~k ~k ~k

This description relates to the technical field of electricity distribution networks and refers in particular to a method and a device for monitoring the electrical power consumption of a domestic electric network.

An interface device is known that is connectible to a domestic electric network and able to communicate with the electronic energy meter of the domestic electric network by powerline communication to acquire power consumption data and display power consumption values for example on a display of the device itself or an external device such as a personal computer or smartphone .

The purpose of the above described type of interface device is to provide a user with data of the power consumed by the domestic electric network, the knowledge of which is particularly useful for user so that he can activate a large loads, such as a washing machine or iron, in such a way as to avoid the automatic disconnection of his domestic electric network from the distribution grid by the electronic energy meter when the power consumed exceeds a certain threshold value. A device of the type described above can also improve the user's awareness of his consumption, leading to energy savings. The known type of interface device, existing both in a version with plug for connection to a common electrical socket and in a version mountable on a DIN rail in an electrical panel, comprises a communication module to communicate with the electronic counter using powerline communication and a control module adapted to control the communication module so as to poll the electronic energy meter at a predetermined fixed frequency to acquire power values .

The interface device comprises a USB port for connection to a personal computer, on which a program is installed that processes the acquired values to calculate power consumption values and that displays the power consumption values.

The frequency of polling of the electronic energy meter by the interface device cannot be too high because the powerline communication band of a home network is typically limited. Consequently, the power consumption data provided through the interface device may not be updated with sufficient speed. In other words, in case of sudden actuation of large loads, the interface device would not be able to inform the user in time to prevent the disconnection of the domestic network. The same problem could occur if the electronic energy meter and the interface device communicate with each other on a communication channel other than powerline communication, for example, if such a channel were shared channel and/or a channel with band limitation requirements. Moreover, in other cases also, whether or not independently of the need to reduce the use of a shared communications channel, there may be the need to contain or, in general, optimise the number of polls of the electronic energy meter, for example to optimise the computing/communication resources of the electronic energy meter.

WO2009/013762 describes a controller that reads the instantaneous parameters of a meter at regular intervals and analyses the data to identify abnormal conditions. Once an abnormal condition is identified, the controller searches for some time more for the existence of the anomaly and when a fixed time has elapsed sends a text message to the base station with the instantaneous parameters. WO2011/050212 describes a power node for energy management. Both the aforementioned documents describe solutions with a fixed polling frequency that, as such, must be selected from a compromise between the available bandwidth resources and the required accuracy.

The purpose of the present invention is to provide a method for monitoring, in real time, the electrical power consumed by the domestic electric network that overcomes, or at least reduces, the drawbacks described above with reference to the prior art interface device.

According to the present invention a method and a device are provided for monitoring the electric power consumption of a domestic electric network according to the annexed claims.

According to its more general embodiment, the method for monitoring the electrical power consumed by a domestic electric network comprising an electronic energy meter connected to an electrical power distribution grid, comprises the steps of:

- periodically polling, according to a first polling period, the electronic energy meter on a communication channel by means of a device, in order to receive, at every polling instant, information comprising at least one parameter related to a power consumption measurement, such as, for example, the value of active power or voltage and current values, carried out by the electronic energy meter;

- calculating on-board the device an estimate of said power consumption measurement or obtaining said power consumption measurement on-board the device;

comparing said estimate or measurement of power consumption with at least a first threshold value;

increasing the polling frequency if said power estimate or measurement is higher than, or equal to, said first threshold value. According to its more general embodiment, the device is operatively connectable to an electronic energy meter to monitor the electric power consumed by a domestic electric network comprising said electronic energy meter. The device comprises a communication interface for communication with the electronic energy meter on a communication channel. The device comprises a processing and control unit operatively connected to the communication interface. The device is configured and programmed to poll the electronic energy meter on said communication channel in order to receive at each polling instant information comprising at least one parameter related to a power consumption measurement performed by the electronic energy meter.

The processing and control unit is configured for: - calculating on-board the device an estimate of said power consumption measurement or obtaining said power consumption measurement on-board the device;

- comparing said estimate or said power consumption measurement with at least a first threshold value;

- increasing said interrogation frequency if said power estimate or measurement is higher than, or equal to, said threshold value.

The method and the device described above on a general level will be described below in greater detail with reference to the accompanying drawings, which illustrate a non-limiting implementation example, in which:

Figure 1 schematically illustrates an electric network and an example of a device connected to said domestic electric network for monitoring the electric power consumed by said domestic electric network;

- Figure 2 illustrates an example of division into power bands that is adopted in a possible embodiment of the method of this invention to monitor the electric power consumption of the domestic electric network; and

- Figure 3 illustrates an example of division into power bands and sub-bands that is adopted in a possible embodiment of the method of this invention.

