EE155/255 Green Electronics

Transcription

1 EE155/255 Green Electronics Power Circuits Photovoltaics 10/5/16 Prof. William Dally Computer Systems Laboratory Stanford University

2 HW2 due Monday 10/10 Lab1 signed off this week Lab2 out Course Logistics

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

4 Last Time DC and AC characteristics of MOSFETs, Diodes, and IGBTs Switches in pairs One switch does the work Turn on transient Diode reverse recovery Parasitics Gate drive and Miller capacitance Dead time and shoot through

5 Review - Turn-On Loss I P I D I L Q RR Q D s V DS t 1 t 2 t 3

6 Review - Effect of Miller Cap on Rise Time dv D dt = i G C DG C DG M1 Δt = ΔV DC DG i G i G Example: i G = 0.5A, C = 100pF, DV = 400V

7 Snubbers

8 Dampen Ringing Nodes 40A C j D L D and C j resonate when M is on Parallel R S dampens tank L D R S Series C S limits dissipation G M C S V

9 Inductance on Drain 42uJ turn-off 8uJ turn-on

10 With Snubber (1nF, 5W) 2uJ in snubber 8uJ turn-on 42uJ turn-off

11 Design Procedure C j Pick R S ~ 1/wC j 40A D Pick C S so t >= p/w Or E s = C S V 2 /2 L D R S G M C S V

12 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

13 Critical Loop

14 Critical Loop V G2 G1 M2 M1 i

15 Lab Half-Bridge Module

16 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

17 Bootstrap Supply 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

18 Bootstrap Supply

19 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

20 Drain Voltage Filter 300nH Input Inductance

21 SPICE

22 SPICE Example A Voltage Doubler

23 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}

24 Turn-On Transient

25 Steady State

26 Close up of Drain Current

27 With PID Control

28 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 fine-tune parameters Don t try to design your circuit using SPICE Simulation is not a substitute for thinking

29 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 Parasitic L and C 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 Supply Miller capacitance Bootstrap supply needed for high-side driver Snubbers dampen voltage and current transients Use SPICE as a verification tool, not a design tool

30 Photovoltaics

31 Energy Conversion

32

33 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

34

35

36 Electrons absorb energy from photons

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

38 IV-Curve

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

40 Typical Module

41 IV Curve from SPICE Model

42 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) + Dv Check result: if(p(i+1) < p(i)) v(i+1) = v(i) Try both directions: Dv = -Dv

43 MPP Tracking The Movie

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

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

46 (35.5V, 4.7A) P=166.9 < Bad Move Go Back to (35, 5.5)

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

48 (34.5, 6.2) P=213.9 > Keep move and keep going

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

50 (34.0, 6.7) P=227.8 > Keep move and keep going

51 (33.5, 7.0) P=234.5> Keep move and keep going

52 (33.0, 7.3) P=240.9 > Keep move and keep going

53 (32.5, 7.5) P= > Keep move and keep going

54 (32.0, 7.6) P=243.2 < Abandon Move and Go Back!

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

56 Hillclimbing On the Power Curve

57 Compound Power Curve

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

59 Three Panels

60 Typical String of 10 PV Panels

61 Exhaustion Try every operating point Random Search Strategies for Non-Convex MPPT 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

62 Good Optimization Depends on Understanding The Collect lots of data Problem 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

63 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.

64 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

65 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

66 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)

67 SPICE

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

69 PV Systems

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

71 Store Energy During AC Null

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

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

74 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

75 3-Phase String of Panels V 10A Inverter AC Line 480 V 20 A 3 phase No need for energy storage

76 3-F Inverter Power Path A B C A B C C 1 R CS A B C

77 Transformerless

78 Typical Utility-Scale PV System

79 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

80 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

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

82 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%.

83 Module (and Cell) Mismatch String current limited to current from weakest cell Module current mismatch s = 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?

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

85 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

86 In Upcoming Lectures No Date Topic HW out HW in Lab out Lab ck Lab HW 1 9/26/16Intro (basic converters) 1 1 Intro to ST32F3 Periodic Steady State 2 9/28/16Embedded Prog/Power Elect. 3 10/3/16Power Electronics - 1 (switches) AC Energy Meter Power Devices 4 10/5/16Power Electronics - 2 (circuits) 5 10/10/16Photovoltaics PV MPPT PV SPICE 6 10/12/16Feedback Control 7 10/17/16Electric Motors Motor control Matlab Feedback 8 10/19/16Isolated Converters 9 10/24/16Solar Day 5/PP Motor control - Lab/ Isolated Converters 10 10/26/16Magnetics 11 10/31/16Soft Switching 6 5/PP 6 5 PS Magnetics and Inverters 12 11/2/16Project Discussions 13 11/7/16Inverters, Grid, PF, and Batteries 6 P 6 Project 14 11/9/16Thermal & EMI 15 11/14/16Quiz Review C /16/16Grounding, and Debugging Q 11/16/16Quiz - in the evening C2 11/21/16Thanksgiving Break 11/23/16Thanksgiving Break 17 11/28/ /30/16 C /5/ /7/16Wrapup TBD Project presentations P TBD Project webpage due