LLC resonant converter

Abstract

The invention relates to an LLC resonant converter comprising a primary side bridge circuit configured to convert a received DC input voltage into an AC signal, a resonant circuit configured to generate a resonant signal having a predetermined frequency based on the AC signal provided by the primary side bridge circuit and to transfer the resonant signal to a transformer; the transformer is configured to perform isolation transformation operation on the resonance signal so as to generate a transformed alternating current signal; the secondary side bridge circuit is configured to convert the transformed alternating current signal provided by the transformer into a direct current output signal again; the controller is configured to control the on-off of each bridge arm in the primary side bridge circuit and the secondary side bridge circuit, and the controller is further configured to adjust the topological structure of the primary side bridge circuit based on a direct current input signal provided by an external power supply; therefore, the gain range of the primary side bridge circuit changes along with the change of the voltage range of the direct current input signal.

Description

Technical Field

[0001] The present invention relates to the field of switching converters, and more particularly, to an LLC resonant converter. Background Art

[0002] With the rapid development of power electronics, the application of switching converters is becoming more and more extensive, and people have higher requirements on their performance, including high power density, high reliability and compact size. LLC resonant converters are widely used in various fields due to their advantages such as low noise, low stress and low switching loss.

[0003] LLC resonant converter can be operated by variable frequency control and fixed frequency control. When the input voltage range varies greatly, the LLC resonant converter using variable frequency control will cause a large change in the operating frequency range, thereby increasing the difficulty of designing the magnetic components in its resonant circuit. In addition, in the case of a wide voltage gain, the traditional variable frequency control method may cause the efficiency of the LLC resonant converter to drop significantly.

[0004] The LLC resonant converter that only uses fixed-frequency phase-shift control is relatively easy to design magnetic components because of its fixed operating frequency. However, under the premise of keeping the output voltage unchanged, it is necessary to operate the circuit at a larger phase-shift angle to adapt to a wide range of input voltage changes. However, an excessively large phase-shift angle may make it difficult for the primary bridge arm to achieve zero voltage switching, limiting its practical application.

[0005] In summary, when the LLC resonant converter is applied to a scenario with a wide input voltage variation range, it is difficult for the circuit to achieve high efficiency and a wide gain range at the same time. Summary of the invention

[0006] In view of this, the present invention provides an LLC resonant converter, the LLC resonant converter comprising:

[0007] a primary bridge circuit, wherein the primary bridge circuit is configured to receive a DC input signal from an external power source and convert the received DC input voltage into an AC signal,

[0008] a resonant circuit configured to generate a resonant signal having a predetermined frequency based on an AC signal provided by the primary bridge circuit, and transmit the resonant signal to a transformer;

[0009] A transformer, wherein the transformer is configured to perform an isolation transformation operation on the resonant signal to generate a transformed AC signal;

[0010] a secondary bridge circuit, the secondary bridge circuit being configured to reconvert the transformed AC signal provided by the transformer into a DC output signal; and

[0011] A controller, wherein the controller is configured to control the on / off of each bridge arm in the primary bridge circuit and the secondary bridge circuit,

[0012] The controller is further configured to adjust the topology of the primary bridge circuit based on a DC input signal provided by an external power supply, so that the gain range of the primary bridge circuit changes with the voltage range of the DC input signal.

[0013] According to an optional embodiment, the primary bridge circuit includes four switch tubes and three switching elements.

[0014] Among them, the first switch tube, the second switch tube, the first switching element, the third switch tube, and the fourth switch tube are connected in series between the positive electrode and the negative electrode of the external power supply in sequence, the first end of the second switching element is connected to the positive electrode of the external power supply, the second end of the second switching element is connected to the common node between the first switching element and the third switch tube, the first end of the third switching element is connected to the common node between the second switch tube and the first switching element, the second end of the third switching element is connected to the negative electrode of the external power supply, the common node between the first switch tube and the second switch tube constitutes the positive output terminal of the primary bridge circuit, and the common node between the third switch tube and the fourth switch tube constitutes the negative output terminal of the primary bridge circuit.

[0015] The controller is configured to adjust the connection relationship between the four switch tubes by controlling the on and off of the three switching elements, so as to realize different topological structures of the primary bridge circuit.

