LCLC resonant converter based on inductive coupling design

Abstract

The invention discloses an LCLC resonant converter based on inductive coupling design, which comprises an inversion unit, an LCLC resonant cavity unit, a transformer and a rectification unit which are arranged in sequence, and is characterized in that the inversion unit is composed of an input power supply and a full-bridge switching circuit, and output nodes on the inversion unit are a node A and a node B respectively; the LCLC resonant cavity unit comprises a resonant inductor, an excitation inductor, a resonant capacitor and an excitation capacitor; the transformer is connected to the output end of the LCLC resonant cavity unit; the rectification unit is composed of four power switch tubes. One end of a primary side winding of the transformer is connected with a node A through a resonant inductor; the other end of the primary winding of the transformer is connected with a node B through a resonant capacitor; the excitation inductor and the excitation capacitor are connected in series and then are connected in parallel with a primary side winding of the transformer; the resonant inductor and the excitation inductor are magnetically coupled through a common magnetic core, different-name ends are connected to the same point to generate mutual inductance M, and the mutual inductance M is used for compensating the deviation of leakage inductance Lk generated by the transformer to resonant frequency.

Description

Technical Field

[0001] The present invention relates to the technical field of LCLC resonant converters, and in particular to an LCLC resonant converter based on inductive coupling design. Background Art

[0002] In recent years, with the advancement of science and technology and the continuous breakthroughs in power electronics technology, isolated resonant converters have been widely used in the field of DC buildings and the construction of DC power distribution systems, especially in distributed energy storage and new energy scenarios. The continuous progress and breakthroughs in the application technology of topology transformation technology and new wide bandgap devices have made high efficiency and high power density the development direction of power electronic devices, especially in the application needs of household energy storage and household adaptation, which have strict requirements on efficiency, volume, wide gain and digital control technology. Traditional LLC, CLLC and other resonant topologies have received widespread attention due to their better switching voltage stress and good EMI characteristics. However, the isolated resonant topology often adopts the frequency modulation control method when boosting, and this method is mostly adjusted within the range of 1 to 1.2 times the standardized voltage gain, and the adjustment range is relatively narrow. The working conditions greater than 1.2 require further reduction of the inductance ratio, which often leads to a reduction in the quality factor of the converter and a decrease in efficiency. In this regard, the LCLC topology was proposed. By connecting the Lm and Cm equivalent excitation circuits in parallel at both ends of the transformer, the equivalent excitation inductance can be applied variable with the switching frequency, thereby achieving a high inductance ratio at the rated point. When away from the resonant frequency, the inductance ratio drops rapidly, which broadens the gain range and takes into account both efficiency and gain characteristics. However, this application is often limited to ideal topology analysis. In real applications, the leakage inductance in the LCLC topology transformer cannot be ignored. The leakage inductance will lead to parameter design deviations, destroy the ideal resonant structure, introduce new resonant points, and cause a sharp drop in the rated design efficiency. Therefore, it is urgent to propose a design method for the LCLC topology that effectively suppresses the leakage inductance without introducing external devices, inherit the soft switching and wide gain characteristics, and solve the problem of efficiency loss caused by leakage inductance, and finally take into account the problem of balancing efficiency and wide gain. Summary of the invention

[0003] The purpose of the present invention is to overcome the deficiencies in the prior art. Based on the LCLC resonant topology, the problem of parameter design deviation and low efficiency caused by transformer leakage inductance is addressed. An LCLC resonant converter based on inductive coupling design is provided. The coupling and alienation effect of the same-name terminals of the parallel excitation inductance and the resonant inductance is utilized to equivalently connect the mutual inductance in series on the leakage inductance path. Then, through the design of the coupled inductance coefficient, the mutual inductance and the leakage inductance are offset. The problem of gain deviation and reactive circulating current introduction caused by parameter design deviation caused by leakage inductance when the existing LCLC topology is applied is solved, which ultimately leads to the attenuation of the actual application efficiency. The application of the theoretical idealized model can be realized, the problem of gain and resonance deviation caused by leakage inductance is solved, and the soft switching characteristics and the wide gain advantages of LCLC are inherited, which provides a new idea for the wide gain and high efficiency application of the resonant converter.

