CN114123210A - Transient over-current control method of flexible loop closing - Google Patents
Transient over-current control method of flexible loop closing Download PDFInfo
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- CN114123210A CN114123210A CN202111425143.3A CN202111425143A CN114123210A CN 114123210 A CN114123210 A CN 114123210A CN 202111425143 A CN202111425143 A CN 202111425143A CN 114123210 A CN114123210 A CN 114123210A
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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
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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
- H02J3/007—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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- Emergency Protection Circuit Devices (AREA)
Abstract
A flexible loop closing transient over-current control method is characterized in that a flexible loop closing device is controlled to output current larger than a rated value of the device in a short time, 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 fault side flexible loop closing device controls the alternating current output voltage in a closed loop mode, and the fault side power supply is achieved by adopting a control structure of a voltage outer loop and a current inner loop; 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 overcurrent control process, and then the current inner ring is entered to finish the control; according to the invention, the transient output current capability of the loop closing device can be improved to the maximum extent through the constant current control or the variable current control in the transient current control process according to the running state and the control mode of the power distribution network; on the premise of thermal stability of the flexible loop closing device, the control capability of the flexible loop closing device on output voltage in a short time is guaranteed, and the stability of the system in the transient state condition that voltage fluctuates such as power grid faults, motor starting and transformer excitation occurs is guaranteed.
Description
Technical Field
The invention relates to the technical field of power supply network electric energy conversion, in particular to a transient over-current control method of a flexible loop closing.
Background
The flexible closed loop is an electric energy conversion device based on power electronic technology. The flexible loop is used for connecting two alternating current power grids, not only can realize the interconnection of the power grids with different voltage grades and different voltage frequencies, but also can control the flow direction of power and realize the function of fault side switching power supply. In the aspect of the existing flexible control strategy, most of research schemes at home and abroad refer to a Modular Multilevel Converter (MMC) converting scheme with a back-to-back structure in flexible direct current transmission. And double closed-loop control of the voltage outer loop and the current inner loop is realized under a two-phase static coordinate system through phase locking of the voltage phase of the power grid.
Under the tidal current control mode, the flexible loop closing device controls the output alternating current in a closed loop mode, and the active power flow and the reactive power flow are controlled. When the power grid fails and is powered off, the flexible loop closing device is switched between modes rapidly, the fault side is controlled to output alternating voltage in a closed loop mode, power supply conversion of the fault side is achieved, and the power failure range and the power failure time of the system are reduced. At present, aiming at a flexible loop closing alternating voltage closed-loop control strategy, a double closed-loop mode of a voltage outer loop and a current inner loop is generally adopted, and the amplitude of a current inner loop instruction is limited in the range of rated current of the device. Under the control mode of the output voltage, when the processes of power grid failure, motor starting, transformer excitation and the like occur, transient voltage drop may cause the inner ring of the flexible loop closing current to be saturated, so that the control capability of the output voltage of the flexible loop closing device is lost, and the normal operation of the system is influenced. Therefore, the transient overcurrent control strategy of the flexible loop closing device is researched, the system instability caused by current inner loop saturation is avoided, and the method has important practical significance for the development of the flexible loop closing related technology and industry.
Disclosure of Invention
In order to overcome the defects in the prior art, the present invention provides a transient overcurrent control method for a flexible loop closing system, which can meet the requirement of transient current in a switching power supply mode, improve the stability of the flexible loop closing system, and improve the reliability of power supply.
In order to achieve the purpose, the invention adopts the following technical scheme:
a transient over-current control method of a flexible loop closing specifically comprises the following steps:
and 4, when the flexible loop closing device works in the mode that the flexible loop closing device controls the alternating current output voltage in a closed loop mode in the 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 instruction value, and the current inner loop instruction is preprocessed through a transient over-current control process and enters the current inner loop to complete control.
The specific method in the step 3 comprises the following steps:
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 the flexible loop closing device controls the voltage at the side I of a first port and the current at the side II of a second port in a closed-loop mode to realize power supply transfer;
2) when the distribution network at the voltage source T2 side of the second transformer substation has a fault, the second circuit breaker S2 is disconnected, and the flexible loop closing device controls the voltage at the second port II side and the current at the first port I side in a closed-loop mode to realize power supply transfer.
