Photovoltaic Inverter Research Articles

SOLAR POWER PLANT PLANNING FOR HOUSEHOLD SCALE BY THE AID PVSYST PROGRAM

Geographically, Indonesia is located on the equator, so it is very rich in solar energy sources with an average solar radiation intensity of around 4.8 kWh/m2 per day throughout Indonesia. The main component contained in solar power plants is solar cells which function to convert sunlight into electrical energy This research discusses the Planning of Solar Power Plants for Household Scale Assisted by the PVsyst Program. The purpose of this research is to determine how many solar modules, batteries, solar charger controllers, and inverters are needed for planning solar power plants in households with 900 VA and 1300 VA power. Based on manual calculations and simulations of the PVsyst program, 10 Luxor Ecoline Half Cell 280 Wp polycrystalline modules, 12 Narada EosG 2000 Ah batteries, 1 Victron Energy Mppt 250/100 solar charge controller, and 1 Victron Multiplus Compact 24/1200/25 inverter. The capacity of the solar power plant components for 900 VA and 1300 VA household loads is approximately the same, this is because the average daily energy usage is only slightly different. In 900 VA households, the number of occupants of 6 people uses 7088 Wh/day of energy, while in 1300 VA households with 4 occupants uses 7274.5 Wh/day of energy.

Nonlinear control of two-stage single-phase standalone photovoltaic system.

This paper presents a single-phase Photovoltaic (PV) inverter with its superior and robust control in a standalone mode. Initially, modeling and layout of the Buck-Boost DC-DC converter by adopting a non-linear Robust Integral Back-stepping controller (RIBSC) is provided. The controller makes use of a reference voltage generated through the regression plane so that the operating point corresponding to the maximum power point (MPP) could be achieved through the converter under changing climatic conditions. The other main purpose of the Buck-Boost converter is to act like a transformer and produce an increased voltage at the inverter input whenever desired. By not using a transformer makes the circuit size more compact and cost-effective. The proposed RIBSC is applied to an H-bridge inverter with an LC filter to produce the sinusoidal wave in the presence of variations in the output to minimize the difference between the output voltage and the reference voltage. Lyapunov stability criterion has been used to verify the stability and finite-time convergence of the overall system. The overall system is simulated in MATLAB/Simulink to test the system performance with different loads, varying climatic conditions and inverter reference voltages. The proposed methodology is compared with a back-stepping controller and Proportional Integral Derivative (PID) controller under rapidly varying climatic conditions. Results demonstrated that the proposed technique yielded a tracking time of 0.01s, a total harmonic distortion of 9.71% and a root means square error of 0.3998 in the case of resistive load thus showing superior control performance compared to the state-of-the-art control techniques.

Passivity-based Rieman Liouville fractional order sliding mode control of three phase inverter in a grid-connected photovoltaic system.

Photovoltaic (PV) system parameters are always non-linear due to variable environmental conditions. The Maximum power point tracking (MPPT) is difficult under multiple uncertainties, disruptions and the occurrence of time-varying stochastic conditions. Therefore, Passivity based Fractional order Sliding-Mode controller (PBSMC) is proposed to examine and develop a storage function in error tracking for PV power and direct voltage in this research work. A unique sliding surface for Fractional Order Sliding Mode Control (FOSMC) framework is proposed and its stability and finite time convergence is proved by implementing Lyapunov stability method. An additional input of sliding mode control (SMC) is also added to a passive system to boost the controller performance by removing the rapid uncertainties and disturbances. Therefore, PBSMC, along with globally consistent control efficiency under varying operating conditions is implemented with enhanced system damping and substantial robustness. The novelty of the proposed technique lies in a unique sliding surface for FOSMC framework based on Riemann Liouville (R-L) fractional calculus. Results have shown that the proposed control technique reduces the tracking error in PV output power, under variable irradiance conditions, by 81%, compared to fractional order proportional integral derivative (FOPID) controller. It is reduced by 39%, when compared to passivity based control (PBC) and 28%, when compared to passivity based FOPID (EPBFOPID). The proposed technique led to the least total harmonic distortion in the grid side voltage and current. The tracking time of PV output power is 0.025 seconds in PBSMC under varying solar irradiance, however FOPID, PBC, EPBFOPID, have failed to converge fully. Similarly the dc link voltage has tracked the reference voltage in 0.05 seconds however the rest of the methods either could not converge, or converged after significant amount of time. During solar irradiance and temperature change, the photovoltaic output power has converged in 0.018 seconds using PBSMC, however remaining methods failed to converge or track fully and the dc link voltage has minimum tracking error due to PBSMC as compared to the other methods. Furthermore, the photovoltaic output power converges to the reference power in 0.1 seconds in power grid voltage drop, whereas other methods failed to converge fully. In addition power is also injected from the PV inverter into the grid at unity power factor.

