# Seven-Phase PMSM Drives Operation Post Two Types of Faults
## 1 Introduction  
Multi-phase machines are witnessing an increasing concern in many industrial applications, especially for medium- and high-power applications such as in the marine, aerospace, and railway industries. This interest is related to the fact that the multi-phase machines offer some advantages over the three-phase drives. Firstly, it possible to obtain a higher power rating motor without the need to increase the phase current or the voltage (same IGBT rating). Secondly, it helps to suppress the harmonics in the torque [1, 2, 3]. Finally, it offers a high degree of reliability as it is inherently fault-tolerant. The research on multi-phase motor drives has been devoted in three directions: the first one dedicated on the study of the fault-tolerant design of the multi-phase drive [4, 5, 6, 7, 8]; the second one concentrated on the modelling of these drives [9, 10], and the last one was studying the control of the multi-phase drive [11, 12, 13]. Among the above areas of research of the multi-phase motor drives, the fault-tolerant feature has received most of the interest in the research. The fault-tolerant control techniques (FTC) can be classified into active and passive. The active technique uses the data obtained by the fault-detection and diagnosis unit to reconfigure the controller post the failure in one of the system components such as (sensors, actuators) [14, 15]. The passive FTC depends only on the redundancies of the system and uses only one controller which is robust against the predefined set of failures [16, 17]. As a result, the passive FTC is considered much simpler but on the other hand, its robustness is much lower than the active FTC. The accomplishment of post-fault drive operation requires the suitable choice of references to be applied. The optimal values of reference currents are determined based upon the particular drive arrangement and the type of winding connection. Most of the introduced reference currents calculation procedures were applied offline utilizing the mathematical model of the machine and the required torque production. These techniques can be classified as follows: maximum torque, minimum losses, and minimum torque ripple [18, 19, 20]. However, to control healthy currents of the multi-phase drive post the fault according to the above techniques, many controller types were used. One of these controllers was the hysteresis current controller [21; 22; 23]. Although this technique is very easy to implement, it has a variable switching frequency that makes it undesirable in the motor drives. Another control technique was the using Vector Control technique based on using a modified SVPWM technique post the fault [24; 25].The Vector Control technique is based on using new transformation matrices can be used to control the new multi-phase currents post the fault [26; 27; 28; 29; 30]. In addition to hysteresis and vector control, other control techniques were also used to control the multi-phase motor currents post the fault such as: Direct-Torque Control (DTC) [31], Sliding Mode Control [32], Model predictive control [33]. Another type of fault that has been research in the last couple of years in the multi-phase motor drive was the fault in the speed sensor (i.e., sensorless operation). Many techniques have been suggested to obtain the speed and the position of the multi-phase motor post the fault in the speed sensor including model-based technique, DTC, and voltage and current excitation techniques [34; 35; 36; 37; 38]. In the last two years, some papers have proposed a fault-tolerant five-phase motor drive that able to work post the failure in one phase and the failure in the speed sensor [39; 40]. This is the first paper that is introducing a fault-tolerant seven-phase drive that has the ability to run post the failures in speed sensor and phase 'A' happened at the same time.