Wind power sending-out system control method and device and wind power sending-out system

Abstract

The invention discloses a wind power sending-out system control method and device and a wind power sending-out system, and relates to the technical field of wind power sending-out system control, and the method comprises the steps: obtaining an output current actual value and an output port voltage actual value of an MMC; the actual value of the output current is controlled by a current control loop; determining the virtual impedance of the MMC, and obtaining the voltage compensation amount according to the actual value of the output current and the virtual impedance of the MMC; according to the actual voltage value of the output port, the voltage reference value of the output port of the MMC and the voltage compensation amount, the voltage adjustment amount of the voltage control loop is obtained; wherein the voltage control loop and the current control loop form a voltage and current double-closed-loop control loop; and adjusting the operation parameters of the MMC according to the voltage adjustment amount. According to the invention, the control stability of the wind power sending-out system can be enhanced.

Description

Technical Field

[0001] The present application relates to the technical field of full DC offshore wind power transmission system control, and in particular to a wind power transmission system control method, equipment, and wind power transmission system. Background Art

[0002] The internal equipment of the all-DC offshore wind power transmission system, such as the MMC (Modular Multilevel Converter) and DC transformer, has strong coupling strength and violent response to small signal disturbances, making the system prone to resonance and low-frequency oscillation, resulting in insufficient stability under complex operating conditions. Summary of the Invention

[0003] The main purpose of this application is to provide a wind power transmission system control method, equipment and wind power transmission system, aiming to solve the technical problem of insufficient stability of wind power transmission system control in related technologies.

[0004] To achieve the above objectives, the present application proposes a wind power transmission system control method, which can be applied to a wind power transmission system control device of a wind power transmission system. The wind power transmission system control device is connected to the MMC of a DC wind turbine in the wind power transmission system. The wind power transmission system includes multiple DC wind turbines. The wind power transmission system control method includes:

[0005] Obtain the actual value of the output current and the actual value of the output port voltage of the MMC; the actual value of the output current is controlled by the current control loop;

[0006] Determine the virtual impedance of the MMC, and obtain the voltage compensation amount according to the actual value of the output current and the virtual impedance of the MMC;

[0007] The voltage adjustment value of the voltage control loop is obtained according to the actual value of the output port voltage, the output port voltage reference value of the MMC and the voltage compensation value; wherein the voltage control loop and the current control loop form a voltage-current double closed-loop control loop;

[0008] Adjust the operating parameters of the MMC according to the voltage adjustment amount.

[0009] In one embodiment, the virtual impedance is related to a virtual inductance parameter and a virtual resistance parameter of the MMC;

[0010] The steps for obtaining the voltage compensation amount based on the actual value of the output current and the virtual impedance of the MMC include:

[0011] The voltage compensation amount is obtained according to the actual value of the output current, the virtual inductance parameter and the virtual resistance parameter.

[0012] In one embodiment, the virtual impedance is related to a virtual inductance parameter of the MMC;

[0013] The steps for obtaining the voltage compensation amount based on the actual value of the output current and the virtual impedance of the MMC include:

[0014] The voltage compensation amount is obtained according to the actual value of the output current and the virtual inductance parameters.

[0015] In one embodiment, the method further comprises:

[0016] The virtual inductance parameters are determined based on the target resonant frequency of the DC wind turbine, the actual line inductance of the MMC, and the DC bus capacitance. The wind power transmission system also includes a DC bus capacitance, which is connected in parallel to the DC side output port of the MMC.

[0017] In one embodiment, the method further comprises:

[0018] The virtual inductance parameters are determined based on the target resonant frequency of the DC wind turbine, the actual line inductance of the MMC, and the DC bus capacitance. The wind power transmission system also includes a DC bus capacitance, which is connected in parallel to the DC side output port of the MMC.

[0019] The virtual resistance parameter is determined according to the target damping ratio of the DC fan, the virtual inductance parameter, the DC bus capacitance, and the actual line resistance of the DC fan.

[0020] In one embodiment, before determining the virtual inductance parameter based on the target resonant frequency of the DC fan, the actual line inductance of the MMC, and the DC bus capacitance, the method further includes:

[0021] Obtain the frequency domain characteristic diagram of the wind power transmission system in the open-loop state through the frequency sweep method or small signal modeling method;

[0022] According to the frequency domain characteristic diagram, the open-loop frequency domain parameters of the wind power transmission system in the open-loop state are determined; the open-loop frequency domain parameters include the open-loop resonant frequency point and the open-loop phase margin;

[0023] The target resonant frequency and target damping ratio are determined according to the open-loop frequency domain parameters.

[0024] In one embodiment, before the step of obtaining the voltage adjustment value of the voltage control loop according to the actual value of the output port voltage, the output port voltage reference value of the MMC, and the voltage compensation value, the method further includes:

[0025] According to the virtual impedance, the voltage control coefficient and frequency control coefficient of the MMC droop control model are determined;

[0026] According to the voltage control coefficient and the frequency control coefficient, the MMC is droop controlled to obtain the output port voltage reference value.

