Distributed electrical power measurement system and related method

Abstract

A distributed system for measuring electrical power in an electrical installation powered by circulating alternating electrical signals, the system comprising a device (4) for measuring voltage and at least one device (6) for measuring current adapted to communicate according to a communication protocol. The device (4) for measuring the voltage is configured to encode (30) voltage samples per cycle during a transmission period comprising a plurality of consecutive cycles of the electrical signal to form a codeword and to transmit the codeword to the device for measuring the current. Each device (6) for measuring an electrical current is configured to receive at least two consecutive communication frames, each frame corresponding to a cycle of an electrical signal; for each frame, a decompression method is determined (40) and applied to obtain N decoded voltage samples and a series of power values is calculated (42).

Description

Technical Field

[0001] The present invention relates to a distributed system for measuring electric power in an electrical installation powered by a cyclic alternating electric signal, and to a related method for measuring electric power.

[0002] The invention belongs to the field of systems for measuring electrical power in electrical installations. Background Art

[0003] Power measuring devices, or wattmeters, are known and are used in various electrical installations to monitor the electrical power consumed by the installation and to better protect the electrical installation.

[0004] More specifically, the invention relates to a distributed system for measuring power, comprising a device for measuring voltage and at least one device for measuring current remote from the device for measuring voltage, adapted to communicate via a communication protocol, via a radio or wired communication link.

[0005] One problem that arises in such systems is limiting the power consumption of each measuring device, especially when the measuring devices are self-powered.

[0006] For example, in a distributed measuring system comprising a plurality of self-powered devices for measuring currents adapted to communicate via a radio communication link according to a radio communication protocol such as Bluetooth or ZigBee, it has been found that the modules ensuring the radio communication have a high power consumption.

[0007] Therefore, there is a need to limit the power consumption of such devices for measuring current. Summary of the invention

[0008] To this end, the present invention proposes a distributed system for measuring electric power in electrical facilities powered by a cyclic alternating electrical signal, the system comprising a device for measuring voltage and at least one device for measuring current remote from the device for measuring voltage, the device for measuring voltage being configured to acquire a predetermined number N of voltage samples in each cycle of the electrical signal, each device for measuring current being configured to acquire N current samples in each cycle of the electrical signal, the device for measuring voltage and the or each device for measuring current being suitable for communicating according to a communication protocol.

[0009] The system is such that the device for measuring voltage is configured to, during a transmission period comprising a plurality of consecutive cycles of the electrical signal:

[0010] - for each cycle, encoding the voltage sample to form a codeword and transmitting said codeword in a communication frame of said communication protocol to the or each device for measuring current,

[0011] The or each device for measuring current is configured:

[0012] - receiving at least two consecutive communication frames, each communication frame corresponding to one cycle of the electrical signal,

[0013] - for each frame, determine the decompression method to be applied, and apply the decompression method to obtain the N decoded voltage samples for the corresponding cycle,

[0014] - Use the measured current samples and the decoded voltage samples to calculate a series of N power values ​​for the corresponding cycle.

[0015] Advantageously, the distributed system for measuring electric power uses compression of the voltage samples transmitted to the device for measuring current at each cycle of the electric signal, which makes it possible to reduce the effective communication time and therefore the power consumption of the device for measuring current.

[0016] The distributed system for measuring electric power according to the present invention may also have one or more of the following features, which may be adopted independently or in all technically feasible combinations.

[0017] the plurality of consecutive cycles include an initial cycle and subsequent cycles, and the device for measuring voltage is configured to apply differential compression to voltage samples of each current cycle different from the initial cycle, the differential compression implementing, for at least two consecutive cycles, sample-by-sample calculation of differences between samples of the current cycle and samples of the previous cycle, calculation of a number P of bytes encoding the differences, and formation of a codeword of P bytes;

[0018] The or each device for measuring current is configured:

[0019] - Extracting codewords from each frame and determining the number of bytes received and, based on said number of bytes received, determining the decompression method to apply.

[0020] For a series comprising consecutive first and second cycles, the differential compression implements a sample-by-sample difference calculation between samples of the second cycle and samples of the first cycle for compression of samples of the second cycle so as to form a series of difference values ​​to be encoded.

