A DC converter topology with output voltage regulation capability

Abstract

The present invention discloses a DC converter topology with output voltage regulation capability, which belongs to the technical field of DC-DC converter topology, and includes two transmission paths for transferring energy from an input port to an output port. The main channel is an LLC resonant converter, which operates at a fixed switching frequency and transfers most of the input energy to a load. The auxiliary channel includes two stages, the first stage uses a small LLC resonant converter to achieve efficient isolation conversion, and then a non-isolated PWM DC converter is cascaded therewith, and the output voltage is adjusted by adjusting the PWM DC converter. The main channel and the auxiliary channel are connected in parallel at the input port and in series at the output port. The present invention simplifies the control strategy and synchronous rectification logic, and most of the input energy is transferred to the load by a single-stage main channel, which significantly reduces energy loss. Therefore, the proposed converter topology achieves high efficiency and high power density.

Description

Technical Field

[0001] The present invention belongs to the technical field of DC-DC converter topology structures, and more specifically, relates to a DC converter topology structure with output voltage regulation capability. Background Art

[0002] Thanks to the rapid development of the information industry, data centers are equipped with more servers, which also increases power consumption. As the output power increases, the power supply occupies more server rack space. In order to reduce energy loss and improve space utilization, it is necessary to achieve high efficiency and high power density in the energy conversion stage.

[0003] Traditional hard-switching pulse width modulation (PWM) converters are widely used in industrial power transmission systems. However, the huge losses caused by hard switching hinder the further improvement of efficiency and power density. Therefore, converters under hard switching are not suitable for server power supplies with high requirements for efficiency and power density.

[0004] Single-stage DC-DC LLC resonant converters are widely used in applications that require electrical isolation and high efficiency. Usually, LLC converters can achieve zero voltage turn-on (ZVS) and turn-off with a smaller turn-off current on the primary switch tube, and zero current turn-off (ZCS) on the secondary switch tube. It greatly reduces switching losses and makes high-frequency switching possible. For a single-stage LLC converter, the output voltage can be adjusted by adjusting the phase shift angle, switching frequency, or duty cycle, but this requires a large resonant inductor, sacrificing efficiency and power density. In addition, it is difficult to obtain an effective control strategy for a high-frequency regulated LLC converter with phase-shift modulation or frequency modulation, and the logic of synchronous rectification is also difficult to implement.

[0005] LLC converter can show the best performance at the series resonant frequency, that is, it can simultaneously achieve zero voltage switch-on (ZVS) of the primary side devices, low current shutdown and zero current shutdown (ZCS) of the secondary side synchronous rectifier, thereby achieving high efficiency and high power density. LLC converters with fixed frequency and no voltage regulation function have been proven to work at MHz, but LLC resonant converters with fixed switching frequency can only provide a fixed transformation ratio, so its output voltage will fluctuate with the input voltage and load current.

[0006] In order to make full use of the advantages of LLC resonant converter and meet the requirements of output voltage regulation, some researchers have proposed a two-stage LLC resonant converter solution. By separating the voltage regulation and electrical isolation functions, each stage can be easily optimized and the control strategy and synchronous rectification logic can be easily implemented. However, in the traditional two-stage structure design, the voltage regulation stage needs to transfer the entire load power, which introduces larger components and reduces efficiency and power density. In order to obtain output regulation capability and improve conversion efficiency, another group of researchers proposed a quasi-single-stage structure, that is, in the sigma converter, most of the energy is directly transmitted to the load by the LLC resonant converter, and only part of the energy is regulated by the buck converter, thereby obtaining output regulation capability and higher conversion efficiency. However, the buck converter cannot achieve electrical isolation. In order to achieve electrical isolation, some new structures have been proposed based on the sigma converter, but there are problems such as increased equipment voltage and current stress and reduced efficiency caused by the circulating energy in the converter.

[0007] Therefore, for the LLC resonant converter operating at a fixed switching frequency and having the ability to regulate output voltage, it is necessary to further optimize its structure and control strategy to improve its power density and efficiency, and to simplify its control strategy and the control logic of synchronous rectification as much as possible to obtain good dynamic performance, that is, to maintain the stability of the output voltage when the input voltage and load vary within a certain range. Summary of the invention

[0008] In view of the defects of the prior art, the purpose of the present invention is to provide a DC converter topology with output voltage regulation capability to solve the technical problems that urgently need to be solved, such as insufficient power density, insufficient efficiency, complex control strategy and difficult implementation of synchronous rectification control logic, etc., of the existing LLC resonant converter with output voltage regulation capability due to its topology structure.

