Patent Grant
11121549
This application is the United States National Phase of PCT Patent Application No. PCT/FR2018/051776 filed on 13 Jul. 2018, which claims priority to French Patent Application No. 1756880 filed 20 Jul. 2017, both of which are incorporated herein by reference.
This invention concerns a power flow control device meant to be used in a mesh network. The invented device can particularly be used in a high voltage direct current mesh network.
A network is a set of overhead lines or cables hereinafter referred to as “links” which are meant to connect devices (or terminals) to each other in order for them to exchange energy. In a direct current network, the devices which supply or consume energy are generally electronic power converters called “converter stations”.
If the network is meshed, the current has several possible paths to go from one converter station to another. The currents in the links are distributed based on the characteristics of the links (this characteristic in direct current networks is the resistor of the link).
For example, on the network represented in
Each converter station can inject or extract power from the network. In this configuration, the currents (I1, I2, I3) in each link are not controlled by converter stations. In fact, each converter station imposes a specific voltage to the network and the node to which it is connected. While the current in each converter station is lower than its maximum current, it is possible to reach operating points where a link transmits current that is higher than its maximum current while other links in the network (which could be used to transfer energy) are under-loaded.
In an architecture such as that which is represented in
Its path will particularly be determined based on the values of the resistors of the links and the voltages imposed by the converter stations of the network.
Solutions have already been proposed by previous technical inventions to ensure a better distribution of the current in the links of a mesh network.
One solution which is by the way described in patent application WO2012/037957A1 consists in inserting an electronic power converter in order to modify the voltage at one end of a link.
Other solutions consist in inserting a voltage source in series with a link, as shown by the diagram in
Converters that add a voltage source in series with two alternating links have equally been described in applications EP3007301A1 and EP3007300A1. However, this type of structure has some limitations: the currents (IIN1 and IIN2 in these documents) must be of the same sign (Ic is equal to IIN1 and to −IIN2 alternately), the structure is not extensible to the case where more than two links are connected to the third link (IOUT) and generates more harmonics in operation.
Another solution described in patent application WO2013/178807A1 and diagrammatically represented in
This type of solution presents three levels of freedom while the system must satisfy only two constraints:
It therefore presents more levels of freedom than necessary and therefore turns out to be more complex than necessary.
The first purpose of the invention is to propose a solution which makes it possible to increase the transport capacity of such a mesh network and to avoid the congestion of links (current higher than the nominal current) without having to integrate new links.
The second purpose of the invention is to propose a power flow control device which serves the first purpose and is equally intended to be connected in a direct current mesh network, this device being:
The device of the invention will also be adapted to operate in an alternating current mesh network.
Presentation of the Invention
These two objectives are achieved by a power flow control device intended to be used in a DC mesh network, a mesh comprised of at least three nodes, each with a specific voltage and three links; the first link connecting the first node to the second node, the second link connecting the first node to the third node and the third link connecting the second node to the third node. The said device being described as having:
According to a particular design, the first voltage source shall comprise at least one capacitor.
According to a particular design, the second voltage source shall comprise at least one capacitor.
According to a particular design, the current source shall comprise at least one inductance.
According to a particular design, the afferent switching means shall comprise six switches:
According to a particular design, the inductance is connected between the first midpoint and the second midpoint.
According to a particular design, each switch is chosen according to the sign of the following parameters:
In which:
According to a particular design, the said switching means and the said current source are distributed in several identical conversion blocks, and in that it comprises a first conversion block connected separately to the first terminal, to the second terminal and to the third terminal.
According to a particular design, the device has a system for bypassing said device, controlled by said control means and comprising switching means arranged in parallel with each voltage source.
According to a particular design, the said bypass system includes means for discharging each voltage source.
The invention also relates to the use of the device as defined above in a DC mesh network, the said network comprising at least three nodes which are each at a determined voltage and three links; the first link connecting the first node to the second node, the second link connecting the first node to the third node and the third link connecting the second node to the third node.
Moreover, the device may be adapted to achieve other objectives, such as:
Other characteristics and advantages will be evoked in the detailed description which follows, made with reference to the appended diagrams in which:
The power flow control device of the invention is intended to be used in a mesh network, preferably a high voltage DC network. According to its configuration, it can also be used in an AC mesh network. It will be seen that such is the case when the switching means is comprised of reversible current and voltage power switches.
