Three-level rectifier DC / DC converter

Abstract

The present invention provides a three-level rectifier DC / DC converter, comprising a primary circuit, a resonant cavity circuit, and a secondary circuit. The voltage between the two primary ends of the resonant cavity circuit is a first voltage, and the voltage between the two secondary ends is a second voltage. The secondary circuit comprises a flying capacitor, a switch bridge arm, and a capacitor bridge arm. The switch bridge arm comprises four switches connected in series. The two ends of the flying capacitor are respectively connected between the first and second switches and between the third and fourth switches. The two secondary ends are respectively connected between the second and third switches and between the two output capacitors of the capacitor bridge arm. In two consecutive change cycles of the first voltage, the first and second switches are in the on state for at least a preset time period after two falling edges, and the third and fourth switches are in the on state for at least a preset time period after two rising edges.

Description

Technical Field

[0001] This case relates to a DC / DC converter, and in particular to a three-level rectifier DC / DC converter. Background Art

[0002] The low-voltage / DC / DC converter, bidirectional on-board charger (OBC), and traction inverter are the three primary power conversion units in electric vehicles. The OBC, as the energy conversion unit between AC and DC, replenishes the power battery and is indispensable in electric vehicle configurations. In recent years, as electric vehicle range continues to improve, battery voltages are shifting from the traditional 400V to 800V. Furthermore, as OBCs transition from traditional single-phase charging to three-phase charging, the rectified AC-to-DC voltage will reach 800V. Consequently, both the primary and secondary sides of the DC / DC converter will involve 800V applications.

[0003] When traditional 650V devices are unavailable, 1200V SiC devices are required. However, these devices are expensive, and the resulting high dv / dt ratio can also cause EMI (electromagnetic interference) issues. Furthermore, wide-bandgap GaN semiconductors, a future trend in power devices, are difficult to directly apply to high voltages like 800V due to their limited voltage resistance. Multi-level technology can overcome this limitation, thereby expanding the development and application of practical products.

[0004] Furthermore, for applications involving a wide output voltage range in practical engineering, to meet the requirements of high efficiency and high output voltage gain, fixed-frequency PWM (pulse width modulation) control based on a dual active bridge (DAB) circuit and resonant soft-switching variable frequency control based on an LLC circuit are often used.

[0005] Dual active bridge circuits typically employ multiple phase-shifting techniques to achieve zero-voltage switching (ZVS) over a wide output range. However, this control is relatively complex, and the high turn-off current can lead to high turn-off stress and EMI.

[0006] For LLC circuits, variable frequency control is usually used to enable all switches to achieve ZVS operation, and its control implementation method is relatively simple. However, LLC circuits have difficulty meeting the bidirectional operation requirements in practical applications.

[0007] Therefore, it is an urgent need to develop a three-level rectifier DC / DC converter that can improve the above-mentioned conventional technology. Summary of the Invention

[0008] The purpose of this application is to provide a three-level rectifier DC / DC converter that not only possesses the characteristics of a resonant circuit but also meets the requirements of bidirectional operation. Furthermore, it features secondary-side short-circuit energy storage, enabling high voltage gain output.

[0009] To achieve the above objectives, the present invention provides a three-level rectifier DC / DC converter comprising a primary circuit, a resonant cavity circuit, and a secondary circuit. The primary circuit receives an input voltage and includes multiple primary switches. The resonant cavity circuit includes a resonant inductor, a resonant capacitor, and a transformer. The first and second primary terminals of the resonant cavity circuit are electrically connected to the primary circuit, the primary winding of the transformer is electrically connected between the first and second primary terminals, and the secondary winding of the transformer is electrically connected between the first and second secondary terminals of the resonant cavity circuit. The voltage between the first and second primary terminals is a first voltage, and the voltage between the first and second secondary terminals is a second voltage. The secondary circuit includes a flying capacitor, a switch arm, and a capacitor arm. The switch arm includes a first secondary switch, a second secondary switch, a third secondary switch, and a fourth secondary switch connected in series. The two ends of the flying capacitor are connected to the node between the first and second secondary switches and the node between the third and fourth secondary switches, respectively. The node between the second secondary switch and the third secondary switch is connected to the first secondary terminal. The capacitor bridge arm includes a first output capacitor and a second output capacitor connected in series, and the node between the first output capacitor and the second output capacitor is connected to the second secondary terminal. The two ends of the capacitor bridge arm are respectively connected to the two ends of the switch bridge arm, and the voltage between the two ends of the capacitor bridge arm is the output voltage. The first secondary switch, the second secondary switch, the third secondary switch, and the fourth secondary switch have the same switching frequency. Two consecutive change cycles of the first voltage have two rising edges and two falling edges. The first secondary switch and the second secondary switch are each in an on state for at least a preset time period after the two falling edges, and the third secondary switch and the fourth secondary switch are each in an on state for at least a preset time period after the two rising edges. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 A schematic diagram of the circuit structure of a three-level rectifier DC / DC converter according to a preferred embodiment of the present invention;

