Research On Direct Torque/Suspension Force Control Of Bearingless Brushless DC Motor For Flywheel Batteries

Facing the global problem of energy crisis,the development and utilization of renewable energy and energy storage technology has become a hot research topic in the world.As a high-performance energy storage device,the flywheel battery has many advantages such as high power density,clean and efficient,long life and so on.It has extremely high scientific research and application value in dealing with the energy crisis.As the core component of the flywheel battery system,the drive motor is the key research object of scholars all over the world.Based on the traditional brushless DC motor,the Bearingless Brushless DC Motor(BBLDCM)embeds a set of suspension windings in the stator slot,which realizes the stable suspension of the rotor at two degrees of freedom while generating torque.It has the advantages of high integration,low loss,high critical speed,high power density,etc.,and has important research significance in the field of flywheel batteries.This paper takes BBLDCM as the research object.In order to solve the problem of nonlinear,strong coupling,high pulsation and poor dynamic performance of BBLDCM,this paper completed the following work:Firstly,the structure of the BBLDCM is described.The mechanism of torque and suspension force generation and its coupling relationship are analyzed.The mathematical model of single degree of freedom radial levitation force is derived,and then extended to the mathematical model of suspension force at any rotor position.It lays a good foundation for the construction of the control systemAiming at the problem of large torque ripple in the running of motor,the numerical analysis relationship of flux linkage,voltage and torque is derived.The direct torque control strategy is applied to the torque control subsystem.In view of the fact that the direct torque control is not ideal for the torque ripple suppression of the high-speed running section of the motor,the root cause of the pulsation is further analyzed,and the current prediction control is introduced on the basis of the direct torque control strategy,and The current prediction expression is deduced at high speed and low speed.The torque ripple suppression is realized in the full speed range of the motor.In order to improve the stability of the suspension rotor and reduce the jitter,this paper draws on the basic idea of direct torque control,proposes a new direct suspension force control strategy for the suspension control subsystem,derives the suspension force vector under different states,and gives the suspension winding conduction table.Clarify the principle of the new direct suspension force regulation.In order to minimize the rotor jitter,reduce the influence of external disturbances,and improve the robustness.Based on the proposed direct suspension force control strategy,combined with the super-helical algorithm,the second-order sliding mode displacement controller is designed and improved to realize the high-performance control of the suspension subsystem.In order to meet the high-speed operation control requirements of motor,a digital control system based on DSP is constructed.The torque and suspension subsystem power converter,drive isolation and signal detection circuits are designed,which lays a foundation for the subsequent research.