Multi-phase LLC resonant converter parallel current sharing system and method

Abstract

The invention discloses a multi-phase LLC resonant converter parallel current sharing system and method. The system comprises N phases of LLC modules which are connected in parallel; the circuit also comprises N-1 passive fractional order capacitors. One passive fractional order capacitor is connected in parallel between every two phases of LLC modules, each passive fractional order capacitor is provided with a half-bridge rectification circuit, current sharing among N phases of LLC modules is realized by adjusting phases between the half-bridge rectification circuits and inversion half bridges in the LLC modules, and the LLC converter has the advantages of supporting hot plugging, being low in device stress, small in loss and the like.

Description

Technical Field

[0001] The present invention relates to the field of multi-module converter control, and in particular to a multi-phase LLC resonant converter parallel current sharing system and method. Background Art

[0002] LLC resonant converters have been widely used due to their high efficiency and low electromagnetic interference. However, with the continuous growth of power demand in scenarios such as new energy systems, data centers and communication base stations, single LLC converters face major challenges in the design and selection of switching devices and passive devices. In high-power applications, a single LLC converter is prone to generate large resonant currents, which not only significantly increases the design complexity of resonant inductors and transformers, but also makes device selection difficult and increases system costs.

[0003] To address the above problems, the IPOP structure of the multi-phase LLC converter has gradually become a highly-regarded technical solution. Compared with a single LLC converter, the LLC IPOP system has the advantages of high scalability and high reliability. However, the inherent defect of the LLC IPOP system is that due to the device offset between the resonant networks of different LLC modules, the operating current of the system modules may be unbalanced. Current imbalance will not only seriously reduce the system efficiency and service life, but may also cause system damage. In order to solve the current imbalance problem in the LLC IPOP system, it is necessary to propose a new current balancing solution for the multi-phase LLC resonant converter. Summary of the invention

[0004] The main purpose of the present invention is to overcome the above-mentioned defects in the prior art and to propose a multi-phase LLC resonant converter parallel current sharing system and method, which has the advantages of supporting hot plugging, low device stress, and low loss.

[0005] The present invention adopts the following technical solution:

[0006] A multi-phase LLC resonant converter parallel current sharing system includes N-phase LLC modules connected in parallel; the characteristic is that: it also includes N-1 passive fractional-order capacitors; one passive fractional-order capacitor is connected in parallel between every two phases of the LLC modules, and the passive fractional-order capacitor is provided with a half-bridge rectifier circuit. By adjusting the phase between the half-bridge rectifier circuit and the inverter half-bridge in the LLC module, current sharing between the N-phase LLC modules is achieved.

[0007] The passive fractional capacitor also includes an LC filter, the port where the filter inductor of the LC filter is located is used as the positive electrode of the passive fractional capacitor, and the port where the filter capacitor of the LC filter is located is used as the negative electrode; the LLC module is provided with a resonant capacitor and a resonant inductor, and the positive electrode and the negative electrode of the passive fractional capacitor are respectively connected to the corresponding resonant capacitors of the two LLC modules; the half-bridge rectifier circuit is connected between the filter capacitor and the filter inductor; the parameters of the LC filter are set as follows:

[0008] L c C c =L rn C rn ;

[0009] Among them, L c , C c are the inductance of the filter inductor and the capacitance of the filter capacitor, L rn , C rn They are the inductance of the resonant inductor and the capacitance of the resonant capacitor respectively.

[0010] The passive fractional-order capacitor also includes an energy storage capacitor, one end of the filter inductor is connected to the positive electrode of the passive fractional-order capacitor, and the negative electrode of the energy storage capacitor is connected to the other end of the filter inductor; the half-bridge rectifier circuit includes a transistor Q1 and a transistor Q2, the source of the transistor Q2 is connected to the other end of the filter inductor, and the drain is connected to the positive electrode of the filter capacitor; the source of the transistor Q1 is connected to the positive electrode of the filter capacitor and the drain of the transistor Q2, and the drain is connected to the positive electrode of the energy storage capacitor; the negative electrode of the filter capacitor is connected to the negative electrode of the passive fractional-order capacitor.

