CN114825367A - Control method for islanding operation of flexible direct current transmission system - Google Patents
Control method for islanding operation of flexible direct current transmission system Download PDFInfo
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- CN114825367A CN114825367A CN202110071232.6A CN202110071232A CN114825367A CN 114825367 A CN114825367 A CN 114825367A CN 202110071232 A CN202110071232 A CN 202110071232A CN 114825367 A CN114825367 A CN 114825367A
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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
- H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
- H02J3/241—The oscillation concerning frequency
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
- H02H9/02—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess current
- H02H9/025—Current limitation using field effect transistors
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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
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Abstract
The application provides a control method for island operation of a flexible direct current transmission system. The flexible direct current transmission system is connected with an alternating current system, the flexible direct current transmission system comprises an inverter, and the method comprises the following steps: when the flexible direct current transmission system is operated in an isolated island mode, starting and steady-state operation are realized in an open-loop control mode in a starting and non-fault state; and when the alternating current system fault is detected, the open-loop control mode is converted into a double closed-loop control mode to limit the fault current to inhibit interference.
Description
Technical Field
The application relates to the technical field of flexible direct current transmission of a power system, in particular to a control method for island operation of a flexible direct current transmission system.
Background
In order to solve the problems of increasingly short supply of energy and increasingly severe environment, the development and utilization of new energy sources such as wind power, photovoltaic and the like are rapidly developed. At present, a new energy power generation base is mostly far away from a load center, a local alternating current power grid is weak, and the access of large-scale new energy may cause influences such as reduction of regional power grid electric energy quality, poor system stability, change of transient characteristics and the like. The flexible direct current transmission system adopts a turn-off power electronic device, has the characteristics of flexible control, rapid dynamic response, low harmonic content and the like, can rapidly and independently adjust active power and reactive power, has flexible control coordination capability, is widely considered as one of the technical means for reliable access and effective utilization of new energy, and has wide application prospect.
When no alternating current power supply exists in an alternating current network area accessed by the flexible direct current converter station or a new energy system is accessed, the flexible direct current converter station needs to provide stable alternating current voltage for a passive system or a new energy in an island control mode. Considering that the flexible direct current converter station is easy to cause high-frequency oscillation when being started in an island mode, the island control mode adopts open-loop control to directly output constant alternating voltage to avoid oscillation when being started. Because the open-loop control has no feedback link and can not inhibit interference, when the alternating current system has a fault and needs to limit the current, the control mode is preferably switched to a closed-loop control mode, and the current limiting link is arranged in the controller to control the fault current not to exceed the limit, so that the tripping of the flexible direct current converter station caused by fault overcurrent can be avoided.
Most researches on island operation control strategies of a flexible direct current transmission system in the prior literature are limited to specific open-loop control and closed-loop control, and few researches on control strategies which are flexibly used by combining the advantages of two control modes are carried out in the prior literature. For example, an open-loop constant-voltage and constant-frequency control strategy is proposed in the study on black-start control capability of a flexible direct-current transmission system (Zengdan, YaoJian, modern electric power, 2012), but double-closed-loop control and switching are not involved. Direct voltage control of passive network power supply of MMC type flexible direct-current power transmission system (tube-sensitive, creep-control, power automation, 2012) provides a double closed-loop control strategy of the passive system, and current suppression under the fault condition is realized. But open loop control and switching are not involved.
The problem of system instability caused by combination of open-loop control and closed-loop control also exists, the open-loop control is adopted in the system in the starting and stable operation processes, the closed-loop control integrator is possibly saturated, the integrator has a desaturation process in the switching process, and the closed-loop control fails in the process to cause the system instability.
Disclosure of Invention
The embodiment of the application provides a method for controlling islanding operation of a flexible direct-current power transmission system, wherein the flexible direct-current power transmission system comprises an alternating-current system and a current converter, and the method comprises the following steps: when the flexible direct current transmission system is in isolated island operation, the converter is started and stably operated in an open-loop control mode in a starting and non-fault state; when the alternating current system fault is detected, the converter is switched from the open-loop control mode to the double closed-loop control mode to limit the fault current to inhibit interference.
