LLC eleven-mode time-domain analysis method considering semiconductor junction capacitance size

Abstract

The present application relates to LLC resonant circuit analysis technical field, specifically to a kind of LLC eleven mode time domain analysis method considering the size of semiconductor junction capacitance;The present scheme is based on the design of resonant parameters suitable for the constraint conditions such as resonant capacitance voltage and current value, considers non-ideal factors such as stray capacitance, analyzes the resonance in dead time, i.e. in a switching cycle including dead time, divides the whole process into eleven modes for analysis;In the LLC converter, the present scheme fully considers the adverse effects of parasitic capacitance on the normal operation of the circuit, and compares and analyzes the circuit model under different modes, which has greater reference value for the design of actual circuit, and the method is clearer and simpler, suitable for practical engineering.

Description

Technical Field

[0001] This invention relates to the field of LLC resonant circuit analysis technology, and more specifically to an LLC eleven-mode time-domain analysis method that takes into account the size of the semiconductor junction capacitance. Background Technology

[0002] LLC resonant converters can be cascaded with other DC / DC circuits, significantly improving efficiency and providing isolation. They are widely used in industrial fields such as photovoltaics and urban rail trains. Traditional LLC converters are suitable for wide input voltage ranges. Their design method starts with DC voltage gain, deriving the relationship between gain, the ratio of resonant inductance to magnetizing inductance, and the quality factor. These two key variables are usually selected empirically. However, in practical circuits, neglecting the junction capacitance of the semiconductor often leads to circuit problems.

[0003] At high switching frequencies, LLC converters become highly sensitive to circuit parasitic parameters, and even small magnetizing currents exacerbate the non-ideal characteristics caused by these parameters. The design of high-frequency transformers differs from that of low-frequency transformers, with more complex parasitic parameters. Ignoring this influence during the design process will compromise the performance of the LLC converter. In high-frequency, high-efficiency, high-power converters, traditional LLC modal analysis is no longer sufficient to meet design requirements. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this invention is to provide an LLC eleven-mode time-domain analysis method that takes into account the size of semiconductor junction capacitance.

[0005] To solve the above-mentioned technical problems, the technical solution provided by the present invention is: the LLC eleven-mode time-domain analysis method considering the size of semiconductor junction capacitance, in a full-bridge LLC topology, includes, in sequence, an inverter circuit, a resonant circuit, and a rectifier circuit, wherein the inverter circuit includes a power supply. V in Switching transistor Q 1. Q 2. Q 3. Q 4. The switching transistor Q 1 Intrinsic Diode D Q1 Junction capacitance C 1. The switching transistor Q 2 Intrinsic Diode D Q2 Junction capacitance C 2. The switching transistor Q 3 Intrinsic Diode D Q3 Junction capacitance C 3. The switching transistor Q 4-inherent diodeD Q4 Junction capacitance C 4; The resonant circuit includes a resonant capacitor. C r Resonant inductor L r Magnetizing inductor L m ,transformer T The rectifier circuit includes a load resistor. R Id Output filter capacitor C 0. Rectifier diode D 1. D 2. D 3. D 4. Junction capacitance C D1 , C D2 , C D3 , C D4 ;

[0006] Based on the symmetry of the full-bridge LLC operation, the half-cycle of the full-bridge LLC topology is analyzed; the analysis yields 11 modes, namely:

[0007] Modality 1: [ t 0, t 1];

[0008] Primary circuits S1 and S4 are forward-biased. At this time, the resonant capacitor... C r and resonant inductor L r Resonance occurs, resonant current i Lr Approximately a sine wave, magnetizing inductance L m By output voltage V out clamped in nV out The current flowing through the magnetizing inductor i Lm Because its voltage is constant, it changes linearly. i Lr and i Lm The current difference is transmitted to the secondary side through the transformer, thus transmitting the current difference during this stage. t 0- t 1. Energy transfer time is denoted as t e ;

[0009] in, Cr and L r resonant frequency f r for:

[0010] ;

[0011] exist t Excitation current value at time 1 i m ( t 1) is:

[0012] ;

[0013] The following formulas can be used to calculate the magnitude of the excitation inductor terminal voltage and the excitation current value: t 0- t Excitation current value within 1 i Lm ( t )for:

[0014] ;

[0015] exist t 0- t The time-domain equations for the resonant cavity voltage and current within 1 are:

[0016] ;

[0017] exist t 0- t The voltage and current of the resonant capacitor both reach their resonant peak values ​​within the time period 1. Therefore, this peak value is taken as the upper limit of the entire time period. Let the maximum resonant current of the resonant capacitor within this time period be... I cr_max The maximum resonant voltage is V cr_max ,in I cr_max and I Lr_max Equivalent, I cr_max and V cr_max The relationship between the two is as follows:

[0018] ;

[0019] The voltage and current in the resonant cavity have a phase angle difference, the magnitude of which is determined by the magnetizing inductance. i Lm With resonant current i Lr Solving for the amplitude:

