Phase Utility Grid Research Articles

Adaptive Hybrid NFS-MSOGIQ Control Technique for Improving Power Quality in Solar PV Distributed Generation System

A two-stage circuit configuration with 3-phase utility grid assisted solar power generation system is designed. In order to track the solar PV arrays maximum peak power (MPP), a DC boost converter with Composite Incremental Conductance (InC) MPP technique is employed in first stage. In Second stage, a grid-tied four-leg DC-AC converter, is employed to provide the solar power that was extracted into the utility grid and to enhancing power quality. An adaptive hybrid Multi-Second Order Generalized Integrator-Quadrature (MSOGI-Q) control algorithm, in conjunction with Neuro Fuzzy system (NFS) is proposed for controlling this DC-AC converter. MSOGI-Q reference current generation strategy is designed to mitigate current harmonics by retrieving the fundamental constituents from non-linear load. The Neuro Fuzzy system along with PID controller, by adjusting the voltage from dc link keeps consistent power in between AC and DC sides for varying isolation condition. To get the peak power out of a PV panel even in different environmental conditions, the composite incremental conductance algorithm is used. To upgrade the dynamic performance of voltage variation at Point of Common Coupling (PCC) a feedforward descriptor for Photovoltaic contributions has been implemented. In addition, a comparison between the proposed NFS-MSOGIQ control technique and the existing adaptive control technique is done to assess the effectiveness of the proposed adaptive control technique. The proposed adaptive control technique for the distributed generation system is designed and stimulated in MATLAB/SIMULINK and the simulation outcomes verify the effectiveness of the proposed control technique under various transition circumstances. A laboratory prototype model of the proposed system is developed for theoretical analysis and its results are found to be compliant with IEEE standards. Furthermore, THD values of voltage and current are found to be within standard limits.

Grid-integrated single phase solar PV system employed with single switch high gain boost converter

• This paper deals with a grid-integrated single phase solar photovoltaic system (GISPSPS) employed with a single switched based high gain boost converter. The significant contributions in this paper are; • The dynamic model of HGBC including effective series resistance (ESR) of passive elements is developed for improving accuracy with slight increase in complexity of model. Then its stability analysis is carried out under different solar irradiations (i.e. 300, 500, 800 and 1000 W/m 2 ) using an eigenvalue plot. • The HGBC control is obtained using the sliding mode control (SMC) for PPE under change in solar irradiations. In proposed SMC only two sensing signals PV panel voltage and current (i.e. v pv and i pv ) are needed for PPE in comparison to three sensing signals PV panel voltage, current and DC link voltage (i.e. v pv , i pv and v dc ) require in SMC of ref. [10] . • The control of FBVSC is obtained by a F i OGI controller. The F i OGI provides noise-less extraction of synchronization signal, under presence of DC offset and noise in grid voltage. However, FOGI used in ref. [10] exhibits poor performance under presence of noise in grid supply voltage. This paper presents a grid-integrated single phase solar photovoltaic (PV) system (GISPSPS) with its modeling, design and control. The GISPSPS consists of a single switch based high gain boost converter (HGBC) and full bridge voltage source converter (FBVSC). The HGBC, boost the low PV panel voltage and extracts the optimum PV power. The HGBC allows high voltage conversion ratio and possesses less voltage stresses on power devices. The optimum PV power is extracted via a sliding mode control (SMC) strategy that generates the switching signal for the switch of HGBC. The FBVSC delivers PV power to the single phase utility grid, as well as load connected at point of interfacing (POI). A fifth order generalized integrator (F i OGI) is developed for FBVSC control to ensure harmonic suppression and DC offset rejection capability during extraction of fundamental grid voltage. Experimental validation of proposed GISPSPS and its control is also verified.

