System and method for determining electrical parameters

Abstract

System for determining electrical parameters of consumers (1) in a branched power grid (2), comprising a central control and evaluation unit (3), a central voltage measuring unit (4), and a plurality of decentralized units (5), each having a decentralized current measuring unit (6) with at least one current sensor (7), a decentralized voltage detection means (8) and a decentralized evaluation unit (9), wherein the decentralized units (5) are each assigned to the consumers (1), wherein the central control and evaluation unit (3) is connected via connections (10) to the central voltage measuring unit (4) and to the decentralized units (5), wherein a voltage value can be measured by the central voltage measuring unit (4) and is made available in a transferable manner, and wherein the decentralized evaluation unit (9) is connected via connections (11) to the decentralized current measuring unit (6) and the decentralized voltage detection means (8), wherein instantaneous values ​​of a current can be measured by the decentralized current measuring unit (6) and made available in a transferable manner, and wherein a voltage curve can be detected and made available in a transferable manner by the decentralized voltage detection means (8), and wherein the transmission of the instantaneous values ​​of the current and the transmission of the detected voltage curve takes place through the connections (11) from the decentralized current measuring unit (6) and the decentralized voltage detection means (8) to the decentralized evaluation unit (9), and wherein the decentralized evaluation unit (9) carries out a zero crossing determination of the voltage from the voltage curve, wherein a calculated sine curve of the voltage is provided on the basis of the determined zero crossings, and wherein the decentralized evaluation unit (9) assigns the instantaneous values ​​of the current to the values ​​of the calculated sine curve of the voltage, wherein normative instantaneous values ​​of the power are formed from the instantaneous values ​​of the current and the respectively assigned values ​​of the calculated sine curve of the voltage, and wherein a normative intermediate power value is formed from the normative instantaneous values ​​of the power and made available as an intermediate power value in a transferable manner, and wherein the intermediate power value is transmitted via the connection (10) from the decentralized evaluation unit (9) to the central control and evaluation unit (3), and wherein the central control and evaluation unit (3) queries the voltage value from the central voltage measuring unit (4) and the intermediate power value from the decentralized evaluation unit (9), and wherein the central control and evaluation unit (3) calculates the electrical active power of the respective consumer (1) from the voltage value and the intermediate power value.

Description

The invention relates to a system and the associated method for determining electrical characteristic variables, in particular the active power, of decentralized consumers at any desired positions within an electrical grid.Systems, devices and methods for determining the active power are generally known from the prior art.In this case, what are known as current or energy counters are generally used, which determine the current and the voltage, and the phase shift occurring between them, in the respective power grid, primarily electronically via sensors and circuits.From the determined data for current, voltage and phase shift it is then possible to determine the active power present in the respective power grid.In times of increasing energy costs, it is becoming increasingly important, especially for producing companies, to determine the active power of individual consumers within a power network in order to be able to control these in a targeted manner and to improve their effectiveness.If such a project were to be implemented using the energy counters known from the prior art, it would become necessary to provide such an energy counter separately for each individual consumer and to process the metrological signals or values in a complicated manner.This would involve immense installation and measurement effort and would thus be uneconomical and expensive for power grids with many consumers.In addition, the known energy meters require a correspondingly large installation space and thus subsequent installation of these into existing power grids is often not feasible.In order to eliminate these disadvantages, devices and methods are also known from the prior art which determine only the respective value of the current present at each load, then calculate this with a stored voltage value and determine the active power taking into account a previously determined active factor stored for the respective load.Such a device is disclosed, for example, in the publication DE 198 27 345 B4 and has a plurality of measurement points and a central processing unit.The measurement points are each assigned to a load and record the current values present at the load.The detected current values are then transmitted to the computing unit and are merged there with a voltage signal.For this purpose, the voltage signal is determined at selected points of the power grid.The disclosed invention disadvantageously provides that for conditioning the device and thus for determining the active power, valid characteristic values for the level of the active power reference and the power factor must be determined at each individual consumer for characteristic operating states. The characteristic values determined are then stored in a database for further use and used to calculate the active power of the individual consumers depending on the fluctuation of the mains voltage.This preliminary determination of the characteristic characteristic values of each consumer in different operating states leads to a great effort in preparation and thus to high preparation and trial expenses.A further solution that is advanced in terms of technology for determining electrical characteristic variables is known from the publication DE 10 2011 107 932 B3.Here, the determination of the electrical characteristic variables, in particular the determination of the active energy of a consumer in a branched power grid, takes place by means of a central control and evaluation unit, a central voltage measurement unit and a plurality of decentralized current measurement units.In the solution mentioned, it is possible to dispense with taking account of the phase shift between current and voltage, which usually occurs in the case of inductive or capacitive loads, during the determination of the active power by outputting a time stamp by the central control and evaluation unit and by measuring instantaneous values of the voltage or of the current, respectively, by the voltage measuring unit and the current measuring units, which instantaneous values are assigned to the time stamp and which are assigned to one another on the basis of the time stamp in the central control and evaluation unit and the electrical characteristic variables are subsequently determined from these.Furthermore, the publication JP 2005 189 012 A describes a system for determining electrical characteristic variables in a branched power grid, which system has a central control and evaluation unit, to which a central voltage measurement unit is assigned, which detects zero crossings of the voltage and generates a sine curve of the voltage on the basis thereof. Furthermore, a plurality of decentralized units is described, which are each assigned to a consumer and are connected to the central control and evaluation unit. The decentralized units each have a current sensor and a decentralized evaluation unit. Load-related intermediate values are determined in the respective decentralized evaluation units on the basis of the sine curve of the voltage provided by the central voltage measurement unit and of the current measured decentrally by means of the current sensor. These are subsequently transmitted to the central control and evaluation unit and corrected there by means of the measured voltage values. A disadvantage of a high data transmission rate is required and voltage distortions close to the consumer can impair the accuracy of the detection.The publication DE 10 2009 003 654 B3 proposes assigning a sensor unit with a current and voltage detection as well as a microcomputer unit to the current supply line of a respective consumer, said sensor unit ascertaining energy consumption data and storing it in an intermediate memory, which is preferably designed as a USB memory stick, so that the energy consumption data can subsequently be read out at another location for further evaluation.A