CN112086991B - Power grid frequency modulation method based on multi-terminal flexible direct current transmission system - Google Patents

Power grid frequency modulation method based on multi-terminal flexible direct current transmission system Download PDF

Info

Publication number
CN112086991B
CN112086991B CN202010873966.1A CN202010873966A CN112086991B CN 112086991 B CN112086991 B CN 112086991B CN 202010873966 A CN202010873966 A CN 202010873966A CN 112086991 B CN112086991 B CN 112086991B
Authority
CN
China
Prior art keywords
power
converter station
alternating current
frequency modulation
station
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Active
Application number
CN202010873966.1A
Other languages
Chinese (zh)
Other versions
CN112086991A (en
Inventor
李周
李亚州
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Southeast University
Original Assignee
Southeast University
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Southeast University filed Critical Southeast University
Priority to CN202010873966.1A priority Critical patent/CN112086991B/en
Priority to PCT/CN2020/116995 priority patent/WO2022041366A1/en
Priority to LU500835A priority patent/LU500835B1/en
Publication of CN112086991A publication Critical patent/CN112086991A/en
Application granted granted Critical
Publication of CN112086991B publication Critical patent/CN112086991B/en
Active legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Images

Classifications

    • 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
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H02J3/48—Controlling the sharing of the in-phase component
    • 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]

Landscapes

  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Supply And Distribution Of Alternating Current (AREA)

Abstract

The invention provides a power grid frequency modulation method based on a multi-terminal flexible direct current transmission system.A converter station can automatically select whether a connected alternating current system receives power grid frequency modulation according to the frequency deviation of the connected alternating current system, and can also select whether the connected alternating current system receives power grid frequency modulation according to the instruction of a scheduling system. Meanwhile, the dispatching system can select the alternating current system connected with one or more converter stations to participate in the frequency modulation of the power grid through instructions. The frequency modulation method realizes the combined frequency modulation among a plurality of alternating current systems by changing the control strategy of the converter station and combining a plurality of power balance converter stations adopting the active power balance technology. Compared with the prior art, the method and the device only need to change the control strategy of the local converter station, change the transmission power of the converter station in real time according to the unbalanced power quantity of the alternating current system, can realize smooth switching among different control strategies, and improve the frequency regulation speed and accuracy of the alternating current system.