[0009] The technical solution of the present invention to solve the above technical problems is as follows: A DC-DC converter topology structure in which an LLC resonant converter operates at a fixed switching frequency and has an output voltage regulation capability includes two transmission paths for transferring energy from an input port to an output port. The main channel transfers most of the input energy to the output port. The auxiliary channel includes two stages for processing the regulated portion of the input power. The input ports of the main channel and the auxiliary channel are connected in parallel, and the output ports are connected in series;

[0010] Among them, the main channel is an LLC resonant converter, which operates at a fixed switching frequency and transfers most of the input energy to the output port;

[0011] The auxiliary channel consists of two stages. The first stage uses a small LLC resonant converter to achieve efficient isolation conversion. The second stage uses a non-isolated PWM DC-DC converter cascaded with the small LLC resonant converter. The output voltage is adjusted by adjusting the cascaded non-isolated PWM DC-DC converter of the auxiliary channel.

[0012] The beneficial effects of the present invention are as follows: since the voltage regulation of the topological structure is realized at a fixed switching frequency, the structure simplifies the control strategy and synchronous rectification logic. Compared with the commonly used two-stage solution, most of the energy input by the structure is transferred to the load by the main channel of the single stage, and only a small part of the energy is transferred to the load through the auxiliary channel with a two-stage structure, thereby significantly reducing energy loss. Therefore, the proposed converter topological structure achieves high efficiency and high power density.

[0013] Based on the above technical solution, the present invention can also be improved as follows.

[0014] Furthermore, the LLC resonant converter used in the main energy transmission channel and the LLC resonant converter used in the auxiliary energy transmission channel both operate at the series resonant frequency of their respective resonant cavities.

[0015] Furthermore, the switching frequency of the PWM converter used in the energy transmission auxiliary channel is independent of the two LLC resonant converters.

[0016] A further beneficial effect of the present invention is that the LLC resonant converter of the main energy transmission channel and the auxiliary energy transmission channel can obtain a stable transformation ratio, retaining the advantages of high efficiency and high power density of the LLC resonant converter, and does not require additional control of the LLC resonant converter, but only needs to control the PWM converter to adjust the output voltage.

[0017] Furthermore, the LLC resonant converter used in the main energy transmission channel and the LLC resonant converter used in the auxiliary energy transmission channel are designed with appropriate resonant cavity parameters and operate at the same series resonant frequency and duty cycle. In this structure, two completely identical bridge arms are not used to introduce square wave input voltages to the two energy transmission paths respectively. Instead, the two bridge arms are combined into one bridge arm, and the two energy transmission paths are connected to completely identical square wave DC input voltages and output completely identical square wave voltages.

[0018] A further beneficial effect of the present invention is that the topological structure of the circuit is greatly simplified.

[0019] Furthermore, the LLC resonant converter of the main channel and the LLC resonant converter of the auxiliary channel share a set of half-bridge arms consisting of a first switch tube Q1 and a second switch tube Q2, and the input voltage V in After input filter capacitor C inAfter filtering, the signal is applied to both ends of the half-bridge arm formed by the first switch tube Q1 and the second switch tube Q2, and then output from the midpoint of the half-bridge arm formed by the first switch tube Q1 and the second switch tube Q2.

[0020] The main channel includes a first resonant inductor L r1 , the first resonant capacitor C r1 , with first excitation inductance L m1 The first center-tapped transformer T1, the first synchronous rectifier switch tube S1, the second synchronous rectifier switch tube S2 and the first output filter capacitor C o1 , the first resonant inductor L r1 , the first resonant capacitor C r1 With the first excitation inductance L m1 The primary side of the first center-tapped transformer T1 is connected in series to form a first resonant cavity. The input of the first resonant cavity is the voltage output from the midpoint of the half-bridge arm formed by the first switch tube Q1 and the second switch tube Q2. m1 The secondary side of the first center-tapped transformer T1 is connected to a synchronous rectifier composed of a first synchronous rectifier switch tube S1 and a second synchronous rectifier switch tube S2. The voltage output from the secondary side of the first center-tapped transformer T1 is rectified by the first synchronous rectifier switch tube S1 and the second synchronous rectifier switch tube S2, and then rectified by the first output filter capacitor C o1 Filtering.

