Shutdown control method and shutdown control device of converter

Abstract

The invention relates to the technical field of power electronics, and provides a shutdown control method and a shutdown control device of a converter, and the converter comprises a primary side circuit, a resonance unit, a secondary side circuit and a transformer. The resonance unit is arranged between the primary side circuit and the secondary side circuit and comprises an inductor and a capacitor; the output end of the secondary circuit is connected with an alternating-current load or a power grid; the method comprises the following steps: in response to a received shutdown instruction of the converter, controlling the conduction state of a switching tube in a primary circuit and a secondary circuit, and enabling an inductor to follow current until the inductor current is smaller than a preset current threshold value; and when the voltage of the capacitor is smaller than a preset voltage threshold value, the switch tubes in the primary circuit and the secondary circuit are blocked, so that the converter is shut down. According to the embodiment of the invention, after the power-off instruction is received, the inductor of the resonance unit is subjected to follow current and the capacitor is discharged, so that the energy of the resonance unit is reset, and the safety and stability of the converter are improved.

Description

Technical Field

[0001] This disclosure relates to the field of power electronics technology, and in particular to a power-off control method and device for a converter. Background Technology

[0002] For single-phase frequency converters, the resonant unit is typically composed of capacitors and inductors. Upon receiving a shutdown command from the converter, related technologies usually employ fully enclosed drive-based shutdown logic for shutdown processing.

[0003] Under the aforementioned shutdown logic, upon receiving a shutdown command, the converter will directly shut down all switching transistors, causing it to stop working instantly. However, this shutdown logic can lead to problems such as electromagnetic interference caused by hard shutdown, overcurrent and overvoltage damage to switching transistors, and residual voltage in the resonant capacitor, affecting the safety and stability of the converter. Summary of the Invention

[0004] This disclosure provides a power-off control method and device for a converter, which can enable the inductor of the resonant unit to continue flowing and the capacitor to discharge after receiving the power-off command of the converter, so as to reset the energy of the resonant unit and improve the safety and stability of the converter.

[0005] In a first aspect, this disclosure provides a shutdown control method for a converter, the converter including a primary-side circuit, a resonant unit, a secondary-side circuit, and a transformer; the primary-side circuit is a full-bridge circuit composed of a first bridge arm and a second bridge arm connected in parallel, the first bridge arm and the second bridge arm including a first switch and a second switch connected in series; the two ends of the first bridge arm and the second bridge arm are connected to a DC source, the midpoint of the first bridge arm is connected to the first end of the primary winding of the transformer, and the midpoint of the second bridge arm is connected to the second end of the primary winding; the resonant unit is disposed between the primary-side circuit and the secondary-side circuit, the... The resonant unit includes an inductor and a capacitor; the output terminal of the secondary circuit is connected to an AC load or a power grid; the shutdown control method of the converter includes: in response to receiving a shutdown command of the converter, controlling the conduction state of the switching transistors in the primary circuit and the secondary circuit to allow the inductor to freewheel until the inductor current is less than a preset current threshold; controlling the conduction state of the switching transistors in the primary circuit and the secondary circuit to discharge the capacitor, and when the capacitor voltage is less than a preset voltage threshold, blocking the switching transistors in the primary circuit and the secondary circuit to shut down the converter.

[0006] In one optional implementation, controlling the conduction state of the switches in the primary circuit and the secondary circuit to enable the inductor to freewheel includes: blocking the switches in the primary circuit; obtaining the output voltage at the output terminal of the secondary circuit; and, based on the voltage polarity of the output voltage, turning on the switch in the secondary circuit corresponding to the voltage polarity, and blocking the remaining switches in the secondary circuit; wherein the conducting switches in the secondary circuit and the inductor form a freewheeling loop, enabling the inductor to freewheel.

[0007] In one optional implementation, the secondary circuit is a four-switch bridge arm cyclic circuit. The secondary circuit includes at least one bridge arm, each bridge arm including a first upper bridge arm and a first lower bridge arm. The first upper bridge arm and the first lower bridge arm are connected in series, and the first upper bridge arm and the first lower bridge arm include a bridge arm upper transistor and a bridge arm lower transistor connected in series. The directions of two adjacent switches in the bridge arm are opposite. The two ends of the bridge arm are the output terminals of the secondary circuit, used to connect to a single-phase AC load or the power grid.

[0008] In one optional implementation, based on the voltage polarity of the output voltage, the switching transistor in the secondary circuit corresponding to the voltage polarity is turned on, and the remaining switching transistors in the secondary circuit are turned off, including: when the voltage polarity is positive, turning on the lower bridge arm transistor in the secondary circuit and turning off the upper bridge arm transistor in the secondary circuit; when the voltage polarity is negative, turning on the upper bridge arm transistor in the secondary circuit and turning off the lower bridge arm transistor in the secondary circuit.

[0009] In one optional implementation, controlling the conduction state of the switches in the primary circuit and the secondary circuit to discharge the capacitor includes: turning on a target switch in the secondary circuit and turning off the remaining switches in the secondary circuit; wherein the target switch and the capacitor form a discharge circuit to discharge the capacitor; and when the capacitor voltage is less than a DC voltage threshold, turning on the first switch of the first bridge arm and the second bridge arm in the primary circuit, or turning on the second switch of the first bridge arm and the second bridge arm in the primary circuit; wherein the primary... The conducting switch in the primary circuit, together with the target switch and the capacitor, forms a discharge loop, allowing the capacitor to continue discharging until its voltage is less than a preset voltage threshold. Alternatively, the switching transistor in the secondary circuit remains conducting while the inductor current is less than a preset current threshold, until the capacitor voltage or the output voltage of the secondary circuit reaches a zero-crossing state, and the switching transistor in the primary circuit remains disconnected. The conducting switch in the secondary circuit, together with the capacitor, forms a discharge loop, allowing the capacitor to discharge.

[0010] In one alternative implementation, the secondary circuit includes a bridge arm, and the step of turning on the target switch in the secondary circuit and blocking the remaining switches in the secondary circuit includes: turning on the switch of the first lower bridge arm in the secondary circuit and blocking the switch of the first upper bridge arm in the secondary circuit, wherein the target switch includes the switch of the first lower bridge arm in the secondary circuit.

[0011] In one optional implementation, the secondary circuit includes two parallel bridge arms. Turning on the target switch in the secondary circuit and blocking the remaining switches in the secondary circuit includes: turning on the switch of the first lower bridge arm in the secondary circuit and blocking the switch of the first upper bridge arm in the secondary circuit, wherein the target switch includes the switch of the first lower bridge arm in the secondary circuit; or, turning on the switch of the first upper bridge arm in the secondary circuit and blocking the switch of the first lower bridge arm in the secondary circuit, wherein the target switch includes the switch of the first upper bridge arm in the secondary circuit.

[0012] In one optional implementation, the secondary circuit is a half-bridge frequency circuit composed of a third bridge arm and a fourth bridge arm connected in parallel. The third bridge arm and the fourth bridge arm include a second upper bridge arm and a second lower bridge arm connected in series. The second upper bridge arm includes an upper bridge arm transistor and a lower bridge arm transistor connected in series, and the second lower bridge arm includes a bridge arm capacitor. The connection point between the second upper bridge arm and the second lower bridge arm of the third bridge arm and the fourth bridge arm serves as the output terminal of the secondary circuit and is connected to a single-phase AC load or the power grid.

[0013] In one optional implementation, the step of turning on the switch corresponding to the voltage polarity in the secondary circuit and blocking the remaining switches in the secondary circuit according to the voltage polarity of the output voltage includes: when the voltage polarity is positive, turning on the upper switch of the third bridge arm and the lower switch of the fourth bridge arm, and blocking the lower switch of the third bridge arm and the upper switch of the fourth bridge arm; when the voltage polarity is negative, turning on the lower switch of the third bridge arm and the upper switch of the fourth bridge arm, and blocking the upper switch of the third bridge arm and the lower switch of the fourth bridge arm.

[0014] In one optional implementation, controlling the conduction state of the switching transistors in the primary circuit and the secondary circuit to discharge the capacitor includes: maintaining the conduction state of the switching transistors in the secondary circuit when the inductor current is less than a preset current threshold, until the capacitor voltage is at a zero-crossing state or the output voltage of the secondary circuit is at a zero-crossing state, while maintaining the switching transistors in the primary circuit in an off state; wherein the conducting switching transistors in the secondary circuit and the capacitor form a discharge circuit to discharge the capacitor.

[0015] In one optional implementation, after controlling the conduction state of the switching transistors in the primary circuit and the secondary circuit to enable the inductor to freewheel, the method further includes: after the inductor freewheels for a first preset time, determining that the inductor current is less than the preset current threshold.

[0016] In one optional implementation, after controlling the conduction state of the switching transistors in the primary circuit and the secondary circuit to discharge the capacitor, the method further includes: after the capacitor discharge continues for a second preset time, determining that the capacitor voltage is less than the preset voltage threshold.

[0017] In one optional implementation, before controlling the conduction state of the switches in the primary and secondary circuits to allow the inductor to freewheel, the method further includes: determining whether the real-time inductor current is less than a preset current threshold when a power-off command is received from the converter; if the real-time inductor current is less than the preset current threshold, blocking the switches in the primary circuit and executing the step of controlling the conduction state of the switches in the primary and secondary circuits to discharge the capacitor; if the real-time inductor current is not less than the preset current threshold, executing the step of controlling the conduction state of the switches in the primary and secondary circuits to allow the inductor to freewheel.

[0018] In one optional implementation, before controlling the conduction state of the switching transistors in the primary and secondary circuits to discharge the capacitor, the method further includes: determining whether the real-time capacitor voltage is less than a preset voltage threshold when the inductor current is less than a preset current threshold; if the real-time capacitor voltage is less than the preset voltage threshold, blocking the switching transistors in the secondary circuit to power off the converter; and if the real-time capacitor voltage is not less than the preset voltage threshold, performing the step of controlling the conduction state of the switching transistors in the primary and secondary circuits to discharge the capacitor.

[0019] Secondly, this disclosure provides a power-off control device for a converter, the converter including a primary circuit, a resonant unit, a secondary circuit, and a transformer; the primary circuit is a full-bridge circuit composed of a first bridge arm and a second bridge arm connected in parallel, the first bridge arm and the second bridge arm including a first switch and a second switch connected in series; the two ends of the first bridge arm and the second bridge arm are connected to a DC source, the midpoint of the first bridge arm is connected to the first end of the primary winding of the transformer, and the midpoint of the second bridge arm is connected to the second end of the primary winding; the resonant unit is disposed between the primary circuit and the secondary circuit, the resonant unit including an inductor. The converter includes a capacitor; the output of the secondary circuit is connected to an AC load or the power grid; the power-off control device of the converter includes: a freewheeling control module, used to control the conduction state of the switching transistors in the primary circuit and the secondary circuit in response to receiving the power-off command of the converter, so that the inductor freewheels until the inductor current is less than a preset current threshold; and a discharge control module, used to control the conduction state of the switching transistors in the primary circuit and the secondary circuit, so that the capacitor discharges, and when the capacitor voltage is less than a preset voltage threshold, to block the switching transistors in the primary circuit and the secondary circuit, so that the converter is powered off.

[0020] The power-off control method for a converter provided in this embodiment includes a primary circuit, a resonant unit, a secondary circuit, and a transformer. The primary circuit is a full-bridge circuit composed of a first bridge arm and a second bridge arm connected in parallel. The first and second bridge arms include a first switch and a second switch connected in series. The two ends of the first and second bridge arms are connected to a DC source. The midpoint of the first bridge arm is connected to the first end of the primary winding of the transformer, and the midpoint of the second bridge arm is connected to the second end of the primary winding. The resonant unit is disposed between the primary and secondary circuits and includes an inductor and a capacitor. The output terminal of the secondary circuit is connected to an AC load or the power grid. In this embodiment, in response to receiving a power-off command from the converter, firstly, the conduction state of the switches in the primary and secondary circuits is controlled to allow the inductor to freewheel until the inductor current is less than a preset current threshold. Then, the conduction state of the switches in the primary and secondary circuits is controlled to discharge the capacitor. When the capacitor voltage is less than a preset voltage threshold, the switches in the primary and secondary circuits are blocked, thus powering off the converter.

[0021] Therefore, this embodiment controls the conduction state of the switching transistors in the converter, releasing the inductor's stored energy in the resonant unit, thereby reducing the inductor current to a preset current threshold. Then, it releases the capacitor's stored energy in the resonant unit, causing the capacitor voltage to fall below a preset voltage threshold. Only after the inductor freewheeling and capacitor discharge are complete, i.e., after resetting the resonant unit's energy, is the converter's switching transistors blocked, shutting down the converter. This embodiment effectively avoids hard-switching electromagnetic interference during the converter shutdown process. Furthermore, it avoids damage to the switching transistors in the converter due to overcurrent and overvoltage, as well as the residual voltage problem of the resonant capacitor after the converter shutdown, improving the converter's safety and stability.

