A three-phase isolated converter and control method

Abstract

This application discloses a three-phase isolated converter and its control method, comprising: a primary circuit, a transformer, and a secondary rectifier circuit; the primary circuit includes three bidirectional switches and three capacitors; the first terminals of the three bidirectional switches are respectively connected to the three phases of the AC source; the second terminals of the three bidirectional switches are connected to the first terminal of the primary winding of the transformer; the first terminals of the three bidirectional switches are respectively connected to the second terminal of the primary winding through corresponding capacitors; the secondary winding of the transformer is connected to the secondary rectifier circuit. This technical solution can reduce the number of switching devices in the three-phase isolated converter and reduce hardware costs.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, specifically to a three-phase isolated converter and its control method. Background Technology

[0002] Three-phase isolated converters typically have a complex topology, including a primary circuit, a transformer, and a secondary rectifier circuit. The input of the primary circuit is connected to an AC source, the output is connected to the primary winding of the transformer, and the secondary winding is connected to the secondary rectifier circuit. Traditional three-phase isolated converters have a large number of switching devices in their primary circuit, resulting in a high total number of switching devices and higher hardware costs. Summary of the Invention

[0003] In view of this, this application provides a three-phase isolated converter and control method, which can reduce the number of switching devices in the three-phase isolated converter and reduce hardware costs.

[0004] This application provides a three-phase isolated converter, including: a primary circuit, a transformer, and a secondary rectifier circuit;

[0005] The primary-side circuit includes three bidirectional switches and three capacitors;

[0006] The first terminals of the three bidirectional switches are used to connect to the three phases of the AC source respectively; the second terminals of the three bidirectional switches are connected to the first terminal of the primary winding of the transformer; the first terminals of the three bidirectional switches are respectively connected to the second terminal of the primary winding through the corresponding capacitors.

[0007] The secondary winding of the transformer is connected to the secondary rectifier circuit.

[0008] One possible implementation also includes: a controller;

[0009] The controller is used to control the three bidirectional switches to have the same switching cycle, different duty cycles, and no overlap in their conduction times.

[0010] One possible implementation also includes: a controller;

[0011] The controller is used to control the switching cycles of the three bidirectional switches to be different, and the conduction times do not overlap.

[0012] One possible implementation also includes: a controller;

[0013] The controller is used to ensure that the three bidirectional switches have the same switching cycle, the same duty cycle, and that their conduction times do not overlap.

[0014] One possible implementation also includes: a controller;

[0015] The second end of the primary winding is connected to the three-phase common point of the AC source;

[0016] The controller is configured to, in the event of a one-phase or two-phase fault in the three-phase isolated converter, keep the bidirectional switch in the faulty phase open and keep the switching period and duty cycle of the bidirectional switch in the normal phase unchanged.

[0017] One possible implementation method also includes: a filter inductor;

[0018] The first terminals of the three bidirectional switches are used to connect to the three phases of the AC source through the corresponding filter inductors; all three bidirectional switches are gallium nitride bidirectional switches.

[0019] One possible implementation is that the secondary-side rectifier circuit is any of the following:

[0020] Uncontrolled full-bridge rectifier circuit, controllable full-bridge rectifier circuit, uncontrollable half-wave rectifier circuit, or controllable half-wave rectifier circuit;

[0021] All three bidirectional switches are gallium nitride bidirectional switches.

[0022] This application also provides a control method for a three-phase isolated converter, the converter comprising: a primary circuit, a transformer, and a secondary rectifier circuit; the primary circuit comprising three bidirectional switches and three capacitors; the first terminals of the three bidirectional switches are respectively connected to the three phases of an AC source; the second terminals of the three bidirectional switches are connected to the first terminal of the primary winding of the transformer; the first terminals of the three bidirectional switches are respectively connected to the second terminal of the primary winding through the corresponding capacitors; the secondary winding of the transformer is connected to the secondary rectifier circuit;

[0023] The method includes:

[0024] The three bidirectional switches are controlled to conduct in turn, and the conduction times do not overlap.

[0025] One possible implementation involves using three gallium nitride (GaN) bidirectional switches; controlling the three bidirectional switches to conduct alternately, with no overlap in their conduction times, includes:

[0026] The three bidirectional switches are controlled to have the same switching period, different duty cycles, and no overlap in their conduction times; or, the three bidirectional switches are controlled to have the same switching period, the same duty cycle, and no overlap in their conduction times.

