To ensure the safe, reliable and economic operation of high-speed railway, a multi-dimensional control method for the power supply operation energy of high-speed railway cophase power supply system is proposed. The composition structure and power supply process of the power supply system are analyzed, and a power flow controller is used to compensate the power of the system, thus ensuring its stable operation. Combined with indicators such as three-phase imbalance degree and distortion of voltage and current waveforms, the optimal load model of operation energy is constructed to minimize the loss of transmission energy. Through the active and reactive power compensation for current in two power supply arms, the negative-sequence current is eliminated. A control strategy for the railway power conditioner is formulated, and the changes in the step-down transformer are obtained to ensure a stable DC-side voltage. Afterwards, a proportional integral controller is used to obtain the ideal value of current and get the control signal, thus realizing the multi-dimensional control of power supply operation energy. Simulation results show that the proposed multi-dimensional control method can improve the three-phase current balance degree and achieve an effect of voltage sharing stability.

For evaluating the capacity of wind powers, photovoltaics and other power electronic grid-connected units supporting power systems, the core foundation is to correctly understand the unit's functional role (i.e., the unit characteristics) that unit adjusts its own internal voltage amplitude/frequency according to the active/reactive power imbalance. However, the mainstream PLL-based grid-connection structure in power electronic units seriously hinders the understanding of the unit's functional role. In particular, based on a specific PLL-based grid-connection structure, the industry and academia at present form a "grid following" role perception that the internal voltage of unit follows the grid voltage or terminal voltage, and have not recognized the functional role that the unit should take during the system operation. Therefore, through an in-depth understanding of the independent excitation-response mechanism of current control which is hidden under the PLL-based grid-connection structure, i.e., the internal voltage response depends on current excitation alone, the functional role of PLL-based grid-connected units in which the active/reactive power imbalance independently adjusts the internal voltage amplitude/frequency is clarified. Afterwards, a role characterization method for unit is proposed based on the relationship between active/reactive power imbalance excitation and internal voltage amplitude/frequency response, i.e., the amplitude-frequency motion equation. Finally, the inevitability of characterizing the role of PLL-based grid-connected units through the relationship between power excitation and internal voltage response is elaborated on, and the existing limitations in the understanding of the role of PLL-based grid-connected units in industry and academia are pointed out.

A frequency regulation method for a large number of electric vehicles (EVs) in an isolated grid with high permeability renewable energy sources is proposed. First, a disturbance observer is designed for the system's order reduction model to generate additional frequency control signals for clustered EVs. This order reduction model is obtained by combining the changes in load, wind power, photovoltaic system and clustered EVs, thus generating a lumped disturbance estimated by the disturbance observer. Second, a robust model predictive control method based on the Tube model is proposed to provide effective control signals to improve the responsiveness of clustered EVs. The control signals are generated to obtain the minimum frequency deviation error by means of the minimum control actions while considering various physical constraints on the system operation. Third, the influence of time delay on communication link is studied through the stability analysis, and the time delay margin is obtained. Finally, through simulation analysis, the effectiveness of the proposed method is verified, and the advantages of the proposed method over traditional model predictive control, fuzzy proportional integral control and linear quadratic regulator control are also verified.

In the case of high switching frequency, the bridge arm crosstalk caused by the parasitic parameters of SiC MOSFET in the traditional drive are more serious. However, most of the existing crosstalk suppression drive circuits suppress the crosstalk at the expense of increasing the switching loss, prolonging the switching delay and adding the control complexity. Therefore, based on the idea of reducing the impedance of the drive loop in the process of crosstalk generation, a novel active Miller clamp gate drive design is proposed by adding PNP triodes connected in series with diodes and capacitors between the gate and source, and its working principle is analyzed. The parallel capacitance parameters of the improved drive circuit are also calculated and designed. Finally, an experimental platform of double-pulse test for a synchronous Buck converter with DC bus voltage of 300 V was built, and the novel crosstalk suppression drive circuit was compared with the traditional and typical crosstalk suppression circuits in terms of the positive and negative crosstalk voltage spike suppression effects and the turn-on and turn-off speeds. Experimental results show that compared with those of the traditional and typical crosstalk suppression circuits, the positive and negative voltage spikes of the proposed crosstalk suppression drive circuit were reduced by 80% and 40%, respectively, and the switching delay of the device was reduced by 32% in the meantime.

