AU2016286182B2 - Energy management system for an energy generation system - Google Patents

Abstract

The invention relates to a DC-coupled energy management system (10) for an energy generation plant (100), in particular a photovoltaic system, comprising a control unit (30), a sensor unit (32) for measuring an electrical balance between consumer units (80) of the energy generation plant (100) and a mains power connection (20) of an energy supply network (200), and a DC/DC converter (22), which is connected by a first connector (24) to an electrical connecting line (16) of the energy generation plant (100) between an energy converter (12) and an inverter (14) coupled to the supply network, and is also connected by a second connector (26) to at least one energy storage unit (40). The control unit (30) is designed for communication connection to the sensor unit (32), to the energy storage unit (40), and to the DC/DC converter (22). The energy converter (12) is provided in order to supply a variable DC voltage power in accordance with operating conditions and/or environmental conditions. Furthermore, a withdrawal or a delivery of electrical energy by the DC/DC converter (22) can be controlled by means of the control unit (30), wherein the control unit (30) controls the DC/DC converter (22) according to the electrical balance specified by the sensor unit (32). The invention further relates to an energy generation plant (100) comprising such a DC-coupled energy management system (10), to a DC/DC converter for such a DC-coupled energy management system (10), and to a method for operating such an energy generation plant (100) having such a DC-coupled energy management system (10).

Description

Energy management system for an energy generation system

Cross-Reference to Related Applications

This application is a National phase application of PCT/EP2016/000440 filed on 11 March 2016,

which claims the benefit of German Patent Application No 10 2015 008 305.8 filed on 29 June 2015,

the disclosures of which is incorporated herein by reference in their entirety.

Technical field

This disclosure relates to a DC-coupled energy management system for an energy generation plant,

in particular a photovoltaic plant, an energy generation plant with a DC-coupled energy

management system, a DC/DC converter for a DC-coupled energy management system, and a

method for the operation of an energy generation plant with a DC-coupled energy management

system.

Prior art

The electrical interconnection of photovoltaic modules (PV modules) of a PV plant by means of a

series and/or parallel connection to form so-called strings of a PV unit is known. Depending on the

size of the PV unit and on the PV modules used, the voltage level of these strings lies in the range

between 30 and 1500 V. The typical current in such an electrical connecting line lies in the range

between 0.1 and 30 A. This string is connected by means of a DC cable to a string input of an inverter

that is coupled to a power supply network. The inverter coupled to a power supply network can,

when appropriate, comprise a plurality of such string inputs, to each of which a string can be

connected.

An energy generation apparatus designed as a photovoltaic plant with a converter apparatus with

DC/DC converter is known from DE 10 2012 022 729 Al, wherein the converter apparatus is

connected through a first bidirectional DC terminal to a battery for discharging and charging the

battery and through a second DC terminal to an inverter coupled to a power supply network. The

converter apparatus comprises a third DC terminal with which it is connected directly to the

photovoltaic plant.

The second and third DC terminals can be bypassed through internal or external switches in such a

way that current of the energy generation apparatus can be passed directly to the inverter coupled to a power supply network. A switch is furthermore arranged between the DC/DC converter and the second DC terminal and between the third DC terminal in order todecouple the DC/DC converter from the second DC terminal and the third DC terminal if, for example, the solar module, when in a darkened state or at night, cannot withstand an external voltage.

Any discussion of documents, acts, materials, devices, articles or the like which has been included in

the present specification is not to be taken as an admission that any or all of these matters form part

of the prior art base or were common general knowledge in the field relevant to the present

disclosure as it existed before the priority date of each of the appended claims.

Throughout this specification the word "comprise", or variations such as "comprises" or

"comprising", will be understood to imply the inclusion of a stated element, integer or step, or group

of elements, integers or steps, but not the exclusion of any other element, integer or step, or group

of elements, integers or steps.

Disclosure

It is an advantage to create a DC-coupled energy management system that can be coupled in a

simple manner to an energy generation plant and operated efficiently.

Further advantages are those of designing an energy generation plant in such a way that it can be

operated efficiently with a DC-coupled energy management system, of providing a DC/DC converter

for such a DC-coupled energy management system, and of creating a method for the operation of

such an energy generation plant that permits an operation that is as efficient as possible.

There is provided a DC-coupled energy management system for an energy generation plant, the

energy generation plant being a photovoltaic plant, comprising

- a control unit, - a sensor unit for the measurement of an electrical balance between loads of the energy

generation plant and a network terminal of an energy supply network,

- a DC/DC converter which is connected through a first terminal to an electrical connecting

line of the energy generation plant between a photovoltaic energy converter and an

inverter coupled to a power supply network, and through a second terminal to at least one

energy storage unit, wherein the control unit is designed for communicative connection with the sensor unit, the energy storage unit, and the DC/DC converter wherein the photovoltaic energy converter is provided for the provision of a variable DC power depending on operating and/or environmental conditions, wherein the inverter coupled to a power supply network is provided to feed one or a plurality of loads, and is connected to the power network terminal, wherein the inverter is configured to perform maximum power point tracking (MPPT) by adjusting an internal DC resistance at the electrical connecting line of the inverter, that is connected to the

