The loss and volume of magnetic components in resonant DC-DC converters account for nearly 50%, which seriously restricts the improvement of power density in high-frequency converters. The magnetic integration technology can reduce the loss and volume of magnetic components, so it has been widely studied and applied. However, the traditional magnetic loss measurement methods cannot accurately and conveniently measure and evaluate the magnetic core loss of magnetic components in integrated resonant inductors and transformers, causing difficulties in the optimization of magnetic core loss. In this paper, the magnetic flux distribution in integrated magnetic components is analyzed, and a method is proposed to obtain the magnetic core loss of integrated magnetic components by testing the difference in losses before and after adding auxiliary integrated magnetic components in parallel in a resonant topology. At the same time, a parameter design method for auxiliary magnetic components is also put forward. This method can accurately and conveniently measure the magnetic core loss of integrated magnetic components under actual circuit conditions. Simulation and experimental results verified the effectiveness of the proposed magnetic loss measurement method for integrated magnetic components.

Due to the lower and significantly fluctuating voltage of micro-source modules (e.g., photovoltaic and fuel cells) in DC microgrids, there is a need for a DC-DC converter with a high gain and a high efficiency to serve as an interface circuit. Therefore, a novel active switched capacitor DC-DC converter based on an isolated Sepic topology is proposed. This converter reduces voltage spikes on the switch tube caused by leakage inductance through a clamp circuit and employs multiple boost units to achieve a high voltage gain. In addition, it also has advantages such as electrical isolation, low stress on the main switch tube and passive clamping. The operation modes and boosting mechanism of the proposed converter are studied, the component stresses are analyzed, and the efficiency of this converter is derived. Finally, a 200 W prototype was constructed in the laboratory to verify its performance.

In the wide conversion range applications of traditional DC-DC converters, there is an urgent need for higher voltage gain, efficiency and reliability. A DC-DC converter based on a switching voltage doubling clamping unit is proposed and analyzed. In this topology, the switch voltage stress is low and the inherent duty cycle is small, which helps reduce switch losses and improve the converter efficiency. All the switch devices achieve voltage clamping, thus reducing the voltage spikes generated during switch transitions. Compared with coupled windings, the single-input inductor reduces the size of the converter and the input current ripple. The shared grounding of input and output terminals ensures the output reliability. Through a comparison with other typical converters and performance analysis with a combination of a 200 W experimental prototype, the feasibility and effectiveness of the DC-DC converter based on the switching voltage doubling clamping unit were validated.

Aimed at the problems in traditional quasi-Y-source inverters such as high busbar voltage peaks and high device voltage stress, the circuit topology of an active clamp-type Y-source three-phase inverter is proposed. By adding power switch tube, capacitor and diode to form a clamping circuit, the voltage gain is improved, the voltage stress of the power device is reduced, and the continuous characteristic of input current is maintained. A third-order harmonic injection boost modulation strategy is adopted to improve the utilization rate of DC-link voltage. The working principle for this inverter is analyzed in detail, and the formulas for its voltage gain and the device voltage stress are deduced. In addition, its performance is compared with those of other inverters, and its advantage is theoretically demonstrated. Finally, a simulation model and an experimental prototype were built for verification, and both the simulation and experimental results verified the feasibility of the proposed inverter.

To address the issue of sub-module number errorscaused by harmonics based on nearest level modulation (NLM) when the voltage level is increasing in a modular multilevel matrix converter (M3C), a mathematical model for M3C was established. The operating principle for M3C based on NLM was analyzed, and an optimized sampling NLM strategy was proposed. Asimulation model of M3C consisting of 20 sub-modules was constructed based on MATLAB/Simulink, and a low-power experimental prototype of M3C was also built. Results verified the feasibility and effectiveness of the proposed method for harmonic suppression.

