Showing papers on "Grid-connected photovoltaic power system published in 2000"

Control of parallel inverters in distributed AC power systems with consideration of line impedance effect

Abstract: The authors have developed a new control technique which allows paralleled inverters to share linear or nonlinear load in a distributed AC power supply system. This technique does not require control interconnections and automatically compensates for inverter parameter variations and line impedance imbalances. Experimental results are provided in the paper to prove the concept.

Development and Testing of an Approach to Anti-Islanding in Utility-Interconnected Photovoltaic Systems

Abstract: This report documents the development of an inverter control method that detects and avoids islanding in utility-interconnected photovoltaic installations. This method is applicable to single and multiple inverters connected to a single utility distribution line. The anti-islanding approach is described and its performance is demonstrated on both a theoretical basis and with results from tests conducted at Sandia National Laboratories and Ascension Technology, a division of Applied Power Corporation. It has been demonstrated that this approach is effective for single and multiple photovoltaic inverter installations for the special case where the inverter contains a version of anti-islanding software compatible with IEEE Std 929-2000.The report also describes the anti-islanding technique so that it can be incorporated into photovoltaic systems lacking this feature. A test procedure that ascertains whether an anti-islanding capability exists in a PV inverter is also presented. This page intentionally left blank

Past, present and future of grid connected photovoltaic- and hybrid-power-systems

Abstract: As a short introduction on the general development and forecast of world market in photovoltaics (PV) are presented. The general classification introduces grid connected, stand alone, large scale and roof-top PV-systems. The core of presentation concentrates on the development and trends of converters for grid connected PV-systems. The novel multi-string converter is introduced representing one of the major trends in PV system technology towards modular PV-system design based on string converter technology with low specific costs and optimal energy yield. A brief excursion into the area of hybrid power systems deals with the development of hybrid power system technology using some representative examples installed by SMA around the world. As one of the future trends in that area a new bi-directional battery-converter for a modularly-structured hybrid power system technology is introduced.

Using power line carrier communications to prevent islanding [of PV power systems]

Abstract: Islanding of grid-connected photovoltaic (PV) power systems jeopardizes personnel and equipment and must therefore be prevented. Existing islanding prevention schemes are undesirable because they fail for certain relatively common customer loads and when more than one PV power system is present, degrade PV power quality, reduce system efficiency, and increase system complexity. These problems can be overcome using power line carrier communications. (PLCC) and an inexpensive, purpose-designed receiver. The use of PLCC for islanding prevention is discussed. In this paper, including considerations for maximum anti-islanding effectiveness. Also, a low-cost receiver for a commercial PLCC system is described and demonstrated. This receiver demonstrates the feasibility of PLCC-based islanding prevention.

A grid-interactive photovoltaic uninterruptible power supply system using battery storage and a back up diesel generator

Abstract: This paper presents a practical implementation of a grid interactive photovoltaic uninterruptible power supply (UPS) system using battery storage and a back up diesel generator. The system incorporates 2.5 kWp of photovoltaic arrays, a 10 kVA power conditioning unit capable of operating in both inverting and charging modes, and a 300-Ah battery bank. Two such systems were installed in two Indian cities. The project was implemented using soft loans available in India through a World Bank Loan for photovoltaic market development. The system has been working satisfactorily since May 1997 and has demonstrated the capability of the system to provide uninterrupted power, demand side management function and load voltage stabilization in a grid which experiences frequent blackouts and under/over voltage problems. Some results from the field installation are also included in this paper.

Energy management uninterruptible power supply system

Abstract: A power system is provided in which a grid supplies electrical power to a load and in which backup power is provided from one of a generator and a dc storage device. The power system includes a standalone inverter having an input and an output. The output of the standalone inverter is connected to the load. The power system includes a grid parallel inverter having an input and an output. The output of the grid parallel inverter is connected to the grid. A dc bus is electrically connected to the input of the standalone inverter and to the input of the grid parallel inverter.

