Showing papers on "Grid-connected photovoltaic power system published in 2002"

Inverters for single-phase grid connected photovoltaic systems-an overview

Abstract: An overview on developments and a summary of the state-of-the-art of inverter technology in Europe for single-phase grid-connected photovoltaic (PV) systems for power levels up to 5 kW is provided in this paper. The information includes details not only on the topologies commercially available but also on the switching devices employed and the associated switching frequencies, efficiency, price trends and market share. Finally, the paper outlines issues associated with the development of relevant international industry standards affecting PV inverter technology.

Cascaded DC-DC converter connection of photovoltaic modules

Abstract: New residential scale photovoltaic (PV) arrays are commonly connected to the grid by a single DC-AC inverter connected to a series string of PV modules, or many small DC-AC inverters which connect one or two modules directly to the AC grid. This paper shows that a "converter-per-module" approach offers many advantages including individual module maximum power point tracking, which gives great flexibility in module layout, replacement, and insensitivity to shading; better protection of PV sources, and redundancy in the case of source or converter failure; easier and safer installation and maintenance; and better data gathering. Simple nonisolated per-module DC-DC converters can be series connected to create a high voltage string connected to a simplified DC-AC inverter. These advantages are available without the cost or efficiency penalties of individual DC-AC grid connected inverters. Buck, boost, buck-boost and Cuk converters are possible cascadable converters. The boost converter is best if a significant step up is required, such as with a short string of 12 PV modules. A string of buck converters requires many more modules, but can always deliver any combination of module power. The buck converter is the most efficient topology for a given cost. While flexible in voltage ranges, buck-boost and Cuk converters are always at an efficiency or alternatively cost disadvantage.

Modelling photovoltaic system using PSpice

Abstract: Introduction to Photovoltaic Systems and Pspice Spectral Response and Short Circuit Current Electrical Characteristics of the Solar Cell Solar Cell Arrays PV Modules and PV Generators Interfacing PV Modules to Loads and Battery Modelling Power Conditioning and Inverter Modelling Stand -- Alone PV Systems Grid Connected PV Systems Small Photovoltaics

Maximum power tracking for photovoltaic power system

Abstract: The electric power supplied by a photovoltaic power generation system depends on the solar radiation and temperature. Designing efficient PV systems heavily emphasizes tracking the maximum power operating point. This work develops a novel three-point weight comparison method that avoids the oscillation problem of the perturbation and observation algorithm which is often employed to track the maximum power point. Furthermore, a low cost control unit is developed, based on a single chip to adjust the output voltage of the solar cell array. Finally, experimental results confirm the superior performance of the proposed method.

Power inverter topologies for photovoltaic modules-a review

Abstract: This review-paper focuses on the latest development of inverters for photovoltaic AC-modules. The power range for these inverters is usually within 90 Watt to 500 Watt, which covers the most commercial photovoltaic-modules. Self-commutated inverters have replaced the grid-commutated ones. The same is true for the bulky low-frequency transformers versus the high-frequency transformers, which are used to adapt the voltage level. The AC-module provides a modular design and a flexible behaviour in various grid conditions. It hereby opens the market for photovoltaic-power for everyone at a low cost due to the plug and play concept, which also makes a further enlargement of the system possible.

A flyback-type single phase utility interactive inverter with low-frequency ripple current reduction on the DC input for an AC photovoltaic module system

Abstract: In recent years, interest in natural energy has grown because of increased environmental concerns. Many kinds of inverter circuits and their control schemes for photovoltaic (PV) power generation systems have been studied. In a conventional system, the PV array in which many PV modules are connected in series is used to obtain sufficient DC-bus voltage for generating an AC utility line voltage from an inverter circuit. However, the total power generation of the PV array is sometimes decreased remarkably when a few modules are partially covered by shadows, thereby decreasing its inherent current generation, and preventing the generation current attaining its maximum value on the array. To overcome this drawback, an AC module strategy has been proposed. In this system, a small power DC-AC utility interactive inverter is mounted on each PV module individually. This inverter operates so as to generate the maximum power from its corresponding PV module. This paper proposes a novel flyback-type utility interactive inverter circuit suitable for AC module systems. The features of the proposed system are that it: (1) is small in volume and lightweight; (2) allows stable AC current injection into the utility line; (3) enables the stable parallel operation without AC current sharing control; and (4) enables the capacitance of the DC capacitor to be small. The effectiveness of the proposed system is clarified through simulation and experiments.

