DC / AC converter and control method thereof

Abstract

The invention relates to the field of inversion, in particular to a DC / AC converter and a control method thereof. The DC / AC converter comprises a DC side bridge arm, an AC side bridge arm, a transformer connected between the DC side bridge arm and the AC side bridge arm, and a controller connected with the DC side bridge arm and the AC side bridge arm. In the process that the first characteristic parameter of the AC side of the DC / AC converter is close to 0, the controller controls the absolute value of a first phase shift angle between the DC side bridge arm and the AC side bridge arm to be gradually increased; in the process that the first characteristic parameter is far away from 0, the controller controls the absolute value of the first phase shift angle to be gradually reduced; the first characteristic parameter is alternating current or alternating voltage. According to the technical scheme, the switching frequency is not limited by the maximum switching frequency, the output waveform is improved, and the performance of the DC / AC converter is remarkably improved.

Description

Technical Field

[0001] The present application relates to the field of inversion, and in particular to a DC / AC converter and a control method thereof. Background Art

[0002] DC / AC converters are currently widely used in various power conversion scenarios. Generally, their power is controlled by controlling the phase shift angle and switching frequency of the DC / AC converter.

[0003] In practical applications, when the AC current I ac Approaching 0, the switching frequency f s Will gradually increase. Due to the limitation of the switching frequency allowed for the power devices in the DC / AC converter, the maximum switching frequency f is generally designed. smax To limit the switching frequency of the operation process, such as Figure 1 As shown. Since the maximum switching frequency f smax The limitation leads to the failure of closed-loop control of the switching frequency, causing grid-connected current distortion and affecting the converter THDi (Total Harmonic Current Distortion) performance. Summary of the invention

[0004] Based on this, it is necessary to provide a DC / AC converter and a control method thereof to address the above technical issues.

[0005] In a first aspect, an embodiment of the present invention provides a DC / AC converter, comprising a DC side bridge arm, an AC side bridge arm, a transformer connected between the DC side bridge arm and the AC side bridge arm, and a controller connected to the DC side bridge arm and the AC side bridge arm;

[0006] When the first characteristic parameter of the AC side of the DC / AC converter approaches 0, the controller controls the absolute value of the first phase shift angle between the DC side bridge arm and the AC side bridge arm to gradually increase; when the first characteristic parameter moves away from 0, the controller controls the absolute value of the first phase shift angle to gradually decrease;

[0007] The first characteristic parameter is AC current or AC voltage.

[0008] In some embodiments, when the first characteristic parameter is within a preset threshold range and is close to 0, the controller controls the absolute value of the first phase shift angle to gradually increase; when the first characteristic parameter is within a preset threshold range and is away from 0, the controller controls the absolute value of the first phase shift angle to gradually decrease, and the preset threshold range includes the zero point of the first characteristic parameter.

[0009] In some embodiments, at the zero-crossing point of the first characteristic parameter, the absolute value of the first phase shift angle reaches a maximum value.

[0010] In some embodiments, the first characteristic parameter is one of the AC current and the AC voltage, and the second characteristic parameter of the AC side of the DC / AC converter is the other of the AC current and the AC voltage;

[0011] When the first characteristic parameter and the second characteristic parameter are both positive or negative, the controller controls the first phase shift angle to be positive; when one of the first characteristic parameter and the second characteristic parameter is positive and the other is negative, the controller controls the first phase shift angle to be negative.

[0012] In some embodiments, when the zero-crossing points of the first characteristic parameter and the second characteristic parameter are not synchronized, the controller switches the polarity of the first phase shift angle at the zero-crossing point of the first characteristic parameter or the zero-crossing point of the second characteristic parameter.

[0013] In some embodiments, when the zero-crossing points of the first characteristic parameter and the second characteristic parameter are not synchronized, and the first characteristic parameter is outside the preset threshold range when the second characteristic parameter crosses the zero point:

[0014] When the first characteristic parameter is within the preset threshold range, if its absolute value gradually decreases, the controller controls the absolute value of the first phase shift angle to gradually increase, and when the absolute value of the first characteristic parameter decreases to 0, the controller switches the polarity of the first phase shift angle; if the absolute value of the first characteristic parameter gradually increases, the controller controls the absolute value of the first phase shift angle to gradually decrease.

[0015] In some embodiments, when the zero-crossing points of the first characteristic parameter and the second characteristic parameter are not synchronized, and the first characteristic parameter is within the preset threshold range when the second characteristic parameter crosses the zero point:

[0016] When the first characteristic parameter is within the preset threshold range and its absolute value gradually decreases, the controller controls the absolute value of the first phase shift angle to gradually increase; in this process, if the second characteristic parameter crosses a zero point or the first characteristic parameter crosses a zero point, the controller switches the polarity of the first phase shift angle at the corresponding zero point;

[0017] When the first characteristic parameter is within the preset threshold range and its absolute value gradually increases, the controller controls the absolute value of the first phase shift angle to gradually decrease; in this process, if the second characteristic parameter passes through a zero point, the controller switches the polarity of the first phase shift angle at the zero point of the second characteristic parameter.

[0018] In some embodiments, the value of the first phase shift angle satisfies the soft switching of the switch tubes in the DC side bridge arm and the AC side bridge arm.

[0019] In some embodiments, when the first characteristic parameter is outside the preset threshold range, the controller controls the absolute value of the first phase shift angle to decrease as the absolute value of the second characteristic parameter increases.

[0020] In some embodiments, the first phase shift angle is the phase difference between the bridge arm output voltages of the DC side bridge arm and the AC side bridge arm, and the bridge arm output voltage is the voltage of the ports where the DC side bridge arm and the AC side bridge arm are connected to the transformer.

[0021] In some embodiments, -π≤first phase shift angle≤π.

[0022] In some embodiments, the AC side bridge arm includes a cycloconverter for performing AC-AC conversion.

[0023] In some embodiments, the DC / AC converter further includes a resonant circuit, wherein the resonant circuit is connected between the transformer and the AC side bridge arm or between the transformer and the DC side bridge arm.

[0024] In some embodiments, the DC side bridge arm includes a full-bridge circuit or a half-bridge circuit.

[0025] In a second aspect, an embodiment of the present invention provides a control method for a DC / AC converter, wherein the DC / AC converter includes a DC side bridge arm, an AC side bridge arm, and a transformer connected between the DC side bridge arm and the AC side bridge arm, and the method includes:

[0026] When the first characteristic parameter of the AC side of the DC / AC converter approaches 0, the absolute value of the first phase shift angle between the DC side bridge arm and the AC side bridge arm is controlled to gradually increase; when the first characteristic parameter moves away from 0, the absolute value of the first phase shift angle is controlled to gradually decrease;

[0027] The first characteristic parameter is AC current or AC voltage.

[0028] In some embodiments, when the first characteristic parameter is within a preset threshold range and approaches 0, the absolute value of the first phase shift angle is controlled to gradually increase; when the first characteristic parameter is within a preset threshold range and moves away from 0, the absolute value of the first phase shift angle is controlled to gradually decrease, and the preset threshold range includes the zero point of the first characteristic parameter.