[0021] Furthermore, the auxiliary channel includes a second resonant inductor L r2 , the second resonant capacitor C r2 , with second excitation inductor L m2 The second center-tapped transformer Tx, the third synchronous rectifier switch tube S3, the fourth synchronous rectifier switch tube S4 and the second output filter capacitor C o2 , the second resonant inductor L r2 , the second resonant capacitor C r2 With the second excitation inductor L m2 The primary side of the second center-tapped transformer T2 is connected in series to form a second resonant cavity. The input of the second resonant cavity is the voltage output from the midpoint of the half-bridge arm formed by the first switch tube Q1 and the second switch tube Q2. m2 The secondary side of the second center-tapped transformer T2 is connected to a synchronous rectifier composed of a third synchronous rectifier switch tube S3 and a fourth synchronous rectifier switch tube S4. The voltage output from the secondary side of the second center-tapped transformer T2 is rectified by the third synchronous rectifier switch tube S3 and the fourth synchronous rectifier switch tube S4, and then rectified by the second output filter capacitor C o2 Filtering.

[0022] Furthermore, the primary switch tubes Q1 and Q2 of the topological structure are gallium nitride devices.

[0023] A further beneficial effect of the present invention is that the turn-off loss of the primary switch tube is greatly reduced.

[0024] Furthermore, the synchronous rectifiers S1 - S4 of the topological structure are silicon devices.

[0025] A further beneficial effect of the present invention is that the conduction loss of the secondary rectifier bridge under high output current conditions is greatly reduced.

[0026] Furthermore, the driving signal of the synchronous rectifier of the topological structure is synchronized with the driving signal of the primary switch tube, and has a fixed frequency and duty cycle.

[0027] Through the above technical solutions conceived by the present invention, compared with the prior art, the present invention simplifies the control strategy and synchronous rectification logic, and most of the input energy is transferred to the load by the main channel of the single stage, which significantly reduces the energy loss. Therefore, the proposed converter topology achieves high efficiency and high power density. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a brief schematic block diagram of the DC converter topology proposed in the present invention;

[0029] Figure 2 It is a schematic diagram of the original circuit topology structure of the DC converter proposed in the present invention;

[0030] Figure 3 It is a schematic diagram of a simplified circuit topology structure of a DC converter proposed in the present invention;

[0031] Figure 4 It is the main waveform diagram of the DC converter proposed in the present invention in steady state;

[0032] Figure 5 is the equivalent circuit diagram of each stage of the DC converter proposed in the present invention in steady state, where (a), (b), and (c) are respectively Figure 4 The equivalent circuit diagram corresponding to the time periods t0~t1, t1~t2, and t2~t3;

[0033] Figure 6 It is a schematic diagram of the circuit topology structure of the DC converter provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0035] Figure 1The present invention is a schematic diagram of the topological structure of the DC converter and the principle of adjusting the output voltage thereof. In this topological structure, the process of transferring energy from the input port to the output port can be divided into two transmission paths, and these two paths are respectively called the main channel and the auxiliary channel as channels for energy transfer. Among them, the main channel transfers most of the input energy to the output port, and the main channel is composed of only one LLC resonant converter working at a fixed switching frequency. Specifically, the main channel of energy transmission is composed of a single LLC resonant converter working at a fixed switching frequency, which converts the input DC voltage into the output DC voltage and undertakes most of the work of the converter transmitting energy. The auxiliary channel is only responsible for transferring most of the input energy to the output port in terms of energy transmission, but it also undertakes the task of adjusting the output voltage. Specifically, the auxiliary channel includes two stages in total, the first stage is a small LLC resonant converter, specifically, it is also an LLC resonant converter working at a fixed switching frequency. The small LLC resonant converter also needs to cascade a non-isolated PWM DC-DC converter in the auxiliary channel, such as a Buck converter, a Boost converter, etc. The cascaded DC converter is used to process the regulated part of the input energy. In addition, the input ports of the main channel and the auxiliary channel are connected in parallel, and the output ports are connected in series.

[0036] exist Figure 1 In, V in is the input voltage of the proposed DC converter. Since the main path and the auxiliary path of energy transmission are connected in parallel to form the DC converter, the input voltages of the main path and the auxiliary path of energy transmission are both V in ; V main is the input voltage V in The output voltage of the main energy transmission path obtained by DC-DC conversion through the LLC resonant converter on the main energy transmission path; P main It is the energy of the total input energy that flows out from the output port after passing through the main energy transmission path; V aux is the input voltage V in The output voltage of the energy transmission auxiliary path is obtained after two DC-DC conversions of the LLC resonant converter and the non-isolated PWM DC converter on the energy transmission auxiliary path; P aux It is the energy of the total input energy that flows out from the output port after passing through the energy transmission auxiliary path; the output voltage V o (V out ) is the total voltage output by the proposed DC converter. Since the main path and the auxiliary path of energy transmission are connected in series at the output port, V o =V main +V aux .

