Photovoltaic Generation System Research Articles

System Unbalance Analyses and Improvement for Rooftop Photovoltaic Generation Systems in Distribution Networks

This paper studies the system unbalance caused by rooftop Photovoltaic Generation Systems (PVGSs) in distribution networks and proposes an improved method. The voltage and current unbalance studies for three extreme cases considering all rooftop PVGSs being connected to one single phase and then the stochastic analyses for the integration cases of rooftop PVGSs are considered. These three extreme cases lead to severe system unbalance problems. An improving method that combines the On Load Tap Changer (OLTC) and the optimal phase arrangement of distribution transformers is proposed in this paper to mitigate the system unbalance. The OLTC-based improving method is applied first. If the system unbalance is still out of range, the optimal phase arrangement of distribution transformers is further used to mitigate the system unbalance problem. The objective function of optimal phase arrangement is to minimize the system unbalance with the constraints of voltage limits, line flow limit, etc. Test results show that the proposed method can improve the system unbalance significantly even under very extreme cases.

Optimal planning of distributed photovoltaic generation for the traction power supply system of high-speed railway

The ever-increasing electricity price and energy consumption in high-speed railway industry push railway companies to seek a promising way to realize their sustainable developments. Making full use of the solar resource along with high-speed railways can be a potential solution to cut the electricity bill, bring more profit to railway companies and realize the decarbonization of high-speed railway industry. This paper studies the optimal planning of distributed photovoltaic generation (DPVG) and energy storage system (ESS) for the traction power supply system (TPSS) of high-speed railway. A quantitative method is proposed to study the time and space characteristics of photovoltaic generation and electricity demand of high-speed trains. An integrated cost-benefit analysis framework is developed to evaluate the effect of DPVG and ESS on the economy of TPSS. To derive the optimal planning scheme and energy management strategy of DPVG and ESS, a mathematical programming model with the objective of minimizing the total cost is proposed to seek the most economical solution. A hybrid global optimal solution approach is developed to solve the model. A real-world case of Beijing-Baoding high-speed railway in China is used to illustrate the capability and characteristics of the proposed model. The computational results show that DPVG is able to supply 32.5% electricity demand of high-speed trains. The integration of DPVG and ESS can help railway company save 4.2 million CNY each year in Beijing-Baoding high-speed railway. This paper demonstrates the potential and applicability of DPVG and ESS in high-speed railway industry.

Optimization of the maximum power point of photovoltaic working under partial shading conditions

Photovoltaic is used to convert electricity from solar radiation. The working characteristics of photovoltaic depend on environmental conditions such as temperature, solar radiation intensity, and the surrounding environment. During operation, the photovoltaic generation system (PGS) can be partially or completely shaded due to natural phenomena such as clouds, buildings, dust, animals, electric pillars, trees ... these are changing the characteristics of the system’s power output of PV. This paper proposes a maximum power point tracking algorithm for PGS operating under partially shaded condition (PSC) based on Particle Swarm Optimization (PSO) method, and a configuration comprises of three PV modules type PHM60W36 is used to simulate using PSIM software. The study focused on changing the working characteristics of the photovoltaic system when changing factors such as level, location of the photovoltaic module are shaded. The effectiveness of the proposed method is not only compared with the traditional Perturb and Observe (P&O) method but also compared with those proposed previously under the same operating conditions. In addition, an experimental model was developed to investigate the response of the proposed solution in the real environment with the Chroma-62050H simulator. The results show the superiority of the proposed solution in improving the performance MPPT and convergence speed of the system under complex operating conditions.

Finite-Time Large Signal Stabilization for High Power DC Microgrids With Exact Offsetting of Destabilizing Effects

The interleaved dual boost converter (IDBC) is a promising topology to interface high power solar photovoltaic (PV) generation or energy storage systems to dc microgrids (MGs). It provides a high boost ratio for voltage transformations and helps significantly to reduce ripples in the currents drawn from dc sources. However, the conventional control methods of IDBC cannot guarantee system stability in the presence of tightly regulated and rapidly varying power electronic loads which behave as constant power loads (CPLs). Moreover, the uncertainties of converter systems may further affect the stability of MGs. In this context, a large signal stabilization scheme, which comprises finite-time observers (FTOs) and a finite-time controller (FTC), is proposed. By considering CPLs and parameter dispersions as system disturbances, FTOs are able precisely observe the disturbances in finite time. Then the FTC exactly offsets the estimated values and stabilizes all system states at their designated points in finite time. By doing so, the finite-time large signal stability can be obtained and the corresponding results are proved with Lyapunov theorems. A detailed control parameter selection guideline is provided for practical applications. Simulations show that the proposed method gives a wider stability margin than the conventional PI (proportional-integral) control. Furthermore, experiments verify its effectiveness and feasibility.

