Research On Maximum Torque Per Ampere Control Of Interior PMSM

Due to increasingly severe resource shortages and environmental problems,energy conservation is the theme of our era. As motor consumes a large amout ofenergy, scholars all over the world have focused on improving the efficiency ofmotor, inorder to reduce energy consumption and carbon emissions. Compared withother motors, Interior Permanent Magnet Synchronous Motor (IPMSM) has becomemore and more popular in general industrial fields due to its higher power density,higher efficiency and higher torque density. IPMSM can produce reluctance torquebecause of the structure asymmetric of rotor magnetic circuit. If the reluctancetorque is fully utilized, it can improve the overload output capacity of the motor andincrease the efficency of the system. Therefore, maximum torque per ampere(MTPA) control strategy of interior permanent magnet synchronous motor wasresearched in this paper.MTPA control strategy based on mathematical caculations using the machinemodel was studied. According to the definition of MTPA operations, the partialderivative of torque to stator current vector angle should be zero.The solution of theMTPA equation is the expression of optimal stator current vector angle. In adition,the stator current refrence is the output of speed loop controller. Thus the d-axis andq-axis currents which are supposed to contribute the maximum torque per amperewas caculated, as long as the machine parameters were provided. However, theparameters of an IPMSM vary significantly for a variety of reasons, such astemperature, magnetic sturation and so on, instead of remaining the nominal values.Therefore a further study on the quantitative analysis of the inaccuracy was done.An on-line MTPA control strategy based on signal injection was studied. Viainjecting a small high frequency current signal into the stator current angle, theresponse in the mechanical power reflected the variation of torque. To extract thepower signal which was used to lock the optium current angle through a PIcontroller, digital signal processing was adopt. As many factors would work on themechanical power, a special controller for high frequency current was designed.Mathematical derivation evaluated that the proposed method ignored the variationof the parameters caused by saturation. Thus the MTPA control strategy hadadvantages of robust and high dynamic performance.On the basis of theory analysis, simulations with matlab/Simulink wasprovided to verify the accuracy of the proposed method. Furthermore, MTPAcontrol method was realized on DSP control system and experiments were carriedout through the experimental platform of2.2kW interior permanent magnet synchronous motor drive system. Experiments verified the effectiveness of theproposed online maximum torque per ampere control method again.