The magnetic leakage from an indoor air-core reactor leads to problems such as serious nearby electromagnetic pollution and heat generation by metal equipment. To solve these problems, based on the ANSYS finite element simulation platform, the indoor air-core reactor and its surrounding ancillary facilities and building structure of a 500 kV substation are modeled in three dimensions, and the building roof is equipped with a shielding plate. Through the optimization analysis of shielding materials, thickness and gap width, a scheme is formulated to improve the electromagnetic environment surrounding the indoor reactor. Simulation results show that the magnetic induction intensity of the steel structure can be effectively reduced by adding a shielding plate which is overlapped by 3 mm thick aluminum plates above the steel beam. The temperature change of the reactor during its operation meets the insulation heat resistance requirement for the air-core reactor. The edge section temperature of the shielding device is higher, with a peak of 53.26 °C. The average temperature of surrounding buildings and facilities increases by about 5-10 °C, which meets the requirements of safe operation.

The state of health (SOH) estimation for sodium-ion batteries is crucial for their safe and efficient applications, which is also a key to large-scale energy storage implementations. However, sodium-ion batteries exhibit usage-induced degradation with unclear mechanisms and are sensitive to operating conditions and environmental factors, posing a challenge to the accurate SOH estimation. In this paper, a data-driven SOH estimation method for sodium-ion batteries is proposed. The charging data is correlated with capacity degradation, and variance filtering, grey relational analysis and recursive feature elimination are integrated for feature selection. In addition, four machine learning methods including multiple linear regression, support vector machine, Gaussian process regression and error back propagation neural network are applied to formulate the corresponding estimation methods. Test results reveal that the root mean square errors for the four methods are all less than 1.6%, with Gaussian process regression showing an error rate below 0.8%, indicating a precise SOH estimation for sodium-ion batteries.

A Super-Boost converter can greatly reduce the mass and volume of power supply and improve the corresponding power density by replacing the traditional charging and discharging module, so it has a broad application prospect in space power system. However, due to the existence of multiple power components and the reverse flow characteristics of inductance current, its power supply mode and output ripple voltage are more complex than those of the traditional Boost converter. To provide a theoretical guidance for the analysis and design of the Super-Boost converter, its power supply mode and output ripple voltage are studied. It is found that there exists continuous conduction mode, pseudo continuous conduction mode and pseudo discontinuous conduction mode in both inductor L₁ and L2. The analytical mathematical models of critical inductance and output ripple voltage in each operation mode are established, the relationship between peak current and inductance is discussed, and the minimum capacitance and minimum inductance that meet the design requirements are obtained. On this basis, a design method for the converter parameters is given, and experimental results verify the theoretical analysis.

Aimed at the particularity of an isolated DC/DC converter when it is applied in a space radiation environment, the isolated magnetic feedback circuit is usually used to improve the feedback accuracy and stability. The working principles for several commonly used amplitude modulation magnetic feedback circuits are introduced, and a forward-flyback amplitude modulation bidirectional magnetic feedback circuit is introduced and optimized to solve the problem of the need for an additional secondary power supply voltage. Under the premise of realizing the same function, a two-winding transformer is used to replace the three-winding transformer, which effectively reduces the volume of the magnetic core and simplifies the circuit structure. The working principle for the circuit and the design method for a pulse sampling circuit and a magnetic feedback transformer are analyzed in detail. In addition, based on the magnetic feedback circuit, a DC/DC converter prototype with 100 W output was built. Simulation and experimental results show the effectiveness of the proposed isolated magnetic feedback circuit, providing a theoretical guidance for engineering design.

In this paper, the modulation scheme for a dual active bridge (DAB) bidirectional DC/DC converter is studied. The main advantage of the DAB converter is that it has characteristics such as symmetrical structure, bidirectional power flow capability, wide soft switching range and flexible control capability. The simplest way to control this topology is to control the direction and magnitude of power transmission by adjusting the phase shift angle between the primary and secondary bridges. However, when the input or output voltage of the converter varies widely, a large amount of reactive power will be generated under light load conditions. Meanwhile, the zero voltage switching (ZVS) operation of part of switches cannot be maintained, which directly leads to a low conversion efficiency. Therefore, to improve the efficiency of the DAB converter, a hybrid phase shift modulation (PSM) scheme is proposed, which can reduce the inductor root-mean-square (RMS) current and extend the soft switching range on the basis of keeping the control simple, thereby improving the performance of the converter. First, by making the controllable variables in the extended phase shift(EPS), dual phase shift (DPS) and triple phase shift (TPS) modulation schemes equal, four different PSM schemes are obtained. Then, the steady-state characteristics of these modulation schemes are compared and analyzed, including their transmission power capacity, inductor current level and soft switching performance. On this basis, a hybrid PSM scheme is formulated. Finally, an experimental platform was built to verify the effectiveness and correctness of the proposed modulation scheme.

