A three-phase ac-ac converter topology and method of controlling the same
By improving the topology and control method of the three-phase AC-AC converter, the voltage stress of the rectifier-side switching devices is reduced, the number of devices and conduction losses are reduced, the system efficiency is improved, and the pollution of the input current by the common-mode current is suppressed, thus solving the problems of high voltage stress and common-mode current in the prior art.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SOUTHEAST UNIV
- Filing Date
- 2024-01-23
- Publication Date
- 2026-05-29
AI Technical Summary
Existing three-phase AC-AC converters suffer from problems such as high voltage stress leading to increased costs, high conduction losses, and common-mode current contamination of input current quality.
The system employs a three-phase AC filter and a three-phase controllable rectifier bridge on the rectifier side, and a DC-side freewheeling diode, inductor, and capacitor connection method. Combined with a three-phase AC filter and a controllable inverter bridge on the inverter side, it provides an internal circulation path, reduces the voltage stress of the controllable switching module, and suppresses common-mode current.
It reduces the voltage stress and number of controllable switching modules, reduces conduction losses, improves system conversion efficiency, suppresses high-frequency common-mode current contamination of input current, and improves current quality.
Smart Images
Figure CN117997136B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of power converter technology, specifically to a three-phase AC-AC converter topology and its control method. Background Technology
[0002] With the continuous development of power electronics technology, three-phase AC-AC converters play a crucial role in energy conversion and power control. A three-phase AC-AC converter is a device capable of converting alternating current (AC) energy into electrical energy of different frequencies, amplitudes, or phases. Its main function is to achieve AC modulation and control, making it suitable for various scenarios requiring power conversion. As a key component of power electronics technology, three-phase AC-AC converters play an irreplaceable role in multiple fields such as motor drives, power systems, industrial production, and medical equipment. Through continuous innovation and the introduction of advanced technologies, three-phase AC-AC converters will continue to drive the development of various industries in the future, achieving more efficient and stable power conversion.
[0003] Common AC-AC converter topologies, such as Figure 1 As shown, it mainly includes a rectifier-side filter inductor, a three-phase rectifier circuit composed of controllable switching devices, a DC capacitor, a three-phase inverter circuit composed of controllable switching devices, and a three-phase filter on the inverter side.
[0004] However, the AC-AC converter has the following disadvantages: (1) The higher the voltage stress, the higher the requirements and quantity of controllable switching devices, which will increase the overall cost of the converter; (2) The higher the voltage stress, the higher the conduction loss of the device and the lower the conversion efficiency of the system; (3) Due to the presence of common mode voltage, the input current will have harmonic distortion, which will reduce the quality of the input current. Summary of the Invention
[0005] The problem to be solved by this invention is to propose a three-phase AC-AC converter topology and its control method, which reduces the voltage stress of the rectifier-side switching devices, suppresses the pollution of the input current by high-frequency common-mode current, and improves the quality of the input current.
[0006] The present invention adopts the following technical solution: a three-phase AC-AC converter topology, wherein the rectifier side consists of a three-phase AC filter 1 and a three-phase controllable rectifier bridge 2; the DC side consists of a DC freewheeling diode 3, a DC inductor and a capacitor 4, including a DC inductor, a DC capacitor and a filter capacitor, wherein the midpoint of the DC capacitor and the midpoint of the DC freewheeling diode 3 are connected to each other and then connected to one end of the filter capacitor, and the other end of the filter capacitor is connected to the neutral point of the three-phase AC filter 1 on the rectifier side and the neutral point of the three-phase AC filter 6 on the inverter side; the inverter side consists of a three-phase controllable inverter bridge 5 and a three-phase AC filter 6 on the inverter side.
[0007] Furthermore, the upper and lower arms of the three-phase controllable rectifier bridge 2 each include a controllable switch module and a diode.
[0008] Furthermore, the DC-side freewheeling diode 3 includes two diodes connected in sequence, and the midpoint of their connection is connected to the midpoint of the DC-side capacitor.
