A flexible AC active voltage regulation device and method

Abstract

The application discloses a flexible alternating current active voltage regulating device and method, the device comprising a main transformer and a controllable voltage source, the main transformer comprising a main transformer high-voltage winding and a main transformer low-voltage winding, characterized in that the controllable voltage source is connected in series between the end of the main transformer high-voltage winding and the neutral point or ground of the transformer, the controllable voltage source is set to be capable of flexibly adjusting the voltage amplitude and phase, the controllable voltage source is used for adjusting the voltage across the main transformer high-voltage winding, and then the voltage of the low-voltage winding is adjusted through electromagnetic coupling. The amplitude modulation voltage regulation is used to replace the conventional mechanical turn regulation, the risks of mechanical failure, insulation deterioration, arc ignition and the like caused by frequent operation of the mechanical voltage regulating switch in the existing transformer are avoided, the reliable operation of the AC and DC power transmission system is ensured, and the safety and operation flexibility of the UHV DC power transmission system and the AC power transmission system are effectively improved.

Description

Technical Field

[0001] The present invention relates to the field of electric power system electrical equipment, and in particular to a flexible AC active voltage regulation device and method. Background Art

[0002] The converter transformer is the core of the HVDC transmission system. To meet the needs of DC system voltage regulation, a mechanical on-load tap changer is installed within the converter transformer. By adjusting the number of turns on the converter transformer's high-voltage winding, the voltage on the valve-side winding is regulated. Conventional AC power transformers also require on-load tap changers to maintain load-side voltage stability when system voltage fluctuates, ensuring load-side voltage quality. Transformer on-load tap changers are essential for maintaining the normal operation of both DC and AC systems.

[0003] Currently, on-load tap changers (OLTs) are primarily used to adjust the voltage of the low-voltage winding by changing the number of turns in the high-voltage winding, thereby changing the transformer's turns ratio. OLTs primarily utilize a combination of a selector switch and a transfer switch, along with dual transition resistors. These switches are mechanically complex and require frequent adjustments to their positions during long-term operation. Frequent actuation of internal mechanical components, such as the selector and transfer switches, can easily lead to mechanical failures such as gearbox shaft shake, gearbox ball clamp failure, misalignment, and drive shaft cracks. Furthermore, operational fault detection is difficult, and there is a risk of transformer inter-turn short circuits during the turn adjustment process. Numerous safety incidents involving OLTs in DC converter transformers have occurred, posing significant challenges to the safe operation of HVDC systems. To avoid frequent OLT actuation and mitigate operational risks, UHVDC systems are forced to adopt fixed operating modes, significantly reducing the flexibility of DC system operation and limiting the effective utilization of DC transmission capacity. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defects of the mechanical voltage regulating switch of the transformer in the prior art, such as mechanical failure and insulation degradation caused by frequent operation, thereby providing a flexible AC active voltage regulating device and method.

[0005] To this end, the present invention provides a flexible AC active voltage regulator, comprising:

[0006] A main transformer, comprising a first winding and a second winding, wherein the first winding and the second winding are electromagnetically coupled, a head end of the first winding is used to be connected to an AC system bus, and the second winding is used to be connected to a load or an AC / DC power transmission system;

[0007] A controllable voltage source, one end of which is connected to the end of the first winding, and the other end of which is connected to the neutral point of the transformer or the ground, wherein the controllable voltage source is configured to have an adjustable amplitude or phase of the output voltage.

[0008] A controllable voltage source is connected in series between the end of the main transformer winding and the neutral point or ground of the transformer. By changing the output voltage of the controllable voltage source without changing the turns ratio, the voltage across the first winding can be adjusted, thereby changing the output voltage of the second winding.

[0009] Furthermore, the controllable voltage source outputs a voltage having the same operating frequency as the main transformer.

[0010] Furthermore, the phase adjustment range of the output voltage of the controllable voltage source is 0-360 degrees.

[0011] Furthermore, the first winding is a high-voltage winding, and the second winding is a low-voltage winding.

