CN201134750Y - Single-stage LLC series resonant AC/DC converter - Google Patents

Abstract

A single-stage LLC series resonant AC/DC converter, including an input filter voltage divider circuit (1), a rectifier circuit (2), a power factor (PFC) correction control circuit (3) and an LLC series resonant DC/DC converter ( 4). Its characteristic is that the filter capacitor of the input filter voltage divider circuit uses two capacitors in series, which not only filters but also divides the input voltage equally, and is connected to the AC input end of the rectifier circuit. The power factor (PFC) correction control circuit uses an inductor (Lr ) and a capacitor (Cr) in series, one end of the series connection is connected to the midpoint of the two input voltage dividing capacitors, and the other end is connected to the midpoint of the two inverter switches of the LLC series resonant DC/DC converter. The converter adopts frequency control mode. This converter not only has all the advantages of the LLC series resonant DC/DC converter, but also has a high power factor close to 1, the input current meets the IEC61000-2-3 standard, and, when the input AC voltage is 180-265Vrms, the load is 10 % to 100%, the DC bus voltage is lower than 450V; the utility model has good application prospects in the fields of small and medium power computer power supplies, flat panel TVs, VCDs, DVDs and other power supplies.

Description

Single-stage LLC series resonant AC/DC converter

technical field

The utility model relates to a single-stage LLC series resonant AC/DC converter. Specifically, it is a high power factor AC/DC converter with a single-stage PFC+LLC DC/DC series resonant converter, which belongs to the technical field of electric energy conversion and control.

Background technique

The half-bridge LLC series resonant DC/DC converter disclosed in Chinese patent CN 136878A (see Figure 1), the converter has two resonant characteristic frequencies: one is the resonant frequency fs formed by capacitors Cs and Ls, $f_S=1/2\mathrm{\&pi;}\sqrt{L_S{C}_S},$ The other is the resonant frequency fm formed by capacitor Cs and Ls+Lm, $f_m=1/2\mathrm{\&pi;}\sqrt{(L_S+L_m)C_S},$ Where fm<fs, when the operating frequency of the converter is greater than fm, the converter has the excellent performance of zero-voltage (ZVS) soft switching of the switching tube, high efficiency and low EMI in the full load and full input voltage range, making the converter The converter is very suitable for occasions with high efficiency and high power density. However, in actual application, in order to improve the power factor and reduce the harmonic content of the input current, a power factor correction (PFC) link is usually added. The advantages of this scheme are: high power factor and fast output voltage regulation , but the disadvantages are: two sets of switches and control circuits are required, many components, high cost, and high power consumption. In order to solve the above problems, a single-stage AC/DC converter that integrates the PFC stage and the DC/DC converter is usually used. Currently, there are two typical single-stage high power factor LLC series resonant AC/DC converter technologies:

One is a boost PFC+LLC series resonant DC/DC single-stage AC/DC converter proposed by the Department of Electrical Engineering, Tsinghua University, Taiwan. The problem with this converter is: Since the DC bus voltage is greater than twice the maximum input voltage value at light load and high input voltage, the range of the effective value of the AC input voltage for this converter is 110±20% V (The reference is: Industrial Technology, 2006.ICIT 2006.IEEE International Conference on) It cannot meet the requirement that the effective value range of the AC input voltage is 180-265V.

The second is the boost PFC+three-level LLC series resonant AC/DC converter proposed by the Power Electronics Application Research Office of the Department of Electrical and Computer Engineering, Queen's University, Canada. The number of switching tubes is twice that of the single-level LLC resonant converter, and the structure is complex and the cost is high. (References are: Applied Power Electronics Conference and Exposition, 2006. APEC. Twenty-First Annual IEEE Volume, Issue, 19-23 March 2006 Page(s): 6pp.-)

Contents of the invention

The purpose of this utility model is to provide a DC/DC converter that has all the advantages of LLC series resonant DC/DC converter, but also has a high power factor close to 1, meets the input current of IEC61000-2-3 standard, and has a lower DC bus Voltage, wide input voltage range, low-cost single-stage LLC series resonant AC/DC converter.

The single-stage LLC series resonant AC/DC converter of the utility model is composed of an input filter voltage divider circuit, a power factor (PFC) correction control circuit, a rectification circuit and an LLC series resonant DC/DC converter. It is characterized in that the capacitor of the input filter voltage divider circuit is composed of two capacitors in series, and the power factor (PFC) correction circuit uses an inductance and a capacitor in series, and realizes power factor correction in a resonant mode. The resonant frequency is fr, and the inductance and One end of the capacitor connected in series is connected to the midpoint of the capacitor of the input filter voltage divider circuit, and the other end is connected to the midpoint of the inverter switch of the LLC series resonant DC/DC converter. In addition, the LLC series resonant DC/DC converter The filter voltage dividing capacitor is not only used as a power supply capacitor for the inverter, but also as an energy storage capacitor for power factor correction.

