LLC resonant converter with wide output voltage range based on voltage doubler rectifier

Abstract

This invention discloses an LLC resonant converter with a wide output voltage range based on a voltage doubler rectifier, applicable to DC fast charging of new energy vehicles. The converter achieves primary-side inversion and secondary-side rectification topology reconfiguration through switch drive signals, enabling wide-range voltage output in four operating modes. The primary side can switch between half-bridge and full-bridge inversion modes, while the secondary side can switch between full-bridge, voltage doubler, and voltage quadruple rectifier modes. This invention reduces diode voltage stress, possesses self-balancing capability of the voltage doubler capacitor, and achieves soft switching across the entire voltage range. Ultra-wide voltage gain is achieved within a narrow frequency adjustment range across the entire voltage range through simple pulse frequency modulation (PFM), allowing the converter to adapt to the charging needs of new energy vehicles with different voltage platforms.

Description

Technical Field

[0001] This invention belongs to the field of DC-DC converter technology, and relates to an LLC resonant converter with a wide output voltage range based on a voltage doubler rectifier. Background Technology

[0002] In the field of new energy vehicles, high-voltage fast charging technology has become a core development track in the industry. Currently, the voltage platform of batteries is undergoing a comprehensive iteration from the traditional 400V voltage architecture to the 800V high-voltage architecture, and the forward-looking research and development of the next-generation powertrain architecture has already targeted the 1200V voltage level. The rated voltage and charging operating voltage range of the power batteries of different vehicle classes vary greatly, which places stringent requirements on the output voltage regulation capability and multi-vehicle compatibility of DC fast charging piles. LLC resonant converters have significant advantages such as soft switching over a wide load range, high conversion efficiency, high power density, and low electromagnetic interference. However, when traditional LLC resonant converters use pulse frequency modulation (PFM), if the switching frequency adjustment range is significantly widened to achieve a wide voltage output, the switching frequency will deviate significantly from the series resonant frequency. This not only greatly increases the design difficulty of magnetic components and the size and cost of the device, but also causes the converter to lose its soft switching characteristics and experience a surge in circulating current losses when operating far from the resonant frequency, resulting in a significant decrease in the overall conversion efficiency.

[0003] To address the shortcomings of the existing technologies, this invention proposes an LLC resonant converter with a wide output voltage range based on a voltage doubler rectifier. Through primary-secondary side structure reconstruction and flexible modulation strategies, it achieves wide voltage output, low component stress, and high stability while retaining the advantages of soft switching, thus meeting the charging needs of current and future electric vehicles. Summary of the Invention

[0004] This invention aims to provide an LLC resonant converter with a wide output voltage range based on a voltage doubler rectifier, achieving a normalized voltage gain range of 0.5-4.0, operating stably at a fixed switching frequency, ensuring zero-voltage switching (ZVS) characteristics and seamless mode switching of all switching transistors, and achieving wide voltage gain within a narrow switching frequency adjustment range to meet the charging needs of new energy vehicles with different voltage platforms.

[0005] The present invention solves the above-mentioned technical problems through the following technical solutions: DC voltage source Vin, primary-side full-bridge inverter circuit, resonant cavity, transformer, and secondary-side improved voltage doubler rectifier circuit.

[0006] Primary-side full-bridge inverter circuit: composed of switching transistors S1-S4. The positive terminal of the DC voltage source Vin is connected to the drain of switching transistors S1 and S3 respectively, and the negative terminal of the DC voltage source Vin is connected to the source of switching transistors S2 and S4 respectively. The switching transistors are driven by frequency modulation, with a duty cycle of 50% and a dead time set.

[0007] The resonant cavity consists of a magnetizing inductor Lm, a resonant inductor Lr, and a resonant capacitor Cr connected in series. One end of the resonant inductor Lr is connected to the source of switch S1 and the drain of switch S2, and the other end is connected to the transformer T. One end of the resonant capacitor Cr is connected to the source of switch S3 and the drain of switch S4. The resonant frequency is... .

