Inverter For Grid-connected Photovoltaic System Research Articles

Enhanced FOPID Controller Based Cascaded Inverter for Grid-Connected Photovoltaic System

An enhanced controller is proposed to investigate grid-connected photovoltaic systems employing cascaded two-level inverters. The primary focus is on optimizing power output, achieved through the development, modeling, and testing of photovoltaic systems using the suggested upgraded controller. This advanced controller, specifically a Fractional Order PID (FOPID) controller, incorporates the Ant-Lion Optimizer (ALO) algorithm for enhanced performance compared to conventional controllers. The FOPID controller’s reliability is emphasized, and further improvements are pursued by optimizing gain parameters through the prescribed method. Power supply under both schemes is examined, and the controller’s performance in extracting maximum power under specified operating conditions is deemed satisfactory. To validate the proposed approach, practical implementation is conducted using the MATLAB/Simulink platform. The effectiveness of proposed and conventional methodologies for analyzing the id and iq currents is assessed. A comparison is drawn between the suggested approach and current methods such as the base controller, GSA, and ABC methodologies. In comparison to the existing methods, the suggested FOPID controller demonstrates superior performance in maintaining the DC link voltage, achieving an efficiency of 94%, while the GSA method reaches 91.5%, the ABC method achieves 91%, and the base controller achieves 90%.

Performance enhancement of a three-phase grid-connected PV inverter system using fractional-order integral sliding mode controls

Grid-integrated photovoltaic (PV) systems hold significant promise for sustainable energy production. However, these systems often struggle with maintaining energy quality and stability in the face of fluctuating conditions. To address these challenges, this study proposes the use of fractional-order integral sliding mode control (FO-ISMC) for grid-connected PV systems. The system comprises solar panel arrays, a DC/DC boost converter with its controller, and a three-phase inverter integrated into the utility grid. The primary goals of this study are to maximize power extraction from the PV system and to regulate system currents, thereby improving effectiveness and power quality. The proposed method is further refined using the particle swarm optimization (PSO) algorithm to fine-tune parameter settings. By optimizing the command gains of the FOI-SMC, the PSO algorithm enhances system performance and stability. Leveraging fractional-order and integral terms provides the control signal with additional degrees of freedom, enhancing system performance in the presence of internal and external disturbances. Simulation results demonstrate the effectiveness of the proposed controller compared to the classical controller, where in the case of Irradiation taking the value of 500 W/m2, the proposed strategy reduced the values of constant voltage, active power, and reactive power by percentages estimated at 88.18%, 90%, and 70%, respectively, compared to the traditional strategy. Also, the overshoot value of active power was reduced in all completed cases compared to the traditional strategy by percentages estimated at 53.57%, 66.66%, and 65%, respectively. The proposed strategy reduced the response time of reactive power in all cases compared to the traditional strategy by percentages estimated at 58.59%, 28.80%, and 75%, respectively. These ratios show the high performance of the proposed control in improving the characteristics of the studied system compared to traditional control based on PI control.

Maximum power point tracking and space vector modulation control of quasi-z-source inverter for grid-connected photovoltaic systems

The quasi-Z-source inverter (qZSI) become one of the most promising power electronic converters for photovoltaic (PV) applications, due to its capability to perform a buck-boost conversion of the input voltage in a single stage. The control strategy based maximum power point tracking (MPPT) and proportional integral (PI) controller are well known in grid-connected with traditional configuration but not in qZSI. This paper presents a control strategy for qZSI grid-connected based on the MPPT algorithm and the linear control by PI controllers. This is complemented by the capability to efficiently transfer the harvested power to the grid, ensuring a unity power factor. The proposed control strategy effectively separates the control mechanisms for the direct current (DC) and alternating current (AC) sides by utilizing the two control variables, the shoot-through duty ratio and the modulation index. An adapted space vector modulation technique is then utilized to generate the switching pulse width modulation (PWM) signals, using these two control variables as inputs. The proposed approach was tested and validated under MATLAB/Simulink and PLECS software.

Optimized 9-Level Switched-Capacitor Inverter for Grid-Connected Photovoltaic Systems

Optimized 9-Level Switched-Capacitor Inverter for Grid-Connected Photovoltaic Systems

Fuzzy Fractional order PI Controller for a Multilevel Inverter for Grid-Connected Photovoltaic Systems (PV)

Fuzzy Fractional order PI Controller for a Multilevel Inverter for Grid-Connected Photovoltaic Systems (PV)

Harmonic Suppression Strategy of LCL Grid-Connected PV Inverter Based on Adaptive QPR_PC Control

