Showing papers on "Power optimizer published in 1998"

Implementation of a DSP-controlled photovoltaic system with peak power tracking

Abstract: Photovoltaic systems normally use a maximum power point tracking (MPPT) technique to continuously deliver the highest possible power to the load when variations in the insulation and temperature occur. It overcomes the problem of mismatch between the solar arrays and the given load. A simple method of tracking the maximum power points (MPPs) and forcing the system to operate close to these points is presented. The principle of energy conservation is used to derive the large- and small-signal model and transfer function. By using the proposed model, the drawbacks of the state-space-averaging method can be overcome. The TI320C25 digital signal processor (DSP) was used to implement the proposed MPPT controller, which controls the DC/DC converter in the photovoltaic system. Simulations and experimental results show excellent performance.

Study of maximum power tracking techniques and control of DC/DC converters for photovoltaic power system

Abstract: As the electric power supplied by solar arrays depends on the insolation, temperature and array voltage, it is necessary to control the operating points to draw the maximum power of the solar array. The object of this paper is to investigate the maximum power tracking algorithms which were often used to compare the tracking efficiencies for the system operating under different controls. Besides, different type DC/DC converters were designed to evaluate the converter performance. A simple method which combines a discrete time control and a PI compensator is used to track the maximum power points (MPPs) of the solar array. The implementation of the proposed converter system was based on a digital signal processor (DSP) and the experimental results are presented.

Performance optimization for doubly-fed wind power generation systems

Abstract: Significant variation of the resource kinetic energy, in the form of wind speed, results in substantially reduced energy capture in a fixed speed wind turbine. In order to increase the wind energy capture in the turbine, variable speed generation (VSG) strategies have been proposed and implemented. However, that requires an expensive AC/AC power converter which increases the capital investment significantly. Consequently doubly-fed systems have been proposed to reduce the size of the power converter and thereby the associated cost. Additionally, in doubly-fed systems, at a fixed operating point (power and speed), power flow can be regulated between the two winding systems on the machine. This feature can be utilized to essentially minimize losses in the machine associated with the given operating point or achieve other desired performance enhancements. In this paper, a brushless doubly-fed machine (BDFM) is utilized to develop a VSG wind power generator. The VSG controller employs a wind speed estimation based maximum power point tracker (MPPT) and a heuristic model based maximum efficiency point tracker (MEPT) to optimize the power output of the system. The controller has been verified for efficacy on a 1.5 kW laboratory VSG wind generator. The strategy is applicable to all doubly-fed configurations, including conventional wound rotor induction machines, Scherbius cascades, brushless doubly fed machines, and doubly-fed reluctance machines.

Control strategy for grid-connected DC-AC converters with load power factor correction

Abstract: The paper presents the modelling, analysis and design of a pulse width modulation voltage source inverter (PWM-VSI) to be connected between a DC source, which is supplied from a photovoltaic (PV) array and the AC grid. The control algorithm of the PWM-VSI applies the concepts of the instantaneous p-q (real-imaginary) power theory. The objective is to show that, with an adequate control, the converter can transfer the DC energy from PV array and improve the power factor (and the power quality) of the electrical system. Some design considerations are also discussed. A digital simulation and measurements on a small prototype model verified the feasibility of the proposed control method.

Novel solar cell power supply system using the multiple-input DC-DC converter

Abstract: Recently, clean electric power generation systems have attracted a great deal of social attention to exploit clean energy resources such as solar arrays, wind generators, fuel cells, etc. In this case, the multiple-input DC-DC power converter is useful to combine the several input power sources and to supply the regulated output voltage for the load. The novel solar cell power supply system using the buck-boost type two-input DC-DC converter is proposed, in which the solar array and the commercial AC line are exploited as power sources and they are combined by the two input windings of the energy-storage reactor. Also, its operation principle and performance characteristics are discussed. Furthermore, the solar cell optimum operating point tracker is proposed and examined. It is confirmed by the experiment that the proposed solar cell power supply system has the excellent performance characteristics.

High efficiency lighting system

Abstract: A high efficiency lighting system maintains normal lighting conditions by lighting fixtures requiring DC electrical power. A power control device receives AC electrical power from a public utility converts AC power to DC power and delivers low voltage DC electrical power to lighting fixtures. A standby battery is provided to maintain power during power outages. Optionally, a photovoltaic DC electrical power source may be connected to the power control device, to provide alternate DC electrical power. In a further embodiment, a gas driven cogenerator unit may supply DC electrical power.