[0020] ;

[0021] Therefore, in t 0- t Resonant current within 1 time period i Lr for:

[0022] i Lr ( t )= I Lr_max sin( ω r t + θ )+ i Lr ( t 0);

[0023] Resonant capacitor voltage v Cr ( t )for:

[0024] v Cr ( t )=- V cr_max cos( ω r t + θ )+ v Cr ( t 0);

[0025] in, ω r =2 πf r ;

[0026] [ t 0, t 1] The time period is during an energy transfer process. Let the power transferred from the primary side to the secondary side during this time period be... P te This power P te Represented as:

[0027]

[0028] Mode 2: [ t 1, t 2];

[0029] Resonant current with an approximately sinusoidal trend i Lr Excitation current that varies linearly with a fixed slope iLm exist t They intersect at time 1, at [ t 1, t 2] During the time period, the two remain equal, entering a three-element resonant state. At this time, the primary-side MOSFET does not immediately turn off but remains in the conducting state. The secondary-side rectifier diode achieves zero-current turn-off (ZCS) due to the cessation of energy transfer from the transformer. Its own capacitance still participates in the primary-side resonance, adding a parasitic resonant current to the primary-side resonant current. Considering the secondary-side diode junction capacitance participating in the resonance, we obtain [ t 1, t 2] The time-domain equation for the time period is:

[0030] ;

[0031] The derivation is i Lr The second-order differential equation is:

[0032] ;

[0033] exist[ t 1, t 2] Inside, v Cr Neglecting the changes and treating them as constants, the above equation simplifies to:

[0034] ;

[0035] The solution obtained by Laplace transform is:

[0036] ;

[0037] Therefore, we get:

[0038] ;

[0039] Combining the above equations, we get:

[0040] ;

[0041] Simplified i Lr The expression is:

[0042] ;

[0043] Performing the inverse Laplace transform on the above equation yields... i Lr The time-domain equation is:

[0044] ;

[0045] Modal 3 + Modal 4: [ t2, t 3]

[0046] exist t At time 2, the primary-side MOSFET is turned off, and the resonant current begins to charge and discharge into the primary-side MOSFET junction capacitance. The primary-side junction capacitance then enters the overall resonant process, causing the resonant current to... i r The DC current component decreases, while the AC component continues to resonate at high frequencies, and the primary-side diode junction capacitance... C Q With secondary diode junction capacitance C D The ratio directly affects the DC current distribution, which in turn affects ZVS. High-frequency resonance still exists in the AC part, and the amplitude of the resonant current and the phase angle together affect ZVS.

[0047] During this time period, the junction capacitance of the primary-side SiC MOSFET participates in resonance. Referring to the time-domain equation in mode 2, we can obtain that... t 2, t The time-domain equation of [3] is:

[0048] ;

[0049] same v Cr Treating it as a constant, the second-order differential equation can be derived:

[0050] ;

[0051] Solving using the Laplace transform, we obtain:

[0052] ;

[0053] From the above formula, we can obtain:

[0054] ;

[0055] From the above formula, we can obtain:

[0056] ;

[0057] Among them, in [ t 2, t 3] Within the time period i Lr resonant frequency f 2 is:

[0058] ;

[0059] From the above formula, we can obtain the simplified version. i Lr The expression is:

[0060] ;

[0061] Taking the inverse Laplace transform of the above equation, we get i Lr The time-domain equation is:

[0062]

[0063] Solving the above equations simultaneously i Lr Simplify:

[0064]

[0065] t At time 2, the resonant cavity current and the excitation current are approximately equal, and can be considered as i Lr ( t 2) = i Lm ( t 2), thus we obtain:

[0066]

[0067] Modal 3: [ t 2, t s ];

[0068] During the transient process of mode 3, the time is very short. The influence of junction capacitance resonance is not considered in the mode 3 interval, and the impact on the charging process of the primary junction capacitance is very small. The main effect is that the drop in its resonant current affects the DC component of the current in the next mode, which in turn affects the ZVS of the primary capacitance. The voltages of other capacitors are considered to remain unchanged.

[0069] Modal 4: [ t s , t 4];

[0070] Based on whether the minimum resonant current in mode 4 is greater than zero and the order in which the primary and secondary junction capacitances achieve ZVS, there are four different modes. Each mode has a distinct equivalent circuit transition, which has different effects on ZVS.

