Ac-ac converter and control method thereof
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- FSP POWERLAND TECHNOLOGY INC
- Filing Date
- 2026-04-21
- Publication Date
- 2026-07-21
Smart Images
Figure CN122437397A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of power electronic converter technology, and in particular to an AC-AC converter and its control method. Background Technology
[0002] Traditional three-phase AC-AC converters often adopt a two-stage topology of AC-DC-AC, which requires an intermediate DC bus and electrolytic capacitors. This not only results in a large size and low power density, but also relies on closed-loop control to adjust the switching frequency and duty cycle in real time to achieve regulated output. The control algorithm is complex and the dynamic response speed is limited.
[0003] Existing isolated AC-AC conversion technologies mostly rely on traditional power frequency transformers. While simple in structure, these devices are bulky, have high losses, and poor adjustability, making them unsuitable for the demands of high-density power distribution and smart grid development. Some conversion schemes using LLC resonant topologies offer soft-switching advantages, but still prioritize closed-loop voltage regulation. Switching frequency and duty cycle must be adjusted in real-time according to load and voltage fluctuations, making it impossible to maintain stable operation at the resonant point for extended periods. This leads to increased switching losses and limited operating frequency, hindering improvements in converter power density. Especially in applications like solid-state transformers (SSTs) where a constant power frequency is required and only electrical isolation and voltage amplitude conversion are needed, achieving a high power factor necessitates sampling input voltage and current information. This requires complex closed-loop calculations and multi-loop control algorithms, resulting in high design difficulty and cost for the overall control logic and sampling architecture. Furthermore, the lack of adaptable open-loop control schemes prevents the full utilization of the single-stage isolation, bidirectional energy flow, and miniaturization advantages of SSTs. Summary of the Invention
[0004] This application aims to provide an AC-AC converter and its control method, which achieves high-efficiency, high-power-density AC-AC conversion with bidirectional energy flow through simple open-loop operation.
[0005] To achieve the above objectives, the technical solution of this application is as follows: A control method for an AC-AC converter is provided, which includes: a first conversion unit that converts a filtered first AC current to obtain a primary-side conversion voltage; a resonant unit that performs a resonant conversion on the primary-side conversion voltage to obtain a secondary-side conversion voltage; and a secondary-side conversion unit that converts the secondary-side conversion voltage to output a second AC current; wherein the first AC current is a three-phase AC current. The control method for the AC-AC converter includes: The first AC current sampled shows that the L phase has the largest amplitude, followed by the M phase, and the S phase has the smallest amplitude. Determine the switching drive logic of the primary-side transformation unit; The switching drive logic of the secondary-side transformation unit is determined based on the switching drive logic of the primary-side transformation unit. The switching drive logic for determining the primary-side transformation unit includes: Set the switching frequency of the primary-side converter unit to the resonant frequency; The duty cycle of the primary-side conversion unit is set according to the S-phase voltage and the M-phase voltage.
[0006] Optionally, the switching phase shift duty cycle of the primary-side conversion unit can be set according to the S-phase voltage and the M-phase voltage, as shown below: Among them, D PN Indicates the switch phase shift duty cycle; u S Indicates the voltage of phase S; u M This represents the voltage of phase M.
[0007] Optionally, the first AC current is sampled, with the largest amplitude in phase L, followed by phase M, and the smallest in phase S, including: Calculate the absolute value of the amplitude of the first AC current, select the voltage of the phase with the largest absolute value of amplitude in the first AC current as the L-phase voltage, select the voltage of the phase with the smallest absolute value of amplitude in the first AC current as the S-phase voltage, and select the voltage of the remaining phase in the first AC current as the M-phase voltage, as shown below: in, This represents the input voltage of the resonant unit.
[0008] Optionally, determining the switching drive logic of the primary-side transformation unit further includes: Set the duty cycle of the primary-side transformation unit to 50%.
[0009] Optionally, the switching drive logic of the secondary-side conversion unit is determined based on the switching drive logic of the primary-side conversion unit, including: setting the switching drive logic of the secondary-side conversion unit to be the same as the switching drive logic of the corresponding phase of the primary-side conversion unit, ensuring that the switches corresponding to the same position are turned on and off at the same time, and applying the same switching frequency and duty cycle.
[0010] An AC-AC converter for performing the control method of the AC-AC converter as described above, comprising: The first AC power unit includes a first AC power supply; wherein the first AC power supply is a three-phase AC power supply. A primary-side filtering unit is connected to the first AC power supply and filters the three-phase AC power supply. The primary-side transformation unit transforms the filtered first AC current to obtain the primary-side transformed voltage. A resonant unit, wherein the resonant unit performs a resonant transformation on the primary-side transformed voltage to obtain the secondary-side transformed voltage; The secondary-side transformation unit transforms the secondary-side transformation voltage to obtain secondary-side alternating current; A secondary-side filtering unit filters the secondary-side AC current. The second AC unit outputs the filtered secondary AC power to obtain the second AC power. The control unit has a first terminal connected to a first AC current and a second terminal connected to the primary-side conversion unit and the secondary-side conversion unit. It samples the first AC current, calculates the switching drive logic of the primary-side conversion unit, and determines the switching drive logic of the corresponding phase of the secondary-side conversion unit based on the switching drive logic of the primary-side conversion unit.
[0011] Optionally, the resonant unit includes: a first inductor, a first end of the first inductor connected to a first terminal of the second end of the primary-side conversion unit, a second end of the first inductor connected to a first end of the primary winding of the transformer, a second end of the primary winding of the transformer connected to a first end of a first capacitor, a second end of the first capacitor connected to a second terminal of the second end of the primary-side conversion unit, a second inductor connected in parallel with the primary winding of the transformer, and a secondary winding of the transformer connected to the first end of the secondary-side conversion unit; The first inductor is a resonant inductor, the second inductor is a magnetizing inductor, and the first capacitor is a resonant capacitor.
