EE152 Green Electronics

Transcription

1 EE152 Green Electronics Power Circuits Photovoltaics 9/30/15 Prof. William Dally Computer Systems Laboratory Stanford University

2 Course Logistics HW2 out Today due Monday 10/5 Lab1 signed off this week Lab2 out EE155/255 Lecture 3 - Power Devices

3 Course to Date We need sustainable energy systems At the core they are voltage converters Periodic steady-state analysis, buck and boost Intelligent control + power path Intelligent control done with event-driven embedded software Real devices have switching and conduction loss EE155/255 Lecture 3 - Power Devices

4 Snubbers EE155/255 Lecture 3 - Power Devices

5 Dampen Ringing Nodes 40A C j D L D and C j resonate when M is on Parallel RS dampens tank L D R S Series C S limits dissipation G M C S V EE155/255 Lecture 3 - Power Devices

6 Inductance on Drain 42uJ turn-off 8uJ turn-on EE155/255 Lecture 3 - Power Devices

7 With Snubber (1nF, 5Ω) 2uJ in snubber 8uJ turn-on 42uJ turn-off EE155/255 Lecture 3 - Power Devices

8 Design Procedure C j Pick R S ~ 1/ωC j 40A D Pick C S so τ >= π/ω Or E s = C S V 2 /2 L D R S G M C S V EE155/255 Lecture 3 - Power Devices

9 Move Turn-Off Dissipation to Passive Device 40A D R S D S G M C S V C S slows rise time of drain C S V 2 /2R S dissipated in R S when C S discharges Rarely used today Other forms slow fall time and rising/falling current EE155/255 Lecture 3 - Power Devices

10 Lab Half-Bridge Module EE155/255 Lecture 3 - Power Devices

11 The Half-Bridge Module V12 Hin 1 2 Hin IRS21834 U1 V B HO S V B CSupply D2 15V C2 1 F R3 1 D1 R1 4.7 M1 V D CFilter V D Out GND 4 3 DT Vss V CC LO Com R2 4.7 C1 4.7 F M2 C3 2.2 F 200V D3 56V 5W COM EE155/255 Lecture 3 - Power Devices

12 Bootstrap Supply EE155/255 Lecture 3 - Power Devices

13 Drain Voltage Filter V12 Hin 1 2 Hin IRS21834 U1 V B HO S V B CSupply D2 15V C2 1 F R3 1 D1 R1 4.7 M1 V D CFilter V D Out GND 4 3 DT Vss V CC LO Com R2 4.7 C1 4.7 F M2 C3 2.2 F 200V D3 56V 5W COM EE155/255 Lecture 3 - Power Devices

14 Drain Voltage Filter 300nH Input Inductance EE155/255 Lecture 3 - Power Devices

15 SPICE EE155/255 Lecture 3 - Power Devices

16 SPICE Example A Voltage Doubler EE155/255 Lecture 3 - Power Devices

17 A Voltage Doubler * Simple voltage "doubler".include "gel.lib".param td=100n tr=100n tf=100n tw=2.5u tcy=5u ncy=2.param l1=22uh c1=10uf r1=10 * call half-bridge subcircuit xhb vd mid g g 0 v12 gel_hb * circuit l1 vin mid {l1} c1 vd 0 {c1} r1 vd 0 {r1} * supplies v12 v vin vin 0 24 * stimulus VG g 0 PULSE(0 5 {td} {tr} {tf} {tw} {tcy} {ncy}).ic i(l1)=9.2.ic v(vd)=42.8.tran {ncy*tcy} EE155/255 Lecture 3 - Power Devices

18 Turn-On Transient EE155/255 Lecture 3 - Power Devices

19 Steady State EE155/255 Lecture 3 - Power Devices

20 Close up of Drain Current EE155/255 Lecture 3 - Power Devices

21 With PID Control EE155/255 Lecture 3 - Power Devices

22 A Warning SPICE (or any simulator) is a Verification tool, not a Design tool Design your circuit first Use Excel, Matlab, a calculator etc to calculate component values Then simulate your circuit to check operation and finetune parameters Don t try to design your circuit using SPICE Simulation is not a substitute for thinking EE155/255 Lecture 3 - Power Devices

