A high-order resonant dc-dc converter based on variable inductance

Abstract

The application relates to a high-order resonant DC converter based on variable inductance, which adopts a resonant topology of an LCLCL resonant network; the resonant inductance Lr, the wave-limiting inductance Ls and the excitation inductance Lm in the LCLCL resonant network are all variable inductances; the high-order resonant DC converter further comprises a resonant frequency detection circuit and an inductance control circuit; the resonant frequency detection circuit is connected in the LCLCL resonant network and is used for detecting the actual resonant frequency of the LCLCL resonant network; the inductance control circuit is used for outputting a control current according to the deviation between the actual resonant frequency and the target resonant frequency of the LCLCL resonant network, controlling the inductance values of the resonant inductance Lr, the wave-limiting inductance Lp and / or the excitation inductance Lm, changing the resonant network impedance, and making the actual resonant frequency of the LCLCL resonant network close to the target resonant frequency. The application offsets the influence of parasitic parameters.

Description

Technical Field

[0001] This invention belongs to the field of power supply technology, specifically relating to a high-order resonant DC-DC converter based on a variable inductor. Background Technology

[0002] Currently, the power supply industry has increasingly higher requirements for efficiency. Resonant switching converters, due to their ability to achieve lower switching losses through soft switching and thus higher efficiency, are being used more and more widely. Among them, LLC resonant converters have become popular products in industrial applications due to their small number of components and simple structure. However, LLC resonant converters still have many problems that need to be solved. These include the need to improve the rated input voltage range, high secondary-side rectification losses, large inrush current at startup, poor frequency modulation performance in the high-frequency range, and low efficiency under light load. These problems have limited the application of LLC resonant converters. Therefore, some researchers have proposed higher-order resonant topologies to solve the above-mentioned problems of LLC resonant converters. Nevertheless, some common problems of resonant converters still remain unresolved, including hard-switching at startup and interference from parasitic parameters on the resonant circuit. Summary of the Invention

[0003] Based on the above analysis, the present invention aims to disclose a high-order resonant DC-DC converter based on a variable inductor, which solves the problems of hard switching at startup and interference of parasitic parameters on the resonant circuit.

[0004] This invention discloses a high-order resonant DC-DC converter based on a variable inductor, employing a resonant topology of an LCLCL resonant network; in the LCLCL resonant network, the resonant inductor Lr, the limiting inductor Ls, and the excitation inductor Lm are all variable inductors;

[0005] The high-order resonant DC-DC converter also includes a resonant frequency detection circuit and an inductor control circuit.

[0006] The resonant frequency detection circuit is connected to the LCLCL resonant network and is used to detect the actual resonant frequency of the LCLCL resonant network.

[0007] The inductor control circuit is used to output a control current based on the deviation between the actual resonant frequency and the target resonant frequency of the LCLCL resonant network, control the inductance values ​​of the resonant inductor Lr, the limiting inductor Lp and / or the excitation inductor Lm, change the impedance of the resonant network, and make the actual resonant frequency of the LCLCL resonant network close to the target resonant frequency.

[0008] Furthermore, in the resonant frequency detection circuit, the fundamental resonant frequency and the third harmonic resonant frequency of the LCLCL resonant network are detected respectively.

[0009] In the inductor control circuit, the errors between the fundamental resonant frequency, the third harmonic resonant frequency and the corresponding target resonant frequency of the detected LCLCL resonant network are determined respectively. When the error exceeds the threshold range, the output control current controls the inductance values ​​of the resonant inductor Lr, the wave limiting inductor Ls and / or the excitation inductor Lm.

[0010] Furthermore, in the inductor control circuit,

[0011] When it is determined that the fundamental resonant frequencies differ significantly, the inductance value of the resonant inductor Lr should be adjusted first.

[0012] When the error of the third harmonic resonant frequency is large, the value of the limiting inductor Lp should be adjusted first.

[0013] When it is determined that both the fundamental resonant frequency and the third harmonic resonant frequency are far from the target resonant frequency, the inductance value of the excitation inductor Lm should be adjusted first.

[0014] Through multiple adjustments, the errors in the fundamental resonant frequency and the third harmonic resonant frequency of the detected LCLCL resonant network were made to fall within the threshold range.

