Typical Type-4 wind turbines use DC-link inverters to couple the electrical machine to the power grid. Each wind turbine has two power conversion steps. Therefore, an N-turbine farm will have 2N power converters. This work presents a DC bus collection system for a type-4 wind farm that reduces the overall required number of converters and minimizes the energy storage system (ESS) requirements. This approach requires one conversion step per turbine, one converter for the ESS and a single grid coupling converter, which leads to N + 2 converters for the wind farm which will result in significant cost savings.

However, one of the trade-offs for a DC collection system is the need for increased energy storage to filter the power variations and improve power quality to the grid. This paper presents a novel approach to an effective DC bus collection system design. The DC collection for the wind farm implements a power phasing control method between turbines that filter the variations and improves power quality while minimizing the need for added energy storage system hardware and improved power quality. The phasing control takes advantage of a novel power packet network concept with nonlinear power flow control design techniques that guarantees both stable and enhanced dynamic performance. This paper presents the theoretical design of the DC collection and phasing control. To demonstrate the efficacy of this approach detailed numerical simulation examples are presented.