LLC converter and wide-range voltage regulation method thereof

Abstract

The application provides an LLC converter and a wide-range voltage regulation method thereof. The LLC converter comprises an input voltage, an input inductor L in , a first half-bridge unit, a second half-bridge unit, a resonant cavity, a transformer, a rectifier circuit, an output capacitor and an output load. The first half-bridge unit is composed of a first switch S1, a second switch S2 and a bus capacitor C1, the second half-bridge unit is composed of a third switch S3, a fourth switch S4 and a bus capacitor C2, the resonant cavity is composed of a resonant capacitor C r , a resonant inductor L r and an excitation inductor L m , and the rectifier circuit is composed of a first rectifier diode D1, a second rectifier diode D2, a voltage doubler capacitor C3 and a voltage doubler capacitor C4. The application can realize soft switching of all power devices in a wide voltage gain range, the switching frequency is fixed at a series resonant frequency, which is beneficial to optimization and design of magnetic elements, and the capacitor voltage of the half-bridge unit in the LLC converter can be self-balanced.

Description

Technical Field

[0001] This invention relates to the field of resonant converter technology, and more particularly to an LLC converter and its wide-range voltage regulation method. Background Technology

[0002] LLC converters are widely used in photovoltaic power generation and fuel cells because all power devices can achieve soft switching and improve efficiency. A common voltage regulation method in LLC converters is frequency conversion control, but the design and optimization of magnetic components become difficult over a wide frequency range. LLC converters operating at a fixed frequency at the series resonant frequency act as DC-DC transformers (DCX), achieving high efficiency. However, they cannot regulate the output voltage. Furthermore, traditional LLC converters are voltage-fed converters, requiring considerable electrolytic capacitors to suppress input current ripple. Therefore, current-fed converters have become a popular solution. They not only reduce input current ripple but also reduce the size of filters and transformers. However, the switching elements of traditional current-fed converters are susceptible to high voltage overshoot. Some researchers have proposed active clamping circuits to absorb voltage spikes, but this introduces additional components and drive circuitry. Another popular solution is a two-stage cascaded structure consisting of a Boost converter and an LLC-DCX converter. By controlling the duty cycle of the Boost converter, the output voltage can be easily regulated. However, the Boost stage cannot achieve soft switching, sacrificing system efficiency. The interleaved boost integrated LLC converter with fixed-frequency PWM control enables soft switching of all components with low current ripple. However, the number of boost inductors increases compared to a two-stage cascaded structure. Summary of the Invention

[0003] The main objective of this invention is to provide an LLC converter and its wide-range voltage regulation method, aiming to achieve high efficiency while reducing input current ripple over a wide voltage range. Furthermore, when operating under the proposed fixed-frequency phase-shift control method, not only is the design of magnetic components simplified, but the capacitor voltage of the half-bridge unit in the LLC converter also exhibits self-balancing characteristics, eliminating the need for complex capacitor voltage equalization control.

[0004] To achieve the above objectives, this invention proposes an LLC converter, comprising: an input voltage and an input inductance L. in The components include: first half-bridge unit, second half-bridge unit, resonant cavity, transformer, rectifier circuit, output capacitor, and output load.

[0005] The first half-bridge unit consists of a primary-side first switch S1, a primary-side second switch S2, and a bus capacitor C1; the second half-bridge unit consists of a primary-side third switch S3, a primary-side fourth switch S4, and a bus capacitor C2; and the resonant cavity consists of a resonant capacitor C1. rResonant inductor L r And excitation inductance L m The rectifier circuit consists of a secondary-side first rectifier diode D1, a secondary-side second rectifier diode D2, a voltage multiplier capacitor C3, and a voltage multiplier capacitor C4.