[0015] Furthermore, the structure of the variable inductor includes a central iron core column and two outer iron core columns; two parallel-connected outer coils are wound on the outer iron core columns for connection to an LCLCL resonant network; a control coil is wound on the central iron core column for connection to a control current; by changing the magnitude of the control current in the control coil, the saturation of the outer iron core columns is changed, thereby controlling the inductance value of the variable inductor.

[0016] Furthermore, a bootstrap driving method is adopted to start up the high-order resonant DC-DC converter.

[0017] Furthermore, the switch control circuit employing a bootstrap driving method includes a drive power supply V. driver Bootstrap diode D boot Bootstrap capacitor C boot First gate driver, second gate driver and capacitor C Ls ;

[0018] The driving power supply V driver The positive terminal and the bootstrap diode D boot Anode connection, bootstrap diode D boot The cathode and bootstrap capacitor C boot One end is connected to the bootstrap capacitor C. boot The other end is connected to the source of the high-voltage side switch S1 of the high-order resonant DC-DC converter; the output of the first gate driver is connected to the gate of the high-voltage side switch S1; the output of the second gate driver is connected to the gate of the low-voltage side switch S2 of the high-order resonant DC-DC converter; the drive power supply Vdriver Positive and negative terminals and capacitor C Ls The two ends are connected respectively;

[0019] bootstrap capacitor C boot Connected to the first gate driver, providing operating voltage for the first gate driver;

[0020] Capacitor C Ls It connects to the second gate driver to provide operating voltage for the second gate driver.

[0021] Furthermore, when starting up the high-order resonant DC-DC converter using a bootstrap driving method, the initial voltage of the low-voltage side bus capacitor C2 is controlled to be higher than the initial voltage of the high-voltage side bus capacitor C1.

[0022] Furthermore, it also includes a first balancing resistor R1 and a second balancing resistor R2; the first balancing resistor R1 is connected in parallel with the high-voltage side bus capacitor C1; the second balancing resistor R2 is connected in parallel with the low-voltage side bus capacitor C2; the high-voltage side bus capacitor C1 is connected between the drain and source of the high-voltage side switching transistor S1; the low-voltage side bus capacitor C2 is connected between the drain and source of the low-voltage side switching transistor S2; the resistance value of the first balancing resistor R1 is less than the resistance value of the second balancing resistor R2.

[0023] Furthermore, when starting up a high-order resonant DC-DC converter using a bootstrap driving method, an active method is used to control the gate drive signal.

[0024] Furthermore, in the active mode control of the gate drive signal, when the first gate driver drives the high-voltage side switch S1 or the second gate driver drives the low-voltage side switch S2,

[0025] First, the voltage across the source and drain of the driven switch is detected. If the voltage is zero, a gate control signal is output to turn on the driven switch. If the voltage is higher than zero, no gate control signal is output. The gate control signal is maintained until the voltage drops to zero, and then it is output to the driven switch to turn it on.

[0026] This invention can achieve at least one of the following beneficial effects:

[0027] The high-order resonant DC-DC converter based on variable inductance of the present invention reduces and eliminates the influence of various parasitic parameters in the transformer and circuit on the resonant circuit. By adjusting the inductance value, the influence of parasitic parameters is offset, thereby obtaining resonant parameters that are more consistent with theoretical analysis.

[0028] The two topology improvement methods for bootstrap resonant converters presented in this invention can effectively suppress and improve the voltage imbalance phenomenon that occurs during converter startup, improve and eliminate the hard switching phenomenon that occurs during startup of bootstrap resonant converters, and thus enable the circuit to operate in soft switching mode during startup, thereby improving the safety and reliability of the topology. Attached Figure Description

[0029] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0030] Figure 1 This is a block diagram of the high-order resonant DC-DC converter circuit in an embodiment of the present invention;

[0031] Figure 2 This is a graph showing the influence of parasitic parameter changes on the notch inductor Lp in this embodiment of the invention.

[0032] Figure 3 This is a graph showing the effect of parasitic parameter changes on the resonant inductor Lr in this embodiment of the invention.

[0033] Figure 4 This is a graph showing the influence of parasitic parameter changes on the excitation inductance Lm in an embodiment of the present invention.

[0034] Figure 5 This is a graph showing the voltage and resonant current curves during the first two cycles of the startup period in an embodiment of the present invention.

