CN110856307A - Light flux and chromaticity coordinate tracking control method of RGB (red, green and blue) color mixing system - Google Patents

Abstract

The invention provides a light flux and chromaticity coordinate tracking control method of an RGB color mixing system, which comprises the following steps: firstly, calculating the luminous flux ratio of LED strings with different colors by utilizing a lever principle in a CIE1931 chromaticity space and utilizing a target chromaticity coordinate value and a chromaticity coordinate value of a mixed color point; then, tracking control is carried out on the chromaticity coordinate by utilizing hysteresis control in power electronics and a color theory in colorimetry; the light flux output of the whole system is controlled by controlling the sum of the duty ratios of all channels by the PI method. The control method can control the luminous flux output between 100lm and 600lm, and the error is within +/-2%; any chromaticity coordinate in a triangle formed by the RGB corresponding color mixing points can be accurately controlled, and the distance between the output coordinate and the reference coordinate is less than 0.007 in the whole color gamut of the CIE1976 chromaticity diagram.

Description

Light flux and chromaticity coordinate tracking control method of RGB (red, green and blue) color mixing system

Technical Field

The invention relates to the field of control of color mixing systems, in particular to a light flux and chromaticity coordinate tracking control method for an RGB color mixing system.

Background

The color of the LED lamp may drift over time due to aging and temperature effects. Some previous research efforts have sampled temperature, LED string current, and luminous flux outputs using thermal, current, or light sensors, with the outputs being regulated by various control schemes. The control scheme is temperature feed forward compensation (TFF), LED luminous Flux Feedback (FFB), color temperature or chromaticity coordinate feedback (CTFB or CCFB), or a combination of two or more control strategies, such as TFF & FFB FFB & CTFB, TFF & CCFB, FFB & CTFB, etc. In a dual-channel color mixing system, a PI control method is generally used for color temperature adjustment. However, the PI method is difficult to extend from two-channel color mixing to more-channel color mixing. Therefore, it has been proposed to use three independent PID controllers and three color sensors to regulate the three channels separately. However, this control method requires knowing the ratio of the three channels in advance. For the case of more than three channels, a method of adding one more sensor is proposed to solve the problem, however, the control method needs to know the proportion of the three channels in advance, and the prior art basically only realizes the tracking control of the color temperature along the white luminous point of the planckian locus, and rarely achieves the realization of any color coordinate point in the whole color gamut.

Disclosure of Invention

The invention aims to: aiming at the problems in the prior art, a light flux and chromaticity coordinate tracking control method of an RGB color mixing system is provided.

The invention aims to be realized by the following technical scheme:

a light flux and chromaticity coordinate tracking control method for an RGB color mixing system comprises the following steps:

firstly, according to a lever principle in a CIE1931 chromaticity space, calculating the luminous flux ratio of LED strings with different colors by using a target chromaticity coordinate value and a chromaticity coordinate value of a mixed color point;

then, tracking control is carried out on the chromaticity coordinate by using hysteresis control and a color theory; the light flux output of the whole system is controlled by controlling the sum of the duty ratios of all channels by the PI method.

Further, the method comprises the following steps: the chromaticity coordinates and luminous flux are corrected and adjusted.

Further, the tracking control of the chromaticity coordinate by using hysteresis control and color theory specifically comprises the following steps:

initial determination of RGB duty cycle;

and calculating the duty ratio of the RGB LED string.

Further, the formula for the initial determination of the RGB duty cycle is:

wherein the chromaticity coordinate of R, G, B is (x)_R,y_R)、(x_G,y_G) And (x)_B,y_B) The coordinate of the chromaticity point F after the color B and the color M are mixed is (x)_F,y_F) The coordinate of the chromaticity point M after the color R and the color G are mixed is (x)_M,y_M)。

Further, the formula for calculating the duty ratio of the RGB LED string is:

wherein k is R, G, B, α_k(n +1) represents the luminous flux ratio of the (n +1) th LED string, phi_o(n +1) represents the total luminous flux output by the LED string during the (n +1) th period, η_kFor the luminous efficiency of the kth LED string,

the voltage amplitude of the kth LED string,

the current amplitude of the kth LED string.