In Figure 1, reference number 1 indicates a domestic electric network, which comprises an electronic energy meter 2 connected to the electrical distribution grid and at least one power outlet 3, for example bipolar or tripolar. To the electric network and in particular to the power outlet 3 is preferably connected, i.e., electrically interconnected, a device 5 for monitoring the power consumption of the electric network 1. It is clear that the electric network 1 also comprises one or more loads not shown in the figures, for example based on the appliances connected to the electric network 1 and activated/deactivated by the user.

The device 5 comprises a box-like container 6, in the non-limiting example comprising a power plug 7 adapted to be coupled to the power outlet 3. According to a preferred and not limiting embodiment, the device 5 preferably comprises, housed in the box-like container 6: a communication interface 8 for the powerline communication with the electronic energy meter 2, a coupling circuit 9 for connecting the communication interface 8 to the power plug 7, a user interface 10, a processing and control unit 11 provided with an internal memory and interfaced with the communication interface 8 and with the user interface 10, two USB sockets 12 and 13 connected to the processing and control unit 11 and a power supply module 14 with its own input directly connected to the power plug 7 to electrically power the communication interface 8 and the processing and control unit 11.

In an alternative embodiment, the communication interface 8 could be a radio communication interface, for example a Bluetooth or Wi-Fi communication interface. In the rest of this description, for the sake of simplicity of description and without thereby introducing any limitation, reference will be made to the case in which the communication interface 8 is a powerline communication interface and that therefore the communication between the device 5 and electronic energy meter is a powerline communication on the domestic electric network, which is therefore also a communication channel between the device 5 and the electronic energy meter 2.

The user interface 10 preferably comprises a button

15, and two LEDs 16 and 17 controlled by the processing and control unit 11 to signal the operating status of the device 5, for example to signal that pairing has occurred between the device 5 and the electronic energy meter 2.

The USB socket 12 is for example provided to receive a

USB type A connector and is used to connect the device 5 to an additional device, for example a wireless network interface device, for example Wi-Fi or Bluetooth. The USB socket 13 is for example provided to a USB mini-B type connector and is used for connection of the device 5 to a personal computer.

The processing and control unit is configured for:

- calculating on-board the device an estimate of said power consumption measurement or obtaining said power consumption measurement on-board the device;

- comparing said estimate or said power consumption measurement with at least a first threshold value;

- increasing said polling frequency (i.e., decreasing the polling period Tq) if said power estimate or measurement is higher than, or equal to, said threshold value .

According to an embodiment, the processing and control unit 11 is also configured for:

comparing said power consumption estimate or measurement with at least a second threshold value;

- decreasing said polling frequency (i.e., increasing the polling period Tq) if said power estimate or measurement is lower than, or equal to, said second threshold value.

In this way, the polling frequency can be advantageously increased if power consumption increases and decreased if instead power consumption decreases. By providing a plurality of thresholds, it is possible to establish a plurality of estimated or measured power consumption reference bands and associate a respective polling frequency to each band.

The power measurement can be provided directly by the electronic energy meter, or calculated on board of the device 5 starting from at least the aforesaid parameter provided by the electronic energy meter following polling by the device 5, or it can be estimated by the device 5. In this latter case, the device 5 can, for example, as will be described below, calculate power estimates between two successive pollings of the electronic meter 2 and perform a faster adjustment of the polling frequency by using said estimates. The examples that will be described below will refer to this latter case, it being understood that the teachings of this description are also extended to the previous two cases, i.e., the case in which a power consumption estimate is not made between two successive pollings and, therefore, a fine adjustment of the polling frequency is not made in a plurality of instants comprised between two successive pollings.

According to an advantageous embodiment, in order to obtain an estimate of the power consumption measurement between two successive pollings, and therefore both a fine adjustment of the polling frequency and a more frequent monitoring of the power consumption, the device 5 comprises a voltage measurement circuit 18, which has:

- an input connected to the electric network 1, for example through the power plug 7, for measuring the electrical voltage of the domestic electric network 1 in the point of the network (for example at the power outlet 3) to which the device 5 is connected;

- an output connected to the processing and control unit 11 to provide the measured voltage values to it.

The voltage measurement circuit 18 can be made in a manner in itself substantially known. According to a first embodiment, the voltage measurement circuit 18 includes a shunt resistor, which is connected in a known manner to the input of an analogue/digital converter of the processing and control unit 11. According to a second embodiment, the voltage measurement circuit 18 comprises an integrated circuit of known type based on a transistor element.

