A voltage regulating transformer and power flow control system

Abstract

The present invention discloses a voltage-regulating transformer and power flow control system. The voltage-regulating transformer comprises a transformer and at least one voltage-regulating circuit. The transformer's primary winding is connected to an AC system, one end of its secondary winding is connected in series with the at least one voltage-regulating circuit, and the other end of the secondary winding is connected to the AC system. The voltage-regulating circuit comprises at least one switch module, and the output voltage of the voltage-regulating circuit is controlled by controlling the on-off state of the switch module. The present invention connects the transformer's secondary winding to the at least one voltage-regulating circuit, adjusts the voltage at the output of the voltage-regulating circuit by changing the on-off state of the switch module, and changes the output voltage amplitude when all the voltage-regulating windings are connected to the transformer, thereby achieving multi-level voltage regulation and controlling the voltage amplitude of the AC system's transmission line.

Description

Technical Field

[0001] The present invention relates to electric power equipment technology, and in particular to a voltage regulating transformer and a power flow control system. Background Art

[0002] With rapid economic development, increasing electricity consumption, and increasingly complex and flexible power grid structures, higher requirements are being placed on the safe and economical operation of power systems. Flexible power flow control is essential for safe and economical power grid operation. Flexible AC transmission systems (FACTS) utilize power electronics to adjust grid operating parameters and effectively control power flows along power lines. The Unified Power Flow Controller (UPFC) is the most powerful FACTS device. It can adjust line voltage and line parameters, providing not only rapid and independent power flow control capabilities but also excellent performance in dynamic reactive power compensation and maintaining grid stability. However, UPFCs primarily consist of high-voltage, high-power power electronics, which are expensive, have significantly higher switching losses than traditional electrical devices such as transformers, and offer lower reliability. Due to factors such as cost-effectiveness, UPFCs have not been widely used in high-voltage power grids. Traditional transformer tap changers operate slowly, pose a risk of arcing, and repeated operation shortens their service life. Furthermore, they are unable to address system oscillations and cannot achieve the goal of dynamically and flexibly supporting grid voltage. Summary of the Invention

[0003] Therefore, the technical problem to be solved by the present invention is to overcome the defect in the prior art that the transformer cannot achieve dynamic flexible support for the grid voltage, thereby providing a voltage regulating transformer and a power flow control system.

[0004] In order to achieve the above object, the present invention provides the following technical solutions:

[0005] In a first aspect, an embodiment of the present invention provides a voltage-regulating transformer, comprising: a transformer and at least one voltage-regulating circuit, wherein the primary winding of the transformer is connected to an AC system, one end of its secondary winding is connected in series with at least one voltage-regulating circuit, and the other end of the secondary winding is connected to the AC system; the voltage-regulating circuit comprises at least one switching module, and the output voltage of the voltage-regulating circuit is controlled by controlling the on-off state of the switching module.

[0006] In one embodiment, the voltage regulating circuit includes: a voltage regulating winding, two output ends and four switch modules, wherein one end of the first switch module and the third switch module is connected to one end of the voltage regulating winding, the other end of the first switch module and one end of the second switch module are connected to a first connection point, and a first output end is led out at the first connection point, the other end of the third switch module and one end of the fourth switch module are connected to a second connection point, and a second output end is led out at the second connection point, and the other end of the second switch module and the other end of the fourth switch module are both connected to the other end of the voltage regulating winding.

[0007] In one embodiment, when the secondary winding of the transformer is connected to multiple voltage regulating circuits, the output ends of all the voltage regulating circuits are interconnected in series.

[0008] In one embodiment, the transformer is a single-phase transformer or a three-phase transformer.

[0009] In one embodiment, when the voltage regulating transformer includes a transformer and a voltage regulating circuit, the voltage regulating circuit is connected in series with the secondary winding of the transformer, and by controlling the on-off state of the switch module, the output voltage of the two output ends of the voltage regulating circuit is a three-level voltage.

[0010] In one embodiment, when the voltage-regulating transformer includes a transformer and two voltage-regulating circuits, the two voltage-regulating circuits are connected in series and then connected in series with the secondary winding of the transformer. By controlling the on-off state of the switch module, the output voltage of the two output ends of the two voltage-regulating circuits connected in series is a nine-level voltage.

[0011] In one embodiment, when the voltage-regulating transformer includes a transformer and three voltage-regulating circuits, the three voltage-regulating circuits are connected in series and then connected in series with the secondary winding of the transformer. By controlling the on-off state of the switch module, the output voltage of the two output ends of the three voltage-regulating circuits connected in series is a twenty-seven-level voltage.

[0012] In a second aspect, an embodiment of the present invention provides a power flow control system, comprising the voltage-regulating transformer of the first aspect, and further comprising: a controller and at least one converter, wherein the input side of the converter is connected to the primary winding of the voltage-regulating transformer, and the output side is connected to the output end of the voltage-regulating circuit on the secondary side of the voltage-regulating transformer, and the converter is used to adjust the voltage amplitude and phase of the AC system; the controller is installed on the AC system power line, and is used to collect the voltage and current of its installation point, nodes and branches in a preset adjacent range, or accept superior dispatching instructions, and change the AC system voltage and power flow by coordinating the output voltage amplitude and phase of the voltage-regulating circuit and the converter.

