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Medium-voltage (MV) distribution networks that are spread through larger territory and threatened by extreme weather conditions are sometimes formed by very long underground cable lines. In such circumstances, a significant amount of capacitive reactive power flow can be generated. If, concurrently, there is low power demand in the network, it can result in significant reverse reactive power flows and voltage rise issues. This paper proposes a general approach for analyzing and mitigating voltage rise issues and demonstrates it using an example of a real distribution network that operates under the described conditions. Previous studies that dealt with this problem did not include the allocation of multiple shunt reactors in a larger distribution network, modeling a high number of lines that create reverse reactive power flows, and modeling the main distribution transformers, which are the locations where voltage rise predominantly occurs. In this paper, we demonstrate that precise allocation and placement of multiple shunt reactors in a fully modeled, larger distribution system, including transformer models, can reduce reverse reactive power flows, thereby improving voltage in the distribution system. If hourly control of the power factor from the distributed generation unit is also implemented, the voltage can be further improved. [ABSTRACT FROM AUTHOR]

The goal of reducing greenhouse gas emissions and energy transition has created many favorable conditions to promote solar power generation technology. However, from a technical perspective, integrating solar power into the power grid poses many challenges in grid operation. This study investigates the impact of rooftop solar power in terms of power quality in the urban distribution grid in Vietnam. The current study simulated a typical low-voltage distribution grid with single-phase and three-phase loads to evaluate important power quality issues, such as Total Harmonic Distortion (THD) of voltage and current, voltage unbalance, and voltage rises. A grid simulation grid was developed in Matlab/Simulink under different conditions for the penetration level of solar power and the daily variation of loads. These indexes were compared with the limits specified in Vietnamese standards and the relevant international standards of IEEE and IEC. Compliance with the provisions of these standards was provided, even in the case of solar power systems with a high level of penetration into Vietnam's urban distribution grid. [ABSTRACT FROM AUTHOR]

In this work, we focus on the degradation of membrane electrode assemblies (MEAs) in proton-exchange membrane water electrolysis (PEMWE) induced by different accelerated stress tests (ASTs), including constant-current mode, square-wave mode, and solar photovoltaic mode. In constant-current mode, at continuous testing for 600 h at 80 °C, a degradation of operating voltage increased by the enhanced current density from 22 µV/h (1 A/cm2) to 50 µV/h (3 A/cm2). In square-wave mode, we found that in the narrow fluctuation range (1–2 A/cm2), the shorter step time (2 s) generates a higher degradation rate of operating voltage, but in the wide fluctuation range (1–3 A/cm2), the longer step time (22 s) induces a faster operating voltage rise. In the solar photovoltaic mode, we used a simulation of 11 h sunshine duration containing multiple constant-current and square-wave modes, which is closest to the actual application environment. Over 1400 h ASTs, the solar photovoltaic mode lead to the most serious voltage rise of 87.7 µV/h. These results are beneficial to understanding the durability of the PEM electrolyzer and optimizing the components of MEAs, such as catalysts, membranes, and gas diffusion layers. [ABSTRACT FROM AUTHOR]

Medium-voltage (MV) distribution networks that are spread through larger territory and threatened by extreme weather conditions are sometimes formed by very long underground cable lines. In such circumstances, a significant amount of capacitive reactive power flow can be generated. If, concurrently, there is low power demand in the network, it can result in significant reverse reactive power flows and voltage rise issues. This paper proposes a general approach for analyzing and mitigating voltage rise issues and demonstrates it using an example of a real distribution network that operates under the described conditions. Previous studies that dealt with this problem did not include the allocation of multiple shunt reactors in a larger distribution network, modeling a high number of lines that create reverse reactive power flows, and modeling the main distribution transformers, which are the locations where voltage rise predominantly occurs. In this paper, we demonstrate that precise allocation and placement of multiple shunt reactors in a fully modeled, larger distribution system, including transformer models, can reduce reverse reactive power flows, thereby improving voltage in the distribution system. If hourly control of the power factor from the distributed generation unit is also implemented, the voltage can be further improved.

