Resonant converter based on mode switching and control method thereof

Abstract

The invention relates to a resonant converter based on mode switching and a control method thereof. A main circuit of the resonant converter comprises a DC / AC inversion unit, a resonant network unit, a rectification filtering unit, an isolation transformer and a control unit. DC input voltage is converted into high-frequency AC square wave voltage through the DC / AC inversion unit; after higher harmonic signals in the high-frequency alternating-current square-wave voltage are filtered out through the resonance network unit, high-frequency sinusoidal voltage is output, the high-frequency sinusoidal voltage is output to the rectifying and filtering unit after passing through the isolation transformer, and direct-current voltage is output through the rectifying and filtering unit; the control unit generates a switch control signal in the resonant network unit to realize switching control of working modes 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, the input and output gain of the converter is widened, and the performance of the converter is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a resonant converter based on mode switching and a control method thereof. Background Art

[0002] New energy vehicles have developed rapidly with their economic and environmental advantages as well as the support of national policies. New energy vehicle charging piles are an important part of ensuring convenient travel of new energy vehicles. Since different models have different requirements for the voltage level of charging piles, the converter is required to have wide gain and high efficiency characteristics.

[0003] As an important component of the charging pile, the DC-DC converter is an important guarantee for achieving 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 switch tube operates at a frequency slightly lower than the resonant frequency, PFM is generally used to adjust 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 adjust 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 LLC resonant converter is a technical problem that needs to be solved urgently. Summary of the invention

[0005] The embodiments of the present application provide a resonant converter based on mode switching and a control method thereof, so that the converter has wide gain and high efficiency characteristics.

[0006] The present application provides a resonant converter based on mode switching, wherein 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 after the high-order harmonic signals in the high-frequency AC square wave voltage are removed; 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 switching control of the converter operating mode, controls the disconnection of the second LC series resonant circuit so that the resonant converter operates in the LLC mode, and controls the connection of the second LC series resonant circuit so that the resonant converter operates in the L-LCLC mode.

[0007] Preferably, by changing the structure of the resonant network unit, the transfer function of the resonant converter can be changed to achieve a wide gain, wherein when the second LC series resonant circuit is controlled to be connected, the resonant converter operates in the L-LCLC mode, and the inverse of the voltage gain of the resonant converter is as follows:

[0008] in, 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.

[0009] Preferably, 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.

[0010] Preferably, when the input voltage of the resonant converter U in Greater than the second preset voltageU 2, 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 of the resonant converter U in Less than the first preset voltage U 1, the resonant network unit is controlled to disconnect the second LC series resonant circuit so that the resonant converter operates in LLC mode. in, U 1< U 0< U 2, U 0 is the output voltage of the resonant converter.

[0011] Preferably, the U 1 ranges from 0.97 U 0~0.99 U 0, described U 2 ranges from 1.01 U 0~1.03 U 0.

[0012] Based on the mode switching-based resonant converter, the present application proposes a control method for the resonant converter, specifically: 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.

[0013] Preferably, 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.

[0014] Preferably, when the input voltage of the resonant converter U in Greater than the second preset voltage U 2, 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 of the resonant converter U in 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 LLC mode. in, U 1< U 0< U 2, U 0 is the output voltage of the resonant converter.

[0015] The present application also proposes a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the processor is enabled to execute the control method of the resonant converter based on mode switching.