[0004] The objective of the present invention is achieved through the following technical solutions:

[0005] An LCLC resonant converter based on inductive coupling design includes an inverter unit, an LCLC resonant cavity unit, a transformer and a rectifier unit arranged in sequence, wherein the inverter unit is composed of an input power supply and a full-bridge switch circuit, the full-bridge switch circuit includes four switch tubes, and the output nodes on the inverter unit are respectively A node and B node; the LCLC resonant cavity unit includes a resonant inductor, an excitation inductor, a resonant capacitor and an excitation capacitor; the transformer is connected to the output end of the LCLC resonant cavity unit; the rectifier unit is composed of four power switch tubes for outputting a stable DC voltage; and the characteristics are as follows:

[0006] One end of the primary winding of the transformer is connected to the A node via a resonant inductor;

[0007] The other end of the primary winding of the transformer is connected to the B node through a resonant capacitor;

[0008] The excitation inductor and the excitation capacitor are connected in series and then connected in parallel with the primary winding of the transformer;

[0009] The resonant inductor and the excitation inductor are magnetically coupled through a common magnetic core, and the opposite ends are connected at the same point to generate a mutual inductance M, which is used to compensate for the leakage inductance L generated by the transformer. k Shift from resonant frequency.

[0010] Furthermore, the output voltage is controlled by adjusting the switching frequency to adapt to different load conditions.

[0011] Furthermore, the mutual inductance coefficient of the mutual inductance M ranges from 0 to 1.

[0012] Compared with the prior art, the technical solution of the present invention effectively solves the performance problem caused by leakage inductance in the traditional LCLC topology in practical applications through inductive coupling design, and the beneficial effects brought about are:

[0013] 1. Achieve leakage inductance suppression: By connecting the opposite ends of the excitation inductance and the resonant inductance at the same point, and designing an appropriate coupling coefficient, the mutual inductance M is introduced, so that the mutual inductance and the transformer leakage inductance cancel each other out in the equivalent circuit, effectively suppressing the damage of the leakage inductance to the resonant cavity structure and forming an ideal resonant network. The problem of the resonance point deviating from the theoretical calculated value and the gain characteristic deviation caused by the leakage inductance is solved, ensuring that the circuit works close to the ideal state.

[0014] 2. Improve circuit efficiency: By suppressing the reactive loss introduced by leakage inductance, the present invention inherits the wide gain and soft switching advantages of the LCLC topology, avoids the additional power loss caused by leakage inductance, significantly improves the overall conversion efficiency, and provides a strong guarantee for efficient power conversion.

[0015] 3. Broaden the gain range: The present invention uses coupling design to adjust the equivalent excitation inductance, combined with the narrow bandwidth gain characteristics of LCLC, to achieve efficient operation under a wide gain range, meeting the high gain requirements of scenarios such as energy storage conversion, DC adaptation and photovoltaic applications.

[0016] 4. Reduce design complexity: The present invention does not require the addition of additional inductors or other components. It utilizes the coupling effect of the transformer structure itself for design, which reduces hardware costs and circuit complexity. At the same time, it reduces dependence on component performance, brings convenience to the design of inductor components, further improves circuit working efficiency, and simplifies the circuit design and optimization process.

[0017] 5. Compatible with traditional control strategies: The control method of the present invention is consistent with that of the traditional LLC resonant converter, and there is no need to introduce new complex control algorithms, which facilitates compatibility with existing technologies and promotion and application.

[0018] 6. Improve application adaptability: The present invention is particularly suitable for application scenarios such as energy storage, photovoltaics, and DC adapters that require high efficiency, high gain, and high power density. It can significantly improve the application performance of isolated resonant converters in these fields and meet the development needs of distributed energy storage and new energy equipment.

