A bipolar flexible DC converter station control system

Abstract

The present application provides a bipolar flexible DC converter station control system, which is suitable for a large-scale new energy pure island access bipolar flexible DC transmission system. The present application may include a bipolar AC voltage outer loop controller, a positive and negative valve side current inner loop controller, and a positive and negative DC side combined controller. The bipolar AC voltage outer loop controller is used to realize the control of the AC voltage on the AC side of the bipolar flexible DC converter station and the distribution of positive and negative power reference values; the positive and negative valve side current inner loop controllers respectively realize the effective control of the positive and negative converter valve side current. The present application can effectively provide stable AC voltage and frequency for the access of new energy power stations.

Description

Technical Field

[0001] The present application relates to the technical field of large-scale new energy flexible direct current long-distance power transmission engineering, and in particular to a bipolar flexible direct current converter station control system. Background Art

[0002] Due to the long transmission distance and large capacity of the new energy flexible DC transmission project, the AC side of the sending end is a pure new energy access system, and the new energy power station is connected to the sending end converter station in an isolated manner. Since the pure new energy access system has no power sources such as generators, in order to ensure the normal operation of the new energy flexible DC transmission project, the bipolar flexible DC sending end converter station system with new energy intervention needs to provide stable AC voltage and frequency.

[0003] Therefore, how to provide stable AC voltage and frequency for the bipolar flexible DC sending-end converter station system of the bipolar flexible DC transmission project with new energy access has always been a problem of concern. Summary of the invention

[0004] The present application aims to solve at least one of the above-mentioned technical defects. In view of this, the present application provides a bipolar flexible DC converter station control system, which is used to solve the technical defect in the prior art that it is difficult to provide stable AC voltage and frequency for the bipolar flexible DC sending-end converter station system of the bipolar flexible DC transmission project for new energy access.

[0005] A bipolar flexible DC converter station control system is applied to a bipolar flexible DC power transmission system, the bipolar flexible DC power transmission system comprises: a bipolar flexible DC sending-end converter station and a new energy power station, wherein the bipolar flexible DC sending-end converter station is connected to the new energy power station island, the bipolar flexible DC converter station control system comprises: a positive converter, a negative converter, an AC side double closed-loop controller, and a converter valve control arranged in the bipolar flexible DC sending-end converter station,

[0006] The converter valve control includes positive converter valve control and negative converter valve control, the positive converter valve control includes a positive converter valve hybrid bridge module, the negative converter valve control includes a negative converter valve hybrid bridge module, and the AC side double closed-loop controller includes an AC voltage outer loop controller, a positive valve side current inner loop controller and a negative valve side current inner loop controller;

[0007] The AC voltage outer loop controller controls the AC voltage shared by the AC side of the positive converter and the AC side of the negative converter, and uses its output to control the input of the positive valve side current inner loop controller and the negative valve side current inner loop controller according to a preset power allocation strategy;

[0008] The positive valve-side current inner loop controller controls the valve-side current of the positive converter, and based on its input and a preset frequency, generates a three-phase AC voltage modulation wave reference value and transmits it to the positive converter valve control;

[0009] The negative pole valve-side current inner loop controller controls the valve-side current of the negative pole converter, and based on its input and a preset frequency, generates a three-phase AC voltage modulation wave reference value and transmits it to the negative pole converter valve control;

[0010] The converter valve control controls the switching of the positive converter valve hybrid bridge module and the negative converter valve hybrid bridge module based on the preset rated module voltage and the three-phase AC voltage modulation wave reference value, and generates a target AC side voltage and a target frequency.

[0011] Preferably, it also includes:

[0012] The positive DC side combined controller and the negative DC side combined controller are arranged in the bipolar flexible DC sending end converter station,

[0013] in,

[0014] The positive DC side combined controller controls the voltage of the positive converter valve hybrid bridge module based on the preset rated submodule voltage reference value of the positive converter valve, and outputs the DC voltage reference value of the positive DC side to the positive converter valve control. The positive converter valve control generates a DC voltage on the DC side of the positive converter based on the DC voltage reference value of the positive DC side, and generates a target positive converter valve hybrid bridge submodule voltage through dynamic adjustment of the DC voltage on the positive DC side;

[0015] The negative pole DC side combined controller controls the voltage of the negative pole converter valve hybrid bridge module based on the preset rated submodule voltage reference value of the negative pole converter valve, and outputs the DC voltage reference value of the negative pole DC side to the negative pole converter valve control. The negative pole converter valve control generates a DC voltage on the DC side of the negative pole converter, and generates a target negative pole converter valve hybrid bridge submodule voltage through dynamic adjustment of the DC voltage on the negative pole DC side.