[0022] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of this disclosure, nor is it intended to limit the scope of this disclosure. Other features of this disclosure will become readily apparent from the following description. Attached Figure Description

[0023] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the embodiments of the present disclosure to explain the disclosure and do not constitute a limitation thereof. The above and other features and advantages will become more apparent to those skilled in the art from the detailed description of exemplary embodiments with reference to the accompanying drawings, in which:

[0024] Figure 1 This is a schematic diagram of the converter structure in an embodiment of this disclosure;

[0025] Figure 2 A flowchart of a power-off control method for a converter provided in this embodiment of the disclosure;

[0026] Figure 3 This is a schematic diagram of the first structure of the converter;

[0027] Figure 4 This is a schematic diagram of the current path during the freewheeling phase of an inductor.

[0028] Figure 5 This is a schematic diagram of the second structure of the converter;

[0029] Figure 6 This is a schematic diagram of the current path during the capacitor discharge process.

[0030] Figure 7 This is the first timing diagram for shutdown control;

[0031] Figure 8 This is the second timing diagram for shutdown control;

[0032] Figure 9 This is the third timing diagram for shutdown control;

[0033] Figure 10 This is the fourth timing diagram for shutdown control;

[0034] Figure 11 This is a schematic diagram of the third structure of the converter;

[0035] Figure 12 This is the fifth timing diagram for shutdown control;

[0036] Figure 13 A block diagram of a power-off control device for a converter provided in an embodiment of this disclosure;

[0037] Figure 14 This is a block diagram of an electronic device provided in an embodiment of the present disclosure. Detailed Implementation

[0038] To enable those skilled in the art to better understand the technical solutions of this disclosure, exemplary embodiments of this disclosure are described below with reference to the accompanying drawings, including various details of the embodiments of this disclosure to aid understanding. These should be considered merely exemplary. Therefore, those skilled in the art should recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of this disclosure. Similarly, for clarity and conciseness, descriptions of well-known functions and structures are omitted in the following description.

[0039] Where there is no conflict, the various embodiments of this disclosure and the features thereof in the embodiments may be combined with each other.

[0040] As used herein, the term “and / or” includes any and all combinations of one or more related enumerated entries.

[0041] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. As used herein, the singular forms “a” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that when the terms “comprising” and / or “made of” are used in this specification, the presence of the stated feature, integral, step, operation, element, and / or component is specified, but the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or groups thereof is not excluded. Words such as “connected” or “linked” are not limited to physical or mechanical connections but can include electrical connections, whether direct or indirect.

[0042] Unless otherwise specified, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art. It will also be understood that terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant art and this disclosure, and will not be interpreted as having an idealized or overly formal meaning, unless expressly so defined herein.

[0043] For single-phase frequency converters, the resonant unit is typically composed of capacitors and inductors. Upon receiving a shutdown command from the converter, related technologies usually employ fully enclosed drive-based shutdown logic for shutdown processing.

[0044] The fully enclosed drive shutdown logic refers to directly shutting down all the switching transistors of the converter during shutdown, causing the converter to stop working instantly. However, under this shutdown logic, the inductor current in the resonant unit will be rapidly discharged through the parasitic capacitance of the switching transistors, diodes, and other nonlinear components, resulting in a hard shutdown and generating significant electromagnetic interference. Furthermore, this direct shutdown logic can cause the switching transistors in the converter to experience overvoltage stress and overcurrent surges, potentially damaging them due to overcurrent and overvoltage. Additionally, under the fully enclosed drive shutdown logic, the capacitors in the resonant unit will retain a relatively high voltage. If the converter is restarted, this residual voltage, combined with the input voltage, may cause the voltage stress on the switching transistors to exceed the limit at the moment of startup.

[0045] Therefore, it can be seen that in related technologies, the shutdown method of the converter can lead to problems such as electromagnetic interference caused by hard shutdown, overcurrent and overvoltage damage to the switching transistors, and residual voltage in the resonant capacitor, thus affecting the safety and stability of the converter.

[0046] The power-off control method for a converter provided in this embodiment includes a primary circuit, a resonant unit, a secondary circuit, and a transformer. The primary circuit is a full-bridge circuit composed of a first bridge arm and a second bridge arm connected in parallel. The first and second bridge arms include a first switch and a second switch connected in series. The two ends of the first and second bridge arms are connected to a DC source. The midpoint of the first bridge arm is connected to the first end of the primary winding of the transformer, and the midpoint of the second bridge arm is connected to the second end of the primary winding. The resonant unit is disposed between the primary and secondary circuits and includes an inductor and a capacitor. The output terminal of the secondary circuit is connected to an AC load or the power grid. In this embodiment, in response to receiving a power-off command from the converter, firstly, the conduction state of the switches in the primary and secondary circuits is controlled to allow the inductor to freewheel until the inductor current is less than a preset current threshold. Then, the conduction state of the switches in the primary and secondary circuits is controlled to discharge the capacitor. When the capacitor voltage is less than a preset voltage threshold, the switches in the primary and secondary circuits are blocked, thus powering off the converter.

[0047] Therefore, this embodiment controls the conduction state of the switching transistors in the converter, releasing the inductor's stored energy in the resonant unit, thereby reducing the inductor current to a preset current threshold. Then, it releases the capacitor's stored energy in the resonant unit, causing the capacitor voltage to fall below a preset voltage threshold. Only after the inductor freewheeling and capacitor discharge are complete, i.e., after resetting the resonant unit's energy, is the converter's switching transistors blocked, shutting down the converter. This embodiment effectively avoids hard-switching electromagnetic interference during the converter shutdown process. Furthermore, it avoids damage to the switching transistors in the converter due to overcurrent and overvoltage, as well as the residual voltage problem of the resonant capacitor after the converter shutdown, improving the converter's safety and stability.

[0048] Figure 1 This is a schematic diagram of the converter structure in an embodiment of this disclosure, with reference to... Figure 1 The converter includes: a primary circuit, a resonant unit, a secondary circuit, and a transformer T.

[0049] The primary-side circuit is a full-bridge circuit consisting of a first bridge arm and a second bridge arm connected in parallel. Both the first and second bridge arms include a first switch and a second switch connected in series.

[0050] Specifically, in the primary circuit, the first bridge arm includes a first switch Q1H and a second switch Q1L, and the second bridge arm includes a first switch Q2H and a second switch Q2L. The midpoint of the first bridge arm (i.e., the connection point between the first switch Q1H and the second switch Q1L) is connected to the first end of the primary winding of transformer T. The midpoint of the second bridge arm (i.e., the connection point between the first switch Q2H and the second switch Q2L) is connected to the second end of the primary winding of transformer T. The two ends of the first and second bridge arms are connected to a DC source V. dc .

[0051] In this configuration, the directions of two adjacent switching transistors in the first and second bridge arms are the same. (Refer to...) Figure 1 The source of the first switch Q1H in the first bridge arm is connected to the drain of the second switch Q1L in the first bridge arm, and the source of the first switch Q2H in the second bridge arm is connected to the drain of the second switch Q2L in the second bridge arm. The drains of each first switch Q1H and Q2H in the primary circuit, and the sources of each second switch Q1L and Q2L in the primary circuit, are connected to the DC source at both ends of the bridge arm.

[0052] The resonant unit is disposed between the primary circuit and the secondary circuit. It should be noted that this disclosure does not limit the specific connection method of the resonant unit. For example, the resonant unit can be disposed between the primary circuit and the primary winding, or between the secondary circuit and the secondary winding of the transformer. This disclosure does not impose any limitations on this.

[0053] Furthermore, the resonant unit includes an inductor and a capacitor (not shown in the figure). The inductor and capacitor in the resonant unit can be connected in series at one end of the winding, or they can be separately located at both ends of the winding, etc. This disclosure does not limit the specific arrangements.

[0054] Furthermore, the inductor in the resonant unit can be an independent inductor element, or it can be integrated with one of the windings of the transformer.

[0055] In this embodiment, the secondary circuit of the converter can be a half-bridge circuit or a full-bridge circuit; this disclosure does not limit this. The output terminal of the secondary circuit of the converter is connected to a single-phase AC load or the power grid, thereby outputting voltage to the single-phase AC load or the power grid. Wherein, V g This is the output voltage.

[0056] A filter unit may be provided between the secondary circuit and the single-phase AC load or power grid, so that the output of the secondary circuit can be connected to the single-phase AC load or power grid through the filter unit. The filter unit may include filter elements such as filter capacitors and filter inductors. This disclosure does not impose specific limitations on the structure of the filter unit.

[0057] It should be noted that, unlike the connection method of the switching transistors in the primary circuit, in this embodiment, the switching transistors in the secondary circuit are bidirectional switching transistors. That is, in any arm of the secondary circuit, the directions of two adjacent switching transistors are opposite. For example, if any arm of the secondary circuit includes four switching transistors connected in series, then the two adjacent switching transistors in that arm are connected top-to-bottom. For example, for the series-connected switching transistors Qa, Qb, Qc, and Qd, the sources of Qa and Qb are connected to each other, the sources of Qc and Qd are connected to each other, and the drains of Qb and Qc are connected to each other.

[0058] Figure 2 A flowchart illustrating a power-off control method for a converter provided in an embodiment of this disclosure. (Refer to...) Figure 2 The method includes:

[0059] Step S210: In response to receiving the power-off command of the converter, control the conduction state of the switching transistors in the primary and secondary circuits to allow the inductor to freewheel until the inductor current is less than the preset current threshold.

[0060] In this step, upon receiving the power-off command of the converter, some switches in the converter are turned on and others are turned off, thereby forming a freewheeling circuit with the inductor in the resonant unit, allowing the inductor to continue flowing. The number of switches turned on in the converter can be adaptively determined based on the topology of the secondary circuit and the voltage polarity of the output voltage of the secondary circuit; this embodiment does not impose any limitations on this.

[0061] The preset current threshold is used to evaluate the magnitude of the inductor current in the resonant unit. Specifically, the preset current threshold is the critical current value used to determine the degree of inductor current decay.

[0062] The inductor current can be detected in real time, and if the detected current at any given moment is less than a preset current threshold, it can be determined that the inductor current is less than the preset current threshold. Alternatively, a preset duration for the inductor freewheeling current can be set, and after the inductor freewheeling current has continued for the preset duration, it can be determined that the inductor current is less than the preset current threshold. This embodiment of the present disclosure does not impose any limitations on this.

[0063] Accordingly, in one optional implementation, after controlling the conduction state of the switching transistors in the primary and secondary circuits to enable inductor freewheeling, the method further includes: determining that the inductor current is less than a preset current threshold when the inductor freewheeling continues for a first preset time.

[0064] The first preset time can be adaptively set according to actual application needs, and this embodiment does not limit it. After the inductor freewheeling process continues for the first preset time, it can be determined that the inductor current has dropped below a preset current threshold.

[0065] For example, the initial freewheeling time of the inductor current is t1. After a first preset time, it reaches time t2. Thus, at time t2, it can be determined that the inductor current has dropped to less than the preset current threshold.

[0066] When the inductor current is less than the preset current threshold, it can be determined that the inductor current has decayed to approximately zero. Correspondingly, the energy stored in the inductor in the resonant unit has been basically released. At this point, subsequent control actions can be performed, such as controlling the discharge of the capacitor in the resonant unit.

[0067] If the inductor current is not less than the preset current threshold, it can be determined that there is still unreleased stored energy in the inductor. Therefore, it is necessary to continue the inductor freewheeling control so that the inductor can continue to flow through the freewheeling circuit until the inductor current drops below the preset current threshold.

[0068] Step S220: Control the conduction state of the switching transistors in the primary and secondary circuits to discharge the capacitors. When the capacitor voltage is less than a preset voltage threshold, block the switching transistors in the primary and secondary circuits to shut down the converter.

[0069] In this step, by controlling some switches in the converter to be turned on and others to be turned off, the turned-on switches and the capacitor in the resonant unit form a discharge circuit, causing the capacitor to discharge. The turned-on switches in the converter can be adaptively determined according to the topology of the secondary circuit, and this embodiment does not limit this.

[0070] The preset voltage threshold is used to evaluate the magnitude of the capacitor voltage in the resonant unit. Specifically, the preset voltage threshold is a critical voltage value for judging the degree of capacitor voltage decay.

