ee152 green electronics - stanford universityl2 charges c 4 node m1 falls . a cycle in the life of a...

EE152 Green Electronics

Soft Switching (concluded) Power Factor and Inverters

10/29/13

Prof. William Dally Computer Systems Laboratory

Stanford University

Course Logistics •  Lab 5 PV lab this week •  Solar day is on Thursday 10/31/13 (Halloween)

–  Make sure you are ready to go Wednesday night.

•  Lab 6 out this week •  Homework 4 due today •  Homework 5 out today

•  Don’t fall behind on labs –  Can open lab at other times by appointment

Soft Switched Let Inductor do the “lifting” High on when V(L) > V(IN) High off when I(L) > Imax Inductor pulls L low Low on when V(L) < 0 Low off when I(L) < 0 Inductor pulls L high Repeat 7µJ per cycle vs 140µJ Esw

A CCM Boost Converter with Soft Switching

Waveforms

A Cycle in the Life of a Soft Switching Converter

1.  m2 turns off ZVS L2 charges C4 Node m1 falls


2. m1 turns on ZVS/ZCS L2 slope reverses


3.  D1 turns off mid falls as L2

discharges C3


4. m2 turns on ZVS/ZCS L2 slope reverses


5. m1 turns off ZVS Nodes m1 and mid rise

0.42W FET Losses (vs 18.2W, 43x)

pm1: AVG(ix(1:1)*v(m1))=0.0827113 FROM 0.0001 TO 0.0002!pm2: AVG(ix(2:1)*(v(mid)-v(c2)))=0.332469 FROM 0.0001 TO 0.0002!

Circuit Calculations

Fall time of node M1 L2 current (avg 18A) charges C4 (100nF) Through 42V tm1f = 100nF*42V/18A ~ 230ns


Time to D2 turn off Time for IL2 to ramp from -12A to +7A Slope is Vd/L2 td2off = I*L/V = 19A*0.5u/42V ~230ns


Time for mid to fall L2 discharges C3 and C4 With portion of current not Used to sink L1 tmidf = CV/I = (C3+C4)(42)/(IL2-IL1) = 150nF(42)/(11) ~ 570ns

Waveforms with better parameters

Soft Switching •  Largely eliminates switching loss in FETs •  Adds components

–  L2, M2, C2, and C3

•  Adds conduction loss due to “resonant” current –  L2 current in L2 and M2

•  Requires precise timing –  Narrow windows for M1 on and M2 on after M2 off

•  One step to turn a 70% efficient converter into a 95% efficient converter

Summary of Soft Switching •  Switch FETs (or IGBTs) only with zero voltage, zero currrent, or

both •  Lossless snubbers

–  Series inductance to give ZCS and/or parallel capacitance to give ZVS – recycle energy in L and C

•  Resonate main inductor –  Requires reversal of current to pull switching node “up” –  Requires critical conduction mode –  Gives variable switching frequency –  Can be applied to other topologies –  Requires higher (and negative) currents

•  Active clamp circuit –  LC tank controlled by aux switch in series with main switch –  Requires higher currents and voltages

Power Factor

Energy Star Regulations

Y. Product Family: A highlevel description referring to a group of computers typically sharing one chassis/motherboard combination that often contains hundreds of possible hardware and software configurations.

2) Qualifying Products: Computers must meet the computer definition as well as one of the product type definitions provided in Section 1, above, to qualify as ENERGY STAR. The following table provides a list of the types of computers that are (and are not) eligible for ENERGY STAR.

Products Covered by Version 5.0 Specification

Products Not Covered by Version 5.0 Specification

x Desktop Computers x Integrated Desktop Computers x Notebook Computers x Workstations x Game Consoles x SmallScale Servers x Thin Clients

x Computer Servers (as defined in Version 1.0 Computer Server specification)

x Handhelds, PDAs, and Smartphones

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.

Computers Using an External Power Supply: External Power Supplies sold with ENERGY STAR computers must be ENERGY STAR qualified or meet the noload and active mode efficiency levels provided in the ENERGY STAR Program Requirements for Single Voltage External AcAc and AcDc Power Supplies, Version 2.0. The ENERGY STAR specification and qualified product list can be found at www.energystar.gov/powersupplies. Note: This performance requirement also applies to multiple voltage output external power supplies as tested in accordance to the Internal Power Supply test method referenced in Section 4, below.

(B) Efficiency and Performance Requirements:

1) Desktop, Integrated Desktop, and Notebook Levels:

Desktop Categories for TEC Criteria: For the purposes of determining TEC levels, desktops and integrated desktops must qualify under Categories A, B, C, or D as defined below:

Category A: All desktop computers that do not meet the definition of Category B, Category C, or Category D below will be considered under Category A for ENERGY STAR qualification.

Category B: To qualify under Category B, desktops must have:

� Equal to 2 Physical Cores; and

� Greater than or equal to 2 gigabytes (GB) of System Memory.