power measuring device which proposes voltage detection by means of a voltage measuring device inserted in a plug socket in a simple manner remotely in order to reduce it is described by the publication WO 2009 / 140777 A1. The voltage measuring device is data-connected and synchronized with the current measuring devices close to the load. The consumer-related characteristic variables can be determined from the combined measured values.Furthermore, the publication US 2013 / 0090869 A1 describes a distribution cabinet with an integrated power measuring device, wherein this can preferably be designed in particular for a rack system.A further system with distributed voltage measurement means and current measurement means is described in the publication US 2013 / 0018609 A1, wherein synchronization is described, in particular using the zero voltage crossings, in order to enable a phase-position-correct assignment of voltage measurement values and current measurement values.It is an object of the present invention to provide an alternative approach for providing a system and method for determining electrical characteristic variables, which avoids the disadvantages of the prior art and by means of which a simple and cost-effective determination of the electrical characteristic variables, in particular the active power and the active work of a plurality of electrical loads within an AC voltage grid with a central feed point is made possible.The object is achieved with respect to the system by the features set out in claims 1 and 12. Preferred refinements are evident from the respective dependent claims.With respect to the method, the object is achieved by the features set out in claim 13. Preferred developments of the method are evident from claims 14 to 18.A system according to the invention for determining electrical characteristic variables of consumers in a branched power grid has a central control and evaluation unit, also referred to below as a controller, a central voltage measurement unit, and a plurality of decentralized units.According to the invention, the decentralized units are assigned to the respective consumers.On the other hand, the central control and evaluation unit is connected via connections both to the central voltage measurement unit and to the decentralized units.According to the invention, the central voltage measuring unit measures a voltage value of the voltage U present in the power grid at a central voltage measuring point within the power grid.In contrast to conventional systems, in a system according to the invention only a single voltage measuring point is required within the power network, as a result of which on the one hand the outlay in terms of equipment and installation and on the other hand the necessary measurement outlay is reduced.By measuring the voltage close to the feed point, it is additionally achieved as a particular advantage that the power loss components and distortions occurring in the power network as far as the consumer, in particular due to voltage drop under load, are also detected in the determination of the ultimately resulting active power and active work.The voltage value is measured by the central voltage measuring unit in a manner known per se either digitally or analog.A further advantage of the solution according to the invention is that only an effective value of the voltage has to be measured and provided in a transmittable manner by the central voltage measurement unit. A technically complicated provision and transmission of relevant instantaneous values of the voltage can thus advantageously be dispensed with.According to the invention, the decentralized units each have a decentralized current measuring unit, a decentralized voltage detection means and a decentralized evaluation unit, wherein the decentralized evaluation unit is connected to the decentralized current measuring unit and the decentralized voltage detection means via connections.According to the invention, the decentralised current measuring unit is capable of measuring the value of the current I flowing through the respective conductors for connecting the load.According to the invention, the instantaneous values of the current are measured.If the loads are loads of a polyphase circuit, as is the case, for example, with a three-phase alternating current circuit, a separate decentralized current measuring unit is assigned to each conductor. In such a case, the decentralized current measurement units are either individually connected to the decentralized evaluation unit, respectively, or else, for example, are combined via a serial bus such that a bus line from the decentralized current measurement unit to the decentralized current measurement unit is looped through.The measurement of the current I at the respective load by the decentralised current measurement unit is preferably carried out in a manner known per se using the Hall effect; moreover, however, according to the invention, any other suitable form of current measurement, for example inductive, can also be used. It is expedient to carry out the current measurement in a contactless manner in order to ensure a galvanic isolation of the power line and the current sensor.The measured instantaneous values of the current are provided in a transmittable manner by the decentralized current measuring unit according to the invention and transmitted to the decentralized evaluation unit via the respective connection.In parallel with the measurement of the instantaneous values of the current, according to the invention, the decentralized voltage detection means detects the voltage profile present on the respective conductor for connecting the load.The detected voltage profile is provided such that it can be transmitted by the decentralized voltage detection means and is likewise transmitted to the decentralized evaluation unit via the respective connection.According to the invention, the decentral evaluation unit is capable of carrying out a zero crossing determination of the voltage from the transmitted voltage profile and of providing a calculated sine curve of the voltage on the basis of the zero crossings determined in this case.The calculated sine curve is an idealised voltage curve, for the calculation of which an arbitrary voltage value to be defined, for example 100 V, is assumed, wherein the voltage value to be defined merely represents a calculation aid and can be selected independently of the actual voltage.In addition, the decentralized evaluation unit is particularly advantageously capable of making an assignment of the instantaneous values of the current to the values of the calculated sine curve of the voltage.The assignment is effected here, for example, in the form that the calculated sine curve is first provided and then, at a defined point in time, for example, in the case of an applied zero crossing of the voltage, the measurement of the instantaneous values of the current by the decentralised current measuring unit and the transmission thereof to the decentralised evaluation unit are started. The instantaneous values of the current are now measured for the duration of a specified time interval, which can preferably be specified by the calculated sine curve, and transmitted to the decentralized evaluation unit, so that the latter can assign an instantaneous value of the current to each value of the calculated sine curve of the voltage.Furthermore, according to the invention, the decentralized evaluation unit forms normative instantaneous values of a power of the respectively present load from the instantaneous values of the current and the associated values of the calculated sine curve.The term normative means in the present case that the power values formed at this point have only normative character and no final accuracy on account of the values of the sine curve of the voltage that are calculated in an idealized manner merely on the basis of a defined voltage.In addition, the decentralized evaluation unit is able according to the invention to form a normative intermediate power value from the normative instantaneous values of the power and to make it available such that it can be transmitted as an intermediate power value.The normative intermediate power value is formed by the integral of the normative instantaneous values of the power.The power intermediate value formed is transmitted according to the invention via the respective connection from the decentralised evaluation unit to the central control and evaluation unit after the latter has carried out an interrogation of the power intermediate value and the voltage value.Preferably, an identifier is assigned to the intermediate power value, which allows identification of the respective load belonging to the intermediate power value.The identifier is provided by conventional