Grid Connection Point Research Articles

A Fast Converter Synchronization Speed Method Based on the Frequency Difference on Both Sides of the Grid Connection Point

The challenge of achieving a reliable and safe synchronization process for microgrids under weak communication conditions is a significant issue in distributed grid-connected energy storage. This is also the core motivation of this study. First, the concept of weak communication is introduced, and weak communication conditions are simulated by limiting the number of communications. Additionally, a fast synchronization method based on the frequency difference at the grid connection point is proposed, which allows for the rapid synchronization of converters under weak communication conditions. This method also includes an analysis of the range for key parameters, providing practical and feasible guidance for its real-world application. Finally, the validity of the theory is verified through PSCAD/EMTDC simulations and physical experiments.

Distributed photovoltaic reactive power control strategy based on improved multiobjective particle swarm algorithm

AbstractDistributed power supply access to the distribution network, although it can effectively support the band voltage, will also cause problems such as voltage overruns at the point of grid connection and large network losses, so this paper establishes a reactive power optimization model containing three objectives: network loss, voltage fluctuation rate, and static reactive power generator (SVG) installation capacity in distributed photovoltaic power generation scenarios by taking advantage of the characteristics of SVG that both absorb and send out reactive power. A multiobjective particle swarm algorithm with an adaptive grid and roulette mechanism is introduced to ensure the uniformity and diversity of the Pareto boundaries under the constraint that the output of each device does not exceed the constraints, and to obtain the optimal set of solutions capable of coping with the stochastic fluctuations of distributed power sources. When the algorithm is compared with three other algorithms, such as nondominated sorting genetic algorithm‐II, the results show that it reduces the network loss by about 25% and significantly improves the voltage fluctuation rate.

Fault Tolerant Control of Grid Connected Inverters Based on Low-Voltage Ride Through

To enhance the reliability of new energy grid connected systems, a fault-tolerant model predictive control strategy with low-voltage ride-through capability for grid connected inverter bridge arms has been proposed. Firstly, the operational principles following a single-phase bridge arm fault in the grid-tied inverter are analyzed. Then, a fault-tolerant structure for the grid connected inverter is established by creating a virtual bridge arm using direct current-side capacitors. Subsequently, a current prediction model is established, and control is implemented using redundant vectors. Additionally, by dynamically adjusting reactive current compensation commands based on the relationship between grid voltage drops and reactive current commands, the system is ensured to maintain continuous and stable operation even during grid voltage fluctuations. Finally, experimental results demonstrate that this fault-tolerant control strategy can still maintain the continuous and stable operation of the system when bridge arm faults occur due to grid voltage drops at the inverter grid connection point.

Active Support Pre-Synchronization Control and Stability Analysis Based on the Third-Order Model of Synchronous Machine

When traditional grid-forming converters directly participate in the grid-connected operation of the power grid, due to the lack of a pre-synchronization control system, the voltage amplitude and initial phase on both sides of the grid-connected point will deviate, resulting in voltage and current distortion during grid-connected mode. An active support phase-locked loop free pre-synchronization control strategy based on the third-order model of a synchronous generator is proposed to address the grid-connected problem of the grid-forming converter mentioned above. First, a model of active support control with frequency integral feedback at small signal levels was constructed. The root locus method was employed to examine how system parameters affect the stability of the active support control system. Second, by adding phase pre-synchronization controllers and amplitude pre-synchronization controllers to the active frequency loop and excitation voltage loop of the third-order model, it was ensured that the frequency, phase, and voltage amplitude of the unit are consistent with the power grid, achieving a fast and smooth grid-connected mode of the unit. Finally, by using a DC source to simulate all types of new energy power generation equipment, the active support pre-synchronization control system based on the three-order model of synchronous generator is built in the MATLAB/Simulink simulation environment, and the accuracy and effectiveness of the control strategy in this paper is verified.