Multifunctional UPQC operating as an interface converter between hybrid AC-DC microgrids and utility grids

This paper proposes a multifunctional hybrid unified power quality conditioner (UPQC-H), adapted to operate as an interface converter between utility grids and hybrid microgrids (H-MG). In addition to the generation of both ac and dc buses to the H-MGs, the main structure of the UPQC-H can also integrate distributed generation (DG) systems and energy storage systems (ESS) without the need for changing any control strategy. The proposed UPQC-H is built by including two additional power switches to the conventional three-phase UPQC power circuit, which in its traditional configuration is composed of two three-phase inverters used to operate as series and parallel converters. Some advantages related to the proposed UPQC-H configuration can be highlighted, as follows: 1) versatile application to any H-MG configuration; 2) natural power exchange between the H-MG ac and dc buses of both grid-connected and islanded operating modes; 3) seamless transitions between the islanded and grid-connected operating modes, and vice versa; and 4) smoothing of intermittency issues associated to renewable energy sources. Extended static and dynamic experimental results are presented to evaluate the UPQC-H performance and explore its functionalities when interfacing a 3-phase utility grid and an H-MG with integrating photovoltaic-based DG and ESS.

Improving power quality of single phase utility grid connected to wind–PV system using multilayer‐frequency adaptive fundamental signal extractor

A multilayer frequency adaptive fundamental signal extractor-based filter is used for the improvement of power quality of a single phase utility grid interfaced to a wind–photovoltaic (PV) system. This filter is used for the grid synchronisation, serving multiple objectives such as mitigating the lower-order harmonics, DC offset elimination, load reactive power compensation, and power flow management. As this filtering technique is based on frequency adaptation, it adapts the changes in the grid fundamental frequency. The effectiveness of this filter is studied with simulations using MATLAB Simulink under varying solar irradiance, wind speeds, and loads also validated on the test setup developed in the laboratory.

Grid tied PV- Electric Vehicle Battery Charger using Bidirectional Converter

Research on renewable energy based Electric Vehicle battery charging system is booming in the automobile industry in the recent years. The intermittent nature of the renewable energy sources leads to the grid connected renewable energy systems for Electric vehicle battery charging applications. Hence, an Electric Vehicle battery charger using grid connected PV system is proposed in this paper. The proposed charger is capable of charging the EV battery continuously irrespective of solar irradiations using dc-dc converter and bidirectional ac-dc converter. Sepic converter is preferred for dc-dc converter and Line commutated converter is used as a bidirectional converter with the help of the proposed bidirectional configurator in the charging system. During sunshine hours, PV array power generated is used to charge the EV battery alone and during peak sunshine hours, apart from charging of EV battery, the excess PV array power is fed to the single phase utility grid. During low and non sunshine hours, the EV battery charging was supported by the utility grid through bidirectional ac-dc converter. The proposed electric vehicle battery charger is simulated in the MATLAB/Simulink software and the dynamic response of the system was studied and its results are furnished in this paper.

Optimization The Performance of a Synchronization Controller For a 3-Phase Photovoltaic Grid-Connected System

In a distributed generation system, divers renewable agents are connected to the low voltage 3 phase utility grid by an inverter which is used as power condition and must assurance the higher efficiency of the renewable agent. To achieve this level of efficiency, a unitary power factor between the utility grid voltages and the inverter currents is necessary, and a synchronization algorithm is required for the perfect synchronization between the 3-phase utility grid and the renewable agent. The aim of this paper is to present the optimization of the performance of a Synchronization controller for a 3-phase photovoltaic grid-connected system, assessing its accuracy under different conditions and studying their drawbacks and advantages. A grid connected photovoltaic system with a nominal power of 5 kW is used so as to assess the behavior of the synchronization algorithm when the 3 phase utility grid is affected by some disturbances such as voltage unbalances.

Performance study of three synchronisation algorithms in renewable energy grid connected system

In grid connected applications, the efficiency of systems is strongly affected by the employed phase locked loop (PLL) strategy. This paper presents a comparative study of three PLL structures applied to a grid-connected renewable energy system with a nominal power of 7 MW. To select the suitable structure dedicated to previously mentioned application, we will evaluate the performance of the PLL techniques under distorted and unbalanced supply voltages. Several simulations test with a disturbed three phase utility grid using MATLAB-Simulink/SimpowerSystem are presented to valid the theoretical study.

