Aimed at the problem that the performance of dielectric barrier discharge (DBD) load cannot be fully utilized by the common load resonant-type power supply with continuous waveform and the deficiency that the topologies of existing pulsed power supplies are complicated, a power supply with unipolar forward pulse is proposed in this paper, which consists of one power switch, two diodes and one coupled inductor. Through the analysis of its working modes, it is shown that this power supply can provide a fast-rising pulse voltage for DBD load. In addition, the power switch operates in a soft-switching state. Simulation and experimental results verified the feasibility of the proposed power supply, indicating that it can provide certain reference for the upgrade of the existing power supplies for DBD load.

The converter with constant-power control in a flexible DC distribution system has characteristics of constant-power load, which will reduce the system damping and adversely affect the system stability. To address this problem, a superconducting magnetic energy storage (SMES) device is introduced to improve the system stability. A feed-back control model of the flexible DC distribution system is derived, and the effect of constant-power load characteris-tics of the converter on system stability is investigated by frequency-domain analysis. Combined with a mathematical model and frequency-domain analysis, it is also pointed out that the SMES device can improve the system stability by introducing positive damping to grid and increasing the phase margin of the system's open-loop transfer function at the shear frequency. To prevent over-high voltage at both ends of the superconducting magnet, the DC/DC converter which connects the SMES device with the DC distribution network needs to have certain voltage regulation performance. Therefore, the SMES device with a modular multilevel DC/DC converter (DC-MMC) is studied, which can adjust the number of sub-modules flexibly to set the voltage ratio of the converter. Moreover, the DC-MMC can control the voltage at both ends of the superconducting magnet while realizing a bidirectional flow of energy in the converter, thus protect-ing storage device. The feasibility and effectiveness of the SMES device with DC-MMC in improving the stability of flex-ible DC distribution system is verified by time-domain simula-tion waveforms.

The hybrid energy storage system can effectively alleviate the frequency instability caused by the strong fluctuation and randomness of wind power output. In this paper, a hybrid energy storage system composed of batteries and super capacitors is taken as the research object, and a hybrid energy storage capacity allocation method is proposed. First, adaptive wavelet transform is adopted to perform a primary distribution of the wind power output, and the grid-connected power and energy storage power satisfying the requirements are obtained. Second, HHT transform is used to decompose the energy storage power, and a series of fluctuating power components and the instantaneous frequency of each component are obtained. Third, the cutoff frequency is determined according to the instantaneous frequency, the power components with a frequency higher than the cutoff frequency are allocated to super capacitors, and the rest are allocated to batteries. Finally, the rated capacity and rated power of the energy storage system are configured according to the energy storage power of batteries and super capacitors, respectively. Simulation results show that adaptive wavelet transform and HHT transform can effectively decompose the wind power output, thus realizing the stabilization of wind power output, as well as the capacity and power allocation of hybrid energy storage system.

Due to the duty cycle constraint on the traditional Boost converter, its applications to high-voltage-gain power supply are limited to certain degree. In this paper, a DC-DC converter with high voltage gain based on an isolated Boost converter and Cockcroft-Walton voltage multiplier cell (VMC) is studied, and its working principle and characteristics are analyzed. This converter achieves a conversion with an ultra-high step-up ratio by integrating the isolated Boost converter with the VMC. Compared with the traditional Boost converter, this topology has a high voltage gain in a low duty cycle, a low voltage stress of active switching device, and a simple control circuit with one single switch. Finally, a 35 W prototype with an efficiency of 89.5% was built to achieve a high step-up conversion from 24 V to 1 000 V, and the theoretical analysis results was verified by experimental results.

A shutdown strategy for a low-cost hybrid DC converter based on diode rectifier is studied. The shut-down process of the auxiliary converter is divided into an energy feedback stage and an energy dissipation stage. At the energy feedback stage, part of the energy stored in the capacitors of sub-modules is fed back to grid through the DC transmission line under the active control. At the energy dissipation stage, the resonant capacitor and the capacitors of sub-modules are discharged in sequence through a discharging resistor. The calculation methods for the discharging cur-rent, capacitance voltage, and discharging time are derived, and the design method for the discharging resistor is also given. The capacitors of the auxiliary converter can be discharged quickly and efficiently under the proposed shutdown strategy without a high-voltage and large-capacity discharging resistor, which is conducive to the realization in engineer-ing projects. Finally, a simulation model is constructed in Matlab/Simulink, and the validity of the shutdown strategy is verified by simulation results.

