To solve the device voltage endurance, voltage change rate and series-parallel problems of traditional two-level dual active bridge (DAB) converters under high voltage and high power, the active neutral point clamped (ANPC) topology is integrated into the DAB converter to form a multilevel DC-DC converter. This converter offers four control degrees of freedom, overcoming the shortcomings of traditional topologies and the limitations of modulation methods. It is suitable for medium to high voltage applications with a wide voltage transfer range. To enhance the efficiency of the multilevel converter, a minimal peak current multi-phase shift (MPS) modulation strategy with four degrees of freedom is proposed. Initially, the operational principles of the converter are analyzed, and the peak inductor current for each operational mode is derived. Subsequently, a power transfer model is established, leading to a multi-degree-of-freedom analytical solution. The minimum current stress is optimized using the KKT (Karush-Kuhn-Tucker) algorithm. Finally, an experimental platform is constructed for testing, comparing the optimization effects of different modulation strategies under various operating conditions to validate the effectiveness of the proposed strategy.

In order to improve the performance of DC-DC converter for photovoltaic power generation systems, a Boost converter topology that introduces diode and capacitor units is proposed, which can achieve high voltage gain; at the same time, the two inductors in the new topology are integrated by using the decoupling magnetic integration theory, which forms a new type of integrated inductors based on the EE core to reduce the size of the magnetic components. The feasibility of the topology and the new magnetic parts design proposed is verified by simulation analysis, and finally an experimental prototype is built to verify the effectiveness of the proposed high-performance DC-DC converter.

The traditional electromagnetic bearing power amplifier usually adopts the hard switching circuit topology with simple circuit structure and high practicability, but it has the problems of large switching loss and easy overheating damage of the switch tube, which limits the use scenarios at higher operating frequencies, and will produce serious electromagnetic noise at higher bus voltage and higher switching frequency. Aiming at the defects of hard switching power amplifier in operation, a soft switching power amplifier suitable for electromagnetic bearing system is proposed, and the working principle of the circuit topology is analyzed in detail. Through the comparative analysis of simulation and experiment, the results show that the topology can reduce the switching loss, reduce the electromagnetic noise in the high frequency working state and improve the working efficiency of the system under the condition of meeting the basic performance requirements of the power amplifier.

To solve the problems of current zero-crossing distortion and midpoint voltage offset in three-phase four-wire Vienna rectifiers, two control methods namely the current zero-crossing distortion suppression and active control of midpoint voltage are proposed. First, for the three-phase four-wire Vienna rectifier, the topology structure and operating principle are analyzed, the causes of current zero-crossing distortion are explained in combination with the commutation path, and a control method to suppress current zero crossing distortion is proposed. Then, the variation of DC-side capacitor voltage is analyzed, and a midpoint voltage active control method based on zero-sequence current injection is given. Finally, experiments are performed to verify the effectiveness of the proposed control method. The experimental results show that with the proposed control method, the Vienna rectifier can eliminate current zero-crossing distortion and achieve midpoint potential balance.

Aiming at the problem that the traditional finite control set-model predictive control (FCS-MPC) has poor control effect at low switching frequency and it is difficult to eliminate current distortion, suppress current ripple and adjust neutral point voltage balance when realizing multi-objective control, a model predictive control strategy based on virtual voltage vectors for Vienna rectifiers is proposed. By constructing 8 new virtual voltage vectors to expand the control set, multiple basic vectors are output in one control cycle, which significantly improves the current control accuracy. By analyzing the causes of current distortion, the use of vectors that cause current distortion is restricted to eliminate current distortion. In addition, the virtual vectors and the basic vectors are used to adjust the neutral point potential together without weight factor. Finally, the experimental verification is carried out from multiple dimensions of steady state, dynamic state, neutral point potential balance control and so on. The results show that the proposed method has good steady state and dynamic performance.

