Research On Thrust Ripple Suppression Strategy Of Linear Vernier Permanent Magnet Machines

In the field of high-end equipment manufacturing such as computer numerical control machine tools,linear machines have received widespread attention and have been widely used as the core component.Thrust density and thrust ripple are core performance indicators of linear machine drive systems.It is difficult to take into account the improvement of thrust density and the suppression of thrust ripple by using traditional machine topology and control algorithm,which is one of the bottlenecks restricting the application of linear machines.In this thesis,aiming at the existing problems and technical difficulties of the linear machine drive systems,the principle of thrust density enhancement of the linear vernier permanent magnet motor(LVPMM)based on the principle of magnetic field modulation is studied in depth.The mathematical model of thrust ripple is deduced in detail.From the perspective of control strategy,the suppression of thrust ripple is studied.Firstly,the basic operating principle of the LVPMM is analyzed from the perspective of the magnetic field modulation principle.Then,the thrust ripple of the linear machine is divided into the no-load thrust ripple and the load thrust ripple.Their generation principles are studied respectively,and the mathematical models are derived.The no-load thrust ripple is the inherent disturbance generated by the interaction between the iron core and the permanent magnet,and the load thrust ripple is the disturbance generated by the current.The generation principles of the two thrust ripples are different.It is necessary to conduct decoupling analysis and apply different control algorithms for suppression.A three-module LVPMM and a single-module LVPMM are taken as research objects.The three-module LVPMM completely eliminates the influence of load thrust ripple through the optimization of electromagnetic structure.It can be used for the verification of the no-load thrust ripple suppression algorithm.The single-module LVPMM has a simpler electromagnetic structure,but is affected by both no-load and load thrust ripples.It can be used to verify the load thrust ripple suppression algorithm under the condition that the no-load thrust ripple is excluded.To suppress the no-load thrust ripple,a thrust ripple observer and a high bandwidth current controller are designed to achieve accurate observation and compensation of no-load thrust ripple.In order to achieve accurate observation of no-load thrust ripple,the thrust ripple is regarded as the extended state of the system,and an extended state observer is proposed.Through reasonable design of the parameters,the bandwidth of the observer can cover the main harmonic components of the thrust ripple,and the accurate observation of the thrust ripple is realized.The observed value is converted into harmonic current and injected into the machine.The injected current generates thrust and cancels out no-load thrust ripple,and the compensation of no-load thrust ripple is realized.In order to improve the accuracy of compensation,the resonant current controller is used to replace the traditional current controller.Control accuracy of harmonic current is improved.The experimental results show that the combination of the thrust ripple observer and the high-bandwidth current controller significantly suppresses the influence of no-load thrust ripple on the control system accuracy.The speed control error caused by no-load thrust ripple is reduced by 90%.To suppress the load thrust ripple,the distribution method and control method of harmonic current are studied respectively.In terms of the distribution method of the harmonic current,the thesis innovatively introduces the negative-sequence current into the linear machine control system,and the load thrust ripple is suppressed.The distribution method of the positive-and negative-sequence current is given according to the mathematical model of the load thrust ripple.Through the proposed negative-sequence current injection algorithm,the amplitude of load thrust ripple is reduced by more than60%.On the basis of the negative-sequence current injection algorithm,an asymmetrical back-EMF observer is designed in this thesis.The observed values are used for the calculation of positive-and negative-sequence current distribution,and the load thrust ripple suppression algorithm can be realized online.In terms of harmonic current control methods,a novel harmonic current controller based on the concept of "virtual winding" is proposed.The problem of positive-and negative-sequence current control in the load thrust ripple suppression algorithm is solved.Firstly,taking the dual-three-phase control system based on auxiliary windings as the research object,the feasibility of applying the dual-three-phase topology to dual-frequency current closed-loop control is analyzed.Then the virtual winding is used to replace the auxiliary winding,and the design of a virtual dual three-phase topology controller is completed.Precise closed-loop control of positiveand negative-sequence currents is realized.On the basis of the virtual dual-three-phase topology,more virtual three-phase topologies can be introduced.A harmonic current controller based on the virtual multi-phase topology is constructed.Decoupling and precise closed-loop control of multiple harmonic currents are realized.The proposed controller solves the problems that the traditional harmonic closed-loop control strategy cannot take into account both dynamic response speed and steady-state accuracy.In this thesis,the decoupling analysis of no-load and load thrust ripples in LVPMMs is carried out,and thrust ripple suppression control strategies are designed respectively.The designed control strategies effectively suppress the impact of thrust ripple on the precision of the linear machine control systems.It is helpful for the popularization and application of LVPMMs in the field of high-end equipment manufacturing.