[0016] According to an optional embodiment, the controller is further configured to:

[0017] When the DC input signal provided by the external power supply is within a first voltage range, the first switching element is turned on, and the second switching element and the third switching element are turned off, so that the primary bridge circuit is in a stacked bridge topology.

[0018] According to an optional embodiment, the controller is further configured to:

[0019] When the DC input signal provided by the external power supply is within a second voltage range, the first switching element is disconnected, and the second switching element and the third switching element are connected, so that the primary bridge circuit is in a full-bridge topology structure, wherein the second voltage range is smaller than the first voltage range.

[0020] According to an optional embodiment, the first voltage range is 400V-800V, and the second voltage range is 200V-400V.

[0021] According to an optional embodiment, the four switch tubes and / or the three switching elements in the primary bridge circuit are selected from the group including MOS tubes, IGBTs and BJTs.

[0022] According to an optional embodiment, the secondary bridge circuit includes a half-bridge rectifier circuit composed of two switching tubes and a filter capacitor connected in parallel with the half-bridge rectifier circuit.

[0023] According to an optional embodiment, the two switch tubes in the secondary bridge circuit are selected from the group including MOS tubes, IGBTs and BJTs.

[0024] According to an optional embodiment, the LLC resonant converter further includes a first capacitor connected between the positive electrode of the external power supply and the first end of the third switching element, and a second capacitor connected between the second end of the second switching element and the negative electrode of the external power supply.

[0025] According to an optional embodiment, the resonant circuit is formed by an LLC series resonator.

[0026] The LLC resonant converter according to the present invention can switch between two different circuit topologies, the circuit works more flexibly, and meets the application requirements under a wider range of input voltages of 200 to 800 V, and has a wider output gain range. In addition, the LLC resonant converter can achieve zero voltage switching (ZVS) of the primary switch tube and zero current switching (ZCS) of the secondary switch tube, reducing the switching loss of the switching device, thereby achieving high-efficiency operation under a wide input voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] By incorporating the accompanying drawings and Figure 1 With reference to the specific embodiments used to illustrate certain principles of the present invention, other features and advantages of the method of the present invention will become clear or be described in more detail.

[0028] Figure 1 A circuit diagram of a conventional LLC resonant converter is shown.

[0029] Figure 2 A circuit diagram of an LLC resonant converter according to an exemplary embodiment of the present invention is shown.

[0030] Figure 3 Shows Figure 2 Equivalent circuit diagram of the LLC resonant converter in the first topology.

[0031] Figure 4 Shows Figure 2 Equivalent circuit diagram of the LLC resonant converter in the second topology.

[0032] Figure 5 The current and voltage waveforms in the LLC resonant converter are shown when the input voltage is 800V.

[0033] Figure 6 The current and voltage waveforms in the LLC resonant converter are shown when the input voltage is 400V. DETAILED DESCRIPTION

[0034] The LLC resonant converter according to the present invention will be described below with reference to the accompanying drawings and by way of example. In the following description, many specific details are set forth so that a person skilled in the art can more fully understand the present invention. However, it is obvious to a person skilled in the art that the present invention may be implemented without some of these specific details. Instead, any combination of the following features and elements may be considered to implement the present invention, regardless of whether they relate to different embodiments. Therefore, the following aspects, features, embodiments and advantages are for illustrative purposes only and should not be regarded as elements or limitations of the claims.

[0035] Figure 1 FIG. 2 shows a circuit diagram of a conventional LLC resonant converter. Figure 1 As shown in , for LLC resonant converters with wide input range requirements, the current mainstream method is to use a half-bridge topology to redesign batteries of different voltage levels to achieve the DC conversion process. For example, for a 400V input battery, its operating voltage is usually 200-400V, and the corresponding resonant circuit parameters (mainly Lr, Cr, Lm parameters) need to be designed for this voltage range. For an 800V battery, its operating voltage is usually 400-800V, and new resonant circuit parameters need to be redesigned for this voltage. Due to different voltage gains, the designs of the above two sets of resonant circuit parameters are also different.

[0036] That is to say, the traditional LLC resonant converter usually adjusts the resonant frequency and then adjusts the output gain by redesigning the resonant circuit parameters, thereby achieving high-efficiency output within a certain input voltage range. However, due to the limitations of the resonant circuit, it is impossible to meet the demand for a wider input range. For example, the traditional LLC converter cannot use a single circuit structure to meet the demand for a wide input voltage range of, for example, 200 to 800V, that is, it cannot take into account the application scenarios of both 400V and 800V batteries at the same time.

