CN108988269B - Voltage source type ice melting device, control method and control device - Google Patents
Voltage source type ice melting device, control method and control device Download PDFInfo
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- CN108988269B CN108988269B CN201810957415.6A CN201810957415A CN108988269B CN 108988269 B CN108988269 B CN 108988269B CN 201810957415 A CN201810957415 A CN 201810957415A CN 108988269 B CN108988269 B CN 108988269B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02G—INSTALLATION OF ELECTRIC CABLES OR LINES, OR OF COMBINED OPTICAL AND ELECTRIC CABLES OR LINES
- H02G7/00—Overhead installations of electric lines or cables
- H02G7/16—Devices for removing snow or ice from lines or cables
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02G—INSTALLATION OF ELECTRIC CABLES OR LINES, OR OF COMBINED OPTICAL AND ELECTRIC CABLES OR LINES
- H02G1/00—Methods or apparatus specially adapted for installing, maintaining, repairing or dismantling electric cables or lines
- H02G1/02—Methods or apparatus specially adapted for installing, maintaining, repairing or dismantling electric cables or lines for overhead lines or cables
Abstract
The invention discloses a voltage source type ice melting device, which comprises an alternating current-direct current converter, wherein the alternating current side of the alternating current-direct current converter is connected with an alternating current power supply, the device also comprises at least two current limiting units, each current limiting unit is formed by connecting a current limiting resistor and a bypass switch in parallel, the current limiting units are connected in series, one end of the series connection is connected with the direct current positive electrode or negative electrode of the alternating current-direct current converter, and the other end of the series connection is used as a direct current output port of the device. The invention can realize the large-range regulation of the ice melting current by combining the control of the AC-DC converter and the input of the current limiting unit, solves the problem of small regulation range of the voltage source converter, and has the advantages of low cost, high reliability, easy realization and high cost performance.
Description
Technical Field
The invention belongs to the technical field of high-power electronic converter, and particularly relates to a voltage source type ice melting device, a control method and a control device.
Background
In winter, due to the combined action of air temperature, air humidity and wind speed, the phenomenon of ice coating caused by the formation of ice by liquid water exists. Therefore, ice coating is a freezing phenomenon generated under specific meteorological conditions, and if ice coating is formed on the overhead conductor in a large area, the tower can topple, the conductor ice coating can swing or break, and the normal and safe operation of the overhead line can be directly influenced. At present, the existing ice melting schemes all need to add additional ice melting equipment, so that additional investment is increased, the occupied space of the equipment is increased, and the complexity of the system is also increased. Compared with the traditional current source converter consisting of thyristors, the voltage source converter has the characteristics of small harmonic wave and four-quadrant operation, and can be used as a reactive power compensation device besides ice melting. However, the direct-current voltage operating range of the voltage source converter scheme is limited, because the voltage source converter has a rectifier bridge formed by diodes, a lower voltage cannot be output, the equivalent resistance of the ice melting line has uncertainty, and the value range of the equivalent resistance is large, so that the ice melting by adopting the voltage source converter is likely to cause the output overcurrent of the device; in the scheme, a chopper circuit is added at the rear stage of the voltage source converter, so that a certain operation range can be improved, but the efficiency and the cost of the device are greatly increased. The invention aims to solve the problems and provides a voltage source type ice melting device with higher cost performance.
Disclosure of Invention
In order to solve the problems, the invention provides a voltage source type ice melting device, which only realizes the promotion of the direct-current voltage operating range of a voltage source converter with lower cost, and provides a corresponding control method and a corresponding control device.
In order to achieve the above purpose, the present invention adopts the following specific scheme:
a voltage source type ice melting device comprises an alternating current-direct current converter, wherein the alternating current side of the alternating current-direct current converter is connected with an alternating current power supply, the device further comprises at least two current limiting units, each current limiting unit is formed by connecting a current limiting resistor and a bypass switch in parallel, the current limiting units are connected in series, one end of the series connection is connected with the direct current positive pole or the negative pole of the alternating current-direct current converter, and the other end of the series connection is used as the direct current output port of the device.
The device also comprises a starting switch which is connected between the current limiting unit and the direct current output port of the device in series.
The alternating current-direct current converter is a multilevel voltage source converter and comprises a first submodule, a second submodule and a reactor, wherein the first submodule, the second submodule and the reactor comprise power semiconductor devices, the multilevel converter comprises three phases, each phase comprises three bridge arms, the first bridge arm and the second bridge arm are respectively defined as an upper bridge arm and a lower bridge arm, and a middle connecting point of the upper bridge arm and the lower bridge arm is connected with the third bridge arm to form an alternating current output phase; the positive end of the first bridge arm of each phase is connected to form a direct current positive electrode, and the negative end of the second bridge arm of each phase is connected to form a direct current negative electrode; the first bridge arm and the second bridge arm are formed by connecting a reactor and at least two first sub-modules in series; the third bridge arm is formed by connecting at least one second submodule in series.