TSFLC based DC link voltage regulation of grid connected DC micro grid

Integration of micro grid with utility power network has major concerns such as active power control and maintaining desired power quality (PQ) standards. Among several power quality issues, voltage dip and harmonics are critical concerns impacting the overall performance and stability of system. In this paper, a grid connected DC micro grid (DCMG) is designed and controlled to ensure requisite power allocation between the micro-grid and utility grid system vis-à-vis DC link voltage regulation, load balancing and harmonic elimination. The utility grid and DCMG system are interfaced via voltage source converter (VSC). The DC link voltage of VSC is regulated using Takagi-Sugeno fuzzy logic controller (TSFLC) based synchronous reference frame technique to compensate for the reactive power demanded by the load. In the proposed architecture, DCMG consists of 8 kW photovoltaic (PV) energy system with maximum power point tracking (MPPT), 6 kW wind energy generation system with MPPT, 3 kW fuel cell (FC) energy systems and a VSC interfaced to three phase utility grid. Further, the TSFLC is compared with conventional PI controller under different operating conditions. It has advantages over classical controller such as better performance under dynamics and can be expressed in the form of the exact linear function. The effectiveness of proposed control method is validated under MALAB/SIMULINK software under different loading conditions.

TSFLC based DC link voltage regulation of grid connected DC micro grid

Integration of micro grid with utility power network has major concerns such as active power control and maintaining desired power quality (PQ) standards. Among several power quality issues, voltage dip and harmonics are critical concerns impacting the overall performance and stability of system. In this paper, a grid connected DC micro grid (DCMG) is designed and controlled to ensure requisite power allocation between the micro-grid and utility grid system vis-a-vis DC link voltage regulation, load balancing and harmonic elimination. The utility grid and DCMG system are interfaced via voltage source converter (VSC). The DC link voltage of VSC is regulated using Takagi-Sugeno fuzzy logic controller (TSFLC) based synchronous reference frame technique to compensate for the reactive power demanded by the load. In the proposed architecture, DCMG consists of 8 kW photovoltaic (PV) energy system with maximum power point tracking (MPPT), 6 kW wind energy generation system with MPPT, 3 kW fuel cell (FC) energy systems and a VSC interfaced to three phase utility grid. Further, the TSFLC is compared with conventional PI controller under different operating conditions. It has advantages over classical controller such as better performance under dynamics and can be expressed in the form of the exact linear function. The effectiveness of proposed control method is validated under MALAB/SIMULINK software under different loading conditions.

A Fuzzy Assisted Enhanced Control for Utility Connected Rooftop PV

A modified control strategy for enhanced operation for a single phase rooftop PV connected to a single phase utility grid is presented in this paper. The current control is modified such that the quadrature references produced are independent of the grid side harmonics, which aids in the optimal control performance, even in polluted grid conditions. The transformations for the quadrature components are achieved using an inverse park phase locked loop (PLL), which enhances the PV performance, especially in the single phase. To assist the controller actions in the most efficient way, a TS fuzzy control for the DC link voltage regulation is used. Thus an improved performance for the rooftop PV With the proposed control topology is observed over the conventional control. The efficacy of the control scheme is tested in the MATLAB/SIMULINK® environment.

Overview and comparative study of two control strategies used in 3-phase grid-connected inverters for renewable systems

In this paper, an overview of grid-connected renewable systems is presented, then two current-control strategies for 3-phase grid-connected inverters are analyzed: firstly, the well-known d–q control in the rotating synchronous reference frame (d–q axes) using Proportional Integral regulators is described, and secondly, the Proportional Resonant controller in the Stationary Reference Frame (αβ axes). In order to obtain a high efficiency of the system when the 3-phase utility grid voltages are affected by harmonic pollution, a Harmonic Compensator (HC) structure is used with the Proportional Resonant controller, this due to the ease way to compensate harmonics when a Proportional Resonant control is utilized instead of a d–q control. Then both control strategies (d–q control and PR + HC) are analyzed under harmonic pollution condition. For both strategies, a Positive Sequence Detector plus a Synchronous Reference Frame Phase-Look Loop (PSD + dqPLL) is used as the synchronization algorithm. After the study, it was observed that the PR controller provides a greater facility for carrying out the harmonic compensation process helping to fulfill with the international standards. A model of a grid-connected photovoltaic system with a nominal power of 10 kW is used to evaluate and compare the performance of the current-control strategies. For this, a Real-Time Digital Simulator (RTDS) platform is used.

