Multi-phase LLC resonant converter current sharing system based on fractional order capacitor

Abstract

The invention discloses a multi-phase LLC resonant converter current sharing system based on a fractional order capacitor, and the system comprises a reference phase resonant circuit and at least one offset phase resonant circuit, and the reference phase resonant circuit and the offset phase resonant circuit are connected in parallel. The reference phase resonant circuit comprises a first LLC resonant converter; each offset phase resonant circuit comprises a second LLC resonant converter and a power-free fractional order capacitor P-FOC; the P-FOC is connected in parallel with a resonant capacitor Cri in the second LLC resonant converter, a positive port of the P-FOC is connected with a primary side of a transformer in the second LLC resonant converter, and a negative port of the P-FOC is connected with a negative electrode of the input voltage. By controlling the phase between the half-bridge rectifier circuit in the power-free fractional capacitor and the inverter half-bridge in the LLC resonant converter, the current sharing among the multi-phase LLC resonant converters can be realized, and compared with the traditional current sharing method, the method has the advantages of supporting hot plugging, being simple to control, low 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 current sharing system based on fractional-order capacitors. 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 and DC current ripples, which not only significantly increases the design complexity of the resonant inductor and transformer, but also leads to difficulties in device selection and increased system costs. In order to address the above problems, the IPOP structure of the multi-phase LLC converter has gradually become a technical solution that has attracted much attention. Compared with a single LLC converter, the LLC IPOP system has the advantages of low ripple and high reliability. However, the inherent defect of the LLC IPOP system is that the operating current of the system modules may be unbalanced due to the device offset between the resonant networks of different LLC modules. Current imbalance will not only seriously reduce the system efficiency and working life, but also may cause system damage. Summary of the invention

[0003] The main purpose of the present invention is to overcome the above-mentioned defects in the prior art and propose a multi-phase LLC resonant converter current sharing system based on fractional-order capacitors, which can solve the current unevenness problem in the LLC IPOP (multi-phase LLC module input parallel output parallel) system.

[0004] The present invention adopts the following technical solution:

[0005] A multi-phase LLC resonant converter current sharing system based on fractional-order capacitors, comprising: a reference phase resonant circuit and at least one offset phase resonant circuit, wherein the reference phase resonant circuit and the offset phase resonant circuit are connected in parallel; the reference phase resonant circuit comprises a first LLC resonant converter; each of the offset phase resonant circuits comprises a second LLC resonant converter and a power-free fractional-order capacitor P-FOC; the P-FOC and the resonant capacitor C in the second LLC resonant converter are connected in parallel; ri Connected in parallel, the positive port of P-FOC is connected to the primary side of the transformer in the second LLC resonant converter, and the negative port of P-FOC is connected to the negative pole of the input voltage; i∈[2,N], N represents the total number of reference phase resonant loops and offset phase resonant loops.

[0006] Preferably, the P-FOC includes an LC filter, a half-bridge rectifier circuit and an energy storage capacitor C d ; The LC filter includes a filter inductor Lc And filter capacitor C c The half-bridge rectifier circuit includes a MOS tube Q1 and a MOS tube Q2; the positive terminal of the P-FOC and the filter inductor L c One end of the filter inductor L c The other end is connected to the source of MOS tube Q2 and the energy storage capacitor C d The negative electrodes of the MOS tube Q2 are connected to the drain electrode of the filter capacitor C c The positive electrode of the MOS tube Q1 is connected to the source of the MOS tube Q1, and the drain of the MOS tube Q1 is connected to the energy storage capacitor C d The positive electrode of the filter capacitor C c The negative electrode of is connected to the negative terminal of P-FOC.

[0007] Preferably, the P-FOC includes an LC filter, a half-bridge rectifier circuit and an energy storage capacitor C d ; The LC filter includes a filter inductor L c And filter capacitor C c The half-bridge rectifier circuit includes a MOS tube Q1 and a MOS tube Q2; the positive terminal of the P-FOC and the filter capacitor C c One end of the filter capacitor C c The other end is connected to the source of MOS tube Q1 and energy storage capacitor C d The negative electrodes of the MOS tube Q1 are connected to the drain electrode of the filter inductor L c The positive electrode of the MOS tube Q2 is connected to the source of the MOS tube Q2, and the drain of the MOS tube Q2 is connected to the energy storage capacitor C d The positive pole is connected to the filter inductor L c The negative electrode of is connected to the negative terminal of P-FOC.

