Grid-connected Photovoltaic Generation Research Articles

New Islanding Detection for Grid-connected PV Generation System Based on the Voltage Harmonic Sequence Components

The islanding problem in grid-connected photoltaics system and traditional islanding detecting method are studied in this paper. Based on the technology of passive islanding detection, a new method of islanding detection is proposed which is implemented by using the voltage harmonic sequence component. According to the principle that the power quality of inverter-side is unequal to power quality of the grid-side at PCC point, the characteristic harmonic frequency sequence components of voltage can be extracted by FFT at PCC when islanding state is occurring. Theoretically, non-detection zone can be thoroughly eliminated by the extraction and recognition of microscopic variables. Simulation model of grid-connected PV generation system is established in PSCAD/EMTDC, and algorithm is carried out by MTALB. The simulation results show that the method is effective and fast. The method proposed has high response speed and no influence on the power quality of the system.

Comprehensive synchronous reference frame discrete-time modelling of a grid-connected PV for fast DC-side voltage control

This paper presents a novel comprehensive discrete-time model of a three-phase single stage grid-connected photovoltaic generation system. The detailed model is carried out on synchronous reference frame. It is shown that both converter's AC and DC-side discrete time model differs from the continuous time one. The main differences are the AC-side current and voltage cross coupling, and the DC-side voltage non-minimum phase behaviour for small active power injected into the grid. Based on the new model, digital internal current and external DC-link voltage controllers are designed. Experimental results show that the proposed controllers provide fast transient response and disturbance rejection. Small errors obtained comparing experimental and simulation waveforms for both DC-side voltage and AC-side current corroborate to validate the model and the designed controllers.

Voltage Equalizing of Solar Modules for Shadowing Compensation

This paper proposes a shadowing compensation method for the solar modules of grid-connected photovoltaic generation systems. The shadowing compensator (SC) implemented by the proposed shadowing compensation method is used only for the solar modules that can be shaded by predictable sources of shading. The proposed SC can simplify both the power circuit and the control circuit as well as improve power efficiency and utilizes a voltage equalizer configured by a modified multi-winding fly-back converter. The proposed SC harvests energy from the entire solar cell array to compensate for the shaded sub-modules of the solar cell array, producing near-identical voltages of all shaded and un-shaded sub-modules in the solar cell array. This setup prevents the formation of multiple peaks in the P-V curve under shaded conditions. Hardware prototypes are developed for the SCs implemented by the conventional and modified multi-winding fly-back converters, and their performance is verified through testing. The experimental results show that both SCs can overcome the multiple peaks in the P-V curve. The proposed SC is superior to the SC implemented by the conventional multi-winding fly-back converter.

Spatial matching of large-scale grid-connected photovoltaic power generation with utility demand in Peninsular Malaysia

Deployment of large-scale grid-connected photovoltaics (PV) power plants requires very reliable technical evaluation to reduce electricity demand and achieve efficient utilization of electricity generated from PV. At lower PV penetration levels, it is likely that the energy mix could under-supply utility demand, thus requiring extra units of generators, while at higher penetration levels it may oversupply demands, thus wasting generator capacity. Thus, determining the optimum installed capacity, technical limits, and economic benefits of large-scale PV systems are the main issues for both power utilities and decision makers. This study describes the development and validation of an alternative method (called the generation-demand matching model, GDMM) for evaluating the large-scale implementation of grid-connected PV power plants in Peninsular Malaysia relative to its interface with the traditional power grid system. The method explicitly provides a detailed assessment of the temporal and spatial factors that facilitate the match between PV generated electricity and electricity demand. These evaluation factors are analyzed using simulations of PV performance located at optimal sites. Optimal sites along with physical constraints were mapped using geographic information systems (GIS) for visualization and representation by location. PV electricity generation at different levels of penetration was predicted hourly for a year using time series analysis. This allowed comparison of electricity generation with electricity demand to evaluate the impacts of increasing levels of PV penetration. A novel feature of the proposed method is its combination of topographical and topological map data with metric data. The ability of the new method to accurately predict the performance of PV compared to PVWatts demonstrates the robustness of the method in evaluating the technical limits of PV systems in conventional power systems.

