Converter control method and converter

Abstract

The invention relates to a converter control method and a converter, the converter comprises a cyclic wave conversion circuit used for AC-AC conversion, the cyclic wave conversion circuit comprises a plurality of groups of switch elements, and each group of switch elements comprises at least two reversely connected switch elements. The method comprises the following steps: controlling two corresponding groups of switch elements in the plurality of groups of switch elements to be complementarily conducted, and after one group of switch elements in the two groups of switch elements which are complementarily conducted is disconnected, controlling the switch elements for follow current in the other group of switch elements to be conducted later than the other switch elements in the other group of switch elements, the problem of turn-on loss and high-frequency noise caused by hard turn-on of a bidirectional switching tube in the prior art is solved.

Description

Technical Field

[0001] The present application relates to the field of power electronics, and in particular to a control method of a converter and a converter. Background Art

[0002] The isolated DC / AC conversion circuit based on the cycloconverter can reduce the number of circuit levels and only use one-stage structure to realize the power conversion from DC low voltage to AC voltage, which can reduce the complexity of the circuit and is widely used in the field of photovoltaic power generation. The cycloconverter uses bidirectional switching tubes to realize the chopping operation of the bridge arm voltage under different polarities. During the switching process of the bridge arm voltage polarity, the bidirectional switching tubes of the upper and lower bridge arms need to switch the working mode. Once the bridge arm voltage polarity is inconsistent with the working mode of the bidirectional switching tube, it will cause the bridge arm to short-circuit, the device will fail due to overcurrent, and cause the cycloconverter to fail.

[0003] The related technology provides a commutation control scheme of simultaneous opening and closing, that is, the bidirectional switch tubes of the same bridge arm are opened and closed at the same time. This control scheme can disconnect the short-circuit loop by turning off the bidirectional switch tube, avoiding the short-circuit risk during the bridge arm voltage polarity switching process. However, this technical solution causes the bidirectional switch tube to be hard-opened, generating opening loss and high-frequency noise, which seriously affects the efficiency and electromagnetic interference performance of the converter. Summary of the invention

[0004] The present application provides a control method of a converter and a converter to solve the problem of turn-on loss caused by hard turn-on of a bidirectional switch tube existing in the related art.

[0005] In a first aspect, a control method of a converter is provided in this embodiment, wherein the converter includes a cycloconversion circuit for AC-AC conversion, the cycloconversion circuit includes a plurality of groups of switch elements, each group of switch elements includes at least two reversely connected switch elements, and the method includes:

[0006] Corresponding two groups of switch elements among the multiple groups of switch elements are controlled to be complementary turned on, wherein, after one group of switch elements among the two groups of switch elements that are complementary turned on is turned off, the switch elements for freewheeling in another group of switch elements are controlled to be turned on later than other switch elements in the another group of switch elements.

[0007] In some embodiments, controlling the switch element for freewheeling in another group of switch elements to be turned on later than other switch elements in the another group of switch elements comprises:

[0008] A switch element for freewheeling in another group of switch elements is controlled to be turned on after a first dead time, and other switch elements in the another group of switch elements are controlled to be turned on after a second dead time, wherein the first dead time is greater than the second dead time.

[0009] In some of the embodiments, the switch element for freewheeling is determined based on the polarity of the current flowing to the connection point of the two groups of switch elements.

[0010] In some embodiments, the first group of switch elements in the two groups of switch elements includes a first switch element and a second switch element, the second group of switch elements includes a third switch element and a fourth switch element, each switch element is connected to the output end of the cycloconversion circuit, the second switch element is reversely connected to the third switch element, and after one switch element in the two groups of switch elements that are complementary turned on is turned off, controlling the switch element for freewheeling in the other group of switch elements to be turned on later than other switch elements in the other group of switch elements comprises:

[0011] After the second group of switch elements are disconnected, when the current is positive polarity, the first switch element for freewheeling is controlled to be turned on later than the second switch element; when the current is negative polarity, the second switch element for freewheeling is controlled to be turned on later than the first switch element;

[0012] After the first group of switch elements are disconnected, when the current is positive polarity, the fourth switch element for freewheeling is controlled to be turned on later than the third switch element; when the current is negative polarity, the third switch element for freewheeling is controlled to be turned on later than the fourth switch element.

[0013] In some embodiments, the duration of the first dead time is set to meet the zero voltage turn-on of the switch element for freewheeling.

[0014] In some embodiments, controlling corresponding two groups of switch elements among the plurality of groups of switch elements to be complementary turned on comprises:

[0015] When the AC voltage at the output end of the converter is within a preset voltage threshold range, corresponding two groups of switch elements in the multiple groups of switch elements are controlled to be complementary turned on, and the voltage threshold range includes a voltage zero crossing point.

[0016] In some embodiments, controlling corresponding two groups of switch elements among the plurality of groups of switch elements to be complementary turned on comprises:

[0017] In each power frequency cycle of the AC voltage at the output end of the converter, corresponding two groups of switch elements among the multiple groups of switch elements are controlled to be complementary and turned on.

[0018] In a second aspect, a converter is provided in this embodiment, including a controller and a cycloconversion circuit for AC-AC conversion, wherein the controller is used to control the switching elements in the cycloconversion circuit based on the control method of the converter described in the first aspect.

[0019] In some of the embodiments, the converter further comprises a resonant circuit connected to the cycloconversion circuit, and an inverter circuit connected to the resonant circuit;

[0020] The converter is used to realize power conversion from direct current to alternating current or from alternating current to direct current.

[0021] In some of the embodiments, the converter further includes a transformer connected between the cycloconversion circuit and the inverter circuit.