Identification of High and Low Voltage Ride-Through Control Parameters for Electromechanical Transient Modeling of Photovoltaic Inverter

The electromechanical transient model of a photovoltaic (PV) inverter’s high and low voltage ride-through has complex operating circumstances and a large number of control parameters, which makes parameter adjustment difficult. Furthermore, it is frequently challenging to identify a single set of control parameters that can successfully handle a variety of operating conditions. The Improved Differential Evolution Particle Swarm Optimization (IDEPSO) algorithm is proposed in this paper to provide a control parameter identification technique for high and low voltage ride-through that addresses these problems. Taking a 320kW PV inverter of a certain company as the research object, based on the specified current control strategy of high and low voltage ride-though, the parameters to be identified were determined by analyzing the influence of model parameters. Secondly, To enhance the algorithm’s capability to solve multidimensional optimization problems, convergence speed, and global search ability, the Differential Evolution (DE) algorithm’s search mechanism is incorporated into the Particle Swarm Optimization (PSO) algorithm, along with a non-fixed gradient inertia weight strategy for the algorithm’s inertia weight and the elite retention idea for the cross factor. Then, the objective function of the IDEPSO algorithm was built based on the concept of minimum deviation between simulation data and various groups of test data, and the significance of various working conditions was distinguished by weight division to improve the robustness of identification parameters. Finally, the identification parameters are imported into the PSASP program type 2 photovoltaic power station model, and the interval division and deviation calculation of the test data and simulation data are carried out. It is confirmed that the identification parameters meet the standards of the maximum variation permitted in GB/T 32892-2016 and are appropriate for a variety of working scenarios.

Characteristics of symmetrical components for high impedance faults in distribution networks with photovoltaic inverters

This work models a photovoltaic (PV) inverter connected to an IEC microgrid system. The purpose of this study was to find the characteristics of symmetrical components before and after a high impedance single phase short-circuit fault. The IEC microgrid system is tailored to the distribution system in Indonesia, where the applied voltage is 20 kV. Only parameters related to the short-circuit study are included in the model. A second-order generalized integrator frequency-locked-loop is utilized to represent the 3-phase PV inverter. The inverter model, previously treated as an ideal current source, and positive sequence current are no longer employed, as they fail to depict the characteristics of symmetric components during a phase-to-ground short-circuit fault. The IEC microgrid system connected to the PV inverter is simulated using ATPDraw-electro magnetic transient program (EMTP). Simulation results reveal that the changes in the symmetric component values of current after a fault experience a very insignificant increase. Meanwhile, the positive sequence voltage values following the short-circuit fault exhibit a negligible decrease. In contrast, the negative sequence and zero sequence voltage components after the short-circuit fault undergo a significant increase.

Analysis of fault current contributions from small‐scale single‐phase photovoltaic inverters and their impacts on the protection of electric power distribution systems

AbstractThis paper presents an analysis of the fault current contributions of small‐scale single‐phase photovoltaic inverters under grid‐connected operation and their potential impact on the protection of distribution systems. To conduct this analysis, an autotransformer‐based voltage dip generator is proposed as a means to test the photovoltaic inverters' contribution to short‐circuit currents. Laboratory tests are then performed to obtain the short‐circuit current contribution of eight single‐phase photovoltaic inverters. Using the short‐circuit current data obtained, a behaviour model is developed and simulated on Matlab‐Simulink. The model is then applied to a real distribution system and case studies are conducted to simulate the potential impacts on the protection system. Results indicate that while the massive penetration of small‐scale single‐phase photovoltaic inverters can alter the protection system's operating time, the impacts are not significant. Only in very specific scenarios, such as events related to high impedance faults, some impact can be observed. In these situations, the presence of photovoltaic inverters further complicates the already difficult task of identifying high impedance faults through conventional overcurrent protections. This study provides valuable insights into the integration of photovoltaic inverters into distribution systems, and can aid in the development of effective protection measures for future grid designs.