The hybrid cascaded nine-level inverter can output more levels using fewer H-bridge units. Under the mixed carrier cascaded modulation strategy, the quality of output voltage waveform is higher, but the output power is not balanced, which will lead to uneven heating and shorten the service life of the equipment. Under the mixed carrier phase-shift modulation strategy, the power self-balancing can be completed, but the power balancing time is too long. Aimed at these problems, a novel hybrid modulation strategy is proposed, where the high-voltage unit is modulated by a stepped wave and voltage constraints are added, and the carrier wave of the low-voltage unit is reconstructed. Compared with the traditional modulation strategy, this strategy can achieve the power balance of three units in the full modulation regime after adding voltage constraints, and reduce the time required for the power balance of the low-voltage unit. Simulation and experimental results verified the feasibility of the proposed modulation strategy.

As an excellent front-end rectifier for power supply, the VIENNA rectifier is widely used in medium-to-high voltage and high-power scenarios such as electric vehicle charging piles and wind power generation systems. However, due to the unidirectional flow of its topological energy, there may be current zero-crossing distortion under traditional control methods, resulting in weak reactive power compensation capability. Therefore, based on the analysis of current zero-crossing distortion, a control scheme integrating zero-crossing distortion suppression and reactive power compensation was adopted, with a focus on analyzing the constraints faced by the VIENNA rectifier when providing maximum reactive power compensation capability, as well as the capability of the VIENNA rectifier to provide additional reactive power compensation when delivering different active power to load. Simulation results verify that the adopted control scheme can effectively suppress the zero-crossing distortion of input current of the VIENNA rectifier and thus enhance its reactive power compensation capability.

Cascaded H-bridge photovoltaic (PV) inverters are susceptible to problems such as shading of PV modules and aging of devices. As a result, an imbalance in the output power between H-bridge units will appear, and over-modulation may occur in some units due to excessive power, resulting in a poor performance of grid-connected current and triggering the instability of the inverter system as a whole. Aimed at this problem, a segmented improved control strategy for enhancing the operating range of the PV inverter is proposed. This method compensates the third-order harmonic and multiple harmonics for some of the overmodulated units. For the severely overmodulated units, their output power are reduced at first, and then the multiple harmonics are compensated. This strategy expands the operating range of the inverter, and it ensures that no overmodulation occurs in all the units under severe power imbalance. In addition, the waveform of grid-connected current is good. The theoretical analysis and simulation results prove the feasibility and effectiveness of the novel control strategy.

Aimed at the problem that the charging and discharging state switching frequency is too high and the life is reduced during the process of wind power fluctuation suppression by energy storage, a fluctuation suppression control strategy based on the hybrid energy storage of dual battery packs is proposed. First, the adaptive moving average filter method is used to decompose the wind power to obtain the grid-connected power. Second, the wavelet packet decomposition of the energy storage target power is carried out to obtain the hybrid energy storage reference power, and the fuzzy control is used to optimize the energy storage target power, so as to prevent the energy storage from overcharge or overdischarge and make the energy storage run at the optimal depth of discharge (DOD). To make the battery run at the optimal DOD while reducing the switching times of working states, a circuit structure of dual battery packs running separately for charging and discharging tasks is adopted, and an adaptive power complementary control strategy is designed to realize power scheduling between battery packs. In addition, a power allocation strategy is also introduced to ensure the state-of-charge balance among each unit in the same battery pack. Finally, the control strategy is simulated and analyzed, and the rainflow counting method is used to evaluate the life of energy storage. Results show that the proposed control strategy can reduce the charging and discharging times of energy storage and prolong its life.

To reduce the carbon emissions of a microgrid system under operation and with the consideration of influences of uncertainties in renewable energy output on the system’s scheduling results, a two-layer optimal low-carbon economic scheduling model for microgrids containing liquid carbon dioxide (CO₂) energy storage is proposed. This model introduces a tiered carbon trading mechanism into the operation and scheduling stage of the system, so as to reduce carbon emissions of the microgrid system. Under a carbon trading scenario, the carbon emissions and scheduling cost data generated by two models of liquid CO₂ energy storage and conventional energy storage during the operation of microgrids are compared and analyzed, and results verify that the proposed model can effectively reduce carbon emissions and improve the economic efficiency after the introduction of liquid CO₂ energy storage.