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Design and implementation of testing system of LED driver power based on LabVIEW
Optik - International Journal for Light and Electron Optics 200 (2020) 163411
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.com/locate/ijleo
Original research article
Design and implementation of testing system of LED driver power based on LabVIEW
T
⁎
Yue Hua,1, Tianhu Wanga,1, , Tianyu Chena, Naiping Songb, Keming Yaoa, Yinsheng Luoa a b
School of Electrical and Information Engineering, Jiangsu University of Technology, Changzhou City, Jiangsu Province 213001, PR China School of Computer Engineering, Jiangsu University of Technology, Changzhou City, Jiangsu Province 213001, PR China
A R T IC LE I N F O
ABS TRA CT
Keywords: LED driver power LabVIEW Data acquisition Performance testing System evaluation
Due to the risk of failure of LED luminaries induced by the driver power, performance testing is especially important to driver power in some critical industries production and acceptance of work. A test system of LED driver based on LabVIEW is proposed to detect multiple physical parameters, including input voltage, output current, driver power efficiency, peak factor of current ripple and total harmonic distortion etc. The component selection of the system was investigated and the framework of the proposed system was presented. The hardware of this system mainly consists of signal conditioning modules, data acquisition card, test cables and computer. The software is designed by LabVIEW to realize the calculation, display and analysis of the collected data. The experimental results show that the system can realize the test of LED driver, and real-time grade determination of the test results according to relevant standards or the exact level specified by client. In addition, the system has simple structure and high expansibility, which is convenient for early use and later maintenance. The stability and bias was carried out to evaluate the proposed system by Minitab software, which ensured the measurement accuracy.
1. Introduction As the fourth generation of environmental protection light source [1,2], LED has developed rapidly with its advantages of green energy saving and long life, and is widely used in indoor, outdoor and various special occasions lighting [3]. It is known that the LED luminaire consists of LED modules, driver power and heat dissipation structure [4]. The driver power is to convert AC power supply into DC power suitable for the normal operation of LED light source, which is an important factor in affecting the quality of LED light and the overall performance of lighting system [5–7]. With the rapid development of the LED industry chain, the technical specifications and control accuracy requirements of the driver power are becoming higher and higher [8,9]. Therefore, it is important to provide a fast, accurate and fair test method for LED driver. At present, there are many comprehensive instruments for LED driver quality detection on the market, with complete test functions and high test accuracy. However, most of these comprehensive testers are expensive and bulky, and are generally used in high-power applications. They are not suitable for testing the quality of the drive power at the construction acceptance site. In addition, during the development process, researchers need to test the performance parameters of the drive power. For example, ⁎
Corresponding author. E-mail address: [email protected] (T. Wang). 1 These authors contributed equally to this paper. https://doi.org/10.1016/j.ijleo.2019.163411 Received 11 June 2019; Accepted 11 September 2019 0030-4026/ © 2019 Elsevier GmbH. All rights reserved.
Optik - International Journal for Light and Electron Optics 200 (2020) 163411
Y. Hu, et al.
Syifaul Fuada et al. designed a driving circuit for indoor lighting and data transmission [10]. In this research process, an oscilloscope was used to test the output signal waveform under different input signals. Roman Hrbac et al. proposed an LED driver circuit designed for adjustable white light illumination system [11], and used multimeter and oscilloscope to measure the efficiency of power supply at different control frequencies. Lei Han et al. studied the aging process of the driving power supply and used power analysis [12]. The instrument tests the output current and calculates the current ripple as the driving power failure criterion. In these experiments, the traditional testing instruments can only get the test results, and cannot further realize the automatic analysis and judgment of the test results at the same time. Nowadays, LabVIEW software developed by NI Company is widely used in test system because of its convenient use, friendly interface and powerful data processing function [13]. It takes general-purpose computer as its core hardware platform and sets userdefined templates [14]. All testing and calculation processes are implemented by software. It is very convenient to build the required test system and make the use process vivid [15]. In this work, a test system of LED driver based on LabVIEW is proposed to detect multiple physical parameters, including input voltage, output current, driver power efficiency, peak factor of current ripple and total harmonic distortion etc. The principle of methodology is introduced in Section 2. The design of hardware and software systems is presented in Section 3. Function system testing and system evaluation are explained in Section 4. Finally, the conclusion is described in Section 5. The proposed system could test and analyze some important performance parameters of LED driver according to IEC 62384, also provide data reference for R & D and production. 2. Principle of methodology The proposed system is designed to measure the performance parameters of the LED driver. The working principle of the test system is as follows: Voltage and current signals are processed by hardware, and then transformed into voltage signals suitable for computer acquisition and processing. Data acquisition card transmits data to software through USB data line. The data are calculated and analyzed by using the LabVIEW function toolkit and the wave-forms and test results of the collected signals are displayed on the front panel. The test and calculation procedures of the system are in accordance with IEC 62384, including power factor, efficiency, total harmonic distortion and peak-ripple factor of the LED driver. The product quality grade could be automatically evaluated according to the classification of related test items. 2.1. Power factor and efficiency test The power factor is defined as the product of the active power (Pin) at the input of the drive power divided by the effective value of the voltage (U) and current (I). The AC voltage and current are substituted into the formula (1) to calculate the effective value.
