To improve the pulse waveform quality of high-power microwave sources, a pulsed high-voltage modulator capable of delivering 41.2 kV, 44 A required by a klystron in a high-power microwave system was designed. The modulator with a combined architecture consisting of a Marx module and a pulse transformer achieves a high step-up ratio of approximately 100 times. Especially the dual secondary winding in the pulse transformer easily realizes the high-voltage isolation of the filament power supply. Conceptual design and functional verification are achieved through simulation and experimental research. The modulator is tested to be able to generate a high-voltage pulse of 41.2 kV with a droop of about 4.9% on a 936 Ω normally-operating klystron load at a charging voltage of 260 V. Measured pulse rise-time, fall-time and overshoot are about 800 ns, 900 ns and 3.9%, respectively.

Aiming at eliminating the bulky and expensive line-frequency phase-shifting transformer at the input of the traditional medium/high voltage converter for AC motor drives, a new unidirectional power flow mining converter topology for open-end winding motors is proposed. The rectifier stage of the proposed converter topology adopts three single-phase diode rectifiers + Boost converter circuit structure without line-frequency transformer isolation, which is characterized by high input power factor, low input current harmonics and low switching device voltage stress. The inverter stage is connected to the AC motor by adopting stator open-winding connection for the isolation between phases. On the basis of the proposed topology, further investigates a low common-mode voltage space vector pulse width modulation (SVPWM) strategy, which achieves unity power factor operation of the system, the suppression of the common mode voltage in the rectifier stage, and the elimination of the zero sequence voltage in the open winding motor.

Efficient diagnosis of IGBT open-circuit faults in grid-tied inverters is helpful for quickly detecting the fault and ensuring the stable operation of the grid-tied inverter system and the safety of equipment. The existing IGBT open-circuit fault diagnosis methods have problems such as difficult feature extraction and poor diagnosis accuracy. On this basis, a method is proposed for IGBT open-circuit fault diagnosis of grid-tied inverter based on modified random forest. First, the wavelet packet energy of each frequency band of three-phase current signal is extracted by maximum overlapping discrete wavelet (MODWT) decomposition as the characteristic values for IGBT open-circuit fault diagnosis; Then, the modified random forest method is used to identify different types of faults; Finally, the various IGBT open-circuit faults of grid-tied inverters are diagnosed. The experimental results show that the proposed method has higher diagnosis accuracy and is suitable for IGBT open-circuit fault diagnosis of grid-tied inverters compared with the traditional diagnosis methods such as back propagation (BP) neural network and support vector machine (SVM).

Power electronic transformer (PET) insulation system continue to deteriorate in high frequency, high voltage, short rise time pulse electrical stress and high temperature and other harsh environments; insulation discharge and breakdown risks are increasing significantly. In order to study the effect of high temperature thermal aging for PET on insulation deterioration under real operating conditions, the typical insulation polyimide (PI) of PET was aged at 250 ℃ for 3, 6, 9, 12 days, and then 20 kHz, 4 kV, 300 ns pulsed voltage was used to simulate PET operating conditions. The partial discharge and breakdown voltage of insulation were tested, and time-resolved partial discharge spectrum (TRPD), discharge times, average discharge amplitude, and maximum discharge amplitude were used to characterize the degree of insulation deterioration. The results show that after aging, the TRPD pattern of PI films changes from single peak to multiple peaks, showing a phenomenon of clustering. At the same time, with the increase of aging time, the number of partial discharges, average discharge amplitude and maximum discharge amplitude increase by 47.3%, 61.1% and 41.9%, respectively, and the degree of insulation deterioration was significantly deepened. The breakdown voltage distribution of PI film conforms to Weibull distribution and decreases with aging time, from the initial 4 667 V to 4 457 V, a decrease of 4.5%. Therefore, the effect of aging time on the deterioration of PET insulation is obtained, which has certain guiding significance for the reliability analysis and optimal design of PET insulation.

The difference in characteristic parameters of an IGBT module is an important factor leading to the difference in control circuit parameters, which has a significant impact on the dynamic current-sharing characteristics of IGBT parallel applications. When the device parameters cannot be changed, some drive compensation control can make up for the influence of device differences on dynamic current-sharing, and the key to this method is accurately identifying the characteristic parameters of the IGBT module. The influence of parameter (e.g., gate resistance) identification accuracy differences on the dynamic current-sharing characteristics is studied when a synchronous pulse-asynchronous drive method is used. The correlation characteristics of characteristic parameters of IGBT devices are studied, and the characteristic models of each parameter and influencing variables are constructed. The working model of PSpice device parallel switch is established, and the variation curve of IGBT device parameters and influence factors is fitted by combining with the device manual data comparison and multi-working condition test parameter correction. Through the parallel switching characteristic experiments on two groups of modules 1 200 V/200 A and 1 700 V/300 A IGBT, the judgment on the influence of the difference in IGBT characteristic parameters on parallel current-sharing was verified. Finally, the influence of the difference in characteristic parameter identification accuracy on dynamic current-sharing characteristics was summarized.

