Wind power ac fault ride-through method, device and equipment under hybrid architecture and medium

Abstract

The application discloses a wind power AC fault ride-through method under a hybrid architecture, relates to the technical field of new energy grid connection and high-voltage direct current transmission, and is used for solving the problem that existing methods cannot be stably controlled. The method comprises the following steps: a fault transient state analysis model of the offshore wind power system is constructed and is used for analyzing voltage support capability; the voltage of an offshore AC bus is detected in real time, and an AC fault stage is judged; when the fault stage belongs to a fault period, a wind turbine generator unit grid-connected converter and a wind farm side MMC are controlled to switch to a fixed AC current control mode, and an AC fault current is injected; when the fault stage belongs to a fault recovery period, a current amplitude limiting value is controlled by the wind turbine generator unit grid-connected converter, and the current amplitude limiting value is gradually recovered to a steady-state amplitude limiting value. The application further discloses a wind power AC fault ride-through device under a hybrid architecture, an electronic device and a computer storage medium. Through cooperative control, the application realizes smooth and impact-free transition from fault ride-through to steady-state operation.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of new energy grid connection and high-voltage direct current transmission technology, and particularly relates to a wind power alternating current fault ride-through method and device under a hybrid architecture, equipment and a medium. BACKGROUND

[0002] The traditional alternating current transmission mode is susceptible to factors such as capacitive effect, reactive power limitation and poor voltage stability in long-distance scenarios, and is difficult to meet the requirements of efficient and reliable power transmission. The existing technology begins to use high-voltage direct current transmission (HVDC) as a power transmission mode.

[0003] Compared with the traditional transmission mode, high-voltage direct current transmission (HVDC) has advantages such as low loss, long transmission distance and controllable power flow, and has become the mainstream transmission technology for offshore wind power. Among many HVDC schemes, the flexible direct current transmission system (VSC-HVDC) based on modular multilevel converter (MMC) has the ability to adjust reactive power, grid black start and rapid control, and the technology is mature, but the construction cost of the offshore converter station is high, the structure is complex, and the operation and maintenance burden is large, which restricts its large-scale promotion. In recent years, in order to improve the economy, a scheme of "diode rectifier unit (DRU) + MMC" hybrid transmission architecture has been proposed. This scheme uses DRU to bear most of the active power transmission, and a small-capacity wind farm side MMC (WFMMC) is connected in parallel for voltage support, reactive power compensation and harmonic control, and takes into account the control ability and system cost, and has become an important development direction for medium and long-distance wind power transmission.

[0004] However, the hybrid architecture faces severe challenges under alternating current fault conditions, and its operating characteristics are fundamentally different from those of traditional VSC-HVDC systems.

[0005] Insufficient voltage support during faults: DRU is a passive device, and its commutation process is highly dependent on the alternating current bus voltage. Once a short-circuit fault occurs in the system, causing a voltage drop, the DRU will immediately lock out and exit operation, and cannot provide any fault current. At this time, the voltage stability of the entire offshore alternating current system completely depends on the fault current injection capability of the GSC and WFMMC. If the support is insufficient, the bus voltage will collapse, causing the system to be disconnected.

[0006] There is a risk of instability in the fault recovery phase: after the fault is cleared, the system enters the recovery phase. The output of the wind turbine can be quickly restored due to its small inertia, while the recovery of the DRU lags behind the reconstruction of the alternating current voltage. This asynchronous power recovery causes a large amount of surplus power to flow into the WFMMC, which can easily cause its alternating current to quickly reach the controller amplitude limit and saturate. Once the WFMMC is saturated, it will lose its voltage regulation capability, which may cause a secondary drop or sustained oscillation of the alternating current voltage, seriously hindering the smooth recovery of the system.

[0007] In summary, the existing scheme fails to systematically consider GSC and WFMMC as a unified fault support whole, cannot maximize the utilization of the overall current injection margin of the system, generally ignores the power dynamic balance problem between GSC and WFMMC in the fault recovery stage, and fails to design an effective cooperative recovery strategy to fundamentally avoid the saturation out of control of WFMMC.

[0008] Therefore, the prior art cannot meet the whole-process stability control requirements of the DRU-MMC hybrid architecture under AC fault for "ride-through" and "recovery". A complete, phase-adaptive cooperative ride-through control strategy is urgently needed to solve the above-mentioned inherent defects and ensure the safe and stable operation of the offshore wind power transmission system. SUMMARY

[0009] In order to overcome the deficiencies of the prior art, one of the purposes of the present application is to provide a wind power AC fault ride-through method under a hybrid architecture, which adopts GSC and WFMMC cooperative constant current support to ride through the fault, and adopts GSC ramp recovery to smoothly transition, realizing the whole-process stability of the system from fault to recovery.

