Conventional dc amplitude-phase modulation topology and control method based on parallel current converter

Abstract

This application belongs to the field of power system transmission and distribution technology, specifically disclosing a conventional DC amplitude and phase voltage regulation topology and control method based on parallel converters. The topology includes: a DC line, a conventional DC converter valve group, a conventional DC converter transformer, two auxiliary flexible DC converters, two auxiliary flexible DC converter transformers, and a receiving-end AC bus. The DC sides of the two auxiliary flexible DC converters are connected in parallel with the DC sides of the low-voltage valves at the positive and negative terminals of the conventional DC converter valve group. The AC side is connected in series with the auxiliary flexible DC converter transformers to the grounding lines of the grid-side windings of the conventional DC converter transformers corresponding to the low-voltage valves at the positive and negative terminals. The auxiliary flexible DC converters are used to regulate the amplitude and phase of the voltage on the receiving-end AC bus. This application enables rapid and precise regulation of the amplitude and phase of the valve-side voltage of the conventional DC converter transformers, while also considering the economic efficiency of the grid-connected system.

Description

Technical Field

[0001] This application belongs to the field of smart grid technology, specifically relating to power system transmission and distribution, and more specifically, to a conventional DC amplitude-phase voltage regulation topology and control method based on parallel converters. Background Technology

[0002] High-voltage direct current (HVDC) transmission systems based on conventional DC converter stations are the main technical solution for large-scale, long-distance transmission of clean / green energy, offering advantages such as long transmission distance, large transmission capacity, low operating losses, and high economic efficiency. However, with the continuous increase in the proportion of new energy sources and DC transmission capacity, the strength of the receiving-end AC grid is showing a decreasing trend, and the problem of system voltage stability is becoming increasingly prominent, while also exacerbating the risk of commutation failure in conventional DC transmission systems.

[0003] Currently, conventional DC converter stations mainly rely on mechanical on-load tap changers on converter transformers for voltage regulation. This method has three major technical drawbacks: First, mechanical on-load tap changers have slow response speeds, small voltage regulation ranges, and large step sizes, making them unsuitable for the rapid and precise voltage regulation requirements of renewable energy sources with their strong volatility and randomness. Second, they lack phase regulation capabilities, increasing engineering complexity and safety risks. Third, mechanical switches have a high failure rate, easily causing converter station outages and seriously threatening the safe operation of the system. To improve the stability of the receiving-end AC system, the industry has proposed auxiliary solutions such as Static Synchronous Compensators (STATCOMs) with dynamic reactive power compensation capabilities. However, such solutions require additional parallel converters, as well as additional filtering circuits and protection devices, resulting in complex maintenance and high unit capacity costs. Furthermore, the technical maturity and reliability of this solution still face challenges in ultra-high voltage scenarios.

[0004] Therefore, existing technical solutions cannot simultaneously achieve rapid and precise adjustment of AC voltage amplitude and phase, as well as the economic efficiency of grid-connected systems. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this application is to achieve rapid and precise adjustment of the voltage amplitude and phase of the valve side of the conventional DC converter transformer by introducing an auxiliary flexible DC converter and a specific transformer connection method without changing the main structure of the existing conventional DC converter station, while taking into account the economy of the grid-connected system.

[0006] To achieve the above objectives, in a first aspect, this application provides a conventional DC amplitude-phase voltage regulation topology based on a parallel converter, comprising: a DC line, a conventional DC converter valve group, a conventional DC converter transformer, an auxiliary flexible DC converter, an auxiliary flexible DC converter transformer, and a receiving-end AC bus. DC lines are used to transmit DC power to conventional DC converter valve assemblies; A conventional DC converter valve assembly is used to convert the received DC power to AC power, and then feed the converted AC power into the receiving-end AC bus via a conventional DC converter transformer. The conventional DC converter valve group is equipped with high-pressure valves and low-pressure valves at the positive and negative poles; the topology is configured with two auxiliary flexible DC converters, namely an auxiliary positive flexible DC converter and an auxiliary negative flexible DC converter; the topology is configured with two auxiliary flexible DC converter transformers. The DC side of the auxiliary positive flexible DC converter is connected in parallel with the DC side of the low-pressure valve of the positive electrode of the conventional DC converter valve group, and the DC side of the auxiliary negative flexible DC converter is connected in parallel with the DC side of the low-pressure valve of the negative electrode of the conventional DC converter valve group. The AC side of the auxiliary positive flexible DC converter is connected in series with an auxiliary flexible DC converter transformer to the grounding line of the grid-side winding of the conventional DC converter transformer corresponding to the low-voltage valve of the positive pole of the conventional DC converter valve group. The AC side of the auxiliary negative flexible DC converter is connected in series with another auxiliary flexible DC converter transformer to the grounding line of the grid-side winding of the conventional DC converter transformer corresponding to the low-voltage valve of the negative pole of the conventional DC converter valve group. An auxiliary flexible DC converter is used to adjust the amplitude and phase of the voltage on the receiving-end AC bus. An auxiliary flexible DC converter transformer is used to match the AC side output voltage of the auxiliary flexible DC converter with the voltage regulation requirements of the receiving-end AC bus.

[0007] Specifically, DC lines are used to transmit DC power generated from long-distance clean energy (green energy) bases to conventional DC converter valve assemblies.

[0008] A conventional DC converter valve assembly is used to convert the received DC power to AC power, and then feed the converted AC power into the receiving-end AC bus via a conventional DC converter transformer.