[0027] One possible implementation involves using three gallium nitride (GaN) bidirectional switches; controlling the three bidirectional switches to conduct alternately, with no overlap in their conduction times, includes:

[0028] The switching cycles of the three bidirectional switches are different, and their conduction times do not overlap.

[0029] The beneficial effects of the embodiments of this application are as follows:

[0030] The primary circuit of the three-phase isolated converter provided in this application embodiment includes three bidirectional switches. The first terminals of the three bidirectional switches are respectively connected to the three phases of the AC source; the second terminals of the three bidirectional switches are connected to the first terminal of the primary winding of the transformer; the first terminals of the three bidirectional switches are respectively connected to the second terminal of the primary winding through corresponding capacitors; the secondary winding of the transformer is connected to the secondary rectifier circuit. Each phase of the primary circuit of the three-phase isolated converter provided in this application embodiment includes one bidirectional switch, thus achieving bidirectional current blocking and bidirectional current flow. Compared with the primary circuit of a traditional three-phase isolated converter, the three-phase isolated converter of this application reduces the number of switching devices in the primary circuit, thereby reducing hardware costs. Attached Figure Description

[0031] Figure 1 A schematic diagram of a first type of three-phase isolated converter provided in the embodiments of this application;

[0032] Figure 2a This is a schematic diagram of a second type of three-phase isolated converter provided in the embodiments of this application;

[0033] Figure 2b A schematic diagram of a third type of three-phase isolated converter provided in the embodiments of this application;

[0034] Figure 3 A schematic diagram of the driving timing of the bidirectional switch of the first type of three-phase isolated converter provided in this application embodiment;

[0035] Figure 4 A schematic diagram of the driving timing of the bidirectional switch of the second type of three-phase isolated converter provided in the embodiments of this application;

[0036] Figure 5 A schematic diagram of the driving timing of the bidirectional switch of the third type of three-phase isolated converter provided in this application embodiment;

[0037] Figure 6 A schematic diagram of a fourth type of three-phase isolated converter provided in the embodiments of this application;

[0038] Figure 7 A schematic diagram of the fifth type of three-phase isolated converter provided in the embodiments of this application;

[0039] Figure 8 A schematic diagram of the sixth type of three-phase isolated converter provided in the embodiments of this application;

[0040] Figure 9A schematic diagram of the seventh type of three-phase isolated converter provided in the embodiments of this application;

[0041] Figure 10 A flowchart illustrating a control method for a three-phase isolated converter provided in an embodiment of this application. Detailed Implementation

[0042] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the embodiments of this application will be further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0043] Traditional three-phase isolated converters typically use a matrix-style primary-side circuit, which includes 12 switching devices. The large number of switching devices in the primary-side circuit results in a large size and high cost.

[0044] To reduce the number of switching devices in the primary circuit, this application provides a three-phase isolated converter in which the topology of the primary circuit is changed and a matrix configuration is not used, which can reduce the number of switching devices and reduce hardware costs.

[0045] The embodiments of this application do not specifically limit the application scenarios of the three-phase isolated converter. For example, it can be applied to vehicle charging scenarios, charging pile charging scenarios, or uninterruptible power supply scenarios, etc.

[0046] The following is a detailed description with reference to the accompanying drawings.

[0047] See Figure 1 The figure is a schematic diagram of the first type of three-phase isolated converter provided in the embodiments of this application.

[0048] The three-phase isolated converter provided in this application includes: a primary circuit 100, a transformer T, and a secondary rectifier circuit 200.

[0049] The primary circuit 100 includes three bidirectional switches and three capacitors; the three bidirectional switches are all gallium nitride bidirectional switches; the first terminals of the three bidirectional switches are used to connect to the three phases of the AC source 300 respectively; the second terminals of the three bidirectional switches are connected to the first terminal of the primary winding of the transformer T; the first terminals of the three bidirectional switches are connected to the second terminal of the primary winding through the corresponding capacitors respectively; the secondary winding of the transformer T is connected to the secondary rectifier circuit 200.