Recent years have seen a rapid uptake in distributed energy resources (DER). Such technologies pose a number of challenges to network operators, which ultimately can limit the amount of rooftop solar photovoltaic (PV) systems that can be connected to a network. The objective of this industry-based research was to determine the potential network effects of forecast levels of customer-owned rooftop solar PV on Energy Queensland's distribution network and formulate functions that can be used to determine such effects without the requirement for detailed network modeling and analysis. In this research, many of Energy Queensland's distribution feeders were modeled using DIgSILENT PowerFactory and analyzed with forecast levels of solar PV and customer load. Python scripts were used to automate this process, and quasi-dynamic simulation (QDSL) models were used to represent the dynamic volt–watt and volt–var response of inverters, as mandated by the Australian Standard AS/NZS 4777. In analyzing the results, linear relationships were revealed between the number of PV systems on a feeder and various network characteristics. Regression was used to form trend equations that represent the linear relationships for each scenario analyzed. The trend equations provide a way of approximating network characteristics for other feeders under various levels of customer-owned rooftop solar PV without the need for detailed modeling. [ABSTRACT FROM AUTHOR]

• Novel methods for mitigating undesired voltage rises in modern-day transmission power systems. • Comparison of methods. • Application on two actual power systems. • Very promising results and showcase of major contribution by renewable energy sources. This paper proposes some novel methods for mitigating undesired voltage rises in modern-day power systems. Some older approaches are also revisited in the light of new developments including the proliferation of power-electronic interfaced equipment. The analysis is performed using both power flow technique as well as long-term simulation employing quasi-steady-state approximation of short-term dynamics. Guidelines and mitigation countermeasures that may be utilized during either system planning or operation are investigated, such as optimal placement of new reactor installations, special transformer load-tap-changer (LTC) controls and reactive power absorption by renewable energy sources, such as wind farms connected through power converters in distribution feeders. Several case studies are investigated in two test systems: a sub-transmission area of the French Transmission Grid, and the Hellenic transmission power system, for which a number of different operating points is considered. [ABSTRACT FROM AUTHOR]

Recent years have seen a rapid uptake in distributed energy resources (DER). Such technologies pose a number of challenges to network operators, which ultimately can limit the amount of rooftop solar photovoltaic (PV) systems that can be connected to a network. The objective of this industry-based research was to determine the potential network effects of forecast levels of customer-owned rooftop solar PV on Energy Queensland’s distribution network and formulate functions that can be used to determine such effects without the requirement for detailed network modeling and analysis. In this research, many of Energy Queensland’s distribution feeders were modeled using DIgSILENT PowerFactory and analyzed with forecast levels of solar PV and customer load. Python scripts were used to automate this process, and quasi-dynamic simulation (QDSL) models were used to represent the dynamic volt–watt and volt–var response of inverters, as mandated by the Australian Standard AS/NZS 4777. In analyzing the results, linear relationships were revealed between the number of PV systems on a feeder and various network characteristics. Regression was used to form trend equations that represent the linear relationships for each scenario analyzed. The trend equations provide a way of approximating network characteristics for other feeders under various levels of customer-owned rooftop solar PV without the need for detailed modeling.

This paper proposes an optimal voltage regulation scheme (OVRS) for distribution systems with rich photovoltaic (PV). Various regulation devices are optimally controlled in a coordinated manner: PV inverter, D-STATCOM, step voltage regulator (SVR), and on-load-tap-changer (OLTC). A data structure algorithm is proposed to split the distribution system into layered zones considering the radial structure of the system. The solution process of the proposed scheme is accomplished by a meta-heuristic optimizer. OVRS addresses the voltage violations while yielding a coordinated operation of the various control devices. The proposed OVRS involves three control levels to completely prevent voltage violations. In the first control level, the PV inverter and D-STATCOM mitigate rapidly the local voltage deviation through injecting/absorbing optimized reactive power. The second control level is a decentralized-based control scheme that utilizes the voltage control devices in each zone to handle the voltage violations if any. For each zone, the control devices in the upper-stream zones (parent zones) are managed by the third control level to ensure cooperative control actions. The simulation results on the 119-bus distribution system, with clear, low fluctuation, and high fluctuation of solar radiation profiles, demonstrate the effectiveness of the proposed OVRS. [ABSTRACT FROM AUTHOR]

