GB2585883A

GB2585883A - Control of local injection of power in a power over cable system

Info

Publication number: GB2585883A
Application number: GB1910363.9A
Authority: GB
Inventors: Merlet Hervé; Lagrange Pascal
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2019-07-19
Filing date: 2019-07-19
Publication date: 2021-01-27
Also published as: GB201910363D0

Abstract

A method concerns controlling local power injection at a first powered device PD3 connected to at least one second powered device PD2, PD1 on a power segment 330 connected to a main power supply 320, which may be a power over cable system, such as Power over Ethernet (PoE) or Power over Coax (PoC) having a power sourcing equipment (PSE). The first device PD3 injects power in the power segment, the power being drawn from a local power source 315, and measures an electrical value such as current I3 at a port connecting the first device to the segment. Upon determining, based on the measured value, that the main power source does not currently supply power to the segment, the first device interrupts the injection of power, thereby allowing the reset of both the first and second PDs, such as when a software update is performed. The determination may involve comparing the measured value to a reference value, computed during an initialization phase and corresponding to the value when the main source does not supply power. The PDs may include analogue, IP or pan-tilt-zoom (PTZ) cameras, access points (AP), or VoIP phones.

Description

CONTROL OF LOCAL INJECTION OF POWER IN A POWER OVER CABLE SYSTEM

FIELD OF THE INVENTION

The present invention relates to a power over cable system. More specifically, the present invention relates to methods allowing the reset of a set of devices interconnected on a power segment despite the presence of a powered device locally injecting power among them.

BACKGROUND OF THE INVENTION

In power over cable systems, such as Power over Ethernet (PoE) and Power over Coax (PoC), one or more devices are powered over network cables by an item of power sourcing equipment.

The power sourcing equipment (PSE) is a device such as a network switch that is able to provide (i.e. to source) power on the network cable. A powered device (PD) refers to an apparatus that can be powered by the PSE and thus consumes energy when being powered. Examples of powered devices include analog cameras, IP cameras including pan-tilt-zoom (PTZ) cameras, wireless access points (AP), and VoIP phones.

Generally speaking, the power over cable technology allows removal of separate data cables and power supplies requirements which would otherwise be needed to power the devices. This allows for more time and cost efficient installation for installers. However, the power distribution over data cables suffers from limitations on the total power that can be carried, and from a significant power loss in the cables due to the relatively low carried voltage (e.g. a typical voltage being comprised between 48 and 56 V). As known in the art, the total power consumption on one network segment is the accumulation of the power consumption of each device and the power dissipated in the cable due to the resistivity of the cable (Joule effect).

In some situations, it may be of interest to have a local power supply at the PD level, in addition to the main power supply from the PSE.

For instance, in large-scale systems in which the cable length is long, the power loss due to the cable resistance may be such that the last device(s) connected on the power segment cannot receive enough power for normal operation. In this case, a local power supply may be advantageously provided at the last device(s) level to allow for normal operation.

In some applications such as video surveillance, the PDs run in continue without service interruption. However, sometimes there may be a need to reset a given set of PDs, for instance to perform some update of the software. In critical applications, the reset must be done in a very short time. For this purpose, the reset may be performed remotely by powering OFF and then powering ON the power supply of the port connected to the PDs to reset.

However, when power is also injected locally at a PD, the reset cannot be done in such a way, i.e. only by cutting the power at the PSE port, as the PD is additionally powered locally.

There is therefore a need to provide for a method allowing quick remote reset of PDs connected to a PSE port when additional power is locally supplied at the PD level.

SUMMARY OF THE INVENTION

The present invention has been devised to address at least one of the foregoing concerns.

According to a first aspect of the invention, there is provided a method of controlling local injection of power at a first powered device interconnected with at least one second powered device on a power segment on which a main power source is connected to supply power to the first and second powered devices, the method comprising, at the first powered device: injecting power in the power segment, the power being drawn from a local power source locally connected to the first powered device; measuring an electrical value at a port connecting the first powered device to 25 the power segment; upon determining, based on the measured electrical value, that the main power source does not currently supply power on the power segment, interrupting the injection of power by the first powered device thereby allowing the reset of the first and second powered device interconnected on the power segment.

Thanks to the first aspect, the reset of the first and second PDs interconnected on the power segment can be performed remotely and quickly by powering OFF and then ON the PSE port.

This is permitted by cutting the local injection of power when it is determined that power is not currently supplied by the PSE port on the power segment, which may mean that an operator tries to perform a remote reset on the power segment, by cutting the power supply from the PSE port.

