In an energy storage system, the voltage level on the DC bus side is usually higher, while the voltage level on the battery side is lower with a wide variation range. Under this background, a three-level bidirectional full-bridge multi-resonant DC-DC converter topology is proposed, in which a three-level structure is adopted on the high-voltage side to reduce the voltage stress of the switch. The resonant cavity is designed as an LLCLC multi-resonant structure with auxiliary inductance, so that the left and right sides of the equivalent circuit is symmetrical, thus realizing the peer-to-peer driving control of forward and reverse operations and the bidirectional transmission of power. An improved synchronous pulse-frequency-modulation control strategy is adopted, so that the full-range zero-voltage-switch can be realized for switches on the high- and low-voltage side regardless of the forward or reverse operation. Compared with the traditional LLC resonant topologies, the proposed topology can achieve a wider range of voltage gain in a narrower frequency range. Through the optimization design of resonant cavity parameters, the converter can transmit the current fundamental wave and third harmonic power at the same time, thereby improving the energy transmission efficiency. Finally, a 2 kW experimental prototype was built, and experimental results verified the theoretical analysis.

The constant-current power supply system is suitable for remote seabed power supply in a harsh environment owing to its strong anti-failure capability. As all the seabed equipment adopts constant-voltage power supply, a constant-current to constant-voltage conversion device is needed to convert constant-current input into constant-voltage output to provide electric energy for the seabed equipment. To solve the problem that an efficient conversion from constant-current to constant-voltage in a wide load range as well as a high-pressure isolation control, a constant-current to constant-voltage converter topology with cascade of a shunt regulator circuit and a DC transformer is proposed to achieve the efficient conversion from constant-current to constant-voltage in a wide range. Aimed at the output control problem under high-pressure isolation, an indirect control strategy for output voltage based on input-side detection is studied to achieve an accurate control of output voltage without the need of high-cost and large-volume output isolation detection devices. Finally, an experimental prototype with input of 1 A and rated power of 500 W was built to verify the feasibility of the power conversion technology of constant-current to constant-voltage converter.

With the large-scale network entry of electric vehicles (EVs), their disorder charging further increases the load peak-valley gap, which has a negative impact on the stable operation of power system. A two-stage optimization scheduling strategy which takes into account the EV load and the energy storage system of batteries is proposed. First, an orderly charging scheduling model for EV is established, which aims at minimizing the absolute peak-valley gap between user charging cost and load. The improved particle swarm optimization algorithm is used to solve this model to avoid peak charging. Second, an optimal scheduling model of peak-shaving and valley-filling for the energy storage system is established with an objective of minimizing the variance of load and the combined cost of energy storage life, which is solved by the improved Harris Hawks optimization algorithm to reduce the peak-valley gap of load. In addition, the optimization results are evaluated and analyzed based on the evaluation index of peak-shaving and valley-filling. Finally, a simulation experiment is carried out with the measured load power of one power network as an example. Results show that under the proposed two-stage optimization scheduling strategy, the peak load decreases by about 147 kW, the valley load increases by about 223 kW, and the peak-valley gap deceases by 46.73%, indicating that this strategy can effectively improve the load curve, alleviate the pressure on power supply during the peak load period and ensure the safe and stable operation of power grid.

With the continuous advancement of medical technology, implantable medical devices (IMD) are increasingly applied in clinical practice. Since the traditional battery-powered method will bring additional tissue damage and surgical costs to patients, the use of wireless power transfer (WPT) technology to power IMD will become a trend in the future. However, how to design a high-efficiency IMD-WPT system in a limited space is very challenging. To this end, the performance characteristics of five WPT technologies suitable for IMD are compared. Then, the magnetic resonance WPT technology is taken as an example to introduce the key issues in the design of a magnetic resonance IMD-WPT system. Finally, the application status of part of the magnetic resonance WPT technologies in some typical IMD is combined, and the research direction of IMD-WPT technology in the future is discussed.

Compared with the traditional silicon(Si) devices, the gallium nitride(GaN) devices have lower parasitic parameters, a faster switching speed and a smaller on-resistance, which will easily lead to the phenomenon of continuous oscillation during their switching-on process and further result in the circuit instability. Therefore, it is necessary to suppress this phenomenon in practical circuits. Under this background, a negative conductance model of a bridge circuit under the conventional driving scheme is established at first, and the oscillation stability of the circuit is analyzed. Then, by adding optimization to the conventional driving scheme, the corresponding negative conductance model is established. The optimization schemes of series damping represented by changing the resistance and adding ferrite beads and those of parallel low impedance represented by adding RC snubber are selected, respectively. With this model, the influence of adding the driving optimization schemes on the oscillation stability of the circuit can be identified, and the changes in the stability before and after the addition were verified by experimental results, providing a reference for the driving circuit to select its appropriate driving optimization scheme.

