Research on Photovolta Array Emulator System Based on A Novel Zero-Voltage Zero-Current Switching Converterer

Considering the characteristics of rooftop photovoltaic (PV) array, a new mathematical model of PV array that is suitable for partial shading condition is built based on an engineering model of a solar cell. It is derived theoretically that output voltage of PV array can be expressed by piecewise function. Moreover, a global maximum power point tracking (MPPT) control method based on particle swarm optimisation (PSO) and incremental conductance algorithm (INC) coordination control is put forward under partial shading. When the environmental conditions are stable, MPPT can be achieved by INC control; otherwise, when the external conditions change, global maximum power point of PV systems can be located fast and accurately by PSO. So, the tracking efficiency is improved. Simulation results show that the PSO and INC coordination control methods have better tracking precision. It can be achieved easily and reduce hardware input costs. It also improves the PV array output efficiency.

The integration of photovoltaic (PV) arrays to the power grid has continued to increase globally. Large PV array installations in the order of 100s of megawatt have already been installed. One of such large PV array installations is the Topaz PV array with an installed capacity of 500MW. With the increasing penetration of PV arrays, it is important to develop an accurate model for PV arrays. Such model will aid in performing state estimation, condition monitoring, load flow analysis, and other analytical studies. Several models for the PV module have been proposed in various publications. However, these models are written in a form that is effective for analyzing the PV module as an individual device. To analyze the PV array in an integrated power system, the form of the PV array model needs to be modified. This modification enables the establishment of connectivity between power system devices, and the definition of the admittance between the buses of the power system network. Consequently, computations such as load flow analysis and state estimation can be performed seamlessly. In this paper, a novel method for modeling a two-diode PV module is proposed. This model applies a scaling factor to the Taylor series expansion of the PV array model exponential terms. Next, the higher order terms of series expansion is reduced to at most second order terms using quadratization technique. This modeling method can also be applied to other PV array models, such as the one-diode and three-diode models. The form of the proposed PV array model enables seamless simulation of the PV array system in an integrated power system network.

Solar ship, which integrates the solar photovoltaic (PV) system into its own ship power system, is becoming one kinds of most promising and fastest developing green ship. Since the electric energy transformed by PV system is provided to the power load through the ship's distribution system, the output power of synchronous generator will be reduced in proportion. Especially, if the matching relationship among solar PV system, energy storage system and the power load requirement is precisely analyzed and the operation characteristics and reliability of solar inverter have already meet the strict test standards for marine equipment, the design capacity of synchronous generators could also be reduced. The off-grid mode and grid mode are the main way of integrated application of solar power photovoltaic system of ship. And the solar PV system is a kind of inverter power supply, which is essentially based on the electronic inverted technology, so PV system can be regarded as a ‘fragile power source’ with ‘zero inertia’. Therefore, the influence of solar photovoltaic grid-connected system to the power flow and power quality of the ship power system cannot be ignored. And the effect of photovoltaic system on the power quality of transient and steady-state and flow calculation remains to be studied. This paper mainly research the changes of power load flow calculation(PLFC) on the system, using the toolbox PSAT of MATLAB Simulink. This paper research the PLFC on the system of different solar photovoltaic systems access points, and analysis the experimental results. The results show that, under the premise of the normal operation of the ship electric power system, the improvement of the capacity of solar photovoltaic system in ship , and different access modes of photovoltaic grid-connected system, have slight impact on the power flow of power system, indicating that the photovoltaic grid-connected system in ship is stable, an appropriate increase in the capacity of PV system is feasible. The results is of certain significance of secure application of grid connected photovoltaic system in this paper.