[0016] Therefore, compared with the prior art, the present invention has the following beneficial effects: In the present invention, by changing the converter unit structure of LLC resonance, a wide input-output gain is achieved, and the wide input-output gain effect is particularly obvious in a range greater than the LLC resonance frequency; In the present invention, by adopting a mode state switching strategy, when the input-output gain is greater than 1, it works in the LLC resonant type resonant type converter mode, and when the input-output gain is less than 1, it works in the L-LCLC resonant type resonant type converter mode. When the input-output gain is greater than 1, the LLC resonant type resonant type converter and the L-LCLC resonant type resonant type converter voltage input-output gain versus frequency curve are similar, and both can achieve soft switching, but compared to the L-LCLC resonant type resonant type converter mode, the LLC resonant type resonant type converter has fewer devices and lower energy consumption, and the efficiency of the resonant type converter is improved by adopting a mode state switching strategy; In the present invention, the LLC resonant type resonant type converter and the L-LCLC resonant type resonant type converter are switched when the input-output gain is 1. At this time, the operating frequencies of the two resonant type converters are the same and the input-output gains are the same, which greatly reduces the impact of voltage and current when the mode state is switched; In the present invention, a hysteresis control strategy is adopted to solve the problem of voltage fluctuation near the switching point and frequent mode switching of the resonant converter, thereby ensuring that the circuit can stably switch the mode state. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1is a structural schematic diagram of a mode switching-based resonant converter provided in one embodiment of the present application; Figure 2 is a structural schematic diagram of a mode switching-based resonant converter provided in yet another embodiment of the present application; Figure 3 is a switching curve diagram of the resonant converter of the present application; Figure 4 It is a schematic diagram of the hysteresis control loop of the present application; Figure 5 This is a capacitor at a voltage level in this application C r1 Current flowing I cr1 And output voltage simulation waveform; Figure 6 This is another voltage level capacitor in this application C r1 Current flowing I cr1 And output voltage simulation waveform; Figure 7 This is a schematic diagram of the LLC mode gain simulation of this application; Figure 8 This is a schematic diagram of the simulated L-LCLC mode gain of the present application; Fig. 9 This is a simulation diagram of the LLC mode switching to the L-LCLC mode of the present application; Fig.10 This is a simulation diagram of the L-LCLC mode switching to LLC mode in this application; Fig.11 It is a simulation diagram under the hysteresis control loop of this application. DETAILED DESCRIPTION

[0019] Example 1 like Figure 1 As shown, the mode switching-based resonant converter provided in the embodiment of the present application includes a DC / AC inverter unit 1, a resonant network unit 2, a rectifier filter unit 3 and a second control unit, and the resonant network unit 2 includes a basic resonant network and an LC series resonant circuit 21; 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 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; A DC / AC inverter unit 1, used for converting a DC voltage into a high-frequency AC square wave voltage and outputting it to a resonant network unit 2; The resonant network unit 2 is used to convert the high-frequency AC square wave voltage into a high-frequency sinusoidal current and output it to the rectification and filtering unit 3; The rectifier and filter unit 3 is used to convert the high-frequency sinusoidal current into a DC voltage and output it; A second control unit is used to control the LC series resonant circuit 21 to connect to the basic resonant network when the switching condition is met, so that the resonant converter operates in the L-LCLC mode, or to control the LC series resonant circuit 21 to disconnect from the basic resonant network, so that the resonant converter operates in the LLC mode; The LC series resonant circuit 21 is used to be controlled by the second control unit and connected to or disconnected from the basic resonant network.

[0020] In the application, the DC / AC inverter unit 1 is used to convert the 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 MOSFET or IGBT), which generate the required high-frequency AC square wave voltage by controlling the conduction and shutdown of these switching tubes. This high-frequency AC square wave voltage is then transmitted to the resonant network unit 2 for processing.

[0021] In the application, the resonant network unit 2 is used to convert the high-frequency AC square wave voltage from the DC / AC inverter unit 1 into a high-frequency sinusoidal current and output it to the rectifier 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 ,capacitance C r1 and resonant inductor L m The LC series resonant circuit 21 can be composed of an additional inductor. L r2 and capacitor C r2 It can be connected to the basic resonant network or disconnected from the basic resonant network under the control of the second control unit. When the LC series resonant circuit 21 is connected, the resonant network unit 2 works in the L-LCLC mode; when it is disconnected, the resonant network unit 2 works in the LLC mode. This mode switching strategy enables the converter to operate efficiently in different gain ranges.

