Power conversion circuit, control method thereof, intelligent device and storage medium

Abstract

The invention relates to a control method for a power conversion circuit, the power conversion circuit, intelligent equipment and a computer readable storage medium. The power conversion circuit comprises a transformer, an input circuit and an output circuit. The method comprises the following steps: determining a current section and selecting a non-control phase according to the size relation and the positive and negative of phase voltage; selecting a first control phase and a second control phase according to a desired power flow direction; and periodically and alternately conducting the upper bridge arm and the lower bridge arm of the non-control phase in the section, and switching the correspondingly conducted lower bridge arm from the lower bridge arm of the first control phase to the lower bridge arm of the second control phase when the upper bridge arm of the non-control phase is conducted, during the conduction period of the lower bridge arm of the non-control phase, the correspondingly conducted upper bridge arm is switched from the upper bridge arm of the first control phase to the upper bridge arm of the second control phase, and before switching, a controllable switch used for controlling on-off of current in the first direction on the lower bridge arm or the upper bridge arm of the second control phase is in a conduction state.

Description

Technical Field

[0001] This application relates to the field of charge and discharge control. More specifically, this application relates to a control method for a power conversion circuit, a power conversion circuit, an intelligent device, and a computer-readable storage medium. Background Art

[0002] With the rapid development of electric vehicle technology, the continuous improvement of the intelligent level, and the continuous optimization of the driving space, on-board chargers (OBCs) face higher technical requirements. During the charging and discharging process of electric vehicles, OBCs need to precisely control the conduction and disconnection of a large number of controllable switches. However, in the currently widely used hard-switching technology, there may be voltage and current on both sides of the switch at the moment of conduction and disconnection of the controllable switch, which not only causes large switching losses but also generates electromagnetic interference (EMI), affecting the stability and safety of the system.

[0003] It should be noted that the information disclosed in the above background art section is only used to enhance the understanding of the background of this application, and thus may include information that does not constitute the prior art known to those of ordinary skill in the art. Summary of the Invention

[0004] In order to solve or at least alleviate one or more of the above problems, the following technical solutions are provided. This application provides a control method for a power conversion circuit, a power conversion circuit, an intelligent device, and a computer-readable storage medium, which can achieve soft-switching of some controllable switches during power transmission by adjusting the on-state and timing of the controllable switches in each arm of the power conversion circuit, thereby reducing the loss of the controllable switches and extending their service life.

[0005] According to a first aspect of the present application, a control method for a power conversion circuit is provided. The power conversion circuit includes a transformer, an input circuit coupled to the primary side of the transformer, and an output circuit coupled to the secondary side of the transformer. The input circuit includes a plurality of bridge arm groups. The upper and lower bridge arms in each bridge arm group include two controllable switches connected back-to-back. One of the controllable switches is used to control the on-off of the current in the first direction, and the other controllable switch is used to control the on-off of the current in the second direction. The first direction is the direction in which the current flows into the bridge arm, and the second direction is the direction opposite to the first direction. The method includes: determining the section in the power frequency period of the input voltage where it is currently located and selecting a non-control phase according to the magnitude relationship and positive and negative of the phase voltages applied to the respective bridge arm groups of the input circuit; selecting a first control phase and a second control phase according to the desired power flow direction; and within the currently located section, making the upper and lower bridge arms of the non-control phase conduct periodically and alternately, and during the conduction of the upper bridge arm of the non-control phase, switching the correspondingly conducting lower bridge arm from the lower bridge arm of the first control phase to the lower bridge arm of the second control phase, and during the conduction of the lower bridge arm of the non-control phase, switching the correspondingly conducting upper bridge arm from the upper bridge arm of the first control phase to the upper bridge arm of the second control phase, wherein, before the switching, making the controllable switch for controlling the on-off of the current in the first direction on the lower or upper bridge arm of the second control phase in a conducting state.

[0006] As an alternative or supplement to the above solution, in the control method according to an embodiment of the present application, the power frequency period of the input voltage includes twelve sections. In each section, the magnitude relationship and positive and negative of the phase voltages of each phase of the input voltage remain unchanged, and the non-control phase is the phase with the largest phase voltage amplitude in the currently located section.

[0007] As an alternative or supplement to the above solution, in the control method according to an embodiment of the present application, the input circuit includes three bridge arm groups, and the three bridge arm groups are respectively connected to the three phase lines of the three-phase power supply; and wherein, selecting the first control phase and the second control phase according to the desired power flow direction includes: if the desired power flow direction is from the primary side of the transformer to the secondary side of the transformer, selecting the phase with the second largest phase voltage amplitude in the currently located section as the first control phase, and selecting the phase with the smallest phase voltage amplitude in the currently located section as the second control phase; if the desired power flow direction is from the secondary side of the transformer to the primary side of the transformer, selecting the phase with the second largest phase voltage amplitude in the currently located section as the second control phase, and selecting the phase with the smallest phase voltage amplitude in the currently located section as the first control phase.

[0008] As an alternative or supplement to the above solution, in the control method according to an embodiment of the present application, the input circuit includes four bridge arm groups, three of the four bridge arm groups are respectively connected to three phase lines of a three-phase power supply, and the other bridge arm group is connected to the neutral phase line of the three-phase power supply. And among them, selecting the first control phase and the second control phase according to the desired power flow direction includes: if the desired power flow direction is from the primary side of the transformer to the secondary side of the transformer, select the phase with the second largest phase voltage amplitude in the current section as the first control phase, and select the phase with the smallest phase voltage amplitude in the current section as the second control phase, and the method further includes: selecting the neutral phase as the third control phase; if the desired power flow direction is from the secondary side of the transformer to the primary side of the transformer, select the neutral phase as the first control phase, and select the phase with the smallest phase voltage amplitude in the current section as the second control phase, and the method further includes: selecting the phase with the second largest phase voltage amplitude in the current section as the third control phase.

[0009] As an alternative or supplement to the above solution, in the control method according to an embodiment of the present application, during the conduction period of the upper bridge arm of the non-control phase, switching the correspondingly conducting lower bridge arm from the lower bridge arm of the first control phase to the lower bridge arm of the second control phase includes: turning on the controllable switch on the lower bridge arm of the second control phase for controlling the on-off of the current in the first direction; turning off the lower bridge arm of the first control phase; and turning on another controllable switch on the lower bridge arm of the second control phase.

[0010] As an alternative or supplement to the above solution, in the control method according to an embodiment of the present application, during the conduction period of the lower bridge arm of the non-control phase, switching the correspondingly conducting upper bridge arm from the upper bridge arm of the first control phase to the upper bridge arm of the second control phase includes: turning on the controllable switch on the upper bridge arm of the second control phase for controlling the on-off of the current in the first direction; turning off the upper bridge arm of the first control phase; and turning on another controllable switch on the upper bridge arm of the second control phase.

[0011] As an alternative or supplement to the above solution, in the control method according to an embodiment of the present application, the method further includes: during the conduction period of the upper bridge arm of the non-control phase, further switching the correspondingly conducting lower bridge arm from the lower bridge arm of the second control phase to the lower bridge arm of the third control phase; during the conduction period of the lower bridge arm of the non-control phase, further switching the correspondingly conducting upper bridge arm from the upper bridge arm of the second control phase to the upper bridge arm of the third control phase, where, before the further switching, the controllable switch on the lower bridge arm or the upper bridge arm of the third control phase for controlling the on-off of the current in the first direction is in the on state.

[0012] As an alternative or supplement to the above solution, in the control method according to an embodiment of the present application, during the conduction of the upper arm of the non-control phase, further switching the corresponding lower arm from the lower arm of the second control phase to the lower arm of the third control phase includes: turning on a controllable switch on the lower arm of the third control phase for controlling the on and off of the current in the first direction; turning off the lower arm of the second control phase; and turning on another controllable switch on the lower arm of the third control phase.

[0013] As an alternative or supplement to the above solution, in the control method according to an embodiment of the present application, during the conduction of the lower arm of the non-control phase, further switching the corresponding upper arm from the upper arm of the second control phase to the upper arm of the third control phase includes: turning on a controllable switch on the upper arm of the third control phase for controlling the on and off of the current in the first direction; turning off the upper arm of the second control phase; and turning on another controllable switch on the upper arm of the third control phase.

