Method and device for suppressing direct current continuous commutation failure

Abstract

The invention provides a method and a device for suppressing a direct current continuous commutation failure, which are used for a scene that a double-fed fan unit and a photovoltaic unit are connected to a direct current receiving end together, and comprise the following steps: judging whether a commutation failure fault occurs in a direct current power transmission system according to an operation state of the direct current power transmission system; if a fault occurs, the main control station is used for controlling the double-fed fan unit and the photovoltaic unit to carry out reactive power adjustment on the direct-current power transmission system, and the main control station is used for coordinating and distributing values of reactive power output by the double-fed fan unit and the photovoltaic unit according to the power grid voltage drop degree caused by the commutation failure fault of the direct-current power transmission system. When the direct current system is in the commutation failure fault state, through reactive power coordination control of the double-fed fan unit and the photovoltaic unit, the system has the capability of directly responding to system voltage fluctuation caused by the direct current system fault, and the direct current continuous commutation failure fault of the system is effectively and flexibly inhibited.

Description

Technical Field

[0001] The present invention relates to the field of power systems, and in particular to a method and device for suppressing direct current continuous commutation failure. Background Art

[0002] In the relevant technologies, the energy resources and electricity demand in many regions are geographically distributed in a counter-trend. For example, the wind energy resources in a certain region are mostly concentrated in the western, northern and eastern coastal areas, which are suitable for large-scale centralized development. Solar energy resources are mainly distributed in the northwest region with rich light resources, as well as in the north and coastal areas, which have geographical conditions for the widespread application of photovoltaic power generation technology. The distribution areas of the two energy sources overlap, and both show the characteristics of large-scale centralized access and long-distance transmission. The distance between the above-mentioned wind power and photovoltaic energy bases and the eastern and central load centers exceeds 2000m. UHVDC (Line Commutated Converter Based High Vltage Direct Current, LCC-HVDC) as a mature and reliable technology is the main means of undertaking long-distance, large-capacity and low-loss power transmission. Therefore, the use of wind power and photovoltaic bundling and DC transmission can not only meet the basic requirements of large-scale traditional energy and renewable energy transmission, but also ensure the safe and stable operation of the DC transmission channel to transmit power.

[0003] With the large-scale grid connection of new energy sources such as wind and solar, the dynamic support capacity of wind, solar and hydroelectric transmission systems has been declining. If the DC continuous commutation fails, on the one hand, the transmission power will be lost, and on the other hand, it will bring a greater impact to the weak AC power grid at the transmission end. Since the group removal delay of the converter station filter takes at least 1 second, the failure of DC continuous commutation will cause continuous overvoltage in the AC system, seriously endangering the reliability of new energy power electronic devices such as wind power and photovoltaics.

[0004] Therefore, it is urgent to take necessary measures to improve the dynamic reactive power support capability of the wind and solar power sending-end system to reduce the hidden dangers of system voltage.

[0005] The current focus of the suppression of DC continuous commutation failure is on improving DC control strategies, installing reactive power compensation devices, and optimizing unit operation modes. However, DC control strategy improvement methods such as optimizing low-voltage current limiting controllers cannot take into account all aspects of system operation and pose safety risks. Installing reactive power compensation devices will increase production and maintenance costs, resulting in reduced economic benefits.

[0006] Therefore, in view of the above-mentioned problems, it is particularly necessary to propose an effective and safe method to suppress DC continuous commutation failure. Summary of the invention

[0007] In view of the problems in the prior art, the embodiments of the present invention provide a method and device for suppressing the failure of DC continuous commutation, so as to solve the problems in the prior art that the dynamic reactive power support capability of the wind and solar power sending-end system is weak and the system voltage potential is large.

[0008] Specifically, the embodiment of the present invention provides the following technical solutions:

[0009] In a first aspect, an embodiment of the present invention provides a method for suppressing a DC continuous commutation failure, which is used in a scenario where a doubly-fed wind turbine unit and a photovoltaic unit are connected to a DC receiving system together, comprising:

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

[0011] According to the operating state of the DC power transmission system, determining whether a commutation failure occurs in the DC power transmission system;

[0012] If a commutation failure occurs in the DC power transmission system, a commutation failure fault signal is sent to the master control station, so that the master control station controls the double-fed wind turbine unit and the photovoltaic unit to perform reactive power regulation on the DC power transmission system according to the commutation failure fault signal.

[0013] The master control station coordinates and distributes the values ​​of reactive power output by the double-fed wind turbine unit and the photovoltaic unit according to the degree of grid voltage drop caused by the commutation failure of the direct current transmission system.

[0014] In a possible implementation, the operating state of the DC power transmission system includes an AC bus voltage level and a shutdown angle signal monitored in real time by a DC converter station;

[0015] The determining, according to the operating state of the DC power transmission system, whether a commutation failure occurs in the DC power transmission system comprises:

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

[0017] Wherein, the critical voltage is:

[0018]

[0019] Among them, U min is the critical value of bus voltage for the first commutation failure, which is calculated based on U min Sure,

[0020] β is the leading trigger angle, k is the transformer ratio, X r is the commutation reactance, I dis the DC current, θ is the phase angle deviation of the commutation voltage, γ min is the minimum turn-off angle.