[0022] In application, the rectifier and filter unit 3 is used to convert the high-frequency sinusoidal current output from the resonant network unit 2 into a DC voltage, and output a stable DC voltage after filtering. The rectifier and filter unit 3 usually includes a rectifier diode or a synchronous rectifier switch tube and a filter capacitor to ensure the stability and quality of the output voltage.

[0023] In application, the second control unit is responsible for controlling the connection or disconnection of the LC series resonant circuit 21 when a specific switching condition is met. Specifically, when the voltage gain range needs to be increased, the second control unit controls the LC series resonant circuit 21 to connect to the basic resonant network, so that the resonant converter enters the L-LCLC mode; and when no additional gain is required, the LC series resonant circuit 21 is controlled to be disconnected, so that the resonant converter operates in the LLC mode. This mode switching strategy not only improves the wide gain capability of the converter, but also optimizes the efficiency in different operating modes.

[0024] In application, the LC series resonant circuit 21 can be controlled by the second control unit to flexibly connect or disconnect the basic resonant network. When the LC series resonant circuit 21 is connected, it works together with the basic resonant network to change the overall characteristics of the resonant network, thereby achieving a wider voltage gain range. When the LC series resonant circuit 21 is disconnected, the basic resonant network works alone, maintaining the original high-efficiency performance. This structure enables the converter to automatically adjust according to actual working conditions to achieve the best working state.

[0025] The embodiment of the present application can achieve efficient operation in a wide gain range by introducing the LC series resonant circuit 21 and controlling it to connect or disconnect the basic resonant network by the second control unit. This structural change enables the converter to switch flexibly between different operating modes, thereby improving overall efficiency and performance. At the same time, by controlling the connection and disconnection of the LC series resonant circuit 21, the characteristics of the resonant network can be optimized, further enhancing the adaptability and stability of the converter.

[0026] Example 2 like Figure 2 As shown, the LC series resonant circuit 21 includes a second inductor, a second capacitor and a switch tube, 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, and 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 switch tube, the source of the switch tube is connected to the midpoint of the lower half bridge of the DC / AC inverter unit 1, and the gate of the switch tube is connected to the control end of the second control unit.

[0027] In application, the LC series resonant circuit 21 is composed of a second inductor L r2 , the second capacitor C r2 and switch tube Q5. The second inductor L r2 One end 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 switch tube Q1 and the drain of the switch tube Q2; the other end is connected to the second capacitor C r2 The second capacitor Cr2 The other end is then connected to the drain of the switch tube Q5, and the source of the switch tube 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 switch tube Q3 and the drain of the switch tube Q4. In order to achieve effective control of the LC series resonant circuit 21, the gate of the switch tube Q5 is connected to the control end of the second control unit. By controlling the state of the switch tube Q5, the LC series resonant circuit 21 can be flexibly connected or disconnected from the basic resonant network, thereby adjusting the working mode of the converter as needed.

[0028] The embodiment of the present application defines in detail the specific composition of the LC series resonant circuit 21, including the second inductor, the second capacitor and the switch tube, and points out their connection methods. This structure enables the LC series resonant circuit 21 to effectively connect or disconnect the basic resonant network, thereby achieving mode switching. In this way, the converter can smoothly switch between different operating modes, improving the overall efficiency and performance.

[0029] In one embodiment, the basic resonant 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, and 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.

[0030] In the application, the basic resonant network consists of the first inductor L r1 , the first capacitor C r1 And the third inductor L m The first inductor (i.e. Figure 2 Inductance 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 switch tube Q1 and the drain of the switch tube Q2; the other end is connected to the first capacitor (that is Figure 2 Capacitor in C r1 ) is connected to one end of the capacitor. C r1 The other end of the third inductor L m (Right now Figure 2 The magnetizing inductance L m ) is connected to one end, and L m The other end of 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 switch tube Q3 and the drain of the switch tube Q4. This connection method forms a typical LLC resonant structure, in whichL r1 and C r1 Together they form a resonant circuit, and L m It acts as the transformer's excitation inductance and participates in the entire energy transfer process.

