A magnetizing inductor design method to ensure soft switching of CLLC resonant converter
By analyzing the dead-zone equivalent circuit of the CLLC resonant converter and using Laplace transform, the resonant current is controlled to drop to zero, and the excitation inductance is reasonably set. This solves the problem of soft switching failure caused by too small resonant current, and achieves reduced converter loss and improved efficiency.
Patent Information
- Application Number
- CN202510538196.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-27
- Publication Date
- 2025-09-16
- Estimated Expiration
- 2045-04-27
AI Technical Summary
The resonant current of the existing CLLC resonant converter during the dead zone may be too small, resulting in soft switching failure and thus reducing efficiency.
By analyzing the dead zone equivalent circuit and using Laplace transform to obtain the resonant current waveform, the current is accurately controlled to drop to zero. The excitation inductance is reasonably set to ensure that the parasitic capacitance is completely discharged, ensuring that soft switching is effective.
Effectively reduce converter losses, ensure the effectiveness of soft switching, and improve the operating efficiency of the CLLC resonant converter.
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Figure CN120090453B_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of power electronic converters, and in particular relates to a method for designing an excitation inductor for ensuring soft switching of a CLLC resonant converter. Background Art
[0002] CLLC resonant converters can be widely used in various applications, such as DC microgrids, electric vehicles, renewable energy generation, and uninterruptible power supplies. For applications requiring higher DC voltages, the CLLC resonant converter can be used to boost the voltage using its inherent voltage gain. Operating efficiency is a key performance indicator for resonant converters. Improving efficiency and reducing costs are particularly crucial when using the resonant converter as a DC transformer. Therefore, while ensuring soft switching, the mainstream approach is to maximize the magnetizing inductance to reduce the converter's resonant current. However, excessively low resonant current can prevent the switching device from completing charging and discharging during the dead time, leading to soft switching failure and, in turn, reduced efficiency. Summary of the Invention
[0003] The object of the present invention is to provide a method for designing an excitation inductor to ensure soft switching of a CLLC resonant converter.
[0004] The technical solution for achieving the purpose of the present invention is: a method for designing an excitation inductor to ensure soft switching of a CLLC resonant converter, comprising:
[0005] Obtaining a dead-time equivalent circuit of a CLLC resonant converter during a dead-time period;
[0006] According to the fixed-frequency analysis principle of CLLC resonant converter, the capacitor voltage and inductor current at the dead zone start time are obtained;
[0007] According to the fixed-frequency control characteristics of the resonant converter, the resonant capacitor is determined as a constant voltage source and the excitation inductor is determined as a constant current source. The resonant inductor is Laplace transformed, and a calculation matrix is constructed and solved to obtain the resonant current in the dead zone.
[0008] According to the parasitic capacitance of the switch tube, the discharge power required to achieve soft switching and the actual discharge power are calculated, and the maximum excitation inductance is determined based on the discharge power required to achieve soft switching and the actual discharge power.
[0009] Preferably, the dead zone circuit includes an input side DC power supply , parasitic capacitance of the primary switch tube , primary side series resonant inductor , primary side series resonant capacitor , excitation inductance , secondary side series resonant inductor , secondary side series resonant capacitor , output side DC power supply , parasitic capacitance of the secondary switch tube ,transformer , the input side DC power supply Parasitic capacitance between the positive electrode and the primary switching tube One end is connected to the input side DC power supply Negative electrode and primary side series resonant capacitor One end of the switch tube parasitic capacitance is connected to The other end is connected in series with the primary side resonant inductor One end of the primary side series resonant inductor is connected to The other end of the excitation inductor One end and the transformer The primary same-name terminal of the transformer is connected The primary opposite end and the excitation inductance The other end and the primary side series resonant capacitor The other end of the transformer is connected The secondary same-name terminal and the secondary side series resonant inductor One end of the secondary side is connected to the series resonant inductor The parasitic capacitance between the secondary opposite terminal and the secondary switch tube One end is connected to the parasitic capacitance of the secondary switch tube The other end of the DC power supply is connected to the output side The positive connection of the output side DC power supply The negative pole and the secondary side series resonant capacitor One end of the secondary side is connected to the series resonant capacitor The other end is connected to the secondary opposite-name terminal of transformer T.