[0027] In one embodiment, after the step of adjusting the operating parameters of the MMC according to the voltage adjustment amount, the method further includes:

[0028] Obtaining a frequency domain output result of the wind power transmission system under closed-loop control; the frequency domain output result includes at least one of a phase margin, an amplitude peak, and a dynamic response time;

[0029] When the frequency domain output result does not meet the preset system stability condition, the virtual impedance is adjusted and the process returns to the step of obtaining the voltage compensation amount based on the actual output current value and the virtual impedance of the MMC until the frequency domain output result of the wind power transmission system under closed-loop control meets the preset system stability condition.

[0030] In addition, to achieve the above-mentioned purpose, the present application also proposes a wind power transmission system control device, which is connected to the MMC. The device includes: a memory, a processor, and a computer program stored in the memory and runnable on the processor. The computer program is configured to implement the steps of the wind power transmission system control method as described above.

[0031] In addition, to achieve the above objectives, the present application also proposes a wind power transmission system, which includes:

[0032] Multiple DC fans; and

[0033] Like the above-mentioned wind power transmission system control device, the wind power transmission system control device is connected to the modular multilevel converter MMC of the DC wind turbine.

[0034] One or more technical solutions proposed in this application have at least the following technical effects:

[0035] In the wind power transmission system control method proposed in this application, a virtual impedance is introduced between the voltage and current dual closed-loop control loops of the MMC, providing a wind power transmission system stability enhancement solution based on virtual impedance control. The voltage compensation amount is calculated according to the actual value of the output current of the MMC and the virtual impedance, and the voltage compensation amount is superimposed on the voltage adjustment amount of the voltage control loop (outer loop), so that the MMC can respond to the actual dynamic changes of the system current and realize the voltage regulation of the MMC, thereby suppressing the voltage instability problem caused by current fluctuations. Then, the output current is quickly tracked through the current control loop (inner loop), forming a hierarchical regulation mechanism, improving the system's ability to suppress voltage and current disturbances, thereby achieving stability control of the wind power transmission system. At the same time, the introduction of virtual impedance indirectly adjusts the equivalent output impedance of the MMC, avoiding the resonance problem that may be caused by traditional fixed impedance control. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the following briefly introduces the drawings required for use in the embodiments or related technical descriptions. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0038] Figure 1 This is the topological structure diagram of the full DC offshore wind power transmission system;

[0039] Figure 2 This is the topological structure diagram of the DC fan;

[0040] Figure 3 A flow chart illustrating a first embodiment of a wind power transmission system control method according to the present application;

[0041] Figure 4 Schematic diagram of the virtual impedance control principle of MMC;

[0042] Figure 5 Bode diagram after virtual impedance optimization design;

[0043] Figure 6 Schematic diagram of the equipment structure of the hardware operating environment involved in the wind power transmission system control method in the embodiment of the present application.

[0044] The realization of the objectives, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0045] It should be understood that the specific embodiments described herein are merely used to explain the technical solutions of the present application and are not intended to limit the present application.

[0046] In order to better understand the technical solution of the present application, a detailed description will be given below in conjunction with the accompanying drawings and specific implementation methods.

[0047] Fully direct current (DC) offshore wind power transmission systems are a key development direction for offshore wind power grid integration. These systems utilize DC to collect and transmit electrical energy, offering advantages such as high energy conversion efficiency, compact system structure, and adaptability to long-distance transmission.

[0048] The internal equipment of the full DC offshore wind power transmission system, such as MMC and DC transformers, has strong coupling strength and violent response to small signal disturbances, which makes the system prone to resonance and low-frequency oscillation, resulting in insufficient stability under complex operating conditions.

[0049] In related technologies, common methods for improving the stability of all-DC wind power systems rely primarily on adjusting controller parameters or adding hardware filters. However, this approach not only increases design complexity but also potentially incurs additional costs.

[0050] Virtual impedance control, an advanced technology that improves system stability by adjusting converter output impedance characteristics, has been widely researched and applied in AC systems. However, its application in all-DC wind power transmission systems remains limited, lacking targeted designs and systematic stability enhancement strategies.

[0051] For example, Figure 1 Figure 2 shows a topological structure of a full DC offshore wind power transmission system. Figure 1 As shown, the transmission voltage level of this full DC offshore wind power transmission system is ±320kV, and the capacity is 1000MW; Figure 1 The wind power transmission system shown may include: a DC wind turbine, a DC bus, and a DC transformer.

[0052] In this example, the DC wind turbines can be divided into two groups, with each group comprising 10 in series and 5 in parallel. The DC wind turbines (DC-WT) are connected in series, then boosted to ±100 kV. They are then connected in parallel at the DC busbar and fed into the DC transformer at the offshore substation. The DC transformer adopts a dual-port input topology to connect and aggregate the two groups of DC wind turbines. The DC transformer achieves ±100 kV / ±320 kV boosting, which can then be inverted at the onshore converter station using HVDC (High Voltage Direct Current) technology and fed into the grid.

[0053] like Figure 2 As shown, the aforementioned DC wind turbine generally includes a wind turbine, a medium-frequency transformer, and a machine-side MMC. The DC wind turbine can be connected to the DC bus via the MMC's DC-side output port, which is connected in parallel with a DC bus capacitor. Under complex operating conditions, the high coupling strength between the MMC, DC transformer, and other equipment in the wind power transmission system, as well as the sharp response to small signal disturbances, can cause resonance and low-frequency oscillation in the wind power transmission system, affecting its operational stability. In the following description, the wind power transmission system will be referred to simply as the system.