[0021] In a possible implementation, in addition to sending a commutation failure fault signal to the master control station, the method further includes:

[0022] Transmitting a reactive power reference signal required by the DC converter station to the master control station through a channel, wherein the reactive power reference signal carries a reactive power reference value required by the DC converter station;

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

[0024]

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

[0026] In a possible implementation, the master control station includes a voltage detection module and a voltage drop judgment module, and the voltage drop judgment module judges the degree of grid voltage drop according to the value of the input voltage of the voltage detection module;

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

[0028] In a possible implementation, the voltage drop judgment module is used to detect when the input signal of the voltage detection module is greater than the minimum voltage limit value U L0 , it is determined that the power grid system is in normal operation mode, and the voltage drop judgment module outputs a drop signal S v =0;

[0029] When the voltage detection module input signal is less than the minimum voltage limit value U of the normal operation of the power grid system L0 And greater than the boundary voltage U g , it is determined that the power grid system has a shallow voltage drop, and the voltage drop judgment module outputs a drop signal S v =1;

[0030] When the voltage detection module input signal is less than the boundary voltage U g , it is determined that the power grid system has a deep voltage drop, and the voltage drop determination module outputs a drop signal Sv=2.

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

[0032] The master control station is used to control the double-fed wind turbine unit to perform reactive power compensation when the grid voltage is in a shallow voltage drop;

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

[0034] In a possible implementation, the master control station is used to transmit the reactive power reference signal required by the DC converter station to the reactive outer loop controller of the double-fed wind turbine unit through a channel when the grid voltage drops slightly, so as to control the grid-side converter of the double-fed wind turbine unit to provide reactive power.

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

[0036] In a possible implementation, the master control station is also used to determine the reactive current command value I of the photovoltaic unit during the fault period when the grid voltage drops deeply. q for:

[0037]

[0038] Among them, I q is the reactive current command value, U L is the actual effective value of the bus voltage, U g is the boundary voltage, I N It is the total rated current of the PV station inverter.

[0039] In a second aspect, an embodiment of the present invention provides a device for suppressing a DC continuous commutation failure, which is used in a scenario where a double-fed wind turbine unit and a photovoltaic unit are connected to a DC receiving system together, comprising:

[0040] An acquisition module, used for acquiring the operating status of the DC transmission system;

[0041] A judgment module, used for judging whether a commutation failure occurs in the DC power transmission system according to the operating state of the DC power transmission system;

[0042] A reactive power regulation module, for sending a commutation failure fault signal to a master control station if a commutation failure fault occurs in the DC power transmission system, so that the master control station controls the double-fed wind turbine unit and the photovoltaic unit to perform reactive power regulation on the receiving end of the DC power transmission system according to the commutation failure fault signal;

[0043] The master control station coordinates and distributes the values ​​of reactive power output by the double-fed wind turbine unit and the photovoltaic unit according to the degree of grid voltage drop caused by the commutation failure of the direct current transmission system.

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

[0045] The master control station is used to control the double-fed wind turbine unit to perform reactive power compensation when the grid voltage is in a shallow voltage drop;

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

[0047] The present invention provides a method and device for suppressing continuous DC commutation failure, wherein, according to the operating state of the DC transmission system, it is determined whether a commutation failure occurs in the DC transmission system; if a commutation failure occurs in the DC transmission system, the main control station is controlled to control the double-fed wind turbine unit and the photovoltaic unit to adjust the reactive power of the DC transmission system according to the commutation failure fault signal, wherein the main control station coordinates and distributes the values ​​of the reactive power output by the double-fed wind turbine unit and the photovoltaic unit according to the degree of grid voltage drop caused by the commutation failure of the DC transmission system. When the DC system is in a commutation failure fault state, the present invention coordinates the reactive power of the double-fed wind turbine unit and the photovoltaic unit through reactive coordination control, so that the system has the ability to directly respond to the system voltage fluctuation caused by the DC system fault, and effectively and flexibly suppresses the system DC continuous commutation failure. The present invention improves the commutation conditions of the converter by allowing the main control station to determine the reactive compensation size based on the bus voltage drop amplitude according to the degree of voltage drop of the receiving-end commutation bus. Since this method does not require year-round 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

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

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

[0051] Figure 3 A schematic diagram of a reactive power and voltage coordinated control strategy in a method for suppressing direct current continuous commutation failure provided by an embodiment of the present invention;

[0052] Figure 4 A schematic diagram of the main circuit and control system structure of a doubly-fed wind turbine unit provided in one embodiment of the present invention;

[0053] Figure 5 A schematic diagram of the main circuit and control system structure of a photovoltaic unit provided by an embodiment of the present invention;

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

[0055] Figure 7 A structural diagram of a DC receiving system example including a doubly-fed wind turbine unit and a photovoltaic unit for verifying the coordinated control strategy of the doubly-fed wind turbine unit and the photovoltaic unit provided in an embodiment of the present invention;