[0013] In one embodiment, the power flow control system further includes: at least one bypass switch module, the voltage regulating circuit and the converter are both connected in parallel with a bypass switch, the bypass switch module is used to quickly cut off the fault point when any voltage regulating circuit or converter fails; or the output end of the voltage regulating circuit is connected to the converter through the bypass switch module, and the bypass switch module is used to cut off the current loop between the voltage regulating circuit and the converter when the voltage regulating circuit or converter fails.

[0014] In one embodiment, when the voltage-regulating transformer is a single-phase transformer, one end of the primary winding of the single-phase transformer is connected to any phase transmission line of the AC system, the other end of the primary winding of the single-phase transformer and the autocoupler output are connected to the input side of the converter, and one end of the converter output is connected to the output end of the voltage-regulating circuit on the secondary side of the single-phase transformer.

[0015] In one embodiment, when the voltage-regulating transformer is a three-phase transformer and the converter is a single-phase converter, the autocoupler output end of the primary winding of each phase of the three-phase transformer is connected to one end of the input side of a converter, the other ends of the three converter input sides are connected to each other, and one end of each converter output side is connected to the output end of the voltage-regulating circuit on the secondary side of the corresponding phase of the three-phase transformer.

[0016] In one embodiment, the power flow control system further includes: at least one additional transformer; when the voltage regulating transformer is a three-phase transformer and the converter is a three-phase converter, the autocoupler output end of the primary winding of each phase of the three-phase transformer is connected to each phase of the converter input side, each phase of the converter output side is connected to one end of the primary winding of an additional transformer, the other end of the primary winding of each additional transformer is interconnected, one end of the secondary winding of each additional transformer is respectively connected to the low potential output end or the high potential output end of the voltage regulating circuit on the secondary side of the corresponding phase of the three-phase transformer, and the other ends of the secondary windings of the three additional transformers are interconnected.

[0017] In one embodiment, when one end of the secondary winding of each additional transformer is respectively connected to the high-potential output end of the voltage regulating circuit on the secondary side of the corresponding phase of the three-phase transformer, one end of the secondary winding of each phase of the three-phase transformer is connected to the ground, and the other end is connected to the secondary winding of the corresponding additional transformer, and the low-potential output end of the voltage regulating circuit on the secondary side of the corresponding phase of the three-phase transformer is connected to the corresponding AC system transmission line.

[0018] In one embodiment, when one end of the secondary winding of each additional transformer is respectively connected to the low-potential output end of the voltage regulating circuit on the secondary side of the corresponding phase of the three-phase transformer, one end of the secondary winding of each phase of the three-phase transformer is connected to the corresponding AC system transmission line, the other end of the secondary winding of each phase of the three-phase transformer is connected to the voltage regulating circuit, and the high-potential output end of the voltage regulating circuit on the secondary side of the corresponding phase of the three-phase transformer is connected to the corresponding AC system transmission line.

[0019] The technical solution of the present invention has the following advantages:

[0020] 1. The voltage-regulating transformer provided by the present invention connects the secondary winding of the transformer to at least one voltage-regulating circuit. By changing the on-off state of a switch module, the output voltage of the voltage-regulating circuit is adjusted. By also changing the output voltage amplitude when all the voltage-regulating windings are connected to the transformer, multi-level voltage regulation is achieved, as well as control of the voltage amplitude of the AC system transmission line.

[0021] 2. The power flow control system provided by the present invention, based on the voltage-regulating transformer, introduces a converter in parallel with the primary side of the transformer to draw energy, and the output end of the converter is connected in series with the secondary side of the transformer. By controlling the operating state of the converter, parallel reactive compensation of the AC system and control of the voltage amplitude and phase of the AC system transmission line are achieved, thereby enhancing the power flow control capability of the AC system; when the voltage-regulating transformer is a three-phase transformer, the converter can be a single-phase transformer or a three-phase transformer; when the voltage-regulating transformer is a single-phase transformer, the converter can be a single-phase transformer, thereby improving the flexibility and adaptability of the power flow control system; the controller controls the operating state of the converter, thereby improving the stability of the power flow control system and its power flow control capability. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 A schematic diagram of a specific example of a voltage regulating transformer provided by an embodiment of the present invention;

[0024] Figure 2 A schematic diagram of a specific example of a voltage regulating circuit provided by an embodiment of the present invention;

[0025] Figure 3 A schematic diagram of a specific example of a bypass switch module provided in an embodiment of the present invention;

[0026] Figure 4 A schematic diagram of a specific example of a power flow control system provided by an embodiment of the present invention;

[0027] Figure 5 The voltage regulation range of the voltage regulating transformer and converter provided in the embodiment of the present invention;

[0028] Figure 6 A schematic diagram of another specific example of a voltage regulating circuit provided by an embodiment of the present invention;

[0029] Figure 7 A schematic diagram of another specific example of a power flow control system provided by an embodiment of the present invention;

[0030] Figure 8 A schematic diagram of another specific example of a power flow control system provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0031] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0032] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; internal connections between two components; wireless connections or wired connections. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0033] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0034] Example 1

[0035] The embodiment of the present invention provides a voltage regulating transformer 1, which is used in situations where voltage regulation of a power transmission line is required, such as Figure 1 As shown, it includes: a transformer 11 and at least one voltage regulating circuit 12.