[0019] In summary, the present invention, while inheriting the advantages of LCLC wide gain and soft switching, further overcomes the limitations brought by leakage inductance, and provides a new technical solution for the efficient wide gain application of resonant converters. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a comparison diagram of voltage gain curves of LLC circuits with different k values ​​and LCLC circuits of the present invention;

[0021] Figure 2 It is a schematic diagram of the structure of the LCLC circuit in the present invention when the leakage inductance exists during actual operation;

[0022] Figure 3 The present invention is a waveform diagram of each resonant cavity current, key switch tube current and output voltage when the LCLC circuit has leakage inductance during actual operation;

[0023] Figure 4 It is a structural schematic diagram of the present invention when the LCLC circuit uses a coupled inductor;

[0024] Figure 5 It is a schematic structural diagram of the present invention using an LCLC circuit to perform decoupling equivalent when using a coupled inductor;

[0025] Figure 6 It is a schematic diagram of the structure of the LCLC circuit of the present invention when there is no transformer leakage inductance;

[0026] Figure 7 The present invention is a waveform diagram of each resonant cavity current, key switch tube current and output voltage of the circuit after decoupling equivalent when the LCLC circuit uses a coupled inductor;

[0027] Figure 8 The present invention is a waveform diagram of each resonant cavity current, key switch tube current and output voltage of the LCLC circuit when there is no transformer leakage inductance. DETAILED DESCRIPTION

[0028] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0029] This embodiment is based on the LCLC resonant topology, inherits the advantages of LCLC wide gain and soft switching, and adopts a coupled inductor method to provide an LCLC resonant converter based on inductor coupling design. The specific topology is shown in the attached figure. Figure 4 As shown, it includes an inverter unit, an LCLC resonant cavity unit, a transformer and a rectifier unit which are arranged in sequence, the inverter unit is composed of an input power supply and a full-bridge switch circuit, the full-bridge switch circuit includes four switch tubes, and the output nodes on the inverter unit are respectively A node and B node; the LCLC resonant cavity unit includes a resonant inductor, an excitation inductor, a resonant capacitor and an excitation capacitor; the transformer is connected to the output end of the LCLC resonant cavity unit; the rectifier unit is composed of four power switch tubes for outputting a stable DC voltage;

[0030] One end of the primary winding of the transformer is connected to the A node through a resonant inductor;

[0031] The other end of the primary winding of the transformer is connected to the B node through a resonant capacitor;

[0032] The excitation inductor and the excitation capacitor are connected in series and then connected in parallel with the primary winding of the transformer;

[0033] The resonant inductor and the excitation inductor are magnetically coupled through a common magnetic core, and the opposite ends are connected at the same point to generate a mutual inductance M, which is used to compensate for the leakage inductance L generated by the transformer. k Shift from resonant frequency.

[0034] The LCLC resonant converter of this embodiment can effectively suppress the influence of transformer leakage inductance in actual working conditions, so that the circuit operates in an ideal state strategy close to that with no leakage inductance, avoiding the damage of the leakage inductance to the resonant cavity structure and the deviation caused by the parameter design, thereby affecting the efficiency.

[0035] Specifically, the LCLC resonant topology adopted in this embodiment is different from the conventional LLC resonant topology in that the conventional ideal LCLC converter structure is as shown in the attached figure. Figure 6 As shown, its structural feature is that L is connected in parallel at both ends of the transformer. m and C m The series structure acts as an excitation inductor, making it have a variable excitation inductance, whose size changes with the frequency. The calculation formula is:

[0036]

[0037] Where L m is the magnetizing inductance, C m is the excitation capacitance, f s is the switching frequency, L m_eq is the equivalent magnetizing inductance of the LCLC circuit.

[0038] Attached Figure 1 Taking the voltage gain curves of different k values ​​for LLC circuits and LCLC circuits respectively, it can be clearly seen that the slope of the gain curve of the LCLC converter is steeper, its gain range is wider, the introduced reactive loss is smaller, and it is more conducive to the realization of wide gain and high efficiency; combined with the LLC gain characteristics, the voltage gain range can be successfully expanded within a narrow frequency range without sacrificing efficiency.

[0039] In the actual circuit, LCLC is due to the leakage inductance of the transformer and the parallel connection L m , C m The impact of L cannot be incorporated into r The real topological structure is as follows Figure 2 As shown. Leakage inductance L k The influence of leakage inductance cannot be ignored. The existence of leakage inductance makes the resonance point deviate from the theoretical calculation point, introduces a new resonance point, and reduces the circuit efficiency. r =80uH, C r =24nF, L m =420uH, C m =47nF, L k=30uH, n=8, after simulation, we can get i 12 、i3、i S1 、i SR1 、V out The waveform is as Figure 3 As shown, the existence of leakage inductance makes the current distortion through the resonant cavity no longer a standard sine waveform, and the resonance point deviates from the theoretical calculation point, which reduces the circuit working efficiency.