Description

Power grid frequency modulation method based on multi-terminal flexible direct current transmission system
Technical Field
The invention belongs to the technical field of power systems, relates to a safety and stability analysis technology of a power system, and particularly relates to a power grid frequency modulation method based on a multi-terminal flexible direct-current power transmission system.
Background
The Voltage Source Converter based High Voltage Direct Current Transmission (VSC-HVDC) technology is also called as flexible Direct Current Transmission technology, has the advantages of realization of active power and reactive power decoupling control, capability of supplying power to a passive network, no commutation failure, no need of communication among Converter stations, easiness in forming a multi-terminal Direct Current system and the like, is one of important technologies for constructing an intelligent power grid, and can be widely applied.
With the development of the flexible direct-current transmission technology, a flexible direct-current transmission system develops to a higher voltage level and a larger transmission capacity, and the topology of a direct-current power grid is more complex. Compared with the traditional alternating current power grid, the flexible direct current power transmission system is constructed based on a large number of power electronic devices, has the capability of quickly adjusting transmission power, can be used for frequency adjustment among interconnected alternating current power grids, realizes rotary standby sharing among the interconnected power grids, and improves the frequency stability of the interconnected alternating current power grids.
Aiming at the direct current power grid with a future complex structure, the most direct method is that the converter station directly adjusts the actual transmission power value of the converter station according to the unbalanced power of the alternating current system to realize the frequency balance of the interconnected power grid. However, the direct introduction of the unbalanced power of the ac power grid into the dc power grid will affect the voltage stability of the dc power grid.
Disclosure of Invention
In order to solve the problems, the invention provides a power grid frequency modulation method based on a multi-terminal flexible direct current transmission system, which can adjust the transmission power of a converter station according to the unbalanced power of an alternating current system, and meanwhile, a direct current power grid can have stronger voltage stability.
In order to solve the technical problems, the invention is realized by the following technical scheme:
a power grid frequency modulation method based on a multi-terminal flexible direct current transmission system comprises the following steps: switching a converter station connected with an alternating current system receiving power grid frequency modulation into an alternating current balance node control mode, and resetting an output integral value of a proportional counter when a converter station control strategy is switched; setting a maximum value for the transmission power of the convertor station working in an alternating current balance node control mode, and changing the control of the convertor station into a power-limited transmission control mode when the transmission power of the frequency modulation convertor station is detected to exceed the maximum value; the dispatching system selects an alternating current system connected with one or more converter stations to participate in power grid frequency modulation through an instruction; and detecting the transmission power of each converter station, calculating the unbalanced power of the direct-current transmission system, and dynamically adjusting the power reference value of the power balance station according to the unbalanced power to realize power balance.
Further, the method also comprises the following precondition steps: and when the frequency deviation of the connected alternating current system exceeds an upper threshold value, the converter station automatically selects the alternating current system to receive the power grid frequency modulation, or selects whether the connected alternating current system receives the power grid frequency modulation according to the instruction of the scheduling system.
Further, the method also comprises the following subsequent steps: after receiving the frequency modulation of the power grid, when the frequency deviation of the alternating current system receiving the frequency modulation of the power grid, which is connected with the converter station, is smaller than a lower threshold value, the converter station receiving the frequency modulation of the power grid is automatically switched to a constant active power control mode, or the converter station receiving the frequency modulation of the power grid is switched to the constant active power control mode by a scheduling system instruction, so that the alternating current system does not receive the frequency modulation of the power grid any more; and resetting the output integral value of the proportional counter when the control strategy of the converter station is switched.
Further, the method specifically comprises the following steps:
switching a converter station into an alternating current balance node control mode, and controlling a voltage amplitude value and a phase angle at an alternating current outlet side of the converter station instead of a PCC (point of charge control) point, so that the converter station becomes a balance node, and the condition that the power shortage of an alternating current system is led into a direct current system without delay and deviation is ensured;
and under the dq coordinate system, the alternating-current side outlet voltage of the converter station controlled by the alternating-current balance node is as follows:
Figure BDA0002652028180000021
where s is the Laplace operator, UsdAnd UsqIs the dq-axis component, U, of the AC voltage at the point of common connectioncdAnd UcqIs the dq-axis component, i, of the AC-side outlet voltage of the converter stationsdAnd isqIs the dq-axis component, k, of the current on the AC side of the converter stationpAnd kiIs the proportional and integral coefficient of a proportional-integrator, RcAnd XcIs the equivalent resistance and the converter reactance of the converter station;
in the process of switching the control strategy, resetting the output integral value of the proportional counter:
Figure BDA0002652028180000022
wherein, UsAnd UcIs the effective value of the voltage at the AC side outlet of the converter station and the effective value of the AC voltage at the point of common connection, vdresetAnd vqresetIs the integrator reset value in d-axis control and the integrator reset value in q-axis control, PsAnd QsActive and reactive power injected at a Point of Common Coupling (PCC);
step (2), setting the maximum value of the transmission power of the converter station working under the control mode of the alternating current balance node
Figure BDA0002652028180000023
And
Figure BDA0002652028180000024
detecting the transmission power of the FM converter station if the transmission power P of the converter stationsExceed
Figure BDA0002652028180000025
Changing the control of the converter station into limited power transmission control, and setting the outlet voltage of the alternating current side of the converter station;
in dq coordinate axis, when the transmission power P of the converter stationsExceedance
Figure BDA0002652028180000031
And during the process, setting the outlet voltage of the alternating current side of the converter station as follows:
Figure BDA0002652028180000032
in dq coordinate axis, when the transmission power P of the converter stationsExceed and exceed