Aimed at the voltage distortion and current distortion of power grid with pulse load, a three-level unified power quality conditioner(UPQC) with supercapacitor energy storage is designed. A method based on artificial neural network is proposed to control the series and shunt compensation units, and a method based on double closed-loop PI control is used to control the supercapacitor energy storage unit. The series compensation unit compensates voltage to maintain the stability of load voltage and ensure the power demand of load, while the shunt compensation unit compensates current to maintain the stability of supply current and avoid the continuous and large impact on power grid. The supercapacitor energy storage unit charges and discharges on the DC side to maintain a constant voltage on the DC side and ensure the normal operation on the series and shunt sides. The proposed method eliminates the complicated coordinate transformation process and avoids the phase lag caused by multiple filters. Simulation experiment results show that the proposed topology and control strategy are helpful for improving the power quality of power grid with pulse load.

Aimed at the problem of low efficiency of a dual active bridge (DAB) converter in the wide voltage range of single phase shift modulation strategy, a one-sided asymmetric duty modulation strategy is proposed in this paper, which significantly improves the efficiency of DAB converter, especially in the case of light load. First, the principle of one-sided asymmetric duty modulation scheme is described, and two operation modes are obtained according to the relationship of control degrees of freedom. Second, based on the time-domain analysis, the steady-state characteristics in the two operation modes are derived, including inductance current and transmission power. Third, in order to find the optimal combination of control degrees of freedom, the peak-to-peak value of inductance current is selected as the optimization objective, and the optimal one-sided asymmetric duty modulation strategy is obtained by applying the KKT condition. Finally, an experimental platform for DAB converter based on SiC device was built, and experimental results verified the effectiveness of the proposed one-sided asymmetric duty modulation strategy.

Aimed at the low conversion efficiency and all the load power that needs to be processed by converters at different stages in the two-stage architecture of a DC transformer cascaded PWM converter, a quasi single-stage DC-DC conversion method with partial power active regulation based on a split-sigma structure is proposed. By splitting the output port of the DC transformer into two ports, the power of one port is directly transmitted to load without being processed by the back-stage PWM converter, thus realizing the quasi single-stage power conversion equivalently. In addition, the power capacity and loss of the PWM converter are effectively reduced, and the system efficiency is improved. The principle and circuit implementation method for the split-sigma structure are analyzed in detail, and the principle and characteristics of system output voltage regulation are also studied. One of the circuits is taken as an example, and its working principle, voltage regulation characteristics and design method for key parameters are analyzed. Finally, experimental results verified the effectiveness and correctness of the proposed scheme.

For a traditional Boost power factor correction (PFC) converter, its output voltage must be greater than its input voltage, which limits its applications in light emitting diode (LED) drivers to a certain degree. Meanwhile, due to the existence of a rectifier bridge at the input end of the traditional LED driver, the improvement of its efficiency is also confined. In this paper, a bridgeless Boost LED driver based on passive current balancing is proposed, which is based on the topology of a resonant Boost PFC converter. With the introduction of a resonant capacitive current-balancing network, the output current of each LED string can be balanced. In addition, the elimination of the rectifier bridge further improves the system efficiency. Finally, a 140 W prototype with a peak efficiency of 93.64% was built, and experimental results verified the correctness and feasibility of theoretical analysis.

Aimed at the poor voltage regulation performance and large circulating current of the traditional frequency-controlled LLC resonant converter in wide voltage applications, a six-switch dual-resonant LLC converter is designed, which is a hybrid combination of two full-bridge LLC resonant converters sharing one bridge arm. Compared with the traditional frequency control, fixed-frequency phase-shift control is employed in this converter to adjust the output voltage and reduce the switching frequency range. According to different connection modes of two transformers, the converter has two topological forms. When the two transformers are connected in series in the forward polarity, the converter's gain range is 0-1, which can achieve an ultra-wide output voltage range. When the two transformers are connected in series in the reverse polarity, the gain range is 1-2, and the circulating current loss during the working process is small. Under the two topological forms, the ZVS turn-ON of the primary switch tube and ZCS turn-OFF of the secondary diodes can be achieved, respectively. Finally, the validity of the research in this paper was verified by Simulink simulations and experimental results.