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.

The parameter identification method for the equivalent circuit model of lithium-ion battery has a great impact on the model accuracy. To solve the problems of low convergence accuracy and slow convergence speed in a satin bowerbird optimization(SBO) algorithm, an improved satin bowerbird optimization (ISBO) algorithm is proposed. The inertial weights, Cauchy mutation, Gaussian mutation and greedy selection strategies are used to improve the convergence accuracy of the ISBO algorithm, and its convergence performance is verified by standard test functions. Based on the battery charging and discharging data, the proposed ISBO algorithm is applied to the parameter identification of the equivalent circuit model of lithium-ion battery. Experimental results show that compared with the SBO and adaptive weight particle swarm optimization algorithms, the ISBO algorithm has a higher accuracy when it is used in identifying the model parameters and the identification accuracy is not affected by the working conditions of battery.

As the number of charge and discharge cycles of a lithium-ion battery increases, its state-of-health (SOH) will degrade to some degree accordingly. Aimed at this problem, a method for estimating the SOH of lithium-ion battery based on an improved multi-objective Cuckoo search (IMOCS)-BP neural network is designed, which adaptively changes the update probability and search step size of the Cuckoo search (CS) algorithm while avoiding the algorithm from falling into the local optimum, thereby solving the problems of slow convergence speed and low solution accuracy in the CS algorithm. The IMOCS algorithm is combined with BP neural network to conduct a global search in the node space, reduce the influence of initial values of weight and threshold on BP neural network, and realize the parameter optimization. Through Matlab simulations, it is verified that the SOH estimation algorithm based on IMOCS-BP neural network has a low error and a strong performance, thus realizing an accurate SOH prediction of lithium-ion battery.

Aimed at the problems of fast loss and high capacity configuration of battery energy storage equipment in microgrid, an optimal configuration model of battery energy storage capacity of microgrid considering life loss is established in this paper. In addition, a cost calculation method for the battery energy storage life loss based on fixed daily cycle times is also proposed. This method combines the piecewise linearization idea and the scenario analysis method, and it can effectively extend the lifetime by optimizing the discharging depth and daily cycle times of battery energy storage. Moreover, considering the uncertainties in wind power output and load power, a two-stage robust optimization model is introduced, which is further solved by the column-and-constraint generation algorithm. Finally, the effectiveness of the novel model under different uncertainties and different unit prices of battery energy storage is verified by numerical examples.

Aimed at the problem that the influencing mechanism of configuration size of a differential pressure channel in proton exchange membrane fuel cell(PEMFC) for the cell's electrochemical performance is unclear, the influences of channel height and rib width on the oxygen concentration, water concentration distribution characteristics, current density, power density, and pressure drop of a differential pressure channel and a straight channel are studied, and a comparative analysis of the two kinds of channels is performed. Results show that channel height has little effect on both channels, but the differential pressure channel has an obvious advantage when its rib width is 1.25 mm or 1.5 mm. The influence of pressure converter area on the performance of the differential pressure channel is further studied, and results show that its peak power density is the highest when the height and length of the pressure converter area are 0.05 mm and 1.5 mm, respectively. With the comprehensive consideration of influences on power density and pressure drop, the differential pressure channel with a height of 0.4 mm, width of 1.25 mm, rib width of 1.25 mm, and a pressure converter area with a length of 1.5 mm and height of 0.05 mm is selected. In this case, its peak power density is 0.366 1 W/cm², which is 6.3% higher than that of the straight channel.

The insulated-gate bipolar transistors (IGBTs) have been widely applied in the modern power electronics technology, and the paralleling of IGBTs has become an economical and feasible method in some working scenarios where one single device cannot meet the design requirements. The paralleling of IGBT modules can simplify the circuit structure, increase the converter output power, and improve the power density of devices. During the operation of IGBTs in parallel, the current imbalance, which may be caused by the difference in IGBTs' characteristics in a static or dynamic mode, the inconsistency of junction temperature, the asymmetry of a drive circuit or power loop, as well as the aging or failure of IGBTs due to long-term use, will affect the system's reliability and stability. The research hotspots of parallel-operating IGBTs at home and abroad are investigated. The principle and influence of static and dynamic current imbalance are summarized, and the difference in the current-sharing control principles is analyzed. The performance characteristics of current-sharing control are summarized and compared from the aspects of power loop current-sharing control and drive circuit current-sharing control. Furthermore, the development of current-sharing technologies for parallel-operating IGBTs in the future is also prospected.

