Methods and apparatus for suppressing continuous DC commutation failure

Abstract

This invention provides a method and apparatus for suppressing continuous DC commutation failures, applicable to scenarios where doubly-fed induction generator (DFIG) wind turbines and photovoltaic (PV) units are connected to a DC receiving end. The method includes: determining whether a commutation failure fault has occurred in the DC transmission system based on its operating status; if a fault occurs, using a main control station to control the DFIG wind turbines and PV units to regulate the reactive power of the DC transmission system. The main control station coordinates and allocates the reactive power output values ​​of the DFIG wind turbines and PV units based on the degree of voltage drop in the grid caused by the commutation failure fault. This invention, when the DC system is in a commutation failure state, enables the system to directly respond to system voltage fluctuations caused by DC system faults through reactive power coordination control of the DFIG wind turbines and PV units, effectively and flexibly suppressing continuous DC commutation failure faults.

Description

Technical Field

[0001] This invention relates to the field of power systems, and more particularly to a method and apparatus for suppressing continuous DC commutation failure. Background Technology

[0002] In related technologies, energy resources and electricity demand in many regions exhibit a geographically inverse distribution pattern. For example, wind energy resources in a certain region are concentrated in the western, northern, and eastern coastal areas, suitable for large-scale centralized development. Solar energy resources are mainly distributed in the solar-rich northwest region, as well as several northern and coastal areas, providing geographical conditions for the widespread application of photovoltaic power generation technology. The overlapping distribution areas of these two energy sources both exhibit characteristics of large-scale centralized access and long-distance transmission. The distance between the aforementioned wind and photovoltaic energy bases and the load centers in the east and central regions exceeds 2000m. Ultra-high voltage direct current (LCC-HVDC) transmission, as a mature and reliable technology, is the main means of undertaking long-distance, large-capacity, and low-loss power transmission. Therefore, bundling wind and photovoltaic power and transmitting it via DC not only meets the basic requirements for large-scale transmission of traditional and renewable energy but also ensures the safe and stable operation of the DC transmission channel.

[0003] With the large-scale grid connection of new energy sources such as wind and solar, the dynamic support capability of wind, solar, and hydropower transmission systems is continuously declining. If continuous DC commutation fails, it will not only result in a loss of transmission power but also cause a significant impact on the weak AC power grid at the sending end. Since the filter grouping and clearing delay at the converter station requires at least 1 second, continuous DC commutation failure will cause continuous overvoltage in the AC system, seriously jeopardizing the reliability of power electronic devices in new energy sources such as wind and solar power.

[0004] Therefore, it is urgent to take necessary measures to improve the dynamic reactive power support capability of the wind and solar power transmission system in order to reduce potential system voltage risks.

[0005] Current methods for suppressing continuous DC commutation failure mainly focus on three aspects: improving DC control strategies, installing reactive power compensation devices, and optimizing unit operation. However, methods such as optimizing low-voltage current limit controllers and other DC control strategy improvements cannot address all aspects of system operation and pose safety risks. Installing reactive power compensation devices increases production and maintenance costs, thereby reducing economic benefits.

[0006] Therefore, it is particularly necessary to propose a method for effectively and safely suppressing DC continuous commutation failure in response to the aforementioned problems. Summary of the Invention

[0007] To address the problems in the prior art, embodiments of the present invention provide a method and apparatus for suppressing continuous DC commutation failure, thereby solving the problems of weak dynamic reactive power support capability and significant system voltage risks in the prior art wind and solar power transmission systems.

[0008] Specifically, the embodiments of the present invention provide the following technical solutions:

[0009] In a first aspect, embodiments of the present invention provide a method for suppressing continuous DC commutation failure, used in scenarios where a doubly-fed induction generator (DFIG) wind turbine and a photovoltaic (PV) unit are connected together to a DC receiving-end system, including:

[0010] Obtain the operating status of the DC transmission system;

[0011] Based on the operating status of the DC transmission system, determine whether the DC transmission system has experienced a commutation failure.

[0012] If a commutation failure occurs in the DC transmission system, a commutation failure fault signal is sent to the main control station, so that the main control station can control the doubly-fed induction generator (DFIG) wind turbines and photovoltaic (PV) units to regulate the reactive power of the DC transmission system based on the commutation failure fault signal.

[0013] The main control station coordinates and allocates the reactive power output of the doubly-fed wind turbine and photovoltaic unit based on the degree of grid voltage drop caused by the commutation failure of the DC transmission system.

[0014] In one possible implementation, the operating status of the DC transmission system includes the AC bus voltage level and turn-off angle signal monitored in real time by the DC converter station;

[0015] The step of determining whether a commutation failure fault has occurred in the DC transmission system based on its operating status includes:

[0016] When the turn-off angle is less than the critical turn-off angle, it is determined that a commutation failure fault has occurred in the DC transmission system; and / or, when the AC bus voltage is less than the critical voltage, it is determined that a commutation failure fault has occurred in the DC transmission system.

[0017] The magnitude of the critical voltage is:

[0018]

[0019] Among them, U min The critical value of the bus voltage for the first commutation failure is defined by U. min Sure,

[0020] β is the lead firing angle, k is the converter transformer turns ratio, and X r For commutation reactance, I dγ is the DC current, θ is the phase angle offset of the commutation voltage, and γ is the DC current. min It is the minimum shut-off angle.

[0021] In one possible implementation, in addition to sending a commutation failure fault signal to the main control station, it also includes:

[0022] The reactive power reference signal required by the DC converter station is transmitted to the main control station through the channel. The reactive power reference signal carries the reactive power reference value required by the DC converter station.

[0023] The required reactive power reference value for the DC converter station is:

[0024]

[0025] Among them, Q ref U is the reference value of reactive power required by the DC converter station, or the input signal of the reactive power outer loop controller. ref U is the reference value for the AC bus voltage of the DC converter station. L Let be the actual effective value of the AC bus voltage of the DC converter station, K and T be the proportional and integral coefficients of the proportional-integral controller, respectively, and s be the complex frequency variable in the Laplace transform domain.