As already mentioned above in reference to
Each node is advantageously connected directly or indirectly to one or more converter stations. The converter station A is thus connected to the first node. The converter station B is thus connected to the second node of the network. The converter station C is therefore connected to the third node of the network.
Each converter station is intended to either inject power into the network or extract power from the network.
Each converter station is intended to either inject a current into the network or extract a current from the mesh network. For the converter station A, it is the current Ia, for the converter station B it is the current Ib and the current Ic for converter station C.
A voltage is imposed on each node by the station connected to the node. The voltage Va is applied to the first node of the network. The voltage Vb is applied to the second node of the network. The voltage Vc is applied to the third node of the network.
A first link 11 connects the first node to the second node. A second link 12 connects the first node to the third node. A third link 13 connects the second node to the third node.
Each link may be formed by an overhead line, a cable or any other means used to transport current.
As already described above, in a configuration where stations B and C provide energy on the mesh network and where station A receives this energy, the currents Ib and Ia can have two paths to get to station A.
With reference to
Of course, we must consider that the three terminals B1, B2, B3 are equivalent. The connection of the three terminals B1, B2, B3 of the device to the three links 11, 12, 13 respectively is therefore unlimited. The device can be inserted into the network so as to connect its terminals to the links differently. Given that the device has three terminals and that the network has three links, there will thus be six permanent connection configurations of the device in the network.
The said control means 21 are not detailed in the present application. They advantageously include a processing unit intended to generate control signals for alternating control and optionally control units (“drivers”) adapted to the switching means used. These control means advantageously form part of the device 20 of the invention.
The first voltage source may have at least a first capacitor C1 having a determined capacity.
The second voltage source may have at least a second capacitor C2 having a determined capacity.
The current source may include an inductor L.
The switching means shall particularly have one or more electronic power switches.
The two capacitors C1, C2 are both connected to the third terminal B3 of the device 20 and have their other terminal connected respectively to the first terminal B1 and to the second terminal B2 of the device so as to connect to the two links 11, 12 whose currents we want to control (I1, I2).
In an alternate design, one of the two capacitors (C1, C2) could be connected between the terminals B1 and B2 while the other capacitor would remain connected between terminals B1 and B3 or B2 and B3.
The composition of the electronic power switches and their positioning depends on the signs of the currents (I1 and I2) which circulate in the links on the one hand, and on the sign of the voltage (Vx=V1−V2) which must be inserted in the mesh whose current wants to be controlled on the other hand. The structure of the switching means is therefore chosen based on the network in which the device will be inserted and the expected operating points.
The three conversion blocks are identical and each of them has at least an inductor and a switching means. The architecture of each conversion block and their association in the device makes it possible in particular to carry out all the layouts which will be described below, to meet the needs of all possible operating cases or requirements.
This modular architecture with several identical conversion blocks makes it particularly possible to ensure operation in degraded mode if a block is faulty and to reduce manufacturing costs with the production of a particular converter by combining elementary converters produced in series.
Furthermore, this architecture, thanks to the command option, presents certain advantages in terms of oscillations in the currents in the links and in the voltages across the capacitors. It is therefore possible to easily shift the commands of the conversion blocks 200, 201, 202 from one to another (N controlled blocks with a period T with orders shifted of T/N). It is also possible to couple the inductances (on the same magnetic circuit) of the conversion blocks, making it possible to limit the number of magnetic circuits used.
In the continuation of the description and the accompanying diagrams, a transistor should be understood as being either a single transistor or several transistors placed in series and/or in parallel to ensure the operation of the device. It is the same for each diode which could equally be a group of several diodes connected in series and/or in parallel, or each capacitor which could be a group of several capacitors connected in series and/or in parallel.
In a bipolar network or in a symmetrical monopolar network, the structure of the proposed device is to be installed on the two poles.
In the most general architecture of the device, as presented in
In this general architecture, the inductance L is connected between the first midpoint and the second midpoint.
Each switch of the switching means can then be chosen according to the sign of the following values:
The signs of these values define what is hereinafter referred to as an “operating case”. Moreover, some switches specified in the general architecture can be deleted (open circuit) depending on the number of operating cases desired.
