CN111355255A - Virtual modulation-based DC overvoltage suppression method and system after lockout fault - Google Patents
Virtual modulation-based DC overvoltage suppression method and system after lockout fault Download PDFInfo
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- CN111355255A CN111355255A CN202010104816.4A CN202010104816A CN111355255A CN 111355255 A CN111355255 A CN 111355255A CN 202010104816 A CN202010104816 A CN 202010104816A CN 111355255 A CN111355255 A CN 111355255A
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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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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
- H02H7/268—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured for dc systems
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- 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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Abstract
The invention discloses a method for restraining direct current overvoltage after a latching fault based on additional virtual modulation, which comprises the following steps: measuring a direct-current voltage signal when the new energy island is accessed through a flexible direct-current power grid; judging whether an additional virtual modulation control strategy is put into use or not based on the direct-current voltage signal; and the time reaching the DC voltage limit value is prolonged by utilizing the input or non-input of an additional virtual modulation control strategy, and the DC overvoltage after the locking fault is restrained. Aiming at a system that a new energy island is accessed into the system through a multi-terminal true bipolar flexible direct current power grid, when a receiving end converter station or an alternating current system fails to cause power output blockage, an additional virtual modulation control strategy is put into, the power flowing into the direct current power grid is reduced, the time reaching a direct current voltage limit value is prolonged, the direct current voltage rising speed is inhibited, and the economic cost is low. And the additional virtual modulation control strategy is automatically switched in and automatically switched out according to the direct-current voltage condition.
Description
Technical Field
The invention belongs to the technical field of flexible direct current power transmission protection and control, and particularly relates to a virtual modulation-based method and a virtual modulation-based system for restraining direct current overvoltage after a blocking fault.
Background
The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.
In recent years, renewable energy, especially wind and light energy, is rapidly developed, and a large amount of wind and light new energy is connected to a power grid. However, the new energy alternating current grid connection faces the bottlenecks of poor power transmission stability, low efficiency and the like, and the large-scale new energy power generation grid connection requirements are difficult to meet only by depending on the power transmission mode of the traditional alternating current power grid. The flexible direct current transmission has the advantages of being capable of achieving passive grid connection of new energy power generation, supplying power to passive loads and the like, and can provide voltage and frequency support for a new energy island. In the flexible direct current transmission project which is put into operation or is built, about one third of the flexible direct current transmission projects target the island access of a wind power plant.
For a new energy source system represented by wind power and sent out through a flexible direct current power grid, a current converter connected with a new energy source island is generally controlled by constant alternating current voltage and constant frequency, and constant voltage and frequency support is provided for the new energy source. When the converter at the receiving end of the flexible direct current power grid has a locking fault, the power of new energy received by the sending end cannot be changed, and the input power in the direct current power grid is higher than the output power, so that the direct current voltage is increased.
The inventor finds in research that, aiming at the problems, the existing engineering generally adopts a power consumption resistor to consume surplus power in a direct current network, but the power consumption resistor is large in cost and large in occupied area.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a method for restraining the DC overvoltage after the locking fault based on additional virtual modulation, which fully considers the economic requirement on the basis of ensuring the safe and stable operation of the system, starts from the aspect of a control strategy to reduce the redundant power in the DC network, and further restrains the DC overvoltage.
To achieve the above object, in one aspect, one or more embodiments of the present invention provide the following technical solutions:
the DC overvoltage suppression method after the latch-up fault based on the additional virtual modulation comprises the following steps:
measuring a direct-current voltage signal when the new energy island is accessed through a flexible direct-current power grid;
judging whether an additional virtual modulation control strategy is put into use or not based on the direct-current voltage signal;
and the time reaching the DC voltage limit value is prolonged by utilizing the input or non-input of an additional virtual modulation control strategy, and the DC overvoltage after the locking fault is restrained.
In another aspect, one or more embodiments of the present invention provide the following:
a post-latch-up DC overvoltage suppression system based on additional virtual modulation includes: a voltage measuring unit and a controller;
the voltage measuring unit measures a direct-current voltage signal when the new energy island is accessed through a flexible direct-current power grid;
the controller judges whether an additional virtual modulation control strategy is put into use based on the direct-current voltage signal;
the time reaching the DC voltage limit value is prolonged by using the input or not of the additional virtual modulation control unit, and the DC overvoltage after the locking fault is restrained.
