CN106918759B - MMC direct current short-circuit fault detection method and device - Google Patents
MMC direct current short-circuit fault detection method and device Download PDFInfo
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Abstract
The invention relates to a method and a device for detecting a direct-current short-circuit fault of an MMC (modular multilevel converter). The method comprises the steps of dividing converter stations into a master station mode and a slave station mode, selecting one converter station as a master station, taking other converter stations as slave stations, gradually raising direct-current voltage by the master station, tracking and recovering the direct-current voltage of the master station by the slave stations through the difference between a direct-current feedback value and a direct-current reference value, and judging that the direct-current short-circuit fault still exists when the time that the direct-current voltage raised by the master station is continuously less than a first set value is T1. According to the invention, inter-station communication is not required in the whole fault detection process, other detection equipment is not required, the detection of the short-circuit fault can be realized only by means of the original direct-current voltage and current sensors, the reliable guarantee is provided for the direct-current voltage improvement after the direct-current short-circuit fault is not completely cleared, and the problems of secondary short circuit, quick discharge of the sub-module, bypass and converter locking tripping are not caused.
Description
Technical Field
The invention belongs to the technical field of direct current transmission, and particularly relates to a method and a device for detecting a direct current short-circuit fault of an MMC (modular multilevel converter).
Background
At present, with the development of fully-controlled power electronic devices and the application of power electronic technology in power systems, the flexible direct-current power transmission technology based on a voltage source converter is increasingly emphasized. The Modular Multilevel Converter (MMC) is one of voltage source converters applied to flexible direct current transmission systems, is formed by connecting a plurality of sub-modules according to a certain mode, and enables alternating current voltage output by the converter to approach sine waves by controlling the input and cut-off states of IGBT groups of the sub-modules, so that efficient transmission of energy is realized.
In a conventional modular multilevel converter, a half-bridge sub-module is generally used as a basic unit to reduce the construction cost of the converter. The traditional half-bridge submodule MMC can not rapidly restrain fault current through self characteristics when a direct current short circuit fault occurs, and the fault current can be cleared only by depending on an alternating current breaker or a direct current breaker. The disadvantages of this method are: because the response time of the alternating current circuit breaker is long, overcurrent damage of the current converter can be caused when the protection is not in time; in addition, the configuration of the dc circuit breaker increases the technical requirements for the equipment and increases the system cost.
In order to solve the above problems, some researchers propose to solve the problem of overcurrent damage of the current converter by adopting a full-bridge submodule or a clamping double-submodule MMC: after short-circuit fault, the converter is locked rapidly, and fault current is restrained rapidly by utilizing the reverse blocking capability of the diodes in the full-bridge submodule, so that the direct-current fault is cleared. However, after the converter is locked, the voltage of the sub-module is gradually reduced along with the loss of the converter, and finally the sub-module is bypassed due to insufficient voltage, so that the converter trips, the flexible direct current transmission system cannot be quickly recovered from the fault, and the recovery time of the flexible direct current transmission system from the fault is prolonged. Therefore, another scholars proposes to add a sufficient number of full-bridge submodules into a conventional half-bridge submodule MMC, as shown in fig. 1, to reduce the dc voltage to zero while maintaining the ac side grid connection by using the capability of the full-bridge submodule to output a negative level, thereby rapidly suppressing the fault current and realizing the dc fault ride-through without locking.
However, before the dc voltage is reestablished after the fault, the method needs to detect whether the dc short-circuit fault is completely cleared or not, otherwise, the dc voltage is raised when the dc short-circuit fault is not completely cleared, which inevitably causes a secondary short-circuit fault, causing the sub-module to quickly discharge and be tripped by the bypass and the converter lock, and therefore, the voltage can be boosted only when the dc short-circuit fault is confirmed to be cleared.