According to the invention, the processing and control unit 11 is programmed and configured to implement the following method for monitoring the electric power consumption of the domestic electric network 1.

The device 5 periodically polls the electronic energy meter 2 to receive at each polling instant information useful to obtain or calculate first voltage values and first current values. This information comprises at least one parameter related to a consumption measurement performed by the electronic energy meter 2. According to an embodiment, said at least one parameter comprises a power value, for example, active power, measured by the electronic energy meter 2. In this case the device 5 is such as to calculate or determine for each polling a respective first voltage value and a respective first current value starting from said measured power value. According to an alternative embodiment, said at least one parameter comprises a current value and a voltage value measured by the electronic energy meter 2, thus in this case the device 5 obtains the first current values and the first voltage values directly from electronic energy meter 2.

The polling period Tq with which the device 5 polls the electronic energy meter 2 has a value comprised between 1 minute and 60 minutes in such a way that the band (limited) of the powerline communication transmission channel does not hinder the communication between the device 5 and electronic energy meter 2.

The sampling through the voltage measurement circuit 18, takes place according to a fixed or variable sampling period Ts less than the polling period Tq and allows the device 5 to obtain second voltage values. It is clear that such second values are obtained from the device 5 in an autonomous way with respect to the electronic energy meter 2, i.e., without polling the electronic energy meter 2, but by sampling the network voltage directly. Advantageously, to simplify the implementation of the method, the voltage at the power plug 7 is sampled synchronously with the polling of the electronic energy meter 2 and with a sampling period Ts of a value equal to an integer sub- multiple of the polling period value Tq.

According to an embodiment, at the i-th polling instant the power value Pcei measured by the electronic energy meter 2 value is read, for example an active power value, or a first voltage value and a first current value.

Assuming that the difference between the detected voltage across the electronic energy meter 2 Vcei, and that read by the voltage measurement circuit 18 Vdevi is negligible, then:

Vcei = Vde i

Therefore it is assumed:

We define

Alcei = Ice± - Icei-i

where i and i-1 indicate two consecutive polling instants of the electronic energy meter 2.

According to an embodiment, in an initial step of the monitoring method, as soon as the value of Alcei, which represents a current variation between two successive pollings of the electronic energy meter 2, exceeds a certain threshold value ItO, the first current values Icei and the first voltage values Vcei are used by the device 5 to obtain a resistance, indicated below by Req, which is indicative of the equivalent resistance seen by the electronic energy meter 2 towards the electrical power distribution grid. The threshold value ItO is, for example, between 2A-8A, extremes included.

More in detail, at each polling instant (i-th polling instant) in which the value Alee exceeds the threshold value ItO, the processing and control unit calculates an instantaneous resistance Reqi as the ratio between the absolute value of a variation between the last two voltage values and a variation between the last two current values provided directly or indirectly by the electronic energy meter 2 , i.e.,

Reqi = I AVce _± | / | AIce _± |

where

AVcei = Vcei - Vcei-i

Alcei = Ice± - Icei-i.

Preferably, the equivalent resistance Req is calculated as the sliding window arithmetic average of the instantaneous resistances Reqi as these are progressively calculated. The sliding window used for the calculation of the arithmetic average has an amplitude comprised, for example, between 100 and 400 samples.

The voltage and current values are directly provided by the electronic energy meter 2 in the case in which the meter 2 is such as to measure said values and provide them in output following the pollings performed by the device 5. In this case, the device 5 obtains on-board the first current values and first voltage values directly from the electronic energy meter 2.

The voltage and current values are indirectly provided by the electronic energy meter 2 in the case in which the meter 2 is not such as to measure said values and/or provide them in output following the pollings performed by the device 5 and in the case in which it is the device 5 that calculates such values starting from information provided by the electronic energy meter 2. In this case, the device 5 is such as to calculate on board for each polling a respective first voltage value and a respective first current value starting from at least one parameter related to a consumption measurement made by the electronic energy meter 2. As already explained, according to an embodiment, said at least one parameter comprises a measured power value, for example, active power.

The intermediate data for the calculation of the sliding window arithmetic average are preferably stored in the memory of the processing and control unit 11.

For each sampling instant of the network voltage by the voltage measurement circuit 18 (j-th sampling instant), the voltage variation AVdevji is calculated as the difference between the voltage value read at that sampling instant (j-th polling instant) and the voltage value read at time of the last polling of the electronic energy meter 2 (i-th polling instant), and a current variation AldeV _j i as the ratio between said voltage variation AVdevji and the equivalent resistance Req, i.e.:

AVdeV _j i = Vdev _j - Vdevi

AldeV _j i = - AVdeV _j i/Req,

where the j-th sampling instant is comprised between the i-th polling instant and the i+l-th polling instant.