[0071] Stage 4a:

[0072] i Lr ( t s If ) > 0, the resonant current is always greater than 0, that is dv CQ / dtThe primary junction capacitance is always greater than 0, and it first reaches ZVS. At this point, the primary side diode clamps and conducts, and the input voltage of the primary resonant cavity is changed from... V in Become - V in This enables input voltage commutation;

[0073] Stage 4b:

[0074] i Lr ( t s When the resonant current is less than 0, there are two possibilities: First, the resonant current has a zero-crossing point, meaning there are waveforms on both the positive and negative half-axis during this time period, causing the resonant current to alternate between positive and negative directions. Additionally, the secondary side completes ZVS first, after which the resonant current's period and amplitude change. Therefore, this mode corresponds to four circuit states, which are... i Lr ( t s When the value is less than 0, the secondary diode is clamped to conduct at the midpoint. i Lr ( t s If the value is less than 0, the secondary diode did not operate at the midpoint of the time interval. i Lr ( t s When the value is greater than 0, the secondary diode is clamped to conduct at the midpoint. i Lr ( t s >0, the secondary diode did not operate at the middle moment; the second is the extreme case where the resonant current is all located in the negative half axis, which does not have ZVS, so it is not considered;

[0075] Stage 4c:

[0076] The resonant current lies entirely on the positive half-axis, and the secondary side first achieves ZVS. The corresponding circuit has two equivalent circuit topologies, namely... i Lr ( t s When the value is greater than 0, the secondary diode is clamped to conduct at the midpoint. i Lr ( t s If the value is greater than 0, the secondary diode does not operate at the midpoint of the time interval; the topologies corresponding to the two equivalent circuits have different resonant amplitudes and periods, which have a certain impact on ZVS.

[0077] Stage 4d:

[0078] The minimum resonant current is less than 0, meaning there is a current zero-crossing point. The case where it is completely in the negative half-cycle is no longer considered. The current repeats, and the primary junction capacitance first achieves ZVS, corresponding to two circuit modes, which are respectively i Lr ( t s When the value is less than 0, the secondary diode is clamped to conduct at the midpoint. i Lr ( t s If the value is less than 0, the secondary diode did not operate at the midpoint of the time interval.

[0079] Modality 5: [ t 3, t 4];

[0080] Stage 5:

[0081] This mode is based on i Lr Crossing zero t z Is the time in [ t 3, t 4] can be divided into two possibilities, the first being t 4< t z For 5a and 5b, the current remains greater than 0 throughout the dead time, and there is no reverse charging. The second type is... t 4> t z This divides the time of mode 5 into two segments: 5a' is the one that works normally, and 5b' is the one where the transistor is not turned on in time, causing the original side to lose ZVS.

[0082] Mode 5a: [ t 3, t z ], Mode 5a': [ t z , t 4];

[0083] exist t At time 3, the commutation of the primary junction capacitor voltage is completed in the previous mode time, i.e., soft switching is achieved, and the primary magnetizing inductor voltage just reaches approximately -n. V out Therefore, it is reverse clamped, the secondary rectifier bridge pair is turned on, the parasitic capacitance of the rectifier diode stops participating in the primary resonance, it leaves the three-element resonance state and enters the two-element resonance state. The resonant current drops rapidly under the negative voltage of the resonant cavity. In this state, the primary pair needs to be turned on immediately; mode 5a', enter the next switching cycle. This state is the normal mode and can be regarded as part of the reverse of mode 1.

[0084] The expression for the resonant inductor voltage is:

[0085] ;

[0086] ;

[0087] Modal 5b: [ t 3, t z ], Modality 5b': [ t z , t 4];

[0088] t z < t 4. In t z At that moment, the resonant current i Lr The current still remained normal after crossing zero, but... i Lr Mode 5b' after the zero crossing is an abnormal mode, and the primary and secondary junction capacitances simultaneously participate in resonance. Q 2. Q The junction capacitor begins charging, corresponding to... Q 1. Q 4. The junction capacitance begins to discharge, and the full-bridge LLC system loses ZVS.

[0089] Furthermore, the resonant current in modes 2 and 3... i Lr Time-domain analysis allows for indirect measurement of the primary-side SiC MOSFET junction capacitance and the secondary-side diode parasitic junction capacitance, which are difficult to measure directly. This is achieved under the given condition of a known transformer resonant inductance. L r Under the condition of inductance, the resonant frequencies in mode 2 and mode 3 + mode 4 were measured respectively. f 1. f 2. The junction capacitance of the SiC MOSFET can be obtained by combining the following steps. C Q Diode junction capacitance C D The expression is:

[0090]

[0091] .

[0092] Compared with existing technologies, the significant advantages of this solution are:

[0093] This solution fully considers the adverse effects of parasitic capacitance on the normal operation of the LLC converter. It also compares and analyzes the dead time under different modes, which has greater reference value for the design of actual circuits. The method is clearer and simpler and is suitable for practical engineering. Attached Figure Description

[0094] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0095] Figure 1 This is the topology diagram of the full-bridge LLC circuit in this scheme;

[0096] Figure 2 This is a diagram of mode 1 of the LLC circuit model considering the secondary junction capacitance in this scheme;

[0097] Figure 3 This is the equivalent circuit diagram of mode 1 of the LLC circuit model considering the secondary junction capacitance in this scheme;

[0098] Figure 4 This is a diagram of mode 2 of the LLC circuit model considering the secondary junction capacitance in this scheme;

