WO2015176789A1

WO2015176789A1 - System for feeding electricity to an electrical grid, and method for operating a system of said type

Info

Publication number: WO2015176789A1
Application number: PCT/EP2015/000806
Authority: WO
Inventors: Alfred Gause; Bernhard Pfaff
Original assignee: AMK Arnold Müller GmbH & Co. KG
Priority date: 2014-05-22
Filing date: 2015-04-17
Publication date: 2015-11-26
Also published as: EP3146607A1; DE102014007640A1

Abstract

The invention relates to a system (1) for feeding electricity to an electrical grid (2), said system (1) comprising an electrical DC link (10), to the input side of which a plurality of generators (12, 14) and/or current accumulators (16) can each be connected via one respective electronic power converter (22, 24, 26), and the output side of which can be connected to the electrical grid (2) via an electronic power converter (20) at the output end. The system (1) further comprises a voltage supply unit (42) for operating at least some of the electrical components and operating means of the system (1), the voltage supply unit (42) being connected to and being fed by the electrical DC link (10). Also disclosed is a method for operating a system of said type.

Description

System for feeding electrical energy into a power supply network and operating method for such a system

The invention relates to a system for feeding electrical energy into a power supply network and an operating method for such a system. Such systems are used, for example, for feeding the electrical energy generated by a photovoltaic system into the low-voltage power supply network. In this case, each solar module is assigned as part of the photovoltaic system, an inverter which converts the photovoltaic DC voltage into a power grid synchronous

AC voltage converted.

The invention has for its object to provide an improved system and associated operating method, which makes it possible to feed electrical energy that can be obtained as DC or AC voltage from different energy sources in an efficient manner in the power grid. In one embodiment, the technical apparatus and control engineering effort for the supply of electrical energy obtained from different energy sources to be reduced while still ensuring a high availability of the system and high reliability of the process with reduced external control effort. This object is achieved by the system defined in claim 1 and by the method defined in the independent claim. Particular embodiments of the invention are defined in the subclaims. In one embodiment, the system has an intermediate circuit, with the input side of which several current generators and / or current accumulators can be connected via a respective converter, and whose output side can be connected to the power supply network via an inverter. Furthermore, the system has a voltage supply connected to the intermediate circuit and fed by the intermediate circuit for the operation of at least part of the electrical equipment of the system.

The power generators may be, for example, photovoltaic modules or fuel cells, or mechanically-electric generators, for example, wind turbines, water wheels or

Internal combustion engines, which may also be part of a combined heat and power plant or a biogas plant. In the power storage can be

For example, to act preferably rechargeable storage for electrical energy on an electrochemical basis. The converters on the input side of the DC link may be

DC converters act, in particular for the connection of photovoltaic modules or electrochemical energy stores, or to inverters, preferably bidirectional inverters / or rectifiers, in particular for the connection of mechanical-electric generators.

A particular advantage of the system according to the invention is that the electrical energy obtained from different energy carriers is combined on a common intermediate circuit. This allows a central control of the feed of the various

Energy sources gained electrical energy. This allows the System availability can be increased, in particular with such a system during the day the photovoltaic energy can be fed and at night or insufficient solar radiation can be used by the system independently other forms of energy for feeding, for example by burning biogas or other biofuels and operating a mechanical electrical

Generator, or by removing energy from one

electrochemical energy storage. In addition, by the connected to the DC link

Power supply system is self-sufficient and preferably no external power supply needed. Furthermore, the system recognizes autarkic when one of the power generators feeds energy into the system and can thus turn on automatically and switch off again automatically in the absence of energy input. The switching on can be effected exclusively by the introduction of energy into the system via the current generators, in particular triggered by the occurrence of a sufficiently high, possibly even unstabilized, voltage on the DC link. In one embodiment, the electrical voltage is on the

DC link, which is preferably a DC link, more than 200 V, in particular more than 300 V and preferably more than 400 V. In a particular embodiment, the voltage is between 500 V and 800 V, in particular about 600 V.

As a result, the electrical energy obtained from different energy sources is particularly advantageous in the

Power supply grid feedable. For example, the

Voltage level of the high-voltage batteries used in electric cars between 400 V and 600 V. Also the mechanical-electrical

Generators can easily generate voltages at this altitude. This allows the converter losses when connecting the Power generators are minimized to the DC link. In addition, the converter losses on the AC converter side of the high-voltage DC link for feeding the electrical energy into the power grid, which may be, for example, a public 230/380 V low-voltage network, also minimal.

