Control method, control device and resonant converter

Abstract

The invention discloses a control method, a control device and a resonant converter, under the working condition that the load of the resonant converter is lower than a first set value, the resonant converter comprises three control variables, namely a first electric parameter representing the duration of a first pulse, a third electric parameter representing the duration of a second pulse and a fourth electric parameter representing the Burstoff turn-off time, the control frequency is equal to the frequency corresponding to the Burst period, and the first electric parameter is a control variable of a switching tube located in a first input loop in the inverter switching circuit; the second electric parameter is a control variable of a switching tube located in a second input loop in the inverter switching circuit; during the Burstoff turn-off time, all switching tubes in the inverter switching circuit are turned off; the Burst period is the sum of the continuous first pulse duration time, the second pulse duration time and the Burstoff turn-off time. The gain adjusting capacity of the resonant converter can be improved, switching loss is reduced, resonant capacitor voltage stress and resonant inductor current stress are reduced, and output voltage ripples are reduced.

Description

Technical Field

[0001] The invention relates to a switching power supply, and in particular to a control method, a control device and a resonant converter. Background Art

[0002] In low-loss, high-performance DC-DC switching power supply applications, traditional hard-switching pulse width modulation (PWM) control can no longer meet the needs of industrial production. LLC resonant converters have natural soft switching characteristics, high power density, easy soft switching and high efficiency, and are widely used in automated production lines, energy storage systems, electric vehicles, data centers, and medical power supplies.

[0003] LLC resonant converter is a typical isolated soft-switching high-efficiency DC-DC converter that achieves electrical isolation through a transformer. It is very popular in civil electronic applications. Under full load conditions, the primary switch tube of the resonant converter achieves zero voltage turn-on (ZVS), and the secondary rectifier diode achieves zero current turn-off (ZCS). At the same time, it has the advantages of simple structure, magnetic integration, high conversion efficiency, and high power density.

[0004] However, under light load or no-load conditions, due to the influence of parasitic capacitance, the LLC resonant converter will produce high-frequency gain distortion, causing the output voltage to pump up, and the overall performance is a non-monotonic gain phenomenon. Therefore, regarding the problem of LLC resonant converter light no-load conditions, many experts and scholars have proposed a variety of control methods.

[0005] In order to improve the efficiency of the resonant converter and reduce the impact of gain non-monotonicity, relevant researchers and inventors have proposed different improvement methods. Among them, Yu Shan, Dong Jiqing and others published an online paper entitled "Research on Voltage Gain Distortion of LLC Resonant Converter under Light Load". This paper is based on the circuit topology of the half-bridge LLC converter. In order to solve the problem of non-monotonic voltage gain under light load conditions, a fixed-frequency mode Burst control is adopted, that is, there are several pulses with a duty cycle of 50% in the Burst_on stage, and the driving pulse stops in the Burst_off stage. This traditional intermittent control mode can effectively control the light-load output voltage, and can also reduce the average operating frequency, effectively improving the converter efficiency under light load. However, such a control strategy only focuses on reducing the average operating frequency and controlling the output voltage, and does not pay attention to the efficiency problem in the energy transmission stage, and does not achieve more optimized efficiency.

[0006] Compared with this traditional Burst control, some scholars have proposed three-pulse control with fewer switching pulses. Weiyi Feng, Fred C Lee and others published an online paper titled "Optimal Trajectory Control of Burst Mode for LLC Resonant Converter". The paper is based on a half-bridge LLC topology. During the Burst_on period, there are only three drive pulses. This control method reduces switching losses under light-load conditions and improves the efficiency of the converter. However, the three-pulse control based on the optimal trajectory has high requirements on the controller's operating speed. Summary of the invention

[0007] In view of this, the technical problem to be solved by the present invention is to provide a control method, a control device and a resonant converter, which can at least to some extent solve the deficiencies of the above-mentioned prior art problems.

[0008] As a first aspect of the present invention, an embodiment of the control method provided is as follows:

[0009] A control method is applied to a resonant converter, wherein the primary side of the resonant converter is a DC input, and comprises an inverter switch circuit, wherein the inverter switch circuit comprises at least one bridge arm; wherein:

[0010] The control method is applied to the working condition where the load of the resonant converter is lower than the first set value, and includes three control quantities, namely, a first electrical parameter θ1 representing the duration of the first pulse, a third electrical parameter θ3 representing the duration of the second pulse, and a fourth electrical parameter φ representing the Burst_off off time, and the control frequency is equal to the frequency corresponding to the Burst period, wherein:

[0011] The first electrical parameter θ1 is a control variable of a switch tube in a first input loop of the inverter switch circuit;

[0012] The second electrical parameter θ3 is a control variable of the switch tube located in the second input loop of the inverter switch circuit;

[0013] During the Burst_off time, all switch tubes in the inverter switch circuit are turned off;

[0014] The Burst period is the sum of a continuous first pulse duration, a second pulse duration and a Burst_off off time.

[0015] Furthermore, the control quantity also includes a second electrical parameter θ2 characterizing the duration of the interval, wherein the interval is the interval between the first pulse and the second pulse, during which all switching tubes in the inverter switch circuit are also turned off, and the Burst cycle is the sum of a continuous first pulse duration, an interval duration, a second pulse duration and a Burst_off turn-off time.

[0016] Preferably, the first electrical parameter θ1, the second electrical parameter θ2, the third electrical parameter θ3 and the fourth electrical parameter φ are all phase angles, and the inverter switch circuit includes two bridge arms, wherein the driving pulse duty cycle of the switch tube located in the first input loop is θ1 / 2π ignoring the dead time, and the phase difference is zero; the driving pulse duty cycle of the switch tube located in the second input loop is θ3 / 2π ignoring the dead time, and the phase difference is zero; the driving pulse of the switch tube located in the second input loop of the inverter switch circuit is lagged relative to the driving pulse of the switch tube located in the first input loop of the inverter switch circuit, and the lag phase angle is θ2.

