CN114123210B - Transient over-current control method for flexible loop closing - Google Patents
Transient over-current control method for flexible loop closing Download PDFInfo
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- CN114123210B CN114123210B CN202111425143.3A CN202111425143A CN114123210B CN 114123210 B CN114123210 B CN 114123210B CN 202111425143 A CN202111425143 A CN 202111425143A CN 114123210 B CN114123210 B CN 114123210B
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- 230000033228 biological regulation Effects 0.000 claims description 3
- 230000003750 conditioning effect Effects 0.000 claims description 3
- 238000006798 ring closing metathesis reaction Methods 0.000 abstract description 5
- 230000005284 excitation Effects 0.000 abstract description 2
- 238000006243 chemical reaction Methods 0.000 description 8
- 238000011217 control strategy Methods 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
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Classifications
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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
- H02J3/04—Circuit arrangements for ac mains or ac distribution networks for connecting networks of the same frequency but supplied from different sources
- H02J3/06—Controlling transfer of power between connected networks; Controlling sharing of load between connected networks
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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
-
- 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
- H02J3/007—Arrangements for selectively connecting the load or loads to one or several among a plurality of power lines or power sources
- H02J3/0073—Arrangements for selectively connecting the load or loads to one or several among a plurality of power lines or power sources for providing alternative feeding paths between load and source when the main path fails, e.g. transformers, busbars
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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
- H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
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- Power Engineering (AREA)
- Emergency Protection Circuit Devices (AREA)
Abstract
The transient over-current control method for the flexible loop closing device outputs current larger than the rated value of the device in a short time by controlling the flexible loop closing device, so that the requirement of a system on large current in a transient condition caused by fluctuation of the voltage of a power distribution network is met, and the control capability of the flexible loop closing device on output voltage is ensured; when one side of the power distribution network fails, the flexible loop closing device at the failure side performs closed-loop control on alternating-current output voltage, and a control structure of a voltage outer loop and a current inner loop is adopted to realize failure side transfer power supply; the output of the voltage outer ring is the instruction value of the current inner ring, the instruction of the current inner ring is preprocessed through the transient over-current control process, and then the current inner ring is entered to complete the control; according to the running state and the control mode of the power distribution network, the transient output current capacity of the loop closing device can be improved to the greatest extent through the fixed overcurrent control or the variable overcurrent control in the transient current control process; on the premise of thermal stability of the flexible ring closure, the control capability of the flexible ring closure device on output voltage in a short time is ensured, and the stability of the system in the transient condition that voltage fluctuation occurs, such as power grid fault, motor starting, transformer excitation and the like is ensured.
Description
Technical Field
The invention relates to the technical field of power supply network electric energy conversion, in particular to a flexible loop closing transient state overcurrent control method.
Background
The flexible ring closure is an electric energy conversion device based on the power electronics technology. The flexible ring is used for connecting two alternating current power grids, so that power grid interconnection with different voltage grades and different voltage frequencies can be realized, the flow direction of power can be controlled, and the function of fault side transfer power supply is realized. In the aspect of the existing flexible control strategy, most of research schemes at home and abroad refer to the current conversion scheme of modular multilevel converters (MMCs, modular Multilevel Converter) with back-to-back structures in flexible direct current transmission. And the voltage phase of the phase-locked power grid is utilized to realize double closed-loop control of the voltage outer loop and the current inner loop under a two-phase static coordinate system.
