Active smoothing voltage regulation method and system for ultra-high voltage direct current system converter transformer

Abstract

The application relates to an active smooth voltage regulation method and system of an extra-high voltage direct current system converter transformer, which comprises the following steps: determining the voltage regulation range of the converter transformer configured with a smooth voltage regulation device, and determining the number of a plurality of parallel bridge arm sub-modules in the smooth voltage regulation device according to the voltage regulation range; after the direct current system is unlocked, the direct current side of the smooth voltage regulation device is electrified; under different operation modes of the direct current system, the number of the bridge arm sub-modules is controlled to be switched to regulate the alternating current side voltage, and valve side voltage regulation is realized. The application can simultaneously consider the smooth voltage regulation demand and the smooth regulation characteristic of the extra-high voltage direct current system, improves the operation characteristic of the extra-high voltage direct current transmission system, and can be applied in the high voltage direct current transmission field.

Description

Technical Field

[0001] This invention relates to the field of high voltage direct current transmission technology, and in particular to an active smooth voltage regulation method and system for converter transformers in ultra-high voltage direct current systems. Background Technology

[0002] Ultra-high voltage direct current (UHVDC) transmission projects adopt a dual twelve-pulse converter main wiring topology based on thyristor valves. The rectifier side uses constant firing angle control, while the inverter side uses constant turn-off angle control or constant DC voltage control. When the transmission power increases, the firing angle on the rectifier side continuously decreases, requiring adjustment of the converter transformer tap changer to a range of 15°±2.5°. On the inverter side, the converter transformer tap changer also needs adjustment to control the turn-off angle or DC voltage. Similarly, when the transmission power decreases, the tap changers on both the rectifier and inverter sides require extensive adjustment. Traditional UHVDC transmission projects use mechanical on-load tap changers to regulate tap position and valve-side voltage in converter transformers. The control and protection system monitors the rectifier-side firing angle and inverter-side turn-off angle or DC voltage in real time. Once the steady-state operating range is exceeded, an up / down tap command is sent to the converter transformer tap changer. After receiving the command, the tap changer adjusts from the current tap position to the target tap position. The adjustment range between each tap position is 1.25% of the grid-side rated voltage. During the tap jump, the valve-side voltage will change "step-like", causing the DC voltage to fluctuate "sawtooth". In addition, the traditional tap changer is a mechanical structure with slow adjustment speed response and poor following characteristics when the DC system needs to increase / decrease power. Summary of the Invention

[0003] To address the aforementioned problems, the purpose of this invention is to provide an active smooth voltage regulation method and system for converter transformers in ultra-high voltage direct current (UHVDC) systems. This method can simultaneously meet the smooth voltage regulation requirements and smooth regulation characteristics of UHVDC systems, thereby improving the operational characteristics of UHVDC transmission systems.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: an active smooth voltage regulation method for a converter transformer in an ultra-high voltage direct current (UHVDC) system, comprising: determining the voltage regulation range of the converter transformer equipped with a smooth voltage regulation device; determining the number of parallel bridge arm sub-modules in the smooth voltage regulation device according to the voltage regulation range; the smooth voltage regulation device is connected in series between the end of the grid-side winding of the converter transformer and the grounding point; the high and low voltage buses on the DC side are respectively connected in parallel to the DC pole line and the neutral line; after the DC system is unlocked, the DC side of the smooth voltage regulation device is energized; under different operating modes of the DC system, the AC side voltage is adjusted by controlling the number of bridge arm sub-modules switched on and off, thereby realizing valve-side voltage regulation.

[0005] Furthermore, the bridge arm submodule is composed of several IGBT fully controlled power electronic devices connected in series.

[0006] Furthermore, determining the voltage regulation range of the converter transformer includes:

[0007] Determine the highest and lowest steady-state voltages of the AC bus of the converter station based on the voltage fluctuation range of the connected AC system;

[0008] Based on the DC-side main circuit parameters and operating mode of the DC system, determine the upper and lower limits of the valve-side voltage of the converter transformer;

[0009] Based on the determined upper and lower limits of the valve-side voltage, and in conjunction with the highest and lowest steady-state voltages of the AC bus of the converter station, the voltage regulation range of the converter transformer is determined.

[0010] Furthermore, the determination of the upper and lower limits of the converter transformer valve-side voltage is based on different operating modes of the DC system, including:

[0011] Under the condition that the DC system is operating at full voltage and in the first minimum power mode, determine the lower limit value of the converter transformer valve side voltage under this operating condition;

[0012] Determine the upper limit of the converter transformer valve side voltage under the following operating conditions: The DC system is operating at full voltage and first rated power.

[0013] Determine the upper limit of the converter transformer valve side voltage under the condition that the DC system is operating at full voltage and under long-term overload.