[0036] In embodiments of the present invention, the transformer's primary winding is connected to an AC system. One end of its secondary winding is connected in series with at least one voltage-regulating circuit, and the other end of the secondary winding is connected to the AC system. The voltage-regulating circuit includes at least one switching module, which controls the output voltage of the voltage-regulating circuit by controlling the on / off state of the switching module. The transformer's primary side can be either the primary or the secondary side, and the secondary side is the side opposite the primary.

[0037] Figure 1 The transformer in the circuit is a single-phase transformer, the primary side of which is connected to a single-phase transmission line of the AC system, and one end of the secondary winding (one end of the conventional winding) is connected to at least one voltage regulating circuit connected in series ( Figure 2Take one end of the secondary winding being connected to two voltage regulating circuits connected in series as an example), and the other end of the conventional winding being connected to the corresponding phase transmission line of the AC system.

[0038] When the transformer is a three-phase transformer, the primary side of the three-phase transformer is connected to the AC system, one end of each phase winding on its secondary side (one end of the conventional winding) is connected to at least one voltage regulating circuit, and the other end of each phase conventional winding on the secondary side is connected to the transmission line of the corresponding phase of the AC system.

[0039] like Figure 2 As shown, the voltage regulating circuit includes: a voltage regulating winding 121, two output terminals, and four switch modules 122. One end of the first switch module S1 and the third switch module S3 is connected to one end of the voltage regulating winding. The other end of the first switch module S1 is connected to one end of the second switch module S2 at a first connection point, and a first output terminal is led out at the first connection point. The other end of the third switch module S3 is connected to one end of the fourth switch module S4 at a second connection point, and a second output terminal is led out at the second connection point. The other end of the second switch module S2 and the other end of the fourth switch module S4 are both connected to the other end of the voltage regulating winding.

[0040] Figure 2 The invention relates to a voltage regulating circuit including a voltage regulating winding and four controllable switch modules. The voltage regulating circuit includes two output terminals, and multiple voltage regulating circuits are connected in series via the output terminals. Figure 2 In the circuit, four controllable switch modules S1, S2, S3, and S4 form an H-bridge structure. Each controllable switch module can be composed of anti-parallel thyristors, or bidirectional conducting IGBTs connected in series with each other and their anti-parallel diodes. Figure 2 The switch module is composed of a bidirectional conducting IGBT and an anti-parallel diode thereof, which is only an example and is not limited to this.

[0041] It should be noted that the number of voltage regulating circuits connected in series with the conventional winding on the secondary side of the transformer and the number of turns of the voltage regulating winding can be set according to actual conditions, and when the conventional winding on the secondary side of the transformer is connected to multiple voltage regulating circuits, the number of turns of each voltage regulating winding can be different.

[0042] Figure 2 In the figure, one end of S1 and S3 is connected to the first end of the voltage regulating winding, the other end of S1 is connected to one end of S2, and then they are connected together and lead out to the first output end; the other end of S3 is connected to one end of S4, and then they are connected together and lead out to the second output end, and the other ends of S2 and S4 are both connected to the second end of the voltage regulating winding.

[0043] It should be noted that the number of switch modules in the embodiment of the present invention can be not only 4, but also other numbers. Multiple switch modules can not only constitute an H-bridge structure. At the same time, according to the actual situation of the voltage-regulating transformer application site, multiple switch modules can constitute multiple H-bridge structures, or the switch module is connected to the first end, the second end and the autocoupler output end of the voltage-regulating winding. By changing the on-off state of the switch module, the voltage-regulating winding can be fully forward-connected, or reverse-connected, or partially forward-connected and partially reverse-connected to the secondary winding of the transformer, thereby changing the total voltage output after the secondary side of the transformer is connected in series with the voltage-regulating circuit.

[0044] In a specific embodiment, the voltage regulating transformer further includes: at least one bypass switch module, each voltage regulating circuit is connected in parallel with a bypass switch, and the bypass switch module is used to quickly cut off all voltage regulating circuits when any voltage regulating circuit is disconnected, such as Figure 3 As shown, two ends of the bypass switch module are respectively connected to two output ends of a plurality of voltage regulating circuits connected in series, and one end of the bypass switch module is grounded. Figure 3 The bypass switch module in the system is a controlled thyristor switch, designed to quickly bypass the fault point. It can also include a mechanical switch for reliable fault bypass and a lightning arrester for overvoltage protection between terminals. When the voltage regulation circuit is located at the transformer's low-potential terminal, one end of the bypass switch module can be directly grounded, providing a stable and reliable grounding point for the transformer when the bypass switch module is turned on.

[0045] In the embodiment of the present invention, by changing the number of turns of the voltage regulating winding, the output voltage amplitudes of the two output terminals after all the voltage regulating windings are connected to the secondary side of the transformer can be changed.

[0046] In an embodiment of the present invention, when the voltage regulating transformer includes a transformer and a voltage regulating circuit, the voltage regulating circuit is connected in series with the secondary winding of the transformer. By controlling the on-off state of the switch module, the output voltage of the two output ends of the voltage regulating circuit is a three-level voltage.

