WO2019224583A1

WO2019224583A1 - Electric energy supply system

Info

Publication number: WO2019224583A1
Application number: PCT/IB2018/053680
Authority: WO
Inventors: Blanka Andrea CSIZMADIA; Zoltán CSIZMADIA; László Zsolt SÁNDOR; József Lajos ORMÓS
Original assignee: Microwatt Energetikai És Szaktanácsadói Kft.
Priority date: 2018-05-24
Filing date: 2018-05-24
Publication date: 2019-11-28

Abstract

The invention relates to an electric energy supply system, suitable for meeting the continuous electric power demand of residential consumers with ad-hoc electric power demand, belonging primarily to the same household. The system is connected to at least two independent energy sources (6, 5), wherein one of the sources is a renewable, direct current (DC) energy source (6), and the other energy source is an alternating current (AC) energy source (5). The system contains at least one DC/DC converter (1), a DC/AC inverter (2), a rectifier (3), and a consumer (4), wherein the elements of the system are connected to each other by electric wire (7). The system according to the invention is analogue controlled, and its analogue circuit ensures that the meeting of the power demand of the consumer (4) is shared between the energy sources, and that no power produced by the DC energy source and not used by the consumer (4) can be fed in the AC energy source.

Description

Electric energy supply system

The patent application relates to an electric energy supply system with analogue process control, suitable for meeting the continuous electric power demand of residential consumers with ad-hoc electric power demand, belonging primarily to the same household, which system is connected to at least two independent electric energy sources, and one of the energy sources is a renewable direct current energy source, while the other energy source is an alternating current energy source. An analogue circuit formed in the system ensures that the electric power demand of the consumer is always met by electric power coming from the energy source having the higher voltage.

The patent application further relates to a new commercial method for the settlement of electric power using the energy supply system based on the conversion of a non-stockable renewable energy source and the drawing of electric power.

Power plants meeting the electric power demand of large communities, supplying the public utility network, are usually very high-capacity power plants, they most often convert heat energy or flowing mechanical energy into electric energy, and the electric energy so produced is supplied to the electric power line system. Electric energy is difficult to store in an efficient manner.

Most often rotating machines are used in the process of conversion into large community electric power. In such high-capacity power plants, therefore, the process of conversion, excitation is often controlled. The electric power, process controlled in the excitation circuit, is transmitted through power lines to the consumers. Rotational excitation is controlled on the basis of the load data of the electric distribution network. In large community power plants operated normally for conversion into electric energy, electric energy is often produced from fossil energy carriers, by thermally driven rotating machines. In nuclear power plants electric energy is also produced thermally, by using heat exchangers and rotating machines, to meet the energy demand of various electricity consumers. Low-capacity power plants suitable for supplying electric energy to households or small communities have recently appeared and are now commercially available. These low-capacity household power plants usually convert the energy of a renewable energy source into electric power and have digital process control, their digital process control is made suitable for distributing electric power.

Public utility direct current (DC) networks are rarely constructed to meet a special electric energy demand. Where DC supply is needed, the DC electric power is usually produced on-site from the alternating current (AC) network. DC networks are often designed in such a way that the AC network is converted into a DC network by rectifiers in a local power plant close to the place of consumption. A typical DC network is the network transmitting electric power to tramways, it is not used for supplying household consumers. From the point of view of the place of consumption, DC networks can usually be considered as closed and technically bounded subnetworks. Recently, due to the increasing use of renewable energy sources, the use of controlled direct current networks and small community networks, DC grids and DC microgrids has come to the fore of interest.

Suppliers use AC public utility networks to meet the residential electric energy demand.

Household and small community residential power plants are usually multi-purpose power plants, which are suitable for performing the complex task of energy production and energy distribution. One of their subtasks is to produce electric power from a renewable energy source, used primarily for meeting the energy demand of the own consumers. For this the purpose, the conversion into electric power is controlled. The other task of current household and small community residential power plants is to distribute the produced instantaneous electric energy. When the electric power from own conversion covers the own demand, the system supplies consumers belonging to the own household. When the electric power produced from a renewable energy source exceeds the instantaneous value of the own electric power demand, the remaining surplus is measured and sold, fed into the public utility electricity network. The sold surplus can be used for meeting the power demand of external consumers belonging to another household. In such systems there are separate subunits isolated by technical measures for measuring the drawn - bought - power, there are separate subsystems for producing own produced electric power output from a renewable energy source with the most favourable values, for measuring the surplus power, for taking the technical measures necessary for selling the surplus power, and for calculating the price of the fed-in power.

In order to ensure the safe operation of the public utility supply, household and small community residential power plants need to be approved and licensed by the public utility supplier. Licensing ensures the smooth operation of the public utility supply, as well as the protection of life and property. In the case of such electric power plants installation and operation is conditional not only on compliance with the technical parameters - cycle time, synchronized state, potential relative to the ground -, but household and small community power plants should also be properly prevented from operating as an island. The installation of public utility power plants and residential power plants connected to the distribution network is limited by the fact that the takeover of electric power is not unlimited.

In order to ensure the safe operation of the public utility supply, household and small community residential power plants are designed to automatically disconnect from the public utility network upon reaching a predetermined degree of deviation. Therefore, in such electric power plants, the recovery of the regular and normal operation of the household and small community residential power plant usually requires separate process control and intervention.

