A bidirectional wide-output-voltage multi-resonant converter and a control method thereof

Abstract

The application discloses a bidirectional wide-output-voltage multi-resonance converter and a control method. p and an auxiliary resonant branch composed of an auxiliary switch S1, an inductor L p and a capacitor C m2 are connected in parallel at the midpoint of the two bridge arms of the primary side of the transformer, so that the bidirectional resonant topology is symmetrical, and the soft switching performance is improved. When the converter is in heavy load operation, it works in a double-resonant-cavity (DRT) mode, when the converter is in light load operation, it works in a single-resonant-cavity (SRT) mode, and when the converter is in reverse operation, it works in the DRT mode. The application realizes bidirectional power conversion, and with the aid of mode switching, a wide output voltage range can be realized in a relatively narrow switching frequency variation range. The proposed topology utilizes a multi-resonance network, improves the conversion efficiency in the full load range, and reduces the voltage / current stress of the resonant inductor and the resonant capacitor.

Description

Technical Field

[0001] This invention relates to the field of bidirectional isolated DC-DC converter technology, and in particular to a bidirectional wide output voltage multiresonant converter and its control method. Background Technology

[0002] In energy storage systems and electric vehicle charging systems, energy can flow bidirectionally between the energy storage device and the DC bus. Therefore, research on isolated bidirectional DC-DC converters has significant research value and application prospects. Since the terminal voltage of the energy storage unit fluctuates considerably with changes in state of charge (SOC), the converter needs to have a wide voltage gain capability. For example, in the on-board charger (OBC) system of new energy vehicles, the voltage of the power battery pack typically varies within the range of 250V to 450V. As the charging process progresses, the battery terminal voltage gradually increases. Therefore, the DC-DC converter needs to maintain high efficiency operation over a wide output voltage range to meet the requirements of the battery's full charging process. To achieve a wide voltage gain range, two main approaches are explored: first, improving the existing LLC converter topology; and second, optimizing the modulation strategy and control algorithm of the LLC converter. These two methods often complement and permeate each other in practical designs. However, existing improved LLC resonant converters often suffer from difficulty in achieving soft-switching characteristics, leading to efficiency degradation; simultaneously, the resonant elements experience high current and voltage stresses, placing higher demands on device selection and overcurrent and overvoltage protection capabilities. The goal is to improve the voltage gain over a wide range, at the expense of converter efficiency. Therefore, scholars both domestically and internationally have conducted extensive research on wide output voltage ranges.

[0003] To address the issues inherent in LLC resonant converters, the published paper "Hybrid Variable Frequency LLC Resonant Converter With Wide Output Voltage Range" proposes a hybrid variable frequency LLC resonant converter. This converter achieves a 7:1 voltage ratio through three-mode hybrid modulation (low gain LG, medium gain MG, and high gain HG), covering a wide range of charging needs, including electric vehicles and supercapacitors. However, it fails to achieve wide gain across a narrow switching frequency range in high-gain mode during light-load operation, and the large magnetizing inductor requirement poses a significant challenge to the design of magnetic components.

[0004] The published paper, "A Novel Multiresonant DC-DC Converter With Wide Output-Voltage Range," achieves a wide gain range of 0.28 to 1.41 within a narrow switching frequency range by introducing a multiresonant network. It also utilizes the reuse of third harmonic energy to transmit active power, reducing reactive circulating current losses and improving efficiency. However, the circulating current is relatively large, and the voltage and current stress on the resonant components is high, placing higher demands on component selection and overcurrent and overvoltage protection design. Summary of the Invention