The alternating current-direct current converter is a multi-level voltage source converter and comprises a first submodule and a reactor, the multi-level converter comprises three phases, each phase comprises two bridge arms, the first bridge arm and the second bridge arm are respectively defined as an upper bridge arm and a lower bridge arm, and a middle connecting point of the upper bridge arm and the lower bridge arm is used as one phase of alternating current side output; the positive end of the first bridge arm of each phase is connected to form a direct current positive electrode, and the negative end of the second bridge arm of each phase is connected to form a direct current negative electrode; the first bridge arm and the second bridge arm are formed by connecting a reactor and at least two first sub-modules in series.
The alternating current-direct current converter is a multi-level voltage source converter and comprises a second submodule and a reactor, the multi-level converter comprises three phases, each phase comprises two bridge arms, the first bridge arm and the second bridge arm are respectively defined as an upper bridge arm and a lower bridge arm, and a middle connecting point of the upper bridge arm and the lower bridge arm is used as one phase of alternating current side output; the positive end of the first bridge arm of each phase is connected to form a direct current positive electrode, and the negative end of the second bridge arm of each phase is connected to form a direct current negative electrode; the first bridge arm and the second bridge arm are formed by connecting a reactor and at least two second submodules in series.
The alternating current-direct current converter is a multi-level voltage source converter and comprises a first submodule, a second submodule and a reactor, the multi-level converter comprises three phases, each phase comprises two bridge arms, the first bridge arm and the second bridge arm are respectively defined as an upper bridge arm and a lower bridge arm, and a middle connecting point of the upper bridge arm and the lower bridge arm is used as one phase of alternating current side output; the positive end of the first bridge arm of each phase is connected to form a direct current positive electrode, and the negative end of the second bridge arm of each phase is connected to form a direct current negative electrode; the first bridge arm and the second bridge arm are formed by connecting a reactor, at least one first submodule and at least one second submodule in series.
The first submodule is a half-bridge module formed by at least two power semiconductor switching devices and a capacitor.
The second submodule is a full-bridge module formed by at least four power semiconductor switching devices and a capacitor.
The alternating current-direct current converter is a two-level voltage source converter.
The alternating current-direct current converter is a three-level voltage source converter.
Wherein the bypass switch is a mechanical switch.
Wherein the bypass switch is a semiconductor switch.
The invention also comprises a control method of the ice melting device, which comprises the following steps:
(1) when the ice melting device is started, the control method comprises the following steps:
step 1: connecting a direct current output port of the ice melting device with an ice melting line;
step 2: by-pass switch for separating all current-limiting units
And step 3: starting an alternating current power supply of the ice melting device, and gradually increasing the direct current voltage of the alternating current-direct current converter;
and 4, step 4: after the direct-current voltage of the alternating-current/direct-current converter is stabilized, a bypass switch of one current-limiting unit is closed, and the direct current output by the ice melting device is increased;
and 5: after the direct current output by the alternating current-direct current converter is stable, closing a bypass switch of a current limiting unit to further increase the direct current output by the ice melting device;
step 6: repeating the step 4, and closing the bypass switches of all the current limiting units;
and 7: and a power semiconductor switching device in the AC-DC converter starts to work, and the output current of the AC-DC converter is regulated to be stabilized at the current value required by ice melting.
(2) When the ice melting device is started and enters an operating state, the ice melting line has a short-circuit fault, and the control method comprises the following steps:
step 1: when a sudden increase in output current is detected;
step 2: a bypass switch for disconnecting one of the current limiting units;
and step 3: when the output current is detected to be still higher than the maximum current value allowed by the AC-DC converter;
and 4, step 4: then a bypass switch of a current limiting unit is switched off;
and 5: repeating the step 4 until the direct current output current of the ice melting device is reduced to an allowable range;
step 6: if the line fault is an instantaneous fault, detecting that the fault is cleared, closing the bypass switches one by one until the normal running current is recovered;
and 7: if the line fault is a permanent fault, the alternating current power supply of the ice melting device is separated, all the bypass switches are separated, and the ice melting device is stopped.
(3) When the ice melting device finishes starting and enters an operating state, and the output of the device is over-current due to small equivalent resistance of an ice melting line, the control method comprises the following steps:
step 1: when an output overcurrent is detected;
step 2: adjusting the duty ratio of power semiconductor devices in a first bridge arm and a second bridge arm of the AC-DC converter to reduce the DC voltage of the AC-DC converter, thereby reducing the output current;
and step 3: if the output direct current of the ice melting device is still detected to exceed the allowable value, the duty ratio of a power semiconductor device in a third bridge arm of the alternating current-direct current converter is adjusted, so that the direct current voltage of the alternating current-direct current converter is further reduced, and the output current is further reduced;
and 4, step 4: if the direct current output by the ice melting device is still detected to exceed the allowable value, a bypass switch of one current limiting unit is disconnected;
and 5: and if the direct current output by the ice melting device is still detected to exceed the allowable value, a bypass switch of a current limiting unit is turned off, and the step 4 is repeated until the direct current output by the device is reduced to the allowable range.