태양광 인버터 소손 사고조사 및 현장 진단 사례 연구

태양광 인버터 소손 사고조사 및 현장 진단 사례 연구

Probing Leakage Current Suppression Techniques for Non-Isolated Photovoltaic Inverters

The evolution of photovoltaic (PV) inverters has witnessed distinct trade-offs between isolated and non-isolated configurations. While isolated PV inverters grapple with challenges such as increased volume and suboptimal system efficiency due to transformer inclusions, their non-isolated counterparts offer a solution by eliminating these transformers. However, this lack of electrical isolation in non-isolated inverters engenders a distinct predicament: significant leakage currents. Such currents not only impede system operation but also curtail operational efficiency. Recognizing this, the suppression of leakage current has catapulted to the forefront of contemporary research. This manuscript elucidates the operational intricacies of non-isolated PV inverters. It then embarks on a panoramic review of prevailing leakage current suppression techniques, both domestic and international, contextualizing them with state-of-the-art inverter topologies such as the H7, H10, three-level neutral point clamped (NPC) and three-phase four-bridge arm configurations. The paper culminates with a prospective glance at future research trajectories in leakage current suppression, proffering seminal recommendations for academic and industry fraternities.

Leakage Current Analysis of Non-Isolated Photovoltaic Grid-Connected System

Amidst mounting concerns over energy scarcity and the environmental repercussions of fossil fuels, renewable sources, spearheaded by solar energy, have garnered substantial societal attention, thereby propelling advancements in photovoltaics (PVs). In the realm of grid-connected (GC) PV systems, a pressing issue is the leakage current suppression in non-isolated GC PV inverters. As a ubiquitous architecture in PV systems, the non-isolated GC configuration is of paramount importance in practical applications. Yet, intrinsic attributes of PV systems have amplified the leakage current challenge within this setup. This paper endeavors to dissect the leakage currents in non-isolated PV GC systems, delving into the salient factors influencing them. It embarks on an exploration of the origins of leakage currents, subsequently analyzing the repercussions of LC filter parameters—spanning filter capacitance, Y capacitance, and common-mode inductance—on these currents. Drawing insights from extant scholarly discourse on leakage current mitigation, this study offers a synthesized perspective accentuated with augmented strategies, elucidating a comprehensive path forward for leakage current suppression.

The effect of inrush transients on PV inverter’s grid impedance measurement based on inter-harmonic injection

This paper addresses a cause for false tripping of photovoltaic inverters with anti-islanding protection based on impedance measurement with inter-harmonic injection. Earlier discussions about tripping problems happening when several devices are doing the measurement at the same time are supplemented with a problem caused by inrush transients of nearby devices. A series of experiments was conducted in the Power Quality laboratory of the TU/e, on a PV inverter which complies with the DIN VDE 0126 standard. Impedance measurement was done in parallel with the inverter and measurement results are presented. A criterion for false tripping caused by transients is explored. Also, influences of network impedance and grid harmonic pollution on false tripping were analyzed. In the end, some signal processing techniques are proposed to avoid this problem.

Who pays for harmonic network losses caused by PV inverters?

The even growing number of small power (household rate) PV sets and the connecting inverters should warn utility companies to make a reconsideration on the network losses. Of course the main portion of the network losses is in connection with the fundamental current flow along the network. In our former papers [1], [2] and [3] it was pointed out that the harmonic network losses caused by non-linear loads generating harmonic currents actually are paid, because the non-linear loads receive as additional fundamental power the network losses originating by their generated harmonic currents. The PV inverter is a fundamental current power generator, but as a nonlinear element it generates harmonic currents as well. The fundamental current network loss cannot be separated into parts caused by consumption and generation; therefore the utility pays for the total energy supplied by the PV installation including the network loss. And what is the situation regarding the harmonic network loss? The paper gives a theoretical overview of the problem, furthermore – based on laboratory measurements – a proper computer simulation model was developed. Using computer simulations different practical scenarios are discussed.

