Method for structuring an existing grid for distributing electric energy

Abstract

In a method for structuring an existing grid (11) for distributing electric energy, wherein the grid (11) comprises, as grid components, at least sources, loads, lines, sensor, switching and converter components which are connected to one another in a starting topology, on the basis of property variables of the grid components and predefinable regulation limits, the grid components are combined in a plurality of local, self-regulating functional groups (30.1, 30.2, 30.3). Each local functional group (30.1, 30.2, 30.3) is assigned regulation processes comprising actions which are carried out upon reaching trigger criteria for complying with the regulation limits. Starting from an existing grid for distributing electric energy, the method results in a grid which is newly structured in terms of the regulation and, as far as possible, dispenses with a hierarchical structure with respect to the regulation and instead is constructed from local functional groups (30.1, 30.2, 30.3) which are self-regulating during normal operation. This reduces the susceptibility to faults and thereby increases the operational safety and supply reliability, inter alia.

Claims

1. A method for structuring an existing grid for distributing electric energy, wherein the grid comprises, as grid components, at least sources, loads, lines, sensor, switching and converter components which are connected to one another in a starting topology, wherein, on the basis of property variables of the grid components and predefinable regulation limits, a) the grid components are combined in a plurality of local, self-regulating functional groups, and b) each local functional group is assigned regulation processes comprising actions which are carried out upon reaching trigger criteria for complying with the regulation limits, the actions comprising local actions, which influence operation of the components in the respective local functional group, and non-local actions, which comprise a transmission of data to another local functional group or to a cross-functional-group control center, and wherein for operating the structured grid sensor components in the local functional groups are used to monitor whether trigger criteria for the actions assigned to the respective local functional group are reached, and wherein one of the actions assigned to the respective functional group for complying with the regulation limits is carried out upon reaching a trigger criterion.

2. The method as claimed in claim 1, comprising a definition of a potential local functional group and a check in order to determine whether the potential local functional group can be locally regulated while complying with the predefinable regulation limits, wherein the potential local functional group is accepted if local regulability is determined, and wherein the potential local functional group is expanded with further grid components if local regulability is absent.

3. The method as claimed in claim 1, wherein a need for additional grid components for creating additional local functional groups and/or for ensuring the predefinable regulation limits is determined.

4. The method as claimed in claim 3, wherein the target function is dependent on costs of the additional grid components, and in that the numerical optimization favors minimization of these costs.

5. The method as claimed in claim 1, wherein a target topology is determined on the basis of the starting topology.

6. The method as claimed in claim 5, wherein the target function is dependent on costs of an adaptation between a starting topology and a target topology, and in that the numerical optimization favors minimization of these costs.

7. The method as claimed in claim 1, the predefinable regulation limits comprising maximum latencies for transmitting data between local functional groups and/or different grid components.

8. The method as claimed in claim 1, comprising numerical optimization of a target function for combining the grid components in the local functional groups.

9. The method as claimed in claim 8, wherein the target function is dependent on a volume of data transmitted between grid components for regulating the grid, and in that the numerical optimization favors minimization of this volume of data.

10. The method as claimed in claim 9, wherein the target function is dependent on costs of the additional grid components, and in that the numerical optimization favors minimization of these costs.

11. The method as claimed in claim 9, wherein the target function is dependent on costs of an adaptation between a starting topology and a target topology, and in that the numerical optimization favors minimization of these costs.

12. The method as claimed in claim 1, wherein local prices for the local functional groups are determined, in that the target function is dependent on the local prices, and in that the numerical optimization favors minimization of these costs.

13. The method as claimed in claim 1, the existing grid comprising at least components in two adjacent levels of the following grid levels: a) extra-high voltage grid with a voltage of 380 or 220 kV: b) high-voltage grid with a voltage of 36-150 kV; c) medium-voltage grid with a voltage of 1-36 kV; and d) low-voltage grid with a voltage of 400 V-1 kV.

14. The method as claimed in claim 1, wherein the property variables of the grid components and/or the starting topology is/are received from a geographical information system.

15. The method as claimed in claim 14, wherein a maintenance requirement is detected and maintenance services are automatically requested.

16. The method as claimed in claim 15, wherein automatic ordering processes are initiated via a logistics interface.

17. A computer program for carrying out the method as claimed in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The drawings used to explain the exemplary embodiment show in:

(2) FIG. 1 a schematic illustration of an existing distribution grid for electric energy with central control;

(3) FIG. 2 a flowchart of a method according to the invention;

(4) FIG. 3 a schematic illustration of a distribution grid structured using the method according to the invention with local regulation; and

(5) FIG. 4 a block diagram of a system for carrying out a method according to the invention for operating a distribution grid for electric energy.

