METHODS AND SYSTEMS FOR DETERMINING AN ELECTRICAL QUANTITY IN AN ELECTRICAL SYSTEM

Description

[0001] The invention relates to a method for determining an electrical quantity in an electrical installation and to a corresponding system.

[0002] The invention relates more particularly to communicating sensors installed within electrical installations, such as electricity distribution networks.

[0003] For example, we know of wireless sensors capable of measuring electrical quantities, such as electrical voltage or electrical current.

[0004] The electrical quantities measured by the sensors can be used to control and supervise the electrical installation, but also to determine other electrical quantities which can be calculated from the measured electrical quantities.

[0005] For example, an electrical power value or a phase shift value can be calculated from the current and voltage values measured by the sensors.

[0006] Measurements are made by sensors repeatedly, by successive sampling over time. In many applications, it is necessary to know precisely when an electrical quantity was measured by a sensor, for example when data from several different sensors are combined.

[0007] A common problem in such sensor networks is that the sensors are not always properly synchronized. Although each sensor is usually equipped with an internal clock, it is common for these clocks to drift over time, causing a loss of synchronization between the sensors.

[0008] There are systems in which a synchronization signal is sent from a main sensor to the other sensors, so that these sensors can recalibrate their clock to a reference clock signal.

[0009] Patent applications EP 3 761 046 A1 and US 2021 / 356501 A1 relate to distributed power computing systems.

[0010] Patent application US 2017 / 08379 A1 describes an example of synchronization, which, however, has the disadvantage of requiring a wired connection between the sensors. Such a solution is not applicable to wireless sensor networks.

[0011] Additionally, in the case of wireless sensors, repeatedly sending a synchronization message can congest the network used by the sensors to communicate with each other. Indeed, it is common for these sensors to be connected to each other by low-speed, short-range radio communication means.

[0012] Additionally, the electronic components used by sensors to process data introduce a processing time that can vary from sensor to sensor. This can lead to errors, which vary from sensor to sensor.

[0013] Ultimately, the sensors are difficult to synchronize, and it is difficult to know for sure whether the values supposed to have been measured at the same time by all the sensors were actually measured simultaneously. When the measured data is used to calculate other electrical quantities, such as electrical power, there is a risk that the calculation will be distorted by this loss of synchronization.

[0014] It is therefore desirable to be able to determine electrical quantities, in particular electrical quantities calculated from measurements made by sensors, in a simple and reliable manner.

[0015] For this purpose, one aspect of the invention relates to a method for determining an electrical quantity in an electrical installation according to claim 1.

[0016] Thanks to the invention, by time-stamping the current and voltage measurements and taking into account the intrinsic delay specific to the measurement chain of each sensor, it is possible to compensate for any delays after the measurement has been made.

[0017] Specifically, instead of trying to synchronize the current and voltage sensors so that they measure the signals at the same time, it is the voltage and current signals measured by the sensors that are virtually synchronized.

[0018] According to advantageous but not mandatory aspects, such a method may incorporate one or more of the features of dependent claims 2 to 12.

[0019] According to another aspect, the invention relates to a system for determining an electrical quantity in an electrical installation according to claim 13.

[0020] The invention will be better understood and other advantages thereof will appear more clearly in the light of the following description of an embodiment of a method and a system for determining an electrical quantity in an electrical installation, given solely by way of example and with reference to the appended drawings, in which: [ Fig 1 ] there figure 1 is a schematic illustration of a system for measuring electrical quantities according to an embodiment of the invention, this system comprising at least one voltage measurement module and a plurality of current measurement modules; [ Fig 2 ] there figure 2 schematically illustrates steps implemented by the voltage measurement module of the figure 1 ; [ Fig 3 ] there figure 3 is a schematic illustration of a synchronization process implemented by the measurement modules of the system of the figure 1 to determine an electrical quantity; [ Fig 4 ] there figure 4 schematically illustrates the steps implemented by each current measurement module of the figure 1 ; [ Fig 5 ] there figure 5 is a schematic illustration showing a delay for each measurement in the current and voltage sensors of the system of the figure 1 ; [ Fig 6 ] there figure 6 is a schematic illustration of a calibration process implemented by the current sensors of the system of the figure 1 .

[0021] There figure 1 schematically represents a measuring system 2 for measuring electrical quantities.

[0022] The system 2 is intended to be associated with an electrical installation, such as an electricity distribution installation, to measure electrical quantities within this electrical installation. Preferably, the electrical quantities measured include at least the electric current and the electric voltage.

[0023] System 2 is also configured to determine at least one electrical quantity from the measured quantities.

[0024] For example, said calculated electrical quantity is an electrical power (in particular an average electrical power, or an instantaneous electrical power, or other) calculated from values of electrical current and electrical voltage measured by the sensors. Alternatively, it could be a reactive power, or a phase shift, or a power factor of the electrical installation, or an energy value, or any other useful electrical quantity.

[0025] The system 2 comprises at least one voltage measurement module 4 and at least one current measurement module 6.

[0026] In practice, the system 2 preferably comprises a plurality of current measurement modules 6.

[0027] For example, measuring modules 4 and 6 are distributed throughout the electrical installation.

[0028] In certain variants, the system 2 could comprise several voltage measurement modules 4 but in this case these modules will preferably operate independently of each other, so that the description which will be given below can be transposed to these embodiments.

[0029] Preferably, the measurement modules 4 and 6 are connected sensors (or communicating sensors) which incorporate information processing means and communication means. The measurement modules 4 and 6 can thus form a sensor network.