Method of operating a power supply system having parallel-connected inverters, and power converting system

Abstract: A method whereby a plurality of inverters (14) for converting DC power outputted from a DC power supply, such as solar cells (1) or fuel cells, to AC power are operated efficiently without being biased to particular inverters. The number of inverters (14) to be run is determined in correspondence with at least one output value of the DC output or AC output, and the determined number of inverters are selected and made to run from among the plurality of inverters (14) on the basis of a predetermined rule. In addition, a parallel-connected system is disclosed for enabling efficient and appropriate parallel-in operation by the use of inverters, with one of the inverters controlling the remaining inverters and effecting system interconnection protection.

Interconnection of a photovoltaic panels array to a single-phase utility line from a static conversion system

Abstract: This paper presents the analysis of a static conversion system for treatment of the solar energy from photovoltaic panels. This system is interconnected with the mains power supply, contributing to the generation of the electrical energy. The power structure is composed of a current-fed push-pull converter, a buck converter, and a current inverter. The main features of the system are: simple control strategy, robustness, lower harmonic distortion of the current and natural isolation. The principle of operation, design procedure and experimental results are presented.

Real-time maximum power point tracking for grid-connected photovoltaic systems

Abstract: The paper presents a model-based method for photovoltaic array maximum power point prediction. The method was tested successfully on a small grid-connected PV system. A three-phase IGBT-voltage-source inverter is used as the power conditioner and a DSP-controller is employed to perform real-time control and prediction functions. The system and experimental results obtained are presented in the paper.

Photovoltaic converter system suitable for use in small scale stand-alone or grid connected applications

Abstract: Of the commercially-available solutions for the conversion of energy from photovoltaic arrays into a usable form, a large number consist of systems which have been developed for a dedicated application and are thus very inflexible. Those that are available as a generic module for use in a variety of environments are often restricted to a single mode of operation, for example utility supply only. A generic modular photovoltaic power conversion system is presented, aimed at single-phase applications which can supply passive AC and DC loads with a regulated voltage or by way of a maximum power tracking system with the maximum power available from the array. In addition a live AC load such as the utility can be supplied with maximum array power. The system is small, light and can be constructed from readily available components.

Power supply system for distributed source

Abstract: PROBLEM TO BE SOLVED: To provide a power supply system for a distributed source, installing a distributed power source system in a plot of a power user by a power supply provider to perform power supply to the user, diagnosis of system operation, etc. SOLUTION: This system includes a distributed power source system 16, supplying power of commercial frequency to a load 8 of a specific user, additionally performing system linkage and a system managing means 15 connected to each distributed power source system via a communication network 12; the distributed power source system 16 includes a solar battery 1, a fuel cell 2, a storage battery 3, a power converter means 4 for system-linking power output from these power-generating means, a power condition monitor means 6, and a system control means 7; and the system control means 7 communicates operating information of the distributed power source system 16 to the system managing means 15 and controls the operating condition of the power converter means 4, according to the indication received from the system-managing means 15.

Grid-linked power supply

Abstract: A grid-linked power supply is described. An inverter, at least one distributed energy source to meet normal, non-peak power demand, a connection to a public utility grid to meet peak power demand requirements, and a converter for regulating delivery of power from the distributed energy source or the public utility grid are connected by bus lines. A topology for the grid-linked power supply has an inverter and a DC/DC converter that is connected to the distributed energy source. The inverter and converter are connected by bus lines, and a bias voltage is provided to select drawing power from the distributed energy source or the public utility grid.

Analysis of utility interactive photovoltaic generation system using a single power static inverter

Abstract: This paper presents the analysis of a static conversion system for treatment of the solar energy from photovoltaic panels. This system is interconnected with the mains power supply, contributing to the generation of the electrical energy. The power structure is composed of a current-fed push-pull converter, a buck converter, and a current inverter. The main features of the system are: simple control strategy, robustness, lower harmonic distortion of the current and natural isolation. The principle of operation, design procedure and experimental results are presented.

