Power converter and control method thereof

Abstract

The invention relates to the technical field of power electronics, in particular to a power converter and a control method thereof. The power converter comprises a primary side bridge arm, a secondary side bridge arm, a resonance circuit connected between the primary side bridge arm and the secondary side bridge arm, and a controller connected with the primary side bridge arm and the secondary side bridge arm. The controller is used for controlling an absolute value of a current angle of the resonant cavity to be smaller than or equal to an absolute value of a first phase shift angle between the primary side bridge arm and the secondary side bridge arm so as to realize soft switching of switching tubes in the primary side bridge arm and the secondary side bridge arm; the resonant cavity current angle is the phase difference between the resonant cavity current and the bridge arm output voltage of the primary side bridge arm, and the polarity of the resonant cavity current angle is the same as that of the first phase shift angle. The soft switching of the switching tubes in the primary side bridge arm and the secondary side bridge arm can be ensured, and the power converter can work in the optimal state under different working conditions.

Description

Technical Field

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

[0002] Resonant power converters are used for power conversion. For example, they can invert direct current into alternating current, or convert low-voltage direct current into high-voltage direct current, etc. Currently, they have been widely used in photovoltaic power generation systems, energy storage systems, etc.

[0003] In order to improve the efficiency and EMI performance of resonant power converters, resonant power converters are generally designed to operate in an optimal state of soft switching, minimum resonant cavity current, and lowest switching frequency. Since the control model of resonant power converters is generally obtained by fundamental wave analysis, and the control quantities of resonant power converters, such as phase shift angles and switching frequencies, are obtained by predictive control. However, the fundamental wave analysis ignores the harmonic content, and there are differences between the fundamental wave waveform used for analysis and the actual excitation waveform. At the same time, there are also differences between the driving signals and parameters of the power converter and the theory. Therefore, the control quantities obtained by predictive control cannot ensure that the resonant converter operates in soft switching and achieves the optimal operation. Summary of the Invention

[0004] Based on this, it is necessary to provide a power converter and its control method for the above technical problems.

[0005] In a first aspect, an embodiment of the present invention provides a power converter, including a primary side bridge arm, a secondary side bridge arm, a resonant circuit connected between the primary side bridge arm and the secondary side bridge arm, and a controller connected to the primary side bridge arm and the secondary side bridge arm;

[0006] The controller is configured to control the absolute value of the resonant cavity current angle to be less than or equal to the absolute value of a first phase shift angle between the primary side bridge arm and the secondary side bridge arm to achieve soft switching of the switching tubes in the primary side bridge arm and the secondary side bridge arm. The resonant cavity current angle is the phase difference between the resonant cavity current and the bridge arm output voltage of the primary side bridge arm, where the resonant cavity current angle has the same polarity as the first phase shift angle.

[0007] In some embodiments, when there is a second phase shift angle between the arms of the primary side bridge arm, the controller further controls the absolute value of the resonant cavity current angle to be greater than or equal to half of the second phase shift angle, and the second phase shift angle is greater than or equal to 0.

[0008] In some embodiments, when there is a third phase shift angle between the arms of the secondary side bridge arm, the controller further controls the absolute value of the resonant cavity current angle to be less than or equal to the difference between the absolute value of the first phase shift angle and half of the third phase shift angle, and the third phase shift angle is greater than or equal to 0.

[0009] In some embodiments, when the voltage gain of the power converter is less than or equal to 1, the controller controls the absolute value of the difference between the resonant cavity current angle and the first phase shift angle to be less than or equal to a first threshold.

[0010] In some embodiments, when the voltage gain of the power converter is greater than 1, the controller further controls the absolute value of the resonant cavity current angle to be less than or equal to a second threshold.

[0011] In some embodiments, when there is a second phase shift angle between the arms of the primary side bridge arm and the voltage gain of the power converter is greater than 1, the controller further controls the second phase shift angle to be equal to 0.

[0012] In some embodiments, when there is a third phase shift angle between the arms of the secondary side bridge arm and the voltage gain of the power converter is less than or equal to 1, the controller further controls the third phase shift angle to be equal to 0.

[0013] In some embodiments, when there is a second phase shift angle between the arms of the primary side bridge arm, the controller further controls the absolute value of the difference between the resonant cavity current angle and half of the second phase shift angle to be less than or equal to a third threshold, where the second phase shift angle is greater than or equal to 0.

[0014] In some embodiments, if there is a third phase shift angle in the secondary side bridge arm, the controller further controls the absolute value of the difference between the first phase shift angle and the sum of half of the third phase shift angle and the absolute value of the resonant cavity current angle to be less than or equal to a fourth threshold, where the third phase shift angle is greater than or equal to 0.

[0015] In some embodiments, when the voltage gain of the power converter is less than or equal to 1 and the power converter operates in the forward direction, the controller controls the difference between the first phase shift angle and the resonant cavity current angle to be less than a first threshold, and both the first phase shift angle and the resonant cavity current angle are greater than or equal to 0.

[0016] In some embodiments, when the voltage gain of the power converter is greater than 1 and the power converter operates in the forward direction, the controller controls the resonant cavity current angle to be less than a second threshold, and the resonant cavity current angle is greater than or equal to 0.

[0017] In some embodiments, when the voltage gain of the power converter is less than or equal to 1 and the power converter operates in the reverse direction, the controller controls the difference between the resonant cavity current angle and the first phase shift angle to be less than a first threshold, and both the first phase shift angle and the resonant cavity current angle are less than 0.

[0018] In some embodiments, when the voltage gain of the power converter is greater than 1 and the power converter operates in reverse, the controller controls the absolute value of the resonant cavity current angle to be less than a second threshold, and the resonant cavity current angle is less than 0.

[0019] In some embodiments, the controller performs closed-loop control based on the resonant cavity current angle to obtain an adjustment value of the phase shift angle of the power converter, and obtains a final value of the phase shift angle based on the adjustment value of the phase shift angle and the initial value of the phase shift angle. The phase shift angle of the power converter includes at least one of a first phase shift angle between the primary bridge arm and the secondary bridge arm, a second phase shift angle of the primary bridge arm, or a third phase shift angle of the secondary bridge arm.

[0020] In some embodiments, the controller calculates the initial value of the phase shift angle and the switching frequency of the power converter based on the voltage gain of the power converter and an instantaneous control instruction, and generates a control signal of the power converter based on the switching frequency and the final value of the phase shift angle, where the instantaneous control instruction is an instantaneous current instruction or an instantaneous power instruction.

