Resonant Converter Based on Mode Switching and Its Control Method

Abstract

The present invention relates to a resonant converter based on mode switching and its control method. The main circuit of the resonant converter includes a DC / AC inverter unit, a resonant network unit, a rectifier and filter unit, an isolation transformer, and a control unit; the DC input voltage is converted into a high-frequency AC square wave voltage by the DC / AC inverter unit; the high-frequency AC square wave voltage outputs a high-frequency sine voltage after filtering out the high-order harmonic signals in the high-frequency AC square wave voltage by the resonant network unit, and the high-frequency sine voltage is output to the rectifier and filter unit through the isolation transformer, and a DC voltage is output through the rectifier and filter unit; the control unit generates a switching control signal in the resonant network unit to realize the switching control of the working mode of the converter; the resonant network unit is composed of an inductor, a capacitor, and a switch, and the structure of the resonant network unit can be changed by controlling the switch of the resonant network unit, so that the converter works in different modes, broadens the input-output gain of the converter, and improves the performance of the converter.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and particularly to a resonant converter based on mode switching and its control method. Background Art

[0002] New energy vehicles have developed rapidly due to advantages such as economy and environmental protection, as well as the support of national policies. The charging piles for new energy vehicles are an important part to ensure the convenient travel of new energy vehicles. Since different vehicle models have different requirements for the voltage levels of charging piles, it is required that the converter has the characteristics of wide gain and high efficiency.

[0003] As an important part of the charging pile, the DC-DC DC converter is an important guarantee for realizing the excellent characteristics of the charging pile. As a DC transformer, the LLC resonant converter is widely used due to its advantages such as high efficiency and wide soft-switching range. When the switching tube operates slightly below the resonant frequency, PFM is generally used to regulate the output voltage. However, in the range where the switching frequency is greater than the resonant frequency, the voltage gain curve of the converter changes more and more slowly as the switching frequency increases. If PSM is used to regulate the output voltage when the switching frequency is greater than the resonant frequency, problems such as duty cycle loss will occur when the phase-shift angle exceeds a certain value.

[0004] Therefore, how to optimize the performance of the LLC resonant converter is a technical problem to be solved urgently. Summary of the Invention

[0005] The embodiments of the present application provide a resonant converter based on mode switching and its control method, enabling the converter to have the characteristics of wide gain and high efficiency.

[0006] The present application provides a resonant converter based on mode switching. The main circuit of the resonant converter includes a DC / AC inverter unit, a resonant network unit, a rectifier and filter unit, an isolation transformer, and a control unit; the DC input voltage is converted into a high-frequency AC square-wave voltage by the DC / AC inverter unit; after the high-frequency AC square-wave voltage filters out the high-order harmonic signals in the high-frequency AC square-wave voltage through the resonant network unit, a high-frequency sine voltage is output, and the high-frequency sine voltage is output to the rectifier and filter unit through the isolation transformer, and a DC voltage is output through the rectifier and filter unit.

[0007] The resonant network unit is composed of an inductor, a capacitor, and a switch. By controlling the switch of the resonant network unit, the structure of the resonant network unit can be changed, enabling the converter to operate in different modes and broadening the input-output gain of the converter. The resonant network unit is composed of a first LC series resonant circuit and a second LC series resonant circuit connected in parallel. Among them, the inductor L1 and the capacitor C1 are connected in series to form the first LC series resonant circuit, and the inductor L2, the capacitor C2, and the switch Q5 are connected in series to form the second LC series resonant circuit. One end of the parallel connection of the first LC series resonant circuit and the second LC series resonant circuit is connected to one end of the output terminal of the DC / AC inverter unit, and the other end of the parallel connection of the first LC series resonant circuit and the second LC series resonant circuit is connected to one end of the input terminal of the isolation transformer. The other end of the output terminal of the DC / AC inverter unit is connected to the other end of the input terminal of the isolation transformer.

[0008] The control unit generates the switch control signal in the resonant network unit to realize the switching control of the converter working mode, controls the disconnection of the second LC series resonant circuit to enable the resonant converter to work in the LLC mode, and controls the connection of the second LC series resonant circuit to enable the resonant converter to work in the L-LCLC mode.

[0009] Preferably, by changing the structure of the resonant network unit, the transfer function of the resonant converter can be changed to achieve wide gain. Among them, when the second LC series resonant circuit is controlled to be connected, the resonant converter works in the L-LCLC mode, and the reciprocal of the voltage gain of the resonant converter is as follows:

[0010]

[0011] Among them, R ac represents the equivalent resistance , n represents the turns ratio of the transformer, R o is the output resistance, L m is the equivalent inductance of the transformer, ω represents the angular frequency, L r1 , L r2 are the inductance values of the inductors L1 and L2, C r1 , C r2 are the capacitance values of the capacitors C1 and C2.

