A bipolar bidirectional resonant converter with double LLC structure and control method thereof

Abstract

The application provides a bipolar bidirectional resonant converter with a double LLC structure and a control method thereof, the converter is composed of two primary input capacitors, a primary full-bridge module, two resonant cavity circuits, a secondary full-bridge module, two secondary output capacitors, and the primary and the secondary are connected through an isolation transformer. The control method of the converter contains two control modes, the control mode is determined according to the real-time value and the change trend of the input voltage of the converter, the driving mode of each switch tube is controlled according to different control modes, and a wider voltage gain range is provided through the switching of the two control modes. In addition, the switch tubes of the same bridge arm of the secondary full-bridge module are driven in a complementary and duty cycle of 50% mode, the driving configuration applies a time-same bipolar output voltage to the excitation inductance, and the voltage-second balance characteristic of the excitation inductance current of the isolation transformer is utilized to realize the voltage equalization of the two-end output voltage.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology, specifically relating to a bipolar bidirectional resonant converter with a dual LLC structure and its control method. Background Technology

[0002] Currently, some distributed DC distribution network systems use bipolar converters to drive DC loads of different power levels. Bipolar converters can reduce voltage to ground while ensuring higher reliability and have the ability to connect DC buses of different voltage levels. When there are differences in converter line parameters or loads, voltage deviations may occur between the two stages. A common voltage equalization method is to add an independent voltage equalization circuit at the bipolar output of the converter, using the voltage transfer characteristics of the independent voltage equalization circuit to eliminate the voltage deviation at the bipolar output. Wuhan University has conducted research on a four-port DC bipolar series LC voltage equalization device for power transfer in the form of a low-voltage DC distribution network (Y. Lei, Y. Zhuang, F. Liu, X. Diao and Y. Huang, "A General Four-Port Converter With Series LC Voltage Balancer for Bipolar DC Microgrid," in IEEE Transactions on Industrial Electronics, vol. 70, no. 12, pp. 12311-12321, Dec. 2023.). The aforementioned research on low-voltage DC bipolar voltage equalization devices conducted by Wuhan University involves adding a series LC voltage equalization device to the bipolar distribution network to equalize the voltage of the DC buses of both polarities. However, the additional voltage equalization device increases the size of the distribution network and the implementation cost, which is detrimental to reducing power density. To reduce power density, Central South University has conducted research on self-equalizing buck-type bipolar converters based on coupled inductors, integrating the coupled inductor into the output of the bipolar converter, thereby reducing the power density of the bipolar converter. (G. Ning, J. Chen, Y. Liu, G. Xu, W. Xiong and M. Su, "Coupled-Inductor-Based Buck-Type Converter With Autonomous Voltage Balancing for Bipolar DC Microgrid," in IEEE Transactions on Power Electronics, vol.39, no. 10, pp. 11937-11942, Oct. 2024.). The voltage equalization strategy based on coupled inductors conducted by Central South University does not require additional voltage equalization devices. However, this converter can only perform unidirectional power transfer, which limits its application scenarios. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention proposes a bipolar bidirectional resonant converter with a dual LLC structure, which addresses the problems of existing bipolar converters relying on additional voltage equalization devices and being unable to achieve bidirectional power flow. This converter uses a pulse frequency modulation strategy to regulate voltage and power.

[0004] The present invention adopts the following technical solution.

