Emergency droop control method and device suitable for flexible direct current interconnection system

Abstract

The invention relates to the technical field of power systems, and discloses an emergency droop control method and device suitable for a flexible direct current interconnection system, and the method comprises the steps: monitoring the bus voltage of the flexible direct current interconnection system in real time through a voltage monitor, and judging whether the bus voltage fluctuates severely; if the bus voltage fluctuates severely, it is judged that the flexible direct current interconnection system is in an abnormal working condition, an emergency control loop is adopted to replace a voltage droop control loop and a power control loop in a traditional droop control strategy, a power reference is directly input to a current control loop through the emergency control loop, and therefore the dynamic response speed of the flexible direct current interconnection system is increased. According to the method, the operation condition of the system is automatically judged through the voltage monitor, the control loop is changed in time after the abnormal working condition is detected, the emergency control loop is used for replacing the voltage droop control loop and the power control loop, the dynamic response speed of the control system is improved, and then the operation performance of the flexible direct current interconnection under the abnormal working condition is improved.

Description

Technical Field

[0001] This invention relates to the field of power system technology, and in particular to an emergency droop control method and device suitable for flexible DC interconnection systems. Background Technology

[0002] With the continuous growth of electricity demand, the power capacity and voltage level of flexible DC interconnection systems suitable for long-distance power transmission are constantly increasing. To meet power quality requirements, appropriate control strategies are needed to maintain the bus voltage and switching power of the flexible DC interconnection system within a reasonable range. As a commonly used control strategy, the droop control strategy allocates power between converter stations connected to the system in real time and regulates the system's DC bus voltage based on the droop characteristic curve. The droop control strategy does not require master and slave converter stations, nor does it rely on high-speed communication between converter stations. It has the advantages of high flexibility and stability and is widely used in flexible DC interconnection systems.

[0003] However, in actual power transmission and distribution processes, abnormal operating conditions such as large power fluctuations and abnormal shutdowns of converter stations occur frequently, generally manifesting as sudden changes in system bus voltage. For example... Figure 1 As shown, the droop control strategy is a three-loop control structure, consisting of a current control loop, a power control loop, and a voltage droop control loop from the inside out. This multi-loop coupling increases the difficulty of setting control parameters and reduces the system's dynamic response speed to some extent. Under abnormal operating conditions, flexible DC interconnect systems employing the droop control strategy are constrained by the complex multi-loop control structure, making it difficult to quickly stabilize the system voltage or power, which may lead to abnormal operation of the converter station and affect the normal operation of the system. Summary of the Invention

[0004] To address the issue of slow dynamic response speed in traditional droop control strategies when the system is under abnormal operating conditions, this invention proposes an emergency droop control method and device suitable for flexible DC interconnection systems. This method optimizes the control loop under emergency conditions, improves the dynamic response speed of the system, and enables the system to adjust voltage and power in a timely manner under abnormal operating conditions. This avoids voltage over-limits or power imbalances, ensuring stable operation of the flexible DC interconnection system and continuous delivery of high-quality power.

[0005] The technical solution adopted in this invention is as follows: An emergency droop control method applicable to flexible DC interconnection systems includes: The bus voltage of the flexible DC interconnection system is monitored in real time by a voltage monitor, and it is determined whether there are drastic fluctuations in the bus voltage. If there are severe fluctuations in the bus voltage, the flexible DC interconnection system is determined to be in an abnormal operating condition. An emergency control loop is used to replace the voltage droop control loop and power control loop in the traditional droop control strategy. The power reference is directly input to the current control loop through the emergency control loop, thereby improving the dynamic response speed of the flexible DC interconnection system.

[0006] Furthermore, the step of monitoring the bus voltage of the flexible DC interconnection system in real time using a voltage monitor and determining whether there are drastic fluctuations in the bus voltage includes: sampling the instantaneous value of the bus voltage of the flexible DC interconnection system in real time using a voltage monitor. U dc And calculate the average bus voltage over the latest minute. U dc_avg Compare the instantaneous values ​​of the bus voltage. U dc and average bus voltage U dc_avg To determine whether voltage fluctuations exceed a threshold.