[0016] Preferably, the positive DC side combined controller comprises a positive DC side submodule voltage controller and a positive DC current controller;

[0017] Based on this, the positive DC side combined controller controls the voltage of the positive converter valve hybrid bridge module and outputs the DC voltage reference value of the positive DC side to the positive converter valve control; including:

[0018] The positive DC side submodule voltage controller controls the voltage average value of the positive converter valve hybrid bridge module, and outputs a positive DC current control reference value to the positive DC current controller;

[0019] The positive DC current controller outputs a positive DC voltage control reference value based on the positive DC current reference value and outputs it to the positive converter valve control.

[0020] Preferably, the negative DC side combined controller includes a negative DC side submodule voltage controller and a negative DC current controller;

[0021] Based on this, the negative electrode DC side combined controller controls the voltage of the negative electrode converter valve hybrid bridge module and outputs the DC voltage reference value of the negative electrode DC side to the negative electrode converter valve control; including:

[0022] The negative DC side submodule voltage controller controls the voltage average value of the negative converter valve hybrid bridge module, and outputs a negative DC current control reference value to the negative DC current controller;

[0023] The negative electrode DC current controller outputs a negative electrode DC voltage control reference value based on the negative electrode DC current reference value and outputs it to the negative electrode converter valve control.

[0024] Preferably, the preset rated module voltage includes a rated positive converter valve hybrid bridge module voltage generated by the positive DC side combined controller and a rated negative converter valve hybrid bridge module voltage generated by the negative DC side combined controller.

[0025] The positive pole converter valve valve control controls the switching of the positive pole converter valve hybrid bridge module based on the positive pole DC voltage control reference value and the three-phase AC voltage modulation wave, and the negative pole converter valve valve control controls the switching of the negative pole converter valve hybrid bridge module based on the negative pole DC voltage control reference value and the three-phase AC voltage modulation wave, and generates a target positive pole converter valve hybrid bridge submodule voltage, a target negative pole converter valve hybrid bridge submodule voltage, a target AC side voltage and a target frequency.

[0026] Preferably, the AC voltage outer loop controller controls the AC voltage of the positive converter and the negative converter, and outputs the AC voltage to control the input of the positive valve side current inner loop controller and the negative valve side current inner loop controller according to a preset power allocation strategy, including:

[0027] The AC voltage outer loop controller outputs a target current reference value based on a preset rated voltage reference value;

[0028] The AC voltage outer loop controller uses the target current reference value as input to the positive valve side current inner loop controller and the negative valve side current inner loop controller respectively according to a preset power allocation strategy.

[0029] Preferably, the positive valve-side current inner loop controller controls the valve-side current of the positive converter, and based on its input and a preset frequency, generates a three-phase AC voltage modulation wave reference value and transmits it to the positive converter valve control, including:

[0030] The positive valve side current inner loop controller generates a three-phase AC voltage modulation wave reference value based on the target current reference value and the preset frequency and transmits it to the positive current converter valve control.

[0031] Preferably, the negative valve-side current inner loop controller controls the valve-side current of the negative converter, and based on its input and a preset frequency, generates a three-phase AC voltage modulation wave reference value and transmits it to the negative converter valve control, including:

[0032] The negative pole valve side current inner loop controller generates a three-phase AC voltage modulation wave reference value based on the target current reference value and the preset frequency and transmits it to the negative pole converter valve control.

[0033] Preferably, the preset power allocation strategy includes:

[0034] The current output by the AC voltage outer loop controller is distributed to the positive valve side current inner loop controller and the negative valve side current inner loop controller according to a set ratio.

[0035] Preferably, the positive pole converter valve hybrid bridge module and the negative pole converter valve hybrid bridge module both include a full-bridge submodule and a half-bridge submodule.

[0036] It can be seen from the above technical solutions that the embodiment of the present application can be applied to a bipolar flexible direct current transmission system, and the bipolar flexible direct current transmission system may include: a bipolar flexible direct current sending end converter station and a new energy power station, wherein the bipolar flexible direct current sending end converter station is connected to the new energy power station island, and the present application may include: a positive converter, a negative converter, an AC side double closed-loop controller, and a converter valve control arranged in the bipolar flexible direct current sending end converter station,