Further, the specific steps of controlling the luminous flux output of the whole system by controlling the sum of the duty ratios of all channels by using the PI method are as follows: measuring the output luminous flux phi with a photosensor_oAnd with a reference value phi for the luminous flux_refThe comparison is performed and the error is handled by the PI controller.

Further, the output result of the PI controller is the sum of duty ratios of all the LED strings_T，d_TWatch capable of showingShown as

Total duty cycle d of the next cycle_T(n +1) is regulated by a PI controller, and the regulation formula is as follows:wherein K_pIs the proportional gain, K_iIs the integral gain, Δ Φ [ j ]]＝Φ_ref-Φ_o[j]，T_samIs the sampling period.

Compared with the prior art, the system adopts a method of combining luminous flux feedback and chromaticity coordinate feedback control strategies, namely FFB & CCFB, so that the aging and temperature effects are compensated. Therefore, the proposed RGB color mixing system luminous flux and chromaticity coordinate tracking control method has the following significant advantages:

1) an accurate photoelectric system model is not required;

2) any color coordinate point within the entire gamut encompassed by the RGB points can be realized;

3) with the FFB & CCFB feedback control, color difference drift due to aging and temperature to the LEDs can be compensated using only RGB color sensors.

Experiments prove that the control method can control the luminous flux output to be between 100lm and 600lm, and the error is within +/-2%; any chromaticity coordinate in a triangle formed by the RGB corresponding color mixing points can be accurately controlled, and the distance between the output coordinate and the reference coordinate is less than 0.007 in the whole color gamut of the CIE1976 chromaticity diagram.

Drawings

FIG. 1 illustrates the application of the control method of the present invention to a topology;

FIG. 2 is a block diagram of chromaticity coordinate control in a CIE1931 chromaticity diagram;

FIG. 3 is a graph of luminous flux versus forward current for different color LEDs;

FIG. 4 is a graph of luminous flux versus junction temperature for different color LEDs;

FIG. 5 shows current amplitudes of LED strings under different duty ratios of RGB LED stringsAnd Q₁And Q₂A graph of switching frequency;

FIG. 6 is a flow chart of the control of the current amplitude adjustment of the LED string;

FIG. 7 is a graph of maximum luminous flux for each chromaticity coordinate value;

FIG. 8 is a control framework diagram of the overall system;

fig. 9 is a detailed control flowchart of luminous flux and chromaticity coordinate values;

FIG. 10 shows (x)_ref,y_ref)＝(0.33,0.33)andΦ_refWhen the voltage is 200lm, a current waveform diagram of the RGB LED string;

FIG. 11 shows (x)_ref,y_ref)＝(0.33,0.33)andΦ_ref600lm, the current waveform diagram of the RGB LED string;

FIG. 12 shows (x)_ref,y_ref)＝(0.25,0.45)andΦ_refWhen the voltage is 200lm, a current waveform diagram of the RGB LED string;

FIG. 13 shows (x)_ref,y_ref)＝(0.5,0.35)andΦ_refWhen the voltage is 200lm, a current waveform diagram of the RGB LED string;

FIG. 14 is (u'_ref,v′_ref) (0.2095,0.4714), luminous flux reference value Φ_refLuminous flux output phi in the variation between 100lm and 600lm_oError change of (u) &'_o,v′_o) And (u'_ref,v′_ref) A graph of distance changes between;

FIG. 15 is a plot of the experimental test plots of FIGS. 16 and 17;

FIG. 16 is phi_ref＝400lm，(u′_ref,v′_ref) Light flux phi varies over the color gamut_oThe output error map of (1);

FIG. 17 is phi_ref＝400lm，(u′_ref,v′_ref) (u 'when varied throughout the gamut'_o,v′_o) And (u'_ref,v′_ref) Distance change map of (2).

Detailed Description

The invention is described in detail below with reference to the figures and specific embodiments.

Examples

The invention combines hysteresis control in power electronics and a lever principle in a colorimetry theory, and provides a novel chromaticity coordinate control strategy for tracking any color coordinate point in the whole gamut formed by RGB. According to the lever principle in the CIE1931 chromaticity space, the luminous flux ratio of the LED strings with different colors can be calculated by utilizing the target chromaticity coordinate point and the RGB mixed color coordinate point. And the chromatic aberration drift caused by aging and temperature is compensated to the maximum extent by introducing a hysteresis control method. Meanwhile, a PI method is introduced into a color mixing system to control the output of the luminous flux of the whole system.

