With the rapid development of new energy technology, the performance of DC-DC converters continuously increases. In this paper, a novel high-gain DC-DC converter is proposed, which is improved based on the quasi-Z-source topology. Owing to the use of the topology in which three capacitors discharge together to the load, a higher voltage gain is obtained while the voltage stress of capacitors is reduced. The proposed converter has advantages of the traditional quasi-Z-source converter such as simple control, continuous current and small current ripple. The working principle for this converter is analyzed. In addition, its performance was verified through simulation experiments and prototype experiments.

Temperature sensitive electrical parameter method has characteristics such as strong online capacity, non-invasiveness, and rapid response, so it has become a research hotspot at present. The on-state voltage drop is taken as a temperature sensitive electrical parameter, and an online monitoring method for IGBT junction temperature is studied based on the on-state voltage drop. First, the data of on-state voltage drop, collector current, and junction temperature of IGBT is obtained through the double-pulse test circuit. Then, based on the measured data, a three-dimensional mapping representation model of IGBT collector current, junction temperature, and on-state voltage drop is constructed. Finally, a novel on-state voltage drop sampling circuit was designed, and an online monitoring experimental of IGBT junction temperature was conducted. Experimental results verified the accuracy and validity of the obtained three-dimensional junction temperature representation model.

Aimed at the thermal runaway accident of lithium-ion batteries in the process of civil aviation transportation, through the simulation of a low-temperature and low-pressure environment during the civil aircraft flight, the thermal runaway of a lithium-ion battery is triggered by contact heating of an external heat source, and the thermal runaway characteristics of lithium-ion battery in a variable pressure and variable temperature environment are explored. Results show that the thermal runaway time of lithium-ion battery advances with an increase in the flight altitude. Within a certain temperature range, temperature has a greater impact on the thermal runaway time than air pressure. When the ambient temperature decreases to a certain extent, it will no longer affect the peak temperature of thermal runaway. The CO concentration increases with an increase in the flight altitude. The solid particles produced by thermal runaway are different at a limit of 0 °C. When the flight altitude is 8 km (80 kPa, 10 °C), the combustion of thermal runaway products is stronger.

When a grid-connected inverter (unit) is connected to a weak grid, the wide range of grid impedance variation may lead to system instability. To solve this problem, a centralized active damping device is configured in parallel at the point of common coupling (PCC) to simulate the external characteristics of damping resistance, thus realizing the suppression of resonance between the grid-connected inverter and grid. In this paper, an adaptive adjustment method for virtual impedance value based on active damping device is proposed, which not only ensures the system stability, but also minimizes the current flowing in the active damping device. At the same time, a current harmonic reference compensation method is proposed, which can reduce the influence of current closed-loop on the virtual impedance characteristics and further improve the damping effect. A 5 kW grid-connected inverter and a 1 kW active damping device were built in a laboratory to verify the effectiveness of the proposed control scheme.

To solve the problem of performance degradation in automotive lithium-ion batteries at low temperatures, a self-heating method based on electric vehicle traction motor and inverter reconfiguration was developed, in which the traction motor windings were utilized as energy storage units to realize AC heating of batteries at low temperatures without additional hardware. First, a detailed mathematical description of AC heating topology was given, and the analytical relationship among the battery voltage, current and heating control parameters was obtained. Then, an adaptive fuzzy PI controller was designed to regulate both the heating current and the charge/discharge voltages of batteries dynamically, so that the heating rate can be guaranteed while avoiding the aging of batteries. In addition, in order to relieve the mechanical vibration and noise from the traction motor during internal heating, a torque ripple canceling scheme based on the clamped rotor position was also proposed, thus ensuring the passenger comfort and the motor durability. Experimental results demonstrate that under the proposed strategy, the tested batteries warmed up from-20 °C to above 0 °C within 403 s without permanently damaging the battery life.

When the grid voltage is unbalanced, the phase-locked loop (PLL) needs to retrack the grid voltage. At this moment, an inaccurate phase lock or an overlong phase lock time will cause the degradation of control performance for the subsequent flexible DC transmission system. Therefore, to avoid the adverse effects caused by PLL, an improved control strategy for converter without PLL is proposed. First, the difference between the traditional PLL scheme and the proposed scheme without PLL is analyzed, and an instantaneous positive-and negative-sequence component extraction scheme is put forward in an environment without PLL. Second, a converter control system without PLL is designed, and the compensation of negative-sequence current is taken as its control target. Finally, the validity and correctness of the proposed strategy was verified by the experimental results of a prototype.

To better compensate for the voltage drop of DC-side bus in an electric vehicle (EV) fast charging station and limit the power ramp rate of power grid, a nonlinear control strategy of flywheel energy storage system for the DC fast charging station is proposed based on the immersion and invariance theory. First, considering the power balance relationship of the power supply system in the fast charging station, the impact characteristics caused by the charging load instantaneous access under the traditional control strategy of flywheel energy storage system are analyzed, and the voltage stability of DC-side bus is determined as the optimization objective. Then, the effect of bus voltage control and the control accuracy of energy storage output current are considered, an affine nonlinear model of flywheel energy storage is established, the manifold surface and control law are constructed using the immersion and invariance method to provide the capability to quickly respond to the charging load current mutation and flywheel speed change, and a charging and discharging control strategy for the energy storage system is designed. Finally, a simulation model is built to compare and analyze different control strategies under single-and multi-EV access, and results show that the proposed control strategy can effectively suppress the influence of electric vehicle access and flywheel speed change on the bus voltage, thereby alleviating the impact on the distribution network.

To study the influence of electron irradiation on the reliability of silicon carbide metal-oxide-semiconductor field-effect transistor(SiC MOSFET) with different aging degrees of the gate oxide, the electrical characteristics of SiC MOSFET were analyzed by combining high-temperature gate bias and electron irradiation experiments. The influence of electron irradiation on the threshold voltage of SiC MOSFET after the gate oxide was stressed by high temperature and a strong electric field was discussed. To avoid the impact of the packaging material on the threshold voltage under high temperature and electron irradiation, the device under test was exposed to air during the experiment. Experimental results show that the threshold voltage after the high-temperature positive gate bias experiment was more sensitive to electron irradiation. The exponential relationship of the influence of electron irradiation on the threshold voltage of SiC MOSFET after the high-temperature gate bias aging was proposed. The threshold voltage after the high-temperature gate bias at 39 V and 150 °C for 2 h can be restored to the initial value by 0.2 MeV and 300 kGy electron irradiation. A basic numerical model of SiC MOSFET was established in the Sentaurus TCAD simulator. By setting the electron concentration and hole traps in the oxide, the effect of high-temperature gate bias and electron irradiation on the threshold voltage of the device was simulated, and the threshold voltage recovery mechanism was discussed.

The three-phase inverter is an important part of the motor drive system in an electric vehicle (EV). When a fault occurs, the fault sample size will be limited due to the short occurrence time, resulting in sample imbalance. To solve this problem, an inverter fault diagnosis method combining conditional generative adversarial network (CGAN) and convolutional neural network (CNN) is proposed in this paper. First, the phase current is taken as a fault sensitive signal, its frequency-domain characteristics are obtained by fast Fourier transform, and normalized preprocessing is carried out. Then, each sample is labeled and input into the CGAN model for countermeasure training to generate new samples in each fault mode. Finally, the CNN model is used to distinguish various fault modes of inverter. Through experimental research, it is found that the fault diagnosis accuracy based on CGAN-CNN can reach more than 98%, indicating that the proposed sample generation method is better than the traditional Smote and GAN methods. The results in this paper provide theoretical support for the intelligent operation and maintenance of new energy EVs.

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.