[0017] Preferably, the first electrical parameter θ1, the third electrical parameter θ3 and the fourth electrical parameter φ are all phase angles, the driving pulse duty cycle of the switch tube located in the first input loop of the inverter switch circuit is θ1 / 2π, and the driving pulse duty cycle of the switch tube located in the second input loop of the inverter switch circuit is θ2 / 2π.

[0018] Further, when the gain of the resonant converter is lower than a second set value, the resonant converter is controlled to operate in a two-element resonant mode of resonance of a resonant inductor and a resonant capacitor during the first pulse duration. In the two-element resonant mode, the excitation inductor is clamped, and the resonant converter outputs energy to the secondary side during the first pulse duration.

[0019] Furthermore, when the gain of the resonant converter is lower than the second set value, within the same Burst cycle, the resonant current and the excitation current within the first pulse of duration are controlled to increase from zero at the same time, and the two are not equal. After the second pulse is turned off, the resonant current and the excitation current drop to zero at the same time.

[0020] Further, when the gain of the resonant converter is higher than a third set value, the resonant converter is controlled to operate in a three-element resonant mode of resonance of the resonant inductor, the resonant capacitor and the excitation inductor during the first pulse duration. In the three-element resonant mode, the resonant converter charges the resonant inductor and the resonant capacitor during the first pulse duration, and does not output energy to the secondary side.

[0021] Furthermore, when the gain of the resonant converter is higher than a third set value, within the same Burst cycle, the resonant current and the excitation current within the duration of the first pulse are controlled to increase from zero, and the two remain equal, and the resonant current and the excitation current within the duration of the second pulse are not equal. After the second pulse is turned off, the resonant current and the excitation current drop to zero at the same time.

[0022] As a second aspect of the present invention, an embodiment of the control device provided is as follows:

[0023] A control device is applied to a resonant converter, wherein the primary side of the resonant converter is a DC input, and comprises an inverter switch circuit, wherein the inverter switch circuit comprises at least one bridge arm; wherein:

[0024] The control device is configured to be applied to a condition where the load of the resonant converter is lower than a first set value, and includes three control quantities, namely, a first electrical parameter θ1 representing the duration of the first pulse, a third electrical parameter θ3 representing the duration of the second pulse, and a fourth electrical parameter φ representing the Burst_off off time, and the control frequency is equal to the frequency corresponding to the Burst period, wherein:

[0025] The first electrical parameter θ1 is a control variable of a switch tube in a first input loop of the inverter switch circuit;

[0026] The second electrical parameter θ3 is a control variable of the switch tube located in the second input loop of the inverter switch circuit;

[0027] During the Burst_off time, all switch tubes in the inverter switch circuit are turned off;

[0028] The Burst period is the sum of a continuous first pulse duration, a second pulse duration and a Burst_off off time.

[0029] As a third aspect of the present invention, an embodiment of a resonant converter is provided as follows:

[0030] A resonant converter, wherein the primary side of the resonant converter is a DC input, and comprises an inverter switch circuit, wherein the inverter switch circuit comprises at least one bridge arm; wherein the resonant converter also comprises the control device described in the second aspect above.

[0031] The embodiment of the present invention meets the output voltage requirement by adjusting the first electrical parameter θ1 characterizing the first pulse duration, the third electrical parameter θ3 characterizing the second pulse duration, and the fourth electrical parameter φ characterizing the Burst_off off time, and has at least the following beneficial effects compared with the prior art:

[0032] (1) The embodiment of the present invention controls the switch tube in the primary inverter switch circuit by adjusting the first electrical parameter θ1 representing the first pulse duration and the third electrical parameter θ3 representing the second pulse duration, thereby increasing the gain adjustment range, optimizing the transformer design, and improving the conversion efficiency and power density of the converter in light-load applications;

[0033] (2) The embodiment of the present invention can reduce the impact of the resonant inductor current and the resonant capacitor voltage by adjusting the first electrical parameter θ1 representing the duration of the first pulse and the third electrical parameter θ3 representing the duration of the second pulse. The device is less stressed and easy to select.

[0034] (3) The embodiment of the present invention can also determine the gain of the resonant converter and the output voltage ripple by adjusting the fourth electrical parameter φ representing the Burst_off turn-off time. In addition, at the moment of entering the burst_off, if the fourth electrical parameter φ is adjusted so that the resonant current is exactly zero, the electromagnetic interference of di / dt and du / dt can be reduced;

[0035] (4) The embodiment of the present invention is a two-pulse Burst control, which is simpler and easier to implement than a three-pulse Burst control scheme. In addition, since the number of pulses is reduced, the driving loss of the switch tube can be significantly reduced, thereby improving the efficiency of the entire machine.

[0036] (5) The embodiment of the present invention can reduce the output current peak value and reduce the difficulty of selecting the secondary rectifier tube by adjusting the second electrical parameter θ2 that represents the intermittent duration.