[0009] Furthermore, the inductor and capacitor in the DC-side inductor and capacitor 4 are symmetrically connected to the circuit, and the midpoint of the capacitor is connected to the midpoint of the DC-side freewheeling diode 3 and one end of the filter capacitor, respectively. The other end of the filter capacitor is connected to the neutral point of the rectifier-side three-phase AC filter 1 and the neutral point of the inverter-side three-phase AC filter 6.
[0010] Furthermore, the upper and lower arms of the three-phase controllable inverter bridge both include controllable switch modules.
[0011] Furthermore, the rectifier-side three-phase AC filter includes three-phase filter inductors and three-phase filter capacitors. The three-phase filter inductors include a first-phase filter inductor L1, a second-phase filter inductor L2, and a third-phase filter inductor L3. The three-phase filter capacitors include a first-phase filter capacitor C1, a second-phase filter capacitor C2, and a third-phase filter capacitor C3. One end of the first-phase filter capacitor C1 is connected to the first-phase AC input side of the three-phase controllable rectifier bridge 2. One end of the second-phase filter capacitor C2 is connected to the second-phase AC input side of the three-phase controllable rectifier bridge 2. One end of the third-phase filter capacitor C3 is connected to the third-phase AC input side of the three-phase controllable rectifier bridge 2. The other ends of the first-phase filter capacitor C1, the second-phase filter capacitor C2, and the third-phase filter capacitor C3 are connected to the neutral point O1 of the rectifier-side three-phase AC filter.
[0012] Furthermore, the inverter-side three-phase AC filter includes three-phase filter inductors and three-phase filter capacitors. The three-phase filter inductors include a first-phase filter inductor L4, a second-phase filter inductor L5, and a third-phase filter inductor L6. The three-phase filter capacitors include a first-phase filter capacitor C4, a second-phase filter capacitor C5, and a third-phase filter capacitor C6. One end of the first-phase filter inductor L4 is connected to the first-phase AC output side of the three-phase controllable inverter bridge 6, and the other end is connected to the first-phase filter capacitor C4. One end of the second-phase filter inductor L5 is connected to the second-phase AC output side of the three-phase controllable inverter bridge 6, and the other end is connected to the second-phase filter capacitor C5. One end of the third-phase filter inductor L6 is connected to the third-phase AC output side of the three-phase controllable inverter bridge 6, and the other end is connected to the third-phase filter capacitor C6. The other ends of the first-phase filter capacitor C4, the second-phase filter capacitor C5, and the third-phase filter capacitor C6 are connected to the neutral point O2 of the inverter-side three-phase AC filter.
[0013] The technical solution of the present invention also includes a control method for any of the above-mentioned three-phase AC-AC converter topologies, wherein the specific steps of the rectifier-side control are as follows:
[0014] S1, The three-phase input voltage on the rectifier side is u a u b u c The three-phase input current is i a i b i c The DC side voltage and current are u dc and i dc ;
[0015] S2. Taking phase A as an example, the duty cycle d of phase A is defined by the current application time. A :
[0016]
[0017] Regarding power conservation, the duty cycle d of phase A A It is expressed as follows:
[0018]
[0019] Where k is the proportionality coefficient.
[0020] S3. Perform rectifier-side control: The three-phase controllable rectifier bridge 2 controls the controllable switching modules in the upper and lower bridge arms to generate trigger signals based on the absolute value of the three-phase input voltage.
[0021] The process is as follows: The trigger signal generation process of the upper bridge arm switch module on the rectifier side is as follows: The three-phase input voltage is divided into u according to the magnitude of its absolute value. max u mid u min For the phase with the largest absolute value of the input voltage, when u max When the value is greater than 0, the upper bridge arm switch module of this phase is turned on, the lower bridge arm switch module is turned off, and the on-time is k. d u max Conversely, if the upper bridge arm switch module is turned off, the lower bridge arm switch module is turned on, and the on-time is k. d u max For the phase with the second largest absolute value of the input voltage, when u mid When the value is greater than 0, the upper bridge arm switch module of this phase is turned on, the lower bridge arm switch module is turned off, and the on-time is k. d u mid Conversely, if the upper bridge arm switch module is turned off, the lower bridge arm switch module is turned on, and the on-time is k. d u mid For the phase with the smallest absolute value of the input voltage, when u min When the value is greater than 0, the upper bridge arm switch module of this phase is turned on, the lower bridge arm switch module is turned off, and the on-time is k. d umin Conversely, if the upper bridge arm switch module is turned off, the lower bridge arm switch module is turned on, and the on-time is k. d u min Within one switching cycle, excluding the conduction time of the three-phase upper bridge arm, all upper and lower bridge arm switching modules are turned off. At this time, the DC side freewheeling diode 3 is turned on for a conduction time of T. s -k d u max T s Sampling time.