[0030] Each measuring module includes a measuring element, also called a sensor, or “sensor” strictly speaking.

[0031] For example, for the voltage measurement module 4 intended to measure an electrical voltage, the measuring element is a voltage sensor 10 (denoted "U" in the figure), for example a divider bridge, or a voltage transformer, or a capacitive sensor, or any other suitable sensor. For the current measurement module 6, the measuring element is a current sensor 20 (denoted "I" in the figure), such as a Rogowski torus, or a current transformer, or a Hall effect sensor, or a shunt measurement sensor, also called a "shunt", or any other equivalent element.

[0032] In addition, each measuring module 4, 6 comprises an electronic processing circuit comprising a processor, a memory, a clock and a communication interface.

[0033] Each measuring module 4, 6 preferably comprises a housing in which all or part of the components of said measuring module are housed. The measuring modules 4, 6 may also optionally comprise any means necessary for their operation, such as a power supply or a battery.

[0034] When the system 2 is operational, the measuring modules 4 and 6 are coupled to the installation. For example, the respective measuring elements of the modules 4, 6 are associated with electrical conductors of the electrical installation. The electrical installation is not shown in the figure 1 for the sake of legibility of the drawings.

[0035] The sensors 4 and 6 may be distributed throughout the installation at different locations. For example, in many embodiments, the current sensors are associated with branches of the installation formed by electrical conductors, and the voltage sensor is placed upstream of the current sensors. In practice, preferably, the branches of the installation on which the current sensors are installed share the same voltage source.

[0036] According to an illustrative and non-limiting example, the electrical installation comprises a primary electrical line and several secondary electrical lines which are derived from the first electrical line. The primary line is for example connected to an electrical source, such as a generator or a distribution transformer, or to another electrical network. Each secondary line connects the primary line to a customer entity, for example comprising an electrical load. The modules 4, 6 are then associated with electrical conductors of the electrical installation, for example mounted on or around the electrical conductors forming the main and secondary lines, to measure one or more electrical quantities relating to these electrical lines.In particular, in the case of a polyphase installation, in particular three-phase, then each primary or secondary electrical line may comprise several phase conductors, each associated with an electrical phase or possibly with a neutral line. Preferably, each measurement module 4, 6 is then configured to individually measure the current and voltage values associated with each of the phases on this electrical line.

[0037] However, other configurations are possible.

[0038] In many embodiments, in each measurement module 4 and 6, the data processing circuit is implemented by one or more electronic circuits.

[0039] The processor of each measuring module 4 and 6 is a microprocessor or a programmable microcontroller. The processor is coupled to a computer memory, or to any computer-readable data recording medium, which comprises executable instructions and / or software code intended to implement, among other things, a method for determining one or more electrical quantities when these instructions are executed by the processor.

[0040] The use of the term "processor" in this description does not prevent, as a variant, at least part of the functions of each measurement module 4, 6 from being carried out by other electronic components, such as a signal processing processor (DSP), or a reprogrammable logic component (FPGA), or a specialized integrated circuit (ASIC), or any equivalent element, or any combination of these elements.

[0041] The electronic processing circuit of each measurement module 4, 6 may also include components for shaping and / or filtering the signals measured by the measurement element before their processing by the processor, such as an analog-to-digital converter (ADC).

[0042] The clock of each measuring module 4, 6 comprises an electronic oscillator, for example a crystal oscillator, such as a quartz oscillator. For example, the clock may be integrated into the processor of said measuring module 4, 6.

[0043] The communication interface of each measurement module 4, 6 makes it possible to exchange data with other measurement modules 4, 6 and / or with one or more other elements, such as a data concentrator or telecommunications equipment, or computer equipment.

[0044] In preferred embodiments, the communication interface is a wireless interface, for establishing a wireless communication link, for example a radio link. For example, the radio link may be a short-range radio link, such as a Bluetooth Low Energy (registered trademark) link or the like. Alternatively, it may be a low-speed, long-range radio link, such as a Zigbee (registered trademark) link, or the like.

[0045] In other embodiments, the communication interface is configured to establish a wired communication link, for example by means of one or more cables, such as Ethernet cables or the like. The wired link may, for example, be a data bus.

[0046] In the illustrated example, the processing circuit and the communication interface of the first measurement module 4 bear the references “12” and “14” respectively. The processing circuit, the memory and the communication interface of the second measurement module 6 bear the numerical references “22”, “24” and “26” respectively.

[0047] Generally, each measurement module 4, 6 is configured to measure an electrical quantity such as voltage or current repeatedly over time, for example by sampling (measuring) this electrical quantity periodically with a fixed sampling frequency.

[0048] In practice, electric voltage and electric current can be alternating quantities which evolve periodically over time, for example with a sinusoidal shape.

[0049] For example, the voltage measurement module 4 periodically measures an electric voltage with a first sampling frequency. Each current measurement module 6 periodically measures an electric current with a second sampling frequency. The first sampling frequency and the second sampling frequency are higher than the frequency of the measured signal.

[0050] In many examples, the first sampling rate is chosen to be equal to the second sampling rate. But this is not essential and, alternatively, the first sampling rate could be different from the second sampling rate.

[0051] The system 2 is in particular configured to determine at least one electrical quantity, such as an electrical power, from the current and the voltage measured by the different measuring modules 4, 6. For example, the electrical power (for example an instantaneous value or an average value) can be calculated for different branches of the electrical installation.

[0052] This calculation is performed from the current and voltage values sampled over time. For example, for each instant, a value of the said quantity (such as power) is calculated from the current and voltage values sampled for that instant.