[0029] In some embodiments, at the zero-crossing point of the first characteristic parameter, the absolute value of the first phase shift angle reaches a maximum value.

[0030] In some embodiments, the first characteristic parameter is one of the AC current and the AC voltage, and the second characteristic parameter of the AC side of the DC / AC converter is the other of the AC current and the AC voltage;

[0031] When the first characteristic parameter and the second characteristic parameter are both positive or negative, the first phase shift angle is positive; when one of the first characteristic parameter and the second characteristic parameter is positive and the other is negative, the first phase shift angle is negative.

[0032] In some embodiments, when the zero-crossing points of the first characteristic parameter and the second characteristic parameter are not synchronized, the polarity of the first phase shift angle is switched at the zero-crossing point of the first characteristic parameter or the zero-crossing point of the second characteristic parameter.

[0033] In some embodiments, when the zero-crossing points of the first characteristic parameter and the second characteristic parameter are not synchronized, and the first characteristic parameter is outside the preset threshold range when the second characteristic parameter crosses the zero point:

[0034] When the first characteristic parameter is within the preset threshold range, if its absolute value gradually decreases, the absolute value of the first phase shift angle is controlled to gradually increase. When the absolute value of the first characteristic parameter gradually decreases to 0, the polarity of the first phase shift angle is switched; if the absolute value of the first characteristic parameter gradually increases, the absolute value of the first phase shift angle is controlled to gradually decrease.

[0035] In some embodiments, when the zero-crossing points of the first characteristic parameter and the second characteristic parameter are not synchronized, and the first characteristic parameter is within the preset threshold range when the second characteristic parameter crosses the zero point:

[0036] When the first characteristic parameter is within the preset threshold range and its absolute value gradually decreases, the absolute value of the first phase shift angle is controlled to gradually increase; in this process, if the second characteristic parameter crosses a zero point or the first characteristic parameter crosses a zero point, the polarity of the first phase shift angle is switched at the corresponding zero point;

[0037] When the first characteristic parameter is within the preset threshold range and its absolute value gradually increases, the absolute value of the first phase shift angle is controlled to gradually decrease; in this process, if the second characteristic parameter passes through a zero point, the polarity of the first phase shift angle is switched at the zero point of the second characteristic parameter.

[0038] In some embodiments, the value of the first phase shift angle satisfies the soft switching of the switch tubes in the DC side bridge arm and the AC side bridge arm.

[0039] In some embodiments, when the first characteristic parameter is outside the preset threshold range, the absolute value of the first phase shift angle is controlled to decrease as the absolute value of the second characteristic parameter increases.

[0040] In some embodiments, the first phase shift angle is the phase difference between the bridge arm output voltages of the DC side bridge arm and the AC side bridge arm, and the bridge arm output voltage is the voltage of the ports where the DC side bridge arm and the AC side bridge arm are connected to the transformer.

[0041] In some embodiments, -π≤first phase shift angle≤π.

[0042] In the present application, when the first characteristic parameter on the AC side of the DC / AC converter approaches 0, the absolute value of the first phase shift angle between the DC side bridge arm and the AC side bridge arm is controlled to gradually increase; when the first characteristic parameter moves away from 0, the absolute value of the first phase shift angle is controlled to gradually decrease, so that the switching frequency will not be limited by the maximum switching frequency, thereby improving the output waveform and significantly improving the performance of the DC / AC converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 The switching frequency f of the prior art s With AC current I ac The changing waveform diagram of

[0044] Figure 2 is a schematic structural block diagram of a DC / AC converter in some embodiments of the present application;

[0045] Figure 3 is a schematic structural block diagram of a DC / AC converter in some other embodiments of the present application;

[0046] Figure 4 A schematic diagram of a control method of a DC / AC converter in some embodiments of the present application;

[0047] Figure 5 A schematic circuit diagram of a DC / AC converter in some exemplary embodiments of the present application;

[0048] FIG. 6( a ) shows θ ≥ 0 in some exemplary embodiments of the present application. The timing diagram of the switch tube in the DC / AC converter when ;

[0049] FIG. 6( b ) shows that θ ≥ 0 in some exemplary embodiments of the present application. The timing diagram of the switch tube in the DC / AC converter when ;

[0050] Figure 7 This is a control block diagram of a controller in some example embodiments of the present application;

[0051] Figure 8 This is a schematic diagram of key waveforms of a DC / AC converter under the control method proposed in this application, PF=1;

[0052] Fig. 9 This is a schematic diagram of the key waveforms of the DC / AC converter under the control method proposed in this application, PF = +0.8;

[0053] Fig.10 This is a schematic diagram of the key waveforms of the DC / AC converter under the control method proposed in this application, PF = -0.8;

[0054] Fig.11 Schematic diagram of key waveforms of the DC / AC converter under the control method proposed in this application, PF = +0.99;

[0055] Fig.12 This is a schematic diagram of the key waveforms of the DC / AC converter under the control method proposed in this application, PF = -0.99;

[0056] Fig.13 Schematic circuit diagrams of DC / AC converters in other exemplary embodiments of the present application;

[0057] Fig.14 Schematic circuit diagram of a DC / AC converter in some further exemplary embodiments of the present application;

[0058] Fig.15 Schematic circuit diagram of a DC / AC converter in some further exemplary embodiments of the present application;

[0059] Fig.16 Schematic circuit diagram of a DC / AC converter in some further exemplary embodiments of the present application;

[0060] Fig.17 Schematic circuit diagrams of DC / AC converters in some further exemplary embodiments of the present application. DETAILED DESCRIPTION

[0061] In order to make the purpose, technical solutions and advantages of the present application clearer, 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 intended to limit the present application. Based on the embodiments provided in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application. In addition, it can also be understood that although the efforts made in this development process may be complex and lengthy, for ordinary technicians in the field related to the contents disclosed in the present application, some changes such as design, manufacturing or production based on the technical contents disclosed in the present application are only conventional technical means, and should not be understood as insufficient contents disclosed in the present application.

[0062] Reference to "embodiments" in this application means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those of ordinary skill in the art that the embodiments described in this application may be combined with other embodiments without conflict.

[0063] Unless otherwise defined, the technical terms or scientific terms involved in this application should be understood by people with ordinary skills in the technical field to which this application belongs. The words "one", "a", "a", "the" and the like involved in this application do not indicate a quantitative limitation, and may represent the singular or plural. The terms "include", "comprise", "have" and any of their variations involved in this application are intended to cover non-exclusive inclusions; for example, a process, method, system, product or device that includes a series of steps or modules (units) is not limited to the listed steps or units, but may also include steps or units that are not listed, or may also include other steps or 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 direct or indirect. The "multiple" involved in this application refers to greater than or equal to two. "And / or" describes the association relationship of associated objects, indicating that there can be three relationships, for example, "A and / or B" can represent: A exists alone, A and B exist at the same time, and B exists alone. The terms "first", "second", "third" and the like involved in the present application are merely used to distinguish similar objects and do not represent a specific ordering of the objects.