The control method of the utility model is: the driving signal applied to the two switches of the LLC resonant circuit is a complementary signal with a constant duty ratio of 50%, and the frequency of the driving signal is changed to adjust the output voltage, the DC bus voltage and the output voltage of the converter. power. The working range of the driving signal frequency f is fmin-fs, and the value range of fr is: fm<fr<fmin.

The beneficial effects of the utility model are: the use of a single-stage circuit realizes power factor correction close to 1 and high-efficiency power conversion, and the DC bus voltage is lower than 450V, and all the advantages of the LLC series resonant DC/DC converter are guaranteed. The utility model has good application prospects in the fields of small and medium power computer power supplies, flat panel TVs, VCDs, DVDs and other power supplies.

Description of drawings

Fig. 1 is a circuit diagram of a known LLC series resonant DC/DC converter;

Fig. 2 is the circuit diagram of the utility model single-stage LLC series resonant AC/DC converter;

Fig. 3 is the typical operating waveform of the single-stage LLC series resonant AC/DC converter of the utility model;

Fig. 4 is the equivalent circuit diagram of the utility model single-stage LLC series resonant AC/DC converter in stage 1;

Fig. 5 is the equivalent circuit diagram of the utility model single-stage LLC series resonant AC/DC converter in stage 2;

Fig. 6 is the equivalent circuit diagram of the utility model single-stage LLC series resonant AC/DC converter in stage 3;

Fig. 7 is the equivalent circuit diagram of the utility model single-stage LLC series resonant AC/DC converter in stage 4;

Fig. 8 is the equivalent circuit diagram of the utility model single-stage LLC series resonant AC/DC converter in stage 5;

Fig. 9 is the equivalent circuit diagram of the utility model single-stage LLC series resonant AC/DC converter in stage 6;

Fig. 10 is the equivalent circuit diagram of the utility model single-stage LLC series resonant AC/DC converter in stage 7;

Fig. 11 is the equivalent circuit diagram of the utility model single-stage LLC series resonant AC/DC converter in stage 8;

Fig. 12 is the equivalent circuit diagram of the utility model single-stage LLC series resonant AC/DC converter in stage 9;

Fig. 13 is the equivalent circuit diagram of the utility model single-stage LLC series resonant AC/DC converter in stage 10;

Fig. 14 is a block diagram of the actual application of the single-stage LLC series resonant AC/DC converter in the liquid crystal TV power supply of the utility model.

Detailed ways

FIG. 2 is a circuit diagram of a single-stage LLC series resonant AC/DC converter of the present invention. The converter includes an input filter voltage divider circuit (1), a power factor (PFC) correction control circuit (2), a rectification circuit (3) and an LLC series resonant DC/DC converter (4). In the illustration, the input filter voltage divider circuit (1) is composed of an inductor Lin and two equivalent capacitors Cin connected in series. After the two equivalent capacitors Cin are connected in series, the upper end is connected to the inductor Lin and the bridge rectifier circuit (3) AC input terminal ( x ₁ ) confluence, the lower end of the two equivalent capacitors Cin connected in series with the bridge rectifier circuit (3) the other end of the AC input (x ₂ ), the AC voltage source N terminal confluence, the front end of the inductor Lin and the AC input voltage source L Connected to the terminals, two equal-value capacitors Cin are used to filter the high-frequency components of the input current and generate two voltage sources that are only half of the input voltage. The power factor (PFC) correction control circuit (2) is composed of an inductor (Lr) and a capacitor (Cr) in series. One end of the series connection is connected to the midpoint of the input voltage dividing capacitor Cin, and the other end is connected to the LLC series resonant DC/DC The source of the inverter switch S1 and the drain of S2 of the converter are connected to realize power factor correction in a resonant mode. The rectifier circuit (3) is connected into a bridge form by four diodes D1, D2, D3 and D4. The LLC series resonant DC/DC converter (4) consists of two equivalent filter capacitors C1, C2, inverter switches (S1, S2), resonant circuits (Cs, Ls, Lm), isolation transformer T, output rectification filter circuit and Composed of a frequency controller to achieve high-efficiency DC/DC conversion, the filter voltage dividing capacitors C1 and C2 of the LLC series resonant DC/DC converter are not only used as power supply capacitors for the inverter, but also as energy storage capacitors for power factor correction.