[0026] In one possible implementation, the master control station includes a voltage detection module and a voltage drop judgment module, wherein the voltage drop judgment module judges the degree of grid voltage drop based on the value of the input voltage of the voltage detection module.

[0027] The main control station determines the reactive power reference values ​​allocated to the doubly-fed wind turbine and the photovoltaic unit respectively based on the degree of grid voltage drop and the reactive power reference value required by the DC converter station, and transmits the reactive power reference signal corresponding to the reactive power reference value to the doubly-fed wind turbine and / or the photovoltaic unit.

[0028] In one possible implementation, the voltage drop detection module is used to determine when the input signal of the voltage detection module exceeds the minimum voltage limit U for normal operation of the power grid system. L0 If the power grid system is determined to be in normal operating mode, the voltage sag detection module outputs a sag signal S. v =0;

[0029] When the input signal of the voltage detection module is less than the minimum voltage limit U for normal operation of the power grid system L0 And greater than the boundary voltage U g The system determines that a shallow voltage dip has occurred in the power grid system, and the voltage dip determination module outputs a dip signal S. v =1;

[0030] When the input signal of the voltage detection module is less than the threshold voltage U g The system determines that a deep voltage drop has occurred in the power grid system, and the voltage drop determination module outputs a voltage drop signal Sv = 2.

[0031] In one possible implementation, the degree of the grid voltage drop includes shallow voltage drop and deep voltage drop;

[0032] The main control station is used to control the doubly fed wind turbine unit to perform reactive power compensation when the grid voltage experiences a shallow voltage drop.

[0033] When the grid voltage experiences a deep voltage drop, the doubly fed wind turbine and the photovoltaic unit are controlled to perform coordinated reactive power compensation.

[0034] In one possible implementation, the master control station is used to transmit a reactive power reference signal required by the DC converter station to the reactive power outer loop controller of the doubly-fed induction generator (DFIG) unit via a channel when the grid voltage experiences a shallow voltage drop, thereby controlling the grid-side converter of the DFIG unit to provide reactive power.

[0035] If the reactive power demand of the DC converter station exceeds the upper limit of the reactive power output of the grid-side converter, the stator-side converter of the doubly-fed wind turbine unit is controlled to compensate for the remaining reactive power demand.

[0036] In one possible implementation, the master control station is further configured to determine the reactive current command value I of the photovoltaic unit during a fault when the grid voltage experiences a deep voltage drop. q for:

[0037]

[0038] Among them, I q U is the reactive current command value. L U is the actual effective value of the bus voltage. g For the boundary voltage, I N The total rated current for the inverters in the photovoltaic power station.

[0039] Secondly, embodiments of the present invention provide a device for suppressing continuous DC commutation failure, used in scenarios where a doubly-fed induction generator (DFIG) wind turbine and a photovoltaic unit are connected together to a DC receiving-end system, including:

[0040] The acquisition module is used to acquire the operating status of the DC transmission system;

[0041] The judgment module is used to determine whether the DC transmission system has experienced a commutation failure fault based on the operating status of the DC transmission system.

[0042] The reactive power regulation module is used to send a commutation failure signal to the main control station if a commutation failure fault occurs in the DC transmission system, so that the main control station can control the doubly-fed wind turbine and photovoltaic unit to regulate the reactive power of the DC transmission system at the receiving end according to the commutation failure fault signal.

[0043] The main control station coordinates and allocates the reactive power output of the doubly-fed wind turbine and photovoltaic unit based on the degree of grid voltage drop caused by the commutation failure of the DC transmission system.

[0044] In one possible implementation, the degree of the grid voltage drop includes shallow voltage drop and deep voltage drop;

[0045] The main control station is used to control the doubly fed wind turbine unit to perform reactive power compensation when the grid voltage experiences a shallow voltage drop.

[0046] When the grid voltage experiences a deep voltage drop, the doubly fed wind turbine and the photovoltaic unit are controlled to perform coordinated reactive power compensation.

[0047] This invention provides a method and apparatus for suppressing continuous DC commutation failure. The method involves determining whether a commutation failure fault has occurred in the DC transmission system based on its operating status. If a commutation failure fault occurs, the main control station controls the doubly-fed induction generator (DFIG) wind turbines and photovoltaic (PV) units to regulate the reactive power of the DC transmission system based on the commutation failure fault signal. The main control station coordinates and allocates the reactive power output of the DFIG wind turbines and PV units based on the degree of voltage drop in the grid caused by the DC transmission system's commutation failure fault. This invention, when the DC system is in a commutation failure fault state, enables the system to directly respond to system voltage fluctuations caused by DC system faults through reactive power coordination control of the DFIG wind turbines and PV units, effectively and flexibly suppressing continuous DC commutation failure faults. Furthermore, this invention improves the converter commutation conditions by allowing the main control station to determine the reactive power compensation magnitude based on the voltage drop amplitude at the receiving end converter bus. Since this method does not require constant phase adjustment operation or additional dynamic reactive power compensation equipment, it has strong dynamic reactive power support capability and reduces system voltage risks. This control strategy has economic and practical value. Attached Figure Description

[0048] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0049] Figure 1 A flowchart illustrating an exemplary method for suppressing continuous DC commutation failure according to an embodiment of the present invention;

[0050] Figure 2 A flowchart illustrating another exemplary method for suppressing continuous DC commutation failure, provided as an embodiment of the present invention;

[0051] Figure 3 This is a schematic diagram of the reactive voltage coordination control strategy in a method for suppressing DC continuous commutation failure provided in an embodiment of the present invention;

[0052] Figure 4 This is a schematic diagram of the main circuit and control system structure of a doubly fed wind turbine unit according to an embodiment of the present invention;

[0053] Figure 5 This is a schematic diagram of the main circuit and control system structure of a photovoltaic unit according to an embodiment of the present invention;

[0054] Figure 6 This is a schematic diagram of the main circuit and control system structure of a photovoltaic unit provided in another embodiment of the present invention;

[0055] Figure 7 This is a structural diagram of a DC receiving-end system containing a doubly fed wind turbine and a photovoltaic unit, provided as an embodiment of the present invention for verifying the coordinated control strategy of the doubly fed wind turbine and the photovoltaic unit;

[0056] Figure 8 In a DC receiving-end system containing a doubly fed wind turbine and a photovoltaic unit provided in an embodiment of the present invention, a voltage dip occurs and a DC commutation failure occurs. The dynamic response comparison diagram of reactive power before and after configuring the coordinated control strategy of the doubly fed wind turbine is shown. In the figure, (a) and (b) are the converter bus voltage and the reactive power output of the doubly fed wind turbine, respectively.

