# Performance Analysis of Direct Torque Controllers in Five-Phase Electrical Drives
## 1 Introduction  
It is expected that about 80% of all the produced energy will be used by electric drives by 2030, playing a major role in the automotive field, where they will dominate almost 50% of the market by that year. Furthermore, electric drives are the basis of locomotive traction, electric ship propulsion, electric aircraft with various auxiliary functions (e.g., fuel pumps, starter/generator solutions, etc. ), and renewable energy production. Although conventional three-phase drives represent the principal choice for industrial applications, multiphase ones have recently aroused the interest of practitioner engineers and researchers in the field. Any energy conversion system formed by a multiphase electric machine and converter and regulated by a certain control technique is called a multiphase drive. The first application of such a system, particularly for a five-phase drive, was used in the late 1960s [1], showing the advantages of multiphase systems over conventional three-phase ones. The main interest in the proposal was that the higher number of phases yields a torque ripple three times lower with respect to the equivalent three-phase case due to a better power distribution per phase, this being one of the most reported problems in conventional drives at that time. However, it was not until the end of the 20 th and the beginning of the 21 st centuries that the interest of researchers in multiphase machines was renewed due to two main reasons. First, the development of high-power and high-frequency semiconductors and, consequently, the appearance of pulse width modulation (PWM) methods to control the ON and OFF states of these electronic devices, as well as theenergy conversion process. Second, there is the development of microelectronic technology and the appearance of powerful electronic devices with the ability to implement control algorithms in real time, such as digital signal processors (DSPs) and field-programmable gate arrays (FPGAs). Notwithstanding the above, the crucial reason for the renewed interest in multiphase drives can be found in the intrinsic benefits that they provide versus the conventional three-phase ones. These benefits are based on the extra degrees of freedom introduced by the higher number of phases and are principally the following:  
* The fault-tolerant capability against a fault situation in the machine and/or the power converter, first presented in [2]. An n-phase machine can operate after one or several fault occurrences without any external equipment, as long as the number of healthy phases remains greater than or equal to three (assuming a single isolated neutral connection). Consequently, the system reliability is enhanced at the expense of a reduction in the post-fault electrical torque production. * The capability of increasing the power density in healthy operation by injecting specific current harmonics, exposed in [3]. This is possible in certain multiphase machine configurations based on concentrated windings, where the lower current harmonic components can be used to increase the torque production. These advances and advantages underlie the adoption of multiphase drives in specific industry applications such as variable-speed drives [4; 5]. Electric propulsion of ships, electric vehicle traction (hybrid/electric vehicles and locomotives), wind energy generation, and low-power electric systems for more electric aircrafts are fields where research has been focused in the last 20 years [6; 7]. The interest of multiphase machines in the cited applications, instead of the conventional three-phase counterparts, arises from the high-torque/current production and/or more robust and cheaper fault-tolerant capability that are usually required.