[0005] The purpose of this invention is to provide a bidirectional wide-output-voltage multiresonant converter and its control method. This converter utilizes the characteristics of a notch filter to achieve low voltage gain, has a wide voltage range adjustment capability, avoids cyclic energy loss, and improves efficiency. Simultaneously, it offers advantages such as lower voltage and current stress on its resonant elements. By switching the operating mode of the switching transistor S1, high efficiency is achieved under light load in SRT mode, along with good soft-switching characteristics and the ability to operate near the resonant frequency. Furthermore, this converter supports bidirectional energy flow between the input and output sides, thus addressing the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A bidirectional wide output voltage multi-resonant converter includes a main circuit and a control circuit. The main circuit includes an input-side voltage divider sampling circuit, an input-side bridge circuit, an L-LLC resonant network, an auxiliary resonant branch, a high-frequency isolation transformer T1, an output-side bridge circuit, and an output-side voltage and current sampling circuit. The auxiliary resonant branch is connected in parallel across the L-LLC resonant network. The control circuit includes a signal conditioning circuit, a DSP digital controller, and a PWM drive circuit in sequence along the signal flow direction. The analog electrical signals collected by the input-side voltage divider sampling circuit and the output-side voltage and current sampling circuit are sent to the signal conditioning circuit for preprocessing and then transmitted to the DSP digital controller. The DSP digital controller outputs multiple PWM control signals to the PWM drive circuit, which drives the input-side bridge circuit switch, the output-side bridge circuit switch, and the auxiliary switch S1, respectively.

[0008] Furthermore, the auxiliary resonant branch consists of the auxiliary switch S1 and the resonant inductor L. p and resonant capacitor C p The high-frequency isolation transformer T1 consists of an additional inductor L connected in parallel at the midpoint of the two bridge arms on the primary side. m2 .

[0009] Furthermore, the converter includes two operating modes: single-cavity mode and dual-cavity mode.

[0010] Under heavy load conditions during forward operation of the converter, the DSP digital controller outputs a drive signal to turn on the auxiliary switch S1, and the auxiliary resonant branch is connected in parallel with the L-LLC resonant network, operating in dual resonant cavity mode.

[0011] Under light load conditions during forward operation of the converter, the DSP digital controller outputs a drive signal to turn off the auxiliary switch S1, the auxiliary resonant branch is disconnected, the L-LLC resonant network works, and it operates in single resonant cavity mode.

[0012] When the converter is running in reverse, the operating mode is switched by controlling the on / off state of the auxiliary switch S1, achieving a wide output voltage range within a narrow switching frequency range, and operating in dual resonant cavity mode.

[0013] Furthermore, the input-side bridge circuit is composed of switching transistors Q1 to Q4 forming a full-bridge inverter circuit, and the output-side bridge circuit is composed of switching transistors Q5 to Q8 forming a full-bridge circuit. When running in the forward direction, it functions as a rectifier circuit, and when running in the reverse direction, it functions as an inverter circuit.

[0014] Furthermore, the L-LLC resonant network includes a resonant inductor L r Resonant capacitor C r and transformer magnetizing inductance L m1 Resonant inductor L r With resonant capacitor C r The first resonant branch is formed to generate the first resonant frequency f. r1 Resonant inductor L p With resonant capacitor C p The second resonant branch is formed to generate the second resonant frequency f. r2 The two branches, when connected in parallel, form a parallel resonant frequency f. rp The second resonant frequency f r2 Matching input-side bridge circuit outputs square wave V ab The third harmonic frequency is used to generate a third harmonic current in the auxiliary resonant branch, which together with the fundamental current of the L-LLC resonant network transmits active power.

[0015] Furthermore, the first resonant frequency f r1 The second resonant frequency f r2 and parallel resonant frequency f rp The calculation formulas can be expressed as follows:

[0016]

[0017]

[0018]

[0019] When the operating frequency fs =f r1 At this time, the converter output voltage corresponds to the rated value. At this point, the voltage gain in both single-cavity and dual-cavity modes is 1. When the operating frequency f... s <f r1 At this time, the single-cavity mode and the dual-cavity mode have similar voltage gain characteristics. The auxiliary resonant branch forms a notch filter structure, which widens the overall voltage gain adjustment range of the converter.

[0020] Furthermore, the additional inductance L m2 Inductance value and transformer magnetizing inductance L m1 same.

[0021] Furthermore, the auxiliary resonant branch calculates the output reference power by sampling the output voltage and output current in real time, and then uses a preset switching power P. switch As a mode switching threshold, when the output reference power is lower than P switch When the output reference power is higher than P, the converter operates in single-cavity mode, suitable for light-load operation; when the output reference power is higher than P... switch When the load is high, the system switches to dual-resonant cavity mode to meet heavy-load requirements. The preset switching power P... switch The calculation formula is as follows:

[0022]

[0023] Where n is the transformer turns ratio, V o The output voltage is given by k, where k is the ratio of the magnetizing inductance to the resonant inductance in SRT mode, and G is the output voltage. max L is the maximum voltage gain. r C represents the resonant inductance value in single-cavity mode. r This represents the resonant capacitance value in single-cavity mode.

