Boost single-phase single-stage AC-AC converter

Abstract

The invention provides a boost single-phase single-stage AC-AC converter, and relates to the technical field of converters. The boost single-phase single-stage AC-AC converter comprises a first inductor, an intermediate capacitor, a second inductor, a first bidirectional switch group and a second bidirectional switch tube group, the first end of the first inductor is connected with the second end of the load, and the second end of the first inductor is connected to the first end of the load through the intermediate capacitor and the second inductor; the first end of the first bidirectional switch group is connected to the common end of the first inductor and the intermediate capacitor; the second end is connected to the common end of the first inductor and the load through the input power supply; the first end of the second bidirectional switch group is connected to the common end of the second inductor and the intermediate capacitor; the second end is connected to the common end of the first bidirectional switch group and the input power supply; according to the invention, one-stage energy type AC / AC conversion can be realized only by controlling the two switching tube groups which work complementarily, the efficiency is high, the control mode is simple, and the converter function can be realized by using fewer peripheral circuits.

Description

Technical Field

[0001] The present invention relates to the technical field of converters, and particularly relates to a boost single-phase single-stage AC-AC converter. Background Art

[0002] The power quality of the distribution network substation area will affect the power supply quality. Low-quality power supply will lead to problems such as increased power grid line loss, equipment failure, and power outage accidents. Too high or too low voltage will cause the user's electrical equipment to malfunction.

[0003] To address the problem of too low supply voltage at the distribution transformer or the end of the line in the substation area, the existing technology generally adjusts the voltage through a UPQC (Unified Power Quality Conditioner) device based on the series-parallel structure of transformers, such as Figure 1 As shown, the UPQC device based on the series-parallel structure of transformers first connects a rectifier in parallel at the grid end to generate a DC voltage, and then converts the DC voltage into an alternating current through an inverter. This alternating current is added to the grid through a coupling transformer connected in series in the grid, so that the load-side voltage is superimposed with an alternating voltage generated by the inverter on the basis of the grid voltage, thereby achieving the adjustment of the grid voltage. When the grid voltage is too low, adding a voltage in the same phase as the grid voltage by using the UPQC can achieve voltage boost and restore the load voltage to the standard voltage (220V).

[0004] However, the UPQC device based on the series-parallel structure of transformers adopts two-stage energy conversion of AC / DC + DC / AC, with low efficiency. Summary of the Invention

[0005] (1) Technical Problems to be Solved

[0006] Aiming at the deficiencies of the existing technology, the present invention provides a boost single-phase single-stage AC-AC converter, which solves the technical problem of low efficiency of the existing UPQC device.

[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 boost single-phase single-stage AC-AC converter, including a first inductor, an intermediate capacitor, a second inductor, a first bidirectional switch group, and a second bidirectional switch tube group;

[0010] The first end of the first inductor is connected to the second end of the load, and the second end of the first inductor is connected to the first end of the load via the intermediate capacitor and the second inductor;

[0011] The first end of the first bidirectional switch group is connected to the common end of the first inductor and the intermediate capacitor; the second end is connected to the first end of the input power supply, and the second end of the input power supply is connected to the common end of the first inductor and the load;

[0012] The first end of the second bidirectional switch group is connected to the common end of the second inductor and the intermediate capacitor; the second end is connected to the common end of the first bidirectional switch group and the input power supply;

[0013] Both the first bidirectional switch group and the second bidirectional switch group are connected to a plurality of control terminals, and are adapted to operate in a complementary conduction mode with a fixed duty cycle under the control of a control signal applied to the control terminals, so that the voltage across the load is higher than the input voltage.

[0014] Preferably, both the first bidirectional switch group and the second bidirectional switch group are switching devices capable of satisfying a bidirectional current path.

[0015] Preferably, both the first bidirectional switch group and the second bidirectional switch group include a pair of opposed switches.

