CN112952845A - Low-frequency power transmission system with transformer isolation and control method thereof - Google Patents
Low-frequency power transmission system with transformer isolation and control method thereof Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/30—Reactive power compensation
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Abstract
The application provides a low-frequency power transmission system with transformer isolation and a control method thereof. The low-frequency power transmission system with the transformer isolation comprises a three-phase power frequency system, a low-frequency system and an AC-AC converter; the system comprises a first isolation switch connected with a three-phase power frequency port of an AC-AC converter; the second isolation switch is connected with a low-frequency port of the AC-AC converter; the system also comprises at least one isolation transformer which is positioned between the first isolation switch and the three-phase power frequency system or between the second isolation switch and the low-frequency system. The voltage of the two sides of the AC-AC converter is changed by changing the transformation ratio and the position of the isolation transformer, so that the AC system is suitable for AC systems with different voltage grades and frequencies, the number of modules of each chain link of the AC-AC converter can be timely reduced, and the system cost is reduced. In addition, this application has set up isolation switch operation, can handle AC/AC converter for reactive compensation equipment, has increased the availability of equipment.
Description
Technical Field
The application relates to the technical field of power electronic application, in particular to a low-frequency power transmission system with transformer isolation and a control method thereof.
Background
When the traditional power frequency transmission system adopts 50/60Hz, the transmission distance is limited compared with a direct current power supply system, and the problems of system reactive power and distribution parameters are also considered. The popularization of the direct current power supply system has considerable advantages in the fields of new energy application and electric energy transmission, but the cost of devices such as a direct current breaker and a direct current transformer is high, and most direct current systems need to be newly built. Therefore, under the conditions that some transmission distances are far relative to power frequency application, but cost requirements are limited, or some equipment needs to be transformed and operated, low-frequency power transmission can be beneficial to improving the problems of system reactive power and distributed parameters due to the fact that power transmission frequency is reduced, and therefore certain long-distance power transmission is achieved. Meanwhile, the power frequency circuit of the power transmission line can still be reserved, so that the reconstruction cost is lower than that of a direct current system.
The low-frequency power transmission system is an AC-AC converter used for power frequency and low-frequency voltage conversion. At present, a common mature ac-ac converter is a modular multilevel matrix converter (M3C), but the converter uses 9 chain links, and in the field of high-voltage application, the number of used modules is large, and the equipment cost is high. For this reason, a 6-chain topology, such as a hexagonal structure of CN110601201A, is proposed, but this topology is prone to cause a serious harmonic problem in the system when the single-phase voltage is unbalanced.
In addition, when one side of the ac system fails, the multiple circuit arms of the M3C converter will stop working, which also reduces the availability of the device.
In summary, the M3C converter still needs to be studied more in terms of reducing the cost and increasing the availability of the equipment.
Disclosure of Invention
In order to solve the above problems, the present application provides a low frequency power transmission system with transformer isolation and a control method thereof, and the specific scheme is as follows:
in a first aspect, the present application provides a low frequency power transmission system with transformer isolation, comprising:
the three-phase power frequency system comprises a three-phase power supply system;
a low frequency system comprising at least one phase power supply system;
the AC-AC converter comprises a three-phase power frequency port and a low-frequency port, and the phase number of the low-frequency port is consistent with that of a low-frequency system;
the first isolation switch is used for connecting the three-phase power frequency system and a three-phase power frequency port of the AC-AC converter;
the second isolation switch is used for connecting the low-frequency system and the low-frequency port of the AC-AC converter;
the isolation transformer is positioned between the first isolation switch and the three-phase power frequency system or between the second isolation switch and the low-frequency system; when the isolation transformer is positioned between the first isolation switch and the three-phase power frequency system, the isolation transformer is a three-phase power frequency transformer; and when the isolation transformer is positioned between the second isolation switch and the low-frequency system, the isolation transformer is a low-frequency transformer.
In a preferred scheme, the system comprises at least two isolation transformers, wherein one isolation transformer is positioned between a first isolation switch and a three-phase power frequency system, and the other isolation transformer is positioned between a second isolation switch and a low-frequency system.