Long term supporting schemes for photovoltaic (PV) system installation have led to accommodating large numbers of PV systems within load pockets in distribution grids. High penetrations of PV systems can cause new technical challenges, such as voltage rise due to reverse power flow during light load and high PV generation conditions. Therefore, new strategies are required to address the associated challenges. Moreover, due to these changes in distribution grids, a different response behavior of the distribution grid on the transmission side can be expected. Hence, a new equivalent model of distribution grids with high penetration of PV systems is needed to be addressed for future power system studies. The thesis contributions lie in three parts. The first part of the thesis copes with the PV modelling. A non-proprietary PV model of a three-phase, single stage PV system is developed in PSCAD/EMTDC and PowerFactory. Three different reactive power regulation strategies are incorporated into the models and their behavior are investigated in both simulation platforms using a distribution system with PV systems. In the second part of the thesis, the voltage rise problem is remedied by use of reactive power. On the other hand, considering large numbers of PV systems in grids, unnecessary reactive power consumption by PV systems first increases total line losses, and second it may also jeopardize the stability of the network in the case of contingencies in conventional power plants, which supply reactive power. Thus, this thesis investigates and develops the novel schemes to reduce reactive power flows while still keeping voltage within designated limits via three different approaches: 1. decentralized voltage control to the pre-defined set-points 2. developing a coordinated active power dependent (APD) voltage regulation Q(P) using local signals 3. developing a multi-objective coordinated droop-based voltage (DBV) regulation Q(V) using local signals In the third part of the thesis, furthermore, a gray-box load modeling is used to develop a new static equivalent model of a complex distribution grid with large numbers of PV systems embedded with voltage support schemes. In the proposed model, variations of voltage at the connection point simulate variations of the model’s active and reactive power. This model can simply be integrated into load-flow programs and replace the complex distribution grid, while still keeping the overall accuracy high. The thesis results, in conclusion, demonstrate: i) using rms-based simulations in PowerFactory can provide us with quite similar results using the time domain instantaneous values in PSCAD platform; ii) decentralized voltage control to specific setpoints through the PV systems in the distribution grid is fundamentally impossible due to the high level voltage control interaction and directionality among the PV systems; iii) the proposed APD method can regulate the voltage under the steady-state voltage limit and consume less total reactive power in contrast to the standard characteristic Cosf (P) proposed by German Grid Codes; iv) the proposed optimized DBV method can directly address voltage and successfully regulate it to the upper steady-state voltage limit by causing minimum reactive power consumption as well as line losses; v) it is beneficial to address PV systems as a separate entity in the equivalencing of distribution grids with high density of PV systems.

In order to use photovoltaic cell effectively and improve its photoelectric conversion efficiency, the maximum power point of photovoltaic generation system should be tracked rapidly and stably. In this paper after comparison and analysis common methods used in controller of photovoltaic systems such as Fuzzy and P&O, proposed an approach combined from FLC and particle swarm optimization algorithm (PSO) as an appropriate method to achieve maximum power point tracking (MPPT). Indeed Fuzzy logic control can cope with photovoltaic system using heuristic knowledge rules, but tuning the control parameters is not straightforward. PSO performs an on-line haphazard global search for input and output scaling factors of a PD-type fuzzy controller. The objective function of the PSO algorithm has been defined to minimize slope of P-V curve. The simulation results in SIMULINK of MATLAB indicate that proposed method can effectively eliminate the power oscillation around MPP and raise stability and reach steady state of the system.

Photovoltaic (PV) generation system is an important way to promote energy transformation and to cope with environmental challenges, firstly, based on the steady-state power flow equations of the PV system AC side connected to weak grid, the influence of power grid structure parameters on their maximum transmission power is studied, which provides a theoretical basis for the design of subsequent virtual impedance; secondly, a time-domain small-signal model for PV system connected to weak grid is established, and based on the proposed small-signal model, eigenvalue analysis is employed to study the stability of PV system connected to weak grid within different grid strength. The results show that: in the case of a given SCR, the smaller the impedance angle is, the greater the maximum transmission power of the system is; when the output power of PV system is rated, the smaller grid impedance angle makes the PV system can operate under the weaker grid conditions; with the decreasing of the grid strength, the PV system prone to power oscillation Finally a virtual resistance control strategy is proposed to improve the operation stability of PV system The validity of the theoretical analysis and the feasibility of the control strategy are verified by time domain simulation.

A comprehensive state-space model of two-stage grid-connected PV systems in transient network analysis

Photovoltaic (PV) system output power greatly depends on environmental operating conditions. Partial shaded condition (PSC) operates PV string under mismatch. PV module mismatch has been one of the major causes for reduced amount of output power. Maximizing the amount of energy extraction from PV system under mismatch greatly influenced by conversion efficiency as well as the mismatch mitigation topology used. Differential power processing (DPP) is one of the advanced techniques to deal with mismatch conditions and enhance power output from a PV system. In this paper hybrid modular DPP topology is presented. The proposed technique mitigates the effect of mismatches at submodule and enhance power extraction from PV string. Since in majority shading on a PV module is nonuniform. The conversion efficiency of module level DPP shading mitigation techniques enhanced using submodule level DPP architecture. To demonstrate its applicability simulation study is carried out in MATLAB Simulink and results are compared with traditional bypass method and module level DPP. Simulation results showed the reduction in mismatch loss and improvement in efficiency and power output.