A fuzzy logic based photovoltaic peak power tracking control

Abstract: This paper describes the analysis, modeling and implementation of a fuzzy based photovoltaic peak power tracking system. The maximum power of a photovoltaic system changes with temperature, solar intensity and load. An analytical model is built for the solar cell on the basis of the manufacturer characteristics. The solar panel is integrated with the converter model and a fuzzy algorithm is developed so as to perform an on-line search procedure to track the maximum power continuously. The system is implemented by an inexpensive RISC microcontroller. Experimental results have shown excellent performance, robustness with parameter variation, modularity for parallel operation at higher power, and ready to retrofit existing installations.

Network node with internal battery backup

Abstract: A method and apparatus for providing uninterrupted DC power for network nodes. The uninterrupted DC power is derived from modular, stackable uninterruptible power supplies that fit within the housing of the network node. Because the battery of the uninterruptible power supply is charged from a DC output of a main power supply, only one AC/DC power converter is required. A high degree of efficiency is therefore obtained.

Solar power generation inverter device

Abstract: PROBLEM TO BE SOLVED: To improve the use efficiency of power at the time of independent operation and low output linking operation by stably executing the maximum power point tracking control in spite of the large change of sunshine. SOLUTION: A controller 19 receives a limit signal from a limit circuit 60 and limits a reference current value ID1* in the case of VD2L*

An artificial neural network-based real time maximum power tracking controller for connecting a PV system to the grid

Abstract: This work deals with the application of a neural network-based controller for tracking the point of maximum power of a photovoltaic (PV) system interconnected to the utility grid. The neural network is used to identify, in real time, the voltage for maximum output power of the system. The controller, through the information supplied by the neural network, generates a control signal that will be applied to a DC/DC (boost) converter in such a way to take the voltage of the system to a value which guarantees the operation of the PV system at maximum power. The boost converter duty-cycle is generated by a PI controller based on the information supplied by the neural network. In order to connect the PV system to the electric distribution system a three-phase voltage source inverter (VSI) is used operating with optimized sinusoidal PWM strategy with harmonics elimination at the output voltage up to the 17/sup th/ harmonic. The inverter uses IGBT as power switches, and is microcontroller operated.

Wind turbine power converters: a comparative study

Abstract: Two of the most promising types of power converter applicable to the task of interfacing variable-voltage DC energy sources to the grid are compared. The converters studied are first a DC/DC power converter with a current-controlled voltage source inverter and, secondly, the line-commutated SCR with an active compensator for reduction of harmonic current and reactive power demand. The comparison is drawn with particular reference to use with variable-speed permanent-magnet wind turbine generators. The optimal power transfer, reactive power/voltage regulation and harmonic minimisation are addressed. Experimental results from laboratory models are presented alongside simulation results, which are in good agreement, to demonstrate the power control and harmonic performance of these systems. Power losses and semiconductor costs are also discussed.

Wind speed estimation based variable speed wind power generation

Abstract: Significant variation of the resource kinetic energy, in the form of wind speed, results in a substantially reduced energy capture in a fixed speed wind turbine. In order to increase the wind energy capture in the turbine, variable speed generation (VSG) strategies have been proposed and implemented. Typically, VSG strategies vary the rotational speed of the turbine, by controlling either a mechanical or electrical parameter to maintain a constant tip-speed ratio of the turbine. This is known as a maximum power point tracking (MPPT) controller. Traditionally, the MPPT controller is based upon a simple, but slow, search or perturbation algorithm to determine the optimal rotational speed of operation. In this paper, a wind speed estimation-based MPPT algorithm is proposed that employs a heuristic model of both the turbine and the generator to estimate the wind speed. A local search/perturbation of the rotational speed is employed to attain fine tuning of the desired optimal tip-speed ratio tracking. While this algorithm is more complicated than the search based method, it can still be implemented inexpensively. The ease of implementation guarantees fast control updates and ensures maximum power point operation for all wind speeds within the design limitations. The controller has been verified for efficacy on a 1.5 kW laboratory VSG wind generator.

A buck-boost DC-AC converter: operation, analysis, and control

Abstract: The main purpose of this paper is to analyze a four quadrant DC to AC switched mode inverter, using a buck-boost DC to DC converter. The buck-boost inverter is intended to be used in UPS design, whenever an AC voltage larger than DC link voltage is needed, with no need of a second power conversion stage. Operation, control strategy, simulation results are included in this paper.

A novel utility interactive photovoltaic inverter with generation control circuit

Abstract: This paper describes a novel utility interactive photovoltaic inverter. Since photovoltaic modules in photovoltaic power generation systems in urban areas are installed on roofs, shadows created by neighboring homes, utility poles, and trees may sometimes cover some part of the photovoltaic modules. In this case, power generated from each photovoltaic module becomes unbalanced and its total generation power is greatly decreased, especially when the photovoltaic modules are connected in series. These problems cannot be solved in conventional systems. We developed a novel utility interactive inverter with generation control circuit. In this proposed inverter system, each of these photovoltaic modules is individually operated at its corresponding maximum power point. By using this inverter, the efficiency of the photovoltaic system can be improved.