[0047] The embodiment of the present invention can realize the module outputting three states of forward winding voltage, reverse winding voltage and zero voltage by controlling the on-off state of the switch module in the H-bridge structure. Figure 2 As shown in the figure, when the primary and secondary currents of the transformer both flow into the windings from the same terminals, assuming that the voltage regulating winding is connected to the transformer in the forward direction, the voltage between the first output terminal and the second output terminal is U1, and when the voltage regulating winding is connected to the transformer in the reverse direction, the voltage between the first output terminal and the second output terminal is -U1, and the voltage across the normal winding on the secondary side of the transformer is U. The control method of the voltage regulating circuit is as follows:

[0048] ① By controlling S1 and S4 to be turned on and S2 and S3 to be turned off, the forward voltage of the voltage regulating winding is output between the first output terminal and the second output terminal of the voltage regulating circuit. At this time, the voltage output after the transformer conventional winding is connected in series with the voltage regulating circuit is U+U1;

[0049] ② By controlling S2 and S3 to be turned on and S1 and S4 to be turned off, the negative voltage of the voltage regulating winding is output between the first output terminal and the second output terminal of the voltage regulating circuit. At this time, the voltage output after the transformer conventional winding is connected in series with the voltage regulating circuit is U-U1;

[0050] ③ When S1 and S3 are controlled to be turned on, or S2 and S4 are controlled to be turned on, the voltage output of the voltage regulating winding between the first output terminal and the second output terminal of the voltage regulating circuit is 0. At this time, the voltage output after the conventional winding of the transformer is connected in series with the voltage regulating circuit is U.

[0051] In an embodiment of the present invention, when the voltage-regulating transformer includes a transformer and two voltage-regulating circuits, the two voltage-regulating circuits are connected in series and then connected in series with the secondary winding of the transformer. By controlling the on-off state of the switch module, the output voltage of the two output ends of the two voltage-regulating circuits connected in series is a nine-level voltage.

[0052] like Figure 1 As shown, when the conventional winding on the secondary side of the transformer is connected to the two voltage regulating circuits, the two voltage regulating circuits form a double H-bridge structure. Assuming that the voltage across the conventional winding on the secondary side of the transformer is U, when the A voltage regulating circuit in the two voltage regulating circuits is forwardly connected to the transformer, the voltage between the first output terminal and the second output terminal of the A voltage regulating circuit is U1, and when the voltage regulating winding is reversely connected to the transformer, the voltage between the first output terminal and the second output terminal of the A voltage regulating circuit is -U1. By changing the on-off state of the switch modules in the two voltage regulating circuits, the voltage between the first output terminal and the second output terminal of the A voltage regulating circuit is U1, -U1, and 0; when the B voltage regulating circuit is forwardly connected to the transformer, the voltage between the first output terminal and the second output terminal of the B voltage regulating circuit is U2, and the voltage regulating winding is reversely connected to the transformer. When connected to the transformer, the voltage between the first output terminal and the second output terminal of the B voltage regulating circuit is -U2. By changing the on-off state of the switch modules in the two voltage regulating circuits, the voltage between the first output terminal and the second output terminal of the B voltage regulating circuit is U2, -U2, 0; then the two output terminals after the two voltage regulating circuits are connected in series can obtain the output voltages of U1+U2, U1, U1-U2, U2, U, -U2, -(U1-U2), -U1, -(U1+U2). Therefore, by changing the on-off state of the switch modules in the two voltage regulating circuits, the voltage output after the conventional winding on the secondary side of the transformer is connected in series with the two voltage regulating circuits can be quickly switched between nine voltage levels.

[0053] Furthermore, if Figure 1The voltages between the first and second output terminals of the A voltage regulating circuit of the two voltage regulating circuits shown are U1, -U1, and 0, and the voltages between the first and second output terminals of the B voltage regulating circuit are 3U1, -3U1, and 0. This allows the output voltage of the transformer secondary side conventional winding connected in series with the two voltage regulating circuits to be continuously adjusted between nine voltage levels. The output status of the dual H-bridge multi-level voltage output combination is shown in the following table.

[0054]

[0055] In an embodiment of the present invention, when the voltage-regulating transformer includes a transformer and three voltage-regulating circuits, the three voltage-regulating circuits are connected in series and connected in series with the secondary winding of the transformer. By controlling the on-off state of the switch module, the output voltage of the two output ends of the three voltage-regulating circuits connected in series is a twenty-seven-level voltage.