Maximum power point tracking using adaptive fuzzy logic control for grid-connected photovoltaic system

Abstract: In this paper proposed method of maximum power point tracking using adaptive fuzzy logic control for grid connected photovoltaic system. The system composed of boost converter single-phase inverter connected to utility grid. The maximum power point tracking control is based on adaptive fuzzy logic to control MOSFET switch of boost converter and single phase inverter uses predicted current control to control four IGBTs switch for grid-connected control. Adaptive fuzzy logic controllers provide attractive features such as fast response, good performance and it can also change fuzzy parameter for improving control system. The fuzzy logic predicted current control provide current with sinusoidal waveshape and inphase with voltage. This system can provide energy with low harmonics and high power factor.

Prediction-data-based maximum-power-point-tracking method for photovoltaic power generation systems

Abstract: A new maximum-power-point-tracking (MPPT) method for a photovoltaic (PV) power generation system was studied which can efficiently generate PV power even under changing weather conditions. In order to research a method suitable for the actual photovoltaic power system, PV characteristics of the maximum power point were measured for more than six months using a PV curve tracer. The actual maximum power points vary with conditions such as the surface temperature and the quantity of solar radiation. So, relationships between the maximum power point and circuit variables such as open circuit voltage and short circuit current were examined under various conditions appearing in the PV power generation system. It was found through measurements that the relationship between the maximum power and the current that the output power was almost a linear function in the actual solar arrays, regardless of the weather conditions. The MPPT method was proposed based on the obtained findings. It was verified through simulations and experiments that the proposed method enables the solar arrays to quickly generate the maximum power as determined by weather conditions at the time.

Probabilistic assessment of photovoltaic (PV) generation systems

Abstract: The sizing of photovoltaic (PV) power systems for remote offshore loads has been the concern of end users. This is because of the space constraints associated with the application and the expensive cost of panels and batteries. This paper evaluates the design of the PV system using three probabilistic methods. One is considering fixed days of battery back up and recharge and the other is based on loss of load probability (LOLP). The third is based on Markov chain modeling. LOLP distinctly shows reduction in the number of panels and size of batteries while providing a detailed view of the system performance.

Mini-optics solar energy concentrator

Abstract: This invention deals with the broad general concept for focussing light. A mini-optics tracking and focusing system is presented for solar power conversion that ranges from an individual's portable system to solar conversion of electrical power that can be used in large scale power plants for environmentally clean energy. It can be rolled up, transported, and attached to existing man-made, or natural structures. It allows the solar energy conversion system to be low in capital cost and inexpensive to install as it can be attached to existing structures since it does not require the construction of a superstructure of its own. This novel system is uniquely distinct and different from other solar tracking and focusing processes allowing it to be more economical and practical. Furthermore, in its capacity as a power producer, it can be utilized with far greater safety, simplicity, economy, and efficiency in the conversion of solar energy.

Implementation and testing of anti-islanding algorithms for IEEE 929-2000 compliance of single phase photovoltaic inverters

Abstract: Electrical system islanding occurs when the utility grid is removed but local sources continue to operate and provide power to local loads. This can present safety hazards and the possibility of damage to other electric equipment. Anti-islanding functionality is a key requirement for grid-interactive inverters used in PV systems that function as distributed generation sources. The IEEE Std. 929-2000 "Recommended Practice for Utility Interface of Photovoltaic (PV) Systems" (IEEE 929) sets testing requirements for these systems which includes an anti-islanding requirement. UL has adopted this practice in UL-1741. This paper provides a description of Xantrex anti-islanding algorithms and examples of inverter testing. Inverters tested were the Xantrex SW with GTI and ST models. Testing was performed at the Sandia National Laboratories Distributed Energy Technologies Laboratory. Data is provided for single and multiple units with additional data on power quality.

Grid connected PV system using two energy processing stages

Abstract: In this work a simple and robust system to be used with electrical energy generated by photovoltaic modules is proposed. Through this system, the produced energy is directly injected into the electric grid utility. It does not need batteries since it operates connected to the grid. The energy supply occurs in periods where the sunlight is present, with the system in standby when light is not supplied. The adopted control strategy allowed the production of a current with little harmonic distortion, simplifying and reducing the size and the number of components, both in the control as well as in the output filter. The high frequency operation permitted the size reduction of the magnetic components and the capacitors. The system is composed by two stages: a flyback converter and a full-bridge voltage inverter. This system operates with commercially available modules being necessary no adaptation of these to be connected. Design procedure and experimental results are shown.