DC/DC converter, to maximize power generated by the photovoltaic energy converter,

wherein the DC/DC converter is of bidirectional design, so that electrical energy can be drawn from

the electrical connecting line and/or electrical energy can be supplied to the electrical connecting

line,

wherein the drawing off or supply of electrical energy through the DC/DC converter can be

controlled by means of the control unit, wherein the control unit controls the DC/DC converter

according to the electrical balance determined by the sensor unit,

wherein the DC/DC converter is designed to emulate a voltage/current characteristic of the

photovoltaic energy converter when feeding electrical energy into the electrical connecting line

and to supply the electrical energy in relation to the target supply in line with a relationship of

transported current as a function of the voltage according to a current/voltage characteristic of the

energy converter and as indicated by the MPPT.

There is further provided an energy generation plant being a photovoltaic plant with a DC-coupled

energy management system, comprising

- a photovoltaic energy converter, in particular a photovoltaic unit, which is provided for the

provision of a variable DC power depending on operating and/or environmental conditions,

- an inverter coupled to a power supply network that is provided to feed one or a plurality of

loads, and that is connected to a power network terminal of an energy supply network,

- a control unit, - a sensor unit for the measurement of an electrical balance between loads and the network

terminal of the energy supply network,

- a DC/DC converter which is connected through a first terminal to an electrical connecting

line between the energy converter and the inverter coupled to a power supply network,

and through a second terminal to at least one energy storage unit,

- wherein the inverter is configured to perform maximum power point tracking (MPPT) by

adjusting an internal DC resistance at the electrical connecting line of the inverter, that is

connected to the DC/DC converter, to maximize power generated by the photovoltaic

energy converter,

- wherein the control unit is designed for communicative connection with the sensor unit,

the energy storage unit, and the DC/DC converter,

- wherein the DC/DC converter is of bidirectional design, so that electrical energy can be

drawn from the electrical connecting line and/or electrical energy can be supplied to the

electrical connecting line,

- wherein the drawing off or supply of electrical energy through the DC/DC converter can be

controlled by means of the control unit, wherein the control unit controls the DC/DC

converter according to the electrical balance determined by the sensor unit,

- wherein the DC/DC converter is designed to emulate a voltage/current characteristic of the

photovoltaic energy converter when feeding electrical energy into the electrical connecting

line and to supply the electrical energy in relation to the target supply in line with a

relationship of transported current as a function of the voltage according to a

current/voltage characteristic of the energy converter and as indicated by the MPPT.

The disclosure proceeds on the basis of a DC-coupled energy management system for an energy

generation plant, in particular of a photovoltaic plant, comprising a control unit, a sensor unit for the

measurement of an electrical balance between loads of the energy generation plant, and a network

terminal of an energy supply network, as well as a DC/DC converter which is connected through a

first terminal to an electrical connecting line of the energy generation plant between an energy

converter and an inverter coupled to a power supply network, and through a second terminal to at

least one energy storage unit.

The control unit is in communicative connection with the sensor unit, the energy storage unit, and

the DC/DC converter. The energy converter is provided for the provision of a variable DC power

depending on operating and/or environmental conditions. The inverter coupled to a power supply

network is provided to feed one or a plurality of loads, and is connected to the power network

terminal.

The DC/DC converter is, furthermore, of bidirectional design, so that electrical energy can be drawn

from the electrical connecting line and/or electrical energy can be supplied to the electrical connecting line. The drawing off or supply of electrical energy through the DC/DC converter can be controlled by means of the control unit, wherein the control unit controls the DC/DC converter according to the electrical balance determined by the sensor unit.

The energy supply network may, in particular, be a public or private energy supply network, in

particular a commercially accounted energy supply network. In accordance with its specific and, in

some cases, material-dependent characteristic current/voltage curve, a PV plant with PV modules in

operation, i.e. in the presence of solar radiation, generates a DC voltage and a direct current

corresponding to the respective operating state, which is converted into alternating current by

means of the inverter coupled to a supply network. The internal DC resistance of the inverter

coupled to a supply network is in this instance at any given time adjusted by the control logic of the

inverter such that a maximum electrical power can be generated in the respective instantaneous

operating state of the PV module. This control strategy is referred to as "Maximum Power Point

Tracking" (MPPT). The MPPT method leads to the result that the inverter coupled to a supply

network is always in a position to reduce the instantaneous actual power of the PV module down to

a power of zero by changing its internal electrical resistance. The inverter coupled to a supply

network is not, however, in a position to generate more electrical power than the PV modules can

make available in their respective, instantaneous operating state at maximum efficiency according to

the MPPT method. The respective instantaneous maximum power of the PV modules depends to a

large extent on the irradiation intensity, the module temperature and the degree of ageing of the

modules. If the modules are operated at the MPP point, a further rise in the electrical power of

these modules is not possible. While in a usual PV plant coupled to a supply network there is a

possibility of reducing the PV power down to zero; it is not, however, possible to provide more AC

power than is physically possible according to the influencing variables explained.