The invention also provides a control device of the voltage source type ice melting device, which comprises the following components: connecting element, bypass switch breaking unit, alternating current power supply start unit, current-limiting bypass switch closing unit, output current regulating unit, wherein:
the connecting unit is used for connecting the direct current output port of the ice melting device with the ice melting line; then enabling a bypass switch breaking unit;
the bypass switch breaking unit is used for separating the bypass switches in all the current limiting units; then enabling the alternating current power supply starting unit;
the alternating current power supply starting unit is used for starting an alternating current power supply of the ice melting device, and the direct current voltage of the alternating current-direct current converter is gradually increased; then enabling the current-limiting bypass switch closing unit;
the current-limiting bypass switch closing unit is used for closing a bypass switch of one current-limiting unit after the direct-current voltage of the alternating-current/direct-current converter is stabilized, so that the direct-current output by the ice melting device is increased; after the direct current output by the alternating current-direct current converter is stable, closing a bypass switch of a current limiting unit to further increase the direct current output by the ice melting device; until all the bypass switches of the current limiting units are closed; then enabling the output current regulating unit;
and the output current regulating unit is used for controlling a power semiconductor switching device in the AC-DC converter to start working and regulating the output current of the AC-DC converter to be stabilized at a current value required by ice melting.
The invention also provides a control device of the voltage source type ice melting device, the control device is used for processing the short-circuit fault of the ice melting line after the ice melting device is started and enters the running state, and the control device comprises: current surge detecting element, bypass switch disconnection unit, output current overcurrent detecting element, fault handling unit, wherein:
the current surge detection unit: for detecting whether the output current suddenly increases; when the sudden increase of the output current is detected, starting a bypass switch disconnection unit;
the bypass switch disconnecting unit is used for disconnecting a bypass switch of one current limiting unit; and starting an output current overcurrent detection unit;
the output current overcurrent detection unit is used for detecting whether the output current is higher than the maximum current value allowed by the AC-DC converter or not; if yes, starting a bypass switch disconnection unit, otherwise, starting a fault processing unit;
the fault processing unit is used for detecting whether the fault is cleared or not, and if so, closing the bypass switches one by one until the normal operation current is recovered; otherwise, the alternating current power supply of the ice melting device is separated, all the bypass switches are separated, and the ice melting device is stopped.
The invention also provides a control device of the voltage source type ice melting device when the AC/DC converter is a multi-level voltage source converter, the control device is used for limiting the output overcurrent of the ice melting device caused by small equivalent resistance of an ice melting line after the ice melting device is started and enters an operating state, and the control device comprises:
the output overcurrent detection unit is used for detecting whether the output direct current of the ice melting device is greater than a set threshold value; if yes, starting a first duty ratio adjusting unit; if the output is still larger than the set threshold value, starting a second duty ratio adjusting unit; if the output is still larger than the set threshold value, starting a current-limiting bypass switch disconnection unit;
the duty ratio adjusting unit I is used for adjusting the duty ratios of power semiconductor devices in a first bridge arm and a second bridge arm of the AC-DC converter to reduce the DC voltage of the AC-DC converter, so that the output current is reduced;
the duty ratio adjusting unit II is used for adjusting the duty ratio of a power semiconductor device in a third bridge arm of the AC-DC converter to further reduce the direct-current voltage of the AC-DC converter, so that the output current is further reduced;
the current-limiting bypass switch disconnecting unit is used for sequentially disconnecting the bypass switches of the current-limiting unit; until the DC output current of the ice melting device is reduced to an allowable range.
The invention has the beneficial effects that:
1. the invention provides a voltage source type ice melting device, when the device is started, because the equivalent resistance of an ice melting line is unknown, the device is prevented from being damaged due to overcurrent impact in the starting process by a starting mode with a current-limiting current unit, the effect of zero-current starting of the current source type ice melting device is achieved by a mode of gradually withdrawing from the current-limiting unit, the risk in the starting process is reduced to the maximum extent, and the mode is low in cost, simple and practical.
2. The multi-level converter is adopted in the AC/DC converter, two different sub-modules are applied in the converter, the full-bridge module realizes negative voltage output by controlling the duty ratio, and can play a role in reducing the DC voltage output by the ice melting device so as to reduce the ice melting current.
3. When the ice melting line has a fault, the short-circuit current can be limited through the rapid input of the current limiting unit, if an instantaneous fault occurs, the current limiting unit can be bypassed, fault ride-through is realized, the device is prevented from being stopped, and the continuous operation capability of the system is improved.
4. The device also has the function of reactive compensation, and when ice melting is not needed, reactive compensation is carried out, so that the equipment utilization rate is improved.
