Showing papers on "Grid-connected photovoltaic power system published in 2001"

Development of a microcontroller-based, photovoltaic maximum power point tracking control system

Abstract: Maximum power point tracking (MPPT) is used in photovoltaic (PV) systems to maximize the photovoltaic array output power, irrespective of the temperature and irradiation conditions and of the load electrical characteristics. A new MPPT system has been developed, consisting of a buck-type DC/DC converter, which is controlled by a microcontroller-based unit. The main difference between the method used in the proposed MPPT system and other techniques used in the past is that the PV array output power is used to directly control the DC/DC converter, thus reducing the complexity of the system. The resulting system has high-efficiency, lower-cost and can be easily modified to handle more energy sources (e.g., wind-generators). The experimental results show that the use of the proposed MPPT control increases the PV output power by as much as 15% compared to the case where the DC/DC converter duty cycle is set such that the PV array produces the maximum power at 1 kW/m/sup 2/ and 25/spl deg/C.

Novel maximum-power-point-tracking controller for photovoltaic energy conversion system

Abstract: A novel maximum-power-point-tracking (MPPT) controller for a photovoltaic (PV) energy conversion system is presented. Using the slope of power versus voltage of a PV array, the proposed MPPT controller allows the conversion system to track the maximum power point very rapidly. As opposed to conventional two-stage designs, a single-stage configuration is implemented, resulting in size and weight reduction and increased efficiency. The proposed system acts as a solar generator on sunny days, in addition to working as an active power line conditioner on rainy days. Finally, computer simulations and experimental results demonstrate the superior performance of the proposed technique.

Generation control circuit for photovoltaic modules

Abstract: Photovoltaic modules must generally be connected in series in order to produce the voltage required to efficiently drive an inverter. However, if even a very small part of photovoltaic module (PV module) is prevented from receiving light, the generation power of the PV module is decreased disproportionately. This greater than expected decrease occurs because PV modules which do not receive adequate light cannot operate on the normal operating point, but rather operate as loads. As a result, the total power from the PV modules is decreased if even only a small part of the PV modules are shaded. In the present paper, a novel circuit, referred to as the generation control circuit (GCC), which enables maximum power to be obtained from all of the PV modules even if some of the modules are prevented from receiving light. The proposed circuit enables the individual PV modules to operate effectively at the maximum power point tracking, irrespective of the series connected PV module system. In addition, the total generated power is shown experimentally to increase for the experimental set-up used in the present study.

A battery management system for stand-alone photovoltaic energy systems

Abstract: It is estimated that about 80% of all photovoltaic (PV) modules are used in stand-alone applications. Continuous power is obtained from PV systems by using a storage buffer, typically in the form of a lead acid battery. Batteries used in PV applications have different performance characteristics compared with batteries used in more traditional applications. In PV applications, lead acid batteries do not reach the cycle of lead acid batteries used in other applications such as uninterruptible power supplies or electric vehicles. The shortened battery life contributes significantly to the costs of a PV system. In some PV systems the battery accounts for more than 40% of the life cycle costs. An increase in the lifetime of the battery will result in improved reliability of the system and a significant reduction in operating costs. The life of a lead acid battery can be extended by avoiding critical operating conditions such as overcharge and deep discharge. This paper presents a battery management system for such applications.

Local area grid for distributed power

Abstract: The invention in the simplest form is a system for managing distributed power sources connected to a power grid. The present invention manages power flow to/from the power grid whether for a stand-alone power sourece or for local area utility grid or microgrid. When two or more power sources are interconnected by the local grid, each source has a power conditioning unit and a circuit breaker manager for controlling and regulating the electric flow to/from the grid. The individual power sources are able to independently draw power from the grid when required without extensive master control schemes. In a preferred embodiment the power sources are reformer equipped fuel cells and the heat from the fuel cell is used as a heat source for efficiency.

Power converting apparatus, control method therefor, and solar power generation apparatus

Abstract: The object is to reliably detect a ground fault of a solar battery. To detect a ground fault position to take an efficient measure against the ground fault, DC power input from a solar battery is converted into AC power and supplied to a system. In a system interconnection inverter (utility connected inverter) having non-insulated input and output, the input voltage of a converter circuit and/or the intermediate voltage between the converter circuit and an inverter circuit are varied to control the potential to ground at each portion of the solar battery to a value other than a value close to zero.