[0024] A control method applied to a bidirectional wide-output voltage multiresonant converter includes the following steps:

[0025] Step 1: The output voltage and current sampling circuit samples the output voltage and current of the main circuit. The sampled signal is converted from digital to analog by the signal conditioning circuit and finally input to the DSP digital controller.

[0026] Step two: During forward operation of the converter, the DSP digital controller determines whether the system is operating in CC mode or CV mode based on the detected converter output voltage. Once the converter completes CC mode, it enters CV mode and outputs power P... o With switching power P switchThe comparison is made to determine whether the converter has entered the light load working state. The output PWM modulation signal is used to control the auxiliary switch S1 to turn on and off. The converter switches between the single resonant cavity and dual resonant cavity working modes. When the converter is running in reverse, it operates in the dual resonant cavity mode. Its working characteristics are consistent with those of the converter when it is running in forward heavy load.

[0027] Step 3: Employ a closed-loop negative feedback mechanism to reduce the converter's output voltage V. o Compared with the reference output voltage V ref A dynamic comparison is performed to generate an error signal. After phase correction and gain adjustment, the error signal is input to the PWM controller to control the primary and secondary side switching transistors Q1~Q8 to conduct alternately, thereby realizing power transmission control.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] 1. This invention proposes a system consisting of an auxiliary switch S1 and a resonant inductor L. p and resonant capacitor C p The multi-resonant network composed of components allows the converter to operate in DRT mode at high power and SRT mode at low power by controlling the on / off state of auxiliary switch S1. The control structure is simple. In DRT mode, L r C r With L p C p Parallel connection to form a notch filter enables wide voltage gain adjustment within a narrow switching frequency range and provides excellent soft-switching characteristics, supporting soft-start and overcurrent protection. Furthermore, the introduced auxiliary resonant branch reduces the voltage and current stress on the resonant elements under the same transmission power, decreasing the effective value of the loop current and thus reducing the conduction losses of the switching devices.

[0030] 2. This invention proposes that the converter controls the on / off state of the main switch and auxiliary switch S1 through PWM modulation signal. The topology switching mechanism (SRT or DRT mode switching) reduces the resonant cavity loss under light load. Combining the efficiency advantages of SRT and DRT modes, and the use of the third harmonic to transmit active power in DRT mode to reduce reactive circulating current loss, the converter maintains high overall efficiency across the entire load range and is always in the optimal operating state. The multi-resonant network characteristics of DRT mode allow it to adjust the output with only frequency conversion control, simplifying the control process. The auxiliary inductor also plays a role in balancing the topology symmetry.

[0031] 3. The additional inductance L introduced in this invention m2 This not only optimizes the soft-switching performance of the converter but also effectively improves the asymmetry of its bidirectional operating performance. During forward operation, L, connected in parallel to the midpoint of the primary side bridge arm... m2The voltage at the midpoint clamps the circuit and prevents it from participating in the resonance process, thus not affecting the forward gain characteristics. Similarly, during reverse operation, the magnetizing inductance L on the secondary side... m1 It is also clamped by the midpoint voltage of the secondary bridge arm and does not participate in resonance, so it does not affect the reverse gain characteristics. This makes the converter have completely consistent gain characteristics in both forward (DRT mode) and reverse operation states. Therefore, it is only necessary to analyze the forward power transmission direction to fully characterize its gain behavior. Attached Figure Description

[0032] Figure 1 This is a topology diagram of a bidirectional LLC-LC multiresonant converter;

[0033] Figure 2 This is a partial circuit structure diagram of the SRT mode;

[0034] Figure 3 This is a partial circuit structure diagram of the DRT mode;

[0035] Figure 4 V is in forward operation DRT working mode in 400V, V o The main operating waveform at 450V;

[0036] Figure 5 The equivalent circuit diagram of the multiresonator converter obtained using the fundamental wave analysis method is shown below.