means, for example a corresponding coding.After transmission of the intermediate power value and the voltage value, the central control and evaluation unit is, according to the invention, capable of calculating the exact electrical active power of the respective consumer from these values, wherein in the present case the intermediate power value is preferably multiplied by a corresponding correction value.The correction value represents a value for the deviation of the voltage value determined by the central voltage measuring unit from a normative voltage value of the calculated sine curve of the voltage.The solution according to the invention offers the particular advantage that, for determining the active power of a consumer in a branched power grid, the actually present voltage values need only be recorded at a single central point, which is preferably close to the feed point, and thus a current and a voltage measurement unit need not be provided for each consumer.In addition, only a relatively low outlay is required here for data collection and transmission, since in particular during the voltage value determination at the central voltage measurement unit only the effective value of the voltage and at the decentralised voltage detection means only the zero crossings of the voltage have to be determined and transmitted. A measurement and transmission of a plurality of specific instantaneous values is therefore not necessary according to the invention.The data transmission effort can also be kept low in the solution according to the invention in particular by the fact that the intermediate power value is already formed in the decentralized unit and therefore only this intermediate power value has to be transmitted to the central control and evaluation unit via the corresponding connection.In addition, a further technological advantage of the invention is that a determination of the phase angle φ (phi) of a consumer-neither in advance nor during the determination of the characteristic variables-is not necessary, since the active power results from the sine curve calculated on the basis of the determined zero crossings of the voltage in relation to the instantaneous values of the current. However, the phase angle φ (phi) can optionally also be determined from this as additional information.In a further embodiment, it is possible according to the invention that the ascertained value of the electrical active power of the respective consumer can be output by the central control and evaluation unit.The output of the electrical active power is effected, for example, in a visualizable or archiveable manner. The output value of the electrical active power can also be used for control purposes, for example for carrying out priority switching to avoid load gear profiles being exceeded or for emergency shutdowns in the event of detected faults in a load.A system according to the invention thus allows not only the determination of the electrical active power but also an assessment and evaluation of the consumers in a power grid with regard to their efficiency, economics and technical operating behavior.Although the invention is primarily aimed at the use of power grids with consumers such as electric motors or production machines, this can also be used in all other conceivable electric consumers in a power grid.Especially in power grids with a plurality of electrical consumers, as is the case, for example, in production plants of companies, the system according to the invention provides an uncomplicated and above all cost-effective solution for detecting the electrical active power of a connected consumer and for evaluating its efficiency, or for correctly energyally evaluating an overall system comprising a plurality of consumers in the respective power grid.In addition, the operations are made possible by the technical solution presented to transfer the energy costs incurred in the production of their products specifically to the individual consumers and the process steps effected by them. As a result, the respective process steps can be optimized and the production costs for the respectively produced product can thus be reduced overall.In a preferred development of the invention, the central voltage measuring unit and / or the respective decentralised unit are assigned storage elements, by means of which measured voltage values or determined intermediate power values can be temporarily stored.Such intermediate storage of the measured values is advantageous in particular when the transmission of the values to the central control and evaluation unit is to be performable not in real time but in a time-offset manner with respect to the actual measurement or determination process of the values.In this case, a voltage value or an intermediate power value is transmitted to the controller only when the controller queries the respective value from the respective buffer.In an advantageous embodiment of the invention, the voltage or power intermediate value is transmitted to the central control and evaluation unit by modulating the respective values, as digitized values, to the power network.The method of modulation onto the power grid is considered in this context to be known from the prior art, for which reason it will not be discussed in more detail here.The modulation of the voltage and power intermediate values onto the existing power network has the particular advantage that no additional connections need to be provided between the controller and the central voltage measuring unit, or between the controller and the respective decentralised unit.The installation outlay required for a system according to the invention can thus be reduced efficiently.In an equally preferred development of the invention, the connection of the control and evaluation unit to the central voltage measurement unit and the respective decentralised unit is configured wirelessly.In this case, the central voltage measuring unit and the respective decentralised unit each have separate transmitters for transmitting the measured values and the control and evaluation unit has a corresponding receiver for receiving the transmitted values. Such a wireless connection can be implemented, for example, by radio or by a W-LAN network. Moreover, all other types of wireless connections are also conceivable.In any case, the use of a wireless connection particularly advantageously eliminates additional connecting lines between the control and evaluation unit and the voltage measurement unit or the respective decentralised unit.A further preferred variant of the system according to the invention provides that the central voltage measuring unit is integrated into the central control and evaluation unit.On the one hand, this makes it possible to further advantageously reduce the installation outlay for a system according to the invention, and on the other hand, the installation space required for installing the system is reduced by integrating the central voltage measurement unit into the control and evaluation unit.This is advantageous in particular if a system according to the invention is to be installed subsequently in an existing power grid with few structural free spaces.In the case of an integration of the central voltage measurement unit into the control and evaluation unit, an equally advantageous development of the invention provides for the connection between the control and evaluation unit and the central voltage measurement unit to take place via an internal processor bus within the controller. Since a processor bus is usually present in any case in the control and evaluation unit for data transmission and / or control purposes, this is used particularly advantageously simultaneously in the refinement described here for the transmission of the data between the central voltage measurement unit and the controller. The need to transmit the voltage values externally, for example via the external bus, is dispensed with.Furthermore, in a further advantageous variant of the invention, a decentralized unit is designed as a decentralized master unit which is connected to the central control and evaluation unit and to at least one further decentralized unit via a respective corresponding connection.In the following, at least one further decentralised unit, which is not decentralised master unit, is referred to as decentralised unit for short.In the variant shown here, the connection of the decentralised unit to the central control and evaluation unit thus exists indirectly via the decentralised master unit, so that an intermediate power value is transmitted from the decentralised unit to the decentralised master unit and from this to the central control and evaluation unit.According to the invention, the intermediate power value can be transmitted from the decentralized