LLC resonant conversion circuit

Abstract

The invention discloses an LLC resonant conversion circuit, which belongs to the technical field of electric energy conversion and comprises a primary side conversion module, a resonant conversion module, a first secondary side conversion module, a second secondary side conversion module and a switch module, the first end of the primary side conversion module is connected with input voltage, and the second end is connected with the first end of the resonant conversion module; the second end of the resonant conversion module is connected with the first end of the first secondary side conversion module, and the third end of the resonant conversion module is connected with the first end of the second secondary side conversion module; the first terminal of the second end of the first secondary side conversion module is connected with the second terminal of the second end of the second secondary side conversion module and the second terminal of the switch module; the first terminal of the second end of the second secondary side conversion module is connected with the first terminal of the switch module. According to the LLC resonant conversion circuit, the voltage gain of the LLC resonant conversion circuit is expanded, and high efficiency in the whole voltage output range is ensured.

Description

Technical Field

[0001] The present application relates to the technical field of electric energy conversion, and in particular to an LLC resonant conversion circuit. Background Art

[0002] LLC resonant circuits are widely used in switching power supplies due to their high efficiency and good EMC characteristics. However, the disadvantage of LLC topology is that the gain range is relatively narrow. Generally, when the input voltage or output voltage is particularly wide (more than 2 times), LLC topology does not have obvious advantages and cannot achieve high efficiency in the entire voltage range.

[0003] At present, there are generally two solutions for wide input and wide output application scenarios. The first is to use PWM circuits such as phase-shifted full-bridge, but its peak efficiency is not as good as LLC; the second is to use LLC circuits and achieve wide gain through PFM / PWM hybrid control. PFM control is adopted when the gain requirement is high, and PWM control is adopted when the gain requirement is low. However, the conversion efficiency of LLC topology working in PWM mode is relatively low. Therefore, there is an urgent need for a high-efficiency and wide-gain LLC resonant circuit. Summary of the invention

[0004] The present application aims to provide an LLC resonant conversion circuit which broadens LLC gain and improves efficiency.

[0005] In order to achieve the above-mentioned purpose, the technical solution of this application is: An LLC resonant conversion circuit comprises: a primary side conversion module, a resonant conversion module, a first secondary side conversion module, a second secondary side conversion module and a switch module; The first end of the primary conversion module is connected to the input voltage, the second end of the primary conversion module is connected to the first end of the resonant conversion module; the second end of the resonant conversion module is connected to the first end of the first secondary conversion module, the third end of the resonant conversion module is connected to the first end of the second secondary conversion module, the first terminal of the second end of the first secondary conversion module is connected to the second terminal of the second end of the second secondary conversion module and the second terminal of the switch module, the first terminal of the second end of the second secondary conversion module is connected to the first terminal of the switch module, and the output voltage is connected between the third terminal of the switch module and the second terminal of the second end of the first secondary conversion module.

[0006] Optionally, the switch module includes: a first switch and a second switch; The first terminal of the first switch is the first terminal of the switch module, the second terminal of the first switch is connected to the first terminal of the second switch, the second terminal of the second switch is the second terminal of the switch module, and the second terminal of the first switch is the third terminal of the switch module.

[0007] Optionally, the switch module further includes: a first diode; A cathode of the first diode is connected to a first terminal of the second switch, and an anode of the first diode is connected to a second terminal of the second switch.

[0008] Optionally, the first switch and the second switch include MOSFETs.

[0009] Optionally, the first switch and the second switch are implemented by relays.

[0010] Optionally, the first secondary side conversion module includes: a full-bridge rectifier circuit structure, a full-wave rectifier circuit structure, or a voltage doubler rectifier circuit structure.

[0011] Optionally, the second secondary side conversion module includes: a full-bridge rectifier circuit structure, a full-wave rectifier circuit structure, or a voltage doubler rectifier circuit structure.

[0012] Optionally, the primary side conversion module includes: a half-bridge conversion circuit structure or a full-bridge conversion circuit structure.