In a preferred scheme, the winding transformation ratio of the isolation transformer connected with the alternating-current/alternating-current converter side is smaller than that of the other side.
In a preferred scheme, the ac-ac converter is a matrix converter and comprises N chain links, wherein N is a positive integer and is an integer multiple of 3, each chain link comprises M ac-dc conversion modules and a resonant branch, each ac-dc conversion module comprises an ac port and a dc port, the dc port is connected to a capacitor, and the M ac-dc conversion modules are connected in series through the ac ports and then connected in series with the resonant branch to form a chain link; every three chain links are divided into a group, one end of each chain link in the same group is connected with the three-phase power frequency port, and the other end of each chain link is connected with one phase of the low-frequency port.
In a preferred embodiment, the low frequency system comprises at least three structural forms:
the structure form I: when the low-frequency system only has a one-phase power supply system, the three-phase power frequency system also comprises a neutral line; one end of phase voltage of the low-frequency system is connected with a low-frequency port of the AC-AC converter, and the other end of the phase voltage of the low-frequency system is connected with a neutral line of the three-phase power frequency system;
the structural form II is as follows: when the low-frequency system only has a two-phase power supply system, the AC-AC converter comprises at least 6 chain links, and every three chain links are divided into two groups; one end of each of the three chain links in the same group is respectively connected with the three-phase power frequency port, the other end of each of the three chain links is commonly connected with one phase of the low-frequency port, and the two groups of chain links are respectively connected with different phases of the low-frequency port; two phases of voltages of the low-frequency system are respectively connected with different phases of the low-frequency port of the AC-AC converter;
the structural form is three: when the low-frequency system only has a three-phase power supply system, the AC-AC converter comprises at least 9 chain links, and each three chain links are divided into three groups; one end of each of three chain links in the same group is respectively connected with a three-phase power frequency port, the other ends of the three chain links are commonly connected with one phase of the low-frequency port, and the three groups of chain links are respectively connected with different phases of the low-frequency port; and the three-phase voltage of the low-frequency system is respectively connected with different phases of the low-frequency port of the AC-AC converter.
In a preferred scheme, the first isolation disconnecting link and the second isolation disconnecting link are both circuit breakers or switch groups consisting of circuit breakers and isolating switches.
In a preferred scheme, the resonance branch is a direct-connected wire or a branch formed by a capacitor or an inductor or a branch formed by a capacitor and an inductor.
In a preferred embodiment, the ac-dc conversion module is a full bridge circuit or a three-level circuit.
In a second aspect, the present application further provides a control method for the low-frequency power transmission system with transformer isolation, where the power flow direction is from a three-phase power frequency system to a low-frequency system, the following steps are adopted:
closing the first isolation switch and the second isolation switch;
collecting voltage and current of a three-phase power frequency system;
collecting voltage and current of a low-frequency system;
adjusting the power angle between the power frequency component voltage of the output voltage of each chain link of the AC-AC converter and the voltage of the three-phase power frequency system, and controlling the power of the three-phase power frequency system flowing into the AC-AC converter;
and adjusting the power angle between the low-frequency component voltage of the output voltage of each chain link of the AC-AC converter and the voltage of the low-frequency system, controlling the power flowing out from the AC-AC converter to the low-frequency system, and ensuring that the power flowing into the AC-AC converter from the three-phase power frequency system is equal to the power flowing out from the AC-AC converter to the low-frequency system.
In a third aspect, the present application also provides a method for controlling the transformer-isolated low-frequency power transmission system, where the power flow direction is from the low-frequency system to the three-phase power frequency system, the method includes the following steps:
closing the first isolation switch and the second isolation switch;
collecting voltage and current of a low-frequency system;
collecting voltage and current of a three-phase power frequency system;
adjusting the power angle between the low-frequency component voltage of the output voltage of each chain link of the AC-AC converter and the voltage of a low-frequency system, and controlling the power of the low-frequency system flowing into the AC-AC converter;
adjusting the power frequency component voltage of the output voltage of each chain link of the AC-AC converter and the power angle of the voltage of the three-phase power frequency system, and controlling the power flowing out from the AC-AC converter to the three-phase power frequency system; and the power of the low-frequency system flowing into the AC-AC converter is ensured to be equal to the power of the AC-AC converter flowing out to the three-phase power frequency system.