As a result of this relationship, PV plants coupled to a supply network are not in a position 24 hours

per day to make electrical energy available to meet the need. An attempt is therefore often made to

solve the problem through the use of electrical energy stores, in particular through the use of

batteries.

A DC-coupling of the energy store between the PV unit and the AC output of the inverter coupled to

a supply network is therefore possible. With DC-coupling, electrical power for the charging or

discharging of the batteries is drawn off or supplied before, in the direction of current flow, the AC

output of the inverter coupled to a supply network, either by means of a bidirectional DC/DC converter or of a pair of unidirectional DC/DC converters connected in parallel. The advantage of this technology is a favourably higher efficiency in comparison with a known AC coupling of the energy store. The disadvantage, however, is that according to the prior art, the charging or discharging of the battery makes a communication with the central control logic of the inverter coupled to a supply network necessary, since an uncontrolled supply of or drawing off of power on the DC side of the inverter coupled to a supply network can lead to current/voltage constellations in the DC string between the PV unit and the inverter coupled to a supply network that are not in conformity with the current/voltage control according to the MPPT control method that is implemented in the inverter coupled to a supply network. An uncontrolled input of electrical energy before the AC output of the inverter coupled to a supply network can lead to total powerdecoupling of the PV unit. If, for example, the voltage in the electrical connecting line during the input of energy from the battery reaches the no-load voltage of the PV modules, the power of the PV modules becomes zero.

Conversely, during a power input significantly below the MPPT working point of the PV modules, the

power potential of the PV modules is not fully exploited, since the voltage of the electrical

connecting line is lower than what would correspond to the MPP point. For this reason a

communication interface to the control electronics of the inverter coupled to a supply network is

necessary with DC-coupling according to the prior art, so that the full power capacity of the PV unit

is not impaired through the use of the battery.

As a result of this relationship, the integration of a battery on the DC side of the inverter coupled to

a supply network without access to the central control unit of the inverter is only possible at the cost

of significant losses in the power capacity of the PV unit or of the overall efficiency of the energy

generation system.

The energy management system advantageously permits an operation of the energy generation

plant even with reduced power of the energy converter, so that an operation of the energy

generation plant is even possible for 24 hours per day, and where the disadvantages of the DC

coupling of a connected energy store corresponding to the prior art is avoided.

In the energy management system for the provision of electrical energy according to need from

predominantly renewable energy sources, a bidirectional DC converter (DC/DC converter) is

connected at at least one electrical connecting line of an energy converter, for example a

photovoltaic (PV unit) to an inverter coupled to a supply network, for example by way of a T-shaped

connecting point. The electrical connecting line in a PV plant is also referred to as a PV string, since the PV modules, wired in parallel and/or in series, are connected to form so-called strings of a PV unit. The T-shaped connecting point can expediently comprise, on the side facing the energy converter, a suitable unidirectional blocking element which prevents unwanted return feed from the energy storage unit into the energy converter, in particular a diode or a suitable circuit that prevents such a return feed from the energy storage unit into the energy converter and which is connected to the energy converter in the blocking direction.

The DC/DC converter comprises a maximum of two power-carrying terminals, one each for a positive

and negative pole. One power-carrying electrical terminal is connected to the electrical connecting

line, and the second power-carrying electrical terminal is connected to an energy storage unit, for

example a rechargeable battery system or a capacitor unit.

The bidirectional DC/DC converter is in this way in a position to carry electrical energy generated in

the energy converter to the energy storage unit and/or to carry electrical energy from the at least

one energy storage unit to the inverter coupled to a supply network. The DC/DC converter is

provided here for voltage matching between the electrical connecting line and the electrical storage

unit. The DC/DC converter and the energy storage unit are, furthermore, connected via a

communication line to the central control unit of the energy management system. In this case there

is no communication line or other kind of communication structure to the inverter coupled to a

supply network.

The central control unit is in communicative connection with a suitable sensor unit, for example an

alternating-current (AC) sensor. The AC sensor is arranged in this instance behind, in the current flow

direction, the inverter coupled to a supply network, and at least one, preferably all, loads of the

relevant electrical balance space are arranged between the inverter coupled to a supply network

and the AC sensor. The sensor detects, with a specified temporal resolution in the relevant electrical

balance space, between the loads of the energy generation plant and the network terminal, at least

the relevant AC network data: current and/or voltage and/or frequency in each phase. This data is

conveyed to the central control unit via the communication line. The evaluation of this data in the

central control unit yields the instantaneous electrical energy flow with the specified temporal

resolution, and thus the net electrical balance of the energy generation plant. The control unit is

thereby in a position to control the DC/DC converter according to the electrical balance determined

by the sensor unit. The internal resistance of the inverter coupled to a supply network can thus be

suitably influenced, by means of the electrical balance to which the DC/DC converter is regulated, in such a manner as if all of the energy that is supplied on the input side to the inverter coupled to a supply network came from the energy converter.