The above one or more technical solutions have the following beneficial effects:
the invention fully considers the economic requirement on the basis of ensuring the safe and stable operation of the system, starts to reduce the redundant power in the direct current network from the perspective of a control strategy, and further inhibits the direct current overvoltage.
In a system in which a new energy island is accessed through a flexible direct current power grid, whether an additional virtual modulation control strategy is put into use is judged by measuring a direct current voltage signal, and the time for reaching a direct current voltage limit value is prolonged.
Aiming at a system that a new energy island is accessed into the system through a multi-terminal true bipolar flexible direct current power grid, when a receiving end converter station or an alternating current system fails to cause power output blockage, an additional virtual modulation control strategy is put into, the power flowing into the direct current power grid is reduced, the time reaching a direct current voltage limit value is prolonged, the direct current voltage rising speed is inhibited, and the economic cost is low. And the additional virtual modulation control strategy is automatically switched in and automatically switched out according to the direct-current voltage condition.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention.
FIG. 1 is a schematic diagram illustrating additional virtual modulation control according to an embodiment of the present invention;
fig. 2 is a flowchart of a post-latch-up dc overvoltage suppression method based on additional virtual modulation according to an embodiment of the present invention.
Detailed Description
It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
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 invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
The embodiments and features of the embodiments of the present invention may be combined with each other without conflict.
Example one
Referring to fig. 2, the present embodiment discloses a method for suppressing a dc overvoltage after a latch-up fault based on additional virtual modulation, which includes:
measuring a direct-current voltage signal when the new energy island is accessed through a flexible direct-current power grid;
judging whether an additional virtual modulation control strategy is put into use or not based on the direct-current voltage signal;
and the time reaching the DC voltage limit value is prolonged by utilizing the input or non-input of an additional virtual modulation control strategy, and the DC overvoltage after the locking fault is restrained.
The technical scheme of the embodiment of the invention can inhibit the direct current overvoltage problem existing in the multi-terminal direct current network, inhibit the rising speed of the direct current voltage and prolong the time reaching the direct current overvoltage limit value.
In a specific embodiment, the method specifically comprises the following steps:
step (1): detecting the running condition of a flexible direct current power grid, judging whether surplus power exists in the flexible direct current power grid or not according to the judgment that whether direct current voltage exceeds an upper limit or whether a receiving end converter station is locked or not, executing the step (2) when the surplus power exists, and when the flexible direct current power grid is normally operated (the direct current voltage is kept in a normal fluctuation range in normal operation), adding virtual modulation control without input, wherein an input signal is selected to be 0;
step (2): judging the reason for generating the surplus power, and analyzing the reason for the influence of the surplus power on the change of the direct-current voltage;
the surplus power can cause the direct-current voltage to rise, the influence of single-station locking and single-pole locking of the current converter at the receiving end on the direct-current voltage is different, the single-station locking can cause the direct-current voltage of the positive pole and the negative pole to rise, the single-pole locking only causes the direct-current voltage of the fault pole to rise, and therefore the fault is judged according to the situation, and a corresponding control strategy is selected.
And (3): surplus power exists in the direct current network, when the direct current voltage of the two poles is higher than an upper limit value, the sending end converter station puts into additional virtual modulation control, meanwhile, the outlet voltage of the alternating current side of the two pole converter is reduced, and the power flowing into the direct current network is reduced;
and (4): when the single pole in the direct current network has redundant power and the single pole direct current voltage is higher than an upper limit value, the sending end fault pole converter is subjected to additional virtual modulation control, the healthy pole converter is not subjected to additional virtual modulation control, the outlet voltage of the alternating current side of the fault pole converter is increased, the outlet voltage of the alternating current side of the healthy pole converter is unchanged, and the power of the fault pole flowing into the power network is reduced;
and (5): and after the fault is cleared, the direct current voltage is automatically quitted after being lower than the upper limit value.
In the step (1), the condition of voltage and current of the flexible direct current power grid connected with the alternating current system is detected in real time, the direct current voltage condition of the direct current power grid, namely the direct current voltage condition of the positive and negative pole converters, is detected, the working state of the converters is detected, and if the direct current voltage is increased, whether surplus power exists or not is judged.