[0035] Figure 6 This is a waveform diagram of the active control gate drive signal in an embodiment of the present invention. Detailed Implementation

[0036] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and, together with the embodiments of the present invention, serve to illustrate the principles of the present invention.

[0037] One embodiment of the present invention discloses a high-order resonant DC-DC converter based on a variable inductor, such as... Figure 1 As shown, the resonant topology uses an LCLCL resonant network;

[0038] The LCLCL resonant network includes a resonant capacitor Cr, a resonant inductor Lr, a magnetizing inductor Lm, a band-stop filter inductor Lp, and a band-stop filter capacitor Cp.

[0039] The excitation inductor Lm and the primary side of the transformer T form the first parallel circuit. The resistive filter inductor Lp and the resistive filter capacitor Cp are connected in parallel to form the second parallel circuit. The resonant capacitor Cr and the resonant inductor Lr are connected in series, and then connected in series with the first parallel circuit and the second parallel circuit.

[0040] In the LCLCL resonant network, the resonant inductor Lr, the wave limiting inductor Ls, and the excitation inductor Lm are all variable inductors;

[0041] The high-order resonant DC-DC converter also includes a resonant frequency detection circuit and an inductor control circuit.

[0042] The resonant frequency detection circuit is connected to the LCLCL resonant network and is used to detect the actual resonant frequency of the LCLCL resonant network.

[0043] The inductor control circuit is used to output a control current based on the deviation between the actual resonant frequency and the target resonant frequency of the LCLCL resonant network, control the inductance values ​​of the resonant inductor Lr, the limiting inductor Lp and / or the excitation inductor Lm, change the impedance of the resonant network, and make the actual resonant frequency of the LCLCL resonant network close to the target resonant frequency.

[0044] exist Figure 1 It also includes power supply Vin, switch drive circuit, high-voltage side switch S1, low-voltage side switch S2, high-voltage side protection diode D1, low-voltage side protection diode D2, high-voltage side bus capacitor C1, and low-voltage side bus capacitor C2.

[0045] The high-voltage side switch S1 and the low-voltage side switch S2 are connected in series. The drain of the high-voltage side switch S1 is connected to the positive terminal of the power supply Vin. The source of the low-voltage side switch S2 is connected to the negative terminal of the power supply Vin. The switch drive circuit is connected to the gates of the high-voltage side switch S1 and the low-voltage side switch S2.

[0046] The high-voltage side protection diode D1 and the high-voltage side bus capacitor C1 are connected in parallel with the high-voltage side switching transistor S1;

[0047] The low-voltage side protection diode D2 and the low-voltage side bus capacitor C2 are connected in parallel with the low-voltage side switching transistor S2.

[0048] exist Figure 1 It also includes diodes D3 and D4, output capacitor C0, and load resistor RL connected to the secondary side of the transformer;

[0049] One end of the secondary side of transformer T is connected to the anode of diode D3, the cathode of diode D3 is connected to the cathode of diode D4, and the anode of diode D4 is connected to the other end of the secondary side of transformer T. The output capacitor C0 is connected between the center tap of the secondary side of transformer T and the cathode of diode D4. The output capacitor C0 is connected in parallel with the load resistor RL.

[0050] In an LCLCL resonant network, there are many resonant inductors, each with different characteristics and functions. Therefore, this embodiment analyzes the characteristics of each resonant inductor and proposes... Figure 1In this scheme, the resonant inductor Lr, the wave limiting inductor Ls, and the excitation inductor Lm are set as variable inductors; by adjusting the inductance values ​​of each inductor, the influence of various parasitic parameters in the transformer and circuit on the resonant circuit is reduced and eliminated.

[0051] By analyzing the variation law of inductance, the change of gain of the resonance curve, especially the change of peak gain, was obtained when the inductance changes. This allowed us to observe the working state of the resonant network and determine the control scheme of variable inductance to achieve reasonable adjustment of the topology.

[0052] In this embodiment, the impact of parasitic parameters caused by changes in the inductance value of the notch inductor Lp on the resonant network was simulated, such as... Figure 2 As shown, the curves illustrate the influence of parasitic parameter variations on the notch filter inductor Lp.

