CN115663764A - Method and system for protecting cascaded power electronic transformer body - Google Patents
Method and system for protecting cascaded power electronic transformer body Download PDFInfo
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- CN115663764A CN115663764A CN202211431647.0A CN202211431647A CN115663764A CN 115663764 A CN115663764 A CN 115663764A CN 202211431647 A CN202211431647 A CN 202211431647A CN 115663764 A CN115663764 A CN 115663764A
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Abstract
The invention provides a method and a system for protecting a cascaded power electronic transformer body, wherein the method comprises the following steps: after the short-circuit fault of the low-voltage direct current side of the cascade power electronic transformer is judged, the low-voltage H-bridge converter of the input stage and the isolation stage of the cascade power electronic transformer is locked; and locking the high-voltage H-bridge converter of the isolation stage of the cascade power electronic transformer after the preset time. The invention solves the problems that the protection cost of the power electronic transformer body is too high and direct and complete locking easily causes overvoltage of an internal capacitance element in the related technology.
Description
Technical Field
The invention relates to the technical field of automatic relay protection of power systems, in particular to a method and a system for protecting a cascaded power electronic transformer body.
Background
With the continuous enlargement of the scale of an AC/DC hybrid Power grid, a cascade Power Electronic Transformer (Power Electronic Transformer with Cascaded H-Bridge, CHB-PET) can be efficiently connected with an AC/DC Power supply and a DC load, flexibly control the Power, reduce the volume and the cost, and is an important component part of an AC/DC Power distribution network. When a bipolar short-circuit fault occurs on the low-voltage direct-current side of the CHB-PET, the IGBT device inside the CHB-PET bears a very large short-circuit current and needs to be quickly locked to protect the power electronic equipment body, but the problem that overvoltage occurs on an internal capacitance element of the CHB-PET is easily caused by directly and completely locking the CHB-PET.
At present, main body protection methods aiming at CHB-PET are mainly divided into two methods, one method focuses on improving the topology and the control strategy of a power electronic equipment body, and the other method focuses on matching the power electronic equipment with a line direct current breaker and a current-limiting inductor. For the improvement of the topology and the control strategy of the power electronic equipment body, the device cost and the control complexity are increased, and the wide use of the power electronic equipment is not facilitated. The power electronic equipment is matched with the line direct current breaker and the current-limiting inductor, is only suitable for specific electric scenes, and has high manufacturing cost and poorer universality. Therefore, the problems that the protection cost of the power electronic transformer body is too high and direct and complete locking easily causes overvoltage of an internal capacitance element exist in the prior art.
Disclosure of Invention
The invention provides a method and a system for protecting a cascaded power electronic transformer body, which at least solve the problems that the protection cost of the power electronic transformer body is too high and direct and complete locking easily causes overvoltage of an internal capacitance element in the related technology.
According to a first aspect of the embodiments of the present invention, there is provided a method for protecting a cascaded power electronic transformer body, the method including: after the short-circuit fault on the low-voltage direct-current side of the cascade power electronic transformer is judged, the low-voltage H-bridge converters of the input stage and the isolation stage of the cascade power electronic transformer are locked; and locking the high-voltage H-bridge converter of the isolation stage of the cascade power electronic transformer after preset time.
Optionally, after the low-voltage direct-current side of the cascaded power electronic transformer is judged to have the short-circuit fault, before the low-voltage H-bridge converters of the input stage and the isolation stage of the cascaded power electronic transformer are locked, the method further includes: acquiring a fault current value in the cascade power electronic transformer; and judging whether the locking starting condition is met or not according to the fault current value and the protection starting value.
Optionally, the obtaining of the fault current value in the cascaded power electronic transformer includes: and acquiring a current value on the low-voltage winding of the isolation stage of the cascade power electronic transformer.
Optionally, the determining whether the locking start condition is satisfied according to the fault current value and the protection start value includes: when the current value of the isolation-level low-voltage winding of the cascade power electronic transformer is larger than the current rated value of the isolation-level low-voltage winding of the cascade power electronic transformer, judging that a locking starting condition is met; and when the current value of the low-voltage winding of the isolation level of the cascade power electronic transformer is less than or equal to the current rated value of the low-voltage winding of the isolation level of the cascade power electronic transformer, judging that the locking starting condition is not met.
