Integrated LLC structure for realizing displacement current equalization and suppression

Abstract

The invention discloses an integrated LLC resonant converter structure for realizing displacement current equalization and suppression, and belongs to the field of power electronic conversion. The resonant inductors are divided into two independent resonant inductors Lr1 and Lr2, the two resonant inductors are equal in inductance value and are arranged on the upper bridge arm and the lower bridge arm of the LLC converter respectively, the magnetic coupling characteristic of a circuit is optimized, it is guaranteed that a resonant network is completely symmetrical, and therefore the resonance current unbalance degree is theoretically eliminated. Under the condition that the symmetry degree of resonance current is consistent, the capacitance value of the resonance capacitor is halved, the number of the resonance capacitors is reduced by one time, and implementation of primary side ZVS is guaranteed. Meanwhile, the resonant capacitor Cr is placed between the primary sides of the second matrix transformer and the third matrix transformer in series, the resonant capacitor Cr is combined with the first matrix transformer, the second matrix transformer, the third matrix transformer and the fourth matrix transformer through integration, and the position of the resonant capacitor determines that the system has natural integration advantages, so that the overall stability and the response speed of the system are enhanced.

Description

Technical Field

[0001] The invention relates to the field of power electronic power converter topology, in particular to an integrated LLC structure for achieving displacement current balancing and suppression. Background Art

[0002] In current switching power supply applications, especially in secondary devices, there is an urgent need for high frequency, high power density and high efficiency. High-reliability converters have become an important solution to meet these needs. This type of structure has been widely used in many industries such as consumer electronics (such as laptops, mobile phones and LCD TVs), automotive industry (including chargers and power supply systems for electric vehicles), telecommunications (servers), and space and military applications (such as rugged and compact power supplies), especially in the new energy industry.

[0003] In the traditional LLC design, the resonant inductor Lr and the resonant capacitor Cr are arranged in the upper bridge arm and the lower bridge arm respectively. However, due to the high-frequency displacement current, the impedance of the upper bridge arm and the lower bridge arm is asymmetric, and the impedance on the resonant capacitor side is smaller than the impedance on the resonant inductor side. This asymmetry causes more displacement current to flow to the bridge arm where the resonant capacitor is located, resulting in current superposition and causing distortion of the high-frequency displacement current. During the dead time, the distorted displacement current cannot provide sufficient charging and discharging energy for the junction capacitance of the switching device on the bridge arm on the resonant capacitor side, making primary side soft switching difficult.

[0004] In order to solve the problem of displacement current, the document "X. Ren et al.," A 1-kV Input SiC LLC Converter With Split Resonant Tanks and Matrix Transformers," in IEEE Transactions on Power Electronics, vol. 34, no. 11, pp. 10446-10457, Nov. 2019." proposes to divide the resonant inductor Lr into resonant inductors Lr1 and Lr2, and the inductance of each inductor is half of the resonant inductor Lr. At the same time, the resonant capacitor Cr is divided into resonant capacitors Cr1 and Cr2, and their capacitances are twice that of the resonant capacitor Cr. The resonant inductor Lr1 and the resonant capacitor Cr1 are placed in the upper arm of the LLC, while the resonant inductor Lr2 and the resonant capacitor Cr2 are placed in the lower arm. This design increases the footprint of the capacitor. Although it improves the system performance, it also limits the further improvement of the power density of the equipment. Summary of the invention

[0005] The purpose of the present invention is to optimize the traditional LLC resonant converter and propose a new topology. Compared with the traditional LLC resonant converter, the displacement current is balanced on the upper and lower bridge arms. The resonant current has no burrs during the non-dead time. The displacement current oscillation is effectively suppressed during the dead time, realizing soft switching.

[0006] The present invention adopts the following technical solutions to solve the above technical problems:

[0007] An integrated LLC structure for achieving displacement current balancing and suppression is characterized in that, in the proposed integrated LLC structure, a power supply end inverter is composed of four switch tubes Q1, Q2, Q3, and Q4, an upper bridge arm and a lower bridge arm are respectively led out from the midpoints of Q1 and Q2 and the midpoints of Q3 and Q4, resonant inductors Lr1 and Lr2 are placed in the upper bridge arm and the lower bridge arm of the LLC converter, a resonant capacitor Cr is placed between the primary sides of the second and third matrix transformers, and the resonant capacitor Cr is integrated with the first, second, third, and fourth matrix transformers.

[0008] Furthermore, an integrated LLC structure for achieving displacement current balancing and suppression is characterized in that the resonant capacitor Cr is placed in series between the primary sides of the second and third matrix transformers.

[0009] Furthermore, an integrated LLC structure for achieving displacement current balancing and suppression is provided, characterized in that the resonant capacitor Cr is integrated with the first, second, third and fourth matrix transformers, the integrated structure consists of a centrally hollowed-out magnetic core and a PCB winding, the PCB uses an 8-layer board with a copper thickness of 2OZ, and each layer is named L1 to L8.