[0054] In view of this, the present application provides a solution, which introduces virtual impedance between the voltage and current dual closed-loop control loops of the MMC, and provides a wind power transmission system stability enhancement solution based on virtual impedance control. The voltage compensation amount is calculated according to the actual value of the output current of the MMC and the virtual impedance, and the voltage compensation amount is superimposed on the voltage adjustment amount of the voltage control loop (outer loop), so that the MMC can respond to the actual dynamic changes of the system current and realize voltage regulation of the MMC, thereby suppressing the voltage instability problem caused by current fluctuations. Then, the output current is quickly tracked through the current control loop (inner loop), forming a hierarchical regulation mechanism, which improves the system's ability to suppress voltage and current disturbances, thereby achieving stability control of the wind power transmission system. At the same time, the introduction of virtual impedance indirectly adjusts the equivalent output impedance of the MMC, avoiding the resonance problem that may be caused by traditional fixed impedance control.

[0055] The execution subject of this embodiment is a wind power transmission system control device. The wind power transmission system control device can be a computing service device with data processing and program execution functions. The wind power transmission system control device can be connected to the MMC or can also be configured in the MMC.

[0056] The wind power transmission system control method provided in the embodiments of the present application is described below with reference to the accompanying drawings.

[0057] Reference Figure 3 The wind power transmission system control method provided in the embodiment of the present application includes steps S100 to S400:

[0058] Step S100 , obtaining an actual value of the output current and an actual value of the output port voltage of the MMC; the actual value of the output current is controlled by a current control loop.

[0059] Step S200 , determining the virtual impedance of the MMC, and obtaining a voltage compensation amount according to the actual value of the output current and the virtual impedance of the MMC.

[0060] Step S300 , obtaining a voltage adjustment value of a voltage control loop according to an actual value of the output port voltage, a reference value of the output port voltage of the MMC, and a voltage compensation value; wherein the voltage control loop and the current control loop form a voltage-current dual closed-loop control loop.

[0061] Step S400: adjusting the operating parameters of the MMC according to the voltage adjustment amount.

[0062] Specifically, in this embodiment, a virtual impedance loop is added between the current control loop and the voltage control loop of the MMC. Figure 4 The schematic diagram of the virtual impedance control principle of MMC is shown in FIG. Figure 4 As shown, V ref is the output port voltage reference value of the MMC, that is, the reference voltage signal of the voltage control loop, Vdc is the actual value of the output port voltage, G v is the voltage controller corresponding to the voltage control loop, G c is the current controller corresponding to the current control loop, I ref is the output current reference value of MMC, I o is the actual value of the output current of the MMC, that is, the output current signal of the current control loop, I c is the capacitive current of the MMC DC port, Z v (s) is the transfer function corresponding to the virtual impedance; the actual value of the output current is converted through Z v (s), generate voltage compensation △V; △V=Z v (s)·I o ; The obtained voltage compensation amount and the actual value of the output port voltage V dc And the output port voltage reference value V ref Substituting into the relevant transfer function of the voltage control loop, the actual voltage adjustment of the voltage control loop can be determined as: V ref -V dc -△V, voltage controller G v According to the voltage adjustment amount, the corresponding I ref The operation of the MMC is adjusted through the voltage and current dual closed-loop control loop presented by the voltage control loop and the current control loop.

[0063] It is not difficult to see that this embodiment introduces virtual impedance into the voltage outer loop and current inner loop control architecture of the system, and obtains the following Figure 4 The three-level architecture control design of "voltage control loop-virtual resistance loop-current control loop" shown in the figure uses virtual impedance to compensate for voltage fluctuations caused by current changes, etc., to achieve precise control of the MMC output port voltage; this decoupling adjustment form of virtual impedance injection realizes the joint optimization of the current control loop impedance, DC bus voltage dynamic response and circulation path, which can adapt to variable disturbance conditions under different operating points, improve the system's robustness and response speed in high ripple and high-frequency disturbance scenarios, and ensure the system's stability and adaptability in engineering operation.

[0064] In other words, by injecting virtual impedance, the equivalent impedance of the MMC can be indirectly changed, reducing the risk of resonance with the grid under fixed impedance conditions. Voltage compensation is generated by combining virtual impedance and the actual output current value, achieving subtle voltage adjustments for the MMC. Virtual impedance control is implemented at the MMC port and can respond quickly to disturbances in the DC bus, helping the MMC quickly resume stable operation and achieve stable control of the wind power transmission system. For example, grid voltage fluctuations during grid connection can cause disturbances in the DC bus, leading to distortion in the actual output current of the MMC. Generating voltage compensation by combining the actual output current and virtual impedance can suppress grid voltage fluctuations. Alternatively, in the event of an asymmetric grid fault, a negative-sequence component can be generated, leading to double-frequency fluctuations in the DC bus voltage. By independently designing virtual impedance in the negative-sequence rotating coordinate system and introducing MMC control, the impact of negative-sequence current on the system can be eliminated, better maintaining system stability.

[0065] It is easy to understand that the virtual impedance is related to the virtual inductance parameter and the virtual resistance parameter of the MMC. Therefore, in one embodiment, step S200 may include: obtaining a voltage compensation value according to the actual value of the output current, the virtual inductance parameter and the virtual resistance parameter.