[0056] When the voltage regulating transformer contains three voltage regulating circuits, assuming that the voltage across the conventional winding on the secondary side of the transformer is U, when the A voltage regulating circuit in the three voltage regulating circuits is connected to the transformer in the forward direction, the voltage between the first output terminal and the second output terminal of the A voltage regulating circuit is U1, and when the voltage regulating winding is connected to the transformer in the reverse direction, the voltage between the first output terminal and the second output terminal of the A voltage regulating circuit is -U1. By changing the on-off state of the switch modules in the two voltage regulating circuits, the voltage between the first output terminal and the second output terminal of the A voltage regulating circuit is U1, -U1, 0; when the B voltage regulating circuit is connected to the transformer in the forward direction, the voltage between the first output terminal and the second output terminal of the A voltage regulating circuit is U1, -U1, 0. When the voltage regulating winding is connected to the transformer in the forward direction, the voltage between the first output terminal and the second output terminal of the B voltage regulating circuit is U2. When the voltage regulating winding is connected to the transformer in the reverse direction, the voltage between the first output terminal and the second output terminal of the B voltage regulating circuit is -U2. By changing the on-off state of the switch modules in the two voltage regulating circuits, the voltage between the first output terminal and the second output terminal of the B voltage regulating circuit is U2, -U2, 0. When the C voltage regulating circuit is connected to the transformer in the forward direction, the voltage between the first output terminal and the second output terminal of the C voltage regulating circuit is U3. When the voltage regulating winding is connected to the transformer in the reverse direction, the voltage between the first output terminal and the second output terminal of the C voltage regulating circuit is The voltage between the output terminals is -U3. By changing the on-off state of the switch modules in the two voltage regulating circuits, the voltage between the first output terminal and the second output terminal of the C voltage regulating circuit is U3, -U3, 0. The two output terminals of the three voltage regulating circuits connected in series can obtain the voltages of the three voltage regulating circuits connected in series. The output voltages can be U1+U2+U3, U2+U3, U2+U3-U1, U1+U3, U3, U3-U1, U3+U1-U2, U3-U2, U3-U2-U1, U1+U2, U2, U2-U1, U1, 0, –(U1+U2+U3), -(U2+U3), -(U2+U3-U1), -(U1+U3), -U3, -(U3-U1), -(U3+U1-U2), -(U3-U2), -(U3-U2-U1), -(U1+U2), -U2, -(U2-U1), -U1. Therefore, by changing the on-off state of the switch modules in the three voltage regulating circuits, the output voltage after the secondary side conventional winding of the transformer is connected in series with the three voltage regulating circuits can be quickly switched between twenty-seven voltage levels.

[0057] When there are three or more voltage regulating circuits, the voltage amplitude at the two output terminals after all the voltage regulating windings are connected to the transformer can be changed by changing the number of turns of each voltage regulating winding, thereby achieving more levels of voltage regulation. For example, when there are three voltage regulating circuits, the voltage amplitude ratio at the two output terminals after all the voltage regulating windings are connected to the transformer can be 1:1:1 or 1:2:4, so that more voltages can be adjusted. Taking the number of voltage regulating circuits as an example, when the voltage amplitude ratio at the two output terminals after all the voltage regulating windings are connected to the transformer is 1:2:4, and the minimum voltage amplitude at the two output terminals after all the voltage regulating windings are connected to the transformer is U, then when the three voltage regulating circuits are connected in series, the total output voltage can be 7U, 6U, 5U, 4U, 3U, 2U, U, 0, -U, 2U, 3U, 4U, 5U, 6U, 7U, a total of 15 levels; when the voltage amplitude at the two output terminals after all the voltage regulating windings are connected to the transformer is The value ratio is 1:3:9, and the minimum voltage amplitude at the two output terminals after all the voltage regulating windings are connected to the transformer is U. Then, when the three voltage regulating circuits are connected in series, the total output voltage can be 13U, 12U, 11U, 10U, 9U, 8U, 7U, 6U, 5U, 4U, 3U, 2U, 1U, 0, -1U, -2U, -3U, -4U, -5U, -6U, -7U, -8U, -9U, -10U, -11U, -12U, -13U, a total of 27 levels. Therefore, from the above, it can be seen that when the transformer is connected in series with more voltage regulating circuits, and the voltage amplitude at the two output terminals after all the voltage regulating windings of the voltage regulating circuits are connected to the transformer has more levels, the transformer can output more voltage levels after being connected in series with the voltage regulating circuits.

[0058] The voltage-regulating transformer provided in an embodiment of the present invention connects the secondary winding of the transformer to at least one voltage-regulating circuit, adjusts the output voltage of the voltage-regulating circuit by changing the on-off state of a switch module, and changes the output voltage amplitude when all the voltage-regulating windings are connected to the transformer, thereby achieving multi-speed voltage regulation and controlling the voltage amplitude of the AC system transmission line.

[0059] Example 2

[0060] An embodiment of the present invention provides a flow control system, which is applied to situations where flow control of an AC system is required. The flow control system includes: a controller 2, at least one converter 3 and the voltage-regulating transformer 1 of embodiment 1. The voltage-regulating transformer can be a single-phase voltage-regulating transformer or a three-phase voltage-regulating transformer. When the voltage-regulating transformer is a single-phase transformer and the converter is a single-phase converter, a voltage-regulating transformer is combined with a converter and connected to a single-phase transmission line of the AC system; when the voltage-regulating transformer is a three-phase transformer and the converter is a single-phase converter, a flow control system formed by connecting a voltage-regulating transformer with three converters is connected to the AC system transmission line; when the voltage-regulating transformer is a three-phase transformer and the converter is a three-phase converter, a flow control system formed by connecting a voltage-regulating transformer with a converter is connected to the AC system transmission line. Figure 4 The example shown is when the voltage regulating transformer is a single-phase transformer, the converter is a single-phase converter, the voltage regulating transformer contains two voltage regulating circuits, and the converter consists of two single-phase converter units. This is just an example, but not limited to this.

