Method for determining measured variable in mesh of low-voltage network, mesh current regulator, system and use of mesh current regulator

Abstract

The invention relates to a method (100) for determining a measured variable in a mesh (7) of a low-voltage network (1), the method (100) comprising: providing a mesh current regulator (9) in the mesh (7) of the low-voltage network (1), the mesh current regulator (9) having an adjustable current / or voltage source (29). The method (100) further comprises determining at least one measured variable of the mesh (7) by means of the mesh current regulator (9) using a current / or voltage source (27). Furthermore, a mesh current regulator (9) for regulating a voltage in the mesh (7) is shown and described, the mesh current regulator (9) having an adjustable current / or voltage source (29) and being designed to carry out the method (100) according to the invention independently. The invention further relates to a system (27) for determining a measured variable in a mesh (7) of a low-voltage network (1) and for regulating a voltage in the mesh (7), the system (27) having a mesh current regulator (9), which comprises a determination unit (29) on the mesh current regulator (9) for determining a measured variable in the mesh (7). Finally, the use of the mesh current regulator (9) in the mesh (7) of the low-voltage network (1) is shown and described, and no measurement point for determining the measurement variable is applied in the mesh (7) outside the mesh current regulator (9) for the mesh current regulator (9).

Description

TECHNICAL FIELD

[0001] The invention relates to a method for determining a measurement variable in a cell of a low-voltage network, a cell current regulator, a system and the use of a cell current regulator. BACKGROUND

[0002] Low-voltage networks, such as for example local networks, usually have three phases and are often implemented as a mesh structure, so that the possible loads of the low-voltage network can be supplied with alternative branches. The loads at the load connection points in the low-voltage network can for example be single- or multi-family homes or commercial enterprises. The cells in the low-voltage network have hitherto often been supplied by a central transformer from the medium-voltage level. The central supply by the transformer has hitherto been sufficient, since only loads were connected to the cells whose power output could be well estimated. With the increasing feed-in of solar or small wind power plants, it has become apparent that the estimation of the power output is made difficult. Furthermore, for example due to the increasing use of charging stations for electric vehicles, the consumption is difficult to predict. Overloads can thus occur at individual output points in the cell. In order to avoid this, cell current regulators are used which are known from the prior art and which can apply an additional voltage to the cell step by step by means of a transformer. In order to regulate the transformer, measurement points within the cell are required, so that the known cell current regulators are not sufficient without external measurement means. The methods for determining the power output within the cell which are known from the prior art likewise have a plurality of decentralized measurement units within the cell.

[0003] Generally, it is desirable in a meshed low-voltage network that the measurement variables in the cells can be determined in a particularly simple manner, for which no decentralized or distributed arrangement of measurement units in the cells is necessary, so that extensive retrofitting measures within the cells are not necessary.

[0004] Furthermore, it is generally desirable in a meshed low-voltage network that a high supply security is achieved, in a manner such that the throughflow in the cells is controlled in a particularly simple manner, ideally for which extensive retrofitting measures within the cells are not necessary, such as for example by installing decentralized or distributed arrangement of measurement units or large, heavy and cost-intensive transformers. SUMMARY

[0005] It is therefore the task of the present invention to provide a method and a cell current regulator, by means of which the measurement variables in the cells can be determined in a particularly simple manner, in particular for which no decentralized or distributed arrangement of measurement units in the cells is necessary, so that in particular extensive retrofitting measures within the cells are not necessary. Furthermore, in particular it should be possible to achieve that a high supply security of the low-voltage network is achieved as far as possible, for example in a manner such that the throughflow in the cells can be controlled in an advantageously simple manner, preferably for which extensive retrofitting measures within the cells are not necessary.

[0006] This task is solved by the features of independent claims. Further advantageous design options of the solution presented here are presented in the dependent claims. It is pointed out here that the individually listed features in the dependent claims can be combined with one another in any technically meaningful manner and can define further design options of the application. Furthermore, the features presented in the claims are further clarified and elucidated in the description, in which further preferred design options of the application can also be shown.

[0007] According to a first aspect of the application, the task is solved by a method having the features of claim 1. The method serves to determine a measurement variable in a mesh of a low-voltage network. The method has provision of a mesh current regulator in the mesh of the low-voltage network, wherein the mesh current regulator has an adjustable current source and / or voltage source. Furthermore, the method has determination of at least one measurement variable of the mesh with the mesh current regulator with application of the current source and / or voltage source. Preferably, the method is implemented with the mesh current regulator presented here or the system presented here.

[0008] The method serves to determine a measurement variable in a mesh of a low-voltage network. The method advantageously enables determination of the measurement variable in different locations within the mesh or in different regions within the mesh, without an explicit decentralized or separate measurement unit being required for this at the different locations. Rather, the determination is effected by the mesh current regulator itself or by itself. In other words, in particular this can also be described as follows: the method serves to determine a measurement variable at or for a location or region of a mesh of a low-voltage network, wherein the location or region is spaced apart or spatially remote from the original measurement entity, the mesh current regulator provided according to the application. In particular, a determination unit of the mesh current regulator can determine the measurement variable within the mesh, which is located outside the determination unit in the mesh. The mesh current regulator can in principle be arranged in the middle or decentralized with respect to the mesh or with respect to the (power) coupling point into the mesh of the transformer arranged between the medium-voltage line and the mesh. The mesh current regulator can be set up to determine the measurement variable for a location or region of the mesh, which is arranged decentralized with respect to the mesh or the mesh current regulator. This can be described as decentralized determination of the measurement variable in the mesh. The term decentralized in particular relates here to a location or region for which the measurement variable is determined. The original measurement is advantageously however (centrally) effected by the mesh current regulator. The determination can thus in particular be effected by the mesh current regulator in the manner of an indirect determination (indirect measurement), wherein the determination / measurement of the mesh current regulator in particular represents the measurement variable at the respective decentralized location within the mesh. In other words, this in particular means that the measurement variable can be determined within the mesh with a single determination unit. It is thereby possible that the measurement variable can be determined within the mesh without a decentralized, external and / or separate measurement unit from the perspective of the determination unit.

[0009] The method has the provision of a cell current regulator in a cell of the low voltage network. Usually, a single or exactly one cell current regulator is provided in the cell. The provision is preferably to be understood as the cell current regulator being installed or connected in the cell. The provision of the cell current regulator can thus comprise the installation, connection and commissioning of the cell current regulator in the cell. In the case of installation, the cell is usually first switched to black mode, so that no current flows in the cell. The connection usually comprises the separation of the cables of the cell at the coupling points of the cell current regulator, wherein one end is connected to the input of the cell current regulator and the other end is connected to the output of the cell current regulator, so that the cell current regulator is preferably connected in series. For commissioning, the cell is again switched to white mode, so that current flows through the cell and the cell current regulator can be switched on. After commissioning, the cell current regulator is operated, so that the measured variables in the cell are determined, and the current in the cell can be regulated, preferably by the coupling of the current or voltage at the coupling points of the cell current regulator.

