Three-phase current source type flexible power transmission unit

Abstract

The utility model belongs to the technical field of converters, and particularly discloses a three-phase current source type flexible power transmission unit. According to the application, the isolation transformer is used at one end to ensure that the whole circuit structure is in an electrically isolated state, and the self-coupling transformer is used at the other end, so that under the same rated capacity, the main size of the self-coupling transformer is relatively small, effective materials and structural materials are reduced, and copper loss and iron loss of the transformer are correspondingly reduced. Therefore, under the same load power, the volume, weight, cost and loss of the whole device can be obviously reduced by using the self-coupling transformer. According to the converter, alternating-current electric energy can be transmitted to the alternating-current bus on the other side by the alternating-current bus on any side to be scheduled at will, switching through any electrical switch is not needed, and therefore mutual flexible scheduling of the alternating-current electric energy can be achieved through the converter in flexible interconnection between different medium-voltage buses.

Description

Technical Field

[0001] The present application belongs to the technical field of converters, and more specifically, relates to a three-phase current source type flexible power transmission unit. Background Art

[0002] Flexible power transmission units (FPTUs) are key devices that convert power signals from one power grid to another. In modern energy systems, FPTUs play a vital role, enabling power conversion between different voltages and frequencies. Three-phase FPTUs, the most common type, possess unique characteristics and applications.

[0003] The three-phase flexible power transmission unit consists of two power electronic converters: a main converter and an auxiliary converter. The main converter converts the AC power from one grid into an intermediate DC power source, while the auxiliary converter converts the intermediate DC power back into AC power for the other grid, enabling power signals to be transmitted between the two grids.

[0004] However, traditional three-phase flexible power transmission units are connected to two power grids through isolation transformers at both ends. This has the problems of large space occupation, high cost, and high transformer losses. Especially in medium and high voltage scenarios, the insulation requirements for the isolation transformer are very high. The isolation transformer is usually large in size and weight, which increases the cost and difficulty of system design. In addition, the isolation transformer's own losses also increase with the increase of voltage level, reducing system efficiency. Utility Model Content

[0005] In response to the defects of the existing technology, the purpose of this application is to provide a three-phase current source type flexible power transmission unit, which aims to solve the problems of large space occupation and transformer self-loss of traditional three-phase flexible power transmission units in medium and high voltage application scenarios.

[0006] To achieve the above object, the present application provides a three-phase current source type flexible power transmission unit, comprising: an isolation transformer, an autotransformer, a first three-phase bridge circuit, a second three-phase bridge circuit and a smoothing reactor;

[0007] The primary side of the isolation transformer is connected to an AC bus, and the secondary side is connected to the AC end of the first three-phase bridge circuit;

[0008] The primary side of the autotransformer is connected to another AC bus, and the secondary side is connected to the AC end of the second three-phase bridge circuit;

[0009] The first three-phase bridge circuit and the second three-phase bridge circuit are symmetrical in structure, and the positive and negative poles on the DC side are connected end to end through a smoothing reactor.

[0010] Preferably, the first and second three-phase bridge circuits are three-phase fully-controlled bridge six-pulse rectification / inversion circuits.

[0011] Preferably, the first three-phase bridge circuit and the second three-phase bridge circuit have the same structure.

[0012] Preferably, the first three-phase bridge circuit and the second three-phase bridge circuit have different structures.

[0013] Preferably, the three-phase current source type flexible power transmission unit supports transmitting AC power from the AC bus on either side to the AC bus on the other side.

[0014] Preferably, the isolation transformer and the autotransformer have the same or different voltage amplitudes at their input ends, and the same voltage amplitudes at their output ends.

[0015] Preferably, the isolation transformer and the autotransformer are connected to the AC bus at the same or different frequencies.

[0016] Preferably, the three-phase current source type flexible power transmission unit is applied to a medium or high voltage power distribution system.

[0017] In general, the above technical solutions conceived by this application have the following beneficial effects compared with the existing technologies:

[0018] The present application proposes a three-phase current source type flexible power transmission unit, in which an isolation transformer is used at one end to ensure that the entire circuit structure is in an electrically isolated state, and an autotransformer is used at the other end. Under the same rated capacity, the main size of the autotransformer is smaller, the effective material and structural material are reduced, and the copper loss and iron loss of the transformer are also reduced accordingly. Therefore, under the same load power, the use of an autotransformer can significantly reduce the volume, weight, cost and loss of the entire device. The flexible power transmission unit can transmit AC power from the AC bus on either side to the AC bus on the other side without the need for switching through any electrical switch, so that the converter can realize the mutual and flexible scheduling of AC power in the flexible interconnection between different medium voltage buses. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a structural schematic diagram of a three-phase current source type back-to-back flexible power transmission unit provided in an embodiment of the present application.