[0037] Among them, the converter valve control may include positive converter valve control and negative converter valve control, the positive converter valve control may include a positive converter valve hybrid bridge module, the negative converter valve control may include a negative converter valve hybrid bridge module, the AC side dual closed-loop controller may include an AC voltage outer loop controller, a positive valve side current inner loop controller and a negative valve side current inner loop controller; the AC voltage outer loop controller may control the AC voltage shared by the positive converter AC side and the negative converter AC side, so that its output can control the input of the positive valve side current inner loop controller and the negative valve side current inner loop controller according to a preset power distribution strategy. The positive valve side current inner loop controller can control the valve side current of the positive converter, and based on its input and a preset frequency, can generate a three-phase AC voltage modulation wave reference value and transmit it to the positive converter valve control; the negative valve side current inner loop controller can control the valve side current of the negative converter, and based on its input and a preset frequency, can generate a three-phase AC voltage modulation wave reference value and transmit it to the negative converter valve control; the converter valve control can control the switching of the positive converter valve hybrid bridge module and the negative converter valve hybrid bridge module based on a preset rated module voltage and the three-phase AC voltage modulation wave reference value, so as to generate a target AC side voltage and a target frequency.

[0038] This application can effectively provide stable AC voltage and frequency for the flexible DC system of the bipolar flexible DC sending-end converter station of the new energy flexible DC transmission project. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0040] Figure 1 A schematic diagram of an architecture for implementing a bipolar flexible DC sending-end converter station control system provided in an embodiment of the present application;

[0041] Figure 2 A schematic diagram of the structure of a hybrid bridge module provided in an embodiment of the present application. DETAILED DESCRIPTION

[0042] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0043] As a new generation of DC transmission technology, flexible DC transmission is similar to HVDC transmission in structure and is still composed of converter stations and DC transmission lines. Unlike the current source converter type HVDC transmission based on phase-controlled commutation technology, the converter stations at both ends of the flexible DC transmission system are all composed of converters, converter transformers, converter reactors, etc. The converter in the flexible DC transmission is a voltage source converter, and its biggest feature is the use of turn-off devices (usually IGBT) and high-frequency modulation technology. Among them, the most critical core part is the voltage source converter, which is composed of a rectifier bridge and a DC capacitor. In the system, considering the topological structure of its main circuit and the type of switching devices, sinusoidal pulse width modulation technology can be used. This technology compares the data of the modulated reference wave with the triangular carrier. When the latter data is relatively small, the lower bridge arm switch will be triggered to turn on and turn off the lower bridge arm. This is mainly because both floating values ​​and phases can be intelligently regulated using pulse width modulation technology. Therefore, the amplitude and phase of the fundamental frequency component of the AC output voltage of the voltage source converter can also be adjusted by the pulse width.

[0044] The sending-end AC side of the bipolar flexible DC transmission system under pure renewable energy access is a renewable energy island access system. Since there is no power source such as a generator, the bipolar flexible DC sending-end converter station flexible DC system is required to provide a stable AC voltage.

[0045] To this end, the applicant has studied a flexible DC converter station control scheme, which can be applied to a bipolar flexible DC power transmission system, which can include: a bipolar flexible DC sending-end converter station and a new energy power station, wherein the bipolar flexible DC sending-end converter station is connected to the new energy power station island. The purpose is to provide a stable AC voltage and frequency for the bipolar flexible DC sending-end converter station flexible DC system of the new energy flexible DC power transmission project.

[0046] Combine the following Figure 1 , introduces an optional system architecture that can realize the control of a flexible DC converter station given in an embodiment of the present application, such as Figure 1 As shown, the system architecture may include: a positive converter, a negative converter, an AC side double closed-loop controller, and a converter valve control arranged at the bipolar flexible DC sending-end converter station.

[0047] Among them, the converter valve control may include positive converter valve control and negative converter valve control, the positive converter valve control may include a positive converter valve hybrid bridge module, the negative converter valve control may include a negative converter valve hybrid bridge module, and the AC side dual closed-loop controller may include an AC voltage outer loop controller, a positive valve side current inner loop controller and a negative valve side current inner loop controller.

[0048] The AC voltage outer loop controller can control the AC voltage shared by the AC side of the positive converter and the AC side of the negative converter, and can use its output to control the input of the positive valve side current inner loop controller and the negative valve side current inner loop controller according to a preset power distribution strategy.

[0049] Specifically, since the new energy flexible DC transmission system adopts a bipolar DC transmission control system, only one AC voltage control point is set for the bipolar flexible DC sending-end converter station, and only one AC voltage outer-loop controller is designed in the bipolar DC transmission control system, so that the output result of the AC voltage outer-loop controller can be distributed to the inner-loop controller corresponding to the bipolar transmission line according to a preset power allocation strategy.

