Coordination control method and system for island new energy through flexible direct current sending-out system

Abstract

The invention discloses a coordinated control method and system for island new energy through a flexible direct current sending-out system. The method comprises the following steps: adjusting an alternating current voltage phase output by a receiving end flexible direct current converter by adopting a network construction type control mode; the alternating-current voltage phase output by the receiving-end flexible direct-current converter is associated with the direct-current voltage; a voltage frequency slope control mode is adopted to adjust the alternating voltage frequency output by the sending-end island flexible direct current converter; the AC voltage frequency output by the sending end island flexible DC converter is associated with the DC voltage; according to the DC voltage of the sending-end new energy unit, adjusting the active power output by the sending-end new energy unit; the active power output by the sending-end new energy unit is associated with the frequency of the island new energy power grid; according to the invention, the island new energy can rapidly and actively support the receiving-end power grid in a short-time active manner through the flexible direct-current sending-out system, emergency support can be carried out under the condition that the receiving-end power grid breaks down and the frequency is unstable, and the stability of the receiving-end power grid is improved.

Description

Technical Field

[0001] This invention relates to the field of flexible DC transmission technology, and in particular to a coordinated control method and system for an isolated renewable energy transmission system via flexible DC transmission. Background Technology

[0002] Transmitting large-scale isolated renewable energy sources via flexible DC transmission is one of the important forms of long-distance transmission of large-scale renewable energy in the future. In the future, large-scale renewable energy transmission from desert and Gobi areas and deep-sea wind power transmission will mainly adopt flexible DC transmission as the transmission route.

[0003] Flexible DC transmission possesses the capability to actively support the active power of the AC grid. When the AC grid frequency changes, it can adjust its active power output to support the grid frequency, thus providing emergency support in the event of grid failure and frequency instability, preventing low-frequency load shedding. However, for isolated renewable energy systems transmitted via flexible DC, the receiving-end converter station uses constant DC voltage control, making it difficult for the sending-end isolated system to quickly support the grid as needed. Adding energy storage would significantly increase system costs. Therefore, it is difficult for isolated renewable energy systems transmitted via flexible DC to achieve active support of the receiving-end AC grid. Summary of the Invention

[0004] To address the problems existing in the prior art, embodiments of the present invention provide a coordinated control method and system for isolated renewable energy transmitted via flexible DC transmission. This system can meet the needs of isolated renewable energy transmitted via flexible DC transmission for rapid and proactive short-term active power support of the receiving-end power grid. Thus, it can provide emergency support in the event of frequency instability due to faults in the receiving-end power grid, prevent low-frequency load shedding in the receiving-end power grid, and improve the stability of the receiving-end power grid.

[0005] In a first aspect, embodiments of the present invention provide a coordinated control method for an isolated renewable energy transmission system via a flexible DC transmission system, comprising: A network-based control mode is used to adjust the phase of the AC voltage output from the receiving-end flexible DC converter; wherein the phase of the AC voltage output from the receiving-end flexible DC converter is related to the DC voltage of the DC link. The AC voltage frequency output of the sending-end islanded flexible DC converter is adjusted using a voltage frequency slope control mode; wherein, the AC voltage frequency output of the sending-end islanded flexible DC converter is related to the DC voltage of the DC link. The active power output of the sending-end renewable energy unit is adjusted according to the DC voltage of the sending-end renewable energy unit; wherein the active power output of the sending-end renewable energy unit is related to the frequency of the islanded renewable energy grid.

[0006] As an improvement to the above scheme, the adjustment of the AC voltage phase output by the receiving-end flexible DC converter using a grid-type control mode includes: Detect the DC voltage of the receiving-end flexible DC converter and the frequency of the receiving-end AC grid; Calculate the first operating angular velocity of the receiving-end AC power grid based on the frequency of the receiving-end AC power grid; Calculate the first phase angle of the receiving-end flexible DC converter for Parker transformation based on the DC voltage of the receiving-end flexible DC converter and the first operating angular velocity of the receiving-end AC grid; Based on the first phase angle, Parker transformation is performed on the three-phase AC voltage of the receiving-end flexible DC converter to obtain the first AC voltage parameter and the first AC current parameter under the dq axis. The phase of the AC voltage output by the receiving-end flexible DC converter is adjusted according to the first AC voltage parameter and the first AC current parameter.

[0007] As an improvement to the above scheme, the step of calculating the first phase angle based on the DC voltage of the receiving-end flexible DC converter and the first operating angular velocity of the receiving-end AC grid includes: Calculate the first DC voltage squared deviation based on the DC voltage of the receiving-end AC grid and the first rated operating DC voltage; Calculate the first angular velocity deviation based on the first operating angular velocity and the first rated angular velocity of the receiving-end AC power grid; Based on the first DC voltage square deviation, the first angular velocity deviation, and the preset first damping coefficient, the second operating angular velocity of the receiving-end AC power grid is calculated through virtual inertia and integration. The first phase angle is calculated by integrating the second operating angular velocity.

[0008] As an improvement to the above scheme, adjusting the phase of the AC voltage output by the receiving-end flexible DC converter based on the first AC voltage parameter and the first AC current parameter includes: The first AC voltage adjustment is calculated based on the preset first d-axis AC voltage component setting value, the preset first reactive power setting value, and the reactive power of the receiving-end flexible DC converter. Calculate the first d-axis current component setting value based on the first AC voltage adjustment amount and the d-axis AC voltage component in the first AC voltage parameter. Based on the q-axis AC voltage component in the first AC voltage parameter and the preset first q-axis AC voltage component setting value, calculate the first q-axis AC current component setting value; The first desired voltage parameter is calculated based on the first q-axis AC current component setting value, the first d-axis current component setting value, the q-axis AC current component and d-axis AC current component in the first AC current parameter, and the q-axis AC voltage component and d-axis voltage component in the first AC voltage parameter. The phase of the AC voltage output by the receiving-end flexible DC converter is adjusted according to the first desired voltage parameter.

[0009] As an improvement to the above scheme, the method of adjusting the AC voltage frequency output of the sending-end islanded flexible DC converter using voltage frequency slope control includes: Detect the DC voltage of the sending-end islanded flexible DC converter; Calculate the second phase angle of the sender-end islanded flexible DC converter for Parker transformation based on the DC voltage of the sender-end islanded flexible DC converter; Based on the second phase angle, Parker transformation is performed on the three-phase AC voltage of the sending-end islanded flexible DC converter to obtain the second AC voltage parameter and the second AC current parameter under the dq axis. The frequency of the AC voltage output by the sending-end islanded flexible DC converter is adjusted according to the second AC voltage parameter and the second AC current parameter.

[0010] As an improvement to the above scheme, the step of calculating the second phase angle of the sending-end islanded flexible DC converter for Parker conversion based on the DC voltage of the sending-end islanded flexible DC converter includes: Calculate the second DC voltage squared deviation based on the DC voltage of the sending-end islanded flexible DC converter and the preset second rated operating DC voltage; The second phase angle of the sending-end islanded flexible DC converter for Parker conversion is calculated based on the second DC voltage squared deviation, the preset first proportional coefficient, and the preset second rated angular velocity.