Energy management system which includes on-site energy supply

Abstract: An energy management system includes one or more electric power generators (14) located at or near a consumer's premises (10), to provide power which is dedicated to the needs of that consumer The power provided by the on-site generators (14) complements that which is delivered via a centralized power grid network (12) In the event that the power grid (12) is disabled, or is otherwise unable to provide adequate power to the consumer (10), the on-site generators (14) are switched to provide power to critical equipment In one embodiment, a computer-driven control facility (18) selectively actuates the on-site generator (14) to intelligently arbitrage between the locally generated power and that which is provided via the grid network, based on a variety of factors The instantaneous cost of power supplied via the grid network is compared against stored costs of operating the on-site generators, such as the price of fuel required to run the generators, maintenance expenses, other types of service and installation expenses, and finance charges When these costs are less than the charges for the power provided by the grid network, the central control system actuates the on-site generators, to partially or totally replace power delivered via the grid Other factors are also employed in the decision whether to activate the on-site generators, such as data relating to weather conditions and peak usage periods Historical data regarding the consumer's power usage is employed to predict times when the usage requirements are likely to be high, and thereby actuate the generators to supplement or replace the power provided from the grid

Control of multiple fuel cell power plants at a site to provide a distributed resource in a utility grid

Abstract: A site management system (11) is provided for a power system (8) at site in a utility distribution grid (10). The power system (8) includes multiple fuel cell power plants (18) and one or more loads (14), for selective connection/disconnection with the grid (10). The site management system (11) operates to control the power plants (18) in an integrated manner, alternatively in a grid connected mode and in a grid independent mode. The utility is able to view and treat the multiple power plants (18) at the site as a single, unified distributed resource on the grid (10). The site management system (11) provides signals representative of the present power capability (Kw Capacity—88) of each of the power plants (18), and a signal (Total Kw Capacity—95) representative of the total present power capability at the site. These power representations are used to appropriately assign power dispatch loadings to the respective fuel cells (18) in the grid connected mode and in the grid independent mode. The site management system (11) also functions in the grid independent mode to monitor present demand of the loads (14) and, if necessary, to shed loads (14) in accordance with a predetermined schedule.

Solar power management system

Abstract: A solar power management system includes a plurality of photovoltaic cell panels, and a solar power cell manager coupled to the photovoltaic cell panels. The solar power cell manager includes an input stage for combining current draws from the photovoltaic cells, and a load manager in communication with the input stage for managing the combined current draw.

A novel AC photovoltaic module system based on the impedance-admittance conversion theory

Abstract: A novel photovoltaic (PV) power generation system based on impedance-admittance conversion theory is described in this paper. AC photovoltaic module systems (AC modules) have attracted interest for their application in PV power generation systems. An AC module has an integrated inverter that allows the module to supply AC power to the utility power line. One distinctive feature of system proposed in this paper is that the output current supplied to the utility line has a similar waveform to the utility voltage, and is proportional only to the output voltage of the voltage source inverter on the AC module. This effect is achieved through use of the impedance-admittance conversion theory, by which the voltage source is converted to the current source, and vice versa. Therefore, in the proposed system, the output current supplied to the utility line can be controlled without being affected by the utility line voltage. Hence, it is not necessary to use current feedback control. The effectiveness of the proposed system is confirmed through simulations and experiments.

Integration of Electric Drive Vehicles with the Electric Power Grid -- a New Value Stream

Abstract: Battery-electric vehicles and grid-connected hybrid vehicles rely on the power grid for energy -- they have to plug in to charge their batteries. With power alerts and blackouts a recent reality in California, it is easy to conclude that the energy requirements of grid-connected electric vehicles will make the energy crisis worse. Actually, quite the opposite may be true. With a bi-directional grid power interface, virtually any vehicle that can plug into the grid can potentially provide beneficial support to the grid. Battery electric vehicles can support the grid exceptionally well by providing any of a number of functions known collectively as ancillary services. These services are vital to the smooth and efficient operation of the power grid. A hybrid vehicle can provide ancillary services, and can also generate power. Fuel cells are already being commercialized for small stationary power sources, so a vehiclemounted fuel cell could also serve as a vehicle-to-grid power source. Sharing power assets between transportation and power generation functions can create a compelling new economics for electrically-propelled vehicles.

Novel inverter topologies for single-phase stand-alone or grid-connected photovoltaic systems

Abstract: Photovoltaic and battery systems often operate in small stand-alone or grid-connected applications, where the generator voltage is lower than the grid voltage. To boost the voltage up to the grid level a further element, either a DC/DC converter or 50 Hz transformer, is connected in series with a PWM inverter. To reduce the high cost of such low power systems, the costs of the power electronics should be minimized. In this paper, several new low-cost inverters with and without HF-transformers are presented. Simulation and experimental results of their operation and control for stand-alone as well for grid-connected applications are discussed.

