Step-down active area transformer

Abstract

The invention provides a step-down type active area transformer, and relates to the technical field of transformers. The step-down active area transformer comprises a distribution transformer, a capacitor and an AC / AC converter, and the AC / AC converter comprises two bridge arms and an inductor; wherein the two bridge arms are connected with a plurality of control ends and are suitable for being disconnected or connected under the control of control signals connected to the control ends, the change of the states of the bridge arms promotes the inductor to charge or discharge, energy is absorbed and released through the inductor, so that the voltage at the output end is smaller than the voltage at the secondary side of the distribution transformer; and a corresponding voltage value is provided for a device connected with the output end. The step-down active area transformer provided by the invention is a hybrid distribution transformer, the circuit structure of the transformer is simple, the control is easy to realize, a primary architecture is adopted, under the condition of realizing voltage treatment, the number of devices is reduced, and the cost is greatly reduced while the efficiency is improved and the size is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of transformers, and particularly to a step-down active substation transformer. Background Art

[0002] With the rapid economic development and the increasing access of new energy such as photovoltaic power, the problem of voltage over-limit in the distribution network (voltage higher than the specified voltage value and voltage lower than the specified voltage) is significant. The traditional use of a single distribution transformer to control the voltage over-limit problem has limitations such as slow operation speed, arc generation, low efficiency, large volume, low adjustment accuracy, and inability to smoothly adjust the voltage. Therefore, there is an urgent need for technological innovation to meet the development needs of the new power system.

[0003] The hybrid distribution transformer voltage regulation technology has emerged as a new type of voltage regulation solution, which has significant advantages such as fast response speed, diverse functions, and flexible voltage regulation methods. The hybrid distribution transformer integrates a power electronic voltage regulator with a distribution transformer, optimizing the traditional voltage regulation mode. Currently, its main technical principle is as Figure 1 shown. In the hybrid distribution transformer, the power electronic circuit uses a unified power quality conditioner (UPQC), which is composed of two three-phase full-bridge circuits, and is connected in series and parallel with the output terminal of the distribution transformer respectively. The parallel part (CV t ) can essentially be regarded as a three-phase fully controlled rectifier circuit, which is connected to the auxiliary windings (W 3a , W 3b , W 3c ) of the low-voltage auxiliary side of the distribution transformer. This connection method enables it to achieve key functions such as power factor control, harmonic suppression, and DC bus voltage control. The series part (CV p ) is connected in series with the high-voltage side of the distribution transformer through the power frequency voltage regulating transformer windings (W 5a , W 5b , W 5c ). By means of PWM modulation technology, the series voltage is precisely controlled to achieve flexible adjustment of the output voltage.

[0004] However, although the hybrid distribution transformer exhibits many advantages, the existing UPQC device (UPQC) in the hybrid distribution transformer adopts a two-stage structure design of rectification first and then inversion, resulting in low efficiency. Summary of the Invention

[0005] (1) Technical Problems to be Solved

[0006] Aiming at the deficiencies of the prior art, the present invention provides a step-down active substation transformer, which solves the problem of low efficiency of the existing hybrid distribution transformer.

[0007] (2) Technical Solutions

[0008] To achieve the above object, the present invention is realized through the following technical solutions:

[0009] In a first aspect, the present invention provides a step-down active substation transformer, including a distribution transformer, a capacitor, and an AC / AC converter. Among them, the AC / AC converter includes two bridge arms and an inductor; the primary side of the distribution transformer is connected to an AC source, the first connection end of the secondary side is connected to the first output end via a capacitor, the second connection end of the secondary side is connected to the second output end through a wire, and a connection port a is provided on the wire.

[0010] The first end of the first bridge arm of the AC / AC converter is connected to the common end of the capacitor and the secondary side of the distribution transformer, and the second end is connected to the connection port a via the second bridge arm.

[0011] The first end of the inductor is connected to the common end of the capacitor and the first output end, and the second end is connected to the common end of the first bridge arm and the second bridge arm.

[0012] The two bridge arms are connected with a number of control ends, and are adapted to be disconnected or conducted under the control of the control signals applied to the control ends. The change of the bridge arm state causes the inductor to charge or discharge. By absorbing and releasing energy through the inductor, the voltage at the output end is made less than the voltage at the secondary side of the distribution transformer, providing a suitable voltage value for the device connected to the output end.