[0010] The cell current regulator has an adjustable current source and / or voltage source. The voltage source is preferably used for the coupling of a series voltage in the line of the cell. Such a voltage source can also be called DVR ("digital voltage restorer") or voltage regulator and is suitable for controlling the series voltage. This can also be called longitudinal voltage coupling. Such a voltage source can be used in the cell for longitudinal voltage coupling in order to control the current in the cell, since the longitudinal coupling of the voltage changes the current distribution in the cell. This can also be called UPFC ("unified power flow controller"). The advantage of the adjustable voltage source is that the regulated voltage value can be set in a particularly simple manner, whereby a high flexibility in the coupling of a defined current value can be achieved.

[0011] The current source is preferably used for providing a defined current value in the line of the cell. The current value can be increased or decreased if necessary. The advantage of the current source is that the current can be coupled directly.

[0012] Preferably, the adjustable current source and / or voltage source has a power electronic circuit. The power electronic circuit is in particular adapted and / or set up for setting a determined (desired or predetermined) current or voltage difference in the mesh. The current or voltage difference in particular determines the taking of at least one measurement variable. Furthermore preferably, the current source and / or voltage source has (only) switching elements, such as for example transistors (power transistors, switching transistors, metal oxide semiconductor field effect transistors (MOSFETs), insulated gate bipolar transistors (IGBTs)). The adjustable current source and / or voltage source is in particular preferably configured to (as required) increase or decrease the amplitude of the voltage in the line and / or to shift the phase of the voltage and / or to feed in harmonics having a determined frequency, phase and / or amplitude, in particular such that the voltage in the line is adaptable and / or the through current in the line is controllable.

[0013] As described above, the method has the taking of at least one measurement variable of the mesh using the mesh current regulator in the case of the application of the current source and / or voltage source. A plurality or a large number of measurement variables can be taken during the operation of the mesh current regulator. The taking can be carried out repeatedly a plurality of times during the operation of the mesh current regulator. In particular, the taking can be carried out continuously or repeatedly at time intervals from one another. It is also conceivable for the method to be carried out at predetermined times during the course of a day, a week or a month or after a predetermined period of time. For the taking of the measurement variables in the mesh, the current source and / or voltage source can preferably have current and voltage measuring means. Using the current and voltage measuring means, the current and voltage values present at the current source and / or voltage source can be taken. The taking of at least one measurement variable of the mesh using the mesh current regulator in the case of the application of the current source and / or voltage source preferably has a (targeted) change of the coupled current or voltage values, so that using the current and voltage measuring means a variety of current and voltage values can be taken. From the variety of current and voltage values, further measurement variables in the mesh can preferably be taken. These measurement variables preferably include the values of the current, the voltage and / or the impedance in the mesh. In the taking of the impedance, a separate taking of the real and imaginary parts of the impedance can in particular preferably be implemented. The taking of the measurement variables can preferably be implemented on all three phases (in particular simultaneously or at least partially in parallel in time). This has the advantage that the taking of the measurement variables can be implemented in particular time-efficiently. Furthermore preferably, the taking of the measurement variables can be carried out sequentially on the individual phases. This has the advantage that the measurement variables can be taken in particular accurately.

[0014] It can thus be summarized that a method is provided by which the measurement variable in the mesh can be determined in a particularly simple manner, in particular without the need for a distributed or distributedly arranged (additional) measurement unit in the mesh, so that in particular extensive retrofitting measures are not necessary in the mesh. Furthermore, in particular it is possible to achieve a high degree of supply security of the low-voltage power grid in that the throughflow current in the mesh is controlled in an advantageously simple manner, preferably without the need for extensive retrofitting measures in the mesh.

[0015] In one embodiment, the method has determining a loop impedance. To determine the loop impedance, the voltage source can preferably be operated as an alternating voltage source in phase with the grid voltage of the mesh and in particular can be set such that a zero current occurs at the coupling point of the mesh current regulator. In addition to the coupled voltage, which is set such that a zero current occurs, a first voltage difference can be applied by the voltage source. First, the first voltage difference can be applied as a positive voltage, so that a first current value occurring at the mesh current regulator can be measured. Next, the first voltage difference can be applied as a negative voltage, and next the first current value occurring at the mesh current regulator can be measured again. This process can be repeated several times, so that a plurality of first current values can be generated. From the generated plurality of first current values, a first current average value can be formed. The loop impedance can be formed from the quotient of the voltage and the current average value.

[0016] In one embodiment, the method has the step of determining at least one section impedance from the loop impedance. The mesh can be divided into a first section and a second section, wherein, for example, the first section can form the route between the transformer and the input side of the mesh current regulator and the second section can form the route between the transformer and the output side of the mesh current regulator. The loop impedance can represent the sum of the impedance of the first section, which can be referred to as the first section impedance, and the impedance of the second section, which can be referred to as the second section impedance. To determine the first and second section impedances, the voltage source can be adjusted to zero volts. The grid voltage and the grid current of the low voltage grid can now be determined. The mesh current regulator can then be preset with a value for the target reactive current. Once the mesh current regulator has been set up in this way, so that the target reactive current has been generated, the grid voltage and the grid current of the low voltage grid can be determined again and the second differential grid voltage and the second differential grid current can be calculated from the determined values, respectively. Once the second differential grid voltage and the second differential grid current have been calculated, the target reactive current can again be set to zero. This procedure can be repeated several times and the average values for the differential grid voltage and the differential grid current can be formed from the generated differential grid voltages and differential grid currents, respectively. With the determined measurement variables (now), the first section impedance can be determined in such a way that the loop impedance is multiplied by the quotient formed from the current difference and the target reactive current. The second section impedance can be determined in a similar manner to the first section impedance or from the difference between the loop impedance and the first section impedance.

[0017] In one embodiment, the method has the step of determining the transformer impedance. First, the total grid impedance can be determined therefrom the quotient of the determined average values of the differential grid voltage and the differential grid current, such as, for example, the quotient of the previously determined average values of the differential grid voltage and the differential grid current. The total grid impedance (now) can be used to determine the transformer impedance. To this end, the local section parallel impedance can be determined (first) from the parallel impedance of the first and second section impedances. The transformer impedance can now be determined from the quotient of the total grid impedance and the determined section parallel impedance.

