Condition monitoring method and device for LCC resonant converter

Abstract

The present invention provides a state monitoring method and device for an LCC resonant converter. The method comprises: obtaining the modes of the LCC resonant converter within a switching cycle through a phase-shift control strategy, and obtaining the state trajectory equations under each mode; calculating the peak current of the resonant cavity through an extended fundamental approximation method; calculating the analytical solution of the current and voltage variables at each mode switching point, and obtaining the trajectory circle radius under each mode, thereby obtaining a state trajectory model of the converter and a state monitoring result. By implementing this application, the state trajectory equations under each mode are obtained through a phase-shift control strategy; the peak current of the resonant cavity is calculated through an extended fundamental approximation method, thereby obtaining a final state trajectory model. Compared with existing technical solutions targeting fundamental components, the analytical accuracy of state modeling during the monitoring process is improved, and the state of the resonant cavity of the phase-shift controlled LCC resonant converter under steady-state operation can be accurately monitored.

Description

Technical Field

[0001] The present invention relates to the field of power supply status monitoring, and in particular to a method and device for monitoring the status of an LCC resonant converter. Background Art

[0002] With the development of power electronics technology, a large number of power semiconductor devices have been applied to the field of power conversion. Compared with traditional industrial frequency power supplies, switching power supplies offer advantages such as smaller size, lower output current ripple, faster dynamic response, and higher power density. DC transformer calibration power supplies (also known as test power supplies) are essential equipment in the development and design of DC transformers. Currently, LCC resonant converters are widely used as test power supplies for high-voltage DC transformers.

[0003] Existing technical solutions primarily use the fundamental wave approximation method to model LCC resonant converters. This method exploits the frequency-selective nature of the LCC resonant converter's resonant cavity. By applying Fourier decomposition to the square wave signal output by the inverter bridge, it is decomposed into a fundamental component and higher-order harmonic components. The resulting higher-order harmonic components are then ignored and the circuit modeling and analysis is performed. While this method effectively describes the converter's output gain and input impedance characteristics, its accuracy decreases as the switching frequency deviates from the resonant frequency. Summary of the Invention

[0004] The present invention provides a state monitoring method and device for an LCC resonant converter, so as to solve the technical problem of how to improve the accuracy of state modeling analysis during the monitoring process.

[0005] In order to solve the above technical problems, an embodiment of the present invention provides a state monitoring method for an LCC resonant converter, comprising:

[0006] The mode of the LCC resonant converter within one switching cycle is obtained through a phase-shift control strategy. The mode is divided according to the input and output levels of the resonant cavity, and the state trajectory equation under each mode is obtained.

[0007] The peak value of the resonant cavity current is calculated based on the state trajectory equations under each mode by using the extended fundamental wave approximation method;

[0008] Based on the calculated resonant cavity current peak value, the analytical solution of the current and voltage variables at each mode switching point is calculated, and the trajectory circle radius under each mode is obtained. Based on the obtained trajectory circle radius, the operation sequence of the LCC resonant converter under phase shift control is combined to obtain the state trajectory model of the LCC resonant converter and the state monitoring result.

[0009] As a preferred solution, the mode of the LCC resonant converter within one switching cycle is obtained by the phase shift control strategy, specifically:

[0010] The phase shift angle between the switching tubes of the inverter full-bridge arm of the LCC resonant converter is controlled to adjust the gain of the LCC resonant converter and obtain the mode within the one switching cycle.

[0011] As a preferred solution, the peak value of the resonant cavity current is calculated based on the state trajectory equation under each mode by using the extended fundamental wave approximation method, specifically:

[0012] By utilizing the frequency selection characteristics of the resonant cavity circuit of the LCC resonant converter, it is set that only the fundamental component of the switching frequency is input into the resonant cavity; the secondary side rectification network of the LCC resonant converter is equivalent to an RC parallel circuit and converted into the primary side circuit. Based on the obtained equivalent circuit, the peak value of the resonant cavity current is derived and calculated.