Figure BDA0002652028180000033
And during the process, setting the outlet voltage of the alternating current side of the converter station as follows:
Figure BDA0002652028180000034
wherein the content of the first and second substances,
Figure BDA0002652028180000035
and
Figure BDA0002652028180000036
for transmitting a maximum value of power to the converter station, wherein
Figure BDA0002652028180000037
Figure BDA0002652028180000038
Representing the maximum value of the transmission power in the rectifying direction, namely representing that active power is injected into the converter station by the alternating current system;
Figure BDA0002652028180000039
Figure BDA00026520281800000310
the maximum value of the transmission power in the inversion direction is represented, namely the active power is injected into an alternating current system by a converter station;
step (3), the dispatching system selects one or more alternating current systems with frequency modulation capability as a power balance station through an instruction;
step (4), detecting the transmission power of each converter station, calculating the unbalanced power delta P of the direct-current transmission system through an active power balance technology, and dynamically adjusting the power reference value of the power balance station according to the delta P;
unbalanced power Δ P of the dc power transmission system:
ΔP＝∑(Pref1,Pref2,...,Prefm,Pm+1,Pm+2,...,Pn)
in the above formula, n is the number of converter stations in the system, the first m converter stations are power balance stations, and the (m + 1) th to nth converter stations adopt an alternating current balance node to control or fix an active power to control the actual value of the transmission power of the converter stations;
dynamically adjusting the power reference value of the power balancing station according to the delta P:
Figure BDA00026520281800000311
wherein, PrefiFor the initial active power reference value of the ith converter station,
Figure BDA00026520281800000312
i is more than or equal to 1 and less than or equal to m, and K is the active power reference value adjusted for the ith converter stationiIs the droop coefficient of the power balancing station.
Further, the method also comprises the following precondition steps:
step 1, acquiring an actual value f of alternating voltage frequency of a public connection point of an alternating current system;
step 2, calculating the AC system connected with the converter stationSystem voltage frequency f and standard frequency frefAnd an upper threshold value deltaf is set for the frequency deviation of the alternating voltagemaxAnd a lower threshold value Δ fmin；
Step 3, when the frequency deviation delta f of the alternating current system connected with the converter station does not exceed delta f yetmaxWhen the frequency modulation is carried out, the converter station automatically selects to utilize the self-regulating capability of the alternating current system to carry out frequency regulation, or the alternating current system connected with the converter station can be selected by a command of a dispatching system to accept the frequency modulation of the power grid; when Δ f exceeds Δ fmaxAnd when the frequency modulation is carried out, the converter station automatically selects the connected alternating current system to receive the frequency modulation of the power grid.
Further, the alternating current system comprises an alternating current system connected with the converter station adopting the constant active power control mode and the converter station adopting the constant direct current voltage control mode.
Further, the method also comprises the following subsequent steps:
step 4, when the frequency deviation delta f of the received power grid frequency modulation alternating current system is smaller than delta fminWhen the system is used, the dispatching system automatically switches the converter station receiving the power grid frequency modulation into a constant active power control mode, so that the connected alternating current system does not receive the power grid frequency modulation any more; or the dispatching system switches the converter station receiving the power grid frequency modulation into a constant active power control mode through an instruction according to the requirement, so that the connected alternating current system does not receive the power grid frequency modulation any more;
in the process of switching the control strategy, the output integral value of the proportional counter is reset, and the reset value of the integrator in the outer loop control is as follows:
Figure BDA0002652028180000041
wherein v isdresetAnd vqresetIntegrator reset values in the outer loop control for the d-axis and q-axis, respectively;
the integrator in the inner loop control is reset to:
Figure BDA0002652028180000042
wherein v isdresetAnd vqresetIntegrator reset values in the inner loop control for the d-axis and q-axis, respectively.
Further, let the active power reference value PrefEqual to the actual value P of the active power transmitted by the current converter station.
Compared with the prior art, the invention has the following advantages and beneficial effects:
(1) the frequency modulation strategy provided by the invention can automatically perform frequency modulation control according to the frequency deviation of the alternating current system, and can also perform frequency modulation control according to the actual demand by a scheduling instruction;
(2) when the frequency deviation of the alternating current system is caused by power shortage, the alternating current balance node control provided by the invention enables the converter station to become a balance node, and the power shortage of the alternating current system can be directly led into the direct current system without delay or deviation;
(3) when the converter station switches the control strategy, the integrator value is reset, so that the state matching of the control system parameters and the electric parameters of the direct current system is ensured, the impact and the oscillation in the switching control process are reduced, and the stable operation of the system is ensured;
(4) the power limiting strategy provided by the invention limits the active power allowed to be injected into the direct current system according to the upper limit of the capacity of the converter station, thereby ensuring the safety of the direct current system;
(5) according to the active power balance technology provided by the invention, the dispatching system designates one or more alternating current systems to participate in the frequency adjustment of the alternating current systems, so that the flexibility of frequency modulation control and the dynamic stability of power and voltage are improved;
(6) compared with the prior art, the method and the device only need to change the control strategy of the local converter station, change the transmission power of the converter station in real time according to the unbalanced power of the alternating current system, and improve the frequency regulation speed and accuracy of the alternating current system.
Drawings
FIG. 1 is a schematic diagram of the system of the present invention.
Fig. 2 is a diagram of an ac balance node control structure.
Fig. 3 is a structural diagram of active and reactive decoupling control, in which (a) an outer ring control structural diagram of active power control, (b) an outer ring control structural diagram of reactive power control, (c) an inner ring control structural diagram of active power control, and (d) an inner ring control structural diagram of reactive power control are determined.
Fig. 4 is a diagram of a simulation model of a six-terminal flexible direct-current power transmission system.