Event-Based Networked Islanding Detection for Distributed Solar PV Generation Systems

This paper proposes an event-based networked set-membership filtering method to detect islanding fault for distributed grid-connected solar photovoltaic generation systems. The method enables each set-membership filter to offer an ellipsoidal estimation set, which is used to judge whether or not the islanding fault happens. When islanding fault happens, the intersection of the ellipsoids is empty, and when islanding fault is free, the intersection of the ellipsoids is nonempty. In the filtering scheme, a novel event-triggered mechanism is proposed to reduce the transmission frequency for saving the communication resources. The condition of the existence of the set-membership algorithm is derived by a time-varying convex optimization approach. A simulation experiment and a comparative experiment are provided using Sim-Power-Systems implementation based on a 2-kW single-phase grid-connected power generation system to illustrate the effectiveness of the proposed method for the detection of the islanding fault and the reduction of the resource consumption, respectively.

Analysis of Harmonic Effect on Grid-connected Photovoltaic Generation System applying Hybrid Transformer Circuit Modeling

Analysis of Harmonic Effect on Grid-connected Photovoltaic Generation System applying Hybrid Transformer Circuit Modeling

A High Efficiency Two-stage Inverter for Photovoltaic Grid-connected Generation Systems

A High Efficiency Two-stage Inverter for Photovoltaic Grid-connected Generation Systems

Coordinated Control of Superconducting Fault Current Limiter and Superconducting Magnetic Energy Storage for Transient Performance Enhancement of Grid-Connected Photovoltaic Generation System

In regard to the rapid development of renewable energy sources, more and more photovoltaic (PV) generation systems have been connected to main power networks, and it is critical to enhance their transient performance under short-circuit faults conditions. This paper proposes and studies the coordinated control of a flux-coupling-type superconducting fault current limiter (SFCL) and a superconducting magnetic energy storage (SMES), to improve the fault ride through (FRT) capability and smooth the power fluctuation of a grid-connected PV generation system. Theoretical analyses of the device structure, operating principle and control strategy are conducted, and a detailed simulation model of 100 kW class PV generation system is built in MATLAB/SIMULINK. During the simulations of the symmetrical and asymmetrical faults, the maximum power point tracking (MPPT) control is disabled, and four different cases including without auxiliary, with SFCL, with SMES, and with SFCL-SMES, are compared. From the demonstrated results, the combination of without MPPT and with SFCL-SMES can more efficiently improve the point of common coupling (PCC) voltage sag, inhibit the DC-link overvoltage and alleviate the power fluctuation. Finally, a preliminary parameter optimization method is suggested for the SFCL and the SMES, and it is helpful to promote their future application in the real PV projects.

Research on simulated devices for Solar photovoltaic grid-connected generation system

On the standpoint of energy conservation and emission reduction, one device simulated photovoltaic grid-connected generation system based on SPWM was designed in the paper. And DC/AC inverter could transduce efficiently direct current to alternating current. The MCU(Micro-Control-Unit), in this system could achieve the control method for maximum-power-point and tracking for frequency and phase. Moreover, the MCU could implement PWM (Plus-Width Modulating) through programming. The system showed clearly the whole photovoltaic grid-connected generation system using simulated methods and ways.

