A direct current voltage synchronous control method and related device

Abstract

This application discloses a DC voltage synchronization control method and related equipment, applied to the receiving-end converter station of a flexible DC transmission system. By acquiring the deviation between the measured and reference values ​​of the submodule capacitor energy, and combining this with a droop control coefficient to generate an angular frequency deviation, and simultaneously integrating real-time grid angular frequency adjustment, the receiving-end converter station is endowed with grid control capabilities, enhancing its adaptability to weak grids and its active voltage support capabilities. By setting a frequency dead-zone control loop, the reference angular frequency is dynamically corrected, avoiding deviations caused by a fixed reference frequency, stabilizing the DC voltage within the allowable range, and preventing voltage exceedances. Through the synergy of dead-zone control and droop control, without increasing the droop coefficient or introducing integral control, both inertia support capabilities and second-order response characteristics of the control loop are maintained, reducing parameter design complexity and balancing control performance with engineering practicality. This effectively improves the operational stability of the flexible DC transmission system, providing a guarantee for long-distance transmission of clean energy.

Description

Technical Field

[0001] This application relates to the field of flexible DC control technology, and more specifically, to a DC voltage synchronization control method and related equipment. Background Technology

[0002] In the construction of new power systems, flexible DC transmission systems have become the core carrier for feeding clean energy power from desert areas and deep-sea regions to load centers over long distances. A typical structure involves a sending-end flexible DC converter station connected to a receiving-end converter station via a long-distance overhead line. The sending-end converter station focuses on active and reactive power control, ensuring that the active power command of the flexible DC transmission system matches the output characteristics of the clean energy source. The receiving-end converter station bears the crucial responsibility of maintaining the DC voltage stability of the entire flexible DC transmission system while also controlling reactive power; its control performance directly determines the safe and stable operation of the entire transmission system.

[0003] In current engineering designs, receiving-end converter stations generally adopt a grid-following control mode. This mode has significant shortcomings, namely, it lacks inertia and active voltage support capabilities, and has poor adaptability to weak power grids. With the increasing electronic sophistication of the receiving-end power grid and the growing trend of power source hollowing out, flexible DC receiving-end converter stations urgently need grid-connection control capabilities to cope with complex changes in grid operating conditions. Furthermore, the allowable range of DC voltage variation in flexible DC transmission systems is limited. Under scenarios with large-scale grid frequency fluctuations, existing control methods are prone to causing DC-side voltage to exceed the allowable range.

[0004] In existing research, two main solutions are used to address this problem: one is to increase the droop coefficient, which can reduce voltage deviation caused by frequency changes, but will severely limit the inertia support capability of the grid control; the other is to introduce integral control into the droop control loop to form a proportional-integral control architecture to achieve zero-error regulation, but this will change the control loop from a second-order response to a third-order response, which will greatly increase the difficulty of control parameter design and make it difficult to meet the needs of practical engineering applications.

[0005] Therefore, a new DC voltage synchronization control method is urgently needed to overcome the shortcomings of existing technologies, achieve the goals of improving the adaptability of power grid frequency changes, avoiding DC voltage overshooting, and not affecting the inertia support capability, so as to ensure the safe and stable operation of flexible DC transmission systems. Summary of the Invention

[0006] This application provides a DC voltage synchronization control method and related equipment. By obtaining the energy deviation of the submodule capacitor and combining it with the droop control coefficient to generate the angular frequency deviation, and then using the frequency dead zone control link to dynamically correct the reference angular frequency, the synchronization angular frequency is generated by superposition and integrated to obtain the synchronization phase angle. This achieves the goal of improving the adaptability of the power grid frequency change, avoiding DC voltage over-limit, and not affecting the inertia support capability, thus ensuring the safe and stable operation of the flexible DC transmission system.

[0007] A DC voltage synchronization control method, applied to the receiving-end converter station of a flexible DC transmission system, includes:

[0008] The measured value of the capacitor energy of the receiving-end converter station submodule is obtained and compared with the preset reference value of the submodule capacitor energy to obtain the energy deviation.

[0009] Multiply the energy deviation by a preset droop control coefficient to generate the angular frequency deviation.

[0010] The phase information of the voltage at the grid connection point of the receiving-end converter station is obtained, and the real-time angular frequency of the power grid is obtained through phase-locked loop processing.

[0011] The real-time angular frequency is processed by a frequency dead-zone control circuit to obtain a reference angular frequency correction amount. The frequency dead-zone control circuit is used to compare the real-time angular frequency with a preset reference angular frequency. When the deviation between the two is within the preset dead-zone range, the original reference angular frequency is maintained. When the deviation between the two exceeds the dead-zone range, the real-time angular frequency is output as the corrected reference angular frequency.

[0012] The angular frequency deviation is superimposed with the reference angular frequency correction to generate a synchronous angular frequency;

[0013] Integrating the synchronization angular frequency generates a synchronization phase angle for converter valve control.

[0014] Optionally, the phase-locked loop is configured as a low-bandwidth phase-locked loop, with a control bandwidth lower than the grid rated frequency and set to below 5Hz, in order to suppress the impact of grid voltage transient disturbances on control stability when tracking grid frequency changes.

[0015] Optionally, the dead zone range of the frequency dead zone control loop is symmetrically set with the reference angular frequency as the center, and the range of the power grid frequency change corresponding to the dead zone width is ±0.1Hz to ±0.2Hz.

[0016] Optionally, after the step of multiplying the energy deviation by a preset droop control coefficient to generate the angular frequency deviation, the method further includes:

[0017] Multiply the energy deviation by a preset energy feedforward coefficient to generate a feedforward compensation angle.