The method proposed by the present invention is validated on a structure as shown in figure 1. In this configuration, the average current amplitude of the LED string is:

let η_kThe luminous efficiency of the kth LED string is the luminous flux phi emitted by the kth LED string_kComprises the following steps:

when two or more colors are mixed, the chromaticity coordinates after mixing are:

wherein (x)_k,y_k) (k is 1,2, …, N) is the chromaticity coordinate of the mixed color, phi_kThe corresponding luminous flux.

The luminous flux and the chromaticity coordinate are controlled by the duty ratio of a switching tube in the module. In order to reduce the influence of aging and temperature on the color difference drift of the LED, the total luminous flux of the system is adjusted by the sum of the duty ratios of all the switching tubes, and the x chromaticity coordinate and the y chromaticity coordinate are controlled by the luminous flux ratio of the LED lamps with different colors. In order to minimize the color difference caused by the current amplitude of the LED, the current amplitude of the LED is adjusted by controlling the total current using the Bang-Bang control method.

The method comprises the following specific steps:

A. correction adjustment of chromaticity coordinates and luminous flux

Color sensors with IR filters (e.g., TCS3472) typically have four output channels, a C channel without an IR filter (Cdata), a red output channel (Rdata), a green output channel (Gdata), and a blue output channel (Bdata). The output of the color sensor is transmitted to the MCU through the IIC bus and then corrected by the following formula.

CIE tristimulus values XYZ and RGB have the following relationship:

wherein

Is a correlation matrix

To obtain the coefficients of the correlation matrix C defined in equation (5) above, we measured three different combinations. The first combination is that only the green LED is on and both the red and blue LEDs are off. Obtaining tristimulus values (X) by integrating sphere and color sensor respectively₁,Y₁,Z₁) And three channel values (R)₁,G₁,B₁). The second combination is that both the red and blue LEDs are on, the green LED is off, and the same way yields (X)₂,Y₂,Z₂) And (R)₂,G₂,B₂) The value is obtained. The third combination is that the red, green and blue LEDs are all on, and the same method gives (X)₃,Y₃,Z₃) And (R)₃,G₃,B₃) The value is obtained. The values obtained by the above three combinations are substituted into formula (5), and the values of the correlation matrix can be obtained.

The coefficients of the correlation matrix C are related to the relative positions of the light sensors and the LED lamps. If the relative positions of the two are changed, the matrix C will change. Otherwise, the matrix C will be fixed. In practice, the light sensor should be fixed in the lighting device, the relative position is fixed, and thus the matrix C will be fixed by the manufacturer.

The chromaticity coordinates were obtained as follows

The luminous flux phi can be calculated by multiplying the constant Y by epsilon

Φ＝εY (9)

The luminous flux of the whole system can be obtained by an integrating sphere test, and Y can be calculated by the formula (5). The parameter epsilon can be derived by training a set of data phi from the integrating sphere and data Y from the light sensor. The above mentioned test values can be obtained by using an EverfineHAAS-2000 high precision spectrum tester with the addition of an integrating sphere.

B. Control of chromaticity coordinates

In a CIE1931-xy chromaticity diagram, two lights with different colors are mixed according to a certain proportion, and a color coordinate obtained after mixing is positioned on a straight line of a connecting line of the two points; any three colors are mixed in a certain proportion, and color coordinates obtained after mixing are necessarily located in a triangle formed by the three colors; similarly, the color coordinates obtained by mixing any four colors must be located within the quadrangle enclosed by the four colors. RGB blending is the most common blending scheme, and the triangle surrounded by three RGB points occupies most of the whole CIE1931 chromaticity diagram. Thus, RGB color mixing control is chosen herein to analyze and validate the proposed color mixing tracking control method.

Initial determination of RGB duty cycle

To improve the tracking speed of the chromaticity coordinates after power-up, the initial value of the duty ratio of each channel is estimated before entering the feedback loop.