master unit to the central control and evaluation unit either directly following the transmission of the intermediate power value from the decentralized unit to the decentralized master unit or only after intermediate storage of the intermediate power value in the decentralized master unit.The particular advantage of the variant shown here is in particular that a direct connection does not have to be provided between each decentralized unit and the central control and evaluation unit. In particular in the case of large spatial distances between the central control and evaluation unit and a plurality of decentralized units, the required installation outlay can be significantly reduced in this way.In a further advantageous embodiment of the invention, the decentralised unit of the system is capable of determining and making available a phase angle φ (phi) for the relevant load such that it can be transmitted or optionally output on the basis of the assignment of the instantaneous values of the current to the values of the calculated sine curve of the voltage.The phase angle is preferably output directly at the decentralised unit, for example via a corresponding display. From the knowledge of the phase angle, conclusions can be drawn about the operating behavior. As a particular advantage, no separate determinations of the phase angle have to be carried out, but rather this is available as an additional benefit of the system according to the invention and can also be evaluated and archived in a uniform data processing and data holder.Furthermore, in a particularly advantageous development, the decentralized unit forms the basis of a rated voltage value for the calculated sine curve.In this context, a value is preferably assumed as the rated voltage value, which approximates sufficiently accurately to the setpoint voltage which is present at the load and is assigned to the local power grid. For example, a rated voltage value of 230 V is used as the basis for this.The advantage resulting therefrom is in particular that, by basing the approximately correct voltage value, an approximately correct value for the active power of the consumer can be determined and transmitted or provided in a outputable manner already in the decentralized unit.In this case, the approximately correct value of the active power can be output directly via a display of the decentralized unit, for example.In this case, a correction of the active power value determined on the basis of a denominator voltage value can be carried out in the central control and evaluation unit on the basis of the actual voltage value transmitted by the central voltage measurement unit.A further advantageous variant of the invention provides that the decentralised voltage detection means is formed by the current sensor of the decentralised current measurement unit.In this case, a voltage signal which is coupled capacitively to the current sensor can be evaluated by the decentral evaluation unit for the detection of the voltage profile as a particular advantage.The variant listed here includes, according to the invention, the capacitively coupled-in voltage signal being in turn initially phase-corrected on account of its capacitive phase shift.The particular advantage in this case is that such a voltage detection also uses the technical means for decentral current measurement which are necessary in any case and can therefore be implemented particularly cost-effectively.In addition, in an advantageous development, the central voltage measuring unit can assign additional information about a detection time window of the voltage value to the voltage value.The additional information can also be provided such that it can be transmitted together with the voltage value and is transmitted to the central control and evaluation unit via the corresponding connection.In addition, the decentralized unit can assign additional information about a detection time window of the underlying instantaneous values of the current to the intermediate power value.This additional information can also be provided such that it can be transmitted together with the intermediate power value and is transmitted according to the invention via the corresponding connection to the central control and evaluation unit.In the present development, the central control and evaluation unit is capable of ascertaining the exact electrical active power from a voltage value and an intermediate power value with respectively matching capture time windows.The particular advantage of the development shown here is, in particular, that the respective intermediate voltage and power value is appended with time information about the time or period of the measurement, which allows the central control and evaluation unit to be assigned exactly over time to one another and thus to determine exactly over time the active electrical power. This exact determination can be carried out in particular in a time-shifted and real-time-independent manner and allows precise analyses of the operating behavior.Alternatively, a system for determining electrical characteristic variables of a consumer in a branched power grid is formed by a decentralised unit which is assigned to the consumer.According to the invention, the decentralized unit has a decentralized current measuring unit having at least one current sensor, a decentralized voltage detection means and a decentralized evaluation unit, wherein the decentralized evaluation unit is connected via connections to the decentralized current measuring unit and to the decentralized voltage detection means, wherein instantaneous values of a current can be measured and are made available in a transmittable manner by the decentralized current measuring unit, and wherein a voltage profile can be detected and is made available in a transmittable manner by the decentralized voltage detection means.According to the invention, the instantaneous values of the current and of the detected voltage profile are transmitted via the connections from the decentralized current measurement unit and the decentralized voltage detection means to the decentralized evaluation unit.Furthermore, the decentralized evaluation unit is able according to the invention to carry out a zero crossing determination of the voltage from the voltage profile, wherein a calculated sine curve of the voltage is provided on the basis of the determined zero crossings.Furthermore, according to the invention, the decentralized evaluation unit carries out an assignment of the instantaneous values of the current to the values of the calculated sine curve of the voltage, normative instantaneous values of the power being formed from the instantaneous values of the current and the respectively assigned values of the calculated sine curve of the voltage, and an intermediate normative power value of the load being formed from the normative instantaneous values of the power and made available in a outputable manner.The output of the intermediate power value is effected, for example, via a display which is assigned to the decentralized evaluation unit and which represents the intermediate power value as a number or alternatively, for example, within a diagram.Alternatively or cumulatively, the output can also take place in the form of forwarding the intermediate power value, for example to a corresponding data processing and output unit.The solution shown here is used in particular when an approximately exact statement about the active power of the consumer on the basis of the intermediate power value is sufficient.A method according to the invention for determining electrical characteristic variables, in particular for determining the active power, of consumers in a branched power grid is carried out by means of a central control and evaluation unit, by means of a central voltage measurement unit and by means of a plurality of decentralized units, wherein the central control and evaluation unit is connected via connections to the central voltage measurement unit and to the decentralized units, and wherein the decentralized units are assigned to the consumers and each have a decentralized current measurement unit, a decentralized voltage detection means and a decentralized evaluation unit, wherein the respective decentralized evaluation unit is connected via connections to the respective decentralized current measurement unit and the respective decentralized voltage detection means.The method according to the invention has the following method steps: a) measuring a voltage value by the central voltage measuring unit, b) measuring instantaneous values of the current by the decentralised current measuring unit, c) detecting a voltage profile by the decentralised voltage detecting means, d) transmitting the instantaneous values of the current and the