[0064] Figure 2A schematic diagram of the structure of a DC / AC converter in some embodiments provided in the present application, wherein the DC / AC converter includes a DC side bridge arm 101, an AC side bridge arm 102, a transformer 103 connected between the DC side bridge arm 101 and the AC side bridge arm 102, and a controller (not shown in the figure) connected to the DC side bridge arm 101 and the AC side bridge arm 102.

[0065] The DC side bridge arm 101 includes an inverter circuit, including at least two switching tubes, for inverting DC power into AC power, and may be a full-bridge circuit or a half-bridge circuit.

[0066] The AC side bridge arm 102 includes, for example, at least one cycloconverter. Specifically, the AC side bridge arm 102 includes a plurality of bidirectional switch tubes for AC-AC conversion. Each switch tube group includes at least two switch tubes connected in reverse. The output end of the AC side bridge arm 102 provides an AC output, for example, to a load or a power grid.

[0067] The controller is used to control the DC side bridge arm 101 and the AC side bridge arm 102 to achieve power conversion.

[0068] The primary side of the transformer 103 is connected to the DC side bridge arm 101 , and the secondary side is connected to the AC side bridge arm 102 , for stepping up or down the voltage.

[0069] In some embodiments, there may be multiple transformers, and the primary winding of each transformer is correspondingly connected to a DC side bridge arm, and the secondary winding is correspondingly connected to the same AC side bridge arm.

[0070] In some embodiments, Figure 3 As shown, the DC / AC converter further includes a resonant circuit 104 connected between the transformer 103 and the AC side bridge arm 102 .

[0071] The resonant circuit 104 is used to realize soft switching of the switch tube in the DC / AC converter, thereby reducing circuit loss. In some embodiments, the resonant circuit 104 can be connected between the DC side bridge arm 101 and the transformer 103, or can be omitted.

[0072] The resonant circuit 104 may be in various circuit forms such as single L, LC, and CLLC.

[0073] In some embodiments, the DC / AC converter further includes a filter circuit 105 connected to the output end of the AC side bridge arm 102 for filtering.

[0074] In some embodiments, the DC / AC converter may be a bidirectional converter or a unidirectional converter, which can realize the conversion from DC to AC, in which case it works in the inverter mode, or it can realize the conversion from AC to DC, in which case it works in the rectification mode.

[0075] Based on the above DC / AC converter, the present application proposes a control method for a DC / AC converter, such as Figure 4 As shown, the method includes:

[0076] S402: When the first characteristic parameter of the AC side of the DC / AC converter approaches 0, the absolute value of the first phase shift angle between the DC side bridge arm and the AC side bridge arm is controlled to gradually increase; when the first characteristic parameter moves away from 0, the absolute value of the first phase shift angle is controlled to gradually decrease.

[0077] Wherein, the first characteristic parameter is AC current or AC voltage.

[0078] In this embodiment, when the first characteristic parameter on the AC side of the DC / AC converter approaches 0, the controller controls the absolute value of the first phase shift angle between the DC side bridge arm and the AC side bridge arm to gradually increase; when the first characteristic parameter moves away from 0, the controller controls the absolute value of the first phase shift angle to gradually decrease, so that the switching frequency will not be limited by the maximum switching frequency, thereby improving the output waveform and significantly improving the THD performance of the DC / AC converter.

[0079] In some embodiments, when the first characteristic parameter is within a preset threshold range and approaches 0, the absolute value of the first phase shift angle is controlled to gradually increase; when the first characteristic parameter is within a preset threshold range and moves away from 0, the absolute value of the first phase shift angle is controlled to gradually decrease, and the preset threshold range includes the zero point of the first characteristic parameter.

[0080] The preset threshold range can be set according to the actual limit range of the switching frequency.

[0081] In some embodiments, at the zero-crossing point of the first characteristic parameter, the absolute value of the first phase shift angle reaches a maximum value.

[0082] In some embodiments, the first characteristic parameter is one of the AC current and the AC voltage, and the second characteristic parameter of the AC side of the DC / AC converter is the other of the AC current and the AC voltage. In this case, the polarity of the first phase shift angle is determined based on the polarities of the first characteristic parameter and the second characteristic parameter.

[0083] Specifically, when the first characteristic parameter and the second characteristic parameter are both positive or negative, the first phase shift angle is positive; when one of the first characteristic parameter and the second characteristic parameter is positive and the other is negative, the first phase shift angle is negative.

[0084] It can be understood that when the first phase shift angle is positive, its value is greater than 0; when the first phase shift angle is negative, its value is less than 0.

[0085] In some embodiments, when the zero-crossing points of the first characteristic parameter and the second characteristic parameter are not synchronized, the polarity of the first phase shift angle is switched at the zero-crossing point of the first characteristic parameter or the zero-crossing point of the second characteristic parameter.

[0086] In some embodiments, when the zero-crossing points of the first characteristic parameter and the second characteristic parameter are not synchronized, and the first characteristic parameter is outside the preset threshold range when the second characteristic parameter crosses the zero point:

[0087] When the first characteristic parameter is within the preset threshold range, if its absolute value gradually decreases, the absolute value of the first phase shift angle is controlled to gradually increase. When the absolute value of the first characteristic parameter gradually decreases to 0, the polarity of the first phase shift angle is switched; if the absolute value of the first characteristic parameter gradually increases, the absolute value of the first phase shift angle is controlled to gradually decrease.

[0088] In some embodiments, when the zero-crossing points of the first characteristic parameter and the second characteristic parameter are not synchronized, and the first characteristic parameter is within the preset threshold range when the second characteristic parameter crosses the zero point:

[0089] When the first characteristic parameter is within the preset threshold range and its absolute value gradually decreases, the absolute value of the first phase shift angle is controlled to gradually increase; in this process, if the second characteristic parameter crosses a zero point or the first characteristic parameter crosses a zero point, the polarity of the first phase shift angle is switched at the corresponding zero point;

[0090] When the first characteristic parameter is within the preset threshold range and its absolute value gradually increases, the absolute value of the first phase shift angle is controlled to gradually decrease; in this process, if the second characteristic parameter passes through a zero point, the polarity of the first phase shift angle is switched at the zero point of the second characteristic parameter.

[0091] In some embodiments, the absolute value of the first phase shift angle satisfies preset soft switching conditions of the switch tubes in the DC side bridge arm and the AC side bridge arm.

[0092] In some embodiments, when the first characteristic parameter is outside the preset threshold range, the absolute value of the first phase shift angle is controlled to decrease as the absolute value of the second characteristic parameter increases.

[0093] In some embodiments, the first phase shift angle is the phase difference between the bridge arm output voltages of the DC side bridge arm and the AC side bridge arm, and the bridge arm output voltage is the voltage of the ports where the DC side bridge arm and the AC side bridge arm are connected to the transformer.

[0094] It can be understood that the “first characteristic parameter zero-crossing point” mentioned in the present application means that the value of the first characteristic parameter becomes 0; and the “second characteristic parameter zero-crossing point” means that the value of the second characteristic parameter becomes 0.