[0014] As an alternative or supplement to the above solution, in the control method according to an embodiment of the present application, the two controllable switches included in the upper arm and the lower arm of each arm group are two parts of a bidirectional controllable switch, and the two parts respectively have control terminals to respectively control the conduction and disconnection of the current in two directions.

[0015] According to a second aspect of the present application, there is provided a power conversion circuit, the power conversion circuit includes a transformer, an input circuit coupled to the primary side of the transformer, and an output circuit coupled to the secondary side of the transformer. The input circuit includes a plurality of arm groups, and the upper arm and the lower arm in each arm group include two controllable switches connected back to back. Wherein, the power conversion circuit further includes a controller configured to execute any one of the control methods according to the first aspect of the present application.

[0016] According to a third aspect of the present application, there is provided an intelligent device, the intelligent device includes the power conversion circuit according to the second aspect of the present application.

[0017] According to a fourth aspect of the present application, there is provided a computer-readable storage medium, the computer-readable storage medium includes instructions, and when the instructions are running, any one of the control methods according to the first aspect of the present application is executed.

[0018] The control method for a power conversion circuit according to one or more embodiments of the present application selects an unregulated phase, a first control phase, and a second control phase by considering the magnitude and sign of the phase voltage and combining the desired power flow direction, thereby ensuring that the voltage differences between the unregulated phase and the first and second control phases change sequentially in accordance with the power flow direction, providing conditions for the soft switching of controllable switches during the voltage switching process; and realizes the soft switching of specific controllable switches by adjusting the turn-on timing of the controllable switches during the periodically alternating voltage switching. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and / or other aspects and advantages of the present application will become clearer and easier to understand through the following descriptions of various aspects in conjunction with the accompanying drawings, where the same or similar units are denoted by the same reference numerals. In the said drawings:

[0020] Figure 1 is a schematic block diagram of a power conversion circuit 100 according to an embodiment of the present application;

[0021] Figure 2 is an exemplary circuit diagram of a power conversion circuit 200 according to an embodiment of the present application;

[0022] Figure 3 is a three-phase voltage waveform diagram of a three-phase power supply connected to an input circuit according to an embodiment of the present application;

[0023] Figure 4 is a flowchart of a control method 400 for a power conversion circuit according to an embodiment of the present application;

[0024] Figure 5 is according to an embodiment of the present application during Figure 3 when charging a vehicle in section 12 of Figure 2 a schematic diagram of the current of the transformer in the circuit, the primary and secondary voltages of the transformer, and the control timing of the controllable switches of each bridge arm;

[0025] Figure 6 is according to an embodiment of the present application during Figure 3 when discharging from a vehicle in section 1 of Figure 2 a schematic diagram of the current of the transformer in the circuit, the primary and secondary voltages of the transformer, and the control timing of the controllable switches of each bridge arm. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The following description of the detailed embodiments is essentially only exemplary and is not intended to limit the disclosed technology or the application and use of the disclosed technology. In addition, there is no intention to be bound by any theory, whether explicit or implicit, presented in the foregoing technical field, background art, or the following detailed embodiments.

[0027] In the following detailed description of the embodiments, numerous specific details are set forth in order to provide a more thorough understanding of the disclosed technology. However, it will be apparent to one of ordinary skill in the art that the disclosed technology may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description.

[0028] Terms such as "comprising" and "including" mean that in addition to the units (modules) and steps directly and explicitly recited in the specification and claims, the technical solutions of the present application do not exclude the case of having other units (modules) and steps not directly or explicitly recited. Terms such as "first" and "second" do not denote the order of the units in terms of time, space, size, etc., but are merely used to distinguish the units. Also, the steps herein are not limited to being implemented in the written order, but the steps written later can also be implemented simultaneously with the steps written earlier, or prior to the steps written earlier.

[0029] Hereinafter, various exemplary embodiments according to the present application will be described in detail with reference to the accompanying drawings.

[0030] Figure 1 is a schematic block diagram of a power conversion circuit 100 according to an embodiment of the present application. As Figure 1 shown, the power conversion circuit 100 includes a transformer 104, an input circuit 102 coupled to the primary side of the transformer 104, an output circuit 106 coupled to the secondary side of the transformer 104, and a controller 108. The input circuit 102 includes a plurality of bridge arm groups (e.g., 3 or 4 bridge arm groups), each bridge arm group includes an upper and a lower bridge arm, and each bridge arm includes two controllable switches (such as MOSFETs, IGBTs, etc.) connected back-to-back. The two controllable switches connected back-to-back can include two structural configurations. In an embodiment where the controllable switch is a MOSFET, the two MOSFETs can be configured in a common-source structure, or the two MOSFETs can be configured in a common-drain structure. Both of these structural configurations can achieve the control of the on / off of the current in two directions. For the purpose of distinction, the first direction is defined as the direction in which the current flows into the bridge arm, and the second direction is defined as the direction opposite to the first direction. One of the two controllable switches is used to control the on / off of the current in the first direction, and the other controllable switch is used to control the on / off of the current in the second direction. It can be understood that when the direction in which the current flows into the same bridge arm (i.e., the first direction) changes, correspondingly, the controllable switch used to control the on / off of the current in the first direction on the same bridge arm also changes. For example, taking Figure 2Taking the upper arm of phase A shown in the figure as an example, when the current flows from bottom to top (from LA to LR) in the upper arm of phase A, the first direction is from LA to LR. The controllable switch for controlling the on / off of the current in the first direction is a_g_n, and the controllable switch for controlling the on / off of the current in the second direction is a_g_p; when the current flows from top to bottom (from LR to LA) in the upper arm of phase A, the first direction is from LR to LA. The controllable switch for controlling the on / off of the current in the first direction is a_g_p, and the controllable switch for controlling the on / off of the current in the second direction is a_g_n. Return Figure 1 , in some embodiments, the two back-to-back connected controllable switches included in each arm can be implemented by a bidirectional controllable switch. Such a bidirectional controllable switch has two parts, and each part has a control terminal to respectively control the conduction and disconnection of the current in two directions.

[0031] The controller 108 is configured to: determine the section in the current input voltage power frequency period and select the non-control phase according to the magnitude relationship and positive / negative of the phase voltages connected to each arm group of the input circuit; select the first control phase and the second control phase; and periodically and alternately turn on the upper arm and the lower arm of the non-control phase within the current section, and switch the correspondingly turned-on lower arm from the lower arm of the first control phase to the lower arm of the second control phase during the conduction of the upper arm of the non-control phase, and switch the correspondingly turned-on upper arm from the upper arm of the first control phase to the upper arm of the second control phase during the conduction of the lower arm of the non-control phase. The following refers to Figures 2 - 6 to detail the control principle and possible implementation manners of the power conversion circuit 100. It should be noted that Figures 2 - 6 In some of the figures, parts of the controller are omitted, and the connection manners of the transformer, the input circuit, and the output circuit are emphasized.

[0032] Figure 2 The exemplary circuit diagram of the power conversion circuit 200 according to an embodiment of the present application is shown.

[0033] The input circuit includes A, B, C, and N arm groups. The upper arms and the lower arms of the A, B, C, and N arm groups each include two back-to-back connected controllable switches (as Figure 2 shown, the upper arm of the A arm group includes a_g_p and a_g_n, the lower arm of the A arm group includes a_h_p and a_h_n, the upper arm of the B arm group includes b_g_p and b_g_n, the lower arm of the B arm group includes b_h_p and b_h_n, the upper arm of the C arm group includes c_g_p and c_g_n, the lower arm of the C arm group includes c_h_p and c_h_n, the upper arm of the N arm group includes n_g_p and n_g_n, and the lower arm of the N arm group includes n_h_p and n_h_n). In some embodiments, as in Figure 2In the power conversion circuit 200, the two MOSFETs on each arm are configured in a common-source structure, where the upper MOSFET can control the on / off of the current in the upward-to-downward direction of the arm, and the lower MOSFET can control the on / off of the current in the downward-to-upward direction of the arm. In other embodiments, the two MOSFETs on each arm can also be configured in a common-drain structure. In the common-drain structure configuration, the upper MOSFET can control the on / off of the current in the downward-to-upward direction of the arm, and the lower MOSFET can control the on / off of the current in the upward-to-downward direction of the arm. Alternatively, in other embodiments, two back-to-back connected controllable switches can be equivalently replaced by a bidirectional controllable switch, where the bidirectional controllable switch has two control terminals that can receive drive signals (for example, taking the upper arm of the A arm group as an example, two controllable switches can be equivalently replaced by a bidirectional controllable switch, where the bidirectional controllable switch has two control terminals a_g_p and a_g_n).