[0013] As a preferred solution, the modes within one switching cycle include the first ZO mode, ZN mode, PN mode, PO mode, the second ZO mode, ZP mode, NP mode and NO mode in sequence;

[0014] The state trajectory equations under each mode are specifically:

[0015] The state trajectory equation of the first ZO mode is:

[0016] ;

[0017] The state trajectory equation of ZN mode:

[0018] ;

[0019] The state trajectory equation of PN mode:

[0020] ;

[0021] The state trajectory equation of PO mode:

[0022] ;

[0023] The trajectory equation of the second ZO mode is:

[0024] ;

[0025] The state trajectory equation of ZP mode:

[0026] ;

[0027] The state trajectory equation of NP mode:

[0028] ;

[0029] The state trajectory equation of NO mode:

[0030] ;

[0031] Among them, i LrN (t) is the normalized value of the resonant inductor Lr current, V CrN (t) is the normalized value of the voltage of the series resonant capacitor Cr, V CpN (t) is the normalized value of the parallel resonant capacitor Cp, Z r is the resonant impedance of the two components, Z e is the three-element resonant impedance, r0 is the trajectory radius of the ZO mode, r1 is the trajectory radius of the ZN mode, r2 is the trajectory radius of the PN mode, r3 is the trajectory radius of the PO mode, r5 is the trajectory radius of the ZP mode, r6 is the trajectory radius of the NP mode, and r7 is the trajectory radius of the NO mode.

[0032] As a preferred solution, the trajectory circle radius under each mode is specifically:

[0033] The trajectory radius of the first ZO mode and the second ZO mode is:

[0034] ;

[0035] The trajectory radius of the ZN mode and the ZP mode is:

[0036] ;

[0037] The trajectory radius of the PN mode and the NP mode is:

[0038] ;

[0039] The trajectory radius of the PO mode and the NO mode is:

[0040] ;

[0041] Among them, V o is the output voltage of the LCC resonant converter, I o is the output current of the LCC resonant converter, f s is the switching frequency, V in is the input voltage of the LCC resonant converter, V oN is the output voltage V o After normalization, n is the transformation ratio of the primary and secondary sides of the transformer.

[0042] Accordingly, an embodiment of the present invention further provides a state monitoring device for an LCC resonant converter, comprising an acquisition module, a current peak value calculation module, and a modeling module; wherein,

[0043] The acquisition module is used to obtain the mode of the LCC resonant converter within a switching cycle through a phase shift control strategy, and divide it according to the input level and output level of the resonant cavity to obtain the state trajectory equation under each mode;

[0044] The current peak calculation module is used to calculate the resonant cavity current peak value based on the state trajectory equation under each mode by using the extended fundamental wave approximation method;

[0045] The modeling module is used to calculate the analytical solution of the current and voltage variables at each mode switching point based on the calculated resonant cavity current peak value, and obtain the trajectory circle radius under each mode, so as to obtain the state trajectory model of the LCC resonant converter and the state monitoring result by combining the obtained trajectory circle radius according to the operation order of the LCC resonant converter under phase shift control.

[0046] As a preferred solution, the acquisition module obtains the mode of the LCC resonant converter within a switching cycle through a phase shift control strategy, specifically:

[0047] The acquisition module controls the phase shift angle between the switching tubes of the inverter full-bridge arm of the LCC resonant converter to adjust the gain of the LCC resonant converter and obtain the mode within the one switching cycle.

[0048] As a preferred solution, the current peak calculation module calculates the resonant cavity current peak value by using the extended fundamental wave approximation method based on the state trajectory equation under each mode, specifically:

[0049] The current peak calculation module utilizes the frequency selection characteristics of the resonant cavity circuit of the LCC resonant converter to set only the fundamental component of the switching frequency to be input into the resonant cavity; the secondary side rectifier network of the LCC resonant converter is equivalent to an RC parallel circuit and converted into the primary circuit; based on the obtained equivalent circuit, the resonant cavity current peak is derived and calculated.