Drawings
FIG. 1 is a first embodiment of the voltage source ice melting apparatus of the present invention.
FIG. 2 is a second embodiment of the voltage source ice-melting device of the present invention.
FIG. 3 is a third embodiment of the voltage source ice-melting device of the present invention.
FIG. 4 is a fourth embodiment of the voltage source ice-melting device of the present invention.
FIG. 5 is one embodiment of a first sub-module of the present invention.
FIG. 6 is one embodiment of a second sub-module of the present invention.
Number designation in the figures: 1. an AC-DC converter; 2. a current limiting unit; 3. a bypass switch; 4. a current limiting resistor; 5. starting a switch; 6. melting ice circuit equivalent resistance;
Detailed Description
The invention will be further explained with reference to the drawings.
A voltage source type ice melting device comprises an alternating current-direct current converter 1, wherein the alternating current side of the alternating current-direct current converter is connected with an alternating current power supply, and the device further comprises at least two current limiting units 2; each current-limiting unit is formed by connecting a current-limiting resistor 4 and a bypass switch 3 in parallel, the current-limiting units are connected in series, one end of the series connection is connected with the direct current positive electrode or the direct current negative electrode of the alternating current-direct current converter, and the other end of the series connection is used as a direct current output port of the device.
The present embodiment further includes a start switch 5, and the start switch is connected in series between the current limiting unit and the dc output port of the apparatus.
As shown in fig. 1, a first embodiment of the present invention: the alternating current-direct current converter is a multilevel voltage source converter and comprises a first submodule X, a second submodule Y and a reactor, wherein the first submodule X, the second submodule Y and the reactor comprise power semiconductor devices, the multilevel converter comprises three phases, each phase comprises three bridge arms, the first bridge arm and the second bridge arm are respectively defined as an upper bridge arm and a lower bridge arm, and a middle connecting point of the upper bridge arm and the lower bridge arm is connected with the third bridge arm to form an alternating current output phase; the positive end of the first bridge arm of each phase is connected to form a direct current positive electrode, and the negative end of the second bridge arm of each phase is connected to form a direct current negative electrode; the first bridge arm and the second bridge arm are formed by connecting a reactor and at least two first sub-modules in series; the third bridge arm is formed by connecting at least one second submodule in series.
Fig. 2 is a second embodiment of the present invention, in which the ac-dc converter is a multilevel voltage source converter, and includes a first sub-module and a reactor, the multilevel converter includes three phases, each phase includes two legs, the first and second legs are respectively defined as an upper and a lower legs, and a middle connection point of the upper and lower legs is used as a phase of the ac side output; the positive end of the first bridge arm of each phase is connected to form a direct current positive electrode, and the negative end of the second bridge arm of each phase is connected to form a direct current negative electrode; the first bridge arm and the second bridge arm are formed by connecting a reactor and at least two first sub-modules in series.
Fig. 3 is a third embodiment of the present invention, including a second submodule and a reactor, where the multilevel converter includes three phases, each phase includes two legs, the first and second legs are respectively defined as an upper and a lower legs, and a middle connection point of the upper and lower legs is used as a phase of an ac side output; the positive end of the first bridge arm of each phase is connected to form a direct current positive electrode, and the negative end of the second bridge arm of each phase is connected to form a direct current negative electrode; the first bridge arm and the second bridge arm are formed by connecting a reactor and at least two second submodules in series.
Fig. 4 is a fourth embodiment of the present invention, which includes a first sub-module, a second sub-module, and a reactor, where the multi-level converter includes three phases, each phase includes two bridge arms, the first and second bridge arms are respectively defined as an upper and a lower bridge arms, and a middle connection point of the upper and lower bridge arms is used as a phase of an ac side output; the positive end of the first bridge arm of each phase is connected to form a direct current positive electrode, and the negative end of the second bridge arm of each phase is connected to form a direct current negative electrode; the first bridge arm and the second bridge arm are formed by connecting a reactor, at least one first submodule and at least one second submodule in series.
The first sub-module is a half-bridge module formed by at least two power semiconductor switching devices and a capacitor, and as shown in fig. 5, the power semiconductor switching devices are IGBTs with anti-parallel diodes.
The second submodule is a full-bridge module formed by at least four power semiconductor switching devices and a capacitor. As shown in fig. 6, the power semiconductor switching device is an IGBT with an anti-parallel diode.
The alternating current-direct current converter can also be a two-level voltage source converter.
The alternating current-direct current converter can also be a three-level voltage source converter.
Wherein the bypass switch may be a mechanical switch.
Wherein the bypass switch may be a semiconductor switch.
