EE152 Green Electronics

Embedded Software9/28/16

Prof. William DallyComputer Systems Laboratory

Stanford University

Logistics• Class is NOT full. See me for “permission numbers”• Lab group assignments

– Sign up. Tentative assignments will be announced next week.• Sign up for Lab signoff time

– Lab 1 must be signed off next week - individually• Homework 1 due next Monday 10/3• Sign up for Piazza

– piazza.com/stanford/fall2016/ee155• Discussion sections

– Fridays 4:30-5:50PM– Herrin T185

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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

EE155/255 Lecture 3 - Power Devices

Today• Logicstics• Brief Review• Embedded software• Power Devices

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Review of Monday– PSSA, Buck, Boost• Green energy systems are made from voltage converters

– PV systems, electric/hybrid cars, wind power, etc…– Power path + intelligent control

• Separate behavior into fast and slow– Fast – within switching cycle– Slow – f << fcy

• Within cycle solve for periodic steady state– State variables the same at start and end of cycle.

• For slow transient response– Write difference equations

• Buck/Boost Topologies

L

V2

+-

iLV1

+-

a

b

L

V2+-

V1+-

a

b

iL

V1 =V2Da

=V2

1−Db( )V2 =V1Da

0 5 10 15 20 25 30 35 400

0.5

1

1.5

2

2.5

3

3.5

time (µs)

V 2 (V)

ω =1e+06ζ =0.2

f = 1.59e+05Q = 2.5

0 5 10 15 20 25 30 35 40

−0.1

−0.05

0

0.05

0.1

0.15

I L (V)

ip

i0

t0 tb tcy

iL

b/a

tb ta

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How Does This Work?

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VS

+

- vC Load

+

C

a b

iLoadLiL

Another View

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VS

+

-

vC Load

+

C

a b

iLoad

LiL

Embedded Software

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Embedded Software• Most software is embedded

– 50 microprocessors in the average car– Several in many appliances– At the heart of most green electronic systems

• Embedded software forms the “slow” but “complex” part of most control loops– The fast, simple parts are in hardware (analog or digital)

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Embedded System

Microcontroller

Fast Hardware

Sensors Actuators

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Example: PV Maximum Power Point Tracker

MicrocontrollerPanel Voltage

PWM to Boost ConverterPanel Current

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Sometimes Embedded Systems Interact with Humans

Microcontroller

Fast Hardware

Sensors Actuators

User Interface Debug Log

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UI Design• It should be obvious how it works• Minimum number of “modes” (1 is best)• Display clearly indicates

– Current mode– Relevant data– Progress indicator if “waiting”– “Button” labels

• If the user needs to read the manual it’s a bad UI• Refresh display every 50ms• Check buttons and update “state machine” every 50ms

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Event Driven• Embedded systems execute code in response to events

– A real-time clock interrupt (e.g., every 1ms)– An I/O device completes an operation (e.g., A/D converter)– An input transitions (logic low-high, or analog threshold)

• Code is of the form– When trigger, do action– When 1ms clock tick, refresh display– When A/D completes, process data & start next conversion– When current over limit, shut down PWM

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Embedded vs Conventional Software

Embedded• Event driven

– Most code runs in response to interrupts

• Real-world I/O– A/D in, D/A and PWM out

• Real-time– Update PWM within one cycle

Conventional• Run code in program order

– In response to user input (e.g. mouse click)

• User Interface I/O• No hard time constraints

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Real-Time Clock• Microcontroller has a counter-timer that can be programmed to interrupt

the processor periodically (e.g., every 1ms).

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STM32 Timers

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Advanced-control timers (TIM1) RM0364

381/1121 DocID025177 Rev 1

Figure 106. Advanced-control timer block diagram

1. The internal break event source can be:- A clock failure event generated by CSS. For further information on the CSS, refer to Section 7.2.7: Clock security system (CSS)- A PVD output- SRAM parity error signal- Cortex-M4 LOCKUP (Hardfault) output.- COMPx output, x = 1,2,3,5 and 6.