[0022] Compared with the prior art, the present invention, employing the above technical solution, has the following technical effects:
[0023] (1) The present invention proposes a medium-high voltage converter topology for motor drive, wherein the maximum voltage stress borne by the controllable switching module on the rectifier side is u. i -u O It is the input phase voltage minus the DC-side capacitor neutral point voltage u. O This reduces the voltage stress on the controllable switching module, thereby reducing the requirements and quantity of the controllable switching module, and thus reducing the overall cost of the converter; it also reduces the conduction loss of the switching module and improves the conversion efficiency of the system.
[0024] (2) This invention provides an internal circulation path for common-mode current, avoiding the flow of common-mode current to input and output current, thereby suppressing the pollution of input and output current by high-frequency common-mode current, reducing the distortion rate of current, and improving current quality. Attached Figure Description
[0025] Figure 1 This is a topology diagram of a traditional AC converter;
[0026] Figure 2 This is a circuit diagram of the three-phase AC-AC converter topology of the present invention;
[0027] Figure 3 This is the current flow path when the three-phase rectifier side bridge arm switch modules S1 and S4 are turned on in a specific embodiment of the present invention.
[0028] Figure 4 This is the current flow path when the three-phase rectifier side bridge arm switch modules S1 and S6 are turned on in a specific embodiment of the present invention.
[0029] Figure 5 This is the current flow path when the three-phase rectifier side bridge arm switch module is fully turned off in a specific embodiment of the present invention.
[0030] Figure 6 This is a schematic diagram of the voltage stress distribution of the switching transistor S1 in a specific embodiment of the present invention;
[0031] Figure 7 The three-phase input voltage and current are specified in the specific embodiment of this invention.
[0032] Figure 8 This refers to the three-phase output voltage and current in a specific embodiment of the present invention. Detailed Implementation
[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0034] This specific embodiment discloses a three-phase AC-AC converter topology, which is an improvement on the commonly used topology, such as... Figure 2 As shown, the system includes: a rectifier-side three-phase AC filter 1, a three-phase controllable rectifier bridge 2, a DC-side freewheeling diode 3, a DC-side inductor and capacitor 4, a three-phase controllable inverter bridge 5, and an inverter-side three-phase AC filter 6. Each phase of the three-phase controllable rectifier bridge 2 includes upper and lower arms, and each upper and lower arm has a controllable switch module and a diode. Each phase of the three-phase controllable inverter bridge 5 includes upper and lower arms, and each upper and lower arm has a controllable switch module. The three-phase power supply is connected to the three-phase controllable rectifier bridge 2 through the rectifier-side three-phase AC filter 1, and the DC-side freewheeling diode 3... The three-phase controllable rectifier bridge 2 is connected to the DC bus, and its midpoint is connected to the midpoint of the DC side capacitor 4. The DC side inductor and capacitor 4 are connected to the DC side freewheeling diode 3, and the midpoint of the capacitor is connected to the midpoint of the DC side freewheeling diode 3 and one end of the filter capacitor, respectively. The other end of the filter capacitor is connected to the neutral point of the rectifier side three-phase AC filter 1 and the neutral point of the inverter side three-phase AC filter 6. The three-phase controllable inverter bridge 5 is connected to the DC side inductor and capacitor 4 via the DC bus, and the AC output side of the three-phase controllable inverter bridge 5 is connected to the inverter side three-phase AC filter 6.