In a fourth aspect, the present application provides a control method for the transformer-isolated low-frequency power transmission system, where the following steps are adopted to make the system equivalent to a reactive power compensation device of a three-phase power frequency system:
closing the first isolation switch and opening the second isolation switch;
collecting voltage and current of a three-phase power frequency system;
and starting the AC-AC converter, and controlling the reactive power of the three-phase power frequency system to be a set value based on the voltage and the current of the three-phase power frequency system.
In a fifth aspect, the present application provides a method for controlling the low-frequency power transmission system with transformer isolation, which is characterized in that the system is equivalent to a reactive power compensation device of the low-frequency system after the following steps are adopted:
closing the second isolation switch and disconnecting the first isolation switch;
collecting voltage and current of a low-frequency system;
and starting the AC-AC converter, and controlling the reactive power of the low-frequency system to be a set value based on the voltage and the current of the low-frequency system.
According to the technical scheme provided by the embodiment of the application, the alternating-current voltage at two sides of the alternating-current/alternating-current converter is reduced by reasonably setting the transformation ratio of the power frequency transformer and the low-frequency transformer, so that the number of modules of a single chain link of the alternating-current/alternating-current converter is reduced, and the system cost is reduced; in addition, the isolation switch that this application set up can realize through the cooperation of rationally breaking absolutely that M3C converter turns into reactive power compensation equipment (SVG or STATCOM) and uses, has improved equipment utilization. The control method provided by the application can realize the controllable operation of the power and the voltage on two sides of the AC-AC converter and can be converted into reactive compensation equipment for use.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
Fig. 1 is a schematic diagram of a low-frequency power transmission system according to an embodiment of the present application.
Fig. 2 is a schematic diagram of another low-frequency power transmission system proposed in an embodiment of the present application.
Fig. 3 is a schematic diagram of another low-frequency power transmission system according to an embodiment of the present application.
Fig. 4 is a schematic circuit diagram of an ac-to-ac converter according to an embodiment of the present disclosure.
Fig. 5 is a schematic circuit diagram of another ac-ac converter according to an embodiment of the present application.
Fig. 6 is a schematic circuit diagram of another ac-to-ac converter according to an embodiment of the present application.
Fig. 7 is a schematic diagram of an ac-dc conversion module according to an embodiment of the present disclosure.
Fig. 8 is a schematic diagram of another ac-dc conversion module according to an embodiment of the present disclosure.
Fig. 9 is a schematic diagram of another ac-dc conversion module according to an embodiment of the present application.
Fig. 10 is a flow chart of a low frequency power transmission system control method.
Fig. 11 is a flow chart of a low frequency power transmission system control method two.
Fig. 12 is a flow chart of a low frequency power transmission system control method three.
Fig. 13 is a fourth flow chart of a low frequency power transmission system control method.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some, but not all, embodiments of the present application. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
It should be understood that the terms "first", "second", etc. in the claims, description, and drawings of the present application are used for distinguishing between different objects and not for describing a particular order. The terms "comprises" and "comprising," when used in the specification and claims of this application, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
As shown in fig. 1 and fig. 2, the low-frequency power transmission system with transformer isolation according to the embodiment of the present application includes:
the three-phase power frequency system 101 comprises a three-phase power supply system;
a low frequency system 103 comprising at least one phase power supply system;
the AC-AC converter 102 comprises a three-phase power frequency port and a low-frequency port, and the phase difference number of the low-frequency port is consistent with that of a low-frequency system;
the first isolation switch 109 is used for connecting the three-phase power frequency system and a three-phase power frequency port of the AC-AC converter;
a second isolation switch 110 for connecting the low frequency system and the low frequency port of the ac-ac converter;
at least one isolation transformer is arranged between the first isolation switch 109 and the three-phase power frequency system 101 or between the second isolation switch 110 and the low-frequency system 103; when the isolation transformer is located between the first isolation switch and the three-phase power frequency system, the isolation transformer is a three-phase power frequency transformer 104, as shown in fig. 1; when the isolation transformer is located between the second isolation switch and the low frequency system, it is a low frequency transformer 105, as shown in fig. 2.
