Since DC bias is one of the main reasons for increases in the vibration and noise of a large-scale transformer, it is essential to fully understand the vibration and noise characteristics of large-scale transformers under DC bias for the evaluation of the operating state of transformers and the reduction of noise and vibration. A 406 MVA EHV large-scale transformer is taken as the research objective, and its vibration and noise characteristics are studied. First, based on the field-circuit coupling finite element method, the no-load operation characteristics under different DC bias currents are simulated and analyzed, and the law of excitation current under different DC biases is analyzed. Second, a multi-physics coupling model of circuit-magnetic field-solid mechanics-pressure acoustics is established, and the effective value of vibration displacement and the time-frequency characteristics of noise signal at different measuring points of the transformer under DC bias are obtained considering the influence of magnetostriction. Third, the sound level is measured at different measuring points around the transformer, and the simulated value is compared with the actual measured value to verify the effectiveness of the proposed calculation method for transformer vibration and noise. Finally, the Hilbert-Huang transform method is used to extract the vibration and noise characteristic quantities of one large-scale transformer under DC bias, and a transformer vibration characteristic recognition method based on the energy ratio of the noise signal intrinsic mode function is proposed. This method can effectively recognize the severity of DC bias of the transformer and accurately grasp its operating state, providing a theoretical basis for timely taking measures to suppress the DC bias.

Limited by the switching frequency, the frequency-controlled LLC resonant converter is difficult to achieve a wide output voltage range. To solve this problem, an expandable variable-mode interleaved parallel LLC resonant converter is studied. The secondary-side of this converter adopts a voltage doubling rectifier circuit, which can work in a parallel or series mode according to different switch combinations of two half-bridges on the primary-side, and it can adapt to the wide output voltage range of 1-3N times. A fixed-frequency PWM control method is proposed. In the middle region between the parallel and series modes, the fixed switching frequency is taken as the resonant frequency, and the duty cycle of one bridge arm is changed to realize voltage control. PSIM simulation results show that the wide output voltage range of 1-3N times can be realized by expanding 2N resonator cavities. The experimental results of a 100 W prototype demonstrate that the wide output voltage range of 1-3 times can be achieved with two half-bridges and two resonant cavities, and the effectiveness of the proposed converter and its control strategy was verified.

To enhance the accuracy of a lithium battery model and realize accurate state estimation of the lithium battery, a fractional-order electric model of the lithium battery was built, and the model parameters were identified using adaptive genetic algorithm. Based on the fractional-order electric model, the unscented Kalman filter was adopted to estimate the lithium battery’s state-of-charge (SOC) and state-of-health (SOH). Stimulation results show that, the established fractional- order electric model of the lithium battery can more accurately describe its dynamic characteristics during charging and discharging, and the accuracy of the proposed state estimation strategy was higher than that the conventional control strategy.

An improved incremental conductance method with a variable step size is proposed to solve the problem that the traditional maximum power point tracking (MPPT) algorithm cannot strike a balance between the tracking speed and steady-state oscillation. The MPPT speed can be increased by the improved incremental conductance method using a zonal variable step size. Meanwhile, the steady-state oscillation problem is optimized by using the incomplete partial differential theory, thus improving the efficiency of photovoltaic power generation. The feasibility and effectiveness of the improved incremental conductance method is verified by comparing the traditional control algorithm with the improved incremental conductance method.

An anti-offset method for a wireless power transmission (WPT) system based on constant-voltage output interval tracking is proposed to deal with the problem of output voltage fluctuation when the coupling mechanism in the WPT system is shifted. First, a model of a CLC-S WPT system is established, and the relationship between the mutual inductance and output voltage gain in resonant and non-resonant states of the system is analyzed. Based on the analysis, it is found that the system has a stronger anti-offset capability in the constant-voltage output interval when it works in the non-resonant state. Second, an inductance compensation sequence is designed, and a constant-voltage output interval tracking control strategy is proposed to realize the constant output voltage control of the WPT system and improve its anti-offset capability. Finally, a simulation model and a test platform were built, and simulation and experimental results show that the constant-voltage output interval tracking control strategy can effectively reduce the output voltage fluctuation, thus verifying the robustness of the system under strong mutual inductance interference. Compared with the WPT system without constant-voltage output interval tracking, the CLC-S WPT system has a better dynamic regulation capability of output voltage.