[0057] Figure 9 In a DC receiving-end system containing a doubly-fed induction generator (DFIG) wind turbine and a photovoltaic (PV) unit, a deep voltage sag and a DC commutation failure occur. The diagram compares the dynamic response of reactive power before and after implementing a coordinated control strategy for the variable-speed pumped-storage unit. In the diagram, (a) and (b) represent the converter bus voltage, and the reactive power output of the DFIG wind turbine and PV unit, respectively.

[0058] Figure 10 This is a block diagram of a device for suppressing continuous DC commutation failure according to an embodiment of the present invention. Detailed Implementation

[0059] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0060] To address the issues of weak dynamic reactive power support and significant system voltage vulnerabilities in existing wind-solar power transmission systems, this application proposes a method to suppress continuous DC commutation failures. Based on a coordinated reactive power and voltage control strategy between the doubly-fed induction generator (DFIG) wind turbine and photovoltaic (PV) unit, this method suppresses continuous DC commutation failures. Through the coordinated control of reactive power and voltage by the DFIG wind turbine and PV unit and the interaction with the DC converter station, this method achieves real-time response to system voltage fluctuations caused by commutation failure faults, suppressing the occurrence of continuous commutation failures and effectively improving the voltage stability of the DC receiving-end system of the DFIG wind turbine and PV unit.

[0061] First, refer to Figure 1 This illustrates a flowchart of a method for suppressing continuous DC commutation failure provided by an exemplary embodiment of the present invention. Figure 1 As shown, the method for suppressing continuous DC commutation failure provided in this embodiment of the invention includes the following steps:

[0062] Step 110: Obtain the operating status of the DC transmission system.

[0063] Step 120: Determine whether a commutation failure fault has occurred in the DC transmission system based on its operating status.

[0064] Step 130: If a commutation failure fault occurs in the DC transmission system, a commutation failure fault signal is sent to the main control station so that the main control station can control the doubly-fed induction generator (DFIG) wind turbines and photovoltaic (PV) units to regulate the reactive power of the DC transmission system based on the commutation failure fault signal. The main control station coordinates and allocates the reactive power output values ​​of the DFIG wind turbines and PV units based on the degree of grid voltage drop caused by the commutation failure fault in the DC transmission system.

[0065] In step 110, the operating status of the DC transmission system includes the AC bus voltage level and the turn-off angle. In one example, the AC bus voltage level and turn-off angle are monitored in real time at the DC converter station. The AC bus voltage level and turn-off angle are used as the basis for subsequent determination of whether a commutation failure fault has occurred in the DC transmission system.

[0066] In step 120, after obtaining the operating status of the HVDC transmission system, a commutation failure detection step is used to determine whether a commutation failure fault has occurred. In the commutation failure detection step, the operating status of the HVDC transmission system is used to determine whether a commutation failure fault has occurred.

[0067] In one example, determining whether a DC transmission system has experienced a commutation failure includes determining whether the DC transmission system is in normal operation or in a commutation failure state.

[0068] In one example, the commutation failure detection stage uses both the turn-off angle and the critical voltage to determine whether a commutation failure has occurred. In another example, the commutation failure detection stage uses the critical voltage to determine whether a commutation failure has occurred. In yet another example, the commutation failure detection stage uses the turn-off angle to determine whether a commutation failure has occurred. In yet another example, a commutation failure is determined to have occurred if either the turn-off angle or the critical voltage fails to meet a predetermined condition.

[0069] This application incorporates a turn-off angle criterion for auxiliary control based on the critical voltage. When the turn-off angle is less than the critical turn-off angle, a commutation failure fault is identified in the DC system. If any of the above criteria is met, a commutation failure is determined, and a coordinated control strategy involving the doubly-fed induction generator (DFIG) wind turbine and photovoltaic (PV) units to supplement the power of the DC receiving-end system is activated. This control strategy, with the addition of the turn-off angle criterion, is more accurate and sensitive to system voltage fluctuations caused by commutation failure faults, and more quickly suppresses the occurrence of consecutive commutation failures, effectively improving the voltage stability of the DC receiving-end system of the DFIG wind turbine and PV units.

[0070] In step 130, if a commutation failure fault occurs in the DC transmission system, a commutation failure fault signal is sent to the main control station so that the main control station can control the doubly-fed induction generator (DFIG) wind turbine and photovoltaic (PV) generator to regulate the reactive power of the DC transmission system based on the commutation failure fault signal. The main control station coordinates and allocates the reactive power output values ​​of the DFIG wind turbine and PV generator based on the degree of grid voltage drop caused by the commutation failure fault in the DC transmission system.

[0071] The main control station includes a voltage detection module and a voltage sag judgment module. The voltage sag judgment module uses the voltage detection module to detect the line voltage value to determine the degree of voltage sag in the power grid. The degree of voltage sag is categorized as no voltage sag, shallow voltage sag, and deep voltage sag. Based on these three voltage sag scenarios, the system controls the doubly-fed induction generator (DFIG) wind turbine units and photovoltaic (PV) units to coordinate reactive power compensation. In one example, controlling the coordinated reactive power compensation between the DFIG wind turbine units and PV units includes selecting which unit will perform reactive power compensation and determining the reactive power value for coordinated reactive power compensation between the DFIG wind turbine units and PV units.