[0066] That is, the transfer function of the virtual impedance can be expressed as Z v (s)=R v +sL v ; Among them, R v is the virtual resistance parameter, L v is the virtual inductor parameter, s is the Laplace operator. The virtual resistance parameter R in the transfer function v It can provide damping to suppress low-frequency oscillation, and the virtual inductance parameter L v The inductive impedance can be enhanced to suppress mid- and high-frequency resonance.

[0067] Therefore, the voltage compensation amount △V can be adjusted by the virtual impedance to the actual value of the output current I o Dynamic response generation: R v I o It can offset the resistive voltage drop caused by current ripple in real time and improve steady-state accuracy; It can suppress current mutation and delay voltage drop.

[0068] The system also includes a DC bus capacitor connected in parallel to the DC output port of the MMC. This allows the virtual inductance parameters to be determined based on the DC fan's target resonant frequency, the actual MMC line inductance, and the DC bus capacitor. The virtual resistance parameters can also be determined based on the DC fan's target damping ratio, virtual inductance parameters, DC bus capacitor, and the actual line resistance of the DC fan.

[0069] Specifically, the target resonant frequency of the DC fan can be determined based on the characteristics of the system. The target resonant frequency is a frequency point in the frequency band that can support the safe operation of the system. For example, the current system resonant frequency is 10Hz, which is in an unstable frequency band. The current resonant frequency of 10Hz needs to be shifted right to the safe range of 50Hz to 70Hz. At this time, the target resonant frequency can be determined to be 50Hz. Then, based on this target resonant frequency, the actual inductance of the line, and the DC bus capacitance, the virtual inductance parameters can be determined. Specifically, the virtual inductance parameters can be determined using formula 1, which is:

[0070] Among them, L v is the virtual inductance parameter, f desired is the target resonant frequency, L line is the actual inductance of the line, C dc is the DC bus capacitor.

[0071] It is understandable that according to the impedance matching theory, the resonant frequency is generally inversely proportional to the total inductance of the system, that is, the relationship between the resonant frequency and the total inductance can be expressed as:

[0072] Among them, f res is the resonant frequency, L total is the total inductance of the system, generally L total =L line +L v , L line is the actual inductance of the line, L v is the virtual inductance parameter, C dc is the DC bus capacitor.

[0073] Transforming the above equation for resonant frequency and total inductance yields Equation 1, used in this application to calculate the virtual inductance parameter. Virtual inductance is a key parameter for adjusting the system's frequency response and suppressing low-frequency oscillations. Accurately setting the target resonant frequency effectively controls the system's oscillation characteristics, providing a foundation for subsequent control and optimization.

[0074] After obtaining the virtual inductance parameter, the corresponding virtual resistance parameter is determined based on the target damping ratio, the determined virtual inductance parameter, the DC bus capacitance, and the actual line resistance of the DC fan. In a feasible implementation, the virtual resistance parameter can be determined using Formula 2; Formula 2 is:

[0075] Among them, R v is the virtual resistance parameter, ξ is the target damping ratio, L v is the virtual inductance parameter, C dcis the DC bus capacitance, R line is the actual resistance of the line.

[0076] The damping ratio is an important indicator for measuring the system's response speed and stability. By selecting an appropriate target damping ratio, the system's transition process and adaptability to external disturbances can be determined, thus avoiding amplitude surges in high-frequency bands.

[0077] The target damping ratio typically ranges from 0.7 to 1.0. A damping ratio of 0.7 is a good engineering compromise, resulting in an acceptable overshoot of approximately 5%, which prevents drastic voltage and current fluctuations in the system. It also offers a fast response and short rise time, meeting the system's requirements for rapid power regulation. Therefore, a suitable target damping ratio can be selected within the range of 0.7 to 1.0 to calculate the virtual resistance parameters.

[0078] By determining the virtual inductor parameters based on the target resonant frequency, the system's resonance point can be moved to a safe range, making the system's dynamic response more stable in the low-frequency band, with higher phase margin and gain margin, reducing the risk of low-frequency oscillation. This can reduce the negative impact of the introduction of virtual impedance on the system's low-frequency performance (less than 10Hz): Although the amplitude can remain basically stable in the low-frequency band, the phase margin is small, resulting in a slower dynamic response of the system in the low-frequency band. In particular, when responding to large disturbances, the system's recovery time may increase. This hysteresis effect will be more significant under rapidly changing power requirements, which may affect the system's transient response capability.

[0079] However, a larger virtual impedance may cause high-frequency oscillations in the high-frequency band, with the amplitude rising rapidly in the high-frequency band, reaching more than 50dB, and the phase also changing sharply. After the frequency exceeds 100kHz, the violent fluctuations in amplitude and phase may cause additional instability in the system at high frequencies. This situation may cause the switching equipment or power electronic devices to be affected by resonance at high frequencies, thereby affecting their reliable operation. The virtual resistance parameters determined by the target damping ratio can achieve enhanced damping of the virtual impedance, thereby suppressing the above-mentioned amplitude surge and phase mutation phenomena.

[0080] For all-DC systems, virtual inductance is typically dominant. Therefore, in another embodiment, the inductive characteristics of the output impedance can be directly enhanced by virtual inductance, shifting the system's resonance point to the right. In other words, the virtual impedance is related to the MMC's virtual inductance parameters; the voltage compensation value can be obtained based on the actual output current and the virtual inductance parameters.

