Control method of cycloconversion circuit, cycloconversion circuit and isolated converter

Abstract

The present application discloses a control method of a cycloconversion circuit, a cycloconversion circuit and an isolated converter, and belongs to the field of power control technology. The cycloconversion circuit is configured to realize AC-AC conversion, and includes a plurality of switch elements connected into a plurality of current paths, the plurality of switch elements are divided into a plurality of groups of switch elements, each group of switch elements includes at least one switch element arranged on each current path, and the control method of the present application includes: when the cycloconversion circuit is in the zero-crossing detection stage, the first group of switch elements are controlled to be complementary turned on, and the second group of switch elements are switched between the on state and the off state; within the dead time of the driving signal of the first group of switch elements, the first target switch element in the second group of switch elements is turned on, and a freewheeling circuit is provided for the switch element on the same current path as the switch element in the first group of switch elements that is turned on after the dead time, so as to release the leakage inductance current and reduce the voltage overstress risk of the switch tube.

Description

Technical Field

[0001] The present application belongs to the technical field of power control, and in particular relates to a control method of a cyclotron conversion circuit, a cyclotron conversion circuit and an isolated converter. Background Art

[0002] In new energy photovoltaic, energy storage and charging scenarios, high-efficiency conversion circuits are required. Among the topology schemes of various conversion circuits, the isolated single-stage topology of the DC side active full-bridge and cycloconverter has the advantages of few circuit components, high conversion efficiency and input and output electrical isolation, which has attracted attention in the industry.

[0003] The cycloconverter divides the switch tubes into high-frequency tubes and low-frequency tubes during the control process, and swaps the high-frequency tubes and low-frequency tubes at the zero-crossing point of the grid voltage. In practical applications, in order to avoid direct conduction during the swap process and cause a short circuit in the bridge arm, a dead time is set during the swap process. During the dead time, all switch tubes are turned off, but this also leads to the risk of overstressing the switch tubes. Summary of the invention

[0004] The present application aims to solve at least one of the technical problems existing in the prior art. To this end, the present application proposes a control method for a cycloconversion circuit, a cycloconversion circuit and an isolated converter, which reduce the voltage overstress risk of the switch tube and make it easier to meet the soft switching condition of zero voltage opening.

[0005] In a first aspect, the present application provides a control method for a cycloconversion circuit, wherein the cycloconversion circuit is configured to realize AC-AC conversion and includes a plurality of switch elements connected into a plurality of current paths, wherein the plurality of switch elements are divided into a plurality of groups of switch elements, each group of switch elements includes at least one switch element arranged on each current path, and the control method for the cycloconversion circuit includes:

[0006] When the cycloconversion circuit is in the zero-crossing detection stage, the first group of switch elements are controlled to be complementary turned on, and the second group of switch elements are switched between an on state and an off state;

[0007] Among them, during the dead time of the driving signal of the first group of switch elements, the first target switch element in the second group of switch elements is turned on, and the first target switch element is a switch element located on the same current path as the switch element in the first group of switch elements that is turned on after the dead time.

[0008] According to the control method of the cycloidal converter circuit of the present application, when the cycloidal converter circuit is in the zero-crossing detection stage, the first target switch element in the second group of switch elements is turned on within the dead time of the drive signal of the first group of switch elements, thereby providing a freewheeling circuit for the switch elements of the first group of switch elements that are turned on after the dead time, releasing the leakage inductance current, reducing the voltage overstress risk of the switch tube, and making it easier to meet the soft switching condition of zero voltage turn-on.

[0009] According to an embodiment of the present application, the first target switching element remains in an on state at least until the dead time ends.

[0010] According to one embodiment of the present application, the first target switching element is turned on before the dead time starts.

[0011] According to an embodiment of the present application, in the zero-crossing detection phase, the driving signal of the second group of switch elements is a pulse signal, and the driving signal of the second group of switch elements is ahead in phase with respect to the driving signal of the first group of switch elements.

[0012] According to an embodiment of the present application, the phase lead of the drive signal of the second group of switch elements relative to the drive signal of the first group of switch elements is greater than or equal to the dead time of the drive signal of the first group of switch elements.

[0013] According to an embodiment of the present application, the driving signal of the second group of switch elements has the same duty cycle and / or the same period as the driving signal of the first group of switch elements.

[0014] According to one embodiment of the present application, the control method further includes:

[0015] Obtaining the voltage at the output side of the frequency conversion circuit;

[0016] Determine a first group of switch elements and a second group of switch elements from each group of switch elements of the cycloconversion circuit according to the positive and negative polarities of the voltage;

[0017] The grouping relationship of each group of switch elements when the voltage is positive polarity is opposite to the grouping relationship when the voltage is negative polarity.

[0018] According to one embodiment of the present application, after obtaining the voltage at the output side of the frequency conversion circuit, the method further includes:

[0019] When the absolute value of the voltage is less than or equal to the first voltage threshold, it is determined that the cycloconversion circuit enters the zero-crossing detection phase.

[0020] In a second aspect, the present application provides an isolated converter, which includes a transformer, a control unit and a frequency conversion circuit connected to a first side of the transformer, the control unit is connected to the frequency conversion circuit and is configured to execute the aforementioned control method.

[0021] According to the isolated converter of the present application, when the cycloconversion circuit is in the zero-crossing detection stage, the first target switching element in the second group of switching elements is turned on within the dead time of the driving signal of the first group of switching elements, thereby providing a freewheeling circuit for the switching elements of the first group of switching elements that are turned on after the dead time, releasing the leakage inductance current, reducing the voltage overstress risk of the switching tube, and making it easier to meet the soft switching conditions of zero voltage turn-on.

[0022] In a third aspect, the present application provides a cyclotron conversion circuit, which is configured to achieve AC-AC conversion and includes a plurality of switching elements connected into a plurality of current paths, wherein the plurality of switching elements are divided into a plurality of groups of switching elements, each group of switching elements includes at least one switching element arranged on each current path, and during a zero-crossing detection phase, a first group of switching elements are complementarily turned on, a second group of switching elements are complementarily turned on, and a driving signal of the second group of switching elements is phase-leading relative to a driving signal of the first group of switching elements.