[0053] For this calculation, it is desirable that the current and voltage values used to calculate such an electrical quantity for each given instant correspond to simultaneous or quasi-simultaneous instants.

[0054] For example, in this description, by "quasi-simultaneously" we mean that the measurements are made for the same instant to within 0.1 microseconds (µs).

[0055] Advantageously, the method could be generalized to any clock synchronization and time adjustment mechanism carried out by exchanging messages between the measurement modules 4 and 6 to time-stamp the samples, which satisfies the measurement accuracy requirement.

[0056] In practice, the calculation of said quantity (such as power) is carried out by a processor, for example by one of the current measurement modules, or by dedicated computer equipment which is in communication with the measurement modules 4, 6.

[0057] Generally, the system 2 is configured (and programmed) to implement a method comprising steps consisting of: by the voltage measurement module 4: periodically measure an electrical voltage (U) in the electrical installation, periodically send to at least one of the current measurement modules 6 a synchronization signal (Top signal), send to said current measurement module(s) 6 a message comprising a master time stamp (TopMasterTime) indicating the instant at which the voltage measurement module emitted the synchronization signal, this instant being measured by the voltage measurement module with its clock, send to said current measurement module(s) 6 a message comprising at least one measured voltage value, by current measurement module 6: periodically measure an electrical current in the electrical installation, upon receipt of the synchronization signal sent by the voltage measurement module 4, calculate, by means of the clock of said current measurement module 6,a local time stamp data (TopLocalTime) indicating the instant at which the current measurement module 6 received said synchronization signal, determining successive delay correction values from the main time stamp data received (TopMasterTime) and the local time stamp data calculated for each synchronization signal received from the voltage measurement module, the successive current measurements carried out by the current measurement module being time stamped by the current measurement module 6, by means of its clock, taking into account the delay correction values thus determined.

[0058] Then, using a processor, calculate at least one value of an electrical quantity from the successive current and voltage values from the measurement modules.

[0059] The current and voltage values measured independently by the voltage 4 and current 6 measurement modules are not synchronous, because the respective clocks of these modules are independent.

[0060] However, as will be seen below, the calculation step involves a correction which makes it possible to resynchronize the measured current values a posteriori with the measured voltage values, in particular with a view to realigning the current values (which are measured at discrete instants) on the same time scale as the measured voltage values.

[0061] For example, missing current values are interpolated for the times when voltage values were measured, in order to resample current values between measured data. The current and voltage values then appear to have been measured simultaneously, which allows the said electrical quantity to be calculated with good accuracy. In other words, current values are calculated by interpolation between the actually measured (sampled) values, to obtain current values synchronous with the voltage values from the voltage measurement module 6.

[0062] Advantageously, as explained in more detail in the description which follows, timestamp data of the voltage values are measured by the voltage module, from the clock of the voltage module.

[0063] The voltage timestamp data corresponds to the instant when the voltage measurement was made, or to a close instant with the most stable time offset possible. Each timestamp data is preferably sent by the voltage measurement module with the measured voltage value.

[0064] An example of a method of operating system 2 is now described with reference to figures 2 , 3 And 4 . Alternatively, the steps of the method to be described could be performed in a different order. Some steps could be omitted. The described example does not preclude other steps from being performed in other embodiments in conjunction and / or sequentially with the described steps.

[0065] The diagram of the figure 2 represents the steps implemented by at least one voltage measurement module 4. The diagram of the figure 4 represents the steps implemented by a voltage measurement module 6.

[0066] Diagram 50 of the figure 3 represents both steps implemented by at least one voltage measurement module 4 (reference 52) and by one of the current measurement modules 6 (reference 54).

[0067] The steps illustrated in these figures are, for example, implemented by the respective processors of the voltage measurement module 4 and the current measurement modules 6.

[0068] The method is described for one of the current measurement modules 6, but it is understood that in practice each of the current measurement modules 6 implements similar steps, independently of the other current measurement modules 6.

[0069] The voltage measurement module 4 and each of the current measurement modules 6 are in communication by means of communication links 56 which can form a communication network. This communication is enabled by the communication interfaces 14 and 26 previously described.

[0070] Initially, the voltage measuring module 4 and each of the current measuring modules 6 are installed in the electrical installation.

[0071] In practice, the steps of the method are repeated periodically during an operating phase of the system 2. However, to simplify the description, only one iteration of these steps is described in detail.

[0072] Moreover, on the diagram of the figure 3 , only the steps relating to time management and synchronization are explained in detail, the steps relating to current and voltage measurements are not explained in detail in this figure.

[0073] The method begins at step 60, in which the voltage measurement module 4 emits a synchronization signal. For example, this synchronization signal marks the start of a periodically repeated cycle.

[0074] The synchronization signal is sent over the communication link 56 (step 61). In practice, it is the sending of this message over the communication link that acts as the synchronization signal. In this case, steps 60 and 61 are combined.

[0075] The measuring module 4 then performs, in step 62, a time stamp using its clock. In doing so, the measuring module 4 determines a time stamp data item, called “main time stamp data item” to date, in the time reference system of the measuring module 4, the instant (Top time) at which the synchronization signal is emitted.

[0076] In this description, the term timestamping is used to designate an operation consisting of measuring at what time an event seen by the measurement module occurs using its clock, then associating this measured time with the event in question.

[0077] For example, timestamp data (the values of measured instants) are associated with measured values by being stored in memory in a list, or an array, or in any suitable data structure.

[0078] In other words, the main timestamp data indicates the instant at which the voltage measurement module emits the synchronization signal, this instant being measured by the voltage measurement module with its clock, in its time reference.