Partial shading conditions (PSCs) can significantly reduce the output energy produced by photovoltaic (PV) systems. Moreover, when such conditions occur, conventional and advanced maximum power point tracking (MPPT) systems fail to operate the PV system at its peak because the bypassing diodes may cause the PV system to become trapped at a low power point when they are in conduction mode. The PV system can be operated at the global maximum power point (MPP) with the help of global peak searching tools. However, the frequent use of these tools will reduce the output of PV systems since they force the PV system to operate outside its power region while scanning the I-V curve in order to determine the global MPP. Thus, the global peak searching tools should be deployed only when a PSC occurs. In this paper, a simple and accurate method is proposed for detecting PSCs by means of monitoring the sign of voltage changes (positive or negative). The method predicts a PSC if the sign of successive voltage changes is the same for a certain number of successive changes. The proposed method was tested on two types of PV array configurations (series and series–parallel) with several shading patterns emulated on-site. The proposed method correctly and timely identified all emulated shading patterns. It can be used to trigger the global MPP searching techniques for improving the PV system’s output under PSCs; furthermore, it can be used to notify the PV system’s operator of the occurrence of PSCs.

Photovoltaic (PV) array which is composed of modules is considered as the fundamental power conversion unit of a PV generator system. The PV array has nonlinear characteristics and it is quite expensive and takes much time to get the operating curves of PV array under varying operating conditions. In order to overcome these obstacles, common and simple models of solar panel have been developed and integrated to many engineering software including Matlab/Simulink. However, these models are not adequate for application involving hybrid energy system since they need a flexible tuning of some parameters in the system and not easily understandable for readers to use by themselves. Therefore, this paper presents a step-by-step procedure for the simulation of PV cells/modules/arrays with Tag tools in Matlab/Simulink. A DS-100M solar panel is used as reference model. The operation characteristics of PV array are also investigated at a wide range of operating conditions and physical parameters. The output characteristics curves of the model match the characteristics of DS-100M solar panel. The output power, current and voltage decreases when the solar irradiation reduces from 1000 to 100 W/m2. When the temperature decreases, the output power and voltage increases marginally whereas the output current almost keeps constant. Shunt resistance has significant effect on the operating curves of solar PV array as low power output is recorded if the value of shunt resistance varies from 1000 ohms to 0.1 ohms. The proposed procedure provides an accurate, reliable and easy-to-tune model of photovoltaic array. Furthermore, it also robust advantageous in investigating the solar PV array operation from different physical parameters (series, shunt resistance, ideality factor, etc.) and working condition ( varying temperature, irradiation and especially partial shadow effect) aspects.

Solar photovoltaic (PV) technology has the versatility and flexibility for developing off-grid electricity system for different regions, especially in remote rural areas. While conventionally straight forward designs were used to set up off-grid PV-based system in many areas for wide range of applications, it is now possible to adapt a smart design approach for the off-grid solar PV hybrid system. A range of off-grid system configurations are possible, depending upon load requirements and their electrical properties as well as on site-specific available energy resources. The overall goal of the off-gird system design should be such that it should provide maximum efficiency, reliability and flexibility at an affordable price. In this chapter, three basic PV systems, i.e. stand-alone, grid-connected and hybrid systems, are briefly described. These systems consider different load profiles and available solar radiations. A systematic approach has then been presented regarding sizing and designing of these systems. Guidelines for selection of PV components and system sizing are provided. Battery energy storage is the important component in the off-grid solar PV system. Due to load and PV output variations, battery energy storage is going to have frequent charging and discharging. So the type of battery used in a PV system is not the same as in an automobile application. Detailed guidelines for selection of battery are therefore also provided. At present, most of the world-wide PV systems are operating at maximum power points and not contributing effectively towards the energy management in the network. Unless properly managed and controlled, large-scale deployment of PV generators in off-grid system may create problems such as voltage fluctuations, frequency deviations, power quality problems in the network, changes in fault currents and protections settings, and congestion in the network. A possible solution to these problems is the concept of active generator. The active generator will be very flexible and able to manage the power delivery as in a conventional generator system. This active generator includes the PV array with combination of energy storage technologies with proper power conditioning devices. The PV array output is weather dependent, and therefore the PV power output predictability is important for operational planning of the off-grid system. Many manufacturers of PV system power condition devices are designing and developing new type of inverters, which can work for delivering the power from PV system in coordination with energy storage batteries as conventional power plant.