The phenomenon of dynamic avalanche occurring during the IGBT turn-off process is one of the important reasons for its failure. To study the dynamic avalanche failure mechanism of IGBT, the Silvaco software was used to simulate and analyze this mechanism. Through the simulation and analysis of the breakdown mechanism, current density distribution and temperature distribution of dynamic avalanche, it is concluded that dynamic avalanche can generate moving current filaments and dead filaments which are either moving slowly or fixed. However, the failure of the device is caused by the dead filaments formed by dynamic avalanche. The dead filaments will lead to a sharp increase of local temperature in the IGBT, and the IGBT will eventually fail because the local temperature is too high to burn the device. On this basis, the causes of dead filaments are analyzed, and specific measures to prevent the dynamic avalanche failure of IGBT are also put forward.

The development of power modules towards high temperature, high power and high density raises higher requirements for the packaging structures of modules. Compared with the traditional wire-bond structure, the double-sided structure has attracted more and more attention owing to its characteristics such as high heat dissipation capacity and low parasitic inductance. However, the mismatch of thermal expansion coefficient between materials used in the double-sided structure makes the structure suffer tremendous thermo-mechanical stress, thus reducing the reliability of power module. Therefore, to develop double-sided bi-directional modules with low thermo-mechanical stress, the effects of chip layouts on the heat dissipation performance of modules and the parasitic inductance were analyzed by simulations at first. Then, a flexible buffering spacer with low Young's modulus is proposed accordingly. The feasibility of reducing the thermo-mechanical stress and improving the reliability of the module was preliminarily proved by simulation and experimental results.

Silicon carbide (SiC) is a promising wide-bandgap semiconductor material owing to its excellent electrical and thermal characteristics. Power metal-oxide-semiconductor field-effect transistors (MOSFETs) based on SiC are suitable for high-power fields, and their high-temperature gate oxide reliability is one of the most concerned characteristics. In this paper, the high-temperature gate oxide reliability of self-developed SiC MOSFETs is compared with that of the foreign SiC MOSFETs of the same specification by positive and negative high-temperature gate bias (HTGB) tests. The negative HTGB test results show that the deviation of threshold voltage of self-developed SiC MOSFETs is almost equal to that of the foreign SiC MOSFETs, and the maximum discrepancy between them is about 4.52%. However, the positive HTGB test results show that the deviation of threshold voltage of self-developed SiC MOSFETs is smaller than that of the foreign SiC MOSFETs, with a maximum discrepancy of 11%. The reason for the better performance of self-developed devices is that an appropriate amount of nitrogen is added to the SiC/SiO2 interface, which can passivate interface defects and reduce the generation of fast interface states, so that the total interface state density is minimized.

A modeling data and optimization algorithm driven electrothermal behavior model of gallium nitride high electron mobility transistor (GaN HEMT) is proposed to facilitate the quantitative analysis of problems caused by high speed switching, such as turn-on overvoltage, false turn-on, oscillation and EMI noise. Compared with the traditional behavior models of GaN HEMT, the proposed model can precisely depict the electrothermal characteristics of GaN HEMT in a wide temperature range in both the first and third quadrants by only two compact equations. Meanwhile, the nonlinear parasitic capacitances of GaN HEMT can be accurately modeled by one compact equation. In addition, an optimization algorithm combing the genetic algorithm and Levenberg-Marquardt algorithm is put forward, and a one-step extraction of modeling parameters is realized based on this optimization algorithm and modeling data, which can reduce the modeling time and work load to a certain degree. Results show that the proposed modeling method can precisely model multiple types of GaN HEMT devices manufactured by different companies. Finally, the correctness and effectiveness of the proposed modeling method was verified by the well-matched simulated dynamic waveforms and experimental measurement data.