[0053] In the figure, the curve shifts significantly to the left as Lp increases in the mid-frequency range, while there is almost no effect in the low-frequency and high-frequency ranges.

[0054] In the LCLCL resonant network, the limiting inductor Lp and the limiting capacitor Cp constitute the notch filter structure in the higher-order resonant network, and its main functions are twofold:

[0055] One advantage is that its notch characteristic allows the voltage gain to decay rapidly between the fundamental resonant point and the notch point.

[0056] Secondly, it can be used with other resonant elements to form a high-order resonant cavity, providing a third harmonic resonant point and reducing the reactive circulating current of the system.

[0057] Although notch capacitors and notch inductors are also involved in the fundamental resonance, the main body is still the reactive power exchange of the resonant capacitors and resonant inductors. This explains why the fluctuations of Lp and Cp have little effect on the fundamental resonance point, but only have a significant effect on the notch point and the third harmonic resonance point.

[0058] In this embodiment, the impact of parasitic parameters caused by changes in the inductance value of the resonant inductor Lr on the resonant network was simulated, such as... Figure 3 As shown, the curves illustrate the influence of parasitic parameter variations on the resonant inductor Lr.

[0059] As can be seen from the figure, Lr has little effect on system gain in the mid-to-low frequency range.

[0060] Calculations based on the curves near the fundamental and third harmonic resonance points revealed that for the resonant inductor Lr, a 10% error corresponds to a frequency shift of only 2%. At the same frequency, the shift in system voltage gain is less than 0.1%. The influence of different values ​​for Lp and Cp on the system voltage gain is more pronounced in the high-frequency range, and the impact of parasitic parameters becomes more significant with increasing frequency. However, since current resonant converters typically operate in the range of tens of kHz to one megaHz, and the frequency modulation range is well-limited due to the presence of notch filters, they generally do not operate at such high frequencies. Therefore, slight changes or errors in the resonant inductor do not significantly affect the converter's system gain or operating status.

[0061] In this embodiment, the impact of parasitic parameters caused by changes in the inductance value of the magnetizing inductor Lm on the resonant network was simulated, such as... Figure 4 As shown, this is the curve showing the effect of parasitic parameter changes on the magnetizing inductance Lm.

[0062] The effect of the magnetizing inductance on system gain is similar to that of the resonant capacitor, primarily affecting the peak voltage gain. However, unlike the resonant capacitor, the system voltage gain increases as the magnetizing inductance decreases. This is because as the magnetizing inductance increases, the proportion of reactive excitation current on the primary side increases, resulting in a decrease in the current transferred to the secondary side and thus a lower system gain. On the other hand, with the resonant inductance constant, the change in magnetizing inductance is equivalent to a change in the inductance coefficient. Therefore, the curve in the figure can also be considered as the effect of the inductance coefficient on the DC voltage gain of the system. For this set of parameters, calculations show that when the magnetizing inductance changes by 10%, the peak voltage gain changes by approximately 5%, with the high-frequency curves essentially overlapping.

[0063] Based on the above analysis, the resonant frequency detection circuit added to the LCLCL resonant network in this embodiment determines the resonant frequency by detecting the resonant current. The signal is then sent to the inductor control circuit of the variable inductor. When the resonant frequency deviates from the target frequency, the sampled signal is fitted to the gain curve function, thereby adjusting the control current of the variable inductor, influencing the inductance value, adjusting the impedance of the resonant network, and changing its operating state. This allows for the design of a high-order resonant topology with a variable resonant frequency and eliminates the influence of parasitic parameters, which are particularly important in high-frequency topologies and greatly limit the efficiency and output quality of the resonant converter. The resonant frequency detection circuit, which determines the resonant frequency by detecting the resonant current, can be implemented using existing technologies, such as methods for detecting signal frequency from current changes.

[0064] More specifically, in the resonant frequency detection circuit, the fundamental resonant frequency and the third harmonic resonant frequency of the LCLCL resonant network are detected respectively.

[0065] In the inductor control circuit, the errors between the fundamental resonant frequency, the third harmonic resonant frequency and the corresponding target resonant frequency of the detected LCLCL resonant network are determined respectively. When the error exceeds the threshold range, the output control current controls the inductance values ​​of the resonant inductor Lr, the wave limiting inductor Ls and / or the excitation inductor Lm.