[0010] One of the purposes of the present application is achieved by adopting the following technical solutions:

[0011] A wind power AC fault ride-through method under a hybrid architecture, comprising the following steps:

[0012] A fault transient analysis model of the offshore wind power system is constructed, which is used to analyze the voltage support capability of the diode converter DRU, the wind turbine grid-connected converter GSC and the wind farm side MMC to the offshore AC bus under three-phase symmetrical AC fault;

[0013] The voltage of the offshore AC bus is detected in real time, and the AC fault stage is judged according to the voltage;

[0014] When the fault stage belongs to the fault period, the wind turbine grid-connected converter and the wind farm side MMC are controlled to switch to the constant AC current control mode and inject AC fault current to support the voltage of the offshore AC bus;

[0015] When the fault stage belongs to the fault recovery period, the current amplitude limiting value is gradually recovered to the steady-state amplitude limiting value through the wind turbine grid-connected converter control. The method provides a complete, cooperative and phased fault ride-through solution, which fundamentally solves the two core problems of voltage collapse and recovery instability faced by the DRU-MMC hybrid architecture under AC fault.

[0016] Further, in order to provide accurate theoretical basis and design basis for the control strategy, the fault transient analysis model of the offshore wind power system includes a fault voltage analytical mathematical model and a fault power balance model established based on the topological parameters of the offshore wind power system.

[0017] Further, the voltage support capability is specified and quantified, and the calculation of the voltage support capability includes:

[0018]

[0019] wherein, and are the DC side current and voltage of the DRU respectively, and are the DC voltage of the upper and lower bridge arms of the DRU respectively, is the commutation reactance of the DRU converter, is the transformer ratio, indicates the on state of the DRU, is the PCC voltage, is the onshore MMC DC side voltage, is the wind farm MMC DC current, is the submarine DC cable resistance, is the active power absorbed by the short circuit point, and indicate the fault current provided by the DRU, the wind farm MMC and the wind farm respectively, indicates the fault grounding resistance.

[0020] Further, the AC fault stage is determined according to the voltage, including:

[0021] detecting the RMS of the offshore AC bus;

[0022] when the RMS is less than a first threshold, it is determined that a fault occurs;

[0023] calculating the rising rate according to the RMS, if the rising rate is greater than a second threshold, it is determined that it is during the fault recovery, otherwise it is during the fault. Using the voltage RMS as the criterion, the anti-interference ability is strong, the detection is reliable, and the "voltage rising rate" is introduced as the criterion of the recovery stage, which can sensitively and quickly identify the fault clearing moment, ensure that the system can be switched from "support mode" to "recovery mode" in time, and avoid slow recovery or misoperation caused by delay in judgment.

[0024] Further, the rising rate is calculated by sampling time and sampling frequency, and the calculation satisfies:

[0025] wherein, is the rising rate, indicates the sampling time, indicates the sampling frequency, indicates the RMS of the offshore AC bus voltage. ​​

[0026] Further, when the fault phase belongs to the fault period, the wind turbine grid-connected converter and the wind farm side MMC are switched to the fixed AC current control mode, and the AC fault current is injected to support the voltage of the offshore AC bus, including: freezing the steady-state power outer loop control of the wind turbine grid-connected converter GSC and the wind farm side MMC, and enabling the inner loop fixed AC current controller during the fault period;

[0027] Wherein, the current limiting value of the wind turbine grid-connected converter GSC is set to K vmax times of the rated steady-state value; the current limiting value of the fixed AC current control of the wind farm side MMC is set to K mvq times of the rated steady-state value, K vmax and K mvq is a proportional coefficient.

[0028] The current potential of the GSC and the WFMMC power electronic devices is fully and safely tapped, and the maximum possible support strength is provided for the bus voltage within the safe range of the equipment.

[0029] Further, when the fault phase belongs to the fault recovery period, the current limiting value of the wind turbine grid-connected converter is gradually restored to the steady-state limiting value, including: the wind turbine grid-connected converter GSC remains in the fixed AC control, and the current limiting value is linearly increased from the initial value according to the preset lifting rate until it is restored to the steady-state limiting value. The smooth and controlled recovery of the GSC output is realized.

[0030] The second purpose of the present application is to provide a wind power AC fault ride-through device under a hybrid architecture, which cooperatively supports the current of the GSC and the wind farm side MMC during the fault period, and the GSC slope limiting value is recovered during the recovery period, solving the problem of voltage collapse and MMC saturation instability of the DRU-MMC hybrid architecture under AC fault.

[0031] The second purpose of the present application is achieved by the following technical solutions:

[0032] A wind power AC fault ride-through device under a hybrid architecture, comprising:

[0033] An analysis module for constructing a fault transient analysis model of an offshore wind power system to analyze the voltage support capability of a diode rectifier DRU, a wind turbine grid-connected converter GSC and a wind farm side MMC for an offshore AC bus under three-phase symmetrical AC fault;

[0034] A detection module for real-time detection of the voltage of the offshore AC bus, and judging the AC fault phase according to the voltage;

[0035] a processing module configured to control the wind turbine grid-connected converter and the wind farm side MMC to switch to a fixed AC current control mode and inject an AC fault current to support the voltage of the offshore AC bus when the fault stage belongs to a fault period, and gradually recover the current limiting value to a steady-state limiting value through the wind turbine grid-connected converter when the fault stage belongs to a fault recovery period.