[0011] As an improvement to the above scheme, adjusting the AC voltage frequency output by the sending-end islanded flexible DC converter based on the second AC voltage parameter and the second AC current parameter includes: The second AC voltage adjustment is calculated based on the preset second d-axis AC voltage component setting value, the preset second reactive power setting value, and the reactive power of the sending-end islanded flexible DC converter. Calculate the setting value of the second d-axis current component based on the second AC voltage adjustment amount and the d-axis AC voltage component in the second AC voltage parameter; Based on the q-axis AC voltage component in the second AC voltage parameter and the preset setting value of the second q-axis AC voltage component, calculate the setting value of the second q-axis AC current component; The second desired voltage parameter is calculated based on the second q-axis AC current component setting value, the second d-axis current component setting value, the q-axis AC current component and d-axis AC current component in the second AC current parameter, and the q-axis AC voltage component and d-axis voltage component in the second AC voltage parameter. The frequency of the AC voltage output by the sending-end islanded flexible DC converter is adjusted according to the second desired voltage parameter.

[0012] As an improvement to the above scheme, the step of adjusting the active power output of the sending-end renewable energy unit based on the DC voltage of the sending-end renewable energy unit includes: Detect the DC voltage of the sending-end renewable energy unit and the frequency of the isolated renewable energy grid; Calculate the third operating angular velocity of the isolated new energy power grid based on its frequency. Based on the DC voltage of the sending-end renewable energy unit and the third operating angular velocity of the islanded renewable energy grid, calculate the third phase angle of the sending-end renewable energy unit for Parker transformation; Based on the third phase angle, Parker transformation is performed on the three-phase AC voltage of the sending-end new energy unit to obtain the third AC voltage parameter and the third AC current parameter under the dq axis. The active power output of the sending-end new energy unit is adjusted according to the third AC voltage parameter and the third AC current parameter.

[0013] As an improvement to the above scheme, adjusting the active power output of the sending-end renewable energy unit based on the third AC voltage parameter and the third AC current parameter includes: The third d-axis current component setting value is calculated based on the preset third reactive power setting value and the reactive power of the sending-end new energy unit. Based on the q-axis AC voltage component in the third AC voltage parameter and the preset setting value of the third q-axis AC voltage component, calculate the setting value of the third q-axis AC current component; The third desired voltage parameter is calculated based on the third q-axis AC current component setting value, the third d-axis current component setting value, the q-axis AC current component and d-axis AC current component in the third AC current parameter, and the q-axis AC voltage component and d-axis voltage component in the third AC voltage parameter. The active power output of the sending-end new energy unit is adjusted according to the third expected voltage parameter.

[0014] Secondly, embodiments of the present invention provide a coordinated control system for an isolated renewable energy transmission system via a flexible DC transmission system, comprising: The receiving-end control module is used to adjust the phase of the AC voltage output by the receiving-end flexible DC converter using a network-type control mode; wherein the phase of the AC voltage output by the receiving-end flexible DC converter is related to the DC voltage of the DC link. The first sending-end control module is used to adjust the AC voltage frequency output of the sending-end islanded flexible DC converter using a voltage frequency slope control mode; wherein, the AC voltage frequency output of the sending-end islanded flexible DC converter is related to the DC voltage of the DC link. The second sending-end control module is used to adjust the active power output of the sending-end renewable energy unit according to the DC voltage of the sending-end renewable energy unit; wherein the active power output of the sending-end renewable energy unit is related to the frequency of the islanded renewable energy grid.

[0015] Compared to existing technologies, this invention provides a coordinated control method and system for an islanded renewable energy transmission system via flexible DC transmission. This method adjusts the phase of the AC voltage output from the receiving-end flexible DC converter using a grid-based control mode; wherein the phase of the AC voltage output from the receiving-end flexible DC converter is related to the DC voltage of the DC link; and adjusts the frequency of the AC voltage output from the sending-end islanded flexible DC converter using a voltage frequency slope control mode; wherein the frequency of the AC voltage output from the sending-end islanded flexible DC converter is related to the DC voltage of the DC link; and adjusts the frequency of the AC voltage output from the sending-end renewable energy unit based on the DC voltage of the sending-end renewable energy unit. The active power output of the sending-end renewable energy unit is adjusted by DC voltage; wherein the active power output of the sending-end renewable energy unit is related to the frequency of the isolated renewable energy grid; the embodiment of the present invention realizes the electrical quantity transmission of the active power demand of the receiving-end AC grid through DC voltage, thereby realizing the adjustment of the active power of the sending-end renewable energy unit, which can realize the short-term active power rapid active support demand of isolated renewable energy to the receiving-end grid through the flexible DC transmission system, thereby providing emergency support in the event of frequency instability due to faults in the receiving-end grid, preventing low-frequency load shedding in the receiving-end grid, and improving the stability of the receiving-end grid. Attached Figure Description

[0016] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a flowchart of a coordinated control method for an isolated renewable energy transmission system via a flexible DC transmission system, provided by an embodiment of the present invention. Figure 2 This is a schematic diagram of the grid-type control mode of the receiving-end flexible DC converter provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the voltage-frequency slope control mode of the sender-end islanded flexible DC converter provided in an embodiment of the present invention; Figure 4 This is a control schematic diagram of the sending-end new energy unit provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of the overall process of coordinated control of isolated new energy through a flexible DC transmission system provided in an embodiment of the present invention; Figure 6 This is a structural block diagram of a coordinated control system for an isolated new energy transmission system via flexible DC transmission, provided in an embodiment of the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] It is understood that the various numerical designations used in the embodiments of this invention are merely for descriptive convenience and are not intended to limit the scope of this application. The order of the process numbers does not imply the order of execution; the execution order of each process should be determined by its function and internal logic.

[0020] Please see Figure 1 , Figure 1 This is a flowchart illustrating a coordinated control method for isolated renewable energy transmitted via a flexible DC transmission system, as provided in an embodiment of the present invention. The coordinated control method for isolated renewable energy transmitted via a flexible DC transmission system specifically includes: S11: The phase of the AC voltage output by the receiving-end flexible DC converter is adjusted using a network-type control mode; wherein, the phase of the AC voltage output by the receiving-end flexible DC converter is related to the DC voltage of the DC link. S12: The AC voltage frequency output of the sending-end islanded flexible DC converter is adjusted using a voltage frequency slope control mode; wherein, the AC voltage frequency output of the sending-end islanded flexible DC converter is related to the DC voltage of the DC link. S13: Adjust the active power output of the sending-end renewable energy unit according to the DC voltage of the sending-end renewable energy unit; wherein the active power output of the sending-end renewable energy unit is related to the frequency of the islanded renewable energy grid.

