Adaptive Frequency Estimation Technique for Grid Connected Photovoltaic System

As the penetration level of grid-connected Photovoltaic (PV) systems increases, the power quality is one of the major concerns for system operators and the demands are becoming even stricter. The impact of interharmonics on the grid has been acknowledged in recent research when considering a large-scale adoption of PV inverters. However, the origins of interharmonics remain unclear. Thus, this paper performs tests on a commercial PV inverter to explore interharmonic generation and more important investigates the mechanism of interharmonic emission. The investigation reveals that the perturbation of the Maximum Power Point Tracking (MPPT) algorithm is one of the sources that induce interharmonics in the grid current, especially at low-power operating conditions. Accordingly, three mitigation solutions are discussed to address this issue, and simulations have been carried out to verify the effectiveness of the solutions. Simulation results indicate that the constant-voltage MPPT method is the most suitable solution to the mitigation of interharmonics introduced by the MPPT operation, as it avoids the perturbation in the PV voltage during operation.

This study introduces a novel methodology aimed at minimising total harmonic distortion (THD) in grid-connected photovoltaic (PV) systems (GCPVs) through the implementation of a maximum power point tracking (MPPT) approach based on artificial neural networks (ANN). High THD levels in PV systems can lead to inefficiencies, power quality issues, and potential damage to the grid infrastructure. Although traditional MPPT methods effectively optimise the power output, they often fail to address harmonics. The proposed ANN-based MPPT algorithm improves PV power harvesting while actively minimising the harmonic distortions. The ANN was trained using a comprehensive dataset that included various environmental conditions, ensuring robust performance in diverse operational scenarios. Simulation results demonstrate that the ANN-based MPPT approach significantly reduces THD to below 1% across various irradiance levels, in contrast to the 1.18% to 2.72% observed with conventional methods such as perturb and observe (PO), while simultaneously preserving optimal power output. Reducing harmonic distortion improves the power quality, system efficiency, and lifespan of grid-connected components. This study highlights ANN-based control strategies for addressing the challenge of maximising energy harvesting and maintaining power quality in modern PV systems, offering a solution for the sustainable integration of solar energy into the grid.

<p><span lang="EN-US">This work proposes an adaptive filter based on a new least mean sixth control approach with incremental conductance method of MPP for 3-phase grid-incorporated photovoltaic (PV) system. The proposed system comprises a PV array, 3-phase DC to AC converter, maximum power point tracker (MPPT), three-phase electronic load, and a 3-phase grid. The combination of solar PV array and the voltage source converter (VSC) supplies power to the grid. The 3-phase inverter as a distribution static synchronous compensator (D-STATCOM) improves the quality of the system performance in case of zero solar irradiation. D-STATCOM also reduces total harmonic distortion (THD) in grid currents, improves power factor, and maintainsa constant voltage at the point of common coupling (PCC). The system modelling and simulation is achieved on MATLAB/Simulink. The proposed system performance has been found satisfactory and conform to IEEE-519 standards.</span></p>

Solar Photovoltaic (SPV) offers alternative sources of energy which is in general pollution free, environment friendly, sustainable and unlimited in nature. The concerns of environment due to green house gases and global warming force research communities to develop a smart power system that has capability to integrate Solar Photovoltaic with the power grid. There are many challenges in integrating SPV generation with the grid like efficiency, power quality, stability, cost of the energy conversion, load management, reliability etc. Moreover, power quality problems at distribution level like harmonics, unbalanced supply, unbalanced loads, reactive power, load management etc. affect the operation of grid connected SPV systems. Single stage grid connected PV systems has the advantage of use of a single VSC for MPPT (Maximum Power Point Tracking) and inverter operation. The proposed grid interfaced SPV generating system consists of a SPV array, VSC (Voltage Source Converter), three-phase grid and linear/nonlinear loads. The SPV energy is injected in to the DC bus of VSC during sunshine hours. The DC bus voltage of a three- phase VSC is regulated for MPPT from the PV array. Secondly, this system serves to provide harmonics elimination, load balancing, power factor correction (PFC) and regulating the terminal voltage at the PCC (Point of Common Coupling). In this paper, a SRF (Synchronous Reference Frame) based control of a single stage dual purpose grid connected SPV system is proposed and simulation based on MATLAB and Simpower System Blockset demonstrates the dual purpose of the system.