[0012] 8. The AC-AC converter as described in claim 7, wherein the primary-side filtering unit comprises: A third inductor, the first end of which is connected to the first phase A AC power supply, and the second end of which is connected to the first end of the second capacitor and the first terminal of the first end of the primary-side conversion unit; a fourth inductor, the first end of which is connected to the first phase B AC power supply, and the second end of which is connected to the first end of the third capacitor and the second terminal of the first end of the primary-side conversion unit; a fifth inductor, the first end of which is connected to the first phase C AC power supply, and the second end of which is connected to the first end of the third capacitor and the third terminal of the first end of the primary-side conversion unit; the second ends of the second capacitor, the second ends of the third capacitor, and the second ends of the fourth capacitor are connected together. The original-side transformation unit includes: The first switch has its source connected to the source of the second switch, the drain of the second switch connected to the drain of the third switch, the source of the third switch connected to the source of the fourth switch, and the midpoint of the connection between the drain of the second switch and the drain of the third switch is the first terminal of the first end of the primary-side transformation unit. The fifth switch has its source connected to the source of the sixth switch, its drain connected to the drain of the seventh switch, and its source connected to the source of the eighth switch. The midpoint of the connection between the drain of the sixth switch and the drain of the seventh switch is the second terminal of the first end of the primary-side transformation unit. The ninth switch has its source connected to the source of the tenth switch, its drain connected to the drain of the eleventh switch, and its source connected to the source of the twelfth switch. The midpoint of the connection between the drains of the tenth and eleventh switches is the third terminal of the first end of the primary-side conversion unit. The drains of the first switch, the fifth switch, and the primary-side switch are connected. The drains of the primary-side switch, the primary-side switch, and the ninth switch are connected. The drain of the ninth switch is the first terminal of the second end of the primary-side conversion unit, and the drain of the twelfth switch is the second terminal of the second end of the primary-side conversion unit.
[0013] Optionally, the second AC power is three-phase AC power; The secondary transformation unit includes: The thirteenth switch, the source of the thirteenth switch is connected to the source of the fourteenth switch, the drain of the fourteenth switch is connected to the drain of the fifteenth switch, the source of the fifteenth switch is connected to the source of the sixteenth switch, and the midpoint of the connection between the drain of the fourteenth switch and the fifteenth switch is the first terminal of the second end of the secondary-side conversion unit. The seventeenth switch, the source of the seventeenth switch is connected to the second terminal of the eighteenth switch, the drain of the eighteenth switch is connected to the drain of the nineteenth switch, the source of the nineteenth switch is connected to the source of the twentieth switch, and the midpoint of the connection between the drain of the eighteenth switch and the drain of the nineteenth switch is the second terminal of the second end of the secondary-side conversion unit. The source of the 21st switch is connected to the second terminal of the 22nd switch, the drain of the 22nd switch is connected to the drain of the 23rd switch, the source of the 23rd switch is connected to the source of the 24th switch, and the midpoint of the connection between the drains of the 22nd and 23rd switches is the third terminal of the second terminal of the secondary-side conversion unit; the drains of the 13th switch, the 17th switch, and the 21st switch are connected, and the drains of the 16th switch, the 20th switch, and the 24th switch are connected, with the drains of the 21st and 24th switches forming the first terminal of the secondary-side conversion unit; The secondary filtering unit includes: The sixth inductor has its first end connected to the second phase A AC power supply; its second end is connected to the first end of the fifth capacitor and the first terminal of the second end of the secondary-side conversion unit; the seventh inductor has its first end connected to the second phase B AC power supply; its second end is connected to the first end of the sixth capacitor and the second terminal of the second end of the secondary-side conversion unit; the eighth inductor has its first end connected to the second phase C AC power supply; its second end is connected to the first end of the seventh capacitor and the third terminal of the first end of the secondary-side conversion unit; and the second ends of the fifth, sixth, and seventh capacitors are connected together.
[0014] Optionally, the second AC power is single-phase AC power; The secondary transformation unit includes: The source of the 25th switch is connected to the source of the 26th switch, the drain of the 26th switch is connected to the drain of the 27th switch, the source of the 27th switch is connected to the source of the 28th switch, and the midpoint of the connection between the drain of the 26th switch and the 27th switch is the first terminal of the second end of the secondary-side conversion unit. The source of the 29th switch is connected to the source of the 30th switch, the drain of the 30th switch is connected to the drain of the 31st switch, the source of the 31st switch is connected to the source of the 32nd switch, and the midpoint of the connection between the drains of the 30th and 31st switches is the second terminal of the second end of the secondary-side conversion unit; the drain of the 25th switch is connected to the drain of the 29th switch, the drain of the secondary-side switch is connected to the drain of the secondary-side switch, and the drain of the 32nd switch and the drain of the 28th switch constitute the first end of the secondary-side conversion unit; The secondary filtering unit includes: The ninth inductor has its first terminal connected to the first terminal of the eighth capacitor and the first terminal of the second terminal of the secondary-side conversion unit, and its second terminal connected to the first terminal of the second AC power supply. The tenth inductor has its first terminal connected to the first terminal of the ninth capacitor and the second terminal of the second terminal of the secondary-side conversion unit, and its second terminal connected to the second terminal of the second AC power supply; the second terminal of the ninth capacitor is connected to the second terminal of the eighth capacitor.