[0021] For a series comprising a first cycle, a second cycle and a third cycle, differential compression is performed on the compression of samples of the third cycle:

[0022] - a sample-by-sample first difference calculation between the samples of the third cycle and the samples of the second cycle to form a series of first differences,

[0023] - a sample-by-sample second difference calculation between the samples of the second cycle and the samples of the first cycle to form a series of second differences,

[0024] - The difference between the series of first differences and the series of second differences is calculated to form a series of difference values ​​to be encoded.

[0025] The device for measuring voltage is further configured to determine a minimum value and a maximum value in the series of difference values ​​to be encoded, and then determine a number B of bits for encoding each of the series of difference values ​​based on the minimum value and the maximum value.

[0026] The device for measuring voltage is further configured to determine a gain value according to the minimum value and the maximum value in the series of difference values ​​to be encoded, and to encode the gain value.

[0027] A coding table is pre-stored by the device for measuring voltage and the or each device for measuring current, which indicates, for each of multiple intervals of difference values, the number of bits B and the associated number of encoded bytes P used to encode each of a series of difference values ​​to be used for the interval.

[0028] To determine the decompression method to be applied, the or each device for measuring current determines whether the received number of bytes belongs to the encoding table and, in the event of a positive response, determines the number of bits B used to encode each value in the series of difference values.

[0029] In the initial cycle, each voltage sample has an amplitude value and a phase value, which are encoded to form a codeword.

[0030] According to another aspect, the invention relates to a method for measuring electric power implemented by a distributed electric power measurement system as briefly described above. The method comprises steps implemented by an electronic computing unit of a device for measuring voltage, comprising encoding voltage samples during a transmission period comprising a plurality of consecutive cycles of said electric signal to form a codeword, and transmitting said codeword to said or each device for measuring current in a communication frame of said communication protocol,

[0031] and comprises the steps implemented by at least one electronic computing unit of a device for measuring electric current:

[0032] - receiving at least two consecutive communication frames, each communication frame corresponding to one cycle of the electrical signal,

[0033] - for each frame, determining the decompression method to be applied and applying said decompression method to obtain N decoded voltage samples for the corresponding cycle,

[0034] - Calculate a series of N power values ​​for the corresponding cycle using the measured current samples and the decoded voltage samples.

[0035] According to another aspect, the present invention relates to a software program comprising a first software program comprising code instructions and a second software program comprising code instructions, which implement the method for measuring electrical power in an electrical installation as briefly described above when the first software program is executed on a device for measuring voltage and the second software program is executed on at least one device for measuring current. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Other characteristics and advantages of the invention will become apparent from the following description given as non-limiting examples with reference to the accompanying drawings, in which:

[0037] Figure 1 Schematically represents a distributed system for measuring electric power according to the present invention;

[0038] Figure 2 is an overview of the main steps used by the device for measuring voltage according to the first embodiment;

[0039] Figure 3 is an overview of the main steps used by the apparatus for measuring current according to the first embodiment;

[0040] Figure 4 is a schematic diagram of steps of a second embodiment used by an apparatus for measuring voltage, which are different from the steps of the first embodiment;

[0041] Figure 5 is a schematic diagram of steps of a second embodiment used by an apparatus for measuring current, which are different from the steps of the first embodiment. DETAILED DESCRIPTION

[0042] Figure 1 An embodiment of a distributed system 2 for measuring electric power is schematically represented, the system being adapted to provide electric power measurements in an electrical installation (not shown) powered by a cyclic alternating electric signal.

[0043] The system 2 comprises a device 4 for measuring voltage and a plurality of devices 6 for measuring current remote from the device 4 for measuring voltage, the devices 4 and 6 being digital devices for electronic measurement of voltage and current.

[0044] For example, the device 4 for measuring voltage is placed at one location in the electrical installation, while the devices 6 for measuring current are distributed at a plurality of other locations in the electrical installation.