[0050] As a preferred solution, the modes within one switching cycle include the first ZO mode, ZN mode, PN mode, PO mode, the second ZO mode, ZP mode, NP mode and NO mode in sequence;

[0051] The state trajectory equations under each mode are specifically:

[0052] The state trajectory equation of the first ZO mode is:

[0053] ;

[0054] The state trajectory equation of ZN mode:

[0055] ;

[0056] The state trajectory equation of PN mode:

[0057] ;

[0058] The state trajectory equation of PO mode:

[0059] ;

[0060] The trajectory equation of the second ZO mode is:

[0061] ;

[0062] The state trajectory equation of ZP mode:

[0063] ;

[0064] The state trajectory equation of NP mode:

[0065] ;

[0066] The state trajectory equation of NO mode:

[0067] ;

[0068] Among them, i LrN (t) is the normalized value of the resonant inductor Lr current, V CrN (t) is the normalized value of the voltage of the series resonant capacitor Cr, V CpN (t) is the normalized value of the parallel resonant capacitor Cp, Z r is the resonant impedance of the two components, Z e is the three-element resonant impedance, r0 is the trajectory radius of the ZO mode, r1 is the trajectory radius of the ZN mode, r2 is the trajectory radius of the PN mode, r3 is the trajectory radius of the PO mode, r5 is the trajectory radius of the ZP mode, r6 is the trajectory radius of the NP mode, and r7 is the trajectory radius of the NO mode.

[0069] As a preferred solution, the trajectory circle radius under each mode is specifically:

[0070] The trajectory radius of the first ZO mode and the second ZO mode is:

[0071] ;

[0072] The trajectory radius of the ZN mode and the ZP mode is:

[0073] ;

[0074] The trajectory radius of the PN mode and the NP mode is:

[0075] ;

[0076] The trajectory radius of the PO mode and the NO mode is:

[0077] ;

[0078] Among them, V o is the output voltage of the LCC resonant converter, I o is the output current of the LCC resonant converter, f s is the switching frequency, V in is the input voltage of the LCC resonant converter, V oN is the output voltage V o After normalization, n is the transformation ratio of the primary and secondary sides of the transformer.

[0079] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0080] An embodiment of the present invention provides a state monitoring method and device for an LCC resonant converter. The state monitoring method includes: obtaining a mode within a switching cycle of the LCC resonant converter through a phase-shift control strategy, and dividing the mode according to the input level and output level of the resonant cavity to obtain a state trajectory equation under each mode; calculating the resonant cavity current peak value based on the state trajectory equation under each mode through an extended fundamental approximation method; calculating the analytical solution of the current and voltage variables at each mode switching point based on the calculated resonant cavity current peak value, and obtaining the trajectory circle radius under each mode, thereby combining the obtained trajectory circle radius according to the operating order of the LCC resonant converter under phase-shift control to obtain a state trajectory model of the LCC resonant converter and obtain a state monitoring result. By implementing the embodiments of the present application, the state trajectory equations under each mode are obtained through the phase-shift control strategy; the peak value of the resonant cavity current is calculated through the extended fundamental wave approximation method, thereby obtaining the final state trajectory model. Compared with the existing technical solutions for the fundamental wave component, the analysis accuracy of the state modeling during the monitoring process is improved, and the state of the resonant cavity of the LCC resonant converter with phase-shift control under steady-state operation can be accurately monitored, which facilitates relevant technical personnel to protect it in a timely manner and provides a reference for testing the nonlinear control of the power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0081] Figure 1: A flow chart of an embodiment of a state monitoring method for an LCC resonant converter provided by the present invention.

[0082] Figure 2 : A structural diagram of an embodiment of a common topology of the LCC resonant converter provided by the present invention.

[0083] Figure 3 : A schematic diagram of an embodiment of the state trajectory of the LCC resonant converter provided by the present invention.

[0084] Figure 4 : A schematic diagram of an embodiment of an equivalent circuit of the LCC resonant converter provided by the present invention.

[0085] Figure 5 : A schematic diagram of the effect of an embodiment of the state trajectory model of the LCC resonant converter provided by the present invention.

