DC / ac converter and control method therefor

Abstract

A direct current (DC) / alternating current (AC) converter and a control method therefor. 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 to the DC side bridge arm and the AC side bridge arm. The controller is configured to: control, during a process in which a first characteristic parameter of an AC side of the DC / AC converter approaches 0, the absolute value of a first phase shift angle between the DC side bridge arm and the AC side bridge arm to gradually increase; and control, during a process in which the first characteristic parameter moves away from 0, control the absolute value of the first phase shift angle to gradually decrease, wherein the first characteristic parameter is an AC current or an AC voltage.

Description

DC / AC converter and control method thereof

[0001] Related applications

[0002] The present application claims priority to the Chinese patent application No. 202411359075.9, filed on September 26, 2024, and entitled "DC / AC converter and control method thereof", the contents of which are hereby incorporated by reference in their entirety. TECHNICAL FIELD

[0003] The present application relates to the field of inverter, and in particular, to a DC / AC converter and a control method thereof. BACKGROUND

[0004] DC / AC converters have been widely applied to various power conversion scenarios. Generally, the power of a DC / AC converter is controlled by controlling the phase shift angle and the switching frequency of the DC / AC converter.

[0005] In actual applications, when the AC current I ac of the DC / AC converter approaches 0, the switching frequency f s will gradually increase. Due to the limitation of the allowable switching frequency of the power device in the DC / AC converter, the maximum switching frequency f smax is generally designed to limit the switching frequency during operation, as shown in FIG. 1. Due to the limitation of the maximum switching frequency f smax , the closed-loop control of the switching frequency is invalid, which causes the grid current to be distorted and affects the THDi (Total Harmonic Current Distortion) performance of the converter. SUMMARY

[0006] According to various embodiments of the present application, a DC / AC converter and a control method thereof are provided.

[0007] In a first aspect, the embodiments of the present application provide 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 with the DC side bridge arm and the AC side bridge arm.

[0008] The controller is configured to gradually increase the absolute value of a first phase shift angle between the DC side bridge arm and the AC side bridge arm when a first characteristic parameter on the AC side of the DC / AC converter approaches 0, and gradually decrease the absolute value of the first phase shift angle when the first characteristic parameter is away from 0.

[0009] The first characteristic parameter is an AC current or an AC voltage.

[0010] In some embodiments, the controller is configured to gradually increase the absolute value of the first phase shift angle when the first characteristic parameter is within a preset threshold range and approaches zero, and gradually decrease the absolute value of the first phase shift angle when the first characteristic parameter is within the preset threshold range and is away from zero, the preset threshold range including zero of the first characteristic parameter.

[0011] In some embodiments, the absolute value of the first phase shift angle reaches a maximum value at zero crossing point of the first characteristic parameter.

[0012] 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.

[0013] The controller is configured to control the first phase shift angle to be positive when both the first characteristic parameter and the second characteristic parameter are positive or negative, and control the first phase shift angle to be negative when one of the first characteristic parameter and the second characteristic parameter is positive and the other is negative.

[0014] In some embodiments, the controller is configured to switch the polarity of the first phase shift angle at zero crossing point of the first characteristic parameter or zero crossing point of the second characteristic parameter when the zero crossing points of the first characteristic parameter and the second characteristic parameter are not synchronized.

[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 outside the preset threshold range when the second characteristic parameter crosses zero:

[0016] The controller is configured to gradually increase the absolute value of the first phase shift angle when the first characteristic parameter is within the preset threshold range and the absolute value of the first characteristic parameter gradually decreases, and switch the polarity of the first phase shift angle when the absolute value of the first characteristic parameter decreases to zero, and gradually decrease the absolute value of the first phase shift angle when the absolute value of the first characteristic parameter gradually increases.

[0017] 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 zero:

[0018] The controller is configured to control the first phase shift angle to gradually increase in absolute value when the first characteristic parameter is within the preset threshold range and the absolute value of the first characteristic parameter gradually decreases; in this process, 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.

[0019] The controller is further configured to control the first phase shift angle to gradually decrease in absolute value when the first characteristic parameter is within the preset threshold range and the absolute value of the first characteristic parameter gradually increases; in this process, the polarity of the first phase shift angle is switched at the zero-crossing point of the second characteristic parameter.

[0020] In some embodiments, the first phase shift angle satisfies soft switching of the switching tubes in the DC side bridge arm and the AC side bridge arm.

[0021] In some embodiments, the controller is configured to control the absolute value of the first phase shift angle to decrease with the increase of the absolute value of the second characteristic parameter when the first characteristic parameter is outside the preset threshold range.

[0022] In some embodiments, the first phase shift angle is a phase difference between bridge arm output voltages of the DC side bridge arm and the AC side bridge arm, and the bridge arm output voltage is a voltage of a port connected to the transformer.

[0023] In some embodiments, -π≤ the first phase shift angle ≤π.

[0024] In some embodiments, the AC side bridge arm includes a cycloconverter for AC / AC conversion.

[0025] In some embodiments, the DC / AC converter further includes a resonant circuit connected between the transformer and the AC side bridge arm or connected between the transformer and the DC side bridge arm.

[0026] In some embodiments, the DC side bridge arm includes a full-bridge circuit or a half-bridge circuit.

[0027] In a second aspect, the embodiments of the present application provide a control method of a DC / AC converter, the DC / AC converter including 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:

[0028] In a process in which a first characteristic parameter at the AC side of the DC / AC converter approaches 0, the absolute value of a first phase shift angle between the DC side bridge arm and the AC side bridge arm is gradually increased; in a process in which the first characteristic parameter is away from 0, the absolute value of the first phase shift angle is gradually decreased.

[0029] The first characteristic parameter is an alternating current or an alternating voltage.

[0030] In some embodiments, when the first characteristic parameter is within a preset threshold range and approaches zero, the absolute value of the first phase shift angle is gradually increased; when the first characteristic parameter is within the preset threshold range and is away from zero, the absolute value of the first phase shift angle is gradually decreased, and the preset threshold range includes a zero point of the first characteristic parameter.

[0031] 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.

