Flexible DC grid-connected system and offshore wind power plant cooperative control method and system

Abstract

The invention provides a flexible direct-current grid-connected system and offshore wind power plant cooperative control method and system, and the method comprises the steps: determining a to-be-reduced active power value of a land alternating-current power grid according to the frequency of the land alternating-current power grid when the land alternating-current power grid is an island power grid and the generated output is greater than a load; according to the to-be-reduced active power value, calculating a to-be-consumed active power instruction value of the flexible direct current grid-connected system connected with the land alternating current power grid; according to the active power value to be reduced, determining an output reduction difference value of an offshore wind plant connected with the flexible direct current grid-connected system; according to the to-be-consumed active power instruction value of the flexible DC grid-connected system and the output reduction difference value of the offshore wind plant, updating the to-be-consumed active power instruction value, and according to the updated to-be-consumed active power instruction value, performing frequency response on the land AC power grid; through cooperative control of the flexible direct-current grid-connected system and the offshore wind power plant, quick response and continuous stability can be taken into account, so that the stability of the power grid is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible direct current (DC) transmission technology, and in particular to a method and system for coordinated control of a flexible DC grid-connected system and an offshore wind farm. Background Art

[0002] Currently, flexible direct current (HVDC) transmission technology based on voltage source converters (VSCs), a new type of direct current (HVDC) transmission technology, offers the advantages of rapid decoupling and independent control of active and reactive power. It can power passive systems without the commutation failure issues of conventional HVDC transmission technology, making it the primary means of integrating offshore wind power into the grid. However, wind power generation is volatile and uncertain. When the onshore AC system does not require significant wind power generation, the excess power must be dissipated. Otherwise, it can cause problems such as DC overvoltage or AC system overcurrent. Relying solely on the wind turbine's own power reduction control has a long response time and cannot meet the needs of short-term power reduction. Therefore, DC energy dissipation devices are generally installed on the DC side of the onshore converter station in flexible HVDC grid-connected systems.

[0003] When a partial disconnection occurs in the onshore AC grid, an active island grid containing some synchronous generators and loads may form, creating an imbalance between power generation and load. If the load exceeds the power generation output, the frequency of the island grid will drop. Removing some load can maintain the frequency within the normal operating range. If the load falls below the power generation output, the frequency of the island grid will rise, necessitating reductions in generator output and the transmission power of the flexible DC grid-connected system. Because offshore wind turbines are remote from the onshore AC grid and the flexible DC grid-connected system decouples them from the onshore AC grid, they cannot directly sense the status of the onshore AC grid. Therefore, the flexible DC grid-connected system must communicate with the offshore wind farm to reduce power. Upon receiving this signal, the offshore wind farm control system must adjust the output of individual wind turbines. This entire process involves the flexible DC system control, the offshore wind farm, and the offshore wind turbine control. The communication link is lengthy, making it impossible to quickly reduce the output of offshore wind power transmitted to the onshore island grid via the flexible DC system. This can lead to a continued rise in frequency, impacting grid stability. Summary of the Invention

[0004] To address the problem of frequency rise caused by the onshore AC grid being disconnected, forming an islanded grid, and the inability of conventional offshore wind turbine power reduction responses to quickly suppress frequency rise, thereby affecting grid stability, due to the decoupling of offshore wind farms from the onshore grid and the long communication link. The present invention proposes a method for coordinated control of a flexible DC grid-connected system and an offshore wind farm, including:

[0005] When the onshore AC power grid is an island power grid and the power generation output of the onshore AC power grid is greater than the load, determining the active power value to be reduced of the onshore AC power grid according to the calculated frequency of the onshore AC power grid;

[0006] Calculating an active power command value to be consumed of a flexible DC grid-connected system connected to the onshore AC power grid according to the active power value to be reduced;

[0007] determining an output reduction difference of an offshore wind farm connected to the flexible DC grid-connected system according to the active power value to be reduced;

[0008] The active power command value to be consumed is updated according to the active power command value to be consumed of the flexible DC grid-connected system and the output reduction difference of the offshore wind farm, and a frequency response is performed on the onshore AC power grid according to the updated active power command value to be consumed.

[0009] Optionally, determining the active power value to be reduced of the onshore AC power grid according to the calculated frequency of the onshore AC power grid includes:

[0010] When the calculated frequency of the onshore AC power grid is less than or equal to a preset frequency threshold, the active power value to be reduced of the onshore AC power grid is 0;

[0011] When the calculated frequency of the onshore AC power grid is greater than the frequency threshold and less than the set frequency upper limit, the active power value to be reduced of the onshore AC power grid is the set power consumption command value;

[0012] When the calculated frequency of the onshore AC grid is greater than the frequency upper limit, the active power value to be reduced of the onshore AC grid is the inverse of the rated power of the flexible DC grid-connected system.

[0013] Optionally, the expression for determining the active power value to be reduced of the onshore AC power grid may be as follows:

[0014]

[0015] Where,

[0016] k=(0-P rate ) / (f max -f0);

[0017] Wherein, ΔP represents the active power value to be reduced in the onshore AC power grid; f represents the frequency of the onshore AC power grid; f0 represents the fundamental wave rated frequency; f dead Indicates the preset dead zone frequency; k indicates the proportional coefficient; f max Indicates the upper frequency limit; p rate Indicates the rated power of the flexible DC grid-connected system.

