| The Telescope is an observer system, which involves a mix of optical, mechanical and electronic system. In order to track the task accurately, the precision of servo control system is required to arcsecond. With the increasing of telescope diameter and resolution, it is required that the motor could provid torque more than 105N·m. In this situation, the brushed motor can’t meet the requirement of the telescopes’ tracking precision on power, volume and low speed. The permanent magnet synchronous motor(PMSM) is used widely in the international telescope, for its higher power density, less volume and better low speed performance. At present, the application of PMSM in the home telescope is at primary stage. So the problem of telescope servo control system design based on PMSM, is urgent to solve. In this paper, we will put mian force on the following four problems:(1) how to design the specified driver;(2) how to start the motor smoothly and identify the control model;(3) how to design the control strategy based on the control model;(4) how to increase the telescope low speed tracking accuracy.Compared with the direct torque control method, the space vector control method has less torque ripple, which is good for the telescope low speed tracking. Firstly, a PMSM simulation model, based on the space vector control, is built for the decoupling control. Using the result of the simulation, we can verify the theory of space vector control, and guide the hardware control system design on the capacity of max drive current and voltage.Based on the simulation result, the PMSM diver and controller are designed. The driver uses the intelligent power module made by Mitsubishi, which has the protect functions of over voltage, under voltage, over current and over temperature. The controller contains DSP and FPGA, as the main controller, DSP is responsible for the control algorithm. FPGA is used as assist controller, for the acquisition of motor phase current, encoder data and fault handling. In order to increase real time of the current loop, parallel hardware circuit is adopt to realize the current loop. The result of experiment verifies that the hardware system has higher detection accuracy and meets the requirement of the telescope control system.Based on the hardware design, the key technologies of telescope servo control system are studied, which are the smooth start and control model identification. Firstly, the pole position detection method is designed. With injection of current vector, changing the position angle of the current vector based on the motor direction and the angle of current vector. In the process of positioning, the rotor has small movement and meets the requirement of non-impact machine. Secondly, the white noise signal is used as the incentive signal, and the response of the system is recorded. Then the frequency feature is obtained through the DFT. In order to identify the control model, the eigensystem realization algorithm is used to fit the frequency feature curve. The result of experiment indicates that the result of control model identification fits the theory analysis. The identification of control model provides basis for the controller design.On the basis of control model identification, In order to reduce the modal resonance, a structure filter is designed. Then the lead-lag controller is designed for the telescope main axis control system. An adaptive sliding mode controller(ASMC) is designed for increasing the low speed tracking performance, the varying system parameters are evaluated by the adaptive law. The integral action contained in the sliding surface can ensure the steady state error of tracking velocity zero. And the boundary layer is employed to suppress the chattering of sliding mode control. The result of experiment indicates that the tracking accuracy reach to 0.489″ after using ASMC, compared with the traditional controller, the accuracy increases by 40%.In this chapter, the factors, which affect the telescope tracking performance, are modeled and compensated. Firstly, the friction of the telescope axis is modeled through Lu Gre model. Then the identification model is used for the low speed performance simulation. In order to reduce the influence of friction, the extended stated observer is adopted to estimate the disturbance and compensate the friction. Secondly, the harmonic model is built. Then the least squares method is used to identify that model. At last, that model is used to iteratively improve the cancellation. The result of simulation verifies the validity of the cogging compensation method. Thirdly, Kalman filter is used to increase the speed detection accuracy, and the filter could estimate the low speed more accurately than numerical difference. Lastly, the above low speed compensation methods are analyzed and evaluated. |
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