[0066] In the inductor control circuit,

[0067] When it is determined that the fundamental resonant frequencies differ significantly, the inductance value of the resonant inductor Lr should be adjusted first.

[0068] When the error of the third harmonic resonant frequency is large, the value of the limiting inductor Lp should be adjusted first.

[0069] When it is determined that both the fundamental resonant frequency and the third harmonic resonant frequency are far from the target resonant frequency, the inductance value of the excitation inductor Lm should be adjusted first.

[0070] Through multiple adjustments, the errors in the fundamental resonant frequency and the third harmonic resonant frequency of the detected LCLCL resonant network were made to fall within the threshold range.

[0071] Preferably, the threshold range is an error of no more than 5%.

[0072] In this embodiment, the structure that can be adopted for the variable inductance of the resonant inductor Lr, the limiting inductor Ls, and the magnetizing inductor Lm is also given:

[0073] The variable inductor includes a central core column and two outer core columns; two parallel-connected outer coils are wound on the outer core columns for connection to the LCLCL resonant network; a control coil is wound on the central core column for connection to the control current; by changing the magnitude of the control current in the control coil, the saturation of the outer core columns is changed, thereby controlling the inductance value of the variable inductor.

[0074] like Figure 1 As shown in this embodiment, the bootstrap driving method is used in the switch driving circuit to start the high-order resonant DC-DC converter.

[0075] Specifically, the switch control circuit using a bootstrap driving method includes a drive power supply V. driver Bootstrap diode D boot Bootstrap capacitor C boot First gate driver, second gate driver and capacitor C Ls ;

[0076] The driving power supply V driver The positive terminal and the bootstrap diode D boot Anode connection, bootstrap diode Dboot The cathode and bootstrap capacitor C boot One end is connected to the bootstrap capacitor C. boot The other end is connected to the source of the high-voltage side switch S1 of the high-order resonant DC-DC converter; the output of the first gate driver is connected to the gate of the high-voltage side switch S1; the output of the second gate driver is connected to the gate of the low-voltage side switch S2 of the high-order resonant DC-DC converter; the drive power supply V driver Positive and negative terminals and capacitor C Ls The two ends are connected respectively;

[0077] bootstrap capacitor C boot Connected to the first gate driver, providing operating voltage for the first gate driver;

[0078] Capacitor C Ls It connects to the second gate driver to provide operating voltage for the second gate driver.

[0079] like Figure 5 As shown, the voltage and resonant current during the first two cycles of the switch drive circuit startup are shown.

[0080] In the diagram, it is assumed that the high-voltage side switch is turned on first under ideal conditions. Before t0, when the input DC voltage Vin increases and the switch is closed, the initial voltage on the low-voltage side bus capacitor C2 (Vcr), based on the voltage divider, is approximately Vin / 2, because the high-voltage side bus capacitor C2 and the low-voltage side bus capacitor C1 have the same capacitance within the tolerance range. The initial current through the resonant inductor Lr is 0A. Since the switching frequency during the startup phase is usually much higher than the steady state, such as 300kHz, for the sake of simplifying the analysis, Vcr can be considered constant in the first few switching cycles. Furthermore, the initial voltage on the large-capacity output capacitor is zero, so it can be assumed that the induced voltage on the primary side of the transformer is zero in the first few switching cycles. From t0 to t1, the high-voltage side switch is turned on for the first time, and the voltage on Lr becomes Vcr. The current Il begins to rise from zero to a local peak I1.

[0081] The switching time of the high-voltage side switch is T. on .

[0082] From t1 to t2, the low-voltage side switch is turned on, and the voltage across Lr becomes -Vcr. The current Il begins to decrease and reaches its peak value I2.