[0021] In some embodiments, the controller calculates the first phase shift angle based on the voltage gain of the power converter, an instantaneous control instruction, and a preset difference, where the preset difference is the difference between the resonant cavity current angle and a reference value of the resonant cavity current angle, and the reference value is the first phase shift angle or 0.

[0022] In some embodiments, the primary bridge arm is a half-bridge circuit or a full-bridge circuit.

[0023] In some embodiments, the secondary bridge arm includes a cycloconverter or a rectifier circuit.

[0024] In a second aspect, an embodiment of the present invention provides a control method for a power converter. The power converter includes a primary bridge arm, a secondary bridge arm, and a resonant circuit connected between the primary bridge arm and the secondary bridge arm. The method includes:

[0025] Controlling the absolute value of the resonant cavity current angle to be less than or equal to the absolute value of the first phase shift angle between the primary bridge arm and the secondary bridge arm to implement soft switching of the switching tubes in the primary bridge arm and the secondary bridge arm. The resonant cavity current angle is the phase difference between the resonant cavity current and the bridge arm output voltage of the primary bridge arm, where the resonant cavity current angle has the same polarity as the first phase shift angle.

[0026] In some embodiments, the method further includes: when there is a second phase shift angle between the arms of the primary bridge arm, further controlling the absolute value of the resonant cavity current angle to be greater than or equal to half of the second phase shift angle, and the second phase shift angle is greater than or equal to 0.

[0027] In some embodiments, the method further includes: when there is a third phase shift angle between the arms of the secondary side bridge arm, further controlling the absolute value of the resonant cavity current angle to be less than or equal to the difference between the absolute value of the first phase shift angle and half of the third phase shift angle, where the third phase shift angle is greater than or equal to 0.

[0028] In some embodiments, the method further includes: when the voltage gain of the power converter is less than or equal to 1, controlling the absolute value of the difference between the resonant cavity current angle and the first phase shift angle to be less than or equal to a first threshold.

[0029] In some embodiments, the method further includes: when the voltage gain of the power converter is greater than 1, further controlling the absolute value of the resonant cavity current angle to be less than or equal to a second threshold.

[0030] In some embodiments, the method further includes: when there is a second phase shift angle between the arms of the primary side bridge arm and the voltage gain of the power converter is greater than 1, further controlling the second phase shift angle to be equal to 0.

[0031] In some embodiments, the method further includes: when there is a third phase shift angle between the arms of the secondary side bridge arm and the voltage gain of the power converter is less than or equal to 1, further controlling the third phase shift angle to be equal to 0.

[0032] In some embodiments, the method further includes: when there is a second phase shift angle between the arms of the primary side bridge arm, further controlling the difference between the absolute value of the resonant cavity current angle and half of the second phase shift angle to be less than or equal to a third threshold, where the second phase shift angle is greater than or equal to 0.

[0033] In some embodiments, the method further includes: if there is a third phase shift angle in the secondary side bridge arm, further controlling the difference between the absolute value of the first phase shift angle, half of the third phase shift angle, and the absolute value of the resonant cavity current angle to be less than or equal to a fourth threshold, where the third phase shift angle is greater than or equal to 0.

[0034] By controlling the resonant cavity current angle in the present application, the absolute value of the resonant cavity current angle is less than or equal to the absolute value of the first phase shift angle between the primary side bridge arm and the secondary side bridge arm, which can ensure the realization of soft switching of the switching tubes in the primary side bridge arm and the secondary side bridge arm, and helps the power converter to work in an optimal state under different working conditions. Description of the Drawings

[0035] Figure 1 It is a schematic structural block diagram of a power converter in an embodiment of the present application;

[0036] Figure 2 It is a schematic structural block diagram of a power converter in another embodiment of the present application;

[0037] Figure 3 Schematic diagram of the circuit of the power converter in an exemplary embodiment of the present application;

[0038] Figure 4 Schematic diagram of the waveform when the power converter operates in reverse in an exemplary embodiment of the present application;

[0039] Figure 5 Schematic diagram of the waveform when the power converter operates in the forward direction in an exemplary embodiment of the present application;

[0040] Figure 6 Schematic diagram of the circuit of the power converter in another exemplary embodiment of the present application;

[0041] Figure 7 Vector diagram when M≤1 and the power converter operates in the state of minimum resonant cavity current in an exemplary embodiment of the present application;

[0042] Figure 8 Vector diagram when M>1 and the power converter operates in the state of minimum resonant cavity current in an exemplary embodiment of the present application;

[0043] Figure 9 Schematic diagram of the control logic of the controller in an exemplary embodiment of the present application;

[0044] Figure 10 Schematic diagram of the control logic of the controller in another exemplary embodiment of the present application;

[0045] Figure 11 Schematic diagram of the control logic of the controller in yet another exemplary embodiment of the present application. Detailed implementation manners

[0046] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be described and explained below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments provided in the present application without creative efforts fall within the scope of protection of the present application. In addition, it can also be understood that although the efforts made in such a development process may be complex and lengthy, for those of ordinary skill in the art related to the content disclosed in the present application, some design, manufacturing or production changes based on the technical content disclosed in the present application are only conventional technical means and should not be understood that the content disclosed in the present application is insufficient.

[0047] As used herein, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment can be included in at least one embodiment of the present application. The phrase may not necessarily refer to the same embodiment when it appears in various places in the specification, 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 the present application can be combined with other embodiments without conflict.

[0048] Unless otherwise defined, technical terms or scientific terms involved in the present application shall have the ordinary meaning as understood by those of ordinary skill in the technical field to which the present application pertains. The words such as "a", "an", "one", "the" and the like involved in the present application do not denote a limitation of quantity and may represent a singular or plural number. The terms "comprising", "including", "having" and any variations thereof involved in the present application are intended to cover non-exclusive inclusion; 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 further include unlisted steps or units, or may further include other steps or units inherent to these processes, methods, products or devices. The terms "connected", "coupled" and the like involved in the present application are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The term "plurality" involved in the present application means greater than or equal to two. "And / or" describes the association relationship of associated objects and indicates that three relationships may exist. For example, "A and / or B" may represent: A exists alone, A and B exist simultaneously, and B exists alone. The terms "first", "second", "third" and the like involved in the present application are only used to distinguish similar objects and do not represent a specific order of the objects.

[0049] As described above, since the fundamental wave analysis method ignores the harmonic content, there is a difference between the fundamental wave waveform used for analysis and the actual excitation waveform. At the same time, there are also differences between the actual and theoretical drive signals and parameters of the power converter. Therefore, the preset values of the phase shift angle and the switching frequency obtained by predictive control cannot ensure that the power converter operates in soft switching.