[0036] A third object of the present application is to provide an electronic device for implementing one of the above-mentioned wind power AC fault ride-through methods under a hybrid architecture, which comprises a processor, a storage medium and a computer program stored in the storage medium and executable by the processor.

[0037] A fourth object of the present application is to provide a computer-readable storage medium storing one of the above-mentioned wind power AC fault ride-through methods under a hybrid architecture.

[0038] Compared with the prior art, the present application has the following advantages:

[0039] The present application utilizes the coordinated current injection of the wind turbine and the wind farm side MMC to compensate for the failure during the DRU fault period, improve the system fault ride-through capability, avoid the current saturation risk of the MMC through the current recovery limiting, ensure the smooth recovery of the AC bus voltage, and form a closed-loop control from the fault occurrence to the complete recovery through the coordinated maximum current support of the GSC of the wind turbine and the WFMMC during the fault period and the slope limiting recovery of the GSC during the recovery period, effectively preventing the bus voltage collapse and system oscillation instability, and ensuring the safe and stable operation of the offshore wind power transmission system under fault conditions; during the fault period, the GSC and the WFMMC are controlled to switch to a fixed AC current control mode, integrating the originally independent two converters into a unified and powerful fault support source, this coordinated current injection strategy not only compensates for the support gap caused by the lack of DRU, but also fully utilizes the current output potential of the entire system, achieving the most effective support for the AC bus voltage; in addition, the present application introduces a precise identification of the fault recovery stage based on the voltage rise rate, and combines the slope recovery mechanism of the GSC current limiting value to balance the recovery speed and control stability. This design not only avoids the impact of the rapid recovery of the GSC power on the WFMMC and prevents its current saturation out of control, but also ensures that the system power can return to the steady state at the fastest and safest speed, realizing a smooth and impact-free transition from fault ride-through to steady-state operation. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 is the DRU-MMC hybrid offshore wind power transmission system topology of the present application;

[0041] Figure 2 is a flow chart of a wind power AC fault ride-through method under the hybrid architecture of embodiment one;

[0042] Figure 3 is a fixed AC current control block diagram during fault ride-through of WTG SC of embodiment one;

[0043] Figure 4 is a fixed AC current control block diagram during fault ride-through of WFMMC of embodiment one;

[0044] Figure 5 is a simulation result diagram of the fault transient response of the DRU-MMC hybrid offshore wind power transmission system under the proposed fault ride-through strategy of embodiment two;

[0045] Figure 6 is a structural block diagram of a wind power AC fault ride-through device under the hybrid architecture of embodiment three;

[0046] Figure 7 is a structural block diagram of an electronic device of embodiment four. DETAILED DESCRIPTION

[0047] The application will be described in more detail below with reference to the accompanying drawings, and it should be noted that the following description of the application with reference to the accompanying drawings is merely illustrative and not limiting. The various embodiments can be combined with each other to form other embodiments not shown in the following description.

[0048] Embodiment one

[0049] Embodiment one provides a wind power AC fault ride-through method under a hybrid architecture, which aims to support through GSC and WFMMC, and cooperate with the linkage control strategy of GSC ramp recovery, to solve the two core problems of “inability to support” during fault and “easy instability” during recovery of the DRU-MMC hybrid architecture, and to realize safe and stable operation of the system from fault ride-through to smooth recovery.

[0050] In view of the problems of weak bus voltage support capability, failure of diode uncontrolled rectifier unit (DRU), and saturation of modular multilevel converter (MMC) current of the existing offshore wind power transmission system under the DRU-MMC hybrid architecture under AC fault conditions, the embodiment proposes a cooperative ride-through control strategy for offshore wind power AC faults under the hybrid DRU-MMC architecture. This method can realize coordinated injection of current by wind turbine generators and WFMMC during faults, thereby providing support for the offshore AC system during faults, and can avoid WFMMC AC current from reaching the amplitude saturation during fault recovery, so as to realize smooth and rapid recovery from faults, and has good engineering practicability and system compatibility.