Library Code

void my_callback1();timer_init();timer_id_t my_timer1 = timer_register(1, &my_callback1, GE_PERIODIC);timer_start(my_timer1);

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Make sure to check my_timer1 for error code

/** * @brief Registers a callback function to an internal Timer* @details Sets up a timer based on the required period. The* function will then assign the callback function to the* appropriate timer interrupt. The function uses TIM3 to generate* the interrupts.* * @param ms Period in milliseconds (int)* @param function Callback function* @param type SINGLE_SHOT or PERIODIC* @return Timer ID of associate timer or error code.*/

timer_id_t timer_register(uint32_t period, void (*function)(void), uint8_t type) {

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Timer Interrupt

rtc

RTC interrupt

Every 1ms

Every 3ms

Every 50ms

rtc rtc rtc

rd rd

tick50()

rtc

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I/O Completion• I/O devices interrupt when they complete an operation• Handler should

– Process input data (if an input device)– Start next operation

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Analog-to-digital converters (ADC) RM0316

220/1037 DocID022558 Rev 3

13.4 ADC functional description

13.4.1 Block diagram of a single ADCFigure 28 shows the ADC block diagram and Table 36 gives the ADC pin description.

Figure 28. ADC block diagram

A/Dvoid my_adc_callback(uint16_t *buf) ;

adc_set_fs(10000); // 10kHz sample frequencyadc_callback(&my_adc_callback); // register callbackadc_enable_channels(chan_to_conv, NUM_ADC); // specify channels adc_initialize_channels(); adc_start();

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A/D Timing

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ADC Start Clk

ADC1ADC2

Convert VConvert I

compute_power()

20us100us

• What happens if timer interrupt handler is still running when ADC interrupt occurs?

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• Make sure your interrupt driven code runs quickly!!!

• You can toggle a GPIO pin at entry and exit of your code to see how long it takes on a scope.

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Volatile Variables• If you run code with “interrupts enabled” other code may run “at the same

time”.– And long running code (more than 200us) should not disable interrupts– Enable interrupts after “critical section”.

• That “other code” may change variables• Don’t expect variables to be stable while “background” code runs!

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Integer Arithmetic• Much embedded code uses fixed-point arithmetic. • Floating-point takes too long (on an integer uC)

– Some modern uCs (e.g., STM32F3) have fast FP• Fixed point has plenty of precision for typical control values

– int (16 bits) [-32,768, 32,767]– long (32 bits) [-2,147,483,648, 2,147,483,647]

• But you need to scale your variables and check for overflow– Example – 16b represents voltage in mV, current in mA– Multiply mV and mA to get 32b power in uW– Divide by 1,000 and truncate to get 16b power in mW

• Shift and multiply – don’t really divide – its expensive• Multiply by 1.024 and shift right 10

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Fixed-Point Arithmetic• Scale numbers to be in [-1,1)• Binary point is just to the right of the sign bit

– s.bbbbbbb…• On multiply retain high half of result• General fixed-point representation

– saaaaaaaaa.bbbbbb…– Represents a value to 1/64– Need to shift after a multiply to put binary point in the correct place

• Need to think about the range and precision of your variables

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Floating Point• ST32F3 has fast 32-bit floating point• Max value of ~ +/-3 x 1038

• Min non-zero value of ~ 1.2 x 10-38

• Represents numbers to better than six sigfigs

• Scale inputs and outputsfloat_volts = (float) int_volts * VOLTS_PER_DIV ;

– 12b ADC with 3V range – 3V/4096 = 0.000732 volts/div

• Always check for range, never equality

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Organization of Code• Control• User Input• Display• Monitoring• Housekeeping

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Layered Control: Example Battery Charger

State Selection

Target Selection

State

Current 3A

PWM Control PWM to Buck

Battery V, IInput V

Battery V, I

Driver I

User Interface

Mode Status

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Layered Control: Example Battery Charger

State Selection50ms

Target Selection1ms

State

Current 3A

PWM Control10us FPGA

100ns - ComparatorPWM to Buck

Battery V, IInput V

Battery V, I

Driver I

User Interface50ms (or foreground)

Mode Status

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Example Photovoltaic Controller• Mode selection

– Line test, Panel test, MPPT, etc…• Monitors

– Line (current, voltage, frequency, …) (anti-islanding)– Internal operation (voltages, currents, temps) – Panels (current, voltage)

• Maximum Power-Point Tracking– Search algorithm for peak power point

• Inverter control– Convert 400V DC to 240V AC – in sync with line

• User interface– Display status, serial output, network connections, …

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Summary – Embedded Software• Embedded software consists of event handlers

– When trigger do action• Timer is used to perform periodic tasks

– Schedule A/D converter every 20us– Report status on serial port every 10ms– Update mode every 50ms– Etc…

• I/O devices trigger handler on completion– Process input data– Start next I/O operation

• Layered Control– High-level control loop sets parameters of lower level control loops– Fastest loops may be in hardware

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Power ElectronicsPart 1 – Power Devices

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Real Switches

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L

V2

iLV1

+-

a

b

R

C

+

_

M1

M2

V1

High-SideGate Drive

Low-SideGate Drive

VGL

VGH

inH

inL

GND

X

G1

G2

Real Switches• Finite switching time• Finite voltage blocking• Non-zero on resistance• Parasitic L and C