The specific working process of the utility model single-stage LLC series resonant AC/DC converter is as follows. In the following analysis, the AC voltage source expression of the converter is _Vin = V _m sin (2πf _L t), where f _L and V _m are the frequency and amplitude of the input voltage, respectively. In a steady state, the DC bus voltage V _d of the LLC series resonant DC/DC converter is greater than the input voltage amplitude V _m . One switching cycle of the converter is divided into 10 stages. When the input power is in the positive half cycle, the 10 equivalent circuits shown in Fig. 4-13 are respectively shown in Fig. 3. The corresponding working waveform is shown in Fig. 3. The principles are described as follows:

(1) Phase 1: t _o ~ t ₁ (the equivalent circuit is shown in Figure 4). At time t _o , both S1 and S2 are turned off, the resonant current is and ir charge the body capacitance CS2 of S2, and the drain-source voltage VDS2 of S2 rises from zero. Therefore, the turn-off of S2 is zero-voltage turn-off. The circuit resonant current discharges the body capacitance CS1 of S1, and the drain-source voltage VDS1 of S1 begins to drop. When VDS1 drops to zero, the body diode DS1 of S1 conducts, and the resonant current ir charges C1 and C2 through D4, two Cin, and DS1 , transfer the energy stored in Lr and Cr to C1 and C2, the voltage Vab at both ends of Lr and Cr is -Vd+Vi/2, and the resonant current is charges C1 through DS1, and the resonant circuit Ls and Cs transfer power to the load. The stage ends until the resonant current is to zero.

(2) Phase 2: t ₁ ~t ₂ (the equivalent circuit is shown in Figure 5). Part of the resonant current ir continues to charge C1 and C2 through D4, two Cin and DS1, and the remaining part flows through Ls and Cs, and the resonant circuit Ls and Cs output power to the load. The voltage Vab at both ends of Lr and Cr at this stage is -Vd+ Vi/2, until the resonant current ir is equal to is.

(3) Stage 3: t ₂ ~t ₃ (the equivalent circuit is shown in Figure 6). At time _t2 , S1 conducts with zero voltage, the resonant current is flows through S1, and the resonant circuits Ls and Cs output power to the load. And the resonant current ir continues to charge C2 through Ls, Cs, D4, and two Cins. At this stage, the voltage Vab across Lr and Cr is -Vd+Vi/2.

(4) Stage 4: t ₃ ˜t ₄ (the equivalent circuit is shown in FIG. 7 ). At the time _t3 , the resonant current is still flows through S1, ir is reversed, and rises sinusoidally from zero at the resonant frequency fr, and passes through D1, and the two Cin also flow through S1. At this stage, the resonant circuit Lr and Cr start from the power To absorb power, the voltage Vab across Lr and Cr is -Vi/2, and the resonant circuit Ls and Cs output power to the load.

(5) Phase 5: t ₄ ˜t ₅ (the equivalent circuit is shown in FIG. 8 ). At time _t4 , the resonant current is equal to the current of the excitation inductance Lm, the output side is completely separated from the resonant circuit, and the resonant circuit Ls and Cs do not output power to the load. The resonant circuit Lr and Cr still flow through D1 and two Cin through S1 to absorb power from the power supply, and the Vab voltage at both ends of Lr and Cr is still -Vi/2. Until _t5 , S1 is turned off, and the next half of the working cycle begins.

(6) Stage 6: t ₅ ˜t ₆ (the equivalent circuit is shown in FIG. 9 ). At time _t5 , S1 is turned off. Since the resonant current is and ir cannot change suddenly, it starts to charge the body capacitance CS1 of S1 and discharge the body capacitance CS2 of S2. The drain-source voltage VDS2 of S2 begins to drop. When VDS2 drops to zero, The body diode DS2 of S2 is turned on, and the resonant current ir charges C1 and C2 through D1, DS2 and two Cin, and transfers the energy stored in Lr and Cr to C1 and C2, and the voltage Vab at both ends of Lr and Cr is Vd-Vi/ 2. The resonant current is charges C2 through DS2, and the resonant circuits Ls and Cs transmit power to the load. This stage ends until the resonant current is reaches zero.

(7) Stage 7: t ₆ ˜t ₇ (the equivalent circuit is shown in FIG. 10 ). Part of the resonant current ir continues to charge C1 and C2 through D1, DS2 and two Cins, and the rest flows through Ls and Cs, and the resonant circuit Ls and Cs output power to the load. The voltage Vab at both ends of Lr and Cr is still Vd- Vi/2, until the resonant current ir is equal to is.

