Optimal Voltage Regulation of Unbalanced Distribution Networks with Coordination of OLTC and PV Generation

Photovoltaic (PV) smart inverters can regulate voltage in distribution systems by modulating reactive power of PV systems. In this paper, an optimization framework for optimal coordination of reactive power injection of smart inverters and tap operations of voltage regulators for multi-phase unbalanced distribution systems is proposed. Optimization objectives are minimization of voltage deviations and tap operations. A novel linearization method convexifies the problem and speeds up the solution. The proposed method is validated against conventional rule-based autonomous voltage regulation (AVR) on the highly-unbalanced IEEE 37 bus test system. Simulation results show that the proposed method estimates feeder voltage accurately, voltage deviation reductions are significant, over-voltage problems are mitigated, and voltage imbalance is reduced.Comment: IEEE Power and Energy Society General Meeting 201

Coordination of OLTC and Smart Inverters for Optimal Voltage Regulation of Unbalanced Distribution Networks

Photovoltaic (PV) smart inverters can improve the voltage profile of distribution networks. A multi-objective optimization framework for coordination of reactive power injection of smart inverters and tap operations of on-load tap changers (OLTCs) for multi-phase unbalanced distribution systems is proposed. The optimization objective is to minimize voltage deviations and the number of tap operations simultaneously. A novel linearization method is proposed to linearize power flow equations and to convexify the problem, which guarantees convergence of the optimization and less computation costs. The optimization is modeled and solved using mixed-integer linear programming (MILP). The proposed method is validated against conventional rule-based autonomous voltage regulation (AVR) on the highly-unbalanced modified IEEE 37 bus test system and a large California utility feeder. Simulation results show that the proposed method accurately estimates feeder voltage, significantly reduces voltage deviations, mitigates over-voltage problems, and reduces voltage unbalance while eliminating unnecessary tap operations. The robustness of the method is validated against various levels of forecast error. The computational efficiency and scalability of the proposed approach are also demonstrated through the simulations on the large utility feeder.Comment: Accepted for Electric Power Systems Research. arXiv admin note: text overlap with arXiv:1901.0950

The Coordination and control of smart inverters utilizing Volt-VAr and Volt-Watt in low voltage networks, and opportunities for South Africa

Thesis (MEng)--Stellenbosch University, 2022.ENGLISH ABSTRACT: Increasing photovoltaic (PV) penetration in the low-voltage (LV) distribution network leads to grid-interconnection issues for electric utilities. These issues include voltage violations, equipment overloading and frequency instability. To mitigate these problems, advanced smart inverter functionality is becoming increasingly popular in states and countries with high renewable energy penetration levels. Although smart inverters have a wide range of benefits for the utility, these benefits are limited to the local level due to autonomous inverter control. This research investigates the benefits of coordinated inverter control in mitigating voltage violations in LV feeders due to increasing PV penetrations. A critical literature review on the grid interconnection requirements and smart inverter functionality guidelines informs on the gaps that need to be addressed to allow for increased smart inverter deployment in South Africa. The literature review also explores the benefits of distributed energy resource management systems (DERMS) and virtual power plants (VPPs), and the requirements for each platform. Based on the literature review’s findings, a simulation has been conducted to investigate the benefits of coordinated smart inverter voltage regulation control, particularly Volt-VAr and Volt-Watt, to increase hosting capacity in LV networks. The proposed methodology considers the feeder-wide voltage conditions instead of local point of connection (PoC) conditions using sensor measurements, and the fairness of voltage regulation and active power curtailment among customers on a feeder. This proposed methodology can be used as an intermediate solution for coordinating smart inverters without the use of extensive communication infrastructure and advanced aggregating platforms. The simulation results show an improvement in voltage profiles using coordinated Volt-VAr and Volt Watt inverter control and feeder-wide awareness. The improved voltage profiles can accommodate higher levels of PV penetration and thus increase hosting capacities in LV feeders.AFRIKAANSE OPSOMMING: Toenemende fotovoltaïese (PV) penetrasie in die laagspanning (LV) verspreidings netwerk lei tot probleme vir die elektrisiteitverskaffer. Hierdie kwessies sluit spanning skendings, oorlading van toerusting en onstabiliteit in frekwensie in.Gevorderde slim-omsetter funksionaliteit word gebruik om hierdie probleme te verlig en raak dus al hoe meer gewild in state en lande met ʼn hoë opname van hernubare energie. Alhoewel slim omsetters 'n wye verskeidenheid voordele vir die kragstelsel inhou, is hierdie voordele beperk tot die plaaslike vlak as gevolg van outonome omsetter-beheer. Hierdie navorsing ondersoek die voordele van gekoördineerde omsetterbeheer om spanningskendings in LV-netwerke te minimeer. 'n Kritiese literatuuroorsig in netwerkverbindingsvereistes en riglyne vir slim-omsetter funksionaliteit lig uit die leemtes wat opgelos moet word om 'n groter implementering van slimomsetters in Suid Afrika moontlik te maak. Die literatuuroorsig ondersoek ook die voordele van verspreide energiehulpbronbestuurstelsels en virtuele kragstasies, en die vereistes vir elke platform. Op grond van die bevindinge van die literatuurstudie is 'n simulasie uitgevoer om die voordele van gekoördineerde slim-omsetter spanningsreguleringsbeheer, veral Volt-VAr en Volt-Watt, in LV-netwerke te ondersoek om gasheervermoë te verhoog. Die voorgestelde metodologie neem in ag die toevoer-wye spanningstoestande, die billikheid van spanning regulering, en die aktiewe kragbeperking onder kliënte. Hierdie voorgestelde metodologie kan gebruik word as 'n intermediêre oplossing vir die koördinering van slim-omsetters sonder die gebruik van uitgebreide kommunikasie-infrastruktuur en gevorderde samevoegings platforms. Die simulasie resultate van om die gekoördineerde Volt-Watt-omsetterbeheer en netwerk-wye bewustheid te gebruik, toon 'n verbetering in spanningsprofiele. Die verbeterde spanningsprofiele kan hoër vlakke van PV-opname akkommodeer en dus gasheer kapasiteit in LVnetwerke vergroot.Master

