CN108923658B - LLC resonant converter - Google Patents

Abstract

The invention discloses an LLC resonant converter, which comprises a power supply input end, a first switch bridge arm, a resonant network, a second switch bridge arm, a rectification output circuit and a load output end, wherein two ends of the first switch bridge arm are connected with the power supply input end, and the midpoint of the first switch bridge arm is connected with one end of the resonant network; the other end of the resonant network is connected with the midpoint of the second switch bridge arm; one end of the second switch bridge arm is connected with the negative electrode of the power supply input end, the other end of the second switch bridge arm is connected with the output end of the rectification output circuit, and the load output end is connected with the rectification output circuit. The invention has simple structure and can realize the wide voltage input to supply power for the load under narrow frequency. The invention is suitable for any load needing stable high-voltage direct current power supply.

Description

LLC resonant converter

technical field

The invention belongs to the field of load power supply, and relates to a converter for providing stable direct current for application, in particular to an LLC resonant converter.

Background technique

At present, the power battery that supplies power to the load has the characteristics of high output voltage and wide range. For example, the output voltage of lithium battery is generally 200-400V. However, most communication systems, UPS and DC motors require a stable high-voltage DC power supply, so a DC/DC converter with a wide voltage input must be connected to the lithium battery to provide stable DC power for the load. Therefore, we need to study a high-efficiency unidirectional DC/DC converter suitable for a wide voltage range input.

The LLC converter in the prior art has the advantages of easy soft switching and high transmission efficiency, so it is widely used in switching power supplies. How to improve the voltage range of LLC converter in load power supply so that it can provide high voltage DC for load is the focus of current research.

SUMMARY OF THE INVENTION

In order to solve the above deficiencies in the prior art, the present invention aims to provide an LLC resonant converter to improve the voltage range of the LLC converter.

For achieving the above object, the technical scheme adopted in the present invention is as follows:

An LLC resonant converter, comprising a power input end, a first switch bridge arm, a resonant network, a second switch bridge arm, a rectifier output circuit, and a load output end, wherein both ends of the first switch bridge arm are connected to the power supply input end, The midpoint of the first switch bridge arm is connected to one end of the resonant network; the other end of the resonant network is connected to the midpoint of the second switch bridge arm; one end of the second switch bridge arm is connected to the negative pole of the power input terminal, The other end is connected to the output end of the rectification output circuit, and the load output end is connected to the output end of the rectification output circuit.

As a limitation of the present invention: the first switch bridge arm and the second switch bridge arm are both half-bridge power switch transistor structures, and the first switch bridge arm includes a first switch transistor and a second switch transistor connected in series, so The second switch bridge arm includes a third switch tube and a fourth switch tube connected in series, wherein the frequency of the first switch tube to the fourth switch tube is the same, and the duty ratio is 0.5, and the first switch tube and the third switch tube are all 0.5. The phases of the tubes are the same, the phases of the second switch tube and the fourth switch tube are the same, and the phase difference between the first switch tube and the second switch tube is 180°.

As a limitation of the resonant network in the present invention: the resonant network includes a resonant inductor, a primary side of a transformer, and a resonant capacitor connected in series in sequence.

As a limitation to the rectifier output circuit in the present invention: the rectifier output circuit includes the secondary side of a transformer with a center tap, and a first diode and a second diode connected in parallel; the first diode One end of the diode is connected to one end of the secondary side of the transformer, one end of the second diode is connected to the other end of the secondary side of the transformer, and the other ends of the first diode and the second diode not connected to the secondary side of the transformer are both connected to the load output One end of the load output end is connected to the tap on the secondary side of the transformer.

As a limitation on the transformer in the present invention: the tap on the negative side of the transformer is located at the center of the secondary side of the transformer.

As a further limitation to the transformer in the present invention, the tap on the negative side of the transformer is located at the center of the secondary side of the transformer.

As the last limitation of the present invention: the first switch tube, the second switch tube, the third switch tube, and the fourth switch tube are one of a MOSFET power tube, an IGBT power tube, and a GTO power tube.

Due to adopting the above-mentioned technical scheme, compared with the prior art, the present invention has the following beneficial effects:

In the present invention, the first switch transistor S1 and the second switch transistor S2 are used to form the first switch bridge arm, while the third switch transistor S3 and the fourth switch transistor S4 form the second switch bridge arm. In application, the LLC converter When the input voltage and transmission power are in the normal range, the output voltage can be stabilized by changing the switching frequency of the four switching tubes.

