| Due to the energy and environment issues, the conventional automobileindustry is changing to “electric”. Most countries and automobile companieshave invested a lot of money to do the research on electric vehicles. ThePermanent Magnet Synchronous Machine has gradually become the mainstreamof the electric vehicles drive system due to its small size, light weight, highefficiency, high power density, widely range of velocity modulation and theadvantages of simple maintenance. As a result of using permanent magnets in therotor of the Permanent Magnet Synchronous Machine, the excitation magneticfield can’t be adjusted, which is a challenge in the application of vehicle motordrive with the requirements of persistent power and wide range of velocitymodulation, which has drawn a great attention of scholars at home and abroad.Therefore, in order to improve the stability of the torque output in high speedoperation and the dynamic response characteristics when the torque response hasa mutation of the Hybrid Electric Vehicles (HEV), further research work has beendone regarding the Flux Weakening control system of the Permanent MagnetSynchronous Machine in this dissertation.Perfect flux weakening control system consists of the inner loop of currenttracing control and the outer loop of flux weakening current commandadjustment. Permanent magnet synchronous machine is a multivariate, nonlinear,and strong coupling system, which is very sensitive to parameters andinterference, so the traditional linear control method can not accurately describethe adjustment process of current tracking in the inner loop and has a difficulty inensuring the stability of the output torque within the range of high speed operating. This paper has a depth analysis of the Feedback Linearization theory,and conduct a research through applying Lie Derivative to the output variables toget the desired coordinate transformation and the state feedback variables ofnonlinear system, so the Input-Output Linearization control method of thePermanent Magnet Synchronous Machine can be realized and the inner loopcontroller to adjust current based on the Input-Output Feedback Linearizationalgorithm is designed in this thesis. The current controller has the advantages offast dynamic response, small error of steady state tracking, simpleimplementation etc. This control method, however, has inevitable problems withdepending on motor parameters. In order to improve its robustness of motorparameters change, this article analyzes and compares a number of on-line andoff-line calculation methods of typical motor parameters and proposes the inputand output feedback linearization of current control algorithm based on motorvoltage, flux estimation of current fundamental information. This methodreconfigures the system input, feedback variable information and the systemcontrol equations and selects motor Flux linkage as the input control informationof the current regulator. Through the offline calculation of the parameters of themotor flux according to the voltage and current fundamental component, not onlyeffectively reduce the complexity of the parameter estimation, and fully considerthe influence of the permanent magnet synchronous motor harmonic componentof the calculated parameters. The inner loop current controller improved hasimproved the characteristics of anti-disturbance of parameters significantly.The regulation and control mode of outer loop flux weakening currentcommand of the Permanent magnet synchronous machine adopt the Feedback(Closed-loop) regulating or Feedforward (Open-loop) adjustment in most cases.The traditional adjustment method of feedforward open-loop uses the real-timeinformation on the speed, voltage and torque of the current motor, and uses themathematical formula to calculate the best expectations of the dq-axis current,this type of algorithm is characterized by good real-time controlling and dynamicresponse of the system, but the system characteristic of anti-disturbance is poordue to the using of open-loop control. The traditional regulation of closed-loopoften uses the deviation of output voltage command and the allowable limit valueof inverter to adjust the PI regulator and the output of the regulator as the compensation given by the dq-axis current is amended. This characteristic of thealgorithm is that the feedback regulation of the link does not depend on motorparameters, and the robustness of the system is increased, but the drawback isthat the capacity of dynamic response of the system declined. In view of theabove analysis, a control method on feedforward/feedback hybrid flux weakeningcurrent command that contains the compensation link of the flux weakeningvoltage command is proposed in this paper. This method contains a two-dimensional form of the motor flux and torque/current in its feedforward channel,which can check the dq-axis current expectations based on the current demandfor torque and flux quickly, so as to ensure the system requirements of real-timeand dynamic characteristics. The feedback channel uses PI regulator for voltageoutput command and voltage command compensation link to get the current fluxinformation of the current motor, which ensures that the anti-disturbancecharacteristics of the system and stability requirements of high-speed fluxweakening operation.In this dissertation, simulation and experimental studies on PMSM fluxweakening control system have been carried out. Simulation and experimentalresults show that the system has strong robustness against load disturbances, andobtains good steady characteristics and dynamic tracking performances. Thedesigned methods and controllers are simple in structure and practical inengineering, so they are applicable for motor drive system for HEV. |
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