Photovoltaic Conversion System Research Articles

Control of the photoelectric generator for used in feeding of the independent wind turbine system

In this paper, a hybrid power system is proposed to eliminate any interruption caused to absence of power supply network by the Fusion between the wind source and the photovoltaic source to create a hybrid system with internal power supply autonomy. The hybrid power system includes a solar and wind source whose wind energy conversion system is based on a doubly fed induction generator. The photovoltaic conversion system extracts the maximum power from the sun. A part of this power is used to supply the rotor of a doubly fed induction generator; the rest is injected in the grid. The connection between the two conversion systems is made by means of static converters (chopper/inverter). In the photovoltaic conversion chain, a controller for tracking the maximum power point is designed using the direct search approach the Perturb and observe method. The wind energy conversion system contains a doubly fed asynchronous generator with a control system of generated powers by the technique of the fuzzy logic. The simulation was done to prove the validity of the strategy and of the control method used for the control of the power generated by the hybrid system.

Comparison of Maximum Power Point Tracking (MPPT) Algorithms to Control DC-DC Converters in Photovoltaic Systems

Background: Using the solar energy by photovoltaic arrays is constantly increasing and has been considered as one of the cleanest sources of energy in recent years. One of the ways to reduce the cost of photovoltaic systems is to maximize the power delivered to the load. On the other hand, changing the load leads to change the operating point of the solar conversion system and causes deviation from the maximum power point (MPP). Methods: For this reason, in various research studies, attention has been paid to MPPT methods applicable in photovoltaic systems. In this paper, a comparison is performed between conventional MPPT methods including Perturb and Observe (P&O), Incremental Conductance (INC), Fractional Open Circuit Voltage (FOCV), Ripple Correlation Control (RCC) and Extremum Seeking Control (ESC). Only current and voltage parameters of the PV panel are measured instantly and used to generate control signals. However, the output voltage of the PV cells is relatively low without using the DC-DC converters. Results: Therefore, high-performance DC-DC converters need to convert the low voltage PV arrays into high DC voltages to handle the 220 VAC systems. Conclusion: Accordingly, in this study, conventional DC-DC converters including Boost, Buck and Buck-Boost converters are investigated, and each of them is simulated using different MPPT controllers and the results are compared together. It is worth noting that all of the simulations are carried out using MATLAB/Simulink.

Solar Energy a Promising Source for E-Vehicles

The demand and availability of energy is growing day by day in the whole world. Renewable energy resources will play an important role in the future as the conventional energy sources like coal and petroleum are limited and declining. In the present situation, energy crisis is an important very critical problem hence necessary to address. Basically, it is to verify the availability to increase the generation or to install additional generators. Alternatively, load management known as demand side management (DSM) strategy must be adopted. In the current scenario, the uses of fossil fuel for the domestic transport are rapidly increasing and indicate the threat in the near future. The adverse effects of the practice of such vehicles and means leads to the environment pollution and health issues related to the living habitats. In line with this the upcoming mode of transport is E-vehicles keeping concerned about the environment pollution. The drawback of this mode of transport is the use of electric energy for the propulsion and going to create additional burden on the existing power system setup and infrastructure. But the use of power electronics and controls in Electric vehicles (EVs) along with latest technologies is fostering and supporting the green transportation systems.E-Vehicle charger is the role player in reducing the dependence on fossil fuels and is the natural evolution of our energy infrastructure significantly. Consumer incentives are also important to make the purchase of an electric vehicle and home fast-charging station more affordable and attractive. To address this issue most of the developed countries have taken up an initiative to extract solar photovoltaic conversion systems to store and transfer to the grid.The present rate of use of E-vehicles is 70% compared to the earlier decade. From the perspective of solar energy basically, it is extracted as either heat or light energy. But the storage system is the bottle neck issue in this regard due to technical, economic barriers and challenges. The power electronics interfaces male E-vehicle battery to get charged from the grid if there is no source solar energy known as grid to vehicle (G2V). The other mode is to transfer the stored energy from the storage battery to grid (V2G) as and when grid finds the deficit of energy to meet its loads. Then the solar PV systems installed on the roof top of the vehicle generate the electricity and is used for their operation by the battery support.Therefore, the E-vehicles fitted with solar PV panels can even transfer electricity to the grid (V2G). Hence, the suitable design and implementation can prove the solar photovoltaic source as a promising source for such E vehicle application in the very near future. This creates an opportunity to the engineers and enterprises.

