发展新能源是应对环境污染和能源危机的根本性措施,有助于推动“双碳”目标的实现。可再生能源发电固有的间歇性、波动性给电网规划和运行带来严峻挑战。针对高比例新能源电力系统,分析了以最小功率波动为目标的新能源和储能容量最佳配比。立足风光资源的互补性,构建了最小化系统功率波动的风光最优配比模型,并提出了基于线性规划的求解算法。最后建立了面向平滑新能源出力的储能容量配置参数线性规划模型,得到波动性指标关于储能容量的解析表达式,并根据成本确定了最优储能容量。所提方法为政策制定提供了可视化工具以及比单一最优解更加丰富的信息。

The development of renewable energy is a fundamental measure to resolve environmental pollution and energy crisis, and achieve the carbon peaking and carbon neutrality goals. However, the inherent volatility and fluctuation of renewable energy output bring unprecedented challenges to the planning and operation of the power grid. This paper studies the optimal ratio of renewable energy and energy storage, aiming to minimize power fluctuation. According to the complementary nature of wind and solar resources, the mode of optimal ratio of wind and solar power that leads to minimal power fluctuation is established and is further transformed into linear programming. The optimization problem of energy storage capacity aiming to smooth the renewable energy output is formulated as a multi-parameter linear program, where storage charging power and energy capacities are parameters. The power fluctuation index is expressed as an analytical function in storage parameters, which is convex and piecewise linear. On the basis of the fluctuation index function, the optimal storage capacities can be determined according to the costs. The proposed method provides an illustrative tool and more abundant information for policy and decision-making.

为解决配网中分布式光伏渗透率持续升高引起的网损增加、功率倒送、电压越限等问题,在对分布式光伏进行集群划分的基础上,提出了一种综合考虑新能源消纳和网损的分布式光伏集群出力评估方法。首先,以基于电气距离的模块度指标和有功平衡度指标作为综合划分指标,利用遗传算法对配网中的分布式光伏进行集群划分;然后,在集群划分结果的基础上,考虑储能的调节作用及网络安全稳定约束,以包含网损成本和弃光成本的配电系统经济成本最低为优化目标,提出了分布式光伏集群出力评估方法;最后,通过在扬州某地实际41节点系统上进行仿真分析,证明了所提评估方法的可行性和有效性,所提评估方法可以根据调度中心的需求提供分布式光伏集群出力评估数据。

In order to solve the problems of the increasing power loss of network, power reverse transmission, voltage out-of-limit and so on, caused by the continuous increase of distributed photovoltaic penetration in distribution network, according to the cluster division of distributed photovoltaic generation, an output evaluation method of distributed photovoltaic cluster considering renewable energy accommodation and power loss of network is proposed. Firstly, the modular index based on electrical distance and active-power balance index are used as comprehensive division indices, and the distributed photovoltaic generation in distribution network is divided into clusters by using genetic algorithm. Then, on the basis of the cluster division results, considering the regulation effect of energy storage and the constraints of network security and stability, the output evaluation method of distributed photovoltaic cluster is proposed with the lowest economic cost of distribution system including the power-loss cost of network and distributed photovoltaic generation. Finally, the feasibility and effectiveness of the evaluation method proposed in this paper are proved by simulation analysis on an actual 41-node system in Yangzhou. The proposed method can provide output evaluation data of distributed photovoltaic cluster according to the demand of dispatching center.

The virtual synchronous generator (VSG) is a promising technology for future utility grids, since it can mimic the output characteristics of a synchronous generator, which provides the necessary inertia to a utility grid. However, the large-scale application of VSGs is limited due to the harmonic interaction between VSGs and the utility grid. Therefore, in order to investigate the stability issue as well as improve the practical application for large-scale power stations, the harmonic interaction mechanism between the VSG cluster and the utility grid is addressed. Firstly, the output impedance model of a single VSG is established, and it is found that the resonance frequency is related to parameters including the output filter, controller, and grid impedance. On this basis, the capacitor current control for a grid-connected inverter based on a VSG is proposed to enhance the resonance suppression. Furthermore, the output impedance of the VSG cluster is established, which reveals the harmonic interaction characteristics between the VSG cluster and the utility grid. In addition, in order to suppress the resonance and improve the stability, an inner-loop control strategy of VSG is introduced. Finally, the simulation and experimental results verified the correctness of the established modeling and analysis of the harmonic interaction between the clustered VSGs and the utility grid. The results show that the proposed impedance model is correct and can predict the resonant point accuracy (which is around 2.3 kHz in the simulation and experimental cases). The total harmonic distortion (THD) can be reduced to 3.2% which meets the requirements of IEEE standard 519.

This study addresses the output impedance model of the LCL-type grid-connected converter considering the dead-time effects and the digital control delay. The model shows that the digital control delay will affect the accuracy of the output impedance of the grid-connected converter, and the dead-time effects are only equivalent to superimposing a disturbance voltage on the original output impedance model. The derived output impedance model is verified by comparing it with the switching model in the PSIM simulation environment. The harmonic interaction between converter cluster and utility grid is modeled and analyzed based on the output impedance model. A combined harmonic suppression strategy is incorporated into every converter control scheme to suppress the harmonic interaction. Simulation results are presented to demonstrate the correctness of harmonic interaction analysis and the effectiveness of the proposed suppression strategy.

Impedance-based stability analysis is an effective method for addressing a new type of SSO accidents that have occurred in recent years, especially those caused by the control interaction between a DFIG and the power grid. However, the existing impedance modeling of DFIGs is mostly focused on a single converter, such as the GSC or RSC, and the influence between the RSC and GSC, as well as the frequency coupling effect inside the converter are usually overlooked, reducing the accuracy of DFIG stability analysis. Hence, the entire impedance is proposed in this paper for the DFIG-based WECS, taking coupling factors into account (e.g., DC bus voltage dynamics, asymmetric current regulation in the dq frame, and PLL). Numerical calculations and HIL simulations on RT-Lab were used to validate the proposed model. The results indicate that the entire impedance model with frequency coupling is more accurate, and it is capable of accurately predicting the system’s possible resonance points.