paper, a new medium-voltage (MV) wind turbine generator (WTG) - energy storage grid interface converter topology with medium-frequency (MF) link transformer isolation is introduced. The system forms a 3-port network in which several series stacked AC-AC converters transform the low-frequency (50/60 Hz) utility MV into MF (0.4 to 2 kHz) AC voltage by modulating it with MF square wave. This voltage is then fed to the MF transformer primary windings. The secondary and tertiary windings interface with the WTG side and the battery energy storage side respectively after power conversion. The power generated by WTG is transferred to the MF transformer secondary windings through a 3-phase PWM rectifier and a 3-phase PWM inverter, whereas the power transfer between the energy storage and the tertiary winding occurs through a 3-phase PWM inverter. It is shown that the utility grid sinusoidal currents, the battery current and the WTG output currents can be controlled to be of good quality using PI and DQ control strategies. Thus, the proposed MF transformer based 3-port topology results in smaller converter weight/volume. Moreover, the control can effectively handle voltage sags/swells and provide low voltage ride through (LVRT) capability without significant change in the topology. Simulation waveforms along with preliminary experimental results are discussed in this paper.