Operational performance stability of grid-connected photovoltaic generator via DC–DC converter and 48-pulse voltage source inverter

This paper presents detailed steady-state stability analysis of PV generator interfaced to grid via DC–DC buck–boost converter, 48-pulse DC–AC sinusoidal Voltage Source Inverter (VSI), LC filter and transmission line. The main purpose of the DC–DC converter implementation is to inject the voltage corresponding to the Maximum Power Point of the PV generator. 48-pulse VSI is chosen as the harmonic contents in the output voltage are far away from the fundamental frequency with very small magnitudes. For numerical simulations, the complete nonlinear dynamical mathematical model in dq stationary reference frame is used including that of the terminal characteristics of the PV generator. The study comprises eigenvalues of the linearized model at various solar intensities. The robustness of the system operating point is checked by time domain simulations after small perturbations in the gird voltage and step changes on the solar insolations. Historically, series compensation of transmission lines has been used to increase the power transfer capability of the power system. In this study, the impact of equipping the transmission line with series capacitor on the system performance is highlighted. Furthermore, the effect of partial shading of the PV modules on the stability of the proposed power plant is investigated.

Impact of Rural Grid-Connected Photovoltaic Generation Systems on Power Quality

Photovoltaic (PV) generation systems have been increasingly used to generate electricity from renewable sources, attracting a growing interest. Recently, grid connected PV micro-generation facilities in individual homes have increased due to governmental policies as well as greater attention by industry. As low voltage (LV) distribution systems were built to make energy flow in one direction, the power feed-in of PV generation in rural low-voltage grids can influence power quality (PQ) as well as facility operation and reliability. This paper presents results on PQ analysis of a real PV generation facility connected to a rural low-voltage grid. Voltage fluctuations and voltage harmonic contents were observed. Statistical analysis shows a negative impact on PQ produced by this PV facility and also that only a small fraction of the energy available during a sunny day is converted, provoking losses of revenue and forcing the converter to work in an undesirable operating mode. We discuss the disturbances imposed upon the grid and their outcome regarding technical and economic viability of the PV system, as well as possible solutions. A low-voltage grid strengthening has been suggested and implemented. After that a new PQ analysis shows an improvement in the impact upon PQ, making this facility economically viable.

Power Synchronization Control for Grid-Connected Current-Source Inverter-Based Photovoltaic Systems

Current-source converters (CSCs) have a promising potential to interface the large-scale photovoltaic (PV) generators to electric grids. In order to overcome several drawbacks associated with the conventional vector-controlled CSC-based PV systems, this paper presents for the first time, the power synchronization control (PSC) scheme for the single-stage grid-connected CSC-based PV generator. A detailed small-signal model for the complete CSC-based PV system with the PSC strategy is developed to investigate the system stability, characterize the converter interactions with the electric grid, and design the controller parameters. The PSC of the CSC-based PV system reflects a stable performance under different operating conditions and following sudden variations in the insolation level. Due to the inherent synchronizing feature of the PSC, the phase-locked loop is eliminated and, hence, the integration to the very weak grids is seamlessly achieved. Although there is no direct control on the injected ac current to the grid, the inherent self-current-limiting feature of the CSC through the modulation of the regulated dc-choke current offers an overcurrent protection. Detailed nonlinear time-domain simulations results validate the theoretical analysis and show the effectiveness of the PSC strategy.

An Analysis of the Failure Modes Impacts in Grid-connected Photovoltaic Power Generation System below 20KW

이 연구는 20KW이하 태양광발전시스템에 대한 구성부품별 위험성에 대하여 고장모드영향분석과 중요도 등을 활용하여 위험우선순위를 결정하는 자료를 도출하는데 그 목적이 있다. 중요도 분석 결과 중요도는 총 4개의 고장모드로 인버터의 Fails to transfer(521), 필터(C)의 Shorted(541), 통신의 Shorted(551)와 Function Failure(552)로 나타났다. 중요도를 통한 위험우선순위가 높은 부품은 통신과 관련되어 있었다. 인버터의 Degraded output를 일으키는 주요 부품은 IGBT이다. IGBT는 24시간 풀가동하며 성능이 저하되었을 때 이를 감지하기도 어렵다. 따라서 내구성 및 수명이 높은 IGBT의 선택이 필요하다. 태양광발전시스템의 경우 모든 설비들이 통신과 연계되어 있어서 통신과 연결되는 다량의 커넥터와 해당 커넥터의 기능적 고장에서 초래됨을 확인하였다. 또한 통신의 경우 RS-422의 4선이 사용되고 있고 외부잡음에 영향을 많이 받는다. 따라서 2선 방식과 외부잡음에 강한 RS-485를 사용하여 기능적 고장에 대한 신뢰성을 확보해야 할 것으로 판단이 된다. 본 데이터는 태양광발전시스템의 유지 및 보수를 위한 기초자료로 활용가능하다.This study is intended to obtain the data for determining the risk priority by using criticality, analysis of failure mode effects, and the like regarding the risk involving component parts of photovoltaic power systemwith capacity of 20kw or below. According to the results of criticality analysis, a total of 4 failure modesare reported such as fails to transfer of an inverter (521), shorted (541) filter (C), shorted (551) communication,and function failure (552). Based on criticality, component parts having a high risk priority are related tocommunication. In the case of photovoltaic power system, as all of its devices are connected to communication, it is found that failures are caused by the failure of multiple connectors attached to communication. Thisdata can be utilized as baseline data for the maintenance of photovoltaic power system.