[0018] Optionally, the calculation formula corresponding to the active power command value to be consumed of the flexible DC grid-connected system is as follows:

[0019]

[0020] Among them, p ch represents the active power command value to be consumed by the flexible DC grid-connected system; ΔP represents the active power value to be reduced in the onshore AC power grid; and P0 represents the transmission power of the flexible DC grid-connected system.

[0021] Optionally, determining, according to the active power value to be reduced, an output reduction difference of the offshore wind farm connected to the flexible DC grid-connected system includes:

[0022] Calculating a target power value of the offshore wind farm according to the active power value to be reduced;

[0023] An output reduction difference of the offshore wind farm is obtained according to a difference between the target power value of the offshore wind farm and the acquired current output value of the offshore wind farm.

[0024] Optionally, the target power value of the offshore wind farm is calculated as follows:

[0025]

[0026] Among them, P wtarget represents the target power value of the offshore wind farm; p w0 represents the current output value of the offshore wind farm; Δp represents the active power value to be reduced in the onshore AC power grid; and P1 represents a preset transmission power comparison value.

[0027] Optionally, updating the active power command value to be consumed according to the active power command value to be consumed of the flexible HVDC grid-connected system and the output reduction difference of the offshore wind farm includes:

[0028] Subtracting the active power command value to be consumed of the flexible DC grid-connected system from the output reduction difference of the offshore wind farm to obtain a coordinated control frequency value;

[0029] The coordinated control frequency value is used as the updated active power command value to be consumed.

[0030] Based on the same inventive concept, the present invention also provides a flexible DC grid-connected system and an offshore wind farm coordinated control system, comprising:

[0031] an onshore power calculation module, configured to determine, when the onshore AC power grid is an island power grid and the power generation output of the onshore AC power grid is greater than the load, a value of the onshore AC power grid's active power to be reduced based on the calculated frequency of the onshore AC power grid;

[0032] a flexible direct current power consumption module, configured to calculate an active power command value to be consumed of a flexible direct current grid-connected system connected to the onshore alternating current grid according to the active power value to be reduced;

[0033] an offshore output reduction module, configured to determine an output reduction difference of an offshore wind farm connected to the flexible DC grid-connected system according to the active power value to be reduced;

[0034] A collaborative control module is configured to update the active power command value to be consumed based on the active power command value to be consumed of the flexible DC grid-connected system and the output reduction difference of the offshore wind farm, and perform frequency response on the onshore AC power grid based on the updated active power command value to be consumed.

[0035] Optionally, the onshore power calculation module includes:

[0036] a first range power calculation submodule, configured to set the active power value to be reduced of the onshore AC power grid to 0 when the calculated frequency of the onshore AC power grid is less than or equal to a preset frequency threshold;

[0037] a second range power calculation submodule, configured to, when the calculated frequency of the onshore AC power grid is greater than the frequency threshold and less than a set frequency upper limit, set the active power value to be reduced of the onshore AC power grid to a set consumption power command value;

[0038] The third range power calculation submodule is configured to, when the calculated frequency of the onshore AC grid is greater than the upper frequency limit, calculate the active power value of the onshore AC grid to be reduced to the inverse of the rated power of the flexible DC grid-connected system.

[0039] Optionally, the expression for determining the active power value to be reduced of the onshore AC power grid is as follows:

[0040]

[0041] Where,

[0042] k=(0-p rate ) / (f max -f0);

[0043] Wherein, ΔP represents the active power value to be reduced in the onshore AC power grid; f represents the frequency of the onshore AC power grid; f0 represents the fundamental wave rated frequency; f deadIndicates the preset dead zone frequency; k indicates the proportional coefficient; f max Indicates the upper frequency limit; P rate Indicates the rated power of the flexible DC grid-connected system.

[0044] Optionally, the calculation formula corresponding to the active power command value to be consumed of the flexible DC grid-connected system is as follows:

[0045]

[0046] Among them, P ch represents the active power command value to be consumed by the flexible DC grid-connected system; ΔP represents the active power value to be reduced in the onshore AC power grid; and P0 represents the transmission power of the flexible DC grid-connected system.

[0047] Optionally, the offshore output reduction module includes:

[0048] a target power calculation submodule, configured to calculate a target power value of the offshore wind farm according to the active power value to be reduced;

[0049] The output difference calculation submodule is configured to obtain an output reduction difference of the offshore wind farm according to a difference between a target power value of the offshore wind farm and the acquired current output value of the offshore wind farm.

[0050] Optionally, the target power value of the offshore wind farm is calculated as follows:

[0051]

[0052] Among them, P wtarget Represents the target power value of the offshore wind farm; P w0 represents the current output value of the offshore wind farm; ΔP represents the active power value to be reduced in the onshore AC power grid; and P1 represents a preset transmission power comparison value.

[0053] Optionally, the collaborative control module includes:

[0054] a frequency interaction submodule, configured to obtain a coordinated control frequency value by subtracting the active power command value to be consumed of the flexible DC grid-connected system from the output reduction difference of the offshore wind farm;

[0055] The frequency updating submodule is configured to use the coordinated control frequency value as an updated active power instruction value to be consumed.

[0056] In another aspect, the present invention further provides an electronic device, comprising: at least one processor and a memory; the memory and the processor are connected via a bus;

[0057] The memory is used to store one or more programs;

[0058] When the one or more programs are executed by the at least one processor, the aforementioned method for coordinated control of a flexible DC grid-connected system and an offshore wind farm is implemented.