Output light flux phi_oCan be represented by the following formula:

final chromaticity coordinate (x) of the output light_o,y_o) From the ratio phi₁,φ₂,…,φ_N-1,φ_NDetermining

The luminous flux ratio of the kth LED string is

α_R,α_GAnd α_BRespectively α_R,i,α_G,iAnd α_B,iAnd (4) showing. In fig. 2, R, G, B has chromaticity coordinates of (x)_R,y_R)，(x_G,y_G) And (x)_B,y_B) And (4) showing. The reference chromaticity coordinate of point F is (x)_F,y_F)。

In fig. 2, point M is the intersection of two straight lines RG and BF, and point M is on the line RG and BF. The determinant for 2x2 can be listed as follows:

det[RG,MG]＝0 (12)

det[BF,FM]＝0 (13)

expanding the formula (12) and the formula (13)

(y_G-y_R)x_M-(x_G-x_R)y_M＝(y_G-y_R)x_G-(x_G-x_R)y_G(14)

(y_F-y_B)x_M-(x_F-x_B)y_M＝(y_F-y_B)x_F-(x_F-x_B)y_F(15)

Writing equations (14) and (15) in the form of a matrix equation:

solving equation (16), the point M (x) can be obtained_M,y_M) The following were used:

the tristimulus values of color R, G, B are X, respectively_R,Y_R,Z_R,X_G,Y_G,Z_GAnd X_B,Y_B,Z_B,

In fig. 2, the M point is a chromaticity point after the color R and the color G are mixed, and F is a chromaticity point after the color B and the color M are mixed. According to the lever principle in CIE1931 chromaticity space, the method can be obtained

Tristimulus value X_kAnd Z_kRespectively by chromaticity coordinate values x_kAnd y_kAnd tristimulus value Y_k(where k ═ R, G, B) the reverse can yield:

substituting the equations (20) and (21) into the equations (18) and (19)

From the formula (22) and the formula (23), it can be derived

According to the linear superposition relationship of the mixed color and the tristimulus values of the two primary colors, the method can obtain

Y_M＝Y_R+Y_G(26)

From the equations (25) and (26), it can be obtained

The distance between two points is taken into account and is given by the formula (24) and the formula (27)

Tristimulus value Y_k(where k is R, G, B) and luminous flux phi_kLinearly proportional, and can be converted into

According to the definition of formula (11), we have

α_R+α_G+α_B＝1 (32)

By rewriting the equations (30) to (32) in a matrix form, as shown in (33), the initial value α can be obtained by solving the equation (33)_R,i,α_G,iAnd α_B,iSuch as formulas (34) - (36).

According to the formula (11), the initial value of the luminous flux of the LED string can be obtained.

φ_k,i＝α_k,iΦ_o,where k＝R,G,B (37)

Substituting equation (36) into equation (2) yields

2. Feedback control method

It can be seen from fig. 3 that the luminous efficiency varies with the forward current of the LED. Therefore, in order to reduce the color difference caused by the forward current of the LED, the total current is controlled in the circuit topology, and a current balancing mechanism is introduced to maintain the amplitude of the LED current constant. However, current equalization errors can cause tracking errors in chromaticity coordinates. As can be seen from fig. 4, the luminous efficiency varies with the junction temperature of the LED. And thus will cause an error in accurate tracking of the chromaticity coordinates. In order to solve the problem of color difference drift caused by unpredictable factors such as temperature, aging, forward current, current balance error and the like, the patent provides a novel control strategy based on hysteresis control of power electronics and a color theory of colorimetry.

The chromaticity coordinate O (x) of the final system output due to the existence of chromatic aberration drift_O,y_O) Coordinates (x) with the target point F in FIG. 2_F,y_F) Is different. M 'is the intersection of the straight lines RG and BO, with M' on the straight lines RG and BO. Similarly, the coordinates of M' can be found as follows:

let

For delta_oAnd delta_ref-Δδ_refA/2 and a_ref+Δδ _ref2 two reference boundary values are compared, Delta delta_refIs the bandwidth, the luminous flux ratio of the red LED string α in the next period_R(n +1) is:

wherein, Delta α_RIs a predefined value that can control the loop gain and the sensitivity of the chromaticity coordinates.

Let

For chi o and chi_ref-Δχ_refA/2 and a%_ref+Δχ _ref2 two reference boundary values are compared, Δ χ_refIs the bandwidth. Luminous flux ratio p of blue LED string in next period_B(n +1) is:

wherein, Delta α_BIs a predefined value and can control the loop gain and the sensitivity of the chromaticity coordinates.