According to a second aspect of the invention, there is provided a first powered device interconnected with at least one second powered device on a power segment on 5 which a main power source is connected to supply power to the first and second powered devices, the first powered device being configured to perform the following steps: injecting power in the power segment, the power being drawn from a local power source locally connected to the first powered device; measuring an electrical value at a port connecting the first powered device to 10 the power segment; upon determining, based on the measured electrical value, that the main power source does not currently supply power on the power segment, interrupting the injection of power by the first powered device thereby allowing the reset of the first and second powered device interconnected on the power segment.

The powered device according to the second aspect has the same advantages as the method according to the first aspect aforementioned.

Since the present invention may be implemented in software, the present invention may be embodied as computer-readable code for provision to a programmable apparatus on any suitable carrier medium, and in particular a suitable tangible carrier medium or suitable transient carrier medium. A tangible carrier medium may comprise a storage medium such as a floppy disk, a CD-ROM, a hard disk drive, a magnetic tape device or a solid state memory device or the like. A transient carrier medium may include a signal such as an electrical signal, an electronic signal, an optical signal, an acoustic signal, a magnetic signal or an electromagnetic signal, e.g. a microwave or RF signal.

Therefore, according to another aspect of the invention, there is provided a computer program product for a programmable apparatus, the computer program product comprising instructions for carrying out the method aforementioned when the program is loaded and executed by a programmable apparatus.

According to another aspect of the invention, there is provided a non-transitory 30 computer-readable medium storing a program which, when executed by a microprocessor or computer system in a device of a power-over-cable system, causes the device to perform the method aforementioned.

Optional features of the invention are further defined in the dependent appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Other particularities and advantages of the invention will also emerge from the following description, illustrated by the accompanying drawings, in which: Figures la, lb and lc illustrate examples of power over cable systems comprising a PSE and a plurality of PDs with local injection of power according to embodiments of the invention; Figure 2 is a flowchart illustrating general steps of a method according to embodiments of the invention; Figures 3a and 3b represent equivalent electrical diagrams of the power over cable system shown in figure la, at different steps of the method according to embodiments of the invention; Figure 4a is a flowchart illustrating steps of an initialization phase according to embodiments; Figure 4b is a flowchart illustrating steps of a control method according to embodiments of the invention; and Figure 5 is a time diagram showing the signals across the devices when implementing embodiments of the invention.

The same references are used across different figures when designating same 20 elements.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION Figures la, lb and lc illustrate examples of power over cable systems comprising a PSE as a main power source and a plurality of PDs with local injection of power from a local power source according to embodiments of the invention.

In these examples, the power over cable system comprises a PSE 120, a plurality of PDs 110, 111, 112, 113, 114 and 115. Network cables 130 and 131 connect, according to a linear bus topology, a plurality of PDs 110-115 to one port of the PSE 120. Each network cable and associated PDs form a power segment.

In the first example shown in Figure la, the PD 110 is also connected to a local power supply 116 from which it can receive power in addition to the power provided by the PSE port to which its power segment is connected. In this first example, the locally powered PD is the last one of the power segment, i.e. the last PD of the power segment receiving power from the PSE port.

In a second example shown in Figure 1 b, the PD 111 is connected to a local power supply 117 from which it can receive power in addition to the power provided by the PSE port to which its power segment is connected. In this second example, the locally powered PD is not the last one of the power segment. It can be any of the PD connected on the power segment.

In a third example shown in Figure lc, both PDs 110 and 111 are each connected to a local power supply 116 and 117 from which they can receive power in addition to the power provided by the PSE port to which their power segment is connected. In this last example, several PDs may receive additional power locally.

Embodiments of the present invention are not limited to these three examples, which are provided for illustration purpose only. The number of PDs may be different and there may be more than two PD connected to a local power supply.

Figure 2 is a flowchart illustrating general steps of a method according to embodiments of the invention. These steps are for instance performed by the locally powered PD 110 shown in Figure la or the locally powered PD 111 shown in Figure lb or one of the locally powered PDs 110 and 111 shown in Figure 1c.

In the following example, the locally powered PD performing the steps is referred to as the first PD while the other PDs of the power segment are referred to as second PDs.

According to general embodiments, the first PD drawn power from a local power source to which it is connected, as shown in Figures la to lc.

At step S201, the first PD injects power in its power segment 130.

At step S202, the first PD measures an electrical value at its port connecting to the power segment. This electrical value is for instance a voltage, current or tension.

At step S203, the first PD determines whether power is currently supplied by the PSE port (which is the main power source) on the power segment.

