EE152 Green Electronics

Transcription

1 EE152 Green Electronics Power Factor and Inverters 10/28/14 Prof. William Dally Computer Systems Laboratory Stanford University

2 Lab 5 PV lab this week Course Logistics Solar day is on Thursday 10/30/14 Make sure you are ready to go Wednesday night. If weather is good, meet on Packard patio on Thursday at 4:15 be ready to go. Project Proposal Assignment out Today Please come to office hours or make an appointment if you want to talk about the project Please discuss ideas before submitting your proposal Homework 5 due today Homework 6 out today Lab 6 out today

3 Summary of Soft Switching Switch FETs (or IGBTs) only with zero voltage, zero currrent, or both Full-bridge Start each transition by turning opposing switch off Use current in leakage inductance to drive voltage transitions before turn-on Add capacitance to slow transitions during turn-off Phase shift between bridge drives is control input QSW Add a capacitor to conventional buck Current in inductor forced to reverse V Three of four switching events driven by voltage or current S High-side turn-off is only free event Variable frequency Quasi-Resonant ZCS Cell with LC tank replaces switch Fixed pulse each time switch is turned on Off-time is free variable Active clamp V S + - D M 1 H H L L r i r M 1 M 2 D 1 D 2 UL C X LL C r D 1 L i L L i L C C UR LR + v C - Load + v C - i Load Load i Load

4 Dealing with the AC Line 60Hz AC is just slowly moving DC Drawing power from AC line need to make current proportional to voltage Driving the AC line need to make current proportional to voltage Synthesizing AC make voltage follow 60Hz sine wave

5 Power factor corrector AC input, DC output Three Cases Make AC current proportional to voltage (unity power factor) Need to store energy Grid tied inverter DC input, AC output Grid defines voltage Drive current to be proportional to voltage (unity power factor) Need to store energy Free-standing inverter Synthesize 60Hz sine wave

6 Example: Stanford Littlebox 450VDC Buck 240V 120Hz rectified sine Unfold 240V AC 60Hz Boost V 120Hz Bidir Buck

7 Example: Stanford Littlebox 450VDC Buck 240V 120Hz rectified sine Unfold 240V AC 60Hz Boost V 120Hz Bidir Buck

8 Some Details VP M1 L1 Input bypass network D1 30uH 12A RS V DC SC Storage capacitor 60x 2.2uF 450V X7T M6 M8 OA VN Inrush Prot L2 100uH 7A D2 M2 C1 M3 M4 L3 100uH 7A C2 0.47uF 600V M5 M7 0.47uF 600V C3 240V AC OB

9 Power Factor

10 Energy Star Regulations 3) Energy Efficiency and Power Management Criteria: Computers must meet the requirements below to qualify as ENERGY STAR. The Version 5.0 effective date is covered in Section 5 of this specification. (A) Power Supply Efficiency Requirements - Requirements are applicable to all product categories covered by the ENERGY STAR Computer Specification: Computers Using an Internal Power Supply: 85% minimum efficiency at 50% of rated output and 82% minimum efficiency at 20% and 100% of rated output, with Power Factor > 0.9 at 100% of rated output. Power Factor >= 0.9 at 100% rated output

11 IEC/EN

12 Definition PF = Real P ower Apparent P ower Apparent Power = V rms x I rms PF = P p P 2 + Q 2 PF = 1 p 1+THD 2 = I 1,rms I rms

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16 Power Factor in Littlebox Must drive load with PF between 0.7 and 1 Current waveform may lead or lag voltage by 45 degrees.

17 PF = Voltage Current

18 PF = Voltage Current

19 PFC

20 Power Factor Correction Correct power factor by regulating input current To be instantaneously proportional to input voltage I = kv Makes circuit look like a resistor May change the constant k over time Often done in a separate input stage Trivially achieved with DCM boost input stage Can be accomplished with CCM boost input stage and current-mode control