[0037] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structure or control timing specifically pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 A typical circuit diagram of a resonant converter applicable to the control method of the first embodiment;

[0039] Figure 2 The control method of the first embodiment is applied to Figure 1 The circuit includes a schematic diagram of four control quantities;

[0040] Figure 3 The control method of the first embodiment is applied to Figure 1 The switch tube driving waveform and key working waveform under the resonant mode of two components of the circuit;

[0041] Figure 4 The control method of the first embodiment is applied to Figure 1Soft switching waveform of the switch tube in the resonant mode of two components of the circuit;

[0042] Figure 5 The control method of the first embodiment is applied to Figure 1 Comparison waveform of output voltage ripple under two-element resonant mode of the circuit and output voltage ripple under traditional Burst control;

[0043] Figure 6 The control method of the first embodiment is applied to Figure 1 Comparison waveform of the resonant current and voltage peaks under the resonant mode of the two components of the circuit and the resonant current and voltage peaks under traditional Burst control;

[0044] Figure 7 The control method of the first embodiment is applied to Figure 1 The switch tube driving waveform and key working waveform under the circuit three-element resonant mode;

[0045] Figure 8 The control method of the first embodiment is applied to Figure 1 Comparison waveform of output voltage ripple under the circuit three-element resonant mode and output voltage ripple under traditional Burst control;

[0046] Fig. 9 The control method of the first embodiment is applied to Figure 1 Comparison waveform of the resonant current and voltage peaks under the three-element resonant mode of the circuit and the resonant current and voltage peaks under traditional Burst control. DETAILED DESCRIPTION

[0047] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0048] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present application.

[0049] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application are described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, the process, method, system, product or equipment comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or equipment.

[0050] It should be understood that, in the specification, claims and drawings, when a step is described as being connected to another step, the step may be directly connected to the other step, or be connected to the other step through a third step; when an element / unit is described as being "connected" to another element / unit, the element / unit may be "directly connected" to the other element / unit, or be "connected" to the other element / unit through a third element / unit.

[0051] First embodiment

[0052] This embodiment provides a control method, which is applied to a resonant converter, wherein the primary side of the resonant converter is a DC input, and includes an inverter switch circuit, and the inverter switch circuit includes at least one bridge arm; wherein:

[0053] The control method of this embodiment is applied to the working condition where the load of the resonant converter is lower than the first set value, and includes three control quantities, namely, a first electrical parameter θ1 representing the duration of the first pulse, a third electrical parameter θ3 representing the duration of the second pulse, and a fourth electrical parameter φ representing the Burst_off off time, and the control frequency is equal to the frequency corresponding to the Burst period, wherein:

[0054] The first electrical parameter θ1 is a control variable of the switch tube located in the first input loop of the inverter switch circuit;

[0055] The second electrical parameter θ3 is a control variable of the switch tube in the second input loop of the inverter switch circuit; during the Burst_off off time, all the switch tubes in the inverter switch circuit are turned off;

[0056] The Burst period is the sum of a continuous first pulse duration, a second pulse duration, and a Burst_off off time.

[0057] like Figure 1, which is a typical circuit diagram of a resonant converter applicable to the control method of the first embodiment, wherein the resonant converter is a DC input, and includes a transformer T, an inverter switch circuit and an LLC resonant cavity on the primary side, and a rectifier circuit and a filter output circuit on the secondary side;

[0058] The DC input is connected to the DC input source V in ;

[0059] The inverter switch circuit includes a first bridge arm composed of a first switch tube S1 and a second switch tube S2, and a second bridge arm composed of a third switch tube S3 and a fourth switch tube S4. The first switch tube S1 and the fourth switch tube S4 are switch tubes located in a first input loop, and the second switch tube S2 and the third switch tube S3 are switch tubes located in a second input loop.

[0060] The LLC resonant cavity includes a resonant capacitor C r , resonant inductor L r and the magnetizing inductance L m ;

[0061] Transformer T is a high-frequency isolation transformer with a center tap on the secondary side, which has the functions of voltage regulation and electrical isolation;

[0062] The rectifier circuit includes a fifth active switch tube S5 and a sixth active switch tube S6;

[0063] The filter output circuit includes the output filter capacitor C o .

[0064] It should be noted that Figure 1 The resonant converter shown is only a typical circuit diagram of a resonant converter applicable to the control method of the first embodiment. The control method used in the control method of this embodiment is also applicable to other resonant converter topologies, for example, the inverter switch circuit only includes the first bridge arm, the two rectifier tubes in the rectifier circuit are diodes, or the rectifier circuit is a full-bridge rectifier circuit, etc.

[0065] The control method of this embodiment has the following beneficial effects:

[0066] (1) By adjusting the first electrical parameter θ1 representing the duration of the first pulse and the third electrical parameter θ3 representing the duration of the second pulse to control the switch tube in the primary inverter switch circuit, the gain adjustment range can be increased, the transformer design can be optimized, and the conversion efficiency and power density of the converter can be improved in light-load applications.

[0067] (2) By adjusting the first electrical parameter θ1 representing the duration of the first pulse and the third electrical parameter θ3 representing the duration of the second pulse, the impact of the resonant inductor current and the resonant capacitor voltage can be reduced, the device is subjected to less stress, and the selection is easy;

[0068] (3) By adjusting the fourth electrical parameter φ that represents the Burst_off turn-off time, the gain of the resonant converter can be determined, and the output voltage ripple can also be determined. In addition, at the moment of entering the burst_off, if the fourth electrical parameter φ is adjusted to make the resonant current exactly zero, the electromagnetic interference of di / dt and du / dt can be reduced;

[0069] (4) The control method of this embodiment is a two-pulse Burst control, which is simpler and easier to implement than the three-pulse Burst control scheme. In addition, the driving loss of the switch tube can be significantly reduced due to the reduction in the number of pulses, thereby improving the efficiency of the entire machine. Furthermore, the control quantity of the control method of this embodiment also includes a second electrical parameter θ2 that characterizes the duration of the interval. The interval is the interval between the first pulse and the second pulse. During the interval, all the switches in the inverter switch circuit are also turned off. The Burst period is the sum of a continuous first pulse duration, an interval duration, a second pulse duration, and a Burst_off off time.

