Introduction LED Lamp Review Supplying LEDs Off-Line Power Supplies for LED Lamps Conclusions

Transcription

1 efficient energy conversion, industrial electronics and lighting Universidad de Oviedo J. Marcos Alonso Universidad de Oviedo, Spain Campus de Viesques, Edificio 3, Sala Gijón, Asturias Introduction LED Lamp Review Supplying LEDs Off-Line Power Supplies for LED Lamps Conclusions 1

2 Fire Candle Oil Lamp Incandescent Discharge COMBUSTION ELECTRIC CONVERSION Solid State Lamp (LED) SEMICONDUCTORS Visible Radiation (W) Lumen Takes into account the eye response Electric energy (W) Able to excite the human eye Heat (W) Non-visible radiation (IR, UV) (W) The sensitivity of human eye is different for each wavelength 2

3 Defines the ability of a light to reproduce the different colors of an object The higher the CRI the better the color reproduction: Lamp with CRI < 60 Lamp With CRI > 80 Light Source CRI Sun light (best CRI) 100 Incandescent >95 Fluorescent 85 HP Sodium 25 Metal Halide 80 LED LEDs are based on a PN semiconductor structure Free carriers (e- y h) circulate through the junction Some recombinations e-/h generate visible radiation (light) but not all of them. 3

4 Types of e-/h recombinations: Radiative recombination: generates a photon with energy equal to the material band gap, E g = h f Non-radiative recombination: generates energy that is transformed into vibration in the lattice and finally heat (usually known as phonon). vibration e- Photon lattice e- h h Radiative recombination Non-radiative recombination Not desired Produced due to lattice defects (dislocations, impurities, etc.) Long life: 40, ,000 hours Small size Robust against vibrations and bumps Instant restart Low voltage operation Multicolor light source 4

5 LEDs do not emit IR/UV radiation All losses are transformed in heat Most of heat is evacuated by conduction through the LED case Cooling is a most important issue when working with LEDs Heatsink is an important element in the LED lamp structure 5

6 Light Source Efficacy (lm/w) 10/12/2018 White Light LEDs Traditional Light Sources LED technology has evolved spectacularly in the last years White LED (0.1W) H.P. Na (400W) Metal Halide (35W) Fluorescent (40W) CFL (6W) Halogen incand. (100W) Incandesc. (40W) Efficacy (lm/w) LEDs have achieved the highest efficacy at the present time 6

7 LED current 10/12/2018 Automotive Lighting and Signaling Backlighting, TV, Computers, etc. Road Signals Architectural applications General Lighting: Street, portable, office, etc. LEDs cannot be supplied with a voltage source typ min max I LED V BAT LED V LED - LED voltage LEDs exhibit very low series resistance The LED current would be nearly unlimited A very small variation of input voltage or LED characteristic would produce a great variation in LED current 7

8 LED current 10/12/2018 Current limitation using series resistance typ min max R LIM I LED V BAT LED - V LED I LED = (V BAT -V LED )/ R LIM LED voltage Very simple. Low cost. No EMI Low efficiency: losses in the series resistance Poor LED current regulation against input voltage variations, temperature, LED characteristic, etc. Not suitable for high power due to low efficiency Linear Current Source Linear PWM Switching Power Supplies ILED RLIM ISRC VBAT LED VBAT PWM LED VBAT Control RS Current regulation Simple. Low number of components No EMI generation Low efficiency LED power control Luminous flux variation (dimming) Constant peak current Used to avoid changes in color coordinates and color temperature Low losses. High Efficiency Higher cost. Higher number of components LED current regulation and control Efficient dimming Flexible: multiple functions can be implemented EMI generation 8

9 Adjustable output current up to 500 ma (± 5%) PWM dimming Input voltage up to 42 V Low voltage drop Several protections: open circuit, short circuit, thermal, inverse polarity. Wide temperature range: -40 ºC 150 ºC Buck Output voltage versus Duty cycle Boost Ideal Real Buck-Boost SEPIC Duty cycle 9

10 Hysteretic control for LED lamps P MOSFET Buck Converter Sensor Hysteretic control (6% accuracy) Input voltage: 4.5V 35V Switching frequency up to 1.5 MHz Programmable maximum current Analog and PWM Dimming Typical diagram of a LED power supply A C M a i n s P o w e r F a c t o r C o r r e c t i o n L E D D r i v e r L E D s Harmonic Current Standard: IEC Class C High quality power factor correction is necessary, especially for power above 25W Street Lighting 10

11 Classifies the different equipment into four different classes Class C corresponds specifically to lighting equipment Active power lower than 25 W 11

12 Active power higher than 25 W i g i s L a m p v g P F C Single Stage V B C B v g i g p g P g Input and output power vary with double the line frequency (100 Hz) A big filter capacitor C B is employed to smooth lamp current Usually electrolytic capacitors are required 12

13 Vled Iled Time (s) 10/12/2018 v g i g i g v g P F C Single Stage i s V B p g C B L a m p P g Bus Voltage Ripple, ^ VB ( V ) f L = 5 0 H z Pv ( W / V ) Bus Capacitance, C B ( F ) Voltage Ripple (peak value): The output ripple depends on output power, output voltage and filter capacitance The ripple increases for higher output power and lower bus voltage L i n e S L i 206 LED lamp voltage, V LED lamp current, A C O Lamp voltage (V) Lamp current (A) V g R g LED lamp Line: 230 V / 50 Hz LED lamp: 200 V/0.35 A fs= 50 khz Li= 0.9 mh Co= 130 uf T i m e, s A capacitor of 130 uf is required for a 30% ripple current 0.1 A 13