[0045] Figure 1 The example of includes three devices for measuring the current 6 , but in practice the number of devices for measuring the current 6 is arbitrary. Figure 1Only one device 6 for measuring current is shown in detail, but all devices 6 for measuring current have similar structures and functions.

[0046] The device 4 for measuring a voltage is supplied with electrical energy by a schematically indicated electrical energy source 8 .

[0047] The source of electrical energy 8 has been schematically shown outside the device 4 for measuring a voltage, but according to an alternative embodiment the source of electrical energy 8 is placed inside the device 4 for measuring a voltage.

[0048] In one embodiment, the electrical energy source 8 is a 24V power source.

[0049] According to a variant, the source of electrical energy 8 is a power distribution network, the voltage of which is measured.

[0050] In another variant, the electrical energy source 8 is a battery, for example placed inside the device 4 for measuring voltage.

[0051] The device 4 for measuring voltage further comprises a voltage sensor 10 which is suitable for carrying out voltage measurements on command or at set time intervals.

[0052] For example, the voltage sensor 10 is suitable for measuring the voltage value of a cyclic alternating electrical signal.

[0053] In a known manner, this electric signal is substantially periodic, for example substantially sinusoidal, and comprises cycles, each cycle corresponding to a sinusoidal period.According to a variant, the electric signal is a triangular or square signal.

[0054] For example, the voltage sensor 10 is configured to acquire a predetermined number N of voltage samples in each cycle of the electrical signal.

[0055] The number N is chosen, for example N=40 per cycle of the electrical signal, so as to comply with the requirements of performance standards for digital electronic measuring equipment, in particular standard IEC 61557-12.

[0056] The device 4 for measuring a voltage further comprises an electronic storage unit 12 , an electronic calculation unit 14 , for example a processor or a microcontroller, and a communication module 16 .

[0057] In one embodiment, the measured voltage samples are time stamped and stored in the electronic storage unit 12 along with the associated time stamp information.

[0058] In one embodiment, the communication module 16 is a radio communication module adapted to communicate in transmission and reception according to a given radio communication protocol.

[0059] The radio communication protocol is, for example, Bluetooth, Bluetooth Low Energy (BLE) or ZigBee.

[0060] In another embodiment, the communication module 16 enables communication according to a wired protocol (eg Ethernet, Modbus, CAN).

[0061] According to a variant, the device 4 comprises a plurality of communication modules 16 configured to communicate according to radio and wired communication protocols.

[0062] Each device 6 for measuring current also comprises a communication module 18 , as well as an electronic storage unit 24 and an electronic calculation unit 26 , for example a processor or a microcontroller.

[0063] The communication module 18 is adapted to communicate according to the same communication protocol (radio and / or wired) as the communication module 16 .

[0064] Thereby, the device for measuring a voltage 4 is configured to communicate with each device for measuring a voltage 6 according to the selected communication protocol.

[0065] Each device for measuring current 6 also comprises a current sensor 22 adapted to carry out current measurements at set time intervals or in other words at set time sampling steps.

[0066] Each device 6 for measuring current is a device which is self-powered by a current sensor 22 .

[0067] For example, the current sensor 22 is adapted to measure the current value of the cyclic alternating electric signal.

[0068] Preferably, the current sensor 22 is configured to obtain N current samples per cycle of the electrical signal, for example, N=40.

[0069] In other words, the device for measuring voltage and each device for measuring current obtain the same number N of voltage and current samples, respectively.

[0070] The system 2 is configured to transmit voltage samples (preferably time-stamped) measured by the device 4 for measuring voltage to the device 6 for measuring current.

[0071] In one embodiment, a measured voltage sample is transmitted at each cycle of the electrical signal.

[0072] Each device 6 for measuring current also acquires a current sample for each cycle, thereby performing a distributed calculation of the voltage measurement for each cycle of the electrical signal from the received voltage samples and the acquired current samples.

[0073] In order to save power consumed by the devices for measuring voltage and current, the system 2 is configured to perform compression of the voltage samples before they are transmitted to the device 4 for measuring voltage and decompressed by each device 6 for measuring current.