[0011] Figure 2 Shown Figure 1 The equivalent circuit of the three-level rectifier DC / DC converter;

[0012] Figure 3A for Figure 1Schematic diagram of key waveforms of a three-level rectifier DC / DC converter when positive sequence control is adopted on its secondary side switches;

[0013] Figure 3B for Figure 1 Schematic diagram of key waveforms of a three-level rectifier DC / DC converter when negative sequence control is adopted on its secondary side switches;

[0014] Figures 4A to 4L Shown Figure 1 The working state of the three-level rectifier DC / DC converter in one cycle when its secondary side switch adopts positive sequence control;

[0015] Figure 5A Shown Figure 1 An equivalent circuit of a three-level rectifier DC / DC converter during a period in which the first voltage on its primary side is at a high level and the secondary side switch is forward-conducting;

[0016] Figure 5B Shown Figure 1 An equivalent circuit of a three-level rectifier DC / DC converter during a period in which the first voltage on its primary side is at a low level and the secondary side switch is forward-conducting;

[0017] Figure 6A for Figure 1 Schematic diagram of key waveforms of a three-level rectifier DC / DC converter when its secondary side switches adopt positive sequence control and partial synchronous rectification;

[0018] Figure 6B for Figure 1 Schematic diagram of key waveforms of a three-level rectifier DC / DC converter when its secondary side switches adopt negative sequence control and partial synchronous rectification;

[0019] Figure 7A for Figure 1 Schematic diagram of key waveforms of a three-level rectifier DC / DC converter when its secondary side switches adopt positive sequence control and full synchronous rectification;

[0020] Figure 7B for Figure 1 Schematic diagram of key waveforms of a three-level rectifier DC / DC converter when its secondary side switches adopt negative sequence control and full synchronous rectification;

[0021] Figure 8A For Figure 1 The control block diagram of the three-level rectifier DC / DC converter using variable frequency control;

[0022] Figure 8B For Figure 1 The control block diagram of the three-level rectifier DC / DC converter adopting fixed frequency control;

[0023] Figure 9 An example is shown Figure 1 A specific implementation of the resonant cavity circuit;

[0024] Figure 10 An example is shown Figure 1 A specific implementation of the primary circuit;

[0025] Figure 11 for Figure 10 Schematic diagram of key waveforms of a three-level rectifier DC / DC converter when positive sequence control is adopted on its secondary side switches;

[0026] Figure 12 for Figure 10 Schematic diagram of key waveforms of a three-level rectifier DC / DC converter when its secondary side switches adopt positive sequence control and partial synchronous rectification;

[0027] Figure 13 for Figure 10 Schematic diagram of key waveforms of a three-level rectifier DC / DC converter when its secondary side switches adopt positive sequence control and full synchronous rectification;

[0028] Figure 14 An example is shown Figure 1 Another specific implementation of the primary circuit;

[0029] Figure 15 for Figure 14 Schematic diagram of key waveforms of a three-level rectifier DC / DC converter when positive sequence control is adopted on its secondary side switches;

[0030] Figure 16 for Figure 14 Schematic diagram of key waveforms of a three-level rectifier DC / DC converter when its secondary side switches adopt positive sequence control and partial synchronous rectification;

[0031] Figure 17 for Figure 14 Schematic diagram of the key waveforms of a three-level rectifier DC / DC converter when its secondary side switches adopt positive sequence control and fully synchronous rectification.

[0032]