[0016] Preferably, when the voltage of the first end of the input power supply is negative and the voltage of the second end is positive, the boost single-phase single-stage AC-AC converter includes two operating modes:

[0017] Operating mode one: The first bidirectional switch group is turned off, and the second bidirectional switch group conducts from the first end to the second end. There are two current flow paths in the circuit, which are: input power supply current, load, second inductor, second bidirectional switch group; intermediate capacitor current passes through the input power supply, first inductor, and second bidirectional switch group; at this time, the voltage of the first end of the load is negative and the voltage of the second end is positive;

[0018] Operating mode two: The second bidirectional switch group is turned off, and the first bidirectional switch group conducts from the first end to the second end. There are two current flow paths in the circuit, which are: input power supply current passes through the load, second inductor to charge the intermediate capacitor and then flows to the first bidirectional switch group; input power supply flows to the first inductor and the first bidirectional switch group; at this time, the voltage of the first end of the load is negative and the voltage of the second end is positive.

[0019] Preferably, when the voltage of the first end of the input power supply is positive and the voltage of the second end is negative, the boost single-phase single-stage AC-AC converter includes two operating modes:

[0020] Operating mode three: The second bidirectional switch group conducts from the second end to the first end, and the first bidirectional switch group is turned off. There are two current flow paths in the circuit, which are: input power supply current passes through the second bidirectional switch group, second inductor, and load; intermediate capacitor current passes through the first inductor; at this time, the voltage of the first end of the load is positive and the voltage of the second end is negative;

[0021] Operating mode four: The second bidirectional switch group is turned off, and the first bidirectional switch group conducts from the second end to the first end. There are two current flow paths in the circuit, which are respectively: the input power supply current flows through the first bidirectional switch group, the intermediate capacitor, the second inductor, and the load; the input power supply current flows through the first bidirectional switch group and the first inductor. At this time, the voltage at the first end of the load is positive, and the voltage at the second end is negative.

[0022] Preferably, when the duty cycle of the first bidirectional switch group is 1 - D and the duty cycle of the second bidirectional switch group is D, the voltage V out across the load and the input voltage V ac have the following quantitative relationship:

[0023] V out = V ac / D.

[0024] In a second aspect, the present invention provides a boost - type AC - AC converter applied to a three - phase circuit, which includes three boost - type single - stage single - phase AC - AC converters. Each boost - type single - stage single - phase AC - AC converter includes a first inductor, an intermediate capacitor, a second inductor, a first bidirectional switch group, and a second bidirectional switch group;

[0025] The common ends of the first bidirectional switch groups and the second bidirectional switch groups of the three boost - type single - stage single - phase AC - AC converters are respectively connected to the first ends of the A, B, and C three - phase power supplies. The second ends of the A, B, and C three - phase power supplies are connected together as the common end of the three - phase power supply;

[0026] The second ends of the second inductors of the three boost - type single - stage single - phase AC - AC converters are respectively connected to the first ends of their respective loads. The second ends of the loads are connected together and then connected to the common end of the three - phase power supply;

[0027] The second end of the first inductor of each boost - type single - stage single - phase AC - AC converter is connected to the first end of the load via the intermediate capacitor and the second inductor; the first end of the first bidirectional switch group is connected to the common end of the first inductor and the intermediate capacitor; the first end of the second bidirectional switch group is connected to the common end of the second inductor and the intermediate capacitor; the second end is connected to the second end of the first bidirectional switch group;

[0028] The first bidirectional switch group and the second bidirectional switch group in each boost - type single - stage single - phase AC - AC converter are each connected to a plurality of control terminals. Adapted to be controlled by the control signals applied to the control terminals, the first bidirectional switch group and the second bidirectional switch group operate in a complementary conduction mode according to a fixed duty cycle, so that the voltage across the load of each phase is greater than the corresponding phase voltage.

[0029] Preferably, both the first bidirectional switch group and the second bidirectional switch group are switch devices capable of satisfying bidirectional current paths;

[0030] Preferably, both the first bidirectional switch group and the second bidirectional switch group include a pair of opposing switches.

[0031] Preferably, in any one-phase circuit, when the duty cycle of the first bidirectional switch group is 1 - D and the duty cycle of the second bidirectional switch group is D, the voltage V out across each phase load and the input voltage V x of this phase have the following quantitative relationship:

[0032] V out = V x / D

[0033] where x = a, b, c, and V x represents the three-phase voltages of V a , V b , and V c .

[0034] (III) Beneficial Effects

[0035] The present invention provides a step-up single-phase single-stage AC-AC converter. Compared with the prior art, it has the following beneficial effects:

[0036] The step-up single-phase single-stage AC-AC converter of the present invention can achieve first-level energy-based AC / AC conversion only by controlling two switch tube groups that work complementarily, with high efficiency and a simple control method, and can implement the converter function with fewer peripheral circuits. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] 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 following drawings 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.

