• Energy Research

Lightning strikes are one of the main causes of power system trip-outs. When the overhead transmission line (TL) connected to a wind farm is struck by lightning, large currents propagate to the substation, resulting in severe problems. To enhance the performance of wind farm substations, the transient behavior during lightning must be analyzed. The main contribution of this paper is to study the lightning behavior of wind farm substations whose design is different from other conventional substations. The lightning surge overvoltages caused by back flashover and shielding-failure of the 132 kV overhead TL connected to the 33/132 kV air-insulated substation (AIS) of Miramar wind farm are calculated. This wind farm has been built in Argentina to achieve grid connection and power transmission with a total capacity of 98.7 MW. The work investigates the fast-front lightning transient overvoltages in the AIS caused by lightning flashes striking the 132 kV overhead TL. The distributed parameter model of the TL, including towers, phase-conductors, the shielding-wire, insulators, and the span, is investigated using Digsilent Power Factory software. In addition, the AIS apparatus, including surge arresters (SAs), two 60 MVA transformers, and circuit breakers, are also considered in the model. The strike is applied first at the shielding-wire, and the impact on the transient overvoltages at the TL and the substation during the back flashover phenomenon are analyzed. On the other hand, the shielding-failure is studied and the transient overvoltages at the TL and the substation are analyzed. The impact on the transient overvoltages at the TL and the substation is investigated, taking into account the SA protection operation, and its dissipated energy during lightning flashes is calculated. The study results are important for the lightning protection systems design of wind farm substations connected to overhead TLs.