[0022] Compared with the related art, the control method of the converter provided in the present application controls the corresponding two groups of switch elements in the multiple groups of switch elements in the cycloidal conversion circuit to be complementary turned on, wherein after one group of switch elements in the two groups of switch elements that are complementary turned on is disconnected, the switch elements for freewheeling in the other group of switch elements are controlled to be turned on later than the other switch elements in the other group of switch elements, thereby avoiding the short circuit of the cycloidal conversion circuit caused by the switching of the polarity of the AC voltage, and at the same time avoiding the hard turning-on of the bidirectional switch tube, reducing the turning-on loss and high-frequency noise generated by the hard turning-on of the bidirectional switch tube, and improving the electromagnetic interference performance of the converter.

[0023] Details of one or more embodiments of the present application are set forth in the following drawings and description to make other features, objects, and advantages of the present application more readily apparent. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0025] Figure 1 is a circuit topology diagram of a cycloconversion circuit of some embodiments of the present application;

[0026] Figure 2 is a schematic diagram of the structure of a converter in some embodiments of the present application;

[0027] Figure 3 is a schematic diagram of the structure of a converter of other embodiments of the present application;

[0028] Figure 4 is a schematic diagram of a circuit topology of a converter in some embodiments of the present application;

[0029] Figure 5 is a switching timing diagram of two groups of switching elements when the bridge arm voltage is positive in some embodiments of the present application;

[0030] Figure 6 It is a schematic diagram of the operation of the cycloconversion circuit in each stage when the bridge arm voltage of some embodiments of the present application is positive and current is commutated from the lower bridge arm to the upper bridge arm;

[0031] Figure 7 It is a schematic diagram of the operation of the cycloconversion circuit in each stage when the bridge arm voltage is positive and current is commutated from the upper bridge arm to the lower bridge arm in some embodiments of the present application;

[0032] Figure 8 is a switching timing diagram of two groups of switch elements when the bridge arm voltage is negative in some embodiments of the present application;

[0033] Fig. 9 It is a schematic diagram of the operation of the cycloconversion circuit at each stage when the bridge arm voltage of some embodiments of the present application is negative and current is commutated from the lower bridge arm to the upper bridge arm;

[0034] Fig.10 It is a schematic diagram of the operation of the cycloconversion circuit at each stage when the bridge arm voltage of some embodiments of the present application is negative and current is commutated from the upper bridge arm to the lower bridge arm;

[0035] Fig.11 is a schematic diagram of circuit topology of converters of other embodiments of the present application;

[0036] Fig.12 is a circuit topology diagram of a converter of some other embodiments of the present application;

[0037] Fig.13 is a circuit topology diagram of a converter of some other embodiments of the present application;

[0038] Fig.14 Schematic diagram of circuit topology of converters according to some other embodiments of the present application. DETAILED DESCRIPTION

[0039] In order to more clearly understand the purpose, technical solutions and advantages of the present application, the present application is described and illustrated below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0040] Unless otherwise defined, the technical terms or scientific terms involved in this application shall have the general meaning understood by people with ordinary skills in the technical field to which this application belongs. The words "one", "a", "a", "the", "these" and the like in this application do not represent quantitative restrictions, and they can be singular or plural. The terms "include", "comprise", "have" and any variants thereof involved in this application are intended to cover non-exclusive inclusions; for example, a process, method and system, product or device comprising a series of steps or modules (units) is not limited to the listed steps or modules (units), but may include unlisted steps or modules (units), or may include other steps or modules (units) inherent to these processes, methods, products or devices. The words "connect", "connected", "coupled" and the like involved in this application are not limited to physical or mechanical connections, but may include electrical connections, whether directly or indirectly. The "multiple" involved in this application refers to two or more. "And / or" describes the association relationship of associated objects, indicating that there can be three relationships. For example, "A and / or B" can mean: A exists alone, A and B exist at the same time, and B exists alone. Usually, the character " / " indicates that the objects associated with each other are in an "or" relationship. The terms "first", "second", "third", etc. involved in this application are only used to distinguish similar objects and do not represent a specific ordering of the objects.

[0041] The control method of the converter provided in the embodiment of the present application can be executed in the controller of the converter. The converter includes a controller and a cycloconversion circuit 102 for AC-AC conversion. Figure 1 Schematic diagram of the circuit topology of the frequency conversion circuit of some embodiments of the present application. Figure 1 As shown, the frequency conversion circuit 102 includes a plurality of switch elements 1021 ( Figure 1 Each group of switch elements 1021 includes at least two reversely connected switch elements Qa and Qb. The switch element Qa includes a body diode and a junction capacitor Ca connected in parallel between the drain and the source. The switch element Qb includes a body diode and a junction capacitor Cb connected in parallel between the drain and the source. It can be understood by those skilled in the art that Figure 1 The structure shown is only for illustration and does not limit the structure of the above-mentioned frequency conversion circuit. Figure 1 As shown in FIG. 1 , more groups of switch elements are shown, each group may also include more switch elements, or the connection relationship between the multiple groups of switch elements is the same as Figure 1 different( Figure 1 The two groups of switch elements 1021 are connected in series with each other).

[0042] In a further embodiment, Figure 2Schematic diagram of the structure of the converter of some embodiments of the present application. Figure 2 As shown, the converter also includes a resonant circuit 106 connected to the frequency conversion circuit 102, and an inverter circuit 101 connected to the resonant circuit 106. The converter can achieve power conversion from DC to AC or from AC to DC. Further, the converter also includes a controller (not shown in the figure) for controlling the switching elements in the frequency conversion circuit 102 and the inverter circuit 101 to achieve power conversion.

[0043] The controller may be any one of a microcontroller unit (MCU), a central processing unit (CPU), a field programmable gate array (FPGA), and a digital signal processor (DSP). Of course, the specific form of the controller is not limited to the above examples.