[0034] The four arm groups of the input circuit can be connected to the three phase lines and the neutral line of the three-phase power supply (for example, the A arm group is connected to the phase line LA, the B arm group is connected to the phase line LB, the C arm group is connected to the phase line LC, and the N arm group is connected to the neutral line N). In some other embodiments, the input circuit may not include the N arm group. By turning on one of the upper arms and one of the lower arms in the input circuit, different voltages can be applied to the primary side of the transformer, and the voltage of the primary side of the transformer is represented by Vp.

[0035] The output circuit includes two arm groups, and each arm group includes two controllable switches (for example, SA and SB, SC and SD), which can receive instructions from the controller to turn on and off. The output circuit can be connected to the battery inside the vehicle, and the voltage of the battery is represented by Vo. By turning on one of the upper arms and one of the lower arms in the output circuit, different voltages can be applied to the secondary side of the transformer, and the voltage of the secondary side of the transformer is represented by Vs. When it is necessary to charge the vehicle from an external power supply, the power flows in from the input circuit and then is supplied to the vehicle's battery via the transformer. At this time, the desired power flow direction in the transformer is from the primary side of the transformer to the secondary side of the transformer; when it is necessary to discharge from the vehicle to the outside, the power is transported from the vehicle's battery through the output circuit, the transformer, and the input circuit to the outside. At this time, the desired power flow direction in the transformer is from the secondary side of the transformer to the primary side of the transformer.

[0036] Figure 3It is a three-phase voltage waveform diagram of a three-phase power supply connected to an input circuit according to an embodiment of the present application. A common three-phase power supply has three phases A, B, and C, and the three-phase voltages of A, B, and C are three sinusoidal voltages with the same frequency, equal amplitude, and a phase difference of 120° from each other. In the current power system, the operating frequency of the three-phase voltage is usually 50 Hz. Correspondingly, the power frequency period of the three-phase voltage is 0.02 seconds. As Figure 3 shown in the figure, the input three-phase voltage changes periodically, and each power frequency period (for example, 0.02 seconds) can be divided into twelve sections according to the magnitude relationship and positive and negative of the three-phase voltage. In each section, the magnitude relationship and positive and negative of the phase voltages of each phase and the magnitude relationship of the amplitudes of each phase voltage remain unchanged. For example, in section 1, Va > Vb > Vc, and Vb < 0; in section 2, Va > Vb > Vc, and Vb > 0; in section 3, Vb > Va > Vc, and Va > 0; in section 4, Vb > Va > Vc, and Va < 0; in section 5, Vb > Vc > Va, and Vc < 0; in section 6, Vb > Vc > Va, and Vc > 0; in section 7, Vc > Vb > Va, and Vb > 0; in section 8, Vc > Vb > Va, and Vb < 0; in section 9, Vc > Va > Vb, and Va < 0; in section 10, Vc > Va > Vb, and Va > 0; in section 11, Va > Vc > Vb, and Vc > 0; in section 12, Va > Vc > Vb, and Vc < 0. Correspondingly, by judging the magnitude relationship and positive and negative of each phase voltage, it is possible to determine which specific section in the power frequency period of the input voltage is currently in.

[0037] Figure 4 It is a flowchart of a control method 400 for a power conversion circuit according to an embodiment of the present application. The method 400 aims to achieve soft-switching control of a specific controllable switch during the voltage switching process. Compared with the traditional hard-switching technology, the soft-switching technology can reduce the voltage across the controllable switch to zero before the controllable switch conducts, and then conduct, thereby significantly reducing the turn-on loss and electromagnetic interference.

[0038] As Figure 4As shown in the figure, in step 402, according to the magnitude relationship and positive / negative of the phase voltages connected to each bridge arm group of the input circuit, the section in the power frequency cycle of the input voltage where it is currently located is determined and the non-controlled phase is selected. As described above, according to the magnitude relationship and positive / negative of the phase voltages of the three-phase power supply connected to each bridge arm group of the input circuit, the section in the power frequency cycle of the input voltage where it is currently located can be determined. Among them, the power frequency cycle of the input voltage includes twelve sections, and within each section, the magnitude relationship and positive / negative of each phase voltage of the input voltage and the magnitude relationship of the amplitudes of each phase voltage remain unchanged. For example, if the controller determines through detecting the input voltage that Va > Vb > Vc and Vb < 0, it can be determined that it is currently in section 1. Then, the non-controlled phase can be selected according to the magnitude relationship of the amplitudes of each phase voltage. Exemplarily, the non-controlled phase is determined as the phase with the largest phase voltage amplitude in the currently located section. For example, in section 1, the non-controlled phase is phase A. Correspondingly, if the currently located section is known, the magnitude relationship and positive / negative of each phase input voltage and the magnitude relationship of the amplitudes of each phase voltage can be determined, and the non-controlled phase can be selected accordingly.

[0039] Then, in step 404, the first control phase and the second control phase are selected according to the desired power flow direction. As mentioned above, when it is necessary to charge the vehicle from an external power supply, the desired power flow direction is from the primary side of the transformer to the secondary side of the transformer. When it is necessary to discharge from the vehicle to the outside, the desired power flow direction is from the secondary side of the transformer to the primary side of the transformer. The selection strategies corresponding to different desired power flow directions are different.

[0040] In an embodiment where the input circuit has three bridge arm groups and does not include an N bridge arm group, the three bridge arm groups are respectively connected to the three phase lines of the three-phase power supply. In step 402, the phase with the largest phase voltage amplitude in the currently located section has been selected as the non-controlled phase. At this time, according to the desired power flow direction, the first control phase and the second control phase are selected from the remaining two phases (the phase with the second largest phase voltage amplitude and the phase with the smallest phase voltage amplitude). If the desired power flow direction is from the primary side of the transformer to the secondary side of the transformer, the phase with the second largest phase voltage amplitude in the currently located section is selected as the first control phase, and the phase with the smallest phase voltage amplitude in the currently located section is selected as the second control phase; if the desired power flow direction is from the secondary side of the transformer to the primary side of the transformer, the phase with the second largest phase voltage amplitude in the currently located section is selected as the second control phase, and the phase with the smallest phase voltage amplitude in the currently located section is selected as the first control phase.

[0041] In an embodiment where the input circuit has four bridge arm groups (including A, B, C, and N bridge arm groups), three of the four bridge arm groups, namely A, B, and C, are respectively connected to three phase lines LA, LB, and LC of a three-phase power supply, and the other bridge arm group N is connected to the neutral phase line N of the three-phase power supply. In step 402, the phase with the largest phase voltage amplitude in the currently located section has been selected as the non-control phase. At this time, in some embodiments, selecting the first control phase and the second control phase according to the desired power flow can become a situation of selecting two of the three phases, and the remaining unselected phase will be used as the third control phase. Specifically, if the desired power flow is from the primary side of the transformer to the secondary side of the transformer, the phase with the second largest phase voltage amplitude in the currently located section is selected as the first control phase, the phase with the smallest phase voltage amplitude in the currently located section is selected as the second control phase, and the neutral phase is selected as the third control phase. By selecting the control phases as described above, it can be ensured that: in the case of charging the vehicle, the voltage difference between the non-control phase and the first control phase (i.e., the magnitude of the potential difference between the two phases), the voltage difference between the non-control phase and the second control phase, and the voltage difference between the non-control phase and the third control phase decrease in sequence, so as to achieve soft switching of a specific controllable switch during the voltage switching process. On the contrary, if the desired power flow is from the secondary side of the transformer to the primary side of the transformer, the neutral phase is used as the first control phase, the phase with the smallest phase voltage amplitude in the currently located section is selected as the second control phase, and the phase with the second largest phase voltage amplitude in the currently located section is selected as the third control phase. By selecting the control phases as described above, it can be ensured that: in the case of discharging from the vehicle, the voltage difference between the non-control phase and the first control phase, the voltage difference between the non-control phase and the second control phase, and the voltage difference between the non-control phase and the third control phase increase in sequence, so as to achieve soft switching of a specific controllable switch during the voltage switching process.