1 N
XRMS =
N −1
∑ x j2 (1)
j=0
The power factor (PF) is calculated as follows:
Pin =
PF =
1 N
N −1
∑ uj i j (2)
j=0
Pin × 100% UI
(3)
Efficiency is defined as the ratio of output power to input active power, and it is an index to measure the effective utilization rate of electric energy. Under the rated input voltage, frequency and output conditions, the input power and output power of the LED driver are measured after 15 min of stable operation. The efficiency formula is as follows:
η=
U0 I0 × 100% Pin
(4)
2.2. Total harmonic distortion (THD) test The total harmonic distortion rate is defined as the ratio of the effective value of the harmonic component to the effective value of the fundamental current. According to IEC 61000-3-2 (2018), the system proposed in this paper should consider the 2 ˜ 40th harmonic current components. In the communication system, if f(t) is a periodic non-sinusoidal signal with distortion, which can be decomposed into Fourier series: ∞
f (t ) =
∑ Ah sin(hωt+ϕh) = A0 h=0
∞
+
∑ (ah cosh ωt+bh sinh ωt ) h=1
(5)
A0 is the DC component, Ah and φh are the amplitude and initial phase angle of h order harmonic, and ah and bh are the cosine and sine terms of the h order harmonic. Using the FFT algorithm, the real part Ir(h) and the imaginary part Ii(h) of the fundamental wave 2
Optik - International Journal for Light and Electron Optics 200 (2020) 163411
Y. Hu, et al.
Fig. 1. System Structure Block Diagram.
and each harmonic are calculated, so that the content of each harmonic component can be obtained, and the total harmonic content (THDI) can be calculated by using Eq. (6). 40
THDI =
∑h = 2 (Ih)2 I1
40
× 100% =
∑h = 2 (Ir2 (h) + Ii2 (h)) I1
× 100%
(6)
2.3. Peak-ripple factor test The peak-ripple factor is defined as the ratio of the difference between the ripple peak and the trough of the wave to the absolute value of the DC component. The current signal collected at the output of the driver power is filtered by an FIR band-pass filter to obtain preliminary ripple information. Calculating the difference (IΔ) between the maximum and minimum of ripple crest and trough by using statistical function in LabVIEW. The peak-ripple factor is calculated as follows:
Peak − ripple factor =
IΔ I − Imin = max |I0 | |I0 |
(7)
3. System design The block diagram of the system is shown in Fig. 1. The test system includes hardware and software design. Hardware mainly includes input and output signal conditioning circuits, data acquisition card, test cables and computer. Software is based on LabVIEW platform in computer. It includes calculating, displaying and analyzing the data collected by the data acquisition card. 3.1. System hardware 3.1.1. Selection of data acquisition card Data acquisition card (Fig. 2) is the core of hardware design. Choosing suitable data acquisition card is the key factor to realize the test function of the system. The data acquisition card selected in this paper is a USB-3102A data acquisition card launched by Beijing Altai Company.
Fig. 2. Data Acquisition Card. 3
Optik - International Journal for Light and Electron Optics 200 (2020) 163411
Y. Hu, et al.
Fig. 3. System software function module diagram.
USB-3102A is a multifunctional data acquisition card. It has the ability to input 16 analog signals at the same time. It meets the requirement of the test system to collect 4 analog signals at the same time. The other channels can be used as standby channels to add extended functions later. Its sampling frequency can reach 250 Ksps. In addition, the data acquisition card can collect both AC voltage and DC voltage, and the range of input voltage can be collected is −10V+10 V.
3.1.2. Selection of input voltage transformer and current-voltage converter According to the system structure diagram, 220 V AC is used as the signal input of the LED driver. Therefore, the precise voltage transformer (Model: LXYA) produced by Huayi Electronics Co., Ltd. is selected. The original input voltage range is 0–250 V, the secondary output range is 0–7.07 V, the level of accuracy is 0.2. At the same time, the special current-voltage converter (Model: LXLA) for testing is selected to collect AC current. According to the test range, the input range of the primary side is 0–1 A, the output range of the secondary side is 0–7.07 V, the level of accuracy is 0.1. In order to protect the safety of operators and test equipment, the dielectric strength of the selected voltage transformer and current-voltage converter reaches 3000 V, which has the function of electrical isolation.
3.2. System software The software is developed on LabVIEW platform. Data processing in LabVIEW is used to calculate and analyze the collected data. In order to ensure that only authorized users can access the main interface of the test system, the user login SubVI was set up. The system software function module diagram is shown in Fig. 3. The user interface of the driving power test platform mainly includes user login, data acquisition, performance testing, data processing and exit. The tested signals are transmitted to the computer through the data acquisition card. In the data acquisition program, the analog signals are sampled continuously by using the special functions provided by Altai Company. Then four voltage values of the input data acquisition card are calculated by using the two program files of LabVIEW, including Averaged DC_RMS.vi and Amplitude and Level Measurements.vi. The test system data acquisition program is shown in Fig. 4.