According to some embodiments, as shown in fig. 3, a low frequency transmission system with transformer isolation comprises at least two isolation transformers, one isolation transformer being located between a first isolation switch and a three-phase power frequency system, and another isolation transformer being located between a second isolation switch and the low frequency system.
According to some embodiments, the low frequency transmission system with transformer isolation has a lower winding transformation ratio of the isolation transformer connection ac-to-ac converter side than the other side. Specifically, the transformation ratio of the winding on one side of the three-phase power frequency transformer connected with the AC-AC converter is smaller than that of the winding connected with the three-phase power frequency system; the transformation ratio of the winding of the low-frequency transformer connected with the AC-AC converter is smaller than that of the winding of the low-frequency system.
According to some embodiments, the low-frequency power transmission system with transformer isolation comprises an ac-dc converter, an ac-dc converter and a resonant branch, wherein the ac-dc converter is a matrix converter and comprises N chain links, N is a positive integer and is an integer multiple of 3, each chain link comprises M ac-dc conversion modules and a resonant branch, each ac-dc conversion module comprises an ac port and a dc port, the dc ports are connected with a capacitor, and the M ac-dc conversion modules are connected in series through the ac ports and then connected in series with the resonant branch to form a chain link; every three chain links are divided into a group, one end of each chain link in the same group is connected with the three-phase power frequency port, and the other end of each chain link is connected with one phase of the low-frequency port. As shown in fig. 1-3, the assemblies 106, 107 and 108 are three links of an ac-to-ac converter, the assembly 1061 is one of the ac-to-dc conversion modules, and the assembly 1062 is a resonant branch. Fig. 4 to 6 are schematic diagrams of 3, 6, and 9 link ac-ac converters provided in the embodiments of the present application.
According to some embodiments, the low frequency power transmission system with transformer isolation comprises at least three of the following structural forms:
the structure form I: when the low-frequency system only has a one-phase power supply system, the three-phase power frequency system also comprises a neutral line; one end of the phase voltage of the low-frequency system is connected with the low-frequency port of the AC-AC converter, and the other end of the phase voltage of the low-frequency system is connected with the neutral line of the three-phase power-frequency system, as shown in FIG. 4.
The structural form II is as follows: when the low-frequency system only has a two-phase power supply system, the AC-AC converter comprises at least 6 chain links, and every three chain links are divided into two groups; one end of each of the three chain links in the same group is respectively connected with the three-phase power frequency port, the other end of each of the three chain links is commonly connected with one phase of the low-frequency port, and the two groups of chain links are respectively connected with different phases of the low-frequency port; the two phases of voltages of the low frequency system are respectively connected with different phases of the low frequency port of the ac-ac converter, as shown in fig. 5,
the structural form is three: when the low-frequency system only has a three-phase power supply system, the AC-AC converter comprises at least 9 chain links, and each three chain links are divided into three groups; one end of each of three chain links in the same group is respectively connected with a three-phase power frequency port, the other ends of the three chain links are commonly connected with one phase of the low-frequency port, and the three groups of chain links are respectively connected with different phases of the low-frequency port; the three-phase voltages of the low-frequency system are respectively connected with different phases of the low-frequency port of the AC-AC converter, as shown in FIG. 6.
According to some embodiments, the low frequency transmission system with transformer isolation is provided, wherein the first isolation switch and the second isolation switch are both circuit breakers or switch groups consisting of circuit breakers and isolation switches.
According to some embodiments, the low frequency power transmission system with transformer isolation, wherein the resonant branch is a direct-connected conductor or a capacitor or an inductor or a branch consisting of a capacitor and an inductor.