[0014] When the DC system is operating at reduced voltage and in the second minimum power mode, determine the lower limit of the converter transformer valve side voltage under this operating condition;

[0015] Determine the upper limit of the converter transformer valve side voltage under the following operating conditions: DC system is operating at reduced voltage and second rated power.

[0016] The minimum value of the lower limit under each operating condition is taken to obtain the minimum value of the converter transformer valve side voltage under each operating mode of the DC system, which is taken as the lower limit value; the maximum value of the upper limit under each operating condition is taken to obtain the maximum value of the converter transformer valve side voltage under each operating mode of the DC system, which is taken as the upper limit value.

[0017] Furthermore, determining the voltage regulation range of the converter transformer based on the determined upper and lower limits of the valve-side voltage, combined with the highest and lowest steady-state voltages of the AC bus of the converter station, includes:

[0018] Based on the highest steady-state voltage of the converter station bus and the minimum voltage on the valve side of the converter transformer, the lower limit value of the smooth voltage regulating device is obtained;

[0019] Based on the minimum steady-state voltage of the converter station bus and the maximum voltage on the valve side of the converter transformer, the upper limit value of the smooth voltage regulating device is obtained;

[0020] Based on the lower and upper limits of the smooth voltage regulator, the voltage regulation range of the smooth voltage regulator is obtained.

[0021] Furthermore, the regulation of AC side voltage by controlling the number of bridge arm sub-modules switched includes: the DC system coordinating with the smooth voltage regulation device to regulate AC side voltage during the process of unlocking the DC system and increasing its power to the rated value;

[0022] When the grid-side circuit breaker is closed, the main winding, voltage regulating winding, and valve-side winding of the converter transformer grid side are all energized. The smooth voltage regulating device starts the sub-module to actively charge. After the sub-module voltage rises to the first rated power, it is ready to be unlocked.

[0023] When the smooth voltage regulating device is unlocked, a voltage opposite in phase to that of the main winding is output on the grid-side voltage regulating winding, thereby increasing the valve-side voltage and effectively raising the tap changer position.

[0024] The DC system is unlocked and operates at the first minimum power.

[0025] When the power of a DC system is increased, the smooth voltage regulation device controls the voltage on the valve side, using the firing angle, shutdown angle, or DC voltage as the control target, until the power is increased to the first rated power, and the DC system enters rated operation.

[0026] Furthermore, the regulation of AC side voltage by controlling the number of bridge arm sub-modules switched includes: the DC system coordinating with the smooth voltage regulation device to regulate AC side voltage during the process of unlocking the DC system and increasing its power to the rated value;

[0027] After the DC blocking command is issued, the DC transmission power gradually decreases from the first rated power to the first minimum power. The smooth voltage regulation device controls the valve side voltage to ensure that the firing angle, turn-off angle or DC voltage is the control target.

[0028] The DC system operates at the first minimum power, at which point the commutator ratio is grid-side main winding / valve-side winding, the voltage at the grid-side regulating winding terminal is zero, and the equivalent gear is gear 1.

[0029] DC system lockout;

[0030] With the smooth voltage regulator locked, there is no output voltage on the AC side, and the submodule is in active charging mode.

[0031] When the grid-side circuit breaker trips, the main winding, voltage regulating winding, and valve-side winding of the converter transformer on the grid side are de-energized.

[0032] An active smoothing voltage regulation system for a converter transformer in an ultra-high voltage direct current (UHVDC) system includes: a processing module, which determines the voltage regulation range of the converter transformer equipped with a smoothing voltage regulation device, and determines the number of parallel bridge arm sub-modules in the smoothing voltage regulation device based on the voltage regulation range; and a voltage regulation module, which, after the DC system is unlocked, energizes the DC side of the smoothing voltage regulation device, and regulates the AC side voltage by controlling the number of bridge arm sub-modules switched on and off under different operating modes of the DC system, thereby achieving valve-side voltage regulation.

[0033] A computer-readable storage medium storing one or more programs, the one or more programs including instructions that, when executed by a computing device, cause the computing device to perform any of the methods described above.

[0034] A computing device includes: one or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, and the one or more programs include instructions for performing any of the methods described above.

[0035] A converter transformer for an ultra-high voltage direct current system includes the aforementioned active smooth voltage regulation system with a smooth voltage regulation device.

[0036] The present invention has the following advantages due to the adoption of the above technical solutions:

[0037] 1. This invention employs a smooth voltage regulating device based on IGBT fully controlled power electronic devices. This device is connected in series between the end of the grid-side winding of the converter transformer and the grounding point. By controlling the switching of submodules, it regulates the AC side voltage. Under different operating modes of the DC system, the voltage regulating device dynamically adjusts the AC side port voltage in real time, achieving valve-side voltage regulation. The converter transformer does not require a mechanical on-load tap changer, thus avoiding the problem of on-load tap changer failure in principle.