Optionally, the high-voltage H-bridge converter for locking the isolation stages of the cascaded power electronic transformer after a preset time includes: and locking the high-voltage H-bridge converter of the isolation stage of the cascade power electronic transformer after 2-4 ms.
According to a second aspect of the embodiments of the present invention, there is also provided a protection system for a cascaded power electronic transformer body, the system including: a cascaded power electronic transformer and a controller; the controller is used for locking the low-voltage H-bridge converters of the input stage and the isolation stage of the cascade power electronic transformer after judging that the low-voltage direct-current side of the cascade power electronic transformer has a short-circuit fault, and locking the high-voltage H-bridge converter of the isolation stage of the cascade power electronic transformer after preset time.
Optionally, the cascaded power electronic transformer comprises: a plurality of input stage rectifiers and a plurality of isolation stage dc transformers; the input stage rectifier consists of an H-bridge module and is used for converting medium-voltage alternating current into medium-voltage direct current; the isolation-level direct-current transformers are composed of double active bridge converters, and the isolation-level direct-current transformers are respectively connected with the input-level rectifiers and used for converting medium-voltage direct current output by the input-level rectifiers into low-voltage direct current.
Optionally, the controller is further configured to, after it is determined that a short-circuit fault occurs on the low-voltage direct-current side of the cascaded power electronic transformer, obtain a fault current value in the cascaded power electronic transformer before the low-voltage H-bridge converters of the input stage and the isolation stage of the cascaded power electronic transformer are locked, and determine whether the cascaded power electronic transformer meets a locking start condition according to the fault current value and a protection start value.
Optionally. The controller is further used for obtaining a current value on the low-voltage winding of the isolation stage of the cascade power electronic transformer.
Optionally, the controller is further configured to determine that the cascaded power electronic transformer satisfies a lockout start condition when a current value of the cascaded power electronic transformer isolation-level low-voltage winding is greater than a current rating of the cascaded power electronic transformer isolation-level low-voltage winding, and determine that the cascaded power electronic transformer does not satisfy the lockout start condition when the current value of the cascaded power electronic transformer isolation-level low-voltage winding is less than or equal to the current rating of the cascaded power electronic transformer isolation-level low-voltage winding.
In the embodiment of the invention, after the cascade power electronic transformer has a direct current fault, the input stage of the cascade power electronic transformer and the low-voltage H-bridge converter of the isolation stage are firstly locked in a step-by-step locking mode, and the high-voltage H-bridge converter of the isolation stage is locked after the preset time. Due to the adoption of step locking, a discharge path can be provided for the input stage direct current side capacitor of the cascade power electronic transformer in a short time, so that the purpose of eliminating overvoltage of the internal capacitor element of the cascade power electronic transformer can be realized; the method is simple in principle, does not need to change the topological structure of the cascade power electronic transformer, and can effectively realize the body protection of the cascade power electronic transformer without additional devices and complex control strategies. The problem of power electronic transformer body protection cost among the correlation technique too high is solved.
In the embodiment of the invention, a time delay locking mode is adopted, and the high-voltage H-bridge converter of the isolation stage of the cascade power electronic transformer is locked after the preset time, so that the aim of providing fault voltage and current information for low-voltage direct-current line protection within the preset time after the fault occurs is fulfilled, and conditions are provided for fault analysis.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and together with the description, serve to explain the principles of the invention.
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without inventive exercise.
Fig. 1 is a schematic flow chart of an alternative method for protecting a cascaded power electronic transformer body according to an embodiment of the present invention;
FIG. 2-1 is a schematic diagram of a first step of a method for alternative protection of a cascaded power electronic transformer body according to an embodiment of the invention;
fig. 2-2 is a second latch-up schematic diagram of an alternative cascaded power electronic transformer body protection method according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of bridge arm currents of an input stage of a cascaded power electronic transformer after an optional step-by-step locking measure according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of the DC-side capacitor voltage of the input stage of the cascaded power electronic transformer after an alternative step-by-step blocking measure according to the embodiment of the invention;
FIG. 5 is a schematic diagram of the DC-side capacitor voltage at the input stage of the cascaded power electronic transformer after direct full latching;
fig. 6 is a schematic diagram of a CHB-PET topology in an alternative cascaded power electronic transformer body protection system according to an embodiment of the present invention;
fig. 7 is a schematic diagram of a CHB-PET topology in an alternative cascaded power electronic transformer body protection system according to an embodiment of the invention;
fig. 8 is a schematic diagram of an alternative exemplary ac/dc interconnected power distribution network fault according to an embodiment of the present invention.