(6) In principle, identical parts in the figures are provided with identical reference signs.

WAYS OF IMPLEMENTING THE INVENTION

(7) FIG. 1 is a schematic illustration of an existing grid for distributing electric energy with central control. The grid 1 is subdivided into a plurality of grid levels 1.1 . . . 1.7. In the grid levels 1.1, 1.3, 1.5, 1.7, which correspond to transmission or distribution grids, the voltage decreases from the top to the bottom:

(8) grid level 1.1: extra-high voltage grid (for example 380 or 220 kV);

(9) grid level 1.3: high-voltage grid (for example 36-150 kV);

(10) grid level 1.5: medium-voltage grid (for example 1-36 kV); and

(11) grid level 1.7: low-voltage grid (for example 400 V-1 kV).

(12) Voltage converters (transformers) are respectively arranged in between as grid levels 1.2, 1.4, 1.6. Conventional power plants feed electric power into the grid levels 1.1, 1.3, 1.5 and the end consumers are generally connected to the low-voltage grid in grid level 1.7.

(13) The grid 1 comprises a control center 2 which centrally performs management tasks for the grid. For this purpose, information is transmitted across all grid levels 1.1 . . . 1.7 between the control center 2 and components in the grid levels 1.1 . . . 1.7. Namely, measurement data are transmitted from measuring points to the control center 2 and control data are transmitted from the control center 2 to individual components of the grid. In addition, communication takes place between adjacent transmission or distribution grid levels 1.1, 1.3, 1.5, 1.7 and between the transmission or distribution grid levels and directly adjacent voltage converters in the grid levels 1.2, 1.4, 1.6.

(14) The sequence of a method according to the invention for structuring an existing grid for electric energy is described below. The corresponding flowchart is illustrated in FIG. 2.

(15) It is first of all necessary to define which system is under consideration (step 101). For example, information relating to the existing grid is obtained from a grid-based geographical information system (GIS). Optionally or additionally, data are read from a database or are manually added. The components under consideration are selected in a manner known per se using a graphical user interface, for example by marking those parts of the grid which are to be structured. It is also possible to define the system via the grid level, for instance by a restriction to particular grid levels, or on the basis of other technical properties. For example, that entire section of the grid which is operated by a particular grid operator can be structured. However, cross-grid-operator structuring and the structuring of a section of the grid are also readily possible.

(16) A second step 102 determines which variables in the system can be regulated. This information also arises from the GIS, from other databases and/or manual inputs. Those variables which should also actually be regulated during the structuring are then selected from these regulable variables (step 103). In principle, a few, a larger number or else all variables which can actually be regulated can be selected.

(17) Classes are also defined (or adopted from an already existing class library) (step 104). Each class represents a grid section (that is to say a contiguous area of the grid with associated grid components) which has particular properties with respect to measurement variables and measurement range and possibly regulability. In this case, it should be noted that a class can possibly also represent only a single grid component.

(18) The grid section under consideration can then be represented by a selection of entities in the existing classes which are connected in a starting topology. If this is initially not possible when using existing classes from a class library, it is possible to define additional classes. However, it is not compulsory for the entire grid to be represented using entities in defined classes. In this case, components and grid sections which have not been represented would be conventionally regulated and would not be autonomously operated or combined to form autonomously operated functional groups.

(19) For all classes (or all classes, from which at least one entity is available in the grid), the desired ranges of the variables to be regulated are then stipulated; in principle, this information can also be automatically taken from a library. Particular classes or combinations of classes may have already been identified by this time as autonomously acting functional groups on the basis of predefined criteria (for example with respect to the expected frequency of an external regulation requirement).

(20) The desired operation of the regulation variables defines the rules, possible actions and the necessary information in order to be able to check whether the trigger criteria for the actions have been met. The limits which should be complied with in terms of the operating parameters during desired operation are determined in step 105 a) by the grid operator; b) by specifications in the software; and/or c) in the case of a GIS-based grid information system in which the component is stored with the operating data: automatically by means of software. The knowledge of the actually available (maximum) power or other dynamic parameters is not necessary as a result of the knowledge of the component and its known or calculable maximum load.