[0074] Thus, advantageously, the amount of data transmitted by the device 4 for measuring voltage and received by the or each device 6 for measuring current is reduced, which makes it possible to reduce the communication time of the corresponding communication modules 16 and 18, the power consumption of which is greater than the power consumption of the calculation units 14 and 26, which are, for example, calculation processors such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit).

[0075] The electronic calculation unit 14 is configured to execute the encoding module 30 for encoding the voltage samples into a codeword for each cycle of the electrical signal. The voltage samples of each cycle are stored in the electronic storage unit 12 for at least two consecutive cycles.

[0076] In one embodiment, the voltage samples reconstructed by decoding are stored in the electronic storage unit 12 for at least one cycle before the current cycle.

[0077] The encoding module 30 starts with the second cycle of the transmission period of the selected duration and, for consecutive first and second cycles, uses the module 32 to calculate the differences between the samples of the second cycle and the samples of the first cycle sample by sample to form a series of difference values ​​to be encoded.

[0078] According to a variant, the module 32 uses a difference of differences (or double differences) calculation to form a series of difference values ​​to be encoded over a series of three cycles, respectively comprising a first cycle, a second cycle and a third cycle, as described in more detail below.

[0079] Module 30 also uses module 34 to determine the minimum and maximum values ​​in a series of difference values ​​to be encoded and then, based on the minimum and maximum values, determines the number of bits B to encode each value in the series of difference values. Module 34 further calculates the number of bytes P used to encode the samples of the current cycle.

[0080] In one embodiment, the number P is obtained by multiplying the number of bits B by the number of voltage samples per cycle N.

[0081] According to a variant, the number P also depends on the gain value to be encoded.

[0082] Finally, the module 30 implements a module 36 for encoding the series of differences into a P-bit codeword. The codeword is transmitted to the communication module 16 for transmission in a communication frame according to the selected communication protocol.

[0083] In one embodiment, the module 30 also uses a decoding module 38 that calculates the value of the voltage samples reconstructed by decoding, similar to the voltage samples decoded by the device for measuring current.

[0084] In one embodiment, modules 32, 34, 36, and 38 each include a first software.

[0085] In a variant (not shown), the modules 32 , 34 , 36 and 38 are each produced in the form of a programmable logic component, such as an FPGA (Field Programmable Gate Array), or further in the form of a dedicated integrated circuit, such as an ASIC (Application Specific Integrated Circuit).

[0086] The first software is also susceptible to being stored on a non-volatile medium (not shown) readable by a programmable electronic device in the form of an executable program including software instructions.

[0087] Each device 6 for measuring current receives a code word representing a voltage sample for each cycle.

[0088] The electronic computing unit 26 is configured to execute a decompression module 40 which determines for each received codeword the decompression method to be applied as a function of the number of bytes encoding the received codeword and applies the selected decompression method to obtain N decoded voltage samples of the current cycle.

[0089] The electronic computing unit 26 is also configured to execute a module 42 for power calculation, which calculates a series of power values ​​from the current samples acquired by the sensor 22 and the decoded voltage samples.

[0090] In one embodiment, modules 40, 42 are each comprised of a second software.

[0091] In a variant (not shown), the modules 40 , 42 each comprise a programmable logic component, such as an FPGA (Field Programmable Gate Array), or further comprise an application specific integrated circuit, such as an ASIC (Application Specific Integrated Circuit).

[0092] The second software is also susceptible to being stored on a non-volatile medium (not shown) readable by a programmable electronic device in the form of an executable program including software instructions.

[0093] The first software and the second software are adapted to cooperate and form software (or a computer program) implementing a distributed method of measuring electrical power.

[0094] Figure 2 is an overview of the main steps of a distributed method for measuring electric power implemented by the device for measuring voltage in the first embodiment.

[0095] The method comprises an initialization 50 during which the index i of the current cycle of the transmission period is initialized to zero.

[0096] Index 0 corresponds to the first cycle of the transmission period, also called the initial cycle.

[0097] The transmission period has a chosen duration, for example equal to 1 second. Thus, for an electrical signal with a frequency equal to 50 Hz, the transmission period comprises 50 cycles.