An estimated value of power consumed or absorbed by the domestic electric network 1 between two consecutive pollings, i.e., at the j-th sampling instant between the i- th polling instant and the i+l-th polling instant, is obtained with the following formula:

PL _j i = (Vcei + AVdeV _j i) -(Icei + Aldev _j i) ,

where Vcei and Icei are first voltage and current values, i.e., the values obtained or calculated by the device 5 thanks to the polling of the electronic energy meter 2 at the i-th instant. In reality, the voltage variations AVdevji also comprise random components that are not due to the connection or disconnection of a load in the domestic electric network and are, for example, due to the switching on or off of a load upstream of the electronic energy counter 2. These random components introduce some error in the calculation of the estimated power consumption value PL _j i, this error, however, being cancelled at each sampling carried out at the polling instants of the electrical energy meter 2. In fact, at the polling instants, the voltage variations AVdevji, and consequently the current variations Aldevji, are null by definition.

According to an advantageous embodiment, to reduce the noise contribution between two successive pollings of the electronic energy meter 2, a moving average <PL _j i> is performed on a given average time interval Tav of the estimated power consumption values PL _j i. For example, Tav is comprised in the range of 10-30 seconds, extremes included.

For example, the estimated power consumption values PL _j i or the averages <PL _j i>, calculated at each sampling step according to the period Ts are made available to the USB sockets 12 and 13 so that they can be acquired and processed by an appropriate program installed on a personal computer in order to display the power consumption data and/or generate audio and/or visual alarms in relation to such data. Henceforth, for simplicity of description, reference will be made to the estimated power consumption values PL _j i both in the case in which these values are not average and when these values are averaged to reduce noise, as described above.

According to an embodiment of this invention, the polling period Tq of the electronic energy meter 2 is regulated by the device 5 as a function of the estimated power consumption values PL _j i so as to increase the accuracy of the estimate of the power consumed in the most critical situations. In particular, the polling frequency is progressively increased with as the estimated power consumption values PL _j i increase, since the closer the power is to the threshold value that causes automatic disconnection, the more critical the situation becomes and, thus, the power is estimated with greater precision.

More in detail, in the above embodiment, the power range that can be supplied by electronic energy meter 2 is divided into several power bands by means of a certain number N of power threshold values, each of which is associated with a respective hysteresis interval. Therefore, the number of power bands is equal to N+l. The k-th power band in which said estimated power consumption values PL _j i are found is identified by the device 5 on the basis of a comparison between the estimated power consumption PL _j i and the N threshold values. Preferably, this comparison is performed by the device 5 at each sampling step to allow a quick adjustment of the polling period Tq.

Figure 2 illustrates an example with 3 threshold values (N=3), indicated with PI, P2 and P3, which divide the power range into four power bands.

According to a possible embodiment, to each power band is associated an initial polling time tqO _k (or "first polling time"), where k is the band index comprised between 1 and N+l, which consists of the time that must elapse from when the estimated power consumption value PL _j i enters the k-th band as a result of an increase in power (transition from the k-l-th band to the k-th band) before performing the first polling of the electronic energy meter 2 in the k-th band. Preferably, the above logic is not applied in the case of a decrease of the estimated power consumption towards a lower band, since the decrease in the estimated power consumption is considered a moving away from the critical situation. According to an advantageous embodiment, the value of the first polling times tqO _k decreases passing from the lowest power band (k=l) to the highest power band (k=N+l) :

TqO _k+1 < TqO _k .

Moreover, to each power band is associated a respective value Tq _k of the polling period in such a way that when the estimated power consumption value PLji enters the k-th power band, the polling period Tq is adjusted to the related value Tq _k , i.e., Tq=Tq _k . The values Tq _k assigned to the polling period Tq upon entering a power band decrease, passing from the lowest power band (k=l) to the highest power band (k=N+l) :

Tq _k+ i < Tq _k .

The values Tq _k are for example comprised between a minimum value of 10 minutes for the highest power band up to a maximum of 60 minutes for the lowest power band.

As long as the estimated power consumption values PL _j i remain in the k-th band, the electronic energy counter 2 is polled according to the respective polling period Tq=Tq _k .

According to a further embodiment of this invention, each of the N power bands below the highest threshold value (N-th) is divided into two related sub-bands of equal amplitude by a related further threshold value. Therefore, the number of power sub-bands is equal to 2N.