[0038] 2. The present invention employs a method that has the ability to continuously and smoothly adjust the valve-side voltage of the converter transformer, thereby avoiding the “step-like” changes in the valve-side voltage during the adjustment process of the mechanical on-load tap changer, which would cause “sawtooth” fluctuations in the DC voltage.

[0039] 3. This invention fully utilizes the fast and flexible control capability of the smooth voltage regulating device, and can coordinate with the DC system to achieve active support control of the AC voltage on the valve side of the converter transformer, solving the problems of slow adjustment response and poor following characteristics of traditional mechanical on-load tap changers. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the active smooth voltage regulation method for the converter transformer of the ultra-high voltage direct current system in an embodiment of the present invention;

[0041] Figure 2 This is a schematic diagram of the topology of the converter transformer smooth voltage regulation device provided in this embodiment of the invention;

[0042] Figure 3a This is a timing diagram of unlocking and power increase of a DC system using a converter transformer smooth voltage regulation device provided in an embodiment of the present invention;

[0043] Figure 3b This is a timing diagram of power reduction and blocking of a DC system using a converter transformer smooth voltage regulation device provided in an embodiment of the present invention. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0045] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0046] This invention provides an active smooth voltage regulation method and system for converter transformers in ultra-high voltage direct current (UHVDC) systems. The system includes: replacing the traditional mechanical on-load tap changer in the converter transformer with a smooth voltage regulation device. This device is connected in series between the end of the grid-side winding and the grounding point. The high and low voltage buses on the DC side are connected in parallel to the DC pole line and the neutral line, respectively. After the incoming switch of the converter transformer is closed, the DC converter valve is unlocked, the DC side voltage is established, and the DC pole line and neutral line charge the bridge arm sub-modules of the smooth voltage regulation device. Once the sub-module voltage reaches the rated level, the smooth voltage regulation device is unlocked. By controlling the switching of the bridge arm sub-modules, the AC side voltage is regulated, changing the voltage between the end of the grid-side winding and the grounding point of the converter transformer. This controls the voltage of the valve-side winding of the converter transformer, thus achieving the regulation of the valve-side voltage of the converter transformer. This invention can be widely applied in the field of high-voltage direct current transmission technology.

[0047] In one embodiment of the present invention, an active smooth voltage regulation method for a converter transformer in an ultra-high voltage direct current system is provided. In this embodiment, as... Figure 1 As shown, the method includes the following steps:

[0048] 1) Determine the voltage regulation range of the converter transformer equipped with a smooth voltage regulation device, and determine the number of several parallel bridge arm sub-modules in the smooth voltage regulation device based on the voltage regulation range;

[0049] 2) After the DC system is unlocked, the DC side of the smooth voltage regulator is energized. Under different operating modes of the DC system, the AC side voltage is adjusted by controlling the number of switching bridge arm sub-modules, thereby realizing valve side voltage regulation.

[0050] In step 1) above, if Figure 2 As shown, this embodiment uses a 6-pulse converter (equipped with a converter transformer smooth voltage regulation device) in an ultra-high voltage direct current system as an example for illustration.

[0051] In this embodiment, the UHVDC primary system includes a converter transformer 1, a DC converter valve 4, a smoothing voltage regulating device 5, a grounding point 8, DC pole lines 9, a DC neutral line 10, and a DC grounding electrode 11. The converter transformer 1 includes a grid-side winding 2 and a valve-side winding 3. The valve-side winding 3 is connected to the DC converter valve 4. The high and low voltage buses of the DC converter valve 4 are connected in parallel to the DC pole line 9 and the DC neutral line 10, respectively, and the DC neutral line 10 is connected to the DC grounding electrode 11. The converter transformer 1 eliminates the traditional mechanical on-load tap changer and is equipped with a smoothing voltage regulating device 5. The smoothing voltage regulating device 5 is connected in series between the end of the grid-side winding 2 and the grounding point 8, and the DC high and low voltage buses are connected in parallel to the DC pole line 9 and the neutral line 10, respectively.

[0052] The smoothing voltage regulating device 5 also includes several bridge arm reactors 6, with the upper and lower ends of each bridge arm connected to the DC pole line 9 and the DC neutral line 10 respectively via a bridge arm reactor 6. Moreover, each bridge arm sub-module in the smoothing voltage regulating device 5 is composed of several IGBT fully controlled power electronic devices connected in series.

[0053] In step 1) above, preferably, in the DC converter valve 4, the converter valve located on the rectifier side adopts a thyristor device or a reverse-resistance type IGCT (integrated gate commutator thyristor) device, and the converter valve on the inverter side adopts a reverse-resistance type IGCT device, which can solve the problems of commutation failure on the inverter side of conventional DC transmission systems and the difficulty in self-clearing DC short-circuit faults in flexible DC transmission systems.