Detailed Description
In order to make those skilled in the art better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, shall fall within the protection scope of the present invention.
It should be noted that, in the description of the present invention, the terms "first", "second", and the like are used for distinguishing similar objects, and are not necessarily used for describing a particular order or sequence. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus. The terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," "outer," and the like are used in the orientation or positional relationship indicated in the drawings for convenience in describing the invention and for simplicity in description, and do not indicate or imply that the referenced device or element must have a particular orientation, be constructed and operated in a particular orientation, and are therefore not to be construed as limiting the invention. The terms "mounted," "connected," and "coupled" are to be construed broadly and may, for example, be fixedly coupled, detachably coupled, or integrally coupled; can be mechanically or electrically connected; the two elements may be directly connected or indirectly connected through an intermediate medium, or may be communicated with each other inside the two elements, or may be wirelessly connected or wired connected. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
According to a first aspect of the embodiments of the present invention, a method for protecting a cascaded power electronic transformer body is provided. Fig. 1 is a schematic flow chart of an alternative method for protecting a cascaded power electronic transformer body according to an embodiment of the present invention, and as shown in fig. 1, the method may include the following steps:
step S201, after it is determined that a short-circuit fault occurs on the low-voltage dc side of the cascaded power electronic transformer, the low-voltage H-bridge converters of the input stage and the isolation stage of the cascaded power electronic transformer are locked. Optionally, fig. 2-1 and 2-2 are a first step locking schematic diagram and a second step locking schematic diagram, that is, a partial locking schematic diagram, of an optional method for protecting a body of a cascaded power electronic transformer according to an embodiment of the present invention, where AC/DC is an input stage of the cascaded power electronic transformer, and is connected to three-phase power sources Ea, eb, and Ec through an inductor Lg, DAB (dual-active-bridge) is an isolation stage of the cascaded power electronic transformer, S1-S12 are IGBTs, and C is a DC-side capacitance of the input stage of the cascaded power electronic transformer. Specifically, after it is determined that a short-circuit fault occurs on the low-voltage dc side of the cascaded power electronic transformer, as shown in fig. 2-1, the low-voltage H-bridge converters of the input stage and the isolation stage of the cascaded power electronic transformer are first locked, that is, the IGBTs S1-S4 of the input stage of the cascaded power electronic transformer and the low-voltage H-bridge converters IGBTs S9-S12 of the isolation stage are controlled to be locked. The determination method of the short-circuit fault may be implemented by using the prior art, and is not described herein again.
Step S202, the high-voltage H-bridge converter of the isolation stage of the cascade power electronic transformer is locked after the preset time. Alternatively, after a preset time, as shown in fig. 2-2, the high voltage H-bridge converters of the isolation stages of the cascaded power electronic transformer, i.e. the high voltage H-bridge converters IGBTs S5-S8 controlling the isolation stages of the cascaded power electronic transformer, are locked.
In the embodiment of the invention, after the cascade power electronic transformer has a direct current fault, the input stage of the cascade power electronic transformer and the low-voltage H-bridge converter of the isolation stage are firstly locked in a step-by-step locking mode, and the high-voltage H-bridge converter of the isolation stage is locked after the preset time. Due to the adoption of step-by-step locking, a discharge path can be provided for the input stage direct-current side capacitor C of the cascade power electronic transformer in a short time, so that the aim of eliminating overvoltage of the internal capacitor element of the cascade power electronic transformer can be fulfilled; the method is simple in principle, does not need to change the topological structure of the cascade power electronic transformer, and can effectively realize the body protection of the cascade power electronic transformer without additional devices and complex control strategies. The problem of power electronic transformer body protection cost among the correlation technique too high is solved.