detected voltage profile via the connections from the decentralised current measuring unit and the decentralised voltage detecting means to the decentralised evaluation unit, e) determining zero crossings of the voltage from the voltage profile in the decentralised evaluation unit, f) providing a calculated sine curve on the basis of the determined zero crossings by the decentralised evaluation unit, g) assigning the instantaneous values of the current to the values of the calculated sine curve of the voltage by the decentralised evaluation unit, h) Formation of normative instantaneous values of the power from the instantaneous values of the current and the associated values of the calculated sine curve by the decentralized evaluation unit, i) Formation of a normative intermediate power value from the normative instantaneous values of the power and provision of the intermediate power value as an intermediate power value by the decentralized evaluation unit, j) Interrogation of the voltage value and the intermediate power value of the current by the central control and evaluation unit via the connections and transmission of the voltage value from the central voltage measurement unit and of the intermediate power value from the decentralized evaluation unit via the connections to the central control and evaluation unit, k) Calculation of the active electrical power from the voltage value and the intermediate power value by the central control and evaluation unit.In the first method step a), a voltage value is measured by the central voltage measuring unit.The voltage value is measured either analog or digital, wherein according to the invention it is only necessary to measure an effective value of the voltage.In the further method step b), instantaneous values of the current are measured by the decentralized current measuring unit, wherein the measurement is preferably carried out in parallel with respect to time with the measurement of the voltage value in method step a).In addition, in method step c), a voltage profile at the respective load is detected by the decentralized voltage detection means.The measured instantaneous values of the current and the detected voltage profile are transmitted in method step d) from the decentralized current measurement unit and the decentralized voltage detection means to the decentralized evaluation unit.According to the invention, it is not absolutely necessary for the instantaneous values of the current and the voltage profile to be transmitted simultaneously to the decentralized evaluation unit.Rather, in the present case, a time-shifted transmission of the instantaneous values of the current and of the voltage profile is also possible.After the detected voltage profile has been transmitted to the decentralised evaluation unit, these then carry out in method step e) a determination of zero crossings of the voltage present at the respective load from the voltage profile and in method step f) a provision of a calculated sine curve on the basis of the determined zero crossings.Method steps b) to f) are not defined according to the invention in a temporal sequence in that first of all, the voltage curve according to method steps c) and d) can be detected and transmitted and the zero crossing determination according to method step e) and the calculated sine curve according to method step f) can be provided, and then first the measurement and the transmission of the instantaneous values of the current according to method steps b) and d) are carried out.After both the instantaneous values of the current and the voltage profile have been transmitted to the decentralised evaluation unit, these are used in method step g) to assign the instantaneous values of the current to the values of the calculated sine curve of the voltage.In method step h), normative instantaneous values of the power of the load are formed from the instantaneous values of the current and the associated values of the sine curve of the voltage by the decentralized evaluation unit, wherein the normative instantaneous values of the power still do not have a final accuracy on the basis of the calculated sine values, which is based according to the invention on a voltage to be defined as desired, and therefore have only normative character.Subsequently, in method step i), a normative intermediate power value is formed in the decentralized evaluation unit from the normative instantaneous values of the power and the intermediate power value is provided as an intermediate power value for transmission to the central control and evaluation unit.The intermediate power value is formed in the present case by the integral of the normative instantaneous values of the power.The voltage value measured by the central voltage measuring unit and the intermediate power value determined by the decentralised evaluation unit are transmitted to the central control and evaluation unit in method step j). According to the invention, it is not necessary for the voltage value and the intermediate power value to be transmitted simultaneously into the central control and evaluation unit.Rather, in this context, it is possible to transmit these two values in a time-shifted manner.Furthermore, the intermediate power value is preferably assigned an identifier which enables identification of the respective load belonging to the intermediate power value.In the final method step k), the central control and evaluation unit calculates the exact electrical active power of the load from the voltage value and the intermediate power value. In the present case, the exact electrical active power is preferably calculated by multiplying the intermediate power value by a corresponding correction value, wherein the correction value here represents a value for the deviation of the voltage value determined by the central voltage measuring unit from a normative voltage value of the calculated sine curve of the voltage.In a particularly advantageous development of the method, the central voltage measuring unit and / or the decentralized units are assigned storage elements, wherein after method step a) an additional method step a1) can be carried out and after method step i) an additional method step i1) can be carried out, and wherein in method step a1) the measured voltage value is temporarily stored and in method step i1) the determined intermediate power value is temporarily stored in the respective storage element.Furthermore, an advantageous variant of the method provides that a decentralized unit is designed as a decentralized master unit, wherein the connection between at least one decentralized unit and the central control and evaluation unit exists indirectly via the decentralized master unit, and wherein the decentralized master unit is connected to the at least one decentralized unit via a connection, and that method steps a) to i) are each carried out both by the decentralized master unit and by the decentralized unit, and that an additional method step i1) can be carried out before method step j), in which a transmission of the formed intermediate power value from the decentralized unit to the decentralized master unit takes place. In addition, method steps j) and k) are carried out by the central control and evaluation unit for the performance values of the decentralized unit and of the decentralized master unit.Furthermore, in a preferred development of the method, an additional method step g 1) is carried out after method step g), wherein in method step g 1), on the basis of the assignment of the instantaneous values of the current to the values of the calculated sine curve of the voltage, a phase angle φ (phi) is ascertained by the decentralised unit and wherein the phase angle φ (phi) is provided such that it can be transmitted or optionally output.In addition, a particularly advantageous embodiment of the method provides that the decentralized unit in method step f) forms the basis for the calculated sine curve a nominal voltage value and that the central control and evaluation unit in method step k) carries out a correction of the intermediate power value on the basis of the voltage value transmitted by the central voltage measuring unit.The underlying rated voltage value is preferably selected to be a value which approximates sufficiently accurately to the setpoint voltage present at the load and thus an intermediate power value which approximates comparatively accurately to the actual value of the active power of the load can already be determined in the decentralised unit.In an advantageous development of the method, the measured voltage value in method step a) and the intermediate power value in method step i) are each assigned additional information about a detection time window, wherein, in the case of the intermediate power value, the additional