Multi-mode LLC resonant converter based on split bus

Abstract

The invention provides a multi-mode LLC resonant converter based on a split bus, and belongs to the technical field of switching power supplies. Comprising a first bus capacitor Cin, a first switch bridge arm, a second switch bridge arm, a second bus capacitor Cb, a boost inductor Lb, a resonant cavity formed by a resonant capacitor Cr and a resonant inductor Lr, a transformer T, an output rectification circuit and an output capacitor Co. The boost inductor Lb and the second switch bridge arm are multiplexed to form a Boost circuit, so that the input voltage of the second switch bridge arm can be increased, the voltage of the resonant cavity is increased, and the current of the resonant cavity is reduced. And meanwhile, a wide voltage gain range can be realized by changing the duty ratio of the second switch bridge arm. In addition, the circuit can also be used for prolonging the holding time of the circuit.

Description

Technical Field

[0001] The present invention belongs to the technical field of switching power supplies, and in particular relates to a multi-mode LLC resonant converter based on a split bus. Background Art

[0002] In recent years, with the rapid development of the power electronics industry, switching converters have been increasingly used, and high power density and high efficiency have become the development trend of the industry. In power electronic converters, increasing the switching frequency can effectively reduce the size of the converter, but it will increase switching losses. In order to reduce switching losses, soft switching technology has emerged. The traditional LLC resonant converter has occupied an important position in the power supply industry due to its many advantages such as simple structure, wide soft switching range, low switching loss, and high efficiency. The large-scale application of renewable energy, on-board chargers, and charging piles has dramatically increased the demand for wide-range voltage regulation converters, but traditional LLC resonant converters are difficult to achieve wide-range voltage regulation due to their gain characteristics. The specific reasons are as follows:

[0003] Traditional LLC resonant converters typically adjust their output voltage by varying the switching frequency. However, resonant topologies, such as the LLC, typically operate within a narrow range of 1 to 1.2 times the normalized voltage gain when using frequency modulation. Operating conditions exceeding 1.2 require further reductions in the inductance ratio, which often results in a reduction in the converter's quality factor and efficiency. There is an urgent need for a new topology or control method that can achieve both wide gain adjustment capability and high-efficiency operation. Summary of the Invention

[0004] The present invention relates to a multi-mode LLC resonant converter based on a split bus, which aims to compensate for the problem of insufficient voltage regulation range in a traditional LLC resonant topology to meet the requirement of wide voltage output.

[0005] The present invention proposes a multi-mode LLC resonant converter based on a split bus, comprising:

[0006] The first bus capacitor Cin receives a DC input voltage.

[0007] The first switch bridge arm is composed of a switch tube Q1 and a switch tube Q2. The drain of the switch tube Q1 is connected to the positive end of the first bus capacitor Cin, the source of the switch tube Q1 is connected to the drain of the switch tube Q2; and the source of the switch tube Q2 is connected to the negative end of the first bus capacitor Cin.

[0008] The negative end of the second bus capacitor Cb is connected to the positive end of the first bus capacitor Cin.

[0009] The second switch bridge arm is composed of a switch tube Q3 and a switch tube Q4. The drain of the switch tube Q3 is connected to the positive end of the second bus capacitor Cb, the source of the switch tube Q3 is connected to the drain of the switch tube Q4, and the source of the switch tube Q4 is connected to the negative end of the first bus capacitor Cin.

[0010] The boost inductor Lb has one end connected to the drain of the switch tube Q1 , and the other end connected to the source of the switch tube Q3 and the drain of the switch tube Q4 .

[0011] The resonant cavity is composed of the resonant inductor Lr and the resonant capacitor Cr. One end of the resonant inductor Lr is connected to the source of the switch tube Q1 and the drain of the switch tube Q2, and the other end of the resonant inductor Lr is connected to one end of the resonant capacitor Cr. The other end of the resonant capacitor Cr is simultaneously connected to one end of the primary winding of the transformer T and one end of the excitation inductor Lm. The other end of the primary winding of the transformer T and the other end of the excitation inductor Lm are commonly connected to the source of the switch tube Q3 and the drain of the switch tube Q4.

[0012] The output rectifier circuit is used to convert the AC power output by the secondary winding of the transformer into DC power for use by the subsequent load. The two input terminals of the output rectifier circuit are coupled to the secondary winding of the transformer T.

[0013] An output capacitor Co, wherein two terminals of the output capacitor Co are connected to the output end of the output rectifier circuit 102 .