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

[0057] Fig. 9 This is a comparison diagram of the dynamic response of reactive power before and after the coordinated control strategy of variable speed pumped storage units is configured in a DC receiving system containing a doubly fed wind turbine unit and a photovoltaic unit, when a deep voltage drop occurs and a DC commutation failure occurs. In the figure, (a) and (b) are the commutation bus voltage, the reactive output of the doubly fed wind turbine unit and the photovoltaic unit, respectively; and

[0058] Fig.10 A block diagram of a device for suppressing DC continuous commutation failure provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0059] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0060] In view of the problems of weak dynamic reactive power support capability and great hidden danger of system voltage in the wind and solar sending-end system in the prior art, the present application proposes a method for suppressing continuous DC commutation failure, which is based on the coordinated reactive power voltage control strategy of the doubly-fed wind turbine unit and the photovoltaic unit to suppress the continuous DC commutation failure. The method realizes real-time response to the system voltage fluctuation caused by the commutation failure through the coordinated control of reactive voltage between the doubly-fed wind turbine unit and the photovoltaic unit and the interaction with the DC converter station, suppresses the occurrence of continuous commutation failure, and can effectively improve the voltage stability of the DC receiving-end system of the doubly-fed wind turbine unit and the photovoltaic unit.

[0061] First, refer to Figure 1 , which shows a flow chart of a method for suppressing DC continuous commutation failure provided by an exemplary embodiment of the present invention. Figure 1 As shown, the method for suppressing DC continuous commutation failure provided by the embodiment of the present invention comprises the following steps:

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

[0063] Step 120: Determine whether a commutation failure occurs in the DC power transmission system according to the operating state of the DC power transmission system.

[0064] Step 130: If a commutation failure occurs in the DC power transmission system, a commutation failure fault signal is sent to the master control station, so that the master control station controls the double-fed wind turbine unit and the photovoltaic unit to perform reactive power regulation on the DC power transmission system according to the commutation failure fault signal, wherein the master control station coordinates and distributes the values ​​of reactive power output by the double-fed wind turbine unit and the photovoltaic unit according to the degree of grid voltage drop caused by the commutation failure of the DC power transmission system.

[0065] In step 110, the operating state of the DC power transmission system includes the AC bus voltage level and the cut-off angle. In one example, the AC bus voltage level and the cut-off angle are monitored in real time by the DC converter station. The AC bus voltage level and the cut-off angle are used as the basis for determining whether a commutation failure occurs in the DC power transmission system.

[0066] In step 120, after the operating state of the DC power transmission system is obtained, a commutation failure detection link is used to determine whether a commutation failure fault occurs. In the commutation failure detection link, it is determined whether a commutation failure fault occurs in the DC power transmission system according to the operating state of the high voltage DC power transmission system.

[0067] In one example, determining whether a commutation failure fault occurs in the DC power transmission system includes determining whether the DC power transmission system is in a normal operating state or a commutation failure fault state.

[0068] In one example, in the phase-change failure detection link, whether a phase-change failure fault occurs is determined by the turn-off angle and the critical voltage. In one example, in the phase-change failure detection link, whether a phase-change failure fault occurs is determined by the critical voltage. In one example, in the phase-change failure detection link, whether a phase-change failure fault occurs is determined by the turn-off angle. In one example, as long as one of the turn-off angle and the critical voltage does not meet the predetermined condition, it is determined that a phase-change failure fault occurs.

[0069] The present application adds a cut-off angle criterion to perform auxiliary control on the basis of the critical voltage. When the cut-off angle is less than the critical cut-off angle, it is judged that a commutation failure occurs in the DC system. If any of the above criteria is met, it is judged that a commutation failure occurs, and a coordinated control strategy for the double-fed wind turbine unit and the photovoltaic unit is put into operation to supplement the power of the DC receiving system. This control strategy adds a cut-off angle criterion for auxiliary control, which is more accurate and sensitive to the system voltage fluctuation caused by the commutation failure, and suppresses the occurrence of continuous commutation failure more quickly, which can effectively improve the voltage stability of the DC receiving system of the double-fed wind turbine unit and the photovoltaic unit.

[0070] In step 130, if a commutation failure occurs in the DC power transmission system, a commutation failure fault signal is sent to the master control station, so that the master control station controls the double-fed wind turbine unit and the photovoltaic unit to perform reactive power regulation on the DC power transmission system according to the commutation failure fault signal, wherein the master control station coordinates and distributes the values ​​of reactive power output by the double-fed wind turbine unit and the photovoltaic unit according to the degree of grid voltage drop caused by the commutation failure of the DC power transmission system.