[0015] The AC-AC converter and its control method proposed in this application achieve three-phase AC to three-phase AC or single-phase AC conversion in a single stage. The equivalent AC-to-AC voltage ratio is changed by adjusting the transformer turns ratio. The resonant converter unit adopts an LLC structure, does not handle voltage regulation, and can always operate at the resonant point, thus achieving high efficiency. Simultaneously, the primary and secondary converter units maintain soft-switching operation with low turn-off current, allowing for a significant increase in switching frequency. No voltage or current loops are required; the switching frequency and phase shift duty cycle are obtained through simple open-loop calculations, greatly reducing the complexity of control and sampling while achieving high power density and a power factor close to 1. Furthermore, energy can flow bidirectionally in the AC-AC converter, enabling bidirectional AC-AC conversion. The AC-AC converter and its control method proposed in this application can be applied to solid-state transformers, for example, converting 13.8kV medium-voltage AC to 380V AC while maintaining the same AC frequency. This is suitable for applications where the power frequency remains constant and only isolation and voltage regulation are required.
[0016] To make the above-mentioned features and advantages of the application more apparent and understandable, specific embodiments are provided below, and detailed descriptions are given in conjunction with the accompanying drawings. Attached Figure Description
[0017] Figure 1 This is a circuit diagram of the AC-AC converter proposed in this application.
[0018] Figure 2 This is an analog control circuit diagram of the control module of the AC-AC converter proposed in this application.
[0019] Figure 3 Circuit diagram of an AC-AC converter that converts three-phase AC to three-phase AC.
[0020] Figure 4 The circuit diagram of an AC-AC converter that converts three-phase AC to single-phase AC.
[0021] Figure 5 This is a flowchart of the control method for an AC-AC converter.
[0022] Figure 6 Three-phase alternating current u A u B u C with u L u M u S Transformation relationship diagram between them.
[0023] Figure 7 The diagram shows the switching drive and voltage / current waveforms of the primary-side conversion unit 13. Detailed Implementation
[0024] To make the objectives and technical solutions of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the described embodiments of this application without creative effort are within the scope of protection of this application.
[0025] This application discloses an AC-AC converter; please refer to [link / reference]. Figure 1 , Figure 1 This is a circuit diagram of the AC-AC converter proposed in this application. The AC-AC converter includes: First AC power unit 11, the first AC power unit 11 includes a first AC power supply. A u B u C ; Primary-side filter unit 12, the primary-side filter unit 12 and the first AC current u A u B u C Connection, for three-phase alternating current u A u B u C Perform filtering; Primary-side transformation unit 13, the first transformation unit 13 filters the first AC current u A u B u C The transformation is performed to obtain the primary-side transformed voltage; Resonant unit 14, wherein the resonant unit 14 performs resonant transformation on the primary side transformed voltage to obtain the secondary side transformed voltage; Secondary-side conversion unit 15, which converts the secondary-side conversion voltage to obtain secondary-side alternating current; Secondary-side filtering unit 16, wherein the secondary-side filtering unit 16 filters the secondary-side AC current; The second AC unit 17 outputs the filtered secondary AC power to obtain the second AC power. Control unit 18, the first terminal of which is connected to the first AC power supply u A u B u C The second terminal of the control unit 18 is connected to the primary-side conversion unit 13 and the secondary-side conversion unit 15 to sample the first AC current u. A u B u CThe switching drive logic of the primary-side conversion unit 13 is calculated, and the switching drive logic of the corresponding phase of the secondary-side conversion unit 15 is determined based on the switching drive logic of the primary-side conversion unit 13.
[0026] As an example, the first alternating current u A u B u C It is a three-phase alternating current.
[0027] As an example, the resonant unit 14 includes: an inductor L r Inductor L m Capacitor C r and transformer T r Inductor L r The first end is connected to the first terminal of the second end of the primary-side transformation unit 13, and the inductor L r The second terminal is connected to transformer T r The first end of the primary winding is connected to the transformer T. r The second terminal of the primary winding is connected to the capacitor C r The first terminal is connected to capacitor C. r The second end is connected to the second terminal of the second end of the primary-side transformation unit 13, and the inductor L m With transformer T r The primary windings are connected in parallel, and the transformer T r The secondary winding is connected to the first end of the secondary transformation unit 15.
[0028] As an example, inductor L r It is a resonant inductor, passing through inductor L r The current is the resonant current i Lr .
[0029] As an example, inductor L m It is the magnetizing inductor.
[0030] As an example, capacitor C r It is a resonant capacitor.
[0031] As an example, control unit 18 can be an analog control circuit; see [link to relevant documentation]. Figure 2 , Figure 2 This is an analog control circuit diagram of the control module for the AC-AC converter proposed in this application. The control unit 18 includes: The sampling module 181, absolute value calculation module 182, frequency and duty cycle calculation module 183, and switch drive logic determination module 184 are connected sequentially. The first terminal of the sampling module 181 is the first terminal of the control module 18. The second terminal of the sampling module 181 is connected to the first terminal of the absolute value calculation module 182. The second terminal of the absolute value calculation module 182 is connected to the first terminal of the frequency and duty cycle calculation module 183. The second terminal of the frequency and duty cycle calculation module 183 is connected to the first terminal of the switch drive logic determination module 184. The second terminal of the switch drive logic determination module 184 outputs a switch drive signal that is connected to the primary-side conversion module 13 and the secondary-side conversion module 15.
[0032] As an example, the control unit 18 may also be a digital signal processing chip (DSP) that integrates a control method for an AC-AC converter proposed in this application.
[0033] As an example, the model of the digital signal processing chip includes: TMS320C6000.
[0034] As an example, the primary-side filtering unit 12 includes: Primary inductor L a1 Primary inductor L b1 Primary inductor L c1 Primary capacitor C 1. Primary capacitor C 2 and primary capacitor C 3. Primary inductor L a1 The first terminal is connected to the first phase A alternating current u A The first end is connected; the primary inductor L a1 The second end is connected to the primary capacitor respectively. C The first terminal of the first end of the primary-side conversion unit 13 is connected to the first terminal of the primary-side inductor; L b1 The first terminal is connected to the first phase B alternating current u B The first end is connected to the primary inductor. L b1 The second end is connected to the primary capacitor respectively. C The first terminal of 2 is connected to the second terminal of the first terminal of the primary-side conversion unit 13; the primary-side inductor L c1 The first terminal is connected to the first C-phase AC current u C The first end is connected to the primary inductor. L c1The second end is connected to the primary capacitor respectively. C The first terminal of 3 and the third terminal of the first terminal of the primary-side transformation unit 13 are connected, and the primary-side capacitor... C The second terminal of 1, primary-side capacitor C 2. Second terminal and primary side capacitor C The second end of 3 is connected.