[0051] Referring to Figure 1 Fig. 1 shows a DRU-MMC hybrid offshore wind power transmission system topology and Figure 2 Fig. 2 shows a flow chart, wherein the offshore grid-connected wind farm is composed of permanent magnet synchronous machines and back-to-back wind turbine converters, the offshore converter station is composed of large-capacity DRUs and small-capacity auxiliary WFMMCs, the DC line adopts submarine high-voltage DC cables, and the onshore inverter station is composed of large-capacity MM Cs. A wind power AC fault ride-through method under a hybrid architecture includes the following steps:

[0052] S1, a fault transient analysis model of the offshore wind power system is constructed, which is used to analyze the voltage support capability of the diode converter DRU, the grid-connected converter GSC of the wind turbine and the WFMMC on the offshore AC bus under three-phase symmetrical AC fault;

[0053] The fault transient analysis model of the offshore wind power system in S1 includes a fault voltage analytical mathematical model and a fault power balance model established based on the topology parameters of the offshore wind power system. The WFMMC DC side and AC side at the offshore wind power collection bus are connected in parallel with the diode valve, the DC side is connected to the onshore AC grid side MMC (GSMMC) through the DC submarine cable, the steady-state active power is transmitted by the diode valve, and the WFMMC provides reactive power support and AC filtering effect. Specifically, the fault voltage analytical mathematical model and the fault power balance model of the offshore AC system are established. By using circuit analysis theories such as Kirchhoff's voltage law and Kirchhoff's current law on the system after the fault, the fault voltage analytical mathematical model and the fault power balance model of the offshore AC system can be obtained. The support capability of the DRU, the GSC and the WFMMC on the bus voltage during the fault under three-phase symmetrical fault is analyzed in combination with the unidirectional current flow characteristic of the DRU:

[0054] ,

[0055] wherein, and are the DC side current and voltage of the DRU, and are the DC voltages of the upper and lower bridge arms of the DRU, is the commutation reactance of the DRU converter, is the transformer ratio, represents the conduction state of the DRU, is the PCC voltage, is the onshore MMC DC side voltage, is the wind farm MMC DC current, is the submarine DC cable resistance, is the active power absorbed by the short-circuit point, , and respectively represent the fault current provided by the DRU, the wind farm MMC and the wind farm, represents the fault grounding resistance.

[0056] S2, real-time detection of the voltage of the offshore AC bus, determining the AC fault stage according to the voltage;

[0057] S2, determining the AC fault stage according to the voltage, comprising:

[0058] detecting the effective value of the offshore AC bus;

[0059] When the effective value is less than the first threshold value, it is determined that a fault occurs;

[0060] According to the effective value, if the rising rate is greater than the second threshold value, it is determined that it is in the fault recovery period, otherwise it is in the fault period.

[0061] The effective value of the AC bus mentioned above can be directly detected by a voltage measuring device, which will not be described here. The first threshold value is selected as 0.8 in this embodiment, and can also be set according to the actual situation, and is not limited to the selection of this embodiment. The effective value of the AC bus voltage The rising rate greater than the second threshold value should be determined according to the sampling frequency of the control system and the specific parameters of the project, and the specific value of the second threshold value is not limited in this embodiment.

[0062] The rising rate is calculated by sampling time and sampling frequency, which satisfies:

[0063] , wherein, is the rising rate, represents the sampling time, represents the sampling frequency, represents the effective value of the offshore AC bus voltage.

[0064] S21, when the fault stage belongs to the fault period, controlling the wind turbine generator set grid-connected converter and the wind farm side MMC to switch to the constant AC current control mode, and injecting the AC fault current to support the voltage of the offshore AC bus;

[0065] In S21, the steady-state power outer loop control of the wind turbine generator set GSC (WTGSC) and the wind farm side MMC (WFMMC) is frozen during the fault period, and the constant AC current control module as shown in Figure 3 and Figure 4 is used for constant AC current control. Figure 3 In the formula, WTGSC represents the wind turbine generator set GSC, I vmax represents the maximum value of the GSC current amplitude, I vN represents the rated value of the GSC current amplitude, and Ug represents the effective value of the offshore AC bus voltage, and respectively represent the d-axis current and q-axis current command values of the GSC, K vq represents the reactive current proportion coefficient of the GSC, which can be set according to the actual scene combined with simulation, and is generally not more than 1.5, Figure 3 SPWM in the formula (1) represents SPWM modulation. Figure 4 MMC in the formula (2) refers to the wind farm side MMC, I mvN represents the WFMMC current amplitude rated value, Ug represents the offshore AC bus voltage effective value, and respectively represent the d-axis current and q-axis current command values of the WFMMC, K mvq represents the reactive current proportion coefficient of the WFMMC, which can be set according to the actual scene combined with simulation, and is generally not more than 1.5, Figure 4 NLM in the formula (3) represents nearest level modulation. The current amplitude limit value of the wind turbine GSC constant AC current control is set to K vmax times of the rated steady-state value, and the current amplitude limit value of the WFMMC constant AC current control is set to K mvq times of the rated steady-state value. The proportion coefficient K vmax and K mvq is less than the maximum tolerable current threshold of the power electronic device in the GSC and the maximum tolerable current threshold of the power electronic device in the WFMMC ; the minimum value of the proportion coefficient K vmax and K mvq is and According to the actual engineering requirement of the reactive power support capacity provided combined with simulation analysis:

[0066] ,

[0067] Figure 3 and Figure 4In the shown direct alternating current control module, the d / q axis component distribution method of the alternating current reference value is as follows: first, the q-axis current reference value is given according to the minimum q-axis current limit specified in the national standard, then the d-axis current reference value is solved according to the relationship that the square of the current limit value is equal to the sum of the squares of the d / q axis currents, then the d / q axis current reference values are input into the inner loop current controller, the current controller adopts proportional-integral control, controls the valve side alternating current of the converter transformer to track the current command value, and generates the differential mode voltage command value of the converter, finally the differential mode voltage command value is sent to the modulation module to generate the valve switch signal, wherein the fan converter adopts SPWM modulation, and the WFMMC adopts nearest level approximation modulation (NLM).

[0068] S22, when the fault stage belongs to the fault recovery period, the current limit value is gradually restored to the steady-state limit value through the wind turbine generator set grid-connected converter.

[0069] In S22, when the fault stage belongs to the fault recovery period, the current limit value is gradually restored to the steady-state limit value through the wind turbine generator set grid-connected converter, including: the wind turbine generator set grid-connected converter GSC remains direct alternating current control, the current limit value starts from an initial value and increases linearly at a preset boost rate until it is restored to the steady-state limit value. During the recovery period, the wind turbine generator set GSC still adopts direct alternating current control, and the limit value is increased through a ramp-up link K vmax0 The steady-state limit value is increased at a boost rate K vimax The steady-state limit value is gradually restored, and the proportional coefficient in the parameter of the ramp-up link K vmax0 And the boost rate K vimax According to the principle of not reaching the limit saturation of the WFMMC alternating current during the recovery period while accelerating the fault recovery speed as much as possible, the parameters are selected through simulation analysis.

[0070] Embodiment two

[0071] Embodiment two is a specific simulation description of the method of embodiment one.

[0072] The sending-out system involved in this embodiment includes a wind turbine generator set, a wind farm side modular multilevel converter (WFMMC), a diode rectifier unit (DRU), a submarine DC cable, a land side converter (GSMMC), and a land alternating current grid. The DRU and the WFMMC are connected in parallel at the alternating current side and the direct current side, the DRU is responsible for transmitting all active power, and the WFMMC undertakes the task of reactive power support and alternating current filtering. The system parameters of the DRU-MMC hybrid offshore wind power sending-out system are shown in Table 1:

[0073] Table 1

[0074]

[0075] The offshore AC three-phase short-circuit fault ride-through strategy in the DRU-MMC hybrid offshore wind power transmission system is designed according to the following method:

[0076] (1) When a three-phase symmetrical fault occurs in the offshore AC system, the DRU cannot commutate due to the one-way conduction characteristic of the diode, and the output current quickly drops to zero. The fault current of the AC system completely depends on the output of the wind turbine generator system (GSC) and the WFMMC. Therefore, a fault transient analysis model needs to be established, considering the irreversible conduction characteristics of the DRU, the power response characteristics of the wind power side, and the current control characteristics of the MMC. The analytical expression of the relationship between the PCC voltage and the injected current is constructed, and the system power balance equation is established by combining the cable resistance, the MMC DC voltage, and the wind turbine output power modeling system, providing a mathematical basis for subsequent controller design.

[0077] (2) Since the correct implementation of system fault ride-through is based on accurate determination of the system state, real-time detection of the offshore AC bus voltage is required to determine whether an AC fault has occurred and whether it has entered the fault recovery phase.

[0078] When the voltage is less than 0.8 p.u., it is determined that the system has entered a fault state. Based on this, if the voltage recovery rate exceeds the threshold K t , it is determined that the fault has been cleared and the recovery control phase is switched to. The above voltage recovery rate threshold K t can be set in combination with the controller sampling period and simulation analysis results, and is usually in the range of 1-15 kV / ms in engineering applications.

[0079] (3) After the fault occurs, the GSC and WFMMC of the wind turbine will freeze their steady-state active and reactive power outer loop control logic, and switch to a constant AC current control mode. At this time, the current reference limit value of the wind power GSC is set to K vmax times its rated steady-state value, and the current limit value of the WFMMC is set to K mvq times its rated value, K vmax and K mvqThe value range of the amplitude limit value should meet the maximum allowable current of the internal power electronic devices of each converter, and the minimum value under the condition of meeting the minimum reactive power support capability is determined through simulation. The controller adopts a fixed amplitude and phase current control structure, and the d / q axis reference value distribution mode of the alternating current is that under the premise of meeting the minimum reactive power injection ratio of the q axis specified in the national standard, the remaining current is distributed to the d axis to improve the bus voltage support capability during the fault as much as possible. The GSC and the WFMMC cooperatively output alternating currents with as similar phase as possible to jointly support the PCC voltage and realize system fault stable crossing.