[0008] Transformer: One end of the primary winding of transformer T is connected to the negative terminal of resonant capacitor Cr, and the other end of the primary winding of transformer T is connected to resonant inductor Lr; one end of the secondary winding of transformer T is connected to the negative terminal of stacked capacitor Co1 and the positive terminal of Co2, and the other end of the secondary winding of transformer T is connected to the anode of diode D1, the source of auxiliary switch S5, and the cathode of diode D2. The turns ratio is 1:1.

[0009] Secondary-side improved voltage doubler rectifier circuit: consisting of diode D1 The transformer consists of diode D6, voltage multiplier capacitors Co1 and Co2, and auxiliary switching transistors S5 and S6. One end of the secondary winding of the transformer is connected to the anode of diode D1, the cathode of diode D2, and the source of auxiliary switching transistor S5, and the other end is connected to the anode of diode D4, the cathode of diode D5, and the source of auxiliary switching transistor S6. The cathode of diode D1 is connected to the anode of diode D3, the cathode of diode D4, and the positive terminal of voltage multiplier capacitor Co1. The anode of diode D2 is connected to the anode of diode D5, the anode of diode D6, and the negative terminal of voltage multiplier capacitor Co2. The positive terminal of voltage multiplier capacitor Co2 is connected to the negative terminal of voltage multiplier capacitor Co1 and the drain of auxiliary switching transistor S5. The positive terminal of output capacitor C1 is connected to the cathode of diode D3, the drain of switching transistor S6, and the positive terminal of output capacitor C2. The negative terminal of output capacitor C1 is connected to the anode of diode D6.

[0010] Furthermore, Lr represents the resonant inductance involved in the resonance, Cr represents the resonant capacitance involved in the resonance, and Lm represents the magnetizing inductance. The formula for calculating the resonant frequency fr of the resonant converter is as follows:

[0011] The inductance ratio of the resonant converter is calculated using the following formula:

[0012] Ro represents the load, N represents the transformer turns ratio, and Req represents the equivalent resistance of the secondary side referred to the primary side. The calculation formula is as follows:

[0013] The formula for calculating the quality factor of the resonant converter described in this invention is as follows:

[0014] fs represents the switching frequency, and the formula for calculating the normalized frequency fn is shown below:

[0015] The gain calculation formula for the resonant converter, where A is the product of the inverter and voltage multiplier modes, is as follows:

[0016] Furthermore, the specific operating mode control of the LLC resonant converter with a wide output voltage range based on a voltage doubler rectifier is as follows: Primary-side half-bridge, secondary-side full-bridge mode (HB-FVR): Primary-side switch S3 is always off and switch S4 is always on, forming a half-bridge structure. Switches S1 and S2 are complementary and conduct with a 50% duty cycle. Secondary-side auxiliary switches S5 and S6 are always off, forming a full-bridge rectification mode.

[0017] Primary-side full-bridge and secondary-side full-bridge mode (FB-FVR): Primary-side switches S1, S4 and S2, S3 conduct complementaryly with a 50% duty cycle, forming a full-bridge structure; secondary-side auxiliary switches S5 and S6 are always off, forming a full-bridge rectification mode.

[0018] Primary-side full-bridge, secondary-side voltage doubler mode (FB-DVR): Primary-side switches S1, S4 and S2, S3 conduct complementaryly with a 50% duty cycle, forming a full-bridge structure; secondary-side auxiliary switch S5 is always on, and switch S6 is always off, forming a voltage doubler rectification mode.

[0019] Primary-side full-bridge, secondary-side quadruple voltage mode (FB-QVR): Primary-side switches S1, S4 and S2, S3 conduct complementaryly with a 50% duty cycle, forming a full-bridge structure; secondary-side auxiliary switches S5 and S6 are always on, forming a quadruple voltage rectification mode.

[0020] The voltage balance analysis of an LLC resonant converter with a wide output voltage range based on a voltage doubler rectifier is as follows: On the reconfigurable secondary side, stacked capacitors Co1 and Co2 are charged by the positive and negative voltage amplitudes of the transformer. Based on the principle of magnetic flux conservation, the voltage amplitude is automatically corrected to ensure voltage balance.

