High Penetration Of Photovoltaic Generation Research Articles

Dynamic Reserve Power Point Tracking in Grid-Connected Photovoltaic Power Plants

This paper introduces a dynamic power reserve control methodology called reserve power point tracking (RPPT) for grid-connected photovoltaic (PV) plants. The proposed RPPT methodology is employed to ensure availability of the required power reserve to support the grid and accordingly facilitate high penetration of PV generation in the grid. Implementing this control methodology does not require any extra hardware. The proposed methodology regulates the average PV power dynamically by periodically operating on and off the maximum power point (MPP) in order to inject a constant desired power into the grid. Tracking a desired power reference implies that the proposed methodology, is a form of flexible power point tracking (FPPT). However, unlike a traditional FPPT, the proposed methodology also provides updated information of the available maximum PV power. Hence, the RPPT fulfills both FPPT and maximum power point tracking (MPPT) functionalities simultaneously. The proposed methodology extracts the MPP information and uses this information to calculate and regulate the amount of PV reserve power. One of the main advantages of the proposed algorithm is its applicability under partial shading conditions. Its effectiveness is demonstrated by experimental results under changing solar irradiance, grid frequency deviation and partial shading conditions.

Photovoltaics literature survey (No. 181)

Photovoltaics literature survey (No. 181)

An Efficient EMS for BESS in Monopolar DC Networks with High Penetration of Renewable Generation: A Convex Approximation

This research presents an efficient energy management system (EMS) for battery energy storage systems (BESS) connected to monopolar DC distribution networks which considers a high penetration of photovoltaic generation. The optimization model that expresses the EMS system with the BESS and renewable generation can be classified as a nonlinear programming (NLP) model. This study reformulates the NLP model as a recursive convex approximation (RCA) model. The proposed RCA model is developed by applying a linear approximation for the voltage magnitudes only at nodes that include constant power loads. The nodes with BESS and renewables are approximated through the relaxation of their voltage magnitude. Numerical results obtained in the monopolar version of a 33-bus system, which included three generators and three BESS, demonstrate the effectiveness of the RCA reformulation when compared to the solution of the exact NLP model via combinatorial optimization techniques. Additional simulations considering wind power and diesel generators allow one to verify the effectiveness of the proposed RCA in dealing with the efficient operation of distributed energy resources in monopolar DC networks via recursive convex programming.

Robust Co-Optimization of Droop and Affine Policy Parameters in Active Distribution Systems With High Penetration of Photovoltaic Generation

Legacy distribution systems need to adapt quickly to upcoming operating scenarios. The expected growth of electromobility and distributed generation will bring forth many challenges regarding efficient operation. Additionally, the limited communication infrastructure of these networks hinders the applicability of heavily centralized control strategies. In this context, this paper proposes a distributed control scheme for photovoltaic generators. The scheme comprises a local real–time control layer for the synthesis of active and reactive power references, using traditional voltage droop control, along with affine policies to handle the uncertainty associated to solar irradiance and demand levels. The characterization and periodic adaptation of such control scheme is achieved via a global, computationally tractable robust model able to co–optimize both droop and affine policy parameters. Performance is benchmarked via extensive computational experiments against other state–of–the–art distributed and local control strategies. Results suggest the proposed scheme is able to outperform all competitive frameworks. Its performance is also evaluated as a strictly local control scheme obtaining superior voltage regulation as compared to the recommendations in the Standard IEEE 1547.8.

Data-driven distributionally robust unbalanced operation of distribution networks with high penetration of photovoltaic generation and electric vehicles

The uncertainties associated with the large-scale integration of electric vehicles (EV) and renewable energy resources introduce new challenges to operating the unbalanced three-phase distribution networks. In this paper, a data-driven distributionally robust optimization framework is proposed for the operation of the distribution network considering the uncertainties associated with the interconnected EV fleets and solar photovoltaic (PV) generation. The proposed framework leverages the column-and-constraint generation (C&CG) approach to minimize the operation cost considering the worst-case probability distributions of PV generation, the available energy in EV fleets, the arrival and departure times of EV fleets as well as their minimum and maximum energy capacities. The proposed approach is applied to the modified three-phase unbalanced IEEE 34-bus and IEEE 123-bus networks. To evaluate the performance of the proposed distributionally robust optimization framework, the results are compared to those procured by solving scenario-based stochastic programming and robust optimization problems. Furthermore, the impact of vehicle-to-grid capability on the operation of the distribution network is investigated and the in-sample and out-of-sample performances of the proposed framework are evaluated.