[0059] On the other hand, the present invention further provides a computer-readable storage medium having an execution program stored thereon. When the execution program is executed, the method for coordinated control of a flexible DC grid-connected system and an offshore wind farm as described above is implemented.

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] The present invention provides a method and system for collaborative control of a flexible direct current (DC) grid-connected system and an offshore wind farm, comprising: when an onshore AC grid is an island grid and the power generation output of the onshore AC grid is greater than the load, determining the active power value to be reduced of the onshore AC grid according to the calculated frequency of the onshore AC grid; calculating the active power instruction value to be consumed of the flexible DC grid-connected system connected to the onshore AC grid according to the active power value to be reduced; determining the output reduction difference of the offshore wind farm connected to the flexible DC grid-connected system according to the active power value to be reduced; and calculating the active power instruction value to be consumed of the flexible DC grid-connected system according to the active power value to be reduced. The output of the offshore wind farm is reduced by the difference between the power command value and the output reduction of the offshore wind farm, the active power command value to be consumed is updated, and the frequency response of the onshore AC power grid is performed according to the updated active power command value to be consumed; the application uses the fast action characteristics of the flexible DC grid-connected system to quickly reduce the output power of the flexible DC grid-connected system and suppress the rapid increase of frequency; by reducing the output of the offshore wind farm, the frequency fluctuation range can be made within a stable range, and a smooth power transition can be achieved; therefore, the present invention can take into account both fast response and continuous stability through the coordinated control of the flexible DC grid-connected system and the offshore wind farm, thereby significantly improving the stability of the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 A flow chart of a coordinated control method of a flexible DC grid-connected system and an offshore wind farm provided by the present invention;

[0063] Figure 2 A schematic diagram of the composition principle of the flexible DC grid-connected system provided by the present invention;

[0064] Figure 3 A schematic diagram of the control framework of the flexible DC grid-connected system provided by the present invention;

[0065] Figure 4 A schematic diagram of the phase-locked loop control principle in the flexible DC grid-connected system provided by the present invention;

[0066] Figure 5A schematic diagram of the control principle of a DC energy consumption device in the flexible DC grid-connected system provided by the present invention;

[0067] Figure 6 A schematic diagram of the principle of a wind farm controller in an offshore wind farm provided by the present invention;

[0068] Figure 7 A schematic diagram of voltage fluctuations in an offshore wind farm provided by the present invention;

[0069] Figure 8 A schematic diagram of voltage and operating mode fluctuations in an offshore wind farm provided by the present invention;

[0070] Figure 9 A schematic diagram of the structure of a flexible DC grid-connected system and an offshore wind farm coordinated control system provided by the present invention;

[0071] Figure 10 This is a structural diagram of an electronic device provided by the present invention. DETAILED DESCRIPTION

[0072] The present invention provides a method, system, device and medium for coordinated control of a flexible DC grid-connected system and an offshore wind farm. Specific implementations of the present invention are further described in detail below with reference to the accompanying drawings.

[0073] Example 1:

[0074] The present invention provides a method for collaborative control of a flexible DC grid-connected system and an offshore wind farm, the flow chart of which is shown as follows: Figure 1 Shown, including:

[0075] Step 1: When the onshore AC power grid is an island power grid and the power generation output of the onshore AC power grid is greater than the load, determining the active power value to be reduced of the onshore AC power grid according to the calculated frequency of the onshore AC power grid;

[0076] Step 2: Calculate the active power command value to be consumed of the flexible DC grid-connected system connected to the onshore AC grid based on the active power value to be reduced;

[0077] Step 3: Determine the output reduction difference of the offshore wind farm connected to the HVDC Flexible grid-connected system based on the active power value to be reduced;

[0078] Step 4: Update the active power command value to be consumed according to the active power command value to be consumed of the flexible DC grid-connected system and the output reduction difference of the offshore wind farm, and perform frequency response on the onshore AC power grid according to the updated active power command value to be consumed.

[0079] Generally, when a partial disconnection occurs in the onshore AC grid, an active island grid containing some synchronous generators and loads may form, creating an imbalance between power generation output and load. If the load exceeds the power generation output, the frequency of the island grid will drop. Removing some of the load will maintain the frequency within the normal operating range. If the load is less than the power generation output, the frequency of the island grid will rise. At this point, it is necessary to reduce the generator output and the transmission power of the offshore wind turbine flexible direct current (FDC) grid-connected system. Because offshore wind turbines are far from the onshore AC grid, and the FDC grid-connected system decouples them from the onshore AC grid, offshore wind turbines cannot directly sense the state of the onshore AC grid. Therefore, the FDC grid-connected system needs to communicate with the offshore wind farm to reduce power. After receiving the signal, the offshore wind farm control system needs to adjust the output of a single wind turbine. The entire process involves the control of the flexible DC grid-connected system, the offshore wind farm, and the offshore wind turbines. The communication link time is long, and it is impossible to quickly reduce the output of offshore wind power transmitted to the onshore island power grid through the flexible DC system. The frequency may continue to rise, affecting the stability of the power grid. To solve the above technical problems, it is possible to consider using the DC energy consumption devices in the flexible DC grid-connected system to quickly absorb excess power and adjust the output of the offshore wind farm in a coordinated manner. This can achieve dual optimization of power balance and frequency stability. Specifically:

[0080] In one implementation, the process of determining the active power value to be reduced of the onshore AC power grid based on the calculated frequency of the onshore AC power grid in step 1 may include:

[0081] When the calculated frequency of the onshore AC power grid is less than or equal to a preset frequency threshold, the active power value to be reduced of the onshore AC power grid is 0;

[0082] When the calculated frequency of the onshore AC power grid is greater than the frequency threshold and less than the set frequency upper limit, the active power value to be reduced of the onshore AC power grid is the set power consumption command value;

[0083] When the calculated onshore AC grid frequency is greater than the upper frequency limit, the active power value to be reduced in the onshore AC grid is the inverse of the rated power of the flexible DC grid-connected system.