[0071] The main control station includes a voltage detection module and a voltage drop judgment module. The voltage drop judgment module determines the degree of voltage drop in the power grid by detecting the value of the line voltage by the voltage detection module. The degree of voltage drop includes no voltage drop, shallow voltage drop and deep voltage drop. According to the above three voltage drop conditions, the double-fed wind turbine unit and the photovoltaic unit are controlled to coordinate reactive power compensation. In one example, controlling the double-fed wind turbine unit and the photovoltaic unit to coordinate reactive power compensation includes selecting which unit to perform reactive power compensation, and the value of reactive power of the double-fed wind turbine unit and the photovoltaic unit for coordinated reactive power compensation.

[0072] In one example, when the voltage detection module input signal is greater than the normal operating minimum voltage limit U L0 , the judgment module outputs a drop signal S v =0, it is considered that the system is still in normal operation mode; when the input signal of the voltage detection module is less than the minimum voltage limit of normal operation U L0 And greater than the boundary voltage U g , the judgment module outputs a drop signal S v =1, it is considered that a shallow voltage drop occurs in the power grid; when the input signal of the voltage detection module is less than the boundary voltage U g , the judgment module outputs a drop signal S v =2, it is considered that the power grid has a deep voltage drop; the master control station determines that the module outputs a drop signal S v =1, the grid voltage drops slightly, and only the doubly fed wind turbine unit needs to perform reactive power compensation; the reactive power reference signal required by the grid bus is transmitted to the reactive outer loop controller of the doubly fed wind turbine unit through the channel; the grid-side converter of the doubly fed wind turbine unit preferentially allocates 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; the master control station determines that the module outputs a drop signal S v =2, the grid voltage drops deeply, and the double-fed wind turbine unit and the photovoltaic unit need to coordinate reactive power compensation. Among them, the degree of grid voltage drop corresponding to the deep voltage drop is greater than the degree of grid voltage drop corresponding to the shallow voltage drop.

[0073] The present invention outputs drop signals to the doubly-fed wind turbine unit and the photovoltaic unit respectively through a main control station, and changes the voltage of the excitation system by setting the excitation controllers on the rotor side and the grid side of the doubly-fed wind turbine unit, thereby adjusting the reactive power output by the doubly-fed wind turbine unit, and changes the power control of the inverter of the photovoltaic unit, thereby adjusting the reactive power output by the photovoltaic unit; necessary power distribution is performed in this link, so that the doubly-fed wind turbine unit and the photovoltaic unit can participate in the reactive coordinated control and voltage regulation of the power system.

[0074] In this embodiment, when the DC system is in a normal operating state, the doubly fed wind turbine unit and the photovoltaic unit do not participate in the voltage regulation of the DC receiving system; when the DC system is in a commutation failure fault state, the doubly fed wind turbine unit and the photovoltaic unit interact with the DC converter station, and the AC bus voltage error signal of the DC converter station is transmitted through the channel, and is coordinated and controlled by the doubly fed wind turbine unit and the photovoltaic unit, so that the system has the ability to directly respond to system voltage fluctuations caused by DC system faults, and effectively and flexibly suppress the system DC continuous commutation failure fault.

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

[0076] Step S1: Acquire the operating status of the high voltage direct current transmission system, where the operating status includes the AC bus voltage level and the shutdown angle.

[0077] Step S2: Commutation failure detection.

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

[0079] Step S4: reactive power distribution of the master control station.

[0080] Among them, in step S1: the AC bus voltage level and the shutdown angle signal of the DC converter station are monitored in real time, and the collected voltage and shutdown angle signals are used to determine whether a commutation failure fault occurs through a commutation failure detection link.

[0081] In step S2, in the phase change failure detection link, the critical voltage and the turn-off angle are used to determine whether a phase change failure fault occurs. In one example, when the turn-off angle is less than the critical turn-off angle, it is determined that a phase change failure fault occurs in the DC power transmission system; and / or when the AC bus voltage is less than the critical voltage, it is determined that a phase change failure fault occurs in the DC power transmission system. In one example, when the bus voltage is less than the critical voltage, it is determined that a phase change failure fault occurs in the DC system. The critical bus voltage for phase change failure can be obtained by calculation, and the formula is:

[0082]

[0083] Where U min is the critical value of bus voltage for the first commutation failure, β is the leading trigger angle,

[0084] θ is the current phase angle, k is the transformer ratio, X r is the commutation reactance, I d is the DC current, U L is the commutation bus voltage, is the phase angle offset of the commutation voltage, γ min is the minimum turn-off angle.

[0085] In one example, a turn-off angle criterion is added on the basis of the critical voltage to perform auxiliary control, and when the turn-off angle is less than the critical turn-off angle, it is determined that a commutation failure occurs in the DC system.

[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 a critical voltage or the shutdown angle is less than a critical shutdown angle, it is determined that a commutation failure has occurred in the DC system.

[0087] In step S3, refer to Figure 3-Figure 6When the commutation failure detection link determines that the DC system is in normal operation, the DC converter station only transmits a digital 0 signal to the master control station through the channel; when the commutation failure detection link determines that the DC system has a commutation failure, the DC converter station transmits the reactive power reference signal required by the DC converter station to the master control station through the channel. The signal carries the reactive power reference value required by the DC converter station. The master control station sends signals to the double-fed wind turbine unit and the photovoltaic unit respectively according to the voltage drop degree and the reactive power reference value required by the DC converter station for reactive voltage coordinated control.