[0013] Preferably, when reducing the voltage at the output end by absorbing energy through the inductor, the operating modes of the step-down active substation transformer include:

[0014] Operating mode 1: The first bridge arm is conducted, the second bridge arm is disconnected, and the current flow path is the secondary side of the transformer → the first bridge arm → the inductor → the device connected to the output end. At this time, the secondary side of the distribution transformer supplies power to the inductor and the device connected to the output end, and the inductor absorbs energy.

[0015] Preferably, when releasing energy through the inductor to supply power to the device connected to the output end, the operating modes of the step-down active substation transformer include:

[0016] Operating mode 2: The second bridge arm is conducted, the other first bridge arm is turned off, and the main current flow path is the inductor → the device connected to the output end → the second bridge arm, and the device connected to the output end is supplied power through the inductor.

[0017] Preferably, it further includes a bypass switch, and both ends of the bypass switch are respectively connected to both ends of the capacitor. When the voltage of the AC source is normal, the voltage at the secondary side of the distribution transformer is equal to the voltage required by the device connected to the output end. After closing the bypass switch and disconnecting the two bridge arms of the AC / AC converter, the AC / AC converter is removed.

[0018] Preferably, each of the two arms includes a connected anti-top switch group, and the two arms are controlled to be disconnected or connected by turning off or on the anti-top switch group.

[0019] Preferably, each of the two arms includes a double-control switch, and the double-control switch includes a first diode, a second diode, a third diode, a fourth diode, and a switch tube.

[0020] Wherein, the anode of the first diode is connected to the cathode of the second diode, and their common terminal serves as the first connection terminal of the arm.

[0021] The cathode of the first diode is connected to the cathode of the third diode, and their common terminal is connected to the first end of the switch tube.

[0022] Wherein, the anode of the third diode is connected to the cathode of the fourth diode, and their common terminal serves as the second connection terminal of the arm.

[0023] The anode of the fourth diode is connected to the anode of the second diode, and their common terminal is connected to the second end of the switch tube.

[0024] Preferably, the device connected to the output terminal includes a distribution network or a load.

[0025] In a second aspect, the present invention provides a step-down active substation transformer applied in a three-phase system, including three step-down active substation transformers as described above.

[0026] Wherein, the primary sides of the distribution transformers in the three step-down active substation transformers are connected to a three-phase AC power supply; the first connection terminal of the primary side of the distribution transformer of the first step-down active substation transformer and the second connection terminal of the primary side of the distribution transformer of the third step-down active substation transformer are connected together and commonly connected to phase A; the second connection terminal of the primary side of the distribution transformer of the first step-down active substation transformer and the first connection terminal of the primary side of the distribution transformer of the second step-down active substation transformer are connected together and commonly connected to phase B; the second connection terminal of the primary side of the distribution transformer of the second step-down active substation transformer and the first connection terminal of the primary side of the distribution transformer of the third step-down active substation transformer are connected together and commonly connected to phase C;

[0027] The second connection terminals of the secondary sides of the three distribution transformers are connected together.

[0028] In a third aspect, the present invention provides a step-down active substation transformer applied in a three-phase system, including three step-down active substation transformers.

[0029] Wherein, each step-down active substation transformer includes a distribution transformer, a capacitor, and an AC / AC converter, and the AC / AC converter includes two arms and an inductor.

[0030] Among them, the first connection end on the primary side of the distribution transformer of the first step-down active substation area transformer and the second connection end on the primary side of the distribution transformer of the third step-down active substation area transformer are connected together and jointly connected to phase A; the second connection end on the primary side of the distribution transformer of the first step-down active substation area transformer and the first connection end on the primary side of the distribution transformer of the second step-down active substation area transformer are connected together and jointly connected to phase B; the second connection end on the primary side of the distribution transformer of the second step-down active substation area transformer and the first connection end on the primary side of the distribution transformer of the third step-down active substation area transformer are connected together and jointly connected to phase C;

[0031] The first connection end of the secondary side of each distribution transformer is connected to the output end via a capacitor; and the second connection ends of the secondary sides of the three distribution transformers are connected together;

[0032] The first end of the first bridge arm of the AC / AC converter is connected to the common end of the capacitor and the secondary side of the distribution transformer, and the second end is connected to the second connection end of the secondary side of the distribution transformer via the second bridge arm;

[0033] The first end of the inductor is connected to the common end of the capacitor and the first output end, and the second end is connected to the common end of the first bridge arm and the second bridge arm;

[0034] Among them, the output ends of the three step-down active substation area transformers are respectively connected to the first end of the distribution network or the load, and the second ends of the distribution network or the load are connected together;

[0035] The two bridge arms are connected with a plurality of control ends and are adapted to be turned off or on under the control of the control signals accessed at the control ends. The change of the bridge arm state prompts the inductor to charge or discharge. By absorbing and releasing energy through the inductor, the output end voltage is made less than the voltage of the secondary side of the distribution transformer, so as to provide a compliant voltage value for the device connected to the output end.