[0031] In application, when the LC series resonant circuit 21 is in the disconnected state, the entire system works in the traditional LLC resonant mode. L r1 , C r1 and L m Once the LC series resonant circuit 21 is activated and connected to the circuit, that is, the switch tube Q5 is turned on, L r2 and C r2 It is 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 over a wider frequency range, especially when the gain is less than 1, which can significantly improve efficiency and stability.

[0032] The embodiment of the present application describes 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 conjunction 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 a wide gain technical solution based on mode switching is implemented, but also efficient energy conversion can be maintained regardless of whether it is in LLC mode or L-LCLC mode. This capability is particularly important for applications such as new energy vehicle charging piles, 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.

[0033] By changing the structure of the resonant network unit and the transfer function of the resonant converter, the purpose of wide gain can be achieved. The inverse of the voltage gain of the L-LCLC resonant converter in the frequency domain is shown in formula (1). The equivalent resistance in formula (1) is R ac The expression is formula (2).

[0034] (1) (2) in, u in Indicates the input voltage, Up represents the resonant cavity input voltage, U m represents the resonant cavity output voltage, U o represents the output voltage of the entire resonant converter; 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.

[0035] From formula (1), the gain curve of the L-LCLC resonant converter can be obtained as follows: Figure 3 As shown. It can be seen that the LLC converter structure can achieve ZVS of the primary side and ZCS of the secondary side in a range slightly less than the resonant frequency, with high efficiency and excellent characteristics. However, when it is slightly greater than the resonant frequency, the ZCS of the secondary side switch cannot be achieved and the voltage gain changes slowly with the frequency. If the phase shift control strategy is adopted in the range where the gain is less than 1, when the phase shift angle exceeds a certain range, the problem of duty cycle loss and the inability to achieve soft switching characteristics is prone to occur. Although the L-LCLC structure can achieve ZVS of the primary side and ZCS of the secondary side in a range slightly less than the resonant frequency and the gain curve is similar to the LLC structure, it has more devices and greater power loss than the LLC structure. By switching the mode, the efficiency of the converter is improved. In this application, the modes of the converter are all variable frequency control, and the two modes have a common frequency resonance point. At the switching frequency, the voltage gains of the two modes are both 1. At the resonance point, the voltage gain is the same and there is no frequency offset. Therefore, the resonance point is selected as the mode switching point, which greatly reduces the impact of voltage and current during mode switching.

[0036] Example 3 The second control unit is also used for: when the gain of the resonant converter is less than 1, controlling the LC series resonant circuit 21 to access the basic resonant network, so that the resonant converter works in the L-LCLC mode; When the gain of the resonant converter is greater than 1, the LC series resonant circuit 21 is controlled to be disconnected from the basic resonant network so that the resonant converter operates in LLC mode.

[0037] 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 tube Q5 to turn it on. L r2 and capacitor Cr2 will be connected to the basic resonant network and the original LLC resonant structure (composed of inductors L r1 ,capacitance C r1 And the excitation inductance L m The two components (constituents) work together to form a more complex L-LCLC resonant network. In this mode, the converter can achieve smoother and more stable voltage conversion in a lower gain range. At the same time, due to the addition of additional resonant components, the gain curve of the entire system becomes more flexible, thereby expanding the applicable voltage range.

[0038] On the other hand, when the gain of the resonant converter is greater than 1, that is, 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 action, that is, control the switch tube Q5 to turn off. This causes the LC series resonant circuit 21 to be disconnected from the basic resonant network, leaving only the original LLC resonant structure 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 is worth noting that in LLC mode, the converter can utilize its inherent soft switching characteristics to maintain high-efficiency operation even in a wider operating frequency range, and the overall energy consumption is further reduced due to the reduction in the number of components involved in the work.