[0054] In step 1) above, the method for determining the voltage regulation range of the converter transformer includes the following steps:

[0055] 1.1) Determine the highest and lowest steady-state voltages of the AC bus of the converter station based on the voltage fluctuation range of the connected AC system;

[0056] 1.2) Based on the DC-side main circuit parameters and operating modes of the DC system, including minimum power operation, rated power operation, and step-down operation, determine the upper and lower limits of the valve-side voltage of the converter transformer;

[0057] 1.3) Based on the determined upper and lower limits of the valve-side voltage, and in conjunction with the highest and lowest steady-state voltages of the AC bus of the converter station, determine the voltage regulation range of the converter transformer.

[0058] In this embodiment, based on the determined voltage regulation range of the converter transformer, the number of bridge arm sub-modules and the IGBT model are further determined.

[0059] In step 1.2) above, the upper and lower limits of the converter transformer valve-side voltage are determined according to different operating modes of the DC system, including the following steps:

[0060] 1.2.1) Determine the lower limit of the converter transformer valve-side voltage under the full-voltage operation and first minimum power (0.1 pu) mode of the DC system;

[0061] 1.2.2) Determine the upper limit of the voltage on the valve side of the converter transformer when the DC system is operating at full voltage and at the first rated power (1.0 pu);

[0062] 1.2.3) Determine the upper limit of the converter transformer valve side voltage under the DC system operating at full voltage and long-term overload (1.05 pu) mode;

[0063] 1.2.4) When the DC system is in step-down operation and the second minimum power (0.08 pu) mode, determine the lower limit of the voltage on the valve side of the converter transformer;

[0064] 1.2.5) When the DC system is in step-down operation and second rated power (0.8pu) mode, determine the upper limit of the voltage on the valve side of the converter transformer;

[0065] 1.2.6) Take the minimum lower limit value under each operating condition to obtain the minimum value of the converter transformer valve side voltage under each operating mode of the DC system, and take it as the lower limit value; take the maximum upper limit value under each operating condition to obtain the maximum value of the converter transformer valve side voltage under each operating mode of the DC system, and take it as the upper limit value; based on the obtained maximum and minimum values ​​of the converter transformer valve side voltage, obtain the range of valve side voltage variation.

[0066] In step 1.3) above, based on the determined upper and lower limits of the valve-side voltage, and in conjunction with the highest and lowest steady-state voltages of the AC bus of the converter station, the voltage regulation range of the converter transformer is determined, including the following steps:

[0067] 1.3.1) Based on the highest steady-state voltage of the converter station bus and the minimum voltage of the converter transformer valve side, the required turns ratio of the converter transformer grid side and valve side under the current operating conditions can be obtained; combined with the number of turns of the converter transformer grid side and valve side windings, the voltage value that the smooth voltage regulating device needs to output can be obtained, that is, the lower limit value of the smooth voltage regulating device.

[0068] 1.3.2) Based on the minimum steady-state voltage of the converter station bus and the maximum voltage of the converter transformer valve side, the required turns ratio of the converter transformer grid side and valve side under the current operating conditions can be obtained; combined with the number of turns of the converter transformer grid side and valve side windings, the voltage value that the smooth voltage regulating device needs to output can be obtained, that is, the upper limit value of the smooth voltage regulating device.

[0069] 1.3.3) Based on the obtained lower and upper limits of the smooth voltage regulator, the voltage regulation range of the smooth voltage regulator is obtained.

[0070] In step 1) above, determining the number of parallel bridge arm sub-modules and IGBT models in the smoothing voltage regulating device based on the voltage regulation range includes the following steps:

[0071] I) Determine the number of sub-modules required for each bridge arm based on the voltage regulation range of the converter transformer smoothing voltage regulation device and the steady-state operating voltage of each sub-module;

[0072] Ⅱ) Determine the current carrying capacity of the submodule based on the converter transformer side current required for the maximum operating power of the DC system;

[0073] Ⅲ) Based on the obtained voltage and current values, determine the selection of IGBT devices.

[0074] In step 2) above, by adjusting the voltage output on the grid-side voltage regulating winding that is in the same / opposite phase to the main winding, the valve-side voltage decreases / increases, which is equivalent to lowering / raising the tap position.

[0075] Different operating modes of a DC system include the process of unlocking the DC system and increasing its power to rated capacity, and the process of locking the DC system after reducing its power. Among them:

[0076] During the process of unlocking the DC system and increasing its power to rated capacity, the AC side voltage is regulated in coordination with the smoothing voltage regulator, such as... Figure 3a As shown, it includes the following steps:

[0077] 2.1.1) When the grid-side circuit breaker is closed, the main winding, voltage regulating winding and valve-side winding of the converter transformer grid side are all energized. The smooth voltage regulating device starts the sub-module to charge actively. After the sub-module voltage rises to the first rated power, it is ready to unlock.