[0050] like Figure 1As shown, the three bidirectional switches are: a first bidirectional switch Sa, a second bidirectional switch Sb, and a third bidirectional switch Sc; the three capacitors are: a first capacitor Ca, a second capacitor Cb, and a third capacitor Cc. Specifically, the first terminal of the first bidirectional switch Sa is connected to phase A of the AC source 300, and the first terminal of the first bidirectional switch Sa is connected to the second terminal of the primary winding through the first capacitor Ca; the first terminal of the second bidirectional switch Sb is connected to phase B of the AC source 300, and the first terminal of the second bidirectional switch Sb is connected to the second terminal of the primary winding through the second capacitor Cb; the first terminal of the third bidirectional switch Sc is connected to phase C of the AC source 300, and the first terminal of the third bidirectional switch Sc is connected to the second terminal of the primary winding through the third capacitor Cc.

[0051] The three capacitors provide filtering support for the primary circuit 100, filtering out the ripple generated when the bidirectional switch operates. The second terminals of the three capacitors are all connected to the second terminal of the primary winding of the transformer T, providing a current loop for the primary circuit 100.

[0052] The magnetizing inductance Lm is the equivalent inductance in the primary winding of transformer T used to establish the magnetic field; it is not a real inductance. The magnetizing inductance Lm is connected in parallel across the primary winding of transformer T, and it stores energy when the primary circuit 100 is operating. This application does not specifically limit the type of transformer T; for example, transformer T can be a step-up transformer or a step-down transformer.

[0053] The three-phase isolated converter obtains energy from the AC source 300. The bidirectional switch in the primary circuit 100 and the primary winding of the transformer T form a flyback switching power supply to deliver AC energy to the transformer T. The transformer T performs energy conversion and outputs the energy. The secondary rectifier circuit 200 rectifies the AC energy flow converted by the transformer T and outputs DC energy.

[0054] The primary circuit of the three-phase isolated converter provided in this application embodiment includes three bidirectional switches. The first terminals of the three bidirectional switches are respectively connected to the three phases of the AC source; the second terminals of the three bidirectional switches are connected to the first terminal of the primary winding of the transformer; the first terminals of the three bidirectional switches are respectively connected to the second terminal of the primary winding through corresponding capacitors; the secondary winding of the transformer is connected to the secondary rectifier circuit. Each phase of the primary circuit of the three-phase isolated converter provided in this application embodiment includes one switching device, thus achieving bidirectional current blocking and bidirectional current flow. Compared with the primary circuit of a traditional three-phase isolated converter, the three-phase isolated converter of this application reduces the number of switching devices in the primary circuit, thereby reducing hardware costs.

[0055] To further reduce the number of switching devices in the primary circuit, bidirectional switches can be made using gallium nitride (GaN) bidirectional switches. Traditionally, to achieve bidirectional current blocking and bidirectional current flow, two switching devices are connected in series back-to-back with a common source or common drain configuration, thus forming a bidirectional switch. Figure 1 The primary circuit of the three-phase isolated converter shown uses back-to-back switching transistors to form a bidirectional switch, requiring six switching transistors. This results in a relatively large number of switching devices.

[0056] The three-phase isolated converter provided in this application uses a gallium nitride (GaN) bidirectional switch to achieve bidirectional current blocking and bidirectional current flow. Three bidirectional switches can be implemented using only three single transistors, thereby reducing the number of switching devices. In the off state, the GaN bidirectional switch maintains a reliable blocking state regardless of whether the voltage applied across it is forward or reverse. In the on state, the current flowing through the GaN bidirectional switch can flow in either a first direction (e.g., from the first terminal to the second terminal) or the opposite direction (e.g., from the second terminal to the first terminal).

[0057] Figure 1 The second end of the primary winding shown is not connected to the three-phase common point of the AC source 300. In order to ensure that the normal phase of the three-phase isolation converter can still operate normally in the event of a one-phase or two-phase failure of the three-phase isolation converter, the second end of the primary winding can be connected to the three-phase common point of the AC source 300.

[0058] See Figure 2a This figure is a schematic diagram of a second type of three-phase isolated converter provided in an embodiment of this application.

