CN103138580B

CN103138580B - DC-to-DC converter, power converter and control method thereof

Info

Publication number: CN103138580B
Application number: CN201110393877.8A
Authority: CN
Inventors: 忽培青; 金红元; 甘鸿坚; 应建平
Original assignee: Delta Electronics Shanghai Co Ltd
Current assignee: Delta Electronics Shanghai Co Ltd
Priority date: 2011-12-01
Filing date: 2011-12-01
Publication date: 2015-08-19
Anticipated expiration: 2031-12-01
Also published as: CN103138580A

Abstract

The invention provides a kind of DC-to-DC converter, power converter and control method thereof.This DC-to-DC converter comprises output circuit, square-wave generator, resonant slots, detecting unit and control unit.Square-wave generator has a brachium pontis, and this brachium pontis comprises one first switch and second switch electric property coupling each other.Detecting unit is for detecting the state of load, when the state of load be underloading or unloaded time, control unit controls the keying of first, second switch to convert an input voltage at least one square wave to resonant slots with a Wave-wide regulation controlled electric pattern, the complementary duty cycle of the duty ratio of second switch and this first switch, makes the gain of DC-to-DC converter be greater than 1.Adopt the present invention, work in switch batch (-type) PWM control mode by underloading with time unloaded, therefore effectively can reduce the master switch number of times of converter within the unit interval, effectively improve light-load efficiency, meet the requirement of loss during restriction underloading.

Description

DC-DC converter, power converter and control method thereof

Technical Field

The present invention relates to power electronics technologies, and in particular, to a dc-dc converter, a power converter, and a control method thereof.

Background

In recent years, due to the widespread implementation of energy saving movement worldwide, more and more customers require that the switching mode converter can achieve high conversion efficiency in a wide load range, so that high requirements are also made on the efficiency of the converter under light load and no load. In this regard, international energy organizations (IEA), countries and organizations such as the united states and europe have or are making relevant standards to limit the losses of electrical products such as switching mode converters during light and no load.

The series resonance DC/DC converter adopts resonance conversion technology, can realize zero voltage switching-on of the switch tube, has small power loss and high efficiency when being fully loaded. Fig. 1 is a basic form of an LLC series-resonant DC/DC converter. The topology generally adopts a frequency conversion modulation mode, the output voltage is stabilized by changing the working frequency of the rectangular wave, and the duty ratio is 50%, as shown in fig. 2. The relationship between the power output voltage gain M and the working frequency is as follows:

M = \frac{2 n * V_{o}}{V_{in}} = \frac{1}{\sqrt{{1 + \frac{L_{s}}{L_{m}} [1 - {(\frac{f_{s}}{f})}^{2}]}^{2} + Q^{2} {(\frac{f}{f_{s}} - \frac{f_{s}}{f})}^{2}}}

wherein the resonant frequency

Wherein L is_sIs a resonant inductance value, L_mFor transformer exciting inductance value, C_sIs the resonant capacitance value, f is the rectangular wave working frequency value, n is the primary and secondary side turn ratio of the transformer, R_LIs the output load resistance value.

As shown in fig. 3, the operation mode of this control mode at light load is: the load condition is detected, the operating frequency of the rectangular wave of the series resonant converter is controlled to increase as the load becomes smaller, and the operating frequency is maintained after the frequency increases to a certain value, and the switching intermittent control mode (i.e., hiccup mode) is entered.

The existing method for improving the light load efficiency comprises the following steps:

1. the operating frequency of the converter is reduced. Since the switching loss and the driving loss of the power device occupy a large proportion of the loss at the time of light load, reducing the switching frequency can effectively reduce these losses, thereby reducing the light load loss. The method is suitable for PWM circuits.

2. The switch operates intermittently. By detecting the voltage error amplification signal, the converter is operated intermittently under light load, so that the total switching times of the converter in unit time can be reduced, and the standby loss can be reduced.

The first method is not applicable since the output voltage cannot be effectively controlled in the resonant circuit by merely lowering the operating frequency; the second method can improve the light load efficiency to a certain extent, but when the working frequency of the converter is higher, the gain is lower (less than 1) (as shown in fig. 4), so the transmission energy in each working period is lower, the total switching times are still too much, the switching loss and the driving loss are still higher, and the standard that the light load loss is more and more limited cannot be reached.

Therefore, it is obvious that the above-mentioned existing control mechanism still has inconveniences and disadvantages, and needs to be further improved. In order to solve the above problems, the related art has not been able to make a thorough effort to solve the above problems, but has not been developed in an applicable manner for a long time. Therefore, how to further improve the light load efficiency is one of the important research and development issues, and is also an urgent need for improvement in the related art.

Disclosure of Invention

In order to meet the strict requirements of light load and high efficiency, the invention provides a novel direct current-direct current converter, a power converter and a control method thereof.

According to an embodiment of the present invention, a dc-dc converter is provided, which includes a load, a rectangular wave generator, a resonant tank, a detection unit, and a control unit. The output circuit is provided with a load, the resonant tank is electrically coupled with the output circuit, and the rectangular wave generator is electrically coupled with the resonant tank. The rectangular wave generator has at least one bridge arm, and the bridge arm comprises a first switch and a second switch which are electrically coupled with each other. The detection unit is used for detecting the state of the load, and when the state of the load is light load or no load, the control unit controls the on and off of the first switch and the second switch in a wave width modulation mode so as to convert an input voltage into at least one rectangular wave to the resonant tank. The duty ratio of the first switch is in a first preset interval or a second preset interval, and the duty ratio of the second switch is complementary with the duty ratio of the first switch, so that the gain of the DC-DC converter is larger than 1.