[0018] The feedforward compensation angle is superimposed on the synchronization phase angle to improve the damping characteristics of the synchronization loop.

[0019] Optionally, the measured value of the capacitor energy of the submodule is calculated based on the measured value of the DC side voltage of the receiving-end converter station and the number of submodules put into operation.

[0020] Optionally, the frequency dead-time control circuit further includes:

[0021] In the initial stage of a disturbance in the power grid frequency, the real-time angular frequency is within the dead zone of the frequency dead zone control loop. The reference angular frequency correction is maintained at the original reference angular frequency, and the energy deviation is supported by the droop control coefficient.

[0022] After the disturbance continues and the grid frequency change exceeds the dead zone range, the reference angular frequency correction amount is switched to the real-time angular frequency to correct the synchronization angular frequency, reduce the energy deviation, and thus limit the DC voltage deviation to within the allowable range.

[0023] A DC voltage synchronization control device, comprising:

[0024] The energy deviation module is used to obtain the measured value of the capacitor energy of the submodule of the receiving-end converter station, and compare it with the preset reference value of the capacitor energy of the submodule to obtain the energy deviation amount.

[0025] The droop control module is used to multiply the energy deviation by a preset droop control coefficient to generate the angular frequency deviation.

[0026] The phase-locked loop control module is used to acquire the phase information of the voltage at the grid connection point of the receiving-end converter station and obtain the real-time angular frequency of the power grid through phase-locked loop processing.

[0027] The frequency dead zone control module is used to process the real-time angular frequency through the frequency dead zone control loop to obtain the reference angular frequency correction amount. The frequency dead zone control loop is used to compare the real-time angular frequency with the preset reference angular frequency. When the deviation between the two is within the preset dead zone range, the original reference angular frequency is maintained. When the deviation between the two exceeds the dead zone range, the real-time angular frequency is output as the corrected reference angular frequency.

[0028] The synchronous angular frequency module is used to superimpose the angular frequency deviation amount with the reference angular frequency correction amount to generate a synchronous angular frequency.

[0029] The synchronization phase angle module is used to integrate the synchronization angular frequency to generate a synchronization phase angle for converter valve control.

[0030] A DC voltage synchronous control device includes a memory and a processor;

[0031] The memory is used to store programs;

[0032] The processor is configured to execute the program to implement the various steps of the DC voltage synchronization control method as described in any of the preceding claims.

[0033] A readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the DC voltage synchronization control method as described in any of the preceding claims.

[0034] A computer program product includes a computer program that, when executed by a processor, performs the steps of the DC voltage synchronization control method as described in any of the preceding claims.

[0035] As can be seen from the above technical solutions, the DC voltage synchronization control method and related equipment provided in this application embodiment are applied to the receiving-end converter station of a flexible DC transmission system. Specifically, it includes: obtaining the measured value of the capacitor energy of the receiving-end converter station submodule and comparing it with a preset reference value to obtain the energy deviation; multiplying the energy deviation by a preset droop control coefficient to generate the angular frequency deviation; obtaining the grid connection point voltage phase information and processing it through a phase-locked loop to obtain the real-time angular frequency of the power grid; processing the real-time angular frequency through a frequency dead-zone control loop to obtain a reference angular frequency correction, wherein the loop maintains the original reference angular frequency when the deviation between the real-time angular frequency and the preset reference angular frequency is within the dead zone, and uses the real-time angular frequency as the corrected reference angular frequency when it exceeds the dead zone; superimposing the angular frequency deviation and the reference angular frequency correction to generate the synchronization angular frequency; and integrating the synchronization angular frequency to generate the synchronization phase angle required for converter valve control.

[0036] This application obtains the energy deviation by comparing the measured value of capacitor energy with the reference value, and generates the angular frequency deviation by combining it with a preset droop control coefficient. Simultaneously, it performs synchronous adjustment based on the real-time angular frequency of the power grid, endowing the receiving-end converter station with grid control capabilities and effectively improving its adaptability to weak power grids and its active voltage support capabilities. By setting a frequency dead-zone control loop, the deviation between the real-time angular frequency of the power grid and the preset reference angular frequency is dynamically judged and the reference angular frequency is corrected accordingly. This avoids the angular frequency deviation caused by a fixed reference frequency, ensuring that the DC voltage is stably controlled within the allowable range, effectively preventing DC voltage exceedances and ensuring DC side voltage stability. Through the coordinated operation of dead-zone control and droop control, there is no need to increase the droop coefficient or introduce integral control in the droop control loop. This ensures both the inertia support capability of the receiving-end converter station's grid control and maintains the second-order response characteristics of the control loop, significantly reducing the design difficulty of control parameters. It balances control performance with practical engineering application needs, significantly improving the overall operational stability and reliability of the flexible DC transmission system, and providing strong support for the long-distance and efficient transmission of clean energy. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0038] Figure 1 This is a flowchart of a DC voltage synchronization control method disclosed in an embodiment of this application;

[0039] Figure 2 This is a schematic diagram of a basic architecture for DC voltage synchronization control disclosed in an embodiment of this application;

[0040] Figure 3 This is a schematic diagram of a frequency dead-zone control curve disclosed in an embodiment of this application;

[0041] Figure 4 This is a schematic diagram of a DC voltage synchronization control device disclosed in an embodiment of this application;

[0042] Figure 5 This is a hardware structure block diagram of a DC voltage synchronization control device disclosed in an embodiment of this application. Detailed Implementation

[0043] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0044] The following section introduces the solution proposed in this application. The technical solution is as follows, and details are provided below.

