Buck-boost active area transformer

Abstract

The invention provides a buck-boost active area transformer, and relates to the technical field of transformers. The buck-boost active area transformer comprises a distribution transformer, a capacitor and an AC / AC converter, and the AC / AC converter comprises four bridge arms and an inductor. The four bridge arms are connected with a plurality of control ends and are suitable for being switched off or switched on under the control of control signals accessed by the control ends, and the change of the states of the bridge arms promotes the capacitor and the inductor to charge or discharge, so that when the voltage of the secondary side of the distribution transformer is greater than the voltage required by a device connected with the output end, the capacitor and the inductor can be switched off. When the voltage of the secondary side is lower than the voltage required by a device connected with the output end, the AC / AC converter reduces the voltage of the output end, and when the voltage of the secondary side is lower than the voltage required by the device connected with the output end, the AC / AC converter boosts the voltage of the output end. The buck-boost active area transformer provided by the invention adopts a primary framework, so that 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-up / step-down active substation transformer. Background Art

[0002] With the rapid economic development and the increasing access of new energy sources 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) has become prominent. The traditional method of using 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 voltage regulation solution, which has significant advantages such as fast response speed, diverse functions, and flexible voltage regulation methods. The hybrid distribution transformer integrates the power electronic voltage regulator with the 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 and is connected to the low-voltage auxiliary winding (W 3a , W 3b , W 3c ) 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 regulation transformer windings (W 5a , W 5b , W 5c ). By means of PWM modulation technology, the series voltage is accurately 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-up / 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 implemented through the following technical solutions:

[0009] In a first aspect, the present invention provides a buck-boost active substation area transformer, including a distribution transformer, a capacitor, and an AC / AC converter. The AC / AC converter includes four bridge arms and an inductor;

[0010] Among them, 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 two connection ports a and b are provided on the wire;

[0011] The first end of the first bridge arm of the AC / AC converter is connected to the common end of the transformer and the capacitor. The second end is connected to the connection port a via the second bridge arm. The first end of the third bridge arm of the AC / AC converter is connected to the common end of the capacitor and the first output end. The second end is connected to the connection port b via the fourth bridge arm; The first end of the inductor is connected to the common end of the first bridge arm and the second bridge arm, and the second end is connected to the common end of the third bridge arm and the fourth bridge arm;

[0012] The four bridge arms are connected to a number of control terminals, and are adapted to be disconnected or conducted under the control of a control signal applied to the control terminals. The change of the bridge arm state causes the capacitor and the inductor to be charged or discharged, so that when the voltage on the secondary side of the distribution transformer is greater than the voltage required by the device connected to the output end, the AC / AC converter steps down the voltage at the output end. When the voltage on the secondary side is lower than the voltage required by the device connected to the output end, the AC / AC converter steps up the voltage at the output end.

[0013] Preferably, when the voltage on the secondary side of the distribution transformer is higher than the voltage required by the device connected to the output end, the buck-boost active substation area transformer switches between working mode 1 and working mode 2 to step down the voltage at the output end:

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

[0015] Working mode 2: The second and third bridge arms are conducted, and the first and fourth bridge arms are disconnected. The current flow path is the second bridge arm → the inductor → the third bridge arm → the device connected to the output end, and the device connected to the output end is supplied with power through the inductor.

[0016] Preferably, when the voltage on the secondary side of the distribution transformer is less than the voltage required by the device connected to the output terminal, the step-up / step-down active substation area transformer switches between operating mode 3 and operating mode 4 to boost the voltage at the output terminal:

[0017] Operating mode 3: The first and fourth bridge arms are conducting, and the second and third bridge arms are off. The current flow path is the secondary side of the distribution transformer → the first bridge arm → the inductor → the fourth bridge arm and the secondary side of the distribution transformer → the capacitor → the device connected to the output terminal. At this time, the power grid charges and stores energy in the inductor, and the secondary side of the distribution transformer and the capacitor supply power to the device connected to the output terminal;

[0018] Operating mode 4: The first and third bridge arms are conducting, and the second and fourth bridge arms are off. The current flow path is the secondary side of the distribution transformer → the first bridge arm → the inductor → the third bridge arm → the device connected to the output terminal and the inductor → the third bridge arm → the capacitor → the first bridge arm. At this time, the secondary side of the distribution transformer and the inductor supply power to the device connected to the output terminal simultaneously, and the capacitor absorbs energy.