[0005] This invention discloses a bipolar resonant converter with a dual LLC structure, comprising two primary-side input capacitors. C i1 and C i2 Primary-side full-bridge module, two resonant cavity circuits, secondary-side full-bridge module, two secondary-side output capacitors C o1 and C o2 Specifically: Both the primary-side full-bridge module and the secondary-side full-bridge module are full-bridge structures composed of two bridge arms. First primary-side input capacitor C i1 Second primary-side input capacitor C i2 The series structure is connected in parallel between the high-voltage side bus and the low-voltage side bus of the primary-side full-bridge module; the first secondary-side output capacitor C o1 Secondary output capacitor C o2 The series structure is connected in parallel between the high-voltage side bus and the low-voltage side bus of the secondary full-bridge module; The midpoint of the first bridge arm of the primary-side full-bridge module is connected to the first input terminal of the first resonant cavity circuit, and the midpoint of the second bridge arm of the primary-side full-bridge module is connected to the first input terminal of the second resonant cavity circuit. The first primary-side input capacitor... C i1 Second primary-side input capacitor C i2 The connection point is connected to the second input terminal of the first resonant cavity circuit, and the first primary-side input capacitor... C i1 Second primary-side input capacitor C i2 The connection point is connected to the second input terminal of the second resonant cavity circuit; the midpoint of the first bridge arm of the secondary full-bridge module is connected to the first output terminal of the first resonant cavity circuit, and the midpoint of the second bridge arm of the secondary full-bridge module is connected to the first output terminal of the second resonant cavity circuit. The first secondary output capacitor... C o1 Secondary output capacitor C o2The connection point is connected to the second output terminal of the first resonant cavity circuit, and the first secondary output capacitor... C o1 Secondary output capacitor C o2 The connection point is connected to the second output terminal of the second resonant cavity circuit. More preferably, Both resonant cavity circuits consist of a primary-side resonant capacitor, a primary-side resonant inductor, and an isolation transformer. The first input terminal of the first resonant cavity circuit is connected in series with a first primary-side resonant capacitor. C r1 and the first primary resonant inductor L r1 , with the first isolation transformer T 1. The first input terminal of the primary side is connected; the first isolation transformer. T The second input terminal of the primary side serves as the second input terminal of the first resonant cavity circuit; the first magnetizing inductor L m1 With the first isolation transformer T Connect the primary edges of 1 in parallel; The first input terminal of the second resonant cavity circuit is connected in series with the second primary-side resonant capacitor. C r2 Second primary resonant inductor L r2 With the second isolation transformer T 2. The first input terminal of the primary side is connected; the second isolation transformer T The second input terminal of the primary side serves as the second input terminal of the second resonant cavity circuit; the second magnetizing inductor L m2 With the second isolation transformer T The primary edges of 2 are connected in parallel; First isolation transformer T The first output terminal of the secondary side serves as the first output terminal of the first resonant cavity circuit, and the first isolation transformer... T The second output terminal of the secondary side serves as the second output terminal of the first resonant cavity circuit; the second isolation transformer T The first output terminal of the second secondary side serves as the first output terminal of the second resonant cavity circuit, and the second isolation transformer... T The second output terminal of the secondary side serves as the second output terminal of the second resonant cavity circuit. First isolation transformer T 1. The first input terminal of the primary side and the first output terminal of the secondary side are of the same name; the second isolation transformer T 2. The first input terminal of the primary side and the second output terminal of the secondary side are terminals with the same name.

[0006] More preferably, The first bridge arm of the primary-side full-bridge module is controlled by a first switching transistor. Q 1 and second switching transistors Q The bridge consists of two forward-connected series components, with the second arm consisting of a third switching transistor. Q 3 and the fourth switching transistor Q The four-phase forward series connection is used; the first bridge arm of the secondary full-bridge module is composed of the fifth switch. Q 5 and the sixth switching transistor Q The bridge consists of 6 forward-connected transistors, with the second arm consisting of the seventh switch. Q 7 and 8 switch transistors Q It consists of 8 forward series connections.

[0007] More preferably, First isolation transformer T 1 and the second isolation transformer T The primary windings of two circuits have the same number of turns, and the secondary windings also have the same number of turns; the first primary resonant capacitor... C r1 Second primary resonant capacitor C r2 With equal capacitance values, the first primary-side resonant inductor L r1 Second primary resonant inductor L r2 The inductance values ​​are equal, and the specific values ​​are determined based on the range of variation between the converter's input and output voltages; the first primary-side input capacitor C i1 Second primary-side input capacitor C i2 The capacitance values ​​are equal, and the first secondary output capacitor... C o1 Secondary output capacitor C o2 The capacitance values ​​are equal, and the specific values ​​are set according to the input voltage and output voltage ripple of the converter.

[0008] This invention discloses, in one aspect, a control method for a bipolar resonant converter with a dual LLC structure, comprising: The control method includes two control modes: control mode 1 and control mode 2. These two control modes are determined based on the real-time value and trend of the input voltage of the converter, specifically: Set low voltage switching threshold V l and high voltage switching threshold V h When the input voltage of the converter V in Decline, and V in < V lWhen the converter switches from control mode 1 to control mode 2; when V in Rising, and V in > V h When the converter switches from control mode 2 to control mode 1; when V l ≤ V in ≤ V h At this time, the converter maintains the current control mode.

[0009] More preferably, The low voltage switching threshold V l and high voltage switching threshold V h ,satisfy V l < nV ref < V h ,in n This refers to the primary-to-secondary turns ratio of an isolation transformer. V ref This is the target output voltage of the converter.