[0071] It should be noted that there are various ways to determine whether the capacitor voltage is less than the preset voltage threshold, and the embodiments disclosed herein do not limit this.

[0072] In one embodiment, the voltage across the capacitor can be detected in real time, thereby determining that the capacitor voltage is less than the preset voltage threshold if the detected voltage is less than the preset voltage threshold.

[0073] In one embodiment, the AC voltage output by the secondary circuit can be sampled. Since the capacitor voltage changes with the AC voltage, when the output voltage of the secondary circuit is less than a preset voltage threshold, it can be determined that the capacitor voltage is less than the preset voltage threshold.

[0074] In one embodiment, a preset duration for capacitor discharge can also be set, and after the capacitor discharge continues for the preset duration, it is determined that the capacitor voltage is less than a preset voltage threshold.

[0075] Accordingly, in one optional implementation, after controlling the conduction state of the switching transistors in the primary and secondary circuits to discharge the capacitor, the method further includes: determining that the capacitor voltage is less than a preset voltage threshold when the capacitor discharge continues for a second preset time.

[0076] The second preset time can be adaptively set according to actual application needs, and this embodiment does not impose any limitations on it. After the capacitor discharge process continues for the second preset time, it can be determined that the capacitor voltage has dropped below the preset current threshold.

[0077] For example, the initial discharge time of the capacitor voltage is t2. After a second preset time, it reaches time t3. Therefore, at time t3, it can be determined that the capacitor voltage has dropped to less than the preset voltage threshold.

[0078] When the capacitor voltage is less than a preset voltage threshold, it can be determined that the capacitor voltage has decayed to approximately zero. Correspondingly, the energy stored in the capacitor in the resonant unit has been largely released, and the energy reset of the resonant unit is complete. Therefore, all conducting switches in the primary and secondary circuits of the converter can be blocked, shutting down the converter.

[0079] If the capacitor voltage is not less than the preset voltage threshold, it can be determined that the capacitor still has unreleased stored energy. Therefore, it is necessary to continue capacitor discharge control to discharge the capacitor through the discharge circuit until the capacitor voltage drops below the preset voltage threshold.

[0080] In this embodiment of the present disclosure, in response to receiving a power-off command from the converter, firstly, the conduction state of the switching transistors in the primary and secondary circuits is controlled to allow the inductor to freewheel until the inductor current is less than a preset current threshold; then, the conduction state of the switching transistors in the primary and secondary circuits is controlled to allow the capacitor to discharge, and when the capacitor voltage is less than a preset voltage threshold, the switching transistors in the primary and secondary circuits are blocked to power off the converter.

[0081] Therefore, this embodiment controls the conduction state of the switching transistors in the converter, releasing the inductor's stored energy in the resonant unit, thereby reducing the inductor current to a preset current threshold. Then, it releases the capacitor's stored energy in the resonant unit, causing the capacitor voltage to fall below a preset voltage threshold. Only after the inductor freewheeling and capacitor discharge are complete, i.e., after resetting the resonant unit's energy, is the converter's switching transistors blocked, shutting down the converter. This embodiment effectively avoids hard-switching electromagnetic interference during the converter shutdown process. Furthermore, it avoids damage to the switching transistors in the converter due to overcurrent and overvoltage, as well as the residual voltage problem of the resonant capacitor after the converter shutdown, improving the converter's safety and stability.

[0082] In one alternative implementation, in order to achieve freewheeling control of the inductor in the resonant unit, the switching transistors of the primary circuit can be blocked, and the switching transistors in the secondary circuit corresponding to the voltage polarity of the output voltage can be turned on according to the output voltage of the secondary circuit, while the remaining switching transistors of the secondary circuit are blocked.

[0083] Correspondingly, controlling the conduction state of the switching transistors in the primary and secondary circuits to enable the inductor to freewheel includes: blocking the switching transistors in the primary circuit; obtaining the output voltage at the output terminal of the secondary circuit; and, based on the voltage polarity of the output voltage, turning on the switching transistor in the secondary circuit corresponding to the voltage polarity, while blocking the remaining switching transistors in the secondary circuit. The conducting switching transistors in the secondary circuit and the inductor form a freewheeling loop, enabling the inductor to freewheel.

[0084] The output voltage polarity can be positive or negative. In the output voltage V... gIf the value is greater than 0, the voltage polarity can be determined to be positive. At the output voltage V... g When the value is less than 0, the voltage polarity can be determined to be negative. When the output voltage is equal to 0, the voltage polarity can be determined to be either positive or negative.

[0085] In order to enable the inductor freewheeling in the resonant unit, it is necessary to block all the switches in the primary circuit and turn on the switch in the secondary circuit corresponding to the voltage polarity according to the voltage polarity of the output voltage of the secondary circuit, while blocking the other switches in the secondary circuit.

[0086] It should be noted that, since there are multiple topologies for the secondary circuit in this embodiment, under different secondary circuit topologies, a switch corresponding to the voltage polarity of the output voltage can be adaptively selected in the secondary circuit for the topology and turned on, while the other switches in the secondary circuit are blocked, so that the switched transistors in the secondary circuit and the inductor form a freewheeling loop, allowing the inductor to continue flowing.

[0087] It should also be noted that since the voltage polarity of the output voltage of the secondary circuit may change over time, the output voltage of the secondary circuit can be obtained in real time during the inductor freewheeling stage. Based on the voltage polarity of the real-time obtained output voltage, the switching transistors in the secondary circuit corresponding to that voltage polarity can be turned on adaptively, while the other switching transistors in the secondary circuit can be turned off.

[0088] For example, at the first moment, the voltage polarity is positive, thus turning on the switch corresponding to the positive polarity in the secondary circuit and turning off the other switches in the secondary circuit. At the second moment, the voltage polarity changes to negative, thus turning on the switch corresponding to the negative polarity in the secondary circuit and turning off the other switches in the secondary circuit.

[0089] In one optional implementation, the secondary circuit is a four-switch bridge arm cyclic circuit. The secondary circuit includes at least one bridge arm, and each bridge arm includes a first upper bridge arm and a first lower bridge arm. The first upper bridge arm and the first lower bridge arm are connected in series, and the first upper bridge arm and the first lower bridge arm include a bridge arm upper transistor and a bridge arm lower transistor connected in series. The directions of two adjacent switches in the bridge arm are opposite. The two ends of the bridge arm are the output terminals of the secondary circuit, which are used to connect to a single-phase AC load or the power grid.

[0090] The secondary-side circuit of the converter may include one bridge arm or two bridge arms, and this embodiment does not limit this. For each bridge arm of the secondary-side circuit, its first upper bridge arm and first lower bridge arm both include a bridge arm upper transistor and a bridge arm lower transistor connected in series. Thus, each bridge arm of the secondary-side circuit is composed of four series-connected switching transistors.

[0091] Specifically, the first upper bridge arm and the first lower bridge arm, comprising a bridge arm upper pipe and a bridge arm lower pipe connected in series, mean that the first upper bridge arm has a bridge arm upper pipe and a bridge arm lower pipe, and the bridge arm upper pipe and the bridge arm lower pipe are connected in series. The first lower bridge arm has a bridge arm upper pipe and a bridge arm lower pipe, and the bridge arm upper pipe and the bridge arm lower pipe are connected in series.

[0092] In the case of a four-switch bridge arm cyclic circuit in the secondary circuit, in order to achieve inductor freewheeling, the switches in the primary circuit must be blocked. When the output voltage of the secondary circuit is positive, the lower bridge arm transistor in the secondary circuit is turned on and the upper bridge arm transistor in the secondary circuit is blocked. When the output voltage of the secondary circuit is negative, the upper bridge arm transistor in the secondary circuit is turned on and the lower bridge arm transistor in the secondary circuit is blocked.

[0093] Among them, the four-switch bridge arm cyclic circuit refers to a secondary circuit with four switches on one of the bridge arms. These four switches form two bidirectional switches, and each bidirectional switch is composed of two switches.

[0094] Specifically, on a bridge arm, the directions of two adjacent switching transistors are opposite. For example, for the first upper bridge arm and the first lower bridge arm in any bridge arm, on the first upper bridge arm, the directions of the upper and lower switching transistors are opposite, and on the first lower bridge arm, the directions of the upper and lower switching transistors are opposite. Furthermore, since the first upper bridge arm and the first lower bridge arm are connected in series, the direction of the lower switching transistor of the first upper bridge arm is opposite to that of the upper switching transistor of the first lower bridge arm.

[0095] The description above, where two adjacent switching transistors are in opposite directions, means that the two adjacent switching transistors are connected top to top. For example, in the first upper bridge arm and the first lower bridge arm, the sources of the upper and lower transistors of the bridge arm are connected to each other. The drains of the lower transistor of the first upper bridge arm and the upper transistor of the first lower bridge arm are connected to each other.

[0096] Correspondingly, in the case of a four-switch bridge arm cyclic circuit in the secondary circuit, in one optional implementation, the switch corresponding to the voltage polarity in the secondary circuit is turned on and the other switches in the secondary circuit are turned off according to the voltage polarity of the output voltage. This includes: when the voltage polarity is positive, turning on the lower bridge arm switch in the secondary circuit and turning off the upper bridge arm switch in the secondary circuit; when the voltage polarity is negative, turning on the upper bridge arm switch in the secondary circuit and turning off the lower bridge arm switch in the secondary circuit.

[0097] To facilitate understanding of the inductor freewheeling current handling process described above in a four-switch bridge arm frequency circuit on the secondary side, Figure 3 A schematic diagram of the first structure of the converter is shown.

[0098] Reference Figure 3The secondary circuit of the converter is a four-switch bridge arm cyclic circuit. Furthermore, the secondary circuit of the converter includes only one bridge arm, which includes a first upper bridge arm and a first lower bridge arm. The first upper bridge arm is composed of the upper bridge arm transistor Q3 and the lower bridge arm transistor Q4 connected in series, and the first lower bridge arm is composed of the upper bridge arm transistor Q5 and the lower bridge arm transistor Q6 connected in series.

[0099] In this bridge arm, the directions of adjacent switching transistors are opposite. The sources of the upper transistor Q3 and the lower transistor Q4 of the first upper bridge arm are connected together; the drains of the lower transistor Q4 and the upper transistor Q5 of the first lower bridge arm are connected together; and the sources of the upper transistor Q5 and the lower transistor Q6 of the first lower bridge arm are connected together. The drains of the upper transistor Q3 and the lower transistor Q6 of the first upper bridge arm serve as the output terminals of the secondary circuit.

[0100] A filter capacitor C can also be set at the output of the secondary circuit. f and filter inductor L f This causes its output voltage to pass through the filter capacitor C. f and filter inductor L f Output to a single-phase AC load or the power grid. Cin is the first capacitor.

[0101] Furthermore, Figure 3 In the diagram, Lr represents the inductance of the resonant unit, and Cr represents the capacitance of the resonant unit. Figure 3 The diagram only shows the connection state of the inductor and capacitor in the resonant unit, connected in series between the secondary winding and the midpoint of the bridge arm of the secondary circuit (i.e., the connection point between the upper and lower bridge arms). The connection state of the inductor and capacitor in the resonant unit can be adaptively set according to actual application needs, and this disclosure does not limit this.

[0102] Correspondingly, targeting Figure 3 With this topology, when performing inductor freewheeling processing, all switches Q1H, Q1L, Q2H, and Q2L in the primary circuit can be directly blocked, and the switch corresponding to the voltage polarity of the output voltage in the secondary circuit can be turned on according to the voltage polarity of the output voltage in the secondary circuit, while the remaining switches in the secondary circuit are blocked.

[0103] The output voltage of the secondary circuit can be directly sampled from the output voltage V. g Alternatively, the sample filter capacitor C can be used. f The voltage at both ends, etc., are not limited in the embodiments disclosed herein.

[0104] For example, when the output voltage at the output terminal of the secondary circuit is positive, all lower bridge arm transistors Q4 and Q6 in the secondary circuit are turned on, and all upper bridge arm transistors Q3 and Q5 in the secondary circuit are turned off. When the output voltage at the output terminal of the secondary circuit is negative, all upper bridge arm transistors Q3 and Q5 in the secondary circuit are turned on, and all lower bridge arm transistors Q4 and Q6 in the secondary circuit are turned off.

[0105] It should be noted that the aforementioned switching actions of the transistors can be performed simultaneously or in a time-sharing manner, and this embodiment does not impose any limitations on this. For example, all upper transistors Q3 and Q5 in the secondary circuit can be turned off simultaneously, while all lower transistors Q4 and Q6 in the secondary circuit can be turned on simultaneously. Another example is that a dead time can be set between the turn-off and turn-on actions. Yet another example is that the aforementioned transistors can be turned on or off in a time-sharing manner, i.e., Q4 and Q6 are not turned off simultaneously, and Q3 and Q5 are not turned on simultaneously.