[0019] Preferably, it further includes a bypass switch. The two ends of the bypass switch 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 terminal. After closing the bypass switch and disconnecting the four bridge arms of the AC / AC converter, the AC / AC converter is removed.

[0020] Preferably, each of the four bridge arms includes a pair of opposing switch groups, and the four bridge arms are controlled to be off or on by the turning off or on of the pair of opposing switch groups.

[0021] Preferably, each of the four bridge arms includes a double-control switch. The double-control switch includes a first diode, a second diode, a third diode, a fourth diode, and a switch tube.

[0022] Among them, the anode of the first diode is connected to the cathode of the second diode, and their common terminal serves as the first connection end of the bridge arm;

[0023] 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;

[0024] 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 end of the bridge arm;

[0025] 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.

[0026] Preferably, the device connected to the output terminal includes a power distribution network or a load.

[0027] Second aspect, the present invention provides a step-up / step-down active substation transformer applied in a three-phase system, characterized by including three step-up / step-down active substation transformers as described above;

[0028] Among them, the primary sides of the distribution transformers in the three step-up / step-down active substation transformers are connected to a three-phase AC power supply; the first connection end of the primary side of the distribution transformer of the first step-up / step-down active substation transformer and the second connection end of the primary side of the distribution transformer of the third step-up / 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-up / step-down active substation transformer and the first connection end of the primary side of the distribution transformer of the second step-up / 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-up / step-down active substation transformer and the first connection end of the primary side of the distribution transformer of the third step-up / step-down active substation transformer are connected together and commonly connected to phase C;

[0029] The second connection ends of the secondary sides of the three distribution transformers are connected together.

[0030] Third aspect, the present invention provides a step-up / step-down active substation transformer applied in a three-phase system, including three step-up / step-down active substation transformers;

[0031] Among them, each step-up / step-down active substation transformer includes a distribution transformer, a capacitor, and an AC / AC converter, and the AC / AC converter includes four bridge arms and an inductor;

[0032] Among them, the first connection end of the primary side of the distribution transformer of the first step-up / step-down active substation transformer and the second connection end of the primary side of the distribution transformer of the third step-up / 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-up / step-down active substation transformer and the first connection end of the primary side of the distribution transformer of the second step-up / 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-up / step-down active substation transformer and the first connection end of the primary side of the distribution transformer of the third step-up / step-down active substation transformer are connected together and commonly connected to phase C;

[0033] 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;

[0034] The first end of the first arm of the AC / AC converter is connected to the common end of the transformer and the capacitor, and the second end is connected to the second connection end of the secondary side via the second arm. The first end of the third arm of the AC / AC converter is connected to the common end of the capacitor and the output terminal, and the second end is connected to the second connection end of the secondary side via the fourth arm. The first end of the inductor is connected to the common end of the first arm and the second arm, and the second end is connected to the common end of the third arm and the fourth arm.

[0035] Among them, the output terminals of the three buck-boost active distribution 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.

[0036] Four arms of the three buck-boost active distribution transformers are all connected with a plurality of control terminals, and are adapted to be turned off or on under the control of the control signals input at the control terminals. The change of the arm state prompts the capacitor and the inductor to charge or discharge, so that when the voltage on the secondary side of the distribution transformer is greater than the voltage required by the distribution network or the load connected to the output terminal, the AC / AC converter steps down the output terminal voltage, and when the voltage on the secondary side is lower than the voltage required by the distribution network or the load connected to the output terminal, the AC / AC converter steps up the output terminal voltage.

[0037] Preferably, each of the four arms includes a pair of opposing switch groups, and the four arms are turned off or on by controlling the turn-off or turn-on of the pair of opposing switch groups.

[0038] Or,

[0039] Each of the four 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.

[0040] 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 arm.

[0041] 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.

[0042] Among them, the anode of the third diode is connected to the cathode of the fourth diode, and their common end serves as the second connection end of the arm.

[0043] The anode of the fourth diode is connected to the anode of the second diode, and their common end is connected to the second end of the switch tube.