23 Summary of Power Circuits Real switches have limitations Conduction losses (R ON for FETs, V CE for IGBTs, Diode drop) Switching losses (finite t on, t off, t rr ) With current source load, current ramps, then voltage falls And voltage rises before current falls May be dominated by reverse recovery time Complicated by inductance Power MOSFETs Switch quickly, have linear I-V, integral diode IGBTs Diode-like I-V, slower switching Diodes Have reverse recovery time Switches operate in pairs For one-way converters, one switch may be a diode Synchronous rectification make both switches FETs to reduce loss Need dead time to avoid shoot through current Gate-drive circuits control rise and fall times Bootstrap supply needed for high-side driver Snubbers dampen voltage and current transients Use SPICE as a verification tool, not a design tool EE155/255 Lecture 3 - Power Devices

24 Photovoltaics EE155/255 Lecture 3 - Power Devices

25 Energy Conversion

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27 Photovoltaic System Solar Panel Solar Panel Solar Panel Solar Panel 400V DC PV Controller and Inverter 240V AC 60 Hz To Grid Solar Panel Solar Panel 48V DC Photovoltaic Array Batteries 27

28 28

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30 Electrons absorb energy from photons

31 Equivalent Circuit R S + I SC D1 D2 R SH V C _

32 IV-Curve

33 Typical Module CS6P 60 cells in series ~0.5V per cell 3 strings of 20 with bypass diode on each string

34 Typical Module

35 IV Curve from SPICE Model

36 Peak-Power Tracking Find point on IV curve where power is maximized. Start at any point (v(0),i(0)) Dither v, v(i+1) = v(i) + Δv Check result: if(p(i+1) < p(i)) v(i+1) = v(i) Try both directions: Δv = -Δv

37 MPP Tracking The Movie

38 Start at (35 V, 5.5A) P=192.5

39 Dither by DV = 0.5V to V = 35.5V (35.5V, 4.7A) P=166.9 < 192.5

40 (35.5V, 4.7A) P=166.9 < Bad Move Go Back to (35, 5.5)

41 Dither by -0.5V to 34.5V (34.5, 6.2) P=213.9 > 192.5

42 (34.5, 6.2) P=213.9 > Keep move and keep going

43 Move to 34.0 (34.0, 6.7) P=227.8 > 213.9

44 (34.0, 6.7) P=227.8 > Keep move and keep going

45 (33.5, 7.0) P=234.5> Keep move and keep going

46 (33.0, 7.3) P=240.9 > Keep move and keep going

47 (32.5, 7.5) P= > Keep move and keep going

48 (32.0, 7.6) P=243.2 < Abandon Move and Go Back!

49 Operate at (32.5, 7.5) P=243.8 With occasional forays to 32.0 and 33.0

50 Hillclimbing On the Power Curve

51 Compound Power Curve

52 Compound Power Curve (2 Panels) Not convex How do you find maximum power point?

53 Three Panels

54 Typical String of 10 PV Panels

55 Search Strategies for Non-Convex MPPT Exhaustion Try every operating point Random Randomly pick new points keep if better Hierarchical Try every point with coarse spacing Try every point near best point with finer spacing Repeat Acquire and Track One of the above to acquire MPPT (e.g., hierarchical) Then gradient search to track Periodically revisit (devote some fraction of string time to this) Optimal method depends on Shape of curve How fast the curve changes How the curve changes

56 Good Optimization Depends on Understanding The Problem Collect lots of data Time series of IV curves from typical strings Understand the data What causes dips Bad panels Static offset in current Fixed shading trees, buildings, etc Periodic offset same time each day Variable shading clouds, etc Unpredictable shading but shifts across panels in one direction Develop algorithms Test on data

57 An Example of Optimization Trade-off parameters against one another to maximize a figure of merit. In this case, parameters are panel voltage and current. Figure of merit is power. Optimization is done real-time because temperature and irradiance change. Sometimes optimization is done at design time, or calibration time.

