KR20190095733A - Asymmetric single-stage llc resonant converter for wide range dimming - Google Patents

Abstract

The present invention relates to an asymmetric single-stage LLC resonant converter for wide range dimming, capable of controlling dimming in a wide range to sufficiently exhibit high light efficiency and electric power. The single-stage LLC resonant converter includes: a power factor improving circuit unit; an LLC resonant circuit unit generating resonance output by being connected to the power factor improving circuit unit; an output circuit unit rectifying the output of the resonant circuit unit and supplying the rectified output to an LED; and a control unit individually applying a switching signal to a first switching element and second switching element. The power factor improving circuit unit includes: an inductor for correcting a power factor, installed in a rectifying output end of commercial power; the first switching element and second switching element, installed on an output side of the inductor for correcting a power factor; and a first bus capacitor and a second bus capacitor, which are individually connected to the first switching element and second switching element.

Description

Asymmetric SINGLE-STAGE LLC RESONANT CONVERTER FOR WIDE RANGE DIMMING for wide range dimming

The present invention relates to an LLC resonant converter, and more particularly, to an asymmetric single stage LLC resonator for wide range dimming for high efficiency using a single stage topology and an LLC resonant circuit in which a PFC stage and a DC-DC stage are combined. Type converter.

Depletion of fossil fuels and environmental issues are on the rise and minimizing power losses across the industry has been a major goal. In the lighting field, which occupies about 19% of the total power consumption, the use of LEDs as luminaires has become a big issue to replace fluorescent and incandescent lamps in order to increase power efficiency. LED lighting fixtures have the advantage that they can be used in a wide range of applications, such as plant cultivation, medical, lighting fixtures.

Korean Patent No. 10-1043476 proposes a PWM dimming driving circuit for an LED. Referring to this prior document, the present invention relates to a PWM dimming driving circuit for combining a power factor correction (PFC) power supply with a DC-DC converter and an LED driver. The control command using fast response solves the hard switching problem.

However, the PWM control method has a disadvantage in that the output gain can be adjusted as the frequency is increased, and the frequency cannot be increased indefinitely in order to prevent the loss from being increased. This disadvantage causes the dimming range to be narrowed (eg, 100). Range from% to 50%).

Republic of Korea Patent No. 10-1043476

The present invention is to provide an LLC resonant converter that can maximize the dimming range of the LED to maximize the advantages of the LED, by applying an asymmetric single stage LLC resonant converter to reduce the number of switching elements and improve the efficiency of the device It can increase the voltage stress of the bus capacitors while increasing the widest possible range by combining the switching frequency control area, switching duty ratio control area and the ON / OFF control area of the upper switching element while operating the PFC in the normal range. It is an object of the present invention to provide an asymmetric single stage LLC resonant converter for wide range dimming which enables dimming control.

An asymmetric single stage LLC resonant converter for wide range dimming according to an embodiment of the present invention includes a power factor correction inductor installed at a rectifying output stage of a commercial power supply, a first switching element installed at an output side of the power factor correction inductor, and a first switching element. A power factor correction circuit including a second switching element, a first bus capacitor and a second bus capacitor connected to each of the first switching element and the second switching element; An LLC resonant circuit portion coupled to the power factor correction circuit portion to generate a resonant output; An output circuit unit rectifying the output of the resonant circuit unit and supplying the LED to the LED; And a control unit for separately applying a switching signal to the first switching element and the second switching element, wherein the control unit comprises: (a) the first switching element and the second switching element; A switching frequency control mode for controlling a current supplied to the LED load by applying a PWM signal whose switching frequency is controlled to the device, and (b) a turn on time of the first switching device and a turn on time of the second switching device. A switching duty ratio control mode for asymmetrically controlling the switching duty ratio corresponding to the ratio; and (c) fixing the on / off duty ratio of the second switching element and controlling only the on / off duty ratio of the first switching element. And an on / off control mode, and operate in any one of the switching frequency control mode, the switching duty ratio control mode, and the on / off control mode.

In the asymmetric single stage LLC resonant converter for wide range dimming according to another embodiment of the present invention, the control unit initially operates in the frequency control mode, and the switching duty when the switching frequency exceeds the upper limit of the switching frequency. Switch to non-control mode.

In the asymmetric single stage LLC resonant converter for wide range dimming according to another embodiment of the present invention, the control unit operates in the switching duty ratio control mode, when the switching duty ratio is greater than or equal to a predetermined switching duty ratio upper limit. The switching duty ratio control mode is switched to the on / off duty ratio control mode, and when the switching duty ratio is less than a predetermined switching duty ratio lower limit, the switching duty ratio is switched to the switching frequency control mode.