[0012] Preferably, when the gain of the resonant converter is less than 1, the resonant network unit is controlled to connect the second LC series resonant circuit to enable the resonant converter to work in the L-LCLC mode;

[0013] When the gain of the resonant converter is greater than 1, the resonant network unit is controlled to disconnect the second LC series resonant circuit to enable the resonant converter to work in the LLC mode.

[0014] Preferably, when the input voltage of the resonant converterU in Greater than the second preset voltage U When it is greater than 2, control the resonant network unit to access the second LC series resonant circuit so that the resonant converter operates in the L-LCLC mode;

[0015] When the input voltage of the resonant converter U in Less than the first preset voltage U When it is less than 1, control the resonant network unit to disconnect the second LC series resonant circuit so that the resonant converter operates in the LLC mode,

[0016] Wherein, U 1 < U 0 < U 2, U 0 is the output voltage of the resonant converter.

[0017] Preferably, the U The range of 1 is 0.97 U 0 to 0.99 U 0, the U The range of 2 is 1.01 U 0 to 1.03 U 0.

[0018] Based on the resonant converter based on mode switching, the present application proposes a control method for the resonant converter, specifically:

[0019] By collecting the converter input voltage signal and the switch state signal in the resonant network unit, comparing the given voltage signal and the input voltage signal to obtain an error signal, and combining the switch state signal, generating a switch control signal in the resonant network unit to realize the switching control of the converter working mode; including: controlling to disconnect the second LC series resonant circuit so that the resonant converter operates in the LLC mode, and controlling to access the second LC series resonant circuit so that the resonant converter operates in the L-LCLC mode.

[0020] Preferably, when the gain of the resonant converter is less than 1, control the resonant network unit to access the second LC series resonant circuit so that the resonant converter operates in the L-LCLC mode;

[0021] When the gain of the resonant converter is greater than 1, control the resonant network unit to disconnect the second LC series resonant circuit so that the resonant converter operates in the LLC mode.

[0022] Preferably, when the input voltage of the resonant converter U in Greater than the second preset voltage UWhen it is 2, control the resonant network unit to access the second LC series resonant circuit so that the resonant converter operates in the L-LCLC mode;

[0023] When the input voltage of the resonant converter U in is less than the first preset voltage U 1, control the resonant network unit to disconnect the second LC series resonant circuit so that the resonant converter operates in the LLC mode.

[0024] wherein, U 1 < U 0 < U 2, U 0 is the output voltage of the resonant converter.

[0025] This application also proposes a computer-readable storage medium. The computer-readable storage medium stores a computer program. When the computer program is executed by a processor, the processor can execute the control method of the resonant converter based on mode switching.

[0026] Thus, compared with the prior art, the present invention has the following beneficial effects:

[0027] In the present invention, by changing the structure of the converter unit of LLC resonance, wide input-output gain is achieved, and the wide input-output gain effect is particularly obvious in the range greater than the LLC resonance frequency;

[0028] In the present invention, by adopting a mode state switching strategy, when the input-output gain is greater than 1, it operates in the resonant converter mode of the LLC resonant type, and when the input-output gain is less than 1, it operates in the resonant converter mode of the L-LCLC resonant type. When the input-output gain is greater than 1, the voltage input-output gain curves of the resonant converter of the LLC resonant type and the resonant converter of the L-LCLC resonant type with respect to frequency are similar, and both can achieve soft switching. However, compared with the resonant converter mode of the L-LCLC resonant type, the resonant converter of the LLC resonant type has fewer devices and lower energy consumption. By adopting the mode state switching strategy, the efficiency of the resonant converter is improved;

[0029] In the present invention, the resonant converter of the LLC resonant type and the resonant converter of the L-LCLC resonant type are switched when the input-output gain is 1. At this time, the operating frequencies and input-output gains of the two resonant converters are the same, greatly reducing the impact of voltage and current during mode state switching;

[0030] In the present invention, a hysteresis control strategy is adopted to solve the problem of voltage fluctuations near the switching point and the problem that the resonant converter frequently switches modes, ensuring that the circuit can stably perform mode state switching. Brief Description of the Drawings

[0031] To more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0032] Figure 1 It is a schematic structural diagram of a resonant converter based on mode switching provided by an embodiment of the present application;

[0033] Figure 2 It is a schematic structural diagram of a resonant converter based on mode switching provided by another embodiment of the present application;

[0034] Figure 3 It is a switching curve diagram of the resonant converter of the present application;

[0035] Figure 4 It is a schematic diagram of the hysteresis control loop of the present application;

[0036] Figure 5 It is the capacitor under a voltage level of the present application C r1 The current flowing through I cr1 And the simulation waveforms of the output voltage;

[0037] Figure 6 It is the capacitor under another voltage level of the present application C r1 The current flowing through I cr1 And the simulation waveforms of the output voltage;

[0038] Figure 7 It is a schematic diagram of the simulation LLC mode gain of the present application;

[0039] Figure 8 It is a schematic diagram of the simulation L-LCLC mode gain of the present application;

[0040] Figure 9 It is a simulation diagram of the LLC mode switching to the L-LCLC mode of the present application;