[0059] The three-phase isolated converter provided in this application embodiment also includes a controller 400, the second end of the primary winding is connected to the three-phase common point N of the AC source 300; the controller 400 is configured to control the normal phase to operate in the event of a one-phase or two-phase failure of the three-phase isolated converter, that is, the three-phase isolated converter can operate with a missing phase.

[0060] The second end of the primary winding of transformer T is connected to the three-phase common point N of AC source 300 to form a three-phase four-wire input structure, providing a loop for zero-sequence current. This ensures that even if one or two phases of the three-phase isolation converter fail, the normal phase can still operate normally.

[0061] When a single phase of a three-phase isolated converter fails, taking a phase A failure as an example, the controller 400 blocks the signal from phase A. The controller 400 no longer sends a drive signal to the first bidirectional switch Sa, meaning the first bidirectional switch Sa is open, isolating phase A. The controller 400 then controls the bidirectional switches of phases B and C to continue operating, maintaining energy transfer from phases B and C to the transformer T. Specifically, the controller 400 can keep the drive signals of the second bidirectional switch Sb of phase B and the third bidirectional switch Sc of phase C unchanged, continuing to operate according to the previous switching cycle and duty cycle.

[0062] In the event of a two-phase fault in a three-phase isolated converter, taking a fault in phases A and B as an example, the controller 400 blocks the waveforms of phases A and B. The controller 400 ceases to send drive signals to the first bidirectional switch Sa and the second bidirectional switch Sb, meaning the first bidirectional switch Sa and the second bidirectional switch Sb remain open, isolating phases A and B. The controller 400 then controls phase C to continue operating, maintaining energy transfer to the transformer T. Specifically, the controller 400 can keep the drive signal of the third bidirectional switch Sc of phase C unchanged, allowing it to continue operating according to the previous switching cycle and duty cycle.

[0063] The three-phase isolated converter provided in this application embodiment also includes a controller. The second end of the primary winding of the transformer is connected to the three-phase common point of the AC source. When one or two phases of the three-phase isolated converter fail, the controller controls the normal phase to maintain normal operation.

[0064] To filter out harmonics generated during bidirectional switching, the three-phase isolated converter provided in this application embodiment also includes a filter inductor.

[0065] The three-phase isolated converter provided in this embodiment also includes a filter inductor. The first terminals of the three bidirectional switches are used to connect to the three phases of the AC source 300 through the corresponding filter inductors.

[0066] The first terminal of the first bidirectional switch Sa is connected to phase A of the AC source 300 through the first filter inductor La; the first terminal of the second bidirectional switch Sb is connected to phase B of the AC source 300 through the second filter inductor Lb; and the first terminal of the third bidirectional switch Sc is connected to phase C of the AC source 300 through the third filter inductor Lc.

[0067] The filter inductor filters out harmonics generated during bidirectional switching, improving the quality of the input current of the three-phase isolated converter.

[0068] Figure 2a The rest of the middle part and Figure 1 Same, see Figure 1 The description will not be repeated here.

[0069] When the second end of the primary winding of the three-phase isolated converter is not connected to the three-phase common point of the AC source 300, in order to filter out the harmonics generated when the bidirectional switch is operated, the three-phase isolated converter provided in this application embodiment also includes a filter inductor.

[0070] See Figure 2b This figure is a schematic diagram of a third type of three-phase isolated converter provided in the embodiments of this application.

[0071] Figure 2b The rest of the middle part and Figure 2a Same, see Figure 2a The description will not be repeated here.

[0072] The switching cycles of the three bidirectional switches in the three-phase isolated converter provided in this application embodiment can be the same or different, as long as the three bidirectional switches are turned on alternately and the turn-on times do not overlap.

[0073] The following describes how to implement a three-phase isolated converter where the switching cycles of the three bidirectional switches are the same.

[0074] See Figure 3 The figure is a schematic diagram of the driving timing of the bidirectional switch of the first type of three-phase isolated converter provided in the embodiment of this application.

[0075] The converter provided in this application embodiment also includes a controller 400. The controller 400 is used to control three bidirectional switches to have the same switching period, different duty cycles, and no overlap in their conduction times.