[0013] Optionally, the resonant conversion module includes: a first capacitor, a first inductor and a first transformer, and the first transformer includes: a primary winding, a first secondary winding and a second secondary winding; The first capacitor, the first inductor and the primary winding are connected in series, and two ends of the series connection of the first capacitor, the first inductor and the primary winding are the first ends of the resonant conversion module; the two ends of the first secondary winding are the second ends of the resonant conversion module; and the two ends of the second secondary winding are the third ends of the resonant conversion module.

[0014] Optionally, the LLC resonant conversion circuit further includes a second capacitor and a first resistor, the second capacitor is connected in parallel across the output voltage, and the second capacitor is connected in parallel with the first resistor.

[0015] The LLC resonant conversion circuit designed in the present application expands the voltage gain of the LLC resonant conversion circuit, and can adopt PFM mode control in the entire output voltage range, thereby ensuring the high efficiency of the LLC resonant conversion circuit in the entire voltage output range.

[0016] In order to make the above features and advantages of the present application more obvious and easy to understand, embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a structural block diagram of the LLC resonant conversion circuit proposed in this application.

[0018] Figure 2 This is a circuit diagram of the first specific embodiment of the LLC resonant conversion circuit proposed in this application.

[0019] Figure 3 This is a circuit diagram of the second specific embodiment of the LLC resonant conversion circuit proposed in this application.

[0020] Figure 4 This is a circuit diagram of the third specific embodiment of the LLC resonant conversion circuit proposed in this application. DETAILED DESCRIPTION

[0021] In order to make the purpose and technical solution of the embodiment of the present application clearer, the technical solution of the embodiment of the present application will be clearly and completely described in conjunction with the drawings of the embodiment of the present application. Obviously, the described embodiment is a part of the embodiment of the present application, not all of the embodiments. Based on the described embodiment of the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0022] In one embodiment of the present application, please refer to Figure 1 , Figure 1 This is a structural block diagram of the LLC resonant conversion circuit proposed in the present application. The LLC resonant conversion circuit proposed in the present application includes: a primary side conversion module 11, a resonant conversion module 12, a first secondary side conversion module 13, a second secondary side conversion module 14 and a switch module 15.

[0023] As an example, the first terminal of the primary side conversion module 11 is connected to the input voltage V in The second end of the primary conversion module 11 is connected to the first end of the resonant conversion module 12, the second end of the resonant conversion module 12 is connected to the first end of the first secondary conversion module 13, the third end of the resonant conversion module 12 is connected to the first end of the second secondary conversion module 14, the first terminal of the second end of the first secondary conversion module 13 is connected to the second terminal of the second end of the second secondary conversion module 14 and the second terminal of the switch module 15, the first terminal of the second end of the second secondary conversion module 14 is connected to the first terminal of the switch module 15, and the output voltage V is connected between the third terminal of the switch module 15 and the second terminal of the second end of the first secondary conversion module 13 o .

[0024] Optionally, the LLC resonant conversion circuit further includes a capacitor C o With resistor R o , capacitor C oConnect in parallel to the output voltage V o The two ends of the capacitor C o With resistor R o in parallel.

[0025] The resonant conversion module 12 includes: a capacitor C r 、Inductance L r And transformer T1, transformer T1 includes: primary winding N1, secondary winding N2 and secondary winding N3; capacitor C r 、Inductance L r The two ends of the primary winding N1 are connected in series, and the two ends of the series connection are the first ends of the resonant conversion module 12; the two ends of the secondary winding N2 are the second ends of the resonant conversion module 12; and the two ends of the secondary winding N3 are the third ends of the resonant conversion module 12. The resonant conversion module 12 also includes: an inductor L m , inductance L m Connected in parallel at both ends of the primary winding N1, where the inductor L m is the magnetizing inductance.

[0026] The switch module 15 includes a switch S1, a switch S2 and a diode D1, the first terminal of the switch S1 is the first terminal of the switch module 15, the second terminal of the switch S1 is connected to the first terminal of the switch S2, the second terminal of the switch S2 is the second terminal of the switch module 15, the second terminal of the switch S1 is the third terminal of the switch module 15, the cathode of the diode D1 is connected to the first terminal of the switch S2, and the anode of the diode D1 is connected to the second terminal of the switch S2.