In the asymmetric single stage LLC resonant converter for wide-range dimming according to another embodiment of the present invention, the switching duty ratio is a turn-on time of the first switching device relative to the turn-on time of the second switching device. Is set longer.

In the asymmetric single stage LLC resonant converter for wide-range dimming according to another embodiment of the present invention, the upper limit of the switching duty ratio is that the turn-on time of the second switching device is greater than the turn-on time of the first switching device. 0.9: 0.1 ', and the lower switching duty ratio is a value at which the turn-on time of the second switching device is' 0.8: 0.2' compared to the turn-on time of the first switching device.

In the asymmetric single stage LLC resonant converter for wide range dimming according to another embodiment of the present invention, while the control unit is operating in the on / off control mode, the on / off duty ratio of the first switching device is predetermined When the on duty upper limit value is exceeded, the switching duty ratio is reduced and then the switching duty ratio control mode is switched.

According to the asymmetric single stage LLC resonant converter for a wide range of dimming of the present invention, by applying the asymmetric single stage LLC resonant converter, the voltage stress of the bus capacitor can be reduced while reducing the number of switching elements and increasing the efficiency of the device. The advantages of LEDs are as much as possible by controlling the output gain by combining the switching frequency control area, switching duty ratio control area and the ON / OFF control area of the upper switching element while operating the PFC in the normal range. The maximum dimming range of the LED can be maximized.

1 is a circuit diagram illustrating a two-stage LLC resonant converter, which is a general-purpose circuit for LED dimming control.
2 is a circuit diagram illustrating a single stage LLC resonant converter to which the present invention is applied;
3 is a flow chart illustrating a method of operating an asymmetric single stage LLC resonant converter for wide range dimming in accordance with the present invention;
4 is a waveform diagram illustrating an operation waveform according to an on / off control mode in the present invention;
5 is a waveform diagram showing a waveform of a converter operation in a switching frequency control mode;
6 is a waveform diagram showing a converter operation waveform in a switching duty ratio control mode;
7 is a waveform diagram showing a waveform of a converter operation in an on / off control mode;
8 illustrates an LED load used to experiment the present invention;
9 illustrates a prototype of an asymmetric single stage LLC resonant converter;
10 is a waveform diagram showing an experimental waveform of an asymmetric single stage LLC resonant converter in switching frequency control mode.
FIG. 11 is a waveform diagram illustrating a waveform representing a single stage LLC resonant converter in a switching duty ratio control mode. FIG.
12 is a waveform diagram illustrating an experimental waveform of an asymmetric single stage LLC resonant converter in an on / off control mode.
FIG. 13 is a waveform diagram showing an operation waveform of each control region of an asymmetric single stage LLC resonant converter for LED lighting having a wide dimming range according to the present invention; and
14 is a view showing the operating characteristics according to the load variation of the asymmetric single stage LLC resonant converter for LED lighting having a wide dimming range according to the present invention.

Hereinafter, with reference to the accompanying drawings will be described a specific embodiment according to the present invention. However, this is not intended to limit the present invention to the specific embodiments, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

The same reference numerals are used for parts having similar configurations and operations throughout the specification. And the drawings attached to the present invention is for convenience of description, the shape and relative measures may be exaggerated or omitted.

In describing the embodiments in detail, overlapping descriptions or descriptions of obvious technology in the art are omitted. In addition, in the following description, when a portion "includes" another component, it means that the component can be further included in addition to the described component unless otherwise stated.

 In addition, the terms "~", "~", "~ module" described in the specification means a unit for processing at least one function or operation, which may be implemented by hardware or software or a combination of hardware and software. Can be. In addition, when a part is electrically connected to another part, this includes not only the case where it is directly connected, but also the case where it is connected through the other structure in the middle.

Terms including ordinal numbers such as first and second may be used to describe various components, but the components are not limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the second component may be referred to as the first component, and similarly, the first component may also be referred to as the second component.

FIG. 1 is a circuit diagram illustrating a two stage LLC resonant converter, and illustrates a circuit diagram generally used for LED dimming control.

Referring to FIG. 1, a two-stage LLC resonant converter operates by being supplied with a commercial power supply 110, and includes a filter circuit unit 120, an input stage rectifier circuit unit 130, and a power factor correction circuit unit 140. And an LLC resonant circuit unit 150 and an output stage rectifier circuit unit 170.