[0070] (5) The purpose of adding the second electrical parameter θ2 representing the intermittent duration as the control variable is to reduce the output current peak value and reduce the difficulty of selecting the secondary rectifier tube by adjusting the second electrical parameter θ2 representing the intermittent duration.

[0071] like Figure 2 As shown, the control method of the first embodiment is applied to Figure 1 The circuit includes a schematic diagram of four control quantities, which are the first electrical parameter θ1 characterizing the duration of the first pulse, the second electrical parameter θ2 characterizing the duration of the interval, the third electrical parameter θ3 characterizing the duration of the second pulse, and the fourth electrical parameter φ characterizing the Burst_off turn-off time, wherein: Vgs1 is the drive pulse of the first switch tube S1; Vgs2 is the drive pulse of the second switch tube S2; Vgs3 is the drive pulse of the third switch tube S3; Vgs4 is the drive pulse of the fourth switch tube S4; Burst_on is the Burst on turn-on time, including the sum of the first pulse duration, the interval duration and the second pulse duration; Burst_off is the Burst off turn-on time.

[0072] The inventor of this application has concluded through theoretical analysis that Figure 2 The mathematical model when the variables are θ1, θ2, θ3 and φ is as follows:

[0073]

[0074] 0=2·sin(θ1-2·θ2)+sin(2·θ2)+2·sin(2·θ2-2·θ3)-M·sin(2·θ2)-Vcr0n·sin(2·θ2)+2·M·sin(θ2)

[0075] 0=M-Vcr0n+2·cos(θ1-2·θ2)-cos(2·θ2)-2·cos(2·θ2-θ3)+M·cos(2·θ2)+Vcr0n·cos(2·θ2)-2·M·cos(θ2)+1

[0076]

[0077]

[0078] Among them, ω r is the resonant angular frequency, t0 is the initial working moment, t1 is the first working moment, t2 is the second working moment, t3 is the third working moment 3, θ0 = ω r t0, θ1 = ω r t1, θ2 = ω r t2 and θ3 = ω r ·t3 is the per-unit value of the operating frequency of the resonant converter at the corresponding time; fr is the resonant frequency of the resonant cavity; n is the transformer ratio, Vo is the nominal output voltage of the resonant converter, Vin is the nominal input voltage of the resonant converter, M is the normalized gain of the resonant converter; Lm is the excitation inductance, Lr is the resonant inductance, λ is the inductance ratio; vCr0 is the initial value of the resonant capacitor voltage; vCrn is the per-unit value of the resonant capacitor voltage, and vCr0n is the initial value of the resonant capacitor voltage at t0.

[0079] The per-unit value refers to a numerical notation method commonly used in engineering calculations, which represents the relative values ​​of various physical quantities and parameters. When performing engineering calculations in power system calculations, the actual values ​​of various physical quantities are often not used. Instead, the ratio of the actual value to a selected reference value with the same unit (i.e., the per-unit value) is used for calculation.

[0080] The inductance ratio λ is related to the parameters of the resonant converter and is a known quantity.

[0081] The variables in the mathematical model are θ1, θ2, θ3 and φ. The mathematical model is a set of equations for the independent variables θ1, θ2, θ3 and φ. The independent variables θ1, θ2, θ3 and φ can be solved by using mathematical analysis tools.

[0082] When the variables in the mathematical model are θ1, θ3 and φ, the mathematical model is as follows:

[0083] ωr=2π·fr

[0084]

[0085]

[0086]

[0087]

[0088] The variables in the mathematical model are θ1, θ3, and φ. The mathematical model is a set of equations for the independent variables θ1, θ3, and φ. The independent variables θ1, θ3, and φ can be solved by using mathematical analysis tools.

[0089] Furthermore, the first electrical parameter θ1, the second electrical parameter θ2, the third electrical parameter θ3 and the fourth electrical parameter φ are all phase angles, and the inverter switch circuit includes two bridge arms, wherein the duty cycle of the driving pulse of the switch tube in the first input loop is θ1 / 2π ignoring the dead time, and the phase difference is zero; the duty cycle of the driving pulse of the switch tube in the second input loop is θ3 / 2π ignoring the dead time, and the phase difference is zero; the driving pulse of the switch tube in the second input loop of the inverter switch circuit is delayed relative to the driving pulse of the switch tube in the first input loop of the inverter switch circuit, and the delayed phase angle is θ2. Since there is a relationship between the phase angle and time (θ0=ω r t0, θ1 = ω r t1, θ2 = ω r t2 and θ3 = ω r ·t3), the first electric parameter θ1, the second electric parameter θ2, the third electric parameter θ3 and the fourth electric parameter φ are all phase angles. When writing the mathematical model analysis equation, it is easy to normalize the phase angle variable to simplify the subsequent calculation processing.

[0090] Preferably, the first electrical parameter θ1, the third electrical parameter θ3 and the fourth electrical parameter φ are all phase angles, the driving pulse duty cycle of the switch tube located in the first input loop of the inverter switch circuit is θ1 / 2π, and the driving pulse duty cycle of the switch tube located in the second input loop of the inverter switch circuit is θ2 / 2π. The first electrical parameter θ1, the third electrical parameter θ3 and the fourth electrical parameter φ are all phase angles, which is also for the purpose of easily normalizing the phase angle variable in the mathematical model analysis equation and simplifying subsequent calculation processing.