The disadvantages of an AC-coupled and of a DC-coupled energy store described above can be

avoided with the energy management system described, so that an operation of an energy

generation plant is thus possible even at a heavily reduced operation of the energy converter, and

loads can thus nevertheless be supplied.

According to an advantageous embodiment, the DC/DC converter can be designed to emulate a

voltage/current characteristic of the energy converter when feeding electrical energy into the

electrical connecting line. In order that the MPPT method of the inverter coupled to a supply

network, as described above, is not unfavourably influenced during operation of the DC/DC

converter, and that the inverter coupled to a supply network continues to run even, for example,

during the night, when a PV module does not generate any energy, the DC/DC converter

conveniently works, in relation to the target supply or drawing off of power in line with the

relationship of transported current as a function of the voltage according to a current/voltage

characteristic of the energy converter, i.e. for example of a photovoltaic cell based on silicon or also

of other suitable materials with a photovoltaic effect.

According to an advantageous embodiment, the electrical connecting line can comprise a

unidirectional blocking element which prevents unwanted return feed from the energy storage unit

into the energy converter, in particular a diode or a suitable circuit that prevents such a return feed,

which is arranged in the electrical connecting line between an output of the energy converter and a

connecting point of the DC/DC converter, and is connected to the energy converter in the blocking

direction. In this way it is possible to prevent the electrical energy fed in from the DC/DC converter

from leading to a malfunction of the energy converter and/or of the energy management system, in

that as a result the output voltage of the energy converter is, so to speak, increased.

According to an advantageous embodiment, the sensor unit comprises at least one AC sensor,

wherein the sensor unit preferably detects current and/or voltage and/or frequency of the electrical

power at the network terminal with a temporal resolution less than 200 ms, preferably less than 100

Ms.

The connected loads of the energy generation plant usually work as AC-operated components, since

they are connected to a conventional network supply into which the energy generation plant is

connected via the inverter coupled to a supply network. It is therefore advantageous if the AC power

of the loads is also detected with a suitable time resolution in order to represent the electrical

balance of the energy generation plant.

According to an advantageous embodiment, the energy storage unit can comprise a rechargeable

battery system and/or a capacitor unit and/or a flywheel store. Storage systems that allow electrical

energy to be taken up and to be stored in a suitable form, possibly including mechanical or chemical

energy, as well as outputting the stored energy directly as electrical energy or converting the stored

energy form back into electrical energy and emitting it, are conceivable here.

According to an advantageous embodiment the DC/DC converter can be connected via the second

terminal to one or a plurality of energy generation units, in particular an energy generation unit

consisting of a fuel cell system, an AC combined heat and power plant, a DC combined heat and

power plant, a motor generator or the like. On a DC bus between the DC/DC converter and the

energy storage unit, the energy management system can comprise a further T-shaped connecting

point as an electrical connection to further electrical energy generation units. These energy

generation units can, for example, be wind turbines, fuel cells, biogas plants, micro-combined heat

and power plants as well as conventional fossil-fuel driven motor generators. These energy

generation units are advantageously operated unidirectionally, i.e. with a flow of power to the DC

bus. All of these energy generation units are connected to the central control unit of the energy

management system.

According to an advantageous embodiment, the one or a plurality of energy generation units can be

operated as constant voltage sources. The operation of the AC/DC or DC/DC converters of the

energy generation units that are connected to the DC bus of the energy storage unit is carried out

with regard to the output voltage to the DC bus of the energy storage unit as a quasi-constant

source.

The energy management system is in this way favourably to be operated via the DC/DC converter

controlled by the control unit.

According to an advantageous embodiment, the energy storage unit and/or the DC/DC converter

and/or the inverter for the operation of the one or a plurality of energy generation units can be

controlled by the control unit. The energy generation units are not connected to the control unit of

the inverter coupled to a supply network, and thus neither receive any information from it nor send

any signals to it. The control unit in this instance controls the advantageous use of the various

energy generation units according to the current operation of energy converters and loads in

accordance with the current electrical balance determined by the sensor unit.

According to a further aspect, an energy generation plant is proposed, in particular a photovoltaic

plant with a DC-coupled energy management system, comprising an energy converter, in particular a

photovoltaic unit, which is provided for the provision of a variable DC power depending on operating

and/or environmental conditions, as well as an inverter coupled to a supply network that is provided

for feeding one or a plurality of loads, and is connected to a network terminal of an energy supply

network. The energy generation plant comprises a control unit, a sensor unit for the measurement

of an electrical balance between loads and the network terminal, as well as a DC/DC converter which

is connected through a first terminal to an electrical connecting line between the energy converter

and the inverter coupled to a power supply network, as well as through a second terminal to at least

one energy storage unit. The control unit is designed for a communicative connection with the

sensor unit, the energy storage unit, and the DC/DC converter. The DC/DC converter is of

bidirectional design, so that electrical energy can be drawn from the electrical connecting line

and/or electrical energy can be supplied to the electrical connecting line. The drawing off or supply

of electrical energy through the DC/DC converter can be controlled by means of the control unit,

wherein the control units controls the DC/DC converter according to the electrical balance

determined by the sensor unit.

