Research On Control Strategy Of Grid Side Converter For Flywheel Energy Storage In Non-ideal Power Grid

Due to the large number of nonlinear loads and renewable energy connected to the power grid,it may lead to non ideal conditions such as voltage imbalance,low order harmonics,and DC components in the power grid.This will further lead to the problem of phase lock out of synchronization of the flywheel energy storage grid side converter and may cause significant distortion of the grid side current,resulting in the grid side converter being unable to operate safely and reliably.Long term operation may lead to overcurrent damage.In view of this,this article studies the control strategy of the flywheel energy storage grid side converter in non ideal power grids with phase-locked loops and unbalanced grid voltage.The research mainly includes the following aspects:(1)Introduced the research background and significance of this topic,determined the topology structure of the flywheel energy storage grid side converter,elaborated on the research status of phase-locked loop technology,grid side converter conventional control technology,and model predictive control technology,and clarified the main research content of this article.(2)Based on the topology structure of the flywheel energy storage grid side converter,establish its mathematical model under voltage balance and imbalance in the power grid.And simulation analysis was conducted on the control strategies of traditional voltage oriented vector control and traditional single vector model predictive control aimed at suppressing negative sequence current under unbalanced power grid voltage.The results showed that traditional control strategies still have problems such as complex parameter adjustment,slow dynamic response,and large current ripple.(3)To address the issue of conventional phase-locked loops losing synchronization in non ideal power grids.Based on the study of traditional second-order generalized integrator phase-locked loops and second-order generalized integrator phase-locked loops with low-pass filters,this paper proposes an improved second-order generalized integrator phase-locked loop through structural cascading;According to the analysis of the Bode diagram and simulation comparison,the results indicate that the power grid voltage is in a non ideal state.The improved second-order generalized integrator phase-locked loop can achieve precise phase-locked,and has better suppression effect when the power grid voltage contains DC components.(4)Given the fixed direction and amplitude of the output voltage vector in traditional single vector model predictive control under unbalanced power grid voltage,which leads to the problem of large current ripple on the grid side.By increasing the number of voltage vectors,a dual vector and three vector model predictive control algorithm has been proposed,which can effectively solve the problem of large current ripple.However,increasing the number of voltage vectors results in a high number of optimization times and computational complexity in the control process.On the basis of the three vector model predictive control,this article proposes an optimized three vector model predictive control algorithm based on the idea of vector synthesis.By synthesizing adjacent basic voltage vectors in each sector,six expected voltage vectors in any amplitude direction are obtained,achieving global 360 ° optimization.The action time of adjacent vectors is calculated using the dq axis deadbeat calculation method,achieving accurate tracking of the reference current,It can still meet the requirements of suppressing negative sequence current while reducing the amount of online optimization calculation.The correctness of the proposed optimized three vector model predictive control was verified through simulation comparison.(5)To verify the feasibility and correctness of the control strategy,a hardware in the loop experimental platform based on Real Time Digital Simulation System(RTDS)/Rapid Control Prototyping(RCP)and an RCP based network side converter experimental platform were built.It has been verified that the improved second-order generalized integrator phase-locked loop performs better than traditional second-order generalized integrator phase-locked loops and second-order generalized integrator phase-locked loops with low-pass filters in non ideal power grids;The optimized three vector model predictive control algorithm is superior to the dual vector and three vector model predictive control algorithms in current ripple,optimization times,computational complexity,and other issues under the voltage balance state of the power grid.