Fig. 5 is a simulated waveform diagram, in which fig. 5(a) is an alternating voltage frequency, fig. 5(b) is a direct voltage at each terminal, fig. 5(c) is an active power transmission at each terminal, and the non-frequency modulation control is represented by a dotted line.
Detailed Description
The technical solutions provided by the present invention will be described in detail below with reference to specific examples, and it should be understood that the following specific embodiments are only illustrative of the present invention and are not intended to limit the scope of the present invention.
In the power grid frequency modulation method based on the multi-terminal flexible direct current transmission system, the converter station can automatically select whether the alternating current system receives power grid frequency modulation according to the frequency deviation of the connected alternating current system, and can also select whether the connected alternating current system receives power grid frequency modulation according to the instruction of the scheduling system. Meanwhile, the dispatching system can select one or more alternating current systems connected with the converter stations to participate in the frequency modulation of the power grid through instructions, change the control strategy of the converter stations and realize the combined frequency modulation among the multiple alternating current systems. The power system for realizing the control method comprises a plurality of power balance converter stations capable of adopting an active power balance technology, a plurality of converter stations capable of adopting a fixed active power control mode and a plurality of converter stations capable of adopting an alternating current balance node control mode. The control method of the invention comprises the following steps:
step 1, acquiring an actual value f of alternating voltage frequency of a public connection point of an alternating current system, wherein the alternating current system comprises a converter station controlled by constant active power and an alternating current system connected with the converter station controlled by constant direct current voltage;
step 2, calculating the voltage frequency f and the standard frequency f of the alternating current system connected with the converter stationrefAnd an upper threshold value deltaf is set for the frequency deviation of the alternating voltagemaxAnd a lower threshold value Δ fmin；
Step 3, when the frequency deviation delta f of the alternating current system connected with the converter station does not exceed delta f yetmaxWhen the frequency modulation is carried out, the converter station automatically selects to utilize the self-regulation capability of the alternating current system to carry out frequency regulation, or the alternating current system connected with the converter station can be selected by the instruction of a scheduling system to accept the frequency modulation of the power grid; when Δ f exceeds Δ fmaxWhen the frequency modulation is carried out, the converter station automatically selects the connected alternating current system to receive the frequency modulation of the power grid; the condition for receiving the frequency modulation of the power grid can be further set to be other conditions according to the requirement.
Specifically, when an alternating current system connected with the converter station needs to receive power grid frequency modulation, the method comprises the following steps:
and (1) switching the converter station into an alternating current balance node control mode, wherein the principle is shown in figure 2. Controlling the amplitude and the phase angle of the voltage at the AC outlet side of the converter station instead of a PCC point, so that the converter station becomes a balance node, and the power shortage of the AC system is ensured to be led into the DC system without delay and deviation;
and in the dq coordinate system, the alternating-current side outlet voltage of the converter station controlled by the alternating-current balance node is as follows:
Figure BDA0002652028180000061
where s is the Laplace operator, UsdAnd UsqIs the dq-axis component, U, of the AC voltage at the point of common connectioncdAnd UcqIs the dq-axis component, i, of the outlet voltage at the ac-side of the converter stationsdAnd isqIs the dq-axis component, k, of the current on the AC side of the converter stationpAnd kiIs the proportional and integral coefficient of a proportional-integrator, RcAnd XcIs the equivalent resistance and the converter reactance of the converter station.
In the process of switching the control strategy, the output integral value of the proportional counter is reset:
Figure BDA0002652028180000062
wherein, UsAnd UcIs a converter station ACEffective value of the voltage at the side outlet and the effective value of the alternating voltage at the point of common connection, vdresetAnd vqresetIs the integrator reset value in d-axis control and the integrator reset value in q-axis control, PsAnd QsIs the active and reactive power injected at the Point of Common Coupling (PCC). The resetting of the integrator ensures the state matching of the control system parameters and the electric parameters of the direct current system, reduces the impact caused by switching the control strategy to the maximum extent, reduces the system oscillation and ensures the safety and stability of the system. If the initialization is not performed, the initial value of the integrator is 0, and the output of the controller is not matched with the state of the electrical parameter of the direct current system, which may cause large oscillation and even instability of the system.
Step (2), setting the maximum value of the transmission power of the converter station working under the control mode of the alternating current balance node
Figure BDA0002652028180000063
And
Figure BDA0002652028180000064
detecting the transmission power of the FM converter station if the transmission power P of the converter stationsExceed
Figure BDA0002652028180000065
Changing the control of the converter station to a power limited transmission control;
in dq coordinate axis, when the transmission power P of the converter stationsExceedance
Figure BDA0002652028180000066
And during the process, setting the outlet voltage of the alternating current side of the converter station as follows:
Figure BDA0002652028180000071
in dq coordinate axis, when the transmission power P of the converter stationsExceed and exceed
Figure BDA0002652028180000072
While setting the commutation of the converter stationThe flow side outlet voltage is:
Figure BDA0002652028180000073
power P transmitted by converter station in figure 1sExceedance
Figure BDA0002652028180000074
The case of (c) is an example.
According to the upper limit of the transmission capacity of the converter station, the phase angle difference between the Pcc point and the voltage on the AC outlet side of the converter station is calculated, so that the phase angle of the voltage on the AC outlet side of the converter station is adjusted, and the synchronous change of the phase angles is ensured, thereby achieving the power limiting effect, further restraining the active power injected into a direct current system by the converter station, and ensuring the safety of the converter station; meanwhile, the capacity of the current converter can be utilized to the maximum extent, and the safety and the stability of a direct current system are improved.
Step (3), the dispatching system selects one or more alternating current systems with frequency modulation capability as a power balance station through an instruction;
step (4), detecting the transmission power of each converter station, calculating the unbalanced power delta P of the direct-current transmission system through an active power balance technology, and dynamically adjusting the power reference value of the power balance station according to the delta P;
