To solve the problems of constant-voltage output instability and low efficiency caused by load resistance and coupling coefficient fluctuations in the dynamic charging process of an electric vehicle, a novel dual-side control scheme is proposed. In this scheme, the constant-voltage control output is realized by adjusting the pulse width angle θ of a high-frequency inverter at the transmitter, and the maximum efficiency tracking (MET) control of the system is realized by adjusting the pulse width angle φ of a controllable rectifier at the receiver. Through theoretical analysis, it is proved that when the derivative ∂[sin(θ/2)]/∂[sin(φ/2)] is a specific constant, the system can always work under the operating condition of maximum efficiency. Compared with the same type of MET control scheme, the proposed scheme does not need to install expensive current or power sensors on the transmitter, which reduces the system’s development cost to a certain extent. To verify the rationality of the proposed scheme, an experimental verification device with a rated power of 360 W was built, and experimental results fully proved the rationality and effectiveness of this scheme.

In the traditional power module automatic layout optimization algorithm, the electrical evaluation is inefficient and takes up a lot of computing time. To solve this problem, lattice Boltzmann method (LBM) is used to replace the traditional evaluation method. Since LBM does not need to solve multiple invertible matrices, it can quickly judge the rationality of electrical interconnection and calculate the voltage/current. With the program of automatic layout design based on the genetic algorithm, an evaluation method of two-dimensional layout is established by using a D2Q4 lattice type, and the accuracy of the evaluation result under the layout scheme is verified by ANSYS Q3D software simulation. A comparative test was conducted in Python 3.10, and results show that LBM reduces the total time of scheme evaluation by 75.4% on average. Moreover, the more the number of loops in the evaluation scheme, the greater the computing advantage of LBM.

According to the demand of enterprises which produce UPS, a condition based maintenance(CBM) management system of UPS based on extended Kalman filter(EKF)-Markov is designed. Under the permission of users, the status data of online position and real-time operation of the equipment is visualized by using the geographic information system. Compared with the traditional post-maintenance scheme, the weighted method is used in data preprocessing to model the CBM of the data-driven collected information and reduce differences caused by different types of data. The EKF is used to eliminate the influence of noise on the sampling results, and the average error of state-of-charge(SOC)predicted using the algorithm is 0.434 3%. Combined with the Markov decision process, the UPS battery state is analyzed, the health management and CBM strategy in charge-change mode is implemented, and the maintenance time is reduced by 57.12% on average. Results show that compared with the traditional maintenance, the state prediction and health management system can improve the maintenance efficiency and accelerate the transformation from traditional planned maintenance to CBM mode.

To satisfy the low sampling frequency, low computational cost and high accuracy requirements of renewable energy generation systems in the grid voltage detection link, a high-precision discrete-time frequency-locked loop (FLL) which does not need to call trigonometric functions is proposed. First, the open-loop transfer function of discrete-time reduced-order generalized integrator (d-ROGI) is derived according to the expression of voltage based on complex numbers under the static coordinate system. Then, a d-ROGI with a low approximation error is derived according to the relationship between the unknown parameter of the open-loop transfer function and frequency. On this basis, the FLL for estimating the unknown parameter is constructed, the second-order small-signal model of the FLL is established, and the corresponding parameter tuning method is given. Finally, experimental results show that the FLL has a higher detection accuracy at a low sampling frequency than the most commonly used third-order numerical integrator discretization method. At the same time, it has a lower computational cost and requires less storage according to the comparison of computation cost.

The energy storage battery pack consists of a large number of low-voltage battery cells. The states-of-charge (SOC) of cells are different due to the difference in their characteristics, which causes some cells to be over-discharged during the charging process. To avoid this phenomenon, a equalizing charger based on multi-winding transformer and cascaded double-voltage rectifiers is proposed, and its characteristics are compared with those of a centralized passive equalizing charger. Its operation principle is analyzed, and its equivalent circuit is obtained. The buffer inductance of the novel equalizing charger and the turn ratio of the transformer are also optimized. A control strategy of single voltage-loop is put forward, which can guarantee the charging at two stages, i.e., constant-current and constant-voltage. In addition, the influence of the voltage difference between cells on the transformer operation is analyzed. Simulation results show that the proposed charger can achieve a high charging efficiency while satisfying the requirement of voltage equalization between cells.