[0050] According to an embodiment of the present application, a power converter is provided. By controlling the angle of the resonant cavity current of the power converter, the absolute value of the angle of the resonant cavity current is made less than or equal to the absolute value of the phase shift angle between the primary bridge arm and the secondary bridge arm, which can ensure the realization of soft switching of the switching tubes in the primary bridge arm and the secondary bridge arm, and helps the power converter to operate in an optimal state under different working conditions.

[0051] Figure 1A schematic structural diagram of a power converter according to an embodiment provided by this application, including a primary bridge arm 101, a secondary bridge arm 102, a resonant circuit 103 connected between the primary bridge arm 101 and the secondary bridge arm 102, and a controller (not shown in the figure) connected to the primary bridge arm 101 and the secondary bridge arm 102.

[0052] The primary bridge arm 101 is an inverter circuit, including at least two switching tubes, for inverting direct current into alternating current.

[0053] In some embodiments, the power converter is a DC / AC converter. The secondary bridge arm 102 includes, for example, a cycloconverter, and the cycloconverter includes multiple groups of switching tubes for performing AC-AC conversion. Among them, each group of switching tubes includes at least two switching tubes connected in reverse. The output end of the secondary bridge arm 102 provides an AC output, for example, to a load or the power grid.

[0054] In some other embodiments, the power converter is a DC / DC converter, such as a dual-active-bridge DC / DC converter. At this time, the secondary bridge arm 102 includes a rectifier circuit for rectifying alternating current into direct current and can supply power to a DC load.

[0055] The resonant circuit 103 is used to realize soft switching of the switching tubes in the power converter, thereby reducing circuit losses.

[0056] The circuit form of the resonant circuit 103 can be various structures such as single-L, LC, and CLLC.

[0057] The controller is used to control the primary bridge arm 101 and the secondary bridge arm 102 to achieve power conversion.

[0058] In some embodiments, as Figure 2 shown, the power converter further includes a transformer 104 connected between the resonant circuit 103 and the primary bridge arm 101. The transformer 104 can be used for boosting.

[0059] In some embodiments, the transformer 104 can also be arranged between the resonant circuit 103 and the secondary bridge arm 102.

[0060] In some embodiments, there can be multiple transformers 104. The primary winding of each transformer 104 is correspondingly connected to a primary bridge arm 101, and the secondary winding is correspondingly connected to the same secondary bridge arm 102.

[0061] In some embodiments, the power converter further includes a filter circuit 105 connected to the output end of the secondary bridge arm 102 for filtering.

[0062] In some embodiments, the power converter can work bidirectionally to realize bidirectional energy flow.

[0063] To ensure that the power converter operates in soft switching, the controller controls the angle of the resonant cavity current such that the absolute value of the angle of the resonant cavity current is less than or equal to the absolute value of the phase shift angle between the primary bridge arm 101 and the secondary bridge arm 102, which can ensure the realization of soft switching of the switching tubes in the primary bridge arm 101 and the secondary bridge arm 102, and helps the power converter to operate in the optimal state under different working conditions.

[0064] The following takes the power converter as a DC / AC converter as an example for illustration.

[0065] Figure 3 FIG. is a schematic circuit diagram of a power converter in an exemplary embodiment. The power converter is a resonant type DC / AC converter. The primary bridge arm 101 of the DC / AC converter adopts an H-bridge structure (i.e., a full-bridge circuit). A capacitor Cin is connected in parallel at the input end of the primary bridge arm 101. The primary 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 of the primary bridge arm 101 to form a half-bridge arm. The midpoint of this half-bridge arm provides an output voltage v1 to the ground. The switching tube Q2H and the switching tube Q2L are connected in series at the input end of the primary bridge arm 101 to form the other half-bridge arm. The midpoint of this half-bridge arm provides an output voltage v2 to the ground. The arm output voltage v of the primary bridge arm 101 x is the difference between the output voltages of the two half-bridge arms, that is, the voltage of the port connected to the transformer 104; the secondary bridge arm 102 is a half-bridge type cycloconverter, which is composed of two groups of switching tubes connected in a common-source manner in series. Specifically, the two groups of switching tubes are connected in series between the two output terminals of the secondary bridge arm 102 to form a half-bridge arm. The first group of switching tubes of the secondary bridge arm 102 includes a switching tube Q3 and a switching tube Q4 connected in a common-source manner. The second group of switching tubes includes a switching tube Q5 and a switching tube Q6 connected in a common-source manner. The two groups of switching tubes are commonly connected to the midpoint of the bridge arm. One end of the secondary winding of the transformer 104 is connected to the midpoint of the bridge arm of the secondary bridge arm 102 through a resonant circuit 103, and the other end is connected to an output terminal of the secondary bridge arm 102. The arm output voltage v of the secondary bridge arm 102 o is the voltage between the midpoint of the bridge arm of the secondary bridge arm 102 and an output terminal of the secondary bridge arm 102, that is, the voltage of the port connected to the transformer 104. The two output terminals of the secondary bridge arm 102 are connected to a filter circuit 105. The filter circuit 105 includes a capacitor C f and an inductor L f , and the resonant circuit 103 includes an inductor Lr and a capacitor Cr connected in series. i rs is the resonant cavity current. The turns ratio of the primary and secondary windings of the transformer 104 is 1:n, V in is the input voltage, and V out is the output voltage.

[0066] Figure 3 In the DC / AC converter shown, the primary bridge arm 101 is a full-bridge circuit. When the primary bridge arm 101 adopts phase-shift control, there is a phase-shift angle θ between the two half-bridge arms of the primary bridge arm 101. The phase-shift angle θ can be the phase difference between the output voltages (output voltage v1 and output voltage v2) of the two half-bridge arms of the primary bridge arm 101; the secondary bridge arm 102 is a half-bridge cycloconverter, and there is a phase-shift angle between the output voltages of the primary bridge arm 101 and the secondary bridge arm 102 Phase-shift angle can be the phase difference between the zero-crossing point of the fundamental component of the output voltage v x of the primary bridge arm 101 and the zero-crossing point of the fundamental component of the output voltage v o of the secondary bridge arm 102; the resonant cavity current angle β is defined as the phase difference between the zero-crossing point of the resonant cavity current i rs and the zero-crossing point of the fundamental component of the bridge arm output voltage v x .

