CN117526397B - Flexible direct-current inner-loop-free network construction control method and system with current limiting function - Google Patents

Flexible direct-current inner-loop-free network construction control method and system with current limiting function Download PDF

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CN117526397B
CN117526397B CN202410011765.9A CN202410011765A CN117526397B CN 117526397 B CN117526397 B CN 117526397B CN 202410011765 A CN202410011765 A CN 202410011765A CN 117526397 B CN117526397 B CN 117526397B
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current
converter
axis
value
voltage
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CN117526397A (en
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赵峥
李探
李明
牛翀
郑宽
薛英林
李政
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State Grid Economic And Technological Research Institute Co LtdB412 State Grid Office
State Grid Corp of China SGCC
State Grid Qinghai Electric Power Co Ltd
Xian XJ Power Electronics Technology Co Ltd
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State Grid Economic And Technological Research Institute Co LtdB412 State Grid Office
State Grid Corp of China SGCC
State Grid Qinghai Electric Power Co Ltd
Xian XJ Power Electronics Technology Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • H02J3/241—The oscillation concerning frequency
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/388—Islanding, i.e. disconnection of local power supply from the network
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/40—Synchronising a generator for connection to a network or to another generator
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
    • H02M5/40—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc
    • H02M5/42—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters
    • H02M5/44—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac
    • H02M5/453—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M5/458—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M5/4585—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only having a rectifier with controlled elements
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/28—The renewable source being wind energy
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Control Of Eletrric Generators (AREA)

Abstract

The invention relates to a flexible direct current inner loop-free network construction control method and system with a current limiting function, wherein the method comprises the following steps: determining the amplitude and the phase of the converter voltage to generate a voltage command value U dref0 of a d-axis component and a voltage command value U qref0 of a q-axis component of the converter output voltage in a rotating coordinate system, and determining intermediate variables delta x d0 and delta x q0 of the d-axis and the q-axis respectively by U dref0 and U qref0; setting the output of the difference value of the maximum current limit i dmax of the d-axis and the component i d of the actual value of the current of the alternating current side on the d-axis of the rotating coordinate system as the upper limit value of the intermediate variable after passing through the PI controller, and obtaining the d-axis intermediate variable after the limit value; setting the output of the difference value of the maximum current limit i qmax of the q-axis and the component i q of the actual value of the current of the alternating current side on the q-axis of the rotating coordinate system as the upper limit value of the intermediate variable, and obtaining the q-axis intermediate variable after the limit value; the voltage command value U dref for the d-axis component and the voltage command value U qref for the q-axis component are recalculated based on the upper limit value of the intermediate variable.

Description

Flexible direct-current inner-loop-free network construction control method and system with current limiting function
Technical Field
The invention relates to the technical field of direct current transmission, in particular to a flexible direct current inner loop-free network control method and system with a current limiting function.
Background
The offshore wind power resources in China are rich, but the intermittent and uncontrollable wind power characteristics enable the distributed power supply to be continuously increased. The conventional distributed grid-connected power generation control adopts power electronic devices, and the mode does not show inherent inertia, frequency modulation and voltage regulation control characteristics of a conventional power system, so that the method brings serious challenges to safe and stable operation of a power grid.
The synchronous generator has the advantage of being natural and friendly to the power grid, combines the flexibility of power electronic equipment and the operation mechanism of the synchronous generator by using the virtual synchronous generator control technology of the operation experience of the traditional power system, can realize the plug-and-play and autonomous operation of new energy, and can effectively solve the problems of underdamping and low inertia of the system. The VSC-HVDC adopting the virtual synchronous control can well solve the stability problem of the voltage frequency of the alternating current system under the island operation, and realizes reasonable power distribution of the multi-flexible direct island and smooth switching of the island/networking operation, so that the method is widely applied to the grid-connected field of the converter station.
However, the converter stations exhibit weak/negative damping characteristics over a wide frequency range, and the system is prone to oscillation problems. The virtual synchronous control structure is a double closed loop, and in the middle frequency range, the current inner loop plays a decisive role in the impedance characteristic of the converter, but single change of the inner loop parameters or additional damping control is difficult to realize oscillation suppression in a wider frequency range. The virtual synchronous control strategy adopting voltage single loop control can not limit the alternating current amplitude of the converter, and the system reliability is reduced.
Disclosure of Invention
Aiming at the problems, the invention aims to provide a flexible direct current inner loop-free network control method and system with a current limiting function, so as to effectively solve the problems that the double closed loop control is difficult to inhibit broadband oscillation and the voltage single loop control cannot limit the current amplitude.