The process control of household and small community power plants is made more difficult by the fact that consumers are switched on and operated in an ad-hoc manner. Residential electric consumers can be motor-driven devices, such as kitchen appliances, vacuum cleaners, refrigerators, washing machines; can be electric heating and warming devices, such as hot plates, microwave ovens, water heaters; can also be light sources, such as incandescent lamps, fluorescent lamps or LED lamps; as well as other devices, such as communications and entertainment devices. The simultaneous use of household consumers changes the demand to be met simultaneously from instant to instant in an ad-hoc manner. For controlling the whole process of energy conversion and distribution in order to supply more consumers simultaneously, the production of electric power produced locally from a renewable energy source, and the connection to the public utility network for drawing-selling energy, has to be controlled according to several parameters varying with time, in accordance with the instantaneous direction of the aggregate power balance.

In US Patent No. 8 612 062 lino Yutaka et al. disclose an energy management system and energy management method, which system comprises an energy supply device, an energy demand device, storage sections storing conditions relating to the energy supply, and calculating sections executing negotiation functions, calculating an energy amount satisfying the condition. This reference discloses a system made of digital devices, and a digital method operating such a system.

In US Patent Application published under No. 20090019299, Deng Duo et al. disclose a method and apparatus for adjusting wakeup time in electric power converter systems and transformer isolation, comprising a controller implemented in software, hardware and/or firmware, enabling a Maximum Power Point Tracking (MPPT) algorithm. This reference also discloses a digital design and digital control.

The invention published under No. PL 407538 discloses a direct current grid connecting multiple components. A design similar to the one disclosed is used for connecting electric distribution networks according to the HVAC system, primarily for transmitting electric power through specially designed undersea cables. The current HVAC networks are installed for special electric energy distribution network purposes. The published invention offers the solution used on an industrial scale for special purposes, and scaled specifically for the purpose, for smaller scale residential use in households. According to the solution disclosed in the specification, a direct current distribution network with multiple supplies, supplied by a renewable energy source as well, is supplied using a circuit controlled to a constant voltage unvarying with time and a constant power, and is also connected to a device for storing electric power. A common disadvantage of the disclosed solution and the residential wind power plants and solar power plants used in practice is that in residential or small community electric power distribution networks electric energy cannot be stored, or only to a very limited extent. The instantaneous surplus electric power is usually stored in batteries. In the case of small community or household power plants the direct storage of electric power in batteries is difficult to ensure, not only because the storage capacity is finite, but also for reasons of fire and property protection. The storage through conversion of electric power presents other obstacles, for example the combined losses of back-and- forth conversion are not always covered by surplus energy from the renewable energy source. Another difficulty in use, however, is that the balancing of the difference in time between the storing and drawing of the electric energy produced by conversion, and the occurrence of the consumption demand is not solved in all cases either. The current price of an efficient battery suitable for meeting the electric power demand of a single household makes the mass installation of residential power plant systems storing electric power uneconomical. In addition, the general problem of smart grids - electricity distribution networks that can monitor the flow of electricity - is that the instantaneous surplus electric power has to be used somewhere immediately, or the instantaneous electric power needs to be stored. As residential power plants supplying small communities are usually not equipped with a technical solution for the storage of electric power, recently, for practical reasons, public utility suppliers have incorporated storage power plants into their own network. Public utility suppliers usually implement the storage power plants with a battery solution. Recently, public utility power plants using fuel cells for storing electric power for a shorter or longer period of time have also appeared. The solutions used in storage power plants for storing electric power are direct current systems with a non-linear behaviour varying along a polarization curve. In addition to the non-linear behaviour, control is made more difficult by the time and place of switch on-off events occurring within the network compared to the instant of zero-crossing of the public utility network, and their frequency compared to the network frequency. Which in other words means the distance between the storage power plant with storage capacity and the electricity consumer causing an electric energy event of switch on-off voltage change, and the phase angle corresponding to this distance in the branch supplying the given load. The zero-crossing distance corresponding to a full cycle of one phase in the case of 50 Hz, the standard frequency in Europe, is 6000 km, however, in the case of a 60 Hz public utility environment, in Japan or in the USA, it is only 5000 km. 1/8 cycle points are 750 or 625 km away, the 1/16 cycle points are 375 or 312.5 km away, the 1/32 cycle points are 187.5 or 156.25 km away and the 1/64 cycle points are 93.75 or 78.125 km away from each other on a sine curve of theoretical accuracy, which also means that there is no phase difference between zero-crossing public utility network points of the same switching distance and direct current points. Batteries do not follow Ohm's general law, therefore the accuracy of the measured electric parameter and the display of the meter reading also influence the electric parameter to be measured, obtained as a product. That is, the data are suitable for measurement and control of reference accuracy, but the digitally measured values and the instantaneous values calculated on their basis are not necessarily matching values in every instant, because they may depend on phase angle type data as well, therefore, at different distances there are different powers, which change according the frequency determined by the own public utility supplier, when there is neither feed-in, nor outgoing supply on the given section.

DC microgrids are usually designed with voltage droop or frequency droop control. Such designs can be DC microgrids with either central or distributed control.