Dans le cadre de l'expansion progressive de la nouvelle génération distribuée d'énergie, le système de micro-réseau à convertisseurs multiples insulaire joue un grand rôle. La stabilité de la tension et de la fréquence des systèmes à convertisseurs multiples en mode îlot et la coordination de l'allocation de puissance entre de nombreux systèmes de convertisseurs sont devenues des points de recherche essentiels. En se concentrant sur le problème de partage de puissance réactive du système à convertisseurs multiples pour différentes impédances de ligne et perturbations de charge, cet article propose une stratégie de contrôle de chute améliorée consensuelle pour atteindre le partage de puissance et la stabilité de tension et de fréquence, et le mécanisme et la performance en régime permanent de la stratégie de contrôle proposée sont analysés et étudiés. Dans ce travail, un modèle de simulation de système à convertisseurs multiples composé de six onduleurs est construit dans le logiciel PLECS, qui vérifie que le schéma de contrôle d'affaissement amélioré consensuel peut compenser les lacunes du contrôle d'affaissement traditionnel. En outre, la configuration expérimentale matérielle du système d'onduleur triphasé est en outre effectuée pour valider les résultats de simulation. En cas de perturbation de la charge, les effets de contrôle du contrôle de l'affaissement amélioré par consensus proposés dans cet article sont analysés et étudiés, et les bonnes caractéristiques dynamiques de la stratégie de contrôle de l'affaissement amélioré par consensus sont vérifiées. Enfin, la grande robustesse de la stratégie de contrôle coordonné proposée est en outre illustrée par le saut de charge déséquilibrée. Cet article clarifie l'efficacité de la stratégie de contrôle proposée basée sur un algorithme de consensus dans la résolution du problème de partage de la puissance réactive des différentes impédances de ligne et des perturbations de charge autour du système multi convertisseur en mode îlot. En outre, le travail dans le document peut assurer un partage efficace de la puissance réactive dans diverses conditions de travail avec une grande robustesse. Bajo la expansión gradual de la nueva generación distribuida de energía, el sistema de microrred multiconvertidor de isla juega un gran papel. La estabilidad del voltaje y la frecuencia de los sistemas multiconvertidores en modo isla y la coordinación de la asignación de potencia entre muchos sistemas convertidores se han convertido en puntos de investigación vitales. Centrándose en el problema del uso compartido de potencia reactiva del sistema multiconvertidor para diferentes impedancias de línea y perturbaciones de carga, este documento propone una estrategia de control de caída mejorada de consenso para lograr el uso compartido de potencia y la estabilidad de voltaje y frecuencia, y se analizan y estudian el mecanismo y el rendimiento en estado estacionario de la estrategia de control propuesta. En este trabajo, se construye en el software PLECS un modelo de simulación de sistema multiconvertidor compuesto por seis inversores, que verifica que el esquema de control de caída mejorado por consenso puede compensar las deficiencias del control de caída tradicional. Además, la configuración experimental de hardware del sistema inversor trifásico se lleva a cabo para validar los resultados de la simulación. Bajo perturbación de carga, se analizan y estudian los efectos de control del control de caída mejorado por consenso propuestos en este documento, y se verifican las buenas características dinámicas de la estrategia de control de caída mejorada por consenso. Finalmente, la alta robustez de la estrategia de control coordinado propuesta se ilustra aún más con el salto de carga desequilibrada. Este documento aclara la efectividad de la estrategia de control propuesta basada en el algoritmo de consenso para resolver el problema de compartir la potencia reactiva de diferentes impedancias de línea y perturbaciones de carga alrededor del sistema multiconvertidor de modo isla. Además, el trabajo en el documento puede garantizar un intercambio efectivo de energía reactiva en diversas condiciones de trabajo con alta robustez. Under the gradual expansion of the new energy distributed generation, the islanding multi converter microgrid system plays a great role. The stability of voltage and frequency of multi converter systems in islanding mode and the coordination of power allocation among many converter systems have become vital research points. Focusing on the reactive power sharing problem of multi converter system for different line impedances and load disturbances, this paper proposes a consensus enhanced droop control strategy to achieve power sharing and voltage and frequency stability, and the mechanism and steady-state performance of the proposed control strategy are analyzed and studied. In this work, a multi converter system simulation model composed of six inverters is built in the software PLECS, which verifies that the consensus enhanced droop control scheme can make up for the shortcomings of the traditional droop control. Moreover, the hardware experimental setup of three-phase inverter system is further conducted to validate the simulation results. Under load disturbance, the control effects of consensus enhanced droop control proposed in this paper are analyzed and studied, and the good dynamic characteristics of consensus enhanced droop control strategy are verified. Finally, the high robustness of the proposed coordinated control strategy is further illustrated by the jump of unbalanced load. This paper clarifies the effectiveness of the proposed control strategy based on consensus algorithm in solving the reactive power sharing problem of different line impedances and load disturbances around the island mode multi converter system. Furthermore, the work in the paper can ensure effective reactive power sharing under various working conditions with high robustness. في ظل التوسع التدريجي للجيل الجديد الموزع للطاقة، يلعب نظام الشبكة الدقيقة متعددة المحولات دورًا كبيرًا. أصبح استقرار الجهد والتردد لأنظمة المحولات المتعددة في وضع الجزر وتنسيق تخصيص الطاقة بين العديد من أنظمة المحولات نقاطًا بحثية حيوية. مع التركيز على مشكلة مشاركة الطاقة التفاعلية لنظام المحول المتعدد لمعاوقات الخطوط المختلفة واضطرابات الحمل، تقترح هذه الورقة استراتيجية تحكم معززة بالإجماع لتحقيق مشاركة الطاقة واستقرار الجهد والتردد، ويتم تحليل ودراسة آلية وأداء الحالة الثابتة لاستراتيجية التحكم المقترحة. في هذا العمل، تم بناء نموذج محاكاة نظام محول متعدد يتكون من ستة محولات في برنامج PLECS، والذي يتحقق من أن مخطط التحكم في التدلي المعزز بالإجماع يمكن أن يعوض عن أوجه القصور في التحكم التقليدي في التدلي. علاوة على ذلك، يتم إجراء الإعداد التجريبي للأجهزة لنظام المحول ثلاثي الطور للتحقق من صحة نتائج المحاكاة. في ظل اضطراب الحمل، يتم تحليل ودراسة تأثيرات التحكم في التحكم المعزز بالإجماع المقترح في هذه الورقة، ويتم التحقق من الخصائص الديناميكية الجيدة لاستراتيجية التحكم المعزز بالإجماع. أخيرًا، تتضح المتانة العالية لاستراتيجية التحكم المنسقة المقترحة بشكل أكبر من خلال قفزة الحمل غير المتوازن. توضح هذه الورقة فعالية استراتيجية التحكم المقترحة بناءً على خوارزمية الإجماع في حل مشكلة مشاركة الطاقة التفاعلية لمعاوقات الخطوط المختلفة واضطرابات الحمل حول نظام المحول المتعدد لوضع الجزيرة. علاوة على ذلك، يمكن أن يضمن العمل في الورقة المشاركة الفعالة للسلطة التفاعلية في ظل ظروف العمل المختلفة بقوة عالية.