Voltage control using fuzzy logic for radial distribution network with high penetration of photovoltaic generators

Voltage control scheme to enhance the stability for current distribution networks connecting with distributed generation (DG). The increasing demand of energy in recent years transformed traditional distribution grids, which have unidirectional power flow to Active Distribution Networks (ADN), including significant penetration of renewable distributed generators (DGs), such as photovoltaic (PV) modules where the power flow became bidirectional due to the high excess DGs active power that reverses to the power grid. Therefore, this ADN comes with a significant challenge, which is voltage regulation problem. To interconnect PV Generators into distribution systems a robust control approach needs to be adopted, there are different Voltage control scheme can be carried out in variety of methods, such as control by using On Load Tap changers (OLTC), using PV inverters reactive power injection/absorption, real power curtailment process, storage batteries and more. This article proposed a reactive power compensation by PV inverters based on fuzzy logic for voltage control along with the feeders. The control approach was tested and simulated, and it was observed that it can guarantee of maintaining the voltage profile of the distribution network within acceptable range. The MATLAB and Simulink platforms are used to model the system.

Harmonic Effects Due to the High Penetration of Photovoltaic Generation into a Distribution System

The growth in global electricity demand has expanded the search for new energy resources. Renewable sources such as photovoltaic (PV) systems have proven to be major alternatives. PV generators connected to distribution grids have exhibited significant growth in the last decade, so it is essential to analyse the impacts resulting from this increase. This work investigated the influence of high PV system penetration in distribution grids in terms of harmonic levels. In particular, this study addressed the distortions in voltage and current waveforms in the presence and absence of PV generators connected to a distribution grid. Additionally, the total harmonic content and the individual harmonic frequencies of voltage and current were analysed. This study was performed with an IEEE 37 bus distribution system and the Open Distribution System Simulator software (OpenDSS). The results show that the voltage limits of some phases far away from a substation can exceed the limits. Furthermore, the total harmonic distortion (THD) and individual harmonic distortion (IHD) levels for voltage and current were significantly high for harmonics of the 3rd, 5th, and 7th orders, where current levels violate the standard levels.

Predictive Voltage Control Scheme Based on Estimation of Short‐Time‐Ahead Voltage Fluctuation in Distribution System with PVs

This paper proposes a predictive voltage control scheme baseda on short‐time‐ahead voltage fluctuation estimation in a distribution system for achieving high penetration of photovoltaic generation. In the proposed control scheme, the short‐time‐ahead voltage fluctuation is estimated from the previously measured voltage of the sensor, and the voltage regulator operates to minimize the expected voltage violation risk in the entire distribution system. Because there is no requirement for real‐time sensor‐measured voltage values, as required in centralized voltage control schemes, the proposed scheme is an autonomous control scheme that uses only the present secondary voltage of the voltage regulator. The proposed control scheme was tested on a large‐scale distribution system model to which thousands of customers are connected, and the voltage control performance was evaluated using the monthly measurement data that was in terms of voltage violation amount and number of tap operations. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Oscillation analysis of low-voltage distribution systems with high penetration of photovoltaic generation

The use of renewable power generation brings new challenges related to power quality issues. Furthermore, with the changing power system nature due to the presence of new components such as power electronics in large numbers and distributed generation systems, the tools used for more than a century to analyze signals in this type of systems are no longer providing accurate information with a good resolution in time and frequency domain. To contribute with a new view of the problem, this paper presents a hybrid technique for the analysis of oscillations in low voltage distribution systems considering photovoltaic generation. The aim is to characterize the behavior of the system in a time–frequency domain and get the different instantaneous frequencies that appear. The results obtained with this technique are compared with three well-known methods of analysis. The validation of the methodology is carried out in a real-time digital simulator of a distributed system with photovoltaic generation.

Photovoltaic generator model for power system dynamic studies

Photovoltaic (PV) power generation has developed very rapidly worldwide in the recent years. There is a possibility that the PV power generation will switch from an auxiliary power supply, as of today, to a main power source in many power grids in the future. Naturally, dynamic studies on power grids with a high penetration of PV generators have become increasingly important, and thus have attracted major attentions from both the power industry and the academia. Consequently, dynamic modeling of PV generators has been investigated widely. However, among various proposed models, there is a confusion on the model applicability and a lack of the clarification on the required level of details on the modeling work, which severely limit the real industrial applications of the developed models. This paper reviews the state-of-the-art PV generator dynamic modeling work, with a focus on the modeling principles of PV generator for the power system dynamic studies. The paper presents the detailed modeling process for the recommended PV generator dynamic model, and clarifies the assumptions and simplifications made in the modeling process, thus raises the discussion on the model applicability. Studies that require further attentions on developing the dynamic models of PV generators for power system dynamic studies are identified and presented in the paper. However, this work does not intend to conclude the research work in this important field, instead, it aims to provoke more discussions on developing guidelines on building or selecting the appropriate models to fit into the purpose of the targeted dynamic studies.