The electrical connecting line can comprise a unidirectional blocking element which prevents

unwanted return feed from the energy storage unit into the energy converter, in particular a diode

or a suitable circuit that prevents such a return feed from the energy storage unit into the energy

converter, said circuit being arranged in the electrical connecting line between an output of the

energy converter and a connecting point of the DC/DC converter, and is connected to the energy

converter in the blocking direction.

According to a further aspect, a DC/DC converter for a DC-coupled energy management system is

proposed, with a first terminal that is connected to an electrical connecting line of an energy generation plant between an energy converter and an inverter coupled to a supply network and with a second terminal that is connected to at least one energy storage unit, whereby a drawing off of electrical energy from the electrical connecting line, or a feed of electrical energy to the electrical connection line, can be controlled by means of a control unit. The control unit controls in this instance the DC/DC converter in accordance with an electrical balance, determined by a sensor unit, between loads of the energy generation plant and a network connection. At least one load of the energy generation plant, preferably all loads of the energy generation plant, are advantageously taken into account for detection of the electrical balance.

According to a further, a method for the operation of an energy generation plant with a DC-coupled

energy management system is proposed, comprising the detection of the electrical balance between

loads of the energy generation plant and a network terminal of an energy supply network by means

of a sensor unit, the control of a DC/DC converter that is connected to at least one energy storage

unit by means of a control unit according to the electrical balance determined by the sensor unit,

along with the drawing off or supply of electrical energy through the DC/DC converter to an

electrical connecting line between an energy converter and an inverter coupled to a supply network

of the energy generation plant.

The operation of the energy management system proceeds as described below. The sensor unit,

preferably designed as an AC sensor, detects, with a temporal resolution of, in particular, less than

200 ms, preferably less than 100 ms in the relevant electrical balance space between the loads of

the energy generation plant and the network terminal, at least the relevant AC network data:

current, voltage, frequency in each phase. This data is conveyed to the central control unit via the

communication line. The evaluation of this data in the central control unit yields the instantaneous

electrical energy flow with the specified temporal resolution.

In addition to this data, the central control unit evaluates all the other state variables of the further

energy stores and energy generation units attached to the DC bus of the energy storage unit, and

then decides which operation the DC/DC converter should carry out in the following regulation

interval. The decision of the central control unit is based here on the consideration of the state

variables of the connected components, taking into account the specific instantaneous power

capacity of the connected components, and taking into account the specific costs of the electrical

energy that the various connected components cause. The aim of this is to minimise the total costs

of the provision of electrical energy as needed from the energy converter in particular of the renewable energy source, and in that way to optimise the overall profitability of the energy generation plant.

Through the control of the DC/DC converter performed by means of the electrical balance detected

by means of the sensor unit by the control unit, the internal resistance of the inverter coupled to a

supply network can be suitably influenced in such a manner as if all of the energy that is supplied on

the input side to the inverter coupled to a supply network came from the energy converter.

The bidirectionally designed DC/DC converter then performs the necessary operations, wherein

there are two operating states of the DC/DC converter. These are the drawing off of electrical energy

from the electrical connecting line and the supply of electrical energy to the electrical connecting

line.

In order that the MPPT method of the inverter coupled to a supply network, as described above, is

not unfavourably influenced during operation of the DC/DC converter, and that the inverter coupled

to a supply network continues to run even, for example, during the night, when a PV module does

not generate any energy, the DC/DC converter works, in relation to the target supply or drawing off

of power in line with the relationship of transported current as a function of the voltage according to

a current/voltage characteristic of the energy converter, i.e. for example of a silicon-based

photovoltaic cell. The MPPT control logic of the inverter coupled to a supply network is not in any

way negatively influenced by this control strategy of the DC/DC converter, so that the inverter

coupled to a supply network does not register any difference between the "true" electrical power of

the energy converter and the resulting electrical power provided by the energy management

system. As a result, any desired inverter coupled to a supply network can be used for the AC feed of

any desired kind of renewable electrical energy for the use of the energy management system. The

disclosed solution is therefore particularly suitable for the further integration of renewable electrical

energy generation units, since no special devices are necessary for the DC/AC conversion, and the AC

feed is thus based on a device technology that has already been used successfully for many decades.

According to an advantageous embodiment, the operation of the DC/DC converter can take place in

parallel with the operation of the energy converter. In this instance it is possible, in particular for

both operating states of the DC/DC converter, namely the drawing off of electrical energy from the

electrical connecting line and the supply of an electrical energy into the electrical connecting line, to

be carried out in parallel with the operation of the energy converter, so that energy converted by the inverter coupled to the supply network can consist in part of energy delivered from the energy converter and in part of energy delivered from the energy storage unit.