Owing to their merits including continuous input and output current, high efficiency and high power density, non-isolated Superboost converters are widely applied in spacecraft power systems. However, the switching loss of the device will increase in a scenario with a high step-up ratio, resulting in a decrease in the converter efficiency. To solve this problem, a zero-voltage switching pulse-width modulation (ZVS-PWM) Superboost converter with low voltage stress is proposed. By introducing a resonant tank, the main switch can be turned on or off under ZVS, and the auxiliary switch can be turned on under zero current switching and turned off under ZVS. Besides, all the diodes are operating under soft-switching. As a result, the switching loss is reduced effectively, and the converter efficiency is improved without increasing the voltage and current stress of the main power device. The operation principle, soft-switching conditions and device stress are analyzed in detail, and the state-space averaging approach is used to estimate the steady-state and dynamic characteristics of the proposed converter. In addition, its feasibility was verified by a prototype with 100 kHz and 400 W.

A novel low delay and low power consumption low-to-high level shift circuit with a logic correction function is proposed, which uses a low delay level shift circuit and a low power consumption level shift circuit to work in parallel. After the logic is corrected, the low level between 1 V and 1.5 V is converted to a high level of 5 V, so this circuit can be widely applied in GaN driver circuits. Based on the 0.5 µm BCD process, 1.5 V power supply low voltage and 5 V power supply high voltage, the circuit is verified at 5 MHz. Results show that although the layout area of this circuit increases as a whole, the rise and fall delays are reduced to 2.3 ns and 1.8 ns, respectively, with a total power consumption current of only 11 μΑ.

Since the existing capacity load ratio calculation methods do not take into account the impact of different voltage levels on AC grid, they cannot ensure the optimization of the reliability and economy of AC grid at the same time. To solve this problem, a capacity load ratio calculation method for AC grid at multiple voltage levels is proposed on the basis of considering voltage levels. The power supply capacities of AC grid in high-and low-voltage modes are calculated, respectively. According to the power supply capacity, the discrete particle swarm optimization algorithm is used to calculate the particle number of capacity load ratio at different voltage levels, and the optimal capacity load ratio calculation results of AC grid at multiple voltage levels are obtained, so as to realize the capacity configuration optimization of AC grid at multiple voltage levels. Experimental results show that the proposed method can optimize the transformer's capacity load ratio, and the power supply reliability, economy and satisfaction score of AC grid are higher.

When the improved droop control based on virtual impedance is adopted in island microgrid, the problem of inaccurate distribution of reactive power and reactive power circulation will still occur with the changing line impedance due to the fixed value of virtual impedance. To solve this problem, a virtual impedance prediction model based on partial least squares regression (PLSR) is proposed, which uses the line impedance value and the system impedance value before compensation to predict the virtual impedance value and realizes the adaptive virtual impedance, thus overcoming the problem in the improved droop control based on virtual impedance. There is no need to detect the real-time power value and circulation value, and the use of communication network is not required. Furthermore, from a comparison with the prediction results obtained by neural network models, it is proved that the prediction accuracy of the virtual impedance prediction model based on PLSR is better. At last, a simulation system of microgrid is constructed in MATLAB/Simulink to verify the adaptive virtual impedance, and simulation results show the superiority of the proposed model.

The smooth switching between grid-connected and islanded microgrid operation modes and the stability of system frequency are important guarantees for the safe and stable operation of a master-slave microgrid system. Combined with the operating characteristics of the microgrid system, an off-grid switching method based on phase angle switching is proposed, and a pre-synchronization control module is added to make sure that the grid phase is quickly tracked and compensated when the islanded mode is switched to the grid-connected mode, thereby solving the problem of shocks in the output voltage and current from master and slave inverters in switching. To ensure the frequency stability of the microgrid system, a V-F frequency control strategy based on fuzzy droop control is proposed and further applied to the smooth switching based on phase angle switching, so that the system frequency is basically maintained at 50 Hz and the problems of large oscillations in voltage and current and frequency shocks in switching are avoided. Finally, an experimental platform was built to verify the effectiveness and stability of the proposed method.