The grid-connected operation of an energy storage system is realized by a converter. Due to the low switching frequency of the conventional converter, there exists time delay in sampling and calculation, which will lead to poor transient characteristics of the energy storage system and even instability of the whole power grid. In this paper, model predictive control(MPC) is used to achieve a fast power response of energy storage system and avoid the influence of time delay. A power weight value function is introduced to calculate the optimal output voltage of energy storage converter in the MPC control of active and reactive power. To solve the problem of inaccurate MPC model caused by the parameter deviation of filter inductor, inductance error compensation control is used to improve the model accuracy. Through Matlab/Simulink simulations and experimental results, it is verified that the proposed scheme can improve the transient characteristics of energy storage system and effectively eliminate the influence of error on the MPC control performance.

Aimed at the problem of low efficiency of a dual active bridge (DAB) converter in the wide voltage range of single phase shift modulation strategy, a one-sided asymmetric duty modulation strategy is proposed in this paper, which significantly improves the efficiency of DAB converter, especially in the case of light load. First, the principle of one-sided asymmetric duty modulation scheme is described, and two operation modes are obtained according to the relationship of control degrees of freedom. Second, based on the time-domain analysis, the steady-state characteristics in the two operation modes are derived, including inductance current and transmission power. Third, in order to find the optimal combination of control degrees of freedom, the peak-to-peak value of inductance current is selected as the optimization objective, and the optimal one-sided asymmetric duty modulation strategy is obtained by applying the KKT condition. Finally, an experimental platform for DAB converter based on SiC device was built, and experimental results verified the effectiveness of the proposed one-sided asymmetric duty modulation strategy.

Aimed at the voltage distortion and current distortion of power grid with pulse load, a three-level unified power quality conditioner(UPQC) with supercapacitor energy storage is designed. A method based on artificial neural network is proposed to control the series and shunt compensation units, and a method based on double closed-loop PI control is used to control the supercapacitor energy storage unit. The series compensation unit compensates voltage to maintain the stability of load voltage and ensure the power demand of load, while the shunt compensation unit compensates current to maintain the stability of supply current and avoid the continuous and large impact on power grid. The supercapacitor energy storage unit charges and discharges on the DC side to maintain a constant voltage on the DC side and ensure the normal operation on the series and shunt sides. The proposed method eliminates the complicated coordinate transformation process and avoids the phase lag caused by multiple filters. Simulation experiment results show that the proposed topology and control strategy are helpful for improving the power quality of power grid with pulse load.

Due to the duty cycle constraint on the traditional Boost converter, its applications to high-voltage-gain power supply are limited to certain degree. In this paper, a DC-DC converter with high voltage gain based on an isolated Boost converter and Cockcroft-Walton voltage multiplier cell (VMC) is studied, and its working principle and characteristics are analyzed. This converter achieves a conversion with an ultra-high step-up ratio by integrating the isolated Boost converter with the VMC. Compared with the traditional Boost converter, this topology has a high voltage gain in a low duty cycle, a low voltage stress of active switching device, and a simple control circuit with one single switch. Finally, a 35 W prototype with an efficiency of 89.5% was built to achieve a high step-up conversion from 24 V to 1 000 V, and the theoretical analysis results was verified by experimental results.

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.

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 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 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.

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.

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.