Method for analyzing influence factors of current sharing capability of parallel secondary winding of CLLLC resonant converter

Abstract

The invention discloses a method for analyzing influence factors of current sharing capability of a parallel secondary winding of a CLLLC resonant converter. The method comprises the following steps of: obtaining an equivalent circuit diagram from a parallel secondary winding topology of the CLLLC resonant converter; obtaining resonance current of the two parallel windings based on the equivalent circuit diagram; based on the resonance current, combining the working frequency of a resonant cavity, analyzing the current sharing capability influence factors of the parallel secondary winding, and obtaining a preliminary analysis result; simulating the equivalent circuit diagram to obtain a simulation waveform; and obtaining a final analysis result based on the simulation waveform and the preliminary analysis result. According to the method, a circuit equation is greatly simplified through reasonable order of magnitude approximation, the calculation efficiency is improved while the precision is guaranteed, the method has remarkable circuit design guidance value, and finally the correctness of the scheme is verified through interaction of theories and simulation.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of isolated DC-DC converter, and particularly relates to a method for analyzing factors influencing current sharing capability of parallel secondary winding of CLLLC resonant converter. BACKGROUND

[0002] The CLLLC resonant converter is very suitable for bidirectional working scene, and in a high-power application scene, the output current of the secondary side is large, and parallel winding design is often adopted. Analyzing the current sharing capability of the parallel secondary winding of the CLLLC converter is fundamentally significant to ensure that the converter can safely, reliably and efficiently operate at the designed power level. It is directly related to the thermal stability, long-term life, energy conversion efficiency, power density potential and design robustness of the system, but the current sharing analysis is not considered in the prior art, and ignoring the current sharing analysis may lead to design hazards, causing overheating, failure or substandard performance in actual application. Therefore, there is an urgent need for a method for analyzing factors influencing current sharing capability of parallel secondary winding of CLLLC resonant converter. SUMMARY

[0003] To solve the above technical problems, the application provides a method for analyzing factors influencing current sharing capability of parallel secondary winding of CLLLC resonant converter, which can obtain the main factors influencing current sharing capability at different switching frequencies.

[0004] To achieve the above purpose, the application provides a method for analyzing factors influencing current sharing capability of parallel secondary winding of CLLLC resonant converter, comprising:

[0005] obtaining an equivalent circuit diagram from the parallel secondary winding topology of the CLLLC resonant converter;

[0006] based on the equivalent circuit diagram, obtaining resonant currents of two parallel windings;

[0007] based on the resonant currents, combining the resonant cavity working frequency, analyzing factors influencing current sharing capability of the parallel secondary winding, and obtaining preliminary analysis results;

[0008] simulating the equivalent circuit diagram to obtain simulation waveforms;

[0009] based on the simulation waveforms and the preliminary analysis results, obtaining final analysis results.

[0010] Optionally, the resonant currents of the two parallel windings are respectively:

[0011]

[0012] wherein, v in is the input voltage of the parallel winding, v o is the output voltage, ir1 i is the resonant current of the first winding. r2 L is the resonant current of the second winding. s1 L s2 For a two-winding resonant inductor, C s1 C s2 For the two-winding resonant capacitor, L k1 L k2 For a two-winding circuit inductance, R s1 R s2 Let ω be the resistance of the two windings, j be the complex unit, and ω be the switching angular frequency.

[0013] Optionally, based on the resonant current and the operating frequency of the resonant cavity, the factors affecting the rated current sharing capability of the parallel secondary winding are analyzed, and preliminary analysis results are obtained, including:

[0014] Based on the operating frequency of the resonant cavity, it is divided into three different operating conditions: resonant point, over-resonance, and under-resonance.

[0015] The factors affecting the rated current sharing capacity of the parallel secondary winding at the resonance point, over-resonance, and under-resonance are analyzed respectively, and preliminary analysis results are obtained.