[0042] Then, after determining the non-control phase through step 402 and determining the first control phase and the second control phase (and potentially the third control phase) through step 404, in step 406, within the currently located section, the upper and lower bridge arms of the non-control phase are periodically and alternately turned on. This periodic and alternate turning on is achieved at a switching control frequency higher than the power frequency (for example, 5 kHz to 50 kHz). Therefore, the formed period is also a high-frequency switching control period smaller than the power frequency period (for example, 0.02 s) (for example, 0.02 ms to 0.2 ms). Further, the high-frequency switching control period can be divided into a first half cycle and a second half cycle according to the positive and negative of the voltage on the primary side of the transformer.

[0043] In addition, during the conduction period of the upper arm of the non-control phase (corresponding to half of the high-frequency switching control period), the conducting lower arm is switched from the lower arm of the first control phase to the lower arm of the second control phase; and during the conduction period of the lower arm of the non-control phase (corresponding to the other half of the high-frequency switching control period), the conducting upper arm is switched from the upper arm of the first control phase to the upper arm of the second control phase. For example, in section 12, at the beginning of the first half of the high-frequency period, the upper arm of the non-control phase and the lower arm of the first control phase are made to conduct. Then, after a period of time, the lower arm of the first control phase is turned off, and the lower arm of the second control phase is made to conduct until the end of the first half, thereby switching the lower arm corresponding to the conducting upper arm of the non-control phase from the lower arm of the first control phase to the lower arm of the second control phase. Then, at the beginning of the second half, the lower arm of the non-control phase and the upper arm of the first control phase are made to conduct. Then, after the said period of time, the upper arm of the first control phase is turned off, and the upper arm of the second control phase is made to conduct until the end of the second half, thereby switching the upper arm corresponding to the conducting lower arm of the non-control phase from the upper arm of the first control phase to the upper arm of the second control phase. Next, a new high-frequency period starts, and a new round of repetition begins. In other sections, when the positive and negative of the voltage of the non-control phase change, the order of conducting the upper and lower arms of the non-control phase in the first half and the second half is opposite to that in section 12.

[0044] When the input circuit includes an N-bridge arm group, in some embodiments, after switching the lower arm corresponding to the conducting upper arm of the non-control phase from the lower arm of the first control phase to the lower arm of the second control phase, the lower arm corresponding to the conducting upper arm of the non-control phase can be further switched from the lower arm of the second control phase to the lower arm of the third control phase; and after switching the upper arm corresponding to the conducting lower arm of the non-control phase from the upper arm of the first control phase to the upper arm of the second control phase, the upper arm corresponding to the conducting lower arm of the non-control phase can be further switched from the upper arm of the second control phase to the upper arm of the third control phase.

[0045] Through these operations, the voltage of the primary side of the transformer changes from a first voltage between the non - controlled phase and the first controlled phase to a second voltage between the non - controlled phase and the second controlled phase (and may further continue to change to a third voltage between the non - controlled phase and the third controlled phase) in the first half - cycle, and changes from the reversed first voltage to the reversed second voltage (and may further continue to change to the reversed third voltage) in the second half - cycle. It should be noted that in step 404, the selection of the first controlled phase, the second controlled phase (and possibly the third controlled phase) ensures that the voltage difference between the non - controlled phase and them changes sequentially (decreases or increases, depending on charging or discharging), thus forming a periodically alternating stepped voltage waveform. On the primary side of the transformer, this periodically alternating stepped voltage waveform can make the current waveform flowing through the primary side of the transformer smoother compared with a single - square - wave voltage waveform and provides conditions for the realization of soft - switching of specific controllable switches in this process.

[0046] Further, in order to be able to achieve soft - switching of specific controllable switches, the switching of the lower arm or the upper arm corresponding to the conduction of the upper arm or the lower arm of the non - controlled phase can be completed according to specific timing requirements. The specific timing requirements include: before the switching, the controllable switch used to control the on - off of the current in the first direction on the lower arm or the upper arm of the second controlled phase (and possibly the third controlled phase) is in the on - state. The control timing of the controllable switch will be exemplified below in combination with Figure 5 and Figure 6 For example, the control timing of the controllable switch will be described.

[0047] Reference Figure 5 , Figure 5 is a schematic diagram of the current of the transformer, the primary - side and secondary - side voltages of the transformer, and the control timing of the controllable switches of each arm (including the upper arm and the lower arm of the N - arm group) in the circuit when charging a vehicle in section 12 according to an embodiment of the present application. As mentioned above, in section 12, Va > Vc > Vb, and Vc < 0, where phase A is the non - controlled phase. Further, since Figure 3 is the situation of a high - frequency cycle in section 12 when charging a vehicle, at this time the power flow direction is from the primary side of the transformer to the secondary side of the transformer. According to the control - phase selection strategy described above, at this time, phase B is the first controlled phase, phase C is the second controlled phase, and phase N is the third controlled phase. Figure 2 Figure 5

[0048]

[0048] As Figure 5As shown in the figure, ILR is the current flowing through the primary side (LR) of the transformer, and Vp and Vs are the voltages of the primary side and secondary side of the transformer respectively. In the first half cycle, the voltage Vp of the primary side of the transformer is a positive voltage. At this time, the current ILR flowing through the transformer is basically in the positive direction (from the left side of LR to the right side of LR), but slightly lags (due to the external phase shift angle φ). In the second half cycle, the voltage Vp of the primary side of the transformer is a negative voltage. At this time, the current ILR flowing through the transformer is basically in the negative direction (from the right side of LR to the left side of LR).

[0049] Sg represents the timing of the drive signal of the controllable switch of the upper bridge arm of the input circuit in the power conversion circuit (for example, Figure 2 the power conversion circuit 200), Sh represents the timing of the drive signal of the controllable switch of the lower bridge arm of the input circuit in the power conversion circuit, and SA, SB, SC, and SD respectively represent the timing of the drive signals of the controllable switches of each bridge arm of the output circuit in the power conversion circuit. As shown in the figure, within the high-frequency switching control period, the upper and lower bridge arms of phase A conduct alternately. Specifically, in the first half cycle (t0 to t4), a_g_p and a_g_n remain conducting (i.e., the upper bridge arm of phase A conducts), and in the second half cycle (t4 to t8), a_h_p and a_h_n remain conducting (i.e., the lower bridge arm of phase A conducts), where there is an overlapping conduction of the upper and lower bridge arms of phase A during t3 - t4 and t7 - t8 (due to the internal phase shift angle on the input circuit side). During the conduction of the upper bridge arm of phase A, the lower bridge arms corresponding to the upper bridge arm of phase A switch from the lower bridge arms of phase B (b_h_p and b_h_n) to the lower bridge arms of phase C (c_h_p and c_h_n) and then to the lower bridge arms of phase N (n_h_p and n_h_n); during the conduction of the lower bridge arm of phase A, the upper bridge arms corresponding to the lower bridge arm of phase A switch from the upper bridge arms of phase B (b_g_p and b_g_n) to the upper bridge arms of phase C (c_g_p and c_g_n) and then to the upper bridge arms of phase N (n_g_p and n_g_n).

[0050] Before a period of time before the moment t1 when the lower arm of phase B switches to the lower arm of phase C, the current ILR in the primary side of the transformer flows in from LA, and then successively passes through a_g_n, a_g_p, LR, b_h_n, b_h_p, and then flows out from LB. At the moment t1, the lower arm of phase B is disconnected, and at the same time, the lower arm of phase C is turned on. Then, the current in the primary side of the transformer flows in from LA, and then successively passes through a_g_n, a_g_p, LR, c_h_n, c_h_p, and then flows out from LC. In this process, the current path through the upper arm of phase A and the primary side LR of the transformer remains unchanged, but the path through the lower arm switches from b_h_n, b_h_p to c_h_n, c_h_p. For the lower arm of phase C, after the switch, the current will flow into the lower arm of phase C from LR, and then flow out of the lower arm of phase C to LC (that is, at this time, the first direction of the lower arm of phase C is from LR to LC, and the second direction is from LC to LR), where c_h_n is a controllable switch on the lower arm of phase C used to control the on and off of the current in the first direction (from LR to LC), and c_h_p is a controllable switch on the lower arm of phase C used to control the on and off of the current in the second direction (from LC to LR). During the switching process, disconnecting b_h_n can achieve the disconnection of the lower arm of phase B, and to turn on the lower arm of phase C, both c_h_n and c_h_p need to be turned on. As shown in the figure, before switching the lower arm of phase B to the lower arm of phase C, c_h_n is in the on state.

