Excitation inductor design method for guaranteeing soft switching of CLLC resonant converter

Abstract

The invention discloses an excitation inductance design method for guaranteeing soft switching of a CLLC resonant converter, and the method comprises the steps: carrying out the qualitative analysis of a dead-zone equivalent circuit of the CLLC resonant converter, and carrying out the Laplace coordinate transformation. And according to the constant frequency analysis principle of the CLLC resonant converter, obtaining the electric quantity values of the capacitor and the inductor at the dead zone moment. And obtaining a resonance current time domain expression in a dead zone period by adopting a mesh current method. And calculating the period of the resonance current according to the parasitic capacitance values of the primary and secondary side switching tubes. And calculating the discharge time of the parasitic capacitor by considering the electric quantity of the capacitor. And calculating the excitation inductance value required when the resonance current just drops to zero when the dead time is ended. Soft switching of the resonant converter can be effectively guaranteed, the amplitude of the resonant current is reduced, the efficiency of the resonant converter is improved, and the universality is high.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronic converters, and specifically relates to a design method for the exciting inductance to ensure 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, new energy power generation, and uninterruptible power supplies. For applications that require a relatively high DC voltage, the voltage gain of the converter itself can be used to achieve step-up. For resonant converters, the operating efficiency is one of the core indicators. Especially in the application of using a resonant converter as a DC transformer, it is very necessary to improve efficiency and reduce costs. Therefore, on the basis of ensuring soft switching of the converter, the idea of increasing the exciting inductance value as much as possible to reduce the resonant current of the converter has become the mainstream. However, an overly small resonant current may cause the switching devices to be unable to complete charging and discharging during the dead time, resulting in the failure of soft switching and a decrease in efficiency instead. Summary of the Invention

[0003] The purpose of the present invention is to provide a design method for the exciting inductance to ensure soft switching of a CLLC resonant converter.

[0004] The technical solution for achieving the purpose of the present invention is as follows: A design method for the exciting inductance to ensure soft switching of a CLLC resonant converter, including:

[0005] Obtaining the dead-time equivalent circuit of the CLLC resonant converter during the dead time;

[0006] Obtaining the capacitor voltage and inductor current at the dead-time opening moment according to the fixed-frequency analysis principle of the CLLC resonant converter;

[0007] According to the fixed-frequency control characteristics of the resonant converter, determining that the resonant capacitor is a constant voltage source and the exciting inductance is a constant current source, performing Laplace transform on the resonant inductance, constructing a calculation matrix and solving to obtain the resonant current under the dead time;

[0008] Calculating the discharge charge required to achieve soft switching and the actual discharge charge according to the capacitance value of the parasitic capacitor of the switching tube, and determining the maximum exciting inductance value according to the discharge charge required to achieve soft switching and the actual discharge charge.

[0009] Preferably, the dead-time circuit includes a DC power supply on the input side , the parasitic capacitor of the primary-side switching tube , the primary-side series resonant inductor , the primary-side series resonant capacitor , the exciting inductance , the secondary-side series resonant inductor , the secondary-side series resonant capacitor , and a DC power supply on the output side , Parasitic capacitance of the secondary side switching transistor , Transformer , The DC power supply on the input side has its positive pole connected to one end of the parasitic capacitance of the primary side switching transistor , The DC power supply on the input side has its negative pole connected to one end of the series resonant capacitance on the primary side , The parasitic capacitance of the switching transistor has its other end connected to one end of the series resonant inductor on the primary side , The other end of the series resonant inductor on the primary side is connected to one end of the exciting inductor and the primary side's same - name terminal of the transformer , The primary side's different - name terminal of the transformer is connected to the other end of the exciting inductor and the other end of the series resonant capacitance on the primary side , The secondary side's same - name terminal of the transformer is connected to one end of the series resonant inductor on the secondary side , The other end of the series resonant inductor on the secondary side is connected to one end of the parasitic capacitance of the secondary side switching transistor , The other end of the parasitic capacitance of the secondary side switching transistor is connected to the positive pole of the DC power supply on the output side , The DC power supply on the output side has its negative pole connected to one end of the series resonant capacitance on the secondary side , The other end of the series resonant capacitance on the secondary side is connected to the secondary side's different - name terminal of the transformer T.

[0010] Preferably, according to the CLLC resonant converter fixed - frequency analysis principle, the resonant capacitor voltage at the dead - zone opening moment and the exciting inductor current are obtained. The specific formulas are:

[0011] ;

[0012] ;

[0013] In the formula, is the power of the resonant converter, is the input voltage of the resonant converter, is the capacitance value of the resonant capacitor, is the switching frequency of the resonant converter, is the inductance value of the exciting inductor.