[0076] like Figure 3 As shown, the switching periods of the three bidirectional switches are all the same, Ts; the current flowing through the magnetizing inductor Lm is denoted as i. Lm The phase A voltage of AC source 300 is represented by Va, the phase B voltage of AC source 300 is represented by Vb, and the phase C voltage of AC source 300 is represented by Vc. Figure 3This is only a partial example, showing only the case where phase A voltage Va is greater than 0, phase B voltage Vb is greater than 0, and phase C voltage Vc is less than 0. Since the sign of the three-phase voltages depends on the AC source, such as a three-phase power grid, it depends on the phase of the grid voltage at the current moment. If the three-phase power grid is symmetrical, the sum of the three-phase voltages is 0. In short, one voltage can be positive and two negative, or two positive and one negative. This application does not specifically limit the sign of the three-phase voltages. For example, it can also include the case where phase A voltage Va is greater than 0, phase B voltage Vb is less than 0, and phase C voltage Vc is greater than 0; or, phase A voltage Va is greater than 0, phase B voltage Vb is less than 0, and phase C voltage Vc is less than 0; the three-phase voltage can also include the case where phase A voltage Va is less than 0, phase B voltage Vb is less than 0, and phase C voltage is greater than 0; or, phase A voltage Va is less than 0, phase B voltage Vb is greater than 0, and phase C voltage is greater than 0; or, phase A voltage Va is less than 0, phase B voltage Vb is greater than 0, and phase C voltage is less than 0; other cases will not be elaborated here.

[0077] The three bidirectional switches have different duty cycles, which are determined by the phase voltage of the AC source 300 corresponding to the three bidirectional switches and the transmission power of the converter. In order to achieve power factor correction of the three-phase isolated converter, the three bidirectional switches are turned on in turn, and the turn-on time does not overlap with each other, ensuring that the primary winding of transformer T is energized by only one phase at the same time, avoiding coupling conflict caused by simultaneous energization of the three phases.

[0078] The on state of the bidirectional switch is represented by ON, and the off state is represented by OFF. When the bidirectional switch is on, the magnetizing inductor Lm is charged; when the bidirectional switch is off, the magnetizing inductor Lm is discharged. To ensure that the energy on the magnetizing inductor Lm is fully released to the secondary winding of the transformer T, the switching period Ts should be greater than the current i of the magnetizing inductor Lm. Lm The time required for the peak value to drop to zero; the current i in the magnetizing inductor Lm during the current bidirectional switch operating cycle. Lm Once the current drops to zero, the next bidirectional switch will begin to conduct, ensuring that the three-phase isolated converter can achieve zero-current turn-on, reducing switching losses and improving the converter's energy conversion efficiency.

[0079] The current i of the magnetizing inductor Lm Lm The rising slope is determined by the three-phase voltage of the AC source 300, and the current i of the magnetizing inductor Lm. Lm The rate of descent is determined by the output voltage of the secondary rectifier circuit 200.

[0080] The following description uses the operation of phase A as an example.

[0081] When the phase A voltage Va is positive, the first bidirectional switch Sa is turned on, and the first bidirectional switch Sa applies a positive voltage to the magnetizing inductor Lm to charge it; when the current i flowing through the magnetizing inductor Lm... Lm When the current reaches the threshold, the first bidirectional switch Sa is turned off, and the magnetizing inductor Lm discharges to the secondary winding of transformer T. At this time, the direction of the discharge from the magnetizing inductor Lm to the secondary winding of transformer T is recorded as positive.

[0082] When the phase A voltage Va is negative, the first bidirectional switch Sa is turned on, and the first bidirectional switch Sa applies a negative voltage to the magnetizing inductor Lm to charge it; when the current i flowing through the magnetizing inductor Lm... Lm When the current reaches the threshold, the first bidirectional switch Sa is turned off, and the magnetizing inductor Lm discharges in reverse to the secondary winding of the transformer T in the opposite direction to the forward discharge direction.

[0083] Regardless of whether the excitation inductor Lm discharges forward or reverse to the secondary winding of the transformer T, after rectification by the secondary rectifier circuit 200, the output side of the secondary rectifier circuit 200 can be charged, ultimately achieving control of the output voltage.

[0084] The working conditions of phases B and C are similar to those of phase A, and will not be described in detail here.