In one embodiment, at least a part of the power converters and / or the output-side power converters and / or a control unit of the system is connected to the voltage supply supplied by the DC link. In particular, the power supply can be the supply of all controllable components and resources of the system

take. This is also achieved that with the shutdown of the

Power supply, the power consumption of the system is essentially zero. The system preferably removes the electrical energy necessary for its operation by more than 50% or even

exclusively the input connected to the system

Power generators and / or power storage.

It is particularly advantageous if the power supply is an am

Intermediate circuit pending unstabilized DC link voltage in a stabilized voltage for the operation of the converter and the

output converter converts, in particular in a stabilized DC voltage. Preferably, the voltage supply provides at least one stabilized DC voltage with a rated voltage of less than 120 V, in particular less than 60 V and preferably 24 V. Thus all components of the system essential for the control can be supplied with electrical energy from the power supply. The invention also relates to a method for operating such

System, wherein in one embodiment, the system based on a turned off state, in particular starting from a

switched off state of the output side power converter, in the case of an energy input through one of the power generators in the system in the intermediate circuit generates an initially unregulated voltage through which the power supply for the operation of at least a portion of the electrical equipment of the system is activated. This results in an energy-autonomous start-up of the system from standstill or a stand-by state, without the system requires an external power supply.

After activation of the power supply, the system takes a synchronization of the output side converter with the

Power supply network and then connects the

output-side converter with the power supply network.

Preferably only now done an electrical load of

DC link and thus a power extraction from the

Power generator. This achieves a very stable feed-in operation and improved energy utilization. In one embodiment, the power grid includes a public power grid and a local area network, both with the

Inverters are connectable. The system has a controllable disconnecting switch arranged between the inverter and the public power grid, by means of which the inverter

preferably all-pole disconnectable from the public power grid. As a result, the system can be self-sufficient, for example when detecting a fault on the public power grid or failure of the

public power grid, and / or manually or automatically controlled to disconnect the system from the public power grid and then feed eih m off-grid mode, the electrical energy only in the local network. In one embodiment, the system switches in the case of island operation, in which the output-side converter from the public

Power supply network is disconnected and the system feeds electrical energy into the local network, the occurrence of an electrical overload on the output side converter from and preferably after a predetermined period of time also automatically on again. This enables the system to autonomously respond to an overload and automatically disconnect from the grid and then start up again. It is advantageous if the generator is operated by the system during the shutdown of the system from the grid at idle, even to provide the system with electrical energy.

In one embodiment, the output side stabilizes in particular

Converter the voltage in the DC link to a predefinable value. In a single-phase load, the DC link is used as a short-term energy storage, also to even the load on the power generator to equalize. The speed control of the power generator is preferably carried out via the input-side converter. occurring

Fluctuations in torque can be buffered by speed fluctuations or electrically through the DC link. Corresponding maps for the control can be stored in the control unit of the system. Further advantages, features and details of the invention will become apparent from the subclaims and the following description in which several embodiments are described in detail with reference to the drawings. The features mentioned in the claims and in the description may each be essential to the invention individually or in any desired combination. Fig. 1 shows an embodiment of a system according to the invention, and

Figs. 2 to 4 show different operating states of another

Embodiment of the system according to the invention.

Fig. 1 shows an embodiment of a system 1 according to the invention for feeding electrical energy into a power grid 2. The power grid 2 consists in the embodiment of a public three-phase power grid 4 and a local three-phase network 6, for example, for the supply of a residential building or a farm. Both subnetwork 4, 6 have a matching low voltage level 230/380 V.

The system 1 has an electrical intermediate circuit 10, in

Embodiment a DC intermediate circuit, with its input side in the embodiment, two current generators 12, 14 and a current memory 16 via a respective power converter 22, 24, 26 are connected, and its output side via an output side converter 20, in the case of a DC link via a

Three-phase inverter, to which the power supply network 2 can be connected. The system 1 has a modular design and can be extended, in particular in the manner of a construction kit, by further power converters for the connection of further current generators or current storages. The first power generator 12 has two solar modules 18, the

are connected together to a first power converter 22, which in the exemplary embodiment is a DC-DC converter (DC / DC), which unidirectionally coupled to the DC link 10, the DC voltage generated by the solar modules 18. The second power generator 14 is a preferably permanent-magnet synchronous generator, which may be convection-cooled or liquid-cooled; Alternatively or additionally, an asynchronous generator can be used as a current generator. The second power generator 14 may be driven, for example, by an internal combustion engine, which in turn may be operated with biogas or other biologically produced or even a fossil fuel.

