ADRC-based control strategy for DC-link voltage of flywheel energy storage system

The direct current (DC)-link voltage control of the flywheel energy storage system plays an important role in realizing high-quality grid connection. With the traditional proportional-integral control, the DC-link voltage cannot track its reference value quickly and smoothly when the flywheel energy storage system switches from the charging stage to other working stages. Therefore, a DC-link voltage control strategy for the flywheel energy storage system based on active disturbance rejection control is proposed in this paper to deal with this issue. The DC-link voltage and its differential value are considered as the state variables in this strategy. The internal and external disturbances, such as load power, switching loss, and parameter uncertainty, are regarded as an expanded state. By inputting the voltage error and the observed disturbance into the nonlinear state feedback control law, the rapidity and anti-interference of the DC-link voltage control are ensured under different States of Charge of the flywheel energy storage system. Then, the coefficient freezing method is used to analyze the effects of the disturbance observation bandwidth by nonlinear gain and pole position changes. The DC-link voltage can track the reference value over a wider frequency range of disturbances. By configuring the appropriate observer structure parameters, the disturbance observation bandwidth under the nonlinear function gain variation is always higher than the expected bandwidth. The effectiveness of the proposed control strategy is verified by simulation results at last. The study focuses on the direct current (DC)-link voltage fluctuation problem caused by frequent charging/discharging switching of the back-to-back dual pulse width modulation converter of the flywheel energy storage system (FESS). An active disturbance rejection control (ADRC)-based DC-link voltage control strategy is proposed to deal with this problem for the operating stage switching process considering that the FESS is always at different speeds. Simulation results show that the proposed strategy can effectively improve the DC-link voltage's fast response capability and anti-disturbance performance, and smooth the burrs of FESS power output.image