[0014] Preferably, the output rectifier circuit is a voltage doubler rectifier circuit composed of diodes D1 and D2 and capacitors C1 and C2.

[0015] Preferably, the output rectifier circuit is a full-bridge rectifier circuit composed of diodes D1 to D4.

[0016] Preferably, the output rectifier circuit is a full-wave rectifier circuit.

[0017] Preferably, the split-bus based multi-mode LLC resonant converter of the present invention operates in operating mode 1, that is, the switch tubes Q1 and Q2 are complementary turned on, with a fixed duty cycle of 0.5, and the switch tubes Q3 and Q4 are complementary turned on, and duty cycle control is adopted.

[0018] Preferably, the multi-mode LLC resonant converter based on a split bus of the present invention operates in operating mode 2, i.e., a variable frequency control mode in which the switch tubes Q1 and Q2 are complementary turned on, with a fixed duty cycle of 0.5, the switch tube Q3 is constantly off, and the switch tube Q4 is constantly on.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The split-bus based multi-mode LLC resonant converter of the present invention can operate in multiple operating modes. By changing or combining the operating modes, a voltage gain adjustment range greater than 4 times can be achieved, and it has a natural power-off time extension function, providing a new solution for realizing a wide-gain, high-efficiency, and multi-scenario adaptable DC converter, and has significant engineering application value and market prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0022] Figure 1 Shows a schematic diagram of the structure of a traditional full-bridge LLC resonant converter;

[0023] Figure 2 A schematic structural diagram of a first embodiment of a multi-mode LLC resonant converter based on a split bus according to the present invention is shown;

[0024] Figure 3 A schematic structural diagram of a second embodiment of a multi-mode LLC resonant converter based on a split bus according to the present invention is shown;

[0025] Figure 4 A schematic structural diagram of a third embodiment of a multi-mode LLC resonant converter based on a split bus according to the present invention is shown;

[0026] Figure 5 The diagram shows the switch control signals and key waveforms of the split-bus-based multi-mode LLC resonant converter of the present invention when it operates in operating mode 1 and has a duty cycle D<0.5;

[0027] Figure 6 The diagram shows the switch control signals and key waveforms of the split-bus-based multi-mode LLC resonant converter of the present invention when it operates in operating mode 1 and has a duty cycle D>0.5;

[0028] Figure 7 The equivalent circuit of the split-bus-based multi-mode LLC resonant converter circuit of the present invention operating in operating mode 2 is shown;

[0029] Figure 8 The waveform diagram shows that the power supply implements the holdover function when the AC input power is lost. DETAILED DESCRIPTION

[0030] In order to make the technical solution of the present invention clearer, the technical solution of the present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0031] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features therein may be combined with each other.

[0032] The traditional full-bridge LLC resonant converter structure is as follows: Figure 1 As shown, see Figures 2 to 4 An embodiment of a split-bus-based multi-mode LLC resonant converter of the present invention is shown. The split-bus-based multi-mode LLC resonant converter of the present invention includes:

[0033] The first bus capacitor Cin receives a DC input voltage.

[0034] The first switch bridge arm is composed of a switch tube Q1 and a switch tube Q2. The drain of the switch tube Q1 is connected to the positive end of the first bus capacitor Cin, the source of the switch tube Q1 is connected to the drain of the switch tube Q2; and the source of the switch tube Q2 is connected to the negative end of the first bus capacitor Cin.

[0035] The second switch bridge arm is composed of a switch tube Q3 and a switch tube Q4. The drain of the switch tube Q3 is connected to the positive end of the first bus capacitor Cin, the source of the switch tube Q3 is connected to the drain of the switch tube Q4, and the source of the switch tube Q4 is connected to the negative end of the first bus capacitor Cin.

[0036] The negative end of the second bus capacitor is connected to the positive end of the first bus capacitor Cin.

[0037] The boost inductor Lb has one end connected to the drain of the switch tube Q1 , and the other end connected to the source of the switch tube Q3 and the drain of the switch tube Q4 .

[0038] A resonant cavity 101 is formed by a resonant inductor Lr and a resonant capacitor Cr. One end of the resonant inductor Lr is connected to the source of the switch tube Q1 and the drain of the switch tube Q2, and the other end of the resonant inductor Lr is connected to one end of the resonant capacitor Cr. The other end of the resonant capacitor Cr is connected to one end of the primary winding of the transformer T. The other end of the primary winding of the transformer T is connected to the source of the switch tube Q3 and the drain of the switch tube Q4.

