A CLLC resonant converter soft-start device and method
By employing a transformer-coupled H-bridge structure and asymmetric duty cycle control in the CLLC resonant converter, the current spike problem during startup is solved, achieving stable output voltage and stable diode turn-off, thus avoiding resonant current oscillation.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SICHUAN ENERGY INTERNET RES INST TSINGHUA UNIV
- Filing Date
- 2022-12-29
- Publication Date
- 2026-06-23
AI Technical Summary
Existing CLLC resonant converters have excessive inrush current and stress during startup. Traditional soft-start methods cannot effectively suppress current spikes and are greatly affected by the load, making it impossible to achieve voltage gain changes from zero.
A transformer-coupled H-bridge structure with primary and secondary sides is adopted. The switching transistor is controlled by asymmetric duty cycle, which ensures that the switching transistor achieves ZVS turn-on and the rectifier diode achieves ZCS turn-off, thus avoiding parasitic capacitance from participating in resonance.
It effectively suppresses overcurrent during startup, achieves stable output voltage establishment, avoids high-frequency oscillation of resonant current, and is unaffected by load, ensuring stable operation of the rectifier-side diodes.
Smart Images
Figure CN115864813B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of converter technology, and more specifically, to a soft-start device and method for a CLLC resonant converter. Background Technology
[0002] High-frequency isolated bidirectional DC / DC converters, as the hub of energy transfer, are indispensable energy conversion devices for achieving high-efficiency, high-reliability flexible urban power supply systems. CLLC resonant converters, as one of the most promising topologies, can achieve bidirectional energy flow, wide-range voltage transformation, and soft switching. However, due to the charging of the filter capacitor during startup and the large voltage difference across the resonant cavity, this process generates excessive inrush current, causing significant stress on the resonant components and switching devices. To reduce inrush current and stress, soft-start of CLLC resonant converters has been proposed. Soft-start can be broadly categorized into three methods: frequency conversion, phase shifting, and duty cycle variation. However, existing frequency conversion soft-start methods are limited by the switching frequency of the power devices, and the frequency cannot be too high. Furthermore, the gain characteristics of CLLC resonant converters limit the ability to adjust voltage gain at high frequencies, making it impossible to achieve a voltage gain change from zero. This results in a large current spike still occurring at startup when using frequency conversion soft-start. Phase shifting soft-start is more complex to implement, involves slight overcurrent during startup, and the resonant current is significantly affected by the load, losing the ZCS (zero-current switch) turn-off of the secondary diode under full load. Variable duty cycle soft starters lack ZVS (zero voltage) turn-on characteristics and cannot change from zero in practical applications, resulting in current spikes at startup. During the period of small duty cycle, the freewheeling time of the resonant current is long, which leads to repeated zero-crossing switching of the diode. The parasitic capacitance connected in parallel on it is repeatedly charged and discharged, affecting the switching performance of the diode. Summary of the Invention
[0003] In view of this, this specification proposes a soft-start device and method for a CLLC resonant converter, which can effectively suppress the overcurrent during startup, achieve the purpose of smoothly establishing the output voltage, has ZVS turn-on characteristics, and is not affected by the load size. It always ensures that half of the diodes on the rectifier side achieve ZCS turn-off, and can avoid high-frequency oscillation of resonant current caused by parasitic capacitance participating in resonance.
[0004] The present invention aims to provide a soft-start device for a CLLC resonant converter, comprising a primary side and a secondary side coupled by a transformer. The primary side includes a first H-bridge; the secondary side includes a second H-bridge. The first arm of the first H-bridge is composed of a series connection of switches S1 and S2; the second arm of the first H-bridge is composed of a series connection of switches S3 and S4; the first arm of the second H-bridge is composed of a series connection of switches S5 and S6; and the second arm of the second H-bridge is composed of a series connection of switches S7 and S8. The pulses of the corresponding switches S1 and S4, and S3 and S2 on the first H-bridge are identical, and the upper and lower switches on the same arm are alternately turned on. The second H-bridge is an uncontrolled rectifier, and no drive signal is applied to the corresponding switches. The duty cycles of the pulse signal and the complementary pulse signal on the first H-bridge are asymmetrically varied. The pulse signal is the pulse passing through switches S1 and S4; the second pulse is the pulse passing through switches S3 and S2.