[0095] In an exemplary embodiment, the circuit schematic diagram of the DC / AC converter is as follows: Figure 5 As shown, the DC voltage on the DC side of the DC / AC converter is V in , the AC voltage on the AC side is V ac , the AC current is I ac The DC side bridge arm 101 adopts an H-bridge structure (i.e., a full-bridge circuit), and a capacitor Cin is connected in parallel at the input end. The DC side bridge arm 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 at the input end to form a half bridge arm, and the switch tube Q2H and the switch tube Q2L are connected in series at the input end to form the other half bridge arm. The AC side bridge arm 102 includes a cycloconverter composed of two groups of switch tubes connected in series in a common source connection mode. Specifically, the two groups of switch tubes are connected in series between two AC terminals of the AC side bridge arm 102 to form a bridge arm. The first group of switch tubes of the AC side bridge arm 102 includes switch tubes Q3 and Q4 connected in common source, and the second group of switch tubes includes switch tubes Q5 and Q6 connected in common source. The two groups of switch tubes are connected to the midpoint of the bridge arm. The AC end of the AC side bridge arm 102 is connected to the filter circuit 105. The filter circuit 105 includes a capacitor C connected in parallel with the output end of the AC side bridge arm 102. f and an inductor L connected to the first AC terminal of the AC side bridge arm 102 f At the same time, the second AC terminal of the AC side bridge arm 102 is connected to one end of the secondary winding of the transformer 103, and the other end of the secondary winding of the transformer 103 is connected to the bridge arm midpoint of the AC side bridge arm 102 through the resonant circuit 104. The resonant circuit 104 includes an inductor Lr and a capacitor Cr connected in series. The turns ratio of the primary and secondary windings of the transformer 103 is 1:n.

[0096] It should be noted that the switch tubes in the DC side bridge arm 101 and the AC side bridge arm 102 of the present application are described by taking MOS tubes as an example, but are not limited thereto and may also be other types of semiconductor switch devices such as IGBTs.

[0097] by Figure 5 Taking the DC / AC converter shown in FIG. 1 as an example, the DC side bridge arm 101 is an H-bridge structure, the AC side bridge arm 102 is a half-bridge cycloconverter, and the first phase shift angle between the DC side bridge arm 101 and the AC side bridge arm 102 is the bridge arm output voltage v of the DC side bridge arm 101. x The fundamental wave component zero crossing point and the bridge arm output voltage v of the AC side bridge arm 102y The phase difference between the zero-crossing points of the fundamental component of The phase difference between the output voltages of the two half-bridge arms of the DC side bridge arm 101 (between the output voltage v1 and the output voltage v2) is the second phase shift angle, denoted as θ. As shown in FIG6(a), θ≥0, When the converter works in rectification mode, the timing diagram of each switch tube is shown in Figure 6(b) when θ≥0. The timing diagram of each switch tube when the converter works in the inverter mode. s Represents a switching cycle, the first phase shift angle The value range of is:

[0098] In some embodiments, to achieve optimal efficiency of the converter, the second phase shift angle θ and the first phase shift angle θ are set to Satisfy the soft switching condition. Specifically, the soft switching condition may be:

[0099]

[0100] in, is the step-up ratio of the converter.

[0101] It can be seen that in at least one embodiment of the present application, by controlling the first phase shift angle, the switching frequency of the DC / AC converter will not be limited to the maximum switching frequency, thereby preventing output waveform distortion and improving the performance of the converter. At the same time, each switch tube in the DC side bridge arm and the AC side bridge arm can achieve soft switching under the entire operating condition, which can reduce switching losses and improve the working efficiency of the converter.

[0102] like Figure 7 As shown, the controller includes a phase shift angle control unit and a frequency determination unit. The phase shift angle control unit determines a first phase shift angle based on a voltage step-up ratio M. and a second phase shift angle θ; the frequency determination unit is based on the first phase shift angle The second phase shift angle θ, the DC voltage V of the DC / AC circuit in , AC voltage V ac , the resonance parameters Lr, Cr of the resonance circuit, the instantaneous control command, and the turns ratio n of the transformer determine the switching frequency f of the switch tube in the DC side bridge arm and the AC side bridge arm s .

[0103] The instantaneous control instruction may be an instantaneous power instruction P savg Or instantaneous current command I savg, which can be calculated based on the grid voltage phase, system power command and power factor. The system power command can be positive or negative, representing the two directions of power flow (from the DC side to the AC side or from the AC side to the DC side).

[0104] The system power instruction may be preset or obtained through other means.

[0105] The following will take the first characteristic parameter as the alternating current I ac The second characteristic parameter is the AC voltage V ac For example, combined with Figure 5 The DC / AC converter shown is illustrated.

[0106] In a possible implementation manner, the DC / AC converter operates under a condition where the power factor PF is 1, and the AC current I ac With AC voltage V ac The zero-crossing synchronization, the first phase shift angle Greater than 0, such as Figure 8 As shown, the AC current I ac As the first phase shift angle approaches 0, The absolute value of the AC current I ac In the process of moving away from 0, the first phase shift angle The absolute value of decreases gradually.

[0107] Furthermore, the preset threshold range can be set to [I th2 ,I th1 ], in the alternating current I ac In the process of changing from positive to negative, when the AC current I ac From I th1 Starts to decrease gradually, that is, when the AC current I ac In the process of approaching 0, the controller controls the first phase shift angle Start from Gradually increases; when the AC current I ac When it is equal to 0, the first phase shift angle Get the maximum value For example, set it to π. Depend on Increase to During the process, the switching frequency f s First it increases and then decreases, and it is never limited to the maximum switching frequency f smax .

[0108] When the AC current I ac It continues to decrease from 0, that is, when the AC current I ac In the process of moving away from 0, the controller controls the first phase shift angle Start from Gradually decreases; when the AC current I ac Reduce to I th2 , the first phase shift angle Reduce to For example, set to In controlling the first phase shift angle Depend on Reduce to During the process, the switching frequency f s First it increases and then decreases, and it is never limited to the maximum switching frequency f smax .

[0109] like Figure 8 As shown, the AC current I ac In the process of changing from negative to positive, when the AC current I ac From I th2 Starts to increase gradually, that is, when the AC current I ac As it approaches 0, the controller starts to control the first phase shift angle from Gradually increases; when the AC current I ac When it is equal to 0, the first phase shift angle Get the maximum value For example, set it to π. Depend on Increase to During the process, the switching frequency f s First it increases and then decreases, and it is never limited to the maximum switching frequency f smax .

[0110] When the AC current I ac It continues to increase from 0, that is, when the AC current I ac In the process of moving away from 0, the controller controls the first phase shift angle begins to decrease gradually; when the AC current I ac Change to I th1 , the first phase shift angle Reduce to For example, set to In controlling the first phase shift angle Depend on Reduce to During the process, the switching frequency f s First it increases and then decreases, and it is never limited to the maximum switching frequency f smax .