[0032] In some embodiments, the first characteristic parameter is one of the alternating current and the alternating voltage, and a second characteristic parameter on an alternating current side of a DC / AC converter is the other of the alternating current and the alternating voltage.

[0033] 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.

[0034] 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.

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

[0036] When the first characteristic parameter is within the preset threshold range and the absolute value of the first characteristic parameter is gradually decreased, the absolute value of the first phase shift angle is gradually increased, and the polarity of the first phase shift angle is switched when the absolute value of the first characteristic parameter gradually decreases to zero; if the absolute value of the first characteristic parameter is gradually increased, the absolute value of the first phase shift angle is gradually decreased.

[0037] In some embodiments, when the zero crossing points of the first characteristic parameter and the second characteristic parameter are not synchronized, and when the second characteristic parameter crosses zero, the first characteristic parameter is within the preset threshold range:

[0038] when the first characteristic parameter is in the preset threshold range and the absolute value of the first characteristic parameter gradually decreases, the absolute value of the first phase shift angle is gradually increased; in the process, if the second characteristic parameter zero-crossing point or the first characteristic parameter zero-crossing point, the polarity of the first phase shift angle is switched at the corresponding zero-crossing point.

[0039] when the first characteristic parameter is in the preset threshold range and the absolute value of the first characteristic parameter gradually decreases, the absolute value of the first phase shift angle is gradually increased; in the process, if the second characteristic parameter zero-crossing point or the first characteristic parameter zero-crossing point, the polarity of the first phase shift angle is switched at the corresponding zero-crossing point.

[0040] In some embodiments, the value of the first phase shift angle satisfies the soft switching of the switch tube in the DC side bridge arm and the AC side bridge arm.

[0041] In some embodiments, when the first characteristic parameter is outside the preset threshold range, the absolute value of the first phase shift angle is decreased with the increase of the absolute value of the second characteristic parameter.

[0042] In some embodiments, the first phase shift angle is the phase difference between the bridge arm output voltage of the DC side bridge arm and the AC side bridge arm, and the bridge arm output voltage is the voltage of the port connected with the transformer of the DC side bridge arm and the AC side bridge arm.

[0043] In some embodiments, -π≤ the first phase shift angle ≤π.

[0044] The details of one or more embodiments of the present application are presented in the following drawings and description to make other features, objects and advantages of the present application more clear and easy to understand. BRIEF DESCRIPTION OF DRAWINGS

[0045] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0046] Fig. 1 is a related art switching frequency f s with the change waveform of the AC current I ac .

[0047] Fig. 2 is a schematic structural block diagram of a DC / AC converter in some embodiments of the present application.

[0048] Fig. 3 is a schematic structural block diagram of a DC / AC converter in some other embodiments of the present application.

[0049] Figure 4 is a schematic diagram of a control method of a DC / AC converter in some embodiments of the application.

[0050] Figure 5 is a schematic circuit diagram of a DC / AC converter in some example embodiments of the application.

[0051] Figure 6A is a timing diagram of the switching transistors in a DC / AC converter when θ≥0, in some example embodiments of the application.

[0052] Figure 6B is a timing diagram of the switching transistors in a DC / AC converter when θ≥0, in some example embodiments of the application.

[0053] Figure 7 is a control block diagram of a controller in some example embodiments of the application.

[0054] Figure 8 is a schematic diagram of key waveforms of a DC / AC converter when PF = 1 under the control method proposed in the application.

[0055] Figure 9 is a schematic diagram of key waveforms of a DC / AC converter when PF = +0.8 under the control method proposed in the application.

[0056] Figure 10 is a schematic diagram of key waveforms of a DC / AC converter when PF = -0.8 under the control method proposed in the application.

[0057] Figure 11 is a schematic diagram of key waveforms of a DC / AC converter when PF = +0.99 under the control method proposed in the application.

[0058] Figure 12 is a schematic diagram of key waveforms of a DC / AC converter when PF = -0.99 under the control method proposed in the application.

[0059] Figure 13 is a schematic circuit diagram of a DC / AC converter in some other example embodiments of the application.

[0060] Figure 14 is a schematic circuit diagram of a DC / AC converter in some further example embodiments of the application.

[0061] Figure 15 is a schematic circuit diagram of a DC / AC converter in some further example embodiments of the application.

[0062] Figure 16 is a schematic circuit diagram of a DC / AC converter in some further example embodiments of the application.

[0063] Figure 17 is a schematic circuit diagram of a DC / AC converter in some further example embodiments of the application. DETAILED DESCRIPTION

[0064] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be described and explained in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present application and should not be used to limit the present application. Based on the embodiments provided by the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of the present application. In addition, it should be understood that, although the efforts made in this development process can be complex and lengthy, some design, manufacture or production changes made on the basis of the technical content disclosed in the present application by those of ordinary skill in the art related to the content disclosed in the present application are only routine technical means and should not be understood as insufficient disclosure of the present application.

[0065] Reference to "an embodiment" in this application means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily mutually exclusive or alternative embodiments. It is explicitly contemplated that embodiments described herein can be combined with other embodiments in a non- conflicting manner.

[0066] Unless otherwise defined, technical terms or scientific terms used in the present application should be understood as having the common meaning understood by one of ordinary skill in the art to which the present application pertains. The terms "a", "an", "one", "this", and similar terms in the present application do not denote a quantity limitation, but can denote a single or multiple quantity. The terms "include", "contain", "have", and any variation thereof in the present application are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or device including a series of steps or modules (units) is not limited to the listed steps or units, but can further include steps or units not listed or can further include other steps or units inherent to the process, method, product, or device. The terms "connect", "connected", "couple", and similar terms in the present application are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. The term "multiple" in the present application means greater than or equal to two. The term "and / or" describes the association relationship of the associated objects, which means that there can be three relationships, for example, "A and / or B" can mean that A exists alone, A and B exist together, and B exists alone. The terms "first", "second", "third", and the like in the present application are only to distinguish similar objects, and do not represent a specific order of the objects.