[0021] It should be noted that the islanded renewable energy transmission system via flexible DC transmission includes sending-end renewable energy units, sending-end islanded flexible DC converter DC links, and receiving-end flexible DC converters. Sending-end renewable energy units can be sending-end renewable energy wind turbines, photovoltaic units, etc., used to provide AC power to form the islanded renewable energy grid. The sending-end islanded flexible DC converter is the converter connecting the islanded renewable energy grid and the DC link, used to rectify AC power into DC power, and is also responsible for stabilizing the voltage and frequency of the islanded renewable energy grid. The DC link, composed of DC cables or overhead lines, is responsible for transmitting the DC power output from the sending-end islanded flexible DC converter over long distances with low loss to the receiving-end flexible DC converter. The receiving-end flexible DC converter is the converter connecting the DC link and the receiving-end AC grid, used to invert DC power into AC power, and simultaneously adjust the output voltage and frequency to match the receiving-end AC grid. The receiving-end AC grid is the power consumer at the load center.

[0022] This invention employs a grid-type control mode (also known as active power control) for the receiving-end flexible DC converter, which has both DC voltage control capability and AC grid power support capability. The phase of the AC voltage output by the flexible DC converter is related to the DC voltage. For the sending-end islanded flexible DC converter, a voltage-frequency slope control mode (VF control mode) is used, where the frequency of the AC voltage output by the sending-end islanded flexible DC converter is related to the DC voltage. The active power output of the sending-end renewable energy units is adjusted based on the electrical quantity of the receiving-end AC grid's active power demand transmitted through the DC voltage. The active power output of the sending-end renewable energy wind turbines is related to the frequency of the islanded renewable energy grid. This enables the islanded renewable energy to quickly and actively support the receiving-end grid's short-term active power demand via the flexible DC transmission system. This allows for emergency support in the event of a fault in the receiving-end grid causing frequency instability, preventing low-frequency load shedding in the receiving-end grid and improving its stability.

[0023] In one optional embodiment, adjusting the phase of the AC voltage output from the receiving-end flexible DC converter using a grid-type control mode includes: Detect the DC voltage of the receiving-end flexible DC converter and the frequency of the receiving-end AC grid; Calculate the first operating angular velocity of the receiving-end AC power grid based on the frequency of the receiving-end AC power grid; Calculate the first phase angle of the receiving-end flexible DC converter for Parker transformation based on the DC voltage of the receiving-end flexible DC converter and the first operating angular velocity of the receiving-end AC grid; Based on the first phase angle, Parker transformation is performed on the three-phase AC voltage of the receiving-end flexible DC converter to obtain the first AC voltage parameter and the first AC current parameter under the dq axis. The phase of the AC voltage output by the receiving-end flexible DC converter is adjusted according to the first AC voltage parameter and the first AC current parameter.

[0024] Specifically, calculating the first phase angle based on the DC voltage of the receiving-end flexible DC converter and the first operating angular velocity of the receiving-end AC grid includes: Calculate the first DC voltage squared deviation based on the DC voltage of the receiving-end AC grid and the first rated operating DC voltage; Calculate the first angular velocity deviation based on the first operating angular velocity and the first rated angular velocity of the receiving-end AC power grid; Based on the first DC voltage square deviation, the first angular velocity deviation, and the preset first damping coefficient, the second operating angular velocity of the receiving-end AC power grid is calculated through virtual inertia and integration. The first phase angle is calculated by integrating the second operating angular velocity.

[0025] Specifically, adjusting the phase of the AC voltage output from the receiving-end flexible DC converter based on the first AC voltage parameter and the first AC current parameter includes: The first AC voltage adjustment is calculated based on the preset first d-axis AC voltage component setting value, the preset first reactive power setting value, and the reactive power of the receiving-end flexible DC converter. Calculate the first d-axis current component setting value based on the first AC voltage adjustment amount and the d-axis AC voltage component in the first AC voltage parameter. Based on the q-axis AC voltage component in the first AC voltage parameter and the preset first q-axis AC voltage component setting value, calculate the first q-axis AC current component setting value; The first desired voltage parameter is calculated based on the first q-axis AC current component setting value, the first d-axis current component setting value, the q-axis AC current component and d-axis AC current component in the first AC current parameter, and the q-axis AC voltage component and d-axis voltage component in the first AC voltage parameter. The phase of the AC voltage output by the receiving-end flexible DC converter is adjusted according to the first desired voltage parameter.

[0026] In this embodiment of the invention, the specific process for adjusting the phase of the AC voltage output by the receiving-end flexible DC converter is as follows: The first rated operating DC voltage of the receiving-end flexible DC converter is set as follows: The first rated angular velocity of the receiving-end AC power grid is .

[0027] The DC voltage of the receiving-end flexible DC converter is detected as follows: The frequency of the receiving-end AC power grid Among them, the first operating angular velocity of the receiving-end AC power grid can be obtained based on the conversion formula of frequency and angular velocity. .

[0028] The first rated operating DC voltage of the receiving-end flexible DC converter The square of the DC voltage is Subtracting the squares of the two values ​​yields the first square deviation of the DC voltage. .

[0029] Calculate the first rated angular velocity of the receiving-end AC power grid With the first running angular velocity The deviation is used to obtain the first angular velocity deviation. .

[0030] First angular velocity deviation After damping, the deviation from the square of the first DC voltage The sum is used as input to the virtual inertia component. After passing through the virtual inertia J and the integration stage, the second operating angular velocity of the receiving-end AC power grid is obtained. This second operating angular velocity is used to update the first operating angular velocity. Both represent the operating angular velocity of the receiving-end AC power grid; therefore, the second operating angular velocity can also be expressed as... The specific calculation process is as follows: (1); Where D is the first damping coefficient of the damping element, and s represents the Laplace operator of the integral element.

[0031] The angular velocity obtained after calculation using the above formula (1) After integration, the first phase angle of the receiving-end flexible DC converter for Parker transformation (i.e., abc-dq transformation) is obtained. .

[0032] The three-phase (a, b, and c phases) AC voltage of the converter transformer side of the receiving-end flexible DC converter will be... , , With three-phase alternating current , , After an abc-dq transformation, the first AC voltage parameter and the first AC current parameter along the dq axis are obtained. The first AC voltage parameter includes the q-axis AC voltage component. AC voltage component along the d-axis The first AC current parameter includes the q-axis AC current component. and d-axis AC current component The specific transformation formula is as follows: (2).

[0033] The first d-axis AC current component setting value of the AC voltage Set to 1 to increase the first reactive power setting value. The measured reactive power of the receiving-end flexible DC converter The deviation between the two values ​​is multiplied by the proportional coefficient K to obtain the first AC voltage adjustment amount, which serves as the overall command value for the AC voltage. This value is then compared with the measured d-axis AC voltage component. Subtraction, followed by PI (proportional balancing) control, yields the setpoint value for the first d-axis current component. .

