1Power Electronics Lab.
Minimization Technologies for Passive Components based on Circuit Topology and Its Control
Jun-ichi ItohNagaoka University of Technology, Japan
One of the most famous firework festivals in Japan is held in Nagaoka on begin of August every year.
Phoenix (width 2000m)
Sho-sanjakuDiameter 600m, altitude 600m
2Power Electronics Lab.
Contents
1. Introduction-Importance of minimization of passive components
2. Approach I: Matrix converter-Circuit topology and features-Latest technologies: Three-phase to Single phase--Matrix converter in Market: general purpose drive/air conditioner/quick charger
3. Approach II: Active power decoupling for Single-phase converter-Principle-Integrated to PFC or Inverter-Integrated to Chopper
4. Approach III: Discontinuous Current Mode converter-Principle: Robustness for inductor -Single-phase inverter with DCM-Three-phase inverter with DCM
5. Approach IV: FRT capability of grid-tied inverter with minimized inductor-Mr. Nagai presents his projects
6. Conclusion
3Power Electronics Lab.
Road to Innovation
Innovation is born when convenience is more important than price;
New applications will be invented by size reductionSize reduction realizes cost reduction because of decrease of material cost.
such as LCD, Smart phone, LED light
The door will be opened to new world!
High power density converter has possibilities;
4Power Electronics Lab.
High efficiency = low loss =small heat think High power density
4
Toward High power density
Pow
er d
ensi
ty HEV inverter
Air conditioner inverter
Unit Pw. Sup.
Gene. Inv.
On board PS
SiC inverter
Package Power Supply
Break through technologies1)Loss reduction with SiC2)High temp. operation3)Size redc. and high temp.for passive components and heat
think4)High current density: DLB,DCB
This is not true ! Passive components can not be neglected
5Power Electronics Lab.
High power density in product –Switching Power Supply-
Passive components
Control PCB
Air flow
TDK Lambda HFE2500-48semiconductor
Passive components dominates large ratio of power system
6Power Electronics Lab.
Items for size reduction of passive components
Development of new materialMagnetic and capacitive materials are developing; however…
High frequency switching by WBG device (SiC,GaN)
Maximum frequency is limited by passive components materials
Rel
ativ
e P
erm
eabi
lity
Frequency(MHz)
Implementation of PCBwill be difficult
because parasitic capacitance and inductance can not be neglected.
Cooling method will bedifficult
Consideration of best circuit topology is important. (Two level inverter is not best way in all purpose)
7Power Electronics Lab.
Three-level output voltage waveform→Equivalent switching frequency: Double
Ref:http://www.jpubb.com/press/137261/
T-type 3-level
High frequency technique with circuit topology
Multi-level topology (series connection)
Interleave topology(parallel connection)
Loss
2-level
3-level Others
Filter
Switching
Conduction
Four-phase
K. Mino, R. Yamada, H. Kimura, Y. Matsumoto: "Power electronics equipments applying novel SiC power semiconductor modules", Proc. IPEC2014, pp. 1920-1924 (2014)
Input current is composed by triangle waveforms of four-phase current
Equivalent switching frequency:Four times
Reduction of switching loss and filter loss are achieved by circuit topology
8Power Electronics Lab.
Contents
1. Introduction-Importance of minimization of passive components
2. Approach I: Matrix converter for reduction of capacitor-Circuit topology and features-Latest technologies: Three-phase to Single phase--Matrix converter in Market: general purpose drive/air conditioner/quick charger
3. Approach II: Active power decoupling for Single-phase converter-Principle-Integrated to PFC or Inverter-Integrated to Chopper
4. Approach III: Discontinuous Current Mode converter-Principle: Robustness for inductor -Single-phase inverter with DCM-Three-phase inverter with DCM
5. Approach IV: FRT capability of grid-tied inverter with minimized inductor-Mr. Nagai presents his projects
6. Conclusion
9Power Electronics Lab.
Approach I: Matrix converter
Direct power conversion from line frequency AC to other AC
Motor
Input current
0
Output current
0
Input voltage
0 Matrix converter
Output voltage
0
Output voltage: composed by chopping three-phase input voltage with AC switches
Circuit type: four types
Inpu
t:
Output:
Single
Three
Single Three
o
o
o
o
The matrix converter can be applied to three-phase and single-phase input and/or output.
10Power Electronics Lab.
Feature 1: Simple AC to AC direct conversion
AC DC ACAC AC
Diode Rec. +Inverter Matrix converter
Initial charging unit, DCL, Breaking unit, and Smoothing capacitor: Not necessary for MC
Drastic size reduction will be achieved
11Power Electronics Lab.