[0067] Figure 2 is a schematic diagram of a DC / AC converter according to some embodiments of the present application, which 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 connected to the DC side bridge arm 101 and the AC side bridge arm 102.

[0068] The DC side bridge arm 101 includes an inverter circuit, which includes at least two switching tubes, for converting DC to AC, and can be a full-bridge circuit or a half-bridge circuit.

[0069] The AC side bridge arm 102 includes, for example, at least one cycloconverter, and specifically includes multiple groups of bidirectional switching tubes for AC / AC conversion. Each group of switching tubes includes at least two anti-parallel switching tubes, and the output of the AC side bridge arm 102 provides AC output, for example, to a load or a power grid.

[0070] The controller is used to control the DC side bridge arm 101 and the AC side bridge arm 102 to achieve power conversion.

[0071] 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 voltage step-up or step-down.

[0072] In some embodiments, there can be multiple transformers, and the primary winding of each transformer is connected to a DC side bridge arm, while the secondary winding is connected to the same AC side bridge arm.

[0073] In some embodiments, as shown in Figure 3, the DC / AC converter further includes a resonant circuit 104 connected between the transformer 103 and the AC side bridge arm 102.

[0074] The resonant circuit 104 is used to achieve soft switching of the switching tubes 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.

[0075] The resonant circuit 104 can have various structures, such as single-L, LC, and CLLC.

[0076] In some embodiments, the DC / AC converter further includes a filter circuit 105 connected to the output of the AC side bridge arm 102, for filtering.

[0077] In some embodiments, the DC / AC converter can be a bidirectional converter or a unidirectional converter. It can achieve DC / AC conversion, in which case it works in inverter mode; or it can achieve AC / DC conversion, in which case it works in rectifier mode.

[0078] Based on the DC / AC converter, the application provides a control method of a DC / AC converter, as shown in FIG. 4, the method comprises:

[0079] S402: In the process that the first characteristic parameter of the AC side of the DC / AC converter is close to 0, the absolute value of the first phase shift angle between the DC side bridge arm and the AC side bridge arm is gradually increased; in the process that the first characteristic parameter is far away from 0, the absolute value of the first phase shift angle is gradually decreased.

[0080] The first characteristic parameter is the AC current or the AC voltage.

[0081] In the embodiment, 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 the first phase shift angle between the DC side bridge arm and the AC side bridge arm to gradually increase; 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 gradually decrease, so that the switching frequency is not limited by the maximum switching frequency, the output waveform is improved, and the THD (Total Harmonic Distortion) performance of the DC / AC converter is significantly improved.

[0082] In some embodiments, in the process that the first characteristic parameter is in a preset threshold range and close to 0, the absolute value of the first phase shift angle is gradually increased; in the process that the first characteristic parameter is in the preset threshold range and far away from 0, the absolute value of the first phase shift angle is gradually decreased, and the preset threshold range includes the zero point of the first characteristic parameter.

[0083] The preset threshold range can be set according to the actual limit range of the switching frequency.

[0084] In some embodiments, at the zero crossing point of the first characteristic parameter, the absolute value of the first phase shift angle reaches the maximum value.

[0085] 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. At this time, the polarity of the first phase shift angle is determined based on the polarity of the first characteristic parameter and the second characteristic parameter.

[0086] Specifically, when the first characteristic parameter and the second characteristic parameter are both positive polarity or negative polarity, the first phase shift angle is positive polarity; when one of the first characteristic parameter and the second characteristic parameter is positive polarity and the other is negative polarity, the first phase shift angle is negative polarity.

[0087] It can be understood that the first phase shift angle is positive when its value is greater than 0; the first phase shift angle is negative when its value is less than 0.

[0088] In some embodiments, when the zero-crossing points of the first characteristic parameter and the second characteristic parameter are asynchronous, 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.

[0089] In some embodiments, when the zero-crossing points of the first characteristic parameter and the second characteristic parameter are asynchronous, and the first characteristic parameter is outside the preset threshold range when the second characteristic parameter crosses zero:

[0090] When the first characteristic parameter is within the preset threshold range, and the absolute value of the first characteristic parameter gradually decreases, the absolute value of the first phase shift angle is gradually increased, and 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 gradually reduced.

[0091] In some embodiments, when the zero-crossing points of the first characteristic parameter and the second characteristic parameter are asynchronous, and the first characteristic parameter is within the preset threshold range when the second characteristic parameter crosses zero:

[0092] When the first characteristic parameter is within the preset threshold range, and the absolute value of the first characteristic parameter gradually decreases, the absolute value of the first phase shift angle is gradually increased; during this process, if the second characteristic parameter crosses zero or the first characteristic parameter crosses zero, the polarity of the first phase shift angle is switched at the corresponding zero-crossing point.

[0093] 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 gradually reduced; during this process, when the second characteristic parameter crosses zero, the polarity of the first phase shift angle is switched.

[0094] In some embodiments, the absolute value of the first phase shift angle satisfies a preset soft switching condition of the switch in the DC side bridge arm and the AC side bridge arm.

[0095] 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 with the increase of the absolute value of the second characteristic parameter.

[0096] In some embodiments, the first phase shift angle is a phase difference between bridge arm output voltages of the DC side bridge arm and the AC side bridge arm, the bridge arm output voltages being voltages of the DC side bridge arm and the AC side bridge arm at a port connected with the transformer.

[0097] It can be understood that the "first characteristic parameter zero-crossing point" in the present application refers to the value of the first characteristic parameter becoming 0; and the "second characteristic parameter zero-crossing point" refers to the value of the second characteristic parameter becoming 0.