[0084] This implementation utilizes flexible DC technology, specifically optimized for the isolated state of the onshore AC grid, and meticulously adjusts the active power level to be reduced. This allows for flexible adjustments based on different frequency states, enabling timely response to load changes and significantly improving the stability and security of the onshore AC grid. When the frequency falls below a preset threshold, the power value is set to zero, enabling a rapid and stable restoration of the grid state and avoiding the risks associated with low frequency. This implementation optimizes the balance between power generation and load by precisely adjusting power consumption within the normal frequency range. When the frequency exceeds the limit, the power is set to the opposite of the system's rated power, effectively consuming excess energy to protect the system. This approach ensures that the onshore AC grid can effectively adjust under various operating conditions, maintains frequency stability, and prevents grid collapse due to frequency fluctuations, significantly improving grid reliability.

[0085] The above steps can accurately determine the active power value to be reduced in the onshore AC power grid, and the power grid can be effectively adjusted under various frequency conditions to avoid grid instability caused by frequency fluctuations. In order to better understand the working principle of the flexible DC grid-connected system and its role in the grid frequency response, the specific components and working mechanisms of the flexible DC grid-connected system can be further studied, specifically:

[0086] In one implementation, the schematic diagram of the composition principle of the flexible DC grid-connected system connected to the onshore AC grid in step 2 above can be as follows: Figure 2 As shown in the figure, the main components include: offshore converter station, DC cable, DC energy consumption device and onshore converter station. The offshore wind farm (i.e., offshore wind power system, including multiple wind turbines) can be directly connected to the offshore converter station, or connected to the offshore converter station after being stepped up by a step-up transformer; the onshore AC power grid can be directly connected to the onshore converter station; the DC energy consumption device is mainly used to consume surplus power and maintain the DC voltage at a safe level when the flexible DC grid-connected system implements fault ride-through under the condition of onshore AC grid-connected fault, so as to avoid triggering overvoltage protection and causing the flexible DC grid-connected system to stop operating.

[0087] The control block diagram of the above-mentioned onshore converter station is as follows: Figure 3 As shown, the control mode can mainly include outer loop control and inner loop control, wherein the outer loop control mode can include: DC voltage control, reactive power control or AC voltage control; the inner loop control can be AC ​​current control, and the inner loop output is the modulation voltage of the onshore converter station, which ultimately generates the trigger signal of the onshore converter station switch device (in the figure, U dc1 Indicates the voltage value of the first DC bus; U dc2 Indicates the voltage value of the second DC bus; i rabc Indicates the three-phase current on the AC side; u gabc Indicates the measured value of the three-phase voltage on the AC side; igabc Indicates the measured value of the three-phase current on the AC side; PWM means pulse width modulation; PLL means phase-locked loop; u gd Indicates the DC voltage control signal; u gq Indicates the output voltage control signal of the inverter side; θ g Indicates the AC voltage phase angle; u rabc Indicates the three-phase voltage of the inner loop control output after coordinate system transformation; u rd Indicates the voltage on the DC side of the onshore converter station; u rq Represents the voltage signal for controlling reactive power; i rd Indicates the current value running on the DC side; i rq Represents the reactive power component current; i rdref Indicates the desired DC current reference setting value; i rqref Indicates the desired reactive current reference setting value; dq / abc indicates the transformation from the dq coordinate system to the abc coordinate system; abc / dq indicates the transformation from the abc coordinate system to the dq coordinate system; i rdmax Indicates the maximum allowable value of DC current; i rdmin Indicates the minimum allowable value of DC current; i rqmax Indicates the maximum allowable value of reactive current; i rqmin Indicates the minimum allowable value of reactive current; U dc2ref Indicates the reference setting value of the second DC bus voltage; U dc2 Indicates the actual voltage value of the second DC bus; Q gref Indicates the expected output value of reactive power; Q g Indicates the reactive power value provided by the system; U gmref Indicates the voltage reference value of the AC side; U gm Indicates the actual measured AC voltage value; fixed U dc +Constant Q means the control mode combining constant DC voltage and constant reactive power, which aims to maintain DC voltage stability and reactive power output; U ac Control refers to the control method of AC voltage, focusing on maintaining voltage stability on the AC side). In addition, the phase-locked loop of the onshore converter station has a control structure such as Figure 4 As shown, by collecting the voltage signal of the onshore AC power grid (for example, u a 、u b 、u c Indicated), not only the coordinate transformation required for control (from abc coordinate system to dq coordinate system) is obtained to obtain the d-axis component (for example, x d ) and the q-axis component (e.g., x q ), and x qThe phase error is detected by the phase-locked loop to generate an error signal. The phase error is adjusted by the integrator in the PI controller to generate the grid frequency (for example, it can be represented by ω) and the phase angle (for example, it can be represented by θ). The frequency of the onshore AC grid can be calculated according to the calculation formula f=ω / 2π (for example, it can be represented by f). Based on the frequency of the onshore AC grid calculated by the phase-locked loop, the relationship between the frequency and the active power to be reduced (which can also be expressed as the active power value to be reduced) is designed, that is, the frequency-power controller. The control structure diagram is shown as follows: Figure 5 As shown, dead-band control is performed according to the grid frequency f and the fundamental wave rated frequency f0. When the onshore AC grid is in the interval between the fundamental wave rated frequency f0 (which can be set to 50 Hz, for example) and the dead-band frequency (which can be set to 0.1 Hz, for example), the dead-band control is performed according to the grid frequency f and the fundamental wave rated frequency f0. dead ), the output is zero, when the frequency f exceeds f0+f dead When f reaches f max (For example, it can be set to 52Hz), the active power that needs to be reduced is -P rate (Indicates that the active power needs to be reduced P rate , ΔP output sets a limit), ΔP is used as the output signal of the frequency-power controller to adjust the power consumption of the flexible DC grid-connected system or the output of the offshore wind farm;