[0044] Furthermore, the frequency conversion circuit 102 can be connected to the power grid to provide the output AC power to the power grid, or to obtain AC power from the power grid in reverse. Specifically, when power is transferred from the inverter circuit 101 to the frequency conversion circuit 102, the converter can realize power conversion from DC to AC, and the converter works in the inverter mode; when power is transferred from the frequency conversion circuit 102 to the inverter circuit 101, the converter can realize power conversion from AC to DC, and the converter works in the rectification mode.

[0045] The resonant circuit 106 may be in various circuit forms such as single L, LC, and CLLC.

[0046] In a further embodiment, Figure 3 Schematic diagram of the structure of the converter of some other embodiments of the present application. Figure 3 As shown, the converter further includes a transformer 105 connected between the frequency conversion circuit 102 and the inverter circuit 101. The transformer 105 is used for stepping up and down the voltage, for example, stepping up the output voltage of the inverter circuit 101.

[0047] Furthermore, the converter may further include a filter circuit connected to the frequency conversion circuit 102 .

[0048] In some specific embodiments, Figure 4 Schematic diagram of the circuit topology of the converter in some embodiments of the present application. Figure 4As shown, the converter includes an inverter circuit 101, a transformer 105, a resonant circuit 106, a frequency conversion circuit 102 and a filter circuit 104 connected in sequence, and also includes an input capacitor Cin. Among them, the inverter circuit 101 includes a switch tube Q1H, a switch tube Q1L, a switch tube Q2H, and a switch tube Q2L. Specifically, the switch tube Q1H and the switch tube Q1L are connected in series to form a half bridge arm, and the switch tube Q2H and the switch tube Q2L are connected in series to form the other half bridge arm. The midpoints of the two half bridge arms are respectively connected to the two ends of the primary winding of the transformer 105. The primary side voltage of the transformer 105 is v x .

[0049] The frequency conversion circuit 102 is composed of two groups of switch elements connected in series in a common source connection mode. Specifically, the two groups of switch elements are connected in series to form a bridge arm. The first group of switch elements in the two groups of switch elements includes switch tubes Q3 and Q4 connected in common source, and the second group of switch elements includes switch tubes Q5 and Q6 connected in common source. The connection point of the two groups of switch elements is the midpoint of the bridge arm. The frequency conversion circuit 102 is connected to the AC side power grid through the filter circuit 104. The filter circuit 104 includes a capacitor C connected in parallel with both ends of the frequency conversion circuit 102. f and an inductor L connected to the first connection terminal of the frequency conversion circuit 102 f At the same time, the second connection end of the frequency conversion circuit 102 is connected to one end of the secondary winding of the transformer 105, and the other end of the secondary winding of the transformer 105 is connected to the midpoint of the bridge arm of the frequency conversion circuit 102 through the resonant circuit 106. The resonant circuit 106 includes an inductor Lr and a capacitor Cr connected in series. The voltage across the capacitor Cr is the bridge arm voltage V cf .

[0050] It can be understood that the type of switch tube in the present application is described by taking MOS tube as an example, but is not limited to this, and can also be other types of semiconductor switch devices such as IGBT.

[0051] Figure 4 In the embodiment, the bidirectional switch tubes Q3 and Q4 constitute the upper bridge arm of the frequency conversion circuit 102, and the bidirectional switch tubes Q5 and Q6 constitute the lower bridge arm. Each switch tube realizes the bridge arm voltage V cf Chopping operation under different polarities. cf During the polarity switching process, the bidirectional switch tubes of the upper and lower bridge arms need to switch the working mode.

[0052] In this embodiment, a control method of a converter is provided, which can be applied to the frequency conversion circuit of the above converter. The method includes:

[0053] Two corresponding groups of switch elements in a plurality of groups of switch elements are controlled to be complementary turned on, wherein after one group of switch elements in the two complementary turned-on groups of switch elements is turned off, a switch element for freewheeling in another group of switch elements is controlled to be turned on later than other switch elements in the another group of switch elements.

[0054] The frequency conversion circuit can be used to achieve the frequency conversion of AC power, for example, it can be used to convert high-frequency AC power into industrial frequency AC power. Figure 4 As shown, the corresponding two groups of switch elements can be a first group of switch elements and a second group of switch elements connected in series. Complementary conduction means that in a switching cycle, when one of the corresponding two groups of switch elements is turned on, the other group of switch elements is turned off; when one group of switch elements is turned off, the other group of switch elements is turned on. Wherein, when one group of switch elements is turned off, it means that all switch elements in the group are turned off at the same time; when one group of switch elements is turned on, it means that all switch elements in the group are turned on after the other group of switch elements is turned off.

[0055] Each group of switch elements includes at least two switch elements connected in reverse, one of which is a switch element for freewheeling. The switch element for freewheeling refers to a switch element whose body diode has the same forward conduction direction as the direction of the current flowing through the bridge arm.

[0056] When one group of the two groups of switch elements that are complementarily conducted is disconnected, the other switch elements in the other group of switch elements except the switch element used for freewheeling are controlled to be turned on first. The switch element that is turned on first can constitute a discharge path for the junction capacitance of the switch element used for freewheeling, so that the voltage across the junction capacitance of the switch element used for freewheeling decreases, thereby reducing the VDS (i.e., the voltage between the drain and source of the switch tube) of the switch element used for freewheeling to 0. At this time, the switch element used for freewheeling is controlled to be turned on, so that the zero voltage turn-on of the switch element can be achieved.

[0057] The control method of the converter of the present embodiment controls corresponding two groups of switch elements in a plurality of groups of switch elements in a frequency conversion circuit to be complementary turned on; wherein after one group of switch elements in the two groups of switch elements that are complementary turned on is disconnected, the switch elements for freewheeling in the other group of switch elements are controlled to be turned on later than other switch elements in the other group of switch elements, so that the voltage drop across the junction capacitance of the switch elements for freewheeling is 0, thereby realizing zero voltage turn-on of the switch elements for freewheeling, avoiding hard turn-on of the switch elements, solving the problem of turn-on loss and high-frequency noise caused by hard turn-on of the bidirectional switch tube, and improving the electromagnetic interference performance of the converter.