[0039] The embodiment of the present application controls the connection and disconnection of the LC series resonant circuit 21 by setting a specific gain condition. The present invention not only achieves efficient operation within a wide gain range, but also optimizes the performance under different operating modes. When the gain is less than 1, the LC series resonant circuit 21 is connected, so that the converter operates in the L-LCLC mode, expanding the gain range; and when the gain is greater than 1, the LC series resonant circuit 21 is disconnected, so that the converter operates in the LLC mode, reducing the number of components and energy consumption, thereby improving the overall efficiency.

[0040] Example 4 The second control unit is also used for: When the input voltage of the resonant converter U in Greater than the second preset voltage U 2, the LC series resonant circuit 21 is controlled to be connected to the basic resonant network so that the resonant converter works in L-LCLC mode; When the input voltage of the resonant converter U in Less than the first preset voltage U 1, the LC series resonant circuit 21 is controlled to be disconnected from the basic resonant network so that the resonant converter operates in LLC mode; in, U 1< U 0< U 2, U 0 is the output voltage of the resonant converter.

[0041] In the application, in order to solve the voltage fluctuation problem that may occur during the mode switching process, a hysteresis control strategy is introduced. This strategy sets two specific switching points U 1 and U 2, respectively, slightly lower and slightly higher than the voltage value at the theoretical gain of 1, in order to avoid frequent mode switching caused by small fluctuations. Specifically, when the resonant converter is in LLC mode and the gain gradually decreases to close to 1, once the input voltage drops to the set U 2, the trigger mode switches to L-LCLC immediately; conversely, if the system is in L-LCLC mode and the gain starts to increase, only when the input voltage rises above U 1 before switching back to LLC mode. This design not only helps stabilize circuit operation, but also effectively reduces the impact on the circuit during mode switching, thus extending the service life of the device.

[0042] Example 5 Figure 4 It is a schematic diagram of the hysteresis control loop. In actual control design, if the resonant converter gain is 1 point as the switching point between LLC variable frequency control and L-LCLC variable frequency control, when voltage fluctuation occurs near this point, it will cause the converter to switch modes frequently, affecting the efficiency of the converter. Therefore, the present invention sets a switching point at which the resonant converter gain is 1 point. U Reset two switching points near 0 U 1 and U 2, U 1 is slightly less than U 0, U 2 Slightly larger than U 0, U 0 is the theoretical input voltage value when the gain is 1. U in Sampling is performed according to U in The converter operating mode is switched according to the size of the switching point. When the converter works in LLC frequency conversion mode, the switching point is U 2. When U in > U 2, switch to L-LCLC frequency conversion control; when the converter works in L-LCLC frequency conversion mode, the switching point is U 1. When U in < U1, switch to LLC frequency conversion control. In the mixed control mode, as long as the minimum gain of LLC frequency conversion mode is lower than the maximum gain of L-LCLC frequency conversion mode, the circuit can stably switch modes.

[0043] In the embodiment of the present application, a specific input voltage threshold is set U 1 and U 2. A hysteresis interval is formed, which can stably switch modes when the voltage fluctuates. This not only ensures a smooth transition between the two modes and reduces the voltage and current impact 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.

[0044] In one embodiment, U 1 ranges from 0.97 U 0~0.99 U 0, U 2 ranges from 1.01 U 0~1.03 U 0.

[0045] The embodiment of the present application is precisely set U 1 and U 2 specific range (0.97 U 0~0.99 U 0 and 1.01 U 0~1.03 U 0), further refines the conditions for mode switching, ensuring accurate and stable mode switching in actual operation. This precise control avoids frequent mode switching caused by voltage fluctuations and improves the operating stability of the converter.

[0046] Example 6 It also includes a first control unit, a control end of the first control unit is connected to the controlled end of the DC / AC inverter unit 1, and the first control unit is used to control the switching tube frequency of the DC / AC inverter unit 1 to achieve gain conversion.

[0047] In the application, the control end of the first control unit is connected to the controlled end of the DC / AC inverter unit 1, and its main function is to achieve gain conversion by adjusting the operating frequency of the switch tubes (such as Q1, Q2, Q3 and Q4) in the DC / AC inverter unit 1. This frequency control strategy is crucial to ensure the efficient operation of the converter in different working modes.