Optimal Selection of Photovoltaic Generation for a Community of Electricity Prosumers

In Brazil, in the lasts five years there has been a significant growth of photovoltaic generation installed in the consumer side of me-ters, the so-called prosumers. However, most of these installations occur in an individual way, as self-consumption, with net-metering billing. The possibility of forming a community grouping several consumer units is little used. This paper analyzes the eco-nomic benefit obtained by prosumers acting individually and by prosumers grouped in a community when investing in photovolta-ic generation. A mixed integer linear programming model was used to select photovoltaic generation systems, considering the Brazilian net-metering billing, in order to minimize the annualized total cost to meet the demand of the prosumers. Tests were con-ducted for prosumers connected individually and in communities, for two tariff modalities, conventional and time of use. The results show that there is an increase in the economic benefit obtained by some of the individually connected prosumers when they install photovoltaic generation. However, when the option is to form a community the economic benefit can be 120% higher.

Operation of the Hybrid Photovoltaic-Battery System on the Electricity Market—Simulation, Real-Time Tests and Cost Analysis

This paper presents research on a hybrid photovoltaic-battery energy storage system, declaring its hourly production levels as a member of a balancing group submitting common scheduling unit to the day-ahead market. It also discusses the variability of photovoltaic system generation and energy storage response. The major research questions were whether the operation of a hybrid photovoltaic-battery energy storage system is viable from the technical and economic viewpoint and how to size battery energy storage for that purpose. The DIgSILENT PowerFactory environment was used to develop the simulation model of postulated hybrid system. Then, tests were conducted on real devices installed in the LINTE^2 laboratory at Gdańsk University of Technology, Poland. Firstly, power generation in the photovoltaic system was modeled using hardware in the loop technique and tested in cooperation with emulated photovoltaic and real battery energy storage system (lithium-ion battery, 25 kWh). Secondly, a real photovoltaic power plant (33 kW) and real battery energy storage were applied. The results obtained from laboratory experiments showed that market operation of hybrid photovoltaic-battery energy storage system is feasible. However, developing a control strategy constitutes a great challenge, as the operator is forced to intervene more frequently than the simulation models indicate in order to keep the parameters of battery storage within accepted ranges, especially in view of a sudden weather breakdown. Levelized cost of electricity from photovoltaic-battery energy storage system varied from 314 to 455 $/MWh, which has proven to be from two to three times higher than the current annual average day-ahead market price in Poland.

Loss of Utility Detection and Seamless Operation of Distributed Generation System

In this article, a protection method for photovoltaic distributed generation (DG) system to fend off from islanding condition caused by the loss of the utility grid has been proposed along with a control scheme. The proposed islanding protection scheme is developed with a parametric time-frequency analysis technique for detection and an optimal probabilistic neural network for classification of events. Along with the islanding protection, a nested loop robust control scheme has been proposed for the seamless operation of the DG system during different uncertainty scenarios. The proposed system with islanding protection and robust control scheme has been implemented in MATLAB/SIMULINK environment. The practical feasibility of the proposed method is verified with an experimental setup and dSPACE control kit. For demonstrating the superiority of the proposed islanding protection method and robust control scheme for the DG system, a discussion of the results is presented.

Multilevel Common-Ground Transformerless Inverter for Photovoltaic Applications

Transformerless inverters have attracted great attention since they became a compact and economic solution for photovoltaic (PV) generation systems. On the other hand, the common-mode (CM) leakage current issue needs to be addressed in order to meet safety requirements. This article proposes a new multilevel common-ground inverter for transformerless systems. The leakage current is eliminated by the electric connection between the grid neutral point and the PV negative terminal. Furthermore, the operation modes of the proposed inverter, as well as the design guidelines, are analyzed in detail. In addition, a feedforward modulation strategy to decouple the output variables from the voltage–capacitor oscillations is proposed. Experimental results are presented to verify the performance and practicability of the proposed inverter in grid-connected operation.

