Low-frequency oscillation flexible DC converter control method and device

Abstract

The invention provides a low-frequency oscillation flexible DC converter control method and device, and the method is applied to a synchronous generator, and comprises the steps: taking a q-axis voltage controlled by a current inner loop of a flexible DC MMC as output feedback, and connecting the q-axis voltage with a high-pass filter module; connecting the high-pass filter module with a proportionality coefficient module; and adding the output of the proportionality coefficient module to the voltage feedforward of the d-axis voltage so as to suppress the low-frequency oscillation of the synchronous generator. According to the scheme, the technical problem that the cost is too high due to the fact that an existing additional oscillation suppression device is used for suppressing the low-frequency oscillation of the synchronous generator is solved, and the technical effect that the low-frequency oscillation of the synchronous generator is effectively suppressed while the cost is not increased additionally is achieved.

Description

Technical Field

[0001] This application belongs to the technical field of power system security and stability control, and particularly relates to a control method and device for a flexible direct current (DC) converter for low-frequency oscillation. Background Art

[0002] The problem of low-frequency oscillation in the power grid dominated by synchronous generators is an important security and stability risk faced by the power system. At present, the problem of low-frequency oscillation of synchronous generators is mainly solved by adding a power system stabilizer (PSS) to the excitation control. In addition, for the problem of low-frequency oscillation of synchronous generators involving new energy, currently, it is generally solved by adding devices such as static var compensators and energy storage, or by changing the control characteristics of new energy generating units to improve the damping of the low-frequency oscillation of the system. However, although adding additional oscillation suppression devices can effectively suppress the low-frequency oscillation of synchronous generators, this method will increase the implementation cost and has poor economy. In addition, due to the large number of new energy units, if the damping of low-frequency oscillation is improved by changing the control characteristics of new energy units, the implementation cost is too high.

[0003] It can be seen that although adding additional oscillation suppression devices can effectively suppress the low-frequency oscillation of synchronous generators, it will additionally increase the cost. Regarding how to effectively suppress the low-frequency oscillation of synchronous generators without additional cost, no effective solution has been proposed yet. Summary of the Invention

[0004] The purpose of this application is to provide a control method and device for a flexible DC converter for low-frequency oscillation, which can effectively suppress the low-frequency oscillation of synchronous generators without additional cost.

[0005] The control method and device for a flexible DC converter for low-frequency oscillation provided by this application are implemented as follows:

[0006] A control method for a flexible DC converter for low-frequency oscillation, which is applied to a synchronous generator, and the method includes:

[0007] Connect the q-axis voltage of the flexible modular multilevel converter (MMC) current inner loop control as the output feedback to a high-pass filter module;

[0008] Connect the high-pass filter module to a proportional coefficient module;

[0009] Add the output of the proportional coefficient module to the voltage feedforward of the d-axis voltage to suppress the low-frequency oscillation of the synchronous generator.

[0010] In one embodiment, before connecting the high-pass filter module to the proportional coefficient module, it further includes:

[0011] Obtain the low-frequency oscillation frequency of the power grid dominated by the synchronous generator;

[0012] Use the low-frequency oscillation frequency as the cut-off frequency of the high-pass filter module;

[0013] Set the high-pass filter module with the determined cut-off frequency.

[0014] In one embodiment, before connecting the high-pass filter module to the proportional coefficient module, it further includes:

[0015] Obtain the rated output power and the maximum amplitude of the oscillation power of the synchronous generator;

[0016] Determine the proportional coefficient of the proportional coefficient module according to the rated output power and the maximum amplitude of the oscillation power of the synchronous generator;

[0017] Set the proportional coefficient module with the determined proportional coefficient.

[0018] In one embodiment, determine the proportional coefficient of the proportional coefficient module according to the following formula:

[0019]

[0020] where, P N represents the rated output power of the synchronous generator, P LO represents the maximum amplitude of the oscillation power of the synchronous generator.

