Reduction And Measurement Of Non-ideal Electromagnetic Torque Of Reaction Wheel

The reaction wheel is one of the main executive components in the control system of satellite attitude which possess the features of high control accuracy, low fuel consumption and great application flexibility. The reaction torque in the process of acceleration and deceleration is utilized to control the satellite attitude. The non-ideal electromagnetic torques in the output torque of the reaction wheel which disturbs the control of the satellite attitude needs to be restrained from the aspects of both the motor design and system control. On the other hand, the measurement of the electromagnetic torque is the inevitable means to evaluate the effect of the restrain in the reaction wheel. Since there is no shaft extension in the reaction wheel and its output torque is in small magnitude which brings in the difficulty in the measurement of the torque, therefore it is necessary to study on the measurement method of the torque in the reaction wheel. Therefore the research of reduction of non-ideal electromagnetic torque and the measurement of the torque is of great significance in the control system of satellite attitude.The non-ideal electromagnetic torque of reaction wheel includes torque ripple and torque drop-out. In this paper, the control system of satellite attitude which takes dynamic torque into account was set up. The influence of the non-ideal electromagnetic torque on satellite attitude was quantified through simulation research. Simulation results show that torque ripple leads to the fluctuation of the same frequency in satellite attitude, the fluctuation increases with the decreasing of order of ripple and with the increasing of the coefficient of the torque ripple. Torque drop-out leads to the deviation of the satellite attitude, the maximum deviation increases with the increasing of the amplitude and lasting time of the torque drop-out. Therefore the influence of non-ideal electromagnetic torque should be taken into account when high control precision was required.The strategy of magnet splice was proposed to restrain the torque ripple of reaction wheel. The influences of the magnetizing style with different air gap and pole pitch in magnet circuit were analyzed; the distribution of flux density with different splices number and different splice angles were studied. The analysis show that small odd number of magnet splices is beneficial to improve the distribution of the flux density. The coefficient of torque ripple can be reduced by 5% through adopting reasonable splice number and splice angle while keeping the same winding structure and driving mode.The four-quadrant operation control program was improved to restrain torque drop-out of reaction wheel. The joint driving mode of dynamic braking and plug braking was realized through adding dynamic braking circuit into existing servo control system. Torque drop-out at zero crossing speed was effectively restrained with reasonable design of control program. Experiment results of four-quadrant operation demonstrated the validity of the improved control program.The strategy of torque measurement which denotes itself as torque balancing coreless torquer was proposed to solve the difficulty of measuring the torque of reaction wheel. On the basis of the overall strategy of the torque measurement, studies are mainly focused on the design and choice of position sensor, the design of the magnet pole and winding of the torquer, the selection of the rotor programs and other related aspects. Comparisons of system response were made between the moving coil program and the moving core program when measurement noise and resolution of feedback element was considered. The analysis show that the moving coil program is less sensitive to measurement noise and feedback element thus is suitable for the measurement of torque. The measurement range of the proposed torque measuring system is from -0.5N?m to 0.5N?m, the resolution and accuracy are 0.126% and±1.494%,respectively, which illustrate the fitness of the measuring system on the measurement of small magnitude torque of reaction wheel.The control system of the torque measurement based on the disturbance observer (DOB) was studied. The model of torque measurement based on the DOB was set up and the influence of the DOB on the system response was analyzed. In the process of the design of position closed-loop controller, the determination method of the transfer function of the closed-loop disturbance was improved based on the synthesis design method with traditional constant adjustable system. On the basis of double closed-loop control system, one DOB was designed and its approximate design method was proposed. The step response of the torque measurement system shows that DOB can improve the anti-disturbance of the position response and the dynamic characteristic of the system. Experiment results show that the torque measurement system can realize the measurement of the torque ripple, the torque drop-out and other dynamic torque in the reaction wheel.