Input /output waveforms
TH
D o
f in
put
curr
ent
(%)
Load torque (%)0 50 100
10
20
30
Inpu
t po
wer
fac
tor
(%)
Load torqure (%)0 50 100
80
90
100
Input current THD(less than 20th )
Input power factor
Input power factor over 99% at over 50% load
THD 5% at rated load
99
5
Power line200V、50Hz
Matrix converter
Motor
電源電圧
入力電流
出力電流
5ms/div
5A/div
5A/div
200V/div
0
0
0
vr
ir
iu
Feature 2: Low input current harmonics
Sinusoidal input current waveform as well as PWM rectifier
Ditto
Ditto
12Power Electronics Lab.
Realizing drastic energy saving for the applications which has regenerating power flow such as
lifts, cleans and rapid adjustable speed drives with large inertia load
Power line 2
00V、50Hz
Matrix converter Motor
Line voltage)250V/div
Input current 5A/div
Output current5A/div
Line voltage250V/div
Input current5A/div
Output current5A/div
Motoring Regenerating
Feature 3: Bidirectional power flow
Regenerated power of motor can be returned to power linewith sinusoidal current
Ditto
Ditto
13Power Electronics Lab.
Comparison among AC-AC converters
Items Diode rec. + Inv. PWM rec. + Inv. Matrix converter
Circuit configuration
Num. of arms Rec:6, INV:6, DB:1 Rec:6, INV:6 CONV:18
Circuit stricture Simple Complicate Complicate
Regeneration Impossible Possible Possible
Semiconductor loss Low Large Middle
Efficiency Middle Low High
Input current harmonics
Large Small Small
Input voltage distortion
Large Small Small
Size Small Large Middle
Cost Low High Middle?
初期充電
ブレーキユニット
DCL
初期充電
同上
同上
Performance of MC is the same to PWM rectifier although smaller size
14Power Electronics Lab.
Limitation of Matrix converter
Maximum Output voltage: 0.866 of Input voltageOutput voltage is composed by three-phase input voltage within envelope curve
Output voltage is limited to less than 0.866 of input voltageOutput voltage becomes 170V at 200V input voltageOutput voltage can be increased by over modulation technique;however input current harmonics will be increased.
0.866
Instantaneous power interruptionNot continuing the operation for instantaneous power interruptiondue to no large energy storage.
Possible to stop and automatic restart without tripSpeedy restart after power return due to no initial charging .Control power supply have to keep during interruptionwith larger capacitors in control board.
Input voltage dropMaximum output voltage is decreased in input voltage drop due to no boost up capability.
PWM rectifier can keep DC voltage even voltage drop.Possible to keep the performance for input voltage distortion, voltage imbalance
Input voltage
Output current
Interruption
Power return
Stop without tripAutomatic restart
It is important to use MC to the applications which can neglect these limitations
15Power Electronics Lab.
R
S
T
U V W
OR
RB-IGBT
IGBT + FWD
Main circuit configuration
9-swtich matrix converter Indirect Matrix converter
Three-phaseAC to AC
AC to DC to AC
Three-phase to single-phase Matrix converter topology is separated intodirect type and indirect type
Indirect matrix converter has no DC link capacitor although snubber capacitor3-1 matrix converter is used for high power application with modular structure and for medium frequency changer
16Power Electronics Lab.
Isolated AC-DC converter with matrix converter
One of disadvantage of matrix converter does not appearin this application because output voltage is adjusted by turn ratio of transformer
Circuit configuration
vr
vsvt
vrvsvt
Inductor
Output sideDC
TransformerSide AC
Step-down
Buck-boost
Inpu
t fil
ter
Output voltage
Boost-up Input sideAC
Control
Simple
Simple
Complicate
Three-types converters according to location of inductor
17Power Electronics Lab.
Step-down isolated matrix converter with DC inductor
DCMediumfrequency Line frequency AC3/1 AC1/DC
requirementSize reduction of
inductor
Current ripple increasing
Solution 1: PWM method considering large DC current ripple [4]
Solution 2: DC current ripple reduction with zero vector distribution of matrix converter [5]
Problems: current ripple reduction with small DC inductor
[5]J. Afsharian, D. D. Xu, B. Wu, B. Gong and Z. Yang, "Analysis of one phase loss operation of three-phase isolated buck matrix-type rectifierwith a boost switch," 2018 IEEE Applied Power Electronics Conference and Exposition (APEC), San Antonio, TX, 2018, pp. 30-36.
[4]S. Takuma, K. Kusaka, J. Itoh: "DC Ripple Component Cancelation Method of Isolated AC-DC Converter with Matrix Converter for Input Current Harmonics Reduction", Energy Conversion Congress Exposition 2019, pp. 6754-6762 (2019)
18Power Electronics Lab.
Dual active bridge type Isolated Matrix converter
or
However, the input voltage is fluctuated by three-phase ac voltage
Basic operating concept is the same to dual active bridge converter
Low EMI and size reduction are achieved by soft switching and increase of frequency
Suitable for high-power isolated power supply, EV charger, aircraft applications etc..
19Power Electronics Lab.