[0035] As an example, the first phase A alternating current u A The second terminal, the first B-phase AC power u B The second terminal and the first C-phase AC power u C The second end is connected.
[0036] As an example, the first phase A alternating current u A Output the first A-phase input current i A The first phase B alternating current u B Output the first B-phase input current i B The first C-phase AC power u C Output the first C-phase input current i C .
[0037] As an example, the original-side transformation unit 13 includes: primary side switch S a1 Primary-side switch S a2 Primary-side switch S a3 Primary-side switch S a4 Primary-side switch S b1 Primary-side switch S b2 Primary-side switch S b3 Primary-side switch S b4 Primary-side switch S c1 Primary-side switch S c2 Primary-side switch S c3 and primary side switch S c4 .
[0038] In phase A bridge arm, the primary side switch S a1 Source and primary side switches S a2 Source-level connection, primary-side switch S a2drain and primary side switch S a3 Drain connection, primary-side switch S a3 Source and primary side switches S a4 Source-level connection, primary-side switch S a2 The drain and primary side switch S a3 The midpoint of the drain connection is the first terminal of the first end of the primary-side transformation unit 13.
[0039] Specifically, primary-side switch S a1 With primary side switch S a2 Construct a bidirectional switch, primary-side switch S a3 With primary side switch S a4 It forms a two-way switch.
[0040] In phase B bridge arm, primary side switch S b1 Source and primary side switches S b2 Source-level connection, primary-side switch S b2 drain and primary side switch S b3 Drain connection, primary-side switch S b3 Source and primary side switches S b4 Source-level connection, primary-side switch S b2 The drain and primary side switch S b3 The midpoint of the drain connection is the second terminal of the first end of the primary-side transformation unit 13.
[0041] Specifically, primary-side switch S b1 With primary side switch S b2 Construct a bidirectional switch, primary-side switch S b3 With primary side switch S b4 It forms a two-way switch.
[0042] In the C-phase bridge arm, the primary-side switch S c1 Source and primary side switches S c2 Source-level connection, primary-side switch S c2drain and primary side switch S c3 Drain connection, primary-side switch S c3 Source and primary side switches S c4 Source-level connection, primary-side switch S c2 The drain and primary side switch S c3 The midpoint of the drain connection is the third terminal of the first end of the primary-side switching unit 13. Primary-side switch S a1 drain and primary side switch S b1 Drain and primary side switch S c1 Drain connection, primary-side switch S a4 drain and primary side switch S b4 Drain and primary side switch S c4 The drain connection. Primary-side switch. S c1 The drain is the first terminal of the second end of the primary-side switching unit 13, and the primary-side switch is... S c4 The drain is the second terminal of the second end of the primary-side transformation unit 13.
[0043] Specifically, primary-side switch S c1 With primary side switch S c2 Construct a bidirectional switch, primary-side switch S c3 With primary side switch S c4 It forms a two-way switch.
[0044] As an example, the second AC unit 17 may include a second AC power supply. A1 u B1 u C1 Or the second alternating current u A2 .
[0045] In a specific embodiment of this application, please refer to Figure 3 , Figure 3 This is a circuit diagram of an AC-AC converter for converting three-phase AC to three-phase AC. The second AC unit 27 includes a second AC power supply. A1 u B1 u C1 The AC-AC converter provided in this application converts the first AC power u A u Bu C Perform conversion to output the second AC voltage u A1 u B1 u C1 .
[0046] As an example, the AC-AC converter includes: a first AC power unit 21, a primary-side filter unit 22, a primary-side converter unit 23, a resonant unit 24, a secondary-side converter unit 25, a secondary-side filter unit 26, a second AC power unit 27, and a control unit 28. The connection relationship between the first AC power unit 21, the primary-side filter unit 22, the primary-side converter unit 23, the resonant unit 24, and the control unit 28 is the same as that between the first AC power unit 11, the primary-side filter unit 12, the primary-side converter unit 13, the resonant unit 14, and the control unit 18, and will not be described again here.
[0047] As an example, the secondary side transformation unit 25 includes: Secondary switch S a11 Secondary switch S a21 Secondary switch S a31 Secondary switch S a41 Secondary switch S b11 Secondary switch S b21 Secondary switch S b31 Secondary switch S b41 Secondary switch S c11 Secondary switch S c21 Secondary switch S c31 and secondary switch S c41 .
[0048] In phase A bridge arm, secondary switch S a11 Source and secondary switches S a21 Source-level connection, secondary-side switch S a21 drain and secondary switch S a31 Drain connection, secondary switch S a31 Source and secondary switches S a41 Source-level connection, secondary-side switch S a21 Drain and secondary switchS a31 The connection midpoint is the first terminal of the second end of the secondary side transformation unit 25.
[0049] Specifically, secondary switch S a11 With secondary switch S a21 Constitutes a bidirectional switch, secondary switch S a31 With secondary switch S a41 It forms a two-way switch.
[0050] In phase B bridge arm, secondary switch S b11 Source and secondary switches S b21 The second end is connected to the secondary switch. S b21 drain and secondary switch S b31 Drain connection, secondary switch S b31 Source and secondary switches S b41 Source-level connection, secondary-side switch S b21 Drain and secondary switch S b31 The midpoint of the drain connection is the second terminal of the second end of the secondary-side conversion unit 25.
[0051] Specifically, secondary switch S b11 With secondary switch S b21 Constitutes a bidirectional switch, secondary switch S b31 With secondary switch S b41 It forms a two-way switch.