[0034] The first q-axis AC current component setting value of the AC voltage Set to 0, corresponding to the measured q-axis AC voltage component. The first q-axis current component setting value is obtained after subtraction and PI control. .

[0035] Subsequently, based on the first d-axis current component tuning value obtained above... First q-axis current component setting value Combined with the measured q-axis AC current component and d-axis AC current component q-axis AC voltage component AC voltage component along the d-axis After PI control and cross decoupling ( L, where L represents inductance), and then through the dq-abc transformation (as shown in the above formula (2), the three-phase voltage is obtained. (i.e., the first desired voltage parameter), the receiving-end flexible DC converter adjusts the AC voltage to the three-phase voltage by controlling the switching of power electronic devices. The corresponding value enables adjustment of the output AC voltage phase, and the control process of the flexible DC converter is as follows: Figure 2 As shown.

[0036] In one optional embodiment, adjusting the AC voltage frequency output of the sending-end islanded flexible DC converter using a voltage frequency slope control mode includes: Detect the DC voltage of the sending-end islanded flexible DC converter; Calculate the second phase angle of the sender-end islanded flexible DC converter for Parker transformation based on the DC voltage of the sender-end islanded flexible DC converter; Based on the second phase angle, Parker transformation is performed on the three-phase AC voltage of the sending-end islanded flexible DC converter to obtain the second AC voltage parameter and the second AC current parameter under the dq axis. The frequency of the AC voltage output by the sending-end islanded flexible DC converter is adjusted according to the second AC voltage parameter and the second AC current parameter.

[0037] Specifically, the step of calculating the second phase angle of the sender-end islanded flexible DC converter for Parker conversion based on the DC voltage of the sender-end islanded flexible DC converter includes: Calculate the second DC voltage squared deviation based on the DC voltage of the sending-end islanded flexible DC converter and the preset second rated operating DC voltage; The second phase angle of the sending-end islanded flexible DC converter for Parker conversion is calculated based on the second DC voltage squared deviation, the preset first proportional coefficient, and the preset second rated angular velocity.

[0038] Specifically, adjusting the AC voltage frequency output by the sending-end islanded flexible DC converter based on the second AC voltage parameter and the second AC current parameter includes: The second AC voltage adjustment is calculated based on the preset second d-axis AC voltage component setting value, the preset second reactive power setting value, and the reactive power of the sending-end islanded flexible DC converter. Calculate the setting value of the second d-axis current component based on the second AC voltage adjustment amount and the d-axis AC voltage component in the second AC voltage parameter; Based on the q-axis AC voltage component in the second AC voltage parameter and the preset setting value of the second q-axis AC voltage component, calculate the setting value of the second q-axis AC current component; The second desired voltage parameter is calculated based on the second q-axis AC current component setting value, the second d-axis current component setting value, the q-axis AC current component and d-axis AC current component in the second AC current parameter, and the q-axis AC voltage component and d-axis voltage component in the second AC voltage parameter. The frequency of the AC voltage output by the sending-end islanded flexible DC converter is adjusted according to the second desired voltage parameter.

[0039] In this embodiment of the invention, the specific procedure for adjusting the AC voltage frequency of the sending-end islanded flexible DC converter is as follows: The second rated operating DC voltage of the sender-end islanded flexible DC converter is set to The second rated angular velocity of the isolated new energy power grid is Among them, the second rated angular velocity of the isolated new energy power grid is The first rated angular velocity of the AC power grid at the receiving end is match.

[0040] The DC voltage of the islanded flexible DC converter at the sending end is detected as follows: .

[0041] The second rated operating DC voltage of the islanded flexible DC converter at the sending end The square of the DC voltage is Subtracting the squares of the two values ​​yields the second square deviation of the DC voltage. After the proportional circuit, the second rated angular velocity is... Adding them together, we obtain the operating angular velocity of the isolated renewable energy grid. The specific calculation process is as follows: (3); Where K is the first damping coefficient of the proportional element.

[0042] The angular velocity obtained by the above formula (3) After integration, the second phase angle of the islanded flexible DC converter at the sending end is obtained for the Parker transformation (i.e., the abc-dq transformation). .

[0043] The three-phase (a, b, and c phases) AC voltage of the converter transformer side of the islanded flexible DC converter at the sending end will be... , , With three-phase alternating current , , After an abc-dq transformation, the second AC voltage parameter and the second AC current parameter in the dq axis are obtained. The second AC voltage parameter includes the q-axis AC voltage component. AC voltage component along the d-axis The second AC current parameter includes the q-axis AC current component. and d-axis AC current component The specific transformation formula can be found in formula (2) above, and will not be repeated here.

[0044] The setting value of the second d-axis AC current component of the AC voltage Set to 1 to increase the second reactive power setting value. The measured reactive power of the islanded flexible DC converter at the sending end The deviation between the two values ​​is multiplied by the proportional coefficient K to obtain the second AC voltage adjustment amount, which serves as the overall command value for the AC voltage. This value is then compared with the measured d-axis AC voltage component. Subtraction, followed by PI (proportional balancing) control, yields the setpoint value for the second d-axis current component. .

[0045] The setting value of the second q-axis AC current component of the AC voltage Set to 0, corresponding to the measured q-axis AC voltage component. The second q-axis current component setting value is obtained after subtraction and PI control. .

[0046] Subsequently, based on the above-obtained tuning values ​​for the second d-axis current component... Second q-axis current component setting value Combined with the measured q-axis AC current component and d-axis AC current component q-axis AC voltage component AC voltage component along the d-axis After PI control and cross decoupling, and then through dq-abc transformation (as shown in formula (2) above), the three-phase voltage is obtained. (i.e., the second desired voltage parameter), the sending-end islanded flexible DC converter adjusts the AC voltage to the three-phase voltage by controlling the switching of power electronic devices. The corresponding value enables adjustment of the output AC voltage frequency. The control process of the islanded flexible DC converter at the sending end is as follows: Figure 3 As shown.

[0047] In one optional embodiment, adjusting the active power output of the sending-end renewable energy unit based on its DC voltage includes: Detect the DC voltage of the sending-end renewable energy unit and the frequency of the isolated renewable energy grid; Calculate the third operating angular velocity of the isolated new energy power grid based on its frequency. Based on the DC voltage of the sending-end renewable energy unit and the third operating angular velocity of the islanded renewable energy grid, calculate the third phase angle of the sending-end renewable energy unit for Parker transformation; Based on the third phase angle, Parker transformation is performed on the three-phase AC voltage of the sending-end new energy unit to obtain the third AC voltage parameter and the third AC current parameter under the dq axis. The active power output of the sending-end new energy unit is adjusted according to the third AC voltage parameter and the third AC current parameter.

