Device and method for stabilising an ac voltage grid
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- SIEMENS ENERGY GLOBAL GMBH & CO KG
- Filing Date
- 2025-12-11
- Publication Date
- 2026-08-06
Smart Images
Figure EP2025086641_06082026_PF_FP_ABST
Abstract
Description
[0001] 2024PF00637
[0002] 1
[0003] Description
[0004] Device and procedure for stabilizing a
[0005] Alternating voltage network
[0006] The invention relates to a device for stabilizing an AC voltage network, which is arranged in series in the AC voltage network during operation, in particular in an overhead line for electrical power transmission, and comprises a capacitor branch with a capacitor arrangement.
[0007] Such a device is often referred to as a fixed series capacitor (ESC) and is used to generate reactive power in the AC power grid. A disadvantage of this solution is its limited flexibility in the event of changing requirements of the transmission network.
[0008] WO 2022 / 167071 Al describes three known variants of the ESC. According to the first variant, a fixed capacitor is inserted into an AC voltage line. According to the second variant, antiparallel thyristors are arranged in parallel with the capacitor, which can control the current flow through the capacitor. This variant is commonly referred to as a 'thyristor-controlled series capacitor' (TCSC). According to the third variant, a switching module with power semiconductors is additionally arranged in series with the capacitor.
[0009] The object of the present invention is to propose a device of the aforementioned type that is as flexible and reliable as possible.
[0010] In a suitable setup, the task is solved by a control branch in a parallel circuit to the capacitor branch, wherein the control branch comprises a series circuit of control modules, each of which is a switchable power semiconductor switch and a control module-2024PF00637
[0011] The energy storage device (e.g., a capacitor) comprises an energy storage device, wherein more than 50%, preferably more than 70%, of the maximum capacitive reactive power that can be generated by the device during operation can be generated by the capacitor arrangement (or is generated during operation). The remaining portion of the capacitive reactive power can be generated by the control modules (for example, (at most) 50% or 30% of the capacitive reactive power can be generated by the control modules).
[0012] During operation, the device draws a capacitive base power from one or more capacitor banks (corresponding to an ESC). This base power accounts for at least 50% of the maximum power that can be generated. Simultaneously, the energy storage devices of the control modules in the control branch can be either bypassed or, alternatively, connected to a current path in the control branch using the switchable power semiconductors. The respective control module energy storage devices can be connected to the current path in both positive and negative directions (i.e., polarity). In this way, the required inductive reactive power for compensating or controlling the capacitive base power can be generated not by a reactance, but by the control modules. For example, the capacitor bank can be configured to generate a capacitive reactive power of 80 MVar.The control modules are also configured to generate capacitive or inductive power of ±20 MVar. Thus, in this example, at least 80% of the maximum achievable capacitive reactive power can be generated by the capacitor array and at most 20% by the control modules. In another example, the capacitor array can provide 100 MVar, which can be supplemented by the control modules with ±40 MVar. During operation, the capacitor array can, of course, temporarily provide 100% of the (instantaneous) power at any given time (for example, if all energy storage devices of the control modules are bypassed). 2024PF00637.
[0013] 3
[0014] The controllability via the control modules advantageously increases the flexibility of the system. Furthermore, by arranging the control modules (i.e., the power electronics) in parallel with the capacitor array, it can be advantageously achieved that a major portion of the load current during operation flows through the (FSC) capacitor array, but not through the control modules. In this way, higher losses can be avoided. Moreover, the maximum load current (and thus the amount of power that can be transmitted via the overhead line) is advantageously independent of the power electronics used.
[0015] Preferably, more than 70% of the maximum capacitive reactive power that can be generated by the device during operation can be generated by the capacitor arrangement. In this way, the relatively expensive control modules can be designed to be smaller, thereby reducing the cost of the device.
[0016] According to one embodiment of the invention, the control branch comprises a reactance for limiting the current rise, which includes, for example, an inductor preferably designed as a choke (e.g., an air choke). Dividing the required inductance into two reactances and / or arranging the reactances before and after the control modules is also possible.
[0017] Furthermore, the control branch can include a charging device for recharging the energy storage devices, preferably comprising a parallel connection of a resistive element and a switching element. The energy storage devices of the control modules can be recharged by means of the charging device.
[0018] Suitablely, the system also includes a control system configured to control the control modules, so that the control modules can be used to achieve a 2024PF00637
[0019] 4
[0020] A virtual impedance can be generated. A virtual impedance is an artificially generated reactance created by the control system. This can be flexibly adjusted to control the load flow in the AC grid, particularly overhead lines, with high dynamics and to increase its stability. Through targeted control of the control modules, the virtual impedance can also be used to improve system damping and avoid resonance problems. This means that even with fluctuating load conditions or grid faults, a stable grid voltage and load flow can be maintained. The virtual impedance acts like a real reactance, but with the advantage that its values can be dynamically and quickly adapted to the current grid conditions. This increases the flexibility and reliability of the entire system.