When the load is in a light load or no load state, the operating frequency of the rectangular wave is higher than the resonant frequency of the resonant tank.

When the load is in a heavy load or full load state, the control unit controls the rectangular wave generator in a frequency modulation mode.

The duty ratio of the first switch is between a first preset upper limit value less than 50% and a first preset lower limit value, and the duty ratio of the second switch is between a second preset lower limit value greater than 50% and a second preset upper limit value. Or the duty ratio of the second switch is between a first preset upper limit value smaller than 50% and a first preset lower limit value, and the duty ratio of the first switch is between a second preset lower limit value larger than 50% and a second preset upper limit value.

The load includes a resistor.

The output circuit further includes a transformer and a rectifier electrically coupled to the resistor.

The resonant tank is a series resonant circuit or a parallel resonant circuit.

The series resonant circuit is an LC series resonant circuit or an LLC series resonant circuit.

The LLC series resonant circuit includes an exciting inductor, a resonant inductor, and a resonant capacitor connected in series with each other, wherein the exciting inductor is connected in parallel with the transformer.

The excitation inductor, the resonance inductor and the resonance capacitor are connected with the second switch in parallel, the control unit controls the duty ratio of the first switch to be less than 50%, and when the control unit switches on the first switch and switches off the second switch, the transformer transmits energy to the secondary side by virtue of the clamping voltage on the excitation inductor. When the control unit turns off the first switch and turns on the second switch, the transformer cannot transmit energy to the secondary side. The sum of the duty cycle of the first switch and the duty cycle of the second switch is 1, the duty cycle of the first switch is between a first predetermined upper limit value which is less than 50% and a first predetermined lower limit value, and the duty cycle of the second switch is between a second predetermined lower limit value which is greater than 50% and a second predetermined upper limit value.

Or the control unit controls the duty ratio of the first switch to be more than 50%, and when the control unit switches on the first switch and switches off the second switch, the transformer cannot transmit energy to the secondary side. When the control unit closes the first switch and turns on the second switch, the transformer transfers energy to the secondary side by the clamping voltage on the exciting inductor. The sum of the duty cycle of the first switch and the duty cycle of the second switch is 1, the duty cycle of the second switch is between a first predetermined upper limit value which is less than 50% and a first predetermined lower limit value, and the duty cycle of the first switch is between a second predetermined lower limit value which is greater than 50% and a second predetermined upper limit value.

According to another embodiment of the present invention, a power converter is provided, which includes the dc-dc converter, a power factor correction device and an electromagnetic interference filter. The power factor correction device is electrically coupled with the DC-DC converter, and the electromagnetic interference filter is electrically coupled with the power factor correction device. The electromagnetic interference filter is used for receiving an alternating current, and the alternating current is converted by the electromagnetic interference filter and the power factor correction device and then provides the input voltage for the direct current-direct current converter.

When the load state is light load or no load, the power factor correction device reduces the input voltage provided to the DC-DC converter.

When the load state is light load or no load, the power factor correction device is closed.

The power factor correction device comprises a bridge rectifier and a power factor corrector, wherein the power factor corrector is electrically coupled with the bridge rectifier. Alternatively, the power factor correction device comprises a bridgeless power factor corrector.

According to another embodiment of the present invention, there is provided a control method of a power converter, the control method including the steps of: detecting a signal reflecting a state of the load; when the load is in a light load or no-load state, the on-off of a first switch and a second switch on a bridge arm are controlled in a wave width modulation mode to convert an input voltage into at least one rectangular wave to a resonant tank, the duty ratio of the first switch falls in a first preset interval or a second preset interval, and the duty ratio of the second switch is complementary with the duty ratio of the first switch, so that the gain of the power converter is larger than 1.

In the control method, when the load is in a light load or no load state, the working frequency of the rectangular wave is higher than the resonant frequency of the resonant tank.

In the control method, when the load state is heavy load or full load, the rectangular wave is modulated in a frequency modulation mode.

In the control method, the duty ratio of the first switch is between a first preset upper limit value which is less than 50% and a first preset lower limit value, and the duty ratio of the second switch is between a second preset lower limit value which is more than 50% and a second preset upper limit value; or the duty ratio of the second switch is between a first preset upper limit value smaller than 50% and a first preset lower limit value, and the duty ratio of the first switch is between a second preset lower limit value larger than 50% and a second preset upper limit value.

The load comprises a transformer, the resonant tank comprises an excitation inductor, a resonant inductor and a resonant capacitor which are connected in series with each other, wherein the excitation inductor is connected with the transformer in parallel, and the excitation inductor, the resonant inductor and the resonant capacitor are connected with a second switch in parallel, and the control method comprises the following steps: controlling the duty ratio of the first switch to be less than 50%, when the first switch is turned on and the second switch is turned off, the transformer transmits energy to the secondary side by virtue of the clamping voltage on the exciting inductor, and when the first switch is turned off and the second switch is turned on, the transformer cannot transmit energy to the secondary side, wherein the sum of the duty ratio of the first switch and the duty ratio of the second switch is 1, the duty ratio of the first switch is between a first preset upper limit value less than 50% and a first preset lower limit value, and the duty ratio of the second switch is between a second preset lower limit value more than 50% and a second preset upper limit value.