A new backstepping finite time sliding mode control of grid connected PV system using multivariable dynamic VSC model

This paper presents independent active and reactive power management of a three-phase grid-connected photovoltaic (PV) generation system using a new nonlinear control approach for the voltage source converter (VSC). Instead of controlling the direct and quadrature-axis currents of the VSC, the instantaneous active and reactive powers are used as error estimation parameters. This mode of control dispenses the unmodelled dynamics of the VSC phase-locked loop system and produces a robust control for the active–reactive power, and dc voltage excursions. This approach reduces computational time as well as complexity by avoiding unnecessary PLL phase calculation in the beginning. However, the PLL is used only to obtain the frequency component needed to generate the PWM signal. Further to improve the stability and robust tracking of the grid connected PV array, backstepping finite time fast sliding mode (BFTSM) control strategy is presented in this paper. The proposed controller offers invariant stability to modeling uncertainties due to converter parameter changes, changes in system frequency and exogenous inputs. Also the finite time sliding mode control offers an important tool for designing continuous finite time control laws. Comprehensive computer simulations are carried out in MATLAB/Simulink to verify the proposed control scheme under several system disturbances like changes in solar insolation, changes in local load, converter parametric changes, and faults on the converter and inverter buses, and partial shading condition of PV array. EMTDC/PSCAD model is established as confirmative study.

Analysis of PV Cell-based DG involving Improved Power Quality Converter for voltage control

The research investigated the impact on the power system with an extensive penetration of photovoltaic (PV) generation. A model of PV generation suitable for studying its interactions with the power system was developed. The dynamic response of a PV generation system to rapid changes in irradiance was investigated. An aggregated model of grid-connected PV generation was built, and it was used for simulating the integration of PV generation on a large-scale. Voltage control technique was investigated by simulation. Distributed Generation (DG) units are connected to the grid increasing nowadays for several reasons. Most DG units are relatively small and connected to the distribution network. A large part of the DG units connected to the grid via power electronic converters. The main task of the converters is to convert the power that is available from the prime source to the correct voltage and frequency of the grid. The general objective of this paper is to investigate how the power electronic converters can support the grid and solve power quality problems. An IEEE-5 bus system considered for this work to validate the power electronic converter using MATLAB/ Simulink.

An efficiency comparative analysis of isolated multi-source grid-connected PV generation systems based on a HF-link micro-inverter approach

For solar photovoltaic grid-connected generation systems, four inverter configurations are currently available in the market for different power ranges of the required system. However, a power gap exists within the lower range of the commercial power scale, particularly between micro-inverters and string inverters, leaving room for innovation and development of flexible and modular converters in this power range. This paper presents three different isolated multi-source grid-connected PV generation systems based on a single-phase high-frequency link micro-inverter scheme, to evaluate the feasibility for reducing the mentioned power gap by using higher power density systems based on a micro-inverter approach instead of derating the currently available string inverters, which are optimized for higher input voltage and power conditions compared with micro-inverters. Losses estimations, peak and weighted efficiencies are presented for Multiple-Input Multiple-Output, Multiple-Input Single-Output and Single-Input Single-Output generation systems with different number of input power sources. Analysis and discussion for each system are presented, showing that a Multiple-Input Single-Output system scheme presents a feasible alternative to a higher power density converter, reducing the inverter market power gap, with attractive features for renewable energy sources such as modularity and flexibility.