According to an advantageous embodiment, the energy management system can carry out at least

one of the operating states of (i) generating electrical energy by the energy converter and feeding

electrical energy through the DC/DC converter to the electrical connecting line, (ii) generating

electrical energy by the energy converter and removing electrical energy through the DC/DC

converter from the electrical connecting line, or (iii) feeding electrical energy to the electrical

connecting line through the DC/DC converter. These operating states of the energy management

system result, in particular, with reference to the common operation of the energy converter and

DC/DC converter and thereby, in particular, to the two operating states of the DC/DC converter for

the drawing off of electrical energy from the electrical connecting line as well as the supply of

electrical energy to the electrical connecting line. The third operating state of the energy

management system (iii), feeding electrical energy to the electrical connecting line through the

DC/DC converter, represents in particular the night-time operation of the energy generation plant.

According to an advantageous embodiment, the control unit can control the DC/DC converter with

the aim of a net electrical balance of zero determined by the sensor unit. Such an operation is

advantageous, because the energy used by the loads is thus completely drawn from the operation of

the energy generation plant, and no energy at all has to be drawn from the energy supply network,

for example a public or private, in particular a commercially accounted network. As a result, the

operation of the loads with respect to the energy generation unit is autonomous. On the other hand,

no energy is supplied to the energy supply network either, which, under certain conditions, which

can depend on appropriate energy supply contracts, can be favourable. It is alternatively also

conceivable that another target variable is chosen instead of the target variable of a net electrical

balance of zero.

According to another advantageous embodiment, the control unit can also control the DC/DC

converter with the aim of a maximum power yield of the energy generation plant on the basis of the

available DC power at the input of the inverter coupled to a supply network.

Such a mode of operation of the energy management system can be advantageous if the maximum

deliverable power should be drawn from the energy generation plant under the conditions given at the time, for example the current weather, condition of the plant, or current electricity costs. It is possible that a cost-optimised operation of the energy generation plant is realised in this way.

Drawing

Further advantages emerge from the following description of the drawing. The drawing, description

and the claims contain numerous features in combination. Those skilled in the art will expediently

also consider the features individually and combine them to form useful further combinations.

By way of example here:

Fig. 1 shows a block diagram of an energy generation plant with an energy management system

according to an exemplary embodiment.

Embodiment

The figure shows one example only and is not to be understood restrictively.

The only figure, Figure 1, shows a block diagram of an energy generation plant 100 with an energy

management system 10.

The energy generation plant 100, which in particular can represent a photovoltaic plant, is designed

with the DC-coupled energy management system 10. The energy generation plant 100 comprises the

energy converter 12, which can in particular be a photovoltaic unit, which is provided for the

provision of a variable DC power depending on operating and/or environmental conditions. The

energy generation plant 100 further comprises the inverter 14 coupled to a supply network which is

provided for the feed of one or a plurality of loads 80, and which is connected to the network

terminal 20 of the energy supply network 200. In the exemplary embodiment drawn in Figure 1,

three loads 81, 82, 83 are connected to the line 56 between the output 18 of the inverter 14 coupled

to a supply network and the network terminal 20.

The DC-coupled energy management system 10 comprises the control unit 30, which is connected

via the communication line 36 to the sensor unit 32 for the measurement of an electrical balance

between the loads 80 and the network terminal 20 of the energy supply network 200, as well as the

DC/DC converter 22 which is connected to the first terminal 24 via the T-shaped connecting point 54

to the electrical connecting lines 16 between the output 62 of the energy converter 12 and the input

28 of the inverter 14 coupled to a supply network, and with the second terminal 26 via the line 62

the energy storage unit 40. The sensor unit 32 comprises at least one AC sensor, wherein the sensor

unit 32 preferably detects current and/or voltage and/or frequency of the electrical power between

the loads 80 and the network terminal 20 with a temporal resolution less than 200 ms, preferably

less than 100 ms.

The energy storage unit 40 can comprise a rechargeable battery system and/or a capacitor unit

and/or a flywheel store.

The electrical connecting line 16 of the energy generation plant 100 comprises the unidirectional

blocking element 52, for example a diode, which prevents unwanted return feed from the energy

storage unit 40 into the energy converter 12, and is arranged in the electrical connecting line 16

between the output 62 of the energy converter 12 and the connecting point 54 of the DC/DC

converter 22, and is connected to the energy converter 12 in the blocking direction.

The DC/DC converter 22 is of bidirectional design, so that electrical energy can be drawn from the

electrical connecting line 16 and/or electrical energy can be supplied to the electrical connecting line

16. The drawing off or supply of electrical energy through the DC/DC converter 22 can be controlled

by means of the control unit 30, said controller 30 controlling the DC/DC converter 22 via the

communication line 34 according to the electrical balance determined by the sensor unit 32

between loads 80 of the energy generation plant of the network terminal 20.

The DC/DC converter 22 is designed to emulate a voltage/current characteristic of the energy

converter 12 when feeding electrical energy into the electrical connecting line 16.

The DC/DC converter 22 is connected via the second terminal 26 to the T-shaped connecting point

58 to a plurality of energy generation units, here to the fuel cell system 41, the AC combined heat

and power plant 42, the DC combined heat and power plant 43, and the motor generator 44, which

can be used for the additional feed of electrical energy via the DC/DC converter 22 into the electrical

connecting line 16, and thus into the inverter 14 coupled to a supply network for the supply to loads

80. The energy generation units 41, 42, 43, 44 can be operated as constant voltage sources. The

DC/DC converter 70 and inverter 72 for the operation of the energy generation unit 41, 42, 43, 44

can also be driven in this instance by the control unit 13 via the communication line 38.

