Battery-utility interface using soft switched AC link buck boost converter

In this paper a novel soft switched high frequency AC link converter is proposed for use as a battery-utility interface. The proposed configuration uses 10 bi-directional switches interfacing with an AC link consisting of an inductor and a parallel capacitance. The capacitance produces soft turn off in all operating conditions, and turn on always occurs with zero voltage. Utility scale battery systems are being developed to improve grid stability, provide peaking power, and to improve the penetration of renewable energy sources. In order to provide the required grid stabilization, power converters which can switch in a few milliseconds from charging batteries to supplying power to the electric grid are required, and this must be done at low cost with high powered converters. The AC link converter proposed is capable of such rapid switching speeds, due to its high frequency of internal operation. Power reversal speed is only limited by the resonance period of the input/output filters, which have low per unit reactance due to the current sourced nature of the converter and its high frequency of internal operation, which is made possible by the fully soft switched converter. Power reversal times of less than 1 ms are demonstrated by simulation.