[0106] Correspondingly, Figure 4 A schematic diagram of the current path during the freewheeling phase of the inductor is shown. (Refer to...) Figure 4 :

[0107] in, Figure 4 In (a), the output voltage is positive and the inductor current i is... rs A schematic diagram showing the inductor freewheeling current when the current is ≥0. Figure 3 In this topology, all lower transistors Q4 and Q6 in the secondary circuit are turned on, while all upper transistors Q3 and Q5 in the primary circuit are turned off. The switches in the primary circuit are also turned off. The diodes of the turned-on switch Q4 in the secondary circuit, the turned-off switch Q3, and the diodes of the turned-off switches Q1L and Q2H in the primary circuit form a freewheeling circuit, allowing the inductor current of the resonant unit to continue flowing.

[0108] in, Figure 4 In (b), the output voltage is positive and the inductor current i rs A schematic diagram of the inductor freewheeling path when the current is ≤0. Figure 3 In this topology, all lower transistors Q4 and Q6 in the secondary circuit are turned on, while all upper transistors Q3 and Q5 are turned off, and the switches in the primary circuit are also turned off. The diodes of the turned-on switch Q6 in the secondary circuit, the turned-off switch Q5, and the diodes of the turned-off switches Q1H and Q2L in the primary circuit form a freewheeling circuit, allowing the inductor current of the resonant unit to continue flowing.

[0109] in, Figure 4 In the middle (c), the output voltage is negative and the inductor current i rsA schematic diagram of inductor freewheeling when the current is ≥0. In this case, all upper transistors Q3 and Q5 in the secondary circuit are turned on, while all lower transistors Q4 and Q6 are turned off. The switches in the primary circuit are also turned off. The diodes of the turned-on switch Q5 in the secondary circuit, the turned-off switch Q6, and the turned-off switches Q1L and Q2H in the primary circuit form a freewheeling loop, allowing the inductor current of the resonant unit to freewheel.

[0110] in, Figure 4 In the middle (d), the output voltage is negative and the inductor current i rs A schematic diagram showing the inductor freewheeling current when the current is ≤0. Figure 3 In this topology, all upper transistors Q3 and Q5 in the secondary circuit are turned on, while all lower transistors Q4 and Q6 are turned off. The switches in the primary circuit are also turned off. The diodes of the turned-on switch Q3 in the secondary circuit, the turned-off switch Q4, and the diodes of the turned-off switches Q1H and Q2L in the primary circuit form a freewheeling circuit, allowing the inductor current of the resonant unit to continue flowing.

[0111] Figure 5 A schematic diagram of a second type of converter structure is shown.

[0112] Reference Figure 5 The secondary circuit of this converter is a four-switch bridge-arm frequency circuit, and it includes two parallel bridge arms. Each bridge arm consists of a first upper bridge arm and a first lower bridge arm. Specifically, for the first bridge arm, the first upper bridge arm is composed of upper transistor Q31 and lower transistor Q41 connected in series. The first lower bridge arm is composed of upper transistor Q51 and lower transistor Q61 connected in series. For the second bridge arm, the first upper bridge arm is composed of upper transistor Q32 and lower transistor Q42 connected in series. The first lower bridge arm is composed of upper transistor Q52 and lower transistor Q62 connected in series.

[0113] In this secondary circuit, the two adjacent switches in each bridge arm are in opposite directions. (Refer to...) Figure 5 For the first bridge arm of the secondary circuit, the sources of the upper bridge arm transistor Q31 and the lower bridge arm transistor Q41 are connected together, the drain of the lower bridge arm transistor Q41 and the upper bridge arm transistor Q51 are connected together, and the sources of the upper bridge arm transistor Q51 and the lower bridge arm transistor Q61 are connected together. The drains of the upper bridge arm transistor Q31 and the lower bridge arm transistor Q61 serve as the output terminals of the secondary circuit.

[0114] For the second bridge arm of the secondary circuit, the sources of the upper bridge arm transistor Q32 and the lower bridge arm transistor Q42 are connected together, the drains of the lower bridge arm transistor Q42 and the upper bridge arm transistor Q52 are connected together, and the sources of the upper bridge arm transistor Q52 and the lower bridge arm transistor Q62 are connected together. The drains of the upper bridge arm transistor Q32 and the lower bridge arm transistor Q62 serve as the output terminals of the secondary circuit.

[0115] A filter capacitor C can also be set at the output of the secondary circuit. f and filter inductor L f This causes its output voltage to pass through the filter capacitor C. f and filter inductor L f Output to single-phase AC load or power grid.

[0116] Furthermore, Figure 5 In the diagram, Lr represents the inductance of the resonant unit, and Cr represents the capacitance of the resonant unit. Figure 5 The diagram only shows the connection state of the inductor and capacitor in the resonant unit, connected in series between the secondary winding and the midpoint of the bridge arm of the secondary circuit (i.e., the connection point between the upper and lower bridge arms). The connection state of the inductor and capacitor in the resonant unit can be adaptively set according to actual application needs, and this disclosure does not limit this.

[0117] Correspondingly, targeting Figure 5 With this topology, when performing inductor freewheeling processing, all switches Q1H, Q1L, Q2H, and Q2L in the primary circuit can be directly blocked, and the switch corresponding to the voltage polarity of the output voltage in the secondary circuit can be turned on according to the voltage polarity of the output voltage in the secondary circuit, while the remaining switches in the secondary circuit are blocked.

[0118] For example, when the output voltage of the secondary circuit is positive, all the lower transistors Q41, Q42, Q61, and Q62 in the secondary circuit are turned on, and all the upper transistors Q31, Q32, Q51, and Q52 in the secondary circuit are turned off. When the output voltage of the secondary circuit is negative, all the upper transistors Q31, Q32, Q51, and Q52 in the secondary circuit are turned on, and all the lower transistors Q41, Q42, Q61, and Q62 in the secondary circuit are turned off.

[0119] In this embodiment of the disclosure, for a converter with a secondary circuit consisting of a four-switch bridge arm cyclic circuit, the inductor current of the resonant unit is freewheeled through the diodes of the primary circuit switching transistors, the diodes of the secondary circuit blocking switching transistors, and the conducting switching transistors, thereby dissipating the inductor energy stored in the resonant unit in the DC side, AC side voltage sources, and loop resistance, causing the inductor current to rapidly decay to less than a preset current threshold.

[0120] Furthermore, regarding the above Figure 3 , Figure 5In a converter with this structure, to achieve capacitor discharge, the switching transistors in the secondary circuit can be kept in the ON state while the inductor current is below a preset current threshold, until the capacitor voltage or the output voltage of the secondary circuit reaches a zero-crossing state. At this point, the capacitor voltage of the resonant unit is below the preset voltage threshold. Alternatively, the target switching transistor in the secondary circuit can be turned on first, while the remaining switching transistors in the secondary circuit are turned off, allowing the capacitor in the resonant unit to discharge to below the DC voltage threshold. Then, some switching transistors in the primary circuit can be turned on to continue discharging the capacitor until its voltage is below the preset voltage threshold.

[0121] Correspondingly, for a converter with a four-switch bridge arm cyclotron circuit in its secondary circuit, in one optional implementation, controlling the conduction state of the switches in the primary and secondary circuits to discharge the capacitor includes: turning on the target switch in the secondary circuit and turning off the remaining switches in the secondary circuit; wherein the target switch and the capacitor form a discharge circuit to discharge the capacitor; when the capacitor voltage is less than a DC voltage threshold, turning on the first switch of the first and second bridge arms in the primary circuit, or turning on the second switch of the first and second bridge arms in the primary circuit; wherein the conducting switches in the primary circuit, together with the target switch and the capacitor, form a discharge circuit to continue discharging the capacitor until the capacitor voltage is less than a preset voltage threshold; or, keeping the inductor current less than a preset current threshold, keeping the switches in the secondary circuit in the conduction state until the capacitor voltage reaches a zero-crossing state or the output voltage of the secondary circuit reaches a zero-crossing state, and keeping the switches in the primary circuit in the off state; wherein the conducting switches in the secondary circuit and the capacitor form a discharge circuit to discharge the capacitor.

[0122] In other words, for converters with a four-switch bridge-arm cyclotron circuit on the secondary side, there are two ways to implement capacitor discharge control. One method is to keep the switches in the primary side circuit off and directly maintain the switching state of the switches in the secondary side circuit when the inductor current is less than a preset current threshold. In this case, it is not necessary to turn on the switches in the secondary side circuit. The capacitor voltage in the resonant unit will change according to the output voltage of the secondary side circuit. Therefore, when the output voltage of the secondary side circuit is at a zero-crossing state, the capacitor voltage will also be less than the preset voltage threshold. Accordingly, the converter can be shut down when the capacitor voltage or the output voltage of the secondary side circuit is at a zero-crossing state.

[0123] Another method is to first turn on the target switch in the secondary circuit and turn off the other switches in the secondary circuit. Then, when the capacitor voltage is less than the DC voltage threshold, turn on the first switch of the first bridge arm and the second bridge arm in the primary circuit, or turn on the second switch of the first bridge arm and the second bridge arm in the primary circuit, so that the capacitor continues to discharge until the capacitor voltage is less than the preset voltage threshold. Once the capacitor discharge process is complete, the converter is shut down.

[0124] The DC voltage threshold can be determined based on the DC voltage. When the capacitor voltage is less than the DC voltage threshold, it indicates that the capacitor voltage of the resonant unit has been discharged to approximately the DC voltage. Therefore, in this case, it is necessary to turn on the first switch of the first bridge arm and the second bridge arm in the primary circuit, or turn on the second switch of the first bridge arm and the second bridge arm in the primary circuit, so that the capacitor can continue to discharge.

[0125] One method is to detect the voltage across the capacitor in the resonant unit; if this detected voltage is lower than a DC voltage threshold, the capacitor voltage is determined to be below the DC voltage threshold. Alternatively, the output voltage of the secondary circuit can be sampled; if this output voltage is lower than the DC voltage threshold, the capacitor voltage is determined to be below the DC voltage threshold.

[0126] In addition, the continuous discharge time of the capacitor can be set. If the capacitor discharges for a third preset time, it is determined that the capacitor voltage is less than the DC voltage threshold. This embodiment does not limit this.

[0127] It should be noted that, in the embodiments of this disclosure, when the secondary circuit is a four-switch bridge arm cyclotron circuit, the secondary circuit may include one bridge arm or two bridge arms. Therefore, under different secondary circuit topologies, a target switch can be adaptively selected in the secondary circuit for conduction processing, and the remaining switches in the secondary circuit can be blocked, so that the conducting switches in the secondary circuit and the capacitor form a discharge circuit, thereby discharging the capacitor.

[0128] In one alternative implementation, regarding the above... Figure 3 In the four-switch bridge arm cyclic circuit structure, the secondary circuit includes one bridge arm. If the target switch in the secondary circuit is turned on while the capacitor discharge of the other switches in the secondary circuit is blocked, the switch in the first lower bridge arm of the secondary circuit can be turned on.

[0129] Correspondingly, in the case of a four-switch bridge arm cyclic circuit, if the secondary circuit includes one bridge arm, turning on the target switch in the secondary circuit and blocking the other switches in the secondary circuit includes: turning on the switch of the first lower bridge arm in the secondary circuit and blocking the switch of the first upper bridge arm in the secondary circuit, wherein the target switch includes the switch of the first lower bridge arm in the secondary circuit.

[0130] For example, targeting Figure 3 In the capacitor discharge process, all the switches Q1H, Q1L, Q2H, and Q2L in the primary circuit of the given topology are kept blocked. First, all the switches Q5 and Q6 in the first lower bridge arm of the secondary circuit are turned on, and all the switches Q3 and Q4 in the first upper bridge arm of the secondary circuit are blocked. Under these circumstances, the capacitor of the resonant unit will discharge rapidly, thereby making the capacitor voltage less than the DC voltage threshold. Figure 6 A schematic diagram of the current path during the capacitor discharge process is shown. (Refer to...) Figure 6 :

[0131] in, Figure 6 In (a), the current i in the inductor is... rs A schematic diagram of capacitor discharge when the voltage is ≥0. At this time, all switches Q5 and Q6 in the first lower bridge arm of the secondary circuit are turned on, all switches Q3 and Q4 in the first upper bridge arm are turned off, and the switches in the primary circuit are turned off. The turned-on switches Q5 and Q6 in the secondary circuit, the turned-off switches Q1L and Q2H diodes in the primary circuit form a discharge circuit, causing the capacitor of the resonant unit to discharge until the capacitor voltage is less than the DC voltage threshold.