[0021] In one embodiment, determine the d-axis voltage feedforward of the current inner loop according to the following formula:

[0022]

[0023] where, u md represents the modulation voltage of the current inner loop, u sd represents the d-axis voltage feedforward of the current inner loop, I Gdref represents the d-axis current reference value of the current inner loop, i d represents the d-axis current of the current inner loop, K p represents the proportional coefficient of the current inner loop, K i represents the integral coefficient of the current inner loop, s represents the Laplace operator, u sq represents the q-axis voltage feedforward of the current inner loop, K v represents the proportional coefficient of the proportional coefficient module, f v represents the cut-off frequency of the high-pass filter module.

[0024] In one embodiment, the flexible DC MMC adopts a constant DC voltage outer loop control and a current inner loop control, and realizes synchronization with the power grid dominated by the synchronous generator through a phase-locked loop.

[0025] In one embodiment, adding the output of the proportional coefficient module to the voltage feed-forward of the d-axis voltage to suppress the low-frequency oscillation of the synchronous generator includes:

[0026] Determine whether the synchronous generator has a low-frequency oscillation within a preset frequency range;

[0027] When it is determined that the synchronous generator has a low-frequency oscillation within a preset frequency range, add the output of the proportional coefficient module to the voltage feed-forward of the d-axis voltage to suppress the low-frequency oscillation of the synchronous generator.

[0028] A control device for a flexible DC converter with low-frequency oscillation, which is applied in a synchronous generator, includes:

[0029] A feedback unit for connecting the q-axis voltage of the current inner loop control of the flexible DC MMC as an output feedback to a high-pass filter module;

[0030] A connection unit for connecting the high-pass filter module to a proportional coefficient module;

[0031] An addition unit for adding the output of the proportional coefficient module to the voltage feed-forward of the d-axis voltage to suppress the low-frequency oscillation of the synchronous generator.

[0032] An electronic device includes a processor and a memory for storing processor-executable instructions, and when the processor executes the instructions, the steps of the above method are implemented.

[0033] A computer-readable storage medium stores a computer program / instructions, and when the computer program / instructions are executed by a processor, the steps of the above method are implemented.

[0034] The control method for the flexible DC converter with low-frequency oscillation provided by this application is applied in a synchronous generator. First, connect the q-axis voltage of the current inner loop control of the flexible DC MMC as an output feedback to a high-pass filter module; then, connect the high-pass filter module to a proportional coefficient module; and then add the output of the proportional coefficient module to the voltage feed-forward of the d-axis voltage to suppress the low-frequency oscillation of the synchronous generator. Through the above solution, the technical problem of high cost caused by using an additional oscillation suppression device to suppress the low-frequency oscillation of the synchronous generator is solved, and the technical effect of effectively suppressing the low-frequency oscillation of the synchronous generator without additional cost is achieved. Description of the Drawings

[0035] To more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments recorded in the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0036] Figure 1 is a flowchart of a method for a flexible DC converter control method for low-frequency oscillation provided by the present application;

[0037] Figure 2 is a schematic diagram of the flexible DC MMC control structure provided by the present application;

[0038] Figure 3 is a schematic diagram of the low-frequency oscillation waveform of power when the output of the synchronous generator provided by the present application is 0.9 p.u.;

[0039] Figure 4 is a schematic diagram of the low-frequency oscillation waveform at the synchronous generator port when the output of the synchronous generator provided by the present application is 0.9 p.u. and the flexible DC is connected, but no oscillation suppression measures are adopted for the flexible DC MMC;

[0040] Figure 5 is a schematic diagram of the power waveform at the synchronous generator port when the output of the synchronous generator provided by the present application is 0.9 p.u. and the flexible DC adopts the oscillation suppression measures of this example;

[0041] Figure 6 is a hardware structure block diagram of an electronic device for a flexible DC converter control method for low-frequency oscillation provided by the present application;

[0042] Figure 7 is a schematic diagram of the module structure of an embodiment of a flexible DC converter control device for low-frequency oscillation provided by the present application. Detailed implementation manners

[0043] In order to enable those skilled in the art to better understand the technical solutions in the present application, the following will clearly and completely describe the technical solutions in the embodiments of the present application in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0044] In this example, a flexible DC MMC (Modular Multilevel Converter) is used to suppress its low-frequency oscillation. Specifically, in the current inner loop of the flexible DC MMC, the q-axis voltage of the control is connected to a high-pass filter and the proportional coefficient is used as the output, which is added to the voltage feedforward of the d-axis voltage, so as to effectively suppress the low-frequency oscillation of the synchronous generator without additional cost.