information about the detection time window relates to the underlying instantaneous values of the current.Furthermore, in the development shown here, the central control and evaluation unit is capable of ascertaining the electrical active power from matching capture time windows in method step k).The particular advantage of this development is that, in particular when temporary memories are provided at the central voltage measuring unit and the respective decentralised unit, the respective voltage value and the respective intermediate power value do not necessarily have to be transmitted to the central control and evaluation unit directly after they have been measured or determined.Rather, in this context, it is possible to provide the respective value with the additional information of the detection time window and to store it in the buffer memory.The central control and evaluation unit can then carry out an interrogation of a plurality of stored voltage or power intermediate values and the relevant active power of the load can subsequently be determined from the values with identical detection time windows.The development thus enables a particularly exact determination of the active power, in particular for the purposes of analyzing the operating behavior of consumers.The invention is described in exemplary embodiments by way of example. FIG. 1 is a schematic diagram with a separate central voltage measuring unit FIG. 2 shows a schematic diagram with an integrated central voltage measurement unit FIG. 3 is a schematic diagram with a decentralized master unitThis will be explained in more detail.FIG. 1 shows a basic illustration of a load 1 in an existing power grid 2, wherein in the present exemplary embodiment the power grid 2 is a commercially available three-phase alternating current circuit having three outer conductors L 1 to L 3, a neutral conductor N and a central feed point 13.A system according to the invention for determining the electrical active power provides that a central control and evaluation unit 3, a central voltage measurement unit 4, a decentral unit 5, having a decentral current measurement unit 6 with three current sensors 7 and a decentral voltage detection means 8 and a decentral evaluation unit 9 are connected to the existing power grid 2.The connection of the system according to the invention is effected in such a way that the central voltage measuring unit 4 is connected to a single defined point close to the feed within the power grid 2 and that the decentralized units 5 are assigned to the respective consumer 1, wherein a current sensor 7 of the decentralized current measuring unit 5 is assigned to one of the outer conductors L 1 to L 3 in each case.The central voltage measuring unit 4 and the decentralised unit 5 are connected to the central control and evaluation unit 3 via connections 10, wherein storage elements 12 are respectively assigned to both the voltage measuring unit 4 and the decentralised unit 5.The connections 10 between the central voltage measuring unit 4, the decentralised unit 5 and the central control and evaluation unit 3 are realized in the present case by modulation to the power grid 2 or by wireless connections.Alternatively, the connections 10 are realized by means of a network, in particular a LAN.In the exemplary embodiment shown here, the voltage measuring unit 4 and the associated storage element 12.1 are structurally separate from the control and evaluation unit 3 and are thus present as separate components.FIG. 2 shows an identical power grid 2 with a load 1 and a system according to the invention for determining the active electrical power.In contrast to the exemplary embodiment in FIG. 1, however, the central voltage measuring unit 4 and the associated storage element 12.1 are not present here as separate components, but rather are integrated into the central control and evaluation unit 3.This integration can reduce the installation effort for a system according to the invention, on the one hand, and in this case, on the other hand, the connection between central voltage measurement unit 4 and central control and evaluation unit 3 is formed via an internal processor bus (not shown) of control and evaluation unit 3.In addition, FIG. 3 shows a preferred embodiment of the system according to the invention, in which a decentralized unit is designed as a decentralized master unit 5.1.In the present case, decentralized master unit 5.1 is connected to further decentralized units 5 and to central control and evaluation unit 3, so that the connection of further decentralized units 5 to central control and evaluation unit 3 exists indirectly via decentralized master unit 5.1.The intermediate power values determined in the decentralized units 5 are thus transmitted in the present embodiment first to the decentralized master unit 5.1 and then from the latter to the central control and evaluation unit 3.At the same time, the decentralized master unit 5.1 is likewise capable of ascertaining intermediate power values for its part and of transmitting these to the central control and evaluation unit.The connection between the decentralized master unit 5.1 and the further decentralized units 5 is designed in the present case such that each further decentralized unit 5 is connected to the decentralized master unit 5.1.Alternatively, there is the possibility here that the further decentralized units 5, for example within a bus system, are connected to one another and the respective intermediate power values of a decentralized unit 5 are thus looped through via a further decentralized unit 5 and are transmitted to the decentralized master unit 5.1 on this path.With the presented exemplary embodiments, a method according to the invention for determining the electrical active power as an electrical characteristic variable is carried out in the sequence described below, wherein the following method steps are carried out in the present case:a) measuring a voltage value by the central voltage measurement unit 4,a1) temporarily storing the voltage value in the storage element 12.1,b) measuring instantaneous values of the current through the decentral current measuring unit 6, wherein the current values for each conductor L 1 to L 3 are detected by the respective current sensor 7,c) Detection of a voltage curve close to the consumer by the decentralized voltage detection means 8,d) Transfer of the instantaneous values of the current and of the detected voltage profile via the connections 11 from the decentralised current measuring unit 6 and the decentralised voltage detection means 8 to the decentralised evaluation unit 9,e) Determination of zero crossings of the voltage from the voltage profile in the decentralised evaluation unit 9,f) Providing a calculated sine curve on the basis of the determined zero crossings by the decentralised evaluation unit 9,g) Assignment of the instantaneous values of the current to the values of the calculated sine curve of the voltage by the decentralised evaluation unit 9,g1) determining a phase angle φ (phi) based on the assignment of the instantaneous values of the current to the values of the calculated sine curve of the voltage by the decentralised unit 5 and outputting the phase angle as a value cos φ via the output device 14,h) Formation of normative instantaneous values of the power from the instantaneous values of the current and the associated values of the calculated sine curve by the decentralised evaluation unit 9,i) forming a normative intermediate power value from the normative instantaneous values of the power and providing the intermediate power value as an intermediate power value by the decentralized evaluation unit 9,i1) latching the intermediate power value in the memory element 12.2,j) Querying the voltage value and the intermediate power value of the current through the central control and evaluation unit 3 via the connections 10 and transmitting the voltage value and the intermediate power value from the storage elements 12 of the central voltage measurement unit 4 and the decentralised unit 5 via the connections 10 to the central control and evaluation unit 3,k) Calculation of the active electric power from the voltage value and the intermediate power value by the central control and evaluation unit 3.In the first method step a), according to the invention, a voltage value present in the power grid 2 is measured by the central voltage measuring unit 4, which voltage value is subsequently temporarily stored in the storage element 12.1 assigned to the central voltage measuring unit 4 in method step a1).Preferably, in parallel with the measurement of the voltage value by the central voltage measurement unit 4 in method step b), instantaneous values of the current are measured by the current sensors 7 of the decentralised current