Week-ahead dispatching of active distribution networks using hybrid energy storage systems

This paper presents a week-long scheduling approach to address the issues associated with uncertain stochastic generation. Specifically, the method is designed for active distribution networks (ADNs) hosting hybrid energy storages, composed by a hydrogen energy storage system (HESS) and a battery energy storage system (BESS). The inclusion of a pressurized HESS allows to balance energy over longer time periods, as opposed to methods considering only BESSs. To this end, this paper combines linearized models for the electricity grid with linearized models of the HESS to solve a tractable scheduling problem. The proposed optimal schedule consists of an active power trajectory at the grid connection point (GCP), called the dispatch plan, and the unit commitment schedule of a PEM fuel cell and electrolyzer system interfacing the electricity network with the HESS. Additionally, a bilevel model predictive control strategy is proposed, where the upper layer MPC computes a storage target accounting for the full horizon, while the lower layer computes the controllable resource setpoints to minimize the dispatch tracking error in each period. A numerical experiment shows the effectiveness of the proposed scheduling and control to accurately compute and track a dispatch plan over a full week. The results clearly show the benefits of combining a HESS with a BESS especially in periods where the prosumption is highly uncertain. Finally, we discuss the computational challenges associated with the weekly horizon and the use of a HESS that exhibits different dynamics than a BESS and propose an approach to mitigate the computational cost.

Empowering offshore wind with ES-STATCOM for stability margin improvement and provision of grid-forming capabilities

Offshore wind power plants (WPPs) play a pivotal role in achieving a CO2-neutral electricity sector. However, their grid connection presents significant challenges and costs. High-voltage alternating current (HVAC) offers a cost-effective solution, but it may necessitate the installation of a static synchronous compensator (STATCOM) at the onshore bus to ensure stability and compliance with connection requirements. Integrating energy storage into the STATCOM (ES-STATCOM) enables the provision of ancillary services, such as inertial response and frequency support, which require active power. This paper utilizes the generalized Nyquist criterion to demonstrate that operating the ES-STATCOM with grid-forming control enhances the stability margin of the grid-connected WPP when compared to operating it with grid-following control. Furthermore, it illustrates through network frequency perturbation (NFP) plots that the overall WPP, comprising grid-following wind turbines and a grid-forming ES-STATCOM, imparts grid-forming behavior at the grid-connection point.

Modelling and Assessing the Advantages of Integrating Wind, Solar, and Coal Systems within an Annual Bilateral Trading Setting

The integration and co-location of new energy sources and thermal power generation within the same grid connection point, under the management of a single market operator, provide noteworthy potential for exploration in the northern part of our nation. This method is based on the premise of allocating new energy resources primarily for generating contracted electricity, while using thermal power to offer ancillary services. This strategy aims to integrate and use the distinct benefits of both thermal power and new energy sources. The yearly bilateral trade market has significant potential for growth and development. In order to model and evaluate the income generated by the interconnected system’s involvement in the yearly bilateral trading market, this study first establishes the definition of the interconnected system and examines its research significance in engaging in annual bilateral trading. This study utilizes the theoretical framework of master-slave games to analyze the involvement of a coupled system in yearly bilateral trade. The specific case examined in this research is a wind-solar-thermal coupling system located in a particular location of Liaoning Province. This study examines the economic advantages of engaging in the electricity market by considering the marginal cost and LCOE (Levelized Cost of Electricity) perspectives. The findings suggest a notable enhancement in the advantages of the integrated system inside the yearly bilateral trade market, in contrast to conventional power sources present in the market, as well as instances when these sources function autonomously without integration.

Research on optimization and improvement method of new energy access grid stability based on transient stability margin index

Abstract This paper focuses on the potential local voltage stability risks and transient stability margin decline in the power grid after the large-scale integration of new energy. Based on the transient stability margin index of the power grid, a method for evaluating and optimizing the transient stability margin after the integration of wind power into the power grid is proposed. This paper provides guidance for the grid connection points and voltage level determination of the wind power access system during the planning phase, as well as the configuration of reactive power compensation devices such as SVGs.

Research on reactive voltage control strategy for substations connected to photovoltaic systems

Abstract The reactive voltage control of conventional substations is mainly realized by adjusting the switching of capacitors or reactors and changing the transformer ratio, which can only be controlled discretely. The PV inverter can carry out continuous reactive power control, and the reactive voltage control strategy of the conventional substation does not consider the reactive power control of the PV. In this paper, the nine-zone diagram control strategy of the traditional substation is used as a reference, and the reactive voltage optimization control strategy of a substation with a photovoltaic power generation system is constructed considering the characteristics that photovoltaic inverter can continuously regulate reactive power. Taking the internal power grid of an enterprise as an example, the simulation analysis verifies the effectiveness of the control strategy, which can ensure that the voltage and power factor of the grid-connected access point are qualified. At the same time, the voltage fluctuation of the grid-connected point can be reduced, and the network consumption can be reduced.

