Many domain adaptation models have been explored for fault transfer diagnosis. However, most of them only consider global domain adaptation of two domains while neglecting the fine-grained class-wise distribution alignment between the source and target domains. Thus, these models cannot satisfy the diagnostic requirement in some cases. A new ensemble weighting subdomain adaptation network (EWSAN) diagnostic model is established in this paper to improve the degree of domain confusion. In EWSAN, an enhanced joint distribution alignment (EJDA) mechanism is proposed. A multiscale top classifier with multiple diverse branches is designed based on ensemble learning to better achieve EJDA. Ensemble voting with the multiscale top classifier can obtain more reliable pseudo labels in the EJDA mechanism. An ensemble weighting maximum mean discrepancy (EWMMD) with the class weight is constructed to enhance the fine-grained domain confusion. Moreover, the closed and partial transfer diagnostic tasks are made available. Furthermore, the information entropy is introduced to increase the confidence coefficient of the pseudo label. The proposed EWSAN diagnostic model is evaluated via multiple closed, and partial fault transfer diagnosis experiments cross machines. The experimental results validate its effectiveness and superiority.

Phase-locked loop (PLL) is essential for the grid-connected inverter to ensure grid synchronization. Since the PLL introduces an negative-resistive admittance to be in parallel with the original inverter output admittance, it poses an instability risk for the grid-connected inverter under weak grid. The system stability can be evaluated by the return ratio matrix, which is the ratio of the inverter output admittance to the grid admittance. Due to the non-singular and non-diagonal properties of this matrix, its eigenvalues are irrational functions, leading to inconvenience of stability analysis and PLL parameters design. To address this issue, this paper reconstructs the return ratio matrix to make it singular. Thus, the eigenvalues become simpler, including a zero eigenvalue and a non-zero eigenvalue. Based on the non-zero eigenvalue, the relation between the gain margin and the PLL parameters is established, and an optimizing design method of the PLL parameters is proposed to achieve system stability and satisfactory PLL dynamic response. Finally, experimental results from a 10-kVA prototype of three-phase grid-connected inverter are provided to verify the validity of the proposed design method.

<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Transformerless series-connected current source converters (SC-CSCs) were recently proposed. Compared with existing ones, they eliminate the transformer, giving significant reductions in cost and size. However,</i> they need the use of series-connected switches in medium/high-voltage applications, and as a result, very complicated voltage balancing schemes are required. To address this challenge, a modified transformerless SC-CSC is proposed. In the modified one, the series-connected switches are replaced with a cascaded half-bridge converter, while the left remains the same as existing ones. By doing so, the need for series-connected switches is eliminated, while the advantages of original converters are well retained. In addition, the cascaded half-bridge converter has inherent voltage balancing, reduced switching frequencies, and a unique zero-load feature. The operation principle of the modified converter is presented. The performance is verified by both simulations and lab-scaled experiments.

Overvoltage protection technology is critical to the safe and stable operation of power electronics equipment and power systems. In this study, based on the characteristics of lightning traveling waves, a novel lightning overvoltage protection scheme was proposed using magnetic rings (MRs) for transmission line systems (TLSs). First, the dynamic inductance of the lightning protection scheme using MRs was theoretically derived by combining the ampere loop law and the infinitesimal method. The finite element method (FEM) was then used to verify the theoretical derivation of dynamic inductance (TDDI) of the lightning protection scheme. Furthermore, the TDDI was integrated into the electromagnetic transient program, and the electromagnetic transient model (ETM) of the TLS with the lightning protection scheme was established. Subsequently, the effects of MR characteristics under the influence of various factors on the protection performance of the lightning protection scheme were investigated. Finally, the MR string in the lightning overvoltage protection scheme with optimal physical structure was used for field application. The results confirmed the feasibility of the lightning overvoltage protection scheme and ETM accuracy.

In this paper, the concept of fusion topology is proposed to tackle the development trend and control issue of hybrid parallel multi-converter applications and to achieve better performance in transient and steady-state operations. Compared to previously fixed frequency compensation strategies, data-driven finite-state machine (FSM) control can determine which voltage source converter (VSC) dominates the operation or whether two VSCs operate simultaneously rather than giving the specific target operation to each VSC alone. The results are verified by a real-time digital simulator (RTDS) with the hardware-in-the-loop (HIL) experiments. The 20kVA RTDS experimental results show that the transient time is shorter by 53.8%− 85.7%, and power loss is smaller by 28.6%− 78.3%, respectively, compared with the previous methods.