Control of PV systems for distribution network voltage regulation with communication delays

Various approaches including the real power control through photovoltaic (PV) inverters have been proposed to address voltage issues due to high penetration of PV generators (PVs). However, most of the existing methods did not include communication delays in the control loop. Communication delays, short or long, are inevitable in the PV voltage regulation loop and can not only deteriorate the system performance with undesired voltage quality but also cause system instability. In this paper, a novel approach is presented to convert the overvoltage control problem via PV inverters for multiple PVs into a problem of single-input–single-output (SISO) systems. The method can handle multiple PVs and different communication delays. The impact of communication delays is then systematically analyzed and the maximum tolerable delay is rigorously obtained. Different from linear matrix inequality (LMI) techniques that have been extensively studied in handling systems with communication delays, the proposed method gives the necessary and sufficient condition for obtaining a controller and the design procedure is explicitly and constructively given in the paper. The effectiveness of the proposed method is verified by simulation studies on a distribution feeder and the widely-used 33-bus distribution test system.

An Interval Arithmetic-Based State Estimation Framework for Power Distribution Networks

An enormous challenge for state estimation (SE) in power distribution networks with high penetration of photovoltaic generators lies in how to deal with measurement uncertainty. Driven by this motivation, an interval arithmetic (IA) based SE is proposed in this paper, which considers interval modeling for measurement uncertainty. The proposed SE is formulated as two interval optimization models based on the unknown-but-bounded theory, and solution bounds of state variables are obtained using a two-stage linear programming approach. In particular, the proposed SE is extended to realistic power distribution networks with mixed microphasor measurement units (μPMU), voltage magnitude, smart meters and feeder terminal units. Case studies and results are illustrated and discussed to demonstrate the performance of the proposed IA-based SE. It could provide the operators intuitive and effective bounds of system states for advanced power industrial applications under consideration of uncertainty.

Optimal probabilistic planning of passive harmonic filters in distribution networks with high penetration of photovoltaic generation

In recent years, distribution networks have been increasingly affected by the random nature of harmonic sources introduced by nonlinear load and renewable energy sources (RES) such as photovoltaic (PV) systems. This paper presents an approach based on Genetic Algorithm (GA) and Monte-Carlo Simulation (MCS) for the optimal planning of single-tuned passive harmonic filters (PHFs) in a distribution network. The resistance and inductance of the lines within the network are modeled by frequency dependent characteristics. The probabilistic characteristics of the load and PV system currents are also considered for optimal planning of PHFs. In our optimization model, the objective function minimizes the total PHF installation cost and the energy losses, by considering the total harmonic distortion (THD) of bus voltages and maximum capacity of PHF as constraints. The proposed method is validated by a simulation study using an unbalanced three-phase real distribution system. An advantage of this method over most of the conventional approaches is that both harmonic current magnitude and phase angle of real PV systems are taken into account. Numerical results show the applicability and effectiveness of the proposed method.

Robust Operation of Soft Open Points in Active Distribution Networks With High Penetration of Photovoltaic Integration

Distributed generators including photovoltaic (PV) panels have been integrated dramatically in active distribution networks (ADNs). Due to the strong volatility and uncertainty, the high penetration of PV generation immensely exacerbates the conditions of voltage violation in ADNs. However, the emerging flexible interconnection technology based on soft open points (SOPs) provides increased controllability and flexibility to the system operation. For fully exploiting the regulation ability of SOPs to address the problems caused by PV, this paper proposes a robust optimization method to achieve the robust optimal operation of SOPs in ADNs. A two-stage adjustable robust optimization model is built to tackle the uncertainties of PV outputs, in which robust operation strategies of SOPs are generated to eliminate the voltage violations and reduce the power losses of ADNs. A column-and-constraint generation algorithm is developed to solve the proposed robust optimization model, which are formulated as second-order cone program to facilitate the accuracy and computation efficiency. Case studies on the modified IEEE 33-node system and comparisons with the deterministic optimization approach are conducted to verify the effectiveness and robustness of the proposed method.