New power conversion topology for battery-less PV generation system with the functions of grid-connection and isolated grid

This paper proposes a photovoltaic power conversion topology (PVPCT). The proposed PVPCT is connected to the utility grid, a PV array and emergency loads. The proposed PVPCT comprises a boost DC-DC power converter (DDPC) and a three-port power converter (TPPC). The TPPC has three ports: a DC port, a grid port and an isolated grid port. The input for the boost DDPC is connected to a PV array and the output from the boost DDPC is connected to the DC port of the TPPC. The grid port connects to the utility grid, and the isolated grid connects to emergency loads. The isolated grid port continuously supplies an uninterruptible voltage with constant amplitude and constant frequency for emergency loads, without the need of battery regardless of whether the utility grid is nominal or interrupted in the condition of sunshine. Hence, the proposed PVPCT can continuously supply high-quality uninterruptible power to the emergency loads, such as charger of cell phone during the natural disasters. In addition, the power circuit is simplified and isolating transient is smooth due to the use of TPPC, and the initial cost and maintenance cost are reduced due to no use of battery. The proposed PVPCT has six operation modes for four conditions. A prototype is set-up for validating the performance of proposed PVPCT. The experimental results of the proposed PVPCT have the expected performance.

Development of fast simulation models of photovoltaic generation system based on MATLAB

Based on the mathematical model of photovoltaic power generation system, the simulation model based on MATLAB/Simulink is given. Traditional simulation models have the drawbacks of rapidity and poor robustness. In this paper, two equivalent simplified models based on inverters are established—the equivalent switch model and the average model. In this paper, the above three models are compared comprehensively from different aspects such as simulation speed, simulation precision and robustness, and the applicable occasions of each method are proposed.

Snapshot of Photovoltaics—February 2020

Since the demonstration of the first modern silicon solar cells at Bell Labs in 1954, it took 58 years until the cumulative installed photovoltaic electricity generation capacity had reached 100 GW by the end of 2012. Then, it took another five years to reach an annual installation capacity of over 100 GW in 2017 and close to 120 GW in 2019. As a consequence, the total world-wide installed photovoltaic electricity generation capacity exceeded 635 GW at the end of 2019. Although it witnessed a 20% and 25% decrease in annual installations in 2018 and 2019, respectively, China was again the largest market with 30 GW of annual installations. The number of countries in the club with more than 1 GW annually has increased to 18 countries in 2019. The use of local battery storage systems in solar farms as well as decentralized photovoltaic electricity generation systems combined has again increased, due to the falling storage system costs.

Dynamic performance evaluation and improvement of PV energy generation systems using Moth Flame Optimization with combined fractional order PID and sliding mode controller

The output power of Photovoltaic (PV) energy generation systems depends mainly on operating conditions that include climatic conditions and occurrence of faults. Current-Voltage characteristic curves show different operating regions that are characterized by different transient responses in varying operating conditions and in the special case of the presence of the partial shading condition. In this paper, a dynamic performance evaluation of the PV system is performed both in open loop and in the presence of a feedback controller. Analysis shows that the PV system is affected when operating in different regions and environmental conditions and is characterized by a complex dynamic behavior. To improve the PV system dynamics, an adapted control strategy is proposed where the PV voltage is regulated using a Fractional Order PID controller tuned in various regions and partial shading patterns using Particle Swarm Optimization, whereas the PV current is regulated using a sliding mode controller that does not require using Pulse Width Modulation (PWM). In the present study, it is also shown that MPPT algorithms are affected by the conventional tuning approach of the feedback controller. To remedy to this issue, the Moth Flame Optimization based MPPT technique is implemented associated with the proposed control strategy to improve the performance PV system in different operating conditions. The proposed dynamic performance improvement strategy shows excellent transient responses in various operating scenarios.

Active distribution system state estimation incorporating photovoltaic generation system model

The inherently intermittent and varying power generation of distributed energy resources (DER) makes the situational awareness of active distribution systems (ADS) a challenging issue. Considering the detailed photovoltaic (PV) system model and environmental influencing factors including solar irradiance and temperature, this paper develops a state estimation model for the ADS with integrated PV power generation systems. Firstly, in order to achieve high computational efficiency, an explicit function fitting model of PV arrays is proposed and used to accurately approximate the conventional five-parameter model. Then, the state variables of a PV generation system are selected, and the measurement equations and the Jocobian matrix are derived. Finally, combined with the conventional distribution network model, state estimation and bad data processing of an ADS with PV systems are realized. A generalized per unit system is also developed for unified standardization of electrical and non-electrical quantities. Simulation results in the IEEE 33-bus system show that the proposed model significantly expands the scopes and capabilities of state estimation and bad data processing in ADSs, which facilitates comprehensive and reliable monitoring of ADSs.