[0012] Furthermore, the controllable voltage source includes:

[0013] The energy transformer includes a third winding and a fourth winding, wherein the third winding and the fourth winding are electromagnetically coupled, and the third winding is connected to an external AC power source;

[0014] The voltage regulating converter valve has an output side connected in series between the end of the first winding and the neutral point of the transformer or the ground, and an input side connected to the fourth winding.

[0015] The controllable voltage source may be realized by a power electronic converter.

[0016] Furthermore, the voltage regulating converter valve includes several power modules, the input sides of the several power modules are respectively connected to the fourth winding, and the output sides of the several power modules are cascaded and connected in series between the end of the first winding and the neutral point or ground of the transformer.

[0017] The voltage-regulating converter valve is composed of several power modules based on fully controlled power electronics, achieving AC-DC-AC power conversion. Cascading multiple power modules allows for adaptability to different voltage ranges, adjusting the transformer winding's output voltage without changing the turns ratio.

[0018] Furthermore, the external AC power supply includes a fifth winding, which is electromagnetically coupled to the first winding and connected to the third winding.

[0019] Furthermore, the controllable voltage source includes a bypass switch, which is connected in series between the end of the first winding and the neutral point of the transformer or the ground.

[0020] The bypass switch ensures that the normal operation of the main transformer is not affected when the controllable voltage source fails.

[0021] A flexible AC active voltage regulation method comprises the following steps:

[0022] A main transformer is provided, the main transformer including a first winding and a second winding, the first winding and the second winding are electromagnetically coupled, a head end of the first winding is used to be connected to an AC system bus, and the second winding is used to be connected to a load or an AC / DC power transmission system;

[0023] A voltage with adjustable amplitude or phase is provided between the end of the first winding and the neutral point of the main transformer.

[0024] The technical solution of the present invention has the following advantages:

[0025] 1. This invention connects a controllable voltage source with flexible amplitude and phase adjustment in series between the end of the main transformer winding and the transformer's neutral point or ground. By adjusting the output voltage of the controllable voltage source, the voltage across the first winding of the main transformer is adjusted, thereby changing the output voltage of the second winding of the main transformer. This approach replaces traditional turn-to-turn voltage regulation with amplitude modulation, completely eliminating the operational risks associated with turn-to-turn voltage regulation.

[0026] 2. The controllable voltage source in the present invention is installed between the end of the main transformer winding and the neutral point or ground of the transformer. The insulation requirements for the controllable voltage source are low, the current is small, and it is easy to apply in engineering;

[0027] 3. The controllable voltage source of the present invention can be composed of multiple power modules. Multiple modules can be cascaded to achieve applications under different voltages and are easy to expand.

[0028] 4. The controllable voltage source in the present invention is based on power electronic devices, which has flexible control, fast response, unlimited adjustment times, and no arc risk;

[0029] 5. In addition to continuous voltage regulation under normal operating conditions, the present invention can also quickly output a controllable voltage source to compensate for the AC system voltage when the system voltage drops, effectively improving the operational reliability of the AC and DC systems;

[0030] 6. The present invention can timely and effectively perform status monitoring, and can avoid problems such as failure to detect faults in mechanical switches and gradual insulation degradation.

[0031] 7. The present invention achieves the purpose of active voltage regulation through the aforementioned power modules. The voltage is adjusted through a control strategy. The cascaded power modules can be applied to different voltage ranges to change the transformer winding voltage. The voltage-regulating converter valve adopts module cascade technology, and the output voltage can be flexibly expanded to achieve the purpose of flexible voltage regulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] 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.