[0010] More preferably, The converter controls the driving mode of each switching transistor according to different control modes. The two control modes are as follows: When operating in control mode 1, all the switches in the primary-side full-bridge module are driven with the same fixed duty cycle of 0.5. The switches in the same bridge arm of the primary-side full-bridge module are driven complementaryly, and the switches in the corresponding bridge arms are driven 180 degrees out of phase. The switches in the first bridge arm of the secondary-side full-bridge module are driven in the same way as the corresponding switches in the first bridge arm of the primary-side full-bridge module. The switches in the second bridge arm of the secondary-side full-bridge module are driven in the same way as the corresponding switches in the second bridge arm of the primary-side full-bridge module. When operating in control mode 2, all switches in the primary-side full-bridge module are driven with the same fixed duty cycle of 0.5. The switches in the same bridge arm of the primary-side full-bridge module are driven complementaryly, and the switches in the corresponding bridge arms are driven the same way. The switches in the first bridge arm of the secondary-side full-bridge module are driven the same way as the corresponding switches in the first bridge arm of the primary-side full-bridge module, and the switches in the second bridge arm of the secondary-side full-bridge module are driven the same way as the corresponding switches in the second bridge arm of the primary-side full-bridge module.

[0011] More preferably, In control mode 1, the switching frequency of all switching transistors is:f s First primary resonant inductor L r1 Second primary resonant inductor L r2 First primary resonant capacitor C r1 Second primary resonant capacitor C r2 First excitation inductor L m1 and the second magnetizing inductor L m2 Together they form a resonant cavity, and the resonant frequency of the resonant cavity is... f r1 Switching frequency f s > f r1 Through closed-loop control f s It enables the adjustment of output power and output voltage.

[0012] More preferably, In control mode 2, the switching frequency of all switching transistors is: f s First primary resonant inductor L r1 First primary resonant capacitor C r1 First primary-side input capacitor C i1 With the first magnetizing inductor L m1 The first resonant cavity and the second primary-side resonant inductor constitute the first resonant cavity. L r2 Second primary resonant capacitor C r2 Second primary-side input capacitor C i2 With the second magnetizing inductor L m2 This forms a second resonant cavity, and the resonant frequencies of both resonant cavities are... f r2 Switching frequency f s > f r2 Through closed-loop control f s It enables the adjustment of output power and output voltage.

[0013] The beneficial effects of this invention are as follows: 1. Compared to bipolar DC-DC converters that use additional voltage equalization circuits, this converter does not require additional voltage equalization devices. It utilizes the magnetizing inductance of the isolation converter to achieve voltage equalization at the bipolar output terminals under unbalanced loads, resulting in higher power density.

[0014] 2. The converter has two different operating modes under two control methods. The components participating in resonance are different in the two operating modes, and the voltage transfer ratio is also different accordingly, thus providing a wider voltage gain range. Attached Figure Description