Design and operation of grid-connected photovoltaic system with power-factor control and active islanding detection

Abstract: An approach to power-factor control and islanding detection of a grid-connected photovoltaic system is proposed. With the designated control circuit, deviation at the output of the inverter can be observed. Coupled with the algorithm developed, this deviation serves as a useful aid to detect islanding more effectively. The proposed method has been tested through different scenarios, including the loss of grid and operation in parallel. Simulation studies and hardware circuits were both made to validate the effectiveness of the method. With the test results they help consolidate the feasibility and practicality of the approach for the applications considered.

Method and apparatus for a solar power conditioner

Abstract: A method and apparatus for supplementing electrical power production during peak demand power consumption is presented. A solar power conditioner converts DC electrical power provided by solar panels (or otherwise) to AC power and uses this to supplement main AC electrical power generated by a power utility (or otherwise) when needed. Both the DC power and the main AC power are digitalized by analog to digital (A/D) converters and continuously monitored by a central processor (CPU). The CPU aims to match the generated AC power of the inverter to that of the main AC power and, after tripping a breaker, supplements the main AC power with that of the converted power provided by the solar panels. In such a supplementary role, the solar power conditioner can be inserted into a utility's distributed power grid.

Photovoltaic energy processing for utility connected system

Abstract: In this work the study of a system for exploitation of the energy provided from photovoltaic panels is presented. Through this system the energy is converted, adapted and injected into the electric utility grid. In this way an amount of electrical energy consumed by one given customer is produced, having the advantage that it can be installed easily in the proper place of consumption, dispensing with the use of a transmission system. The current has sinusoidal shape in the system output, taking as reference the electric grid, obtaining low total harmonic distortion, thus the quality of the electric energy is preserved. Moreover, other requirements are achieved, as the galvanic isolation between the panels and the utility grid, and the protection against energy failure. The power stages, the control strategy, the system's operation principle, the simulation and experimental results acquired with the prototype constructed in the laboratory are presented.

Photovoltaic Power Systems and the National Electrical Code: Suggested Practices

Abstract: This suggested practices manual examines the requirements of the National Electrical Code (NEC) as they apply to photovoltaic (PV) power systems. The design requirements for the balance of systems components in a PV system are addressed, including conductor selection and sizing, overcurrent protection ratings and location, and disconnect ratings and location. PV array, battery, charge controller, and inverter sizing and selection are not covered, as these items are the responsibility of the system designer, and they in turn determine the items in this manual. Stand-alone, hybrid, and utility-interactive PV systems are all covered.

Inverter controlled, parallel connected asynchronous generator for distributed generation

Abstract: A distributed generation system is disclosed that is capable of conditioning power from a utility grid, providing backup power in the event the utility grid fails, and exporting excess power to the utility grid. The system comprises an engine coupled to an asynchronous generator, an energy storage device, an engine controller capable of managing the engine and controlling its torque or speed or power, and an inverter for generating an AC output and also capable of controlling the frequency and voltage of the generator to match the frequency of a coupled utility grid.

Evaluation of LFC capacity for output fluctuation of photovoltaic power generation systems based on multi-point observation of insolation

Abstract: The output of a photovoltaic power generation system (PV system) fluctuates depending on weather conditions. Large-scale introduction of PV systems may cause some difficulties in the operation of an electric power system. The evaluation of the influence of PV systems on the power system operation should consider the smoothing effect of the outputs by the dispersed introduction of PV systems. This paper discusses the LFC (load frequency control) capacity for output fluctuation of PV systems based on the insolation data simultaneously observed at 5 points around Nagoya, Japan. As a result, when the weather was clear but clouds moved frequently, the capacity. for LFC based on the regional averaged insolation was evaluated less than a half of that evaluated by the insolation at one point. Furthermore, LFC capacity might be dominated by the speed factor rather than the magnitude factor of load fluctuation including PV system's output when a large capacity of PV systems is installed.

Solar power generation system having storage battery

Abstract: PROBLEM TO BE SOLVED: To provide an optimum system which can reduce peak power demand, using a small storage battery. SOLUTION: A solar power generation system, which is linked to a power system, supplies the power generated at a solar cell device to an inverter device for conversion to alternating current, and feeds it to a power consumption part, comprises a storage battery to charge power from the solar cell device, and a changeover control means to output the power from the solar cell device to the storage battery or to the inverter device upon changing over; and supplies the power to the inverter device in addition to generated energy from the solar cell device, by controlling to charge the storage battery with one or more of power selected from the generated power by the solar cell device during off-peak time of power demand after sun rising or power from the power system during night time, and by controlling discharge of energy stored in the storage battery corresponding to a fluctuation curve of the power demand in a particular time zone the power demand is high.