Rodrigo A. F. Ferreira et ah, in their article of 5-7th November 2012 entitled Analysis of Voltage Droop Control Method for DC Microgrids with Simulink: Modelling and Simulation, Industry Applications, 2012 lOth IEEE/IAS International Conference disclosed DC microgrid designs. In a master - slave system the communication between interfaces is decisive, the master converter controls the voltage of the DC bus, and sends reference signals to the other converters. The voltage droop control also requires some communication between the units. According to computer modelling data, proportional voltage droop controllers are quicker, while proportional integral controllers have better voltage stability, and both solutions provide good load sharing.

Jinxin Zhao et al. disclose a Distributed control and optimization in DC microgrids on pages 18 - 26 of the November 2015 issue of Vol. 61 of Automatica. Various solutions are discussed through a simplified mathematical model, covering the voltage droop and frequency droop solutions, which are examined with the simplification of real operation, in a constant current or constant impedance load - or purely resistive, or Ohm-capacitive, P - model, omitting the disturbing factors existing in reality. It is easy to see on the basis of the thorough and detailed examination of the simplified operation that even within a single household there are a lot of electric power demand related events that arise from the everyday use of the household appliances and that need to be managed by the control. These ad-hoc events, such as the switching on, use and switching off of appliances used within the household can be learned, but the mathematical modelling of simultaneous operation is yet another separate task to be used for the control. Therefore, due to simultaneous use, process control based on organizing elementary pre-stored event-driven processes into an algorithm requires a lot of computing resources.

Fenil V Gadhethariya et al., in their article entitled Analysis of Voltage Droop Control of DC Microgrid, published in May 2014 in Issue 5 of Volume 4 of the Indian Journal of Applied Research (ISSN 2249-555x), deal in detail with a DC microgrid design, comprising a photovoltaic (PV) device, a DC-DC converter, an inverter and a fuel cell, and the computer simulation thereof, capable of operation in a feed-in system and in island operation as well. In addition to the general DC microgrid topology, the article also covers simple and complex PV device designs, emphasizing that the integration of a stand-alone PV device solution into a system requires a battery as well, which is charged and discharged by a charging device.

The invention of GB Patent No. 2519823 discloses a method and system for powering a load, wherein the power may be provided to said load by DC and AC voltage sources. The specification discloses a system and method for controlling an electrical power supply to a load, comprising the use of a first, renewable electrical power source to generate a first amount of power for supply to the load, the comparison of the first amount of power to the power demand of the load, and the determination of whether to supply power to the load from a second, different electrical power source, such as the AC grid. The specification discloses a digital system design and method for controlling the subprocesses of the generation of power, the comparison of the generated power and the power demand, and the determination of whether to use a second power source. A disadvantage of the solution is that it uses a lot of computing resources, and leaves a lot of room for errors. According to the method, the first amount of power generated by the first electrical power source is maximised using MPPT, and when the comparison step indicates that there is a shortfall amount between the first amount of power generated by the first electrical power source for supply to the load and the power demand, the output of the second electrical power source is controlled so that the second amount of power is as close as possible to said shortfall amount. The solution according to the invention uses computer software for MPPT, and a computer can be configured or adapted to perform the described method.

Contrary to previously known solutions, a device for energy conversion and electric power distribution, and a method for local load sharing can be implemented not only with a DC microgrid with battery or feed-in, but systems made for this purpose with a suitably designed analogue circuit device can also be controlled in an analogous manner. All subprocesses of such process control can be performed on-site, and thus load sharing can also be performed fully at the place of consumption through the operation of the system. Surprisingly, such an electric energy system requires little human and little computing resources, and is suitable for meeting ad-hoc household consumption demand both in island operation and in power drawing operation, and can be operated without equipment suitable for the storage of electric power.

With the solution according to the invention, for residential small community power plants converting a non-stockable renewable energy source at the place of consumption, a commercial method for the settlement of the electric power can be implemented under more favourable conditions compared to previously known residential power plants. With the solution according to the invention, electric power is only drawn from the public utility network, therefore there is no need for a feed-in metering device. Due to eliminating the option of feed-in, the number of computing devices required for the settlement - the number of metering devices to be installed, the demand for the use of data storing and data processing computing resources - can be reduced to a half.

An object of the invention is to eliminate the disadvantages of the currently known solutions, and to develop an electric energy supply system, which system draws the energy required for its operation simultaneously on the one hand from a renewable energy source available locally, and on the other hand from an externally owned electricity network, preferably a public utility network, and which system ensures continuous and safe power supply to the electric consumers of a household or small community. Another object of the invention is to ensure that the sytem is capable of operating autonomously, in an island-like manner, independently of the network of the public utility supplier, and is also capable of cooperating with it, and that, if necessary, it is capable of supplying power independently to consumers belonging to a household.

The system does not allow the electric power produced from a renewable source and not used by the consumers to be fed in the public utility network.

Furthermore, the system ensures that, when a sufficient amount of renewable energy is available, the power supply to the own consumers is provided through the distribution of electric power from the renewable energy source, by producing the highest instantaneous power at the highest efficiency, or if the amount of renewable energy available at a given instant is lower than the energy demand, only the necessary amount is drawn from the public utility network.