[0018] In one embodiment, the method has the determination of a (virtual) position factor of the load connection end connected in the mesh and the derivation of at least one route factor from the position factor and the segment impedance. Further characteristic values can be derived from the previously derived measurement variables, which can be used for real-time calculation of the load situation in the mesh. Segments can be divided into sub-segments (virtually or computationally for the purpose of derivation). In this embodiment, the first segment and the second segment can each be divided into two (or more) sub-segments, for example a first sub-segment and a second sub-segment. Segments can be divided into the same number of sub-segments or a different number of sub-segments. The respective sub-segments can be of the same length or so determined that they have different lengths. It is preferably possible to set that the sub-segments have varying lengths. On the one hand, the first sub-segment can differ in its length from the second sub-segment. Alternatively or cumulatively, the first sub-segment of the plurality of first sub-segments and / or the second sub-segment of the plurality of second sub-segments can each have a different length from one another. Here, the sum of the respective sub-segments generally (always) results in the length of the respective segment. It is furthermore preferably possible to variably select the sub-segments, for example depending on or independently of (preferably depending on) the location or region of the load connection end. It is particularly preferably selected that at least one load connection end is located in or on one of the sub-segments. It is furthermore particularly preferably selected that (at most) one load connection end is located in or on each of the sub-segments. This can advantageously contribute to the measurement variables derived for the respective sub-segments being always assigned to at most one load connection end located in the respective sub-segment. In an (alternative) embodiment, the segments are divided into more than two sub-segments. In practice, it can prove advantageous to divide into 5 to 30 sub-segments, respectively. This can contribute to a more accurate allocation of the load within one of the segments. It can be assumed in principle that the more sub-segments a segment has, the more accurately the load can be allocated within the segment. With an increasing number of sub-segments, however, the computational requirement for deriving the measurement variables within the mesh or the sub-segments also generally increases, so that it has proven particularly advantageous for a segment to be divided into, for example, ten sub-segments. It is advantageous here to set the number of sub-segments in one or more segments to a value between 5 and 20.

[0019] As mentioned above, each of the segments can be divided into sub-segments, wherein the sum of the sub-segments of the respective segment usually again results in the length of the respective segment. In other words, this can also be described as follows, that each sub-segment can be assigned a virtual position factor, which can also be called a relative scaling factor. The scaling factor can be specified by a value between 0 and 1, which corresponds to the relative scaling of the length of the segment (relative length of the sub-segment). For example, a sub-segment with a scaling factor of 0.5 corresponds to half the length of the respective segment. The division of the segment into sub-segments is preferably related to or represents the real length of the segment, wherein the number of sub-segments can increase with increasing length of the segment. If the segment has a length of for example 1 km, the segment can be divided into 10 sub-segments, which each have a length of 100 m. In the case of a respective shorter segment, it can be sufficient or advantageous that the segment is divided into fewer sub-areas, wherein the sub-segments can in particular preferably have a length of at least 50 m. This has the advantage that it is thereby possible that in one sub-segment there is only one load with a particularly high power requirement. Loads which can be considered to have a particularly high power requirement are for example multiple single-family or multi-family homes with a respective plurality of households. Loads with a particularly high power requirement can also be for example commercial enterprises. Commercial enterprises usually have a higher power requirement than for example single-family or multi-family homes. From the position factor or scaling factor (now) the sub-segment impedance can be determined. For this purpose, the respective scaling factor can be multiplied by the respective segment impedance of the respective segment. From the calculated sub-segment impedance (now) the route factor can be calculated for each sub-segment. For this purpose, the route factor for a sub-segment can divide the sub-segment parallel impedance by the sub-segment impedance of the sub-segment. The route factor is in particular used as a dimensionless characteristic quantity in order to determine how much of the load current of a load connected in a sub-segment or at a respective virtual point - the virtual point can be defined by the position factor or scaling factor - would naturally flow (i.e. without influence by the mesh current regulator itself) at the installation location of the mesh current regulator. The route factor preferably remains the same in the case of constant impedance. In the idealized case of a homogeneous line (along the length of which a line cross section remains the same), the position factor is essentially synonymous with the assumed (real) distance between the point defined by the position factor (for example the connection point of the load or the area in which the load is connected to the mesh) and the mesh current regulator.

[0020] For storing the calculated values, these values can preferably be saved in tables, wherein for each section a table of its own can be saved, so that a first table can be set up for noting the values of the first section and a second table for noting the values of the second section. The tables can each comprise three columns, in which the local load current, the position factor or the scale factor and the route factor are saved. In the case of creating the tables, the value zero can first be stored for the local load current. This is because the method can advantageously identify and calculate load changes within the cell, for which the actual load does not necessarily have to be known. This has the advantage that the method can be carried out without an initial parameterization.

[0021] In one embodiment, the method has an adjustable current target value of an adjustable voltage source by two voltage vectors, wherein one of the voltage vectors runs in phase and in the same direction as the grid voltage and the other of the two voltage vectors runs orthogonally to the first voltage vector. The adjustment of the current target value can here be effected with the two voltage vectors. One of the vectors can run in phase or in the same direction as the grid voltage, wherein preferably the output of an integrator or of an integrator and a proportional element determines the amplitude of the active current component on the basis of the target value difference of the target value of the active current component (I or PI regulator). The second vector can run orthogonally to the first vector and thus also orthogonally to the grid voltage, wherein furthermore preferably the output of an integrator or of an integrator and a proportional element adjusts the amplitude of the reactive current component on the basis of the target value difference of the target value of the reactive current component (I or PI regulator). The resulting adjustment variable is typically a voltage, which is delivered to the voltage source (voltage source converter). This adjustment variable is here in particular generated by vector addition of the two components.

[0022] In one embodiment, the method has a determination of the natural point of coupling current. As described above, a large load change or a current coupling on the load connection can cause a load increase or a load decrease in the section. In order to be able to advantageously compensate a possible load increase or load decrease, with the method a load-compensated point of coupling current target value can advantageously be determined. The point of coupling current target value typically specifies a target value for the point of coupling current. For this purpose, a change in the natural point of coupling current can be determined (first). The natural point of coupling current here typically represents the current change which would arise due to the load change at the point of coupling of the cell current regulator without direct coupling and without the effect of the cell current regulator. The natural point of coupling current is in particular calculated from the product of the regulated point of coupling current of the cell current regulator and the quotient of the voltage value of the voltage source and the loop impedance.

[0023] In one embodiment, the method has: determining a line voltage difference from the segment impedance and the natural point of coupling current variation. To determine the natural point of coupling current variation, which can also be called the natural point of coupling current variation, the natural point of coupling current at a first time and at a second time can be determined. The natural point of coupling current variation can be determined from the difference of the two values. The line voltage variation can be calculated in such a way that the product of the natural point of coupling current variation and the segment impedance is formed.

[0024] In one embodiment, the method has: determining a transformer voltage variation from the connection point voltage variation and the line voltage difference. Preferably, a first connection point voltage variation can be determined at both connection points of the segment in such a way that the voltage is determined at a first time at the connection point of the first segment and at a second time at the connection point of the second segment. In a similar manner, a second connection point voltage variation can also preferably be determined at the connection point of the second segment. Based on the two connection point voltage variations, a dominant load change can be determined. For this purpose, in particular (first) it is determined in which segment a load change has occurred. This is preferably achieved in accordance with the following cases. In the case of a consumption current from the first segment to the second segment via the coupling point becoming positive, a load decrease in the second segment can be assumed in the case of an increase in the first connection point voltage variation. If the first connection point voltage variation decreases, a load increase in the first segment can be assumed. In the case of a consumption current from the first segment to the second segment via the coupling point becoming negative, a load decrease in the first segment can be assumed in the case of an increase in the second connection point voltage variation. If the second connection point voltage variation decreases, a load increase in the second segment can be assumed. The transformer voltage variation is in particular generated from the difference of the connection point voltage variation and the line voltage difference. Based on this determination, the compensation current can now be calculated.