[0045] Figure 1 FIG. is a flowchart of a method of an embodiment of a control method for a flexible DC converter for low-frequency oscillation provided by the present application. Although the present application provides method operation steps or device structures as shown in the following embodiments or drawings, more or fewer operation steps or module units may be included in the method or device based on routine or non-creative labor. In steps or structures where there is no necessary causal relationship logically, the execution order of these steps or the module structure of the device is not limited to the execution order or module structure described in the embodiments of the present application and shown in the drawings. When the method or module structure is applied to an actual device or terminal product, it can be executed sequentially or in parallel according to the method or module structure connection shown in the embodiments or drawings (for example, in an environment of parallel processors or multi-threaded processing, or even a distributed processing environment).

[0046] Specifically, as Figure 1 shown, the above control method for a flexible DC converter for low-frequency oscillation, when applied to a synchronous generator, may include the following steps:

[0047] Step 101: Connect the q-axis voltage of the current inner loop control of the flexible DC MMC as the output feedback to a high-pass filter module;

[0048] Step 102: Connect the high-pass filter module to a proportional coefficient module;

[0049] Step 103: Add the output of the proportional coefficient module to the voltage feedforward of the d-axis voltage to suppress the low-frequency oscillation occurring in the synchronous generator.

[0050] Specifically, the cut-off frequency f v of the high-pass filter can be determined by the frequency of the low-frequency oscillation occurring in the synchronous generator, and the proportional coefficient K v of the proportional coefficient module can be determined according to the amplitude of the low-frequency oscillation of the synchronous generator power. Specifically, when implementing, before connecting the high-pass filter module to the proportional coefficient module, it may further include:

[0051] S1: Obtain the low-frequency oscillation frequency of the power grid dominated by the synchronous generator;

[0052] S2: Use the low-frequency oscillation frequency as the cut-off frequency of the high-pass filter module;

[0053] S3: Set the high-pass filter module with the determined cut-off frequency.

[0054] Alternatively, before connecting the high-pass filter module to the proportional coefficient module, it may further include:

[0055] S1: Obtain the rated output power of the synchronous generator and the maximum amplitude of the oscillation power;

[0056] S2: Determine the proportional coefficient of the proportional coefficient module according to the rated output power of the synchronous generator and the maximum amplitude of the oscillation power;

[0057] S3: Set the proportional coefficient module with the determined proportional coefficient.

[0058] For example, the proportional coefficient of the proportional coefficient module can be determined according to the following formula:

[0059]

[0060] where P N represents the rated output power of the synchronous generator, and P LO represents the maximum amplitude of the oscillation power of the synchronous generator.

[0061] Furthermore, the d-axis voltage feedforward of the inner current loop can be determined according to the following formula:

[0062]

[0063] where u md represents the modulation voltage of the inner current loop, u sd represents the d-axis voltage feedforward of the inner current loop, I Gdref represents the d-axis current reference value of the inner current loop, i d represents the d-axis current of the inner current loop, K p represents the proportional coefficient of the inner current loop, K i represents the integral coefficient of the inner current loop, s represents the Laplace operator, u sq represents the q-axis voltage feedforward of the inner current loop, K v represents the proportional coefficient of the proportional coefficient module, and f v represents the cut-off frequency of the high-pass filter module.

[0064] To achieve efficient low-frequency oscillation suppression, the above-mentioned flexible DC MMC can adopt a constant DC voltage outer loop control and an inner current loop control, and achieve synchronization with the power grid dominated by the synchronous generator through a phase-locked loop.

[0065] Considering that when a low-frequency oscillation of 0.1 Hz - 2.5 Hz occurs in a synchronous generator, the flexible DC MMC can suppress the low-frequency oscillation without deteriorating the safe and stable operation of the flexible DC MMC itself. Based on this, adding the output of the proportional coefficient module to the voltage feed-forward of the d-axis voltage to suppress the low-frequency oscillation occurring in the synchronous generator may include: determining whether the synchronous generator has a low-frequency oscillation within a preset frequency range; in the case of determining that the synchronous generator has a low-frequency oscillation within the preset frequency range, adding the output of the proportional coefficient module to the voltage feed-forward of the d-axis voltage to suppress the low-frequency oscillation occurring in the synchronous generator. Among them, the above preset frequency range may be 0.1 Hz - 2.5 Hz.