[0037] Based on the above background, the present invention proposes an LLC resonant converter that can adapt to a wider range of input voltages (e.g., 200-800V). The converter designs the resonant circuit parameters based on the 800V half-bridge LLC resonant converter. Due to the voltage doubling characteristics of the full-bridge LLC converter, the above resonant circuit parameters are the same as the 400V full-bridge LLC resonant circuit parameters. The converter is based on the stacked bridge LLC converter, with the addition of S1, S2, and S3 switches (see Figure 2 ), thus realizing two different circuit topologies, thus meeting the application requirements under a wider input voltage range of 200-800V. The LLC resonant converter can realize zero voltage switching (ZVS) of the primary switch tube and zero current switching (ZCS) of the secondary switch tube, reducing the switching loss of the switching device, thereby realizing high-efficiency operation under a wide input voltage.

[0038] Figure 2 FIG. 2 shows a circuit diagram of an LLC resonant converter according to an exemplary embodiment of the present invention. Figure 2 As shown in , the LLC resonant converter is mainly composed of five parts: a primary bridge circuit 10, a resonant circuit 20, a transformer T, a secondary bridge circuit 30 and a controller 40.

[0039] The primary bridge circuit 10 is actually an inverter bridge circuit composed of four switch tubes Q1 to Q4, which can receive a DC input signal Vin from an external power source and convert the received DC input voltage into an AC signal. The on and off of each switch tube in the primary bridge circuit 10 is controlled by the controller 40.

[0040] The AC signal output by the primary bridge circuit 10 can be further transmitted to the resonant circuit 20 downstream thereof, which is the core part inside the LLC converter and is composed of a resonant inductor Lr, a resonant capacitor Cr, and an excitation inductor Lm in the transformer. Therefore, the LLC resonant circuit has two frequency resonance points, the first frequency is composed of Lr and Cr, and the second frequency is composed of Lr / Lm and Cr. The resonant circuit makes the input AC signal oscillate between the two frequency resonance points. This oscillation phenomenon makes energy transfer more efficient and reduces the loss of the switching device.

[0041] The resonant signal provided by the resonant circuit 20 may be further transferred to a transformer T, which may isolate the input and the output and adjust the voltage level (eg, perform a step-up or step-down operation) to generate a transformed AC signal.

[0042] The AC signal output by the transformer T can finally be transmitted to the secondary bridge circuit 30, which may include a half-bridge rectifier circuit composed of two switch tubes Q5 and Q6 and a filter capacitor C0 connected in parallel with the half-bridge rectifier circuit. The on and off of each switch tube in the secondary bridge circuit 30 can usually be controlled by the controller 40. At the secondary bridge circuit 30, the AC signal can be reconverted into a DC output signal Vout.

[0043] The special feature of this embodiment is that the controller 40 can adjust the topology of the primary bridge circuit 10 based on the DC input signal Vin (especially its voltage range) provided by the external power supply, so that the gain range of the primary bridge circuit 10 changes with the change of the voltage range of the DC input signal Vin.

[0044] The specific implementation method of the above topological structure change is that, in addition to the four switch tubes Q1-Q4, the primary bridge circuit 10 may also include three additional switching elements S1-S3. By controlling the on-off of the three switching elements S1-S3 with the help of the controller 40, the connection relationship between the four switch tubes Q1-Q4 can be adjusted, thereby realizing different topological structures of the primary bridge circuit 10.

[0045] Figure 2 It is shown that the switch tubes Q1-Q6 and the switching elements S1-S3 are all N-channel MOS tubes, but the N-channel MOS tube is only an example, and it is conceivable that in other examples, these switch tubes and switching elements can also be implemented as P-channel MOS tubes, or BJT, IGBT, etc. In short, the electrical components mentioned in this article are not limited to the listed types, but can be replaced by any other component type that can achieve the same function.