(21) In order to define the limits, there is an orientation to existing components and/or to standards (for instance maximum permissible current for a cable) or for instance—in the case of a new construction—to the connections and a requested maximum power.

(22) The following table lists, for example, parameters for the desired operation in a local distribution grid. The action listed in the left-hand column is respectively carried out if the operating range is not complied with, that is to say a corresponding trigger criterion is satisfied:

(23) TABLE-US-00001 Lower Upper operating operating Unit Parameter range range Action PV meter with Frequency 49.5 Hz 50.5 Hz Reduce P.sub.active, disconnect control output and from the grid above 52 Hz interrupter PV meter with Voltage 207 V 253 V Obtain reactive power, control output and reduce power if this does not interrupter suffice PV meter with Current 0 A 100 A Disconnect from the control output and grid/change tariff/send interrupter message PV meter with Harmonic 0 20 Store number of times the control output and value is exceeded; if more interrupter than 10, send message to grid operator/connect short-circuit current amplifier or filter/contact customer and change tariff Lower Upper operating operating Unit Parameter range range Rule Action Meter with Voltage, EN 50160 EN 50160 Action when Reduce voltage customer having a current 0 x the time to the lowest moderate, information value according temporally limited is received to EN50160 if load limit the load limit is exceeded Meter with Current 0 x Comply with Limit current to customer having a upper the upper load limit operating operating range range

(24) Actions are also defined (or adopted from an already existing action library) (step 106). As explained above, an action comprises one or more measures, in particular the activation of an actuator and/or the sending of a message to other components. The actions are assigned to the individual entities. If actions which relate to a plurality of entities (in particular in different classes) have been defined, actions can also be assigned to specific combinations of entities (connected to one another).

(25) It is then determined which information must be provided in order to be able to actually perform the regulation (step 107). The variables to be measured and the calculable variables are defined therefrom.

(26) On the basis of this, it is therefore then identified which measurement variables can be used for regulation (step 108). Regulation processes ultimately comprise the determination of one or more measurement variables, the processing for the purpose of determining the action(s) to be taken and the performance of the action until the regulation variable is influenced. A certain information transmission time results depending on the complexity of the regulation process, the distribution of the components involved in the grid and the time requirement for processing the measurement variables. This information transmission time is determined and is compared with a maximum permitted information transmission time (step 109). The latter need not be the same for all regulation processes because certain regulation operations must take place more quickly than others if the operation of the grid is not intended to be negatively influenced.

(27) In a similar manner to the measurement variables, it is also possible to stipulate the extent to which the selection and the topology of the grid components can be changed. For example, optimization limited to the dynamic variables can be carried out, or the possible changes to the infrastructure can be restricted to the addition of particular actuators and sensors.

(28) The physically smallest possible information latencies optionally determined (step 110). This makes it possible to immediately eliminate particular scenarios which are not compatible with the required latencies, for example the real-time control of a smart grid by means of smart meters if “real time” is in the seconds range or if data are transmitted only once a day (for example from the household meter) and “real time” means a maximum of 10 minutes.

(29) On the basis of the starting topology with the entities in the different classes and the associated desired ranges, the variables to be regulated and the available measurement variables and actions, the grid is then numerically optimized taking into account the permissible transmission times (step 111). As stated above, various approaches known per se can be pursued for this purpose, even in combination. In particular. (non-linear) numerical optimization of a target function is carried out, in which the relevant criteria are included. Limits to be observed in any case can be included in the target function as secondary conditions, for example by means of Lagrange multipliers. The criteria are generally both of a technical and of an economic nature.

(30) The optimization can be carried out with regard to the broadest possible decentralization of the grid since it can be expected that the operational safety (namely the robustness with respect to local faults) is maximized in such a case. A combination of a plurality of entities (even entities which typically cannot be locally regulated), including associated actions (and trigger criteria), in local functional groups therefore follows from the optimization.

(31) As mentioned above, the addition of further components to the existing infrastructure can also be directly checked as part of the numerical optimization. If, in contrast, optimization with regard to the dynamic variables is first of all carried out, it is possible to check, if a rule is violated, on the basis of the stipulated actions whether the necessary infrastructure, in particular sensors and actuators, is already available. Alternatively, after stipulating the desired operation, it is possible to advisorily check which actions are possible or to automatically calculate which functional groups are physically possible and—if a technology or a product is stored with characteristic values (for example based on a GIS)—which actions are required. If the technology or product information is not immediately available, the comparison is advisorily carried out, in which case hypotheses can be checked for their feasibility with the aid of the method according to the invention.