[0067] In some other embodiments, if the primary bridge arm 101 in the power converter is a half-bridge circuit, it can be considered that there is no phase-shift angle θ in the primary bridge arm 101, or it can be considered that the phase-shift angle θ is 0

[0068] In some embodiments, the power converter can perform unidirectional conversion or bidirectional conversion; it can perform rectification or inversion

[0069] It should be noted that the switching tubes in the embodiments of the present application can be selected from one or more of various types of switching tubes such as Metal Oxide Semiconductor Field Effect Transistor (MOSFET) and Insulated Gate Bipolar Transistor (IGBT). In the present application, the switching tube is taken as an MOSFET as an example for illustration

[0070] Figure 4 is a waveform schematic diagram when the DC / AC converter operates in the reverse direction. At this time, θ≥0, β≤0, β is the angle between the zero-crossing point when the resonant cavity current i rs changes from positive to negative and the zero-crossing point of the fundamental component of the bridge arm output voltage v x . The DC / AC converter performs rectification, and energy flows from the AC side to the DC side Figure 5 is a waveform schematic diagram when the DC / AC converter operates in the forward direction. At this time, θ≥0, β≥0, β is the resonant cavity current i rsThe angle between the zero-crossing point from negative to positive and the zero-crossing point of the fundamental component of the arm output voltage v x During this period, the DC / AC converter performs inversion, and energy flows from the DC side to the AC side. The phase-shift angle θ ranges from 0 to π, and the phase-shift angle ranges from -π to π, and the resonant cavity current angle β ranges from -π / 2 to π / 2.

[0071] To achieve zero-voltage turn-on of the switching tubes Q1L, Q2H, Q1H, and Q2L, it is necessary to control the resonant cavity current i rs > 0 at the turn-on moments of the switching tubes Q1L and Q2H; at the turn-on moments of the switching tubes Q1H and Q2L, control the resonant cavity current i rss < 0.

[0072] To achieve zero-voltage turn-on of the switching tubes Q3, Q4, Q5, and Q6, it is necessary to control the resonant cavity current i rs > 0 at the turn-on moments of the switching tubes Q3 and Q6; at the turn-on moments of the switching tubes Q4 and Q5, control the resonant cavity current i rs < 0.

[0073] Since the magnitude of the resonant cavity current i rs is related to θ, and β, through fundamental wave analysis, the resonant cavity current i rs can be expressed as an expression related to θ, and β. Further, according to the above zero-voltage turn-on conditions, it is necessary to control so that the resonant cavity current i rs meets the zero-voltage turn-on requirements of each switching tube, and realizes the soft switching of the switching tubes of the primary arm 101 and the secondary arm 102.

[0074] Figure 6 FIG. is a schematic circuit diagram of a power converter in another exemplary embodiment. The power converter is a resonant DC / AC converter. The secondary arm 102 of the DC / AC converter is a full-bridge cycloconverter, including two half-bridge arms. One half-bridge arm includes switching tubes Q31, Q41, Q51, and Q61. The midpoint of this half-bridge arm is connected to one end of the secondary winding of the transformer 104 through a resonant circuit 103; the other half-bridge arm includes switching tubes Q32, Q42, Q52, and Q62, and the midpoint of this half-bridge arm is connected to the other end of the secondary winding of the transformer 104.

[0075] When the secondary bridge arm 102 is a full-bridge cycloconverter, if the secondary bridge arm 102 also adopts phase-shift control, that is, a phase-shift angle δ, δ≥0, is controlled to exist between the two half-bridge arms of the secondary bridge arm 102. The phase-shift angle δ can be the phase difference between the output voltages (output voltage v3 and output voltage v4) of the two half-bridge arms of the secondary bridge arm 102. At this time, in order for the zero-voltage turn-on of each switch tube in the secondary bridge arm 102, it is necessary to control the resonant cavity current i rs >0 at the turn-on moments of switch tubes Q31, Q61, Q42, and Q52; at the turn-on moments of switch tubes Q41, Q51, Q32, and Q62, control the resonant cavity current i rs <0. At this time, it is necessary to control β to satisfy: so that the resonant cavity current i rs meets the zero-voltage turn-on requirements of each switch tube.

[0076] Among them, θ and The value of can be determined according to the following boundary conditions:

[0077]

[0078] Among them, is denoted as the voltage gain of the power converter, and |V out | is the absolute value of the instantaneous value of the output voltage V out .

[0079] When the primary bridge arm 101 is a half-bridge circuit, the voltage gain M is

[0080] In the embodiments of the present application, the controller controls the relationship between the resonant cavity current angle β and each phase-shift angle, realizes the soft switching of each switch tube in the power converter, and optimizes the working state of the power converter.

[0081] In order to further optimize the working state of the power converter, the relationship between the resonant cavity current angle and each phase-shift angle can be optimized and controlled, and at the same time, the resonant cavity current is minimized to further reduce the conduction loss of the power converter.

[0082] In order to minimize the resonant cavity current, it is necessary to control the resonant cavity to only transfer active power and not transfer reactive power. Taking the forward operation of the power converter (θ≥0, β≥0) as an example, when the voltage gain M≤1, the vector schematic diagram of the power converter working in the state of minimum resonant cavity current is as Figure 7 shown. At this time, the reactive power transferred by the resonant cavity to the AC side is zero. As can be seen from the figure, in order to minimize the resonant cavity current, it is necessary to control

[0083] For the embodiment where the secondary bridge arm 102 is a full-bridge cycloconverter, it is also necessary to further control the phase-shift angle δ = 0.

[0084] When the voltage gain M > 1, the vector schematic diagram of the power converter operating in the state of minimum resonant cavity current is as shown in Figure 8 At this time, the reactive power transferred from the resonant cavity to the DC side is zero. It can be known from Figure 8 that to achieve the minimum resonant cavity current, it is necessary to control β = 0.

[0085] For the embodiment where the secondary bridge arm 102 is a full-bridge type cycloconverter, correspondingly, it is also necessary to control the phase shift angle

[0086] In some embodiments, when the resonant cavity current is the smallest, due to the deviation of the actual system, the resonant cavity current angle β is not necessarily the value mentioned above. The deviation of the actual system can be considered for further correction to further ensure that the power converter operates in the desired optimal state. Considering the influence of the non-linear parasitic capacitance of the switching tubes in the actual system, it is necessary to retain a certain negative current to fully discharge the parasitic capacitance and turn on the freewheeling diode. Therefore, the specific correction method is as follows:

[0087] When the voltage gain M ≤ 1 and the power converter operates in the forward direction, the controller controls the resonant cavity current angle β to be slightly smaller than the phase shift angle The difference is When the voltage gain M ≤ 1 and the power converter operates in the reverse direction, the controller controls the resonant cavity current angle β to be slightly larger than the phase shift angle The difference is When the voltage gain M > 1 and the power converter operates in the forward direction, the controller controls the resonant cavity current angle β to be slightly larger than 0, and the difference is Δβ2 = β; when the voltage gain M > 1 and the power converter operates in the reverse direction, the controller controls the resonant cavity current angle β to be slightly smaller than 0, and the difference is Δβ2 = -β.