[0085] The three-phase isolated converter provided in this application provides a simple and easy-to-implement control for the three bidirectional switches. The duty cycles of the three bidirectional switches are less than 100%, and since they are turned on sequentially, a conduction interval naturally exists, eliminating the need for a dead zone and allowing for flexible control.

[0086] When the switching cycles of the three bidirectional switches of the three-phase isolated converter provided in this application embodiment are the same, the duty cycles of the three bidirectional switches can be the same.

[0087] See Figure 4 The figure is a schematic diagram of the driving timing of the bidirectional switch of the second type of three-phase isolated converter provided in the embodiment of this application.

[0088] The three-phase isolated converter provided in this application embodiment also includes a controller 400. The controller 400 is used to control the three bidirectional switches to have the same switching cycle, the same duty cycle, and no overlap in their conduction times.

[0089] like Figure 4 As shown, the switching cycles of the three bidirectional switches are the same, all being Ts, and the duty cycles of the three bidirectional switches are also the same. The duty cycle is determined by the three-phase voltage of the AC source 300 and the transmission power of the converter. Having the same duty cycle facilitates control by the controller 400.

[0090] Figure 4 The rest of the middle part and Figure 3 Same, see Figure 3 The description will not be repeated here.

[0091] The following describes how to implement the different switching cycles of the three bidirectional switches in a three-phase isolated converter.

[0092] See Figure 5 The figure is a schematic diagram of the driving timing of the bidirectional switch of the third type of three-phase isolated converter provided in the embodiments of this application.

[0093] The three-phase isolated converter provided in this application embodiment also includes a controller 400. The controller 400 is used to control the switching cycles of the three bidirectional switches to be different, and the conduction times do not overlap.

[0094] The conduction period of the first bidirectional switch Sa is Tsa, the conduction period of the second bidirectional switch Sb is Tsb, and the conduction period of the third bidirectional switch Sc is Tsc. The different switching periods of the three bidirectional switches can reduce the discontinuity of the magnetizing inductor Lm and reduce the current i in the magnetizing inductor Lm when the bidirectional switches are turned off. Lm The peak value can be adjusted according to the actual needs under different operating conditions or the three-phase fault condition of the three-phase isolation converter, thereby reducing the zero current time.

[0095] Figure 5 The rest of the middle part and Figure 3 Same, see Figure 3 The description will not be repeated here.

[0096] The implementation of the secondary rectifier circuit is described below.

[0097] The secondary rectifier circuit 200 of the three-phase isolated converter provided in this application embodiment is any one of the following: an uncontrolled full-bridge rectifier circuit, a controlled full-bridge rectifier circuit, an uncontrolled half-wave rectifier circuit, or a controlled half-wave rectifier circuit.

[0098] See Figure 6 This figure is a schematic diagram of the fourth type of three-phase isolated converter provided in the embodiments of this application.

[0099] like Figure 6 As shown, the secondary rectifier circuit 200 of the three-phase isolated converter is an uncontrolled full-bridge rectifier circuit. The energy stored in the primary circuit 100 is transferred to the secondary rectifier circuit 200 through the transformer T. The diagonal diodes of the secondary rectifier circuit 200 conduct alternately, delivering the rectified energy to the downstream load. Since the secondary rectifier circuit 200 is implemented by diodes, it is low in cost and does not require control, thus saving on the control process.

[0100] See Figure 7This figure is a schematic diagram of the fifth type of three-phase isolated converter provided in the embodiments of this application.

[0101] like Figure 7 As shown, the secondary rectifier circuit 200 of the three-phase isolated converter is a controllable full-bridge rectifier circuit. Each controllable switch in this controllable full-bridge rectifier circuit simulates the operation of a diode. The working effect of the controllable full-bridge rectifier circuit is equivalent to that of an uncontrolled full-bridge rectifier circuit. The advantage of the controllable full-bridge rectifier circuit compared to the uncontrolled full-bridge rectifier circuit is that it can reduce switching losses and improve power conversion efficiency.

[0102] See Figure 8 This figure is a schematic diagram of the sixth type of three-phase isolated converter provided in the embodiments of this application.

