Bidirectional output L2c3 resonant converter

Abstract

The application relates to a bidirectional output L2C3 resonant converter, which comprises two excitation sources and a resonant cavity, wherein the excitation sources are both half-wave bridge circuits; the resonant cavity comprises a transformer, three capacitors and two inductors; the primary winding of the transformer is connected in parallel with a resonant capacitor C p 1; the same end of the primary winding of the transformer is connected with a resonant capacitor C1 and an inductor L1 in series connection; the other end of the inductor L1 is connected with the connection point of the first excitation source and two switch tubes in series connection; the same end of the secondary winding of the transformer is connected with a resonant capacitor C2; the other end of the resonant capacitor C2 is connected with the connection point of the second excitation source and two switch tubes in series connection; the leakage inductor L g of the secondary winding of the transformer is used as a resonant inductor; the other ends of the same ends of the primary and secondary windings of the transformer are respectively connected with the negative poles of the direct-current power supplies of the corresponding excitation sources. Energy bidirectional transmission and synchronous rectification are realized through a brand-new circuit topology. All active switches can realize soft switching, and the working efficiency is improved. In an open-loop control state, the output current does not change with the change of a load, and the application is suitable for a bidirectional constant current working mode.

Description

TECHNICAL FIELD

[0001] The present application relates to a converter technology, in particular to a bidirectional output L2C3 resonant converter. BACKGROUND

[0002] Bidirectional DC / DC converter is an important component of energy storage system, which is a channel for its integration into the power grid. The bidirectional energy channel of the bidirectional converter can ensure the flexible switching of the energy storage system in the charging and discharging mode, so as to eliminate the phenomenon of power flow interruption or instability at the load end. In addition, the bidirectional converter is widely used in electric vehicles, battery management systems, aerospace devices and large-capacity uninterruptible power supplies, and has broad application prospects.

[0003] Among them, the bidirectional resonant converter has many advantages: ZVS realization reduces switching loss and improves efficiency, high frequency helps to reduce the size of the converter. However, the traditional bidirectional LLC resonant converter is sensitive to load changes in constant current output mode, and needs to change the switching frequency in real time, so it needs higher control complexity in constant current output applications. SUMMARY

[0004] In view of the problems existing in the resonant converter, a bidirectional output L2C3 resonant converter is proposed, which can realize bidirectional constant current output under open-loop control and improve efficiency through synchronous rectification.

[0005] The technical scheme of the present application is: a bidirectional output L2C3 resonant converter, comprising two excitation sources and a resonant cavity, the excitation sources are both half-wave bridge circuits, which are composed of a DC power supply and two switching tubes in series; the resonant cavity includes a transformer, three capacitors and two inductors; the transformer primary winding is connected in parallel with the resonant capacitor C p , the same end of the transformer primary winding is connected in series with the resonant capacitor C1 and the inductor L1, the other end of the inductor L1 is connected to the connection point of the first excitation source and the two switching tubes in series; the same end of the transformer secondary winding is connected with the resonant capacitor C2, the other end of the resonant capacitor C2 is connected to the connection point of the second excitation source and the two switching tubes in series, and the leakage inductance L g of the transformer is used as the resonant inductor; the other end of the same end of the primary and secondary windings of the transformer is connected to the negative pole of the corresponding excitation source DC power supply.

[0006] Preferably, the resonant cavity has two resonant frequencies, a primary resonant frequency and a secondary resonant frequency, the primary resonant frequency is a series resonant circuit composed of the series resonant inductor L1, the resonant capacitor C1 and the parallel resonant capacitor C p , and the secondary resonant frequency is a series resonant circuit composed of the series resonant capacitor C2, the transformer complex leakage inductance L g and the parallel resonant capacitor C p .

[0007] Preferably, the two excitation sources are connected through a resonant cavity, the switching frequency is controlled, the ratio of the switching frequency / working resonant frequency is adjusted, and the two excitation sources are energy output end and energy input end.

[0008] Preferably, the working resonant frequency of the resonant cavity is the excitation end resonant frequency.

[0009] Preferably, the two switch tubes in series in the one excitation source are used as excitation switch tubes, the two switch tubes in series in the other excitation source are used as rectifier switch tubes, the excitation switch tubes and the rectifier switch tubes have the same switching frequency, and the resonant cavity resonates and synchronously rectifies at the same time.