[0045] The DC voltage synchronization control method disclosed in this application is applied to the receiving-end converter station of a flexible DC transmission system. It aims to solve the problem that the existing DC voltage synchronization control is prone to DC voltage exceeding the limit under large-scale changes in grid frequency, and improve the system's adaptability to grid frequency changes. The specific implementation process of each step is as follows, and each step works together to form a complete synchronization control closed loop, ensuring that the receiving-end converter station has grid construction control capability, inertia support capability, and voltage stability control capability.

[0046] Figure 1 This is a flowchart of a DC voltage synchronization control method disclosed in an embodiment of this application.

[0047] like Figure 1 As shown, this method, applied to the receiving-end converter station of a flexible DC transmission system, may include:

[0048] Step S1: Obtain the measured value of the capacitor energy of the receiving-end converter station submodule and compare it with the preset reference value of the submodule capacitor energy to obtain the energy deviation.

[0049] Specifically, the measured value of the submodule capacitor energy is not directly obtained through sensor acquisition, but is precisely calculated based on the measured value of the DC side voltage of the receiving-end converter station and the number of submodules in operation, using a preset formula. Combining the technical solution disclosed in this patent application, the measured value E of the submodule capacitor energy is calculated as E∝U²×N, where U is the measured value of the DC side voltage of the flexible DC transmission system, and N is the number of DC side submodules in operation. In practical applications, the instantaneous value of the DC side voltage can be collected in real time using voltage sensors installed on the DC side of the receiving-end converter station. Simultaneously, the number of currently operational submodules can be obtained in real time through the converter station control system. Substituting these two parameters into the above formula yields the accurate measured value of the submodule capacitor energy. The preset reference value E of the submodule capacitor energy is based on the flexible DC transmission system... Rated operating parameters (including rated DC voltage and rated power), DC voltage control targets (typically within ±10% of the allowable DC voltage variation range), and submodule rated capacitor parameters are determined through simulation calculations and engineering tests. Their core function is to provide an ideal reference state for the energy of the submodule capacitors, ensuring stable operation of the system under rated conditions and preventing overcharging or over-discharging of the submodule capacitors. The energy deviation ΔE is calculated as the difference between the measured value and the reference value. This difference calculation can accurately reflect the degree to which the energy of the submodule capacitors deviates from the ideal state, providing a precise basis for subsequent angular frequency adjustment. At the same time, this energy deviation can also serve as an indirect indicator of the DC voltage stability. When the deviation exceeds the preset threshold, it indicates that there is a risk of DC voltage instability, requiring adjustment through subsequent steps.

[0050] Step S2: Multiply the energy deviation by a preset droop control coefficient to generate the angular frequency deviation.

[0051] Specifically, the preset droop control coefficient K is one of the key parameters of the control method in this application. Its value needs to comprehensively consider the inertia support requirements of the flexible DC transmission system, the sensitivity of DC voltage regulation, and actual engineering operation experience. Usually, the value range needs to be determined through multiple sets of simulation tests to ensure that both the DC voltage can be quickly regulated and the system has sufficient inertia support capability. This avoids the coefficient being too large, which would limit the inertia support capability, or the coefficient being too small, which would cause the DC voltage regulation to lag and the response to be slow. The angular frequency deviation Δω is generated by multiplying the energy deviation and the droop control coefficient, i.e., Δω=ΔE×K. The core purpose of this operation is to convert the energy deviation into an angular frequency regulation signal that can be used for synchronous control, so as to realize the one-to-one correspondence between the energy deviation and the angular frequency regulation, so that the deviation of the submodule capacitor energy can be compensated by the angular frequency regulation, thereby realizing the stable control of DC voltage. At the same time, this angular frequency deviation is also the core regulation component for the subsequent generation of synchronous angular frequency, which directly affects the accuracy and response speed of synchronous control.

[0052] Step S3: Obtain the phase information of the voltage at the grid connection point of the receiving-end converter station, and obtain the real-time angular frequency of the power grid through phase-locked loop processing.

[0053] Specifically, the three-phase voltage signal at the grid connection point is first acquired in real time using a high-precision voltage transformer installed at the receiving-end converter station. The acquisition frequency must meet the control accuracy requirements, typically not lower than 1kHz. The acquired voltage signal contains grid harmonics, electromagnetic interference, and other noise, so it needs to be preprocessed, including filtering, amplitude normalization, and phase synchronization. Specifically, a second-order low-pass filter can be used to remove high-frequency noise, and amplitude normalization adjusts the voltage signal amplitude to a preset range to ensure the accuracy of subsequent phase extraction. The preprocessed voltage phase information is then input into a phase-locked loop (PLL) for further processing. The PLL is configured as a low-bandwidth PLL, with a control bandwidth lower than the grid's rated frequency and set below 5Hz to suppress the impact of grid voltage transients on control stability when tracking grid frequency changes. The core purpose of this bandwidth setting is to reduce the response speed of the phase-locked loop (PLL), weaken the impact of rapid PLL changes on the stability of the entire control architecture, effectively suppress the interference of transient voltage disturbances (such as voltage fluctuations, harmonic interference, three-phase imbalance, etc.) on control stability when tracking changes in grid frequency, and ensure that the real-time grid angular frequency output by the PLL is accurate, stable, and without significant fluctuations, providing a reliable and accurate basis for subsequent correction of the reference angular frequency. At the same time, the control logic of the PLL adopts proportional-integral (PI) control, and its PI parameters need to be matched with the PLL bandwidth to further improve the PLL's anti-interference capability and output stability.