[0021] By comparing the preset thresholds VFF (HB-FVR and FB-FVR switching threshold), VFD (FB-FVR and FB-DVR switching threshold), and VDQ (FB-DVR and FB-QVR switching threshold) of the output voltage Vout, the reconstruction of the primary-side inverter mode and the secondary-side rectification mode is triggered; during the mode switching process, the output current is kept stable through a PI closed-loop control modulation strategy.

[0022] Compared with existing technologies, this invention has the following advantages: it has an ultra-wide adjustable voltage range, achieving a normalized voltage gain range of 0.5-4. By controlling the on and off of the primary and secondary switches, the LLC resonant converter can operate in four modes: primary-side half-bridge, secondary-side full-bridge mode (HB-FVR), primary-side full-bridge, secondary-side full-bridge mode (FB-FVR), primary-side full-bridge, secondary-side double voltage mode (FB-DVR), and primary-side full-bridge, secondary-side quadruple voltage mode (FB-QVR). The rectifier of this converter can reduce the voltage stress on the diodes by half and has the ability to self-balance the voltage of the stacked capacitors. It achieves wide voltage gain within a narrow switching frequency adjustment range, meeting the ultra-wide voltage charging requirements of different electric vehicles. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a topology diagram of an LLC resonant converter with a wide output voltage range based on a voltage doubler rectifier, as described in this invention.

[0025] Figure 2 This is a topology diagram of the resonant converter in this invention operating in primary-side half-bridge and secondary-side full-bridge modes.

[0026] Figure 3 This is a waveform diagram of the resonant converter in this invention operating in primary-side half-bridge and secondary-side full-bridge modes.

[0027] Figure 4 This is a diagram showing the positive and negative half-cycle rectification operation of the resonant converter in this invention, operating in primary-side half-bridge and secondary-side full-bridge modes.

[0028] Figure 5 This is a topology diagram of the resonant converter in this invention operating in primary-side full-bridge and secondary-side full-bridge modes.

[0029] Figure 6 This is a waveform diagram of the resonant converter in this invention operating in primary-side full-bridge and secondary-side full-bridge modes.

[0030] Figure 7 This is a diagram showing the positive and negative half-cycle rectification operation of the resonant converter in the primary-side full-bridge and secondary-side full-bridge modes of this invention.

[0031] Figure 8 This is a topology diagram of the resonant converter in this invention operating in primary-side full-bridge and secondary-side double-voltage mode; Figure 9 This is a waveform diagram of the resonant converter in this invention operating in primary-side full-bridge and secondary-side double-voltage mode.

[0032] Figure 10 This is a diagram showing the positive and negative half-cycle rectification operation of the resonant converter in this invention, operating in primary-side full-bridge and secondary-side double voltage doubling mode.

[0033] Figure 11 This is the topology diagram of the resonant converter in this invention operating in primary-side full-bridge and secondary-side quadruple voltage multiplier mode; Figure 12 This is a waveform diagram of the resonant converter in this invention operating in primary-side full-bridge and secondary-side quadruple voltage multiplier mode.

[0034] Figure 13 This is a diagram showing the positive and negative half-cycle rectification operation of the resonant converter in this invention, operating in primary-side full-bridge and secondary-side quadruple voltage mode. Detailed Implementation

[0035] To make the technical solution, objectives, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention. In this invention, the switching device uses a silicon-based MOSFET.

[0036] like Figure 1 As shown, a topology diagram of an LLC resonant converter with a wide output voltage range based on a voltage doubler rectifier is presented. Its primary side is a traditional full-bridge inverter circuit, and its secondary side is a novel rectifier circuit composed of six diodes, four capacitors, and two fully controlled switching devices. The primary and secondary sides are connected through a high-frequency transformer and an LC series resonant cavity.

[0037] like Figure 2 The diagram shows the topology of the resonant converter operating in primary-side half-bridge and secondary-side full-bridge mode. In this mode, primary-side switch S3 is always off, and switch group S4 is always on. S1 and S2 form a half-bridge inverter circuit. Secondary-side auxiliary switches S5 and S6 are always off, which is the full-bridge rectification mode.