[0078] In this embodiment, the first rated power is 1.0 pu;

[0079] 2.1.2) The smooth voltage regulating device is unlocked, and a voltage opposite to that of the main winding is output on the grid-side voltage regulating winding, thereby increasing the valve-side voltage and effectively raising the tap changer position.

[0080] 2.1.3) Unlock the DC system and operate at the first minimum power level;

[0081] In this embodiment, the first minimum power is 0.1 pu;

[0082] 2.1.4) When the DC system increases power, the smooth voltage regulating device controls the valve side voltage, using the firing angle, shutdown angle or DC voltage as the control target, until the power is increased to the first rated power and the DC system enters rated operation.

[0083] In this embodiment, due to the adoption of a flexible smooth voltage regulation device, the converter transformer no longer has the tap positions of the traditional mechanical tap changer. Instead, the DC open-circuit voltage Udi0 is used as the state description quantity. However, for ease of understanding and comparison with the traditional tap changer, the concept of "equivalent tap position" will still be used to describe the DC state in this embodiment.

[0084] During the power reduction and blocking process in the DC system, the AC side voltage is adjusted in coordination with the smoothing voltage regulator, such as... Figure 3b As shown, it includes the following steps:

[0085] 2.2.1) After the DC blocking command is issued, the DC transmission power gradually decreases from the first rated power (1.0 pu) to the first minimum power (0.1 pu). The smooth voltage regulation device controls the valve side voltage to ensure that the firing angle, turn-off angle or DC voltage is the control target.

[0086] 2.2.2) The DC system operates at the first minimum power (0.1 pu), at which time the commutator ratio is grid-side main winding / valve-side winding, the voltage at the grid-side regulating winding terminal is zero, and the equivalent gear is 1.

[0087] 2.2.3) DC system interlock;

[0088] 2.2.4) When the smooth voltage regulation device is locked, there is no output voltage on the AC side, and the submodule is in active charging state;

[0089] 2.2.5) When the grid-side circuit breaker is tripped, the main winding, voltage regulating winding, and valve-side winding of the converter transformer grid side are not energized.

[0090] In summary, during operation, after the incoming switch of converter transformer 1 is closed, the DC converter valve 4 is unlocked, the DC side voltage is established, and the DC pole line 9 and neutral line 10 charge the bridge arm submodule 7 of the smooth voltage regulating device 5. After the voltage of the bridge arm submodule 7 reaches the rated level, the smooth voltage regulating device 5 is unlocked. By controlling the switching of the bridge arm submodule 7, the AC side voltage is regulated, changing the voltage between the end of the grid-side winding 2 of converter transformer 1 and the grounding point 8, thereby controlling the voltage of the valve-side winding 3 of converter transformer 1, that is, realizing the regulation of the valve-side voltage of the converter transformer.

[0091] In one embodiment of the present invention, an active smoothing voltage regulation system for a converter transformer in an ultra-high voltage direct current system is provided, comprising:

[0092] The processing module determines the voltage regulation range of the converter transformer equipped with the smooth voltage regulation device, and determines the number of several parallel bridge arm sub-modules in the smooth voltage regulation device according to the voltage regulation range; the smooth voltage regulation device is connected in series between the end of the grid-side winding of the converter transformer and the grounding point, and the DC side high and low voltage buses are connected in parallel to the DC pole line and the neutral line, respectively.

[0093] After the DC system is unlocked, the DC side of the smooth voltage regulating device is energized. Under different operating modes of the DC system, the AC side voltage is adjusted by controlling the number of switching bridge arm sub-modules, thereby realizing valve side voltage regulation.

[0094] In the above embodiments, the bridge arm submodule is composed of several IGBT fully controlled power electronic devices connected in series.

[0095] In the above embodiments, the determination of the voltage regulation range of the converter transformer in the processing module includes:

[0096] The first determining module determines the highest and lowest steady-state voltages of the AC bus of the converter station based on the voltage fluctuation range of the connected AC system.

[0097] The second determining module determines the upper and lower limits of the converter transformer valve-side voltage based on the DC-side main circuit parameters and operating mode of the DC system.

[0098] The voltage regulation range determination module determines the voltage regulation range of the converter transformer based on the determined upper and lower limits of the valve-side voltage, combined with the highest and lowest steady-state voltages of the AC bus of the converter station.

[0099] In the above embodiments, in the second determining module, the upper and lower limits of the converter transformer valve-side voltage are determined according to different operating modes of the DC system, including:

[0100] The first submodule determines the lower limit of the converter transformer valve side voltage under the condition that the DC system is operating at full voltage and in the first minimum power mode.