[0037] Figure 6 Normalized DC voltage gain curves for DRT and SRT modes;

[0038] Figure 7 The logic control flowchart for switching the operating modes of a multi-resonant converter;

[0039] Figure 8 The closed-loop control block diagram for mode switching of a multi-resonant converter;

[0040] Figure 9 A graph showing the charging characteristics of the charging power supply.

[0041] In the attached diagram: V gs1 V gs4 V is the drive signal for switching transistors Q1 and Q4. gs2 V gs3 V is the drive signal for switching transistors Q2 and Q3. gs5 V gs8 This is the drive signal for switching transistors Q5 and Q8, V gs6 V gs7 This is the drive signal for switching transistors Q6 and Q7, V gs_S1 S1 is the drive signal, i Lm1 i is the magnetizing inductance current of the transformer.Lm2 To assist the inductor current, i Lp For the resonant inductor current, V s i is the secondary voltage of the transformer. s V is the secondary current of the transformer. in I is the primary input voltage. in V is the primary input current. o For the secondary output voltage, I o This is the secondary-side output current. Detailed Implementation

[0042] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] like Figure 1 As shown, a bidirectional wide output voltage multi-resonant converter includes a main circuit 1 and a control circuit 2. The main circuit 1 includes an input-side voltage divider sampling circuit 3, an input-side bridge circuit 4, an L-LLC resonant network 5, an auxiliary resonant branch 6, a high-frequency isolation transformer T17, an output-side bridge circuit 8, and an output-side voltage and current sampling circuit 9. The auxiliary resonant branch 6 is connected in parallel across the L-LLC resonant network 5. The control circuit 2 includes a signal conditioning circuit 10, a DSP digital controller 11, and a PWM drive circuit 12 in sequence along the signal flow direction. The analog electrical signals collected by the input-side voltage divider sampling circuit 3 and the output-side voltage and current sampling circuit 9 are sent to the signal conditioning circuit 10 for preprocessing and then transmitted to the DSP digital controller 11. The DSP digital controller 11 outputs multiple PWM control signals to the PWM drive circuit 12. The PWM drive circuit 12 drives the switching transistors of the input-side bridge circuit 4, the output-side bridge circuit 8, and the auxiliary switch S1, respectively.

[0044] Furthermore, this converter employs a multi-resonant topology, utilizing the resonant inductor L of a traditional LLC resonant converter. r Resonant capacitor C r A parallel circuit consisting of an auxiliary switch S1 and a resonant inductor L is connected. p and resonant capacitor C p The auxiliary resonant branch 6, which is composed of this circuit, utilizes its notch filter characteristics to broaden the output voltage gain of the proposed converter. An additional inductor L is connected in parallel at the midpoint of the two bridge arms on the primary side of the high-frequency isolation transformer T17. m2 Inductance value and transformer magnetizing inductance L m1 Similarly, it achieves symmetry in the bidirectional resonant topology and improves the soft-switching performance of the converter.

[0045] It should be noted that the additional inductance L m2 Connected in parallel to the midpoint of the two arms of the transformer primary side, it is clamped by the midpoint voltage during forward operation and does not participate in the resonance process, thus not affecting the forward gain characteristics; during reverse operation, the magnetizing inductance L on the secondary side... m1 The voltage clamped at the midpoint of the secondary bridge arm prevents it from participating in resonance and does not affect the reverse gain characteristics, thus ensuring that the converter has completely consistent gain characteristics in both forward and reverse operation states.

[0046] The converter includes two operating modes: single-cavity mode and dual-cavity mode.

[0047] Under heavy load conditions during forward operation of the converter, the DSP digital controller 11 outputs a drive signal to turn on the auxiliary switch S1, and the auxiliary resonant branch 6 is connected in parallel with the L-LLC resonant network 5, operating in dual resonant cavity mode.

[0048] Under light load conditions during forward operation of the converter, the DSP digital controller 11 outputs a drive signal to turn off the auxiliary switch S1, the auxiliary resonant branch 6 is disconnected, the L-LLC resonant network 5 is working, and it operates in single resonant cavity mode.

[0049] When the converter is running in reverse, the operating mode is switched by controlling the on / off state of the auxiliary switch S1, achieving a wide output voltage range within a narrow switching frequency range, and operating in dual resonant cavity mode.

