IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 33, NO. 4, JULY/AUGUST 1997 983 High-Performance Control of Synchronous Reluctance Motors Alfredo Vagati, Senior Member, IEEE, Michele Pastorelli, and Giovanni Franceschini Abstract— Based on a synchronous frame, the control problems of synchronous reluctance motors are outlined. In par- ticular, the effect of magnetic saturation, core loss, and angular measurement errors of various types are evidenced. A flux- observer-based control scheme, capable of overcoming most of the above problems, is proposed. The proposed control has been implemented on a prototype drive, adopting a 17-N m 8000-r/min motor. The experimental results show quite a good performance, with particular emphasis on those applications which require a large constant-power speed range. Index Terms— Electrical drives, observer-based control, syn- chronous reluctance motor. I. INTRODUCTION T HE CONTROL of the synchronous reluctance motor exhibits peculiar features in comparison with other fre- quently used ac motors. This is due to its particular flux-current relationship, which allows very fast variations of the main flux [19], [21]. In recent years, several different approaches have been proposed in the literature [1]–[23] concerning control schemes for this motor. In most of these approaches, a frame synchronous to the rotor is chosen as the control frame. An exception is presented in [4] and [6], where an frame is adopted, synchronous to stator flux. This frame gives better performance with reference to full exploitation of the supply voltage. However, the electrical equations become nonlinear, in this case, even when shaft speed is constant. This can represent a drawback for control purposes. On the contrary, a -frame-based control exhibits a linear behavior in this case. For this reason, only the frame will be considered in this paper. In general, control of both torque and total flux linkage is wanted. This is generally done through the control of two intermediate variables. The most straightforward choice in this sense is represented by the control of components of the current vector as shown by block B in Fig. 1. The current vector control can be implemented both on stationary or synchronous frames, leading to different per- formance. A detailed analysis of this point can be found in [21]. In the following, only the results of that analysis will Paper IPCSD 97–16, approved by the Industrial Drives Committee of the IEEE Industry Applications Society for presentation at the 1996 Industry Ap- plications Society Annual Meeting, San Diego, CA, October 6–10. Manuscript released for publication February 10, 1997. A. Vagati and M. Pastorelli are with the Dipartimento di Ingegneria Elettrica Industriale, Politecnico di Torino, I-10129 Torino, Italy. G. Franceschini is with the Dipartimento di Ingegneria dell’Informazione, Universit` a di Parma, I-43100 Parma, Italy. Publisher Item Identifier S 0093-9994(97)04822-6. Fig. 1. -based control scheme. be summarized. Although very simple and intuitive, the - based control presents several drawbacks, which are related in particular to high-speed, flux-weakened conditions. The aim of this paper is to give evidence to the above- mentioned drawbacks and to propose a control solution which gives superior performance with respect to the Fig. 1 scheme. This solution is based on a different choice of the intermediate control variables which also implies simplification of block A in Fig. 1. A completely different approach is also possible, i.e., direct control of and variables (examples can be found in [7], [14], and [23]). II. CURRENT-VECTOR CONTROL The performance of block B is briefly summarized here, with the aim of illustrating its limitations. Reference is given, in this case, to the simplified motor model shown in Fig. 2, where the effect of iron loss is disregarded. The related equations are given by (1) and (2). The meaning of the symbols is straightforward. Reference is made to a frame, as suggested by the subscript. A vector notation is adopted, for conciseness. Differently from (1), (2) is written in a form which implies that magnetic saturation is disregarded. The operator is a diagonal matrix, with different values, of course: (1) (2) In Fig. 3, the corresponding vector block scheme is shown. The block is drawn by a double line, to remind one of the nonlinear relationship existing in practice between flux and current; this is one of the points to be discussed later. In the ideal case of linear magnetic circuit, to feed back the current vector is equivalent to a feedback of the flux vector, 0093–9994/97$10.00  1997 IEEE