A Novel Stability Analysis Method for Large-Scale Photovoltaic System

Multi-inverter systems have been widely used for grid-connected large-scale centralized photovoltaic (LSCPV) plants. However, the problem of how time delays affect the stability of digitally controlled grid-connected LSCPV plants with multi-inverter systems has not been investigated sufficiently. This paper models a grid-connected LSCPV system as a cascade system and conducts a systematic study of the relationship between the time delay and the stability of a grid-connected LSCPV system. The analysis intuitively reveals the influence of the time delay on the stability of the grid-connected LSCPV system. The impact of the time delay on the stability range of the number of grid-connected inverters in LSCPV plants is discussed for the first time, and the stability range for a specific time delay is obtained from the root locus. In addition, considering the damping performance is negatively affected by the time delay, an improved capacitor-current-feedback active damping method is proposed to reduce the effects of the delay on the damping region and the robustness against variations in the grid impedance. Simulations and experimental results are presented to validate the theoretical analysis and the effectiveness of the proposed delay compensation method.

A review of generation dispatch with large-scale photovoltaic systems

The objective of this paper is to explore the role of generation dispatch strategy and spinning and non-spinning reserve methods in solving challenges posed by grid-connected large-scale PV systems as opposed to the commonly used approaches such as voltage, rotor angle and frequency control methods. The investigation covers the issues associated with the inherent intermittent of PV output, which results in additional operational challenges such as load-following requirements, spinning reserve requirements, load frequency excursions and system stability. A detailed performance evaluation of generation dispatch with large-scale PV systems is carried out in this research work based on the IEEE 14-bus test system using the MATLAB-based Power System Analysis Toolbox (PSAT). An analysis is conducted by using the power flow analysis methods such as power flow (PF), continuation power flow (CPF) and time domain (TD) analysis to gain an understanding of the influence that large-scale PV systems have on sub-transmission and transmission networks. The outputs of the study can be used to work out the appropriate penetration level of large-scale PV systems that can minimize their negative impacts on sub-transmission and transmission systems.

Agricultural Photovoltaic Systems are a key technology to achieve sustainable development goals by reducing competition between land for food and electricity. In addition, Agricultural Photovoltaic Systems are at the heart of the link between power generation, crop production and irrigation water conservation. The main ecophysiological constraint on crop production under photovoltaics is the reduction of light. It is difficult to recommend shade tolerance for some plant varieties due to insufficient information on shading conditions for most plants. The use of shading panels (photovoltaic panels) requires more crop-specific research to determine the optimal percentage of panels and their placement that will not reduce agricultural yields. Crop yield variation versus field shading and availability to maximize the system require extensive research. This study aims to develop a standard procedure for designing an agricultural grid-connected photovoltaic power generation system for solar power generation in an agricultural area in Bahteem, Egypt. The technical and annual performance of the grid-connected PV system was simulated using PV Syst software. The paper started with a pre-feasibility study of a grid-connected photovoltaic system using PV Syst. Software with an extensive database of meteorological data, including global daily horizontal solar irradiance, and a database of various renewable energy system components from different manufacturers. In this work, a comprehensive literature review of agricultural solar photovoltaic systems is conducted, with a particular focus on grid-connected systems, followed by a design procedure for grid-connected solar photovoltaic systems. The planned photovoltaic system will generate a total of 400 KWp of electricity. This generated electricity can drive down electricity prices by exporting excess electricity to the national grid. In addition, solar power systems are fuel-efficient and have a low environmental impact.

Renewable energy systems (RESs), such as photovoltaic (PV) systems, are providing increasingly larger shares of power generation. PV systems are the fastest growing generation technology today with almost ~30% increase since 2015 reaching 509.3 GWp worldwide capacity by the end of 2018 and predicted to reach 1000 GWp by 2022. Due to the fluctuating and intermittent nature of PV systems, their large-scale integration into the grid poses momentous challenges. This paper provides a review of the technical challenges, such as frequency disturbances and voltage limit violation, related to the stability issues due to the large-scale and intensive PV system penetration into the power network. Possible solutions that mitigate the effect of large-scale PV system integration on the grid are also reviewed. Finally, power system stability when faults occur are outlined as well as their respective achievable solutions.