[0088] In one example, after the DC converter station detects the voltage level and the cut-off angle of the monitored AC bus and determines that the DC transmission system is in a normal operating state or a commutation failure fault state based on the AC bus voltage level and the cut-off angle, the DC converter station transmits a specific signal to the master control station through a channel. The specific signal corresponds to the operating state of the high-voltage DC transmission system. In one example, the specific signal is 0 and 1, where 0 indicates that the operating state of the high-voltage DC transmission system is normal; 1 indicates that the high-voltage DC transmission system is in a commutation failure fault state.

[0089] After determining that the high-voltage direct current transmission system is in a commutation failure state, in addition to transmitting the above-mentioned specific signals, the direct current converter station also transmits the reactive power reference signal required by the direct current converter station to the master control station through the channel. The master control station sends signals to the double-fed wind turbine unit and the photovoltaic unit for reactive voltage coordinated control according to the reactive power reference required by the direct current converter station and the voltage drop degree.

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

[0091]

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

[0093] In step S4, in the reactive power distribution link of the master control station, the master control station determines the reactive reference values ​​respectively allocated to the double-fed wind turbine group and the photovoltaic group according to the degree of grid voltage drop and the reactive power reference value required by the DC converter station, and transmits the corresponding reactive reference values ​​to the double-fed wind turbine group and / or the photovoltaic group.

[0094] In one example, the main control station outputs drop signals to the doubly-fed wind turbine unit and the photovoltaic unit respectively, and the excitation system voltage is changed by setting the excitation controllers on the rotor side and the grid side of the doubly-fed wind turbine unit to adjust the reactive power output of the doubly-fed wind turbine unit and by changing the power control of the inverter of the photovoltaic unit to adjust the reactive power output of the photovoltaic unit; necessary power distribution is performed in this link to realize the function of the doubly-fed wind turbine unit and the photovoltaic unit participating in the reactive coordinated control and voltage regulation of the power system.

[0095] In one example, the master control station includes a voltage detection module and a voltage drop judgment module. The voltage detection module is used to detect the voltage value of the DC system, and the voltage drop judgment module judges the degree of grid voltage drop according to the input voltage value of the voltage detection module.

[0096] In one example, when the voltage detection module input signal is greater than the normal operating minimum voltage limit U L0 , the judgment module outputs a drop signal S v =0, it is considered that the system is still in normal operation mode; when the input signal of the voltage detection module is less than the minimum voltage limit of normal operation U L0 And greater than the boundary voltage U g , the judgment module outputs a drop signal S v =1, it is considered that a shallow voltage drop occurs in the power grid; when the input signal of the voltage detection module is less than the boundary voltage U g , the judgment module outputs a drop signal S v =2, it is considered that the power grid has a deep voltage drop; the master control station determines that the module outputs a drop signal S v =1, the grid voltage drops slightly, and only the doubly fed wind turbine unit needs to perform reactive power compensation; the reactive power reference signal required by the grid bus is transmitted to the reactive outer loop controller of the doubly fed wind turbine unit through the channel; the grid-side converter of the doubly fed wind turbine unit preferentially allocates 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; the master control station determines that the module outputs a drop signal S v =2, the grid voltage drops deeply, and the double-fed wind turbine unit and the photovoltaic unit need to coordinate reactive power compensation.

[0097] In summary, the voltage drop judgment module judges the degree of grid voltage drop according to the value of the input voltage of the voltage detection module, including:

[0098] When the input signal of the voltage detection module is greater than the minimum voltage limit U of the normal operation of the power grid system L0 , it is judged that the power grid system is in normal operation mode, and the voltage drop judgment module outputs a drop signal S v =0;

[0099] When the input signal of the voltage detection module is less than the minimum voltage limit U of the normal operation of the power grid system L0 And greater than the boundary voltage U g , it is judged that the power grid system has a shallow voltage drop, and the voltage drop judgment module outputs a drop signal S v =1;

[0100] When the voltage detection module input signal is less than the boundary voltage U g , judge that the power grid system has a deep voltage drop, and the voltage drop judgment module outputs a drop signal S v =2.

[0101] In one example, the specific strategy of the reactive power distribution link of the master control station includes the following steps:

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

[0103] S42: The master station determines that the module outputs a drop signal S v =1, the grid voltage drops slightly, and only the doubly fed wind turbine unit needs to perform reactive power compensation; the reactive power reference signal required by the grid bus is transmitted to the reactive outer loop controller of the doubly fed wind turbine unit through the channel; the grid-side converter of the doubly fed wind turbine unit preferentially allocates reactive power, and 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 master station determines that the module outputs a drop signal S v =2, the grid voltage drops deeply, and the double-fed wind turbine unit and the photovoltaic unit need to coordinate reactive power compensation; during the fault period, the reactive current command value of the photovoltaic unit I q The formula is:

[0105]

[0106] In the formula, I q is the reactive current command value, U L is the actual effective value of the bus voltage, U g is the boundary voltage, IN It is the total rated current of the PV station inverter.