unbalanced power Δ P of the dc power transmission system:
ΔP＝∑(Pref1,Pref2,...,Prefm,Pm+1,Pm+2,...,Pn)
in the above formula, n is the number of converter stations in the system, the first m converter stations are power balance stations, and the (m + 1) th to nth converter stations adopt an ac balance node to control or fix an active power to control the actual value of the transmission power of the converter stations.
Dynamically adjusting the power reference value of the power balancing station according to the delta P:
Figure BDA0002652028180000075
wherein, PrefiIs the initial active power reference value of the ith converter station (i is more than or equal to 1 and less than or equal to m),
Figure BDA0002652028180000076
the adjusted active power reference value K of the ith converter station (i is more than or equal to 1 and less than or equal to m)iIs the droop coefficient of the power balancing station.
The step can calculate the unbalanced power in the direct current system in real time, the accuracy of frequency adjustment is guaranteed, and meanwhile, the scheduling system designates one or more alternating current systems to participate in the frequency adjustment of the alternating current system, so that the flexibility of frequency modulation control and the dynamic stability of power and voltage are improved.
Step 4, when the frequency deviation delta f of the received power grid frequency modulation alternating current system is smaller than delta fminIn the process, the dispatching system automatically switches the converter station receiving the power grid frequency modulation into a constant active power control mode, so that the connected alternating current system does not receive the power grid frequency modulation any more, and the principle is shown in fig. 3. The dispatching system can flexibly switch the converter station receiving the power grid frequency modulation into a constant active power control mode according to the demand, so that the connected alternating current system does not receive the power grid frequency modulation any more.
For realizing stable switching of control strategies of the converter station, the active power reference value P is enabledrefEqual to the actual value P of the active power transmitted by the current converter station. In the process of switching the control strategy, the output integral value of the proportional counter should be reset, and the reset value of the integrator in the outer loop control is as follows:
Figure BDA0002652028180000081
wherein v isdresetAnd vqresetIntegrator reset values in the outer loop control for the d-axis and q-axis, respectively.
The integrator in the inner loop control is reset to:
Figure BDA0002652028180000082
wherein v isdresetAnd vqresetIntegrator reset values in the inner loop control for the d-axis and q-axis, respectively.
The coordination control strategy proposed by the present invention is specifically described by taking the six-terminal flexible dc power transmission system shown in fig. 4 as an example. Direct current voltage droop control is adopted to converter station VSC2, VSC3, VSC4 and VSC5, and VSC1 links to each other with the wind field and VSC6 links to each other with passive electric network, all adopts amplitude and phase control to active power is the positive direction by alternating current system injection direct current system. The transmission power of each converter station ranges from-750 MW to 750 MW.
The traditional master-slave control strategy is compared with the novel coordination control strategy. Under the master-slave control strategy, the VSC3 station is used as a master station, constant direct-current voltage control is adopted, the VSC2 station, the VSC4 station and the VSC5 station are used as control slave stations, constant active power control is adopted, and voltage control work is sequentially undertaken after the master station quits. The VSC1 and the VSC6 adopt amplitude-phase control, and the voltage grade of the multi-end flexible direct-current transmission system is +/-500 kV.
Case (2): in the simulation scenario, the transmission power of the VSC1, the VSC2, the VSC3, the VSC4, the VSC5 and the VSC6 is 700MW, 600MW, 230MW, -400MW, -450MW and-600 MW at the initial time. The load of an alternating current system connected with the VSC5 station is suddenly increased by 200MW at 6s, and the load of 200MW is cut off by an alternating current power grid at 16 s. The power reference value of the control system is 750WVA, the alternating voltage reference value is 500kV, the direct current voltage reference value is 500kV, and the unit value of the commutation reactance is 0.15.
For the novel frequency modulation control strategy provided by the invention:
when the frequency of an alternating current power grid connected with the VSC5 station changes at 6s, and when the frequency change exceeds a threshold value delta fmax equal to 0.05Hz, the control strategy of the VSC5 station is switched to alternating current balance node control. In the control switching process, the reset values of the d-axis voltage and the q-axis voltage are as follows: v. ofdreset＝0.996，vqreset＝0。
And when the load of an alternating current power grid connected with the VSC5 station is adjusted for 16s, 200MW active load is cut, the power shortage of the alternating current power grid is lower than the lower limit Pmin of transmission power of the VSC3, the lower limit Pmin is-750 MW, and the control strategy of the VSC5 station is still controlled by an alternating current balance node.
At 26s, the system stabilized. The power transmitted by VSC5 needed by the system after load shedding is known to be 450MW, at this time, the system is switched to constant active power control and constant reactive power control, the active power reference value is-450 MW, the reactive power reference value is 0MVA, and in the control switching process, the reset value of each integrator is as follows: i.e. iqreset＝-0.6，idreset＝0，vdreset＝0.007，vqreset＝0.012。
The simulation waveforms are shown in fig. 5, where fig. 5(a) shows the frequency of the ac voltage, fig. 5(b) shows the transmission of active power at each terminal, and fig. 5(c) shows the dc voltage at each terminal.
As can be seen from fig. 5, the novel frequency modulation control strategy: in an alternating current system (AC grid5) with power disturbance, an unbalanced power converter station of the alternating current system directly flows into a direct current power grid, unbalanced power is quickly led into a proper alternating current system to complete supplement under a direct current power grid quick power regulation strategy, and the response speed of frequency regulation is high. The lowest frequency value of 49.78Hz has smaller deviation than 49.09Hz of the traditional frequency control; meanwhile, the dynamic stability of the direct-current voltage is ensured by the active power balance technology.
The simulation verifies that the coordination control strategy of the invention is superior to the traditional control strategy, the dynamic response speed is high, the direct current voltage of the system is at the standard working voltage in a steady state, the power of each converter station except the amplitude-phase control converter station is a reference value, and the steady-state control performance is good.
The technical means disclosed in the invention scheme are not limited to the technical means disclosed in the above embodiments, but also include the technical scheme formed by any combination of the above technical features. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and such improvements and modifications are also considered to be within the scope of the present invention.