As an optional embodiment, after determining that a short-circuit fault occurs on the low-voltage dc side of the cascaded power electronic transformer, before locking the low-voltage H-bridge converters of the input stage and the isolation stage of the cascaded power electronic transformer, the method further includes: acquiring a fault current value in a cascade power electronic transformer; and judging whether the locking starting condition is met or not according to the fault current value and the protection starting value.
Optionally, after the short-circuit fault on the low-voltage direct-current side of the CHB-PET is determined, before the low-voltage H-bridge converter of the input stage and the isolation stage of the CHB-PET is locked, it is determined whether the CHB-PET meets a locking starting condition, and first, a fault current value flowing through the CHB-PET is acquired, and then, whether the locking starting condition is met is determined according to the fault current value and a protection starting value. In the embodiment of the invention, after the fault occurs and before the first step of locking is adopted, the reliability of step-by-step locking is improved by judging whether the locking starting condition is met.
As an alternative embodiment, obtaining the fault current value in the cascade power electronic transformer comprises: and obtaining the current value on the low-voltage winding of the isolation stage of the cascade power electronic transformer. Optionally, when determining whether the CHB-PET meets the latch-up starting condition, first obtaining a fault current value flowing through the CHB-PET, selecting a current of the CHB-PET isolation-level high-voltage winding or a current of the low-voltage winding, and preferably, using the current of the isolation-level low-voltage winding as a determination basis.
As an alternative embodiment, the determining whether the latch-up enabling condition is satisfied according to the fault current value and the protection enabling value includes: when the current value of the isolation-level low-voltage winding of the cascade-type power electronic transformer is larger than the rated current value of the isolation-level low-voltage winding of the cascade-type power electronic transformer, judging that a locking starting condition is met; and when the current value of the low-voltage winding of the isolation stage of the cascade power electronic transformer is less than or equal to the current rated value of the low-voltage winding of the isolation stage of the cascade power electronic transformer, judging that the locking starting condition is not met.
Optionally, when the current of the low-voltage winding of the CHB-PET isolation stage is taken as a judgment basis, the current of the low-voltage winding is recorded as i 2 The current rated value of the low-voltage winding of the CHB-PET isolation stage is taken as a corresponding protection starting value and is marked as I N Then the latch-up enabling condition at this time can be expressed as:
i 2 ＞I N
when the current value of the CHB-PET isolation level low-voltage winding is larger than the current rated value of the isolation level low-voltage winding of the cascade power electronic transformer, judging that the locking starting condition is met, and starting step-by-step locking; otherwise, judging that the locking starting condition is not met.
As an alternative embodiment, the high voltage H-bridge converter for blocking the isolation stages of the cascaded power electronic transformer after a preset time comprises: and locking the high-voltage H-bridge converter of the isolation stage of the cascade power electronic transformer after 2-4 ms. Preferably, when the short-circuit fault occurs on the low-voltage direct-current side of the CHB-PET, the high-voltage H bridge converter of the CHB-PET isolation stage is locked after 3ms after the low-voltage H bridge converter of the input stage and the low-voltage H bridge converter of the isolation stage of the CHB-PET are locked. In the embodiment of the invention, a time delay locking mode is adopted, and the high-voltage H-bridge converter of the isolation stage of the cascade power electronic transformer is locked after the preset time, so that the aim of providing fault voltage and current information for low-voltage direct-current line protection within the preset time after the fault occurs is fulfilled, and conditions are provided for fault analysis. The 2ms-4ms is selected as the preset time, so that overvoltage can be eliminated, and the protection of the cascaded power electronic transformer body is not influenced.
According to the second aspect of the embodiment of the invention, the invention also provides a protection system for the body of the cascaded power electronic transformer. The system comprises a cascade power electronic transformer and a controller; the controller is used for locking the low-voltage H-bridge converter of the input stage and the isolation stage of the cascade power electronic transformer after judging that the low-voltage direct-current side of the cascade power electronic transformer has a short-circuit fault, and locking the high-voltage H-bridge converter of the isolation stage of the cascade power electronic transformer after preset time.