[0006] The drain of the first switching transistor S1 is connected to one end of the bus capacitor C1, and the source of the first switching transistor S1 is connected to the drain of the second switching transistor S2 and the input inductor L. in One end of the input inductor is connected to one end of the resonant cavity. The source of the second switch S2 is connected to the other end of the bus capacitor C1, the source of the third switch S3, and the drain of the fourth switch S4. The drain of the third switch S3 is connected to one end of the bus capacitor C2. The source of the fourth switch S4 is connected to the other end of the bus capacitor C2 and the negative terminal of the input voltage. in The other end is connected to the positive terminal of the input voltage, the other end of the resonant cavity is connected to the other end of the primary side of the transformer, one end of the secondary side of the transformer is connected to the anode of the first rectifier diode D1 in the rectifier bridge, the other end of the secondary side of the transformer is connected to one end of the voltage multiplier capacitor C4 in the rectifier bridge, and the output capacitor is connected to the output of the rectifier bridge and the output load respectively.

[0007] A further technical solution of the present invention is that the first switch S1 and the second switch S2 are complementaryly connected, the third switch S3 and the fourth switch S4 are complementaryly connected, and the dead time is denoted as T. d The switching frequencies of the first switch S1 to the fourth switch S2 are equal and constant, and the switching period is denoted as T. s The period of each physical quantity is T. f The duty cycle of the second switch S2 and the fourth switch S4 is fixed at 0.5 during the first fundamental period T. f The fourth switch S4 lags the second switch S2 by an angle β, and in the second fundamental period T f The fourth switch S4 leads the second switch S2 by an angle β, for two fundamental periods T. f This constitutes a switching cycle T s That is, T s =2T f The input voltage V of the resonant cavity AB It is a three-level wave with a duty cycle of 1 / 2-β.

[0008] To achieve the above objectives, this invention also proposes a wide-range voltage regulation method for an LLC converter. This method is applied to the LLC converter described above, wherein the converter has ten operating modes within one fundamental cycle Tf, [t0, t5] represents the five operating modes in the first half of the first fundamental cycle, and [t5, t10] represents the five operating modes in the second half of the first fundamental cycle. The operating modes of the LLC converter in the [t5, t10] phase are the same as those in the [t0, t5] phase. The method includes the following steps:

[0009] Step S10, Mode 1 [t0, t1]: At t = t0, the second switch S2 is turned off, and simultaneously the first rectifier diode D1 is turned on, and the resonant current iL r With current iL in Together, they discharge the junction capacitance Coss1 of the first switch S1 and charge the junction capacitance Coss2 of the second switch S2. After the charging and discharging are completed, the voltage of the capacitor Coss1 drops to 0, which creates the conditions for the ZVS turn-on of the first switch S1. In addition, the input voltage of the resonant cavity is doubled in this mode.

[0010] Step S20, Mode 2 [t1,t2], at t=t1, the first switch S1 achieves ZVS turn-on; resonant current iL r Specific excitation current iL m Large, resonant current iL r With excitation current iL m The difference is supplied to the secondary side through the transformer, and the magnetizing inductor L m The voltage across the terminals is clamped to Vo / (2n), therefore the excitation current iL m Linear rise, input inductance L in The voltage across the terminals is clamped to -V in Current iL in Linear descent, only the inductor L in this mode r With the capacitor C r Resonance occurs;

[0011] Step S30, Mode 3 [t2, t3], at t = t2, the first switch S1 is turned off. In this mode, the resonant current iL r With current iL in The junction capacitance Coss1 of the first switch S1 and the junction capacitance Coss2 of the second switch S2 are charged and discharged together until the voltage across the capacitor Coss2 is 0, in preparation for the ZVS conduction of the second switch S2 at time t3. During this stage, the input voltage of the resonant cavity is halved.

[0012] Step S40, Mode 4 [t3, t4], at t = t3, the second switch S2 achieves ZVS turn-on, and the resonant current iL r Greater than the excitation current iL m The first rectifier diode D1 continues to conduct; the inductor L m The voltage across the terminals continues to be clamped by the voltage Vo / (2n), and it still does not resonate, so the current iLm continues to rise linearly, and the inductor L... in The voltage across the terminals is clamped to 0, and the current iL in Remain unchanged;

[0013] Step S50, mode 5 [t4, t5], at t = t4, the current iL m With current iL r Equal, excitation inductor voltage vL m No longer limited by Vo / (2n), the first rectifier diode D1 achieves ZCS turn-off, and the inductor L m Resonance is introduced at this stage, and the transformer T r Both the primary and secondary sides are disconnected from the main circuit, and the first rectifier diode D1 and the second rectifier diode D2 are both turned off. Therefore, the primary side no longer transfers energy to the output, and the inductor L... in The voltage across the terminals is still clamped to 0, and the current iL in It will remain unchanged.