[0038] Figure 1 is a framework diagram of an existing UPQC device based on transformer series-parallel connection;

[0039] Figure 2 is a framework diagram of a step-up single-phase single-stage AC-AC converter in Embodiment 1;

[0040] Figure 3 is Figure 2 the specific circuit diagram of the shown framework diagram;

[0041] Figure 4 isFigure 3 Schematic diagram of operating mode 1 of the shown circuit;

[0042] Figure 5 is Figure 3 Schematic diagram of operating mode 2 of the shown circuit;

[0043] Figure 6 is Figure 3 Schematic diagram of operating mode 3 of the shown circuit;

[0044] Figure 7 is Figure 3 Schematic diagram of operating mode 4 of the shown circuit;

[0045] Figure 8 is to Figure 3 Circuit diagram of applying the shown boostable single-phase single-stage AC-AC converter in a three-phase circuit. Specific implementation manners

[0046] 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 described clearly and completely. Obviously, 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 making creative efforts shall fall within the protection scope of the present invention.

[0047] It should be noted that for the convenience of description, the switch IGBT is used as a representative of the controllable (conducting and turning 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 the embodiments of the present invention, to ensure the normal operation of each switching device, a freewheeling diode needs to be connected in parallel with 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.

[0048] The embodiments of the present application provide a boostable single-phase single-stage AC-AC converter, which solves the technical problem of low efficiency of the existing UPQC device, realizes one-stage AC / AC conversion, saves the number of devices, and improves the operation efficiency.

[0049] The technical solutions in the embodiments of the present application to solve the above technical problems are generally as follows:

[0050] Regarding the problem of too low supply voltage at the distribution transformer or the end of the line in the substation area, the traditional passive solutions include the on-load tap-changing scheme of the transformer, which adjusts the output voltage by changing the turns ratio of the transformer. However, the number of adjustment steps is limited, and the flexibility and reliability are poor. The method of switching capacitors uses the method of incorporating capacitors to achieve reactive power support for the line inductance, thereby improving the low voltage. However, it cannot be adjusted seamlessly, and the flexibility and real-time performance are poor. The active solutions are based on power electronics technology. Commonly used ones include bidirectional AC / DC + DC / AC, or AC / AC solutions. All the power of this type of solution passes through the power electronic converter, which has disadvantages such as low efficiency and high cost.

[0051] To overcome the defects of traditional passive and active solutions, the current mainstream technical path is to adopt the UPQC solution based on the series-parallel structure of the transformer. This solution compensates the current through the shunt side and realizes voltage compensation with the help of the series transformer, and then completes the power electronic conversion of part of the power. However, this solution still uses the two-stage energy conversion mode of AC / DC + DC / AC, and this mode has poor efficiency. In addition, the power frequency transformer used in the solution is not only bulky, but also leads to low overall efficiency and a significant increase in cost.

[0052] As Figure 1 is known, the UPQC device first connects a rectifier in parallel at the grid end to generate a DC voltage, and then inversely converts the DC voltage into an alternating current through an inverter. This alternating current is added to the grid through a coupling transformer connected in series in the grid, so that the load-side voltage is superimposed with an alternating voltage generated by the inverter on the basis of the grid voltage, thereby achieving the adjustment of the grid voltage. When the grid voltage is too low, adding a voltage in the same phase as the grid voltage by using UPQC can realize voltage boost and restore the load voltage to the standard voltage (220V).

[0053] In summary, due to the two-stage architecture of rectification first and then inversion adopted by UPQC, and the need to connect a coupling transformer in series in the grid, it not only greatly improves the control complexity of the device, but also causes significant problems such as low efficiency, large volume, and high cost.

[0054] To solve the above problems, the embodiment of the present invention proposes a boost single-phase single-stage AC-AC converter, which can realize single-stage energy AC / AC conversion only by controlling two complementary working switch groups S1 and S2 with a fixed duty cycle, has high efficiency, and the control method is simple, and the converter function can be realized with fewer peripheral circuits.

[0055] To better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings of the specification and specific embodiments.