[0091] Furthermore, when the gain of the resonant converter is lower than the second set value, the resonant converter is controlled to operate in a two-element resonant mode of resonance between the resonant inductor and the resonant capacitor within the first pulse duration. In the two-element resonant mode, the excitation inductor is clamped, and the resonant converter outputs energy to the secondary side within the first pulse duration, thereby reducing the circulating current power of the primary circuit of the transformer and further improving the energy conversion efficiency of the resonant converter.

[0092] Specifically, when the gain of the resonant converter is lower than the second set value, within the same Burst cycle, the resonant current and the excitation current within the first pulse duration are controlled to increase from zero at the same time, and the two are not equal. After the second pulse is turned off, the resonant current and the excitation current drop to zero at the same time.

[0093] Figure 3 The control method of the first embodiment is applied to Figure 1 The switch tube driving waveform and key working waveform under the resonant mode of the two components of the circuit, Figure 3 Medium V gs1 、V gs2 、V gs3 、V gs4 Respectively represent the driving pulses of the first switch tube S1, the second switch tube S2, the third switch tube S3, and the fourth switch tube S4; the driving pulse V gs1 and V gs4 Same; driving pulse V gs2 and V gs3 Same; V AB Represents the voltage at the midpoint of the two bridge arms of the primary side. Its operating waveform is related to the control strategy of the primary switch tube. V TP represents the transformer primary voltage and i Lr Represents the current flowing through the resonant inductor L r The resonant current, i Lm Indicates the current flowing through the magnetizing inductance L m The interval between the first pulse and the second pulse is zero, the first pulse is the driving pulse of the first switch tube S1 and the fourth switch tube S4, and the second pulse S2 is the driving pulse of the second switch tube and the third switch tube S3.

[0094] At light load (I o =10%I oN ,I oN In the working condition of full load current, after calculation, the first pulse, the second pulse and the Burst_off turn-off time φ are 1.25 microseconds, 1.189 microseconds, and 18.712 microseconds respectively.

[0095] Before the first pulse, the resonant inductor current is equal to the excitation inductor current, and both are zero. During the duration of the first pulse, the resonant inductor and the resonant capacitor resonate. The resonant current of the primary side of the transformer is not equal to the excitation current during the duration of the first pulse. The input voltage of the resonant cavity is the power supply voltage. At the same time, the primary voltage of the transformer is the converted value of the secondary voltage. The excitation inductor is clamped, and the resonant current and the excitation current increase. At this time, the energy of the converter is transferred from the primary side of the transformer to the secondary side. During the duration of the second pulse, the resonant current and the excitation current are also not equal. In this stage, the excitation inductor is clamped by the output voltage, and the excitation current decreases linearly. When the second pulse is turned off, the excitation current just drops to zero. Therefore, the converter transfers energy to the secondary side in the Burst_on stage, and the output capacitor outputs power to the load in the Burst_off stage.

[0096] Figure 4 The control method of the first embodiment is applied to Figure 1 Soft switching waveform of the switch tube in the resonant mode of two components of the circuit. Figure 4 Where Vds1 represents the drain-source voltage of the first switch tube S1, Vgs1 represents the driving voltage of the first switch tube S1, Vds2 represents the drain-source voltage of the second switch tube S2, and Vgs2 represents the driving voltage of the second switch tube S2. The basic condition for achieving soft switching is that during the dead time, the current of the resonant circuit can draw away the charge on the junction capacitance of the primary switch tube. After adding light load control (i.e., the control method provided in this embodiment when the load of the resonant converter is lower than the first set value), the turn-off currents of the switches S1 and S2 of the first bridge arm and the switches S3 and S4 of the second bridge arm are different, and the difficulty of achieving ZVS in the first bridge arm driven by the first pulse and the second bridge arm driven by the second pulse is no longer the same. Figure 4 The driving voltage signals Vgs1 and Vgs2 of the switches S1 and S2, as well as the drain-source voltages Vds1 and Vds2 are shown respectively. During the Burst_off time before the switch S1 is turned on, the resonant cavity current is zero, and it is impossible to charge the drain-source junction capacitance C1 of the switch S1, nor to discharge the drain-source junction capacitance C2 of the switch S2. Therefore, during the first pulse duration, the switches S1 and S2 are hard-on, and ZVS cannot be achieved. During the dead time after the switch S1 is turned off and before the switch S2 is turned on, the resonant cavity current is not zero, and the resonant current charges the drain-source junction capacitance C1 of the switch S1 and discharges the drain-source junction capacitance C2 of the switch S2. Therefore, during the second pulse duration, the switch is soft-on, and ZVS is achieved. In the light-load Burst control of the resonant converter, the first pulse is inevitably hard switching, and the second pulse achieves soft switching.

[0097] Figure 5 The control method of the first embodiment is applied to Figure 1The output voltage ripple under the circuit two-element resonant mode is compared with the output voltage ripple under traditional Burst control. Figure 5 In the figure, Vo1 represents the output voltage waveform of the conventional light-load burst control; Vgs11 represents the driving voltage waveform of the first switch tube S1 and the fourth switch tube S4 of the conventional light-load burst control; Vgs21 represents the driving voltage waveform of the second switch tube S2 and the third switch tube S3 of the conventional light-load burst control. Vgs1 represents the driving voltage waveform of the first switch tube S1 and the fourth switch tube S4 of the light-load burst control of this embodiment, Vgs2 represents the driving voltage waveform of the second switch tube S2 and the third switch tube S3 of the light-load burst control of this embodiment, and Vo represents the output voltage waveform of the light-load burst control of this embodiment; from the comparison of the figures, it can be concluded that the light-load burst control of this embodiment is more conducive to reducing the output voltage ripple, reducing the ripple loss, and improving the energy conversion efficiency of the light-load control of the converter.