[0058] In some embodiments, controlling the switch element for freewheeling in another group of switch elements to be turned on later than other switch elements in another group of switch elements comprises:

[0059] The switch element for freewheeling in another group of switch elements is controlled to be turned on after a first dead time, and the other switch elements in another group of switch elements are controlled to be turned on after a second dead time, wherein the first dead time is greater than the second dead time.

[0060] The first dead time refers to the time required from the disconnection of one group of switch elements to the turn-on of the switch elements for freewheeling in another group of switch elements, and its duration can be set to meet the zero voltage turn-on of the switch elements for freewheeling. The second dead time refers to the time required from the disconnection of one group of switch elements to the turn-on of other switch elements (non-freewheeling switch elements) in another group of switch elements, and its duration can be set to meet the VDS of other switch elements (non-freewheeling switch elements) Small enough to avoid hard turn-on. In a specific embodiment, for a frequency conversion circuit with an operating frequency of hundreds of kHz, the first dead time can be hundreds of ns, and the second dead time can be tens of ns.

[0061] The control method of the converter of this embodiment, through the setting of the first dead time and the second dead time, ensures that the switch elements used for freewheeling in another group of switch elements and other switch elements do not have the problem of hard turning on, and the freewheeling switch elements achieve zero voltage conduction, further avoiding the turn-on loss and high-frequency noise caused by the hard turning on of the bidirectional switch tube, thereby improving the electromagnetic interference performance of the converter.

[0062] In some embodiments, it also involves how to determine a switch element for freewheeling in another group of switch elements. The method includes:

[0063] The switching element used for freewheeling is determined based on the polarity of the current flowing to the connection point of the two groups of switching elements.

[0064] In some embodiments, the first group of switch elements in the two groups of switch elements includes a first switch element and a second switch element, the second group of switch elements includes a third switch element and a fourth switch element, each switch element is sequentially connected to the output end of the cycloconverter, the second switch element is reversely connected to the third switch element, and after one switch element in the two groups of switch elements that are complementary turned on is turned off, controlling the switch element for freewheeling in the other group of switch elements to be turned on later than the other switch elements in the group includes:

[0065] After the second group of switch elements are disconnected, when the current is positive polarity, the first switch element for freewheeling is controlled to be turned on later than the second switch element; when the current is negative polarity, the second switch element for freewheeling is controlled to be turned on later than the first switch element;

[0066] After the first group of switch elements are disconnected, when the current is positive polarity, the fourth switch element for freewheeling is controlled to be turned on later than the third switch element; when the current is negative polarity, the third switch element for freewheeling is controlled to be turned on later than the fourth switch element.

[0067] Specifically, in Figure 4 In the embodiment shown, the current flowing to the connection point of the two groups of switch elements may be the resonant current i rs . Taking the direction indicated by the arrow in the figure as the reference positive direction, when the resonant current i rs When the flow direction is consistent with the arrow direction, the resonant current i rs The polarity is positive, when the resonant current i rs When the flow direction is opposite to the arrow direction, the resonant current i rs The polarity is negative.

[0068] After the second set of switching elements is turned off, when the resonant current i rs When the polarity is positive, the switch tube Q3 used for freewheeling is turned on later than the switch tube Q4; when the resonant current i rs When the polarity is negative, the switch tube Q4 used for freewheeling is controlled to be turned on later than the switch tube Q3;

[0069] After the first set of switching elements is turned off, when the resonant current i rs When the polarity is positive, the switch tube Q6 used for freewheeling is turned on later than the switch tube Q5; when the resonant current i rs When the polarity is negative, the switch tube Q5 used for freewheeling is controlled to be turned on later than the switch tube Q6.

[0070] The working principle of this application will be described in detail below with reference to the accompanying drawings. Figure 5 is a switching timing diagram of two groups of switch elements when the bridge arm voltage is positive in some embodiments of the present application. Figure 5 As shown, in the inverter mode and rectification mode, the resonant current i rs The typical waveforms are shown in the figure. 1 is the first dead time, T 2 is the second dead time.

[0071] When the resonant current i rs When the bidirectional switch tubes Q5 and Q6 of the lower bridge arm are commutated to the bidirectional switch tubes Q3 and Q4 of the upper bridge arm, the resonant current i of the inverter mode and the rectifier mode rs The switch tube Q4 is a non-freewheeling tube, and the switch tube Q3 is a freewheeling tube. After the second dead time T 2 After the switch tube Q3 is turned on, the first dead time T 1 After opening; if the resonant current i rsis less than zero (i.e. negative polarity), the switch tube Q3 is a non-freewheeling tube, the switch tube Q4 is a freewheeling tube, and the switch tube Q3 passes through the second dead time T 2 After that, the switch tube Q4 is turned on, and after the first dead time T 1 Opened later.

[0072] Figure 6 The schematic diagram of the operation of the cycloconversion circuit in each stage when the bridge arm voltage of some embodiments of the present application is positive and the current is commutated from the lower bridge arm to the upper bridge arm. When commutating, the resonant current i rs For example, if it is greater than 0, Figure 6 As shown, t 0 -t 1 In the stage, the switch tubes Q5 and Q6 are turned off, and the resonant current i rs The parallel capacitor of the switch tube Q3 is discharged through the body diode of the switch tube Q6, and the parallel capacitors of the switch tubes Q4 and Q5 are charged; t 1 -t 2 In the stage, the switch tube Q4 is turned on, and the resonant current i rs Through the body diode of switch tube Q6 and switch tube Q4, the parallel capacitor of switch tube Q3 is discharged and the parallel capacitor of switch tube Q5 is charged; t 2 -t 3 In the stage, the parallel capacitor of the switch tube Q3 is discharged to zero, and the parallel capacitor of the switch tube Q5 is charged to the bridge arm voltage V cf , resonant current i rs Through the body diodes of switch tube Q4 and switch tube Q3; t 3 -t 4 In the stage, the switch tube Q3 is turned on with zero voltage, and the resonant current i rs Through the switch tube Q4 and the switch tube Q3.

