In order to cope with power quality problems and low utilization rate of regenerative braking energy(RBE) in double-modes traction system, a power transfer device integrating supercapacitor(PTDS) is proposed in this paper. A hierarchical control strategy containing an energy management layer and a converter control layer is presented, which can realize the rapid and accurate control performance. Based on the different operation states of the AC and DC traction systems, the energy management layer is divided into three working modes and ten working scenarios. The converter control layer realizes the reactive power compensation by controlling the AC-DC converter. Furthermore, by controlling the back-to-back converter in PTDS, the energy interconnection between the AC and the DC traction system is achieved. Moreover, the supercapacitor(SC), connecting at the DC bus, can store the RBE and release it to effectuate the peak clipping and valley filling. Finally, the feasibility of improving the power quality and utilizing the RBE of the proposed PTDS and its control strategy is verified.

In this work, a 13-level inverter is proposed based on the switched-capacitor(SC) technique. The proposed topology(PT) consists of thirteen power switches, four capacitors, and two diodes and achieves a voltage gain of six. The circuit design, operation, and power losses analysis of the PT are described in detail. The most significant features of the PT include: capacitors’ voltages are inherently self-balanced, high voltage gain, low component count per level, and ability to supply an inductive load. A simple logic-based multicarrier pulse width modulation technique has been utilized to control the switching operation. More importantly, the overall merit of the PT in terms of the cost function is established using a comparative study with the prior art topologies. Finally, simulation and experimental results have been presented for a rated output of 1.4 kW to validate the performance of the PT at steady-state and dynamic conditions.

High-altitude electromagnetic pulse(HEMP) can produce Electromagnetic interference(EMI) on the generator system. Without a precise machine model, over-voltage on the stator winding of generator cannot be accurately evaluated, and this is a new challenge for the design of nuclear power plant generator system. Therefore, the paper establishes the motor model by considering multi-conductor transmission line, and employs this model to design a set of precautions. At first, the expression of HEMP and coupling channel of HEMP are performed to analyze magnitude and waveform of over-voltage caused by HEMP. Then, a novel stator winding model is developed which bases on the analysis for multi-conductor transmission line. This model considers the influence of E1 on frequency-dependent parameters, and the voltage of winding per turn under HEMP can be calculated fast and accurately via it. The proposed approach can be validated through a three-dimensional electromagnetic simulation software based on the finite integration method. Finally, couple of precautions are derived based on the existing lightning protection measures and the above analysis.

This paper presents a new five-level converter with capacitor voltage control capability. The topology is relatively simple and the required blocking voltages of all switching devices are the same without the need of device series-connection, so the five-level converter is suitable for medium-voltage power conversion systems. Meanwhile, the five-level converter only needs to control the flying capacitor(FC) voltages and the capacitor voltage control can be achieved with a proposed simple control method based on the level-shifted pulse width modulation(LS-PWM), which reduces the control complexity. Simulation and experimental results demonstrate the voltage control ability and the performance of the converter under various operating conditions including various modulation indexes, power factors, steady-state and dynamic response, which verifies the feasibility of the topology and the effectiveness of the control method.

This paper proposes a novel seven-level inverter for renewable energy applications with voltage boosting capability. The proposed inverter is based on a full-bridge(FB) inverter, whose two half-bridge legs are cascaded with a three-level T-type (3LTT) inverter, respectively. It is supplied by a single dc source in series with an input inductor. The inductor is charged by the dc source internally through the FB inverter without using extra switches. It then transfers energy to capacitors that directly supply the 3LTT inverters. Auxiliary circuits for balancing the voltages of capacitors are not required, since each capacitor can be charged by the inductive dc-link with the same step-up average voltage. Carrier-based phase-shift pulse-width modulation (PWM) scheme is applied to the FB inverter to produce an inductive-charge duty ratio and generate suitable voltage gain. The operating principles of the proposed inverter are described. Key inverter parameters including voltage gain and voltage stresses on devices are analyzed and compared with those of the prior-art solutions. Simulations and experimental results verify the feasibility of the proposed single-stage dc-to-ac power conversion for producing a boosted seven-level output voltage with relatively high efficiency.