[0039] The output rectifier circuit 102 is used to convert the AC power output by the secondary winding of the transformer into DC power for use by the subsequent load. The two input terminals of the output rectifier circuit 102 are coupled to the secondary winding of the transformer T.

[0040] An output capacitor Co, wherein two terminals of the output capacitor Co are connected to the output end of the output rectifier circuit 102 .

[0041] Preferably, Figure 2As shown, the output rectifier circuit 102 is a voltage doubler rectifier circuit composed of diodes D1 and D2 and capacitors C1 and C2.

[0042] Preferably, Figure 3 As shown, the output rectifier circuit 102 is a full-bridge rectifier circuit composed of diodes D1 to D4.

[0043] Preferably, Figure 4 As shown, the output rectifier circuit 102 is a full-wave rectifier circuit.

[0044] Combined with different control modes of the switch tube, the multi-mode LLC resonant converter based on the split bus of the present invention has multiple operating modes and can meet different application requirements.

[0045] Control mode 1: the switch tubes Q1 and Q2 are complementary turned on, with a fixed duty cycle of 0.5, and the switch tubes Q3 and Q4 are complementary turned on and duty cycle controlled. The circuit operates in working mode 1.

[0046] In this working mode, the input voltage Vin, the boost inductor Lb, the switches Q3 and Q4 form a Boost circuit, and the first switch bridge arm, the second switch bridge arm, the resonant cavity 101, the transformer T, the output rectifier circuit 102 and the output capacitor form an LLC resonant converter.

[0047] According to the characteristics of the Boost circuit,

[0048] Vcb+Vin=Vin / (1-D) (1)

[0049] Wherein, D is the duty cycle of the switch tube Q4. The resonant cavity voltage of the multi-mode LLC resonant converter based on the split bus has three levels in one working cycle.

[0050] When D varies between (0, 1), the converter can obtain the characteristics shown in Table 1.

[0051] Table 1 shows the relationship between converter characteristics and duty cycle

[0052]

[0053] It can be seen from Table 1 that, by only controlling the duty cycle without changing the operating frequency, the multi-mode LLC resonant converter based on the split bus of the present invention can obtain a voltage gain of 4 times in the operating mode.

[0054] Figure 5 and Figure 6 The switch control signals and key waveforms of the split-bus based multi-mode LLC resonant converter of the present invention are shown respectively when the switch control signals are in the working mode 1 with a duty cycle of D<0.5 and a duty cycle of D>0.5.

[0055] Control mode 2: The switches Q1 and Q2 are complementary turned on, with a fixed duty cycle of 0.5. The switches Q1 and Q2 adopt a variable frequency control mode, the switch Q3 is always off, and the switch Q4 is always on. In this case, the first embodiment of the multi-mode LLC resonant converter based on split bus of the present invention is taken as an example, and its equivalent circuit is as follows: Figure 7 As shown in Figure 2, under this control mode, the circuit operates in operating mode 2. Since the voltage Vcb across the second bus capacitor Cb is zero, the circuit is equivalent to a half-bridge LLC resonant converter. Therefore, the output voltage gain can be adjusted using conventional LLC resonator frequency conversion control to a value less than 0.5, further expanding the output voltage regulation range.

[0056] The split-bus based multi-mode LLC resonant converter of the present invention also naturally has the function of extending the power-off time, overcoming the shortcomings of traditional LLC resonant converters. It can be used as a post-stage DC-DC conversion link of a server power supply to extend the power-off holding time.

[0057] Figure 8 The waveform diagram shows the power supply's holdover function when the AC input is lost. The voltage of capacitor Cin is the intermediate bus voltage between the front-stage PFC circuit and the back-stage DC-DC converter. The stored energy formula is:

[0058]

[0059] Where E is the energy stored in the capacitor, C is the capacitance of the input capacitor Cin, and v is the voltage of the input capacitor Cin. When the input source voltage is lost for some reason, the input capacitor Cin takes on the task of maintaining power. According to the formula:

[0060]

[0061] Wherein, T is the holding time, C is the capacitance of the energy storage capacitor Cin, v1 is the voltage of the capacitor Cin at the start of power failure, v2 is the voltage of the capacitor Cin at the end of power failure, and Pout is the output power.