[0025] In one embodiment, the method has: determining a load current variation from the transformer voltage variation and the transformer impedance. The load current variation, which can also be called the dominant load current variation, is in particular generated from the quotient of the transformer voltage variation and the transformer impedance.

[0026] In one embodiment, the method has: determining a load proportion from the natural point of coupling current variation and the load current variation. To advantageously obtain the load proportion at the coupling point from the load current variation, the natural point of coupling current variation can be divided by the load current variation.

[0027] In one embodiment, the method has: determining a load distribution from the load ratio, the loop impedance and the segment impedance. The load distribution can be determined by a quotient resulting from the loop impedance and the product of the load distribution and the segment impedance. The load distribution preferably specifies a value range between 0 and 1, wherein the value corresponds to a location or area within the first segment. The value 0 generally corresponds to the location of the output of the first segment and the value 1 to the location on the connection terminal of the cell current regulator on the first segment. The values of the detected loads can be entered in the aforementioned (created) table for each load distribution. For this, the entered values of the local load currents can be updated for the respective load distribution. As described above, the method can detect load changes, so that the table generally contains the value 0 in the column of the local load currents in the case of the first execution. By the updating of the table, changes in the load in the sub-areas can advantageously always be tracked.

[0028] In one embodiment, the method has: determining an output current from the load distribution and the load current change. The point of coupling current can be recalculated from the determined loads. The point of coupling current generally results from the sum of all entries of the table for the local load currents. From the calculated value for the point of coupling current, a load correction can be calculated (now) in the case of the application of the natural point of coupling current. The load distribution can be formed by the quotient of the point of coupling current and the natural point of coupling current. The calculated load correction can be calculated for updating (now) with each value of the local load currents, in particular in such a way that each value of the table is multiplied by the load correction. From the updated values of the table, the first output current and the second output current can be calculated from the sum of the values of the multiplication of the local load currents with the respective route factor.

[0029] In one embodiment, the method has: determining a point of coupling current target value from the natural point of coupling current and the output currents. The point of coupling current target value of the load compensation to be set by the cell current regulator (now) can be determined from the half of the difference of the natural point of coupling current and the two output currents. For this, the natural point of coupling current can be added to the half of the difference of the two output currents.

[0030] According to a second aspect of the application, the task is solved by a mesh current regulator having the features of claim 15. The mesh current regulator is used for regulating the voltage in a mesh, wherein the mesh current regulator has an adjustable current source and / or voltage source and is set up to independently carry out the method described herein. Furthermore, the mesh current regulator can have, for example, single or multiple (or even all) of the following elements: connection terminals for the connection of the mesh current regulator on or in the mesh; inputs and outputs for connecting external sensors or signal sources in order to (obtain) information about the system operating state or other relevant parameters; a power supply for powering the mesh current regulator or its electronics; a signal processing component for processing and / or filtering the detected signals; a protection component or protection mechanism for protection against overload, overvoltage or other faults; a measuring unit for detecting a measured variable in the mesh; a regulator for regulating the output of the mesh current regulator; an actuator for influencing the through-current in the mesh, such as, for example, a power transistor or a power switch; an interface for communication of the mesh current regulator with other system or control components; a feedback loop for feedback and adaptation of the values of the regulation of the current in the mesh. The details, features and advantageous design solutions discussed in connection with the method can accordingly also occur in the mesh current regulator presented here, and vice versa. Reference is made in this regard to the explanations there of the further characterization of the features.

[0031] According to a third aspect of the application, the task is solved by a system having the features of claim 16. The system is used for detecting a measured variable in a mesh of a low-voltage power grid and for regulating the voltage and current in the mesh, wherein the system has a mesh current regulator. Furthermore, the system has a detection unit on the mesh current regulator for detecting the measured variable in the mesh. The details, features and advantageous design solutions discussed in connection with the method can accordingly also occur in the system presented here, and vice versa. Reference is made in this regard to the explanations there of the further characterization of the features.

[0032] According to a fourth aspect of the application, the task is solved by an application having the features of claim 17. The application has the application of a mesh current regulator in a mesh of a low-voltage power grid, wherein no measuring point for detecting a measured variable for the mesh current regulator is applied in the mesh other than the mesh current regulator. The details, features and advantageous design solutions discussed in connection with the method can accordingly also occur in the application presented here, and vice versa. Reference is made in this regard to the explanations there of the further characterization of the features. BRIEF DESCRIPTION OF DRAWINGS

[0033] Further features, advantages and applications of the present application can result from the following description of embodiments and the drawings. All features described and / or illustrated herein form the subject-matter of the present application in their own right, both independently and in any combination, and independently of their combination in the respective claims or their reference. In the drawings, like reference numerals represent the same or similar objects.

[0034] Figure 1 a schematic diagram showing one embodiment of the method described herein for determining a measurement quantity in a mesh cell of a low-voltage power grid;

[0035] Figure 2 a schematic diagram showing a meshed low-voltage power grid;

[0036] Figure 3 a schematic diagram showing one embodiment of the mesh cell current regulator described herein. DETAILED DESCRIPTION

[0037] Figure 1 a schematic diagram showing one embodiment of the method 100 described herein for determining a measurement quantity in a mesh cell of a low-voltage power grid. The order of the method steps shown by means of blocks 101 and 102 is principally exemplary and can occur, for example, in the normal operating flow of the method. It is furthermore conceivable that the method steps can be implemented at least partially in parallel or simultaneously. It is furthermore conceivable that the method steps are implemented directly consecutively or with a time interval between one another. The method step according to block 101 can be performed, for example, in the context of the installation or commissioning of a mesh cell current regulator. The method step according to block 102 can be implemented repeatedly several times during the operation of a mesh cell current regulator. In particular, the method step according to block 102 can be performed more frequently than the method step according to block 101.

[0038] The method 100 has, in a first step 101, providing a mesh cell current regulator in a mesh cell of a low-voltage power grid, wherein the mesh cell current regulator has an adjustable current source and / or voltage source. In a second step 102, the method 100 has determining at least one measurement quantity of the mesh cell with the mesh cell current regulator using the current source and / or voltage source. As described above, the method 100 described herein is applied in a mesh cell of a low-voltage power grid. Exemplary mesh cells in which the method can be applied are shown in Figure 2 and are therefore described in further detail below with respect to Figure 2 the method 100.

[0039] Figure 2A schematic diagram of an exemplary low-voltage grid 1 is shown, which is connected to a medium-voltage line 3. Between the low-voltage grid 1 and the medium-voltage line 3 a transformer 5 for voltage transformation is provided. The low-voltage grid 1 is an electrical power grid which is operated at a low voltage, usually less than 1 kV, and is mostly used in distribution grids. For the distribution of the voltage, the voltage is usually first distributed over a long distance in the medium-voltage grid before it is fed via the transformer 5 from the medium-voltage line 3 into the low-voltage grid 1.