Technologies for the new millennium: photovoltaics as a distributed resource

Abstract: As we enter the new millennium, photovoltaics (PV) is emerging as an important distributed resource. PV gives both the benefits of a distributed resource and a clean power source. Because PV can be located at both residential and commercial locations, it can be used to reduce peak demand when its output is properly matched with load usage. It can also improve asset utilization by requiring less large capital generation spending and delaying some equipment replacement. With the price of some grid-connected PV systems expected to reach $3/W in the next 5 years, PV will become an economical option for distributed power generation. One of the most important aspects of establishing PV as a distributed resource is standardizing the requirements for grid connection. IEEE Standards Coordinating Committee (SCC) 21 has published IEEE Std 929 "Recommend Practice for Utility Interface of Photovoltaic Systems." This recommended practice details power quality, safety, and protection requirements for connection to the utility grid. This paper describes what types of PV systems are available, what the benefits are for PV systems, and what the interconnection issues and solutions are for using PV as a distributed resource.

Photovoltaic power generation apparatus and control method thereof

Abstract: A photovoltaic power generation apparatus having a plurality of power converters, respectively connected to a plurality of solar battery arrays, for converting direct-current power generated by the solar battery arrays to alternating-current power so as to provide the alternating-current power to a commercial power system. The photovoltaic power generation apparatus is so constructed that the plurality of power converters do not simultaneously suspend operation when an abnormal state is detected, in order to prevent generation of an electrical stress or reduction of the power generation amount caused by simultaneous operation suspension of the power converters or repeated operation suspension and operation resume. When the power generation amount of each solar battery array is different, a power converter connected to the solar battery array of the smallest power generation amount is set in the first-to-suspend condition.

Maximum output control of photovoltaic (PV) array

Abstract: A photovoltaic (PV) system output depends on environmental parameters such as the solar insolation and the PV module temperature. If it is possible to predict the maximum power point under the outdoor environment and to operate at that point, the PV system can generate the maximum output every time. In this paper, a maximum power point control method that maximizes the output of a PV array is proposed. This method determines the maximum output operation point from the I-V characteristics introducing empirically the effects of the solar insolation and the module temperature. The authors derived two main parameters from this analysis; one is the power gain G, and another is the environmental operation parameter X. At the operation point determined by this method, G becomes larger than that of under the same environmental conditions. G becomes large with the increase of X, and the large X mainly means low solar insolation. The characteristics of PV module which will supply more power especially at large X should satisfy the following points; the fill factor of the module should be lower and the short circuit current of the module should be larger than those of arrays currently available in the market.

Control and interfacing of bi-directional inverters for off-grid and weak grid photovoltaic power systems

Abstract: Photovoltaics (PV) is one of the most cost-effective, reliable and durable energy sources to provide electricity in remote areas not connected to a grid. In some parts of the world grid-connected PV systems also help utilities to alleviate the need to install or operate costly power plants by supplementing and meeting high peak hours of electricity demand. The key to the widespread application of PV power plants is the availability of efficient and low cost power electronic equipment. A photovoltaic generator is a current source depending on solar radiation intensity and temperature. Simple charge controllers and DC-DC converters with maximum power point tracking are used to interface solar panels with batteries. There are different types of inverters for converting the DC power from batteries and/or solar panels to AC power. This paper describes the application of bi-directional inverters for remote area power systems using PV, diesel generators and battery storage. Use of bidirectional inverters to improve power quality and reliability in weak grids is also presented.

A new solar energy conversion scheme implemented using grid-tied single phase inverter

Abstract: A new utility-connected photovoltaic inverter is presented in this paper. Simulation and implementation of the new solar energy conversion scheme has been demonstrated. The solar energy conversion unit consists of an array of solar panels, DC-DC converter, single-phase inverter, and AC mains power source. The inverter converts DC power generated by the photovoltaic cells into AC power and provides it to the load connected to the utility line, when the photovoltaic power is greater than the load; the excess power is fed to the utility line through a reverse power flow. With this new approach we can reduce the use of the power from the grid and even make a contribution to the mains supply. Simulation and experimental results are provided to demonstrate the effectiveness of the design.