The embodiment also comprises a control method of the ice melting device, which comprises the following steps:
(1) when the ice melting device is started, the control method comprises the following steps:
step 1: connecting a direct current output port of the ice melting device with an ice melting line;
step 2: by-pass switch for separating all current-limiting units
And step 3: starting an alternating current power supply of the ice melting device, and gradually increasing the direct current voltage of the alternating current-direct current converter;
and 4, step 4: after the direct-current voltage of the alternating-current/direct-current converter is stabilized, a bypass switch of one current-limiting unit is closed, and the direct current output by the ice melting device is increased;
and 5: after the direct current output by the alternating current-direct current converter is stable, closing a bypass switch of a current limiting unit to further increase the direct current output by the ice melting device;
step 6: repeating the step 4, and closing the bypass switches of all the current limiting units;
and 7: and a power semiconductor switching device in the AC-DC converter starts to work, and the output current of the AC-DC converter is regulated to be stabilized at the current value required by ice melting.
(2) When the ice melting device is started and enters an operating state, the ice melting line has a short-circuit fault, and the control method comprises the following steps:
step 1: when a sudden increase in output current is detected;
step 2: a bypass switch for disconnecting one of the current limiting units;
and step 3: when the output current is detected to be still higher than the maximum current value allowed by the AC-DC converter;
and 4, step 4: then a bypass switch of a current limiting unit is switched off;
and 5: repeating the step 4 until the direct current output current of the ice melting device is reduced to an allowable range;
step 6: if the line fault is an instantaneous fault, detecting that the fault is cleared, closing the bypass switches one by one until the normal running current is recovered;
and 7: if the line fault is a permanent fault, the alternating current power supply of the ice melting device is separated, all the bypass switches are separated, and the ice melting device is stopped.
(3) When the ice melting device finishes starting and enters an operating state, and the output of the device is over-current due to small equivalent resistance of an ice melting line, the control method comprises the following steps:
step 1: when an output overcurrent is detected;
step 2: adjusting the duty ratio of power semiconductor devices in a first bridge arm and a second bridge arm of the AC-DC converter to reduce the DC voltage of the AC-DC converter, thereby reducing the output current;
and step 3: if the output direct current of the ice melting device is still detected to exceed the allowable value, the duty ratio of a power semiconductor device in a third bridge arm of the alternating current-direct current converter is adjusted, so that the direct current voltage of the alternating current-direct current converter is further reduced, and the output current is further reduced;
and 4, step 4: if the direct current output by the ice melting device is still detected to exceed the allowable value, a bypass switch of one current limiting unit is disconnected;
and 5: and if the direct current output by the ice melting device is still detected to exceed the allowable value, a bypass switch of a current limiting unit is turned off, and the step 4 is repeated until the direct current output by the device is reduced to the allowable range.
The scheme and method of the present invention are further illustrated with the topology of fig. 1 as an example.
The system parameters are as follows: the voltage of an alternating current side input by the device is 35kV, and the required line ice melting current is 3 kA.
The device parameters were as follows: the alternating current bridge arm of the device is composed of half-bridge modules, the upper bridge arm and the lower bridge arm are composed of full-bridge modules, wherein the alternating current bridge arm is composed of 10 modules, one alternating current bridge arm can output equivalent alternating current lateral line voltage of 10kV, 4 current limiting units are arranged in the device, the resistance value of a current limiting resistor 1 in each current limiting unit 1 is 5 omega, the resistance value of a current limiting resistor 2 in each current limiting unit 2 is 100 omega, the resistance value of a current limiting resistor 3 in each current limiting unit 3 is 1900 omega, and the resistance value of a current limiting resistor 4 in each current limiting unit 4 is 8000 omega.
The equivalent resistance 6 of the ice-melting line is variable according to the length of the line, the line can be selected through a switch in the ice-melting process, and the impedance of the ice-melting line is initially set to be 20 omega.
At device startup:
after an alternating current power supply of the device is started, alternating current voltage charges a direct current side through a diode rectifier bridge of the IGBT; in this embodiment it may be raised to about 49 kV. Since the current limiting resistors are all put into use at this time, the total resistance value is about 10k omega. The device output current at this time was 4.9A. The limited limit limits the inrush current at device start-up.
Gradually closing the bypass switch, and closing the bypass switches in the current limiting unit 4, the current limiting unit 3, the current limiting unit 2 and the current limiting unit 1 in sequence, wherein the ice melting current gradually rises to 25A, 392A, 1960A and 2450A; after the starting is finished, the IGBT in the alternating current-direct current converter of the device is unlocked, the direct current voltage is gradually increased, and the ice melting current is stabilized at 3 kA. The output dc voltage of the device at this time was 60 kV.
When the ice melting line has a fault, the direct current rapidly rises, the bypass switch of the current limiting unit 2 can be disconnected at the moment, the current limiting resistor is connected in series into a loop, the direct current is limited to 600A, if the fault is an instantaneous fault, the bypass switch of the current limiting unit 2 is closed after the fault is eliminated, and if the fault is a permanent fault, the alternating current switch is separated, and all the bypass switches are separated.