[0072] In one example, when the voltage detection module input signal is greater than the minimum normal operating voltage limit U... L0 The judgment module outputs a drop signal S. v =0 indicates that the system is still in normal operating mode; when the input signal of the voltage detection module is less than the minimum normal operating voltage limit U... L0 And greater than the boundary voltage U g The judgment module outputs a drop signal S. v =1 indicates a shallow voltage drop in the power grid; when the input signal of the voltage detection module is less than the threshold voltage U g The judgment module outputs a drop signal S. v =2, indicating a deep voltage dip in the power grid; the main control station's judgment module outputs a dip signal S. v =1, the grid voltage drops slightly, requiring only reactive power compensation from the doubly-fed induction generator (DFIG) wind turbine. A reference signal for the reactive power required by the grid bus is transmitted via a channel to the DFIG wind turbine's outer reactive power controller. The grid-side converter of the DFIG wind turbine prioritizes reactive power allocation. If the reactive power demand of the DC converter station exceeds the upper limit of the grid-side converter's output reactive power, the stator side of the DFIG wind turbine compensates for the remaining reactive power demand. The main control station's judgment module outputs a voltage drop signal S. v =2, a deep voltage sag in the grid requires coordinated reactive power compensation between doubly-fed induction generator (DFIG) wind turbines and photovoltaic (PV) units. The degree of grid voltage sag corresponding to a deep voltage sag is greater than that corresponding to a shallow voltage sag.

[0073] This invention outputs sag signals to both the doubly-fed induction generator (DFIG) wind turbine and the photovoltaic (PV) unit via a main control station. It adjusts the reactive power output of the DFIG wind turbine by changing the excitation system voltage through rotor-side and grid-side excitation controllers on both sides. Similarly, it adjusts the reactive power output of the PV unit by modifying the inverter's power control. This process performs necessary power allocation, enabling both the DFIG wind turbine and the PV unit to participate in the reactive power coordination and voltage regulation of the power system.

[0074] In this embodiment, when the DC system is in normal operation, the doubly-fed induction generator (DFIG) wind turbine and photovoltaic (PV) unit do not participate in the voltage regulation of the DC receiving-end system. When the DC system is in a commutation failure state, the DFIG wind turbine and PV unit interact with the DC converter station. The AC bus voltage error signal of the DC converter station is transmitted through the channel and controlled by the reactive power coordination of the DFIG wind turbine and PV unit. This enables the system to directly respond to system voltage fluctuations caused by DC system faults, effectively and flexibly suppressing continuous DC commutation failure faults in the system.

[0075] The following is another exemplary embodiment of this application, with reference to Figure 2 The following embodiments of the present invention provide a method for suppressing continuous DC commutation failure, comprising:

[0076] Step S1: Obtain the operating status of the high voltage direct current transmission system, including the AC bus voltage level and the turn-off angle.

[0077] Step S2: Commutation failure detection.

[0078] Step S3: Channel transmission fault related signals.

[0079] Step S4: Reactive power allocation at the main control station.

[0080] In step S1: the AC bus voltage level and turn-off angle signal of the DC converter station are monitored in real time. The collected voltage and turn-off angle signals are used to determine whether a commutation failure fault has occurred through the commutation failure detection circuit.

[0081] In step S2, during the commutation failure detection stage, a commutation failure fault is determined by the critical voltage and the turn-off angle. In one example, when the turn-off angle is less than the critical turn-off angle, a commutation failure fault is determined to have occurred in the DC transmission system; and / or, when the AC bus voltage is less than the critical voltage, a commutation failure fault is determined to have occurred in the DC transmission system. In one example, a bus voltage less than the critical voltage is considered a commutation failure fault in the DC system. The critical bus voltage at which commutation failure occurs can be calculated using the following formula:

[0082]

[0083] In the formula, U min The threshold value for the bus voltage during the first commutation failure is given by β, where β is the leading trigger angle.

[0084] θ is the current phase angle, k is the converter transformer turns ratio, and X r For commutation reactance, I d For direct current, U L γ is the converter bus voltage, γ is the phase angle offset of the commutation voltage, and γ is the phase angle offset of the commutation voltage. min It is the minimum shut-off angle.

[0085] In one example, a turn-off angle criterion is added to the critical voltage for auxiliary control. When the turn-off angle is less than the critical turn-off angle, it is determined that the DC system has experienced a commutation failure fault.

[0086] In one example, if any one of the criteria is met, it is determined that a commutation failure has occurred, and a coordinated control strategy is activated. When the bus voltage is less than the critical voltage or the turn-off angle is less than the critical turn-off angle, it is determined that a commutation failure fault has occurred in the DC system.

[0087] In step S3, refer to Figures 3-6When the commutation failure detection stage determines that the DC system is in normal operation, the DC converter station only transmits a digital 0 signal to the main control station through the channel. When the commutation failure detection stage determines that a commutation failure has occurred in the DC system, the DC converter station transmits a reactive power reference signal required by the DC converter station to the main control station through the channel. This signal carries the reactive power reference value required by the DC converter station. The main control station then sends signals to the doubly-fed induction generator (DFIG) wind turbine and photovoltaic unit respectively to coordinate reactive power and voltage control based on the voltage drop and the reactive power reference value required by the DC converter station.

[0088] In one example, after the DC converter station detects the monitoring AC bus voltage level and turn-off angle, and determines whether the DC transmission system is in normal operation or a commutation failure state based on these parameters, the DC converter station transmits a specific signal to the master control station via a channel. This specific signal corresponds to the operating status of the HVDC transmission system. In one example, the specific signal is 0 and 1, where 0 indicates that the HVDC transmission system is operating normally; and 1 indicates that the HVDC transmission system is in a commutation failure state.