To improve the performance of modern unipolar power diodes and further break through the "Silicon limit", by increasing the junction depth of P+ region in traditional JBS diodes and introducing a super junction structure to reduce the chip thickness, the contradiction between on-state voltage drop and reverse blocking voltage of traditional unipolar devices is alleviated and the conduction current density of devices per unit area is improved. The effects of P-pillar concentration, N-pillar width and N-pillar concentration of super junction JBS diode on the forward conduction and reverse blocking characteristics are analyzed using a numerical method. The forward conduction and reverse blocking mechanism of super junction JBS diode is analyzed using the theory of electric field coupling effect, and a super junction JBS diode with 300 V is designed.

The junction temperature monitoring of power devices in a solid-state power controller(SSPC) plays a vital role in the SSPC reliability. The thermal model method is widely used owing to its contactless measurement and simplicity. However, the aging of the power chip will lead to the degradation of the thermal path, and the junction-to-case thermal resistance of the device will increase. As a result, the actual junction temperature may far exceed the value estimated by the thermal network model, leading to an optimistic estimation of the device's state-of-health. The failure of the solder layer is considered to be one of the main reasons for the aging failure of SSPC power devices. In this paper, the device's aging state is monitored in real time during the life of SSPC, and the thermal model of the power device is adaptively updated online. The thermal impedance taken as an update basis is calculated by measuring the temperature-sensitive electrical parameters which are not affected by the degradation of the solder layer, and the thermal impedance information is associated with the aging state of the solder layer to update the thermal model. Using the proposed method, the thermal model can be updated in real time without affecting the normal operation of SSPC, and experimental results verified the effectiveness of this method.

The diode-rectifer-based high voltage direct current(DR-HVDC) system is a promising low-cost scheme for the connection of offshore wind power, which can deliver wind energy from remote offshore wind farms to onshore power systems. However, the increasing number of offshore DR-HVDC systems may lead to a growing difficulty in controlling wind turbine(WT) converters and a poor system stability. On this basis, a novel grid-formation control method for the connection of DR-HVDC to offshore WT converters is proposed. Two positive-sequence control loops are used to adjust the active power output from WTs and maintain the frequency and voltage of offshore AC grid, in which the first controller can adjust the active power error of each WT to the voltage angle deviation and thus cause frequency changes, and the second controller counteracts frequency changes by adjusting the AC voltage amplitude of WT. The converter's internal current control loop is used to limit the fault current and eliminate high-frequency resonance in the system. Finally, the effectiveness and superiority of the proposed control method are verified by electromagnetic transient simulations in terms of fault crossing, WT power change, reactive power disturbance and WTs shutdown.

Since the existing distribution network technology increases the active power loss of distribution network system, problems such an increase in the network loss value and a lower penetration rate will arise. To solve these problems, the research on the optimal control method for the flexible soft switch in distribution network considering demand-side response is proposed. First, a demand-side response model and an optimal control model of flexible soft switch are established. Then, the particle swarm optimization algorithm is used to solve these models, and the design of load transfer in distribution network is completed. Finally, the constraint conditions such as the operation of flexible soft switch, power flow in distribution network system and output from renewable energy power generation are set, thereby realizing the optimization of the control of flexible soft switch in distribution network. Experimental results show that after the application of the proposed method, the load of distribution network system can be effectively transferred, the active power loss of distribution network system and the overall network loss can be greatly reduced, and the penetration rate of distribution network system and the consumption of renewable energy power generation can be improved. As a result, the operation optimization of distribution network system is realized, providing a guarantee for its safe and economic operation.

