A Hybrid AC/DC microgrid (MG) can integrate distributed generation sources and distributed loads on the AC and DC side of the MG by eliminating many unnecessary power conversion devices, which is more flexible and efficient. However, to achieve reliable and economic operation of a hybrid AC/DC MG is challenging due to its complex structure. In this paper, a novel distributed event-triggered hierarchical control strategy is proposed to improve the economic operation of a hybrid AC/DC MG. For the primary control, distributed local controls of AC DGs, DC DGs, and interlinking converters (ICs) are realized by adopting the droop control method. For the secondary control, the distributed economic dispatch, distributed average bus voltage discovery, and distributed proportional power-sharing algorithms are first proposed; then, control objectives of voltage and frequency restoration and economic operation of the hybrid AC/DC MG are realized based upon the developed algorithms. Furthermore, the distributed secondary control is built upon an event-triggered mechanism developed in this paper, which can reduce the communication burden. The simulation results demonstrate the effectiveness of the proposed control strategy.

Demagnetization fault in a permanent magnet synchronous motor (PMSM) degrades its performance and may cause serious catastrophes. Fault localization technique can improve the reliability and safety of PMSM and provide important information for developing operation and maintenance strategies. Thus, a fault localization method is so important. Mainstream is a common method that uses search coil installed on every stator tooth to diagnose fault location. Due to the use of a large number of search coils, the method is limited in terms of invasiveness, implementation cost, and installation. Moreover, the method can only diagnose the fault location in PMSM with one demagnetized permanent magnet (PM). This article proposes a novel method which can detect the specific location of demagnetized PMs in PMSM with any types of demagnetization faults. The method only needs three additional toroidal yoke coils wound around the stator yoke. Toroidal yoke coils are used to measure the back electromotive force (EMF). The demagnetization fault localization signals (DFLSs) are produced by basic calculation of the output signals of three search coils. The DFLSs are partitioned according to the electrical period. The location of demagnetization fault can be diagnosed through analyzing each electric period waveform of DFLSs. First, the arrangement of toroidal-yoke-type search coil and the construction method of DFLSs are introduced. Second, a partitioned analytical model of DFLSs is developed. Third, waveforms in one electric period of DFLSs under preset fault types are investigated. Finally, the method for diagnosing demagnetization fault in PMSM is proposed. The simulation and experimental results justify the precision of the proposed search coil which shows the maximum error of back EMF to be 4.1%. It also shows the ability of the method to locate demagnetized PMs when the demagnetization severity (the ratio of the change in coercive force of PM to the normal coercive force) is 10%. This study provides a new method for diagnosing demagnetization fault, as well as provides a significant reference for fault post-processing and fault-tolerant control of PMSM.

The voltage-source grid-supporting inverters (GSIs) are important to establish and support the frequency and voltage of a microgrid (MG) in both islanded and grid-connected modes. Traditionally, a cascaded control strategy that includes an external droop-based control loop and an inner proportional-integral (PI)-based voltage and current control loop is adopted to control a GSI, which barely shows inertia and limited control performance. In this article, a novel cascaded control strategy is proposed for a GSI. In the external loop, a VSG-based control strategy is adopted to increase the frequency stability of the MG, and a novel synchronization control method that does not use a complex PLL unit is proposed to satisfy the plug-and-play requirements of a GSI. In the inner voltage and current control loop, this article proposes an SMC-based vector control strategy which uses the fixed switching frequency and inherits the robustness and fast response speed of the SMC control. Both simulation and experiments demonstrate the effectiveness and improved performance of the proposed control strategy.

To decrease the cost, enhance the torque performance, and improve the system reliability, this paper puts forward a novel position sensorless torque control strategy for switched reluctance machines (SRMs) with fewer current sensors. In the proposed drive, a developed direct torque control (DTC) strategy is proposed for the torque ripple mitigation, where a hybrid chopping mode is employed and the torque is online compensated according to the torque error. A developed current sensing scheme with fewer current sensors is presented. The phase current in a whole period can be easily detected for both the torque control and sensorless control. The position sensor is removed from the proposed drive. The real-time rotor position of each phase can be obtained by implementing a flux linkage-current based method. According to the current and position, the instantaneous phase torque and torque sharing function (TSF) can be determined for the DTC. Therefore, system reliability can be significantly improved due to the simplified sensor part. With the proposed scheme, a compact, high-reliable, and high-performance SRM drive can be achieved. A 3-phase 12/8 SRM prototype is employed for the experiment to verify the feasibility of the proposed system.

The inverter-interfaced renewable energy is increasing in future new power systems, both the system rotary inertia and frequency regulation capacity of traditional units are decreasing and becoming increasingly insufficient. It is urgent to explore various types of frequency regulation resources, especially for inverter-interfaced units that show fast response speed. The heterogeneous frequency regulation resources generally have different system models, capacities, and response speeds, which challenges the automatic generation control (AGC). In this paper, to make the heterogeneous frequency regulation resources provide improved frequency regulation performance, a novel distributed cooperative AGC method is proposed. Firstly, a distributed consensus-based area control error (ACE) discovery algorithm is proposed. Then, each frequency regulation unit can participate in the frequency regulation with an individual PI controller based on the discovered ACE information. Finally, by controlling the low-speed AGC units to generate more power, it can release the power capacity of the high-speed AGC units to prepare for the following round of AGC services. Furthermore, the communication delays are also considered for the proposed distributed AGC algorithm design. The improved performance of the proposed AGC method is verified based on the simulation study of a two-area power system with five different kinds of frequency regulation units.

The original fuzzy-based Taguchi method is restricted with the number of objective functions. Aiming to solve this problem, this paper describes an improved fuzzy-based Taguchi method (IFBTM) coupled with finite-element analysis (FEA) for the multi-objective optimization of direct-drive permanent magnet synchronous motors (DDPMSMs). To reduce the number of dimensions in the fuzzy rule base, the IFBTM uses a factor stratification method to establish multilayer fuzzy rule base. The fuzzy inference system with multilayer fuzzy rule base is introduced to translate the multiple optimization objectives to a single objective. After optimal selection analysis, the best combination of motor structure factors is obtained with small FEA computation. Finally, the performances of DDPMSM are analyzed and compared with those of IFBTM. The results certify the superiority and validity of IFBTM.