Therefore, it is very necessary to provide a safe and efficient dc short-circuit fault state detection method, which can effectively solve the contradiction between zero dc voltage control and dc voltage boosting, and accurately determine whether the dc short-circuit fault has been cleared on the premise that the dc side has no overvoltage and overcurrent, and the ac side maintains grid connection and reactive compensation, so as to prepare for dc voltage recovery.
Disclosure of Invention
The invention aims to provide an MMC direct-current short-circuit fault detection method and device, which are used for solving the problem of secondary short-circuit fault caused by the fact that direct-current voltage is increased when a direct-current short-circuit fault is not completely cleared.
In order to solve the technical problem, the invention provides an MMC direct current short-circuit fault detection method, which comprises the following method schemes:
The first method scheme comprises the following steps:
selecting one converter station as a master station and other converter stations as slave stations; the master station boosts the direct-current voltage from zero, detects the direct-current voltage in real time in the boosting process, and synchronously tracks the direct-current voltage of the master station according to the difference between a direct-current feedback value and a direct-current reference value; when the time that the direct-current voltage continues to be less than the first set value is T1, it is determined that the direct-current short-circuit fault still exists.
And in a second method scheme, on the basis of the first method scheme, when the direct-current short-circuit fault still exists, the main station is controlled to be in a zero direct-current voltage control state.
and a third method scheme, on the basis of the first method scheme, when the time that the direct-current voltage is continuously greater than or equal to the first set value is T2, the direct-current short-circuit fault is judged to be cleared, and the main station continues to boost the direct-current voltage until the direct-current voltage is boosted to the rated value of the direct-current voltage.
In a fourth method scheme, on the basis of the first method scheme, the main station raises the direct-current voltage from zero according to a set first direct-current bias, and when the time when the direct-current voltage is smaller than a first set value is T1, it is determined that the direct-current short-circuit fault still exists; and the first direct current bias is used for generating the bridge arm voltage of the main station by combining the three-phase modulation wave.
In the fifth method scheme, on the basis of the first method scheme, the slave station generates a second direct current bias of the bridge arm modulation instruction through a proportional controller or a proportional-integral controller after the direct current feedback value is subtracted from the direct current reference value; and the second direct current bias is used for generating a bridge arm voltage of the slave station converter by combining the three-phase modulation wave.
And in the sixth and seventh method schemes, on the basis of the fourth and fifth method schemes respectively, the bridge arm voltage calculation formula is as follows:
In the formula, when v arm is the bridge arm voltage of the master station converter, U dc_rated is the rated value of the direct-current voltage, k is the per unit value of the first direct-current bias, and e abc is the three-phase modulation wave, and when v arm is the bridge arm voltage of the slave station converter, U dc_rated is the rated value of the direct-current voltage, k is the per unit value of the second direct-current bias, and e abc is the three-phase modulation wave.
method solutions eight and nine are respectively based on the method solutions six and seven, when k is the first direct current offset, k is obtained by adding a command value k ref and a command value k err, k ref is a command value gradually increasing from 0 to 1 according to a specified slope, and k err is a command value limiting direct current.
and a tenth method scheme and an eleventh method scheme, respectively based on the eighth method scheme and the ninth method scheme, wherein when the direct current is greater than a set upper limit or less than a set lower limit in the direct current voltage of the master station in the boosting process, the first direct current bias is corrected, and the direct current is controlled between the upper limit and the lower limit.
In order to solve the above technical problem, the present invention further provides an MMC direct current short circuit fault detection apparatus, including the following apparatus schemes:
The device scheme one comprises the following units:
A selection unit: the system comprises a master station, a slave station, a converter station, a plurality of slave stations and a plurality of communication terminals, wherein the master station is used for selecting one converter station and the other converter stations are used as the slave stations;
A judging unit: the slave station is used for synchronously tracking the direct-current voltage of the master station according to the difference between a direct-current feedback value and a direct-current reference value; when the time that the direct-current voltage continues to be less than the first set value is T1, it is determined that the direct-current short-circuit fault still exists.
And the device scheme II further comprises a unit for controlling the main station to be in a zero direct current voltage control state when the direct current short circuit fault still exists on the basis of the device scheme I.