[0044] (III) Beneficial effects

[0045] The present invention provides a buck-boost active distribution transformer. Compared with the prior art, it has the following beneficial effects:

[0046] Compared with traditional equipment such as UPQC, the buck-boost active substation area transformer 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, which saves the number of devices while achieving voltage regulation, and greatly reduces the cost while improving efficiency and reducing volume. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] 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 use in 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, other drawings can be obtained based on these drawings without creative efforts.

[0048] Figure 1 is the circuit diagram of an existing hybrid distribution transformer;

[0049] Figure 2 is the architecture diagram of a buck-boost active substation area transformer in Embodiment 1;

[0050] Figure 3 is Figure 2 the first specific circuit diagram of the architecture diagram of;

[0051] Figure 4 is Figure 3 the state diagram of the switching tubes of the circuit shown in working mode 1 and working mode 4;

[0052] Figure 5 is Figure 3 the state diagram of the switching tubes of the circuit shown in working mode 2;

[0053] Figure 6 is Figure 3 the state diagram of the switching tubes of the circuit shown in working mode 3;

[0054] Figure 7 is Figure 2 the second specific circuit diagram of the architecture diagram of;

[0055] Figure 8 is the architecture diagram of a buck-boost active substation area transformer in Embodiment 2;

[0056] Figure 9 is the architecture diagram of applying the buck-boost active substation area transformer in a three-phase system in Embodiment 3, and its connection method is a star connection method;

[0057] Figure 10 is the architecture diagram of applying the buck-boost active substation area transformer in a three-phase system in Embodiment 3, and its connection method is a delta connection method. Detailed implementation manners

[0058] 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 will be clearly and completely described. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0059] It should be noted that for the sake of convenience of description, the switching IGBT is used as a representative of the controllable (turn-on and turn-off) switching tube in the embodiments of the present invention. However, the switching tube in the present invention is not limited to the IGBT. The IGBT is taken 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 switching tube in the embodiments of the present invention. For the sake of simplicity, it will not be elaborated hereinafter. The power switching tube in the embodiments of the present invention can also be implemented by other controllable switching tube devices other than the IGBT, such as MOSFET. At the same time, in the embodiments of the present invention, to ensure the normal operation of each switching device, 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 it will be pointed out in this embodiment in special cases.

[0060] The embodiments of the present application provide a buck-boost type active distribution transformer, which solves the problem of low efficiency of some hybrid distribution transformers, realizes AC / AC conversion by using a single-stage energy conversion, replaces the mainstream AC / DC + DC / AC two-stage architecture, and achieves high efficiency and low cost.

[0061] The technical solutions in the embodiments of the present application to solve the above technical problems are generally as follows:

[0062] By integrating a power electronic voltage regulator with a distribution transformer, the hybrid distribution transformer optimizes the traditional voltage regulation mode and has 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, the large number of power electronic devices required by the two-stage structure significantly increases 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 require an auxiliary winding 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.

[0063] To solve the above problems, the embodiment of the present invention proposes a step-up / step-down active substation area transformer that combines a traditional on-load voltage regulating transformer with 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, achieving high efficiency and low cost. At the same time, there is a bridging capacitor in the topology of the step-up / 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 achieve a standard AC voltage output with good waveform quality by using control technology.

[0064] To better understand the above technical solutions, the following will explain the above technical solutions in detail in conjunction with the accompanying drawings of the specification and specific implementation manners.

[0065] Embodiment 1:

[0066] This embodiment provides a step-up / 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 four 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 terminal O1 via a capacitor, and the second connection end of the secondary side is connected to the second output terminal O2 through a wire (in the specific implementation process, the two output terminals are connected to the distribution network or load, and in Figure 2In the case where two output terminals are connected to both sides of the load, two connection ports a and b are 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 transformer and the capacitor, and the second end is connected to the connection port a via the second bridge arm; the first end of the third bridge arm of the AC / AC converter is connected to the common end of the capacitor and the first output terminal, and the second end is connected to the connection port b via the fourth bridge arm; the first end of the inductor is connected to the common end of the first bridge arm and the second bridge arm, and the second end is connected to the common end of the third bridge arm and the fourth bridge arm;

[0067] The four 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 capacitor and the inductor to be charged or discharged, so that when the voltage on the secondary side of the distribution transformer is greater than the voltage required by the device connected to the output terminal, the AC / AC converter steps down the output terminal voltage, and when the voltage on the secondary side is lower than the voltage required by the device connected to the output terminal, the AC / AC converter steps up the output terminal voltage.