[0014] Preferably, the specific method for performing Laplace transform on the resonant inductor, constructing a calculation matrix and solving to obtain the resonant current under the dead - zone is:

[0015]

[0016] Wherein, is the s-domain form of the resonant current, is the s-domain form of the secondary mesh current, is the inductance value of the primary resonant inductor, is the equivalent inductance value of the secondary series resonant inductor referred to the primary side of the transformer, is the turns ratio of the transformer, is the capacitance value of the parasitic capacitance of the primary and secondary switching transistors, is the voltage of the primary resonant capacitor, is the equivalent resonant capacitor voltage of the secondary resonant capacitor voltage referred to the primary side, is the exciting inductance 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 under dead time:

[0018]

[0019] Wherein is the inductance value of the primary resonant inductor, is the equivalent inductance value of the secondary series resonant inductor referred to the primary side of the transformer, is the turns ratio of the transformer, is the capacitance value of the parasitic capacitance of the primary and secondary switching transistors, is the voltage of the primary resonant capacitor, is the equivalent resonant capacitor voltage of the secondary resonant capacitor voltage referred to the primary side, is the exciting inductance current;

[0020] Preferably, the discharge charge required to achieve soft switching and the actual discharge charge are respectively:

[0021] ;

[0022] ;

[0023] Wherein, is the discharge charge required to achieve soft switching, is the actual discharge charge of the resonant current during dead time, is the dead time, is the input voltage of the converter, is the resonant current, is the capacitance value of the parasitic capacitance of the primary and secondary switching transistors.

[0024] Preferably, the maximum exciting inductance value is specifically:

[0025] ;

[0026] Among them, represents the maximum exciting inductance value at which the converter achieves the lowest loss, is the primary resonant inductance value, is the equivalent resonant inductance value of the secondary series resonant inductance referred to the primary side of the transformer, is the transformer turns ratio, is the capacitance value of the parasitic capacitances of the primary and secondary switching transistors, is the primary resonant capacitor voltage, is the equivalent resonant capacitor voltage of the secondary resonant capacitor voltage referred to the primary side, is the exciting inductance current, is the dead time, is the input voltage of the CLLC converter.

[0027] Compared with the prior art, the significant advantages of the present invention are as follows: By analyzing the dead-time equivalent circuit of the CLLC resonant converter, the present invention obtains the detailed waveform of the resonant current using Laplace transform, and then by accurately controlling the time when the resonant current drops to zero and reasonably setting the exciting inductance to ensure complete discharge of the parasitic capacitance, the loss of the converter can be effectively reduced, the soft-switching can be ensured to take effect, and the universality is strong.

[0028] The present invention will be further described in detail below with reference to the accompanying drawings. Description of the Drawings

[0029] Figure 1 is the dead-time circuit diagram of the CLLC resonant converter.

[0030] Figure 2 is the equivalent Laplace circuit diagram of the dead time of the CLLC resonant converter.

[0031] Figure 3 is a schematic diagram of the fixed-frequency control of a CLLC resonant converter.

[0032] Figure 4 is the dead-time soft-switching simulation result diagram of the CLLC resonant converter.

[0033] Figure 5 is the waveform comparison diagram between the traditional exciting inductance design method and the exciting inductance design method proposed by the present invention. Detailed Embodiments

[0034] The present invention will be described in detail below with reference to specific examples.

[0035] In order to more clearly describe the object, technical solution and advantages of the present invention, the detailed embodiments are illustrated by examples and the accompanying drawings. Obviously, the described embodiments are only used to explain the present invention and are not limited to the present invention.

[0036] A design method of exciting inductance to ensure soft switching of CLLC resonant converter, which specifically includes:

[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-time circuit includes the input-side DC power supply , the parasitic capacitance of the primary-side switch , the primary-side series resonant inductor , the primary-side series resonant capacitor , the exciting inductance , the secondary-side series resonant inductor , the secondary-side series resonant capacitor , the output-side DC power supply , the parasitic capacitance of the secondary-side switch , the transformer , the positive pole of the input-side DC power supply is connected to one end of the parasitic capacitance of the primary-side switch , the negative pole of the input-side DC power supply is connected to one end of the primary-side series resonant capacitor , the other end of the parasitic capacitance of the switch is connected to one end of the primary-side series resonant inductor , the other end of the primary-side series resonant inductor is connected to one end of the exciting inductance and the primary-side homonymous terminal of the transformer , the primary-side heteronymous terminal of the transformer is connected to the other end of the exciting inductance and the other end of the primary-side series resonant capacitor , the secondary-side homonymous terminal of the transformer is connected to one end of the secondary-side series resonant inductor , the secondary-side heteronymous terminal of the secondary-side series resonant inductor is connected to one end of the parasitic capacitance of the secondary-side switch , the other end of the parasitic capacitance of the secondary-side switch is connected to the positive pole of the output-side DC power supply , the negative pole of the output-side DC power supply is connected to one end of the secondary-side series resonant capacitor , the other end of the secondary-side series resonant capacitor is connected to the secondary-side heteronymous terminal of the transformer .