[0056] An embodiment of the present invention provides a boostable single-phase single-stage AC-AC converter, as Figure 2 shown, which includes a first inductor, an intermediate capacitor, a second inductor, a first bidirectional switch group, and a second bidirectional switch group;

[0057] The first end of the first inductor is connected to the second end of the load, and the second end of the first inductor is connected to the first end of the load via the intermediate capacitor and the second inductor;

[0058] The first end of the first bidirectional switch group is connected to the common end of the first inductor and the intermediate capacitor; the second end is connected to the common end of the first inductor and the load via the input power supply;

[0059] The first end of the second bidirectional switch group is connected to the common end of the second inductor and the intermediate capacitor; the second end is connected to the common end of the first bidirectional switch group and the input power supply;

[0060] Both the first bidirectional switch group and the second bidirectional switch group are connected to a plurality of control terminals, and are adapted to work in a complementary conduction mode with a fixed duty cycle under the control of the control signals applied to the control terminals, so that the voltage across the load is higher than the input voltage.

[0061] As Figure 3 shown, in this embodiment, both the first bidirectional switch group S1 and the second bidirectional switch group S2 adopt two opposing IGBTs. It should be noted that in the specific implementation process, other forms of switching tubes such as MOSFETs can also be used to form an opposing switch group, or other switching devices that can satisfy the bidirectional current path. In Figure 3 it, the load is represented by an RC load, but it does not mean that the load can only be an RC load, and it can also be other forms of loads.

[0062] Next, taking the Figure 3 shown circuit topology as an example, the modal analysis of the boostable single-phase single-stage AC-AC converter in this embodiment is as follows:

[0063] When the input power supply is negative (the input voltage is considered to be positive at the top and negative at the bottom in the reference direction):

[0064] Operating mode one: As Figure 4 shown, the first bidirectional switch group S1 is turned off (i.e., both T1 and T2 are turned off), and the second bidirectional switch group S2 conducts from the first end to the second end (i.e., T3 conducts, T4 conducts, and the anti-parallel diode conducts). There are two current flow paths in the circuit, which are respectively: the input power supply current, the load, the second inductor L2, the second bidirectional switch group S2; the current of the intermediate capacitor C passes through the input power supply, the first inductor L1, and the second bidirectional switch group S2; at this time, the output voltage is positive at the bottom and negative at the top.

[0065] Operating mode two: AsFigure 5 As shown, the second bidirectional switch group S2 is turned off (i.e., both T3 and T4 are turned off), and the first bidirectional switch group S1 conducts from the first end to the second end (i.e., T1 conducts, and the antiparallel diode of T2 conducts). There are two current flow paths in the circuit, which are respectively: the input power supply current passes through the load, the second inductor L2, charges the intermediate capacitor C, and then flows to the first bidirectional switch group S1; the input power supply flows to the first inductor L1 and the first bidirectional switch group S1. At this time, the output voltage is positive at the bottom and negative at the top.

[0066] When the input power supply is positive (i.e., the input voltage is considered to be positive at the top and negative at the bottom in the reference direction):

[0067] Operating mode three: As Figure 6 shown, the second bidirectional switch group S2 conducts from the second end to the first end (i.e., T4 conducts, and the antiparallel diode of T3 conducts), and the first bidirectional switch group S1 is turned off. There are two current flow paths in the circuit, which are respectively: the input power supply current passes through the second bidirectional switch group S2, the second inductor L2, and the load; the current of the intermediate capacitor C passes through the first inductor L1. At this time, the output voltage is positive at the top and negative at the bottom.

[0068] Operating mode four: As Figure 7 shown: The second bidirectional switch group S2 is turned off, and the first bidirectional switch group S1 conducts from the second end to the first end (i.e., T2 conducts, and the antiparallel diode of T1 conducts). There are two current flow paths in the circuit, which are respectively: the input power supply current passes through the intermediate capacitor, the second inductor L2, and the load; the power supply charges the first inductor L1. At this time, the output voltage is positive at the top and negative at the bottom.

[0069] Since the first bidirectional switch group S1 and the second bidirectional switch group S2 conduct complementarily, assume that the duty cycle of the first bidirectional switch group S1 is 1 - D, the duty cycle of the second bidirectional switch group S2 is D, and the capacitor voltage is V c , positive on the left and negative on the right.