Behind-the-meter solar photovoltaics (PV) have the ability to impact the distribution system due to the significant fluctuations in energy production and potential reverse power flow. While these phenomena are well understood, this research will investigate the level of solar penetration at which voltage rise and flicker are observed on a real-world distribution network. Using solar power data measured at four second intervals from the Renewable Energy and Smart Grid Laboratory at Louisiana State University alongside detailed feeder data provided by a local utility, we investigate the impact of increasing levels of solar PV penetration on voltage rise and long-term flicker. Results suggest that feeders can handle up to 10% of customers installing 7-kW behind-the-meter solar systems before voltage rise and flicker are observed. For levels above 30% penetration, feeders experience significant power quality issues. We find that the safe penetration level of a specific feeder depends on the system's topology. • The paper addresses the impact of solar growth on voltage rise and long-term flicker. • The study has been conducted on three actually existing feeders in Louisiana. • One can identify vulnerable nodes within a feeders highly penetrated by solar. • Policy considerations are discussed for future planning of power systems. [ABSTRACT FROM AUTHOR]

This paper presents the details of exhaustive investigations on a typical Saudi distribution network showing the effectiveness of various control techniques to mitigate the voltage rise issues due to high penetration of solar photovoltaic (PV) systems. One of the major goals of Saudi Arabia future economic plans is to expand on renewable energy installations throughout the Kingdom. It is planned to generate 9.5 GW of electric power from renewable energy sources by 2023. Further, energy regulators in the Kingdom have announced policies and regulations govern the integration of small- and large-scale solar PV. However, distributed solar PV systems come with technical challenges, especially during high level of integration including grid stability, voltage rise, flickering, frequency fluctuation, and protection and coordination schemes. One issue is that the voltage profile is expected to change and rise to unacceptable level, especially with high solar PV penetration. Various voltage rise mitigation techniques investigated include active power curtailment, reactive power injection, and also a hybrid combination of these two methods. The paper reports the results of both steady-state and dynamic analyses of the Saudi distribution network at various load levels. The investigations reveal that the hybrid approach is more effective in the voltage rise mitigation. [ABSTRACT FROM AUTHOR]

In recent years, a rapid spread of residential photovoltaic power systems (PVs) causes voltage imbalance in distribution systems. For this reason, it has become difficult to control voltage in distribution systems to within the allowable range. Therefore, the authors have proposed a system for suppressing the voltage unbalance using single‐phase static capacitors (SCs). The purpose of the system (SC system) is to suppress voltage imbalance by controlling single‐phase SCs in each phase, and its effect has been confirmed by the previous authors' study. On the other hand, as a result of analyzing the voltage measured on some distribution lines, the authors found that it is not necessary to control single‐phase SCs in each phase because the voltage imbalance hardly changes throughout a day. In this paper, an alternative method for suppressing the voltage imbalance by constantly installing single‐phase SCs on distribution lines is proposed in order to realize at a lower cost than the previous SC system. In addition, the authors verify the effect of the method on the actual distribution lines. © 2020 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