[0099] Figure 5 This is the equivalent circuit diagram of mode 2 of the LLC circuit model considering the secondary junction capacitance in this scheme;

[0100] Figure 6 This is a diagram of mode 3 of the LLC circuit model considering the secondary junction capacitance in this scheme;

[0101] Figure 7 This is the equivalent circuit diagram of mode 3 of the LLC circuit model considering the secondary-side capacitor in this scheme;

[0102] Figure 8 This is a diagram of mode 5 of the LLC circuit model considering the secondary junction capacitance in this scheme;

[0103] Figure 9 This is the equivalent circuit diagram of mode 5 of the LLC circuit model considering the secondary junction capacitance in this scheme;

[0104] Figure 10 The diagram shows mode 5b' of the LLC circuit model considering the secondary junction capacitance in this scheme.

[0105] Figure 11 The equivalent circuit diagram of mode 5b' of the LLC circuit model considering the secondary-side capacitor in this scheme;

[0106] Figure 12 This is a schematic diagram of the modal analysis of the full-bridge LLC.

[0107] Figure 13 This is the modal flowchart of this scheme. Detailed Implementation

[0108] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0109] The present invention describes an LLC eleven-mode time-domain analysis method considering the semiconductor junction capacitance, with a full-bridge LLC topology as follows: Figure 1 As shown, from left to right, the circuit includes an inverter circuit, a resonant circuit, and a rectifier circuit. The inverter circuit includes a power supply. V in Switching transistor Q 1. Q 2. Q 3. Q 4. The switching transistor Q 1 Intrinsic Diode D Q1 Junction capacitance C 1. The switching transistor Q 2 Intrinsic Diode D Q2 Junction capacitance C 2. The switching transistor Q 3 Intrinsic Diode D Q3 Junction capacitance C 3. The switching transistor Q 4-inherent diode D Q4 Junction capacitance C 4; The resonant circuit includes a resonant capacitor. C r Resonant inductor L r Magnetizing inductor L m ,transformer T The rectifier circuit includes a load resistor. R Id Output filter capacitor C 0. Rectifier diode D 1. D 2. D 3. D 4. Junction capacitance C D1 , C D2 , C D3 , C D4 ;

[0110] Based on the symmetry of the full-bridge LLC operation, the half-cycle of the full-bridge LLC topology is analyzed; the analysis yields 11 modes, namely:

[0111] Modality 1: [ t 0, t 1];

[0112] like Figure 2 and 3 As shown, Figure 2 For the LLC circuit model that takes into account the secondary junction capacitance, Figure 3 For the equivalent circuit of the LLC circuit model considering the secondary junction capacitance, primary side S1 and S4 are forward-biased. At this time, the resonant capacitance... C r and resonant inductor L r Resonance occurs, resonant current i Lr Approximately a sine wave, magnetizing inductance L m By output voltage V out clamped in nV out The current flowing through the magnetizing inductor i Lm Because its voltage is constant, it changes linearly. i Lr and i Lm The current difference is transmitted to the secondary side through the transformer, thus transmitting the current difference during this stage. t 0- t 1. Energy transfer time is denoted as t e ;

[0113] in, C r and L r resonant frequency f r for:

[0114] ;

[0115] exist t Excitation current value at time 1 i m ( t 1) is:

[0116] ;

[0117] The following formulas can be used to calculate the magnitude of the excitation inductor terminal voltage and the excitation current value: t 0- t Excitation current value within 1i Lm ( t )for:

[0118] ;

[0119] exist t 0- t The time-domain equations for the resonant cavity voltage and current within 1 are:

[0120] ;

[0121] exist t 0- t The voltage and current of the resonant capacitor both reach their resonant peak values ​​within the time period 1. Therefore, this peak value is taken as the upper limit of the entire time period. Let the maximum resonant current of the resonant capacitor within this time period be... I cr_max The maximum resonant voltage is V cr_max ,in I cr_max and I Lr_max Equivalent I cr_max and V cr_max The relationship between the two is as follows:

[0122] ;

[0123] The voltage and current in the resonant cavity have a phase angle difference, the magnitude of which is determined by the magnetizing inductance. i Lm With resonant current i Lr Solving for the amplitude:

[0124] ;

[0125] Therefore, in t 0- t Resonant current within 1 time period i Lr for:

[0126] i Lr ( t )= I Lr_max sin( ω r t + θ )+ i Lr ( t 0);

[0127] Resonant capacitor voltage v Cr ( t )for:

[0128] v Cr ( t )=- V cr_max cos( ω r t + θ )+ v Cr ( t 0);

[0129] in, ω r =2 πf r ;

[0130] [ t 0, t 1] The time period is during an energy transfer process. Let the power transferred from the primary side to the secondary side during this time period be... P te This power P te Represented as:

[0131]

[0132] Mode 2: [ t 1, t 2];