To reduce the influence of voltage harmonics on the grid current, a control strategy based on adaptive quasi-proportional phase compensated resonance (QPR_PC) is proposed. Firstly, the LCL grid-connected photovoltaic inverter system model is established, and the stability performance of the three-level inverter system under double closed-loop control is analyzed using the output impedance model of the inverter. Then, a QPR regulator for the zero steady-state error tracking of AC signals is studied. To solve the problem that the system has poor robustness against frequency changes when the traditional QPR regulator is used in the static coordinate system, this paper improves the traditional QPR regulator to optimize the response characteristics of the closed-loop system. Based on the QPR regulator, a phase margin compensation structure is introduced to form QPR_PC control. Then adaptive frequency design is added to ensure good control even when the power grid frequency drifts, which is the control strategy proposed in this paper. Verification shows that the proposed method improves the phase margin of output impedance at a specific frequency, restrains the interference of the 3rd, 5th, and 7th harmonics of grid voltage, and improves the dynamic performance of the system and the quality of grid-connected current. Finally, the simulation results show that the total harmonic distortion rate of grid-connected current is reduced by 1.03% after adopting this strategy, which verifies the effectiveness and correctness of the proposed method.

A Multilevel Inverter for Grid-Connected Photovoltaic Systems Optimized by Genetic Algorithm

This article introduces a grid-connected photovoltaic (PV) source combined with a multi-level inverter. A converter five-level neutral point (NPC) can be used to integrate the PV power into the power grid with minimum harmonic distortions and high power capacity. If the output voltage of the PV generator varies significantly with solar radiation, the output voltage of the ripple must be fixed. For this reason, a regulation loop was used. In this study, we used a classical PI regulator. It is difficult to determine the PI controller transaction values, so Genetic Algorithm was used to optimize the PI controller parameters. The Matlab/Simulink simulation results show the better performance and efficiency of the PI controller optimized by the GA, in comparison to the stand-alone PI controller, regarding stability and accuracy, and the reduction of Total Harmonic Distortions (THD) of the current injected into the grid for any difference in solar radiation.

Cascade feedforward neural network and deep neural network controller on photovoltaic system with cascaded multilevel inverters: Comparison on standalone and grid integrated system

The introduction of a micro-grid-based power generation network will help to meet the demands of consumers while reducing environmental impact. Several industrialized and emerging countries allocate considerable resources to renewable energy-based power generation and invest significant sums of money in this area. This study examines the challenges involved with electricity generation through photovoltaic (PV) systems and the integration of the same with the grid to mitigate power quality issues and improve the power factor for various loading conditions. An innovative multilayer inverter for grid-connected PV systems has been developed to enhance the voltage profile and resulted in a drop in total harmonic distortion (THD). A cascade multilevel inverter (associated with a grid-integrated PV system and managed using multiple innovative artificial intelligence controllers) was developed in this research project. Various advanced intelligent controllers, such as cascade feedforward neural networks (CFFNN) and deep neural networks (DNN), have been analyzed under various operating situations and observed that the THD of voltage, current at the grid, and the load is less than 3 % as per the IEEE 519 standards along with this power factor is maintained nearly unity for the grid-connected system. The quality of power in terms of voltage, frequency, total harmonics distortion, and power factor are improved by using a novel deep neural network algorithm in a cascaded multilevel inverter and verified according to IEEE 1547 and IEEE 519 standards to determine the efficacy of the proposed system.

DC/DC Stage Contribution to Bus Voltage in 1000- and 1500-V Grid-Connected Solar Inverters

Modern architectures of transformerless, three-phase-grid-connected photovoltaic (PV) inverter for 1000- and 1500-V commercial/residential applications are analyzed and compared from the point of view of the energy harvested during one year period, system efficiency, and power density. Scenarios for different ac grid voltage levels and inverters topologies are analyzed based on one- and two-stage solutions. The architectures with and without included dc/dc stage are compared from the point of view of the optimized power density. In the case of the two-stage PV inverter architecture, the mini-boost converter concept, presented in previous publications, is extended and the standard boost topology that employs 1200-V rated IGBTs and diodes is replaced by a multilevel, hybrid power converter topology that exhibits high efficiency due to the partial power processing and new classes of 900- and 650-V SiC and GaN devices employed. The inverter’s output filter design space (DS) has been researched from the point of view of the dc bus voltage variation. The cases are analyzed for fully controlled bus voltage at its minimum value and when allowed to vary in the full MPP range. Optimization results of the output filter DSs for the minimum and maximum operating dc bus voltage are compared in terms of the occupied volume in order to investigate whether it is possible to obtain more compact inverter stage by better control of dc bus voltage. The results show that in the case of controlled low dc bus voltage level, it is feasible to design a filter that occupies up to 50% less volume than the filter designed for the full MPP voltage variation. Even more, this can be achieved by maintaining the system efficiency. The simulation and experimental results complement the analysis of the 1000- and 1500-V grid-connected PV inverter systems.