[0023] According to the cyclic conversion circuit of the present application, in the zero-crossing detection stage, the first target switching element in the second group of switching elements is turned on within the dead time of the driving signal of the first group of switching elements, thereby providing a freewheeling circuit for the switching elements of the first group of switching elements that are turned on after the dead time, releasing the leakage inductance current, reducing the voltage overstress risk of the switching tube, and making it easier to meet the soft switching conditions of zero voltage turn-on.

[0024] According to one embodiment of the present application, the phase lead of the drive signal of the second group of switch elements relative to the drive signal of the first group of switch elements is greater than or equal to the dead time of the drive signal of the first group of switch elements.

[0025] According to one embodiment of the present application, the zero-crossing detection stage includes a positive voltage stage and a negative voltage stage, and the grouping relationship of the switching elements in the positive voltage stage and the negative voltage stage is opposite. The grouping relationship of the switching elements is the corresponding relationship between the first group of switching elements and the second group of switching elements and each switching element in the frequency conversion circuit.

[0026] In a fourth aspect, the present application provides an isolated converter, which includes a transformer and the aforementioned cyclotron conversion circuit, wherein the cyclotron conversion circuit is electrically connected to a first side of the transformer.

[0027] According to the isolated converter of the present application, when the cycloconversion circuit is in the zero-crossing detection stage, the first target switching element in the second group of switching elements is turned on within the dead time of the driving signal of the first group of switching elements, thereby providing a freewheeling circuit for the switching elements of the first group of switching elements that are turned on after the dead time, releasing the leakage inductance current, reducing the voltage overstress risk of the switching tube, and making it easier to meet the soft switching conditions of zero voltage turn-on.

[0028] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0030] Figure 1 It is one of the topological structure diagrams of the cycloconversion circuit provided in the embodiment of the present application;

[0031] Figure 2 It is one of the driving signal waveform diagrams of the frequency conversion circuit in the related technology;

[0032] Figure 3 This is the second driving signal waveform diagram of the frequency conversion circuit in the related art;

[0033] Figure 4 It is one of the flow charts of the control method of the cycloconversion circuit provided in the embodiment of the present application;

[0034] Figure 5 This is the second topological structure diagram of the frequency conversion circuit provided in the embodiment of the present application;

[0035] Figure 6 This is the third topological structure diagram of the frequency conversion circuit provided in the embodiment of the present application;

[0036] Figure 7 It is one of the driving signal waveform diagrams of the cycloconversion circuit provided in the embodiment of the present application;

[0037] Figure 8 This is the second driving signal waveform diagram of the cycloconversion circuit provided in the embodiment of the present application;

[0038] Fig. 9 This is the second flow chart of the control method of the cycloconversion circuit provided in the embodiment of the present application;

[0039] Fig.10 This is the third driving signal waveform diagram of the cycloconversion circuit provided in the embodiment of the present application;

[0040] Fig.11 This is the fourth driving signal waveform diagram of the cycloconversion circuit provided in the embodiment of the present application;

[0041] Fig.12 This is one of the freewheeling path schematic diagrams of the cycloconversion circuit provided in the embodiment of the present application;

[0042] Fig.13This is the second schematic diagram of the freewheeling path of the cycloconversion circuit provided in the embodiment of the present application;

[0043] Fig.14 This is the third schematic diagram of the freewheeling path of the cycloconversion circuit provided in the embodiment of the present application;

[0044] Fig.15 This is the fourth schematic diagram of the freewheeling path of the cycloconversion circuit provided in the embodiment of the present application.

[0045] Reference numerals:

[0046] Transformer T, first to twelfth switch tubes S1 to S12, first to fourth capacitors C1 to C4, first to fourth parasitic capacitors C oss1 ~C oss4 . DETAILED DESCRIPTION

[0047] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be understood as limiting the present application.

[0048] In the following description, "circuit" refers to a conductive loop composed of at least one element or subcircuit through electrical connection or electromagnetic connection. When an element or circuit is said to be "coupled to" or "connected to" another element or an element / circuit is said to be "coupled to" or "connected to" two nodes, it can be directly coupled or connected to another element or there can be an intermediate element, and the connection between the elements can be physical, logical, or a combination thereof. On the contrary, when an element is said to be "directly coupled to" or "directly connected to" another element, it means that there is no intermediate element between the two.

[0049] In the description, the terms "first", "second", etc. are used to distinguish similar objects, and are not used to describe a specific order or sequence. It should be understood that the numerical descriptors used in this way are interchangeable where appropriate, so that the embodiments of the present application can be implemented in an order other than those illustrated or described herein, and the objects distinguished by "first", "second", etc. are generally of the same type, and the number of objects is not limited. For example, the first object can be one or more. In addition, "and / or" in the specification and claims represents at least one of the connected objects, and the character " / " generally indicates that the objects associated with each other are in an "or" relationship.

[0050] In addition, descriptions with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0051] Reference Figure 1 , Figure 1 The topological structure of a frequency conversion circuit is shown. The frequency conversion circuit includes a first switch tube S1, a second switch tube S2, a third switch tube S3 and a fourth switch tube S4. The first switch tube S1, the second switch tube S2, the third switch tube S3 and the fourth switch tube S4 are connected in series in sequence and electrically connected between power lines. The frequency conversion circuit also includes a first capacitor C1 and a second capacitor C2, the first capacitor C1 and the second capacitor C2 are connected in series and electrically connected between power lines. The first end of the secondary winding of the transformer T is electrically connected to the connection node of the second switch tube S2 and the third switch tube S3, and the second end of the secondary winding of the transformer T is electrically connected to the connection node of the first capacitor C1 and the second capacitor C2.