The third device scheme is based on the first device scheme, and further comprises a unit for judging that the direct current short-circuit fault is cleared when the direct current voltage is continuously greater than or equal to the first set value for T2, and the main station continues to boost the direct current voltage until the direct current voltage is boosted to the rated value of the direct current voltage.
A fourth device scheme, based on the first device scheme, the method further includes that the main station raises the dc voltage from zero according to a set first dc bias, and when the duration of the dc voltage being less than a first set value is T1, it is determined that the dc short-circuit fault still exists; and the first direct current bias is used for generating a unit of bridge arm voltage of the main station by combining the three-phase modulation wave.
in the fifth device scheme, on the basis of the first device scheme, the slave station generates a second direct current bias of the bridge arm modulation instruction through a proportional controller or a proportional-integral controller after the direct current feedback value and the direct current reference value are subjected to difference; and the second direct current bias is used for generating a unit of bridge arm voltage of the slave station converter by combining the three-phase modulation wave.
and on the basis of the fourth and fifth device schemes respectively, the bridge arm voltage calculation formula is as follows:
In the formula, when v arm is the bridge arm voltage of the master station converter, U dc_rated is the rated value of the direct-current voltage, k is the per unit value of the first direct-current bias, and e abc is the three-phase modulation wave, and when v arm is the bridge arm voltage of the slave station converter, U dc_rated is the rated value of the direct-current voltage, k is the per unit value of the second direct-current bias, and e abc is the three-phase modulation wave.
the eighth and ninth device configurations further include, on the basis of the sixth and seventh device configurations, respectively, a unit configured to add the command value k ref to the command value k err when k is the first dc offset, k ref is a command value gradually increasing from 0 to 1 with a predetermined slope, and k err is a command value for limiting the dc current.
The tenth and eleventh device schemes further include a dc current control unit on the basis of the eighth and ninth device schemes, respectively: and when the direct current is greater than a set upper limit or less than a set lower limit in the direct current voltage of the main station in the boosting process, correcting the first direct current bias and controlling the direct current between the upper limit and the lower limit.
The invention has the beneficial effects that: the converter station is divided into a master station mode and a slave station mode, one converter station is selected as a master station, other converter stations are selected as slave stations, the master station gradually raises direct current voltage, the slave stations track and recover the direct current voltage of the master station through the difference between a direct current feedback value and a direct current reference value, and when the time that the direct current voltage raised by the master station is continuously smaller than a first set value is T1, the direct current short-circuit fault still exists. According to the invention, inter-station communication is not required in the whole fault detection process, other detection equipment is not required, the detection of the short-circuit fault can be realized only by means of the original direct-current voltage and current sensors, the reliable guarantee is provided for the direct-current voltage improvement after the direct-current short-circuit fault is not completely cleared, and the problems of secondary short circuit, quick discharge of the sub-module, bypass and converter locking tripping are not caused.
Drawings
FIG. 1 is a schematic topology diagram of a half-bridge and full-bridge sub-module hybrid MMC;
FIG. 2 is a flow chart of sub-module hybrid MMC direct current short circuit fault detection of the present invention;
FIG. 3 is a master station inverter control block diagram;
fig. 4 is a slave inverter control block diagram;
FIG. 5 is a control schematic of the DC current limit controller;
FIG. 6 is a waveform of the electrical quantities of the primary station under a condition where the DC fault has been cleared;
FIG. 7 is a waveform of the electrical quantities from the station under the condition that the DC fault is cleared;
FIG. 8 is a waveform diagram of the electrical quantities of the primary station under a DC fault uncleared condition;
FIG. 9 is a waveform of the electrical quantities from the station under an uncleared DC fault condition.
Detailed Description
the following further describes embodiments of the present invention with reference to the drawings.