The filter circuit unit 120 includes a filter inductor Lf provided at one side of the power input terminal and a filter capacitor Cf connected in parallel to the filter inductor Lf. The filter circuit 120 is a circuit for removing and filtering harmonic components with respect to the current generated by the power factor correction inductor Lin, which will be described later.

The input stage rectifier circuit 130 may be configured to rectify AC input power and convert the AC input power into a DC component. For example, the input stage rectifier circuit 130 may be configured as a full bridge diode for full-wave rectifying the AC input.

The power factor correction circuit unit 140 is connected to a power factor correcting inductor Lin installed at one side of the DC input terminal, three switching elements Q1, Q2, and Q3 connected to the output side of the power factor correcting inductor Lin, and the switching element Q1. It consists of a bus capacitor (Cbus) connected in parallel.

The controller (not shown) applies a trigger signal to each of the three switching elements Q1, Q2, and Q3 to control the output current of the power factor correction circuit 140.

The LLC resonant circuit unit 150 includes a resonant capacitor Cr, a resonant inductor Lr, a magnetized inductor Lm, and a transformer 160. The resonant capacitor Cr and the resonant inductor Lr resonate the frequency of the current output from the power factor correction circuit 140. The transformer 160 supplies the output to the load while maintaining an insulation state between the output of the resonant frequency and the load side. Transformer 160 may be designed to include a resonant inductor (Lr) and a magnetized inductor (Lm).

The output stage rectifier circuit unit 170 is composed of a half wave or full wave rectifier circuit, and an output capacitor Co is installed in parallel to the output stage rectifier circuit unit 170 to smooth the output current to provide the LED array 180.

The two stage LLC resonant converter shown in FIG. 1 has excellent power factor improvement performance by controlling three switching elements Q1 to Q3, but there is a problem that unnecessary switching loss occurs due to a large volume of the driving circuit and a large number of switching elements. . On the other hand, the single stage LLC resonant converter is more suitable for showing the long life and high efficiency characteristics of the LED by reducing the switching elements compared to the two stage LLC resonant converter. However, the voltage stress on the switching device and the bus capacitor may be a problem.

The present invention solves the above problem by asymmetrical operation, and proposes a converter and a method of operating the single-stage LLC resonant converter in three control modes to maximize the dimming range.

2 is a circuit diagram illustrating a single stage LLC resonant converter to which the present invention is applied.

Referring to FIG. 2, the single-stage LLC resonant converter operates by receiving commercial power 210 as described above, and includes a filter circuit 220, an input stage rectifier circuit 230, and a power factor correction circuit. 240, an LLC resonant circuit 250, and an output stage rectifier circuit 270 to drive the LED array 280.

Other circuit configurations are the same as the two stage LLC resonant converter described above, but the power factor correction circuitry 240 consists of a single stage.

Referring to FIG. 2, the power factor correction circuit 240 includes a power factor correcting inductor Lin, a first switching element Q1, a second switching element Q2, a first bus capacitor Cbus1, and a second power factor correction circuit 240. It consists of a bus capacitor Cbus2.

The first switching element Q1 is connected between the output side (plus end) of the power factor correction inductor Lin and the negative end of the input stage rectifying circuit unit 230, and the second switching element Q2 is connected to the first switching element Q1. Is connected between the minus and plus ends of the. The first bus capacitor Cbus1 is connected in parallel with the first switching element Q1 between the positive and negative ends, and the second bus capacitor Cbus2 is connected in parallel with the second switching element Q2 between the negative and positive ends. do.

The controller (not shown) controls the turn on / off by transmitting the first trigger signal to the first switching device Q1, and controls the turn on / off by transferring the second trigger signal to the second switching device Q2. do. The first trigger signal and the second trigger signal are not simultaneously applied.

The power factor correction inductor Lin receives the voltage rectified by the input rectifier circuit unit 230, charges the magnetism by the current flow when the first switching element Q1 is turned on, and the second switching element Q2 is When turned on, the current can be output according to the charged magnetism.

Preferably, the first switching element Q1 and the second switching element Q2 are zero voltage switched (ZVS) in order to reduce a loss that may occur in on / off. ZVS reduces switching losses while minimizing the components affected by the switching frequency.

When the second switching device Q2 is turned on, the first bus capacitor Cbus1 and the second bus capacitor Cbus2 receive a voltage of a current output across the capacitor. In this case, the voltage applied may be a breakdown voltage applied to the first switching element Q1.

3 is a flow chart illustrating a method of operating an asymmetric single stage LLC resonant converter for wide range dimming in accordance with the present invention.