[0050] For example, an AC side double closed-loop controller can be set at the bipolar flexible DC sending-end converter station, and the AC side double closed-loop controller can be controlled by the AC voltage d-axis component and q-axis component, and the positive valve side current inner loop controller and the negative valve side current inner loop controller can be controlled by the valve side current d-axis component and q-axis component. When the bipolar DC power transmission system operates normally, the AC side double closed-loop controller can achieve stable control of the AC side voltage and frequency of the bipolar flexible DC sending-end converter station, and evenly distribute the power of the positive DC transmission line and the negative DC transmission line.

[0051] For example, the AC voltage outer loop controller can control the input of the positive valve side current inner loop controller and the negative valve side current inner loop controller according to a preset power distribution strategy, so that the current and power of the positive valve side current inner loop controller and the negative valve side current inner loop controller can be evenly distributed.

[0052] Compared with the single-loop control strategy, the dual closed-loop control strategy can control the valve-side current within the limiting range while achieving stable control of the AC voltage and frequency, thereby preventing the current of the bridge arm of the hybrid bridge module from exceeding the limited current.

[0053] The positive valve-side current inner loop controller can control the valve-side current of the positive converter, and based on its input and a preset frequency, generate a three-phase AC voltage modulation wave reference value and transmit it to the positive converter valve control.

[0054] The negative pole valve side current inner loop controller can control the valve side current of the negative pole converter, and can generate a three-phase AC voltage modulation wave reference value based on its input and a preset frequency and transmit it to the negative pole converter valve control.

[0055] Specifically, since the positive valve side current inner loop controller and the negative valve side current inner loop controller respectively correspond to the positive DC transmission system and the negative DC transmission system of the bipolar DC transmission system, under the control of the AC voltage outer loop controller, the positive valve side current inner loop controller and the negative valve side current inner loop controller can generate a three-phase AC voltage modulation wave reference value based on the input controlled by the AC voltage outer loop controller and a preset frequency, and transmit it to the converter valve control, so that the converter valve control can generate a stable voltage and frequency.

[0056] The preset power allocation strategy may be as follows:

[0057] The current output by the AC voltage outer loop controller is distributed to the positive valve side current inner loop controller and the negative valve side current inner loop controller according to a set ratio.

[0058] The three-phase AC voltage modulation wave reference value is that the positive valve side current inner loop controller and the negative valve side current inner loop controller convert the d-axis and q-axis components of the output voltage of the AC voltage outer loop controller into abc three-phase AC components. The three-phase AC signals are the bridge arm modulation wave signals of the hybrid bridge module controlled by the three-phase converter valve.

[0059] For example, the preset frequency can be set to 50 Hz, and the positive valve side current inner loop controller and the negative valve side current inner loop controller can generate a three-phase AC voltage modulation wave reference value based on the current reference value controlled by the AC voltage outer loop controller and the frequency of 50 Hz, and transmit it to the converter valve control so that the converter valve control can generate stable voltage and frequency.

[0060] The converter valve control can control the switching of the positive converter valve hybrid bridge module and the negative converter valve hybrid bridge module based on the preset rated module voltage and the three-phase AC voltage modulation wave reference value to generate the target AC side voltage and target frequency.

[0061] Specifically, the converter valve control can control the voltage of the hybrid bridge module. After receiving the three-phase AC voltage modulation wave reference value transmitted by the positive valve side current inner loop controller and the negative valve side current inner loop controller, the converter valve control can control the switching of the hybrid bridge module voltage based on the rated hybrid bridge module voltage and the three-phase AC voltage modulation wave reference value to generate a stable AC side voltage and frequency.

[0062] The hybrid bridge module may include a full-bridge submodule and a half-bridge submodule.

[0063] In the above Figure 1 middle,

[0064] U d and U q can represent the d-axis and q-axis components of the AC voltage, U d and U q It can be obtained by abc / dq transformation for three-phase AC voltage;

[0065] I dref ,I qref Can represent the current reference value of the valve side current controller, I dref can be the d-axis current reference value, I qref It can be the q-axis current reference value;

[0066] f can be the frequency;

[0067] U cavg It can be the average voltage of the submodule;

[0068] m dc It can be a DC voltage reference value output by the DC side combined controller;

[0069] U iref It can be the reference value of the three-phase voltage modulation wave.

[0070] It can be seen from the technical solution introduced above that the embodiment of the present application can utilize the converter valve control based on the preset rated module voltage and the three-phase AC voltage modulation wave reference value to control the switching of the positive converter valve hybrid bridge module and the negative converter valve hybrid bridge module, generate the target sub-module voltage and the target AC side voltage and target frequency, and effectively provide stable AC voltage and frequency for the bipolar flexible DC sending end converter station flexible DC system of the new energy flexible DC transmission project.