[0098] In an example embodiment, a circuit schematic diagram of the DC / AC converter is shown in FIG. 5, a DC voltage at the DC side of the DC / AC converter is V in , an AC voltage at the AC side is V ac , and an AC current is I ac The DC side bridge arm 101 adopts an H-bridge structure (i.e., a full-bridge circuit), and an input end is connected in parallel with a capacitor Cin. The DC side bridge arm 101 includes a switching tube Q1H, a switching tube Q1L, a switching tube Q2H, and a switching tube Q2L. Specifically, the switching tube Q1H and the switching tube Q1L are connected in series at the input end to form a half-bridge bridge arm, and the switching tube Q2H and the switching tube Q2L are connected in series at the input end to form another half-bridge bridge arm. The AC side bridge arm 102 includes a cycloconverter formed by two groups of switching tubes connected in series in a common-source mode. Specifically, the two groups of switching 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 switching tubes of the AC side bridge arm 102 includes a switching tube Q3 and a switching tube Q4 connected in a common-source mode, and the second group of switching tubes includes a switching tube Q5 and a switching tube Q6 connected in a common-source mode. The two groups of switching tubes are commonly connected to a bridge arm midpoint. The AC terminals of the AC side bridge arm 102 are connected with a filter circuit 105. The filter circuit 105 includes a capacitor C f connected in parallel with an output end of the AC side bridge arm 102, and an inductor L f connected with a first AC terminal of the AC side bridge arm 102. Meanwhile, a second AC terminal of the AC side bridge arm 102 is connected with one end of a secondary winding of a transformer 103, and the other end of the secondary winding of the transformer 103 is connected with the bridge arm midpoint of the AC side bridge arm 102 through a resonance circuit 104. The resonance circuit 104 includes an inductor Lr and a capacitor Cr connected in series. A turn ratio of the primary winding and the secondary winding of the transformer 103 is 1: n.

[0099] It should be noted that the switching tubes in the DC side bridge arm 101 and the AC side bridge arm 102 are taken as MOS (Metal Oxide Semiconductor) tubes for illustration, but are not limited thereto, and can also be other types of semiconductor switching devices such as IGBT (Insulate-Gate Bipolar Transistor).

[0100] Taking the DC / AC converter shown in Figure 5 as an example, the DC-side bridge arm 101 is an H-bridge structure, and the AC-side bridge arm 102 is a half-bridge cycloconverter. 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 component crosses zero at the point of intersection with the output voltage v of the bridge arm 102 on the AC side. y The phase difference between the zero-crossing points of the fundamental component is denoted as . The phase difference between the output voltages of the two half-bridge arms of the DC-side bridge arm 101 (between output voltage v1 and output voltage v2) is the second phase shift angle, denoted as θ. Figure 6A shows an angle ≥ 0. The timing diagram of each switch when the converter is operating in rectification mode; Figure 6B shows the timing diagram when θ≥0. Timing diagram of each switch when the converter is operating in inverter mode. Where T... s This represents one switching cycle, the first phase shift angle. The range of values ​​for is:

[0101] In some embodiments, to achieve optimal converter efficiency, a second phase shift angle θ and a first phase shift angle are set. The soft-switching condition must be met. Specifically, the soft-switching condition can be:

[0102] in, This represents the boost ratio of the converter.

[0103] Therefore, in at least one embodiment of this application, by controlling the first phase shift angle, the switching frequency of the DC / AC converter is not limited to the maximum switching frequency, which prevents output waveform distortion and improves the performance of the converter. At the same time, each switching transistor in the DC-side bridge arm and the AC-side bridge arm can achieve soft switching under the whole operating condition, which can reduce switching losses and improve the working efficiency of the converter.

[0104] As shown in Figure 7, the controller includes a phase shift angle control unit and a frequency determination unit. The phase shift angle control unit determines the first phase shift angle based on the boost ratio M. The second phase shift angle θ; the frequency determination unit is based on the first phase shift angle. The second phase shift angle θ, and the DC voltage V of the DC / AC circuit. in AC voltage V ac The resonant parameters Lr and Cr of the resonant circuit, the instantaneous control command, and the transformer turns ratio n determine the switching frequency f of the switching transistors in the DC-side bridge arm and the AC-side bridge arm. s .

[0105] The instantaneous control command can be an instantaneous power command P. savg Or instantaneous current command I savg It 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 two directions of power flow (from DC side to AC side or from AC side to DC side).

[0106] System power commands can be preset or obtained through other means.

[0107] The first characteristic parameter will be the alternating current I. ac The second characteristic parameter is the AC voltage V. ac For example, let's take the DC / AC converter shown in Figure 5 as an example.

[0108] In one possible implementation, the DC / AC converter operates with a power factor PF of 1, and the alternating current I... ac With AC voltage V ac Zero-crossing synchronization, first phase shift angle Greater than 0, as shown in Figure 8, in the alternating current I ac During the process of approaching 0, the first phase shift angle The absolute value gradually increases; in the alternating current I ac During the process of moving away from 0, the first phase shift angle The absolute value gradually decreases.

[0109] Furthermore, a preset threshold range can be set to [I] th2 ,I th1 ], in alternating current I ac During the process of changing from positive to negative, when the alternating current I... ac From I th1 It begins to gradually decrease, that is, at the alternating current I ac During the process of approaching 0, the controller controls the first phase shift angle. Start from Gradually increase; when the alternating current I ac When equal to 0, the first phase shift angle Get the maximum value For example, set it to π. In controlling the first phase shift angle... Depend on Increase to During the process, the switching frequency f s It first increased and then decreased, but was never limited to the maximum switching frequency f. smax .

[0110] When the alternating current I ac Starting from 0, it continues to decrease, that is, in the alternating current Iac During the process of moving away from 0, the controller controls the first phase shift angle. Start from Gradually decrease; when the alternating current I ac Reduce to I th2 First phase shift angle Reduce to For example, set to Controlling the first phase shift angle Depend on Reduce to During the process, the switching frequency f s It first increased and then decreased, but was never limited to the maximum switching frequency f. smax .

[0111] As shown in Figure 8, under alternating current I ac During the process of changing from negative to positive, when the alternating current I... ac From I th2 It begins to gradually increase, that is, in the alternating current I ac As the phase approaches zero, the controller begins to control the first phase shift angle. from Gradually increase; when the alternating current I ac When equal to 0, the first phase shift angle Get the maximum value For example, set it to π. In controlling the first phase shift angle... Depend on Increase to During the process, the switching frequency f s It first increased and then decreased, but was never limited to the maximum switching frequency f. smax .

