Hybrid active neutral-point-clamped (HANPC) converters are receiving more attentions owing to considerable cost-effectiveness and high efficiency. However, when open-circuit fault occurs in multiple switches, the existing fault-tolerant schemes cannot support the HANPC converter to operate at rated output voltage and satisfactory neutral-point voltage balancing. To address this issue, an advanced fault-tolerant HANPC (FT-HANPC) converter is proposed, which is equipped with shared fault management unit (SFMU) and voltage ripple suppression unit (VRSU). The proposed discontinuous space vector modulation strategy enables SFMU to take over the multiple faulty switches with minimal redundant active switches. Moreover, the VRSU with proposed control strategy is activated to effectively regulate neutral-point voltage for full power factor range under fault condition. The operation principle and fault-tolerant control of proposed topology are elaborated, respectively. Experimental results are presented to validate the effectiveness of the proposed topology.

The flexible traction power supply system (FTPSS) based on the railway power conditioner (RPC), photovoltaic (PV), and energy storage system (ESS) can realize energy exchange between substations while providing an opportunity for efficient use of PV and regenerative braking energy (RBE). However, the power of PV and traction loads (TL) has multi-directional, large amplitude, and high-frequency fluctuation characteristics in the FTPSS. Thus, realizing efficient and high-quality dispatch for FTPSS has become a pressing challenge under the real-time energy management requirements. To this end, a real-time hierarchical energy management strategy (EMS) for FTPSS to improve the PV/RBE utilization and power supply quality is designed. First, a cooperative mechanism for energy hierarchical management is developed. That is, the multi-station level carries out cluster management in 10s, and the substation level carries out autonomy management in 1s. Secondly, a unified active-reactive power flow model for FTPSS is established at the multi-station cluster management level, determining the optimal power flow for the FTPSS and the line power losses. Meanwhile, a combined rule-based and optimization EMS is proposed at the substation autonomy management level, which combines the advantages of high timeliness of rule-based EMS with the multi-objective synchronization gain of optimization EMS. Finally, the performance of the proposed strategy is verified on the MATLAB simulation platform and RT-LAB semi-physical platform based on measured data.

The problem of grounding fault arc suppression is the key to the safe operation of distribution network, but the existing voltage and current arc suppression methods are difficult to effectively deal with different grounding faults. This paper proposes an adaptive grounding fault regulation method considering the influence of line impedance. Firstly, the variation of residual voltage and residual current with grounding resistance and fault distance is deduced, and the mechanism of voltage arc suppression affected by line impedance is verified. Secondly, the difference of line characteristic parameters between complete arc suppression and incomplete arc suppression in distribution network is compared. Further, the deviation between load current and line current of fault phase is converted into residual voltage compensation of fault point, then the influence of the line impedance voltage drop on the arc suppression can be offset. This method can adapt to the different grounding fault condition and accurately suppress the voltage of fault point to zero. The analysis of the transfer function and Bode diagram of the control system proves that the control method has strong stability and adaptability to line parameter changes. Finally, the reliability and feasibility of the proposed arc suppression control strategy are verified by MATLAB/Simulink simulation.

Multi-energy complementary DC micro-grid is of great significance to realize sustainable energy development. Based on the typical DC micro-grid with various energy forms including wind, solar, gas and battery, this paper aims at the problem that the Micro-Turbine(MT) has large inertia and cannot respond quickly to load changes, and proposes a control method that inertia complements of the MT and battery, which makes up for the lack of dynamic characteristics of MT by using the fast dynamic response of battery. Make full use of the power adjustment function of the MT, improve the utilization rate of new energy, reduce the system cost and maintain the stable operation of the DC micro-grid system. Finally, the effectiveness and correctness of the proposed control strategy are verified by simulation.

Under weak grid conditions, the grid impedance and phase-locked loop (PLL) affects the robust stability of grid-connected inverters, leading to harmonic resonance, or even instability in the system. In this paper, a impedance remodeling control method is proposed to enhance the stability of grid-connected inverters with high grid impedance. First, the output impedance of the PLL is reshaped by connecting a complex-coefficient filter (CCF) structure in series with the input of a typical SRF-PLL. The purpose is to broaden the range of feasible phase angles that can maintain grid-connected inverters stability. Then, the output impedance of the current control loop is reshaped, to ensure that the system has sufficient phase margin. The introduction of the impedance reshaping control method enables the grid-connected inverter to adapt to a wider grid impedance range, which more friendly to weak grid. Experimental measurements verify the proposed strategy.

Aiming at improving the voltage-based power quality issues and maximizing the utilization of renewable generation (RG) simultaneously, this paper proposes a microgrid multifunctional dynamic voltage restorer (MFDVR). Whether the grid voltage disturbances (such as sag, swell) happen or not, the MFDVR can always work by adopting vector control. Based on it, MFDVR realizes the full utilization of RG when the normal grid voltage happens, and it can utilize RG along with ensuring the stability for the voltage of critical loads during grid voltage disturbances, both of which expand the function of device. In addition, the constraint problem between output power and output voltage of the inverter can be solved by adding a series coupling capacitor in structure. This method, which can apparently reduce the output voltage of inverter combining the multifunctional method mentioned above, thereby reduce the voltage demand of DC side and the voltage stress of switch. All of those broaden the operating range and improve the performance of device effectively. The operating principle of the proposed MFDVR, power flow under different conditions and the optimization mechanism of the coupling capacitor are analyzed in detail. Simulation results verify the effectiveness of the proposed topology and control strategy.

In this paper, an improved topology for unified power quality conditioner (UPQC) is proposed. By adding a coupling capacitor to the LC filter branch in series side of UPQC, the improved topology can reduce the output voltage of the inverter, and provide a large part of the load-reactive power, thereby effectively reducing the overall capacity and dc-link voltage level of the UPQC system. Because of these prominent characteristics, the overall utilization and the cost performance of the device can be improved. Firstly, the circuit topology and working principle of the proposed UPQC are introduced. Secondly, the two working modes of UPQC under different working conditions are introduced in detail, including: power regulation mode under the normal steady-state condition and voltage compensation mode under the voltage sag condition. Then, the proposed topology is compared with other topologies to show its advantages in reducing overall capacity. Finally, the validity and feasibility of the proposed topology are verified by experimental results.