Grid-tied Photovoltaic Generation Research Articles

Improvement of Power Quality Using Reduced Switch Count Eleven-Level Inverter in Smart Grid

This article proposed a hybrid control topology to cascaded multilevel-inverter (CMLI) using 11-level for the grid-tied photovoltaic generation system. The proposed hybrid technique combines an archerfish hunting optimiser (AHO) and Spike Neural Network (SNN); hence, it is called the AHO-SNN technique. The proposed control technique is to maintain the regulation of power or maximal energy conversion of the solar subsystem and reduce total harmonic distortion (THD). Here, the AHO is utilised to construct the optimum control signal dataset. The best control signals are estimated using a data set performed by SNN. The resultant control signals will regulate insulated-gate-bi-polar-switches (IGBT) of Cascaded MLI. The proposed AHO-SNN control topology determines the converter switching states by constructing the operating modes of the generation system. The system parameter changes and outside disturbances are optimally minimised with this control strategy. The proposed AHO-SNN control is done in MATLAB platform, and it evaluated their performance by using existing methods, like War Strategy Optimization Algorithm (WSO) Fuzzy Wavelet Neural Network (FWNN), Side-Blotched Lizard Algorithm (SBLA), Adaptive Neuro-Fuzzy Inference System (ANFIS), and Memetic Fire-Fly Algorithm (MFA). The result shows that the proposed approach based on THD is less than existing approaches.

A Three-Port Energy Router for Grid-Tied PV Generation Systems With Optimized Control Methods

In grid-tied photovoltaic (PV) generation systems, intelligent energy management is required to maximize its performance. In this article, a novel three-port energy router with optimized control is proposed for this application. The proposed converter can interface among three ports (PV source, battery, and dc-link) with high integration. The PV panel is connected to the battery through an interleaved boost structure on the primary side. The primary-side PV-battery system and secondary-side dc-link are connected through a dual-active-bridge (DAB) converter. The battery operates as an energy buffer to compensate for the power mismatch due to the intermittent nature of the PV source. According to the daily power profile and intelligent power management between the grid and battery, six operating modes are possible. Optimized control strategies are customized in different operating modes. The maximum-power-point-tracking (MPPT) of the PV panel can be always realized. The zero-voltage-switching (ZVS) condition for all <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> s, reducing circulating current over a wide range, and flexible energy flow among three ports are all taken into considerations in the design. To verify the proposed concept, a 500 W rated prototype is designed. The designed prototype exhibits high efficiency in various operating modes. The experimental results agree well with the theoretical analysis.

Modeling and Mechanism Investigation of Inertia and Damping Issues for Grid-Tied PV Generation Systems with Droop Control

Inertia effect and damping capacity, which are the basic characteristics of traditional power systems, are critical to grid frequency stability. However, the inertia and damping characteristics of grid-tied photovoltaic generation systems (GPVGS), which may affect the frequency stability of the grid with high proportional GPVGS, are not yet clear. Therefore, this paper takes the GPVGS based on droop control as the research object. Focusing on the DC voltage control (DVC) timescale dynamics, the mathematical model of the GPVGS is firstly established. Secondly, the electrical torque analysis method is used to analyze the influence law of inertia, damping and synchronization characteristics from the physical mechanism perspective. The research finds that the equivalent inertia, damping and synchronization coefficient of the system are determined by the control parameters, structural parameters and steady-state operating point parameters. Changing the control parameters is the simplest and most flexible way to influence the inertia, damping and synchronization ability of the system. The system inertia is influenced by the DC voltage outer loop proportional coefficient Kp and enhanced with the increase of Kp. The damping characteristic of the system is affected by the droop coefficient Dp and weakened with the increase of Dp. The synchronization effect is only controlled by DC voltage outer loop integral coefficient Ki and enhanced with the increase of Ki. In addition, the system dynamic is also affected by the structural parameters such as line impedance X, DC bus capacitance C, and steady-state operating point parameters such as the AC or DC bus voltage level of the system and steady-state operating power (power angle). Finally, the correctness of the above analysis are verified by the simulation and experimental results.