[0037] When the input voltage is Figure 1 As shown in V in When the line graph changes, since the LLC resonant converter on the main energy transmission path operates at a fixed switching frequency, the gain of the output voltage on the main path remains unchanged, that is, V main The changing trend and V in Same, at this time, only V aux The changing trend of V aux The polyline Figure 1 The output voltage V o In this structure, due to V main With V o The two energy transmission paths are very close, and the two energy transmission paths are connected in series, so only a small part of the total input energy passes through the two-stage DC conversion structure of the auxiliary energy transmission path, that is, the energy lost in the hard-switched non-isolated PWM converter is very small. Within a certain adjustment range, the power loss is very small.

[0038] Figure 2 Schematic diagram of the original circuit topology of the DC converter proposed in the present invention, LLC1 is an LLC resonant converter operating at a fixed switching frequency in the main energy transmission path, wherein Q1 and Q2 together constitute a bridge arm for generating an input square wave voltage on the primary side of the transformer, Q1 is the upper switch tube of the bridge arm, Q2 is the lower switch tube of the bridge arm, and L r1 is the resonant inductance of LLC1, C r1 is the resonant capacitor of LLC1, L m1 is the magnetizing inductor of LLC1, T1 is the center-tapped transformer of LLC1, with a turns ratio of n∶1∶1, S1 and S2 are the secondary synchronous rectifier switches of LLC1, V o1 is the output voltage of the main energy transfer path, C o1 It is a capacitor used for output voltage regulation and filtering in the main path of energy transmission.

[0039] LLC2 is a small LLC resonant converter operating at a fixed switching frequency in the auxiliary path of energy transmission. Q3 and Q4 together form a bridge arm for generating an input square wave voltage on the primary side of the transformer. Q3 is the upper switch tube of the bridge arm, and Q4 is the lower switch tube of the bridge arm. r2 is the resonant inductance of LLC2, C r2 is the resonant capacitor of LLC2, L m2 is the excitation inductor of LLC2, T2 is the center-tapped transformer of LLC2, and its turns ratio is m∶1∶1, S3 and S4 are the secondary synchronous rectifier switch tubes of LLC2, V o2 is the output voltage of LLC2, C o2 It is the capacitor used for LLC2 output voltage regulation and filtering. o3is the output voltage of the PWM converter in the auxiliary path of energy transfer, C o3 It is a capacitor used for output voltage regulation and filtering in the auxiliary path of energy transmission. C in is a capacitor used for input voltage regulation and filtering, R L is the load resistance of the proposed converter.

[0040] exist Figure 2 In the proposed circuit topology, the switching frequency of the non-isolated PWM converter is independent of the two LLC resonant converters. By changing the duty cycle of the PWM converter, the output voltage of the auxiliary energy transmission path can be adjusted, thereby adjusting the output voltage of the entire converter. Since the factors that cause the output voltage change in the proposed circuit topology are mainly the input voltage and the load current, the duty cycle of the PWM converter is jointly determined by the output voltage and the load current through a feedback control loop.

[0041] Figure 3 This is a simplified circuit topology diagram of the DC converter proposed in the present invention. In the present invention, since LLC1 and LLC2 both operate at a fixed switching frequency, and the LLC resonant converter can turn on the primary switch tube at zero voltage and turn off at low voltage when the switching frequency is equal to the series resonant frequency of the resonant cavity, and the secondary rectifier can turn off at zero current, it has the highest efficiency and power density and the best performance. Therefore, in the present invention, LLC1 and LLC2 both operate at the series resonant frequency of their respective resonant cavities. By designing the parameters of their respective resonant cavities, the series resonant frequencies of LLC1 and LLC2 are the same, that is, the switching frequencies of LLC1 and LLC2 are the same, so Figure 2 The bridge arm composed of Q1 and Q2 and the bridge arm composed of Q3 and Q4 are combined into Figure 3 The bridge arm is composed of Q1 and Q2.

[0042] By making the two bridge arms work at the same switching frequency, and the switching frequency is the series resonant frequency of LLC1 and LLC2, LLC1 and LLC2 can obtain the best performance, that is, high efficiency and high power density, and the driving signals required by the primary switch tubes and secondary rectifiers of LLC1 and LLC2 are completely consistent, which greatly simplifies the control strategy and control logic of synchronous rectification. Figure 2 The two bridge arms are combined into Figure 3 A bridge arm in the circuit can greatly reduce the complexity of the circuit.