Flatness-Based Control for the Maximum Power Point Tracking in a Photovoltaic System

Solar energy harvesting using Photovoltaic (PV) systems is one of the most popular sources of renewable energy, however the main drawback of PV systems is their low conversion efficiency. An optimal system operation requires an efficient tracking of the Maximum Power Point (MPP), which represents the maximum energy that can be extracted from the PV panel. This paper presents a novel control approach for the Maximum Power Point Tracking (MPPT) based on the differential flatness property of the Boost converter, which is one of the most used converters in PV systems. The underlying idea of the proposed control approach is to use the classical flatness-based trajectory tracking control where a reference voltage will be defined in terms of the maximum power provided by the PV panel. The effectiveness of the proposed controller is assessed through numerical simulations and experimental tests. The results show that the controller based on differential flatness is capable of converging in less than 0.15 s and, compared with other MPPT techniques, such as Incremental Conductance and Perturb and Observe, it improves the response against sudden changes in load or weather conditions, reducing the ringing in the output of the system. Based on the results, it can be inferred that the new flatness-based controller represents an alternative to improve the MPPT in PV systems, especially when they are subject to sudden load or weather changes.

Reduced Switches Multilevel Inverter Integration with Boost Converters in Photovoltaic System

Multilevel inverters (MLIs) are developed to meet medium voltage and high power applications in flexible power systems. The conventional configuration of multilevel inverter requires more switches and has limitation to its wide range application. This paper reports the performed work on 1-phase 7-level reduced switch multilevel inverter (RS MLI) in photovoltaic (PV) system. RS MLI configuration integration with PV system which uses less number of switching components for specified number of voltage output levels as compared to that of conventional multilevel inverter topology. To performed enhanced operation of PV cells and maximize the solar energy extraction an incremental conductance (IC) based maximum power point tracking (MPPT) scheme is used. To improve the quality of RS MLI output parameters mainly total harmonic distortion (THD) and switching losses, selected harmonic elimination (SHE) based genetic algorithm (GA) method is consider for control the gating pulse of PV based RS MLI. This work is performed using MATLAB/ SIMULINK software.

Electromagnetic Transient Modeling and Simulation of Power Converters Based on a Piecewise Generalized State Space Averaging Method

Large-scale photovoltaic (PV) power plants connected to the grid leads to the complex calculations in modeling and simulation of the power system, especially in the electromagnetic transient progress. Common averaging methods are studied for modeling a grid-connected converter to simplify the calculation and balance accuracy and efficiency in the simulation. The piecewise technique is applied to the generalized state space averaging model of converters, which combine time segment with similar operating characteristic. In addition, a new piecewise generalized state space averaging (P-GSSA) model is derived and a multi time scale modeling is achieved for the grid-connected converters in PV systems. The model error and accuracy of the P-GSSA model are analyzed, the physical significance and the influence factors in the model error of P-GSSA model are discussed. The proposed P-GSSA model is flexible to be used in a PVs system simulation, and it can accurately reflect the steady-state and transient characteristics of a converter. The research shows that P-GSSA model improved the simulation efficiency over 20% by the index of consumed time, meanwhile, the model error analysis is under 5%. The analysis of the P-GSSA model is verified by simulating a DC/AC converter and a photovoltaic system.

Design and implementation of a 31 level asymmetrical cascaded MLI with DC-DC flyback converter for photovoltaic system using P&O technique for electric traction application

This paper proposes a design and implementation of 31-Level MLI (Multi-Level Inverter) which is supplied from a single solar panel with multioutput flyback converter for transformer-less railway traction drive. The multioutput flyback converter provides isolation for the circuit and also produces four different supply voltages based on the transformer turns ratio. In asymmetrical MLI the DC source magnitudes are unequal and it is designed with binary form of voltage such as 15Vdc, 30Vdc, 60Vdc and 120Vdc. In this proposed technique, we are using a single solar panel and single fly back converter, from this four DC output voltages are obtained in the ratio of 1 : 2 : 4 : 8. Our proposed technique requires fewer switches, i.e., seven switches for more levels, i.e., 31 levels, and it also gives less total harmonic distortion (THD). The results are verified in MATLAB, PROTEUS and realtime system using TMS320F2802 and ATMEGA328.