[0103] like Figure 8 As shown, the secondary rectifier circuit 200 of the three-phase isolated converter is an uncontrolled half-wave rectifier circuit. The secondary rectifier circuit 200 outputs pulsating DC. When the primary circuit 100 outputs a positive voltage, the diodes within the secondary rectifier circuit 200 conduct, transferring energy to the load. The advantage of the uncontrolled half-wave rectifier circuit is that it saves on the number of diodes, reducing hardware costs.

[0104] See Figure 9 This figure is a schematic diagram of the seventh type of three-phase isolated converter provided in the embodiments of this application.

[0105] like Figure 9 As shown, the secondary rectifier circuit 200 of the three-phase isolated converter is a controllable half-wave rectifier circuit. In this case, each controllable switch in the controllable half-wave rectifier circuit simulates the operation of a diode. The advantage of the controllable half-wave rectifier circuit is reduced switching losses, a reduction in the number of switches, and a decrease in hardware costs.

[0106] Based on the three-phase isolated converter provided in the above embodiments, this application also provides a control method for the three-phase isolated converter.

[0107] See Figure 10 The figure is a flowchart of a control method for a three-phase isolated converter provided in an embodiment of this application.

[0108] The control method for a three-phase isolated converter provided in this application embodiment includes a primary circuit, a transformer, and a secondary rectifier circuit. The primary circuit includes three bidirectional switches and three capacitors. The first terminals of the three bidirectional switches are respectively connected to the three phases of the AC source. The second terminals of the three bidirectional switches are connected to the first terminal of the primary winding of the transformer. The first terminals of the three bidirectional switches are respectively connected to the second terminal of the primary winding through corresponding capacitors. The secondary winding of the transformer is connected to the secondary rectifier circuit.

[0109] The method includes:

[0110] S101: Controls three bidirectional switches to conduct in turn, and the conduction times do not overlap.

[0111] The primary circuit of the three-phase isolated converter provided in this application embodiment includes three bidirectional switches. The first terminals of the three bidirectional switches are respectively connected to the three phases of the AC source; the second terminals of the three bidirectional switches are connected to the first terminal of the primary winding of the transformer; the first terminals of the three bidirectional switches are respectively connected to the second terminal of the primary winding through corresponding capacitors; the secondary winding of the transformer is connected to the secondary rectifier circuit. Each phase of the primary circuit of the three-phase isolated converter provided in this application embodiment includes one bidirectional switch, thus achieving bidirectional current blocking and bidirectional current flow. Compared with the primary circuit of a traditional three-phase isolated converter, the three-phase isolated converter of this application reduces the number of switching devices in the primary circuit, lowering hardware costs. Moreover, the control method is simple and easy to implement; it only requires ensuring that the conduction times of the three switching transistors do not overlap.

[0112] Three bidirectional switches are turned on alternately to ensure that the energy in the magnetizing inductor is fully released to the secondary winding of the transformer. The switching cycle should be longer than the time required for the current in the magnetizing inductor to drop from its peak value to zero. The conduction times of the three bidirectional switches do not overlap, ensuring that only one phase of the primary winding of transformer T is energized at any given time, avoiding coupling conflicts caused by simultaneous three-phase energization. Within the current bidirectional switch's operating cycle, the next bidirectional switch only begins to conduct after the current in the magnetizing inductor drops to zero, ensuring that the three-phase isolated converter can achieve zero-current turn-on, reducing switching losses and improving the converter's energy conversion efficiency.

[0113] The control method for a three-phase isolated converter provided in this application includes controlling three bidirectional switches to conduct in turn, with no overlap in their conduction times. The next bidirectional switch only begins to conduct after the magnetizing inductance drops to zero, ensuring that the three-phase isolated converter can achieve zero-current turn-on, reducing switching losses, and improving the converter's energy conversion efficiency.

[0114] To further reduce the number of switching devices in the primary circuit, gallium nitride (GaN) bidirectional switches can be used. A GaN bidirectional switch, as a single transistor, can achieve both bidirectional current blocking and bidirectional current flow.

[0115] One possible implementation, the control method provided in this application embodiment, includes: controlling the three bidirectional switches to have the same switching period, different duty cycles, and no overlap in their conduction times.

[0116] The duty cycle of the three bidirectional switches is determined by the phase voltage of the AC source corresponding to the three bidirectional switches and the transmission power of the converter, and can be determined according to different operating conditions.