[0005] Furthermore, the switching transistors S1, S2, S3, S4, S5, S6, S7, and S8 have the same structure, including an NMOS transistor, a diode, and a non-polarized capacitor; the drain of the NMOS transistor is connected to the cathode of the diode and one end of the non-polarized capacitor; the source of the NMOS transistor is connected to the anode of the diode and the other end of the non-polarized capacitor.
[0006] Furthermore, the primary side also includes an input power supply V. in Primary resonant inductance L r1 Primary resonant capacitor C r1 Excitation inductor L m The input power supply V in The positive terminal is connected to the drain of the NMOS transistor in switching transistors S1 and S3; the input power supply V in The negative terminal is connected to the source of the NMOS transistor in the switching transistors S2 and S4; the primary-side resonant inductor L r1 One end is connected to the source of the NMOS transistor in switch S1 and the drain of the NMOS transistor in switch S2; the primary resonant inductor L r1 The other end is connected to the excitation inductor L m One end of the excitation inductor is connected to the corresponding end of the primary coil; the excitation inductor L m The other end is connected to the primary resonant capacitor C. r1 One end is connected to the opposite end of the primary coil; the primary resonant capacitor C r1The other end is connected to the source of the NMOS transistor in the switching transistor S3 and the drain of the NMOS transistor in the switching transistor S4.
[0007] Furthermore, the input power supply V in The expression for the fundamental wave is:
[0008]
[0009] Where vAB,FHA represents the fundamental frequency, and D represents the duty cycle at time t. Uin represents the initial phase of the fundamental wave, and Uin represents the input voltage.
[0010] Furthermore, the secondary side also includes a secondary resonant inductor L. r2 Secondary resonant capacitor C r2 , filter capacitor C0 and voltage equalizing resistor R0; the corresponding terminal of the secondary coil and the secondary resonant inductor L r2 One end is connected; the secondary resonant inductor L r2 The other end is connected to the source of the switching transistor S7 and the drain of the switching transistor S8; the opposite end of the secondary coil is connected to the secondary resonant capacitor C. r2 One end is connected; the secondary resonant capacitor C r2 The other end is connected to the source of the switching transistor S5 and the drain of the switching transistor S6; the filter capacitor C0 is connected in parallel with the voltage equalization resistor R0, one end of the filter capacitor C0 is connected to the drain of the NMOS transistor in the switching transistor S7 and the switching transistor S5; the other end of the filter capacitor C0 is connected to the source of the switching transistor S6 and the switching transistor S8.
[0011] Furthermore, the duty cycle of the pulse signal and the complementary pulse signal changes asymmetrically: the duty cycle of the pulse signal and the complementary pulse signal changes in opposite directions, and the total duty cycle is 1.
[0012] Furthermore, the duty cycle of the pulse signal gradually increases, while the duty cycle of the complementary pulse signal gradually decreases.
[0013] Furthermore, the duty cycle of the pulse signal gradually increases from 0.001 to 0.5; the duty cycle of the complementary pulse signal gradually decreases from 0.999 to 0.5.
[0014] Furthermore, the resonant frequency of the resonant converter is equal to the switching frequency of the resonant converter.
[0015] This specification proposes a method for a soft-start device for a CLLC resonant converter as described in any of the above claims, comprising: determining the resonant frequency of the resonant converter based on its switching frequency; determining a start-up time, an initial duty cycle of a pulse signal, and an initial duty cycle of a complementary pulse signal; applying the pulse signal to switches S1 and S4 on the primary side; applying the complementary pulse signal to switches S2 and S3 on the primary side; and after the start-up time ends, the resonant converter enters a stable operation phase.