[0070] Write the potential balance equations for the inductor and capacitor. Ignoring the high-frequency transformation quantity and approximately considering that the voltage is a constant quantity within adjacent switching cycles, for the inductor L1, we get 0 = V ac *(1 - D)+(V ac+ V c )*D, and for the inductor L2, we get V out＝ D*V ac +(V ac - V c )*(1 - D)

[0071] Then the relationship between the output voltage V out and the input voltage V ac is:

[0072] V out = Vac / D

[0073] Therefore, the converter can achieve step-up by only controlling the first bidirectional switch group S1 and the second bidirectional switch group S2 that work complementarily with a fixed duty cycle.

[0074] Embodiment 2:

[0075] In this embodiment, the step-up single-phase single-stage AC-AC converter in Embodiment 1 is applied to a three-phase structure, as Figure 8 shown (in this figure, the two bidirectional switch groups in each step-up single-phase single-stage AC-AC converter take the top-to-bottom switches as an example). The second ends of the second inductors of the three step-up single-phase single-stage AC-AC converters are respectively connected to the first ends of their respective loads, the second ends of the loads are connected together, and then connected to the common end of the three-phase power grid. The common ends of the first bidirectional switch group and the second bidirectional switch group of the three step-up single-phase single-stage AC-AC converters are respectively connected to the first ends of the A, B, and C phases of the three-phase power grid, and the second ends of the A, B, and C phases of the three-phase power grid are connected together to serve as the common end of the three-phase power grid. Of course, in the specific implementation process, the top-to-bottom switch tube groups in the three step-up single-phase single-stage AC-AC converters in the three-phase structure can also adopt other switching devices that satisfy the bidirectional current path. Its working mode is similar to that of Embodiment 1 and will not be elaborated here.

[0076] In summary, compared with the prior art, the following beneficial effects are achieved:

[0077] 1. The step-up single-phase single-stage AC-AC converter according to the embodiment of the present invention can achieve first-level energy-based AC / AC conversion by only controlling two switch tube groups that work complementarily, has high efficiency, and a simple control method, and can realize the function of the converter with fewer peripheral circuits.

[0078] 2. The output voltage and output current of this circuit are continuous, with few voltage and current harmonics, and are easier to filter.

[0079] 3. By controlling the duty cycles of the first bidirectional switch group and the second bidirectional switch group, the step-up amplitude can be controlled. The control method is simple, and the required voltage can be flexibly output.

[0080] It should be noted that, in this document, 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 terms "comprising", "including" or any other variant thereof are 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 elements inherent to such process, method, article or device. Without further limitation, an element defined by the phrase "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or device comprising said element.

[0081] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; 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 cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A boostable single-phase single-stage AC-AC converter, characterized in that, It includes a first inductor, an intermediate capacitor, a second inductor, a first bidirectional switch group, and a second bidirectional switch group; The first end of the first inductor is connected to the second end of the load, and the second end of the first inductor is connected to the first end of the load via the intermediate capacitor and the second inductor; The first end of the first bidirectional switch group is connected to the common end of the first inductor and the intermediate capacitor; the second end is connected to the first end of the input power supply, and the second end of the input power supply is connected to the common end of the first inductor and the load; The first end of the second bidirectional switch group is connected to the common end of the second inductor and the intermediate capacitor; the second end is connected to the common end of the first bidirectional switch group and the input power supply; Both the first bidirectional switch group and the second bidirectional switch group are connected to a plurality of control terminals, and are adapted to work in a complementary conduction mode with a fixed duty cycle under the control of the control signal applied to the control terminals, so that the voltage across the load is higher than the input voltage.

2. The boostable single-phase single-stage AC-AC converter according to claim 1, wherein Both the first bidirectional switch group and the second bidirectional switch group are switching devices capable of satisfying a bidirectional current path.

3. The boostable single-phase single-stage AC-AC converter according to claim 2, wherein Both the first bidirectional switch group and the second bidirectional switch group include a set of opposite switches.