Optionally, the protection system for the cascaded power electronic transformer body comprises a CHB-PET and a controller, wherein the controller controls the CHB-PET to be locked after a direct-current short-circuit fault occurs, specifically, after receiving information of the short-circuit fault occurring on the low-voltage direct-current side of the CHB-PET, the controller locks the low-voltage H-bridge converter of the input stage and the isolation stage of the CHB-PET, and locks the high-voltage H-bridge converter of the isolation stage of the CHB-PET after preset time.
Fig. 3 is a schematic diagram of bridge arm currents of an input stage of a cascaded power electronic transformer after an optional step-by-step locking measure is adopted, where it should be noted that, as shown in fig. 2-1, the shape of the CHB-PET input stage is similar to the letter "H", and is called an "H bridge" like a bridge, and the positions of 4 switches are called "bridge arms". As shown in fig. 3, at the time t =0, a short-circuit fault occurs on the low-voltage dc side of the cascade power electronic transformer and the latch start condition is satisfied, so that at the time t =0, the low-voltage H-bridge converter of the input stage and the isolation stage of the cascade power electronic transformer is latched, and the high-voltage H-bridge converter of the isolation stage of the cascade power electronic transformer is latched after a preset time of 3ms, and it can be seen that the bridge arm currents Ia, ib, and Ic of the input stage of the cascade power electronic transformer gradually decrease after the start of the step-by-step latch, and become 0 after the step-by-step latch is completed, that is, the latch is completed. And Ia, ib and Ic respectively represent the input stage bridge arm currents connected with Ea, eb and Ec, and pu represents the multiple of the input stage bridge arm currents relative to the steady-state current value.
Fig. 4 and 5 are schematic diagrams of the voltage of the capacitor at the input stage dc side of the cascaded power electronic transformer after the step-by-step locking measure is adopted and schematic diagrams of the voltage of the capacitor at the input stage dc side of the cascaded power electronic transformer after direct and complete locking is adopted, respectively. The time t =0 is a fault time, ua, ub and Uc respectively indicate voltages of the input stage direct current side capacitors connected with Ea, eb and Ec after step locking, and Ua1, ub1 and Uc1 respectively indicate voltages of the input stage direct current side capacitors connected with Ea, eb and Ec after direct and complete locking. As shown in fig. 4, step-by-step latching is started at the time t =0, since the dc side capacitor voltage can be discharged to a short-circuit point through an IGBT of a high-voltage H-bridge converter of the CHB-PET isolation stage and a diode of a current converter of a low-voltage H-bridge converter, and step-by-step latching is completed after 3ms, since discharging cannot be continued, the voltage slowly rises, but does not exceed the maximum withstand voltage, the purpose of eliminating overvoltage of the capacitor element inside the CHB-PET is achieved by step-by-step latching. When direct full latch-up is adopted, as shown in fig. 5, the dc-side capacitor voltage of the CHB-PET input stage rapidly rises to 1.2 times the steady-state value, which is liable to damage the capacitor element.
In the embodiment of the invention, after the cascade power electronic transformer has a direct current fault, the input stage and the low-voltage H-bridge converter of the isolation stage of the cascade power electronic transformer are firstly locked in a step-by-step locking mode, and then the high-voltage H-bridge converter of the isolation stage is locked after the preset time. Due to the adoption of step-by-step locking, a discharge path can be provided for the input stage direct-current side capacitor of the cascade power electronic transformer in a short time, so that the aim of eliminating overvoltage of the internal capacitor element of the cascade power electronic transformer can be fulfilled; the method is simple in principle, does not need to change the topological structure of the cascade power electronic transformer, and can effectively realize the body protection of the cascade power electronic transformer without additional devices and complex control strategies. The problem of power electronic transformer body protection cost too high that exists among the correlation technique is solved.