[0035] Preferably, the upper and lower arms of the three-phase controllable rectifier bridge 2 each include a controllable switch module and a diode. Each phase is as follows: the first phase upper arm controllable switch module S1 and diode D1, the first phase lower arm controllable switch module S2 and diode D2, the second phase upper arm controllable switch module S3 and diode D3, the second phase lower arm controllable switch module S4 and diode D4, the third phase upper arm controllable switch module S5 and diode D5, and the third phase lower arm controllable switch module S6 and diode D6. The midpoint is connected to the AC input side of the corresponding phase.
[0036] Preferably, the DC-side freewheeling diode 3 includes two diodes D connected in sequence.F1 D F2 And its midpoint is connected to the midpoint of DC side capacitor 4.
[0037] Preferably, the DC-side inductor L P L N and capacitor C P C N The inductor and capacitor are symmetrically connected in the circuit, with the midpoint of the capacitor connected to the midpoint of the DC-side freewheeling diode 3 and the filter capacitor C, respectively. m One end is connected to the filter capacitor C. m The other end is interconnected with the neutral points of both the three-phase AC filter 1 and the three-phase AC filter 6. This connection method provides an internal circulation path for the common-mode current, preventing it from flowing into the input and output currents, thereby suppressing the contamination of the input and output currents by high-frequency common-mode current, reducing the current distortion rate, and improving current quality.
[0038] Preferably, the upper and lower arms of the three-phase controllable inverter bridge 5 both include controllable switch modules. Each phase comprises: a first-phase upper arm controllable switch module S7, a first-phase lower arm controllable switch module S8, a second-phase upper arm controllable switch module S9, and a second-phase lower arm controllable switch module S1. 10 Third phase upper bridge arm controllable switch module S 11 The third phase lower bridge arm controllable switch module S 12 The midpoint connects to the AC output side of the corresponding phase.
[0039] Preferably, the rectifier-side three-phase AC filter 1 includes three-phase filter inductors and three-phase filter capacitors. The three-phase filter inductors include a first-phase filter inductor L1, a second-phase filter inductor L2, and a third-phase filter inductor L3. The three-phase filter capacitors include a first-phase filter capacitor C1, a second-phase filter capacitor C2, and a third-phase filter capacitor C3. One end of the first-phase filter capacitor C1 is connected to the first-phase AC input side of the three-phase controllable rectifier bridge 2. One end of the second-phase filter capacitor C2 is connected to the second-phase AC input side of the three-phase controllable rectifier bridge 2. One end of the third-phase filter capacitor C3 is connected to the third-phase AC input side of the three-phase controllable rectifier bridge 2. The other ends of the first-phase filter capacitor C1, the second-phase filter capacitor C2, and the third-phase filter capacitor C3 are connected to the neutral point O1 of the three-phase AC filter 1, which is preferred.
[0040] Preferably, the inverter-side three-phase AC filter 6 includes three-phase filter inductors and three-phase filter capacitors. The three-phase filter inductors include a first-phase filter inductor L4, a second-phase filter inductor L5, and a third-phase filter inductor L6. The three-phase filter capacitors include a first-phase filter capacitor C4, a second-phase filter capacitor C5, and a third-phase filter capacitor C6. One end of the first-phase filter inductor L4 is connected to the first-phase AC output side of the three-phase controllable inverter bridge 5, and the other end is connected to the first-phase filter capacitor C4. One end of the second-phase filter inductor L5 is connected to the second-phase AC output side of the three-phase controllable inverter bridge 5, and the other end is connected to the second-phase filter capacitor C5. One end of the third-phase filter inductor L6 is connected to the third-phase AC output side of the three-phase controllable inverter bridge 5, and the other end is connected to the third-phase filter capacitor C6. The other ends of the first-phase filter capacitor C4, the second-phase filter capacitor C5, and the third-phase filter capacitor C6 are connected to the neutral point O2 of the inverter-side three-phase AC filter 6.
[0041] Based on the above three-phase AC-AC converter topology, this specific embodiment also provides a control method for the rectifier side. The inverter side adopts a traditional control method, which will not be elaborated here. The control method for the rectifier side includes:
[0042] 1) The three-phase input voltage is u a u b u c The three-phase input current is i a i b i c The DC side voltage and current are u dc and i dc .