[0088] where, |Δβ1| ≤ the first threshold T h1 , the first threshold T h1 is usually set within 30°, that is, 0° ≤ T h1 ≤ 30°.

[0089] |Δβ2| ≤ the second threshold T h2 , the second threshold T h2 is usually set within 30°, and its value is T h2_min ≤ T h2 ≤ 30°, and its minimum value T h2_min satisfies: in the value range of the second threshold, the integral of the resonant cavity current i rs with respect to time t is equal to 2 times the input voltage V in multiplied by the equivalent output capacitance of the switching tube, that is, ∫i rs dt = 2V inC oss ,T h2_min ≤T h2 ≤30°, where C oss is the equivalent output capacitance value of the switching device.

[0090] It should be noted that the difference values Δβ1 and Δβ2 can each take a fixed value or a variable value in the intervals where the voltage gain M is less than 1 and the voltage gain M is greater than 1, respectively.

[0091] In some other embodiments, in order to further optimize the operating state of the power converter on the basis of achieving soft switching of the power converter, the relationship between the resonant cavity current angle and each phase-shift angle can be controlled to minimize the switching frequency of the power converter.

[0092] To minimize the switching frequency, it is necessary to control the amplitude of the fundamental component of the arm output voltage v x to be as equal as possible to the amplitude of the fundamental component of the arm output voltage v o and the phase-shift angle value to be as small as possible. Taking the embodiment shown in Figure 3 as an example, when the voltage gain M ≤ 1, by controlling the switching frequency can be minimized; when the voltage gain M > 1, by controlling the switching frequency can be minimized.

[0093] According to the angular relationship when the resonant cavity current is minimized, it can be known that when the switching frequency of the power converter is minimized, the resonant cavity current of the power converter is also minimized. In summary, when the voltage gain M ≤ 1, by controlling the power converter can operate in the optimal state of soft switching, minimum resonant cavity current, and lowest switching frequency; when the voltage gain M > 1, by controlling the power converter can operate in the optimal state of soft switching, minimum resonant cavity current, and lowest switching frequency.

[0094] For the secondary arm 102 being a full-bridge cycloconverter, if the secondary arm 102 also adopts phase-shift control, to minimize the switching frequency, when the voltage gain M ≤ 1, it is also necessary to control When the voltage gain M > 1, it is also necessary to control

[0095] Considering the influence of the non-linear parasitic capacitance of the switching device in the actual system, when the voltage gain M is less than or equal to 1, the absolute value of the resonant cavity current angle β can be controlled to be slightly greater than θ / 2, and the difference between the two is less than or equal to the third threshold T h3 , and the third threshold T h3 is usually set within 30°, and its value is T h3_min ≤Th3 ≤ 30°, and its minimum value T h3_min satisfies: such that in the value range of the third threshold, the integral of the resonant cavity current i rs with respect to time t is equal to 2 times the input voltage V in multiplied by the equivalent output capacitance of the switching tube, that is, ∫i rs dt = 2V in C oss , T h3_min ≤ T h3 ≤ 30°.

[0096] When the secondary bridge arm 102 is a full-bridge type cycle converter and there is a third phase shift angle δ and the voltage gain M is greater than 1, the phase shift angle absolute value can be controlled to be slightly greater than δ / 2, and the difference between the absolute value of the first phase shift angle and half of the third phase shift angle δ and the absolute value β of the resonant cavity current angle is less than or equal to the fourth threshold T h4 , that is, it satisfies the fourth threshold T h4 is usually set within 30°, and its value is T h4_min ≤ T h4 ≤ 30°, and its minimum value T h4_min satisfies: such that in the value range of the fourth threshold, the integral of the resonant cavity current i rs with respect to time t is equal to 2 times the input voltage V in multiplied by the equivalent output capacitance of the switching tube, that is, ∫i rs dt = 2V in C oss , T h4_min ≤ T h4 ≤ 30°.

[0097] It should be noted that the third threshold T h3 and the fourth threshold T h4 can take a fixed value respectively in the intervals where the voltage gain M is less than or equal to 1 and M is greater than 1, or can be a variable value.

[0098] The following will take controlling Figure 3 the power converter shown to work in the optimal state as an example to specifically illustrate the control strategy of this application.

[0099] Based on the fundamental wave analysis method, the expression of the resonant cavity current angle β can be obtained as follows:

[0100]

[0101] From the expression of the resonant cavity current angle β, it can be seen that the resonant cavity current angle β is related to the phase shift angle , and the controller controls the phase shift angle It is possible to control the resonant cavity current angle β, and further enable the power converter to operate in the desired optimal state.

[0102] In some embodiments, a closed-loop control can be performed on the resonant cavity current angle β. Figure 9 It is a schematic diagram of the control logic of the controller in some embodiments. As Figure 9 shown, the controller includes a predictive control module and a closed-loop control module. The predictive control module is used to calculate the phase shift angle θ, the initial value of the phase shift angle and the switching frequency f s based on the instantaneous control command and the voltage gain M of the power converter; the closed-loop control module performs closed-loop control on the resonant cavity current angle β to obtain the adjustment value of the phase shift angle . After that, the controller adjusts the initial value of the phase shift angle based on the adjustment value of the phase shift angle to obtain the final value of the phase shift angle .

[0103] The instantaneous control command can be the instantaneous current command I savg or the instantaneous power command P savg .

[0104] Specifically, the predictive control module includes a frequency determination unit and a phase shift angle determination unit. The phase shift angle determination unit calculates the phase shift angle θ and the initial value of the phase shift angle based on the voltage gain M. The frequency determination unit calculates the switching frequency f savg through a preset control model according to the instantaneous current command I savg , the phase shift angle θ and the initial value of the phase shift angle . The final value of the phase shift angle s can be the sum of its adjustment value and the initial value .