Alternatively, the second power generator 14 may also be driven, for example, by a wind turbine or a water turbine. The second current generator 14 supplies a three-phase in the exemplary embodiment

AC voltage, by means of the second power converter 24 in a

DC voltage is converted, wherein the second power converter 24 is connected with its DC output to the DC link 10. The second power converter 24 may have a load-dependent vector control of the second generator 14 sensorless for optimum energy utilization.

In the power storage 16 is in the embodiment to a battery of electrochemical energy storage, for example, a high-voltage battery with a rated voltage of more than 100 V in

Embodiment of about 400 V. The power storage 16 is via the third power converter 26, which is a bidirectional

DC-DC converter is connected to the intermediate circuit 10. On the output side, the intermediate circuit 10 via an output-side converter 20, which in the exemplary embodiment is a

Inverter is that converts the DC voltage of the DC link 10 in a three-phase AC voltage with the

Power supply network 2 connected. The output-side converter 20 can be any within its power range

Provide reactive power component for the St ömversorgungsnetz 2, the System 1 can automatically regulate. The connection to the

Power supply network 2 is fully automatic. To compensate for an optionally phase unbalanced load of

Power supply network 2, the system can have 1 balancing elements. Between the output-side converter 20 and the power supply network 2, a transformer 28 is arranged.

The system 1 has a control unit 30, which is connected via unidirectional or bidirectional control lines to the input-side converters 22, 24, 26 and to the output-side converter 20. In the exemplary embodiment, the control unit 30 is directly on

output side converter 20 arranged or even formed in a unit with this. The control unit 30 is further connected via a

Network connection line 32 is connected to the public power grid 4 and therefore can detect a failure or failure of the public power grid 4. In addition, the control unit 30 is connected to a circuit breaker 34 and can disconnect the system 1 in a fault, preferably all-pole from the public power grid 4. Furthermore, the control unit 30 has an optionally wireless interface 36 for connection to a public data network 38. Via the public data network 38, the control unit 30 can preferably exchange bidirectional data with a terminal 40 that is connected to the public data network 38. Parallel to the electrical intermediate circuit 10, the system 1 may have a heat circuit, not shown in FIG. 1, which may be branched similar to the electrical intermediate circuit 10, in particular may be connected to the heat circuit several or even all power converters 20, 22, 24, 26 be and dissipate their waste heat to the heat circuit.

In addition, the power generators 12, 14 and / or the

Power storage 16 may be connected to the heat circuit. The heat circle The system 10 can be used as a thermal energy source either only within the system 1 or have a connection to a secondary heating network, in particular to a local heating network, for example, supply of living space or hot water provision.

FIGS. 2 to 4 show different operating states of a further exemplary embodiment of the system 1 according to the invention. FIG. 2 shows the system 1, for example in an off state, in which the system 1 does not require an external power supply. Although the

Disconnector 34 is open, recognizes the system 1 via the

Network link 32 the presence of a public

Power supply network 4. In the network connection line 32, a manually or automatically operated by the control unit 30 of the system 1 switch 44 is arranged, which is closed in the state of Fig. 2. The closed state of the switch 44 gives the control unit 30 the possibility to synchronize to the mains voltage after starting the system 1 and to close the circuit breaker 34 and thus to run a grid parallel operation. In contrast, an open switch 44 indicates that no network parallel operation is possible or desired, but an isolated operation of the local area network 6 by the system 1 is connected only to the local network 6.

On the input side, the second power generator 14 is connected to the system 1 via the second power converter 24, which in the illustrated

Embodiment of an internal combustion engine 46 is driven. To the intermediate circuit 10, a power supply 42 is connected, which on your output side a DC voltage of in

Embodiment provides 24 V as a system voltage, with which the various components and electrical equipment of the system 1 are supplied with electrical energy. In the exemplary embodiment is at the power supply 42 to a switching power supply.

If, starting from the operating state of FIG. 2, the internal combustion engine 46 starts up and introduces energy into the system 1, comparable to the irradiation of sunlight onto a photovoltaic module, the second current generator 14 initially generates an electrical voltage on the intermediate circuit 10 uncontrolled activated, which in turn provides the output side, the supply voltage for the components and resources of the system 1, including the control unit 30. Then recognizes the control unit 30 via the network connection line 32 the queuing of the public power grid 4 and closes after synchronization of the output side converter 20th generated AC voltage to the public

Power supply network 4, the circuit breaker 34. Thus, the

Operating state of FIG. 3 reached. Only now is the second power generator 14 and thus the internal combustion engine 46 loaded in terms of performance.

The system 1 is thus able to start autonomously and to connect to the public power grid 4. As an alternative to starting the engine 46, the second power generator 14 may also be set in motion, for example, by the advent of wind or by the flow of water through a water turbine connected to the second power generator 14.