The idea of the invention is based on the fact that, contrary to the previous general technical practice, a method of analogue process control is preferable to a method of digital process control for the combined control of such complex processes as the subprocesses of the production of electric power from a renewable energy source and the distribution of the electric power drawn from the public utility electricity network, which control processes are required in currently available residential electric power plants in the process control of processes related to conversion into electric power, and to the distribution and drawing of electric power according to the instantaneous values, which processes are executed in the devices currently available in the market, forming an integral part of the operation of devices designed for the performance of such a complex task. In addition, the invention also simplifies the commercial method for the settlement of electric power for residential power plants made exclusively for supplying consumers belonging to a household or a small community, because contrary to power plants of previous designs converting non-stockable energy sources into electric power, the operation of which also requires uninterrupted and continuous public utility supply, and the use of previously known solutions for conversion efficiency based on an at least three-dimensional function, with the value of the instantaneous conversion of the surplus convertible power of the renewable energy source exceeding the limit value, the lower limit under the instantaneous household parameters, our power drawing power plant of analogous design will not feed-in power under any circumstances. Therefore, there is no need for the technical solutions and organizational knowledge required for the previously known solutions, either for their operation or for the settlement of the electric power.

The idea of the invention is based on the recognition that an electric energy supply system, to be operated in a household, or according to the small community distribution model, producing electric power from a renewable energy source using a direct current converter, preferably a PV device or a small wind turbine, for supplying residential consumers found in households or small plants, preferably for supplying AC consumers that can be connected to and operated by it, and for performing load sharing between the public utility electricity network and the locally produced electric energy, preferably especially in the electric power range of < 15 kW, can be implemented by assembling analogue circuit elements and by using exclusively analogue process control.

When in a household electric power plant system a DC supply supplied from two directions is designed in such a way that the electric power flows in the supply branches only in the direction of consumers demanding electric power, belonging to the own supplied household, and is blocked towards the source of the supply branches, all subprocesses related to the conversion of a renewable energy source into electric power and electric load sharing can be performed preferably with little instrumentation and without additional digital computing resources, even if the consumer demand belonging to the own household needs to be met in an ad-hoc manner. Several devices are available for making the flow of electric power unidirectional, and a so designed DC supply, supplied at least from two directions, can supply a DC/ AC inverter that can meet the ad-hoc electric power demand belonging to the own household.

Thus, the invention relates to an electric energy supply system, suitable for meeting the continuous electric power demand of residential consumers with ad-hoc electric power demand, belonging primarily to the same household. The system is connected simultaneously to at least two independent electric energy sources, which supply electric energy to the system. One of the energy sources is a renewable, direct current (DC) energy source, and the other energy source is an alternating current (AC) energy source.

The electric power of at least one of the selected energy sources is sufficient in itself to meet the demand of the own household at all times.

The system contains the following elements: at least one DC/DC converter, a DC/ AC inverter, a rectifier and a consumer, wherein the elements of the system are connected to each other by electric wire. The DC energy source is connected by electric wire to the direct current input point of the DC/DC converter, the AC energy source is connected by electric wire to the alternating current input point of the rectifier.

The electric wires coming from the direct current output point of the DC/DC converter and direct current output point of the rectifier are connected to each other, forming a node. The electric wires of the system conducting direct current come into this node. The electric wire coming from the node is connected to the direct current input point of the DC/ AC inverter.

The direct current output point of the DC/DC converter, the direct current output point of the rectifier, the node and the direct current input point of the DC/ AC inverter, and the electric wires connecting these points with correct polarity, form a circuit designed as an analogue device within the system. The circuit designed as an analogue device ensures that from the energy sources the current can flow only in the direction of the consumer. The design of the system prevents the current instantaneous voltage of the node from appearing either at the converter input point, at the rectifier input point or at the alternating current output point.

The renewable energy source is a solar panel known in itself, or a known rotating machine producing electric power.

In a preferred embodiment the energy source supplying the DC/DC converter is a solar panel or a PV device formed by connecting solar panels in an array, which converts the light of the Sun into electric power. The solution according to the invention allows the system to contain more than one DC/DC converters, then each DC/DC converter is connected to a machine converting into electric power, which can be machines operating on the same principle, or can be machines operating on a different principle, such as the combined use of a PV device and a small wind turbine. Each electric wire coming from the converter direct current output points of the DC/DC converters is connected to the node. It is easy to see that there is no need for the installation of separate data connection or data transmission.

In the solution according to the invention, the AC energy source can be any source that has properties corresponding to the network voltage signal, preferably the public utility network, or energy drawn from it, but the AC energy source can also be a generator, where appropriate.

The solution according to the invention is described in detail with reference to the following figures, without being limited thereto:

Figure 1 : shows the elements of the system according to the invention and their connection to each other, in a linear representation;

Figure 2: shows the elements of the system according to the invention and their connection to concrete energy sources, in a linear representation.