According to some embodiments, the ac-dc conversion module is a full bridge circuit. A block diagram of a full bridge circuit is schematically shown in fig. 7. The circuit comprises a first semiconductor switch, a second semiconductor switch, a third semiconductor switch and a fourth semiconductor switch; the first semiconductor switch and the third semiconductor switch are connected in series; the second semiconductor switch and the fourth semiconductor switch are connected in series; the capacitor is connected in parallel with the two series branches; the connection point of the first semiconductor switch and the third semiconductor switch and the connection point of the second semiconductor switch and the fourth semiconductor switch form an alternating current port of the alternating current-direct current conversion module. Another block diagram of the full bridge circuit is schematically shown in fig. 8. The circuit comprises a first semiconductor switch, a second semiconductor switch, a first capacitor and a second capacitor; the first semiconductor switch and the second semiconductor switch are connected in series; the first capacitor and the second capacitor are connected in series to form a capacitor on the direct current side of the alternating current-direct current converter; and the connecting point of the first semiconductor switch and the second semiconductor switch and the connecting point of the first capacitor and the second capacitor form an alternating current port of the alternating current-direct current conversion module.
According to some embodiments, the ac-dc conversion module is a three-level circuit. A block diagram of a three-level circuit is schematically shown in fig. 9. The circuit comprises a first semiconductor switch, a second semiconductor switch, a third semiconductor switch, a fourth semiconductor switch, a first diode, a second diode, a first capacitor and a second capacitor; the first semiconductor switch, the second semiconductor, the third semiconductor switch and the fourth semiconductor switch are sequentially connected in series from top to bottom; the first capacitor and the second capacitor are connected in series to form a capacitor on the direct current side of the alternating current-direct current converter; the cathode of the first diode is connected with the connection point of the first semiconductor switch and the second semiconductor switch, and the anode of the first diode is connected with the connection point of the first capacitor and the second capacitor; the cathode of the second diode is connected with the connection point of the first capacitor and the second capacitor, and the anode of the second diode is connected with the connection point of the third semiconductor switch and the fourth semiconductor switch; and the connecting point of the second semiconductor switch and the third semiconductor switch and the connecting point of the first capacitor and the second capacitor form an alternating current port of the alternating current-direct current conversion module.
Fig. 10 is a flowchart illustrating system control when power flows from a three-phase power frequency system to a low frequency system according to the embodiment of the present application. A control method of a low-frequency power transmission system with transformer isolation comprises the following steps when the power flow direction is from a three-phase power frequency system to a low-frequency system:
s11: and closing the first isolation switch and the second isolation switch.
S12: and collecting voltage and current of the three-phase power frequency system.
S13: and collecting the voltage and current of the low-frequency system.
S14: and adjusting the power angle between the power frequency component voltage of the output voltage of each chain link of the AC-AC converter and the voltage of the three-phase power frequency system, and controlling the power of the three-phase power frequency system flowing into the AC-AC converter.
S15: and adjusting the power angle between the low-frequency component voltage of the output voltage of each chain link of the AC-AC converter and the voltage of the low-frequency system, controlling the power flowing out from the AC-AC converter to the low-frequency system, and ensuring that the power flowing into the AC-AC converter from the three-phase power frequency system is equal to the power flowing out from the AC-AC converter to the low-frequency system.
Fig. 11 is a flowchart illustrating system control when power flows from a low-frequency system to a three-phase power-frequency system according to the embodiment of the present application. The control method of the low-frequency power transmission system with the transformer isolation comprises the following steps when the power flow direction is from a low-frequency system to a three-phase power frequency system:
s21: and closing the first isolation switch and the second isolation switch.
S22: and collecting the voltage and current of the low-frequency system.
S23: and collecting voltage and current of the three-phase power frequency system.
S24: and adjusting the power angle between the low-frequency component voltage of the output voltage of each chain link of the AC-AC converter and the voltage of a low-frequency system, and controlling the power of the low-frequency system flowing into the AC-AC converter.
S25: adjusting the power frequency component voltage of the output voltage of each chain link of the AC-AC converter and the power angle of the voltage of the three-phase power frequency system, and controlling the power flowing out from the AC-AC converter to the three-phase power frequency system; and the power of the low-frequency system flowing into the AC-AC converter is ensured to be equal to the power of the AC-AC converter flowing out to the three-phase power frequency system.