[0117] One possible implementation, the control method provided in this application embodiment includes: controlling the three bidirectional switches to have the same switching period, the same duty cycle, and no overlap in conduction time; or, controlling the three bidirectional switches to have the same switching period, different duty cycles, and no overlap in conduction time.

[0118] When the duty cycle is the same, it is easy for the controller to control the device and the response is rapid.

[0119] One possible implementation, the control method provided in this application embodiment, includes: controlling the switching cycles of the three bidirectional switches to be different, and ensuring that the conduction times do not overlap.

[0120] The three bidirectional switches have different switching cycles, which can reduce the discontinuity of the magnetizing inductor and the peak current of the magnetizing inductor when the bidirectional switches are turned off. The duty cycle of the three bidirectional switches can be adjusted according to the actual needs under different operating conditions or the three-phase fault situation of the three-phase isolation converter to reduce the zero current time.

[0121] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0122] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A three-phase isolated converter, characterized in that, include: Primary circuit, transformer and secondary rectifier circuit; The primary-side circuit includes three bidirectional switches and three capacitors; The first terminals of the three bidirectional switches are used to connect to the three phases of the AC source respectively; the second terminals of the three bidirectional switches are connected to the first terminal of the primary winding of the transformer; the first terminals of the three bidirectional switches are respectively connected to the second terminal of the primary winding through the corresponding capacitors. The secondary winding of the transformer is connected to the secondary rectifier circuit.

2. The converter according to claim 1, characterized in that, Also includes: Controller; The controller is used to control the three bidirectional switches to have the same switching cycle, different duty cycles, and no overlap in their conduction times.

3. The converter according to claim 1, characterized in that, Also includes: Controller; The controller is used to control the switching cycles of the three bidirectional switches to be different, and the conduction times do not overlap.

4. The converter according to claim 1, characterized in that, Also includes: Controller; The controller is used to ensure that the three bidirectional switches have the same switching cycle, the same duty cycle, and that their conduction times do not overlap.

5. The converter according to claim 1, characterized in that, Also includes: Controller; The second end of the primary winding is connected to the three-phase common point of the AC source; The controller is configured to, in the event of a one-phase or two-phase fault in the three-phase isolated converter, keep the bidirectional switch in the faulty phase open and keep the switching period and duty cycle of the bidirectional switch in the normal phase unchanged.

6. The converter according to any one of claims 1 to 5, characterized in that, Also includes: Filter inductor; The first terminals of the three bidirectional switches are used to connect to the three phases of the AC source through the corresponding filter inductors; all three bidirectional switches are gallium nitride bidirectional switches.

7. The converter according to any one of claims 1 to 5, characterized in that, The secondary-side rectifier circuit is any one of the following: Uncontrolled full-bridge rectifier circuit, controllable full-bridge rectifier circuit, uncontrollable half-wave rectifier circuit, or controllable half-wave rectifier circuit; All three bidirectional switches are gallium nitride bidirectional switches.

8. A control method for a three-phase isolated converter, characterized in that, The converter includes: a primary circuit, a transformer, and a secondary rectifier circuit; the primary circuit includes three bidirectional switches and three capacitors; the first terminals of the three bidirectional switches are respectively connected to the three phases of the AC source; the second terminals of the three bidirectional switches are connected to the first terminal of the primary winding of the transformer; the first terminals of the three bidirectional switches are respectively connected to the second terminal of the primary winding through the corresponding capacitors; the secondary winding of the transformer is connected to the secondary rectifier circuit. The method includes: The three bidirectional switches are controlled to conduct in turn, and the conduction times do not overlap.

9. The control method according to claim 8, characterized in that, All three bidirectional switches are gallium nitride bidirectional switches; controlling the three bidirectional switches to conduct alternately, with no overlap in their conduction times, includes: The three bidirectional switches are controlled to have the same switching period, different duty cycles, and no overlap in their conduction times; or, the three bidirectional switches are controlled to have the same switching period, the same duty cycle, and no overlap in their conduction times.

10. The control method according to claim 8, characterized in that, All three bidirectional switches are gallium nitride bidirectional switches; controlling the three bidirectional switches to conduct alternately, with no overlap in their conduction times, includes: The switching cycles of the three bidirectional switches are different, and their conduction times do not overlap.

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