Interleaving of parallel DC-DC converters using sliding mode control

Abstract: This paper introduces a new approach to interleaving parallel power converters using a multi-input sliding-mode control scheme The control approach is based on sliding surfaces which naturally provide interleaving between cells of a modular power supply system Moreover, the sliding surfaces provide equal current distribution among the power converter modules and a regulated voltage in the output The technique is also effective if there is a varying number of cells in the system, each as the failure of one or more cells Simulation and experimental results are presented for a parallel structure based on three buck power converters

Development of a single-phase inverter for small wind turbines

Abstract: This paper reports the development of a single-phase, delta modulated IGBT inverter for wind energy conversion applications.

Hybrid power systems with diesel and wind turbine generation

Abstract: We present a modular simulation system developed to study the dynamics and to aid in the design of hybrid power systems with diesel and wind turbine generation. The emphasis is placed on the representation of the dynamics of the elements of a real system and on the control aspects of the modules. Each module represents a component of the hybrid power system such as the diesel generator, wind turbine generator, village load, etc. Various system configurations with different load and wind resource profiles can be simulated. This tool can be used to study the transient and the steady-state interaction of the various components of a hybrid system. It is especially useful when a new configuration of a power system is to be analyzed, a new load or wind speed profile has to be included, additional modules have been installed in an existing power system, or an old control strategy is to be replaced by a new one.

Assessment of wind turbines impact on the power quality of autonomous weak grids

Abstract: Wind turbines' impact on the power quality of autonomous weak power grids is investigated in terms of variations in the frequency and the voltage, flicker and harmonics. Laboratory measurements on a wind-diesel hardware simulator are presented for various operational scenarios with different characteristics of the wind speed and the wind turbine. In order to assess the effect of the different parameters of a wind power plant to the power quality of an existing diesel powered system the followed methodology was to compare the power system's behaviour operating with and without wind turbines. Results for all scenarios considering all power quality characteristics are presented and discussed.

Digital control of power supplies-opportunities and constraints

Abstract: In this paper, we present a study of the opportunities and constraints of digital control in power supplies The advantages and disadvantages between analog and digital controllers in switched-mode power supplies are discussed in detail The effects of a digital controller on device reliability and integration level are also discussed A 48 V, 500 W rectifier having a switching frequency of 100 kHz was used as a practical case example This switched-mode rectifier consists of two converter stages, ie, AC/DC and DC/DC converters Dynamic characteristics for digital controllers in both converters were studied by extensive simulations Based on the simulation results, the values of the required sampling frequencies were determined According to the obtained results and careful analyses made in our study, it can be stated that digital control is certainly a viable alternative also in power supplies However, before digital controllers will become dominant in high-volume power supply products, low cost microcontrollers or signal processors, which are tailored for the specific application, are needed to reduce the existing cost barrier

Hybrid wind turbine power generating system provided with solar battery

Abstract: PROBLEM TO BE SOLVED: To construct a hybrid power generating system which is fully economically efficient and capable of fully utilizing a sunlight power output and a wind turbine power output. SOLUTION: The DC output, converted output of a wind turbine power generator 1 with a rectifying diode 3 constituting a wind power generation control panel 18 and the output of a battery 9, are inputted to a converter 12 which has an output drop characteristic approximating the output characteristic of a solar battery 2, and are converted into AC power in a first inverter 13. Moreover, the output of the solar battery 2 is converted into AC power in a second inverter 10 via a collector box 17 comprising a switch 5 and a reverse current blocking diode 4, and after the AC output of first and second inverters 10, 13 is combined, system linkage operation with an external power system is performed by a breaker 16 provided with a synchronous parallel function. COPYRIGHT: (C)2000,JPO

Wind turbine and method for operating a wind turbine

Abstract: The invention relates to a method for operating a wind turbine with an electric generator which can be driven by a rotor in order to output electric power to an electric consumer, especially an electric network. The invention also relates to a wind turbine with a rotor and an electric generator coupled to the rotor in order to output electric power to an electric consumer, especially an electric network. The aim of the invention is to provide a wind turbine and a method for operating a wind turbine which avoid the disadvantages pertaining to prior art, which especially avoid excess fluctuations of voltage to consumers, especially to an electric network, and which avoid an undesired disconnection of the wind turbine. To this end, the inventive method is provided such that the power supplied to the network by the wind turbine is regulated according to the relevant network voltage of the supply network.

Design of high quality AC/DC converter with high efficiency based on half bridge topology

Abstract: A single stage AC/DC converter based on a half bridge topology suitable for low power level applications is proposed. The proposed converter has high power factor, low harmonic distortion, and tight output regulations. An asymmetrical control and synchronous rectification are employed to reduce the switching and rectification losses, respectively. The modelling and detailed analysis are performed to derive the design equations. Based on these design equations, a prototype converter has been designed and experimented upon. This prototype meets the IEC 555-2 regulations with near unity power factor and high efficiency.

