Point Of Interconnection Research Articles

Design and Real-Time Implementation of a Centralized Microgrid Control System With Rule-Based Dispatch and Seamless Transition Function

With reference to the newly released microgrid standards, design and real-time implementation of a centralized microgrid control system is presented in this article. In the grid-connected mode, the utility grid will provide the voltage and frequency reference at the point of connection. The assets within the microgrid will follow power command references provided by the control system. In the islanded mode, the energy storage system (ESS) can provide the voltage and frequency reference to all other generators. Based on the state-of-charge of the ESS, a rule-based dispatch is proposed, with priority given to diesel generator and then the storage in the middle state of charge range. To alleviate power fluctuations, meet smooth planned islanding requirement, and compensate for the feeder losses ignored in dispatch algorithm, a supplementary slack-bus power control based on closed-loop feedback and first-order filter is proposed. The potential of the storage system in firming short-time power fluctuation and providing long-term load shifting capabilities is exploited. An emergency dispatch function for unplanned islanding considering the speed of response limitation of a diesel generator is also proposed. The proposed control strategy is implemented and tested on a controller hardware-in-the-loop test bench. It demonstrates the capability of the control system to reduce load shedding and renewable curtailment, and to implement power management at the point of interconnection.

Improved Widrow–Hoff Based Adaptive Control of Multiobjective PV-DSTATCOM System

This article presents an adaptive control algorithm for a multiobjective grid-tied solar photovoltaic (PV)-distribution static compensator. The multiobjective system extracts the maximum energy available across the solar PV array and delivers it to the load and the grid connected at the common point of interconnection (PIC). In addition to this, the system reduces the losses on the distribution network and improves the quality of the voltage at the PIC by maintaining the grid currents balanced with THD value less than 5%. The perturb and observe-based maximum power point tracking method is used to extract the maximum energy, while the voltage source converter (VSC) is controlled by the presented improved Widrow-Hoff algorithm. This control algorithm improves the grid current power quality by estimating the fundamental component of the load current. It uses two weight to track the desired signal as compared to the other existing similar algorithms, which improves its tracking accuracy, reduces the steady-state error, and oscillation form the desired output signal. The same algorithm is used for synchronization of the VSC with the distribution network. Hence, it eliminates the need for another algorithm for the synchronization, which further improves its performance in dynamic conditions. An additional feed-forward term corresponding to the solar PV array (IPVFF) power is added in the VSC control to improve its dynamic response in the severe atmospheric conditions. The performance of the system is validated through simulated and test results in various dynamic conditions.

GAFA’s Information Infrastructure Distribution: Implications for the Global South

We address the implications of GAFA’s choice of points of interconnection in the global North versus the global South to understand the degree to which the global South is underserved, if at all. We find that more than twice as many countries in the global South have no GAFA presence at all than countries in the global North. Apple has approximately 92% of its points of interconnection in the North, followed by Amazon (82.5%), Facebook (73%), and Google (72%). We assert that regulatory authorities investigate the information infrastructure to understand the implications of GAFA’s market concentration at a global level.

Robustness and adaptability analysis for equivalent model of doubly fed induction generator wind farm using measured data

As many large wind farms connected to the power grid, it is necessary to develop a robust and adaptable dynamic equivalent model of the wind farm for system analysis and control. In this paper, the trajectory sensitivity of time-varying parameters of the equivalent model is analyzed. Then the non-time- varying parameters of the equivalent model are fixed as aggregated values, while the time-varying parameters are identified using the genetic learning particle swarm optimization based on phasor measurement unit data at the point of interconnection. The robustness and adaptability of the equivalent model under different scenarios are analyzed. The simulation results using the Western Electricity Coordinating Council benchmark test system show that the global searching capability to find the optimal point of the proposed method is higher than canonical particle swarm optimization and genetic algorithm by 2 orders. Further, the biggest mismatch between the identification results of the proposed method and the true values is within 10% for parameters with high sensitivity which is much better than previous work.