The intermittent photovoltaic (PV) units significantly affect the performance of distribution systems, and they often cause several operational problems, most importantly, voltage rise/drop. At high PV penetration, excessive tap movements of transformers and high curtailed PV power are expected to completely solve the voltage violation problem. In this paper, we propose an optimal voltage control method for distribution systems considering the number of tap movements of transformers and the active power curtailment of PV units. The objective function of the proposed method comprises: 1) voltage drop violation, 2) voltage rise violation, 3) tap movement rate (TMR) of transformers, and 4) curtailed power of PV (CPPV). A multiobjective grey wolf optimizer integrated with a Lévy mutation operator (GWO-Lévy) is formulated to accurately solve the voltage control problem. A 24-h simulation is performed on the 119-bus distribution system with PV and different types of loads. The performance of GWO-Lévy is compared with three other optimizers, finding that it achieves the best performance. The simulation results demonstrate the efficacy of the proposed method for solving the voltage violation problem with PV while simultaneously optimizing TMR and CPPV. [ABSTRACT FROM AUTHOR]

A major concern associated with the connection of distributed generators (DGs) to distribution systems is the voltage rise problem. A solution introduced in many voltage control schemes is DG active power curtailment. However, this measure has a negative effect on both DG revenue and DG investment. This paper proposes the use of existing system resources to mitigate the voltage rise problem. Based on the big bang-big crunch optimization and the reactive power compensation method, the new technique controls the distribution system voltage profile while avoiding DG active power curtailment. The proposed method minimizes voltage deviations by determining the regulator taps and reactive power contributions of both the capacitors and the DGs. The approach is implemented online by a central control unit that optimally determines appropriate control decisions and then communicates them to the voltage regulators, capacitors, and DGs. Eliminating the voltage deviation problem associated with the network installation of DGs provides a cost-effective means of increasing DG penetration. The new algorithm was implemented and tested on the 33-bus test feeder. The results demonstrate the effective control of the voltage profile and fast convergence speed provided by the developed technique. [ABSTRACT FROM AUTHOR]

Renewable Distributed Generation (RDG), when connected to a Distribution Network (DN), suffers from power quality issues because of the distorted currents drawn from the loads connected to the network over generation of active power injection at the Point of Common Coupling (PCC). This research paper presents the voltage rise regulation strategy at the PCC to enhance power quality and continuous operation of RDG, such as Photovoltaic Arrays (PVAs) connected to a DN. If the PCC voltage is not regulated, the penetration levels of the renewable energy integration to a DN will be limited or may be ultimately disconnected in the case of a voltage rise issue. The network is maintained in both unity power factor and voltage regulation mode, depending on the condition of the voltage fluctuation occurrences at the PCC. The research investigation shows that variation in the consumer’s loads (reduction) causes an increase in the power generated from the PVA, resulting in an increase in the grid current amplitude, reduction in the voltage of the feeder impedance and an increase in the phase voltage amplitude at the PCC. When the system is undergoing unity power factor mode, PCC voltage amplitude tends to rises with the loads. Its phase voltage amplitude rises above an acceptable range with no-loads which are not in agreement, as specified in the IEEE-1547 and Southern Africa grid code prerequisite. Incremental Conduction with Integral Regulator bases (IC + PI) are employed to access and regulate PVA generation, while the unwanted grid current distortions are attenuated from the network using an in-loop second order integral filtering circuit algorithm. Hence, the voltage rise at the PCC is mitigated through the generation of positive reactive power to the grid from the Distribution Static Compensator (DSTATCOM), thereby regulating the phase voltage. The simulation study is carried out in a MATLAB/Simulink environment for PVA performance.

Growing penetrations of distributed photovoltaic (PV) generation in low-voltage electrical networks are raising new challenges for electricity industry operation. Voltage rise is a particular concern and new distributed voltage management techniques have been proposed in the literature. In this study, a novel distributed voltage control method is presented. The method is designed to be used by both PV systems and controllable loads and uses both a voltage and a power set point to manage control. These set points, along with a voltage sensitivity measure, are then used to control PV system generation and load-shedding. The objective of the control is to keep voltage levels within operational limits with reasonable accuracy. The method is practical; local measurements of net-power and voltage are used with no additional communication infrastructure required. The proposed method is compared to a power set point only and a voltage set point only control method. Results show the proposed method improves on both methods in terms of both voltage accuracy and the equity of intervention.