[0015] Figure 1 This is a circuit diagram of the bipolar bidirectional resonant converter with a dual LLC structure in this invention; Figure 2 This is the equivalent circuit diagram of the resonant cavity of the bipolar bidirectional resonant converter in control mode 1 of this invention; Figure 3 It is the second switching transistor in control mode 1 of this invention. Q 2 anti-parallel diodes, third switching transistor Q Current flow diagram of the anti-parallel diode during freewheeling; Figure 4 It is the first switching transistor in control mode 1 of this invention. Q 1. Anti-parallel diode, fourth switching transistor Q Current flow diagram of a 4-pin anti-parallel diode during freewheeling; Figure 5 This is the equivalent circuit diagram of the resonant cavity of the bipolar bidirectional resonant converter in control mode 2 of this invention; Figure 6 It is the second switching transistor in control mode 2 of this invention. Q 2 anti-parallel diodes, fourth switching transistor Q Current flow diagram of a 4-pin anti-parallel diode during freewheeling; Figure 7 It is the first switching transistor in control mode 2 of this invention. Q 1. Anti-parallel diode, third switching transistor Q Current flow diagram of the anti-parallel diode during freewheeling; Figure 8 It is the fifth switching transistor in control mode 1 of this invention. Q 5. Eighth switching transistor Q 8. Secondary current flow diagram during turn-on; Figure 9 It is the sixth switch in control mode 1 of this invention. Q 6. Seventh switching transistor Q 7. Secondary current flow diagram during turn-on; Figure 10 It is the fifth switching transistor in control mode 2 of this invention.Q 5. Seventh switching transistor Q 7. Secondary current flow diagram during turn-on; Figure 11 It is the sixth switch in control mode 2 of this invention. Q 6. Eighth switching transistor Q 8. Diagram of secondary current flow when the circuit is turned on. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0017] Example 1: This invention discloses a bipolar bidirectional resonant converter with a dual LLC structure, such as... Figure 1 As shown, it includes two primary-side input capacitors. C i1 and C i2 Primary-side full-bridge module, two resonant cavity circuits, secondary-side full-bridge module, two secondary-side output capacitors C o1 and C o2 Specifically: Both the primary-side full-bridge module and the secondary-side full-bridge module are full-bridge structures composed of two bridge arms. First primary-side input capacitor C i1 Second primary-side input capacitor C i2 The series structure is connected in parallel between the high-voltage side bus and the low-voltage side bus of the primary-side full-bridge module; the first secondary-side output capacitor C o1 Secondary output capacitor C o2 The series structure is connected in parallel between the high-voltage side bus and the low-voltage side bus of the secondary full-bridge module; The midpoint of the first bridge arm of the primary-side full-bridge module is connected to the first input terminal of the first resonant cavity circuit, and the midpoint of the second bridge arm of the primary-side full-bridge module is connected to the first input terminal of the second resonant cavity circuit. The first primary-side input capacitor... C i1 Second primary-side input capacitor C i2 The connection point is connected to the second input terminal of the first resonant cavity circuit, and the first primary-side input capacitor...C i1 Second primary-side input capacitor C i2 The connection point is connected to the second input terminal of the second resonant cavity circuit; the midpoint of the first bridge arm of the secondary full-bridge module is connected to the first output terminal of the first resonant cavity circuit, and the midpoint of the second bridge arm of the secondary full-bridge module is connected to the first output terminal of the second resonant cavity circuit. The first secondary output capacitor... C o1 Secondary output capacitor C o2 The connection point is connected to the second output terminal of the first resonant cavity circuit, and the first secondary output capacitor... C o1 Secondary output capacitor C o2 The connection point is connected to the second output terminal of the second resonant cavity circuit. Specifically, Both resonant cavity circuits consist of a primary-side resonant capacitor, a primary-side resonant inductor, and an isolation transformer. The first input terminal of the first resonant cavity circuit is connected in series with a first primary-side resonant capacitor. C r1 and the first primary resonant inductor L r1 , with the first isolation transformer T 1. The first input terminal of the primary side is connected; the first isolation transformer. T The second input terminal of the primary side serves as the second input terminal of the first resonant cavity circuit; the first magnetizing inductor L m1 With the first isolation transformer T Connect the primary edges of 1 in parallel; The first input terminal of the second resonant cavity circuit is connected in series with the second primary-side resonant capacitor. C r2 Second primary resonant inductor L r2 With the second isolation transformer T 2. The first input terminal of the primary side is connected; the second isolation transformer T The second input terminal of the primary side serves as the second input terminal of the second resonant cavity circuit; the second magnetizing inductor L m2 With the second isolation transformer T The primary edges of 2 are connected in parallel; First isolation transformer T The first output terminal of the secondary side serves as the first output terminal of the first resonant cavity circuit, and the first isolation transformer... T The second output terminal of the secondary side serves as the second output terminal of the first resonant cavity circuit; the second isolation transformer TThe first output terminal of the second secondary side serves as the first output terminal of the second resonant cavity circuit, and the second isolation transformer... T The second output terminal of the secondary side serves as the second output terminal of the second resonant cavity circuit. First isolation transformer T 1. The first input terminal of the primary side and the first output terminal of the secondary side are of the same name; the second isolation transformer T 2. The first input terminal of the primary side and the second output terminal of the secondary side are terminals with the same name.

[0018] Specifically, The first bridge arm of the primary-side full-bridge module is controlled by a first switching transistor. Q 1 and second switching transistors Q The bridge consists of two forward-connected series components, with the second arm consisting of a third switching transistor. Q 3 and the fourth switching transistor Q The four-phase forward series connection is used; the first bridge arm of the secondary full-bridge module is composed of the fifth switch. Q 5 and the sixth switching transistor Q The bridge consists of 6 forward-connected transistors, with the second arm consisting of the seventh switch. Q 7 and 8 switch transistors Q It consists of 8 forward series connections.

[0019] Specifically, First isolation transformer T 1 and the second isolation transformer T The primary windings of two circuits have the same number of turns, and the secondary windings also have the same number of turns; the first primary resonant capacitor... C r1 Second primary resonant capacitor C r2 With equal capacitance values, the first primary-side resonant inductor L r1 Second primary resonant inductor L r2 The inductance values ​​are equal, and the specific values ​​are determined based on the range of variation between the converter's input and output voltages; the first primary-side input capacitor C i1 Second primary-side input capacitor C i2 The capacitance values ​​are equal, and the first secondary output capacitor... C o1 Secondary output capacitor C o2 The capacitance values ​​are equal, and the specific values ​​are set according to the input voltage and output voltage ripple of the converter.