The method for the operation of the energy generation plant 100 with the DC-coupled energy

management system 10 comprises the detection of the electrical balance between the loads 80 of

the energy generation plant 100 and the network terminal 20 of the energy supply network 200 by

means of the sensor unit 32, the control of the DC/DC converter 22 that is connected to the energy

storage unit 40 by means of the control unit 30 according to the electrical balance determined by

the sensor unit 32, and, further, the drawing off or feed of electrical energy by the DC/DC converter

22 at the electrical connecting lines 16 between the energy converter 12 and the inverter 14 coupled

to a supply network of the energy generation plant 100. The operation of the DC/DC converter 22

can take place here in parallel with the operation of the energy converter 12.

The energy management system 10 can respectively carry out at least one of the operating states of

(i) generating electrical energy through the energy converter 12 and feeding electrical energy

through the DC/DC converter 22 to the electrical connecting line 16, (ii) generating electrical energy

through the energy converter 12 and removing electrical energy through the DC/DC converter 22

from the electrical connecting line 16, or (iii) feeding electrical energy to the electrical connecting

line 16 through the DC/DC converter 22.

The control unit 30 can thus control the DC/DC converter 22 with the aim of a net electrical balance

of zero determined by the sensor unit 32, or with another target variable. Alternatively, the control

unit 20 can, for example, also control the DC/DC converter 22 with the aim of a maximum power

yield of the energy generation plant 100 on the basis of the available DC power at the input 28 of the

inverter 14 coupled to a supply network.

Reference numbers

Energy management system

12 Energy converter

14 Inverter

16 Connecting line

18 Output

Network terminal

22 DC/DC converter

24 First terminal

26 Second terminal

28 Input

Control unit

32 Sensor unit

34 Communication line

36 Communication line

38 Communication line

Energy storage unit

41 Fuel cell system

42 AC heat and power plant

43 DC heat and power plant

44 Motor generator

52 Unidirectional blocking element

54 Connecting point

56 Line

58 Connecting point

Line

62 Output

DC/DC converter

72 Inverter

Load

81 First load

82 Secondload

83 Third load

100 Energy generation plant

200 Energy supply network

Claims (15)

Claims

1. DC-coupled energy management system for an energy generation plant, the energy

generation plant being a photovoltaic plant,

comprising

- a control unit, - a sensor unit for the measurement of an electrical balance between loads of the energy

generation plant and a network terminal of an energy supply network,

- a DC/DC converter which is connected through a first terminal to an electrical connecting

line of the energy generation plant between a photovoltaic energy converter and an

inverter coupled to a power supply network, and through a second terminal to at least

one energy storage unit,

wherein the control unit is designed for communicative connection with the sensor unit, the

energy storage unit, and the DC/DC converter

wherein the photovoltaic energy converter is provided for the provision of a variable DC power

depending on operating and/or environmental conditions,

wherein the inverter coupled to a power supply network is provided to feed one or a plurality of

loads, and is connected to the power network terminal,

wherein the inverter is configured to perform maximum power point tracking (MPPT) by adjusting

an internal DC resistance at the electrical connecting line of the inverter, that is connected to the

DC/DC converter, to maximize power generated by the photovoltaic energy converter,

wherein the DC/DC converter is of bidirectional design, so that electrical energy can be drawn

from the electrical connecting line and/or electrical energy can be supplied to the electrical

connecting line,

wherein the drawing off or supply of electrical energy through the DC/DC converter can be

controlled by means of the control unit, wherein the control unit controls the DC/DC converter

according to the electrical balance determined by the sensor unit,

wherein the DC/DC converter is designed to emulate a voltage/current characteristic of the

photovoltaic energy converter when supplying electrical energy to the electrical connecting line

and to supply the electrical energy in relation to the target supply in line with a relationship of

transported current as a function of the voltage according to a current/voltage characteristic of

the energy converter and as indicated by the MPPT.

2. The energy management system according to claim 1 or 2, wherein the electrical

connecting line comprises a unidirectional blocking element, which prevents unwanted return

feed from the energy storage unit into the photovoltaic energy converter, and which is arranged

in the electrical connecting line between the output of the photovoltaic energy converter and a

connecting point of the DC/DC converter, and is connected to the photovoltaic energy converter

in the blocking direction.

3. The energy management system according to one of the preceding claims, wherein the

sensor unit comprises at least one AC sensor, wherein the sensor unit preferably detects current

and/or voltage and/or frequency of the electrical power at the network terminal with a temporal

resolution less than 200 ms, preferably less than 100 ms.

4. The energy management system according to one of the preceding claims, wherein the

energy storage unit comprises a rechargeable battery system and/or a capacitor unit and/or a

flywheel store.

