In high-performance servo applications a rapid and accurate torque control is desired, preferably without the use of a motion-state sensor。 The use of permanent magnet synchronous motors (PMSMs) combined with the direct torque control (DTC)scheme offers many opportunities to achieve this goal。 Recently several authors have proposed possible implementations of direct torque control for permanent magnet synchronous motors。 In this paper an overview is given。 The basic principles of DTC for PMSMs are explained。 Topologies and algorithms described in the literature for interior PMSMs as well as surface mounted PMSMs are discussed。 Estimations of stator flux linkage and initial rotor position are needed in these control schemes。 Techniques to achieve these estimations are discussed in this paper as well。 The main goal of the paper is to give an outline of what is already achieved and to determine points of interest for further research。83563

I。 INTRODUCTION

Permanent magnet synchronous motor (PMSM) drives are replacing classic dc and induction machine (IM) drives in a variety of industrial applications, such as industrial robots and machine tools。 Advantages of PMSMs include low inertia, high efficiency, high power density and reliability。 Because of these advantages, PMSMSs are indeed excellent for use in high-performance servo drives where a fast and accurate torque response is required。 In PMSM drives, the electromagnetic torque is usually controlled indirectly via the stator current components in a reference frame fixed to the rotor flux field。 This field orientation creates the need for a position sensor, which reduces there liability and increases the cost of the drive。

For induction motors, direct torque control (DTC) was proposed as an alternative control scheme in [1] and became very popular in the past two decades。 DTC for induction machines is inherently motion-state sensor less as the calculations are executed in a stationary reference frame。 Moreover DTC uses no current controller and no motor parameters other than the stator resistance, which yields a faster torque response and a lower parameter dependence than with field oriented control。论文网

The idea of combining the advantages of DTC and PMSMs into a highly dynamic drive appeared in the literature in the late 1990’s [2], [3]。 In the past decade several authors have proposed ways to adapt DTC to work with PMSMs。

In this paper an overview of the research in this field is given。 The possible

implementations are given in section III, for interior PMSMs (IPMSMs) as well as surface mounted PMSMs (SPMSMs)。Problems of implementation are discussed in sections IV and V。 Points of interest for further research are summarized in section VI。

II。 PRINCIPLES OF DTC FOR PMSMS

Neglecting cogging torque, the steady-state electromagnetic torque T of a PMSM can be written as where denotes the load angle。 The load angle is defined as the angle between the stator flux linkage vector and permanent magnet flux linkage vector , as shown in Fig。1。The number of pole pairs is denoted by。 Equation (1) is applicable for PMSMs with saliency, i。e。 IPMSMs, where the direct axis stator inductance is smaller than the quadrature axis stator inductance。For PMSMs without saliency, i。e。 SPMSMs, is equal to  and (1) becomes

From (1) and (2) it can be seen that for a constant level of the stator flux linkage, the torque can be changed by altering the load angle 。 A three-phase two-level voltage source inverter (VSI) can generate eight voltage vectors as shown in Fig。1, six active vectorsand two zero vectors。The stator flux vector can be calculated as where denotes the stator resistance, and denote the stator voltage and current space vector respectively。 It follows that, when the stator resistance is neglected, the variation of the stator flux linkage vector is given as