[0050] By controlling the on / off state of the auxiliary switch S1, the operating mode can be switched, achieving a wide output voltage range within a narrow switching frequency variation range.

[0051] Dual-cavity resonant (DRT) mode enables a wide voltage gain range, which is beneficial for obtaining inherent overcurrent protection capabilities. The added inductance L... m2 This not only optimizes the soft-switching performance of the converter but also improves the asymmetry of bidirectional operating performance. By controlling the on / off state of the auxiliary switch S1, the operating mode can be switched: heavy load operation in dual-cavity resonant (DRT) mode and light load operation in single-cavity resonant (SRT) mode, thus achieving both a wide output voltage range and high efficiency within a narrow switching frequency range.

[0052] This resonant network achieves bidirectional symmetrical operation and efficient energy transfer through parameter configuration. Resonant inductor L r With resonant capacitor C r Determine the first resonant frequency f r1 Resonant inductor L p With resonant capacitor C p Determine the second resonant frequency f r2 The resonant frequency of the two in parallel is f rpTo achieve bidirectional symmetry, the values ​​of the transformer's magnetizing inductance and auxiliary inductance must satisfy L. m1 =L m2 Compared to traditional resonant converters that only utilize the fundamental frequency for energy transmission, the proposed multi-resonant converter, through reasonable design of resonant parameters, achieves a second resonant frequency f. r2 Designed to output a square wave voltage V close to that of a primary-side bridge topology circuit. ab The third harmonic frequency excites the auxiliary resonant branch to generate a third harmonic current, which, together with the fundamental current of the original resonant circuit, shares the energy transmission, thereby improving the power transmission capability of the resonant cavity. Since the parallel-operating auxiliary resonant branch bears part of the resonant energy, it reduces the resonant capacitance C. r The proposed multi-resonant topology effectively suppresses high-order harmonic current components and improves the resonant current waveform by mitigating voltage stress. Simultaneously, the converter switches to single-resonant-cavity (SRT) mode under light load conditions, avoiding the circulating current problem between resonant cavities in traditional multi-resonant topologies, thereby improving the converter's energy transfer efficiency and operating performance across the entire load range.

[0053] like Figures 2-3 As shown, the converter detects the output reference power in real time and switches it to a preset power switching point P. switch By comparing and dynamically adjusting the PWM modulation signal of the auxiliary switch S1, the operating mode is automatically switched: under light load, it operates in SRT mode, where the converter utilizes its advantages of high efficiency under light load and good soft-switching characteristics, operating near the resonant frequency, and thus achieving high-efficiency operation at the rated operating point; under heavy load, it switches to DRT mode. In DRT mode, the auxiliary inductor L... m2 The notch filter, composed of a resonant capacitor, widens the voltage gain range, thereby achieving a wide voltage output within a narrow switching frequency range. Simultaneously, under the condition of transmitting the same power, the DRT mode reduces the effective value of the primary-side current compared to the SRT mode. This not only reduces the conduction losses of the switching devices and the voltage and current stress on the resonant elements, but also further improves the overall efficiency of the converter.

[0054] Furthermore, the auxiliary resonant branch calculates the output reference power by sampling the output voltage and output current in real time, and then uses a preset switching power P. switch As a mode switching threshold, when the output reference power is lower than P switch When the output reference power is higher than P, the converter operates in single-cavity mode, suitable for light-load operation; when the output reference power is higher than P... switch When the load is high, the system switches to dual-resonant cavity mode to meet heavy-load requirements. The preset switching power P... switch The calculation formula is as follows:

[0055]

[0056] Where n is the transformer turns ratio, V o The output voltage is given by k, where k is the ratio of the magnetizing inductance to the resonant inductance in SRT mode, and G is the output voltage. max L is the maximum voltage gain. r C represents the resonant inductance value in single-cavity mode. r This represents the resonant capacitance value in single-cavity mode.