[0016] Optionally, the analysis of factors affecting the rated current sharing capability of the parallel secondary winding at the resonant point includes:

[0017]

[0018] Based on ω=2πf, we get

[0019] Among them, L s For secondary resonant inductance, C s Here, f is the secondary resonant capacitor, and f is the switching frequency.

[0020] The value of Δi depends only on the line resistance R of the two windings. s1 R s2 If the switching frequency is equal to the resonant frequency, the key factor affecting the current sharing capability of the parallel secondary windings of a CLLLC is the line resistance.

[0021] Optionally, the method for analyzing the influencing factors of the rated current sharing capacity of the parallel secondary winding in the over-resonance is as follows:

[0022] When the switching frequency is greater than the resonant frequency Will denoted as jωL σ1 We can obtain:

[0023]

[0024] Based on Rs and ωL σ of the order of magnitude, we have:

[0025]

[0026] where L σ1 is the total equivalent inductance of the first circuit, L σ2 is the total equivalent inductance of the second circuit, R s is the circuit resistance;

[0027] Based on the fact that △i is only related to the circuit inductance, when the switching frequency is greater than the resonance frequency, the key factor affecting the current sharing capability of the CLLLC two-phase parallel secondary winding is the circuit inductance.

[0028] Optionally, the method for analyzing the factors affecting the rated current sharing capability of the under-resonant middle parallel secondary winding is:

[0029] When the switching frequency is less than the resonance frequency Let be

[0030]

[0031] Based on the distance between the switching frequency and the resonance frequency and the circuit inductance value, we have:

[0032]

[0033] where C σ is the total equivalent capacitance of the circuit;

[0034] Based on the fact that the value of △i is only related to the circuit resistance R s1 , R s2 , when the switching frequency is less than the resonance frequency, the key factor affecting the current sharing capability of the CLLLC two-phase parallel secondary winding is the circuit resistance.

[0035] Compared with the prior art, the present application has the following advantages and technical effects:

[0036] The present application clearly distinguishes the key parameters of the dominant current sharing capability under different switching frequencies by establishing an equivalent circuit model and based on frequency condition segmentation analysis; through reasonable order of magnitude approximation, the circuit equation is greatly simplified, the calculation efficiency is improved while the accuracy is ensured, and the present application has significant circuit design guiding value, and finally the correctness of the present solution is verified through interactive verification of theory and simulation. BRIEF DESCRIPTION OF DRAWINGS

[0037] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application and are incorporated in and constitute a part of this application. The embodiments of this application, and of which specific embodiments will be described and illustrated by the accompanying drawings, are shown schematically in the drawings:

[0038] Figure 1 is a flow chart of an analysis method of factors affecting the current sharing capability of the parallel secondary winding of the CLLL resonant converter according to an embodiment of the application;

[0039] Figure 2 is a power topology diagram of the CLLL resonant converter with parallel secondary winding according to an embodiment of the application;

[0040] Figure 3 is a simplified equivalent circuit diagram of the parallel secondary winding according to an embodiment of the application;

[0041] Figure 4 is a simulation waveform diagram at the resonant point when the difference between the two-phase line resistances is 5mΩ according to an embodiment of the application;

[0042] Figure 5 is a simulation waveform diagram at the resonant point when the difference between the two-phase line inductances is 10nH according to an embodiment of the application;

[0043] Figure 6 is a simulation waveform diagram at the under-resonance when the difference between the two-phase line resistances is 5mΩ according to an embodiment of the application;

[0044] Figure 7 is a simulation waveform diagram at the under-resonance when the difference between the two-phase line inductances is 10nH according to an embodiment of the application;

[0045] Figure 8 is a simulation waveform diagram at the over-resonance when the difference between the two-phase line resistances is 5mΩ according to an embodiment of the application;

[0046] Figure 9 is a simulation waveform diagram at the over-resonance when the difference between the two-phase line inductances is 10nH according to an embodiment of the application. DETAILED DESCRIPTION

[0047] It should be noted that the embodiments and features of the embodiments in the present application can be combined with each other without conflict. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0048] It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases, the steps shown or described herein can be executed in an order different from that shown herein.