[0020] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0021] 1-Medium-voltage busbar at end I, 2-Medium-voltage busbar at end II, 3-Isolation transformer, 4-Autotransformer, 5-First three-phase bridge circuit, 6-Second three-phase bridge circuit, 7-Smoothing reactor. DETAILED DESCRIPTION

[0022] For ease of understanding, the English abbreviations and related technical terms involved in the embodiments of this application are explained and described below.

[0023] Autotransformer: A transformer with a common winding on the primary and secondary sides is called an autotransformer.

[0024] The embodiments of the present application are described below in conjunction with the drawings in the embodiments of the present application.

[0025] like Figure 1 As shown, the present application provides a three-phase current source type flexible power transmission unit, including: an isolation transformer 3, an autotransformer 4, a first three-phase bridge circuit 5, a second three-phase bridge circuit 6 and a smoothing reactor 7. The primary side of the isolation transformer 3 is connected to the medium-voltage bus 1 at end I, and the secondary side is connected to the AC end of the bridge arm of the first three-phase bridge circuit 5. The primary side of the autotransformer 4 is connected to the medium-voltage bus 2 at end II, and the secondary side is connected to the AC end of the bridge arm of the second three-phase bridge circuit 6. The first three-phase bridge circuit 5 and the second three-phase bridge circuit 6 are symmetrical in structure, and the positive and negative poles on the DC side are connected end to end through the smoothing reactor 7, that is, a flexible interconnection between different busbars is formed.

[0026] The three-phase current source type flexible power transmission unit can be used between two different medium voltage busbars to form mutual support and call of energy between different medium voltage busbars.

[0027] Preferably, the first and second three-phase bridge circuits are three-phase bridge six-pulse rectifier / inverter circuits. The six-pulse rectifier circuit is composed of six thyristors, each of which is connected to a phase and triggered to conduct in a certain order, and the DC output is connected to a smoothing inductor. Thyristors can withstand high voltages and high currents and are suitable for high-power power conversion scenarios. Thyristors have a fast switching speed and can complete the on and off operations in a short time, thereby quickly responding to changes in the input signal, which is conducive to application in flexible interconnection scenarios.

[0028] Preferably, the first three-phase bridge circuit 5 and the second three-phase bridge circuit 6 have the same or different structures.

[0029] The smoothing reactor 7 primarily stores energy and smoothes the DC voltage in the DC link. Using a smoothing reactor on the DC side allows it to withstand a certain degree of overcurrent and overvoltage during operation, reducing the probability of failures caused by external interference. During the rectification process, the DC voltage still has some ripple, which the reactor smooths. During load changes or system switching, the DC reactor acts as an energy buffer, absorbing or releasing energy to help maintain system stability.

[0030] The three-phase current-source flexible power transmission unit operates as follows: Under control commands from the control module, the three-phase current-source back-to-back power conversion unit can transfer AC power from either side of the AC bus to the other side in any scheduling manner, without the need for any electrical switches. Active power transmission can only be regulated in a single-phase manner, from left to right or right to left, to avoid circulating current.

[0031] Next, the dispatching of AC power from left to right will be explained.

[0032] The first three-phase bridge circuit 5 is a rectifier bridge. Its AC side is connected to the medium-voltage busbar via the isolation transformer 3, and its DC side is connected to a smoothing reactor. The rectifier section first determines the magnitude of the DC voltage output by the rectifier bridge. It then obtains a synchronization signal from the AC power grid to determine the starting point of each cycle and the triggering time of each thyristor. Finally, based on the trigger angle calculated based on the DC voltage magnitude and system status, it generates the corresponding trigger pulses and sends them to the thyristors at the correct time to control their conduction and shutdown.

[0033] The second three-phase bridge circuit 6 is an inverter bridge. Its AC side is connected to the medium-voltage busbar via the autotransformer 4, and its DC side is connected to a smoothing reactor. The inverter section first needs to determine the amplitude, frequency, and phase of the inverter bridge's output voltage. It then obtains a synchronization signal from the AC grid to determine the phase and frequency of the inverter bridge's output AC power. Finally, based on the required output AC voltage and the trigger angle calculated from the system state, it generates the corresponding trigger pulses and sends them to the thyristors at the correct time to control their conduction and shutdown.