The embodiment of the invention relates to an MMC direct current short-circuit fault detection method, which comprises the following steps:
According to the double-end or multi-end flexible direct current transmission system formed by the half-bridge and full-bridge sub-module hybrid modular multilevel converter shown in the figure 1, the number of full-bridge and half-bridge sub-modules in the system is N, M respectively, wherein N is more than or equal to 2, M is more than or equal to 2, in the figure 1, U sm is sub-module voltage, U dc is direct current voltage, HBSM (half-bridge sub-module) is a half-bridge sub-module, FBSM (full-bridge sub-module) is a full-bridge sub-module, when a direct current double-pole short-circuit fault is detected, the full-bridge sub-module can output negative voltage, the direct current voltage U dc of the system can be more flexibly controlled on the premise that the amplitude of the alternating current voltage is kept unchanged by utilizing the characteristic, the direct current fault current passing is carried out by the converter in a mode of not locking the converter, the fault current is limited to 0, and the voltage U sm of the sub-bridge sub-module is always kept at.
After the direct current is limited to 0, the short-circuit fault is cleared, the direct-current voltage of the direct-current power transmission system starts a recovery process, and before the direct-current voltage starts to recover, the direct-current short-circuit fault state detection needs to be performed according to the following steps:
As shown in fig. 2, the grid-connected state of the converter is maintained, one of the converter stations is selected as a master station, the fixed dc voltage station in normal operation is used as the master station, and the rest are used as slave stations; for a main station, while controlling the voltage of a sub-module of the main station, gradually increasing a first direct current bias according to a set slope, and gradually increasing the direct current voltage from zero; the slave station controls the voltage of a submodule of the slave station, and generates a second direct current bias of a bridge arm modulation instruction through a proportional controller or a proportional-integral controller according to the difference between a direct current feedback value and a direct current reference value so as to enable the slave station to track the direct current voltage of the master station; the first direct current bias and the second direct current bias are respectively bridge arm voltages used for generating a master station and a slave station by combining three-phase modulation waves, and the calculation formula of the bridge arm voltages is as follows:
In the formula, when v arm is the bridge arm voltage of the master station converter, U dc_rated is the rated value of the direct-current voltage, k is the per unit value of the first direct-current bias, and e abc is the three-phase modulation wave, and when v arm is the bridge arm voltage of the slave station converter, U dc_rated is the rated value of the direct-current voltage, k is the per unit value of the second direct-current bias, and e abc is the three-phase modulation wave.
When the fault is judged, when the duration time that the actual direct-current voltage detected by the main station is less than 90% of the first direct-current bias set value is longer than the set time T1, the direct-current short-circuit fault still exists, namely the direct-current short-circuit fault is not cleared up yet, the control mode of the main station is changed, the main station is controlled to be in zero direct-current voltage control, and the direct-current voltage is not increased any more; the set time T1 is related to the rising slope of the first dc offset and the control parameter; and when the actual direct-current voltage detected by the master station is always greater than 90% of the first direct-current offset set value, or the duration time less than 90% of the first direct-current offset set value is less than the set time T2, judging that the direct-current short-circuit fault is cleared, continuing to improve the first direct-current offset of the master station, and continuing to track the direct-current voltage of the master station by the slave station according to the second direct-current offset. And after the direct-current voltage reaches the rated value and is stabilized, each converter station is switched back to the original normal running state, and the master station and the slave station are both restored to the working modes before the fault.