14 They are cheap and compact but: The lifetime specifications for aluminum electrolytic capacitors operating at maximum permitted core temperature are typically 1,000 to 10,000 hours. LED lamps can reach a lifetime up to 100,000!! Longer life, but: Higher cost Higher volume It is important to reduce the capacitance in order to save space and money!! 14

15 For the purpose of further reducing the storage capacitance, a method of injecting the third harmonic current into the input current flow is proposed. While ensuring that the input power factor is always higher than 0.9 to comply with regulation standards such as ENERGY STAR, the storage capacitance can be reduced to 65.6% of that with an input power factor of 1. A bidirectional buck-boost converter is connected at the output of the typical single phase PWM rectifier. An auxiliary capacitor with capacitance Cs is used as an energy storage element. We control the bidirectional converter as a buck mode when ripple energy needs to be stored in the Cs. It is controlled as a boost mode when ripple energy needs to be released back to the dc link 15

16 It consists of two power conversion stages: The first stage is a buck converter operating in discontinuous capacitor voltage mode, so that the input current is continuous. It is used to deliver a regulated current for the second stage. The second stage is a current-fed inverter, in which the semiconductor switches are operated at constant switching frequency and constant duty cycle of 0.5. The power supplying to the LED string is regulated by controlling the duty cycle of the main switch in the front-stage buck converter. The two stages are interconnected by an LC filter, which is designed to attenuate harmonics at double of the line frequency. Instead of using an electrolytic capacitor for the filter, a polyester capacitor of better lifetime expectancy is used. i g i s L a m p i g i s L a m p v g I d e a l PFC Stage V B C B D C / D C v g Q u a s i PFC Stage V B C B D C / D C v g p g v g i g i g P g a p - a V B p g P g The second stage compensates the bus voltage ripple, usually via duty cycle regulation The bus ripple can be increased so that bus capacitance can be reduced Higher complexity, higher cost, lower efficiency 16

17 i g v g - I n t e g r a t e d P F C / D C - D C S t a g e i o v o - L a m p C B Both stages share the same controlled switch Both stages operate at same switching frequency and duty cycle Higher voltage/current in the shared controlled switch Lower complexity, lower cost First Stage D 1 D 2 M 2 L i n e L i C B L O C O M 1 Natural Power Factor Corrector in DCM Output voltage higher/lower than input voltage 17

18 First Stage Second Stage D 1 D 2 L i n e L i C B L O C O M 1 M 2 Natural Power Factor Corrector in DCM Output voltage higher/lower than input voltage Corrects the sign inversion of the first stage Operation in DCM or CCM DCM is investigated in this work First Stage Second Stage D 1 D 2 L i n e L i C B L O C O M 1 M 2 The two switches can be integrated in a single switch 18

19 D 1 D 2 D 3 L i C B L i n e DCM L O C O M 1 DCM Single-stage converter with high power factor Li operates in DCM to provide power factor correction Lo operates also in DCM i g ( Not to scale) Line Current D 1 D 2 D 3 D T s Line Semiperiod ( T L / 2 ) C B Input Power L i L O C O Output Power M 1 Output Voltage and Bus Voltage Output Current: 19

20 Bus voltage low frequency ripple is transferred to the output: D 1 D 2 D 3 Bus Voltage C B Output Voltage L i L O C O M 1 Bus Voltage low frequency ripple: Output voltage versus bus voltage in output stage: Ripple voltage transformation ratio: Taking derivative i D 1 ( Not to scale) i D 1 _ p e a k Input Inductor Bus Capacitor t 1 Line Semiperiod ( T L / 2 ) D 1 D 2 D 3 C B L i L O C O M 1 Output Inductor Output Capacitor LED Current Ripple 20

21 LED Lamp 60 LED Osram Golden Dragon LW W5SG Power Rating: 70 W Voltage and Current: 200 V / 350 ma Luminous Flux: 1500 lm Equivalent Circuit: Vg = 170 V, Rg = 87 L i n e E M I F i l t e r Laboratory Prototype and List of Materials 4 x H E R G D 1 D 2 D 3 H E R G L i 0. 9 m H E F D 3 0 / N 8 7 D r i v e r L M H E R G C B 1 2 u F L O 1. 9 m H E F D 3 0 / N 8 7 M 1 S T P 1 2 N K 8 0 Z H E R G C O 3 u F V L o a d Error Amplifier ( O T A ) C r e g 9 k 1 k 1 V C C R e f e r e n c e 1 k n F L M n F Power Stage D 1 D 2 D 3 EMI Filter L i C B L O C O M 1 21

22 Experimental Results MOSFET Waveforms Bus Voltage and Output Voltage Drain: 500 V/div Bus: 100 V/div Output: 50 V/div Gate: 10 V/div 10 ms/div Peak voltage: ~700 V 5 ms/div Bus Voltage Ripple: 60 Vpp Output Voltage Ripple: 10 Vpp Experimental Results Line Waveforms Lamp Voltage and Current Voltage 100 V/div Voltage: 50 V/div Current 0.5 A/div Current: 0.1 A/div 5 ms/div 5 ms/div Power Factor: 0.99 Line Current THD: 12 % LED Voltage Ripple: 10 Vpp LED Current Ripple: 0.1 App Efficiency: ~ 86 % 22

23 Conclusions Drivers for LEDs is a hot topic of research: Power factor correction avoiding the use of electrolytic capacitors Multi-string LED lamps with current equalization Thermal and photometrical modeling of LED lamps Dimming Retrofit applications High efficient dc drivers for emergency and portable applications Color mixing and color generation PT-based power supplies for LED lamps Thank you! Questions? Campus de Viesques, Gijón, Asturias, España Asturias Gijón 23