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PROGRAM ROZWOJOWY

^1 POLITECHNIKI WARSZAWSKIEJ

Only for the linear case (no magnetic saturation) the instantaneous torque T_e(t) is:

T_e(t)

Y 1 Ej )ij

" 7¹2 a> '

(1.21)

As usually heavy magnetic saturation is present, E, {co,d,\) as of (1.19) is a pseudo emf as it includes also a part related to the magnetic energy storage. Conseąuently the torąue is to be calculated only from the coenergy formula.

1.3. CONTROL

Summarizing, the instantaneous torque T_ej per phase may be obtained through the known coenergy, W’f(#), formula:

rswTOTT	; W' = fl
l ^d0 Jii=cons.a,	K o

(1.22)

Equation (1.22) demonstrates the necessity of knowing, through calculations or test, the family of curves The total instantaneous torque is (m - number of phases):

T„=£t_5j. (1.23)

Only in the absence of saturation the instantaneous torque is:

(1.24)

_T ylfdWjW

• Be

SRM drives are controlled by synchronizing the energization of the motor phases with the rotor position. Fig. 1.8 illustrates the basie strategy.

As equation (1.12) suggests, positive (or motoring) torque is produced when the motor inductance is rising as the shaft angle is inereasing, dL/d&>0. Thus, the desired operation is to have current in the SRM winding during this period of time. Similarly, a negative (or braking) torque is produced by supplying the SRM winding with current while dL/d0<O. The exact choice of the tum-on and turn-off angles and the magnitude of the phase current, determine the ultimate performance of the SRM. The design of commutation angles, sometimes called firing angles, usually involves the resolution of two conflicting concerns - maximizing the torque output of the motor or maximizing the efficiency of the motor. In generał, efficiency is optimized by minimizing the dwell angle (the dwell angle is the angle traversed while the

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