[0098] The method comprises a step 52 of acquiring N voltage samples of the current cycle and storing the voltage samples.

[0099] The number of samples N in each cycle is predetermined, for example N=40.

[0100] Adjust the time sampling step of the voltage sensor to obtain N samples per cycle.

[0101] According to a variant, the temporal sampling step of the voltage sensor is different from N and an interpolation calculation is used during step 52 in order to obtain N samples per cycle.

[0102] The method then comprises a test step 54 for determining whether the current cycle is the first cycle (or initial cycle) of the transmission cycle.

[0103] For the test, the value of the loop index i is compared to an initialization value, thus zero in this embodiment.

[0104] In case of a positive response, ie if the cycle index i is equal to zero, the specific encoding method of the voltage samples of the first cycle is applied to the step 56 of encoding the samples.

[0105] For example, since the electrical signal is a sinusoidal signal, the amplitude and phase values ​​of each voltage sample are encoded. In one embodiment, the amplitude value is encoded on 2 bytes and the phase is encoded on 2 bytes.

[0106] In case of a negative response to test step 54, the current cycle is the second cycle or a subsequent cycle.

[0107] The method comprises a step 58 of differential compression using previously stored sample-by-sample difference calculations between the voltage samples of the current cycle of index i and the voltage samples of the cycle of index i-1 to form a series of difference values ​​to be encoded.

[0108] If a series of N samples of loop index i is given by Represented by, then a series of differences are given by: express.

[0109] In one embodiment, a difference is taken between the amplitude value of the voltage sample of the current cycle of index i and the voltage amplitude value of the previous cycle reconstructed by decoding and stored at each cycle.

[0110] The reconstruction (or decoding) is performed according to the calculations described below with reference to the decoding step 82 .

[0111] Then, during a step 60 of determining the number of bits B used to encode each difference value, the method determines the minimum and maximum value in the series of difference values ​​to be encoded. The number of bits B used to encode each value in the series of difference values ​​is derived therefrom.

[0112] For example, a coding table is used that relates the number of bits B to the difference value interval. In other words, the selected coding interval is the interval to which the minimum and maximum values ​​in a series of difference values ​​to be coded belong.

[0113] In one embodiment, Table 1 is used.

[0114] Table 1: Coding interval and number of bits B to be encoded for each difference value

[0115] Minimum Maximum B P -1 0 1 5 -2 1 2 10 -4 3 3 15 -8 7 4 20 -16 15 5 25 -32 31 6 30 -64 63 7 35 -128 127 8 40

[0116] In Table 1, the number of bytes P used to form a codeword per cycle is also indicated.

[0117] It can be seen that P=BxN / 8, and N=40 in this example.

[0118] It should be understood that Table 1 is given as an example and other tables may be used, such as the minimum and maximum values ​​offset by + 1. This offset keeps the average value of each interval centered around 0.

[0119] In one embodiment, if the minimum value V min Less than -128 or if the maximum V max If the value V is greater than 127, the coding is modified by adding a gain value G, which is additionally coded. The gain G is, for example, a divider which allows the corresponding value V to be divided by min and V max Substitute each of into the interval under consideration: and Each difference value to be encoded is then divided by G, which results in a slight loss of precision.

[0120] For example, the gain value is encoded on an additional byte, added to the P = 40 bytes of the last interval [128, 127]. In this case, for the gain encoding, the encoding table is increased by a number of bytes P equal to 41.

[0121] Then, during an encoding step 62, each difference value is encoded on B bits, for example based on a predetermined encoding table, such as Table 1 given above.

[0122] The method finally comprises step 64 of shaping the codewords in the communication frame according to the selected communication protocol and transmitting the codewords.

[0123] For example, the selected communication protocol is the Bluetooth protocol or the ZigBee protocol.

[0124] Step 64 is followed by step 66, which consists in verifying whether all loops of the transmission cycle have been processed. For example, the loop index i is compared with a predetermined maximum loop index value for each transmission cycle, and during step 66 it is verified whether the current loop index is equal to the predetermined maximum value.

[0125] If the response is negative, step 66 is followed by step 68 during which the current loop index is incremented by 1 for the next loop of processing. Step 68 is followed by step 52 as previously described.