[0112] When the alternating current I ac Starting from 0 and continuing to increase, that is, in the alternating current I ac During the process of moving away from 0, the controller controls the first phase shift angle. It begins to gradually decrease; when the alternating current I... ac Change to I th1 First phase shift angle Reduce to For example, set to Controlling the first phase shift angle Depend on Reduce to During the process, the switching frequency f s It first increased and then decreased, but was never limited to the maximum switching frequency f. smax .

[0113] In some embodiments, when the current threshold relationship is designed as I th1 = -I th2 , the first phase shift angle

[0114] In the technical solution, when the AC current I ac is equal to 0, the first phase shift angle is not limited to be equal to π, but must be greater than

[0115] It can be understood that the application realizes the control of the switching frequency f s by the above-mentioned manner of controlling the first phase shift angle , so that the switching frequency f s is not limited by the maximum switching frequency f smax , the output performance of the DC / AC converter is improved, and meanwhile, the first phase shift angle after control satisfies the soft switching condition, soft switching can be realized under different working conditions, the switching loss is reduced, and the efficiency of the converter is improved.

[0116] In a possible embodiment, the DC / AC converter works under the working condition that the power factor PF is equal to +0.8, the AC current I ac is asynchronous with the zero-crossing point of the AC voltage V ac , the AC current I ac lags behind the AC voltage V ac , and when the AC voltage V ac crosses zero, the AC current I ac is out of the preset threshold range [I th2 , I th1 ] or [I th3 , I th4 ]. Wherein, the first phase shift angle , and the waveform of the switching frequency f s changes with the AC current I ac is shown in FIG. 9, wherein the dashed line represents the absolute value of the first phase shift angle .

[0117] During the process that the AC current I ac changes from positive to negative, when the AC current I ac begins to gradually decrease from I th1 , i.e., during the process that the AC current I ac is close to 0, the first phase shift angle is less than 0, and the controller controls the absolute value of the first phase shift angle to begin to gradually increase (as shown by the dashed line), corresponding to the control of the first phase shift angle from gradually decreases to for example to -π; in controlling the first phase shift angle by decreases to (i.e. the absolute value of the first phase shift angle increases from to ) the switching frequency f s gradually increases, but is always limited to the maximum switching frequency f smax . When the alternating current I ac is equal to 0, the polarity of the first phase shift angle is switched, the first phase shift angle is controlled from to (i.e. from to and for example can be mutually opposite.

[0118] When the alternating current I ac continues to decrease from 0, i.e. in the course of said alternating current I ac moving away from 0, the controller controls the first phase shift angle to gradually decrease from ; when the alternating current I ac changes to I th2 , the first phase shift angle decreases to for example to In controlling the first phase shift angle by decreases to the switching frequency f s gradually decreases, is always limited to the maximum switching frequency f smax .

[0119] In the course of the alternating voltage V ac tending towards 0 from positive, the first phase shift angle is greater than 0, the first phase shift angle is controlled to gradually increase to In the alternating voltage V ac is equal to 0, the polarity of the first phase shift angle is switched, the first phase shift angle is controlled from to and for example can be mutually opposite, from the moment when the alternating voltage V ac is equal to 0 to the moment when the alternating current I ac is equal to I th1At the moment when the alternating current I ac Outside the preset threshold range, and the AC voltage V ac As the absolute value gradually increases, the first phase shift angle is controlled. The absolute value gradually decreases due to the first phase shift angle. During this period, the first phase shift angle is less than 0. from Gradually increase to During this period, the switching frequency f s It gradually increases, but is never limited to the maximum switching frequency f. smax .

[0120] In alternating current I ac During the process of changing from negative to positive, when the alternating current I... ac From I th3 It begins to gradually increase, that is, in the alternating current I ac During the process of approaching 0, the controller controls the first phase shift angle. The absolute value begins to gradually increase due to the first phase shift angle. A value less than 0 corresponds to controlling the first phase shift angle. from Gradually decrease to For example, it can be set to -π; in controlling the first phase shift angle Depend on Reduce to (i.e., the first phase shift angle) The absolute value from Increase to During the process, the switching frequency f s Although it gradually increased, it was never limited to the maximum switching frequency f. smax When the alternating current I ac When the value is 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 opposites.

[0121] When the alternating current I ac Continue to increase from 0, that is, in the alternating current I ac During the process of moving away from 0, the controller controls the first phase shift angle. Start from Gradually decrease; when the alternating current I ac Change to I th4 First phase shift angle Reduce to For example, set to Controlling the first phase shift angle Depend on Reduce to During the process, the switching frequency f s It gradually decreased, but was never limited to the maximum switching frequency f. smax .

[0122] In AC voltage V ac During the process of the phase shifting from negative to 0, the first phase shift angle is controlled. Gradually increase to In AC voltage V ac When the value is 0, switch the first phase shift angle. The polarity controls the first phase shift angle. from Switch to and For example, they can be opposites, from AC voltage V ac From the moment when it equals 0 until the alternating current I ac equals I th3 At the moment when the alternating current I ac Outside the preset threshold range, and the AC voltage V ac As the absolute value gradually increases, the first phase shift angle is controlled. The absolute value gradually decreases due to the first phase shift angle. During this period, the first phase shift angle is less than 0. from Gradually increase to During this period, the switching frequency f s Although it gradually increased, it was never limited to the maximum switching frequency f. smax .

[0123] In some specific implementations, when the current threshold relationship is I th1 =-I th3 I th4 =-I th2 At that time, you can set

[0124] In one possible implementation, the DC / AC converter operates with a power factor PF of -0.8, and the AC current I... ac With AC voltage V ac The zero-crossing points are not synchronized, and the alternating current I ac Leading AC voltage V ac And AC voltage V ac AC current I at zero crossing acIt is outside the preset threshold range, which is [I th2 ,I th1 ]、[I th3 ,I th4 ]. Among them, the first phase shift angle Switching frequency f s With alternating current I ac The changing waveform is shown in Figure 10.