This paper focuses on the control design of a differential boost inverter when used in single-stage grid-tied PV systems. The inverter performs both Maximum Power Point Tracking (MPPT) at the DC side and Power Factor Correction at the AC side. At first, the state-space time-domain averaged model of the inverter is derived and the small signal frequency domain model is obtained using a quasi-static approximation in which the inverter is treated as a DC–DC converter with a slowly varying output voltage. Then, the controllers are designed using a three-loop strategy in which the inverter inductor currents loop is used for suitable compensation, the DC Photovoltaic (PV) voltage loop is used for MPPT and the output grid current loop is used for Power Factor Correction (PFC) and active power control. The selection of the control parameters is based on a compromise among suitable system performances such as settling time of the input PV voltage, the sampling period of the MPPT, total harmonic distortion of the output grid current, power factor as well as suppression of subharmonic oscillation for all the range of the operating duty cycle. The resulting design ensures that the oscillations of the voltage, current and power at the DC side and the grid current at the AC side are effectively controlled. The validity of the proposed control design is verified by numerical simulations performed on the switched model of the system demonstrating its robustness and fast response under irradiance variations and MPPT perturbations despite the nonlinearity and complexity of the system.

The main purpose of this paper is to model, study and analyze the effect of shading with different Photovoltaic (PV) array configurations on a three-phase two-stage grid connected PV system. The first stage is a boost converter, which serves the purpose of MPPT (maximum power point tracking) and feeding the extracted solar energy, whereas the second stage is a two-level VSC (voltage source converter) serving as PV inverter which feeds power from a boost converter into the grid. The Incremental Conductance technique was used to track the Maximum Power Point (MPP). The two PV configurations used through this paper are Series-Parallel (SP) and Total Cross Tied (TCT) configurations, which showed best performance among other configurations (Series, Parallel, Bridge-linked and Honey-Comb configurations) [1]. The results showed that TCT configuration PV array Grid connected PV system has better efficiency under partial shading effect than SP, and that validated by simulation in the Matlab-Simulink environment.

This paper proposes the use of a variable step based improved least sum of exponentials (VS-ILSE) control algorithm for single stage three phase grid connected photovoltaic (PV) system. The VS-ILSE algorithm provides a fundamental weight of active and reactive power components of load currents which are used to generate reference grid currents. This control algorithm provides the power quality improvement of distribution network likes load balancing, power factor correction. The perturb and observe (P&O) MPPT (Maximum Power Point Tracking) algorithm is used to obtain reference DC link voltage of VSC and also used to extract maximum power from the SPV array during varying environmental conditions. The proposed system is simulated in MATLAB®/Simulink based environment of simpower system toolbox. The proposed algorithm is verified on a developed hardware and obtained responses are found satisfactory. The total harmonics distortions (THDs) of the grid currents and CCP (Common Coupling Point) voltages are found well according to an IEEE-519 and IEEE-929 standards.

This paper introduces the simulation and analysis of a three-phase large-scale grid-connected solar Photovoltaic (PV) system in order to assess the effect of integrated PV grid-connected mode on the power quality of the utility grid. The study takes into account the effect of solar system power variation as well as the PV inverter's introduction of penetrating harmonics into the system. The simulation of the system is done in MATLAB software using the SIMULINK environment and is tested by the Pysyst program. Where it is done in real-time with an actual case study on a 1620-kW PV array connected to an 11-kV grid via a three-level Voltage Source Converter (VSC). The technical data was recorded, and the system's power quality was examined. The grid-connected PV system's Performance Ratio (PR) is assessed to determine the PV system's reliability and grid connectivity.

Control of multi-functional grid-connected PV systems with load compensation under distorted and unbalanced grid voltages

This paper presents the grid interfaced 3P3W (Three-Phase Three- Wire) solar PV (Photovoltaic) system. The MDF (Modified Digital Filter) control technique is used for fundamental load current extraction and providing the VSC (Voltage Source Converter) switching. The grid interfaced VSC is used to provide active power to the load and surfeit power fed to the grid. Moreover, VSC provides reactive power compensation, harmonic mitigation, and load balancing. Simulated results of the proposed system have shown a good response under steady-state and dynamic-state conditions. The grid current THDs (Total Harmonic Distortion) are well within recommended IEEE-519 limits.