[0111] In some specific embodiments, when the design current threshold relationship is I th1 =-I th2 , you can set

[0112] In this technical solution, for the alternating current I ac When it is equal to 0, the first phase shift angle Whether it is equal to π is not limited, but it must be

[0113]

[0114] It can be understood that the present invention controls the first phase shift angle The switching frequency f is realized by s The control makes the switching frequency f s will not be affected by the maximum switching frequency f smax The limitation of the DC / AC converter improves the output performance of the DC / AC converter and ensures the first phase shift angle after control. The soft switching conditions are met and soft switching can be achieved under different working conditions, which reduces switching losses and improves converter efficiency.

[0115] In a possible implementation manner, the DC / AC converter operates under a condition where the power factor PF is ≥ 0.8, and the AC current I ac With AC voltage V ac The zero crossing point of the AC current I ac Lagging AC voltage V ac , and the AC voltage V ac When the AC current crosses zero, I ac Outside the preset threshold range, the preset threshold range is [I th2 ,I th1 ]、[I th3 ,I th4 ]. Among them, the first phase shift angle Switching frequency f s With AC current I ac The changing waveform is as follows Fig. 9 As shown, the dotted line in the figure represents the first phase shift angle The absolute value of .

[0116] In the alternating current I ac In the process of changing from positive to negative, when the AC current I ac From I th1 Starts to decrease gradually, that is, when the AC current I ac In the process of approaching 0, the first phase shift angle Less than 0, the controller controls the first phase shift angle The absolute value of begins to increase gradually (as shown by the dotted line in the figure), corresponding to the control of the first phase shift angle from Gradually decrease to For example, set it to -π; when controlling the first phase shift angle Depend on Reduce to (i.e. the first phase shift angle The absolute value of Increase to ) process, the switching frequency f s Gradually increases, but is never limited to the maximum switching frequency f smax When the AC current I ac When it is equal to 0, switch the first phase shift angle The polarity controls the first phase shift angle from Switch to ( greater than 0), and For example, they are opposite numbers.

[0117] When the AC current I ac Continue to decrease from 0, that is, when the AC current I ac In the process of moving away from 0, the controller controls the first phase shift angle Start from Gradually decreases; when the AC current I ac Change to I th2 , the first phase shift angle Reduce to For example, set to In controlling the first phase shift angle Depend on Reduce to During the process, the switching frequency f s gradually decreases, but is never limited to the maximum switching frequency f smax .

[0118] At the AC voltage V ac In the process from positive to 0, the first phase shift angle Greater than 0, controls the first phase shift angle Gradually increase to At the AC voltage V ac When it is equal to 0, switch the first phase shift angle The polarity controls the first phase shift angle from Switch to and For example, they can be opposite to each other, from the AC voltage V ac From the moment when the AC current I ac Equal to I th1 At the moment when the AC current I ac is outside the preset threshold range, and the AC voltage V ac As the absolute value of the first phase shift angle increases, The absolute value of the first phase shift angle During this period, it is less than 0, corresponding to the first phase shift angle from Gradually increase to During this period, the switching frequency f s Gradually increases, but is never limited to the maximum switching frequency f smax .

[0119] In the alternating current I ac In the process of changing from negative to positive, when the AC current I ac From I th3 Starts to increase gradually, that is, when the AC current I ac In the process of approaching 0, the controller controls the first phase shift angle The absolute value of the first phase shift angle Less than 0, corresponding to the control of the first phase shift angle from Gradually decrease to For example, set it to -π; when controlling the first phase shift angle Depend on Reduce to (i.e. the first phase shift angle The absolute value of Increase to ) process, the switching frequency f s Although it gradually increases, it is never limited to the maximum switching frequency f smax When the AC current I ac When it is equal to 0, switch the first phase shift angle The polarity controls the first phase shift angle from Switch to ( is greater than 0). and For example, they are opposite numbers.

[0120] When the AC current I ac Continue to increase from 0, that is, when the AC current I ac In the process of moving away from 0, the controller controls the first phase shift angle Start from Gradually decreases; when the AC current I ac Change to I th4 , the first phase shift angle Reduce to For example, set to In controlling the first phase shift angle Depend on Reduce to During the process, the switching frequency f sgradually decreases, but is never limited to the maximum switching frequency f smax .

[0121] At the AC voltage V ac In the process from negative to 0, control the first phase shift angle Gradually increase to At the AC voltage V ac When it is equal to 0, switch the first phase shift angle The polarity controls the first phase shift angle from Switch to and For example, they can be opposite to each other, from the AC voltage V ac From the moment when the AC current I ac Equal to I th3 At the moment when the AC current I ac is outside the preset threshold range, and the AC voltage V ac As the absolute value of the first phase shift angle increases, The absolute value of the first phase shift angle During this period, it is less than 0, corresponding to the first phase shift angle from Gradually increase to During this period, the switching frequency f s Although it gradually increases, it is never limited to the maximum switching frequency f smax .

[0122] In some embodiments, when the current threshold relationship is I th1 =-I th3 ,I th4 =-I th2 When

[0123]

[0124] In a possible implementation manner, the DC / AC converter operates under a condition where the power factor PF is -0.8, and the AC current I ac With AC voltage V ac The zero crossing point of the AC current I ac Leading AC voltage V ac , and the AC voltage V ac When the AC current crosses zero, I ac Outside the preset threshold range, the preset threshold range is [I th2 ,I th1 ]、[I th3 ,I th4 ]. Among them, the first phase shift angle Switching frequency fs With AC current I ac The changing waveform is as follows Fig.10 shown.

[0125] In the alternating current I ac In the process of changing from positive to negative, when the AC current I ac From I th1 In the process of decreasing to 0, that is, when the AC current I ac In the process of approaching 0, the first phase shift angle Greater than 0, the controller controls the first phase shift angle from Gradually increase to For example, set it to π; when controlling the first phase shift angle Depend on Increase to During the process, the switching frequency f s Although it gradually increases, it is never limited to the maximum switching frequency f smax When the AC current I ac When it is equal to 0, switch the first phase shift angle The polarity controls the first phase shift angle from Switch to ( less than 0), and For example, they are opposite numbers.

[0126] When the AC current I ac Continue to decrease from 0, that is, when the AC current I ac In the process of moving away from 0, the controller controls the first phase shift angle The absolute value of the phase shift angle Less than 0, the corresponding control first phase shift angle from Gradually increases; when the AC current I ac Reduce to I th2 , control the first phase shift angle Increase to For example, set to In controlling the first phase shift angle Depend on Increase to During the process, the switching frequency f s gradually decreases, but is never limited to the maximum switching frequency f smax .

[0127] At the AC voltage V ac As the AC current I ac Equal to I th2From the moment to the AC voltage V ac When the AC current I ac is outside the preset threshold range, and the AC voltage V ac As the absolute value of the first phase shift angle decreases, The absolute value of the first phase shift angle increases gradually during this period. Less than 0, the corresponding control first phase shift angle from Reduce to During this period, the switching frequency f s gradually decreases, but is never limited to the maximum switching frequency f smax . At the AC voltage V ac When it is equal to 0, switch the first phase shift angle The polarity controls the first phase shift angle from Switch to and For example, they can be opposite numbers.