[0040] The low-voltage grid 1 can be designed as a three-phase AC grid. In the low-voltage grid there are usually technical possibilities for forming a mesh 7. The mesh 7 serves to ensure a high supply security, since possible loads can thus be supplied with power via alternative branches. In order to regulate the current in the mesh 7, a mesh current regulator 9 can be installed. The mesh current regulator 9 serves to change the voltage level of the low-voltage grid 1. By means of the change in the voltage level, the current in the mesh 7 can be controlled, since the coupling of the voltage changes the current distribution in the mesh 7. The mesh 7 can have a plurality of load connection points 11, on which a plurality of loads 13 and / or current sources 15, for example in the form of photovoltaic devices or small wind power devices, can be connected. The loads 13 in the load connection points 11 can be, for example, single- or multi-family homes or commercial enterprises, wherein the loads 13 can each have one or more current sources 15. It often occurs that a plurality of loads 13 and / or current sources 15 are connected at the load connection points 11. Due to the plurality of loads 13 and / or current sources 15, large load changes can occur within the low-voltage grid 1, which in extreme cases can lead to an overload of the load connection points 11 or the entire mesh 7. In order to prevent this, the mesh current regulator 9 can regulate the through current in the mesh 7.

[0041] As mentioned above, the mesh current regulator 9 can serve to ensure an even distribution of the current in the mesh 7. For this it is necessary that the mesh current regulator 9 knows or can determine different currents, for example the output current at the coupling point on the transformer 5 or the output current at different points within the mesh 7. In addition, the mesh current regulator 9 can have means for current and voltage measurement, preferably for each phase of the mesh 7.

[0042] Now in order to be able to determine the current to be coupled in, the method 100 exemplarily applies various measurement variables of the mesh 7 in the case of an applied current and / or voltage source. The various measurement variables are explained in the following. In the following the method 100 is described according to the mesh current regulator 9 with an adjustable voltage source, but the method 100 is similarly executable with the mesh current regulator 9 with an adjustable current source.

[0043] In Figure 2The loop 17 is shown in Fig. 1 and illustrates the assumed current flow for the method 100. First, the loop impedance Z 17 of the loop 17 can be determined with the method 100. To determine the loop impedance Z 17 , the voltage source can be operated as an alternating voltage source in phase with the network voltage of the network cell 7 and so adjusted that a zero current occurs at the coupling point of the network cell current regulator 9. In addition to the coupled-in voltage adjusted to produce the zero current, a first voltage difference U d9 can be applied by the voltage source. First, the first voltage difference U d9 is applied as a positive voltage, so that a first current value I 17 occurring at the network cell current regulator 9 can be measured. Next, the first voltage difference U d9 is applied as a negative voltage, and next the first current value I 17 occurring at the network cell current regulator 9 is measured again. This procedure can be repeated several times, so that a plurality of first current values I 17 can be produced. From the plurality of first current values I 17 produced, a first current average value Ī 17 can be formed. The loop impedance Z 17 is formed from the quotient of the voltage U d9 and the current average value Ī 17 according to the following formula.

[0044]

[0045] The determination can be carried out simultaneously on all three phases or sequentially on the individual phases. The method 100 or the determination of the measured variables is preferably carried out separately for each phase and thus applies to a single-phase or multi-phase network cell 7. For simplicity, the following example is explained only on the basis of one phase, however, the example applies analogously to the remaining phases.

[0046] The network cell 7 can be divided into a first section 19 and a second section 21, wherein, for example, the first section 19 forms the route between the transformer 5 and the input side of the network cell current regulator 9 and the second section 21 forms the route between the transformer 5 and the output side of the network cell current regulator 9.

[0047] The loop impedance Z 17 represents the sum of the impedance of the first section 19, which can be referred to as the first section impedance Z 19 , and the impedance of the second section 21, which can be referred to as the second section impedance Z 21 . To determine the first and second section impedances Z 19 , Z 21The voltage source can be adjusted to zero volts. The grid voltage U1 and the grid current I1 of the low voltage grid 1 can now be determined. The mesh current regulator 9 can then be preset with the value of the target reactive current. Once the mesh current regulator 9 has been set in this way, the target reactive current I qs , the grid voltage U1 and the grid current I1 of the low voltage grid 1 can be determined anew and the second differential grid voltage U 1d and the second differential grid current I 1d can be calculated from the determined values, respectively. 1d Once the second differential grid voltage U 1d and the second differential grid current I qs have been calculated, the target reactive current I 1d can again be set to zero. This procedure can be repeated several times and the plurality of differential grid voltages U 1d and differential grid currents I 1d can form an average value for the differential grid voltage Ū 1d and the differential grid current Ī 19 , respectively. The first partial impedance Z 21 can now be determined from the determined measurement variables according to the following formula.

[0048]

[0049] The second partial impedance Z 17 is generated from the difference between the loop impedance Z 19 and the first partial impedance Z 1d according to the following formula.

[0050]

[0051] The total grid impedance Z1 can be determined from the determined average values of the differential grid voltage Ū 1d and the differential grid current Ī 19 according to the following formula.

[0052]

[0053] The total grid impedance Z1 can now be used to determine the transformer impedance Z5. To this end, the local partial parallel impedance Z 21 is first determined from the parallel impedance of the first and second partial impedances Z sp according to the following formula.

[0054]

[0055] The transformer impedance Z5 can now be determined from the quotient of the total grid impedance Z1 and the determined partial parallel impedance Z sp according to the following formula.

[0056]

[0057] From the previously determined measurement variables further characteristic values can be determined which are used for the real-time calculation of the load situation in the cell 7. For the calculation, the segments 19, 21 are virtually divided into sub-segments 23, 23', 25, 25'. In the present embodiment, the first segment 19 is divided into first sub-segments 23, 23' and the second segment 21 is divided into second sub-segments 25, 25', respectively. The sub-segments 23, 23', 25, 25' can be of equal length or so determined that they have varying lengths. For example, it can be provided that the sub-segments 23, 23', 25, 25' have different lengths. On the one hand, the first sub-segments 23, 23' can differ in their length from the second sub-segments 25, 25', and on the other hand the first sub-segments 23, 23' or the second sub-segments 25, 25' can have different lengths from each other, wherein the sum of the first sub-segments 23, 23' always results in the length of the first segment 19 and the sum of the second sub-segments 25, 25' always results in the length of the second segment 21. The sub-segments 23, 23', 25, 25' can also be variably selected, for example in particular independently of the location of the load connection 11. Preferably, the sub-segments 23, 23', 25, 25' are so selected that at least one load connection 11 is located in one of the sub-segments 23, 23', 25, 25'. Particularly preferably, the sub-segments 23, 23', 25, 25' are so selected that at most one load connection 11 is located in each of the sub-segments 23, 23', 25, 25'. This has the advantage that the measurement variables determined for the respective sub-segments 23, 23', 25, 25' can always be assigned to at most one load connection 11 which is located in the respective sub-segment 23, 23', 25, 25'.