[0041] Figure 10 It is a simulation diagram of the L-LCLC mode switching to the LLC mode of the present application;

[0042] Figure 11 It is a simulation diagram under the hysteresis control loop of the present application. Detailed Embodiments

[0043] Embodiment 1

[0044] As shown Figure 1 in the figure, the resonant converter based on mode switching provided by the embodiment of the present application includes a DC / AC inverter unit 1, a resonant network unit 2, a rectifier and filter unit 3, and a second control unit. The resonant network unit 2 includes a basic resonant network and an LC series resonant circuit 21;

[0045] The DC / AC inverter unit 1 is connected to the input end of the resonant network unit 2, the output of the resonant network unit 2 is connected to the input end of the rectifier and filter unit 3, and the control end of the second control unit is connected to the controlled end of the LC series resonant circuit 21;

[0046] The DC / AC inverter unit 1 is configured to convert a DC voltage into a high-frequency AC square wave voltage and output it to the resonant network unit 2;

[0047] The resonant network unit 2 is configured to convert the high-frequency AC square wave voltage into a high-frequency sine current and output it to the rectifier and filter unit 3;

[0048] The rectifier and filter unit 3 is configured to convert the high-frequency sine current into a DC voltage and output it;

[0049] The second control unit is configured to control the LC series resonant circuit 21 to be connected to the basic resonant network when the switching condition is satisfied, so that the resonant converter operates in the L-LCLC mode, or control the LC series resonant circuit 21 to disconnect from the basic resonant network, so that the resonant converter operates in the LLC mode;

[0050] The LC series resonant circuit 21 is configured to be controlled by the second control unit to be connected to or disconnected from the basic resonant network.

[0051] In application, the DC / AC inverter unit 1 is configured to convert a DC voltage into a high-frequency AC square wave voltage and output it to the resonant network unit 2. This unit is usually composed of switching tubes (such as MOSFETs or IGBTs), and the required high-frequency AC square wave voltage is generated by controlling the on and off of these switching tubes. This high-frequency AC square wave voltage is then transmitted to the resonant network unit 2 for processing.

[0052] In application, the resonant network unit 2 is configured to convert the high-frequency AC square wave voltage from the DC / AC inverter unit 1 into a high-frequency sine current and output it to the rectifier and filter unit 3. The resonant network unit 2 includes a basic resonant network and an LC series resonant circuit 21. The basic resonant network can be composed of an inductor L r1 , a capacitor C r1 and a resonant inductor L mComposed to generate a resonance effect, thereby filtering out high-order harmonic signals in the high-frequency AC square-wave voltage. The LC series resonance circuit 21 can be composed of an additional inductor L r2 and a capacitor C r2 Composed, it can be connected to the basic resonance network or disconnected from the basic resonance network under the control of the second control unit. When the LC series resonance circuit 21 is connected, the resonance network unit 2 operates in the L-LCLC mode; when it is disconnected, the resonance network unit 2 operates in the LLC mode. This mode switching strategy enables the converter to operate efficiently within different gain ranges.

[0053] In an application, the rectifier and filter unit 3 is used to convert the high-frequency sinusoidal current output from the resonance network unit 2 into a DC voltage, and after filtering, a stable DC voltage is output. The rectifier and filter unit 3 usually includes rectifier diodes or synchronous rectifier switching tubes and filter capacitors to ensure the stability and quality of the output voltage.

[0054] In an application, the second control unit is responsible for controlling the connection or disconnection of the LC series resonance circuit 21 when specific switching conditions are met. Specifically, when it is necessary to increase the voltage gain range, the second control unit will control the LC series resonance circuit 21 to connect to the basic resonance network, making the resonant converter enter the L-LCLC mode; when additional gain is not required, it will control the LC series resonance circuit 21 to disconnect, making the resonant converter operate in the LLC mode. This mode switching strategy not only improves the wide gain ability of the converter but also optimizes the efficiency in different operating modes.

[0055] In an application, the LC series resonance circuit 21 can be controlled by the second control unit to flexibly connect to or disconnect from the basic resonance network. When the LC series resonance circuit 21 is connected, it acts together with the basic resonance network, changing the overall characteristics of the resonance network, thereby achieving a wider voltage gain range. When the LC series resonance circuit 21 is disconnected, the basic resonance network works alone, maintaining its original high efficiency. This structure enables the converter to automatically adjust according to the actual working conditions to achieve the best working state.

[0056] In the embodiment of this application, by introducing the LC series resonance circuit 21 and controlling its connection or disconnection to the basic resonance network by the second control unit, efficient operation within a wide gain range can be achieved. This structural change enables the converter to flexibly switch between different operating modes, thereby improving the overall efficiency and performance. At the same time, by controlling the connection and disconnection of the LC series resonance circuit 21, the characteristics of the resonance network can be optimized, further enhancing the adaptability and stability of the converter.