Generator control system to accommodate a decrease in a power grid voltage

Abstract: A system includes a generator and a circuit. The generator is coupled to provide power to a power grid. The circuit is coupled to the generator and is adapted to use a scheme to detect a shut down of the power grid and prevent the generator from providing power to the power grid in response to the detection of the shut down of the power grid. The circuit is also adapted to receive an indication to modify the scheme and modify the scheme based on the indication.

Uninterruptible power generation system

Abstract: A power delivery system (102) including a primary power bus (103) for transferring power to the facility (100) from on-site generators (104), and a secondary power bus (106) for transferring power to the facility (100) from a utility (108). The system (102) further includes a static disconnect switch (110) capable of quickly isolating the facility (100) from the utility power grid, and a controller (112) for controlling the overall operation of the power delivery system. In a normal mode of operation, the utility (108) supplies power approximately in the mount of the single largest load in the facility (100), with the remaining power being supplied by the on-site generators (104). If one or more of the generators (104) goes off-line, the power supplied by the utility drops below a predetermined level, the static disconnect switch (112) quickly opens and islands the facility (100), whereupon 100 % of the power is supplied by the generators (104).

Analysis and control of PWM converter with V-I output characteristics of solar cell

Abstract: In this paper, the virtual implementation of a solar cell (VISC) was proposed to solve problems such as the reappearance and repetition of situations in photovoltaic power system experiments, and to achieve reliable experimental results on PV power systems. VISC emulates the solar cell output characteristics, and can substitute for solar cells in laboratory experiment systems. To realize the VISC, a mathematical model of solar cell for the driving power converter was studied and the buck and buck-boost power converters were compared from the viewpoint of the tracking error of the characteristic curve of solar cells using computer simulation.

A novel simulation method for PV power generation systems using real weather conditions

Abstract: In PV power generation systems, huge system apparatus are needed in order to verify the effect of system efficiency and stability considering the size of solar panel, the sort of converter and the load condition. Also, under the same weather and load conditions, it is almost impossible to compare a certain MPPT control scheme with another. In order to remedy the above, one must realize the transient simulation of PV power systems using real field weather conditions. In this paper, the authors introduce how to apply real field weather conditions to EMTP and EMTDC, which are the most generalized transient analysis simulators. First of all, a solar cell is simulated with a V-I characteristic equation of the solar cell, and real field data of weather conditions are interfaced to EMTP and EMTDC programs using a Fortran program interface method. As a result, comparing real data of a PV panel and the simulated data, the authors obtained hopeful answers and made the simulation of PV power generation system much closer to reality. As a merit of using this proposed simulation method, stability and efficiency analyses according to various MPPT controls are possible under the same weather conditions.

Solar cell module, photovoltaic power generation system and method of implementing the same

Abstract: PROBLEM TO BE SOLVED: To provide a solar cell module whose arrangement design, wiring design and construction to a roof face are simplified, by which the roof face can be used effectively, which can be executed to the roof face in a small area, which restrains the volume of a cable and which can simplify a connecting operation inside a connection box, to provide a photovoltaic power generation system, and to provide a method of implementing the photovoltaic power generation system. SOLUTION: The solar cell module is used for the photovoltaic power generation system, in which a plurality of solar cell modules are connected in parallel and which comprises an interconnection used to integrate their power generation outputs. A connection part for their parallel connections is installed at the inside of the solar cell module. COPYRIGHT: (C)2002,JPO

Solar cell power supply system

Abstract: PROBLEM TO BE SOLVED: To effectively utilize a generated power at a low output. SOLUTION: When the generated power of a solar battery is discriminated by a discrimination circuit 504 that it exceeds a predetermined value, charging by a charging circuit 501 is invalidated; and the generated power of the solar battery 1 is outputted to an interconnection inverter 4 via a step-up chopper 3, and the power stored in a storage battery 502 is outputted to the interconnection inverter 4 via a step-up/step-down chopper 503; and the output power of the step-up chopper 3 or the step-up/step-down chopper 503 is fed to a power supply system 6 or a load 7, upon converting to AC power by the interconnection inverter 4. When the generating power of the solar battery 1 is discriminated that it is the predetermined value or lower, operation of the step-up chopper 3 is stopped, and the generating power of the solar battery 1 is stored in the storage battery 502. COPYRIGHT: (C)2003,JPO