An integrated LLC structure implementing displacement current balancing and suppression

Abstract

The application discloses an integrated LLC resonant converter structure realizing displacement current balance and suppression, and belongs to the field of power electronic conversion. The resonant inductance is divided into two independent resonant inductances Lr1 and Lr2, and the two inductance values are equal. The two resonant inductances are arranged on the upper bridge arm and the lower bridge arm of the LLC converter respectively, the magnetic coupling characteristics of the circuit are optimized, the resonant network is completely symmetrical, and thus the resonant current imbalance degree is theoretically eliminated. In the case of ensuring the consistency of the resonant current symmetry degree, the capacitance value of the resonant capacitor is halved, and the number of the resonant capacitor is reduced by half, so that the primary side ZVS is ensured. Meanwhile, the resonant capacitor Cr is placed in series between the primary sides of the second and third matrix transformers. The resonant capacitor Cr is combined with the first, second, third and fourth matrix transformers through integration, the position of the resonant capacitor determines that the resonant capacitor has a natural integrated advantage, so that the overall stability and response speed of the system are enhanced.

Description

Technical Field

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

[0002] In current switching power supply applications, especially in secondary equipment, there is an urgent need for high frequency, high power density, and high efficiency. High-reliability converters have become an important solution to address these needs. These structures are widely used in various industries, including consumer electronics (such as laptops, mobile phones, and LCD TVs), the automotive industry (including chargers and power supply systems for electric vehicles), telecommunications (servers), and aerospace and military applications (such as rugged, compact power supplies), particularly in the new energy industry.

[0003] In traditional LLC designs, the resonant inductor Lr and resonant capacitor Cr are positioned on the upper and lower bridge arms, respectively. However, due to high-frequency displacement current, the impedances of the upper and lower bridge arms are asymmetrical, with the impedance on the resonant capacitor side being less than that on the resonant inductor side. This asymmetry causes more displacement current to flow to the bridge arm containing the resonant capacitor, resulting in current superposition and distortion of the high-frequency displacement current. During the dead time, the distorted displacement current cannot provide sufficient charging and discharging energy to the junction capacitance of the switching devices on the resonant capacitor side of the bridge arm, making primary-side soft switching difficult.

[0004] To address the displacement current issue, the paper "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 dividing the resonant inductor Lr into two resonant inductors, Lr1 and Lr2, with each inductor having an inductance value half that of Lr. Similarly, the resonant capacitor Cr is divided into two resonant capacitors, Cr1 and Cr2, each with a capacitance value twice that of Cr. The resonant inductor Lr1 and capacitor Cr1 are placed on the upper arm of the LLC, while the resonant inductor Lr2 and capacitor Cr2 are placed on the lower arm. This design increases the capacitor footprint, which, while improving system performance, limits further increases in power density. Summary of the Invention

[0005] The purpose of this invention is to optimize the traditional LLC resonant converter by proposing a new topology. Compared to the traditional LLC resonant converter, the displacement current is more balanced across the upper and lower bridge arms. There are no glitches in the resonant current during the non-dead time. Displacement current oscillations are effectively suppressed during the dead time, achieving soft switching.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] An integrated LLC structure for achieving displacement current balancing and suppression is characterized in that, in the proposed integrated LLC structure, the power-side inverter consists of four switching transistors Q1, Q2, Q3, and Q4, with the upper and lower bridge arms leading out from the midpoints of Q1 and Q2 and Q3 and Q4, respectively. Resonant inductors Lr1 and Lr2 are placed in the upper and lower bridge arms of the LLC converter, and a resonant capacitor Cr is placed between the primary sides of the second and third matrix transformers. 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 a 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 characterized in that the resonant capacitor Cr is integrated with the first, second, third, and fourth matrix transformers. This integrated structure consists of a hollowed-out magnetic core and PCB windings. 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 characterized in that L1, L4, and L8 are primary windings, connected in parallel in each layer; L2 and L6 are secondary upper windings, connected in parallel in each layer; and L3 and L7 are secondary lower windings, connected in parallel in each layer.

[0011] Furthermore, an integrated LLC structure for achieving displacement current balancing and suppression is characterized in that the primary winding is designed such 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.

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

[0013] Furthermore, the rectifier diode can be replaced with 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 provided in this invention, which realizes displacement current balancing and suppression, ensures that the resonant network is completely symmetrical, thereby theoretically eliminating the resonant current imbalance. It also ensures the realization of ZVS on the primary side.

[0016] (2) The present invention provides an integrated LLC structure for achieving displacement current balance 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 downstream transformer on the displacement current.

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

[0018] (4) The integrated LLC structure provided in this invention, which achieves displacement current balancing and suppression, 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. Attached Figure Description

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

[0020] Figure 2 This is a classic quaternary integrated matrix transformer layout;

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

[0022] Figure 4 This is the layout of the quaternary integrated matrix transformer of the present invention;

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

[0024] Figure 6 This is the circuit diagram corresponding to the quaternary integrated matrix transformer structure of the present invention;

[0025] Figure 7 This invention relates to a method for winding the secondary winding of a quaternary integrated matrix transformer.

[0026] Figure 8 This invention relates to a method for winding the lower secondary winding of a quaternary integrated matrix transformer.

[0027] Figure 9 This is a schematic diagram of the overall structure of the quaternary integrated matrix transformer of the present invention;

[0028] Figure 10 This is the circuit diagram corresponding to the parasitic parameters of the present invention;

[0029] Figure 11 This is a schematic diagram of the prototype built for this invention;

[0030] Figure 12 This is the current waveform of the LLC resonant tank proposed in this invention;

[0031] Figure 13 The results are finite element simulations of the integrated structure proposed in this invention.

