Feeder Voltage Regulation Research Articles

Northern goshawk optimization for optimal reactive power compensation in photovoltaic low-voltage radial distribution networks

In recent years, photovoltaic systems (PVs) have been increasingly integrated into radial distribution networks (RDNs). However, network operators experience significant issues because they are sporadic. To reduce the load on the main grid and improve the network performance, capacitor banks (CBs) are frequently employed for power factor correction and VAr compensation. However, a large number of CBs must be switched at once in accordance with variations in load and PV generation to maintain feeder voltage regulation and improve its performance. This study's optimization strategy for CB control considers a variety of goals. Using seasonal load profiles and PV generation patterns, a novel and efficient northern goshawk optimization (NGO) was created to determine the appropriate control of CBs. By resolving the typical CBs allocation problem in EDNs and comparing the findings with those in the literature, the effectiveness of NGO was initially cross-verified. In the second stage, an NGO is used to maximize annual net savings while maintaining the best possible control over CBs. Considering the PVs and CBs of the network, a modified IEEE 33-bus test system was used to evaluate the effectiveness of the suggested methodology.

A Method for Calculating the Adjustable Capacity of Feeder Load Aggregators Considering the User’s Wishes

Abstract With the deepening of China’s energy reform, large-scale renewable energy access has put forward higher requirements for the flexible adjustment ability of the power system. The research and application of mining flexible and adjustable resources on the user side to participate in the peak regulation and frequency regulation of the power grid have received extensive attention. With the gradual opening of the power market and the deepening of the reform of the power system, the feeder load aggregator has gradually become a new role in the power market, and the feeder load aggregator plays an important role in the centralized management of users, the optimization of distribution, and the realization of market-oriented transactions. However, the research on the participation of feeder loads in the auxiliary services of power grid peak regulation and frequency regulation is not perfect. In this context, this paper proposes a method for calculating the adjustable capacity of feeder load aggregators considering the wishes of users, in which the maximum voltage adjustable at the feeder and the change of the capacity of each user caused by the feeder voltage regulation are calculated by the feeder load aggregator through the power flow relationship, and finally the adjustable capacity declaration for the ancillary service market is completed.

A robust control scheme for voltage and reactive power regulation in islanded AC microgrids

In multi-feeder microgrid systems, accurate power sharing and voltage regulation at each load feeder is more challenging than the conventional single-feeder microgrids. This paper presents an enhanced resilient control strategy for multi-feeder micro-network systems by considering the load feeder voltage regulation and power balancing as a quadratic optimization problem. The proposed control strategy is composed of impedance estimator and optimal controller. However, the impedance estimator obtains each load feeder impedance while optimal controller computes the voltage commands for each distributed generator. One of the important aspects of the proposed control scheme is that only the voltage magnitude information is required to transfer at each inverter's controller, with primary aim to achieve the two-fold objectives. This control strategy is also extended to approximate the whole network impedance into solitary load feeder for micro-networks with extensive number of load feeders. This makes the system computationally less burdening. The MATLAB/Simulink and experimental results are obtained under varying load conditions and line parameter uncertainties for radial type multi-feeder microgrid configuration that reflects the effectiveness of the proposed scheme. The verification outcomes prove the proposed method capability of accurate reactive power sharing, regulation of load feeder voltages, and frequency restoration.

Cooperative Peak Shaving and Voltage Regulation in Unbalanced Distribution Feeders

This paper considers the co-operation of distributed generators (DGs), battery energy storage systems (BESSs) and voltage regulating devices for integrated peak shaving and voltage regulation in distribution grids through a co-optimization framework, which aims to minimize the operational costs while fulfilling the operational constraints of network and devices. To account for the uncertainties of load demand and generation, we then convert the co-optimization model into a two-stage stochastic program where state-of-charge (SoC) trajectories of BESSs and operation of voltage regulating devices are optimized at the first stage for day-ahead scheduling, while the reactive powers of DGs and BESSs are left at the second stage for potential intra-day scheduling to handle short-term voltage issues. The proposed co-optimization scheme is validated on the IEEE 37-node test feeder and compared with other practices.

