Showing papers on "Maximum power point tracking published in 1989"

Combined low-cost, high-efficient inverter, peak power tracker and regulator for PV applications

Abstract: A novel compound power converter that serves as a DC-to-AC inverter, maximum power point tracker (MPPT), and battery charger for stand-alone photovoltaic (PV) power systems is introduced. A theoretical analysis of the proposed converter is performed, and the results are compared with experimental results obtained from a 1.5 kW prototype. The overall cost of PV systems can thus be reduced by using load management control and efficiency-optimization techniques. Power flow through the converter is controlled by means of a combination of duty cycle and output frequency control. With load management, large domestic loads, such as single phase induction motors for water pumping, hold-over refrigerators, and freezers, can be driven by day at a much higher energy efficiency. This is due to the high efficiency of the inverter with high insolation, and because the inverter uses the energy directly from the solar array. The battery loss component is thus reduced. >

Modeling and Dynamic Performance of a Line-Commutated Photovoltaic Inverter System

Abstract: Interest in utility-interactive photovoltaic (PV) inverter systems has increased over the past decade and numerous central-station PV systems have been installed. It is anticipated that as PV system costs decrease, residential systems will be installed in increased numbers. Although a substantial amount of literature is available concerning the design, protection, safety, economics, and operating experience of residential and central-station PV systems, little information is available regarding their dynamic electrical characteristics and the computer modeling of these systems. Moreover, most of the available literature concerning modeling and/or dynamic performance focuses either upon the long-term dynamic behavior as it affects power system scheduling or upon the steady-state harmonic characteristics. In recent work, highly detailed computer models of a representative set of PV systems have been developed and several of these models have been verified by comparison with system measurements [1, 2]. However, the models described in [1, 2] are more complex than necessary for large-scale power system studies in which the fast switching transients associated with the dc-to-ac inverter are of little concern and only the slower cycle-to-cycle behavior of the PV system is of interest. In fact, it is not possible to incorporate these detailed models into conventional transient stability programs due, in part, to the very small time-step requirements associated with these models. In this paper, a three-phase self-commutated utility-interactive photovoltaic inverter system is described including its associated control system. A schematic diagram of the selected PV inverter system is depicted in Fig. 1.

Simulation studies of islanded behavior of grid-connected photovoltaic systems

Abstract: Simplified computer models are presented for predicting the run-on time of self-commutated inverters operating in a utility interactive mode. The inverter receives DC power from a photovoltaic (PV) array and delivers AC power to a local load or the utility lines. The models represent the dynamics of a phase-locked loop control circuit that is designed to destabilize the inverter operation and shut down the power-conditioning subsystem when a phase discrepancy between the line and some reference signal is detected. The sustained isolated operation (or islanding) of the PV system poses a possible safety concern to utility personnel and potential damage to utility-connected equipment. Two computer models, the TESLACO model and the APCC model, were implemented on an IBM PC using Pascal. They provide results compatible with experimental evidence and more elaborate computer modeling techniques. >

Maximum power point tracking technique

Abstract: It is noted that to overcome the problem of mismatch between solar cells and a given load, maximum power-point tracking should be used. A simple efficient maximum power-point tracking technique is developed. The connection strategy depends on a very simple criterion which is the measurement of the solar radiation level. The control strategy is based on appropriate logic that compares the signs of dP/dt and dV/dt. The proposed technique is applied to the cases of resistive load, resistive load with battery, and dynamic load. >

The operation of permanent magnet DC motors powered by a common source of solar cells

Abstract: In a photovoltaic water-pumping system, the solar cell array is usually designed to power a single motor-load pump Several water-pumping systems of the same or different types that are in close proximity to each other can be powered by separate solar cell arrays (sources) for each one, or, alternatively, by a common solar cell source for all the water pumping systems The authors introduce a procedure for comparing the performances of these two setups One system includes a permanent magnet DC motor and a volumetric pump, and the other a permanent magnet DC motor and a centrifugal pump The comparison was also done for the same systems when a maximum-power point tracker (MPPT) was included for both the separate and the common solar cell source It is shown, for example, that in systems not including MPPTs the total performance of the two motor-pumps in the common source system is improved as compared to the performance of the two motor-pumps when they are powered separately by individual sources >

Enhancing the Utilization of Photovoltaic Power Generation by Superconductive Magnetic Energy Storage