Claims (7)

1. A power grid frequency modulation method based on a multi-terminal flexible direct current transmission system is characterized by comprising the following steps: switching a converter station connected with an alternating current system receiving power grid frequency modulation into an alternating current balance node control mode, and controlling the voltage amplitude and the phase angle of an alternating current outlet side of the converter station to enable the converter station to become a balance node, so that the power shortage of the alternating current system is led into a direct current system without delay and deviation; resetting the output integral value of the proportional integrator when the control strategy of the converter station is switched; setting a maximum value for the transmission power of the convertor station working in an alternating current balance node control mode, detecting the transmission power of the frequency modulation convertor station, and changing the control of the convertor station into a power-limited transmission control mode when the transmission power exceeds the maximum value; the dispatching system selects an alternating current system connected with one or more converter stations to participate in power grid frequency modulation through an instruction; detecting the transmission power of each converter station, calculating the unbalanced power of the direct-current transmission system, and dynamically adjusting the power reference value of the power balance station according to the unbalanced power to realize power balance;
the method specifically comprises the following steps:
switching a converter station into an alternating current balance node control mode, and controlling the voltage amplitude and the phase angle of an alternating current outlet side of the converter station to enable the converter station to become a balance node, so that the power shortage of an alternating current system is led into a direct current system without delay and deviation;
and in the dq coordinate system, the alternating-current side outlet voltage of the converter station controlled by the alternating-current balance node is as follows:
Figure FDA0003586937510000011
where s is the Laplace operator, UsdAnd UsqIs the dq-axis component, U, of the AC voltage at the point of common connectioncdAnd UcqIs the dq-axis component, i, of the AC-side outlet voltage of the converter stationsdAnd isqIs the dq-axis component, k, of the current on the AC side of the converter stationpAnd kiProportional and integral coefficients, R, of a proportional integratorcAnd XcRespectively the equivalent resistance and the converter reactance of the converter station;
in the process of switching the control strategy, resetting the output integral value of the proportional integrator:
Figure FDA0003586937510000012
wherein, UsAnd UcRespectively, the effective value of the alternating voltage at the point of common connection and the effective value of the voltage at the outlet of the alternating side of the station, vdresetAnd vqresetAre the integrator reset value in d-axis control and the integrator reset value in q-axis control, PsAnd QsRespectively the active power and the reactive power injected at the common connection point;
step (2), setting the maximum value of the transmission power of the converter station working in the alternating current balance node control mode
Figure FDA0003586937510000013
And
Figure FDA0003586937510000014
detecting the transmission power of the frequency-modulated converter station, if the transmission power Ps of the converter station exceeds
Figure FDA0003586937510000021
Changing the control of the converter station into limited power transmission control, and setting the outlet voltage of the alternating current side of the converter station;
in dq coordinate axis, when the transmission power P of the converter stationsExceedance
Figure FDA0003586937510000022
And during the process, setting the outlet voltage of the alternating current side of the converter station as follows:
Figure FDA0003586937510000023
in dq coordinate axis, when the transmission power P of the converter stationsExceed and exceed
Figure FDA0003586937510000024
And during the process, setting the outlet voltage of the alternating current side of the converter station as follows:
Figure FDA0003586937510000025
wherein the content of the first and second substances,
Figure FDA0003586937510000026
and
Figure FDA0003586937510000027
for the absolute value of the maximum value of the transmission power of the converter station, wherein
Figure FDA0003586937510000028
Figure FDA0003586937510000029
Representing the maximum value of the transmission power in the rectifying direction, namely representing that active power is injected into the converter station by the alternating current system;
Figure FDA00035869375100000210
Figure FDA00035869375100000211
the maximum value of the transmission power in the inversion direction is represented, namely the active power is injected into an alternating current system by a converter station;
step (3), the dispatching system selects one or more alternating current systems with frequency modulation capability as a power balance station through an instruction;
step (4), detecting the transmission power of each converter station, calculating the unbalanced power delta P of the direct-current transmission system through an active power balance technology, and dynamically adjusting the power reference value of the power balance station according to the delta P;
unbalanced power Δ P of the dc power transmission system:
ΔP＝∑(Pref1,Pref2,...,Prefm,Pm+1,Pm+2,...,Pn)
in the above formula, n is the number of converter stations in the system, the first m converter stations are power balance stations, and the (m + 1) th to nth converter stations are converter stations adopting alternating current balance node control or constant active power control;
dynamically adjusting the power reference value of the power balancing station according to the delta P:
Figure FDA00035869375100000212
wherein, PrefiFor the initial active power reference value of the ith converter station,
Figure FDA00035869375100000213
i is more than or equal to 1 and less than or equal to m and K is an active power reference value adjusted by the ith converter stationiIs the droop coefficient of the power balancing station.
2. The grid frequency modulation method based on the multi-terminal flexible direct current transmission system according to claim 1, characterized by further comprising the following prerequisite steps: and when the frequency deviation of the connected alternating current system exceeds an upper threshold value, the converter station automatically selects the alternating current system to receive the power grid frequency modulation, or selects whether the connected alternating current system receives the power grid frequency modulation according to the instruction of the scheduling system.
3. The method for modulating the frequency of a power grid based on a multi-terminal flexible direct current transmission system according to claim 1 or 2, further comprising the following subsequent steps: after receiving the frequency modulation of the power grid, when the frequency deviation of the alternating current system receiving the frequency modulation of the power grid, which is connected with the converter station, is smaller than a lower threshold value, the converter station receiving the frequency modulation of the power grid is automatically switched to a constant active power control mode, or the converter station receiving the frequency modulation of the power grid is switched to the constant active power control mode by a scheduling system instruction, so that the alternating current system does not receive the frequency modulation of the power grid any more; the output integral value of the proportional-integrator is reset when the converter station control strategy switches.
4. The grid frequency modulation method based on the multi-terminal flexible direct current transmission system according to claim 1, characterized by further comprising the following prerequisite steps:
step 1, acquiring an actual value f of alternating voltage frequency of a public connection point of an alternating current system;
step 2, calculating the voltage frequency f and the standard frequency f of the alternating current system connected with the converter stationrefAnd an upper threshold value deltaf is set for the frequency deviation of the alternating voltagemaxAnd a lower threshold value Δ fmin；
Step 3, when the frequency deviation delta f of the alternating current system connected with the converter station does not exceed delta f yetmaxWhen the frequency modulation is carried out, the converter station automatically selects to utilize the self-regulation capability of the alternating current system to carry out frequency regulation, or the alternating current system connected with the converter station can be selected by the instruction of a scheduling system to accept the frequency modulation of the power grid; when Δ f exceeds Δ fmaxAnd when the frequency modulation is carried out, the converter station automatically selects the connected alternating current system to receive the frequency modulation of the power grid.
5. The method according to claim 4, wherein the AC system comprises an AC system connected to the converter station with constant active power control mode and the converter station with constant DC voltage control mode.
6. The method for modulating the frequency of a power grid based on a multi-terminal flexible direct current transmission system according to claim 4 or 5, further comprising the following subsequent steps:
step 4, when the frequency deviation delta f of the received power grid frequency modulation alternating current system is smaller than delta fminWhen the system is used, the dispatching system automatically switches the converter station receiving the power grid frequency modulation into a constant active power control mode, so that the connected alternating current system does not receive the power grid frequency modulation any more; or the dispatching system switches the converter station receiving the power grid frequency modulation into a constant active power control mode through an instruction according to the requirement, so that the connected alternating current system does not receive the power grid frequency modulation any more;
in the process of switching the control strategy, the output integral value of the proportional integrator is reset, and the reset value of the integrator in the outer loop control is as follows:
Figure FDA0003586937510000031
wherein idresetAnd iqresetIntegrator reset values, P, in outer loop control of d-and q-axes, respectivelyrefAs active power reference value, QrefIs a reactive power reference value;
the integrator in the inner loop control is reset to:
Figure FDA0003586937510000041
wherein v isdresetAnd vqresetThe integrator reset values in the inner loop control are d-axis and q-axis, respectively, omega is the angular frequency of the ac system and L is the value of the converter inductance of the ac part of the converter station.
7. The method according to claim 6, wherein the active power reference value P is set asrefEqual to the actual value P of the active power transmitted by the current converter station.
CN202010873966.1A 2020-08-26 2020-08-26 Power grid frequency modulation method based on multi-terminal flexible direct current transmission system Active CN112086991B (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
CN202010873966.1A CN112086991B (en) 2020-08-26 2020-08-26 Power grid frequency modulation method based on multi-terminal flexible direct current transmission system
PCT/CN2020/116995 WO2022041366A1 (en) 2020-08-26 2020-09-23 Multi-terminal flexible direct current transmission system-based power grid frequency modulation method
LU500835A LU500835B1 (en) 2020-08-26 2020-09-23 Grid frequency regulation method based on multi-terminal flexible direct current transmission system