Delay-Tolerant Predictive Power Compensation Control for Photovoltaic Voltage Regulation

Voltage regulation is imperative for the successful operation of electricity distribution networks, especially with a high penetration level of photovoltaic (PV) systems. Power compensation control (PCC) that uses both reactive power compensation and active power curtailment has shown promising results in alleviating voltage rise problems. It crucially relies on real-time communications among distributed PV systems. However, the transmission of state measurements and control signals in PCC is hampered by inevitable communication delays. Therefore, it is important to not only estimate the maximum tolerable communication delay (MTCD) but also develop an alternative technique for PCC under abnormal communication delay (ACD) conditions. This article presents a delay-tolerant predictive PCC for voltage regulation in distribution feeders. After estimating the MTCD based on voltage and power mutation, it uses normal PCC for effective operation when communication delay is within MTCD, or switches to predictive PCC under ACD conditions. An accurate prediction is achieved using a double neural network with online adjustment of weights and samples. Simulations on a sample distribution network demonstrate the effectiveness of our presented approach.

Distribution feeder costs as a function of the penetration of distributed generation – key drivers and trends

Distributed generation (DG) has experienced extraordinary growth in installed capacity in many countries. DG can have a significant impact on both the investment and operational costs of distribution feeders. However, in many contexts, such impact is still not clear. Moreover, the impact of DG could be positive or negative and could be different for different levels of DG penetration. This paper proposes a high-level approach to estimate the cost of distribution feeders as a function of the DG penetration scenario, for different types of medium voltage grids. Grid scenarios include urban and rural feeders, intermittent and conventional DG technologies, different distributions of loads and DG along the feeder, and passive and active voltage regulation. For each grid scenario, we build the curve of total feeder cost as a function of the penetration of DG. We identify the levels of the penetration that create savings and the levels that drive additional costs. We find that, for all the explored medium voltage grids, DG creates savings for low penetration scenarios, but increases the total feeder cost for higher penetrations, which is largely driven by the increase in power losses. We finally discuss the possible policy implications of the resulting cost curves.

Decoupled Control Strategy for Electric Springs: Dual Functionality Feature

Smart grid philosophy recommends a wide spread of residential roof-top installed grid-connected photovoltaic (PV) systems as a benchmark for renewable energy (RE) emphasis to future power generation. These systems must adopt power electronic-based converters to perform grid integration function. On the other side, concerns about voltage fluctuations, which are directly related to power system stability, have arisen from the increasing use of intermittent renewable energy sources (RES) distributed in the grid. Hence, a power electronic-based converter topology, known as Electric Spring (ES), has been developed to be additively connected in series with non-critical residential loads. It has the ability to regulate the mains voltage via reactive power compensation. In this paper, a novel control scheme is proposed for ESs operation. The presented control technique offers conventional ES a decoupled dual functionality. Besides, its inherent ability of feeder voltage regulation, the ES can, under the proposed control technique, simultaneously inject locally available PV power into the grid via the same power electronic converter. The system analysis and mathematical modeling of the proposed control scheme are demonstrated in detail. To verify the proposed technique effectiveness, both simulation and experimental investigation are carried under various bus voltage levels' cases: normal, sag, and swell. Moreover, the system performance is attested under irradiance changes. The results from simulations and experimental setup prove the applicability of the ES dual functionality even under severe disturbances.