Frequency jitter technology is commonly used to mitigate electromagnetic compatibility issues in LLC converters. However, the traditional frequency jitter technology has certain limitations in the processing of load characteristics when adapting to frequency changes, which leads to the reduction of the working efficiency of LLC converters, especially in single-phase hybrid inverters, where the fixed frequency disturbance makes the above problems more significant. In view of this situation, a frequency jitter control method based on the load power characteristics is proposed, which aims to improve the efficiency of LLC converters, and the key is to achieve the matching of “source impedance” and “load impedance”. First, the characteristics of “source” and “load” in single-phase hybrid inverter are analyzed, and the characteristics of “source impedance” and “load impedance” are deeply explored. Then, combining with the impedance characteristics of LLC converter at different frequencies, this frequency jitter control method based on load power characteristics is proposed. Finally, the effectiveness of the proposed method is verified by experiments. Experimental results show that the proposed method can effectively improve the working efficiency of LLC converter.

The large-scale application of megawatt-level off-board chargers faces problems such as high energy consumption, low dynamic accuracy, and lack of multi-module collaborative detection capabilities existing in traditional detection methods. A model prediction test method integrating model-in-the-loop (MIL) simulation and orthogonally optimized long short-term memory network (Orthogonal-LSTM) is proposed, aiming to break through the power bottleneck of test platform and improve detection adaptability under complex working conditions. By constructing a virtual charger model driven by model predictive control (MPC), the dynamic characteristics of the charger under test are simulated. However, in the face of the superposition of charging modules and the increase in power, the error between the model and the actual test results increases. To solve this problem, the LSTM model parameters are optimized in combination with the orthogonal test method to achieve the error prediction-compensation of the model. Experimental results show that the proposed method provides a high-precision, low-energy-consumption and scalable detection solution for megawatt-class chargers with a single-unit multi-module structure, and has great value for engineering promotion.

The bidirectional switch-based current source converter (BDS-CSC) has broad application prospects for high-frequency bidirectional operation (rectification/inversion), which meets the requirements for reliable, efficient, and high-power-density three-phase AC-DC converter in systems such as electrified transportation and energy storage systems. High-quality operation of the BDS-CSC relies on reliable and efficient commutation and control, both of which require AC side phase voltage information. Based on this analysis, the relationship among active current vectors, the DC-link voltage and the phase voltage are firstly analyzed. a phase voltage reconstruction method is proposed that utilizes vector decomposition characteristics. Then, to suppress the effect of blind zone caused by low modulation ratio and sector boundary regions, a complementary vector strategy based on vector injection is further proposed to achieve high-quality-reconstruction. Finally, the effectiveness of the proposed method is validated on a 3 kW current source inverter.

In conventional cascaded H-bridge converters, each unit contains large-value capacitors and voltage sensors, which increases system size and cost. The operation of these converters is examined, with a comprehensive analysis conducted on the capacitor charge/discharge cycle and its self-balancing voltage control in the level-doubling network. A single DC-side transducer control strategy is introduced, which uses a single transducer to monitor the voltage of the first H-bridge cell and automatically balances the voltage of the subsequent cells to half the capacitor voltage of the previous cell. This strategy reduces the number of voltage sensors, simplifies the control, and increases the power density of the system. The effectiveness of this approach is demonstrated through simulation and experimentation.

During the fault recovery phase of a direct-drive wind turbine, the delayed withdrawal of reactive current leads to transient overvoltage of the turbine after the fault recovery, which affects the safe and stable operation of the grid-connected system. In order to suppress the transient overvoltage, an electromagnetic transient model for the direct-drive wind turbine is established, the mechanism of transient overvoltage occurrence is quantitatively analyzed, and a three-stage coordinated control strategy is proposed. The first stage optimizes the active/reactive current during fault ride-through to reduce the active/reactive power fluctuations before and after fault recovery; the second stage introduces the rate of change of terminal voltage to assist in accurately identifying the fault clearance and accelerating the reactive current withdrawal speed. The third stage controls the wind turbine to proportionally absorb reactive power, eliminating the accumulated reactive power surplus. Furthermore, a simulation platform based on MATLAB/Simulink and Speedgoat is built to verify the suppression effect of the proposed strategy on the transient overvoltage after fault recovery. Simulation and experimental results show that, compared with traditional control strategies, this strategy reduces transient overvoltage by 9.3% without sacrificing the reactive power support capability of the wind turbine.