Fig. 4. Data acquisition program. 4
Optik - International Journal for Light and Electron Optics 200 (2020) 163411
Y. Hu, et al.
Table 1 Parameters of LED driver. Parameter
Range
Input Voltage Output Constant Current Output Voltage Rated Load Efficiency Power Factor
AC 220˜240 V, 50/60Hz DC 340mA 6˜12V 3W ＞78% ＞50%
4. Results and discussions 4.1. Performance testing The input voltage rating, output type, power range and other parameters of the sample were systematically selected for testing within the system test range. For the purpose of performance system testing, the main interface of the system can be opened in a computer embedded with LabVIEW development platform. The waveform controls were added to the front panel to simulate the oscilloscope, which can be used to display the collected signal wave-forms. The computer calculates and analyses the signal according to IEC 62384, industry standard or customer's self-set demands. Before the use of this automatic testing system, the process calibration of the data acquisition part was carried out by using 5½ digit multifunction multimeter Fluke 8808A. Then this system is used to complete the automatic detection and grade determination of the tested sample. The specific parameters of the test sample are shown in Table 1. In this case, the test and result determination procedures of the system are in accordance with the IEC 62384 standard [16]. The evaluation of energy efficiency grade conforms to GB/T 24825 standard [17]. At the same time, the ranking evaluation procedure of the peak-ripple factor refers to the relevant industry standards. The contents of test standards in system programs are shown in Table 2. Before the test, the driver to be tested works continuously for 20 min according to its standard output to preheat. If the driver to be tested meets the requirements of the standard according to the technical indicators measured by the above test methods, it will be judged to meet the requirements of the standard. If it exceeds the technical indicators, the test interface will alarm and display, and record the wrong data. After debugging the hardware and software separately, the test system is run and the test parameters in the test interface are set according to the factory value of the sample. The test data and signal wave-forms obtained are directly displayed on the front panel of LabVIEW. Fig. 5 shows the front panel of LED driver test system. On the left side of the front panel, the parameters of the sample are set according to Table 1. The wave-forms on the right side of the figure are the voltage and current signals of the driving power supply to be measured collected through the data acquisition card, and the wave-forms displayed are selected through the tab. The specific physical parameters of the test are displayed in the lower half of the test interface. Boolean controls were added to the right side of the measuring sub-components to alarm for exceeding the limit value. At the same time, some performance test results were re-graded according to the grading in the setting standards, so as to reduce the harm caused by some manufacturers' false labeling of driver power. The results of system testing are shown in Table 3. It can be seen from Fig. 5 and Table 3 that the automatic test system can calculate the process quantity of the collected signal by using the function library in the LabVIEW software, so as to obtain the specific values of the power factor, efficiency, THD and peakripple factor of the LED driving power source. Furthermore, according to the relevant standards, the efficiency value was in the level 2 and the peak-ripple factor value was in the level 3. At the same time, the grade judgment results were displayed in yellow light on the right side of the corresponding test results in the front panel. Since data acquisition of test system directly affects the quality of test results, the manual test results obtained by the multimeter are compared with the system automatic test results to further verify the accuracy of the data collected by the test system proposed in this paper. The comparison results of the test data are shown in Table 4. As can be seen from the table above, the relative errors of the input and output current and voltage values of the test system are less than 1%.
Table 2 Testing standards. Input Voltage
Efficiency (Isolated Output)
Rated value ( ± 10%) Frequency: rated ± 3 Hz Total harmonic distortion rate≤ ± 5%
(power≤5W) Level 1: ≥78.5% Level 2: ≥75% Level 3: ≥67%
Peak-ripple factor Single-stage circuit Level 1: ≤50% Level 2: ≤100% Level 3: ≤150%
5
Double-stage circuit Level 1: ≤5% Level 2: ≤10% Level 3: ≤20%
Optik - International Journal for Light and Electron Optics 200 (2020) 163411
Y. Hu, et al.
Fig. 5. Front panel of LED driver test system. Table 3 The results of system testing. Parameter
Result
Input Voltage Output Constant Current Output Voltage Output Power Efficiency Power Factor Total harmonic distortion (THD) Current Peak-ripple factor
AC 222.86 V, 50.02Hz DC 332mA DC 9.41V 3.19W 78.32% 54.28% 1.66% 0.1901
Table 4 Comparisons of Test Data. Project
Manual testing (X)
Automatic testing (Y)
Error (Y-X)
Relative Error
Input voltage Input current Output voltage Output current
221.28V 34.222mA 9.38V 333.2mA
222.86 V 33.94mA 9.41V 331.6mA
1.58 −0.282 0.03 −1.6
0.7% 0.8% 0.3% 0.5%
4.2. Systematic evaluation In order to ensure that the test data of the system can be used and meet the quality inspection requirements, it is necessary to systematically evaluate the test system. Because the data acquisition of the signals at both ends of the driver directly affects the test system's efficiency of the driver, this system evaluation takes the efficiency of the driver as the test object. This paper analyses and evaluates the efficiency of system testing from two perspectives of stability and bias.
6
Optik - International Journal for Light and Electron Optics 200 (2020) 163411
Y. Hu, et al.
Fig. 6. Xbar-R chart.