[0058] In Figure 2 the first segment 19 is exemplarily divided into two sub-segments 23, 23' and the second segment 21 is exemplarily divided into two sub-segments 25, 25'. Preferably, the segments 19, 21 are divided into more than two sub-segments, wherein in practice it has proven advantageous to divide into 5 to 30 sub-segments, respectively. This has the advantage that the load can be more accurately distributed within one of the segments 19, 21. In general, it applies that the more sub-segments a segment has, the more accurately the load can be distributed within the segment. With increasing number of sub-segments, the computational demand for determining the measurement variables within the cell 7 or the sub-segments 23, 23', 25, 25' also increases, so that particularly preferably it has proven particularly advantageous that a segment is divided into ten sub-segments.

[0059] As described above, each of the segments 19, 21 is divided into subsegments 23, 23', 25, 25', wherein the sum of the subsegments 23, 23', 25, 25' of the respective segment 19, 21 again yields the length of the respective segment 19, 21. That is, for each subsegment 23, 23', 25, 25' a relative scaling factor A 23 25 23‘ 25‘ The scaling factor A corresponds to the scaled, relative length of the segment 19, 21. For example, a subsegment with a scaling factor of 0.5 corresponds to half the length of the respective segment 19, 21. The division of the segments 19, 21 into subsegments 23, 23', 25, 25' can preferably be related to the actual length of the segments 19, 21, wherein the number of subsegments can increase with increasing length of the segments. If a segment has a length of, for example, 1 km, this segment can be divided into 10 subsegments, which each have a length of 100 m. In the case of correspondingly shorter segments, it is sufficient for the segment to be divided into fewer subareas, wherein the subsegments particularly preferably have a length of at least 50 m. This has the advantage that only one load with a particularly high power requirement is present in one subsegment. Loads which can be considered to have a particularly high power requirement are, for example, multiple single-family or multi-family homes with a respective plurality of households. Loads with a particularly high power requirement can also be, for example, commercial enterprises. Commercial enterprises generally have a higher power requirement than, for example, single-family or multi-family homes.

[0060] The subsegment impedance Z 23 25 23‘ 25‘ The subsegment impedance Z 23 23‘ 25 25‘ can now be determined. To this end, the respective scaling factor A 23 25 23‘ 25‘ is multiplied by the respective segment impedance Z 19 21 of the respective segment 19, 21.

[0061]

[0062] The calculation of the subsegment impedances Z 23‘ 25 25‘ of the remaining subsegments 23', 25, 25' can be carried out analogously. Alternatively, the subsegment impedance Z​​​​​​​​​​​​​​​23 .

[0063]

[0064] from the calculated sub-section impedance Z 23 , Z 23‘ , Z 25 , Z 25‘ Now the route factor SF(A 23 ), SF(A 23‘ ), SF(A 25 ), SF(A 25‘ ) can be calculated for each sub-section. To this end, for example, the route factor SF(A 23 ) for the sub-section 23 is the sub-section parallel impedance Z 23p divided by the sub-section impedance Z 23‘ . The route factor SF(A 23 ) for the sub-section 23 is calculated, for example, using the following formula.

[0065]

[0066]

[0067] The route factor SF(A x ) serves as a dimensionless characteristic quantity in order to determine how much of the load current of a load connected in the sub-section 23, 23', 25, 25' or at the corresponding virtual point (which can be defined by the scaling factors A 23 , A 23‘ , A 25 , A 25‘ ) would flow naturally at the installation location of the mesh current regulator 9, i.e. without being influenced by the mesh current regulator itself. The route factor SF(A x ) preferably remains the same in the case of constant impedance.

[0068] In order to store the calculated values, these values can be saved in a table Tx, wherein for each section 19, 21 a table T 19 , T 21 of its own can be saved, so that a first table T 19 for the values of the first section 19 and a second table T 21 for the values of the second section 21 can be set up. The tables T 19 , T 21 may each contain three columns, in which the partial load current I Ax , the scaling factor A x and the route factor SF(A x). In the case of creating a table, for the local load current I Ax The value zero can first be stored. This is because the method 100 can identify and calculate load changes within the cell 7, for which it is not necessary to know the actual load. This has the advantage that the method 100 can be performed without an initial parameterization.

[0069] As described above, a load increase or a load decrease in the segments 19, 21 can be caused by a large load change or a current coupling-in on the load connection 11. In order to be able to compensate a possible load increase or load decrease, with the method 100 the load-compensated point-of-coupling current target value I 9s is now determined. The point-of-coupling current target value I 9s is explained. For this the change in the natural point-of-coupling current I 9n is first determined. The natural point-of-coupling current I 9n represents the current change which would arise on the point of coupling of the cell current regulator 9 due to a load change without direct coupling and without the action of the cell current regulator 9. The natural point-of-coupling current I 9n is calculated from the adjusted point-of-coupling current I9 of the cell current regulator 9, the voltage value U q of the voltage source and the loop impedance Z 17 .

[0070]

[0071] In order to determine the change in the natural point-of-coupling current I 9n , which can also be called the natural point-of-coupling current change I d9n , the natural point-of-coupling currents I 9n at a first time T1 and a second time T2 can be determined. The following calculation of the difference of the two values results in the natural point-of-coupling current change I d9n .

[0072] ;

[0073]

[0074] In addition to determining the natural point-of-coupling current change I d9n , first connection end voltage changes U 19d , U 21d can be determined on the two connection points of the segments 19, 21 in such a way that the voltage is determined on the connection point of the first segment 19 at the time T1 and the voltage is determined on the connection point of the first segment 19 at the time T2. In a similar manner, second connection end voltage changes U 21d can also be determined on the connection points of the second segment 21. Based on the two connection end voltage changes U19d U 21d The dominant load change can be determined. To do this, first determine in which segment the load change has occurred. This can be achieved, for example, by differentiating based on the following criteria.

[0075] When the current consumption from the first segment 19 to the second segment 21 via the coupling point becomes positive, the voltage change U at the first connection terminal... 19d In the case of an increase, the load in the second segment 21 is considered to decrease. If the voltage at the first connection terminal changes U... 19d If the current decreases, then the load in the first segment 19 is considered to have increased. When the current consumption from the first segment 19 to the second segment 21 via the coupling point becomes negative, the voltage change U at the second connection terminal... 21d In the case of an increase, the load in the first segment 19 is considered to decrease. If the voltage at the second connection terminal changes U... 21d If the load decreases, then it is assumed that the load in the second segment 21 increases.

[0076] Based on this determination, the compensation current I can now be calculated. 9d Subsequently, the compensation current I can be calculated based on the measured values ​​of the first segment 19. 9d However, the subsequent steps apply similarly to the second segment.