Impedance-Based Method for Predictive Stability Assessment

Impedance-based analysis methods enable a more specific and earlier foundation for assessing harmonic stability in decentralized converter-based power plants compared to the conventional compliance testing in the grid connection process. Essentially, they can be implemented as black-box model approaches without the necessity to disclose internal control models. Initially, only knowledge of the input impedances of the planned grid connection point and the planned PV system is required for application. For this purpose, the method of impedance spectroscopy for inverters has already been developed as a means to determine the effective impedance profile and the internal harmonic sources of inverters, allowing for the description of the frequency-dependent behavior of individual units. The time- and frequency-dependent grid impedance at the grid connection point (GCP) has also been successfully measured in several campaigns on medium and low-voltage grids. Through the coordinated application of both measurement methods, a predictive harmonic assessment is intended in the future, ensuring high planning reliability and grid quality even in grids with a high penetration of power electronics-coupled systems. This paper provides an overview of the current state of research on impedance-based stability criteria and presents measurement methods for practical implementation. Furthermore, it outlines remaining open questions until application in the field.

Assessment of the locational potential of floating offshore wind energy in South Africa

Expanding floating wind into new markets could support emission reduction targets in several national contexts. It furthers the need for adequate assessments to gain a full understanding of the technology’s potential in future markets. South Africa is a prime case study as it has seen limited industry and policy developments despite its huge technical potential for floating offshore wind (FOW). This paper assessed the locational potential of floating wind in South Africa through a three-phased approach that evaluated the key technical drivers/barriers of the technology, conducted a Geographic Information System analysis (GIS) using ArcMap 10.8 to exclude unsuitable sites based on a predetermined exclusion criteria (including marine protected zones, underwater cables, major oil and gas deposits, etc.), and estimated the total harvestable capacity in the feasible sites. The study found that 2% (246,105.4 km2) of South Africa’s entire Exclusive Economic Zone (EEZ) is suitable for hosting floating wind turbines, with a potential to generate a maximum of 142.61 GW of floating wind power. Although the Western Cape province holds the highest potential (80.52 GW) for floating wind in the country, the Eastern Cape region, with a locational potential of 20.04 GW, is considered most suitable for early-stage developments due to the availability of grid connection points, limited marine traffic, and proximity to appropriate port facilities. Future work can conduct techno-economic assessments to evaluate the technical and economic implications of developing floating wind in distinct sites in the country’s EEZ.

Analysis of the influence of large‐scale offshore wind power on the steady‐state voltage of the vicinity region of grid connection point

AbstractThe power characteristics of offshore wind power will change the regional power flow distribution and affect the regional voltage. Here, the direct‐drive wind turbine generator controlled by unity power factor is selected as the research object, and the influence of change of wind power on voltage at the grid connection point is analyzed from the simple integration model. Based on the two critical states of the external equivalent power of the grid connection point, an analytical expression of the output of wind power in the corresponding state is obtained, and the relationship among the critical state outputs, the output of wind power and the parameters at the grid connection point is drawn, hence the related influence laws is analyzed. The influence of change of wind power on voltage and regional reactive power and the reactance distribution of transmission lines near the grid connection point is considered to analyze the influence of offshore wind power on the vicinity region of grid connection point. The rationality of the conclusion is verified by study the cases of the integration of offshore wind power into Guangdong power grid, and some suggestions are put forward for the planning of offshore wind power integration.

Multifunctional Single-Phase Single-Stage Grid-Connected PV System

This paper presents the analysis of a multifunctional single-phase single-stage grid connected photovoltaic (PV) system. The primary function of the grid connected inverter in a single stage (PV) system is to supply active power to both load and grid in a way that complies with the applied grid connection standards. The added functions to the grid connected inverter are compensation for reactive power requirements and mitigation of the harmonics produced by the nonlinear loads connected to the point of grid connection. The single stage topology utilized in the grid connected PV system has the advantages of high efficiency and low cost compared with the two stage topology. Maximum power point tracking (MPPT) is achieved using perturb and observe algorithm. A test system composed of the PV array, single phase inverter, single phase supply, and three different types of single phase loads is modeled to evaluate the performance of the multifunctional operation of the PV grid connected system. The results of the test system simulation, using MATLAB/Simulink environment, validate the effectiveness of the system to perform the multifunctional operation of the grid connected inverter.