[0014] The beneficial effects of the LLC converter and its wide-range voltage regulation method of this invention are:

[0015] This invention enables soft switching of all power devices over a wide voltage gain range; under the proposed fixed-frequency phase-shift control method, the output voltage can be adjusted and the capacitor voltage of the half-bridge unit in the LLC converter can achieve self-balancing; the switching frequency is fixed at the series resonant frequency, which is beneficial for the optimization and design of magnetic components. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the circuit structure of a preferred embodiment of the LLC converter of the present invention.

[0017] Figure 2 This is the main working waveform diagram of the fixed-frequency phase-shift control method.

[0018] Figure 3 This is the equivalent circuit diagram at [t0, t1].

[0019] Figure 4 This is the equivalent circuit diagram at [t1,t2].

[0020] Figure 5 This is the equivalent circuit diagram at [t2,t3].

[0021] Figure 6 This is the equivalent circuit diagram at [t3,t4].

[0022] Figure 7 This is the equivalent circuit diagram at [t4,t5].

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. Detailed Implementation

[0024] It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0025] To address the problems of large frequency adjustment range, difficulty in designing and optimizing magnetic components, and large input current ripple in LLC converters operating over a wide range of input and output, this invention proposes an LLC converter and its wide-range voltage regulation method, achieving wide-range voltage regulation at a fixed frequency and with low input current ripple.

[0026] The LLC converter of this invention can reduce input current ripple. The proposed input inductor and transformer are designed together to achieve soft switching of all power devices over a wide voltage gain range. Under the proposed fixed-frequency phase-shift control method, the output voltage can be adjusted and the capacitor voltage of the half-bridge unit in the LLC converter can achieve self-balancing. The switching frequency is fixed at the series resonant frequency, which is beneficial for the optimization and design of magnetic components.

[0027] Specifically, such as Figure 1 As shown, a preferred embodiment of the LLC converter of the present invention includes: input voltage 1, input inductor Lin2, first half-bridge unit 3, second half-bridge unit 4, resonant cavity 5, transformer 6, rectifier circuit 7, output capacitor 8, and output load 9.

[0028] The first half-bridge unit 3 consists of a primary-side first switch S1, a primary-side second switch S2, and a bus capacitor C1; the second half-bridge unit 4 consists of a primary-side third switch S3, a primary-side fourth switch S4, and a bus capacitor C2; and the resonant cavity 5 consists of a resonant capacitor C1. r Resonant inductor L r And excitation inductance L m The rectifier circuit 7 is composed of a secondary-side first rectifier diode D1, a secondary-side second rectifier diode D2, a voltage multiplier capacitor C3, and a voltage multiplier capacitor C4.

[0029] The drain of the first switching transistor S1 is connected to one end of the bus capacitor C1. The source of the first switching transistor S1 is connected to the drain of the second switching transistor S2, one end of the input inductor Lin2, and one end of the resonant cavity 5. The source of the second switching transistor S2 is connected to the other end of the bus capacitor C1, the source of the third switching transistor S3, and the drain of the fourth switching transistor S4. The drain of the third switching transistor S3 is connected to one end of the bus capacitor C2. The source of the fourth switching transistor S4 is connected to the other end of the bus capacitor C2 and the negative terminal of the input voltage 1. The other end of the input inductor Lin2 is connected to the positive terminal of the input voltage 1. The other end of the resonant cavity 5 is connected to the other end of the primary side of the transformer 6. One end of the secondary side of the transformer 6 is connected to the anode of the first rectifier diode D1 in the rectifier bridge. The other end of the secondary side of the transformer 6 is connected to one end of the voltage multiplier capacitor C4 in the rectifier bridge. The output capacitor 8 is connected to the output of the rectifier bridge and the output load 9, respectively.

[0030] Please refer to Figure 2 , Figure 2 The following are the main operating waveforms of the fixed-frequency phase-shift control method proposed in this invention, in conjunction with... Figure 2 The working principle of the fixed-frequency phase-shift control of the LLC converter of this invention is introduced.