[0034] The rectifier bridge and the inverter bridge are connected via a smoothing reactor 7. Using a smoothing reactor on the DC side can reduce the DC voltage ripple and make the DC voltage more stable.

[0035] Preferably, the voltage amplitudes at the input terminals of the isolation transformer and the autotransformer can be the same or different, and the voltage amplitudes at the output terminals are the same. The isolation transformer and the autotransformer can be connected to medium voltage buses of the same or different voltage levels, and the voltages at the output terminals of the transformers must be the same.

[0036] Preferably, the isolation transformer and the autotransformer can be connected to the same or different AC bus frequencies. The isolation transformer and the autotransformer can be connected to medium voltage buses of the same or different frequencies.

[0037] It should be understood that expressions such as "include" and "may include" used in this application indicate the existence of the disclosed functions, operations, or constituent elements, and do not limit one or more additional functions, operations, and constituent elements. In this application, terms such as "include" and / or "have" may be interpreted as indicating specific characteristics, numbers, operations, constituent elements, components, or combinations thereof, but may not be interpreted as excluding the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components, or combinations thereof.

[0038] In addition, in this application, the expression "and / or" includes any and all combinations of the associated listed words. For example, the expression "A and / or B" may include A, may include B, or may include both A and B.

[0039] In the description of the embodiments of the present application, it should be noted that, unless otherwise clearly specified and limited, the term "connection" should be understood in a broad sense. For example, "connection" can be a detachable connection or a non-detachable connection; it can be a direct connection or an indirect connection through an intermediate medium. Among them, "fixed connection" means that the two are connected to each other and the relative position relationship after the connection remains unchanged. "Rotational connection" means that the two are connected to each other and can rotate relative to each other after the connection. "Sliding connection" means that the two are connected to each other and can slide relative to each other after the connection. The directional terms mentioned in the embodiments of the present application, such as "top", "bottom", "inside", "outside", "left", "right", etc., are only reference to the directions of the accompanying drawings. Therefore, the directional terms used are for better and clearer explanation and understanding of the embodiments of the present application, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0040] In addition, in the embodiments of the present application, the mathematical concepts mentioned include symmetry, equality, parallelism, and perpendicularity. These limitations are all for the current state of the art, rather than being absolutely strict definitions in a mathematical sense. A small amount of deviation is allowed, and it is possible to be approximately symmetric, approximately equal, approximately parallel, or approximately perpendicular. For example, A and B are parallel, which means that A and B are parallel or approximately parallel, and the angle between A and B can be between 0 and 10 degrees. A and B are perpendicular, which means that A and B are perpendicular or approximately perpendicular, and the angle between A and B can be between 80 and 100 degrees.

[0041] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A three-phase current source type flexible power transmission unit, characterized in that: include: Isolation transformer, autotransformer, first three-phase bridge circuit, second three-phase bridge circuit and smoothing reactor; The primary side of the isolation transformer is connected to an AC bus, and the secondary side is connected to the AC end of the bridge arm of the first three-phase bridge circuit; The primary side of the autotransformer is connected to another AC bus, and the secondary side is connected to the AC end of the bridge arm of the second three-phase bridge circuit; The first three-phase bridge circuit and the second three-phase bridge circuit are symmetrical in structure, and the positive and negative poles on the DC side are connected end to end through a smoothing reactor.

2. The three-phase current source type flexible power transmission unit according to claim 1, characterized in that: The first and second three-phase bridge circuits are three-phase bridge six-pulse rectification / inversion circuits.

3. The three-phase current source type flexible power transmission unit according to claim 1, characterized in that: The first three-phase bridge circuit and the second three-phase bridge circuit have the same structure.

4. The three-phase current source type flexible power transmission unit according to claim 1, characterized in that: The first three-phase bridge circuit and the second three-phase bridge circuit have different structures.

5. The three-phase current source type flexible power transmission unit according to claim 1, characterized in that: The three-phase current source type flexible power transmission unit supports transmitting AC power from the AC bus on either side to the AC bus on the other side.

6. The three-phase current source type flexible power transmission unit according to claim 1, characterized in that: The voltage amplitudes at the input ends of the isolation transformer and the autotransformer are the same or different, and the voltage amplitudes at the output ends are the same.

7. The three-phase current source type flexible power transmission unit according to claim 1, characterized in that: The isolation transformer and the autotransformer are connected to the AC bus with the same or different frequencies.

8. The three-phase current source type flexible power transmission unit according to any one of claims 1 to 7, characterized in that: The three-phase current source type flexible power transmission unit is applied to medium and high voltage power distribution systems.

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