[0046] The following takes N-channel MOS as an example to explain in detail Figure 2 The circuit structure shown in . Figure 2As shown in the figure, the first switch tube Q1, the second switch tube Q2, the first switching element S1, the third switch tube Q3, and the fourth switch tube Q4 are connected in series between the positive electrode and the negative electrode of the external power supply in sequence, the first end of the second switching element S2 is connected to the positive electrode of the external power supply, the second end of the second switching element S2 is connected to the common node between the first switching element S1 and the third switch tube Q3 (that is, the drain of Q3), the first end of the third switching element S3 is connected to the common node between the second switch tube Q2 and the first switching element S1 (that is, the source of Q2), the second end of the third switching element S3 is connected to the negative electrode of the external power supply, the common node between the first switch tube Q1 and the second switch tube Q2 (which is both the source of Q1 and the drain of Q2) constitutes the positive output terminal of the primary bridge circuit 10, and the common node between the third switch tube Q3 and the fourth switch tube Q4 (which is both the source of Q3 and the drain of Q4) constitutes the negative output terminal of the primary bridge circuit 10.

[0047] Optionally, the LLC resonant converter may further include a first capacitor C1 connected between the positive electrode of the external power source and the first end of the third switching element S3, and a second capacitor C2 connected between the second end of the second switching element S2 and the negative electrode of the external power source.

[0048] exist Figure 2 What is not shown is that the control terminals of the switch tubes Q1 to Q4 (in Figure 2 Taking the MOS tube in the example, the control end is the gate of the MOS tube) and can be connected to the controller 40.

[0049] Figure 2 The LLC resonant converter shown in the figure is based on the stacked bridge LLC converter, with the addition of switches S1, S2, and S3 (see Figure 2 ), thereby realizing two different circuit topologies according to different input voltage ranges.

[0050] Specifically, when the DC input signal Vin provided by the external power supply is within a first voltage range (for example, 400V to 800V), the controller 40 can turn on the first switching element S1 and disconnect the second switching element S2 and the third switching element S3 to place the primary bridge circuit 10 in a first topology structure (specifically a stacked bridge structure). Figure 3 Shows Figure 2 Equivalent circuit diagram of the LLC resonant converter in the first topology.

[0051] When the DC input signal Vin provided by the external power supply is within the second voltage range, the controller 40 can disconnect the first switching element S1 and connect the second switching element S2 and the third switching element S3 to make the primary bridge circuit 10 in a second topology structure (specifically a full-bridge structure), wherein the second voltage range is smaller than the first voltage range, and can be, for example, 200V to 400V. Figure 4 Shows Figure 2 Equivalent circuit diagram of the LLC resonant converter in the second topology.

[0052] Figure 5 The current and voltage waveforms in the LLC resonant converter are shown when the input voltage is 800V. Figure 6 The current and voltage waveforms in the LLC resonant converter are shown when the input voltage is 400V.

[0053] according to Figure 5 and Figure 6 The simulation results show that Figure 3 and Figure 4 In both topological structures, the primary resonant circuit in the converter can operate near the resonance point, and the secondary side can operate in a zero current switching state, so high-efficiency operation of the converter can be achieved in both modes.

[0054] The LLC resonant converter according to the present invention can switch between two different circuit topologies, the circuit works more flexibly, and meets the application requirements under a wider range of input voltages of 200 to 800 V, and has a wider output gain range. In addition, the LLC resonant converter can achieve zero voltage switching (ZVS) of the primary switch tube and zero current switching (ZCS) of the secondary switch tube, reducing the switching loss of the switching device, thereby achieving high-efficiency operation under a wide input voltage.

[0055] Those skilled in the art can understand that, in this article, the expression "the second voltage range is less than the first voltage range" specifically means that the upper limit value of the second voltage range is less than the lower limit value of the first voltage range, that is, any value in the first voltage range is less than any value in the first voltage range. In addition, the terms such as "comprising" and "including" indicate that in addition to the steps directly and clearly stated in the specification and claims, the technical solution of the present application does not exclude the situation of having other steps that are not directly or clearly stated.

[0056] Although the present invention has been disclosed as above with preferred embodiments, the present invention is not limited thereto. Any changes and modifications made by any person skilled in the art without departing from the spirit and scope of the present invention should be included in the protection scope of the present invention, and therefore the protection scope of the present invention should be subject to the scope defined by the claims.