In order to achieve the above purpose, the present invention adopts the following technical scheme: a flexible direct current inner loop-free network control method with a current limiting function comprises the following steps: aiming at the converter, a control loop for simulating a synchronous generator rotor operation equation and excitation control is established; determining the amplitude and the phase of the converter voltage according to the established simulation synchronous generator rotor operation equation and a control loop of excitation control, as well as the command of the active power and the command of the reactive power of the converter, so as to generate a voltage command value U dref0 of a d-axis component and a voltage command value U qref0 of a q-axis component of the converter output voltage in a rotating coordinate system, and determining intermediate variables delta x d0 and delta x q0 of the d-axis and the q-axis respectively by U dref0 and U qref0; setting the output of the current actual value of the alternating current side of the converter at the upper limit value of an intermediate variable Deltax d0 after passing through the PI controller as the difference value between a maximum current limit i dmax of the current actual value of the alternating current side at the d axis of the rotating coordinate system and a component i d of the current actual value of the alternating current side at the d axis of the rotating coordinate system to obtain a d-axis intermediate variable Deltax d after the limit value; setting the output of the current actual value of the alternating current side of the converter at the upper limit value of an intermediate variable Deltax q0 after passing through the PI controller as the difference value between a maximum current limit i qmax of the current actual value of the alternating current side at the q axis of the rotating coordinate system and a component i q of the current actual value of the alternating current side at the q axis of the rotating coordinate system to obtain a q-axis intermediate variable Deltax q after the limit value; the voltage command value U dref for the d-axis component and the voltage command value U qref for the q-axis component are recalculated based on the upper limit Δχ d、Δxq for the intermediate variable after the limit.
Further, the simulated synchronous generator rotor operation equation is:
Wherein J is a virtual rotor time constant, D is a virtual generator damping factor, P ref is an instruction value of active power of the converter, P e is actual power of the converter, omega 0 is a rotating speed reference value of the rotor, Is the actual value of the rotating speed of the rotor,/>Is the phase angle of the output voltage of the converter.
Further, the excitation control equation is:
Wherein Q ref is a reactive power command value of the converter, U ac_ref is an ac voltage command value of the converter, U ac is an actual ac voltage amplitude of the ac bus, s is a complex frequency, Q is a reactive power actual value of the converter, k q is a reactive power deviation gain coefficient, k ac is an ac voltage deviation gain coefficient, k p is a virtual internal potential controller proportional gain, T i is a virtual internal potential controller integral time constant, E 0 is a virtual internal potential reference value, and E is an amplitude of the converter voltage.
Further, the d-axis maximum current limit i dmax and the q-axis maximum current limit i qmax are set by the maximum value of the bridge arm current in the converter transient state and the maximum value of the short circuit current that the converter feeds into the ac system.
Further, the method comprises the steps of: the arrangement of i dmax and i qmax includes:
determining the clearing time t fault of the fault of the alternating current system;
Calculating the maximum value I armmax of bridge arm current corresponding to the junction temperature of the converter device T jmax at T fault;
Determining the corresponding maximum current I max of the alternating current side of the converter according to the maximum value I armmax of the bridge arm current;
When the converter is connected into an alternating current system with short-circuit current not exceeding limit, i dmax and i qmax are limited according to preset proportion:
wherein k is a proportionality coefficient;
When the converter is connected into an alternating current system with out-of-limit short circuit current, determining I qmax according to the maximum limit of the short circuit current fed into the alternating current system by the converter, and obtaining according to the determined I qmax and I max 。
Further, intermediate variables Δx d0 and Δx q0 of the d-axis and q-axis are determined by U dref0 and U qref0, respectively, by the following formula, including:
Wherein L, R is the equivalent impedance of the converter, and U sd、Usq is the component of the voltage of the AC bus of the converter on the d and q axes.