[0071] From the above introduction, it can be known that the converter valve control can control the switching of the positive converter valve hybrid bridge module and the negative converter valve hybrid bridge module based on the rated hybrid bridge module voltage and the three-phase AC voltage modulation wave reference value to generate the target AC side voltage and target frequency. In practical applications, in order to ensure that the converter valve control can operate normally, the bipolar flexible DC converter station control system also includes: a positive DC converter and a negative DC converter, and a positive DC side combined controller and a negative DC side combined controller arranged at the bipolar flexible DC sending end converter station,

[0072] in,

[0073] The positive DC side combined controller controls the voltage of the positive converter valve hybrid bridge module based on the preset rated submodule voltage reference value of the positive converter valve, and outputs the DC voltage reference value of the positive DC side to the positive converter valve control. The positive converter valve control generates a DC voltage on the DC side of the positive converter based on the DC voltage reference value of the positive DC side, and generates a target positive converter valve hybrid bridge submodule voltage through dynamic adjustment of the DC voltage on the positive DC side.

[0074] Specifically, in order to ensure the normal operation of the converter valve control, the positive DC side combined controller controls the voltage of the positive converter valve hybrid bridge module based on the preset rated submodule voltage reference value of the positive converter valve, and outputs the DC voltage reference value of the positive DC side to the positive converter valve control, so that the converter valve control can generate a DC voltage on the DC side of the positive converter at the voltage reference value of the positive DC side, and effectively maintain stable operation through dynamic adjustment of the DC voltage on the positive DC side, thereby generating a stable target positive converter valve hybrid bridge submodule voltage.

[0075] The negative pole DC side combined controller controls the voltage of the negative pole converter valve hybrid bridge module based on the preset rated submodule voltage reference value of the negative pole converter valve, and outputs the DC voltage reference value of the negative pole DC side to the negative pole converter valve control. The negative pole converter valve control generates a DC voltage on the DC side of the negative pole converter, and generates a target negative pole converter valve hybrid bridge submodule voltage through dynamic adjustment of the DC voltage on the negative pole DC side.

[0076] Specifically, in order to ensure the normal operation of the converter valve control, the negative DC side combined controller controls the voltage of the negative converter valve hybrid bridge module based on the preset rated submodule voltage reference value of the negative converter valve, and outputs the DC voltage reference value of the negative DC side to the negative converter valve control, so that the converter valve control can effectively maintain stable operation at the voltage reference value of the negative DC side, so as to generate a DC voltage on the DC side of the negative converter. The target negative converter valve hybrid bridge submodule voltage is generated by dynamically adjusting the DC voltage on the negative DC side.

[0077] It can be seen from the technical solutions introduced above that the positive DC side combined controller of the embodiment of the present application controls the target positive converter valve hybrid bridge submodule voltage based on the preset rated submodule voltage reference value of the positive converter valve, and the negative DC side combined controller controls the target negative converter valve hybrid bridge submodule voltage based on the preset rated submodule voltage reference value of the negative converter valve, and outputs the voltage reference value of the positive DC side and the voltage reference value of the negative DC side to the converter valve control respectively, so as to ensure that the converter valve control can operate normally.

[0078] In actual application, the positive DC side combined controller may include a positive DC side submodule voltage controller and a positive DC current controller, and the negative DC side combined controller may include a negative DC side submodule voltage controller and a negative DC current controller. Then the positive DC side combined controller controls the voltage of the positive converter valve hybrid bridge module based on the preset rated submodule voltage reference value of the positive converter valve, and the negative DC side combined controller controls the voltage of the negative converter valve hybrid bridge module based on the preset rated submodule voltage reference value of the negative converter valve, and the process of outputting the voltage reference value of the positive DC side and the voltage reference value of the negative DC side to the converter valve control may include the following:

[0079] The positive DC side module voltage controller can control the voltage average value of each submodule of the positive converter valve hybrid bridge module, and output a positive DC current control reference value to the positive DC current controller;

[0080] The positive DC current controller can output a positive DC voltage control reference value based on the positive DC current reference value and output it to the converter valve control.

[0081] The negative DC side module voltage controller can control the voltage average value of each submodule of the negative converter valve hybrid bridge module, and output a negative DC current control reference value to the negative DC current controller;

[0082] The negative DC current controller can output a negative DC voltage control reference value based on the negative DC current reference value and output it to the converter valve control.

[0083] It can be seen from the technical solution introduced above that the positive DC side combined controller of the embodiment of the present application controls the voltage of the positive converter valve hybrid bridge module based on the preset rated submodule voltage reference value of the positive converter valve, and the negative DC side combined controller controls the voltage of the negative converter valve hybrid bridge module based on the preset rated submodule voltage reference value of the negative converter valve, and respectively outputs the voltage reference value of the positive DC side and the voltage reference value of the negative DC side to the converter valve control to ensure that the converter valve control can operate normally.