[0043] 2) Taking phase A as an example, the duty cycle d of phase A is defined by the duration of current application. A :
[0044]
[0045] For power conservation, the following conditions must be met:
[0046] u dc i dc =u a i a +u b i b +u c i c
[0047] If the three-phase input voltage and current are in phase, then the following condition must be met:
[0048] i a =ku a
[0049] i b =kub
[0050] i c =ku c
[0051] Where k is the proportionality coefficient.
[0052] Therefore, the power conservation formulas can be listed as follows:
[0053] u dc i dc =k(u a ×u a +u b ×u b +u c ×u c )
[0054] Combining the four formulas above, we can list the following expressions:
[0055]
[0056] in:
[0057]
[0058] 3) The trigger signal generation process of the upper bridge arm switch module on the rectifier side is as follows:
[0059] Three-phase input voltage is classified into u according to its absolute value. max u mid u min For the phase with the largest absolute value of the input voltage, when u max When the value is greater than 0, the upper bridge arm switch module of this phase is turned on, the lower bridge arm switch module is turned off, and the on-time is k. d u max Conversely, if the upper bridge arm switch module is turned off, the lower bridge arm switch module is turned on, and the on-time is k. d u max For the phase with the second largest absolute value of the input voltage, when u mid When the value is greater than 0, the upper bridge arm switch module of this phase is turned on, the lower bridge arm switch module is turned off, and the on-time is k. d u mid Conversely, if the upper bridge arm switch module is turned off, the lower bridge arm switch module is turned on, and the on-time is k. d u mid For the phase with the smallest absolute value of the input voltage, when u min When the value is greater than 0, the upper bridge arm switch module of this phase is turned on, the lower bridge arm switch module is turned off, and the on-time is k. d u minConversely, if the upper bridge arm switch module is turned off, the lower bridge arm switch module is turned on, and the on-time is k. d u min Within one switching cycle, excluding the conduction time of the three-phase upper bridge arm, all upper and lower bridge arm switching modules are turned off. At this time, the DC side freewheeling diode 3 is turned on for a conduction time of T. s -k d u max T s Sampling time.
[0060] The following uses a three-phase input voltage u a >0>u b >u c Taking [example] as an example, the above method will be explained in detail.
[0061] In this case, during one switching cycle T s Inside, the conduction time of the upper arm of phase A is The lower arms of phases B and C are sequentially turned on, with the following turn-on times: and In a switching cycle T s For the remaining time, all controllable switching modules on the rectifier side are turned off, at which point the freewheeling diode D... F1 D F2 Conduction.
[0062] like Figure 3 , Figure 4 and Figure 5 As shown in the figure, the dashed lines with arrows indicate the three states of the DC bus current flow path under this control method.
[0063] At this time, because of u a >0>u b >u c Therefore, the A-phase controllable switch module S1 is turned on, the B-phase and C-phase upper arm controllable switch modules S3 and S5 are both turned off, the lower arm A-phase controllable switch module S2 is turned off, and the B-phase and C-phase lower arm controllable switch modules S4 and S6 are turned on alternately.
[0064] exist Figure 5 Since all controllable switching modules on the rectifier side are turned off, the freewheeling diode D... F1 D F2 When the diode is conducting, if the voltage drop across the diode is ignored, the freewheeling diode D will continue to conduct in this state. F1 The upper end and freewheeling diode D F2 The tail voltage and the neutral point voltage u of the DC side capacitor o The voltage stresses on controllable switch modules S1, S4, and S6 are equal, at which point they are u, ... a -u o u o-u b and u o -u c The voltage stress in other cases is similar and will not be elaborated here.
[0065] Input phase voltage u a Controllable switch module voltage u S1 and the neutral point voltage u of the DC side capacitor o The simulation results, such as Figure 6 As shown, taking this result as an example, it can be seen that under the control method, the maximum voltage stress borne by the flow-side controllable switch module of the topology proposed in this invention is u. i -u O It is the input phase voltage minus the DC-side capacitor neutral point voltage u. O This reduces the voltage stress on the controllable switching module.