[0080] (4) After the fault is cleared, the system enters the recovery phase. In this phase, the GSC of the wind turbine remains in the constant alternating current control mode, but the amplitude limit value is gradually increased from the initial value during the fault K vmax0 times the steady-state current, and is gradually restored to the normal steady-state current through a ramp-up module at a set ramp-up rate. K vimax K vmax0 K vimax The setting of the above parameters needs to ensure that the WFMMC does not enter the amplitude saturation state during the entire recovery process, so as to always maintain its voltage source characteristics and bus voltage building capability, and complete the fault recovery of the system in the shortest time. The above parameters can be optimized through electromagnetic transient simulation, taking into account the fault recovery speed and stability.

[0081] Based on the simulation model built based on the parameters in Table 1, a metallic offshore alternating current three-phase symmetrical short circuit is set to occur at t=2.0s, and the fault is cleared at t=2.2s. The simulation results are as follows Figure 5 , Figure 5 (a) in FIG. 1 shows the three-phase instantaneous value of the offshore alternating bus voltage, Figure 5 (b) in FIG. 1 shows the effective value of the offshore alternating bus voltage, Figure 5 (a) in FIG. 1 shows the three-phase component of the grid-side voltage, the blue line represents the instantaneous voltage of the offshore grid-side alternating bus A phase, the orange line represents the instantaneous voltage of the B phase, and the yellow line represents the instantaneous voltage of the C phase, Figure 5 (c) and (d) in FIG. 1 respectively show the active power and the reactive power of the DRU, the offshore MMC and the wind farm WF, Figure 5 (e) and (f) in FIG. 1 respectively show the DC side voltage and the DC side current of the offshore and land MMCs and the DRU. Figure 5 The electromagnetic transient simulation results of (f) in FIG. 1 for the AC side current of the DRU show that after the occurrence of the metallic AC three-phase short circuit, the AC current of the DRU rapidly decreases to zero and does not provide any fault current during the entire fault period, verifying the constructed fault characteristic model. In addition, Figure 5 ​​The transient simulation result of the offshore AC bus voltage shows that under the proposed fault ride-through control strategy, the offshore PCC voltage is effectively supported during the fault, and the current reference value of the MMC controller does not reach the saturation limit value during the fault recovery stage, and the system realizes a fast and stable fault recovery process, further verifying the effectiveness of the strategy.

[0082] Embodiment three

[0083] Embodiment three discloses a device corresponding to the wind power AC fault ride-through method under the hybrid architecture of the above-mentioned embodiment, for the virtual device structure of the above-mentioned embodiment, please refer to Figure 6 , which comprises:

[0084] The analysis module 310 is configured to construct a fault transient analysis model of the offshore wind power system to analyze the voltage support capability of the diode converter DRU, the grid-side converter GSC and the wind farm side MMC to the offshore AC bus under three-phase symmetrical AC fault.

[0085] The detection module 320 is configured to detect the voltage of the offshore AC bus in real time, and determine the AC fault stage according to the voltage.

[0086] The processing module 330 is configured to control the grid-side converter and the wind farm side MMC to switch to the fixed AC current control mode and inject AC fault current to support the voltage of the offshore AC bus when the fault stage belongs to the fault period, and gradually recover the current limiting value to the steady-state limiting value through the grid-side converter when the fault stage belongs to the fault recovery period.

[0087] Preferably, the fault transient analysis model of the offshore wind power system comprises a fault voltage analytical mathematical model and a fault power balance model established based on the topological parameters of the offshore wind power system.

[0088] Preferably, the calculation of the voltage support capability comprises:

[0089]

[0090] wherein, and are the DC side current and voltage of the DRU, and are the DC voltages of the upper and lower bridge arms of the DRU, is the commutation reactance of the DRU converter, is the transformer ratio, represents the conduction state of the DRU, is the PCC voltage, is the DC side voltage of the onshore MMC, is the DC current of the wind farm MMC,​ Rsea is the resistance of the submarine DC cable, Pabs is the active power absorbed by the short circuit point, , and I DRU, I MMC and I WFC represent the fault current provided by the DRU, the wind farm MMC and the wind farm respectively, Rg represents the fault ground resistance.

[0091] Preferably, determining the AC fault phase according to the voltage comprises:

[0092] detecting the RMS of the offshore AC bus;

[0093] determining that a fault occurs when the RMS is less than a first threshold value;

[0094] calculating a rising rate according to the RMS, and determining that the fault recovery period if the rising rate is greater than a second threshold value, otherwise the fault period.

[0095] Preferably, the rising rate is calculated by sampling time and sampling frequency, and the calculation satisfies:

[0096] wherein, r is the rising rate, t is the sampling time, f is the sampling frequency, V is the RMS of the offshore AC bus voltage.

