Research On Control Method Of Moving-coil Linear Motor For Electromagnetic Launcher For Unmanned Aerial Vehicles

As a new type of UAV take-off mode,the electromagnetic ejection system requires full-range control,small thrust fluctuation and strong flexibility.Moving coil linear motor meets the design requirements of electromagnetic ejection system because of its high power density and high thrust density,but there are some problems of thrust fluctuation.And the control method plays a decisive role in further improving its performance.So there are four aspects: full-range control,load and resistance,commutation control and braking control being researched.With the structure of electromagnetic ejection system based on moving coil linear motor analyzed,in order to realize the full-range control and meet the requirements of the system for the acceleration distance and the end speed,this paper proposes a method,which designs the control target curve to make UAV tracking target curve movement.In order to facilitate tracking control of the system,the control target curve is decomposed into a number of equally constant acceleration motion curves.In order to achieve constant acceleration motion in each segment,the solutions for the change of thrust fluctuation and load resistance are discussed.The predictive voltage control method is proposed to solve the problem of thrust fluctuation caused by non-ideal back EMF and electronic commutation.And the correlation model between thrust deviation and system input voltage is established,the thrust is realized effectively.Aiming at the problem that the external resistance of the system is different in different take-off environments,and the internal resistance of the system such as cogging force and friction is difficult to measure,the resistance observer based on sliding mode theory is designed to observe the system resistance quickly and in real time.The simulation results show that the combination of the above two methods can adjust the output thrust of the system in real time to control the acceleration and the system can make UAV follow the target curve to accelerate take-off in different environments,with the full-range controllable characteristics.In view of the fact that position sensors are susceptible to strong magnetic field,humidity and other environmen,and the number of them increases significantly with the extension of track,this paper proposes a position sensorless commutation control method based on the principle of line zero-potential zero-crossing.Through the qualitative analysis of the waveform and the theoretical formula of the series,it is proved that even if the back EMF is distorted,the zero point of the line back EMF still corresponds to the actual electronic commutation point of the system.In order to avoid the miss detection of line back EMF zero-crossing point,the S-function-based mover position detection method is further constructed.The simulation results show that the method can effectively guarantee the normal commutation control of the system..In order to achieve short-distance braking of the system and make the rotor coil "soft landing" in the braking process,this paper adopts the method,which contains that the integrated control scheme in that eddy current braking without mechanical contact is headed,reverse brake is used as the adjustment control and rubber damping brake is an emergency means.And the control strategy for designing the brake reference curve is proposed to solve the problem that the braking process is uncontrollable.The simulation results show that the integrated braking scheme meets the requirements of relevant systems.At last,the hardware platform of electromagnetic launcher system based on moving-coil linear motor is built,and the thrust control method described in this paper is tested and verified,which proves that the method is effective.