The present invention employs the single stage LLC resonant converter illustrated in FIG. 2 to fully exhibit the advantages of LEDs, such as long lifespan and high power and light efficiency. Single stage LLC resonant converter can reduce the number of switching elements to minimize the loss in the switching element, and has the advantage of making the device thin and light.

In a single stage LLC resonant converter, the voltage stress on the switching element can be relieved by ZVS operation. In addition, ZVS enables the compact design of devices that are affected by the switching frequency.

In addition, the present invention provides a switching frequency control mode (ST100), switching duty ratio control mode (ST200), the first switching device (PFC) while operating in the normal range in order to enable dimming control over the entire range in the LED drive circuit A method of operating the control unit in three operation modes combining the ON / OFF control mode (ST300) of Q1) is proposed. Hereinafter, a process of operating the single stage LLC resonant converter of FIG. 2 in asymmetric operation and the above three operating modes will be described.

Referring to FIG. 3, the controller initially starts operation in the switching frequency control mode (ST110). In the switching frequency control mode, the controller applies a trigger signal to the first switching element Q1 and the second switching element Q2 through a pulse width modulation (PWM) signal. The operation process in the switching frequency control mode is as follows.

It is determined whether the output current I_out is greater than or equal to the reference current I_ref by comparing the preset reference current I_ref and the output current I_out measured by the output capacitor Co (ST120). If no, the process proceeds to step ST130 to decrease the switching frequency Fs of the PWM signal applied to each of the switching elements Q1 and Q2 (ST130). If YES, the flow proceeds to step ST140 to increase the switching frequency Fs (ST140).

After performing step ST130 or ST140, it is determined whether the switching frequency Fs exceeds a predetermined switching frequency upper limit value Fs_MAX (ST150). PWM dimming control has the advantage of adjusting the output gain as the switching frequency (Fs) is increased, but the switching frequency (Fs) cannot be increased indefinitely because of loss. Therefore, limit the switching frequency (Fs) to minimize losses. Such a limitation causes the dimming range to be narrowed in the LED driving circuit. The switching frequency upper limit (Fs_MAX) can be set as a limit to adjust the output gain with minimal loss.

If NO is determined in step ST150, that is, if the switching frequency Fs does not exceed the switching frequency upper limit value Fs_MAX, the process returns to step ST110 to continue the switching frequency control mode. If it is determined as YES in step ST150, the process proceeds to step ST210 to switch to the switching duty ratio control mode.

In step ST210, the switching duty ratio control mode is started (ST210). The switching duty ratio is determined by a ratio of the turn on time of the first switching device Q1 which is the upper switching device and the turn on time of the second switching device Q2 which is the lower switching device. In this case, the switching duty ratio is determined in an asymmetric manner in which the turn-on time of the first switching device Q1 is relatively longer. For example, the switching duty ratio varies fluidly from '0.8: 0.2' to '0.9: 0.1'.

In operation ST220, it is determined whether the switching duty ratio Duty_s is less than the predetermined switching duty ratio upper limit Duty_MAX (ST220). The switching duty ratio upper limit Duty_MAX is, for example, a value representing a duty ratio of '0.9: 0.1'. The limit of the switching duty ratio upper limit (Duty_MAX) is defined as such that when the switching duty ratio (Duty_s) becomes extremely large, that is, when the difference between the upper and lower switching duty becomes extremely large, the PFC operation may not be performed normally. Because. This problem occurs because the single stage converter topology performs the PFC operation and the converter operation together. Due to this limitation, there is a limitation on the dimming range in the switching duty ratio control.

If it is determined as NO in the determination of step ST220, the flow advances to step ST310 to switch to the ON / OFF control mode. A detailed description of the ON / OFF control mode will be described later. If it is determined in step ST220 that YES, the flow proceeds to step ST230.

In operation ST230, the reference current I_ref and the output current I_out are compared to determine whether the output current I_out is greater than or equal to the reference current I_ref (ST230). If no, the process proceeds to step ST240 to reduce the switching duty ratio Duty_s (ST240). If YES, the flow proceeds to step ST250 to increase the switching duty ratio Duty_s (ST250).

After performing step ST240 or ST250, it is determined whether the switching duty ratio Duty_s is less than the predetermined switching duty ratio lower limit Duty_MIN (ST260). The switching duty ratio lower limit Duty_MIN is, for example, a value representing a duty ratio of '0.8: 0.2'. When the switching duty ratio Duty_MIN is lower than the lower limit, the voltage across the bus capacitors Cbus1 and Cbus2 may increase and the voltage stress of the switching elements Q1 and Q2 may increase. The switching duty ratio lower limit Duty_MIN may be determined such that the turn-on time of the first switching device Q1 is sufficiently maintained to prevent an increase in voltage stress of the switching devices Q1 and Q2.