[0020] Example 2: This invention discloses a control method for a bipolar resonant converter with a dual LLC structure, comprising: The control method includes two control modes: control mode 1 and control mode 2. These two control modes are determined based on the real-time value and trend of the input voltage of the converter, specifically: Set low voltage switching threshold V l and high voltage switching threshold V h When the input voltage of the converter V in Decline, and V in < V l When the converter switches from control mode 1 to control mode 2; when V in Rising, and V in > V h When the converter switches from control mode 2 to control mode 1; when V l ≤ V in ≤ V h At this time, the converter maintains the current control mode.

[0021] Specifically, the low voltage switching threshold V l and high voltage switching threshold V h ,satisfy V l < nV ref < V h ,in n This refers to the primary-to-secondary turns ratio of an isolation transformer. V ref The target output voltage of the converter; Specifically, When operating in control mode 1, all switches in the primary-side full-bridge module are driven with the same fixed duty cycle of 0.5. Switches in the same bridge arm of the primary-side full-bridge module have complementary drives, with corresponding switches in two bridge arms having a 180-degree phase difference. The drives of switches in the first bridge arm of the secondary-side full-bridge module are the same as those in the corresponding first bridge arm of the primary-side full-bridge module, and the drives of switches in the second bridge arm of the secondary-side full-bridge module are the same as those in the corresponding second bridge arm of the primary-side full-bridge module. The switching frequency of all switches is... f s First primary resonant inductor L r1 Second primary resonant inductorL r2 First primary resonant capacitor C r1 Second primary resonant capacitor C r2 First excitation inductor L m1 and the second magnetizing inductor L m2 Together they form a resonant cavity; see the resonant cavity structure for details. Figure 2 The resonant frequency of the resonant cavity is f r1 Switching frequency f s > f r1 Through closed-loop control f s It enables the adjustment of output power and output voltage.

[0022] (1) When the load size of the bipolar output terminals is the same The current flow diagram during switch switching is as follows: Figure 3 , Figure 4 As shown. Due to symmetry, the zero-voltage switching within half a switching cycle will be explained in detail below. To achieve zero-voltage turn-on of the primary-side full-bridge module switch, the anti-parallel diode of the switch to be turned on needs to be turned on before the switch transistor is turned on. When the switching frequency... f s Greater than f r1 At that time, the resonant cavity is inductive as a whole, and the voltage input to the resonant cavity is... v in Leading the input current i in When the first switching transistor Q 1. Fourth switching transistor Q 4. Fifth switching transistor Q 5 and the eighth switch Q After switch 8 is turned off, the current in the resonant cavity is switched by the second switch. Q 2. Third switching transistor Q 3. Sixth switching transistor Q 6 and the seventh switch Q 7. Before activation, the flow direction is negative, which will cause the second switching transistor to... Q 2. Third switching transistor Q 3. Sixth switching transistor Q 6 and the seventh switch Q The anti-parallel diode corresponding to 7 is turned on, thereby realizing the second switching transistor. Q 2. Third switching transistor Q 3. Sixth switching transistor Q 6 and the seventh switchQ Similarly, zero-voltage turn-on of transistor 7 can also achieve the first switching transistor. Q 1. Fourth switching transistor Q 4. Fifth switching transistor Q 5 and the eighth switch Q Zero-voltage turn-on of 8.

[0023] (2) When the loads at the bipolar output terminals are not the same Let's assume the first secondary output capacitor C o1 Connected load R 1 is for heavy load, second secondary output capacitor C o2 Connected load R 2 represents a light load. Using Ohm's law, it can be calculated that when the first magnetizing inductance... L m1 With the second magnetizing inductor L m2 When the circuit is broken, the load R voltage of 1 v o1 Greater than the load R 2 voltage v o2 At this time, the first magnetizing inductor L m1 With the second magnetizing inductor L m2 It can be analyzed through the following two modal analyses.

[0024] Mode 1: The current flow diagram for this mode is as follows. Figure 8 As shown, the fifth switching transistor Q 5. Eighth switching transistor Q 8 is turned on, sixth switch tube Q 6. With the seventh switch transistor Q 7. When the first magnetizing inductor is turned off, L m1 The voltage across the terminals is supplied by the load. R 1. Provides the first magnetizing inductor. L m1 High current rise rate, first secondary output capacitor C o1 Energy decreases, output voltage decreases v o1 The rate of decrease is high. Second magnetizing inductance. L m2 The voltage across the terminals is supplied by the load. R 2. Provides a second magnetizing inductor. L m2 Low current rise rate, second secondary output capacitor C o2 Energy decreases, output voltage decreasesv o2 It decreased, and the rate of decrease was low.