Aiming at the voltage rise due to the photovoltaic generation system (PVGS) at the point of common coupling (PCC), the cause is analysed with power transmission theory. Here, the principle and strategies of voltage regulation based on active and reactive power in PVGS are proposed. In this control strategy, the voltage of PCC is tracked by PV system in real time. When the voltage of PCC is normal, inverter will output in the way of maximum power point tracking (MPPT).When the voltage of PCC exceeds the upper limit, the inverter will regulate the voltage using the remaining capacity preferentially. If the remaining capacity is insufficient, the inverter will adjust active output and dynamically calculate the active and reactive best out values. In this way, the voltage of PCC is adjusted in an appropriate range to achieve the active output minimisation and reactive output optimisation of inverter. The experimental results validate the effectiveness of the proposed control scheme for voltage regulation.

Under the influence of series compensation (SC) capacitance and rated voltage rise, when ultra high voltage (UHV) high SC line occurs inner fault, the short-circuit current through the SC line is greater and the residual voltage across the SC is higher, which cause the electromagnetic transient process excited by high amplitude current and voltage to be more serious in the event of fault occurrence and removal. The security of circuit breaker (CB) equipment is threatened, which make it need further research on the characteristics and put forward some effective solutions. In this study, the characteristics of macroscopic statistical distribution of peak value via short-circuit current of transient recovery voltage (TRV) across CB fracture during switching after short-circuit current zero crossing for UHV high SC line are put forward, and also of the microscopic characterization parameter of waveform rise rate and peak value time. It shows that the TRV switching capability of existing UHV CBs can not cover all the fault scenarios of high SC line. Solutions including comprehensive comparison of TRV optimal suppression measures and increase of the UHV CB switching expected TRV test requirements are put forward, which provide feasible technical scheme for CBs reliable switching of UHV high SC line.

Distributed energy resources (DERs) are a new class of disruptive technologies with rapidly increasing adoption levels due to favorable government policies and subsidies. However, these emerging technologies come with technical challenges for utilities and system operators; for instance, voltage rise issues in residential secondary distribution systems with high penetration of DERs. One of the low-cost mitigation options to alleviate the overvoltage problem is reactive power absorption. Nevertheless, secondary feeders exhibit a high R/X ratio more noticeably than primary distribution systems, requiring large amount of reactive power for voltage regulation that cannot be entirely provided by the DERs alone. It is also necessary to minimize the reactive power drawn from the primary distribution system to prevent any stress on the network and reduce extra system losses, while at the same time ensuring the voltage within admissible limits. To address these critical issues, this paper proposes a distributed reactive power management, where additional source is provided from inexpensive devices such as switchable shunt reactors. The proposed overvoltage mitigation is accompanied by detailed analytical investigation that estimates the minimum amount of required reactive power to manage the voltage with user specified voltage rise tolerances. Case studies have also been conducted on real residential distribution systems subjected to severe voltage rise issues provoked by large adoption of DERs. [ABSTRACT FROM AUTHOR]

Aiming at the voltage rise due to the photovoltaic generation system (PVGS) at the point of common coupling (PCC), the cause is analysed with power transmission theory. Here, the principle and strategies of voltage regulation based on active and reactive power in PVGS are proposed. In this control strategy, the voltage of PCC is tracked by PV system in real time. When the voltage of PCC is normal, inverter will output in the way of maximum power point tracking (MPPT).When the voltage of PCC exceeds the upper limit, the inverter will regulate the voltage using the remaining capacity preferentially. If the remaining capacity is insufficient, the inverter will adjust active output and dynamically calculate the active and reactive best out values. In this way, the voltage of PCC is adjusted in an appropriate range to achieve the active output minimisation and reactive output optimisation of inverter. The experimental results validate the effectiveness of the proposed control scheme for voltage regulation. [ABSTRACT FROM AUTHOR]