Abstract: The authors demonstrate that a superconductive magnetic energy storage (SMES) system can enhance large-scale utilization of photovoltaic (PV) generation. Results show that power output from a SMES system can be used to smooth out PV power fluctuations so that the combined PV/SMES output is dispatchable and free from fluctuations. Power generated from PV arrays is shown to be fully utilized under different weather conditions, and PV penetration is increased to significant levels without adversely affecting the power system. Coupled with PV generation, a SMES system is even more effective in performing diurnal load leveling. A coordinated PV/SMES operation scheme is proposed, and its demonstration under different weather conditions is discussed. >

Current and voltage harmonic measurements and modeling at the Gardner photovoltaic project

Abstract: Measurements on harmonics taken at the Gardner photovoltaic (PV) project during the summer of 1987 are reported. The project includes 28 PV homes, each with a roof-mounted 2 kW PV system, connected to one phase of a 13.8 kV three-phase feeder. The measurements discussed pertain to voltage and current distortion and power flow. Theoretical calculations were carried out in order to study the effects of PV inverters other than the type installed for this study. Computer modeling of the feeder in Gardner indicates, and measurements confirm, that small increases (0.2%) in voltage total harmonic distortion will occur on this feeder with the indicated penetration of PV systems using high-quality, forced-commutation inverters. >

Three phase parallel processing UPS using multi-functional inverter

Abstract: A parallel processing uninterruptible power supply (UPS) system is proposed in which a three-phase pulse-width modulation (PWM) inverter is connected in parallel to a utility power source through an inductance and an electronic switch. In this system, when the utility power is on, the inverter controls the voltage regulation of the inductance so as to control the output voltage constantly in synchronization with the utility. The batteries are charged by the inverter at the same time. The inverter also absorbs the load harmonics so as to obtain a sinusoidal output voltage. When a power failure happens, the electronic switch in the input line is turned off and the inverter operates alone with no break of power supply to the load. Using only one inverter, the parallel processing UPS realizes a combined system of a constant voltage power source, an uninterruptible power supply, and a harmonics absorbing active filter. This system can also link new types of DC power sources, such as fuel cells or photovoltaic cells, to utility power systems. >

No break power transfer control for a vscf power generating system

Abstract: In aircraft applications, it may be necessary or desirable to transfer one or more loads between a variable speed, constant frequency (VSCF) power generating system and a further source of AC power. Prior controls for effecting such transfer, however, have been unduly complex. In order to overcome this problem, a control (30) for a VSCF system (10) senses the deviation of a parameter of the power developed by an inverter (22) of the system (10) relative to a parameter of the power developed by an AC power source (28) and controls the inverter (22) in accordance with such deviation to cause the parameter of the power developed thereby to approach the parameter of the power developed by the AC power source (28). The inverter (22) and the AC power source (28) are connected in parallel across one or more loads (27) when the parameter deviation is within a certain range. Either the inverter (22) or the AC power source (28) is thereafter disconnected a certain time after the two were connected in parallel to complete the power transfer.

Large-signal analysis of spacecraft power systems

Abstract: A large-signal analysis of the direct energy transfer power system is performed to predict the main bus dynamics in various modes of operation. Stability criteria for the operating points on the solar-array I-V curve are identified in each mode. The large-signal trajectories of the system's operating point for a complete orbit cycle are analyzed, employing a qualitative graphical representation. The analyses are verified through computer simulation. The results of the analysis are presented and discussed in great detail. >

A flexible control strategy to interface solar system with privileged load and utility line

Abstract: An intermediate photovoltaic power system (160 kVA, 380 V three-phase) that could be used as a stand-alone energy power supply and as an AC back up system has been designed. For this purpose it was necessary to use self-commuted inverters; a suitable power control logic was also required in order to compensate for reactive power and optimize power flow from the photovoltaic array to the AC power line. Good agreement between theoretical studies and simulation results confirms the validity of the proposed power control logic. >

Current controlled active flywheel type neutral point clamped inverter

Abstract: A power inverter having a neutral clamping circuit which is controlled for low harmonic output. The power inverter includes power transistors, a current sensor at the inverter output and a neutral clamping circuit connected between the inverter output and a neutral point in a DC power source which supplies the inverter. A controller circuit is connected to the current sensor, to the power transistors and to the neutral clamping circuit to selectively enable and disable the power transistors in the neutral clamping circuit in accordance with the inverter operation and current direction at the inverter output to minimize current transients at the load.