[0128] In the alternating current I ac In the process of changing from negative to positive, when the AC current I ac From I th3 In the process of increasing to 0, that is, when the AC current I ac In the process of approaching 0, the first phase shift angle Greater than 0, the controller controls the first phase shift angle Gradually increases, corresponding to the control of the first phase shift angle from Gradually increase to For example, set it to π; when controlling the first phase shift angle Depend on Increase to During the process, the switching frequency f s Although it gradually increases, it is never limited to the maximum switching frequency f smax When the AC current I ac When equal to 0, control the first phase shift angle from Switch to ( less than 0), and For example, they are opposite numbers.

[0129] When the AC current I a Continue to increase from 0, that is, when the AC current I ac In the process of moving away from 0, the controller controls the first phase shift angle The absolute value of the first phase shift angle from Gradually increases; when the AC current I ac Increase to I th4 , the first phase shift angle Increase to For example, set to In controlling the first phase shift angle Depend on Increase to During the process, the switching frequency f s gradually decreases, but is never limited to the maximum switching frequency f smax .

[0130] At the AC voltage V ac In the process of going from negative to 0, the AC current I ac Equal to I th4 From the moment to the AC voltage V ac When the AC current I ac is outside the preset threshold range, and the AC voltage V ac As the absolute value of the first phase shift angle decreases, The absolute value of the first phase shift angle increases gradually during this period. Less than 0, the corresponding control first phase shift angle from Reduce to During this period, the switching frequency f s gradually decreases, but is never limited to the maximum switching frequency f smax . At the AC voltage V ac When it is equal to 0, switch the first phase shift angle The polarity controls the first phase shift angle from Switch to and For example, they can be opposite numbers.

[0131] In some embodiments, when the current threshold relationship is I th1 =-I th3 , I th4 =-I th2 When

[0132]

[0133] In a possible implementation, the DC / AC converter operates under the condition that the power factor PF is ≥ 0.99, and the AC current I ac Lagging AC voltage V ac , and the AC voltage V ac When the AC current crosses zero, I ac Within the preset threshold range, the preset threshold range is [I th2,I th1 ]、[I th3 ,I th4 ]. Among them, the first phase shift angle Switching frequency f s The waveform changes with the alternating current. Fig.11 shown.

[0134] and Fig. 9 The embodiment shown differs in that the AC voltage V ac In the alternating current I ac From I th1 Decrease to 0, and from I th3 The controller needs to pass the zero point during the process of increasing to 0, so the AC voltage V ac The zero-crossing point switches the first phase shift angle polarity.

[0135] Specifically, when the AC current I ac From I th1 In the process of decreasing to 0, that is, when the AC current I ac In the process of approaching 0, the controller controls the first phase shift angle The absolute value of the first phase shift angle from begins to increase gradually; when the AC voltage V ac When it is equal to 0, the first phase shift angle Increase to At the same time, the controller switches the polarity of the first phase shift angle and controls the first phase shift angle from Switch to ( less than 0), and For example, they are opposite to each other; in the alternating current I ac In the process of continuing to decrease to 0, control the first phase shift angle The absolute value of continues to increase, corresponding to the control of the first phase shift angle from Gradually decrease to When the AC current I ac When equal to 0, control the first phase shift angle from Switch to ( greater than 0), and For example, they are opposite numbers.

[0136] In the alternating current I ac From I th3 In the process of increasing to 0, that is, when the AC current I acIn the process of approaching 0, the controller controls the first phase shift angle The absolute value of the first phase shift angle from begins to increase gradually; when the AC voltage V ac When it is equal to 0, the first phase shift angle Increase to At the same time, the controller switches the polarity of the first phase shift angle and controls the first phase shift angle from Switch to ( less than 0), and For example, they are opposite to each other; in the alternating current I ac As it continues to increase to 0, control the first phase shift angle The absolute value of continues to increase, corresponding to the control of the first phase shift angle from Gradually decrease to When the AC current I ac When it is equal to 0, the controller switches to the first phase shift angle The polarity controls the first phase shift angle from Switch to ( greater than 0), and For example, they are opposite numbers.

[0137] In the above AC current I ac During the change of the switching frequency f s is never limited to the maximum switching frequency f smax .

[0138] In a possible implementation, the DC / AC converter operates under the condition that the power factor PF is -0.99, and the AC current I ac Leading AC voltage V ac , and the AC voltage V ac When the AC current crosses zero, I ac Within the preset threshold range, the preset threshold range is [I th2 ,I th1 ]、[I th3 ,I th4 ]. Among them, the first phase shift angle Switching frequency f s The waveform changes with the alternating current. Fig.12 shown.

[0139] and Fig.10 The embodiment shown differs in that the AC voltage V ac In the alternating current Iac Decrease from 0 to I th2 , and increases from 0 to I th4 The controller needs to have an AC voltage V ac The zero-crossing point switches the first phase shift angle polarity.

[0140] Specifically, when the AC current I ac Decrease from 0 to I th2 During the process, that is, when the alternating current I ac In the process of moving away from 0, the controller controls the first phase shift angle The absolute value of the first phase shift angle from begins to increase gradually; when the AC voltage V ac When it is equal to 0, the first phase shift angle Increase to At the same time, the controller switches the polarity of the first phase shift angle and controls the first phase shift angle from Switch to ( greater than 0), and For example, they are opposite to each other; in the alternating current I ac Continue to reduce I th2 In the process of controlling the first phase shift angle from Gradually decrease to

[0141] When the AC current I ac Increase from 0 to I th4 During the process, that is, when the alternating current I ac In the process of moving away from 0, the controller controls the first phase shift angle The absolute value of the first phase shift angle from begins to increase gradually; when the AC voltage V ac When it is equal to 0, the first phase shift angle Increase to When the controller switches the polarity of the first phase shift angle, the first phase shift angle from Switch to ( greater than 0), and For example, they are opposite to each other; in the alternating current I ac Continue to increase to I th4 In the process of controlling the first phase shift angle from Gradually decrease to

[0142] In the above AC current I ac During the change of the switching frequency f s is never limited to the maximum switching frequency f smax .

[0143] In some embodiments, the first characteristic parameter is the AC voltage V ac The second characteristic parameter is the AC current I ac , the corresponding controller uses AC voltage V ac As a condition, set the corresponding preset threshold range, when the AC voltage V ac Within the preset threshold range, the controller adjusts the first phase shift angle Adjustment of the switching frequency f s is never limited to the maximum switching frequency f smax .

[0144] Specifically, when the AC voltage V ac In the process of changing from the voltage threshold to 0, the first phase shift angle is controlled The absolute value of the AC voltage V ac In the process of changing from 0 to the voltage threshold, the first phase shift angle is controlled The absolute value of decreases gradually.

[0145] It should be noted that the control method proposed in this application can also be used for DC / AC converters with other topologies.