Further, the voltage command value U dref of the d-axis component and the voltage command value U qref of the q-axis component are recalculated by the following formulas:
。
A flexible dc non-inner loop network control system with current limiting function, comprising: the control loop establishing module is used for establishing a control loop for simulating a synchronous generator rotor operation equation and excitation control aiming at the converter; determining the amplitude and the phase of the converter voltage according to the established simulation synchronous generator rotor operation equation and a control loop of excitation control, as well as the command of the active power and the command of the reactive power of the converter, so as to generate a voltage command value U dref0 of a d-axis component and a voltage command value U qref0 of a q-axis component of the converter output voltage in a rotating coordinate system, and determining intermediate variables delta x d0 and delta x q0 of the d-axis and the q-axis respectively by U dref0 and U qref0; the d-axis limiting module is used for setting the output of the current limiter module of the current converter after passing through the PI controller as the upper limit value of the intermediate variable Deltax d0 to obtain a d-axis intermediate variable Deltax d after limiting the difference value between the maximum current limit i dmax of the current actual value of the current converter on the d axis of the rotating coordinate system and the component i d of the current actual value of the current on the alternating side on the d axis of the rotating coordinate system; the q-axis limiting module is used for setting the output of the current limiter module of the current converter after passing through the PI controller as the upper limit value of an intermediate variable Deltax q0 to obtain a q-axis intermediate variable Deltax q after limiting the difference value between a maximum current limit i qmax of an actual value of an alternating current side current of the current converter on the q-axis of a rotating coordinate system and a component i q of the actual value of the current side current on the q-axis of the rotating coordinate system; the calculation module recalculates the voltage command value U dref of the d-axis component and the voltage command value U qref of the q-axis component according to the intermediate variable Deltax d、Δxq after the limit value.
Further, the simulated synchronous generator rotor operation equation is:
Wherein J is a virtual rotor time constant, D is a virtual generator damping factor, P ref is an instruction value of active power of the converter, P e is actual power of the converter, omega 0 is a rotating speed reference value of the rotor, Is the actual value of the rotating speed of the rotor,/>Is the phase angle of the output voltage of the converter.
Further, the excitation control equation is:
Wherein Q ref is a reactive power command value of the converter, U ac_ref is an ac voltage command value of the converter, U ac is an actual ac voltage amplitude of the ac bus, s is a complex frequency, Q is a reactive power actual value of the converter, k q is a reactive power deviation gain coefficient, k ac is an ac voltage deviation gain coefficient, k p is a virtual internal potential controller proportional gain, T i is a virtual internal potential controller integral time constant, E 0 is a virtual internal potential reference value, and E is an amplitude of the converter voltage.
Further, the d-axis maximum current limit i dmax and the q-axis maximum current limit i qmax are set by the maximum value of the bridge arm current in the converter transient state and the maximum value of the short circuit current that the converter feeds into the ac system.
Further, the method comprises the steps of: the arrangement of i dmax and i qmax includes:
determining the clearing time t fault of the fault of the alternating current system;
Calculating the maximum value I armmax of bridge arm current corresponding to the junction temperature of the converter device T jmax at T fault;
Determining the corresponding maximum current I max of the alternating current side of the converter according to the maximum value I armmax of the bridge arm current;
When the converter is connected into an alternating current system with short-circuit current not exceeding limit, i dmax and i qmax are limited according to preset proportion:
wherein k is a proportionality coefficient;
When the converter is connected into an alternating current system with out-of-limit short circuit current, determining I qmax according to the maximum limit of the short circuit current fed into the alternating current system by the converter, and obtaining according to the determined I qmax and I max 。
Further, intermediate variables Δx d0 and Δx q0 of the d-axis and q-axis are determined by U dref0 and U qref0, respectively, by the following formula, including:
Wherein L, R is the equivalent impedance of the converter, and U sd、Usq is the component of the voltage of the AC bus of the converter on the d and q axes.
Further, the voltage command value U dref of the d-axis component and the voltage command value U qref of the q-axis component are recalculated by the following formulas:
。
A computer readable storage medium storing one or more programs, the one or more programs comprising instructions, which when executed by a computing device, cause the computing device to perform any of the methods described above.
A computing apparatus, comprising: one or more processors, memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, the one or more programs comprising instructions for performing any of the methods described above.
Due to the adoption of the technical scheme, the invention has the following advantages:
1. The invention not only ensures the capacity of providing inertia for the system by the network construction control, but also avoids a brand new solution of the overcurrent risk of the converter.
2. The invention does not need a virtual synchronous generator control strategy of the current inner ring, effectively solves the difficult problem of flexible and straight broadband oscillation caused by the selection of the current inner ring and parameters thereof, and reduces the complexity of a control system.
3. The current limiting method solves the problem that single loop control cannot be used for limiting current rapidly in fault, and the method does not act on the system in steady operation, so that the stability of the control system is improved.
Drawings
FIG. 1 is a flow chart of the whole method for controlling the current limiting without an inner loop of the offshore wind power flexible direct current output system in the embodiment of the invention;
FIG. 2 is a block diagram of a flexible DC output system for offshore wind power in an embodiment of the invention;
FIG. 3 is a control block diagram of the offshore wind power flexible direct current output system no-inner-loop current limiting method in the embodiment of the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. It will be apparent that the described embodiments are some, but not all, embodiments of the invention. All other embodiments, which are obtained by a person skilled in the art based on the described embodiments of the invention, fall within the scope of protection of the invention.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the present invention. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.