System interconnection electric power generator and control method therefor

Abstract: In a solar energy generator including a solar battery a microcomputer for controlling at least a boosting circuit and an inverter circuit so that AC power suitably usable as the AC power of a commercial power supply system can be supplied to the commercial power supply system, the power to be supplied to the various kinds of equipment of the solar energy generator is selectively supplied from one of the solar battery and the commercial power supply system. The microcomputer stores the operational status data of the solar energy generator into an external storage device, and these data can be used for maintenance or trouble shooting of the solar energy generator.

Power conditioner for solar power generation system

Abstract: An inverter unit converts power from a solar battery into AC power and interconnects the AC power with a utility power supply. A control circuit manages the time during which the inverter unit stops. If the time is equal to or longer than a predetermined time, it is determined that one day has passed. Data for one day stored in a memory is accordingly cleared and data is newly stored in the memory.

High-frequency DC link inverter for grid-connected photovoltaic system

Abstract: This paper proposes an inverter for the grid-connected photovoltaic system based on the transformerless inverter. This system consists of a high frequency inverter bridge, high frequency transformer, diode bridge rectifiers, a DC filter, a low frequency inverter bridge, and an AD filter. The high frequency inverter bridge switching at 20 kHz is used to generate bipolar PWM pulse, which is subsequently rectified by diode bridge rectifiers to result in a full-wave rectified sine wave. Finally, it is unfolded by a low frequency inverter bridge to result in a 60 Hz sine wave power output. In this paper, the control algorithm for synchronous current feedback control method and a maximum power point tracking (MPPT) method using DSP are described. The simulation and experimental results are shown to verify the validity of the proposed system.

Space solar-power stations, wireless power transmissions, and biological implications

Abstract: The concept of SPS-WPT envisions the generation of electric power by solar energy in space for use on earth. The system would consist of an orbiting platform to gather solar energy and convert it to electric and microwave power in space. A microwave transmission system would be employed to send the electric power to earth. A power-receiving antenna (rectenna), on the ground or offshore, would convert and collect the transmitted microwave energy in a form of electricity suitable for the common electric utility distribution infrastructure. Some environmental and health concerns are discussed.

Novel concept of a PV power generation system adding the function of shunt active filter

Abstract: Novel concept of a photovoltaics (PV) power generation system adding the function of active filter (AF) is proposed in this paper. So far, because the PV power generation system can be treated to a harmonics source for the power distribution systems, the PV system combined the function of AF systems as well as the AF systems using the PV module as the power source have never been reported. Here, the control strategy of PV-AF system is for the first time introduced. Also, in order to stabilize the output current of VSI, the reference voltage MPPT control is applied. Using simulation analysis, it is confirmed that it is possible to combine AF theory to the three phase PV system connected up to utility, and results gave us that it was theoretically positive to actualize the PV-AF system.

Flyback type inverter for small scale photovoltaic power system

Abstract: This paper presents a newly developed flyback type inverter for a small scale (low power) photovoltaic power system and a maximum power point tracking (MPPT) controller without a current sensor for this system. As the small scale photovoltaic power systems are used in parallel, cost reduction with high reliability is strongly required. In the proposed inverter, the current is controlled with open loop, and then the generated power of photovoltaic array is calculated by an equation using the voltage of the photovoltaic array. Therefore, the system can obtain the power by detecting only the voltage of the photovoltaic array. As a result, we may obtain the performance of the MPPT without a current sensor as well as with a current sensor.

Solar cell module, solar cell array, and photovoltaic power generation system

Abstract: PROBLEM TO BE SOLVED: To provide a solar cell module which is improved in durability and reliability and reduced in cost. SOLUTION: A plurality of single cell converters 4, each composed of a solar cell 2 and a DC/DC converter 3 fitted to the solar cell 2, are connected in parallel in the solar cell module 1. The electrical output of the solar cell modules 1 are collected through a connection box 57 and inputted into a link inverter 56. COPYRIGHT: (C)2004,JPO

Implementation of three-phase grid connected inverter for photovoltaic solar power generation system

Abstract: Detailed analysis, simulation and hardware results of a new solar photovoltaic inverter configuration interconnected to the grid are presented. From the simulation and experimental results it is confirmed that the harmonic distortion of the output current waveform of the inverter fed to the grid is within the stipulated limits laid down by the utility companies. To harvest the vast solar energy, it would be desirable if the energy conversion units are simple, reliable, and of low cost and high efficiency. High efficiency can be achieved by the use of all the power generated for the unit and even contribute to the gird while the energy is not used.