The Combined Effect of Photovoltaic and Electric Vehicle Penetration on Conservation Voltage Reduction in Distribution System

Global conditions over the past dozen years have led to an expanded appetite for renewable energy sources: The diminishing fossil fuel supply, the political instability of countries producing these fossil fuels, the ever-more destructive effects of global warming, and the lowering of costs for renewable energy technologies have made countries around the world reconsider their sources of energy. The proliferation of photovoltaic (PV) systems especially has surged dramatically with the decreasing initial costs for installation, and increasing government support in the form of renewable energy portfolios, feed-in-tariffs, tax incentives, etc. Furthermore, electric vehicles (EV) are also becoming widespread due to recent advances in battery and electric drive technologies, and the desperate need to reduce air pollution in urban areas. Meanwhile, electric utilities are always making an effort to run their system more efficiently by encouraging the use of energy-efficient appliances and customer participation in demand-side management programs. In an attempt to further reduce load demand; many utilities regulate the voltage along their distribution feeders in a particular way that is referred to as conservation voltage reduction (CVR). The key principle of CVR operation is that the ANSI standard voltage band between 114 and 126 volts can be compressed via regulation to the lower half (114–120) instead of the upper half (120–126), producing measurable energy savings at low cost and without harm to consumer appliances. As the penetration of distributed PV and EV charging station increases, this can dramatically change the conventional demand profile as PV system act as negative loads during the daylight hours, and EVs significantly increase load demand during charging. Consequently, traditional means of controlling the voltage by capacitor switching and voltage regulators can be improved in this “smart” grid era by adding a fleet of enabling devices including the smart PV inverter functionalities, such as Volt/VAR control, and intelligent EV charging schemes. This thesis explores how better energy conservation is achieved by CVR in a modern distribution system with advanced distributed PV systems inverters and EV loads. Then it summarizes computer simulations that are conducted on the IEEE 37 and IEEE 123 node test feeders using OpenDSS interfaced with MATLAB

Dynamic Weight-Based Collaborative Optimization for Power Grid Voltage Regulation

Power distribution grids with high PV generation are exposed to voltage disturbances due to the unpredictable nature of renewable resources. Smart PV inverters, if controlled in coordination with each other and continuously adapted to the real-time conditions of the generation and load, can effectively regulate nodal voltages across the feeder. This is a fairly new concept and requires communication and a distributed control logic to realize a fair utilization of reactive power across all PV systems. In this paper, a collaborative reactive power optimization is proposed to minimize voltage deviation under changing feeder conditions. The weight matrix of the collaborative optimization is updated based on the reactive power availability of each PV system, which changes over time depending on the cloud conditions and feeder loading. The proposed updates allow PV systems with higher reactive power availability to help other PV systems regulate their nodal voltage. Proof-of-concept simulations on a modified IEEE 123-node test feeder are performed to show the effectiveness of the proposed method in comparison with four common reactive power control methods