[0073] When the resonant current i rs When the bidirectional switch tubes Q3 and Q4 of the upper bridge arm are commutated to the bidirectional switch tubes Q5 and Q6 of the lower bridge arm, the resonant current i of the inverter mode and the rectifier mode is rs The switch tube Q6 is a non-freewheeling tube, and the switch tube Q5 is a freewheeling tube. After the second dead time T 2 After opening, Q5 passes the first dead time T 1 After opening; if the resonant current i rs is greater than zero (i.e. positive polarity), the switch tube Q5 is a non-freewheeling tube, the switch tube Q6 is a freewheeling tube, and the switch tube Q5 passes through the second dead time T 2 After the first dead time T 1 Opened later.

[0074] Figure 7The schematic diagram of the operation of the cycloconversion circuit in each stage when the bridge arm voltage of some embodiments of the present application is positive and the current is commutated from the upper bridge arm to the lower bridge arm. When commutating, the resonant current i rs Less than 0, for example, Figure 7 As shown, t 4 -t 5 In the stage, the switch tubes Q3 and Q4 are turned off, and the resonant current i rs The parallel capacitor of the switch tube Q5 is discharged through the body diode of the switch tube Q4, and the parallel capacitors of the switch tubes Q3 and Q6 are charged; t 5 -t 6 In the stage, the switch tube Q6 is turned on, and the resonant current i rs Through the body diode of switch tube Q4 and switch tube Q6, the parallel capacitor of switch tube Q5 is discharged and the parallel capacitor of switch tube Q3 is charged; t 6 -t 7 In the stage, the parallel capacitor of the switch tube Q5 is discharged to zero, and the parallel capacitor of the switch tube Q3 is charged to the bridge arm voltage V cf , resonant current i rs Through the body diodes of switch tube Q6 and switch tube Q5; t 7 -t 8 In the stage, the switch tube Q5 is turned on with zero voltage, and the resonant current i rs Through switch tube Q6 and switch tube Q5.

[0075] Figure 8 is a switching timing diagram of two groups of switch elements when the bridge arm voltage is negative in some embodiments of the present application. Figure 8 As shown, in the inverter mode and rectification mode, the resonant current i rs The typical waveforms are shown in the figure.

[0076] When the resonant current i rs When the bidirectional switches Q5 and Q6 of the lower bridge arm commutate to the bidirectional switches Q3 and Q4 of the upper bridge arm, the resonant currents in the inverter mode and the rectifier mode are both less than zero, the switch Q3 is a non-freewheeling tube, the switch Q4 is a freewheeling tube, and the switch Q3 passes through the first dead time T 1 After that, the switch tube Q4 is turned on, and after the second dead time T 2 After opening; if the resonant current i rs If it is greater than zero, the switch tube Q4 is a non-freewheeling tube, the switch tube Q3 is a freewheeling tube, and the switch tube Q4 passes through the first dead time T 1 After that, the switch tube Q3 is turned on, and after the second dead time T 2 Opened later.

[0077] Fig. 9The schematic diagram of the operation of the cycloconversion circuit in each stage when the bridge arm voltage of some embodiments of the present application is negative and the current is commutated from the lower bridge arm to the upper bridge arm. When commutating, the resonant current i rs Less than 0, for example, Fig. 9 As shown, t 0 -t 1 In the stage, the switch tubes Q5 and Q6 are turned off, and the resonant current i rs The parallel capacitor of the switch tube Q4 is discharged through the body diode of the switch tube Q5, and the parallel capacitors of the switch tubes Q3 and Q6 are charged; t 1 -t 2 In the stage, the switch tube Q3 is turned on, and the resonant current i rs Through the body diode of switch tube Q5 and switch tube Q3, the parallel capacitor of switch tube Q4 is discharged and the parallel capacitor of switch tube Q6 is charged; t 2 -t 3 In the stage, the parallel capacitor of switch tube Q4 is discharged to zero, and the parallel capacitor of switch tube Q6 is charged to -V cf , resonant current i rs Through the body diodes of switch tube Q3 and switch tube Q4; t 3 -t 4 In the stage, the switch tube Q4 is turned on with zero voltage, and the resonant current i rs Through the switch tube Q4 and the switch tube Q3.

[0078] When the resonant current i rs When the bidirectional switches Q3 and Q4 of the upper bridge arm commutate to the bidirectional switches Q5 and Q6 of the lower bridge arm, the resonant currents in the inverter mode and the rectifier mode are both greater than zero, the switch Q5 is a non-freewheeling tube, the switch Q6 is a freewheeling tube, and the switch Q5 passes the second dead time T 2 After the first dead time T 1 After opening; if the resonant current i rs is less than zero, the switch tube Q6 is a non-freewheeling tube, the switch tube Q5 is a freewheeling tube, and the switch tube Q6 passes through the second dead time T 2 After the switch Q5 is turned on, the switch Q5 passes through the first dead time T 1 Opened later.