Under the influence of series compensation (SC) capacitance and rated voltage rise, when ultra high voltage (UHV) high SC line occurs inner fault, the short-circuit current through the SC line is greater and the residual voltage across the SC is higher, which cause the electromagnetic transient process excited by high amplitude current and voltage to be more serious in the event of fault occurrence and removal. The security of circuit breaker (CB) equipment is threatened, which make it need further research on the characteristics and put forward some effective solutions. In this study, the characteristics of macroscopic statistical distribution of peak value via short-circuit current of transient recovery voltage (TRV) across CB fracture during switching after short-circuit current zero crossing for UHV high SC line are put forward, and also of the microscopic characterization parameter of waveform rise rate and peak value time. It shows that the TRV switching capability of existing UHV CBs can not cover all the fault scenarios of high SC line. Solutions including comprehensive comparison of TRV optimal suppression measures and increase of the UHV CB switching expected TRV test requirements are put forward, which provide feasible technical scheme for CBs reliable switching of UHV high SC line. [ABSTRACT FROM AUTHOR]

The increasing amount of photovoltaic (PV) systems leads to a voltage rise in the distribution grid. By providing reactive power, PV and battery inverters can reduce the voltage. For this purpose, most inverters have implemented a voltage‐dependent reactive power curve, which is often parameterised once during the installation of the system. In most cases, the parameterisation does not take into account the position of the system in the grid. As a result, inverters closer to the distribution transformer provide less or no reactive power as the voltage at the beginning of a feeder is much smaller. This study presents a regulation tool, which parameterises the reactive power curve in dependence on the position in the grid. This leads to a coordinated behaviour of all inverters in a distribution grid and ensures that all inverters provide a similar amount of reactive power. Moreover, the regulation tool notices if the grid topology has changed and adapts the reactive power control to this change. [ABSTRACT FROM AUTHOR]

Transient overvoltage represents a high magnitude voltage surge of a short duration which has to be considered when performing proper insulation coordination. Overhead line energisation is found to be a fundamental cause of transients. Both normal and faulty conditions are possible during line energisation. The latter implies the existence of an asymmetrical phase‐to‐ground fault and facing with two asymmetrical processes which take place concurrently. This type of energisation results in severe overvoltage, as well as in a voltage rise at the line receiving end. However, in practice, measuring devices are usually placed at the line sending end, which points to difficulties in determination of phase‐voltages at the opposite end of the line. This study offers a solution for the aforementioned issue by proposing the frequency‐dependent voltage transfer functions (TFs). By using the functions any voltage value at the sending line end will obtain the corresponding value at the receiving end. The functions are derived through complex mathematical modelling and by signal processing based on the empirical mode decomposition method. The TFs validity is confirmed through performed simulation in MATLAB Simulink and real‐site measurements. [ABSTRACT FROM AUTHOR]

The increasing deployment of Distributed Generation (DG) technologies introduces power quality challenges to the grid, in particular steady state voltage rise at the connection point for DG units. In most distribution networks, control and monitoring of grid parameters is missing, as well as system security is at risk. Smart grid technologies have the capability to realize the real-time measurements and on-load voltage controls. With the steady implementation of smart grid technologies throughout the existing distribution networks, the online voltage control can be achieved ensuring the power quality and voltage levels within the statutory limits. This study presents a methodology for the estimation of voltage profile in a smart distribution network with DG for the online voltage control, taking into account different line $X/R$ ratios and laterals. This method is based on maximum and minimum voltage estimation by remote terminal units (RTUs) placed only at DG connected bus and at capacitor connected bus. Voltage regulation is carried out based on RTUs estimated values. This work is tested on two radial distribution networks with/without DGs and laterals. Comparative results for voltage magnitudes estimated with different methodology are presented. The reported simulation results show that the method presented is capable of estimating the voltage profile along the distribution network with DGs for the online voltage control, considering different line $X/R$ ratios and laterals.