Control Methods on Three-phase Power Converters in Photovoltaic Systems

<span lang="EN-US">In this paper, a three-phase load connected to a NPC three-level inverter is presented. To generate gate signals for the multilevel inverter, two commands are developed and compared: the phase disposition pulse width modulation (PDPWM) and the space vector pulse width modulation (SVPWM). DC supply is provided by photovoltaic cells. Boost converter controls the power transfer from photovoltaic generator. Due to nonlinear I-V characteristics of photovoltaic cells, a maximum power point tracking algorithm is adopted to maximize the output power, the nonlinear controller (sliding mode) is developed and simulated. To verify the effectivnesse of the introdueced controller, it is compared with the fuzzy logic controller. Matlab-simulink is used for simulation, analysis and interpretation the results of these controllers.</span>

Stability Study of Output Voltages of Two-Stage PV System Based Three Levels Inverter

This paper presents an algorithm of regulation of AC voltage of photovoltaic conversion system composed by PV generator-boost converter-three phases three levels inverter for stand-alone application without introduced any system to regulate the fluctuation of the DC bus. The maximum power point tracking based on the “perturb & observe” (P&O) approach as a control strategy of a boost DC-DC converter is applied. In order to get the best AC voltage waveform, the simplified space vector pulse width modulation technique is used in this paper. To maintain the two capacitors voltages of DC bus equal, the redundant vectors of space vector diagram of three levels inverter are used. Without any system to regulate the fluctuation of the DC bus and to get a stable output inverter voltage, authors in this paper propose a proportional regulator of inverter modulation index. A theoretical analysis with a complete simulation of the system with different profiles of irradiance is presented to prove the excellent performance of the proposed technique.

A High-Efficiency Isolated-Type Three-Port Bidirectional DC/DC Converter for Photovoltaic Systems

This paper proposes a novel high-efficiency isolated three-port bidirectional DC/DC device for photovoltaic (PV) systems. The device contains a high step-up converter for PV modules to supply power to the DC bus, and a bidirectional charge/discharge control circuit for the battery with an improved boost-flyback converter. When the PV modules supply sufficient energy, their output can be stepped up and energy supply to the DC bus and charging of the battery can be achieved simultaneously. However, when the energy supplied is insufficient, the battery provides energy to the DC bus. When the proposed converter is operated in the step-down mode, the DC-blocking capacitor on the high-voltage side is used to reduce the voltage on the transformer and achieve high step-down performance. Moreover, to improve the overall efficiency of the system, the energy stored in the leakage inductance is recycled and supplied to the DC-blocking capacitor during operation in the step-up mode. Finally, to verify the feasibility and practicability of the proposed devices, a 500 W three-port bidirectional DC/DC devices was implemented. The highest efficiencies achieved for operation in different modes were as follows: high step-up mode for the PV modules, 95.2%; battery step-up mode, 94.2%; and step-down mode, 97.6%.

Novel control algorithm for MPPT with Boost converters in photovoltaic systems

The great advances in efficiency and performance of photovoltaic modules would not be very useful if they do not work close to their maximum power point (MPP). In this paper a novel Sliding Mode Control (SMC) based algorithm is proposed to be implemented in a DC/DC converter in order to make an autonomous photovoltaic system to work at the MPP. Once that the design of the novel algorithm has been detailed (especially the novel part relative to the current reference signal) and its stability has been demonstrated, its performance has been compared with two of the most commonly used algorithms in this scope, i.e., Perturbation & Observation (P&O) and Incremental Conductance (IC) algorithms, in addition to a PI controller because it is one of the preferred controllers in industrial applications. This comparison has been carried out taking into account both simulated and experimental tests. The first focused on their behavior when sudden changes in irradiance and temperature, while the lasts analyzed them when the load resistance was varying arbitrarily in actual facilities (composed of a photovoltaic module Mitsubishi PV-TD185MF5, a Boost converter, a variable load and a real-time data acquisition card dSPACE DSP1104 used as the interface between the control algorithm implemented in Simulink/Matlab and the real photovoltaic module). After completing tests under different conditions, we found that the proposed SMC based algorithm outperforms the PI controller and the P&O and IC algorithms, especially in experiments carried out using actual facilities.

Novel Switch Adaptive Control to Improve the Efficiency of Boost Converter in Photovoltaic Systems

The efficiency of photovoltaic power generation is affected by the changeable weather conditions. This paper improves the efficiency of a standalone PV system over a wider range of operating conditions by employing novel switch adaptive control to an interleaved boost converter. With various loads, simulation and experimental results show that the interleaved boost converter with novel switch adaptive control offers better performance and higher conversion efficiency under changeable weather conditions.