[0132] in, Figure 6 In (b), the current in the inductor is... rs A schematic diagram of capacitor discharge when the voltage is ≤0. At this time, all switches Q5 and Q6 in the first lower bridge arm of the secondary circuit are turned on, all switches Q3 and Q4 in the first upper bridge arm are turned off, and the switches in the primary circuit are turned off. The conducting switches Q5 and Q6 in the secondary circuit, the turned-off switches Q1H and Q2L in the primary circuit form a discharge circuit, causing the capacitor of the resonant unit to discharge until the capacitor voltage is less than the DC voltage threshold.

[0133] When the capacitor voltage is less than the DC voltage threshold, the first switch Q1H and Q2H in the primary circuit or the second switch Q1L and Q2L in the primary circuit are turned on. Thus, the switched switch in the primary circuit and the target switch and capacitor in the secondary circuit form a discharge circuit, allowing the capacitor to continue discharging until the capacitor voltage is less than the preset voltage threshold.

[0134] Reference Figure 6 In step (c), when the capacitor voltage is less than the DC voltage threshold, the second switches Q1L and Q2L in the primary circuit are turned on. Thus, the switches Q5 and Q6 in the secondary circuit and the switches Q1L and Q2L in the primary circuit form a discharge circuit, causing the capacitor of the resonant unit to discharge until the capacitor voltage is less than the preset voltage threshold.

[0135] For ease of understanding, regarding the above Figure 3The converter topology, Figure 7 The first timing diagram for shutdown control is shown, refer to Figure 7 :

[0136] The time period from T1 to T3 is the inductor freewheeling period. (Regarding...) Figure 3 The converter topology is such that all the switches of the converter are in normal operation before time T1. At time T1, a power-off command is received, which directly blocks all the switches Q1H, Q1L, Q2H, and Q2L of its primary circuit.

[0137] During the time period T1 to T2, the output voltage V of the secondary circuit g When the voltage is ≥0, the lower transistors Q4 and Q6 in the secondary circuit are turned on, while the upper transistors Q3 and Q5 are turned off. At time T2, the output voltage V g The voltage polarity changes from positive to negative. Correspondingly, during the time period T2 to T3, the upper transistors Q3 and Q5 in the secondary circuit are turned on, while the lower transistors Q4 and Q6 are turned off. After the inductor freewheeling process during the time period T1 to T3, the inductor current is less than the preset current threshold at time T3.

[0138] The period from T3 to T5 is the capacitor discharge period. Figure 3 In the converter topology, during the time period from T3 to T4, the switches Q1H, Q1L, Q2H, and Q2L of the primary circuit remain blocked, while the switches Q5 and Q6 of the first lower bridge arm in the secondary circuit are turned on, and the switches Q3 and Q4 of the first upper bridge arm in the secondary circuit are blocked.

[0139] At time T4, the capacitor voltage of the resonant unit is less than the DC voltage threshold. This turns on either the second switch Q1L or Q2L in the primary circuit, or the first switch Q1H or Q2H in the primary circuit. The capacitor continues to discharge until, at time T5, the capacitor voltage is less than the preset voltage threshold. Therefore, after time T5, all switches in the primary and secondary circuits of the converter are turned off, completing the converter shutdown and resetting the resonant cavity.

[0140] Furthermore, it should be noted that during the capacitor discharge process from T3 to T5, the switches in the primary circuit can be kept off, and the switches in the secondary circuit can be kept on while the inductor current is less than a preset current threshold. Specifically, at time T3, the upper bridge arms Q3 and Q5 in the secondary circuit are on, while the lower bridge arms Q4 and Q6 are off, until the capacitor voltage or the output voltage of the secondary circuit reaches zero. At this point, all on switches in the secondary circuit can be off, completing the converter shutdown and resetting the resonant cavity.

[0141] The duration of the inductor freewheeling period can be set to a first preset time, so that starting from time T1, after the first preset time, time T3 is reached, at which point the inductor current is less than a preset current threshold. Alternatively, the inductor current in the resonant unit can be detected, and when the detected current is less than the preset current threshold, that time is determined as time T3.

[0142] The duration of the capacitor discharge period can be set to a second preset time, so that starting from time T3, time T5 is reached after the second preset time. Alternatively, the capacitor voltage or the output voltage of the secondary circuit can be detected, and when the capacitor voltage or the output voltage of the secondary circuit is less than a preset voltage threshold, that time is defined as time T5. Furthermore, the capacitor voltage or the output voltage of the secondary circuit can be detected, and when the capacitor voltage or the output voltage of the secondary circuit is at a zero-crossing state, that time is defined as time T5.

[0143] The duration of the capacitor discharge to the DC voltage threshold can be set to a third preset time. Thus, starting from time T3, after this third preset time, time T4 is reached, at which point the capacitor voltage is less than the DC voltage threshold. Alternatively, the capacitor voltage or the output voltage of the secondary circuit can be detected, and when the capacitor voltage or the output voltage of the secondary circuit is less than the DC voltage threshold, that time is defined as time T4.

[0144] In one alternative implementation, regarding the above... Figure 5 The four-switch bridge arm cyclic circuit in the structure includes two parallel bridge arms. If the target switch in the secondary circuit is turned on and the capacitor discharge method of blocking the other switches in the secondary circuit is adopted, the switch of the first lower bridge arm in the secondary circuit or the switch of the first upper bridge arm in the secondary circuit can be turned on.

[0145] Correspondingly, for a converter whose secondary circuit is a four-switch bridge arm cyclic circuit, if the secondary circuit includes two parallel bridge arms, turning on the target switch in the secondary circuit and blocking the remaining switches in the secondary circuit includes: turning on the switch of the first lower bridge arm in the secondary circuit and blocking the switch of the first upper bridge arm in the secondary circuit, wherein the target switch includes the switch of the lower bridge arm in the secondary circuit; or, turning on the switch of the first upper bridge arm in the secondary circuit and blocking the switch of the first lower bridge arm in the secondary circuit, wherein the target switch includes the switch of the first upper bridge arm in the secondary circuit.

[0146] For example, targeting Figure 5In the capacitor discharge stage of the topology, the primary-side switches Q1H, Q1L, Q2H, and Q2L remain blocked. First, the switches Q51, Q52, Q61, and Q62 of the first lower bridge arm of each bridge arm in the secondary circuit are turned on, while the switches Q31, Q32, Q41, and Q42 of the first upper bridge arm of each bridge arm in the secondary circuit are blocked. Under these circumstances, the capacitor of the resonant unit will discharge rapidly, thereby making the capacitor voltage less than the DC voltage threshold.

[0147] When the capacitor voltage is less than the DC voltage threshold, the first switch Q1H and Q2H in the primary circuit or the second switch Q1L and Q2L in the primary circuit are turned on. Thus, the switched switch in the primary circuit and the target switch and capacitor in the secondary circuit form a discharge circuit, allowing the capacitor to continue discharging until the capacitor voltage is less than the preset voltage threshold.

[0148] For ease of understanding, regarding the above Figure 5 The converter topology, Figure 8 The second timing diagram for shutdown control is shown. Figure 9 The third timing diagram for shutdown control is shown, refer to Figure 8 , Figure 9 :

[0149] The time period from T1 to T3 is the inductor freewheeling period. (Regarding...) Figure 5 The converter topology is such that all the switches of the converter are in normal operation before time T1. At time T1, a power-off command is received, which directly blocks all the switches Q1H, Q1L, Q2H, and Q2L of its primary circuit.

[0150] During the time period T1 to T2, the output voltage V of the secondary circuit g ≥0, all lower transistors Q41, Q42, Q61, and Q62 in the secondary circuit are turned on, and all upper transistors Q31, Q32, Q51, and Q52 are turned off. At time T2, the output voltage V g The voltage polarity changes from positive to negative. Correspondingly, during the time period T2 to T3, all upper-side transistors Q31, Q32, Q51, and Q52 in the secondary circuit are turned on, while all lower-side transistors Q41, Q42, Q61, and Q62 are turned off. After the inductor freewheeling process during the time period T1 to T3, the inductor current is less than the preset current threshold at time T3.

[0151] The period from T3 to T5 is the capacitor discharge period. Figure 5 In the converter topology, during the time period T3 to T4, the primary-side circuit switches Q1H, Q1L, Q2H, and Q2L remain blocked, as shown in the reference. Figure 8This allows all switches Q51, Q52, Q61, and Q62 in the first lower bridge arm of the secondary circuit to be turned on, while blocking all switches Q31, Q32, Q41, and Q42 in the first upper bridge arm of the secondary circuit; see reference. Figure 9 It can also turn on all the switches Q31, Q32, Q41, and Q42 in the first upper arm of the secondary circuit, and turn off all the switches Q51, Q52, Q61, and Q62 in the first lower arm of the secondary circuit.

[0152] At time T4, the capacitor voltage of the resonant unit is less than the DC voltage threshold. This turns on either the second switch Q1L or Q2L in the primary circuit, or the first switch Q1H or Q2H in the primary circuit. The capacitor continues to discharge until, at time T5, the capacitor voltage is less than the preset voltage threshold. Therefore, after time T5, all switches in the primary and secondary circuits of the converter are turned off, completing the converter shutdown and resetting the resonant cavity.

[0153] Among them, regarding the above Figure 8 , Figure 9 The duration of the inductor freewheeling period can be set to a first preset time, so that starting from time T1, after the first preset time, time T3 is reached, at which point the inductor current is less than a preset current threshold. Alternatively, the inductor current in the resonant unit can be detected, and when the detected current is less than the preset current threshold, that time is determined as time T3.

[0154] The duration of the capacitor discharge period can be set to a second preset time, so that starting from time T3, time T5 is reached after the second preset time. Alternatively, the capacitor voltage or the output voltage of the secondary circuit can be detected, and when the capacitor voltage or the output voltage of the secondary circuit is less than a preset voltage threshold at a certain time, that time is determined as time T5.

[0155] The duration of the capacitor discharge to the DC voltage threshold can be set to a third preset time. Thus, starting from time T3, after this third preset time, time T4 is reached, at which point the capacitor voltage is less than the DC voltage threshold. Alternatively, the capacitor voltage or the output voltage of the secondary circuit can be detected, and when the capacitor voltage or the output voltage of the secondary circuit is less than the DC voltage threshold, that time is defined as time T4.

[0156] In addition, it should be noted that, regarding the above... Figure 5 The capacitor discharge process of the structure can also maintain the switching transistor in the secondary circuit in the on state when the inductor current is less than the preset current threshold, until the capacitor voltage is at zero crossing or the output voltage of the secondary circuit is at zero crossing.

[0157] For ease of understanding, regarding the above Figure 5 The converter topology, Figure 10 The fourth timing diagram for shutdown control is shown, refer to Figure 10 :

[0158] The time period from T1 to T3 is the inductor freewheeling period. (Regarding...) Figure 5 The converter topology is such that all the switches of the converter are in normal operation before time T1. At time T1, a power-off command is received, which directly blocks all the switches Q1H, Q1L, Q2H, and Q2L of its primary circuit.

[0159] During the time period T1 to T2, the output voltage V of the secondary circuit g ≥0, all lower transistors Q41, Q42, Q61, and Q62 in the secondary circuit are turned on, and all upper transistors Q31, Q32, Q51, and Q52 are turned off. At time T2, the output voltage V g The voltage polarity changes from positive to negative. Correspondingly, during the time period T2 to T3, all upper-side transistors Q31, Q32, Q51, and Q52 in the secondary circuit are turned on, while all lower-side transistors Q41, Q42, Q61, and Q62 are turned off. After the inductor freewheeling process during the time period T1 to T3, the inductor current is less than the preset current threshold at time T3.

[0160] The period from T3 to T4 is the capacitor discharge period. During this period, the upper-side transistors Q31, Q32, Q51, and Q52 in the secondary circuit are kept in the ON state at time T3, while the lower-side transistors Q41, Q42, Q61, and Q62 are kept in the OFF state until the output voltage of the secondary circuit reaches zero at time T4. At this point, the ON transistors in the secondary circuit can be switched off, completing the converter shutdown and resetting the resonant cavity.

[0161] Among them, targeting Figure 10 The duration of the inductor freewheeling period can be set to a first preset time, so that starting from time T1, after the first preset time, time T3 is reached, at which point the inductor current is less than a preset current threshold. Alternatively, the inductor current in the resonant unit can be detected, and when the detected current is less than the preset current threshold, that time is determined as time T3.