If NO is determined in step ST260, it means that the switching duty ratio Duty_s is within the set range, and the flow returns to step ST220 to repeat the switching duty ratio control mode. If it is determined as YES in step ST260, the flow advances to step ST110 to switch to the switching frequency control mode described above.

As described above, when the switching duty ratio Duty_s rises above the switching duty ratio upper limit Duty_MAX, the switching duty mode is switched to the on / off control mode. The on / off control mode is started in step ST310 (ST310).

Here, the on / off control mode is to maintain the normal PFC function by fixing the on / off duty ratio for the second switching device (Q2) to perform a continuous boost and PFC operation, the first switching device (Q1) ) Is a mode of controlling the output gain by controlling only the variable on / off duty ratio (Duty_onoff). By adding such an on / off control mode, it is possible to control the LED dimming to the maximum possible width when applied to the LED driving circuit.

In operation ST320, the reference current I_ref and the output current I_out are compared to determine whether the output current I_out is greater than or equal to the reference current I_ref (ST320). If no, the process proceeds to step ST330 to increase the on / off duty ratio Duty_onoff for the first switching device Q1 (ST330). If YES, the flow proceeds to step ST340 to reduce the on / off duty ratio Duty_s for the first switching device Q1 (ST340).

After performing step ST330 or step ST340, it is determined whether the on / off duty ratio Duty_onoff for the first switching element Q1 exceeds the on duty upper limit value OnDuty_MAX (ST350). If the on duty upper limit value OnDuty_MAX is not exceeded, the process returns to step ST320 and the on / off control mode is repeated.

If the on / off duty ratio Duty_onoff for the first switching element Q1 exceeds the on duty upper limit OnDuty_MAX, the switching duty ratio Duty_s is reduced (ST360), and the flow proceeds to step ST210 to the switching duty. Adjust the output gain by switching to non-control mode.

4 is a waveform diagram illustrating an operating waveform according to the on / off control mode in the present invention.

Referring to FIG. 4, the on / off duty ratio for the first switching device Q1 is exemplified as '0.5: 0.5', and the first switching device Q1 is turned on in the on / off period off period at the top of the waveform diagram. Not. In the on / off period on period, the first switching element Q1 and the second switching element Q2 are alternately turned on by the switching duty ratio Duty_s.

In order to simulate and experiment asymmetric single stage LLC resonant converter and its operation method for wide range dimming according to the present invention, the following parameters are used. The input power was applied to 110V corresponding to half of the commercial power 210, the range of the switching frequency is 40kHz to 100kHz, the period of the on / off frequency is set to 500Hz. The bus capacitors (Cbus1, Cbus2) and output capacitors (Co) used in the simulations and experiments were sufficiently large so that the effects of voltage ripple were small. The transformer 260 used in the experiment was used based on the results of modeling the leakage inductance and the magnetizing inductance, and the simulation and the experiment were performed accordingly.

 Single Stage LLC Resonant Converter Design Conditions Parameter Value

Switching frequency,

40 to 100 [kHz] Resonant frequency,

60 [kHz] Boost Inductance,

34.8 [uH] Resonant Inductance,

7.16 [uH] Magnetizing inductance,

1.05 [mH] Resonant Capacitance,

33 [nF] Bus Capacitance,

820 [uF] Output Capacitance,

470 [uF] Input Voltage,

110 [Vrms] Output Voltage,

180 [V] Output Cuttent,

0.7 [A]

The simulation uses PSIM's DLL feature to control the output gain through switching frequency, switching duty ratio, and duty cycle between ON / OFF periods. When the lower and upper limit conditions were set in each control mode, the control mode was changed and the operation and output gain of the single stage LLC resonant converter operating asymmetrically were checked.

FIG. 5 is a waveform diagram illustrating an operation waveform of a converter in a switching frequency control mode. FIG. 5A illustrates an operation waveform when the switching frequency is 40 kHz, and FIG. 5B illustrates an operation waveform when the switching frequency is 100 kHz.

In the switching frequency control mode, the output gain decreases as the switching frequency of the asymmetric single stage LLC resonant converter gradually increases, so that the converter operates normally in accordance with the gain characteristics of the conventional LLC resonant converter. It can be seen from the waveform diagram of FIG. 5 that dimming is possible through switching frequency control within a switching frequency range set to 40 kHz to 100 kHz.