[0086] Figure 6 : A waveform diagram of an embodiment of modeling of the LCC resonant converter provided by the present invention.

[0087] Figure 7 : A structural diagram of an embodiment of a state monitoring device for an LCC resonant converter provided by the present invention. DETAILED DESCRIPTION

[0088] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0089] Example 1

[0090] Please refer to Figure 1 , a state monitoring method for an LCC resonant converter provided by an embodiment of the present invention, comprising steps S1 to S3; wherein,

[0091] Step S1: Obtain the mode of the LCC resonant converter within a switching cycle through a phase-shift control strategy, and divide it according to the input level and output level of the resonant cavity to obtain the state trajectory equation under each mode.

[0092] The LCC resonant converter of this embodiment is the main power circuit, which undertakes the task of power conversion and is the main control object of this embodiment. It includes a full-bridge inverter, an LCC resonant cavity circuit, a high-voltage transformer and a rectifier circuit. Its basic topology diagram can be referred to Figure 2 .

[0093] Figure 2 As an example only, this embodiment provides a common topology. The parasitic parameters of the high-voltage transformer are converted into the resonant capacitor Cp and resonant inductor Lr within the resonant cavity circuit. Power conversion is achieved by controlling the switching of the four switches Q1 to Q4 in the inverter full bridge. The switches on the same bridge arm are not turned on simultaneously, i.e., Q1 and Q2 are turned on in a complementary manner, and Q3 and Q4 are turned on in a complementary manner.

[0094] Regarding the phase-shift control strategy of this embodiment: this strategy is a fixed-frequency modulation strategy, which adjusts the output gain of the LCC resonant converter by changing the phase-shift angle d between the pairs of tubes Q1, Q4 and Q2, Q3 on the bridge arm, and can effectively reduce the reactive circulating current of the LCC resonant converter.

[0095] By using the phase shift control strategy, the modal diagram of the LCC resonant converter within one switching cycle can be obtained, as shown in Figure 3 As shown. According to the division of the input level and output level of the resonant cavity, the state trajectory equation under each mode can be obtained. The modes in one switching cycle are the first ZO mode-ZN mode-PN mode-PO mode-second ZO mode-ZP mode-NP mode-NO mode, a total of eight modes. It should be noted that according to the input and output levels of the primary inverter bridge and the secondary rectifier bridge, the working mode of the LCC resonant converter can be divided into nine states. This embodiment defines the positive level of the primary inverter bridge output or the secondary rectifier bridge input as P mode, defines the negative level of the primary inverter bridge output or the secondary rectifier bridge input as N mode, defines the zero level of the primary inverter bridge output as Z mode, and defines the zero level of the secondary rectifier bridge input as O mode. Therefore, there are a total of nine possible modes of the LCC resonant converter: PP, PN, PO, NP, NN, NO, ZP, ZN and ZO. In this embodiment, based on the phase-shift control, the modes within one switching cycle mainly include: the first ZO mode, the ZN mode, the PN mode, the PO mode, the second ZO mode, the ZP mode, the NP mode, and the NO mode, totaling eight modes (of which two ZO modes are required, namely the first ZO mode and the second ZO mode).

[0096] The state trajectory equation of the first ZO mode is:

[0097] ;

[0098] The state trajectory equation of ZN mode:

[0099] ;

[0100] The state trajectory equation of PN mode:

[0101] ;

[0102] The state trajectory equation of PO mode:

[0103] ;

[0104] The trajectory equation of the second ZO mode is:

[0105] ;

[0106] The state trajectory equation of ZP mode:

[0107] ;

[0108] The state trajectory equation of NP mode:

[0109] ;

[0110] The state trajectory equation of NO mode:

[0111] ;

[0112] Among them, i LrN (t) is the normalized value of the resonant inductor Lr current (current state variable), V CrN (t) is the normalized value of the voltage of the series resonant capacitor Cr (voltage state variable), V CpN (t) is the normalized value of the parallel resonant capacitor Cp (voltage state variable), Z r is the resonant impedance of the two components, Z e is the three-element resonant impedance, r0 is the trajectory radius of the ZO mode, r1 is the trajectory radius of the ZN mode, r2 is the trajectory radius of the PN mode, r3 is the trajectory radius of the PO mode, r5 is the trajectory radius of the ZP mode, r6 is the trajectory radius of the NP mode, r7 is the trajectory radius of the NO mode, and t is time.