[0162] The converter can detect the capacitor voltage or the output voltage of the secondary circuit. When the capacitor voltage or the output voltage of the secondary circuit is at a zero-crossing state at a certain moment, that moment is defined as time T4. In an optional implementation, the secondary circuit of the converter can also be a half-bridge frequency circuit composed of a third bridge arm and a fourth bridge arm connected in parallel. The third bridge arm and the fourth bridge arm include a second upper bridge arm and a second lower bridge arm connected in series. The second upper bridge arm includes an upper bridge arm transistor and a lower bridge arm transistor connected in series, and the second lower bridge arm includes a bridge arm capacitor. The upper bridge arm transistor and the lower bridge arm transistor in the second upper bridge arm have opposite directions. The connection point between the second upper bridge arm and the second lower bridge arm in the third and fourth bridge arms serves as the output terminal of the secondary circuit and is connected to a single-phase AC load or the power grid.

[0163] In the case that the secondary circuit in the converter is the aforementioned half-bridge cyclic circuit, in order to achieve inductor freewheeling, the switching transistors of the primary circuit must be blocked. When the voltage polarity of the output voltage of the secondary circuit is positive, the upper transistor of the third bridge arm and the lower transistor of the fourth bridge arm in the secondary circuit are turned on, and the remaining switching transistors in the secondary circuit are blocked. When the voltage polarity of the output voltage of the secondary circuit is negative, the lower transistor of the third bridge arm and the upper transistor of the fourth bridge arm in the secondary circuit are turned on, and the remaining switching transistors in the secondary circuit are blocked.

[0164] Accordingly, when the secondary circuit in the converter is the aforementioned half-bridge frequency circuit, in one optional implementation, the switching transistors in the secondary circuit corresponding to the voltage polarity are turned on and the remaining switching transistors in the secondary circuit are turned off according to the voltage polarity of the output voltage. This includes: when the voltage polarity is positive, turning on the upper transistor of the third bridge arm and the lower transistor of the fourth bridge arm, and turning off the lower transistor of the third bridge arm and the upper transistor of the fourth bridge arm; when the voltage polarity is negative, turning on the lower transistor of the third bridge arm and the upper transistor of the fourth bridge arm, and turning off the upper transistor of the third bridge arm and the lower transistor of the fourth bridge arm.

[0165] In the case where the secondary circuit of the converter is the aforementioned half-bridge frequency circuit, to facilitate understanding of the inductor freewheeling current handling process of this converter, Figure 11 A schematic diagram of the third structure of the converter is shown.

[0166] Reference Figure 11 The secondary circuit of this converter consists of a half-bridge frequency circuit composed of a third bridge arm and a fourth bridge arm connected in parallel. Specifically, the second upper bridge arm of the third bridge arm includes a series-connected upper bridge arm transistor Q. 4’ and bridge arm lower tube Q 3’ Its second lower bridge arm is the bridge arm capacitor C1. For the fourth bridge arm, its second upper bridge arm includes the series-connected upper bridge arm transistor Q. 5’ and bridge arm lower tube Q 6’Its second lower bridge arm is the bridge arm capacitor C2.

[0167] In this secondary circuit, the two adjacent switches in each second upper bridge arm are in opposite directions. (Refer to...) Figure 11 For the third bridge arm of the secondary circuit, the upper transistor Q of its bridge arm... 4’ With bridge arm lower tube Q 3’ The sources are interconnected, and the lower arm of the bridge tube Q is connected. 3’ The drain of the bridge arm capacitor C1 is connected. For the fourth bridge arm of the secondary circuit, its upper transistor Q... 5’ With bridge arm lower tube Q 6’ The sources are interconnected, and the lower arm of the bridge tube Q is connected. 6’ The drain of the bridge arm capacitor C2 is connected.

[0168] In this circuit, the connection point between the second upper arm and the second lower arm of the third and fourth bridge arms serves as the output terminal of the secondary circuit, connected to a single-phase AC load or the power grid. That is, the lower arm transistor Q... 3’ Drain, lower bridge arm Q 6’ The drain terminal is the output terminal of the secondary circuit.

[0169] In this circuit, a first inductor L can be set at the output terminal of the secondary circuit, so that its output voltage is output to a single-phase AC load or the power grid through the first inductor L.

[0170] Furthermore, Figure 11 In the diagram, Lr represents the inductance of the resonant unit, and Cr represents the capacitance of the resonant unit. Figure 11 The diagram only shows the connection schematic of the inductor and capacitor in the resonant unit, which are respectively located at the first and second ends of the secondary winding. The connection relationship of the inductor and capacitor in the resonant unit can be adapted according to the actual application needs, and this disclosure does not limit this.

[0171] Correspondingly, targeting Figure 11 With this topology, when performing inductor freewheeling processing, all switches Q1H, Q1L, Q2H, and Q2L in the primary circuit can be directly blocked, and the switch corresponding to the voltage polarity of the output voltage in the secondary circuit can be turned on according to the voltage polarity of the output voltage in the secondary circuit, while the remaining switches in the secondary circuit are blocked.

[0172] For example, when the output voltage at the output terminal of the secondary circuit is positive, the upper transistor Q of the third bridge arm in the secondary circuit is turned on. 4’ and the lower tube Q of the fourth bridge arm 6’ And block the lower transistor Q of the third bridge arm in the secondary circuit. 3’ And the upper tube Q of the fourth bridge arm 5’ When the output voltage at the output terminal of the secondary circuit is negative, the lower transistor Q of the third bridge arm in the secondary circuit is turned on. 3’And the upper tube Q of the fourth bridge arm 5’ And block the upper transistor Q of the third bridge arm in the secondary circuit. 4’ and the lower tube Q of the fourth bridge arm 6’ .

[0173] Furthermore, regarding the above Figure 11 In order to achieve capacitor discharge, the converter structure can keep the switching transistor in the secondary circuit in the on state when the inductor current is less than a preset current threshold until the output voltage of the secondary circuit reaches the zero-crossing state. At this time, the capacitor voltage of the resonant unit is less than the preset voltage threshold.

[0174] Accordingly, when the secondary circuit in the converter is the aforementioned half-bridge cyclic circuit, in one optional implementation, controlling the conduction state of the switching transistors in the primary and secondary circuits to discharge the capacitor includes: maintaining the conduction state of the switching transistors in the secondary circuit when the inductor current is less than a preset current threshold until the capacitor voltage is at a zero-crossing state or the output voltage of the secondary circuit is at a zero-crossing state, while keeping the switching transistors in the primary circuit in an off state; wherein, the conducting switching transistors in the secondary circuit and the capacitor form a discharge circuit to discharge the capacitor.

[0175] In this context, a voltage being in a zero-crossing state at a given moment means that the instantaneous value of the voltage at that moment is 0, and that this moment represents the critical point for the voltage to switch from positive to negative polarity or vice versa. For example, during the process of changing from positive to negative voltage polarity, the voltage is considered to be in a zero-crossing state at the moment when its instantaneous value is 0. For ease of understanding, the above... Figure 11 The converter topology, Figure 12 The fifth timing diagram for shutdown control is shown, refer to... Figure 12 :

[0176] The time period from T1 to T3 is the inductor freewheeling period. (Regarding...) Figure 11 The converter topology is such that all the switches of the converter are in normal operation before time T1. At time T1, a power-off command is received, which directly blocks all the switches Q1H, Q1L, Q2H, and Q2L of its primary circuit.

[0177] During the time period T1 to T2, the output voltage V of the secondary circuit g ≥0, Q of the upper transistor of the third bridge arm in the secondary circuit 4’ and the lower tube Q of the fourth bridge arm 6’ When the circuit is turned on, the lower transistor Q of the third bridge arm in the secondary circuit is activated. 3’ And the upper tube Q of the fourth bridge arm 5’ Blocked. At time T2, the output voltage V gThe voltage polarity changes from positive to negative. Correspondingly, during the time period T2 to T3, the lower transistor Q of the third bridge arm in the secondary circuit... 3’ And the upper tube Q of the fourth bridge arm 5’ Conduction, the upper tube Q of the third bridge arm 4’ and the lower tube Q of the fourth bridge arm 6’ Blocking. After inductor freewheeling processing during periods T1 to T3, the inductor current is less than the preset current threshold at time T3.

[0178] The period from T3 to T4 is the capacitor discharge period. During this period, the switch in the primary circuit remains off, and the Q value in the secondary circuit remains unchanged at time T3. 3’ Q 5’ The conduction state of Q 4’ Q 6’ The secondary circuit remains in a blocked state until the output voltage of the secondary circuit reaches zero at time T4. At this point, all the conducting switches in the secondary circuit of the converter can be blocked, completing the converter shutdown and resetting the resonant cavity.

[0179] Among them, targeting Figure 12 The duration of the inductor freewheeling period can be set to a first preset time, so that starting from time T1, after the first preset time, time T3 is reached, at which point the inductor current is less than a preset current threshold. Alternatively, the inductor current in the resonant unit can be detected, and when the detected current is less than the preset current threshold, that time is determined as time T3.

[0180] Among them, the capacitor voltage or the output voltage of the secondary circuit can be detected. When the capacitor voltage or the output voltage of the secondary circuit is at a zero-crossing state at a certain moment, that moment is determined as time T4.

[0181] In one alternative implementation, if the inductor current is less than a preset current threshold when a shutdown command is received, the step of controlling the conduction state of the switching transistors in the primary and secondary circuits to allow the inductor to freewheel can be skipped. Instead, the switching transistors in the primary circuit can be directly blocked, and the control step of discharging the resonant capacitor can be executed.

[0182] Accordingly, before controlling the conduction state of the switching transistors in the primary and secondary circuits to allow the inductor to freewheel, the method further includes: determining whether the real-time inductor current is less than a preset current threshold when the power-off command of the converter is received; if the real-time inductor current is less than the preset current threshold, blocking the switching transistors in the primary circuit and controlling the conduction state of the switching transistors in the primary and secondary circuits to discharge the capacitor; if the real-time inductor current is not less than the preset current threshold, controlling the conduction state of the switching transistors in the primary and secondary circuits to allow the inductor to freewheel.

[0183] When the power-off command of the converter is received, if the converter is operating under no-load or light-load conditions, its resonant cavity energy is relatively small. Therefore, when the power-off command of the converter is received, the real-time inductor current of the resonant unit in the converter may be less than the preset current threshold.

[0184] Correspondingly, when the power-off command of the converter is received, if the real-time inductor current of the resonant unit in the converter is less than the preset current threshold, the step of controlling the conduction state of the switching transistors in the primary and secondary circuits to allow the inductor to freewheel can be skipped. Instead, after blocking the switching transistors in the primary circuit, the step of controlling the conduction state of the switching transistors in the primary and secondary circuits to allow the capacitor to discharge can be executed directly.

[0185] It should be noted that when only the capacitor discharge control step is executed, and the inductor freewheeling control step is not performed, the discharge process involving the conduction state of the switching transistors in the secondary circuit when the inductor current is kept below the preset current threshold during the capacitor discharge phase can be handled according to the following procedure. At the initial moment of the capacitor discharge phase, referring to the switching transistor conduction control method corresponding to the inductor freewheeling control step, some switching transistors in the secondary circuit of the converter are turned on, while the remaining switching transistors are turned off. During the duration of the capacitor discharge phase, the conduction state of each switching transistor at the initial moment is maintained until the output voltage of the secondary circuit or the capacitor voltage reaches a zero-crossing state.

[0186] For example, at the initial moment of the capacitor discharge phase, the switching transistors of the primary circuit are turned off, and the switching transistors corresponding to the voltage polarity of the output voltage of the secondary circuit are turned on, while the remaining switching transistors of the secondary circuit are turned off. During the duration of the capacitor discharge phase, the conducting state of each switching transistor at the initial moment is maintained until the output voltage of the secondary circuit or the capacitor voltage reaches a zero-crossing state.

[0187] When the power-off command of the converter is received, if the real-time inductor current of the resonant unit in the converter is not less than the preset current threshold, it indicates that inductor freewheeling processing is required. This requires controlling the conduction state of the switching transistors in the primary and secondary circuits to enable inductor freewheeling.

[0188] In one alternative implementation, if the capacitor voltage is already less than a preset voltage threshold when the inductor current is less than a preset current threshold, the capacitor discharge control step can be skipped, and the switching transistors of the primary and secondary circuits can be directly blocked to shut down the converter.

[0189] Accordingly, before controlling the conduction state of the switching transistors in the primary and secondary circuits to discharge the capacitor, the method further includes: determining whether the real-time capacitor voltage is less than a preset voltage threshold when the inductor current is less than a preset current threshold; if the real-time capacitor voltage is less than the preset voltage threshold, blocking the switching transistors in the secondary circuit to shut down the converter; if the real-time capacitor voltage is not less than the preset voltage threshold, executing the step of controlling the conduction state of the switching transistors in the primary and secondary circuits to discharge the capacitor.