4.2.1. Stability Stability refers to the total variation obtained by multiple measurements of a known sample over a long period of time using the same test system. To study the stability of the automatic test system proposed in this paper, a standard sample of driver power is selected as the object of stability analysis. In the measurements, the same surveyor is selected to measure the same standard sample in the same 15 time periods on the same day under the same environmental conditions, and three data were tested each time. The test results were explored by Minitab software to calculate the average ( X ) and mean deviation (R ), and then the Xbar-R chart (Fig. 6) was generated by the software. The chart includes upper control line (UCL), lower control line (LCL) and central line (CL). The range chart reflects the change of repeatability of the measurement system with time, and the mean chart shows the bias stability of the measurement system. Fig. 6 shows that all the test points are within the control boundary, and there is no sudden change in the control area. So it can be explained that the stability of the system in this paper is acceptable, and the bias analysis can be carried out in the next step. 4.2.2. Bias Bias refers to the difference between the mean and the actual value of the same operator's repeated test results for the same characteristics of the same sample. In this paper, the independent sample method is selected to test the bias of the efficiency test of the test system. When analyzing the bias of the measurement system, the above selected driver power was taken as the standard sample. Under the optimum test conditions, the operator used the test system to test the sample efficiency 15 times and takes the mean value, which was recorded as X. Each test minus x was the basic data for analysis, and the histogram was drawn with Minitab software. When the histogram is "high in the middle, low in both sides and symmetrical in left and right", it shows that the measurement process is in a statistic control stable state. The bias analysis histogram is shown in Fig. 7. As can be seen from the above figure, the bias analysis histogram of the efficiency testing of the system satisfies the required state, and there is no abnormal situation in the test process. Then continuing to test 15 data with significant T-test, and setting the hypothesis bias to be 0, the mean value could be obtained as 0.0333, the standard error of the mean value could be obtained as 0.0810. The 95% confidence interval (-0.1404, 0.2070), including 0 and P = 0.687 > 0.05, which indicates that the hypothesis of
Fig. 7. Bias analysis histogram. 7
Optik - International Journal for Light and Electron Optics 200 (2020) 163411
Y. Hu, et al.
accepting bias 0 is accepted. The above analysis shows that the bias of the system is acceptable. 5. Conclusions Design and implementation is presented of a testing system for LED driver. The system is designed to test the most important electrical performance parameters of LED driver. The measured parameters include input voltage, output current, driver power efficiency, peak factor of current ripple and total harmonic distortion etc. The implementation is based on LabVIEW, which can develop simple man-machine interface, scalable and low-cost testing system. The test data of each test LED driver is displayed intuitively by waveform diagram, and the test results are stored in the database for creating test reports. The test results and system evaluation show that the test system could accordance with the quality testing needs of the driving power supply and complete the grade evaluation of the test results. However, due to the limited operating conditions, there are still many detection indicators not implemented in the system. The reserved channel of data acquisition card can be used for later functional expansion to further enrich the test interface. Acknowledgments The authors would like to thank the funding support from the Natural Science Foundation of Jiangsu Province (Grants No.BK20150247), Six Talent Peaks Project in Jiangsu Province (No.2017-XNY-015), the Prospective Joint Program of Jiangsu Province (grant numbers BY2016030-07), Jiangsu Government Scholarship for Overseas Studies, and the Postgraduate Research & Practice Innovation Program of Jiangsu Province (SJCX18_1026 & SJCX18_1016). References [1] D. Jafrancesco, L. Mercatelli, P. Sansoni, et al., Optical design of a light-emitting diode lamp for a maritime lighthouse, Appl. Opt. 54 (11) (2015) 3252–3262. [2] X.J. Hu, K.Y. Qian, Optimal design of optical system for LED road lighting with high illuminance and luminance uniformity, Appl. Opt. 52 (24) (2013) 5888–5893. [3] A. Nardelli, E. Deuschle, L.D. Azevedo, et al., Assessment of light emitting diodes technology for general lighting: a critical review, Renew. Sustain. Energy Rev. 75 (2017) 368–379. [4] N. Yeh, T.J. Ding, P. Yeh, Light-emitting diodes’ light qualities and their corresponding scientific applications, Renew. Sustain. Energy Rev. 51 (2015) 55–61. [5] A. Pollock, H. Pollock, C. Pollock, High efficiency LED power supply, IEEE J. Emerg. Selected Topics Power Electron. 3 (3) (2015) 617–623. [6] B. Poorali, E. Adib, H. Farzanehfard, A single-stage single-switch soft-switching power-factor- correction LED driver, IEEE Trans. Power Electron. 32 (10) (2017) 7932–7940. [7] T.N. Gücin, B. Fincan, M. Biberoğlu, A series resonant converter-based multi-channel LED driver with inherent current balancing and dimming capability, IEEE Trans. Power Electron. 34 (3) (2019) 2693–2703. [8] J.L. Liu, J.L. Zhang, G.X. Wang, et al., Status of GaN-based green light-emitting diodes, Chin. Phys. B 24 (6) (2015) 1–8. [9] S. Nakamura, Nobel Lecture: Background story of the invention of efficient blue InGaN light emitting diodes, Rev. Mod. Phys. 87 (4) (2015) 1139–1152. [10] S. Fuada, T. Adiono, A.P. Putra, et al., LED driver design for indoor lighting and low-rate data transmission purpose, Optik 156 (2018) 847–856. [11] R. Hrbac, V. Kolar, T. Novak, et al., Low-cost solution of LED driving, designed for tunable white lighting systems, IFAC. Pap. OnLine 51 (6) (2018) 396–401. [12] L. Han, N. Narendran, An accelerated test method for predicting the useful life of an LED driver, IEEE Trans. Power Electron. 26 (8) (2011) 2249–2257. [13] P. Otomański, A. Szlachta, The evaluation of expanded uncertainty of measurement results in direct measurements using the LabVIEW environment, J. Electron. Meas. Instrum. 8 (6) (2008) 147–150. [14] V.D. Ćatić, N.M. Lukić, I.M. Salom, et al., An automated environment for hardware testing using PXI instrumentation and LabVIEW software, Telfor J. 9 (2) (2017) 98–103. [15] K.L. Xu, The design concept of a virtual experiment teaching platform for digital logic based on LabVIEW, Int. J. Hybrid Inf. Technol. 8 (2) (2015) 229–236. [16] IEC, DC Or AC Supplied Electronic Control Gear for LED Module-Performance Requirements, (2011) IEC 62384. [17] GB, DC Or AC Supplied Electronic Control Gear for LED Module-Performance Requirements, (2009) GB/T 24825-14.