[0105] In some embodiments, the phase shift angle determination unit can calculate the phase shift angle θ and the initial value of the phase shift angle according to the above boundary conditions and the voltage gain M. The voltage gain M can be specifically calculated according to the input voltage V in of the power converter, the output voltage V out and the turns ratio n of the transformer.

[0106] The closed-loop control module is based on the voltage gain M, the resonant cavity current angle β, and the phase shift angle of the previous cycle. The final value of adjustment value of the last adjustment value and the initial value are added to obtain the phase shift angle of the current beat The final value of so that the relationship between the resonant cavity current angle β and the phase shift angle

[0107] It can be understood that in this application, the "beat" in the current beat and the previous beat is a sampling period or a control period or a switching period when digital control is adopted.

[0108] In some embodiments, when the voltage gain M is less than or equal to 1, the closed-loop control module uses the opposite value of the output value after adjustment by the closed-loop controller for the difference between the phase shift angle and the resonant cavity current angle β as the adjustment value of the phase shift angle of When the voltage gain M is greater than 1, the controller uses the output value after adjustment by the closed-loop controller for the difference between 0 and the resonant cavity current angle β as the adjustment value of the phase shift angle of

[0109] Among them, the closed-loop controller can be a proportional-integral controller, but it is not limited thereto.

[0110] In some other embodiments, the frequency determination unit can also calculate the switching frequency f according to the instantaneous control command, the phase shift angle θ and the phase shift angle s .

[0111] In some embodiments, taking the instantaneous control command as the instantaneous power command P savg as an example. The frequency determination unit can also determine the switching frequency fs according to the following formula:

[0112]

[0113] Among them, L r represents the value of the resonant inductor Lr, and C r represents the value of the resonant capacitor Cr.

[0114] In some other embodiments, closed-loop control can be performed on the phase shift angle θ and the phase shift angle according to the resonant cavity current angle β. As shown in Figure 10 , the controller includes a predictive control module and a closed-loop control module. The predictive control module is used to calculate the initial value θ1 of the phase shift angle θ and the initial value of the phase shift angle of ​and the switching frequency f s ; The closed-loop control module performs closed-loop control on the phase-shift angle θ and the phase-shift angle according to the resonant cavity current angle β, and respectively obtains the adjustment value of the phase-shift angle and the adjustment value Δθ of the phase-shift angle θ; Then, based on the adjustment value of the phase-shift angle the controller adjusts the initial value of the phase-shift angle to obtain the final value of the phase-shift angle , and adjusts the initial value θ1 of the phase-shift angle θ based on the adjustment value Δθ of the phase-shift angle θ to obtain the final value of the phase-shift angle θ.

[0115] Specifically, the closed-loop control module obtains the adjustment value of the current beat phase-shift angle according to the voltage gain M of the previous beat, the resonant cavity current angle β, and the final value of the phase-shift angle . Finally, the adjustment value of the phase-shift angle and the initial value of the phase-shift angle are added to obtain the final value of the phase-shift angle of the current beat, so that the magnitude relationship between the resonant cavity current angle β and the phase-shift angle meets the requirements of the optimal operating state of the power converter.

[0116] The closed-loop control module obtains the adjustment value Δθ of the phase-shift angle θ of the current beat according to the voltage gain M of the previous beat, the resonant cavity current angle β, and the final value of the phase-shift angle θ. Finally, the adjustment value Δθ of the phase-shift angle θ and the initial value θ1 of the phase-shift angle θ are added to obtain the final value of the phase-shift angle θ of the current beat, so that the magnitude relationship between the resonant cavity current angle β and the phase-shift angle θ meets the requirements of the optimal operating state of the power converter.

[0117] In some other embodiments, when the secondary bridge arm 102 is a full-bridge cycloconverter and there is a third phase-shift angle δ, compared with the embodiment Figure 10 shown, the predictive control module is further configured to calculate the initial value δ1 of the phase-shift angle δ according to the instantaneous control instruction and the voltage gain M of the power converter, and the closed-loop control module further obtains the adjustment value Δδ of the phase-shift angle δ of the current beat according to the voltage gain M of the previous beat, the resonant cavity current angle β, and the final value of the phase-shift angle δ. Finally, the adjustment value Δδ and the initial value δ1 are added to obtain the final value of the phase-shift angle δ of the current beat, so that the magnitude relationship between the resonant cavity current angle β and the phase-shift angle δ meets the requirements of the optimal operating state of the power converter.

[0118] In some embodiments, the controller further includes a signal generation module, and the signal generation module is based on the phase-shift angle θ, the phase-shift angle Switching frequency f s Generate a control signal for the power converter to control the power converter to operate in an optimal state.

[0119] It should be noted that when the primary bridge arm 101 is a half-bridge circuit, the signal generation module generates a control signal for the power converter based on the switching frequency f s and the phase shift angle to generate a control signal for the power converter.

[0120] The controller can be any one of a microcontroller unit (MCU), a central processing unit (CPU), a digital signal processing (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), etc., or any combination of one or more of other programmable logic devices, transistor logic devices, and hardware components.

[0121] Among them, the resonant cavity current angle can be obtained by sampling the resonant cavity current or can be obtained according to time domain analysis.

[0122] In some other embodiments, an open-loop control can also be performed on the resonant cavity current angle β Figure 11 is a schematic diagram of the control logic of the controller in some other embodiments. Different from the Figure 9 shown embodiment, the resonant cavity current angle closed-loop control module is omitted, and the phase shift angle determination unit directly obtains the phase shift angle θ and the phase shift angle according to the voltage gain M and the preset difference Δβ Among them, the preset difference Δβ is the difference between the resonant cavity current angle β and its reference value, generally taken within 30°.

[0123] Specifically, in some possible implementation manners, when the voltage gain M≤1 and the power converter operates in the forward direction, β = θ / 2 can be taken, and the reference value of the resonant cavity current angle is taken as Then the difference At this time:

[0124]

[0125] When the voltage gain M>1 and the power converter operates in the forward direction, θ = 0 can be set, the reference value of the resonant cavity current angle is 0, and then Δβ = β - 0.

[0126] At this time:

[0127]

[0128] It should be noted that in the embodiments of the present application, it is not limited that the power fixed converter operates in the above optimal state in all switching cycles within one power frequency cycle. For example, within the 30° intervals before and after the grid voltage and grid current cross zero, in order to control the switching frequency, it does not operate in the optimal state.