[0051] Therefore, during the conduction period of the upper arm of phase A, switching the corresponding conducting lower arm from the lower arm of phase B to the lower arm of phase C includes: turning on the controllable switch on the lower arm of phase C used to control the on and off of the current in the first direction; disconnecting the lower arm of phase B; and turning on the controllable switch on the lower arm of phase C used to control the on and off of the current in the second direction.

[0052] When ILR is along the positive direction and the voltage Vp on the primary side of the transformer changes from large to small (Vab to Vac), turning on c_h_n before the lower arm of phase B is disconnected (at moment t1) can provide a freewheeling path for the current at the moment of disconnection through the lower arm of phase C (the MOSFET of c_h_n and the diode of c_h_p) to LC, so that when the MOSFET of c_h_p is turned on at moment t1, the voltage difference across c_h_p is almost zero, thus realizing the soft switching of c_h_p. On the contrary, if c_h_n and c_h_p are both turned on at moment t1, at the moment of t1, the voltage difference across c_h_n and c_h_p is Vbc. At this time, hard switching technology must be used to turn on the controllable switch of the lower arm of phase C.

[0053] Turning to the second half cycle, during a period of time before the moment t5 when the upper bridge arm of phase B switches to the upper bridge arm of phase C, the current ILR in the primary side of the transformer flows in from LA, then successively passes through a_h_p, a_h_n, LR, b_g_p, b_g_n, and then flows out from LB. At the moment t5, the upper bridge arm of phase B is disconnected, and at the same time, the upper bridge arm of phase C is turned on. Then, the current in the primary side of the transformer flows in from LA, then successively passes through a_h_p, a_h_n, LR, c_g_p, c_g_n, and then flows out from LC. During this process, the current path through the lower bridge arm of phase A and the primary side LR of the transformer remains unchanged, but the path through the upper bridge arm switches from b_g_p, b_g_n to c_g_p, c_g_n. For the upper bridge arm of phase C, after the switching, the current will flow into the upper bridge arm of phase C from LR, and then flow out of the upper bridge arm of phase C to LC (that is, at this time, the first direction of the upper bridge arm of phase C is from LR to LC, and the second direction is from LC to LR), where c_g_p is a controllable switch on the upper bridge arm of phase C for controlling the on-off of the current in the first direction (from LR to LC), and c_g_n is a controllable switch on the upper bridge arm of phase C for controlling the on-off of the current in the second direction (from LC to LR). During the switching process, disconnecting b_g_p can achieve the disconnection of the upper bridge arm of phase B, and to turn on the upper bridge arm of phase C, it is necessary to turn on both c_g_p and c_g_n. As shown in the figure, before switching the upper bridge arm of phase B to the upper bridge arm of phase C, c_g_p is in the on state.

[0054] Therefore, switching the corresponding turned-on upper bridge arm from the upper bridge arm of phase B to the upper bridge arm of phase C during the conduction period of the lower bridge arm of phase A includes: turning on the controllable switch on the upper bridge arm of phase C for controlling the on-off of the current in the first direction; disconnecting the upper bridge arm of phase B; and turning on the controllable switch on the upper bridge arm of phase C for controlling the on-off of the current in the second direction.

[0055] When ILR is along the negative direction and the voltage Vp in the primary side of the transformer changes from small to large (-Vab to -Vac), keeping c_g_p in the on state before the upper bridge arm of phase B is disconnected (at the moment t5) can provide a freewheeling path for the current at the moment of disconnection via the upper bridge arm of phase C (the MOSFET of c_g_p and the diode of c_g_n) to LC, so that when the MOSFET of c_g_n is turned on at the moment t5, the voltage difference across c_g_n is almost zero, thus realizing the soft switching of c_g_n. On the contrary, if c_g_p and c_g_n are both turned on at the moment t5, at the moment of t5, the voltage difference across c_g_p and c_g_n is Vbc, and at this time, hard switching technology must be used to turn on the controllable switch of the upper bridge arm of phase C.

[0056] Continue to refer to Figure 5, similar to the switching at time t1, before the moment t2 when the lower arm of phase C is further switched to the lower arm of phase N (during the period from t1 to t2), the current ILR in the primary side of the transformer flows in from LA, then successively passes through a_g_n, a_g_p, LR, c_h_n, c_h_p, and then flows out from LC. At time t2, the lower arm of phase C is disconnected, and at the same time, the lower arm of phase N is turned on. Then, the current in the primary side of the transformer flows in from LA, then successively passes through a_g_n, a_g_p, LR, n_h_n, n_h_p, and then flows out from the N line. During this process, the current path through the upper arm of phase A and the primary side LR of the transformer remains unchanged, but the path through the lower arm switches from c_h_n, c_h_p to n_h_n, n_h_p. For the lower arm of phase N, after the switching, the current will flow into the lower arm of phase N from LR, and then flow out from the lower arm of phase N to the N line (that is, at this time, the first direction of the lower arm of phase N is from LR to the N line, and the second direction is from the N line to LR), where n_h_n is a controllable switch on the lower arm of phase N used to control the on / off of the current in the first direction (from LR to the N line), and n_h_p is a controllable switch on the lower arm of phase N used to control the on / off of the current in the second direction (from the N line to LR). During the switching process, disconnecting c_h_n (here c_h_p is also disconnected at the same time) can achieve the disconnection of the lower arm of phase C, and to turn on the lower arm of phase N, both n_h_n and n_h_p need to be turned on. As shown in the figure, before switching the lower arm of phase C to the lower arm of phase N, n_h_n is in the on state.

[0057] Therefore, switching the corresponding turned-on lower arm from the lower arm of phase C to the lower arm of phase N during the conduction period of the upper arm of phase A includes: turning on the controllable switch on the lower arm of phase N used to control the on / off of the current in the first direction; disconnecting the lower arm of phase C; and turning on the controllable switch on the lower arm of phase N used to control the on / off of the current in the second direction.

[0058] When ILR is along the positive direction and the voltage Vp in the primary side of the transformer changes from large to small (from Vac to Van), turning on n_h_n before the lower arm of phase C is disconnected (at time t2) can provide a freewheeling path for the current at the moment of disconnection via the lower arm of phase N (the MOSFET of n_h_n and the diode of n_h_p) to the N line, so that when the MOSFET of n_h_p is turned on at time t2, the voltage difference across n_h_p is almost zero, thus achieving soft switching of n_h_p. On the contrary, if n_h_n and n_h_p are turned on together only at time t2, at the moment of time t2, the voltage difference across n_h_n and n_h_p is Vcn, and at this time, hard switching technology must be used to turn on the controllable switch of the lower arm of phase N.

[0059] Turning to the second half cycle, similar to the switching at time t5, before the moment t6 when the upper bridge arm of phase C switches to the upper bridge arm of phase N (during the time period from t5 to t6), the current ILR in the primary side of the transformer flows in from LA, then successively passes through a_h_p, a_h_n, LR, c_g_p, c_g_n, and then flows out from LC. At time t6, the upper bridge arm of phase C is disconnected, and at the same time, the upper bridge arm of phase N is turned on. Then, the current in the primary side of the transformer flows in from LA, then successively passes through a_h_p, a_h_n, LR, n_g_p, n_g_n, and then flows out from the N line. During this process, the current path through the lower bridge arm of phase A and the primary side LR of the transformer remains unchanged, but the path through the upper bridge arm switches from c_g_p, c_g_n to n_g_p, n_g_n. For the upper bridge arm of phase N, after the switching, the current will flow into the upper bridge arm of phase N from LR, and then flow out from the upper bridge arm of phase N to the N line (that is, at this time, the first direction of the upper bridge arm of phase N is from LR to the N line, and the second direction is from the N line to LR), where n_g_p is a controllable switch on the upper bridge arm of phase N for controlling the on-off of the current in the first direction (from LR to the N line), and n_g_n is a controllable switch on the upper bridge arm of phase N for controlling the on-off of the current in the second direction (from the N line to LR). During the switching process, disconnecting c_g_p (and at the same time disconnecting c_g_n here) can achieve the disconnection of the upper bridge arm of phase C, and to turn on the upper bridge arm of phase N, it is necessary to turn on both n_g_p and n_g_n. As shown in the figure, before switching the upper bridge arm of phase C to the upper bridge arm of phase N, n_g_p is turned on.