[0036] Preferably, each of the two bridge arms includes a connected antipodal switch group, and the two bridge arms are turned off or on by the turn-off or turn-on of the antipodal switch group;

[0037] Or,

[0038] Each of the two bridge arms includes a double-control switch, and the double-control switch includes a first diode, a second diode, a third diode, a fourth diode and a switch tube,

[0039] Among them, the anode of the first diode is connected to the cathode of the second diode, and their common end serves as the first connection end of the bridge arm;

[0040] The cathode of the first diode is connected to the cathode of the third diode, and their common end is connected to the first end of the switch tube;

[0041] Among them, the anode of the third diode is connected to the cathode of the fourth diode, and their common terminal serves as the second connection terminal of the bridge arm.

[0042] The anode of the fourth diode is connected to the anode of the second diode, and their common terminal is connected to the second terminal of the switching transistor.

[0043] (III) Beneficial Effects

[0044] The present invention provides a step-down active distribution transformer area. Compared with the prior art, it has the following beneficial effects:

[0045] Compared with traditional equipment such as UPQC, the step-down active distribution transformer area proposed by the present invention is a hybrid distribution transformer. The circuit structure of this transformer is simple, and the control is easy to implement. It adopts a first-level architecture. While achieving voltage regulation, the number of devices is saved, and the cost is greatly reduced while improving efficiency and reducing volume. Description of the Drawings

[0046] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0047] Figure 1 is the circuit diagram of the existing hybrid distribution transformer;

[0048] Figure 2 is the architecture diagram of a step-down active distribution transformer area in Embodiment 1;

[0049] Figure 3 is Figure 2 the first specific circuit diagram of the architecture diagram of;

[0050] Figure 4 is Figure 3 the state diagram of the switching transistor when the circuit shown is in operating mode 1;

[0051] Figure 5 is Figure 3 the state diagram of the switching transistor when the circuit shown is in operating mode 2;

[0052] Figure 6 is Figure 2 the second specific circuit diagram of the architecture diagram of;

[0053] Figure 7 is the architecture diagram of a step-down active distribution transformer area in Embodiment 2;

[0054] Figure 8 It is the architecture diagram of applying the buck-type active substation area transformer in a three-phase system in Embodiment 3, and its connection mode is the star connection mode;

[0055] Figure 9 It is the architecture diagram of applying the buck-type active substation area transformer in a three-phase system in Embodiment 3, and its connection mode is the delta connection mode. Specific implementation manners

[0056] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0057] It should be noted that for the convenience of description, the switch IGBT is used as a representative of the controllable (on and off) switch tube in the embodiments of the present invention, but the switch tube in the present invention is not limited to IGBT. Taking IGBT as an example for illustration. The first end of the IGBT refers to the collector, the second end refers to the emitter, and the control end refers to the gate. A drive control signal is applied to the control end of each switch tube in the embodiments of the present invention. For the sake of simplicity, it will not be elaborated hereinafter. The power switch tube in the embodiments of the present invention can also be implemented by other controllable switch tube devices other than IGBT, such as MOSFET. At the same time, in order to ensure the normal operation of each switching device in the embodiments of the present invention, a freewheeling diode needs to be connected in parallel to each switching device. The parallel connection direction of the freewheeling diode is related to the type of the switching device, and those skilled in the art can set it according to the type of the switching device, which is not limited herein. If not specified, the switching device is default to include a freewheeling diode, and this embodiment will point it out in special cases.

[0058] By providing a buck-type active substation area transformer in the embodiments of the present application, the technical problem of low efficiency of some hybrid distribution transformers is solved. The AC / AC conversion is realized by using a single-stage energy conversion, replacing the mainstream AC / DC + DC / AC two-stage architecture, and achieving high efficiency and low cost.

