Control Of Grid-connected Photovoltaic System Research Articles

New Trends in the Control of Grid-Connected Photovoltaic Systems for the Provision of Ancillary Services

The gradual displacement of conventional generation from the energy mix to give way to renewable energy sources represents a paradigm shift in the operation of future power systems: on the one hand, renewable technologies are, in general, volatile and difficult to predict; and on the other hand, they are usually connected to the grid through electronic power converters. This decoupling due to power converters means that renewable generators lack the natural response that conventional generation has to the imbalances between demand and generation that occur during the regular operation of power systems. Renewable generators must, therefore, provide a series of complementary services for the correct operation of power systems in addition to producing the necessary amount of energy. This paper presents an overview of existing methods in the literature that allow photovoltaic generators to participate in the provision of ancillary services, focusing on solutions based on power curtailment by modifying the traditional maximum power point tracking algorithm.

Indirect power control of grid-connected photovoltaic system using fuzzy control with a three-level inverter

This paper proposes an enhanced study of a photovoltaic generator (PVG) connected to the grid. A fuzzy maximum power point tracking (MPPT) is used to extract maximum power. The control strategy adopted gives the possibility to control separately the active and reactive power. the voltage control at the input of the three levels inverter allows fixing the reference currents in the DQ frame to control indirectly the power injected into the grid. The use of a three-level neutral point clamped voltage source inverter (3L-NPC-VSI) with space vector pulse width modulation (SVPWM) control and the RL filter allows to have a quality current and voltage wave with a minimum total harmonic distortion (THD). The simulation results on MATLAB/Simulink confirm the performance of this proposed strategy in the steady-state with high efficiency.

Nonlinear control of grid-connected PV systems using active power filter with three-phase three-level NPC inverter

Grid-connected photovoltaic (PV) systems have become a significant area of interest for research scientists. Given this, this article presents a nonlinear control of grid-connected PV systems using active power filter (APF) with three-phase three-level neutral point clamped (NPC) inverter. The control objectives involve: (1) Forcing the PV output voltage to track a reference signal provided by the MPPT block in order to produce their maximum power, (2) Regulating the DC link voltage to satisfy a correct operation mode of the three-phase active power filter, and (3) Satisfying power factor correction (PFC) objective at the point of common coupling, PCC. Therefore, the suggested control strategy includes a cascade structure of two loops. The inner-loop regulator is designed using the sliding mode control technique and Lyapunov approaches to ensure the PFC objective by forcing the grid current to follow a given reference signal. The Outer-loop consists mainly of a proportional-integral (PI) regulator so that to regulate the output voltage. Further, the theory of instantaneous real power is used to calculate reference harmonics. The effectiveness of the proposed controller is demonstrated through simulation results using MATLAB/Simulink.

Current model predictive fault-tolerant control for grid-connected photovoltaic system

<abstract><p>This paper investigates the performance of the current model predictive control (CMPC) for controlling a two-stage transformerless grid-connected photovoltaic (PV) system under grid fault conditions. A maximum power point tracking (MPPT) controller was used to extract the maximum power of the PV panel. To stabilize the DC link and generate the reference current values, a proportional-integral (PI) controller was used. The CMPC strategy was implemented to control the output current of the inverter that connects the PV system to the utility grid. The system and control strategy were simulated via a MATLAB/Simulink environment. The performance of the proposed control strategy was investigated under fault conditions between the three-phase two-level inverter and the grid. Moreover, to validate the capability of the CMPC, comparative case studies were conducted between CMPC, PI, and sliding mode control (SMC) under grid fault. Case studies' results showed that under grid fault, CMPC did not introduce any overshoot or undershoot in the PV output DC current and power. However, PI and SMC produced undershoots of almost 15 kW for the output power and 45 A for the output current. Under the fault conditions, the active output power and three-phase current recovery time of the inverter was 50 ms using CMPC, compared to PI and SMC with recovery times of 80 ms and 60 ms, respectively. Moreover, a voltage dip of 75 V at the DC link voltage was recorded with CMPC under faulty conditions, while the voltage dips for PI and SMC were around 180 V.</p></abstract>