Parallel active power filter based on single-phase independent control

With the rapid development of high-voltage power grids and power electronics technology, the integration of numerous power electronic devices has led to a significant increase in harmonic pollution in power grids. Consequently, the demand for high-voltage and large-capacity active power filters has become increasingly urgent. This article introduces a novel approach using single-phase independent control and proposes a parallel active power filter based on magnetic flux compensation. This filter not only enhances power quality but also achieves three-phase decoupling control. It is specifically designed for medium and high-voltage three-phase three-wire power systems. Simulation experiments were conducted to validate the efficacy of the proposed active power filter, demonstrating its ability to effectively reduce the total harmonic distortion rate at the grid connection point and subsequently improve power quality.

Two-stage AGC Control Method for Wind Farm Considering Power Forecast and Theoretical Power Error

With the large-scale wind farm connected to the power system, the uncertainty and fluctuation of its output bring challenges to the power grid dispatching and operation, especially in the automatic generation control. The problem of inaccurate theoretical power upper limit and power forecast has always been prominent. Therefore, this paper proposes a two-stage AGC control method for wind farms. In the first stage, the power control target value of the wind turbine group is determined by comprehensively considering the grid connection point of the station, the power consumption of the station, the loss in the station, and the theoretical power error. In the second stage, the power control of the wind turbine group is divided according to the proportion of the maximum power generation capacity and sent to the wind turbine, to realize the closed-loop control. Based on the measured data of a typical wind farm in Jiangsu province, the calculation results show that the control strategy proposed in this paper is effective and can greatly improve the response speed and accuracy of wind farm AGC.

Improved Methodology for Power Transformer Loss Evaluation: Algorithm Refinement and Resonance Risk Analysis

The decline in power quality within electrical networks is adversely impacting the energy efficiency and safety of transmission elements. The growing prevalence of power electronics has elevated harmonic levels in the grid to an extent where their significance cannot be overlooked. Additionally, the increasing integration of renewable energy sources introduces heightened fluctuations, rendering the prediction and simulation of working modes more challenging. This paper presents an improved algorithm for calculating power transformer losses attributed to harmonics, with a comprehensive validation against simulation results obtained from the Power Factory application and real-world measurements. The advantages of the algorithm are that all evaluations are performed in real-time based on single-point measurements, and the algorithm was easy to implement in a Programmable Logic Controller (PLC). This allows us to receive the exchange of information to energy monitoring systems (EMSs) or with Power factor Correction Units (PFCUs) and control it. To facilitate a more intuitive understanding and visualization of potential hazardous scenarios related to resonance, an extra Dijkstra algorithm was implemented. This augmentation enables the identification of conditions, wherein certain branches exhibit lower resistance than the grid connection point, indicating a heightened risk of resonance and the presence of highly distorted currents. Recognizing that monitoring alone does not inherently contribute to increased energy efficiency, the algorithm was further expanded to assess transformer losses across a spectrum of Power Factory Correction Units power levels. Additionally, a command from a PLC to a PFCU can now be initiated to change the capacitance level and near-resonance working mode. These advancements collectively contribute to a more robust and versatile methodology for evaluating power transformer losses, offering enhanced accuracy and the ability to visualize potentially critical resonance scenarios.

Power-System Flexibility: A Necessary Complement to Variable Renewable Energy Optimal Capacity Configuration

Comprehending the spatiotemporal complementarity of variable renewable energy (VRE) sources and their supplemental ability to meet electricity demand is a promising move towards broadening their share in the power supply mix without sacrificing either supply security or overall cost efficiency of power system operation. Increasing VRE share into the energy mix has to be followed with measures to manage technical challenges associated with grid operations. Most sub-Saharan countries can be considered ‘greenfield’ due to their relatively low power generation baseline and are more likely to be advantaged in planning their future grids around the idea of integrating high VRE sources into the grid from the outset. An essential measure for achieving this objective entails exploring the possibility of integrating renewable hybrid power plants into the existing hydropower grid, leveraging on existing synergies and benefiting from the use of existing infrastructure and grid connection points. This study evaluates the potential for hybridizing existing hydropower-dominated networks to accommodate solar- and wind-energy sources. The existing synergy is quantified using correlation and energy indicators by evaluating complementarity at daily, monthly and annual intervals. The proposed metric serves as a tool to improve planning on increasing the VRE fraction into the existing systems with the aim to achieve optimal power mixes. In comparison to cases in which the same kind of resource is over-planted while expanding installed capacity, the results demonstrate that wind and solar resources hold a positive degree of complementarity, allowing a greater share of VRE sources into the grid. The study shows that Kenya bears favorable climatic conditions that allow hybrid power plant concepts to be widely explored and scaled up on a large and efficient scale. The results can be applicable in other regions and represent an important contribution to promoting the integration of VRE sources into sub-Saharan power grids.