[0054] like Figure 2 As shown, the basic architecture of DC voltage synchronization control includes the measured values ​​of the capacitor energy of the sub-modules. Reference value of energy of submodule capacitor The deviation, multiplied by the droop coefficient The angular frequency deviation is obtained, and the angular frequency deviation is superimposed on the angular frequency reference value. The phase angle is obtained by integration. .Will and The deviation, multiplied by This is directly superimposed on the phase angle element to improve the damping of the synchronization loop. Based on this, the frequency is optimized from a fixed 50Hz to a frequency feedforward with a dead-zone phase-locked loop, which can follow the grid frequency under large variations in grid frequency and reduce frequency difference. The q-axis component of the grid connection point voltage is then superimposed with the reference frequency through a proportional and integral controller. Angular frequency is obtained , The angular frequency is obtained through a frequency dead-time control circuit. .

[0055] Step S4: Process the real-time angular frequency through a frequency dead-zone control circuit to obtain a reference angular frequency correction amount. The frequency dead-zone control circuit is used to compare the real-time angular frequency with a preset reference angular frequency. When the deviation between the two is within the preset dead-zone range, the original reference angular frequency is maintained. When the deviation between the two exceeds the dead-zone range, the real-time angular frequency is output as the corrected reference angular frequency.

[0056] Specifically, the frequency dead-zone control loop compares the real-time angular frequency with a preset reference angular frequency. When the deviation is within the preset dead-zone range, the original reference angular frequency is maintained. When the deviation exceeds the dead-zone range, the real-time angular frequency is output as the corrected reference angular frequency. Specifically, the preset reference angular frequency ω corresponds to the rated angular frequency of the power grid, calculated using ω=2πf, where f is the reference frequency of the power grid, defaulting to 50Hz. This reference angular frequency is the fundamental reference for synchronization control. The core function of the frequency dead-zone control loop is to prevent frequent corrections of the reference angular frequency due to small fluctuations in the power grid frequency, thereby improving the stability of the entire control architecture. Its control logic is similar to... Figure 3 The frequency dead-zone control curves shown are consistent, meaning a dead-zone range symmetrical about the reference angular frequency is preset, and the corresponding grid frequency variation Δf is set within the range of ±0.1Hz to ±0.2Hz. For example... Figure 3 As shown, if exist( , Within the frequency dead zone, Values If it exceeds the frequency dead zone range, Values The frequency dead zone range is determined by combining the allowable fluctuation range of the power grid frequency, the accuracy of DC voltage control, and actual engineering needs. It avoids frequent adjustments caused by small frequency fluctuations while ensuring timely response to large fluctuations in the power grid frequency. In practice, the difference Δf = ff between the real-time angular frequency and the power grid frequency f and the reference frequency f is first calculated. If Δf is within the dead zone range of (-0.2Hz, 0.2Hz), or can be adjusted to ±0.1Hz as needed, it is considered a normal small fluctuation in the power grid, and the frequency dead zone control loop outputs the original reference angular frequency as a correction value. If Δf exceeds this dead zone range, it is considered a large fluctuation in the power grid frequency, and the real-time angular frequency is immediately output as the corrected reference angular frequency. This ensures that the reference angular frequency can track changes in the power grid frequency in a timely manner, providing a reference that closely matches the actual operating state of the power grid for the subsequent generation of the synchronization angular frequency.

[0057] Step S5: The angular frequency deviation is superimposed with the reference angular frequency correction to generate a synchronous angular frequency.

[0058] Specifically, the synchronization angular frequency is generated by superimposing the angular frequency deviation and the reference angular frequency correction. This superposition operation achieves coordinated control of submodule capacitor energy deviation adjustment and grid frequency change tracking. The angular frequency deviation obtained in step S2 is an adjustment signal reflecting the submodule capacitor energy deviation, used to compensate for the deviation and stabilize the DC voltage. The reference angular frequency correction obtained in step S4 is an adjustment signal reflecting the real-time frequency change of the grid, used to track grid frequency fluctuations and avoid angular frequency deviations caused by a fixed reference frequency. Through the superposition of these two, the synchronization angular frequency can respond to the submodule capacitor energy deviation to achieve stable DC voltage control, and also track grid frequency changes, improving the system's adaptability to grid frequency fluctuations and ensuring precise matching between the synchronization angular frequency and the grid operating state and the system's own state. Simultaneously, this superposition logic also achieves an improvement by replacing the fixed reference frequency with frequency feedforward using a dead-zone phase-locked loop, avoiding the DC voltage limit exceeding problem caused by a fixed reference frequency in existing technologies.

[0059] Step S6: Integrate the synchronization angular frequency to generate a synchronization phase angle for converter valve control.