[0079] Fig.10 The schematic diagram of the operation of the cycloconversion circuit in each stage when the bridge arm voltage of some embodiments of the present application is negative and the current is commutated from the upper bridge arm to the lower bridge arm. When commutating, the resonant current i rs For example, if it is greater than 0, Fig.10 As shown, t 4 -t 5 In the stage, the switch tubes Q3 and Q4 are turned off, and the resonant current i rsThe parallel capacitor of the switch tube Q6 is discharged through the body diode of the switch tube Q3, and the parallel capacitors of the switch tubes Q4 and Q5 are charged; t 5 -t 6 In the stage, the switch tube Q5 is turned on, and the resonant current i rs Through the body diode of switch tube Q3 and switch tube Q5, the parallel capacitor of switch tube Q6 is discharged and the parallel capacitor of switch tube Q4 is charged; t 6 -t 7 In the stage, the parallel capacitor of the switch tube Q6 is discharged to zero, and the parallel capacitor of the switch tube Q4 is charged to -V cf , resonant current i rs Through the body diodes of switch tubes Q5 and Q6; t 7 -t 8 In the stage, the switch tube Q6 is turned on with zero voltage, and the resonant current i rs Through switch tube Q6 and switch tube Q5.

[0080] In some embodiments, the implementation conditions for controlling corresponding two groups of switch elements in the plurality of groups of switch elements to be complementary conductive include:

[0081] When the AC voltage at the output end of the converter is within a preset voltage threshold range, corresponding two groups of switch elements in the plurality of switch elements are controlled to be complementary turned on, and the voltage threshold range includes a voltage zero crossing point.

[0082] When the AC voltage at the output end of the converter passes through the zero point, if the positive and negative half-cycle driving logic of the cycloconversion circuit is not switched in time, there will be a short circuit risk between the output ends of the cycloconversion circuit. In this embodiment, when the AC voltage at the output end of the converter is within a preset voltage threshold range, corresponding two groups of switch elements in the multiple groups of switch elements are controlled to be complementary and turned on, wherein the voltage threshold range includes the voltage zero point, thereby avoiding the short circuit risk of the cycloconversion circuit.

[0083] When the AC voltage at the output end of the converter is within a preset voltage threshold range, corresponding two groups of switch elements in the plurality of groups of switch elements are controlled to perform high-frequency switching actions.

[0084] When the output end of the converter is connected to the grid, the AC voltage at the output end of the converter is the grid voltage.

[0085] The voltage threshold range may be set according to actual needs, and specifically may be a range between two positive and negative thresholds near the voltage zero crossing point. Usually, the absolute values ​​of the two thresholds are the same.

[0086] In some embodiments, when the AC voltage at the output of the converter is outside the preset voltage threshold range, the two groups of switch elements can be controlled based on the positive half cycle and the negative half cycle of the AC voltage. When the AC voltage is in the positive half cycle or the negative half cycle and is not within the threshold range, one switch element in each group of switch elements is controlled to be in a normally on state, and the other switch element performs a high-frequency switching action.

[0087] Specifically, for Figure 4 In the cyclic conversion circuit shown, when the AC voltage at the output of the converter is in the positive half cycle and outside the preset voltage threshold range, the positive half cycle driving logic is adopted, the switch tube Q4 and the switch tube Q6 remain in the normally on state, and the switch tube Q3 and the switch tube Q5 work complementary with a duty cycle of 50%, for example. When the AC voltage at the output of the converter is in the negative half cycle and outside the preset voltage threshold range, the negative half cycle driving logic is adopted, that is, the switch tube Q3 and the switch tube Q5 remain in the normally on state, and the switch tube Q4 and the switch tube Q6 work complementary with a duty cycle of 50%. The cyclic conversion circuit is controlled by the above driving logic to realize AC-AC conversion.

[0088] In other embodiments, corresponding two groups of switch elements in the plurality of switch elements are controlled to be complementary turned on in each power frequency cycle of the AC voltage at the output end of the converter. That is, regardless of whether the AC voltage at the output end of the converter is within the preset voltage threshold range, corresponding two groups of switch elements in the plurality of switch elements are controlled to be complementary turned on, without the need to adopt a control method of controlling one switch element in each group of switch elements to be in a normally-on state and the other switch element to perform a high-frequency switching action, which can quickly respond to the rapid and multiple flipping of the polarity of the bridge arm voltage under working conditions such as grid short circuit and lightning surge, and is conducive to fault ride-through.

[0089] In some specific embodiments, Fig.11 Schematic diagram of the circuit topology of the converter of some other embodiments of the present application. Fig.11 As shown, the inverter circuit 101 of the converter is connected in parallel with the capacitor C4, and the inverter circuit 101 includes switch tubes Q7H, Q7L, Q8H, and Q8L; one end of the secondary winding of the transformer 105 is connected to the frequency conversion circuit 102 through the resonant circuit 106, and the resonant unit 106 includes an inductor L3 and a capacitor C5 connected in series; the first group of switch elements of the frequency conversion circuit 102 includes reversely connected switch tubes Q9 and Q12, and the second group of switch elements includes switch tubes Q10 and Q11 connected to a common drain. Figure 4Compared with the embodiment shown in the figure, one end of the secondary winding of the transformer 105 is connected to the connection point of the switch tube Q9 of the first group of switch elements and the switch tube Q10 of the second group of switch elements through the resonant circuit 106, and the other end of the secondary winding of the transformer 105 is connected to the connection point of the switch tube Q11 of the second group of switch elements and the switch tube Q12 of the first group of switch elements. The frequency conversion circuit 102 is connected to the AC side power grid V through the filter circuit 104. g The filter circuit 104 includes a capacitor C6 connected in parallel with the frequency conversion circuit 102 and an inductor L4 connected to the first connection end of the frequency conversion circuit 102 .

[0090] After the second set of switch elements Q10 and Q11 are disconnected, when the current flowing to the connection point of the two sets of switch elements is positive (i.e., the current i rs When the current is in the negative polarity (i.e., the current i rs When the flow direction is opposite to the direction of the arrow), the switch element Q12 used for freewheeling is controlled to be turned on later than the switch element Q9.

[0091] After the first group of switch elements Q9 and Q12 are disconnected, when the current flowing to the connection point of the two groups of switch elements is positive polarity, the switch element Q10 used for freewheeling is controlled to be turned on later than the switch element Q11; when the current is negative polarity, the switch element Q11 used for freewheeling is controlled to be turned on later than the switch element Q10.