(32) In one application, the steps presented are carried out as follows, for example. Step 101 stipulates that all consumers on grid level 1.7, that is to say in the low-voltage grid, are intended to be considered. In principle, the power resulting from voltage and maximum currents and the frequency can be regulated here as dynamic variables according to step 102.

(33) Within the scope of the exemplary application, the energy requirement on grid level 1.7 is intended to be limited by regulating phase currents and voltages while complying with the European standard EN 50160. This may be useful, for example, if peak load times cause high costs because energy must be purchased at unfavorable prices or if materials such as cables reach their operational limits and there is a risk of property and personal damage or grid failures. In step 104, the consumers are classified according to minimum and maximum currents and voltages, for instance in private households having operating voltages of 230 V and maximum currents of 100 A and businesses having operating voltages of 400 V and higher maximum currents. Step 105 defines the desired operation, in this case while complying with EN 50160 and restricting the maximum power. In a simple variant of the method, all consumers are restricted to the same extent, for instance to 80% of the maximum current. In an extended variant, the voltage can be taken into account. In a further variant, the power can be limited based on a connection string of a transformer station and the maximum power of the connected consumers can be adapted based on the total power.

(34) Actions are now defined according to step 106. These actions comprise, in particular, the limitation of the current if the maximum current stipulated according to step 105 is exceeded.

(35) Step 107 stipulates the information needed to implement the regulation task. In the simple variant, this information is the currents of the home connections, in the extended variant, it is also the voltages and, in the variant of the string-based power limitation, it is the calculated sum of the instantaneous string power. It is accordingly identified which measurement variables can be used and whether additional measuring points are required or would be advantageous (step 108).

(36) Step 109 comprises the determination of the maximum permitted time for transmitting information for each regulation process. In the present case, this could be selected in the seconds or else minutes range depending on the infrastructure and costs. The stipulation of the physically possible information latency according to step 110 can be disregarded In the present case. This step would be necessary in a conventional architecture in which regulation processes should be carried out for such limitations on the basis of a central control center—locally optimized power limitation would not be possible or would be possible only with considerable outlay depending on the solution.

(37) Step 111 comprises the optimization of the existing grid according to the above steps. Numerical optimization is possible but is not compulsory in the present case. A comparison with a grid topology or a measuring infrastructure can take place manually or in an automated manner here. If appropriate, following a cost analysis, smart meters with appropriate measuring capabilities and/or actuators for power limitation are then retrofitted or grid reinforcements are carried out. The resulting orders and installation orders can be effected using an automated logistics interface.

(38) In order to structure a grid for distributing electric energy with respect to the dynamic variables in the grid, the following procedure is used in a specific case, for example: 1. The entire grid which is operated by a grid operator is first determined as the grid section to be structured. 2. The following results for the energy in this grid:
E.sub.electric,grid=E.sub.Consumption+E.sub.Production+E.sub.Transmission+E.sub.Transformation+E.sub.Import+E.sub.Export where E=P*t;P=U*I etc. The available electric energy from renewable energy sources can be regulated by being limited to a maximum. This maximum can also be dynamically or locally optimized or both. 3. Individual energy values readily result from the power values:
E.sub.n=P.sub.n*t 4. And therefore also the regulation limits:
E.sub.n,min.sup.max=P.sub.n,min.sup.max*t 5. If these limits are exceeded or undershot, there is a need for action:
E.sub.n(t)<E.sub.n.sup.min: fault message
E.sub.n(t)>E.sub.n.sup.max: curtailment 6. This results in requirements imposed on the individual power, voltage and current values P.sub.n(t), U.sub.n(t), I.sub.n(t). 7. For P.sub.n, (A, ρ, I, t), the time to the earliest possible occurrence of a cable fire or a device fault results as the maximum time before the effect of a regulation process; for P.sub.min, the intention is to comply with a maximum tolerated time for fault messages. 8. The required information transmission time is calculated as follows:
t.sub.min=t.sub.Measurement+t.sub.AD/conversion+2*t.sub.Transmission+t.sub.Algorithm+I.sub.Actuator
Based on this information, the various possible solutions are then assessed in order to find out, for example, whether it is more useful to carry out the regulation by means of a microprocessor and an actuator on the component itself or whether regulation in a transformer station is more expedient. In addition to technical criteria (for example with respect to the operational safety of the grid), economic criteria (for example with respect to conversion and operating costs) also play a role in this assessment.