The adjustment of energy structure is an important issue for China's energy development in the 21st century, in which the development of renewable new energy is an important means to optimize the energy structure and reduce environmental pollution. Nowadays, lithium-based batteries are still the main devices that can achieve reversible storage of renewable energy, whose electrochemical performance is often affected under harsh environmental conditions such as different temperatures, mechanical stress and humidity. As a result, problems including the damage of battery components, capacity fading, short-circuit explosion, and thermal runaway will occur. The failure mechanism of lithium-based batteries under harsh environmental conditions is systematically analyzed. Then, the main methods for improving their electrochemical and safety performance are reviewed. Finally, the urgent problems to be solved are summarized. This paper provides ideas for the failure mechanism research on lithium-based batteries as well as the development and applications under harsh environmental conditions.

The cables of switching power supply which are connected in parallel is an important radiated electromag-netic interference(EMI) source for the switching power supply. Aimed at the problem of inaccurate prediction of radiated EMI of cables connected in parallel due to an unclear mutual-coupling effect, a radiated EMI model of cables of switch-ing power supply is proposed by taking into account the mutual-coupling effect between cables. Through the modeling of mutual-impedance which describes the mutual-coupling effect between cables, the radiated EMI input impedance model de-scribing the radiation characteristics of cables of switching power supply is obtained. Then, the radiated EMI model of cables of switching power supply is obtained considering the mutual-coupling effect. Finally, an experimental platform for measuring the radiated EMI was built, and experimental results show that the proposed radiated EMI model which takes the mutual-cou-pling effect into account can predict the radiated EMI of cables of switching power supply more accurately.

With the development of industrial demand, higher requirements are put forward for the reliability of power transistors. The real-time measurement of device junction temperature can ensure the normal operation of the device, so it is very important. Through the research on the on-line measurement method for turn-on delay time, a measurement circuit is designed. By measuring the turn-on delay time at different junction temperatures, the relationship between them is established, the on-line measurement of device junction temperature is realized by measuring the turn-on delay time under actual working conditions, and the device junction temperature is deduced. The results measured using the proposed method are similar to those obtained by an infrared temperature gun. In this way, an on-line measurement method for MOSFET junction temperature based on turn-on delay time is proposed, providing a new idea for the on-line measurement of junction temperature in the future.

The traditional coupling mechanism of multi-directional wireless power transfer (WPT) often adopts an xyz orthogonal circular coil structure, which requires three power supplies and has a charging area limited by the coil structure. To solve this problem, a novel multi-directional WPT coupling mechanism composed of two groups of 8-shaped coils and one group of circular coils is proposed. It presents five circular rings in different directions as a whole and only needs one single power supply. Based on the S-S type transmitter topology, the magnetic field distribution in the coil is changed by controlling the circuit, thus realizing power transfer inside and outside the coil and broadening the charging area. Based on the coil structure, a mathematical model of the proposed coupling mechanism is established, and the calculation formulas for mutual inductance and efficiency at any spatial position are derived. The best working area of the coupling mechanism is determined according to simulation and experimental results.

Virtual DC motor(VDCM) control has been widely applied in suppressing the power fluctuations of DC microgrid and improving the voltage stability of DC bus. Due to the randomness and uncertainty of distributed generations in microgrid, as well as the load switching in microgrid, the DC bus voltage will fluctuate greatly. To improve the regulation capability of bus voltage, a virtual energy storage control strategy based on the coordination of VDCM control and controllable load is proposed by using the regulation capability of controllable load and the virtual motor control of load converter. By adjusting the angular speed of the virtual motor, the power consumption of the controllable load can be adjusted to compensate the fluctuation of bus power and improve the stability of bus voltage. In addition, the relationship between the rotational kinetic energy of VDCM and the charging and discharging energy of the DC capacitor is established. Finally, a simulation model is built on the MATLAB/Simulink platform to verify the effectiveness of the proposed control strategy.

The common-mode(CM) inductor is composed of windings and a magnetic core. Mn-Zn ferrite can be used as the magnetic core of CM inductor, and the frequency-dependent characteristics of its high-frequency parameters make the CM inductor exhibit non-linearity within a range of 150 kHz-30 MHz. It is difficult to accurately predict the impedance characteristics of the CM inductor in a high-frequency band due to the large deviation between the traditional lumped circuit model of CM inductor and the measured impedance characteristics. The effects of material parameters of the magnetic core and the winding scheme on the high-frequency impedance characteristics of CM inductor are analyzed, and the mechanism of magnetic material parameters and the winding structure affecting the distributed capacitance is described from the perspective of the distributed capacitance characteristics of CM inductor. A wide-band impedance simulation modeling method for CM inductor with the consideration of related frequency-dependent parameters of magnetic core was proposed, and its validity was verified by combining with the impedance test result.