CN102497700A - Power factor correction method for LED (light-emitting diode) lighting - Google Patents

Power factor correction method for LED (light-emitting diode) lighting Download PDF

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CN102497700A
CN102497700A CN2011103978239A CN201110397823A CN102497700A CN 102497700 A CN102497700 A CN 102497700A CN 2011103978239 A CN2011103978239 A CN 2011103978239A CN 201110397823 A CN201110397823 A CN 201110397823A CN 102497700 A CN102497700 A CN 102497700A
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input
signal
voltage
current
power factor
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姜岩峰
赵帆
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North China University of Technology
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Abstract

The invention discloses a power factor correction method for LED (light-emitting diode) lighting, which adopts an average current control mode in a CCM (continuous conduction mode). The method comprises the following steps that: after an input alternating voltage is rectified, the rectified voltage is converted into a first current signal (IAC) by a resistor (RAC); the waveform of the first current signal (IAC) is the envelope of the input rectified voltage, the signal and a detection current (ISENSE) of an inductor are superposed, and after the superposed current is corrected, a second current signal (I) is outputted, and the second current signal (I) is used as an input end of an operation module; and an input-end predicted voltage signal (VRMS) obtained by scaling down in equal proportion and filtering an average value of input voltages is taken as an input end of the operation module.

Description

A kind of power factor correcting method that is used for the LED illumination
Technical field
The invention belongs to the solid light source field, relate more specifically to the LED lighting field.
Background technology
High-brightness LED is as a kind of solid light source; With its long-life, environmental protection, low-power consumption, high light efficiency, how photochromic, tunable optical, response rapidly, switch sudden strain of a muscle many advantages such as break, can under the safety low-voltage, work continuously; Day by day develop towards the direction that becomes lighting source of new generation, be called as the 4th generation lighting source.The application of LED is from initial indicator light, to traffic signals, large scale display in recent years, the then increasing at present functional lighting fields such as Landscape Lighting, road lighting and tunnel illumination that are applied to.
See that from state is external the U.S. maintains the leading position always, is the leader of LED technology in the industrial technology exploitation of LED illumination.Japan is being in the leading level in the world aspect the development of power type high brightness LED and epitaxial wafer thereof, chip and the industrialization development.Taiwan is through introducing the technology of the U.S. and Japan, developed rapidly at aspects such as epitaxial wafer and chip production, device package, application product exploitations, becomes maximum in the world LED production base.
From domestic, under the increasingly serious situation of energy situation, quicken to eliminate the vital task that incandescent lamp becomes China.Government has released a series of relevant policies and has promoted China's Green Lighting Project, and the LED Lighting Industry is developed rapidly, has welcome new revolution.
But the LED Lighting Industry is in fast development; Still also exist lack independent research and development capacity, lack industry standard, problems such as product homogeneity is serious, blind investment; How to improve reliability, prolong bulb life, become the important research contents of LED lighting field.In addition, cost also is to influence the main aspect that such light fixture uses, and under the condition that LED bulb production technology is ripe relatively at home, the cost decline space of bulb part is little, is lowered into and should mainly concentrates on drive circuit and light fixture external form aspect.
Summary of the invention
The present invention proposes a kind of new LED lighting circuit power factor correcting method, this method improvement because of the complicated of original LED chip for driving PFC control circuit or there are not these a series of problems of drive circuit of PFC module.
A kind of power factor correcting method that is used for the LED illumination proposed by the invention, it adopts the CCM pattern, Average Current Control, said method comprises: at input ac voltage after rectification, via a resistance (R AC) be converted into first current signal (IAC); The waveform of said first current signal (IAC) is the envelope of input rectifying voltage, and the detection electric current (ISENSE) of this signal and inductance superposes, and proofreaies and correct back output second current signal (I), and this second current signal (I) is as an input of computing module; Will be by the input of the input predicted voltage signal (VRMS) that obtains after input voltage mean value scaled down and the filtering as computing module.
When power factor correcting method proposed by the invention, wherein said input predicted voltage signal (VRMS) are fed forward to the voltage circuit gain, the correction of an open circuit is provided.
Power factor correcting method proposed by the invention wherein for the sustaining voltage loop gain is a definite value, does not change with average input voltage, said input predicted voltage signal (VRMS) signal through square after participate in computing.
Power factor correcting method proposed by the invention; Wherein since said input predicted voltage signal (VRMS) induction of signal of computing module be the line voltage signal; Little in order to guarantee the computing module input noise; The place need adopt a current mirror of 2: 1 to reduce input noise at said input predicted voltage signal (VRMS) signal, improves the performance of computing module.