[0079] Then, the measuring module 4 sends, to at least one of the current measuring modules 6, a message comprising the main timestamp data (step 64).

[0080] In parallel, during a step 63, the voltage measurement module 4 measures an electrical voltage in the electrical installation, preferably periodically with the first sampling frequency. For example, the voltage measurement module 4 samples the voltage with its voltage sensor 10.

[0081] In doing so, during a step 65, the measurement module 4 determines a time stamp for each voltage measurement (for each sampling) to date the instant of the voltage measurement in the time reference of the voltage measurement module 4. In other words, each measured voltage value is time stamped by the measurement module 4 with its clock.

[0082] Then, the measuring module 4 sends, to each of the corresponding current measuring modules 6, a message containing the measured voltage value (step 67), preferably with its time stamp.

[0083] In practice, in a preferred embodiment, the voltage measurement module 4 sends the synchronization signal, the main time stamp data and the measured voltage values in a single message. In other words, steps 61, 64 and 67 are combined.

[0084] For example, this message acts as a synchronization signal and includes, recorded in the body of the message, the measured voltage values and the main timestamp data associated with the previous synchronization signal (i.e. the one that initiated the previous cycle).

[0085] However, in other embodiments, the voltage measurement module 4 could send the synchronization signal, the main timestamp data and the measured voltage values in separate messages.

[0086] In other embodiments, the messages could be partially combined, for example as in the figure 3 , with during each cycle, a first message for the synchronization signal and a second message to send the rest of the data.

[0087] In many embodiments, the frequency of sending the message may be lower than the first sampling frequency and the second sampling frequency. For example, the frequency of sending the message is at least ten times lower than the first sampling frequency and / or the second sampling frequency. For example, each message sent by the voltage measurement module 4 comprises a number of voltage samples (of measurement values) of between twenty and one hundred, or even between thirty and fifty. In the case where the measurement module is associated with several electrical conductors and comprises as many voltage sensors, for example in a polyphase installation, then each message sent may comprise the values measured for these different conductors at the same time.

[0088] In the following, the voltage measuring module 4 may be referred to as the “main module”.

[0089] Furthermore, as will be seen later, the main timestamp data contained in the messages sent by the voltage measurement module 4 are subsequently used to compensate for delay variations and time drifts between the different measurement modules 4 and 6.

[0090] During a step 70, the current measurement module 6 receives the synchronization signal sent by the voltage measurement module 4. For example, this corresponds to the reception of a message on the communication interface 56.

[0091] In practice, the synchronization signal can be detected by all current measurement modules 6. Detection can be done with more or less delay by the different current measurement modules 6, provided that this delay is fixed for each measurement.

[0092] Upon receipt of the synchronization signal sent by the voltage measurement module 4, the current measurement module 6 measures (step 72), by means of its clock, a local time stamp indicating the instant at which the current measurement module 6 received said synchronization signal.

[0093] According to the possible embodiments, the time of detection of reception of the synchronization signal can be taken as the time from which the preamble of the message is received by the communication interface 56, or the time from which the body of the message is received. Other examples are possible as a variant, provided that the method used is consistent and that it generates the least possible variability in the processing time upon reception of the message between successive measurement cycles.

[0094] More preferably, to limit such variability, the message is sent by the voltage measurement module 4 by limiting or even omitting any bidirectional communication between the respective communication interfaces 14 and 26 of the measurement modules 4 and 6 (for example by omitting bidirectional communication routines of the “handshake” or “discovery” type).

[0095] Preferably, said message is sent by a broadcast method by the voltage measurement module 4.

[0096] More preferably, said message has a fixed length header.

[0097] Then, during a step 74, the main timestamp data (previously generated by the module 4) contained in the received message are extracted. The main timestamp data received from the voltage sensor 4 and being associated with the sending of the synchronization signal is for example associated with the local timestamp data calculated during the reception of the synchronization signal.

[0098] In step 76, the current measurement module 6 automatically determines parameters which will make it possible to estimate the time difference between the local clock of the current measurement module 6 and the clock of the voltage measurement module 4. In other words, the current measurement module 6 determines parameters aimed at expressing the time measured locally by its clock in the time reference frame corresponding to the voltage measurement module 4.

[0099] This makes it possible in particular to calculate the time drift of measurement module 6 compared to measurement module 4.

[0100] This mainly allows the current measurement module 6 to estimate the time reference of the main module 4 and to convert the timestamp of the current measurements into this estimated reference. However, the estimation of the synchronization of the current and voltage samples contains an error, which will only be known or corrected when the calibration process described below has been implemented.

[0101] In many embodiments, an offset between the modules 4 and 6 is calculated from the difference between the times of sending the message. A time drift of the current measurement module 6 is estimated from the ratio between the time interval between two consecutive sendings of the message by the voltage measurement module 4 as determined from the main timestamp data, and the time interval between the reception of two consecutive messages by the current measurement module 6.

[0102] In some examples, for each current measurement module 6, the duration between two consecutive messages received can be counted and used as information to determine this correction. This makes it possible to date the instant of reception of said message in the time reference of the current measurement module 6.

[0103] Generally, the delay correction applied to the timestamp data associated with the measured current values is calculated based on the difference between the main timestamp data received and the local timestamp data calculated for the same synchronization signal.

[0104] For example, measurement module 6 calculates the time drift coefficient (denoted “Slope”) using the following formula: Slope = MasterTimeBetweenTops LocalTimeBetweenTops where: “MasterTimeBetweenTops” designates the time interval between two consecutive sendings of the synchronization signal by the voltage measurement module 4, this time interval being determined from the main timestamp data contained in the messages sent successively, and where

[0105] “LocalTimeBetweenTops” means the time interval between the reception of two consecutive synchronization signals by the measurement module 6.