[0016] The technical solutions of the embodiments of the present invention have at least the following advantages and beneficial effects:
[0017] The soft-start device for CLLC resonant converters provided in some embodiments of this specification uses asymmetrical duty cycle to perform soft start, which simplifies the operating mode and makes it easy to implement in practical applications. It can effectively suppress current overcurrent during startup, achieve the purpose of smoothly establishing the output voltage, has ZVS turn-on characteristics, and is not affected by the load size, always ensuring that half of the diodes on the rectifier side achieve ZCS turn-off.
[0018] Some embodiments in this specification ensure that the resonant current always flows through the switching transistors by using asymmetrical variable duty cycle startup and complementary switching actions of the upper and lower switching transistors on the same bridge arm. The port voltage of the resonant cavity is always equal to the input voltage, thereby avoiding high-frequency oscillation of the resonant current caused by parasitic capacitance participating in the resonance. Attached Figure Description
[0019] Figure 1 An exemplary schematic diagram of a soft-start device for a CLLC resonant converter provided for some embodiments of the present invention;
[0020] Figure 2 Exemplary schematic diagrams of pulse signals and complementary pulse signals provided for some embodiments of the present invention;
[0021] Figure 3 An exemplary schematic diagram of the main theoretical operating waveforms of asymmetric variable duty cycle provided for some embodiments of the present invention;
[0022] Figure 4 Simulation waveforms of the output voltage and transformer secondary current of the CLLC resonant converter under full load and no-load conditions during soft start, provided for some embodiments of the present invention;
[0023] Figure 5 The primary current i of the CLLC resonant converter provided in some embodiments of the present invention during light-load and heavy-load soft-start processes, respectively. p Excitation current i m and secondary current i s The simulation waveform unfolded diagram;
[0024] Figure 6 This is an exemplary flowchart of a soft-start method for a CLLC resonant converter provided for some embodiments of the present invention. Detailed Implementation
[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.
[0026] Figure 1 This is an exemplary schematic diagram of a soft-start device for a CLLC resonant converter provided for some embodiments of the present invention. Figure 1 As shown, the soft-start device of the CLLC resonant converter is coupled to the primary and secondary sides through a transformer. The primary side includes a first H-bridge, and the secondary side includes a second H-bridge.
[0027] The first arm of the first H-bridge consists of switches S1 and S2 connected in series; the second arm consists of switches S3 and S4 connected in series; the first arm of the second H-bridge consists of switches S5 and S6 connected in series; the second arm consists of switches S7 and S8 connected in series. In the first H-bridge, the pulses of the opposite switches S1 and S4, and S3 and S2, are identical, and the upper and lower switches on the same arm conduct alternately. The second H-bridge is an uncontrolled rectifier, and no drive signal is applied to the switches. The duty cycles of the pulse signal and the complementary pulse signal on the first H-bridge change asymmetrically. The pulse signal is the pulse passing through switches S1 and S4; the second pulse is the pulse passing through switches S3 and S2. The diodes and parasitic capacitances connected in reverse parallel are VD1-VD8 and C1-C8, respectively.
[0028] In some embodiments, the switching transistors S1, S2, S3, S4, S5, S6, S7, and S8 have the same structure, including an NMOS transistor, a diode, and a non-polarized capacitor; the drain of the NMOS transistor is connected to the cathode of the diode and one end of the non-polarized capacitor; the source of the NMOS transistor is connected to the anode of the diode and the other end of the non-polarized capacitor.
[0029] In some embodiments, the primary side also includes an input power supply V. in Primary resonant inductance L r1 Primary resonant capacitor C r1 Excitation inductor L m Input power supply V inThe positive terminal is connected to the drain of the NMOS transistor in switching transistors S1 and S3; the input power supply V in The negative terminal is connected to the source of the NMOS transistor in switching transistors S2 and S4; the primary resonant inductor L r1 One end is connected to the source of the NMOS transistor in switch S1 and the drain of the NMOS transistor in switch S2; the primary resonant inductor L r1 The other end is connected to the excitation inductor L m One end is connected to the corresponding end of the primary coil; the excitation inductor L m The other end is connected to the primary resonant capacitor C. r1 One end is connected to the opposite end of the primary coil; the primary resonant capacitor C r1 The other end is connected to the source of the NMOS transistor in switch S3 and the drain of the NMOS transistor in switch S4.