[0007] Furthermore, if the voltage fluctuation does not exceed the threshold, it is determined that the bus voltage does not fluctuate drastically, the flexible DC interconnection system is operating under normal conditions, and a three-loop control structure with a traditional droop control strategy is adopted, in which the voltage droop control loop calculates and outputs the active power reference value. P droop Then, the power command is input to the current control loop through the power control loop.

[0008] Furthermore, the active power reference value P droop The calculation methods include: (1) in, K droop The set droop coefficient, U dc_ref This is the set reference value for the bus voltage.

[0009] Furthermore, if the voltage fluctuation exceeds the threshold, it is determined that there is a severe fluctuation in the bus voltage, and the flexible DC interconnection system is in an abnormal operating condition. The emergency power value is then calculated through the emergency control loop. P temp And directly input to the current control loop.

[0010] Furthermore, the emergency power value P temp The calculation methods include: (2) in, γ tempThe preset emergency compensation coefficient is determined based on the expected time for the bus voltage to return to normal and the power capacity of each converter station. P ref This is the set power reference value.

[0011] Furthermore, the current control loop is based on the active power reference value of the converter station. P ref_out and reactive power reference value Q ref The current reference value of the converter station in the dq coordinate system is calculated. The calculation method includes: (3) in, The median value. i sd_ref This is the reference value of the converter station current on the d-axis of the two-phase coordinate system. i sq_ref This is the reference value of the converter station current on the q-axis of the two-phase coordinate system; u sd This represents the actual AC voltage component of the converter station on the d-axis. u sq This represents the actual value component of the AC voltage of the converter station on the q-axis.

[0012] Furthermore, when the bus voltage of the flexible DC interconnect system returns to normal after adjustment by the emergency control loop from an abnormal operating condition, the emergency control loop is switched to the voltage droop control loop and power control loop in the droop control strategy. A buffer is then used to ensure that the power reference value output by the power control loop is within the specified range. P droop_ref During the buffer time T buffer The internal power gradually replaces the emergency power value. P temp This completes the flexible exit of the emergency control loop.

[0013] Furthermore, the power reference value output by the power control loop through the buffer circuit... P droop_ref During the buffer time T buffer The internal power gradually replaces the emergency power value. P temp ,include: (4) in, The power reference value is the one before the update.

[0014] An emergency droop control device for flexible DC interconnection systems includes a voltage monitor, an automatic control mode switching module, an emergency control loop, a voltage droop control loop, a power control loop, and a current control loop. The voltage monitor is configured to monitor the bus voltage of the flexible DC interconnection system in real time. The automatic control mode switching module is configured to determine whether there are drastic fluctuations in the bus voltage. If drastic fluctuations are found, the flexible DC interconnection system is determined to be in an abnormal operating condition. The emergency control loop is then used to replace the voltage droop control loop and the power control loop. The power reference is directly input to the current control loop through the emergency control loop, thereby improving the dynamic response speed of the flexible DC interconnection system.

[0015] The beneficial effects of this invention are as follows: 1. This invention focuses on flexible DC interconnection systems. It addresses the problem that the traditional complex three-loop control structure of droop control has a slow response speed and difficulty in timely suppressing voltage and power fluctuations when the system is under abnormal conditions. An emergency control loop is proposed to improve the dynamic response speed of the control system by simplifying the control loop, which greatly improves the stability and sensitivity of the system in dealing with abnormal conditions.

[0016] 2. Based on the characteristic of large voltage fluctuations in flexible DC interconnection systems under abnormal operating conditions, this invention introduces a voltage monitor to monitor in real time whether there are jumps in the system bus voltage, thereby determining the system's operating status, and selecting different control loops for normal and abnormal operating conditions.

[0017] 3. This invention enables the system to maintain the three-loop structure of the traditional droop control strategy under normal operating conditions through system condition judgment and control mode switching, so as to smoothly regulate the system voltage and power; under abnormal operating conditions, the control strategy will automatically switch to the emergency control loop, directly inputting the power reference to the current control loop, improving the system response speed, and ensuring that the system can cope with short-term large fluctuations caused by abnormal operating conditions.