[0052] Reference Figure 2 , Figure 2 The driving signal waveform of the frequency conversion circuit in the related art is shown. In the traditional driving scheme, in the positive half-cycle of the grid voltage, the first switch tube S1 and the third switch tube S3 work as high-frequency tubes to complement each other, and the second switch tube S2 and the fourth switch tube S4 are normally turned on as low-frequency tubes; in the negative half-cycle of the grid voltage, the second switch tube S2 and the fourth switch tube S4 work as high-frequency tubes to complement each other, and the first switch tube S1 and the third switch tube S3 are normally turned on as low-frequency tubes. In the above two working modes, near the zero-crossing point of the grid voltage, if the grid polarity is misjudged due to sampling errors and delays, the bridge arm will be directly connected, resulting in the risk of short circuit in the frequency conversion circuit near the zero-crossing point of the grid voltage, and then overstress of the electronic components.

[0053] Reference Figure 3 , Figure 3 The driving signal waveform of the frequency conversion circuit in the related art is shown. In the related art, in order to solve the risk of short circuit in the aforementioned frequency conversion circuit, the driving signal of the low-frequency tube in the positive half-cycle and negative half-cycle of the grid voltage is adjusted to the same frequency as the high-frequency tube and is turned on complementarily. Since the switch tubes in the same direction are turned on complementarily and have a dead zone in the frequency conversion circuit, there will be no bridge arm short-circuit path even if the grid polarity is misjudged. However, during the dead zone time, all switch tubes are turned off, and the secondary leakage inductance current loses the freewheeling path, which will introduce the risk of overstress of the switch tube voltage.

[0054] Reference Figure 4 , Figure 4 A flow chart of a control method of a cycloconversion circuit proposed in an embodiment of the present application is shown. An embodiment of the present application proposes a control method of a cycloconversion circuit, the cycloconversion circuit is configured to realize AC-AC conversion, and includes a plurality of switch elements connected into a plurality of current paths, the plurality of switch elements are divided into a plurality of groups of switch elements, each group of switch elements includes at least one switch element arranged on each current path, and the control method of the cycloconversion circuit includes step 10.

[0055] Step 10, when the frequency conversion circuit is in the zero-crossing detection stage, the first group of switch elements are controlled to be turned on complementary, and the second group of switch elements are switched between the on state and the off state; wherein, within the dead time of the driving signal of the first group of switch elements, the first target switch element in the second group of switch elements is turned on, and the first target switch element is a switch element located on the same current path as the switch element in the first group of switch elements that is turned on after the dead time.

[0056] The first group of switch elements and the second group of switch elements refer to different switch tubes when the topology of the cycloconversion circuit is different, or when the polarity of the voltage at the output side of the cycloconversion circuit is different.

[0057] exist Figure 1 In the topological structure of the cycloconversion circuit shown, in the zero-crossing detection stage, when the output side of the cycloconversion circuit is a positive voltage, the first group of switch elements refers to the first switch tube S1 and the third switch tube S3, and the second group of switch elements refers to the second switch tube S2 and the fourth switch tube S4; when the output side of the cycloconversion circuit is a negative voltage, the first group of switch elements refers to the second switch tube S2 and the fourth switch tube S4, and the second group of switch elements refers to the first switch tube S1 and the third switch tube S3.

[0058] Reference Figure 5 , Figure 5 The topological structure of a frequency conversion circuit is shown. The frequency conversion circuit includes a fifth switch tube S5, a sixth switch tube S6, a seventh switch tube S7 and an eighth switch tube S8. The fifth switch tube S5, the sixth switch tube S6, the seventh switch tube S7 and the eighth switch tube S8 are connected in series in sequence and electrically connected between power lines. The frequency conversion circuit also includes a third capacitor C3, which is electrically connected between power lines. The first end of the secondary winding of the transformer T is electrically connected to the connection node of the sixth switch tube S6 and the seventh switch tube S7, and the second end of the secondary winding of the transformer T is electrically connected to the connection node of the eighth switch tube S8 and the power line.

[0059] exist Figure 5In the topological structure of the cycloconversion circuit shown, in the zero-crossing detection stage, when the output side of the cycloconversion circuit is a positive voltage, the first group of switch elements refers to the fifth switch tube S5 and the seventh switch tube S7, and the second group of switch elements refers to the sixth switch tube S6 and the eighth switch tube S8; when the output side of the cycloconversion circuit is a negative voltage, the first group of switch elements refers to the sixth switch tube S6 and the eighth switch tube S8, and the second group of switch elements refers to the fifth switch tube S5 and the seventh switch tube S7.

[0060] Reference Figure 6 , Figure 6 The topological structure of a frequency conversion circuit is shown. The frequency conversion circuit includes a ninth switch tube S9, a tenth switch tube S10, an eleventh switch tube S11 and a twelfth switch tube S12. The ninth switch tube S9, the tenth switch tube S10, the eleventh switch tube S11 and the twelfth switch tube S12 are connected in series in sequence and electrically connected between power lines. The frequency conversion circuit also includes a fourth capacitor C4, which is electrically connected between power lines. The first end of the secondary winding of the transformer T is electrically connected to the connection node of the ninth switch tube S9 and the tenth switch tube S10, and the second end of the secondary winding of the transformer T is electrically connected to the connection node of the eleventh switch tube S11 and the twelfth switch tube S12.

[0061] exist Figure 6 In the topological structure of the cycloconversion circuit shown, in the zero-crossing detection stage, when the output side of the cycloconversion circuit is a positive voltage, the first group of switch elements refers to the ninth switch tube S9 and the eleventh switch tube S11, and the second group of switch elements refers to the tenth switch tube S10 and the twelfth switch tube S12; when the output side of the cycloconversion circuit is a negative voltage, the first group of switch elements refers to the tenth switch tube S10 and the twelfth switch tube S12, and the second group of switch elements refers to the ninth switch tube S9 and the eleventh switch tube S11.

[0062] The oscillator circuit also includes a controller, which is electrically connected to the driving end of each switch tube and is mainly used to apply a driving signal to the driving end of each switch tube to drive each switch tube to operate.