Figure 3 illustrates the sub-bands in the same example of bands (N = 3) of Figure 2.

To each of the sub-bands is associated a respective value Tq _kz of the polling period, where k is the band index comprised between 1 and N and, within the k-th band, z is the sub-band index, which is 1 or 2. The values Tq _kz for k comprised between 1 and N of the embodiment of Figure 3 replace the values Tq _k of the same index k of the embodiment of Figure 2. The values Tq _kz of the polling period decrease passing from the lower sub-band of the first band (k=l) to the upper sub-band of the penultimate band (z=N) . The value Tq _N+ i associated to the last band is smaller than the values of Tq _kz of all the sub-bands (k comprised between 1 and N) .

The values Tq _kz are for example comprised between a minimum value of 10 minutes for the highest power band up to a maximum of 60 minutes for the lowest power band.

The presence of the sub-bands allows further optimising the frequency of polling the electronic energy meter in order to increase it only in the most critical power situations that could lead to a disconnection of the electronic energy meter 2. To two sub-bands belonging to the same band k, is preferably associated the same first polling time T _0k -

There are further possible embodiments, complementary to those already described, that allow further optimising the polling of the electronic meter, which will be described below.

According to a first further embodiment, the polling of the electronic energy meter 2, occurs in correspondence of a power variation greater than a determined fixed value. More in detail, for example, the average value of the average values <PL _j i> is calculated using a number of Lv of previous average values <PL _j i>. This average value is indicated with <<PL _j i>> and stored for later processing. Then, the difference A<PL _j i> between <PL _j± > And <<PL _j i» is calculated .

A<PL _j i> = <PL _j i> - «PL _j i».

Two counting variables, m and d are defined and initially set to 0

m, d = 0.

If the difference A<PL _j i> is greater than the pre-set power value PV (e.g., 1000 W) or less than the pre-set power value PN (e.g., -500 W) , the counting variables m and d are set to one and zero, respectively.

If A<PL _j i> > PV or A<PL _j i> < PN then

m = 1; d = 0

At each sampling instant q > j, the difference A<PL _j i> between <PL _j i> And <<PL _j i>> is calculated.

A<PL _qi > = <PL _qi > - «PL _j i».

If A<PL _q i> is greater than the pre-set power value PV or less than the pre-set power value PN, the counting variables m and d are set to zero. If neither of these conditions has occurred, d is increased by one. Therefore: If A<PL _qi > > PV or A<PL _qi > < PN then

d = 0

else d = d+1

If the value of d exceeds a pre-set value DMAX, m is set to zero, i.e., it is reset. Otherwise, m is increased by one .

If d > DMAX Then

m = 0

else m = m+1

If m assumes the pre-set value MMAX, m is set to zero, d is set to zero, and at the next processing instant the electronic energy meter 2 is polled. Therefore:

If m = MMAX then

m = 0; d = 0

polling meter at instant

According to a second further embodiment, complementary to the first further embodiment described above, the polling of the electronic energy meter 2, takes place in correspondence to the detection of a difference between the local maximum <PL> _max and the local minimum <PL> _min of the power curve <PL _j i> greater than a pre-set amount. More in detail, the average power value <PL _j i> and the value <PL _j _i _{; ±} > related to the preceding sampling instant are compared.

If <PL _j i> is greater than <PL _j _i, i>, the trend is increasing, otherwise it is decreasing.

If the trend detected at instant j differs from that detected at instant j-1, the difference APL is calculated APL = <PL> _max -<PL> _min .

If this difference is greater than a pre-set value LTMAX, at the next processing instant the electronic energy meter 2 is polled. If the trend detected is increasing, the value <PL _j i> is stored in the variable <PL> _max . If the trend detected is decreasing, the value <PL _j i> is stored in the variable <PL> _min .

According to a third further embodiment of this invention, combinable with the first further embodiment of embodiment described above and/or with the second embodiment described above, to each power band is associated a minimum polling time TM0 _k , where k is the band index comprised between 1 and N+l. This minimum polling time indicates the minimum time interval that must elapse between two successive pollings of the electronic energy meter 2. The value of the minimum polling times tqO _k decreases passing from the lowest power band (k=l) to the highest power band (k=N+l) :

TmO _k+ i < TmO _k .

Although the invention described above makes particular reference to very specific embodiments, it should not be considered limited to these examples, since its scope includes all those variations, modifications or simplifications that would be evident to an expert in the field, such as for example implementation in a device mountable on a DIN rail and connectible at a point of the electric network immediately downstream of the electronic energy meter 2 by means of appropriate connection terminals .