Aiming at the problem that oscillation suppression in a wider frequency domain is difficult to realize in the prior art, the invention provides a flexible direct-current inner-loop-free network control method and system with a current limiting function, and the specific contents comprise two steps: 1) The control system can quickly play a role in limiting current during faults, and a brand new solution is provided for ensuring the capacity of providing inertia for the system by the network-structured control and avoiding the overcurrent risk of the converter; 2) The current limiting does not play a role in the steady state, and the voltage single loop operates. Because the current inner loop and the parameter selection thereof become the accepted factors causing the difficult problem of soft and straight broadband oscillation, compared with the traditional method with the inner loop, the amplitude limiting method can thoroughly solve the difficult problem of broadband oscillation.
In one embodiment of the invention, a flexible direct current inner loop-free network control method with a current limiting function is provided. In this embodiment, as shown in fig. 1, the method includes the following steps:
1) Establishing a control loop for simulating synchronous generator rotor operation equation and excitation control aiming at the converter, determining the amplitude and the phase of the converter voltage according to the established control loop for simulating synchronous generator rotor operation equation and excitation control and the instructions of active power and reactive power of the converter so as to generate a voltage instruction value U dref0 of a d-axis component and a voltage instruction value U qref0 of a q-axis component of the converter output voltage in a rotating coordinate system, and respectively determining intermediate variables delta x d0 and delta x q0 of d-axis and q-axis by U dref0 and U qref0;
2) Setting the output of the current actual value of the alternating current side of the converter at the upper limit value of an intermediate variable Deltax d0 after passing through the PI controller as the difference value between a maximum current limit i dmax of the current actual value of the alternating current side at the d axis of the rotating coordinate system and a component i d of the current actual value of the alternating current side at the d axis of the rotating coordinate system to obtain a d-axis intermediate variable Deltax d=lim(Δxd0 after the limit value;
3) Setting the output of the current actual value of the alternating current side of the converter at the upper limit value of an intermediate variable Deltax q0 after passing through the PI controller as the difference value between a maximum current limit i qmax of the current actual value of the alternating current side at the q axis of the rotating coordinate system and a component i q of the current actual value of the alternating current side at the q axis of the rotating coordinate system to obtain a q-axis intermediate variable Deltax q=lim(Δxq0 after the limit value;
4) And recalculating a voltage command value U dref of the d-axis component and a voltage command value U qref of the q-axis component according to the upper limit value Deltax d、Δxq of the intermediate variable after the limit value so as to realize flexible direct current inner loop-free network control with a current limiting function.
In the step 1), determining the phase of the converter voltage, specifically, determining the phase of the converter voltage according to the operation equation of the analog synchronous generator rotor and the instruction of the active power; the running equation of the rotor of the simulated synchronous generator is as follows:
Wherein J is a virtual rotor time constant, D is a virtual generator damping factor, P ref is an active power instruction value of the converter (the inflow of an alternating current system is in a positive direction), P e is the actual power of the converter, omega 0 is a rotating speed reference value of the rotor, Is the actual value of the rotating speed of the rotor,/>Is the phase angle of the output voltage of the converter.
Determining the amplitude of the converter voltage according to an excitation control equation and a reactive power instruction, wherein the excitation control equation is as follows:
Wherein Q ref is a reactive power command value of the converter, U ac_ref is an ac voltage command value of the converter, U ac is an actual ac voltage amplitude of the ac bus, s is a complex frequency, Q is a reactive power actual value of the converter, k q is a reactive power deviation gain coefficient, k ac is an ac voltage deviation gain coefficient, k p is a virtual internal potential controller proportional gain, T i is a virtual internal potential controller integral time constant, E 0 is a virtual internal potential reference value, and E is an amplitude of the converter voltage.
In the above step 1), the intermediate variables Δx d0 and Δx q0 of the d-axis and q-axis are determined by U dref0 and U qref0 by the following formulas, respectively, including:
Wherein L, R is the equivalent impedance of the converter, and U sd、Usq is the component of the voltage of the AC bus of the converter on the d and q axes.
In the above steps 2) -3), the d-axis maximum current limit i dmax and the q-axis maximum current limit i qmax are set by the maximum value of the bridge arm current in the transient state of the converter valve and the maximum value of the system short-circuit current.