Protection coordination scheme for distribution networks with high penetration of photovoltaic generators

The installation of photovoltaic (PV) systems is gaining great attention due to the matured PV technology and the lowered price of PV modules. With an increasing penetration of PV systems, the selectivity of distribution network protection may be affected which results in undesirable de-energisation of loads, damage of network equipment, and reduction of reliability. This study presents a method to preserve the protection coordination considering future PV systems installation with any penetration level and different locations along the distribution feeder. Depending on the accessibility of protection device settings or PV control parameters, the proposed method modifies the existing characteristic curve of overcurrent devices or limits the output current of PV sources, respectively. The proposed strategy does not change the structure of existing distribution network protection system and can also be implemented in the old and non-programmable relays. Meanwhile, it does not need the communication links. The merits of the proposed method are demonstrated through several case studies using the Isfahan distribution network.

Mitigation of Fast Voltage Variations During Cloud Transients in Distribution Systems With PV Solar Farms

Since photovoltaic (PV) generators have no mechanical inertia, fast solar irradiance changes associated with cloud transients cause instantaneous variations in PV power output, resulting in rapid and possibly significant voltage changes in systems with high penetration of PV generators. In addition to characterizing this emerging power-quality issue, this paper proposes and investigates techniques to mitigate these fast voltage variations caused by cloud transients in distribution system with PV solar farms. The investigated approaches are based on the PV inverter capacity for fast reactive power compensation without the need to oversize the inverter or curtail the active power by using only the available reserve. Real measurement data characterize the issue and time-series power-flow simulations evaluate the mitigation techniques.

Impact of fault‐ride‐through strategy on dynamic characteristics of photovoltaic power plant

The large-scale grid-connected photovoltaic (PV) power plant is growing rapidly these years. For power system with high penetration of PV generation, the dynamic characteristic analysis of PV plant is a key factor in system stability studies. In this study, the impact of fault-ride-through (FRT) strategy on dynamic characteristics of PV plant is studied. First, the mathematic relationship between plant active/reactive power, point of interconnection voltage and inverter current is deduced. Second, the impact of dynamic reactive current support logic, active current limit logic and active current restore logic is investigated, respectively. Finally, the dynamic response of PV plant and synchronous generator is compared. The simulation results show that PV plant is an important controllable power source, and a reasonable FRT strategy can improve power system stability.

Static Voltage Stability Analysis in a Distribution System with High Penetration of Photovoltaic Generation

Static Voltage Stability Analysis in a Distribution System with High Penetration of Photovoltaic Generation

Optimal Power Scheduling for Smart Grids Considering Controllable Loads and High Penetration of Photovoltaic Generation

The distributed generator (DG) has a huge economical and environmental potential, especially if it is based on renewable energy sources (RESs). It is very important for the future development of smart grids. However, high penetration of DGs into distribution systems can cause voltage deviations beyond the statutory range, and reverse power flow toward the substation transformer. Consequently, it can increase the distribution system losses if it is not well supervised. Thus, in order to meet smart grid objectives, DGs have to be controlled in coordination with other power resources existing in the distribution system. Controllable loads (CLs) can also help in promoting smart grids through demand response (DR) application. Therefore, this paper proposes a decision technique of an optimal reference schedule for DGs, battery energy storage system (BESS), CLs, and tap changing transformers. The main objective of the proposed optimization problem is to achieve loss reduction in the distribution system. However, other aims such as voltage control and power flow smoothing have been achieved. The optimization is performed based on predicted values of load demand and DG generation. Simulations are conducted for one operation day to illustrate the optimality of the proposed scheduling method and to assess the impact of CLs in smart grids.

Southern California Edison's Advanced Distribution Protection Demonstrations

A novel advanced protection system was developed and demonstrated on SCE's 12 kV Circuit of the Future. This system used fiber optic communications to coordinate the operation of fault interrupting switches located along the circuit. One of the creative components of this project is the study of the circuit with a superconducting fault current limiter (FCL) connected in series with the feeder. The details of the FCL are described in this paper. Knowledge gained from this demonstration was used to design a second generation advanced distribution protection system. This system replaced fiber with radio communications and looped two radial 12 kV circuits together to reduce cost and improve reliability. This system shows promise in helping with protection of circuits with high penetrations of photovoltaic generation. Implementation is planned in 2013 as part of SCE's Irvine Smart Grid Demonstration.