[0038] like Figure 3 The figure shows the waveform of the resonant converter operating in primary half-bridge and secondary full-bridge mode. In this mode, primary switch S3 is always off, switch S4 is always on, and switches S1 and S2 are complementary in conducting with a 50% duty cycle. Secondary auxiliary switches S5 and S6 are always off.

[0039] like Figure 4The diagram shows the positive and negative half-cycle rectification operation of the resonant converter in primary-side half-bridge and secondary-side full-bridge mode. In this mode, the primary-side switches S1 and S2 form a half-bridge inverter circuit, while the secondary-side transformer windings and diodes D1, D2, D3, D4, D5, and D6 form a full-bridge rectifier. The positive half-cycle current flows through the transformer windings, diodes D1, D3, D5, and D6, and output capacitors C1 and C2. The negative half-cycle current flows through the transformer windings, diodes D4, D3, D6, and D2, and output capacitors C1 and C2. Therefore, the sum of the voltages across output capacitors C1 and C2 is U. Together, output capacitors C1 and C2 supply power to the load, and the load voltage is U.

[0040] like Figure 5 The diagram shows the topology of the resonant converter operating in primary-side full-bridge and secondary-side full-bridge modes. In this mode, primary-side switches S1, S2, S3, and S4 form a full-bridge inverter circuit. Secondary-side auxiliary switches S5 and S6 are always off, operating in full-bridge rectification mode.

[0041] like Figure 6 The figure shows the waveforms of the resonant converter operating in primary-side full-bridge and secondary-side full-bridge modes. In this mode, the primary-side switches S1, S4 and S2, S3 are complementary and conduct with a 50% duty cycle, forming a full-bridge structure; the secondary-side auxiliary switches S5 and S6 are always off.

[0042] like Figure 7 The diagram shows the positive and negative half-cycle rectification operation of the resonant converter in primary-side full-bridge and secondary-side full-bridge modes. In full-bridge rectification mode, the primary-side switches S1, S2, S3, and S4 form a full-bridge inverter circuit. The secondary-side transformer windings, along with diodes D1, D2, D3, D4, D5, and D6, form a full-bridge rectifier. During the positive half-cycle, the current flows through the transformer windings, diodes D1, D3, D5, and D6, and output capacitors C1 and C2. During the negative half-cycle, the current flows through the transformer windings, diodes D4, D3, D6, and D2, and output capacitors C1 and C2. Therefore, the sum of the voltages across output capacitors C1 and C2 is U. Together, output capacitors C1 and C2 supply power to the load, and the load voltage is U.

[0043] like Figure 8 The diagram shows the topology of the resonant converter operating in primary-side full-bridge and secondary-side voltage doubler mode. In this mode, primary-side switches S1, S2, S3, and S4 form a full-bridge inverter circuit. Secondary-side auxiliary switches S5 and S6 are always on, operating in voltage doubler rectification mode.

[0044] like Figure 9The figure shows the waveform of the resonant converter operating in primary-side full-bridge and secondary-side double voltage doubling mode. In this mode, the primary-side switches S1, S4 and S2, S3 are complementary and conduct with a 50% duty cycle; the secondary-side auxiliary switch S5 is always on and the secondary-side switch S6 is always off.

[0045] like Figure 10 The diagram shows the resonant converter operating in primary-side full-bridge and secondary-side voltage doubler mode during the positive and negative half-cycle rectification. In voltage doubler rectification mode, the transformer windings, auxiliary switch S5, voltage doubler capacitors CO1 and CO2, and diodes D3, D4, D5, and D6 form a voltage doubler rectifier, which charges the voltage doubler capacitors CO1 and CO2, thus achieving voltage doubler. During both the positive and negative half-cycles, the current has two flow paths. In the positive half-cycle, one path is where the current flows from the transformer windings through auxiliary switch S5, voltage doubler capacitor CO2, and diode D5, charging voltage doubler capacitor CO2; the other path is where the current flows from the transformer windings through auxiliary switch S5, voltage doubler capacitor CO1, diodes D3, D5, D6, and output capacitors C1 and C2, supplying power to the load. During the negative half-cycle, one path involves current flowing from the transformer winding through auxiliary switch S5, voltage multiplier capacitor Co1, and diode D4, charging voltage multiplier capacitor Co1. The other path involves current flowing from the transformer winding through auxiliary switch S5, voltage multiplier capacitor Co2, diodes D3, D4, and D6, and output capacitors C1 and C2. Therefore, the sum of the voltages across output capacitors C1 and C2 is 2U. Output capacitors C1 and C2 together supply power to the load, with a load voltage of 2U.

