An alternative method of estimating the stator flux linkage is presented in [21]。The method is based on the monitoring of the scalar product of estimated stator flux and the measured stator current。 The ac part is extracted, filtered and used for the correction of the estimated stator flux linkage。 Both simple LPF and adaptive filtering are discussed。 Other methods to estimate the stator flux linkage are extended Kalman filtering(EKF) as in [22], which allows also to estimate the mechanical state of the considered SPMSM, and observers based on sliding mode as in [23]。

V。 INITIAL ROTOR POSITION ESTIMATION

As mentioned earlier in section II, the initial rotor position must be known in a DTC drive as it is required for the estimation of the initial stator flux linkage。 If the initial-position information in the controller is too inaccurate, the motor may initially rotate in the wrong direction。

In [19] and [24] a technique is discussed to estimate the initial rotor position of an IPMSM。 The method is based on the relation between the amplitude of a high-frequency (300 Hz) stator current and the angular position of the rotor due to the saliency。 The magnetic-pole orientation is found by the effect of saturation on the stator currents。 A method using rectangular pulsed voltages is described in [25] and is valid for salient PMSMs, i。e。 IPMSMs, only。

For nonsalient PMSMs the sensor less estimation of the initial rotor position is more difficult。 Methods as described in [19] and [24] possibly can be adapted to work with SPMSMs, when saturation effects are considered。

VI。 UTURE RESEARCH

The influence of saturation and parameter-estimation errors on the performance of DTC for PMSMs, especially on model-based estimators and controllers has to be investigated。 A focus on sensorless controllers and estimators is intended。 Sensor less position estimation also has applications other than DTC PMSM。

Digital implementation of DTC PMSM and associated discrete modelling of PMSM, together with new DTC schemes offers many opportunities for more research 。In conjunction with the research on DTC schemes, research into the most appropriate switching strategies has to be undertaken。 Many implementations are reported in literature。 However, apart from [26], the stability of the DTC PMSM drive has not much been studied yet, in spite of the fact that instability can occur due to the maximum in the torque-load angle characteristic。 With m the load angle corresponding with maximum orque, a load angle will result in a lower torque。 If the direct torque controller tries to increase the torque by increasing the load angle, the torque will decrease further thus resulting in instability。 Two methods of avoiding this instability are discussed in [26]。 Both are based on controlling the load angle m 。 However besides this static instability, the overall stability of the drive should be considered as well。 In [27] a mathematical analysis of the stabilization mechanism of DTC for induction machines is given and used to understand the observed behavior of DTC schemes。 As such a thorough investigation concerning the stability of DTC for PMSMs still has to be undertaken。

ACKNOWLEDGEMENT

The research of Thomas Vyncke is funded by a Ph。D。 grant from the Special Research Fund (BOF) of Ghent University。
永磁同步电动机的矢量控制——综述摘要 在高性能伺服应用中，最理想的方法莫过于不使用运动状态传感器的快速精确的转矩控制。结合直接转矩控制器的永磁同步电动机使用计划为实现这一目标提供了许多机会。最近，已经有一些作者提出了可能实现的永磁同步电动机的直接转矩控制。本文给出了一些概述，解释了永磁同步电动机的基本原则。讨论了内嵌式和面贴式的拓扑结构和算法描述。在这些控制计划需要估计定子磁链和初始转子位置。本文也讨论了实现这些估计的技术。本文的主要目标是对已经取得的成果给出一个大纲，同时为进一步研究确定兴趣点。