For instance, this may be done by comparing the electrical value measured with a reference electrical value determined during an initialization phase and corresponding to the electrical value measured at the PD port when the PSE port is OFF. In other words, the reference electrical value corresponds to a situation in which an operator tries to perform a remote reset on the power segment by cutting the power supply from the PSE port.

An example of implementation of this step is described in further detail with reference to Figures 3a and 3b.

If it is determined that power is currently supplied by the PSE port on the power segment, it means that the power segment is operating normally and that there is no tentative of reset by the PSE port currently.

Otherwise, if it is determined that power is not currently supplied by the PSE port on the power segment, it may mean that an operator tries to perform a remote reset on the power segment, by cutting the power supply from the PSE port. Therefore, the first PD interrupts the injection of power on the power segment at step S204 to allow the reset to be done.

Doing so, the reset of the first and second PDs interconnected on the power 10 segment can be performed remotely and quickly by powering OFF and then ON the PSE port.

One may note that in the case of Figure 1c where several first PDs of a same power segment receive additional power locally, a preliminary step is performed during which one first PD (called "master") determines the topology of the power segment before injecting power at step S201. For example, the master is choosen among the first PDs as the one located at the last position on the segment, i.e. at the bounds of which the lowest voltage is measured during the preliminary step.

During this preliminary step, all the first PD provide their electrical parameters (cable resistance, voltage, current, power, etc.) to the master first PD. In order to calculate the electrical parameters properly and therefore to limit the number of unknown variables in the electrical equation system, the first PDs may start one after the other according to a predetermined order. For instance, the order may be by increasing voltage value, these voltage values being measured before any power injection in the power segment. As the first PDs have provided their electrical parameters, the multi-injection of power can be taken into account during the calculation at step S203, which is performed by the master first PD. In function of the result of step S203, the master first PD may send the result of the determining step to the other first PDs so that they can cut their own injection of power if needed.

Figures 3a and 3b represent equivalent electrical diagrams of the power over cable system shown in figure la, at different steps of the method according to embodiments of the invention.

The equivalent electrical diagram shown in Figure 3a corresponds to the normal operating of the power over cable system.

The PSE port is here represented as a voltage source E (e.g. 56V). The cable 330 is represented here by its equivalent electrical diagram with serial resistors Rcl, Rc2 and Rc3 between each PD (or node) and the PSE port E. In this example, the current in the resistors Rc1, Rc2 and Rc3 are represented respectively by I', I" and I"'. The power consumption of the PD 1, PD 2 and PD 3 are represented respectively by the electrical currents 11, 12 and 13 and the voltages VI, V2, and V3. In this example, the PD 3 (which thus has the role of the first PD aforementioned) is powered by a local power supply 315, and injects the electrical current 13 on the power segment.

One may note that in this case, the value 1-= -13.

A preliminary calculation may be performed to evaluate the cable resistors Rc1, Rc2 and Rc3 between the devices and to deduce the topology of the cable segment, notably the position of the first PD (locally powered).

An exemplary implementation of this preliminary calculation is now provided.

First, a voltage measurement may be done across each PD to know V1, V2, and V3. One may thus know the classification V1 > V2 > V3. The value of the currents 11, 12, 13 may then be deduced from I = P / V where "P" is the power consumption of the PD. If needed the "Injector" PD3 switch-ON the Local power supply on the line. In this case, the current 13 becomes an output current. This current 13 is measured internally in the "Injector" PD 3. It is noted 13,0.

Next, the voltage operating point may be computed using these parameters. For this purpose, the PDs communicate their power characteristics and voltage measurements to the first PD ( PD 3 in this example). Power is then injected by the PD 3, such as V3 = E. Then, the value E is set as follows: [1] E = RCI * + RC2* I" + RC3* I"' +V3 As there is: I"' = -13 and V3 = E; Then from [1] we know that: [2] RC1 * + RC2* I" -RC3 * 13 =0 The cable resistance computation starts by the Rc3 calculation. As the PD power characteristic are known respectively: P1 = V1 *11 for the PD 1, P2 = V2 *12 for the PD 2, Then the values Rc1, Rc2 and Rc3 can be deduced as follows: [3] RC3 = [V3-V2] /13 As: 12 = 1" + 13 => 1" = 12 -13, Then: [4] RC2 = [V1 -V2] /1" As: l' =I" +II Then: [5] RC1 = [E -V1] / At this point, all the electrical parameters are known on this cable in the normal operating mode. The cable resistors Rc1, Rc2, Rc3, the current II, 12, 13, the voltages V1, V2, and V3 are thus known.