[0009] The auxiliary flexible DC converter is used to achieve rapid, accurate and continuous adjustment of the amplitude and phase of the AC bus voltage at the receiving end, ensuring the stability of the AC bus voltage at the receiving end and reducing the risk of commutation failure in conventional DC transmission systems.

[0010] Conventional DC converter transformers are used to transform the valve-side AC voltage and the receiving-end AC bus voltage of a conventional DC converter station, suppress the injection of specific characteristic harmonics generated during the operation of the conventional DC converter station into the receiving-end AC grid, and achieve electrical isolation between the valve-side AC line of the conventional DC converter station and the receiving-end AC grid.

[0011] The auxiliary flexible DC converter transformer is used to match the AC side output voltage of the auxiliary flexible DC converter with the voltage regulation requirements of the AC bus at the receiving end, ensuring that the compensation voltage output can be accurately injected according to the target amplitude and phase, while realizing electrical isolation between the auxiliary flexible DC converter and the AC grid at the receiving end.

[0012] The receiving-end AC bus is used to receive and distribute AC power transmitted from the conventional DC transmission system to the receiving-end AC grid; at the same time, the amplitude and phase stability of its AC voltage directly provides the necessary commutation voltage support for the reliable commutation of the conventional DC converter station.

[0013] In one possible implementation, the conventional DC converter valve group adopts a cascaded grid-commutated converter structure with symmetrical bipolar wiring, and both its positive and negative poles contain high- and low-pressure valves.

[0014] Here is an example of the "symmetrical bipolar connection cascaded grid phase-commutator structure": the positive DC side of the positive high-pressure valve is connected to the positive DC line, and the negative DC side of the positive high-pressure valve is connected to the positive DC side of the positive low-pressure valve; the negative DC side of the positive low-pressure valve is connected to the positive DC side of the negative low-pressure valve; the negative DC side of the negative low-pressure valve is connected to the positive DC side of the negative high-pressure valve; the negative DC side of the negative high-pressure valve is connected to the negative DC line; the positive DC side of the positive high-pressure valve and the negative DC side of the negative high-pressure valve constitute the DC input terminal (DC port) of a conventional DC converter station.

[0015] The AC sides of the high and low pressure valves of the positive and negative poles are respectively connected to the valve-side windings of a conventional DC converter transformer. The grid-side windings of all conventional DC converter transformers are connected in parallel to the receiving-end AC bus to form the AC output terminal of the conventional DC converter station.

[0016] In one possible implementation, the high- and low-voltage valves for the positive and negative terminals can be constructed using either a grid-commutated converter (LCC) or a controllable grid-commutated converter (CLCC). A conventional DC transmission system constructed using LCCs is called an LCC-HVDC, and a conventional DC transmission system constructed using CLCCs is called a CLCC-HVDC. If the high- and low-voltage valves for the positive and negative terminals of a conventional DC converter valve group are LCCs, then the conventional DC converter valve group can be called a conventional DC converter valve group LCC. If the high- and low-voltage valves for the positive and negative terminals of a conventional DC converter valve group are CLCCs, then the conventional DC converter valve group can be called a conventional DC converter valve group CLCC.

[0017] In one possible implementation, the MMC includes multiple sub-modules, which can be a half-bridge MMC based on half-bridge sub-modules (HBSM) or a hybrid MMC based on both half-bridge sub-modules and full-bridge sub-modules (FBSM).

[0018] In one possible implementation, the conventional DC converter transformer can consist of three single-phase double-winding transformer groups or one three-phase double-winding transformer. Specifically, the conventional DC converter transformer connected to the AC side of the positive and negative high-voltage valves of the conventional DC converter valve group adopts a Y / Yn connection, meaning the valve-side winding is star-connected with an ungrounded neutral point, while the grid-side winding is star-connected and grounded via the neutral point. The conventional DC converter transformer connected to the AC side of the positive and negative low-voltage valves of the conventional DC converter valve group adopts a Δ / Yn connection, meaning the valve-side winding is delta-connected, while the grid-side winding is star-connected and grounded via the neutral point. Specifically, one end of each of the three-phase (A-phase, B-phase, C-phase) grid-side windings is connected to the receiving-end AC bus, and the other end is connected in series with the grid-side windings of the corresponding auxiliary flexible DC converter transformers, and then grounded via the neutral point.

[0019] In one possible implementation, the conventional DC converter transformer can also be composed of three single-phase three-winding transformer groups or one three-phase three-winding transformer. In this case, the AC sides of the high and low voltage valves on the positive end of the conventional DC converter valve group are connected to the receiving-end AC bus via a single conventional DC converter transformer, and the AC sides of the high and low voltage valves on the negative end of the conventional DC converter valve group are also connected to the receiving-end AC bus via a single conventional DC converter transformer. The three single-phase three-winding transformer groups or the single three-phase three-winding transformer adopt a Δ / Y / Yn connection method, that is, the primary and secondary windings on the valve side of the transformer are delta connected and star connected respectively, with the neutral point ungrounded, while the grid-side windings are star connected and grounded through the neutral point.

[0020] In one possible implementation, the auxiliary flexible DC converter transformer consists of three single-phase dual-winding transformer groups or one three-phase dual-winding transformer. The transformer windings adopt a Yn / Yn connection, meaning that both the valve-side winding and the grid-side winding are star-connected and grounded via a neutral point. The valve-side winding of the auxiliary flexible DC converter transformer is connected to the AC side of the auxiliary flexible DC converter, while the grid-side winding is connected in series to the grounding line of the grid-side winding of the conventional DC converter transformer.