Figure 1 shows the elements of the system: a DC/DC converter 1 , a DC/ AC inverter 2, a rectifier 3 and a consumer 4, where these are connected to each other by electric wire 7. The DC/DC converter 1 has a converter input point 11 and a converter output point 12, to which electric wires 7 are connected. The DC/AC inverter 2 has an inverter input point 21 and an inverter output point 22, to which electric wires 7 are connected. The rectifier 3 also has a rectifier input point 31 and a rectifier output point 32, to which electric wires 7 are connected. The electric wire 7 coming from the converter output point 12 and the electric wire 7 coming from the rectifier output point 32 are connected to each other, forming a node 10. The electric wire 7 coming from the node 10 is connected to the DC/AC inverter 2 through the inverter input point 21 thereof. The electric wire 7 coming from the inverter output point 22 of the DC/ AC inverter 2 is connected to the connection point 41 of the consumer 4. The connection point 41 is the supply point of the internal circuit of the own household, which supplies electric energy to the electric household appliances connected to it.

The electric wire 7 coming into the converter input point 11 is connected to a DC energy source supplied with electric power from a renewable energy source, while the electric wire 7 coming into the rectifier input point 31 is connected to an AC energy source. Within the system the converter output point 12, the rectifier output point 32, the node 10 and the inverter input point 21, and the electric wires 7 connected to these points form a circuit designed as an analogue device. The voltages present at the converter output point 12, the rectifier output point 32, the node 10 and the inverter input point 21 form the energy sources of the circuit within the analogue device.

In the Figure arrows show the direction of electricity flowing in the electric wires 7, it can be seen that the end point of the electric powers starting from the energy sources is the consumer 4. In the specification the terms„output” and„input” are used in accordance with the direction of electricity flow indicated in the Figures, and the voltage conditions of the individual elements are also shown in the Figures.

Figure 2 shows, in addition to the elements of the system, the DC and AC energy sources as well, and their connection to the system according to the invention. In the shown embodiment the DC energy source can be a simple solar panel, or a PV device 6 formed by connecting solar panels. The electric wire 7 coming from the direct current output point 62 of the PV device 6 is connected to the converter input point 11.

In the shown embodiment the AC energy source is the public utility network 5, the electric wire 7 coming from the alternating current output point 52 thereof is connected to the rectifier input point 31. At the rectifier output point 32 the rectifier 3 supplies a constant effective DC1 voltage of constant direction.

In the solution according to the invention the function of the DC/DC converter 1 is to convert the voltage of the direct current (DC) energy source to a DC2 voltage, to prevent the voltage of the node 10 from appearing at the converter input point 11, and to adjust it to the DC voltage demanded by the DC/ AC inverter 2.

In the solution according to the invention, the DC/DC converter 1 is designed is such a way that for the rated terminal voltage measurable at the output of the converter, when converting environmental potential at the rated power of the renewable energy source, a predetermined DC2 voltage appears at the converter output point 12. This DC2 voltage depends on the instantaneous value of the environmental potential of the non-stockable renewable energy source, and also on the instantaneous efficiency of conversion, therefore it is a DC voltage of constant direction and variable size, the value of which is proportional to the instantaneous available electric power. Therefore, the DC/DC converter 1 is designed in such a way that during conversion under rated environmental conditions, when supplied with the rated voltage of the direct current output point 62, the DC2 voltage is higher than the DC1 voltage.

The rated voltage of the direct current output point 62 of the DC energy source, measured at the converter input point 11, is adjusted by the DC/DC converter 1 to the required value. During its operation, the DC/DC converter does not change the direct current nature of the voltage present at the converter input point 11, its function is to adjust it to the value of the DC input demanded by the DC/ AC inverter 2, to prevent the current instantaneous voltage of the node 10 from appearing at the converter input point 11 , and to ensure that the load present at the direct current output point 62 as instantaneous terminal voltage is changed as little as possible by the current value of the ad-hoc change in the set of consumers 4.

Therefore, the DC2 voltage always depends on the instantaneous renewable energy source potential, on the instantaneous efficiency of the given energy source conversion, and also on the instantaneous impedance. This is also true when several renewable energy sources available on site are used in such a way in the DC supply branch that the different types of energy sources, by taking into account their own characteristics, are connected by electric wire 7 to an own DC/DC converter to form a separate supply branch by converter, which produces a DC2 voltage at its own output when converting the rated potential, and the so formed converter output point 12 is used as the DC supply branch. With this design of a supply branch from a renewable energy source, several branches of DC2 voltage can be connected by electric wire 7 to the node 10 simultaneously, thus allowing the use of several types of renewable energy sources to supply the set of ad-hoc consumers 4 of the own internal network simultaneously, while the normal household use of the elements of the set of consumers 4 does not affect significantly the preferable utilization of the renewable energy source potentials.

The electric wire 7 coming from the converter output point 12 of the DC/DC converter 1 is connected directly to the node 10. From the point of view of the node 10, it is one of the input power components thereof. The electric wire 7 coming from the rectifier output point 32 of the rectifier 3 is connected to the node 10, from the point of view of the node 10, it is another of the input power components thereof.

The AC/DC rectifier 3 can be any device that converts alternating current into direct current, irrespective of its input and/or output form. Its function, in addition to converting the voltage of the alternating current (AC) energy source to the DC voltage demanded by the inverter input point 21 of the DC/AC inverter 2, is to prevent the current instantaneous voltage of the node 10 from appearing in the section bounded by the alternating current output point 52 and the rectifier input point 31. It is easy to see that the solution according to the invention is not suitable for feed- in operation, however, it is capable of island operation according to the instantaneous potential of the renewable energy source.