[0057] like Figure 4 As shown, during forward operation, it is in DRT working mode, and switch S1 remains on. The primary-side full-bridge inverter circuit consists of two sets of switches, Q1, Q4 and Q2, Q3, which alternately and complementaryly conduct under the drive of the frequency modulation control signal. At this time, the secondary-side switches are all off, and the secondary-side rectification function is achieved by relying on the rectifier diodes. During the dead time, the resonant current charges and discharges the parasitic capacitance of the primary-side MOSFET, so that the primary-side MOSFET F achieves zero-voltage conduction. The output-side bridge circuit (8) consists of switches Q5~Q8 forming a full-bridge circuit, which acts as a rectifier circuit during forward operation and as an inverter circuit during reverse operation.

[0058] Furthermore, the L-LLC resonant network 5 includes a resonant inductor L r Resonant capacitor C r and transformer magnetizing inductance L m1 Resonant inductor L r With resonant capacitor C r The first resonant branch is formed to generate the first resonant frequency f. r1 Resonant inductor L p With resonant capacitor C p The second resonant branch is formed to generate the second resonant frequency f. r2 The two branches, when connected in parallel, form a parallel resonant frequency f. rp The second resonant frequency f r2 Matching input-side bridge circuit outputs square wave V ab The third harmonic frequency is used to generate the third harmonic current in the auxiliary resonant branch 6, which together with the fundamental current of the L-LLC resonant network 5 transmits active power.

[0059] like Figure 5 As shown, in dual-cavity resonant converter (DRT) mode, series resonance occurs. When the impedance is zero, the first resonant frequency f is... r1 The second resonant frequency f r2 They can be represented as:

[0060]

[0061]

[0062] In dual-cavity resonant converter (DRT) mode, parallel resonance occurs. When the impedance is infinite, the resonant frequency f is... rp They can be represented as:

[0063]

[0064] When the operating frequency f s =f r1 At this time, the converter output voltage corresponds to the rated value. At this point, the voltage gain in both single-cavity and dual-cavity modes is 1. When the operating frequency f... s <f r1 At this time, the single-cavity mode and the dual-cavity mode have similar voltage gain characteristics. The auxiliary resonant branch 6 forms a notch filter structure, which widens the overall voltage gain adjustment range of the converter.

[0065] The equivalent resistance of the secondary side in SRT and DRT modes is:

[0066]

[0067] Where R is the load resistance and n is the transformer turns ratio.

[0068] like Figure 6 As shown, the normalized voltage gain of the converter resonant cavity in DRT mode is:

[0069]

[0070] In the formula, , , , , ,

[0071] The normalized voltage gain of the converter in SRT mode is:

[0072]

[0073] Among them, L r It is a resonant inductor. L p To assist the resonant inductor, C r For resonant capacitance, C p As an auxiliary resonant capacitor, L m For the magnetizing inductance, f s This refers to the operating frequency.

[0074] like Figure 7As shown, initial parameters are first set according to the system design specifications. The inductance ratio k and quality factor Q are then determined based on the minimum and maximum voltage gain requirements, and the gain requirements are iteratively checked to determine if they are met. Once the gain requirements are met, the device stress and soft-switching conditions are further verified; if not, the design parameters are readjusted. Finally, based on satisfying all constraints, the parameters of each component in the resonant network are calculated, completing the converter parameter design.

[0075] like Figure 8 As shown, the input and output voltages of the converter are acquired in real time and dynamically compared with a reference value to generate an error signal. This signal, after phase correction and gain adjustment, is input to the PWM controller to control the primary and secondary side switches to alternately conduct in order to achieve power transfer. At the same time, the DSP digital controller compares the output power with the preset switching power to determine the operating mode, and outputs a PWM modulation signal accordingly to control the on / off state of the auxiliary switch S1, enabling the converter to switch between SRT and DRT modes.

[0076] like Figure 9 As shown, the system initially operates in constant current charging mode. When the output voltage reaches the constant voltage operating set value V... o_cv When charging mode switches to constant voltage operation, the output power reaches its maximum value. During constant voltage operation, if the output power P... o The switching power P drops below the preset value. switch Then, the resonant cavity operating mode is switched, changing from DRT mode to SRT mode.

[0077] The control method for a bidirectional wide-output voltage multiresonant converter includes the following steps:

[0078] The output voltage and current sampling circuit 9 samples the output voltage and current of the main circuit. The sampled signal is converted from digital to analog by the signal conditioning circuit 10 and finally input to the DSP digital controller 11.

