Direct current (DC) power grids based on flexible high-voltage DC technology have become a common solution of facilitating the large-scale integration of distributed energy resources (DERs) and the construction of advanced urban power grids. In this study, a typical topology analysis is performed for an advanced urban medium-voltage DC (MVDC) distribution network with DERs, including wind, photovoltaic, and electrical energy storage elements. Then, a multi-time scale optimal power flow (OPF) strategy is proposed for the MVDC network in different operation modes, including utility grid-connected and off-grid operation modes. In the utility grid-connected operation mode, the day-ahead optimization objective minimizes both the DER power curtailment and the network power loss. In addition, in the off-grid operation mode, the day-ahead optimization objective prioritizes the satisfaction of loads, and the DER power curtailment and the network power loss are minimized. A dynamic weighting method is employed to transform the multi-objective optimization problem into a quadratically constrained quadratic programming (QCQP) problem, which is solvable via standard methods. During intraday scheduling, the optimization objective gives priority to ensure minimum deviation between the actual and predicted values of the state of charge of the battery, and then seeks to minimize the DER power curtailment and the network power loss. Model predictive control (MPC) is used to correct deviations according to the results of ultra short-term load forecasting. Furthermore, an improved particle swarm optimization (PSO) algorithm is applied for global intraday optimization, which effectively increases the convergence rate to obtain solutions. MATLAB simulation results indicate that the proposed optimization strategy is effective and efficient.

中文翻译：

---

考虑不同运行方式的中压直流电网多时标最优潮流策略

基于柔性高压直流技术的直流（DC）电网已成为促进大规模集成分布式能源（DER）和建设高级城市电网的通用解决方案。在这项研究中，对具有DER的高级城市中压DC（MVDC）配电网络进行了典型的拓扑分析，包括风力，光伏和电能存储元素。然后，针对MVDC网络在不同的运行模式下提出了多时间尺度的最优潮流（OPF）策略，包括公用电网并网和离网运行模式。在公用事业并网运行模式下，提前优化目标可以最大程度地减少DER功率削减和网络功率损耗。另外，在离网运行模式下，提前优化目标优先考虑满足负载的需求，并最大程度地降低了DER功率消耗和网络功率损耗。采用动态加权方法将多目标优化问题转换为二次约束二次规划（QCQP）问题，该问题可以通过标准方法解决。在日内调度期间，优化目标将优先考虑以确保电池充电状态的实际值与预测值之间的最小偏差，然后寻求将DER功率限制和网络功率损耗最小化。模型预测控制（MPC）用于根据超短期负荷预测的结果来校正偏差。此外，将改进的粒子群优化（PSO）算法应用于全局日内优化，有效地提高了收敛速度以获得解决方案。MATLAB仿真结果表明，所提出的优化策略是有效和高效的。