Integration of electric drive vehicles with the power grid-a new application for vehicle batteries

Abstract: Summary form only given as follows. Most personal transportation vehicles sit parked about 22 hours each day, during which time they represent an idle asset. Vehicles that incorporate electric propulsion could be utilized as power sources while parked because the drive systems include the fundamental elements for generating AC power. Utilizing idle vehicles to provide valuable electric power functions can produce a positive net revenue stream and create a powerful economic incentive to own an electrically-propelled vehicle. Production of valued power services from electrically-propelled vehicles has been demonstrated. The range of services is broad, and includes mobile AC power, backup power for homes or businesses, power generation during peak demand periods, and grid ancillary services such as spinning reserves, regulation, reactive power, and transmission stabilization. Most of these functions already have established economic value when procured from nonvehicular sources. Battery EVs and grid connected hybrid vehicles could provide the energy and power capabilities of their battery packs to the grid. On a daily basis, the battery energy throughput resulting from these grid services will be larger than the energy throughput resulting from driving. The income stream generated from the grid services is expected to more than cover the amortized wear-out costs of the battery for both grid services and driving. Because of the increased usage resulting from grid services, battery packs will have to be replaced more often for battery suppliers but the cost of the battery replacement will be covered by the value of the grid services provided for consumers and automakers. With vehicle-to-grid services, there is the potential to create a compelling new economic rationale for electric drive vehicles.

AC-LFR concept applied to modular photovoltaic power conversion chains

Abstract: Modular inverters are presented for grid-connected photovoltaic systems based on the loss-free resistor concept. The basic module consists of a cascade connection of a buck-boost converter operating in discontinuous conduction mode and a push-pull switching inverter. The DC power of the photovoltaic module is transferred by the buck-boost stage to the push-pull converter, which transforms this power into AC power compatible with grid connection. Maximum power point tracking is achieved by matching the panel impedance at the maximum power point and the buck-boost input impedance. Two alternatives for building modular structures for N panels are investigated. Experimental and simulation results of both modular alternatives are presented.

A modelling method for building-integrated photovoltaic power supply:

Abstract: Models of photovoltaic (PV) module electrical characteristics are well developed, because of the precise knowledge of the physics of semiconductor behaviour. The PV cell current-voltage characteristic is well known, and used in many models of array output. However, in many practical cases such as building-integrated photovoltaics, a model of power output only is required. Current-voltage revious researchers on which particular model should be used. This contrasts with the case of the diode model for I-V characteristics. In this work, an ef. ciency model of power output will be developed based on an adaptation of the established PV. fill factor method, and attempts are made to ground the irradiance and temperature characteristics in established theory in order to make a general PV power ef. ciency model. The model is validated using measured data from a 39.5-kW building-integrated PV array.

Islanding behaviour of grid-connected PV inverters operating under different control schemes

Abstract: This paper compares the islanding behaviour of different inverter implementations, which have current source or voltage source characteristics. Measurements were made on a number of commercially available inverters, and simulation models were developed to enable further investigation of the influence of the type of control system on islanding operation. Additionally, a modified active-frequency-drift detection method is presented which reduces the amount of distortion introduced to the grid compared with the conventional approach often described in the literature.

Design considerations for three-phase grid connected photovoltaic inverters

Abstract: This paper discusses the design considerations for three-phase inverters for grid connected photovoltaic systems. Specific performance considerations are addressed including topology trade-offs, efficiency trade-offs, and maximum power point tracking. Additionally, utility interconnect issues are examined including power quality and anti-islanding. Testing results are provided for the Xantrex PV series of inverter products. These systems operate with a variety of PV panels and are designed to meet the UL-1741 utility interconnection standard. Power levels are from 5 kW to 300 kW, and the output is a nominal 208 VAC. Experimental results showing successful operation are given for the 10 kW system. Testing was performed at the Sandia National Laboratories Photovoltaic Systems Evaluation Lab in Albuquerque, NM.