[0048] Specifically, adjusting the active power output of the sending-end renewable energy unit based on the third AC voltage parameter and the third AC current parameter includes: The third d-axis current component setting value is calculated based on the preset third reactive power setting value and the reactive power of the sending-end new energy unit. Based on the q-axis AC voltage component in the third AC voltage parameter and the preset setting value of the third q-axis AC voltage component, calculate the setting value of the third q-axis AC current component; The third desired voltage parameter is calculated based on the third q-axis AC current component setting value, the third d-axis current component setting value, the q-axis AC current component and d-axis AC current component in the third AC current parameter, and the q-axis AC voltage component and d-axis voltage component in the third AC voltage parameter. The active power output of the sending-end new energy unit is adjusted according to the third expected voltage parameter.

[0049] In this embodiment of the invention, the specific procedure for adjusting the AC voltage frequency of the sending-end renewable energy unit is as follows: The third rated operating DC voltage of the sending-end new energy unit is set as follows: .

[0050] The DC voltage of the sending-end new energy unit is detected as follows: Frequency of isolated renewable energy grid Among them, the third operating angular velocity of the isolated renewable energy grid can be obtained based on the conversion formula of frequency and angular velocity. .

[0051] The third rated operating DC voltage of the sending-end new energy unit The square of the DC voltage is Subtracting the squares of the first two values ​​yields the third DC voltage square deviation. .

[0052] Calculate the second rated angular velocity of the isolated renewable energy grid With the third angular velocity The deviation is used to obtain the third angular velocity deviation. .

[0053] Third angular velocity deviation After damping, the deviation from the square of the third DC voltage The sum is used as input to the virtual inertia part. After passing through the virtual inertia J and the integration stage, the fourth operating angular velocity of the isolated new energy grid is obtained. This fourth operating angular velocity is used to update the third operating angular velocity. Both represent the operating angular velocity of the receiving-end AC power grid; therefore, the fourth operating angular velocity can also be expressed as... The specific calculation process is as follows: (4); The angular velocity obtained after calculation using the above formula (4) After integration, the third phase angle of the sending-end renewable energy unit used for Parker transformation (i.e., abc-dq transformation) is obtained. .

[0054] The three-phase (a, b, and c phases) AC voltage of the converter transformer side of the sending-end new energy unit will be... , , With three-phase alternating current , , After the abc-dq transformation, the third AC voltage parameter and the third AC current parameter in the dq axis are obtained. The third AC voltage parameter includes the q-axis AC voltage component. AC voltage component along the d-axis The third AC current parameter includes the q-axis AC current component. and d-axis AC current component The specific transformation formula can be found in formula (2) above, and will not be repeated here.

[0055] Set the third reactive power setting value The measured reactive power of the sending-end renewable energy unit After subtraction, the setting value of the third d-axis current component is obtained through PI control. .

[0056] The setting value of the third q-axis AC current component of the AC voltage. Set to 0, corresponding to the measured q-axis AC voltage component. The third q-axis current component setting value is obtained after subtraction and PI control. .

[0057] Subsequently, based on the above-obtained tuning values ​​for the second d-axis current component... Second q-axis current component setting value Combined with the measured q-axis AC current component and d-axis AC current component q-axis AC voltage component AC voltage component along the d-axis After PI control and cross decoupling, and then through dq-abc transformation (as shown in formula (2) above), the three-phase voltage is obtained. (i.e., the third desired voltage parameter), the sending-end renewable energy unit adjusts the AC voltage to three-phase voltage by controlling the switching of power electronic devices. The corresponding values ​​are used to adjust the output active power. The control process of the sending-end new energy unit is as follows: Figure 4 As shown.

[0058] Based on the above-mentioned coordinated control method, in the scenario where the flexible DC voltage level is ±400kV, the sending-end islanded flexible DC converter is connected to a new energy wind farm (i.e., an islanded new energy grid), and the receiving-end flexible DC converter is connected to a receiving-end AC grid with a voltage level of 500kV.

[0059] The receiving-end flexible DC converter adopts a grid-type control mode, where the damping coefficient D is set to a specific value. Due to the power output of the isolated new energy wind farm at the sending end, the active power received by the receiving-end flexible DC converter is 0 MW.

[0060] Suppose that the frequency of the receiving-end AC grid drops from 50Hz to 48.5Hz due to a fault or other reasons. At this time, according to the grid-type control mode of the receiving-end flexible DC converter, its DC voltage U dc1 Upgraded to 820kV.

[0061] The sending-end flexible DC converter adopts an AC voltage frequency slope control mode, where the proportional coefficient K is selected. This is because the receiving-end flexible DC converter's DC voltage U... dc1 Upgraded to 820kV, based on the AC voltage frequency slope control mode, the DC voltage U of the sending-end islanded converter... dc2 The voltage will be gradually increased to 825kV, and the frequency of the new energy wind farm at the sending end will be reduced to 49Hz.

[0062] When the frequency of the sending-end new energy wind turbine and AC energy storage is detected to be low, the output active power is actively adjusted and increased from 10MW to 1000MW within 40ms.

[0063] The active power output of the receiving-end flexible DC converter to the receiving-end AC grid increases from 0MW to 1000MW, and the frequency of the receiving-end AC grid recovers to 49.8Hz, thus enabling the islanded new energy flexible DC transmission system to actively support the frequency of the receiving-end AC grid.

[0064] Similarly, in the scenario where the flexible DC voltage level is ±400kV, the sending-end islanded flexible DC converter is connected to a new energy wind farm (i.e., an islanded new energy grid), and the receiving-end flexible DC converter is connected to a receiving-end AC grid with a voltage level of 500kV.

[0065] The receiving-end flexible DC converter adopts a grid-type control method, where the damping coefficient D is set to a specific value. The receiving-end flexible DC converter receives 1000MW of active power.

[0066] Assuming the frequency of the receiving-end AC grid rises from 50Hz to 51.5Hz due to load shedding or other reasons, at this time, according to the DC voltage U of the receiving-end flexible DC converter in the grid-type control mode... dc1 It dropped to 790kV.

[0067] The sending-end islanded flexible DC converter adopts an AC voltage frequency slope control mode, where the proportional coefficient K is selected. Due to the DC voltage U of the receiving-end flexible DC converter... dc1 The voltage drops to 790kV. Based on the AC voltage frequency slope control mode, the DC voltage U of the sending-end islanded flexible DC converter... dc2 The voltage will be gradually reduced to 792kV, and the frequency of new energy wind farms will be increased to 50.5Hz.

[0068] After detecting a decrease in frequency, the sending-end new energy wind turbines and AC energy storage actively adjust their output active power, reducing it from 1000MW to 200MW within 40ms.

[0069] The active power output of the receiving-end flexible DC converter to the receiving-end AC grid is reduced from 1000MW to 190MW, and the frequency of the receiving-end AC grid is restored to 50.1Hz, thus enabling the islanded new energy flexible DC transmission system to actively support the frequency of the receiving-end AC grid.

