High-efficiency Operation Control Method Of Asynchronous Motor Based On Magnetic Energy Recovery Switch(MERS)

In recent years,with the development of productivity and the growth of energy consumption,energy issue has been listed as one of the major issues in the world,among various energy sources,the application of electrical energy is very extensive.The motor is an energy conversion device closely related to electrical energy,which can realize the mutual conversion of electrical energy and mechanical energy.Among different types of motors,induction motors have become widely used power machinery because of having the characteristics of simple structure and manufacturing process,affordable price,durability and reliable operation.Although the asynchronous motor has a higher energy conversion efficiency when operating under rated conditions,the efficiency will decrease significantly when operating at light loads,which results in waste of energy.With the increasingly serious energy problem,how to improve the efficiency of asynchronous motors under light load conditions has attracted increasing attention.This paper studies the problem of low efficiency of asynchronous motors under light load,and the main work focuses on the following aspects.First,according to the general electrical model of asynchronous motor,the main factors affecting the efficiency of asynchronous motor are analyzed,and the mathematical model of asynchronous motor considering iron loss is established.Based on the model analysis,we found that the loss of the asynchronous motor under different load conditions is related to the stator terminal voltage.By changing the size of the stator terminal voltage reasonably,the efficiency optimal operation of the asynchronous motor under different load conditions can be achieved.The relationship between the loss of the asynchronous motor and the stator terminal voltage is derived quantitatively,and the optimal value of the stator terminal voltage at the minimum loss under different load conditions of the asynchronous motor is obtained.Taking the stator terminal voltage of the asynchronous motor as the control variable in efficiency optimization is an innovation in this paper.The simulation results show that the mathematical model of the asynchronous motor established in this paper considering the iron loss is more in line with the actual operation of the motor,when the load rate of the asynchronous motor does not exceed 70%,the efficiency of the asynchronous motor is increased by an average of 14% when it is running at the deduced stator terminal voltage when the loss is minimum,and the smaller the loading rate,thegreater the efficiency increase.Secondly,this paper proposes a high efficiency operation control method of the asynchronous motor under light load in which a variable capacitive reactance is connected in series between the power supply and the asynchronous motor system to change the stator terminal voltage.It introduces a new variable capacitive reactance topology structure based on Magnetic Energy Recovery Switch(MERS),analyzes the working principle of MERS as variable capacitive reactance,and based on the phase control method,the relationship between the equivalent capacitive reactance and phase shift angle of MERS in different working modes is qualitatively clarified.The electrical model of the asynchronous motor system with MERS is established.Based on the phasor analysis,the relationship between terminal voltage of asynchronous motor and equivalent capacitive reactance of MERS is revealed,and then the quantitative relationship between terminal voltage of asynchronous motor and the control variable of MERS is obtained.A closed-loop phase-shifting control strategy based on MERS changing the terminal voltage of asynchronous motor is proposed and verified by simulation.The control performance of the system is analyzed,and a reasonable design method of MERS structural parameter is proposed.It is another innovation of this paper to realize the regulation of the stator terminal voltage of the asynchronous motor through the closed-loop phase-shifting control of MERS.Compared with the traditional asynchronous motor efficiency optimization method,the method proposed in this paper only uses a PI controller,and it avoids the problem of difficult choice of hysteresis loop width,and the control is simpler.The simulation results show that the load terminal voltage will change with the change of the MERS phase shift angle,and under different load conditions,by performing closed-loop phase-shifting control on the asynchronous motor system containing MERS,the efficiency of the motor system can be optimized.Finally,an experimental platform is built for software and hardware design and experimental verification.The experimental results show that the phase voltage of MERS can adjust its load terminal voltage.The above simulation and experimental results show that the new topology of MERS-asynchronous motor and its efficiency optimization control method proposed in this paper are correct and effective,which is of great significance to further study the efficiency optimization control strategy of asynchronous motor.