[0084] It can be known from the technical solution introduced above that the converter valve control can control the switching of the positive converter valve hybrid bridge module and the negative converter valve hybrid bridge module based on the preset rated module voltage and the three-phase AC voltage modulation wave reference value, and generate the target positive converter valve hybrid bridge submodule voltage and the target negative converter valve hybrid bridge submodule voltage as well as the target AC side voltage and the target frequency, and the preset rated module voltage can include the rated positive converter valve hybrid bridge module voltage generated by the positive DC side combination controller and the rated negative converter valve hybrid bridge module voltage generated by the negative DC side combination controller. Therefore, the converter valve control can control the switching of the positive converter valve hybrid bridge module and the negative converter valve hybrid bridge module based on the preset rated module voltage and the three-phase AC voltage modulation wave reference value, and generate the target positive converter valve hybrid bridge submodule voltage and the target negative converter valve hybrid bridge submodule voltage as well as the target AC side voltage and the target frequency. The process can include the following:

[0085] The positive pole converter valve valve control can be based on the positive pole DC voltage control reference value and the three-phase AC voltage modulation wave, thereby controlling the switching of the positive pole converter valve hybrid bridge module. The negative pole converter valve valve control can be based on the negative pole DC voltage control reference value and the three-phase AC voltage modulation wave, thereby controlling the switching of the negative pole converter valve hybrid bridge module, thereby generating the target positive pole converter valve hybrid bridge submodule voltage and the target negative pole converter valve hybrid bridge submodule voltage as well as the target AC side voltage and the target frequency.

[0086] It can be seen from the technical solution introduced above that the converter valve control of the present application can control the switching of the positive converter valve hybrid bridge module and the negative converter valve hybrid bridge module based on the preset rated module voltage and the three-phase AC voltage modulation wave reference value, and generate the target positive converter valve hybrid bridge submodule voltage and the target negative converter valve hybrid bridge submodule voltage as well as the target AC side voltage and target frequency, which can effectively provide stable AC voltage and frequency for the bipolar flexible DC sending end converter station flexible DC system of the new energy flexible DC transmission project.

[0087] It can be seen from the technical solution introduced above that the AC voltage outer loop controller of the embodiment of the present application can control the input of the positive valve side current inner loop controller and the negative valve side current inner loop controller according to the preset power allocation strategy. The process is introduced below, and the process may include the following:

[0088] The AC voltage outer loop controller can output a target current reference value based on a preset rated voltage.

[0089] After obtaining the target current reference value, the AC voltage outer loop controller can use the target current reference value as input to the positive valve side current inner loop controller and the negative valve side current inner loop controller respectively according to a preset power allocation strategy.

[0090] The preset power allocation strategy may be set with reference to the target current reference value and the operation status of the bipolar transmission line.

[0091] Based on this, the positive valve-side current inner loop controller controls the valve-side current of the positive converter, and based on its input and a preset frequency, generates a three-phase AC voltage modulation wave reference value and transmits it to the positive converter valve control process, which may include the following:

[0092] The positive valve side current inner loop controller and the negative valve side current inner loop controller can generate a three-phase AC voltage modulation wave reference value based on a preset frequency and the target current reference value and transmit it to the converter valve control.

[0093] The process in which the negative pole valve-side current inner loop controller controls the valve-side current of the negative pole converter and generates a three-phase AC voltage modulation wave reference value based on its input and a preset frequency and transmits the reference value to the negative pole converter valve control may include the following:

[0094] The negative valve side current inner loop controller can generate a three-phase AC voltage modulation wave reference value based on the target current reference value and the preset frequency and transmit it to the negative current converter valve control.

[0095] It can be seen from the technical solution introduced above that the AC voltage outer loop controller in the embodiment of the present application can control the input of the positive valve side current inner loop controller and the negative valve side current inner loop controller according to a preset power distribution strategy, so that the positive valve side current inner loop controller and the negative valve side current inner loop controller can generate a three-phase AC voltage modulation wave reference value based on their input and a preset frequency and transmit it to the converter valve control, so that the converter valve control can generate a stable AC side voltage and frequency on the AC side based on the three-phase AC voltage modulation wave reference value, which can effectively provide stable AC voltage and frequency for the bipolar flexible DC sending end converter station flexible DC system of the new energy flexible DC transmission project.

[0096] As can be seen from the above introduction, the embodiment of the present application includes a hybrid bridge module, Figure 2 The structural schematic diagram of the hybrid bridge module is illustrated. The hybrid bridge module may include several full-bridge sub-modules and several half-bridge sub-modules.

