Showing papers on "Maximum power point tracking published in 1995"

Multilevel cascade voltage source inverter with seperate DC sources

Abstract: A multilevel cascade voltage source inverter having separate DC sources is described herein. This inverter is applicable to high voltage, high power applications such as flexible AC transmission systems (FACTS) including static VAR generation (SVG), power line conditioning, series compensation, phase shifting and voltage balancing and fuel cell and photovoltaic utility interface systems. The M-level inverter consists of at least one phase wherein each phase has a plurality of full bridge inverters equipped with an independent DC source. This inverter develops a near sinusoidal approximation voltage waveform with only one switching per cycle as the number of levels, M, is increased. The inverter may have either single-phase or multi-phase embodiments connected in either wye or delta configurations.

Identification of optimal operating point of PV modules using neural network for real time maximum power tracking control

Abstract: This paper presents an application of a neural network for the identification of the optimal operating point of PV modules for the real time maximum power tracking control. The output power from the modules depends on the environmental factors such as insolation, cell temperature, and so on. Therefore, accurate identification of optimal operating point and real time continuous control are required to achieve the maximum output efficiency. The proposed neural network has a quite simple structure and provides a highly accurate identification of the optimal operating point and also a highly accurate estimation of the maximum power from the PV modules. >

Evaluation of neural network based real time maximum power tracking controller for PV system

Abstract: This paper presents a neural network based maximum power tracking controller for interconnected PV power systems The neural network is utilized to identify the optimal operating voltage of the PV power system The controller generates the control signal in real-time, and the control signal is fed back to the voltage control loop of the inverter to shift the terminal voltage of the PV power system to its identified optimum, which yields maximum power generation The controller is of the PI type The proportional and the integral gains are set to their optimal values to achieve fast response and also to prevent overshoot and also undershoot Continuous measurement is required for the open circuit voltage on the monitoring cell, and also for the terminal voltage of the PV power system Because of the accurate identification of the optimal operating voltage of the PV power system, more than 99% power is drawn from the actual maximum power >

Power conditioning system for a four quadrant photovoltaic array with an inverter for each array quadrant

Abstract: A photovoltaic (PV) power system having distributed square wave current DC to AC inverters integral with strings of PV cells in a PV array. The PV array is arranged into four quadrants and phase-shifted and summed AC voltages from each quadrant are further summed in a 12-phase to 3-phase transformer to produce a sinusoidal 3-phase AC voltage with a total harmonic distortion of less than 5 percent.

200 W low cost module integrated utility interface for modular photovoltaic energy systems

Abstract: This paper describes the design of a utility interface for a 200 W solar cell array. The interface comprises high frequency soft switching PWM power conversion, analog and logic control and protection circuits and an analog maximum power point tracker (MPPT). All circuits are implemented with standard components (no microcontroller) and thus facilitates integration into ASIC components at a later development stage. The design emphasis is on module integration, low cost production and compliance with standards on utility interfacing. The special requirements of utility interfacing and solar cell array utilization are described and the design of the components of the utility interface is described. The theory and design are verified with the implemented laboratory prototype, which shows excellent performance and verifies the operation of the interface.

Photovoltaic inverter with a novel cycloconverter for interconnection to a utility line

Abstract: A PV (photovoltaic) inverter is the power conversion equipment that converts DC power generated by PV cells into isolated AC power and interconnects it to a utility line. This paper describes a PV inverter with a novel cycloconverter for interconnection to a utility line. The authors developed this novel cycloconverter as a way of frequency conversion so that a small, high-frequency transformer can be used to minimize the size of the PV inverter. They manufactured a 3 kW PV inverter as an experimental model with this novel cycloconverter for interconnection to a utility line. This equipment is 25% the size in volume and 17% the weight compared to previous commercial-frequency isolation type inverters. In rated operations, excellent results were obtained; the output current distortion factor was less than 5.0% and conversion efficiency was as high as 92.1%.

Power quality of wind turbines and their interaction with the grid

Abstract: The interaction of wind turbines (WT) with the grid has an evident influence on the voltage of the grid. The loss of power quality is depending directly on the intensity of the interference related to the capacity of the grid. In near future a certificate for power quality will be claimed by German utilities. This certificate will demonstrate the quality of power generation of a WT with respects to harmonics, power peaks, power factor and flicker for normal operation as well as for extreme and switching operation conditions. In this paper we present examples of the measurements according to the guideline. We show the grid interactions occurring during the operation of different WTs and how they possibly could be diminished. In addition the interaction effects of single WTs and wind farms will be compared.