[0081] In the case where virtual inductance is dominant, the transfer function of virtual impedance Z v (s)=R v +sL vThe virtual resistance parameter in is much smaller than the virtual inductance parameter, so it can be approximated as Z v (s)=sL v The voltage compensation value △V at this time can be adjusted by virtual impedance to the actual value of the output current I o Dynamic response generation: The voltage compensation amount △V is then superimposed on the voltage control loop.

[0082] In this embodiment, the virtual inductance parameter can also be determined based on the target resonant frequency of the DC fan, the actual line inductance of the MMC, and the DC bus capacitance. For details, please refer to the description of the above embodiment, which will not be repeated here.

[0083] It is not difficult to see that the virtual inductor introduced in this embodiment shifts the resonance point from low frequency (such as 10Hz) to the right to a higher frequency (such as 50Hz~70Hz), avoiding the low-frequency unstable area and improving the system stability. Moreover, since the full DC system is dominated by the virtual inductor, the impedance of the virtual inductor is significantly increased, which can effectively suppress high-frequency current fluctuations and reduce the risk of high-frequency oscillation.

[0084] It is worth mentioning that before determining the virtual inductance parameters based on the target resonant frequency of the DC wind turbine, the actual line inductance of the MMC, and the DC bus capacitance, the frequency domain characteristic diagram of the wind power transmission system in the open-loop state can be obtained by a frequency sweep method or a small signal modeling method; based on the frequency domain characteristic diagram, the open-loop frequency domain parameters of the wind power transmission system in the open-loop state are determined; wherein the open-loop frequency domain parameters include the open-loop resonant frequency point and the open-loop phase margin; based on the open-loop frequency domain parameters, the target resonant frequency and the target damping ratio are determined.

[0085] That is, the system's original impedance characteristics are determined without closed-loop control, and the target resonant frequency and target damping ratio are determined accordingly. The aforementioned frequency sweep method observes the system's frequency response by applying a series of sinusoidal signals (generally sweeping from low to high frequencies). By controlling the system's input frequency and recording the corresponding output amplitude and phase, a curve showing the system's amplitude and phase varying with frequency is obtained. Alternatively, a small-signal model of the system can be established: typically a linearized system model that ignores large-amplitude nonlinear effects. The system's response to small-amplitude perturbations is then calculated to obtain the system's gain and phase response at different frequencies. After obtaining a frequency domain characteristic diagram (such as a Bode plot) of the system in the open-loop state, the system's open-loop frequency domain parameters can be extracted from the frequency domain characteristic diagram. These parameters include the open-loop resonant frequency, open-loop phase margin, and open-loop amplitude peak (resonance peak dB value). The open-loop resonant frequency (the frequency at which the phase crosses -180°) typically corresponds to the frequency at which the system's amplitude and phase response change. Identifying the system's resonant frequency effectively understands the system's resonant characteristics.

[0086] Determining the system's frequency-domain parameters in the open-loop state can help design a virtual impedance target, further improving system robustness. For example, the target resonant frequency can be determined based on the open-loop resonant frequency. The target resonant frequency is typically shifted rightward from the open-loop resonant frequency to meet control requirements. Since the open-loop phase margin is small, the system is prone to approaching the critical point of oscillation, so it is necessary to increase the phase margin. This can be achieved by increasing the target damping ratio. The above steps can predetermine the system's original impedance characteristics, allowing for more targeted virtual impedance design.

[0087] In addition, the introduction of virtual impedance changes the output impedance characteristics of the MMC. Virtual impedance is the core of droop control and can be used to simulate the impedance characteristics of the synchronous generator to achieve autonomous power distribution. Therefore, after determining the virtual impedance, in order to achieve real-time autonomous adjustment of the MMC power distribution, it is necessary to convert the virtual impedance into the actual droop control instructions of the system.

[0088] Therefore, in one embodiment, the voltage control coefficient and frequency control coefficient of the MMC droop control model can be determined according to the virtual impedance; the MMC is droop controlled according to the voltage control coefficient and the frequency control coefficient to obtain the output port voltage reference value.

[0089] Among them, the voltage control coefficient mainly adjusts the response strength of the DC bus voltage, and the frequency control coefficient is mainly used to suppress the frequency deviation of power oscillation.

[0090] In a feasible implementation, the maximum output current value and the maximum output apparent power value of the MMC can be obtained; the voltage control coefficient is determined based on the virtual impedance, the maximum output current value, the maximum output apparent power value and the preset droop active power adjustment coefficient; and the frequency control coefficient is determined based on the maximum output apparent power value and the preset droop reactive power adjustment coefficient.

[0091] Specifically, the voltage control coefficient and the frequency control coefficient can be determined by the following calculation formula 3; the calculation formula 3 is:

[0092] Among them, δ Vmax is the voltage control coefficient, δ fmax is the frequency control coefficient, R D is the magnitude of the virtual impedance (i.e. |Z v |), k pmax is the preset droop active power adjustment coefficient, k qmax is the preset droop reactive power adjustment coefficient, i omax is the maximum output current value of MMC, S max is the maximum output apparent power value of MMC.