A novel self-boosting 5-level inverter for grid-connected photovoltaic system

Renewable energy systems are presently recognized as the primary alternative power source due to increased electricity demand and the depletion of fossil resources. The photovoltaic (PV) system is a rapidly growing renewable energy system. Inverters are used to integrate PV systems to the utility grid. Multilevel inverters are the most popular option for PV application due to reduced total harmonic distortion (THD), switching stress, and electromagnetic interference. This work presents a 5-Level grid-connected inverter while minimizing the cost. The proposed inverter uses six unidirectional switches and one diode with a single switched capacitor. Furthermore, it removes the requirement of multiple isolated DC sources. A simple modulation technique generates a suitable switching pulse for the inverter. Additionally, the comparison of the proposed inverter with the other topologies existing in the literature shows that it has reduced power devices, total standing voltage (TSV), and cost function. The PV connected grid system is investigated with specified controlling and implemented in MATLAB/Simulink and validated through hardware-in-the-loop (HIL) real-time simulation in OPAL-RT. In addition, the laboratory setup of the proposed structure is built and tested to verify its effectiveness.

Optimization of Grid-Connected Photovoltaic Power Generation Technology Based on Nonlinear Back-Stepping Controller

To address the issue of energy scarcity and to use solar photovoltaic energy as a renewable source, a three-phase grid-connected photovoltaic inverter system with uncertain system model parameters is investigated, which converts DC power into AC power, feeds it into the grid, and maintains the grid-connected part’s quality. An enhanced back-stepping approach is proposed to explore the control strategy of three-phase solar grid-connected inverter, which includes adaptive control, dissipative theory, sliding mode control, and rapid terminal sliding mode control, respectively. It is verified that the system is subjected to external interference F = 5 during 0.5 s–0.8 s. As per the simulation results, the improved adaptive terminal sliding mode control method can suppress the interference to a certain extent and has strong robustness to the external interference. When compared with the adaptive sliding mode control approach, the anti-interference ability is better, and the system stability is improved. Then, to improve the above approach, a high speed terminal sliding mode control method is proposed, which can swiftly converge in finite time and the estimated value of uncertain parameters is closer to the actual value, thereby boosting the system’s robustness.

Transformerless Six-Switch (H6)-Based Single-Phase Inverter for Grid-Connected Photovoltaic System With Reduced Leakage Current

Due to the advancements of power electronic devices and photovoltaic (PV) power systems, there has been an increasing interest in transformerless grid-connected PV inverters, which offer lower cost, smaller volume, and higher efficiency than the one with the transformer. However, transformerless inverters with conventional topologies suffer from leakage current problem, which needs to be handled carefully. To overcome the conduction loss and leakage current problem associated with conventional transformerless inverters, a new transformerless H6 (six-switch-based) inverter topology is proposed in this article that can maintain constant common-mode (CM) voltage. At the same time, reduce or eliminate the leakage current problem. The proposed inverter topology is simulated using MATLAB/Simulink software to validate the proposed system's accuracy. The proposed topology's effectiveness is verified through the comparative results of CM voltage, CM leakage current, and conduction loss of the proposed topology with the conventional H6-I, H6-II, and H5 topologies. Finally, to validate the proposed topology, a laboratory prototype is also built and tested. The experimental results validate the theoretical analysis and simulation results.

Research on LCL-type three-phase photovoltaic grid-connected inverter based on passive damping

The traditional LCL filter has resonance phenomenon in the working process of three-phase photovoltaic grid-connected inverter system. Based on the analysis of the frequency characteristics of LCL filter equivalent circuit before and after the introduction of passive damping resistor, it is concluded that the resonance of the system can be suppressed after the introduction of passive damping resistor. In the meantime, the current double closed-loop control strategy used in the system is introduced in detail. Finally, the simulation model is built by Matlab/Simulink simulation platform to verify the feasibility of the research method of LCL-type three-phase photovoltaic grid-connected inverter based on passive damping.

Research on New Energy Power Generation Technology under Smart Grid

The paper introduces the new energy solar photovoltaic grid-connected power generation technology and system composition in the smart grid, and describes the basic working principles and functions of photoelectric conversion components and inverters. The article introduces the single-phase photovoltaic grid-connected inverter system and its control system design, tests and analyzes the harmonics generated by the inverter system after grid-connected, and proposes some further improvements and research and development work for the system in the future view.

Research on the Influence of Photovoltaic Module Power Generation Efficiency and Manufacturing Technology on Power Grid Connection

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.