Calculation of phase angle diversity for time-varying harmonic currents from grid measurement

Phase angle diversity of harmonic currents emitted by different equipment, like electronic power supplies, modern lamps with electronic ballast, chargers for electrical cars or photovoltaic inverters, results in cancellation effects which represent an efficient way of managing harmonic levels in LV grids. Different methods have been presented in the last decades to quantify and evaluate the summation of harmonic currents based on grid measurements. There is not a general consensus about which method or index should be preferred, especially if time-variation of harmonic currents is considered. The paper discusses the impact of measurement accuracy and aggregation parameters on the calculation of the two main diversity indices, namely diversity factor and summation exponent. In case of time varying harmonics an additional statistical post-processing is required which also depends on several parameters and calculation methods. Based on the results of the application of different methods to real grid measurement data, some guidance on suitability and limitations of the different methods are given.

Reactive power management in photovoltaic installations connected to low-voltage grids to avoid active power curtailment.

Photovoltaic (PV) inverters are traditionally designed to operate with unity power factors. In order to use reactive power capabilities of smart inverters, in this work two strategies are analysed: limiting the amount of active power delivered or oversizing the inverter. The first of these options implies a reduction in the PV production and therefore, it would lead to reduced earnings for the PV system owner. On the other hand, oversizing the PV inverter allows having reactive power compensation capabilities, while delivering full power output from its PV field.

Real Problems in Utility High Voltage Network due to Grid Connected Photovoltaic Power Generation. The experience of Endesa.

Photovoltaic (PV) systems require connection to a utility power grid to work effectively as energy sources. Numerous problems and unusual configurations have been detected in those connections: Some problems are due to a dysfunction of the faulted-phase relay protection on Substations (Sub.) not originated in all cases by phase imbalance of the PV inverters, other problems are related to an abnormal stationary (resonant) state of generation just after islanding of the plant, where frequency and amplitude of the power signal are in a corrupted stable state caused by the inverters. The final problem to be discussed is related to switch-on sequencing and associated starting inverter’s problems.

A review of linear advanced current control techniques for grid connected PV inverters

The following paper presents the work being done on the comparative design, simulation and experiments concerning advanced digital linear control techniques for power inverters. Based on an existing inverter topology being developed and implemented, with a conventional DSP-programmed PI control, a research is done on more advanced linear control techniques that might improve the PI response, allowing at the same time a separate regulation of active and reactive power for electricity connection to the grid.

A partial soft-switching SiC-based ANPC single-phase inverter with loss model-based dead time optimization for grid-tied PV systems

Single-phase string inverter has been widely applied to grid-tied photovoltaic (PV) rooftop applications for its renewable energy. However, the inherent attribute of intermittency in solar energy may induce instability and unqualified power. To meet the grid-interconnection standards, high demands of efficiency and harmonic distortion need to be imposed on DC/AC inverters. Conventional soft-switching inverters used to sacrificing auxiliary resonant circuits to exchange for soft switching. This requires additional costs as well as sufficient dead time to discharge junction capacitances of all switches, which exacerbates total harmonics distortion (THD) induced by dead-time effect. To improve, this paper proposes a partial soft-switching silicon carbide (SiC) -based active neutral-point-clamped (ANPC) inverter, which possesses high efficiency, eligible dead time, and no auxiliaries. 650-V SiC MOSFET is adopted for its smaller output capacitance compared with Si device. Hybrid PWM modulation is utilized to achieve partial soft switching. Whereas, the soft switching realization range and power losses highly depend on the dead time. To achieve less power loss and improved dead time effect, this paper proposes a loss model-based dead time algorithm through a Power Loss VS. Dead Time mathematical loss model. Moreover, the mechanism of the dead time affected by soft switching is explored. The transition modes, dead time configurable boundaries, and design procedure are also analyzed in detail. A 1-kW prototype is demonstrated with the input of 800 V and the rated output of 220 V/ 4.5 A. Its efficiency could reach 99.6% with THD=0.95% at full power level.