[0030] In some embodiments, the resonant frequency of the resonant converter is equal to the switching frequency of the resonant converter. In some embodiments, when the duty cycle changes asymmetrically, the input power supply V... in The expression for the fundamental component is:
[0031]
[0032] Where vAB,FHA represents the fundamental frequency, and D represents the duty cycle at time t. Uin represents the initial phase of the fundamental wave, and Uin represents the input voltage.
[0033] Initial phase of the fundamental wave The expression is:
[0034]
[0035] The gain expression for the input / output voltage is as follows:
[0036]
[0037] As can be seen from the gain expression, changing the duty cycle D allows the voltage gain to change from zero. This method can achieve zero-voltage switching (ZVS) of the inverter-side switching transistors by setting the dead time. Here, M(wn,D) represents the gain expression for the input / output voltage when using asymmetrical duty cycle soft-start, where w... n w represents the normalized angular frequency. n =w s / w1, ws represents the switching frequency of the converter, w1 represents the resonant frequency of the converter, and M(wn) represents the gain expression of the input / output voltage under frequency conversion control.
[0038] In some embodiments, the secondary side also includes a secondary resonant inductor L.r2 Secondary resonant capacitor C r2 1. Filter capacitor C0 and voltage equalizing resistor R0; the same-name terminal of the secondary coil and the secondary resonant inductor L r2 One end is connected; secondary resonant inductor L r2 The other end is connected to the source of switch S7 and the drain of switch S8; the opposite end of the secondary coil is connected to the secondary resonant capacitor C. r2 One end is connected; secondary resonant capacitor C r2 The other end is connected to the source of switch S5 and the drain of switch S6; the filter capacitor C0 is connected in parallel with the voltage equalization resistor R0, one end of the filter capacitor C0 is connected to the drain of the NMOS transistor in switch S7 and switch S5; the other end of the filter capacitor C0 is connected to the source of switch S6 and switch S8. Where L... r1 and L r2 These respectively include the leakage inductance on the primary and secondary sides of the transformer, transformer T. r The transformation ratio is n. The theoretical operating waveform of the CLLC converter using this drive pulse is as follows: Figure 3 As shown, a switching cycle is divided into 6 typical operating stages. Because the upper and lower switches of the same bridge arm conduct alternately with unequal duty cycles, the operating principles of the first and second halves of the cycle are not entirely the same.
[0039] like Figure 2 As shown, the initial duty cycle of the pulse signal is less than the initial duty cycle of the complementary pulse signal. In some embodiments, the duty cycles of the pulse signal and the complementary pulse signal change in opposite directions, with a total duty cycle of 1. For example, the duty cycle of the pulse signal gradually increases, while the duty cycle of the complementary pulse signal gradually decreases. Exemplarily, the duty cycle of the pulse signal gradually increases from 0.001 to 0.5; the duty cycle of the complementary pulse signal gradually decreases from 0.999 to 0.5.
[0040] In some embodiments, the parameters of the filter capacitor C0 can be 1650μF, and the resonant inductor L... r1 The parameters of L1 and L2 can be 14μH and 0.2μH respectively, the parameters of the resonant capacitors C1 and C2 can be 0.1μF and 5.6μF respectively, and the magnetizing inductance L... m The parameters can be 120μH, the high-frequency transformer turns ratio n can be 7.8, and the converter resonant frequency f. r It can be 142kHz, with a dead time t. dead It can be 0.7ns.