[0088] For example, the expression for determining the active power value to be reduced of the above-mentioned onshore AC power grid may be as follows:

[0089]

[0090] Where,

[0091] k=(0-P rate ) / (f max -f0);

[0092] Wherein, ΔP represents the active power value to be reduced in the onshore AC power grid; f represents the frequency of the onshore AC power grid; f0 represents the fundamental wave rated frequency; f dead Indicates the preset dead zone frequency; k indicates the proportional coefficient; f max Indicates the upper frequency limit; P rate It represents the rated power of the flexible DC grid-connected system. Through this expression, it can be found that when the onshore power grid is disconnected and the onshore converter station detects that the onshore AC grid frequency f rises and exceeds f0+f dead When ΔP signal is generated.

[0093] The control block diagram of the DC energy consumption device of the flexible DC grid-connected system is as follows: Figure 6As shown in FIG, it is composed of a DC bus, an energy dissipation device, a switch module (SM in the figure is the switch module), a control module, a feedback sensor, a protection circuit and a communication interface. Each part works together to achieve efficient management of excess power and safe and stable operation of the system. During normal operation, the DC energy dissipation device operates in Mode 1 (i.e., Mode = 1). By detecting the DC voltage overvoltage, the control duty cycle of the DC energy dissipation device is output. Duty = 1 means that the DC energy dissipation device consumes the rated power of the flexible DC grid-connected system (i.e., full power P rate ), duty = 0 means that the DC energy consumption device is not started and does not consume energy; duty is adjusted between 0 and 1, which can realize flexible adjustment of the power of the DC energy consumption device; the present invention can operate the DC energy consumption device in mode 2, by calculating the active power instruction (which can also be expressed as the active power instruction value to be consumed P ch ) divided by the rated active power of the flexible DC grid-connected system to calculate the duty instruction; Figure 7 Expresses the DC energy consumption device in the control voltage (for example, the voltage can be used as U dc The waveform shows periodic fluctuations, reflecting the voltage fluctuation characteristics of the offshore wind farm. Through real-time monitoring and dynamic adjustment, the DC energy consumption device can effectively control voltage fluctuations and maintain system stability. Figure 8 The voltage fluctuation characteristics of offshore wind farms under different working modes are shown, with duty being used to represent the duty cycle, t d The delay time of the switching action is represented by t1 and t2, which represent the on-time and off-time of the switch within a cycle, respectively. The length of this time directly affects the average current and power output of the system, thereby affecting the energy efficiency and responsiveness of the entire energy-consuming device. When the voltage rises, the control module increases the duty, prolongs t1 (on-time), increases energy dissipation, and thus reduces the bus voltage. When the voltage is normal, the duty may be reduced, shortening t1 and prolonging t2 (off-time) to avoid excessive energy consumption. This diagram shows the dynamic process of DC energy-consuming devices during switching control, which can effectively cope with the challenges of voltage fluctuations and load changes in DC power systems.

[0094] For example, the calculation formula corresponding to the active power command value to be consumed of the flexible DC grid-connected system can be as follows:

[0095]

[0096] Among them, P chrepresents the active power command value to be consumed by the flexible DC grid-connected system; ΔP represents the active power value to be reduced in the onshore AC grid; P0 represents the transmission power of the flexible DC grid-connected system. This expression shows that the onshore converter station transmits the generated ΔP signal to the DC energy consumption device. When the DC energy consumption device detects that ΔP is greater than 0, the operation mode is switched from 1 to 2, and the active power command consumed by the DC energy consumption device is P ch If the current transmission power P0 of the flexible DC grid-connected system is greater than ΔP, then P ch =ΔP; if the current transmission power of the flexible DC grid-connected system P0≤ΔP, then P ch =P0; In this example, power coordination and dynamic adjustment between the onshore AC grid and the flexible DC system can be effectively achieved. First, the active power value to be reduced ΔP of the onshore AC grid is used as an input signal to reflect the power demand caused by grid load changes or other factors. This signal is transmitted from the onshore converter station to the DC energy consumption device, so that the device can respond in time when it detects that ΔP is greater than zero and automatically switch the operating mode, thereby ensuring the flexibility and adaptability of the system. Through this example, it can be ensured that if the transmission power P0 of the flexible DC grid-connected system is greater than ΔP, the active power command value to be consumed P ch If P0 is less than or equal to ΔP, then P ch It is set to the current transmission power P0 to ensure that excessive demand will not be forced in the state of insufficient power. Through this mechanism, it can adapt to the power fluctuations of the power grid and enhance the responsiveness and reliability of the system.