[0089] After determining that the high-voltage direct current transmission system is in a commutation failure state, in addition to transmitting the aforementioned specific signals, the DC converter station also transmits the reactive power reference signal required by the DC converter station to the main control station through the channel. The main control station then sends signals to the doubly-fed induction generator (DFIG) wind turbine units and photovoltaic units respectively to perform reactive power and voltage coordination control based on the reactive power reference required by the DC converter station and the voltage drop level.

[0090] The reactive power reference signal required by the DC converter station is defined as the difference between the reference value and the actual effective value of the AC bus voltage of the DC converter station. In one example, the required reactive power reference value for the current system is generated through proportional-integral control. The formula is:

[0091]

[0092] In the formula, Q ref This is the reactive power reference signal required by the DC converter station, and also the input signal for the reactive power outer loop controller, U ref U is the reference value for the AC bus voltage of the DC converter station. L Let be the actual effective value of the AC bus voltage of the DC converter station, K and T be the proportional and integral coefficients of the proportional-integral controller, respectively, and s be the complex frequency variable in the Laplace transform domain.

[0093] In step S4, in the reactive power allocation process of the main control station, the main control station determines the reactive power reference values ​​to be allocated to the doubly-fed wind turbine and the photovoltaic unit respectively based on the degree of grid voltage drop and the reactive power reference value required by the DC converter station, and transmits the corresponding reactive power reference values ​​to the doubly-fed wind turbine and / or photovoltaic unit.

[0094] In one example, the main control station outputs sag signals to both the doubly-fed induction generator (DFIG) wind turbine and the photovoltaic (PV) unit. By setting excitation controllers on the rotor side and grid side of the DFIG wind turbine to change the excitation system voltage, the reactive power output of the DFIG wind turbine is adjusted. Similarly, by changing the power control of the inverter of the PV unit, the reactive power output of the PV unit is adjusted. Necessary power allocation is performed in this stage to enable the DFIG wind turbine and PV unit to participate in the reactive power coordination control and voltage regulation of the power system.

[0095] In one example, the aforementioned master control station includes a voltage detection module and a voltage sag detection module. The voltage detection module is used to detect the voltage value of the DC system, and the voltage sag detection module determines the degree of grid voltage sag based on the input voltage value of the voltage detection module.

[0096] In one example, when the voltage detection module input signal is greater than the minimum normal operating voltage limit U... L0 The judgment module outputs a drop signal S. v =0 indicates that the system is still in normal operating mode; when the input signal of the voltage detection module is less than the minimum normal operating voltage limit U... L0 And greater than the boundary voltage U g The judgment module outputs a drop signal S. v =1 indicates a shallow voltage drop in the power grid; when the input signal of the voltage detection module is less than the threshold voltage U g The judgment module outputs a drop signal S. v =2, indicating a deep voltage dip in the power grid; the main control station's judgment module outputs a dip signal S. v =1, the grid voltage drops slightly, requiring only reactive power compensation from the doubly-fed induction generator (DFIG) wind turbine. A reference signal for the reactive power required by the grid bus is transmitted via a channel to the DFIG wind turbine's outer reactive power controller. The grid-side converter of the DFIG wind turbine prioritizes reactive power allocation. If the reactive power demand of the DC converter station exceeds the upper limit of the grid-side converter's output reactive power, the stator side of the DFIG wind turbine compensates for the remaining reactive power demand. The main control station's judgment module outputs a voltage drop signal S. v =2, the grid voltage drops deeply, requiring coordinated reactive power compensation between the doubly fed wind turbine and photovoltaic units.

[0097] In summary, the voltage sag detection module determines the degree of grid voltage sag based on the input voltage value of the voltage detection module, including:

[0098] When the input signal of the voltage detection module is greater than the minimum voltage limit for normal operation of the power grid system, U L0 To determine if the power grid system is in normal operating mode, the voltage sag detection module outputs a sag signal S. v =0;

[0099] When the input signal of the voltage detection module is less than the minimum voltage limit U for normal operation of the power grid system L0 And greater than the boundary voltage U g The system detects a shallow voltage dip in the power grid and outputs a voltage dip signal S. v =1;

[0100] When the input signal of the voltage detection module is less than the threshold voltage U g The system detects deep voltage drops in the power grid system, and the voltage drop detection module outputs a voltage drop signal S. v =2.

[0101] In one example, the specific strategy for reactive power allocation in the master control station includes the following steps:

[0102] S41: When the input signal of the voltage detection module is greater than the minimum normal operating voltage limit U L0 The judgment module outputs a drop signal S. v =0 indicates that the system is still in normal operating mode; when the input signal of the voltage detection module is less than the minimum normal operating voltage limit U... L0 And greater than the boundary voltage U g The judgment module outputs a drop signal S. v =1 indicates a shallow voltage drop in the power grid; when the input signal of the voltage detection module is less than the threshold voltage U g The judgment module outputs a drop signal S. v =2, indicating a deep voltage drop in the power grid;

[0103] S42: The main control station's judgment module outputs a drop signal S v =1, the grid voltage drops slightly, and only the doubly fed wind turbine unit needs to compensate for reactive power; the reactive power reference signal required by the grid bus is transmitted to the reactive power outer loop controller of the doubly fed wind turbine unit through the channel; the grid-side converter of the doubly fed wind turbine unit gives priority to allocating reactive power. If the reactive power demand of the DC converter station exceeds the upper limit of the reactive power output of the grid-side converter, the stator side of the doubly fed wind turbine unit compensates for the remaining reactive power demand.

[0104] S43: The main control station's judgment module outputs a drop signal S v =2, grid voltage deep sag, requiring coordinated reactive power compensation between doubly-fed induction generator (DFIG) wind turbines and photovoltaic (PV) units; reactive current command value I of PV units during the fault. q The formula is:

[0105]

[0106] In the formula, I q U is the reactive current command value. L U is the actual effective value of the bus voltage. g For the boundary voltage, IN The total rated current for the inverters in the photovoltaic power station.