Droop Control Methods for PV-Based Mini Grids with Different Line Resistances and Impedances

Different droop control methods for PV-based communal grid networks (minigrids and microgrids) with different line resistances (R) and impedances (X) are modelled and simulated in MATLAB to determine the most efficient control method for a given network. Results show that active power-frequency (P-f) droop control method is the most efficient for low voltage transmission networks with low X/R ratios while reactive power-voltage (Q-V) droop control method is the most efficient for systems with high X/R ratios. For systems with complex line resistances and impedances, i.e. near unity X/R ratios, P-f or Q-V droop methods cannot individually efficiently regulate line voltage and frequency. For such systems, P-Q-f droop control method, where both active and reactive power could be used to control PCC voltage via shunt-connected inverters, is determined to be the most efficient control method. Results also show that shunt-connection of inverters leads to improved power flow control of interconnected communal grids by allowing feeder voltage regulation, load reactive power support, reactive power management between feeders, and improved overall system performance against dynamic disturbances.

Model-Free Optimal Coordination of Distributed Energy Resources for Provisioning Transmission-Level Services

Collective control of distributed energy resources (DER)—such as photovoltaic (PV) inverters or battery storage—have the potential to provide regulation services to the bulk electric grid. While optimal power flow techniques may be used to coordinate DER for this purpose, these approaches typically rely on accurate network models and a large number of system measurements. In this paper, we consider an approach that alleviates these modeling and measurement requirements. Here, we consider a two-dimensional adaptive control scheme known as extremum seeking, or ES, to perform optimization without knowledge of a model of the distribution network. We apply this scheme to enable simultaneous feeder head active power and voltage magnitude reference tracking, as well as feeder voltage regulation. From the perspective of the transmission grid, this approach essentially transforms the distribution feeder into a controllable (P,V) bus. Simulation results confirm the ability of the approach to track substation real power and voltage reference signals while maintaining distribution system voltages within acceptable tolerances.

Impacts of Voltage Control Methods on Distribution Circuit’s Photovoltaic (PV) Integration Limits

The widespread integration of photovoltaic (PV) units may result in a number of operational issues for the utility distribution system. The advances in smart-grid technologies with better communication and control capabilities may help to mitigate these challenges. The objective of this paper is to evaluate multiple voltage control methods and compare their effectiveness in mitigating the impacts of high levels of PV penetrations on distribution system voltages. A Monte Carlo based stochastic analysis framework is used to evaluate the impacts of PV integration, with and without voltage control. Both snapshot power flow and time-series analysis are conducted for the feeder with varying levels of PV penetrations. The methods are compared for their impacts on (1) the feeder’s PV hosting capacity; (2) the number of voltage violations and the magnitude of the largest bus voltage; (3) the net reactive power demand from the substation; and (4) the number of switching operations of feeder’s legacy voltage support devices i.e., capacitor banks and load tap changers (LTCs). The simulation results show that voltage control help in mitigating overvoltage concerns and increasing the feeder’s hosting capacity. Although, the legacy control solves the voltage concerns for primary feeders, a smart inverter control is required to mitigate both primary and secondary feeder voltage regulation issues. The smart inverter control, however, increases the feeder’s reactive power demand and the number of LTC and capacitor switching operations. For the 34.5-kV test circuit, it is observed that the reactive power demand increases from 0 to 6.8 MVAR on enabling Volt-VAR control for PV inverters. The total number of capacitor and LTC operations over a 1-year period also increases from 455 operations to 1991 operations with Volt-VAR control mode. It is also demonstrated that by simply changing the control mode of capacitor banks, a significant reduction in the unnecessary switching operations for the capacitor banks is observed.

LV Grid Voltage Regulation Using Transformer Electronic Tap Changing, With PV Inverter Reactive Power Injection