[0146] In some other example embodiments, Fig.13 As shown, the AC side bridge arm 102 of the DC / AC converter includes a cycloconverter composed of two groups of switch tubes. Figure 5 Compared with the DC / AC converter shown in the figure, the first group of switch tubes includes switch tubes Q8 and switch tube Q9 connected in reverse series, the second group of switch tubes includes switch tubes Q7 and switch tube Q10 connected in reverse through the first group of switch tubes, one end of the secondary winding of the transformer 103 is connected to the connection midpoint of the switch tubes Q7 and Q8 through the resonant circuit 104, the other end of the secondary winding of the transformer 103 is connected to the midpoint of the switch tubes Q9 and Q10, the source of the switch tube Q7 is connected to the source of the switch tube Q8, and the source of the switch tube Q9 is connected to the source of the switch tube Q10.

[0147] In some further example embodiments, Fig.14 As shown, the AC side bridge arm 102 of the DC / AC converter includes a cycloconverter composed of two groups of switch tubes connected in series. Figure 5Compared with the DC / AC converter shown in FIG. 1 , the first group of switch tubes includes switch tubes Q12 and Q13 connected with a common source, and the second group of switch tubes includes switch tubes Q11 and Q14 connected in reverse through the first group of switch tubes. One end of the secondary winding of the transformer 103 is connected to the connection midpoint of the switch tubes Q11 and Q12 through the resonant circuit 104, and the other end of the secondary winding of the transformer 103 is connected to the midpoint of the switch tubes Q13 and Q14. The drain of the switch tube Q12 is connected to the source of the switch tube Q11, and the drain of the switch tube Q13 is connected to the source of the switch tube Q14.

[0148] In some further example embodiments, Fig.15 As shown, the AC side bridge arm 102 of the DC / AC converter includes two groups of switch tubes connected in reverse series, and each group of switch tubes is connected in series with a capacitor. Figure 5 Compared with the DC / AC converter shown in FIG. 1 , the first group of switch tubes includes switch tubes Q15 and Q16 connected with a common source, and the second group of switch tubes includes switch tubes Q17 and Q18 connected with a common source, and the connection point of switch tubes Q15 and Q17 serves as the midpoint of the bridge arm. The first group of switch tubes and capacitor Cr1 are connected to a node, which serves as the first AC terminal of the AC side bridge arm 102; the second group of switch tubes and capacitor Cr2 are connected to another node, which serves as the second AC terminal of the AC side bridge arm 102. One end of the secondary winding of the transformer 103 is connected to the midpoint of the bridge arm of the AC side bridge arm 102 through the inductor Lr, and the other end is connected to the connection point of the capacitor Cr1 and the capacitor Cr2, and the inductor Lr, the capacitor Cr1 and the capacitor Cr2 form a resonant circuit 104.

[0149] In some further example embodiments, Fig.16 As shown, the AC side bridge arm 102 of the DC / AC converter is a full-bridge topology structure. Figure 5 Compared with the DC / AC converter shown in FIG. 1 , the AC side bridge arm 102 includes a first upper bridge arm, a first lower bridge arm, a second upper bridge arm and a second lower bridge arm, the connection point of the first upper bridge arm and the first lower bridge arm is connected to the first end of the secondary winding of the transformer 103 through the resonant circuit 104, and the connection point of the second upper bridge arm and the second lower bridge arm is connected to the second end of the secondary winding of the transformer 103. The first upper bridge arm includes two reversely connected switch tubes Q19 and Q20; the first lower bridge arm includes two reversely connected switch tubes Q23 and Q24; the second upper bridge arm includes two reversely connected switch tubes Q21 and Q22; the second lower bridge arm includes two reversely connected switch tubes Q25 and Q26.

[0150] In some further example embodiments, Fig.17As shown, the DC / AC converter is a three-phase DC / AC converter that provides a three-phase AC output. Figure 5 Compared with the DC / AC converter shown in FIG. 1 , the AC side bridge arm 102 of the DC / AC converter includes three groups of switch tubes connected in reverse series, and each group of switch tubes is connected in series with a capacitor. The first group of switch tubes includes switch tubes Q27 and Q28 connected to a common source, the second group of switch tubes includes switch tubes Q29 and Q30 connected to a common source, and the third group of switch tubes includes switch tubes Q31 and Q32 connected to a common source, and the three groups of switch tubes are connected together at one point. The first group of switch tubes and capacitor Cr3 are connected to a node, which serves as the first AC terminal of the AC side bridge arm 102; the second group of switch tubes and capacitor Cr4 are connected to another node, which serves as the second AC terminal of the AC side bridge arm 102; the second group of switch tubes and capacitor Cr5 are connected to another node, which serves as the third AC terminal of the AC side bridge arm 102. One end of the secondary winding of the transformer 103 is connected to the common connection point of the three groups of switch tubes through the inductor Lr, and the other end is connected to the common connection point of the capacitor Cr3, the capacitor Cr4, and the capacitor Cr5. The inductor Lr, the capacitor Cr3, the capacitor Cr4, and the capacitor Cr5 form a resonant circuit 104. In some other embodiments, the capacitor Cr3, the capacitor Cr4, and the capacitor Cr5 can also be replaced by two switch tubes connected to a common source, or a capacitor connected in series with the inductor Lr can be added to form a resonant circuit.

[0151] Above Figure 13-Figure 17 In the DC / AC converters of the exemplary embodiments shown, the controller may adopt the control method of the embodiments described above, and when the AC current or AC voltage on the AC side of the DC / AC converter approaches 0, the absolute value of the first phase shift angle between the DC side bridge arm and the AC side bridge arm is controlled to gradually increase; when the AC current or AC voltage is away from 0, the absolute value of the first phase shift angle is controlled to gradually decrease, and the switching frequency f s is never limited to the maximum switching frequency f smax .

[0152] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0153] The above 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 the invention patent. 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 protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A DC / AC converter, characterized in that: It includes a DC side bridge arm, an AC side bridge arm, a transformer connected between the DC side bridge arm and the AC side bridge arm, and a controller connected to the DC side bridge arm and the AC side bridge arm; When the first characteristic parameter of the AC side of the DC / AC converter approaches 0, the controller controls the absolute value of the first phase shift angle between the DC side bridge arm and the AC side bridge arm to gradually increase; when the first characteristic parameter moves away from 0, the controller controls the absolute value of the first phase shift angle to gradually decrease; The first characteristic parameter is AC current or AC voltage.

2. The DC / AC converter according to claim 1, characterized in that: When the first characteristic parameter is within a preset threshold range and is close to 0, the controller controls the absolute value of the first phase shift angle to gradually increase; when the first characteristic parameter is within a preset threshold range and is away from 0, the controller controls the absolute value of the first phase shift angle to gradually decrease, and the preset threshold range includes the zero point of the first characteristic parameter.

3. The DC / AC converter according to claim 1 or 2, characterized in that: At the zero-crossing point of the first characteristic parameter, the absolute value of the first phase shift angle reaches a maximum value.

4. The DC / AC converter according to claim 1 or 2, characterized in that: The first characteristic parameter is one of the AC current and the AC voltage, and the second characteristic parameter of the AC side of the DC / AC converter is the other of the AC current and the AC voltage; When the first characteristic parameter and the second characteristic parameter are both positive or negative, the controller controls the first phase shift angle to be positive; when one of the first characteristic parameter and the second characteristic parameter is positive and the other is negative, the controller controls the first phase shift angle to be negative.