[0060] Therefore, switching the corresponding turned-on upper bridge arm from the upper bridge arm of phase C to the upper bridge arm of phase N during the conduction period of the lower bridge arm of phase A includes: turning on the controllable switch on the upper bridge arm of phase N for controlling the on-off of the current in the first direction; disconnecting the upper bridge arm of phase C; and turning on the controllable switch on the upper bridge arm of phase N for controlling the on-off of the current in the second direction.

[0061] When ILR is along the negative direction and the voltage Vp in the primary side of the transformer increases from small to large (-Vac to -Van), turning on n_g_p before the disconnection of the upper bridge arm of phase C (at time t6) can provide a freewheeling path for the current at the moment of disconnection via the upper bridge arm of phase N (the MOSFET of n_g_p and the diode of n_g_n) to the N line, so that the voltage difference across n_g_n is almost zero when the MOSFET of n_g_n is turned on at time t6, thereby realizing the soft switching of n_g_n. On the contrary, if n_g_p and n_g_n are turned on together only at time t6, at the moment of time t6, the voltage difference across n_g_p and n_g_n is Vcn, and at this time, hard switching technology must be used to turn on the controllable switch of the upper bridge arm of phase N.

[0062] Next, refer to Figure 6 to discuss the situation when discharging from the vehicle, Figure 6 which is a schematic diagram of the current of the transformer in the circuit, the primary and secondary voltages of the transformer, and the control timing of the controllable switches of each bridge arm when discharging from the vehicle in section 1 according to an embodiment of the present application. Figure 3 in section 1 Figure 2 The meanings represented by the symbols in Figure 6 are the same as those represented by the same symbols in Figure 5 and will not be repeated here.

[0063] In section 1, Va > Vb > Vc, and Vb < 0, where the amplitude of Va is the largest, so phase A is the non - controlled phase. Further, since Figure 6 shows the situation of a high - frequency cycle in section 1 when discharging from the vehicle. At this time, the power flow is from the secondary side of the transformer to the primary side of the transformer. Therefore, phase N is the first controlled phase, phase B is the second controlled phase, and phase C is the third controlled phase.

[0064] In Figure 6 during the first half - cycle, the voltage Vp of the primary side of the transformer is a positive voltage. At this time, the current ILR flowing through the transformer is basically in the negative direction (from the right side of LR to the left side of LR), but slightly ahead (due to the external phase - shift angle φ). During the second half - cycle, the voltage Vp of the primary side of the transformer is a negative voltage. At this time, the current ILR flowing through the transformer is basically in the positive direction (from the left side of LR to the right side of LR).

[0065] As shown in the figure, within the high - frequency cycle, the upper and lower arms of phase A conduct alternately. Specifically, during the first half - cycle (t0 to t4), a_g_p and a_g_n remain conducting (i.e., the upper arm of phase A conducts). During the second half - cycle (t4 to t8), a_h_p and a_h_n remain conducting (i.e., the lower arm of phase A conducts). There is an overlap conduction of the upper and lower arms of phase A during the periods of t3 - t4 and t7 - t8 (due to the internal phase - shift angle ap on the input circuit side). During the conduction of the upper arm of phase A, the corresponding lower arms that conduct with the upper arm of phase A switch from the lower arms of phase N (n_h_p and n_h_n) to the lower arms of phase B (b_h_p and b_h_n) and then to the lower arms of phase C (c_h_p and c_h_n); during the conduction of the lower arm of phase A, the corresponding upper arms that conduct with the lower arm of phase A switch from the upper arms of phase N (n_g_p and n_g_n) to the upper arms of phase B (b_g_p and b_g_n) and then to the upper arms of phase C (c_g_p and c_g_n).

[0066] Before the moment t1 when the lower arm of the N phase switches to the lower arm of the B phase (during the period t0 to t1), the current ILR in the primary side of the transformer flows in from the N line, then successively passes through n_h_p, n_h_n, LR, a_g_p, a_h_n, and then flows out from LA. At the moment t1, the lower arm of the N phase is disconnected, and at the same time, the lower arm of the B phase is turned on. Then, the current in the primary side of the transformer flows in from LB, then successively passes through b_h_p, b_h_n, LR, a_g_p, a_g_n, and then flows out from LA. During this process, the current path through the upper arm of the A phase and the primary side LR of the transformer remains unchanged, but the path through the lower arm switches from n_h_p, n_h_n to b_h_p, b_h_n. For the lower arm of the B phase, after the switch, the current will flow into the lower arm of the B phase from LB, and then flow out through the lower arm of the B phase to LR (that is, at this time, the first direction of the lower arm of the B phase is from LB to LR, and the second direction is from LR to LB), where b_h_p is a controllable switch on the lower arm of the B phase for controlling the on-off of the current in the first direction (from LB to LR), and b_h_n is a controllable switch on the lower arm of the B phase for controlling the on-off of the current in the second direction (from LR to LB). During the switching process, disconnecting n_h_p (disconnecting n_h_n at the same time here) can achieve the disconnection of the lower arm of the N phase, and to turn on the lower arm of the B phase, it is necessary to turn on both b_h_n and b_h_p. As shown in the figure, before switching the lower arm of the N phase to the lower arm of the B phase, b_h_p is turned on.

[0067] Therefore, switching the corresponding lower arm that is turned on during the conduction of the upper arm of the A phase from the lower arm of the N phase to the lower arm of the B phase includes: turning on the controllable switch on the lower arm of the B phase for controlling the on-off of the current in the first direction; disconnecting the lower arm of the N phase; and turning on the controllable switch on the lower arm of the B phase for controlling the on-off of the current in the second direction.

[0068] When ILR is along the negative direction and the voltage Vp in the primary side of the transformer increases from small to large (from Van to Vab), turning on b_h_p before the lower arm of the N phase is disconnected (at the moment t1) can provide a freewheeling path for the current at the moment of disconnection via the lower arm of the B phase (the MOSFET of b_h_p and the diode of b_h_n) to LR, so that when the MOSFET of b_h_n is turned on at the moment t1, the voltage difference across b_h_n is almost zero, thus achieving soft switching of b_h_n. On the contrary, if b_h_p and b_h_n are turned on together only at the moment t1, at the instant of t1, the voltage difference across b_h_p and b_h_n is Vbn, and at this time, hard switching technology must be used to turn on the controllable switch of the lower arm of the B phase.

[0069] Turning to the second half cycle, before the moment t5 when the upper arm of the N phase switches to the upper arm of the B phase (during the time period t4 to t5), the current ILR in the primary side of the transformer flows in from the N line, then successively passes through n_g_n, n_g_p, LR, a_h_n, a_h_p, and then flows out from LA. At the moment t5, the upper arm of the N phase is disconnected, and at the same time, the upper arm of the B phase is turned on. Then, the current in the primary side of the transformer flows in from LB, then successively passes through b_g_n, b_g_p, LR, a_h_n, a_h_p, and then flows out from LA. During this process, the current path through the lower arm of the A phase and the primary side LR of the transformer remains unchanged, but the path through the upper arm switches from n_g_n, n_g_p to b_g_n, b_g_p. For the upper arm of the B phase, after the switching, the current will flow into the upper arm of the B phase from LB, and then flow out of the upper arm of the B phase to LR (i.e., at this time, the first direction of the upper arm of the B phase is from LB to LR, and the second direction is from LR to LB). Among them, b_g_n is a controllable switch on the upper arm of the B phase for controlling the on / off of the current in the first direction (from LB to LR), and b_g_p is a controllable switch on the upper arm of the B phase for controlling the on / off of the current in the second direction (from LR to LB). During the switching process, disconnecting n_g_n (here n_g_p is also disconnected simultaneously) can achieve the disconnection of the upper arm of the N phase, and to turn on the upper arm of the B phase, it is necessary to turn on both b_g_p and b_g_n. As shown in the figure, before switching the upper arm of the N phase to the upper arm of the B phase, b_g_n is in the on state.

[0070] Therefore, during the conduction period of the lower arm of the A phase, switching the corresponding conducting upper arm from the upper arm of the N phase to the upper arm of the B phase includes: turning on the controllable switch on the upper arm of the B phase for controlling the on / off of the current in the first direction; disconnecting the upper arm of the N phase; and turning on the controllable switch on the upper arm of the B phase for controlling the on / off of the current in the second direction.