[0107] In summary, the main control station coordinates and allocates the reactive power output of the doubly-fed induction generator (DFIG) wind turbines and photovoltaic (PV) units based on the degree of grid voltage drop caused by commutation failure in the DC transmission system.

[0108] When the grid voltage experiences a shallow voltage drop, only the doubly fed wind turbine units provide reactive power compensation.

[0109] When the grid voltage experiences a deep voltage drop, the doubly fed wind turbine and the photovoltaic unit work together to coordinate reactive power compensation.

[0110] When the grid voltage experiences a slight voltage dip, only the doubly-fed induction generator (DFIG) wind turbine units provide reactive power compensation, including:

[0111] The reactive power reference signal required by the grid bus is transmitted through the channel to the reactive power outer loop controller of the doubly-fed induction generator (DFIG) wind turbine unit, where the grid-side converter of the DFIG wind turbine unit prioritizes providing reactive power.

[0112] If the reactive power demand of the DC converter station exceeds the upper limit of the reactive power output of the grid-side converter, the stator-side converter of the doubly-fed wind turbine unit will compensate for the remaining reactive power demand.

[0113] This application determines the reactive power reference values ​​allocated to the doubly-fed induction generator (DFIG) wind turbine units and photovoltaic (PV) units respectively based on the degree of grid voltage sag and the reactive power reference value required by the DC converter station. This scheme not only performs reactive power control based on the reactive power required by the DC converter station but also on the degree of grid voltage sag, thus optimizing the reactive power control strategy, making reactive power control more accurate, and enhancing the voltage stability of the DC receiving-end system. Real-time, coordinated reactive power control of the DFIG wind turbine units and PV units effectively improves the voltage stability of the DC receiving-end system for both units.

[0114] Feasibility verification of the invention

[0115] Engineering simulation example system model such as Figure 7 As shown, the simulation comparison results are as follows: Figure 8 , Figure 9 As shown, the effectiveness of the present invention is verified. Figure 8 The diagram shows the dynamic response of reactive power before and after the reactive power voltage is coordinated and controlled by the doubly-fed induction generator (DFIG) wind turbine unit in a DC receiving-end system, where the converter bus voltage drops slightly and the DC commutation failure occurs. (a) and (b) show the converter bus voltage and the reactive power output of the DFIG wind turbine unit, respectively. Figure 9In a DC receiving-end system, the converter bus voltage drops sharply, and a DC commutation failure occurs. The dynamic response of reactive power before and after configuring a reactive power and voltage coordination control strategy for the doubly-fed induction generator (DFIG) wind turbine and photovoltaic unit is compared. (a) and (b) show the converter bus voltage and the reactive power output of the DFIG wind turbine and photovoltaic unit, respectively.

[0116] After adopting a coordinated control strategy, the commutation failure detection stage extracts the AC bus voltage signal of the DC converter station and sends a real-time determination of whether a commutation failure has occurred to the master control station. When the commutation failure detection stage determines a fault, the master control station transmits the reactive power reference signal to the appropriate object based on the drop signal.

[0117] Depend on Figure 8 As shown in (a) and (b), when the converter bus voltage experiences a shallow drop, the doubly-fed induction generator (DFIG) can quickly respond to the reactive power demand of the DC system after implementing the proposed coordinated control strategy, rapidly increasing reactive power generation by approximately 3 pu during the recovery period from commutation failure. Compared to the condition without the coordinated control strategy, the converter bus voltage increases by approximately 0.2 pu, effectively increasing the commutation margin of the converter. Due to the increase in bus voltage, the minimum turn-off angle during recovery increases from 4° to 10°, and the number of commutation failures decreases from 2 to 1. This demonstrates that the coordinated control strategy effectively suppresses continuous commutation failures and improves the DC transmission power recovery speed under conditions of a shallow drop in bus voltage.

[0118] Depend on Figure 9 As shown in (a) and (b), after implementing the coordinated control strategy, during the transient period, the photovoltaic units generate approximately 5 pu of reactive power, the doubly-fed induction generator (DFIG) units generate approximately 2 pu of reactive power, and the bus voltage rises by approximately 0.8 pu. The minimum turn-off angle increases from 0° to 12°, the number of commutation failures decreases from 2 to 1, and the recovery of DC transmission power is accelerated. Under the condition of deep bus voltage drop, the coordinated control strategy proposed in this invention still demonstrates good effectiveness.

[0119] In summary, this invention provides a reactive power and voltage coordination control strategy for doubly-fed induction generator (DFIG) wind turbines and photovoltaic (PV) units to suppress continuous DC commutation failures. This strategy involves the main control station outputting a corresponding voltage drop signal based on the voltage drop at the receiving end converter bus, which is applied to both the DFIG wind turbine and PV unit. During commutation failure recovery, the main control station can determine the magnitude of reactive power compensation based on the bus voltage drop amplitude, thereby improving the converter commutation conditions. Since this method does not require year-round phase adjustment operation or additional dynamic reactive power compensation equipment, this control strategy is both economical and practical.

[0120] like Figure 10 As shown, the present invention also provides a device 100 for suppressing continuous DC commutation failure, used in scenarios where a doubly-fed wind turbine unit and a photovoltaic unit are connected together to a DC receiving-end system, including:

[0121] The acquisition module 110 is used to acquire the operating status of the DC transmission system;

[0122] The judgment module 120 is used to determine whether a commutation failure fault has occurred in the DC transmission system based on the operating status of the DC transmission system.

[0123] The reactive power regulation module 130 is used to send a commutation failure signal to the main control station if a commutation failure fault occurs in the DC transmission system, so that the main control station can control the doubly fed wind turbine and photovoltaic unit to regulate the reactive power of the DC transmission system at the receiving end according to the commutation failure fault signal.

[0124] The main control station coordinates and allocates the reactive power output of the doubly-fed wind turbine and photovoltaic unit based on the degree of grid voltage drop caused by the commutation failure of the DC transmission system.