A medium power PV-array simulator with a robust control strategy

Abstract: This paper introduces strategies to simulate photovoltaic arrays with arbitrary and reproducible insolation conditions. The operating point of the simulator can be controlled and it is stable, so electrical tests and comparisons can be made with high accuracy. Medium power units (1 kW) were built using an efficient switch-mode strategy together with a novel control strategy having superior performance under variable load conditions. This new control strategy can also be used in many other applications in power electronics.

Photovoltaic systems for small-scale remote power supplies

Abstract: This article considers the technical aspects of using photovoltaic systems for small power supplies where a connection from a main electricity distribution network is not appropriate. The technology of the various components of a photovoltaic power system is discussed and the overall system design considered. Typical applications of photovoltaic systems are described.

Method and apparatus for adaptive and corrective determination of battery run-time in uninterruptible power systems

Abstract: The run-time available from an uninterruptible power system is accurately determined both during supply of power from the battery to the load and during the time where power is supplied directly from an AC power system to the load. During power outages, where power is supplied from the battery through the inverter to the load, the remaining run-time is first estimated by calculation and then corrected by modification of the calculated value according to the reciprocal of the run-time slope. Alternatively, a scaling factor is used as part of the first run-time calculations and a correction factor which applies more corrective weight as the time on inverter progresses may be used. During power outages and when power is supplied from the AC power system to the load the maximum available run-time is extrapolated from a table of values representing maximum available run-times at various levels of power being supplied to the load from a fully charged battery. These values are updated after inverter runs to reflect actual system run-times. The maximum run-times are thereby adapted to reflect battery aging and other unique characteristics of the system.

Inverter for pumps and a pump unit therewith

Abstract: An inverter unit having a simple circuit configuration which provides reliable control over the performance of a fluid handling pump is presented. An application of the inverter unit to a motor-driven peripheral flow type pump is demonstrated. The inverter unit is constructed so that the inverter unit isolates a three-phase commercial alternative power source from the pump driving alternative power source such that the problems, such as a misconnection of phase relationship, in the commercial power source do not affect the performance of the motor. The pump is powered by an internally-generated power produced within the inverter unit. The inverter unit thus includes: a converter section which rectifies the three-phase commercial power and converts the alternating current power to direct current power; and an inverter section which generates pulse signals having specific frequency and voltage values using the direct current power produced in the converter section. The three-phase alternating current thus generated by the inverter unit are applied to the motor, independent of the phases in the commercial three-phase alternative power source, so as to produce optimum performance of the motor in each of the start-up, steady-state and stopping stages. The pump is thus able to perform reliably at its peak efficiency without the problems encountered in the pumps incorporating conventional inverters.

Characteristics of a parallel-module high power-factor AC-to-DC converter system with current-balancing controllers

Abstract: Characteristics of a parallel-module high power-factor AC-to-DC power converter system using current-balancing controllers are presented. Problems caused by the parallel connection of power factor correction (PFC) power converter modules are discussed. Two types of current-balancing controllers, i.e. conventional and improved, are applied to the parallel-module PFC system to share the load current between the power converter modules. The effectiveness of the current-balancing controllers for the PFC power converter system is confirmed by experiment. The current-balancing controller improved here has fast transient response to load current sharing under dynamic conditions.

Linked inverter having solar battery output inspection function and inspection method

Abstract: PROBLEM TO BE SOLVED: To perform the maintenance and inspection concerning the output of a solar battery safely and easily by a method wherein the output characteristics of the solar battery are evaluated by using a linked inverter and a current detecting sensor. SOLUTION: When a linked inverter is operating in a normal operation state, the output control of a solar battery is performed by following a maximum power point and the semiconductor switches 14 of all strings 3 are in the off-states. At that time, an LED 11 lights to indicate that the respective strings 3 of a solar battery are in generating states. On the other hand, when the linked inverter is off, the semiconductor switches 14 of all the strings 3 are in OFF state. Therefore, even in this case, if the solar battery is outputting a power, the LED 11 lights. With this process, it is detected that the output power of the solar battery exists. When the short-circuit current of the solar battery is detected, a short-circuit current detected by a current sensor 15 in the closed loop of the short-circuited string 3 is measured and the measured datum is also indicated optionally.

Dc power source system

Abstract: PURPOSE: To provide a DC power source system capable of supplying a required minimum of load by converting the output of a storage battery to AC power by high efficiency even when the storage battery having small capacity is mounted as an emergency power source. CONSTITUTION: In a DC power source system, a storage battery 7 having small capacity is connected to the output terminal of a DC power source 1 made of a solar cell via a charge/discharge controller 6, a small-capacity inverter 8 having lower rated output than that of a main inverter 2 is connected between the controller 6 and the battery 7, and an emergency plug socket 9 is connected to the output terminal of the inverter 8.