[0061] The input side of the converter is connected to the primary winding of the voltage regulating transformer, and the output side is connected to the output end of the voltage regulating circuit on the secondary side of the voltage regulating transformer. The converter is used to adjust the voltage amplitude and phase of the AC system.

[0062] If the voltage-regulating transformer is connected in series alone in the AC system, since it can only change the amplitude of the AC voltage but cannot change the phase of the AC voltage, an inverter is provided in an embodiment of the present invention, and the input side of the inverter is connected to the primary side of the voltage-regulating transformer, that is, the inverter and the transformer are connected in parallel to obtain energy, and the output side of the inverter is connected to the output end of the voltage-regulating module on the secondary side of the voltage-regulating transformer.

[0063] The controller is installed on the AC system power line and is used to collect the voltage and current of its installation point, nodes and branches in a preset proximity, or receive superior dispatching instructions to change the AC system voltage and power flow by coordinating the output voltage amplitude and phase of the voltage regulating circuit and converter.

[0064] The controller is used to collect voltage and current at the installation point or nearby nodes (nodes can include balancing nodes, PQ nodes, PV nodes, etc.) and branches, and use voltage and current to calculate power flow. When the power flow calculation is abnormal, the output voltage amplitude and phase of the converter at the abnormal location are controlled, and combined with the output voltage amplitude of the voltage regulating transformer, the AC system voltage and power flow can be changed.

[0065] In a specific embodiment, if Figure 4As shown, when the voltage regulating transformer is a single-phase transformer, one end of the primary winding of the single-phase transformer is connected to any phase transmission line of the AC system, the other end of the primary winding of the single-phase transformer and the autocoupler output end are connected to the input side of the converter, and one end of the converter output side is connected to the output end of the voltage regulating circuit on the secondary side of the single-phase transformer.

[0066] When the voltage regulating transformer is a single-phase transformer, the converter is a single-phase converter. The input side of the converter is connected in parallel with the primary side of the voltage regulating transformer to obtain energy, so that the converter is an active converter. The output side of the converter is connected to the output end of the voltage regulating circuit at the low potential end of the secondary side of the voltage regulating transformer. A voltage regulating transformer and a converter are combined and connected to a single-phase transmission circuit of the AC system.

[0067] The conventional winding on the secondary side of the transformer in the embodiment of the present invention is not only connected in series with at least one voltage regulating module, but also a converter can be connected in series at the low-voltage output end of the voltage regulating module. The converter is composed of at least two converter units with a common busbar. At least one converter unit is connected in parallel with the transformer winding to obtain energy, providing dynamic reactive compensation for the system and stabilizing the node voltage level. The AC output voltage output by the AC side of the converter unit on the output side of the converter is connected in series with the output end of the voltage regulating circuit. The converter has a small-capacity voltage amplitude and phase rapid adjustment capability, and can achieve a wide range of rapid power flow adjustment capability in a point-to-surface combination with the voltage regulating circuit. The voltage adjustment range of the two-stage on-load voltage regulation and the active converter is as follows: Figure 5 As shown in the figure, A is the output voltage amplitude of the power flow control system, U tap Output voltage vector for power flow control system.

[0068] In a specific embodiment, the power flow control system also includes: at least one bypass switch module 4, each voltage regulating circuit and converter is connected in parallel with a bypass switch, the bypass switch module is used to quickly cut off the fault point when any voltage regulating circuit or converter fails; or the output end of the voltage regulating circuit is connected to the converter through a bypass switch module, and the bypass switch module is used to cut off the current loop between the voltage regulating circuit and the converter when the voltage regulating circuit or converter fails.

[0069] like Figure 6 As shown, the output end of the voltage regulating circuit is connected to the converter via a bypass switch module 4. The bypass switch module is used to cut off the current loop between the voltage regulating circuit and the converter when the voltage regulating circuit or the converter fails. Figure 3 As shown, Figure 3The bypass switch module in the circuit is a controllable thyristor switch, which is used to quickly bypass the fault point. In addition, the bypass switch module can also include a mechanical switch for reliable bypass of the fault point; a lightning arrester for overvoltage protection between terminals. When the voltage regulating circuit is located at the low potential end of the transformer, one end of the bypass switch module can be directly grounded, so that the transformer has a stable and reliable grounding point when the bypass switch module is turned on. In addition, the voltage regulating circuit in the voltage regulating transformer in the power flow control system is connected in parallel with the bypass switch module. The specific connection method is as follows: Figure 3 shown.

[0070] In a specific embodiment, when the voltage regulating transformer is a three-phase transformer and the converter is a single-phase converter, the autocoupler output end of the primary winding of each phase of the three-phase transformer is connected to one end of the input side of a converter, the other ends of the three converter input sides are connected to each other, and one end of each converter output side is connected to the output end of the voltage regulating circuit on the secondary side of the corresponding phase of the three-phase transformer.