[0101] The second submodule determines the upper limit of the converter transformer valve side voltage under the condition that the DC system is operating at full voltage and at the first rated power.

[0102] The third submodule determines the upper limit of the converter transformer valve side voltage under the condition that the DC system is operating at full voltage and under long-term overload.

[0103] The fourth submodule determines the lower limit of the converter transformer valve-side voltage under the DC system operating at reduced voltage and in the second minimum power mode.

[0104] The fifth submodule determines the upper limit of the converter transformer valve side voltage under the DC system operating at reduced voltage and second rated power.

[0105] The upper and lower limit determination module takes the minimum lower limit value under each operating condition to obtain the minimum value of the converter transformer valve side voltage under each operating mode of the DC system, which is taken as the lower limit value; and takes the maximum upper limit value under each operating condition to obtain the maximum value of the converter transformer valve side voltage under each operating mode of the DC system, which is taken as the upper limit value.

[0106] In the above embodiments, in the voltage regulation range determination module, the voltage regulation range of the converter transformer is determined based on the determined upper and lower limits of the valve-side voltage, combined with the highest and lowest steady-state voltages of the AC bus of the converter station, including:

[0107] Based on the highest steady-state voltage of the converter station bus and the minimum voltage on the valve side of the converter transformer, the lower limit value of the smooth voltage regulating device is obtained;

[0108] Based on the minimum steady-state voltage of the converter station bus and the maximum voltage on the valve side of the converter transformer, the upper limit value of the smooth voltage regulating device is obtained;

[0109] Based on the lower and upper limits of the smooth voltage regulator, the voltage regulation range of the smooth voltage regulator is obtained.

[0110] In the above embodiments, the process of unlocking the DC system and increasing its power to the rated value in different operating modes of the DC system, and coordinating with the smooth voltage regulator to adjust the AC side voltage, includes:

[0111] When the grid-side circuit breaker is closed, the main winding, voltage regulating winding, and valve-side winding of the converter transformer grid side are all energized. The smooth voltage regulating device starts the sub-module to actively charge. After the sub-module voltage rises to the first rated power, it is ready to be unlocked.

[0112] When the smooth voltage regulating device is unlocked, a voltage opposite in phase to that of the main winding is output on the grid-side voltage regulating winding, thereby increasing the valve-side voltage and effectively raising the tap changer position.

[0113] The DC system is unlocked and operates at the first minimum power.

[0114] When the power of a DC system is increased, the smooth voltage regulation device controls the voltage on the valve side, using the firing angle, shutdown angle, or DC voltage as the control target, until the power is increased to the first rated power, and the DC system enters rated operation.

[0115] In the above embodiments, the process of unlocking the DC system and increasing its power to the rated value in different operating modes of the DC system, and coordinating with the smooth voltage regulator to adjust the AC side voltage, includes:

[0116] After the DC blocking command is issued, the DC transmission power gradually decreases from the first rated power to the first minimum power. The smooth voltage regulation device controls the valve side voltage to ensure that the firing angle, turn-off angle or DC voltage is the control target.

[0117] The DC system operates at the first minimum power, at which point the commutator ratio is grid-side main winding / valve-side winding, the voltage at the grid-side regulating winding terminal is zero, and the equivalent gear is gear 1.

[0118] DC system lockout;

[0119] With the smooth voltage regulator locked, there is no output voltage on the AC side, and the submodule is in active charging mode.

[0120] When the grid-side circuit breaker trips, the main winding, voltage regulating winding, and valve-side winding of the converter transformer on the grid side are de-energized.

[0121] The system provided in this embodiment is used to execute the above-described method embodiments. For specific processes and details, please refer to the above embodiments, which will not be repeated here.

[0122] In one embodiment of the present invention, a converter transformer for an ultra-high voltage direct current system is also provided, which includes an active smooth voltage regulation system with a smooth voltage regulation device in the above embodiments.