The step (2) specifically comprises the following substeps:
2-1) determining a direct current voltage upper limit threshold according to the protection fixed value, and setting the allowable upper limit value of the normal operation of the direct current voltage to be 1.05 p.u;
2-2) judging the fault type, if the direct current voltages of the positive pole and the negative pole are higher than the upper limit value, turning to the step (3), and if not, turning to the step 2-3);
2-3) judging whether the direct current voltage of the single pole (anode or cathode) is higher than an upper limit value, if the direct current voltage of the single pole (anode or cathode) exceeds the upper limit value, turning to the step (4), and if the direct current voltage of the single pole (anode or cathode) does not exceed the limit value, turning to the step (5);
in the step (3), according to the judgment result in the step (2), the sending end converters are subjected to additional virtual modulation control, control signals are all selected to be 1, the alternating-current voltage reference value is reduced, the alternating-current outlet voltage reference value of the converters is reduced through the traditional double closed-loop control, the power flowing into a direct-current power grid is reduced, and the direct-current voltage rising speed is restrained.
In the step (3), the additional virtual modulation control is put into the sending end converter, specifically:
a direct current voltage measured value is acquired, and is subtracted from a given direct current voltage reference value to obtain a direct current voltage difference value; the DC voltage difference is modulated by adding a virtual modulation-kpvThe proportional controller obtains an alternating voltage correction value;
and adding the alternating voltage reference value and the alternating voltage correction value to reduce the alternating voltage reference value of the positive and negative pole current converters.
In the step (4), according to the judgment result in the step (2), when the fault pole in the direct current network has redundant power and the direct current voltage of the fault pole is higher than the upper limit value, the sending end fault pole converter is put into an additional virtual modulation controller, a control signal is selected to be 2, the healthy pole converter is not put into the additional virtual modulation controller, the control signal is selected to be 0, the reference value of the alternating voltage of the fault pole is increased, the reference value of the alternating voltage of the healthy pole is not changed, the reference value of the alternating current outlet voltage of the healthy pole converter is not changed, the reference value of the alternating current outlet voltage of the fault pole converter is increased through the traditional double closed loop control, the power flowing into the direct current network by the fault pole converter is reduced, and the direct current voltage increasing speed.
In the step (4), the additional virtual modulation control of the sending end fault pole converter is specifically as follows:
the direct current voltage difference value is added with a virtual modulation proportion link kpvObtaining an alternating voltage correction value; k is a radical ofpvIn order to add a virtual scaling link, a value between 0.8 and 1.0 is generally selected, which is related to the actual modulation ratio range, and parameters of the actual system modulation ratio can be directly selected.
And adding the alternating voltage reference value and the alternating voltage correction value to increase the alternating voltage reference value of the fault electrode.
And (5) constantly detecting the direct-current voltage condition of the direct-current power grid, wherein the direct-current voltage measured value is lower than an upper limit value, and the additional virtual modulation control strategy exits the operation.
And (3) detecting the conditions of the positive and negative direct-current voltages of the direct-current power grid in real time, and when the measured values of the positive and negative direct-current voltages are lower than the upper limit value, adding a virtual modulation control strategy to quit the operation, wherein the control signal is selected to be 0.
The above embodiment of the present invention determines whether surplus power exists in the flexible direct current power grid by detecting the operation condition of the flexible direct current power grid; judging the reason for the surplus power and analyzing the reason for the change of the direct current voltage; surplus power exists in the direct current network, when the direct current voltage of the two poles is higher than an upper limit value, the sending end converter station puts into additional virtual modulation control, meanwhile, the outlet voltage of the alternating current side of the two pole converter is reduced, and the power flowing into the direct current network is reduced; when the single pole in the direct current network has redundant power and the single pole direct current voltage is higher than an upper limit value, the sending end fault pole converter is subjected to additional virtual modulation control, the healthy pole converter is not subjected to additional virtual modulation control, the outlet voltage of the alternating current side of the fault pole converter is increased, the outlet voltage of the alternating current side of the healthy pole converter is unchanged, and the power of the fault pole flowing into the power network is reduced; and after the fault is cleared, the direct current voltage is automatically quitted after being lower than the upper limit value. The method can inhibit the rising speed of the direct current voltage when the latching fault of the receiving end occurs, prolong the time of reaching the direct current overvoltage limit value and strive for time for the safety control action of the system.
Example two
Referring to fig. 1, the present embodiment is directed to a post-latch-up dc overvoltage suppression system based on additional virtual modulation, including: a voltage measuring unit and a controller;
the voltage measuring unit measures a direct-current voltage signal when the new energy island is accessed through a flexible direct-current power grid;
the controller judges whether an additional virtual modulation control strategy is put into use based on the direct-current voltage signal;
the time reaching the DC voltage limit value is prolonged by using the input or not of the additional virtual modulation control unit, and the DC overvoltage after the locking fault is restrained.