[0107] In summary, the master control station includes the following values ​​for coordinating and allocating the reactive power output by the double-fed wind turbine and photovoltaic units according to the degree of grid voltage drop caused by the commutation failure of the DC transmission system:

[0108] When the grid voltage drops slightly, only the double-fed wind turbine unit performs reactive power compensation;

[0109] When the grid voltage experiences a deep voltage drop, the doubly-fed wind turbine unit and the photovoltaic unit jointly perform coordinated reactive power compensation.

[0110] When the grid voltage drops slightly, only the double-fed wind turbine unit performs reactive power compensation including:

[0111] The reactive power reference signal required by the grid bus is transmitted through the channel to the reactive outer loop controller of the doubly-fed wind turbine unit, where the grid-side converter of the doubly-fed wind turbine unit provides reactive power first.

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

[0113] The degree of grid voltage drop of the present application and the reactive power reference value required by the DC converter station determine the reactive reference values ​​respectively allocated to the double-fed wind turbine unit and the photovoltaic unit. The scheme not only performs reactive power control based on the reactive power required by the DC converter station, but also performs reactive power control based on the degree of grid voltage drop, which optimizes the reactive control strategy, makes reactive control more accurate, and makes the voltage stability of the DC receiving system stronger. The real-time and coordinated reactive coordination control of the double-fed wind turbine unit and the photovoltaic unit effectively improves the voltage stability of the DC receiving system of the double-fed wind turbine unit and the photovoltaic unit.

[0114] Technical feasibility verification of the present invention

[0115] The system model of the engineering simulation example is as follows Figure 7 The simulation comparison results are shown in Figure 8 , Fig. 9 As shown, the effectiveness of the present invention is verified. Figure 8 In the DC receiving system, the commutation bus voltage drops slightly and the DC commutation failure occurs. The dynamic response comparison diagram of reactive power before and after the reactive voltage coordinated control strategy is implemented using only the doubly fed wind turbine unit. (a) and (b) are the commutation bus voltage and the reactive output of the doubly fed wind turbine unit, respectively. Fig. 9In the DC receiving system, the commutation bus voltage drops deeply and the DC commutation failure occurs. The dynamic response comparison diagram of reactive power before and after the reactive voltage coordinated control strategy is configured for the doubly fed wind turbine unit and the photovoltaic unit. (a) and (b) are the commutation bus voltage, the reactive output of the doubly fed wind turbine unit and the photovoltaic unit, respectively.

[0116] After adopting the coordinated control strategy, the commutation failure detection link extracts the AC bus voltage signal of the DC converter station, and determines in real time whether a commutation failure has occurred and sends it to the master control station. When the commutation failure detection link determines that it is a fault, the master control station transmits the reactive reference signal to the corresponding object according to the drop signal.

[0117] Depend on Figure 8 (a) and (b) show that when the commutation bus voltage drops slightly, after the coordinated control strategy proposed in this paper is put into use, the doubly fed wind turbine unit can quickly respond to the reactive power demand of the DC system and quickly increase the reactive power by about 3pu during the recovery period of commutation failure. Compared with the working condition without the coordinated control strategy, the commutation bus voltage is raised by about 0.2pu, which effectively increases the commutation margin of the converter. Due to the increase in bus voltage, the minimum shutdown angle during the recovery period is increased from 4° to 10°, and the number of commutation failures is reduced from 2 times to 1 time. This shows that the configuration of the coordinated control strategy enables the doubly fed wind turbine unit to effectively suppress the occurrence of continuous commutation failures under the condition of shallow bus voltage drops, and improve the recovery speed of DC transmission power.

[0118] Depend on Fig. 9 (a) and (b) show that when the commutation bus voltage drops deeply, after the coordinated control strategy is put into use, the photovoltaic unit generates about 5pu of reactive power during the transient period, the doubly fed wind turbine unit generates about 2pu of reactive power, and the bus voltage rises by about 0.8pu. The minimum value of the shutdown angle is increased from 0° to 12°, the number of commutation failures is reduced from 2 times to 1 time, and the DC transmission power recovery is accelerated. Under the condition of deep bus voltage drop, the coordinated control strategy proposed by the present invention is still relatively effective.

[0119] In summary, the reactive voltage coordinated control strategy of the doubly-fed wind turbine unit and the photovoltaic unit to suppress the failure of continuous DC commutation of the present invention is that the control strategy outputs the corresponding drop signal from the master control station according to the voltage drop degree of the receiving-end commutation bus, and acts on the doubly-fed wind turbine unit and the photovoltaic unit; during the recovery period of commutation failure, the master control station can determine the reactive compensation size based on the bus voltage drop amplitude to improve the commutation conditions of the converter. Since this method does not require year-round phase adjustment operation or additional dynamic reactive compensation equipment, this control strategy has economic and practical value.