As an alternative embodiment, a cascaded power electronic transformer comprises: a plurality of input stage rectifiers and a plurality of isolation stage dc transformers; the input-stage rectifier consists of an H-bridge module and is used for converting medium-voltage alternating current into medium-voltage direct current; the isolation-level direct-current transformer consists of double active bridge converters, and the isolation-level direct-current transformers are respectively connected with the input-level rectifiers and used for converting medium-voltage direct current output by the input-level rectifiers into low-voltage direct current. Alternatively, as shown in fig. 6 and 7, are alternative CHB-PET topology schematics according to embodiments of the present invention, the CHB-PET comprising multiple input stages, CHB, and multiple isolation stages, DAB. The input stage rectifier is composed of an H-bridge module, is connected with the isolation stage direct current transformer and is used for converting medium-voltage alternating current from three-phase alternating current power supplies Ea, eb and Ec into medium-voltage direct current. The isolation-stage direct-current transformer consists of a double-active-bridge converter, is connected with the input-stage rectifier and is used for converting the medium-voltage direct current output by the CHB into low-voltage direct current. In addition, the left side of the CHB is provided with 10kV medium-voltage alternating current, and the right side of the DAB is provided with 750kV low-voltage direct current.
Fig. 8 is a schematic diagram of an alternative exemplary ac/DC interconnected power distribution network fault according to an embodiment of the present invention, as shown in fig. 8, the CHB-PET provides a medium voltage ac port and a low voltage DC port, the ac power source is connected to the CHB-PET through the power transformer, the voltage level is converted into 750V low voltage DC through the input stage CHB rectification and the isolation stage DAB, and then the voltage level is connected to the low voltage DC bus through the DC main line l, and the distributed power source such as the photovoltaic PV, the energy storage BESS, and the Load are connected through the DC/DC branch line l and the DC/DC branch line l 1 、l 2 、l 3 Is connected to the low voltage dc bus.
As an optional embodiment, the controller is further configured to, after it is determined that a short-circuit fault occurs at the low-voltage dc side of the cascaded power electronic transformer, obtain a fault current value in the cascaded power electronic transformer before the low-voltage H-bridge converters at the input stage and the isolation stage of the cascaded power electronic transformer are locked, and determine whether the cascaded power electronic transformer meets a locking start condition according to the fault current value and the protection start value. Optionally, the controller is configured to determine whether the CHB-PET satisfies a latch-up start condition, and specifically, the controller obtains a fault current value flowing in the CHB-PET, and then determines whether the latch-up start condition is satisfied according to the fault current value and a protection start value. In the embodiment of the invention, after the fault occurs and before the first step of locking is adopted, the reliability of step-by-step locking is improved by judging whether the locking starting condition is met.
As an alternative embodiment, the controller is further configured to obtain a current value on the low-voltage winding of the isolation stage of the cascaded power electronic transformer. Optionally, when determining whether the CHB-PET satisfies the lockout start condition, the controller needs to obtain a fault current value flowing in the CHB-PET, preferably, a current value of the isolation stage low voltage winding, as shown in fig. 8, and obtains a current value i of the isolation stage DAB low voltage winding 2 Due to CHB-After the current of the PET isolation level low-voltage winding breaks down on the low-voltage direct-current side, the current rises fastest and is the most sensitive, and the quick action of the locking protection can be ensured and the method is more accurate and reliable as a judgment basis.
As an alternative embodiment, the controller is further configured to determine that the cascade-type power electronic transformer satisfies the lockout start condition when a current value of the low-voltage winding of the isolation stage of the cascade-type power electronic transformer is greater than a current rating of the low-voltage winding of the isolation stage of the cascade-type power electronic transformer, and determine that the cascade-type power electronic transformer does not satisfy the lockout start condition when the current value of the low-voltage winding of the isolation stage of the cascade-type power electronic transformer is less than or equal to the current rating of the low-voltage winding of the isolation stage of the cascade-type power electronic transformer. Optionally, the controller determines i 2 ＞I N And (4) whether the current value of the low-voltage winding of the CHB-PET isolation level is greater than the current rating of the low-voltage winding of the isolation level of the cascade power electronic transformer or not is judged by the controller to meet the locking starting condition, and step locking is started. As shown in FIG. 8, a fault f occurs on the main line l 1 And then, starting line protection, and acquiring a current value i of the isolation-level DAB low-voltage winding by the controller 2 When judging i 2 ＞I N And if the direct current breaker is established, step-by-step locking is started, and the direct current breaker and the load switch normally act according to self configuration. In the embodiment of the invention, after the short-circuit fault occurs in the direct current region, the CHB-PET can realize the protection of the body by means of step-by-step locking.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (10)
1. A protection method for a cascaded power electronic transformer body is characterized by comprising the following steps:
after the short-circuit fault of the low-voltage direct current side of the cascade power electronic transformer is judged, the low-voltage H-bridge converter of the input stage and the isolation stage of the cascade power electronic transformer is locked;
and locking the high-voltage H-bridge converter of the isolation stage of the cascade power electronic transformer after preset time.