[0057] Embodiment 2

[0058] AsFigure 2 As shown, the LC series resonance circuit 21 includes a second inductor, a second capacitor, and a switching transistor. One end of the second inductor is used to connect to the midpoint of the upper half-bridge of the DC / AC inverter unit 1, the other end is connected to one end of the second capacitor, the other end of the second capacitor is connected to the drain of the switching transistor, the source of the switching transistor is connected to the midpoint of the lower half-bridge of the DC / AC inverter unit 1, and the gate of the switching transistor is connected to the control terminal of the second control unit.

[0059] In application, the LC series resonance circuit 21 consists of the second inductor L r2 , the second capacitor C r2 and the switching transistor Q5. One end of the second inductor L r2 is connected to the midpoint of the upper half-bridge of the DC / AC inverter unit 1, that is, the node between the source of the switching transistor Q1 and the drain of the switching transistor Q2; the other end is connected to one end of the second capacitor C r2 . One end of the second capacitor C r2 is then connected to the drain of the switching transistor Q5, and the source of the switching transistor Q5 is directly connected to the midpoint of the lower half-bridge of the DC / AC inverter unit 1, that is, the node between the source of the switching transistor Q3 and the drain of the switching transistor Q4. To achieve effective control of the LC series resonance circuit 21, the gate of the switching transistor Q5 is connected to the control terminal of the second control unit. By controlling the state of the switching transistor Q5, the LC series resonance circuit 21 can be flexibly connected to or disconnected from the basic resonance network, thereby adjusting the working mode of the converter as needed.

[0060] The embodiment of the present application details the specific composition of the LC series resonance circuit 21, including the second inductor, the second capacitor, and the switching transistor, and points out their connection methods. This structure enables the LC series resonance circuit 21 to effectively connect to or disconnect from the basic resonance network, thereby realizing mode switching. In this way, the converter can smoothly switch between different working modes, improving the overall efficiency and performance.

[0061] In one embodiment, the basic resonance network includes a first inductor, a first capacitor, and a third inductor. The first inductor is connected to the midpoint of the upper half-bridge of the DC / AC inverter unit 1, the other end is connected to one end of the first capacitor, the other end of the first capacitor is connected to one end of the third inductor, and the other end of the third inductor is connected to the midpoint of the lower half-bridge of the DC / AC inverter unit 1.

[0062] In application, the basic resonance network consists of the first inductor L r1 , the first capacitor C r1 and the third inductor Lm is composed of. One end of the first inductor (i.e., the inductor Figure 2 in L r1 ) is connected to the midpoint of the upper half-bridge of the DC / AC inverter unit 1, that is, the node between the source of the switching transistor Q1 and the drain of the switching transistor Q2; the other end is connected to one end of the first capacitor (i.e., the capacitor Figure 2 in C r1 ). The other end of the capacitor C r1 is connected to one end of the third inductor L m (i.e., the exciting inductor Figure 2 in L m ), and the other end of L m is connected to the midpoint of the lower half-bridge of the DC / AC inverter unit 1, that is, the node between the source of the switching transistor Q3 and the drain of the switching transistor Q4. Such a connection method constitutes a typical LLC resonant structure, in which L r1 and C r1 act together to form a resonant circuit, and L m acts as the exciting inductor of the transformer and participates in the whole energy transfer process.

[0063] In application, when the LC series resonant circuit 21 is in the off state, the whole system works in the traditional LLC resonant mode. At this time, the voltage conversion is mainly completed by L r1 , C r1 and L m . Once the LC series resonant circuit 21 is activated and connected to the circuit, that is, after the switching transistor Q5 is turned on, L r2 and C r2 will be added to the original resonant path to form a more complex L-LCLC resonant network. The L-LCLC resonant network allows the converter to maintain good gain characteristics in a wider frequency range. Especially when the gain is less than 1, it can significantly improve the efficiency and stability.

[0064] The embodiments of this application describe in detail the composition of the basic resonant network, including a first inductor, a first capacitor, and a third inductor. This structure ensures that the basic resonant network can work in cooperation with the LC series resonant circuit 21 to jointly achieve efficient operation within a wide gain range. By optimizing the configuration of these components, the overall performance of the converter is improved. Through the above configuration, not only is the wide-gain technical solution based on mode switching achieved, but also it is ensured that efficient energy conversion can be maintained whether in the LLC mode or the L-LCLC mode. Especially for application scenarios such as new energy vehicle chargers, this ability is particularly important because it means that the charging facilities can adapt to more types of vehicles and can provide stable and reliable power supply under different input voltage conditions.

[0065] By changing the structure of the resonant network unit and changing the transfer function of the resonant converter, the purpose of wide gain can be achieved. The reciprocal of the voltage gain of the L-LCLC resonant converter in the frequency domain is as shown in Equation (1). In Equation (1), the equivalent resistance R ac The expression is Equation (2).