[0011] The driving signals of the transistors Q1 and Q2 are 50% complementary square waves; the operating frequency of the half-bridge rectifier circuit is set to be the same as the operating frequency of the inverter half-bridge of the LLC module. fs same:

[0012]

[0013] The inverter half bridge of the LLC module is provided with a transistor S n1 and transistor S n1 , the transistor S n1 The source of the transistor S n2 The drain of the transistor S n2 The source of the transistor Q1 is connected to the resonant capacitor, and the transistor Q1 is set to lag behind the transistor S n1 Phase The transistor Q2 is set to lag behind the transistor S n1 Phase and exists

[0014] The two-phase LLC modules connected to the passive fractional capacitor need to achieve current balancing. and Phase They are configured to satisfy the following formulas:

[0015]

[0016] |Z Cα | represents the equivalent impedance of the passive fractional capacitor, L r1 , L r2 are the resonant inductors of the two-phase LLC modules connected to the passive fractional-order capacitors, C r1 , C r2 are the capacitance values ​​of the resonant capacitors of the two-phase LLC modules connected to the passive fractional-order capacitors, Z1 and Z2 are the equivalent impedances of the subsequent stages of the two-phase LLC modules connected to the passive fractional-order capacitors, |Z1| and θ Z1 Respectively represent the modulus and phase angle of Z1, |Z2| and θ Z2 They represent the modulus and phase angle of Z2 respectively, ω represents the angular frequency, ω=2πf s , fs is the operating frequency. D1, D2, D3, D4, They are all intermediate variables in calculation and have no actual physical meaning.

[0017] The equivalent impedance of the passive fractional capacitor is:

[0018]

[0019] Among them, L r1 , L r1 are the resonant inductance of the LLC module of the two phases, C r1 , C r1 are the capacitance values ​​of the resonant capacitors of the two-phase LLC modules connected to the passive fractional-order capacitors, Z1 and Z2 are the equivalent impedances of the subsequent stages of the two-phase LLC modules connected to the passive fractional-order capacitors, and |Z1| and θ Z1 Respectively represent the modulus and phase angle of Z1, |Z2| and θ Z2 Respectively represent the modulus and phase angle of Z2; ω represents the angular frequency, ω=2πf s , fs is the operating frequency. A, B, and C are all intermediate variables in calculation and have no actual physical meaning.

[0020] A method for parallel current balancing of multi-phase LLC resonant converters is disclosed. N-1 passive fractional-order capacitors are added to parallel N-phase LLC modules, and the configuration is such that one passive fractional-order capacitor is connected in parallel between every two phases of the LLC modules. The passive fractional-order capacitor is provided with a half-bridge rectifier circuit. Current balancing between the N-phase LLC modules is achieved by adjusting the phase between the half-bridge rectifier circuit and the inverter half-bridge in the LLC module.

[0021] It can be seen from the above description of the present invention that, compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention connects passive fractional capacitors in parallel between multi-phase LLC modules, and by adjusting the phase between the rectifier half-bridge in the power-free fractional capacitor and the inverter half-bridge in the LLC resonant converter, current sharing between multi-phase LLC modules can be achieved, which has the advantages of easy installation, simple control, low loss, good current sharing effect, etc. Compared with the traditional current sharing method, the method of the present invention also has the advantages of supporting hot plugging, low device stress, low loss, etc.

[0023] The power-free fractional capacitor P-FOC constructed by the present invention has low current and voltage stress requirements for the required switching devices, which not only greatly reduces the hardware cost of the P-FOC but also improves the system working life. In addition, the realization of ZVS further reduces the working loss caused by the P-FOC. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a system circuit diagram of the present invention;

[0025] Figure 2 is the equivalent circuit diagram using Δ-Y transformation;

[0026] Figure 3 It is the key waveform diagram of the system;

[0027] Figure 4(a) and Figure 4(b) are the phasor diagrams of the ZVS implementation of Q1 / Q2;

[0028] Figure 5(a) and Figure 5(b) show the different offsets. Relationship diagram;

[0029] Figure 6(a) and Figure 6(b) show the different offsets. Relationship diagram;

[0030] Figure 7 This is the system control block diagram;

[0031] FIG8(a), FIG8(b) and FIG8(c) are output current waveforms of the system working under 25% / 50% / 100% load before adding P-FOC;

[0032] FIG9(a), FIG9(b) and FIG9(c) are output current waveforms of the system working under 25% / 50% / 100% load after adding P-FOC;

[0033] FIG. 10( a ) and FIG. 10 ( b ) are port / internal operating waveforms of the P-FOC when the system operates at 50% load.