[0190] When the inductor current is less than the preset current threshold, the real-time capacitor voltage of the resonant unit in the converter may be less than the preset voltage threshold.

[0191] Correspondingly, when the inductor current is less than the preset current threshold and the real-time capacitor voltage of the resonant unit in the converter is less than the preset voltage threshold, the step of controlling the conduction state of the switching transistors in the primary and secondary circuits to discharge the capacitor can be skipped. Instead, the switching transistors in the secondary circuit that are in the conduction state can be directly blocked, thus shutting down the converter.

[0192] If the inductor current is less than the preset current threshold, and the real-time capacitor voltage of the resonant unit in the converter is not less than the preset voltage threshold, then capacitor discharge is required. This requires controlling the conduction state of the switching transistors in the primary and secondary circuits to discharge the capacitor.

[0193] Furthermore, if the converter malfunctions upon receiving a shutdown command, such as a relay disconnecting and causing the grid to disconnect, the aforementioned capacitor discharge control steps may be omitted. Instead, when the inductor current is less than a preset current threshold, the switching transistor in the secondary circuit can be directly blocked to shut down the converter. This disclosure does not impose any limitations on this aspect.

[0194] It is understood that the various method embodiments mentioned above in this disclosure can be combined with each other to form combined embodiments without violating the principle and logic. Due to space limitations, this disclosure will not elaborate further. Those skilled in the art will understand that in the above methods of specific implementation, the specific execution order of each step should be determined by its function and possible internal logic.

[0195] In addition, this disclosure also provides a power-off control device, electronic device, and computer-readable storage medium for a converter. All of the above can be used to implement any power-off control method for a converter provided in this disclosure. The corresponding technical solutions and descriptions are described in the corresponding descriptions in the method section and will not be repeated here.

[0196] Figure 13 This is a block diagram of a power-off control device for a converter provided in an embodiment of the present disclosure.

[0197] Reference Figure 13 This disclosure provides a power-off control device for a converter, which includes a primary circuit, a resonant unit, a secondary circuit, and a transformer. The primary circuit is a full-bridge circuit composed of a first bridge arm and a second bridge arm connected in parallel. The first and second bridge arms include a first switch and a second switch connected in series. The two ends of the first and second bridge arms are connected to a DC source. The midpoint of the first bridge arm is connected to the first end of the primary winding of the transformer, and the midpoint of the second bridge arm is connected to the second end of the primary winding. The resonant unit is disposed between the primary circuit and the secondary circuit, and includes an inductor and a capacitor. The output terminal of the secondary circuit is connected to an AC load or a power grid. The power-off control device for this converter includes:

[0198] The freewheeling control module 1301 is used to control the conduction state of the switching transistors in the primary circuit and the secondary circuit in response to receiving the power-off command of the converter, so that the inductor freewheels until the inductor current is less than a preset current threshold.

[0199] The discharge control module 1302 is used to control the conduction state of the switching transistors in the primary circuit and the secondary circuit, so as to discharge the capacitor, and when the capacitor voltage is less than a preset voltage threshold, to block the switching transistors in the primary circuit and the secondary circuit, so as to shut down the converter.

[0200] In one optional implementation, controlling the conduction state of the switches in the primary circuit and the secondary circuit to enable the inductor to freewheel includes: blocking the switches in the primary circuit; obtaining the output voltage at the output terminal of the secondary circuit; and, based on the voltage polarity of the output voltage, turning on the switch in the secondary circuit corresponding to the voltage polarity, and blocking the remaining switches in the secondary circuit; wherein the conducting switches in the secondary circuit and the inductor form a freewheeling loop, enabling the inductor to freewheel.

[0201] In one optional implementation, the secondary circuit is a four-switch bridge arm cyclic circuit. The secondary circuit includes at least one bridge arm, each bridge arm including a first upper bridge arm and a first lower bridge arm. The first upper bridge arm and the first lower bridge arm are connected in series, and the first upper bridge arm and the first lower bridge arm include a bridge arm upper transistor and a bridge arm lower transistor connected in series. The directions of two adjacent switches in the bridge arm are opposite. The two ends of the bridge arm are the output terminals of the secondary circuit, used to connect to a single-phase AC load or the power grid.

[0202] In one optional implementation, based on the voltage polarity of the output voltage, the switching transistor in the secondary circuit corresponding to the voltage polarity is turned on, and the remaining switching transistors in the secondary circuit are turned off, including: when the voltage polarity is positive, turning on the lower bridge arm transistor in the secondary circuit and turning off the upper bridge arm transistor in the secondary circuit; when the voltage polarity is negative, turning on the upper bridge arm transistor in the secondary circuit and turning off the lower bridge arm transistor in the secondary circuit.

[0203] In one optional implementation, controlling the conduction state of the switches in the primary circuit and the secondary circuit to discharge the capacitor includes: turning on a target switch in the secondary circuit and turning off the remaining switches in the secondary circuit; wherein the target switch and the capacitor form a discharge circuit to discharge the capacitor; and when the capacitor voltage is less than a DC voltage threshold, turning on the first switch of the first bridge arm and the second bridge arm in the primary circuit, or turning on the second switch of the first bridge arm and the second bridge arm in the primary circuit; wherein the primary... The conducting switch in the primary circuit, together with the target switch and the capacitor, forms a discharge loop, allowing the capacitor to continue discharging until its voltage is less than a preset voltage threshold. Alternatively, the switching transistor in the secondary circuit remains conducting while the inductor current is less than a preset current threshold, until the capacitor voltage or the output voltage of the secondary circuit reaches a zero-crossing state, and the switching transistor in the primary circuit remains disconnected. The conducting switch in the secondary circuit, together with the capacitor, forms a discharge loop, allowing the capacitor to discharge.

[0204] In one optional implementation, the secondary circuit includes a bridge arm, and the step of turning on the target switch in the secondary circuit and blocking the remaining switches in the secondary circuit includes: turning on the switch of the first lower bridge arm in the secondary circuit and blocking the switch of the first upper bridge arm in the secondary circuit, wherein the target switch includes the switch of the first lower bridge arm in the secondary circuit.

[0205] In one optional implementation, the secondary circuit includes two parallel bridge arms. Turning on the target switch in the secondary circuit and blocking the remaining switches in the secondary circuit includes: turning on the switch of the first lower bridge arm in the secondary circuit and blocking the switch of the first upper bridge arm in the secondary circuit, wherein the target switch includes the switch of the first lower bridge arm in the secondary circuit; or, turning on the switch of the first upper bridge arm in the secondary circuit and blocking the switch of the first lower bridge arm in the secondary circuit, wherein the target switch includes the switch of the first upper bridge arm in the secondary circuit.

[0206] In one optional implementation, the secondary circuit is a half-bridge frequency circuit composed of a third and a fourth bridge arm connected in parallel. The third and fourth bridge arms include a second upper bridge arm and a second lower bridge arm connected in series. The second upper bridge arm includes an upper and a lower bridge arm connected in series, and the second lower bridge arm includes a bridge arm capacitor. The upper and lower bridge arms in the second upper bridge arm are in opposite directions. The connection point between the second upper and the second lower bridge arms in the third and fourth bridge arms serves as the output terminal of the secondary circuit and is connected to a single-phase AC load or the power grid.

[0207] In one optional implementation, the step of turning on the switch corresponding to the voltage polarity in the secondary circuit and blocking the remaining switches in the secondary circuit according to the voltage polarity of the output voltage includes: when the voltage polarity is positive, turning on the upper switch of the third bridge arm and the lower switch of the fourth bridge arm, and blocking the lower switch of the third bridge arm and the upper switch of the fourth bridge arm; when the voltage polarity is negative, turning on the lower switch of the third bridge arm and the upper switch of the fourth bridge arm, and blocking the upper switch of the third bridge arm and the lower switch of the fourth bridge arm.

[0208] In one optional implementation, controlling the conduction state of the switching transistors in the primary circuit and the secondary circuit to discharge the capacitor includes: maintaining the conduction state of the switching transistors in the secondary circuit when the inductor current is less than a preset current threshold, until the capacitor voltage is at a zero-crossing state or the output voltage of the secondary circuit is at a zero-crossing state, while maintaining the switching transistors in the primary circuit in an off state; wherein the conducting switching transistors in the secondary circuit and the capacitor form a discharge circuit to discharge the capacitor.

[0209] In one optional implementation, after controlling the conduction state of the switching transistors in the primary circuit and the secondary circuit to enable the inductor to freewheel, the device is further configured to: determine that the inductor current is less than the preset current threshold when the inductor freewheel continues for a first preset time.

[0210] In one optional implementation, after controlling the conduction state of the switching transistors in the primary circuit and the secondary circuit to discharge the capacitor, the device is further configured to: determine that the capacitor voltage is less than the preset voltage threshold when the capacitor discharge continues for a second preset time.

[0211] In one optional implementation, before controlling the conduction state of the switches in the primary and secondary circuits to allow the inductor to freewheel, the device is further configured to: determine whether the real-time inductor current is less than a preset current threshold when the power-off command of the converter is received; if the real-time inductor current is less than the preset current threshold, block the switches in the primary circuit and execute the step of controlling the conduction state of the switches in the primary and secondary circuits to discharge the capacitor; if the real-time inductor current is not less than the preset current threshold, execute the step of controlling the conduction state of the switches in the primary and secondary circuits to allow the inductor to freewheel.

[0212] In one optional implementation, before controlling the conduction state of the switching transistors in the primary and secondary circuits to discharge the capacitor, the device is further configured to: determine whether the real-time capacitor voltage is less than a preset voltage threshold when the inductor current is less than a preset current threshold; if the real-time capacitor voltage is less than the preset voltage threshold, block the switching transistors in the secondary circuit to shut down the converter; if the real-time capacitor voltage is not less than the preset voltage threshold, execute the step of controlling the conduction state of the switching transistors in the primary and secondary circuits to discharge the capacitor.

[0213] The various modules in the shutdown control device of the aforementioned converter can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in the processor of a computer device in hardware form or independent of it, or stored in the memory of a computer device in software form, so that the processor can call and execute the operations corresponding to each module.

[0214] Figure 14 This is a block diagram of an electronic device provided in an embodiment of the present disclosure.

[0215] Reference Figure 14 This disclosure provides an electronic device, which includes: at least one processor 1401; at least one memory 1402; and one or more I / O interfaces 1403 connected between the processor 1401 and the memory 1402; wherein the memory 1402 stores one or more computer programs that can be executed by the at least one processor 1401, and the one or more computer programs are executed by the at least one processor 1401 to enable the at least one processor 1401 to perform the above-described power-off control method for the converter.

[0216] The modules in the aforementioned electronic devices can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in the processor of a computer device in hardware form or independent of it, or stored in the memory of a computer device in software form, so that the processor can call and execute the operations corresponding to each module.

[0217] This disclosure also provides a computer-readable storage medium storing a computer program thereon, wherein the computer program, when executed by a processor, implements the aforementioned power-off control method for the converter. The computer-readable storage medium may be volatile or non-volatile.

[0218] This disclosure also provides a computer program product, including computer-readable code, or a non-volatile computer-readable storage medium carrying computer-readable code, wherein when the computer-readable code is run in a processor of an electronic device, the processor in the electronic device executes the above-described power-off control method for the converter.

[0219] Those skilled in the art will understand that all or some of the steps, systems, and apparatuses disclosed above, and their functional modules / units, can be implemented as software, firmware, hardware, or suitable combinations thereof. In hardware implementations, the division between functional modules / units mentioned above does not necessarily correspond to the division of physical components; for example, a physical component may have multiple functions, or a function or step may be performed collaboratively by several physical components. Some or all physical components may be implemented as software executed by a processor, such as a central processing unit, digital signal processor, or microprocessor, or as hardware, or as an integrated circuit, such as an application-specific integrated circuit (ASIC). Such software can be distributed on a computer-readable storage medium, which may include computer storage media (or non-transitory media) and communication media (or transient media).

[0220] As is known to those skilled in the art, the term computer storage medium includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storing information, such as computer-readable program instructions, data structures, program modules, or other data. Computer storage media includes, but is not limited to, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM), static random access memory (SRAM), flash memory or other memory technologies, portable compact disc read-only memory (CD-ROM), digital versatile disc (DVD) or other optical disc storage, magnetic cartridges, magnetic tape, disk storage or other magnetic storage devices, or any other medium that can be used to store desired information and is accessible to a computer. Furthermore, it is known to those skilled in the art that communication media typically contain computer-readable program instructions, data structures, program modules, or other data in modulated data signals such as carrier waves or other transmission mechanisms, and may include any information delivery medium.

