Single-phase Photovoltaic System Research Articles

A modified carrier-based PWM technique for minimization of leakage current in transformer less single-phase grid-tied PV system

This paper discusses the impact of leakage current and its dependency on common mode voltage in transformer less single-phase grid connected photovoltaic (PV) system. Further a new carrier-based PWM method is derived for H bridge single-phase grid-tied PV inverter to minimize leakage current. The proposed modulation strategy is compared with conventional techniques through simulation in MATLAB R2018a. The superiority of the proposed technique is validated in laboratory prototype of a 500 W single-phase grid-tied PV system. The hardware results validate the theoretical findings in appropriate.

Single phase PV system operating under Partially Shaded Conditions with ABC-PO as MPPT algorithm for grid connected applications

Single phase transformerless grid connected Photovoltaic (PV) systems have become prevalent in recent years because of the reduced size & volume and enhanced working efficacy. A single phase two stage grid connected PV system is successfully implemented under Partially Shaded Condition (PSC), Standard Test Conditions (STC) and load variations in this work. The first stage includes the use of a MPPT controller-based DC–DC boost converter. Artificial Bee Colony integrated Perturb & Observe (ABC-PO) MPPT algorithm is used to obtain maximum power from the photovoltaic module. ABC-PO is capable of tracking Global Maximum Power Peak (GMPP) even under PSC. A DC–AC inverter along with LC filter and Phase Locked Loop (PLL) is used in the second stage to synchronize with the grid. A small scale grid connected solar power generation system with a maximum capacity of 1kW power output has been considered for analysis. The simulation results validate the efficient maximum power point tracking characteristics of ABC-PO algorithm over ABC algorithm for a grid connected network. Moreover, the successful synchronization of grid current with grid voltage under variations in irradiance as well as load has been carried out. The result shows the satisfactory performance of the entire system.

Performance and Implementation of Grid Connected Single Phase Photovoltaic System and FPGA-Design Based MPPT

Solar Photo Voltaic system are used for power generation by the process of photovoltaic effect. The solar power is varying continuously on a particular day due the variations in the temperature and irradiances. To overcome the power loss of PV system maximum power point tracking techniques are used to generate maximum solar power . Generally digital signal processors are used for implementing maximum power point tracking algorithms, but the performance is limited. The high degree of flexibility is achieved by the use of field-programmable gate arrays (FPGA) chips. The PV systems are used to provide stable and reliable power. The paper presents the single-phase implementation of the grid connected PV system and FPGS based P&O MPPT algorithm. The proposed system consists of P&O MPPT algorithm for maximum solar power extraction, bi-directional DC-DC converter for is used for controlling the battery. The solar power is used to serve the connected load and the excess power is used for serving grid utility. The single-phase inverter is used for DC-AC conversion. The Xilinx ISE is used for simulation of MPPT algorithm. The grid connected PV system is simulated using MATLAB/SIMULINK.

A DQ Synchronous Reference Frame Current Control for Grid Connected Photovoltaic Systems using Single Phase Cascaded H Bridge Multilevel Inverter

This paper projects a high performance decoupled current control using a dq synchronous reference frame for single-phase inverter. For the three-phase inverter the conversion from AC to DC with Proportional Integral controller grants to obtain steady state error for AC Voltages and currents but has a few challenges with the single-phase systems. Hence, an orthogonal pair (β) is created by shifting the phase by one quarter cycle with respect to the real component (α) which is needed for the transformation from stationary to rotating frame. The synchronous reference frame control theory helps in controlling the AC voltage by using DC signal as the reference with the proportional integrator controllers. The implementation of the control is done with two-stage converter with LCL filter for a single-phase photovoltaic system. A modified MPPT Incremental conductance algorithm along with decoupled current control helps in regulating the active and reactive power infused into the grid where the power factor is improved, the efficiency of the system is increased above 95% and total harmonic distortion for current is also reduced to3%. The results have been validated using MATLAB.