This paper proposes a wireless open-winding motor (WOWM) system, where noncontact operation can be achieved with the magnetic coupler. Thus, the flexibility and reliability of the WOWM system can be improved. Two isolated DC voltage ports for the open-winding motor can be obtained with only one DC voltage source, which facilitates the application of the system. The zero-sequence current in the motor winding can be suppressed and the DC link voltage utilization rate can be maximized owing to the isolated DC link structure. Besides, the operation characteristics of the WOWM system are analyzed in detail. The decoupled dual-receivers are designed, which ensures that the ratio of DC link voltages is load-independent. Moreover, the influences of misalignment on the WOWM system, including the overmodulation and increased phase current ripple are presented. The DC link voltage regulation (DVR) and active power allocation (APA) strategy are further proposed. The DC link voltage reference is identified based on the operating state of the motor for high performance operation. The allocation coefficient, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> is adjusted according to the extent of misalignment, which improves the anti-misalignment capability. The feasibility of the WOWM system and the effectiveness of the DVR and APA strategy are verified by experiments.

Speed-sensorless control (SSC) techniques enhance the overall reliability while reducing the cost, and thus become attractive in induction motors (IMs). Simplicity and flexibility are the main features that make phase-locked loop (PLL)- and frequency-locked loop (FLL)-based speed estimation schemes stand out among considerable estimation methods. However, many PLL and FLL schemes exhibit a poor estimation accuracy in the cases of acceleration and deceleration (AaD). Accordingly, an adaptive second-order generalized integrator-FLL (SOGI-FLL)-based scheme is introduced. While, the issue of the estimated speed feedback (ESF) in the adaptive SOGI-FLL scheme remains an obstacle. With the above, a speed estimation scheme that combines the super-twisting algorithm with an FLL (STA-FLL) is proposed for the SSC of IM drives in this paper. In the proposed STA-FLL scheme, an STA-based quadrature signal generator (STA-QSG) is properly designed, in which the ESF is cancelled to further ensure speed estimation. Moreover, a closed-loop flux observer is adopted in the implementation to enhance the proposed STA-FLL scheme in terms of disturbance mitigation. Experimental tests are performed to validate the proposed STA-FLL scheme.

In this paper, an optimized space vector modulation (SVM) method is proposed for the isolated three-phase matrix-type AC/DC converter, where the four-quadrant operation ability of the bidirectional power switch can be fully used. The primary-side transformer current can be eliminated naturally during zero current vectors without extra switching actions. Therefore, the conduction loss of matrix converter (MC) is reduced and the efficiency can be increased. Moreover, the proposed method can avoid the shoot-through operation in MC, and the common-mode voltage can be mitigated effectively. As the zero current vector is kept with the proposed modulation strategy, the current harmonics will not be increased. Thirdly, both the DC-link inductor current and DC-bias current of high-frequency transformer (HFT) are measured through the secondary-side current of HFT. Therefore, the DC-bias current and the saturation of HFT are avoided by closed-loop control with the proposed modulation strategy. The experiments have been carried on a 1-kW laboratory prototype to verify the validity of the proposed modulation scheme.

Induction motor powertrains are emerging as a cost-effective option for high-power electric vehicles (EVs). A differential four-wheel drive (D4WD) EV based on two open end winding induction motor (OEWIM) propulsion is presented in this paper. Each OEWIM is driven by two 2-level voltage source inverters (VSI) with two isolated battery packs as the source. The proposed drive control algorithm integrates the uniform state-of-charge (SoC) distribution and fault-tolerant operation. A two-stage look-up table (LUT) based direct torque control (DTC) scheme is proposed to balance the SoC of batteries by selecting the suitable redundant VSI voltage vectors. The proposed LUT-DTC scheme is less sensitive to variations in motor parameters and provides excellent steady-state and transient performance. The results show the superiority of the proposed controller in terms of battery SoC balancing. The performance of the EV drive with the proposed LUT-DTC is validated by both simulation and laboratory experiments for the FTP75 and HFET driving cycles under different operating modes under normal and fault conditions. The dual motor driven D4WD with the proposed LUT-DTC is found to achieve 89.2% efficiency.

Two adaptive notch filters (ANFs) based on the double integrators (ANF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</sub> ) and the unbalanced synchronous reference frame control (ANF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</sub> ) were applied to the bus voltage control of a single-phase grid-connected inverter. This paper also proposes a non-invasive prognostic function for the degradation of the bus capacitance using the difference between the bus ripple amplitudes estimated from the ANFs and the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> -axes currents with the nominal bus capacitance. The ANF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</sub> , ANF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</sub> , and conventional notch filters were experimentally validated with a 220-V, 50-Hz, 2.5-kW two-stage inverter. The bus voltage control schemes using the three notch filters tuned at a fast bandwidth of 30 Hz exhibited identical performance with the grid current harmonics complied with the IEEE 1547 standard. Moreover, the ANF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</sub> and ANF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</sub> control schemes maintain low current distortion with a variable grid frequency of 45-55 Hz. The capacitance degradation prognostic function accurately responded to a 27% reduction in the bus capacitance. Considering the control performance and computational effort, the ANF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</sub> is suitable for bus voltage control of the single-phase inverter.