[0070] This invention supports the power supply to the receiving-end AC grid by increasing the DC voltage through grid configuration control of the receiving-end flexible DC converter when a decrease in the AC grid frequency is detected; decreasing the AC voltage frequency through VF control when the sending-end islanded flexible DC converter detects an increase in the DC voltage; and increasing the output power of the sending-end renewable energy units through grid configuration control when a decrease in the AC voltage frequency is detected. Conversely, if the receiving-end AC grid frequency increases abnormally, the power transmitted by the sending-end renewable energy units can be reduced through corresponding control measures to meet the power balance requirements of the receiving-end AC grid.

[0071] To more clearly illustrate the coordinated control process of the islanded new energy transmission system via flexible DC transmission according to the embodiments of the present invention, the following is in conjunction with... Figure 5 The overall coordination and control process of the system is described in detail below: Step a: Assume that the frequency of the receiving-end AC power grid drops due to a fault or other reason; Step b: After detecting a frequency drop, the receiving-end flexible DC converter based on the grid-type control mode automatically increases the active power injected into the receiving-end AC grid to support the frequency. Step c: Due to the increase in active power, the capacitor voltage of the receiving-end flexible DC converter decreases, resulting in a decrease in DC voltage; Step d: Subtract the square of the measured DC voltage value from the square of the command value (i.e., the corresponding rated operating DC voltage) calculated by the receiving-end flexible DC converter to obtain the square deviation of the DC voltage. If this value is less than 0, bidirectional regulation is triggered. Step e1: Based on the grid-type control mode, the output three-phase AC voltage angular velocity of the flexible DC converter at the receiving end decreases, and the output active power level decreases to coordinate the balance between active power and DC voltage. It should be noted that the control strategy for the receiving-end flexible DC converter based on the grid-type control mode can be found in the above description and... Figure 2 As shown, I will not repeat the details here; Step e2: The DC voltage of the islanded flexible DC converter at the sending end decreases synchronously; Step f: Since the DC voltage drop of the receiving-end flexible DC converter will be transmitted to the sending end through the DC link, the DC voltage of the sending-end islanded flexible DC converter will drop synchronously. After the DC voltage of the sending-end islanded flexible DC converter based on VF control mode drops, in order to maintain its own AC side power balance, the frequency of the output AC voltage will be reduced. It should be noted that the control strategy for the send-end islanded flexible DC converter based on VF control mode can be found in the above description and... Figure 3 As shown, I will not repeat the details here; Step g: After the frequency of the AC voltage output by the islanded flexible DC converter at the sending end decreases, the active power output of the new energy unit at the sending end increases based on the frequency-active power characteristics. Step h: The active power of the new energy generator at the sending end increases, which leads to a decrease in the DC voltage of its inverter; Step i: The rectifier side of the sending-end renewable energy unit detects a drop in DC voltage and controls the output active power to increase; it should be noted that the control strategy of the sending-end renewable energy unit can be found in the above description and... Figure 4 As shown, I will not repeat the details here; Step j: At this time, the active power received by the islanded flexible DC converter side at the sending end increases, and the overall DC voltage of the system increases; Step k: The active power output of the receiving-end flexible DC converter increases, and the system frequency returns to normal.

[0072] Compared to existing technologies, this invention uses DC voltage as the electrical medium to enable rapid sensing of frequency changes in the sending-end renewable energy grid when the receiving-end frequency of the isolated renewable energy system undergoes a flexible DC transmission. This eliminates the need for a communication system, allowing for rapid power generation to meet the rapid power support requirements of the receiving-end AC grid. Furthermore, this invention supports the receiving-end AC grid by increasing active power generation when the receiving-end AC grid frequency decreases. When the receiving-end AC grid frequency decreases, the DC voltage is increased, thus avoiding a significant increase in the IGBT device current of the flexible DC converter during power generation, thereby preventing system overload. In this invention, the sending-end isolated renewable energy station can achieve short-term rapid power support through the energy storage capacitors in the wind turbine itself. This invention has a wide range of applications and can be widely used in deep-sea wind power flexible DC transmission projects, large-scale renewable energy islands via UHV flexible DC transmission projects, and other scenarios.

[0073] Please see Figure 6 , Figure 6 This invention provides a structural block diagram of a coordinated control system for an isolated renewable energy source transmitted via a flexible DC transmission system. The coordinated control system includes: The receiving-end control module 11 is used to adjust the phase of the AC voltage output by the receiving-end flexible DC converter using a network-type control mode; wherein the phase of the AC voltage output by the receiving-end flexible DC converter is related to the DC voltage of the DC link. The first sending-end control module 12 is used to adjust the AC voltage frequency output of the sending-end islanded flexible DC converter using a voltage frequency slope control mode; wherein, the AC voltage frequency output of the sending-end islanded flexible DC converter is related to the DC voltage of the DC link. The second sending-end control module 13 is used to adjust the active power output of the sending-end renewable energy unit according to the DC voltage of the sending-end renewable energy unit; wherein the active power output of the sending-end renewable energy unit is related to the frequency of the islanded renewable energy grid.

[0074] In one optional embodiment, the receiving-end control module 11 includes: The first detection unit is used to detect the DC voltage of the receiving-end flexible DC converter and the frequency of the receiving-end AC grid. The first calculation unit is used to calculate the first operating angular velocity of the receiving-end AC power grid based on the frequency of the receiving-end AC power grid. The second calculation unit is used to calculate the first phase angle of the receiving-end flexible DC converter for Parker transformation based on the DC voltage of the receiving-end flexible DC converter and the first operating angular velocity of the receiving-end AC grid. The first transformation unit is used to perform Parker transformation on the three-phase AC voltage of the receiving-end flexible DC converter according to the first phase angle to obtain the first AC voltage parameter and the first AC current parameter under the dq axis. An AC voltage adjustment unit is used to adjust the phase of the AC voltage output by the receiving-end flexible DC converter according to the first AC voltage parameter and the first AC current parameter.

[0075] In one optional embodiment, the second computing unit includes: The first calculation subunit is used to calculate the first DC voltage square deviation based on the DC voltage of the receiving-end AC grid and the first rated operating DC voltage; The second calculation subunit is used to calculate the first angular velocity deviation based on the first operating angular velocity and the first rated angular velocity of the receiving-end AC power grid. The third calculation subunit is used to calculate the second operating angular velocity of the receiving-end AC power grid based on the first DC voltage square deviation, the first angular velocity deviation, and the preset first damping coefficient, through virtual inertia and integration. The fourth calculation subunit is used to calculate the first phase angle based on the second operating angular velocity through an integration process.