[0008] Preferably, the parameter design of the LC filter and the parameter design of the first LLC resonant converter satisfy the following formula:

[0009] L c C c =L r1 C r1

[0010] Among them, L r1 represents the resonant inductance in the first LLC resonant converter; C r1 represents the resonant capacitor in the first LLC resonant converter.

[0011] Preferably, the driving signals of the MOS transistors Q1 and Q2 are 50% complementary square waves, and the operating frequency of the half-bridge rectifier circuit is the same as the operating frequency f of the LLC inverter half-bridge in the first LLC resonant converter. s Consistent, f s Satisfy the following formula:

[0012]

[0013] Among them, L r1 represents the resonant inductance in the first LLC resonant converter; C r1 represents the resonant capacitor in the first LLC resonant converter.

[0014] Preferably, is the phase angle of P-FOC, and the phase angle of the half-bridge rectifier circuit in P-FOC ahead of the LLC inverter half-bridge in the second LLC resonant converter is The current balancing of the multi-phase LLC resonant converter is achieved by adjusting accomplish, Satisfy the following formula:

[0015]

[0016] in, ω=2πf s , R eq =8n 2 R L / π;f s represents the operating frequency of the LLC inverter half-bridge in the first LLC resonant converter; n represents the transformer turns ratio; R L Indicates load resistance; L ri represents the resonant inductance in the second LLC resonant converter; L r1 represents the resonant inductance in the first LLC resonant converter; C r1 represents the resonant capacitor in the first LLC resonant converter; R ri is the total parasitic resistance of the offset phase resonant circuit; L mi represents the transformer excitation inductance in the second LLC resonant converter.

[0017] Preferably, the phase angle of the half-bridge rectifier circuit in the P-FOC ahead of the LLC inverter half-bridge in the second LLC resonant converter is Specifically:

[0018] MOS tube Q1 leads the MOS tube S of the LLC inverter half bridge in the second LLC resonant converter. i1 The phase angle is

[0019] Preferably, the P-FOC port is capacitive. When the system is stable, the voltage V across the P-FOC is Cα Inverter voltage V in hysteresis LLC resonant converter p2 Phase And the voltage across P-FOC V CαThe resonant current I of the second LLC resonant converter is lagging behind Lri Phase When P-FOC is charging, When P-FOC releases energy,

[0020] Preferably, P-FOC and resonant capacitor C ri The equivalent impedance after parallel connection is Z eq Satisfy the following formula:

[0021]

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The present invention connects the power-free fractional capacitor in parallel with the resonant capacitor in the second LLC resonant converter, and controls the phase between the half-bridge rectifier circuit in the power-free fractional capacitor and the inverter half-bridge in the second LLC resonant converter to achieve current balancing between multi-phase LLC resonant converters. Compared with the traditional current balancing method, the present invention has the advantages of supporting hot plugging, simple control, and low loss.

[0024] (2) The present invention selects one phase LLC resonant converter as the reference phase, and the resonant capacitor C of the other phase LLC resonant converters rx Both need to be connected in parallel with P-FOC as the offset phase, and the control signal Q of the offset phase resonant circuit i1 / Q i2 The adjustment method is consistent, which greatly reduces the complexity of system control and can achieve better current sharing effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A topological diagram of a current sharing system of a multi-phase LLC resonant converter based on fractional-order capacitors according to an embodiment of the present invention;

[0026] Figure 2 The equivalent circuit of the P-FOC connected in parallel with the LLC resonant circuit according to the embodiment of the present invention;

[0027] Figure 3 1 is a system phase diagram of the P-FOC of the embodiment of the present invention when it is working in different states; wherein (a) represents working in charging state, (b) represents working in stable state, and (c) represents working in releasing state;

[0028] Figure 4 This is a key waveform diagram of the system according to an embodiment of the present invention;

[0029] Figure 5 The embodiment of the present invention under different loads / C eq Relationship diagram;

[0030] Figure 6 is the Load (load) of the reference phase under different offsets of the embodiment of the present invention. Relationship diagram; where (a) is the r1 / C r1 The relationship diagram under the offset, (b) is the relationship diagram under L r2 / C r2 Relationship diagram under offset;

[0031] Figure 7 The output current waveform diagram of the system working under different loads before adding P-FOC in the embodiment of the present invention; wherein (a) is under 25% load, (b) is under 50% load, and (c) is under 100% load;

[0032] Figure 8 The output current waveforms of the system working under different loads after adding P-FOC in the embodiment of the present invention; wherein (a) is under 25% load, (b) is under 50% load, and (c) is under 100% load;

[0033] Fig. 9 It is a port / internal working waveform diagram of the P-FOC when the system according to the embodiment of the present invention works at 50% load. DETAILED DESCRIPTION