Large-scale photovoltaic system (PV) installation can affect power system operation, stability, and reliability because of the non-linear characteristic of the PV system installation. DC/AC and DC/DC converters are the major devices use in connecting PV into the grid. These converters are liable to power quality problem if the proper control mechanism is not adopted. This study presents an optimal control technique to improve dynamic operation of PV grid-connected system. An optimal control method with use of Manta ray foraging optimization (MRFO), is implemented as a control strategy for tuning the proportional-integral (PI) controllers of DC/DC and DC/AC converters for the integration of the PV system into the grid. The MRFO is chosen because of its ease of implementation and requirement of less adjusting parameters. The effectiveness of the proposed technique is studied under irradiance variation. The obtained results demonstrate the superior performance of the MRFO over five other metaheuristic algorithms (i.e., grey wolf optimization, whale optimization, grasshopper optimization, atom search optimization, and salp swarm algorithm) in terms of convergence rate and optimal global solution capture. The entire simulation model is established using MATLAB editor and Simulink. The acquired transient result shows the functionality and viability of the MRFO approach.

In photovoltaic (PV) systems, a wide variety of power converter topologies and PV configurations have been developed in order to increase the system efficiency. Traditionally, grid-connected PV systems use one or two conversion stages. The single conversion stage is mainly used for large-scale PV systems working with only a DC-AC converter. Whereas, for small and medium-scale, two conversion stages are used. The advantages working with a DC-stage are mainly the distributed maximum power point tracking (MPPT) algorithm and the elevation capability, but it presents a reduced conversion efficiency compared with the single stage configurations. On the other hand, the single conversion stage presents a reduced overall efficiency produced by partial shading. The proposed work presents a Partial Power DC-DC converter (PPC) which process only a portion of the whole power, reducing the conversion losses. It includes the benefits of two stage configurations so that it performs individual MPPT. Besides, due to the modularity of the architecture, it allows the parallel connection of many strings as required to use in large-scale PV systems. Simulations are performed in order to evaluate the converter performance.

The purpose of this paper is to study large-scale PV system with pumped storage systems (PSS). It is proposed a new method for PSS to store the electric power from PV system in the daytime and discharge in the nighttime as base power supply. Moreover, it should be concerned with the installing position of PSS, the capacity of PSS, the transmission capacity, the land and personnel cost, and the base power supply. The results indicate that PSS has possibility to be electric storage system in large-scale PV system. It can be used as base power supply to satisfy demand and to reduce or stop the output of nuclear or fuel oil electricity stations. It is possible that use base power supply from PV power instead of electricity from nuclear or fuel oil electric power stations.

Chapter 9 - Grid-connected solar PV power systems

The impact of the installation of a large-scale photovoltaic (PV) system to the electric power grid management is analyzed in a series of two works: Part 1 and Part 2. The PV generation is estimated in Part 1. By applying the results of Part 1, the Guatemala’s electric power grid management is simulated with a virtually-installed large-scale PV system using a nonlinear analysis model in this work, Part 2. The thermal power plants reduced their operation in the simulation by installing the PV system, however the effect of the PV system installation to the plants is different in each thermal power plant. The contribution of the PV installation to the reduction of operation of the largest generation thermal plants is very limited or null, because of their high efficiency and low cost in operation. On the other hand, the middle-large generation thermal power plants reduce their operation after installing PV system in this simulation. The reduction of thermal plants’ operation becomes large, but its reduction gradient becomes small as the PV installing capacity becomes large.