ENERGY STAR Program Requirements for Computers: Version 5.0 9

Power Factor >= 0.9 at 100% rated output

IEC/EN61000-3-2

Definition

�I = (Vin �DhVd)tcyL

i(s) = �dh(s)hVdisL

� vd(s)hDhisL

�Vd =

✓DhI �

Vd

R

◆tcyC

vd(s) =hDhii(s)

sC� vd(s)

sRC

vd(s)

✓1 +

1

sRC

◆=

hDhii(s)sC

vd(s) (sRC + 1) = hDhiRi(s)

vd(s) =hDhiRi(s)

sRC + 1=

hDhii(s)sC + 1

R

vd(s) = �hDhihVdidh(s) + hDhi2vd(s)s2LC + sL

R

vd(s)

✓s2LC + s

L

R+ hDhi2

◆= �hDhihVdidh(s)

vd(s)

dh(s)= � hDhihVdi

s2LC + sLR + hDhi2

vd(s)

dh(s)= �

hDhihVdiLC

s2 + s 1RC + hDhi2

LC

PF =Real Power

Apparent Power

PF =Pp

P 2 +Q2

PF =1p

1 + THD2=

I1,rms

Irms

1

Apparent Power = Vrms x Irms

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

PFC Input Stage

PFC Boost Forward Output

Stage

DCM of Flyback 1kHz Input Frequency Constant Pulse Width

Two Other Strategies

11

LT1248

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

300W, 382V Preregulator

Kool Mµ is a registered trademark of Magnetics, Inc.

–

+

–

+

IM = IA2 IB

200µA2

VAOUT

7.5V

7.9V

12µA 5V

EA

VREF

–

+

–

+ –

+

2.2V

32k

IA

IB

7µA

IM

7.5VVREF

–

+VCC

16V TO 10V

2.6V/2.2V –

+

0.7V–

+

OSC

RRS

Q

CSET RSET

6

11

10

7 9 5 4 2 1 15

16

1214

SS

OVP

IAC

VSENSE

EN/SYNC

MOUT ISENSE3

CAOUT

VCC

RUN

CA

RUN

16V

GND

–

+

GTDR

1000pF

SYNC

1N5819†4.7nF

1M

20k 0.47µF

0.047µF

330k

0.1µF1nF

8

0.01µF

13

100pF

PKLIM

20k1%

RREF4k

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180µF

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90VTO

270V

EMIFILTER

+

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750µH*

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MURH860

VCC = 18V**

56µF35V

10Ω

15k

–

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1248 TA01

IRF840

ONE SHOT200ns

6A

M1

1. COILTRONICS CTX02-12236-1 (TYPE 52 CORE) AIR MOVEMENT NEEDED AT POWER LEVEL GREATER THAN 250W.2. COILTRONICS CTX02-12295 (MAGNETICS Kool Mµ® 77930 CORE) SEE START-UP AND SUPPLY VOLTAGE SECTION FOR VCC GENERATOR.THIS SCHOTTKY DIODE IS TO CLAMP GTDR WHEN MOS SWITCH TURNS OFF. PARASITIC INDUCTANCE AND GATE CAPACITANCE MAYTURN ON CHIP SUBSTRATE DIODE AND CAUSE ERRATIC OPERATIONSIF GTDR IS NOT CLAMPED.

*

**†

+

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A

O

PPLICATITYPICAL

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

Inverters

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

Basic Inverter Make a Square Wave and Filter

But Filtering a 60Hz Square Wave is Hard

Spectrum of a 60Hz Square Wave

0 100 200 300 400 500 600 700 800 900 10000

200

400

600

800

1000

1200

1400

f (Hz)

Mag

Make a PWM Sine Wave and Filter

PWM Waveform

0 2 4 6 8 10 12 14 16

−1

−0.8

−0.6

−0.4

−0.2

0

0.2

0.4

0.6

0.8

1

V PWM

(V)

t (ms)

PWM Synthesis

0 2 4 6 8 10 12 14 16−1

−0.5

0

0.5

1

1.5

V AC, V

Saw (V

)

0 2 4 6 8 10 12 14 16−1

−0.5

0

0.5

1

V PWM

(V)

0 2 4 6 8 10 12 14 16−1.5

−1

−0.5

0

0.5

1

1.5

V Out

(V)

0 2 4 6 8 10 12 14 16−1

−0.5

0

0.5

1

I L (A)

t (ms)

x = sine > saw y = -sine > saw

Digitally generate sine with quarter-wave table

100kHz PWM, 60Hz Sine (1667:1)

2 2.02 2.04 2.06 2.08 2.1 2.12 2.14 2.160

0.5

1

1.5

V AC, V

Saw (V

)

2 2.02 2.04 2.06 2.08 2.1 2.12 2.14 2.16−1

−0.5

0

0.5

1

V PWM

(V)

2 2.02 2.04 2.06 2.08 2.1 2.12 2.14 2.160.68

0.7

0.72

0.74

0.76

V Out

(V)

2 2.02 2.04 2.06 2.08 2.1 2.12 2.14 2.160.5

0.6

0.7

0.8

0.9

I L (A)

t (ms)

Spectrum of 100kHz PWM Signal

101 102 103 104 105 1060

1

2

3

4

5

6

7

8

9x 105

f (Hz)

Mag

Circuit Simulation

SPICE Waveforms

Close Up of 2 PWM Cycles

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

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?

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

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

Questions?

In Upcoming Lectures •  Batteries •  Experimental Technique •  Guest Lectures from Tesla and Enphase

ee152 green electronics - stanford universityl2 charges c 4 node m1 falls . a cycle in the life of a...

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