[0126] If the response is affirmative, step 66 is followed by step 50 as previously described.

[0127] In other words, when the last cycle of a transmission cycle is processed, the method returns to step 50 for the subsequent transmission cycle.

[0128] Advantageously, the result is that the voltage samples of the initial cycle of a new transmission period can be encoded, resulting in a more efficient differential encoding.

[0129] It should be noted that, in addition to a series of differences for each cycle, timestamp information is also transmitted for synchronization of the devices measuring the current, more specifically, for synchronization between the clocks of the device measuring the voltage and each device measuring the current. For example, the timestamp information is also compressed, for example by double difference compression. Any known synchronization method can be implemented to achieve this synchronization.

[0130] Figure 3 is an overview of the main steps of a distributed method for measuring electrical power implemented by a device for measuring electric current in a first embodiment.

[0131] In a first embodiment, each device for measuring current receives a frame comprising codewords, each codeword comprising data representing a voltage sample for each cycle, the data being transmitted by reference to Figure 2 Described method steps are obtained.

[0132] The method comprises a step 70 of receiving communication frames, each frame comprising a codeword corresponding to a cycle of the electrical signal, and a step 72 of storing the extracted codewords.

[0133] Then, during a step 74 of determining the number of bytes, the number P of bytes representing the codeword extracted from the current frame is determined.

[0134] Based on the number of bytes P, the method determines a decompression method to obtain N decoded voltage samples of the corresponding cycle from the codeword.

[0135] During a test step 75, it is verified whether the quantity P belongs to the coding table used during the coding, for example Table 1, as referenced Figure 2 described.

[0136] If the number P does not belong to the encoding table used during encoding (negative response during step 75), it is concluded that the current cycle is the first cycle (or initial cycle) of the transmission cycle.

[0137] During a step 76 , the amplitude and phase values ​​of the N voltage samples of the first cycle of the transmission period are decoded and stored.

[0138] The decoding is a specific decoding corresponding to the specific encoding method of the first cycle samples used during step 56 .

[0139] If the number P is a number belonging to the coding table used, shared with the device for measuring the voltage which transmits a coded sample of the voltage, the number of bits B used to code each difference is derived during a step 78 .

[0140] In a variant, without using a stored coding table, during step 75 it is verified whether the number of bytes P multiplied by 8 and divided by the number of samples per cycle N is an integer between 1 and 8, and this number is the number of bits B per difference value.

[0141] Step 78 is followed by a decoding step 80 to obtain N decoded difference values, which are stored.

[0142] For example, according to the coding table used for encoding, the received codeword is divided into N words of B bits, each word of B bits representing a difference value.

[0143] Then, during a decoding step 82 , a decoded voltage sample is obtained from the decoded difference value and the voltage value sample previously stored for the previous cycle.

[0144] For example, if the current cycle has an associated index i, the decoded values ​​of the voltage samples of the cycle with index i-1 and the previously stored values ​​are used.

[0145] In other words, if represents a series of decoded differences, represents a series of N decoded voltage samples of cycle (i-1), the sample value is obtained by the following formula:

[0146]

[0147] During the storing step 84 , the N values ​​of the decoded voltage samples of the current cycle of index i are also stored.

[0148] Steps 76 and 84 are followed by step 86 of calculating N power values ​​from N decoded voltage samples and N corresponding current samples acquired by a current sensor of the device for measuring current.

[0149] In addition to the steps of the above method, the aim is to obtain decoded voltage samples to perform calculation of power values, the method comprises synchronizing according to the received timestamp information by any suitable method.

[0150] Steps 70 to 86 are repeated for each new frame received.

[0151] Thus, upon receipt of a frame corresponding to the first cycle of a transmission period, a series of N decoded voltage samples are obtained for each consecutive cycle.

[0152] Reference Figure 2 and Figure 3 The first embodiment described implements compression by differences between samples of successive cycles.

[0153] According to a second embodiment, in a variant, the distributed method for measuring electric power uses differential compression of differences (or double differences).

