Page 10 - IJOCTA-15-4

M. A. Aman et al. / IJOCTA, Vol.15, No.4, pp.549-577 (2025)
2. Fundamentals of switched reluctance 3. Control strategies of switched
motors reluctance motors

The fundamental electromagnetic equation that The switched reluctance motor is an admirable so-
determines the behavior of the SRM individual lution for enhancing traction motor applications,
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phase is as follows : including e-bikes and EVs, due to its robustness,
reliability, and a wide constant-power operating
dθ dθ range. However, it suffers issues such as acous-
V = iR m + L (θ, i) + KB(θ, i) (1)
dt dt tic noise and torque ripple caused by the dou-
ble salient structure, leading to discontinuous cur-
where V represents the phase voltage, i represents
rent commutation and highly nonlinear magnetic
the phase current, R m represents the phase resis-
characteristics, 20 as illustrated in Figure 6.
tance, L(θ, i) represents the instantaneous induc-
tance, and KB(θ, i) represents the instantaneous Torque ripples can be reduced by employing
back emf. different control techniques or improving motor
Upon excitation of each stator pole, the cor- design. Various control strategies are available
responding adjacent rotor pole tends to align it- to enhance SRM performance by increasing effi-
self in a configuration that minimizes reluctance. ciency, minimizing torque ripple, and providing
The torque generated by the current in a desig- a wide speed range. Figure 7 illustrates existing
nated phase serves to drive the rotor in a direction machine-controlling schemes employed in SRM.
that minimizes reluctance, thereby improving in-
ductance. The torque generated by the motor, 3.1. Torque control strategy
excluding the effects of magnetic saturation, can
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be expressed as follows : Due to advancements in semiconductors, inte-
grated circuits, and power electronics convert-
dL ers, control technologies have become the optimal
2
T em = i /2 (2)
dθ strategy for mitigating torque ripple. These ad-
From Equation (2), it is evident that torque vancements have significantly increased the po-
remains unaffected by the polarity of the stator tential for controlling and enhancing SRM per-
current, as indicated by the square term. Fur- formance. Based on SRM operating principles,
thermore, torque generation is contingent upon a small inductance gradients between the minimum
variation in inductance. Consequently, a positive and maximum inductance zones lead to low phase
torque is generated in the region with rising in- torque in these regions. Consequently, torque
ductance, whereas a negative torque is observed decreases in the phase commutation region, re-
in the area of decreasing inductance. sulting in significant torque ripple. 20 This subsec-
tion provides a review of various control strategies
By using the Maxwell stress tensor, the radial
used to reduce SRM torque ripple, including indi-
force, F r , and tangential force, F t , as shown in
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Figure 5, can be calculated as follows : rect torque control, direct torque control (DTC),
and AI-based torque control.
Z
1 2 2
F r = (B − B )ds (3)
t
r
2µ◦ s 3.1.1. Indirect torque control strategy
1 Z
F t = B r B t ds (4) Indirect torque control is a widely used strategy in
µ◦ s electric drive systems, designed to achieve accu-
In Equation (3), B r , B t , µ 0 , and ds represent rate torque regulation by decoupling the control
the radial flux density, tangential flux density, of flux and torque components. Unlike DTC, indi-
vacuum permeability, and infinite increment of rect torque control utilizes mathematical models
the integral surface area, respectively. The torque and reference frame transformations to determine
is generated by the tangential force exerted on the voltage commands indirectly. This strategy offers
rotor poles. lower torque ripple, better steady-state perfor-
The nonlinear properties of the intrinsic dou- mance, and higher efficiency, making it ideal for
ble salient structure make it difficult to represent high-performance industrial applications. From
flux linkage, torque, and inductance as functions the recent literature, some of the most used indi-
of phase current and rotational angle. Therefore, rect torque control strategies are discussed in the
several numerical and analytical methods have following subsections.
been developed to obtain an exact model. 19 Ta-
ble 1 summarizes various methods; the details are 3.1.1.1. Average torque control
available in the previous review. 19 A new strategy for estimating and controlling the
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