[0021] Secondly, this application provides a control method for a conventional DC amplitude-phase voltage regulation topology based on a parallel converter, applicable to the topology described in the first aspect or any possible implementation of the first aspect, the control method comprising: Conventional DC converter valve groups adopt a control mode with a constant DC port voltage and an additional backup control mode with a constant turn-off angle. The auxiliary flexible DC converter employs compensation voltage amplitude control and compensation voltage phase control.

[0022] Understandably, once the amplitude and phase changes of the AC bus voltage at the receiving end and the valve-side voltage of the conventional DC converter transformer are detected to exceed the threshold, the control method can quickly adjust the amplitude and phase of the AC output voltage of the auxiliary flexible DC converter, thereby achieving dynamic compensation for the valve-side voltage of the conventional DC converter transformer to maintain the stability of the valve-side voltage of the conventional DC converter transformer.

[0023] It is understandable that the beneficial effects of the second aspect mentioned above can be found in the relevant descriptions in the first aspect mentioned above, and will not be repeated here.

[0024] Overall, the technical solutions conceived in this application have the following beneficial effects compared with the prior art: (1) By connecting an auxiliary flexible DC converter in parallel on the low-voltage valve side of a conventional DC converter valve group and utilizing a specific transformer connection method, the voltage amplitude and phase of the conventional DC converter transformer valve side can be rapidly, accurately, and continuously adjusted. This application enables conventional DC converter stations to have millisecond-level, wide-range amplitude and phase continuous voltage regulation capability and grid voltage support capability, effectively improving the voltage stability of conventional DC transmission systems and reducing the risk of commutation failure.

[0025] (2) The topology provided in this application does not require changes to the main structure of existing conventional DC converter stations. By using an "incremental" modification method—connecting an auxiliary flexible DC converter in parallel only on the low-voltage valve side of the conventional DC converter station and connecting an auxiliary flexible DC converter transformer in series on the winding grounding line of its connecting transformer grid side—flexible control of the valve-side voltage of the conventional DC converter transformer is achieved. This scheme avoids large-scale equipment replacement or main structure modification, and has high economic and engineering application value.

[0026] It should be noted that only two auxiliary flexible DC converters are required. These auxiliary flexible DC converters can be small-capacity MMCs with low DC voltage levels. Their equipment capacity and voltage level are significantly lower than traditional solutions such as directly connecting STATCOMs in parallel on the AC bus side, thereby greatly reducing the investment cost and operating losses of the main power electronic equipment, resulting in high economic efficiency. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the LCC-HVDC amplitude-phase voltage regulation topology based on parallel converters and dual-winding transformers provided in the embodiments of this application; Figure 2 This is a schematic diagram of the LCC-HVDC amplitude-phase voltage regulation topology based on parallel converters and three-winding transformers provided in the embodiments of this application; Figure 3 This is a schematic diagram of the CLCC-HVDC amplitude-phase voltage regulation topology based on parallel converters and dual-winding transformers provided in the embodiments of this application; Figure 4 This is a schematic diagram of the CLCC-HVDC amplitude-phase voltage regulation topology based on parallel converters and three-winding transformers provided in the embodiments of this application; Figure 5 This is a schematic flowchart of a conventional DC converter valve group control method provided in the embodiments of this application; Figure 6 This is a flowchart illustrating the auxiliary flexible DC converter control method provided in the embodiments of this application.

[0028] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein: S1 is the positive high-pressure valve of the conventional DC converter valve group LCC; S2 is the positive low-pressure valve of the conventional DC converter valve group LCC; S3 is the negative low-pressure valve of the conventional DC converter valve group LCC; S4 is the negative high-pressure valve of the conventional DC converter valve group LCC; S5 is an auxiliary flexible DC converter (or auxiliary positive flexible DC converter) connected in parallel to the DC side of the positive low-pressure valve of the conventional DC converter valve group; S6 is an auxiliary flexible DC converter (or auxiliary negative flexible DC converter) connected in parallel to the DC side of the negative low-pressure valve of the conventional DC converter valve group; S7 is a submodule of the auxiliary flexible DC converter; S8 is the converter transformer of the positive high-pressure valve of the conventional DC converter valve group; S9 is the converter transformer of the positive low-pressure valve of the conventional DC converter valve group; S10 is the converter transformer of the negative low-pressure valve of the conventional DC converter valve group. S11 is the converter transformer for the negative high-voltage valve of the conventional DC converter valve group; S12 is the auxiliary positive flexible DC converter transformer; S13 is the auxiliary negative flexible DC converter transformer; S14 is the receiving-end AC bus; S15 is the receiving-end AC power grid; S16 is the DC line; S17 is a three-winding converter transformer connected to the AC side of the high and low voltage valves of the positive pole of the conventional DC converter valve group; S18 is a three-winding converter transformer connected to the AC side of the high and low voltage valves of the negative pole of the conventional DC converter valve group; S19 is the positive high-voltage valve of the conventional DC converter valve group CLCC; S20 is the positive low-voltage valve of the conventional DC converter valve group CLCC; S21 is the negative low-voltage valve of the conventional DC converter valve group CLCC; S22 is the negative high-voltage valve of the conventional DC converter valve group CLCC. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0030] In this application, the terms "first" and "second," etc., are used to distinguish different objects, not to describe a specific order of objects. For example, "first configuration" and "second configuration," etc., are used to distinguish different configurations, not to describe a specific order of configurations.