[0066] In a specific embodiment, before connecting the high-pass filter module and the proportional coefficient module, it may further include: constructing a digital twin model of the synchronous generator and flexible DC MMC combined system, and using this digital twin model to simulate the low-frequency oscillation propagation path and the low-frequency oscillation suppression effect in real time; in the case of determining that the suppression effect meets the preset suppression requirements, the cut-off frequency of the determined high-pass filter module and the proportional coefficient of the proportional coefficient module can be used to set the high-pass filter module and the proportional coefficient module. If it is determined that the suppression effect does not meet the preset suppression requirements, the cut-off frequency of the high-pass filter module and the proportional coefficient of the proportional coefficient module can be adjusted until the suppression effect meets the preset suppression requirements.

[0067] In order to achieve real-time and efficient suppression, in a specific embodiment, before connecting the high-pass filter module and the proportional coefficient module, it may further include: constructing a digital twin model of the synchronous generator and flexible DC MMC combined system, and using this digital twin model to predict the oscillation trend in the future time period (3 to 5 seconds) in real time. Based on the predicted oscillation trend in the future time period (3 to 5 seconds), the cut-off frequency of the high-pass filter module and the proportional coefficient of the proportional coefficient module are adjusted in advance to achieve the technical effect of real-time and efficient suppression of low-frequency oscillation.

[0068] Furthermore, in order to achieve lead control, in this example, the feed-forward compensation of the prediction can be increased. Specifically, the suppression effect of the current scheme on the low-frequency oscillation can be predicted, and a feed-forward compensation signal is generated according to the determined suppression effect on the low-frequency oscillation. Then, this feed-forward compensation signal is superimposed on the d-axis voltage feed-forward (u sd ) of the current inner loop to achieve lead control.

[0069] In this example, considering that the existing PI (Proportional-Integral) control strategy can be combined to perform closed-loop control on the d-axis current. Specifically, the output of the adaptive high-pass filter can be combined with the q-axis voltage signal adjusted by the dynamic proportional coefficient as one of the input signals of the PI controller to jointly generate the modulation voltage u of the inner current loop. md Then, the modulation voltage u of the inner current loop md is used as the driving signal of the MMC to control the output current of the MMC, thereby achieving precise control of the inner current loop while suppressing high-frequency oscillations.

[0070] The above method will be described below in conjunction with a specific embodiment. However, it should be noted that this specific embodiment is only for better explaining the present application and does not constitute an improper limitation to the present application.

[0071] Considering that although the existing additional oscillation suppression device can effectively suppress the low-frequency oscillation of the synchronous generator, it will increase the cost additionally. In this example, the flexible controllability of the flexible DC converter is used to suppress the low-frequency oscillation of the power grid, with lower cost. Specifically, the existing control strategy of the MMC is mainly used to improve its own stability or the stability of the wind farm - flexible DC interconnected system. In this example, the multi-module converter is applied to suppress the low-frequency oscillation phenomenon of the synchronous machine.

[0072] Based on this, in this example, a flexible DC converter stability control method for suppressing the low-frequency oscillation of the synchronous generator is provided, which can suppress the low-frequency oscillation of the synchronous generator without deteriorating the stable operation of the flexible DC system itself. Specifically, in this example, the flexible MMC adopts a constant DC voltage outer loop control and a current inner loop control, and synchronizes with the power grid through a phase-locked loop. Specifically, in a permanent magnet synchronous motor, the current can be decomposed into two components: the q-axis current and the d-axis current. Among them, the q-axis current is the current component perpendicular to the rotor magnetic field, and the d-axis current is the current component parallel to the rotor magnetic field. By decomposing the current into the q-axis and d-axis, the operating state of the motor can be better controlled. Then, returning to the voltage equation of the motor dq-axis, the dq-axis forms a 90-degree relationship. When the q-axis current lags by another 90 degrees, the dq-axis just forms 180 degrees. Therefore, the coupling of the q-axis current on the d-axis is just negative.