Accurate Sizing of Residential Stand-Alone Photovoltaic Systems Considering System Reliability

In rural areas or in isolated communities in developing countries it is increasingly common to install micro-renewable sources, such as photovoltaic (PV) systems, by residential consumers without access to the utility distribution network. The reliability of the supply provided by these stand-alone generators is a key issue when designing the PV system. The proper system sizing for a minimum level of reliability avoids unacceptable continuity of supply (undersized system) and unnecessary costs (oversized system). This paper presents a method for the accurate sizing of stand-alone photovoltaic (SAPV) residential generation systems for a pre-established reliability level. The proposed method is based on the application of a sequential random Monte Carlo simulation to the system model. Uncertainties of solar radiation, energy demand, and component failures are simultaneously considered. The results of the case study facilitate the sizing of the main energy elements (solar panels and battery) depending on the required level of reliability, taking into account the uncertainties that affect this type of facility. The analysis carried out demonstrates that deterministic designs of SAPV systems based on average demand and radiation values or the average number of consecutive cloudy days can lead to inadequate levels of continuity of supply.

Clustering-Based Self-Imputation of Unlabeled Fault Data in a Fleet of Photovoltaic Generation Systems

This work proposes a fault detection and imputation scheme for a fleet of small-scale photovoltaic (PV) systems, where the captured data includes unlabeled faults. On-site meteorological information, such as solar irradiance, is helpful for monitoring PV systems. However, collecting this type of weather data at every station is not feasible for a fleet owing to the limitation of installation costs. In this study, to monitor a PV fleet efficiently, neighboring PV generation profiles were utilized for fault detection and imputation, as well as solar irradiance. For fault detection from unlabeled raw PV data, K-means clustering was employed to detect abnormal patterns based on customized input features, which were extracted from the fleet PVs and weather data. When a profile was determined to have an abnormal pattern, imputation for the corresponding data was implemented using the subset of neighboring PV data clustered as normal. For evaluation, the effectiveness of neighboring PV information was investigated using the actual rooftop PV power generation data measured at several locations in the Gwangju Institute of Science and Technology (GIST) campus. The results indicate that neighboring PV profiles improve the fault detection capability and the imputation accuracy. For fault detection, clustering-based schemes provided error rates of 0.0126 and 0.0223, respectively, with and without neighboring PV data, whereas the conventional prediction-based approach showed an error rate of 0.0753. For imputation, estimation accuracy was significantly improved by leveraging the labels of fault detection in the proposed scheme, as much as 18.32% reduction in normalized root mean square error (NRMSE) compared with the conventional scheme without fault consideration.

Extended operating range of PV module-level CHB inverter

In this paper an enhanced distributed maximum power point tracking (DMPPT) algorithm, along with an improved hybrid modulation method for a photovoltaic (PV) module-level Cascaded H­Bridge (CHB) inverter, is proposed. The advantages and drawbacks of the CHB topology in distributed PV generation systems are highlighted. The main benefits are related to the higher granularity of the PV power control, which mitigates mismatch effects, thus increasing the power harvesting. Nevertheless, heavy unbalanced configurations need to be properly addressed by means of dedicated control action. The proposed control strategy allows to overcome the operating limits of PV CHB inverter, by integrating in the MPPT algorithm a limitation of the individual cell modulation index. Experimental tests carried out on a laboratory prototype of a single­phase seven­level PV CHB inverter, evidence the effectiveness of the proposed control and modulation approach in terms of extended operating range and MPPT efficiency.

Shading simulation for two photovoltaics solar generation residential systems (SPV) using SAM (System Advisor Model)

In this document, shading models are developed for photovoltaic solar generationsystems located in two environments, a rural one, in the Cundiboyacense savanna,and the other one within the con-urban area of the Colombian capital. Both systemsconsider a typical electrical load for an average home. The photovoltaic generationsystems and their components are dimensioned based on this estimation, for which,in this case, there are not considered any battery energy storage system. Shading onthe panels is done using SAM, inserting objects of considerable height in both environments.The results of this modeling confirm that indeed, power losses are greaterwhen considering the area of panels affected by shade. Therefore, a comparative simulationcase is presented for the two considered environments, including and excludinglosses due to the effect of shading, and the respective conclusions for this researchare finally written. Keywords: Renewable Energies, Photovoltaic Solar Energy, Losses, System AdvisorModel, Simulation, Shading.