[0027] As an example, the LLC resonant conversion circuit designed in the present application expands the voltage gain of the LLC resonant conversion circuit, and can adopt PFM mode control in the entire output voltage range, thereby ensuring the high efficiency of the LLC resonant conversion circuit in the entire voltage output range.

[0028] See also Figure 2 , Figure 2 This is a circuit diagram of the first specific embodiment of the LLC resonant conversion circuit proposed in this application. In this specific embodiment, the primary conversion module 21 adopts a half-bridge conversion circuit structure, the secondary conversion module 23 adopts a full-bridge rectifier circuit structure, the secondary conversion module 24 adopts a full-wave rectifier circuit structure, and the switch S1 and switch S2 of the switch module 25 are implemented by a single-pole double-throw relay.

[0029] Specifically, the primary side conversion module 21 includes: a switch S3 and a switch S4, the switch S3 and the switch S4 are connected in series, and the first terminal of the switch S3 is connected to the input voltage V in The positive terminal of switch S3 is connected to the first terminal of switch S4, and the second terminal of switch S4 is connected to the input voltage V in The negative electrode of capacitor C r、Inductance L r , the series branch of the primary winding N1 is connected in parallel with the switch S4.

[0030] The first secondary conversion module 23 includes: a diode D2, a diode D3, a diode D4, a diode D5 and a capacitor C1; the cathode of the diode D2 is connected to the cathode of the diode D4, the anode of the diode D2 is connected to the cathode of the diode D3, the anode of the diode D3 is connected to the anode of the diode D5, and the cathode of the diode D5 is connected to the anode of the diode D4; the midpoint of the series branch of the diode D2 and the diode D3 is connected to the first terminal of the secondary winding N2, and the midpoint of the series branch of the diode D4 and the diode D5 is connected to the second terminal of the secondary winding N2; the capacitor C1 is connected in parallel with the series branch of the diode D4 and the diode D5, the first terminal of the capacitor C1 is the first terminal of the second end of the first secondary conversion module 23, and the second terminal of the capacitor C1 is the second terminal of the second end of the first secondary conversion module 23. Among them, the output voltage V at both ends of the capacitor C1 o1 .

[0031] The second secondary conversion module 24 includes: a diode D6, a diode D7 and a capacitor C2; the anode of the diode D6 is connected to the first terminal of the secondary winding N3, the cathode of the diode D6 is connected to the cathode of the diode D7, the anode of the diode D7 is connected to the second terminal of the secondary winding N3, the first terminal of the capacitor C2 is connected to the cathode of the diode D6, and the second terminal of the capacitor C2 is connected to the midpoint of the secondary winding N3 and the first terminal of the capacitor C1. The output voltage V across the capacitor C2 is o2 .

[0032] The switch module 25 includes: a relay Re1 and a diode D1; the relay Re1 includes an input terminal 1, an output terminal 2 and an output terminal 3, and the switch composed of the input terminal 1 and the output terminal 2 of the relay Re1 is equivalent to Figure 1 The switch S1 in the figure, the switch composed of the input terminal 1 and the output terminal 3 of the relay Re1 is equivalent to Figure 1 The switch S2 in the circuit is connected, the cathode of the diode D1 is connected to the input terminal 1, and the anode of the diode D1 is connected to the output terminal 3. The input terminal 1 is the third terminal of the switch module 25, the output terminal 2 is the first terminal of the switch module 25, the output terminal 3 is the second terminal of the switch module 25, and the output voltage V is connected between the input terminal 1 and the second terminal of the capacitor C1. o .

[0033] As an example, for an actual charging pile module, assuming the output voltage range is 200V~500V, an LLC resonant circuit with mixed control of PFM mode and PWM mode is adopted, and the LLC resonance point is designed to be around 350V output; when the output voltage is around 280V~500V, the LLC resonant circuit is controlled in PFM mode, and the full load efficiency can reach more than 96%; when the output voltage is around 200V~280V, the LLC resonant circuit enters PWM mode, and the full load efficiency drops below 94%, and the lowest is only around 92%.

[0034] Furthermore, by using the LLC resonant conversion circuit designed in this application, the circuit efficiency will be greatly improved. Figure 2 Describes how this application works.