[0073] In this example, as Figure 2 shown, the q-axis voltage of the flexible MMC current inner loop control is connected to the high-pass filter and the proportional coefficient as the output. Then, the output of the proportional coefficient is added to the voltage feedforward of the d-axis voltage. Correspondingly, the modulation voltage u of the inner current loop md can be expressed as:

[0074]

[0075] where usd is the d-axis voltage feedforward of the inner current loop, u sq is the q-axis voltage feedforward of the inner current loop, u md is the modulation voltage of the inner current loop, i d is the d-axis current of the inner current loop, I Gdref is the d-axis current reference value of the inner current loop, K p is the proportional coefficient of the inner current loop, K i is the integral coefficient of the inner current loop, f v is the cut-off frequency of the high-pass filter, K v is the proportional coefficient.

[0076] That is, as Figure 2 shown, add a u sq to the high-pass filter. By introducing the high-pass filter and the proportional coefficient, due to the introduction of these two parameters, because the parameters are determined according to the oscillation frequency, therefore, low-frequency oscillations can be effectively suppressed.

[0077] Among them, the cut-off frequency f v of the above high-pass filter can be the frequency of the low-frequency oscillation that appears in the synchronous generator, and the above proportional coefficient K v can be determined according to the amplitude of the low-frequency oscillation of the synchronous generator power. Specifically, the proportional coefficient K v can be determined according to the following formula:

[0078]

[0079] Among them, P N represents the rated output power of the synchronous generator, and P LO represents the maximum amplitude of the oscillation power.

[0080] Furthermore, the cut-off frequency f v of the above high-pass filter can be automatically matched through real-time spectrum analysis to obtain the optimal cut-off frequency f v , thereby solving the limitations of a single fixed cut-off frequency. The above proportional coefficient K v can be dynamically adjusted according to the oscillation mode (for example: oscillation energy, phase shift), and further, the proportional coefficient can be adaptively optimized by combining fuzzy logic or reinforcement learning algorithms. When implementing, the q-axis voltage feedforward u sq of the inner current loop can be fused with the power angle deviation signal of the synchronous generator, thereby forming a hybrid control input to enhance the direct suppression ability of the oscillation source.

[0081] To achieve real-time and efficient suppression, a digital twin model of the combined system of a synchronous generator and a flexible DC MMC can be constructed. Through this digital twin model, the oscillation trend in the future time period (3 to 5 seconds) can be predicted in real time. Based on the predicted oscillation trend in the future time period (3 to 5 seconds), the cut-off frequency of the high-pass filter module and the proportional coefficient of the proportional coefficient module can be adjusted in advance to achieve the technical effect of real-time and efficient suppression of low-frequency oscillations.

[0082] As Figure 3 shown in the schematic diagram of the low-frequency oscillation waveform of the power when the output of the synchronous generator is 0.9 p.u., as Figure 4 shown in the schematic diagram of the low-frequency oscillation waveform at the port of the synchronous generator when the output of the synchronous generator is 0.9 p.u. and the flexible DC is connected, but the flexible DC MMC does not adopt any oscillation suppression measures, as Figure 5 shown in the schematic diagram of the power waveform at the port of the synchronous generator when the output of the synchronous generator is 0.9 p.u. and the flexible DC adopts the oscillation suppression measures of this example; it can be seen that the oscillation suppression method provided in this example can effectively suppress low-frequency oscillations.

[0083] The method embodiments provided in the above embodiments of the present application can be executed on a mobile terminal, a computer terminal or a similar computing device. Taking running on an electronic device as an example, Figure 6 is the hardware structure block diagram of an electronic device for a flexible DC converter control method of low-frequency oscillation provided by the present application. As Figure 6 shown, the electronic device 10 may include one or more (only one is shown in the figure) processors 02 (the processor 02 may include, but is not limited to, a processing device such as a microprocessor MCU or a programmable logic device FPGA), a memory 04 for storing data, and a transmission module 06 for communication functions. Those of ordinary skill in the art can understand that, Figure 6 the structure shown is only schematic and does not limit the structure of the above electronic device. For example, the electronic device 10 may further include more or fewer components than those Figure 6 shown, or have a different configuration from that Figure 6 shown.