[0125] In alternating current I ac During the process of changing from positive to negative, in the alternating current I ac From I th1 During the process of decreasing to 0, that is, during the alternating current I... ac During the process of approaching 0, the first phase shift angle If the value is greater than 0, the controller controls the first phase shift angle. from Gradually increase to For example, set it to π; in controlling the first phase shift angle Depend on Increase to During the process, the switching frequency f s Although it gradually increased, it was never limited to the maximum switching frequency f. smax When the alternating current I ac When the value is 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 opposites.

[0126] When the alternating current I ac It continues to decrease from 0, that is, in the alternating current I ac During the process of moving away from 0, the controller controls the first phase shift angle. The absolute value begins to decrease during this period due to the first phase shift angle. Less than 0, corresponding to the first phase shift angle of control from Gradually increase; when the alternating current I ac Reduce to I th2 Control the first phase shift angle Increase to For example, set to Controlling the first phase shift angle Depend on Increase to During the process, the switching frequency f sIt gradually decreased, but was never limited to the maximum switching frequency f. smax .

[0127] In AC voltage V ac During the process of the alternating current I approaching 0, ac equals I th2 From the moment until the AC voltage V ac The moment when the current I equals 0, i.e., when the alternating current I... ac Outside the preset threshold range, and the AC voltage V ac As the absolute value gradually decreases, the first phase shift angle is controlled. The absolute value gradually increases during this period, due to the first phase shift angle. Less than 0, corresponding to the first phase shift angle of control from Reduce to During this period, the switching frequency f s It gradually decreased, but was never limited to the maximum switching frequency f. smax At AC voltage V ac When the value is 0, switch the first phase shift angle. The polarity controls the first phase shift angle. from Switch to and For example, they can be opposites.

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

[0129] When the alternating current I a is increased from 0, i.e. in the course of the alternating current I ac moving away from 0, the controller controls the first phase shift angle whose absolute value begins to decrease, specifically the first phase shift angle is gradually increased from When the alternating current I ac is increased to I th4 , the first phase shift angle is increased to for example to In the course of the first phase shift angle being increased from to , the switching frequency f s is gradually decreased and is not limited to the maximum switching frequency f smax at any time.

[0130] In the course of the alternating voltage V ac tending towards 0 from negative, from the moment when the alternating current I ac equals I th4 to the moment when the alternating voltage V ac equals 0, i.e. in the course of the alternating current I ac being outside the predetermined threshold range and the absolute value of the alternating voltage V ac gradually decreasing, the controller controls the first phase shift angle whose absolute value is gradually increased, since in this period the first phase shift angle is less than 0, the corresponding first phase shift angle is decreased from to In this period the switching frequency f s is gradually decreased and is not limited to the maximum switching frequency f smax at any time. At the moment when the alternating voltage V ac equals 0, the polarity of the first phase shift angle is switched, the first phase shift angle is switched from to and for example can be mutually opposite.

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

[0132] In one possible implementation, the DC / AC converter operates with a power factor PF of +0.99 and an AC current I... ac Lagging AC voltage V ac And AC voltage V ac AC current I at zero crossing 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 that varies with alternating current is shown in Figure 11.

[0133] The difference from the embodiment shown in Figure 9 is that the AC voltage V ac In alternating current I ac From I th1 Decrease to 0, and from I th3 The voltage increases to zero during the process of crossing zero, therefore the controller needs an AC voltage V during this process. ac Zero-crossing switching of the first phase angle The polarity of.

[0134] Specifically, in alternating current I ac From I th1 During the process of reducing to 0, that is, during the alternating current I ac During the process of approaching 0, the controller controls the first phase shift angle. The absolute value of the value begins to gradually increase, corresponding to the control of the first phase shift angle. from It begins to gradually increase; when the AC voltage V ac When equal to 0, the first phase shift angle Increase to Simultaneously, the controller switches the polarity of the first phase shift angle, controlling the first phase shift angle. from Switch to ( Less than 0), and For example, they are opposites; in alternating current I ac During the process of continuing to decrease to 0, control the first phase shift angle. As the absolute value continues to increase, the corresponding control first phase shift angle... from Gradually decrease to When the alternating current I ac When the value is 0, control the first phase shift angle. from Switch to ( (greater than 0), and For example, they are opposites.

[0135] In alternating current I ac From I th3 During the process of increasing to 0, that is, during the alternating current I ac During the process of approaching 0, the controller controls the first phase shift angle. The absolute value of the value begins to gradually increase, corresponding to the control of the first phase shift angle. from It begins to gradually increase; when the AC voltage V ac When equal to 0, the first phase shift angle Increase to Simultaneously, the controller switches the polarity of the first phase shift angle, controlling the first phase shift angle. from Switch to ( Less than 0), and For example, they are opposites; in alternating current I ac As the phase angle continues to increase to 0, control the first phase shift angle. As the absolute value continues to increase, the corresponding control first phase shift angle... from Gradually decrease to When the alternating current I ac When the value is 0, the controller switches the first phase shift angle. The polarity controls the first phase shift angle. from Switch to ( (greater than 0), and For example, they are opposites.

[0136] In the above alternating current I ac During the change process, the switching frequency f s It was never limited to the maximum switching frequency f. smax .

[0137] In one possible implementation, the DC / AC converter operates with a power factor PF of -0.99 and an AC current I... ac Leading AC voltage V ac And AC voltage V ac AC current I at zero crossing ac Within the preset threshold range, the preset threshold range is [I th2 ,Ith1 ]、[I th3 ,I th4 ]. Among them, the first phase shift angle Switching frequency f s The waveform that varies with alternating current is shown in Figure 12.

[0138] The difference from the embodiment shown in Figure 10 is that the AC voltage V ac In alternating current I ac Decrease from 0 to I th2 and increasing from 0 to I th4 During the process, the voltage crosses zero, therefore the controller needs an AC voltage V during this process. ac Zero-crossing switching of the first phase angle The polarity of.

