CN110829855A - LLC converter switching over wide voltage range based on alternating current switch - Google Patents

Abstract

The invention relates to a wide-voltage range LLC converter based on AC switch switching, and belongs to the technical field of converters. Including the primary side H bridge circuit, the DC capacitor bridge arm including the neutral point, the AC switch circuit, the secondary side half bridge circuit, the LLC resonant cavity sharing the split resonant capacitor and the isolation transformer; the primary side H bridge circuit and the DC capacitor bridge arm are connected Both ends of the input power supply; the primary side of the isolation transformer with the same name is connected to the left half-bridge midpoint of the primary H-bridge circuit, and the non-identical terminal of the isolation transformer is connected to the right half-bridge of the primary H-bridge circuit. Connect the left half-bridge circuit of the primary H-bridge and the neutral point of the DC capacitor bridge arm; the secondary side of the isolation transformer with the same name is connected to one end of the resonant inductor of the LLC resonant cavity, and the other end of the resonant inductor is connected to the midpoint of the secondary side half-bridge; the secondary side of the isolation transformer The non-synonymous side is terminated to the midpoint of the split resonant capacitor string. The circuit of the invention has the advantages of small switching loss, high efficiency, bidirectional power supply and the like.

Description

A Wide Voltage Range LLC Converter Based on AC Switching

technical field

The invention relates to a wide-voltage range LLC converter based on AC switch switching, and belongs to the technical field of converters.

Background technique

In recent years, in order to increase the switching frequency of the converter to improve the power density of the converter, soft switching technologies such as zero voltage switching (ZVS) or zero current switching (ZCS) have been widely used. The switching losses are reduced and the converter efficiency is improved. Scholars have proposed a phaseshift full-bridge (PSFB) DC-DC converter based on PWM technology, which can control the output voltage of the PSFB DC-DC converter by controlling the phase-shift angle of the driving pulses of the two bridge arms; PSFB DC-DC converters have the advantages of simple structure, easy implementation of soft switching, and high efficiency. However, the soft switching area will become smaller at low load, and even cannot achieve soft switching, resulting in converter failure. LLC resonant soft-switching converters generally use pulse frequency modulation (PFM) to control the output voltage. Soft-switching can be achieved at any load rate, but when the input voltage changes greatly, it often results in a large frequency change.

SUMMARY OF THE INVENTION

The purpose of the present invention is to address the above shortcomings, to provide a wide-voltage range LLC converter based on AC switching, utilizing the advantages of switching and LLC frequency conversion and voltage regulation from practical requirements, and combining AC switching to realize full-bridge Fast switching with half bridges, stable output in a wide range of converters, and voltage regulation control and soft switching in a wide voltage range of converters.

The present invention is achieved by adopting the following technical solutions:

A wide voltage range LLC converter based on AC switching, the internal circuit includes a primary side H bridge circuit, a DC capacitor bridge arm including a neutral point, an AC switch circuit, and a secondary side half bridge circuit, an LLC resonant cavity sharing a split resonant capacitor, and an isolation transformer;

The primary side H bridge circuit and the DC capacitor bridge arm including the neutral point are respectively connected to both ends of the input power supply;

The primary side H-bridge circuit is constructed by 4 MOSFET tubes; the secondary side half-bridge circuit is constructed by 2 MOSFET tubes;

The LLC resonant cavity sharing the split resonant capacitor is composed of a resonant inductance, two split resonant capacitors and the excitation inductance of the isolation transformer;

The primary side of the isolation transformer with the same name is connected to the left half-bridge midpoint of the primary side H-bridge circuit, the primary side of the isolation transformer is not connected to the right half-bridge midpoint of the primary side H-bridge circuit, and the AC switch is connected to the primary side H. The left half-bridge of the bridge circuit and the neutral point of the DC capacitor bridge arm; the primary side of the isolation transformer with the same name is connected to the left half-bridge of the primary side of the H-bridge circuit; the secondary side of the isolation transformer with the same name and the corresponding LLC resonant cavity resonant inductance One end is connected, the other end of the resonant inductor is connected to the midpoint of the secondary half-bridge; the secondary side of the isolation transformer is not connected to the midpoint of the split resonant capacitor string;

The AC switch circuit is composed of two MOSFETs in reverse series;

The DC two ends of the secondary side half-bridge circuit and the split resonance capacitor string are respectively connected with the output DC two ends, and the output DC two ends are connected in parallel with the output capacitor and the equivalent load resistance.