Performance study of three synchronisation algorithms in renewable energy grid connected system

In grid connected applications, the efficiency of systems is strongly affected by the employed phase locked loop (PLL) strategy. This paper presents a comparative study of three PLL structures applied to a grid-connected renewable energy system with a nominal power of 7 MW. To select the suitable structure dedicated to previously mentioned application, we will evaluate the performance of the PLL techniques under distorted and unbalanced supply voltages. Several simulations test with a disturbed three phase utility grid using MATLAB-Simulink/SimpowerSystem are presented to valid the theoretical study.

Design, Simulation and Implementation of Current Fed Isolated Full Bridge DC-DC with Voltage Multiplier for Fuel Cell Grid Applications

Abstract This paper proposes novel current fed converter full bridge isolated DC-DC converter with voltage multiplier and active clamp circuit for fuel cell grid connected applications. The proposed converter is best suited for fuel cells and their interfacing to utility three phase grid. Active clamp concept introduced on the primary side of isolation transformer to reduce the turn-off voltage spikes of full bridge active devices. Innate soft-switching with elongated range can be achieved in the recommended converter by using the parasitic capacitance of MOSFET switches and leakage inductance of the high frequency transformer. Zero Voltage Switching(ZVS) is achieved for all the primary devices which allow greater switching frequency operation and improvement in over-all efficiency of the converter for utility interface. Cost, size and weight of the converter minimizes for the higher switching operation of the converter. Half-wave Cockcroft-Walton Voltage Multiplier (H-W C-W VM) having minimum number of multiplying stages is used on the secondary side of the designed converter in order toget the required DC-link voltage for three phase utility grid connection. The converter's switching frequency is maintained at 100 KHz. This paper is organized as introduction, steady state operation, simulation results with two different cases i.e. full load and half load conditions and finally, test result validation of a 250 Watt experimental setup with the proposed converter.

Design and control of LCL filter interfaced grid connected solar photovoltaic (SPV) system using power balance theory

Abstract In this paper solar photovoltaic (SPV) system connected to the utility grid is designed and simulated. The utility grid and SPV system are coupled with current controlled voltage source converter (VSC) and LCL filter. The design of LCL filter, MPPT algorithm and power quality improvements are discussed and simulation results are shown for the performance analysis of grid-coupled PV system under different load condition. The system is controlled through power balance theory method. The principle behind the control implementation is to evacuate the solar power generated during the daytime and the reactive power demand for the load should be supplied by the PV. The grid coupled system consists of SPV system, dc–dc boost converter, maximum power point tracking (MPPT), voltage source converter (VSC), LCL filter, different loads and three phase utility grid. This system is capable of eliminating harmonic and load balancing by supplying unbalanced current from the PV as a compensator. The system is simulated with 10 kW SPV array using indirect current control scheme.

Performance study of a synchronization algorithm for a 3-phase photovoltaic grid-connected system under harmonic distortions and unbalances

In a distributed generation (DG) system, several renewable agents are connected to the low-voltage 3-phase utility grid through an inverter which is used as power condition and must guarantee the higher efficiency of the renewable agent. To attain this level of efficiency, a unitary power factor (FP) between the inverter currents and the utility grid voltages is necessary, and a synchronization algorithm is needed for the perfect synchronization between the renewable agent and the 3-phase utility grid. Within this context, this paper gives a performance study of the Positive Sequence Detector plus a Synchronous Reference Frame Phase-Locked Loop (PSD+dqPLL) as the synchronization algorithm, evaluating its accuracy under different conditions and studying their advantages and drawbacks. A grid-connected photovoltaic system with a nominal power of 6kW is used so as to evaluate the behavior of the synchronization algorithm when the 3-phase utility grid is affected by some disturbances such as voltage unbalances, frequency variations and harmonic distortions. Firstly, several simulations with a disturbed 3-phase utility grid using MATLAB/SIMULINK from The MathWorks, Inc. are shown, and secondly, the previous tests are run in a Real-Time Digital Simulation (RTDS) platform in order to validate the obtained results with simulations.