the master station and the slave station are controlled by the current converter controller as follows:
The method comprises the following steps that a controller inner ring still adopts a current PI controller under a traditional dq rotation coordinate system, a d-axis current instruction value is generated by a submodule voltage control outer ring and is obtained by comparing a submodule voltage average value with an instruction value and sending the submodule voltage average value into the PI controller, a q-axis current instruction value is generated by a reactive power control outer ring and is obtained by comparing a reactive power feedback value with the instruction value and sending the reactive power feedback value into the PI controller, a three-phase modulation wave e abc obtained by controlling the inner ring needs to be processed according to the following formula to obtain output voltages of 6 bridge arms:
In the formula, v arm is output voltage of each bridge arm, U dc_rated is rated value of direct current voltage, e abc is three-phase modulation wave, k is per unit value of first direct current bias or second direct current bias, k is 1 in normal operation, a calculation method of the k value is different according to whether a converter station is a main station or a slave station when a system detects whether a direct current short-circuit fault is cleared, for the main station, k is controlled to gradually rise from 0 to the rated value according to a set slope, for the slave station, k is obtained through direct current negative feedback through a proportional controller or a proportional integral controller, values of positive and negative signs in the formula are related to positions of each bridge arm, for example, in fig. 1, when the output voltage of a calculated bridge arm is calculated, the upper formula takes a negative sign, and when the output voltage of a lower bridge arm is calculated, the upper formula takes a positive sign.
in order to avoid that the direct current is overlarge due to the fact that the first direct current bias of the main station is lifted under the condition that the direct current short-circuit fault is not cleared, and the impact current is generated, the command value of the per unit value of the first direct current bias of the main station is divided into two parts, one part is the command value which gradually rises from 0 to a rated value according to a set slope, the other part is the command value output by the direct current limiting controller, and the calculation formula is as follows:
k1＝kref+kerr
in the formula, k 1 is a first dc offset after the master station has applied current limit control, k ref is a command value gradually increasing from 0 to a rated value according to a set slope, and k err is a command value output by the dc current limit controller.
The control principle of the direct current limiting controller is shown in fig. 5, the controller is divided into an upper limit controller and a lower limit controller, the upper limit controller compares the upper limit value of the direct current with a direct current sampling value and sends the direct current sampling value to a PI controller, an integrator in the PI controller works only when the output is less than 0 and greater than-1, the lower limit controller compares the lower limit value of the direct current with the direct current sampling value and sends the direct current sampling value to the PI controller, the integrator in the PI controller works only when the output is greater than 0 and less than 1, and the final output k err is obtained by adding the output values of the two PI controllers.
The DC current limit controller is characterized in that the output is 0 when the DC current does not reach the set upper limit and lower limit, the normal control is not influenced, the controller starts to work when the DC current crosses the upper limit and the lower limit, the first DC bias in the controller is corrected, and the DC current is limited in an allowable range. Therefore, secondary fault current caused by the fact that the direct current voltage is increased when the direct current short-circuit fault is not cleared is avoided, and the direct current voltage of the main converter station is increased too fast after the direct current short-circuit fault is cleared, and the other converter stations cannot track the direct current voltage in time to cause impact current.
During the detection period of the direct-current short-circuit fault, a control block diagram of the converter station as a main station is shown in fig. 3, and on the basis of a traditional current inner ring, a sub-module voltage controller is adopted as an active current outer ring and used for stabilizing the sub-module voltage of the converter; meanwhile, a reactive power controller is used as a reactive current outer ring, so that the converter can provide reactive power support for a connected power grid in the whole fault recovery process.
As shown in fig. 4, a control block diagram of a converter station as a slave station is that, like a master station, on the basis of a conventional current inner loop, a sub-module voltage controller is used as an active current outer loop for stabilizing the sub-module voltage of the converter; and a reactive power controller is adopted as a reactive current outer ring, so that the converter can provide reactive power support for a power grid.
when the slave station calculates the output voltage of each bridge arm, the direct current bias per unit value is determined as shown in fig. 4, and is calculated through a proportional controller or a proportional-integral controller after being compared with a direct current reference value through direct current feedback, wherein the direct current reference value can be set to be 0 usually, and the positive direction of the current is selected to be the direction of flowing into the converter. At this time, when the dc voltage output by the master station rises, the dc current sampled from the slave station side increases, and after being compared with a reference value and amplified by a proportional-integral controller (or a proportional controller), the dc bias of the slave station rises, and the dc voltage of the slave station side rises accordingly, so that the function of following the dc voltage of the master station is achieved.
taking a double-end flexible direct-current power transmission system as an example, MATLAB/SIMULINK simulation is adopted to verify the MMC direct-current short-circuit fault detection method.