To the throw light on requirement of permanent power control of LED, the power factor correcting method that is used for the LED illumination proposed by the invention, this has following characteristics:
● be applicable to the LED lamp of 3W to 20W, power factor can reach more than 99%;
● adopt the multi-mode control mode, no matter can both keep high conversion efficiency under underloading, the heavily loaded situation;
● in the total solution, the power supply that adopts this technological PFC chip to make up, its whole conversion efficiency is up to 96%;
● because power supply conversion efficiency is high, greatly alleviated the heat dissipation problem of LED, had obvious effect for improving the LED life-span;
This technology is applied in the LED illumination application based on the BOOST framework, and the basic principle block diagram is as shown in Figure 4.
Description of drawings
Accompanying drawing 1 is a DCM-PFC step-up transformer circuit diagram;
Accompanying drawing 2 is DCM inductive current figure;
Accompanying drawing 3 is I-V characteristic curve diagrams of actual measurement LED lamp;
Accompanying drawing 4 is PFC module frame charts;
Accompanying drawing 5 is that PFC half period internal inductance detects current waveform figure;
Accompanying drawing 6 is commutating voltage sampled value IAC oscillograms;
Accompanying drawing 7 is voltage and current waveforms in the PFC half period;
Accompanying drawing 8 is PFC duty ratio control associated voltage and current waveform figure;
Accompanying drawing 9 is PFC chip theory diagrams;
Accompanying drawing 10 is PFC Chip Packaging figure.
Embodiment
(Power Factor Correction PFC) refers to relation between effective power and the total power consumption (apparent power) to power factor, and just effective power is divided by the ratio of total power consumption (apparent power).Basically power factor can be weighed the degree that electric power is used effectively, and when the power factor (PF) value is big more, represents its electric power utilance high more.
Be used at present that the Active Power Factor Correction Technology of LED lighting field adopts be work in DCM (Discontinuous Conduction Mode, DCM) or critical conduction mode (Critical Mode, two kinds of schemes CRM).
DCM control model operating frequency is constant, and the electric current of process inductance is a high frequency triangle wave, and after inductive current dropped to zero, switch VT was not conducting at once, causes inductive current to exist for zero dead band, is not continuous flow.As shown in Figure 1.
DCM control model work characteristics: the peak inrush current of inductance surpasses 2 times of maximum average current input; Therefore need to select bigger power MOSFET tube and the booster diode of the magnitude of current; And high peak current is quite responsive to noise, influences the stability of whole system; Because the modulation of input inductance current discharge time, the mean value of input current can not be directly proportional with input voltage, thereby input current can present distortion to a certain degree, can't satisfy the requirement of low THD.
The PFC controlling schemes of CRM pattern control adopts VFC, i.e. ON time T ONConstant, cycle T is changing all the time.Work characteristics: the CRM pattern is controlled with respect to constant frequency, and the input current waveform discontinuity of VFC is slightly improved, but since under this pattern operating frequency changing all the time, just caused bigger EMI.
The two kinds of control models of DCM and CRM of comparing, the work characteristics of CCM mode is: adopt the control of fixed frequency average-current mode; The peak value of power current is the mean value of high-frequency current, so the peak value of the peakedness ratio power current of high-frequency current wants high; Error between inductive current peak and the mean value is little, and THD is very little, to insensitive for noise.
Compare with the PFC technology of DCM and CRM, under identical input power, the CCM pattern adopts average-current mode control, and the current stress that on PFC power MOSFET switch tube and booster diode constant power device, produces is smaller, and EMI handles easily; Control loop is because there is current filtering insensitive to conducted noise; Frequency stabilization does not need oblique wave compensation; Be applicable to the international AC supply line input of 85V-264V, almost can realize unity power factor, THD is usually less than 5%.
LED (abbreviation of light emitting diode) light-emitting diode belongs to the solid-state semiconductor device that is converted into electric energy luminous energy.LED belongs to diode from the kind of device, has the unilateral conduction of diode, and electric current and voltage are followed
Figure BSA00000628244600031
I wherein SBe diode reverse saturation current, V TBe thermal voltage.V generally speaking BEChange 60mV, electric current I changes about 10 times.
Fig. 3 is the I-V indicatrix of actual measurement OSRAM LW W5SM LED.
As shown in Figure 3, when the electric current of LED lamp is 350mA, its forward voltage drop V BEBe 3.12V, this moment, dynamic electric resistor did
Figure BSA00000628244600041
All the junction temperature along with PN junction is different and different with optical characteristics for the electrology characteristic of LED, when temperature raises, and the V of LED lamp BECan be with 2mV/ ℃ of decline, the light output variable of LED lamp also reduces thereupon, and optical wavelength moves to the long wave direction.In illuminator, generally can select three frequency: 67KHz, 85KHz, 100KHz.
LED throws light on to the requirement of PFC:
(1) 220VAC input voltage, the PF value keeps more than 0.95;
(2) THD is below 10%;
(3) illumination begins from 5W;
(4) must isolate;
For the permanent power output of LED illumination, the theoretical foundation of its control is:
P = 1 2 η I p L p f - - - ( 1 )
P is the power output of LED;
η is the efficient of transducer;
I pAverage current for former limit transformer;
L pFormer limit inductance for transformer;
F is a switching frequency.