After the computing of the electrical values of the circuit in the normal operating mode (Figure 3a), the first PD performs calculation of these electrical values in case of a tentative reset by the PSE port by cutting the power supply from the PSE port (Figure 3b).

The equivalent electrical diagram shown in Figure 3b corresponds to an initialization phase during which the reference electrical value used at step S203 may be computed. It corresponds to a situation in which the PSE port is OFF. In other words, the reference electrical value corresponds to an electrical value measured at the first PD port when there is no power supplied by the PSE on the power segment. It also corresponds to the situation where an operator tries to perform a remote reset on the power segment by cutting the power supply from the PSE port.

Hence, during this phase, a prediction is done to evaluate the current excursion 13, 1 during the voltage drop on the PSE-port when E is cut-off.

For instance, the determination of the electrical operating point is such that: If E is OFF, then: 13,1 >13,0 With: V3 = RC3* (12,1 +11,1) + RC2 *11,1 + V1 13,1 = 11,1 +12,1 At this point the current 13,1 at the first PD port (here PD3) when the PSE port is OFF is known. Consequently, at step S203, when the first PD (here PD3) detects a current 13 equal or superior to the current 13,1, it may identify a situation in which the PSE port is OFF, meaning that there may be currently a tentative reset by shutting down power from the PSE port on the corresponding power segment.

For illustration purposes only, a numerical example is now provided.

For a PSE port voltage E = 56 volts, and Rc1 = 21 ohms corresponding to a RG9 coaxial cable of 300 meters, and Rc2, Rc3 = 6.8 ohms for a cable length of 100 meters each, for a camera consumption of 10 watts, the voltage across the camera 3 is 32 volt, and the camera 2 at 34 volts. This means a risk to have a power down of this camera, or a non-start. This is why the installer may put a local power supply to power the camera 3 but also to power the other cameras connected to the power cable. The injector PD may for instance inject a current value of 493 mA.

Then the computation of the extra current supply by the local injection is done in the case where the PSE-port cuts off the power supply on the power segment. The computation gives a current value of 626 mA, therefore the difference between the two currents is 133 mA.

Figure 4a shows steps of an initialization phase 400 according to embodiments, during which a locally powered PD (first PD) as computes the reference electrical value used at step S203 to determine whether the PSE port is OFF. These steps are for instance performed by the locally powered PD 110 shown in Figure la or the locally powered PD 111 shown in Figure 1 b or one of the locally powered PDs 110 and 111 shown in Figure lc.

At step S401, the main power source, i.e. the PSE port and the local power source are started and all the PDs start. The first PD, which is connected to the local power source, injects power on the power segment.

After the starting phase, the voltage is stabilized at step S402. The necessary time to have a stabilized voltage across the equipment items is around one minute for a video surveillance equipment, for instance.

Next, at step S403, the PDs may measure the voltage and the current at their own port with the power segment. The results of the voltage and current measurements may be recorded in the memory of each PD at step S404.

At step S405, the PSs communicate their measurement results and their electrical characteristics (i.e. their power consumption) to the first PD(s).

At step S406, the first PD(s) computes different electrical parameters (cable resistance, voltage, current) first in the normal operating mode, and then deduce(s) the reference values characterizing a tentative reset by the PSE port (i.e. where the PSE port voltage E = 0). The detailed calculation is described with reference to Figures 3a and 3b.

Next, at step S407, the first PD(s) are (is) ready to detect a tentative reset by cutting power from the PSE port.

Figure 4b is a flowchart illustrating steps 410 of a control method according to embodiments of the invention.

At first step S411, the first PD continuously (or by sampling) measures the output current at its port connecting the power segment.

At step S412, a comparison is done between the measured output current and the reference value (or threshold) previously determined. If the injected current increases up to a current level around the previously calculated reference value, the first PD detects a situation that may correspond to a tentative reset from the PSE-port at step S412. There may be a decision interval to determine if the measured current may correspond to a tentative reset. This interval depends on the precision of the calculation and the accuracy of the measurement.

Next, as a tentative reset mode may have been detected, the first PD stops to inject current in its power segment at step S413. Hence, the voltage across all the PDs becomes zero.