[0059] The technical solutions in the embodiments of the present application to solve the above technical problems are generally as follows:

[0060] The hybrid distribution transformer integrates a power electronic voltage regulator and a distribution transformer, optimizing the traditional voltage regulation mode and having significant advantages such as fast response speed, diverse functions, and flexible voltage regulation methods. However, the UPQC device (UPQC) in the existing hybrid distribution transformer adopts a two-stage structure design of rectification first and then inversion, which inevitably brings a series of problems. From the control level, the two-stage structure makes the control logic intricate, greatly increasing the operation and maintenance difficulty and technical threshold of the system; during operation, the two-stage energy conversion leads to a reduction in the operating efficiency of the transformer; moreover, a large number of power electronic devices required by the two-stage structure significantly increase the volume of the equipment, not only occupying more installation space but also further increasing the equipment cost. In addition, the required power frequency voltage regulating transformer and DC bus capacitor in the existing hybrid distribution transformer are bulky, and an auxiliary winding needs to be added on the low-voltage side, changing the original structure of the distribution transformer, so the cost is still much higher than that of the traditional mechanical on-load voltage regulating distribution transformer. These defects seriously restrict the popularization and application of hybrid distribution transformers in a wider range of scenarios.

[0061] To solve the above problems, an embodiment of the present invention proposes a step-down active substation area transformer that combines a traditional on-load voltage regulating transformer and a power electronic transformer. It adopts a single-stage energy conversion to achieve AC / AC conversion, replacing the mainstream AC / DC + DC / AC two-stage architecture, realizing high efficiency and low cost. At the same time, there is a bridging capacitor in the topology of the step-down active substation area transformer of the embodiment of the present invention. Because the voltage of the capacitor cannot change suddenly, the modulation technology of high-frequency power switching tubes can be used to control the smooth change of the capacitor voltage. Finally, the voltage on the capacitor is superimposed on the input voltage, which can effectively ensure the smoothness of the AC output, and a standard AC voltage output is achieved by using control technology, and the waveform quality is good.

[0062] To better understand the above technical solutions, the above technical solutions will be described in detail below in conjunction with the accompanying drawings of the specification and specific implementation manners.

[0063] Embodiment 1:

[0064] This embodiment provides a step-down active substation area transformer, as Figure 2 shown, including a distribution transformer, a capacitor, and an AC / AC converter. Among them, the AC / AC converter includes two bridge arms and an inductor; the primary side of the distribution transformer is connected to an AC source, and the first connection end of the secondary side is connected to the first output terminal O 1 through a capacitor, and the second connection end of the secondary side is connected to the second output terminal O 2 (In the specific implementation process, the two output terminals are connected to the distribution network or the load. In Figure 2In the case where two output terminals are connected to both sides of the load, a connection port a is set on the wire; the first end of the first bridge arm of the AC / AC converter is connected to the common end of the capacitor and the secondary side of the distribution transformer, and the second end is connected to the connection port a via the second bridge arm; the first end of the inductor is connected to the common end of the capacitor and the first output terminal, and the second end is connected to the common end of the first bridge arm and the second bridge arm;

[0065] The two bridge arms are connected to a number of control terminals and are adapted to be turned off or on under the control of a control signal applied to the control terminals. The change in the state of the bridge arms causes the inductor to charge or discharge. By absorbing and releasing energy through the inductor, the voltage at the output terminal is made less than the voltage on the secondary side of the distribution transformer, providing a suitable voltage value for the device connected to the output terminal.

[0066] During the implementation process, when the voltage on the secondary side of the distribution transformer is greater than the voltage required by the power grid or the load, the circuit can operate to reduce the voltage at the output terminal and stabilize the output terminal voltage. The circuit has the following working modes:

[0067] Working mode 1: The first bridge arm is turned on and the second bridge arm is turned off. The current flow path is: secondary side of the transformer → first bridge arm → inductor → load. At this time, the secondary side of the distribution transformer supplies power to the inductor and the load, and the inductor absorbs energy.

[0068] Working mode 2: The second bridge arm is turned on and the first bridge arm is turned off. The current flow path is: inductor → load → second bridge arm, and the inductor supplies power to the load.

[0069] In the specific implementation process, the AC / AC converter includes two bridge arms, and each can adopt two opposite switching tubes, as Figure 3 shown. The first switching tube T 1 and the second switching tube T 2 form the first bridge arm, and the third switching tube T 3 and the fourth switching tube T 4 form the second bridge arm. The AC / AC converter has a total of three working modes. The states of the switching tubes in each mode are as Figure 4 、 5 shown.