With reference to
In each operating case, the switches S1 to S6 are chosen according to a particular design in order to respond to the expressed need. In a non-exhaustive and unrestricted way, each switch will then be chosen based on one of the layouts listed below:
A first series of designs presented below relates to the fact that the currents I1 and I2 are always of identical signs.
In this layout, we have:
In the
The transistor T is controlled on closing with a duty cycle α. When the transistor T is on, we have VL=V1. When the transistor is open, with the assumption that the current in the inductance never vanishes, the diode D is on, we have V1=V2. In a steady-state, the average voltage at the terminals of the inductance which is expressed as aV1+(1−α) V2 must be zero. V1 and V2 are therefore of different signs.
With the average current in the capacitors being zero in a steady-state, the average of IL is therefore equal to I. The average current in the transistor is equal to I1 and α IL and therefore to I1=α I. Similarly, we have I2=(1−α) I. The duty cycle α therefore makes it possible to adjust the distribution of the current I in the connections 11 and 12, which is the expected effect.
For this case, the positions of the transistor and the diode are exchanged. The operating principle is the same as in the previous case.
It is a simple adaptation of the previous cases.
It is a simple adaptation of the previous cases.
For this need, the switches must be voltage reversible. Thus, we will use transistors in series with diodes (as shown in
It is an adaptation of the previous operation case.
In this case, the switches are current-reversible but not voltage-reversible. We will use field effect transistors possibly in parallel with diodes or IGBT type transistors in parallel with diodes or GTO type transistors (possibly asymmetrical) in parallel with diodes or IGCT type transistors (possibly asymmetrical) in parallel with diodes.
It is an adaptation of the previous operation case.
For this need, we will use voltage and current reversible switches (placed in series and parallel to transistors and diodes or antiparallel to GTO, IGCT or connected in series in opposition to MOSFETs).
A second series of designs presented below relates to the fact that the currents I1 and I2 are always of different signs.
In this operation case, we then have the following configuration:
For this design, a possible control mode is as follows. Transistors T1 and T2 are simultaneously controlled at the closing with a duty cycle α. When the transistors are closed, the voltage VL is then equal to V1. Assuming that there is continuous conduction (IL is never zero), when the transistors are controlled at the opening, the diodes start conducting, the voltage VL is then equal to −V2. The average voltage across the inductor is aV1−(1−a) V2.
In steady-state, this voltage is zero on average. We therefore have:
V1=(1−a)/aV2.
The voltages V1 and V2 are therefore of the same sign (necessarily positive considering the switches chosen here) and the voltage inserted in the network mesh is:
Vx=V1−V2=(1−2a)/(1−a)V1=(1−2a)/aV2
This voltage therefore changes sign depending on whether a is greater than 0.5 or not.
In steady-state, the average current in the capacitors is zero. The average current in the transistor T1 (which is transmitting a fraction of a in the period) is equal to I1 (actually I1/α when conducting and 0 the rest of the time). When the transistor T1 is conducting, the current flowing through it is equal to IL. We therefore find that I1/0 and IL are equal. Similarly, −I2/(1−α) and IL are equal. We therefore have:
I1=aI2/(1−α)
This last result clearly shows that the currents I1 and I2 must therefore be of opposite signs.
Since I=I1+I2, we deduce that:
I1=−(1−2α)/αIand I2=(1−2α)/(1−α)I
It can therefore be seen that the adjustment of the duty cycle a makes it possible to adjust the distribution of the current I between the links 11 and 12, which is the expected effect.
We also note that current I (current in converter station A) can change sign even if the direction of the current in links 11, 12 does not change. The design presented here works for V1, V2, I1 positive and I2 negative, with the value of a enabling the distribution of the current of the converter station between links 11 and 12. The current I in the converter station A and the voltage inserted in the mesh Vx can change sign but we must always have I/Vx<1 (signs of any value but different) because Vx=(1−2α)/αV2 and I=−α/(1−2α) I1 and the switches were chosen for V2>0 and I1>0. Therefore:
The operating principle is the same as in the previous case. It is just a question of swapping indices 1 and 2 of the different parameters.
The operating principle is the same as in the two previous cases, except that V1 and V2 are negative.
It is an adaptation of the previous design.
The operating principle is the same but V1 and V2 change sign depending on the voltage Vx inserted. Voltage reversible switches are therefore chosen.
It is an adaptation of the previous design.