[0077] First, the change in current I at the natural coupling point d9n With segmented impedance Z 19 The product of the line voltage change U is used to calculate the line voltage change. dl .

[0078]

[0079] Due to line voltage change U dl and the voltage change U at the first connection terminal 19d The transformer voltage change U 5d .

[0080]

[0081] Dominant load current variation I 7d Now, the voltage change U of the transformer... 5d This is generated in relation to the transformer impedance Z5.

[0082]

[0083] To obtain the load current change I 7d Obtain the load ratio R at the coupling point x The change in natural coupling point current I d9n Divided by the load current change I 7d .

[0084]

[0085] The load distribution A x can be determined from the load ratio R 17 , the loop impedance Z 19 and the segment impedance Z Rx using the following equation.

[0086]

[0087] The load distribution A Rx is similar to the scaling factor A 23 , A 25 , A 23‘ , A 25‘ specifies a value in the range between 0 and 1, wherein the value corresponds to a location within the first segment 19. The value 0 corresponds here to the location of the output of the first segment 19, and the value 1 corresponds to the location on the connection terminal of the mesh current regulator 9 on the first segment 19. The load distribution A Rx can now be entered in the aforementioned tables T 19 , T 21 . For this, the entered value of the local load current I Ax is updated for the corresponding load distribution A Rx . As described above, the method 100 detects load changes, so that the tables T 19 , T 21 contain the value 0 in the column of the local load current I Ax in the case of the first execution. The update of the local load current I Ax is calculated as follows.

[0088]

[0089] By the update of the tables T 19 , T 21 , the changes in the load in the sub-areas 23, 23', 25, 25' can always be tracked. The coupling point current I9 can be recalculated from the loads determined. The coupling point current I9 results from the sum of all entries of the tables T Ax , T 19 , T 21 for the local load currents I 19 and can be formed as follows.

[0090]

[0091] Here n stands for all entries of the first table T 19 , and m stands for all entries of the second table T 21 . From the value calculated for the coupling point current I9, the natural coupling point current I 9nThe load correction D is calculated in the following way in the case of I .

[0092]

[0093] The calculated load correction D I In order to update the now prevailing local load current I Ax each value is calculated in such a way that the table T 19 , T 21 each value is multiplied by the load correction.

[0094]

[0095] From the updated values, the first output current I 19 , T 21 the sum of the values of the local load current can be calculated in the following way the first output current I 19 and the second output current I 21 .

[0096]

[0097]

[0098] The load-compensated point-of-coupling current target value I 9s The now prevailing natural point-of-coupling current I 9n and the difference between the two output currents I 19 , I 21 half.

[0099]

[0100] As mentioned above, the method 100 can also utilize separate determination of the real part and the imaginary part for the determination of the measurement values. In this case, the aforementioned method steps of the method 100 can separately determine the active power and the reactive power. This has the advantage that thereby a more accurate determination of the measurement quantities is made possible.

[0101] The aforementioned method 100 for determining the measurement quantities in the mesh 7 is run iteratively, preferably purely iteratively. This is to be understood in the sense that the method 100 maintains the load state of the mesh 7 without the exact load state of the mesh 7 being required. This has the advantage that the method 100 is sufficient without initialization and without input of possible measurement values in the mesh 7. Thus, no external measurement values or measurement points in the mesh 7 are required in order to implement the method 100.

[0102] As mentioned above, the method 100 is carried out by the cell current regulator 9. Normally, the cell 7 or the lines of the cell 7, on which the cell current regulator 9 is installed, are switched to the black mode, so that no current flows. The method 100 can then be carried out if the cell current regulator 9 is in operation. Since an overload situation normally does not exist in the case of the cell current regulator 9 being in operation in the cell 7, the method 100 is able to maintain the load state, so that an overload situation cannot occur. The method 100 thus reacts to changes within the cell 7. As mentioned above, the changes are determined by taking various measured variables. The method 100 reacts to possible changes with the coupling point current I9, which is compensated for. In a preferred embodiment of the method 100, the load-compensated coupling point current I9 is changed only if the method 100 detects a change in the measured variables in the cell 7.

[0103] As mentioned above, the method 100 is carried out by the cell current regulator 9. In Figure 3 An exemplary cell current regulator 9, which is suitable for carrying out the method 100, is shown in Fig. 1.

[0104] Figure 3 A schematic diagram of an embodiment of a system 27, which comprises the cell current regulator 9 described herein, is shown. The cell current regulator 9 has a voltage source 29, which is coupled in, which is adjustable by a determination unit 31. Instead of a voltage source 29, a current source can also be provided. The voltage source 29 has a power supply 33 for this purpose, which has bidirectional power. The cell current regulator 9 is connected to the three phases of the cell 7. The determination unit 31 is likewise connected to the three phases of the cell 7 and has for this purpose a current and voltage measuring device 35 for each phase. Furthermore, the determination unit 31 is connected to the voltage source 29 via a first connection line 37. The determination unit 31 provides the target value of the voltage, which is to be coupled in, to the voltage source 29 via the first connection line 37 in order to achieve the target value of the load-compensated coupling point current I 9s For the case in which a current source is provided instead of a voltage source 29, the determination unit 31 provides the load-compensated coupling point current I 9s via the first connection line 37. The determination unit 31 is connected to the power supply 33 via a second connection line 39, via which the determination unit 31 provides the target reactive current I qs to the power supply 33.

[0105] The cell current regulator 9 has an internal regulating circuit, which provides the voltage target value to the voltage source 29. With the voltage target value, the target value of the load-compensated coupling point current I 9s is achieved. The determination unit 31 obtains the measured variables, which are coupled in, by means of the current and voltage measuring device 35 at regular intervals, so that it can always be determined whether the load-compensated coupling point current I 9sthe target value. In a preferred embodiment, the internal regulating circuit has an update rate of 100 μs.

[0106] In order to determine the load-compensated point-of-coupling current I 9s , the mesh current regulator 9 has an external regulating circuit. Preferably, the external regulating circuit is an open-loop regulating circuit. The external regulating circuit provides a value for the load-compensated point-of-coupling current I 9s , which is used as an input variable by the internal regulating circuit. The internal regulating circuit can preferably be implemented as a current regulator. The current regulator operates a voltage source (actuator, voltage source converter) with its set value and regulates to the load-compensated point-of-coupling current I 9s , which is obtained by the external regulating circuit. The current regulator has a high update rate and thus keeps the current of the mesh current regulator, which represents the grid coupling, on the predetermined value even in the event of load changes in the grid. This is very advantageous, since the overloading of the point of coupling is thus actively prevented. The regulation of the current is achieved by two voltage vectors, one of which is in phase or in the same direction as the grid voltage, wherein an integrator or the output of an integrator and the output of a proportional element determine the amplitude of the active current component on the basis of the target value difference of the target value (I or PI regulator). The second vector is orthogonal to the first vector and thus also to the grid voltage, wherein an integrator or the output of an integrator and the output of a proportional element adjust the amplitude of the reactive current component on the basis of the target value difference of the target value (I or PI regulator). The resulting regulating variable is a voltage, which is delivered to the voltage source (voltage source converter). The regulating variable is produced by vector addition of the two components.