Determining the Hosting Capacity of Solar Photovoltaic in a Radial Distribution Network Using an Analytical Approach

Integrating high photovoltaic (PV) on distribution grid system has a positive impact by significantly reducing the losses and improving the voltage profile at the same time reducing the pollution of the environment However, integrating high proportions of PV in the distribution grid can bring the grid to its operational limits and result in power quality issues. The maximum PV capacity that can be integrated without incurring any grid impacts is referred to as the PV hosting capacity of the grid. This paper intends to evaluate the hosting capacity of solar PV in Dodhara-Chandani (DoC) distribution feeder as one of the feeder of Integrated Nepal Power System (INPS), considering grid parameters and operating condition in Nepal. Three main criteria were investigated for determining the hosting capacity of PV; reverse power flow, maximum voltage deviation of feeder and current carrying limit of conductor. The analysis has been performed by means of static load-flow simulation in Electrical Transient & Analysis Program (ETAP) and coding in MATLAB R2017a. The study shows that PV of rated capacity 687kWp can be installed at a point of interconnection (POI) whereas an optimal placement of solar PV is found to be at 18th node (in between starting and end of the feeder) considering minimum system losses. The minimum voltage profile at end of the feeder has improved by 8 % while the active power loss reduction of network has reduced by 83.6 % after the integration of solar PV. The results indicate voltage at different buses and the ampacity of most of the conductors have been improved after the integration of PV system into DoC feeder.

Second harmonic impedance drift‐based islanding detection method

Islanding detection is an important operational aspect of microgrids. Early detection of islanding is essential to avoid unsynchronised reclosing. The possibility for minimal or near zero power mismatch between generation and load of a microgrid is high in a modern reconfigurable distribution network. Hence, at the instant of islanding, the voltage at the Point of Interconnection (PoI) will not change significantly and may lead to failure of over/under voltage and frequency relays in detecting islanding. In this work, second harmonic voltage at PoI of a voltage source inverter-based distributed generation (DG) is extracted through a sliding window discrete Fourier transform and is used for generating a second harmonic current reference, through virtual admittance. The second harmonic impedance at DG terminal is estimated. This second harmonic impedance remains insignificant in the case of grid-connected mode but drifts beyond a threshold in islanding mode. The proposed method is validated on two test cases, and the comparative results from simulation studies indicate that the islanding detection is achieved in less time with minimal effect on the power quality, fundamental voltage, and frequency at the PoI.

ANOVA Kernel Kalman Filter for Multi-Objective Grid Integrated Solar Photovoltaic-Distribution Static Compensator

In this paper, a novel ANOVA Kernel Kalman Filter (AKKF)-based adaptive control algorithm is introduced which is used for accurate harmonics support during operation of grid-integrated solar energy conversion system (SECS). For grid integrated SECS, a single-phase two-stage topology is considered, where local loads are attached on common point of interconnection (CPI), and a battery is attached on DC link. The AKKF is the improved form of Kalman Filter (KF), where the ANOVA Kernel (AK) trick is hybridized to improve the estimation accuracy of the KF. The objective of proposed control technique is to use this solar power to fulfil the load requirement. After satisfying the load requirement, the rest of solar power is fed to the grid. However, when the solar power is not available (in nighttime), then the system operates as Distribution Static Compensator (DSTATCOM), which provides reactive power support to the grid. The performance of the developed control technique is validated through experimentation on a developed prototype. During testing, adverse grid conditions, solar insolation variation, and load unbalance conditions are considered for satisfying the motive of the developed control technique.

Placement of photovoltaic and capacitors in the 20 kV Jeneponto Distribution Network

Indonesia is located on the equator which has a good intensity of solar radiation throughout the year. This radiation condition gives the potential for photovoltaic placement in Indonesia. Jeneponto Regency is one of the areas in South Sulawesi that has the high potential for the construction of photovoltaic (PV) with irradiation levels reaching 5.404 kWh/m2/day. This research aims to determine the location of photovoltaic and capacitor interconnection points in the 20 kV Jeneponto distribution system for optimizing voltage stability and minimizing power losses. The optimal simulation of the determination of interconnection points is carried out by simulating photovoltaic placement in different main buses, which are Jeneponto main distribution substation, Jeneponto switching substation, Tolo switching substation and Benteng switching substation. The results analysis showed that the photovoltaic interconnection point in Benteng switching substation produces the smallest power losses and all loads have a voltage profile that complies with both IEEE and PLN voltage standards.