[0097] Preferably, when the fault phase belongs to the fault period, controlling the wind turbine grid-connected converter and the wind farm side MMC to switch to the fixed AC current control mode and inject the AC fault current to support the voltage of the offshore AC bus comprises: freezing the steady-state power outer loop control of the wind turbine grid-connected converter GSC and the wind farm side MMC, and enabling the inner loop fixed AC current controller during the fault period;

[0098] wherein the current limiting value of the wind turbine grid-connected converter GSC is set to K vmax times of its rated steady-state value; and the current limiting value of the fixed AC current control of the wind farm side MMC is set to K mvq times of its rated steady-state value, K vmax and K mvq k is a proportional coefficient.

[0099] Preferably, when the fault stage belongs to the fault recovery period, the current limit value gradually recovers to the steady-state limit value through the wind turbine grid-connected converter, including: the wind turbine grid-connected converter GSC keeps the fixed AC control, and the current limit value starts from an initial value and linearly increases at a preset increasing rate until it recovers to the steady-state limit value.

[0100] Embodiment four

[0101] Figure 7 A structural schematic diagram of an electronic device provided for embodiment four of the present application is shown in the figure, which includes a processor 410, a memory 420, an input device 430 and an output device 440; the number of processors 410 in the computer device can be one or more, Figure 7 and an example of one processor 410 is taken in the figure; the processor 410, the memory 420, the input device 430 and the output device 440 in the electronic device can be connected through a bus or other means, Figure 7 and an example of connection through a bus is taken in the figure. Figure 7

[0102] The memory 420 as a kind of computer readable storage medium can be used to store software programs, computer executable programs and modules, such as program instructions / modules of the wind power AC fault ride-through method under the hybrid architecture in the embodiment of the present application. The processor 410 executes the software programs, instructions and modules stored in the memory 420, thereby performing various functional applications and data processing of the electronic device, i.e. implementing the wind power AC fault ride-through method under the hybrid architecture of the above-mentioned embodiment one to embodiment two.

[0103] The memory 420 can mainly include a program storage area and a data storage area, wherein the program storage area can store an operating system and at least one application program required by a function; the data storage area can store data created according to the use of the terminal, etc. In addition, the memory 420 can include a high-speed random access memory, and can also include a non-volatile memory, such as at least one magnetic disk storage device, a flash memory device, or other non-volatile solid-state storage device. In some examples, the memory 420 can further include a memory remotely arranged with respect to the processor 410, which can be connected to the electronic device through a network. Examples of the above-mentioned network include but are not limited to the Internet, an intranet, a local area network, a mobile communication network and a combination thereof.

[0104] The input device 430 can be used to receive input user identity information, offshore wind power system data, etc. The output device 440 can include a display device such as a display screen.

[0105] Embodiment five

[0106] ​The fifth embodiment of the present application also provides a storage medium containing computer executable instructions, which can be used for a computer to execute the wind power AC fault ride-through method under a hybrid architecture, and the method comprises the following steps of:

[0107] constructing a fault transient analysis model of the offshore wind power system, for analyzing voltage support capabilities of the diode rectifier (DRU), the wind turbine grid-connected converter (GSC) and the wind farm side MMC to the offshore AC bus under three-phase symmetric AC faults;

[0108] detecting a voltage of the offshore AC bus in real time, and determining an AC fault stage according to the voltage;

[0109] when the fault stage belongs to a fault period, controlling the wind turbine grid-connected converter and the wind farm side MMC to switch to a fixed AC current control mode and inject an AC fault current to support the voltage of the offshore AC bus;

[0110] when the fault stage belongs to a fault recovery period, gradually recovering a current limiting value controlled by the wind turbine grid-connected converter to a steady-state limiting value.

[0111] Of course, the computer executable instructions of the storage medium provided by the embodiment of the present application are not limited to the method operations described above, and can also perform related operations in the wind power AC fault ride-through method under the hybrid architecture provided by any embodiment of the present application.

[0112] From the above description of the embodiments, those skilled in the art can clearly understand that the present application can be realized by means of software and necessary general hardware, and of course can also be realized by hardware, but in many cases the former is a better embodiment. Based on this understanding, the technical solutions of the present application or the parts that contribute to the prior art can be embodied in the form of a software product, which can be stored in a computer readable storage medium, such as a floppy disk, a read-only memory (ROM), a random access memory (RAM), a FLASH, a hard disk or an optical disk, etc., including a plurality of instructions to make an electronic device (which can be a mobile phone, a personal computer, a server or a network device, etc.) execute the method described in each embodiment of the present application.

[0113] It is worth noting that in the above embodiments of the wind power AC fault ride-through method and device under the hybrid architecture, each unit and module is only divided according to the functional logic, but is not limited to the above division, as long as the corresponding functions can be realized; in addition, the specific names of each functional unit are only for easy distinction, and do not limit the protection scope of the present application.