[0097] Since the converter valve may include 6 bridge arms, each bridge arm may be composed of a plurality of full-bridge sub-modules and half-bridge sub-modules connected in series.

[0098] The full-bridge submodule can be composed of 4 fully controlled devices IGBT and capacitors. Due to the increase in the number of IGBTs, the full-bridge submodule can include three states: positive input state, reverse input state and cut-off state. When the full-bridge submodule is in the positive input state, the voltage in the series circuit of the full-bridge submodule is positive; when the full-bridge submodule is in the reverse input state, the voltage of the full-bridge submodule is negative; when the full-bridge submodule is in the cut-off state, the voltage of the full-bridge submodule is 0.

[0099] The half-bridge submodule can be composed of two fully controlled devices IGBT and capacitor, and the half-bridge submodule can include two states: the on state and the off state. When the half-bridge submodule is in the on state, the voltage in the series circuit of the half-bridge submodule is positive, and when the half-bridge submodule is in the off state, the voltage of the half-bridge submodule is 0;

[0100] Since the converter functions to convert AC to DC, the modules used in the upper and lower bridge arms are fixed. If the converter valves are composed entirely of half-bridge sub-modules, the DC side voltage of the converter does not have the ability to be adjusted, and the DC side voltage of the converter can be 1pu; if they are all composed of full-bridge sub-modules, the DC side voltage of the converter can be adjusted in the range of [-1pu, 1pu]. However, if the converter valves are all composed of full-bridge sub-modules, although the DC side voltage of the converter can be flexibly adjusted, the cost is relatively high. Considering the economic applicability of electrical equipment and the need to achieve a certain negative voltage on the DC side voltage, in order to clear DC side faults, it is possible to consider using full-bridge sub-modules and half-bridge sub-modules to form a hybrid bridge module in a certain proportion.

[0101] For example, the full-bridge submodule and the half-bridge submodule may be arranged in a ratio of 7:3 to form a hybrid bridge module, so that the DC side voltage range of the converter can be [-0.4pu, 1pu].

[0102] It can be seen from the technical solution introduced above that the hybrid bridge module 3 of the embodiment of the present application may include a number of full-bridge sub-modules and half-bridge sub-modules, thereby ensuring that the DC side voltage range of the converter is within a preset range, which is beneficial for the converter valve control to generate stable voltage and current on the AC side.

[0103] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0104] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0105] The above description of the disclosed embodiments enables professionals and technicians in the field to implement or use the present application. Various modifications to these embodiments will be apparent to professionals and technicians in the field, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. The various embodiments can be combined with each other. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A bipolar flexible DC converter station control system, characterized in that: The invention is applied to a bipolar flexible direct current power transmission system, which comprises: a bipolar flexible direct current sending end converter station and a new energy power station, wherein the bipolar flexible direct current sending end converter station is connected to the island of the new energy power station, and the bipolar flexible direct current converter station control system comprises: a positive converter, a negative converter, an AC side double closed-loop controller, a converter valve control, a positive DC side combined controller and a negative DC side combined controller arranged in the bipolar flexible direct current sending end converter station, The converter valve control includes positive converter valve control and negative converter valve control, the positive converter valve control includes a positive converter valve hybrid bridge module, the negative converter valve control includes a negative converter valve hybrid bridge module, and the AC side double closed-loop controller includes an AC voltage outer loop controller, a positive valve side current inner loop controller and a negative valve side current inner loop controller; The AC voltage outer loop controller controls the AC voltage shared by the AC side of the positive converter and the AC side of the negative converter, and uses its output to control the input of the positive valve side current inner loop controller and the negative valve side current inner loop controller according to a preset power allocation strategy; The positive valve-side current inner loop controller controls the valve-side current of the positive converter, and based on its input and a preset frequency, generates a three-phase AC voltage modulation wave reference value and transmits it to the positive converter valve control; The negative pole valve-side current inner loop controller controls the valve-side current of the negative pole converter, and based on its input and a preset frequency, generates a three-phase AC voltage modulation wave reference value and transmits it to the negative pole converter valve control; The converter valve control controls the switching of the positive converter valve hybrid bridge module and the negative converter valve hybrid bridge module based on the preset rated submodule voltage and the three-phase AC voltage modulation wave reference value, and generates a target AC side voltage and a target frequency; The positive DC side combined controller controls the voltage of the positive converter valve hybrid bridge module based on the preset rated submodule voltage reference value of the positive converter valve, and outputs the DC voltage reference value of the positive DC side to the positive converter valve control. The positive converter valve control generates a DC voltage on the DC side of the positive converter based on the DC voltage reference value of the positive DC side, and generates a target positive converter valve hybrid bridge submodule voltage through dynamic adjustment of the DC voltage on the positive DC side; The negative pole DC side combined controller controls the voltage of the negative pole converter valve hybrid bridge module based on the preset rated submodule voltage reference value of the negative pole converter valve, and outputs the DC voltage reference value of the negative pole DC side to the negative pole converter valve control. The negative pole converter valve control generates a DC voltage on the DC side of the negative pole converter, and generates a target negative pole converter valve hybrid bridge submodule voltage through dynamic adjustment of the DC voltage on the negative pole DC side.