[0066] Compared with the traditional rectifier where the switching module needs to withstand the phase voltage, the present invention can effectively reduce the voltage stress of the switching module, thereby reducing the requirements and number of controllable switching modules, thus reducing the overall cost of the converter; reducing the conduction loss of the switching module and improving the conversion efficiency of the system.
[0067] The three-phase input voltage and current and the three-phase output voltage and current are respectively as follows: Figure 7 and Figure 8 As shown in the figure, taking this result as an example, it can be seen that the topology proposed in this invention can generate normal three-phase voltage and current waveforms under this control method.
[0068] It should be noted that, through Figure 2 It can be seen that the midpoint of the DC capacitor in the topology of this invention is respectively connected to the midpoint of the DC freewheeling diode 3 and the filter capacitor C. m One end is connected to the filter capacitor C. m The other end is interconnected with both the neutral point of three-phase AC filter 1 and the neutral point of three-phase AC filter 6. This connection method provides an internal circulation path for common-mode current, preventing common-mode current from flowing into the input and output currents, and the filter capacitor C... m It can further suppress the pollution of input and output current by high-frequency common-mode current, reduce the current distortion rate, and improve current quality.
[0069] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.
[0070] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.
Claims
1. A control method for a three-phase AC-AC converter topology, characterized in that, The rectifier-side control is as follows: S1, the three-phase input voltage on the rectifier side is , , The three-phase input current is , , The DC side voltage and current are respectively and ; S2. Taking phase A as an example, the duty cycle of phase A is defined by the duration of current application. : (1) Regarding power conservation, the following conditions must be met: (2) If the three-phase input voltage and current are in phase, then the following conditions must be met: (3) Where k is the proportionality coefficient; Combining formula (2), the power is expressed as follows: (4) Combining formulas (1)-(4), the duty cycle of phase A It is expressed as follows: (5) in, (6) S3, Three-phase controllable rectifier bridge (2) controls the controllable switch modules in the upper and lower bridge arms according to the absolute value of the three-phase input voltage to generate trigger signals; The three-phase AC-AC converter topology includes a rectifier-side three-phase AC filter (1), a three-phase controllable rectifier bridge (2), a DC-side freewheeling diode (3), a DC-side inductor and capacitor (4), a three-phase controllable inverter bridge (5), and an inverter-side three-phase AC filter (6). The three-phase power supply is connected to the three-phase controllable rectifier bridge (2) through the rectifier-side three-phase AC filter (1). The DC-side freewheeling diode (3) is connected to the three-phase controllable rectifier bridge (2) via a common DC bus. The DC-side inductor and capacitor (4) are connected to the DC bus. The freewheeling diode (3) is connected, and the DC side inductor and capacitor (4) include: DC inductor, DC capacitor and filter capacitor. One end of the DC capacitor is connected to the DC side freewheeling diode (3), and the other end is connected to the neutral point of the rectifier side three-phase AC filter (1) and the neutral point of the inverter side three-phase AC filter (6) through the filter capacitor. The three-phase controllable inverter bridge (5) is connected to the DC side inductor and capacitor (4) via the same bus. The AC output side of the three-phase controllable inverter bridge (5) is connected to the inverter side three-phase AC filter (6).
2. The control method for a three-phase AC-AC converter topology according to claim 1, characterized in that: Each phase of the three-phase controllable rectifier bridge (2) includes two bridge arms, an upper bridge arm and a lower bridge arm, and both the upper and lower bridge arms include a controllable switch module and a diode.
3. The control method for a three-phase AC-AC converter topology according to claim 1, characterized in that: The DC-side freewheeling diode (3) includes two diodes connected in sequence, and the midpoint of the connection between the two diodes is connected to the midpoint of the DC-side inductor and capacitor (4).
4. The control method for a three-phase AC-AC converter topology according to claim 1, characterized in that: The DC inductor and DC capacitor in the DC side inductor and capacitor (4) are symmetrically connected to the circuit, and the midpoint of the DC capacitor is connected to the midpoint of the DC side freewheeling diode (3) and one end of the filter capacitor, respectively. The other end of the filter capacitor is connected to the neutral point of the rectifier side three-phase AC filter (1) and the neutral point of the inverter side three-phase AC filter (6).