[0041] The converter was subjected to asymmetrical variable duty cycle soft-start under full load and no-load conditions: maintaining a switching frequency of 142kHz, the pulses of switches S1 and S4 were gradually increased from an initial duty cycle of 0.001 to 0.5, while the pulses of complementary switches S2 and S3 were gradually decreased from an initial duty cycle of 0.999 to 0.5, yielding the output voltage V0 and transformer secondary current is under full load and no-load conditions. The simulated waveforms of the output voltage V0 and transformer secondary current is under full load and no-load conditions are shown below. Figure 4 As shown, the output voltage rise process of the asymmetric variable duty cycle soft start is consistent with the result of the input / output voltage gain expression. As the duty cycle gradually increases, the output voltage is steadily established, and the peak current at startup is greatly reduced.
[0042] Figure 5 The primary current i of the CLLC resonant converter provided in some embodiments of the present invention during light-load and heavy-load soft-start processes, respectively. p Excitation current i m and secondary current i s The simulation waveform unfolded diagram.
[0043] like Figure 5 As shown in the waveform diagram, the complementary switching action of the upper and lower switching transistors on the same bridge arm ensures that the resonant current always flows through the switching transistors, and the port voltage of the resonant cavity is always equal to the input voltage. This avoids the high-frequency oscillation of the resonant current caused by the participation of parasitic capacitance in the resonance in the traditional variable duty cycle method. Furthermore, regardless of light or heavy load, it can ensure that half of the diodes on the rectifier side achieve ZCS turn-off.
[0044] Figure 6 This is an exemplary flowchart illustrating a soft-start method for a CLLC resonant converter, provided for some embodiments of the present invention. Figure 6 As shown, the process of the soft-start method for a CLLC resonant converter may include the following:
[0045] Step 610: Determine the resonant frequency of the resonant converter based on its switching frequency. For example, the switching frequency can be used as the resonant frequency. In some embodiments, the fundamental frequency approximation method can also be used to calculate the resonant frequency f of the converter. r For more information on step 610, see [link to relevant documentation]. Figure 1 And its related descriptions.
[0046] Step 620: Determine the startup time, the initial duty cycle of the pulse signal, and the initial duty cycle of the complementary pulse signal. In some embodiments, the startup time can be set to 0.4s, the initial duty cycle is 0.001, and the converter's duty cycle linearly increases from 0.001 to 0.5 during the startup time, while the duty cycle of the complementary pulse signal in the same bridge arm linearly decreases from 0.999 to 0.5. For more information on step 620, see [link to step 620]. Figure 1 And its related descriptions.
[0047] Step 630: Apply the pulse signal to the primary side switches S1 and S4. For more details on step 630, see [link to relevant documentation]. Figure 1 And its related descriptions.
[0048] Step 640: A complementary pulse signal is applied to switches S2 and S3 on the primary side. The secondary side of the converter is uncontrolled rectification; no drive signal is applied to the secondary-side switches, and the output-side filter capacitor begins to charge slowly. For more information on step 640, see [link to relevant documentation]. Figure 1 And its related descriptions.
[0049] Step 650: After the startup time ends, the resonant converter enters the stable operation phase. For example, 0.4 seconds after startup, the output-side filter capacitor of the converter has finished charging, the output voltage V0 has reached stability, the startup process ends, and the converter enters the stable operation phase. For more information on step 650, please refer to [link to relevant documentation]. Figure 1 And its related descriptions.
[0050] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A soft-start device for a CLLC resonant converter, comprising a primary side and a secondary side coupled via a transformer, wherein the primary side includes a first H-bridge; and the secondary side includes a second H-bridge, characterized in that, The first arm of the first H-bridge is composed of a switching transistor. and switching transistor The first H-bridge is composed of series components; the second arm of the first H-bridge consists of a switching transistor. and switching transistor Composed of series connections; The first arm of the second H-bridge is composed of a switching transistor. and switching transistor The second H-bridge is composed of series connections; the second arm of the second H-bridge consists of a switching transistor. and switching transistor Composed of series connections; Among them, the corresponding switches on the first H bridge and , and The pulses are the same, and the upper and lower switches on the same bridge arm are turned on alternately; the second H bridge is an uncontrolled rectifier, and no drive signal is applied to the corresponding switch. The duty cycles of the pulse signal and the complementary pulse signal on the first H-bridge change asymmetrically, and the magnitudes of the duty cycles of the pulse signal and the complementary pulse signal change in opposite directions, with a total duty cycle of 1. The pulse signal is transmitted through the switching transistor. and the switching transistor The complementary pulse is the pulse that passes through the switching transistor. and the switching transistor The pulse; The resonant frequency of a resonant converter is equal to its switching frequency.