[0043] Figure 4 is the main waveform diagram of the circuit topology of the DC converter proposed in the present invention, Figure 5 (a), (b), and (c) are Figure 4 The equivalent circuit diagram corresponding to the time periods t0~t1, t1~t2, and t2~t3. Figure 4 Medium Vgs_Q1 With V gs_Q2 They are the driving signals of the primary switch tubes Q1 and Q2, respectively. Their frequencies are the series resonant frequencies of LLC1 and LLC2 resonant cavities. V ds_Q is the drain-source voltage of the primary switch tube Q2. r1 is the resonant current of LLC1, i m1 is the excitation current of LLC1, i s1 、i s2 are the currents of the secondary rectifier tube of LLC1. r2 is the resonant current of LLC2, i m2 is the excitation current of LLC2, i s3 、i s4 They are respectively the currents of the secondary rectifier tube of LLC2.

[0044] Figure 5 (a) is the proposed circuit topology. Figure 4 The equivalent circuit diagram of the time period t0 to t1, where Q1 is turned on at t0, the resonant cavity begins to oscillate, and the resonant current is a sine wave. At the same time, the secondary rectifiers S1 and S3 are turned on at t0, and the excitation inductance L m1 is clamped by the output voltage, L m1 The voltage across the two ends is nV o1 , that is, V in / 2; excitation inductance L m2 Also clamped by the output voltage, L m2 The voltage across the two ends is mV o2 , that is, V in / 2. Therefore L m1 and L m2 The current flowing through it increases linearly, the resonant current and the excitation current are offset, and the energy is transferred to the load through Q1, T1, T2, S1, and S3.

[0045] Figure 5 (b) shows the proposed circuit topology. Figure 4 In the equivalent circuit diagram of the time period t1 to t2, during the period t1 to t2, the resonant current and the excitation current are equal, and the current i flowing through the secondary rectifier tube is s1 and i s3When the current is equal to 0, the secondary rectifier tubes S1 and S3 are turned off, realizing the zero current shutdown of the secondary rectifier tube. At the same time, the excitation inductor is no longer clamped by the output voltage, but resonates with the resonant inductor and the resonant capacitor. At time t2, the primary switch tube Q1 is turned off. During the dead time from t1 to t2, the input voltage no longer transfers energy from the primary side to the output side, and the output voltage is maintained by the output capacitor. The most important purpose of setting the dead time is to discharge the body capacitance of the primary switch tube Q2 and the secondary rectifier tubes S2 and S4 through the excitation current until their respective drain-source voltages are equal to 0, thereby realizing zero voltage turn-on in the next stage.

[0046] Figure 5 (c) is the proposed circuit topology. Figure 4 In the equivalent circuit diagram of the time period t2 to t3, at time t2, the primary switch tube Q2 and the secondary rectifier tubes S2 and S4 are turned on, the input voltage is applied to the resonant cavity again, the resonant inductor and the resonant capacitor continue to resonate, and the resonant current is a sine wave. m1 is clamped by the output voltage, L m1 The voltage across the two ends is -nV o1 , that is -V in / 2; excitation inductance L m2 Also clamped by the output voltage, L m2 The voltage across the two ends is -mV o2 , that is -V in / 2. Therefore L m1 and L m2 The current flowing through the upper circuit changes linearly, and the slope of the change is negative. The resonant current and the excitation current are offset, and the energy is transferred to the load through Q2, T1, T2, S2, and S4. At time t3, the resonant current and the excitation current are equal, and the primary switch tube Q2 and the secondary rectifier tubes S2 and S4 are turned off with zero current.

[0047] exist Figure 4 During the time period from t3 to t4, since the primary switch tube Q2 and the secondary rectifier tubes S2 and S4 have been turned off at zero current at t3, the circuit enters another dead time at t3. The equivalent circuit at this time is Figure 5 The excitation inductor is no longer clamped by the output voltage, but resonates with the resonant inductor and the resonant capacitor. At t4, the primary switch Q2 is turned off. During the dead time from t3 to t4, the input voltage no longer transfers energy from the primary side to the output side, and the output voltage is maintained by the output capacitor. During the time period from t3 to t4, the body capacitance of the primary switch Q1 and the secondary rectifiers S1 and S3 are discharged through the excitation current until their respective drain-source voltages are equal to 0, thereby achieving zero voltage turn-on in the next stage.