Finally, at step S414, each PD can be reset by the power-ON of the PSE port and / or the local injection of power by the first PD. Equally, the first PD can apply itself a hardware reset during the power shutdown. This hardware reset is not a power-reset because the injector PD is locally and permanently power supplied. This hardware reset is classically based on the watchdog system well known of the person skilled in the art. Figure 5 is a time diagram 500 showing the signals across the devices when implementing embodiments of the invention. In this example, it is assumed that only one PD of the power segment is connected to an additional local power supply. It corresponds for instance to the PD 110 shown in Figure 1a or the PD 111 shown in Figure lb. The time diagram 500 shows a first signal 501, which corresponds to the voltage across the PSE port. During the period 502, the power on the port is shut down (E = 0), and then the power is ON again (E = 56V). The duration of this period is for example one second (1 s).

The current I (signal 503) corresponds to the current across the PD locally connected to an additional local power supply. In practice, the PD needs some time to detect the PSE port power shut down. As described before, this detection may be based on the measurement of the current coming from 10 to the current increase up to 11 (signal 503) during the period 504. Additionally, this period 504 may allow to integrate the signal, i.e. to capture many measurement samples and then to calculate the average level of the signal, and therefore to filter the signal 503 to get rid of the ripple or other spurious.

According to embodiments, the PD stops the injection of the current 12 during a period 505 when a tentative reset has been detected. The voltage across the PD is thus at zero. Then the PD may inject again the current 13 at the instant 506, in the same time the PSE port may power-ON.

In practice, there is no need of a perfect synchronization between the two signals 501 and 503. This is because the power-ON phase is a transient phase and the behaviors of each devices during this starting phase may be different.

It should be noted that when a PD is shutdown in order to be removed from the system, the current measured by the locally powered PD decreases. Therefore, this situation can be distinguished from the detection of a tentative reset by the PSE port since in this latter case, the current measured by the locally powered PD should increase.

In case of such removal, the locally powered PD may update the new electrical values (in particular the reference electrical values used latter in the determination step S203) of the circuit by performing a new initialization phase.

Although the present invention has been described hereinabove with reference to specific embodiments, the present invention is not limited to the specific embodiments, and modifications, which lie within the scope of the present invention, will be apparent to a person skilled in the art. In particular, different features from different embodiments may be interchanged, where appropriate. Many further modifications and variations will suggest themselves to those versed in the art upon making reference to the foregoing illustrative embodiments, which are given by way of example only and which are not intended to limit the scope of the invention as determined by the appended claims.

Claims

CLAIMS1. A method of controlling local injection of power at a first powered device interconnected with at least one second powered device on a power segment on which a main power source is connected to supply power to the first and second powered devices, the method comprising, at the first powered device: injecting power in the power segment, the power being drawn from a local power source locally connected to the first powered device; measuring an electrical value at a port connecting the first powered device to the power segment; upon determining, based on the measured electrical value, that the main power source does not currently supply power on the power segment, interrupting the injection of power by the first powered device thereby allowing the reset of the first and second powered device interconnected on the power segment.
2. The method of claim 1, wherein determining that the main power source does not currently supply power on the power segment includes comparing the measured electrical value to a reference electrical value.
3. The method of claim 2, wherein the reference electrical value corresponds to the electrical value at the port connecting the first powered device to the power segment when the main power source does not supply power on the power segment.
4. The method of claim 2 or 3, comprising an initialization phase during which the reference electrical value is computed.
5. The method of any one of claims 2 to 4, wherein the reference electrical value is computed based on the cable resistance of the power segment.
6. A first powered device interconnected with at least one second powered device on a power segment on which a main power source is connected to supply power to the first and second powered devices, the first powered device being configured to perform the following steps: injecting power in the power segment, the power being drawn from a local power source locally connected to the first powered device; measuring an electrical value at a port connecting the first powered device to the power segment; upon determining, based on the measured electrical value, that the main power source does not currently supply power on the power segment, interrupting the injection of power by the first powered device thereby allowing the reset of the first and second powered device interconnected on the power segment.
7. The method of claim 6, wherein determining that the main power source does not currently supply power on the power segment includes comparing the measured electrical value to a reference electrical value.
8. The method of claim 7, wherein the reference electrical value corresponds to the electrical value at the port connecting the first powered device to the power segment when the main power source does not supply power on the power segment.
9. The method of claim 7 or 8, comprising an initialization phase during which the reference electrical value is computed.
10. The method of any one of claims 7 to 9, wherein the reference electrical value is computed based on the cable resistance of the power segment.
11. A computer program product for a programmable apparatus, the computer program product comprising instructions for carrying out the method according to any one of claims 1 to 10 when the program is loaded and executed by a programmable apparatus.
12. A non-transitory computer-readable medium storing a program which, when executed by a microprocessor or computer system in a device of a power-over-cable system, causes the device to perform the method of any one of claims 1 to 10.