Despite increasing levels of solar-Photovoltaic (PV) penetration in electrical distribution networks, to date the inverters of these PV systems have not been significantly utilized for distribution network control. One particular area of interest for these inverters is their potential to inject/absorb reactive power to/from grid to help manage the voltage profile of their distribution feeder. Various reactive power management strategies have been proposed to address this issue using different voltage-reactive power relationships, but their effectiveness can be limited by competing performance objectives, or simply because the higher resistance characteristics of a typical Low Voltage feeder constrain the range of voltage regulation that can be achieved by reactive power injection. This paper addresses this issue by proposing a combined strategy, where an electronic tap-changer is incorporated into the feeder distribution transformer to provide the feeder voltage regulation function, and the PV distributed generation systems at each feeder bus are then used to minimize feeder losses by providing local load reactive power support. The investigation considers a variety of issues such as feeder impedance, dynamic transformer tap changing, different load types, and levels of PV penetration. The results obtained from a detailed distribution feeder simulation model show that the combined strategy can very effectively regulate the distribution feeder voltage throughout an entire 24 h period even with high solar irradiance fluctuations, while still significantly reducing feeder losses.

English

This paper mainly deals the impact of relays on feeder protection also different factors used to control the active power, reactive power, power reversals, fault current magnitude and balancing condition of power system to protect the distribution system. when Distributed Generation sources are integrated in to the grid above all problems are occurs along with the feeder voltage regulation and feeder protection for effective operation of DG connected Distribution networks needs control the above factors for this Solid Oxide Fuel Cell (SOFC) is modeled and integrated in to the grid, Rectifier inverter pair (PCU) is consider for controlling the all factors to give protection, simulation are performed using Matlab/Simulink.

A Study on Compensating Voltage Drop in Distribution Systems due to Nighttime Simultaneous Charging of Electric Vehicles Utilizing Charging Power Adjustment and Reactive Power Injection

SUMMARYTo reduce the environment load, electric vehicles (EV) have been attracting attention and expectations. since they can run with at good fuel efficiency and without exhaust gases. It is expected that EV will become more and more popular. Generally, EVs would be used for driving during daytime and be charged during the nighttime, considering lifestyle and time‐of‐use patterns. If most EV owners adopt this use pattern, feeder voltage profiles could be greatly affected, causing severe voltage drops. The battery charger for EVs described in this papers consists of a self‐commutated inverter, which in principle can control not only active power but also reactive power. We propose a basic feeder voltage regulation algorithm, “PQ control”, using EVs which involves adjustment of the EV charging schedule and reactive power injection. In addition, we propose “prediction control”, which is based on “PQ control” and is takes account of prediction of the receiving voltage. Advanced “communication control” regulation algorithms, utilizing communication among EVs and the distribution system operator, are also proposed. The purpose of this paper is to confirm the effectiveness of the three proposed algorithms by simulations.

EV Charging Facilities and Their Application in LV Feeders With Photovoltaics

Low-voltage (LV) grid feeders with high penetration of photovoltaics (PVs) are often affected by voltage magnitude problems. To solve such issues, previous research has shown that reactive power methods, active power curtailment and grid reinforcement can be used for voltage support, yet showing several limits. We introduce the use of electric vehicle (EV) public charging stations with energy storage system (ESS) as a solution for voltage regulation in LV feeders with PV. A novel method is proposed to determine the ESS charging load required for voltage regulation and compare the results for the different locations in the feeder. With time-series simulations, we quantify the energy size required for a station ESS. A Belgian LV residential grid, modeled using real PV generation and load profiles, is used as case study. The method and simulation results show the effectiveness of using public EV charging facilities with the additional function of voltage regulation in feeders with PV.

A Study on Compensating Voltage Drop in Distribution Systems due to Nighttime Simultaneous Charging of Electric Vehicles Utilizing Charging Power Adjustment and Reactive Power Injection

To realize reduction in environment load, electric vehicles (EV) have been attracting great attentions and expectations since they can run at good fuel efficiency without exhaust gases. It is expected that the EVs will become more and more popular. Generally, EVs would be used for driving during daytime and be charged during nighttime considering our lifestyle and time-of-use program. If most of EV owner adopt the use pattern, feeder voltage profiles could be greatly affected. It would cause severe voltage drop.In this paper, battery charger for EV consists of self-commutated inverter, which can control not only active power but also reactive power in principle. We propose a basic feeder voltage regulation algorithm, “PQ control”, using EVs by means of adjustment of EV charging schedule and reactive power injection. In addition, we propose “prediction control” which is based on “PQ control” and is considering prediction of receiving voltage. And advanced regulation algorithms, “communication control”, utilizing communication among EVs and the distribution system operator are proposed. The purpose of this paper is to confirm the effectiveness of the three proposed algorithms by simulations.