21 AC current in DC current out

22 PFC Input Stage PFC Boost Forward Output Stage

23 DCM of Flyback 1kHz Input Frequency Constant Pulse Width

24 Two Other Strategies

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26 LT1248 TYPICAL APPLICATI O U 300W, 382V Preregulator 90V TO 270V T 6A EMI FILTER + 750µH* IRF840 MURH860 1M 1% + V OUT 180µF 0.047µF R S 0.2Ω 20k 1% 20k 0.47µF 330k R REF 4k 0.1µF 4k 1nF 100pF 20k V CC = 18V** + 56µF 35V VA OUT V REF M OUT I SENSE PK LIM GND CA OUT V CC V CC 16V TO 10V + 7.5V V REF RUN V/2.2V + EN/SYNC 2.2V + M1 7µA 1M 4.7nF 50k 11 V SENSE 6 I AC 7.5V 7.9V 8 OVP 12µA 5V SS 13 EA k I A I B ONE SHOT 200ns I M = I A 2 I B 200µA 2 I M CA V + RUN OSC SYNC R R S Q 16V GTDR 16 10Ω 1N µF C SET 14 R SET 12 * ** 1. COILTRONICS CTX (TYPE 52 CORE) AIR MOVEMENT NEEDED AT POWER LEVEL GREATER THAN 250W. 2. COILTRONICS CTX (MAGNETICS Kool Mµ CORE) SEE START-UP AND SUPPLY VOLTAGE SECTION FOR V CC GENERATOR. THIS SCHOTTKY DIODE IS TO CLAMP GTDR WHEN MOS SWITCH TURNS OFF. PARASITIC INDUCTANCE AND GATE CAPACITANCE MAY TURN ON CHIP SUBSTRATE DIODE AND CAUSE ERRATIC OPERATIONS IF GTDR IS NOT CLAMPED. 1000pF 15k 1248 TA01

27 Summary of PFC Input current must be proportional to input voltage Harmonics limited by regulation PFC input stage regulates input current DCM constant pulse width CCM multiply input voltage by voltage error signal and regulate current to this value CrCM Constant on-time variable frequency Feedback tracks Input current to make it proportional to input voltage Output voltage sets constant of proportionality

28 Inverters

29 Inverter PFC regulates an AC input current Converts AC power to DC power Inverter regulates an AC output voltage Converts DC power to AC power Particularly useful for motor drives

30 Basic Inverter Make a Square Wave and Filter

31 Basic Inverter Make a Square Wave and Filter

32 But Filtering a 60Hz Square Wave is Hard

33 Spectrum of a 60Hz Square Wave Mag f (Hz)

34 Make a PWM Sine Wave and Filter

35 PWM Waveform V PWM (V) t (ms)

36 PWM Synthesis V AC, V Saw (V) V PWM (V) x = sine > saw y = -sine > saw Digitally generate sine with quarterwave table V Out (V) I L (A) t (ms)

37 100kHz PWM, 60Hz Sine (1667:1) 1.5 V AC, V Saw (V) V PWM (V) V Out (V) I L (A) t (ms)

38 Spectrum of 100kHz PWM Signal 9 x Mag f (Hz)

39 Circuit Simulation

40 SPICE Waveforms

41 Close Up of 2 PWM Cycles

42 Inverter Details Can operate independently or drive the grid. Grid connected inverters use the AC line as a sine-wave reference. This gives the proper phase It also compensates for distortion of the sine wave Current-mode control often used To give close to unity power factor into AC line This is the same as a PFC circuit but the current is flowing the other way

43 Anti-Islanding Grid-connected inverters need to turn off when the grid goes down. Safety issue for firemen, linemen, etc How do you detect when the grid goes down?

44 Anti-Islanding Line monitoring Voltage limits, frequency limits. Rate of change of frequency Rapid phase shift Active detection Impedance measurement Forced phase shift/frequency shift

45 Littlebox Inverter VP M1 L1 Input bypass network D1 30uH 12A RS V DC SC Storage capacitor 60x 2.2uF 450V X7T M6 M8 OA VN Inrush Prot L2 100uH 7A D2 M2 C1 M3 M4 L3 100uH 7A C2 0.47uF 600V M5 M7 0.47uF 600V C3 240V AC OB Generates rectified sinewave (RS) then unfolds it with a FET bridge why?

46 Inverters Summary Convert a DC Voltage to an AC Voltage AC is just slowly changing DC Use a full-bridge to generate a PWM Sine Wave Pulse width proportional to sin(x) LC Filter to reject high frequencies

47 Questions?

48 Upcoming Lectures HW Lab Lecture Date Topic out in out in Lab Descrip3on Homework Descrip3on Sep Introduc3on to Green Electronics, Boost, 1 1 Introduc3on to AVR Microcontroller Periodic Steady State Buck, and periodic steady state analysis Sep Real- 3me embedded sojware Sep Motors and Modeling AC energy meter Motor Calcula3ons 4 2- Oct Power MOSFETs, SPICE simula3on 5 7- Oct Power circuits Motor control - Matlab Power devices 6 9- Oct Feedback Control Oct PV Cells, Op3miza3on, Finding Peak Power Motor control - Lab Feedback Oct Transformers and bridge converters Oct Magne3cs PV power- point tracker PV Oct SoJ switching Oct Inverters Power supply part 1/Project Magne3cs design Proposal Oct Solar Day l Nov Ba\eries Power supply part 2 Bridge converter Nov Grounding and debugging Nov Review for Midterm 6 P 7 Project Nov Mar3n Fornage (Enphase) MT 13- Nov Midterm Nov Colin Campbell (Tesla) C Nov Andrew Ponec (SunPower/Dragonfly) Dec Wrapup Lecture C Dec Project Presenta3ons P Project Report Due - Website