Development of Simulation Program of Electric Power Generated by PV System Using New I-V Curve Construction Method

Abstract: In the design, operation and evaluation of a photovoltaic power generation systems (PV systems), it is particularly important to accurately estimate the total amount of annual electric power generated by PV system. The authors applied a new I-V curve construction method developed for the calculation of output power from a photovoltaic array in order to develop a practical “simulation program for the calculation of the amount of electric power generated by PV system.” The following items were clarified by this research.

Space-vector modulated PWM converters for photo-voltaic interface applications: analysis, power management and control issues

Abstract: This paper presents new power management and control concepts for power converters that interface a photovoltaic (PV) system to an electric utility power system. The interface circuit is a space-vector modulated (SVM), high-frequency, 3/spl phi/, PWM buck-type inverter. Decoupled control of DC voltage for peak power tracking, and the quadrature component of AC output current for reactive power flow control is achieved. The inner current loop maintains a preset flow of reactive power from the power converter to the local load and the utility power system. The peak power tracking loop sets the reference value of the outer voltage loop. Small-signal model of the switching power converter, derived in rotating d-q coordinates is used to design the control loops. >

Novel control strategy for grid-connected dc-ac converters with load power factor and MPPT control

Abstract: This paper presents a modeling, analysis and design of a PWM voltage source inverter (VSI) to be connected between a dc source and the ac grid. The control algorithm of the PWM-VSI applies the concept of the instantaneous p-q (real-imaginary) power theory and the converter dc source is supplied by a photovoltaic array (PC). 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 of the electrical system. Some design considerations are also discussed. The feasibility of the proposed control method was verified by a digital simulation and measurements on a small prototype model. (author) 5 refs., 12 figs., 1 tab.

Photovoltaic system using buck‐boost PWM power inverter

Abstract: This paper presents a buck-boost PWM power inverter and its application for the residential photovoltaic system. The PWM power inverter is realized by driving an inverter constructed with a high-frequency buck-boost chopper in the discontinuous conduction mode (DCM). The photovoltaic system with the power inverter has the following advantages: (1) the power generated by the photovoltaic array can be transferred to the load and the utility line under any array voltage; (2) isolation between the photovoltaic array and the utility line is performed by a small high-frequency reactor operating as energy storage element; (3) there is no need of a reactor to link the utility line; (4) unity power factor operation is provided; and (5) the system configuration is very simple. the input-output characteristics of the system are analyzed. As a result, the ripple component of the array current and the power flow between the interface and the utility line are derived and verified experimentally.

Photovoltaic water pumps coupled with dc/ac inverter

Abstract: Proper sizing of photovoltaic (PV) array and motor/pump subsystem are essential for maximum utilisation of PV water pumping systems. A proper matching of electromechanical loads to a PV array is a great problem in many PV systems. This is mainly related to the non-linear, solar irradiance and cell temperature-dependent voltage and current characteristics of the PV array generator. In a proper matching system, the electrical energy supplied to the load is close to the maximum available array energy. The load matching factor is one of the basic comparison method used in the optimisation of PV water pumping systems. Optimisation of PV pumping system can be made from a simple non-linear mathematical model and from experimental data. From this optimisation technique, array configuration can be determined using the required rated power of the motor/pump subsystem and the I-V characteristic of a single cell. Conversely, the optimal size of motor/pump subsystem can be determined from a known array configuration. ...

A New maximum Power Point Tracking of Photovoltaic with Fuzzy Controller

Abstract: The purpose of this paper is to develop a new maximum power point tracker(MPPT) using fuzzy set theory, it is proposed to improve energy conversion efficiency. Fuzzy algorithm based on linguistic rules describing the operator's control strategy is applied to control step-up chopper for MPPT. Temperature compensation effect means that Photovoltaic voltage is change in condition (irradiation, temperature and etc.. Fuzzy algorithm is applied to control boost MPPT converter by temperature compensation effect. In this paper, temperature compensation range is -40℃ ~ +100℃.

Analysis of a photovoltaic water pumping system

Abstract: A solar powered photovoltaic water pumping system has been installed and field tested at James Cook University of North Queensland, Australia. The results of the experiment are discussed based on field measurements and computer modeling of the various system components in order to investigate the efficiency of each component and the performance of the entire system.