[0129] Based on the above power converter, the present application proposes a control method for a power converter, and the method includes:

[0130] Controlling the absolute value of the resonant cavity current angle to be less than or equal to the absolute value of the first phase shift angle between the primary bridge arm and the secondary bridge arm to achieve soft switching of the switching tubes in the primary bridge arm and the secondary bridge arm. The resonant cavity current angle is the phase difference between the resonant cavity current and the bridge arm output voltage of the primary bridge arm, where the polarity of the resonant cavity current angle is the same as that of the first phase shift angle.

[0131] In some embodiments, the method further includes: when there is a second phase shift angle between the arms of the primary bridge arm, further controlling the absolute value of the resonant cavity current angle to be greater than or equal to half of the second phase shift angle, and the second phase shift angle is greater than or equal to 0.

[0132] In some embodiments, the method further includes: when there is a third phase shift angle between the arms of the secondary bridge arm, further controlling the absolute value of the resonant cavity current angle to be less than or equal to the difference between the absolute value of the first phase shift angle and half of the third phase shift angle, and the third phase shift angle is greater than or equal to 0.

[0133] In some embodiments, the method further includes: when the voltage gain of the power converter is less than or equal to 1, controlling the absolute value of the difference between the resonant cavity current angle and the first phase shift angle to be less than or equal to a first threshold.

[0134] In some embodiments, the method further includes: when the voltage gain of the power converter is greater than 1, further controlling the absolute value of the resonant cavity current angle to be less than or equal to a second threshold.

[0135] In some embodiments, the method further includes: when there is a second phase shift angle between the arms of the primary bridge arm and the voltage gain of the power converter is greater than 1, further controlling the second phase shift angle to be equal to 0.

[0136] In some embodiments, the method further includes: when there is a third phase shift angle between the arms of the secondary bridge arm and the voltage gain of the power converter is less than or equal to 1, further controlling the third phase shift angle to be equal to 0.

[0137] In some embodiments, the method further includes: when there is a second phase shift angle between the arms of the primary side bridge arm, further controlling the difference between the absolute value of the resonant cavity current angle and half of the second phase shift angle to be less than or equal to a third threshold, where the second phase shift angle is greater than or equal to 0.

[0138] In some embodiments, the method further includes: if there is a third phase shift angle in the secondary side bridge arm, further controlling the difference between the absolute value of the first phase shift angle and the sum of half of the third phase shift angle and the absolute value of the resonant cavity current angle to be less than or equal to a fourth threshold, where the third phase shift angle is greater than or equal to 0.

[0139] In some embodiments, the method further includes: when the voltage gain of the power converter is less than or equal to 1 and the power converter is operating in the forward direction, controlling the difference between the first phase shift angle and the resonant cavity current angle to be less than a first threshold, and both the first phase shift angle and the resonant cavity current angle are greater than or equal to 0.

[0140] In some embodiments, the method further includes: when the voltage gain of the power converter is greater than 1 and the power converter is operating in the forward direction, controlling the resonant cavity current angle to be less than a second threshold, and the resonant cavity current angle is greater than or equal to 0.

[0141] In some embodiments, the method further includes: when the voltage gain of the power converter is less than or equal to 1 and the power converter is operating in the reverse direction, controlling the difference between the resonant cavity current angle and the first phase shift angle to be less than a first threshold, and both the first phase shift angle and the resonant cavity current angle are less than 0.

[0142] In some embodiments, the method further includes: when the voltage gain of the power converter is greater than 1 and the power converter is operating in the reverse direction, controlling the absolute value of the resonant cavity current angle to be less than a second threshold, and the resonant cavity current angle is less than 0.

[0143] In some embodiments, the method further includes: performing closed-loop control based on the resonant cavity current angle to obtain an adjustment value of the phase shift angle of the power converter, and obtaining a final value of the phase shift angle based on the adjustment value of the phase shift angle and the initial value of the phase shift angle. The phase shift angle of the power converter includes at least one of the first phase shift angle between the primary side bridge arm and the secondary side bridge arm, the second phase shift angle of the primary side bridge arm, or the third phase shift angle of the secondary side bridge arm.

[0144] In some embodiments, the method further includes: calculating the initial value of the phase shift angle and the switching frequency of the power converter based on the voltage gain of the power converter and the instantaneous control instruction, and generating a control signal of the power converter based on the switching frequency and the final value of the phase shift angle, where the instantaneous control instruction is an instantaneous current instruction or an instantaneous power instruction.

[0145] In some embodiments, the method further includes: calculating the first phase shift angle based on the voltage gain of the power converter, the instantaneous control instruction, and a preset difference, where the preset difference is the difference between the resonant cavity current angle and a reference value of the resonant cavity current angle, and the reference value is the first phase shift angle or 0.

[0146] Since the control method of the power converter in this embodiment corresponds to the foregoing embodiments, principles, and examples of the power converter, for the details not described in the description of this embodiment, reference may be made to the relevant descriptions in the foregoing embodiments and will not be elaborated herein.

[0147] The technical features of the above embodiments can be combined arbitrarily. For the sake of concise description, 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, it should be considered as the scope recorded in this specification.

[0148] The above embodiments only represent several implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, 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 appended claims.

Claims

1. A power converter, characterized in that, It includes a primary side bridge arm, a secondary side bridge arm, a resonant circuit connected between the primary side bridge arm and the secondary side bridge arm, and a controller connected to the primary side bridge arm and the secondary side bridge arm; The controller is used to control the absolute value of the resonant cavity current angle to be less than or equal to the absolute value of the first phase shift angle between the primary side bridge arm and the secondary side bridge arm to achieve soft switching of the switching tubes in the primary side bridge arm and the secondary side bridge arm. The resonant cavity current angle is the phase difference between the resonant cavity current and the bridge arm output voltage of the primary side bridge arm. Among them, the polarities of the resonant cavity current angle and the first phase shift angle are the same.

2. The power converter according to claim 1, characterized in that, When there is a second phase shift angle between the arms of the primary side bridge arm, the controller also controls the absolute value of the resonant cavity current angle to be greater than or equal to half of the second phase shift angle, and the second phase shift angle is greater than or equal to 0.

3. The power converter according to claim 1 or 2, characterized in that, When there is a third phase shift angle between the arms of the secondary side bridge arm, the controller also controls the absolute value of the resonant cavity current angle to be less than or equal to the difference between the absolute value of the first phase shift angle and half of the third phase shift angle, and the third phase shift angle is greater than or equal to 0.

4. The power converter according to claim 1, characterized in that, When the voltage gain of the power converter is less than or equal to 1, the controller controls the absolute value of the difference between the resonant cavity current angle and the first phase shift angle to be less than or equal to a first threshold.