[0040] The specific structure of the present invention is shown in the attached Figure 4 As shown, the LCLC structure diagram with coupled inductance, resonant inductor L r With the excitation inductance L m Magnetic coupling is achieved by sharing the magnetic core, and the resonant inductor L r With the excitation inductance L m The opposite ends are connected at the same point, and the mutual inductance between them is M. By properly designing the resonant inductor L r With the excitation inductance L m The coupling coefficient between them makes the mutual inductance close to the actual leakage inductance value. The equivalent structure circuit is shown in the attached figure. Figure 5 As shown, by making a decoupling equivalent circuit diagram, it can be found that the leakage inductance branch can be simplified into mutual inductance -M and leakage inductance L k The equivalent inductance of the series circuit is L k -M, by adjusting the mutual inductance coefficient to make M close to L k , thus eliminating the influence of leakage inductance and achieving the application effect of the ideal LCLC topology. And the control method of the LCLC circuit is consistent with the traditional LLC circuit control method.

[0041] Specifically, for Figure 4 The circuit shown with coupled inductors can be described according to Kirchhoff's voltage-current law:

[0042]

[0043] The decoupling equivalent circuit is obtained from equation (2): Figure 5 Coupling factor If the coupling factor k of the two is reasonably designed during parameter design, the size of the mutual inductance M can be obtained. k -M=0, so the influence of leakage inductance on the circuit can be eliminated, and the result is as follows Figure 6 The circuit without leakage inductance is shown.

[0044] for Figure 5 , Figure 6 The two circuits are simulated and verified in PSIM respectively, with mutual inductance M = 30uH and other parameters kept the same as above. 12 、i3、i S1 、iSR1 、V out The waveform is as Figure 7 , Figure 8 As shown, the two waveforms are compared and found to be basically the same, which can prove the effectiveness of the method proposed in the present invention.

[0045] The present invention is not limited to the embodiments described above. The above description of the specific embodiments is intended to describe and illustrate the technical solution of the present invention. The above specific embodiments are merely illustrative and not restrictive. Without departing from the scope of the present invention and the scope of protection of the claims, a person of ordinary skill in the art can also make many forms of specific changes under the guidance of the present invention, which all fall within the scope of protection of the present invention.

Claims

1. An LCLC resonant converter based on inductive coupling design, comprising an inverter unit, an LCLC resonant cavity unit, a transformer and a rectifier unit arranged in sequence, wherein the inverter unit is composed of an input power supply and a full-bridge switch circuit, the full-bridge switch circuit includes four switch tubes, and the output nodes on the inverter unit are respectively A node and B node; the LCLC resonant cavity unit includes a resonant inductor (L r )、Magnetic inductance(L m )、resonant capacitor (C r ) and the excitation capacitor (C m ); the transformer is connected to the output end of the LCLC resonant cavity unit; the rectifier unit is composed of four power switch tubes for outputting a stable DC voltage; it is characterized in that, One end of the primary winding of the transformer is connected via a resonant inductor (L r ) is connected to node A; The other end of the primary winding of the transformer is connected through a resonant capacitor (C r ) is connected to Node B; Excitation inductance (L m ) and the excitation capacitor (C m ) are connected in series and then in parallel with the primary winding of the transformer; Resonant inductance (L r ) and magnetizing inductance (L m ) Magnetic coupling is achieved by sharing a magnetic core, and the opposite ends are connected at the same point to generate a mutual inductance M, which is used to compensate for the leakage inductance L generated by the transformer. k Shift from resonant frequency.

2. The LCLC resonant converter based on inductive coupling design according to claim 1, characterized in that: The output voltage is controlled by adjusting the switching frequency to adapt to different load conditions.

3. The LCLC resonant converter based on inductive coupling design according to claim 1, characterized in that: The mutual inductance coefficient of the mutual inductance M ranges from 0 to 1.

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