[0062] Compared to traditional full-bridge LLC circuits, the split-bus-based multi-mode LLC resonant converter of the present invention has a wider output voltage gain adjustment range. Therefore, with a smaller capacitance value for Cin, the output voltage can be maintained constant when Vin is within the voltage range of v1 to v2. While maintaining the same output voltage and power, the boundary voltage v2 of the input capacitor Cin can be smaller, meaning the input capacitor can provide the required voltage output and power at a lower voltage, thereby increasing the circuit's holdup time. While maintaining the same output voltage holdup time, the capacitance value of Cin can be reduced, thereby reducing circuit cost.

[0063] Well-known implementation methods and operating means are not described in detail herein to avoid confusing the various technical implementation schemes of the present invention. However, for those skilled in the art, the lack of one or more specific details or components does not affect the understanding and implementation of the present invention.

[0064] The specific implementation methods and methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A multi-mode LLC resonant converter based on a split bus, characterized in that: include: The first bus capacitor Cin receives the DC input voltage, the first switch bridge arm composed of the switch tube Q1 and the switch tube Q2, the second bus capacitor Cb, the second switch bridge arm composed of the switch tube Q3 and the switch tube Q4, the boost inductor Lb, the resonant cavity composed of the resonant inductor Lr and the resonant capacitor Cr, the output rectifier circuit, and the output capacitor Co.

2. The multi-mode LLC resonant converter based on split bus according to claim 1, characterized in that: The first switch bridge arm is composed of a switch tube Q1 and a switch tube Q2, wherein the drain of the switch tube Q1 is connected to the positive terminal of the first bus capacitor Cin, the source of the switch tube Q1 is connected to the drain of the switch tube Q2; and the source of the switch tube Q2 is connected to the negative terminal of the first bus capacitor Cin; The negative end of the second bus capacitor Cb is connected to the positive end of the first bus capacitor Cin; The second switch bridge arm is composed of a switch tube Q3 and a switch tube Q4, the drain of the switch tube Q3 is connected to the positive terminal of the second bus capacitor Cb, the source of the switch tube Q3 is connected to the drain of the switch tube Q4, and the source of the switch tube Q4 is connected to the negative terminal of the first bus capacitor Cin; The boost inductor Lb has one end connected to the drain of the switch tube Q1 and the other end connected to the source of the switch tube Q3 and the drain of the switch tube Q4; The resonant cavity formed by the resonant inductor Lr and the resonant capacitor Cr has one end of the resonant inductor Lr connected to the source of the switch tube Q1 and the drain of the switch tube Q2, the other end of the resonant inductor Lr is connected to one end of the resonant capacitor Cr, the other end of the resonant capacitor Cr is simultaneously connected to one end of the primary winding of the transformer T and one end of the excitation inductor Lm, the other end of the primary winding of the transformer T and the other end of the excitation inductor Lm are commonly connected to the source of the switch tube Q3 and the drain of the switch tube Q4.

3. The multi-mode LLC resonant converter based on split bus according to claim 2, characterized in that: The output rectifier circuit is used to convert the AC power output by the secondary winding of the transformer into DC power for use by the subsequent load. The two input terminals of the output rectifier circuit are coupled to the secondary winding of the transformer T; The two terminals of the output capacitor Co are connected to the output end of the output rectifier circuit.

4. The multi-mode LLC resonant converter based on split bus according to claim 3, characterized in that: The output rectifier circuit is a voltage doubler rectifier circuit composed of diodes D1 and D2 and capacitors C1 and C2.

5. The multi-mode LLC resonant converter based on split bus according to claim 3, characterized in that: The output rectifier circuit is a full-bridge rectifier circuit composed of diodes D1 to D4.

6. The multi-mode LLC resonant converter based on split bus according to claim 3, characterized in that: The output rectifier circuit is a full-wave rectifier circuit.

7. The multi-mode LLC resonant converter based on split bus according to any one of claims 1 to 6, characterized in that: When the multi-mode LLC resonant converter based on the split bus operates in the first operating mode, the switch tubes Q1 and Q2 are complementary turned on with a fixed duty cycle of 0.5, and the switch tubes Q3 and Q4 are complementary turned on with duty cycle control; When the split-bus based multi-mode LLC resonant converter operates in the second operating mode: the switching tubes Q1 and Q2 are complementary turned on in a variable frequency control mode, the fixed duty cycle is 0.5, the switching tube Q3 is constantly turned off, and the switching tube Q4 is constantly turned on.

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