5. The control method for a three-phase AC-AC converter topology according to claim 1, characterized in that: Each phase of the three-phase controllable inverter bridge (5) includes two bridge arms, an upper one and a lower one, and both the upper and lower bridge arms include a controllable switch module.
6. The control method for a three-phase AC-AC converter topology according to claim 1, characterized in that: The rectifier-side three-phase AC filter (1) includes a three-phase filter inductor and a three-phase filter capacitor. The three-phase filter inductor includes a first-phase filter inductor (L1), a second-phase filter inductor (L2), and a third-phase filter inductor (L3). The three-phase filter capacitor includes a first-phase filter capacitor (C1), a second-phase filter capacitor (C2), and a third-phase filter capacitor (C3). One end of the first-phase filter capacitor (C1) is connected to the first-phase AC input side of the three-phase controllable rectifier bridge (2). One end of the second-phase filter capacitor (C2) is connected to the second-phase AC input side of the three-phase controllable rectifier bridge (2). One end of the third-phase filter capacitor (C3) is connected to the third-phase AC input side of the three-phase controllable rectifier bridge (2). The other ends of the first-phase filter capacitor (C1), the second-phase filter capacitor (C2), and the third-phase filter capacitor (C3) are connected as the neutral point (O1) of the rectifier-side three-phase AC filter (1).
7. The control method for a three-phase AC-AC converter topology according to claim 1, characterized in that: The inverter-side three-phase AC filter (6) includes three-phase filter inductors and three-phase filter capacitors. The three-phase filter inductors include a first-phase filter inductor (L4), a second-phase filter inductor (L5), and a third-phase filter inductor (L6). The three-phase filter capacitors include a first-phase filter capacitor (C4), a second-phase filter capacitor (C5), and a third-phase filter capacitor (C6). One end of the first-phase filter inductor (L4) is connected to the first-phase AC output side of the three-phase controllable inverter bridge (5), and the other end is connected to the first-phase filter capacitor (C4). The second-phase... One end of the filter inductor (L5) is connected to the second phase AC output side of the three-phase controllable inverter bridge (5), and the other end is connected to the second phase filter capacitor (C5); one end of the third phase filter inductor (L6) is connected to the third phase AC output side of the three-phase controllable inverter bridge (5), and the other end is connected to the third phase filter capacitor (C6); the other ends of the first phase filter capacitor (C4), the second phase filter capacitor (C5), and the third phase filter capacitor (C6) are connected to the neutral point (O2) of the three-phase AC filter (6) on the inverter side.
8. The control method for the three-phase AC-AC converter topology according to claim 1, characterized in that... In step S3, the trigger signal generation process is as follows: In a three-phase controllable rectifier bridge (2), the three-phase input voltages are divided into u according to their absolute values. max u mid u min ; For the phase with the largest absolute value of the input voltage u max , when u max When the value is greater than 0, the upper bridge arm switch module of this phase is turned on, the lower bridge arm switch module is turned off, and the on-time is k. d u max Conversely, if the upper bridge arm switch module is turned off, the lower bridge arm switch module is turned on, and the on-time is k. d u max ; For the second largest absolute value of the input voltage, u mid , when u mid When the value is greater than 0, the upper bridge arm switch module of this phase is turned on, the lower bridge arm switch module is turned off, and the on-time is k. d u mid Conversely, if the upper bridge arm switch module is turned off, the lower bridge arm switch module is turned on, and the on-time is k. d u mid ; For the phase with the smallest absolute value of the input voltage u min , when u min When the value is greater than 0, the upper bridge arm switch module of this phase is turned on, the lower bridge arm switch module is turned off, and the on-time is k. d u min Conversely, if the upper bridge arm switch module is turned off, the lower bridge arm switch module is turned on, and the on-time is k. d u min ; Within one switching cycle, excluding the conduction time of the three-phase upper bridge arm, the upper and lower bridge arm switching modules are all turned off. At this time, the DC side freewheeling diode (3) is turned on, and the conduction time is T. s -k d u max T s Sampling time.