Alternatively, the control method comprises: controlling the duty ratio of the first switch to be more than 50%, when the first switch is closed and the second switch is turned on, the transformer transmits energy to the secondary side by virtue of the clamping voltage on the exciting inductor, and when the first switch is turned on and the second switch is turned off, the transformer cannot transmit energy to the secondary side, wherein the sum of the duty ratio of the first switch and the duty ratio of the second switch is 1, the duty ratio of the second switch is between a first preset upper limit value which is less than 50% and a first preset lower limit value, and the duty ratio of the first switch is between a second preset lower limit value which is more than 50% and a second preset upper limit value.

In the control method, a power factor correction device can be used for receiving an alternating current, and the alternating current is converted by an electromagnetic interference filter and the power factor correction device to provide an input voltage.

When the load state is light load or no load, the input voltage provided by the power factor correction device is reduced. Or, when the load state is light load or no load, the power factor correction device is turned off.

In summary, the technical scheme of the present invention has obvious advantages and beneficial effects compared with the prior art, by operating in the switching intermittent pulse width modulation control mode during light load and no load, the operating frequency is higher than the resonant frequency, but the gain is greater than 1, so that the total switching times of the converter in unit time can be effectively reduced, the light load efficiency can be effectively improved, and the requirement of limiting the loss during light load can be satisfied.

Drawings

The various aspects of the present invention will become more apparent to the reader after reading the detailed description of the invention with reference to the attached drawings. Wherein,

FIG. 1 shows a block diagram of an LLC series resonant DC/DC converter;

FIG. 2 shows conventional LLC series resonant cavity drive waveforms;

FIG. 3 illustrates a conventional LLC series resonant DC/DC converter control scheme;

FIG. 4 shows a gain curve under a conventional LLC series resonant DC/DC converter control mode;

FIG. 5 shows a block diagram of a power converter according to an embodiment of the invention;

FIG. 6 is a block diagram of a power factor correction device according to an embodiment of the present invention;

FIG. 7 is a block diagram of the DC-DC converter shown in FIG. 5 according to an embodiment of the present invention;

FIG. 8 is a circuit diagram of a rectangular wave generator according to an embodiment of the present invention;

fig. 9 is a circuit diagram of a transformer and a rectifier according to an embodiment of the invention;

fig. 10 shows a circuit block diagram of an LLC series resonant converter in accordance with an embodiment of the invention;

FIG. 11 shows a novel high gain control main current voltage waveform (D < 50%);

FIG. 12 shows the circuit operating diagram with S1 turned on (D < 50%);

FIG. 13 shows an equivalent circuit diagram of S1 when it is turned on (D < 50%);

FIG. 14 shows a current diagram for gain calculation;

fig. 15 shows a gain curve for the novel LLC series resonant DC/DC converter control scheme.

[ description of main reference symbols ]

100: DC-DC converter

110: rectangular wave generator

120: resonance tank

130: output circuit

131: transformer and rectifier

140: detection unit

150: control unit

160: power factor correction device

170: electromagnetic interference filter

161: bridge rectifier

162: power factor corrector

163: bridgeless power factor corrector

200: power converter

C_s: resonant capacitor

L_m: excitation inductor

L_s: resonant inductor

R_L: load(s)

Detailed Description

In order to make the present disclosure more complete and complete, reference is made to the accompanying drawings, in which like references indicate similar or analogous elements, and to the various embodiments of the invention described below. However, it will be understood by those of ordinary skill in the art that the examples provided below are not intended to limit the scope of the present invention. In addition, the drawings are only for illustrative purposes and are not drawn to scale.

In the present application, reference to a "coupled with" is intended to generally mean that one element is indirectly coupled to another element through another element or that one element is directly coupled to another element without the other element.

In this application, the articles "a" and "an" may be used broadly to mean "a single or a plurality unless the context specifically indicates otherwise.

As used herein, "about" or "approximately" is used to modify the amount of any slight variation, but such slight variation does not alter the nature thereof. Unless otherwise specified, the range of error for values modified by "about", "about" or "approximately" is generally tolerated within twenty percent, preferably within ten percent, and more preferably within five percent.

The new technical solution proposed by the invention is to meet the strict requirements of light load and high efficiency. As shown in fig. 5, the power converter 200 includes the dc-dc converter 100, the power factor correction device 160 and the electromagnetic interference filter 170. Structurally, the emi filter 170 is electrically coupled to the pfc device 160, and the pfc device 160 is electrically coupled to the dc-dc converter 100. In use, the EMI filter 170 is used to receive an AC power, and the AC power is converted by the EMI filter 170 and the PFC device 160 to provide the input voltage V to the DC-DC converter 100_iTo the dc-dc converter 100.

As shown in fig. 6, the pfc device 160 may be composed of a bridge rectifier 161 and a conventional pfc 162, or may be implemented by a bridgeless pfc 163, but is not limited thereto.

As shown in fig. 7, the dc-dc converter 100 includes a rectangular wave generator 110, a resonant tank 120, an output circuit 130, a detection unit 140, and a control unit 150. Structurally, the rectangular wave generator 110 is electrically coupled to the resonant tank 120, the resonant tank 120 is electrically coupled to the output circuit 130, the output circuit 130 is electrically coupled to the detection unit 140, the detection unit 140 is electrically coupled to the control unit 150, and the control unit 150 is electrically coupled to the rectangular wave generator 110.