[0034] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. DETAILED DESCRIPTION

[0035] The present invention is further described below through specific implementation modes.

[0036] join Figure 1 A multi-phase LLC resonant converter parallel current sharing system includes N-phase LLC modules connected in parallel and N-1 passive fractional-order capacitors. A passive fractional-order capacitor P-FOC is connected in parallel between each two adjacent phases of LLC modules. The passive fractional-order capacitor P-FOC is provided with a half-bridge rectifier circuit. By adjusting the phase between the half-bridge rectifier circuit and the inverter half-bridge in the LLC module, current sharing between the N-phase LLC modules is achieved.

[0037] The LLC module of the present invention includes a transformer T N , transistor S N1 , transistor S N2 , resonant capacitor C rN and resonant inductor L rN Etc., N represents the LLC module of the Nth phase. Transistor S N1 And transistor S N2 Constitute an inverter half bridge, transistor S N1 The source of transistor S N2 The drain and resonant inductance L rN One end is connected to the transistor S N2 The source of the resonant capacitor C rN One end, resonant capacitor C rN The other end and the resonant inductor L rN The other end is connected to the transformer T N .

[0038] The passive fractional capacitor also includes a storage capacitor Cd and an LC filter. The LC filter includes a filter inductor and a filter capacitor, the port where the filter inductor is located is used as the positive electrode of the passive fractional capacitor, and the port where the filter capacitor of the LC filter is located is used as the negative electrode. One end of the filter inductor is connected to the positive electrode of the passive fractional capacitor, and the negative electrode of the energy storage capacitor is connected to the other end of the filter inductor. The half-bridge rectifier circuit is connected between the filter capacitor and the filter inductor, and includes a transistor Q1 and a transistor Q2, the source of the transistor Q2 is connected to the other end of the filter inductor, and the drain is connected to the positive electrode of the filter capacitor; the source of the transistor Q1 is connected to the positive electrode of the filter capacitor and the drain of the transistor Q2, and the drain is connected to the positive electrode of the energy storage capacitor; the negative electrode of the filter capacitor is connected to the negative electrode of the passive fractional capacitor.

[0039] In passive fractional order capacitors P-FOC, such as filter inductors L c 、Filter capacitor C c If the positions are swapped, the drive signals of transistors Q1 and Q2 are also swapped. d It only provides voltage support, not energy. The energy storage capacitor C d The parameter can be set to one to ten microfarads, but is not limited thereto. Therefore, under normal operation, the P-FOC branch current is smaller than the main resonant circuit current. (In the present invention,

[0040] Furthermore, the positive and negative electrodes of the passive fractional-order capacitor P-FOC are respectively connected to the resonant capacitors of the corresponding two LLC modules. If there are three or more LLC modules, the positive electrode of the passive fractional-order capacitor P-FOC is connected to the positive electrode of the resonant capacitor of the N-th phase LLC module, and its negative electrode is connected to the positive electrode of the resonant capacitor of the N-1-th phase LLC module. Therefore, the current balancing of the N-phase LLCIPOP system requires N-1 P-FOCs. For example, for the passive fractional-order capacitor connected to the first-phase LLC module and the second-phase LL module, the negative electrode of the passive fractional-order capacitor is connected to the resonant capacitor C of the first-phase LLC module. r1 The positive electrode of the passive fractional capacitor is connected to the resonant capacitor C of the second phase LLC module. r2 connected.

[0041] The LC filter parameter design should meet the same resonant frequency as the LLC module, that is, the LC filter parameters are set as follows:

[0042] L c C c =L rn C rn ;

[0043] Among them, L c , C c are the inductance of the filter inductor and the capacitance of the filter capacitor, L rn , Crn They are the inductance of the resonant inductor and the capacitance of the resonant capacitor respectively.

[0044] In the passive fractional capacitor P-FOC, the driving signals of transistors Q1 and Q2 of the half-bridge rectifier circuit can be set to 50% complementary square waves; the operating frequency of the half-bridge rectifier circuit is set to the operating frequency of the inverter half-bridge of the LLC module. fs Same, f s The following should be satisfied:

[0045]

[0046] right Figure 1 By simplifying the circuit with the offset phase in the Figure 2 . Where V P In the system of the present invention, the fundamental wave of the output voltage of the LLC module inverter is represented, and the fundamental waves of the output voltages output by the first-phase LLC module and the second-phase LLC module are V p1 、V p2 , V Cα represents the voltage across the passive fractional-order capacitor P-FOC, while Z1 and Z2 represent the equivalent impedance of the first and second phase LLC resonant converter. Therefore, the system satisfies the following equation:

[0047]

[0048] Among them, V in is the input voltage, and V Cd C in the passive fractional capacitor P-FOC d The voltage across the terminals, and |Z1| and θ Z1 Respectively represent the modulus and phase angle of Z1, |Z2| and θ Z2 Similarly. ω=2πf s , R eq =16n 2 R L / π 2 ; n is the transformer turns ratio, R L is the load resistance, L m is the transformer excitation inductance, R r1 , R r2 are the total parasitic resistance of the resonant circuit of the first and second phase LLC modules respectively. When the system is working stably, looking from the passive fractional capacitor P-FOC port to the LLC module resonant circuit, the voltage V Cα Leading LLC module inverter voltage V p Phase

[0049] refer to Figure 2, the two-phase LLC module can be decoupled using the Δ-Y transformation, and the impedance in the figure satisfies:

[0050]

[0051] Where Z eq1 , Z eq2 , Z eq3 are the equivalent port impedances after Δ-Y transformation. Cr1 , Z Cr2 , Z Cα C r1 , C r2 , P-FOC impedance. Figure 2 Using KCL, the neutral point N of the Y-type circuit can be obtained:

[0052]

[0053] Where V N is the voltage between point N and the negative pole of the power supply, that is, the equivalent port impedance Z eq3 At the same time, it is noted that in order to achieve the balance of the two-phase LLC output current after decoupling, the following formula should be satisfied:

[0054]

[0055] V o1 、V o2 Indicates the first-phase LLC output voltage and the second-phase LLC output voltage after the system decoupling is completed by Δ-Y transformation. Further, the transistor Q1 in the half-bridge rectifier circuit is set to the transistor S in the lagging inverter half-bridge. n1 Phase Transistor Q2 is set to lag transistor S n1 Phase Since Q1 and Q2 are complementary, there exists

[0056] According to the previous formula, the equivalent impedance of the passive fractional capacitor |Z Cα |For:

[0057]

[0058] Among them, L r1 , L r1 are the resonant inductance of the two-phase LLC module connected to the passive fractional-order capacitor, C r1 , C r1 are the capacitance values ​​of the resonant capacitors of the two-phase LLC modules connected to the passive fractional-order capacitors, Z1 and Z2 are the equivalent impedances of the subsequent stages of the two-phase LLC modules connected to the passive fractional-order capacitors, and |Z1| and θ Z1Respectively represent the modulus and phase angle of Z1, |Z2| and θ Z2 Respectively represent the modulus and phase angle of Z2; ω represents the angular frequency, ω=2πf s , f s is the operating frequency. A, B, and C are all intermediate variables in calculation and have no actual physical meaning.

[0059] The above formula is a quadratic equation with one variable, and its Δ has the following characteristics:

[0060]

[0061] Defining λ L =L r2 / L r1 ,λ C =C r2 / C r1 , so when λ L =λ C =1, the equation has a unique solution -B / 2A, otherwise the passive fractional-order capacitor P-FOC has two stable operating points under any offset condition.

[0062] Figure 4(a) shows the P-FOC working at λ L λ C <1, while Figure 4(b) shows the phasor diagram of P-FOC working at λ L λ C >1. Note that regardless of the offset, P-FOC achieves ZVS, |Z Cα | should be as capacitive as possible. Therefore, according to the ZVS constraint, |Z can be selected Cα |The unique root of the quadratic equation is as follows:

[0063]

[0064] |Z Cα |Lianli The following formula is obtained. According to this formula, The relationship is shown in Figure 5(a) and Figure 5(b). From Figure 5(a) and Figure 5(b), we can conclude that: or The phase impedance balance can be achieved, where C eq Compared with the traditional variable capacitor, the C of the P-FOC eq It can realize the mutual conversion between capacitance and inductance, and at the same time satisfy the phase angle Therefore, it is more appropriate to use fractional order theory to describe the structural characteristics.