In this embodiment, the setting of i dmax and i qmax includes the following steps:
(1) Determining the clearing time t fault of the fault of the alternating current system;
(2) Calculating the maximum value I armmax of bridge arm current corresponding to the junction temperature of the converter device T jmax at T fault;
(3) Determining the corresponding maximum current I max of the alternating current side of the converter according to the maximum value I armmax of the bridge arm current;
Wherein, I max is:
In the method, in the process of the invention, Is a direct current.
(4) When the converter is connected into an alternating current system with short-circuit current not exceeding limit, i dmax and i qmax are limited according to a preset proportion;
for example, the ratio set is k:1, then there are:
(5) When the converter is connected into an alternating current system with out-of-limit short circuit current, determining I qmax according to the maximum limit of the short circuit current fed into the alternating current system by the converter, and further determining I dmax according to I qmax and I max: 。
In this embodiment, the parameter of the PI controller may be set to a fixed value, or the adjustable PI parameter may be determined according to the magnitude of the deviation, when the deviation is large, the PI parameter is set to a larger value to suppress the current more quickly, and when the deviation is small, the PI parameter is set to a smaller value to avoid large overshoot or instability.
In the above step 4), the voltage reference value U dref of the d-axis component and the voltage reference value U qref of the q-axis component are recalculated by the following formulas:
。
In the embodiment, as shown in fig. 2, the offshore wind power flexible direct current output system adopts an end-to-end flexible direct current transmission system, the system consists of a transmitting end offshore converter station and a receiving end land converter station, an island of the offshore converter station is connected with an offshore wind power field, the land converter station is connected with an alternating current system, and the flexible direct current converter adopts a half-bridge modular multilevel converter. The method of the present invention will be described in further detail below with respect to a + -500 kV/2000MW double-ended back-to-back flexible DC delivery system.
1. And (3) establishing a control loop for simulating a synchronous generator rotor operation equation and excitation control, determining the amplitude and the phase of the converter voltage according to the instructions of active power and reactive power, generating the converter output voltage, and performing dq conversion to obtain the instruction values U dref0 and U qref0 of components on the d and q axes of a rotating coordinate system.
The specific calculation process of the phase and the amplitude of the output voltage is shown as a virtual rotor motion equation and a virtual excitation control in fig. 3. The virtual rotor equation of motion is as follows:
In the rotor operation equation, J is a virtual rotor time constant, D is a virtual generator damping factor, P ref is an inverter active power command value (the inflow of an alternating current system is in a positive direction), and omega 0 is a rotating speed reference value of the rotor.
The virtual excitation control equation is as follows:
Wherein Q ref is a converter reactive power command value, U ac_ref is a converter ac voltage command value, k q is a reactive power deviation gain factor, k ac is an ac voltage deviation gain factor, k p is a virtual internal potential controller proportional gain, T i is a virtual internal potential controller integration time constant, and E 0 is a virtual internal potential command value.
2. The U dref0、Uqref0, the component i d、iq of the ac side current actual value on the d and q axes of the rotating coordinate system, and the maximum current limits i dmax and i qmax of the d and q axes are input into the inner loop free current limiting calculation module.
The maximum current limits i dmax and i qmax of the d and q axes are set by the maximum value of bridge arm current and the maximum value of system short circuit current under the transient state of the converter valve. The method comprises the following steps:
1) Determining the clearing time t fault of the fault of the alternating current system;
2) Calculating the maximum value I armmax of bridge arm current corresponding to the junction temperature of the converter device T jmax at T fault;
3) Determining a corresponding converter ac side maximum current ；
4) When the converter is connected into an alternating current system with short-circuit current not exceeding limit, i dmax and i qmax are in a certain proportion k:1, specifically:
5) When the converter is connected into an alternating current system with out-of-limit short circuit current, i qmax is determined according to the system requirement, and i dmax is further determined: 。
3. the inner-loop-free current limiting calculation module firstly calculates intermediate variables delta x d0=Lid/dt+Rid0 and delta x q0=Liq/dt+Riq according to a dynamic current equation of the converter, and the specific calculation process is as follows:
Wherein L, R is the equivalent impedance of the converter, and U sd、Usq is the component of the voltage of the AC bus of the converter on the d and q axes.
4. The upper limit value calculation process of the intermediate variable Deltax d0 is that the difference is made between i dmax and i d, and the output of the difference after passing through the PI controller is set as the upper limit value of the intermediate variable Deltax d0; the upper limit value of the intermediate variable Deltax q0 is calculated by taking the difference between i qmax and i q, and the output of the difference after passing through the PI controller is set as the upper limit value of the intermediate variable Deltax q0.
The parameter of the PI controller may be set to a fixed value, or the adjustable PI parameter may be determined according to the deviation amount, when the deviation amount is large, the PI parameter is set to a larger value to suppress the current more quickly, and when the deviation amount is small, the PI parameter is set to a smaller value to avoid large overshoot or instability.
