Synchronous reference frame-based vector control (SRF-VC) is widely adopted by single stage photovoltaic (PV) inverter to transfer powers into power grids. However, the overshoot effect and power coupling in SRF-VC, i.e., real and reactive powers coupling (RRPC), may cause oscillation amplification and forced oscillation issues when interharmonics of real power reference (P_ref) occur, which is induced by Maximum Power Point Tracking (MPPT) control. In this paper, a frequency domain analytical model is proposed to analyze the effect of overshoot and RRPC on forced oscillation when there is an oscillation source of P_ref induced by MPPT. Firstly, interharmonics of P_ref induced by MPPT is introduced, which can be the oscillation source of forced oscillation. Then, the power coupling mechanisms of SRF-VC are analyzed by visual phasor diagram, which is induced by slow dynamics of PLL in weak grids. Next, the frequency domain model considering RRPC channels are derived to analytically analyze its oscillation amplification characteristics when P_ref at sub/super-synchronous resonance frequency occur. Furthermore, forced oscillation magnitudes influenced by different control parameters are investigated by bode diagram of the proposed frequency domain model. Finally, the influences of overshoot and RRPC on forced oscillation are validated by the simulations and control-hardware-in-loop tests.

The large-scale integration of distributed energy resources poses numerous challenges to distribution networks. At present, multi-terminal flexible interconnection has become a key development trend for active distribution networks integrated with high-penetration distributed energy resources. Conventional unified power flow controllers (UPFCs) are mainly designed for high-voltage transmission networks and lack distribution-adapted control strategies, making it difficult for them to meet the networking requirements for multi-terminal interconnection. Moreover, most existing studies still focus on two-terminal devices, soft open points and improved UPFC topologies for transmission networks. Existing multi-port schemes mostly adopt only shunt-side structures without series compensation branches, which fail to regulate voltage magnitude and phase difference, thus failing to suppress closing inrush currents and mitigate busbar voltage sags. Meanwhile, such schemes struggle with three-phase imbalance, feeder load imbalance and bidirectional power flow fluctuations in distribution networks, and lack adaptive power allocation capability among multiple ports. To solve the above problems, this paper proposes a VSC-based series–shunt hybrid multi-terminal flexible interconnection converter. The proposed topology consists of one series-side VSC and n − 1 shunt-side VSCs connected through a common DC capacitor; it removes the shunt-side transformer, and effectively reduces cost and volume, while achieving phase shifting, voltage regulation and power flow control. Meanwhile, dual closed-loop PI cross-decoupling control and a flexible closing strategy are adopted to independently regulate the active and reactive power of each feeder, adapt to three-phase imbalance and load imbalance conditions, suppress inrush currents, and realize flexible power mutual support among multiple ports, thereby significantly enhancing adaptability to distribution networks.

This paper proposes a wideband composite sequence impedance model (WCSIM)-based analysis method to evaluate the interactions in power-electronic-based power systems subjected to unbalanced grid faults or with unbalanced loads. The WCSIM-based method intuitively assesses the impact of the small-signal interconnection among the positive-, negative-, and zero-sequence circuits on the interaction stability of unbalanced power systems. The effectiveness of this method is demonstrated using a permanent magnet synchronous generator-based weak grid system under a single-line-to-ground fault (SLGF). Frequency scanning results and controller hardware-in-loop tests validate both the correctness of the WCSIM and the effectiveness of the WCSIM-based analysis method.

The increasing integration of high-penetration renewable energy has led to prominent issues in power grid stability. This paper proposes a hybrid modeling method that integrates Kernel Density Estimation (KDE) with the Stochastic Response Surface Method (SRSM), addressing the dual challenges of insufficient accuracy in traditional parametric distribution models and the low efficiency of Monte Carlo simulations. By employing non-parametric probabilistic modeling to accurately characterize the spatiotemporal characteristics of wind-solar output, a refined model for wind turbine and photovoltaic generation is established. Combined with SRSM, a coordinated regulation mechanism between hydropower and renewables under fault scenarios is constructed to support system stability control strategies. A case study on a certain hydropower station demonstrates that the proposed method can accurately reflect system responses, providing theoretical support for the secure operation of power grids with high renewable penetration.