THD reduction with reactive power compensation for fuzzy logic DVR based solar PV grid connected system

Dynamic voltage restorer (DVR) is used to protect sensitive loads from voltage disturbances of the distribution generation (DG) system. In this paper, a new control approach for the 200 kW solar photovoltaic grid connected system with perturb and observe maximum power point tracking (MPPT) technique is implemented. Power quality improvement with comparison is conducted during fault with proportional integral (PI) and artificial intelligence-based fuzzy logic controlled DVR. MPPT tracks the actual variable DC link voltage while deriving the maximum power from a photovoltaic array and maintains DC link voltage constant by changing modulation index of the converter. Simulation results during fault show that the fuzzy logic based DVR scheme demonstrates simultaneous exchange of active and reactive power with less total harmonic distortion (THD) present in voltage source converter (VSC) current and grid current with fast tracking of optimum operating point at unity power factor. Standards (IEEE-519/1547), stipulates that the current with THD greater than 5% cannot be injected into the grid by any distributed generation source. Simulation results and validations of MPPT technique and operation of fuzzy logic controlled DVR demonstrate the effectiveness of the proposed control schemes.     

Power quality investigation of a solar PV transformer-less grid-connected system fed DVR

This paper presents a single stage transformer-less grid-connected solar photovoltaic (PV) system with an active and reactive power control. In the absence of active input power, the grid-tied voltage source converter (VSC) is operated in a reactive power generation mode, which powers the control circuitry, and maintains a regulated DC voltage to the VSC. A data-based maximum power point tracking (MPPT) control scheme which performs power quality control at a maximum power by reducing the total harmonic distortion (THD) in grid injected current as per IEEE-519/1547 standards is implemented. A proportional-integral (PI) controller based dynamic voltage restorer (DVR) control scheme is implemented which controls the grid side converter during single-phase to ground fault. The analysis includes the grid current THD along with the corresponding variation of the active and reactive power during the fault condition. The MPPT tracks the actual variable DC link voltage while deriving the maximum power from the solar PV array, and maintains the DC link voltage constant by changing the modulation index of the VSC. Simulation results using Matlab/Simulink are presented to demonstrate the feasibility and validations of the proposed novel MPPT and DVR control systems under different environmental conditions.     

Power quality improvement of solar photovoltaic transformer-less grid-connected system with maximum power point tracking control

This paper presents a transformer-less single-stage grid-connected solar photovoltaic (PV) system with active reactive power control. In the absence of active input power, grid-tied voltage source converter (VSC) is operated in the reactive power generation mode, which powers control circuitry and maintains regulated DC voltage. Control scheme has been implemented so that the grid-connected converter continuously serves local load. A data-based maximum power point tracking (MPPT) has been implemented at maximum power which performs power quality control by reducing total harmonic distortion (THD) in grid-injected current under varying environmental conditions. Standards (IEEE-519/1547) stipulates that current with THD greater than 5% cannot be injected into the grid by any distributed generation (DG) source. MPPT tracks actual variable DC link voltage while deriving maximum power from PV array and maintains DC link voltage constant by changing the converter modulation index. Simulation results with the PV model and MPPT technique validations demonstrate effectiveness of the proposed system.     

Photovoltaic field emulation including dynamic and partial shadow conditions

In this paper the development of a new laboratory prototype for the emulation of a photovoltaic (PV) field is presented. The proposed system is based on a DC/DC step-down converter topology and allows to obtain the solar array I–V curves, taking into account the environmental changes in solar irradiance and cell temperature. The DC/DC converter control strategy is deduced by using a comprehensive mathematical model of the PV field whose parameters are obtained from the knowledge of: (a) maximum power point data, measured when the PV plant power converter is running, (b) open circuit voltage and short-circuit current, measured off-line. This approach allows the most accurate representation of the PV source. Computer simulations and experimental results demonstrate that the proposed circuit acts as a highly accurate and efficient laboratory simulator of the photovoltaic array electrical characteristics both in steady state and transient conditions. Partial shading and fluctuating conditions can be reproduced too. Moreover the dynamic behaviour of the proposed laboratory emulator is suitable to its effective connection to power electronic interface to the utility or to load through a DC/DC boost converter.     