When the ice melting line impedance becomes 10 omega, the ice melting line current becomes 6kA, the IGBTs of the upper bridge arm and the lower bridge arm can be locked, the direct current voltage is reduced to 49kV, the alternating current bridge arm outputs a reverse alternating current voltage, after a part of the alternating current voltage is counteracted, the alternating current voltage input into the three-phase bridge circuit is reduced to 25kV, the direct current voltage is reduced to 35kV, the direct current voltage is reduced to 3.5kA and still higher than 3kA, the bypass switch in the current limiting unit 1 is separated at the moment, the direct current voltage is reduced to 2.33kA, the IGBTs of the upper bridge arm and the lower bridge arm are unlocked again, the direct current voltage is increased, and finally the ice melting current is stabilized at 3 kA.
It can be seen from this embodiment that the present invention can be safely operated under different operating conditions.
When the device starts, because the equivalent resistance of the ice melting circuit is unknown, the device is prevented from being damaged due to overcurrent impact in the starting process by the starting mode with the current-limiting current unit, the zero-current starting effect of the current type ice melting device is achieved by gradually withdrawing from the current-limiting unit, the risk in the starting process is reduced to the maximum extent, and the method is low in cost, simple and practical.
When short-circuit fault occurs in the ice melting line, the short-circuit current can be limited through the rapid input of the current limiting unit, if instantaneous fault occurs, the current limiting unit can be bypassed, fault ride-through is realized, the device is prevented from being stopped, and the continuous operation capacity of the system is improved
When the resistance of the ice melting line is small, the full-bridge module on the alternating current side realizes negative voltage output by controlling the duty ratio, the effect of reducing the direct current voltage output by the ice melting device can be achieved, the ice melting current is reduced, the ice melting current can be effectively limited by matching with the input and exit control of the current limiting unit, the operation range of the ice melting device is greatly increased, and the adaptability of the device to different resistances of the ice melting line is improved.
The invention also provides a control device of the voltage source type ice melting device, and the first embodiment of the control device comprises the following steps:
the control device includes: connecting element, bypass switch breaking unit, alternating current power supply start unit, current-limiting bypass switch closing unit, output current regulating unit, wherein:
the connecting unit is used for connecting the direct current output port of the ice melting device with the ice melting line; then enabling a bypass switch breaking unit;
the bypass switch breaking unit is used for separating the bypass switches in all the current limiting units; then enabling the alternating current power supply starting unit;
the alternating current power supply starting unit is used for starting an alternating current power supply of the ice melting device, and the direct current voltage of the alternating current-direct current converter is gradually increased; then enabling the current-limiting bypass switch closing unit;
the current-limiting bypass switch closing unit is used for closing a bypass switch of one current-limiting unit after the direct-current voltage of the alternating-current/direct-current converter is stabilized, so that the direct-current output by the ice melting device is increased; after the direct current output by the alternating current-direct current converter is stable, closing a bypass switch of a current limiting unit to further increase the direct current output by the ice melting device; until all the bypass switches of the current limiting units are closed; then enabling the output current regulating unit;
and the output current regulating unit is used for controlling a power semiconductor switching device in the AC-DC converter to start working and regulating the output current of the AC-DC converter to be stabilized at a current value required by ice melting.
The invention also provides a control device of the voltage source type ice melting device, and the second embodiment comprises the following steps:
the control device is used for processing the short-circuit fault of the ice melting line after the ice melting device is started to enter the running state, and comprises: current surge detecting element, bypass switch disconnection unit, output current overcurrent detecting element, fault handling unit, wherein:
the current surge detection unit: for detecting whether the output current suddenly increases; when the sudden increase of the output current is detected, starting a bypass switch disconnection unit;
the bypass switch disconnecting unit is used for disconnecting a bypass switch of one current limiting unit; and starting an output current overcurrent detection unit;
the output current overcurrent detection unit is used for detecting whether the output current is higher than the maximum current value allowed by the AC-DC converter or not; if yes, starting a bypass switch disconnection unit, otherwise, starting a fault processing unit;
the fault processing unit is used for detecting whether the fault is cleared or not, and if so, closing the bypass switches one by one until the normal operation current is recovered; otherwise, the alternating current power supply of the ice melting device is separated, all the bypass switches are separated, and the ice melting device is stopped.