[0060] Specifically, the synchronization angular frequency reflects the rate of change of the synchronization phase angle, and its integration logic is similar to... Figure 2 The control architecture shown is consistent, namely, integrating the synchronous angular frequency through an integral stage, with the integral formula θ=∫ωdt. This integration converts the change in angular frequency into the absolute value of the phase angle, ultimately yielding the synchronous phase angle required for converter valve control. The synchronous phase angle is the core control signal for converter valve turn-on and turn-off control; its accuracy directly determines the control effect of the converter valve and the stability of the DC voltage. In specific applications, the synchronous phase angle is used to control the turn-on and turn-off timing of the IGBT devices in the converter valve, ensuring that the switching action of the converter valve is precisely matched with the grid phase and the energy state of the submodule capacitors, thereby achieving synchronous and stable control of the DC voltage in the flexible DC transmission system. Simultaneously, this step can be combined with an energy deviation feedforward coefficient K, multiplying the energy deviation ΔE by K and directly adding it to the phase angle stage, further improving the damping of the synchronization loop and enhancing control stability. Furthermore, in the early stages of frequency disturbance, the frequency phase-locked loop feedforward with dead zone is ineffective. At this time, through integral control of this step, the energy release of the submodule capacitor is called to provide inertia support. In the later stages of frequency disturbance, the frequency phase-locked loop feedforward with dead zone follows the change of grid frequency to prevent excessive release of submodule capacitor. Within the dead zone range set in this application, the energy of the submodule capacitor can be called to provide support in a very short time, taking into account both inertia support and DC voltage stability, and ultimately improving the overall operational stability and reliability of the flexible DC transmission system.

[0061] As can be seen from the above technical solutions, the DC voltage synchronization control method and related equipment provided in this application embodiment are applied to the receiving-end converter station of a flexible DC transmission system. Specifically, it includes: obtaining the measured value of the capacitor energy of the receiving-end converter station submodule and comparing it with a preset reference value to obtain the energy deviation; multiplying the energy deviation by a preset droop control coefficient to generate the angular frequency deviation; obtaining the grid connection point voltage phase information and processing it through a phase-locked loop to obtain the real-time angular frequency of the power grid; processing the real-time angular frequency through a frequency dead-zone control loop to obtain a reference angular frequency correction, wherein the loop maintains the original reference angular frequency when the deviation between the real-time angular frequency and the preset reference angular frequency is within the dead zone, and uses the real-time angular frequency as the corrected reference angular frequency when it exceeds the dead zone; superimposing the angular frequency deviation and the reference angular frequency correction to generate the synchronization angular frequency; and integrating the synchronization angular frequency to generate the synchronization phase angle required for converter valve control.

[0062] This application obtains the energy deviation by comparing the measured value of capacitor energy with the reference value, and generates the angular frequency deviation by combining it with a preset droop control coefficient. Simultaneously, it performs synchronous adjustment based on the real-time angular frequency of the power grid, endowing the receiving-end converter station with grid control capabilities and effectively improving its adaptability to weak power grids and its active voltage support capabilities. By setting a frequency dead-zone control loop, the deviation between the real-time angular frequency of the power grid and the preset reference angular frequency is dynamically judged and the reference angular frequency is corrected accordingly. This avoids the angular frequency deviation caused by a fixed reference frequency, ensuring that the DC voltage is stably controlled within the allowable range, effectively preventing DC voltage exceedances and ensuring DC side voltage stability. Through the coordinated operation of dead-zone control and droop control, there is no need to increase the droop coefficient or introduce integral control in the droop control loop. This ensures both the inertia support capability of the receiving-end converter station's grid control and maintains the second-order response characteristics of the control loop, significantly reducing the design difficulty of control parameters. It balances control performance with practical engineering application needs, significantly improving the overall operational stability and reliability of the flexible DC transmission system, and providing strong support for the long-distance and efficient transmission of clean energy.

[0063] In some embodiments of this application, considering that the damping characteristics of the synchronization loop directly affect the stability, response speed and anti-interference capability of the entire flexible DC transmission system, if the damping of the synchronization loop is insufficient, oscillations are likely to occur when the grid frequency is disturbed or the energy of the submodule capacitor fluctuates, resulting in DC voltage regulation lag and control accuracy reduction. Therefore, this application can also set a feedforward compensation process.

[0064] Specifically, after multiplying the energy deviation by a preset droop control coefficient to generate the angular frequency deviation, the following two specific steps are also included:

[0065] ① Multiply the energy deviation by a preset energy feedforward coefficient to generate a feedforward compensation angle;

[0066] ② The feedforward compensation angle is superimposed on the synchronization phase angle to improve the damping characteristics of the synchronization loop.

[0067] Specifically, the preset energy feedforward coefficient is determined comprehensively based on the damping design requirements of the synchronization loop, the system response speed threshold, and the results of actual engineering simulation tests. Its value needs to be matched with the droop control coefficient to avoid excessive feedforward compensation leading to abnormal fluctuations in the synchronization phase angle, or insufficient compensation failing to achieve the expected damping improvement effect. Typically, multiple sets of comparative tests are needed to calibrate the optimal value range to ensure effective suppression of synchronization loop oscillations. The feedforward compensation angle is generated by directly multiplying the energy deviation by the energy feedforward coefficient. This compensation angle can respond in advance to changes in the energy deviation of the submodule capacitors, thus adjusting the synchronization phase angle. It provides an advance compensation signal, eliminating the need to wait for feedback adjustment from the synchronization loop and effectively shortening the adjustment lag time. After generating the synchronization phase angle for converter valve control, the feedforward compensation angle is superimposed on the synchronization phase angle to obtain the final control phase angle. This superposition operation can significantly improve the damping characteristics of the synchronization loop, suppress the oscillation phenomenon of the synchronization loop when the grid frequency is disturbed or the energy deviation fluctuates, accelerate the response speed of the synchronization loop, and further improve the stability and control accuracy of the entire control system. This ensures that the DC voltage can be quickly and smoothly stabilized within the allowable variation range, avoiding DC voltage fluctuations caused by synchronization loop oscillation.