[0010] The beneficial effects of the present application are that the bidirectional output L2C3 resonant converter realizes bidirectional energy transfer through a brand-new circuit topology, and during energy transfer, synchronous rectification with simple control is adopted, and all active switches can realize soft switching, and the working efficiency of the circuit is improved. The circuit has the characteristics of constant current working, and in the open-loop control state, the output current does not change with the change of the load, and can be well applied to the bidirectional constant current working mode. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 It is a topological structure diagram of the bidirectional output L2C3 resonant converter of the present application;

[0012] Figure 2 It is a corresponding relationship diagram of the circuit current gain and the working frequency of the bidirectional output L2C3 resonant converter of the present application;

[0013] Figure 3a It is a diagram showing the change relationship of the imaginary part (b1) of the resonant cavity impedance with the normalized frequency fn during step-down;

[0014] Figure 3b It is a diagram showing the change relationship of the imaginary part (b1) of the resonant cavity impedance with the normalized frequency fn during step-up;

[0015] Figure 4 It is a working key waveform diagram of the bidirectional output L2C3 resonant converter of the present application in step-down mode;

[0016] Figure 5 It is a working key waveform diagram of the bidirectional output L2C3 resonant converter of the present application in step-up mode;

[0017] Figure 6a It is an output current diagram of the bidirectional output L2C3 resonant converter of the present application in step-down mode;

[0018] Figure 6b It is an output current diagram of the bidirectional output L2C3 resonant converter of the present application in step-up mode;

[0019] Figure 7a Efficiency chart of bidirectional output L2C3 resonant converter in buck mode of the present application;

[0020] Figure 7b Efficiency chart of bidirectional output L2C3 resonant converter in boost mode of the present application. DETAILED DESCRIPTION

[0021] The present application will be described in detail below with reference to the drawings and specific embodiments. The embodiments are implemented on the premise of the technical solution of the present application, and detailed implementation and specific operation processes are given, but the protection scope of the present application is not limited to the following embodiments.

[0022] As shown in the bidirectional output L2C3 resonant converter topology diagram shown in Figure 1 , it includes two excitation sources and a resonant cavity. The excitation sources are both half-wave bridge circuits, which are composed of a DC power supply (battery) in series with two switching tubes. The resonant cavity includes a transformer, three capacitors and two inductors. The primary winding of the transformer is connected in parallel with a resonant capacitor C p . The same end of the primary winding of the transformer is connected in series with a resonant capacitor C1 and an inductor L1, and the other end of the inductor L1 is connected to the connection point a of the first excitation source in series with two switching tubes. The same end of the secondary winding of the transformer is connected with a resonant capacitor C2, and the other end of the resonant capacitor C2 is connected to the connection point c of the second excitation source in series with two switching tubes, Figure 1 The resonant inductor L g is the leakage inductance of the secondary winding of the transformer. The other ends (points b and d) of the same ends of the primary and secondary windings of the transformer are respectively connected to the negative poles of the corresponding excitation sources. The first excitation source includes a DC power supply V DC1 and two switching tubes Q1 and Q2. The second excitation source includes a DC power supply V DC2 and two switching tubes Q3 and Q4. The primary and secondary windings are both active bridges, and the circuit can realize bidirectional energy transfer. The resonant cavity has two resonant frequencies, the primary resonant frequency and the secondary resonant frequency. The primary resonant frequency is a series resonant circuit composed of a resonant inductor L1, a resonant capacitor C1 and a parallel resonant capacitor C p . The secondary resonant frequency is a series resonant circuit composed of a resonant capacitor C2, a transformer complex leakage inductance L g and a parallel resonant capacitor C p . When the circuit is designed symmetrically, i.e. the primary and secondary resonant parameters are the same, the primary and secondary resonant frequencies are equal. When designing the circuit structure, if the primary and secondary symmetrical design is required, the transformer ratio is designed as 1:1, and if the asymmetrical design is required, the prediction and calculation of the synchronous rectification need to be recalculated, and the input and output characteristics also need to be redesigned.

