The hybrid distribution transformer (HDT) achieves a compromise between the low-frequency transformer (LFT) and the solid-state transformer. It combines the LFT's efficiency and reliability with the added advantage of partial power controllability via an integrated converter. However, the existing research on the HDT fault ride-through does not consider the coordination relationship with its own safe operation constraints, while few studies have considered capacity coordination between multiple converters. Therefore, this article proposes an improved hierarchical coordination control of integrated HDT (IHDT), considering grid fault and normal conditions. First, the IHDT topology is proposed, and the operation mechanism of IHDT to realize the voltage support and current compensation is clarified by analyzing the coupling mechanism between the converter and LFT. Furthermore, under complex conditions, the unified expressions of the IHDT winding voltage, current, and power are derived, the safe operation constraints of IHDT are analyzed, and a hierarchical coordination control strategy is proposed. Finally, the correctness and effectiveness of the IHDT topology and control strategy are demonstrated by simulation analysis and experimental verification.

To ensure the safe and stable operation of the power grid, it is necessary to carry out the risk assessment of the main electrical connection in the substation. In traditional methods, the influences of the regional power grid on the main electrical connection scheme are ignored. This paper aims to propose a new method of main electrical connection risk assessment considering the regional grid safety constraints. Firstly, the traditional risk indexes are modified by considering the load shedding in the regional grid, and safety constraints indexes are built by using severity functions. Secondly, the analytic method is adopted to analyze the faults in the substation and determine the consequences, and the external equivalent of the substation is conducted. Finally, the regional grid’s power flow and optimal scheduling are calculated, and the risk assessment results are obtained. To verify the effectiveness of the proposed method, the IEEE-RTBS system and a real 220kV substation and its adjacent grid are taken for analysis. The results show that compared with the traditional method, the risk indexes obtained by the proposed method are more conservative, and the weakness of the main electrical connection under maintenance conditions can be obtained, which proves the proposed method’s feasibility and effectiveness.

The random fluctuation of renewable power generation output makes the frequency and voltage of distribution network fluctuate frequently. And the stable operation performance of the system is decreased. Therefore, the sliding mode control (SMC) strategy of grid-forming (GFM) energy storage converter with fast active support of frequency and voltage is proposed in this paper. Firstly, the virtual synchronous generator (VSG) control possessing the superior GFM performance is applied to single-stage neutral point clamped (NPC) converter of energy storage system. Meantime, the improved comprehensive equivalent circuit model of lithium iron phosphate battery and equivalent model of converter are constructed by means of ampere-hour method and Kirchhoff’s law. Then, the SMC with fast response and strong robustness is utilized into the current inner-loop controller. Combined with VSG control, the SMC strategy of GFM energy storage converter is proposed, so that the converter could play an active supporting role by quickly adjusting the output power while the frequency and voltage are reduced. Finally, the simulation model of GFM energy storage converter SMC system is established. Through the simulation analyses, it can be seen that the response time of the proposed strategy to complete the active support is about 0.65 s.

With the greatly increased penetration rate of wind power, photovoltaic, and other new energy sources in the power system, the proportion of controllable units gradually decreased, resulting in increased system uncertainty. The biogas power generation system can effectively alleviate the pressure caused by source-load uncertainty in such high-permeability systems of new energy sources such as wind power and photovoltaic. Hence, from the perspective of the power system, this paper introduces a capacity demand analysis method for a rural biogas power generation system capable of independent operation amidst source-load uncertainty. To enhance the depiction of pure load demand uncertainty, a scene set generation method is proposed, leveraging quantile regression analysis and Gaussian mixture model clustering. Each scene’s data and probability of occurrence elucidate the uncertainty of pure load demand. An integrated optimal operation model for new energy and biogas-generating units, free from energy storage capacity constraints, is established based on the generated scenario set. Addressing considerations such as biogas utilization rate and system operation cost, a biogas storage correction model, utilizing the gas storage deviation degree index and the cost growth rate index, is developed to determine biogas demand and capacity. The example results demonstrate the significant reduction in gas storage construction costs and charging and discharging imbalances achieved by the proposed model while ensuring systemic operational cost effectiveness.

With large-scale access to distributed new energy, the power flow form of the distribution network tends to be complex. The distribution loop network rate increases, resulting in serious circulation of the distribution network, which places significant pressure on the loss of the distribution network. The problem of network loss change caused by distributed new energy grid connection, coupled with the inconsistency between load fluctuation and output power change of distributed new energy, will have a significant impact on the safety, reliability, and economic operation of the distribution network. Therefore, it is urgent to have good economic and technical means of power flow control. This paper proposes a minimum network loss optimization control strategy for active distribution networks based on a distributed power flow controller. First, according to the characteristics of the distribution network load and the new energy power supply along the distribution line, the multiple sub-modules of the distributed power flow controller are arranged in sections in the distribution loop network line. The regulation effect of the distributed power flow controller on the voltage and power flow of the distribution loop network is analyzed. The loop network current equation and power loss equation after the distributed power flow controller are constructed, and the power equation with the minimum active loss of the active distribution loop network is derived. Second, the control strategy for minimum network loss of the active distribution network based on the distributed power flow controller is proposed. Finally, the simulation model of the active distribution loop network is constructed by PSCAD/EMTDC. The loss of the loop network before and after the distributed power flow controller is simulated and analyzed, and the effectiveness of the proposed strategy is verified.