[0154] refer to Figure 4 , showing steps of a second embodiment different from the steps of the first embodiment, which are performed by an apparatus for measuring voltage.

[0155] In such an embodiment, test 54 is also used to determine whether the current cycle is the third or subsequent cycle of the transmission period.

[0156] The first loop (initial loop) is encoded in a manner similar to the first embodiment, and the second loop is encoded according to the reference Figure 2 The method described is via (simple) difference encoding.

[0157] Starting from the third cycle of the transmission period, step 54 is followed by a series of processes for a first cycle including an index i-2, a second cycle of an index i-1, and a third cycle (current cycle) of an index i.

[0158] The process includes a sample-by-sample first difference calculation (step 55) between samples from the third cycle and samples from the second cycle, so as to form a series of first differences:

[0159]

[0160] In other words, the difference between the sample of the loop of index i and the sample of the loop of index (i-1) is calculated.

[0161] In one embodiment, the samples of the second cycle are reconstructed by decoding.

[0162] Furthermore, a second difference calculation is performed sample by sample between the samples of the second cycle of index (i-1) and the samples of the first cycle of index (i-2) (step 57) so as to form a series of second differences:

[0163]

[0164] In one embodiment, samples of the first cycle are reconstructed by decoding.

[0165] According to a variant, the differences calculated during the first difference calculation are stored sample by sample between the samples of the current cycle and the samples of the previous cycle in each iteration.

[0166] The step 57 of the second calculation of the difference is replaced by a step of reading in a memory the difference stored during the previous step.

[0167] Then, step 59 uses the calculation of the difference between the series of first differences and the series of second differences to form a series of difference values ​​to be encoded:

[0168]

[0169] Step 59 is followed by step 60, determining the number of bits B used to encode each difference value, as previously described with reference to Figure 2 described.

[0170] Advantageously, in the second embodiment, the difference values ​​to be encoded are differences of differences, which serve to increase the compression level.

[0171] For the second embodiment, for a series of cycles including first, second and third consecutive cycles indexed as i-2, i-1 and i, respectively, each device for measuring current uses a corresponding decompression method.

[0172] The specific steps of the second embodiment implemented by the device for measuring current are as follows: Figure 5 is shown in the schematic diagram.

[0173] For the current cycle i, the method implements a decoding step 81 after the previously described step 78 to obtain N decoded difference values ​​corresponding respectively to the differences DD(i-2, i-1, i).

[0174] The method comprises a subsequent step 83 of obtaining the difference between the loop of index (i-1) and the loop of index (i-2) previously decoded and stored, and a step 85 of calculating the decoded difference between the loop of index i and the loop of index (i-1):

[0175]

[0176] The decoded difference values ​​calculated during step 85 are also stored during said step for use in subsequent steps.

[0177] The method then comprises calculating 87 a decoded voltage sample of the current cycle of index i from the decoded difference value DD(i, i-1) and the decoded and stored voltage value samples of the cycle of index (i-1).

[0178] During the previously described storing step 84 , the voltage samples decoded for the current cycle of index i are stored.

[0179] Advantageously, a distributed method for power calculation implements a compression / decompression that is used to obtain a good level of compression, including in the case of fluctuations in the electrical signal, and thus to reduce the power consumption of the various devices used.

[0180] Advantageously, the differential compression or double differential compression used is simple and serves to reduce the computational load.

Claims

1. A distributed system for measuring electric power in an electrical installation powered by a cyclic alternating electric signal, the system (2) comprising a device (4) for measuring voltage and at least one device (6) for measuring current remote from the device (4) for measuring voltage, The device (4) for measuring voltage is configured to acquire a predetermined number N of voltage samples per cycle of the electrical signal, Each device (6) for measuring current is configured to acquire N current samples in each cycle of the electrical signal, the device (4) for measuring voltage and the or each device (6) for measuring current are adapted to communicate according to a communication protocol, The system (2) is characterized in that: The device (4) for measuring voltage is configured to, during a transmission period comprising a plurality of consecutive cycles of the electrical signal: - for each cycle, encoding (30) the voltage samples to form a codeword and transmitting said codeword in a communication frame of said communication protocol to the or each device for measuring current, The or each device (6) for measuring current is configured as follows: - receiving at least two consecutive communication frames, each communication frame corresponding to one cycle of the electrical signal, - for each frame, determining (40) the decompression method to be applied and applying the decompression method to obtain N decoded voltage samples for the corresponding cycle, - Using the measured current samples and the decoded voltage samples, a series of N power values ​​corresponding to the cycle are calculated (42).