[0221] The computer-readable program instructions described herein can be downloaded from computer-readable storage media to various computing / processing devices, or downloaded via a network, such as the Internet, local area network, wide area network, and / or wireless network, to an external computer or external storage device. The network may include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. A network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards them to the computer-readable storage media in the respective computing / processing device.

[0222] Computer program instructions used to perform the operations of this disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, status setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, etc., and conventional procedural programming languages ​​such as the "C" language or similar programming languages. The computer-readable program instructions may execute entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving a remote computer, the remote computer may be connected to the user's computer via any type of network—including a local area network (LAN) or a wide area network (WAN)—or may be connected to an external computer (e.g., via the Internet using an Internet service provider). In some embodiments, electronic circuitry, such as programmable logic circuitry, field-programmable gate arrays (FPGAs), or programmable logic arrays (PLAs), is personalized by utilizing the status information of the computer-readable program instructions to implement various aspects of this disclosure.

[0223] The computer program product described herein can be implemented specifically through hardware, software, or a combination thereof. In one alternative embodiment, the computer program product is specifically embodied in a computer storage medium; in another alternative embodiment, the computer program product is specifically embodied in a software product, such as a software development kit (SDK), etc.

[0224] Various aspects of this disclosure are described herein with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this disclosure. It should be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer-readable program instructions.

[0225] These computer-readable program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing apparatus to produce a machine such that, when executed by the processor of the computer or other programmable data processing apparatus, they create means for implementing the functions / actions specified in one or more blocks of the flowchart and / or block diagram. These computer-readable program instructions can also be stored in a computer-readable storage medium that causes a computer, programmable data processing apparatus, and / or other device to operate in a particular manner; thus, the computer-readable medium storing the instructions comprises an article of manufacture that includes instructions for implementing aspects of the functions / actions specified in one or more blocks of the flowchart and / or block diagram.

[0226] Computer-readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable data processing apparatus, or other device to produce a computer-implemented process, thereby causing the instructions executed on the computer, other programmable data processing apparatus, or other device to perform the functions / actions specified in one or more boxes of a flowchart and / or block diagram.

[0227] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present disclosure. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of an instruction containing one or more executable instructions for implementing a specified logical function. In some alternative implementations, the functions marked in the blocks may occur in a different order than those shown in the drawings. For example, two consecutive blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, may be implemented using a dedicated hardware-based system that performs the specified function or action, or using a combination of dedicated hardware and computer instructions.

[0228] Example embodiments have been disclosed herein, and while specific terminology has been used, it is for illustrative purposes only and should be construed as such, and is not intended to be limiting. In some instances, it will be apparent to those skilled in the art that features, characteristics, and / or elements described in connection with particular embodiments may be used alone, or in combination with features, characteristics, and / or elements described in connection with other embodiments, unless otherwise expressly indicated. Therefore, those skilled in the art will understand that various changes in form and detail may be made without departing from the scope of this disclosure as set forth by the appended claims.

Claims

1. A shutdown control method for a converter, characterized in that, The converter includes a primary-side circuit, a resonant unit, a secondary-side circuit, and a transformer. The primary-side circuit is a full-bridge circuit composed of a first bridge arm and a second bridge arm connected in parallel. The first bridge arm and the second bridge arm include a first switch and a second switch connected in series. The two ends of the first bridge arm and the second bridge arm are connected to a DC source. The midpoint of the first bridge arm is connected to the first end of the primary winding of the transformer, and the midpoint of the second bridge arm is connected to the second end of the primary winding. The resonant unit is disposed between the primary-side circuit and the secondary-side circuit, and the resonant unit includes an inductor and a capacitor. The output terminal of the secondary-side circuit is connected to an AC load or a power grid. The method includes: In response to receiving the power-off command of the converter, the conduction state of the switching transistors in the primary circuit and the secondary circuit is controlled to allow the inductor to freewheel until the inductor current is less than a preset current threshold. The conduction state of the switching transistors in the primary circuit and the secondary circuit is controlled to discharge the capacitor. When the capacitor voltage is less than a preset voltage threshold, the switching transistors in the primary circuit and the secondary circuit are blocked, and the converter is turned off.

2. The method according to claim 1, characterized in that, Controlling the conduction state of the switching transistors in the primary and secondary circuits to enable freewheeling current in the inductor includes: The switching transistor of the primary circuit is blocked; Obtain the output voltage at the output terminal of the secondary circuit; According to the voltage polarity of the output voltage, the switch corresponding to the voltage polarity in the secondary circuit is turned on, and the other switches in the secondary circuit are turned off; wherein, the turned-on switch in the secondary circuit and the inductor form a freewheeling circuit, allowing the inductor to continue flowing.

3. The method according to claim 2, characterized in that, The secondary circuit is a four-switch bridge arm cyclic circuit. The secondary circuit includes at least one bridge arm, and each bridge arm includes a first upper bridge arm and a first lower bridge arm. The first upper bridge arm is connected in series with the first lower bridge arm, and the first upper bridge arm and the first lower bridge arm include a bridge arm upper tube and a bridge arm lower tube connected in series; the two adjacent switching tubes in the bridge arm are in opposite directions; the two ends of the bridge arm are the output terminals of the secondary circuit, which are used to connect to a single-phase AC load or the power grid.

4. The method according to claim 3, characterized in that, The step of turning on the switch corresponding to the voltage polarity of the output voltage and turning off the remaining switches in the secondary circuit according to the voltage polarity of the output voltage includes: When the voltage polarity is positive, the lower bridge arm transistor in the secondary circuit is turned on, and the upper bridge arm transistor in the secondary circuit is blocked. When the voltage polarity is negative, the upper transistor of the bridge arm in the secondary circuit is turned on, and the lower transistor of the bridge arm in the secondary circuit is blocked.

5. The method according to claim 3, characterized in that, Controlling the conduction state of the switching transistors in the primary and secondary circuits to discharge the capacitor includes: The target switch in the secondary circuit is turned on, while the remaining switches in the secondary circuit are turned off. The target switch and the capacitor form a discharge circuit, allowing the capacitor to discharge. If the capacitor voltage is less than a DC voltage threshold, the first switches of the first and second bridge arms in the primary circuit, or the second switches of the first and second bridge arms in the primary circuit, are turned on. The turned-on switches in the primary circuit, along with the target switch and the capacitor, form a discharge circuit, allowing the capacitor to continue discharging until the capacitor voltage is less than a preset voltage threshold. or, When the inductor current is kept less than a preset current threshold, the switching transistor in the secondary circuit remains in the on state until the capacitor voltage is at a zero-crossing state or the output voltage of the secondary circuit is at a zero-crossing state, while the switching transistor in the primary circuit remains in the off state; wherein, the on switching transistor in the secondary circuit and the capacitor form a discharge circuit, causing the capacitor to discharge.

6. The method according to claim 5, characterized in that, The secondary circuit includes a bridge arm, wherein turning on the target switch in the secondary circuit and blocking the remaining switches in the secondary circuit includes: Turn on the switch of the first lower bridge arm in the secondary circuit and block the switch of the first upper bridge arm in the secondary circuit, wherein the target switch includes the switch of the first lower bridge arm in the secondary circuit.

7. The method according to claim 5, characterized in that, The secondary circuit includes two parallel bridge arms. Turning on the target switch in the secondary circuit and blocking the remaining switches in the secondary circuit includes: Turn on the switch of the first lower bridge arm in the secondary circuit and block the switch of the first upper bridge arm in the secondary circuit, wherein the target switch includes the switch of the first lower bridge arm in the secondary circuit; or, Turn on the switch of the first upper bridge arm in the secondary circuit and block the switch of the first lower bridge arm in the secondary circuit, wherein the target switch includes the switch of the first upper bridge arm in the secondary circuit.

8. The method according to claim 2, characterized in that, The secondary circuit is a half-bridge frequency circuit composed of a third bridge arm and a fourth bridge arm connected in parallel. The third bridge arm and the fourth bridge arm include a second upper bridge arm and a second lower bridge arm connected in series. The second upper bridge arm includes an upper bridge arm transistor and a lower bridge arm transistor connected in series. The second lower bridge arm includes a bridge arm capacitor. The upper bridge arm transistor and the lower bridge arm transistor in the second upper bridge arm are in opposite directions. The connection point between the second upper arm and the second lower arm of the third and fourth bridge arms serves as the output terminal of the secondary circuit, which is connected to a single-phase AC load or the power grid.

9. The method according to claim 8, characterized in that, The step of turning on the switch corresponding to the voltage polarity of the output voltage and turning off the remaining switches in the secondary circuit according to the voltage polarity of the output voltage includes: When the voltage polarity is positive, the upper tube of the third bridge arm and the lower tube of the fourth bridge arm are turned on, and the lower tube of the third bridge arm and the upper tube of the fourth bridge arm are blocked. When the voltage polarity is negative, the lower tube of the third bridge arm and the upper tube of the fourth bridge arm are turned on, while the upper tube of the third bridge arm and the lower tube of the fourth bridge arm are blocked.

10. The method according to claim 8, characterized in that, Controlling the conduction state of the switching transistors in the primary and secondary circuits to discharge the capacitor includes: When the inductor current is kept less than a preset current threshold, the switching transistor in the secondary circuit remains in the on state until the capacitor voltage is at a zero-crossing state or the output voltage of the secondary circuit is at a zero-crossing state, while the switching transistor in the primary circuit remains in the off state; wherein, the on switching transistor in the secondary circuit and the capacitor form a discharge circuit, causing the capacitor to discharge.

11. The method according to any one of claims 1-10, characterized in that, After controlling the conduction state of the switching transistors in the primary and secondary circuits to enable freewheeling current in the inductor, the method further includes: If the inductor freewheeling current continues for a first preset time, it is determined that the inductor current is less than the preset current threshold.

12. The method according to any one of claims 1-10, characterized in that, After controlling the conduction state of the switching transistors in the primary and secondary circuits to discharge the capacitor, the method further includes: If the capacitor discharge continues for a second preset time, it is determined that the capacitor voltage is less than the preset voltage threshold.

13. The method according to any one of claims 1-10, characterized in that, Before controlling the conduction state of the switching transistors in the primary-side circuit and the secondary-side circuit to enable the inductor to freewheel, the method further includes: Determine whether the real-time inductor current of the inductor is less than the preset current threshold when the power-off command of the converter is received; When the real-time inductor current is less than the preset current threshold, the switching transistor of the primary circuit is blocked, and the step of controlling the conduction state of the switching transistors in the primary circuit and the secondary circuit is executed to discharge the capacitor. If the real-time inductor current is not less than the preset current threshold, the step of controlling the conduction state of the switching transistors in the primary circuit and the secondary circuit to enable the inductor to freewheel is executed.

14. The method according to any one of claims 1-10, characterized in that, Before discharging the capacitor by controlling the conduction state of the switching transistors in the primary-side circuit and the secondary-side circuit, the method further includes: Determine whether the real-time capacitor voltage of the capacitor is less than the preset voltage threshold when the inductor current is less than the preset current threshold. If the real-time capacitor voltage is less than the preset voltage threshold, the switching transistor in the secondary circuit is blocked, and the converter is shut down. If the real-time capacitor voltage is not less than the preset voltage threshold, the step of controlling the conduction state of the switching transistors in the primary circuit and the secondary circuit is executed to discharge the capacitor.

15. A power-off control device for a converter, characterized in that, The converter includes a primary-side circuit, a resonant unit, a secondary-side circuit, and a transformer. The primary-side circuit is a full-bridge circuit composed of a first bridge arm and a second bridge arm connected in parallel. The first bridge arm and the second bridge arm include a first switch and a second switch connected in series. The two ends of the first bridge arm and the second bridge arm are connected to a DC source. The midpoint of the first bridge arm is connected to the first end of the primary winding of the transformer, and the midpoint of the second bridge arm is connected to the second end of the primary winding. The resonant unit is disposed between the primary-side circuit and the secondary-side circuit, and the resonant unit includes an inductor and a capacitor. The output terminal of the secondary-side circuit is connected to an AC load or a power grid. The device includes: The freewheeling control module is used to control the conduction state of the switching transistors in the primary circuit and the secondary circuit in response to receiving the power-off command of the converter, so that the inductor freewheels until the inductor current is less than a preset current threshold. The discharge control module is used to control the conduction state of the switching transistors in the primary circuit and the secondary circuit, so as to discharge the capacitor. When the capacitor voltage is less than a preset voltage threshold, the module blocks the switching transistors in the primary circuit and the secondary circuit, thereby shutting down the converter.

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