Explanation of symbols

[0033] 1: Three-level rectifier DC / DC converter

[0034] 11: Primary circuit

[0035] 12: Resonant Cavity Circuit

[0036] Lr: resonant inductance

[0037] Cr: resonant capacitor

[0038] Tr: Transformer

[0039] Np: primary winding

[0040] Ns: secondary winding

[0041] 121: First original edge

[0042] 122: Second original edge

[0043] 123: First secondary side

[0044] 124: Second secondary side

[0045] 13: Secondary circuit

[0046] Cf: Flying capacitance

[0047] S21: First secondary side switch

[0048] S22: Second secondary switch

[0049] S23: The third secondary switch

[0050] S24: The fourth secondary switch

[0051] Co1: first output capacitor

[0052] Co2: Second output capacitor

[0053] A, B, C, D: nodes

[0054] VAB: first voltage

[0055] VCD: Second voltage

[0056] Ip: primary current

[0057] Is: secondary current

[0058] Vin: input voltage

[0059] Vo: output voltage

[0060] is21, is22, is23, is24, iCf: current

[0061] t0, t1, t2, t3, t4, t5, t6, t7, t8, t9, t10, t11, t12: time

[0062] 14a, 14b: Control module

[0063] 141: Regulator

[0064] 142: Voltage Controlled Oscillator

[0065] 143: Controller

[0066] 144: PWM controller

[0067] Io: output current

[0068] Vin_FB: input voltage signal

[0069] Vo_FB: output voltage signal

[0070] Io_FB: output current signal

[0071] Vo_ref: output reference voltage

[0072] Io_ref: output reference current

[0073] fs: switching frequency

[0074] n: turns ratio

[0075] Ton: On time

[0076] Lrp: primary resonant inductance

[0077] Lrs: secondary side resonant inductor

[0078] Crp: primary resonant capacitor

[0079] Crs: secondary side resonant capacitor

[0080] 11a, 11b: Primary circuit

[0081] Cin: input capacitance

[0082] S11: First primary switch

[0083] S12: Second primary switch

[0084] S13: Third primary switch

[0085] S14: Fourth primary switch

[0086] Cf2: Flying capacitor

[0087] C1: First input capacitor

[0088] C2: Second input capacitor DETAILED DESCRIPTION

[0089] Some typical embodiments that embody the features and advantages of this invention will be described in detail in the following description. It should be understood that this invention is capable of various variations in various aspects without departing from the scope of this invention, and that the descriptions and illustrations herein are intended to be illustrative in nature and not to limit this invention.

[0090] Figure 1This is a schematic diagram of the circuit structure of a three-level rectifier DC / DC converter in a preferred embodiment of the present invention. Figure 2 Shown Figure 1 The equivalent circuit of the three-level rectifier DC / DC converter. Figure 1 and Figure 2 As shown, the three-level rectifier DC / DC converter 1 includes a primary circuit 11 , a resonant cavity circuit 12 and a secondary circuit 13 . It has the characteristics of a resonant circuit and can also meet the requirements of bidirectional operation.

[0091] The primary circuit 11 receives an input voltage Vin and includes a plurality of primary switches configured to provide a first voltage V AB . Note that, since the actual configuration of the primary circuit 11 is not limited, this embodiment illustrates the primary circuit 11 as a voltage source providing the first voltage V AB . Specific implementations of the primary circuit 11 will be exemplified in the subsequent description.

[0092] The resonant cavity circuit 12 includes a resonant inductor Lr, a resonant capacitor Cr, and a transformer Tr. The first primary terminal 121 and the second primary terminal 122 of the resonant cavity circuit 12 are electrically connected to the primary circuit 11. The primary winding Np of the transformer Tr is electrically connected between the first primary terminal 121 and the second primary terminal 122. The secondary winding Ns of the transformer Tr is electrically connected between the first secondary terminal 123 and the second secondary terminal 124 of the resonant cavity circuit 12. The voltage between the first primary terminal 121 and the second primary terminal 122 is a first voltage VAB, and the voltage between the first secondary terminal 123 and the second secondary terminal 124 is a second voltage VCD. Figure 1 and Figure 2 In the figure, Ip is the primary current and Is is the secondary current.

[0093] The secondary circuit 13 includes a flying capacitor Cf, a switch arm, and a capacitor arm. The switch arm includes a first secondary switch S21, a second secondary switch S22, a third secondary switch S23, and a fourth secondary switch S24, connected in series. The two ends of the flying capacitor Cf are connected to the node between the first and second secondary switches S21 and S22, and the node between the third and fourth secondary switches S23 and S24, respectively. A node C between the second and third secondary switches S22 and S23 is connected to the first secondary terminal 123. The capacitor arm includes a first output capacitor Co1 and a second output capacitor Co2, connected in series. A node D between the first and second output capacitors Co1 and Co2 is connected to the second secondary terminal 124. The two ends of the capacitor arm are connected to the two ends of the switch arm, and the voltage between the two ends of the capacitor arm is the output voltage Vo.