FIG. 6 is a waveform diagram illustrating an operation waveform of a converter in a switching duty ratio control mode. In case of rising to a frequency above 100 kHz higher than the previously set switching frequency, the frequency limit is set so that the switching frequency is fixed to 100 kHz and the switching duty ratio control is performed. Indicates the waveform operated through

FIG. 6A is an operating waveform when the switching duty ratio indicating the turn on ratio for each of the first switching element Q1 and the second switching element Q2 is '0.9: 0.1', and (b) is switching The PFC waveform is displayed when the duty ratio is operated at '0.9: 0.1' or higher.

As a result of the simulation, as the duty ratio of the second switching device Q2 contributing to the boost operation decreases, the output gain decreases and changes. That is, as the duty ratio of the first switching element Q1 increases, a wide range of dimming operation is possible. However, when the switching duty ratio control is continued for dimming, it can be seen that a problem occurs in which the PFC operation is not normally performed as shown in FIG. This is a problem caused by simultaneously acting as a PFC and a DC / DC converter in a single stage converter topology. Therefore, in order to solve such a problem and to enable a wider dimming, the normal operation in the switching duty ratio control mode, the switching duty ratio is fixed to the upper limit in the region where the PFC does not operate normally, the first switching device (Q1) Only on / off control allows the PFC operation to perform normally while simultaneously dimming.

FIG. 7 is a waveform diagram illustrating an operation waveform of a converter in an on / off control mode. FIG. 7A illustrates an operation waveform when the on / off duty of the first switching element Q1 is 0.8. Denotes a PFC waveform in the on / off control mode of the present invention. In the simulation result of FIG. 7, the on / off period of the first switching device Q1 is set to 500 Hz.

Referring to FIG. 7, it can be seen that the problem of the inoperability of the PFC, which was the problem of the switching duty ratio control mode described above, is solved. Although the ripple occurs somewhat due to the on / off period as in the waveform shown in FIG. 7B, the PFC operates normally.

That is, the PFC can be normally operated by fixing the switching duty ratio to an upper limit in the region in which the PFC operation becomes unstable while operating in the switching duty ratio control mode and controlling ON / OFF only the first switching element Q1. This allows for wider dimming.

In addition, it can be seen from FIG. 7A that the output gain is changed to be lower than the previous switching duty ratio control mode. In the on / off control mode, it was confirmed that the output gain decreases as the ratio of the section in which the first switching element Q1 is turned on decreases, and thus, dimming in a wider range is possible.

FIG. 8 is a diagram illustrating an LED load used to experiment the present invention, and FIG. 9 is a diagram illustrating a prototype of an asymmetric single stage LLC resonant converter.

The prototype used a control board with TI's TMS320F28335 with a 150M clock. Through the AD board, the current flowing through the input voltage Vac, input current Iac, and resonant current Lr was measured.

The switching element applied to the converter prototype illustrated in FIG. 9 is CREE's 'KIT8020-CRD-8FF1217P-1' (SiC MOSFET Module) having excellent characteristics of heat dissipation, and the same CREE SiC MOSFETs 'C2M0080120D' and SiC. Schottky Diode 'C4D20120D' is embedded as a device. The LED load used in the experiment is the LED module of LG Innotek Co., Ltd. as shown in FIG. 8, and is rated at 30 [V], 0.7 [A], 2.5 [W], 60 [Hz], 2465 [lm], and color temperature of 5700 K, maximum operation. Six products of temperature Tc 80 were used in series.

10 is a diagram illustrating an experimental waveform of an asymmetric single stage LLC resonant converter in a switching frequency control mode, in which (a) is an experimental waveform in a frequency control mode, and (b) is an symmetrical experiment. Waveforms (c) show experimental waveforms when operated asymmetrically, respectively.

Prior to full-scale experiments, in order to verify the gain characteristics and normal operation of the experimental set consisting of a single stage LLC resonant converter, the switching frequency is set from 40 kHz to 100 kHz as shown in FIG. Set to and sweep to see the resulting output. As a result of the experiment, the lower the switching frequency, the higher the output gain. Therefore, it was confirmed that it operates normally in accordance with the characteristics of the conventional LLC resonant converter. Through this, it was confirmed that dimming is possible in the frequency range from 40kHz to 100kHz set using switching frequency control.