[0070] Working mode 1: As Figure 4 shown, the switching tubes T 1 , T 2 are turned on, and the other switching tubes are turned off. The main current flow path is: secondary side of the transformer → T 1 → T 2 → L → load. At this time, the secondary side of the transformer supplies power to the load and charges the inductor.

[0071] Working mode 2: As Figure 5 shown, the switching tubes T 3 , T4 conducts, other switching tubes are turned off, and the main current flow path is L → load → T 4 → T 3 , and the load is powered by the inductor.

[0072] It should be noted that in this circuit, the capacitor does not transfer the main power but only the harmonic power. Therefore, the main power current does not pass through the capacitor. The main power current in both modes passes through the inductor, but in one mode the inductor is charging and in the other mode the inductor is discharging.

[0073] In the specific implementation process, the bridge arm included in the AC / AC converter can also adopt a dual-control switch composed of four diodes and one switching tube, as Figure 6 shown. It should be noted that when constructing the two bridge arms of the AC / AC converter, it is not limited to the above two specific switching component designs. Multiple other switches can also be used to achieve the conduction and cut-off of the bridge arms, as long as these switches meet the following requirements: when the switch is in the off state, during the negative half-cycle of the AC source connected to the primary side of the distribution transformer, the phenomenon of direct connection of the bridge arm must be avoided. At the same time, multiple switches can also be mixed and combined, such as using an opposite-switch group for the first bridge arm and a dual-control switch composed of four diodes and one switching tube for the second bridge arm.

[0074] Figure 6 The circuit operation mode shown in Figure 3 is the same as that of the circuit shown, and will not be elaborated here.

[0075] Embodiment 2:

[0076] This embodiment provides a buck-type active distribution transformer, as Figure 7 shown. On the basis of the circuit shown in Figure 2 , a bypass switch is added. When the voltage of the AC source (power grid) is normal, the voltage on the secondary side of the distribution transformer is equal to the voltage required by the device (distribution network or load) connected to the output terminal. Then, it is not necessary for the AC / AC converter to boost the voltage at the output terminal, and this AC / AC converter needs to be removed to avoid unnecessary losses. Therefore, a bypass switch needs to be connected in parallel to the capacitor on the basis of the above circuit.

[0077] After closing the bypass switch, all the two bridge arms of the AC / AC converter are turned off, and the AC / AC converter can be removed from the grid side.

[0078] The circuit form of the AC / AC converter in this embodiment is the same as that in Embodiment 1, and will not be elaborated here.

[0079] Embodiment 3:

[0080] In this embodiment, the step-down active substation transformer in Embodiment 1 or Embodiment 2 can be applied to a three-phase system, and its connection methods include a star connection method and a delta connection method. For the star connection method, as shown in Figure 8 , the primary sides of the distribution transformers in the three step-down active substation transformers are connected to a three-phase AC power supply. Among them, the first connection end of the primary side of the distribution transformer of the first step-down active substation transformer and the second connection end of the primary side of the distribution transformer of the third step-down active substation transformer are connected together and commonly connected to phase A; the second connection end of the primary side of the distribution transformer of the first step-down active substation transformer and the first connection end of the primary side of the distribution transformer of the second step-down active substation transformer are connected together and commonly connected to phase B; the second connection end of the primary side of the distribution transformer of the second step-down active substation transformer and the first connection end of the primary side of the distribution transformer of the third step-down active substation transformer are connected together and commonly connected to phase C. The second connection ends of the secondary sides of the three distribution transformers are connected together, and the connection methods of the other devices in the circuit topology of the step-down active substation transformer are the same as those in Embodiment 1 and will not be elaborated here.

[0081] For the delta connection method, as shown in Figure 9 , the primary sides of the distribution transformers in the three step-down active substation transformers are connected to a three-phase AC power supply. Among them, the first connection end of the primary side of the distribution transformer of the first step-down active substation transformer and the second connection end of the primary side of the distribution transformer of the third step-down active substation transformer are connected together and commonly connected to phase A; the second connection end of the primary side of the distribution transformer of the first step-down active substation transformer and the first connection end of the primary side of the distribution transformer of the second step-down active substation transformer are connected together and commonly connected to phase B; the second connection end of the primary side of the distribution transformer of the second step-down active substation transformer and the first connection end of the primary side of the distribution transformer of the third step-down active substation transformer are connected together and commonly connected to phase C. The second connection ends of the secondary sides of the three distribution transformers are connected together. The connection methods of the two output ends of the three step-down active substation transformers to the load or the power grid are different from those of the step-down active substation transformer connected to the load or the power grid in a single-phase circuit. In the delta connection method, the first output ends of the step-down active substation transformers are respectively connected to the load or the power grid and then connected together. After the wires led out from the second connection ends of the secondary sides of the three distribution transformers are connected to the second bridge arm, no wires are led out as the second output end.