[0066] (1)

[0067] (2)

[0068] Among them, u in represents the input voltage, U p represents the input voltage of the resonant cavity, U m represents the output voltage of the resonant cavity, U o represents the output voltage of the entire resonant converter; n represents the turns ratio of the transformer, R o is the output resistance, L m is the equivalent inductance of the transformer, ω represents the angular frequency, L r1 、L r2 are the inductance values of inductors L1 and L2, C r1 、C r2 are the capacitance values of capacitors C1 and C2.

[0069] From Equation (1), the gain curve of the L-LCLC resonant converter is as Figure 3As shown, it can be seen that the LLC converter structure can achieve ZVS on the primary side and ZCS on the secondary side within a range slightly less than the resonant frequency, with high efficiency and excellent characteristics. However, when the frequency is slightly greater than the resonant frequency, ZCS of the secondary side switch cannot be achieved and the voltage gain changes slowly with frequency. If the phase-shift control strategy is adopted within the range where the gain is less than 1, when the phase-shift angle exceeds a certain range, problems such as duty-cycle loss and inability to achieve soft-switching characteristics are likely to occur. Although the L-LCLC structure can achieve ZVS on the primary side and ZCS on the secondary side within a range slightly less than the resonant frequency and the gain curve is similar to that of the LLC structure, compared with the LLC structure, it has more components and greater power loss. By switching modes, the efficiency of the converter is improved. In this application, the modes of the converter are all frequency-variable control, and the two modes have a common frequency resonance point. At this switching frequency, the voltage gains of the two modes are both 1. At this resonance point, the voltage gains are the same and there is no frequency offset. Therefore, this resonance point is selected as the mode switching point, greatly reducing the impact of voltage and current during mode switching.

[0070] Embodiment 3

[0071] The second control unit is further configured to: when the gain of the resonant converter is less than 1, control the LC series resonant circuit 21 to be connected to the basic resonant network so that the resonant converter operates in the L-LCLC mode;

[0072] When the gain of the resonant converter is greater than 1, control the LC series resonant circuit 21 to be disconnected from the basic resonant network so that the resonant converter operates in the LLC mode.

[0073] In application, when it is detected that the gain of the resonant converter is less than 1, it means that the output voltage is lower than the input voltage. At this time, in order to maintain efficient energy conversion and good output characteristics, the second control unit will send an instruction to the switch Q5 to make it conduct. In this way, the inductor L r2 and capacitor C r2 in the LC series resonant circuit 21 will be connected to the basic resonant network and act together with the original LLC resonant structure (formed by the inductor L r1 , capacitor C r1 and the magnetizing inductor L m ) to form a more complex L-LCLC resonant network. In this mode, the converter can achieve smoother and more stable voltage conversion within a lower gain range. At the same time, due to the addition of extra resonant components, the gain curve of the entire system becomes more flexible, thus expanding the applicable voltage range.

[0074] On the other hand, when the gain of the resonant converter is greater than 1, that is, when the output voltage is higher than the input voltage, in order to reduce unnecessary losses and improve efficiency, the second control unit will take the opposite operation, that is, control the switch tube Q5 to turn off. This causes the LC series resonant circuit 21 to disconnect from the basic resonant network, and only the original LLC resonant structure remains to continue working. At this time, by adjusting the frequency of the AC square wave generated by the inverter unit, the output voltage can be effectively controlled to ensure that it meets the preset requirements. It should be noted that in the LLC mode, the converter can utilize its inherent soft-switching characteristics, and can maintain high-efficiency operation even within a wide operating frequency range. Moreover, due to the reduction in the number of components participating in the work, the overall energy consumption is further reduced.

[0075] In the embodiment of the present application, by setting specific gain conditions to control the access and disconnection of the LC series resonant circuit 21, the present invention not only realizes high-efficiency operation within a wide gain range, but also optimizes the performance under different operating modes. When the gain is less than 1, by connecting the LC series resonant circuit 21, the converter operates in the L-LCLC mode, expanding the gain range; when the gain is greater than 1, the LC series resonant circuit 21 is disconnected, and the converter operates in the LLC mode, reducing the number of components and energy consumption, thereby improving the overall efficiency.

[0076] Embodiment 4

[0077] The second control unit is further configured to:

[0078] When the input voltage of the resonant converter U in is greater than the second preset voltage U 2, control the LC series resonant circuit 21 to access the basic resonant network, so that the resonant converter operates in the L-LCLC mode;

[0079] When the input voltage of the resonant converter U in is less than the first preset voltage U 1, control the LC series resonant circuit 21 to disconnect from the basic resonant network, so that the resonant converter operates in the LLC mode;

[0080] Wherein, U 1 < U 0 < U 2, U 0 is the output voltage of the resonant converter.

[0081] In the application, in order to solve the problem of voltage fluctuation that may occur during the mode switching process, a hysteresis control strategy is introduced. This strategy sets two specific switching points U 1 and U2, slightly lower and slightly higher than the voltage value at which the theoretical gain is 1 point, respectively, to avoid frequent mode switching caused by small fluctuations. Specifically, when the resonant converter is in the LLC mode and the gain gradually decreases to approach 1, once the input voltage drops below the set U 2, the mode is immediately switched to L-LCLC; conversely, if the system is in the L-LCLC mode and the gain starts to rise, the mode will only switch back to the LLC mode when the input voltage rises above U 1. This design not only helps to stabilize the circuit operation but also effectively reduces the impact on the circuit during mode switching, extending the service life of the device.

