Research On Current Reconstruction And Model Predictive Control Of T-type Three-level Grid-tied Converter

The grid-tied technology of new energy power generation can alleviate the environmental problems caused by traditional energy and has been widely concerned.T-type three-level gridtied converter,as the key equipment of new energy grid-tied,is widely used in high voltage and high power grid-tied situations because of its advantages of high conversion efficiency,uniform switching loss and large capacity.However,T-type three-level grid-tied converter will encounter problems such as current sensor failure and strong parameter dependence in actual operation,which will affect the stable operation of grid-tied system.In addition,model predictive control is applied to new energy power electronic grid-tied converter because of its fast dynamic response and easy realization of multi-objective control.In order to solve the problems of current sensor failure and strong dependence on model parameters,a current reconstruction model predictive control strategy for T-type three-level grid-tied converter is proposed.Specific research contents are as follows:Firstly,a model predictive control strategy based on current reconstruction is proposed to improve the fault tolerance of T-type three-level grid-tied converter.This strategy analyzes the relationship between phase current and voltage vector,and reconstructs fault phase current from DC current,normal phase current and predicted current respectively.The required voltage vector is divided into two voltage vector sets according to the reconstruction method.Continuous use of the predicted current to reconstruct the fault phase current can lead to accumulated errors.Therefore,it is necessary to detect the voltage vector set at the current time to ensure that a different voltage vector set is selected at the next time to reduce the accumulation of errors.Secondly,in order to improve the grid-tied performance of T-type three-level grid-tied converter,virtual vectors are added to the voltage vector set.In order to study the method of adding virtual vectors,based on the structure of T-type three-level grid-tied converter,the method of synthesizing virtual vectors from basic voltage vectors is analyzed.According to the mathematical model of T-type three-level grid-tied converter,the grid-tied current error is analyzed,and the visual graph of current error coverage Angle under different virtual vector control is obtained.The Angle of the desired virtual vector is obtained by overlaying the Angle visualization.The virtual vector is determined when the Angle range of the error current covers the entire vector diagram.The proposed strategy can determine the optimal virtual vector and improve the performance of grid connection.Finally,in order to solve the problem that T-type three-level virtual synchronous generator is sensitive to model parameters during operation,a parameterless model predictive control strategy based on Runge-Kutta Algorithm(RKA)is proposed.Firstly,the principle of T-type three-level virtual synchronous generator is analyzed,the model of virtual synchronous generator is constructed,and the model predictive control strategy is designed.Secondly,the influence of parameter mismatch of T-type three-level virtual synchronous generator is analyzed.Then,the Lagrange difference function is used to fit the RKA coefficient,the lumped disturbance is calculated by RKA,the hyperlocal model is determined,and the no-parameter model predictive control strategy is designed,which improves the parameter robustness of Ttype three-level virtual synchronous generator operation.Based on Typhoon HIL602+ and My Way-Expert4,a hardware-in-the-loop experiment platform was built to verify the proposed control strategy.The experimental results validate the effectiveness of the proposed control strategy.