[0010] Preferably, the resonant capacitor voltage at the dead zone opening moment is obtained according to the fixed frequency analysis principle of the CLLC resonant converter. and the magnetizing inductor current , the specific formula is:
[0011] ;
[0012] ;
[0013] Where, is the resonant converter power, is the resonant converter input voltage, is the resonant capacitor value, is the resonant converter switching frequency, is the excitation inductance value.
[0014] Preferably, the specific method of performing Laplace transform on the resonant inductor, constructing a calculation matrix and solving to obtain the resonant current in the dead zone is:
[0015]
[0016] Where, is the s-domain form of the resonant current, is the s-domain form of the secondary mesh current, is the primary resonant inductance value, The equivalent resonant inductance of the secondary side resonant inductance converted to the primary side of the transformer is: is the transformer turns ratio, is the capacitance of the parasitic capacitance of the original secondary side switch tube, is the primary resonant capacitor voltage, is the equivalent resonant capacitor voltage converted from the secondary resonant capacitor voltage to the primary side, is the magnetizing inductor current;
[0017] Solve the calculation matrix to obtain the s-domain expression of the resonant current, and finally obtain the time-domain expression of the resonant current in the dead zone:
[0018]
[0019] In the formula is the primary resonant inductance value, The equivalent resonant inductance of the secondary side resonant inductance converted to the primary side of the transformer is: is the transformer turns ratio, is the capacitance of the parasitic capacitance of the original secondary side switch tube, is the primary resonant capacitor voltage, is the equivalent resonant capacitor voltage converted from the secondary resonant capacitor voltage to the primary side, is the magnetizing inductor current;
[0020] Preferably, the discharge amount required to achieve soft switching and the actual discharge amount are:
[0021] ;
[0022] ;
[0023] in, To achieve the required discharge amount for soft switching, is the actual discharge amount of the resonant current during the dead zone, is the dead time, is the converter input voltage, is the resonant current, It is the capacitance of the parasitic capacitance of the original secondary side switch tube.
[0024] Preferably, the maximum excitation inductance value is specifically:
[0025] ;
[0026] in, Indicates the maximum excitation inductance value for the converter to achieve the lowest loss. is the primary resonant inductance value, The equivalent resonant inductance of the secondary side resonant inductance converted to the primary side of the transformer is: is the transformer turns ratio, is the capacitance of the parasitic capacitance of the original secondary side switch tube, is the primary resonant capacitor voltage, is the equivalent resonant capacitor voltage converted from the secondary resonant capacitor voltage to the primary side, is the magnetizing inductor current, is the dead time, is the input voltage of the CLLC converter.
[0027] Compared with the existing technology, the present invention has the following significant advantages: by analyzing the dead-zone equivalent circuit of the CLLC resonant converter, the present invention uses Laplace transform to obtain the detailed waveform of the resonant current, and then accurately controls the time for the resonant current to drop to zero, reasonably sets the excitation inductance to ensure that the parasitic capacitance is completely discharged, which can effectively reduce the converter loss, ensure the effectiveness of soft switching, and has strong versatility.
[0028] The present invention is further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS
[0029] Figure 1 This is the dead zone circuit diagram of the CLLC resonant converter.
[0030] Figure 2 This is the dead zone equivalent Laplace circuit diagram of the CLLC resonant converter.
[0031] Figure 3 It is a schematic diagram of fixed frequency control of a CLLC resonant converter.
[0032] Figure 4 This is the simulation result of the CLLC resonant converter dead zone soft switching.
[0033] Figure 5 It is a waveform comparison diagram of the traditional excitation inductance design method and the excitation inductance design method proposed by the present invention. DETAILED DESCRIPTION
[0034] The present invention is described in detail below with reference to specific examples.