[0071] When ILR is along the positive direction and the voltage Vp in the primary side of the transformer changes from large to small (-Van to -Vab), turning on b_g_n before the disconnection of the upper arm of the N phase (at the moment t5) can provide a freewheeling path for the current at the moment of disconnection via the upper arm of the B phase (the MOSFET of b_g_n and the diode of b_g_p) to LR, so that when the MOSFET of b_g_p is turned on at the moment t5, the voltage difference across b_g_p is almost zero, thereby realizing the soft switching of b_g_p. On the contrary, if b_g_n and b_g_p are turned on together at the moment t5, at the moment of t5, the voltage difference across b_g_n and b_g_p is Vbn. At this time, hard switching technology must be used to turn on the controllable switch of the upper arm of the B phase.

[0072] Continue to refer to Figure 6, similar to the switching at time t1, before the moment t2 when the lower arm of phase B is further switched to the lower arm of phase C (during the period from t1 to t2), the current ILR in the primary side of the transformer flows in from LB, then successively passes through b_h_p, b_h_n, LR, a_g_p, a_g_n, and then flows out from LA. At time t2, the lower arm of phase B is disconnected, and at the same time, the lower arm of phase C is turned on. Then, the current in the primary side of the transformer flows in from LC, then successively passes through c_h_p, c_h_n, LR, a_g_p, a_g_n, and then flows out from LA. During this process, the current path through the upper arm of phase A and the primary side LR of the transformer remains unchanged, but the path through the lower arm switches from b_h_p, b_h_n to c_h_p, c_h_n. For the lower arm of phase C, after the switching, the current will flow into the lower arm of phase C from LC, and then flow out from the lower arm of phase C to LR (that is, at this time, the first direction of the lower arm of phase C is from LC to LR, and the second direction is from LR to LC), where c_h_p is a controllable switch on the lower arm of phase C for controlling the on-off of the current in the first direction (from LC to LR), and c_h_n is a controllable switch on the lower arm of phase C for controlling the on-off of the current in the second direction (from LR to LC). During the switching process, disconnecting b_h_p (here b_h_n is also disconnected simultaneously) can achieve the disconnection of the lower arm of phase B, and to turn on the lower arm of phase C, it is necessary to turn on both c_h_n and c_h_p. As shown in the figure, before switching the lower arm of phase B to the lower arm of phase C, c_h_p is in the on state.

[0073] Therefore, switching the corresponding turned-on lower arm from the lower arm of phase B to the lower arm of phase C during the conduction period of the upper arm of phase A includes: turning on the controllable switch on the lower arm of phase C for controlling the on-off of the current in the first direction; disconnecting the lower arm of phase B; and turning on the controllable switch on the lower arm of phase C for controlling the on-off of the current in the second direction.

[0074] When ILR is along the negative direction and the voltage Vp in the primary side of the transformer increases from small to large (Vab to Vac), turning on c_h_p before the disconnection of the lower arm of phase B (at time t2) can provide a freewheeling path for the current at the moment of disconnection through the lower arm of phase C (the MOSFET of c_h_p and the diode of c_h_n) to LR, so that when the MOSFET of c_h_n is turned on at time t2, the voltage difference across c_h_n is almost zero, thereby realizing the soft switching of c_h_n. On the contrary, if c_h_p and c_h_n are turned on together only at time t2, at the moment of time t2, the voltage difference across c_h_p and c_h_n is Vcb, and at this time, hard switching technology must be used to turn on the controllable switch of the lower arm of phase C.

[0075] Turning to the second half cycle, similar to the switching at time t5, before the moment t6 when the upper bridge arm of phase B switches to the upper bridge arm of phase C (during the period from t5 to t6), the current ILR in the primary side of the transformer flows in from LB, then successively passes through b_g_n, b_g_p, LR, a_h_n, a_h_p, and then flows out from LA. At time t6, the upper bridge arm of phase B is disconnected, and at the same time, the upper bridge arm of phase C is turned on. Then, the current in the primary side of the transformer flows in from LC, then successively passes through c_g_n, c_g_p, LR, a_h_n, a_h_p, and then flows out from LA. During this process, the current path through the lower bridge arm of phase A and the primary side LR of the transformer remains unchanged, but the path through the upper bridge arm switches from b_g_n, b_g_p to c_g_n, c_g_p. For the upper bridge arm of phase C, after the switching, the current will flow into the upper bridge arm of phase C from LC, and then flow out to LR through the upper bridge arm of phase C (that is, at this time, the first direction of the upper bridge arm of phase C is from LC to LR, and the second direction is from LR to LC). Among them, c_g_n is a controllable switch on the upper bridge arm of phase C for controlling the on-off of the current in the first direction (from LC to LR), and c_g_p is a controllable switch on the upper bridge arm of phase C for controlling the on-off of the current in the second direction (from LR to LC). During the switching process, disconnecting b_g_n (here b_g_p is also disconnected simultaneously) can achieve the disconnection of the upper bridge arm of phase B, and to turn on the upper bridge arm of phase C, it is necessary to turn on both c_g_p and c_g_n. As shown in the figure, before switching the upper bridge arm of phase B to the upper bridge arm of phase C, c_g_n is in the on state.

[0076] Therefore, switching the corresponding upper bridge arm from the upper bridge arm of phase B to the upper bridge arm of phase C during the conduction period of the lower bridge arm of phase A includes: turning on the controllable switch on the upper bridge arm of phase C for controlling the on-off of the current in the first direction; disconnecting the upper bridge arm of phase B; and turning on the controllable switch on the upper bridge arm of phase C for controlling the on-off of the current in the second direction.

[0077] When ILR is along the positive direction and the voltage Vp in the primary side of the transformer changes from large to small (-Vab to -Vac), turning on c_g_n before the disconnection of the upper bridge arm of phase B (at time t6) can provide a freewheeling path for the current at the moment of disconnection via the upper bridge arm of phase C (the MOSFET of c_g_n and the diode of c_g_p) to LR, so that when the MOSFET of c_g_p is turned on at time t6, the voltage difference across c_g_p is almost zero, thus achieving soft switching of c_g_p. On the contrary, if c_g_n and c_g_p are turned on together only at time t6, at the moment of time t6, the voltage difference across c_g_n and c_g_p is Vcb. At this time, hard switching technology must be used to turn on the controllable switch of the upper bridge arm of phase C.

[0078] Combination Figure 5 and Figure 6 From the embodiments, it can be seen that during the conduction period of the upper arm of the non - control phase, when switching the corresponding conducting lower arm from the lower arm of the first control phase to the lower arm of the second control phase, in order to achieve soft switching of the controllable switch for controlling the on - off of the current in the second direction on the lower arm of the second control phase, it is necessary to make the controllable switch for controlling the on - off of the current in the first direction on the lower arm of the second control phase in the conducting state before the switching; during the conduction period of the lower arm of the non - control phase, when switching the corresponding conducting upper arm from the upper arm of the first control phase to the upper arm of the second control phase, in order to achieve soft switching of the controllable switch for controlling the on - off of the current in the second direction on the upper arm of the second control phase, it is necessary to make the controllable switch for controlling the on - off of the current in the first direction on the upper arm of the second control phase in the conducting state before the switching.

[0079] Additionally, during the conduction period of the upper arm of the non - control phase, when further switching the corresponding conducting lower arm from the lower arm of the second control phase to the lower arm of the third control phase, in order to achieve soft switching of the controllable switch for controlling the on - off of the current in the second direction on the lower arm of the third control phase, it is necessary to make the controllable switch for controlling the on - off of the current in the first direction on the lower arm of the third control phase in the conducting state before the further switching; during the conduction period of the lower arm of the non - control phase, when further switching the corresponding conducting upper arm from the upper arm of the second control phase to the upper arm of the third control phase, in order to achieve soft switching of the controllable switch for controlling the on - off of the current in the second direction on the upper arm of the third control phase, it is necessary to make the controllable switch for controlling the on - off of the current in the first direction on the upper arm of the third control phase in the conducting state before the further switching.

[0080] In addition, the present application can also be implemented as a power conversion circuit, the power conversion circuit includes a transformer, an input circuit coupled to the primary side of the transformer, and an output circuit coupled to the secondary side of the transformer. The input circuit includes a plurality of bridge arm groups, and the upper arm and the lower arm in each bridge arm group include two controllable switches connected back - to - back. Wherein, the power conversion circuit further includes a controller configured to execute the control method of any one of the foregoing embodiments. In addition, the present application can also be implemented as an intelligent device, and the intelligent device includes the above - mentioned power conversion circuit.

