Coordinated DC Voltage Control of Wind Turbine With Embedded Energy Storage System

This paper investigates dc voltage control strategies for output power smoothing of a fully rated converter-based wind turbine with energy storage device connected to the common dc link via a bidirectional dc/dc converter. Since the dc link voltage ripple reflects power oscillation, coordinated dc voltage control schemes are used for the ac network side converter and energy storage system to ensure that generated high-frequency power fluctuation is absorbed by the energy storage system, whereas the low-frequency components are transmitted to the connected ac network. Two methods have been proposed: one is based on proportional-integral (PI) voltage controller and low-pass filter with large time constant, and the other is based on PI with low natural frequency and droop controller with large droop gain. The detailed controller designs are described and system stability is assessed and shown to be stable. Both the MATLAB/Simulink simulations and experimental results are presented to demonstrate the effectiveness of the proposed methods for power smoothing.