Design and development of new control technique for standalone PV system

A Sub-Maximum Power Point Tracking (S-MPPT) algorithm improves the performance of Photo Voltaic (PV) systems. This S-MPPT is used in single-phase PV system to test the tracking accuracy and its impact on the consistency of the whole system. Single phase PV Deadbeat Scheduler is proposed in this paper. The Deadbeat scheduler is a linear system. It initializes each initial state of the system to zero in shortest time possible. A single phase PV structure configuration is proposed to decrease the partial shading effect by changing the parameters of S-MPPT control algorithm. Thus, voltage sensor based S-MPPT algorithm through voltage reference control technique with the help of controller is developed for minimizing the tracking time and steady state oscillations. Selection of the objective function to mitigate the drawbacks associated with voltage sensor based algorithm for a decrease in solar irradiance are also demonstrated. The proposed MPPT algorithm with the designed controller is tested for a step change in irradiance from 270 to 480 W/m2 with a perturbation time of 20 ms and ∆V = 0.5 V (perturbation of voltage). From the simulation results, the proposed method with S-MPPT plus deadbeat control algorithm is compared with other existing algorithms.

Single Phase Photovoltaic System with Maximum Power Point Tracking

Due to the increase in demand of electric energy, people are shifting towards renewable energy resources. Among the various renewable sources, solar power is growing at a faster rate due to its abundant availability. Solar panel characteristics show that the output power from the panel peaks only at one operating point. For extracting maximum power from the panel, tracking of the operating point has to be done continuously by a control algorithm. In this work, a solar system connected to the grid is considered, where there is a necessity of synchronizing the solar inverter with the grid apart from MPPT. Hysteresis current control is implemented in the inverter for synchronization and for tracking the maximum power, perturb and observe algorithm is applied. Grid connected PV systems are used in main cities by domestic and industrial consumers, where the excess power can be sold to the utility. Simulation of the grid connected PV system is done in Simulink and the results are presented.

Fault Ride-Through Capability Enhancement for Microinverter Applications

Due to the fast growth of single-phase grid-connected photovoltaic (PV) systems, the existing grid codes are expected to be modified to guarantee the availability, quality, and reliability of the electrical system. Therefore, the future single-phase PV systems should become smarter and support low voltage ride-through (LVRT) capability, which are required for three-phase wind power systems. In this paper, the operation principle of a flyback inverter in a low-voltage ride-through operation is demonstrated in order to map future challenges. The steady state performance of the flyback inverter under voltage rise and drop conditions at boundary conduction mode (BCM) and discontinues conduction mode (DCM) is studied theoretically. The simulation results of the flyback inverter for various grid faults are presented to verify the theoretical analyses. The results indicate the fact that the flyback inverter at BCM condition can provide LVRT capability for photovoltaic microinverter applications in distributed generation (DG) systems, even though it does not need any auxiliary control branches and any limitations in components design.

An Adaptive Control Scheme for Flexible Power Point Tracking in Photovoltaic Systems

One of the major concerns associated with the increasing penetration of grid-connected photovoltaic (PV) power plants is the operational challenges (e.g., overloading and overvoltage), imposed due to the variability of PV power generation. A flexible power point tracking (FPPT), which can limit the PV output power to a specific value, has thus been defined in grid-connection regulations to tackle some of the integration challenging issues. However, the conventional FPPT algorithm based on the perturb and observe method suffers from slow dynamics. In this paper, an adaptive FPPT algorithm is thus proposed, which features fast dynamics under rapidly changing environmental conditions (e.g., due to passing clouds), while maintaining low power oscillations in steady state. The proposed algorithm employs an extra measured sampling at each perturbation to observe the change in the operating condition (e.g., solar irradiance). Afterwards, the voltage-step is adaptively calculated following the observed condition (e.g., transient or steady state) in a way to improve the tracking performance. Experimental results on a 3-kVA grid-connected single-phase PV system validate the effectiveness of the proposed algorithm in terms of fast dynamics and high accuracy under various operational conditions.