Analysis and enhancement of PV efficiency with incremental conductance MPPT technique under non-linear loading conditions

This paper presents experimental evaluations for variation in the efficiency of energy extracted from a photovoltaic (PV) module (under non-linear loading) incorporated with an incremental conductance(IC) maximum power point tracking (MPPT) algorithm. The focus is on the evaluation of the PV panel under non-linear loading conditions using the experimental installation of a 100W_p photovoltaic array connected to a DC–DC converter and a KVA inverter feeding a non-linear load. Under the conditions of non-linear loading, both the simulation and experiment show that the MPPT technique fails to attain maximum power point due to the presence of ripples in the current leading eventually to a reduction in efficiency. In this paper, panel current is taken as a function of load impedance in the MPPT algorithm to eradicate power variation, as load impedance varies with supply voltage under non-linear conditions. The system is simulated for different non-linear loads using MATLAB-Simulink. A TMDSSOLAREXPKIT was used for MPPT control. In case 2, the inverter is connected to a single phase grid. When a voltage swell occurs in the grid, PV power drops. This power loss is reduced using the proposed MPPT method. The results of simulations and experimental measurements and cost efficiency calculations are presented.     

Adaptive fuzzy control with an optimization by using genetic algorithms for grid connected a hybrid photovoltaic–hydrogen generation system

The integration of significant amounts of renewable-storage hybrid power generation systems to the electric grid poses a unique set of challenges to utilities and system operators. This article deals with the designing methodology of an intelligent control based grid-connected a hybrid system composed of renewable energy source (RES) and storage system (SS). RES is a photovoltaic (PV) source and SS is a process of hydrogen transformation system (H₂TS) which composed of alkaline water electrolysis (AWE) for decomposition water by using the PV power, a tank used for gas storage and a proton exchange membrane (PEM) fuel cell (FC) to transform the H₂ to the electrical energy. The interconnection of the grid with the power generation system (PGS) is ensured through using a DC/AC hysteresis converter and it can synchronize current with the grid voltage among an independent control of active (P) and reactive (Q) power through a possibility of the Q compensation. In the proposed system, three algorithms are applied; two used inside generation and the third is used inside the grid. Perturb and observe (P&O) maximum power point tracking (MPPT) control algorithm always finds optimal power in the PV generator. A simple cascade controls loop of DC-DC boost converter and operate the FC generator to ensure maximum power and to regulate the DC Bus voltage. In addition, adaptive fuzzy logic control (FLC) unit is developed to control the DC/AC inverter, with adopting an off-line optimization based on genetic algorithms (GAs) applauded for tune different issues as scaling factors of the FLC and PIDs gains of the PV and the H₂TS control loops. Simulated results prove a big success of the proposed controls of the grid connected the hybrid PV-H₂TS with good performance.     

Fuzzy dispatching of solar energy in distribution system

This paper presents a novel approach for solar energy using in distribution system as distributed generation (DG) unit. A nonlinear fuzzy controller tunes the modulation index of PWM inverter to feed the load in the grid via photovoltaic arrays. The controller also dispatches two dc sources to control input of inverter. The proposed system controls the voltage even during changing sunlight voltage condition or unbalanced load. A low pass LC filter is linked to the output of voltage source converter to bypass switching harmonics. The evolutionary method based on fuzzy theory is used to determine the value of modulation index and disperse the sources from a fuzzy rule-based defined on load voltage error of the point of common coupling. This system gives a full flexibility to the grid to obtain power from the solar photovoltaic units depending on its cost and load requirement at any given time. Simulation results illustrate the effectiveness of performance of proposed method.     