[0021] According to one embodiment of the invention, the device comprises a plurality of capacitor assemblies arranged in series within the capacitor branch. Each capacitor assembly suitably includes a capacitor bank. The capacitor bank comprises several capacitor units connected in series and / or parallel configurations to achieve the desired voltage and capacitance values. The components of the capacitor assembly are mounted on a (at least partially insulated) support structure that provides mechanical support and ensures proper electrical insulation (particularly from ground potential). The design of the support structure takes into account factors such as environmental conditions, ease of maintenance, and accessibility for inspections. The ESC, or even the entire device, can be housed in a common container.
[0022] Advantageously, the resonant frequency of a resonant circuit formed by the capacitor arrangement(s) and the reactance is at least twice the 2024PF00637
[0023] 5
[0024] a mains frequency of the AC power grid. The electrical resonant frequency is chosen to be greater than twice the mains frequency, since the corresponding frequency of the energy oscillation is then greater than the bandwidth of the
[0025] Inverter energy control is a feature that prevents unintended interactions (excitation of the resonant circuit). This also eliminates the need for additional (physical) damping structures.
[0026] According to one embodiment of the invention, at least some of the control modules are designed as full-bridge control modules. A full-bridge control module comprises four switching elements (for example, IGBTs, IGCTs, or other switchable power semiconductors) and an energy storage device, arranged in a bridge circuit. This arrangement makes it possible to control the current flow through the energy storage device in both directions. This is particularly advantageous for applications where flexible and precise control of the alternating voltage is required.
[0027] Preferably, the device includes a protection branch connected in parallel to the capacitor branch and the control branch, in which a surge arrester and preferably a spark gap or other fast-switching elements are arranged. To ensure the safety and longevity of the capacitor bank, various protective devices can be integrated into the device. These include, for example, varistors, voltage dividers, limiting chokes, and surge capacitors.
[0028] Metal oxide varistors (MOVs) protect capacitors from overvoltage conditions by clamping the voltage at a safe level. Spark-gap-free surge arresters provide continuous overvoltage protection without the need for maintenance or replacement.
[0029] Current limiting chokes can be installed in series with the capacitor bank and limit the 2024PF00637
[0030] 6
[0031] Fault current under short-circuit conditions.
[0032] Surge capacitors protect the equipment from high-frequency transient overvoltages.
[0033] The device described above is preferably used in an electrical energy transmission system comprising an AC power grid, preferably an overhead line, designed for a voltage of more than 60 kV. The AC power grid can be a transmission or distribution network with a multitude of power generation plants and consumers. The device improves the efficiency and stability of the AC power grid by means of highly dynamic load flow control. Reactive power compensation increases energy efficiency by reducing parasitic reactive power consumers on the transmission lines and thus reducing losses. Furthermore, it improves voltage stability because the reactive power is adapted to the current grid conditions, resulting in a constant and safe grid voltage.Furthermore, transmission losses can be reduced because the overall current flow is decreased. This also increases grid capacity, as more active power can be transmitted. Improving the power factor allows for more efficient use of electrical energy. Additionally, resonance problems can be avoided and reactive power flow optimized. Modern technologies enable dynamic adjustment of reactive power, which increases the flexibility and reliability of the grid.
[0034] The invention further relates to a method for stabilizing an alternating current network.
[0035] The object of the invention is to provide a method that allows for the most flexible and reliable stabilization of the network. 2024PF00637
[0036] 7
[0037] The problem is solved by using a device according to the invention to perform (continuous) highly dynamic load flow control in the AC network.
[0038] The advantages of the method according to the invention result in particular from the advantages of the device according to the invention described above.
[0039] The invention is further explained below with reference to Figures 1 to 3.
[0040] Figure 1 shows a schematic representation of an embodiment of the device according to the invention;
[0041] Figure 2 shows an example of a control module in a schematic representation;
[0042] Figure 3 shows another embodiment of the device according to the invention in a schematic representation.
[0043] Figure 1 shows a device 1 for stabilizing an AC voltage network. The device 1 is arranged in series in an AC voltage network 2.
[0044] If the AC power network is multi-phase, the device 1 can be arranged in one phase line of the AC power network. Advantageously, each phase line of the multi-phase AC power network has a device as shown in Figure 1.
[0045] The device 1 comprises a capacitor branch 4 with a capacitor arrangement 3, which has a parallel connection of series-connected capacitors. The device can include several such capacitor arrangements in the capacitor branch 4, which are connected in series with each other. 2024PF00637
[0046] 8
[0047] The device 1 further comprises a control branch 5 connected in parallel to the capacitor branch 4. The control branch 5 has a series connection of control modules 6a-6c, each comprising switchable power semiconductor switches and a control module energy storage device. The number of control modules in the control branch is generally freely selectable and can be adapted to the respective application. The design of the capacitor arrangement 3 and the control modules 6a-c is chosen such that more than 50% of the capacitive reactive power generated by the device during operation can be generated by the capacitor arrangement.