Fractional-Order Control of Grid-Connected Photovoltaic System Based on Synergetic and Sliding Mode Controllers

Starting with the problem of connecting the photovoltaic (PV) system to the main grid, this article presents the control of a grid-connected PV system using fractional-order (FO) sliding mode control (SMC) and FO-synergetic controllers. The article presents the mathematical model of a PV system connected to the main grid together with the chain of intermediate elements and their control systems. To obtain a control system with superior performance, the robustness and superior performance of an SMC-type controller for the control of the udc voltage in the DC intermediate circuit are combined with the advantages provided by the flexibility of using synergetic control for the control of currents id and iq. In addition, these control techniques are suitable for the control of nonlinear systems, and it is not necessary to linearize the controlled system around a static operating point; thus, the control system achieved is robust to parametric variations and provides the required static and dynamic performance. Further, by approaching the synthesis of these controllers using the fractional calculus for integration operators and differentiation operators, this article proposes a control system based on an FO-SMC controller combined with FO-synergetic controllers. The validation of the synthesis of the proposed control system is achieved through numerical simulations performed in Matlab/Simulink and by comparing it with a benchmark for the control of a grid-connected PV system implemented in Matlab/Simulink. Superior results of the proposed control system are obtained compared to other types of control algorithms.

Stability improvement and control of grid-connected photovoltaic system during faults using supercapacitor

This paper describes the stability improvement of grid-connected photovoltaic (PV) system using supercapacitor (SC). The proposed technique is applied on PV system which using maximum power point tracking of perturbation and observation (P&O) algorithm. The P&O algorithm is used to extract the maximum power from the studied PV system. The effect of SC as a type of storage device on PV system appears at the abnormal conditions of grid faults. This technique is used to compensate the system parameters at different fault conditions. The control strategy of SC technique is developed for continuously charging and discharging to achieve its objective. In addition, the control system is presented in order to maintain the DC link voltage and to manage the power transit between the SC and the grid. The whole grid-connected PV system with SC energy storage system (ESS) is modeled and simulated using MATLAB/SIMULINK software and also the control system strategies are demonstrated. The effects of different fault conditions on the behaviors of studied grid-connected PV system with the SC ESS technique are investigated. A comparison between the behaviors of studied PV system in cases of without SC and with SC technique is studied. Also, the variations of DC voltage, active power, and reactive power for the studied PV system equipped without and with SC technique are investigated. The simulation results present a clear improvement for the system stability in case of using SC. Numerical results illustrate the validity of proposed technique with satisfactory values.

Robust Control of Grid-Connected Photovoltaic Systems Under Unbalanced Faults Without PLL

This paper presents the design of a robust control scheme for grid-connected photovoltaic systems subjected to severe operating conditions such as grid faults, abrupt set-point changes, parametric uncertainties, and unknown disturbances. During unbalanced faults, the scheme is able to deliver either constant real and reactive powers, or constant real power with sinusoidal currents to the grid, without requiring a phase-locked loop or symmetrical component decomposition. Moreover, the same controllers are used under normal operation and grid faults. These feats result in a control system having lesser computational requirements and complexity, and a lower number of design steps in comparison to some existing schemes. The dc-link voltage controller is based on active disturbance rejection control, and phase currents are controlled using repetitive control based on the internal model principle. The controllers are designed using linear matrix inequality constraints that can be solved by readily available tools. A number of simulation test cases are presented using the SimPowerSystems toolbox of the MATLAB/Simulink computing environment to demonstrate the performance of the control scheme under various types of grid faults, parametric uncertainties, and abrupt changes under operating conditions. Controller performance is also validated through digital implementation on a low-cost microcontroller.