To solve the problem of poor transient response of a traditional capacitor-less low dropout linear regulator (LDO), a transient enhanced capacitor-less LDO with low power consumption was proposed, which used a push-pull Class AB operational amplifier as an error amplifier to improve the charging and discharging rate of current at the gate of a power tube. In addition, a novel type of transient enhanced circuit was designed in the LDO to detect the fluctuation of load current under the premise of low power consumption and provide extra charging and discharging current for the gate of the power tube, so as to reduce the transient fluctuation of output voltage. Based on the 0.18 μm CMOS process, the circuit, layout and simulation of the LDO were completed. Simulation results show that the output voltage of LDO was 1.5 V in the input voltage range of 1.6–4 V. Under the rated input voltage, the static current was 9.4 μA, the load current varied in the range of 0–50 mA, the output overshoot voltage and undershoot voltage of the LDO were 56 mV and 55 mV, respectively, and the stable time was within 1.7 μs. In the full-load range of 0–50 mA, the output overshoot voltage and undershoot voltage of the LDO were reduced, and the transient performance was greatly improved. As a result, the designed LDO can meet the application requirements.

A wide-voltage hybrid bridge bidirectional DC-DC converter is proposed. Compared with the CLLC converter, the proposed converter adds linear bridge arms on both sides, so as to improve its gain range and reduce the switching frequency and feedback current. A dynamic control method of pulse-shift modulation is put forward, which can effectively suppress the overvoltage at the inductor terminal in the energy transmission process. In addition, this method also has a function of control initialization. In all of its operating modes, the converter can realize soft switching. A prototype of a bidirectional DC-DC converter with a wide-voltage hybrid bridge was designed, and the correctness and effectiveness of the proposed converter topology and control strategy were verified by experimental results.

To achieve efficient and reliable interconnection in bipolar DC distribution systems, a novel fault tolerant quad active bridge (FT-QAB) converter featuring low power conversion stages and its operation control strategy are proposed. First, the operation control strategy for the FT-QAB under normal operation conditions and the fault reconfiguration operation strategy under pole-to-ground fault (PTGF) conditions on the high- and low-voltage side are presented. Second, the power transmission characteristics and zero-voltage switching operation conditions of the FT-QAB converter during normal and fault-tolerant operations are analyzed. In addition, the flow chart of parameter design and control block diagram of the converter are also given. Third, by comparing the FT-QAB topology with the existing typical converter topologies in the case of bipolar system interconnection, the advantages of the FT-QAB converter in terms of efficiency and fault-tolerant operation capability are clarified, which are realized by reducing the power conversion stages. Finally, the effectiveness of the proposed FT-QAB converter topology and its effectiveness innormal and fault-tolerant operation modes were validated by experimental results.

HVDC transmission systems based on modular multilevel converters (MMCs) face many problems, e.g., the DC fault current cannot be cleared by a half-bridge submodule topology, and the submodule capacitor voltage sequencing requires too much computation and high real-time performance of sensors. Aimed at these problems, a modified full-bridge MMC with fault current self-clearing and module capacitor voltage self-balancing capabilities is proposed in this paper. By accessing a branch consisting of two IGBTs in reverse series on the same side of the adjacent full-bridge submodule, a path is provided for directly connecting the capacitors of adjacent submodules in parallel. In addition, its operating modes in different states are analyzed, and the corresponding dynamic distribution voltage balancing control strategy is designed. By adding the parallel operation state of capacitors, the modified full-bridge MMC can realize voltage self-balancing between the capacitors of different submodules on the same bridge arm without monitoring the submodule capacitor voltage, thus effectively reducing the complexity and calculation amount of the controller. Meanwhile, the parallel input of capacitors can also reduce the output from individual capacitors, thereby reducing the capacitor voltage fluctuations. Finally, the simulation results in RT-LAB show that the DC fault current self-clearing and submodule capacitor voltage self-balancing can be realized simultaneously by using the proposed voltage balancing control strategy.

A novel active-neutral-point-clamped seven-level inverter based on the principle of switched-capacitor is proposed. The operation principle for the proposed topology and the mechanism of self-balancing for capacitors are discussed in detail. Through a comparison with other topologies, the advantages of the proposed topology such as reduced components, higher Boost capability, lower overall voltage stress and self-balancing capability of capacitors are also demonstrated, showing its suitability for distributed generation, electric vehicles and other applications. Finally, the Boost capability of the topology and the self-balancing capability of capacitors were verified by simulation and experimental results.