(8) Stage 8: t ₇ ˜t ₈ (the equivalent circuit is shown in FIG. 11 ). At time _t7 , S2 conducts with zero voltage, C2 discharges to the resonant circuit Ls, Cs, the resonant current is flows through S2, and the resonant circuit Ls, Cs outputs power to the load. The resonant current ir continues to charge C2 through Ls, Cs, D1, and two Cins, and the voltage Vab at both ends of Lr and Cr is still Vd-Vi/2. This mode ends until the resonant current ir reaches zero.

(9) Stage 9: t ₈ ˜t ₉ (the equivalent circuit is shown in FIG. 12 ). At time _t8 , the resonant current is still flows through S2, ir is reversed, through D4, and the two Cin also flow through S2. At this stage, the resonant circuit Lr and Cr absorb power from the power supply, and the voltage Vab at both ends of Lr and Cr is Vi/2, the resonant circuit Ls, Cs output power to the load.

(10) Stage 10: t ₉ ˜t ₁₀ (the equivalent circuit is shown in FIG. 13 ). At time _t9 , the resonant current is equal to the current of the excitation inductance Lm, the output side is completely separated from the resonant circuit, and the resonant circuit Ls and Cs do not output power to the load. The resonant circuit Lr and Cr still flow through D4 and two Vi/2 through S2 to absorb power from the power supply, and the voltage Vab at both ends of Lr and Cr is still Vi/2. Until time t ₁₀ , S2 is turned off.

From the analysis of the above 10 working stages, the switches S1 and S2 are both working in the ZVS state; the voltage Vab applied to the resonant circuit Lr and Cr varies between Vd-|Vin|, so that the resonant current ir of a switching cycle The average value of depends on Vin; in all stages, regardless of the direction of the resonant current ir, there is always ir/2 resonant current flowing from the power supply Vin, therefore, the input current i _in follows the input voltage and has the same phase, the expression of i _in The formula is as follows:

${\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\sqrt{\frac{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}}{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}}}}{{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; f</span>}}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}}{\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; )</span>}\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; -</span>{<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}$

The actual application block diagram of the utility model in LCD TV power supply is shown in Figure 14, the input voltage is 180Vac-265Vac, and the output DC voltage is: 30V/1A; 24V/6A; 12V/3A. The main parameters of the circuit are shown in Table 1

Table 1 main parameters of the circuit

component value Lin 1mH Cin 2uF Lr 113uH Cr 66nF Ls 113uH Cs 22nF Lm 818uH S1, S2 IRFP450

Claims (4)

1. Single-stage LLC series resonant AC/DC converter, including: input filter voltage divider circuit (1), power factor (PFC) correction control circuit (2), rectification circuit (3) and LLC series resonant DC/DC converter (4); -Input filter voltage divider circuit (1), composed of an inductor Lin and two equivalent capacitors Cin in series, the upper end of the two equivalent capacitors Cin is connected in series with the inductor Lin, bridge rectifier circuit (3) AC input terminal (x ₁ ) Junction, the lower end of the two equivalent capacitors Cin connected in series with the bridge rectifier circuit (3) the other end of the AC input (x ₂ ), the N end of the AC voltage source, the front end of the inductor Lin and the L end of the AC input voltage source Connected, two equivalent capacitors Cin are used to filter the high-frequency component of the input current and generate two voltage sources that are half of the input voltage; -The power factor (PFC) correction circuit (2) includes: a correction inductor (Lr), a correction capacitor (Cr), the two are connected in series, one end of the series connection is connected to the midpoint of the input voltage dividing capacitor, and the series connection The other end is connected to the source of the inverter switch S1 of the LLC series resonant DC/DC converter; - a rectification circuit (3) consisting of four diodes for rectifying the input voltage into a pulsating direct current; -LLC series resonant DC/DC converter (4) includes: two equivalent bus filter capacitors C1, C2, inverter switches (S1, S2), resonant circuits (Cs, Ls, Lm), isolation transformer T, output rectifier filter circuit and frequency controller. 2. The single-stage LLC series resonant AC/DC converter according to claim 1, wherein the resonant frequency formed by the capacitor Cr and the inductance Lr is fr, and the resonant frequency formed by the capacitor Cs and the inductance Ls is fs, The resonant frequency formed by the capacitor Cs, Ls and Lm is fm, where fm<fs. 3. The single-stage LLC series resonant AC/DC converter according to claim 1, characterized in that the output power is controlled by controlling the frequency of the inverter switches (S1, S2), and the operating range of the frequency f is fmin˜fs. 4. The single-stage LLC series resonant AC/DC converter according to claim 1, the range of fr is: fm<fr<fmin.

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