Next, FIG. 10 (b) shows a waveform when the single-stage LLC resonant converter is operated symmetrically with a switching duty ratio of '0.5: 0.5', and (c) shows a switching duty ratio of '0.8: 0.2'. Waveform when operated asymmetrically. Comparing the waveform of the gate waveform of the first switching element Q1 of CH1 with the resonant current of CH2, the first switching element Q1 turns when the current flows in reverse through the body diode of the first switching element Q1. You can see that ZVS is on and in both symmetric and asymmetric behavior. In addition, when comparing the bus capacitor voltage of CH3 and the voltage across the first switching element Q1 of CH4, the time required to charge the bus capacitor through the boost operation is reduced when driving asymmetrically than when driving the symmetrically, It was confirmed that the magnitudes of the bus capacitor voltage and the voltage applied to the first switching device Q1 are reduced. Since the voltage stress can be thought of as the magnitude of the bus capacitor voltage and the voltage applied to the switching device, it can be said that the voltage stress is reduced when driven asymmetrically.

FIG. 11 is a waveform diagram illustrating a waveform representing a single stage LLC resonant converter in a switching duty ratio control mode, in which FIG. 11A illustrates a case where the switching duty ratio is 0.8: 0.2, and FIG. The cases where the ratio is '0.9: 0.1' are shown, respectively.

Although the dimming is possible when the switching frequency control is performed within the set frequency range through the experimental results of FIG. 10, the switching frequency is continuously increased when the output gain is continuously lowered for a wider dimming range. Therefore, the frequency is limited by the loss and additional problems.

Accordingly, the present invention provides an asymmetric operation in which the switching frequency is fixed and the switching duty ratio of the first switching element Q1 and the second switching element Q2 is operated at a ratio of 0.8: 0.2 in the region where the switching frequency is limited. By changing the switching ratio to '0.9: 0.1', the output gain is reduced to enable dimming.

Referring to FIG. 11, CH1 and 2 of each waveform represent gate signals of the first switching element Q1 and the second switching element Q2, respectively, and CH3 and 4 represent the resonance current and the output current. In the frequency-limited region, the switching duty ratio control shows that the output gain gradually decreases, allowing dimming over a wider range.

12 and 13 illustrate that the PFC operation is normally performed by controlling ON / OFF only the first switching element Q1 in a state in which the switching duty ratio is limited to solve the problem in which the PFC operation is abnormally operated as described above. This waveform confirms that dimming is possible over a wider range. In this case, since the second switching element Q2 contributes to the boost operation and the PFC, the second switching element Q2 is turned on / off by a normal duty regardless of the on / off waveform illustrated in FIG. 4.

FIG. 12 is a waveform diagram illustrating an experimental waveform of an asymmetric single stage LLC resonant converter in an on / off control mode. FIG. 12A illustrates a ratio of an on / off period of 0.8 to a first switching device Q1. (B) shows the case where the application ratio of the on / off period is 0.3, respectively.

CH1 and 2 of each waveform represent gate signals of the first switching element Q1 and the second switching element Q2, and CH3 and 4 represent resonance current and output current. As a result of the experiment, the output current decreases as the section in which the first switching device Q1 is turned off increases. According to this result, it can be confirmed that dimming is wider than the existing range according to the duty cycle of the on / off period.

FIG. 13 is a waveform diagram illustrating an operation waveform of each control region of an asymmetric single stage LLC resonant converter for LED lighting having a wide dimming range according to the present invention. FIG. 13A illustrates an operation waveform of a switching frequency control mode. (b) shows an operating waveform of the switching duty ratio control mode, and (c) shows an operating waveform of the on / off control mode.

As the phase of CH1 and 2 of the waveform of each mode coincides with the phase of the current, it can be confirmed that PFC is operating normally. As the output current of CH3 decreases, the brightness of LED decreases and dimming is possible. can confirm. The dimming range, PF, THD analysis, and voltage of the bus capacitor according to each control mode can be checked in FIG. 14.

14 is a view showing the operating characteristics according to the load variation of the asymmetric single stage LLC resonant converter for LED lighting having a wide dimming range according to the present invention, Figure 14 (a) is a case where the load resistance is 100 Ohm, (b ) Indicate the case of LED load, respectively.

Referring to FIG. 14, as a result of analyzing the PF and THD operation according to the load variation, the power factor (PF) in all the operating ranges is maintained at 90% or more, which is the international standard, from 0.95% to 0.99%, and the THD is about 6-11. % Was maintained. The total amount of bus capacitor voltage directly connected to the stress of the switch was confirmed to be from 260V minimum to 480V maximum. The dimming range of LED load is 50% or more as switching frequency control area, 10% or more switching duty ratio control area, and less than 10% as on / off control area. This result proved that the dimming range is wider than the conventional dimming method.