[0082] It should be noted that, for the purpose of drawing, the AC / AC converters in the step-down active substation transformers in Figure 8 and Figure 9 adopt a simplified drawing method.

[0083] In summary, compared with the prior art, the following beneficial effects are achieved:

[0084] 1. Compared with traditional equipment such as UPQC, the step-down active substation area transformer proposed in the embodiment of the present invention is a hybrid distribution transformer. The circuit structure of this transformer is simple, and the control is easy to implement. It adopts a first-level architecture. While achieving voltage governance, the number of components is saved, and the cost is greatly reduced while improving efficiency and reducing volume.

[0085] 2. There is a bridging capacitor (i.e., capacitor C) in the topology of the step-down active substation area transformer in the embodiment of the present invention. Since the voltage of the capacitor cannot change suddenly, the modulation technology of the high-frequency power switch tube can be used to control the smooth change of the capacitor voltage. Finally, the voltage on the capacitor is superimposed on the input voltage, which can effectively ensure the smoothness of the AC output. The control technology is used to achieve the standard AC voltage output, and the waveform quality is good.

[0086] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including a..." does not exclude the existence of additional identical elements in the process, method, article or device including the said element.

[0087] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A step-down active transformer, characterized in that: The invention comprises a distribution transformer, a capacitor and an AC / AC converter, wherein the AC / AC converter comprises two bridge arms and an inductor; the primary side of the distribution transformer is connected to an AC source, the first connection end of the secondary side is connected to a first output end via a capacitor, the second connection end of the secondary side is connected to a second output end via a wire, and a connection port a is provided on the wire; A first end of the first bridge arm of the AC / AC converter is connected to a common end of the capacitor and the secondary side of the distribution transformer, and a second end is connected to the connection port a via the second bridge arm; The first end of the inductor is connected to the common end of the capacitor and the first output end, and the second end of the inductor is connected to the common end of the first bridge arm and the second bridge arm; The two bridge arms are connected to a number of control terminals, and are suitable for disconnecting or connecting the two bridge arms under the control of the control signal connected to the control terminal. The change of the bridge arm state prompts the inductor to charge or discharge, and the inductor absorbs and releases energy, so that the output terminal voltage is less than the secondary side voltage of the distribution transformer, providing a suitable voltage value for the device connected to the output terminal.

2. The step-down active transformer according to claim 1, characterized in that: When the voltage at the output is reduced by absorbing energy through inductance, the operating modes of the step-down active transformer include: Working mode 1: The first bridge arm is turned on and the second bridge arm is turned off. The current flow path is the secondary side of the transformer → the first bridge arm → the inductor → the device connected to the output end. At this time, the secondary side of the distribution transformer supplies power to the inductor and the device connected to the output end, and the inductor absorbs energy.

3. The step-down active transformer according to claim 1, characterized in that: When releasing energy through inductance to power the connected devices at the output end, the working modes of the step-down active transformer include: Working mode 2: The second bridge arm is turned on, and the other first bridge arms are turned off. The main current flow path is inductor → device connected to the output end → second bridge arm, and the device connected to the output end is powered through the inductor.

4. The step-down active transformer according to any one of claims 1 to 3, characterized in that: It also includes a bypass switch, the two ends of which are respectively connected to the two ends of the capacitor. When the AC source voltage is normal, the voltage on the secondary side of the distribution transformer is equal to the voltage required by the device connected to the output end. After the bypass switch is closed, the two bridge arms of the AC / AC converter are disconnected, and the AC / AC converter is cut off.

5. The step-down active transformer according to any one of claims 1 to 3, characterized in that: The two bridge arms each include a top switch group connected thereto, and the two bridge arms are controlled to be disconnected or turned on by turning off or on the top switch group.