[0120] like Fig.10 As shown, the present invention also provides a device 100 for suppressing DC continuous commutation failure, which is used in a scenario where a double-fed wind turbine unit and a photovoltaic unit are connected to a DC receiving system together, comprising:

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

[0122] A judging module 120, configured to judge whether a commutation failure occurs in the DC power transmission system according to the operating state of the DC power transmission system;

[0123] The reactive power regulation module 130 is used to send a commutation failure fault signal to the master control station if a commutation failure fault occurs in the DC power transmission system, so that the master control station controls the double-fed wind turbine unit and the photovoltaic unit to perform reactive power regulation on the receiving end of the DC power transmission system according to the commutation failure fault signal;

[0124] Among them, the master control station coordinates and distributes the output reactive power values ​​of the doubly-fed wind turbine units and photovoltaic units according to the degree of grid voltage drop caused by the commutation failure of the DC transmission system.

[0125] In one example, the extent of the grid voltage sag includes a shallow voltage sag and a deep voltage sag;

[0126] The master control station is used to control the double-fed wind turbine units to perform reactive power compensation when the grid voltage drops slightly;

[0127] When the grid voltage experiences a deep voltage drop, the double-fed wind turbine unit and the photovoltaic unit are controlled to perform coordinated reactive power compensation.

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

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

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

[0131] Wherein, the critical voltage is:

[0132]

[0133] Among them, U min is the critical value of bus voltage for the first commutation failure, which is calculated based on U min Sure,

[0134] β is the leading trigger angle, k is the transformer ratio, X r is the commutation reactance, I d is the DC current, O is the phase angle offset of the commutation voltage, γ min is the minimum turn-off angle.

[0135] In one example, the reactive power regulation module 130 is further configured to:

[0136] Transmitting a reactive power reference signal required by the DC converter station to the master control station through a channel, wherein the reactive power reference signal carries a reactive power reference value required by the DC converter station;

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

[0138]

[0139] Among them, Q ref is the reactive power reference value required by the DC converter station, or the reactive power outer loop controller input signal, U ref is the reference value of the AC bus voltage of the DC converter station, U L is the actual effective value of the AC bus voltage of the DC converter station, K and T are the proportional and integral coefficients of the proportional-integral controller respectively, and s is 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, and the voltage drop judgment module judges the degree of grid voltage drop according to the value of the input voltage of the voltage detection module;

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

[0142] In one example, the voltage drop judgment module is used to detect when the input signal of the voltage detection module is greater than the minimum voltage limit value U of the normal operation of the power grid system. L0 , it is determined that the power grid system is in normal operation mode, and the voltage drop judgment module outputs a drop signal S v =0;

[0143] When the voltage detection module input signal is less than the minimum voltage limit value U of the normal operation of the power grid system L0 And greater than the boundary voltage U g , it is determined that the power grid system has a shallow voltage drop, and the voltage drop judgment module outputs a drop signal S v =1;

[0144] When the voltage detection module input signal is less than the boundary voltage U g , it is determined that the power grid system has a deep voltage drop, and the voltage drop determination module outputs a drop signal Sv=2.

[0145] In one example, the master control station is used to transmit the reactive power reference signal required by the DC converter station to the reactive outer loop controller of the double-fed wind turbine unit through a channel when the grid voltage drops slightly, so as to control the grid-side converter of the double-fed wind turbine unit to provide reactive power.

[0146] If the reactive power demand of the DC converter station exceeds the reactive power upper limit of the grid-side converter output, the stator-side converter of the double-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 the fault period when the grid voltage drops deeply. q for:

[0148]

[0149] Among them, I q is the reactive current command value, U L is the actual effective value of the bus voltage, U g is the boundary voltage, I N It is the total rated current of the PV station inverter.

[0150] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0151] Those of ordinary skill in the art will appreciate that the templates, units, and algorithm steps of each example 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 performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0152] If the module / unit is implemented in the form of 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, the present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by the processor, the steps of the above-mentioned method embodiments for suppressing the failure of DC continuous commutation can be implemented. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium may include: any entity or device that can carry the computer program code, recording medium, U disk, mobile hard disk, disk, optical disk, computer memory, read-only memory, random access memory, electrical carrier signal, telecommunication signal and software distribution medium.

[0153] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A method for suppressing DC continuous commutation failure, characterized in that: It is used in scenarios where doubly-fed wind turbines and photovoltaic units are connected to the DC receiving system together, including: Obtain the operating status of the DC transmission system; According to the operating state of the DC power transmission system, determining whether a commutation failure occurs in the DC power transmission system; If a commutation failure occurs in the DC power transmission system, a commutation failure fault signal is sent to the master control station, so that the master control station controls the double-fed wind turbine unit and the photovoltaic unit to perform reactive power regulation on the DC power transmission system according to the commutation failure fault signal. The master control station coordinates and distributes the values ​​of reactive power output by the double-fed wind turbine unit and the photovoltaic unit according to the degree of grid voltage drop caused by the commutation failure of the direct current transmission system.