According to some embodiments, the open-loop control mode comprises: the method comprises the steps that a preset converter network side alternating voltage and a preset frequency reference value are used as input of an open-loop controller, a constant converter alternating voltage reference wave is output after the regulation of the open-loop controller, and the control of alternating current side current waveform and phase of the converter is achieved.
According to some embodiments, the double closed loop control mode comprises an outer loop control and an inner loop control, wherein the outer loop control inputs the network side alternating voltage and frequency of the converter, and outputs an inner loop active current reference value and an inner loop reactive current reference value through a proportional integral controller; and the inner ring control receives an inner ring active current reference value and an inner ring reactive current reference value from the outer ring control, and quickly tracks the inner ring active current reference value and the inner ring reactive current reference value, so that the direct control of the alternating current side current waveform and the phase of the converter is realized.
According to some embodiments, the dual closed-loop control further includes a current limiting link, and the current limiting link controls the fault current of the ac system not to exceed a limit.
According to some embodiments, the input of the integrator controlled by the outer loop is initialized when the open-loop control mode is changed to the double closed-loop control mode. The situations of control failure and system instability caused by the desaturation process of the integrator are avoided.
According to some embodiments, the detecting of the ac system failure includes: according to the voltage criterion, when the system voltage U s <System voltage preset low value U s_setL Or U s >High value U is predetermine to system voltage s_setH Or when a DC voltage U DC <DC voltage preset low value U DC_setL Or U DC >DC voltage preset high value U DC_setH Or when the zero sequence voltage U is on the AC valve side 0 >Zero sequence voltage threshold value U of alternating current valve side 0_set When the system is in use, the open-loop control mode is converted into double closed-loop control; according to the current criterion, when the network side current I s >Grid side current threshold I s_set Or bridge arm current I b >Bridge arm current threshold I b_set When the system is in use, the open-loop control mode is converted into double closed-loop control; according to the power criterion, when there is active power P<Active power threshold P _set When the system is in the open-loop control mode, the system is converted into double closed-loop control; according to the frequency criterion, when the system frequency f<System frequency preset low value f _setL Or f>System frequency preset high value f _setH Meanwhile, the system is changed from an open-loop control mode to a double closed-loop control mode.
According to some embodiments, the system voltage is preset to a low value U s_setL Less than or equal to 1pu, system voltageSet high value U s_setH More than or equal to 1 pu; DC voltage preset low value U DC_setL Less than or equal to 1pu, and a preset high value U of direct current voltage DC_setH More than or equal to 1 pu; zero sequence voltage threshold value U of alternating current valve side 0_set Not less than 0pu, net side current threshold I s_set Not less than 1pu, bridge arm current threshold I b_set More than or equal to 1pu, active power threshold P _set Less than or equal to 1pu, and a preset low value f of system frequency _setL <50Hz, high preset value f of system frequency _setH >50Hz, where pu is the unit of the per unit value, where the per unit value is the relative value of the actual value to the nominal value.
According to some embodiments, the flexible direct current transmission system operates in an islanded mode, with or without load.
According to the technical scheme, the island open-loop mode is operated to avoid high-frequency oscillation caused by connection of a transformer or a short no-load circuit, and the system is switched from the open-loop mode to the double-closed-loop control mode during fault, so that fault overcurrent is effectively inhibited.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
Fig. 1 is a schematic diagram of a flexible dc power transmission system according to an embodiment of the present application.
Fig. 2 is a schematic flow chart of a control method for islanding operation of a flexible direct current power transmission system according to an embodiment of the present application.
Fig. 3 is a schematic flow chart of an open-loop control method of an islanding operation control method according to an embodiment of the present application.
Fig. 4 is a schematic diagram of a dual closed-loop control method of an islanding operation control method according to an embodiment of the present application.