[0010] Furthermore, an integrated LLC structure for achieving displacement current balancing and suppression is provided, characterized in that L1, L4, and L8 are primary windings, each layer is connected in parallel; L2 and L6 are secondary upper windings, each layer is connected in parallel; and L3 and L7 are secondary lower windings, each layer is connected in parallel.

[0011] Furthermore, an integrated LLC structure for achieving displacement current balancing and suppression is provided, characterized in that the primary winding is designed by connecting the resonant capacitor Cr pin 1 when the second transformer winding is wound out, and leading out the resonant capacitor pin 2 to be wound into the third transformer winding.

[0012] Furthermore, an integrated LLC structure for achieving displacement current balancing and suppression is provided, characterized in that the secondary winding design method is to wind one turn around the central column of each matrix transformer, and input and output from both sides of the integrated structure.

[0013] Furthermore, the rectifier diode can be replaced by a MOSFET for synchronous rectification without affecting the specific implementation of the present invention.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] (1) The integrated LLC structure for achieving displacement current balancing and suppression provided in the present invention ensures that the resonant network is completely symmetrical, thereby theoretically eliminating the imbalance of the resonant current and ensuring the realization of primary side ZVS.

[0016] (2) The present invention provides an integrated LLC structure for achieving displacement current balancing and suppression. The displacement current suppression degree of the proposed structure is less affected by the transformer conduction capacitance Cps, which avoids the influence of the parasitic parameters of the subsequent transformer on the displacement current.

[0017] (3) The integrated LLC structure for achieving displacement current balancing and suppression provided in the present invention reduces the capacitance of the resonant capacitor by half and reduces the number by half while ensuring the symmetry of the resonant current, compared with the existing symmetrical resonant network method.

[0018] (4) The integrated LLC structure for achieving displacement current balancing and suppression provided in the present invention has a natural integration advantage due to the location of the resonant capacitor. It can be integrated inside the matrix transformer, completely eliminating the footprint. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a structural diagram of an integrated LLC for achieving displacement current balancing and suppression according to the present invention;

[0020] Figure 2 It is a classic four-element integrated matrix transformer layout;

[0021] Figure 3 It is the LLC displacement current conduction path of the present invention;

[0022] Figure 4 The layout of the four-element integrated matrix transformer of the present invention;

[0023] Figure 5 It is a schematic diagram of the connection between the primary winding of the quaternary integrated matrix transformer and the resonant capacitor Cr of the present invention;

[0024] Figure 6 The circuit diagram corresponding to the structure of the four-element integrated matrix transformer of the present invention;

[0025] Figure 7 A method for winding a secondary winding of a quaternary integrated matrix transformer according to the present invention;

[0026] Figure 8 A method for winding a secondary lower winding of a quaternary integrated matrix transformer according to the present invention;

[0027] Fig. 9 It is an overall schematic diagram of the structure of the quaternary integrated matrix transformer of the present invention;

[0028] Fig.10 The circuit diagram corresponding to the parasitic parameters of the present invention;

[0029] Fig.11 A schematic diagram of a prototype built for the present invention;

[0030] Fig.12 The LLC resonant tank current waveform proposed by the present invention;

[0031] Fig.13 This is the finite element simulation result of the integrated structure proposed in the present invention;

[0032] Fig.14 It is a traditional LLC structure;

[0033] Fig.15 It is a four-element integrated matrix transformer structure without resonant capacitor;

[0034] Fig.16 This is the current waveform of the traditional LLC resonant tank. DETAILED DESCRIPTION

[0035] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings of the specification. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work are within the scope of protection of the present invention.

[0036] As attached Figure 1 The figure shows an integrated LLC structure proposed to realize displacement current balancing and suppression, which is characterized by Fig.14 The original resonant inductor Lr of the traditional LLC structure is separated into two resonant inductors Lr1 and Lr2, each with half the inductance of the original resonant inductor. The two resonant inductors are arranged in the upper bridge arm and the lower bridge arm of the LLC converter respectively; the resonant capacitor Cr is placed in series between the primary sides of the second and third matrix transformers, and the resonant capacitor Cr is integrated with the first, second, third, and fourth matrix transformers. Suppress and balance the displacement current ips conducted by the primary and secondary capacitors Cps of the planar LLC converter. As shown in the attached figure Figure 3 As shown, the resonant capacitor is integrated with the post-stage matrix transformer to eliminate the area occupied by the resonant capacitor and improve the power density of the device.

[0037] An integrated LLC structure that realizes displacement current balancing and suppression. In actual design, the resonant inductance is usually determined by experiment or simulation to ensure that the circuit can meet the required performance requirements; the transformer turns ratio is designed to be close to the ratio of the rated output voltage to the rated input voltage, so that under rated conditions, the LLC frequency is near the resonant frequency. The general form of the LLC resonant capacitance calculation formula is:

[0038]

[0039] Where C is the desired capacitance in Farads (F), f is the resonant frequency in Hertz (Hz), and L is the inductance in Henrys (H).

[0040] Further, as attached Figure 4 As shown, the resonant capacitor Cr is integrated with the first, second, third and fourth matrix transformers. The integrated structure consists of a central hollowed-out magnetic core and a PCB winding. The PCB uses an 8-layer board with a copper thickness of 2OZ, and each layer is named L1 to L8.

