Department of Electrical Engineering Southern Taiwan University Robot and Servo Drive Lab. 2016/6/13 Design of a Synchronous Reluctance Motor Drive T. J. E. Miller, Senior Member, ZEEE, Alan Hutton, Calum Cossar, and David A. Staton IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 21, NO. 4, JULYIAUGUST 1991 學生 : Guan Ting Lin 指導老師 : Ming Shyan Wang

Department of Electrical Engineering Southern Taiwan University Outline Abstract Introduction Basic theory Evolution of the design Electronic control Conclusion References 2016/6/13 Robot and Servo Drive Lab. 2

Department of Electrical Engineering Southern Taiwan University 2016/6/13 Robot and Servo Drive Lab. 3 Abstract segmental-rotor synchronous reluctance motor is used in a variable-speed drive with current-regulated PWM control. The low-speed torque capability is compared with those of an induction motor, a switched reluctance motor, and a brushless dc PM motor of identical size and copper weight.

Department of Electrical Engineering Southern Taiwan University 2016/6/13 Robot and Servo Drive Lab. 4 Introduction The rotor is potentially less expensive than the PM rotor. Because it requires no cage winding, it is lighter and possibly cheaper than an induction-motor rotor. The torque per ampere is independent of rotor temperature, unlike that of the PM or induction motors. The stator and the inverter power circuit are identical to those of the induction motor or PM synchronous motor drives. The control is simpler than that of the field-oriented induction motor drive, although shaft position feedback is necessary. The main features of the synchronous reluctance motor are as follows:

Department of Electrical Engineering Southern Taiwan University 2016/6/13 Robot and Servo Drive Lab. 5 Basic theory No starting cage is necessary. The rotor can therefore be designed purely for synchronous performance. Electronic control makes the motor autosynchronous. Therefore, the torque angle can be set to maximize torque per ampere at all loads and speeds without concern for pullout. There is no need for amortisseur currents to prevent rotor oscillations. This makes it possible to design for the highest possible ratio of the synchronous reactances x, and x d without concern for stability. The inverter-fed SYNCHREL motor is freed from the old constraints of the line-start version as follows:

Department of Electrical Engineering Southern Taiwan University Basic theory Because the SYNCHREL motor is a classical synchronous machine, its electromagnetic torque is given by (l), where Id and I, are components of the rms phase current I resolved along the d and q axes of the phasor diagram; they correspond to the space-vector components of stator mmf along the d and q axes of the rotor: 2016/6/13 Robot and Servo Drive Lab. 6

Department of Electrical Engineering Southern Taiwan University The torque per ampere is maximized if the phase current is oriented at 45° to the q axis so that Id and I, are equal in magnitude. Since L d < L q, I d must be negative, and therefore, the current leads the q axis in the phasor diagram (Fig. 2). 2016/6/13 Robot and Servo Drive Lab. 7 Basic theory

Department of Electrical Engineering Southern Taiwan University For a peak airgap flux density of 0.8 T and a saturation density of around 1.7 T, t must be limited to the order of 0.5. Now, the synchronous reactance X, is inversely proportional to the airgap length g, the linear magnetic theory developed it can be shown that X d is inversely proportional to the sum of g and the combined thickness of the flux barriers, which is very roughly equal to tR, where R is the rotor radius. Therefore, the saliency is given approximately by 2016/6/13 Robot and Servo Drive Lab. 8 Basic theory

Department of Electrical Engineering Southern Taiwan University Evolution of the design 2016/6/13 Robot and Servo Drive Lab. 9 Three rotors have been built, and the cross sections of two of these are shown in Fig. 4. The pole pieces are held by two thin ribs that attach to the q axis webs in the same way as in the interior magnet motor described by Jahns.

Department of Electrical Engineering Southern Taiwan University Fig. 6(a) and (b) show typical d- and q-axis finite-element flux plots. The calculation of magnetization curves is a straightforward exercise of the finite-element method once the magnetization characteristics of the core steel are accurately known. 2016/6/13 Robot and Servo Drive Lab. 10 Evolution of the design

Department of Electrical Engineering Southern Taiwan University Electronic control 2016/6/13 Robot and Servo Drive Lab. 11 The configuration of the electronic control for two-phase motor is shown in Fig. 9. A 360-pulse magnetoresistive encoder mounted on the motor shaft generates an indexed pulse count representing the rotor position. This count is used to address two EPROM's: one for the d axis and one for the q axis

Department of Electrical Engineering Southern Taiwan University Conclusion These results have been achieved with a single flux-barrier design capable of accommodating permanent magnets. The inductance ratio is much smaller than theoretically possible in a pure SYNCHREL motor, and much better results would be expected with an axially laminated construction or equivalent. The comparison of motor types underlines the superiority of the PM brushless dc motor in raw torque production at low speed and its ability to tolerate a large airgap length. The comparison also highlights the weakness of the induction motor in this small size range. 2016/6/13 Robot and Servo Drive Lab. 12