The primary-side H-bridge circuit and the secondary-side half-bridge circuit of the converter are controlled by a high-frequency PWM signal with a 50% duty cycle, and the high-frequency PWM signal is used to control the primary-side H-bridge circuit and the secondary-side half-bridge circuit The MOSFETs in the circuit are turned on alternately.

When the primary side H-bridge circuit applies PWM signal, the secondary side half-bridge circuit operates in synchronous rectification to realize LLC power forward mode; when the secondary side half-bridge circuit applies PWM signal, the primary side H-bridge circuit operates in synchronous rectification to realize LLC power reverse mode.

The transformation ratio of the isolation transformer is n:1, wherein n is greater than 0.

When the AC switch circuit is blocked, the four MOSFETs of the primary H-bridge circuit work in full-bridge mode; when the AC switch circuit is running, the left half-bridge circuit of the primary H-bridge is blocked, and the two right half-bridge circuits of the primary H-bridge are blocked. The MOSFETs work in half-bridge mode.

When the voltage gain is between 0.5-0.75, the converter operates in half-bridge mode; when the voltage gain is between 0.75-1.3, the converter operates in full-bridge mode.

The voltage gain is also the amplification factor of the voltage, and the calculation formula is: Au=output voltage/input voltage; in the present invention, when the power is forward, the voltage gain is the product of the reference value of the output value Uo and n and the actual input The ratio of the value Ui; when the power is reversed, the voltage gain is the ratio of the reference value of the input value Ui to the product of the output values Uo and n.

Compared with the prior art, the present invention has the advantages of small switching loss, high efficiency and simple structure, and specifically has the following advantages:

1. Give full play to the variable frequency voltage regulation function of LLC circuit, simple control, high efficiency at light load or rated voltage point;

2. Utilize the AC switch switching function to realize voltage regulation with a large range of voltage changes;

3. The soft switching technology is realized in the full load range and the full working voltage range.

Description of drawings

The present invention will be further described below in conjunction with the accompanying drawings:

FIG. 1 is a circuit schematic diagram of a wide voltage range LLC converter based on AC switching according to the present invention.

FIG. 2 is a PWM signal diagram when the present invention operates in a forward full-bridge LLC mode.

FIG. 3 is a PWM signal diagram when the present invention operates in a forward half-bridge LLC mode.

FIG. 4 is a schematic circuit diagram of the present invention when the present invention operates in the forward full-bridge LLC mode and the current is forward.

FIG. 5 is a schematic circuit diagram of the present invention when the present invention operates in the forward full-bridge LLC mode and the current is reversed.

6 is a schematic circuit diagram of the present invention when the present invention operates in a forward half-bridge LLC operation mode and the current is forward.

FIG. 7 is a schematic circuit diagram of the present invention when the present invention operates in the forward half-bridge LLC operating mode and the current is reversed.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the following embodiments are only used to illustrate the technical solutions of the present invention more clearly, and cannot be used to limit the protection scope of the present invention.

Referring to FIG. 1, a wide-voltage range LLC converter based on AC switching of the present invention consists of a primary H-bridge circuit, a DC capacitor bridge arm including a neutral point, an AC switch circuit, and a secondary Side half bridge circuit, 1 LLC resonant cavity sharing split resonant capacitor and 1 isolation transformer.