According to α_R(n+1)+α_G(n+1)+α_B(n +1) ═ 1, the luminous flux ratio of the green LED string α_G(n +1) may be represented as:

α_G(n+1)＝1-α_R(n+1)-α_B(n+1) (46)

according to equation (32) and equation (9), the duty cycles of the rgb led strings are:

control of current amplitude and luminous flux of LED string

In order to minimize the color drift, the amplitude of the LED string current is controlled by controlling the switch tube Q₁And Q₂Switching frequency f_QTo make the total current i_TKept constant and then passed through a current balancing network so that the current of each LED string is kept constant, rather than being kept constant by sampling the current of each LED string. Taking the RGB LED string as an example,

and

respectively represent switches S_R,S_GAnd S_BThe duty cycle of (c). The current amplitude and Q of the LED string can be obtained by the formula (1)₁And Q₂The switching frequency relationship is shown in fig. 5. Since this structure can realize the function of current equalization, the currents flowing through all the LED strings are approximately equal, i.e., the current flowing through all the LED strings is approximately equal

The red, green and blue lines in FIG. 5 respectively indicate

Andthe amplitude of the LED string current. It can be seen that the magnitude of the LED string current follows the switch Q₁And Q₂Is decreased with an increase in the switching frequency of and switch S_R,S_GAnd S_BIs substantially independent of the duty cycle of the circuit. Thus, the switch Q₁,Q₂And S_kIs independent of the control of (a). FIG. 6 is a control flow chart for adjusting the amplitude of the current in the LED string by controlling the switch Q₁And Q₂Switching frequency of (1) and amplitude of current of LED string i_T,refSet to 300 mA.

Measuring the output luminous flux phi with a photosensor_oAnd with a reference value phi for the luminous flux_refA comparison is made and the error is processed by a proportional-integral (PI) controller. The output result of the PI controller is the sum of all the LED string duty ratios, d_TCan be expressed as

Total duty cycle d of the next cycle_T(n +1) is regulated by PI control, and the regulation formula is as follows:

wherein, Δ Φ [ j]＝Φ_ref-Φ_o[j],Φ_o[j]Is phi_oJ sample of (1), K_pIs the proportional gain, K_iIs the integral gain, T_samIs the sampling period.

The duty cycle of the kth LED string may be expressed as:

to ensure chromaticity coordinates at the output luminous flux phi_oThe duty cycles of the modules must be increased or decreased at the same rate while changing, which remains the same. Switch S_kDuty ratio of

Must be between 0 and 1, so the total duty cycle d_TIs finite, the maximum value of the total duty cycle being

According to the formulas (3) and (50), the maximum luminous flux Φ_o,maxIs composed of

Substituting equation (51) into equation (52)

The maximum luminous flux at each chromaticity coordinate value is shown in fig. 7 according to the parameters given in table two. It can be seen that the maximum output luminous flux is different at different chromaticity coordinate values. Output light flux Φ for uniformity_oCan only be adjusted from 0 to the minimum light flux value phi in all chromaticity coordinate values in the whole color gamut_o,max。