Fig. 12 is a control flowchart of the reactive power compensation device for converting the ac-ac converter into the three-phase power frequency system according to the embodiment of the present application. The control method of the low-frequency power transmission system with the transformer isolation is characterized in that the system is equivalent to a reactive power compensation device of a three-phase power frequency system after the following steps are adopted:
s31: closing the first isolation switch and opening the second isolation switch;
s32: collecting voltage and current of a three-phase power frequency system;
s33: and starting the AC-AC converter, and controlling the reactive power of the three-phase power frequency system to be a set value based on the voltage and the current of the three-phase power frequency system.
Fig. 13 is a control flowchart of the conversion of the ac/ac converter into the reactive power compensation device of the low frequency system according to the embodiment of the present application. The control method of the low-frequency power transmission system with the transformer isolation is characterized in that the system is equivalent to reactive compensation equipment of the low-frequency system after the following steps are adopted:
s41: closing the second isolation switch and disconnecting the first isolation switch;
s42: collecting voltage and current of a low-frequency system;
s43: and starting the AC-AC converter, and controlling the reactive power of the low-frequency system to be a set value based on the voltage and the current of the low-frequency system.
The foregoing detailed description of the embodiments of the present application has been presented to illustrate the principles and implementations of the present application, and the description of the embodiments is only intended to facilitate the understanding of the methods and their core concepts of the present application. Meanwhile, a person skilled in the art should, according to the idea of the present application, change or modify the embodiments and applications of the present application based on the scope of the present application. In view of the above, the description should not be taken as limiting the application.
Claims (12)
1. A low frequency power transmission system with transformer isolation, comprising:
the three-phase power frequency system comprises a three-phase power supply system;
a low frequency system comprising at least one phase power supply system;
the AC-AC converter comprises a three-phase power frequency port and a low-frequency port, and the phase number of the low-frequency port is consistent with that of a low-frequency system;
the first isolation switch is used for connecting the three-phase power frequency system and a three-phase power frequency port of the AC-AC converter;
the second isolation switch is used for connecting the low-frequency system and the low-frequency port of the AC-AC converter;
the isolation transformer is positioned between the first isolation switch and the three-phase power frequency system or between the second isolation switch and the low-frequency system; when the isolation transformer is positioned between the first isolation switch and the three-phase power frequency system, the isolation transformer is a three-phase power frequency transformer; and when the isolation transformer is positioned between the second isolation switch and the low-frequency system, the isolation transformer is a low-frequency transformer.
2. A low frequency transmission system with transformer isolation according to claim 1 comprising at least two isolation transformers, one isolation transformer being located between the first isolation switch and the three phase power frequency system and another isolation transformer being located between the second isolation switch and the low frequency system.
3. A low frequency transmission system with transformer isolation according to claim 1, wherein the isolation transformer connects the ac-to-ac converter side with a smaller winding transformation ratio than the other side.
4. The low frequency power transmission system with transformer isolation of claim 1, wherein the ac-to-ac converter is a matrix converter comprising N chain links, N being a positive integer and an integer multiple of 3, each chain link comprising M ac-to-dc conversion modules and a resonant branch, each ac-to-dc conversion module comprising an ac port and a dc port, wherein the dc port is connected to a capacitor, and the M ac-to-dc conversion modules are connected in series via the ac ports and then connected in series to the resonant branch to form a chain link; every three chain links are divided into a group, one end of each chain link in the same group is connected with the three-phase power frequency port, and the other end of each chain link is connected with one phase of the low-frequency port.
5. A low frequency power transmission system with transformer isolation according to claim 1, wherein the low frequency system comprises at least three of the following configurations:
the structure form I: when the low-frequency system only has a one-phase power supply system, the three-phase power frequency system also comprises a neutral line; one end of phase voltage of the low-frequency system is connected with a low-frequency port of the AC-AC converter, and the other end of the phase voltage of the low-frequency system is connected with a neutral line of the three-phase power frequency system;
the structural form II is as follows: when the low-frequency system only has a two-phase power supply system, the AC-AC converter comprises at least 6 chain links, and every three chain links are divided into two groups; one end of each of the three chain links in the same group is respectively connected with the three-phase power frequency port, the other end of each of the three chain links is commonly connected with one phase of the low-frequency port, and the two groups of chain links are respectively connected with different phases of the low-frequency port; two phases of voltages of the low-frequency system are respectively connected with different phases of the low-frequency port of the AC-AC converter;
the structural form is three: when the low-frequency system only has a three-phase power supply system, the AC-AC converter comprises at least 9 chain links, and each three chain links are divided into three groups; one end of each of three chain links in the same group is respectively connected with a three-phase power frequency port, the other ends of the three chain links are commonly connected with one phase of the low-frequency port, and the three groups of chain links are respectively connected with different phases of the low-frequency port; and the three-phase voltage of the low-frequency system is respectively connected with different phases of the low-frequency port of the AC-AC converter.