5. The command values U dref and U qref are calculated from the limited intermediate variables Δx d and Δx q, as shown in the no inner loop limit calculation section of fig. 3. The calculation process is as follows:
。
In one embodiment of the present invention, there is provided a flexible direct current endoless loop network control system having a current limiting function, comprising:
the control loop establishing module is used for establishing a control loop for simulating a synchronous generator rotor operation equation and excitation control aiming at the converter;
The intermediate variable acquisition module is used for determining the amplitude and the phase of the converter voltage according to the established control loop for simulating the synchronous generator rotor running equation and excitation control and the command of the active power and the command of the reactive power of the converter so as to generate a voltage command value U dref0 of a d-axis component and a voltage command value U qref0 of a q-axis component of the converter output voltage in a rotating coordinate system, and the U dref0 and the U qref0 are used for respectively determining intermediate variables delta x d0 and delta x q0 of the d-axis and the q-axis;
The d-axis limiting module is used for setting the output of the current limiter module of the current converter after passing through the PI controller as the upper limit value of the intermediate variable Deltax d0 to obtain a d-axis intermediate variable Deltax d=lim(Δxd0 after limiting the difference value between the maximum current limit i dmax of the current actual value of the current converter on the d-axis of the rotating coordinate system and the component i d of the current actual value of the current on the alternating current side on the d-axis of the rotating coordinate system;
The q-axis limiting module is used for setting the output of the current limiter module of the q-axis of the current converter after passing through the PI controller as the upper limit value of the intermediate variable Deltax q0 to obtain a q-axis intermediate variable Deltax q=lim(Δxq0 after limiting the difference value between the maximum current limit i qmax of the current actual value of the current converter on the q-axis of the rotating coordinate system and the component i q of the current actual value of the current on the alternating current side on the q-axis of the rotating coordinate system;
The calculation module recalculates the voltage command value U dref of the d-axis component and the voltage command value U qref of the q-axis component according to the limited intermediate variable Deltax d、Δxq.
In the above embodiment, determining the phase of the inverter voltage includes:
Determining the phase of the converter voltage according to an analog synchronous generator rotor operation equation and an active power instruction:
Wherein J is a virtual rotor time constant, D is a virtual generator damping factor, P ref is an instruction value of active power of the converter, P e is actual power of the converter, omega 0 is a rotating speed reference value of the rotor, Is the actual value of the rotating speed of the rotor,/>Is the phase angle of the output voltage of the converter.
In the above embodiment, determining the magnitude of the inverter voltage includes:
determining the amplitude of the converter voltage according to the excitation control equation and the reactive power instruction:
Wherein Q ref is a reactive power command value of the converter, U ac_ref is an ac voltage command value of the converter, U ac is an actual ac voltage amplitude of the ac bus, s is a complex frequency, Q is a reactive power actual value of the converter, k q is a reactive power deviation gain coefficient, k ac is an ac voltage deviation gain coefficient, k p is a virtual internal potential controller proportional gain, T i is a virtual internal potential controller integral time constant, E 0 is a virtual internal potential reference value, and E is an amplitude of the converter voltage.
In the above embodiment, the d-axis maximum current limit i dmax and the q-axis maximum current limit i qmax are set by the maximum value of the bridge arm current in the transient state of the inverter and the suppression requirement of the short-circuit current fed into the ac system by the inverter.
Specifically, the setting of i dmax and i qmax includes:
determining the clearing time t fault of the fault of the alternating current system;
Calculating the maximum value I armmax of bridge arm current corresponding to the junction temperature of the converter device T jmax at T fault;
Determining the corresponding maximum current I max of the alternating current side of the converter according to the maximum value I armmax of the bridge arm current;
When the converter is connected into an alternating current system with short-circuit current not exceeding limit, i dmax and i qmax are limited according to a preset proportion;
when the converter is connected to the alternating current system with the out-of-limit short circuit current, determining I qmax according to the maximum limit of the short circuit current fed into the alternating current system by the converter, and determining according to the determined I qmax and I max 。
In the above embodiment, the d-axis and q-axis intermediate variables Δx d0 and Δx q0 are determined by U dref0 and U qref0, respectively, by the following formulas, including:
Wherein L, R is the equivalent impedance of the converter, and U sd、Usq is the component of the voltage of the AC bus of the converter on the d and q axes.
In the above embodiment, the voltage command value U dref of the d-axis component and the voltage command value U qref of the q-axis component are recalculated by the following formulas:
。
the system provided in this embodiment is used to execute the above method embodiments, and specific flow and details refer to the above embodiments, which are not described herein.