[0018] 4. This invention incorporates a buffer loop, enabling the emergency control loop to exit flexibly and smoothly switch to the traditional droop control loop, effectively avoiding sudden power command changes and potential system oscillations during the switching process.

[0019] 5. This invention only changes the input power reference of the current control loop and does not modify other control parameters, so it will not have a significant impact on the stability of the control system. Attached Figure Description

[0020] Figure 1 This is a simplified structural diagram of the traditional droop control strategy for flexible DC interconnect systems.

[0021] Figure 2 This is a schematic diagram of an emergency droop control method applicable to a flexible DC interconnection system according to Embodiment 1 of the present invention. Detailed Implementation

[0022] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments are now described. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of the invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0023] Example 1 like Figure 2 As shown, this embodiment provides an emergency droop control method suitable for flexible DC interconnection systems, including: real-time monitoring of the bus voltage of the flexible DC interconnection system using a voltage monitor, and determining whether there are severe fluctuations in the bus voltage; if there are severe fluctuations in the bus voltage, the flexible DC interconnection system is determined to be in an abnormal operating condition, and an emergency control loop is used to replace the voltage droop control loop and power control loop in the traditional droop control strategy. The power reference is directly input to the current control loop through the emergency control loop, thereby improving the dynamic response speed of the flexible DC interconnection system.

[0024] Preferably, in this embodiment, the instantaneous value of the bus voltage of the flexible DC interconnection system is sampled in real time using a voltage monitor. U dc And calculate the average bus voltage over the latest minute. U dc_avg By comparing the instantaneous values ​​of the bus voltage U dc and average bus voltage U dc_avg This allows us to determine whether voltage fluctuations exceed a threshold.

[0025] More preferably, if the voltage fluctuation does not exceed a threshold (e.g., ±5%) U dc_avg If the bus voltage does not fluctuate drastically, the flexible DC interconnection system is operating under normal conditions. A three-loop control structure using a traditional droop control strategy is employed, where the voltage droop control loop calculates and outputs the active power reference value. P droop The power command is then input to the current control loop via the power control loop. If the voltage fluctuation exceeds the threshold, it is determined that there is a severe fluctuation in the bus voltage, and the flexible DC interconnection system is in an abnormal operating condition. The emergency power value is then calculated via the emergency control loop. P temp And directly input to the current control loop.

[0026] Specifically, active power reference value Pdroop The calculation methods include: (1) in, K droop The set droop coefficient, U dc_ref This is the set reference value for the bus voltage.

[0027] Specifically, emergency power value P temp The calculation methods include: (2) in, γ temp The preset emergency compensation coefficient is determined based on the expected time for the bus voltage to return to normal and the power capacity of each converter station. P ref This is the set power reference value.

[0028] In this embodiment, the current control loop is based on the active power reference value of the converter station. P ref_out and reactive power reference value Q ref The current reference value of the converter station in the dq coordinate system is calculated. The calculation method includes: (3) in, The median value. i sd_ref This is the reference value of the converter station current on the d-axis of the two-phase coordinate system. i sq_ref This is the reference value of the converter station current on the q-axis of the two-phase coordinate system; u sd This represents the actual AC voltage component of the converter station on the d-axis. u sq This represents the actual q-axis component of the AC voltage at the converter station. Furthermore, in... Figure 2 In this context, P represents the actual active power of the converter station; i sd These are the actual components of the converter station current on the d and q axes of the two-phase coordinate system. u differ_d This refers to the d-axis differential mode voltage output by the converter station. u differ_q This is the output q-axis differential mode voltage of the converter station.

[0029] It should be noted that once the DC bus voltage returns to normal after the system has been regulated by the emergency control loop from an abnormal operating condition, the emergency control loop will be withdrawn. When switching from the emergency control loop to the three-loop control structure with the droop control strategy, the power command input to the current control loop will change abruptly, which may disrupt system stability and cause sudden changes in DC bus voltage or converter station power.