A study of impact on power system stability originated from new islanding detection method in PV systems

AbstractIn Japan, a unique islanding detection method, named New Islanding Detection Method, is widely equipped with grid-tied photovoltaic generation systems (PVs) to accurately detect their islanding operation. However, some research results show that the extensive installation of new islanding detection method brings negative impacts on stability of main power grids. This is because the islanding detection method has a possibility to detect frequency fluctuation caused by main grid’s faults, and the resulting undesirable operation intensifies the frequency fluctuations more. The authors especially focus on a frequency feedback mechanism in the islanding detection method, and then clarify some impacts on the stability of main grids which are originated from the growth in penetration of the islanding detection method in PVs. Through numerical simulations and discussions on their results, the authors concluded as, (1) the transient stability can be improved when active power output of PVs are set to const...

Parallel Operation of Modular Single-Phase Transformerless Grid-Tied PV Inverters With Common DC Bus and AC Bus

In order to enhance the efficiency and reliability of dc-module-type photovoltaic (PV) generation systems, the single-phase transformerless full-bridge grid-tied inverters with a common dc bus and ac bus are utilized as the dc–ac stage. The high-frequency circulating current issue of parallel-operated single-phase grid-tied inverters with different topologies and modulation strategies are investigated. The conditions of high-frequency circulating currents elimination without additional hardware costs are revealed and presented. The analysis indicates that there are no high-frequency circulating currents between parallel-operated inverters with bipolar pulsewidth modulation (PWM). The parallel-operated inverters with unipolar double frequency PWM have high-frequency circulating currents, but the effects of the high-frequency circuiting currents on the fundamental components of split-filter inductor currents can be mitigated. The parallel-operated inverters with a unipolar PWM also have high-frequency circulating currents, but their effects on the fundamental components of split-filter inductor currents cannot be reduced. The single-phase transformerless full-bridge inverters with low-leakage currents, such as H5 and highly efficient and reliable inverter concept, meet the elimination conditions of the high-frequency circulating currents. Hence, these inverters are free of high-frequency circulating currents. A prototype of dc module-type grid-tied PV generation system is built up, and experimental tests with different topologies and PWM methods verify the analysis.

The &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$H_{\infty }$ &lt;/tex-math&gt;&lt;/inline-formula&gt; Control Method of Grid-Tied Photovoltaic Generation

Microgrid allows high penetration of renewable energy sources, and provides technical foundation for the grid connection and operation of distributed generations (DGs). The negative impacts caused by DGs should be reduced inside the microgrid. Photovoltaic (PV) generation is one of the major distributed energy sources, and the performance of PV generation systems connected to microgrid directly affects power quality and other technical indexes of the microgrid. Thus, the research of flexible microgrid connection control for PV generation system has both theoretical significance and practical value. This paper makes a concise exposition on the H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> control theory and applies this theory to the flexible microgrid connection control for PV generation systems. This paper focuses on the specific situation where the microgrid is grid tied to the main power grid. We establish the mathematical model of PV generation system and adopt the H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> control theory to design a voltage tracking controller. Theoretical analysis proved that our control system is internally stable. Simulations under six different conditions are performed using MATLAB/Simulink, and the results demonstrate that the grid-tied PV generation system using H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> controller has high control accuracy and robustness.

Modelling robustness for a flexible grid‐tied photovoltaic generation system

Robustness to modelling inaccuracy is a vital characteristic of a controller, because no matter how accurate a model is, modelling inaccuracies always exist. However, it is difficult to achieve satisfactory nominal and robust performance of a grid-tied photovoltaic (PV) generation system at the same time, using traditional controller design methods. To solve this problem, a μ-synthesis control method combined with the application of linear fraction transformation (LFT) is proposed in this study. The proposed method is designed with object transforming and implemented with DK iteration. The μ-analysis and simulation results prove that the objective can be achieved under various microgrid conditions, determined by factors such as grid connection point voltage, load conditions and component parameter perturbations. Compared with traditional controller design methods, the grid-tied PV generation system under μ-synthesis control exhibits comparatively large perturbation margin for nominal performance and robust stability, and simultaneously is capable of guaranteeing the preset perturbation range for robust performance.