A photovoltaic generation system based on wide voltage-gain DC-DC converter and differential power processors for DC microgrids

In this paper, a photovoltaic(PV) generation system based on front-stage differential power processors(DPP) and BACK-stage centralized wide voltage-gain converter is proposed. The resonant switched capacitor(ReSC) converter, which features high power density and high efficiency, is employed as the differential power processor and aims at processing the differential power among series-connected PV modules, avoiding the great power loss caused by power mismatch of PV modules. The ReSC converter in PV system can operate in equalization mode or MPPT mode and both modes are researched. The BACK-stage DC-DC converter is implemented as the dual-phase-shift controlled full-bridge converter(DPS-FBC). It has high conversion efficiency and wide voltage gain, suitable for PV generation applications. The current source control for grid-connected mode and the voltage source control for islanding mode are developed for DPS-FBC. Therefore, for the whole system with front and BACK stage converters, the dual-mode control strategy is proposed. When the system is connected to the grid, DPS-FBC operates as the current source for global MPPT for PV modules while ReSC converters operate in maximum power point tracking(MPPT) mode for local MPPT. When the system operates in an island, DPS-FBC works as the voltage source for constant output voltage control and ReSC converters work in equalization mode. The mode switch is based on the voltage of output DC bus. Simulations and experiments verify the feasibility of the proposed PV generation system and the effectiveness of the proposed control algorithm

Low Cost and High Efficiency Buck-Boost Converter for Photovoltaic Applications

This paper presents low cost and effective implementation of non-inverting buck-boost converter for photovoltaic system. An improved switching scheme is introduced for attaining high efficiency during buck, boost and buck-boost mode. The investigation of system structure for various output current and supply voltage is performed by PSIM software and experimental method. The supply voltage of non-inverting synchronous buck-boost converter range from 9.4 – 16V with its load voltage set to 12V. It can provide the load current up to 1.5A and its maximum efficiency is 92%.

Modeling, Dynamics, Bifurcation Behavior and Stability Analysis of a DC–DC Boost Converter in Photovoltaic Systems

A study of a DC–DC boost converter fed by a photovoltaic (PV) generator and supplying a constant voltage load is presented. The input port of the converter is controlled using fixed frequency pulse width modulation (PWM) based on the loss-free resistor (LFR) concept whose parameter is selected with the aim to force the PV generator to work at its maximum power point. Under this control strategy, it is shown that the system can exhibit complex nonlinear behaviors for certain ranges of parameter values. First, using the nonlinear models of the converter and the PV source, the dynamics of the system are explored in terms of some of its parameters such as the proportional gain of the controller and the output DC bus voltage. To present a comprehensive approach to the overall system behavior under parameter changes, a series of bifurcation diagrams are computed from the circuit-level switched model and from a simplified model both implemented in PSIM© software showing a remarkable agreement. These diagrams show that the first instability that takes place in the system period-1 orbit when a primary parameter is varied is a smooth period-doubling bifurcation and that the nonlinearity of the PV generator is irrelevant for predicting this phenomenon. Different bifurcation scenarios can take place for the resulting period-2 subharmonic regime depending on a secondary bifurcation parameter. The boundary between the desired period-1 orbit and subharmonic oscillation resulting from period-doubling in the parameter space is obtained by calculating the eigenvalues of the monodromy matrix of the simplified model. The results from this model have been validated with time-domain numerical simulation using the circuit-level switched model and also experimentally from a laboratory prototype. This study can help in selecting the parameter values of the circuit in order to delimit the region of period-1 operation of the converter which is of practical interest in PV systems.