[0025] Mode 2: The current flow diagram for this mode is as follows. Figure 9 As shown, the sixth switch transistor Q 6. Seventh switching transistor Q 7 is turned on, fifth switch tube Q 5. Eighth switching transistor Q 8 is turned off, at which point the first magnetizing inductor is switched off. L m1 The voltage across the terminals is supplied by the load. R 2 provides the first magnetizing inductor. L m1 Low current drop rate, second secondary output capacitor C o2 Increased energy, increased output voltage v o2 The rise is high, and the rate of rise is also high. Second magnetizing inductor. L m2 The voltage across the terminals is supplied by the load. R 1. Provides a second magnetizing inductor. L m2 High current drop rate, first secondary output capacitor C o1 Increased energy, increased output voltage v o1 It is rising, but the rate of increase is low.

[0026] As the two modes continuously switch until the output voltage... v o1 and v o2 When they are equal, in mode 1 and mode 2, the first magnetizing inductor L m1 With the second magnetizing inductor L m2 The current rise rate and fall rate are the same, and since the time for both modes is 0.5 switching cycles, the first magnetizing inductor... L m1 With the second magnetizing inductor L m2 The current remains balanced within one cycle, achieving a voltage equalization effect at the bipolar output terminals.

[0027] Specifically, When operating in control mode 2, all switches in the primary-side full-bridge module are driven with the same fixed duty cycle of 0.5. Switches in the same bridge arm of the primary-side full-bridge module have complementary drives, while switches in two different bridge arms have the same drive. The drives of switches in the first bridge arm of the secondary-side full-bridge module are the same as those in the corresponding first bridge arm of the primary-side full-bridge module, and the drives of switches in the second bridge arm of the secondary-side full-bridge module are the same as those in the corresponding second bridge arm of the primary-side full-bridge module. The switching frequency of all switches is... f s First primary resonant inductor L r1 First primary resonant capacitor C r1 First primary-side input capacitor C i1 With the first magnetizing inductor L m1 The first resonant cavity and the second primary-side resonant inductor constitute the first resonant cavity. L r2 Second primary resonant capacitor C r2 Second primary-side input capacitor C i2 With the second magnetizing inductor L m2 This constitutes the second resonant cavity; see the resonant cavity structure below. Figure 5 The resonant frequencies of both resonant cavities are f r2 Switching frequency f s > f r2 Through closed-loop control f s It enables the adjustment of output power and output voltage.

[0028] (1) When the load size of the bipolar output terminals is the same The current flow diagram during switch switching is as follows: Figure 6 , Figure 7 As shown. Due to symmetry, the zero-voltage switching within half a switching cycle will be explained in detail below. To achieve zero-voltage turn-on of the primary-side full-bridge module switch, the anti-parallel diode of the switch to be turned on needs to be turned on before the switch transistor is turned on. When the switching frequency... f s Greater than f r2 At that time, the resonant cavity is inductive as a whole, and the voltage input to the resonant cavity is... v in1 Leading the input current i in1 , v in2Leading the input current i in2 When the first switching transistor Q 1. Third switching transistor Q 3. Fifth switching transistor Q 5 and the seventh switch Q After switch 7 is turned off, the current in the resonant cavity is switched by the second switch. Q 2. Fourth switching transistor Q 4. Sixth switching transistor Q 6 and the eighth switch Q 8. Before it is turned on, the flow direction is negative, which will cause the second switch transistor to... Q 2. Fourth switching transistor Q 4. Sixth switching transistor Q 6 and the eighth switch Q The anti-parallel diode corresponding to 8 is turned on, realizing the second switching transistor. Q 2. Fourth switching transistor Q 4. Sixth switching transistor Q 6 and the eighth switch Q Similarly, zero-voltage turn-on of 8 can be achieved by the first switching transistor. Q 1. Third switching transistor Q 3. Fifth switching transistor Q 5 and the seventh switch Q Zero-voltage turn-on of 7.

[0029] (2) When the loads at the bipolar output terminals are not the same Let's assume the first secondary output capacitor C o1 Connected load R 1 is for heavy load, second secondary output capacitor C o2 Connected load R 2 represents a light load. Using Ohm's law, it can be calculated that when the first magnetizing inductance... L m1 With the second magnetizing inductor L m2 Load during circuit break R voltage of 1 v o1 Greater than the load R 2 voltage v o2 At this time, the first magnetizing inductor L m1 With the second magnetizing inductor L m2 It can be analyzed through the following two modal analyses.

[0030] Mode 1: The current flow diagram for this mode is as follows. Figure 10 As shown, the fifth switching transistor Q 5. Seventh switching transistorQ 7 is turned on, sixth switch tube Q 6. Eighth switching transistor Q 8 is turned off, at which point the first magnetizing inductor is switched off. L m1 Second excitation inductor L m2 The voltage at both ends is supplied by the load. R 1. Provides the first magnetizing inductor. L m1 Current rise, second magnetizing inductor L m2 The current decreases, and the rate of change is high; the first secondary output capacitor... C o1 Energy decreases, output voltage decreases v o1 reduce.