Power controller for battery power supply

Abstract: PROBLEM TO BE SOLVED: To provide a power controller capable of stably taking out the maximum output from a solar battery. SOLUTION: This equipment comprises a battery power supply 1, power conversion means 2 for converting power from the battery power supply and supplying it to a load 3, voltage detection means 4 for detecting a voltage value of the battery power supply, current detection means 5 for detecting a current value of the battery power supply, output value setting means 6 for setting an output value of the battery power supply based on the detected values of the voltage detection means and the current detection means, and control means 7 controlling the power conversion means in such a manner that the output value of the battery power supply coincides with the set point of the output value setting means. And the output value setting means 6 fluctuates the operating point of the battery power supply 1 and samples the voltage value and current value at a plurality of operating points, calculates power value from voltage and current values at each operating point, and the setting method for a set point is selected depending on the curvature of an approximate curve of voltage-power or current-power characteristics curves by polarized functional equations based on the power value and the voltage value of current value. COPYRIGHT: (C)1997,JPO

Rating batteries for initial capacity, charging parameters and cycle life in the photovoltaic application

Abstract: Stand-alone photovoltaic (PV) systems typically depend on battery storage to supply power to the load when there is cloudy weather or no sun. Reliable operation of the load is often dependent on battery performance. This paper presents test procedures for lead-acid batteries which identify initial battery preparation, battery capacity after preparation, charge regulation set-points, and cycle life based on the operational characteristics of PV systems.

A novel islanding protection system for photovoltaic inverters

Abstract: It is very difficult to detect an islanding condition of a power distribution line with conventional voltage or frequency relays while the output power and the load power of utility interactive PV inverter units are in nearly balanced state in both active power and reactive power. This is because a sufficiently large voltage or frequency change cannot be expected at such a balanced state. Many studies have been reported so far to complement dead bands in combination of active and passive methods to prevent the islanding, but none of them has been successful. This paper presents the principle of a new active method called slip mode frequency shift (SMS). With this method the reactive power between the inverter and the load is made unbalanced intentionally to cause the frequency to shift as if it slips down a slide. The performance when the dead bands are eliminated effectively in the range of practical use has been examined through simulation and experiments.

Self-excitation type inverter control circuit for adjusting effective and reactive power

Abstract: PURPOSE: To provide a self-excitation type inverter control circuit for adjusting effective and reactive power which can prevent stop of inverter due to fluctuation of feeding line voltage when an in-rush is generated. CONSTITUTION: In a self-excitation type inverter control circuit for adjusting effective and reactive power which compensates for voltage drop and voltage unbalance in the side of the 3-phase power supply system by connecting the self-excitation type inverter to the power feeding line for AC electrical railway in the output side of the transforer of the 3-phase-2-phase conversion connection system to send and receive the effective power and reactive power, a timer 8 is operated when in-rush is detected to turn off an inverter current output command for a certain period with a switching circuit 9. For in-rush detection, the detected output of a load current is fully rectified and thereafter the peak value is sampled and held to judge whether a difference between the rectified output and sample-and-hold output is higher than the preset value or not. COPYRIGHT: (C)1996,JPO

A model of three phase inverter hybrid IC with 60 V/150 A MOSFET

Abstract: Utilizing the insulated metal substrate technology (IMST), a new 60 V/150 A inverter IC has been developed. At present, a single substrate inverter IC is limited to 75 A for its maximum current carrying capacity, and its applications are primarily in high voltage commercial area. Power utilization of devices for such applications are relatively high and have little influence on the system performance since the supply voltage is much higher in comparison with ON-state saturation voltage of power devices. Unlikely, for battery powered applications where supply voltage and power utilization are low, thus selections of proper power devices are essential to build a better inverter system since the degree of power utilization in inverter ICs determines the performance of the inverter system. Because of the resistance of substrate pattern also has a significant influence on the system performance, the authors increased the thickness of copper foil to twice of the current models. Despite increased thickness, the authors maintained the present fine pattern pitch by the adoption of a new etching process, and succeeded the development of a new high density assembly substrate. Being able to adopt low on-resistance power devices and thick pattern traces, as a result the unit became compact and performed as per design.

Power supply system start-up/stoppage controller

Abstract: PURPOSE:To stably perform the start-up and stoppage of a power supply system at the time of low quantity of solar radiation in which the start-up operation and stopping operation of the power supply system tend to be performed frequently and repeatedly. CONSTITUTION:This controller is constituted of a detecting part 15 which detects the output of a solar battery 1, a maximum power point tracking part 16 which decides the maximum power point of the solar battery from an output voltage, a sine wave pattern control part 17 which generates a sine wave pattern for the control of an inverter 2, a sine wave pattern adjusting part 18 which switches the operation of the sine wave pattern control part 17 and a system start-up/stoppage control part 19 which performs the start-up/stoppage of a system by a prest value for system start-up/stoppage, and when a value exceeds a sine wave pattern adjusting setting preset value set so as to satisfy a condition preset value for system stoppage < preset value for sine wave pattern adjustment < preset value for system start-up, the sine wave pattern which becomes the maximum power point is outputted by the sine wave pattern control part 17, also, when it is reduced lower then that, the sine wave pattern to evade the reduction to be lower than the preset value for system stoppage is outputted.