Enhancing the Dynamic Stability of Integrated Offshore Wind Farms and Photovoltaic Farms Using STATCOM with Intelligent Damping Controllers

To build a large-scale renewable energy integrated system in the power system, power fluctuation mitigation and damping measures must be implemented during grid connection. PID damping controllers and traditional intelligent controllers with pole configuration are usually used for improving damping. Integration of large wind power plants and photovoltaic power plants into the power system faces transient power oscillation and fault ride-through (FRT) capability under fault conditions. Therefore, this paper proposes a static synchronous compensator (STATCOM) damper based on a recurrent Petri fuzzy probabilistic neural network (RPFPNN) to improve the transient stability of the power system when large offshore wind farms and photovoltaic power plants are integrated into the power system, suppress power fluctuation, and increase FRT capability. To verify the effectiveness of the proposed control scheme, a three-phase short circuit fault at the connected busbar is modeled in the time domain as part of a nonlinear model. From the comparison of simulation results, the proposed control scheme can effectively slow down the transient fluctuation of power supply to the grid-connected point when the grid is faulty, reach steady-state stability within 1–1.5 s, and reduce overshoot by more than 50%. It can also provide system voltage support at an 80% voltage drop and assist in stabilizing the system voltage to increase FRT capability. It also improves stability more than PID controllers when disturbances are present. Therefore, it maximizes the stability and safety of the power grid system.

Energy Consumption Optimisation of Emergency Shelters for Ukrainian War Refugees

The paper deals with optimisation of energy consumption of emergency shelters (tiny houses) for Ukrainian War refugees. Significant amount of Ukrainian citizens lost their homes or were forced to leave their properties. These refugees overcrowd the rest of the country and bring huge problems with accommodation and inclusion into existing communities. Accommodation in schools or gyms is just temporary solution with another unpleasant influence on the society. It is necessary to construct new quarters or communities using cheap but energy very efficient constructions. Several variants of tiny house with various equipment features and living or comfort standard are being discussed and compared. These studies are based on real project realised between Ukrainian non-government organisation Synergy and German development agency weChange. Main goal of this research is consumption optimisation of not particular single shelter but rather of large community of shelters containing hundreds or thousands units called shelter city. The tiny houses itself are designed according to passive solar systems standards and with accent to minimal purchasing costs and operational energy needs. Second important requirement is strong optimisation of shelter’s load chart to significantly decrease influence of the shelter city to power grid connection point. Both tasks are important because the Russian attack against Ukraine brings new tasks for power engineering sector. Electricity production, transmission, distribution and consumption must face new challenges. Nowadays more than 35 % of critical infrastructure is being damaged. Remaining infrastructure would be more overloaded, if new customers are connected without energy needs optimisation.

Enhancement of Power Decoupling for Virtual Synchronous Generator: A Virtual Inductor and Virtual Capacitor Approach

The inertia of a power system decreases with the increasing penetration of renewable energy, and the stability of power systems is facing great challenges. A virtual synchronous generator (VSG) has become one of the effective schemes for the high permeability of distributed generation, due to its similar characteristics to a synchronous generator. However, the coupling of the VSG in the power transmission from the actual power output point to the grid-connected point may lead to a steady-state error and dynamic oscillations, which limits the power output capability of the grid-connected converter and the grid support ability. To solve this problem, first, the power coupling mechanism of VSG is studied. Second, a virtual-inductor and virtual-capacitor control strategy is proposed for power decoupling, which eliminates the power coupling and improves their capability in suppressing the reactive power fluctuation. Finally, simulation and laboratory experimental results verify the effectiveness of the proposed decoupling strategy.