2. The bipolar flexible DC converter station control system according to claim 1 is characterized in that: The positive DC side combined controller includes a positive DC side submodule voltage controller and a positive DC current controller; Based on this, the positive DC side combined controller controls the voltage of the positive converter valve hybrid bridge module and outputs the DC voltage reference value of the positive DC side to the positive converter valve control; including: The positive DC side submodule voltage controller controls the voltage average value of the positive converter valve hybrid bridge module, and outputs a positive DC current control reference value to the positive DC current controller; The positive DC current controller outputs a DC voltage reference value on the positive DC side based on the positive DC current control reference value and outputs it to the positive converter valve control.

3. The bipolar flexible DC converter station control system according to claim 1, characterized in that: The negative DC side combined controller includes a negative DC side submodule voltage controller and a negative DC current controller; Based on this, the negative electrode DC side combined controller controls the voltage of the negative electrode converter valve hybrid bridge module and outputs the DC voltage reference value of the negative electrode DC side to the negative electrode converter valve control; including: The negative DC side submodule voltage controller controls the voltage average value of the negative converter valve hybrid bridge module, and outputs a negative DC current control reference value to the negative DC current controller; The negative electrode DC current controller outputs a DC voltage reference value of the negative electrode DC side based on the negative electrode DC current control reference value and outputs it to the negative electrode converter valve control.

4. The bipolar flexible DC converter station control system according to claim 1, characterized in that: The preset rated submodule voltage includes the rated positive converter valve hybrid bridge module voltage generated by the positive DC side combined controller and the rated negative converter valve hybrid bridge module voltage generated by the negative DC side combined controller. The positive pole converter valve valve control controls the switching of the positive pole converter valve hybrid bridge module based on the DC voltage reference value of the positive pole DC side and the three-phase AC voltage modulation wave, and the negative pole converter valve valve control controls the switching of the negative pole converter valve hybrid bridge module based on the DC voltage reference value of the negative pole DC side and the three-phase AC voltage modulation wave, and generates a target positive pole converter valve hybrid bridge submodule voltage, a target negative pole converter valve hybrid bridge submodule voltage, a target AC side voltage and a target frequency.

5. The bipolar flexible DC converter station control system according to claim 1, characterized in that: The AC voltage outer loop controller controls the AC voltage of the positive converter and the negative converter, and uses its output to control the input of the positive valve side current inner loop controller and the negative valve side current inner loop controller according to a preset power allocation strategy, including: The AC voltage outer loop controller outputs a target current reference value based on a preset rated voltage reference value; The AC voltage outer loop controller uses the target current reference value as input to the positive valve side current inner loop controller and the negative valve side current inner loop controller respectively according to a preset power allocation strategy.

6. The bipolar flexible DC converter station control system according to claim 5, characterized in that: The positive valve-side current inner loop controller controls the valve-side current of the positive converter, and based on its input and a preset frequency, generates a three-phase AC voltage modulation wave reference value and transmits it to the positive converter valve control, including: The positive valve side current inner loop controller generates a three-phase AC voltage modulation wave reference value based on the target current reference value and the preset frequency and transmits it to the positive current converter valve control.

7. The bipolar flexible DC converter station control system according to claim 5, characterized in that: The negative pole valve-side current inner loop controller controls the valve-side current of the negative pole converter, and based on its input and a preset frequency, generates a three-phase AC voltage modulation wave reference value and transmits it to the negative pole converter valve control, including: The negative pole valve side current inner loop controller generates a three-phase AC voltage modulation wave reference value based on the target current reference value and the preset frequency and transmits it to the negative pole converter valve control.

8. The bipolar flexible DC converter station control system according to claim 1, characterized in that: The preset power allocation strategy includes: The current output by the AC voltage outer loop controller is distributed to the positive valve side current inner loop controller and the negative valve side current inner loop controller according to a set ratio.

9. The bipolar flexible DC converter station control system according to any one of claims 1 to 8, characterized in that: The positive pole converter valve hybrid bridge module and the negative pole converter valve hybrid bridge module both include a full-bridge submodule and a half-bridge submodule.

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