[0071] When the voltage regulating transformer is a three-phase transformer and the converter is a single-phase converter, each phase on the primary side of the three-phase transformer is connected to a converter input side, and a converter is composed of at least two single-phase converter units connected back to back. The single-phase converter unit can be a converter circuit such as a full-bridge converter circuit, a half-bridge converter circuit, etc. One end of the AC side of the single-phase converter unit on the input side of each converter is connected in parallel with a phase on the primary side of the transformer to obtain energy, and the other end of the AC side of the single-phase converter unit on the input side of each converter is connected to each other to form a neutral point. The AC side output voltage of the AC side of a converter unit on the output side of each converter is connected to the output end of the voltage regulating circuit of the corresponding phase on the secondary side of the three-phase transformer, and can also be connected to one end of the conventional winding of the three-phase transformer. When the output side of the converter is connected to one end of the conventional winding of the three-phase transformer, the output end of the voltage regulating circuit is connected to the AC system line.

[0072] In a specific embodiment, if Figure 7 As shown, the power flow control system also includes:

[0073] At least one additional transformer. When the voltage regulating transformer is a three-phase transformer and the converter is a three-phase converter, the autocoupler output end of the primary winding of each phase of the three-phase transformer is connected to each phase on the input side of the converter, each phase on the output side of the converter is connected to one end of the primary winding of an additional transformer, the other end of the primary winding of each additional transformer is interconnected, one end of the secondary winding of each additional transformer is respectively connected to the low-potential output end or the high-potential output end of the voltage regulating circuit on the secondary side of the corresponding phase of the three-phase transformer, and the other ends of the secondary windings of the three additional transformers are interconnected.

[0074] When the voltage regulating transformer is a three-phase transformer and the converter is a three-phase converter, the converter is composed of at least two three-phase converter units connected back to back, and the three-phase converter unit can be a three-phase rectifier circuit or a three-phase inverter circuit. Figure 7 As shown, the primary side of the three-phase transformer is connected in parallel to the AC system transmission line, and the three-phase secondary side input terminals of the three-phase transformer are respectively connected in series with the conventional windings of their respective phases, the voltage regulating circuit and the adjustable AC voltage output by the converter output side.

[0075] When one end of the secondary winding of each additional transformer is respectively connected to the low-potential output end of the voltage regulating circuit on the secondary side of the corresponding phase of the three-phase transformer, one end of the secondary winding of each phase of the three-phase transformer is connected to the corresponding AC system transmission line, the other end of the secondary winding of each phase of the three-phase transformer is connected to the voltage regulating circuit, and the high-potential output end of the voltage regulating circuit on the secondary side of the corresponding phase of the three-phase transformer is connected to the corresponding AC system transmission line.

[0076] The three-phase AC terminal on the input side of the three-phase converter is connected in parallel with the transformer to perform dynamic reactive compensation on the system nodes. The three-phase AC voltage output on the output side of the three-phase converter is connected to the primary side of the additional transformer, which is an additional three-phase transformer, such as Figure 7 As shown, the secondary winding of the additional transformer is a three-phase single-phase structure with 6 ports, which converts the three-phase AC voltage output by the converter into three single-phase voltages and connects them to the high potential output terminal or low potential output terminal of the corresponding phase of the three-phase secondary side of the three-phase transformer. Figure 7 To connect the additional transformer to the low-potential output terminal, when one end of the secondary side of the additional transformer is connected to the low-potential of the corresponding phase of the secondary side of the three-phase transformer, the other end of the secondary side of the additional transformer is interconnected in a star or triangle connection manner.

[0077] like Figure 8 As shown, when one end of the secondary winding of each additional transformer is respectively connected to the high-potential output terminal of the voltage regulating circuit on the secondary side of the corresponding phase of the three-phase transformer, one end of the secondary winding of each phase of the three-phase transformer is connected to the ground, and the other end is connected to the secondary winding of the corresponding additional transformer. The low-potential output terminal of the voltage regulating circuit on the secondary side of the corresponding phase of the three-phase transformer is connected to the corresponding AC system transmission line. When one end of the secondary side of the additional transformer is connected to the high-potential of the corresponding phase of the secondary side of the three-phase transformer, the other end of the secondary side of the additional transformer is interconnected in a star or delta connection manner. Figure 8 The secondary sides of the additional transformers are interconnected in a delta connection, but can also be interconnected in a star connection.

[0078] The power flow control system provided by the embodiment of the present invention, based on the voltage regulating transformer, introduces a converter to be connected in parallel with the primary side of the transformer to obtain energy, and the output end of the converter is connected in series with the secondary side of the transformer. By controlling the operating state of the converter, parallel reactive compensation of the AC system and control of the voltage amplitude and phase of the AC system transmission line are achieved, thereby enhancing the power flow control capability of the AC system; when the voltage regulating transformer is a three-phase transformer, the converter can be a single-phase transformer or a three-phase transformer; when the voltage regulating transformer is a single-phase transformer, the converter can be a single-phase transformer, thereby improving the flexible adaptability of the power flow control system; the controller controls the operating state of the converter, thereby improving the stability of the power flow control system and its power flow control capability.