Bidirectional energy storage photovoltaic grid-connected inverter application system

A novel topology of the bidirectional energy storage photovoltaic grid-connected inverter was proposed to reduce the negative impact of the photovoltaic grid-connected system on the grid caused by environmental instability. Using the proposed Inverter as a UPS power supply in case of a grid failure, storage electrical energy and regulating the energy delivered to the grid for reducing the pressure on the grid. A new artificial fish-swarm algorithm and variable step voltage perturbation method were presented to track the maximum power point of the solar panels. Analysis was done to reduce the output ripple of the inverter and sinusoidal pulse width modulation (SPWM) was selected to control the inverter. Model simulation was performed using PSpice software to obtain the volt-ampere characteristic curve of the solar panel output. The solar array simulator was used to verify the effect of maximum power point tracking at different light intensities. The study concludes that the maximum power point tracking (MPPT) efficiency of the bidirectional energy storage photovoltaic grid-connected inverter designed was as high as 99.9%. The distortion rate of the grid-connected current waveform was within 2% and the DC current component was less than 0.5%. The output voltage and power were in full compliance with the grid connection standard.     

New control strategy for 2-stage grid-connected photovoltaic power system

This work deals with the performances and responses of a grid-connected photovoltaic (PV) plant in normal and disturbed modes. The system is composed of a solar array, a dc–dc converter and a three-phase inverter connected to the utility grid. On the one hand a suitable control of the dc–dc converter is developed in order to extract the maximum amount of power from the PV generator. On the other hand an active and reactive power control approach (PQ) has been presented for the inverter. This method can provide a current with sinusoidal waveform and ensure a high power factor. Therefore, the grid interface inverter transfers the energy drawn from the PV into the grid by ensuring constant dc link voltage. Modeling and controlling were carried out using the informational graph of causality and the macroscopic energy representation methods. The simulation under MATLAB/SIMULINK and the experimental results show the control performance and dynamic behavior of grid-connected PV system in normal and disturbances modes.     

Single-stage sine-wave inverter for an autonomous operation of solar photovoltaic energy conversion system

This paper proposes a high performance single-stage inverter topology for the autonomous operation of a solar photovoltaic system. The proposed configuration which can boost the low voltage of photovoltaic (PV) array, can also convert the solar dc power into high quality ac power for driving autonomous loads without any filter. An MPPT circuit with parallel connection is implemented so that the part of the energy generated is processed by the dc–dc converter to supply dc loads. The line current total harmonic distortion (THD) obtained using this configuration is quite reasonable. The proposed topology has several desirable features such as low cost and compact size as number of switches used, are limited to four as against six switches used in classical two-stage inverters. In this paper analysis, simulation and experimental results are presented.     

Multilevel converters for single-phase grid connected photovoltaic systems: an overview

Multilevel voltage source inverters offer several advantages compared to their conventional counterparts. By synthesising the AC output terminal voltage from several levels of DC voltages, staircase waveforms can be produced, which approach the sinusoidal waveform with low harmonic distortion, thus reducing filter requirements. The need of several sources on the DC side of the converter makes multilevel technology attractive for photovoltaic applications. This paper provides an overview on different multilevel topologies and investigates their suitability for single-phase grid connected photovoltaic systems. Several transformerless photovoltaic systems incorporating multilevel converters are compared regarding issues such as component count and stress, system power rating and the influence of the photovoltaic array earth capacitance.     

Rapid transaction to load variations of active filter supplied by PV system

This paper deals with the analysis and control of a photovoltaic (PV) system connected to the main supply through a Boost converter and shunt active filter supplied by a PV system providing continuous supply of nonlinear load in variation. A robust control of a PV system connected to the grid while feeding a variable nonlinear load is developed and highlighted. This development is based on the control of the Boost converter to extract the maximum power from the PV system using the Perturb and Observe (P and O) algorithm in the presence of temperature and illumination. The proposed modeling and control strategy provide power to the variable nonlinear load and facilitates the transfer of power from solar panel to the grid while improving the quality of energy (harmonic currents compensation, power factor compensation and dc bus voltage regulation). Validation of the developed model and control strategy is conducted using power system simulator Sim-Power System Blockset Matlab/Simulink. To demonstrate the effectiveness of the shunt active filter to load changes, the method of instantaneous power (pq theory) is used to identify harmonic currents. The obtained results show an accurate extraction of harmonic currents and perfect compensation of both reactive power and harmonic currents with a lower THD and in accordance with the IEEE-519 standard.     