[0034] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0035] The present invention discloses a multi-phase LLC resonant converter current sharing system based on fractional-order capacitors, comprising a reference phase resonant circuit and at least one offset phase resonant circuit, wherein the reference phase resonant circuit and the offset phase resonant circuit are connected in parallel; the reference phase resonant circuit comprises a first LLC resonant converter; each of the offset phase resonant circuits comprises a second LLC resonant converter and a power-free fractional-order capacitor P-FOC; the P-FOC and the resonant capacitor C in the second LLC resonant converter are connected in parallel; ri Connected in parallel, the positive port of P-FOC is connected to the primary side of the transformer in the second LLC resonant converter, and the negative port of P-FOC is connected to the negative pole of the input voltage; i∈[2,N], N represents the total number of reference phase resonant loops and offset phase resonant loops.

[0036] like Figure 1As shown, the multi-phase LLC resonant converter current sharing system based on fractional-order capacitors of this embodiment is described by including a reference phase resonant circuit and an offset phase resonant circuit.

[0037] Specifically, the P-FOC includes an LC filter, a half-bridge rectifier circuit and an energy storage capacitor C d ; The LC filter includes a filter inductor L c And filter capacitor C c The half-bridge rectifier circuit includes a MOS tube Q1 and a MOS tube Q2; the positive terminal of the P-FOC and the filter inductor L c One end of the filter inductor L c The other end is connected to the source of MOS tube Q2 and the energy storage capacitor C d The negative electrodes of the MOS tube Q2 are connected to the drain electrode of the filter capacitor C c The positive electrode of the MOS tube Q1 is connected to the source of the MOS tube Q1, and the drain of the MOS tube Q1 is connected to the energy storage capacitor C d The positive electrode of the filter capacitor C c The negative electrode of is connected to the negative terminal of P-FOC.

[0038] It should be noted that in P-FOC, if L c and C c The positions are interchanged, and the driving signals of Q1 and Q2 are also interchanged. The working mechanism is the same as the original topology, and is considered to be consistent with the present invention.

[0039] In the P-FOC, the LC filter parameter design should satisfy the same resonant frequency as the first LLC resonant converter, that is:

[0040] L c C c =L r1 C r1

[0041] Among them, L r1 represents the resonant inductance in the first LLC resonant converter; C r1 represents the resonant capacitor in the first LLC resonant converter.

[0042] C d It only provides voltage support but not energy. Therefore, under normal operation, the P-FOC branch current is smaller than the main resonant circuit current. d The capacitance value is designed to be ten to one hundred nanofarads to meet the demand, and PFOC has a high power density.

[0043] The driving signals of Q1 and Q2 in the half-bridge rectifier circuit in the P-FOC are 50% complementary square waves, and the resonant frequency of the first LLC resonant converter, the operating frequency of the half-bridge rectifier circuit and the LLC inverter half-bridge operating frequency fs Consistent,f s The following should be satisfied:

[0044]

[0045] Define Q1 Lead S 21 The phase angle is and is defined as the phase angle of the fractional-order capacitor,

[0046] like Figure 2 As shown, it is the equivalent circuit of P-FOC connected in parallel with LLC resonant circuit. P2 represents the inverter bridge output voltage in the second LLC resonant converter, V Cα represents the voltage across P-FOC, and Z2 represents the total equivalent impedance of the subsequent stage (including the resonant inductor L r2 , transformer excitation inductance L m2 And the subsequent equivalent load R eq ).

[0047] The system satisfies the following equation:

[0048]

[0049] Among them, V in is the input voltage, V Cd is C in P-FOC d The voltage across the two ends of The vector representing the LLC inverter output voltage of the reference phase, The vector representing the LLC inverter output voltage of the offset phase, The vector representing the voltage at the P-FOC port, |Z2| is the modulus of the total equivalent impedance of the subsequent stage, is the phase angle of the total equivalent impedance of the subsequent stage.