[0048] Specifically, the DC / AC inverter unit 1 is usually composed of four switching tubes to form 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 generates an error signal by sampling the voltage signal output by the rectifier and filter unit 3 and comparing it with a given target voltage. Based on this error signal, the first control unit adjusts the operating frequency of the switching tube to achieve precise control of the output voltage.

[0049] When the resonant converter operates in LLC mode, the first control unit changes the output voltage by adjusting the switching frequency. The LLC resonant converter can maintain high efficiency in a wide frequency range because it allows soft switching operation within a certain frequency range, that is, the switch tube is turned on and off under zero voltage or zero current conditions, thereby reducing switching losses. The first control unit can ensure that the converter always operates near the optimal efficiency point in LLC mode by real-time monitoring and adjusting the switching frequency.

[0050] 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 resonant network characteristics. Due to the access of the LC series resonant circuit 21, the total inductance and capacitance values ​​of the resonant network change, thereby affecting the resonant frequency. Therefore, the first control unit needs to recalculate and set a suitable switching frequency according to the new resonant parameters to ensure that the converter can maintain efficient energy conversion in the L-LCLC mode.

[0051] In addition, the first control unit is also responsible for handling the smooth frequency transition during the mode switching process. When the second control unit decides to switch from LLC mode to L-LCLC mode or vice versa, the first control unit will gradually adjust 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 equipment.

[0052] Through the above detailed frequency control strategy, the first control unit can ensure that the converter can operate efficiently in different working modes. Whether in LLC mode or L-LCLC mode, the first control unit can achieve precise control of the output voltage through precise frequency regulation to meet the needs of various application scenarios. This frequency control strategy is particularly important in situations where wide gain characteristics are required, such as new energy vehicle charging piles, because it can ensure that charging facilities can provide stable and reliable power supply under different input voltage conditions.

[0053] Example 7 A transformer 4 is also included. 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 .

[0054] The embodiment of the present application connects the resonant network unit 2 and the rectifier filter unit 3 through the transformer 4, thereby achieving electrical isolation and improving the safety and reliability of the system. In addition, the use of the transformer 4 also allows the output voltage to be further adjusted, thereby enhancing the adaptability of the converter and enabling it to be applied to more different application scenarios.

[0055] A second aspect of the present application provides a control method for a resonant converter based on mode switching, comprising: When the switching condition is met, the LC series resonant circuit 21 is controlled to access the basic resonant network so that the resonant converter operates in the L-LCLC mode; Alternatively, the LC series resonant circuit 21 is controlled to be disconnected from the basic resonant network so that the resonant converter operates in the LLC mode.

[0056] Example 8 Also included: When the input voltage of the resonant converter U in Greater than the second preset voltage U 2, the LC series resonant circuit 21 is controlled to be connected to the basic resonant network so that the resonant converter works in L-LCLC mode; When the input voltage of the resonant converter U in Less than the first preset voltage U 1, the LC series resonant circuit 21 is controlled to be disconnected from the basic resonant network so that the resonant converter operates in LLC mode; in, U 1< U 0< U 2, U 0 is the output voltage of the resonant converter.

[0057] Figure 2 Capacitors in circuits C r1 Current flowing I cr1 And the output voltage simulation waveform is as follows Figure 5 and 6 As shown in the figure, the input voltage is 240±80V, the output voltage is 48V and the input voltage is 275±25V, the output voltage is 75V. From top to bottom, the waveforms are input voltage U in , output voltage U o as well as C r1 Current flowingI cr1 From the left figure, we can see that when the voltage drops from 320V to 160V, the output voltage is always maintained at around 48V. From the right figure, we can see that when the voltage drops from 300V to 250V, the output voltage is always maintained at around 75V. It has good stability and can be applied to occasions with different voltage levels. The simulation input and output and the parameter settings of each component are as follows: Rated output voltage V O =48V, rated output power P=600W, transformer ratio n=5; inductance L r1 =27.1μH, capacitance C r1 =36.53nF, inductance L r2 =40.91μH, capacitance C r2 =12.18nF, excitation inductance L m =108.4μH.