Fig. 5 is a schematic diagram of a dual closed-loop control manner of another islanding operation control method according to an embodiment of the present application.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some, but not all, embodiments of the present application. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
It will be understood that the terms "comprises" and/or "comprising," when used in this specification and claims, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
Fig. 1 is a schematic diagram of a flexible dc power transmission system according to an embodiment of the present application.
As shown in fig. 1, the flexible dc transmission system comprises an ac system, an inverter, a coupling transformer 3, a new energy source 1 and dc field equipment 4.
The primary side of the connecting transformer 3 is connected with a new energy source 1 through an inlet wire switch 2, the secondary side of the connecting transformer 3 is connected with a current converter and direct current field equipment 4, the current converter and the direct current field equipment 4 are connected with a current converter and direct current field equipment 6 of the docking station through a direct current circuit 5, and the current converter and the direct current field equipment 6 of the docking station are connected with an alternating current power grid or a power supply 9 through a docking station connecting transformer 7 and a docking station primary side switch 8.
Fig. 2 is a schematic flow chart of a control method for islanding operation of a flexible direct current power transmission system according to an embodiment of the present application.
In S10, when the flexible direct current transmission system is in island operation, the converter is in open loop control mode in starting and non-fault state to realize starting and steady state operation.
And when the flexible direct current transmission system is operated in an isolated island mode, the flexible direct current transmission system is operated with or without a load.
After the flexible direct current transmission system is unlocked in an island mode, the flexible direct current transmission system is started in an open-loop control mode, and as shown in fig. 3, a d-axis component U of alternating voltage at the network side of a converter is preset d * Presetting d-axis component U of AC voltage at converter network side q * And a preset frequency reference value f ref * As the input of the open-loop controller, the constant converter AC voltage reference wave is output after the PI regulation of the open-loop controller, and vd is equal to U d * And vq is 0, and the control of the alternating-current side current waveform and the phase of the converter is realized.
When the flexible direct current transmission system is in island starting, an open-loop control mode is adopted, a voltage reference wave starts from 0kV and rises to a rated voltage U at the speed of alpha kV/s N And kV, after stable alternating current voltage is established, the flexible direct current transmission system keeps open-loop control operation, and stable voltage amplitude and frequency are provided for a new energy system or a passive alternating current system.
The starting mode avoids large disturbance and large impact when the island is started, inhibits high-frequency components and distortion of output voltage and current, and keeps stable operation of the system.
At S20, when an ac system fault in the flexible dc power transmission system is detected, the inverter is switched from the open-loop control mode to the double closed-loop control mode to limit the fault current and suppress the disturbance.
And detecting the fault of the alternating current system in a mode of voltage criterion, current criterion, power criterion and frequency criterion.
According to the voltage criterion, when the system voltage U s <System voltage preset low value U s_setL Or U s >High value U is predetermine to system voltage s_setH Or when a DC voltage U DC <DC voltage preset low value U DC_setL Or U DC >DC voltage preset high value U DC_setH Or when the zero sequence voltage U is on the AC valve side 0 >Zero sequence voltage threshold value U of alternating current valve side 0_set Meanwhile, the system is changed from an open-loop control mode to a double closed-loop control mode.
Wherein the system voltage is preset to a low value U s_setL Less than or equal to 1pu, and a preset high value U of system voltage s_setH More than or equal to 1 pu; DC voltage preset low value U DC_setL Less than or equal to 1pu, and a preset high value U of direct current voltage DC_setH More than or equal to 1 pu; zero sequence voltage threshold value U of alternating current valve side 0_se t More than or equal to 0 pu. Wherein the content of the first and second substances,pu is a unit of per unit, and the per unit is a relative value between an actual value and a rated value.
According to the current criterion, when the network side current I s >Grid side current threshold I s_set Or bridge arm current I b >Bridge arm current threshold I b_set Meanwhile, the system is changed from an open-loop control mode to a double closed-loop control mode.