[0133] like Figure 4 As shown, the resonant current varies with an approximately sinusoidal trend. i Lr Excitation current that varies linearly with a fixed slope i Lm exist t They intersect at time 1, at [ t 1, t [2] During the time period, the two remain equal, entering a three-element resonant state. At this time, the primary-side MOSFET does not immediately turn off but remains in the conducting state. The secondary-side rectifier diode achieves zero-current turn-off (ZCS) because the energy transfer of the transformer stops. Its own capacitance still participates in the primary-side resonance, adding a parasitic resonant current to the primary-side resonant current. Considering the secondary-side diode junction capacitance participating in the resonance, the equivalent circuit is as follows: Figure 5 As shown, we obtain [ t 1, t 2] The time-domain equation for the time period is:

[0134] ;

[0135] The derivation is i Lr The second-order differential equation is:

[0136] ;

[0137] exist[ t 1, t 2] Inside, v Cr Neglecting the changes and treating them as constants, the above equation simplifies to:

[0138] ;

[0139] The solution obtained by Laplace transform is:

[0140] ;

[0141] Therefore, we get:

[0142] ;

[0143] Combining the above equations, we get:

[0144] ;

[0145] Simplified i Lr The expression is:

[0146] ;

[0147] Performing an inverse Laplace transform on the above equation yields... i Lr The time-domain equation is:

[0148] ;

[0149] Mode 3 + Mode 4: [ t 2, t 3]

[0150] exist t At time 2, the primary-side MOSFET is turned off, and the resonant current begins to charge and discharge into the primary-side MOSFET junction capacitance. The primary-side junction capacitance then enters the overall resonant process, causing the resonant current to... i r The DC current component decreases, while the AC component continues to resonate at high frequencies, and the primary-side diode junction capacitance... C Q With secondary diode junction capacitance C DThe ratio directly affects the DC current distribution, and thus the ZVS. High-frequency resonance still exists in the AC section, and the amplitude and phase angle of this resonant current jointly affect the ZVS. A detailed analysis of the changes in both the DC and AC components can further refine the ZVS conditions. Since mode 3 is a transient process with a very short duration, it primarily affects the DC portion of the resonant current.

[0151] During this time period, the junction capacitance of the primary-side SiC MOSFET participates in resonance. Referring to the time-domain equation in mode 2, we can obtain that... t 2, t The time-domain equation of [3] is:

[0152] ;

[0153] same v Cr Treating it as a constant, the second-order differential equation can be derived:

[0154] ;

[0155] Solving using the Laplace transform, we obtain:

[0156] ;

[0157] From the above formula, we can obtain:

[0158] ;

[0159] From the above formula, we can obtain:

[0160] ;

[0161] Among them, in [ t 2, t 3] Within the time period i Lr resonant frequency f 2 is:

[0162] ;

[0163] From the above formula, we can obtain the simplified version. i Lr The expression is:

[0164] ;

[0165] Taking the inverse Laplace transform of the above equation, we get i Lr The time-domain equation is:

[0166]

[0167] Solving the above equations simultaneously iLr Simplify:

[0168]

[0169] t At time 2, the resonant cavity current and the excitation current are approximately equal, and can be considered as i Lr ( t 2) = i Lm ( t 2), thus we obtain:

[0170]

[0171] Modal 3: [ t 2, t s ];

[0172] During the transient process of mode 3, the time is very short. The influence of junction capacitance resonance is not considered in the mode 3 interval, and the impact on the charging process of the primary junction capacitance is very small. The main effect is that the drop in its resonant current affects the DC component of the current in the next mode, which in turn affects the ZVS of the primary capacitance. The voltages of other capacitors are considered to remain unchanged.

[0173] Mode 4: [ t s , t 4];

[0174] Based on whether the minimum resonant current in mode 4 is greater than zero and the order in which the primary and secondary junction capacitances achieve ZVS, there are four different modes. Each mode has a distinct equivalent circuit transition, which has different effects on ZVS.

[0175] Stage 4a:

[0176] i Lr ( t s If ) > 0, the resonant current is always greater than 0, that is dv CQ / dt The primary junction capacitance is always greater than 0, and it first reaches ZVS. At this point, the primary side diode clamps and conducts, and the input voltage of the primary resonant cavity is changed from... V in Become - V in This achieves input voltage commutation; the equivalent circuit for this mode is only one, corresponding to... Figure 6 , Figure 7 This is the equivalent circuit and also the fastest mode for achieving ZVS. The circuit should be operated in this mode as much as possible.