The invention also provides a control device of the voltage source type ice melting device when the alternating current-direct current converter is a multi-level voltage source converter, and the third embodiment comprises the following steps:
the control device is used for limiting the output overcurrent of the ice melting device caused by small equivalent resistance of an ice melting line after the ice melting device is started to enter the running state, and comprises:
the output overcurrent detection unit is used for detecting whether the output direct current of the ice melting device is greater than a set threshold value; if yes, starting a first duty ratio adjusting unit; if the output is still larger than the set threshold value, starting a second duty ratio adjusting unit; if the output is still larger than the set threshold value, starting a current-limiting bypass switch disconnection unit;
the duty ratio adjusting unit I is used for adjusting the duty ratios of power semiconductor devices in a first bridge arm and a second bridge arm of the AC-DC converter to reduce the DC voltage of the AC-DC converter, so that the output current is reduced;
the duty ratio adjusting unit II is used for adjusting the duty ratio of a power semiconductor device in a third bridge arm of the AC-DC converter to further reduce the direct-current voltage of the AC-DC converter, so that the output current is further reduced;
the current-limiting bypass switch disconnecting unit is used for sequentially disconnecting the bypass switches of the current-limiting unit; until the DC output current of the ice melting device is reduced to an allowable range.
The above embodiments are only for illustrating the technical solution of the present invention and not for limiting the same, and various modifications or changes made with reference to the above embodiments are within the scope of the present invention.
Claims (14)
1. A voltage source type ice melting device comprises an AC-DC converter, wherein the AC side of the AC-DC converter is connected with an AC power supply, and the device is characterized by further comprising at least two current limiting units, each current limiting unit is formed by connecting a current limiting resistor and a bypass switch in parallel, the current limiting units are connected in series, one end of the series connection is connected with the DC positive electrode or the DC negative electrode of the AC-DC converter, and the other end of the series connection is used as a DC output port of the device;
the alternating current-direct current converter is a multilevel voltage source converter and comprises a first submodule, a second submodule and a reactor, wherein the first submodule, the second submodule and the reactor comprise power semiconductor devices, the multilevel voltage source converter comprises three phases, each phase comprises three bridge arms, the first bridge arm and the second bridge arm are respectively defined as an upper bridge arm and a lower bridge arm, and a middle connecting point of the upper bridge arm and the lower bridge arm is connected with the third bridge arm to form an alternating current output phase; the positive end of the first bridge arm of each phase is connected to form a direct current positive electrode, and the negative end of the second bridge arm of each phase is connected to form a direct current negative electrode; the first bridge arm and the second bridge arm are formed by connecting a reactor and at least two first sub-modules in series; the third bridge arm is formed by connecting at least one second submodule in series;
the sub-module is a half-bridge module formed by at least two power semiconductor switching devices and capacitors, or a full-bridge module formed by at least four power semiconductor switching devices and capacitors.
2. A voltage source ice melting apparatus as claimed in claim 1, wherein: the device also comprises a starting switch which is connected between the current limiting unit and the direct current output port of the device in series.
3. A voltage source ice melting apparatus as claimed in claim 1, wherein: the first submodule is a half-bridge module formed by at least two power semiconductor switching devices and a capacitor.
4. A voltage source ice melting apparatus as claimed in claim 1, wherein: the second submodule is a full-bridge module formed by at least four power semiconductor switching devices and a capacitor.
5. A voltage source ice melting apparatus as claimed in claim 1, wherein: the AC-DC converter is a two-level voltage source converter.
6. A voltage source ice melting apparatus as claimed in claim 1, wherein: the alternating current-direct current converter is a three-level voltage source converter.
7. A voltage source ice melting apparatus as claimed in claim 1, wherein: the bypass switch is a mechanical switch.
8. A voltage source ice melting apparatus as claimed in claim 1, wherein: the bypass switch is a semiconductor switch.
9. A control method of the voltage source type ice melting device based on any one of claims 1 to 8, characterized in that: when the ice melting device is started, the control method comprises the following steps:
step 1: connecting a direct current output port of the ice melting device with an ice melting line;
step 2: by-pass switch for separating all current-limiting units
And step 3: starting an alternating current power supply of the ice melting device, and gradually increasing the direct current voltage of the alternating current-direct current converter;
and 4, step 4: after the direct-current voltage of the alternating-current/direct-current converter is stabilized, a bypass switch of one current-limiting unit is closed, and the direct current output by the ice melting device is increased;
and 5: after the direct current output by the alternating current-direct current converter is stable, closing a bypass switch of a current limiting unit to further increase the direct current output by the ice melting device;
step 6: repeating the step 4, and closing the bypass switches of all the current limiting units;
and 7: and a power semiconductor switching device in the AC-DC converter starts to work, and the output current of the AC-DC converter is regulated to be stabilized at the current value required by ice melting.
10. A control method of the voltage source type ice melting device based on any one of claims 1 to 8, characterized in that: when the ice melting device is started and enters an operating state, the ice melting line has a short-circuit fault, and the control method comprises the following steps:
step 1: when a sudden increase in output current is detected;
step 2: a bypass switch for disconnecting one of the current limiting units;
and step 3: when the output current is detected to be still higher than the maximum current value allowed by the AC-DC converter;
and 4, step 4: then a bypass switch of a current limiting unit is switched off;
and 5: repeating the step 4 until the direct current output current of the ice melting device is reduced to an allowable range;
step 6: if the line fault is an instantaneous fault, detecting that the fault is cleared, closing the bypass switches one by one until the normal running current is recovered;
and 7: if the line fault is a permanent fault, the alternating current power supply of the ice melting device is separated, all the bypass switches are separated, and the ice melting device is stopped.