measurement unit 6.Furthermore, in method step c), a voltage profile close to the consumer is detected by the decentralized voltage detection means 8.The detected instantaneous values of the current and the detected voltage profile are transmitted in the further method step d) via the connections 11 from the decentralized current measurement unit 6 or the decentralized voltage detection means 8 to the decentralized evaluation unit 9.The decentralized evaluation unit 9 now carries out a determination of zero crossings of the voltage from the transmitted voltage profile in method step e) and provides a calculated sine curve of the voltage on the basis of the determined zero crossings in method step f).The values resulting from the calculated sine curve are then assigned the determined instantaneous values of the current in method step g) and the phase angle φ is determined on the basis of this assignment in method step g1). This phase angle φ is further output as a value cos φ via the output device 14.The output device 14 is designed as a display device, in particular as a display.Parallel to method step g 1), normative instantaneous values of the power are formed by the decentralized evaluation unit 9 in method step h) from the instantaneous values of the current and the associated values of the calculated sine curve of the voltage.Subsequently, in method step i), the decentralized evaluation unit 9 forms a normative intermediate power value from the normative instantaneous values of the power, which intermediate power value is temporarily stored in the storage element 12.2 assigned to the decentralized unit 5 in the subsequent method step i1).Continuing, in method step j), the voltage value and the intermediate power value of the current are interrogated by the central control and evaluation unit 3 via the connections 10 and the voltage value and the intermediate power value are transmitted from the storage elements 12 of the central voltage measurement unit 4 and the decentralised unit 5 via the connections 10 to the central control and evaluation unit 3.Insofar as a decentralized unit, as is shown in FIG. 3, is designed as a decentralized master unit 5.1, the intermediate power value is first transmitted from the further decentralized units 5 to the decentralized master unit 5.1 and then from this to the central control and evaluation unit 3.The central control and evaluation unit 3 is now capable, in the final method step k), of calculating the electrical active power of the load 1 from the voltage value and the intermediate power value by multiplying the intermediate power value by a corresponding correction value, wherein the correction value here represents a value for the deviation of the voltage value determined by the central voltage measurement unit from a normative voltage value of the calculated sine curve of the voltage, and outputting it, for example via a display (not shown). Alternatively, the calculated active power value can also be provided such that it can be transmitted by the central control and evaluation unit 3 for further processing.Reference numerals used1 Consumer 2 Power grid 3 Central control and evaluation unit 4 Central voltage measurement unit 5 5.1 Remote unit Remote master unit 6 Remote current measurement unit 7 Current sensor 8 Remote voltage detection means 9 Remote evaluation unit 10 Connections to central control and evaluation unit 11 Connections to remote evaluation unit 12 Storage element 13 Central feed point 14 Output device

Claims

System for determining electrical characteristic variables of consumers (1) in a branched power grid (2), comprising a central control and evaluation unit (3), a central voltage measurement unit (4) and a plurality of decentralized units (5), each having a decentralized current measurement unit (6) with at least one current sensor (7), a decentralized voltage detection means (8) and a decentralized evaluation unit (9), wherein the decentralized units (5) are each assigned to the consumers (1), wherein the central control and evaluation unit (3) is connected via connections (10) to the central voltage measurement unit (4) and to the decentralized units (5), wherein a voltage value can be measured and is made available in a transmittable manner by the central voltage measurement unit (4), and wherein the decentralized evaluation unit (9) is connected via connections (11) to the decentralized current measurement unit (6) and to the decentralized voltage detection means (8), wherein instantaneous values of a current can be measured and are made available in a transmittable manner by the decentralized current measurement unit (6), and wherein a voltage profile can be detected and is made available in a transmittable manner by the decentralized voltage detection means (8), and wherein the transmission of the instantaneous values of the current and the transmission of the detected voltage profile takes place by the connections (11) from the decentralized current measurement unit (6) and the decentralized voltage detection means (8) to the decentralized evaluation unit (9), and wherein the decentralized evaluation unit (9) carries out a zero-crossing determination of the voltage from the voltage profile, wherein a calculated sine curve of the voltage is provided on the basis of the determined zero-crossings, and wherein the decentralized evaluation unit (9) carries out an assignment of the instantaneous values of the current to the values of the calculated sine curve of the voltage, wherein normative instantaneous values of the power are formed from the instantaneous values of the current and the respectively assigned values of the calculated sine curve of the voltage, and wherein a normative intermediate power value is formed from the normative instantaneous values of the power and is made available such that it can be transmitted as an intermediate power value, and wherein the intermediate power value is transmitted via the connection (10) from the decentralized evaluation unit (9) to the central control and evaluation unit (3), and wherein the central control and evaluation unit (3) carries out an interrogation of the voltage value from the central voltage measurement unit (4) and of the intermediate power value from the decentralized evaluation unit (9), and wherein the central control and evaluation unit (3) calculates the active electrical power of the respective load (1) from the voltage value and the intermediate power value.System according to claim 1, wherein the central voltage measuring unit (4) and / or the decentralised units (5) are assigned storage elements (12), by means of which the measured voltage value and the determined intermediate power value can be temporarily stored.System according to claim 1 or 2, wherein the connection (10) of the central control and evaluation unit (3) to the central voltage measurement unit (4) and the decentralised units (5) is effected by modulation to the power network (2).The system according to claim 1 or 2, wherein the connection (10) of the central control and evaluation unit (3) to the central voltage measurement unit (4) and the decentralized units (5) is configured wirelessly.The system according to claim 1 or 2, wherein the central voltage measurement unit (4) is integrated into the central control and evaluation unit (3).The system according to claim 5, wherein the connection (10) of the central control and evaluation unit (3) to the central voltage measurement unit (4) takes place via an internal processor bus.System according to one of the preceding claims, wherein a decentralised unit is designed as a decentralised master unit (5.1) and wherein the connection between at least one further decentralised unit (5) and the central control and evaluation unit (3) exists indirectly via the decentralised master unit (5.1) and wherein the decentralised master unit (5.1) is connected to the at least one further decentralised unit (5) via a connection and wherein an intermediate power value of the at least one further decentralised unit (5) is transmitted to the decentralised master unit (5.1) and wherein the intermediate power value of the at least one further decentralised unit (5) is made available in the decentralised master unit (5.1) such that it can be transmitted to the central control and evaluation unit (3).System according to one of the preceding claims, wherein the decentralised unit (5) is capable of determining and providing a phase angle φ (phi) in a transmittable manner or optionally in a transmittable manner on the basis of the assignment of the instantaneous values of the current to the values of the calculated sine curve of the voltage.System according to one of the preceding claims, wherein the decentralized unit (5) forms the basis of a rated voltage value for the calculated