A new control method of energy capacitor system in DC-based wind farm

This paper proposes energy capacitor system (ECS) to smoothen the power fluctuation of wind farm composed of variable speed wind generators. Usually, ECS is installed at the terminal of wind farm through a step down transformer, and it is composed of AC-DC converter, DC-link capacitor, buck/boost converter, and EDLC bank. If the desired DC-link voltage is available, then the formation of ECS can be composed of buck/boost converter and EDLC bank only and then becomes very simple and cost-effective. Therefore, in this study, ECS is considered to be connected at the terminal of DC-based wind farm. The variable speed wind turbines driving permanent magnet synchronous generators are considered to be connected to the DC-bus through rectifier and boost converter sets. The DC-bus is connected to the AC network through only one DC-AC inverter. This wind farm topology is also cost-effective since the number of three phase transformers and AC-DC converters can be reduced. A detailed modeling and control strategies for individual component of overall system are presented. Exponential moving average is used to generate the real power reference of ECS. The reference is then adjusted using a look-up table to utilize the stored energy of the EDLC bank in an efficient way. Therefore, the energy storage capacity of EDLC bank can be made small in size, resulting in low system cost of ECS unit and also improvement in the overall performance. The effectiveness of the proposed system is verified with simulation results, which is carried out using PSCAD/EMTDC.