[0084] The memory 04 can be used to store software programs and modules of application software, such as the program instructions / modules corresponding to the control method of the flexible DC converter with low-frequency oscillation in the embodiments of the present application. The processor 02 executes various functional applications and data processing by running the software programs and modules stored in the memory 04, that is, realizes the control method of the flexible DC converter with low-frequency oscillation of the above application program. The memory 04 may include a high-speed random access memory, and may also include a non-volatile memory, such as one or more magnetic storage devices, flash memory, or other non-volatile solid-state memories. In some instances, the memory 04 may further include a memory remotely set relative to the processor 02, and these remote memories can be connected to the electronic device 10 through a network. Examples of the above network include but are not limited to the Internet, enterprise intranet, local area network, mobile communication network, and combinations thereof.

[0085] The transmission module 06 is used to receive or send data via a network. Specific examples of the above network may include the wireless network provided by the communication provider of the electronic device 10. In one instance, the transmission module 06 includes a network adapter (Network Interface Controller, NIC), which can be connected to other network devices through a base station and thus can communicate with the Internet. In one instance, the transmission module 06 can be a radio frequency (RF) module, which is used to communicate with the Internet wirelessly.

[0086] At the software level, the above control device of the flexible DC converter with low-frequency oscillation, when applied in a synchronous generator, can be as Figure 7 shown, including:

[0087] A feedback unit 701, configured to connect the q-axis voltage of the inner current loop control of the flexible MMC as an output feedback to the high-pass filter module;

[0088] A connection unit 702, configured to connect the high-pass filter module to the proportional coefficient module;

[0089] An addition unit 703, configured to add the output of the proportional coefficient module to the voltage feedforward of the d-axis voltage to suppress the low-frequency oscillation occurring in the synchronous generator.

[0090] In one embodiment, before connecting the high-pass filter module to the proportional coefficient module, the control device of the flexible DC converter with low-frequency oscillation can obtain the low-frequency oscillation frequency of the power grid dominated by the synchronous generator; use the low-frequency oscillation frequency as the cut-off frequency of the high-pass filter module; set the high-pass filter module through the determined cut-off frequency.

[0091] In one embodiment, before connecting the high-pass filter module to the proportional coefficient module, the flexible DC converter control device for low-frequency oscillation can obtain the rated output power of the synchronous generator and the maximum amplitude of the oscillation power; determine the proportional coefficient of the proportional coefficient module according to the rated output power of the synchronous generator and the maximum amplitude of the oscillation power; and set the proportional coefficient module with the determined proportional coefficient.

[0092] In one embodiment, the flexible DC converter control device for low-frequency oscillation can specifically determine the proportional coefficient of the proportional coefficient module according to the following formula:

[0093]

[0094] where P N represents the rated output power of the synchronous generator, and P LO represents the maximum amplitude of the oscillation power of the synchronous generator.

[0095] In one embodiment, the flexible DC converter control device for low-frequency oscillation can specifically determine the d-axis voltage feedforward of the current inner loop according to the following formula:

[0096]

[0097] where u md represents the modulation voltage of the current inner loop, u sd represents the d-axis voltage feedforward of the current inner loop, I Gdref represents the d-axis current reference value of the current inner loop, i d represents the d-axis current of the current inner loop, K p represents the proportional coefficient of the current inner loop, K i represents the integral coefficient of the current inner loop, s represents the Laplace operator, u sq represents the q-axis voltage feedforward of the current inner loop, K v represents the proportional coefficient of the proportional coefficient module, and f v represents the cut-off frequency of the high-pass filter module.

[0098] In one embodiment, the above flexible MMC can adopt a constant DC voltage outer loop control and a current inner loop control, and achieve synchronization with the power grid dominated by the synchronous generator through a phase-locked loop.

[0099] In one embodiment, the adding unit 703 can specifically determine whether the synchronous generator has a low-frequency oscillation within a preset frequency range; in the case of determining that the synchronous generator has a low-frequency oscillation within the preset frequency range, add the output of the proportional coefficient module to the voltage feedforward of the d-axis voltage to suppress the low-frequency oscillation of the synchronous generator.

