Battery-utility interface using soft switched ac link supporting low voltage ride through

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 bidirectional 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. This converter has several significant advantages such as: high efficiency, light weight, low cost, very short power reversal time and the low voltage ride through (LVRT) capability. These characteristics make this converter an outstanding option for the battery-utility interface. 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 0.5 ms are demonstrated through simulation. Another important factor in the grid stability is low voltage ride through capability. In this paper, it will be shown that our proposed converter has this capability. Both simulations and experimental results will be included in this paper.