Research On Optimal Model Predictive Control For Low Switching Frequency Of Permanent Magnet Synchronous Motor

Permanent magnet synchronous motors are extensively used in the fields of aerospace and industrial manufacturing due to their advantages of low noise and high power density.Traditional control strategies are difficult to meet the requirements of high-performance motion control systems due to low performance and poor interference immunity.Model predictive control of permanent magnet synchronous motors has become a current research hotspot due to its good dynamic performance and easy addition of various constraints.However,the conventional model predictive control strategy has the problem of large direct axis and quadrature axis current pulsation and poor steady-state performance.The application of multi-vector model predictive control can improve the steady-state performance of the control,but it will enlarge the amount of algorithm operations,while the multi-vector model predictive control has a fixed and high switching frequency,which leads to an increase in inverter losses.Further research is needed on how to reduce the switching frequency of the model predictive control while ensuring its high performance.Therefore,in this thesis,the surface-mounted permanent magnet synchronous motor is used as the control object,and its control method is improved for the problems in the above-mentioned traditional model predictive current control,and theoretical analysis,simulation and experimental research are carried out.The main work of this thesis is classified into the following points:(1)Mathematical modeling of permanent magnet synchronous motors and conventional model predictive control analysis.Firstly,the equations of stator voltage and stator flux linkage for surface-mounted permanent magnet synchronous motors in different coordinate systems are derived,and then model predictive control is investigated and the fundamental features of model predictive control are explained.Starting from the analysis of the basic voltage vector of the inverter,the traditional model predictive current control method is elaborated,its current sampling error is derived,the current sampling error is divided into offset error and gain error,the impact of each part of the sampling accuracy on the d-q axis current measurement is analyzed,and a hardware scheme to improve the current sampling error is proposed.(2)Phase voltage duty cycle modulation model predictive current control(PVDM-MPCC)strategy research.The control principle of PVDM-MPCC is deduced.This method divides the space vector into 3 sectors,applies the current deadbeat principle in each sector to calculate the phase voltage duty cycle,and then predicts the current.This control method Compared with the traditional 6-sector method,it greatly reduces the computational complexity of the algorithm and improves the steady-state performance of the system.The control performance and current loop bandwidth of the PVDM-MPCC strategy were tested by Simulink simulation,and the simulation data was analyzed.(3)Research on two-step PVDM-MPCC strategy with low switching frequency.To address the problem of switching frequency,this paper proposes a two-step prediction method for low switching frequency based on the phase voltage duty cycle modulation model prediction current control method,which takes the more suitable two alternative vectors in each prediction and then performs the prediction at t+2 moments,while adding the term of switching times in the value function of the second prediction step,so as to decrease the switching times as one of the optimization objectives.The effect of decreasing the switching frequency is achieved.Using Simulink to verify the feasibility of the designed control strategy,the simulation indicates that the low switching frequency two-step PVDM-MPCC strategy can significantly decrease the switching frequency.(4)A permanent magnet synchronous motor experimental platform based on FPGA+TMS320F28377D was designed and built for experimental research.In this thesis,the specific design methods of the main circuit,isolation circuit,sampling circuit,and other circuits are explained,and PC upper computer software is written to communicate with the hardware experimental platform for control and experimental data collection.After completing the design and debugging of the control platform,perform experiments on this control platform to validate the effectiveness of low switching frequency two-step PVDM-MPCC.The experimental results prove that in comparison with the conventional model predictive control strategy,the proposed low switching frequency two-step PVDM-MPCC strategy can improve the performance of the permanent magnet synchronous motor control system.