[0123] A schematic diagram of a computing device structure is provided in one embodiment of the present invention. This computing device can be a terminal, and may include: a processor, a communication interface, memory, a display screen, and an input device. The processor, communication interface, and memory communicate with each other via a communication bus. The processor provides computing and control capabilities. The memory includes a non-volatile storage medium and internal memory. The non-volatile storage medium stores an operating system and a computer program. When executed by the processor, the computer program implements an active smooth voltage regulation method for a converter transformer in an ultra-high voltage direct current system. The internal memory provides an environment for the operation of the operating system and computer program in the non-volatile storage medium. The communication interface is used for wired or wireless communication with external terminals. Wireless communication can be achieved through Wi-Fi, a management network, NFC (Near Field Communication), or other technologies. The display screen can be a liquid crystal display or an e-ink display. The input device can be a touch layer covering the display screen, or buttons, a trackball, or a touchpad mounted on the casing of the computing device, or an external keyboard, touchpad, or mouse. The processor can call logic instructions in memory to execute the following methods: determine the voltage regulation range of the converter transformer equipped with a smooth voltage regulation device; determine the number of parallel bridge arm sub-modules in the smooth voltage regulation device according to the voltage regulation range; connect the smooth voltage regulation device in series between the end of the grid winding of the converter transformer and the grounding point; connect the high and low voltage buses on the DC side in parallel to the DC pole line and the neutral line, respectively; after the DC system is unlocked, the DC side of the smooth voltage regulation device is energized; under different operating modes of the DC system, the AC side voltage is adjusted by controlling the number of bridge arm sub-modules switched on and off, thereby realizing valve side voltage regulation.

[0124] Furthermore, the logical instructions in the aforementioned memory can be implemented as software functional units and sold or used as independent products, and can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0125] Those skilled in the art will understand that the structure of the above-described computing device is only a partial structure related to the solution of this application and does not constitute a limitation on the computing device to which the solution of this application is applied. A specific computing device may include more or fewer components, or combine certain components, or have different component arrangements.

[0126] In one embodiment of the present invention, a computer program product is provided, the computer program product including a computer program stored on a non-transitory computer-readable storage medium, the computer program including program instructions, when the program instructions are executed by a computer, the computer can execute the methods provided in the above-described method embodiments, for example including: determining the voltage regulation range of a converter transformer configured with a smooth voltage regulation device, determining the number of several parallel bridge arm sub-modules in the smooth voltage regulation device according to the voltage regulation range; the smooth voltage regulation device is connected in series between the end of the grid-side winding of the converter transformer and the grounding point, and the DC side high and low voltage buses are respectively connected in parallel to the DC pole line and the neutral line; after the DC system is unlocked, the DC side of the smooth voltage regulation device is energized, and under different operating modes of the DC system, the AC side voltage is adjusted by controlling the number of bridge arm sub-modules switched on and off, thereby realizing valve-side voltage regulation.

[0127] In one embodiment of the present invention, a non-transitory computer-readable storage medium is provided, which stores server instructions that cause a computer to execute the methods provided in the above embodiments, such as: determining the voltage regulation range of a converter transformer equipped with a smoothing voltage regulation device; determining the number of parallel bridge arm sub-modules in the smoothing voltage regulation device according to the voltage regulation range; connecting the smoothing voltage regulation device in series between the end of the grid-side winding of the converter transformer and the grounding point; connecting the DC high and low voltage buses in parallel to the DC pole line and the neutral line, respectively; after the DC system is unlocked, the DC side of the smoothing voltage regulation device is energized; and under different operating modes of the DC system, adjusting the AC side voltage by controlling the number of bridge arm sub-modules switched on and off, thereby realizing valve-side voltage regulation.

[0128] The computer-readable storage medium provided in the above embodiments has a similar implementation principle and technical effect to the above method embodiments, and will not be described again here.

[0129] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0130] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0131] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0132] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for active smooth voltage regulation of a converter transformer in an ultra-high voltage direct current system, characterized in that, include: Determine the voltage regulation range of the converter transformer equipped with a smooth voltage regulation device, and determine the number of several parallel bridge arm sub-modules in the smooth voltage regulation device according to the voltage regulation range; wherein, the smooth voltage regulation device is connected in series between the end of the grid-side winding of the converter transformer and the grounding point, and the DC side high and low voltage buses are connected in parallel to the DC pole line and the neutral line, respectively. After the DC system is unlocked, the DC side of the smooth voltage regulator is energized. Under different operating modes of the DC system, the AC side voltage is adjusted by controlling the number of switching bridge arm sub-modules, thereby achieving valve side voltage regulation. The determination of the voltage regulation range of the converter transformer includes: Determine the highest and lowest steady-state voltages of the AC bus of the converter station based on the voltage fluctuation range of the connected AC system; Based on the DC-side main circuit parameters and operating mode of the DC system, determine the upper and lower limits of the valve-side voltage of the converter transformer; Based on the determined upper and lower limits of the valve-side voltage, and in conjunction with the highest and lowest steady-state voltages of the AC bus of the converter station, the voltage regulation range of the converter transformer is determined. In the process of adjusting the AC side voltage by controlling the number of switching bridge arm submodules, the DC system coordinates with the smooth voltage regulating device to adjust the AC side voltage during the process of unlocking the DC system and increasing its power to the rated value. When the grid-side circuit breaker is closed, the main winding, voltage regulating winding, and valve-side winding of the converter transformer grid side are all energized. The smooth voltage regulating device starts the sub-module to actively charge. After the sub-module voltage rises to the first rated power, it is ready to be unlocked. When the smooth voltage regulating device is unlocked, a voltage opposite in phase to that of the main winding is output on the grid-side voltage regulating winding, thereby increasing the valve-side voltage and effectively raising the tap changer position. The DC system is unlocked and operates at the first minimum power. When the DC system increases its power, the smooth voltage regulation device controls the valve side voltage, using the firing angle, turn-off angle, or DC voltage as the control target, until the power is increased to the first rated power and the DC system enters rated operation. In the process of adjusting the AC side voltage by controlling the number of switching bridge arm submodules, the DC system coordinates with the smooth voltage regulating device to adjust the AC side voltage during the process of unlocking the DC system and increasing its power to the rated value. After the DC blocking command is issued, the DC transmission power gradually decreases from the first rated power to the first minimum power. The smooth voltage regulation device controls the valve side voltage to ensure that the firing angle, turn-off angle or DC voltage is the control target. The DC system operates at the first minimum power, at which point the commutator ratio is grid-side main winding / valve-side winding, the voltage at the grid-side regulating winding terminal is zero, and the equivalent gear is gear 1. DC system lockout; With the smooth voltage regulator locked, there is no output voltage on the AC side, and the submodule is in active charging mode. When the grid-side circuit breaker trips, the main winding, voltage regulating winding, and valve-side winding of the converter transformer on the grid side are de-energized.