[0107] In a preferred embodiment, the external regulating circuit has an update rate of 100 milliseconds. In another preferred embodiment, the external regulating circuit has an observation or estimation element, the output of which is an estimate of the load-compensated point-of-coupling current I 9s .

[0108] In Figure 2 , the mesh current regulator 9 is only shown schematically in the middle of the mesh 7, so that the two segments 19, 21 are of equal length. However, the method 100 can be implemented such that the mesh current regulator 9 is installed at any position in the mesh 7. By not having to initialize the mesh current regulator 9 and by not requiring an external measuring point within the mesh 7, the mesh current regulator can be installed and operated at every arbitrary position. As described above, the mesh current regulator 9 reacts to changes within the mesh 7, which changes can be determined at every position in the mesh 7 with the method 100 described herein independently of the installation site of the mesh current regulator 9 described herein.

[0109] In summary it can thus be said that by means of the method 100 described herein the measurement variables in the mesh 7 can be determined in a particularly simple manner, in particular without the need for a distributed or distributedly arranged (additional) measurement unit in the mesh 7, so that in particular extensive retrofitting measures are not necessary in the mesh 7. Furthermore it is in particular possible to achieve a maximum possible supply security of the low-voltage power grid 1 in such a way that the throughflow current in the mesh 7 is controlled in an expediently simple manner, preferably without the need for extensive retrofitting measures in the mesh 7.

[0110] It is additionally pointed out that "having" does not exclude other elements or steps and "one" or "a" does not exclude a plurality. Furthermore it is pointed out that features that have been stated with reference to one of the above embodiments can also be applied in combination with other features of other above embodiments. Reference signs in the claims are not to be interpreted as limiting.

[0111] List of reference signs

[0112] 1 low-voltage power grid

[0113] 3 medium-voltage line

[0114] 5 transformer

[0115] 7 mesh

[0116] 9 mesh current regulator

[0117] 11 load connection

[0118] 13 load

[0119] 15 current source

[0120] 17 loop

[0121] 19 first section

[0122] 21 second section

[0123] 23 first subsection

[0124] 25 second subsection

[0125] 27 system

[0126] 29 voltage source

[0127] 31 determination unit

[0128] 33 power supply

[0129] 35 current and voltage measurement means

[0130] 37 first connection line

[0131] 39 second connection line

[0132] 100 method

[0133] 101 first method step

[0134] 102 second method step

[0135] Z 17 loop impedance

[0136] U d1 first voltage difference

[0137] I 17 first current value

[0138] I 17‘ first current average value

[0139] R 17 real part of loop impedance

[0140] X 17 imaginary part of loop impedance

[0141] Z 19 first segment impedance

[0142] Z 21 second segment impedance

[0143] U1 grid voltage

[0144] I1 grid current

[0145] I qs target reactive current

[0146] U 1d differential grid voltage

[0147] I 1d differential grid current

[0148] Ū 1d average value of differential grid voltage

[0149] Ī 1d average value of differential grid current

[0150] Z1 total grid impedance

[0151] Z sp segment parallel impedance

[0152] Z5 transformer impedance

[0153] A 23 proportionality factor for sub-segment (Lok_rel)

[0154] Z 23 sub-segment impedance

[0155] SF(A x ) route factor

[0156] I9 coupling point current

[0157] I 9n natural coupling point current

[0158] I d9n natural coupling point current variation

[0159] U 19d first connection end voltage variation

[0160] U 21d second connection end voltage variation

[0161] U dl line voltage variation

[0162] U 5d transformer voltage variation

[0163] I 7d load current variation

[0164] R x load proportion

[0165] A x load distribution

[0166] I Ax load current

[0167] T 19 first table

[0168] T 21 second table

[0169] D I load correction

[0170] I 19 first output current

[0171] I 21 second output current

Claims

1. Method (100) for determining a measured variable in a cell (7) of a low-voltage network (1), wherein The method (100) has the following steps: A mesh current regulator (9) is provided in a mesh (7) of a low-voltage network (1), wherein the mesh current regulator (9) has an adjustable current source and / or voltage source (29); and At least one measured variable of the mesh (7) is determined using the mesh current regulator (9) with the application of the current source and / or voltage source (27).

2. The method (100) according to any of the preceding claims, wherein The method (100) has the following step: determining a loop impedance.

3. The method (100) according to any of the preceding claims, wherein The method (100) has the following step: determining at least one section impedance from the loop impedance.

4. The method (100) according to any of the preceding claims, wherein The method (100) has the following step: determining a transformer impedance.

5. The method (100) according to any of the preceding claims, wherein The method (100) has the following steps: determining a virtual position factor of a load connection (11) connected in the mesh (7); and determining at least one route factor from the position factor and the section impedance.

6. The method (100) according to any of the preceding claims, wherein The method (100) has the following step: regulating a current target value of the adjustable voltage source by two voltage vectors, one of the voltage vectors being in phase and in the same direction as the network voltage and the other of the two voltage vectors extending at right angles to the first voltage vector.

7. The method (100) according to any of the preceding claims, wherein The method (100) has the following step: determining a natural coupling point current.

8. The method (100) according to any of the preceding claims, wherein The method (100) has the following step: determining a line voltage difference from the section impedance and the natural coupling point current change.

9. The method (100) according to any of the preceding claims, wherein The method (100) has the following step: determining a transformer voltage change from the connection voltage change and the line voltage difference.

10. The method (100) according to any one of the preceding claims, wherein The method (100) has the following step: determining a load current change from the transformer voltage change and the transformer impedance.

11. The method (100) according to any one of the preceding claims, wherein The method (100) has the following step: determining a load proportion from the natural coupling point current change and the load current change.

12. The method (100) according to any one of the preceding claims, wherein The method (100) has the following step: determining a load distribution from the load proportion, the loop impedance and the section impedance.

13. The method (100) according to any one of the preceding claims, wherein The method (100) has the following step: determining an output current from the load distribution and the load current change.

14. The method (100) according to any one of the preceding claims, wherein The method (100) has the following step: determining a coupling point current target value from the natural coupling point current and the output current.

15. Mesh current regulator (9) for regulating the voltage in a mesh (7), wherein The mesh current regulator (9) has an adjustable current source and / or voltage source (29) and is designed to independently carry out the method (100) according to claims 1 to 14.

16. System (27) for determining a measured variable in a mesh (7) of a low voltage network (1) and for regulating the voltage in the mesh (7), wherein The system (27) has a mesh current regulator (9) which comprises a determination unit (29) on the mesh current regulator (9) for determining a measured variable in the mesh (7).

17. Use of a cell current regulator (9) in a cell (7) of a low voltage electrical network (1), wherein, No measuring point for determining a measured variable for the mesh current regulator (9) is applied in the mesh (7) outside the mesh current regulator (9).

Images