[0094] Figure 3A for Figure 1Schematic diagram of the key waveforms of the three-level rectifier DC / DC converter when its secondary side switches adopt positive sequence control. Figure 3B for Figure 1 Schematic diagram of the key waveforms of the three-level rectifier DC / DC converter when its secondary side switches adopt negative sequence control. Figure 3A and Figure 3B In FIG, S21, S22, S23 and S24 represent the driving signals of the first secondary switch S21, the second secondary switch S22, the third secondary switch S23 and the fourth secondary switch S24 respectively, is21, is22, is23 and is24 represent the currents flowing through the first secondary switch S21, the second secondary switch S22, the third secondary switch S23 and the fourth secondary switch S24 respectively, and iCf represents the current flowing through the flying capacitor Cf. Figure 3A and Figure 3B As shown, in any two consecutive variation cycles of the first voltage VAB, there are two rising edges and two falling edges. The first secondary switch S21 and the second secondary switch S22 are each in an on state for a preset duration after the two falling edges, and the third secondary switch S23 and the fourth secondary switch S24 are each in an on state for a preset duration after the two rising edges. The first secondary switch S21, the second secondary switch S22, the third secondary switch S23, and the fourth secondary switch S24 have the same switching frequency, which is equal to half the frequency of the first voltage VAB. All of the secondary switches in the secondary circuit 13 can achieve zero voltage turn-on. The preset duration is determined based on the input voltage Vin and the output voltage Vo. By controlling the preset duration, the duty cycle of each secondary switch can be adjusted, thereby controlling the gain of the output voltage Vo. In addition, the first voltage VAB is a square wave that is high in half a period and low in the other half a period, wherein the high level and the low level may be equal to +VAB / 2 and -VAB / 2, or equal to +VAB and 0, respectively.

[0095] Figure 3A and Figure 3B The difference in the waveforms shown is whether the secondary side switches use positive sequence control or negative sequence control.

[0096] When the secondary switches adopt positive sequence control, the phases of the fourth secondary switch S24, the first secondary switch S21, the third secondary switch S23 and the second secondary switch S22 are sequentially different by 90 degrees. Figure 3AAs shown, during two consecutive cycles of variation of the first voltage VAB (e.g., the period from time t0 to time t12), a first rising edge, a first falling edge, a second rising edge, and a second falling edge occur in sequence. The first secondary switch S21 and the second secondary switch S22 remain on for a predetermined period of time after the first falling edge and the second falling edge, respectively. The fourth secondary switch S24 and the third secondary switch S23 remain on for a predetermined period of time after the first rising edge and the second rising edge, respectively.

[0097] When the secondary switches adopt negative sequence control, the phases of the second secondary switch S22, the third secondary switch S23, the first secondary switch S21 and the fourth secondary switch S24 are 90 degrees apart in sequence. Figure 3B As shown, during two consecutive variation cycles of the first voltage VAB (e.g., from time t0 to t12), a first rising edge, a first falling edge, a second rising edge, and a second falling edge occur in sequence. The first secondary switch S21 and the second secondary switch S22 remain on for a predetermined period of time after the second falling edge and the first falling edge, respectively. The fourth secondary switch S24 and the third secondary switch S23 remain on for a predetermined period of time after the first rising edge and the second rising edge, respectively.

[0098] At Figure 3A and Figure 3B In the embodiment, the time period from time t0 to time t12 can be regarded as a cycle of the secondary side switch. Figures 4A to 4L Shown Figure 1 The working state of the three-level rectifier DC / DC converter in one cycle when its secondary side switch adopts positive sequence control. Specifically, Figures 4A to 4L The switching state and current flow direction of the three-level rectifier DC / DC converter 1 in each time period within one cycle are shown. Figure 4B ), the time period from time t4 to t5 ( Figure 4E ), the time period from time t7 to t8 ( Figure 4H ) and the time period from time t10 to t11 ( Figure 4K ) corresponds in sequence to the time periods when the fourth secondary switch S24, the first secondary switch S21, the third secondary switch S23, and the second secondary switch S22 are forward-conducting. Figure 4B 、 4E 4H and 4K show the corresponding working states of the three-level rectifier DC / DC converter 1. The equivalent circuit of the three-level rectifier DC / DC converter 1 during the period from time t1 to t2 and from time t7 to t8 is shown as follows: Figure 5A As shown, the equivalent circuit of the three-level rectifier DC / DC converter 1 during the period from time t4 to t5 and from time t10 to t11 is as follows: Figure 5B As shown. Figure 4B 、 4EAs can be seen from Figures 4H, 4K, 5A, and 5B, during the forward conduction period of these secondary switches, the voltage across the flying capacitor Cf and the voltage across the output capacitor Co1 or Co2 are equal in magnitude and opposite in direction, thus canceling each other out. This effectively short-circuits the secondary circuit 13. During this period, the resonant inductor Lr stores energy via the first voltage VAB, thereby preparing for high-gain energy output in the next period.

[0099] Correspondingly, when the secondary side switch adopts negative sequence control, the working state of the three-level rectifier DC / DC converter 1 in one cycle of its secondary side switch can be based on Figures 4A to 4L It can be deduced, so I will not elaborate on it here.

[0100] As can be seen from the above, in the present three-level rectifier DC / DC converter 1, by controlling the cyclic conduction of the four secondary switches, energy can be stored in the resonant inductor Lr during operation, thereby achieving a high-gain voltage output. Furthermore, since the four secondary switches are turned on in rotation, the four secondary switches naturally have equal RMS current and conduction losses, facilitating thermal design and selection of switching components.