[0041] Furthermore, L1, L4, and L8 are primary windings, each layer is connected in parallel; L2 and L6 are secondary upper windings, each layer is connected in parallel; L3 and L7 are secondary lower windings, each layer is connected in parallel; L5 is a primary switching layer, which connects the primary windings of the first, second, third, and fourth transformers.

[0042] Further, as attached Figure 4 As shown, the design method of the primary winding is that when the second transformer winding is wound out, the resonant capacitor Cr pin 1 is connected, and the resonant capacitor pin 2 is led out and wound into the third transformer winding. The circuit diagram corresponding to the integrated structure is shown in the attached Figure 6 shown.

[0043] Further, as attached Figure 7-8 As shown, the secondary winding design method is to wind one turn around the central column of each matrix transformer, and input and output from both sides of the integrated structure. L2 and L6 draw the secondary upper winding, and L3 and L7 draw the secondary lower winding.

[0044] Further, as attached Fig.16 In the conventional LLC resonant tank current waveform shown, the bridge arm on the resonant capacitor side is affected by the displacement current, and the displacement current burrs are superimposed during the non-dead time. During the dead time, the resonant current is superimposed by the oscillating displacement current, which makes it impossible to achieve soft switching of the switch connected to the lower bridge arm.

[0045] In order to verify the validity of the present invention, an experiment is conducted with a set of LLC operating parameters in Table I and a set of LLC parasitic parameters in Table II. Fig.10 The prototype is as attached. Fig.11 shown.

[0046] Table 1 LLC operating parameters

[0047]

[0048] Table 2 LLC parasitic parameters

[0049]

[0050] Using the proposed method prototype, the LLC resonant tank current waveform under full load 200W is shown in the attached figure. Fig.12 As shown in the figure, the displacement current is balanced on the upper and lower bridge arms. The resonant current has no burrs during the non-dead time. The displacement current oscillation is effectively suppressed during the dead time. The prototype achieves soft switching.

[0051] The integrated structure is simulated by ANSYS, and the magnetic flux density distribution is shown in the attached figure. Fig.13 and attached Fig.15 As shown in the figure. The extraction results show that the magnetic flux density after the core is hollowed out is basically unchanged compared to before the core is hollowed out. This means that the proposed integration method does not introduce additional core loss. In addition, the volume of the resonant capacitor is shared with the transformer, eliminating the footprint of the resonant capacitor.

Claims

1. An integrated LLC resonant converter structure for achieving displacement current balancing and suppression, wherein the power supply inverter is composed of four switch tubes Q1, Q2, Q3, and Q4, the upper bridge arm and the lower bridge arm are respectively led from the midpoint of Q1, Q2 and the midpoint of Q3, Q4, the resonant inductors Lr1 and Lr2 are placed in the upper bridge arm and the lower bridge arm of the LLC converter, the resonant capacitor Cr is placed between the primary sides of the second and third matrix transformers, and the resonant capacitor Cr is integrated with the first, second, third, and fourth matrix transformers. The same-name end of the upper winding and the opposite-name end of the lower winding on the secondary side of the integrated transformer are connected to the positive pole of the rectifier diodes D1-D8, the negative pole of the rectifier diodes D1-D8 is connected to the output capacitor and the positive pole of the load, and the four-way center tap of the transformer is connected to the output capacitor and the negative pole of the load.

2. An integrated LLC structure for achieving displacement current balancing and suppression according to claim 1, characterized in that: The LLC resonant inductor includes two resonant inductors Lr1 and Lr2, the two inductances are equal, and the two resonant inductors are respectively arranged in the upper bridge arm and the lower bridge arm of the LLC converter.

3. The integrated LLC structure for achieving displacement current balancing and suppression according to claim 1, characterized in that: The resonant capacitor Cr is placed in series between the primary sides of the second and third matrix transformers.

4. The integrated LLC structure for achieving displacement current balancing and suppression according to claim 1, characterized in that: The resonant capacitor Cr is integrated with the first, second, third and fourth matrix transformers. The integrated structure consists of a centrally hollowed-out magnetic core and a PCB winding. The PCB winding uses an 8-layer board with a copper thickness of 2OZ, and each layer is named L1 to L8.

5. An integrated LLC structure for achieving displacement current balancing and suppression according to claim 4, characterized in that: L1, L4, and L8 are primary windings, each layer is connected in parallel; L2 and L6 are secondary upper windings, each layer is connected in parallel; L3 and L7 are secondary lower windings, each layer is connected in parallel; L5 is the primary switching layer that connects the primary windings of the first, second, third, and fourth transformers.

6. An integrated LLC structure for achieving displacement current balancing and suppression according to claim 5, characterized in that: The design method of the primary winding is to connect the resonant capacitor Cr pin 1 when the second transformer winding is wound out, and lead out the resonant capacitor pin 2 to wind into the third transformer winding.

7. A partially discrete planar integrated LLC structure for achieving displacement current balancing and suppression according to claim 5, characterized in that: The secondary winding design method is to wind one turn around the central column of each matrix transformer, input and output from both sides of the integrated structure.

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