Simulation of single phase photovoltaic system based on fuzzy logic control with multilevel inverter

To control the solar power, reliability and stability are two main challenges. In addition, the total harmonic distortion (THD) must be within limits for optimal operation. In an inverter, the harmonics are produced during the conversion of DC power to AC power, which will affect the power electronic devices. Therefore, to overcome such challenges in high voltage and high power systems multilevel inverter (MLI) topology is more useful. Such type of inverters uses various DC voltage levels to generate the stepped AC at its output, approaching the sinusoidal shape. The cascaded H-bridge, capacitor-clamped, and diode-clamped are the most commonly used multilevel inverters topologies. For photovoltaic (PV) usage, cascaded H-bridge (CHB) MLI is more adaptive among the three topologies, where for each H-bridge unit; each PV model behaves as an isolated DC source. This paper specifically focused on the simulation of PV power as a source to the system and displayed the potential of a single-phase 11-level CHB inverter. For switching the IGBT devices, sinusoidal pulse width modulation (SPWM) is applied. Moreover, the fuzzy logic control (FLC) is introduced to improve the power quality. FLC reduce the THD via finding the appropriate set of IGBT switch signals. To show the improvement in the operation and reduction in the complex harmony signal effects of the CHB 11-level inverter, the proposed system is designed in Matlab/Simulink software. Finally, the results show that the dynamic behavior of the FLC is much better than the traditional proportional integral derivative (PID) controller.

A modified perturb and observe maximum power point tracking algorithm for a standalone single phase photovoltaic system using boost converter

The photovoltaic solar energy becomes more and more one of the most abundant and an alternative source of electric energy. But its efficiency is very low. For this reason, several Maximum Power Point Tracking algorithms are used to track de maximum power. This paper proposes a modified Perturb and Observe (P&O) algorithm using a boost chopper. That algorithm was implemented under Matlab/Simulink/Simpowersystems/Simelectronics platform. Results obtained showed that the proposed algorithm gives better results compared to the conventional P&O algorithm. In fact, the extracted power’s ripple factor using the conventional P&O method varies from 3.35 % to 5.30 %. Whereas the extracted power’s ripple factor using the 'modified P&O' varies from 1.41 % to 2.86 %.

Review of power decoupling methods for micro-inverters used in PV systems

In single-phase photovoltaic(PV) systems, power mismatch between input and output terminal leads to power pulsation, seriously affecting maximum power point tracking (MPPT). Paralleling an electrolytic capacitor(e-cap) across the PV panel to smooth power pulsation seems to be an unreliable method owing to its short lifespan. Various power decoupling methods used in micro-inverters have been proposed to solve the problem. These methods were categorized. Some of them were introduced in this paper regarding efficiency, cost and technical features. Special novel methods proposed in recent years were presented to show the development trend of micro-inverter. Then, conclusion and comparisons were made. Finally, a potential technological route was proposed by author for further study on power decoupling.

Adaptive Intelligent Sliding Mode Control of a Photovoltaic Grid-Connected Inverter

Adaptive intelligent sliding mode control methods are developed for a single-phase photovoltaic (PV) grid-connected transformerless system with a boost chopper and a DC-AC inverter. A maximum power point tracking (MPPT) method is implemented in the boost part in order to extract the maximum power from the PV array. A global fast terminal sliding control (GFTSMC) strategy is developed for an H-bridge inverter to make the tracking error between a grid reference voltage and the output voltage of the inverter converge to zero in a finite time. A fuzzy-neural-network (FNN) is used to estimate the system uncertainties. Intelligent methods, such as an adaptive fuzzy integral sliding controller and a fuzzy approximator, are employed to control the DC-AC inverter and approach the upper bound of the system nonlinearities, achieving reliable grid-connection, small voltage tracking error, and strong robustness to environmental variations. Simulation with a grid-connected PV inverter model is implemented to validate the effectiveness of the proposed methods.