[0098] Figure 6 The control method of the first embodiment is applied to Figure 1 Comparison waveform of the resonant current and voltage peak value under the resonant mode of the two components of the circuit and the resonant current and voltage peak value under traditional Burst control. Figure 6 In the figure, Vcr1 represents the resonant capacitor voltage waveform of the conventional light-load burst control; iLr1 represents the resonant inductor current waveform of the conventional light-load burst control; Vgs11 represents the driving voltage waveform of the first switch tube S1 and the fourth switch tube S4 of the conventional light-load burst control; Vgs21 represents the driving voltage waveform of the second switch tube S2 and the third switch tube S3 of the conventional light-load burst control. Vgs1 represents the driving voltage waveform of the first switch tube S1 and the fourth switch tube S4 of the light-load burst control of this embodiment, Vgs2 represents the driving voltage waveform of the second switch tube S2 and the third switch tube S3 of the light-load burst control of this embodiment, Vcr represents the resonant capacitor voltage waveform of the light-load burst control of this embodiment; iLr represents the resonant inductor current waveform of the light-load burst control of this embodiment. By comparison, it can be seen that under the conventional control, the resonant capacitor voltage stress is as high as six hundred volts, which is seven times that of the control method of this embodiment under the same working condition, and the resonant inductor current stress under the conventional control is thirty amperes, which is eight times that of the control method of this embodiment. Therefore, the control method of this embodiment effectively reduces voltage and current stresses, while reducing the difficulty of device selection.

[0099] Furthermore, when the gain of the resonant converter is higher than the third set value, the resonant converter is controlled to operate in a three-element resonant mode of resonance of the resonant inductor, the resonant capacitor and the excitation inductor within the first pulse duration. In the three-element resonant mode, the resonant converter charges the resonant inductor and the resonant capacitor within the first pulse duration and does not output energy to the secondary side. At this time, the energy stored in the resonant inductor and the resonant capacitor can enable the switch tube to be opened fewer times when the resonant converter outputs a higher gain, thereby reducing the number of drive pulses and thus reducing drive losses.

[0100] Specifically, when the gain of the resonant converter is higher than the third set value, within the same Burst cycle, the resonant current and the excitation current within the first pulse duration are controlled to increase from zero, and the two remain equal. The resonant current and the excitation current within the second pulse duration are not equal. After the second pulse is turned off, the resonant current and the excitation current drop to zero at the same time.

[0101] Figure 7 The control method of the first embodiment is applied to Figure 1 The switch tube driving waveform and key working waveform under the circuit three-element resonant mode, Figure 7 Medium V gs1 、V gs2 、V gs3 、V gs4 Respectively represent the driving pulses of the first switch tube S1, the second switch tube S2, the third switch tube S3, and the fourth switch tube S4; the driving pulse V gs1 and V gs4 Same; driving pulse V gs2 and V gs3 Same; V AB Represents the voltage at the midpoint of the two bridge arms of the primary side. Its operating waveform is related to the control strategy of the primary switch tube. V TP represents the transformer primary voltage and i Lr Represents the current flowing through the resonant inductor L r The resonant current, i Lm Indicates the current flowing through the magnetizing inductance L m The interval between the first pulse and the second pulse is zero, the first pulse is the driving pulse of the first switch tube and the fourth switch tube, and the second pulse is the driving pulse of the second switch tube and the third switch tube.

[0102] At light load (I o =10%I oN ,I oN In the working condition of full load current, after calculation, the first pulse, the second pulse and the Burst_off turn-off time φ are 4.998 microseconds, 2.541 microseconds, and 39.975 microseconds respectively.

[0103] Before the first pulse, the resonant inductor current is equal to the excitation inductor current, and both are zero. During the duration of the first pulse, the resonant inductor, resonant capacitor and excitation inductor resonate. The resonant current of the primary side of the transformer is equal to the excitation current during the duration of the first pulse. The input voltage of the resonant cavity is the power supply voltage. At the same time, the primary voltage of the transformer is the excitation inductor voltage. The excitation inductor is in a free resonance state. The resonant current and the excitation current increase in phase. At this time, the energy of the converter cannot be transferred from the primary side of the transformer to the secondary side. During the duration of the second pulse, the resonant current is not equal to the excitation current. At this stage, the excitation inductor is clamped by the output voltage, and the excitation current decreases linearly. When the second pulse is turned off, the excitation current just drops to zero. Therefore, the converter transfers energy to the secondary side during the second pulse duration of Burst_on, and the output capacitor outputs power to the load during the Burst_off stage.

[0104] The control method of the first embodiment is applied to Figure 1 The soft switching waveform of the switch tube in the three-element resonant mode of the circuit is consistent with the soft switching waveform of the switch tube in the two-element resonant mode, which is also Figure 4 , so I won’t go into details.

[0105] Figure 8 The control method of the first embodiment is applied to Figure 1 The output voltage ripple under the circuit three-element resonant mode is compared with the output voltage ripple under traditional Burst control. Figure 8 In the figure, Vo1 represents the output voltage waveform of the conventional light-load burst control; Vgs11 represents the driving voltage waveform of the first switch tube S1 and the fourth switch tube S4 of the conventional light-load burst control; Vgs21 represents the driving voltage waveform of the second switch tube S2 and the third switch tube S3 of the conventional light-load burst control. Vgs1 represents the driving voltage waveform of the first switch tube S1 and the fourth switch tube S4 of the light-load burst control of this embodiment, Vgs2 represents the driving voltage waveform of the second switch tube S2 and the third switch tube S3 of the light-load burst control of this embodiment, and Vo represents the output voltage waveform of the light-load burst control of this embodiment; from the comparison of the figures, it can be concluded that the light-load burst control of this embodiment is more conducive to reducing the output voltage ripple, reducing the ripple loss, and improving the energy conversion efficiency of the light-load control of the converter.