In a specific embodiment, the additional virtual modulation control unit includes: the device comprises a comparator, a first adder, a second adder, a first proportion controller, a second proportion controller, a selector and a third adder;
the first adder is connected to the selector through a negative proportion unit, the second adder is connected to the selector through a positive proportion unit, the comparator is connected to the selector, and the selector is connected to the third adder;
the comparator compares whether the direct current voltages of the positive pole and the negative pole are both higher than an upper limit value, the corresponding branch is selected by the selector according to the comparison result, the direct current voltage measured value is subtracted from the given direct current voltage reference value by the first adder or the second adder to obtain a direct current voltage difference value, positive and negative additional virtual modulation is carried out on the direct current voltage difference value to obtain an alternating current voltage correction value, and the third adder adds the correction value and the alternating current voltage correction value to inhibit the direct current voltage rising speed.
In this embodiment, the execution device is a controller, and after the reference value of the ac-side voltage of the inverter is reduced, the switching signals input to the sub-modules are also changed, so as to suppress the dc overvoltage.
In FIG. 1; k is a radical ofpacRepresents the proportional parameter, k, of the outer loop PI controlleriacRepresents the integral parameter of the outer loop PI controller; k is a radical ofpiAnd kiiRespectively representing the proportional and integral parameters of the inner loop PI controller. These parameters are selected as well as the parameters of the dual closed-loop controller. To obtain ucdrefAnd ucqredThen, firstly, the u is transformed to be under the abc coordinate system to obtain uca、ucbAnd uccAnd then obtaining the switching signals of each sub-module through a recent level modulation strategy.
In a specific implementation example, the comparator compares whether the direct current voltages of the positive pole and the negative pole are higher than an upper limit value, if so, the selector selects a branch where the first adder and the first proportional controller are located to be connected, the first adder subtracts a direct current voltage measured value from a given direct current voltage reference value to obtain a direct current voltage difference value, and the direct current voltage difference value is subjected to additional virtual modulation-kpvThe first proportional controller obtains an alternating voltage correction value, and the third adder adds the correction value and the alternating voltage correction value to reduce the alternating voltage reference value of the positive and negative pole current converters;
the comparator compares whether the direct current voltages of the positive pole and the negative pole are all higher than an upper limit value, if not, whether the direct current voltages of the single pole are all higher than the upper limit value is judged, if so, the selector selects a branch where a second adder and a second proportional controller are located to be connected, the second adder subtracts a direct current voltage measured value from a given direct current voltage reference value to obtain a direct current voltage difference value, and the direct current voltage difference value is subjected to additional virtual modulation kpvThe second proportional controller obtains an alternating voltage correction value, and the third adder adds the correction value and the alternating voltage correction value to increase the alternating voltage reference value of the fault electrode;
the comparator judges whether the unipolar direct-current voltage is higher than the upper limit value, if not, the selector selects the additional virtual modulation control unit to quit the operation, the healthy pole alternating-current voltage reference value is unchanged, the healthy pole converter alternating-current outlet voltage reference value is unchanged, the fault pole converter alternating-current outlet voltage reference value is increased through double closed-loop control, the power of the fault pole converter flowing into a direct-current power grid is reduced, and the direct-current voltage increasing speed is restrained.
The control strategy of the controller in this embodiment is described in the first embodiment based on the steps of the latch-up post-fault dc overvoltage suppression method based on additional virtual modulation, and will not be described in detail here.
Those skilled in the art will appreciate that the modules or steps of the present invention described above can be implemented using general purpose computer means, or alternatively, they can be implemented using program code that is executable by computing means, such that they are stored in memory means for execution by the computing means, or they are separately fabricated into individual integrated circuit modules, or multiple modules or steps of them are fabricated into a single integrated circuit module. The present invention is not limited to any specific combination of hardware and software.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Although the embodiments of the present invention have been described with reference to the accompanying drawings, it is not intended to limit the scope of the present invention, and it should be understood by those skilled in the art that various modifications and variations can be made without inventive efforts by those skilled in the art based on the technical solution of the present invention.