[0031] Mode 2: The current flow diagram for this mode is as follows. Figure 11 As shown, the sixth switch transistor Q 6. Eighth switching transistor Q 8 is turned on, fifth switch tube Q 5. Seventh switching transistor Q 7. When the first magnetizing inductor is turned off, L m1 Second excitation inductor L m2 The voltage at both ends is supplied by the load. R 2 provides the first magnetizing inductor. L m1 Current decrease, second magnetizing inductor L m2 The current increases, but the rate of change is low, and the second secondary output capacitor... C o2 Increased energy, increased output voltage v o2 Increase.

[0032] As the two modes continuously switch until the output voltage... v o1 and v o2 When they are equal, in mode 1 and mode 2, the first magnetizing inductor L m1 With the second magnetizing inductor L m2 The current rise rate and fall rate are the same, and since the time for both modes is 0.5 switching cycles, the first magnetizing inductor... L m1 With the second magnetizing inductor L m2 The current remains balanced within one cycle, achieving a voltage equalization effect at the bipolar output terminals.

[0033] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A bipolar resonant converter with a dual LLC structure, comprising two primary-side input capacitors. C i1 and C i2 Primary-side full-bridge module, two resonant cavity circuits, secondary-side full-bridge module, two secondary-side output capacitors C o1 and C o2 Its features are: Both the primary-side full-bridge module and the secondary-side full-bridge module are full-bridge structures composed of two bridge arms. First primary-side input capacitor C i1 Second primary-side input capacitor C i2 The series structure is connected in parallel between the high-voltage side bus and the low-voltage side bus of the primary-side full-bridge module; the first secondary-side output capacitor C o1 Secondary output capacitor C o2 The series structure is connected in parallel between the high-voltage side bus and the low-voltage side bus of the secondary full-bridge module; The midpoint of the first bridge arm of the primary-side full-bridge module is connected to the first input terminal of the first resonant cavity circuit, and the midpoint of the second bridge arm of the primary-side full-bridge module is connected to the first input terminal of the second resonant cavity circuit. The first primary-side input capacitor... C i1 Second primary-side input capacitor C i2 The connection point is connected to the second input terminal of the first resonant cavity circuit, and the first primary-side input capacitor... C i1 Second primary-side input capacitor C i2 The connection point is connected to the second input terminal of the second resonant cavity circuit; the midpoint of the first bridge arm of the secondary full-bridge module is connected to the first output terminal of the first resonant cavity circuit, and the midpoint of the second bridge arm of the secondary full-bridge module is connected to the first output terminal of the second resonant cavity circuit. The first secondary output capacitor... C o1 Secondary output capacitor C o2 The connection point is connected to the second output terminal of the first resonant cavity circuit, and the first secondary output capacitor... C o1 Secondary output capacitor C o2 The connection point is connected to the second output terminal of the second resonant cavity circuit; Both resonant cavity circuits consist of a primary-side resonant capacitor, a primary-side resonant inductor, and an isolation transformer. The first input terminal of the first resonant cavity circuit is connected in series with a first primary-side resonant capacitor. C r1 and the first primary resonant inductor L r1 , with the first isolation transformer T 1. The first input terminal of the primary side is connected; the first isolation transformer. T The second input terminal of the primary side serves as the second input terminal of the first resonant cavity circuit; the first magnetizing inductor L m1 With the first isolation transformer T Connect the primary edges of 1 in parallel; The first input terminal of the second resonant cavity circuit is connected in series with the second primary-side resonant capacitor. C r2 Second primary resonant inductor L r2 With the second isolation transformer T 2. The first input terminal of the primary side is connected; the second isolation transformer T The second input terminal of the primary side serves as the second input terminal of the second resonant cavity circuit; the second magnetizing inductor L m2 With the second isolation transformer T The primary edges of 2 are connected in parallel; First isolation transformer T The first output terminal of the secondary side serves as the first output terminal of the first resonant cavity circuit, and the first isolation transformer... T The second output terminal of the secondary side serves as the second output terminal of the first resonant cavity circuit; the second isolation transformer T The first output terminal of the second secondary side serves as the first output terminal of the second resonant cavity circuit, and the second isolation transformer... T The second output terminal of the secondary side serves as the second output terminal of the second resonant cavity circuit. First isolation transformer T 1. The first input terminal of the primary side and the first output terminal of the secondary side are terminals with the same name; Second isolation transformer T 2. The first input terminal of the primary side and the second output terminal of the secondary side are terminals with the same name.