[0125] In one example, the degree of grid voltage drop includes shallow voltage drop and deep voltage drop;

[0126] The main control station is used to control the doubly fed wind turbine units to perform reactive power compensation when the grid voltage experiences a shallow voltage drop.

[0127] When the grid voltage experiences a deep voltage drop, the control system coordinates the reactive power compensation of the doubly fed wind turbine and the photovoltaic unit.

[0128] In one example, the operating status of the DC transmission system includes the AC bus voltage level and turn-off angle signal monitored in real time by the DC converter station.

[0129] The judgment module 120 is specifically used for:

[0130] When the turn-off angle is less than the critical turn-off angle, it is determined that a commutation failure fault has occurred in the DC transmission system; and / or, when the AC bus voltage is less than the critical voltage, it is determined that a commutation failure fault has occurred in the DC transmission system.

[0131] The magnitude of the critical voltage is:

[0132]

[0133] Among them, U min The critical value of the bus voltage for the first commutation failure is defined by U. min Sure,

[0134] β is the lead firing angle, k is the converter transformer turns ratio, and X r For commutation reactance, I d Where is the DC current, O is the phase angle offset of the commutation voltage, and γ is the DC current. min It is the minimum shut-off angle.

[0135] In one example, the reactive power regulation module 130 is also used for:

[0136] The reactive power reference signal required by the DC converter station is transmitted to the main control station through the channel. The reactive power reference signal carries the reactive power reference value required by the DC converter station.

[0137] The required reactive power reference value for the DC converter station is:

[0138]

[0139] Among them, Q ref U is the reference value of reactive power required by the DC converter station, or the input signal of the reactive power outer loop controller. ref U is the reference value for the AC bus voltage of the DC converter station. L Let be the actual effective value of the AC bus voltage of the DC converter station, K and T be the proportional and integral coefficients of the proportional-integral controller, respectively, and s be the complex frequency variable in the Laplace transform domain.

[0140] In one example, the master control station includes a voltage detection module and a voltage drop judgment module. The voltage drop judgment module judges the degree of grid voltage drop based on the value of the input voltage of the voltage detection module.

[0141] The main control station determines the reactive power reference values ​​allocated to the doubly-fed wind turbine and the photovoltaic unit respectively based on the degree of grid voltage drop and the reactive power reference value required by the DC converter station, and transmits the corresponding reactive power reference values ​​to the doubly-fed wind turbine and / or the photovoltaic unit.

[0142] In one example, the voltage drop detection module is used when the input signal of the voltage detection module is greater than the minimum voltage limit U for normal operation of the power grid system. L0 If the power grid system is determined to be in normal operating mode, the voltage sag detection module outputs a sag signal S. v =0;

[0143] When the input signal of the voltage detection module is less than the minimum voltage limit U for normal operation of the power grid system L0 And greater than the boundary voltage U g The system determines that a shallow voltage dip has occurred in the power grid system, and the voltage dip determination module outputs a dip signal S. v =1;

[0144] When the input signal of the voltage detection module is less than the threshold voltage U g The system determines that a deep voltage drop has occurred in the power grid system, and the voltage drop determination module outputs a voltage drop signal Sv = 2.

[0145] In one example, the master control station is used to transmit a reactive power reference signal required by the DC converter station to the reactive power outer loop controller of the doubly-fed induction generator (DFIG) unit via a channel when the grid voltage experiences a shallow voltage drop, thereby controlling the grid-side converter of the DFIG unit to provide reactive power.

[0146] If the reactive power demand of the DC converter station exceeds the upper limit of the reactive power output of the grid-side converter, the stator-side converter of the doubly-fed wind turbine unit is controlled to compensate for the remaining reactive power demand.

[0147] In one example, the master control station is also used to determine the reactive current command value I of the photovoltaic unit during a fault when the grid voltage experiences a deep voltage drop. q for:

[0148]

[0149] Among them, I q U is the reactive current command value. L U is the actual effective value of the bus voltage. g For the boundary voltage, I N The total rated current for the inverters in the photovoltaic power station.

[0150] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0151] Those skilled in the art will recognize that the templates, units, and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0152] If the module / unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the above embodiments of the present invention can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the above embodiments of the method for suppressing continuous DC commutation failure. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, a recording medium, a USB flash drive, a portable hard drive, a magnetic disk, an optical disk, a computer memory, a read-only memory, a random access memory, an electrical carrier signal, a telecommunication signal, and a software distribution medium, etc.

[0153] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for suppressing continuous DC commutation failure, characterized in that, Scenarios for connecting doubly-fed wind turbine units and photovoltaic units together to a DC receiving-end system include: Obtain the operating status of the DC transmission system; Based on the operating status of the DC transmission system, determine whether the DC transmission system has experienced a commutation failure. If a commutation failure occurs in the DC transmission system, a commutation failure fault signal is sent to the main control station, so that the main control station can control the doubly-fed induction generator (DFIG) wind turbines and photovoltaic (PV) units to regulate the reactive power of the DC transmission system based on the commutation failure fault signal. The main control station coordinates and allocates the reactive power output values ​​of the doubly-fed wind turbine and photovoltaic unit based on the degree of grid voltage drop caused by the commutation failure fault of the DC transmission system. In addition to sending a commutation failure fault signal to the main control station, the method also includes: The reactive power reference signal required by the DC converter station is transmitted to the main control station through the channel. The reactive power reference signal carries the reactive power reference value required by the DC converter station. The required reactive power reference value for the DC converter station is: in, Q ref This refers to the required reactive power reference value for the DC converter station, or the input signal for the reactive power outer loop controller. U ref This is a reference value for the AC bus voltage of a DC converter station. U L This represents the actual effective value of the AC bus voltage at the DC converter station. K and T These are the proportional and integral coefficients of the proportional-integral controller, respectively. s is the complex frequency variable in the Laplace transform domain; The main control station includes a voltage detection module and a voltage drop judgment module. The voltage drop judgment module judges the degree of grid voltage drop based on the value of the input voltage of the voltage detection module. The main control station determines the reactive power reference values ​​allocated to the doubly-fed wind turbine and the photovoltaic unit respectively based on the degree of grid voltage drop and the reactive power reference value required by the DC converter station, and transmits the reactive power reference signal corresponding to the reactive power reference value to the doubly-fed wind turbine and / or the photovoltaic unit.