Hierarchical control system for a flexible microgrid with dynamic boundary: design, implementation and testing

The design, implementation, and testing of a control system for a flexible microgrid (MG) is presented in this study. The MG controllers can be implemented in a real-world MG with multiple smart switches, photovoltaic panel system, and battery energy storage systems (BESSs). With the benefits from smart switches, the MG has unique characteristics such as dynamic boundary and flexible point of interconnection (POI) concepts. To control such a unique MG and realise the dynamic boundary, an MG central controller and two types of local controllers are implemented. Compared to the MG with fixed boundary, the MG with dynamic boundary can have smaller BESS capacity, better utilisation of renewable energy, and multiple POI options. Also, compared with IEEE Std 2030.7–2017, the topology identification and active and reactive power balance functions are newly designed to realise the dynamic boundary concept. The planned islanding and reconnection functions are modified to realise the flexible POI concept. These functions are introduced including the software architecture, cooperation, and interaction among them. Finally, a hardware-in-the-loop testing platform based on the Opal-RT real-time simulator is set up to verify the performance, realisation of the dynamic boundary, and flexible POI concepts with four comprehensive test scenarios.

A SUSPICION OF ARCHITECTONIC IN KANT’S TRANSITION PROJECT

This essay explores the undervalued methodological elements underpinning Kant’s Transition from Metaphysical Foundations of Natural Science to Physics in Opus postumum. I do this by drawing a line between the Architectonic of Pure Reason in Critique of Pure Reason and the Transition, although this line is problematized at various points. What emerges is the call for an explicitly architectonic understanding of the concept of transition in Opus postumum. According to the architectonic of Transition, instead of only devising the strict division of metaphysics and physics we must devise systematic ways of building bridges between them and finding their points of interconnection. When extended to the wider critical edifice this implies a radical departure from the Architectonic of Pure Reason as it was understood in Critique of Pure Reason and a complication of Kant’s theorization of metaphysics, physics, and physiology throughout his corpus.

A new STATCOM based Reactive Power Management in Grid Connected DFIG based Wind Farm

This paper displays control based on STATCOM conspire of PQ enlargement in grid associated DFIG (Doubly Fed Induction Generators).The fundamental purpose for utilizing the acceptance generators incorporated with a wind turbine is to excerpt max. Power. DFIG having a capability to operate at wider range of wind speeds and ability to produce more output with available energy , that’s why it is being preferred well than SCIG (Squirrel Cage Induction Generator).The transient reaction is really a basic unique normal for DFIG-based breeze turbines, particularly within the sight of quick transient occasions, for example, power system fault ,abrupt change in load, and so on. Serious issue is found in profile of voltage and deviances in frequency with altering normal conditions, for example, speed of wind & load distincts. This paper shows a near investigation of stabilizing out a DFIG based wind-generating station utilizing its individual Converters for frequency & utilizing a STATCOM. By Simulation it shows a dynamic compensation of Q, when STATCOM utilized at a point of interconnection of WPS and keeping up its voltage level.

Online Decentralized and Cooperative Dispatch for Multi-Microgrids

Microgrid usually associated with distributed renewable energy sources plays a key role in reducing the requirement of traditional power sources and the emission of CO2. Connecting multiple microgrids to the electric power grid can facilitate a more powerful and reliable operation. Microgrids need decentralized dispatch with the requirement of security and privacy, and at the same time, they need to cooperate to satisfy the constraints from the power grid. We consider online decentralized and cooperative dispatch problem in this paper. In order to capture the randomness in the wind and solar power generation and the system dynamics, we formulate the problem as a decentralized Markov decision process (Dec-MDP). We propose a new method to calculate the approximate Q-value functions by constructing the initial feasible policy with reasonable space and time complexity. Bayesian games (BGs) is applied to model the decentralized dispatch with delayed communication in order not to slow down the online decision-making. Also, the alternating minimization method is used to solve this BGs based on the approximate Q-value functions. Numerical results demonstrate that the proposed algorithm is very effective in reducing the state space and computing time and achieving the requirement of real-time scheduling. Motivated by the problem of decentralized dispatch of multi-microgrids in grid-connected mode, we consider the online decentralized operation and pay special attention to the grid tie-line power fluctuation. This problem is challenging due to the randomness of the renewable power generation, the global constraints about multiple microgrids, and the correlation among stages. We model the decentralized dispatch problem as a rolling horizon Dec-MDP and provide an approximate solution method, namely, alternately minimizing among different microgrids at the online stage and calculating approximate value functions in the offline preparation process. The approximate value functions make the online decision turn out to be a single-stage decentralized decision problem. Online decision calculation based on delayed communication is to guarantee all the microgrids to start conducting an action immediately while receiving the information related to them. We hope this paper brings insight onto the tie-line power fluctuation stabilization while multiple microgrids connecting to the same point of interconnection.