[0023] As shown in the bidirectional output L2C3 resonant converter circuit current gain and working frequency correspondence chart shown in Figure 2 ,Figure 2 R1-R5 represent different load impedance in R1-R5, Figure 2 The ordinate represents the output current to input voltage (current gain), that is, the higher the ordinate, the greater the output current, only considering current output, the boost and buck depends on the relationship between the two input voltages and the phase shift angle. The buck mode needs the secondary side switch signal to lag behind the primary side signal, and vice versa for the boost mode. fs is the switching frequency, and fr is the resonant frequency. The relationship between fs and fr is determined by whether the switching frequency is greater than or less than the resonant frequency.

[0024] The circuit has two working modes, buck and boost mode.

[0025] Buck mode: primary input, secondary output, that is, the DC power V DC1 is converted to an alternating square wave output by a half-wave bridge circuit, and then to a high-frequency sinusoidal alternating current by a resonant cavity. The high-frequency sinusoidal alternating current output is rectified by two switch tubes in the second excitation source and output to the load V DC2 , the DC power V DC1 discharges, V DC2 charges. From Figure 3a we can see that when the switching frequency is lower than the resonant frequency of the resonant cavity, that is, f n1 = switching frequency / resonant frequency <1, the circuit works in the inductive region, and the switching frequencies of the excitation switches Q1, Q2 and the rectification switches Q3, Q4 are the same, which ensures synchronous rectification. In this way, the two switch tubes Q1, Q2 of the primary half-bridge can realize soft switching to improve the efficiency of the circuit. When the circuit works in constant current output mode, the constant current characteristic will be affected to a certain extent because the switching frequency is lower than the resonant frequency, so the switching frequency cannot deviate too far from the resonant frequency. From Figure 4 we can see that the two rectification switches Q3, Q4 of the secondary side are complementary and phase-shifted by 90°, and the calculation of the phase shift angle is related to the size of the equivalent load. The larger the equivalent load, the larger the phase shift angle of the primary and secondary signals. Therefore, the required phase shift angle for synchronous rectification can be predicted according to the size of the equivalent load, realizing synchronous rectification with low control complexity. Figure 4 v gs1 and v gs2 in are the voltage signals on the two switch tubes Q1, Q2, Figure 4 i3 and i4 in are the current signals on the two switch tubes Q3, Q4.

[0026] Boost mode: secondary input, primary output, that is, the DC power V DC2 is converted to an alternating square wave output by a half-wave bridge circuit, and then to a high-frequency sinusoidal alternating current by a resonant cavity. The high-frequency sinusoidal alternating current output is rectified by two switch tubes in the first excitation source and output to the load V DC1 , the DC power V DC2 discharges, VDC1 Charging. From Figure 3b It can be seen that when the switching frequency is higher than the resonant frequency of the resonant cavity, i.e. f n >1, the circuit works in the inductive region, the switching frequency of the excitation switch tubes Q3, Q4 and the rectifier switches Q1, Q2 is the same, which ensures synchronous rectification. Like the buck mode, the two switch tubes Q3, Q4 of the secondary side half-bridge can achieve soft switching to improve the efficiency of the circuit. Moreover, it cannot be too far above the resonant frequency, which will affect the constant current output characteristics. Figure 5 The key waveforms of the circuit in the boost mode are shown. In the boost mode, the parasitic output capacitance of the switch tube also needs to be considered for synchronous rectification. As can be seen from the waveforms of i1 and i2, there is a negative current for about half a period. When implementing synchronous rectification, the conduction time needs to be removed, otherwise oscillation will occur. Figure 5 v gs3 and v gs4 are the voltage signals on the two switch tubes Q3, Q4, Figure 5 i1 and i2 are the current signals on the two switch tubes Q1, Q2.

[0027] When the transformer is designed with a ratio of 1:1, the resonant frequencies of the primary and secondary sides are equal; when the transformer is designed asymmetrically, the resonant frequency of the resonant cavity is the resonant frequency of the excitation source end. That is, in the buck mode, the primary side is input and the secondary side is output, the primary side is connected to the excitation source and the secondary side is connected to the load. At this time, the resonant frequency of the resonant cavity is the resonant frequency formed by the series resonant of the series resonant inductor L1, the resonant capacitor C1 and the parallel resonant capacitor C p 2 of the transformer; in the boost mode, the secondary side is input and the primary side is output, the secondary side is connected to the excitation source and the primary side is connected to the load. At this time, the resonant frequency of the resonant cavity is the resonant frequency formed by the series resonant of the series resonant capacitor C2, the series resonant inductor L g and the parallel resonant capacitor C p 2 of the transformer.