Wherein, the current threshold value I of the network side s_set Not less than 1pu, bridge arm current threshold I b_set ≥1pu。
According to the power criterion, when there is active power P<Active power threshold P _set Meanwhile, the system is converted from an open-loop control mode to double closed-loop control.
Wherein, the active power threshold value P _set ≤1pu。
According to a frequency criterion when the system frequency f<System frequency preset low value f _setL Or f>System frequency preset high value f _setH Meanwhile, the system is changed from an open-loop control mode to a double closed-loop control mode.
System frequency preset low value f _setL <50Hz, high preset value f of system frequency _setH >50Hz。
The dual closed loop control scheme includes an outer loop control and an inner loop control, as shown in fig. 4.
In outer-loop control, the AC voltage U at the network side of the input converter d Presetting d-axis component U of alternating voltage on converter network side d * And the difference value is input into a proportional-integral controller PI, and an inner loop active current reference value is output through the proportional-integral controller. Input converter network side alternating voltage U q Presetting q-axis component U of AC voltage at converter network side q * And the difference value is input into a proportional-integral controller PI, and an inner loop reactive current reference value is output through the proportional-integral controller PI.
In the inner ring control, an inner ring active current reference value and an inner ring reactive current reference value from the outer ring control are received, and the inner ring active current reference value, the inner ring reactive current reference value and a preset frequency reference value f are quickly tracked ref * And direct control of the alternating current side current waveform and phase of the converter is realized.
In the double closed-loop control mode, the outer loop controls the amplitude and frequency of the output voltage, and the inner loop controls the current.
In the control mode selection, turning to A is an open-loop control mode, and turning to B is a double closed-loop control mode.
Optionally, in order to meet the requirement that the current does not exceed the limit in the fault state, the dual closed-loop control mode further includes a current limiting link Idmax, which controls the fault current of the ac system to not exceed the limit, as shown in fig. 5. The current limiting link is arranged between the channels of the outer ring control and the inner ring control, and tripping of the flexible direct current transmission system caused by overcurrent during fault is avoided.
Optionally, when the open-loop control mode is switched to the double-closed-loop control mode, an initial value is given to the input of the integrator controlled by the outer loop, and the initial value is-2 times to 2 times of the integral value of the integrator in normal operation before the fault, but not limited to this, so that the integrator immediately exits the saturation state. So as to avoid the situations of control failure and system instability caused by the desaturation process of the integrator under closed-loop control.
According to the technical scheme, the island open-loop mode is operated to avoid high-frequency oscillation caused by connection of a transformer or a short no-load circuit, and the system is switched from the open-loop mode to the double-closed-loop control mode during fault, so that fault overcurrent is effectively inhibited. In the control switching process, the conditions of control failure and system instability caused by the desaturation process of the integrator under closed-loop control are avoided by giving an initial value to the input of the integrator under outer-loop control.
The above embodiments are only for illustrating the technical idea of the present application, and the protection scope of the present application is not limited thereby, and any modifications made on the basis of the technical solution according to the technical idea presented in the present application fall within the protection scope of the present application.
Claims (8)
1. A method of controlling islanding operation of a flexible direct current power transmission system connected to an alternating current system, the flexible direct current power transmission system including a converter, the method comprising:
when the flexible direct current transmission system operates in an isolated island mode, the converter is started and operates in a steady state in an open-loop control mode in a starting and non-fault state;
when the alternating current system fault is detected, the converter is switched from the open-loop control mode to the double closed-loop control mode to limit the fault current to inhibit interference.
2. The control method according to claim 1, wherein the open-loop control mode includes:
the method comprises the steps that a preset converter network side alternating voltage and a preset frequency reference value are used as input of an open-loop controller, a constant converter alternating voltage reference wave is output after the regulation of the open-loop controller, and the control of alternating current side current waveform and phase of the converter is achieved.