8
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.com/locate/ijleo
Original research article
Design and implementation of testing system of LED driver power based on LabVIEW
T
⁎
Yue Hua,1, Tianhu Wanga,1, , Tianyu Chena, Naiping Songb, Keming Yaoa, Yinsheng Luoa a b
School of Electrical and Information Engineering, Jiangsu University of Technology, Changzhou City, Jiangsu Province 213001, PR China School of Computer Engineering, Jiangsu University of Technology, Changzhou City, Jiangsu Province 213001, PR China
A R T IC LE I N F O
ABS TRA CT
Keywords: LED driver power LabVIEW Data acquisition Performance testing System evaluation
Due to the risk of failure of LED luminaries induced by the driver power, performance testing is especially important to driver power in some critical industries production and acceptance of work. A test system of LED driver based on LabVIEW is proposed to detect multiple physical parameters, including input voltage, output current, driver power efficiency, peak factor of current ripple and total harmonic distortion etc. The component selection of the system was investigated and the framework of the proposed system was presented. The hardware of this system mainly consists of signal conditioning modules, data acquisition card, test cables and computer. The software is designed by LabVIEW to realize the calculation, display and analysis of the collected data. The experimental results show that the system can realize the test of LED driver, and real-time grade determination of the test results according to relevant standards or the exact level specified by client. In addition, the system has simple structure and high expansibility, which is convenient for early use and later maintenance. The stability and bias was carried out to evaluate the proposed system by Minitab software, which ensured the measurement accuracy.
1. Introduction As the fourth generation of environmental protection light source [1,2], LED has developed rapidly with its advantages of green energy saving and long life, and is widely used in indoor, outdoor and various special occasions lighting [3]. It is known that the LED luminaire consists of LED modules, driver power and heat dissipation structure [4]. The driver power is to convert AC power supply into DC power suitable for the normal operation of LED light source, which is an important factor in affecting the quality of LED light and the overall performance of lighting system [5–7]. With the rapid development of the LED industry chain, the technical specifications and control accuracy requirements of the driver power are becoming higher and higher [8,9]. Therefore, it is important to provide a fast, accurate and fair test method for LED driver. At present, there are many comprehensive instruments for LED driver quality detection on the market, with complete test functions and high test accuracy. However, most of these comprehensive testers are expensive and bulky, and are generally used in high-power applications. They are not suitable for testing the quality of the drive power at the construction acceptance site. In addition, during the development process, researchers need to test the performance parameters of the drive power. For example, ⁎
Corresponding author. E-mail address: [email protected] (T. Wang). 1 These authors contributed equally to this paper. https://doi.org/10.1016/j.ijleo.2019.163411 Received 11 June 2019; Accepted 11 September 2019 0030-4026/ © 2019 Elsevier GmbH. All rights reserved.
Optik - International Journal for Light and Electron Optics 200 (2020) 163411
Y. Hu, et al.
Syifaul Fuada et al. designed a driving circuit for indoor lighting and data transmission [10]. In this research process, an oscilloscope was used to test the output signal waveform under different input signals. Roman Hrbac et al. proposed an LED driver circuit designed for adjustable white light illumination system [11], and used multimeter and oscilloscope to measure the efficiency of power supply at different control frequencies. Lei Han et al. studied the aging process of the driving power supply and used power analysis [12]. The instrument tests the output current and calculates the current ripple as the driving power failure criterion. In these experiments, the traditional testing instruments can only get the test results, and cannot further realize the automatic analysis and judgment of the test results at the same time. Nowadays, LabVIEW software developed by NI Company is widely used in test system because of its convenient use, friendly interface and powerful data processing function [13]. It takes general-purpose computer as its core hardware platform and sets userdefined templates [14]. All testing and calculation processes are implemented by software. It is very convenient to build the required test system and make the use process vivid [15]. In this work, a test system of LED driver based on LabVIEW is proposed to detect multiple physical parameters, including input voltage, output current, driver power efficiency, peak factor of current ripple and total harmonic distortion etc. The principle of methodology is introduced in Section 2. The design of hardware and software systems is presented in Section 3. Function system testing and system evaluation are explained in Section 4. Finally, the conclusion is described in Section 5. The proposed system could test and analyze some important performance parameters of LED driver according to IEC 62384, also provide data reference for R & D and production. 2. Principle of methodology The proposed system is designed to measure the performance parameters of the LED driver. The working principle of the test system is as follows: Voltage and current signals are processed by hardware, and then transformed into voltage signals suitable for computer acquisition and processing. Data acquisition card transmits data to software through USB data line. The data are calculated and analyzed by using the LabVIEW function toolkit and the wave-forms and test results of the collected signals are displayed on the front panel. The test and calculation procedures of the system are in accordance with IEC 62384, including power factor, efficiency, total harmonic distortion and peak-ripple factor of the LED driver. The product quality grade could be automatically evaluated according to the classification of related test items. 2.1. Power factor and efficiency test The power factor is defined as the product of the active power (Pin) at the input of the drive power divided by the effective value of the voltage (U) and current (I). The AC voltage and current are substituted into the formula (1) to calculate the effective value.