The primary side H-bridge circuit includes two MOSFET tubes, which are S1-S4 respectively; the DC capacitor bridge arm including the neutral point has capacitors C1 and C2. The D poles of the MOSFET tubes S1 and S3 and one end of the capacitor C1 are connected to the input positive bus, the S poles of the MOSFET tubes S2 and S4 and one end of the capacitor C2 are connected to the input sub-bus, the S pole of the MOSFET tube S1 and the D pole of the MOSFET tube S2 form the original The midpoint of the left half-bridge on the side, the S pole of MOSFET S3 and the D pole of MOSFET S4 form the midpoint of the right half-bridge on the primary side, and the other end of the capacitor C1 and the other end of the capacitor C2 form the midpoint of the capacitor string.

The D pole of the MOSFET tube Ss1 and one end of the capacitor Cr1 are connected to the output positive bus, the S pole of the MOSFET tube Ss2 and the one end of the capacitor Cr2 are connected to the output sub-bus, the S pole of the MOSFET tube Ss1 and the D pole of the MOSFET tube Ss2 form a secondary side half-bridge circuit. The other end of the capacitor Cr1 and the other end of the capacitor Cr2 form the midpoint of the resonant capacitor string.

The circuit of the LLC resonant cavity includes a resonant inductance Lr1, a resonant capacitor Cr1, a resonant capacitor Cr2, and an excitation inductance Lm1 of the isolation transformer T1. The same-named end of the primary side of the isolation transformer T1 is connected to the midpoint of the left half-bridge circuit of the primary side H-bridge, The non-identical end of the primary side of the isolation transformer T1 is connected to the midpoint of the right half-bridge circuit of the H-bridge on the primary side; the same-named end of the secondary side of the isolation transformer T1 is connected to one end of the resonant inductor Lr1, and the other end of the resonant inductor Lr1 is connected to the secondary side of the half-bridge circuit. The midpoint of the MOSFET tube Ss1 and the MOSFET tube Ss2, and the non-identical end of the secondary side of the isolation transformer T1 is connected to the midpoint of the resonant capacitor strings Cr1 and Cr2.

The AC switch circuit includes 2 MOSFET tubes, which are respectively MOSFET tube S5 and MOSFET tube S6, the D pole of MOSFET tube S5 is connected to the midpoint of capacitor C1 and capacitor C2, and the S pole of MOSFET tube S5 is connected to MOSFET tube S6. S pole, D pole of MOSFET S6 is connected to the midpoint of the left half bridge circuit of the primary side H bridge.

The excitation inductance Lm1 of the isolation transformer T1 is a parasitic characteristic parameter of the transformer itself, and does not need to be separately set outside the transformer.

As shown in Figure 2 and Figure 3, in the present invention, the principle of switching between half-bridge and full-bridge modes is as follows: when operating in half-bridge mode, the driving signals of MOSFET tube S5 and MOSFET tube S6 are normally on, and the MOSFET tube is in a normally-on state. The driving signals of S1 and MOSFET S2 are blocked; when running in full-bridge mode, the driving signals of MOSFET S5 and MOSFET S6 are in a blocking state, the driving signals of MOSFET S3 and MOSFET S4 are complementary, and MOSFET S3 and MOSFET Tube S1 has a certain phase shift angle.

When the converter of the present invention operates in LLC mode, if the small dead time is ignored, the PWM signal with the frequency change is used to control the MOSFET devices in the primary side H-bridge circuit or the secondary side half-bridge circuit to be turned on alternately . According to the output voltage feedback, the output voltage closed-loop controller is used to adjust the switching frequency and the phase shift angle between S1 and S3 in real time to achieve precise control of the output voltage. As shown in Figure 2, when the converter operates in positive power LLC mode, the power device MOSFETs S3-S4 or MOSFETs S1-S4 on the energy side are controlled by a PWM signal with a 50% duty cycle and a changing frequency. MOSFET tube Ss1 and MOSFET tube Ss2 are also controlled by PWM signal corresponding to 50% duty cycle and frequency change, but MOSFET tube Ss1 and MOSFET tube Ss2 operate in synchronous rectifier mode, that is, MOSFET tube Ss1 and MOSFET tube Ss2 are only tracking MOSFET tubes S1 and MOSFET tube S2 signal, and there is a dead zone; if the power is reversed, MOSFET tube Ss1 and MOSFET tube Ss2 are controlled by PWM signal with 50% duty cycle and frequency change, MOSFET tubes S3-S4 or MOSFET tubes S1-S4 operate in synchronous rectifier mode.