[0048] Figure 6A schematic diagram of a circuit topology structure of a DC converter provided in an embodiment of the present invention. Figure 1 , 2 The auxiliary energy transmission channel of the circuit topology structure proposed in 3 and 5 requires a non-isolated PWM converter such as a Buck converter or a Boost converter to be cascaded with DCX2. In this embodiment, the non-isolated PWM converter adopts a Buck converter. The Buck converter consists of a pair of bridge arms composed of switch tubes Q3 and Q4, an inductor L1, and a capacitor C o3 The switch tube Q3 is the upper switch tube of the bridge arm, and the switch tube Q4 is the lower switch tube of the bridge arm. The primary switch tube adopts gallium nitride (GaN) equipment to reduce turn-off loss, and the secondary rectifier adopts silicon (Si) equipment to reduce conduction loss.

[0049] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A DC converter topology with output voltage regulation capability, characterized in that: It includes two transmission paths for transferring energy from an input port to an output port: a main channel and an auxiliary channel, wherein the input ports of the main channel and the auxiliary channel are connected in parallel, and the output ports are connected in series; The main channel is an LLC resonant converter, which operates at a fixed switching frequency; the LLC resonant converter of the main channel and the LLC resonant converter of the auxiliary channel share a group of first switching transistors. And the second switch The half-bridge arm is composed of input voltage Input filter capacitor After filtering, the first switch tube and the second switch tube The two ends of the half-bridge bridge arm are then connected from the first switch tube And the second switch The midpoint output of the half-bridge bridge arm is formed; the main channel includes a first resonant inductor , the first resonant capacitor , with first excitation inductor The first center-tapped transformer , the first synchronous rectifier switch tube , the second synchronous rectifier switch and the first output filter capacitor , the first resonant inductor , the first resonant capacitor With the first excitation inductor The first center-tapped transformer The primary side of the first resonant cavity is connected in series to form the first resonant cavity. The input of the first resonant cavity is the first switch tube. And the second switch The voltage output at the midpoint of the half-bridge arm with the first excitation inductor The first center-tapped transformer The secondary side is connected to the first synchronous rectifier switch , the second synchronous rectifier switch The synchronous rectifier is composed of a first center-tapped transformer The voltage output by the secondary side is rectified by the first synchronous rectifier switch. and the second synchronous rectifier switch After rectification, it passes through the first output filter capacitor Filtering; The auxiliary channel comprises two stages, the first stage adopts an LLC resonant converter, the second stage adopts a non-isolated PWM DC-DC converter cascaded with the first stage, and the output voltage is adjusted by adjusting the cascaded non-isolated PWM DC-DC converter of the auxiliary channel; the auxiliary channel comprises a second resonant inductor , the second resonant capacitor , with second excitation inductor The second center-tapped transformer , the third synchronous rectifier switch tube , the fourth synchronous rectifier switch tube and the second output filter capacitor , the second resonant inductor , the second resonant capacitor With second excitation inductor The second center-tapped transformer The primary side of the second resonant cavity is connected in series to form the second resonant cavity. The input of the second resonant cavity is the first switch tube. And the second switch The voltage at the midpoint of the half-bridge arm is output with the second excitation inductor The second center-tapped transformer The secondary side is connected to the third synchronous rectifier switch , the fourth synchronous rectifier switch tube The synchronous rectifier, the second center-tapped transformer The voltage output by the secondary side is passed through the third synchronous rectifier switch tube and the fourth synchronous rectifier switch After rectification, it passes through the second output filter capacitor Filtering; The LLC resonant converter used by the main channel and the LLC resonant converter used by the auxiliary channel both operate at the series resonant frequency of their respective resonant cavities.

2. The DC converter topology structure according to claim 1, characterized in that: The switching frequency of the PWM converter used in the auxiliary channel is independent of the two LLC resonant converters.

3. The DC converter topology structure according to claim 1, characterized in that: The LLC resonant converter used by the main channel and the LLC resonant converter used by the auxiliary channel operate at the same series resonant frequency and duty cycle. The main channel and the auxiliary channel share a bridge arm, are connected to exactly the same DC input voltage, and output exactly the same square wave voltage.

4. The DC converter topology structure according to claim 1, characterized in that: The driving signal of the synchronous rectifier of the topological structure is synchronized with the driving signal of the primary switch tube, and has the same and fixed frequency and duty cycle.

5. The DC converter topology structure according to claim 1, characterized in that: The PWM DC-DC converter is a Buck converter or a Boost converter.

Images