[0101] In some embodiments, to further improve the operating efficiency of the three-level rectifier DC / DC converter 1, a synchronous rectification control method can be adopted for the secondary side switch, that is, the secondary side switch is driven during the period when the current is flowing in the reverse direction, thereby reducing the conduction loss of the secondary side switch.

[0102] Figure 6A for Figure 1 Schematic diagram of the key waveforms of the three-level rectifier DC / DC converter when its secondary side switches adopt positive sequence control and partial synchronous rectification. Figure 6B for Figure 1 Schematic diagram of the key waveforms of a three-level rectifier DC / DC converter when its secondary side switches adopt negative sequence control and partial synchronous rectification. Figure 6A and Figure 6B As shown, when partial synchronous rectification is adopted, the first secondary switch S21, the second secondary switch S22, the third secondary switch S23 and the fourth secondary switch S24 are Figure 3A and Figure 3B In addition to being in the on-state during the illustrated on-period, the first secondary switch S21, the second secondary switch S22, the third secondary switch S23, and the fourth secondary switch S24 are also in the on-state during portions of the reverse current flow period. In this embodiment, the duty cycles of the first secondary switch S21, the second secondary switch S22, the third secondary switch S23, and the fourth secondary switch S24 are all 25%, and they maintain a 90-degree phase difference with each other. Their switching frequencies are also still equal to half the frequency of the first voltage VAB.

[0103] Figure 7Afor Figure 1 Schematic diagram of the key waveforms of the three-level rectifier DC / DC converter when its secondary side switches adopt positive sequence control and full synchronous rectification. Figure 7B for Figure 1 Schematic diagram of the key waveforms of the three-level rectifier DC / DC converter when its secondary side switches adopt negative sequence control and full synchronous rectification. Figure 7A and Figure 7B As shown, when full synchronous rectification is adopted, the first secondary switch S21, the second secondary switch S22, the third secondary switch S23 and the fourth secondary switch S24 are Figure 3A and Figure 3B In addition to being in the on state during the illustrated conduction period, the first secondary switch S21, the second secondary switch S22, the third secondary switch S23, and the fourth secondary switch S24 are also in the on state during all periods of reverse current flow. In this embodiment, the driving signals of the first secondary switch S21 and the fourth secondary switch S24 are complementary, and the driving signals of the second secondary switch S22 and the third secondary switch S23 are complementary.

[0104] In addition, depending on whether the switching frequency of the primary switch changes or not, the control method of the three-level rectifier DC / DC converter 1 of this embodiment can be divided into variable frequency control and fixed frequency control.

[0105] Figure 8A For Figure 1 The control block diagram of the three-level rectifier DC / DC converter adopts variable frequency control. When variable frequency control is adopted, such as Figure 8A As shown, the three-level rectifier DC / DC converter 1 further includes a control module 14a. The control module 14a is configured to sense an input voltage signal Vin_FB, an output voltage signal Vo_FB, and an output current signal Io_FB, respectively reflecting the input voltage Vin, the output voltage Vo, and the output current Io, and to control the operation of all primary and secondary switches. The control module 14a includes a regulator 141, which generates a regulation signal based on the output voltage signal Vo_FB, the output current signal Io_FB, the output reference voltage Vo_ref, and the output reference current Io_ref. In this embodiment, the control module 14a further includes a voltage-controlled oscillator 142 and a controller 143. The voltage-controlled oscillator 142 is electrically connected to the regulator 141 and generates a switching frequency fs for all primary switches based on the regulation signal. The controller 143 is electrically connected to the voltage-controlled oscillator 142 and generates the on-time Ton of all the secondary switches according to the input voltage signal Vin_FB, the output voltage signal Vo_FB, and the switching frequency fs of all the primary switches. When the turns ratio n of the transformer Tr is constant, the relationship between the on-time Ton of all the secondary switches and the input voltage Vin, the output voltage Vo, and the switching frequency fs of all the primary switches conforms to Figure 8A In practical applications, the on-time Ton of the secondary switch can be obtained by calculation or by looking up a table.

[0106] Figure 8B For Figure 1 The control block diagram of the three-level rectifier DC / DC converter adopts fixed frequency control. When fixed frequency control is adopted, the switching frequency fs of all primary switches is fixed and greater than the resonant frequency of the resonant cavity circuit 12. Figure 8B As shown, the three-level rectifier DC / DC converter 1 further includes a control module 14b. The control module 14b is configured to sense an input voltage signal Vin_FB, an output voltage signal Vo_FB, and an output current signal Io_FB, respectively reflecting the input voltage Vin, the output voltage Vo, and the output current Io, and to control the operation of all primary and secondary switches. The control module 14b includes a regulator 141, which generates a regulation signal based on the output voltage signal Vo_FB, the output current signal Io_FB, the output reference voltage Vo_ref, and the output reference current Io_ref. In this embodiment, the control module 14b further includes a PWM controller 144, which is electrically connected to the regulator 141 and generates drive signals for all primary and secondary switches based on the regulation signal.