[0052] In the C-phase bridge arm, the secondary switch S c11 Source and secondary switches S c21 The second end is connected to the secondary switch. S c21 drain and secondary switch S c31 Drain connection, secondary switch S c31 Source and secondary switches S c41 Source-level connection, secondary-side switch S c21 Drain and secondary switchS c31 The midpoint of the drain connection is the third terminal of the second end of the secondary-side switching unit 25. Secondary-side switch S a11 Drain and secondary switch S b11 Drain and secondary switch S c11 Drain connection, secondary switch S a41 Drain and secondary switches S b41 Drain and secondary switch S c41 The drain connection. Secondary switch. S c11 Drain and secondary switch S c41 The drain of the secondary side forms the first terminal of the secondary-side transformation unit 25.
[0053] Specifically, secondary switch S c11 With secondary switch S c21 Constitutes a bidirectional switch, secondary switch S c31 With secondary switch S c41 It forms a two-way switch.
[0054] As an example, the secondary filtering unit 26 includes: Secondary inductor L a11 Secondary inductor L b11 Secondary inductor L c11 Secondary capacitor C 4. Secondary capacitor C 5 and secondary capacitors C 6. Secondary inductor L a11 The first terminal is connected to the second phase A alternating current u A1 First terminal connection; Secondary inductor L a11 The second end is connected to the secondary capacitor. C The first terminal of the first end of the 6 and the first terminal of the second end of the secondary-side conversion unit 25 are connected; the secondary-side inductor L b11 The first terminal is connected to the second phase B alternating current u B1 The first terminal is connected to the secondary inductor. L b11 The second end is connected to the secondary capacitor. CThe first terminal of the 5 and the second terminal of the second terminal of the secondary-side conversion unit 25 are connected; the secondary-side inductor L c11 The first terminal is connected to the second C-phase AC current u C1 The first terminal is connected to the secondary inductor. L c11 The second end is connected to the secondary capacitor. C The first terminal of 4 and the third terminal of the first terminal of the secondary-side conversion unit 25 are connected, and the secondary-side capacitor... C The second terminal of 6, secondary capacitor C 5's second terminal and secondary capacitor C The second end of 4 is connected.
[0055] As an example, the second phase A alternating current u A1 The second terminal, the second phase B AC power u B1 The second terminal and the second C-phase AC power u C1 The second end is connected.
[0056] As an example, the secondary inductor L a1 The current is i A1 Secondary inductor L b1 The current is i B1 Secondary inductor L c1 The current is i C1 .
[0057] In another specific embodiment of this application, please refer to Figure 4 , Figure 4 This is a circuit diagram of an AC-AC converter that converts three-phase AC to single-phase AC. The second AC unit 37 includes a second AC power supply. A2 The AC-AC converter provided in this application converts the first AC power u A u B u C Perform conversion to output the second AC voltage u A2 .
[0058] As an example, the AC-AC converter includes: a first AC power unit 31, a primary-side filter unit 32, a primary-side conversion unit 33, a resonant unit 34, a secondary-side conversion unit 35, a secondary-side filter unit 36, a second AC power unit 37, and a control unit 38. The connection relationship between the first AC power unit 31, the primary-side filter unit 32, the primary-side conversion unit 33, the resonant unit 34, and the control unit 38 is the same as that between the first AC power unit 11, the primary-side filter unit 12, the primary-side conversion unit 13, the resonant unit 14, and the control unit 18, and will not be described again here.
[0059] As an example, the secondary side transformation unit 35 includes: Secondary switch S a12 Secondary switch S a22 Secondary switch S a32 Secondary switch S a42 Secondary switch S b12 Secondary switch S b22 Secondary switch S b32 Secondary switch S b42 .
[0060] Secondary switch S a12 Source and secondary switches S a22 Source-level connection, secondary-side switch S a22 drain and secondary switch S a32 Drain connection, secondary switch S a32 Source and secondary switches S a42 Source-level connection, secondary-side switch S a22 Drain and secondary switch S a32 The connection midpoint is the first terminal of the second end of the secondary side transformation unit 35.
[0061] Specifically, secondary switch S a12 With secondary switch S a22 Constitutes a bidirectional switch, secondary switch S a32 With secondary switch S a42 It forms a two-way switch.
[0062] Secondary switch S b12 Source and secondary switches S b22 Source-level connection, secondary-side switch S b22 drain and secondary switch S b32 Drain connection, secondary switch S b32 Source and secondary switchesS b42 Source-level connection, secondary-side switch S b22 Drain and secondary switch S b32 The midpoint of the drain connection is the second terminal of the second end of the secondary-side switching unit 35. S a12 Drain and secondary switch S b12 Drain connection, secondary switch S a42 drain and secondary switch S b42 The drain connection. Secondary switch. S b12 Drain and secondary switch S b42 The drain of the secondary-side transformer 35 forms the first terminal of the secondary-side transformer 35.
[0063] Specifically, secondary switch S b12 With secondary switch S b22 Constitutes a bidirectional switch, secondary switch S b32 With secondary switch S b42 It forms a two-way switch.
[0064] As an example, the secondary filtering unit 36 includes: Secondary inductor L a12 Secondary inductor L b12 Secondary capacitor C 7. Secondary capacitor C 8 and secondary capacitors C 6. Secondary inductor L a12 The first end is connected to the secondary capacitor respectively C The first terminal of the first end of the 8 and the first terminal of the second end of the secondary-side conversion unit 35 are connected, and the secondary-side inductor L a12 The second terminal is connected to the second AC current u A2 First terminal connection; Secondary inductor L b12 The first end is connected to the secondary capacitor respectively C The first terminal of 7 and the second terminal of the second terminal of the secondary-side conversion unit 35 are connected, and the secondary-side inductor... L b12 The second terminal is connected to the second AC current u A2 The second terminal is connected; secondary capacitor C The second terminal of 7 and the secondary capacitorC The second end of 8 is connected.