OPTIMAL UTILIZATION OF HYBRID WIND–SOLAR SYSTEM AS DVR FOR VOLTAGE REGULATION AND ENERGY CONSERVATION

This paper presents a novel optimal utilization of hybrid wind–solar system as dynamic voltage restorer (DVR) for voltage sag, voltage swell, outage and unbalanced voltage mitigation. Besides the voltage regulation, the proposed DVR reduces the energy consumption from the three phase utility grid by utilizing the rated inverter capability after excessive or equal real power generation to the load demand during both day time and night time. It reduces the energy consumption from the three phase utility grid. However, the reduction of energy consumption is always desirable for the reduction of panel tariff and electricity demand. The proposed system was simulated using MATLAB-SIMULINK in which the input parameters were selected from the metrological data of the selected location to validate the advantage of the proposed system.

Modelling, simulation and experimental verification for renewable agents connected to a distorted utility grid using a Real-Time Digital Simulation Platform

The large number of Photovoltaic plants and its utilization as agents of a Distributed Generation Systems justified the increasing efforts towards the optimal design of the overall grid-connected System. In a Distributed Generation environment the low voltage 3-phase utility grid could be affected by some disturbances such as voltage unbalanced, variations of frequency and harmonics distortion and it is mandatory that the control algorithms used in the inverter can be able to maintain the power flow between the renewable agent and the low voltage 3-phase utility grid; in addition a unitary power factor must be attained.A Proportional-Resonant regulator is used to performance a current control with the output current of the inverter and a Multiple Second Order Generalized Integrator Frequency-Locked Loop (MSOGI-FLL) is used to detect the frequency of the low voltage 3-phase utility grid. Some low order harmonics are introduced in the low voltage 3-phase utility grid in order to see the effect of the harmonic compensator.In order to validate the model of the Photovoltaic Renewable agent, the synchronization algorithm and the inverter control algorithm, some simulations using MATLAB/SIMULINK from The MathWorks, Inc. are shown firstly, and secondly, some Real-Time Digital Simulation tests using a Real-Time Digital Simulation (RTDS) Platform are carried out.

Power electronic configuration for the operation of PV system in combined grid‐connected and stand‐alone modes

A simple photovoltaic (PV) system capable of operating in both grid-connected mode and stand-alone mode using multilevel boost converter (MBC) and line commutated inverter (LCI) has been developed for extracting the maximum power and feeding it to a single phase utility grid and stand-alone system simultaneously. Theoretical analysis of the proposed system is done and the duty ratio of the MBC is estimated for extracting maximum power from PV array. For a fixed firing angle of LCI, the proposed system is able to track the maximum power with the determined duty ratio which remains the same for all irradiations. This is the major advantage of the proposed system which eliminates the use of a separate maximum power point tracking (MPPT) controller. Experiments have been conducted on a 80 V, 9.4 A PV array feeding a 110 V single phase grid and a 230 V, 100 W DC motor. The MBC extracts maximum power from the PV array and feeds the major portion of power to the single phase utility grid via LCI and the remaining power to separately excited DC motor. It was found that the theoretical analysis, simulation and experimental results closely correlate with each other and proves the effectiveness of the proposed configuration.

Investigations of an improved PV system topology using multilevel boost converter and line commutated inverter with solutions to grid issues

A photovoltaic (PV) system using multilevel boost converter (MBC) and line commutated inverter (LCI), operating in both grid-connected mode and stand-alone mode has been analysed. This proposed system extracts and feeds the maximum power to a single phase utility grid and stand-alone system simultaneously. The duty ratio of the MBC is estimated from the theoretical analysis of the proposed system, for extracting maximum power from PV array. The proposed system tracks the maximum power with the determined duty ratio which remains the same for all irradiations, for a fixed firing angle of LCI. The flexibility of supplying required proportion of extracted power to grid and stand-alone load and the elimination of a separate MPPT controller are the major benefits of the proposed system under normal grid conditions. In addition to it, the grid issues like voltage swell, blackout and brownout are considered and necessary remedial measures have been taken in the proposed system. Based on the issues, either the firing angle of LCI is adjusted or LCI is disconnected and replaced by a battery. Simulation studies have been carried out and the dynamic response of the system is observed. A laboratory prototype is built and experimental investigations have also been carried out. The theoretical analysis, simulation and experimental results are found to be closely associating with each other proving the efficacy of the proposed configuration.