Robust operation of microgrid energy system under uncertainties and demand response program

<span>Microgrid energy systems are one of suitable solutions to the available problems in power systems such as energy losses, and resiliency issues. Local generation by these energy systems can reduce the role of the upstream network, which is a challenge in risky conditions. Also, uncertain behavior of electricity consumers and generating units can make the optimization problems sophisticated. So, uncertainty modeling seems to be necessary. In this paper, in order to model the uncertainty of generation of photovoltaic systems, a scenario-based model is used, while the robust optimization method is used to study the uncertainty of load. Moreover, the stochastic scheduling is performed to model the uncertain nature of renewable generation units. Time-of–use rates of demand response program (DRP) is also utilized to improve the system economic performance in different operating conditions. Studied problem is modeled using a mixed-integer linear programming (MILP). The general algebraic modeling system (GAMS) package is used to solve the proposed problem. A sample microgrid is studied and the results with DRP and without DRP are compared. It is shown that same robustness is achieved with a lower increase in the operation cost using DRP.</span>

Análisis experimental del desempeño de un sistema solar fotovoltaico con inversor centralizado y con microinversores: caso de estudio Manizales

La generación de electricidad amigable con el medio ambiente es un factor fundamental para el crecimiento económico y social de cualquier país. Recientemente la instalación de sistemas de generación fotovoltaicos se ha incrementado a nivel local, aunque su rendimiento depende del lugar de instalación y se ve afectado por diversos parámetros ambientales como la radiación, la temperatura y la precipitación. En el presente trabajo se lleva a cabo un análisis experimental del rendimiento, en términos de potencia generada, de un sistema solar fotovoltaico con inversor centralizado y con microinversores, instalado en la ciudad de Manizales, ubicada a 2.150 m s.n.m., temperatura promedio de 16.4 °C y precipitación de 1.878 mm al año. Históricamente, este municipio presenta dos periodos de tiempo lluviosos con alta nubosidad entre los meses de abril – junio y octubre – diciembre, y dos periodos de tiempo menos lluviosos entre los meses de enero–marzo y julio–septiembre.
 Para el experimento se implementó un sistema de generación solar fotovoltaico conformado por seis paneles solares marca Hybrytec con 270 W de potencia de generación cada uno, y dos sistemas de monitoreo – (i) Wifi – Box® para el arreglo fotovoltaico con inversor centralizado y (ii) EnvoyTM para el arreglo fotovoltaico con microinversores. Los parámetros ambientales recolectados por la estación meteorológica La Nubia, ubicada en los alrededores del sistema solar, y los datos recolectados por los sistemas de monitoreo implementados son analizados en el periodo de tiempo comprendido entre los meses de julio de 2018 y mayo de 2019. Se observa y se concluye que, a pesar de los altos niveles de precipitación promedio acumulada mensual (entre 71 mm y 262,2 mm) y los altos niveles de nubosidad (nublado o mayormente nublado el 76 % del tiempo), el arreglo fotovoltaico con microinversores presenta un 16,5 % de energía generada por encima del arreglo con inversor centralizado.

Simulation on power-flow dispatching cases for Microgrid with PVS and battery energy storage system

Modern Microgrid (MG) mainly consists of distributed generators (DGs), energy storage systems (ESSs), different loads, and protection systems. Microgrid plays an important role not only to ensure the power supply reliability but also to improve the power quality in distribution network. Moreover, deployment of distributed generators such as Photovoltaic Generation System (PVS), wind turbine generation system, and energy storage systems diversifies operation and control modes of AC microgrid in order to meet local demand response. This paper studies on power-flow dispatching cases for a MG with PVS and Battery Energy Storage System (BESS), which considers the maximum power consumption generated by the PVS and minimizes the power received from the utility grid. Simulation results validate the effectiveness of BESS for actively dispatching power-flow of MG in case the PVSs cannot partially or fully meet the local demand response in peak hours. By using ETAP software, real data of the PVSs are used to do simulation and power-flow calculation for the MG, which is to evaluate the feasibility of power-flow dispatch solutions proposed in this paper.