The rectangular wave generator 110 may be implemented by a switching device, such as a half-bridge circuit (a), a full-bridge circuit (B) shown in fig. 8. The control unit 150 controls the on/off of the switching device to output a rectangular wave, wherein the amplitude of the rectangular wave is equal to the input voltage, the duty ratio is D, and the frequency is f. Alternatively, in another embodiment, the amplitude of the square wave may be twice the input voltage, and one skilled in the art can flexibly select the amplitude as required.

The output circuit 130 has a load R_LAnd may comprise a resistor, for example. Alternatively, the output circuit 130 may be composed of a transformer, a rectifier 131 and a load R_LThe rectifier 131 is electrically connected to the resistor, and the rectification manner of the rectifier may be full-wave rectification, center-tap rectification, diode rectification, or synchronous rectification, as shown in fig. 9, but is not limited thereto.

The resonant tank 120 may be a series resonant circuit, such as an LC series resonance circuit, an LLC series resonance circuit, or a parallel resonant circuit. Wherein the output circuit 130 is connected in parallel or in series with a certain resonator device, or several resonator devices, in the resonator tank 120.

The control unit 150, as described above, may be implemented in software, hardware and/or firmware. For example, if execution speed and accuracy are paramount, the unit may be essentially hardware and/or firmware-based; if the design flexibility is taken as the primary consideration, the unit basically can be mainly selected by software; alternatively, the unit may employ software, hardware and firmware in conjunction. It should be understood that the above examples are not intended to limit the invention to any particular type of device, and that one skilled in the art can flexibly select the specific configuration of the control unit 150 as desired.

Taking a half-bridge LLC series resonant dc-dc converter as an example, as shown in fig. 10, a rectangular wave generator 110 is electrically coupled to the resonant tank, the rectangular wave generator has at least one bridge arm, and includes a first switch S1 and a second switch S2 electrically coupled to each other. The resonant tank 120 is an LLC series resonant circuit, the three being connected in series, wherein the magnetizing inductor L_mIn parallel with the output circuit 130, a resonant inductor L_sA resonant capacitor C_sAnd excitation inductor L_mThe three are connected in parallel with a second switch S2.

When the dc-dc converter 100 is in operation, the rectangular wave generator 110 converts an input voltage into at least one rectangular wave to the resonant tank 120, and the detection unit 140 is configured to detect a signal reflecting a state of a load, for example, the detection unit 140 detects a signal related to a load current, which may be a primary current signal of a transformer, a secondary current signal of a transformer, or a resonant inductor L in the resonant tank 120_sOr may be a resonant capacitor C_sThe voltage of (c). When the output circuit 130 is in a light load or no load state, the control unit 150 controls the on/off of the first switch S1 and the second switch S2 in a wave width modulation mode to convert an input voltage into at least one rectangular wave to the resonant tank 120, wherein the operating frequency of the rectangular wave is higher than the resonant frequency of the resonant tank, the duty ratio of the first switch S1 falls within a first predetermined interval or a second predetermined interval, and the duty ratio of the second switch S2 is complementary to the duty ratio of the first switch S1, so that the gain of the dc-dc converter is greater than 1.

On the other hand, when the load is in a heavy load or full load state, the control unit 150 controls the square-wave generator 110 in a frequency modulation mode, that is, the output voltage is stabilized by changing the operating frequency of the square-wave, so as to meet the requirement of high efficiency during heavy load.

When the control unit 150 controls the duty ratio D of the first switch S1 to be less than 50%, the novel high-gain control mode is implemented by the following steps:

state 1: when the control unit 150 turns on the first switch S1 and turns off the second switch S2, the resonant capacitor C_sVoltage of D x V_inAnd n is V_o＜(1-D)*V_inAt this time, the resonant capacitor C_sAnd a resonant inductor L_sResonance, L_mThe upper clamping voltage is clamped at n x V_oThe transformer transfers energy to the secondary side.

State 2: when the control unit 150 turns on the second switch S2 and turns off the first switch S1, the voltage D × V on the resonant capacitor Cs_in＜n*V_oWhen the transformer cannot transfer energy to the secondary side due to insufficient voltage, the resonant capacitor Cs is coupled to the resonant inductor and the magnetizing inductance (L)_s+L_m) Resonate together. The main current voltage waveform is shown in fig. 11.

Similarly, when the control unit 150 controls the duty ratio D of the first switch S1 to be greater than 50%, the novel line operation mode of the high-gain control mode is:

state 1: when the control unit 150 turns on the first switch S1 and turns off the second switch S2, the resonant capacitor C_sVoltage of D x V_inAnd n is V_o＞(1-D)*V_inThe transformer cannot transfer energy to the secondary side due to insufficient voltage, and the resonant capacitor C is used_sWith resonant and excitation inductances (L)_s+L_m) Resonate together.

State 2: when the control unit 150 turns on the second switch S2 and turns off the first switch S1, the resonant capacitor C_sVoltage D V of_in＞n*V_oAt this time, the resonant capacitor C_sAnd a resonant inductor L_sResonance, L_mThe voltage on is clamped at n x V_oThe transformer transfers energy to the secondary side.