A Novel Data Driven Voltage Control Approach for Grid Connected Wind Power Plants

Due to increasing penetration of wind power plants (WPP), power grids are facing significant power quality challenges at the point of interconnection (POI). To achieve stable and robust power system operation, reactive power plays a vital role. Reactive power needed to compensate voltage fluctuations at the POI of the WPP varies with a short-circuit ratio (SCR). The reactive power capability of a WPP is also limited and largely depends on various operating conditions. In a physical system, it is difficult to find the correlation among critical parameters for voltage control. In this paper, a data-driven voltage control approach is proposed for a grid-connected WPP. Two regression models are developed through surface fitting using MATLAB curve fitting toolbox: One model based on simulation data is to determine the required reactive power for grid voltage compensation; another model based on field measurement data is to determine the reactive power characteristics of the WPP. The reactive power compensation device is capacitors in this study. Two controllers, a central WPP controller, and a capacitor controller are designed, and their effectiveness is validated through several case and sensitivity studies.

Solar PV Energy Generation System Interfaced to Three Phase Grid With Improved Power Quality

This paper deals with a multipurpose distributed sparse (DS) control approach for a single stage solar photovoltaic (PV) energy generation system (SPEGS). This SPEGS is interfaced here to the three phase grid at varying solar irradiance and compensating the nonlinear load tied at point of common interconnection. The SPEGS performs multitasks. It feeds the generated solar PV power to the local three phase grid. It reduces the harmonics of loads and furnished balanced currents of local three-phase grid. The SPEGS uses a solar PV array, a voltage source converter (VSC), a nonlinear load, a three phase grid, and a dc-link capacitance. In case, when the solar irradiance is not available, the proposed system works as distribution static compensator by utilizing same VSC. For extracting maximum power from the PV source, the traditional perturb and observe (P&O) scheme is utilized here. The tracking performance and efficiency of P&O technique are also examined here at rapid changing climatic conditions to show the behavior of the P&O scheme. The DS control approach is capable to estimate required fundamental component to find out reference grid currents. The proposed control approach is validated on a developed prototype in the laboratory.

Case study on the effects of partial solar eclipse on distributed PV systems and management areas

Photovoltaic (PV) systems are weather-dependent. A solar eclipse causes significant changes in these parameters, thereby impacting PV generation profile, performance, and power quality of larger grid, where they connect to. This study presents a case study to evaluate the impacts of the solar eclipse of 21 August 2017, on two real-world grid-tied PV systems (1.4 MW and 355 kW) in Miami and Daytona, Florida, the feeders they are connected to, and the management areas they belong to. Four types of analyses are conducted to obtain a comprehensive picture of the impacts using 1 min PV generation data, hourly weather data, real feeder parameters, and daily reliability data. These analyses include: individual PV system performance measurement using power performance index; power quality analysis at the point of interconnection; a study on the operation of voltage regulating devices on the feeders during eclipse peak using an IEEE 8500 test case distribution feeder; and reliability study involving a multilayer perceptron framework for forecasting system reliability of the management areas. Results from this study provide a unique insight into how solar eclipses impact the behaviour of PV systems and the grid, which would be of concern to electric utilities in future high penetration scenarios.

From microgrids to aggregators of distributed energy resources. The microgrid controller and distributed energy management systems

Microgrids are a collection of distributed energy resources (DER) within a specific boundary, with a control system for their management and operations at the point of interconnection with the distribution utility. As microgrid concepts evolve, they are being applied to aggregations of DER outside boundaries with appropriate controls for operation with transmission and distribution utilities and participation in markets. This article marks this evolution and points towards the common functionalities of microgrid controllers and distributed energy management systems for integration of DER into transmission and distribution operations and markets.