Dynamic stability analyses of a photovoltaic array connected to a large utility grid

Abstract: This paper proposes a novel approach based on the eigenvalue method to investigate both transient and steady-state performance of a photovoltaic (PV) system connected to a large utility grid. A DC-to-DC boost converter is employed to step up the output DC voltage of the PV array. A DC-to-AC single-phase inverter is utilized to convert the higher DC voltage from the boost converter's output to the three-phase balanced voltages of utility's distribution system. The dynamic equations of the studied PV-utility's system are derived to examine the dynamic characteristics of the studied system under different operating conditions. The transient responses of the studied PV under different operating conditions are also examined. It can be concluded from the simulated results that the proposed methods are effective to explore the transient performance and dynamic characteristics of the studied combined PV-utility system under different disturbance conditions.

A novel high performance utility interactive photovoltaic inverter system

Abstract: This paper presents a novel photovoltaic inverter system that can achieve not only a sinusoidal AC output current synchronized with the utility line voltage but also a generation power control on each of the photovoltaic modules connected in series. The proposed inverter system is composed of a half bridge inverter and novel generation control circuit that can compensate for the reduction in output power caused by the shadow covering the photovoltaic modules. The proposed generation control circuit can make the operation point on each of the photovoltaic modules correspond to the maximum power point individually, and the generation power control on each of the photovoltaic modules is executed only by detecting the total output power of the photovoltaic system. Furthermore, the low frequency ripple voltages on the series-connected DC bus capacitors caused by the utility interactive inverter operation are reduced owing to the effect of the generation control circuit. Hence, the average value of photovoltaic generation power is much increased. The effectiveness of the proposed system is confirmed experimentally and through simulation results.

Modeling and operation of a 10 kW photovoltaic power generator using equivalent electric circuit method

Abstract: The output power of a photovoltaic power generator system (PV system) changes continuously as it strongly depends on the weather condition (solar radiation and temperature). Large fluctuations of output of PV system result in fluctuation and hence of harmonics in the inverter output. The PV systems are usually connected to the power grid lines, therefore, it is necessary to simulate the effects of the PV power systems on the commercial distribution line. In this paper, the authors have modeled a 10 kW PV module using current-voltage characteristic of a PV module by estimating its equivalent electrical circuit parameters.

Investigation of ground-fault protection devices for photovoltaic power system applications

Abstract: Photovoltaic (PV) power systems, like other electrical systems, may be subject to unexpected ground faults. Installed PV systems always have invisible elements other than those indicated by their electrical schematics. Stray inductance, capacitance and resistance are distributed throughout the system. Leakage currents associated with the PV modules, the interconnected array, wires, surge protection devices and conduit add up and can become large enough to look like a ground-fault. PV systems are frequently connected to other sources of power or energy storage such as batteries, standby generators, and the utility grid. This complex arrangement of distributed power and energy sources, distributed impedance and proximity to other sources of power requires sensing of ground faults and proper reaction by the ground-fault protection devices. The different DC grounding requirements (country to country) often add more confusion to the situation. This paper discusses the ground-fault issues associated with both the DC and AC side of PV systems and presents test results and operational impacts of backfeeding commercially available AC ground-fault protection devices under various modes of operation. Further, the measured effects of backfeeding the tripped ground-fault devices for periods of time comparable to anti-islanding allowances for utility interconnection of PV inverters in the United States are reported.

Solar generator and its control system

Abstract: PROBLEM TO BE SOLVED: To provide a control system, which can readily clear up and detect the drop of the generation capacity of a solar generator and the cause, can detect the abnormal section of that device, and further synthetically controls the working state of two or more solar generators, the abnormality of the device, and others, using a communication line. SOLUTION: This is a solar generator which is equipped with a solar cell 1, a power conditioner 2 having at least a converter 25 for converting the DC power from the solar cell 1 into AC, and a storage part 28. Further, this is equipped with a quantity-of-generated-power measuring means 22 for measuring the quantity of power generated by the solar cell 1, and an illumination meter 3 for measuring the quantity of solar radiation. The measurement results of the quantity of generated power and the quantity of solar radiation are stores as times-series data in a storage 28.