The DC/ AC inverter 2 is a voltage converter that converts the direct current appearing at the inverter input point 21 into alternating voltage of a power suitable for the consumer 4, thus the consumer 4 can be connected and operated within the internal network through the inverter output point 22 of the DC/AC inverter 2.

In the system, the only electric wire 7 coming out from the node 10 is connected to the inverter input point 21 of the DC/ AC inverter 2. The node 10 is a privileged place in the system, which is not bypassed by the power of the electric energy supplied by the elements managing the energy flow of the system according to the invention, and the voltage of which corresponds to the voltage value present at the inverter input point 21 of the DC/ AC inverter 2. This value is a decisive value of the system, the value or value range specified by the manufacturer of the component elements.

The voltage of the node 10 supplies the DC/AC inverter 2, by connecting directly to the inverter input point 21 thereof.

Physically, Kirchhoff’s first law applies to the node 10 at all times, where the current supplied by he output of the DC/DC converter 1 represents the currents flowing into the node 10, and the inverter input point 21 represents the value of the current flowing out of the node 10. According to Kirchhoff’s first law, at a node the sum of the currents flowing into that node is equal to the sum of currents flowing out of that node, which law applies in real time, under all circumstances and without any active or passive intervention, automatically.

This design is an analogue system, which during its operation controls the extent to which the individual energy sources present on the input side prevail as a function of their instantaneous voltage conditions, and forces their input to an extent corresponding to the instantaneous load, in a shared way.

In the device of the analogue system the electric wires 7 coming from the converter output point 12 and the rectifier output point 32 are connected directly to the node 10, that is the currents coming from the individual energy sources are currents flowing into the node 10. The electric wire 7 coming from the node 10 is connected to the inverter input point 21, and thus defines the current demand of the node 10 according to the resultant impedance of the set of consumers 4, which current demand is the current flowing out of the node 10. Within the analogue system, the circuit effect acts at the node 10 in such a way that the supply branches supply it with a voltage corresponding to their instantaneous power. Therefore, at a given instant in time, the output current demand is divided on the input side into components shared between the individual energy sources, the sum of which is equal to the output current demand. The circuit of the device of the analogue system controls the proportions of the division of the current demand into components shared between the individual energy sources by supply branch in such a way, that the output current is always supplied by the energy source having the higher voltage. In the case of same voltages, the input currents supply the required output current together, in a shared way.

Kirchhoff’s first law and Ohm’s law apply in a combined manner to the operation of the analogue system supplied in this way. For the power demand of a consumer 4 at a given instant, the current demand is also known in every instant at the voltage level defined by the inverter output point 22. (I=P/U, where P is the rated instantaneous power demand of the set of consumers operating at a given instant, and U is its operating voltage, which is at the same time the operating voltage of the DC/AC inverter 2 as well, in this case the 230 V of the AC network. Thus, the current demand of the consumer will be determined for the circuit by the two known members.)

This consumer current demand defines the output current of the node 10, which also defines the sum of the input currents of the node 10 supplied by the converter output point 11 of the DC/DC converter 1 and the rectifier output point 32 of the rectifier 3. And the sharing of these currents between the individual energy sources is determined by their voltage conditions, there is no need for the use of switch contacts in the system.

The use of the system does not require measuring instruments and digital control based on organizing event-driven pre-stored processes into algorithms, when the analogue system is loaded and the load is supplied in the given way, the operating conditions are set, by selecting the DC1 and DC2 voltages the analogue control is implemented by itself. Therefore, both on-site conversion into electric power, and on-site electric load sharing can be performed by operating the system.

The term consumer 4 is used to mean a set of electric consumers operating at a given instant, using standardized alternating voltage and not exceeding the normal power demand of households.

Preferably, the DC energy source is a machine or PV device 6 converting the rays of the Sun into electric current using the photovoltaic phenomenon. Its normal operating voltage is low voltage direct current, which can take any value between zero and the so called no-load voltage as a function of the load connected to its terminals and the intensity of radiation at its surface.

The public utility network 5 is a basic energy source with a high power reserve, providing continuous energy supply. The network supplies alternating voltage according to standardized values, it is capable of supplying the consumer directly.

Such a system can be made without switch contacts, preferably from analogue circuit elements. A further advantage of the system is that the branch currently capable of supply can be continuously and simply selected, and the continuous back-and-forth switching of the load between the branches supplying the current power demand can be simply controlled by the DC2 and DC1 values taking into account the input of the DC/ AC inverter 2.

With the solution according to the invention, the system uses a DC energy source supplied with electric power produced from a renewable energy source to supply the consumer, if the DC energy source can meet the power demand of the consumer, then the total electric power demand of the consumer is met by the DC energy source. If the energy amount of the DC energy source is less than the energy amount demanded by the consumer, then the missing energy is supplied by the AC energy source. The power of the public utility network 5 exceeds the demand of household consumers by orders of magnitude, thus the system can use it as the only energy source, if necessary.

Therefore, the voltage of the inverter input point 21 always corresponds to the voltage demanded by the ad-hoc instantaneous impedance belonging to the own household, and thus the DC/ AC inverter 2 is capable of meeting the instantaneous electric power demand in the circuit supplied in the own household.

