ee152 green electronics - stanford universityl2 charges c 4 node m1 falls . a cycle in the life of a...
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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
A Cycle in the Life of a Soft Switching Converter
2. m1 turns on ZVS/ZCS L2 slope reverses
A Cycle in the Life of a Soft Switching Converter
3. D1 turns off mid falls as L2
discharges C3
A Cycle in the Life of a Soft Switching Converter
4. m2 turns on ZVS/ZCS L2 slope reverses
A Cycle in the Life of a Soft Switching Converter
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
Circuit Calculations
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
Circuit Calculations
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
VOUT
180µF
T
90VTO
270V
EMIFILTER
+
–
4k
20k
RS0.2Ω
50k
750µH*
1M1%
MURH860
VCC = 18V**
56µF35V
10Ω
15k
–
+
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.
*
**†
+
+
U
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
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
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