[0063] An embodiment of the present application provides a control method, and the executor of the control method may be the aforementioned controller or a functional module or functional entity in the controller that can implement the control method. The control method provided in the embodiment of the present application is described below using the controller as an example of the executor.

[0064] The following is Figure 1 The topological structure of the cycloconversion circuit shown is taken as an example to illustrate the control method of the cycloconversion circuit proposed in this application.

[0065] The zero-crossing detection stage of the frequency conversion circuit refers to the stage in which the voltage on the output side of the frequency conversion circuit decreases from a positive voltage to a zero voltage and the stage in which the voltage on the output side of the frequency conversion circuit increases from a negative voltage to a zero voltage. When the output side of the frequency conversion circuit is connected to a power grid, the voltage on the output side of the frequency conversion circuit can be the voltage of the power grid.

[0066] Reference Figure 7 When the cycloconversion circuit is in the zero-crossing detection stage and the grid voltage is a positive voltage, the first switch tube S1 and the third switch tube S3 are turned on complementary, and the second switch tube S2 and the fourth switch tube S4 are switched between the on state and the off state. During the dead time of the driving signal of the first switch tube S1 and the third switch tube S3, the fourth switch tube S4 is turned on, so that during the dead time from the first switch tube S1 being turned off to the third switch tube S3 being turned on, the fourth switch tube S4 is the third switch tube S3 maintaining the freewheeling path of the leakage inductance current; during the dead time from the third switch tube S3 being turned off to the first switch tube S1 being turned on, the second switch tube S2 is turned on, and the second switch tube S2 is the first switch tube S1 maintaining the freewheeling path of the leakage inductance current.

[0067] Reference Figure 8 When the cycloconversion circuit is in the zero-crossing detection stage and the grid voltage is a negative voltage, the second switch tube S2 and the fourth switch tube S4 are complementarily turned on, and the first switch tube S1 and the third switch tube S3 are switched between the on state and the off state. During the dead time of the driving signal of the second switch tube S2 and the fourth switch tube S4, the third switch tube S3 is turned on, so that during the dead time from the second switch tube S2 being turned off to the fourth switch tube S4 being turned on, the third switch tube S3 maintains the freewheeling path of the leakage inductance current for the fourth switch tube S4, and during the dead time from the fourth switch tube S4 being turned off to the second switch tube S2 being turned on, the first switch tube S1 is turned on, and the first switch tube S1 maintains the freewheeling path of the leakage inductance current for the second switch tube S2.

[0068] According to the control method of the cycloidal converter circuit of the present application, when the cycloidal converter circuit is in the zero-crossing detection stage, the first target switch element in the second group of switch elements is turned on within the dead time of the drive signal of the first group of switch elements, thereby providing a freewheeling circuit for the switch elements of the first group of switch elements that are turned on after the dead time, releasing the leakage inductance current, reducing the voltage overstress risk of the switch tube, and making it easier to meet the soft switching condition of zero voltage turn-on.

[0069] In some embodiments, the first target switching element remains in the on state at least until the dead time ends.

[0070] Continue to refer to Figure 7When the cycloconversion circuit is in the zero-crossing detection stage and the grid voltage is a positive voltage, during the dead time of the driving signals of the first switch tube S1 and the third switch tube S3, the fourth switch tube S4 remains in an on state until the third switch tube S3 is turned on, and a freewheeling path can be provided for the leakage inductance current during the dead time of the driving signals of the first switch tube S1 and the third switch tube S3 until the third switch tube S3 is turned on. The second switch tube S2 remains in an on state until the first switch tube S1 is turned on, and a freewheeling path can be provided for the leakage inductance current during the dead time of the driving signals of the first switch tube S1 and the third switch tube S3 until the first switch tube S1 is turned on. The flow path of the leakage inductance current will not be interrupted, thereby reducing the stress of the leakage inductance current on the switch tube.

[0071] The implementation principle of the cycloconversion circuit when it is in the zero-crossing detection stage and the grid voltage is a negative voltage is the same as the principle when the grid voltage is a positive voltage, and will not be repeated here.

[0072] In some embodiments, the first target switching element is turned on before the dead time starts.

[0073] When the cycloconversion circuit is in the zero-crossing detection stage and the grid voltage is a positive voltage, before the dead time of the driving signal entering the first switch tube S1 and the third switch tube S3, the fourth switch tube S4 has been turned on and remains in the turned-on state until the dead time ends, or, before the dead time of the driving signal entering the third switch tube S3 and the first switch tube S1, the second switch tube S2 has been turned on and remains in the turned-on state until the dead time ends, which can provide a freewheeling path for the leakage inductance current during the entire dead time, further reducing the stress caused by the leakage inductance current on the switch tube.

[0074] The implementation principle of the cycloconversion circuit when it is in the zero-crossing detection stage and the grid voltage is a negative voltage is the same as the principle when the grid voltage is a positive voltage, and will not be repeated here.

[0075] In some embodiments, during the zero-crossing detection phase, the driving signal of the second group of switch elements is a pulse signal, and the driving signal of the second group of switch elements has a phase lead relative to the driving signal of the first group of switch elements.

[0076] The driving signal of the second group of switching elements is ahead in phase with respect to the driving signal of the first group of switching elements, that is, when the cycloconversion circuit is in the zero-crossing detection stage and the grid voltage is a positive voltage, the second switch tube S2 and the fourth switch tube S4 are turned on earlier than the first switch tube S1 and the third switch tube S3.

[0077] The fourth switch tube S4 is turned on during the dead time from when the first switch tube S1 is turned off to when the third switch tube S3 is turned on, and the second switch tube S2 is turned on during the dead time from when the third switch tube S3 is turned off to when the first switch tube S1 is turned on. The phase difference between the drive signals of the first switch tube S1 and the third switch tube S3 and the drive signals of the second switch tube S2 and the fourth switch tube S4 can ensure that at least one of the second switch tube S2 and the fourth switch tube S4 is in the on state during the dead time when the first switch tube S1 and the third switch tube S3 are complementarily turned on, thereby providing a freewheeling path for the leakage inductance current and simultaneously controlling the phase of the drive signals of the second switch tube S2 and the fourth switch tube S4 to be advanced, so that the control is simple and easy to implement.