H∞ loop-shaping controller design for a grid-connected single-phase photovoltaic system

This paper presents a H∞ loop-shaping controller for controlling dc-link voltage by regulating the switching signal of the inverter associated with a grid-connected single-phase photovoltaic system. To facilitate a robust control design, state-space realisation of the system model is made with uncertainties represented by linear fractional transformation. The controller is achieved through H∞ synthesis followed by obtaining desired loop shapes through the choice of the proper weighting functions. The controller order is reduced by Henkel-norm method for facilitating its practical implementation. Controller performance is evaluated through carrying out simulations on MATLAB/Simulink platform under standard and changing atmospheric conditions, and fault condition.

Common-Ground-Type Transformerless Inverters for Single-Phase Solar Photovoltaic Systems

This paper proposes a family of novel flying capacitor transformerless inverters for single-phase photovoltaic (PV) systems. Each of the new topologies proposed is based on a flying capacitor principle and requires only four power switches and/or diodes, one capacitor, and a small filter at the output stage. A simple unipolar sinusoidal pulse width modulation technique is used to modulate the inverter to minimize the switching loss, output current ripple, and the filter requirements. In general, the main advantages of the new inverter topologies are: 1) the negative polarity of the PV is directly connected to the grid, and therefore, no leakage current; 2) reactive power compensation capability; and 3) the output ac voltage peak is equal to the input dc voltage (unlike neutral-point-clamped and derivative topologies, which requires twice the magnitude of the peak ac voltage). A complete description of the operating principle with modulation techniques, design guidelines, and comprehensive comparisons is presented to reveal the properties and limitations of each topology in detail. Finally, experimental results of 1-kVA prototypes are presented to prove the concept and theoretical analysis of the proposed inverter family for practical applications.

Enhancing PV Penetration in LV Networks Using Reactive Power Control and On Load Tap Changer With Existing Transformers

Voltage rise beyond statuary limits in low voltage (LV) ac networks due to high photovoltaic (PV) penetration and its mitigation using multiple techniques was assessed. Investigations using a real rural domestic overhead LV network were done through load flow simulations. A three-phase four wire medium length LV network with a fixed tap transformer and PV inverters operating at unity power factor was able to host PV between 79%–98% of transformer ratings for five different PV configurations. For the case studied at this penetration level three, limiting factors (voltage, thermal loading limits of lines, and transformer) come together. Three techniques were utilized to control the voltage across the LV network. On load tap changer (OLTC) control was found more robust than reactive power control (RPC). Hybrid control (OLTC and RPC) was found beneficial only for extra high PV penetration scenarios. Replacement of a few critical line spans and the existing transformer with higher capacity conductors and an OLTC equipped transformer (higher size) enabled the network to host an additional 50%–90% PV. The unequal distribution of single-phase PV systems among three phases has negative effects on penetration. Consideration of PV integration while planning new LV networks and retrofitting of OLTCs with existing transformers, could make the LV system more PV friendly. The RPC option, though less effective than OLTC due to increased current, can be beneficial at medium penetrations where OLTC may become a costly solution.

Artificial Neural Network for Control and Grid Integration of Residential Solar Photovoltaic Systems

Residential solar photovoltaic (PV) energy is becoming an increasingly important part of the world's renewable energy. A residential solar PV array is usually connected to the distribution grid through a single-phase inverter. Control of the single-phase PV system should maximize the power output from the PV array while ensuring overall system performance, safety, reliability, and controllability for interface with the electricity grid. This paper has two main objectives. The first objective is to develop an artificial neural network (ANN) vector control strategy for an LCL -filter based single-phase solar inverter. The ANN controller is trained to implement optimal control, based on approximate dynamic programming. The second objective is to evaluate the performance of the ANN-based solar PV system by simulating the PV system behavior for grid integration and maximum power extraction from solar PV array in a realistic residential PV application and building an experimental solar PV system for hardware validation. The results demonstrate that a residential PV system using the ANN control outperforms the PV system using the conventional standard vector control method and proportional resonant control method in both simulation and hardware implementation. This is also true in the presence of noise, disturbance, distortion, and nonideal conditions.