Photovoltaic (PV) system modeling is used throughout the photovoltaic industry for the prediction of PV system output under a given set of weather conditions. PV system modeling has a wide range of uses including: pre-purchase comparisons of PV system components, system health monitoring, and estimation of payback (return on investment) times. In order to adequately model a PV system, the system must be characterized to establish the relationship between given weather inputs (e.g., irradiance, spectrum, temperature) and desired system outputs (e.g., AC power, module temperature). Traditional approaches to system characterization involve characterizing and modeling each component in a PV system and forming a system model by successively using component models. This paper compares a traditional modeling approach using the Sandia Photovoltaic Array Performance Model [1] to a new method of characterization using a recurrent neural network (RNN). The Sandia model predicts system performance from given weather data and individual component characterizations using a defined set of equations, while the RNN “learns” the input/output relationships by training on concurrent weather and performance data. The comparison of a traditional modeling technique and the new RNN method serves to validate the accuracy of the new method in comparison to a widely accepted modeling technique. Modeling using an RNN may be advantageous when component models are not available for the components in a PV system, when the components of a PV system are unknown to the modeler, or when system components are installed or altered in such a fashion that their model parameters are no longer applicable.

Photovoltaic (PV) systems incorporated with sun-tracking technology have been proposed and verified to effectively increase the power harvest. However, the actual power generated from a PV module has not been investigated and compared with that analyzed from theoretical models of the PV material. This study proposes a novel method for estimating the power benefit harvested by a two-axis sun-tracking type (STT) PV system. The method is based on semiconductor theory and the dynamic characteristics, including maximum power point tracking of PV modules that can be integrated with the database of annual solar incidences to predict the power harvested by any STT PV system. The increment of annual energy provided by an STT PV system installed at any arbitrary latitude, compared with that by a fixed-type system, can be accurately estimated using the proposed method. To verify the feasibility and precision performance of this method, a fixed-type and a two-axis STT PV system were installed at 24.92° north latitude in northern Taiwan and tested through long-term experiments. The experimental results show that the energy increments estimated by the theoretical model and actual measurement are 19.39% and 16.74%, respectively. The results demonstrate that the proposed method is capable of predicting the power benefit harvested by an STT PV system with high accuracy. Using our method, a PV system installer can evaluate beforehand the economic benefits of different types of PV systems while taking different construction locations into consideration, thereby obtaining a better installation strategy for PV systems. Copyright © 2012 John Wiley & Sons, Ltd.

Fault identification and detection are important to the safety, reliability, and efficiency of photovoltaic (PV) systems. Although PV systems do not have any moving parts, they are highly susceptible to harsh environmental factors and undergo degradation that increase the risk for faults. PV systems are difficult to shut down because they are always energized when exposed to any level of solar irradiation. Therefore, in the event of a fault, PV systems are dangerous to handle and have an increased risk for injury.This dissertation reviews the challenges, limitations, and improved solutions specifically for arc faults on the DC-side of the PV system. Arc faults are a subset of PV faults which occur between an air gap that may have formed from the loose connectors, junction box terminals, compromised wires, faulty soldering, and other PV degradation factors and have a large risk of causing fires in PV systems. Traditional detection methods require a priori knowledge of the PV system, utilize only a narrowband of the arcing frequencies for detection, or require large training datasets for machine learning techniques. To increase the robustness of the arc fault detection device and avoid false alarms from unwanted tripping conditions, a detailed DC arc fault model characterizing the different arc fault states as it burns in the air and a modified pink noise model corresponding to the physical arc fault states in the time-domain is proposed for detailed simulations. The unique operating point behavior of arc faults in PV systems is discussed and new current demodulation algorithm is proposed to filter the current waveform of other external noise without a priori knowledge of the PV system. An autocorrelation coefficient analysis technique is proposed which observes the entire arcing frequency band for detection analysis and simple threshold violation criteria are developed for the detection of the arc fault. The dissertation demonstrates the effectiveness of the new arc fault feature extraction methods and detection in both simulation and experimental results.--Author's abstract

The analysis presented in this paper focuses on the energetic aspects of the use of photovoltaic (PV) systems in office buildings. Energy generation from PV system has been simulated on an hourly time scale and compared with the energy demand of two office buildings located in Krakow (southern Poland). The buildings’ annual load exceeded 1 GWh in both cases. The analysis dealt with estimating how much energy generated by a PV system can be utilized on-site (self-consumption) and how big the energy surpluses will be (energy generation greater than demand). Capacities of PV systems ranging from 0.1 to 1.0 MW have been considered. Also, the impact of PV generation on the residual load parameters and changes in the maximal monthly and hourly energy demand were investigated. The results show that although the building energy demand is similar (in terms of annual volume of energy consumed) the potential of PV systems to cover it is different. The 100-kW PV system can reduce the observed hourly peak energy demand by 1% in December but by over 30% in June (respectively, from 171 kWh to 169 kWh, and from 333 kWh to 255 kWh). Considering the annual patterns of the office buildings’ energy demand and PV generation (both have their respective peaks in summer), the application of a PV system changes the office building energy demand pattern significantly from the perspective of the power system operator. After installing 500 kW PV in an office building consuming 1 GWh annually, the months with highest demand are no longer in summer but in winter.