[0078] The implementation principle of the cycloconversion circuit when it is in the zero-crossing detection stage and the grid voltage is a negative voltage is the same as the principle when the grid voltage is a positive voltage, and will not be repeated here.

[0079] In some embodiments, the phase lead of the driving signal of the second group of switching elements relative to the driving signal of the first group of switching elements is greater than or equal to the dead time of the driving signal of the first group of switching elements.

[0080] The phase lead of the drive signal of the second group of switch elements relative to the drive signal of the first group of switch elements is equal to the dead time of the drive signal of the first group of switch elements, indicating that the fourth switch tube S4 is turned on at the beginning of the dead time from the first switch tube S1 being turned off to the third switch tube S3 being turned on, and the second switch tube S2 is turned on at the beginning of the dead time from the third switch tube S3 being turned off to the first switch tube S1 being turned on, so that the second switch tube S2 and the fourth switch tube S4 provide a freewheeling path for the leakage inductance current during the dead time of the drive signal of the first switch tube S1 and the third switch tube S3.

[0081] The phase lead of the drive signal of the second group of switch elements relative to the drive signal of the first group of switch elements is greater than the dead time of the drive signal of the first group of switch elements, indicating that the fourth switch tube S4 has been turned on before the dead time from the turn-off of the first switch tube S1 to the turn-on of the third switch tube S3 begins, and the second switch tube S2 has been turned on before the dead time from the turn-off of the third switch tube S3 to the turn-on of the first switch tube S1 begins, providing a time margin for the second switch tube S2 and the fourth switch tube S4 to provide a freewheeling path for the leakage inductance current within the dead time of the drive signal of the first switch tube S1 and the third switch tube S3.

[0082] In some embodiments, the driving signals of the second group of switching elements have the same duty cycle and / or the same period as the driving signals of the first group of switching elements.

[0083] The driving signal of the second group of switching elements can have the same duty cycle as the driving signal of the first group of switching elements, or the driving signal of the second group of switching elements can have the same period as the driving signal of the first group of switching elements, or the driving signal of the second group of switching elements can have the same duty cycle and the same period as the driving signal of the first group of switching elements, so as to facilitate control.

[0084] Reference Fig. 9 In some embodiments, the control method further includes: step 20 and step 30.

[0085] Step 20, obtaining the voltage at the output side of the frequency conversion circuit;

[0086] Step 30, determining the first group of switch elements and the second group of switch elements from each group of switch elements of the cycloconversion circuit according to the positive and negative polarities of the voltage; wherein the grouping relationship of each group of switch elements when the voltage is positive is opposite to the grouping relationship when the voltage is negative.

[0087] exist Figure 1 In the topological structure of the cycloconversion circuit shown, when the output side of the cycloconversion circuit is a positive voltage, the first group of switch elements refers to the first switch tube S1 and the third switch tube S3, and the second group of switch elements refers to the second switch tube S2 and the fourth switch tube S4; when the output side of the cycloconversion circuit is a negative voltage, the first group of switch elements refers to the second switch tube S2 and the fourth switch tube S4, and the second group of switch elements refers to the first switch tube S1 and the third switch tube S3.

[0088] Figure 5 In the topological structure of the cycloconversion circuit shown in FIG. 1 , the grouping relationship of each group of switch elements when the voltage is positive polarity is the same as the grouping relationship when the voltage is negative polarity. Figure 1 The topological structure of the cycloconversion circuit shown is the same and will not be repeated here.

[0089] exist Figure 6 In the topological structure of the cycloconversion circuit shown, when the output side of the cycloconversion circuit is a positive voltage, the first group of switch elements refers to the ninth switch tube S9 and the eleventh switch tube S11, and the second group of switch elements refers to the tenth switch tube S10 and the twelfth switch tube S12; when the output side of the cycloconversion circuit is a negative voltage, the first group of switch elements refers to the tenth switch tube S10 and the twelfth switch tube S12, and the second group of switch elements refers to the ninth switch tube S9 and the eleventh switch tube S11.

[0090] In some embodiments, after obtaining the voltage at the output side of the cyclotron conversion circuit, the method further includes: when the absolute value of the voltage is less than or equal to the first voltage threshold, determining that the cyclotron conversion circuit enters the zero-crossing detection phase.

[0091] The absolute value of the voltage is less than or equal to the first voltage threshold, indicating that the difference between the voltage and the zero voltage is small, which can be regarded as the cycloidal conversion circuit entering the zero-crossing detection stage.

[0092] The first voltage threshold can be selected according to the actual application scenario and is not limited here. For example, the first voltage threshold can be 2V, 3V or 4V.

[0093] An embodiment of the present application provides an isolated converter, which includes a transformer T, a control unit, and a cyclotron conversion circuit connected to a first side of the transformer T. The control unit is connected to the cyclotron conversion circuit and is configured to execute the aforementioned control method.

[0094] The first side of the transformer T may be a side where the secondary winding of the transformer T is located. The frequency conversion circuit may be electrically connected to the secondary winding of the transformer T, and the control unit is electrically connected to the driving end of each switch tube in the frequency conversion circuit, and is mainly used to apply a driving signal to the driving end of each switch tube to drive each switch tube to switch between an on state and an off state.

[0095] The specific steps and principles of the control method can be referred to the aforementioned embodiments and will not be described in detail here.

[0096] According to the isolated converter of the present application, when the cycloconversion circuit is in the zero-crossing detection stage, the first target switching element in the second group of switching elements is turned on within the dead time of the driving signal of the first group of switching elements, thereby providing a freewheeling circuit for the switching elements of the first group of switching elements that are turned on after the dead time, releasing the leakage inductance current, reducing the voltage overstress risk of the switching tube, and making it easier to meet the soft switching conditions of zero voltage turn-on.