[0106] Fig. 9 The control method of the first embodiment is applied to Figure 1 Comparison waveform of the resonant current and voltage peak value under the three-element resonant mode of the circuit and the resonant current and voltage peak value under traditional Burst control. Fig. 9Where Vcr1 represents the resonant capacitor voltage waveform of the traditional light-load burst control; iLr1 represents the resonant inductor current waveform of the traditional light-load burst control; Vgs11 represents the driving voltage waveform of the first switch tube S1 and the fourth switch tube S4 of the traditional light-load burst control; Vgs21 represents the driving voltage waveform of the second switch tube S2 and the third switch tube S3 of the traditional light-load burst control. Vgs1 represents the driving voltage waveform of the first switch tube S1 and the fourth switch tube S4 of the light-load burst control of this embodiment, Vgs2 represents the driving voltage waveform of the second switch tube S2 and the third switch tube S3 of the light-load burst control of this embodiment, Vcr represents the resonant capacitor voltage waveform of the light-load burst control of this embodiment; iLr represents the resonant inductor current waveform of the light-load burst control of this embodiment. By comparison, it can be seen that the resonant capacitor voltage peak and resonant current peak under the traditional control are higher than those of the control method of this embodiment. Therefore, the control scheme of the present invention effectively reduces voltage and current stresses, while reducing the difficulty of device selection.

[0107] Second embodiment

[0108] This embodiment provides a control device, which is applied to a resonant converter, wherein the primary side of the resonant converter is a DC input, and includes an inverter switch circuit, and the inverter switch circuit includes at least one bridge arm; wherein:

[0109] The control device is configured to be applied to a condition where the load of the resonant converter is lower than a first set value, and includes three control quantities, namely, a first electrical parameter θ1 representing the duration of the first pulse, a third electrical parameter θ3 representing the duration of the second pulse, and a fourth electrical parameter φ representing the Burst_off off time, and the control frequency is equal to the frequency corresponding to the Burst period, wherein:

[0110] The first electrical parameter θ1 is a control variable of the switch tube located in the first input loop of the inverter switch circuit;

[0111] The second electrical parameter θ3 is a control variable of the switch tube located in the second input loop of the inverter switch circuit;

[0112] During the Burst_off time, all switches in the inverter switch circuit are turned off;

[0113] The Burst period is the sum of a continuous first pulse duration, a second pulse duration, and a Burst_off off time.

[0114] Furthermore, the control quantity of the control device of this embodiment also includes a second electrical parameter θ2 that characterizes the intermittent duration. The intermittence is the interval between the first pulse and the second pulse. During the intermittent period, all switching tubes in the inverter switch circuit are also turned off. The Burst cycle is the sum of a continuous first pulse duration, an intermittent duration, a second pulse duration and a Burst_off turn-off time.

[0115] Furthermore, the first electrical parameter θ1, the second electrical parameter θ2, the third electrical parameter θ3 and the fourth electrical parameter φ are all phase angles, and the inverter switch circuit includes two bridge arms, wherein the driving pulse duty cycle of the switch tube located in the first input loop is θ1 / 2π ignoring the dead time, and the phase difference is zero; the driving pulse duty cycle of the switch tube located in the second input loop is θ3 / 2π ignoring the dead time, and the phase difference is zero; the driving pulse of the switch tube located in the second input loop of the inverter switch circuit is delayed relative to the driving pulse of the switch tube located in the first input loop of the inverter switch circuit, and the lag phase angle is θ2.

[0116] Preferably, the first electrical parameter θ1, the third electrical parameter θ3 and the fourth electrical parameter φ are all phase angles, the driving pulse duty cycle of the switch tube located in the first input loop of the inverter switch circuit is θ1 / 2π, and the driving pulse duty cycle of the switch tube located in the second input loop of the inverter switch circuit is θ2 / 2π.

[0117] Furthermore, when the gain of the resonant converter is lower than the second set value, the resonant converter is controlled to operate in a two-element resonant mode of resonance between the resonant inductor and the resonant capacitor within the first pulse duration. In the two-element resonant mode, the excitation inductor is clamped, and the resonant converter outputs energy to the secondary side within the first pulse duration.

[0118] Specifically, when the gain of the resonant converter is lower than the second set value, in the same Burst cycle, the resonant current and the excitation current in the first pulse are controlled to increase from zero at the same time, and the two are not equal. After the second pulse is turned off, the resonant current and the excitation current drop to zero at the same time.

[0119] Further, when the gain of the resonant converter is higher than the third set value, the resonant converter is controlled to operate in a three-element resonant mode of resonance of the resonant inductor, the resonant capacitor and the excitation inductor within the first pulse duration. In the three-element resonant mode, the resonant converter charges the resonant inductor and the resonant capacitor within the first pulse duration, and does not output energy to the secondary side.

[0120] Specifically, when the gain of the resonant converter is higher than the third set value, within the same Burst cycle, the resonant current and the excitation current in the first pulse are controlled to increase from zero, and the two remain equal. When the second pulse is turned on, the resonant current and the excitation current are not equal. After the second pulse is turned off, the resonant current and the excitation current drop to zero at the same time.

[0121] The technical means adopted by the control device of this embodiment correspond to and are consistent with the control method of the first embodiment, and have the same beneficial effects.

[0122] Third embodiment

[0123] This embodiment provides a resonant converter, the primary side of the resonant converter is a DC input, including an inverter switch circuit, and the inverter switch circuit includes at least one bridge arm; wherein the resonant converter also includes any one of the control devices in the second embodiment.