Measurement of partial discharge (PD) is a vital method to assess the health of the electrical insulation in high-voltage power equipment. As diagnostic testing at very low frequency (VLF) is increasingly being used, it is important to investigate PD behaviours under such a low-frequency voltage excitation. This study presents the PD characteristics at VLF excitation under different applied voltage waveforms, including sinusoidal and trapezoid-based waves. Also, the effects of cavity size on PD behaviours at VLF are investigated. Experiments were performed to measure PDs in a cylindrical void bounded by solid insulation. The results show that discharge activities at VLF, in general, exhibit lower magnitude and repetition rate when compared with power frequency. Also revealed is the strong dependency of discharge parameters on the rate of voltage rise. Physical mechanisms to explain discharge behaviours are given.

Solar energy from photovoltaic (PV) is among the fastest developing renewable energy systems worldwide. Driven by governmental subsidies and technological development, Europe has seen a fast expansion of solar PV in the last few years. Among the installed PV plants, most of them are situated at the distribution systems and bring various operational challenges such as power quality and power flow management. The paper discusses the modelling requirements for PV system integration studies, as well as the possible techniques for voltage rise mitigation at low voltage (LV) grids for increasing PV penetration. Potential solutions are listed and preliminary results are presented.

A distributed voltage control scheme is proposed in an active distribution network in the presence of a large scale photovoltaic (PV) farm/plant to mitigate high ramp-rate issues. Multiple voltage regulating devices, such as on-load tap changers, step voltage regulators (SVRs), and switched capacitors banks are controlled in various ways based on either a centralized or a distributed coordination management scheme. This paper presents the relationship of the active and reactive power outputs of a PV plant in the presence of the conventional voltage regulating devices, and proposes a distributed control strategy to coordinate the SVRs with the PV smart inverter’s capability to improve power quality. The distributed voltage control schemes are tested on an unbalanced medium voltage feeder located in a California utility service territory with the PV integrated at the far end of the feeder. [ABSTRACT FROM PUBLISHER]

This paper introduces a brief analysis on hosting capacity and related concepts as applied to distribution network systems. Furthermore, it addresses the applicability of hosting capacity study methodologies to harmonic voltage distortion caused by photovoltaic panels (PV) connected at a low-voltage (LV) side of a university campus grid. The analysis of the penetration of new distributed generation technologies, such as PV panels, in the distribution grid of the campus was carried out via measurement processes, and later by computer simulations analyzing a new concept of the hosting capacity approach in relation to voltage harmonics distortion. The voltage rise due to harmonic injection is analyzed and discussed with the aim of validating the discussed model and also putting forward recommendations for connecting PV generation across other network systems. [ABSTRACT FROM AUTHOR]

The hosting capacity approach is presented as a planning, improving, and communication tool for electrical distribution systems operating under specific uncertainties, such as power quality issues, power stabilities, and reliability, among others. In other words, it is an important technique, when renewable sources are present, to answer the amount of power that is possible to supply to the system without trespassing power performance limits. However, the power flow in a distribution system, for instance, can change throughout time due to the penetration of distributed generation, as well as load consumption. Based on the dynamic nature existing in distribution grids nowadays, it is important to highlight that the hosting capacity should not be calculated in a specifically chosen time only, but must be analyzed throughout a period of time. Thus, this paper introduces an extended concept of hosting capacity in relation to an integrated impact of harmonic voltage distortion and voltage rise as a function of time for daily, weekly, monthly, or even yearly periods. This extended concept is named as Dynamic Hosting Capacity (DHC(t)). General aspects of DHC(t) are demonstrated via measured data on a photovoltaic system (PV) connected at a low-voltage (LV) side of a university building.