Experimental investigations into low concentrating line axis solar concentrators for CPV applications

Solar photovoltaic conversion systems with integrated, low concentration ratio, non-imaging reflective concentrators, could be on south facing building roofs used to generate power at a lower cost than currently available proprietary systems. The experimental investigation presented by this research provides information on the optical and energy conversion characteristics of two geometrically equivalent non-imaging concentrators; a compound parabolic concentrator and a V-trough reflector. The aim was to investigate the assumption of uniform cell illumination when PV cells located on the receiver surface with their central axes are aligned parallel with the focal line of the line-axis concentrator. Solar radiation incident was measured at the aperture and the PV cell surface using respectively a pyranometer and photodiodes at six different collector tilt angles of 0°, 10°, 20°, 30°, 40° and 52°. The analysis of the collected experimental data presented demonstrated that the V-trough system had a more even distribution of solar radiation than the CPC and a higher optical concentration ratio (ratio of solar radiation incident on the aperture cover to that incident on the receiver) though the geometrical concentration ratio of the two collectors was equal to 2.2×. Also, the V-trough concentrator had an electrical power output up to 17.2% higher than the CPC system at a specific tilt angle of 30°. The V-trough had a consistently higher receiver plate temperature as it was reflecting larger quantities of solar radiation than the CPC. Over 17 consecutive typical summer days’ similar performance was observed over the range of tilt angles studied. The development of V-trough concentrators should be preferred due to higher power production, reduced complexity, increased uniformity of illumination and lower manufacturing costs compared to CPCs.

Photo-stability of the photons converter applied in the photovoltaic conversion systems

In this work we develop the idea of using a poly methyl methacrylate (PMMA) polymer doped with optically active molecules such as photovoltaic encapsulation materials. The effect of this encapsulation system on the incident solar spectrum has been obtained from direct allowed transition after the samples have been exposed to sunlight. A resulting, the incident solar spectrum at the interface is red-shifted for a better fit with the spectral response of SiO2/Si solar cell structures. The simulation results showed that the short-circuit current density increased by 7%. Therefore the mechanism of the photo-degrading by UV illumination of an LDS has been studied to identify molecular changes that occur in the organic dye when exposed to UV light. The photo-degrading effect of the PMMA layer was measured by CONICA-MINOLTA spectrometer, as a function of increasing exposure time to UV light. The UV Photo-degrading studies revealed that the more photo-stable dye doped in value.

A Function-Based Maximum Power Point Tracking Method for Photovoltaic Systems

In this paper, a novel maximum power point tracking (MPPT) algorithm based on introducing a complex function for photovoltaic (PV) systems is proposed. This function is used for determination of the duty cycle of the dc–dc converter in PV systems to track the MPP in any environment and load condition. It has been suggested based on analyzing the expected behavior of converter controller. The function is formed by a two-dimensional Gaussian function and an Arctangent function. It has been shown that contrary to many algorithms that produce wrong duty cycles in abrupt irradiance changes, the proposed algorithm is able to behave correctly in these situations. In order to evaluate the performance of method, various simulations and experimental tests have been carried out. The method has been compared with some major MPPT techniques with regard to start-up, steady-state, and dynamic performance. The results reveal that the proposed method can effectively improve the dynamic performance and steady-state performance simultaneously.

Implementation of MPPT Techniques for a High Step-up Converter with Voltage Multiplier Module based Photovoltaic System

Renewable energy systems such as Photovoltaic system generate low output, thus, dc/dc converters are widely employed in many renewable energy applications to improve the output voltage. But due to leakage inductance, the conventional step-up converters cannot achieve high step-up conversion with high efficiency. Thus A concept of high step-up conventional converter for photovoltaic system has been explained in this paper. The most important improvement of this step-up converter is that as it is operated with the help of voltage multiplier module, it does not depend on the value of extreme duty ratio. This high step-up converter is designed based on dc-dc boost converter and coupled inductors. This work also proposed the application of Maximum Power Point Tracking (MPPT) techniques to PV system for improvement in output power and overall efficiency. The experimental setup for a high step-up based solar system is worked in Matlab and the results are compared for different types of MPPT techniques which shows that the Fuzzy logic based MPPT controller can meet the load easily and have fewer fluctuations around maximum power point; also this method has well regulated PV output power and has high efficiency when compared to Perturb and Observe and Incremental Conductance methods.

Integrated sizing and scheduling of wind/PV/diesel/battery isolated systems

In this paper we address the optimal sizing and scheduling of isolated hybrid systems using an optimization framework. The hybrid system features wind and photovoltaic conversion systems, batteries and diesel backup generators to supply electricity demand. A Mixed-Integer Linear Programming formulation is used to model system behavior over a time horizon of one year, considering hourly changes in both the availability of renewable resources and energy demand. The optimal solution is achieved with respect to the minimization of the levelized cost of energy (LCOE) over a lifetime of 20 years. Results for a case study show that the most economical solution features all four postulated subsystems.