[0079] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A power flow control system, characterized in that: include: A voltage regulating transformer, a controller and at least one converter, wherein: The voltage-regulating transformer includes a transformer and at least one voltage-regulating circuit, wherein the primary winding of the transformer is connected to the AC system, one end of the secondary winding is connected in series with the at least one voltage-regulating circuit, and the other end of the secondary winding is connected to the AC system; the voltage-regulating circuit includes at least one switch module, and the output voltage of the voltage-regulating circuit is controlled by controlling the on-off state of the switch module; The input side of the converter is connected to the primary winding of the voltage regulating transformer, and the output side is connected to the output end of the voltage regulating circuit on the secondary side of the voltage regulating transformer. The converter is used to adjust the voltage amplitude and phase of the AC system; The controller is installed on the AC system power line and is used to collect the voltage and current of its installation point, nodes in the preset proximity range, and branches. It also receives dispatch instructions from the upper level and changes the AC system voltage and power flow by coordinating the output voltage amplitude and phase of the voltage regulating circuit and converter. At least one additional transformer; when the voltage-regulating transformer is a three-phase transformer and the converter is a three-phase converter, the autocoupler output end of the primary winding of each phase of the three-phase transformer is connected to each phase of the converter input side, each phase of the converter output side is connected to one end of the primary winding of an additional transformer, the other end of each additional transformer primary winding is interconnected, one end of each additional transformer secondary winding is connected to the low-potential output end or the high-potential output end of the voltage-regulating circuit on the secondary side of the corresponding phase of the three-phase transformer, and the other ends of the secondary windings of the three additional transformers are interconnected; When one end of the secondary winding of each additional transformer is respectively connected to the high potential output terminal of the voltage regulating circuit on the secondary side of the corresponding phase of the three-phase transformer, one end of the secondary winding of each phase of the three-phase transformer is connected to the ground, and the other end is connected to the secondary winding of the corresponding additional transformer, and the low potential output terminal of the voltage regulating circuit on the secondary side of the corresponding phase of the three-phase transformer is connected to the corresponding AC system transmission line; At least one bypass switch module, with the voltage regulating circuit and the converter both connected in parallel to a bypass switch, the bypass switch module being used to quickly disconnect the fault point when either the voltage regulating circuit or the converter fails; or the output end of the voltage regulating circuit is connected to the converter via a bypass switch module, the bypass switch module being used to disconnect the current loop between the voltage regulating circuit and the converter when either the voltage regulating circuit or the converter fails; When one end of the secondary winding of each additional transformer is respectively connected to the low-potential output end of the voltage regulating circuit on the secondary side of the corresponding phase of the three-phase transformer, one end of the secondary winding of each phase of the three-phase transformer is connected to the corresponding AC system transmission line, the other end of the secondary winding of each phase of the three-phase transformer is connected to the voltage regulating circuit, and the high-potential output end of the voltage regulating circuit on the secondary side of the corresponding phase of the three-phase transformer is connected to the corresponding AC system transmission line.

2. The power flow control system according to claim 1, characterized in that: When the voltage-regulating transformer is a single-phase transformer, one end of the primary winding of the single-phase transformer is connected to any phase transmission line of the AC system, the other end of the primary winding of the single-phase transformer and the autocoupler output end are connected to the input side of the converter, and one end of the output side of the converter is connected to the output end of the voltage-regulating circuit on the secondary side of the single-phase transformer.

3. The power flow control system according to claim 1, characterized in that: When the voltage-regulating transformer is a three-phase transformer and the converter is a single-phase converter, the autocoupler output end of the primary winding of each phase of the three-phase transformer is connected to one end of the input side of a converter, the other ends of the three converter input sides are connected to each other, and one end of each converter output side is connected to the output end of the voltage-regulating circuit on the secondary side of the corresponding phase of the three-phase transformer.

4. The power flow control system according to claim 1, characterized in that: The voltage regulating circuit includes: a voltage regulating winding, two output terminals and four switch modules, wherein: One end of the first switch module and the third switch module is connected to one end of the voltage regulating winding, the other end of the first switch module is connected to one end of the second switch module at a first connection point, and a first output end is led out at the first connection point, the other end of the third switch module is connected to one end of the fourth switch module at a second connection point, and a second output end is led out at the second connection point, and the other end of the second switch module and the other end of the fourth switch module are both connected to the other end of the voltage regulating winding.

5. The power flow control system according to claim 4, characterized in that: When the secondary winding of the transformer is connected to a plurality of voltage regulating circuits, each voltage regulating circuit is connected in series with other voltage regulating circuits via two output terminals.

6. The power flow control system according to any one of claims 1, 4 and 5, characterized in that: The transformer is a single-phase transformer or a three-phase transformer.

7. The power flow control system according to claim 5, characterized in that: When the voltage regulating transformer includes a transformer and a voltage regulating circuit, the voltage regulating circuit is connected in series with the secondary winding of the transformer. By controlling the on-off state of the switch module, the output voltage of the two output ends of the voltage regulating circuit is a three-level voltage.

8. The power flow control system according to claim 5, characterized in that: When the voltage-regulating transformer includes a transformer and two voltage-regulating circuits, the two voltage-regulating circuits are connected in series and then connected in series with the secondary winding of the transformer. By controlling the on-off state of the switch module, the output voltage of the two output ends of the two voltage-regulating circuits connected in series is a nine-level voltage.

9. The power flow control system according to claim 5, characterized in that: When the voltage-regulating transformer includes a transformer and three voltage-regulating circuits, the three voltage-regulating circuits are connected in series and then connected in series with the secondary winding of the transformer. By controlling the on-off state of the switch module, the output voltage of the two output ends of the three voltage-regulating circuits connected in series is a twenty-seven-level voltage.

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