[0031] In the embodiments of this application, the terms "exemplary" or "for example" are used to indicate that something is an example, illustration, or description. Any embodiment or design that is described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design. Specifically, the use of the terms "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0032] In the description of the embodiments of this application, unless otherwise stated, "multiple" means two or more, for example, multiple processing units means two or more processing units, multiple elements means two or more elements, etc.

[0033] For ease of understanding, the English abbreviations and related technical terms used in the embodiments of this application will be explained and described below.

[0034] LCC stands for Line-Commutated Converter. MMC stands for Modular Multilevel Converter. CLCC stands for Controllable Line-Commutated Converter. VDCOL stands for Voltage Dependent Current Limit Control.

[0035] The embodiments of this application are described below with reference to the accompanying drawings.

[0036] Example 1 This embodiment discloses an LCC-HVDC amplitude-phase voltage regulation topology based on parallel converters, such as... Figure 1As shown, it includes: a positive high-pressure valve S1 of a conventional DC converter valve group LCC, a positive low-pressure valve S2 of a conventional DC converter valve group LCC, a negative low-pressure valve S3 of a conventional DC converter valve group LCC, a negative high-pressure valve S4 of a conventional DC converter valve group LCC, an auxiliary flexible DC converter S5 connected in parallel to the DC side of the positive low-pressure valve of the conventional DC converter valve group, an auxiliary flexible DC converter S6 connected in parallel to the DC side of the negative low-pressure valve of the conventional DC converter valve group, and an auxiliary flexible DC converter. The sub-modules are as follows: S7, S8, S9, S10, S11, S12, S13, S14, S15, S16, S16, S17, S18, S19, S10, S11, S12, S13, S14, S15 ...4, S15, S16, S17, S18, S19, S14, S16, S17, S18, S19, S14, S19, S10, S11, S16, S17, S

[0037] It is understandable that, such as Figure 1 As shown, a conventional DC converter station includes conventional DC converter valve groups (S1-S4), conventional DC converter transformers (S8-S11), auxiliary flexible DC converters (S5, S6), and auxiliary flexible DC converter transformers (S12, S13).

[0038] The conventional DC converter valve group LCC adopts a cascaded grid-commutated converter structure with symmetrical bipolar connection. Both its positive and negative poles contain high- and low-pressure valves (S1-S4 respectively). The high- and low-pressure valves of the positive and negative poles are composed of grid-commutated converters (LCCs). The conventional DC transmission system composed of LCCs is called LCC-HVDC.

[0039] The positive terminal of the positive high-pressure valve S1 is connected to the positive terminal of the DC line, and its negative terminal is connected to the positive terminal of the positive low-pressure valve S2. The negative terminal of the positive low-pressure valve S2 is connected to the positive terminal of the negative low-pressure valve S3. The negative terminal of the negative low-pressure valve S3 is connected to the positive terminal of the negative high-pressure valve S4. The negative terminal of the negative high-pressure valve S4 is connected to the negative terminal of the DC line. The positive terminal of the positive high-pressure valve S1 and the negative terminal of the negative high-pressure valve S4 constitute the DC input terminal of a conventional DC converter station.

[0040] The high and low voltage valves of the positive and negative poles are respectively connected to the valve-side windings of a conventional DC converter transformer (S8-S11). The grid-side windings of all conventional DC converter transformers S8-S11 are connected in parallel to the receiving-end AC bus S14, forming the AC output terminal of the conventional DC converter station.

[0041] The auxiliary flexible DC converters S5 and S6 adopt a modular multilevel converter (MMC) structure, including an auxiliary positive flexible DC converter S5 and an auxiliary negative flexible DC converter S6. Their DC sides are connected in parallel with the DC sides of the low-pressure valves S2 and S3 of the conventional DC converter valve group, respectively, and share the grounding electrode with the conventional DC converter valve group. Their AC sides are connected in series with the grounding lines of the grid-side windings of the conventional DC converter transformers S9 and S10 of the positive and negative low-pressure valves through the auxiliary flexible DC converter transformers S12 and S13, respectively.

[0042] The MMC contains multiple sub-modules S7, which can be a half-bridge MMC based on half-bridge sub-modules (HBSM) or a hybrid MMC based on a combination of half-bridge sub-modules and full-bridge sub-modules (FBSM).

[0043] The conventional DC converter transformers S8-S11 can be composed of three single-phase double-winding transformer groups or one three-phase double-winding transformer. Specifically, conventional DC converter transformers S8 and S11, connected to the AC sides of the positive and negative high-voltage valves of the conventional DC converter valve group, adopt a Y / Yn connection method, meaning the valve-side windings are star-connected with the neutral point ungrounded, while the grid-side windings are star-connected and grounded through the neutral point. Conventional DC converter transformers S9 and S10, connected to the AC sides of the positive and negative low-voltage valves of the conventional DC converter valve group, adopt a Δ / Yn connection method, meaning the valve-side windings are delta-connected, while the grid-side windings are star-connected and grounded through the neutral point. Specifically, one end of each of the three-phase (A-phase, B-phase, C-phase) grid-side windings is connected to the receiving-end AC bus S14, and the other end is connected in series with the grid-side windings of the corresponding auxiliary flexible DC converter transformers S12 and S13, and then grounded through the neutral point.