[0068] During the implementation process, a buck-boost active distribution transformer includes four operating modes:

[0069] The buck-boost active distribution transformer switches between operating mode 1 and operating mode 2 to step down the output terminal voltage:

[0070] Operating mode 1: The first and third bridge arms are turned on, and the second and fourth bridge arms are turned off. The current flow path is the secondary side of the distribution transformer → the first bridge arm → the inductor → the third bridge arm → the device connected to the output terminal. At this time, the secondary side of the distribution transformer (that is, the voltage of the AC source connected to the primary side of the distribution transformer is directly supplied to the output terminal after passing through the distribution transformer) supplies power to the device connected to the output terminal and charges the inductor, and the inductor absorbs energy.

[0071] Operating mode 2: The second and third bridge arms are turned on, and the first and fourth bridge arms are turned off. The current flow path is the second bridge arm → the inductor → the third bridge arm → the device connected to the output terminal. The inductor supplies power to the device connected to the output terminal.

[0072] When the voltage on the secondary side of the distribution transformer is less than the voltage required by the device connected to the output terminal, the buck-boost active distribution transformer switches between operating mode 3 and operating mode 4 to step up the output terminal voltage:

[0073] Working mode 3: The first and fourth bridge arms are conducting, and the second and third bridge arms are off. The current flow path is from the secondary side of the distribution transformer → the first bridge arm → the inductor → the fourth bridge arm and the secondary side of the distribution transformer → the capacitor → the device connected to the output terminal. At this time, the power grid charges and stores energy in the inductor, and the secondary side of the distribution transformer and the capacitor supply power to the device connected to the output terminal;

[0074] Working mode 4: The first and third bridge arms are conducting, and the second and fourth bridge arms are off. The current flow path is from the secondary side of the distribution transformer → the first bridge arm → the inductor → the third bridge arm → the device connected to the output terminal and the inductor → the third bridge arm → the capacitor → the first bridge arm. At this time, the secondary side of the distribution transformer and the inductor supply power to the device connected to the output terminal simultaneously, and the capacitor absorbs energy;

[0075] In the specific implementation process, all four bridge arms of the AC / AC converter can adopt two opposite switching tubes, as Figure 3 shown. The first switching tube T1 and the second switching tube T2 form the first bridge arm, the third switching tube T3 and the fourth switching tube T4 form the second bridge arm, the fifth switching tube T5 and the sixth switching tube T6 form the third bridge arm, and the seventh switching tube T7 and the eighth switching tube T8 form the fourth bridge arm. This AC / AC converter has three working modes. The states of the switching tubes in each mode are as Figure 4 、 5 、6 shown.

[0076] When the voltage on the secondary side of the distribution transformer is higher than the voltage required by the device (distribution network or load) connected to the output terminal, the step-up / step-down active substation transformer switches between working mode 1 and working mode 2, and the states of the switching tubes are as Figure 4 、 5 shown, and the voltage at the output terminal is stepped down.

[0077] Working mode 1: The states of the switching tubes are as Figure 4 shown. The switching tubes T1, T2, T5, and T6 are conducting, and the other switching tubes are off. The current flow path is from the secondary side of the distribution transformer → T1 → T2 → L → T5 → T6 → the load. At this time, the secondary side of the distribution transformer supplies power to the load, charges the capacitor, and the inductor absorbs energy.

[0078] Working mode 2: The states of the switching tubes are as Figure 5 shown. The switching tubes T3, T4, T5, and T6 are conducting, and the other switching tubes are off. The current flow path is T3 → T4 → L → T6 → T5 → the load, and the device connected to the output terminal is supplied power through the inductor.

[0079] When the voltage on the secondary side of the distribution transformer is lower than the voltage required by the device (distribution network or load) connected to the output terminal, the buck-boost active substation area transformer switches between operating mode 3 and operating mode 4, and the states of the switching tubes are as Figure 6 , 4 shown, boosting the voltage of the output terminal.

