Numerical model of photovoltaic drive system with MPP tracker based on positive feedback

The paper deals with numerical model of the system with photovoltaic generator feeding the DC commutator motor with permanent magnet excitement, by DC buck chopper. The motor drives its load of fan characteristic - centrifugal water pump. The system is of Stand-Alone type, and without the electric buffer source (electrochemical accumulator or supercapacitor). The simple circuit for Maximum Power Point tracking, with positive feedback from average value of motor’s armature voltage, has been applied in this system. The real system's diagram is presented and shortly described. The numerical model of the whole real system has been created in TCAD simulation software. This model's diagram is presented and described in details. The model of PV generator enables simple modeling of generator's cells insolation changes, and also different temperatures of the cells, independently. The results of computer simulations of such transient states as: start-ups of the motor for different PV cells insolation and temperature values, and linear increases and decreases of insolation, are presented. The good points and shortcomings of the described system and its model are recapitulated in the conclusions

The optimization of electrical machine's operation in photovoltaic drive system

This article presents essential methods of securing the improvement of electrical machine's operation parameters, during machine's operation in the systems with photovoltaic generator (directly converting sunlight radiation energy into electrical energy) as the basic energy source. The article mainly fixes attention on the aspects that are possible to carry into effect at the stage of project, installation and exploitation of the photovoltaic system. These aspects refer to attaining maximum efficiency of energy conversion by the machine and in the whole system, maximization of machine's lifetime, and also maximization of supply reliability of electrical machine's load. The described problem is very significant for stand-alone system structures (i.e. not co-operating with electroenergetical grid) and simultaneously without electrochemical accumulators as buffer energy sources. Such structures have: systems with direct connection of electrical machine to photovoltaic generator, systems without any electrical buffer energy source but comprising energoelectronical converter between photovoltaic generator and machine, and finally systems with two converters and a capacitor as electrical buffer source

Stand-Alone Photovoltaic Drive System with Single-Phase Induction Motor and without Electric Buffer Source

An off-grid low power drive system with multiple energy conversion is described in the paper. At first, solar irradiation energy is directly converted into low-voltage DC current electrical energy by photovoltaic generator. Then, the generator’s output voltage is increased by DC boost chopper. In the next stage, this voltage is transformed into AC single-phase voltage, with variable frequency and RMS value, by bridge inverter. This voltage feeds single-phase induction motor with capacitor starting coil. Finally, the motor drives its load – in created and tested system this is the propeller of the fan. The described system, with different load machines, can find practical application in recreation, for: cooling and ventilation while hot days, providing operation of fountains, filtration of water in swimming pools.W artykule opisano autonomiczny system napędowy małej mocy, w którym występuje wielokrotna konwersja energii. W pierwszym etapie energia promieniowania słonecznego zamieniana jest w generatorze fotowoltaicznym na niskonapięciową energię elektryczną prądu stałego. Z kolei napięcie wyjściowe generatora zostaje podwyższone przy pomocy przerywacza prądu stałego, a następnie zamienione przez falownik mostkowy na jednofazowe napięcie przemienne o zmiennej częstotliwości i zmiennej wartości skutecznej. Napięcie to zasila jednofazowy silnik indukcyjny z rozruchową fazą kondensatorową. Ostatecznie, silnik napędza maszynę roboczą – w wykonanym i przetestowanym systemie jest to śmigło wentylatora. System ten, dla różnych odbiorników, może znaleźć praktyczne zastosowanie głównie w rekreacji: chłodzenie i wentylacja w upalne dni, zapewnienie pracy fontann, filtracja wody w basenach

Aspects of electrical machines and photovoltaic generators cooperation

The most important aspects, determining the operation possibilities of different kind electrical machines in photovoltaic (PV) driving systems, have been discussed in this article. In such a system a PV generator, directly converting sunlight energy into electrical energy, is the basic energy source for electrical machine. Technically, and presently often economically, reasonable examples of PV driving systems applications, such as driving of pumps, compressors, fans and feeders, have been presented below. The basic properties of PV generators, as low-voltage DC-current energy sources with significantly of fate changing parameters, have been short reminded. The basic features of different kind structures of PV driving systems (grid-connected, stand-alone with accumulators, stand-alone without electrical buffer energy sources) have been presented in brief. Detailed description and analysis of different kind electrical machines properties at an angle of possibilities of their operation in PV driving systems has been done. The instructions for selection of energoelectronical energy converters used between PV generators and electrical machines have been also presented. The application of these converters is necessary, because direct connection of the machine to PV generator is either impossible, or in practice not profitable. The article issues will be much more important in Poland in near future, because of permanent, intensive growth of PV market in the wide world (tens percents yearly) for the last several years. This fact should cause analogous state of affairs in Poland soon

Fluctuations in Time of Onset of la-Motoneuron EPSPs in the Cat

Synaptic delay between Ia fiber volley and motoneuron EPSP was originally estimated at about 0.3-0.4 msec. When averaged individual EPSPs evoked by the action of single Ia fibers were recorded, it became evident that this delay was not constant but varied from synapse to synapse. In general, EPSPs with short rise times were initiated with less delay than EPSPs with long rise times, and this was ascribed to electrotonic conduction time in motoneuron dendrites in accord with the prediction of Rall. All of this work was done using averaged individual EPSPs. Here, we show that the synaptic delays associated with a given Ia-motoneuron synapse exhibit fluctuations, and we examine the properties of these EPSPs with long and short delays. Some evidence from this variability is already available at this synapse

Fluctuations in Time of Onset of la-Motoneuron EPSPs in the Cat

Synaptic delay between Ia fiber volley and motoneuron EPSP was originally estimated at about 0.3-0.4 msec. When averaged individual EPSPs evoked by the action of single Ia fibers were recorded, it became evident that this delay was not constant but varied from synapse to synapse. In general, EPSPs with short rise times were initiated with less delay than EPSPs with long rise times, and this was ascribed to electrotonic conduction time in motoneuron dendrites in accord with the prediction of Rall. All of this work was done using averaged individual EPSPs. Here, we show that the synaptic delays associated with a given Ia-motoneuron synapse exhibit fluctuations, and we examine the properties of these EPSPs with long and short delays. Some evidence from this variability is already available at this synapse

Immediate Increase in Ia-Motoneuron Synaptic Transmission Caudal to Spinal Cord Transection

1. Individual EPSPs recorded from triceps surae motoneurons using the spike-triggered averaging technique were found to be larger in amplitude in cats with acute spinal cord transection than in cats with intact spinal cord. This increase occurred whether transection was at T13 or L5. Very large EPSPs (\u3e400 µV) only rarely observed in intact preparations were commonly found. 2. In preparations studied before and immediately after spinal cord transection, it was observed that the increase in EPSP amplitude did not occur instantaneously but took a few hours to develop. 3. The average proportion of the motoneuron pool contacted by single Ia afferent fibers (projection frequency) was close to 100%, beginning apparently immediately after transection at either level. This represented an increase in comparison to the 80% projection frequency in intact preparations. 4. We conclude that spinal transection acutely enhances the strength of Ia-motoneuron synaptic transmission. The delayed increase in amplitude suggests the action of nonneural factors. The relatively quick increase in projection frequency indicates a functional change in previously inactive synapses, rather than the growth of new connections. Furthermore, the amplitude and projection frequency changes appear to be independent