[0031] In this embodiment, the first switch S1 and the second switch S2 are complementaryly connected, the third switch S3 and the fourth switch S4 are complementaryly connected, and the dead time is denoted as T. d The switching frequencies of the first switch S1 to the fourth switch S2 are equal and constant, and the switching period is denoted as T. s The period of each physical quantity is T. f The duty cycle of the second switch S2 and the fourth switch S4 is fixed at 0.5 during the first fundamental period T. f The fourth switch S4 lags the second switch S2 by an angle β, and in the second fundamental period T f The fourth switch S4 leads the second switch S2 by an angle β, for two fundamental periods T. f This constitutes a switching cycle T s That is, T s =2T f The input voltage of the resonant cavity 5 is 1V. AB It is a three-level wave with a duty cycle of 1 / 2-β.

[0032] In this embodiment, the input power supply V of the resonant cavity 5 is controlled by changing the angle β. ABThis adjusts the voltage gain of the LLC converter, ultimately achieving voltage regulation over a wide voltage range. Furthermore, the larger the phase shift angle β, the smaller the voltage gain.

[0033] The beneficial effects of the LLC converter of this invention are:

[0034] The LLC converter of this invention can reduce input current ripple. The proposed input inductor and transformer are designed together to achieve soft switching of all power devices over a wide voltage gain range. Under the proposed fixed-frequency phase-shift control method, the output voltage can be adjusted and the capacitor voltage of the half-bridge unit in the LLC converter can achieve self-balancing. The switching frequency is fixed at the series resonant frequency, which is beneficial for the optimization and design of magnetic components.

[0035] To achieve the above objectives, this invention also proposes a wide-range voltage regulation method for LLC converters. This method is applied to the LLC converter described in the above embodiment, where [t0, t5] represents the five operating modes in the first half of the first fundamental cycle, and [t5, t10] represents the five operating modes in the second half of the first fundamental cycle. Considering symmetry, the operating modes of the LLC converter in the [t5, t10] stage are the same as those in the [t0, t5] stage. Therefore, this invention only provides a detailed analysis of the operating principle in the [t0, t5] stage. Combined with... Figure 2 The corresponding timing diagrams and equivalent circuits for each stage are as follows: Figures 3 to 7 As shown.

[0036] The method includes the following steps:

[0037] Step S10, Mode 1 [t0,t1], please refer to... Figure 3 At t = t0, the second switch S2 is turned off, and at the same time the first rectifier diode D1 is turned on, and the resonant current iL r With current iL in Together, they discharge the junction capacitance Coss1 of the first switch S1 and charge the junction capacitance Coss2 of the second switch S2. After the charging and discharging are completed, the voltage of the capacitor Coss1 drops to 0, which creates the conditions for the ZVS turn-on of the first switch S1. In addition, the input voltage of the resonant cavity is doubled in this mode.

[0038] Step S20, Mode 2 [t1,t2], please refer to... Figure 4 At t = t1, the first switch S1 achieves ZVS turn-on; the resonant current iL r Specific excitation current iL m Large, resonant current iL r With excitation current iL m The difference is supplied to the secondary side through the transformer, and the magnetizing inductor Lm The voltage across the terminals is clamped to Vo / (2n), therefore the excitation current iL m Linear rise, input inductance L in The voltage across the terminals is clamped to -V in Current iL in Linear descent, only the inductor L in this mode r With the capacitor C r Resonance occurs.

[0039] Step S30, Mode 3 [t2,t3], please refer to Figure 5 At t = t2, the first switch S1 is turned off. In this mode, the resonant current iL r With current iL in The junction capacitance Coss1 of the first switch S1 and the junction capacitance Coss2 of the second switch S2 are charged and discharged together until the voltage across the capacitor Coss2 is 0, which prepares for the ZVS conduction of the second switch S2 at time t3. During this stage, the input voltage of the resonant cavity is halved.