5. The energy management system according to one of the preceding claims, wherein the

DC/DC converter is connected via the second terminal to one or a plurality of energy generation

units, in particular an energy generation unit consisting of a fuel cell system, an AC combined heat

and power plant, a DC combined heat and power plant, a motor generator or the like.

6. The energy management system according to claim 5, wherein the one or plurality of

energy generation units can be operated as constant voltage sources.

7. The energy management system according to claim 5 or 6, wherein the energy storage

unit and/or the DC/DC converter and/or the inverter coupled to a supply network for the

operation of the one or a plurality of energy generation units can be controlled by the control

unit.

8. An energy generation plant being a photovoltaic plant with a DC-coupled energy

management system, comprising

- a photovoltaic energy converter, in particular a photovoltaic unit, which is provided for

the provision of a variable DC power depending on operating and/or environmental

conditions,

- an inverter coupled to a power supply network that is provided to feed one or a plurality of loads, and that is connected to a power network terminal of an energy supply network,

- a control unit, - a sensor unit for the measurement of an electrical balance between loads and the

network terminal of the energy supply network,

- a DC/DC converter which is connected through a first terminal to an electrical connecting

line between the energy converter and the inverter coupled to a power supply network,

and through a second terminal to at least one energy storage unit,

- wherein the inverter is configured to perform maximum power point tracking (MPPT) by

adjusting an internal DC resistance at the electrical connecting line of the inverter, that is

connected to the DC/DC converter, to maximize power generated by the photovoltaic

energy converter,

- wherein the control unit is designed for communicative connection with the sensor unit,

the energy storage unit, and the DC/DC converter,

- wherein the DC/DC converter is of bidirectional design, so that electrical energy can be

drawn from the electrical connecting line and/or electrical energy can be supplied to the

electrical connecting line,

- wherein the drawing off or supply of electrical energy through the DC/DC converter can

be controlled by means of the control unit, wherein the control unit controls the DC/DC

converter according to the electrical balance determined by the sensor unit,

- wherein the DC/DC converter is designed to emulate a voltage/current characteristic of

the photovoltaic energy converter when supplying electrical energy to the electrical

connecting line and to supply the electrical energy in relation to the target supply in line

with a relationship of transported current as a function of the voltage according to a

current/voltage characteristic of the energy converter and as indicated by the MPPT.

9. The energy generation plant according to Claim 8, wherein the electrical connecting line

comprises a unidirectional blocking element, which prevents unwanted return feed from the

energy storage unit into the photovoltaic energy converter, and which is arranged in the electrical

connecting line between the output of the photovoltaic energy converter and a connecting point

of the DC/DC converter, and is connected to the photovoltaic energy converter in the blocking

direction.

10. DC/DC converter for a DC-coupled energy management system according to one of claims

1 to 7, with a first terminal that is connected to an electric connecting line of an energy

generation plant according to claim 8 or 9 between an photovoltaic energy converter and an

inverter coupled to a supply network, as well as to a second terminal that is connected to at least

one energy storage unit, wherein a drawing off of electrical energy from the electrical connecting

line or a feed of electrical energy to the electrical connecting line can be controlled by means of a

control unit, where said control unit controls the DC/DC converter according to the electrical

balance between loads of the energy generation plant and a network terminal determined by a

sensor unit.

11. A method for the operation of an energy generation plant according to claim 9 or 10 with

a DC-coupled energy management system according to one of claims 1 to 8, comprising

- detection of the electrical balance between loads of the energy generation plant and a

network terminal of an energy supply network by means of the sensor unit,

- controlofa DC/DCconverter thatisconnected to at leastone energy storage unit by

means of a control unit according to the electrical balance determined by the sensor unit,

- drawing off or supplying electrical energy through the DC/DC converter to an electrical

connecting line between an photovoltaic energy converter and an inverter coupled to a

supply network of the energy generation plant, and

- emulating a voltage/current characteristic of the photovoltaic energy converter when

supplying electrical energy to the electrical connecting line to supply the electrical energy

in relation to the target supply in line with a relationship of transported current as a

function of the voltage according to a current/voltage characteristic of the energy

converter and as indicated by the MPPT.

12. The method according to claim 11, wherein the operation of the DC/DC converter takes

place in parallel with operation of the photovoltaic energy converter.

13. The method according to one of claims 11 or 12, wherein the energy management system

carries out at least one of the operating states of

(i) generation of electrical energy through the photovoltaic energy converter and supply of electrical energy through the DC/DC converter to the electrical connecting line,

(ii) generation of electrical energy through the photovoltaic energy converter and drawing

off of electrical energy through the DC/DC converter from the electrical connecting line,

(iii) supply of electrical energy to the electrical connecting line through the DC/DC converter.

14. The method according to one of claims 11 to 13, wherein the control unit controls the

DC/DC converter with the aim of a net electrical balance of zero determined by the sensor unit, or

with another target variable.

15. The method according to one of claims 11 to 14, wherein the control unit controls the

DC/DC converter with the aim of a maximum power yield of the energy generation plant on the

basis of the available DC power at the input of the inverter coupled to a supply network.