In the present invention, the first switch S1 to the fourth switch S4 all use power transistors with the same frequency and duty cycle of 0.5, while the first switch S1 and the third switch S3 have the same phase, and the second switch S2 The phase of the fourth switch S4 is the same, and the phase difference between the first switch S1 and the second switch S2 is 180°, and the opening and closing of the first switch S1 to the fourth switch S4 can be controlled, so that the present invention can be When the input voltage is small, the gain of the LLC converter is similar to the gain of the full-bridge LLC converter; and when the input voltage is large, the gain of the LLC converter is similar to the gain of the half-bridge LLC converter , so the LLC converter of the present invention can realize wide voltage input under narrow frequency;

The invention can realize the zero voltage turn-on (ZVS) of the power switch tube and the zero-current turn-off (ZCS) of the rectifier diode.

To sum up, the present invention has a simple structure, and can realize a wide voltage input to supply power to a load under a narrow frequency.

The present invention is suitable for any load requiring stable high-voltage direct current power supply.

Description of drawings

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

1 is a schematic diagram of an electrical structure of an embodiment of the present invention;

2 is a simulation waveform diagram of an embodiment of the present invention;

FIG. 3a is an equivalent circuit diagram of the stage t ₀ to t ₁ according to the embodiment of the present invention;

Fig. 3b is an equivalent circuit diagram of the embodiment of the present invention in stages t ₁ to t ₃ ;

3c is an equivalent circuit diagram of the embodiment of the present invention in _stages t3 to t4 _;

FIG. 3d is an equivalent circuit diagram of the embodiment of the present invention in stages t ₄ to t ₅ ;

Fig. 4a is the equivalent circuit diagram of Fig. 3a;

Fig. 4b is the equivalent circuit diagram of Fig. 3b;

Fig. 4c is an equivalent circuit diagram of Fig. 3c;

Fig. 5 is the waveform of the experimental part of the embodiment of the present invention;

FIG. 6 is a soft switching waveform of an embodiment of the present invention;

FIG. 7 is a waveform comparison of the gain of the embodiment of the present invention with the gain of the half-bridge LLC and the gain of the full-bridge LLC.

Detailed ways

Example LLC resonant converter

This embodiment, as shown in Figure 1, includes:

①Power input terminal.

②The first switch bridge arm is connected to both ends of the power input terminal, including the first switch tube S1 and the second switch tube S2 connected in series in sequence, wherein the first switch tube S1 is connected to the positive pole of the power input terminal, and the second switch tube S2 and The negative poles of the power input terminals are grounded together.

③ The second switch bridge arm includes a third switch S3 and a fourth switch S4 connected in series in sequence, and one end of the third switch S3 not connected to the fourth switch S4 is grounded.

④ The resonant network includes the resonant inductor Lr, the primary winding of the transformer T, and the resonant capacitor Cr connected in series in sequence, wherein the free end of the resonant inductor Lr is used as one end of the resonant network to connect to the midpoint of the first switch bridge arm, and the resonant capacitor Cr The free end of the resonant network is connected to the midpoint of the two switch bridge arms as the other end of the resonant network.

⑤ The rectifier output circuit includes the secondary winding of the transformer T, the first diode D1, and the second diode D2. The secondary winding of the transformer T has a tap, and the position of the tap is located in the middle of the secondary winding. A diode D1 is connected to the cathode of the second diode D2 and then connected to one end of the fourth switch S4 that is not connected to the third switch S3, while the anode of the first diode D1 is connected to one end of the secondary winding of the transformer T, The anode of the second diode D2 is connected to the other end of the secondary winding of the transformer T.

⑥ The load output terminal includes capacitor C and resistor R connected in parallel. One end of the load output terminal is connected to the cathodes of the first diode D1 and the second diode D2, and the other end is connected to the middle tap of the secondary winding of the transformer T.

In the above structure, the first to fourth switch transistors S1 to S4 are power switch transistor structures in the prior art, such as MOSFET power transistors in the prior art, or IGBT power transistors or GTO power transistors. And the frequency of the first switch S1 to the fourth switch S4 is the same, and the duty ratio is 0.5; and the phase of the first switch S1 and the third switch S3 are the same, and the second switch S2 and the fourth switch The phases of the transistors S4 are the same, and the phases of the first switching transistor S1 and the second switching transistor S2 differ by 180°.