In the present invention, in order to maximize the advantages of the LED which is in the spotlight recently, a high efficiency driving circuit including a brightness control function is proposed, and the proposed invention is analyzed through simulation and experiment. This reduces the number of devices compared to conventional two-stage converter topologies, resulting in asymmetrical operation of more efficient single-stage LLC resonant converters to reduce voltage stress on the switch and reduce ZVS. Designed to allow operation. In this topology, LED brightness is controlled by adjusting the output gain by combining switching frequency control area, switching duty ratio control area, and on / off control area to have a wider dimming range while maintaining PFC operation in a normal range. The method was proposed.

In the conventional PWM control method, if dimming was possible only in the range of 100% to 50% based on the limit of the switching frequency, the dimming in the range of 50% to 10% is possible by adding the switching duty ratio control area. It was confirmed that dimming of 10% or less was enabled by adding an on / off control region. As a result, it is possible to provide a driving circuit for LED lighting having a higher efficiency condition and a wider range of dimming than conventional two-stage converters, and is expected to be widely used in fields requiring detailed brightness control and other additional fields.

Various modifications are possible in the invention disclosed above without departing from the basic idea. That is, the above embodiments should all be interpreted as illustrative and not restrictive. Therefore, the protection scope of the present invention should be determined according to the appended claims rather than the above-described embodiments, and if the components defined in the appended claims are replaced by equivalents, they should be regarded as belonging to the protection scope of the present invention.

110: commercial power supply 120: filter circuit
130 input rectifier circuit portion 140 power factor correction circuit portion
150: LLC resonant circuit portion 160: transformer
170: output stage rectifier circuit 180: LED array
210: commercial power 220: filter circuit
230: input stage rectifier circuit portion 240: power factor correction circuit portion
250: LLC resonant circuit portion 260: transformer
270: output stage rectifier circuit portion 280: LED array

Claims (6)

A power factor correcting inductor installed at the rectifying output stage of the commercial power supply, a first switching element and a second switching element installed at an output side of the power factor correcting inductor, and a first first connected to each of the first switching element and the second switching element. A power factor correction circuit unit including a bus capacitor and a second bus capacitor; An LLC resonant circuit portion coupled to the power factor correction circuit portion to generate a resonant output; An output circuit unit rectifying an output of the resonance circuit unit and supplying the LED to the LED; And a control unit for separately applying a switching signal to the first switching element and the second switching element.
The control unit,
(a) a switching frequency control mode for controlling a current supplied to an LED load by applying a PWM signal whose switching frequency is controlled to the first switching element and the second switching element;
(b) a switching duty ratio control mode for asymmetrically controlling a switching duty ratio corresponding to a ratio of a turn on time of the first switching element to a turn on time of the second switching element;
(c) an on / off control mode for fixing the on / off duty ratio of the second switching element and controlling only the on / off duty ratio of the first switching element;
Operating in any one of the switching frequency control mode, the switching duty ratio control mode, and the on / off control mode.
Asymmetric single stage LLC resonant converter for wide range dimming.
The method of claim 1,
And the control unit initially operates in the frequency control mode, and switches to the switching duty ratio control mode when the switching frequency exceeds the upper limit of the switching frequency.
The method of claim 2,
The control unit switches to the on / off duty ratio control mode from the switching duty ratio control mode when the switching duty ratio is equal to or greater than a predetermined switching duty ratio upper limit while operating in the switching duty ratio control mode, and the switching duty ratio is previously set. An asymmetric single stage LLC resonant converter for wide range dimming from the switching duty ratio control mode to the switching frequency control mode when less than a predetermined switching duty ratio lower limit.
The method of claim 3,
The switching duty ratio is an asymmetric single stage LLC resonant converter for wide range dimming wherein the turn on time of the first switching element is set relatively longer than the turn on time of the second switching element.
The method of claim 4, wherein
The switching duty ratio upper limit value is a value in which the turn on time of the second switching device is '0.9: 0.1' relative to the turn on time of the first switching device.
And the switching duty ratio lower limit is a value in which the turn-on time of the second switching device is '0.8: 0.2' relative to the turn-on time of the first switching device.
The method according to any one of claims 1 to 5,
The control unit switches to the switching duty ratio control mode after reducing the switching duty ratio when the on / off duty ratio of the first switching element exceeds a predetermined on duty upper limit value while operating in the on / off control mode. Single stage LLC resonant converter for wide range dimming.

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