In a tide control mode, the flexible loop closing device outputs alternating current in a closed loop control mode, and active and reactive tide control is achieved. When the power grid fails and is powered off, the flexible loop closing device is switched in a rapid mode, the fault side is controlled by a closed loop to output alternating voltage, power supply conversion of the fault side is realized, and the power failure range and the power failure time of the system are reduced. At present, a voltage closed-loop control strategy of a flexible closed-loop alternating current is generally adopted in a double closed-loop mode of a voltage outer loop and a current inner loop, and the amplitude of a current inner loop instruction is limited in the range of rated current of the device. In the output voltage control mode, when a power grid is in fault, a motor is started, a transformer is excited and the like, transient voltage drop can cause the inner ring of the flexible loop closing current to be saturated, so that the flexible loop closing device loses the control capability of the output voltage, and the normal operation of the system is affected. Therefore, the transient over-current control strategy of the flexible ring closing device is researched, the system instability caused by current inner ring saturation is avoided, and the method has important practical significance for the development of related technologies and industries of flexible ring closing.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention aims to provide a transient over-current control method for a flexible loop closing system, which can meet the requirement of transient current in a power supply switching mode, improve the stability of the flexible loop closing system and improve the reliability of power supply.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
The transient over-current control method for the flexible loop closing specifically comprises the following steps:
Step 1, arranging a flexible loop closing device between a first transformer substation voltage source T1 and a second transformer substation voltage source T2, respectively arranging a first port I and a second port II on two sides of the flexible loop closing device, arranging a circuit breaker S1 between the first port I and the first transformer substation voltage source T1, and arranging a circuit breaker S2 between the second port II and the second transformer substation voltage source T2;
Step 2, when the power distribution network has no faults, the flexible loop closing device works in a loop closing operation mode, the circuit breakers S1 and S2 are closed, the flexible loop closing device performs closed-loop control on the alternating-current side output current, namely the flexible loop closing device performs closed-loop control on the current of the first port I and the second port II, and thus the power flow regulation is realized;
Step3, when one side of the power distribution network fails, the flexible loop closing device at the failure side performs closed-loop control on alternating-current output voltage, so that failure side transfer power supply is realized;
And 4, when the flexible loop closing device works in the step 3 and the flexible loop closing device performs closed-loop control on an alternating current output voltage mode, adopting a control structure of a voltage outer loop and a current inner loop, wherein the output of the voltage outer loop is a current inner loop instruction value, preprocessing the current inner loop instruction through a transient over-current control process, and entering the current inner loop to complete control.
The specific method of the step 3 is as follows:
1) When the power distribution network at the side of the voltage source T1 of the first transformer substation fails, the first disconnection switch S1 is disconnected, and the flexible loop closing device performs closed loop control on the voltage at the side of the first port I and the current at the side of the second port II, so that power conversion and power supply are realized;
2) When the power distribution network on the side of the voltage source T2 of the second transformer substation fails, the second circuit breaker S2 is disconnected, and the flexible loop closing device performs closed loop control on the voltage on the side of the second port II and the current on the side of the first port I, so that power conversion and power supply are realized.
The transient over-current control process in the step 4 specifically comprises the following steps: according to the running state and the control mode of the power distribution network in the step 3, further conditioning the current inner loop instruction output by the voltage outer loop through constant overcurrent control or variable overcurrent control:
1) The constant overcurrent control is as follows: after the transient state condition caused by fluctuation of the voltage of the power distribution network, the flexible loop closing device outputs a current larger than the rated value of the device in a short time, and the output overcurrent is kept unchanged; under the control of fixed overcurrent, when the power grid has short-circuit faults, the motor load suddenly starts or other transient conditions cause the voltage of the power distribution network to drop, the output of the voltage outer ring can rise in a step mode, the flexible ring closing device outputs current larger than the rated value of the device in a short time, the requirement of the system on high current in the transient conditions is met, and the transient stability of the system is ensured;
2) The variable overcurrent control is as follows: after the transient state condition caused by fluctuation of the voltage of the power distribution network, the flexible loop closing device outputs a current larger than the rated value of the device in a short time, and the output overcurrent is gradually reduced along with the change of time; under the control of the variable overcurrent, when the power grid comprises short-circuit faults, sudden starting of motor load or voltage drop caused by other transient conditions, the output of the voltage outer ring can rise in a step mode, the flexible ring closing device outputs current larger than the rated value of the device in a short time, the requirement of the system on high current in the transient condition is met, and the transient stability of the system is ensured.
Compared with the prior art, the invention has the following beneficial effects:
According to the running state and the control mode of the power distribution network, the transient output current capacity of the loop closing device can be improved to the greatest extent through the fixed overcurrent control or the variable overcurrent control in the transient current control process. On the premise of thermal stability of the flexible ring closure, the flexible ring closure device is utilized to provide large current in a short time, so that the stability of the system in transient conditions caused by fluctuation of power distribution network voltages such as power grid faults, motor starting, transformer excitation and the like is ensured. The method provided by the invention is an inventive operation method for controlling the output current of the flexible loop closing device.
Drawings
FIG. 1 is a schematic view of a flexible loop closing device according to the present invention.
Fig. 2 is a diagram of the output voltage closed-loop control structure of the present invention.
Fig. 3 is a graph of overcurrent versus duration in the overcurrent control according to the invention.
Fig. 4 is a graph of overcurrent versus duration in variable overcurrent control according to the invention.
In the figure: s1, a first circuit breaker; s2, a second circuit breaker; I. a first port; II. A second port; t1, a first transformer substation voltage source; and T2, a second transformer substation voltage source.