[0093] Based on the determined voltage control coefficient and frequency control coefficient, the MMC is subjected to droop control to generate a real-time voltage reference value. By determining the voltage control coefficient and frequency control coefficient through virtual impedance and using them for droop control, a more accurate voltage reference value can be generated. This method makes full use of the characteristics of virtual impedance, improves the accuracy and stability of MMC control, and can be used in application scenarios with high requirements for voltage regulation and power distribution, such as full DC wind power transmission systems.

[0094] That is, this embodiment sets the virtual impedance through the output impedance analysis of the MMC, and then determines the appropriate control coefficient based on this. By introducing a virtual impedance control mechanism into the system, the output impedance characteristics of key devices such as the MMC are adjusted, and the impedance matching relationship within the system is optimized, thereby effectively weakening the strong coupling effect between the system's MMC, DC transformer and other devices, thereby suppressing voltage and current oscillations under small signal disturbances, improving the overall small signal stability and dynamic robustness of the system, reducing the risk of resonance, and ensuring the reliable operation of long-distance, high-power wind power systems. In addition, this embodiment can achieve system stability control only through virtual impedance injection, without the need to add hardware equipment such as physical filters, which can effectively reduce the design complexity and construction cost of the system.

[0095] In addition, after adjusting the operating parameters of the MMC according to the voltage adjustment amount, the virtual impedance can be further optimized to achieve a better effect of maintaining system stability. Therefore, in one embodiment, the following steps can be performed:

[0096] (1) Obtain the frequency domain output results of the system under the above closed-loop control.

[0097] The closed-loop control mode is Figure 4 The control architecture shown is a “current control loop + voltage control loop + virtual impedance loop”; the frequency domain output result includes at least one of phase margin, peak amplitude, and dynamic response time.

[0098] (2) When the frequency domain output result does not meet the preset system stability condition, the virtual impedance is adjusted, and based on the adjusted virtual impedance, the step of obtaining the voltage compensation amount according to the actual value of the output current and the virtual impedance of the MMC is returned to be executed until the frequency domain output result of the system under closed-loop control meets the preset system stability condition.

[0099] Specifically, if the frequency domain output result does not meet the preset system stability conditions, the current virtual inductance and virtual resistance parameters can be adjusted. For example, the target resonant frequency and / or target damping ratio can be adjusted, and the corresponding virtual inductance and / or virtual resistance parameters can be determined using the aforementioned equations 1 and 2 to achieve adjustment of the virtual inductance and virtual resistance.

[0100] Alternatively, the virtual inductance parameters and the virtual resistance parameters can be directly adjusted, and the adjusted virtual inductance parameters and virtual resistance parameters can be introduced into the above-mentioned closed-loop control to obtain the corresponding frequency domain output results. Then, it is determined again whether the phase margin, amplitude peak value, dynamic response time, etc. in the frequency domain output results meet the preset system stability conditions. Iteration and verification are continuously performed until the frequency domain output results obtained after substituting the virtual inductance parameters and the virtual resistance parameters into the closed-loop control meet the preset system stability conditions.

[0101] In a feasible implementation, the frequency domain output result may include phase margin, amplitude peak and dynamic response time. In this embodiment, the preset system stability conditions include that the phase margin of the system in the mid-frequency band is greater than the preset phase margin, the amplitude peak of the system in the high-frequency band is less than the preset amplitude, and the dynamic response time of the system in the low-frequency band is less than the preset response time. Among them, the mid-frequency band is a frequency band of 10Hz to 100Hz, the high-frequency band is a frequency band greater than 1kHz, and the low-frequency band is a frequency band less than 10Hz. For example, the preset phase margin can be set to 45°, the preset amplitude can be set to 20dB, and the preset response time can be set to 0.5s. The specific setting values ​​can be determined according to specific engineering requirements or industry standards and are not specifically limited here.

[0102] Similarly, the frequency domain characteristic diagram (such as Bode diagram, etc.) obtained by the system after closed-loop control after injecting virtual impedance can be obtained by frequency sweeping method or small signal modeling method, and then the corresponding phase margin, amplitude peak and dynamic response time can be extracted from the diagram; and it is determined whether the phase margin, amplitude peak and dynamic response time meet the above-mentioned preset system stability conditions. If not, the target resonant frequency and / or target damping ratio can be adjusted according to a certain step size to obtain new virtual inductance parameters and virtual resistance parameters, and the above steps can be repeated for iterative verification. The step size can be a preset fixed value or a dynamically changing random value.

[0103] Alternatively, the virtual inductor and resistor parameters can be directly adjusted in steps of a certain size until the frequency-domain output meets the preset system stability conditions. By iteratively adjusting the impedance parameters based on the current frequency-domain output, the system output can be guaranteed to meet the predetermined stability requirements. This rational design and dynamic scheduling of virtual impedance parameters can adapt to changes in electrical characteristics under different operating conditions, providing flexible parameter control and high adjustment accuracy.

[0104] It can be understood that the wind power transmission system control method provided in the embodiment of the present application can calculate the voltage compensation amount based on the actual value of the output current of the MMC and the virtual impedance, and superimpose the voltage compensation amount on the voltage adjustment amount of the voltage control loop (outer loop), so that the MMC can respond to the actual dynamic changes of the system current, realize the voltage regulation of the MMC, and thus suppress the voltage instability problem caused by current fluctuations. Then, the output current is quickly tracked through the current control loop (inner loop), forming a hierarchical regulation mechanism, which improves the system's ability to suppress voltage and current disturbances, thereby achieving stability control of the wind power transmission system. At the same time, the introduction of virtual impedance indirectly adjusts the equivalent output impedance of the MMC, avoiding the resonance problem that may be caused by traditional fixed impedance control.