[0097] An embodiment of the present application provides a cyclotron conversion circuit, which is configured to achieve AC-AC conversion and includes a plurality of switching elements connected into a plurality of current paths, wherein the plurality of switching elements are divided into a plurality of groups of switching elements, each group of switching elements includes at least one switching element arranged on each current path, and during a zero-crossing detection phase, a first group of switching elements are complementarily turned on, a second group of switching elements are complementarily turned on, and a driving signal of the second group of switching elements is phase-leading relative to a driving signal of the first group of switching elements.

[0098] The topology of the frequency conversion circuit can be selected according to the actual application scenario and is not limited here.

[0099] exist Figure 1In the topological structure of the cycloconversion circuit shown, in the zero-crossing detection stage, when the output side of the cycloconversion circuit is a positive voltage, the first switch tube S1 and the third switch tube S3 are turned on complementarily, and the second switch tube S2 and the fourth switch tube S4 are turned on complementarily. The second switch tube S2 and the fourth switch tube S4 are ahead in phase with respect to the driving signal of the first group of switch elements, so that during the dead time from the first switch tube S1 being turned off to the third switch tube S3 being turned on, the fourth switch tube S4 is a freewheeling path for the third switch tube S3 to maintain the leakage inductance current, and during the dead time from the third switch tube S3 being turned off to the first switch tube S1 being turned on, the second switch tube S2 is turned on, and the second switch tube S2 is a freewheeling path for the first switch tube S1 to maintain the leakage inductance current.

[0100] Figure 5 The control method in the topological structure of the frequency conversion circuit shown is similar to Figure 1 The control method of the topological structure of the cycloconversion circuit shown is the same and will not be repeated here.

[0101] Reference Fig.10 ,exist Figure 6 In the topological structure of the cycloconversion circuit shown, in the zero-crossing detection stage, when the output side of the cycloconversion circuit is a positive voltage, the ninth switch tube S9 and the eleventh switch tube S11 are complementarily turned on, the tenth switch tube S10 and the twelfth switch tube S12 are complementarily turned on, and the phase of the tenth switch tube S10 and the twelfth switch tube S12 is ahead of the driving signal of the first group of switch elements, so that during the dead time from the ninth switch tube S9 being turned off to the eleventh switch tube S11 being turned on, the tenth switch tube S10 is a freewheeling path for the eleventh switch tube S11 to maintain the leakage inductance current, and during the dead time from the eleventh switch tube S11 being turned off to the ninth switch tube S9 being turned on, the twelfth switch tube S12 is turned on, and the twelfth switch tube S12 is a freewheeling path for the ninth switch tube S9 to maintain the leakage inductance current.

[0102] Reference Fig.11 The implementation principle of the cycloidal conversion circuit when it is in the zero-crossing detection stage and the grid voltage is a negative voltage is the same as that when the grid voltage is a positive voltage, and will not be repeated here.

[0103] According to the cyclic conversion circuit of the present application, in the zero-crossing detection stage, the first target switching element in the second group of switching elements is turned on within the dead time of the driving signal of the first group of switching elements, thereby providing a freewheeling circuit for the switching elements of the first group of switching elements that are turned on after the dead time, releasing the leakage inductance current, reducing the voltage overstress risk of the switching tube, and making it easier to meet the soft switching conditions of zero voltage turn-on.

[0104] In some embodiments, the phase lead of the drive signal of the second group of switch elements relative to the drive signal of the first group of switch elements is greater than or equal to the dead time of the drive signal of the first group of switch elements.

[0105] Reference Fig.12 ,exist Figure 1 In the topological structure of the cycloconverter circuit shown in FIG. 1 , when the cycloconverter circuit is in the zero-crossing detection stage and the grid voltage is a positive voltage, when the first switch tube S1 is turned off, the secondary leakage inductance current i lk The phase lead of the second switch tube S2 and the fourth switch tube S4 drive signals relative to the first switch tube S1 and the third switch tube S3 drive signals is equal to the dead time of the first switch tube S1 and the third switch tube S3 drive signals, which is the leakage inductance current i lk The freewheeling circuit provides two branches: the first branch includes the first parasitic capacitor C of the first switch tube S1 oss1 and the body diode of the second switch tube S2, the second branch includes the third parasitic capacitor C of the third switch tube S3 oss3 and the fourth switch tube S4, the corresponding branch current directions are respectively as shown in FIG. ZVS12 ,i ZVS34 Therefore, during the dead time from when the first switch tube S1 is turned off to when the third switch tube S3 is turned on, i ZVS12 ,i ZVS34 The first parasitic capacitance C oss1 Charging the third parasitic capacitor C oss3 When the third parasitic capacitor C oss3 When the discharge reaches zero, the body diode of the third switch tube S3 is turned on. At this time, turning on the third switch tube S3 can achieve zero voltage turn-on.

[0106] Reference Fig.13 When the third switch tube S3 is turned off, the secondary leakage inductance current i lk The current flows from the secondary winding of the transformer T into the frequency conversion circuit. Since the phase lead of the second switch tube S2 and the fourth switch tube S4 relative to the first switch tube S1 and the third switch tube S3 is equal to the dead time of the first switch tube S1 and the third switch tube S3 drive signal, the leakage inductance current i lk The freewheeling circuit provides two branches: the first branch includes the first parasitic capacitor C of the first switch tube S1 oss1 The second branch includes a third parasitic capacitor C of the third switch tube S3. oss3 and the body diode of the fourth switch tube S4, and the corresponding branch current directions are respectively as shown in FIG. ZVS12 ,i ZVS34 Therefore, in the dead zone from the third switch tube S3 being turned off to the first switch tube S1 being turned on, i ZVS12 ,i ZVS34 The first parasitic capacitance C oss1 Discharge the third parasitic capacitor C oss3When the first parasitic capacitor C oss1 When the discharge reaches zero, the body diode of the first switch tube S1 is turned on. At this time, turning on the first switch tube S1 can achieve zero voltage turn-on.