2. The active smooth voltage regulation method for converter transformers in ultra-high voltage direct current systems as described in claim 1, characterized in that, The bridge arm submodule is composed of several IGBT fully controlled power electronic devices connected in series.

3. The active smooth voltage regulation method for converter transformers in ultra-high voltage direct current systems as described in claim 1, characterized in that, The determination of the upper and lower limits of the converter transformer valve-side voltage is based on different operating modes of the DC system, including: Under the condition that the DC system is operating at full voltage and in the first minimum power mode, determine the lower limit value of the converter transformer valve side voltage under this operating condition; Determine the upper limit of the converter transformer valve side voltage under the following operating conditions: The DC system is operating at full voltage and first rated power. Determine the upper limit of the converter transformer valve side voltage under the condition that the DC system is operating at full voltage and under long-term overload. When the DC system is operating at reduced voltage and in the second minimum power mode, determine the lower limit of the converter transformer valve side voltage under this operating condition; Determine the upper limit of the converter transformer valve side voltage under the following operating conditions: DC system is operating at reduced voltage and second rated power. The minimum value of the lower limit under each operating condition is taken to obtain the minimum value of the converter transformer valve side voltage under each operating mode of the DC system, which is taken as the lower limit value; the maximum value of the upper limit under each operating condition is taken to obtain the maximum value of the converter transformer valve side voltage under each operating mode of the DC system, which is taken as the upper limit value.

4. The active smooth voltage regulation method for converter transformers in ultra-high voltage direct current systems as described in claim 1, characterized in that, The process of determining the voltage regulation range of the converter transformer based on the determined upper and lower limits of the valve-side voltage, combined with the highest and lowest steady-state voltages of the AC bus of the converter station, includes: Based on the highest steady-state voltage of the converter station bus and the minimum voltage on the valve side of the converter transformer, the lower limit value of the smooth voltage regulating device is obtained; Based on the minimum steady-state voltage of the converter station bus and the maximum voltage on the valve side of the converter transformer, the upper limit value of the smooth voltage regulating device is obtained; Based on the lower and upper limits of the smooth voltage regulator, the voltage regulation range of the smooth voltage regulator is obtained.

5. An active smooth voltage regulation system for a converter transformer in an ultra-high voltage direct current (UHVDC) system, used to implement the active smooth voltage regulation method for a converter transformer in an UHVDC system as described in any one of claims 1 to 4, characterized in that, include: The processing module determines the voltage regulation range of the converter transformer equipped with a smooth voltage regulation device, and determines the number of several parallel bridge arm sub-modules in the smooth voltage regulation device according to the voltage regulation range; wherein, the smooth voltage regulation device is connected in series between the end of the grid-side winding of the converter transformer and the grounding point, and the DC side high and low voltage buses are connected in parallel to the DC pole line and the neutral line, respectively. After the DC system is unlocked, the DC side of the smooth voltage regulating device is energized. Under different operating modes of the DC system, the AC side voltage is adjusted by controlling the number of switching bridge arm sub-modules, thereby realizing valve side voltage regulation.

6. A computer-readable storage medium for storing one or more programs, characterized in that, The one or more programs include instructions that, when executed by a computing device, cause the computing device to perform any of the methods described in claims 1 to 4.

7. A computing device, characterized in that, include: One or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, the one or more programs including instructions for performing any of the methods described in claims 1 to 4.

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