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L

V2

iLV1

+-

a

b

R

C

+

_

M1

M2

V1

High-SideGate Drive

Low-SideGate Drive

VGL

VGH

inH

inL

GND

X

G1

G2

Quick Summary in a Few Pictures

DC I-V Characteristics of On Switches

V(d)0.0V 0.1V 0.2V 0.3V 0.4V 0.5V 0.6V 0.7V 0.8V 0.9V 1.0V 1.1V 1.2V 1.3V 1.4V 1.5V 1.6V 1.7V 1.8V 1.9V 2.0V

0A

5A

10A

15A

20A

25A

30A

35A

40A

45A

50AIx(m:1) Ix(h:2) Ix(i:C) I(Dd)

600V FETFCB36N60

600V IGBTFGH40N60

400V DiodeSTTH20R04

60V FETIRLB3036

FETs CharacterizedBy RON

IGBT Like a DiodeLittle Current Until ~0.7V

HV FET has high RONR ~ kV2

Diode and IGBTResistive at high Current

Transient Response of FET and IGBT

0ns 40ns 80ns 120ns 160ns 200ns 240ns 280ns 320ns0V

50V

100V

150V

200V

250V

300V

350V

400V

450V

500V

550V

0A

5A

10A

15A

20A

0V

50V

100V

150V

200V

250V

300V

350V

400V

450V

500V

550V

0A

5A

10A

15A

20A

0KW

1KW

2KW

3KW

4KW

5KW

6KW

7KW

8KW

9KW

10KW

V(di) Ix(i:C)

V(dm) Ix(h:2)

ix(i:c)*v(di) ix(h:2)*V(dm)

600V FETFCB36N60

InstantaneousPower

Turn On Turn Off

600V IGBTFGH40N60

36µJ 36µJ92µJ 428µJ

Boost Configuration for Transient Test

Diode Reverse Recovery

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I1

IRM

ta tb

trr

Qrr

iD

(Amps)

t(sec)t1

t2

t3

Diode Reverse Recovery

0ns 3ns 6ns 9ns 12ns 15ns 18ns 21ns 24ns 27ns 30ns-220A

-200A

-180A

-160A

-140A

-120A

-100A

-80A

-60A

-40A

-20A

0A

20A

40AI(D1) I(D2) I(D3) I(D4)

0ns 10ns 20ns 30ns 40ns 50ns 60ns 70ns 80ns 90ns 100ns 110ns 120ns-810A

-720A

-630A

-540A

-450A

-360A

-270A

-180A

-90A

0A

90A

180AI(D1) I(D2) I(D3) I(D4) I(D5) I(D6) I(D7)

400V DiodeSTTH20R04

Medium Speed Diode

Area under curve (Charge)is approximately constant QRR

Power MOSFETs

Power MOSFETs are your friends

MOSFET Properties• Fast switching time 10-50ns

– Low switching losses• Low conduction losses at low voltages

– V2/R of 1-2MW • e.g., at 20V R = 0.4mOhm (4mV drop at 10A)

– Typically better than IGBT up to ~400V• Easily paralleled for lower Ron, More I, or easier cooling• Integral body diode in DMOS FET• Avalanche breakdown can be used to “snub” overshoot

MOSFETs are Switches

Gate

Drain

Source

Drain

Source

GateRon

Dbody

(a) (b)

(a)

gaten n

p

VDS

(b)

gaten n

p

VDS

- - - - -

IDS

g=0 g=1

IDSg

s d

g

s dIDS=0

+

−

+

−

How do they Work

VGS

Power MOSFET (DMOS) Structure

n+

p+n+

n-

p+n+

gatesource source

drain

channel

Gate Charge vs VGS

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0 10 20 30 40 50 60 70 80 900

1

2

3

4

5

6

7

8

9

10

QG (nC)

V GS (V

)

CDG

LS

LGRG

LD

CDS

CGS

source

gate

drain

Parasitics

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130 Green Electronics

CDG

LS

LGRG

LD

CDG

CGS

source

gate

drain

Figure 17.4: MOSFET parasitic circuit elements. At high operating frequen-cies these parasitic circuit elements have a large e↵ect on the performance andswitching losses of a MOSFET.

Symbol Value Units DescriptionCDS 200 pF Drain-source capacitanceCDG 70 pF Drain-gate (Miller) capacitanceCGS 3600 pF Gate-source capacitanceQG 86 nC Total gate turn-on chargeQGD 35 nC Gate-drain turn-on chargeLS 7 nH Source inductanceLD 3 nH Drain inductanceLG 7 nH Gate inductanceRG 1.5 ⌦ Gate resistance

Table 17.1: Values of parasitic circuit elements for a typical 600V 100m⌦ powerMOSFET in a TO-220 package.