Simulating the working condition that the direct current short-circuit fault is cleared, wherein the waveform of the main station is as shown in fig. 6, when the time is 0.1s, selecting a main converter station and a slave converter station, adding a direct current limiting controller, starting to lift a first direct current bias according to a set slope, and keeping the direct current voltage and the first direct current bias in a height consistent in the lifting process, so that the direct current short-circuit fault is judged to be completely cleared, the direct current bias is continuously lifted according to the set slope, and the waveform shows the stable lifting of the direct current voltage. The waveforms of the slave stations are shown in fig. 7, and the master station can be tracked well from beginning to end by the dc voltage, in the tracking process, a dc current of about 0.3pu appears due to the influence of the detection delay and the characteristics of the controller, but the dc current is limited to 0.2pu at this time due to the suppression effect of the dc current limiting controller. As can be seen from fig. 6 and 7, the voltage of the sub-module is stable, the reactive power output is normal, the electric quantity is stable, and there is no current or voltage impact.
as shown in fig. 8 and 9, the master station waveform and the slave station waveform of the dc short-circuit fault unremoved working condition are respectively selected and added with the dc current limit controller at 0.1s, and the first dc bias in the boost controller is started, but since the dc short-circuit fault is not recovered, the boost dc bias may cause the dc current to exceed the set value of 0.2pu, so the dc current limit controller starts to operate, the dc voltage is always limited to be near 0pu, and after a while, the system finds that the measured dc voltage value does not reach 90% of the first dc bias in the controller, and therefore, the dc short-circuit fault is determined not to be cleared, and the dc voltage is maintained in the 0 control mode.
As can be seen from fig. 8 and 9, in the whole process, the passing direct current of the master station and the slave station is less than 0.25pu, which does not affect the system safety, and meanwhile, on the premise of not adding additional detection equipment, it is accurately determined that the direct current short circuit fault is still not cleared, which illustrates the safety and effectiveness of the detection method.
in this embodiment, a converter station controlled by a constant dc voltage during normal operation may be used as both a master station and a slave station, and other converter stations may also be used as a master station or a slave station, that is, for a converter station, the converter station has both an ability to boost the first dc bias as the master station and an ability to track the dc voltage as the slave station; when the converter station controlled by the constant direct current voltage is used as a slave station in normal operation, a master station is designated in other converter stations.
The direct-current short-circuit fault detection method is not only suitable for the half-bridge and full-bridge submodule mixed multi-level converter shown in fig. 1, but also suitable for the full-bridge submodule multi-level converter.
According to the invention, inter-station communication is not required in the direct current fault detection process, other detection equipment is not required, the detection of the short circuit fault can be realized only by means of the original direct current voltage and current sensors, the guarantee is provided for the improvement of the direct current voltage after the direct current short circuit fault is not completely cleared, and the problems of secondary short circuit, quick discharge of the submodule, bypass and converter locking tripping are not caused.
The embodiment of the invention relates to an MMC direct current short-circuit fault detection device, which comprises the following steps:
the method comprises the following units:
A selection unit: the system comprises a master station, a slave station, a converter station, a plurality of slave stations and a plurality of communication terminals, wherein the master station is used for selecting one converter station and the other converter stations are used as the slave stations;
A judging unit: the slave station is used for synchronously tracking the direct-current voltage of the master station according to the difference between a direct-current feedback value and a direct-current reference value; when the time that the direct-current voltage continues to be less than the first set value is T1, it is determined that the direct-current short-circuit fault still exists.
The MMC direct-current short-circuit fault detection device referred to in the above embodiments is actually a computer solution based on the method flow of the present invention, that is, a software framework, which can be applied to a converter station, and the above device is a processing process corresponding to the method flow. The method described above is sufficiently clear and complete, and the device claimed in this embodiment is actually a software architecture, and therefore will not be described in detail.