[0107] In addition, in the three-level rectifier DC / DC converter 1 of the present invention, the resonant inductor Lr and the resonant capacitor Cr of the resonant cavity circuit 12 have various implementation aspects. Figure 9 The example shows a specific embodiment of the resonant cavity circuit 12. Figure 9 In the embodiment shown, the resonant inductor Lr, the primary winding Np, and the resonant capacitor Cr are sequentially connected in series between the first primary terminal 121 and the second primary terminal 122. However, this is not limited to the embodiment shown. For example, the resonant capacitor Cr may also be connected in series between the secondary winding Ns and the second secondary terminal 124, and the resonant inductor Lr may also be connected in series between the secondary winding Ns and the first secondary terminal 123. Furthermore, for example, Figure 10 As shown, in some embodiments, the resonant inductor Lr includes a primary resonant inductor Lrp and a secondary resonant inductor Lrs, wherein the primary resonant inductor Lrp is connected in series between the primary winding Np and the first primary terminal 121, and the secondary resonant inductor Lrs is connected in series between the secondary winding Ns and the first secondary terminal 123; in some embodiments, the resonant capacitor Cr includes a primary resonant capacitor Crp and a secondary resonant capacitor Crs, wherein the primary resonant capacitor Crp is connected in series between the primary winding Np and the second primary terminal 122, and the secondary resonant capacitor Crs is connected in series between the secondary winding Ns and the second secondary terminal 124.

[0108] Furthermore, in the three-level rectifier DC / DC converter 1 of the present invention, the actual circuit topology of the primary circuit is not limited and can be, for example, but not limited to, a full-bridge circuit, a half-bridge circuit, a series half-bridge circuit, a flying capacitor three-level circuit, or a mid-point clamped three-level circuit. Two actual circuit topologies of the primary circuit are exemplified below.

[0109] In some embodiments, such as Figure 10 As shown, the primary circuit 11a is a full-bridge circuit, wherein the primary circuit 11a includes an input capacitor Cin, a first bridge arm, and a second bridge arm connected in parallel. The voltage across the input capacitor Cin is the input voltage Vin. The first bridge arm includes a first primary switch S11 and a second primary switch S12 connected in series. Node B between the first and second primary switches S11 and S12 is connected to the second primary terminal 122. The second bridge arm includes a third and fourth primary switch S13 and S14 connected in series. Node A between the third and fourth primary switches S13 and S14 is connected to the first primary terminal 121. All primary switches in the primary circuit 11a can achieve zero voltage turn-on. Figure 11 for Figure 10 Schematic diagram of the key waveforms of the three-level rectifier DC / DC converter when its secondary side switches adopt positive sequence control. Figure 12 for Figure 10 Schematic diagram of the key waveforms of a three-level rectifier DC / DC converter when its secondary side switches adopt positive sequence control and partial synchronous rectification. Figure 13 for Figure 10 The key waveform diagram of the three-level rectifier DC / DC converter when its secondary side switch adopts positive sequence control and full synchronous rectification. Correspondingly, the key waveform diagram of the three-level rectifier DC / DC converter 1 when adopting negative sequence control can be based on Figures 11 to 13 The inference is that I will not elaborate on it here.

[0110] In some embodiments, such as Figure 14As shown, the primary circuit 11b is a flying capacitor three-level circuit, wherein the primary circuit 11b includes a flying capacitor Cf2, a first bridge arm, and a second bridge arm. The voltage across the first bridge arm is the input voltage Vin, and the two ends of the first bridge arm are respectively connected to the two ends of the second bridge arm. The first bridge arm includes a first input capacitor C1 and a second input capacitor C2 connected in series. The second bridge arm includes a first primary switch S11, a second primary switch S12, a third primary switch S13, and a fourth primary switch S14 connected in series. The two ends of the flying capacitor Cf2 of the primary circuit 11b are respectively connected to the node between the first primary switch S11 and the second primary switch S12 and the node between the third primary switch S13 and the fourth primary switch S14. Node A between the second primary switch S12 and the third primary switch S13 is connected to the first primary terminal 121, and node B between the first input capacitor C1 and the second input capacitor C2 is connected to the second primary terminal 122. All primary switches in the primary circuit 11b can achieve zero voltage turn-on. Figure 15 for Figure 14 Schematic diagram of the key waveforms of the three-level rectifier DC / DC converter when its secondary side switches adopt positive sequence control. Figure 16 for Figure 14 Schematic diagram of the key waveforms of a three-level rectifier DC / DC converter when its secondary side switches adopt positive sequence control and partial synchronous rectification. Figure 17 for Figure 14 The key waveform diagram of the three-level rectifier DC / DC converter when its secondary side switch adopts positive sequence control and full synchronous rectification. Correspondingly, the key waveform diagram of the three-level rectifier DC / DC converter 1 when adopting negative sequence control can be based on Figures 15 to 17 The inference is that I will not elaborate on it here.