The novel high gain control modes are: under the light-load intermittent working mode, the purpose of controlling the output voltage is realized by controlling the driving duty ratio and the intermittent time.

The parameters of the LLC series resonant circuit in the novel high-gain control mode are selected as follows:

d is S1 duty cycle, when the value range is 0-0.5, the lower tube S2 duty cycle is (1-D), the value range of D with gain larger than 1 is:

wherein:

<math> <mrow> <mi>θ</mi> <mo>=</mo> <mfrac> <mn>1</mn> <mn>3</mn> </mfrac> <mi>arccos</mi> <mo>[</mo> <mfrac> <mrow> <mn>108</mn> <msub> <mi>fL</mi> <mi>s</mi> </msub> </mrow> <mrow> <msup> <mi>n</mi> <mn>2</mn> </msup> <msub> <mi>R</mi> <mi>L</mi> </msub> <msup> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mfrac> <mn>1</mn> <mi>h</mi> </mfrac> <mo>)</mo> </mrow> <mn>3</mn> </msup> </mrow> </mfrac> <mo>-</mo> <mn>1</mn> <mo>]</mo> <mo>,</mo> </mrow> </math>

and:

\frac{{2 fL}_{s}}{n^{2} R_{L}} < \frac{1}{27} {(1 - \frac{1}{h})}^{3},

h = \frac{L_{s}}{L_{m}} > 1

and when

D = \sqrt[3]{\frac{A}{B} (1 + \sqrt{1 + \frac{A}{B}})} - \sqrt[3]{\frac{A}{B} (1 - \sqrt{1 + \frac{A}{B}})}

In which

A = \frac{{2 fL}_{s}}{n^{2} R_{L}},

B = 1 + \frac{1}{h},

The line gain is maximum.

The reason is as follows:

when D is between 0-0.5, the circuit operation diagram is shown in FIG. 12. The converter transfers energy from input to output in the Stagel stage, the equivalent circuit diagram of which is shown in fig. 13. Since the ripple on the resonant capacitor Cs is small, the currents flowing through the resonant inductor Ls and the magnetizing inductor Lm can be linearized as shown in fig. 14. The voltages and currents on the resonant capacitor Cs, the resonant inductor Ls and the magnetizing inductor Lm can also be calculated by integration. This line gain M can be approximated by calculating the current delivered by the converter as follows:

wherein:

A = \frac{{2 fL}_{s}}{n^{2} R_{L}},

B = 1 + \frac{1}{h}

the gain of the line can of course also be calculated by calculating the energy transmitted by the converter.

Fig. 15 is a graph of the relationship between line gain and duty cycle D at a certain load. When the duty ratio D is within the above-mentioned predetermined range, i.e., the first predetermined section (D1, D3) and the second predetermined section (D4, D2), the line gain is greater than 1. It should be understood that the specific values of the first predetermined lower limit value D1, the first predetermined upper limit value D3, the second predetermined lower limit value D4 and the second predetermined upper limit value D2 may vary with the type of the load RL, and are not a fixed value.

If the gain M is larger than 1Is 2D³+(B-2)D²+A＜0

Let function f (D) 2D³+(B-2)D²+ A, the derivative of the function is f' (D) 6D²+2(B-2) D. When f' (D) is 0, D is 0 or

When D is 0, f (0) ═ a > 0, and when D is 0.5, the upper and lower tube duty cycles are equal, the operating frequency is higher than the resonant frequency, as can be seen from the foregoing discussion, when M < 1, so f (0.5) > 0.

If M > 1, then f (D) < 0. To have f (D) < 0 within a range of 0-0.5, it is necessary to have a point D 'within 0-0.5 such that f' (D ') is 0 and f (D') < 0. And f (D) as shown.

As is clear from D ' e (0, 0.5) and f ' (D ') being 0,

and is

0 < \frac{2 - B}{3} = \frac{1 - \frac{1}{h}}{3} < 0.5,

It can be seen that h > 1. Therefore:

since f (D') < 0, it is preferable that

A < {(\frac{2 - B}{3})}^{3},

Namely, it is

\frac{{2 fL}_{s}}{n^{2} R_{L}} < \frac{1}{27} {(1 - \frac{1}{h})}^{3} .

So whenAnd h > 1, there is an interval within the interval 0-0.5 such that the gain M > 1.

If f (D) is 2D³+(B-2)D²+ A ═ 0, using the cardThe Erdan equation can be solved:

wherein

<math> <mrow> <mi>θ</mi> <mo>=</mo> <mfrac> <mn>1</mn> <mn>3</mn> </mfrac> <mi>arccos</mi> <mo>[</mo> <mfrac> <mrow> <mn>2</mn> <mi>A</mi> </mrow> <msup> <mrow> <mo>(</mo> <mfrac> <mrow> <mn>2</mn> <mo>-</mo> <mi>B</mi> </mrow> <mn>3</mn> </mfrac> <mo>)</mo> </mrow> <mn>3</mn> </msup> </mfrac> <mo>-</mo> <mn>1</mn> <mo>]</mo> <mo>,</mo> </mrow> </math>

A = \frac{{2 fL}_{s}}{n^{2} R_{L}},

B = 1 + \frac{1}{h}

Because of the fact that

Therefore, it is not only easy to use

<math> <mrow> <mi>θ</mi> <mo>&Element;</mo> <mrow> <mo>(</mo> <mn>0</mn> <mo>,</mo> <mfrac> <mi>π</mi> <mn>3</mn> </mfrac> <mo>)</mo> </mrow> <mo>,</mo> </mrow> </math>