[0035] In order to more clearly describe the purpose, technical solutions and advantages of the present invention, the specific implementation methods are illustrated by examples and drawings. Obviously, the described embodiments are only used to explain the present invention and are not limited to the present invention.
[0036] A method for designing an excitation inductor to ensure soft switching of a CLLC resonant converter is provided. The method specifically comprises:
[0037] Step 1: Qualitatively analyze the circuit during the dead time of the CLLC resonant converter to obtain the dead time equivalent circuit;
[0038] The dead zone circuit includes an input side DC power supply , parasitic capacitance of the primary switch tube , primary side series resonant inductor , primary side series resonant capacitor , excitation inductance , secondary side series resonant inductor , secondary side series resonant capacitor , output side DC power supply , parasitic capacitance of the secondary switch tube ,transformer , the input side DC power supply Parasitic capacitance between the positive electrode and the primary switching tube One end is connected to the input side DC power supply Negative electrode and primary side series resonant capacitor One end of the switch tube parasitic capacitance is connected to The other end is connected in series with the primary side resonant inductor One end of the primary side series resonant inductor is connected to The other end of the excitation inductor One end and the transformer The primary same-name terminal of the transformer is connected The primary opposite end and the excitation inductance The other end and the primary side series resonant capacitor The other end of the transformer is connected The secondary same-name terminal and the secondary side series resonant inductor One end of the secondary side is connected to the series resonant inductor The parasitic capacitance between the secondary opposite terminal and the secondary switch tube One end is connected to the parasitic capacitance of the secondary switch tube The other end of the DC power supply is connected to the output side The positive connection of the output side DC power supply The negative pole and the secondary side series resonant capacitor One end of the secondary side is connected to the series resonant capacitor The other end of the transformer The secondary synonym end connection.
[0039] Step 2: Based on the volt-second balance principle of the inductor and the charge conservation principle of the capacitor, the resonant capacitor voltage and the excitation inductor current at the moment the dead zone is turned on are obtained. The specific formula is:
[0040]
[0041]
[0042] Where, is the resonant converter power, is the resonant converter input voltage, is the resonant capacitor value, is the resonant converter switching frequency, is the excitation inductance value.
[0043] Step 3: Based on the principle that the excitation inductance of the resonant converter is much larger than the resonant inductance, and the larger the inductance, the slower the change of its own current, the excitation inductance of the circuit is determined to be a constant current source; based on the principle that the resonant capacitor of the resonant converter is much larger than the parasitic capacitance of the switching tube, and the larger the capacitance, the slower the change of its own voltage, the resonant capacitor of the circuit is determined to be a constant voltage source.
[0044] Performing Laplace transform on the resonant inductor yields the Laplace circuit during the dead zone. The calculation matrix is established using the mesh current method. The specific formula is:
[0045]
[0046] Where, is the s-domain form of the resonant current, is the s-domain form of the secondary mesh current, is the primary resonant inductance value, The equivalent resonant inductance of the secondary side resonant inductance converted to the primary side of the transformer is: is the transformer turns ratio, is the capacitance of the parasitic capacitance of the original secondary side switch tube, is the primary resonant capacitor voltage, is the equivalent resonant capacitor voltage converted from the secondary resonant capacitor voltage to the primary side, is the magnetizing inductor current;
[0047] Solving the calculation matrix, we can get the resonant current expression in the dead zone:
[0048]
[0049] Step 4: Calculate the discharge power required to achieve soft switching and the actual discharge power based on the parasitic capacitance of the switch tube. Then determine the maximum excitation inductance based on the discharge power required to achieve soft switching and the actual discharge power. The specific process is as follows:
[0050] Combined converter input voltage Calculate the discharge capacity required for parasitic capacitance , the corresponding formula is:
[0051]
[0052] Resonant current discharge quantity during dead time The resonant current and dead time Jointly decided:
[0053]
[0054] To achieve soft switching of the resonant converter, the resonant current discharge quantity must be greater than the parasitic capacitance discharge quantity. The corresponding formula is:
[0055]
[0056] The solution can obtain the maximum excitation inductance value that meets the requirements. The corresponding formula is:
[0057]
[0058] Among them, among them, Indicates the maximum excitation inductance value for the converter to achieve the lowest loss. is the primary resonant inductance value, The equivalent resonant inductance of the secondary side resonant inductance converted to the primary side of the transformer is: is the transformer turns ratio, is the capacitance of the parasitic capacitance of the original secondary side switch tube, is the primary resonant capacitor voltage, is the equivalent resonant capacitor voltage converted from the secondary resonant capacitor voltage to the primary side, is the magnetizing inductor current, is the dead time, is the input voltage of the CLLC converter.