[0035] In the case where the output voltage of the LLC resonant conversion circuit does not need to be expanded, the output voltage range is V1~V2, the switch S2 composed of the input terminal 1 and the output terminal 3 of the relay Re1 is turned on, and the switch S1 composed of the input terminal 1 and the output terminal 2 is turned off. At this time, the output of the secondary side conversion module 23 is the output voltage V o , the output voltage V of LLC resonant converter circuit o =V o1 By designing the turns ratio of the secondary winding N2 to the primary winding N1, the first secondary conversion module 23 can be controlled in the PFM mode within the entire output voltage range, so that the efficiency of the LLC resonant conversion circuit is greatly improved.

[0036] For example, when the output voltage of the LLC resonant conversion circuit does not need to be expanded, the output voltage range is 200V~400V. By designing the turns ratio n1:n2 of the secondary winding N2 and the primary winding N1, the resonance point of the LLC resonant conversion circuit is around 270V, and the output voltage range is 200V~400V. In this way, PFM mode control can be used in the entire output voltage range of 200V~400V, and the efficiency of the LLC resonant conversion circuit is greatly improved, with the minimum efficiency reaching more than 94%. Among them, n1 is the number of turns of the primary winding N1, and n2 is the number of turns of the secondary winding N2.

[0037] Further, when the output voltage of the LLC resonant conversion circuit needs to be expanded, the output voltage range is V2~V3, the switch S1 composed of the input terminal 1 and the output terminal 2 of the relay Re1 is turned on, and the switch S2 composed of the input terminal 1 and the output terminal 3 is turned off. At this time, the first secondary side conversion module 23 and the second secondary side conversion module 24 are connected in series, and the output voltage V o =V o1 +V o2 By designing the turns ratio n2:n3 of the secondary winding N2 and the secondary winding N3, the voltage Vo1 With voltage V o2 The voltage of the series output meets the demand for output voltage expansion and ensures that the first secondary conversion module 23 still adopts PFM mode control, thereby ensuring the high efficiency of the LLC resonant conversion circuit. Wherein, V3 = (1 + n3 / n2) * V2. Wherein, n2 is the number of turns of the secondary winding N2, and n3 is the number of turns of the secondary winding N3.

[0038] For example, when the output voltage of the LLC resonant conversion circuit needs to be expanded, the output voltage requirement is 400V~500V, and the turns ratio of the secondary winding N2 to the secondary winding N3 is designed to be 4:1, then: V o1 When it is 320V, V o2 =80V, then V o =V o1 +V o2 =400V, V o1 When V is 400V, o2 =100V, then V o =V o1 +V o2 =500V, Thus, the output voltage range is 400V~500V. At this time, V o1 The range is 320V~400V, which is still within the 200V~400V range that can be controlled by PFM mode.

[0039] Although the secondary winding N3 and components such as the diode D6 and the diode D7 of the second secondary conversion module 24 are added compared to the usual situation, the second secondary conversion module 24 only processes 20% of the output power, so the LLC resonant conversion circuit can continue to maintain a high efficiency within this output voltage range.

[0040] As another example, for constant power output occasions (such as charging pile modules), as the output voltage increases, the output current will decrease year-on-year, so the loss can be further reduced. Even considering the losses of the secondary winding N3, diode D6 and diode D7, the LLC resonant conversion circuit can still achieve a full load efficiency of more than 96% in the output voltage range of 400V~500V.

[0041] Transient analysis of the LLC resonant converter circuit shows that for general charging situations, the battery voltage (output voltage V o ) are all changing from low to high, so when the LLC resonant converter circuit output voltage V oWhen the output voltage is below V2, the switch S2 composed of the input terminal 1 and the output terminal 3 of the relay Re1 is turned on, and the switch S1 composed of the input terminal 1 and the output terminal 2 is turned off. When the output voltage begins to reach V2, the switch S2 composed of the input terminal 1 and the output terminal 3 of the relay Re1 is first turned off. At this time, the output voltage V o1 The diode D1 is used for freewheeling. Then the switch S1 composed of the input terminal 1 and the output terminal 2 of the relay Re1 is turned on. Through the adjustment of the output feedback, the output voltage will soon stabilize at 400V. In other words, the LLC resonant conversion circuit designed in this application can achieve hot switching without stopping and restarting for switching.