A three-phase Vienna rectifier is taken as the research object in this paper. In view of the difficulty in selecting the weight factor when the finite control set model predictive control realizes the neutral-point potential balance control, as well as the problem of large current ripple on grid-side caused by the action of one single vector during the sampling period, an unweighted factor model predictive control strategy based on double vectors is proposed. First, a single-objective cost function based on power prediction is constructed, and the efficiency of single optimization is improved by sector division and unweighted factor. According to the fluctuation of neutral-point potential on DC side, the redundant small vector is selected to realize the unweighted factor neutral-point potential balance control. Then, based on the obtained optimal vector, the double-vector fixed switching frequency control is realized by combining with the zero vector. Finally, the proposed control strategy is verified on a hardware-in-the-loop platform based on RT-LAB from the aspects of steady state, transient state and neutral-point potential fluctuation, and results effectively prove its correctness and effectiveness.

The conventional Buck-type power factor correction (PFC) converter has a disadvantage of high harmonic current, which limits its applications. A Buck-type single-switch integrated PFC converter is proposed and analyzed. This converter is composed of a Buck-type PFC converter and a Buck-Boost PFC converter, and they are integrated by only one active switch, thereby simplifying the control. Under the constant on time (COT) control, the dead zone of input current in the Buck-type PFC converter is eliminated. With advantages of Buck and Buck-Boost converters, this converter can achieve a high power factor and a high efficiency in universal-input applications. The circuit structure, working principle, steady-state characteristics and design considerations of the proposed converter are introduced and analyzed. Finally, a 56 W prototype was built, and experimental results verified the analysis results.

The integrated control of frequency transient stability of multi-microinverter microgrid is studied, which can effectively control the frequency transient stability of microgrid, improve the control accuracy, and shorten the regulation time. By means of excitation control and power frequency control, a virtual synchronous generator(VSG) control method is constructed to realize the frequency transient stability control of microgrid under a small load disturbance. The improved droop control method is used to realize the frequency transient stability control of microgrid under a large load disturbance. By designing a synchronous voltage controller and a double-loop controller, the free switch between the VSG control method and the improved droop control method is completed, and the transient stability of microgrid frequency under different conditions is controlled comprehensively. Experimental results show that the proposed method can effectively control the frequency transient stability of microgrid under different load disturbances. When switching between the off-grid and grid-connected modes, the control methods are effectively switched, the frequency transient stability of microgrid is accurately controlled, and the regulation time is shortened.

The circuit topology of a novel three-phase quasi-Z source AC-AC converter is proposed, and the basic working principle and structure of the circuit are analyzed. In addition, the relationship between input voltage and output voltage is also derived. This circuit topology is controlled by a pulse width modulation method, which can achieve the effect of changing the output voltage. MATLAB/Simulink is used to build a simulation model, and the simulation results are analyzed. Finally, an experimental circuit was built on the basis of the simulation model, and experimental results verified the feasibility of the proposed circuit topology and the correctness of circuit analysis.

The traditional nearest level modulation (NLM) has advantages of simple control and low switching frequency. However, when the number of output levels is small, the harmonic distortion rate of output waveform from a modular multilevel converter(MMC) under the NLM modulation will be large. In this paper, a full-bridge auxiliary sub-module is added to each arm of the traditional three-phase six-leg MMC topology, and the capacitance voltage of the auxiliary sub-module is half of that of the half-bridge sub-module. Aimed at this MMC topology, an improved hybrid modulation strategy is proposed, which can realize the balance control of half-bridge and auxiliary sub-module, reduce the harmonic distortion rate of MMC AC-side output current, and reduce the switching frequency and system loss of the full-bridge sub-module. A detailed simulation model is built in MATLAB/Simulink, and simulation results verify the effectiveness of the proposed MMC topology and the improved hybrid modulation strategy.