[0113] Further for the above parameters:

[0114] ;

[0115] Step S2: calculating the resonant cavity current peak value based on the state trajectory equations under each mode by using the extended fundamental wave approximation method.

[0116] In this embodiment, the extended fundamental approximation method is specifically as follows: by utilizing the frequency selection characteristics of the LCC resonant cavity circuit itself, assuming that only the switching frequency f sThe fundamental component is input into the resonant cavity, and the other high-order harmonic energy is completely attenuated and does not participate in energy transfer. At the same time, the secondary rectifier network is equivalent to an RC parallel circuit and converted into the primary circuit. According to the obtained equivalent circuit, the resonant current peak, output gain defect, and input impedance curve can be derived. The equivalent circuit can be referred to Figure 4 .

[0117] The peak value of the resonant cavity current I Lrmax Specifically:

[0118] ;

[0119] Where N is the turns ratio of the isolation transformer, ω s is the switching angular frequency.

[0120] For the switching angular frequency: ;

[0121] The conduction angle θ of the secondary rectifier bridge within one switching cycle is calculated as follows:

[0122] ;

[0123] Among them, R L is the load resistance value.

[0124] Step S3: Based on the calculated resonant cavity current peak value, the analytical solution of the current and voltage variables at each mode switching point is calculated, and the trajectory circle radius under each mode is obtained. Based on the obtained trajectory circle radius, the operation order of the LCC resonant converter under phase shift control is combined to obtain the state trajectory model of the LCC resonant converter and obtain the state monitoring result.

[0125] Regarding step S3 above, the method for calculating the theoretical trajectory circle radius is specifically as follows: the trajectory radius of the first ZO mode and the second ZO mode is:

[0126] ;

[0127] The trajectory radius of the ZN mode and the ZP mode is:

[0128] ;

[0129] The trajectory radius of the PN mode and the NP mode is:

[0130] ;

[0131] The trajectory radius of the PO mode and the NO mode is:

[0132] ;

[0133] Among them, V o is the output voltage of the LCC resonant converter, I o is the output current of the LCC resonant converter, f s is the switching frequency, V in is the input voltage of the LCC resonant converter, V oN is the output voltage V o After the per-unit value, n is the transformation ratio of the primary and secondary sides of the transformer. The per-unit formula is .

[0134] Then, the trajectory circles corresponding to each mode are combined according to the operating order of the LCC resonant converter under phase-shift control to obtain the state trajectory model of the LCC resonant converter under phase-shift control. Please refer to Figure 5 At the same time, the waveform corresponding to the trajectory modeling method of the LCC resonant converter under phase shift control provided in the embodiment of the present application is as follows: Figure 6 shown.

[0135] Accordingly, refer to Figure 7 The embodiment of the present invention further provides a state monitoring device for an LCC resonant converter, comprising an acquisition module 101, a current peak value calculation module 102 and a modeling module 103; wherein,

[0136] The acquisition module 101 is used to obtain the mode of the LCC resonant converter within a switching cycle through a phase shift control strategy, and divide it according to the input level and output level of the resonant cavity to obtain the state trajectory equation under each mode;

[0137] The current peak calculation module 102 is configured to calculate the resonant cavity current peak value based on the state trajectory equations under each mode by using an extended fundamental wave approximation method;

[0138] The modeling module 103 is used to calculate the analytical solution of the current and voltage variables at each mode switching point based on the calculated resonant cavity current peak value, and obtain the trajectory circle radius under each mode, so as to obtain the state trajectory model of the LCC resonant converter and the state monitoring result by combining the obtained trajectory circle radius according to the operation order of the LCC resonant converter under phase shift control.