[0097] In one implementation, the process of determining the output reduction difference of the offshore wind farm connected to the flexible DC grid-connected system based on the active power value to be reduced in step 3 may include:

[0098] Calculate the target power value of the offshore wind farm according to the active power value to be reduced;

[0099] According to the difference between the target power value of the offshore wind farm and the obtained current output value of the offshore wind farm, the output reduction difference of the offshore wind farm (i.e., the amount of abandoned wind) is obtained;

[0100] In this implementation, when the onshore converter station transmits the ΔP signal to the DC energy consumption device, it also transmits the ΔP signal to the offshore wind farm controller through communication. The offshore wind farm controller receives the ΔP signal, and the wind farm output is P w0 (P w0 ≈P0), the offshore wind farm needs to reduce the power to the target value P wtarget , P wtarget =Pw0 -ΔP, if P w0 -ΔP≤0, then P wtarget =0.

[0101] For example, the target power value of the offshore wind farm can be calculated as follows:

[0102]

[0103] Among them, P wtarget Represents the target power value of the offshore wind farm; P w0 represents the current output value of the offshore wind farm; ΔP represents the active power value to be reduced in the onshore AC power grid; and P1 represents a preset transmission power comparison value.

[0104] In this implementation, the target power value P of the offshore wind farm is first calculated based on the active power value ΔP to be reduced. wtarget , by identifying the current wind power output P w0 The difference from ΔP can accurately determine the output reduction difference, thereby achieving precise control of the amount of wind curtailment. This feedback mechanism not only effectively reduces the waste of resources caused by excess power by coordinating the production of offshore wind power sources with the needs of the power grid, but also improves the efficiency and stability of the overall power system. In addition, this implementation method transmits the ΔP signal at the onshore converter station while also transmitting this signal in real time to the controller of the offshore wind farm, allowing the wind farm to quickly respond to changes in the power demand of the power grid. This instant communication and response capability enables the offshore wind farm to flexibly adjust its output power during operation, ensuring that its power output always matches the actual load demand of the power grid, reducing the safety risks caused by power imbalance.

[0105] In one implementation, the process of updating the active power command value to be consumed in step 4 according to the active power command value to be consumed of the flexible HVDC grid-connected system and the output reduction difference of the offshore wind farm may include:

[0106] The coordinated control frequency value (e.g., ΔP w );

[0107] The coordinated control frequency value is used as the updated active power command value to be consumed (for example, it can be expressed as P ch_new );

[0108] In this implementation, the offshore wind farm reduces its output at a certain rate, and the flexible DC grid-connected system detects the difference value ΔP of the power reduction fed into the offshore wind farm in real time. w(That is, the system control frequency value mentioned above). The difference ΔP that the flexible DC grid-connected system reduces the output of the offshore wind farm w If the active power consumption instruction of the DC energy consumption device is transmitted to the control device, the instruction of the DC energy consumption device to consume active power will be updated based on step 2. The updated instruction value can be expressed as P ch_new =P ch -ΔP w , in order to achieve power balance within the DC system. After the output power of the offshore wind farm reaches the target value, the instructions executed by the energy consumption device will also drop to 0, and the energy consumption operation will be exited. During the entire process, after the flexible DC grid-connected system detects the frequency increase, the DC energy consumption device will be put into operation before the offshore wind farm. Utilizing the fast action characteristics of the DC energy consumption device, it quickly reduces the output power of the flexible DC grid-connected system, quickly maintains the power balance of the island power grid, and suppresses the frequency increase; after the offshore wind farm executes the active power reduction instruction, the DC energy consumption device and the offshore wind farm work together to maintain the flexible DC output power until the offshore wind farm power drops to the target value, and the DC energy consumption device exits operation.

[0109] In summary, the present invention aims to solve the problem that when the onshore AC power grid is decoupled and an island power grid is formed, which causes the frequency to rise, the offshore wind farm is decoupled from the onshore power grid and the communication link is long. The traditional response that relies on the power reduction of the offshore wind turbine cannot quickly suppress the frequency rise, thereby affecting the stability of the power grid. A flexible DC grid-connected system and an offshore wind farm collaborative control method are proposed. The method takes into account the specific working conditions of the onshore AC power grid being decoupled to form an island power grid. When the power generation output is greater than the load, the system can timely adjust the output power of the offshore wind power flexible DC grid-connected system through the coordinated control method to achieve continuous power balance and frequency stability support. The present invention establishes a relationship between the active power and frequency of the flexible DC grid-connected system. When the frequency rises, the DC energy consumption device quickly reduces the grid-connected power of the flexible DC system. In this process, the offshore wind farm control system will also reduce the output of the wind farm accordingly. Once the power of the wind farm is adjusted in place, the DC energy consumption device can be exited, so that the offshore wind power flexible DC grid-connected system can achieve rapid and continuous power regulation in the frequency rise range. Therefore, the present invention can effectively deal with the problem of onshore AC power grid frequency deviating from the normal range through a power coordination control method between DC energy consumption devices and offshore wind farms in a flexible DC grid-connected system, thereby ensuring the rapid and continuous power regulation capability of the offshore wind power flexible DC grid-connected system, thereby maintaining the power balance and frequency stability of the onshore island power grid under abnormal frequency conditions, and effectively maintaining the stable operation of the power grid.