2. The method according to claim 1, wherein after determining that the short-circuit fault occurs on the low-voltage direct-current side of the cascaded power electronic transformer, before locking the low-voltage H-bridge converters of the input stage and the isolation stage of the cascaded power electronic transformer, the method further comprises:
acquiring a fault current value in the cascade power electronic transformer;
and judging whether the locking starting condition is met or not according to the fault current value and the protection starting value.
3. The method of claim 2, wherein said obtaining a fault current value within said cascaded power electronic transformer comprises:
and acquiring a current value on the low-voltage winding of the isolation stage of the cascade power electronic transformer.
4. The method of claim 3, wherein said determining whether a latch-up enabling condition is satisfied based on said fault current value and a protection enabling value comprises:
when the current value of the isolation-level low-voltage winding of the cascade power electronic transformer is larger than the current rating of the isolation-level low-voltage winding of the cascade power electronic transformer, judging that a locking starting condition is met;
and when the current value of the low-voltage winding of the isolation level of the cascade power electronic transformer is less than or equal to the current rated value of the low-voltage winding of the isolation level of the cascade power electronic transformer, judging that the locking starting condition is not met.
5. The method of claim 1, wherein said blocking the high voltage H-bridge converter of the cascaded power electronic transformer isolation stage after a preset time comprises:
and locking the high-voltage H-bridge converter of the isolation stage of the cascade power electronic transformer after 2-4 ms.
6. A protection system for a cascaded power electronic transformer body is characterized by comprising a cascaded power electronic transformer and a controller;
the controller is used for locking the low-voltage H-bridge converters of the input stage and the isolation stage of the cascade power electronic transformer after judging that the low-voltage direct-current side of the cascade power electronic transformer has a short-circuit fault, and locking the high-voltage H-bridge converter of the isolation stage of the cascade power electronic transformer after preset time.
7. A cascaded power electronic transformer body protection system according to claim 6, characterized in that the cascaded power electronic transformer comprises: a plurality of input stage rectifiers and a plurality of isolation stage dc transformers;
the input stage rectifier consists of an H-bridge module and is used for converting medium-voltage alternating current into medium-voltage direct current;
the isolation-level direct-current transformer consists of double active bridge converters, and the isolation-level direct-current transformers are respectively connected with the input-level rectifiers and used for converting the medium-voltage direct current output by the input-level rectifiers into low-voltage direct current.
8. The system of claim 6, wherein the controller is further configured to obtain a fault current value in the cascaded power electronic transformer after determining that the short-circuit fault occurs on the low-voltage dc side of the cascaded power electronic transformer and before locking the low-voltage H-bridge converters of the input stage and the isolation stage of the cascaded power electronic transformer, and determine whether the cascaded power electronic transformer satisfies a locking start condition according to the fault current value and a protection start value.
9. The cascaded power electronic transformer body protection system of claim 8, wherein the controller is further configured to obtain a current value on the low voltage winding of the isolation stage of the cascaded power electronic transformer.
10. The cascaded power electronic transformer body protection system of claim 9, wherein the controller is further configured to determine that the cascaded power electronic transformer satisfies a latch-up start condition when a current value on the low voltage winding of the isolation stage of the cascaded power electronic transformer is greater than a current rating of the low voltage winding of the isolation stage of the cascaded power electronic transformer, and determine that the cascaded power electronic transformer does not satisfy the latch-up start condition when the current value on the low voltage winding of the isolation stage of the cascaded power electronic transformer is less than or equal to the current rating of the low voltage winding of the isolation stage of the cascaded power electronic transformer.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202211431647.0A CN115663764A (en) | 2022-11-16 | 2022-11-16 | Method and system for protecting cascaded power electronic transformer body |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202211431647.0A CN115663764A (en) | 2022-11-16 | 2022-11-16 | Method and system for protecting cascaded power electronic transformer body |
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| CN115663764A true CN115663764A (en) | 2023-01-31 |
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