2. The method for suppressing DC continuous commutation failure according to claim 1, characterized in that: The operating status of the DC power transmission system includes the AC bus voltage level and the shutdown angle signal monitored in real time by the DC converter station; The determining, according to the operating state of the DC power transmission system, whether a commutation failure occurs in the DC power transmission system comprises: When the cut-off angle is less than the critical cut-off angle, it is determined that a commutation failure fault occurs in the DC power transmission system; and / or when the AC bus voltage is less than the critical voltage, it is determined that a commutation failure fault occurs in the DC power transmission system; Wherein, the critical voltage is: Among them, U min is the critical value of bus voltage for the first commutation failure, which is calculated based on U min Sure, β is the leading trigger angle, k is the transformer ratio, X r is the commutation reactance, I d is the DC current, θ is the phase angle deviation of the commutation voltage, γ min is the minimum turn-off angle.

3. The method for suppressing DC continuous commutation failure according to claim 1, characterized in that: In addition to sending a commutation failure fault signal to the master control station, it also includes: Transmitting a reactive power reference signal required by the DC converter station to the master control station through a channel, wherein the reactive power reference signal carries a reactive power reference value required by the DC converter station; The reactive power reference value required by the DC converter station is: Among them, Q ref is the reactive power reference value required by the DC converter station, or the reactive power outer loop controller input signal, U ref is the reference value of the AC bus voltage of the DC converter station, U L is the actual effective value of the AC bus voltage of the DC converter station, K and T are the proportional and integral coefficients of the proportional-integral controller respectively, and s is the complex frequency variable in the Laplace transform domain.

4. The method for suppressing DC continuous commutation failure according to claim 3, characterized in that: The master control station includes a voltage detection module and a voltage drop judgment module, and the voltage drop judgment module judges the degree of grid voltage drop according to the value of the input voltage of the voltage detection module; Among them, the main control station determines the reactive reference values ​​respectively allocated to the doubly fed wind turbine group and the photovoltaic group according to the degree of grid voltage drop and the reactive power reference value required by the DC converter station, and transmits the reactive reference signal corresponding to the reactive reference value to the doubly fed wind turbine group and / or the photovoltaic group.

5. The method for suppressing DC continuous commutation failure according to claim 4, characterized in that: The voltage drop judgment module is used to detect the voltage drop when the input signal of the voltage detection module is greater than the minimum voltage limit value U of the normal operation of the power grid system. L0 , it is determined that the power grid system is in normal operation mode, and the voltage drop judgment module outputs a drop signal S v =0; When the voltage detection module input signal is less than the minimum voltage limit value U of the normal operation of the power grid system L0 And greater than the boundary voltage U g , it is determined that the power grid system has a shallow voltage drop, and the voltage drop judgment module outputs a drop signal S v =1; When the voltage detection module input signal is less than the boundary voltage U g , it is determined that the power grid system has a deep voltage drop, and the voltage drop determination module outputs a drop signal Sv=2.

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

7. The method for suppressing DC continuous commutation failure according to claim 6, characterized in that: The master control station is used to transmit the reactive power reference signal required by the DC converter station to the reactive outer loop controller of the double-fed wind turbine unit through a channel when the grid voltage drops slightly, so as to control the grid-side converter of the double-fed wind turbine unit to provide reactive power. If the reactive power demand of the DC converter station exceeds the reactive power upper limit of the grid-side converter output, the stator-side converter of the double-fed wind turbine unit is controlled to compensate for the remaining reactive power demand.

8. The method for suppressing DC continuous commutation failure according to claim 6, characterized in that: The master control station is also used to determine the reactive current command value I of the photovoltaic unit during the fault period when the grid voltage drops deeply. q for: Among them, I q is the reactive current command value, U L is the actual effective value of the bus voltage, U g is the boundary voltage, I N It is the total rated current of the PV station inverter.

9. A device for suppressing DC continuous commutation failure, characterized in that: It is used in scenarios where doubly-fed wind turbines and photovoltaic units are connected to the DC receiving system together, including: An acquisition module, used for acquiring the operating status of the DC transmission system; A judgment module, used for judging whether a commutation failure occurs in the DC power transmission system according to the operating state of the DC power transmission system; A reactive power regulation module is used for sending a commutation failure fault signal to a master control station if a commutation failure fault occurs in the DC power transmission system, so that the master control station controls the double-fed wind turbine unit and the photovoltaic unit to perform reactive power regulation on the receiving end of the DC power transmission system according to the commutation failure fault signal; The master control station coordinates and distributes the values ​​of reactive power output by the double-fed wind turbine unit and the photovoltaic unit according to the degree of grid voltage drop caused by the commutation failure of the direct current transmission system.

10. The device for suppressing DC continuous commutation failure according to claim 9, characterized in that: The degree of the grid voltage drop includes shallow voltage drop and deep voltage drop; The master control station is used to control the double-fed wind turbine unit to perform reactive power compensation when the grid voltage is in a shallow voltage drop; When the grid voltage experiences a deep voltage drop, the double-fed wind turbine unit and the photovoltaic unit are controlled to jointly perform coordinated reactive power compensation.

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