[0139] Specifically, in alternating current I ac Decrease from 0 to I th2 During the process, that is, in the alternating current I ac During the process of moving away from 0, the controller controls the first phase shift angle. The absolute value of the value begins to gradually decrease, corresponding to the control of the first phase shift angle. from It begins to gradually increase; when the AC voltage V ac When equal to 0, the first phase shift angle Increase to Simultaneously, the controller switches the polarity of the first phase shift angle, controlling the first phase shift angle. from Switch to ( (greater than 0), and For example, they are opposites; in alternating current I ac Continue to reduce I th2 During the process, control the first phase shift angle from Gradually decrease to

[0140] When the alternating current I ac Increase from 0 to I th4 During the process, that is, in the alternating current I ac During the process of moving away from 0, the controller controls the first phase shift angle. The absolute value of the value begins to gradually decrease, corresponding to the control of the first phase shift angle. from It begins to gradually increase; when the AC voltage V ac When 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, controls the first phase shift angle From switches to ( greater than 0), and for example, are opposite numbers; in the alternating current I ac continues to increase to I th4 , the process of controlling the first phase shift angle From gradually decreases to

[0141] In the process of changing the above alternating current I ac , the switching frequency f s is always limited to the maximum switching frequency f smax .

[0142] In some embodiments, the first characteristic parameter is the alternating voltage V ac , the second characteristic parameter is the alternating current I ac , and the corresponding controller sets the corresponding preset threshold range as a condition with the alternating voltage V ac , when the alternating voltage V ac is within the preset threshold range, the controller adjusts the first phase shift angle to achieve that the switching frequency f s is always limited to the maximum switching frequency f smax .

[0143] Specifically, in the process of changing the alternating voltage V ac from the voltage threshold to 0, the absolute value of the first phase shift angle is gradually increased; in the process of changing the alternating voltage V ac from 0 to the voltage threshold, the absolute value of the first phase shift angle is gradually reduced.

[0144] It should be noted that the control method proposed in the present application can also be used for other topological structure DC / AC converters.

[0145] In some example embodiments, as shown in FIG. 13, the AC side bridge arm 102 of the DC / AC converter comprises a cyclo-converter composed of two groups of switch tubes. Compared with the DC / AC converter shown in FIG. 5, the first group of switch tubes comprises switch tube Q8 and switch tube Q9 connected in reverse series, and the second group of switch tubes comprises switch tube Q7 and switch tube Q10 connected in reverse series through the first group of switch tubes. One end of the secondary winding of the transformer 103 is connected to the connection midpoint of switch tube Q7 and switch tube Q8 through the resonant circuit 104, and the other end of the secondary winding of the transformer 103 is connected to the midpoint of switch tube Q9 and switch tube Q10. The source of switch tube Q7 is connected to the source of switch tube Q8, and the source of switch tube Q9 is connected to the source of switch tube Q10.

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

[0147] In some example embodiments, as shown in FIG. 13, the AC side bridge arm 102 of the DC / AC converter comprises a cyclo-converter composed of two groups of switch tubes. Compared with the DC / AC converter shown in FIG. 5, the first group of switch tubes comprises switch tube Q8 and switch tube Q9 connected in reverse series, and the second group of switch tubes comprises switch tube Q7 and switch tube Q10 connected in reverse series through the first group of switch tubes. One end of the secondary winding of the transformer 103 is connected to the connection midpoint of switch tube Q7 and switch tube Q8 through the resonant circuit 104, and the other end of the secondary winding of the transformer 103 is connected to the midpoint of switch tube Q9 and switch tube Q10. The source of switch tube Q7 is connected to the source of switch tube Q8, and the source of switch tube Q9 is connected to the source of switch tube Q10.

[0148] In some example embodiments, as shown in FIG. 16, the AC side bridge arm 102 of the DC / AC converter is a full-bridge topology. Compared with the DC / AC converter shown in FIG. 5, 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 with 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 with the second end of the secondary winding of the transformer 103. The first upper bridge arm includes two reversely connected switch tubes Q19, Q20; the first lower bridge arm includes two reversely connected switch tubes Q23, Q24; the second upper bridge arm includes two reversely connected switch tubes Q21, Q22; and the second lower bridge arm includes two reversely connected switch tubes Q25, Q26.

[0149] In some example embodiments, as shown in FIG. 17, the DC / AC converter is a three-phase DC / AC converter, which provides a three-phase AC output. Compared with the DC / AC converter shown in FIG. 5, the AC side bridge arm 102 of the DC / AC converter includes three groups of reversely connected switch tubes, and each group of switch tubes is connected in series with a capacitor. The first group of switch tubes includes switch tubes Q27, Q28 connected in common source, the second group of switch tubes includes switch tubes Q29, Q30 connected in common source, and the third group of switch tubes includes switch tubes Q31, Q32 connected in common source, and the three groups of switch tubes are connected to a point. The first group of switch tubes and the 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 the capacitor Cr4 are connected to another node, which serves as the second AC terminal of the AC side bridge arm 102; and the third group of switch tubes and the 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 capacitors Cr3, Cr4 and Cr5. The inductor Lr, the capacitors Cr3, Cr4 and Cr5 form a resonant circuit 104. In some other example embodiments, the capacitors Cr3, Cr4 and Cr5 can be respectively replaced by two switch tubes connected in common source, and a capacitor connected in series with the inductor Lr can be added to form a resonant circuit.

[0150] In the DC / AC converters of the example embodiments shown in FIGS. 13-17, the controller can adopt the control method of the example embodiments described above. In the process that the AC current or the AC voltage 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 gradually increased; in the process that the AC current or the AC voltage is far away from 0, the absolute value of the first phase shift angle is gradually decreased, and the switching frequency fs is always not limited to the maximum switching frequency f smax .

Claims

1. A DC / AC converter, characterized by, 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; The controller is configured to gradually increase an absolute value of a first phase shift angle between the DC side bridge arm and the AC side bridge arm when a first characteristic parameter of the AC side of the DC / AC converter approaches 0, and gradually decrease the absolute value of the first phase shift angle when the first characteristic parameter is away from 0. The first characteristic parameter is an AC current or an AC voltage.

2. The DC / AC converter of claim 1, wherein, The controller is configured to gradually increase the absolute value of the first phase shift angle when the first characteristic parameter is within a preset threshold range and approaches 0, and gradually decrease the absolute value of the first phase shift angle when the first characteristic parameter is within the preset threshold range and is away from 0.