Therefore:

<math> <mfenced open='{' close=''> <mtable> <mtr> <mtd> <mn>2</mn> <mi>cos</mi> <mrow> <mo>(</mo> <mi>θ</mi> <mo>-</mo> <mfrac> <mrow> <mn>2</mn> <mi>π</mi> </mrow> <mn>3</mn> </mfrac> <mo>)</mo> </mrow> <mo>-</mo> <mn>1</mn> <mo>&Element;</mo> <mrow> <mo>(</mo> <mo>-</mo> <mn>2,0</mn> <mo>)</mo> </mrow> </mtd> </mtr> <mtr> <mtd> <mn>2</mn> <mi>cos</mi> <mrow> <mo>(</mo> <mi>θ</mi> <mo>+</mo> <mfrac> <mrow> <mn>2</mn> <mi>π</mi> </mrow> <mn>3</mn> </mfrac> <mo>)</mo> </mrow> <mo>-</mo> <mn>1</mn> <mo>&Element;</mo> <mrow> <mo>(</mo> <mo>-</mo> <mn>3</mn> <mo>,</mo> <mo>-</mo> <mn>2</mn> <mo>)</mo> </mrow> </mtd> </mtr> <mtr> <mtd> <mn>2</mn> <mi>cos</mi> <mi>θ</mi> <mo>-</mo> <mn>1</mn> <mo>&Element;</mo> <mrow> <mo>(</mo> <mn>0,1</mn> <mo>)</mo> </mrow> </mtd> </mtr> <mtr> <mtd> </mtd> </mtr> </mtable> </mfenced> </math>

so D₃＜0＜D₁＜D₂。

In summary, when the operating frequency is higher than the resonance frequency, D has a range between 0 and 0.5 such that the gain M > 1 is conditioned by: h is greater than 1, andin this case, the interval D is

Because of the fact that

M (D) = \frac{{2 (1 - D) D}^{2}}{{A + BD}^{2}},

Wherein

A = \frac{{2 fL}_{s}}{n^{2} R_{L}},

B = 1 + \frac{1}{h},

Therefore:

let f (D) be BD³The only real root of +3AD-2A is 0, which can be found by the kardan equation:

D = \sqrt[3]{\frac{A}{B} (1 + \sqrt{1 + \frac{A}{B}})} - \sqrt[3]{\frac{A}{B} (1 - \sqrt{1 + \frac{A}{B}})}

therefore, in the range of 0 to 0.5 when

D = \sqrt[3]{\frac{A}{B} (1 + \sqrt{1 + \frac{A}{B}}) - \sqrt[3]{\frac{A}{B} (1 - \sqrt{1 + \frac{A}{B}})}}

When the temperature of the water is higher than the set temperature,

wherein The line gain M may take a maximum value.

When D ranges between 0.5 and 1, the same method can be used to calculate the range of D when the gain is greater than 1:

wherein:

and:

\frac{{2 fL}_{s}}{n^{2} R_{L}} < \frac{1}{27} {(1 - \frac{1}{h})}^{3},

h = \frac{L_{s}}{L_{m}} > 1

when the line M takes the maximum value, the value of D when the line gain M takes the maximum value can also be calculated by the same method:

D = 1 - \sqrt[3]{\frac{A}{B} (1 + \sqrt{1 + \frac{A}{B}})} + \sqrt[3]{\frac{A}{B} (1 - \sqrt{1 + \frac{A}{B}})},

wherein

A = \frac{{2 fL}_{s}}{n^{2} R_{L}},

B = 1 + \frac{1}{h} .

The novel high gain control mode is used to improve the efficiency of the conventional PFM mode LLC series resonant circuit at light load: the load condition is detected, and the traditional PFM mode is used for controlling during heavy load, so that the efficiency is high; the novel high-gain control mode is used in light load, and the gain is high, so that the circuit action times can be obviously reduced, the loss is reduced, and the light load efficiency is improved.

Novel high gain control modes the control modes for the overall AC/DC converter are: detecting the load condition, wherein the working mode during heavy load is the same as the working mode of the traditional PFC + LLC; during light load, the DC/DC stage operates in a novel high gain control mode, and the gain is high, so that the output voltage of the PFC stage, i.e. the output voltage of the PFC device 160, can be reduced, for example, the control unit 150 reduces the output voltage of the PFC device 160, thereby improving the efficiency of the converter during light load.

Novel high gain control modes the control modes for the overall AC/DC converter are: detecting the load condition, wherein the working mode during heavy load is the same as the working mode of the traditional PFC + LLC; during light load, the DC/DC stage operates in a novel high gain control mode, and the gain is high, so that when the input ac voltage is high, the PFC stage, i.e. the PFC device 160, is turned off, for example, the control unit 150 turns off the PFC device 160, and when the input ac voltage is low, the output voltage of the PFC stage is reduced, thereby improving the converter efficiency during light load.

In summary, another embodiment of the present invention is a control method of the power converter 200, the control method includes the following steps: detecting a load R_LThe state of (1); when the load R_LWhen the state of (1) is light load or no load, the on/off of the first switch S1 and the second switch S2 are controlled in a wave width modulation mode to convert an input voltage into at least one rectangular wave to the resonant tank 120, wherein the operating frequency of the rectangular wave is higher than the resonant frequency of the resonant tank, the duty ratio of the first switch S1 falls within a first predetermined interval or a second predetermined interval, and the duty ratio of the second switch S2 is complementary to the duty ratio of the first switch S1, so that the gain of the power converter 200 is greater than 1.