[0106] Preferably, the coefficient used for subsequent calculations is determined by calculating an average over several cycles (for example by taking the running average calculated from at least ten or fifty previous values).

[0107] However, other calculation methods are possible as a variant.

[0108] For example, measurement module 6 calculates the difference (noted "Offset") between the start of the respective clocks of the two measurement modules 4 and 6 using the following formula: Offset = LastSyncMasterTime where “LastSyncMasterTime” designates the time of sending of the message by the voltage measurement module 4 (called “Top time” in the above), this time being measured (time-stamped) by the voltage measurement module 4 in its time reference, this information being contained in the message received.

[0109] On the figure 5 , this gap is not visible and has already been corrected, the two curves having the same timeline.

[0110] These time drift and deviation values are calculated during step 76, which is preferably repeated periodically.

[0111] In parallel with these steps, during a step 71, the current measurement module 6 measures (samples) the current value. This measurement is for example repeated several times periodically, for example with the second sampling frequency.

[0112] Each current measurement is then time-stamped in a step 73 by the current measurement module 6 with its local clock, taking into account the correction values determined in step 76. The measured values and the corresponding time-stamping data can then be recorded in a step 75.

[0113] In other words, each time the module 6 samples an electric current value with the measuring element 20, the measuring module 6 determines a corresponding local time stamp for each current measurement (for each sampling), this time stamping being carried out taking into account the correction values determined during step 76. This makes it possible to date the instant of the current measurement in a corrected time frame which corresponds to the time frame of the main module 4 (or at least which comes as close as possible to it), and in which the time difference between the modules 4 and 6 is automatically compensated.

[0114] Preferably, the corrected timestamp is achieved by calculating an estimated time (denoted "EstimatedMasterTime") using the following formula: EstimatedMasterTime LocalTime = Offset + Slope × LocalTime − LastSyncLocalTime where: “Offset” and “Slope” are the correction values calculated previously in step 76, “LocalTime” designates the uncorrected local timestamp value (i.e. the time measured using the local clock, similar to what is done in step 70) and “LastSyncLocalTime” designates the time of reception of the message by the current measurement module 6, this time being measured (time-stamped) by the current measurement module 6 in its time reference frame.

[0115] Other calculation formulas can be used.

[0116] For example, the calculation of the estimated time is repeated for, with successive current measurements then being timestamped with this estimated time, until the next update. Alternatively, the estimated time can be recalculated for each current measurement.

[0117] An advantage of these embodiments is that, as the correction values are calculated periodically, then the local timestamps made for the current measurements are updated periodically, for example during each cycle, which makes it possible to automatically compensate for any time drifts that could occur during the operation of each current measurement module 6, such as a clock drift.

[0118] Alternatively, each current measurement could be time-stamped in step 73 by the current measurement module 6 with its local clock, as described previously. Then, the corrected time-stamping data could be calculated separately, in a second step, for each current measurement, from the local time-stamping data and taking into account the correction values determined in step 76.

[0119] In parallel with these steps based on timestamps, in many embodiments, the method advantageously implements steps of correcting the measured current and voltage values based on calibration data already known (for example recorded in memory).

[0120] There figure 5 represents an example illustrating one aspect of the sampling of current and voltage values by measurement modules 4 and 6.

[0121] Graph 30 includes a first curve 32 which represents the evolution of the real voltage (noted U, on the ordinate) in a location of the electrical installation over time (noted t, on the abscissa).

[0122] The second curve 34 represents the evolution of the measured voltage reconstructed from the values sampled by the voltage sensor over time.

[0123] Reference 36 designates a measurement point given as an example to illustrate the existence of a delay, noted “TU” between the moment when the actual voltage takes a certain value and the moment for which the corresponding sampling is finished.

[0124] In practice, this first delay TU corresponds to the duration required by the processing circuit 12 to process the signal measured by the measuring element 10. This delay is generally fixed for a given frequency; it is a characteristic of the measurement chain of the voltage measurement module 4, and depends for example on the properties of the measuring element 10, the analog-digital converter, the processor present in the processing circuit 12, and also the digital filters implemented by the processor, among others.

[0125] Still on the figure 5 , graph 40 includes a first curve 42 which represents the evolution of the real current (noted I, on the ordinate) in a location of the electrical installation over time (noted t, on the abscissa).

[0126] The second curve 44 represents the evolution of the measured current reconstructed from the values sampled by the current sensor 6 over time.

[0127] Reference 46 designates a measurement point given as an example to illustrate the existence of a delay, noted “TI” between the moment when the “real” current takes a certain value and the moment for which the corresponding sampling is finished.

[0128] In practice, this second delay TI corresponds to the duration required by the processing circuit 22 to process the signal measured by the measuring element 20. This delay is generally fixed for a given frequency; it is a characteristic of the measurement chain of the current measurement module 6, and depends for example on the properties of the measuring element 20, the analog-digital converter and the processor present in the processing circuit 22, among others.

[0129] A second aspect therefore aims to correct or compensate at least in part for these delays, thanks to a calibration carried out initially, in particular to automatically compensate for the difference between the second delay TI and the first delay TU.

