Research On The Techniques To Improve The Performance Of Permanent Magnet Synchronous Machines Drive System

The permanent magnet synchronous machine (PMSM) has come to the drive system developers' attention for their merits such as low volume, high power density, high efficiency and simple maintenance. In order to enhance the performance of PMSM drive system, direct torque control (DTC) method with simple structure and fast dynamic response has been applied. Torque adjuster, flux observer and flux weakening control method have been studied deeply in the paper, which set the foundation of improving the performance of PMSM drive system.The theory of PMSM DTC method has been analyzed from the mathematics model of PMSM. With using fixed hysteresis bandwidth to achieve round flux locus, there exist two shortcomings. The first is that round flux locus causes high switching frequency. The second is that fixed hysteresis bandwidth arouses contradiction between switching frequency and torque ripple. In order to overcome the two shortcomings, a method of achieving the torque hysteresis band width by using switching frequency PI adjusting method has been brought forward. The PI adjusting method uses the inverter switching frequency as feedback value and optimal switching frequency as given value. The PI adjusting method not only makes full use of the switching frequency of power device but also solve the contradiction between switching frequency and torque ripple. The effect of zero voltage space vectors has been analyzed. In the low speed region of PMSM drive system, a new voltage space vector selection method has been introduced. The new voltage space vector selection method can be described as: zero voltage space vectors is chose to reduce the torque during the stable state of low speed and non-zero voltage space vectors is chose to reduce the torque during the dynamicstate of low speed. By using the new voltage space vector selection method, the average torque ripple during stable state is reduced and fast torque response is guaranteed during dynamic state.The accurate stator flux linkage observer is one of the most important parts to realize the DTC system. A modified integrator is applied to stator flux observer of PMSM DTC. In order to insure the accuracy of the modified integrator flux observer, the parameter of the controller must be modified with the changing of outside setting. A method is introduced to overcome this shortcoming. The new method uses the modified integrator to obtain the stator flux phase information and uses the state equation of PMSM to acquire the value of stator flux. By doing so, the modified integrator can be used as flux observer with a large-scale of speed.On the base of defining constant item-rotor flux linkage as input variable, a full order state observer is designed to observer PMSM DTC system stator flux. By using full order state flux observer, the performance of PMSM DTC system during low speed range has been improved. The design of full order state flux observer is based on the assumption that the PMSM system is a linear and invariable system. In practical, some parameters of motor will change during the running of the motor. The PMSM system is a variable system but not an invariable system. The error of flux cannot be tended to zero while using full order state flux observer, which is designed on the base of invariable system. In order to observe stator flux accurately even when the parameters of the coefficients are not known, an adaptive stator flux observer is put forward. The results achieved by using adaptive flux observer have been compared with that got from full order state flux observer. The adaptive stator flux observer can observer stator flux more accurately and has more robustness to parameters variation.The full order state observer and adaptive observer of stator flux have observed the flux accurately. But the structures of them are complex and they can't be applied to engineering easily. In order to find a flux observer with simple structure and easyto be realized, a new mixed closed loop stator observer is put forward and the performance has been compared with what got from full order state observer.In order to enhance the performance of PMSM, the flux-weakening control method has been studied. The method of realizing PMSM DTC flux weakening control is to increase negative direct axis current. The realizing method causes two problems. The first is that the parameters of PMSM vary in large-scale. The second is that the efficiency of PMSM reduces rapidly during flux weakening control. Based on the realization of PMSM DTC flux-weakening control system, the parameters variation effect on flux-weakening performance was analyzed. A new fuzzy torque controller is put forward, which make the torque command near to PMSM real ability. In order to improve the torque output ability, a new flux weakening control method has been introduced to insure the maximum output torque ability in each flux-weakening region. A stator flux-linkage compensator is put forward to solve the difference between really flux-linkage and calculate value. The effect of parameters of PMSM on flux-weakening performance was analyzed too, which give a reference to motor design.