[0040] Step S40, mode 4 [t3,t4], please refer to Figure 6 At t = t3, the second switch S2 achieves ZVS turn-on, and the resonant current iL r Greater than the excitation current iL m The first rectifier diode D1 continues to conduct; the inductor L m The voltage across the terminals continues to be clamped by the voltage Vo / (2n), and it still does not resonate, so the current iLm continues to rise linearly, and the inductor L... in The voltage across the terminals is clamped to 0, and the current iL in It remains unchanged.

[0041] Step S50, mode 5 [t4,t5], please refer to Figure 7 At t = t4, the current iL m With current iL r Equal, excitation inductor voltage vL m No longer limited by Vo / (2n), the first rectifier diode D1 achieves ZCS turn-off, and the inductor L m Resonance is introduced at this stage, and the transformer T r Both the primary and secondary sides are disconnected from the main circuit, and the first rectifier diode D1 and the second rectifier diode D2 are both turned off. Therefore, the primary side no longer transfers energy to the output, and the inductor L... in The voltage across the terminals is still clamped to 0, and the current iL in It will remain unchanged.

[0042] The beneficial effects of the wide-range voltage regulation method for the LLC converter of this invention are:

[0043] This invention enables soft switching of all power devices over a wide voltage gain range; under the proposed fixed-frequency phase-shift control method, the output voltage can be adjusted and the capacitor voltage of the half-bridge unit in the LLC converter can achieve self-balancing; the switching frequency is fixed at the series resonant frequency, which is beneficial for the optimization and design of magnetic components.

[0044] The following are Figures 1 to 7 The meanings of the electrical component symbols involved are explained below:

[0045] V in It is an input DC voltage source, L in This is the input inductor. C1 and C2 are the bus capacitors of the two half-bridge units, respectively. S1 to S4 are the primary-side switching transistors from the first to the fourth. Capacitors Coss1 to Coss4 are the junction capacitances of the primary-side switching transistors from S1 to S4. r It is a resonant capacitor, L r It is a resonant inductor, L m It is a magnetizing inductor, T r It's a transformer, 1:n is the transformer's turns ratio, D1 and D2 are the first rectifier diode on the secondary side to the second rectifier diode on the secondary side, C3 and C4 are the first voltage multiplier capacitor and the second voltage multiplier capacitor on the secondary side, respectively. o It is the output capacitor, R L This is the output load. VGS1 to VGS4 are the drive signals for the primary side first switch S1 to the primary side fourth switch S4, respectively. β is the phase shift angle between the primary side fourth switch S4 and the primary side second switch S2. iL in It is the input inductor current, iL r It is the resonant current, iL m It is the magnetizing current, V AB iD1 is the input voltage of the resonant cavity, and iD2 is the current flowing through the first rectifier diode on the secondary side to the second rectifier diode on the secondary side.

[0046] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural changes made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. An LLC converter, characterized in that, include: Input voltage, input inductance Lin, first half-bridge unit, second half-bridge unit, resonant cavity, transformer, rectifier circuit, output capacitor, and output load; The first half-bridge unit consists of a primary-side first switch S1, a primary-side second switch S2, and a bus capacitor C1; the second half-bridge unit consists of a primary-side third switch S3, a primary-side fourth switch S4, and a bus capacitor C2; and the resonant cavity consists of a resonant capacitor C1. r Resonant inductor L r And excitation inductance L m The rectifier circuit consists of a secondary-side first rectifier diode D1, a secondary-side second rectifier diode D2, a voltage multiplier capacitor C3, and a voltage multiplier capacitor C4. The drain of the first switching transistor S1 is connected to one end of the bus capacitor C1, and the source of the first switching transistor S1 is connected to the drain of the second switching transistor S2 and the input inductor L. in One end of the input inductor is connected to one end of the resonant cavity. The source of the second switch S2 is connected to the other end of the bus capacitor C1, the source of the third switch S3, and the drain of the fourth switch S4. The drain of the third switch S3 is connected to one end of the bus capacitor C2. The source of the fourth switch S4 is connected to the other end of the bus capacitor C2 and the negative terminal of the input voltage. in The other end is connected to the positive terminal of the input voltage. The other end of the resonant cavity is connected to the same-name terminal of the primary side of the transformer. The opposite-name terminal of the primary side of the transformer is connected to the drain of the fourth switching transistor S4. The same-name terminal of the secondary side of the transformer is connected to the anode of the first rectifier diode D1 in the rectifier circuit. The opposite-name terminal of the secondary side of the transformer is connected to one end of the voltage multiplier capacitor C4 in the rectifier circuit. The output capacitor is connected to the output of the rectifier circuit and the output load, respectively.