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

4. The DC / AC converter according to claim 1 or 2, wherein, The first characteristic parameter is one of the AC current and the AC voltage, and a second characteristic parameter of the AC side of the DC / AC converter is the other of the AC current and the AC voltage. The controller is configured to control the first phase shift angle to be positive when both the first characteristic parameter and the second characteristic parameter are positive or negative, and control the first phase shift angle to be negative when one of the first characteristic parameter and the second characteristic parameter is positive and the other is negative.

5. The DC / AC converter of claim 4, wherein, The controller is configured to switch the polarity of the first phase shift angle at a zero-crossing point of the first characteristic parameter or a zero-crossing point of the second characteristic parameter when the zero-crossing points of the first characteristic parameter and the second characteristic parameter are asynchronous.

6. The DC / AC converter of claim 5, wherein, When the zero-crossing points of the first characteristic parameter and the second characteristic parameter are asynchronous, and the first characteristic parameter is outside a preset threshold range when the second characteristic parameter is at the zero-crossing point: The controller is configured to gradually increase the absolute value of the first phase shift angle when the first characteristic parameter is within the preset threshold range and the absolute value of the first characteristic parameter gradually decreases, and switch the polarity of the first phase shift angle when the absolute value of the first characteristic parameter decreases to 0; and gradually decrease the absolute value of the first phase shift angle when the absolute value of the first characteristic parameter gradually increases.

7. The DC / AC converter of claim 5, wherein, When the zero-crossing points of the first characteristic parameter and the second characteristic parameter are asynchronous, and the first characteristic parameter is within the preset threshold range when the second characteristic parameter is at the zero-crossing point: The controller is configured to gradually increase the absolute value of the first phase shift angle when the first characteristic parameter is within the preset threshold range and the absolute value of the first characteristic parameter gradually decreases, and switch the polarity of the first phase shift angle at the corresponding zero-crossing point when the second characteristic parameter is at the zero-crossing point or the first characteristic parameter is at the zero-crossing point. The controller is further configured to control the first phase shift angle to gradually decrease in absolute value when the first characteristic parameter is within the preset threshold range and gradually increases in absolute value, and switch the polarity of the first phase shift angle when the second characteristic parameter crosses zero.

8. The DC / AC converter of claim 1 or 2, wherein, The first phase shift angle satisfies soft switching of the switching tubes in the DC side bridge arm and the AC side bridge arm.

9. The DC / AC converter of claim 4, wherein, The controller is configured to control the first phase shift angle to decrease in absolute value as the second characteristic parameter increases in absolute value when the first characteristic parameter is outside the preset threshold range.

10. The DC / AC converter of claim 1 or 2, wherein, The first phase shift angle is a phase difference between bridge arm output voltages of the DC side bridge arm and the AC side bridge arm, and the bridge arm output voltage is a voltage of a port connected to the transformer.

11. The DC / AC converter of claim 1, wherein, -π≤ the first phase shift angle ≤π.

12. The DC / AC converter of claim 1, wherein, The AC side bridge arm comprises a cycloconverter for AC / AC conversion.

13. The DC / AC converter of claim 1, wherein, The DC / AC converter further comprises a resonant circuit 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 of claim 1, wherein, The DC side bridge arm comprises a full-bridge circuit or a half-bridge circuit.

15. A control method of a DC / AC converter including 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, characterized by, The method comprises: controlling the first phase shift angle between the DC side bridge arm and the AC side bridge arm to gradually increase in absolute value when a first characteristic parameter at the AC side of the DC / AC converter is close to 0, and gradually decrease in absolute value when the first characteristic parameter is far from 0; The first characteristic parameter is an AC current or an AC voltage.

16. The method of claim 15, wherein, controlling the first phase shift angle to gradually increase in absolute value when the first characteristic parameter is within a preset threshold range and close to 0, and gradually decrease in absolute value when the first characteristic parameter is within the preset threshold range and far from 0, the preset threshold range including a zero point of the first characteristic parameter.

17. The method of claim 15 or 16, wherein, The first phase shift angle reaches a maximum value in absolute value at the zero crossing point of the first characteristic parameter.

18. The method of claim 15 or 16, wherein, The first characteristic parameter is one of the AC current and the AC voltage, and a second characteristic parameter at the AC side of the DC / AC converter is the other of the AC current and the AC voltage. The first phase shift angle is positive polarity when the first characteristic parameter and the second characteristic parameter are both positive polarity or negative polarity, and is negative polarity when one of the first characteristic parameter and the second characteristic parameter is positive polarity and the other is negative polarity.

19. The method of claim 18, wherein, Switching 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 when the zero crossing points of the first characteristic parameter and the second characteristic parameter are not synchronized.

20. The method of claim 19, wherein, 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 zero, When the first characteristic parameter is within the preset threshold range, and the absolute value of the first characteristic parameter gradually decreases, the absolute value of the first phase shift angle is gradually increased, and 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 gradually reduced.

21. The method of claim 19, wherein, 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 zero: When the first characteristic parameter is within the preset threshold range, and the absolute value of the first characteristic parameter gradually decreases, the absolute value of the first phase shift angle is gradually increased; during this process, if the second characteristic parameter crosses zero or the first characteristic parameter crosses zero, the polarity of the first phase shift angle is switched at the corresponding zero-crossing point; When the first characteristic parameter is within the preset threshold range, and the absolute value of the first characteristic parameter gradually increases, the absolute value of the first phase shift angle is gradually reduced; during this process, when the second characteristic parameter crosses zero, the polarity of the first phase shift angle is switched.

22. The method of claim 15 or 16, wherein, 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 of claim 18, wherein, When the first characteristic parameter is outside the preset threshold range, the absolute value of the first phase shift angle is reduced as the absolute value of the second characteristic parameter increases.

24. The method of claim 15 or 16, wherein, 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 port connected to the transformer.

25. The method of claim 15, wherein, -π≤ first phase shift angle ≤π.

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