[0124] Since the resonant converter of this embodiment includes any one of the control devices in the second embodiment, it reduces switching losses, reduces the voltage stress of the resonant capacitor, reduces the current stress of the resonant inductor, improves the gain adjustment capability of the resonant converter, and reduces the output voltage ripple on the secondary side. It has broad application prospects in light-load situations of series resonant converters.

[0125] The embodiments described above are merely examples of the technical solutions and contents of the present invention. It should be noted that the above embodiments should not be regarded as limiting the present invention. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and scope of the present invention, but they will not deviate from the spirit of the present invention or exceed the scope defined by the attached claims, and should also be regarded as the protection scope of the present invention.

Claims

1. A control method, applied to a resonant converter, wherein the primary side of the resonant converter is a DC input, and comprises an inverter switch circuit, wherein the inverter switch circuit comprises at least one bridge arm; characterized in that: The control method is applied to the working condition where the load of the resonant converter is lower than the first set value, and includes three control quantities, namely, a first electrical parameter θ1 representing the duration of the first pulse, a third electrical parameter θ3 representing the duration of the second pulse, and a fourth electrical parameter φ representing the Burst_off off time, and the control frequency is equal to the frequency corresponding to the Burst period, wherein: The first electrical parameter θ1 is a control variable of a switch tube in a first input loop of the inverter switch circuit; The second electrical parameter θ3 is a control variable of the switch tube located in the second input loop of the inverter switch circuit; During the Burst_off time, all switch tubes in the inverter switch circuit are turned off; The Burst period is the sum of a continuous first pulse duration, a second pulse duration and a Burst_off off time.

2. The control method according to claim 1, characterized in that: The control quantity also includes a second electrical parameter θ2 that characterizes the duration of the interval, where the interval is the interval between the first pulse and the second pulse, during which all switch tubes in the inverter switch circuit are also turned off, and the Burst cycle is the sum of a continuous first pulse duration, an interval duration, a second pulse duration, and a Burst_off turn-off time.

3. The control method according to claim 2, characterized in that: The first electrical parameter θ1, the second electrical parameter θ2, the third electrical parameter θ3 and the fourth electrical parameter φ are all phase angles. The inverter switch circuit includes two bridge arms, wherein the driving pulse duty cycle of the switch tube located in the first input loop is θ1 / 2π ignoring the dead time, and the phase difference is zero; the driving pulse duty cycle of the switch tube located in the second input loop is θ3 / 2π ignoring the dead time, and the phase difference is zero; the driving pulse of the switch tube located in the second input loop of the inverter switch circuit is lagged relative to the driving pulse of the switch tube located in the first input loop of the inverter switch circuit, and the lag phase angle is θ2.

4. The control method according to claim 1, characterized in that: The first electrical parameter θ1, the third electrical parameter θ3 and the fourth electrical parameter φ are all phase angles. The driving pulse duty cycle of the switch tube located in the first input loop of the inverter switch circuit is θ1 / 2π, and the driving pulse duty cycle of the switch tube located in the second input loop of the inverter switch circuit is θ2 / 2π.

5. The control method according to claim 1, characterized in that: When the gain of the resonant converter is lower than a second set value, the resonant converter is controlled to operate in a two-element resonant mode of resonance between a resonant inductor and a resonant capacitor during the first pulse duration. In the two-element resonant mode, the excitation inductor is clamped, and the resonant converter outputs energy to the secondary side during the first pulse duration.

6. The control method according to claim 5, characterized in that: When the gain of the resonant converter is lower than the second set value, within the same Burst cycle, the resonant current and the excitation current within the duration of the first pulse are controlled to increase from zero at the same time, and the two are not equal. After the second pulse is turned off, the resonant current and the excitation current drop to zero at the same time.

7. The control method according to claim 1, characterized in that: When the gain of the resonant converter is higher than a third set value, the resonant converter is controlled to operate in a three-element resonant mode of resonance of the resonant inductor, the resonant capacitor and the excitation inductor during the first pulse duration. Under the three-element resonant mode, the resonant converter charges the resonant inductor and the resonant capacitor during the first pulse duration, and does not output energy to the secondary side.

8. The control method according to claim 7, characterized in that: When the gain of the resonant converter is higher than the third set value, within the same Burst cycle, the resonant current and the excitation current within the duration of the first pulse are controlled to increase from zero, and the two remain equal. The resonant current and the excitation current within the duration of the second pulse are not equal. After the second pulse is turned off, the resonant current and the excitation current drop to zero at the same time.

9. A control device, applied to a resonant converter, wherein the primary side of the resonant converter is a DC input, and comprises an inverter switch circuit, wherein the inverter switch circuit comprises at least one bridge arm; characterized in that: The control device is configured to be applied to a condition where the load of the resonant converter is lower than a first set value, and includes three control quantities, namely, a first electrical parameter θ1 representing the duration of the first pulse, a third electrical parameter θ3 representing the duration of the second pulse, and a fourth electrical parameter φ representing the Burst_off off time, and the control frequency is equal to the frequency corresponding to the Burst period, wherein: The first electrical parameter θ1 is a control variable of a switch tube in a first input loop of the inverter switch circuit; The second electrical parameter θ3 is a control variable of the switch tube located in the second input loop of the inverter switch circuit; During the Burst_off time, all switch tubes in the inverter switch circuit are turned off; The Burst period is the sum of a continuous first pulse duration, a second pulse duration and a Burst_off off time.

10. A resonant converter, wherein the primary side of the resonant converter is a DC input, and comprises an inverter switch circuit, wherein the inverter switch circuit comprises at least one bridge arm; characterized in that: The resonant converter further comprises the control device as claimed in claim 9.

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