[0065] As an example, the secondary inductor L a12 The current is i A2 Secondary inductor L b12 The current is i B2 .
[0066] This application also proposes a control method for an AC-AC converter, applied to the aforementioned AC-AC converter. Please refer to [link to relevant documentation]. Figure 5 , Figure 5 This is a flowchart of the control method for an AC-AC converter, which includes steps S1 to S4.
[0067] Step S1, sample the first AC current u A u B u C The L phase has the largest amplitude, followed by the M phase, and the S phase has the smallest amplitude.
[0068] Step S2: Determine the switching drive logic of the primary-side transformation unit.
[0069] Step S3: Determine the switching drive logic of the secondary-side transformation unit based on the switching drive logic of the primary-side transformation unit.
[0070] The following is combined with Figure 1 This section introduces the specific steps of the control method for AC-AC converters.
[0071] In step S1, the first alternating current u is sampled. A u B u C The L phase has the largest amplitude, followed by the M phase, and the S phase has the smallest amplitude.
[0072] For example, please refer to Figure 6 , Figure 6 Three-phase alternating current u A u B u C with u L u M u S The transformation relationship diagram between them, where u LM u represents the line voltage between phase L and phase M. LS u represents the line voltage between phase L and phase S. MS This represents the line voltage between phase M and phase S. Each power frequency cycle T s Inside, according to the first alternating current u A uB u C The magnitude of the amplitude is determined for the three phases L, M, and S, including: calculating the first AC current u A u B u C The absolute value of the amplitude, select the first AC voltage u A u B u C The voltage of the phase with the largest absolute value of the intermediate amplitude is taken as the L-phase voltage u. L Select the first AC power supply u A u B u C The voltage of the phase with the smallest absolute value of the intermediate amplitude is taken as the voltage of phase S, u. S Select the first AC power supply u A u B u C The voltage of the remaining phase is taken as the M-phase voltage u. M , means as follows: in, This represents the input voltage of the resonant unit 14.
[0073] In step S2, the switching drive logic of the primary-side transformation unit is determined.
[0074] As an example, the switching drive logic of the primary-side transformation unit is determined, including: The duty cycle of the primary-side converter is set to 50%. Set the switching frequency f of the primary-side transformer unit. s =f o ; where f o This represents the resonant frequency, a fixed value for the AC-AC converter. According to the S-phase voltage u S and M-phase voltage u M Set the switching phase shift duty cycle D of the primary-side conversion unit. PN .
[0075] As an example, the switching frequency f of the primary-side transformation unit is set. s =f o At this time, the resonant unit 14 is working at the resonant point, and the AC-AC converter is a solid-state transformer (SST).
[0076] For example, please refer to Figure 7 , Figure 7 The diagram shows the switching drive and voltage / current waveforms of the primary-side conversion unit 13, where u S_gs Indicates the gate switching drive signal; S Lu / dThis represents the drive signal for the upper switch and the drive signal for the lower switch of phase L in the first half of the cycle; S Ld / u This indicates the drive signal of the upper switch and the drive signal of the lower switch of phase L in the second half of the cycle, and S. Lu / d They are complementary; S Md / u This indicates the drive signal for the lower switch of phase M in the first half of the cycle and the drive signal for the lower switch; S Mu / d This indicates the drive signal of the lower switch of phase M in the second half of the cycle and the drive signal of the lower switch, and S. Md / u They are complementary; S Sd / u This indicates the drive signal for the lower switch of phase S in the first half of the cycle and the drive signal for the upper switch; S Su / d This indicates the drive signal of the lower switch of phase S in the second half of the cycle and the drive signal of the upper switch, and S Sd / u They are complementary; i L Indicates the L-phase current, i M Indicates the M-phase current, i S Indicates the S-phase current; D PN T s This indicates the phase shift delay time.
[0077] As an example, since the switching duty cycle of the primary-side converter is 50%, the resonant current i Lr It is almost a standard sine wave, with the L-phase current i L M-phase current i M and S-phase current i S The average value and their respective phase voltages are directly proportional to obtain the switch phase shift duty cycle D. PN , means as follows: Among them, the switch phase shift duty cycle D PN The range is [0.25, 0.5]. The switching frequency f provided in this application... s and phase shift duty cycle D PN By controlling the solid-state transformer, the power factor can be ensured to be close to 1, thus solving the problem of poor power factor in traditional solid-state transformers.
[0078] In a specific embodiment of this application, please refer to the following: Figure 6 With a phase shift angle of 60° ~90 For example, at this time .
[0079] In step S3, the switching drive logic of the secondary-side transformation unit is determined based on the switching drive logic of the primary-side transformation unit.
[0080] As an example, the switching drive logic of the secondary-side conversion unit 15 is set to be the same as the switching drive logic of the corresponding phase of the primary-side conversion unit 13. The switches corresponding to the same position are turned on and off at the same time, and the same switching frequency and duty cycle are applied.
[0081] In a specific embodiment of this application, when converting three-phase AC power to three-phase AC power, please refer to... Figure 3 The circuit diagram shows that the second AC unit 27 includes a second AC power supply. A1 u B1 u C1 The switching drive logic of the secondary-side conversion unit 25 is the same as the switching drive logic of the corresponding phase of the primary-side conversion unit 23. For example, the primary-side switch S a1 The switch drive logic and the secondary switch S a11 The switching drive logic is the same, primary-side switch S a2 The switch drive logic and secondary switch S a21 The switching drive logic is the same, primary-side switch S c3 The switch drive logic and secondary switch S c31 The switching drive logic is the same, primary-side switch S c4 The switch drive logic and secondary switch S c41 The switching drive logic is the same.