600V 0.1W FET TO220 Package

CDG

LS

LGRG

LD

CDS

CGS

source

gate

drain

Parasitics

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CDS – CV2 energyLD, LS – I2L energy

slows switching, overshoot,corrupts gate drive

CDG – slows turn onRG, LG – slow device turn-on

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Typical MOSFETs

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Copyright

(c)

2011-15

by

W.J

Dally,allrights

reserved

133

Device 20V IRLB3036 IRFB4227 FCB36N60N EPC2010 C2M0025120 Units DescriptionVDSmax

20 60 200 600 200 1200 V Maximum VDS

Ron

1.9 20 81 18 25 m⌦ On resistanceQG 91 70 86 5 161 nC Gate chargeCoss 1020 460 80 270 220 pF Output capacitance CSD + CGD

IDmax

195 65 36 12 90 A Maximum continuous drain currentIDM 1100 260 108 60 250 A Maximum pulsed drain currentEAS 290 140 1800 mJ Single-event avalanche energyP

max

380 330 312 463 W Maximum power dissipationV 2/R 1.9 2.0 4.4 2.2 58 MW Figure of meritV 2/RQG 21 29 52 440 360 mV/s Figure of merit

Table 17.2: Key parameters of six field-e↵ect transistors.

GaN SiC

Power MOSFETs should be ON or OFFThey are not happy in between

• IRLB3036 • Can handle 60V (when its off)• Can handle 195A (when its on – if you can cool it)

– I2R = (195)2(0.002) = 76W• But it can’t handle 60V and 195A at the same time

– P = VI = (60)(195) = 11.7kW– At least not for very long

• Turn them on and off quickly• Best circuits are “soft switching”

– Zero-current switching (ZCS) or zero-voltage switching( ZVS) or both.

Power Diodes

Diode Properties• Self-controlling switch

– Allows current in one direction– Turns off when current reaches zero (in theory)

• Relatively fixed voltage drop independent of current– 0.5 to 2.0V– High losses at low voltages

• Care required to operate in parallel– Current hogging

• Turn-off delay– Must clear space charge out of junction

• Turn-on delay– Negligible for most fast diodes, but some are problematic

Key Parameters• Reverse breakdown voltage

• Maximum current

• Reverse recovery time

• Junction capacitance

Diode Reverse Recovery

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I1

IRM

ta tb

trr

Qrr

iD

(Amps)

t(sec)t1

t2

t3

Diode Forward Recovery

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VFP

VF

tfr

vD

(Volts)

t(sec)

1.1VF

Diode Forward Recovery

Good Diode Bad Diode

Two 2A Diodes < One 4A Diode

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0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 1.05 1.10

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

25°C

75°C

125°C

VD (Volts)

i D (A

mps

)

CDG

LS

LGRG

LD

CDS

CGS

source

gate

drain

Summary – Power Devices• Finite, non-zero

– Switching time– Blocking voltage– On-voltage (resistance)

• Parasitics – L and C• MOSFETs – switches

– Turn on/off as fast as gate can be charged

– R = kV2

• Diodes– Self-controlled switches– Reverse recovery loss QRR

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Gate

Drain

Source

Drain

Source

Gate RonDbody

(a) (b)

I1

IRM

ta tb

trr

Qrr

iD

(Amps)

t(sec)t1

t2

t3

No Date Topic HWout HWin Labout Labck Lab HW1 9/26/16Intro(basicconverters) 1 1 IntrotoST32F3 PeriodicSteadyState2 9/28/16EmbeddedProg/PowerElect.3 10/3/16PowerElectronics- 1(switches) 2 1 2 1 ACEnergyMeter PowerDevices4 10/5/16PowerElectronics- 2(circuits)5 10/10/16Photovoltaics 3 2 3 2 PVMPPT PVSPICE6 10/12/16FeedbackControl7 10/17/16ElectricMotors 4 3 4 3 MotorcontrolMatlab Feedback8 10/19/16IsolatedConverters9 10/24/16SolarDay 5/PP 4 5 4 Motorcontrol- Lab/ IsolatedConverters

10 10/26/16Magnetics11 10/31/16SoftSwitching 6 5/PP 6 5 PS MagneticsandInverters12 11/2/16ProjectDiscussions13 11/7/16Inverters,Grid,PF,andBatteries 6 P 6 Project14 11/9/16Thermal&EMI15 11/14/16QuizReview C116 11/16/16Grounding,andDebuggingQ 11/16/16Quiz- intheevening C2

11/21/16ThanksgivingBreak11/23/16ThanksgivingBreak

17 11/28/1618 11/30/16 C319 12/5/1620 12/7/16Wrapup

TBD Projectpresentations PTBD Projectwebpagedue EE155/255 F15 L1 66

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