Research On Low-frequency-ratio Sensorless Control Strategy For Ipmsm Drives

Recent developments in the design of power electronic circuits and permanent-magnet materials have made it possible to replace IMs with more efficient permanent magnet synchronous motors(PMSM).PMSMs provide high power density,excellent efficiency,strong reliability and good environmental adaptability,which are getting more and more used in human production and life.With rapidly improvements in power electronic technology and microelectronics technology,the switching frequency of the inverter has been increased in low and medium power applications.However,in some high power occasions,the frequency of the inverter still can not be improved because of the limitation of the switching loss.On the other hand,the employment of high speed permanent magnet synchronous motors has made the research on the low frequency ratio control of PMSMs popular.The dynamic performance of the motor is restricted due to the influence of the current loop coupling effect under the circumstance of low frequency ratio.At the same time,time delay and discretization methods should be considered into the design of the rotor position observer which can affect the accuracy of the estimation.In this paper,the sensorless control methods of PMSM under low frequency ratio are investigated based on current regulator and rotor position observer.First of all,the mathematical model of the interior permanent magnet synchronous motor in continuous domain is established.Then the complex vector model of the IPMSM is expressed based on the concept of extended electromotive force.By solving the differential equation the complex vector model,the discretization model of the IPMSM is deduced in the rotating coordinate.And the following researches are all on the basis of the above derivation.The coupling effect of the vector control method is analyzed and the solving strategies are proposed in this paper.Theoretical analysis on the traditional PI controller,the feed-forward decoupling controller,the feedback decoupling controller and the complex vector current controller are carried out by the pole-zero map and the Bode diagram.Both simulation and experimental results have proved that the complex vector current controller is superior to other controller s on the decoupling performance.In order to improve the precision of the speed and the rotor position estimation,this paper studies the observation method under low frequency ratio.Also the observer is directly designed in the discrete domain instead of designed in continuous domain firstly and discretized afterwards.The two methods are compared with experiments.In addition,this article adopts the double sampling double update method and digital system delay compensation strategies in order to reduce the negative effect on the control system resulting from the low frequency ratio.Finally,through the simulations on Matlab/Simulink and experiments based on the ARM platform,the sensorless operation of IPMSM under low frequency ratio is implemented.Comparing the decoupling performance of the conventional PI controller,feed-forward decoupling controller,feedback decoupling controller and complex vector current controller,the performance of the complex vector current controller is verified to be optimal.Also the experimental results show that the position and speed estimation accuracy of the discrete domain designed observer is obviously improved after the implementation of the double sampling double update and time delay compensation strategy.