[0082] Embodiment 5

[0083] Figure 4 is a schematic diagram of the hysteresis control loop. In the actual control design, if the point where the gain of the resonant converter is 1 is used as the switching point between LLC variable-frequency control and L-LCLC variable-frequency control, when voltage fluctuations occur near this point, it will cause the converter to frequently switch modes, affecting the efficiency of the converter. Therefore, the present invention re-sets two switching points near the switching point U 0, U 1 and U 2. U 1 is slightly smaller than U 0, U 2 is slightly larger than U 0, U 0 is the theoretical input voltage value when the gain is 1. When the converter is working, the input voltage U in is sampled, and the working mode of the converter is switched according to U in the size. When the converter is working in the LLC variable-frequency mode, the switching point is taken as U 2. When U in > U 2, it is switched to L-LCLC variable-frequency control; when the converter is working in the L-LCLC variable-frequency mode, the switching point is taken as U 1. When U in < U 1, it is switched to LLC variable-frequency control. In the hybrid control mode, as long as the lowest gain of the LLC variable-frequency mode is lower than the highest gain of the L-LCLC variable-frequency mode, it is ensured that the circuit can stably perform mode switching.

[0084] By setting specific input voltage thresholds U 1 and U2. A hysteresis region is formed, enabling stable mode switching during voltage fluctuations. This not only ensures a smooth transition between the two modes, reduces voltage and current surges during mode switching, but also solves the problem of frequent switching near the switching point through the hysteresis control strategy, ensuring the stability and reliability of the circuit.

[0085] In one embodiment, U The range of 1 is 0.97 U 0 to 0.99 U 0, U The range of 2 is 1.01 U 0 to 1.03 U 0.

[0086] In the embodiment of the present application, by precisely setting U 1 and U 2 within specific ranges (0.97 U 0 to 0.99 U 0 and 1.01 U 0 to 1.03 U 0), the conditions for mode switching are further refined, ensuring accurate and stable mode switching during actual operation. This precise control avoids frequent mode switching caused by voltage fluctuations and improves the operating stability of the converter.

[0087] Embodiment 6

[0088] It further includes a first control unit. The control end of the first control unit is connected to the controlled end of the DC / AC inverter unit 1. The first control unit is used to control the switching tube frequency of the DC / AC inverter unit 1 to achieve gain transformation.

[0089] In application, the control end of the first control unit is connected to the controlled end of the DC / AC inverter unit 1. Its main function is to achieve gain transformation by adjusting the operating frequency of the switching tubes (such as Q1, Q2, Q3, and Q4) in the DC / AC inverter unit 1. This frequency control strategy is crucial for ensuring the efficient operation of the converter in different operating modes.

[0090] Specifically, the DC / AC inverter unit 1 usually consists of four switching tubes, forming a full-bridge or half-bridge structure. These switching tubes (such as MOSFET or IGBT) are turned on and off at a specific frequency under the control of the first control unit, thereby converting the DC voltage into a high-frequency AC square wave voltage. The first control unit samples the voltage signal output by the rectifier filter unit 3 and compares it with the given target voltage to generate an error signal. Based on this error signal, the first control unit adjusts the operating frequency of the switching tubes to achieve precise control of the output voltage.

[0091] When the resonant converter operates in the LLC mode, the first control unit changes the output voltage by adjusting the switching frequency. The LLC resonant converter can maintain high efficiency within a wide frequency range because it allows soft-switching operation within a certain frequency range, that is, the switching transistors turn on and off under zero-voltage or zero-current conditions, thereby reducing switching losses. By real-time monitoring and adjusting the switching frequency, the first control unit can ensure that the converter always operates near the optimal efficiency point in the LLC mode.

[0092] When the resonant converter switches to the L-LCLC mode, the first control unit also needs to adjust the switching frequency to adapt to the new characteristics of the resonant network. Due to the access of the LC series resonant circuit 21, the total inductance and capacitance values of the resonant network change, thus affecting the resonant frequency. Therefore, the first control unit needs to recalculate and set an appropriate switching frequency according to the new resonant parameters to ensure that the converter can also maintain efficient energy conversion in the L-LCLC mode.

[0093] In addition, the first control unit is also responsible for handling the smooth transition of the frequency during the mode switching process. When the second control unit decides to switch from the LLC mode to the L-LCLC mode or vice versa, the first control unit gradually adjusts the switching frequency to avoid voltage and current shocks caused by sudden changes. This smooth transition not only improves the stability of the system but also extends the service life of the device.