1 N
XRMS =
N −1
∑ x j2 (1)
j=0
The power factor (PF) is calculated as follows:
Pin =
PF =
1 N
N −1
∑ uj i j (2)
j=0
Pin × 100% UI
(3)
Efficiency is defined as the ratio of output power to input active power, and it is an index to measure the effective utilization rate of electric energy. Under the rated input voltage, frequency and output conditions, the input power and output power of the LED driver are measured after 15 min of stable operation. The efficiency formula is as follows:
η=
U0 I0 × 100% Pin
(4)
2.2. Total harmonic distortion (THD) test The total harmonic distortion rate is defined as the ratio of the effective value of the harmonic component to the effective value of the fundamental current. According to IEC 61000-3-2 (2018), the system proposed in this paper should consider the 2 ˜ 40th harmonic current components. In the communication system, if f(t) is a periodic non-sinusoidal signal with distortion, which can be decomposed into Fourier series: ∞
f (t ) =
∑ Ah sin(hωt+ϕh) = A0 h=0
∞
+
∑ (ah cosh ωt+bh sinh ωt ) h=1
(5)
A0 is the DC component, Ah and φh are the amplitude and initial phase angle of h order harmonic, and ah and bh are the cosine and sine terms of the h order harmonic. Using the FFT algorithm, the real part Ir(h) and the imaginary part Ii(h) of the fundamental wave 2
Optik - International Journal for Light and Electron Optics 200 (2020) 163411
Y. Hu, et al.
Fig. 1. System Structure Block Diagram.
and each harmonic are calculated, so that the content of each harmonic component can be obtained, and the total harmonic content (THDI) can be calculated by using Eq. (6). 40
THDI =
∑h = 2 (Ih)2 I1
40
× 100% =
∑h = 2 (Ir2 (h) + Ii2 (h)) I1
× 100%
(6)
2.3. Peak-ripple factor test The peak-ripple factor is defined as the ratio of the difference between the ripple peak and the trough of the wave to the absolute value of the DC component. The current signal collected at the output of the driver power is filtered by an FIR band-pass filter to obtain preliminary ripple information. Calculating the difference (IΔ) between the maximum and minimum of ripple crest and trough by using statistical function in LabVIEW. The peak-ripple factor is calculated as follows:
Peak − ripple factor =
IΔ I − Imin = max |I0 | |I0 |
(7)
3. System design The block diagram of the system is shown in Fig. 1. The test system includes hardware and software design. Hardware mainly includes input and output signal conditioning circuits, data acquisition card, test cables and computer. Software is based on LabVIEW platform in computer. It includes calculating, displaying and analyzing the data collected by the data acquisition card. 3.1. System hardware 3.1.1. Selection of data acquisition card Data acquisition card (Fig. 2) is the core of hardware design. Choosing suitable data acquisition card is the key factor to realize the test function of the system. The data acquisition card selected in this paper is a USB-3102A data acquisition card launched by Beijing Altai Company.
Fig. 2. Data Acquisition Card. 3
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Fig. 3. System software function module diagram.
USB-3102A is a multifunctional data acquisition card. It has the ability to input 16 analog signals at the same time. It meets the requirement of the test system to collect 4 analog signals at the same time. The other channels can be used as standby channels to add extended functions later. Its sampling frequency can reach 250 Ksps. In addition, the data acquisition card can collect both AC voltage and DC voltage, and the range of input voltage can be collected is −10V+10 V.
3.1.2. Selection of input voltage transformer and current-voltage converter According to the system structure diagram, 220 V AC is used as the signal input of the LED driver. Therefore, the precise voltage transformer (Model: LXYA) produced by Huayi Electronics Co., Ltd. is selected. The original input voltage range is 0–250 V, the secondary output range is 0–7.07 V, the level of accuracy is 0.2. At the same time, the special current-voltage converter (Model: LXLA) for testing is selected to collect AC current. According to the test range, the input range of the primary side is 0–1 A, the output range of the secondary side is 0–7.07 V, the level of accuracy is 0.1. In order to protect the safety of operators and test equipment, the dielectric strength of the selected voltage transformer and current-voltage converter reaches 3000 V, which has the function of electrical isolation.
3.2. System software The software is developed on LabVIEW platform. Data processing in LabVIEW is used to calculate and analyze the collected data. In order to ensure that only authorized users can access the main interface of the test system, the user login SubVI was set up. The system software function module diagram is shown in Fig. 3. The user interface of the driving power test platform mainly includes user login, data acquisition, performance testing, data processing and exit. The tested signals are transmitted to the computer through the data acquisition card. In the data acquisition program, the analog signals are sampled continuously by using the special functions provided by Altai Company. Then four voltage values of the input data acquisition card are calculated by using the two program files of LabVIEW, including Averaged DC_RMS.vi and Amplitude and Level Measurements.vi. The test system data acquisition program is shown in Fig. 4.
