Accurate modeling for power-electronic devices requires power systems to be simulated with considerably small step sizes (typically several microseconds), which causes unnecessary computational burden and reduces efficiency, especially for large-scale power systems. To achieve a balance between simulation precision and efficiency, this paper introduces an innovative multi-rate interface strategy based on the modified time-domain simulation (TDS) method and multi-area data exchange method. The modified TDS method transforms the initialization process into exchange of electric data among different subsystems, while the multi-area data exchange method is able to ensure numerical stability and simulation universality during the multi-rate simulation. The proposed strategy provides a robust interface that allows different subsystems to be engaged in simulations with different step sizes while exchanging data. To validate this strategy, simulations on an integrated system of IEEE 14-bus and 33-bus systems is conducted. In addition, the strategy is further applied to a real-world scenario of the subsystem in the Guangxi Power Grid in China. Analysis of the results indicates that the proposed multi-rate fast simulation strategy can significantly boost simulation efficiency while maintaining accuracy, which marks a notable improvement compared with the traditional single step size simulation.

To harness the strengths and mitigate the limitations of line-commutated converter (LCC) and modular multilevel converter (MMC) HVDC systems, the LCC-MMC hybrid HVDC system has been developed. This paper proposes a holomorphic embedding (HE)-based power flow calculation method for AC/DC power systems with the LCC-MMC hybrid HVDC system. Firstly, the methodology involves establishing the mathematical model of the LCC-MMC hybrid HVDC system and its control modes. Subsequently, the HE formulation for the constructed LCC-MMC model is derived using the HE method. The proposed method simplifies the HE formulation using substitute variables, making it adaptable to various control modes. The designed HE formulation facilitates the derivation of the germ solution and the calculation of high-order power series coefficients. A sequential solution flow chart compatible with AC power flow algorithms is constructed to enhance the practicality of the HE method for real-world large-scale systems. The accuracy and effectiveness of the proposed method are verified through numerical tests on the modified IEEE 14-bus, IEEE 57-bus, and large 2383-bus system. The proposed method provides a reliable and efficient solution for power flow analysis in hybrid HVDC systems.

This paper proposes a reliable and nonintrusive approach for calculating economical operating states and at the same time, maintaining the transient stability of the system. It focuses on providing a preventive control strategy to address transient rotor angle stability and short-term voltage stability issues resulting from severe disturbances. The objective function, steady-state and multiple types transient stability constraints are equivalently and simultaneously reformulated in polynomial expressions of the control variables such that the original differential-algebraic equations in the transient stability-constrained optimal power flow model are eliminated. This reformulation also allows imposing both rotor angle and voltage magnitude bounds that achieve transient stability and reduce the complexity in the optimization stage. A transient constraint reduction strategy is also proposed to address the large number of constraints introduced by the polynomial chaos expansion when transforming multiple types of transient constraints. This strategy enables the elimination of most transient constraints, thereby further simplifying the overall optimization model. The effectiveness of the proposed method is numerically illustrated and validated through the WECC 3-machine 9-bus system and the IEEE 69-machine 300-bus system.

The holomorphic embedding (HE) method has gained significant attention in power flow analysis. However, there is no consensus regarding its computational efficiency compared to the traditional Newton-Raphson (NR) method. This paper presents a comprehensive analysis of the computational complexity of the HE method focusing on key steps such as matrix factorization, higher-order power series calculation, and Padé approximation. A theoretical investigation of these steps is conducted, followed by the implementation of multi-core parallel computing using Numba to enhance performance. Case studies on test systems ranging from 300 to 25,000 buses are used to evaluate the parallel strategies for accelerating computation. The results show a significant improvement in the computational efficiency of the HEM, demonstrating its scalability and practical applicability for large-scale power flow calculations. This study provides both theoretical and practical foundations for the broader adoption of the HE method in power system analysis.