Voltage fluctuation and voltage rise are common issues associated with the massive integration of photovoltaic (PV) technologies in distribution systems. In this paper, sensitivity-based and optimization-based methods are proposed for mitigating voltage fluctuation and rise in the presence of plug-in hybrid electric vehicles (PHEVs). The concept of these methods is to optimize the reactive power of PV inverter and active power from charging station of PHEVs for matching a target voltage profile. The sensitivity-based method is based on the first-order power flow sensitivities around the desired voltage profile. An optimization model is used in optimization-based to minimize the mismatches between the fluctuating and required voltage profiles. The charging/discharging operation of PHEVs and reactive power of PV inverter are simultaneously controlled for compensating power fluctuation during cloud transients and load fluctuations. The results demonstrate the effectiveness of the proposed methods compared with existing methods. [ABSTRACT FROM AUTHOR]

As the photovoltaic (PV) sources capacities in distribution networks continue to grow, more operational challenges are expected to be encountered. One of these challenges is the voltage rise within distribution networks due to reverse power flow from the PV sources toward the grid. In this paper, a simplified analytical approach is presented which allows the voltage rise possibility to be tested and the performance of its mitigation techniques to be evaluated. Equivalent transformations are used to represent complicated power systems using simplified circuits. Then, formulas are derived to determine the PV power limits beyond which a voltage rise will be encountered considering the PV sources capability of absorbing reactive power. Moreover, the system losses in each case are estimated using the proposed formulas. Consequently, the proposed analysis method could be used for a number of applications related to PV sizing and losses minimization. The validity of the proposed method is verified through a number of case studies where its findings are compared with results obtained from DIgSILENT software tools. [ABSTRACT FROM AUTHOR]

Integration of wind power generation into power distribution grid may result in stability and power quality challenges. In this way, this paper first reviews the grid integration issues of wind power generation. Then, as the main contribution, the paper develops in-depth theoretical analyses for examination the grid integration issues such as voltage rise, output power fluctuations, and static and dynamic voltage variations created due to grid integration of wind turbines and corresponding aerodynamic power fluctuations. Besides, the paper addresses these issues by proposing elaborate control approaches and by using the static compensator (STATCOM). The paper first addresses the problem of voltage rise by active power curtailment through pitch control. However, this method may result in a large waste of wind energy that may not be cost effective. Next, the STATCOM is implemented and efficient control approaches are proposed for addressing the problem of voltage rise, improvement of voltage profile and suppression of voltage and power fluctuations. At the end, simulation studies for the study distribution grid are given. The study system is an actual distribution grid in Iran with approximately 7.9 MW wind power generation and 21.9 MW load. [ABSTRACT FROM AUTHOR]

This paper describes the detailed analysis of a reactor application for a power plant to mitigate the voltage rise of a distribution line (DL) caused by the connection of distributed resources (DRs). The maximum capacity of renewable energy generators (REGs) that meets the acceptable voltage rise of a DL and the necessary capacity of the reactor to mitigate that voltage rise according to the different types of REGs are analyzed. The re-coordination of a protection relay and the loss of generation revenue as well as the installation location of a reactor are described. Finally, the ON/OFF conditions of the reactor, such as the magnitudes of the grid voltage and generator voltage, and the duration time of the voltage rise are analyzed. As the voltage rise is mitigated and self-limited in small power plants, it is confirmed that the capacity of the DRs connected to the DL can be increased through a field demonstration. [ABSTRACT FROM AUTHOR]

Conditions on feeders with dispersed generation vary between voltage drop when there is no generation, and voltage rise when the generation exceeds the load. The utility is responsible for keeping the voltage variation within regulatory limits while the location of generation could be determined by investing customers without regard to feeder performance. Therefore, utilities must estimate as a general case how much generation can be connected randomly to a stochastically-loaded LV feeder before the risk of violating voltage limits becomes high enough to require detailed location specific studies. A fast probabilistic analytical core for voltage calculations on a feeder with loads and generation, described in a companion paper, enables Monte Carlo simulation of thousands of scenarios with randomly located generation and low loads to be done quickly, and gives a visual representation of the probable voltage conditions. The implications of choosing various levels of risk are discussed. The results can be used to set indicative penetration limits for photovoltaic generation in grid codes for low voltage feeders. [ABSTRACT FROM AUTHOR]