[0111] In summary, this case provides a three-level rectifier DC / DC converter that not only has the characteristics of a resonant circuit but also meets the requirements of bidirectional operation. In addition, it has a secondary-side short-circuit energy storage characteristic, which can be used to achieve high voltage gain output. The maximum voltage across the secondary-side switch tube is half of the output voltage, so devices with lower voltage resistance can be selected, which facilitates the selection of switching devices and reduces costs. In addition, by controlling the four secondary-side switches to be cyclically turned on, the secondary-side circuit can be equivalent to a short circuit during operation to store energy for the resonant inductor, thereby achieving a high-gain voltage output. Furthermore, since the four secondary-side switches are turned on in turn, the four secondary-side switches can naturally have equal current effective values and conduction losses, which facilitates thermal design and selection of switching devices.

[0112] It should be noted that the above description is merely a preferred embodiment for the purpose of illustrating the present invention. The present invention is not limited to the described embodiment. The scope of the present invention is determined by the appended claims. Furthermore, the present invention is subject to various modifications by those skilled in the art, without departing from the scope of protection intended by the appended claims.

Claims

1. A three-level rectifier DC / DC converter, characterized in that: Include: a primary circuit receiving an input voltage and comprising a plurality of primary switches; a resonant cavity circuit comprising a resonant inductor, a resonant capacitor, and a transformer, wherein a first primary terminal and a second primary terminal of the resonant cavity circuit are electrically connected to the primary circuit, a primary winding of the transformer is electrically connected between the first primary terminal and the second primary terminal, a secondary winding of the transformer is electrically connected between the first secondary terminal and the second secondary terminal of the resonant cavity circuit, and a voltage between the first primary terminal and the second primary terminal is a first voltage, and a voltage between the first secondary terminal and the second secondary terminal is a second voltage; and A secondary circuit includes a flying capacitor, a switch bridge arm, and a capacitor bridge arm, wherein the switch bridge arm includes a first secondary switch, a second secondary switch, a third secondary switch, and a fourth secondary switch connected in series in sequence, and the two ends of the flying capacitor are respectively connected to a node between the first secondary switch and the second secondary switch and a node between the third secondary switch and the fourth secondary switch, and the node between the second secondary switch and the third secondary switch is connected to the first secondary end; the capacitor bridge arm includes a first output capacitor and a second output capacitor connected in series, and the node between the first output capacitor and the second output capacitor is connected to the second secondary end, and the two ends of the capacitor bridge arm are respectively connected to the two ends of the switch bridge arm, and the voltage between the two ends of the capacitor bridge arm is the output voltage. The first secondary switch, the second secondary switch, the third secondary switch, and the fourth secondary switch have the same switching frequency. Two consecutive variation cycles of the first voltage have two rising edges and two falling edges. In the two consecutive variation cycles, the first secondary switch is in an on state for at least a preset time period after one of the two falling edges, the second secondary switch is in an on state for at least the preset time period after the other of the two falling edges, the third secondary switch is in an on state for at least the preset time period after one of the two rising edges, and the fourth secondary switch is in an on state for at least the preset time period after the other of the two rising edges.

2. The three-level rectifier DC / DC converter according to claim 1, characterized in that: During the two consecutive change cycles of the first voltage, a first rising edge, a first falling edge, a second rising edge, and a second falling edge appear in sequence; the first secondary switch is in an on state for at least the preset time period after the first falling edge; the second secondary switch is in an on state for at least the preset time period after the second falling edge; the fourth secondary switch is in an on state for at least the preset time period after the first rising edge; and the third secondary switch is in an on state for at least the preset time period after the second rising edge.

3. The three-level rectifier DC / DC converter according to claim 2, characterized in that: Phases of the fourth secondary switch, the first secondary switch, the third secondary switch, and the second secondary switch are sequentially different by 90 degrees.

4. The three-level rectifier DC / DC converter according to claim 2, characterized in that: The switching frequencies of the first secondary switch, the second secondary switch, the third secondary switch, and the fourth secondary switch are equal to half of the frequency of the first voltage.

5. The three-level rectifier DC / DC converter according to claim 1, characterized in that: In the two consecutive variation cycles of the first voltage, a first rising edge, a first falling edge, a second rising edge, and a second falling edge appear in sequence; the first secondary switch is in an on state for at least the preset time period after the second falling edge; the second secondary switch is in an on state for at least the preset time period after the first falling edge; the fourth secondary switch is in an on state for at least the preset time period after the first rising edge; and the third secondary switch is in an on state for at least the preset time period after the second rising edge.

