###### Abstract
In [17; 18; 19], by limiting the number of the phases simultaneously conducted to no greater than two, the phase currents of a three- or four-phase SRM are reconstructed by using two crossing winding sensors and by solving two linear equations related to the non-zero phase currents and the sensed currents. In [17], each sensor detects the sum of all the phase currents, while in [18; 19] each sensor measures the sum of two-phase currents. By using the two-sensor-based schemes, both the magnetization, freewheeling, and demagnetization phase currents can be reconstructed without pulse injection, voltage penalty, and modification to the AHBC. However, the limitation would most likely compromise the available maximum motor torque, especially at high speeds and especially for multiphase SRMs. In [20], a two-sensor-based scheme for four-phase SRMs is put forward by splitting the upper and lower dc buses of the AHBC into two buses. All the currents through the commutating switches of phases B and D flow through an upper bus and the bus current are detected by a sensor. All the currents through the commutating switches of phases A and C flow through a lower bus and the bus current are detected by another sensor. This scheme can reconstruct the magnetization and freewheeling phase currents without pulse injection and voltage penalty. In [21], the lower dc bus of the AHBC is split into two buses whose currents are detected by two sensors, respectively. One bus current is equal to the sum of the currents through the lower switches, and the other bus current is equal to the sum of the currents through the lower diodes. This scheme can enhance the fault detection ability, but the issue of voltage penalty still exists. In [22], the positions of the power switches in the AHBC are rearranged and two sensors are used to detect the currents through the middle points of the upper and lower dc buses, respectively. This method owns superior thermal stress distribution but still requires pulse injection. All the current detection methods mentioned above with reduced sensors do not consider the multiphase excitation which is common in multiphase SRM drives to suppress torque ripple and increase motor torque, and thus are not very suitable for multiphase SRM drives. To detect the phase currents under multiphase excitation with reduced sensors, several methods are proposed in recent years. In [19], two multiplexed sensors are used to reconstruct the phase currents under the three-phase excitation in five- and six-phase SRM drives which are made equivalent to two independent drives with a single sensor. Phase reconstruction of each independent drive can be achieved using the method in [12; 14]. In [23], \(n/2\) and \((m+1)/2\) crossing-winding sensors are used to detect the phase currents in an even-numbered multiphase SRM (EMSRM) with \(n\) phases and in an odd-numbered multiphase SRM (OMSRM) with \(m\) phases, respectively. Intact phase currents can be reconstructed without pulse injection, voltage penalty, converter modification, additional switching losses, and additional current ripples. However, the methods are not quite suitable for high-speed operation. The reason for this will be detailed in the following sections. The rest of the paper is organized as follows: Section 2 reviews the conventional current detection scheme where each phase current is independently detected by a hall effect sensor. The proposed current detection schemes for EMSRMs and OMSRMs are described in detail in Section 3. In Section 4, the simulation results by using the proposed methods and the methods in [23] are presented and analyzed. In Section 5, the experiments with the proposed method for OMSRMs are conducted. Finally, conclusions are drawn in Section 6.