[0139] As a preferred solution, the acquisition module 101 obtains the mode of the LCC resonant converter within a switching cycle through a phase shift control strategy, specifically:

[0140] The acquisition module 101 controls the phase shift angle between the switching tubes of the inverter full-bridge arm of the LCC resonant converter to adjust the gain of the LCC resonant converter and obtain the mode within the one switching cycle.

[0141] As a preferred solution, the current peak calculation module 102 calculates the resonant cavity current peak value by using the extended fundamental wave approximation method based on the state trajectory equation under each mode, specifically:

[0142] The current peak calculation module 102 uses the frequency selection characteristics of the resonant cavity circuit of the LCC resonant converter to set only the fundamental component of the switching frequency to be input into the resonant cavity; the secondary side rectifier network of the LCC resonant converter is equivalent to an RC parallel circuit and converted into the primary circuit, and the resonant cavity current peak is derived and calculated based on the obtained equivalent circuit.

[0143] As a preferred solution, the modes within one switching cycle include the first ZO mode, ZN mode, PN mode, PO mode, the second ZO mode, ZP mode, NP mode and NO mode in sequence;

[0144] The state trajectory equations under each mode are specifically:

[0145] The state trajectory equation of the first ZO mode is:

[0146] ;

[0147] The state trajectory equation of ZN mode:

[0148] ;

[0149] The state trajectory equation of PN mode:

[0150] ;

[0151] The state trajectory equation of PO mode:

[0152] ;

[0153] The trajectory equation of the second ZO mode is:

[0154] ;

[0155] The state trajectory equation of ZP mode:

[0156] ;

[0157] The state trajectory equation of NP mode:

[0158] ;

[0159] The state trajectory equation of NO mode:

[0160] ;

[0161] Among them, i LrN (t) is the normalized value of the resonant inductor Lr current, V CrN (t) is the normalized value of the voltage of the series resonant capacitor Cr, V CpN (t) is the normalized value of the parallel resonant capacitor Cp, Z r is the resonant impedance of the two components, Z e is the three-element resonant impedance, r0 is the trajectory radius of the ZO mode, r1 is the trajectory radius of the ZN mode, r2 is the trajectory radius of the PN mode, r3 is the trajectory radius of the PO mode, r5 is the trajectory radius of the ZP mode, r6 is the trajectory radius of the NP mode, and r7 is the trajectory radius of the NO mode.

[0162] As a preferred solution, the trajectory circle radius under each mode is specifically:

[0163] The trajectory radius of the first ZO mode and the second ZO mode is:

[0164] ;

[0165] The trajectory radius of the ZN mode and the ZP mode is:

[0166] ;

[0167] The trajectory radius of the PN mode and the NP mode is:

[0168] ;

[0169] The trajectory radius of the PO mode and the NO mode is:

[0170] ;

[0171] Among them, V o is the output voltage of the LCC resonant converter, I o is the output current of the LCC resonant converter, f s is the switching frequency, V in is the input voltage of the LCC resonant converter, V oN is the output voltage V o After normalization, n is the transformation ratio of the primary and secondary sides of the transformer.

[0172] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0173] An embodiment of the present invention provides a state monitoring method and device for an LCC resonant converter. The state monitoring method includes: obtaining a mode within a switching cycle of the LCC resonant converter through a phase-shift control strategy, and dividing the mode according to the input level and output level of the resonant cavity to obtain a state trajectory equation under each mode; calculating the resonant cavity current peak value based on the state trajectory equation under each mode through an extended fundamental approximation method; calculating the analytical solution of the current and voltage variables at each mode switching point based on the calculated resonant cavity current peak value, and obtaining the trajectory circle radius under each mode, thereby combining the obtained trajectory circle radius according to the operating order of the LCC resonant converter under phase-shift control to obtain a state trajectory model of the LCC resonant converter and obtain a state monitoring result. By implementing the embodiments of the present application, the state trajectory equations under each mode are obtained through the phase-shift control strategy; the peak value of the resonant cavity current is calculated through the extended fundamental wave approximation method, thereby obtaining the final state trajectory model. Compared with the existing technical solutions for the fundamental wave component, the analysis accuracy of the state modeling during the monitoring process is improved, and the state of the resonant cavity of the LCC resonant converter with phase-shift control under steady-state operation can be accurately monitored, which facilitates relevant technical personnel to protect it in a timely manner and provides a reference for testing the nonlinear control of the power supply.