[0105] In order to more intuitively understand the effect of introducing the virtual impedance control loop in this application, the following is given: Figure 5 The Bode diagram after virtual impedance optimization design is shown. Figure 5 The red arrow in the figure indicates that the virtual inductance parameter gradually increases from 0mH to 0.2mH, which means that the virtual impedance injection is gradually increased. Figure 5 It can be seen that after the introduction of virtual impedance in MMC, the system equivalent impedance shifts to the right, and the intersection with the DC line impedance shifts from low frequency to high frequency. In the mid-frequency band of 10Hz to 100Hz, the increase in virtual impedance has a significant impact on the amplitude and phase of the system. The amplitude increases slightly in this frequency band. Near the resonant frequency, the increase in virtual impedance suppresses the system's resonant peak, reducing the amplitude drop. Figure 4 The introduction of virtual impedance in the phase diagram alleviates the sharp change of phase, and the phase change gradually recovers from -90° to 0° between 10Hz and 20Hz, which shows that the virtual impedance effectively suppresses the resonance phenomenon in this frequency band.

[0106] Before the introduction of virtual impedance, the phase was close to -180° in the resonant frequency band, the phase margin was almost zero, and the system was on the verge of instability. After the introduction of virtual impedance, the lowest phase point can be restored to approximately -90°, and the phase margin is increased by approximately 90°. This greatly improves the dynamic stability of the system at the resonant frequency. Virtual impedance can effectively improve the robustness of the system and reduce the impact of controller failure or external disturbances on system stability. It can be seen that the addition of virtual impedance increases the inductive impedance of the wind farm, shifts the resonant point to the right, increases the phase margin, and reduces the system's low-frequency oscillation from 68dB to 4dB. The damped oscillation frequency is suppressed, and the phase margin is reduced, which is conducive to enhancing the stability of wind farm output.

[0107] The present application provides a wind power transmission system control device, which is connected to a modular multilevel converter MMC. The wind power transmission system control device includes: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute the wind power transmission system control method in the above-mentioned first embodiment.

[0108] Reference below Figure 6 , which shows a structural schematic diagram of a wind power transmission system control device suitable for implementing the embodiment of the present application. Figure 6 The wind power transmission system control device shown is only an example and should not bring any limitation to the functions and scope of use of the embodiments of the present application.

[0109] like Figure 6 As shown, the wind power transmission system control device may include a processing device 1001 (e.g., a central processing unit, a graphics processing unit, etc.), which can perform various appropriate actions and processes according to a program stored in a read-only memory (ROM) 1002 or a program loaded from a storage device 1003 into a random access memory (RAM) 1004. RAM 1004 also stores various programs and data required for the operation of the wind power transmission system control device. Processing device 1001, ROM 1002, and RAM 1004 are interconnected via a bus 1005. An input / output (I / O) interface 1006 is also connected to the bus. Typically, the following systems can be connected to I / O interface 1006: an input device 1007 including, for example, a sensor; an output device 1008 including, for example, an output port; a storage device 1003 including, for example, a magnetic tape or hard disk; and a communication device 1009. Communication device 1009 can allow the wind power transmission system control device to communicate with other devices wirelessly or by wire to exchange data. Although the figures show a wind power transmission system control device having various systems, it should be understood that it is not required to implement or possess all the systems shown, and more or fewer systems may be implemented or possessed instead.

[0110] In particular, according to the embodiments disclosed in the present application, the processes described above with reference to the flowcharts can be implemented as computer software programs. For example, the embodiments disclosed in the present application include a computer program product comprising a computer program carried on a computer-readable medium, the computer program comprising program code for executing the method shown in the flowchart. In such an embodiment, the computer program can be downloaded and installed from a network via a communication device, or installed from a storage device 1003, or installed from a ROM 1002. When the computer program is executed by the processing device 1001, the above-mentioned functions defined in the method of the embodiment disclosed in the present application are executed.

[0111] The wind power transmission system control device provided in this application utilizes the wind power transmission system control method described in the aforementioned embodiment, resolving the technical issue of insufficient stability in wind power transmission system control in related art. Compared to related art, the beneficial effects of the wind power transmission system control device provided in this application are the same as those of the wind power transmission system control method described in the aforementioned embodiment. Other technical features of the wind power transmission system control device are the same as those disclosed in the aforementioned embodiment and are not further elaborated here.

[0112] It should be understood that the various parts disclosed in this application can be implemented using hardware, software, firmware, or a combination thereof. In the description of the above embodiments, specific features, structures, materials, or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0113] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

[0114] The present application provides a wind power transmission system, comprising multiple DC wind turbines and a wind power transmission system control device as described above; the wind power transmission system control device is connected to a modular multilevel converter (MMC) for the DC wind turbines. It should be noted that the wind power transmission system control device can be internal, i.e., directly disposed within the MMC, or can be connected externally to the MMC.