[0030] Preferably, a buffer is added to avoid voltage or power fluctuations that may occur when the emergency control loop is withdrawn, as shown in Equation 4. Through the buffer, when the system switches from the emergency control loop back to the three-loop control structure, the power reference value output by the power control loop is... P droop_ref During the buffer time T buffer Gradually exit the emergency power reference value P temp This completes the flexible exit of the emergency control loop.

[0031] (4) Among them, buffer time T buffer It depends on the requirements of the actual control system; The power reference value is the one before the update.

[0032] In summary, this method automatically assesses the system's operating status using a voltage monitor and promptly modifies the control loop upon detecting abnormal conditions. It replaces the voltage droop control loop and power control loop with an emergency control loop, thereby improving the dynamic response speed of the control system and ultimately enhancing the performance of the flexible DC interconnect under abnormal conditions. Specifically, this method has the following characteristics: (1) This method utilizes the characteristics of sudden voltage changes in the system under abnormal operating conditions to introduce a voltage monitor, monitors the DC side voltage of the system in real time, and determines whether the system voltage jumps or exceeds the limit, thereby determining the system operating status.

[0033] (2) This method switches to the emergency control loop in abnormal operating conditions, skips the outer voltage droop control loop and power control loop, and retains only the innermost current control loop, which significantly improves the dynamic response speed of the system.

[0034] (3) This method simplifies the control structure when the system is in an abnormal operating condition, introduces an emergency control loop, and directly provides a power reference for the current control loop.

[0035] (4) After the emergency control adjustment is completed and the system voltage and power return to normal, this method sets up a buffer loop that gradually decays over time to achieve a flexible exit of the emergency control loop.

[0036] (5) This method maintains the three-loop control structure of traditional droop control under normal operating conditions, so that the system can operate stably without abnormal fluctuations.

[0037] Example 2 This embodiment is based on embodiment 1: This embodiment provides an emergency droop control device suitable for flexible DC interconnection systems, including a voltage monitor, an automatic control mode switching module, an emergency control loop, a voltage droop control loop, a power control loop, and a current control loop. The voltage monitor is configured to monitor the bus voltage of the flexible DC interconnection system in real time. The automatic control mode switching module is configured to determine whether there are drastic fluctuations in the bus voltage. If there are drastic fluctuations, the flexible DC interconnection system is determined to be in an abnormal operating condition. The emergency control loop is then used to replace the voltage droop control loop and the power control loop. The power reference is directly input to the current control loop through the emergency control loop, thereby improving the dynamic response speed of the flexible DC interconnection system.

[0038] Example 3 This embodiment is based on embodiment 1: This embodiment provides a computer device, including a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the emergency droop control method for flexible DC interconnect systems described in Embodiment 1. The computer program can be in the form of source code, object code, executable file, or some intermediate form.

[0039] Example 4 This embodiment is based on embodiment 1: This embodiment provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the emergency droop control method for flexible DC interconnect systems described in Embodiment 1. The computer program can be in the form of source code, object code, executable file, or some intermediate form. The storage medium includes any entity or device capable of carrying computer program code, a recording medium, a computer memory, a read-only memory (ROM), a random access memory (RAM), an electrical carrier signal, a telecommunication signal, and a software distribution medium. It should be noted that the content of the storage medium can be appropriately added to or subtracted according to the requirements of legislation and patent practice in a jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, the storage medium does not include electrical carrier signals and telecommunication signals.

[0040] The above description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the concept described herein through the above teachings or related technologies or knowledge. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

[0041] It should be noted that, for the sake of simplicity, the foregoing method embodiments are described as a series of actions. However, those skilled in the art should understand that this application is not limited to the described order of actions, as some steps may be performed in other orders or simultaneously according to this application. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and modules involved are not necessarily essential to this application.

Claims

1. An emergency droop control method applicable to flexible DC interconnection systems, characterized in that, include: The bus voltage of the flexible DC interconnection system is monitored in real time by a voltage monitor, and it is determined whether there are drastic fluctuations in the bus voltage. If there are severe fluctuations in the bus voltage, the flexible DC interconnection system is determined to be in an abnormal operating condition. An emergency control loop is used to replace the voltage droop control loop and power control loop in the traditional droop control strategy. The power reference is directly input to the current control loop through the emergency control loop, thereby improving the dynamic response speed of the flexible DC interconnection system.