In Figure 1, Lm is the equivalent excitation inductance of the transformer, i _Lr is the current of the resonant inductance Lr, i _Lm is the current of the excitation inductance Lm, u _cr is the voltage across the resonant capacitor Cr, Vtank is the resonant tank voltage, and i _DO1 is the current flowing through the resonant capacitor Cr. The current of the first diode D1, i _DO2 is the current flowing through the second diode D2. In order to better introduce this embodiment, as shown in FIG. 2 , the working process of this embodiment is divided into 10 stages from 0 to t ₉ , and FIG. 3 a to FIG. 3 d are the specific working circuit principles of this embodiment in different stages. In the figure, the dotted line part in the figure represents that the current does not flow through this line at this stage, so the working principle of each stage is analyzed in detail with reference to Figures 3a-3d.

Stage 1 (t ₀ ~ t ₁ ): As shown in Figure 3a, at time t ₀ , the dead time is over, and the first switch S1 and the third switch S3 are turned on. Since the resonant inductor current i _Lr is negative, i The absolute value of _Lr begins to decrease, a current of i _Lm -i _Lr flows through the transformer T, and is transmitted to the secondary side of the transformer T, the first diode D1 is turned on, the excitation inductance Lm is clamped, and does not participate in the resonance, The equivalent circuit refers to Figure 4a. At this stage, the resonant frequency is fr, and the secondary energy of the transformer T is provided by the resonant inductor Lr. Before this, the resonant current flows through the anti-parallel diodes of the first switch S1 and the third switch S3, and the first switch S1 and the third switch S3 realize ZVS.

Stage 2 (t ₁ ~ t ₂ ): As shown in Figure 3b, at time t ₁ , the absolute value of i _Lr decreases to 0 and rises in the positive direction, starting to flow through the first switch tube S1, and the magnitude of the current flowing through the transformer T It becomes i _Lm +i _Lr , the first diode D1 continues to conduct, the excitation inductance Lm is clamped, and does not participate in the resonance, and the equivalent circuit refers to Fig. 4b. At this stage, the resonant frequency is fr, and the secondary side energy of the transformer T is provided by the input power supply.

Stage 3 (t ₂ ~ t ₃ ): still as shown in Figure 3b, i _Lr maintains the same direction, at t ₂ , i _Lm is commutated, the excitation inductance Lm is in a charged state, the excitation current i _Lm gradually increases, and the current The magnitude of the current through the transformer T becomes i _Lr -i _Lm . At time t ₃ , i _Lm is equal to i _Lr . At this time, there is no current on the primary side of the transformer T, the output current on the secondary side is 0, and the current flowing through the two diodes is 0 , to realize ZCS, and the equivalent circuit is shown in Figure 4b. At this stage, the resonant frequency is fr, and the secondary side energy of the transformer T is still provided by the input power supply.

Stage 4 (t ₃ ~ t ₄ ): As shown in Figure 3c, at this stage, i _Lr and i _Lm continue to be equal, there is no current on the primary side of the transformer T, the excitation inductance Lm is released from the clamp and participates in the resonance, and the resonant frequency becomes fm, the load energy is provided by the filter capacitor C. During the conduction period of the first switch S1 and the second switch S3, the voltage across the second switch S2 is the input voltage V _i , and the voltage across the fourth switch S4 is the output Voltage Vo, the equivalent circuit refers to Figure 4c.

Stage 5 (t ₄ ~ t ₅ ): As shown in FIG. 3d , this embodiment enters the dead zone, the first switch S1 to the fourth switch S4 are all turned off, and the second switch S2 and the fourth switch S4 are parasitic The capacitors Coss2 and Coss4 are discharged and then charged in reverse until the diodes of the second switch S2 and the fourth switch S4 are turned on, and the parasitic capacitances Coss1 and Coss3 of the first switch S1 and the third switch S3 begin to charge to the input voltage Vi and the output voltage Vo. At this stage, the resonant frequency is fm, and the load energy is provided by the filter capacitor.

The second half cycle of this embodiment (ie, stages t ₅ to t ₉ ) is similar to the first half cycle, except that the filter capacitor C acts as an input power supply.

In order to facilitate the understanding of each stage, according to the switching mode of the first switch S1 to the fourth switch S4 and whether the excitation inductance Lm participates in the resonance, regardless of the dead zone, the working mode of the resonant tank in this embodiment is divided into three stages. And calculate the time domain equation expression.