In the case of consumers 4 used at a given instant within the own household, usually the impedance profile changes dynamically with time, and is also modified by the instantaneous status indicators of combined operation. Simple summation is made more difficult by the fact that both the semiconductor elements and the batteries and capacitors, similarly to fuel cells, are ohmically non-linear circuit elements, therefore, by taking into account the inductive components, phase-correct vector summation should be performed for the correct use of the computing resources and algorithms, and load sharing should be selected by taking into account the switching distance as well, which can be avoided with the solution proposed by us.

The previously disclosed residential small community power plant system solutions using non- stockable renewable energy sources usually do not perform vector summation, but are designed in such a way that electric power exceeding the instantaneous electric power demand is fed in the public utility network 5 by using a separate control unit, while the electric power exceeding the own demand is measured by a separate meter. These previous priority-controlled systems draw from the public utility network 5 the total instantaneous electric power demand of the own household in all cases, which demand necessarily includes the electric power demand required for the operation of the given power plant, considered to be constant, and in addition, the instantaneous demand of the consumer 4 operated in an ad-hoc manner in the household. The previous solutions are designed in such a way that a system using some kind of an MPPT algorithm is used to control the efficiency of conversion from the non-stockable renewable energy source - implemented as a separate measurement and process requiring computing resources and electric power - for producing electric power, to control the conversion into electric power, and to perform by means of further circuit elements the parametrisation necessary for feed-in, in order to sell electric power corresponding to the parameters of the public utility network 5, and to be able to feed in at an instant close to the zero-crossing in a phase- synchronized manner. As the solution according to our invention is technically designed in such a way that it is impossible for the own produced electric power to appear in the direction of the public utility network 5, there is no need for the use of a separate MPPT and other resources, including the use of own computing resources, and in addition, the resources required for the installation and operation, technical organization of a branch for selling electric power to the public utility network 5 can be reduced to about a half. Although the previously disclosed solutions are practically considered to be real-time in practice, this real-timeness, however, due to the signal processing required by digitization, and the time required for the execution of the digitized signal algorithms/programs, is never same-instant processing and control, which is an important element in the development of the total process control of the power plant, because the behaviour of power machines converting non-stockable renewable energy sources - especially those based on the photovoltaic effect - is such that in the event of overload the energy conversion process is immediately stopped. As the design according to the invention proposed by us does not receive the energy required for its control from the public utility network 5, in the event of an outage of the public utility network 5 it remains operational to a limited extent, when the instantaneous potential of the non-stockable renewable energy source contains sufficient convertible energy to meet the power demand of the consumers 4 ad-hoc connected in a given instant within the household. This requires the instantaneous value of the potential of the non- stockable energy to be at least so high at all times, that the value given by the instantaneous efficiency corresponds to the ad-hoc consumption demand increased by the operation of the system according to our invention, meeting the demand supplied by the residential power plant according to our invention. When using the power plant designed according to our invention, for settlement it is sufficient to record and manage data on the electric power drawn from the public utility network 5.

The analogue system can be controlled by selecting the value of the DC1 and DC2 voltages, and with such a design, the supply branches can be continuously selected by the stepless back-and- forth switching of the load in the system, in order to supply electric power to the consumers 4 at all times on demand exclusively within the own household. Therefore, the DC/DC converter 1 incorporated into the device of the system is designed in such a way that by taking into account the rated voltage measurable during the conversion of the renewable energy source, performed under rated environmental conditions, while supplying the same voltage to the converter input point 11 as that of the direct current output point 62, the DC2 voltage of the converter output point 12 is some volts higher than the DC1 voltage, which is the voltage of the normal alternating current supply of the rectifier 3, at the rectifier output point 32 thereof, for supplying the node 10 in order to supply the DC/ AC inverter 2 by taking into account the constant continuous electric power demand. Therefore, there is no need either for separate measurement, or to act according to a pre-stored event-driven process organized into a separate algorithm, either during the conversion of the energy, or for the sharing of the electric load, in order to meet the current instantaneous power demand of the set of ad-hoc consumers 4 by operating the device. It is also simple to see that in such a system the load can be continuously switched back-and-forth between the supply branches, always selecting a supply branch that meets the electric power demand, even when supply to the set of ad-hoc consumers within the own household has to be solved by the non-priority distribution of electric power.

The usability of the solution according to our invention, which has been under own testing and development for some years, is characterized by the behaviour of an undersized solar panel embodiment, experienced under blackout conditions, as a stress test, to which our test system was exposed to between 15th and 18th March 2018, in an unmanaged and special period for smart grids. The test system is used in an assisted mode of operation, where the installed solar panel power is less than 1 kW for meeting the daytime energy demand of a normal household. The PV power of the test system under laboratory conditions is about 850 W, from which a real peak power of about 650 W can be expected, and from which 500-550 W can be drawn with the assembly according to the invention, under ideal weather conditions. Weather conditions are considered ideal when the ambient temperature is not extremely high and it is sunny. In the area of operation of the test system there was a total blackout covering a large area, which completely excluded smaller villages and most of the people living in the area from the public utility supply due to short circuits, torn cables and broken poles caused by freezing rain. At a time close to the astronomical equinox, for whole days the temperature was below freezing and it was cloudy, clouds covered a large area. At the place of installation of the test system the total blackout ended in the evening of 18tb March 2018, after lasting for about 20 hours. Because of the total outage of the public utility network 5 starting in the evening hours, during the night most of the homes cooled down, and cooling down continued even after sunrise, the communications networks operated in emergency mode for a long time. The test system, operated under such conditions, during the period between sunrise and sunset, continuously supplied a power of 80 - 100 W, this power proved to be sufficient for operating the about 50 W pump of a gas heating system during the day, and for charging mobile phones, and allowed the use of other consumers as well, for example during the daytime hours the power of our test system was sufficient for operating a television set, while the public utility network 5 branch was under repair.