[0049] The embodiment proposes an analysis method for factors influencing current sharing capability of parallel secondary winding of CLLL resonant converter Figure 1 as shown, specifically comprising the following steps:

[0050] obtaining an equivalent circuit diagram from the parallel secondary winding topology of the CLLL resonant converter;

[0051] obtaining resonant currents of the two parallel windings based on the equivalent circuit diagram;

[0052] based on the resonant currents, combining the resonant cavity working frequency, analyzing factors influencing current sharing capability of the parallel secondary winding, and obtaining preliminary analysis results;

[0053] carrying out simulation on the equivalent circuit diagram, and obtaining simulation waveforms;

[0054] based on the simulation waveforms and the preliminary analysis results, obtaining final analysis results.

[0055] Specifically, the embodiment specifically comprises: step one, obtaining an equivalent circuit diagram from the parallel secondary winding topology of the CLLL resonant converter; step two, writing circuit equations from the equivalent circuit diagram and carrying out reasonable parameter simplification; step three, dividing into three different working conditions of resonant point, over-resonance and under-resonance according to the resonant cavity working frequency, and discussing factors influencing rated current sharing capability of the parallel secondary winding; step four, carrying out circuit simulation according to the above three working conditions with the aid of LTSpice; and step five, analyzing simulation waveforms and drawing conclusions.

[0056] More specifically, the CLLL resonant converter power topology structure with parallel secondary winding in the embodiment is as shown in Figure 2 , and specifically comprises:

[0057] V bus is an input voltage, S1-S4 are primary side switching devices, constituting a primary side full bridge; T is a transformer, C r is a primary side resonant capacitor, L r is a primary side resonant inductor, the above three are connected in series and connected to the two half bridge midpoints of the primary side full bridge; Q1-Q4 are switching devices of the secondary side A phase, constituting a secondary side A phase full bridge; L s1 , C s1 are resonant inductors and resonant capacitors of the secondary side A phase, connected in series to the full bridge of the secondary side A phase; Q5-Q8 are switching devices of the secondary side B phase, constituting a secondary side B phase full bridge; L s2 , C s2 are resonant inductors and resonant capacitors of the secondary side B phase, connected in series to the full bridge of the secondary side B phase; the two secondary side AB phases are connected in parallel and then connected to an output capacitor C o , and finally an output voltage V o is obtained.

[0058] as shown,Figure 3 As shown in step two, in the simplified equivalent circuit diagram, all the subscript suffixes 1 are A phase, and 2 are B phase; V in1 is the A phase secondary winding port voltage, i r1 is the A phase resonant current, L k1 is the A phase line inductance, R s1 is the A phase line resistance, C s1 is the A phase resonant capacitance, the above three are in series in the circuit after simplification; … (the explanation of B phase is the same); finally, the simplified AB two-phase equivalent circuits are connected in parallel, and then connected in series with the output ac resistance R ac .

[0059] Further, the resonant currents of the two parallel windings are respectively:

[0060]

[0061] L s1 ≈L s2 =L s C s1 ≈C s2 =C s

[0062]

[0063] wherein v in is the input voltage of the parallel winding, v o is the output voltage, i r1 is the resonant current of the first winding, i r2 is the resonant current of the second winding, L s1 , L s2 is the resonant inductance of the two windings, C s1 , C s2 is the resonant capacitance of the two windings, L k1 , L k2 is the line inductance of the two windings, R s1 , R s2 is the line resistance of the two windings, j is the complex number unit, and ω is the switching angular frequency.

[0064] Further, based on the resonant current, the influence factors of the rated current sharing capability of the parallel secondary winding are analyzed in combination with the resonant cavity operating frequency, and the preliminary analysis results include:

[0065] According to the resonant cavity operating frequency, it is divided into three different working conditions of resonant point, over-resonance and under-resonance;

[0066] The influence factors of the rated current sharing capability of the parallel secondary winding in the resonant point, over-resonance and under-resonance are analyzed respectively, and the preliminary analysis results are obtained.