[0058] The gain comparison diagram of simulated LLC mode and L-LCLC mode is shown in the figure below: Figure 7 and 8 As shown. Set the input voltage to 240V, the switching frequency to 200KHZ, and simulate the circuit. The left figure is the output voltage curve of the converter in LLC mode, and the right figure is the output voltage curve of the converter in L-LCLC mode. It can be seen that the output voltage of the converter in LLC mode fluctuates around 40V, and the output voltage of the converter in L-LCLC mode fluctuates around 17V. The voltage gain of L-LCLC mode is wider than that of LLC mode, which has a significant improvement effect.

[0059] The simulation diagram of the hysteresis control loop is as follows: Fig. 9 and 10 The figure on the left shows the converter switching from LLC mode to L-LCLC mode and from L-LCLC mode to LLC mode. The figure on the left shows the switching point when the converter works in LLC variable frequency mode. U The value of 2 is U 1.02 times of 0, when U in > U 2, it switches to L-LCLC frequency conversion control; the right figure shows the switching point when the converter works in L-LCLC frequency conversion mode. U The value of 1 is U 0.98 times of 0, when U in < U1, it switches to LLC variable frequency control. It can be seen that the mode is not switched frequently during the mode switching process, and the circuit can switch modes stably.

[0060] The specific simulation diagram of the hysteresis control loop is as follows: Fig.11 As shown, the thresholds of the two switches are switching points U1 and U2 respectively.

[0061] From the analysis of the above simulation waveforms, it can be seen that by adopting a mode switching strategy, when the gain is greater than 1, it works in the LLC resonant converter mode, and when the gain is less than 1, it works in the L-LCLC resonant converter mode. The mode switching point is set to the LLC resonant converter and the L-LCLC resonant converter when the gain is 1. At this time, the operating frequency and gain of the two converters are the same. The circuit state is stable during mode switching, which greatly reduces the impact of voltage and current 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.

[0062] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions 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 switching control of the converter operating mode, controls the disconnection of the second LC series resonant circuit so that the resonant converter operates in the LLC mode, and controls the connection of the second LC series resonant circuit so that the resonant converter operates in the L-LCLC mode.

2. The mode switching resonant converter according to claim 1, characterized in that: 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: in, 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.

3. The mode switching resonant converter according to claim 2, 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.

4. The mode switching resonant converter according to claim 2, characterized in that: When the input voltage of the resonant converter U in Greater than the second preset voltage U 2, 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 of the resonant converter U in Less than the first preset voltage U 1, the resonant network unit is controlled to disconnect the second LC series resonant circuit so that the resonant converter operates in LLC mode. in, U 1< U 0< U 2, U 0 is the output voltage of the resonant converter.

5. The mode switching resonant converter according to claim 4, characterized in that: Said U 1 ranges from 0.97 U 0~0.99 U 0, described U 2 ranges from 1.01 U 0~1.03 U 0.

6. A control method for a resonant converter based on mode switching according to any one of claims 1 to 5, characterized in that: The invention realizes the switching control of the working mode of the converter by collecting the input voltage signal of the converter and the switch state signal in the resonant network unit, comparing the given voltage signal and the input voltage signal to obtain the error signal, and combining the switch state signal to generate the switch control signal in the resonant network unit; comprising: 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.

7. The control method of the resonant converter based on mode switching according to claim 6, 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.

8. The control method of the resonant converter based on mode switching according to claim 6, characterized in that: When the input voltage of the resonant converter U in Greater than the second preset voltage U 2, 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 of the resonant converter U in Less than the first preset voltage U 1, the resonant network unit is controlled to disconnect the second LC series resonant circuit so that the resonant converter operates in LLC mode. in, U 1< U 0< U 2, U 0 is the output voltage of the resonant converter.

9. 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 6 to 8.

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