11. A control method of the voltage source type ice melting device based on claim 1, characterized in that: when the ice melting device finishes starting and enters an operating state, and the output of the device is over-current due to small equivalent resistance of an ice melting line, the control method comprises the following steps:
step 1: when an output overcurrent is detected;
step 2: adjusting the duty ratio of power semiconductor devices in a first bridge arm and a second bridge arm of the AC-DC converter to reduce the DC voltage of the AC-DC converter, thereby reducing the output current;
and step 3: if the output direct current of the ice melting device is still detected to exceed the allowable value, the duty ratio of a power semiconductor device in a third bridge arm of the alternating current-direct current converter is adjusted, so that the direct current voltage of the alternating current-direct current converter is further reduced, and the output current is further reduced;
and 4, step 4: if the direct current output by the ice melting device is still detected to exceed the allowable value, a bypass switch of one current limiting unit is disconnected;
and 5: and if the direct current output by the ice melting device is still detected to exceed the allowable value, a bypass switch of a current limiting unit is turned off, and the step 4 is repeated until the direct current output by the device is reduced to the allowable range.
12. The control device for a voltage source type ice-melting device according to any one of claims 1 to 8, characterized in that: the control device includes: connecting element, bypass switch breaking unit, alternating current power supply start unit, current-limiting bypass switch closing unit, output current regulating unit, wherein:
the connecting unit is used for connecting the direct current output port of the ice melting device with the ice melting line; then enabling a bypass switch breaking unit;
the bypass switch breaking unit is used for separating the bypass switches in all the current limiting units; then enabling the alternating current power supply starting unit;
the alternating current power supply starting unit is used for starting an alternating current power supply of the ice melting device, and the direct current voltage of the alternating current-direct current converter is gradually increased; then enabling the current-limiting bypass switch closing unit;
the current-limiting bypass switch closing unit is used for closing a bypass switch of one current-limiting unit after the direct-current voltage of the alternating-current/direct-current converter is stabilized, so that the direct-current output by the ice melting device is increased; after the direct current output by the alternating current-direct current converter is stable, closing a bypass switch of a current limiting unit to further increase the direct current output by the ice melting device; until all the bypass switches of the current limiting units are closed; then enabling the output current regulating unit;
and the output current regulating unit is used for controlling a power semiconductor switching device in the AC-DC converter to start working and regulating the output current of the AC-DC converter to be stabilized at a current value required by ice melting.
13. The control device for a voltage source type ice-melting device according to any one of claims 1 to 8, characterized in that: the control device is used for processing the short-circuit fault of the ice melting line after the ice melting device is started to enter the running state, and comprises: current surge detecting element, bypass switch disconnection unit, output current overcurrent detecting element, fault handling unit, wherein:
the current surge detection unit: for detecting whether the output current suddenly increases; when the sudden increase of the output current is detected, starting a bypass switch disconnection unit;
the bypass switch disconnecting unit is used for disconnecting a bypass switch of one current limiting unit; and starting an output current overcurrent detection unit;
the output current overcurrent detection unit is used for detecting whether the output current is higher than the maximum current value allowed by the AC-DC converter or not; if yes, starting a bypass switch disconnection unit, otherwise, starting a fault processing unit;
the fault processing unit is used for detecting whether the fault is cleared or not, and if so, closing the bypass switches one by one until the normal operation current is recovered; otherwise, the alternating current power supply of the ice melting device is separated, all the bypass switches are separated, and the ice melting device is stopped.
14. The control device for a voltage source type ice-melting device according to claim 1, characterized in that: the control device is used for limiting the output overcurrent of the ice melting device caused by small equivalent resistance of an ice melting line after the ice melting device is started to enter the running state, and comprises:
the output overcurrent detection unit is used for detecting whether the output direct current of the ice melting device is greater than a set threshold value; if yes, starting a first duty ratio adjusting unit; if the output is still larger than the set threshold value, starting a second duty ratio adjusting unit; if the output is still larger than the set threshold value, starting a current-limiting bypass switch disconnection unit;
the duty ratio adjusting unit I is used for adjusting the duty ratios of power semiconductor devices in a first bridge arm and a second bridge arm of the AC-DC converter to reduce the DC voltage of the AC-DC converter, so that the output current is reduced;
the duty ratio adjusting unit II is used for adjusting the duty ratio of a power semiconductor device in a third bridge arm of the AC-DC converter to further reduce the direct-current voltage of the AC-DC converter, so that the output current is further reduced;
the current-limiting bypass switch disconnecting unit is used for sequentially disconnecting the bypass switches of the current-limiting unit; until the DC output current of the ice melting device is reduced to an allowable range.
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