[0033] Figure 1 This is a principle block diagram of a specific example of the flexible AC active voltage regulator in Example 1 of the present invention;

[0034] Figure 2 A topological structure diagram of a specific example of the flexible AC active voltage regulator in embodiment 2 of the present invention;

[0035] Figure 3 A topological structure diagram of a specific example of the flexible AC active voltage regulator in Example 3 of the present invention;

[0036] Figure 4 This is a flowchart of a specific example of the flexible AC active voltage regulation method in Example 4 of the present invention;

[0037] Reference numerals:

[0038] 01-AC system bus, 02-main transformer, 03-controlled voltage source, 04-other AC power sources, 21-first winding, 22-second winding, 23-fifth winding, 31-voltage regulating valve, 32-energy extraction transformer, 33-bypass switch, 311-power module, 321-third winding, 322-fourth winding. DETAILED DESCRIPTION

[0039] 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.

[0040] In the description of the present invention, it should be noted that the terms "first", "second" and "third" are only used for descriptive purposes and should not be understood as indicating or implying relative importance.

[0041] Example 1

[0042] This embodiment provides an AC voltage regulating device, such as Figure 1As shown, it includes: a main transformer 02, the main transformer 02 includes a first winding 21 and a first winding 22, the first winding 21 and the first winding 22 are electromagnetically coupled, the first end of the first winding 21 is used to be connected to the AC system bus 01, and the second winding 22 is used to be connected to the load or the AC / DC power transmission system; a controllable voltage source 03, one end of which is connected to the end of the first winding 21, and the other end is used to be connected to the neutral point or ground of the main transformer 02, and the controllable voltage source 03 is configured to have an adjustable output voltage amplitude or phase.

[0043] In an optional embodiment, the main transformer 02 may be a converter transformer or a power transformer.

[0044] In an optional implementation, the controllable voltage source 03 outputs a voltage having the same operating frequency as the main transformer 02 .

[0045] In an optional embodiment, the phase of the output voltage of the controllable voltage source 03 can be adjusted in a range of 0-360 degrees.

[0046] In an optional embodiment, the first winding 21 is a high-voltage winding, and the second winding 22 is a low-voltage winding, or the first winding 21 is a low-voltage winding, and the second winding 22 is a high-voltage winding.

[0047] The AC system bus 01, to which the main transformer 02 is connected, provides power to the main transformer 02. The first winding 21 and the second winding 22 cooperate to complete the voltage conversion process. The second winding 22 is responsible for voltage output. When the voltage of the first winding 21 changes, the voltage of the low-voltage winding also changes accordingly.

[0048] A controllable voltage source 03 is connected in series between the end of the first winding 21 of the main transformer 02 and the neutral point (or ground), and the voltage of the AC system bus 01 is u S , the voltage of the first winding of the main transformer 02 is u1, and the output voltage of the controllable voltage source 03 is u X , the second winding voltage is u2, the transformation ratio of the first winding 21 and the second winding 22 of the main transformer 02 is N, then the relationship between the second winding 22 voltage and the output voltage of the controllable voltage source 03 is as follows:

[0049]

[0050] This embodiment adjusts the voltage across the first winding of the main transformer, thereby changing the output voltage of the second winding, by changing the output voltage of the controllable voltage source 03 without changing the turns ratio. A controllable voltage source with flexible amplitude and phase adjustment is connected in series between the end of the first winding of the main transformer 02 and the center point (or ground). This has a low ground potential, low insulation requirements, low current tolerance, and is easy to implement. By adjusting the output voltage of the voltage source, the voltage across the first winding of the transformer is changed, thereby adjusting the voltage of the second winding (low-voltage side) of the transformer. This replaces traditional mechanical turn-to-turn voltage regulation with amplitude modulation and voltage regulation, avoiding the frequent activation of traditional mechanical turn-to-turn voltage regulation switches, reducing safety operational risks, improving the operational flexibility of the DC system, and effectively enhancing the DC transmission capacity of the transformer.

[0051] Example 2

[0052] Based on Example 1, the flexible AC active voltage regulator provided in this embodiment is as follows: Figure 2 As shown, the controllable voltage source 03 includes: an energy-taking transformer 32, including a third winding 321 and a fourth winding 322, the third winding 321 and the fourth winding 322 are electromagnetically coupled, and the third winding 321 is connected to an external AC power supply; a voltage-regulating converter valve 31, the output side of which is connected in series between the end of the first winding 21 and the neutral point (or ground) of the transformer, and the input side is connected to the fourth winding 322.