[0080] Operating mode 3: The states of the switching tubes are as Figure 6 shown. T1, T2, T7, and T8 are conducting, and the other switching tubes are turned off. The current flow path is from the secondary side of the distribution transformer → T1 → T2 → L → T7 → T8 and from the secondary side of the distribution transformer → C → the device connected to the output terminal. At this time, the power grid charges the inductor to store energy, and the secondary side of the distribution transformer and the capacitor supply power to the device connected to the output terminal;

[0081] Operating mode 4: The states of the switching tubes are as Figure 4 shown. Switching tubes T1, T2, T5, and T6 are conducting, and the other switching tubes are turned off. The current flow path is from the secondary side of the distribution transformer → T1 → T2 → L → T6 → T5 → the device connected to the output terminal and L → T6 → T5 → C → T1 → T2. At this time, the secondary side of the distribution transformer and the inductor supply power to the device connected to the output terminal at the same time, and the capacitor absorbs energy.

[0082] 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 7 shown. It should be noted that when constructing the four bridge arms of the AC / AC converter, it is not limited to the above two specific switch component designs. Multiple other switches can also be used to achieve the conduction and turn-off of the bridge arms, as long as these switches meet the following requirements: When the switch is in the off state, a through phenomenon of the bridge arm must be avoided during the negative half cycle of the AC source connected to the primary side of the distribution transformer. At the same time, multiple switches can also be mixed and combined. For example, the first bridge arm and the second bridge arm adopt an opposing switch group, and the third bridge arm and the fourth bridge arm adopt a dual-control switch composed of four diodes and one switching tube.

[0083] Figure 7 The circuit operating mode shown and Figure 3 the operating mode of the circuit shown are the same, and will not be elaborated here.

[0084] Embodiment 2:

[0085] This embodiment provides a buck-boost active substation area transformer, as Figure 8 shown. This transformer is in Figure 2Based on the shown circuit, 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 grid or load) connected to the output terminal. In this case, there is no need for the AC / AC converter to step down or step up 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 with the capacitor based on the above circuit.

[0086] After closing the bypass switch, all four bridge arms of the AC / AC converter are turned off, and the AC / AC converter can be removed from the grid side.

[0087] 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.

[0088] Embodiment 3:

[0089] In this embodiment, the step-up / step-down type active substation area transformer in Embodiment 1 or Embodiment 2 can be applied to a three-phase system, and its connection methods include star connection and delta connection. For the star connection, as Figure 9 shown, the primary sides of the distribution transformers in the three step-up / step-down type active substation area transformers are connected to a three-phase AC power supply. Among them, the first connection end of the primary side of the distribution transformer in the first step-up / step-down type active substation area transformer and the second connection end of the primary side of the distribution transformer in the third step-up / step-down type active substation area transformer are connected together and commonly connected to phase A; the second connection end of the primary side of the distribution transformer in the first step-up / step-down type active substation area transformer and the first connection end of the primary side of the distribution transformer in the second step-up / step-down type active substation area transformer are connected together and commonly connected to phase B; the second connection end of the primary side of the distribution transformer in the second step-up / step-down type active substation area transformer and the first connection end of the primary side of the distribution transformer in the third step-up / step-down type active substation area 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-up / step-down type active substation area transformer are the same as those in Embodiment 1, and will not be elaborated here.

[0090] For the delta connection, as Figure 10As shown in the figure, the primary sides of the distribution transformers in the three buck-boost active substation area 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 buck-boost active substation area transformer and the second connection end of the primary side of the distribution transformer of the third buck-boost active substation area transformer are connected together and jointly connected to phase A; the second connection end of the primary side of the distribution transformer of the first buck-boost active substation area transformer and the first connection end of the primary side of the distribution transformer of the second buck-boost active substation area transformer are connected together and jointly connected to phase B; the second connection end of the primary side of the distribution transformer of the second buck-boost active substation area transformer and the first connection end of the primary side of the distribution transformer of the third buck-boost active substation area transformer are connected together and jointly 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 buck-boost active substation area transformers to the load or the power grid are different from those of the buck-boost active substation area transformer connected in a single-phase circuit to the load or the power grid. In the delta connection method, the first output ends of the buck-boost active substation area 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 and the third bridge arm, no wires are led out as the second output end.