[0083]

[0084] Among them To ffThis refers to the conduction time of the low-voltage side switch. If I2 < 0, the high-voltage side switch can achieve soft switching at t2. If I2 > 0, the high-voltage side switch at t2 will undergo hard switching. Therefore, the condition for ensuring soft switching of the high-voltage side switch during the LLC converter startup phase can be written as follows:

[0085]

[0086] That is

[0087] V cr ≥DV in (3)

[0088] Ideally, if the high-voltage side switch does indeed turn on first at time zero, soft switching can be easily achieved. However, in this embodiment, the bootstrap capacitor C of the bootstrap circuit... boot The first gate driver, which controls the gate power supply of the high-voltage side switch S1, is powered. Bootstrap capacitor C boot The initial voltage on the high-voltage side is zero. To charge it above the supply threshold, the low-voltage side switch must be open for several cycles before the high-voltage side switch can actually open. The low-voltage side switch opens first and remains open for several weeks. During this process, the low-voltage side resonant capacitor Cr1 will discharge through the low-voltage side switch, resulting in a significant voltage drop in Vcr. Then, when the high-voltage side switch is turned on after this, Equation 3 may not be satisfied. Therefore, hard switching is likely to occur at time t2.

[0089] To address the hard-switching problem, this embodiment presents two solutions.

[0090] In one solution, when starting up a high-order resonant DC-DC converter using a bootstrap driving method, the initial voltage of the low-voltage side bus capacitor C2 is controlled to be higher than the initial voltage of the high-voltage side bus capacitor C1.

[0091] Since the voltage drop across capacitor C2 on the low-voltage side bus is the primary cause of hard switching, the initial voltage across capacitor C2 is intentionally increased before startup. This ensures that the initial voltage across C2 is higher than Vin / 2. This suppresses the voltage imbalance that occurs when the high-voltage side switch is first opened.

[0092] Preferably, in this embodiment, a voltage balancing resistor is introduced to ensure that the initial voltage of the low-voltage side bus capacitor C2 is higher than the initial voltage of the high-voltage side bus capacitor C1. For example... Figure 1As shown, the voltage balancing resistors include a first balancing resistor R1 and a second balancing resistor R2; the first balancing resistor R1 is connected in parallel with the high-voltage side bus capacitor C1; the second balancing resistor R2 is connected in parallel with the low-voltage side bus capacitor C2; the resistance of the first balancing resistor R1 is less than the resistance of the second balancing resistor R2. Through the voltage division of resistors R1 and R2 in series, the initial voltage of the low-voltage side bus capacitor C2 is higher than the initial voltage of the high-voltage side bus capacitor C1.

[0093] In another solution, the gate drive signal is controlled actively in the switch control circuit.

[0094] Specifically, in the active mode control of the gate drive signal, when the first gate driver drives the high-voltage side switch S1 or the second gate driver drives the low-voltage side switch S2,

[0095] First, the voltage across the source and drain of the driven switch is detected. If the voltage is zero, a gate control signal is output to turn on the driven switch. If the voltage is higher than zero, no gate control signal is output. The gate control signal is maintained until the voltage drops to zero, and then it is output to the driven switch to turn it on.

[0096] like Figure 6 As shown, the waveform of the gate drive signal is controlled by the active mode. The active control method solves the hard switching phenomenon during bootstrap drive.

[0097] In summary, the high-order resonant DC-DC converter based on variable inductor in this invention reduces and eliminates the influence of various parasitic parameters in the transformer and circuit on the resonant circuit. By adjusting the inductance value, the influence of parasitic parameters is offset, thereby obtaining resonant parameters that are more consistent with theoretical analysis. Furthermore, the two topology improvement methods for bootstrap resonant converters presented can effectively suppress and improve the voltage imbalance phenomenon that occurs during converter startup, and improve and eliminate the hard-switching operation phenomenon that occurs during startup of bootstrap-driven resonant converters. This allows the circuit to operate in soft-switching mode during startup, improving the safety and reliability of the topology.

[0098] 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 changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-order resonant DC-DC converter based on a variable inductor, employing a resonant topology of an LCLCL resonant network; characterized in that, In the LCLCL resonant network, the resonant inductor Lr, the notch filter inductor Lp, and the magnetizing inductor Lm are all variable inductors. The high-order resonant DC-DC converter also includes a resonant frequency detection circuit and an inductor control circuit. The resonant frequency detection circuit is connected to the LCLCL resonant network and is used to detect the actual resonant frequency of the LCLCL resonant network. The inductor control circuit is used to output a control current based on the deviation between the actual resonant frequency and the target resonant frequency of the LCLCL resonant network, control the inductance values ​​of the resonant inductor Lr, notch inductor Lp and / or excitation inductor Lm, change the impedance of the resonant network, and make the actual resonant frequency of the LCLCL resonant network close to the target resonant frequency.