Capacitor impedance estimation utilizing dc‐link voltage oscillations in single phase inverter

Grid tied single-phase solar inverters offer less operational life when compared with the Photovoltaic (PV) panels due to the use of aluminium electrolytic capacitor (AEC). With time, AEC degrades, resulting in an increase in ripple voltage on PV panel. This would reduce the power extraction efficiency of the system, thereby a loss of revenue. This study proposes a simple and cost-efficient online technique for monitoring the health of AECs. The proposed technique suggests evaluating the AEC impedance at twice the grid frequency. Sampling of PV voltage, PV current and inductor current is required to determine the second harmonic impedance of AEC. These voltage and current sensors are present in commercially available solar PV inverters for their control operation. The proposed technique could be extended to other single-phase inverter applications provided that voltage and current sensors are available. Suitable mathematical model of the technique is derived to determine the effect of sampling instant on the accuracy of the results. Criteria for the replacement of capacitor based on impedance monitoring is defined. For validation of the proposed technique, detailed simulation studies are carried out for a single-phase PV system. The technique is verified experimentally on a scaled down solar PV inverter prototype.

English

English

Zero-Voltage Ride-Through Capability of Single-Phase Grid-Connected Photovoltaic Systems

Distributed renewable energy systems play an increasing role in today’s energy paradigm. Thus, intensive research activities have been centered on improving the performance of renewable energy systems, including photovoltaic (PV) systems, which should be of multiple-functionality. That is, the PV systems should be more intelligent in the consideration of grid stability, reliability, and fault protection. Therefore, in this paper, the performance of single-phase grid-connected PV systems under an extreme grid fault (i.e., when the grid voltage dips to zero) is explored. It has been revealed that combining a fast and accurate synchronization mechanism with appropriate control strategies for the zero-voltage ride-through (ZVRT) operation is mandatory. Accordingly, the representative synchronization techniques (i.e., the phase-locked loop (PLL) methods) in the ZVRT operation are compared in terms of detection precision and dynamic response. It shows that the second-order generalized integrator (SOGI-PLL) is a promising solution for single-phase systems in the case of fault ride-through. A control strategy by modifying the SOGI-PLL scheme is then introduced to single-phase grid-connected PV systems for ZVRT operation. Simulations are performed to verify the discussions. The results have demonstrated that the proposed method can help single-phase PV systems to temporarily ride through zero-voltage faults with good dynamics.

The impact of single-phase grid-connected distributed photovoltaic systems on the distribution network using P-Q and P-V models

The gradual emergence of photovoltaic (PV) systems as the most common distributed generation interconnected with the electric power system calls for a detailed power flow analysis with different models especially in the evolving unbalanced active distribution network. This paper is an extension of a previous study carried out on the performance evaluation of a 10kWp grid-connected PV system deployed in a school, with the grid providing a virtual storage and access to upstream markets. For increased adoption of such systems in the unbalanced distribution network, it is pivotal to understand the mode of operation and the type of connection to the system. This article presents an impact analysis of such utility interactive single-phase PV systems distributed on all the single-phase load nodes of the traditional IEEE-13 bus distribution test feeder. The PV distributed generation (PV-DG) can be modelled as constant P-Q or P-V nodes with varied impacts in power flow studies for the unbalanced active distribution network. Results from these models are compared in terms of their impacts on voltage profiles at load buses, voltage unbalance, equipment loading, power losses and the total number of iterations for a converged power flow solution.