[0107] In addition, since the phase lead of the driving signals of the second switch tube S2 and the fourth switch tube S4 relative to the driving signals of the first switch tube S1 and the third switch tube S3 is equal to the dead time of the driving signals of the first switch tube S1 and the third switch tube S3, before the first switch tube S1 is turned off, the second switch tube S2 has been turned off in advance for a dead time, and the current is turned on by the body diode of the second switch tube S2; before the third switch tube S3 is turned off, the fourth switch tube S4 has been turned off in advance for a dead time, and the current is turned on by the body diode of the fourth switch tube S4. Since the turn-on current is small and the dead time is short at this time, the phase lead of the driving signal of the second group of switch elements relative to the driving signal in the first group of switch elements brings very little additional body diode turn-on loss. In addition, when the grid voltage is positive, the second switch tube S2 and the fourth switch tube S4 do not bear the withstand voltage when they are turned off, so there is no hard switch when the second switch tube S2 and the fourth switch tube S4 are switched, thereby ensuring the soft switching characteristics of all switch tubes.

[0108] Reference Fig.14 ,exist Figure 1 In the topological structure of the cycloconverter circuit shown in FIG. 1 , when the cycloconverter circuit is in the zero-crossing detection stage and the grid voltage is a negative voltage, when the second switch tube S2 is turned off, the secondary leakage inductance current i lk The current flows from the secondary winding of the transformer T into the frequency conversion circuit. Since the phase lead of the driving signals of the first switch tube S1 and the third switch tube S3 relative to the driving signals of the second switch tube S2 and the fourth switch tube S4 is equal to the dead time of the driving signals of the second switch tube S2 and the fourth switch tube S4, the leakage inductance current i lk The freewheeling provides two branches: the first branch includes the body diode of the first switch tube S1 and the second parasitic capacitor C of the second switch tube S2. oss2 The second branch includes the fourth parasitic capacitor C of the third switch tube S3 and the fourth switch tube S4. oss4 , the corresponding branch current direction is as shown in Figure i ZVS12 ,i ZVS34 Therefore, in the dead zone from the second switch tube S2 being turned off to the fourth switch tube S4 being turned on, i ZVS12 ,i ZVS34 The second parasitic capacitance C oss2 Charging the fourth parasitic capacitor C oss4 When the fourth parasitic capacitor C oss4 When the discharge reaches zero, the body diode of the fourth switch tube S4 is turned on. At this time, turning on the fourth switch tube S4 can achieve zero voltage turn-on.

[0109] Reference Fig.15 When the fourth switch tube S4 is turned off, the secondary leakage inductance current i lk The phase lead of the driving signals of the first switch tube S1 and the third switch tube S3 relative to the driving signals of the second switch tube S2 and the fourth switch tube S4 is equal to the dead time of the driving signals of the second switch tube S2 and the fourth switch tube S4, which is the leakage inductance current i lk The freewheeling provides two branches: the first branch includes the first switch tube S1 and the second parasitic capacitor C of the second switch tube S2. oss2 The second branch includes the body diode of the third switch tube S3 and the fourth parasitic capacitor C of the fourth switch tube S4. oss4 , the corresponding branch current direction is as shown in Figure i ZVS12 ,i ZVS34 Therefore, in the dead zone from the fourth switch tube S4 being turned off to the second switch tube S2 being turned on, i ZVS12 ,i ZVS34 The second parasitic capacitance C oss2 Discharge the fourth parasitic capacitor C oss4 When the second parasitic capacitor C oss2 When the discharge reaches zero, the body diode of the second switch tube S2 is turned on. At this time, turning on the second switch tube S2 can achieve zero voltage turn-on.

[0110] In addition, since the phase lead of the driving signals of the first switch tube S1 and the third switch tube S3 relative to the driving signals of the second switch tube S2 and the fourth switch tube S4 is equal to the dead time of the driving signals of the second switch tube S2 and the fourth switch tube S4, before the second switch tube S2 is turned off, the first switch tube S1 has been turned off in advance for a dead time, and the current is turned on by the body diode of the first switch tube S1; before the fourth switch tube S4 is turned off, the third switch tube S3 has been turned off in advance for a dead time, and the current is turned on by the body diode of the third switch tube S3. Since the turn-on current is small and the dead time is short at this time, the phase lead of the driving signal of the second group of switch elements relative to the driving signal in the first group of switch elements brings very little additional body diode turn-on loss. In addition, when the grid voltage is negative, the first switch tube S1 and the third switch tube S3 do not withstand the withstand voltage when they are turned off, so there is no hard switch when the first switch tube S1 and the third switch tube S3 are switched, thereby ensuring the soft switching characteristics of all switch tubes.

[0111] The phase lead of the drive signal of the second group of switch elements relative to the drive signal of the first group of switch elements is greater than the dead time of the drive signal of the first group of switch elements, indicating that the fourth switch tube S4 has been turned on before the dead time from the turn-off of the first switch tube S1 to the turn-on of the third switch tube S3 begins, and the second switch tube S2 has been turned on before the dead time from the turn-off of the third switch tube S3 to the turn-on of the first switch tube S1 begins, providing a time margin for the second switch tube S2 and the fourth switch tube S4 to provide a freewheeling path for the leakage inductance current within the dead time of the drive signal of the first switch tube S1 and the third switch tube S3.

[0112] Figure 5 and Figure 6 The corresponding freewheeling path in the dead zone and the soft switch implementation principle in the topological structure of the cycloconversion circuit shown in the figure are Figure 1 The topological structure of the cycloconversion circuit shown is the same and will not be repeated here.

[0113] In some embodiments, the zero-crossing detection stage includes a positive voltage stage and a negative voltage stage, and the grouping relationship of the switching elements in the positive voltage stage and the negative voltage stage is opposite. The grouping relationship of the switching elements is the corresponding relationship between the first group of switching elements and the second group of switching elements and each switching element in the frequency conversion circuit.