The development of industry and economy has caused a huge consumption of energy, which brings serious energy crisis and environmental pollution. Therefore, building a safe and clean energy interconnection network is a way to solve the relationship among social development, environment and energy at present. Nowadays, different countries have proposed their policies for the development of new energy electric vehicles (EVs). As the core component of EVs, lithium-ion batteries are directly related to the driving performance and safety of EVs. The state-of-charge (SOC) estimation is a core parameter of lithium-ion batteries used in various industries, and the estimation accuracy is directly related to the service life and efficiency of batteries. In this paper, the problem of battery SOC estimation accuracy in EV applications is studied, and an SOC estimation method based on the extended Kalman filter (EKF) optimized by the whale optimization algorithm (WOA) is proposed. On the basis of constructing the covariance matrix of system noise and observation noise, the improved and optimized WOA-EKF algorithm is used to optimize the noise covariance matrix under dynamic conditions, thus improving the SOC estimation accuracy. The model parameter identification and comparative simulation verification are carried out in MATLAB/ Simulink. Results show that the SOC estimation of lithium-ion batteries based on the WOA optimized EKF algorithm can control the SOC estimation error to be within 2% under different working conditions, which is of significance to the promotion of develop- ment of batteries in the new energy field.

Aimed at the problem of eddy current loss, a method for the parameter design and optimization of a wireless power transfer (WPT) system in seawater is proposed to optimize the power transmission efficiency of the system. First, based on the analysis of the electromagnetic field of coils under operation in seawater, the equivalent mutual inductance model of the WPT system in a marine environment is obtained by using the equivalent impedance of eddy current loss. Second, when the positions of the primary- and secondary-side coils are fixed, the corresponding relationship between the equivalent impedance of eddy current loss and the operating frequency of the system and the number of coil turns is established, and the feasibility of the calculation method for the equivalent impedance of eddy current loss is verified by using the coils on both sides of the WPT system. Finally, based on the energy model of an LCC/S-type WPT system in seawater, the particle swarm optimization algorithm is used to optimize the transmission efficiency. A test system was built with the optimized parameters, and results show that when it transmitted 1 kW of power in a simulated marine environment, its overall efficiency can reach 84%.

Aimed at the problem that the traditional control methods are difficult to achieve soft-switching in a wide load range due to the limitation of resonant inductor volume and duty cycle loss in phase-shifted full-bridge converters, a hybrid control method based on peak current and Burst mode is proposed. The output voltage is stabilized to a reference value by adjusting the Burst duty cycle, and the phase shift angle is changed to maintain the minimum primary current so as to realize the lagging bridge arm zero voltage switching. A simulation platform was built for the proposed control method, and a 250 W prototype was developed. The hybrid control of a phase-shifted full-bridge converter was realized through a digital signal processor, and the feasibility of the control method was verified by simulation and experimental results.

A novel two-channel light emitting diode (LED) driver is proposed, and its operating principle and characteristics are analyzed in detail. This driver uses a novel Z-source resonant network and an active switch which has the same ground properties as the power supply, and the current balance is automatically realized by balancing capacitors, so its current control is simple. At the same time, owing to the use of Z-source resonant network to transfer energy, the proposed driver has advantages such as soft switching, high efficiency, small volume and low voltage stress. To verify the effectiveness of this driver, a 80 W prototype was built and tested.

Three-phase chain-link energy storage converters (TPCLESCs) are promising in enhancing the controllability of renewable energy in power grid, such as wind and solar power. Aimed at the problem of state-of-charge (SOC) imbalance of energy storage battery among phases of a TPCLESC, a phase-to-phase SOC balance method based on phase-to-phase circulating current power closed-loop control is proposed. Through the zero-sequence voltage injection into phases a, b and c, the active circulating current among phases is generated to realize the SOC balance in the three-phase energy storage battery groups. A mathematical model of the maximum phase-to-phase circulating current power of the chain-link energy storage converter and SOC deviation is established. On this basis, the phase-to-phase SOC balance in battery groups is realized at the maximum circulating current power through the phase-to-phase circulating current active power closed-loop control. As a result, the phase-to-phase SOC reaches its balance at the maximum speed, and the process of phase-to-phase SOC balance is accelerated. Finally, the correctness and feasibility of the proposed method were verified by a MATLAB simulation model and an experimental platform.