[0059] According to the design, the maximum excitation inductance value is obtained. When making a high-frequency transformer, the excitation inductance can be increased to the maximum value by reducing the air gap, and the completed high-frequency transformer is installed in the CLLC resonant converter for test operation. This can not only reduce the operating current of the CLLC resonant converter, but also ensure that the switching device is turned on at zero voltage, thereby maximizing the operating efficiency of the CLLC resonant converter.
[0060] Example
[0061] like Figure 1As shown, the dead zone equivalent circuit of the CLLC resonant converter provided by the embodiment of the present invention includes an input side DC power supply , parasitic capacitance of the primary switch tube , primary side series resonant inductor , primary side series resonant capacitor , excitation inductance , secondary side series resonant inductor , secondary side series resonant capacitor , output side DC power supply , parasitic capacitance of the secondary switch tube ,transformer .
[0062] like Figure 2 The figure shows a dead-zone equivalent Laplace circuit of a CLLC resonant converter provided by an embodiment of the present invention, which includes: a series circuit of a resonant inductor equivalent impedance and a voltage source, a resonant capacitor voltage source circuit, and an excitation inductor constant current source circuit.
[0063] like Figure 3 The figure shows a fixed frequency control diagram of a CLLC resonant converter provided by an embodiment of the present invention. The main process includes: With voltage reference value After the difference is made, it is sent to the PI controller. The output of the PI controller is the voltage compensation amount. , the voltage compensation amount As the input of the voltage controlled oscillator VCO, the output duty cycle of the voltage controlled oscillator VCO is a complementary pulse with 50%.
[0064] In order to illustrate the correctness and effectiveness of the control strategy proposed by the present invention, according to Figures 1 to 3 Build a simulation model.
[0065] Figure 4 The following are simulation results of soft switching in the dead zone of a CLLC resonant converter. The simulation results show that during the dead zone, the resonant current gradually decreases according to the expression. The proposed magnetizing inductance design method can reduce the resonant current to zero at the end of the dead zone. This shows that the proposed design method maximizes the resonant current discharge performance, effectively reducing the losses of the CLLC resonant converter while ensuring soft switching.
[0066] Figure 5 The waveform comparison between the traditional excitation inductance design method and the excitation inductance design method proposed in the present invention shows that the excitation inductance design method proposed in the present invention has accurate results and will not cause the resonant current to be too small to cause soft switching failure. It has obvious advantages over the excitation inductance design method.