[0177] Stage 4b:

[0178] i Lr ( t s When the resonant current is less than 0, there are two possibilities: First, the resonant current has a zero-crossing point, meaning there are waveforms on both the positive and negative half-axis during this time period, causing the resonant current to alternate between positive and negative directions. Additionally, the secondary side completes ZVS first, after which the resonant current's period and amplitude change. Therefore, this mode corresponds to four circuit states, which are... i Lr ( t s When the value is less than 0, the secondary diode is clamped to conduct at the midpoint. i Lr ( t s If the value is less than 0, the secondary diode did not operate at the midpoint of the time interval. i Lr ( t s When the value is greater than 0, the secondary diode is clamped to conduct at the midpoint. i Lr ( t s >0, the secondary diode did not operate at the middle moment; the second is the extreme case where the resonant current is all located in the negative half axis, which does not have ZVS, so it is not considered;

[0179] Stage 4c:

[0180] The resonant current lies entirely on the positive half-axis, and the secondary side first achieves ZVS. The corresponding circuit has two equivalent circuit topologies, namely... i Lr ( t s When the value is greater than 0, the secondary diode is clamped to conduct at the midpoint. i Lr ( t s If the value is greater than 0, the secondary diode does not operate at the midpoint of the time interval; the topologies corresponding to the two equivalent circuits have different resonant amplitudes and periods, which have a certain impact on ZVS.

[0181] Stage 4d:

[0182] The minimum resonant current is less than 0, meaning there is a current zero-crossing point. The case where it is completely in the negative half-cycle is no longer considered. The current repeats, and the primary junction capacitance first achieves ZVS, corresponding to two circuit modes, which are respectively i Lr ( t sWhen the value is less than 0, the secondary diode is clamped to conduct at the midpoint. i Lr ( t s If the value is less than 0, the secondary diode did not operate at the midpoint of the time interval.

[0183] Modality 5: [ t 3, t 4];

[0184] Stage 5:

[0185] like Figure 8 As shown, this mode is based on i Lr Crossing zero t z Is the time in [ t 3, t 4] can be divided into two possibilities, the first being t 4< t z For 5a and 5b, the current is always greater than 0 during the dead time, and there is no reverse charging. This corresponds to an equivalent circuit state as follows: Figure 9 As shown; the second type is t 4> t z This divides the time of mode 5 into two segments: 5a', which operates normally, and 5b', where the transistor fails to conduct in time, causing the primary side to lose ZVS; for example... Figure 12 As shown, this situation should be avoided.

[0186] Mode 5a: [ t 3, t z ], Mode 5a': [ t z , t 4];

[0187] exist t At time 3, the commutation of the primary junction capacitor voltage is completed in the previous mode time, i.e., soft switching is achieved, and the primary magnetizing inductor voltage just reaches approximately -n. V out Therefore, it is reverse clamped, the secondary rectifier bridge pair is turned on, the parasitic capacitance of the rectifier diode stops participating in the primary resonance, it leaves the three-element resonance state and enters the two-element resonance state. The resonant current drops rapidly under the negative voltage of the resonant cavity. In this state, the primary pair needs to be turned on immediately; mode 5a', enter the next switching cycle. This state is the normal mode and can be regarded as part of the reverse of mode 1.

[0188] The expression for the resonant inductor voltage is:

[0189] ;

[0190] ;

[0191] Modal 5b: [ t 3, t z ], Modality 5b': [ t z , t 4];

[0192] like Figure 10-11 As shown, t z < t 4. In t z At that moment, the resonant current i Lr The current still remained normal after crossing zero, but... i Lr Mode 5b' after the zero crossing is an abnormal mode, and the primary and secondary junction capacitances simultaneously participate in resonance. Q 2. Q The junction capacitor begins charging, corresponding to... Q 1. Q 4. The junction capacitance begins to discharge, and the full-bridge LLC system loses ZVS. This state should not occur during normal operation.

[0193] The resonant current in mode 2 and mode 3 i Lr Time-domain analysis allows for indirect measurement of the primary-side SiC MOSFET junction capacitance and the secondary-side diode parasitic junction capacitance, which are difficult to measure directly. This is achieved under the given condition of a known transformer resonant inductance. L r Under the condition of inductance, the resonant frequencies in mode 2 and mode 3 + mode 4 were measured respectively. f 1. f 2. The junction capacitance of the SiC MOSFET can be obtained by combining the following steps. C Q Diode junction capacitance C D The expression is:

[0194]

[0195] .

[0196] Figure 13 This is the flowchart for this solution.