A computing device provided in an embodiment of the present invention may be a terminal, which may include: a processor (processor), a communication interface (Communications Interface), a memory (memory), a display, and an input device. The processor, the communication interface and the memory complete communication with each other through a communication bus. The processor is configured to provide computing and control capabilities. The memory comprises a non-volatile storage medium storing an operating system and a computer program which when executed by the processor implements the methods of the embodiments described above; the internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage media. The communication interface is used for carrying out wired or wireless communication with an external terminal, and the wireless mode can be realized through WIFI, a manager network, NFC (near field communication) or other technologies. The display screen can be a liquid crystal display screen or an electronic ink display screen, the input device can be a touch layer covered on the display screen, can also be a key, a track ball or a touch pad arranged on the shell of the computing equipment, and can also be an external keyboard, a touch pad or a mouse and the like. The processor may invoke logic instructions in memory.
Further, the logic instructions in the memory described above may be implemented in the form of software functional units and stored in a computer-readable storage medium when sold or used as a stand-alone product. Based on this understanding, the technical solution of the present invention may be embodied essentially or in a part contributing to the prior art or in a part of the technical solution, in the form of a software product stored in a storage medium, comprising several instructions for causing a computer device (which may be a personal computer, a server, a network device, etc.) to perform all or part of the steps of the method according to the embodiments of the present invention. And the aforementioned storage medium includes: a usb disk, a removable hard disk, a Read-Only Memory (ROM), a random access Memory (RAM, random Access Memory), a magnetic disk, or an optical disk, or other various media capable of storing program codes.
In one embodiment of the present invention, a computer program product is provided, the computer program product comprising a computer program stored on a non-transitory computer readable storage medium, the computer program comprising program instructions which, when executed by a computer, are capable of performing the methods provided by the method embodiments described above.
In one embodiment of the present invention, a non-transitory computer readable storage medium storing server instructions that cause a computer to perform the methods provided by the above embodiments is provided.
The foregoing embodiment provides a computer readable storage medium, which has similar principles and technical effects to those of the foregoing method embodiment, and will not be described herein.
The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and are not limiting; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (9)

1. The flexible direct current inner loop-free network construction control method with the current limiting function is characterized by comprising the following steps of:
Aiming at the converter, a control loop for simulating a synchronous generator rotor operation equation and excitation control is established;
Determining the amplitude and the phase of the converter voltage according to the established simulation synchronous generator rotor operation equation and a control loop of excitation control, as well as the command of the active power and the command of the reactive power of the converter, so as to generate a voltage command value U dref0 of a d-axis component and a voltage command value U qref0 of a q-axis component of the converter output voltage in a rotating coordinate system, and determining intermediate variables delta x d0 and delta x q0 of the d-axis and the q-axis respectively by U dref0 and U qref0;
Setting the output of the current actual value of the alternating current side of the converter at the upper limit value of an intermediate variable Deltax d0 after passing through the PI controller as the difference value between a maximum current limit i dmax of the current actual value of the alternating current side at the d axis of the rotating coordinate system and a component i d of the current actual value of the alternating current side at the d axis of the rotating coordinate system to obtain a d-axis intermediate variable Deltax d after the limit value;
Setting the output of the current actual value of the alternating current side of the converter at the upper limit value of an intermediate variable Deltax q0 after passing through the PI controller as the difference value between a maximum current limit i qmax of the current actual value of the alternating current side at the q axis of the rotating coordinate system and a component i q of the current actual value of the alternating current side at the q axis of the rotating coordinate system to obtain a q-axis intermediate variable Deltax q after the limit value;
Recalculating a voltage command value U dref of the d-axis component and a voltage command value U qref of the q-axis component according to an intermediate variable Deltax d、Δxq after the limit value;
The maximum current limit of d-axis i dmax and the maximum current limit of q-axis i qmax are set by the maximum value of bridge arm current in the transient state of the converter and the maximum value of short circuit current fed into the alternating current system by the converter;
the control system can quickly play a role in limiting current during faults, so that the capability of providing inertia for the system by the grid-formed control is ensured, and the overcurrent risk of the converter is avoided; the current limiting does not play a role in the steady state, and the voltage single loop operates.
2. The flexible direct current inner loop-free network control method with current limiting function as set forth in claim 1, wherein the simulated synchronous generator rotor operation equation is:
Wherein J is a virtual rotor time constant, D is a virtual generator damping factor, P ref is an instruction value of active power of the converter, P e is actual power of the converter, omega 0 is a rotating speed reference value of the rotor, Is the actual value of the rotating speed of the rotor,/>Is the phase angle of the output voltage of the converter.