sine curve and wherein a correction of an active power value determined on the basis of the rated voltage value can be carried out in the central control and evaluation unit (3) on the basis of the voltage value transmitted by the central voltage measuring unit.System according to one of the preceding claims, wherein the decentralised voltage detection means (8) is formed by the current sensor (7) of the decentralised current measurement unit (5) and wherein a voltage signal which is coupled capacitively to the current sensor (7) can be evaluated by the decentralised evaluation unit (9) as a voltage profile.System according to one of the preceding claims, wherein the central voltage measuring unit (4) can assign and transmit an additional information item to the voltage value over a detection time window of the voltage value, and wherein the decentralized unit (5) can assign and transmit an additional information item to the power intermediate value over a detection time window of the underlying instantaneous values of the current, and wherein the central control and evaluation unit (3) determines the electrical active power from a voltage value and an intermediate power value from matching detection time windows.System for determining electrical characteristic variables of a load (1) in a branched power grid (2), formed by a decentralized unit (5), having a decentralized current measurement unit (6) having at least one current sensor (7), a decentralized voltage detection means (8) and a decentralized evaluation unit (9), wherein the decentralized unit (5) is in each case assigned to the load (1), and wherein the decentralized evaluation unit (9) is connected via connections (11) to the decentralized current measurement unit (6) and to the decentralized voltage detection means (8), wherein instantaneous values of a current can be measured and made available in a transmittable manner by the decentralized current measurement unit (6), and wherein a voltage profile can be detected and made available in a transmittable manner by the decentralized voltage detection means (8), and wherein the transmission of the instantaneous values of the current and the transmission of the detected voltage profile through the connections (11) takes place from the decentralized current measuring unit (6) and the decentralized voltage detection means (8) to the decentralized evaluation unit (9), and wherein the decentralized evaluation unit (9) carries out a zero-crossing determination of the voltage from the voltage profile, wherein a calculated sine curve of the voltage is provided on the basis of the determined zero crossings, and wherein the decentralized evaluation unit (9) carries out an assignment of the instantaneous values of the current to the values of the calculated sine curve of the voltage, wherein normative instantaneous values of the power are formed from the instantaneous values of the current and the respectively associated values of the calculated sine curve of the voltage, and wherein a normative intermediate power value of the load is formed from the normative instantaneous values of the power and is made available in a outputable manner.Method for determining electrical characteristic variables of consumers (1) in a branched power grid (2), by means of a central control and evaluation unit (3), by means of a central voltage measurement unit (4) and by means of a plurality of decentralized units (5), wherein the central control and evaluation unit (3) is connected via connections (10) to the central voltage measurement unit (4) and to the decentralized units (5), and wherein the decentralized units (5) are assigned to the consumers (1) and each have a decentralized current measurement unit (6) having at least one current sensor (7), a decentralized voltage detection means (8) and a decentralized evaluation unit (9), wherein the respective decentralized evaluation unit (9) is connected via connections (11) to the respective decentralized current measurement unit (6) and the respective decentralized voltage detection means (8), having the following method steps: a) measuring a voltage value by the central voltage measuring unit (4), b) measuring instantaneous values of the current by the decentralized current measuring unit (6), c) detecting a voltage profile by the decentralized voltage detecting means (8), d) transmitting the instantaneous values of the current and transmitting the detected voltage profile via the connections (11) from the decentralized current measuring unit (6) and the decentralized voltage detecting means (8) to the decentralized evaluation unit (9), e) determining zero crossings of the voltage from the voltage profile in the decentralized evaluation unit (9), f) providing a calculated sine curve on the basis of the determined zero crossings by the decentralized evaluation unit (9), g) Assignment of the instantaneous values of the current to the values of the calculated sine curve of the voltage by the decentralized evaluation unit (9), h) Formation of normative instantaneous values of the power from the instantaneous values of the current and the assigned values of the calculated sine curve by the decentralized evaluation unit (9), i) Formation of a normative intermediate power value from the normative instantaneous values of the power and provision of the intermediate power value by the decentralized evaluation unit (9), j) Querying the voltage value from the central voltage measuring unit (4) and the intermediate power value of the current from the decentralized evaluation unit (9) by the central control and evaluation unit (3) via the connections (10) and transmitting the voltage value and the intermediate power value from the central voltage measuring unit (4) and the decentralized evaluation unit (9) via the connections (10) to the central control and evaluation unit (3), k) calculating the active electrical power from the voltage value and the intermediate power value by the central control and evaluation unit (3).Method according to Claim 13, wherein the central voltage measuring unit (4) and / or the decentralized units (5) are assigned storage elements (12), and wherein after method step a) an additional method step a1) can be carried out and after method step i) an additional method step i1) can be carried out, wherein in method step a1) the measured voltage value is temporarily stored and in method step i1) the ascertained intermediate power value is temporarily stored in the respective storage element (12).Method according to Claim 13 or 14, wherein a decentralised unit (5) is designed as a decentralised master unit and wherein the connection between at least one decentralised unit (5) and the central control and evaluation unit (3) exists indirectly via the decentralised master unit and wherein the decentralised master unit is connected to the at least one decentralised unit (5) via a connection and wherein the method steps a) to i) are each carried out both by the decentralised master unit and by the decentralised unit (5) and wherein, before the method step j), an additional method step i1) can be carried out in which the power intermediate value formed is transmitted from the decentralised unit (5) to the decentralised master unit and wherein the method steps j) and k) are carried out for the power values of the decentralised unit (5) and of the decentralised master unit.Method according to one of Claims 13 to 15, wherein an additional method step g1) can be carried out after the method step g), wherein in method step g1), on the basis of the assignment of the instantaneous values of the current to the values of the calculated sine curve of the voltage, a phase angle φ (phi) is ascertained by the decentralised unit (5) and wherein the phase angle φ is provided such that it can be transmitted or optionally output.Method according to one of Claims 13 to 16, wherein the decentralized unit (5) in method step f) forms the basis for the calculated sine curve a nominal voltage value, and wherein the central control and evaluation unit (3) carries out a correction of the intermediate power value in method step k) on the basis of the voltage value transmitted by the central voltage measurement unit.Method according to one of Claims 13 to 17, wherein in method step a) the measured voltage value is assigned additional information about a detection time window and wherein in method step i) the intermediate power value can be assigned additional information about a detection time window of the underlying instantaneous values of the current and wherein the central control and evaluation unit (3) determines the electrical active power from a voltage value and an intermediate power value from matching detection time windows in method step k).

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