Conception of a modular multilevel converter for high-scale photovoltaic generation based on efficiency criteria

This work presents the design of a modular multilevel converter for high-scale grid-connected photovoltaic generation. Converter modules are used in order to divide between them the power to deliver, giving more advantages in comparison with using only one total converter. Losses and efficiencies are derived for each stage of a modular component, in order to select the most adequate number of converter modules according to efficiency criteria. First, a modular multilevel converter topology is proposed, rising its advantages over other reported topologies. Second, the calculation of losses of each stage of the converter module is performed. Then, the design of the modular multilevel converter is developed for two practical examples, one for a 10kW–1.32kV generation system, and another one for a 1MW–13.2kV medium-voltage generation system. These designs are developed considering different number of converter modules, and an analysis to select the most adequate number of them is made for both cases. One of the intentions of this work is to draw the highest efficiency possible when implementing a multilevel power converter for interconnecting photovoltaic generation to the grid.

Modified Cascaded Multilevel Grid-Connected Inverter to Enhance European Efficiency and Several Extended Topologies

This paper proposes a modified cascaded multilevel grid-connected inverter (MCM-GCI) suitable for photovoltaic grid-connected generation system, which considers wide operation range, low grid current total harmonics distortion (THD), and high European efficiency. In the proposed topology, a bidirectional power switch is added to the standard single-phase cascaded multilevel inverter (CMI) to implement the transformation between CMI mode and H-bridge inverter (HBI) mode. An online topology transformation approach of the MCM-GCI is proposed to guarantee the topology modes transformed safely and smoothly. The proposed MCM-GCI operates in CMI mode when the PV arrays’ output voltage and power are low, and transforms into HBI mode when the PV arrays’ output voltage and power are high. Experimental results of five-level MCM-GCI are represented to validate the feasibility of the proposed topology and it is also compared with other three classic grid-connected inverters to highlight its advantages. Furthermore, more structures based on hybrid CMI, which possess the topology transformation ability, are shown to further improve the generation range and obtain a higher efficiency of the system.

Life cycle assessment of grid-connected photovoltaic power generation from crystalline silicon solar modules in China

The environmental impacts of grid-connected photovoltaic (PV) power generation from crystalline silicon (c-Si) solar modules in China have been investigated using life cycle assessment (LCA). The life cycle inventory was first analyzed. Then the energy consumption and greenhouse gas (GHG) emission during every process were estimated in detail, and finally the life-cycle value was calculated. The results showed that the energy payback time (TEPBT) of grid-connected PV power with crystalline silicon solar modules ranges from 1.6 to 2.3years, while the GHG emissions now range from 60.1 to 87.3g-CO2,eq/kWh depending on the installation methods. About 84% or even more of the total energy consumption and total GHG emission occupied during the PV manufacturing process. The solar grade silicon (SoG-Si) production is the most energy-consuming and GHG-emitting process, which accounts for more than 35% of the total energy consumption and the total GHG emission. The results presented in this study are expected to provide useful information to enact reasonable policies, development targets, as well as subsidies for PV technology in China.

A New Common-Mode Transformerless Photovoltaic Inverter

Transformerless inverters are being widely used in grid-connected photovoltaic (PV) generation systems. Transformer elimination, in grid-connected PV systems, has many advantages. This not only reduces cost, size, and weight, but also increases the whole system efficiency. However, once the transformer is removed, there is no galvanic isolation between grid and PV array; as a consequence, leakage current appears due to parasitic capacitance to the ground, resulting in prohibitive electromagnetic interference and security issues.