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Two-degree-of-freedom motors are capable of producing linear, rotary, and helical motion, and thus have widespread applications in special industries. In this paper, a new concept-static coupling effect-is studied in the 2-degree-of-freedom direct drive induction motor (2DoFDDIM). The proposed approach is based on the image method and the 3D finite element method. The image method model is established to analyse its reasons and predict the main effects, which are then verified by the proposed 3D finite element static coupling model and experiments. The induced voltages and currents are produced in the static part and induced torque or force is obtained, even though the static part is not energized. It is concluded that the static coupling effect increases with the supply frequency and is influenced by the stator winding configuration. Thus, the existence of the static coupling effect is confirmed, which must be taken into account in future optimization and precise control of the 2DoFDDIM.Index Terms: induction motor, image method, static coupling effect, 3D finite element method, 2-degreeof-freedom.

a b s t r a c tRenewable energy is high on international and national agendas. Currently, grid-connected photovoltaic (PV) systems are a popular technology to convert solar energy into electricity. Existing PV panels have a relatively low and varying output voltage so that the converter installed between the PVs and the grid should be equipped with high step-up and versatile control capabilities. In addition, the output current of PV systems is rich in harmonics which affect the power quality of the grid. In this paper, a new multistage hysteresis control of a step-up DCeDC converter is proposed for integrating PVs into a singlephase power grid. The proposed circuitry and control method is experimentally validated by testing on a 600 W prototype converter. The developed technology has significant economic implications and could be applied to many distributed generation (DG) systems, especially for the developing countries which have a large number of small PVs connected to their single-phase distribution network.

Aiming at obtaining high power density of surface-mounted and interior permanent magnet synchronous motor (SIPMSM), it is important to accurately calculate the temperature field distribution of SIPMSM, and a magnetic-thermal coupling method is proposed. The magnetic-thermal coupling mechanism is analyzed. The thermal network model and finite element model are built by this method, respectively. The effects of power frequency on iron losses and temperature fields are analyzed by the magnetic-thermal coupling finite element model under the condition of rated load, and the relationship between the load and temperature field is researched under the condition of the synchronous speed. In addition, the equivalent thermal network model is used to verify the magnetic-thermal coupling method. Then the temperatures of various nodes are obtained. The results show that there are advantages in both computational efficiency and accuracy for the proposed coupling method, which can be applied to other permanent magnet motors with complex structures. Index Terms-Equivalent thermal network method, magnetic-thermal coupling method, power frequency, iron loss, surface-mounted and interior permanent magnet synchronous motor(SIPMSM), temperature field.

Due to the lack of mature design program for the tubular permanent magnet linear wave generator (TPMLWG) and poor sinusoidal characteristics of the air gap flux density for the traditional surface-mounted TPMLWG, a design method and a new secondary structure of TPMLWG are proposed. An equivalent mathematical model of TPMLWG is established to adopt the transformation relationship between the linear velocity of permanent magnet rotary generator and the operating speed of TPMLWG, to determine the structure parameters of the TPMLWG. The new secondary structure of the TPMLWG contains surface-mounted permanent magnets and the interior permanent magnets, which form a series-parallel hybrid magnetic circuit, and their reasonable structure parameters are designed to get the optimum pole-arc coefficient. The electromagnetic field and temperature field of TPMLWG are analyzed using finite element method. It can be included that the sinusoidal characteristics of air gap flux density of the new secondary structure TPMLWG are improved, the cogging force as well as mechanical vibration is reduced in the process of operation, and the stable temperature rise of generator meets the design requirements when adopting the new secondary structure of the TPMLWG.

As winding short-circuit faults (WSF) in a direct-drive permanent magnet synchronous motor (DDPMSM) degrade its reliability and may cause serious catastrophes, fault detection and diagnosis for the DDPMSM are necessary. The performances analyses of motor under WSF are the basis of fault detection and diagnosis. An efficient and accurate faulty model is a great tool for evaluating motor performances under various WSF. Hence, this paper proposes a novel physical faulty model (PFM) based on the coil sub-element for the DDPMSM with the WSF. Fault position can be examined by differentiating the inductance and the electromotive force of the coil sub-element. This model can evaluate motor performances under various WSF, especially inter-turn short-circuit fault in different positions of the same slot, without changing the internal structure of model. The faults are set by connecting the desired taps as in the practical motor. First, the structure and parameters of the DDPMSM are reported. Second, the inductance calculation matrix, which considers the spatial position of the fault, is constructed. Then, the proposed PFM is established. The motor performances under various WSF are evaluated. Finally, the results of PFM, finite element model and experiment are compared. The results validate the correctness of the proposed PFM. INDEX TERMS Coil sub-element, direct-drive permanent magnet synchronous motor, inductance calculation matrix, physical faulty model, winding short-circuit fault.

Inter‐turn short‐circuit fault (ISF) degrades its reliability and may cause serious catastrophes for direct‐drive permanent magnet synchronous motor (DDPMSM). Fault location technology can reduce maintenance time, increase the mean time between failure (MTBF), and then improve the reliability of DDPMSM. Hence, an intelligent fault locating system for DDPMSM is proposed in this paper. This system proposes a knowledge graph (KG) based diagnostic tool for detection and location of the fault coil. First, the fault model of the DDPMSM with multiple branches parallel winding is established, which is used to analyze the fault characteristics of motor. Second, the BDC and BRC are proposed as the fault indicator. The effectiveness and robustness of fault indicator are analyzed. Then, the KG system are designed and established according to the relationship between fault indicator and location of fault coil. Finally, the system is tested by data under different fault and operation conditions. The test results showed that the proposed fault locating system can detect and locate the fault coil in early stage. The minimum ratio of shorted turns to branch turns that can be detected is 0.52%. The minimum ratio of shorted turns to branch turns that can be located is 6.25%.

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