[0114] As can be apparent to those skilled in the art in the light of the foregoing description, all the changes and modifications of the technical solutions and concepts described above can be made, and all these changes and modifications shall fall within the scope of protection of the claims of the present application.

Claims

1. A wind power AC fault ride-through method under a hybrid architecture, characterized in that, Includes the following steps: A fault transient analysis model of an offshore wind power system is constructed to analyze the voltage support capability of the diode converter (DRU), the grid-connected converter (GSC) of the wind turbine, and the wind farm-side converter (MMC) to the offshore AC bus under a three-phase symmetrical AC fault. The voltage of the offshore AC bus is monitored in real time, and the AC fault stage is determined based on the voltage. When the fault stage is during a fault period, the grid-connected converter of the wind turbine and the MMC on the wind farm side are switched to constant AC current control mode, and AC fault current is injected to support the voltage of the offshore AC bus. When the fault stage is within the fault recovery period, the current limit value of the wind turbine grid-connected converter is gradually restored to the steady-state limit value.

2. The wind power AC fault ride-through method under a hybrid architecture as described in claim 1, characterized in that, The fault transient analysis model of the offshore wind power system includes an analytical mathematical model of fault voltage and a fault power balance model established based on the topology parameters of the offshore wind power system.

3. The wind power AC fault ride-through method under a hybrid architecture as described in claim 1 or 2, characterized in that, The calculation of voltage support capability includes: ， in, and These are the DC-side current and voltage of the DRU, respectively. and These are the DC voltages of the upper and lower bridge arms of the DRU, respectively. For the commutation reactance of the DRU converter, For transformer turns ratio, This indicates the on / off state of the DRU. PCC voltage, This refers to the DC-side voltage of the onshore MMC. For wind farm MMC DC current, For the resistance of the submarine DC cable, Active power absorbed at the short-circuit point , and These represent the fault currents supplied by the DRU, the wind farm MMC, and the wind farm, respectively. This indicates the fault grounding resistance.

4. The wind power AC fault ride-through method under a hybrid architecture as described in claim 1, characterized in that, Determining the AC fault stage based on the voltage includes: Detect the effective value of marine AC busbars; When the effective value is less than the first threshold, it is determined that a fault has occurred; The rise rate is calculated based on the effective value. If the rise rate is greater than the second threshold, it is determined to be a fault recovery period; otherwise, it is a fault period.

5. The wind power AC fault ride-through method under a hybrid architecture as described in claim 4, characterized in that, The rate of increase is calculated using sampling time and sampling frequency, and the calculation satisfies: ,in, For the rate of increase, Indicates the sampling time. Indicates the sampling frequency. This indicates the effective value of the AC bus voltage at sea.

6. The wind power AC fault ride-through method under a hybrid architecture as described in claim 1, characterized in that, When the fault stage is during the fault period, the grid-connected converter of the wind turbine and the MMC on the wind farm side are switched to constant AC current control mode and AC fault current is injected to support the voltage of the offshore AC bus. This includes freezing the steady-state power outer loop control of the grid-connected converter GSC and the MMC on the wind farm side during the fault period and enabling the inner loop constant AC current controller. The current limiting value of the grid-connected converter (GSC) for wind turbine generators is set to its rated steady-state value. K vmax The current limit value for the MMC constant AC current control on the wind farm side is set to its rated steady-state value. K mvq times, K vmax and K mvq This is the proportionality coefficient.

7. The wind power AC fault ride-through method under a hybrid architecture as described in claim 1, characterized in that, When the fault stage is within the fault recovery period, the current limit value of the wind turbine grid-connected converter is gradually restored to the steady-state limit value, including: the wind turbine grid-connected converter GSC maintains constant AC power control, and the current limit value starts from the initial value and increases linearly according to the preset boost rate until it is restored to the steady-state limit value.

8. A wind power AC fault ride-through device with a hybrid architecture, characterized in that, It includes: The analysis module is used to build a fault transient analysis model of the offshore wind power system to analyze the voltage support capability of the diode converter (DRU), the grid-connected converter (GSC) of the wind turbine and the wind farm side converter (MMC) to the offshore AC bus under a three-phase symmetrical AC fault. The detection module is used to detect the voltage of the offshore AC bus in real time and determine the AC fault stage based on the voltage. The processing module is used to control the wind turbine grid-connected converter and the wind farm-side MMC to switch to constant AC current control mode and inject AC fault current when the fault stage is during a fault period, so as to support the voltage of the offshore AC bus. When the fault stage is within the fault recovery period, the current limit value of the wind turbine grid-connected converter is gradually restored to the steady-state limit value.

9. An electronic device comprising a processor, a storage medium, and a computer program, wherein the computer program is stored in the storage medium, characterized in that, When the computer program is executed by the processor, it implements the wind power AC fault ride-through method under the hybrid architecture as described in any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the wind power AC fault ride-through method under the hybrid architecture as described in any one of claims 1 to 7.

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