58 MPPT Power Path (Boost Converter with Energy Meter) V L G M 2 V PV L 1 C O Load PV Panel I PV C i G M 1 R S

59 MPPT Power Path (Boost Converter with Energy Meter) V L G M 2 V PV L 1 C O Load PV Panel I PV C i G M 1 R S MPPT is a boost converter that regulates its INPUT voltage

60 Cycle Waveforms il(a) Size inductor L to set ripple v in (V) 35 Size input cap C i for acceptable ripple v out (V) Size output cap C o for acceptable ripple t (µs)

61 SPICE

62 v in (V) Longer Simulation i pv (A) v out (V) D P (W) t (ms)

63 PV Systems

64 Microinverter 30-40V 0-10A Panel Inverter AC Line 240 Vrms ~1Arms

65 Store Energy During AC Null

66 Approach 1 DC Link 30-40V 0-10A V 0-1A Rectified AC 240V, 1A rms Boost Buck Unfold

67 Approach 2 Single Stage Rectified AC 240V, 1A rms 30-40V 0-10A Convert Unfold

68 Two-Path 400VDC Buck 240V 120Hz rectified sine Unfold 240V AC 60Hz Boost V 120Hz Buck 2/3 of power through main path Lower path levels input current

69 3-Phase String of Panels V 10A Inverter AC Line 480 V 20 A 3 phase No need for energy storage

70 3-Φ Inverter Power Path A B C A B C C 1 R CS A B C

71 Transformerless

72 Typical Utility-Scale PV System

73 Typical Utility-Scale PV System 8,000 Modules 400 strings of 20 modules each 325W/module 2.6MW DC total Central 2MW inverter Central 2MW step-up transformer to 34.5kv Single axis tracking This 2MW block is repeated for larger systems

74 PV Economics 1 Utility scale costs PV Module $0.60/W Inverter $0.10/W Mounting $0.15/W Balance $0.65/W TOTAL $1.50/W Residential costs PV Module $0.60 Microinverter $0.50 Mounting $0.20 Balance $1.70 TOTAL $3.00 Return Hours/year 2,200 Wholesale $0.05/kWh TOTAL $0.11/Wyear 7.3% ROI Return Hours/year 2,200 Retail $0.15-$0.35/kWh TOTAL $ /Wyear 11% - 26% ROI

75 PV Economics 2 Module is only 40% of cost (20% for residential) Real issue is balance-of-system (installation labor)

76 V OC Limiting Typical module (Trina TSM-310-PD14) Vmp = 36V, Voc = 46V (worst-case cold temperature) Inverter input limited to 1kV Limits strings to 21 modules At Vmp could have 27 modules 29% increase Reduces string cost by ~30%.

77 Module (and Cell) Mismatch String current limited to current from weakest cell Module current mismatch σ = 5% Worse for residential installations (partial shading) Two questions: What is the typical mismatch profile of a 10-module string? What power reduction does a X % current mismatch result in?

78 Cell open/short Diode open/short Arc fault Faults and Failures

79 Summary of PV PV cells/strings are voltage-dependent current sources (Diode in parallel with current source) PV controllers regulate their input voltage/current to maximize power Maximum power-point tracking Can apply almost any converter topology Boost used for illustration Regulate input rather than output Gradient search for convex optimization More sophisticated search needed for multi cell/panel string

80 In Upcoming Lectures No Date Topic HW out HW in Lab out Lab ck Lab HW 1 9/21/15 Intro (basic converters) 1 1 Intro to ST32F3 Periodic Steady State 2 9/23/15 Embedded Programming 3 9/28/15 Power Electronics - 1 (switches) AC Energy Meter Power Devices 4 9/30/15 Power Electronics - 2 (circuits) 5 10/7/15 Photovoltaics PV MPPT PV 6 10/9/15 Feedback Control 7 10/12/15 Electric Motors Motor control Matlab Feedback 8 10/14/15 Solar Day 9 10/19/15 Isolated Converters Motor control - Lab Motors 10 10/21/15 MagneTcs 11 10/28/15 SoU Switching 6/PP PS Part 1/Proposal MagneTcs and bridge converter 12 10/30/15 Inverters and Power Factor 13 11/2/15 BaWeries 6/PP 7 6 PS Part /4/15 Thermal Design 15 11/9/15 EMI, Grounding, and Debugging P 7 Project 16 11/11/15 Quiz Review 17 11/16/15 11/16/15 Quiz - in the evening 18 11/18/15 C1 11/23/15 Thanksgiving Break 11/25/15 Thanksgiving Break 19 11/30/15 C /2/15 Wrapup 21 12/4/15 Project presentatons P 12/9/15 Project webpage due EE155/255 Lecture 3 - Power Devices