6. The three-level rectifier DC / DC converter according to claim 5, characterized in that: Phases of the second secondary switch, the third secondary switch, the first secondary switch, and the fourth secondary switch are sequentially different by 90 degrees.

7. The three-level rectifier DC / DC converter according to claim 5, characterized in that: The switching frequencies of the first secondary switch, the second secondary switch, the third secondary switch, and the fourth secondary switch are equal to half of the frequency of the first voltage.

8. The three-level rectifier DC / DC converter according to claim 1, characterized in that: The first secondary switch, the second secondary switch, the third secondary switch and the fourth secondary switch are also in an on state during a portion of the time period when the first secondary switch, the second secondary switch, the third secondary switch and the fourth secondary switch are in reverse current flow.

9. The three-level rectifier DC / DC converter according to claim 8, characterized in that: The duty cycle of the first secondary switch, the second secondary switch, the third secondary switch, and the fourth secondary switch is 25%.

10. The three-level rectifier DC / DC converter according to claim 1, characterized in that: The first secondary switch, the second secondary switch, the third secondary switch and the fourth secondary switch are also in an on state during all time periods when the first secondary switch, the second secondary switch, the third secondary switch and the fourth secondary switch are in reverse current flow.

11. The three-level rectifier DC / DC converter according to claim 10, characterized in that: The driving signals of the first secondary switch and the fourth secondary switch are complementary, and the driving signals of the second secondary switch and the third secondary switch are complementary.

12. The three-level rectifier DC / DC converter according to claim 1, wherein: The preset duration is obtained based on the input voltage and the output voltage.

13. The three-level rectifier DC / DC converter according to claim 1, characterized in that: The primary switch and the secondary switch are turned on at zero voltage.

14. The three-level rectifier DC / DC converter according to claim 1, characterized in that: The first voltage is a square wave that is high in half a period and low in the other half a period.

15. The three-level rectifier DC / DC converter according to claim 1, characterized in that: The primary circuit includes an input capacitor, a first bridge arm, and a second bridge arm connected in parallel. The voltage on the input capacitor is the input voltage. The first bridge arm includes a first primary switch and a second primary switch connected in series. The node between the first primary switch and the second primary switch is connected to the second primary end. The second bridge arm includes a third primary switch and a fourth primary switch connected in series. The node between the third primary switch and the fourth primary switch is connected to the first primary end.

16. The three-level rectifier DC / DC converter according to claim 1, characterized in that: The primary circuit includes a flying capacitor, a first bridge arm, and a second bridge arm. The voltage between the two ends of the first bridge arm is the input voltage, and the two ends of the first bridge arm are respectively connected to the two ends of the second bridge arm. The first bridge arm includes a first input capacitor and a second input capacitor connected in series. The second bridge arm includes a first primary switch, a second primary switch, a third primary switch, and a fourth primary switch connected in series in sequence. The two ends of the flying capacitor of the primary circuit are respectively connected to a node between the first primary switch and the second primary switch and a node between the third primary switch and the fourth primary switch. The node between the second primary switch and the third primary switch is connected to the first primary end, and the node between the first input capacitor and the second input capacitor is connected to the second primary end.

17. The three-level rectifier DC / DC converter according to claim 1, characterized in that: In the resonant cavity circuit, the resonant inductor, the primary winding, and the resonant capacitor are connected in series between the first primary end and the second primary end.

18. The three-level rectifier DC / DC converter according to claim 1, wherein: The invention also includes a control module, wherein the control module is structured to obtain an input voltage signal, an output voltage signal and an output current signal respectively reflecting the input voltage, the output voltage and an output current through sensing, and control the operation of the primary side switches and the secondary side switches; the control module includes a regulator, which generates a regulation signal according to the output voltage signal, the output current signal, an output reference voltage and an output reference current.

19. The three-level rectifier DC / DC converter according to claim 18, characterized in that: The control module further includes a voltage-controlled oscillator and a controller. The voltage-controlled oscillator is electrically connected to the regulator and generates a switching frequency of the multiple primary switches according to the adjustment signal. The controller is electrically connected to the voltage-controlled oscillator and generates a conduction time of the multiple secondary switches according to the input voltage signal, the output voltage signal and the switching frequency of the multiple primary switches.

20. The three-level rectifier DC / DC converter according to claim 18, wherein: The control module further includes a PWM controller. The PWM controller is electrically connected to the regulator and generates driving signals for the primary-side switches and the secondary-side switches according to the regulating signal.

21. The three-level rectifier DC / DC converter according to claim 20, characterized in that: The switching frequencies of the multiple primary switches are fixed and greater than the resonant frequency of the resonant cavity circuit.

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