Fig. 4. Data acquisition program. 4
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Table 1 Parameters of LED driver. Parameter
Range
Input Voltage Output Constant Current Output Voltage Rated Load Efficiency Power Factor
AC 220˜240 V, 50/60Hz DC 340mA 6˜12V 3W ＞78% ＞50%
4. Results and discussions 4.1. Performance testing The input voltage rating, output type, power range and other parameters of the sample were systematically selected for testing within the system test range. For the purpose of performance system testing, the main interface of the system can be opened in a computer embedded with LabVIEW development platform. The waveform controls were added to the front panel to simulate the oscilloscope, which can be used to display the collected signal wave-forms. The computer calculates and analyses the signal according to IEC 62384, industry standard or customer's self-set demands. Before the use of this automatic testing system, the process calibration of the data acquisition part was carried out by using 5½ digit multifunction multimeter Fluke 8808A. Then this system is used to complete the automatic detection and grade determination of the tested sample. The specific parameters of the test sample are shown in Table 1. In this case, the test and result determination procedures of the system are in accordance with the IEC 62384 standard [16]. The evaluation of energy efficiency grade conforms to GB/T 24825 standard [17]. At the same time, the ranking evaluation procedure of the peak-ripple factor refers to the relevant industry standards. The contents of test standards in system programs are shown in Table 2. Before the test, the driver to be tested works continuously for 20 min according to its standard output to preheat. If the driver to be tested meets the requirements of the standard according to the technical indicators measured by the above test methods, it will be judged to meet the requirements of the standard. If it exceeds the technical indicators, the test interface will alarm and display, and record the wrong data. After debugging the hardware and software separately, the test system is run and the test parameters in the test interface are set according to the factory value of the sample. The test data and signal wave-forms obtained are directly displayed on the front panel of LabVIEW. Fig. 5 shows the front panel of LED driver test system. On the left side of the front panel, the parameters of the sample are set according to Table 1. The wave-forms on the right side of the figure are the voltage and current signals of the driving power supply to be measured collected through the data acquisition card, and the wave-forms displayed are selected through the tab. The specific physical parameters of the test are displayed in the lower half of the test interface. Boolean controls were added to the right side of the measuring sub-components to alarm for exceeding the limit value. At the same time, some performance test results were re-graded according to the grading in the setting standards, so as to reduce the harm caused by some manufacturers' false labeling of driver power. The results of system testing are shown in Table 3. It can be seen from Fig. 5 and Table 3 that the automatic test system can calculate the process quantity of the collected signal by using the function library in the LabVIEW software, so as to obtain the specific values of the power factor, efficiency, THD and peakripple factor of the LED driving power source. Furthermore, according to the relevant standards, the efficiency value was in the level 2 and the peak-ripple factor value was in the level 3. At the same time, the grade judgment results were displayed in yellow light on the right side of the corresponding test results in the front panel. Since data acquisition of test system directly affects the quality of test results, the manual test results obtained by the multimeter are compared with the system automatic test results to further verify the accuracy of the data collected by the test system proposed in this paper. The comparison results of the test data are shown in Table 4. As can be seen from the table above, the relative errors of the input and output current and voltage values of the test system are less than 1%.
Table 2 Testing standards. Input Voltage
Efficiency (Isolated Output)
Rated value ( ± 10%) Frequency: rated ± 3 Hz Total harmonic distortion rate≤ ± 5%
(power≤5W) Level 1: ≥78.5% Level 2: ≥75% Level 3: ≥67%
Peak-ripple factor Single-stage circuit Level 1: ≤50% Level 2: ≤100% Level 3: ≤150%
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Double-stage circuit Level 1: ≤5% Level 2: ≤10% Level 3: ≤20%
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Fig. 5. Front panel of LED driver test system. Table 3 The results of system testing. Parameter
Result
Input Voltage Output Constant Current Output Voltage Output Power Efficiency Power Factor Total harmonic distortion (THD) Current Peak-ripple factor
AC 222.86 V, 50.02Hz DC 332mA DC 9.41V 3.19W 78.32% 54.28% 1.66% 0.1901
Table 4 Comparisons of Test Data. Project
Manual testing (X)
Automatic testing (Y)
Error (Y-X)
Relative Error
Input voltage Input current Output voltage Output current
221.28V 34.222mA 9.38V 333.2mA
222.86 V 33.94mA 9.41V 331.6mA
1.58 −0.282 0.03 −1.6
0.7% 0.8% 0.3% 0.5%
4.2. Systematic evaluation In order to ensure that the test data of the system can be used and meet the quality inspection requirements, it is necessary to systematically evaluate the test system. Because the data acquisition of the signals at both ends of the driver directly affects the test system's efficiency of the driver, this system evaluation takes the efficiency of the driver as the test object. This paper analyses and evaluates the efficiency of system testing from two perspectives of stability and bias.
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Fig. 6. Xbar-R chart.