The solar photovoltaic (PV)‐based microgrid is one of the most ideal renewable energy resources. This paper presents a utility grid intertie multi‐PV‐inverter‐based microgrid (MG) control for the solar rooftop application. The main and ancillary voltage source converters (VSCs) DC links are assimilated with PV arrays of independent maximum power point tracking (MPPT) algorithms for the economical and efficacious single‐stage configuration. At the point of common coupling (PCC), parallel VSCs arrangement increases the MG's power rating with distinctive local loads. In normal circumstances, the current control methodology is employed by the main VSC under the grid‐interactive mode. Conversely, in some grid contingency conditions under the isolated mode, its control transfers to the voltage control, which regulates the frequency and the voltage at PCC and acts like a grid‐forming inverter. The ancillary VSC operation is implemented with the current control algorithm. The main VSC supplies the active power towards the grid and accomplishes the load requirement, whereas the ancillary VSC retains its load demand in a grid‐interactive mode and also regulates the load requirement in an islanded mode of operation. The utilization of feed‐forward components for PV arrays powers in the VSCs current control techniques improves the MG dynamic performance. The seamless mode transfer performance of the main VSC is implemented via a power electronics switch. The MATLAB software is used to model a microgrid and its performance is analysed via RT‐LAB in real time through the OPAL‐RT (OP4510) controller for various scenarios, that is, varying solar insolation, load alterations and unbalanced non‐linear loads. The utilization of the modified Kwong's algorithm‐based current control enhances the power quality such as harmonics current elimination and improvement in the power factor. The voltage profile of PCC voltages is enhanced via using a modified Kwong's algorithm‐based filter in the voltage controller. The modified Kwong's algorithm has fast convergence, reduces misadjustments and gives very good performance compared to the least‐mean‐square (LMS) and Kwong's approaches. The total harmonic distortion (THD) of grid currents and PCC voltages THD in an isolated mode is found according to the limits of the IEEE‐519 standard.

This paper presents a single stage solar photo voltaic (PV)-battery based three-phase microgrid in grid connected and isolated modes. The PV-battery system feeds nonlinear load through a voltage source converter (VSC). The battery energy storage (BES) is connected at the DC-link of the VSC through a bidirectional DC-DC buck-boost converter. The proposed control scheme operates the single stage PV system at maximum power point tracking (MPPT) in grid-connected as well as standalone modes. The dual objectives of battery charging and power quality control is implemented through VSC. An adaptive least mean square (LMS) control is used so that grid currents are always maintained balanced and free of harmonics, as per IEEE 519 standards. BES charging, in case of low state of charge (SOC), is implemented by VSC in grid connected mode by using droop based control. Simple and effective perturb & observe (P&O) control for MPPT is executed through the bidirectional DC-DC converter control. The proposed control algorithm is simulated on MATLAB/Simulink with Simscape toolbox and its satisfactory performance is demonstrated in various scenarios.

The lack of control in voltage overshoot, transient response, and steady state error are major issues that are frequently encountered in a grid-connected photovoltaic (PV) system, resulting in poor power quality performance and damages to the overall power system. This paper presents the performance of a control strategy for an inverter in a three-phase grid-connected PV system. The system consists of a PV panel, a boost converter, a DC link, an inverter, and a resistor-inductor (RL) filter and is connected to the utility grid through a voltage source inverter. The main objective of the proposed strategy is to improve the power quality performance of the three-phase grid-connected inverter system by optimising the proportional-integral (PI) controller. Such a strategy aims to reduce the DC link input voltage fluctuation, decrease the harmonics, and stabilise the output current, voltage, frequency, and power flow. The particle swarm optimisation (PSO) technique was implemented to tune the PI controller parameters by minimising the error of the voltage regulator and current controller schemes in the inverter system. The system model and control strategies were implemented using MATLAB/Simulink environment (Version 2020A) Simscape-Power system toolbox. Results show that the proposed strategy outperformed other reported research works with total harmonic distortion (THD) at a grid voltage and current of 0.29% and 2.72%, respectively, and a transient response time of 0.1853s. Compared to conventional systems, the PI controller with PSO-based optimization provides less voltage overshoot by 11.1% while reducing the time to reach equilibrium state by 32.6%. The consideration of additional input parameters and the optimization of input parameters were identified to be the two main factors that contribute to the significant improvements in power quality control. Therefore, the proposed strategy effectively enhances the power quality of the utility grid, and such an enhancement contributes to the efficient and smooth integration of the PV system.

Grid integration improvement for single-phase inverters of small wind turbines under distorted voltage conditions

The industry of solar photovoltaic (PV) energy and its application is still booming to enhance the sustainability of the society. When PV systems are connected to the grid, challenging issues should be addressed. One of the challenges is related to interharmonics in PV systems, especially with a large-scale adoption of PV systems. However, the origins of interharmonics remain unclear, although the impact of interhamonics has been reported in the literature. Thus, this paper explores the generation mechanisms of interharmonics in PV systems and the characteristics. The exploration reveals that the perturbation from the maximum power point tracking (MPPT) algorithm is one of the origins of interharmonics appearing in the grid current. Accordingly, the MPPT controller parameters such as the perturbation step size and the sampling rate have an inevitable impact on the interharmonic characteristics. Furthermore, an approach to characterize the interharmonics in the grid current is proposed. With the proposed model, interharmonics can be predicted according to the designed controller parameters in terms of frequencies and amplitudes. Experimental tests are performed on a single-phase grid-connected PV system. The results are in a close agreement with the analysis and, thus, validate the effectiveness of the proposed model.