[0082] In a specific embodiment of this application, when converting three-phase AC power to single-phase AC power, please refer to... Figure 4 The circuit diagram shows that the second AC unit 37 includes a second AC power supply. A2 The switching drive logic of the secondary-side conversion unit 35 is the same as the switching drive logic of the corresponding phase of the primary-side conversion unit 33. For example, the primary-side switch S a1 The switch drive logic and secondary switch S a12 The switching drive logic is the same, primary-side switch S a2 The switch drive logic and the secondary switch S a22 The switching drive logic is the same, primary-side switch S b3 The switch drive logic and secondary switch S b32 The switching drive logic is the same, primary-side switch S b4 The switch drive logic and secondary switch S b42 The switching drive logic is the same.
[0083] Furthermore, since energy flows automatically in both directions in an AC-AC converter, when energy flows from the secondary side to the primary side, bidirectional AC-AC conversion can be achieved simply by sending a drive signal according to the aforementioned switch drive logic.
[0084] The AC-AC converter and its control method proposed in this application achieve three-phase AC to three-phase AC or single-phase AC conversion in a single stage. The equivalent AC-to-AC voltage ratio is changed by altering the transformer's turns ratio. The resonant converter unit adopts an LLC structure and does not handle voltage regulation, allowing it to always operate at the resonant point, thus achieving high efficiency. Simultaneously, both the primary and secondary converter units maintain soft-switching operation with low turn-off current and a low switching frequency f. s It can significantly improve performance. No voltage or current loop is needed; the switching frequency f is obtained through simple open-loop calculations. s and phase shift duty cycle D PN This significantly reduces the complexity of control and sampling while achieving high power density, bringing the power factor close to 1. Furthermore, energy can flow bidirectionally within the AC-AC converter, enabling bidirectional AC-AC conversion. The AC-AC converter and its control method proposed in this application can be applied to solid-state transformers, for example, to convert 13.8kV medium-voltage AC power... ac Converted to 380V AC power ac It maintains the same AC frequency, making it suitable for applications where the power frequency remains unchanged and only isolation and voltage regulation are required.
[0085] Although this application has been disclosed above with reference to embodiments, it is not intended to limit this application. Anyone skilled in the art may make some modifications and refinements without departing from the spirit and scope of this application. Therefore, the scope of protection of this application shall be determined by the appended claims.
Claims
1. A control method for an AC-AC converter, applied to an AC-AC converter, characterized in that, The AC-AC converter includes: a first conversion unit, which converts the filtered first AC power to obtain a primary-side conversion voltage; a resonant unit performs resonant conversion on the primary-side conversion voltage to obtain a secondary-side conversion voltage; and a secondary-side conversion unit converts the secondary-side conversion voltage to output a second AC power; wherein the first AC power is a three-phase AC power. The control method for the AC-AC converter includes: The first AC current sampled shows that the L phase has the largest amplitude, followed by the M phase, and the S phase has the smallest amplitude. Determine the switching drive logic of the primary-side transformation unit; The switching drive logic of the secondary-side transformation unit is determined based on the switching drive logic of the primary-side transformation unit. The switching drive logic for determining the primary-side transformation unit includes: Set the switching frequency of the primary-side converter unit to the resonant frequency; The duty cycle of the primary-side conversion unit is set according to the S-phase voltage and the M-phase voltage.
2. The control method for an AC-AC converter as described in claim 1, characterized in that, The duty cycle of the primary-side converter is set based on the S-phase voltage and the M-phase voltage, as shown below: Among them, D PN Indicates the switch phase shift duty cycle; u S Indicates the voltage of phase S; u M This represents the voltage of phase M.
3. The control method for an AC-AC converter as described in claim 2, characterized in that, The L, M, and S phases are determined based on the amplitude of the first alternating current, including: Calculate the absolute value of the amplitude of the first AC current, select the voltage of the phase with the largest absolute value of amplitude in the first AC current as the L-phase voltage, select the voltage of the phase with the smallest absolute value of amplitude in the first AC current as the S-phase voltage, and select the voltage of the remaining phase in the first AC current as the M-phase voltage, as shown below: in, This represents the input voltage of the resonant unit.
4. The control method for an AC-AC converter as described in claim 1, characterized in that, Determining the switching drive logic of the primary-side transformation unit also includes: Set the duty cycle of the primary-side transformation unit to 50%.
5. The control method for an AC-AC converter as described in claim 3, characterized in that, The switching drive logic of the secondary-side conversion unit is determined based on the switching drive logic of the primary-side conversion unit, including: setting the switching drive logic of the secondary-side conversion unit to be the same as the switching drive logic of the corresponding phase of the primary-side conversion unit, ensuring that the switches corresponding to the same position are turned on and off at the same time, and applying the same switching frequency and duty cycle.
6. An AC-AC converter for executing the control method of the AC-AC converter as described in any one of claims 1 to 5, characterized in that, include: The first AC power unit includes a first AC power supply; wherein the first AC power supply is a three-phase AC power supply. A primary-side filtering unit is connected to the first AC power supply and filters the three-phase AC power supply. The primary-side transformation unit transforms the filtered first AC current to obtain the primary-side transformed voltage. A resonant unit, wherein the resonant unit performs a resonant transformation on the primary-side transformed voltage to obtain the secondary-side transformed voltage; The secondary-side transformation unit transforms the secondary-side transformation voltage to obtain secondary-side alternating current; A secondary-side filtering unit filters the secondary-side AC current. The second AC unit outputs the filtered secondary AC power to obtain the second AC power. The control unit has a first terminal connected to a first AC current and a second terminal connected to the primary-side conversion unit and the secondary-side conversion unit. It samples the first AC current, calculates the switching drive logic of the primary-side conversion unit, and determines the switching drive logic of the corresponding phase of the secondary-side conversion unit based on the switching drive logic of the primary-side conversion unit.