[0197] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for LLC eleven-mode time-domain analysis considering the size of semiconductor junction capacitance, characterized in that, In a full-bridge LLC topology, the circuit consists of an inverter circuit, a resonant circuit, and a rectifier circuit, in sequence. The inverter circuit includes a power supply. V in Switching transistor Q 1. Q 2. Q 3. Q 4. The switching transistor Q 1 Intrinsic Diode D Q1 Junction capacitance C 1. The switching transistor Q 2 Intrinsic Diode D Q2 Junction capacitance C 2. The switching transistor Q 3 Intrinsic Diode D Q3 Junction capacitance C 3. The switching transistor Q 4-inherent diode D Q4 Junction capacitance C 4; The resonant circuit includes a resonant capacitor. C r Resonant inductor L r Magnetizing inductor L m ,transformer T The rectifier circuit includes a load resistor. R Id Output filter capacitor C 0. Rectifier diode D 1. D 2. D 3. D 4. Junction capacitance C D1 , C D2 , C D3 , C D4 ; Based on the symmetry of the full-bridge LLC operation, the half-cycle of the full-bridge LLC topology is analyzed; the analysis yields 11 modes, namely: Modality 1: [ t 0, t 1]; Primary circuits S1 and S4 are forward-biased. At this time, the resonant capacitor... C r and resonant inductor L r Resonance occurs, resonant current i Lr Approximately a sine wave, magnetizing inductance L m By output voltage V out clamped in nV out The current flowing through the magnetizing inductor i Lm Because its voltage is constant, it changes linearly. i Lr and i Lm The current difference is transmitted to the secondary side through the transformer, thus converting the current difference in this stage into a current difference. t 0- t 1. Energy transfer time is denoted as t e ; in, C r and L r resonant frequency f r for: ; exist t Excitation current value at time 1 i m ( t 1) is: ; The following formulas can be used to calculate the magnitude of the excitation inductor terminal voltage and the excitation current value: t 0- t Excitation current value within 1 i Lm ( t )for: ; exist t 0- t The time-domain equations for the resonant cavity voltage and current within 1 are: ; exist t 0- t The voltage and current of the resonant capacitor both reach their resonant peak values ​​within the time period 1. Therefore, this peak value is taken as the upper limit of the entire time period. Let the maximum resonant current of the resonant capacitor within this time period be... I cr_max The maximum resonant voltage is V cr_max ,in I cr_max and I Lr_max Equivalent, I cr_max and V cr_max The relationship between the two is as follows: ; The voltage and current in the resonant cavity have a phase angle difference, the magnitude of which is determined by the magnetizing inductance. i Lm With resonant current i Lr Solving for the amplitude: ; Therefore, in t 0- t Resonant current within 1 time period i Lr for: i Lr ( t )= I Lr_max sin( ω r t + θ )+ i Lr ( t 0); Resonant capacitor voltage v Cr ( t )for: v Cr ( t )=- V cr_max cos( ω r t + θ )+ v Cr ( t 0); in, ω r =2 πf r ; [ t 0, t 1] The time period is during an energy transfer process. Let the power transferred from the primary side to the secondary side during this time period be... P te This power P te Represented as: ; Mode 2: [ t 1, t 2]; Resonant current with an approximately sinusoidal trend i Lr Excitation current that varies linearly with a fixed slope i Lm exist t They intersect at time 1, at [ t 1, t 2] During the time period, the two remain equal, entering a three-element resonant state. At this time, the primary-side MOSFET does not immediately turn off but remains in the conducting state. The secondary-side rectifier diode achieves zero-current turn-off (ZCS) due to the cessation of energy transfer from the transformer. Its own capacitance still participates in the primary-side resonance, adding a parasitic resonant current to the primary-side resonant current. Considering the secondary-side diode junction capacitance participating in the resonance, we obtain [ t 1, t 2] The time-domain equation for the time period is: ; The derivation is i Lr The second-order differential equation is: ; exist[ t 1, t 2] Inside, v Cr Neglecting the changes and treating them as constants, the above equation simplifies to: ; The solution obtained by Laplace transform is: ; Therefore, we get: ; Combining the above equations, we get: ; Simplified i Lr The expression is: ; Performing an inverse Laplace transform on the above equation yields... i Lr The time-domain equation is: ; Mode 3 + Mode 4: [ t 2, t 3] exist t At time 2, the primary-side MOSFET is turned off, and the resonant current begins to charge and discharge into the primary-side MOSFET junction capacitance. The primary-side junction capacitance then enters the overall resonant process, causing the resonant current to... i r The DC current component decreases, while the AC component continues to resonate at high frequencies, and the primary-side diode junction capacitance... C Q With secondary diode junction capacitance C D The ratio directly affects the DC current distribution, which in turn affects ZVS. High-frequency resonance still exists in the AC part, and the amplitude of the resonant current and the phase angle together affect ZVS. During this time period, the junction capacitance of the primary-side SiC MOSFET participates in resonance. Referring to the time-domain equation in mode 2, we can obtain that... t 2, t The time-domain equation of [3] is: ; same v Cr Treating it as a constant, the second-order differential equation can be derived: ; Solving using the Laplace transform, we obtain: ; From the above formula, we can obtain: ; From the above formula, we can obtain: ; Among them, in [ t 2, t 3] Within the time period i Lr resonant frequency f 2 is: ; From the above formula, we can obtain the simplified version. i Lr The expression is: ; Taking the inverse Laplace transform of the above equation, we get i Lr The time-domain equation is: Solving the above equations simultaneously i Lr Simplify: t At time 2, the resonant cavity current and the