2. The emergency droop control method for a flexible DC interconnection system according to claim 1, characterized in that, The step of monitoring the bus voltage of the flexible DC interconnection system in real time using a voltage monitor and determining whether there are drastic fluctuations in the bus voltage includes: sampling the instantaneous value of the bus voltage of the flexible DC interconnection system in real time using a voltage monitor. U dc And calculate the average bus voltage over the latest minute. U dc_avg Compare the instantaneous values ​​of the bus voltage. U dc and average bus voltage U dc_avg To determine whether voltage fluctuations exceed a threshold.

3. The emergency droop control method for a flexible DC interconnection system according to claim 2, characterized in that, If the voltage fluctuation does not exceed the threshold, it is determined that the bus voltage has no drastic fluctuation, and the flexible DC interconnection system is operating under normal conditions. It adopts a three-loop control structure with a traditional droop control strategy, in which the voltage droop control loop calculates and outputs the active power reference value. P droop Then, the power command is input to the current control loop through the power control loop.

4. The emergency droop control method for a flexible DC interconnection system according to claim 3, characterized in that, The active power reference value P droop The calculation methods include: (1) in, K droop The set droop coefficient, U dc_ref This is the set reference value for the bus voltage.

5. The emergency droop control method for a flexible DC interconnection system according to claim 2, characterized in that, If the voltage fluctuation exceeds the threshold, it is determined that there is a drastic fluctuation in the bus voltage, and the flexible DC interconnection system is in an abnormal operating condition. The emergency power value is calculated through the emergency control loop. P temp And directly input to the current control loop.

6. The emergency droop control method for a flexible DC interconnection system according to claim 5, characterized in that, The emergency power value P temp The calculation methods include: (2) in, γ temp The preset emergency compensation coefficient is determined based on the expected time for the bus voltage to return to normal and the power capacity of each converter station. P ref This is the set power reference value.

7. The emergency droop control method for a flexible DC interconnection system according to claim 1, characterized in that, The current control loop is based on the active power reference value of the converter station. P ref_out and reactive power reference value Q ref The current reference value of the converter station in the dq coordinate system is calculated. The calculation method includes: (3) in, The median value. i sd_ref This is the reference value of the converter station current on the d-axis of the two-phase coordinate system. i sq_ref This is the reference value of the converter station current on the q-axis of the two-phase coordinate system; u sd This represents the actual AC voltage component of the converter station on the d-axis. u sq This represents the actual value component of the AC voltage of the converter station on the q-axis.

8. The emergency droop control method for a flexible DC interconnection system according to claim 1, characterized in that, When the bus voltage of the flexible DC interconnect system returns to normal after adjustment by the emergency control loop from an abnormal operating condition, the emergency control loop is switched to the voltage droop control loop and power control loop in the droop control strategy. A buffer is then used to ensure that the power reference value output by the power control loop is within the specified range. P droop_ref During the buffer time T buffer The internal power gradually replaces the emergency power value. P temp This completes the flexible exit of the emergency control loop.

9. The emergency droop control method for a flexible DC interconnection system according to claim 8, characterized in that, The power reference value output by the power control loop is achieved through a buffer circuit. P droop_ref During the buffer time T buffer The internal power gradually replaces the emergency power value. P temp , include: (4) in, The power reference value is the one before the update.

10. An emergency droop control device suitable for flexible DC interconnection systems, characterized in that, The system includes a voltage monitor, an automatic control mode switching module, an emergency control loop, a voltage droop control loop, a power control loop, and a current control loop. The voltage monitor is configured to monitor the bus voltage of the flexible DC interconnection system in real time. The automatic control mode switching module is configured to determine whether there are drastic fluctuations in the bus voltage. If drastic fluctuations are found, the flexible DC interconnection system is determined to be in an abnormal operating condition. The emergency control loop is then used to replace the voltage droop control loop and the power control loop. The power reference is directly input to the current control loop through the emergency control loop, thereby improving the dynamic response speed of the flexible DC interconnection system.

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