[0067] Further, the method for analyzing the factors affecting the rated current-sharing capability of the parallel secondary winding at the resonance point is:

[0068]

[0069] Since ω = 2πf, f is generally in the order of hundreds of kHz, and thus can be approximated as:

[0070]

[0071] where L s is the secondary resonant inductance, C s is the secondary resonant capacitance, and f is the switching frequency;

[0072] Since △i is only related to the line resistances R s1 and R s2 , when the switching frequency is equal to the resonant frequency, the key factor affecting the current-sharing capability of the parallel secondary winding of the CLLL is the line resistance.

[0073] Further, the method for analyzing the factors affecting the rated current-sharing capability of the parallel secondary winding at the over-resonance point is:

[0074] When the switching frequency is greater than the resonant frequency Let jωL σ1 , and we have:

[0075]

[0076] Since R s is generally in the order of 10 -4 , and ωL σ is generally in the order of 10 -3 , we can further approximate:

[0077]

[0078] where L σ1 is the first total equivalent inductance reactance, L σ2 is the second total equivalent inductance reactance, and R s is the line resistance;

[0079] Since △i is only related to the line inductance, when the switching frequency is greater than the resonant frequency, the key factor affecting the current-sharing capability of the parallel secondary winding of the CLLL is the line inductance.

[0080] Further, the method for analyzing the factors affecting the rated current-sharing capability of the parallel secondary winding at the under-resonance point is:

[0081] When the switching frequency is less than the resonant frequency Let be

[0082]

[0083] In the case of the switching frequency is not far from the resonant frequency, and the line inductance value is not large, The value of this part of the impedance is small, and it may appear at a certain switching frequency The new resonant point appears. Therefore, we have:

[0084]

[0085] Where C σ is the total equivalent capacitance of the line;

[0086] The value of delta i is only related to the line resistance R s1 , R s2 , so when the switching frequency is less than the resonant frequency, the key factor affecting the current sharing capability of the two parallel secondary windings of the CLLLC is the line resistance.

[0087] In summary, when the switching frequency is greater than the resonant frequency, the key factor affecting the current sharing capability of the two parallel secondary windings of the CLLLC is the line inductance; when the switching frequency is less than or equal to the resonant frequency, the key factor affecting the current sharing capability of the two parallel secondary windings of the CLLLC is the line resistance.

[0088] The simulation results obtained in step five are shown in Figures 4-9 , which are consistent with the conclusions obtained in step three, thereby proving the effectiveness of the optimization method.

[0089] The upper subgraph (yellow waveform) is the output voltage waveform, and the lower subgraph (red and blue waveforms) is the resonant current waveform of the two-phase secondary windings. Since the embodiment is the current sharing capability of the two-phase secondary windings, the closer the red and blue waveforms in the lower subgraph are to each other, the higher the degree of coincidence, the stronger the current sharing capability, and vice versa. The output voltage waveform plotted in the upper subgraph represents the simulation working condition of the CLLLC converter, and the output voltages of the three working conditions (resonant point, over-resonance, and under-resonance) are different.

[0090] Next, take Figure 4 and Figure 5 as examples to illustrate how the simulation results are consistent with the conclusions obtained in step three. First, according to the content in the description section, Figure 4 is the simulation waveform diagram of the embodiment of the present application at the resonant point, when the line resistance of the two phases differs by 5mΩ; Figure 5 is the simulation waveform diagram of the embodiment of the present application at the resonant point, when the line inductance of the two phases differs by 10nH.

[0091] As previously deduced, the main factor affecting current sharing at the resonant point is the line resistance. Therefore, it can be seen that... Figure 5 The two-phase current waveforms in ( Figure 5 (Sub-image below) Figure 4 The higher degree of overlap means that when the inductance of the two phase lines differs, it has little impact on the current-sharing capability; however, when the resistance of the two phase lines differs, it has a significant impact on the current-sharing capability, becoming the main influencing factor. This aligns with the results of theoretical analysis. The explanations regarding over-resonance and under-resonance are similar.