[0076] In one optional embodiment, the AC voltage regulation unit includes: The fifth calculation subunit is used to calculate the first AC voltage adjustment amount based on the preset first d-axis AC voltage component setting value, the preset first reactive power setting value, and the reactive power of the receiving-end flexible DC converter. The sixth calculation subunit is used to calculate the setting value of the first d-axis current component based on the first AC voltage adjustment amount and the d-axis AC voltage component in the first AC voltage parameter. The seventh calculation subunit is used to calculate the first q-axis AC current component setting value based on the q-axis AC voltage component in the first AC voltage parameter and the preset first q-axis AC voltage component setting value. The eighth calculation subunit is used to calculate the first desired voltage parameter based on the first q-axis AC current component setting value, the first d-axis current component setting value, the q-axis AC current component and the d-axis AC current component in the first AC current parameter, and the q-axis AC voltage component and the d-axis AC voltage component in the first AC voltage parameter. The first adjustment subunit is used to adjust the phase of the AC voltage output by the receiving-end flexible DC converter according to the first desired voltage parameter.

[0077] In one optional embodiment, the first sending end control module 12 includes: The second detection unit is used to detect the DC voltage of the sending-end islanded flexible DC converter. The third calculation unit is used to calculate the second phase angle of the sender-end islanded flexible DC converter for Parker transformation based on the DC voltage of the sender-end islanded flexible DC converter. The second conversion unit is used to perform Parker transformation on the three-phase AC voltage of the sending-end islanded flexible DC converter according to the second phase angle, so as to obtain the second AC voltage parameters and the second AC current parameters under the dq axis. An AC voltage frequency adjustment unit is used to adjust the AC voltage frequency output by the sending-end islanded flexible DC converter according to the second AC voltage parameter and the second AC current parameter.

[0078] In one optional embodiment, the third computing unit includes: The ninth calculation subunit is used to calculate the second DC voltage square deviation based on the DC voltage of the sending-end islanded flexible DC converter and the preset second rated operating DC voltage. The tenth calculation subunit is used to calculate the second phase angle of the sending-end islanded flexible DC converter for Parker conversion based on the second DC voltage square deviation, the preset first proportional coefficient, and the preset second rated angular velocity.

[0079] In one optional embodiment, the AC voltage frequency adjustment unit includes: The eleventh calculation subunit is used to calculate the second AC voltage adjustment amount based on the preset second d-axis AC voltage component setting value, the preset second reactive power setting value, and the reactive power of the sending-end islanded flexible DC converter; The twelfth calculation subunit is used to calculate the setting value of the second d-axis current component based on the second AC voltage adjustment amount and the d-axis AC voltage component in the second AC voltage parameter. The thirteenth calculation subunit is used to calculate the setting value of the second q-axis AC current component based on the q-axis AC voltage component in the second AC voltage parameter and the preset setting value of the second q-axis AC voltage component; The fourteenth calculation subunit is used to calculate the second desired voltage parameter based on the second q-axis AC current component setting value, the second d-axis current component setting value, the q-axis AC current component and d-axis AC current component in the second AC current parameter, and the q-axis AC voltage component and d-axis voltage component in the second AC voltage parameter; The second adjustment subunit is used to adjust the frequency of the AC voltage output by the sending-end islanded flexible DC converter according to the second desired voltage parameter.

[0080] In one optional embodiment, the second sending end control module 13 includes: The third detection module is used to detect the DC voltage of the sending-end new energy unit and the frequency of the islanded new energy grid. The fourth calculation unit is used to calculate the third operating angular velocity of the isolated new energy power grid based on the frequency of the isolated new energy power grid. The fifth calculation unit is used to calculate the third phase angle of the sending-end renewable energy unit for Parker transformation based on the DC voltage of the sending-end renewable energy unit and the third operating angular velocity of the islanded renewable energy grid. The third transformation unit is used to perform Parker transformation on the three-phase AC voltage of the sending-end new energy unit according to the third phase angle, so as to obtain the third AC voltage parameters and the third AC current parameters under the dq axis. The active power adjustment unit is used to adjust the active power output of the sending-end new energy unit according to the third AC voltage parameter and the third AC current parameter.

[0081] In one optional embodiment, the active power adjustment unit includes: The fifteenth calculation subunit is used to calculate the third d-axis current component setting value based on the preset third reactive power setting value and the reactive power of the sending-end new energy unit. The sixteenth calculation subunit is used to calculate the setting value of the third q-axis AC current component based on the q-axis AC voltage component in the third AC voltage parameter and the preset setting value of the third q-axis AC voltage component. The seventeenth calculation subunit is used to calculate the third desired voltage parameter based on the third q-axis AC current component setting value, the third d-axis current component setting value, the q-axis AC current component and d-axis AC current component in the third AC current parameter, and the q-axis AC voltage component and d-axis AC voltage component in the third AC voltage parameter; The third adjustment subunit is used to adjust the active power output of the sending-end new energy unit according to the third desired voltage parameter.

[0082] It should be noted that the working process of each module in the coordinated control system of the isolated new energy through the flexible DC transmission system described in the embodiments of the present invention can refer to the working process of the coordinated control method of the isolated new energy through the flexible DC transmission system described in the above embodiments, and the technical effect achieved is the same as that of the coordinated control method of the isolated new energy through the flexible DC transmission system described in the above embodiments, and will not be repeated here.

[0083] It should be noted that the system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Furthermore, in the accompanying drawings of the system embodiments provided by this invention, the connection relationships between modules indicate that they have communication connections, which can be specifically implemented as one or more communication buses or signal lines. Those skilled in the art can understand and implement this without any creative effort.

[0084] The above description represents the preferred embodiments of the present invention. It should be noted that, for those skilled in the art, various improvements and modifications can be made without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A coordinated control method for an isolated renewable energy transmission system via flexible DC transmission, characterized in that, include: A network-based control mode is used to adjust the phase of the AC voltage output from the receiving-end flexible DC converter; wherein the phase of the AC voltage output from the receiving-end flexible DC converter is related to the DC voltage of the DC link. The AC voltage frequency output of the sending-end islanded flexible DC converter is adjusted using a voltage frequency slope control mode; wherein, the AC voltage frequency output of the sending-end islanded flexible DC converter is related to the DC voltage of the DC link. The active power output of the sending-end renewable energy unit is adjusted according to the DC voltage of the sending-end renewable energy unit; wherein the active power output of the sending-end renewable energy unit is related to the frequency of the islanded renewable energy grid.

2. The coordinated control method for an isolated new energy transmission system via flexible DC transmission as described in claim 1, characterized in that, The method of adjusting the phase of the AC voltage output from the receiving-end flexible DC converter using a grid-type control mode includes: Detect the DC voltage of the receiving-end flexible DC converter and the frequency of the receiving-end AC grid; Calculate the first operating angular velocity of the receiving-end AC power grid based on the frequency of the receiving-end AC power grid; Calculate the first phase angle of the receiving-end flexible DC converter for Parker transformation based on the DC voltage of the receiving-end flexible DC converter and the first operating angular velocity of the receiving-end AC grid; Based on the first phase angle, Parker transformation is performed on the three-phase AC voltage of the receiving-end flexible DC converter to obtain the first AC voltage parameter and the first AC current parameter under the dq axis. The phase of the AC voltage output by the receiving-end flexible DC converter is adjusted according to the first AC voltage parameter and the first AC current parameter.