Such a system is simple to operate, simple to de-energise, it operates exclusively as a power drawing system in such a way that feed-in is technically impossible. The device is suitable for island-operation as well, and in places where no public utility network 5 is installed, it is suitable for being supplied by an individual AC generator.

The system according to the invention allows the implementation of the set objectives, the energy conversions are performed in a self-controlled manner, by analogue process control.

Claims

1. Method for the operation of an electric energy supply system meeting the ad-hoc electric power demand of consumers belonging to the same household, which system is used exclusively for meeting the ad-hoc electric power demand of consumers belonging to the same household, for the conversion of a renewable energy source available on-site into electric power and for on-site electric load sharing, and which system has analogue process control, and according to this analogue process control method a machine converting a renewable energy source into direct current electric power supplies a DC/DC converter ( 1 ) installed in the system; an AC source, which in itself is capable of supplying power suitable for continuously supplying an ad-hoc set of standard consumers belonging to the own household, supplies a rectifier (3) installed in the system; an analogue device is formed by electrically connecting analogue circuit elements designed without switch contacts, in which all subprocesses related to the conversion of the instantaneous potential of a renewable energy source into electric power and simultaneous supply from an AC source, and related to the distribution of the electric power of the electricity supply to meet the current instantaneous electric power demand of an ad-hoc set of consumers belonging exclusively to the own household, can be performed in the system without organizing them into a separate algorithm; a direct current voltage level is set in the system to supply the DC/AC inverter (2), which is supplied from a node (10), which is formed in the system by selecting and electrically connecting suitable pre-determined DC2 and DC1 supply voltages, in order to ensure that the branch suitable for meeting the instantaneous electric power demand can be continuously selected; continuous branch selection is performed between the branches of voltage DC2 and voltage DC1, resulting in the continuous, stepless back-and-forth switching of the load, in order to be able to meet, by supplying the DC/ AC inverter (2), the current instantaneous AC electric power demand of the set of all ad-hoc connected consumers (4) appearing exclusively in the internal circuit of the own household with an electric power demand, to be supplied on a non-priority basis, by operating the analogue device of the system.

2. The electric energy supply system according to claim 1, suitable for meeting the continuous electric power demand of a set of residential consumers (4) belonging primarily to the same household, characterized in that the system is connected to at least two independent electric energy sources, wherein one of the energy sources is a renewable, direct current (DC) energy source, and the other energy source is an alternating current (AC) energy source; the system comprises at least one DC/DC converter (1), a DC/AC inverter (2), a rectifier (3), and a consumer (4), wherein the elements of the system are connected to each other by electric wire (7) in such a way that the electric wire (7) coming from the direct current output point (62) of the DC energy source is connected to the converter input point (11) of the DC/DC converter (1), the electric wire (7) coming from the alternating current output point (52) of the AC energy source is connected to the input point (31) of the rectifier (3), the electric wires (7) coming from the converter output point (12) of the DC/DC converter (1) and the rectifier output point (32) are connected to each other, forming a node (10); the electric wire (7) coming from the node (10) is connected to the inverter input point (21) of the DC/ AC inverter (2), the electric wire (7) coming from the inverter output point (22) of the DC/ AC inverter (2) is connected to the connection point (41) of the consumer (4); the converter output point (12), the rectifier output point (32), the node (10) and the inverter input point (21), and the electric wires (7) connected to these points are parts of the circuit formed within the analogue system.

3. The system according to claim 2, characterized in that the DC energy source is at least either one solar panel or one PV device (6).

4. The system according to claim 2, characterized in that the AC energy source is energy drawn from the public utility network (5).

5. The system according to claim 2, characterized in that the AC energy source is a generator.

6. Method for the settlement of the electric power of electric consumers belonging to the same household, according to which method an electric energy supply system is operated in such a way that the current electric power demand of an ad-hoc operated ad-hoc set of consumers belonging preferably to a household or a small community is produced on-site by an analogue power plant system installed at the place of consumption, according to which method electric power is produced on-site from a non-stockable renewable energy source by a power machine converting into electric power, using a PV device (6), where appropriate, to which a DC/DC converter (1) is connected, and which is connected by a node (10) to a rectifier (3), which is supplied directly from the public utility network (5); the node (10) supplies a DC/ AC inverter (2), designed exclusively for supplying an ad-hoc set of consumers (4) belonging to the own household; and which process is characterized by the fact that in the process of electric power settlement exclusively the electric power bought from the public utility network (5) is measured and recorded.