It should be understood that the above steps, except the specific sequence described above, may be performed simultaneously or partially simultaneously, with the sequence being adjusted according to the actual requirement. As to the hardware devices for implementing these steps, since the above embodiments are specifically disclosed, they are not described in detail.

In the control method, when the load R is_LWhen the state of (1) is heavy load or full load, the rectangular wave is modulated in a frequency modulation mode.

The sum of the duty cycle of the first switch S1 and the duty cycle of the second switch S2 is 1, the duty cycle of the first switch S1 is between a first predetermined upper limit value D1 and a first predetermined lower limit value D3 which are less than 50%, and the duty cycle of the second switch S2 is between a second predetermined lower limit value D4 and a second predetermined upper limit value D2 which are greater than 50%.

Alternatively, the duty cycle of the second switch S2 is between a first predetermined upper limit D1 and a first predetermined lower limit D3 which are less than 50%, and the duty cycle of the first switch S1 is between a second predetermined lower limit D4 and a second predetermined upper limit D2 which are greater than 50%.

In the control method, the EMI filter 170 is used to receive an AC power, and the AC power is converted by the EMI filter 170 and the PFC device 160 to provide an input voltage V_i。

When the load is in a light load or no-load state, the input voltage V provided by the PFC device 160 is reduced_i。

Alternatively, when the load state is light load or no load, the power factor correction device 160 is turned off.

Therefore, the converter works in a switching intermittent pulse width modulation control mode under light load and no load, the working frequency f is higher than the resonant frequency fs, but the gain is greater than 1, so that the total switching times of the converter in unit time can be effectively reduced, the light load efficiency is effectively improved, and the requirement of limiting the loss under light load is met.

Hereinbefore, specific embodiments of the present invention are described with reference to the drawings. However, those skilled in the art will appreciate that various modifications and substitutions can be made to the specific embodiments of the present invention without departing from the spirit and scope of the invention. Such modifications and substitutions are intended to be included within the scope of the present invention as defined by the appended claims.

Claims

1. A dc-dc converter, comprising:

an output circuit having a load;

a resonant tank electrically coupled to the output circuit;

a rectangular wave generator electrically coupled to the resonant tank, the rectangular wave generator having at least one bridge arm including a first switch and a second switch electrically coupled to each other;

a detection unit for detecting a signal reflecting a state of the load; and

a control unit, for controlling the on/off of the first and second switches in a wave width modulation mode to convert an input voltage into at least a rectangular wave to the resonant tank when the load is in a light load or no load state, wherein the control unit controls the duty ratio of the first switch to fall within a first predetermined interval or a second predetermined interval when the load is in a light load or no load state, and controls the duty ratio of the second switch to be complementary to the duty ratio of the first switch, so as to make the gain of the dc-dc converter greater than 1.

2. The dc-dc converter according to claim 1, wherein the rectangular wave has an operating frequency higher than a resonant frequency of the resonant tank when the load is in a light load or no load state.

3. The dc-dc converter according to claim 1, wherein the control unit controls the rectangular wave generator in a frequency modulation mode when the load is in a heavy load or a full load state.

4. The dc-dc converter according to claim 1, wherein the duty cycle of the first switch is between a first predetermined upper limit value less than 50% and a first predetermined lower limit value, and the duty cycle of the second switch is between a second predetermined lower limit value greater than 50% and a second predetermined upper limit value.

5. The dc-dc converter according to claim 1, wherein the duty cycle of the second switch is between a first predetermined upper limit value less than 50% and a first predetermined lower limit value, and the duty cycle of the first switch is between a second predetermined lower limit value greater than 50% and a second predetermined upper limit value.

6. The dc-dc converter of claim 1, wherein the load comprises a resistor.

7. The DC-DC converter according to claim 6, wherein the load further comprises a transformer and a rectifier electrically coupled to each other and the resistor.

8. The DC-DC converter according to claim 7, wherein the resonant tank is a series resonant circuit or a parallel resonant circuit.

9. A DC-DC converter according to claim 8, characterized in that the series resonant circuit is an LC series resonant circuit or an LLC series resonant circuit.

10. The DC-DC converter according to claim 9, wherein the LLC series resonant circuit comprises an excitation inductor, a resonant inductor and a resonant capacitor connected in series with each other, wherein the excitation inductor is connected in parallel with the transformer.

11. The dc-dc converter according to claim 10, wherein the exciting inductor, the resonant inductor and the resonant capacitor are connected in parallel with the second switch, the control unit controls a duty ratio of the first switch to be less than 50%, and the transformer transfers energy to the secondary side by a clamping voltage on the exciting inductor when the control unit turns on the first switch and turns off the second switch.

12. The dc-dc converter of claim 11, wherein the transformer is unable to transfer energy to the secondary side when the control unit turns off the first switch and turns on the second switch.

13. The dc-dc converter according to claim 12, wherein a sum of a duty cycle of the first switch and a duty cycle of the second switch is 1, the duty cycle of the first switch is between a first predetermined upper limit value less than 50% and a first predetermined lower limit value, and the duty cycle of the second switch is between a second predetermined lower limit value greater than 50% and a second predetermined upper limit value.