2. The method for suppressing continuous DC commutation failure according to claim 1, characterized in that, The operating status of the DC transmission system includes the AC bus voltage level and turn-off angle signal monitored in real time by the DC converter station; The step of determining whether a commutation failure fault has occurred in the DC transmission system based on its operating status includes: When the turn-off angle is less than the critical turn-off angle, it is determined that a commutation failure fault has occurred in the DC transmission system; and / or, when the AC bus voltage is less than the critical voltage, it is determined that a commutation failure fault has occurred in the DC transmission system. The magnitude of the critical voltage is: in, U min The critical value of the bus voltage for the first commutation failure is determined by... U min Sure, It is a leading trigger angle. k For the converter transformer turns ratio, X r For commutation reactance, I d It is direct current. This refers to the phase angle offset of the commutation voltage. It is the minimum shut-off angle.

3. The method for suppressing continuous DC commutation failure according to claim 1, characterized in that, The voltage drop detection module is used when the input signal of the voltage detection module exceeds the minimum voltage limit for normal operation of the power grid system. U L0 If the power grid system is determined to be in normal operating mode, the voltage sag detection module outputs a sag signal. S v =0; When the input signal of the voltage detection module is less than the minimum voltage limit for normal operation of the power grid system U L0 And greater than the threshold voltage U g The voltage sag detection module determines that a shallow voltage drop has occurred in the power grid system and outputs a voltage sag signal. S v =1; When the input signal of the voltage detection module is less than the threshold voltage U g The system determines that a deep voltage drop has occurred in the power grid system, and the voltage drop determination module outputs a voltage drop signal Sv=2.

4. The method for suppressing continuous DC commutation failure according to claim 1, characterized in that, The degree of voltage drop in the power grid includes shallow voltage drop and deep voltage drop; The main control station is used to control the doubly fed wind turbine unit to perform reactive power compensation when the grid voltage experiences a shallow voltage drop. When the grid voltage experiences a deep voltage drop, the doubly fed wind turbine and the photovoltaic unit are controlled to perform coordinated reactive power compensation.

5. The method for suppressing continuous DC commutation failure according to claim 4, characterized in that, The main control station is used to transmit a reactive power reference signal required by the DC converter station to the reactive power outer loop controller of the doubly-fed induction generator (DFIG) unit via a channel when the grid voltage experiences a shallow voltage drop, thereby controlling the grid-side converter of the DFIG unit to provide reactive power. If the reactive power demand of the DC converter station exceeds the upper limit of the reactive power output of the grid-side converter, the stator-side converter of the doubly-fed wind turbine unit is controlled to compensate for the remaining reactive power demand.

6. The method for suppressing continuous DC commutation failure according to claim 4, characterized in that, The main control station is also used to determine the reactive current command value of the photovoltaic unit during a fault when the grid voltage experiences a deep voltage drop. I q for: in, I q This is the reactive current command value. U L This is the actual effective value of the bus voltage. U g This is the boundary voltage. I N The total rated current for the inverters in the photovoltaic power station.

7. A device for suppressing continuous DC commutation failure, characterized in that, Scenarios for connecting doubly-fed wind turbine units and photovoltaic units together to a DC receiving-end system include: The acquisition module is used to acquire the operating status of the DC transmission system; The judgment module is used to determine whether the DC transmission system has experienced a commutation failure fault based on the operating status of the DC transmission system. The reactive power regulation module is used to send a commutation failure signal to the main control station if a commutation failure fault occurs in the DC transmission system, so that the main control station can control the doubly-fed wind turbine and photovoltaic unit to regulate the reactive power of the DC transmission system at the receiving end according to the commutation failure fault signal. The main control station coordinates and allocates the reactive power output values ​​of the doubly-fed wind turbine and photovoltaic unit based on the degree of grid voltage drop caused by the commutation failure fault of the DC transmission system. The reactive power regulation module is also used to: in addition to sending a commutation failure fault signal to the main control station, transmit a reactive power reference signal required by the DC converter station to the main control station through the channel, wherein the reactive power reference signal carries a reactive power reference value required by the DC converter station. The required reactive power reference value for the DC converter station is: in, Q ref This refers to the required reactive power reference value for the DC converter station, or the input signal for the reactive power outer loop controller. U ref This is a reference value for the AC bus voltage of a DC converter station. U L This represents the actual effective value of the AC bus voltage at the DC converter station. K and T These are the proportional and integral coefficients of the proportional-integral controller, respectively. s is the complex frequency variable in the Laplace transform domain; The main control station includes a voltage detection module and a voltage drop judgment module. The voltage drop judgment module judges the degree of grid voltage drop based on the value of the input voltage of the voltage detection module. The main control station determines the reactive power reference values ​​allocated to the doubly-fed wind turbine and the photovoltaic unit respectively based on the degree of grid voltage drop and the reactive power reference value required by the DC converter station, and transmits the reactive power reference signal corresponding to the reactive power reference value to the doubly-fed wind turbine and / or the photovoltaic unit.

8. The apparatus for suppressing continuous DC commutation failure according to claim 7, characterized in that, The degree of voltage drop in the power grid includes shallow voltage drop and deep voltage drop; The main control station is used to control the doubly fed wind turbine unit to perform reactive power compensation when the grid voltage experiences a shallow voltage drop. When the grid voltage experiences a deep voltage drop, the doubly fed wind turbine and the photovoltaic unit are controlled to perform coordinated reactive power compensation.

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