[0079] When the converter is running in the forward direction, the DSP digital controller 11 determines whether the system is operating in CC mode or CV mode based on the detected converter output voltage. After the converter completes CC mode, it enters CV mode and outputs power P. o With switching power P switch The comparison is made to determine whether the converter has entered the light load working state. The output PWM modulation signal is used to control the auxiliary switch S1 to turn on and off. The converter switches between the single resonant cavity and dual resonant cavity working modes. When the converter is running in reverse, it operates in the dual resonant cavity mode. Its working characteristics are consistent with those of the converter when it is running in forward heavy load.

[0080] A closed-loop negative feedback mechanism is adopted to reduce the output voltage V of the converter. o Compared with the reference output voltage Vref A dynamic comparison is performed to generate an error signal. After phase correction and gain adjustment, the error signal is input to the PWM controller to control the primary and secondary side switching transistors Q1~Q8 to conduct alternately, thereby realizing power transmission control.

[0081] In summary, this multiresonant converter improves performance by adding an auxiliary switch S1 to achieve dynamic switching of operating modes (SRT mode and DRT mode), as detailed below:

[0082] In DRT mode, the converter can achieve a wider voltage gain over a narrow switching frequency range, and can achieve soft start and overcurrent protection functions.

[0083] Through this topology switching mechanism, the converter can select the optimal mode based on the load (heavy-load DRT and light-load SRT modes), achieving overall high-efficiency operation. Simultaneously, the multi-resonant network in DRT mode allows for output adjustment primarily through frequency converter control, simplifying the circuit control process. Auxiliary inductor L m2 The introduction of this technology optimizes the bidirectional operational symmetry of the circuit topology. This converter reuses third harmonic energy to transmit active power, reducing reactive circulating current losses and improving efficiency. Furthermore, the introduction of the DRT mode reduces voltage and current stress on resonant components and lowers the effective value of the loop current, thus improving converter efficiency.

[0084] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A bidirectional wide output voltage multiresonant converter, comprising a main circuit (1) and a control circuit (2), characterized in that, The main circuit (1) includes an input-side voltage divider sampling circuit (3), an input-side bridge circuit (4), an L-LLC resonant network (5), an auxiliary resonant branch (6), a high-frequency isolation transformer T1 (7), an output-side bridge circuit (8), and an output-side voltage and current sampling circuit (9). The auxiliary resonant branch (6) is connected in parallel across the L-LLC resonant network (5). The control circuit (2) includes a signal conditioning circuit (10), a DSP digital controller (11), and a PWM drive circuit (12) in sequence along the signal flow direction. The analog electrical signals collected by the input-side voltage divider sampling circuit (3) and the output-side voltage and current sampling circuit (9) are sent to the signal conditioning circuit (10) for preprocessing and then transmitted to the DSP digital controller (11). The DSP digital controller (11) outputs multiple PWM control signals to the PWM drive circuit (12). The PWM drive circuit (12) drives the switching transistors of the input-side bridge circuit (4), the output-side bridge circuit (8), and the auxiliary switch S1, respectively.

2. The bidirectional wide output voltage multiresonant converter according to claim 1, characterized in that, The auxiliary resonant branch (6) consists of the auxiliary switch S1 and the resonant inductor L. p and resonant capacitor C p Composition: A high-frequency isolation transformer T1 (7) has an additional inductor L connected in parallel at the midpoint of the two primary arms of the bridge. m2 .

3. A bidirectional wide output voltage multiresonant converter according to claim 1, characterized in that, The converter includes two operating modes: single-cavity mode and dual-cavity mode. Under heavy load conditions during forward operation of the converter, the DSP digital controller (11) outputs a drive signal to turn on the auxiliary switch S1, and the auxiliary resonant branch (6) is connected in parallel with the L-LLC resonant network (5), operating in dual resonant cavity mode. Under light load conditions during forward operation of the converter, the DSP digital controller (11) outputs a drive signal to turn off the auxiliary switch S1, the auxiliary resonant branch (6) is disconnected, the L-LLC resonant network (5) is working, and it operates in single resonant cavity mode. When the converter is running in reverse, the operating mode is switched by controlling the on / off state of the auxiliary switch S1, achieving a wide output voltage range within a narrow switching frequency range, and operating in dual resonant cavity mode.