[0044] The auxiliary flexible DC converter transformers S12 and S13 consist of three single-phase double-winding transformer groups or one three-phase double-winding transformer. The transformer windings adopt a Yn / Yn connection method, meaning that both the valve-side winding and the grid-side winding are star-connected and grounded through the neutral point. The valve-side windings of the auxiliary flexible DC converter transformers S12 and S13 are connected to the AC sides of the auxiliary flexible DC converters S5 and S6, respectively, while the grid-side windings are connected in series to the grounding lines of the grid-side windings of the conventional DC converter transformers S9 and S10.

[0045] In addition to being able to... Figure 1 The configuration can be either three single-phase double-winding transformer units or one three-phase double-winding transformer. Figure 2The configuration involves three single-phase three-winding transformer groups or one three-phase three-winding transformer. In this configuration, the AC sides of the high- and low-voltage valves S1 and S2 on the positive side of the conventional DC converter valve group are connected to the receiving-end AC bus S14 via a single conventional DC converter transformer S17. Similarly, the AC sides of the high- and low-voltage valves S3 and S4 on the negative side of the conventional DC converter valve group are connected to the receiving-end AC bus S14 via a single conventional DC converter transformer S18. The three single-phase three-winding transformer groups or the single three-phase three-winding transformer adopt a Δ / Y / Yn connection configuration, meaning the primary and secondary windings on the valve side are delta-connected and star-connected respectively, with the neutral point ungrounded. The grid-side windings are star-connected and grounded via the neutral point.

[0046] It is understandable that, such as Figure 2 As shown, a conventional DC converter station includes conventional DC converter valve groups (S1-S4), conventional DC converter transformers (S17, S18), auxiliary flexible DC converters (S5, S6), and auxiliary flexible DC converter transformers (S12, S13).

[0047] The control method for the LCC-HVDC amplitude-phase voltage regulation topology based on parallel converters in this embodiment is designed as follows: The single-pole (positive / negative) high and low pressure valves S1-S4 of the conventional DC converter valve group LCC adopt Figure 5 The control mode shown is a constant DC port voltage control, supplemented by a constant turn-off angle backup control mode. When the system detects that the turn-off angle is lower than the safety threshold, it automatically switches from constant DC voltage control to backup constant turn-off angle control, adjusting the trigger angle to ensure commutation margin and prevent commutation failure.

[0048] exist Figure 5 middle, This refers to the DC voltage at the DC port of a conventional DC converter valve group (the DC input terminal of a conventional DC converter station); VDCOL is the reference value for DC voltage; VDCOL is for low-voltage current limiting control. This refers to the DC current of a conventional DC converter valve group. This is a reference value for DC current; It is the shut-off angle; This is a reference value for the shut-off angle; The inverter angle generated for backup cut-off angle control; The inverter angle generated for constant DC voltage control; The trigger angle is shown in the attached diagram. The adder is used to perform an algebraic sum operation on multiple input signals. The "..." in the adder... "" indicates that the input signal is multiplied by 1 before performing an algebraic sum operation. The "" in the adder The expression "" indicates that the input signal is multiplied by -1 before performing an algebraic sum operation. In the attached diagram, the low-pass filter has a transfer function of 1 / (Ts+1) (where T is a time constant) and its function is to allow low-frequency signals to pass while suppressing high-frequency signals, thus filtering the input signal. In the diagram, the PI controller (Proportional-Integral controller) adjusts the deviation signal through proportional and integral elements to optimize the steady-state accuracy and dynamic response characteristics of the control system. In the attached diagram, the minimum (MIN) module compares multiple input signals and outputs the minimum value. In the attached diagram, the maximum (MAX) module compares multiple input signals and outputs the maximum value.

[0049] The control method that keeps the DC port voltage constant is through and Generate DC current reference value Then through and Generate inverted angle Backup constant turn-off angle control (or constant turn-off angle backup control) is achieved through... and Generate inverted angle ; and The trigger angle is generated through algebraic operations. .

[0050] The auxiliary flexible DC converters S5 and S6 adopt Figure 6 The diagram shows the compensation voltage amplitude control and compensation voltage phase control. Once the amplitude and phase changes of the voltage on the receiving end AC bus S14 and the valve-side voltage of the conventional DC converter transformer are detected to exceed the threshold, the control mode can quickly adjust the amplitude and phase of the AC-side output voltage of the auxiliary flexible DC converter, thereby achieving dynamic compensation for the valve-side voltage of the conventional DC converter transformer to maintain the stability of the valve-side voltage of the conventional DC converter transformer.

[0051] exist Figure 6 middle, and These are the amplitude of the AC bus voltage at the receiving end and its reference value, respectively. and These are the valve-side voltage amplitude and reference value of a conventional DC converter transformer; , These are the compensation voltage and its reference value output from the AC side of the auxiliary flexible DC converter, respectively. and These are the currents on the AC side of the auxiliary flexible DC converter and their reference values, respectively. To compensate for the phase angle of the auxiliary flexible DC converter; and These are the phase angle (phase) of the valve side voltage of a conventional DC converter transformer and its reference value; and These are the phase angle (phase) of the AC bus voltage at the receiving end and its reference value; , and These are the DC voltage unbalance components in the abc coordinate system, respectively. This is the reference value for the rated DC voltage component; and These are the d-axis and q-axis components of the second harmonic circulating current, respectively. and These are the reference values ​​for the d-axis and q-axis components of the second harmonic circulating current, respectively. , and These are the unbalanced components of the second harmonic DC voltage in the abc coordinate system.