Claims (9)
1. A MMC direct current short circuit fault detection method is characterized by comprising the following steps:
Selecting one converter station as a master station and other converter stations as slave stations; the master station boosts the direct-current voltage from zero, detects the direct-current voltage in real time in the boosting process, and synchronously tracks the direct-current voltage of the master station according to the difference between a direct-current feedback value and a direct-current reference value; when the time that the direct-current voltage is continuously less than the first set value is T1, determining that the direct-current short-circuit fault still exists;
the slave station generates a second direct current bias of the bridge arm modulation instruction through a proportional controller or a proportional-integral controller after the direct current feedback value is differentiated from the direct current reference value; and the second direct current bias is used for generating a bridge arm voltage of the slave station converter by combining the three-phase modulation wave.
2. The MMC direct current short circuit fault detection method of claim 1, wherein when a direct current short circuit fault still exists, controlling the master station to a zero direct current voltage control state.
3. The MMC direct current short circuit fault detection method of claim 1, wherein when the direct current voltage continues to be greater than or equal to the first set point for a time T2, it is determined that the direct current short circuit fault has cleared and the primary station continues to ramp up the direct current voltage until the direct current voltage is ramped up to the direct current voltage rating.
4. The MMC direct current short-circuit fault detection method of claim 1, wherein the master station boosts the direct current voltage from zero according to a set first direct current bias, and determines that the direct current short-circuit fault still exists when a time of the direct current voltage being less than a first set value is T1; and the first direct current bias is used for generating bridge arm voltage of the main station converter by combining three-phase modulation waves.
5. the MMC direct current short-circuit fault detection method of claim 4, wherein the bridge arm voltage calculation formula of the master station converter or the slave station converter is as follows:
In the formula, when v arm is the bridge arm voltage of the master station converter, U dc_rated is the rated value of the dc voltage, k is the first dc bias, and e abc is the three-phase modulation wave, and when v arm is the bridge arm voltage of the slave station converter, U dc_rated is the rated value of the dc voltage, k is the second dc bias, and e abc is the three-phase modulation wave.
6. the MMC direct current short circuit fault detection method of claim 5, wherein when k is the first direct current offset, k is obtained by adding a command value k ref to a command value k err, k ref is a command value gradually increasing from 0 to 1 according to a designated slope, and k err is a command value limiting the direct current.
7. The MMC direct current short circuit fault detection method of claim 6, wherein the primary station modifies the first direct current bias to control the direct current between an upper limit and a lower limit when the direct current is greater than a set upper limit or less than a set lower limit during a boost process direct current voltage.
8. the MMC direct current short circuit fault detection device is characterized by comprising the following units:
A selection unit: the system comprises a master station, a slave station, a converter station, a plurality of slave stations and a plurality of communication terminals, wherein the master station is used for selecting one converter station and the other converter stations are used as the slave stations;
a judging unit: the slave station is used for synchronously tracking the direct-current voltage of the master station according to the difference between a direct-current feedback value and a direct-current reference value; when the time that the direct-current voltage is continuously less than the first set value is T1, determining that the direct-current short-circuit fault still exists;
the slave station generates a second direct current bias of the bridge arm modulation instruction through a proportional controller or a proportional-integral controller after the direct current feedback value is differentiated from the direct current reference value; and the second direct current bias is used for generating a bridge arm voltage of the slave station converter by combining the three-phase modulation wave.
9. The MMC direct current short circuit fault detection device of claim 8, further comprising means for controlling the master station to a zero direct current voltage control state when a direct current short circuit fault is still present.
Priority Applications (1)
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| CN108469557B (en) * | 2018-03-07 | 2019-03-15 | 西南交通大学 | High voltage direct current transmission device Fault Locating Method based on inverter differential protection |
| CN112684290B (en) * | 2020-12-16 | 2022-11-04 | 华北电力大学 | Efficient calculation method for interelectrode short-circuit fault current of flexible direct-current power grid |
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