(39) A grid structured according to the method consists of a multiplicity of self-operating, preferably also self-optimizing and self-maintaining, functional groups. The grid may partially or completely consist of such functional groups. Such a grid 11 is schematically illustrated in FIG. 3. It is still subdivided into the known grid levels 11.1 . . . 1.7 which correspond to the grid levels 1.1 . . . 1.7 in FIG. 1. The control center 2 is still present but is required only as an exception, in cases which cannot be regulated using the method presented. In addition to the control center 2, fault management 13 is provided and is used when an event cannot be resolved in a local functional group or on a lower grid level.

(40) Information is transmitted as a priority between the transmission or distribution grid levels 11.1, 11.3, 11.5, 11.7 between local functional groups. Transmission takes place secondarily between the transmission or distribution grid levels 11.1, 11.3, 11.5, 11.7 or, if necessary, over a plurality of grid levels 11.1 . . . 11.7, to the central control center 2.

(41) FIG. 4 shows a block diagram of a system which can be used to carry out the method according to the invention for operating a grid for electric energy. The grid 11 is constructed according to the illustration in FIG. 3. The system comprises a central computer unit 20 on which the method according to the invention for operating the grid 11 runs. The computer unit 20 is connected to a grid-based geographical information system (GIS) 21. The latter comprises a database which stores, inter alia, the present topology of the grid and the components known to the grid operator with their relevant properties. The computer unit 20 is also connected to a logistics interface 22 which can be used to automatically request additional grid components or replacement parts. The computer unit 20 is also connected to a maintenance interface 23 which can be used to request maintenance services for maintenance, fault correction or repair.

(42) The computer unit also communicates with the control center 2 and the fault management 13.

(43) A plurality of local functional groups are defined in the individual grid levels or in a cross-grid-level manner. FIG. 4 illustrates, by way of example, three such functional groups 30.1, 30.2, 30.3. Two of the functional groups 30.1, 30.2 are arranged in the grid level 11.7 and a further functional group extends over the grid levels 11.5-11.7 and comprises, inter alia, a converter 11.6.

(44) Each of the functional groups 30.1 . . . 3 comprises a control unit 31.1, 31.2, 31.3 (symbolized by a rectangle). At least one sensor unit 32.1, 32.2, 32.3 (symbolized by a circle) is likewise present in each of the illustrated functional groups 30.1 . . . 3, which sensor unit measures one or more relevant variables and transmits them to the corresponding control unit 31.1 . . . 3. At least one actuator 33.2, 33.3 (symbolized by a square) is also present in two of the three functional groups 30.2, 30.3 shown, which actuator can be used to influence the method of operation of the respective functional group 30.2, 30.3 in a manner triggered by the respective control unit 31.2, 31.3.

(45) The control units 31.1, 31.2 of the two local functional groups 30.1, 30.2 are connected to one another in the grid level 11.7 and can interchange information when corresponding actions are triggered. The control unit 31.1 of the local functional group 30.1 is also connected to the control unit 31.3 of the cross-grid-level local functional group 30.3. The latter can in turn interchange data with the fault management 13.

(46) The connections illustrated should be understood as examples. The illustration does not mean that (direct) physical connections must exist between the components mentioned, and data can be interchanged, for example, via a bus system or a central router. In the end, it is relevant which actions are assigned to the individual functional groups 30.1 . . . 3. Unidirectional or bidirectional data interchange with further functional groups or components can be enabled by adding an additional action.

(47) The method according to the invention for structuring the grid can be applied to a number of problems, for example can be used to prioritize the consumption of locally available energy, for example energy produced by photovoltaic installations. This makes it possible to reduce the transport route of the energy. The dynamic response expected in the grid with respect to the power to be transmitted is thereby reduced and the design of the grid can accordingly likewise satisfy reduced requirements.

(48) In a further application, it is possible to define a minimum schedule for power plants on grid level 1 and rules for infringements of the desired operation (frequency or production volume not achieved etc.). In the situations which cannot be regulated by means of local actuators, an item of information is transmitted to an external system (control center, fault management). Information for operation may correspond to measured rule violations from other functional groups, in which case the action of the measuring functional group, which is carried out upon reaching a corresponding trigger criterion (for example a frequency disturbance), provides for information to be sent to the receiving functional group (for example on grid level 1).

(49) In summary, it can be stated that the invention provides a method for structuring an existing grid for distributing electric energy, which method can be systematically applied to the existing grid and enables a high degree of operational safety with a low susceptibility to faults.