[0053] In an optional embodiment, the voltage regulating converter valve 31 includes a plurality of power modules 311, the input sides of the plurality of power modules 311 are respectively connected to the fourth winding 322, and the output sides of the plurality of power modules 311 are cascaded and connected in series between the end of the first winding 21 and the neutral point of the transformer.

[0054] The plurality of power modules 311 are commutation power modules to achieve the purpose of active voltage regulation.

[0055] In one optional embodiment, the output sides of the power modules are cascaded to achieve the desired regulated voltage. By adjusting the voltage through a control strategy, the cascaded power modules can be adapted to different voltage ranges, thereby varying the transformer winding voltage. The voltage-regulating converter valve utilizes module cascade technology, allowing for flexible expansion of the output voltage and achieving flexible voltage regulation.

[0056] In an optional embodiment, the controllable voltage source 03 may be implemented by a power electronic converter.

[0057] In an optional embodiment, a bypass switch 33 is further included, and the bypass switch 33 is connected in series between the end of the first winding 21 and the neutral point (or ground) of the transformer.

[0058] The fourth winding 322 (low-voltage side) of the energy extraction transformer 32 is a multi-winding type, with each winding providing energy to each power module. The controllable voltage source 03 can be implemented by a power electronic converter. The third winding 321 (high-voltage side) of the energy extraction transformer 32 is connected to the AC power supply bus of other voltage levels in the substation. The fourth winding 322 (low-voltage side) is connected to the voltage-regulating converter valve 31, converting the voltage of the other power supply bus into an input voltage suitable for the voltage-regulating converter valve 31. The energy extraction transformer 32 is connected to the other AC power source 04 in the substation, reducing the voltage of the other AC power source 04 to a voltage suitable for the input of the voltage-regulating converter valve 31, providing active power support for the voltage-regulating converter valve 31 and achieving electrical isolation between the other AC power source 04 and the voltage-regulating converter valve 31.

[0059] The voltage-regulating converter valve 31 is composed of multiple power modules 311 based on fully controlled power electronic devices, achieving AC-DC-AC power conversion. The input side of each power module 311 is connected to the low-voltage winding of the energy-taking transformer 32, and each power module 311 on the input side is independent of each other. The output side of the power modules 311 is connected in series to the neutral point (or ground) of the high-voltage winding of the transformer 02 through cascading. Multiple modules can be cascaded to accommodate different voltage ranges, allowing the output voltage of the valve-side winding to be adjusted without changing the turns ratio. The voltage-regulating converter valve 31 is located outside the main transformer and connected to the fourth winding 322 (low-voltage side) of the energy-taking transformer 32. The voltage can be adjusted using a control strategy. Multiple modules can be cascaded to accommodate different voltage ranges, used to change the voltage of the high-voltage winding of the main transformer 02, thereby adjusting the output voltage of the low-voltage winding without changing the turns ratio. Several power modules 311 in the voltage-regulating converter valve 31 can be cascaded to achieve flexible output voltage expansion.

[0060] Bypass switch 33 is connected in parallel across the output of active voltage-regulating converter valve 31 to ensure that a failure of valve 31 does not affect the normal operation of transformer 02. When active voltage-regulating converter valve 31 fails, bypass switch 33 closes, allowing main transformer 02 to continue functioning without affecting the continued operation of the AC / DC system.

[0061] Example 3

[0062] Based on embodiment 2, a flexible AC active voltage regulator is provided, such as Figure 3 As shown, the external AC power supply includes a fifth winding 23 , which is electromagnetically coupled to the first winding 21 , and is connected to the third winding 321 .

[0063] The fifth winding 23 is connected to the third winding 321 (input side) of the energy extraction transformer 32 to provide active power support for the energy extraction transformer 32. The energy extraction transformer 32 is connected to the fifth winding 23 to reduce the voltage of the fifth winding 23 to an input voltage suitable for the voltage-regulating converter valve 31, providing active power support for the voltage-regulating converter valve 31 and achieving electrical isolation between the fifth winding 23 and the voltage-regulating converter valve 31.