[0042] In summary, for the LLC resonant conversion circuit provided in the present application, by designing the turns ratio of the secondary winding N2 to the primary winding N1, the output voltage V o The range is V1~V2; then by designing the turns ratio n2:n3 of the secondary winding N2 and the secondary winding N3, the output voltage V o The range is V1~(1+n3 / n2)*V2, thereby expanding the output voltage range of the entire LLC resonant conversion circuit. Among them, n2 is the number of turns of the secondary winding N2, and n3 is the number of turns of the secondary winding N3.

[0043] It should be noted that in actual design, the turns ratio n2:n3 between the secondary winding N2 and the secondary winding N3 cannot be too small, otherwise the second secondary conversion module 24 needs to process too much output power, thereby reducing efficiency.

[0044] Optionally, n2:n3 ranges from 3 to 5.

[0045] See also Figure 3 , Figure 3 This is a circuit diagram of the second specific embodiment of the LLC resonant conversion circuit proposed in this application. This specific embodiment is similar to Figure 2 The difference between the circuits is that Figure 1 The switch S1 and switch S2 of the switch module are implemented by MOSFET. Figure 1 The diode D1 in the circuit can be realized by the body diode of the MOSFET itself, and the switch S2 does not need an additional parallel diode.

[0046] As an example, the first terminal of the switch S1 is connected to the first terminal of the capacitor C4, the second terminal of the switch S1 is connected to the first terminal of the switch S2, the second terminal of the switch S2 is connected to the first terminal of the capacitor C1, and the output voltage V is connected between the second terminal of the switch S1 and the second terminal of the capacitor C1. o .

[0047] Figure 3The working principle of the specific embodiment is Figure 2 The same as in, no further description is given here.

[0048] See also Figure 4 , Figure 4 The circuit diagram of the third specific embodiment of the LLC resonant conversion circuit proposed in this application. In this specific embodiment, Figure 3 The difference between the two circuits is that the primary side conversion module 41 adopts a full-bridge conversion circuit structure, and the first secondary side conversion module 43 adopts a voltage doubler rectifier circuit structure.

[0049] As an example, the primary side conversion module 41 includes a switch S5, a switch S6, a switch S7, and a switch S8; the switch S5 is connected in series with the switch S6, the switch S7 is connected in series with the switch S8, and the first terminal of the switch S5 is connected to the input voltage V in The positive electrode of the switch S5 is connected to the first terminal of the switch S7, the second terminal of the switch S5 is connected to the first terminal of the switch S6, and the second terminal of the switch S6 is connected to the input voltage V in The negative electrode of the switch S7 is connected to the second terminal of the switch S8, and the second terminal of the switch S7 is connected to the first terminal of the switch S8; the capacitor C r 、Inductance L r , two ends of the series branch of the primary winding N1 are connected to the series midpoint of the switch S5 and the switch S6, and the series midpoint of the switch S7 and the switch S8.

[0050] The first secondary conversion module 43 includes: a diode D8, a diode D9, a capacitor C3 and a capacitor C4; the cathode of the diode D8 is connected to the first terminal of the capacitor C3, the anode of the diode D8 is connected to the cathode of the diode D9, the anode of the diode D9 is connected to the second terminal of the capacitor C4, and the first terminal of the capacitor C4 is connected to the second terminal of the capacitor C3; the series midpoint of the diode D8 and the diode D9 is connected to the first terminal of the secondary winding N2, and the series midpoint of the capacitor C3 and the capacitor C4 is connected to the second terminal of the secondary winding N2. The first terminal of the capacitor C3 is connected to the second terminal of the switch S2 and the second terminal of the capacitor C7, and the second terminal of the capacitor C4 is connected to the second terminal of the switch S1. The output voltage V o The output voltage V at both ends of the series connection of capacitors C3 and C4 is o1 .

[0051] Figure 4 The working principle of the specific embodiment is Figure 2 The same as in, no further description is given here.

[0052] As an example, the primary side conversion module of the LLC resonant conversion circuit proposed in the present application may include: a half-bridge conversion circuit structure or a full-bridge conversion circuit structure, etc., but the present invention is not limited thereto.