SummaryThe large integration of distributed generation (DG) and electric vehicles (EVs) facilitates daily life and reduces carbon emissions. However, it brings problems such as increased uncertainty and power electronic permeability to the distribution network. In this context, it is important to solve the line loss optimization problem as closely as possible to the real situation. Therefore, this paper solves the line loss optimization problem based on a probabilistic model of three‐phase unbalanced modern power electrical distribution network. Firstly, the paper proposes a frequency domain model of the distribution network and the optimization problem model. Then, to deal with the uncertainty of the system, the point estimation method (PEM) and Monte Carlo Simulation (MCS) are used. Finally, this paper proposes two optimization schemes considering the power quality when single and multiple DGs are integrated. The simulation results demonstrate that the PEM using the Gram–Charlier series expansion of the fourth‐order statistical moments to estimate the probability density function (PDF) is significantly less time consuming than the traditional MCS method while maintaining accuracy. The comparative analysis reveals that under the optimization scheme with single DG integration, the expected value of system line loss and expected line loss rate are reduced from 283.95 kW to 218.96 kW (22.89% reduction) and from 13.44% to 10.68%, respectively. Under the dual DG integrated optimization scheme, the expected value of line losses and expected line loss rate are reduced from 283.95 kW to 208.88 kW (26.4% reduction) and from 13.44% to 10.25%, respectively. However, after taking the uncertainty into account, the operational reliability of the system has been enhanced under different scenarios. In addition, it is found that the optimization approach incorporating multiple DG units can effectively mitigate the system line loss under diverse operational scenarios while enhancing the system's DG integration capability.

Nowadays, the scale of power grid is remarkably increasing and there is a continuous reinforcement of AC–DC hybrid systems. Thus, the single-phase grounding fault currents on the AC grid-side of rectifier and inverter stations increase significantly, which may exceed the capacity limit of the circuit breakers. The large short-circuit currents would result in problems during equipment selection and threaten the safety of equipment and personnel. To solve such issue, the effect of the converter transformer on the single-phase grounding fault current on the grid-side is analyzed. The mechanism of high short-circuit current in DC near region is revealed. Also, the feasibility of neutral point earthing via small reactor at HVDC converter transformer to suppressing the single-phase grounding fault current is verified. In addition, the principle of selecting the suitable small reactor is summarized. The results show that the neutral point earthing via small reactor at converter transformer can effectively limit the single-phase grounding fault current on the AC-side. However, it would lead to an increase of overvoltage at the neutral point of HVDC transformer. Therefore, neutral grounding by small reactor might be implemented when the insulation level is satisfied.

AbstractIn recent years, with a large number of distributed energy sources connected to the grid, the distribution network has shown a clear trend towards the use of power electronics. As a power conversion interface, the stability of the converter's interaction with the grid has received considerable attention. Adequate admittance (impedance) modeling of the three‐phase grid‐connected converter is a prerequisite for analyzing the stability and resonance characteristics of the grid‐connected system. Understanding the internal mechanisms and proposing effective solutions are crucial to enable power systems to effectively cope with the impact of power electronics. Therefore, by studying the admittance equivalence relationship and equivalent circuit of three‐phase AC systems in various coordinate systems, this paper focuses on solving the non‐uniqueness problem of impedance admittance modeling of three‐phase converter system. It is proposed that the input admittance of the three‐phase asymmetrical system in the dq and fb rotating coordinate systems is a 2‐order matrix and equivalent. The input admittance of the three‐phase unbalanced system in the αβ and “12” static coordinate systems is a 4‐order matrix and equivalent. From both theoretical analysis and simulation verification, it is shown that the number of eigenvalues of the three‐phase asymmetrical system in the stationary coordinate system is twice that in the rotating coordinate system, and the overall damping of the system is improved. The control strategy based on the stationary coordinate system will make the system more stable. The second contribution of this paper is to establish the equivalent circuit of the three‐phase symmetric converter system by the node admittance matrix and extend it to the multi‐machine system to explain the system instability mechanism by the circuit resonance mechanism. Finally, the frequency coupling phenomenon is studied for the three‐phase asymmetrical converter system, and it is explained that it cannot establish an equivalent circuit similar to the three‐phase symmetrical converter system.

Abstract The integration of renewable energy (RE) sources is increasing day by day because of their permanent existence and the limited quantities of fossil fuels. One of the most promising RE sources is photovoltaic (PV) technology, which is developing quickly in many countries worldwide. PV cells generate electricity by converting the sunlight to DC voltage. PV arrays are installed in outdoor areas and on the rooftops of homes to be directly subjected to the sun. Consequently, they are frequently subjected to lightning strikes, which may cause damage to PV arrays, service interruption, and additional cost for PV replacement. Therefore, an adequate lightning protection system (LPS) must be installed to protect the PV panels. In addition, the transient performance of PV panels during lightning strikes must be analyzed well. This paper presents a comprehensive review of the superior modeling methods of PV systems during lightning strikes. In addition, the paper displays the different platforms to simulate the transient effects of lightning strikes on PV systems. The lightning transient effects on PV arrays are studied based on the system modeling to assess the recommended LPS designs studied in the literature. The paper also gives some recommendations about the modeling methods and protection of PV systems during lightning strike.