The step 4 of transient overcurrent control specifically includes: and (3) according to the running state and the control mode of the power distribution network, further conditioning a current inner ring instruction output by the voltage outer ring through a fixed current control or a variable current control:
1) the constant current control comprises the following steps: after the voltage of the power distribution network fluctuates to cause a transient state condition, the flexible loop closing device outputs a current larger than a rated value of the device in a short time, and the magnitude of the output overcurrent is kept unchanged; under the control of constant over-current, when the voltage of the power distribution network drops due to short-circuit fault, sudden start of motor load or other transient conditions of the power grid, the output of a voltage outer ring rises in a step mode, and the flexible loop closing device outputs current larger than the rated value of the device in a short time, so that the requirement of the system on high current in the transient condition is met, and the transient stability of the system is ensured;
2) the change over current control is as follows: after the voltage of the power distribution network fluctuates to cause a transient state condition, the flexible loop closing device outputs a current larger than a rated value of the device in a short time, and the magnitude of the output overcurrent is gradually reduced along with the change of time; under the control of variable overcurrent, when the voltage drops due to the fact that short-circuit faults, sudden starting of motor loads or other transient conditions occur to the power grid, the output of the voltage outer ring rises in a step mode, the flexible loop 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 condition is met, and the transient stability of the system is guaranteed.
Compared with the prior art, the invention has the following beneficial effects:
according to the invention, the transient output current capability of the loop closing device can be improved to the maximum extent through the constant current control or the variable current control in the transient current control process according to the running state and the control mode of the power distribution network. On the premise of flexible loop closing thermal stability, the flexible loop closing device is utilized to provide large current in a short time, and the stability of the system in the transient condition caused by fluctuation of the voltage of the power distribution network 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 diagram of a flexible loop closing device according to the present invention.
FIG. 2 is a diagram of the closed loop control of the output voltage according to the present invention.
FIG. 3 is a diagram showing the relationship between overcurrent and duration in a constant overcurrent control according to the present invention.
Fig. 4 is a diagram showing the relationship between overcurrent and duration in the variable overcurrent control according to the present invention.
In the figure: s1, a first circuit breaking switch; s2, a second circuit breaking switch; I. a first port; II. A second port; t1, first substation voltage source; t2, second substation voltage source.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
Referring to fig. 1, a transient overcurrent control method of a flexible loop specifically includes the following steps:
referring to fig. 2, in step 4, when the flexible loop closing device works in the mode of controlling the alternating current output voltage in the closed loop manner by 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 instruction value, and the current inner loop instruction is preprocessed through the transient overcurrent control process and enters the current inner loop to complete control.
The specific method in the step 3 comprises the following steps:
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 the flexible loop closing device controls the voltage at the side I of a first port and the current at the side II of a second port in a closed-loop mode to realize power supply transfer;
2) when the distribution network at the voltage source T2 side of the second transformer substation has a fault, the second circuit breaker S2 is disconnected, and the flexible loop closing device controls the voltage at the second port II side and the current at the first port I side in a closed-loop mode to realize power supply transfer.
The step 4 of transient overcurrent control specifically includes: according to the operation state and the control mode of the power distribution network in the step 3, further conditioning a current inner ring instruction output by the voltage outer ring through the fixed current control and the variable current control:
1) the constant current control comprises the following steps: after the voltage of the power distribution network fluctuates to cause a transient state condition, the flexible loop closing device outputs a current larger than a rated value of the device in a short time, the magnitude of 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 the control of the fixed overcurrent, when the voltage of the power distribution network drops due to short-circuit fault, sudden starting of motor load or other transient states, the output of the voltage outer ring rises in a step mode, the flexible loop 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 ensured.
Taking fig. 3 as an example, when the current instruction output by the voltage outer ring in the transient state condition caused by the fluctuation of the voltage of the power distribution network is greater than 5 times of the rated current, the output of the transient current control process is 5 times of the rated current, and the duration is 3 seconds; when the current instruction output by the voltage outer ring is more than 4 times of rated current and less than 5 times of rated current, the transient current control process outputs 4 times of rated current for 4 seconds; when the current instruction output by the voltage outer ring is more than 3 times of rated current and less than 4 times of rated current, the transient current control process outputs 3 times of rated current for 6 seconds; when the current instruction output by the voltage outer ring is more than 2 times of rated current and less than 3 times of rated current, the transient current control process outputs 2 times of rated current for 8 seconds.
2) The change over current control is as follows: after the voltage of the power distribution network fluctuates to cause a transient state, the flexible loop closing device outputs a current larger than a rated value of the device in a short time, the magnitude of the output overcurrent is gradually reduced along with the change of time, and the specific numerical value and the shape of a slope curve can be different according to the thermal stability of the flexible loop closing device.
Under the control of variable overcurrent, when the voltage of the power distribution network drops due to short-circuit fault, sudden starting of motor load or other transient states, the output of the voltage outer ring rises in a step mode, the flexible loop 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 stability of the system is ensured.