[0114] exist Figure 1 In the topological structure of the cycloconversion circuit shown, when the output side of the cycloconversion circuit is a positive voltage, the first group of switch elements refers to the first switch tube S1 and the third switch tube S3, and the second group of switch elements refers to the second switch tube S2 and the fourth switch tube S4; when the output side of the cycloconversion circuit is a negative voltage, the first group of switch elements refers to the second switch tube S2 and the fourth switch tube S4, and the second group of switch elements refers to the first switch tube S1 and the third switch tube S3.

[0115] Figure 5 In the topological structure of the cycloconversion circuit shown in FIG. 1 , the grouping relationship of each group of switch elements when the voltage is positive polarity is the same as the grouping relationship when the voltage is negative polarity. Figure 1 The topological structure of the cycloconversion circuit shown is the same and will not be repeated here.

[0116] exist Figure 6 In the topological structure of the cycloconversion circuit shown, when the output side of the cycloconversion circuit is a positive voltage, the first group of switch elements refers to the ninth switch tube S9 and the eleventh switch tube S11, and the second group of switch elements refers to the tenth switch tube S10 and the twelfth switch tube S12; when the output side of the cycloconversion circuit is a negative voltage, the first group of switch elements refers to the tenth switch tube S10 and the twelfth switch tube S12, and the second group of switch elements refers to the ninth switch tube S9 and the eleventh switch tube S11.

[0117] An embodiment of the present application provides an isolated converter. The isolated converter includes a transformer T and the aforementioned cycloconversion circuit. The cycloconversion circuit is electrically connected to a first side of the transformer T.

[0118] The first side of the transformer T may be a side where the secondary winding of the transformer T is located, and the cycloconversion circuit may be electrically connected to the secondary winding of the transformer T.

[0119] The specific structure and principle of the frequency conversion circuit can refer to the above-mentioned embodiment and will not be described in detail here.

[0120] According to the isolated converter of the present application, when the cycloconversion circuit is in the zero-crossing detection stage, the first target switching element in the second group of switching elements is turned on within the dead time of the driving signal of the first group of switching elements, thereby providing a freewheeling circuit for the switching elements of the first group of switching elements that are turned on after the dead time, releasing the leakage inductance current, reducing the voltage overstress risk of the switching tube, and making it easier to meet the soft switching conditions of zero voltage turn-on.

[0121] Although the embodiments of the present application have been shown and described, those skilled in the art will appreciate that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present application, and that the scope of the present application is defined by the claims and their equivalents.

Claims

1. A control method for a cycloconversion circuit, characterized in that: The cycloconversion circuit is configured to realize AC-AC conversion and includes a plurality of switch elements connected to form a plurality of current paths, wherein the plurality of switch elements are divided into a plurality of groups of switch elements, each group of switch elements including at least one switch element arranged on each current path; The control method comprises: When the cycloconversion circuit is in the zero-crossing detection stage, the first group of switch elements are controlled to be turned on in a complementary manner, and the second group of switch elements are controlled to be turned on in a complementary manner; Wherein, during the dead time of the driving signal of the first group of switch elements, the first target switch element in the second group of switch elements is turned on, and remains turned on at least until the dead time ends, and the first target switch element is a switch element located on the same current path as the switch element in the first group of switch elements that is turned on after the dead time; During the zero-crossing detection stage, the drive signals of the first group of switch elements and the second group of switch elements are both pulse signals, the drive signals of the second group of switch elements are phase-advanced relative to the drive signals of the first group of switch elements, and the phase lead amount of the drive signals of the second group of switch elements relative to the drive signals of the first group of switch elements is greater than or equal to the dead time of the drive signals of the first group of switch elements.

2. The control method of the cycloconversion circuit according to claim 1, characterized in that: The driving signals of the second group of switch elements have the same duty cycle and / or the same period as the driving signals of the first group of switch elements.

3. The control method of the cycloconversion circuit according to claim 1 or 2, characterized in that: The control method further comprises: Obtaining the voltage at the output side of the frequency conversion circuit; Determining the first group of switch elements and the second group of switch elements from each group of switch elements of the cycloconversion circuit according to the positive and negative polarities of the voltage; Wherein, the grouping relationship of the switch elements in each group when the voltage is positive polarity is opposite to the grouping relationship when the voltage is negative polarity.

4. The control method of the cycloconversion circuit according to claim 3, characterized in that: After obtaining the voltage at the output side of the frequency conversion circuit, the method further includes: When the absolute value of the voltage is less than or equal to the first voltage threshold, it is determined that the cyclotron conversion circuit enters the zero-crossing detection phase.

5. An isolated converter, characterized in that: The invention comprises a transformer, a control unit and a cycloconversion circuit connected to a first side of the transformer, wherein the control unit is connected to the cycloconversion circuit and is configured to execute a control method for a cycloconversion circuit according to any one of claims 1 to 4.

6. A frequency conversion circuit, characterized in that: The cyclotron conversion circuit includes a first group of switch elements and a second group of switch elements. During the zero-crossing detection stage, the first group of switch elements are complementarily turned on, the second group of switch elements are complementarily turned on, and the drive signals of the second group of switch elements are phase-leading relative to the drive signals of the first group of switch elements; wherein the phase lead of the drive signals of the second group of switch elements relative to the drive signals in the first group of switch elements is greater than or equal to the dead time of the drive signals of the first group of switch elements.

7. The frequency conversion circuit according to claim 6, characterized in that: The zero-crossing detection stage includes a positive voltage stage and a negative voltage stage. The grouping relationship of the switching elements in the positive voltage stage and the negative voltage stage is opposite. The grouping relationship of the switching elements is the corresponding relationship between the first group of switching elements and the second group of switching elements and each switching element in the cycloidal conversion circuit.

8. An isolated converter, characterized in that: It comprises a transformer and a frequency conversion circuit according to claim 6 or 7, wherein the frequency conversion circuit is electrically connected to the first side of the transformer.

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