In power electronic traction transformer, the failure of the single-phase PWM rectifier will lead to performance degradation of the system. Thus, a feasible data-driven method is proposed to realize online fault diagnosis of single-phase PWM rectifier in this paper. The principle of the data-driven method is to construct a signal predictor based on historic database utilizing the nonlinear autoregressive exogenous(NARX) model with a randomized learning algorithm named extreme learning machine (ELM). Besides, the ensemble method is employed to improve the prediction accuracy and robustness against load fluctuation. In online diagnosis, the predictor and sensor operate simultaneously and their residual is generated. Afterward, the fault detection is conducted by comparing the residual with fault threshold and the fault classification is completed based on system fault symptoms and fault residuals analysis. Several hardware-in-loop tests are implemented to verify the applicability of the proposed diagnosis method. Test results show that this data-driven method is effective to perform the online fault diagnosis with fast fault detection speed and high classification accuracy, and robust against load fluctuation.

Bipolar medium-voltage dc(MVDC) distribution systems are of great interests nowadays due to its high availability and reliability. A bipolar MVDC grid can be established by the installation of power-balancers or directly by converters with inherent bipolar operation capability to avoid the extra cost and volume. Therefore, this paper proposes a modular multilevel dc-dc converter(MMDC) with inherent bipolar operation capability for the interconnection of bipolar MVDC grids and LVDC girds. Considering that the MMDC is normally only capable of operating with monopole MVDC distribution systems due to the symmetric structure and operation scheme, a center-tapped high-frequency interface transformer is employed on the MV side of the MMDC. Based on the concept of the flux dc-bias cancellation, a dedicated operation method is proposed, whereby the power flows of the two MVDC poles can be regulated independently with a simple control scheme, and no penalty of increased current rating is imposed on the semiconductor devices or the interface transformer compared to the conventional MMDC with monopole operation. Additionally, the MMDC can realize single-pole operation in case one pole is faulty and deliver at least 50% of the rated power capacity, which significantly enhance the reliability and availability of the power delivery. The validity of the proposed bipolar operation scheme of the MMDC has been verified by both simulations and experiments with a down-scale prototype.

The measurement of the internal temperature rise of high-frequency magnetic components is of key significance in the design, application, and safety regulation of magnetic components. However, the eddy current loss at the metal end of the thermocouple will bring a large additional temperature rise, which distorts the temperature rise measurement in the part with high frequency magnetic field for the high-frequency magnetic element. Firstly, this paper tests the additional temperature rise of thermocouples with different sizes at different frequencies. Through the analysis of the results, the influencing factors and degree of temperature rise error are clarified, which is helpful to select the appropriate thermocouple according to the working frequency in the actual measurement and evaluate and correct errors. In order to further deduct the unpredictable influence of high-frequency magnetic field environment on thermocouples, this paper proposes to correct the additional temperature rise of thermocouples caused by eddy current loss by using the cooling process curve of magnetic components after power failure and combined with the thermal circuit model of the cooling process. At the same time, the neural network method is proposed to deduce the actual temperature rise of the measured point deducting the additional temperature rise of the thermocouple before the data prediction of the cooling characteristic curve, so as to realize the accurate measurement of the hot spot temperature rise in the magnetic element under the high-frequency magnetic field.

A universal control strategy is proposed in this paper to improve the performances of electric springs(ESs) based on current-source inverters(CSIs). The proposed control can realize the functions of voltage regulation, harmonic suppression, and power factor correction(PFC) at the same time. The single-phase topology of ES with CSI is described firstly, and its operating principles are analyzed by means of phasor diagram and current decomposition. Then the proposed control strategy is analyzed in detail. In the proposed control, a cascade generalized integrator (CGI) is used to construct the quadrature signal generator(QSG), in order to enhance the capability of harmonic compensation and PFC of ES. In addition, a dq0 transform module is used to decouple the active power and reactive power of ES. Finally, the effectiveness and feasibility of the proposed control is verified by simulation and experimental results in the case of normal voltage, over-voltage, and under-voltage, respectively.

Aiming at the poor performance of permanent magnet synchronous motor(PMSM) under low carrier wave ratio synchronous modulation caused by low switching frequency of power devices, a pulse width modulation(PWM) analysis method based on the mathematical model of PMSM is proposed. A comparative study of selective harmonic elimination pulse width modulation(SHEPWM) and central 60 degree modulation is carried out, the current harmonic and torque ripple indexes of the two modulation methods under different carrier wave ratios, as well as the advantages, disadvantages and application scope of the two modulation methods are analyzed. Finally, through simulation and experiment, the application of SHEPWM and central 60 degree modulation is realized on the metro traction system, and the correctness of the theoretical analysis is verified.