[0052] AC voltage amplitude control generates a reference value for the compensation voltage amplitude by using the amplitudes of the receiving-end AC bus voltage and the valve-side voltage of a conventional DC converter transformer, along with their reference values. The compensation voltage amplitude control is achieved through... and Generate the current and its reference value on the AC side of the auxiliary flexible DC converter. and Compensation voltage phase control generates the compensation phase angle of the auxiliary flexible DC converter by using the phase of the AC bus voltage and the valve-side voltage of the conventional DC converter transformer, along with their reference values. Acting on the current control circuit, and The DC voltage imbalance component is generated through a current control circuit. , , and The second-harmonic DC voltage imbalance component is generated through circulating current control. The DC voltage imbalance component and the reference value of the rated DC voltage component are input into the modulation strategy control circuit through algebraic operations to generate a modulation signal, which is finally generated into a trigger pulse through the trigger logic circuit.

[0053] Example 2 This embodiment discloses a CLCC-HVDC amplitude-phase voltage regulation topology based on parallel converters, such as... Figure 3As shown, it includes: an auxiliary flexible DC converter S5 connected in parallel to the DC side of the positive low-pressure valve of the conventional DC converter valve group; an auxiliary flexible DC converter S6 connected in parallel to the DC side of the negative low-pressure valve of the conventional DC converter valve group; a submodule S7 of the auxiliary flexible DC converter; a converter transformer S8 for the positive high-pressure valve of the conventional DC converter valve group; a converter transformer S9 for the positive low-pressure valve of the conventional DC converter valve group; a converter transformer S10 for the negative low-pressure valve of the conventional DC converter valve group; and a converter transformer for the negative valve of the conventional DC converter valve group. The converter transformer S11 of the high-pressure valve, the auxiliary positive flexible DC converter transformer S12, the auxiliary negative flexible DC converter transformer S13, the receiving-end AC bus S14, the receiving-end AC power grid S15, the DC line S16, the positive high-pressure valve S19 of the conventional DC converter valve group CLCC, the positive low-pressure valve S20 of the conventional DC converter valve group CLCC, the negative low-pressure valve S21 of the conventional DC converter valve group CLCC, and the negative high-pressure valve S22 of the conventional DC converter valve group CLCC.

[0054] It is understandable that, such as Figure 3 As shown, a conventional DC converter station includes conventional DC converter valve groups (S19-S22), conventional DC converter transformers (S8-S11), auxiliary flexible DC converters (S5, S6), and auxiliary flexible DC converter transformers (S12, S13).

[0055] The conventional DC converter valve group CLCC adopts a cascaded controllable grid-commutated converter structure with symmetrical bipolar connection. Both its positive and negative poles contain high- and low-pressure valves (S19-S22 respectively). The high- and low-pressure valves of the positive and negative poles are composed of controllable grid-commutated converters (CLCC). The conventional DC transmission system composed of CLCC is called CLCC-HVDC.

[0056] The positive DC side of the positive high-pressure valve S19 is connected to the positive DC line, and its negative DC side is connected to the positive DC side of the positive low-pressure valve S20. The negative DC side of the positive low-pressure valve S20 is connected to the positive DC side of the negative low-pressure valve S21. The negative DC side of the negative low-pressure valve S21 is connected to the positive DC side of the negative high-pressure valve S22. The negative DC side of the negative high-pressure valve S22 is connected to the negative DC line. The positive DC side of the positive high-pressure valve S19 and the negative DC side of the negative high-pressure valve S22 constitute the DC input terminal of a conventional DC converter station.

[0057] The high and low voltage valves of the positive and negative poles are respectively connected to the valve-side windings of a conventional DC converter transformer (S8-S11). The grid-side windings of all conventional DC converter transformers S8-S11 are connected in parallel to the receiving-end AC bus S14, forming the AC output terminal of the conventional DC converter station.

[0058] The auxiliary flexible DC converters S5 and S6 adopt a modular multilevel converter (MMC) structure, including an auxiliary positive flexible DC converter S5 and an auxiliary negative flexible DC converter S6. Their DC sides are connected in parallel with the DC sides of the low-pressure valves S2 and S3 of the conventional DC converter valve group, respectively, and share the grounding electrode with the conventional DC converter valve group. Their AC sides are connected in series with the grounding lines of the grid-side windings of the conventional DC converter transformers S9 and S10 of the positive and negative low-pressure valves through the auxiliary flexible DC converter transformers S12 and S13, respectively.

[0059] The MMC contains multiple sub-modules S7, which can be a half-bridge MMC based on half-bridge sub-modules (HBSM) or a hybrid MMC based on a combination of half-bridge sub-modules and full-bridge sub-modules (FBSM).

[0060] The conventional DC converter transformers S8-S11 can be composed of three single-phase double-winding transformer groups or one three-phase double-winding transformer. Specifically, conventional DC converter transformers S8 and S11, connected to the AC sides of the positive and negative high-voltage valves of the conventional DC converter valve group, adopt a Y / Yn connection method, meaning the valve-side windings are star-connected with the neutral point ungrounded, while the grid-side windings are star-connected and grounded through the neutral point. Conventional DC converter transformers S9 and S10, connected to the AC sides of the positive and negative low-voltage valves of the conventional DC converter valve group, adopt a Δ / Yn connection method, meaning the valve-side windings are delta-connected, while the grid-side windings are star-connected and grounded through the neutral point. Specifically, one end of each of the three-phase (A-phase, B-phase, C-phase) grid-side windings is connected to the receiving-end AC bus S14, and the other end is connected in series with the grid-side windings of the corresponding auxiliary flexible DC converter transformers S12 and S13, and then grounded through the neutral point.