[0048] Furthermore, one or more reactances for limiting the current rise are arranged in the control branch 5; in the illustrated example, this is an air choke 7. The control branch 5 also has a charging device 8 for charging the energy storage devices, which comprises a parallel connection of a resistive element 8a and a switching element 8b, by means of which the resistive element 8a can be bypassed.
[0049] A protection branch 9 is arranged in parallel to the capacitor branch 4, in which a surge arrester arrangement 10 and a spark gap 11 are arranged to protect the device from overvoltages.
[0050] By means of a control unit 12, the control modules 6a-c can be controlled such that a virtual impedance can be generated in the AC network 2 by means of the control modules 6a-c. For this purpose, the control unit 12 can access measured values (e.g., current and voltage) from the AC network 2 and / or the unit 1. The virtual impedance to be generated can be specified by predefined setpoint values. The control unit 12 controls the power semiconductor switches of the control modules such that the energy storage devices of the control modules are activated for a predefined period.
[0051] Time and with a suitable polarity switched or bridged in the current path.
[0052] Figure 2 shows a control module 13, which can be used, for example, as one or more of the control modules 6a-c in the device 1 of Figure 1. The control module 13 is a full-bridge control module. The control module 13 comprises a first and a second terminal XI, X2, a first power semiconductor switch (IGBT) S1, a second power semiconductor switch (IGBT) S2, a third power semiconductor switch (IGBT) S3, and a fourth power semiconductor switch (IGBT) S4, each with a freewheeling diode F connected in antiparallel. The power semiconductor switches S1-S4 are interconnected such that an energy storage device C (capacitor) can be connected bipolarly (on both sides) in the current path or bypassed.
[0053] Figure 3 shows a device 13. The components of device 13 correspond to those of device 1 in Figure 1. Device 13 comprises a container 14 in which the capacitor assembly and the control modules of the device are housed. Device 13 is arranged on a support structure 15, by means of which device 13 is isolated from earth potential. Device 13 is inserted in series into an overhead line phase conductor 16 of a transmission line designed for a voltage of 220 kV to 400 kV.
Claims
2024PF00637 10 Patent claims 1. Device ( 1 ) for stabilizing an AC voltage network ( 2 ) which is arranged in series in the AC voltage network ( 2 ) during operation, comprising a capacitor branch ( 4 ) with a capacitor arrangement ( 3 ) , characterized by a control branch ( 5 ) in a parallel connection to the capacitor branch ( 4 ), wherein the control branch ( 5 ) comprises a series connection of control modules ( 6a-c ), each comprising switchable power semiconductor switches ( S l-4 ) and a control module energy storage device ( C ), wherein more than 50% of a maximum capacitive reactive power achievable by the device ( 1 ) in operation can be generated by the capacitor arrangement ( 3 ).
2. Device ( 1 ) according to claim 1, wherein the control branch ( 5 ) has at least one reactance ( 7 ) for limiting the current rise, which is preferably designed as an air throttle.
3. Device ( 1 ) according to one of the preceding claims 1 or 2, wherein the control branch ( 5 ) has a charging device ( 8 ) for charging the control module energy storage device ( C ), which preferably comprises a parallel connection of a resistance element ( 8a ) and a switching element ( 8b ).
4. Device ( 1 ) according to one of the preceding claims, wherein the device ( 1 ) further comprises a control device ( 12 ) which is configured to control the control modules ( 6a-c ) so that a virtual impedance can be generated by means of the control modules ( 6a-c ).
5. Device ( 1 ) according to one of the preceding claims, wherein the device ( 1 ) comprises a plurality of 2024PF00637 11 Capacitor arrangements (3) are included, which are arranged in a series connection in the capacitor branch (4).
6. Device ( 1 ) according to one of the preceding claims, wherein a resonant frequency of a resonant circuit formed by the capacitor arrangement (3) or capacitor arrangements and the reactance (7 ) is at least twice the mains frequency of the AC mains (2 ).
7. Device ( 1 ) according to one of the preceding claims, wherein the control modules ( 6a-c ) are designed as full bridge control modules.
8. Device ( 1 ) according to one of the preceding claims, wherein the device ( 1 ) has a protection branch ( 9) in a parallel circuit to the capacitor branch (4 ) and to the control branch (5), in which a surge arrester arrangement ( 10) and preferably a highly dynamic switching device spark gap ( 11 ) are arranged.
9. System for the transmission of electrical energy comprising an electrical line ( 16 ), preferably an overhead line designed for a voltage of more than 60 kV, an alternating voltage network and a device ( 13 ) according to any one of claims 1 to 8.
10. Method for stabilizing an AC power network, wherein load flow control is carried out in the AC power network (2) by means of a device ( 1 ) according to one of claims 1 to 8.