[0174] The specific embodiments described above further illustrate the objectives, technical solutions, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. In particular, it should be noted that any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included within the scope of protection of the present invention for those skilled in the art.

Claims

1. A method for monitoring the state of an LCC resonant converter, characterized in that: include: The mode of the LCC resonant converter within one switching cycle is obtained through a phase-shift control strategy. The mode is divided according to the input and output levels of the resonant cavity, and the state trajectory equation under each mode is obtained. The peak value of the resonant cavity current is calculated based on the state trajectory equations under each mode by using the extended fundamental wave approximation method; Based on the calculated resonant cavity current peak value, an analytical solution of the current and voltage variables at each mode switching point is calculated, and the trajectory circle radius under each mode is obtained. Based on the obtained trajectory circle radius, the operation sequence of the LCC resonant converter under phase shift control is combined to obtain a state trajectory model of the LCC resonant converter and obtain a state monitoring result. The extended fundamental wave approximation method is used to calculate the peak current of the resonant cavity based on the state trajectory equation under each mode, specifically: By utilizing the frequency selection characteristics of the resonant cavity circuit of the LCC resonant converter, it is set that only the fundamental component of the switching frequency is input into the resonant cavity; the secondary side rectification network of the LCC resonant converter is equivalent to an RC parallel circuit and converted into the primary side circuit. Based on the obtained equivalent circuit, the peak value of the resonant cavity current is derived and calculated.

2. The state monitoring method of an LCC resonant converter according to claim 1, wherein: The mode of the LCC resonant converter within one switching cycle is obtained by the phase shift control strategy, specifically: The phase shift angle between the switching tubes of the inverter full-bridge arm of the LCC resonant converter is controlled to adjust the gain of the LCC resonant converter and obtain the mode within the one switching cycle.

3. The method for monitoring the state of an LCC resonant converter according to claim 1, wherein: The modes within one switching cycle include the first ZO mode, the ZN mode, the PN mode, the PO mode, the second ZO mode, the ZP mode, the NP mode and the NO mode in sequence; The state trajectory equations under each mode are specifically: The state trajectory equation of the first ZO mode is: ； The state trajectory equation of ZN mode: ； The state trajectory equation of PN mode: ； The state trajectory equation of PO mode: ； The trajectory equation of the second ZO mode is: ； The state trajectory equation of ZP mode: ； The state trajectory equation of NP mode: ； The state trajectory equation of NO mode: ； where, v CprN (t)=v CrN (t)+ v CpN (t); Where i LrN (t) is the normalized value of the resonant inductor Lr current, v CrN (t) is the series resonant capacitor C r The voltage is normalized to the value, v CpN (t) is the parallel resonant capacitance C p The normalized value, Z r is the resonant impedance of the two components, Z e is the three-element resonant impedance, r0 is the trajectory radius of the ZO mode, r1 is the trajectory radius of the ZN mode, r2 is the trajectory radius of the PN mode, r3 is the trajectory radius of the PO mode, r5 is the trajectory radius of the ZP mode, r6 is the trajectory radius of the NP mode, and r7 is the trajectory radius of the NO mode.

4. The method for monitoring the state of an LCC resonant converter according to claim 3, wherein: The trajectory circle radius under each mode is specifically: The trajectory radius of the first ZO mode and the second ZO mode is: ； The trajectory radius of the ZN mode and the ZP mode is: ； The trajectory radius of the PN mode and the NP mode is: ； The trajectory radius of the PO mode and the NO mode is: ； Among them, V o is the output voltage of the LCC resonant converter, I o is the output current of the LCC resonant converter, f s is the switching frequency, V in is the input voltage of the LCC resonant converter, V oN is the output voltage V o After normalization, n is the transformation ratio of the primary and secondary sides of the transformer, I Lrmax is the peak value of the resonant cavity current.