[0130] For example, the time compensation aims to compensate for fixed delays present in the measurement chains of the measurement modules 4 and 6, and aims above all to compensate for a fixed overall delay which is equivalent to the sum of the difference between a delay of the measurement module 4 and a delay of the measurement module 6 (these delays being intrinsic to the measurement electronics of the modules 4 and 6), with the difference between the time offset of the measurement module 4 and the time offset of the measurement module 6 (these offsets being the result of the process described in figure 3 , which accidentally generates delays due to the implementation of timestamps and / or message sending).

[0131] For example, the time compensation (Calibration time) is representative of an overall delay given by the following formula: Calibration time = Tu − Ti + TimeSyncOffset _ U − TimeSyncOffset _ I where TU is the delay of measurement module 4 and TI is the delay of measurement module 6 as defined with reference to the figure 5 “TimeSyncOffset _U” is the time offset of measurement module 4 and “TimeSyncOffset _I” is the time offset of measurement module 6.

[0132] For example, time correction is applied by increasing or decreasing the time given by the clock of module 4 or 6 by the predefined calibration value resulting from the calibration.

[0133] This correction is for example carried out by the measurement module 4. However, as a variant, this correction can be carried out after sending the message. The correction can be carried out centrally before calculating the electrical quantity, in particular if this calculation is carried out by an entity of the system 2 separate from the measurement modules 4 and 6.

[0134] In addition, the measured current values are automatically corrected taking into account a time correction value pre-recorded in memory, this time correction value being the result of a prior calibration process.

[0135] For example, measured current values are resampled so that the current values are "realigned" a posteriori to the same time scale as the measured voltage values. This allows the voltage and current values to appear a posteriori during a subsequent calculation as having been measured simultaneously or quasi-simultaneously, even though the measurements were made by separate measurement modules, each with its own clock, and these clocks are not actively synchronized.

[0136] In practice, the number of current samples can be changed so that their number corresponds to the number of voltage values contained in each message.

[0137] In practice, each message can contain the same number of voltage values measured for each cycle (e.g. 40 voltage samples per message).

[0138] This correction is carried out, for example, by the measurement module 6, but here again the correction can be carried out differently, for example a posteriori in a centralized manner.

[0139] Finally, at the end of the method, for example once the voltage and current values have been acquired by the measurement modules 4 and 6 (and corrected using the calibration data), at least one value of the electrical quantity (such as the electrical power) is calculated from the successive current and voltage values from the measurement modules 4 and 6. In other variants, the calculation of the electrical quantity is carried out in real time, as the current values are measured by the measurement modules 6 and the measured voltage values are received by the measurement modules 6.

[0140] For example, to calculate electrical power, each measured voltage value is multiplied with the corresponding current value estimated (by interpolation) at the same time. The operation is repeated to calculate and obtain a succession of values representing the evolution of electrical power over time.

[0141] It is therefore understood that the calculation of said electrical quantity is carried out by taking into account (at least implicitly) the delay correction values calculated for each sensor for each of the measurements. The calculation of said electrical quantity also takes into account (at least implicitly) the calibration corrections made to the measured current and voltage values. Optionally, other corrections can be made on this occasion, for example to adjust the time compensation according to other parameters such as the frequency of the measured signal.

[0142] Thanks to one embodiment of the invention, by time-stamping the current and voltage measurements and taking into account the intrinsic delay specific to the measurement chain of each sensor, it is possible to correct the delay after the measurement has been made.

[0143] In other words, instead of synchronizing the clocks of the current and voltage measurement modules so that they measure voltage and current at the same time, it is the voltage and current signals measured by the sensors that are virtually synchronized, by correcting the time reference of the current measurement modules.

[0144] It is thus possible to determine electrical quantities, in particular electrical quantities calculated from measurements made by the measurement modules, such as electrical power, in a simple and reliable manner.

[0145] Furthermore, using the current and voltage calibration values advantageously makes it possible to compensate for the fixed delays due to the measurement chain of the different measurement modules 4 and 6 (delays generally constant over time for a given frequency, these delays and / or these phase shifts coming from elements such as the analog-digital converter, an analog anti-aliasing filter and the digital filters implemented in the processor, for example).

[0146] Optionally, the measured voltage values can also be corrected in a similar manner, for example before being sent in said message, taking into account a time correction value pre-recorded in memory, this time correction value being derived from a prior calibration process.

[0147] For example, the voltage values measured during a measurement cycle are resampled, for example so that each measurement cycle (and possibly each message sent) contains the same number of measured voltage values (for example 40 voltage samples per measurement cycle). During this resampling, a corrected time base is used which includes time compensation from the calibration process.

[0148] However, such calibration of voltage values remains optional and can be omitted. As with the calibration of current values, described above, the time compensation can be adjusted according to the frequency of the measured signal.

[0149] There figure 6 describes an example of a calibration method implemented to initially calibrate the measurement modules 4 and 6 of the system 2 in order to calculate the current and voltage calibration values used in the previously described method.

[0150] This calibration process is illustrated here in conjunction with the voltage and current measurement steps previously described.

[0151] This calibration process is preferably carried out in the factory before commissioning of the system 2. However, optionally but nevertheless advantageously, the calibration process can be implemented after commissioning of the system 2, for example by repeating the calibration at regular intervals (every year for example).

[0152] Diagram 80 of the figure 6 represents steps implemented by at least one voltage measuring module 4 (upper half of the diagram) and by one of the current measuring modules 6 (lower half of the diagram) during a test phase separate from the operating phase. These steps are, for example, implemented by the respective processors of the voltage measuring module 4 and the current measuring modules 6.

[0153] Again, the steps of the method to be described could be performed in a different order. Some steps could be omitted. The example described does not preclude other steps from being performed in other embodiments in conjunction and / or sequentially with the steps described.