2. The high-order resonant DC-DC converter according to claim 1, characterized in that, In the resonant frequency detection circuit, the fundamental resonant frequency and the third harmonic resonant frequency of the LCLCL resonant network are detected respectively. In the inductor control circuit, the errors between the fundamental resonant frequency, the third harmonic resonant frequency and the corresponding target resonant frequency of the detected LCLCL resonant network are determined respectively. When the error exceeds the threshold range, the output control current controls the inductance values ​​of the resonant inductor Lr, the notch inductor Lp and / or the magnetizing inductor Lm.

3. The high-order resonant DC-DC converter according to claim 2, characterized in that, In the inductor control circuit, When it is determined that the fundamental resonant frequencies differ significantly, the inductance value of the resonant inductor Lr should be adjusted first. When the error of the third harmonic resonant frequency is large, the value of the notch inductor Lp should be adjusted first. When it is determined that both the fundamental resonant frequency and the third harmonic resonant frequency are far from the target resonant frequency, the inductance value of the excitation inductor Lm should be adjusted first. Through multiple adjustments, the errors in the fundamental resonant frequency and the third harmonic resonant frequency of the detected LCLCL resonant network were made to fall within the threshold range.

4. The high-order resonant DC-DC converter according to any one of claims 1-3, characterized in that, The variable inductor has a structure comprising a central core column and two outer core columns; two parallel-connected outer coils are wound on the outer core columns for connection to an LCLCL resonant network; a control coil is wound on the central core column for connection to a control current; by changing the magnitude of the control current in the control coil, the saturation of the outer core columns is changed, thereby controlling the inductance value of the variable inductor.

5. The high-order resonant DC-DC converter according to claim 4, characterized in that, The bootstrap method is used to start up the high-order resonant DC-DC converter.

6. The high-order resonant DC-DC converter according to claim 5, characterized in that, A switch control circuit employing a bootstrap driving method includes a drive power supply V. driver Bootstrap diode D boot Bootstrap capacitor C boot First gate driver, second gate driver and capacitor C Ls ; The driving power supply V driver The positive terminal and the bootstrap diode D boot Anode connection, bootstrap diode D boot Cathode and bootstrap capacitor C boot One end is connected to the bootstrap capacitor C. boot The other end is connected to the source of the high-voltage side switch S1 of the high-order resonant DC-DC converter; the output of the first gate driver is connected to the gate of the high-voltage side switch S1; the output of the second gate driver is connected to the gate of the low-voltage side switch S2 of the high-order resonant DC-DC converter; the drive power supply V driver Positive and negative terminals and capacitor C Ls The two ends are connected respectively; bootstrap capacitor C boot Connected to the first gate driver, providing operating voltage for the first gate driver; Capacitor C Ls It connects to the second gate driver to provide operating voltage for the second gate driver.

7. The high-order resonant DC-DC converter according to claim 6, characterized in that, When starting up a high-order resonant DC-DC converter using a bootstrap driving method, the initial voltage of the low-voltage side bus capacitor C2 is controlled to be higher than the initial voltage of the high-voltage side bus capacitor C1. It also includes a first balancing resistor R1 and a second balancing resistor R2; the first balancing resistor R1 is connected in parallel with the high-voltage side bus capacitor C1; the second balancing resistor R2 is connected in parallel with the low-voltage side bus capacitor C2; the high-voltage side bus capacitor C1 is connected between the drain and source of the high-voltage side switching transistor S1; the low-voltage side bus capacitor C2 is connected between the drain and source of the low-voltage side switching transistor S2; the resistance value of the first balancing resistor R1 is less than the resistance value of the second balancing resistor R2.

8. The high-order resonant DC-DC converter according to claim 6, characterized in that, When starting up a high-order resonant DC-DC converter using a bootstrap driving method, an active method is used to control the gate drive signal. In the active mode control of the gate drive signal, when the first gate driver drives the high-voltage side switch S1 or the second gate driver drives the low-voltage side switch S2... First, the voltage across the source and drain of the driven switch is detected. If the voltage is zero, a gate control signal is output to turn on the driven switch. If the voltage is higher than zero, no gate control signal is output. The gate control signal is maintained until the voltage drops to zero, and then it is output to the driven switch to turn it on.

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