Research On Multi-motor Coordinated Control And Fault-tolerant Strategies

In the industrial applications of heavy load, there are some mechanical equipments such as large tunnel boring machines, rolling machines and strip cold rolling mills. Besides, there are some situations where the space is limited or special so that we can’t use one huge motor. Considering the difficulity of those situations, multi-motor system is often used to replace the single motor. This kind of driving system has the advantage of reducing the moment of inertia, improving speed accuracy and improving system reliablity. This paper starts at reducing the torque imbalance of multi-motor coordination systems and improving the operational reliablity. It discusses the problems of multi-motor torque distribution systems and proposes solutions to the problems.This paper uses the research methods of modeling, experiment, analysis and summary and makes a research on issues related to multi-motor systems. First, considering the problem that the brushless DC motor back EMF is different with the common model, a detailed analysis of the motor body is made based on which this paper gives a new model. The new model is simulated in the Simulink toolbox and the current waveforms are consistent with the result of the hardware experiment which verifies the accuracy of the model.After analysising the operation mechanism of multi-motor system, this paper gives the idea that this system can be obtained by several single motor control systems. Further more, giving the second order transfer function of the motor body, the parameter design method of single motor control system is discussed. After that, taking the system of twomotor with rigid connection as an example, this paper compares two kinds of torque balance control structures in which the master-slave control structure has a better adaptability to changes in the parameters of the motor body. In the given master-slave structure based on master motor phase current sampling, the connection between each motor control hardwares is weaken, and the cost of the hardware is reduced at the same time. On the issues of what relative angle the rotors are connected in, this paper analysises the relationship between the relative angle of the rotors and the flutuation of the total electromagnetic torque and reaches the conclusion that the flutuation of the total electromagnetic torque can be reduced by controlling the relative angle of the rotors, which has been verified by simulaton experiments.Next, the typical vibration problems of systems of multi-motor connected in rigid and flexible way are discussed. In the system of gear transmission with gap, the gap will produce vibration and noise in the multi-motor mode. The analysises indicate that without considering the changes of the mechanical parameters, the vibration only exists during starting process, which has no impact on long time running. However, in the simulations and analysises of flat belt driving system, resonance phenomenon is quite obvious. Two conditons are summarized when the resonance happens in multi-motor belt driving system, which are the alternate torque ripple and commutaton frequency close to the natural frequency.Finally, in order to improve the reliablity of multi-motor coordination control system, the paper discusses several fault tolerance strategies including solutions to one motor fault and hall positon sensor fault. Depending on the number of broken hall sensors, two kinds of solutions are designed including estimating the fault signal and using backup sensors. The former solution is used in one broken hall sensor situation, which can determine and eliminate the fault accurately. The latter way is used in situation where more then one sensors are broken with exact phase difference of defferent motor back EMF privided. After correcting the relative angle, the positon sensor of other motors can be used as backup sensor in order to solve the problem of hall sensor fault.