[0094] Through the above detailed frequency control strategy, the first control unit can ensure that the converter operates efficiently in different operating modes. Whether in the LLC mode or the L-LCLC mode, the first control unit can achieve precise control of the output voltage through precise frequency regulation, thus meeting the requirements of various application scenarios. Especially in application scenarios such as new energy vehicle charging piles that require wide gain characteristics, this frequency control strategy is particularly important because it can ensure that the charging facilities can provide stable and reliable power supply under different input voltage conditions.

[0095] Embodiment 7

[0096] It further includes a transformer 4. The output end of the resonant network unit 2 is connected to the primary side of the transformer 4, and the input end of the rectifying and filtering unit 3 is connected to the secondary side of the transformer 4.

[0097] In the embodiment of the present application, the resonant network unit 2 and the rectifying and filtering unit 3 are connected through the transformer 4, achieving electrical isolation and improving the safety and reliability of the system. In addition, the use of the transformer 4 also allows for further adjustment of the output voltage, enhancing the adaptability of the converter and enabling it to be applied to more different application scenarios.

[0098] The second aspect of the present application provides a control method for a resonant converter based on mode switching, including:

[0099] When the switching condition is satisfied, control the LC series resonant circuit 21 to be connected to the basic resonant network so that the resonant converter operates in the L-LCLC mode;

[0100] Alternatively, control the LC series resonant circuit 21 to disconnect from the basic resonant network so that the resonant converter operates in the LLC mode.

[0101] Embodiment 8

[0102] It further includes: when the input voltage of the resonant converter U in is greater than the second preset voltage U 2, control the LC series resonant circuit 21 to be connected to the basic resonant network so that the resonant converter operates in the L-LCLC mode;

[0103] When the input voltage of the resonant converter U in is less than the first preset voltage U 1, control the LC series resonant circuit 21 to disconnect from the basic resonant network so that the resonant converter operates in the LLC mode;

[0104] Wherein, U 1 < U 0 < U 2, U 0 is the output voltage of the resonant converter.

[0105] Figure 2 The current C r1 flowing through the capacitor I cr1 in the circuit and the simulation waveforms of the output voltage are as shown in Figure 5 and 6 which show the cases of input voltage of 240 ± 80V, output voltage of 48V and input voltage of 275 ± 25V, output voltage of 75V. From top to bottom, the waveforms are the input voltage U in , the output voltage U o and C r1 the current I cr1 . It can be seen from the left figure that during the process of the voltage dropping from 320V to 160V, the output voltage always remains near 48V. It can be seen from the right figure that during the process of the voltage dropping from 300V to 250V, the output voltage always remains near 75V, having good stability and can be applied to occasions with different voltage levels. The simulation input and output as well as the parameter settings of each component are as follows: rated output voltage VO = 48V, the rated output power P = 600W, the transformer turns ratio n = 5; inductance L r1 = 27.1μH, capacitance C r1 = 36.53nF, inductance L r2 = 40.91μH, capacitance C r2 = 12.18nF, exciting inductance L m = 108.4μH.

[0106] The simulation comparison diagram of the gains of the LLC mode and the L-LCLC mode is as Figure 7 and 8 shown. Set the input voltage to 240V and the switching frequency to 200KHZ, and simulate the circuit. The left figure is the output voltage curve of the converter in the LLC mode, and the right figure is the output voltage curve of the converter in the L-LCLC mode. It can be seen that the output voltage of the converter in the LLC mode fluctuates around 40V, and the output voltage of the converter in the L-LCLC mode fluctuates around 17V. The voltage gain of the L-LCLC mode is wider than that of the LLC mode, and there is an obvious improvement effect.

[0107] The simulation diagram of the hysteresis control loop is as Figure 9 and 10 shown. It shows the situation of the converter switching from the LLC mode to the L-LCLC mode and from the L-LCLC mode to the LLC mode. The left figure is when the converter works in the LLC variable-frequency mode, and the value of the switching point U 2 takes U 1.02 times of 0. When U in > U 2, it switches to the L-LCLC variable-frequency control; the right figure is when the converter works in the L-LCLC variable-frequency mode, and the value of the switching point U 1 takes U 0.98 times of 0. When U in < U 1, it switches to the LLC variable-frequency control. It can be seen that the mode does not switch frequently during the mode switching process, and the circuit can stably perform mode switching.

[0108] The specific simulation schematic diagram of the hysteresis control loop is as Figure 11 shown, where the thresholds of the two switches are the switching points U1 and U2 respectively.

[0109] From the analysis of the above simulation waveforms, it can be seen that by adopting the mode switching strategy, when the gain is greater than 1, it operates in the LLC resonant converter mode, and when the gain is less than 1, it operates in the L-LCLC resonant converter mode. The mode switching point is set when the LLC resonant converter and the L-LCLC resonant converter have the same operating frequency and the same gain at a gain of 1. At this time, the circuit state is stable during mode switching, greatly reducing the voltage and current shocks during mode switching. Compared with the LLC resonant converter, the present invention has obvious advantages in voltage gain while achieving a wide range of input and output voltages.