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN202010873966.1A CN112086991B (en) 2020-08-26 2020-08-26 Power grid frequency modulation method based on multi-terminal flexible direct current transmission system

Publications (2)

Publication Number Publication Date
CN112086991A CN112086991A (en) 2020-12-15
CN112086991B true CN112086991B (en) 2022-06-03

Family

ID=73729213

Family Applications (1)

Application Number Title Priority Date Filing Date
CN202010873966.1A Active CN112086991B (en) 2020-08-26 2020-08-26 Power grid frequency modulation method based on multi-terminal flexible direct current transmission system

Country Status (3)

Country Link
CN (1) CN112086991B (en)
LU (1) LU500835B1 (en)
WO (1) WO2022041366A1 (en)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113113929B (en) * 2021-04-14 2022-06-14 南方电网科学研究院有限责任公司 Power grid structure type control method, device and medium for flexible direct current transmission system
CN114914903A (en) * 2022-04-02 2022-08-16 南京南瑞继保电气有限公司 Energy storage system structure for alternating current power grid interconnection and control method
CN115377998A (en) * 2022-09-20 2022-11-22 武汉大学 Power grid frequency control method based on flexible load active power-voltage coupling characteristic
CN115864415B (en) * 2023-02-16 2023-04-25 中国科学院电工研究所 Flexible AC/DC power distribution system stable control method in weak network interconnection scene
CN117878976B (en) * 2024-03-13 2024-05-24 华北电力大学 Receiving end frequency supporting method based on three-terminal flexible direct current transmission system

Family Cites Families (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103119821B (en) * 2010-09-30 2016-01-13 Abb研究有限公司 Multiterminal HVDC system coordination controls
CN105552948B (en) * 2016-02-05 2019-06-25 国网浙江省电力公司湖州供电公司 A kind of power grid frequency modulation method based on flexible HVDC transmission system
US10389125B2 (en) * 2017-03-07 2019-08-20 Thomas Alexander Wilkins Expanded reactive following for distributed generation and loads of other reactive controller(s)
CN108462196A (en) * 2018-02-09 2018-08-28 清华大学 The adaptive droop control methods of new energy VSG auxiliary frequency modulation P-V and system
CN108521139B (en) * 2018-05-11 2020-08-04 国网经济技术研究院有限公司 Frequency and voltage coordination control method and device
CN108923448B (en) * 2018-06-19 2022-04-29 东南大学 Multi-terminal flexible direct current transmission coordination control method and system
CN109120005B (en) * 2018-06-22 2022-04-01 华北电力大学（保定） Power coordination control method for multi-terminal flexible direct current transmission system
CN109638839B (en) * 2019-01-21 2022-07-29 东南大学 Load flow calculation method of bipolar flexible direct-current transmission system
CN110912158A (en) * 2019-12-15 2020-03-24 兰州交通大学 Multi-terminal flexible direct-current power transmission system frequency stability control method with wind power participating in frequency modulation

Also Published As

Publication number Publication date
CN112086991A (en) 2020-12-15
LU500835B1 (en) 2022-03-04
WO2022041366A1 (en) 2022-03-03

Similar Documents

Publication Publication Date Title
CN112086991B (en) Power grid frequency modulation method based on multi-terminal flexible direct current transmission system
AU2018393156B2 (en) Microgrid control system and microgrid
WO2022077847A1 (en) Virtual synchronous machine control method for hybrid microgrid mmc interconnected converter
CN105932706B (en) A kind of control method for coordinating for improving mixing back-to-back DC system
CN108832657A (en) Alternating current-direct current mixing micro-capacitance sensor bidirectional power converter virtual synchronous motor control method
CN108565885A (en) A kind of mesohigh large capacity cascade type energy storage system control method based on VSG
CN107623458B (en) A kind of virtual synchronous electric moter voltage source inverter minimum current stress control method
CN107994620A (en) Flexible ring net controller both-end virtual motor control method
CN108173278B (en) Direct-current voltage control device and method for VSG frequency modulation of new energy and optimization method
US20150260161A1 (en) Control device for voltage source converter and operating method thereof
CN109193797A (en) A kind of inertia matching method and control system based on synchronous generator and virtual synchronous parallel operation of generator microgrid
CN113394819B (en) Coordination control method and system for island offshore wind power plant hybrid direct current grid-connected system
CN112467789B (en) Hybrid microgrid virtual synchronous machine control method based on power transmission principle
CN104734598B (en) Based on band logical Damping voltage type current transformer virtual synchronous motor control method
CN106130055A (en) The lever variable-power control system of HVDC transmission system and method thereof
CN112600232B (en) Extra-high voltage direct current transmission system converter station control system based on virtual synchronous machine
CN106786592B (en) Island switching control method and device suitable for flexible direct current transmission system
CN115296325A (en) Control method for phase-locked loop-network-type MMC converter station parallel power supply system
Torres-Olguin et al. Grid Integration of offshore wind farms using a Hybrid HVDC composed by an MMC with an LCC-based transmission system
Rump et al. Frequency-dependent control of the active power consumption of converter-fed loads for grid support
CN109787267A (en) A kind of double-fed blower accesses the determination method of weak receiving-end system through VSC-HVDC
CN111864783A (en) Direct-current short-circuit fault ride-through control method and related device
CN106374755B (en) A kind of modularization transverter sensorless control method based on phase-shifting carrier wave technology
CN212462806U (en) Power supply system for assisting starting of wind power plant
CN113178893B (en) Inverter parallel soft start method and system based on virtual synchronous generator control

Legal Events

Date Code Title Description
PB01 Publication
PB01 Publication
SE01 Entry into force of request for substantive examination
SE01 Entry into force of request for substantive examination
GR01 Patent grant
GR01 Patent grant