excitation current are approximately equal, and can be considered as i Lr ( t 2) = i Lm ( t 2), thus we obtain: Modal 3: [ t 2, t s ]; During the transient process of mode 3, the time is very short. The influence of junction capacitance resonance is not considered in the mode 3 interval, and the impact on the charging process of the primary junction capacitance is very small. The drop in its resonant current affects the DC component of the current in the next mode, which in turn affects the primary capacitance ZVS. The voltages of other capacitors are considered to remain unchanged. Modal 4: [ t s , t 4]; Based on whether the minimum resonant current in mode 4 is greater than zero and the order in which the primary and secondary junction capacitances achieve ZVS, there are four different modes. Each mode has a distinct equivalent circuit transition, which has different effects on ZVS. Stage 4a: i Lr ( t s If ) > 0, the resonant current is always greater than 0, that is dv CQ / dt The primary junction capacitance is always greater than 0, and it first reaches ZVS. At this point, the primary side diode clamps and conducts, and the input voltage of the primary resonant cavity is changed from... V in Become - V in This enables input voltage commutation; Stage 4b: i Lr ( t s When the resonant current is less than 0, there are two possibilities: First, the resonant current has a zero-crossing point, meaning there are waveforms on both the positive and negative half-axis during this time period, causing the resonant current to alternate between positive and negative directions. Additionally, the secondary side completes ZVS first, after which the resonant current's period and amplitude change. Therefore, this mode corresponds to four circuit states, which are... i Lr ( t s When the value is less than 0, the secondary diode is clamped to conduct at the midpoint. i Lr ( t s If the value is less than 0, the secondary diode did not operate at the midpoint of the time interval. i Lr ( t s When the value is greater than 0, the secondary diode is clamped to conduct at the midpoint. i Lr ( t s >0, the secondary diode did not operate at the middle moment; the second is the extreme case where the resonant current is all located in the negative half axis, which does not have ZVS, so it is not considered; Stage 4c: The resonant current lies entirely on the positive half-axis, and the secondary side first achieves ZVS. The corresponding circuit has two equivalent circuit topologies, namely... i Lr ( t s When the value is greater than 0, the secondary diode is clamped to conduct at the midpoint. i Lr ( t s If the value is greater than 0, the secondary diode does not operate at the midpoint of the time interval; the topologies corresponding to the two equivalent circuits have different resonant amplitudes and periods, which have a certain impact on ZVS. Stage 4d: The minimum resonant current is less than 0, meaning there is a current zero-crossing point. The case where it is completely in the negative half-cycle is no longer considered. The current repeats, and the primary junction capacitance first achieves ZVS, corresponding to two circuit modes, which are respectively i Lr ( t s When the value is less than 0, the secondary diode is clamped to conduct at the midpoint. i Lr ( t s If the value is less than 0, the secondary diode did not operate at the midpoint of the time interval. Modality 5: [ t 3, t 4]; Stage 5: This mode is based on i Lr Crossing zero t z Is the time in [ t 3, t 4] can be divided into two possibilities, the first being t 4< t z For 5a and 5b, the current remains greater than 0 throughout the dead time, and there is no reverse charging. The second type is... t 4> t z This divides the time of mode 5 into two segments: 5a' is the one that works normally, and 5b' is the one where the transistor is not turned on in time, causing the original side to lose ZVS. Mode 5a: [ t 3, t z ], Mode 5a': [ t z , t 4]; exist t At time 3, the commutation of the primary junction capacitor voltage is completed in the previous mode time, i.e., soft switching is achieved, and the primary magnetizing inductor voltage just reaches approximately -n. V out Therefore, it is reverse clamped, the secondary rectifier bridge pair is turned on, the parasitic capacitance of the rectifier diode stops participating in the primary resonance, it leaves the three-element resonance state and enters the two-element resonance state. The resonant current drops rapidly under the negative voltage of the resonant cavity. In this state, the primary pair needs to be turned on immediately; mode 5a', enter the next switching cycle. This state is the normal mode and can be regarded as part of the reverse of mode 1. The expression for the resonant inductor voltage is: ; ; Modal 5b: [ t 3, t z ], Modality 5b': [ t z , t 4]; t z < t 4. In t z At that moment, the resonant current i Lr The current still remained normal after crossing zero, but... i Lr Mode 5b' after the zero crossing is an abnormal mode, and the primary and secondary junction capacitances simultaneously participate in resonance. Q 2. Q The junction capacitor begins charging, corresponding to... Q 1. Q 4. The junction capacitance begins to discharge, and the full-bridge LLC system loses ZVS.

2. The LLC eleven-mode time-domain analysis method considering the semiconductor junction capacitance as described in claim 1, characterized in that, The resonant current in mode 2 and mode 3 i Lr Time-domain analysis allows for indirect measurement of the primary-side SiC MOSFET junction capacitance and the secondary-side diode parasitic junction capacitance, which are difficult to measure directly. This is achieved under the given condition of a known transformer resonant inductance. L r Under the condition of inductance, the resonant frequencies in mode 2 and mode 3 + mode 4 were measured respectively. f 1. f 2. The junction capacitance of the SiC MOSFET can be obtained by combining the following steps. C Q Diode junction capacitance C D The expression is: 。

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