[0110] Example 2:

[0111] Based on the same inventive concept, the present invention also provides a flexible DC grid-connected system and an offshore wind farm coordinated control system, the structural composition diagram of which is shown in FIG. Figure 9 Shown, including:

[0112] an onshore power calculation module, configured to determine a value of the onshore AC power grid to be reduced based on the calculated frequency of the onshore AC power grid when the onshore AC power grid is an island power grid and the power generation output of the onshore AC power grid is greater than the load;

[0113] A flexible DC power consumption module is used to calculate an active power command value to be consumed of a flexible DC grid-connected system connected to the onshore AC power grid according to the active power value to be reduced;

[0114] An offshore output reduction module is used to determine the output reduction difference of the offshore wind farm connected to the flexible DC grid-connected system according to the active power value to be reduced;

[0115] The collaborative control module is used to update the active power command value to be consumed based on the active power command value to be consumed of the flexible DC grid-connected system and the output reduction difference of the offshore wind farm, and to perform frequency response on the onshore AC power grid based on the updated active power command value to be consumed.

[0116] In one implementation, the above-mentioned onshore power calculation module may include:

[0117] A first range power calculation submodule is configured to set the active power value to be reduced of the onshore AC power grid to 0 when the calculated frequency of the onshore AC power grid is less than or equal to a preset frequency threshold;

[0118] a second range power calculation submodule, configured to, when the calculated frequency of the onshore AC power grid is greater than a frequency threshold and less than a set frequency upper limit, reduce the active power value of the onshore AC power grid to a set power consumption command value;

[0119] The third range power calculation submodule is configured to, when the calculated onshore AC grid-connected frequency is greater than the upper frequency limit, calculate the active power value to be reduced of the onshore AC grid to be the inverse of the rated power of the flexible DC grid-connected system.

[0120] For example, the expression for determining the active power value to be reduced of the above-mentioned onshore AC power grid is as follows:

[0121]

[0122] Where,

[0123] k=(0-P rate ) / (f max -f0);

[0124] Wherein, ΔP represents the active power value to be reduced in the onshore AC power grid; f represents the frequency of the onshore AC power grid; f0 represents the fundamental wave rated frequency; f deadIndicates the preset dead zone frequency; k indicates the proportional coefficient; f max Indicates the upper frequency limit; P rate Indicates the rated power of the flexible DC grid-connected system.

[0125] For example, the calculation formula corresponding to the active power command value to be consumed of the flexible DC grid-connected system can be as follows:

[0126]

[0127] Among them, P ch represents the active power command value to be consumed by the flexible DC grid-connected system; ΔP represents the active power value to be reduced in the onshore AC power grid; and P0 represents the transmission power of the flexible DC grid-connected system.

[0128] In one implementation, the offshore power reduction module may include:

[0129] The target power calculation submodule is used to calculate the target power value of the offshore wind farm according to the active power value to be reduced;

[0130] The output difference calculation submodule is used to obtain the output reduction difference of the offshore wind farm according to the difference between the target power value of the offshore wind farm and the obtained current output value of the offshore wind farm.

[0131] For example, the target power value of the offshore wind farm may be calculated as follows:

[0132]

[0133] Among them, P wtarget Represents the target power value of the offshore wind farm; P w0 represents the current output value of the offshore wind farm; ΔP represents the active power value to be reduced in the onshore AC power grid; and P1 represents a preset transmission power comparison value.

[0134] In one implementation, the collaborative control module may include:

[0135] The frequency interaction submodule is used to obtain a coordinated control frequency value by subtracting the active power command value to be consumed of the flexible DC grid-connected system from the output reduction difference of the offshore wind farm;

[0136] The frequency update submodule is used to use the coordinated control frequency value as the updated active power instruction value to be consumed.

[0137] Example 3:

[0138] like Figure 10As shown, the present invention also provides an electronic device, which may be a computer, a single-chip microcomputer, a smart mobile device, or the like. The electronic device in this embodiment may include a processor, a memory, a transceiver component, and the like. The memory, processor, and transceiver component are connected via a bus; the memory may be used to store an execution program, which may include instructions; and the processor may be used to execute the instructions stored in the memory. The memory may also be used to store data, which may be accessed and / or modified during the execution of the instructions.

[0139] The processor may be a central processing unit (CPU), or it may be other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, which is suitable for implementing one or more instructions, specifically suitable for loading and executing one or more instructions in the storage medium to implement the corresponding method flow or corresponding function, so as to realize the steps of a method for coordinated control of a flexible DC grid-connected system and an offshore wind farm in the above-mentioned embodiment.

[0140] Example 4:

[0141] Based on the same inventive concept, the present invention also provides a readable storage medium, specifically an electronic device readable storage medium (Memory), which is a memory device in an electronic device for storing programs and data. It can be understood that the storage medium here can include both built-in storage media in the electronic device and, of course, extended storage media supported by the electronic device. The storage medium provides a storage space, which stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by the processor are also stored in the storage space. These instructions can be one or more execution programs (including program codes). It should be noted that the storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk memory. The processor loads and executes one or more instructions stored in the storage medium, which can implement the steps of a method for coordinated control of a flexible DC grid-connected system and an offshore wind farm in the above embodiment.