[0068] Furthermore, the frequency dead-zone control stage may also include a specific process of dynamically adjusting the reference angular frequency correction amount according to different stages of power grid frequency disturbance, so as to achieve coordinated control of inertia support and DC voltage stability, specifically including the following two stages:

[0069] ① In the initial stage of a disturbance in the power grid frequency, the change in the power grid frequency is relatively small. The real-time angular frequency is located within the dead zone of the frequency dead zone control loop. The correction amount of the reference angular frequency remains unchanged. At this time, the energy deviation amount provides inertial support through the droop control coefficient. That is, through the release or absorption of energy by the submodule capacitor, it quickly responds to the initial disturbance of the power grid frequency, provides instantaneous inertial support for the power grid, alleviates the amplitude of the frequency disturbance, and avoids the frequency from deviating rapidly from the rated range.

[0070] ② When the disturbance continues and the power grid frequency changes beyond the dead zone, it indicates that the power grid frequency is fluctuating significantly. At this time, the reference angular frequency correction is switched to the real-time angular frequency to quickly correct the synchronization angular frequency. The correction of the synchronization angular frequency will further adjust the output of the submodule capacitor energy, thereby reducing the energy deviation and avoiding excessive release or absorption of submodule capacitor energy. This will strictly limit the DC voltage deviation within the allowable range of ±10%, achieving the dual control objectives of inertia support and DC voltage stability.

[0071] Specifically, the division between the initial and sustained phases of grid frequency disturbances is based on whether the deviation between the real-time angular frequency and the reference angular frequency exceeds the dead zone. The dead zone corresponds to a grid frequency change of ±0.1Hz to ±0.2Hz, ensuring priority is given to providing inertia support during the initial disturbance and timely switching to frequency tracking mode when the disturbance intensifies. In the initial stage of the disturbance, maintaining the original reference angular frequency avoids control fluctuations caused by frequent corrections of the reference angular frequency, ensuring the timeliness and stability of inertia support. After the disturbance continues and exceeds the dead zone, switching to the real-time angular frequency as the reference angular frequency correction allows the synchronous angular frequency to quickly track changes in grid frequency, reducing energy deviation and preventing DC voltage from exceeding the allowable range due to excessive energy deviation. This balances the grid inertia support requirements and DC voltage stability control requirements, further enhancing the system's adaptability to grid frequency disturbances.

[0072] The following describes a DC voltage synchronization control device provided in the embodiments of this application. The DC voltage synchronization control device described below and the DC voltage synchronization control method described above can be referred to and correspond to each other.

[0073] See Figure 4 , Figure 4 This is a schematic diagram of a DC voltage synchronization control device disclosed in an embodiment of this application.

[0074] like Figure 4 As shown, the DC voltage synchronization control device may include:

[0075] The energy deviation module 110 is used to obtain the measured value of the capacitor energy of the submodule of the receiving-end converter station, and compare it with the preset reference value of the capacitor energy of the submodule to obtain the energy deviation amount.

[0076] The droop control module 120 is used to multiply the energy deviation by a preset droop control coefficient to generate the angular frequency deviation.

[0077] The phase-locked loop control module 130 is used to acquire the phase information of the voltage at the grid connection point of the receiving-end converter station and obtain the real-time angular frequency of the power grid through phase-locked loop processing.

[0078] The frequency dead zone control module 140 is used to process the real-time angular frequency through the frequency dead zone control loop to obtain the reference angular frequency correction amount. The frequency dead zone control loop is used to compare the real-time angular frequency with the preset reference angular frequency. When the deviation between the two is within the preset dead zone range, the original reference angular frequency is maintained. When the deviation between the two exceeds the dead zone range, the real-time angular frequency is output as the corrected reference angular frequency.

[0079] The synchronous angular frequency module 150 is used to superimpose the angular frequency deviation amount with the reference angular frequency correction amount to generate a synchronous angular frequency.

[0080] The synchronization phase angle module 160 is used to integrate the synchronization angular frequency to generate a synchronization phase angle for converter valve control.

[0081] As can be seen from the above technical solutions, the DC voltage synchronization control method and related equipment provided in this application embodiment are applied to the receiving-end converter station of a flexible DC transmission system. Specifically, it includes: obtaining the measured value of the capacitor energy of the receiving-end converter station submodule and comparing it with a preset reference value to obtain the energy deviation; multiplying the energy deviation by a preset droop control coefficient to generate the angular frequency deviation; obtaining the grid connection point voltage phase information and processing it through a phase-locked loop to obtain the real-time angular frequency of the power grid; processing the real-time angular frequency through a frequency dead-zone control loop to obtain a reference angular frequency correction, wherein the loop maintains the original reference angular frequency when the deviation between the real-time angular frequency and the preset reference angular frequency is within the dead zone, and uses the real-time angular frequency as the corrected reference angular frequency when it exceeds the dead zone; superimposing the angular frequency deviation and the reference angular frequency correction to generate the synchronization angular frequency; and integrating the synchronization angular frequency to generate the synchronization phase angle required for converter valve control.

[0082] This application obtains the energy deviation by comparing the measured value of capacitor energy with the reference value, and generates the angular frequency deviation by combining it with a preset droop control coefficient. Simultaneously, it performs synchronous adjustment based on the real-time angular frequency of the power grid, endowing the receiving-end converter station with grid control capabilities and effectively improving its adaptability to weak power grids and its active voltage support capabilities. By setting a frequency dead-zone control loop, the deviation between the real-time angular frequency of the power grid and the preset reference angular frequency is dynamically judged and the reference angular frequency is corrected accordingly. This avoids the angular frequency deviation caused by a fixed reference frequency, ensuring that the DC voltage is stably controlled within the allowable range, effectively preventing DC voltage exceedances and ensuring DC side voltage stability. Through the coordinated operation of dead-zone control and droop control, there is no need to increase the droop coefficient or introduce integral control in the droop control loop. This ensures both the inertia support capability of the receiving-end converter station's grid control and maintains the second-order response characteristics of the control loop, significantly reducing the design difficulty of control parameters. It balances control performance with practical engineering application needs, significantly improving the overall operational stability and reliability of the flexible DC transmission system, and providing strong support for the long-distance and efficient transmission of clean energy.