[0115] The wind power transmission system provided in this application utilizes the wind power transmission system control method described in the aforementioned embodiment, resolving the technical issue of insufficient stability in wind power transmission system control in related technologies. Compared to related technologies, the wind power transmission system provided in this application offers the same beneficial effects as the wind power transmission system control method described in the aforementioned embodiment. Other technical features of this wind power transmission system are the same as those disclosed in the aforementioned embodiment and are not further elaborated upon here.

[0116] The above descriptions are only some embodiments of the present application and do not limit the scope of protection. All equivalent structural transformations made using the contents of the present application specification and drawings under the technical concept of the present application, or direct / indirect application in other related technical fields are included in the scope of protection.

Claims

1. A wind power transmission system control method, characterized in that: A wind power transmission system control device applied to a wind power transmission system, the wind power transmission system control device being connected to a modular multilevel converter (MMC) of a DC wind turbine in the wind power transmission system, the wind power transmission system comprising a plurality of the DC wind turbines, and the wind power transmission system control method comprising: Obtaining an actual value of the output current and an actual value of the output port voltage of the MMC; the actual value of the output current is controlled by a current control loop; Determining the virtual impedance of the MMC, and obtaining a voltage compensation amount according to the actual value of the output current and the virtual impedance of the MMC; Obtaining a voltage adjustment amount of a voltage control loop according to the actual value of the output port voltage, the output port voltage reference value of the MMC, and the voltage compensation amount; wherein the voltage control loop and the current control loop form a voltage-current dual closed-loop control loop; The operating parameters of the MMC are adjusted according to the voltage adjustment amount.

2. The wind power transmission system control method according to claim 1, characterized in that: The virtual impedance is related to a virtual inductance parameter and a virtual resistance parameter of the MMC; The step of obtaining a voltage compensation amount according to the actual value of the output current and the virtual impedance of the MMC comprises: The voltage compensation amount is obtained according to the actual value of the output current, the virtual inductance parameter, and the virtual resistance parameter.

3. The wind power transmission system control method according to claim 1, characterized in that: The virtual impedance is related to a virtual inductance parameter of the MMC; The step of obtaining a voltage compensation amount according to the actual value of the output current and the virtual impedance of the MMC comprises: A voltage compensation amount is obtained according to the actual value of the output current and the virtual inductance parameter.

4. The wind power transmission system control method according to claim 2 or 3, characterized in that: The method further comprises: The virtual inductance parameter is determined according to the target resonant frequency of the DC wind turbine, the actual line inductance of the MMC, and the DC bus capacitor; wherein the wind power transmission system also includes the DC bus capacitor, and the DC bus capacitor is connected in parallel to the DC side output port of the MMC.

5. The wind power transmission system control method according to claim 2, wherein: The method further comprises: The virtual inductance parameter is determined according to the target resonant frequency of the DC wind turbine, the actual line inductance of the MMC, and the DC bus capacitor; wherein the wind power transmission system further includes the DC bus capacitor, and the DC bus capacitor is connected in parallel to the DC side output port of the MMC; The virtual resistance parameter is determined according to the target damping ratio of the DC fan, the virtual inductance parameter, the DC bus capacitance, and the actual line resistance of the DC fan.

6. The wind power transmission system control method according to claim 5, characterized in that: Before the step of determining the virtual inductance parameter according to the target resonant frequency of the DC fan, the actual line inductance of the MMC, and the DC bus capacitance, the method further includes: Obtain the frequency domain characteristic diagram of the wind power transmission system in the open-loop state through the frequency sweep method or small signal modeling method; Determining the open-loop frequency domain parameters of the wind power transmission system in an open-loop state according to the frequency domain characteristic diagram; the open-loop frequency domain parameters include an open-loop resonant frequency point and an open-loop phase margin; The target resonant frequency and the target damping ratio are determined according to the open-loop frequency domain parameters.

7. The wind power transmission system control method according to claim 1, characterized in that: Before the step of obtaining the voltage adjustment amount of the voltage control loop according to the actual value of the output port voltage, the output port voltage reference value of the MMC, and the voltage compensation amount, the method further includes: Determining a voltage control coefficient and a frequency control coefficient of the MMC droop control model according to the virtual impedance; The MMC is subjected to droop control according to the voltage control coefficient and the frequency control coefficient to obtain the output port voltage reference value.

8. The wind power transmission system control method according to claim 1, wherein: After the step of adjusting the operating parameters of the MMC according to the voltage adjustment amount, the method further includes: Obtaining a frequency domain output result of the wind power transmission system under closed-loop control; the frequency domain output result includes at least one of a phase margin, an amplitude peak, and a dynamic response time; If the frequency domain output result does not meet the preset system stability condition, the virtual impedance is adjusted, and the step of obtaining the voltage compensation amount based on the actual value of the output current and the virtual impedance of the MMC is returned to execution until the frequency domain output result of the wind power transmission system under closed-loop control meets the preset system stability condition.

9. A wind power transmission system control device, characterized in that: The wind power transmission system control device is connected to a modular multilevel converter MMC. The device includes: a memory, a processor, and a computer program stored in the memory and executable on the processor. The computer program is configured to implement the steps of the wind power transmission system control method according to any one of claims 1 to 8.

10. A wind power transmission system, characterized in that: The wind power transmission system includes: Multiple DC fans; and The wind power transmission system control device according to claim 9, wherein the wind power transmission system control device is connected to the modular multilevel converter MMC of the DC wind turbine.

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