[0039] Step 2: According to the volt-second balance principle of the inductor and the charge conservation principle of the capacitor, the resonant capacitor voltage and the magnetizing inductor current at the dead-time start moment are obtained. The specific formulas are as follows:

[0040]

[0041]

[0042] In the formulas, is the power of the resonant converter, is the input voltage of the resonant converter, is the capacitance value of the resonant capacitor, is the switching frequency of the resonant converter, is the inductance value of the magnetizing inductor.

[0043] Step 3: According to the principle that the inductance value of the magnetizing inductor of the resonant converter is much larger than that of the resonant inductor, and the larger the inductance value, the slower the change of its own current, it is determined that the magnetizing inductor of the circuit is a constant current source; according to the principle that the capacitance value of the resonant capacitor of the resonant converter is much larger than the parasitic capacitance value of the switching tube, and the larger the capacitance value, the slower the change of its own voltage, it is determined that the resonant capacitor of the circuit is a constant voltage source.

[0044] The Laplace transform of the resonant inductor is performed to obtain the Laplace circuit during the dead time. A calculation matrix is established by the mesh current method. The specific formulas are as follows:

[0045]

[0046] In the formulas, is the s-domain form of the resonant current, is the s-domain form of the secondary mesh current, is the inductance value of the primary resonant inductor, is the equivalent inductance value of the secondary series resonant inductor referred to the primary side of the transformer, is the turns ratio of the transformer, is the capacitance value of the primary and secondary switching tube parasitic capacitances, is the primary resonant capacitor voltage, is the equivalent resonant capacitor voltage of the secondary resonant capacitor voltage referred to the primary side, is the magnetizing inductor current;

[0047] The calculation matrix is solved to obtain the resonant current expression under the dead time:

[0048]

[0049] Step 4: According to the parasitic capacitance value of the switching tube, the discharge charge required to achieve soft switching and the actual discharge charge are calculated, and the maximum magnetizing inductor value is determined based on the discharge charge required to achieve soft switching and the actual discharge charge. The specific process is as follows:

[0050] Combined with the converter input voltage Calculate the required discharge charge of the parasitic capacitance , and the corresponding formula is:

[0051]

[0052] Discharge charge of the resonant current during the dead time Determined jointly by the resonant current and the dead time :

[0053]

[0054] To achieve soft switching of the resonant converter, the discharge charge of the resonant current needs to be greater than the required discharge charge of the parasitic capacitance. The corresponding formula is:

[0055]

[0056] Solving it can obtain the maximum value of the exciting inductance that meets the requirements. The corresponding formula is:

[0057]

[0058] Among them, among them, represents the maximum value of the exciting inductance for the converter to achieve the lowest loss, is the value of the primary resonant inductance, is the equivalent resonant inductance value of the secondary series resonant inductance referred to the primary side of the transformer, is the turns ratio of the transformer, is the capacitance value of the parasitic capacitances of the primary and secondary switching devices, is the primary resonant capacitor voltage, is the equivalent resonant capacitor voltage of the secondary resonant capacitor voltage referred to the primary side, is the exciting inductance current, is the dead time, is the input voltage of the CLLC converter.

[0059] According to the obtained result of the maximum value of the exciting inductance in the design, when manufacturing the high-frequency transformer, the exciting inductance can be increased to the maximum value by reducing the air gap, etc., and the manufactured high-frequency transformer is installed in the CLLC resonant converter for test operation. This can not only reduce the working current of the CLLC resonant converter, but also ensure that the switching devices achieve zero-voltage turn-on, thereby improving the operating efficiency of the CLLC resonant converter as much as possible.

[0060] Embodiment

[0061] Such as Figure 1As shown, it is the dead-time equivalent circuit of the CLLC resonant converter provided by the embodiment of the present invention, including the input-side DC power supply , the parasitic capacitance of the primary-side switching transistor , the primary-side series resonant inductor , the primary-side series resonant capacitor , the exciting inductor , the secondary-side series resonant inductor , the secondary-side series resonant capacitor , the output-side DC power supply , the parasitic capacitance of the secondary-side switching transistor , the transformer .

[0062] As Figure 2 shown, it is a dead-time equivalent Laplace circuit of the CLLC resonant converter provided by the embodiment of the present invention. It includes: a series circuit of a resonant inductor equivalent impedance and a voltage source, a resonant capacitor voltage source circuit, and an exciting inductor constant current source circuit.