Control Approach of Grid-Connected PV Inverter under Unbalanced Grid Conditions

In grid-connected photovoltaic (PV) systems, power quality and voltage control are necessary, particularly under unbalanced grid conditions. These conditions frequently lead to double-line frequency power oscillations, which worsen Direct Current (DC)-link voltage ripples and stress DC-link capacitors. The well-known dq frame vector control technique, which is effective under normal conditions, struggles with oscillatory component management in unbalanced grid conditions. To address this issue, this paper presents an advanced control approach designed for grid-connected PV inverters. The proposed approach is effective at reducing oscillations in the DC-link voltage at double the grid frequency, thereby enhancing system stability and component longevity. This method introduces a feedback control method designed to regulate oscillatory components that appeared within the dq frame and suppress the DC-link voltage oscillations under imbalance conditions, including single line-to-ground (SLG) faults. Additionally, the control scheme incorporates a maximum power point tracking (MPPT) controller to optimize PV efficiency. Comprehensive simulations demonstrate the effectiveness of this method in maintaining sinusoidal current injections and stabilizing DC-link voltage during unbalanced grid conditions. Simulation results show that the control scheme effectively stabilizes DC-link voltage, maintains balanced grid current, and ensures constant active power under various conditions, including SLG faults and solar irradiance changes.

Impact of a High Penetration of Electric Vehicles and Photovoltaic Inverters on Power Quality in an Urban Residential Grid Part I – Unbalance

This paper presents a measurement-based assessment of the impact of a high penetration of plug-in electric vehicles with on-board charger (EVC) and photovoltaic inverters (PVI) on Power Quality in a public low voltage (LV) network. The paper consists of two parts. This first part is focused on the impact on unbalance, the second part is related to harmonics. The results are based on extensive measurements in an urban residential grid with almost 100 households (HH), 43 PVIs and 36 EVCs. The impact of PVI and EVC on unbalance at different levels of aggregation is described in detail. At first the individual impact of a single PVI and EVC is discussed for different operating conditions. In particular, a sunny day, a cloudy day and hours during the night are used for PVI, while periods of charging and periods of no charging are considered for EVC. Next sections analyse the interaction between PVI, EVC and residual load at household level as well as the overall impact of PVIs and EVCs in the low voltage grid. The analysis considers current unbalance and voltage unbalance.

Power Quality in Renewable Energy Systems  Challenges and Opportunities

Power quality in traditional power systems is concerned with voltage problems caused by abnormal operation or nonlinear load behavior. The integration of renewable energy into the power grid introduces new power quality problems. In addition to the intermittency of renewable production, which leads to more frequent voltage fluctuation, and the switching in the power electronics interfaces, which injects high-frequency harmonics into the system, harmonic resonance and other dynamics power quality problems become more prevalent due to the complex and fast dynamics and control of power electronics interfaces. This paper reviews the sources of harmonic resonance involving renewable energy and presents a systematic method to identify and characterize such dynamic power quality problems. A distributed generation test-bed is also presented as an experimental platform for the study of system harmonic resonance and other control-related power quality and stability problems. Measurement results involving single-phase solar and three-phase wind inverters are presented to validate the analysis method and to demonstrate possible mitigation techniques. The need for advanced autonomous control that enhances system stability and mitigates system harmonic resonance are discussed. Issues related to electromagnetic interference (EMI) generated by renewable energy sources and the need to develop EMI compliance requirements for such sources are also discussed.

Designing Large scale Photovoltaic Systems

This paper presents a plan and procedure for the design and performance analysis of large-scale grid-connected solar Photovoltaic (PV) systems. A 1MW grid-connected PV system was designed and its performance was analyzed over the guaranteed life of the system using a photovoltaic system performance analysis program. In the system designed and analyzed in this paper, half of the produced electricity is fed to the load and the other half is stored to the grid. If the solar system cannot produce electricity for the load, then the load will use power from the grid. A photovoltaic system is a power system designed to supply usable solar power by means of photovoltaic panels. It consists of an arrangement of several components, including solar panels to absorb and convert sunlight into electricity, a solar inverter to change the electric current from DC to AC, as well as mounting, cabling, and other electrical accessories to set up a working system.