[0091] It should be noted that for the purpose of drawing, Figure 9 and Figure 10 the AC / AC converters in the buck-boost active substation area transformers in

[0092] In summary, compared with the prior art, the following beneficial effects are achieved:

[0093] 1. Compared with traditional equipment such as UPQC, the buck-boost 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 realizing voltage governance, the number of devices is saved, and the cost is greatly reduced while improving efficiency and reducing volume.

[0094] 2. There is a bridging capacitor (i.e., capacitor C) in the topology of the buck-boost active substation area transformer in the embodiment of the present invention. Because the voltage of the capacitor cannot change suddenly, the voltage of the capacitor can be controlled to change smoothly through the modulation technology of the high-frequency power switching tube. Finally, the voltage on the capacitor is superimposed on the input voltage, which can effectively ensure the smoothness of the AC output. The standard AC voltage output is realized by using control technology, and the waveform quality is good.

[0095] It should be noted that in this text, 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 comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the said element.

[0096] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than 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 on 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 buck-boost type active distribution transformer, characterized in that It includes a distribution transformer, a capacitor, and an AC / AC converter, and the AC / AC converter includes four bridge arms and an inductor; Among them, 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, and the second connection end of the secondary side is connected to the second output end through a wire. Two connection ports a and b are arranged on the wire; The first end of the first bridge arm of the AC / AC converter is connected to the common end of the transformer and the capacitor, and the second end is connected to the connection port a via the second bridge arm. The first end of the third bridge arm of the AC / AC converter is connected to the common end of the capacitor and the first output end, and the second end is connected to the connection port b via the fourth bridge arm; The first end of the inductor is connected to the common end of the first bridge arm and the second bridge arm, and the second end is connected to the common end of the third bridge arm and the fourth bridge arm; The four bridge arms are connected with a number of control ends and are adapted to be turned off or on under the control of a control signal applied to the control ends. The change of the bridge arm state causes the capacitor and the inductor to be charged or discharged, so that when the voltage on the secondary side of the distribution transformer is greater than the voltage required by the device connected to the output end, the AC / AC converter steps down the output voltage, and when the voltage on the secondary side is lower than the voltage required by the device connected to the output end, the AC / AC converter steps up the output voltage.

2. The buck-boost type active substation transformer according to claim 1, wherein When the voltage on the secondary side of the distribution transformer is higher than the voltage required by the device connected to the output end, the step-up / step-down type active substation area transformer switches between working mode 1 and working mode 2 to step down the output voltage: Working mode 1: The first and third bridge arms are turned on, and the second and fourth bridge arms are turned off. The current flow path is the secondary side of the distribution transformer → the first bridge arm → the inductor → the third bridge arm → the device connected to the output end. At this time, the secondary side of the distribution transformer supplies power to the device connected to the output end and charges the inductor, and the inductor absorbs energy; Working mode 2: The second and third bridge arms are turned on, and the first and fourth bridge arms are turned off. The current flow path is the second bridge arm → the inductor → the third bridge arm → the device connected to the output end, and the device connected to the output end is powered by the inductor.

3. The buck-boost active substation transformer according to claim 1, characterized in that, When the voltage on the secondary side of the distribution transformer is less than the voltage required by the device connected to the output end, the step-up / step-down type active substation area transformer switches between working mode 3 and working mode 4 to step up the output voltage: Working mode 3: The first and fourth bridge arms are turned on, and the second and third bridge arms are turned off. The current flow path is the secondary side of the distribution transformer → the first bridge arm → the inductor → the fourth bridge arm and the secondary side of the distribution transformer → the capacitor → the device connected to the output end. At this time, the power grid charges and stores energy in the inductor, and the secondary side of the distribution transformer and the capacitor supply power to the device connected to the output end; Working mode 4: The first and third bridge arms are turned on, and the second and fourth bridge arms are turned off. The current flow path is the secondary side of the distribution transformer → the first bridge arm → the inductor → the third bridge arm → the device connected to the output end and the inductor → the third bridge arm → the capacitor → the first bridge arm. At this time, the secondary side of the distribution transformer and the inductor supply power to the device connected to the output end at the same time, and the capacitor absorbs energy.

