As an excellent alternative to permanent magnet synchronous motors (PMSMs) or induction motors, switched reluctance motors (SRMs) have the advantages of simple structure, robustness, low cost, long life, etc. At the same time, however, SRMs suffer from the noise and torque ripple, which restrict the application of SRMs. A main reason is that SRMs are conventionally driven by a rectangular winding current, which is generated by the asymmetric H-bridge (AHB) power converter[1]. With this type of driving method, there is only one or two phases windings that are energized at the same time, as a result, the winding current commutation is not smooth enough, which contributes to the noise and torque ripple.

To reduce the noise and torque ripple in the SRM, the space vector pulse width modulation (SVPWM) driving method [2] is considered as an effective solution. An SVPWM driving method is an algorithm for motor control. Based on the real-time position of the rotor and the reference value of the excitation voltage or current vector, the SVPWM is expected to generate sinusoidal currents by means of multiple switching. This type of winding current has a smooth commutation, it is a convenient way to implement a digital control while reducing harmonics.

There have been some researchers who are interested in applying SVPWM to the SRM. By using the asymmetric H-bridge power converter, the authors of [3]and [4] propose an improved voltage vector driving method for SRM, they remove the flux-linkage loop control and added some voltage vectors, then the switching loss and torque are reduced accordingly. The paper [5] describes a space voltage vector driving method, which transforms the basic voltage vectors into equivalent space voltage vectors, to facilitate the implementation of direct force control, here the torque ripple is reduced drastically. The authors of [6] use alpha-beta transformation to estimate the synchronous rotating angle of the space vector and the rotor position of the SRM, then a sensorless SVPWM control are developed.

Instead of the asymmetric H-bridge, the full-bridge power converter is applied to SVPWM for SRM by the authors in [7] and [8], they propose a four-leg converter for a 3-phase SRM, this type of converter is used to control the winding current with both AC and DC components, by using the proposed SVPWM method, the power loss of the SRM is reduced compared to the traditional converter. A direct torque control (DTC) method using an optimized voltage vector for the SRM is proposed in [9]: to reduce the torque ripple, the basic voltage vector in the DTC algorithm is analyzed and the voltage vector is optimized to further reduce the torque ripple. Here, the SRM is driven as a synchronous reluctance motor, and similar equations can be derived. By optimizing the voltage vector, the peak-to-peak value of the torque is reduced also by 10%, which proves that the smooth current waveform helps to reduce the torque ripple.

The literature description above indicates that the methods to implement the SVPWM to the SRM can be classified into two groups: one is using the AHB power converter, the other is using the full-bridge power converter. For the first group, in the asymmetric H-bridge, IGBT with an external diode is required to keep the polarity of the winding currents the same. This type of circuit can only be ordered by customer design, which makes it expensive. For the second group, the full-bridge circuit has a low cost, because this type of circuit is mass produced for different type of motors [10], such as brushless DC motors, induction motors, and permanent magnet AC motors. As a result, full-bridge power converter is a better choice for SRM driving topology.

To apply SVPWM to SRM by full-bridge power converter, however, the existing methods change the internal winding structure, then an SRM is operated as a synchronous reluctance motor. Additionally, the modification of the SRM winding structure leads to an extra cost, and because of the double salient structure, the SRM is unable to generate the low noise and torque ripple as the synchronous reluctance motor.

This paper proposes a three-phase SRM with a ring winding structure, which uses the full-bridge power converter as the driving topology, without changing the internal winding structure. The proposed topology drives the SRM by matching its operating principle, instead of driving as a synchronous reluctance motor. Based on this type of driving topology, the SVPWM method is applied to driving the SRM. Compared to the conventional driving method by AHB power converter, the SVPWM method can generate sinusoidal winding currents and smoother current commutation, as a result, the torque ripple of the SRM is improved.