[0083] Optionally, the phase-locked loop is configured as a low-bandwidth phase-locked loop, with a control bandwidth lower than the grid rated frequency and set to below 5Hz, in order to suppress the impact of grid voltage transient disturbances on control stability when tracking grid frequency changes.

[0084] Optionally, the dead zone range of the frequency dead zone control loop is symmetrically set with the reference angular frequency as the center, and the range of the power grid frequency change corresponding to the dead zone width is ±0.1Hz to ±0.2Hz.

[0085] Optionally, after the step of multiplying the energy deviation by a preset droop control coefficient to generate the angular frequency deviation, the method further includes:

[0086] Multiply the energy deviation by a preset energy feedforward coefficient to generate a feedforward compensation angle.

[0087] The feedforward compensation angle is superimposed on the synchronization phase angle to improve the damping characteristics of the synchronization loop.

[0088] Optionally, the measured value of the capacitor energy of the submodule is calculated based on the measured value of the DC side voltage of the receiving-end converter station and the number of submodules put into operation.

[0089] Optionally, the frequency dead-time control circuit further includes:

[0090] In the initial stage of a disturbance in the power grid frequency, the real-time angular frequency is within the dead zone of the frequency dead zone control loop. The reference angular frequency correction is maintained at the original reference angular frequency, and the energy deviation is supported by the droop control coefficient.

[0091] After the disturbance continues and the grid frequency change exceeds the dead zone range, the reference angular frequency correction amount is switched to the real-time angular frequency to correct the synchronization angular frequency, reduce the energy deviation, and thus limit the DC voltage deviation to within the allowable range.

[0092] The DC voltage synchronization control device provided in this application embodiment can be applied to DC voltage synchronization control equipment. Figure 5 The hardware structure block diagram of the DC voltage synchronization control device is shown. (Refer to...) Figure 5 The hardware structure of a DC voltage synchronization control device may include: at least one processor 1, at least one communication interface 2, at least one memory 3, and at least one communication bus 4;

[0093] In this embodiment of the application, the number of processor 1, communication interface 2, memory 3, and communication bus 4 is at least one, and processor 1, communication interface 2, and memory 3 communicate with each other through communication bus 4;

[0094] Processor 1 may be a central processing unit (CPU), an application-specific integrated circuit (ASIC), or one or more integrated circuits configured to implement embodiments of the present invention.

[0095] Memory 3 may include high-speed RAM, and may also include non-volatile memory, such as at least one disk storage device;

[0096] The memory stores a program, which the processor can call. The program is used for:

[0097] The measured value of the capacitor energy of the receiving-end converter station submodule is obtained and compared with the preset reference value of the submodule capacitor energy to obtain the energy deviation.

[0098] Multiply the energy deviation by a preset droop control coefficient to generate the angular frequency deviation.

[0099] The phase information of the voltage at the grid connection point of the receiving-end converter station is obtained, and the real-time angular frequency of the power grid is obtained through phase-locked loop processing.

[0100] The real-time angular frequency is processed by a frequency dead-zone control circuit to obtain a reference angular frequency correction amount. The frequency dead-zone control circuit is used to compare the real-time angular frequency with a preset reference angular frequency. When the deviation between the two is within the preset dead-zone range, the original reference angular frequency is maintained. When the deviation between the two exceeds the dead-zone range, the real-time angular frequency is output as the corrected reference angular frequency.

[0101] The angular frequency deviation is superimposed with the reference angular frequency correction to generate a synchronous angular frequency;

[0102] Integrating the synchronization angular frequency generates a synchronization phase angle for converter valve control.

[0103] Optionally, the refined and extended functions of the program can be referred to the above description.

[0104] This application embodiment also provides a readable storage medium that can store a program suitable for execution by a processor, the program being used for:

[0105] The measured value of the capacitor energy of the receiving-end converter station submodule is obtained and compared with the preset reference value of the submodule capacitor energy to obtain the energy deviation.

[0106] Multiply the energy deviation by a preset droop control coefficient to generate the angular frequency deviation.

[0107] The phase information of the voltage at the grid connection point of the receiving-end converter station is obtained, and the real-time angular frequency of the power grid is obtained through phase-locked loop processing.

[0108] The real-time angular frequency is processed by a frequency dead-zone control circuit to obtain a reference angular frequency correction amount. The frequency dead-zone control circuit is used to compare the real-time angular frequency with a preset reference angular frequency. When the deviation between the two is within the preset dead-zone range, the original reference angular frequency is maintained. When the deviation between the two exceeds the dead-zone range, the real-time angular frequency is output as the corrected reference angular frequency.

[0109] The angular frequency deviation is superimposed with the reference angular frequency correction to generate a synchronous angular frequency;

[0110] Integrating the synchronization angular frequency generates a synchronization phase angle for converter valve control.

[0111] Optionally, the refined and extended functions of the program can be referred to the above description.