[0100] Embodiments of the present application also provide a specific implementation manner of an electronic device that can implement all steps in the flexible DC converter control method for low-frequency oscillation in the above embodiments. The electronic device specifically includes the following: a processor, a memory, a communications interface, and a bus; wherein, the processor, the memory, and the communications interface complete communication with each other through the bus; the processor is used to call a computer program in the memory, and when the processor executes the computer program, all steps in the flexible DC converter control method for low-frequency oscillation in the above embodiments are implemented. For example, when the processor executes the computer program, the following steps are implemented:

[0101] Step 1: Connect the q-axis voltage of the flexible MMC current inner-loop control as output feedback to a high-pass filter module;

[0102] Step 2: Connect the high-pass filter module to a proportional coefficient module;

[0103] Step 3: Add the output of the proportional coefficient module to the voltage feedforward of the d-axis voltage to suppress the low-frequency oscillation of the synchronous generator.

[0104] Embodiments of the present application also provide a computer-readable storage medium that can implement all steps in the flexible DC converter control method for low-frequency oscillation in the above embodiments. A computer program is stored on the computer-readable storage medium, and when the computer program is executed by a processor, all steps in the flexible DC converter control method for low-frequency oscillation in the above embodiments are implemented. For example, when the processor executes the computer program, the following steps are implemented:

[0105] Step 1: Connect the q-axis voltage of the flexible MMC current inner-loop control as output feedback to a high-pass filter module;

[0106] Step 2: Connect the high-pass filter module to a proportional coefficient module;

[0107] Step 3: Add the output of the proportional coefficient module to the voltage feedforward of the d-axis voltage to suppress the low-frequency oscillation of the synchronous generator.

[0108] As can be seen from the above description, in the embodiment of the present application, the q-axis voltage of the flexible DC MMC current inner-loop control is first used as an output feedback and connected to the high-pass filter module; then, the high-pass filter module is connected to the proportional coefficient module; and then, the output of the proportional coefficient module is added to the voltage feed-forward of the d-axis voltage to suppress the low-frequency oscillation of the synchronous generator. Through the above solution, the technical problem of excessive cost caused by the existing additional oscillation suppression device for suppressing the low-frequency oscillation of the synchronous generator is solved, and the technical effect of effectively suppressing the low-frequency oscillation of the synchronous generator without additional cost is achieved.

[0109] Each embodiment in this specification is described in a progressive manner. The same or similar parts among the embodiments can be referred to each other, and the differences between each embodiment and other embodiments are emphasized. In particular, for the hardware + program type embodiments, since they are basically similar to the method embodiments, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiments.

[0110] The specific embodiments of this specification are described above. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims can be performed in a different order than in the embodiments and still achieve the desired result. Additionally, the processes depicted in the drawings do not necessarily require the specific order or sequential order shown to achieve the desired result. In certain embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0111] Although the present application provides method operation steps as described in the embodiments or flowcharts, more or fewer operation steps may be included based on routine or non-creative labor. The order of steps listed in the embodiments is only one way among many execution orders of the steps and does not represent the only execution order. When the actual device or client product is executed, it can be executed in the order shown in the embodiments or the drawings or in parallel (for example, in an environment of parallel processors or multithreaded processing).

[0112] Although the embodiments of this specification provide method operation steps as described in the embodiments or flowcharts, more or fewer operation steps may be included based on conventional or non-creative means. The order of steps listed in the embodiments is only one way among the execution orders of numerous steps and does not represent the only execution order. When the actual device or terminal product is executed, it may be executed in the order of the method shown in the embodiments or the drawings or executed in parallel (for example, in an environment of parallel processors or multi-threaded processing, or even in a distributed data processing environment). The term "comprise", "include" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, product or device including a series of elements not only includes those elements but also includes other elements not expressly listed, or further includes elements inherent to such process, method, product or device. Without further limitation, it does not exclude the existence of additional identical or equivalent elements in the process, method, product or device including the said elements.

[0113] For convenience of description, the above device is described by dividing it into various modules according to functions. Of course, when implementing the embodiments of this specification, the functions of each module can be implemented in the same or multiple software and / or hardware, or the modules implementing the same function can be realized by a combination of multiple sub-modules or sub-units, etc. The device embodiments described above are only illustrative. For example, the division of the units is only a logical function division, and there may be other division methods in actual implementation. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed coupling or direct coupling or communication connection to each other may be through some interfaces, and the indirect coupling or communication connection of the device or unit may be in electrical, mechanical or other forms.