Claims

1. An LLC resonant converter, characterized in that: The LLC resonant converter includes: A primary bridge circuit (10) is configured to receive a DC input signal (Vin) from an external power source and convert the received DC input voltage into an AC signal. A resonant circuit (20) configured to generate a resonant signal having a predetermined frequency based on the AC signal provided by the primary bridge circuit (10), and transmit the resonant signal to a transformer (T); A transformer (T), wherein the transformer (T) is configured to perform an isolation transformation operation on the resonant signal to generate a transformed AC signal; a secondary bridge circuit (30), the secondary bridge circuit being configured to reconvert the transformed AC signal provided by the transformer (T) into a DC output signal (Vout); and a controller (40), the controller being configured to control the on / off of each bridge arm in the primary bridge circuit (10) and the secondary bridge circuit (30), The controller (40) is further configured to adjust the topology of the primary bridge circuit (10) based on a DC input signal (Vin) provided by an external power supply, so that the gain range of the primary bridge circuit (10) changes as the voltage range of the DC input signal (Vin) changes.

2. The LLC resonant converter according to claim 1, characterized in that: The primary bridge circuit (10) comprises four switch tubes (Q1-Q4) and three switching elements (S1-S3). The first switch tube (Q1), the second switch tube (Q2), the first switching element (S1), the third switch tube (Q3), and the fourth switch tube (Q4) are connected in series between the positive electrode and the negative electrode of the external power supply in sequence; the first end of the second switching element (S2) is connected to the positive electrode of the external power supply; the second end of the second switching element (S2) is connected to a common node between the first switching element (S1) and the third switch tube (Q3); the first end of the third switching element (S3) is connected to a common node between the second switch tube (Q2) and the first switching element (S1); the second end of the third switching element (S3) is connected to the negative electrode of the external power supply; the common node between the first switch tube (Q1) and the second switch tube (Q2) constitutes a positive output terminal of the primary bridge circuit (10); the common node between the third switch tube (Q3) and the fourth switch tube (Q4) constitutes a negative output terminal of the primary bridge circuit (10); The controller (40) is configured to adjust the connection relationship between the four switch tubes (Q1-Q4) by controlling the on-off of the three switching elements (S1-S3), so as to realize different topological structures of the primary bridge circuit (10).

3. The LLC resonant converter according to claim 2, characterized in that: The controller (40) is further configured to: When a DC input signal (Vin) provided by an external power source is within a first voltage range, the first switching element (S1) is turned on, and the second switching element (S2) and the third switching element (S3) are turned off, so that the primary bridge circuit (10) is in a stacked bridge topology.

4. The LLC resonant converter according to claim 3, characterized in that: The controller (40) is further configured to: When a DC input signal (Vin) provided by an external power supply is within a second voltage range, the first switching element (S1) is disconnected, and the second switching element (S2) and the third switching element (S3) are connected, so that the primary bridge circuit (10) is in a full-bridge topology structure, wherein the second voltage range is smaller than the first voltage range.

5. The LLC resonant converter according to claim 4, characterized in that: The first voltage range is 400V to 800V, and the second voltage range is 200V to 400V.

6. The LLC resonant converter according to any one of claims 2 to 5, characterized in that: The four switch tubes (Q1-Q4) and / or the three switching elements (S1-S3) in the primary bridge circuit (10) are selected from a group including MOS tubes, IGBTs and BJTs.

7. The LLC resonant converter according to any one of claims 2 to 5, characterized in that: The secondary bridge circuit (30) comprises a half-bridge rectifier circuit formed by two switch tubes (Q5, Q6) and a filter capacitor (C0) connected in parallel with the half-bridge rectifier circuit.

8. The LLC resonant converter according to claim 7, characterized in that: The two switch tubes (Q5, Q6) in the secondary bridge circuit (30) are selected from a group including MOS tubes, IGBTs and BJTs.

9. The LLC resonant converter according to any one of claims 2 to 5, characterized in that: The LLC resonant converter further includes a first capacitor (C1) connected between the positive electrode of the external power supply and the first end of the third switching element (S3), and a second capacitor (C2) connected between the second end of the second switching element (S2) and the negative electrode of the external power supply.

10. The LLC resonant converter according to any one of claims 2 to 5, characterized in that: The resonant circuit (20) is composed of an LLC series resonator.

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