Design of a low power utility interactive photovoltaic inverter

Abstract: This paper presents a new low power, low cost, single phase utility interactive photovoltaic inverter The proposed inverter configuration has features like unity power factor operation, soft switching of its power devices, fixed frequency operation and matching of the maximum power point of the solar array by simple duty cycle modulation The output sinusoidal current fed to the grid by the inverter also satisfies the current harmonic distortion limits specified by the utility companies The working of the inverter has been verified by suitable simulation and experimental results

Air conditioning system and power converter apparatus for the same

Abstract: An air conditioning system of enhanced cooling and heating capability, allowing finer control for suppressing generation of higher harmonics with relatively simple and generally inexpensive structure is equipped with a refrigerating cycle system (20) in which an electric motor (18) operatively coupled to the compressor (25) is driven through inverter control (8, 12) after converting AC power supplied from an AC power source (1) into a DC power. The system has a switching element (3) disposed in parallel with a DC power source for supplying a DC power derived by rectifying the AC power supplied from the AC power source (1), a DC voltage detecting circuit (10) for detecting a DC voltage (Vdc) derived by the rectification, and a PWM control circuit (11) for controlling the switching element (3) through a PWM control on the basis of a value of the DC voltage (Vdc) detected by the DC voltage detecting circuit (10).

Power generating device

Abstract: PROBLEM TO BE SOLVED: To provide a power generating device, wherein solar energy and wind energy are converted into electrical energy for the continuous supply of electrical energy. SOLUTION: A power generating device 10 comprises a solar light power generating device 20 containing a solar cell panel comprising solar cells which detects sunlight to generate electricity, a windmill power generating means 30 in which the rotation of a rotor 31 of translucent material generates electricity, a charging means 40 where a DC current generated by the solar light power generating device 20 and the windmill power generating means 30 is stored, and a DC to AC converter 50, in which the DC power outputted from the charge means 40 is converted into AC power of a preset frequency. With the power generating device 10, the solar energy such as sunlight and solar heat and wind energy are converted into electric energy for continuous supply of electrical energy.

Small-size wind power generating system interconnection system and protecting device for its automatic drive

Abstract: PROBLEM TO BE SOLVED: To constitute a stable, full-automatic drive system, to materialize system interconnection of a wind power generator, to dispense with complication such as the detection and control of wind speed data, and to provide a necessary protection device by combining the wind power generator, a rectifying circuit, the protection device, and a system interconnection inverter together. SOLUTION: Rotation energy from a wind turbine 1 adopting wind power energy is converted into AC electric power by a synchronous power generator 2, converted into DC by a rectifying circuit 3, and then fed to a power system 5 via an inverter 4. Then, the protecting device 11 utilizes an electromagnetic brake by a short-circuit current of the generator, for example in a three-phase generator, to detect the abrupt rise of the rotation speed by a rotation detecting line 12 and stop the power generation by turning on a short circuiting switch 13 via a relay 16. When the system interconnection inverter 4 is stopped by the internal failure, etc., an inverter abnormality detecting line 14 detects it so as to stop it similarly. In detecting the system voltage detecting line 18, the power generation is stopped by the short circuiting switch 13. COPYRIGHT: (C)2000,JPO

Application of models of the wind energy conversion system to wind power dynamic analysis

Abstract: Due to stochastic variation of the wind energy, the wind power connected to the grid is stochastic. As a result, the voltage of the grid, particularly near a wind farm, fluctuates. According to the characteristics of the wind energy conversion system (WECS), a program including the models of the WECS was developed. The dynamic performances of the startup, shutdown, and running processes of the WECS and the front of the gust could be simulated and investigated. In this paper, a typical WECS connected to a large system (infinite bus) was simulated, and the relationships of the short circuit capacity (SCC) with the wind power penetration were investigated. The results showed that the SCC was one of important factors to affect the wind power penetration. The bigger SCC of the network at the WECS connection, the larger the wind power penetration. There was a maximum penetration level of the wind power to a given SCC. If the wind power of the WECS had exceeded a limit, the grid voltage fluctuation would have been in excess of the allowable value of the grid; in a severe case, the voltage would have been unstable.

Induction heating inverter with power factor correction

Abstract: The design and performance of the power stage for an induction-heating inverter is presented. The inverter is fed by a rectifier without a filter in the DC link; when operated at resonance, at a frequency much higher than the mains frequency, it provides a high power factor without further power stages or switching strategies. Tests show that the harmonic performance is well within the limits set by the applicable standards for low power apparatus.