Detailed Description
The invention is described in further detail below with reference to the accompanying drawings.
Referring to fig. 1, a method for controlling transient over-current of a flexible loop includes the following steps:
Step 1, arranging a flexible loop closing device between a first transformer substation voltage source T1 and a second transformer substation voltage source T2, respectively arranging a first port I and a second port II on two sides of the flexible loop closing device, arranging a circuit breaker S1 between the first port I and the first transformer substation voltage source T1, and arranging a circuit breaker S2 between the second port II and the second transformer substation voltage source T2;
Step 2, when the power distribution network has no faults, the flexible loop closing device works in a loop closing operation mode, the circuit breakers S1 and S2 are closed, the flexible loop closing device performs closed-loop control on the alternating-current side output current, namely the flexible loop closing device performs closed-loop control on the current of the first port I and the second port II, and thus the power flow regulation is realized;
Step3, when one side of the power distribution network fails, the flexible loop closing device at the failure side performs closed-loop control on alternating-current output voltage, so that failure side transfer power supply is realized;
Referring to fig. 2, step 4, when the flexible loop closing device works in the closed loop control ac output voltage mode of the flexible loop closing device in step 3, a control structure of a voltage outer loop and a current inner loop is adopted, the output of the voltage outer loop is a current inner loop command value, and the current inner loop command is preprocessed through a transient over-current control process, and enters the current inner loop to complete control.
The specific method of the step 3 is as follows:
1) When the power distribution network at the side of the voltage source T1 of the first transformer substation fails, the first disconnection switch S1 is disconnected, and the flexible loop closing device performs closed loop control on the voltage at the side of the first port I and the current at the side of the second port II, so that power conversion and power supply are realized;
2) When the power distribution network on the side of the voltage source T2 of the second transformer substation fails, the second circuit breaker S2 is disconnected, and the flexible loop closing device performs closed loop control on the voltage on the side of the second port II and the current on the side of the first port I, so that power conversion and power supply are realized.
The transient over-current control process in the step 4 specifically comprises the following steps: according to the running state and the control mode of the power distribution network in the step 3, further conditioning the current inner loop instruction output by the voltage outer loop through constant overcurrent control and variable overcurrent control:
1) The constant overcurrent control is as follows: after the transient state condition caused by fluctuation of the voltage of the power distribution network occurs, the flexible loop closing device outputs a current larger than the rated value of the device in a short time, the output overcurrent is kept unchanged, and specific numerical values can be different according to the thermal stability of the flexible loop closing device;
Under constant overcurrent control, when the power grid comprises short circuit faults, motor load suddenly starts or other transient states cause the voltage of the power distribution network to drop, the output of the voltage outer ring rises in a step mode, the flexible ring closing device outputs current larger than the rated value of the device in a short time, the requirement of the system on large current in the transient state condition is met, and the transient stability of the system is guaranteed.
Taking fig. 3 as an example, when the current command output by the voltage outer ring is greater than 5 times rated current in the transient state condition caused by the fluctuation of the voltage of the power distribution network, the transient state current control process outputs 5 times rated current for 3 seconds; when the current command output by the voltage outer ring is greater than 4 times rated current and less than 5 times rated current, the transient current control process outputs 4 times rated current for 4 seconds; when the current command output by the voltage outer ring is larger than 3 times rated current and smaller than 4 times rated current, the transient current control process outputs 3 times rated current for 6 seconds; when the current command output by the voltage outer ring is larger than 2 times rated current and smaller than 3 times rated current, the transient current control process outputs 2 times rated current for 8 seconds.
2) The variable overcurrent control is as follows: after the voltage of the power distribution network fluctuates to cause transient conditions, the flexible loop closing device outputs a current larger than the rated value of the device in a short time, the output overcurrent gradually decreases along with the change of time, and the specific numerical value and the shape of the slope curve can be different according to the thermal stability of the flexible loop closing device.
Under the control of the variable overcurrent, when the power grid comprises short-circuit faults, sudden starting of motor loads or voltage drop of the power distribution network caused by other transient states, the output of the voltage outer ring can rise in a step mode, the flexible ring closing device outputs current larger than the rated value of the device in a short time, the requirement for large current in the transient state condition of the system is met, and the transient state stability of the system is guaranteed.
