To study the conducted common-mode (CM) electromagnetic interference (EMI) characteristics of a single-switch forward converter and reduce its CM noise, the analysis of the transmission mechanism of conducted CM noise in the single-switch forward converter is necessary. On this basis, a CM noise transmission path model is established, and a calculation method is proposed to determine the specific external capacitance to reduce the CM noise. In addition, aimed at the defects of the traditional calculation model of induced charge on the secondary side, an improved calculation model is put forward, and simulation results show that the accuracy of the improved model is higher under ideal conditions. Afterwards, the balanced winding method was used to reduce the CM noise flowing through the transformer, and a prototype of single-switch forward converter power supply was used for experimental verification. Results show that the method of calculating the external capacitance was effective, and the accuracy of charge calculated by the improved calculation model was higher when the windings were close or when the number of turns per unit length was relatively large.

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 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.

Aimed at the problems of a traditional LLC resonant converter in wide voltage applications such as a wide switching frequency range and a poor voltage regulation performance, a voltage doubling two-phase parallel resonant converter is proposed. There is a parallel double half-bridge LLC structure on the primary side of this converter, and a bidirectional switch is introduced into the full-bridge rectifier network on its secondary side to form a reconfigurable voltage doubling rectifier network. Fixed frequency control is adopted during operation. The lower half-bridge on the primary side changes the input voltage of the resonant tank by changing the duty cycle, while the upper half-bridge works with a fixed duty cycle. The rectifier network on the secondary side realizes full-bridge and voltage doubling hybrid rectification under the bidirectional switch, which can achieve 4 times of voltage gain. At the same time, this converter has a good soft switching performance, its voltage gain is independent of magnetizing inductance and load, and a larger magnetizing inductance can be selected to reduce the switch-off loss and conduction loss. Finally, the feasibility of the proposed converter was verified by simulation and experimental results.

Phase-shifted full-bridge zero-voltage zero-current switching(ZVZCS) converters are favored in high- power DC conversion applications owing to their advantages such as simple structures and high efficiency. However, high-power phase-shifted full-bridge ZVZCS converters still face problems including difficulty in the current reset and severe duty cycle loss. In response to the above issues, a novel phase-shifted full-bridge ZVZCS converter is put forward, which ensures that it can realize zero-current switching over a wide load range by introducing an auxiliary circuit on the primary side to reset the current to zero before the turn-on of lagging-leg switches. At the same time, it can accelerate the commutation speed on the primary side, reduce the duty cycle loss and realize an optimized design of power supply. Based on the analysis of the circuit structure, working principle and characteristics of the proposed converter, a 1 kW experimental prototype was designed to verify its correctness.

The magnetic integrated coupling technology is introduced into a high-gain converter, and a magnetic integrated Boost converter based on diode clamping is proposed. Through the theoretical analysis of the working principle and performance characteristics of the proposed converter, it is shown that this converter can reduce its volume and inductance current ripple based on the advantages of the original converter, such as a high voltage gain and a simple control strategy. In addition, the voltage gain of the novel converter is further improved by using the switched capacitor technology, the voltage stress of the switch and diode is further reduced, and the energy conversion efficiency of the converter is effectively improved. Finally, the findings were verified by simulation and experimental results.

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.

Single-phase charging systems usually face the problem of secondary power pulsation. To solve this problem, a single-phase electric drive reconstructed onboard charger (EDROC) system with low voltage ripple is proposed, in which a Buck/Boost active filter is placed in parallel on the output side of a traditional single-phase EDROC system to absorb or compensate the secondary power pulsation, thereby obviously reducing the output voltage ripple of the charging system. First, the topology, working principle and secondary power pulsation generation mechanism of the single-phase EDROC system are analyzed. Second, a single-phase EDROC system with low voltage ripple is put forward by combing the Buck/Boost active filter. Meanwhile, the topology, working principle, and selection of inductors and capacitors of the Buck/Boost active filter are analyzed in detail. Third, a control strategy for the proposed EDROC system is designed. Finally, a 200 W experimental prototype was designed, and experimental results verified the feasibility of the proposed charger.

For a hybrid cascade H-bridge inverter with a DC-side voltage ratio of 1:1:2, if the hybrid carrier disp-osition modulation strategy is adopted, the problem of output power imbalance in the low-voltage unit will occur al-though there is no current backflow phenomenon and the harmonic performance of output voltage is good. To solve this problem, the power imbalance is analyzed at first. Then, an improved hybrid modulation strategy is proposed, under which the high-voltage unit performs step wave modulation and the low-voltage unit performs PWM, and two low-voltage units adopt different processing methods for the modulation wave. The good harmonic performance of output voltage is kept, the number of triangular carriers is reduced, and the control process is simplified, with a frequency doubling effect. Third, this strategy is optimized, and the switching signal of low-voltage unit is logically calculated, which can solve the power imbalance problem of low-voltage unit in two carrier cycles. Finally, the feasibility was proved by simulation and experimental results.

Aimed at the problems of current unobservable area and zero drift error in the traditional space vector pulse width modulation with single-sensor phase current reconstruction method, an error self-correction complementary non-zero vector pulse width modulation method is proposed. Through the analysis of the DC bus sample principle, the minimum sample time is defined, the complementary non-zero vector is used to replace the zero voltage vector, and the current sampling window is extended, thus eliminating the sector boundary unobservable area. At the same time, the generation mechanism of error amplification effect is revealed, and the zero drift is detected and self-corrected by means of double-sampling complementary non-zero vector, which realizes the compensation for current zero drift reconstruction. Experimental results show that the reconstruction error of the proposed method was lower than 1.26%, and the phase current THD was lower than 6.15%.