PV systems are considered one of the most important and popular forms of renewable energy sources worldwide. Due to the installation of PV modules on rooftops and outdoor areas, they are frequently subjected to lightning strikes, leading to a deterioration in PV systems. To provide an efficient lightning protection system, the accurate modeling of PV systems during lightning strikes is required. The main objective of this paper is to assess the transient behavior of PV systems when struck by lightning, where the PV system is modeled using the partial element equivalent circuit (PEEC) and finite difference time-domain (FDTD) methods. The PEEC method is one of the accurate methods used to represent the PV system by its equivalent RLC circuit to study lightning transients. Moreover, the FDTD method provides high accuracy when studying lightning transients by analyzing the electric and magnetic fields inside the PV system. The PEEC and FDTD methods are used to calculate the transient overvoltages at different points of the PV system. Then, a small-scale PV system is tested in the laboratory using an impulse generator representing the lightning strike to verify the correctness of the results obtained by simulation. Most of the existing research works introduce low accuracy in PV system modeling during lightning transients by neglecting the effect of the mounting system, metal frame, and mutual coupling, which are considered in this work. Moreover, the high-frequency nature of lightning current is considered when modeling the elements of the grounding system. Verifying the results by laboratory experiments can guarantee the application of the simulation model on large-scale PV systems.

Load mismatch of grid-connected photovoltaic systems: Review of the effects and analysis in an urban context

The power generation efficiency of a photovoltaic power generation system is closely related to factors such as the material of the photovoltaic module, the tilt angle of the module installation, and the power of the module. At present, the output power of large-scale grid-connected photovoltaic power generation systems has large fluctuations and strong randomness. In order to accurately predict the output power of photovoltaic power stations to solve the problems of peaking and dispatching caused by large-scale photovoltaic grid-connected power generation to the grid. The article introduces the design of single-phase photovoltaic grid-connected inverter system and its control system based on big data technology. The research found that the photovoltaic manufacturing and grid-connected algorithms proposed in this paper can achieve the best power generation benefits of photovoltaic power plants, while improving the operation and maintenance efficiency of photovoltaic power plants.

The contribution of solar power in electric power systems has been increasing rapidly due to its environmentally friendly nature. Photovoltaic (PV) systems contain solar cell panels, power electronic converters, high power switching and often transformers. These components collectively play an important role in shaping the reliability of PV systems. Moreover, the power output of PV systems is variable, so it cannot be controlled as easily as conventional generation due to the unpredictable nature of weather conditions. Therefore, solar power has a different influence on generating system reliability compared to conventional power sources. Recently, different PV system designs have been constructed to maximize the output power of PV systems. These different designs are commonly adopted based on the scale of a PV system. Large-scale grid-connected PV systems are generally connected in a centralized or a string structure. Central and string PV schemes are different in terms of connecting the inverter to PV arrays. Micro-inverter systems are recognized as a third PV system topology. It is therefore important to evaluate the reliability contribution of PV systems under these topologies. This work utilizes a probabilistic technique to develop a power output model for a PV generation system. A reliability model is then developed for a PV integrated power system in order to assess the reliability and energy contribution of the solar system to meet overall system demand. The developed model is applied to a small isolated power unit to evaluate system adequacy and capacity level of a PV system considering the three topologies.

When the power grid impedance mutates, the output power of the grid-connected photovoltaic power generation system controlled by drooping will become very unstable. To solve this problem, an improved droop control algorithm based on network impedance detection is proposed. Taking photovoltaic grid-connected power generation system as the research object, the influence of power grid impedance on traditional droop control is firstly expounded by introducing power grid impedance value into traditional droop control. Then the method of real-time network impedance extraction is introduced. Furthermore, according to the bandwidth and phase angle constraints of the equivalent output impedance phase frequency characteristics of the photovoltaic grid-connected inverter, the controller parameters are updated in real time to achieve the purpose of adaptive network impedance mutation. Finally, the proposed method is tested and verified by real-time simulation in the loop respectively. The results show that the proposed method is correct.