[0142] It will be understood by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Thus, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0143] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowcharts and / or block diagrams. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0144] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0145] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0146] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit its scope of protection. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that after reading the present invention, those skilled in the art may still make various changes, modifications or equivalent substitutions to the specific implementation methods of the application, but these changes, modifications or equivalent substitutions are all within the scope of protection of the pending claims.

Claims

1. A method for collaborative control of a flexible DC grid-connected system and an offshore wind farm, characterized in that: include: When the onshore AC power grid is an island power grid and the power generation output of the onshore AC power grid is greater than the load, determining the active power value to be reduced of the onshore AC power grid according to the calculated frequency of the onshore AC power grid; Calculating an active power command value to be consumed of a flexible DC grid-connected system connected to the onshore AC power grid according to the active power value to be reduced; determining an output reduction difference of an offshore wind farm connected to the flexible DC grid-connected system according to the active power value to be reduced; The active power command value to be consumed is updated according to the active power command value to be consumed of the flexible DC grid-connected system and the output reduction difference of the offshore wind farm, and a frequency response is performed on the onshore AC power grid according to the updated active power command value to be consumed.

2. The method according to claim 1, wherein The determining, based on the calculated frequency of the onshore AC power grid, a value of active power to be reduced of the onshore AC power grid includes: When the calculated frequency of the onshore AC power grid is less than or equal to a preset frequency threshold, the active power value to be reduced of the onshore AC power grid is 0; When the calculated frequency of the onshore AC power grid is greater than the frequency threshold and less than the set frequency upper limit, the active power value to be reduced of the onshore AC power grid is the set power consumption command value; When the calculated frequency of the onshore AC grid is greater than the frequency upper limit, the active power value to be reduced of the onshore AC grid is the inverse of the rated power of the flexible DC grid-connected system.

3. The method according to claim 1, wherein The expression for determining the active power value to be reduced of the onshore AC power grid is as follows: Where, k=(0-P rate ) / (f max -f0); Wherein, ΔP represents the active power value to be reduced in the onshore AC power grid; f represents the frequency of the onshore AC power grid; f0 represents the fundamental wave rated frequency; f dead Indicates the preset dead zone frequency; k indicates the proportional coefficient; f max Indicates the upper frequency limit; P rate Indicates the rated power of the flexible DC grid-connected system.

4. The method according to claim 1, wherein The calculation formula corresponding to the active power command value to be consumed of the flexible DC grid-connected system is as follows: Among them, P ch represents the active power command value to be consumed by the flexible DC grid-connected system; ΔP represents the active power value to be reduced in the onshore AC power grid; and P0 represents the transmission power of the flexible DC grid-connected system.

5. The method according to claim 1, wherein The determining, based on the active power value to be reduced, an output reduction difference of the offshore wind farm connected to the flexible DC grid-connected system includes: Calculating a target power value of the offshore wind farm according to the active power value to be reduced; An output reduction difference of the offshore wind farm is obtained according to a difference between the target power value of the offshore wind farm and the acquired current output value of the offshore wind farm.

6. The method according to claim 5, wherein The calculation formula corresponding to the target power value of the offshore wind farm is as follows: Among them, P wtarget Represents the target power value of the offshore wind farm; P w0 represents the current output value of the offshore wind farm; ΔP represents the active power value to be reduced in the onshore AC power grid; and P1 represents a preset transmission power comparison value.

7. The method according to claim 1, wherein The updating of the active power command value to be consumed according to the active power command value to be consumed of the flexible HVDC grid-connected system and the output reduction difference of the offshore wind farm includes: Subtracting the active power command value to be consumed of the flexible DC grid-connected system from the output reduction difference of the offshore wind farm to obtain a coordinated control frequency value; The coordinated control frequency value is used as the updated active power command value to be consumed.

8. A flexible DC grid-connected system and offshore wind farm coordinated control system, characterized in that: include: an onshore power calculation module, configured to determine, when the onshore AC power grid is an island power grid and the power generation output of the onshore AC power grid is greater than the load, a value of the onshore AC power grid's active power to be reduced based on the calculated frequency of the onshore AC power grid; a flexible direct current power consumption module, configured to calculate an active power command value to be consumed of a flexible direct current grid-connected system connected to the onshore alternating current grid according to the active power value to be reduced; an offshore output reduction module, configured to determine an output reduction difference of an offshore wind farm connected to the flexible DC grid-connected system according to the active power value to be reduced; A collaborative control module is configured to update the active power command value to be consumed based on the active power command value to be consumed of the flexible DC grid-connected system and the output reduction difference of the offshore wind farm, and perform frequency response on the onshore AC power grid based on the updated active power command value to be consumed.

9. An electronic device, characterized in that: include: at least one processor and memory; The memory and the processor are connected via a bus; The memory is used to store one or more programs; When the one or more programs are executed by the at least one processor, a coordinated control method of a flexible DC grid-connected system and an offshore wind farm according to any one of claims 1 to 7 is implemented.

10. A computing device readable storage medium, characterized in that: An execution program is stored thereon, and when the execution program is executed, a coordinated control method of a flexible direct current grid-connected system and an offshore wind farm according to any one of claims 1 to 7 is implemented.

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