5. The power converter according to claim 1 or 4, characterized in that, When the voltage gain of the power converter is greater than 1, the controller also controls the absolute value of the resonant cavity current angle to be less than or equal to a second threshold.

6. The power converter according to claim 5, wherein When there is a second phase shift angle between the arms of the primary side bridge arm and the voltage gain of the power converter is greater than 1, the controller also controls the second phase shift angle to be equal to 0.

7. The power converter according to claim 4, characterized in that When there is a third phase shift angle between the arms of the secondary side bridge arm and the voltage gain of the power converter is less than or equal to 1, the controller also controls the third phase shift angle to be equal to 0.

8. The power converter according to claim 4 or 7, characterized in that, When there is a second phase shift angle between the arms of the primary side bridge arm, the controller also controls the absolute value of the difference between the resonant cavity current angle and half of the second phase shift angle to be less than or equal to a third threshold, where the second phase shift angle is greater than or equal to 0.

9. The power converter according to claim 6, characterized in that If there is a third phase shift angle in the secondary side bridge arm, the controller also controls the difference between the absolute value of the first phase shift angle and the sum of half of the third phase shift angle and the absolute value of the resonant cavity current angle to be less than or equal to a fourth threshold, where the third phase shift angle is greater than or equal to 0.

10. The power converter according to claim 4, wherein, When the voltage gain of the power converter is less than or equal to 1 and the power converter is operating in the forward direction, the controller controls the difference between the first phase shift angle and the resonant cavity current angle to be less than the first threshold, and both the first phase shift angle and the resonant cavity current angle are greater than or equal to 0.

11. The power converter according to claim 5, characterized in that, When the voltage gain of the power converter is greater than 1 and the power converter is operating in the forward direction, the controller controls the resonant cavity current angle to be less than the second threshold, and the resonant cavity current angle is greater than or equal to 0.

12. The power converter according to claim 4, characterized in that, When the voltage gain of the power converter is less than or equal to 1 and the power converter is operating in the reverse direction, the controller controls the difference between the resonant cavity current angle and the first phase shift angle to be less than the first threshold, and both the first phase shift angle and the resonant cavity current angle are less than 0.

13. The power converter according to claim 5, characterized in that, When the voltage gain of the power converter is greater than 1 and the power converter operates in reverse, the controller controls the absolute value of the resonant cavity current angle to be less than a second threshold, and the resonant cavity current angle is less than 0.

14. The power converter according to claim 1, characterized in that, The controller performs closed-loop control based on the resonant cavity current angle to obtain an adjustment value of the phase shift angle of the power converter, and obtains a final value of the phase shift angle based on the adjustment value of the phase shift angle and the initial value of the phase shift angle. The phase shift angle of the power converter includes at least one of a first phase shift angle between the primary bridge arm and the secondary bridge arm, a second phase shift angle of the primary bridge arm, or a third phase shift angle of the secondary bridge arm.

15. The power converter according to claim 14, wherein, The controller calculates the initial value of the phase shift angle and the switching frequency of the power converter based on the voltage gain of the power converter and an instantaneous control command, and generates a control signal of the power converter based on the switching frequency and the final value of the phase shift angle, where the instantaneous control command is an instantaneous current command or an instantaneous power command.

16. The power converter according to claim 1, characterized in that, The controller calculates the first phase shift angle based on the voltage gain of the power converter, an instantaneous control command, and a preset difference, where the preset difference is the difference between the resonant cavity current angle and a reference value of the resonant cavity current angle, and the reference value is the first phase shift angle or 0.

17. The power converter according to claim 1, wherein The primary bridge arm is a half-bridge circuit or a full-bridge circuit.

18. The power converter according to claim 1, characterized in that, The secondary bridge arm includes a cycloconverter or a rectifier circuit.

19. A control method for a power converter, the power converter including a primary bridge arm, a secondary bridge arm, and a resonant circuit connected between the primary bridge arm and the secondary bridge arm, characterized in that, The method includes: Controlling the absolute value of the resonant cavity current angle to be less than or equal to the absolute value of the first phase shift angle between the primary bridge arm and the secondary bridge arm to achieve soft switching of the switching tubes in the primary bridge arm and the secondary bridge arm. The resonant cavity current angle is the phase difference between the resonant cavity current and the bridge arm output voltage of the primary bridge arm, where the resonant cavity current angle has the same polarity as the first phase shift angle.

20. The method according to claim 19, characterized in that, The method further includes: when there is a second phase shift angle between the arms of the primary bridge arm, further controlling the absolute value of the resonant cavity current angle to be greater than or equal to half of the second phase shift angle, and the second phase shift angle is greater than or equal to 0.

21. The method according to claim 19 or 20, characterized in that, The method further includes: when there is a third phase shift angle between the arms of the secondary bridge arm, further controlling the absolute value of the resonant cavity current angle to be less than or equal to the difference between the absolute value of the first phase shift angle and half of the third phase shift angle, and the third phase shift angle is greater than or equal to 0.

22. The method according to claim 19, wherein The method further includes: when the voltage gain of the power converter is less than or equal to 1, controlling the absolute value of the difference between the resonant cavity current angle and the first phase shift angle to be less than or equal to a first threshold.

23. The method according to claim 19 or 22, characterized in that, The method further includes: when the voltage gain of the power converter is greater than 1, further controlling the absolute value of the resonant cavity current angle to be less than or equal to a second threshold.

24. The method according to claim 23, wherein The method further includes: when there is a second phase shift angle between the arms of the primary bridge arm and the voltage gain of the power converter is greater than 1, further controlling the second phase shift angle to be equal to 0.

25. The method according to claim 22, wherein The method further includes: when there is a third phase shift angle between the arms of the secondary bridge arm and the voltage gain of the power converter is less than or equal to 1, further controlling the third phase shift angle to be equal to 0.

26. The method according to claim 22 or 25, characterized in that, The method further includes: when there is a second phase shift angle between the arms of the primary side bridge arm, further controlling the difference between the absolute value of the resonant cavity current angle and half of the second phase shift angle to be less than or equal to a third threshold, where the second phase shift angle is greater than or equal to 0.

27. The method according to claim 24, wherein The method further includes: if there is a third phase shift angle in the secondary side bridge arm, further controlling the difference between the absolute value of the first phase shift angle and the sum of half of the third phase shift angle and the absolute value of the resonant cavity current angle to be less than or equal to a fourth threshold, where the third phase shift angle is greater than or equal to 0.

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