[0092] In some specific embodiments, Fig.12 Schematic diagram of the circuit topology of the converter of some other embodiments of the present application. Fig.12 As shown, the inverter circuit 101 of the converter is connected in parallel with the capacitor C7, and the inverter circuit 101 includes a switch tube Q13H, a switch tube Q14L, a switch tube Q15H, and a switch tube Q16L; one end of the secondary winding of the transformer 105 is connected to the frequency conversion circuit 102 through a resonant circuit 106, and the resonant circuit 106 includes an inductor L5 and a capacitor C8 connected in series; and Figure 4 Compared with the embodiment, the first group of switch elements of the frequency conversion circuit 102 includes switch tubes Q18 and Q19 connected with a common source, and the second group of switch elements includes switch tubes Q17 and Q20 connected in reverse series through the first group of switch elements. The drain of the switch tube Q18 is connected to the source of the switch tube Q17, and the drain of the switch tube Q19 is connected to the source of the switch tube Q20. The frequency conversion circuit 102 is connected to the AC side power grid V through the filter circuit 104. g The filter circuit 104 includes a capacitor C9 connected in parallel with the frequency conversion circuit 102 and an inductor L6 connected to the first connection end of the frequency conversion circuit 102 .

[0093] After the second set of switch elements Q17 and Q20 are disconnected, when the current flowing to the connection point of the two sets of switch elements is positive (i.e., the current i rs When the current is in the negative polarity (i.e., the current i rs When the flow direction is opposite to the direction of the arrow), the switch element Q18 used for freewheeling is controlled to be turned on later than the switch element Q19.

[0094] After the first group of switch elements Q18 and Q19 are disconnected, when the current flowing to the connection point of the two groups of switch elements is positive polarity, the switch element Q17 used for freewheeling is controlled to be turned on later than the switch element Q20; when the current is negative polarity, the switch element Q20 used for freewheeling is controlled to be turned on later than the switch element Q17.

[0095] In some specific embodiments, Fig.13 Schematic diagram of the circuit topology of the converter of some other embodiments of the present application. Fig.13 As shown, the inverter circuit 101 of the converter is connected in parallel with the capacitor C14, and the inverter circuit 101 includes a switch tube Q29H, a switch tube Q29L, a switch tube Q30H, and a switch tube Q30L; the frequency conversion circuit 102 includes two groups of switch elements connected in reverse series, and each group of switch elements is connected in series with a capacitor. Specifically, the two groups of switch elements are connected in series between the two connection ends of the frequency conversion circuit 102 to form a bridge arm. The first group of switch elements includes a switch tube Q31 and a switch tube Q32 connected with a common source, and the second group of switch elements includes a switch tube Q33 and a switch tube Q34 connected with a common source. The first group of switch elements and the capacitor C15 are connected to a node and serve as the first connection end of the frequency conversion circuit 102; the second group of switch elements and the capacitor C16 are connected to another node and serve as the second connection end of the frequency conversion circuit 102. One end of the secondary winding of the transformer 105 is connected to the midpoint of the bridge arm of the frequency conversion circuit 102 through the inductor L8. The inductor L8, the capacitor C15 and the capacitor C16 form a resonant circuit 106. The two connection ends of the frequency conversion circuit 102 are connected to the AC side power grid V through the filter circuit 104. g The filter circuit 104 includes a capacitor C17 connected in parallel to two connection terminals of the frequency conversion circuit 102 and an inductor L9 connected to a first connection terminal of the frequency conversion circuit 102 .

[0096] After the second set of switch elements Q33 and Q34 are disconnected, when the current flowing to the connection point of the two sets of switch elements is positive (i.e., the current i rs When the current is in the negative polarity (i.e., the current i rsWhen the flow direction is opposite to the direction of the arrow), the switch element Q31 used for freewheeling is controlled to be turned on later than the switch element Q32.

[0097] After the first group of switch elements Q31 and Q32 are disconnected, when the current flowing to the connection point of the two groups of switch elements is positive polarity, the switch element Q34 used for freewheeling is controlled to be turned on later than the switch element Q33; when the current is negative polarity, the switch element Q33 used for freewheeling is controlled to be turned on later than the switch element Q34.

[0098] In some alternative embodiments, Fig.13 The capacitor C15 and the capacitor C16 in the circuit can be replaced by a group of switch elements connected with a common source.

[0099] In some specific embodiments, Fig.14 Schematic diagram of the circuit topology of the converter of some other embodiments of the present application. Fig.14 As shown, the converter is a three-phase inverter, the inverter circuit 101 of the converter is connected in parallel with a capacitor C10 at the input end, and the inverter unit 101 includes a switch tube Q21H, a switch tube Q21L, a switch tube Q22H, and a switch tube Q22L. The frequency conversion circuit 102 includes three groups of switch elements connected in reverse series, and each group of switch elements is connected in series with a capacitor. Specifically, every two groups of switch elements constitute a bridge arm, and each bridge arm corresponds to one of the three-phase alternating current. The first group of switch elements includes switch tubes Q23 and Q24 connected with a common source, the first group of switch elements and capacitor C11 are connected to node E and serve as the first connection end of the frequency conversion circuit 102; the second group of switch elements includes switch tubes Q25 and Q26 connected with a common source, the second group of switch elements and capacitor C12 are connected to node F and serve as the second connection end of the frequency conversion circuit 102; the third group of switch elements includes switch tubes Q27 and Q28 connected with a common source, the third group of switch elements and capacitor C13 are connected to node G and serve as the third connection end of the frequency conversion circuit 102. One end of the secondary winding of the transformer 105 is connected to the middle point of the bridge arm of the frequency conversion circuit 102 through the inductor L7, and the other end of the secondary winding is connected to the common end of the capacitors C11, C12, and C13.