3. The control method of claim 1, wherein the dual closed-loop control manner comprises:
the outer loop control inputs the alternating voltage and frequency of the converter network side, and outputs an inner loop active current reference value and an inner loop reactive current reference value through a proportional-integral controller;
and the inner ring control is used for receiving the inner ring active current reference value and the inner ring reactive current reference value output by the outer ring control, quickly tracking the inner ring active current reference value and the inner ring reactive current reference value and realizing the direct control of the alternating current side current waveform and the phase of the converter.
4. The control method of claim 1, wherein the dual closed-loop control manner further comprises:
and the current limiting link is used for controlling the fault current of the alternating current system not to exceed the limit.
5. The control method according to claim 1, wherein an input of an integrator of an outer loop control is initialized when the open loop control mode is changed to the double closed loop control mode.
6. The control method of claim 1, wherein the detecting of the ac system fault comprises:
according to the voltage criterion, when the system voltage U s <System voltage preset low value U s_setL Or U s >High value U is predetermine to system voltage s_setH Or when a DC voltage U DC <DC voltage preset low value U DC_setL Or U DC >DC voltage preset high value U DC_setH Or when the zero sequence voltage U is on the AC valve side 0 >Zero sequence voltage threshold value U of alternating current valve side 0_set When the system is in use, the open-loop control mode is converted into double closed-loop control;
according to the current criterion, when the network side current I s >Grid side current threshold I s_set Or bridge arm current I b >Bridge arm current threshold I b_set When the system is in use, the open-loop control mode is converted into double closed-loop control;
according to the power criterion, when there is active power P<Active power threshold P _set When the system is in the open-loop control mode, the system is converted into double closed-loop control;
according to the frequency criterion, when the system frequency f<System frequency preset low value f _setL Or f>System frequency preset high value f _setH Meanwhile, the system is changed from an open-loop control mode to a double closed-loop control mode.
7. Control method according to claim 6, wherein the system voltage is preset low U s_setL Less than or equal to 1pu, and a preset high value U of system voltage s_setH More than or equal to 1 pu; DC voltage preset low value U DC_setL Less than or equal to 1pu, and a preset high value U of direct current voltage DC_setH More than or equal to 1 pu; zero sequence voltage threshold value U of alternating current valve side 0_set Not less than 0pu, net side current threshold I s_set Not less than 1pu, bridge arm current threshold I b_set More than or equal to 1pu, active power threshold P _set Less than or equal to 1pu, and a preset low value f of system frequency _setL <50Hz, high preset value f of system frequency _setH >50Hz, where pu is the unit of the per unit value, which is the relative value of the actual value to the nominal value.
8. The control method according to claim 1, wherein the flexible direct current transmission system is operating in an islanded mode, with or without load.
Priority Applications (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202110071232.6A CN114825367A (en) | 2021-01-19 | 2021-01-19 | Control method for islanding operation of flexible direct current transmission system |
| PCT/CN2022/072571 WO2022156681A1 (en) | 2021-01-19 | 2022-01-18 | Control method and system for island operation of vsc-hvdc system |
| MX2023007693A MX2023007693A (en) | 2021-01-19 | 2022-01-18 | Control method and system for island operation of vsc-hvdc system. |
| EP22742160.9A EP4283816A1 (en) | 2021-01-19 | 2022-01-18 | Control method and system for island operation of vsc-hvdc system |
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| Application Number | Priority Date | Filing Date | Title |
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| CN202110071232.6A CN114825367A (en) | 2021-01-19 | 2021-01-19 | Control method for islanding operation of flexible direct current transmission system |
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| CN114825367A true CN114825367A (en) | 2022-07-29 |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115047333A (en) * | 2022-08-11 | 2022-09-13 | 国网经济技术研究院有限公司 | Passive unlocking test method and system for offshore platform converter valve wharf |
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2021
- 2021-01-19 CN CN202110071232.6A patent/CN114825367A/en active Pending
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115047333A (en) * | 2022-08-11 | 2022-09-13 | 国网经济技术研究院有限公司 | Passive unlocking test method and system for offshore platform converter valve wharf |
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