[0032] Figure 14 It is a traditional LLC structure;

[0033] Figure 15 It is a quaternary integrated matrix transformer structure without resonant capacitors;

[0034] Figure 16 This is the current waveform of a traditional LLC resonant tank. Detailed implementation method:

[0035] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present invention.

[0036] As attached Figure 1 The figure shows an integrated LLC structure for achieving displacement current balancing and suppression, characterized by the following: Figure 14 The original resonant inductor Lr in the traditional LLC structure is discretely divided into two resonant inductors, Lr1 and Lr2, each with an inductance value half that of the original resonant inductor. These two resonant inductors are respectively positioned on the upper and lower arms of the LLC converter. The resonant capacitor Cr is connected in series between the primary and secondary sides of the second and third matrix transformers, and is integrated with the first, second, third, and fourth matrix transformers. This suppresses and balances the displacement current ips conducted by the primary and secondary capacitors Cps of the planar LLC converter. (See attached diagram) Figure 3 As shown, integrating the resonant capacitor with the subsequent matrix transformer eliminates the footprint of the resonant capacitor and increases the power density of the device.

[0037] An integrated LLC structure for achieving displacement current balancing and suppression. In practical design, the resonant inductor is usually determined experimentally or through simulation to ensure the circuit meets the required performance. The transformer turns ratio is designed to be near the ratio of rated output voltage to rated input voltage, so that the LLC frequency is near the resonant frequency under rated operating conditions. The general form of the LLC resonant capacitance calculation formula is:

[0038]

[0039] Where C is the required capacitance value in farads (F), f is the resonant frequency in hertz (Hz), and L is the inductance value in henries (H).

[0040] Further details are attached. Figure 4 As shown, the resonant capacitor Cr is integrated with the first, second, third, and fourth matrix transformers. This integrated structure consists of a hollowed-out magnetic core and PCB windings. 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, connected in parallel in each layer; L2 and L6 are secondary upper windings, connected in parallel in each layer; L3 and L7 are secondary lower windings, connected in parallel in each layer; L5 is the primary transition layer, which connects the primary windings of the first, second, third, and fourth transformers.

[0042] Further details are attached. Figure 4 As shown, the design method for the primary winding is as follows: 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 this integrated structure is attached. Figure 6 As shown.

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

[0044] Further details are attached. Figure 16 The conventional LLC resonant tank current waveform shown exhibits a displacement current effect on the bridge arm located on one side of the resonant capacitor, resulting in displacement current spikes during the non-dead time. During the dead time, the resonant current superimposed on the oscillating displacement current prevents the soft switching of the switching transistor connected to the lower bridge arm from being achieved.

[0045] To verify the validity of this invention patent, experiments were conducted using a set of LLC operating parameters in Table I and a set of LLC parasitic parameters in Table II. The parasitic parameters correspond to the attached table. Figure 10 The prototype is shown in the attached image. Figure 11 As shown.

[0046] Table 1 LLC Operating Parameters

[0047]

[0048] Table 2 LLC parasitic parameters

[0049]

[0050] The current waveform of the resonant tank under a full load of 200W in the LLC of the prototype using the proposed method is shown in the attached figure. Figure 12 As shown, the displacement current is balanced across the upper and lower bridge arms. The resonant current is glitchy outside the dead time. Displacement current oscillations are effectively suppressed within the dead time. The prototype achieves soft switching.

[0051] The integrated structure was simulated using ANSYS, and the magnetic flux density distribution is shown in the attached figure. Figure 13 and attached Figure 15 As shown in the figure, the extraction results indicate that the magnetic flux density remains essentially unchanged after the core is hollowed out compared to before hollowing. This means that the proposed integration method does not introduce additional core losses. Furthermore, the resonant capacitor volume 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 consists of four switching transistors Q1, Q2, Q3, and Q4, with the upper and lower bridge arms leading out from the midpoints of Q1 and Q2 and Q3 and Q4, respectively; resonant inductors Lr1 and Lr2 are placed in the upper and lower bridge arms of the LLC converter; and a resonant capacitor Cr is placed between the primary windings of the second and third matrix transformers, and is integrated with the first, second, third, and fourth matrix transformers; the same-name terminal of the upper winding and the opposite-name terminal of the lower winding on the secondary side of the integrated transformer are connected to the positive terminals of rectifier diodes D1-D8, the negative terminals of rectifier diodes D1-D8 are connected to the output capacitor and the positive terminal of the load, and the four center taps of the transformer are connected to the output capacitor and the negative terminal of the load; The resonant capacitor Cr is integrated with the first, second, third, and fourth matrix transformers. This integrated structure consists of a hollowed-out magnetic core and PCB windings. The PCB windings are made of an 8-layer board with a copper thickness of 2OZ. Each layer is named L1 to L8. Among them, L1, L4, and L8 are the primary windings, which are connected in parallel in each layer; L2 and L6 are the secondary upper windings, which are connected in parallel in each layer; L3 and L7 are the secondary lower windings, which are connected in parallel in each layer; L5 is the primary transition layer that connects the primary windings of the first, second, third, and fourth transformers.

2. The integrated LLC resonant converter structure for achieving displacement current equalization and suppression according to claim 1, characterized in that, The LLC resonant inductors consist of two resonant inductors, Lr1 and Lr2, with equal inductance values. These two resonant inductors are respectively positioned on the upper and lower arms of the LLC converter.

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

5. The integrated LLC resonant converter structure for achieving displacement current equalization and suppression according to claim 1, characterized in that, The secondary winding design method involves winding one turn around the central column of each matrix transformer, with input and output from both sides of the integrated structure.

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