[0154] Calibration is performed by injecting alternating current and voltage signals with known phase shifts. The signals can come from a signal generator within a test setup that is powered by the signal generator. They can also be real signals in an operating setup.

[0155] At block 90, the test signals are emitted.

[0156] In a periodically repeated step (block 92), the voltage measurement module 4 acquires a voltage value by sampling the test signal.

[0157] In block 94, the measured voltage value is timestamped with the clock of module 4, for example with a timestamp data provided by the clock of module 4 (block 96).

[0158] In block 98, the time stamp data associated with the measured voltage values are corrected with correction data provided by a first synchronization module of the measurement module 4 (block 95).

[0159] This allows you to place yourself in an ideal main time frame.

[0160] The synchronization module is here configured to implement the synchronization management functions described with reference to figures 2 , 3 And 4 , for example for managing synchronization signals and for managing time correction parameters.

[0161] For example, the first calibration module 95 emits a synchronization signal and the corresponding instant is time-stamped using the clock of module 4 (block 96). The corresponding main time-stamping data at this stage contains the so-called synchronization delay (TimeSyncOffset _U) associated with module 4.

[0162] In the example illustrated, the synchronization signal is sent over the communication link 56 to the module 6 in the form of a message comprising the main timestamp data (or that measured for the previous synchronization signal).

[0163] The correction data provided in block 98 allows the voltage samples to be timestamped with corrected timestamp information (block 100). In practice, the corrected timestamp data may still contain a generic delay expected for all voltage measurement modules.

[0164] Block 96 here corresponds to the local clock which provides the local timestamp data of module 6.

[0165] This timestamp data is then sent to module 6.

[0166] For example, at block 101, module 4 sends a message over communication link 56 to module 6, this message comprising the time-stamped voltage samples.

[0167] In parallel, for the current measurement module 6, during a periodically repeated step (block 102), the measurement module 6 acquires a current value by sampling the received test signal.

[0168] In block 106, the measured current value is timestamped with the clock of module 6, for example with a timestamp data provided by the clock of module 6 (block 104).

[0169] In block 107, the timestamp data provided by the clock of module 6 are corrected with correction data provided by a calibration module of measurement module 6 (block 105).

[0170] For example, the calibration module 105 initiates a cycle upon receipt of the synchronization signal sent by the module 4. The corresponding instant is time-stamped using the clock of the module 6 (block 104). The corresponding local time-stamping data at this stage contains the so-called synchronization delay (TimeSyncOffset _I) associated with the module 6.

[0171] The module 105 determines an estimated time value, from the local timestamp and the main timestamp data received in the message, in a manner similar to that described previously with reference to the method of the figure 3 .

[0172] This data, provided to block 107, makes it possible to timestamp the current samples with corrected timestamp information (block 110) but this nevertheless includes at this stage the delay TI. Because the estimated time contains the delays coming from the voltage measurement module 4 as well as the delays introduced by the module 6 during timestamping, then the timestamp data are affected by the overall delay previously defined (Calibration Time). It should be noted that in general, the absolute values of these delays will not be known, but it will be ensured that they are identical in all the measurement modules, and that the time differences between the current and voltage values are zero.

[0173] In parallel, at block 113, module 6 receives the voltage samples contained in the received message. The time stamp data is extracted (block 111) and, at block 112, the measured current values are resampled to match them in time with the measured voltage values that were received from module 4 (i.e., so that the measured current values are realigned in time with the voltage values). Next, the phase shift between the measured current and voltage is determined, and this phase is compared with the known phase shift between the input signals to determine the overall delay of the measurement chain. This makes it possible to determine voltage or current correction data (depending on whether a voltage or current reference measurement module was used). The correction data is then provided (by a calculation module illustrated in block 116) to the calibration module 95 and to the calibration module 105.It is also this correction data that is used in the process of the . figure 3 .

[0174] For example, to determine the phase shift between the voltage and current signals, in block 114, the active power and reactive power values are calculated from the measured voltage and current values. However, other methods are possible for determining the phase shift between the voltage and current signals.

[0175] Then, in block 116, a time correction value is calculated for measurement modules 4 and 6 from the calculated active power and reactive power values.

[0176] For example, the time correction value (UCalibTimeCorrection) for voltage measurement module 4 is calculated using the following formula: UCalibTimeCorrection = Arctan Q P − CalibrationTarget 360 × Frequency where "Q" and "P" are, respectively, the previously calculated (averaged) reactive power and active power, "CalibrationTarget" is the value of the phase shift between the voltage input signal and the current input signal and "Frequency" is the oscillation frequency of the test signals.

[0177] For example, the time correction value (ICalibTimeCorrection) for voltage measurement module 4 is calculated in the same way.

[0178] This value is then provided to modules 95 and 105 to shift the time of the signal measured by at least one of the respective modules 4 and 6. For example, the time given by the clock of module 4 or 6 is increased or decreased by this amount UCalibTimeCorrection or ICalibTimeCorrection.

[0179] Preferably, the voltage measurement module 4 and the current measurement module 6 are calibrated separately. For example, when calibrating the voltage measurement module 4, a reference measurement module is used as the current measurement module 6, which, although having an intrinsic delay, is ideally free of additional delays or time drift. The same applies when calibrating a current measurement module 6, taking a reference voltage measurement module 4.

[0180] It is understood that, to calculate the time correction value, the calibration method uses the method for determining an electrical quantity as previously described with reference to figures 2 à 5 in particular. This allows the calibration process to correct for time errors (in particular the time difference) and to be independent of the communication link used.