D. Control flow of output luminous flux and chromaticity coordinate value

In FIG. 1, a switching tube Q₁And Q₂The switching tube S is controlled by the bang-bang control method shown in FIG. 6_k(k ═ 1,2,3, …, N) was controlled by the methods shown in fig. 8 and 9. To compensate for the effects of aging, temperature and certain unpredictable factors, two control loops are used to adjust the output luminous flux and track the chromaticity coordinates, respectively. The control flow chart of the entire system is shown in fig. 8. When the system is powered on, two cycles are always performed,until the system is powered down. The first cycle is to adjust the output luminous flux by using a PI control method, and the second cycle is to perform tracking control on chromaticity coordinates by using a new method proposed by hysteresis control and color theory. Fig. 9 is a detailed control flow chart of the luminous flux and the output chromaticity coordinate value. Reference value of luminous flux phi_refAnd a chromaticity coordinate reference value (x)_F,y_F) Can be set according to the requirements of users. Coordinate (x)_R,y_R),(x_G,y_G) And (x)_B,y_B) The test can be carried out by a high-precision spectral performance analysis tester in advance. When the user inputs a desired color, a chromaticity coordinate reference value (x) is determined_F,y_F). According to the formula (17), the coordinates (x) are obtained_M,y_M) Then the reference values delta are derived separately_refHexix-_ref. Firstly, the optical sensor starts to collect signals and sends data to the single chip microcomputer through the IIC bus. The data sent back to the singlechip by the optical sensor is used for calculating the current output chromaticity coordinate value and output luminous flux. Comparing the measured luminous flux with a reference luminous flux, transmitting the error to a PI controller, and deriving the total duty ratio d by using a formula (48)_T. Then, the coordinates (x) are obtained by the formula (39)_M′,y_M′) Then, δ o and χ o are obtained by equations (41) and (43), respectively. The calculated values δ o and χ o are associated with two reference frequency bands (δ)_ref-Δδ_ref/2,δ_ref+Δδ_ref[ 2 ] and [ chi ]_ref-Δχ_ref/2,χ_ref+Δχ_ref/2) to find the ratio α of the next switching period_R,α_GAnd α_BWhen the ratio α is obtained_R,α_GAnd α_BAnd (3) determining the duty ratio by the formula (47) and controlling the on-off of the switch tube of each module. The closed-loop control of the two cycles is not stopped until the power supply is turned off, so that the output luminous flux and chromaticity coordinate values of the system are monitored all the time, and the color difference drift is effectively reduced.

Experimental verification

For better color uniformity, LEDs of different colors on the LED board are arranged alternately so that LED strings of the same color are not adjacent. Mixed color LEThe D system is composed of LED strings of three colors of red, green and blue. The optical sensor is placed in the upper right corner of the drive board. Meanwhile, the driving board is close to the integrating sphere, so that the optical sensor can collect data information of the LED placed in the integrating sphere. In this experiment, we used an integrating sphere to mix the different colors of LED light so that it was not affected by the external environment. However, in practical applications, the integrating sphere is replaced by a color mixing mask, which functions as an integrating sphere. The output light flux and chromaticity coordinates were measured using the optical sensor TAOS TCS3472 and verified using the high-precision spectral performance analysis tester HAAS-2000. The single chip microcomputer MC9S08QE128 firstly reads data values of Rdata, Gdata, Bdata and Cdata from the optical sensor through the IIC bus. Then proceed to phi_oAnd (x)_O,y_O) And (4) calculating and correcting the high-precision spectrum performance analysis tester. The correction coefficient of the TCS3472 will only vary with the relative positions of the light sensor and the LED light source, and will not vary with the LED junction temperature and power. Therefore, in practical applications, as long as the relative position of the light sensor and the light source is fixed, the correction coefficient of TCS3472 is also fixed.

Table parameters for experimental tests

As can be seen from fig. 10 to 11, under the same reference chromaticity coordinates, the duty ratio of each LED string is substantially the same, and the sum of the duty ratios increases with the increase of the luminous flux. As can be seen from fig. 12 and 13, the duty ratio of each LED string varies under different reference chromaticity coordinates, but if the luminous flux is constant, the sum of the duty ratios remains constant. Fig. 14-17 show the performance of luminous flux and chromaticity coordinate control, and it can be seen that phi is within the entire gamut_maxThe theoretical minimum is 715 lm. In practical application, considerTo the tolerance of the LED performance, the maximum output is set to 600 lm. And, the whole system light is set to be dimmable to 20%, the minimum output is set to 100 lm. Therefore, the present patent sets the adjustment range of the luminous flux to 100lm to 600lm in the entire color gamut. As is well known, the CIE commission recommends CIE1976 as the chromaticity diagram for analyzing light sources, since CIE1976 is the most uniform chromaticity space. Further, CIE technical report 001:2014 "chromatography Difference Specification for Light Sources" refers to: for the color difference analysis of a common illumination source, it is recommended to use a circle in the CIE1976 chromaticity diagram instead of the macadam ellipse in the CIE1931 chromaticity diagram. Thus, instead of the CIE1931 macadam ellipse, the u 'v' circle in the CIE1976 chromaticity diagram is used to visualize the acceptable color difference of the control method. However, when different colors are mixed, the leverage used to calculate the color formula only holds true in CIE1931(x, y). Therefore, CIE1931(x, y) is used for the chromaticity coordinate feedback control. When analyzing the chromaticity tolerance, CIE1931(x, y) should be converted to CIE1976(u ', v').

