The flywheel energy storage system (FESS) is a short-time high-power energy storage technology widely used in various fields. To improve speed and reduce air friction loss, the rotor of the high-speed permanent magnet synchronous machine (HSPMSM) used in FESS operates at a magnetic suspension state in vacuum. It is very difficult for the rotor to dissipate heat, which may even lead to PM demagnetization. In this paper, a 200 kW 20000 r/min HSPMSM is designed for FESS of an uninterruptible power supply (UPS), and a composite PM rotor with multilayer sleeves is proposed. Distinct from the previously proposed retaining sleeve design of the HSPMSM rotor, a silicon steel sleeve is added in the composite PM rotor, which can provide a bypass for alternating flux density harmonic components in the rotor and prevent them from entering the alloy sleeve and PM. Moreover, a post-processing method of finite-element analysis (FEA) results is proposed to obtain the alternating harmonic components in the rotor and further analyze the suppression effect of the silicon steel sleeve on them. As the silicon steel sleeve is introduced, the amplitudes of alternating harmonic components are effectively suppressed, which can mitigate the eddy current loss and heat generation of the HSPMSM rotor from the source.

The flywheel energy storage system (FESS) has high-power density and fast response speed, hence it is widely used as a pulse power supply. For the high-speed permanent magnet synchronous machine (HSPMSM) used in high-power FESS, there are two technical problems that need to be solved, including huge centrifugal forces of the rotor at a high-speed operation region and large phase currents at a low-speed operation region. In this paper, a 5 MW high-speed interior PMSM (HSIPMSM) is designed for FESS. The design goal of this electric machine is to reduce the maximum phase current at the lowest speed as much as possible while ensuring the rotor mechanical strength. Based on the response surface (RS) model and non-dominated sorting genetic algorithm II (NSGA-II), the multiobjective design of the HSIPMSM is accomplished using 29 groups of multiphysical field finite element analysis (FEA) sampling experiments. The computational cost is effectively reduced. In addition, the constant power optimal trajectory and control switching speed of the HSIPMSM are analyzed and discussed, and the reason that the constant power flux weakening region of the designed HSIPMSM is not wide and the maximum torque per ampere (MTPA) mode is adopted at a low-speed operation region is further illustrated.

With the development of electric vehicles and More-Electric/All-Electric aircraft, high reliability is required in motor servo systems. The redundancy technique is one of the most effective methods to improve the reliability of motor servo systems. In this paper, the structure of dual-redundancy permanent magnet synchronous motor (DRPMSM) with weak thermal coupling and no electromagnetic coupling is analyzed and the mathematical model of this motor is established. However, there is little research on how to suppress the torque ripple caused by short-circuited coils in the DRPMSM. The main contribution of this paper is to present the advantages of DRPMSM and to find a way to suppress the torque ripple caused by the short circuit fault in DRPMSM. In order to improve operation quality and enhance the reliability of DRPMSM after a short circuit occurs, the torque ripple caused by the coils inter-turn short circuit fault in DRPMSM is analyzed in detail. Then, a control method for suppressing the electromagnetic torque ripple of a short-circuited coil is proposed for the first time by using an improved adaptive proportional resonant (PR) controller and a proportional integral (PI) controller in parallel. PR control is a method of controlling alternating components without steady-state error, and it can be used to suppress torque ripple. DRPMSM adopts speed and current double closed-loop control strategies. An improved adaptive PR controller and a PI controller are employed in parallel for the speed loop, while traditional PI control is adopted in current loop. From the simulation and experimental results, the torque ripple is reduced from 45.4 to 5.6% when the torque ripple suppression strategy proposed in this paper is adopted, in the case that the speed is 600 r/min. The torque ripple suppression strategy based on the PR controller can quickly and effectively suppress the torque ripple caused by the short-circuited coils, which makes the motor speed more stable.

In the aerospace and military fields, with high reliability requirements, the dual-redundancy permanent magnet synchronous motor (DRPMSM) with weak thermal coupling and no electromagnetic coupling is needed. A common fault in the DRPMSM is the inter-turn short circuit fault (ISCF). However, research on how to diagnose ISCF and the set of faulty windings in the DRPMSM is lacking. In this paper, the structure of the DRPMSM is analyzed and mathematical models of the motor under normal and faulty conditions are established. Then an on-line ISCF detection scheme, which depends on the running modes of the DRPMSM and the average values for the difference of the d-axis voltages between two sets of windings in the latest 20 sampling periods, is proposed. The main contributions of this paper are to analyze the calculation for the inductance of each part of the stator windings and propose the on-line diagnosis method of the ISCF under various operating conditions. The simulation and experimental results show that the proposed method can quickly and effectively diagnose ISCF and determine the set of faulty windings of the DRPMSM.

The Dual-Redundancy Permanent Magnet Synchronous Motor (DRPMSM) with weak thermal coupling and no electromagnetic coupling among phase windings has two sets of three-phase symmetrical windings. Under normal conditions, two sets of windings can operate simultaneously, and once one set has an inter-turn short circuit fault (ISCF), the other set will operate alone, so a DRPMSM can be applied in fields with high reliability requirements. According to the equivalent circuit principle, a simplified model of a DRPMSM when ISCF occurs is established in this paper, and mathematical equations for the equivalent resistance, inductance and induction electromotive force (EMF) are derived. Based on the simplified circuit principle and instantaneous power theory, combined with the analysis of the fundamental wave in the two sets, an online diagnosis method of the ISCF for DRPMSM is proposed based on the reactive power difference and the feasibility of the method is verified by experiments.

Interturn short circuits are a common fault of permanent magnet synchronous motors (PMSMs). This paper proposes a new method to detect the interturn short-circuit fault (ISCF) of a five-phase PMSM. The method first takes the command voltage and measured current of each phase winding as the original signal and then obtains the delay signal orthogonal to the original signal via Hilbert transform. Then, the generalized instantaneous reactive power of each phase can be calculated from the orthogonal voltage and current signals of each phase. Finally, the influence of the ISCF on the generalized instantaneous reactive power of each phase is analyzed under different working conditions. By comparing the difference in the generalized instantaneous reactive power of each phase, it can be determined which phase winding has the ISCF. The proposed method is verified by simulated and experimental results.