3. The flexible direct current inner loop-free network control method with current limiting function as set forth in claim 1, wherein the excitation control equation is:
Wherein Q ref is a reactive power command value of the converter, U ac_ref is an ac voltage command value of the converter, U ac is an actual ac voltage amplitude of the ac bus, s is a complex frequency, Q is a reactive power actual value of the converter, k q is a reactive power deviation gain coefficient, k ac is an ac voltage deviation gain coefficient, k p is a virtual internal potential controller proportional gain, T i is a virtual internal potential controller integral time constant, E 0 is a virtual internal potential reference value, and E is an amplitude of the converter voltage.
4. The flexible direct current inner loop-free network control method with current limiting function as set forth in claim 1, comprising: the arrangement of i dmax and i qmax includes:
determining the clearing time t fault of the fault of the alternating current system;
Calculating the maximum value I armmax of bridge arm current corresponding to the junction temperature of the converter device T jmax at T fault;
Determining the corresponding maximum current I max of the alternating current side of the converter according to the maximum value I armmax of the bridge arm current;
When the converter is connected into an alternating current system with short-circuit current not exceeding limit, i dmax and i qmax are limited according to preset proportion:
wherein k is a proportionality coefficient;
When the converter is connected into an alternating current system with out-of-limit short circuit current, determining I qmax according to the maximum limit of the short circuit current fed into the alternating current system by the converter, and obtaining according to the determined I qmax and I max 。
5. The flexible direct current endoless loop network control method with current limiting function as set forth in claim 1, wherein the d-axis and q-axis intermediate variables Δx d0 and Δx q0 are determined by U dref0 and U qref0, respectively, by the following formula, comprising:
Wherein L, R is the equivalent impedance of the converter, and U sd、Usq is the component of the voltage of the AC bus of the converter on the d and q axes.
6. The flexible direct current no-inner loop network structure control method with current limiting function according to claim 1, wherein the voltage command value U dref of the d-axis component and the voltage command value U qref of the q-axis component are recalculated by the following formula:
。
7. a flexible dc non-inner loop network control system with current limiting function, comprising:
the control loop establishing module is used for establishing a control loop for simulating a synchronous generator rotor operation equation and excitation control aiming at the converter;
The intermediate variable acquisition module is used for determining the amplitude and the phase of the converter voltage according to the established control loop for simulating the synchronous generator rotor running equation and excitation control and the command of the active power and the command of the reactive power of the converter so as to generate a voltage command value U dref0 of a d-axis component and a voltage command value U qref0 of a q-axis component of the converter output voltage in a rotating coordinate system, and the U dref0 and the U qref0 are used for respectively determining intermediate variables delta x d0 and delta x q0 of the d-axis and the q-axis;
The d-axis limiting module is used for setting the output of the current limiter module of the current converter after passing through the PI controller as the upper limit value of the intermediate variable Deltax d0 to obtain a d-axis intermediate variable Deltax d after limiting the difference value between the maximum current limit i dmax of the current actual value of the current converter on the d axis of the rotating coordinate system and the component i d of the current actual value of the current on the alternating side on the d axis of the rotating coordinate system;
The q-axis limiting module is used for setting the output of the current limiter module of the current converter after passing through the PI controller as the upper limit value of an intermediate variable Deltax q0 to obtain a q-axis intermediate variable Deltax q after limiting the difference value between a maximum current limit i qmax of an actual value of an alternating current side current of the current converter on the q-axis of a rotating coordinate system and a component i q of the actual value of the current side current on the q-axis of the rotating coordinate system;
The calculation module recalculates the voltage command value U dref of the d-axis component and the voltage command value U qref of the q-axis component according to the intermediate variable Deltax d、Δxq after the limit value;
The maximum current limit of d-axis i dmax and the maximum current limit of q-axis i qmax are set by the maximum value of bridge arm current in the transient state of the converter and the maximum value of short circuit current fed into the alternating current system by the converter;
the control system can quickly play a role in limiting current during faults, so that the capability of providing inertia for the system by the grid-formed control is ensured, and the overcurrent risk of the converter is avoided; the current limiting does not play a role in the steady state, and the voltage single loop operates.
8. A computer readable storage medium storing one or more programs, wherein the one or more programs comprise instructions, which when executed by a computing device, cause the computing device to perform any of the methods of claims 1-6.
9. A computing device, comprising: one or more processors, memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, the one or more programs comprising instructions for performing any of the methods of claims 1-6.
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