[0061] The auxiliary flexible DC converter transformers S12 and S13 consist of three single-phase double-winding transformer groups or one three-phase double-winding transformer. The transformer windings adopt a Yn / Yn connection method, meaning that both the valve-side winding and the grid-side winding are star-connected and grounded through the neutral point. The valve-side windings of the auxiliary flexible DC converter transformers S12 and S13 are connected to the AC sides of the auxiliary flexible DC converters S5 and S6, respectively, while the grid-side windings are connected in series to the grounding lines of the grid-side windings of the conventional DC converter transformers S9 and S10.

[0062] In addition to being able to... Figure 3 The configuration can be either three single-phase double-winding transformer units or one three-phase double-winding transformer. Figure 4The configuration involves three single-phase three-winding transformer groups or one three-phase three-winding transformer. In this configuration, the AC sides of the high- and low-voltage valves S19 and S20 on the positive side of the conventional DC converter valve group are connected to the receiving-end AC bus S14 via a single conventional DC converter transformer S17. Similarly, the AC sides of the high- and low-voltage valves S21 and S22 on the negative side of the conventional DC converter valve group are connected to the receiving-end AC bus S14 via a single conventional DC converter transformer S18. The three single-phase three-winding transformer groups or the single three-phase three-winding transformer adopt a Δ / Y / Yn connection configuration, meaning the primary and secondary windings on the valve side are delta-connected and star-connected respectively, with the neutral point ungrounded. The grid-side windings are star-connected and grounded via the neutral point.

[0063] It is understandable that, such as Figure 4 As shown, a conventional DC converter station includes conventional DC converter valve groups (S19-S22), conventional DC converter transformers (S17-S18), auxiliary flexible DC converters (S5, S6), and auxiliary flexible DC converter transformers (S12, S13).

[0064] The control method for the CLCC-HVDC amplitude-phase voltage regulation topology based on parallel converters in this embodiment is designed as follows: The single-pole (positive / negative) high and low pressure valves S19-S22 of the conventional DC converter valve group CLCC adopt Figure 5 The control method shown is a constant DC port voltage, with an additional backup control method that is a constant turn-off angle.

[0065] The auxiliary flexible DC converters S5 and S6 adopt Figure 6 The diagram shows the compensation voltage amplitude control and compensation voltage phase control. Once the amplitude and phase changes of the voltage on the receiving end AC bus S14 and the valve-side voltage of the conventional DC converter transformer are detected to exceed the threshold, the control mode can quickly adjust the amplitude and phase of the AC-side output voltage of the auxiliary flexible DC converter, thereby achieving dynamic compensation for the valve-side voltage of the conventional DC converter transformer to maintain the stability of the valve-side voltage of the conventional DC converter transformer.

[0066] It is understood that the various numerical designations used in the embodiments of this application are merely for the convenience of description and are not intended to limit the scope of the embodiments of this application.

[0067] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A conventional DC amplitude-phase voltage regulation topology based on a parallel converter, characterized in that, include: DC lines, conventional DC converter valve assemblies, conventional DC converter transformers, auxiliary flexible DC converters, auxiliary flexible DC converter transformers, and receiving-end AC busbars; DC lines are used to transmit DC power to conventional DC converter valve assemblies; A conventional DC converter valve assembly is used to convert the received DC power to AC power, and then feed the converted AC power into the receiving-end AC bus via a conventional DC converter transformer. The conventional DC converter valve group is equipped with high-pressure valves and low-pressure valves at the positive and negative poles; the topology is configured with two auxiliary flexible DC converters, namely an auxiliary positive flexible DC converter and an auxiliary negative flexible DC converter; the topology is configured with two auxiliary flexible DC converter transformers. The DC side of the auxiliary positive flexible DC converter is connected in parallel with the DC side of the low-pressure valve of the positive electrode of the conventional DC converter valve group, and the DC side of the auxiliary negative flexible DC converter is connected in parallel with the DC side of the low-pressure valve of the negative electrode of the conventional DC converter valve group. The AC side of the auxiliary positive flexible DC converter is connected in series with an auxiliary flexible DC converter transformer to the grounding line of the grid-side winding of the conventional DC converter transformer corresponding to the low-voltage valve of the positive pole of the conventional DC converter valve group. The AC side of the auxiliary negative flexible DC converter is connected in series with another auxiliary flexible DC converter transformer to the grounding line of the grid-side winding of the conventional DC converter transformer corresponding to the low-voltage valve of the negative pole of the conventional DC converter valve group. An auxiliary flexible DC converter is used to adjust the amplitude and phase of the voltage on the receiving-end AC bus. An auxiliary flexible DC converter transformer is used to match the AC side output voltage of the auxiliary flexible DC converter with the voltage regulation requirements of the receiving-end AC bus.

2. The conventional DC amplitude-phase voltage regulation topology based on a parallel converter according to claim 1, characterized in that, The positive terminal of the high-pressure valve of the conventional DC converter valve group is connected to the positive terminal of the DC line; the negative terminal of the high-pressure valve of the conventional DC converter valve group is connected to the positive terminal of the low-pressure valve of the conventional DC converter valve group; the negative terminal of the low-pressure valve of the conventional DC converter valve group is connected to the positive terminal of the low-pressure valve of the conventional DC converter valve group; the negative terminal of the low-pressure valve of the conventional DC converter valve group is connected to the positive terminal of the high-pressure valve of the conventional DC converter valve group; and the negative terminal of the high-pressure valve of the conventional DC converter valve group is connected to the negative terminal of the DC line. The AC side of the following valves in a conventional DC converter valve group is connected to the valve-side winding of the corresponding conventional DC converter transformer: the high-voltage valve of the positive pole, the low-voltage valve of the positive pole, the low-voltage valve of the negative pole, and the high-voltage valve of the negative pole. The grid-side windings of a conventional DC converter transformer are connected in parallel to the receiving-end AC bus.