7. The AC-AC converter as described in claim 6, characterized in that, The resonant unit includes: a first inductor, a first end of which is connected to a first terminal of the second end of the primary-side conversion unit, a second end of which is connected to a first end of the primary winding of the transformer, a second end of the primary winding of the transformer being connected to a first end of a first capacitor, a second end of which is connected to a second terminal of the second end of the primary-side conversion unit, a second inductor being connected in parallel with the primary winding of the transformer, and a secondary winding of the transformer being connected to the first end of the secondary-side conversion unit; The first inductor is a resonant inductor, the second inductor is a magnetizing inductor, and the first capacitor is a resonant capacitor.
8. The AC-AC converter as described in claim 7, characterized in that, The primary-side filtering unit includes: A third inductor, the first end of which is connected to the first phase A AC power supply, and the second end of which is connected to the first end of the second capacitor and the first terminal of the first end of the primary-side conversion unit; a fourth inductor, the first end of which is connected to the first phase B AC power supply, and the second end of which is connected to the first end of the third capacitor and the second terminal of the first end of the primary-side conversion unit; a fifth inductor, the first end of which is connected to the first phase C AC power supply, and the second end of which is connected to the first end of the third capacitor and the third terminal of the first end of the primary-side conversion unit; the second ends of the second capacitor, the second ends of the third capacitor, and the second ends of the fourth capacitor are connected together. The original-side transformation unit includes: The first switch has its source connected to the source of the second switch, the drain of the second switch connected to the drain of the third switch, the source of the third switch connected to the source of the fourth switch, and the midpoint of the connection between the drain of the second switch and the drain of the third switch is the first terminal of the first end of the primary-side transformation unit. The fifth switch has its source connected to the source of the sixth switch, its drain connected to the drain of the seventh switch, and its source connected to the source of the eighth switch. The midpoint of the connection between the drain of the sixth switch and the drain of the seventh switch is the second terminal of the first end of the primary-side transformation unit. The ninth switch has its source connected to the source of the tenth switch, its drain connected to the drain of the eleventh switch, and its source connected to the source of the twelfth switch. The midpoint of the connection between the drains of the tenth and eleventh switches is the third terminal of the first end of the primary-side conversion unit. The drains of the first switch, the fifth switch, and the primary-side switch are connected. The drains of the primary-side switch, the primary-side switch, and the ninth switch are connected. The drain of the ninth switch is the first terminal of the second end of the primary-side conversion unit, and the drain of the twelfth switch is the second terminal of the second end of the primary-side conversion unit.
9. The AC-AC converter as described in claim 8, characterized in that, The second AC power is a three-phase AC power; The secondary transformation unit includes: The thirteenth switch, the source of the thirteenth switch is connected to the source of the fourteenth switch, the drain of the fourteenth switch is connected to the drain of the fifteenth switch, the source of the fifteenth switch is connected to the source of the sixteenth switch, and the midpoint of the connection between the drain of the fourteenth switch and the fifteenth switch is the first terminal of the second end of the secondary-side conversion unit. The seventeenth switch, the source of the seventeenth switch is connected to the second terminal of the eighteenth switch, the drain of the eighteenth switch is connected to the drain of the nineteenth switch, the source of the nineteenth switch is connected to the source of the twentieth switch, and the midpoint of the connection between the drain of the eighteenth switch and the drain of the nineteenth switch is the second terminal of the second end of the secondary-side conversion unit. The source of the 21st switch is connected to the second terminal of the 22nd switch, the drain of the 22nd switch is connected to the drain of the 23rd switch, the source of the 23rd switch is connected to the source of the 24th switch, and the midpoint of the connection between the drains of the 22nd and 23rd switches is the third terminal of the second terminal of the secondary-side conversion unit; the drains of the 13th switch, the 17th switch, and the 21st switch are connected, and the drains of the 16th switch, the 20th switch, and the 24th switch are connected, with the drains of the 21st and 24th switches forming the first terminal of the secondary-side conversion unit; The secondary filtering unit includes: The sixth inductor has its first end connected to the second phase A AC power supply; its second end is connected to the first end of the fifth capacitor and the first terminal of the second end of the secondary-side conversion unit; the seventh inductor has its first end connected to the second phase B AC power supply; its second end is connected to the first end of the sixth capacitor and the second terminal of the second end of the secondary-side conversion unit; the eighth inductor has its first end connected to the second phase C AC power supply; its second end is connected to the first end of the seventh capacitor and the third terminal of the first end of the secondary-side conversion unit; and the second ends of the fifth, sixth, and seventh capacitors are connected together.
10. The AC-AC converter as described in claim 8, characterized in that, The second AC power is single-phase AC power; The secondary transformation unit includes: The source of the 25th switch is connected to the source of the 26th switch, the drain of the 26th switch is connected to the drain of the 27th switch, the source of the 27th switch is connected to the source of the 28th switch, and the midpoint of the connection between the drain of the 26th switch and the 27th switch is the first terminal of the second end of the secondary-side conversion unit. The source of the 29th switch is connected to the source of the 30th switch, the drain of the 30th switch is connected to the drain of the 31st switch, the source of the 31st switch is connected to the source of the 32nd switch, and the midpoint of the connection between the drains of the 30th and 31st switches is the second terminal of the second end of the secondary-side conversion unit; the drain of the 25th switch is connected to the drain of the 29th switch, the drain of the secondary-side switch is connected to the drain of the secondary-side switch, and the drain of the 32nd switch and the drain of the 28th switch constitute the first end of the secondary-side conversion unit; The secondary filtering unit includes: The ninth inductor has its first terminal connected to the first terminal of the eighth capacitor and the first terminal of the second terminal of the secondary-side conversion unit, and its second terminal connected to the first terminal of the second AC power supply. The tenth inductor has its first terminal connected to the first terminal of the ninth capacitor and the second terminal of the second terminal of the secondary-side conversion unit, and its second terminal connected to the second terminal of the second AC power supply; the second terminal of the ninth capacitor is connected to the second terminal of the eighth capacitor.