[0110] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A resonant converter based on mode switching, characterized in that: The main circuit of the resonant converter includes a DC / AC inverter unit, a resonant network unit, a rectifier and filter unit, an isolation transformer and a control unit; the DC input voltage is converted into a high-frequency AC square wave voltage by the DC / AC inverter unit; the high-frequency AC square wave voltage is filtered out by the resonant network unit to output a high-frequency sinusoidal voltage, and the high-frequency sinusoidal voltage is output to the rectifier and filter unit after passing through the isolation transformer, and the DC voltage is output through the rectifier and filter unit; The resonant network unit is composed of an inductor, a capacitor and a switch, and the structure of the resonant network unit can be changed by controlling the switch of the resonant network unit, so that the converter works in different modes and the input and output gain of the converter is widened; the resonant network unit is composed of a first LC series resonant circuit and a second LC series resonant circuit connected in parallel, wherein the inductor L1 and the capacitor C1 are connected in series to form the first LC series resonant circuit, and the inductor L2, the capacitor C2 and the switch Q5 are connected in series to form the second LC series resonant circuit; one end of the first LC series resonant circuit and the second LC series resonant circuit connected in parallel is connected to one end of the output end of the DC / AC inverter unit, and the other end of the first LC series resonant circuit and the second LC series resonant circuit connected in parallel is connected to one end of the input end of the isolation transformer, and the other end of the output end of the DC / AC inverter unit is connected to the other end of the input end of the isolation transformer; The control unit generates a switch control signal in the resonant network unit to implement the switching control of the converter working mode, controls the disconnection of the second LC series resonant circuit so that the resonant converter works in the LLC mode, and controls the connection of the second LC series resonant circuit so that the resonant converter works in the L-LCLC mode; By changing the structure of the resonant network unit, the transfer function of the resonant converter can be changed to achieve a wide gain. When the second LC series resonant circuit is controlled to be connected, the resonant converter works in the L-LCLC mode, and the inverse of the voltage gain of the resonant converter is as follows: Among them, R ac Indicates equivalent resistance n represents the transformer ratio, R o is the output resistance, L m is the transformer equivalent inductance, ω represents the angular frequency, L r1 , L r2 Inductance value of inductors L1 and L2, C r1 , C r2 Capacitance values ​​of capacitors C1 and C2.

2. The mode switching resonant converter according to claim 1, characterized in that: When the gain of the resonant converter is less than 1, the resonant network unit is controlled to be connected to the second LC series resonant circuit so that the resonant converter operates in an L-LCLC mode; When the gain of the resonant converter is greater than 1, the resonant network unit is controlled to disconnect the second LC series resonant circuit, so that the resonant converter operates in LLC mode.

3. The mode switching resonant converter according to claim 1, characterized in that: When the input voltage U in When the voltage is greater than the second preset voltage U2, the resonant network unit is controlled to be connected to the second LC series resonant circuit, so that the resonant converter operates in L-LCLC mode; When the input voltage U in When the voltage is less than the first preset voltage U1, the resonant network unit is controlled to disconnect the second LC series resonant circuit, so that the resonant converter operates in the LLC mode. Among them, U1<U0<U2, U0 is the output voltage of the resonant converter.

4. The mode switching resonant converter according to claim 3, characterized in that: The range of U1 is 0.97U0~0.99U0, and the range of U2 is 1.01U0~1.03U0.

5. A control method for a resonant converter based on mode switching according to any one of claims 1 to 4, characterized in that: By collecting the converter input voltage signal and the switch state signal in the resonant network unit, comparing the given voltage signal and the input voltage signal to obtain an error signal, and combining the switch state signal to generate a switch control signal in the resonant network unit, the switching control of the converter working mode is realized; including: controlling the disconnection of the second LC series resonant circuit so that the resonant converter works in the LLC mode, and controlling the connection of the second LC series resonant circuit so that the resonant converter works in the L-LCLC mode.

6. The control method of the resonant converter based on mode switching according to claim 5, characterized in that: When the gain of the resonant converter is less than 1, the resonant network unit is controlled to be connected to the second LC series resonant circuit so that the resonant converter operates in an L-LCLC mode; When the gain of the resonant converter is greater than 1, the resonant network unit is controlled to disconnect the second LC series resonant circuit, so that the resonant converter operates in LLC mode.

7. The control method of the resonant converter based on mode switching according to claim 5, characterized in that: When the input voltage U in When the voltage is greater than the second preset voltage U2, the resonant network unit is controlled to be connected to the second LC series resonant circuit, so that the resonant converter operates in L-LCLC mode; When the input voltage U in When the voltage is less than the first preset voltage U1, the resonant network unit is controlled to disconnect the second LC series resonant circuit, so that the resonant converter operates in the LLC mode. Among them, U1<U0<U2, U0 is the output voltage of the resonant converter.

8. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the processor executes the control method of the resonant converter based on mode switching according to any one of claims 5 to 7.

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