[0064] Example 4

[0065] This embodiment provides an AC voltage regulation method, such as Figure 4 As shown, the following steps are included:

[0066] S1: Provide a main transformer, which includes a first winding and a second winding. The first winding and the second winding are electromagnetically coupled. The first winding is used to connect to the AC system bus at its head end, and the second winding is used to connect to a load or an AC / DC power transmission system.

[0067] S2: Provides a voltage with adjustable amplitude or phase between the end of the first winding and the neutral point of the main transformer;

[0068] By adjusting the voltage across the first winding, the output voltage of the second winding is adjusted.

[0069] The above-mentioned flexible AC active voltage regulation method connects a controllable voltage source with flexible amplitude and phase adjustment in series between the end of the high-voltage winding of the converter transformer (or power transformer) and the neutral point (or ground) of the transformer. By adjusting the output voltage of the voltage source, the voltage across the high-voltage winding of the transformer is changed, and then the voltage on the low-voltage side of the transformer is adjusted. By replacing the traditional mechanical turn-to-turn voltage regulation with amplitude modulation, the operational risks brought by the use of turn-to-turn voltage regulation can be completely avoided.

[0070] 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 readily appreciate that other variations or modifications based on the above descriptions are possible. 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 flexible AC active voltage regulator, characterized in that: include: A main transformer, comprising a first winding and a second winding, wherein the first winding and the second winding are electromagnetically coupled, a head end of the first winding is used to be connected to an AC system bus, and the second winding is used to be connected to a load or an AC / DC power transmission system; a controllable voltage source, one end of the controllable voltage source being connected to the end of the first winding, and the other end being connected to the neutral point or ground of the transformer, the controllable voltage source being configured to have an adjustable amplitude or phase of an output voltage; Wherein, the controllable voltage source includes: The energy transformer includes a third winding and a fourth winding, wherein the third winding and the fourth winding are electromagnetically coupled, and the third winding is connected to an external AC power source; a voltage regulating valve, the output side of which is connected in series between the end of the first winding and the neutral point of the transformer, and the input side of which is connected to the fourth winding; The voltage regulating converter valve includes a plurality of power modules, the input sides of the plurality of power modules are respectively connected to the fourth winding, and the output sides of the plurality of power modules are cascaded and connected in series between the end of the first winding and the neutral point of the transformer; The controllable voltage source outputs a voltage having the same operating frequency as the main transformer.

2. The flexible AC active voltage regulator according to claim 1, characterized in that: The phase adjustment range of the output voltage of the controllable voltage source is 0-360 degrees.

3. The flexible AC active voltage regulator according to claim 1, characterized in that: The first winding is a high-voltage winding, and the second winding is a low-voltage winding.

4. The flexible AC active voltage regulator according to claim 1, characterized in that: The output sides of the plurality of power modules are cascaded to achieve a voltage that needs to be adjusted.

5. The flexible AC active voltage regulator according to claim 1, characterized in that: The external AC power supply includes a fifth winding, which is electromagnetically coupled to the first winding and connected to the third winding.

6. The flexible AC active voltage regulator according to claim 1, characterized in that: The controllable voltage source includes a bypass switch connected in series between the end of the first winding and the neutral point of the transformer.

7. A flexible AC active voltage regulation method, characterized in that: Based on the flexible AC active voltage regulator according to claim 1, the method comprises the following steps: A main transformer is provided, the main transformer including a first winding and a second winding, the first winding and the second winding are electromagnetically coupled, a head end of the first winding is used to be connected to an AC system bus, and the second winding is used to be connected to a load or an AC / DC power transmission system; A voltage with adjustable amplitude or phase is provided between the end of the first winding and the neutral point of the main transformer, and different voltage ranges are provided by cascading multiple modules.

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