[0046] like Figure 11 The diagram shows the topology of the resonant converter operating in primary-side full-bridge and secondary-side quadruple voltage multiplier mode. In this mode, primary-side switches S1, S2, S3, and S4 form a full-bridge inverter circuit. Secondary-side auxiliary switches S5 and S6 are always on, operating in quadruple voltage multiplier rectification mode.

[0047] like Figure 12 As shown, the waveform diagram of the resonant converter operating in the primary half-bridge and secondary quadruple voltage multiplier mode is shown. In this mode, the primary side switches S1, S4 and S2, S3 are complementary and conduct with a 50% duty cycle, forming a full-bridge structure; the secondary side auxiliary switches S5 and S6 are always on.

[0048] like Figure 13The diagram shows the resonant converter operating in primary-side full-bridge and secondary-side quadruple voltage multiplier mode during the positive and negative half-cycle rectification. In quadruple voltage multiplier mode, the transformer windings, auxiliary switches S5 and S6, voltage multiplier capacitors CO1 and CO2, diodes D3, D4, D5, and D6, and output capacitors C1 and C2 constitute a quadruple voltage multiplier, charging the voltage multiplier capacitors CO1 and CO2 to achieve the quadruple voltage. During both the positive and negative half-cycles, the current has two flow paths. In the positive half-cycle, one path is through the transformer windings, auxiliary switch S5, voltage multiplier capacitor CO2, and diode D5, charging voltage multiplier capacitor CO2. The other path is through the transformer windings, auxiliary switch S5, voltage multiplier capacitor CO1, diode D3, output capacitor C1, and auxiliary switch S6. The voltage across output capacitor C1 is 2U, which, together with output capacitor C2, supplies power to the load. During the negative half-cycle, one path involves current flowing from the transformer winding through auxiliary switch S5, diode D4, and voltage multiplier capacitor Co1, charging Co1. The other path involves current flowing from the transformer winding through auxiliary switch S6, output capacitor C2, diode D6, output capacitor Co2, and auxiliary switch S5. The voltage across output capacitor C2 is 2U, which, together with output capacitor C1, supplies power to the load. Therefore, the sum of the voltages across output capacitors C1 and C2 is 4U, and together they supply power to the load, resulting in a load voltage of 4U.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A wide output voltage range LLC resonant converter based on a voltage doubler rectifier, characterized in that: It includes a full-bridge inverter circuit, a resonant cavity, a transformer, and a rectifier circuit with switchable voltage multiplier mode; The full-bridge inverter circuit includes a first bridge arm and a second bridge arm, wherein the first bridge arm includes a switch S1 and a switch S2, and the second bridge arm includes a switch S3 and a switch S4. The resonant cavity includes a magnetizing inductor Lm, a resonant inductor Lr, and a resonant capacitor Cr; The rectifier circuit includes voltage multiplier capacitors Co1 and Co2, output capacitors C1 and C2, full-bridge rectifier diodes D1, D2, D3, and D4, stacked diodes D5 and D6, and auxiliary switching transistors S5 and S6.

2. The LLC resonant converter with a wide output voltage range based on a voltage doubler rectifier according to claim 1, characterized in that: The positive terminal of the DC voltage source Vin in the full-bridge inverter circuit is connected to the drain of switching transistor S1 and switching transistor S3 respectively, and the negative terminal of the DC voltage source Vin is connected to the source of switching transistor S2 and switching transistor S4 respectively. The switching transistors are driven by frequency modulation with a duty cycle of 50% and a dead time is set.