4.2.1. Stability Stability refers to the total variation obtained by multiple measurements of a known sample over a long period of time using the same test system. To study the stability of the automatic test system proposed in this paper, a standard sample of driver power is selected as the object of stability analysis. In the measurements, the same surveyor is selected to measure the same standard sample in the same 15 time periods on the same day under the same environmental conditions, and three data were tested each time. The test results were explored by Minitab software to calculate the average ( X ) and mean deviation (R ), and then the Xbar-R chart (Fig. 6) was generated by the software. The chart includes upper control line (UCL), lower control line (LCL) and central line (CL). The range chart reflects the change of repeatability of the measurement system with time, and the mean chart shows the bias stability of the measurement system. Fig. 6 shows that all the test points are within the control boundary, and there is no sudden change in the control area. So it can be explained that the stability of the system in this paper is acceptable, and the bias analysis can be carried out in the next step. 4.2.2. Bias Bias refers to the difference between the mean and the actual value of the same operator's repeated test results for the same characteristics of the same sample. In this paper, the independent sample method is selected to test the bias of the efficiency test of the test system. When analyzing the bias of the measurement system, the above selected driver power was taken as the standard sample. Under the optimum test conditions, the operator used the test system to test the sample efficiency 15 times and takes the mean value, which was recorded as X. Each test minus x was the basic data for analysis, and the histogram was drawn with Minitab software. When the histogram is "high in the middle, low in both sides and symmetrical in left and right", it shows that the measurement process is in a statistic control stable state. The bias analysis histogram is shown in Fig. 7. As can be seen from the above figure, the bias analysis histogram of the efficiency testing of the system satisfies the required state, and there is no abnormal situation in the test process. Then continuing to test 15 data with significant T-test, and setting the hypothesis bias to be 0, the mean value could be obtained as 0.0333, the standard error of the mean value could be obtained as 0.0810. The 95% confidence interval (-0.1404, 0.2070), including 0 and P = 0.687 > 0.05, which indicates that the hypothesis of
Fig. 7. Bias analysis histogram. 7
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accepting bias 0 is accepted. The above analysis shows that the bias of the system is acceptable. 5. Conclusions Design and implementation is presented of a testing system for LED driver. The system is designed to test the most important electrical performance parameters of LED driver. The measured parameters include input voltage, output current, driver power efficiency, peak factor of current ripple and total harmonic distortion etc. The implementation is based on LabVIEW, which can develop simple man-machine interface, scalable and low-cost testing system. The test data of each test LED driver is displayed intuitively by waveform diagram, and the test results are stored in the database for creating test reports. The test results and system evaluation show that the test system could accordance with the quality testing needs of the driving power supply and complete the grade evaluation of the test results. However, due to the limited operating conditions, there are still many detection indicators not implemented in the system. The reserved channel of data acquisition card can be used for later functional expansion to further enrich the test interface. Acknowledgments The authors would like to thank the funding support from the Natural Science Foundation of Jiangsu Province (Grants No.BK20150247), Six Talent Peaks Project in Jiangsu Province (No.2017-XNY-015), the Prospective Joint Program of Jiangsu Province (grant numbers BY2016030-07), Jiangsu Government Scholarship for Overseas Studies, and the Postgraduate Research & Practice Innovation Program of Jiangsu Province (SJCX18_1026 & SJCX18_1016). References [1] D. Jafrancesco, L. Mercatelli, P. Sansoni, et al., Optical design of a light-emitting diode lamp for a maritime lighthouse, Appl. Opt. 54 (11) (2015) 3252–3262. [2] X.J. Hu, K.Y. Qian, Optimal design of optical system for LED road lighting with high illuminance and luminance uniformity, Appl. Opt. 52 (24) (2013) 5888–5893. [3] A. Nardelli, E. Deuschle, L.D. Azevedo, et al., Assessment of light emitting diodes technology for general lighting: a critical review, Renew. Sustain. Energy Rev. 75 (2017) 368–379. [4] N. Yeh, T.J. Ding, P. Yeh, Light-emitting diodes’ light qualities and their corresponding scientific applications, Renew. Sustain. Energy Rev. 51 (2015) 55–61. [5] A. Pollock, H. Pollock, C. Pollock, High efficiency LED power supply, IEEE J. Emerg. Selected Topics Power Electron. 3 (3) (2015) 617–623. [6] B. Poorali, E. Adib, H. Farzanehfard, A single-stage single-switch soft-switching power-factor- correction LED driver, IEEE Trans. Power Electron. 32 (10) (2017) 7932–7940. [7] T.N. Gücin, B. Fincan, M. Biberoğlu, A series resonant converter-based multi-channel LED driver with inherent current balancing and dimming capability, IEEE Trans. Power Electron. 34 (3) (2019) 2693–2703. [8] J.L. Liu, J.L. Zhang, G.X. Wang, et al., Status of GaN-based green light-emitting diodes, Chin. Phys. B 24 (6) (2015) 1–8. [9] S. Nakamura, Nobel Lecture: Background story of the invention of efficient blue InGaN light emitting diodes, Rev. Mod. Phys. 87 (4) (2015) 1139–1152. [10] S. Fuada, T. Adiono, A.P. Putra, et al., LED driver design for indoor lighting and low-rate data transmission purpose, Optik 156 (2018) 847–856. [11] R. Hrbac, V. Kolar, T. Novak, et al., Low-cost solution of LED driving, designed for tunable white lighting systems, IFAC. Pap. OnLine 51 (6) (2018) 396–401. [12] L. Han, N. Narendran, An accelerated test method for predicting the useful life of an LED driver, IEEE Trans. Power Electron. 26 (8) (2011) 2249–2257. [13] P. Otomański, A. Szlachta, The evaluation of expanded uncertainty of measurement results in direct measurements using the LabVIEW environment, J. Electron. Meas. Instrum. 8 (6) (2008) 147–150. [14] V.D. Ćatić, N.M. Lukić, I.M. Salom, et al., An automated environment for hardware testing using PXI instrumentation and LabVIEW software, Telfor J. 9 (2) (2017) 98–103. [15] K.L. Xu, The design concept of a virtual experiment teaching platform for digital logic based on LabVIEW, Int. J. Hybrid Inf. Technol. 8 (2) (2015) 229–236. [16] IEC, DC Or AC Supplied Electronic Control Gear for LED Module-Performance Requirements, (2011) IEC 62384. [17] GB, DC Or AC Supplied Electronic Control Gear for LED Module-Performance Requirements, (2009) GB/T 24825-14.
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