5. A state monitoring device for an LCC resonant converter, characterized in that: It includes acquisition module, current peak calculation module and modeling module; among them, The acquisition module is used to obtain the mode of the LCC resonant converter within a switching cycle through a phase shift control strategy, and divide it according to the input level and output level of the resonant cavity to obtain the state trajectory equation under each mode; The current peak calculation module is used to calculate the resonant cavity current peak value based on the state trajectory equation under each mode by using the extended fundamental wave approximation method; The modeling module is configured to calculate an analytical solution of the current and voltage variables at each mode switching point based on the calculated resonant cavity current peak value, and obtain a trajectory circle radius under each mode, thereby combining the obtained trajectory circle radii according to the operating order of the LCC resonant converter under phase shift control to obtain a state trajectory model of the LCC resonant converter and obtain a state monitoring result; The current peak calculation module calculates the resonant cavity current peak value by using the extended fundamental wave approximation method based on the state trajectory equation under each mode, specifically: The current peak calculation module utilizes the frequency selection characteristics of the resonant cavity circuit of the LCC resonant converter to set only the fundamental component of the switching frequency to be input into the resonant cavity; the secondary side rectifier network of the LCC resonant converter is equivalent to an RC parallel circuit and converted into the primary circuit; based on the obtained equivalent circuit, the resonant cavity current peak is derived and calculated.

6. The state monitoring device of an LCC resonant converter according to claim 5, characterized in that: The acquisition module obtains the mode of the LCC resonant converter within a switching cycle through a phase shift control strategy, specifically: The acquisition module controls the phase shift angle between the switching tubes of the inverter full-bridge arm of the LCC resonant converter to adjust the gain of the LCC resonant converter and obtain the mode within the one switching cycle.

7. The state monitoring device for an LCC resonant converter according to claim 5, wherein: The modes within one switching cycle include the first ZO mode, the ZN mode, the PN mode, the PO mode, the second ZO mode, the ZP mode, the NP mode and the NO mode in sequence; The state trajectory equations under each mode are specifically: The state trajectory equation of the first ZO mode is: ； The state trajectory equation of ZN mode: ； The state trajectory equation of PN mode: ； The state trajectory equation of PO mode: ； The trajectory equation of the second ZO mode is: ； The state trajectory equation of ZP mode: ； The state trajectory equation of NP mode: ； The state trajectory equation of NO mode: ； where, v CprN (t) = v CrN (t) + v CpN (t); Where i LrN (t) is the normalized value of the resonant inductor Lr current, v CrN (t) is the series resonant capacitor C r The voltage is normalized to the value, v CpN (t) is the parallel resonant capacitance C p The normalized value, Z r is the resonant impedance of the two components, Z e is the three-element resonant impedance, r0 is the trajectory radius of the ZO mode, r1 is the trajectory radius of the ZN mode, r2 is the trajectory radius of the PN mode, r3 is the trajectory radius of the PO mode, r5 is the trajectory radius of the ZP mode, r6 is the trajectory radius of the NP mode, and r7 is the trajectory radius of the NO mode.

8. The state monitoring device for an LCC resonant converter according to claim 7, wherein: The trajectory circle radius under each mode is specifically: The trajectory radius of the first ZO mode and the second ZO mode is: ； The trajectory radius of the ZN mode and the ZP mode is: ； The trajectory radius of the PN mode and the NP mode is: ； The trajectory radius of the PO mode and the NO mode is: ； Among them, V o is the output voltage of the LCC resonant converter, I o is the output current of the LCC resonant converter, f s is the switching frequency, V in is the input voltage of the LCC resonant converter, V oN is the output voltage V o After normalization, n is the transformation ratio of the primary and secondary sides of the transformer, I Lrmax is the peak value of the resonant cavity current.

Images