[0063] As Figure 3 shown, it is a schematic diagram of the fixed-frequency control of the CLLC resonant converter provided by the embodiment of the present invention. The main process includes: subtracting the output voltage from the voltage reference value and sending the result to the PI controller. The output of the PI controller is the voltage compensation amount . The voltage compensation amount is used as the input of the voltage-controlled oscillator VCO, and the output of the voltage-controlled oscillator VCO is a complementary pulse with a duty cycle of 50%.

[0064] To illustrate the correctness and effectiveness of the control strategy proposed by the present invention, a simulation model is established according to Figures 1 to 3 .

[0065] Figure 4 is the simulation result of the dead-time soft switching of the CLLC resonant converter. It can be seen from the simulation result that during the dead time, the resonant current gradually decreases according to the expression. The design method of the exciting inductor proposed by the present invention can make the resonant current drop to zero at the end of the dead time. It can be seen that the design method proposed by the present invention can make the best use of the discharge performance of the resonant current and effectively reduce the loss of the CLLC resonant converter on the premise of ensuring soft switching.

[0066] Figure 5 is the waveform comparison between the traditional exciting inductor design method and the exciting inductor design method proposed by the present invention. It can be seen that the result of the exciting inductor design method proposed by the present invention is accurate and will not cause the resonant current to be too small to make the soft switching fail, which has obvious advantages over the exciting inductor 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 moment of dead zone opening are obtained; According to the constant frequency control characteristics of the resonant converter, the resonant capacitor is determined as a constant voltage source, the excitation inductor is determined as a constant current source, and the resonant inductor is Laplace transformed to construct a calculation matrix and solve to obtain the resonant current in the dead zone; According to the parasitic capacitance of the switch tube, the discharge amount required to achieve soft switching and the actual discharge amount are calculated, and the maximum excitation inductance is determined according to the discharge amount required to achieve soft switching and the actual discharge amount.

2. The method for designing the excitation inductance for ensuring soft switching of the CLLC resonant converter according to claim 1, characterized in that: The dead zone circuit includes an input side DC power supply , parasitic capacitance of primary switch tube , primary series resonant inductor , primary series resonant capacitor , Excitation inductance , Secondary side series resonant inductor , Secondary side series resonant capacitor , DC power supply on output side , Parasitic capacitance of the secondary switch tube ,transformer , the input side DC power supply Parasitic capacitance between positive electrode and primary switch 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 The other end is connected in series with the primary side resonant inductor One end of the primary series resonant inductor is connected to The other end of the excitation inductor One end and the transformer The primary same-name end of the transformer is connected The primary opposite end and the excitation inductance The other end of the primary side is connected to the series resonant capacitor The other end of the transformer is connected The secondary same-name terminal is connected in series with the secondary side resonant inductor One end of the secondary side is connected to the series resonant inductor The parasitic capacitance between the secondary opposite end and the secondary switch tube The parasitic capacitance of the secondary switch tube is connected to one end of 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 is connected to the secondary side in series with the resonant capacitor One end of the secondary side is connected to the series resonant capacitor The other end is connected to the secondary opposite end of the transformer T.

3. The method for designing the excitation inductance for ensuring soft switching of the CLLC resonant converter according to claim 1, characterized in that: According to the fixed frequency analysis principle of CLLC resonant converter, the resonant capacitor voltage at the dead zone start time is obtained. and the magnetizing inductor current , the specific formula is: ； ； In the formula, is the resonant converter power, is the resonant converter input voltage, is the resonant capacitor value, is the resonant converter switching frequency, is the magnetizing inductance value.

4. The method for designing the excitation inductance for ensuring soft switching of a CLLC resonant converter according to claim 1, characterized in that: The specific method of performing Laplace transform on the resonant inductor, constructing the calculation matrix and solving the resonant current in the dead zone is: ， In the formula, 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, is the equivalent resonant inductance of the secondary side resonant inductance converted to the primary side of the transformer, is the transformer turns ratio, is the capacitance of the parasitic capacitance of the original secondary 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: ， In the formula, is the primary resonant inductance value, is the equivalent resonant inductance of the secondary side resonant inductance converted to the primary side of the transformer, is the transformer turns ratio, is the capacitance of the parasitic capacitance of the original secondary 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.

5. The method for designing the excitation inductance for ensuring soft switching of a CLLC resonant converter according to claim 1, characterized in that: The discharge amount required to achieve soft switching and the actual discharge amount are: ； ； in, To achieve the required discharge amount for soft switching, is the actual discharge amount of the resonant current during the dead time, 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.

6. The method for designing the excitation inductance for ensuring soft switching of the CLLC resonant converter according to claim 5, characterized in that: 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, is the equivalent resonant inductance of the secondary side resonant inductance converted to the primary side of the transformer, is the transformer turns ratio, is the capacitance of the parasitic capacitance of the original secondary 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, It is the input voltage of CLLC converter.

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