Local, global and decentralized fuzzy-based computing paradigms for coordinated voltage control of grid-connected photovoltaic systems

The high penetration of grid-connected PV systems in conventional electrical grids may cause serious technical limitations, which could hinder the pervasion of these systems. In this domain, the decreasing of the power quality levels due to voltage perturbation represents one of the main issues to address. In order to tackle this problem, the application of Fuzzy logic-based voltage control at the point of common coupling is considered as one of the most promising research direction. Although, various computing paradigms based on both local and global information processing could be deployed to address this issue, the selection of the most effective solution, which depends on the available communication facilities and the required control accuracy, is still an open problem requiring further investigations. In trying to solve this problem, in this paper the main features, the expected performances, and the technological requirements of both local and global fuzzy-based computing paradigms for coordinate voltage control are analyzed. Detailed simulation results obtained on a realistic case study are presented and discussed in order to validate the presented argumentations.

Maximum Power Point Tracking Using Fuzzy Logic Control for Grid-Connected Photovoltaic System & Operation of PV Cells under Partial Shading Conditions

Maximum Power Point Tracking Using Fuzzy Logic Control for Grid-Connected Photovoltaic System & Operation of PV Cells under Partial Shading Conditions

Synergetic Control of Grid-Connected Photovoltaic Systems

It is important to improve the dynamic performance and the low-voltage ride-through (LVRT) capability of a grid-connected photovoltaic (PV) system. This paper presents synergetic control for the control of a grid-connected PV system. Modeling of a grid-connected PV system is described, and differential-algebra equations are obtained. Two control strategies are used in normal operation and during LVRT of a PV system. Practical synergetic controllers with two control strategies are synthesized. The mathematical expressions are derived for computing control variables. The design of the synergetic controllers does not require the linearization of the grid-connected PV system. A grid-connected PV system with synergetic controllers is simulated in Simulink surroundings. The control performance is studied in normal operation and during LVRT. Simulation results show that the synergetic controllers are robust and have good dynamic characteristics under different operation states.

FPGA-based real time simulation and control of grid-connected photovoltaic systems

Nowadays, FPGA devices are widely used to build control platforms in various fields of real time applications such as wireless telecommunications, image and signal processing, robotics and renewable energy systems. In grid-connected photovoltaic (PV) systems, an effective control strategy is needed for an efficiently use of solar energy as well as for energy supplies optimization. This paper presents an investigation, modelling and FPGA based digital controller design of a two-stage grid connected photovoltaic (GCPV) system. The basic idea of the proposed control structure is to operate the PV system as an active power generator and reactive power regulator. Firstly, a comprehensive study of dynamic behaviour of a two-stage GCPV system using Matlab/Simulink was presented. Subsequently, a digital circuit design of Incremental Conductance (IncCond) algorithm and decoupled active–reactive power control algorithm is carried out using the Hardware Description Language (VHDL). The simulation results confirm the accuracy of the adopted control strategy as well as the feasibility of the overall FPGA based control circuit.

06/00136 Maximum power point tracking using adaptive fuzzy logic control for grid-connected photovoltaic system: Patcharaprakiti, N. et al. Renewable Energy, 2005, 30, (11), 1771–1788

06/00136 Maximum power point tracking using adaptive fuzzy logic control for grid-connected photovoltaic system: Patcharaprakiti, N. et al. Renewable Energy, 2005, 30, (11), 1771–1788

Maximum power point tracking using adaptive fuzzy logic control for grid-connected photovoltaic system

This paper proposes a method of maximum power point tracking using adaptive fuzzy logic control for grid-connected photovoltaic systems. The system is composed of a boost converter and a single-phase inverter connected to a utility grid. The maximum power point tracking control is based on adaptive fuzzy logic to control a switch of a boost converter. Adaptive fuzzy logic controllers provide attractive features such as fast response, good performance. In addition, adaptive fuzzy logic controllers can also change the fuzzy parameter for improving the control system. The single phase inverter uses predictive current control which provides current with sinusoidal waveform. Therefore, the system is able to deliver energy with low harmonics and high power factor. Both conventional fuzzy logic controller and adaptive fuzzy logic controller are simulated and implemented to evaluate performance. Simulation and experimental results are provided for both controllers under the same atmospheric condition. From the simulation and experimental results, the adaptive fuzzy logic controller can deliver more power than the conventional fuzzy logic controller.