Claims
1. A method for designing an excitation inductor to ensure soft switching of a CLLC resonant converter, characterized in that: include: Obtaining a dead-time equivalent circuit of a CLLC resonant converter during a dead-time period; According to the fixed-frequency analysis principle of CLLC resonant converter, the capacitor voltage and inductor current at the dead zone start time are obtained; According to the fixed-frequency control characteristics of the resonant converter, the resonant capacitor is determined as a constant voltage source and the excitation inductor is determined as a constant current source. The resonant inductor is Laplace transformed, and a calculation matrix is constructed and solved to obtain the resonant current in the dead zone. According to the parasitic capacitance of the switch tube, the discharge power required to achieve soft switching and the actual discharge power are calculated, and the maximum excitation inductance is determined based on the discharge power required to achieve soft switching and the actual discharge power. The discharge power required to achieve soft switching and the actual discharge power are: ； ； in, To achieve the required discharge amount for soft switching, is the actual discharge amount of the resonant current during the dead zone, is the dead time, is the converter input voltage, is the resonant current, is the capacitance of the parasitic capacitance of the primary and secondary switching tubes. The maximum excitation inductance is: ； in, Indicates the maximum excitation inductance value for the converter to achieve the lowest loss. is the primary resonant inductance value, The equivalent resonant inductance of the secondary side resonant inductance converted to the primary side of the transformer is: is the transformer turns ratio, is the capacitance of the parasitic capacitance of the original secondary side switch tube, is the primary resonant capacitor voltage, is the equivalent resonant capacitor voltage converted from the secondary resonant capacitor voltage to the primary side, is the dead time, is the input voltage of the CLLC converter, is the switching frequency of the resonant converter.
2. The method for designing an excitation inductor for ensuring soft switching of a CLLC resonant converter according to claim 1, wherein: The dead zone equivalent circuit includes an input side DC power supply , parasitic capacitance of the primary switch tube , primary side series resonant inductor , primary side series resonant capacitor , excitation inductance , secondary side series resonant inductor , secondary side series resonant capacitor , output side DC power supply , parasitic capacitance of the secondary switch tube ,transformer , the input side DC power supply Parasitic capacitance between the positive electrode and the primary switching tube One end is connected to the input side DC power supply Negative electrode and primary side series resonant capacitor One end of the switch tube parasitic capacitance is connected to The other end is connected in series with the primary side resonant inductor One end of the primary side series resonant inductor is connected to The other end of the excitation inductor One end and the transformer The primary same-name terminal of the transformer is connected The primary opposite end and the excitation inductance The other end and the primary side series resonant capacitor The other end of the transformer is connected The secondary same-name terminal and the secondary side series resonant inductor One end of the secondary side is connected to the series resonant inductor The parasitic capacitance between the secondary opposite terminal and the secondary switch tube One end is connected to the parasitic capacitance of the secondary switch tube The other end of the DC power supply is connected to the output side The positive connection of the output side DC power supply The negative pole and the secondary side series resonant capacitor One end of the secondary side is connected to the series resonant capacitor The other end is connected to the secondary opposite-name terminal of transformer T.
3. The method for designing an excitation inductor for ensuring soft switching of a CLLC resonant converter according to claim 1, wherein: According to the fixed frequency analysis principle of CLLC resonant converter, the resonant capacitor voltage at the dead zone opening time is obtained. and the magnetizing inductor current , the specific formula is: ； ； Where, is the resonant converter power, is the resonant converter input voltage, is the resonant capacitor value, is the resonant converter switching frequency, is the excitation inductance value.
4. The method for designing an excitation inductor for ensuring soft switching of a CLLC resonant converter according to claim 1, wherein: The specific method of performing Laplace transform on the resonant inductor, constructing the calculation matrix and solving to obtain the resonant current in the dead zone is: ， Where, is the s-domain form of the resonant current, is the s-domain form of the secondary mesh current, is the primary resonant inductance value, The equivalent resonant inductance of the secondary side resonant inductance converted to the primary side of the transformer is: is the transformer turns ratio, is the capacitance of the parasitic capacitance of the original secondary side switch tube, is the primary resonant capacitor voltage, is the equivalent resonant capacitor voltage converted from the secondary resonant capacitor voltage to the primary side, is the magnetizing inductor current; Solve the calculation matrix to obtain the s-domain expression of the resonant current, and finally obtain the time-domain expression of the resonant current in the dead zone: ， Where, is the primary resonant inductance value, The equivalent resonant inductance of the secondary side resonant inductance converted to the primary side of the transformer is: is the transformer turns ratio, is the capacitance of the parasitic capacitance of the original secondary side switch tube, is the primary resonant capacitor voltage, is the equivalent resonant capacitor voltage converted from the secondary resonant capacitor voltage to the primary side, is the magnetizing inductor current.