2. The soft-start device for a CLLC resonant converter according to claim 1, characterized in that, The switching transistor The switching transistor The switching transistor The switching transistor The switching transistor The switching transistor The switching transistor and the switching transistor They have the same structure, including NMOS transistors, diodes, and non-polarized capacitors; The drain of the NMOS transistor is connected to the cathode of the diode and one end of the non-polar capacitor. The source of the NMOS transistor is connected to the anode of the diode and the other end of the non-polarized capacitor.
3. The soft-start device for a CLLC resonant converter according to claim 2, characterized in that, The original side also includes an input power supply. Primary resonant inductor Primary resonant capacitor Excitation inductor ; The input power supply The positive electrode and the switching transistor and the switching transistor The drain connection of the NMOS transistor in the circuit; the input power supply The negative terminal of the switch transistor and the switching transistor The source connection of the NMOS transistor in the circuit; primary resonant inductor One end is connected to the switching transistor The source of the NMOS transistor and the switching transistor The drain connection of the NMOS transistor in the circuit; the primary-side resonant inductor The other end is connected to the excitation inductor One end is connected to the corresponding end of the primary coil; The excitation inductor The other end is connected to the primary resonant capacitor. One end is connected to the opposite end of the primary coil; The primary resonant capacitor The other end is connected to the switching transistor The source of the NMOS transistor and the switching transistor The drain connection of the NMOS transistor in the circuit.
4. The soft-start device for a CLLC resonant converter according to claim 3, characterized in that, The input power supply The expression for the fundamental wave is: ； in, Let D represent the fundamental frequency, and D represent the duty cycle at time t. Indicates the initial phase of the fundamental wave. This indicates the input voltage.
5. The soft-start device for a CLLC resonant converter according to claim 2, characterized in that, The secondary side also includes a secondary resonant inductor. Secondary resonant capacitor Filter capacitor and equalizing resistor ; The corresponding terminal of the secondary coil is connected to the secondary resonant inductor. One end is connected; Secondary resonant inductor The other end is connected to the switching transistor The source and the switch transistor Drain connection; The opposite terminal of the secondary coil and the secondary resonant capacitor One end is connected; The secondary resonant capacitor The other end is connected to the switching transistor The source and the switch transistor Drain connection; The filter capacitor With the equalizing resistor The filter capacitors are connected in parallel. One end is connected to the switching transistor and the switching transistor The drain connection of the NMOS transistor in the circuit; the filter capacitor The other end is connected to the switching transistor and the switching transistor The source connection.
6. The soft-start device for a CLLC resonant converter according to claim 1, characterized in that, The duty cycle of the pulse signal gradually increases, while the duty cycle of the complementary pulse signal gradually decreases.
7. The soft-start device for a CLLC resonant converter according to claim 6, characterized in that, The duty cycle of the pulse signal gradually increases from 0.001 to 0.5; the duty cycle of the complementary pulse signal gradually decreases from 0.999 to 0.
5.
8. A method for using a soft-start device for a CLLC resonant converter as described in any one of claims 1-7, characterized in that, include: The resonant frequency of the resonant converter is determined based on its switching frequency. Determine the start time, the initial duty cycle of the pulse signal, and the initial duty cycle of the complementary pulse signal; The pulse signal is applied to the switching transistor on the primary side. and switching transistor ; The complementary pulse signal is applied to the switching transistor on the primary side. and switching transistor ; After the startup time ends, the resonant converter enters the stable operation phase.