[0028] When the circuit works in the buck mode, the capacitor C2 and the inductor L g of the transformer can be regarded as being connected in series with the equivalent load, and it can be known from the derivation of the current gain that when the switching frequency is close to the series resonant frequency of the primary side resonant cavity (C1, L1, C p series resonant), the output current is independent of the load. In the boost mode, the principle is the same, and when the switching frequency is close to the series resonant frequency of the secondary side resonant cavity (C2, L g , C p series resonant frequency), the output current is independent of the load.

[0029] The specific circuit of the example is shown in Figure 1Wherein in low voltage application scenario, the primary input DC voltage is 15V, the output current is 500mA, the resonance frequency is 200kHz, and the switching frequency is 196kHz. The secondary input DC voltage is 4V, the output current is 125mA, the resonance frequency is 200kHz, and the switching frequency is 204.1kHz. The output current of the circuit in two working modes is shown in Figure 6a 、 6b The experiment shows that the circuit still has good constant current output characteristics under open loop control, wherein the equivalent load is the ratio of the terminal voltage of the primary and secondary battery (output voltage source) and the current flowing therethrough. Figure 7a 、 7b The working efficiency of the circuit in two modes is shown, and it can be seen that the peak efficiency of the circuit is 90%.

[0030] The above-described embodiments only express several embodiments of the present application, and the description is relatively specific and detailed, but it cannot be understood as a limitation on the scope of the patent. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, several modifications and improvements can be made, which belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A bidirectional output L2 C3 resonant converter characterized by, The application relates to a double-excitation-source resonant transformer, which comprises two excitation sources and a resonant cavity, wherein each excitation source is a half-wave bridge circuit formed by connecting two switch tubes in series with a direct-current power supply; the resonant cavity comprises a transformer, three capacitors and two inductors; the primary winding of the transformer is connected in parallel with a resonant capacitor C p ; the same end of the primary winding of the transformer is connected with a resonant capacitor C1 and an inductor L1 connected in series; the other end of the inductor L1 is connected with the connection point of two switch tubes in series in the first excitation source; the same end of the secondary winding of the transformer is directly connected with one end of a leakage inductor L g ; the other end of the leakage inductor L g is connected with a resonant capacitor C2; the end of the resonant capacitor C2 far from the leakage inductor L g is connected with the connection point of two switch tubes in series in the second excitation source; the leakage inductor L g of the secondary winding of the transformer serves as a resonant inductor; the other end of the same end of the primary winding and the secondary winding of the transformer is connected with the negative pole of the corresponding excitation source direct-current power supply; the transformer realizes bidirectional constant-current output under open-loop control; the two switch tubes in series in the one excitation source serve as excitation switch tubes, and the two switch tubes in series in the other excitation source serve as rectification switch tubes; the excitation switch tubes and the rectification switch tubes have the same switching frequency, and the resonant cavity resonates and synchronously rectifies at the same time; when the switching frequency is close to the series resonant frequency of the primary resonant cavity, the output current size is independent of the load in the step-down mode; when the switching frequency is close to the series resonant frequency of the secondary resonant cavity, the output current is independent of the load in the step-up mode.

2. The bidirectional output L2 C3 resonant converter of claim 1, wherein, The resonant cavity has two resonant frequencies, a primary resonant frequency and a secondary resonant frequency, the primary resonant frequency being a series resonance constituted by a resonant inductor L1, a resonant capacitor C1 and a parallel resonant capacitor C p 2 in series; the secondary resonant frequency being a series resonance constituted by a resonant capacitor C2, a complex leakage inductance L g L of the transformer and a parallel resonant capacitor C p 2.

3. The bidirectional output L2 C3 resonant converter of claim 2, wherein, The two excitation sources are connected through a resonant cavity, the switching frequency is controlled, the ratio of the switching frequency / working resonant frequency is adjusted, and the two excitation sources are energy output end and energy input end.

4. The bidirectional output L2 C3 resonant converter of claim 2 or 3, wherein, The working resonant frequency of the resonant cavity is the excitation end resonant frequency.

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