A Two Ways Communication-Based Distributed Control for Voltage Regulation in Smart Distribution Feeders

Smart grid initiative is based on several pillars among which integrating a wide variety of distributed generation (DG) is of particular importance. The connection of a large number of DG units among loads may result in a severe voltage regulation problem and the utility-side voltage regulators might no longer be able to use conventional control techniques. In addition, smart grid should provide new digital technologies such as monitoring, automatic control, and two way communication facilities to improve the overall performance of the network. These technologies have been applied in this paper to construct a distributed control that has the capability to provide proper voltage regulation in smart distribution feeders. The functions of each controller have been defined according to the concept of intelligent agents and the characteristics of the individual DG unit as well as utility regulators. To verify the effectiveness and robustness of the proposed control structure, a real time simulation model has been proposed. The simulation results show that distributed control structure has the capability to mitigate the interference between DG facilities and utility voltage regulators.

Assessment of Feeder Voltage Regulation Using Statistical Process Control Methods

Power-quality voltage and current transient waveform data have been explored rather extensively as the primary input data in predictive maintenance, automatic root-cause analysis, and evaluating system performance to indicate potential problems. Unfortunately, very few efforts have been directed toward making use of the voluminous steady-state data collected alongside waveform data. Therefore, this paper proposes to use steady-state data, particularly, rms voltage data to detect abnormal trend behavior that may be indicative of a problem. Specifically, this paper develops a statistical analysis algorithm based on the well-known statistical process control methods for assessing feeder voltage regulation performance. The assessment results can be used to indicate potential regulator problems as well. The efficacy of the method is demonstrated by applications to two sets of actual RMS voltage data.

Dynamic Voltage Collapse Index— Wind Generator Application

Wind-driven induction generators are popular due to their robust construction and performance. They are typically connected to a distribution system through a feeder and may cater to a local load of comparable size. Wind characteristics are unpredictable, sometimes causing large bursts of power flow. During such bursts, the feeder voltage regulation is problematic, possibly leading to a collapse. A robust collapse indicator, with the least possible local measurements, located at the sending or receiving end of the feeder, is desirable to operate protective equipment. This paper presents an implementation of such a dynamic voltage collapse indicator. Simulation results are included to demonstrate the versatility of the proposed method

Voltage control integrated in distribution management system

The voltage control in distribution networks is established as a centralized analytical function in this paper. It is integrated in the Distribution Management System. Control devices consist of under-load and off-voltage tap changing transformers, feeder voltage regulators and buck/boost transformers. On the basis of areas whose voltages are influenced by these control devices and their action speeds, the voltage control problem is decomposed in space and time. The space decomposition enables a solution of the distribution voltage control problem for the medium voltage (MV) network of each supply transformer (substation) separately. As well, the time decomposition enables a solution in the operation planning mode and the real time mode separately. The voltage control is each time stated as a constrained optimization problem. The network voltage profile quality is quantified by the damage (inconvenience) that electric consumers sustain due to steady state voltage deviations. Therefore, this damage is used as the optimization objective. The effectiveness of the voltage control is demonstrated on a real-life DN.

General probabilistic voltage drop calculation method for LV distribution networks based on a beta p.d.f. load model

In previous work, it was shown that a probabilistic approach to the calculation of voltage regulation in low voltage residential distribution feeders is superior to deterministic methods. The probabilistic technique, known as the Herman Beta method, is now being used on a national scale in South Africa for the design of residential distribution circuits. This paper describes enhancements to the Herman Beta method that improves accuracy and particularly addresses the issue of successive risk.