Taking fig. 4 as an example, when the current command output by the voltage outer ring in the transient state condition caused by the fluctuation of the voltage of the power distribution network is 6 times of the rated current, the transient current control process outputs a 6 times current-time curve, 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 the rated value when the current command reaches 8 seconds; when the current output by the voltage outer ring is 3 times of rated current, the transient current control process outputs a 3 times current-time curve, firstly, the 3 times current instruction lasts for 6 seconds, then the current instruction gradually becomes smaller along the slope curve, and when the current instruction reaches 8 seconds, the current instruction becomes the rated value.
Claims (3)
1. A transient over-current control method of a 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 substation voltage source (T1) and a second substation voltage source (T2), wherein a first port (I) and a second port (II) are respectively arranged on two sides of the flexible loop closing device, a disconnecting switch (S1) is arranged between the first port (I) and the first substation voltage source (T1), and a disconnecting switch (S2) is arranged between the second port (II) and the second substation voltage source (T2);
step 2, when the power distribution network has no fault, 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 controls the output current of the alternating current side in a closed loop mode, namely the flexible loop closing device controls the current of the first port (I) and the current of the second port (II) in a closed loop mode, and power flow regulation is achieved;
step 3, when one side of the power distribution network fails, the flexible loop closing device at the fault side controls the alternating current output voltage in a closed loop mode, and power supply is switched at the fault side;
and 4, when the flexible loop closing device works in the mode that the flexible loop closing device controls the alternating current output voltage in a closed loop mode in the 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 instruction value, and the current inner loop instruction is preprocessed through a transient over-current control process and enters the current inner loop to complete control.
2. The transient overcurrent control method for the flexible loop-closing of claim 1, wherein: the specific method in the step 3 comprises the following steps:
1) when a power distribution network at the voltage source (T1) side of a first substation fails, a first circuit breaker (S1) is disconnected, and the flexible loop closing device controls the voltage at the first port (I) side and the current at the second port (II) side in a closed-loop mode to realize power supply transfer;
2) when a distribution network on the voltage source (T2) side of the second substation fails, the second circuit breaker (S2) is disconnected, and the flexible loop closing device controls the voltage on the second port (II) side and the current on the first port (I) side in a closed-loop mode to realize power supply transfer.
3. The transient overcurrent control method for the flexible loop-closing of claim 1, wherein: the step 4 of transient overcurrent control specifically includes: and (3) according to the running state and the control mode of the power distribution network, further conditioning a current inner ring instruction output by the voltage outer ring through a fixed current control or a variable current control:
1) the constant current control comprises the following steps: after the voltage of the power distribution network fluctuates to cause a transient state condition, the flexible loop closing device outputs a current larger than a rated value of the device in a short time, and the magnitude of the output overcurrent is kept unchanged; under the control of constant over-current, when the voltage of a power distribution network drops due to short-circuit faults, sudden starting of motor loads or other transient states, the output of a voltage outer ring rises in a step mode, and the flexible loop closing device outputs current larger than the rated value of the device in a short time, so that the requirement of a system on large current in the transient state condition is met, and the transient stability of the system is ensured;
2) the change over current control is as follows: after the voltage of the power distribution network fluctuates to cause a transient state condition, the flexible loop closing device outputs a current larger than a rated value of the device in a short time, and the magnitude of the output overcurrent is gradually reduced along with the change of time; under the control of variable overcurrent, when the voltage of the power distribution network drops due to short-circuit fault, sudden starting of motor load or other transient states, the output of the voltage outer ring rises in a step mode, the flexible loop 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 stability of the system is ensured.
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| Application Number | Priority Date | Filing Date | Title |
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| CN202111425143.3A CN114123210A (en) | 2021-11-26 | 2021-11-26 | Transient over-current control method of flexible loop closing |
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| CN202111425143.3A CN114123210A (en) | 2021-11-26 | 2021-11-26 | Transient over-current control method of flexible loop closing |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117335578A (en) * | 2023-12-01 | 2024-01-02 | 成都天合一成科技服务有限公司 | Detection and regulation system for loop closing power conversion of low-voltage power distribution |
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- 2021-11-26 CN CN202111425143.3A patent/CN114123210A/en active Pending
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117335578A (en) * | 2023-12-01 | 2024-01-02 | 成都天合一成科技服务有限公司 | Detection and regulation system for loop closing power conversion of low-voltage power distribution |
| CN117335578B (en) * | 2023-12-01 | 2024-02-06 | 成都天合一成科技服务有限公司 | Detection and regulation system for loop closing power conversion of low-voltage power distribution |
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