Recent interest in the synchronous reluctance motor has increased in the context of possible applications in field oriented AC drives. The absence of rotor slip losses and the apparent simplicity of the control suggest the possibility of performance and cost advantages over the induction motor. With field oriented control, and continuous shaft position feedback, the synchronous reluctance motor does not need a starting cage and can be designed for maximum saliency ratio (L/sub d//L/sub q/ ratio). This ratio is by far the most important parameter for achieving high power factor, torque/ampere, and constant-power speed range. This paper analyses the various known forms of the synchronous reluctance motor, to determine the maximum achievable saliency ratio and identify the parameters on which it depends. The main originality is the analysis of the effect of the number of flux guides/barriers. It is shown that a minimum number is required for the performance to surpass that of the induction motor. The analysis also reveals the optimum ratio of flux guide/flux barrier thicknesses and the effects of the tooth/slot geometry and stator saturation. Test results are included from three motors ranging from 50 W at 2000 r.p.m. to 7.5 kW at 1500 r.p.m., covering both axially laminated and transversely laminated types.<
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Maximising the saliency ratio of the synchronous reluctance motor

A segmental-rotor synchronous reluctance motor is used in a variable-speed drive with current-regulated pulse-width-modulated (PWM) control. The low-speed torque capability is compared with that of an induction motor, a switched reluctance motor, and a brushless DC PM motor of identical size and copper weight. A particular point of interest is the comparison of motors of different types, all with essentially the same frame size and tested under identical conditions. The results suggest that many of the desirable properties of the switched reluctance motor can be realized with the synchronous reluctance motor but with using standard AC motor and control components. The torque capability is lower, but so is the noise level. >

Design of a synchronous reluctance motor drive

This paper presents a refined design of a high-speed synchronous reluctance machine with minimized eddy-current losses in the rotor. Design criteria are high power capability, ability of the rotor to withstand high speeds, ability to operate in vacuum, negligible zero-torque spinning losses, high reliability, high efficiency, and low manufacturing cost. The rotor of the synchronous reluctance machine consists of bonded sections of ferromagnetic and nonmagnetic steels. A finite element code, incorporating rotor rotation, has been developed in MATLAB that calculates steady-state motionally-induced eddy currents (and losses) in the rotor. A stator iron and stator winding have been designed to minimize rotor losses, and two such prototype machines have been fabricated. Experimental results show an efficiency of 91% at a 10 kW, 10000 rpm operating point, and negligible rotor heating.

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High-speed synchronous reluctance machine with minimized rotor losses

The paper studies the application of conventional two-axis machine theory to the performance analysis of modern permanent-magnet synchronous motors. A representative motor with radially-oriented samarium-cobalt magnets in a rotor of interior type is considered as an example. Full performance data are measured for the full 360° range of load angles at various supply frequencies. Performance computations using constant motor parameters show significant discrepancies when compared with measurements, particularly at low supply frequency. Detailed determinations of parameter values reveal an important variation of quadrature-axis reactance as a function of quadrature-axis current, owing to magnetic saturation on this axis. When this variation is included within the analysis, together with temperature variation of stator resistance, excellent correlation is shown in all respects.

Parameters and performance of a high-field permanent-magnet synchronous motor for variable-frequency operation

A method for the analysis of a cageless reluctance-synchronous machine with nonsinusoidal space distributions is described. First, general equations for inductances are derived from the winding and permeance distributions in the air gap, which are assumed to have space harmonics. It is shown how the amplitude of ascending order decreases more rapidly for the inductance harmonic than for the harmonic of the permanence or the magnetomotive force. Second, the fundamental components of the inductances that vary with the angular position of the rotor are found to be influenced by the space harmonics. Thus, the variations of the self-inductance and mutual inductance are assumed to be purely sinusoidal with no harmonics. On the basis of this mathematical model, simple equations are derived for the general direct and quadrature-axis inductances. Finally, these equations are used in the single-phase standstill method for measuring the parameters of a 1.3 kW test machine, and it is shown that the measured values agree fairly well with the equations. >

Inductances of cageless reluctance-synchronous machines having nonsinusoidal space distributions

The principles and design method of a new type of reluctance motor are described. The rotor of the new machine has one system of flux barriers per pole pair and is nonsegmented. The machine combines the advantage of simplicity of manufacture with a performance which is satisfactory by any present standard.

J.S.C. Htsui

Papers

New type of reluctance motor