Application of QOCGWO-RFA for maximum power point tracking (MPPT) and power flow management of solar PV generation system

A hybrid technique for solar PV array (SPV) generating system for maximizing the power to load is proposed in this dissertation. The proposed hybrid technique is the joint execution of both the Quasi Oppositional Chaotic Grey Wolf Optimizer (QOCGWO) with Random Forest Algorithm (RFA) and hence it is named as QOCGWO-RFA technique. Here, QOCGWO optimizes the exact duty cycles required for the DC-DC converter of SPV based on the voltage and current parameters. RFA predicts the control signals of the voltage source inverter (VSI) based on the active and reactive power variations in the load side. With this control technique, the system parameter variations and external disturbances are reduced and the load demands are satisfied optimally. The proposed strategy is implemented in MATLAB/Simulink working platform with three different case studies and compared with existing techniques. With these case studies, the proposed technique generates the optimal PV power of 2.1 kW.     

Erratum to “Steady-state analysis of PV supplied separately excited DC motor fed from IDB converter” [Sol. Energy Mater. Sol. Cells 71 (4) (2002) 493–510]

Interleaved dual boost converter is capable of extracting more amount of power from the photovoltaic source than the conventional boost converter. Power extraction capabilities of the conventional boost and interleaved dual boost converters from the photovoltaic array are verified through experimental studies. As an application the effectiveness of this interleaved dual boost converter for PV supplied separately excited DC motor is studied through simulation. Extensive studies are made by formulating the mathematical models for photovoltaic source, interleaved dual boost converter, DC motor and load. Steady-state performance of the motor coupled to centrifugal pump load is analyzed for maximum power, gross mechanical energy operations. From the simulation studies, it is found that the motor performance is improved with gross mechanical energy output operation as compared to maximum power operation of solar cell array. Furthermore, the use of interleaved dual boost converter reduces the ripple content both in the source and load waveforms, thus resulting in reduced filtering requirements and improved photovoltaic array performance.     

Distributed energy storage system‐based control strategy for hybrid DC/AC microgrids in grid‐connected mode

This paper concentrates on the issues with the aim of providing a constant dc‐link voltage and desired power sharing for a distributed energy storage system (DESS)‐based hybrid microgrid under load variations. The hybrid microgrid which is consisted of PV system, lithium battery‐based storage system and a grid‐connected dc/ac converter are controlled by designing a controller based on the zero dynamics‐based mathematical equations of all used converters. Two buck and bidirectional buck‐boost dc/dc converters employed in PV and DESS systems, respectively, are responsible for damping the dc‐link voltage fluctuations, and also the grid‐connected converter is set to enhance the grid power quality and supply continuously the grid‐connected loads. The main contributions of the proposed control technique are simplicity and providing the simultaneous stable performance for both DC and AC sides under both DC and grid‐connected loads variations. Moreover, another contribution of the proposed control technique is providing accurate coordination in both steady‐state and dynamic conditions. To analyze the proposed controller, the dynamic operations of the converters in various operating conditions are evaluated. In this evaluation, several curves based on their zero dynamics are achieved, and their desired operations are completely investigated in different operating conditions. Simulation results in MATLAB/SIMULINK verify the proposed controller ability at reaching the desired zero dynamics and the stable performance of the proposed hybrid microgrid.     