[0065] In the present invention, the two-phase LLC module connected to the passive fractional capacitor needs to achieve current balancing, and the P-FOC port voltage V Cα Leading LLC module inverter voltage V p Phase Angle Therefore, the passive fractional capacitor P-FOC controls the phase angle phase and Phase They are configured to satisfy the following formulas:

[0066]

[0067] L r1 , L r2 are the resonant inductance of the two-phase LLC module connected to the passive fractional-order capacitor, C r1 , C r2 are the capacitance values ​​of the resonant capacitors of the two-phase LLC modules connected to the passive fractional-order capacitors, Z1 and Z2 are the equivalent impedances of the subsequent stages of the two-phase LLC modules connected to the passive fractional-order capacitors, |Z1| and θ Z1 Respectively represent the modulus and phase angle of Z1, |Z2| and θ Z2 They represent the modulus and phase angle of Z2 respectively, ω represents the angular frequency, ω=2πf s , fs is the operating frequency. D1, D2, D3, D4, They are all intermediate variables in calculation and have no actual physical meaning.

[0068] Further, draw the load / control quantity The relationship between is shown in Figure 6(a) and Figure 6(b). It can be seen from Figure 6 It is not only related to the load condition but also to the offset condition. Therefore, multiple current sensors must be used to control P-FOC. The control block diagram is shown in Figure 2. Figure 7 . Figure 7 According to λ L λ C Depending on the size, the control schemes are divided into two categories. L λ C The relationship between I and 1 can be easily measured through open-loop experiments. o1 >I o2 When L λ C >1, on the contrary, when I o1 o2 When L λ C <1.

[0069] ​Based on this, the present invention also proposes a multi-phase LLC resonant converter parallel current equalization method, which is implemented by the above-mentioned multi-phase LLC resonant converter parallel current equalization system, adding N-1 passive fractional-order capacitors in the parallel N-phase LLC modules, and configuring a passive fractional-order capacitor in parallel between every two adjacent phase LLC modules, and the passive fractional-order capacitor is provided with a half-bridge rectifier circuit. By adjusting the phase between the half-bridge rectifier circuit and the inverter half-bridge in the LLC module, current equalization between the N-phase LLC modules is achieved.

[0070] In order to verify the correctness of the above analysis, the above method was experimented. The experimental parameters are shown in the table below (λ L λ C <1):

[0071]

[0072]

[0073] Figure 8(a), Figure 8(b), and Figure 8(c) are the system output current waveforms before adding P-FOC. It can be seen that I o1 and I o2 There is a large difference, and as the output power increases, the difference in the two-phase output current gradually increases, which seriously affects the system's working efficiency and may even damage the system. The output current waveform of the system after adding P-FOC can refer to the P-FOC working waveforms in Figure 9(a), Figure 9(b), and Figure 9(c). It can be seen that after adding P-FOC, the system has achieved a good current sharing effect. Figure 10(a) is the port waveform of P-FOC, V Cα Advanced V p Phase And I Cα is the pulse voltage V Cd Figure 10(b) shows the internal waveform of P-FOC. Note that V Cd The voltage is only V in About 4% of I Cα Compared to I Lr2 It is also small, which means that the current and voltage stress requirements of the switching devices required to build P-FOC are low, which not only greatly reduces the hardware cost of P-FOC but also improves the system working life. In addition, the implementation of ZVS further reduces the working loss caused by P-FOC.

[0074] In the present invention, the terms "first", "second", "third", etc. are only used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence, nor can they be understood as indicating or implying relative importance. In the description, the directions or positional relationships indicated by "upper", "lower", "left", "right", "front", and "back" are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention, and are not intended to indicate or imply that the device referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the scope of protection of the present invention. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0075] In addition, in the description of this application, unless otherwise specified, "plurality" means two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0076] The above is only a specific implementation of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantial changes to the present invention using this concept shall be deemed as an infringement of the protection scope of the present invention.

Claims

1. A multi-phase LLC resonant converter parallel current sharing system, comprising N-phase LLC modules connected in parallel; characterized in that: It also includes N-1 passive fractional-order capacitors; one passive fractional-order capacitor is connected in parallel between every two phases of the LLC modules, and the passive fractional-order capacitor is provided with a half-bridge rectifier circuit. By adjusting the phase between the half-bridge rectifier circuit and the inverter half-bridge in the LLC module, current sharing between the N-phase LLC modules is achieved.