[0050] According to the above formula, draw the phasor diagram of the system as follows Figure 3 When the system is working stably, looking from the P-FOC port to the LLC resonant circuit, the voltage V across the P-FOC should be Cα Inverter voltage V in hysteresis LLC resonant converter p2 Phase P-FOC and C r2 The equivalent impedance after parallel connection is Z eq Satisfy the following formula:

[0051]

[0052] Therefore, the P-FOC port must be capacitive, that is, the stable system also satisfies V Cα Lag resonant current I Lr2 Phase When P-FOC is charging, On the contrary, when P-FOC releases energy,

[0053] like Figure 4 The following is the key working waveform of the system. It can be seen from the waveform that Q1 leads S 21 Phase is And V Cα Hysteresis I Lr2 Phase At the same time, note that the port current I Cα is the pulse voltage V Cd The LC resonant current under excitation, the resonant frequency f α Satisfy the following formula:

[0054]

[0055] P-FOC loop (i.e., C when Q2 is turned on and Q1 is turned off) r2 , C c , L c , C d The characteristic impedance Z of the series circuit α,eq Satisfy the following formula:

[0056]

[0057] The excitation voltage is V Cd The pulse voltage, according to f α and Z α,eq You can calculate I Cα The specific value of C r2 After parallel connection P-FOC, the port equivalent capacitance C eq The following formula can be deduced:

[0058]

[0059] Where ω=2πf s , R eq =8n 2 R L / π; n is the transformer turns ratio, R L is the load resistance, L m2 is the excitation inductance of the offset phase transformer, R r2 is the total parasitic resistance of the offset phase resonant circuit. The equivalent capacitance C of P-FOC can be drawn eq,Cα and Relationship images, reference Figure 5 . Figure 5 C eq,Cα Compared with the traditional variable capacitor, the C of the P-FOC eq,CαIt can realize the mutual conversion between capacitance and inductance, and at the same time satisfy the phase angle is adjustable, so it is more appropriate to use fractional order theory to describe the characteristics of this structure.

[0060] It indicated Figure 5 C eq,Cα The critical phase of capacitance and inductance satisfies the following equation. It is worth noting that in order to achieve C r2 +C eq,Cα =C eq =C r1 , so the control angle in the present invention satisfy

[0061]

[0062] In order to achieve the current balance with the reference phase LLC module, it is necessary to meet the R eq1 =R eq2 =2R eq (R eq1 , R eq2 are the equivalent load resistances of the reference phase and the offset phase respectively; due to the system current sharing, the equivalent load resistance of each phase should be twice the total load resistance) circuit gain, that is, satisfying L r1 C r1 =L r2 C eq ,So The following should be satisfied:

[0063]

[0064] According to the above formula, it is drawn as load / Image, reference Figure 6 . Figure 6 Medium L =L r2 / L r1 ,λ C =C r2 / C r1 .contrast Figure 6 (a) The reference phase offset and Figure 6 (b) is offset from the phase shift, and we can conclude that: Not affected by C r2 Affected by L r2 The influence is small, that is, the control amount Insensitive to offset phase parameters, Only subject to load R L Therefore, this method only needs one current sensor to collect the total output current I o , according to the fixed output voltage Vo , that is, the load R can be calculated L =V o / I o , so that the control quantity can be obtained This method sacrifices a certain degree of current sharing accuracy, but has the advantages of simple control and a small number of sensors. Therefore, this P-FOC current sharing method is extremely suitable for DC transformer (DCX) application scenarios.

[0065] In order to verify the correctness of the above analysis, the above method was experimented. The experimental parameters are shown in Table 1 below.

[0066] Table 1

[0067]

[0068] Figure 7 This is the system output current waveform before adding P-FOC. It can be seen that I o1 and I o2 There is a big difference, and as the output power increases, the difference between the two-phase output currents gradually increases, which seriously affects the working efficiency of the system and may even damage the system. The output current waveform after the system adds P-FOC can be referred to Figure 8 , it can be seen that after adding P-FOC, the system has achieved a good current sharing effect. Fig. 9 This is the working waveform of P-FOC. It can be seen that I Cα is the pulse voltage V Cd The LC resonant current under excitation, and its amplitude is compared with I Lr2 It is smaller, which means that the loss of P-FOC is smaller and there is a larger margin in device selection.

[0069] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A multi-phase LLC resonant converter current sharing system based on fractional-order capacitors, characterized in that: include: a reference phase resonant circuit and at least one offset phase resonant circuit, the reference phase resonant circuit and the offset phase resonant circuit are connected in parallel; the reference phase resonant circuit includes a first LLC resonant converter; each of the offset phase resonant circuits includes a second LLC resonant converter and a power-free fractional order capacitor P-FOC; the P-FOC and the resonant capacitor C in the second LLC resonant converter are connected in parallel; ri Connected in parallel, the positive port of P-FOC is connected to the primary side of the transformer in the second LLC resonant converter, and the negative port of P-FOC is connected to the negative pole of the input voltage; i∈[2,N], N represents the total number of reference phase resonant loops and offset phase resonant loops.

