Due to the requirements of industrial drive system for high output power, uniform torque distribution, and accurate synchronous movement, the synchronous control methods of multimotor system have drawn increasing attention. This article refers to a large number of research on synchronous control methods and summarizes and compares different control structures and algorithms. Based on the evaluation criteria of tacking error, synchronization error, and adjustment time, the advantages and disadvantages of three representative control algorithms, including proportional integral derivative (PID) control, model predictive control, and sliding mode control, are studied through experiments. Finally, the development trend of multimotor synchronous control is summarized and prospected.

Permanent magnet synchronous machines (PMSMs) work with controllers and controller parameters affect the machine's voltages and currents and thus the diagnosis of stator winding fault. One such parameter is the current controller bandwidth that affects the harmonic content in these signals. In the literature, the 2nd harmonics in both dq-axis currents and voltages have been used for fault detection, and the main advantage is that inter-turn short-circuit (ITSC) winding fault with a few shorted turns, specially one turn, can be detected. One indicator that combines the fault information in voltages and currents is the instantaneous reactive power (IRP). However, it has been shown that IRP does not perform robustly with respect to current controller bandwidth. The main contribution of this work is that it proposes and validates a new mathematical function for ITSCs detection, Rayleigh quotient, which combines the fault information present in voltages and currents to make ITSCs detection robust to current controller bandwidth. The validations from both co-simulation and experiment show that the proposed method is robust to the bandwidth and can detect ITSC faults faster than IRP.

With the wide application of inverter-fed motors (IFMs), it is necessary to monitor the groundwall (GW) insulation status to guarantee the reliable operation of motor drive system. This article first proposes a mathematical model of leakage current in IFM to analyze its time domain characteristics, and then an online GW insulation monitoring method is proposed based on the transient characteristics of leakage current. By using the initial oscillation amplitude, oscillation period, and attenuation time of leakage current, the phase, position, and severity of GW insulation degradation can be identified. The proposed method is validated using an IFM, and the experimental results agree well with theoretical analysis.

Incipient interturn short-circuits (ITSCs) in permanent-magnet synchronous machines (PMSMs) develop to direct short-circuit without proper mitigation. This article proposes an ITSC mitigation control for standard three-phase interior PMSMs (IPMSMs) driven by typical three-phase inverters, named as maximum torque per circulating current (MTPCC), to constrain the circulating current (CC) due to ITSC within acceptable limits so as to delay the insulation degradation between shorted turns, and to maximize output torque to support the postfault performance. In the $dq$ current plane, it is shown that for a specific fault severity and machine speed, the operating points with the same CC form a circle, and for constant torque with ITSC is a hyperbola. ITSC is a fast-developing fault that implies the fault severity continues to increase with time, and the positions of the CC circle and torque hyperbola change with the increasing fault severity in the $dq$ current plane. The MTPCC control updates the mitigation operating point automatically, depending on the positions of the CC circle and torque hyperbola with respect to the circle of the machine's maximum current, to produce the maximum possible torque as the fault severity changes, which shows that it is adaptive to the variation of fault severity. The proposed mitigation control is validated through experiments.

A cooperative predictive position control (CPPC) method for dual-motor system is proposed in this paper to improve the synchronization performance, tracking performance and rapidity. The prediction model for dual-motor system is established to predict future behavior of motor, and the position synchronization error is introduced into cost function to establish algorithm-level connection between motors to improve the synchronization performance. The motor operation process is divided into acceleration stage, constant speed stage, deceleration stage and position approaching stage, and the adaptive adjustment method of weight coefficient is proposed for different motor operation stages to realize multi-variable collaborative optimization control. The experimental results of proposed CPPC method are presented to verify its effectiveness and superiority.

Reliable inter-turn short-circuit (ITSC) fault detection is essential for permanent magnet synchronous generators (PMSGs). The harmonics in machine currents and voltages are affected by the bandwidths of dual-loop controllers, which may lead to the failure of ITSC fault detection based on the current or voltage signature analysis. In this article, a robust method for ITSC fault detection is proposed to deal with this problem. First, the mathematical model of PMSG with ITSC fault is established. Then, the behaviors of the second-order harmonics in dq -axis currents, dq -axis voltages, and dc-link voltage with respect to the bandwidths of current and voltage controllers are investigated. After that, a reliable detection method based on two fault detection indicators and adaptive to the bandwidth changes of dual-loop controllers is proposed. The first indicator is simple and easy when only the bandwidth of the current controller changes, and the other one weights and sums the second harmonics in q -axis current, q -axis voltage, and dc-link voltage to ensure the robustness and improve the accuracy of ITSC detection when both the bandwidths of current and voltage controllers change. Finally, the effectiveness of the proposed method is validated by experiments.