The coordinate transformation formula from CIE1931(x, y) to CIE1976(u ', v') is:

the chromaticity tolerance of a light source is generally expressed by the distance between two coordinates in a diagram (u ', v') of the CIE1976 chromaticity diagram, in which Δ u 'v' is (u ', v')₁′,v₁') and (u)₂′,v₂') the distance between two points, can be expressed as

As can be seen from FIG. 14, when the output luminous flux varies in the range of 100lm to 600lm, the luminous flux error is within. + -. 2%, when Φ is_refVarying between 100lm and 600lm, (u'_o,v′_o) And (u'_ref,v′_ref) Is less than 0.006. Selecting a reference coordinate (x)_E,y_E) The reference coordinate is substantially at the midpoint of the RGB color gamut in the CIE1931 chromaticity diagram (0.33 ). According to the formula (54), the coordinate value (x) in CIE1931 chromaticity diagram_E,y_E) (0.33 ) can be converted to coordinate values (u'_ref,v′_ref) = (0.2095, 0.4714). The red dots in fig. 15 represent the test points of the experiment. As can be seen, the test points are uniformly distributed within the triangular color gamut surrounded by the three color points of red, green and blue. As can be seen from FIG. 16, when Φ_ref＝400lm，(u′_ref,v′_ref) Light flux phi varies over the color gamut_oThe error of (c) is kept within ± 1%. As can be seen from FIG. 17, when Φ_ref400lm constant, (u'_ref,v′_ref) (u 'when varied throughout the gamut'_o,v′_o) And (u'_ref,v′_ref) Is less than 0.007. From the above experimental results, it can be seen that the control strategy proposed by the present patent has good luminous flux control and color coordinate tracking performance.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, it should be noted that any modifications, equivalents and improvements made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (7)

1. A light flux and chromaticity coordinate tracking control method for an RGB color mixing system is characterized by comprising the following steps:

firstly, calculating the luminous flux ratio of LED strings with different colors by utilizing a lever principle in a CIE1931 chromaticity space and utilizing a target chromaticity coordinate value and a chromaticity coordinate value of a mixed color point;

then, tracking control is carried out on the chromaticity coordinate by utilizing hysteresis control in power electronics and a color theory in colorimetry; the light flux output of the whole system is controlled by controlling the sum of the duty ratios of all channels by the PI method.

2. A method as claimed in claim 1, wherein the method comprises the following steps: the chromaticity coordinates and luminous flux are corrected and adjusted.

3. The method as claimed in claim 1, wherein the step of using hysteresis control and color theory to control the chromaticity coordinate comprises the steps of:

initial determination of RGB duty cycle;

and calculating the duty ratio of the RGB LED string.

4. A method as claimed in claim 3, wherein the formula for the initial determination of RGB duty cycle is:

wherein the chromaticity coordinate of R, G, B is (x)_R,y_R)、(x_G,y_G) And (x)_B,y_B) The coordinate of the chromaticity point F after the color B and the color M are mixed is (x)_F,y_F) The coordinate of the chromaticity point M after the color R and the color G are mixed is (x)_M,y_M)。

5. The method as claimed in claim 3, wherein the formula for calculating the duty ratio of the RGB LED string is as follows:

wherein k is R, G, B, α_k(n +1) represents the luminous flux ratio of the (n +1) th cycle LED string, phi_o(n +1) represents the total luminous flux output by the LED string during the (n +1) th period, η_kFor the luminous efficiency of the kth LED string,

the voltage amplitude of the kth LED string,

the current amplitude of the kth LED string.

6. The method as claimed in claim 1, wherein the specific steps of controlling the luminous flux output of the whole system by controlling the sum of the duty ratios of all channels by PI method comprises: measuring the output luminous flux phi with a photosensor_oAnd with a reference value phi for the luminous flux_refThe comparison is performed and the error is handled by the PI controller.

7. The method as claimed in claim 6, wherein the output result of the PI controller is the sum of the duty cycles of all the LED strings_T，d_TCan be expressed as

Total duty cycle d of the next cycle_T(n +1) is regulated by a PI controller, and the regulation formula is as follows:wherein K_pIs the proportional gain, K_iIs the integral gain, Δ Φ [ j ]]＝Φ_ref-Φ_o[j]，T_samIs the sampling period.

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