Claims (10)
1. The DC overvoltage suppression method after the latch-up fault based on the additional virtual modulation is characterized by comprising the following steps:
measuring a direct-current voltage signal when the new energy island is accessed through a flexible direct-current power grid;
judging whether an additional virtual modulation control strategy is put into use or not based on the direct-current voltage signal;
and the time reaching the DC voltage limit value is prolonged by utilizing the input or non-input of an additional virtual modulation control strategy, and the DC overvoltage after the locking fault is restrained.
2. The method according to claim 1, wherein the dc overvoltage suppression method after latch-up fault based on additional virtual modulation is characterized in that dc voltages of the positive and negative inverters are obtained by measuring the dc voltage signals, and the inverter operating state is detected to determine whether surplus power exists.
3. The method according to claim 1, wherein the dc overvoltage suppression method after latch-up based on additional virtual modulation is characterized in that when the dc voltage signal rises, it is determined whether surplus power exists in the flexible dc power grid.
4. The additional virtual modulation based post-latch-up dc overvoltage suppression method according to claim 1, wherein when there is surplus power in the dc power grid, causing the dc voltage at both poles to exceed the upper limit, the transmitting converter station applies an additional virtual modulation control strategy, while reducing the ac side outlet voltage of the two pole converter, reducing the power flowing into the dc power grid.
5. The method for suppressing dc overvoltage after latch-up fault based on additional virtual modulation as claimed in claim 1, wherein when excess power exists in a single pole in the dc power network, resulting in a single pole dc voltage higher than an upper limit value, the transmitting end fault pole converter puts into an additional virtual modulation control strategy;
the robust pole converter does not need to be subjected to additional virtual modulation control, the voltage of an outlet at the alternating current side of the fault pole converter is increased, the voltage of the outlet at the alternating current side of the robust pole converter is unchanged, and the power of a fault pole flowing into a power grid is reduced.
6. The post-latch-up dc overvoltage suppression method based on additional virtual modulation as claimed in claim 4, wherein the characteristic is that an upper limit value of a dc voltage normal operation allowance is set; if the direct current voltage of the positive pole and the negative pole is higher than the upper limit value, the sending end converter is subjected to additional virtual modulation control.
7. The post-latch-up dc overvoltage suppression method based on additional virtual modulation as claimed in claim 6, wherein the sending-end converters are all put into additional virtual modulation control specifically:
a direct current voltage measured value is acquired, and is subtracted from a given direct current voltage reference value to obtain a direct current voltage difference value;
the direct current voltage difference value obtains an alternating current voltage correction value through an additional virtual modulation proportion controller;
and adding the alternating voltage reference value and the alternating voltage correction value to reduce the alternating voltage reference value of the positive and negative pole current converters.
8. The method for suppressing post-latch-up dc overvoltage based on additional virtual modulation as claimed in claim 5, wherein the step of putting the sending-end fault pole converter into additional virtual modulation control is specifically as follows:
the direct current voltage difference value obtains an alternating current voltage correction value through an additional virtual modulation proportion link;
and adding the alternating voltage reference value and the alternating voltage correction value to increase the alternating voltage reference value of the fault electrode.
9. The DC overvoltage suppression system after the latch-up fault based on the additional virtual modulation is characterized by comprising the following components: a voltage measuring unit and a controller;
the voltage measuring unit measures a direct-current voltage signal when the new energy island is accessed through a flexible direct-current power grid;
the controller judges whether an additional virtual modulation control strategy is put into use based on the direct-current voltage signal;
the time reaching the DC voltage limit value is prolonged by using the input or not of the additional virtual modulation control unit, and the DC overvoltage after the locking fault is restrained.
10. The post-latch-up dc overvoltage suppression system based on additional virtual modulation as claimed in claim 9 wherein the additional virtual modulation control unit comprises: the device comprises a comparator, a first adder, a second adder, a first proportion controller, a second proportion controller, a selector and a third adder;
the first adder is connected to the selector through a negative proportion unit, the second adder is connected to the selector through a positive proportion unit, the comparator is connected to the selector, and the selector is connected to the third adder;
the comparator compares whether the direct current voltages of the positive pole and the negative pole are both higher than an upper limit value, the corresponding branch is selected by the selector according to the comparison result, the direct current voltage measured value is subtracted from the given direct current voltage reference value by the first adder or the second adder to obtain a direct current voltage difference value, positive and negative additional virtual modulation is carried out on the direct current voltage difference value to obtain an alternating current voltage correction value, and the third adder adds the correction value and the alternating current voltage correction value to inhibit the direct current voltage rising speed.
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