5. The DC / AC converter according to claim 4, characterized in that: In the case where the zero-crossing points of the first characteristic parameter and the second characteristic parameter are not synchronized, the controller switches the polarity of the first phase shift angle at the zero-crossing point of the first characteristic parameter or the zero-crossing point of the second characteristic parameter.

6. The DC / AC converter according to claim 5, characterized in that: In the case where the zero-crossing points of the first characteristic parameter and the second characteristic parameter are not synchronized, and the first characteristic parameter is outside a preset threshold range when the second characteristic parameter crosses the zero point: When the first characteristic parameter is within the preset threshold range, if its absolute value gradually decreases, the controller controls the absolute value of the first phase shift angle to gradually increase, and when the absolute value of the first characteristic parameter decreases to 0, the controller switches the polarity of the first phase shift angle; if the absolute value of the first characteristic parameter gradually increases, the controller controls the absolute value of the first phase shift angle to gradually decrease.

7. The DC / AC converter according to claim 5, characterized in that: In the case where the zero-crossing points of the first characteristic parameter and the second characteristic parameter are not synchronized, and the first characteristic parameter is within a preset threshold range when the second characteristic parameter crosses the zero point: When the first characteristic parameter is within the preset threshold range and its absolute value gradually decreases, the controller controls the absolute value of the first phase shift angle to gradually increase; in this process, if the second characteristic parameter crosses a zero point or the first characteristic parameter crosses a zero point, the controller switches the polarity of the first phase shift angle at the corresponding zero point; When the first characteristic parameter is within the preset threshold range and its absolute value gradually increases, the controller controls the absolute value of the first phase shift angle to gradually decrease; in this process, if the second characteristic parameter passes through a zero point, the controller switches the polarity of the first phase shift angle at the zero point of the second characteristic parameter.

8. The DC / AC converter according to claim 1 or 2, characterized in that: The value of the first phase shift angle satisfies the soft switching of the switch tubes in the DC side bridge arm and the AC side bridge arm.

9. The DC / AC converter according to claim 4, characterized in that: When the first characteristic parameter is outside a preset threshold range, the controller controls the absolute value of the first phase shift angle to decrease as the absolute value of the second characteristic parameter increases.

10. The DC / AC converter according to claim 1 or 2, characterized in that: The first phase shift angle is the phase difference between the bridge arm output voltages of the DC side bridge arm and the AC side bridge arm, and the bridge arm output voltage is the voltage of the ports where the DC side bridge arm and the AC side bridge arm are connected to the transformer.

11. The DC / AC converter according to claim 1, characterized in that: -π≤first phase shift angle≤π.

12. The DC / AC converter according to claim 1, characterized in that: The AC side bridge arm includes a cycloconverter for performing AC-AC conversion.

13. The DC / AC converter according to claim 1, characterized in that: The DC / AC converter further comprises a resonant circuit, which is connected between the transformer and the AC side bridge arm or between the transformer and the DC side bridge arm.

14. The DC / AC converter according to claim 1, characterized in that: The DC side bridge arm includes a full-bridge circuit or a half-bridge circuit.

15. A control method for a DC / AC converter, wherein the DC / AC converter comprises a DC side bridge arm, an AC side bridge arm, and a transformer connected between the DC side bridge arm and the AC side bridge arm, wherein: The method comprises: When the first characteristic parameter of the AC side of the DC / AC converter approaches 0, the absolute value of the first phase shift angle between the DC side bridge arm and the AC side bridge arm is controlled to gradually increase; when the first characteristic parameter moves away from 0, the absolute value of the first phase shift angle is controlled to gradually decrease; The first characteristic parameter is AC current or AC voltage.

16. The method according to claim 15, characterized in that When the first characteristic parameter is within a preset threshold range and approaches 0, the absolute value of the first phase shift angle is controlled to gradually increase; when the first characteristic parameter is within a preset threshold range and moves away from 0, the absolute value of the first phase shift angle is controlled to gradually decrease, and the preset threshold range includes the zero point of the first characteristic parameter.

17. The method according to claim 15 or 16, characterized in that At the zero-crossing point of the first characteristic parameter, the absolute value of the first phase shift angle reaches a maximum value.

18. The method according to claim 15 or 16, characterized in that The first characteristic parameter is one of the AC current and the AC voltage, and the second characteristic parameter of the AC side of the DC / AC converter is the other of the AC current and the AC voltage; When the first characteristic parameter and the second characteristic parameter are both positive or negative, the first phase shift angle is positive; when one of the first characteristic parameter and the second characteristic parameter is positive and the other is negative, the first phase shift angle is negative.

19. The method according to claim 18, characterized in that In the case where the zero-crossing points of the first characteristic parameter and the second characteristic parameter are not synchronized, the polarity of the first phase shift angle is switched at the zero-crossing point of the first characteristic parameter or the zero-crossing point of the second characteristic parameter.

20. The method according to claim 19, characterized in that In the case where the zero-crossing points of the first characteristic parameter and the second characteristic parameter are not synchronized, and the first characteristic parameter is outside a preset threshold range when the second characteristic parameter crosses the zero point: When the first characteristic parameter is within the preset threshold range, if its absolute value gradually decreases, the absolute value of the first phase shift angle is controlled to gradually increase. When the absolute value of the first characteristic parameter gradually decreases to 0, the polarity of the first phase shift angle is switched; if the absolute value of the first characteristic parameter gradually increases, the absolute value of the first phase shift angle is controlled to gradually decrease.

21. The method according to claim 19, characterized in that In the case where the zero-crossing points of the first characteristic parameter and the second characteristic parameter are not synchronized, and the first characteristic parameter is within a preset threshold range when the second characteristic parameter crosses the zero point: When the first characteristic parameter is within the preset threshold range and its absolute value gradually decreases, the absolute value of the first phase shift angle is controlled to gradually increase; in this process, if the second characteristic parameter crosses a zero point or the first characteristic parameter crosses a zero point, the polarity of the first phase shift angle is switched at the corresponding zero point; When the first characteristic parameter is within the preset threshold range and its absolute value gradually increases, the absolute value of the first phase shift angle is controlled to gradually decrease; in this process, if the second characteristic parameter passes through a zero point, the polarity of the first phase shift angle is switched at the zero point of the second characteristic parameter.

22. The method according to claim 15 or 16, characterized in that The value of the first phase shift angle satisfies the soft switching of the switch tubes in the DC side bridge arm and the AC side bridge arm.

23. The method according to claim 18, characterized in that When the first characteristic parameter is outside a preset threshold range, the absolute value of the first phase shift angle is controlled to decrease as the absolute value of the second characteristic parameter increases.

24. The method according to claim 15 or 16, characterized in that The first phase shift angle is the phase difference between the bridge arm output voltages of the DC side bridge arm and the AC side bridge arm, and the bridge arm output voltage is the voltage of the ports where the DC side bridge arm and the AC side bridge arm are connected to the transformer.

25. The method according to claim 15, characterized in that -π≤first phase shift angle≤π.

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