A novel maximum power fuzzy logic controller for photovoltaic solar energy systems

The maximum power tracking problem and efficient energy utilization of a stand-alone photovoltaic array (PVA) feeding voltage controlled linear and nonlinear loads is studied. A novel and simple on-line fuzzy logic-based dynamic search, detection and tracking controller is developed to ensure maximum power point (MPP) operation under excursions in solar insolation, ambient temperature and electric load variations. A computer simulation model of the PVA renewable utilization scheme including the effects of temperature and solar irradiation changes was developed and fully simulated. The load voltage is controlled by a DC chopper and kept constant at the required rated voltage. A permanent magnet DC motor (PMDC) driving a fan-type load was connected in parallel to an RL passive load. A speed control scheme is also used for the PMDC motor drive so that the drive can be operated at specified speeds. Different controllers have been employed in the unified PVA scheme to control three separate loads at MPP tracking condition namely voltage at load bus and speed of the PMDC motor. The main objective of the paper is to present a novel enhanced, cost-effective MPP detector (MPPD) and dynamic MPP tracking (MPPT) controller for a hybrid mix of electric loads.     

Hybrid Control of a Grid-Interactive Wind Energy Conversion System

Without storage provision, a wind energy conversion system (WECS) does not have fault ride-through capability for most temporary faults on the utility feeder. This paper proposes a hybrid valve switching and control strategy for a voltage-sourced converter (VSC) used for interfacing a WECS to the utility grid. The hybrid control of the VSC ensures continuous operation of the system in the presence of temporary single line to ground faults on the utility feeder without the need for a storage provision. The fast acting hybrid control also limits reactive fault current contribution by the converter, and therefore, avoids problems associated with overcurrent protection of the feeder. The hybrid valve switching and control of the VSC consists of: 1) sinusoidal pulse width modulation (SPWM) based valve switching and current-controlled voltage-source operation of the VSC during normal system operating conditions and 2) hysteresis space vector modulation (HSVM) based switching together with controlled current-source operation of the VSC during temporary fault conditions. The hybrid control of the VSC isolates the WECS from the grid side disturbances to ensure uninterrupted operation of the unit. Simulation studies of the grid-interactive WECS in PSCAD/EMTDC confirm the validity of the proposed hybrid control scheme.      

可再生能源交流孤网转并网运行中的电压控制策略

柔性直流远距离输送有仅通过直流送出模式和交直流混联送出模式。两种送出模式下,系统的运行点存在较大差异,直接切换会对电网产生较大冲击。文章首先分析了两种送出模式下系统的调压控制特点,指出并网点电压幅值偏差是切换过程的关键点,设计了以可再生能源集群并网点电压偏差最小为主目标,换流站综合无功裕度最大为次目标的柔性切换策略。最后,基于某柔直电网可再生能源送端规划系统进行仿真,验证了所提策略的有效性。     

Digital power factor control and reactive power regulation for grid-connected photovoltaic inverter

The overall efficiency of photovoltaic (PV) systems connected to the grid depends on the efficiency of direct current (DC) of the solar modules to alternate current (AC) inverter conversion. The requirements for inverter connection include: maximum power point, high efficiency, control power injected into the grid, high power factor and low total harmonic distortion of the currents injected into the grid. An approach to power factor control and reactive power regulation for PV systems connected to the grid using field programmable gate array (FPGA) is proposed. According to the grid demands; both the injected active and reactive powers are controlled.In this paper, a new digital control strategy for a single-phase inverter is carried out. This control strategy is based on the phase shift between the inverter output voltage and the grid voltage, and the digital sinusoidal pulse width modulation (DSPWM) patterns, in order to control the power factor for a wide range of the inverter output current and consequently the control and the regulation of the reactive power will be achieved. The advantage of the proposed control strategy is its implementation around simple digital circuits.In this work, a simulation study of this strategy has been realized using Matlab/Simulink and PSIM. In order to validate its performance, this control has been implemented in a FPGA. Experimental tests have been carried out demonstrating the viability of this control in order to control the power factor and the injected power into the grid.