If, starting from the operating state of Fig. 3, the power of the second power generator 14 drops, for example, because the

Internal combustion engine 46 comes to a standstill or the solar radiation or the wind subsides, the electric voltage drops to the

DC link 10. When the voltage on the intermediate circuit 10 falls below a first voltage value, the output-side converter 20 is switched off by the control unit 30. Accordingly, no Energy is fed into the power grid 2. If the voltage drops to the intermediate circuit 10 below a second voltage value, the power supply 42 is turned off and thus the system 1 is switched off altogether, which then goes into a stand-by mode, the power consumption of the system 1 in stand-by mode preferably is essentially zero.

If, starting from the operating state of FIG. 3, the system 1 detects a loss of the public power supply network 4, or if such a failure is simulated by opening the switch 44 or the separation is to be controlled by the public power supply network 4, the system 1 opens the circuit breaker 34 and thus separates the system 1 from the public power grid 4.

Thereafter, the system 1 continues to supply the local area network 6

electrical energy as long as the system 1 by one of

Power generators 12, 14 or by the power storage 16 on the input side sufficient electrical energy is provided. This corresponds to the operating state of FIG. 4. The further supply of the local network 6 when disconnected from the public power grid 4 takes place without appreciable load interruption, in particular the duration of the switching operation is less than 1 second, in particular less than 0.5 seconds, and preferably less than 0 , 1 second.

Claims

P a n t a n s p r e c h e

System (1) for feeding electrical energy into a

Power supply network (2), wherein the system (1) has an electrical intermediate circuit (10), with its input side a plurality of power generators (1 2, 14) and / or power storage (16) via a respective power converter (22, 24, 26) are connectable , and its

Output side via an output side power converter (20) to the power supply network (2) is connectable, and wherein the system (1) further connected to the intermediate circuit (10) and from the intermediate circuit (10) powered power supply (42) for the operation of at least one Part of the electrical components and resources of the system (1).

System (1) according to Claim 1, characterized in that the voltage supply (42) fed by the intermediate circuit (10) can be switched on automatically starting from a switched-off state of the system (1).

System (1) according to one of the preceding claims, characterized in that at least a part of the power converters (22, 24, 26) and / or the output-side converter (20) and / or a

Control unit (30) of the system (1) is connected to the voltage supply (42) fed by the intermediate circuit (10).

System (1) according to one of the preceding claims, characterized in that the power supply (42) has an am

Intermediate circuit (10) pending unstabilized DC link voltage into a stabilized voltage for the operation of the power converters (22, 24, 26) and the output-side converter (20) converts,

in particular in a stabilized DC voltage. System (1) according to one of the preceding claims, characterized in that the power supply (42) provides at least one stabilized DC voltage with a nominal voltage of less than 120 V, in particular less than 60 V and preferably 24 V.

Method for operating a system (1) according to one of the preceding claims, characterized in that, starting from a switched-off state of the system (1), in particular starting from an off state of the output-side power converter (20), the system (1) in the case of Energy input of one of

Current generators (12, 14) in the intermediate circuit (10) generates an initially unregulated voltage, through which the

Power supply (42) for the operation of at least a part of the electrical equipment of the system (1) is activated.

A method according to claim 6, characterized in that the system (1) after activation of the power supply (42) performs a synchronization of the output side power converter (20) with the power supply network (2) and the output side

Power converter (20) to the power supply network (2) connects.

Method according to Claim 6 or 7, characterized in that the power supply network (2) comprises a public power supply network (4) and a local network (6), both of which can be connected to the output-side power converter (20), and in that the system (1) in case of disruption or loss of publicity

Power supply network (4) the output side converter (20) by a between the output side converter (20) and the public power grid (4) arranged controllable disconnect switch (34) from the public power grid (4) separates.

A method according to claim 8, characterized in that in the case of island operation of the system (1), in which the output-side converter (20) from the public power grid (4) is disconnected and the system (1) electrical energy into the local network (6). fed, the system (1) on the occurrence of an electrical overload, the output side converter (20) turns off and automatically turns on again after a predetermined period of time.

Method according to one of claims 6 to 9, characterized

in that the output-side converter (20) stabilizes the voltage in the intermediate circuit (10) to a predefinable value.

Method according to one of claims 6 to 10, characterized

characterized in that the system (1) in the case of a single-phase load, or a two-phase load, or a

phase unbalanced load on the output side of the

Output side converter (20) uses the intermediate circuit (10) as a temporary storage for electrical energy.