The equivalent models of stage 1, stage 2, and stage 3 are shown in Figure 3a, and their time domain equation expressions are:

,特征阻抗

,n为变压器原副边匝比，Vi为输入电压，Vo为输出电压，

。where, the angular frequency

, the characteristic impedance

, n is the turns ratio of the primary and secondary sides of the transformer, Vi is the input voltage, Vo is the output voltage,

.

The equivalent model of stage four is shown in Figure 3b, and its time domain equation expression is:

，特征阻抗

，

。where, the angular frequency

, the characteristic impedance

,

.

The model of the second half period t ₅ -t ₈ is shown in Figure 3-c, and its time domain equation expression is:

，励磁电感与谐振电感比

，品质因数

，谐振频率

，变压器变比为4:3，稳定输出电压240V, 开关频率在43KHz-60KHz范围内变化，开关频率变化高达17KHz。而传统LLC频率变换61.02KHz。For this LLC converter, the input voltage

, the ratio of excitation inductance to resonant inductance

,Quality factor

,Resonant frequency

, The transformer ratio is 4:3, the stable output voltage is 240V, the switching frequency changes in the range of 43KHz-60KHz, and the switching frequency changes up to 17KHz. The traditional LLC frequency conversion is 61.02KHz.

Fig. 5 shows some experimental waveforms when the input voltage is 400V, the output voltage is 240V, and the power is 1kW according to the embodiment of the present invention. The waveforms are, from top to bottom, the driving signal of the first switch tube S1 and the resonant tank voltage V _tank harmoniously The vibration current i _Lr , at this time, the frequency of the first switch S1 to the fourth switch S4 is 60 kHz, which is equal to the resonant frequency _fr .

Fig. 6 shows the soft switching waveform when the input voltage is 400V, the output voltage is 240V, and the power is 1kW according to the embodiment of the present invention. Due to the symmetry, the driving signals of the second switch S2 and the third switch S3 are measured respectively. V _gs and drain-source voltage V _ds , so as to judge that soft switching can be realized.

Claims (6)

1. An LLC resonant converter, characterized in that: the power supply comprises a power supply input end, a first switch bridge arm, a resonant network, a second switch bridge arm, a rectification output circuit and a load output end, wherein two ends of the first switch bridge arm are connected with the power supply input end, and the middle point of the first switch bridge arm is connected with one end of the resonant network; the other end of the resonant network is connected with the midpoint of the second switch bridge arm; one end of the second switch bridge arm is connected with the negative electrode of the power supply input end, the other end of the second switch bridge arm is connected with the output end of the rectification output circuit, and the load output end is connected with the output end of the rectification output circuit.

2. The LLC resonant converter of claim 1, wherein: the first switch bridge arm and the second switch bridge arm are both half-bridge power switch tube structures, the first switch bridge arm comprises a first switch tube and a second switch tube which are connected in series, the second switch bridge arm comprises a third switch tube and a fourth switch tube which are connected in series, the switching frequencies of the first switch tube to the fourth switch tube are the same, the duty ratios of the first switch tube to the fourth switch tube are 0.5, the phases of the first switch tube and the third switch tube are the same, the phases of the second switch tube and the fourth switch tube are the same, and the phase difference between the first switch tube and the second switch tube is 180 degrees.

3. The LLC resonant converter of claim 2, wherein: the resonance network comprises a resonance inductor, a transformer primary side and a resonance capacitor which are sequentially connected in series.

4. The LLC resonant converter of claim 3, wherein: the rectification output circuit comprises a secondary side of a transformer with a middle tap, and a first diode and a second diode which are connected in parallel; one end of the first diode is connected with one end of the secondary side of the transformer, one end of the second diode is connected with the other end of the secondary side of the transformer, the other ends of the first diode and the second diode, which are not connected with the secondary side of the transformer, are connected with one end of the load output end, and the other end of the load output end is connected with a tap on the secondary side of the transformer.

5. The LLC resonant converter of claim 4, wherein: and the tap on the secondary side of the transformer is positioned in the center of the secondary side of the transformer.

6. LLC resonant converter according to any of claims 2-5, characterized in that: the first switch tube, the second switch tube, the third switch tube and the fourth switch tube are one of MOSFET power tubes, IGBT power tubes and GTO power tubes.

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