2. The bipolar resonant converter with a dual LLC structure according to claim 1, characterized in that: The first bridge arm of the primary-side full-bridge module is controlled by a first switching transistor. Q 1 and second switching transistors Q The bridge consists of two forward-connected series components, with the second arm consisting of a third switching transistor. Q 3 and the fourth switching transistor Q The four-phase forward series connection is used; the first bridge arm of the secondary full-bridge module is composed of the fifth switch. Q 5 and the sixth switching transistor Q The bridge consists of 6 forward-connected transistors, with the second arm consisting of the seventh switch. Q 7 and 8 switch transistors Q It consists of 8 forward series connections.

3. The bipolar resonant converter with a dual LLC structure according to claim 1, characterized in that: First isolation transformer T 1 and the second isolation transformer T The primary windings of two circuits have the same number of turns, and the secondary windings also have the same number of turns; the first primary resonant capacitor... C r1 Second primary resonant capacitor C r2 With equal capacitance values, the first primary-side resonant inductor L r1 Second primary resonant inductor L r2 The inductance values ​​are equal, and the specific values ​​are determined based on the range of variation between the converter's input and output voltages; the first primary-side input capacitor C i1 Second primary-side input capacitor C i2 The capacitance values ​​are equal, and the first secondary output capacitor... C o1 Secondary output capacitor C o2 The capacitance values ​​are equal, and the specific values ​​are set according to the input voltage and output voltage ripple of the converter.

4. A control method applied to the converter according to any one of claims 1-3, characterized in that, include: The control method includes two control modes: control mode 1 and control mode 2. These two control modes are determined based on the real-time value and trend of the input voltage of the converter, specifically: Set low voltage switching threshold V l and high voltage switching threshold V h When the input voltage of the converter V in Decline, and V in < V l When the converter switches from control mode 1 to control mode 2; when V in Rising, and V in > V h When the converter switches from control mode 2 to control mode 1; when V l ≤ V in ≤ V h At this time, the converter maintains the current control mode.

5. The control method according to claim 4, characterized in that: The low voltage switching threshold V l and high voltage switching threshold V h ,satisfy V l < nV ref < V h ,in n This refers to the primary-to-secondary turns ratio of an isolation transformer. V ref This is the target output voltage of the converter.

6. The control method according to claim 4, characterized in that: The converter controls the driving mode of each switching transistor according to different control modes. The two control modes are as follows: When operating in control mode 1, all the switches in the primary-side full-bridge module are driven with the same fixed duty cycle of 0.

5. The switches in the same bridge arm of the primary-side full-bridge module are driven complementaryly, and the switches in the corresponding bridge arms are driven 180 degrees out of phase. The switches in the first bridge arm of the secondary-side full-bridge module are driven in the same way as the corresponding switches in the first bridge arm of the primary-side full-bridge module. The switches in the second bridge arm of the secondary-side full-bridge module are driven in the same way as the corresponding switches in the second bridge arm of the primary-side full-bridge module. When operating in control mode 2, all switches in the primary-side full-bridge module are driven with the same fixed duty cycle of 0.

5. The switches in the same bridge arm of the primary-side full-bridge module are driven complementaryly, and the switches in the corresponding bridge arms are driven the same way. The switches in the first bridge arm of the secondary-side full-bridge module are driven the same way as the corresponding switches in the first bridge arm of the primary-side full-bridge module, and the switches in the second bridge arm of the secondary-side full-bridge module are driven the same way as the corresponding switches in the second bridge arm of the primary-side full-bridge module.

7. The control method according to claim 6, characterized in that: In control mode 1, the switching frequency of all switching transistors is: f s First primary resonant inductor L r1 Second primary resonant inductor L r2 First primary resonant capacitor C r1 Second primary resonant capacitor C r2 First excitation inductor L m1 and the second magnetizing inductor L m2 Together they form a resonant cavity, and the resonant frequency of the resonant cavity is... f r1 Switching frequency f s > f r1 Through closed-loop control f s It enables the adjustment of output power and output voltage.

8. The control method according to claim 6, characterized in that: In control mode 2, the switching frequency of all switching transistors is: f s First primary resonant inductor L r1 First primary resonant capacitor C r1 First primary-side input capacitor C i1 With the first magnetizing inductor L m1 The first resonant cavity and the second primary-side resonant inductor constitute the first resonant cavity. L r2 Second primary resonant capacitor C r2 Second primary-side input capacitor C i2 With the second magnetizing inductor L m2 This forms a second resonant cavity, and the resonant frequencies of both resonant cavities are... f r2 Switching frequency f s > f r2 Through closed-loop control f s It enables the adjustment of output power and output voltage.

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