14. The dc-dc converter according to claim 10, wherein the exciting inductor, the resonant inductor and the resonant capacitor are connected in parallel with the second switch, the control unit controls a duty ratio of the first switch to be greater than 50%, and the transformer cannot transfer energy to the secondary side when the control unit turns on the first switch and turns off the second switch.

15. The dc-dc converter of claim 14, wherein the transformer transfers energy to the secondary side by a clamping voltage across the magnetizing inductor when the control unit turns off the first switch and turns on the second switch.

16. The dc-dc converter of claim 15, wherein a sum of a duty cycle of the first switch and a duty cycle of the second switch is 1, the duty cycle of the second switch is between a first predetermined upper limit value less than 50% and a first predetermined lower limit value, and the duty cycle of the first switch is between a second predetermined lower limit value greater than 50% and a second predetermined upper limit value.

17. A power converter, characterized in that the power converter comprises:

a dc-dc converter according to any one of claims 1 to 16;

a power factor correction device electrically coupled to the DC-DC converter; and

and the electromagnetic interference filter is electrically coupled with the power factor correction device and used for receiving alternating current, and the alternating current is converted by the electromagnetic interference filter and the power factor correction device and then provides the input voltage for the direct current-direct current converter.

18. The power converter as claimed in claim 17, wherein the pfc device decreases the input voltage provided to the dc-dc converter when the load is in a light load or no load state.

19. The power converter according to claim 17, wherein the pfc device is turned off when the load is in a light load or no load state.

20. The power converter of claim 19, wherein the power factor correction device comprises:

a bridge rectifier; and

a power factor corrector electrically coupled to the bridge rectifier.

21. The power converter of claim 19 wherein said pfc device comprises a bridgeless pfc.

22. A method for controlling a power converter, the power converter comprising a load and a resonant tank, the resonant tank being electrically coupled to the load, the method comprising:

detecting a signal reflecting a state of the load; and

when the load is in a light load or no-load state, the on-off of a first switch and a second switch on a bridge arm are controlled in a wave width modulation mode to convert an input voltage into at least one rectangular wave to the resonant tank, the duty ratio of the first switch is controlled to fall in a first preset interval or a second preset interval, and the duty ratio of the second switch is complementary with the duty ratio of the first switch, so that the gain of the power converter is larger than 1.

23. The method of claim 22, further comprising:

24. The method of claim 23, further comprising:

when the load is in a heavy load or full load state, the rectangular wave is modulated in a frequency modulation mode.

25. The control method of claim 23, wherein the duty cycle of the first switch is between a first predetermined upper limit value less than 50% and a first predetermined lower limit value, and the duty cycle of the second switch is between a second predetermined lower limit value greater than 50% and a second predetermined upper limit value.

26. The control method of claim 23, wherein the duty cycle of the second switch is between a first predetermined upper limit value less than 50% and a first predetermined lower limit value, and the duty cycle of the first switch is between a second predetermined lower limit value greater than 50% and a second predetermined upper limit value.

27. The control method of claim 23, wherein the load comprises a transformer, the resonant tank comprises an excitation inductor, a resonant inductor and a resonant capacitor connected in series with each other, wherein the excitation inductor is connected in parallel with the transformer, and the excitation inductor, the resonant inductor and the resonant capacitor are connected in parallel with the second switch, the control method comprising:

the duty ratio of the first switch is controlled to be less than 50%, when the first switch is turned on and the second switch is turned off, the transformer transmits energy to the secondary side by the clamping voltage on the exciting inductor, and when the first switch is turned off and the second switch is turned on, the transformer cannot transmit energy to the secondary side.

28. The control method of claim 27, wherein a sum of a duty cycle of the first switch and a duty cycle of the second switch is 1, the duty cycle of the first switch is between a first predetermined upper limit value less than 50% and a first predetermined lower limit value, and the duty cycle of the second switch is between a second predetermined lower limit value greater than 50% and a second predetermined upper limit value.

29. The control method of claim 23, wherein the load comprises a transformer, the resonant tank comprises an excitation inductor, a resonant inductor and a resonant capacitor connected in series with each other, wherein the excitation inductor is connected in parallel with the transformer, and the excitation inductor, the resonant inductor and the resonant capacitor are connected in parallel with the second switch, the control method comprising:

the duty ratio of the first switch is controlled to be more than 50%, when the first switch is turned off and the second switch is turned on, the transformer transmits energy to the secondary side by the clamping voltage on the exciting inductor, and when the first switch is turned on and the second switch is turned off, the transformer cannot transmit energy to the secondary side.

30. The control method of claim 23, wherein a sum of a duty cycle of the first switch and a duty cycle of the second switch is 1, the duty cycle of the second switch is between a first predetermined upper limit value less than 50% and a first predetermined lower limit value, and the duty cycle of the first switch is between a second predetermined lower limit value greater than 50% and a second predetermined upper limit value.

31. The method of claim 23, further comprising:

an electromagnetic interference filter is used for receiving an alternating current, and the alternating current is converted by the electromagnetic interference filter and a power factor correction device to provide the input voltage.

32. The method of claim 31, further comprising:

when the load is in a light load or no load state, the input voltage provided by the power factor correction device is reduced.

33. The method of claim 31, further comprising:

and when the load is in a light load or no load state, turning off the power factor correction device.