Sensitivity Analysis of Renewable Energy Integration on Stochastic Energy Management of Automated Reconfigurable Hybrid AC–DC Microgrid Considering DLR Security Constraint

This paper aims to investigate the optimal scheduling of stochastic reconfigurable hybrid ac-dc microgrid (MG) in the presence of renewable energies and also considering dynamic line rating (DLR) constraint. DLR is a practical limitation that can potentially affect the ampacity of lines, particularly in the islanded mode when the lines reach their maximum capacity in lack of main generation source at the point of interconnection with the utility. In order to prevent overloading of the lines, the reconfiguration technique is developed to change the topology of the network by some prelocated switches. A linearization technique is adapted to address the nonlinearity of both nodal ac power flow and the DLR constraints. The unscented transform technique is utilized to model uncertainties including renewable energy generations, hourly load demands, and hourly market prices along with the DLR uncertainties such as solar radiation, wind speed, and ambient temperature. Finally, a sensitivity analysis is performed to see the effect of wind speed and solar radiation on the energy management of hybrid ac-dc MG. The performance of the proposed methodology is examined on a modified IEEE-33 bus test system, which demonstrates the high efficiency and importance of the proposed techniques in minimizing the hybrid ac-dc MG operation cost while all of the constraints of the network are satisfied.

Optimal Management of Energy Consumption and Comfort for Smart Buildings Operating in a Microgrid

This paper presents a mixed integer non-linear programming model to optimize, in a centralized fashion, the operation of multiple buildings in a microgrid. The proposed model aims to minimize the total cost of the energy imported from the main grid at the interconnection point, managing the power demand and generation of buildings, while operational constraints of the electrical grid are guaranteed. This approach considers the management of heating, ventilation, and air conditioning units, lighting appliances, photovoltaic generation and energy storage system of each building. Comfortable indoor conditions for the occupants are kept by a set of mathematical constraints. Additionally, a strategy that simplifies the original model is presented, based on a set of linearization techniques and equivalent representations, obtained through a pre-processing stage executed in EnergyPlus software. This strategy allows approximating the proposed model into a mixed integer linear programming formulation that can be solved using commercial solvers. The proposed model was tested in a 13-bus microgrid for different deterministic cases of study with non-manageable loads and smart buildings. A large-size test case is also considered. Finally, a rolling horizon strategy is proposed with the aim of addressing the uncertainty of the data, as well as reducing the amount of forecasting data required.

A method to identify weak points of interconnection of renewable energy resources

The increasing penetration of renewable energy resources (RERs) is challenging power grid planning and operation in maintaining grid reliability. Potential power grid reliability and stability issues may arise when large-scale RERs are connected to a weak power grid. These issues may become more significant due to the mutual interactions among RERs that are interconnected electrically close through a power network. Weakness analysis based on grid strength assessment is useful for identifying the potential weak grid issues. However, when taking into account the impact of the interactions among RERs, the weakness analysis becomes computationally challenging. Different combinations of points of interconnections (POIs) of RERs may have different impacts on grid strength at each POI. Due to the combination nature, such weakness analysis may be time-consuming when identifying the weakest combination of POIs from a large number of potential candidates in realistic power grids. To address this concern, the impact of the power network structure on grid strength is analyzed in this paper. It is found that the impact mainly depends on the impedance ratios at POIs. The findings can be summarized as two criteria to develop a recursive method for fast identification of the weakest combination in this paper. The efficacy of the proposed method is demonstrated through case studies on the IEEE 39-bus system and a realistic power grid.

Transmission Design and Analysis for Large-Scale Offshore Wind Energy Development

The offshore wind resource is very large in many coastal regions, over 80,000 MW capacity in the region studied here. However, the resource cannot be utilized unless distant offshore wind generation can be effectively collected and brought to shore. Based on extensive oceanographic, environmental, and shipping data, a realistic wind energy deployment layout is designed with 160 wind power plants each 500 MW. The power collection and transmission infrastructure required to bring this power to shore and connect it to the electricity grid is designed and analyzed. Three types of connection to shore are compared; high voltage AC to the nearest onshore point of interconnection (POI), high voltage DC with voltage-source converter (HVDC-VSC) to the nearest onshore POI, and connecting to an offshore HVDC backbone running parallel to shore that interconnects multiple wind power plants and multiple POIs ashore. The electrical transmission losses are estimated step by step from the wind turbines to the POI. The results show that such a large system can be built with existing technology in near-load resources, and that losses in the HVDC-VSC systems are approximately 1%-2% lower than that in the AC system for a distance about 120 km from shore.