Permanent power control mode all is the power output P of prevision LED earlier, in theory, in case design of transformer well after, f, L p, η is definite, as long as change primary current I pSize, just can change the size of power output.Again because:
ΔI = UD f L p - - - ( 2 )
U is the voltage that is added in the former limit of transformer, i.e. input voltage; D is a duty ratio; F is a switching frequency; L pFormer limit inductance for transformer.Can know that according to formula 2 Δ I is directly proportional with D,, also just can change the size of power output as long as change the size that duty ratio D just can change primary current.
Wherein main control section is computing module and PWM modulating part, and basic functional principle is: input ac voltage is after rectification, via a resistance R ACBe converted into current signal, represent with IAC, this signal waveform is the envelope of input rectifying voltage, and the detection current IS ENSE of IAC and inductance superposes, and proofreaies and correct current signal I of back output, and its waveform is followed commutating voltage waveform stream.The current signal of this output is as an input of computing module.
By the input predicted voltage signal that obtains after input voltage mean value scaled down and the filtering is that VRMS is (when this signal is fed forward to the voltage circuit gain; The correction of an open circuit is provided) also as an input of computing module; For the sustaining voltage loop gain is a definite value; Do not change with average input voltage, the VRMS signal through square after participate in computing.
VEAO is the output voltage of output voltage feedback sample value after through an error amplifier, because output voltage is relatively stable, therefore feedback can be stablized, and the value of VEAO also can keep substantially constant.Therefore this value is equivalent to an input constant in computing module.When input voltage increases when being twice, the last voltage of IAC increases exponentially, and the square value of VRMS increases and is original four times simultaneously.Suppose that ISENSE went up voltage and do not change as yet this moment, after the signal stack on IAC and the ISENSE, export signal also linearity increase and be twice.The square value of this signal and VRM acts on computing module simultaneously, makes the output signal become original 1/2 times, realizes the constant of power.
Because the input VRMS of computing module induction is the line voltage signal, little in order to guarantee the computing module input noise, need to adopt a current mirror of 2: 1 to reduce input noise at the VRMS place, improve the performance of computing module.
The output signal of computing module and a square wave stack through amplifier output, are played the effect of soft start, the output V of amplifier CReceive IEAO and compensate, and with a ramp signal V SCompare, work as V CValue is greater than ramp signal V SThe time, power tube VT conducting, inductive current increases, and works as V CValue is less than ramp signal V SThe time, switching tube VT turn-offs, and current value reduces on the inductance, and concrete waveform is as shown in Figure 8.
The PFC control loop can be introduced factors such as harmonic distortion and phase shift in the input current waveform; Source of error comprises the ripple in bridge rectifier, computing module and output and the predicted voltage etc.; Should technology carry out relevant control to the harmonic distortion that produces in the system to this, concrete grammar is following:
Predicted voltage is selected from the input voltage after the rectification; The composition that wherein comprises a small amount of second harmonic, this becomes branch to get into computing module, becomes the third harmonic distortion and the phase shift of input current at last; The ripple voltage that therefore must reduce to feedover is to reduce the distortion of input current.Can adopt a filter, can in ripple decay, provide than first order pole transient response time faster with duopole.
In addition, use the PFC of average-current mode control, its voltage circuit has the first order pole falling characteristic to the output transfer function, and therefore the error amplifier of an available flat gain compensates, and this will produce the high stable loop of 90 degree phase margins.Because the ripple voltage phase place that on output capacitance, produces is spent with the phasic difference mutually 90 of input current; So if error amplifier has smooth gain to second harmonic frequency; Voltage-phase differs 90 degree after will making phase place and the rectification of Harmonics of Input; The composition of phase shift is imported voltage error amplifier, can improve the power factor of system.
Use that the present invention proposes based on New LED lighting circuit special power factor correcting method, a power factor correction chip can be proposed out, the general principles block diagram is as shown in Figure 9, its its packing forms is shown in figure 10.
Chip internal contains functions such as overvoltage protection, under-voltage protection, peak current limit, the protection of line voltage detecting, guarantees the chip steady operation.Chip adopts less pin, practices thrift chip area, and circuit structure is more simplified, and greatly reduces chip cost, has improved the market competitiveness of chip.
Chip pin distributes as follows:
Table 2-1
Figure BSA00000628244600061
Though accompanying drawing and above stated specification have provided embodiments of the invention.But it is understandable that, it will be appreciated by those skilled in the art that and can the one or more assemblies in this assembly be combined into the individual feature assembly well.In alternative, specific assembly can be divided into a plurality of functional units, otherwise or.Simultaneously, scope of the present invention does not receive the restriction of these particular instances.Multiple variation all is possible, the difference on structure etc. for example, and no matter whether it is clearly provided in specification.Scope of the present invention is the same wide with the scope that accompanying claims provides at least.

