Research On Interpolation Control Strategy In Low Speed Region Of Permanent Magnet Synchronous Machines

The permanent magnet synchronous machine(PMSM)has been widely used in home appliances,aerospace and other fields because of its high efficiency,energy saving,low noise and good control performance.In both industry and academia,improvements to the control performance of PMSM have conducted by researchers via exploiting the potential of vector control technology.For vector control algorithms,it is necessary to obtain high-precision rotor position in real time to ensure both control accuracy and efficiency.Therefore,it is usually necessary to install an optical encoder or a resolver at the end of rotor shaft to realize the real-time acquisition of rotor position.However,the high accuracy position encoder will increase the manufacturing cost of the system and reduce the system reliability.Thus,existing researches are starting to work on the vector control technology without position sensors.Up to now,the theory of sensorless control has become mature,which are now applied in some industrial applications.However,its reliability is still difficult to fully meet various demands in applications.For example,in applications being sensitive to production costs and reliability such as washing machines,electric vehicles,etc.,the interpolation control of low-precision position encoders can be used as a solution for balancing the control accuracy and cost.In this thesis,the position encoder interpolation control strategy in low-speed region of PMSM is deeply studied,and the position observer-based solution is selected as the research focus.The main content of this thesis is listed as follows:1.The mathematical model of PMSM drive system and parameter determination of controllers are analyzed.Firstly,this thesis analyzes the mathematical model of the machine drive system and deduces the equations of PMSMs under different coordinates.Secondly,the theoretical derivation is carried out for the parameter determination of current loop/speed loop controllers,and the influence of controller bandwidth,electrical and mechanical parameters on the vector control is analyzed by simulation.On this basis,the motor driving system with low-resolution encoder is modeled and analyzed,and the theoretical derivation and simulation verification of the average speed method are carried out.2.A switching control strategy for the position observer with anti-load disturbance capability is proposed.When there is a severe external load disturbance,the conventional flux observer will face significant convergence errors and instability problems.Aiming to solve this problem,this thesis proposes a switching control strategy,which can improve the convergence accuracy and anti-disturbance of conventional position observers,and can finally improve the anti-load disturbance performance of the interpolation algorithm.Experiments show that,compared with the traditional position interpolation method based on flux observer,this strategy shows better position interpolation accuracy in the presence of severe load disturbances.3.A position interpolation control for compensating accumulative errors is proposed.Aiming to solve the cumulative error problem existing in the traditional position interpolation control method based on flux observer,this thesis proposes a compensation strategy based on error prediction.Experiments show that,compared with the traditional interpolation scheme,this method is more effective in reducing the cumulative error generated by the position interpolation calculation of flux observer,and can effectively improve the interpolation position accuracy under both constant and step load conditions.4.An interpolation control strategy considering the compensation of inverter nonlinearities is proposed.The interpolation control and cumulative error compensation strategies proposed in this thesis generally work in the low-speed region,in which the reference voltage distortion caused by the inverter nonlineariry is quite significant,and will affect the steady state and dynamic performances of control algorithm.Therefore,this thesis proposes to consider the influence of inverter nonlinearity in the compensation of cumulative error,of which the performance is verified in experiments.The results show that,after adding the compensation of inverter nonlinearities,the low-speed region interpolation control with cumulative error compensation will have better steady state and dynamic performances under both constant and step load conditions.