[0092] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for analyzing the influencing factors of the current sharing capability of the parallel secondary winding of a CLLLC resonant converter, characterized in that, include: The equivalent circuit diagram is obtained from the parallel secondary winding topology of the CLLLC resonant converter. Based on the equivalent circuit diagram, the resonant current of the two parallel windings is obtained; Based on the resonant current and the operating frequency of the resonant cavity, the factors affecting the current sharing capability of the parallel secondary winding are analyzed, and preliminary analysis results are obtained. The equivalent circuit diagram is simulated to obtain the simulation waveform; Based on the simulation waveforms and preliminary analysis results, the final analysis results are obtained.

2. The method for analyzing the influencing factors of the current sharing capability of the parallel secondary winding of a CLLLC resonant converter according to claim 1, characterized in that, The resonant currents of the two parallel windings are respectively: Among them, v in The input voltage of the parallel winding, v o For the output voltage, i r1 i is the resonant current of the first winding. r2 L is the resonant current of the second winding. s1 L s2 For a two-winding resonant inductor, C s1 C s2 For the two-winding resonant capacitor, L k1 L k2 For a two-winding circuit inductance, R s1 R s2 Let ω be the resistance of the two windings, j be the complex unit, and ω be the switching angular frequency.

3. The method for analyzing the influencing factors of the current sharing capability of the parallel secondary winding of a CLLLC resonant converter according to claim 2, characterized in that, Based on the resonant current and the operating frequency of the resonant cavity, the factors affecting the rated current sharing capability of the parallel secondary winding are analyzed, and the preliminary analysis results include: Based on the operating frequency of the resonant cavity, the operating conditions of the CLLLC resonant converter are divided into three different operating conditions: resonant point, over-resonance, and under-resonance. The factors affecting the rated current sharing capacity of the parallel secondary winding at the resonance point, over-resonance, and under-resonance are analyzed respectively, and preliminary analysis results are obtained.

4. The method for analyzing the influencing factors of the current sharing capability of the parallel secondary winding of a CLLLC resonant converter according to claim 3, characterized in that, The analysis of factors affecting the rated current sharing capability of the parallel secondary winding at the resonant point includes: Based on ω=2πf, we get Among them, L s For secondary resonant inductance, C s Here, f is the secondary resonant capacitor, and f is the switching frequency. The value of Δi depends only on the line resistance R of the two windings. s1 R s2 If the switching frequency is equal to the resonant frequency, the key factor affecting the current sharing capability of the parallel secondary windings of a CLLLC is the line resistance.

5. The method for analyzing the influencing factors of the current sharing capability of the parallel secondary winding of a CLLLC resonant converter according to claim 4, characterized in that, The method for analyzing the influencing factors of the rated current sharing capacity of the parallel secondary winding in the over-resonance is as follows: When the switching frequency is greater than the resonant frequency Will denoted as jωL σ1 We can obtain: Based on R s and ωL σ Order of magnitude, we can obtain: Among them, L σ1 For the total equivalent inductance and inductive reactance of the first line, L σ2 R is the total equivalent inductance and inductive reactance of the second line. s Line resistance; Since Δi is only related to the line inductance, when the switching frequency is greater than the resonant frequency, the key factor affecting the current sharing capability of the parallel secondary winding of the CLLLC is the line inductance.

6. The method for analyzing the influencing factors of the current sharing capability of the parallel secondary winding of a CLLLC resonant converter according to claim 5, characterized in that, The method for analyzing the factors affecting the rated current sharing capability of the underresonant parallel secondary winding is as follows: When the switching frequency is less than the resonant frequency Will Recorded as Based on the distance between the switching frequency and the resonant frequency, and the line inductance value, we obtain: Among them, C σ The total equivalent capacitance and capacitive reactance of the line; The value of Δi depends only on the line resistance R of the two windings. s1 R s2 If the switching frequency is less than the resonant frequency, the key factor affecting the current sharing capability of the parallel secondary windings of a CLLLC is the line resistance.

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