4. A bidirectional wide output voltage multiresonant converter according to claim 1, characterized in that, The input-side bridge circuit (4) is a full-bridge inverter circuit composed of switching transistors Q1 to Q4, and the output-side bridge circuit (8) is a full-bridge circuit composed of switching transistors Q5 to Q8. When running in the forward direction, it serves as a rectifier circuit, and when running in the reverse direction, it serves as an inverter circuit.

5. A bidirectional wide output voltage multiresonant converter according to claim 2, characterized in that, The L-LLC resonant network (5) includes the resonant inductor L r Resonant capacitor C r and transformer magnetizing inductance L m1 Resonant inductor L r With resonant capacitor C r The first resonant branch is formed to generate the first resonant frequency f. r1 Resonant inductor L p With resonant capacitor C p The second resonant branch is formed to generate the second resonant frequency f. r2 The two branches, when connected in parallel, form a parallel resonant frequency f. rp The second resonant frequency f r2 Matching input-side bridge circuit outputs square wave V ab The third harmonic frequency of the auxiliary resonant branch (6) generates the third harmonic current, which together with the fundamental current of the L-LLC resonant network (5) transmits active power.

6. A bidirectional wide output voltage multiresonant converter according to claim 5, characterized in that, The first resonant frequency f r1 The second resonant frequency f r2 and parallel resonant frequency f rp The calculation formulas can be expressed as follows: When the operating frequency f s =f r1 At this time, the converter output voltage corresponds to the rated value. At this point, the voltage gain in both single-cavity and dual-cavity modes is 1. When the operating frequency f... s <f r1 At this time, the single-cavity mode and the dual-cavity mode have similar voltage gain characteristics. The auxiliary resonant branch (6) forms a notch filter structure, which broadens the overall voltage gain adjustment range of the converter.

7. A bidirectional wide output voltage multiresonant converter according to claim 5, characterized in that, Additional inductor L m2 Inductance value and transformer magnetizing inductance L m1 same.

8. A bidirectional wide output voltage multiresonant converter according to claim 5, characterized in that, The auxiliary resonant branch calculates the output reference power by sampling the output voltage and output current in real time, and then uses a preset switching power P. switch As a mode switching threshold, when the output reference power is lower than P switch When the output reference power is higher than P, the converter operates in single-cavity mode, suitable for light-load operation; when the output reference power is higher than P... switch When the load is high, the system switches to dual-resonant cavity mode to meet heavy-load requirements. The preset switching power P... switch The calculation formula is as follows: Where n is the transformer turns ratio, V o The output voltage is given by k, where k is the ratio of the magnetizing inductance to the resonant inductance in SRT mode, and G is the output voltage. max L is the maximum voltage gain. r C represents the resonant inductance value in single-cavity mode. r This represents the resonant capacitance value in single-cavity mode.

9. A control method, applied to the bidirectional wide output voltage multiresonant converter as described in any one of claims 1-8, characterized in that, Includes the following steps: Step 1: The output voltage and current sampling circuit (9) samples the output voltage and current of the main circuit. The sampled signal is converted from digital to analog by the signal conditioning circuit (10) and finally input to the DSP digital controller (11). Step 2: During forward operation of the converter, the DSP digital controller (11) determines whether the system is operating in CC mode or CV mode based on the detected converter output voltage. After the converter completes CC mode, it enters CV mode and outputs power P. o With switching power P switch The comparison is made to determine whether the converter has entered the light load working state. The output PWM modulation signal is used to control the auxiliary switch S1 to turn on and off. The converter switches between the single resonant cavity and dual resonant cavity working modes. When the converter is running in reverse, it operates in the dual resonant cavity mode. Its working characteristics are consistent with those of the converter when it is running in forward heavy load. Step 3, convert the converter's output voltage V o Compared with the reference output voltage V ref A dynamic comparison is performed to generate an error signal. After phase correction and gain adjustment, the error signal is input to the PWM controller to control the primary and secondary side switching transistors Q1~Q8 to conduct alternately, thereby realizing power transmission control.

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