Pwm current source converter and inverter

Abstract: Recent progress made by turn off power semi­conductor devices has been contributing to simplifica­tion of circuit arrangement in power electronic equip­ment This paper summaries important development in power devices and describes novel industrial applica­tions of these semiconductor devices in voltage source and current source converter and inverter.

Inverters for utility interactive photovoltaic power plants

Abstract: An introduction to the more important inverter circuits for photovoltaic (PV) plants is presented. Their relative merits and drawbacks are examined, with particular emphasis on power quality, reliability, and efficiency. It is concluded that transistor circuits will probably conquer the small power field, whereas high-power converters will use thyristors and GTOs. >

A new series of smart controllers [for power convertors]

Abstract: A series of three intelligent power integrated modules for 0.4 to 1.5 kW AC-DC-AC inverted power conversion has been developed. Each of these is fabricated in one common and compact housing to produce a three-phase converter, a three-phase inverter using insulated-gate bipolar transistors, opto-couplers for input-to-output signal interfaces, and monolithic drive/protection logic. The internal architectures, functional and overall performance results, and the advantages of these smart controlling 'black boxes' are presented. >

Design of the Space Station Freedom power system

Abstract: The design of Space Station Freedom's electric power system (EPS) is reviewed, highlighted the key design goals of performance, low cost, reliability and safety. Tradeoff study results that illustrate the competing factors responsible for many of the more important design decisions are discussed. When Freedom's EPS is compared with previous space power designs, two major differences stand out. The first is the size of the EPS, which is larger than any prior system. The second major difference between the EPS and other space power designs is the indefinite expected life of Freedom; 30 years has been used for life-cycle-cost calculations. >

Space Station Freedom photovoltaic power module design status

Abstract: Electric power for the Space Station Freedom will be provided by four photovoltaic (PV) power modules using silicon solar cells during phase I operation. Each PV power module requires two solar arrays with 32800 solar cells generating 18.75 kW of DC power for a total of 75 kW. The design incorporates an optimized thermal control system, pointing and tracking provision with the application of gimbals, and the use of orbital replacement units to achieve modularization. The design status of the PV power module, as derived from major tradeoff studies, is discussed at hardware levels ranging from component to system. Details of the design are presented where appropriate. >

AC three-phase power transmission system for Amtrak's new locomotives F69PH-AC

Abstract: Advances in the field of three-phase drives for rail vehicles are described with reference to the power transmission system for the high-speed four-axle F69PC-AC locomotive. This model of locomotive incorporates state-of-the-art three-phase technology in the traction and head-end power systems. Traction converters, which are of the voltage-source inverter type with gate-turn-off thyristors, supply power to the squirrel-cage three-phase induction motors which are connected in parallel within each bogie. In addition to the two traction inverters, a third inverter is installed to supply power to the passenger cars. All three inverters are identical and utilize the evaporation-bath cooling method to dissipate the heat caused by electrical losses. The locomotive and the inverters are micro-processor-controlled. >

Designing a 1200 Watt multiple output modular power system with high power utilization for the workstation environment

Abstract: The design of a 1200 W multiple-output modular power system for the workstation environment is described. High power utilization (78% efficiency with 80% power factor) is achieved through the use of Victor modules and a passive power factor correction. Emphasis is on the design of the AC-to-DC unit and DC-to-DC converter board (Power System Eurocard) with its controller for use in the Apollo DN 10000 workstation. System considerations, design trade-offs, and problems encountered are described. Future considerations for further enhancements to performance are proposed. >

Control device for system interconnecting power converter

Abstract: PURPOSE: To always accurately operate a system interconnecting power converter by changing a maximum apparent power outputted from the power converter in accordance with the system voltage of an AC system CONSTITUTION: A power control device 300 in the power controller 1000 is constituted of an active power reference setter 71, a reactive power reference setter 72, an active power control circuit 77, a reactive power control circuit 78, active power/reactive power limiters 81, 82, and a control variable converter 90 The limiter 82 changes maximum apparent power by an C system voltage signal V sy Even when voltage on the system side is dropped or boosted in the operating state of the converter 1000 in a rated apparent power range, the operation of the converter 1000 is stably continued without generating excess current COPYRIGHT: (C)1990,JPO&Japio