3. The coordinated control method for an isolated new energy transmission system via flexible DC transmission as described in claim 2, characterized in that, The step of calculating the first phase angle based on the DC voltage of the receiving-end flexible DC converter and the first operating angular velocity of the receiving-end AC grid includes: Calculate the first DC voltage squared deviation based on the DC voltage of the receiving-end AC grid and the first rated operating DC voltage; Calculate the first angular velocity deviation based on the first operating angular velocity and the first rated angular velocity of the receiving-end AC power grid; Based on the first DC voltage square deviation, the first angular velocity deviation, and the preset first damping coefficient, the second operating angular velocity of the receiving-end AC power grid is calculated through virtual inertia and integration. The first phase angle is calculated by integrating the second operating angular velocity.

4. The coordinated control method for an isolated new energy transmission system via flexible DC transmission as described in claim 2, characterized in that, The step of adjusting the phase of the AC voltage output by the receiving-end flexible DC converter according to the first AC voltage parameter and the first AC current parameter includes: The first AC voltage adjustment is calculated based on the preset first d-axis AC voltage component setting value, the preset first reactive power setting value, and the reactive power of the receiving-end flexible DC converter. Calculate the first d-axis current component setting value based on the first AC voltage adjustment amount and the d-axis AC voltage component in the first AC voltage parameter. Based on the q-axis AC voltage component in the first AC voltage parameter and the preset first q-axis AC voltage component setting value, calculate the first q-axis AC current component setting value; The first desired voltage parameter is calculated based on the first q-axis AC current component setting value, the first d-axis current component setting value, the q-axis AC current component and d-axis AC current component in the first AC current parameter, and the q-axis AC voltage component and d-axis voltage component in the first AC voltage parameter. The phase of the AC voltage output by the receiving-end flexible DC converter is adjusted according to the first desired voltage parameter.

5. The coordinated control method for an isolated new energy transmission system via flexible DC transmission as described in claim 1, characterized in that, The method of adjusting the AC voltage frequency output of the sending-end islanded flexible DC converter using voltage frequency slope control includes: Detect the DC voltage of the sending-end islanded flexible DC converter; Calculate the second phase angle of the sender-end islanded flexible DC converter for Parker transformation based on the DC voltage of the sender-end islanded flexible DC converter; Based on the second phase angle, Parker transformation is performed on the three-phase AC voltage of the sending-end islanded flexible DC converter to obtain the second AC voltage parameter and the second AC current parameter under the dq axis. The frequency of the AC voltage output by the sending-end islanded flexible DC converter is adjusted according to the second AC voltage parameter and the second AC current parameter.

6. The coordinated control method for an isolated new energy transmission system via flexible DC transmission as described in claim 5, characterized in that, The step of calculating the second phase angle of the sender-end islanded flexible DC converter for Parker conversion based on the DC voltage of the sender-end islanded flexible DC converter includes: Calculate the second DC voltage squared deviation based on the DC voltage of the sending-end islanded flexible DC converter and the preset second rated operating DC voltage; The second phase angle of the sending-end islanded flexible DC converter for Parker conversion is calculated based on the second DC voltage squared deviation, the preset first proportional coefficient, and the preset second rated angular velocity.

7. The coordinated control method for an isolated new energy transmission system via flexible DC transmission as described in claim 5, characterized in that, The step of adjusting the AC voltage frequency output by the sending-end islanded flexible DC converter according to the second AC voltage parameter and the second AC current parameter includes: The second AC voltage adjustment is calculated based on the preset second d-axis AC voltage component setting value, the preset second reactive power setting value, and the reactive power of the sending-end islanded flexible DC converter. Calculate the setting value of the second d-axis current component based on the second AC voltage adjustment amount and the d-axis AC voltage component in the second AC voltage parameter; Based on the q-axis AC voltage component in the second AC voltage parameter and the preset setting value of the second q-axis AC voltage component, calculate the setting value of the second q-axis AC current component; The second desired voltage parameter is calculated based on the second q-axis AC current component setting value, the second d-axis current component setting value, the q-axis AC current component and d-axis AC current component in the second AC current parameter, and the q-axis AC voltage component and d-axis voltage component in the second AC voltage parameter. The frequency of the AC voltage output by the sending-end islanded flexible DC converter is adjusted according to the second desired voltage parameter.

8. The coordinated control method for an isolated new energy transmission system via flexible DC transmission as described in claim 1, characterized in that, The adjustment of the active power output of the sending-end renewable energy unit based on the DC voltage of the sending-end renewable energy unit includes: Detect the DC voltage of the sending-end renewable energy unit and the frequency of the isolated renewable energy grid; Calculate the third operating angular velocity of the isolated new energy power grid based on its frequency. Based on the DC voltage of the sending-end renewable energy unit and the third operating angular velocity of the islanded renewable energy grid, calculate the third phase angle of the sending-end renewable energy unit for Parker transformation; Based on the third phase angle, Parker transformation is performed on the three-phase AC voltage of the sending-end new energy unit to obtain the third AC voltage parameter and the third AC current parameter under the dq axis. The active power output of the sending-end new energy unit is adjusted according to the third AC voltage parameter and the third AC current parameter.

9. The coordinated control method for an isolated new energy transmission system via flexible DC transmission as described in claim 8, characterized in that, The adjustment of the active power output of the sending-end renewable energy unit based on the third AC voltage parameter and the third AC current parameter includes: The third d-axis current component setting value is calculated based on the preset third reactive power setting value and the reactive power of the sending-end new energy unit. Based on the q-axis AC voltage component in the third AC voltage parameter and the preset setting value of the third q-axis AC voltage component, calculate the setting value of the third q-axis AC current component; The third desired voltage parameter is calculated based on the third q-axis AC current component setting value, the third d-axis current component setting value, the q-axis AC current component and d-axis AC current component in the third AC current parameter, and the q-axis AC voltage component and d-axis voltage component in the third AC voltage parameter. The active power output of the sending-end new energy unit is adjusted according to the third expected voltage parameter.

10. A coordinated control system for an isolated new energy transmission system via flexible DC transmission, characterized in that, include: The receiving-end control module is used to adjust the phase of the AC voltage output by the receiving-end flexible DC converter using a network-type control mode; wherein the phase of the AC voltage output by the receiving-end flexible DC converter is related to the DC voltage of the DC link. The first sending-end control module is used to adjust the AC voltage frequency output of the sending-end islanded flexible DC converter using a voltage frequency slope control mode; wherein, the AC voltage frequency output of the sending-end islanded flexible DC converter is related to the DC voltage of the DC link. The second sending-end control module is used to adjust the active power output of the sending-end renewable energy unit according to the DC voltage of the sending-end renewable energy unit; wherein the active power output of the sending-end renewable energy unit is related to the frequency of the islanded renewable energy grid.

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