[0181] Optionally, the calibration process can also correct the clock of module 4 so that it matches or comes as close as possible to an ideal clock. This improves the measurement of the voltage frequency.

[0182] For example, the calibration value of the time drift (CalibrationDrift) is given by the following formula: CalibrationDrift = Frequency − FrequencyTarget FrequencyTarget where "Frequency" is the oscillation frequency of the test signals and "FrequencyTarget" is a target frequency, for example the frequency of the measurement cycles.

[0183] The embodiments and variants envisaged above may be combined with each other to give rise to new embodiments.

Claims

1. A method for determining an electrical quantity in an electrical installation, by means of a measurement system (2) comprising at least one voltage measurement module (4) and at least one current measurement module (6) coupled to the electrical installation, each of said measurement modules comprising a sensor, a processor, a memory and a clock, the method comprising: • by the voltage measurement module (4): ▪ periodically measuring an electrical voltage (U) in the electrical installation, ▪ periodically sending a synchronisation signal to at least one of the current measurement modules, ▪ sending to said current measurement module a message comprising at least one main timestamp data indicating the instant at which the voltage measurement module transmitted the synchronisation signal, this instant being measured by the voltage measurement module with its clock, ▪ sending a message comprising at least one measured voltage value to said current measurement module, • by a current measurement module (6): ▪ periodically measuring an electrical current (I) in the electrical installation, ▪ on receiving the synchronisation signal sent by the voltage measurement module, calculating, by means of the clock of said current measurement module, a local timestamp data indicating the time at which the current measurement module received said synchronisation signal, ▪ determining successive delay correction values from the main timestamp data received and the local timestamp data calculated for each synchronisation signal received from the voltage measurement module, the successive current measurements carried out by the current measurement module being time-stamped by the current measurement module, by means of its clock, taking into account the delay correction values thus determined, • by a processor, calculating at least one value of an electrical quantity from successive current and voltage values measured by the measurement modules.

2. The method according to claim 1, wherein the delay correction applied to the timestamp data associated with the measured current values is calculated as a function of the difference between the main timestamp data received and the local timestamp data calculated for the same synchronisation signal.

3. The method according to any one of the preceding claims, wherein the calculation of said value of an electrical quantity comprises beforehand an interpolation of the current values for the instants corresponding to the instants for which the voltage values were measured by the voltage measurement module, said interpolation being carried out on the basis of the measured current values and the time-stamp data associated with the measured current values.

4. The method according to any one of the preceding claims, wherein a time drift of the current measurement module is estimated by the ratio between, on the one hand, the time interval between two consecutive transmissions of the synchronisation signal by the voltage measurement module, this time interval being determined from the main time-stamp data, and, on the other hand, the time interval between the reception of two synchronisation signals received consecutively by the current measurement module, this time interval being determined from the local timestamp data.

5. The method according to any one of the preceding claims, wherein each voltage measurement by the voltage measurement module is timestamped by the voltage measurement module, a corresponding timestamp data being sent by the corresponding voltage measurement module, for each voltage value measured.

6. The method according to claim 5, wherein the timestamp data associated with the measured voltage values are automatically corrected, before they are sent in said message, taking into account a time correction value pre-stored in memory, this time correction value coming from a prior calibration method.

7. The method according to any one of claims 1 to 5, wherein timestamp data associated with the measured current values are automatically corrected by taking into account a time correction value pre-stored in memory, this time correction value coming from a prior calibration method.

8. The method according to claim 6 or claim 7, wherein to calculate the time correction value, the calibration method comprises a method for determining an electrical quantity according to any one of the preceding claims.

9. The method according to any one of the preceding claims, wherein the measurement modules of the system are in communication via a wireless communication link, each message sent by the voltage measurement module being a radio message.

10. The method according to any one of claims 1 to 8, wherein the measurement modules of the system are in communication via a wired communication link, such as a data bus.

11. The method according to any one of the preceding claims, wherein the calculation of the value of an electrical quantity is carried out by an electronic circuit for processing at least one of the current measurement modules.

12. The method according to any one of the preceding claims, wherein the value of a calculated electrical quantity is an electrical power calculated from the current and voltage values measured by the measurement modules.

13. A system (2) for determining an electrical quantity in an electrical installation, this system comprising at least one voltage measurement module (4) and at least one current measurement module (6) coupled to the electrical installation, each of said measurement modules comprising a sensor, a processor, a memory and a clock, the system being configured to implement a method for determining an electrical quantity, the method comprising: • by the voltage measurement module (4): ▪ periodically measuring an electrical voltage (U) in the electrical installation, ▪ periodically sending a synchronisation signal to at least one of the current measurement modules ▪ sending to said current measurement module a message comprising at least one main timestamp data indicating the instant at which the voltage measurement module transmitted the synchronisation signal, this instant being measured by the voltage measurement module with its clock, ▪ sending a message comprising at least one measured voltage value to said current measurement module, • by a current measurement module (6): ▪ periodically measuring an electrical current (I) in the electrical installation, ▪ on receiving the synchronisation signal sent by the voltage measurement module, calculating, by means of the clock of said current measurement module, a local timestamp data indicating the time at which the current measurement module received said synchronisation signal, ▪ determining successive delay correction values from the main timestamp data received and the local timestamp data calculated for each synchronisation signal received from the voltage measurement module, the successive current measurements carried out by the current measurement module being timestamped by the current measurement module, by means of its clock, taking into account the delay correction values thus determined, • by a processor, calculating at least one value of an electrical quantity from successive current and voltage values measured by the measurement modules.