2. A multi-phase LLC resonant converter parallel current sharing system as claimed in claim 1, characterized in that: The passive fractional capacitor also includes an LC filter, the port where the filter inductor of the LC filter is located is used as the positive electrode of the passive fractional capacitor, and the port where the filter capacitor of the LC filter is located is used as the negative electrode; the LLC module is provided with a resonant capacitor and a resonant inductor, and the positive electrode and the negative electrode of the passive fractional capacitor are respectively connected to the corresponding resonant capacitors of the two LLC modules; the half-bridge rectifier circuit is connected between the filter capacitor and the filter inductor; the parameters of the LC filter are set as follows: L c C c =L rn C rn ; Among them, L c , C c are the inductance of the filter inductor and the capacitance of the filter capacitor, L rn , C rn They are the inductance of the resonant inductor and the capacitance of the resonant capacitor respectively.

3. A multi-phase LLC resonant converter parallel current sharing system as claimed in claim 2, characterized in that: The passive fractional-order capacitor also includes an energy storage capacitor, one end of the filter inductor is connected to the positive electrode of the passive fractional-order capacitor, and the negative electrode of the energy storage capacitor is connected to the other end of the filter inductor; the half-bridge rectifier circuit includes a transistor Q1 and a transistor Q2, the source of the transistor Q2 is connected to the other end of the filter inductor, and the drain is connected to the positive electrode of the filter capacitor; the source of the transistor Q1 is connected to the positive electrode of the filter capacitor and the drain of the transistor Q2, and the drain is connected to the positive electrode of the energy storage capacitor; the negative electrode of the filter capacitor is connected to the negative electrode of the passive fractional-order capacitor.

4. A multi-phase LLC resonant converter parallel current sharing system as claimed in claim 2, characterized in that: The driving signals of the transistors Q1 and Q2 are 50% complementary square waves; the operating frequency of the half-bridge rectifier circuit is set to be the same as the operating frequency of the inverter half-bridge of the LLC module. fs same:

5. A multi-phase LLC resonant converter parallel current sharing system as claimed in claim 3, characterized in that: The inverter half bridge of the LLC module is provided with a transistor S n1 and transistor S n1 , the transistor S n1 The source of the transistor S n2 The drain of the transistor S n2 The source of the transistor Q1 is connected to the resonant capacitor, and the transistor Q1 is set to lag behind the transistor S n1 Phase The transistor Q2 is set to lag behind the transistor S n1 Phase and exists 6. A multi-phase LLC resonant converter parallel current sharing system as claimed in claim 5, characterized in that: The two-phase LLC modules connected to the passive fractional capacitor need to achieve current balancing. and Phase They are configured to satisfy the following formulas: |Z Cα | represents the equivalent impedance of the passive fractional capacitor, L r1 , L r2 are the resonant inductors of the two-phase LLC modules connected to the passive fractional-order capacitors, C r1 , C r2 are the capacitance values ​​of the resonant capacitors of the two-phase LLC modules connected to the passive fractional-order capacitors, Z1 and Z2 are the equivalent impedances of the subsequent stages of the two-phase LLC modules connected to the passive fractional-order capacitors, |Z1| and θ Z1 Respectively represent the modulus and phase angle of Z1, |Z2| and θ Z2 They represent the modulus and phase angle of Z2 respectively, ω represents the angular frequency, ω=2πf s , fs is the operating frequency; D1, D2, D3, D4, They are all calculated intermediate variables.

7. The multi-phase LLC resonant converter parallel current sharing system according to claim 1, characterized in that: The equivalent impedance of the passive fractional capacitor is: Among them, L r1 , L r1 are the resonant inductance of the LLC module of the two phases, C r1 , C r1 are the capacitance values ​​of the resonant capacitors of the two-phase LLC modules connected to the passive fractional-order capacitors, Z1 and Z2 are the equivalent impedances of the subsequent stages of the two-phase LLC modules connected to the passive fractional-order capacitors, and |Z1| and θ Z1 Respectively represent the modulus and phase angle of Z1, |Z2| and θ Z2 Respectively represent the modulus and phase angle of Z2; ω represents the angular frequency, ω=2πf s , fs is the operating frequency; A, B, and C are all intermediate variables for calculation.

8. A method for current balancing of multi-phase LLC resonant converters in parallel, characterized in that: N-1 passive fractional-order capacitors are added to the parallel N-phase LLC modules, and are configured so that one passive fractional-order capacitor is connected in parallel between every two phases of the LLC modules. The passive fractional-order capacitor is provided with a half-bridge rectifier circuit. By adjusting the phase between the half-bridge rectifier circuit and the inverter half-bridge in the LLC module, current sharing between the N-phase LLC modules is achieved.

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