Performance Improvement of the Grid Connected PV Inverter System with ANN Controller

The implementation of the PV system and its integration into the grid has been increased. In this process some power quality issues arise i.e. harmonics, voltage sags / surges, interruptions, flickers, transients, and this is due to non-linear loads, arc furnaces, frequent starting / stopping of electric motors, oscillating loads and interactions of different semiconductor devices. Within these interharmonics is one of the emerging power quality issues in grid-connected photovoltaic (PV) systems. Based on previous case studies and field measurements, evidence of interharmonic emission from maximum power point tracking is one of the leading causes of interharmonics in PV inverters. In this regard, MPPT parameters such as sampling rate and perturbation step size have a strong impact on the interharmonic characteristic of PV system, and to overcome these problems, a mitigating solution has been previously proposed , namely modifications of the MPPT algorithm so as to randomly select the sampling rate between the fast value and the slow value. By implementing this technique with an artificial neural network controller for the control of the inverter. With the proposed method, the voltage perturbations of the DC-link voltage as well as the harmonics of the grid currents are reduced and the performance of the MPPT and PV system has been increased. The performances of the proposed system has been validated on a MATLAB / SIMULINK software environment.

Three-Phase Filter-Clamped Transformerless Inverter for Grid-Connected Photovoltaic Systems with Low Leakage Current

In this paper, a Filter-Clamped (FC) inverter is employed as a three-phase grid-connected Transformerless Photovoltaic (TLPV) inverter. TLPV inverters are more efficient and more cost-effective compared to the alternatives based on high and low-frequency isolation transformers. On the other hand, TLPV inverters generate high leakage current due to the removal of the isolation transformer. Prior-art TLPV topologies have been developed to overcome this issue by either adding more semiconductor switches to block potential leakage current paths or modifying the control method. In contrast, the FC inverter addresses the leakage current issue without adding any extra component or improving the control technique. Thus, it is a promising solution to TLPV systems. Having decreased the leakage current, the FC inverter improves the THD of grid injected current and the efficiency compared to the conventional three-phase Full-Bridge (FB) inverter. Simulations and experiments are provided to validate the effectiveness of the FC inverter in terms of reduced leakage current, improved grid current THD, and improved overall efficiency.

Adaptive Backstepping-Based H${_{\infty}}$ Robust Controller for Photovoltaic Grid- Connected Inverter

To improve the robustness and stability of the photovoltaic grid-connected inverter system, a nonlinear backstepping-based H ∞ controller is proposed. A generic dynamical model of grid-connected inverters is built with the consideration of uncertain parameters and external disturbances that cannot be accurately measured. According to this, the backstepping H ∞ controller is designed by combining techniques of adaptive backstepping control and L2-gain robust control. The Lyapunov function is used to design the backstepping controller, and the dissipative inequality is recursively designed. The storage functions of the DC capacitor voltage and grid current are constructed, respectively, and the nonlinear H ∞ controller and the parameter update law are obtained. Experimental results show that the proposed controller has the advantage of strong robustness to parameter variations and external disturbances. The proposed controller can also accurately track the references to meet the requirements of high-performance control of grid-connected inverters.

A Feedback-Based Passive Islanding Detection Technique for One-Cycle-Controlled Single-Phase Inverter Used in Photovoltaic Systems

Single-stage, single-phase photovoltaic (PV) distributed generation (DG) systems rated below 5 kW are becoming popular because of the reduction in the cost of PV panels and also due to various policy initiatives. One cycle control (OCC) based inverters are ideally suitable for such DG systems because of its cost-effectiveness, simple structure, and phase-locked loop free implementation. These inverter-based DG systems should have a robust islanding detection method (IDM) incorporated into it and should fulfill the recent standard requirements. This article proposes a novel feedback-based passive IDM, which is suitable for OCC-based grid-connected PV inverter system. The proposed method relies on the inbuilt feedback nature of OCC-based system, which drives the voltage at the point of common coupling outside the normal range of operation during an islanding condition. The proposed IDM works effectively under the new standard requirements with negligible nondetection zone. The IDM does not rely on additional computational effort or injection of external disturbance into the grid. Simulation studies are performed to verify the effectiveness of the proposed IDM. A laboratory prototype has been developed, and experimental studies are conducted to ascertain the viability of the proposed method.

A Model Predictive Power Control Method for PV and Energy Storage Systems With Voltage Support Capability

The cascaded control method with an outer voltage loop and an inner current loop has been traditionally employed for the voltage and power control of photovoltaic (PV) inverters. This method, however, has very limited power regulation capability. With the fast increasing penetration of PV power generation systems in the distribution network, the voltage rise/drop has become a serious problem impacting negatively on the power quality and grid stability. Therefore, flexible power regulation is highly desired for PV inverters to provide ancillary services. This paper proposes a novel model predictive power control (MPPC) scheme to control and coordinate the dc–dc converter and inverter for grid-connected PV systems with energy storage systems (ESS). By regulating the dc-bus voltage and controlling the active and reactive power flows, MPPC can support the power grid to maintain stable voltage and frequency and improve the power factor. Numerical simulation and controller hardware-in-the-loop (CHIL) testing have been conducted on a PV-ESS system to verify the capability and effectiveness of the proposed control strategy.