2. The system of claim 1, wherein the plurality of consecutive cycles comprises an initial cycle and a subsequent cycle, wherein: The device for measuring voltage is configured to apply differential compression to the voltage samples of each current cycle different from the initial cycle, the differential compression implementing, for at least two consecutive cycles, a sample-by-sample calculation of the difference between the samples of the current cycle and the samples of the previous cycle, the calculation of a number P of bytes encoding the difference, and the formation of a codeword of P bytes; The or each device (6) for measuring current is configured as follows: - Extracting codewords from each frame and determining the number of bytes received and, based on said number of bytes received, determining the decompression method to apply.

3. The system according to claim 2, wherein: For a series having a continuous first cycle and a second continuous cycle, the differential compression implements a sample-by-sample difference calculation between samples of the second cycle and samples of the first cycle for compression of samples of the second cycle so as to form a series of difference values ​​to be encoded.

4. The system according to claim 2 or 3, wherein: For a series comprising a first cycle, a second cycle and a third cycle in succession, the differential compression is performed on the compression of samples of the third cycle: - a sample-by-sample first difference calculation between the samples of the third cycle and the samples of the second cycle to form a series of first differences, - a sample-by-sample second difference calculation between the samples of the second cycle and the samples of the first cycle to form a series of second differences, - calculating the differences between the series of first differences and the series of second differences to form a series of difference values ​​to be encoded.

5. The system according to any one of claims 2 to 4, wherein: The device for measuring voltage is further configured to determine a minimum value and a maximum value in the series of difference values ​​to be encoded, and then determine a number B of bits for encoding each of the series of difference values ​​according to the minimum value and the maximum value.

6. The system according to claim 5, wherein: The device for measuring voltage is further configured to determine a gain value according to the minimum value and the maximum value in the series of difference values ​​to be encoded, and to encode the gain value.

7. The system according to claim 5 or 6, wherein: A coding table is pre-stored by the device for measuring voltage and the or each device for measuring current, which indicates, for each of multiple intervals of difference values, the number of bits B and the associated number of encoded bytes P used to encode each of a series of difference values ​​to be used for the interval.

8. The system according to claim 7, wherein: For determining the decompression method to be applied, the or each device for measuring current determines whether the received number of bytes belongs to the encoding table and, in the event of a positive response, determines the number of bits B used to encode each of the series of difference values.

9. A system according to any one of claims 2 to 8, wherein: For the initial cycle, each voltage sample has an amplitude value and a phase value, which are encoded to form a codeword.

10. A distributed method for measuring electric power in an electrical installation, implemented by a distributed system for measuring electric power according to claims 1 to 8, comprising steps implemented by an electronic computing unit of a device for measuring voltage, comprising encoding (56, 58-62, 55-59) voltage samples to form a codeword during a transmission period comprising a plurality of consecutive cycles of said electrical signal, and transmitting (64) said codeword to said or each device for measuring current in a communication frame of said communication protocol, and comprises the steps implemented by at least one electronic computing unit of a device for measuring electric current: - receiving (70) at least two consecutive communication frames, each communication frame corresponding to one cycle of the electrical signal, - for each frame, determining (72-75) the decompression method to be applied and applying (76, 78-82, 81-87) said decompression method to obtain N decoded voltage samples of the corresponding cycle, - Calculate (86) a series of N power values ​​corresponding to the cycle using the measured current samples and the decoded voltage samples.

11. A software program comprising a first software program comprising code instructions and a second software program comprising code instructions, which implements the method for measuring electrical power in an electrical installation according to claim 10 when the first software program is executed on a device for measuring voltage and the second software program is executed on at least one device for measuring current.

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