If the converter of the present invention ignores the tiny dead time, as shown in Figure 4, when the converter operates in full-bridge mode, the forward power and when the current is positive, the resonant inductor Lr1, the resonant capacitor Cr2 and the resonant capacitor are Cr1 participates in the resonance, the power supply provides energy to the primary side of the isolation transformer through MOSFET tube S1 and MOSFET tube S4, so the energy is transferred to the secondary side of the isolation transformer, and the secondary side current starts from the same name terminal of the isolation transformer T1 and passes through the resonant inductor Lr1 and MOSFET tube Ss1 , The resonance capacitors Cr1 and Cr2, the capacitor C3 and the load return to the non-identical end of the isolation transformer T1. As shown in Figure 5, when the forward power is negative and the current is negative, the resonant inductor Lr1, the resonant capacitor Cr2 and the resonant capacitor Cr1 participate in the resonance, and the power supply provides energy for the primary side of the isolation transformer T1 through the MOSFET tube S2 and the MOSFET tube S3, Therefore, the energy is transferred to the secondary side of the isolation transformer T1, and the secondary side current starts from the non-synonymous end of the isolation transformer T1 and returns to the same-named end of the isolation transformer T1 through the MOSFET tube Ss2, the capacitor C3 and the load, the resonant capacitors Cr1 and Cr2, and the resonant inductor Lr1. Similarly, in LLC operation mode and reverse power flow, the drive signal of MOSFET tube Ss1 and MOSFET tube Ss2 are complementary to realize, the MOSFET tubes S1-S4 of the primary side work in synchronous rectification mode, and the power flow transfer path is similar to the above Figure 4, Figure 5.

When the converter of the present invention operates in the half-bridge mode, the forward power and the current are positive, as shown in FIG. 6 , since the MOSFET tube S5 and the MOSFET tube S6 are in the conducting state, the MOSFET tube S1 and the MOSFET tube S2 are in the blocking state , the power supply provides energy for the primary side of the isolation transformer through the MOSFET tube S4 and the capacitor C2, so the energy is transferred to the secondary side of the isolation transformer, and the secondary side current starts from the same name terminal of the isolation transformer T1 and passes through the inductor Lr1, the MOSFET tube Ss1, the capacitor C3 and the load. , The resonance capacitors Cr1 and Cr2 return to the non-identical end of the isolation transformer T1. When the forward power is negative and the current is negative, as shown in Figure 7, since the MOSFET tube S5 and the MOSFET tube S6 are in the conducting state, the MOSFET tube S1 and the MOSFET tube S2 are in the blocking state, and the power supply is the isolation transformer through the MOSFET tube S3 and the capacitor C1. The primary side of T1 provides energy, so the energy is transferred to the secondary side of the isolation transformer T1. The secondary side current starts from the non-identical end of the isolation transformer T1 and returns to the isolation through the MOSFET tube Ss2, the capacitor C3 and the load, the resonant capacitors Cr1 and Cr2, and the inductor Lr1. Transformer T1 has the same name terminal.

The isolation transformer transformation ratio of the converter of the present invention is n:1. When the power is forward, the ratio of the product of Uo and n to the actual input value Ui is between 0.5-0.75; or when the power is reversed, the ratio of the reference value of the input Ui to the product of Uo and n is between 0.5-0.75 time, the converter operates in half-bridge mode. When the above ratios are at other values of 0.75-1.3, the converter operates in full-bridge mode.