2. The LLC converter according to claim 1, characterized in that, The first switch S1 and the second switch S2 are complementaryly turned on, and the third switch S3 and the fourth switch S4 are complementaryly turned on. The dead time is denoted as T. d The switching frequencies of the first switch S1 to the fourth switch S2 are equal and constant, and the switching period is denoted as T. s The period of each physical quantity is T. f The duty cycle of the second switch S2 and the fourth switch S4 is fixed at 0.5 during the first fundamental period T. f The fourth switch S4 lags the second switch S2 by an angle β, and in the second fundamental period T f The fourth switch S4 leads the second switch S2 by an angle β, for two fundamental periods T. f This constitutes a switching cycle T s That is, T s =2T f The input voltage V of the resonant cavity AB It is a three-level wave with a duty cycle of 1 / 2-β.

3. A wide-range voltage regulation method for an LLC converter, characterized in that, The method is applied to the LLC converter as described in claim 2, wherein, in a fundamental period T f The internal converter has ten operating modes. [t0, t5] represents the five operating modes in the first half of the first fundamental cycle, and [t5, t10] represents the five operating modes in the second half of the first fundamental cycle. The LLC converter operates in the same modes as in the [t0, t5] phase during the [t5, t10] phase. The method includes the following steps: Step S10, Mode 1 [t0, t1]: At t = t0, the second switch S2 is turned off, and simultaneously the first rectifier diode D1 is turned on, and the resonant current iL r With current iL in Together, they discharge the junction capacitance Coss1 of the first switch S1 and charge the junction capacitance Coss2 of the second switch S2. After the charging and discharging are completed, the voltage of the capacitor Coss1 drops to 0, which creates the conditions for the ZVS turn-on of the first switch S1. In addition, the input voltage of the resonant cavity is doubled in this mode. Step S20, Mode 2 [t1,t2], at t=t1, the first switch S1 achieves ZVS turn-on; resonant current iL r Specific excitation current iL m Large, resonant current iL r With excitation current iL m The difference is supplied to the secondary side through the transformer, and the magnetizing inductor L m The voltage across the terminals is clamped to Vo / (2n), therefore the excitation current iL m Linear rise, input inductance L in The voltage across the terminals is clamped to -V in Current iL in Linear descent, only the inductor L in this mode r With the capacitor C r Resonance occurs; Step S30, Mode 3 [t2, t3], at t = t2, the first switch S1 is turned off. In this mode, the resonant current iL r With current iL in The junction capacitance Coss1 of the first switch S1 and the junction capacitance Coss2 of the second switch S2 are charged and discharged together until the voltage across the capacitor Coss2 is 0, in preparation for the ZVS conduction of the second switch S2 at time t3. During this stage, the input voltage of the resonant cavity is halved. Step S40, Mode 4 [t3, t4], at t = t3, the second switch S2 achieves ZVS turn-on, and the resonant current iL r Greater than the excitation current iL m The first rectifier diode D1 continues to conduct; the inductor L m The voltage across the terminals continues to be clamped by the voltage Vo / (2n), and it still does not resonate, so the current iLm continues to rise linearly, and the inductor L... in The voltage across the terminals is clamped to 0, and the current iL in Remain unchanged; Step S50, mode 5 [t4, t5], at t = t4, the current iL m With current iL r Equal, excitation inductor voltage vL m No longer limited by Vo / (2n), the first rectifier diode D1 achieves ZCS turn-off, and the inductor L m Resonance is introduced at this stage, and the transformer T r Both the primary and secondary sides are disconnected from the main circuit, and the first rectifier diode D1 and the second rectifier diode D2 are both turned off. Therefore, the primary side no longer transfers energy to the output, and the inductor L... in The voltage across the terminals is still clamped to 0, and the current iL in It will remain unchanged.

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