Taking fig. 4 as an example, when the current command output by the voltage outer ring is 6 times of rated current in the transient state condition caused by the fluctuation of the voltage of the power distribution network, the transient state current control process is output as a 6 times current-time curve, firstly, the 6 times current command lasts for 2 seconds, then, the current command gradually becomes smaller along the slope curve, and the current command becomes a rated value when the current command is 8 seconds; when the current output by the voltage outer ring is 3 times rated current, the transient current control process outputs a 3 times current-time curve, firstly, the 3 times current command lasts for 6 seconds, then, the current command gradually becomes smaller along the slope curve, and the current command becomes rated value when the current is 8 seconds.
Claims (2)
1. A transient over-current control method for flexible loop closing is characterized in that: the method specifically comprises the following steps:
Step 1, arranging a flexible loop closing device between a first transformer substation voltage source (T1) and a second transformer substation voltage source (T2), respectively arranging a first port (I) and a second port (II) on two sides of the flexible loop closing device, arranging a first circuit breaker (S1) between the first port (I) and the first transformer substation voltage source (T1), and arranging a second circuit breaker (S2) between the second port (II) and the second transformer substation voltage source (T2);
Step 2, when the power distribution network has no faults, the flexible loop closing device works in a loop closing operation mode, the first circuit breaker (S1) and the second circuit breaker (S2) are closed, the flexible loop closing device performs closed-loop control on the alternating current side to output current, namely the flexible loop closing device performs closed-loop control on the current of the first port (I) and the second port (II), and thus the current regulation is realized;
Step3, when one side of the power distribution network fails, the flexible loop closing device at the failure side performs closed-loop control on alternating-current output voltage, so that failure side transfer power supply is realized;
Step 4, when the flexible loop closing device works in the step 3 and the flexible loop closing device performs closed-loop control on an alternating-current output voltage mode, a control structure of a voltage outer loop and a current inner loop is adopted, the output of the voltage outer loop is a current inner loop instruction value, the current inner loop instruction is preprocessed through a transient overcurrent control process, and the current inner loop is entered to complete control;
the transient over-current control process specifically comprises the following steps: according to the running state and the control mode of the power distribution network in the step 3, further conditioning the current inner loop instruction output by the voltage outer loop through constant overcurrent control or variable overcurrent control:
1) The constant overcurrent control is as follows: after the transient state condition caused by fluctuation of the voltage of the power distribution network, the flexible loop closing device outputs a current larger than the rated value of the device in a short time, and the output overcurrent is kept unchanged; under the control of fixed overcurrent, when the power grid comprises short-circuit faults, the motor load suddenly starts or other transient states cause the voltage of the power distribution network to drop, the output of the voltage outer ring rises in a step mode, the flexible ring closing device outputs current larger than the rated value of the device in a short time, the requirement of the system on high current in the transient state condition is met, and the transient stability of the system is ensured;
2) The variable overcurrent control is as follows: after the transient state condition caused by fluctuation of the voltage of the power distribution network, the flexible loop closing device outputs a current larger than the rated value of the device in a short time, and the output overcurrent is gradually reduced along with the change of time; under the control of the variable overcurrent, when the power grid comprises short-circuit faults, sudden starting of motor loads or voltage drop of the power distribution network caused by other transient states, the output of the voltage outer ring can rise in a step mode, the flexible ring closing device outputs current larger than the rated value of the device in a short time, the requirement for large current in the transient state condition of the system is met, and the transient state stability of the system is guaranteed.
2. The method for controlling transient over-current of a flexible loop according to claim 1, wherein: the specific method of the step 3 is as follows:
1) When a power distribution network at the side of a voltage source (T1) of a first transformer substation fails, a first circuit breaker (S1) is disconnected, and a flexible loop closing device performs closed loop control on the voltage at the side of a first port (I) and the current at the side of a second port (II), so that power transfer is realized;
2) When the power distribution network at the side of the voltage source (T2) of the second transformer substation fails, the second circuit breaker (S2) is disconnected, and the flexible loop closing device is used for controlling the voltage at the side of the second port (II) and the current at the side of the first port (I) in a closed loop mode, so that power transfer is realized.
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Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106786761A (en) * | 2017-01-10 | 2017-05-31 | 华北电力大学 | The powered operation method of the flexible looped network device based on droop control |
| CN113315123A (en) * | 2021-05-31 | 2021-08-27 | 西安交通大学 | Back-to-back flexible loop closing switch state switching method |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106786761A (en) * | 2017-01-10 | 2017-05-31 | 华北电力大学 | The powered operation method of the flexible looped network device based on droop control |
| CN113315123A (en) * | 2021-05-31 | 2021-08-27 | 西安交通大学 | Back-to-back flexible loop closing switch state switching method |
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