With the development of wide band gap devices, SiC MOSFET has been widely applied, and the research on its short-circuit protection has become an important topic to ensure the reliability of power electronic equipment. In view of the short short-circuit withstand time of SiC MOSFET and the difficulty in short-circuit fault protection, a short-circuit detection method for SiC MOSFET based on a planar differential Rogowski coil is proposed, which realizes a rapid identification of short-circuit fault by measuring the drain source current of the circuit and has advantages such as a fast response speed, a strong anti-interference capability and complete isolation from the main circuit. First, the working process of the SiC MOSFET short-circuit detection method based on the planar Rogowski coil is introduced. The partial element equivalent circuit (PEEC) modeling method for planar Rogowski coil is studied in detail, and an equivalent model which can reflect the coil’s high-frequency characteristics is obtained. At the same time, the influence of the geometric structure of the planar Rogowski coil on its performance is analyzed, and an optimal design scheme considering both the high gain and high bandwidth is proposed. Aimed at the problem of low measurement accuracy of the Rogowski coil in an environment with strong electromagnetic interference, a scheme of using the differential coil is put forward to improve the anti-interference performance. Finally, the anti-interference per-formance of the designed planar differential Rogowski coil and the reliability of short-circuit protection method based on this coil were verified by experimental results.

The bi-directional power transmission with a high efficiency and a high power density can be achieved by employing CLLC resonant converters. However, the traditional parameter design method is cumbersome and requires multiple iterations to obtain appropriate circuit parameters. To solve this problem, the working principle and characteristics of a bi-directional CLLC converter are analyzed, and a novel parameter design method is proposed. By considering the full range of soft switching, design index constraints and high-efficiency optimization conditions, the range of design parameters is narrowed and the design steps are optimized, thus effectively reducing the complexity of the converter parameter design process. Based on the demand for a 48~380 V/kW bi-directional DC-DC converter in industrial applications, specific parameter design steps and results were given, and a prototype was developed. The correctness and effectiveness of the proposed parameter design method was verified through experimental testing.

The power supply load of a high voltage direct current (HVDC) power supply system is prone to be affected by signal interruption, which will result in the unstable operation of power supply system. To effectively improve the management efficiency of power supply system, an optimization method for the management efficiency of HVDC power supply system based on genetic algorithm is proposed. The optimization of management efficiency is transformed into the problem of load distribution, and a load distribution control strategy of efficiency optimization is adopted to reasonably distribute the load current in the HVDC power supply system. The genetic algorithm is used to optimize the management efficiency of the HVDC power supply system, so as to optimize its management efficiency. Experimental results show that the system management efficiency can be adjusted through the independent operation of dual power supplies, thereby improving the efficiency of power supply system. In addition, the running time of this method was maintained at 90-120 s, the optimization time was short, and the efficiency was high.

With the large-scale integration of wind power and other renewable energy sources, the frequency regulation capacity and effect of traditional frequency regulation power sources are difficult to meet the requirements of power grid. To solve this problem, a comprehensive control strategy based on the frequency regulation signal optimization of a battery energy storage system which assists the thermal power unit to participate in secondary frequency regulation is proposed. First, a simulation model of energy storage that meets the power grid’s frequency regulation requirements is established. Based on this model, the allocation mode of area control error signal and area frequency regulation requirement signal is analyzed in the complex frequency domain, and the switching criterion for frequency regulation signal is determined by combining the advantages of the two control signals. Then, considering the economy and efficiency of energy storage frequency regulation, the allocation coefficient is optimized by a decomposed multi-objective evolutionary algorithm to reduce the frequency offset and optimize the cost of frequency regulation. Finally, the effectiveness of frequency regulation signal switching criterion and multi-objective evolutionary algorithm in optimizing the energy storage allocation coefficient is verified by step disturbance simulation. The comprehensive control strategy is verified by continuous disturbance simulation, and results show that it can not only reduce the system frequency offset effectively, but also lower the operating cost of energy storage.

To avoid the dynamic problems caused by dynamic and static loads in the operation of a power electronic power system, which affect the system stability, a modeling and analysis method for the voltage power angle dynamic stability is proposed. The continuation method is used to track the equilibrium solution manifold of the power system, and the small disturbance analysis method is used to calculate the voltage power angle state matrix to judge the dynamic stability of voltage power angle. By means of the power system stability mode discrimination method, the correlation between voltage and power angle state variables in the instability state is analyzed, the system instability category is determined, and the construction and analysis of voltage and power angle dynamic stability model is realized. Experimental results show that the load model is directly related to the category of dynamic instability of power system in an electronic environment. The static load model is easy to cause power angle instability, while the dynamic load model is easy to cause voltage instability. The time-domain simulation results are consistent with the discrimination results of state variable participation factor. Through the tests of power angle instability and voltage instability, the generator angle and node voltage are analyzed. It is proved that the proposed method has a good effect in the analysis of voltage and power angle dynamic stability, providing certain reference value for researches in the field of power system engineering.