6. The low frequency transmission system with transformer isolation of claim 1, wherein the first isolation switch and the second isolation switch are both circuit breakers or switch sets consisting of circuit breakers and disconnectors.
7. A low frequency power transmission system with transformer isolation according to claim 4, wherein said resonant branch is a direct conductor or a branch of a capacitor or an inductor or a branch of a capacitor and an inductor.
8. The low frequency power transmission system with transformer isolation of claim 4, wherein the AC-DC conversion module is a full bridge circuit or a three-level circuit.
9. The method for controlling the low-frequency power transmission system with the transformer isolation according to any one of claims 1 to 8, wherein when the power flows from the three-phase power frequency system to the low-frequency system, the following steps are adopted:
closing the first isolation switch and the second isolation switch;
collecting voltage and current of a three-phase power frequency system;
collecting voltage and current of a low-frequency system;
adjusting the power angle between the power frequency component voltage of the output voltage of each chain link of the AC-AC converter and the voltage of the three-phase power frequency system, and controlling the power of the three-phase power frequency system flowing into the AC-AC converter;
and adjusting the power angle between the low-frequency component voltage of the output voltage of each chain link of the AC-AC converter and the voltage of the low-frequency system, controlling the power flowing out from the AC-AC converter to the low-frequency system, and ensuring that the power flowing into the AC-AC converter from the three-phase power frequency system is equal to the power flowing out from the AC-AC converter to the low-frequency system.
10. The method for controlling the low-frequency power transmission system with the transformer isolation according to any one of claims 1 to 8, wherein when the power flows from the low-frequency system to the three-phase power frequency system, the following steps are adopted:
closing the first isolation switch and the second isolation switch;
collecting voltage and current of a low-frequency system;
collecting voltage and current of a three-phase power frequency system;
adjusting the power angle between the low-frequency component voltage of the output voltage of each chain link of the AC-AC converter and the voltage of a low-frequency system, and controlling the power of the low-frequency system flowing into the AC-AC converter;
adjusting the power frequency component voltage of the output voltage of each chain link of the AC-AC converter and the power angle of the voltage of the three-phase power frequency system, and controlling the power flowing out from the AC-AC converter to the three-phase power frequency system; and the power of the low-frequency system flowing into the AC-AC converter is ensured to be equal to the power of the AC-AC converter flowing out to the three-phase power frequency system.
11. The method for controlling the low-frequency power transmission system with the transformer isolation as claimed in any one of claims 1 to 8, wherein the system is equivalent to a reactive power compensation device of a three-phase power frequency system by adopting the following steps:
closing the first isolation switch and opening the second isolation switch;
collecting voltage and current of a three-phase power frequency system;
and starting the AC-AC converter, and controlling the reactive power of the three-phase power frequency system to be a set value based on the voltage and the current of the three-phase power frequency system.
12. The method for controlling a low-frequency power transmission system with transformer isolation according to any one of claims 1 to 8, wherein the system is equivalent to a reactive power compensation device of the low-frequency system by adopting the following steps:
closing the second isolation switch and disconnecting the first isolation switch;
collecting voltage and current of a low-frequency system;
and starting the AC-AC converter, and controlling the reactive power of the low-frequency system to be a set value based on the voltage and the current of the low-frequency system.
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| CN113381415A (en) * | 2021-07-13 | 2021-09-10 | 全球能源互联网研究院有限公司 | Low-frequency power transmission voltage regulation method and system and electronic equipment |
| CN113595075A (en) * | 2021-08-04 | 2021-11-02 | 全球能源互联网研究院有限公司 | Starting method and device of low-frequency power transmission system |
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