In this design, each switch is replaced by the association of a transistor and a diode in parallel. The switches are placed adjacent to one another to ensure the operation adapts as required.
It is an adaptation of the previous design.
In this design, each switch is replaced by the association of two transistors and two diodes so as to produce a current and voltage reversible switch. The switches are arranged to ensure the operation adapts as required.
For this need, we have the following configuration:
Here, the converter is represented according to the preceding principle suitable for the case where I1, Vx and I are positive and I2 is of a sign that can change. In this case, the switch S3 is not used.
Furthermore, in certain designs, it will also be possible to replace transistors with a simple mechanical contact, especially when one of the currents I1 or I2 changes sign.
When the mechanical contacts CM1 and CM2 are closed, the contacts CM3 and CM4 are open and vice versa. In the first case, the operation is identical to that of the design of
Of course, as mentioned above, it must be understood that there are still other possible designs, not described in the present application but which result, like those already described above, from an adaptation of the general architecture of the device represented in
With reference to
According to another feature of the invention, it is also possible to provide a so-called “bypass” system (that is to say circumvent) of the power flow control device of the invention, in order to bypass it when it is not useful. The “bypass” system avoids the complete powering-off of the network.
This system is visible in
In
The “bypass” system is comprised of a first resistor R1a whose role is to discharge the capacitor C1 and a second resistor R2a meant to discharge the second capacitor C2. The first resistor R1a is connected on the one hand to the first terminal B1 and to the terminal B10. The second resistor R2a is connected on the one hand to the second terminal B2 and to the terminal B20. A first switch CM1a is connected in parallel with the first resistor R1a and a second switch CM2a is connected in parallel with the second resistor R2a. A switch CM1b is connected between the first terminal B1 and the third terminal B3. Another switch CM2b is connected between the second terminal B2 and the third terminal B3.
The switches CM1a, CM1b, CM2a and CM1b can be obtained through the use of mechanical contactors. The device that operates these switches is not shown here.
When the power flow control device is not in use (state 1):
When the power flow control device is in use (state 2):
To switch from state 1 to state 2, switches CM1a and CM2a are closed while switches CM1b and CM2b are opened.
To switch from state 2 to state 1, switches CM1a and CM2a are opened while switches CM1b and CM2b are closed.
As a result, the power flow control device is short-circuited and the capacitors are discharged into the resistors. After the unloading of the capacitors, switches CM1a and CM2a can be closed to prepare for the next power up.
The proposed solution ensures that the current in the links is never interrupted. The sequence to switch from one state to another is performed in such a way that the capacitors are not short-circuited.
In an alternative design, the control applied to the switching means of the power flow control device can cancel the voltage across the capacitors (by acting on the duty cycles). If this control functionality is implemented, resistors and switches CM1a and CM2a can be omitted and only switches CM1b and CM2b will be maintained.
From the above statement, it is understood that the invention solution has a number of advantages. It makes it possible to increase the transport capacity of direct current mesh networks, avoiding the congestion of links without the need to integrate new links.
In addition, the invention solution can be used to perform the following functions:
It should also be noted that no part of the device is subjected to the voltage that exists between the conductors of the links and the ground (as is the case in previous solutions). The voltages that must reach the terminals of the device are of the order of magnitude of the voltage drops that exist in the considered mesh network (R1I1−R2I2+R3I3 for the example being considered), this will involve voltages lower than those between the conductors of the links and the ground (e.g. Va). Moreover, the device does not exchange energy with the alternative network and there is no insulation problem with the latter. It is therefore a converter that is placed at a high potential in relation to the earth but does not receive very high voltages at its terminals.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1756880 | Jul 2017 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2018/051776 | 7/13/2018 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2019/016449 | 1/24/2019 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20080284248 | Raulin | Nov 2008 | A1 |
| 20150180231 | Whitehouse | Jun 2015 | A1 |
| Number | Date | Country |
|---|---|---|
| 2670013 | Dec 2013 | EP |
| 3007300 | Apr 2016 | EP |
| 3007301 | Apr 2016 | EP |
| WO 2010115452 | Oct 2010 | WO |
| WO 2010115453 | Oct 2010 | WO |
| WO 2012037957 | Mar 2012 | WO |
| WO 2013 13858 | Jan 2013 | WO |
| WO 2013178807 | Dec 2013 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20210083473 A1 | Mar 2021 | US |