In view of the fact that the existing methods cannot identify all the effective power supply paths for voltage over-limit, which leads to problems of poor real-time performance and unobvious suppression effect in the voltage over-limit identification in distribution network, the voltage over-limit identification in distribution network with photovoltaic (PV) power supply is studied based on a regulation function, so as to improve the corresponding real-time performance and effectiveness. First, an external characteristic model of PV power supply is constructed by using its physical mechanism, based on which a simulation model of PV power supply is built in the Matlab/Simulink software. According to the power relationship in distribution network with PV power supply, the voltage variation at the grid-connected point before and after the integration of PV power supply is calculated, and the mechanism of voltage over-limit is analyzed, so as to design the equivalent circuit of distribution network with PV power supply. All the effective power supply paths for voltage over-limit are specified, a candidate set of voltage over-limit regulation strategies for distribution network with PV power supply is set up in an decreasing order by means of the regulation function, and the candidate strategies are selected from the candidate set of regulation strategies to realize the voltage over-limit identification. The analysis results of an example show that the proposed method can effectively adjust the voltage of distribution network with PV power supply to a normal state with less iteration times and a short execution time, indicating a high practicability.

The HT-6M Tokamak Reconstruction is an international project of cooperation between China and Thailand for responding to the Belt and Road Initiative. The function of pulse power supply for heating field is to breakdown and produce plasma, and the corresponding power supply scheme adopts the form of capacitor energy storage pulse discharge. To calculate the parameters of power supply that meet the requirements, the discharging process of pulse power supply for heating field is analyzed mathematically, and the core devices are designed and developed according to working parameters of power supply equipment. To verify the theoretical analysis of discharging process, a set of small capacitor energy storage pulse power supply was developed. At the same time, a turn-off experiment on a high-power solid-state circuit breaker was carried out.

To accurately obtain the on-orbit health status of a spacecraft electrical power system, a condition quantitative assessment model for a satellite electrical power system with the fuzzy theory is proposed. First, an index system for evaluating the system condition is established by analyzing the operating characteristics of one satellite electrical power system. Combined with the time-varying characteristics of actual telemetry, the corresponding telemetry pre-processing method for electrical power system and a dimensionless deterioration function are put forward. Then, a hierarchical condition quantitative assessment method for the satellite electrical power system is established through introducing the variable weight theory and fuzzy theory. Finally, the correctness and effectiveness of the proposed condition quantitative assessment method are verified by analyzing the actual on-orbit and simulation data of the satellite and comparing with the traditional method. Moreover, the deteriorated system condition can be assessed by the proposed method two days earlier only based on thresholds.

The problem of high-order nonlinearity in the transient process of a wireless power transmission system is a difficulty in load measurement and identification. When dealing with beat-frequency signals due to the high-order nonlinearity, there are some problems in the existing analog envelope detection method, such as signal distortion, poor circuit flexibility, and limited measurement range. Aimed at these problems, a digital envelope detection method was proposed based on Hilbert transform, and a digital envelope detector was designed to extract the envelope of the voltage beat-frequency signal. In addition, simulations and experiments were conducted to validate the proposed method. Results show that this method can accurately extract the envelope of the voltage beat-frequency signal with different loads, and it achieved an error of less than 5% in the load resistance range of 1-2 000 Ω. The proposed method extends the contactless load measurement range based on characteristic parameters in the transient process, providing a new idea for measuring the internal resistance of batteries in aircraft such as unmanned aerial vehicles.

Aimed at the problem that the failure of electronic components or power off in the current control unit of a short-circuit current protection device will lead to a protection failure, a passive electromagnetic current transformer is proposed. The working principle for the trigger device is analyzed, and the maximum magnetic flux of iron core within the effective working range of the transformer is determined according to the magnetization curve of the core material. Considering that the magnetic flux in the iron core is easily saturated at a large current, simulations are performed to analyze the influence of air gap distribution on magnetic flux intensity in the transformer. An electromagnetic current transformer core structure is designed, which can still effectively work at the 15 kA short-circuit current peak. The 3D transient electromagnetic simulations show that when the short-current rising rate is 20 A/µs and the number of turns in the secondary winding is 30, the output voltage from the secondary winding is not less than 14 V. Finally, an engineering prototype of hybrid current-limiting fuse with a passive electromagnetic current transformer as its trigger device was made, and a short-circuit current detection test was carried out. The experimental results basically agreed with simulations, indicating the accuracy and validity of the design of iron core.