4. The buck-boost type active substation transformer according to any one of claims 1 to 3, characterized in that, It also includes a bypass switch, both ends of which are respectively connected to both 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 terminal. After closing the bypass switch and disconnecting the four bridge arms of the AC / AC converter, the AC / AC converter is removed.

5. The buck-boost type active substation transformer according to any one of claims 1 to 3, characterized in that Each of the four bridge arms includes a pair of top-bottom switch groups connected therein, and the four bridge arms are controlled to be disconnected or conducted by turning off or on the pair of top-bottom switch groups.

6. The buck-boost type active substation transformer according to any one of claims 1 to 3, characterized in that, Each of the four bridge arms includes a dual-control switch, and the dual-control switch includes a first diode, a second diode, a third diode, a fourth diode, and a switching tube. Among them, the anode of the first diode is connected to the cathode of the second diode, and their common terminal 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 their common terminal is connected to the first end of the switching tube. 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 end of the bridge arm. 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 switching tube.

7. The buck-boost active substation transformer according to any one of claims 1 to 3, characterized in that, The device connected to the output terminal includes a power distribution network or a load.

8. A buck-boost type active substation transformer applied in a three-phase system, characterized in that, It includes three step-up / step-down active substation area transformers as described in any one of claims 1 to 7. Among them, the primary sides of the distribution transformers in the three step-up / step-down active substation area transformers are connected to a three-phase AC power source; the first connection end of the primary side of the distribution transformer of the first step-up / step-down active substation area transformer and the second connection end of the primary side of the distribution transformer of the third step-up / step-down active substation area 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-up / step-down active substation area transformer and the first connection end of the primary side of the distribution transformer of the second step-up / step-down active substation area 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-up / step-down active substation area transformer and the first connection end of the primary side of the distribution transformer of the third step-up / step-down active substation area 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.

9. A buck-boost type active substation transformer applied in a three-phase system, characterized in that, It includes three step-up / step-down active substation area transformers. Among them, each step-up / step-down active substation area transformer includes a distribution transformer, a capacitor, and an AC / AC converter. The AC / AC converter includes four bridge arms and an inductor. Among them, the first connection end of the primary side of the distribution transformer of the first step-up / step-down active substation area transformer and the second connection end of the primary side of the distribution transformer of the third step-up / step-down active substation area 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-up / step-down active substation area transformer and the first connection end of the primary side of the distribution transformer of the second step-up / step-down active substation area 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-up / step-down active substation area transformer and the first connection end of the primary side of the distribution transformer of the third step-up / step-down active substation area transformer are connected together and commonly connected to phase C. 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; The first end of the first bridge arm of the AC / AC converter is connected to the common end of the transformer and the capacitor, and the second end is connected to the second connection end of the secondary side via the second bridge arm. The first end of the third bridge arm of the AC / AC converter is connected to the common end of the capacitor and the output end, and the second end is connected to the second connection end of the secondary side via the fourth bridge arm; the first end of the inductor is connected to the common end of the first bridge arm and the second bridge arm, and the second end is connected to the common end of the third bridge arm and the fourth bridge arm; Among them, the output ends of the three buck-boost active substation area 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; Four bridge arms of the three buck-boost active substation area transformers are all connected with a plurality of control ends, and are adapted to be turned off or on under the control of the control signal input at the control ends. The change of the bridge arm state prompts the capacitor and the inductor to charge or discharge, so that when the voltage on the secondary side of the distribution transformer is greater than the voltage required by the distribution network or the load connected to the output end, the AC / AC converter steps down the output end voltage, and when the voltage on the secondary side is lower than the voltage required by the distribution network or the load connected to the output end, the AC / AC converter steps up the output end voltage.

10. The buck-boost active distribution transformer applied to a three-phase system according to claim 9, wherein Each of the four bridge arms includes a connection to an anti-parallel switch group, and the four bridge arms are turned off or on by controlling the turn-off or turn-on of the anti-parallel switch group; Or, Each of the four 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, Among them, the anode of the first diode is connected to the cathode of the second diode, and their common end is used 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 their common end is connected to the first end of the switch tube; Among them, the anode of the third diode is connected to the cathode of the fourth diode, and their common end is used 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 their common end is connected to the second end of the switch tube.

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