3. The conventional DC amplitude-phase voltage regulation topology based on a parallel converter according to claim 1, characterized in that, The following valves in a conventional DC converter valve group are constructed using a grid-commutated converter (LCC) or a controllable grid-commutated converter (CLCC): a high-pressure valve for the positive pole, a low-pressure valve for the positive pole, a low-pressure valve for the negative pole, and a high-pressure valve for the negative pole.

4. The conventional DC amplitude-phase voltage regulation topology based on a parallel converter according to claim 1, characterized in that, The auxiliary flexible DC converter adopts the modular multilevel converter (MMC) structure; Modular multilevel converter (MMC) is a half-bridge MMC based on half-bridge submodule HBSM, or a hybrid MMC based on half-bridge submodule HBSM and full-bridge submodule FBSM.

5. The conventional DC amplitude-phase voltage regulation topology based on a parallel converter according to claim 1, characterized in that, Conventional DC converter transformers are constructed using any of the following methods: The first configuration consists of three single-phase double-winding transformer groups; The second configuration consists of a single three-phase double-winding transformer; The third configuration consists of three single-phase three-winding transformer groups. The fourth configuration consists of a three-phase, three-winding transformer.

6. The conventional DC amplitude-phase voltage regulation topology based on a parallel converter according to claim 5, characterized in that, When the conventional DC converter transformer adopts the first configuration or the second configuration, the conventional DC converter transformer connected to the AC side of the high-voltage valve of the conventional DC converter valve group adopts the Y / Yn connection method; the conventional DC converter transformer connected to the AC side of the low-voltage valve of the conventional DC converter valve group adopts the Δ / Yn connection method. Among them, the Y / Yn connection method is that the valve side winding of the transformer is star-connected and the neutral point is not grounded, while the grid side winding is star-connected and grounded through the neutral point; The △ / Yn wiring method means that the transformer valve-side winding is connected in a delta configuration, while the grid-side winding is connected in a star configuration and grounded through the neutral point.

7. The conventional DC amplitude-phase voltage regulation topology based on a parallel converter according to claim 5, characterized in that, When the conventional DC converter transformer adopts the third or fourth configuration, the AC sides of the two valves on the positive end of the conventional DC converter valve group are connected to the AC bus of the receiving end through a conventional DC converter transformer; the AC sides of the two valves on the negative end of the conventional DC converter valve group are connected to the AC bus of the receiving end through a conventional DC converter transformer; the conventional DC converter transformer adopts the Δ / Y / Yn connection method. In the △ / Y / Yn connection method, the primary and secondary windings on the valve side of the transformer are connected in a delta configuration and a star configuration, respectively, with the neutral point ungrounded. The windings on the grid side are connected in a star configuration and grounded through the neutral point.

8. The conventional DC amplitude-phase voltage regulation topology based on a parallel converter according to claim 1, characterized in that, The auxiliary flexible DC converter transformer consists of three single-phase double-winding transformer groups or one three-phase double-winding transformer. The auxiliary flexible DC converter transformer adopts a Yn / Yn connection method; In the Yn / Yn connection method, both the transformer valve-side winding and the grid-side winding are star-connected and grounded through the neutral point.

9. A control method for a conventional DC amplitude-phase voltage regulation topology based on a parallel converter, characterized in that, Applied to any of the conventional DC amplitude-phase voltage regulation topologies based on parallel converters as described in claims 1-8, the control method includes: Conventional DC converter valve groups adopt a constant DC port voltage control mode, with an additional constant turn-off angle backup control mode; The auxiliary flexible DC converter employs compensation voltage amplitude control and compensation voltage phase control.

10. The control method for a conventional DC amplitude-phase voltage regulation topology based on a parallel converter according to claim 9, characterized in that, Control methods that maintain a constant DC port voltage include: pass and generate Then through and generate ; Backup control methods with a constant shut-off angle include: based on and ,generate ; in, This indicates the DC voltage at the DC port of a conventional DC converter valve assembly. This represents a reference value for the DC voltage of a conventional DC converter valve group. This represents a reference value for the DC current of a conventional DC converter valve assembly. This represents the DC current at the DC port of a conventional DC converter valve assembly. For the shut-off angle, This is a reference value for the shut-off angle. The inverter angle generated for a control method that maintains a constant DC port voltage. The inverter angle generated for a backup control mode with a constant shut-off angle; and The trigger angle is generated through algebraic operations. ; Compensation voltage amplitude control includes: based on and This generates current on the AC side of the auxiliary flexible DC converter. and the corresponding current reference value ; Compensated voltage phase control, including: Phase based on the receiving-end AC bus voltage and the corresponding phase reference value and the phase of the valve-side voltage of a conventional DC converter transformer and the corresponding phase reference value Generate the compensation phase angle of the auxiliary flexible DC converter ; in, and This indicates the compensation voltage output from the AC side of the auxiliary flexible DC converter and the corresponding compensation voltage reference value. It acts on the current control circuit; and The DC voltage imbalance component is generated through a current control circuit.

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