6. The step-down active transformer according to any one of claims 1 to 3, characterized in that: The two bridge arms each include a double-control switch, and the double-control switch includes a first diode, a second diode, a third diode, a fourth diode and a switch tube. Wherein, the anode of the first diode is connected to the cathode of the second diode, and the common end thereof serves as the first connection end of the bridge arm; The cathode of the first diode is connected to the cathode of the third diode, and the common end thereof is connected to the first end of the switch tube; The anode of the third diode is connected to the cathode of the fourth diode, and the common end thereof serves as the second connection end of the bridge arm; The anode of the fourth diode is connected to the anode of the second diode, and the common end thereof is connected to the second end of the switch tube.

7. The step-down active transformer according to any one of claims 1 to 3, characterized in that: The device connected to the output end includes a power distribution network or a load.

8. A step-down active transformer for use in a three-phase system, characterized in that: It comprises three step-down active station transformers as claimed in any one of claims 1 to 7; Among them, the primary side of the distribution transformer in the three step-down active substation transformers is connected to a three-phase AC power supply; the first connection end of the primary side of the distribution transformer of the first step-down active substation transformer and the second connection end of the primary side of the distribution transformer of the third step-down active substation transformer are connected together and are commonly connected to phase A; the second connection end of the primary side of the distribution transformer of the first step-down active substation transformer and the first connection end of the primary side of the distribution transformer of the second step-down active substation transformer are connected together and are commonly connected to phase B; the second connection end of the primary side of the distribution transformer of the second step-down active substation transformer and the first connection end of the primary side of the distribution transformer of the third step-down active substation transformer are connected together and are commonly connected to phase C; The second connection ends on the secondary sides of the three distribution transformers are connected together.

9. A step-down active transformer for use in a three-phase system, characterized in that: It includes three step-down active station area transformers; Wherein, each step-down active area transformer includes a distribution transformer, a capacitor and an AC / AC converter, and the AC / AC converter includes two bridge arms and an inductor; Among them, the first connection end of the primary side of the distribution transformer of the first step-down active substation transformer and the second connection end of the primary side of the distribution transformer of the third step-down active substation transformer are connected together and are commonly connected to phase A; the second connection end of the primary side of the distribution transformer of the first step-down active substation transformer and the first connection end of the primary side of the distribution transformer of the second step-down active substation transformer are connected together and are commonly connected to phase B; the second connection end of the primary side of the distribution transformer of the second step-down active substation transformer and the first connection end of the primary side of the distribution transformer of the third step-down active substation transformer are connected together and are commonly connected to phase C; The first connection terminal of the secondary side of each distribution transformer is connected to the output terminal via a capacitor; and the second connection terminals of the secondary sides of the three distribution transformers are connected together; A first end of the first bridge arm of the AC / AC converter is connected to a common end of the capacitor and the secondary side of the distribution transformer, and a second end is connected to a second connection end on the secondary side of the distribution transformer via a second bridge arm; The first end of the inductor is connected to the common end of the capacitor and the first output end, and the second end of the inductor is connected to the common end of the first bridge arm and the second bridge arm; The output ends of the three step-down active transformers are respectively connected to the first ends of the distribution network or the load, and the second ends of the distribution network or the load are connected together; The two bridge arms are connected to a number of control terminals, and are suitable for disconnecting or connecting the two bridge arms under the control of the control signal connected to the control terminal. The change of the bridge arm state prompts the inductor to charge or discharge, and the inductor absorbs and releases energy, so that the output terminal voltage is less than the secondary side voltage of the distribution transformer, providing a suitable voltage value for the device connected to the output terminal.

10. The step-down active transformer for use in a three-phase system as claimed in claim 9, characterized in that: The two bridge arms each include a top switch group connected thereto, and the two bridge arms are controlled to be disconnected or turned on by turning off or on the top switch group; or, The two bridge arms each include a double-control switch, and the double-control switch includes a first diode, a second diode, a third diode, a fourth diode and a switch tube. Wherein, the anode of the first diode is connected to the cathode of the second diode, and the common end thereof serves as the first connection end of the bridge arm; The cathode of the first diode is connected to the cathode of the third diode, and the common end thereof is connected to the first end of the switch tube; The anode of the third diode is connected to the cathode of the fourth diode, and the common end thereof serves as the second connection end of the bridge arm; The anode of the fourth diode is connected to the anode of the second diode, and the common end thereof is connected to the second end of the switch tube.

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