[0053] The first secondary side conversion module may include: a full-bridge rectifier circuit structure, a full-wave rectifier circuit structure, a voltage doubler rectifier circuit structure, etc., and is not limited to the situation proposed in this application.

[0054] The second secondary side conversion module may include: a full-bridge rectifier circuit structure, a full-wave rectifier circuit structure, a voltage doubler rectifier circuit structure, etc., and is not limited to the situation proposed in this application.

[0055] It should be noted that Figure 1 The switches S1 and S2 in the embodiment include but are not limited to relays, MOSFETs, IGBTs and other switches, but the present invention is not limited thereto.

[0056] In summary, the LLC resonant conversion circuit designed in the present application expands the voltage gain of the LLC resonant conversion circuit, and can adopt PFM mode control in the entire output voltage range, thereby ensuring the high efficiency of the LLC resonant conversion circuit in the entire voltage output range.

[0057] Although the present application has been disclosed as above with the embodiments, it is not intended to limit the present application. Any person with ordinary knowledge in the technical field can make some changes and modifications without departing from the spirit and scope of the present application. Therefore, the scope of protection of the present application shall be determined by the scope of the attached patent application.

Claims

1. An LLC resonant conversion circuit, characterized in that: include: A primary side conversion module, a resonant conversion module, a first secondary side conversion module, a second secondary side conversion module and a switch module; The first end of the primary conversion module is connected to the input voltage, the second end of the primary conversion module is connected to the first end of the resonant conversion module; the second end of the resonant conversion module is connected to the first end of the first secondary conversion module, the third end of the resonant conversion module is connected to the first end of the second secondary conversion module, the first terminal of the second end of the first secondary conversion module is connected to the second terminal of the second end of the second secondary conversion module and the second terminal of the switch module, the first terminal of the second end of the second secondary conversion module is connected to the first terminal of the switch module, and the output voltage is connected between the third terminal of the switch module and the second terminal of the second end of the first secondary conversion module.

2. The LLC resonant converter circuit according to claim 1, characterized in that: The switch module includes: a first switch and a second switch; The first terminal of the first switch is the first terminal of the switch module, the second terminal of the first switch is connected to the first terminal of the second switch, the second terminal of the second switch is the second terminal of the switch module, and the second terminal of the first switch is the third terminal of the switch module.

3. The LLC resonant converter circuit according to claim 2, characterized in that: The switch module further includes: a first diode; A cathode of the first diode is connected to a first terminal of the second switch, and an anode of the first diode is connected to a second terminal of the second switch.

4. The LLC resonant converter circuit according to claim 2, characterized in that: The first switch and the second switch include MOSFETs.

5. The LLC resonant converter circuit according to claim 3, characterized in that: The first switch and the second switch are implemented by relays.

6. The LLC resonant converter circuit according to claim 1, characterized in that: The first secondary side conversion module includes: a full-bridge rectifier circuit structure, a full-wave rectifier circuit structure, or a voltage doubler rectifier circuit structure.

7. The LLC resonant converter circuit according to claim 1, wherein: The second secondary side conversion module includes: a full-bridge rectifier circuit structure, a full-wave rectifier circuit structure, or a voltage doubler rectifier circuit structure.

8. The LLC resonant converter circuit according to claim 1, characterized in that: The primary side conversion module includes: a half-bridge conversion circuit structure or a full-bridge conversion circuit structure.

9. The LLC resonant converter circuit according to claim 1, characterized in that: The resonant conversion module includes: a first capacitor, a first inductor and a first transformer, and the first transformer includes: a primary winding, a first secondary winding and a second secondary winding; The first capacitor, the first inductor and the primary winding are connected in series, and two ends of the series connection of the first capacitor, the first inductor and the primary winding are the first ends of the resonant conversion module; the two ends of the first secondary winding are the second ends of the resonant conversion module; and the two ends of the second secondary winding are the third ends of the resonant conversion module.

10. The LLC resonant converter circuit according to claim 1, characterized in that: The LLC resonant conversion circuit further includes a second capacitor and a first resistor, the second capacitor is connected in parallel across the output voltage, and the second capacitor is connected in parallel with the first resistor.

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