Claims (7)

1. A wide-voltage range LLC converter based on AC switching, is characterized in that: its internal circuit comprises 1 primary side H bridge circuit, 1 DC capacitor bridge arm comprising neutral point, 1 AC switch circuit, 1 secondary half bridge circuit, 1 LLC resonant cavity sharing split resonant capacitor and 1 isolation transformer; The primary side H bridge circuit and the DC capacitor bridge arm including the neutral point are respectively connected to both ends of the input power supply; The primary side H-bridge circuit is constructed by 4 MOSFET tubes; the secondary side half-bridge circuit is constructed by 2 MOSFET tubes; The LLC resonant cavity sharing the split resonant capacitor is composed of a resonant inductance, two split resonant capacitors and the excitation inductance of the isolation transformer; The primary side of the isolation transformer with the same name is connected to the left half-bridge midpoint of the primary side H-bridge circuit, the primary side of the isolation transformer is not connected to the right half-bridge midpoint of the primary side H-bridge circuit, and the AC switch is connected to the primary side H. The left half-bridge of the bridge circuit and the neutral point of the DC capacitor bridge arm; the primary side of the isolation transformer with the same name is connected to the left half-bridge midpoint of the primary H-bridge circuit; the secondary side of the isolation transformer with the same name is connected to the corresponding end of the LLC resonant cavity resonant inductor , the other end of the resonant inductor is connected to the midpoint of the secondary half-bridge; the secondary side of the isolation transformer is not terminated with the same name as the midpoint of the split resonant capacitor string; The AC switch circuit is composed of two MOSFETs in reverse series; The DC two ends of the secondary side half-bridge circuit and the split resonance capacitor string are respectively connected with the output DC two ends, and the output DC two ends are connected in parallel with the output capacitor and the equivalent load resistance. 2 . The wide-voltage range LLC converter based on AC switching according to claim 1 , wherein the primary side H-bridge circuit and the secondary side half-bridge circuit of the converter are controlled by a high frequency of 50% duty cycle. 3 . PWM signal control, the high-frequency PWM signal is used to control the MOSFET transistors in the primary side H-bridge circuit and the secondary side half-bridge circuit to be turned on alternately. 3. The wide voltage range LLC converter based on AC switching according to claim 2, is characterized in that: when the primary side H-bridge circuit applies PWM signal, the secondary side half-bridge circuit operates in synchronous rectification to realize LLC power forward mode; when the secondary side half-bridge circuit applies PWM signal, the primary side H-bridge circuit operates in synchronous rectification to realize LLC power reverse mode. 4 . The wide voltage range LLC converter based on AC switching according to claim 1 , wherein the transformation ratio of the isolation transformer is n:1, wherein n is greater than 0. 5 . 5. The wide voltage range LLC converter based on AC switching according to claim 3, characterized in that: when the power is positive, the voltage gain is defined as the product of the output voltage and the transformation ratio n divided by the input voltage; the power is negative When , the voltage gain is defined as the product of the input voltage divided by the output voltage and the transformation ratio n; the range of the voltage gain is 0.5-1.3. 6. The wide-voltage range LLC converter based on AC switch switching according to claim 3, characterized in that: when the AC switch circuit is blocked, 4 MOSFETs of the primary H-bridge circuit work in full-bridge mode; During operation, the left half-bridge circuit of the primary side H-bridge is blocked, and the two MOSFETs of the right half-bridge circuit of the primary side H-bridge work in the half-bridge mode. 7 . The wide voltage range LLC converter based on AC switching according to claim 6 , wherein: when the voltage gain is at 0.5-0.75, the converter operates in half-bridge mode; when the voltage gain is at 0.75-1.3 , the converter operates in full-bridge mode.

Images