4. The boostable single-phase single-stage AC-AC converter according to any one of claims 1 to 3, characterized in that, When the voltage at the first end of the input power supply is negative and the voltage at the second end is positive, the boostable single-phase single-stage AC-AC converter includes two operating modes: Operating mode one: The first bidirectional switch group is turned off, and the second bidirectional switch group conducts from the first end to the second end. There are two current flow paths in the circuit, which are respectively: input power supply current, load, second inductor, second bidirectional switch group; intermediate capacitor current passes through the input power supply, first inductor, and second bidirectional switch group; at this time, the voltage at the first end of the load is negative and the voltage at the second end is positive; Operating mode two: The second bidirectional switch group is turned off, and the first bidirectional switch group conducts from the first end to the second end. There are two current flow paths in the circuit, which are respectively: input power supply current passes through the load, second inductor to charge the intermediate capacitor and then flows to the first bidirectional switch group; input power supply flows to the first inductor and the first bidirectional switch group; at this time, the voltage at the first end of the load is negative and the voltage at the second end is positive.

5. The boostable single-phase single-stage AC-AC converter according to any one of claims 1 to 3, characterized in that When the voltage at the first end of the input power supply is positive and the voltage at the second end is negative, the boostable single-phase single-stage AC-AC converter includes two operating modes: Operating mode three: The second bidirectional switch group conducts from the second end to the first end, and the first bidirectional switch group is turned off. There are two current flow paths in the circuit, which are respectively: input power supply current passes through the second bidirectional switch group, second inductor, and load; intermediate capacitor current passes through the first inductor; at this time, the voltage at the first end of the load is positive and the voltage at the second end is negative; Operating mode four: The second bidirectional switch group is turned off, and the first bidirectional switch group conducts from the second end to the first end. There are two current flow paths in the circuit, which are respectively: input power supply current flows through the first bidirectional switch group, intermediate capacitor, second inductor, and load; input power supply current flows through the first bidirectional switch group and the first inductor; at this time, the voltage at the first end of the load is positive and the voltage at the second end is negative.

6. The boostable single-phase single-stage AC-AC converter according to any one of claims 1 to 3, characterized in that When the duty cycle of the first bidirectional switch group is 1 - D and the duty cycle of the second bidirectional switch group is D, the voltage V out across the load and the input voltage V ac are related as follows: V out = V ac / D.

7. An AC-AC boost converter applied to a three-phase circuit, characterized in that, It includes three boostable single-phase single-stage AC-AC converters, and each boostable single-phase single-stage AC-AC converter includes a first inductor, an intermediate capacitor, a second inductor, a first bidirectional switch group, and a second bidirectional switch group; The common ends of the first bidirectional switch groups and the second bidirectional switch groups of the three boostable single-phase single-stage AC-AC converters are respectively connected to the first ends of the A, B, and C three-phase power supplies, and the second ends of the A, B, and C three-phase power supplies are connected together to serve as the common end of the three-phase power supply; The second ends of the second inductors of the three boostable single-phase single-stage AC-AC converters are respectively connected to the first ends of their respective loads, and the second ends of the loads are connected together and then connected to the common end of the three-phase power supply; The second end of the first inductor of each boostable single-phase single-stage AC-AC converter is connected to the first end of the load via the intermediate capacitor and the second inductor; the first end of the first bidirectional switch group is connected to the common end of the first inductor and the intermediate capacitor; the first end of the second bidirectional switch group is connected to the common end of the second inductor and the intermediate capacitor; the second end is connected to the second end of the first bidirectional switch group; The first bidirectional switch group and the second bidirectional switch group in each boostable single-phase single-stage AC-AC converter are both connected to a plurality of control terminals, and are adapted to work in a complementary conduction mode with a fixed duty cycle under the control of the control signals applied to the control terminals, so that the voltage across the load of each phase is greater than the corresponding voltage of each phase.

8. The boostable AC-AC converter applied in a three-phase circuit as claimed in claim 7, wherein, The first bidirectional switch group and the second bidirectional switch group are both switching devices capable of satisfying the bidirectional current path.

9. The boostable AC-AC converter applied to a three-phase circuit as claimed in claim 8, wherein, The first bidirectional switch group and the second bidirectional switch group both include a set of opposed switches.

10. The boostable AC-AC converter applied to a three-phase circuit according to any one of claims 7 to 9, characterized in that In any one-phase circuit, when the duty cycle of the first bidirectional switch group is 1 - D and the duty cycle of the second bidirectional switch group is D, the voltage V across each phase load out and the input voltage V x of this phase have the following quantitative relationship: V out = V x / D Among them, x = a, b, c, V x represents V a , V b , V c three-phase voltages.

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