[0081] In addition, as described above, the present application can also be implemented as a computer-readable storage medium in which a program for causing a computer to execute the method described in any of the above embodiments is stored. Here, as the computer-readable storage medium, various types of computer-readable storage media such as disk types (e.g., magnetic disks, optical disks, etc.), card types (e.g., memory cards, optical cards, etc.), semiconductor memory types (e.g., ROM, non-volatile memories, etc.), tape types (e.g., magnetic tapes, cassette tapes, etc.) can be adopted.

[0082] In applicable cases, hardware, software, or a combination of hardware and software can be used to implement the various embodiments provided by the present application. Moreover, in applicable cases, without departing from the scope of the present application, the various hardware components and / or software components described herein can be combined into a composite component including software, hardware, and / or both. In applicable cases, without departing from the scope of the present application, the various hardware components and / or software components described herein can be divided into sub-components including software, hardware, or both. Additionally, in applicable cases, it is contemplated that software components can be implemented as hardware components, and vice versa.

[0083] The software (such as program code and / or data) according to the present application can be stored on one or more computer-readable storage media. It is also contemplated that one or more general-purpose or special-purpose computers and / or computer systems connected via a network and / or in other ways can be used to implement the software identified herein. In applicable cases, the order of the various steps described herein can be changed, combined into composite steps, and / or divided into sub-steps to provide the features described herein.

[0084] The embodiments and examples presented herein are provided so as to best illustrate the embodiments in accordance with the present application and its specific applications, and thereby enable those skilled in the art to implement and use the present application. However, those skilled in the art will know that the above description and examples are provided only for ease of illustration and exemplification. The presented description is not intended to cover all aspects of the present application or to limit the present application to the precise forms disclosed.

Claims

1. A control method for a power conversion circuit, the power conversion circuit comprising a transformer, an input circuit coupled to the primary side of the transformer, and an output circuit coupled to the secondary side of the transformer, the input circuit comprising a plurality of bridge arm groups, an upper bridge arm and a lower bridge arm in each bridge arm group comprising two controllable switches connected back to back, one of the controllable switches being used to control the on-off of a current in a first direction, and the other controllable switch being used to control the on-off of a current in a second direction, the first direction being the direction in which a current flows into the bridge arm, and the second direction being the direction opposite to the first direction, the method comprising: According to the magnitude relationship and positive and negative of the phase voltages connected to each bridge arm group of the input circuit, the current section of the input voltage power frequency cycle is determined and the non-controlled phase is selected; Selecting a first control phase and a second control phase according to a desired power flow direction; as well as In the section, the upper bridge arm and the lower bridge arm of the non-controlled phase are periodically and alternately turned on, and during the period when the upper bridge arm of the non-controlled phase is turned on, the corresponding turned-on lower bridge arm is switched from the lower bridge arm of the first controlled phase to the lower bridge arm of the second controlled phase, and during the period when the lower bridge arm of the non-controlled phase is turned on, the corresponding turned-on upper bridge arm is switched from the upper bridge arm of the first controlled phase to the upper bridge arm of the second controlled phase, Before switching, a controllable switch on the lower bridge arm or the upper bridge arm of the second control phase for controlling the on and off of the current in the first direction is placed in an on state.

2. The method of claim 1, wherein: The input voltage power frequency cycle includes twelve sections, in each section, the magnitude relationship and positive and negative sign of each phase voltage of the input voltage remain unchanged, and the non-controlled phase is the phase with the largest phase voltage amplitude in the current section.

3. The method of claim 2, wherein: The input circuit includes three bridge arm groups, the three bridge arm groups are respectively connected to three phase lines of a three-phase power supply, and wherein selecting the first control phase and the second control phase according to the desired power flow direction includes: If the desired power flow direction is from the primary side of the transformer to the secondary side of the transformer, the phase with the second largest phase voltage amplitude in the current section is selected as the first control phase, and the phase with the smallest phase voltage amplitude in the current section is selected as the second control phase; If the desired power flow is from the secondary side of the transformer to the primary side of the transformer, the phase with the second largest phase voltage amplitude in the current section is selected as the second control phase, and the phase with the smallest phase voltage amplitude in the current section is selected as the first control phase.

4. The method of claim 2, wherein: The input circuit includes four bridge arm groups, three of which are respectively connected to three phase lines of a three-phase power supply, and another bridge arm group is connected to a neutral phase line of the three-phase power supply, and wherein, Selecting the first control phase and the second control phase according to the desired power flow direction includes: if the desired power flow direction is from the primary side of the transformer to the secondary side of the transformer, selecting the phase with the second largest phase voltage amplitude in the current section as the first control phase, selecting the phase with the smallest phase voltage amplitude in the current section as the second control phase, and The method further includes: selecting a neutral phase as a third control phase; If the desired power flow direction is from the secondary side of the transformer to the primary side of the transformer, the neutral phase is selected as the first control phase, the phase with the smallest phase voltage amplitude in the current section is selected as the second control phase, and The method further includes: selecting a phase with the second largest phase voltage amplitude in the current section as a third control phase.

5. The method according to any one of claims 3 or 4, wherein: During the conduction period of the upper bridge arm of the non-controlled phase, switching the corresponding conducted lower bridge arm from the lower bridge arm of the first controlled phase to the lower bridge arm of the second controlled phase comprises: Turning on a controllable switch on the lower bridge arm of the second control phase for controlling the on and off of the current in the first direction; Disconnecting the lower bridge arm of the first control phase; and Another controllable switch on the lower bridge arm of the second control phase is turned on.

6. The method according to any one of claims 3 or 4, wherein: During the conduction period of the lower bridge arm of the non-controlled phase, switching the corresponding conducted upper bridge arm from the upper bridge arm of the first controlled phase to the upper bridge arm of the second controlled phase comprises: Turning on a controllable switch on the upper bridge arm of the second control phase for controlling the on and off of the current in the first direction; Disconnecting the upper bridge arm of the first control phase; and Another controllable switch on the upper bridge arm of the second control phase is turned on.

7. The method of claim 4, further comprising: During the conduction period of the upper bridge arm of the non-controlled phase, the correspondingly conducted lower bridge arm is further switched from the lower bridge arm of the second controlled phase to the lower bridge arm of the third controlled phase; During the conduction period of the lower bridge arm of the non-controlled phase, the corresponding conducted upper bridge arm is further switched from the upper bridge arm of the second controlled phase to the upper bridge arm of the third controlled phase, Before further switching, a controllable switch on the lower bridge arm or the upper bridge arm of the third control phase for controlling the on and off of the current in the first direction is placed in an on state.

8. The method of claim 7, wherein: During the conduction period of the upper bridge arm of the non-controlled phase, further switching the corresponding conducted lower bridge arm from the lower bridge arm of the second controlled phase to the lower bridge arm of the third controlled phase comprises: Turning on a controllable switch on the lower bridge arm of the third control phase for controlling the on and off of the current in the first direction; Disconnecting the lower bridge arm of the second control phase; and Another controllable switch on the lower bridge arm of the third control phase is turned on.

9. The method of claim 7, wherein: During the conduction period of the lower bridge arm of the non-controlled phase, further switching the corresponding conducted upper bridge arm from the upper bridge arm of the second controlled phase to the upper bridge arm of the third controlled phase comprises: Turning on a controllable switch on the upper bridge arm of the third control phase for controlling the on and off of current in the first direction; Disconnecting the upper bridge arm of the second control phase; and Another controllable switch on the upper bridge arm of the third control phase is turned on.

10. The method of claim 1, wherein: The two controllable switches included in the upper bridge arm and the lower bridge arm in each bridge arm group are two parts of a bidirectional controllable switch, and the two parts respectively have control terminals to respectively control the conduction and disconnection of current in the first direction and the second direction.

11. A power conversion circuit, comprising a transformer, an input circuit coupled to the primary side of the transformer, and an output circuit coupled to the secondary side of the transformer, wherein the input circuit comprises a plurality of bridge arm groups, an upper bridge arm and a lower bridge arm in each bridge arm group comprise two controllable switches connected back to back, wherein: The power conversion circuit further includes a controller configured to execute the control method according to any one of claims 1-10.

12. A smart device, characterized in that: The smart device comprises the power conversion circuit as claimed in claim 11.

13. A computer-readable storage medium, characterized in that: The computer-readable storage medium comprises instructions, which, when executed, cause the control method according to any one of claims 1 to 10 to be executed.

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