[0100] Assume that the first group of switch elements and the second group of switch elements are two corresponding groups of switch elements. After the second group of switch elements Q25 and Q26 are disconnected, when the current flowing to the connection point of the two groups of switch elements is positive (i.e., the current i rs When the current is in the negative polarity (i.e., the current i rs The flow direction is opposite to the direction of the arrow), the switch element Q23 used for freewheeling is controlled to be turned on later than the switch element Q24.

[0101] After the first group of switch elements Q23 and Q24 are disconnected, when the current flowing to the connection point of the two groups of switch elements is positive polarity, the switch element Q26 used for freewheeling is controlled to be turned on later than the switch element Q25; when the current is negative polarity, the switch element Q25 used for freewheeling is controlled to be turned on later than the switch element Q26.

[0102] The control method of the third group of switch elements is similar to that of the first group of switch elements and the second group of switch elements, and will not be described in detail here.

[0103] In some alternative embodiments, Fig.14 The capacitors C11, C12, and C13 in the circuit can be replaced by a group of switch elements connected with a common source.

[0104] It should be noted that the specific examples in this embodiment can refer to the examples described in the above embodiments and optional implementation modes, and will not be repeated in this embodiment.

[0105] It should be understood that the specific embodiments described herein are only used to explain the application, rather than to limit it. Based on the embodiments provided in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the protection scope of this application.

[0106] Obviously, the drawings are only some examples or embodiments of the present application. For ordinary technicians in the field, the present application can also be applied to other similar situations based on these drawings without creative work. In addition, it is understandable that although the work done in this development process may be complicated and lengthy, for ordinary technicians in the field, certain changes in design, manufacturing or production based on the technical content disclosed in this application are only conventional technical means and should not be regarded as insufficient content disclosed in this application.

[0107] The term "embodiment" in this application refers to a specific feature, structure or characteristic described in conjunction with the embodiment that can be included in at least one embodiment of the present application. The appearance of this phrase in various locations in the specification does not necessarily mean the same embodiment, nor does it mean that it is mutually exclusive with other embodiments and is independent or optional. It is clearly or implicitly understood by those of ordinary skill in the art that the embodiments described in this application can be combined with other embodiments without conflict.

[0108] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of patent protection. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the scope of protection of the present application. Therefore, the scope of protection of the present application shall be subject to the attached claims.

Claims

1. A control method for a converter, characterized in that: The converter comprises a cycloconversion circuit for AC-AC conversion, the cycloconversion circuit comprises a plurality of groups of switch elements, each group of switch elements comprises at least two reversely connected switch elements, and the method comprises: Corresponding two groups of switch elements among the multiple groups of switch elements are controlled to be complementary turned on, wherein after one group of switch elements among the two groups of switch elements that are complementary turned on is turned off, a switch element for freewheeling in another group of switch elements is controlled to be turned on later than other switch elements in the another group of switch elements.

2. The method according to claim 1, characterized in that The controlling the switch element for freewheeling in another group of switch elements to be turned on later than other switch elements in the another group of switch elements comprises: A switch element for freewheeling in another group of switch elements is controlled to be turned on after a first dead time, and other switch elements in the another group of switch elements are controlled to be turned on after a second dead time, wherein the first dead time is greater than the second dead time.

3. The method according to claim 1, characterized in that The switch element for freewheeling is determined based on the polarity of the current flowing to the connection point of the two groups of switch elements.

4. The method according to claim 3, characterized in that The first group of switch elements in the two groups of switch elements includes a first switch element and a second switch element, the second group of switch elements includes a third switch element and a fourth switch element, each switch element is connected to the output end of the cycloidal conversion circuit, the second switch element is reversely connected to the third switch element, and after one switch element in the two groups of switch elements that are complementary turned on is turned off, controlling the switch element for freewheeling in the other group of switch elements to be turned on later than other switch elements in the other group of switch elements comprises: After the second group of switch elements are disconnected, when the current is positive polarity, the first switch element for freewheeling is controlled to be turned on later than the second switch element; when the current is negative polarity, the second switch element for freewheeling is controlled to be turned on later than the first switch element; After the first group of switch elements are disconnected, when the current is positive polarity, the fourth switch element for freewheeling is controlled to be turned on later than the third switch element; when the current is negative polarity, the third switch element for freewheeling is controlled to be turned on later than the fourth switch element.

5. The method according to claim 2, characterized in that: The duration of the first dead time is set to satisfy the zero voltage conduction of the switch element for freewheeling.

6. The method according to claim 1, characterized in that The controlling corresponding two groups of switch elements among the plurality of groups of switch elements to be complementary turned on comprises: When the AC voltage at the output end of the converter is within a preset voltage threshold range, corresponding two groups of switch elements in the multiple groups of switch elements are controlled to be complementary turned on, and the voltage threshold range includes a voltage zero crossing point.

7. The method according to claim 1, characterized in that The controlling corresponding two groups of switch elements among the plurality of groups of switch elements to be complementary turned on comprises: In each power frequency cycle of the AC voltage at the output end of the converter, corresponding two groups of switch elements among the multiple groups of switch elements are controlled to be complementary and turned on.

8. A converter, characterized in that: It comprises a controller and a cycloconversion circuit for AC-AC conversion, wherein the controller is used to control the switching elements in the cycloconversion circuit based on the control method of the converter according to any one of claims 1 to 7.

9. The converter according to claim 8, characterized in that The converter further comprises a resonant circuit connected to the cycloconversion circuit, and an inverter circuit connected to the resonant circuit; The converter is used to realize power conversion from direct current to alternating current or from alternating current to direct current.

10. The converter according to claim 9, characterized in that The converter further includes a transformer connected between the cycloconversion circuit and the inverter circuit.

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