[0114] Each embodiment in this specification is described in a progressive manner. For the same or similar parts among the embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments. In particular, for system embodiments, since they are basically similar to method embodiments, the description is relatively simple. For relevant parts, reference can be made to the description of the method embodiments. In the description of this specification, the description referring to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the embodiments of this specification. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0115] The above is only the embodiment of the embodiments of this specification and is not used to limit the embodiments of this specification. For those skilled in the art, various changes and modifications can be made to the embodiments of this specification. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the embodiments of this specification shall be included within the scope of the claims of the embodiments of this specification.

Claims

1. A low frequency oscillation flexible DC converter control method, characterized in that: Applied in a synchronous generator, the method comprises: The q-axis voltage of the flexible direct current MMC current inner loop control is connected to the high-pass filter module as output feedback; Connecting the high-pass filter module to the proportional coefficient module; The output of the proportional coefficient module is added to the voltage feedforward of the d-axis voltage to suppress the low-frequency oscillation of the synchronous generator.

2. The method according to claim 1, characterized in that Before connecting the high-pass filter module to the proportional coefficient module, the method further includes: Obtaining a low-frequency oscillation frequency of a power grid dominated by the synchronous generator; Using the low frequency oscillation frequency as the cutoff frequency of the high pass filter module; Sets the high-pass filter module with a defined cutoff frequency.

3. The method according to claim 1, characterized in that Before connecting the high-pass filter module to the proportional coefficient module, the method further includes: Obtaining the rated output power and the maximum amplitude of the oscillation power of the synchronous generator; Determining a proportionality coefficient of a proportionality coefficient module according to the rated output power of the synchronous generator and the maximum amplitude of the oscillation power; The scaling factor module is set by the determined scaling factor.

4. The method according to claim 3, characterized in that Determine the proportional coefficient of the proportional coefficient module according to the following formula: Among them, P N Indicates the rated output power of the synchronous generator, P LO Indicates the maximum amplitude of the oscillating power of the synchronous generator.

5. The method according to claim 1, characterized in that The d-axis voltage feedforward of the current inner loop is determined according to the following formula: Among them, u md represents the modulation voltage of the inner current loop, u sd represents the d-axis voltage feedforward of the current inner loop, I Gdref Indicates the d-axis current reference value of the current inner loop, i d represents the d-axis current of the inner current loop, K p Indicates the proportionality coefficient of the current inner loop, K i represents the integral coefficient of the inner current loop, s represents the Laplace operator, u sq represents the q-axis voltage feedforward of the current inner loop, K v Indicates the proportional coefficient of the proportional coefficient module, f v Represents the cutoff frequency of the high-pass filter module.

6. The method according to any one of claims 1 to 5, characterized in that The flexible DC MMC adopts a constant DC voltage outer loop control and a current inner loop control, and achieves synchronization with the power grid dominated by the synchronous generator through a phase-locked loop.

7. The method according to any one of claims 1 to 5, characterized in that The output of the proportional coefficient module is added to the voltage feedforward of the d-axis voltage to suppress the low-frequency oscillation of the synchronous generator, including: Determining whether the synchronous generator has low-frequency oscillation within a preset frequency range; When it is determined that the synchronous generator has low-frequency oscillation within a preset frequency range, the output of the proportional coefficient module is added to the voltage feedforward of the d-axis voltage to suppress the low-frequency oscillation of the synchronous generator.

8. A low-frequency oscillation flexible DC converter control device, characterized in that: Applications in synchronous generators include: A feedback unit is used to connect the q-axis voltage of the flexible direct current MMC current inner loop control as output feedback to the high-pass filter module; A connecting unit, used to connect the high-pass filter module with the proportional coefficient module; The adding unit is used to add the output of the proportional coefficient module to the voltage feedforward of the d-axis voltage to suppress the low-frequency oscillation of the synchronous generator.

9. An electronic device comprising a processor and a memory for storing instructions executable by the processor, characterized in that: When the processor executes the instructions, the steps of the method according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium having a computer program / instruction stored thereon, characterized in that: When the computer program / instructions are executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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