2. The multi-phase LLC resonant converter current sharing system based on fractional-order capacitors according to claim 1 is characterized in that: The P-FOC includes an LC filter, a half-bridge rectifier circuit and an energy storage capacitor C d ; The LC filter includes a filter inductor L c And filter capacitor C c The half-bridge rectifier circuit includes a MOS tube Q1 and a MOS tube Q2; the positive terminal of the P-FOC and the filter inductor L c One end of the filter inductor L c The other end is connected to the source of MOS tube Q2 and the energy storage capacitor C d The negative electrodes of the MOS tube Q2 are connected to the drain electrode of the filter capacitor C c The positive electrode of the MOS tube Q1 is connected to the source of the MOS tube Q1, and the drain of the MOS tube Q1 is connected to the energy storage capacitor C d The positive electrode of the filter capacitor C c The negative electrode of is connected to the negative terminal of P-FOC.

3. The multi-phase LLC resonant converter current sharing system based on fractional-order capacitors according to claim 1 is characterized in that: The P-FOC includes an LC filter, a half-bridge rectifier circuit and an energy storage capacitor C d ; The LC filter includes a filter inductor L c And filter capacitor C c The half-bridge rectifier circuit includes a MOS tube Q1 and a MOS tube Q2; the positive terminal of the P-FOC and the filter capacitor C c One end of the filter capacitor C c The other end is connected to the source of MOS tube Q1 and energy storage capacitor C d The negative electrodes of the MOS tube Q1 are connected to the drain electrode of the filter inductor L c The positive electrode of the MOS tube Q2 is connected to the source of the MOS tube Q2, and the drain of the MOS tube Q2 is connected to the energy storage capacitor C d The positive pole is connected to the filter inductor L c The negative electrode of is connected to the negative terminal of P-FOC.

4. The multi-phase LLC resonant converter current sharing system based on fractional-order capacitors according to claim 2 or 3, characterized in that: The parameter design of the LC filter and the parameter design of the first LLC resonant converter satisfy the following formula: L c C c =L r1 C r1 Among them, L r1 represents the resonant inductance in the first LLC resonant converter; C r1 represents the resonant capacitor in the first LLC resonant converter.

5. The multi-phase LLC resonant converter current sharing system based on fractional-order capacitors according to claim 2 or 3, characterized in that: The driving signals of the MOS transistors Q1 and Q2 are 50% complementary square waves, and the operating frequency of the half-bridge rectifier circuit is the same as the operating frequency f of the LLC inverter half-bridge in the first LLC resonant converter. s Consistent, f s Satisfy the following formula: Among them, L r1 represents the resonant inductance in the first LLC resonant converter; C r1 represents the resonant capacitor in the first LLC resonant converter.

6. The multi-phase LLC resonant converter current sharing system based on fractional-order capacitors according to claim 2 or 3, characterized in that: make is the phase angle of P-FOC, and the phase angle of the half-bridge rectifier circuit in P-FOC ahead of the LLC inverter half-bridge in the second LLC resonant converter is The current balancing of the multi-phase LLC resonant converter is achieved by adjusting accomplish, Satisfy the following formula: in, ω=2πf s , R eq =8n 2 R L / π;f s represents the operating frequency of the LLC inverter half-bridge in the first LLC resonant converter; n represents the transformer turns ratio; R L Indicates load resistance; L ri represents the resonant inductance in the second LLC resonant converter; L r1 represents the resonant inductance in the first LLC resonant converter; C r1 represents the resonant capacitor in the first LLC resonant converter; R ri is the total parasitic resistance of the offset phase resonant circuit; L mi represents the transformer excitation inductance in the second LLC resonant converter.

7. The multi-phase LLC resonant converter current sharing system based on fractional-order capacitors according to claim 6, characterized in that: The phase angle of the half-bridge rectifier circuit in P-FOC leading the LLC inverter half-bridge in the second LLC resonant converter is Specifically: MOS tube Q1 leads the MOS tube S of the LLC inverter half bridge in the second LLC resonant converter. i1 The phase angle is 8. The multi-phase LLC resonant converter current sharing system based on fractional-order capacitors according to claim 2 or 3, characterized in that: The P-FOC port is capacitive. When the system is stable, the voltage V Cα Inverter voltage V in hysteresis LLC resonant converter p2 Phase And the voltage across P-FOC V Cα The resonant current I of the second LLC resonant converter is lagging behind Lri Phase When P-FOC is charging, When P-FOC releases energy, 9. The multi-phase LLC resonant converter current sharing system based on fractional-order capacitors according to claim 7, characterized in that: P-FOC and resonant capacitor C ri The equivalent impedance after parallel connection is Z eq Satisfy the following formula:

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