[0112] This application also provides a computer program product, including a computer program, wherein the computer program is executed by a processor using the following method:

[0113] The measured value of the capacitor energy of the receiving-end converter station submodule is obtained and compared with the preset reference value of the submodule capacitor energy to obtain the energy deviation.

[0114] Multiply the energy deviation by a preset droop control coefficient to generate the angular frequency deviation.

[0115] The phase information of the voltage at the grid connection point of the receiving-end converter station is obtained, and the real-time angular frequency of the power grid is obtained through phase-locked loop processing.

[0116] The real-time angular frequency is processed by a frequency dead-zone control circuit to obtain a reference angular frequency correction amount. The frequency dead-zone control circuit is used to compare the real-time angular frequency with a preset reference angular frequency. When the deviation between the two is within the preset dead-zone range, the original reference angular frequency is maintained. When the deviation between the two exceeds the dead-zone range, the real-time angular frequency is output as the corrected reference angular frequency.

[0117] The angular frequency deviation is superimposed with the reference angular frequency correction to generate a synchronous angular frequency;

[0118] Integrating the synchronization angular frequency generates a synchronization phase angle for converter valve control.

[0119] Optionally, the refined and extended functions of the program can be referred to the above description.

[0120] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0121] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0122] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A DC voltage synchronization control method, characterized in that, Receiving-end converter stations used in flexible DC transmission systems include: The measured value of the capacitor energy of the receiving-end converter station submodule is obtained and compared with the preset reference value of the submodule capacitor energy to obtain the energy deviation. Multiply the energy deviation by a preset droop control coefficient to generate the angular frequency deviation. The phase information of the voltage at the grid connection point of the receiving-end converter station is obtained, and the real-time angular frequency of the power grid is obtained through phase-locked loop processing. The real-time angular frequency is processed by a frequency dead-zone control circuit to obtain a reference angular frequency correction amount. The frequency dead-zone control circuit is used to compare the real-time angular frequency with a preset reference angular frequency. When the deviation between the two is within the preset dead-zone range, the original reference angular frequency is maintained. When the deviation between the two exceeds the dead-zone range, the real-time angular frequency is output as the corrected reference angular frequency. The angular frequency deviation is superimposed with the reference angular frequency correction to generate a synchronous angular frequency; Integrating the synchronization angular frequency generates a synchronization phase angle for converter valve control.

2. The method according to claim 1, characterized in that, The phase-locked loop is configured as a low-bandwidth phase-locked loop, with a control bandwidth lower than the grid rated frequency and set below 5Hz, in order to suppress the impact of grid voltage transient disturbances on control stability when tracking grid frequency changes.

3. The method according to claim 1, characterized in that, The dead zone range of the frequency dead zone control loop is symmetrically set with the reference angular frequency as the center, and the range of the power grid frequency change corresponding to the dead zone width is ±0.1Hz to ±0.2Hz.

4. The method according to claim 1, characterized in that, After the step of multiplying the energy deviation by a preset droop control coefficient to generate the angular frequency deviation, the method further includes: Multiply the energy deviation by a preset energy feedforward coefficient to generate a feedforward compensation angle. The feedforward compensation angle is superimposed on the synchronization phase angle to improve the damping characteristics of the synchronization loop.

5. The method according to claim 1, characterized in that, The measured value of the capacitor energy of the submodule is calculated based on the measured value of the DC side voltage of the receiving-end converter station and the number of submodules put into operation.

6. The method according to claim 1, characterized in that, The frequency dead-time control circuit also includes: In the initial stage of a disturbance in the power grid frequency, the real-time angular frequency is within the dead zone of the frequency dead zone control loop. The reference angular frequency correction is maintained at the original reference angular frequency, and the energy deviation is supported by the droop control coefficient. After the disturbance continues and the grid frequency change exceeds the dead zone range, the reference angular frequency correction amount is switched to the real-time angular frequency to correct the synchronization angular frequency, reduce the energy deviation, and thus limit the DC voltage deviation to within the allowable range.

7. A DC voltage synchronization control device, characterized in that, include: The energy deviation module is used to obtain the measured value of the capacitor energy of the submodule of the receiving-end converter station, and compare it with the preset reference value of the capacitor energy of the submodule to obtain the energy deviation amount. The droop control module is used to multiply the energy deviation by a preset droop control coefficient to generate the angular frequency deviation. The phase-locked loop control module is used to acquire the phase information of the voltage at the grid connection point of the receiving-end converter station and obtain the real-time angular frequency of the power grid through phase-locked loop processing. The frequency dead zone control module is used to process the real-time angular frequency through the frequency dead zone control loop to obtain the reference angular frequency correction amount. The frequency dead zone control loop is used to compare the real-time angular frequency with the preset reference angular frequency. When the deviation between the two is within the preset dead zone range, the original reference angular frequency is maintained. When the deviation between the two exceeds the dead zone range, the real-time angular frequency is output as the corrected reference angular frequency. The synchronous angular frequency module is used to superimpose the angular frequency deviation amount with the reference angular frequency correction amount to generate a synchronous angular frequency. The synchronization phase angle module is used to integrate the synchronization angular frequency to generate a synchronization phase angle for converter valve control.

8. A DC voltage synchronization control device, characterized in that, Including memory and processor; The memory is used to store programs; The processor is used to execute the program to implement the various steps of the DC voltage synchronization control method as described in any one of claims 1-6.

9. A readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements each step of the DC voltage synchronization control method as described in any one of claims 1-6.

10. A computer program product, comprising a computer program, characterized in that, When the computer program is run by the processor, it executes the steps of the DC voltage synchronization control method as described in any one of claims 1-6.

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