Magnification of starting torques of DC motors by maximum power point trackers in photovoltaic systems

Abstract: A calculation of the starting torque ratio of permanent magnet, series, and shunt-excited DC motors powered by solar cell arrays is presented for two cases, ie with and without a maximum-power-point tracker (MPPT) Defining motor torque magnification by the ratio of the motor torque with an MPPT to the motor torque without an MPPT, a magnification of 3 for the permanent magnet motor and a magnification of 7 for both the series and shunt motors are obtained The study also shows that all motor types are less sensitive to solar insolation variation in systems including MPPTs as compared to systems without MPPTs >

20 kHz main inverter unit

Abstract: A proof-of-concept main inverter unit has demonstrated the operation of a pulse-width-modulated parallel resonant power stage topology as a 20 kHz AC space power source driver, showing simple output regulation, parallel operation, power sharing and short-circuit operation. The use of a two-stage DC input filter controls the electromagnetic compatibility (EMC) characteristics of the DC power bus, and the use of an AC harmonic trap controls the EMC characteristics of the 20 kHz AC power bus. >

Load independent efficient, transformerless inverter for photovoltaic applications

Abstract: The overall efficiency of photovoltaic power systems (PVPS) depends on the efficiency of the PV panels, the storage batteries, and the efficiency of the inverter circuitry. The last is greatly influenced by the connected load, as the efficiencies are severly reduced when operating at low loads. This is especially effective when the PVPS is most likely to operate with a fraction of the full load. The suggested inverter has excellent efficiency characteristics over a wide power range, and because it contains only electronic components further cost reduction can be expected. Experimentally this inverter is designed for a 120 W output using thyristor switching devices; the efficiency obtained is 88% at full load and 85.2% at 10% of full load, with a maximum output voltage of 60 V stepped sinewave with frequency of 50 Hz. However, higher power outputs could also be achieved with this type of inverter.

Series-connected power-line controller

Abstract: A full-bridge transistor inverter is connected at its DC supply-side with an energy-storing capacitor. The inverter's output terminals are connected in series between a source of AC voltage and a load; which load may be an electric motor, a fluorescent lighting system, etc. By controllably switching the transistors of the inverter ON and OFF at some rate higher than, but basically synchronous with, the frequency of the AC voltage, effective control of the flow of power between the AC source and the load is achieved. DC voltage on the energy-storing capacitor is obtained from the AC source and established by way of the timing of the switching action of the inverter. Hence, in contrast with the ordinary situation where an inverter is supplied with net power from its source of DC voltage and where this net power is then supplied to a load connected with the inverter's output, the present invention relates to a situation where generally no net power is supplied to the inverter from its source of DC voltage and where generally no net power is supplied from the inverter's output. Instead, the inverter is used for controlling the waveform, magnitude and phasing of the alternating current flowing through it by way of its output terminals.

High frequency zero voltage switching resonant power inverter with extended line and load range

Abstract: A power inverter efficiency is optimized at high frequency in a fully resonant inverter operating with a range of load impedance that takes into consideration switching loss and conducting loss as a combined overall effect. Within this range of load impedance the inverter is constrained to operate with switching loss which is generally considered unacceptable in a conventional high frequency high efficiency power inverter, but the overall combined high efficiency of the disclosed power inverter has a wider range of load impedances than has been previously achieved in such a resonant power inverter. Non-linear capacitance across switching the device is positively utilized in achieving this goal.

Photovoltaic Power System Using an Orthogonal-Core Type Push-Pull Converter and Characteristics of a Push-Pull Parametric Transformer

Abstract: The authors earlier proposed an orthogonal-core type push-pull converter. The converter was constructed with a pair of orthogonal-cores whose primary sides were excited by square-wave choppers, and the converter had almost sinusoidal output current and high power factor. In this paper we report a photovoltaic power system using the push-pull converter. The test results obtained in the trial system indicate that the orthogonal-core type push-pull converter can be applicable to a practical photovoltaic power system. As another application, an orthogonal-core type push-pull parametric transformer is also described here. It was experimentally clarified that a low distorted input current and high input power factor are obtained in the push-pull parametric transformer.