Design, development and performance of a 50 kW grid connected PV system with three phase current-controlled inverter

Abstract: In order to investigate the system performance for grid connection, a 50 kW photovoltaic power generation system including a three-phase DC/AC inverter is designed, made and constructed. This paper describes the system design and the performance of a 50 kW grid-tied PV plant, which consists of solar cells, DC/AC inverter, utility grid. Especially, the control scheme of a three phase current-controlled PWM inverter using d-q axis transformation is presented, and then the experimental results show that the proposed system has high efficiently stable behavior with a unity power factor in utility-interactive operation. Also the field test results show that the system utilization rate is about 13.4%.

A three-phase grid-connected PV system

Abstract: This work deals with the design and laboratory implementation of a static converter for grid connected PV power systems. The converter is made zip of a DC-DC boost structure controlled by a neural network and a three-phase voltage source inverter (VSI) with optimised sinusoidal PWM strategy. The DC-DC boost converter allows the PV system to operate at maximum power point. The three-phase VSI provides the necessary voltage and frequency for interconnection to the grid. The optimised switching strategy used guarantees harmonics elimination at the VSI output voltage up to the 17/sup th/ harmonic. The DC-DC and DC-AC structures use IGBT as power switches, and the system control signals are generated by a 80X51 microcontroller-based circuit Experimental results are shown to access the performance of the system PV system and its behaviour at the interconnection point.

An improved approach to reduce harmonics in the utility interface of wind, photovoltaic and fuel cell power systems

Abstract: In this paper, an improved approach to reduce harmonics in the utility interface of wind, photovoltaic and fuel cells power systems is presented. The approach is based on circulating third harmonic current injection to reduce utility line current harmonics in SCR converters. In this paper, a new injected current shape is computed from analysis to achieve sinusoidal utility line currents. A controllable single switch boost converter connected in shunt is employed to circulate the new injected current shape. A method to implement the proposed approach under varying load conditions is shown. Analysis, design, limitations, simulation and experimental result are presented.

Solar power generator system with power storage

Abstract: PROBLEM TO BE SOLVED: To provide a solar power generator system which can reverse the flow of the excessive generated power flow to the grid while normally avoiding power flowing out to the grid. SOLUTION: In a solar power generator/storage system provided with a bilateral converter to control the battery, the bilateral converter is controlled so that the usable power is not less than required when making the excessive power flow reverse to the grid. COPYRIGHT: (C)2002,JPO

A multi-function photovoltaic power supply system with grid-connection and power factor correction features

Abstract: A conventional photovoltaic (PV) inverter system with grid-connection feature is usually composed of a full-bridge inverter and a microprocessor. The PV system is idle when there is no insolation (at nighttime). To optimize the use of the existing components, this paper proposes a multi-function PV power supply system with grid-connection, power factor correction and lamp-driving features. With the synchronous switch technique, pulse-width modulation, additional relays and components, an ordinary inverter system can function alternately as an electronic ballast with power factor correction at nighttime. Thus, the power switches, driving circuits and the microprocessor in such a multi-function system are optimally used. Computer simulation results and experimental measurements have verified the feasibility of the proposed system.

An improved method for controlling an EDLC-battery hybrid stand-alone photovoltaic power system

Abstract: Stand-alone photovoltaic power systems are potential power sources for wireless and optical telecommunications equipment and solar home systems. For these systems to be practical, the batteries used to store the power must have a long lifetime. We have proposed a stand-alone photovoltaic power system that uses an electric double-layer capacitor (EDLC) with lead-acid batteries. This system reduces the number of battery charge-and-discharge cycles and maintains the optimal charging voltage by using EDLC discharge power. In this paper, we describe the system's circuit configuration, operation, and conversion efficiency analysis. An improved method is described for controlling the system. It increases the system's power-conversion efficiency by keeping the capacitor voltage high. Simulation of a 250 W photovoltaic system showed that it reduces the power conversion losses in the system by about 35%.