3. The LLC resonant converter with a wide output voltage range based on a voltage doubler rectifier according to claim 1, characterized in that: The resonant cavity includes an excitation inductor Lm, a resonant inductor Lr, and a resonant capacitor Cr arranged in series. One end of the resonant inductor Lr is connected to the source of the switching transistor S3 and the drain of the switching transistor S4, and the other end is connected to the transformer T. One end of the resonant capacitor Cr is connected to the source of switch S1 and the drain of switch S2; the resonant frequency is... .

4. The LLC resonant converter with a wide output voltage range based on a voltage doubler rectifier according to claim 1, characterized in that: One end of the secondary winding of the transformer is connected to the anode of diode D1, the cathode of diode D2, and the source of auxiliary switch S5, and the other end is connected to the anode of diode D4, the cathode of diode D5, and the source of auxiliary switch S6. The cathode of diode D1 is connected to the anode of diode D3, the cathode of diode D4, and the positive terminal of voltage multiplier capacitor Co1. The anode of diode D2 is connected to the anode of diode D5, the anode of diode D6, and the negative terminal of voltage multiplier capacitor Co2. The positive terminal of voltage multiplier capacitor Co2 is connected to the negative terminal of voltage multiplier capacitor Co1 and the drain of auxiliary switch S5. The positive terminal of output capacitor C1 is connected to the cathode of diode D3, the drain of switch S6, and the positive terminal of output capacitor C2. The negative terminal of output capacitor C1 is connected to the anode of diode D6.

5. The LLC resonant converter with a wide output voltage range based on a voltage doubler rectifier according to claim 1, characterized in that: The primary reconfigurable side of the rectifier circuit has two operating modes: full-bridge inverter (FB) and half-bridge inverter (HB). The secondary reconfigurable side has three operating modes: full-bridge rectifier (FVR), voltage doubler rectifier (DVR), and voltage doubler rectifier (QVR). The switching between these three operating modes is achieved by controlling the on / off states of auxiliary switches S5 and S6.

6. The LLC resonant converter with a wide output voltage range based on a voltage doubler rectifier according to claim 1, characterized in that: This converter features four charging modes to adapt to different voltage requirements: Primary-side half-bridge, secondary-side full-bridge mode: Primary-side switch S3 is always off and switch S4 is always on, forming a half-bridge structure; switches S1 and S2 are complementary and conduct with a 50% duty cycle; secondary-side auxiliary switches S5 and S6 are always off, forming a full-bridge rectification mode. Primary-side full-bridge and secondary-side full-bridge modes: Primary-side switches S1, S4 and S2, S3 conduct complementaryly with a 50% duty cycle, forming a full-bridge structure; secondary-side auxiliary switches S5 and S6 are always off, forming a full-bridge rectification mode. Primary-side full-bridge, secondary-side voltage doubler mode: Primary-side switches S1, S4 and S2, S3 conduct complementaryly with a 50% duty cycle, forming a full-bridge structure; secondary-side auxiliary switch S5 is always on, and switch S6 is always off, forming a voltage doubler rectification mode. Primary-side full-bridge, secondary-side quadruple voltage mode: Primary-side switches S1, S4 and S2, S3 conduct complementaryly with a 50% duty cycle, forming a full-bridge structure; secondary-side auxiliary switches S5 and S6 are always on, forming a quadruple voltage rectification mode.

7. The LLC resonant converter with a wide output voltage range based on a voltage doubler rectifier according to claim 1, characterized in that: The voltage multiplier capacitors Co1 and Co2, and the output capacitors C1 and C2 all have voltage self-balancing capabilities. Co1 and Co2 are charged by the positive and negative voltage amplitudes of the transformer. Based on the principle of magnetic flux conservation, the voltage amplitude is automatically corrected to ensure voltage balance.

8. The LLC resonant converter with a wide output voltage range based on a voltage doubler rectifier according to claim 1, characterized in that: The resonant converter includes a mode switching strategy: by comparing the output voltage Vo with preset thresholds VFF (HB-FVR and FB-FVR switching threshold), VFD (FB-FVR and FB-DVR switching threshold), and VDQ (FB-DVR and FB-QVR switching threshold), the reconfiguration of the primary-side inverter mode and the secondary-side rectification mode is triggered; during the mode switching process, a PI closed-loop control modulation strategy is used to ensure that the entire system operates stably and reliably.

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