Claims (4)

1. one kind is used for the power factor correcting method that LED throws light on, and it adopts the CCM pattern, Average Current Control, and said method comprises:
A) at input ac voltage after rectification, via a resistance (R AC) be converted into first current signal (IAC);
B) waveform of said first current signal (IAC) is the envelope of input rectifying voltage, and the detection electric current (ISENSE) of this signal and inductance superposes, and proofreaies and correct back output second current signal (I), and this second current signal (I) is as an input of computing module;
C) will be by the input of the input predicted voltage signal (VRMS) that obtains after input voltage mean value scaled down and the filtering as computing module.
2. according to the power factor correcting method of claim 1, when wherein said input predicted voltage signal (VRMS) is fed forward to the voltage circuit gain, the correction of an open circuit is provided.
3. according to the power factor correcting method of claim 1, wherein, do not change with average input voltage for the sustaining voltage loop gain is a definite value, said input predicted voltage signal (VRMS) signal through square after participate in computing.
4. according to the power factor correcting method of claim 1; Wherein since said input predicted voltage signal (VRMS) induction of signal of computing module be the line voltage signal; Little in order to guarantee the computing module input noise; The place need adopt a current mirror of 2: 1 to reduce input noise at said input predicted voltage signal (VRMS) signal, improves the performance of computing module.
CN2011103978239A 2011-12-05 2011-12-05 Power factor correction method for LED (light-emitting diode) lighting Pending CN102497700A (en)

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103078530A (en) * 2012-12-29 2013-05-01 东南大学 Digital power factor converter with fast transient response function and control method of digital power factor converter
CN105790616A (en) * 2016-05-27 2016-07-20 广东美的制冷设备有限公司 Power factor correction (PFC) circuit and method and device for identifying electric inductor thereof
CN105811791A (en) * 2016-05-27 2016-07-27 广东美的制冷设备有限公司 PFC (power factor correction) circuit and method and device for inductor identification of PFC circuit
CN105871235A (en) * 2016-05-27 2016-08-17 广东美的制冷设备有限公司 Power-factor correction (PFC) circuit and inductor identification method and device thereof
CN112003462A (en) * 2020-08-25 2020-11-27 科华恒盛股份有限公司 Harmonic compensation method and device of PFC circuit and terminal equipment

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Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103078530A (en) * 2012-12-29 2013-05-01 东南大学 Digital power factor converter with fast transient response function and control method of digital power factor converter
CN103078530B (en) * 2012-12-29 2015-09-30 东南大学 A kind of digit power factor converter of fast transient response and control method thereof
CN105790616A (en) * 2016-05-27 2016-07-20 广东美的制冷设备有限公司 Power factor correction (PFC) circuit and method and device for identifying electric inductor thereof
CN105811791A (en) * 2016-05-27 2016-07-27 广东美的制冷设备有限公司 PFC (power factor correction) circuit and method and device for inductor identification of PFC circuit
CN105871235A (en) * 2016-05-27 2016-08-17 广东美的制冷设备有限公司 Power-factor correction (PFC) circuit and inductor identification method and device thereof
CN105811791B (en) * 2016-05-27 2018-07-13 广东美的制冷设备有限公司 PFC pfc circuit and its inductance discrimination method and device
CN105790616B (en) * 2016-05-27 2018-12-18 广东美的制冷设备有限公司 PFC pfc circuit and its inductance discrimination method and device
CN112003462A (en) * 2020-08-25 2020-11-27 科华恒盛股份有限公司 Harmonic compensation method and device of PFC circuit and terminal equipment

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Application publication date: 20120613