Simple duty ratio calculation method by approximation
Easy to calculate duty ratioPossible to power transfer stiffing soft switching conditionsError between ideal voltage and approximate waveform
depending on load conditions = difficult to compensation
Output voltageof inverter
Transformer current
Output voltageof MC
Equivalent circuit
Output voltage of MC is approximated to square waveform as well as DAB
Use of approximationto square waveform
M. A. Sayed, et.,al "Soft-Switching PWM Technique for Grid-Tie Isolated Bidirectional DC–AC Converter With SiC Device," in IEEE Transactions on IA, vol. 53, no. 6, pp. 5602-5614, . 2017.
Problems occur such as increase of output power error, input current distortion, etc.
20Power Electronics Lab.
Asymmetry modulation method
Output voltageof inverter
Transformer current
Output voltageof MC
Circulating
Average current during one switching period becomes constant for power transfer mode
Positive (A-B) and Negative (A’-B’) ripple
Power transfer
The current ripple in positive period is cancelled by ripple in negative period in transformer
Sinusoidal input current, high power factor
in MFT,and Soft switching operation
S. Takuma, K. Kusaka, J. Itoh, Y. Ohnuma, S. Miyawaki: "A Novel Current Ripple Cancellation PWM for Isolated Three-phase Matrix DAB AC-DC Converter", EPE2019, (2019)
Input voltage
Input current
Output current
Output voltage
Input current THD:4.1 %
21Power Electronics Lab.
Input current harmonics is suppressed to 5%
General Purpose Motor Drive: U1000 Yaskawa Electric
Power Range of U1000:From 200V, 9kVA (output current 28A) up to 400V, 770kVA (output current 930A)
Ref: http://www.e-mechatronics.com/en/product/inverter/u1000/feature/power.html
The biggest motivation to use matrix converter is
the input current harmonics reduction.
22Power Electronics Lab.
Ref: http://www.e-mechatronics.com/en/product/inverter/u1000/feature/allinone.html
Size reduction
Panel size can be reduced by 1/2
Matrix converter has big contribution to size reduction of panel in practically.
The number of components: drastically reduced.
The wiring is only 6
23Power Electronics Lab.
Air conditioners Daikin
Ref: K. Sakakibara et.al., :”Application of Indirect matrix converter for Air conditioners”,IEEJ Transaction on IA, Vol. 136, No. 7, p. 471-478, 2016
rpS
rnS
spS
snS
tpS
tnS
upS
unS
vpS
vnS
wpS
wnS
IPM
cS
preS
400V/50Hz, 5.7kW
Main circuit
Active Clamp circuit: Serial/parallel switching operation according to current
directionTo absorb reactive current at low load power factor To reduce inrush current at initial charge
Current source rectifier: unidirectional power flow
24Power Electronics Lab.
CPU →
FPGA →Clump →capacitor
Filter →capacitor
←Filterreactor
←NoiseFilter
OutputInput
NF1
NF2
NF3
Filter PCB INV PCB
OutputInput
NF1
NF2
NF3
NF4
NF5NF6
NF7,8
CPU forConv. →Inv. →
Noise←Filter
Reactor
additionalX
capacitor
ElectrolyticCapacitors→
Filter PCB INV PCB
Comparison of over view between PWM Rec. and IMC
PWM rectifier +Inverter Indirect matrix converter
The weight is reduced by 30% from 12kg to 8.2kg
Same PCB size although the number of switching device is increased.
Additional noise filters are not necessary
25Power Electronics Lab.
Vdc(200V/div)
Vs(200V/div)Is(10A/di
v)
Iu(10A/div)
Vdc:DC link voltage, Vs:Input phase voltage
Is:Input current, Iu:Output current
0
0
0
4mS/div
Operation waveforms
Performance evaluations(1)
Input current harmonics analysis
Unity power factorSinusoidal input and output current
Meeting IEC 61000-3-2 Class A
26Power Electronics Lab.
85
87
89
91
93
95
97
99
0 1000 2000 3000 4000 5000 6000 7000
Effi
cien
cy
[%]
Speed [min-1]
Diode-Rect.
PWM-Rect.
IMC
Meeting CISPR14-1 (QP)without additional noise filters
Note: PWM rec. switching frequency:15kHzIndirect matrix converter:5.9kHz
Conducted emission Efficiency
Improved by 1.5 - 2% in maximum and by 6% in light load condition(Air conditioner has long operation
time in light load)
6%
2%
Performance evaluations(2)
27Power Electronics Lab.
Volume: reduced by 50% Cost: reduced by 30%
to the conventional charger.
Rapid Charger for EV
The number of products: over 6000 units
Conventional charger Matrix converter charger
co1
1700
mm
750
640
1840
mm
380 670
15kUSD 10kUSD
Anti-series connection IGBT module
28Power Electronics Lab.
PWM rectifier inverter
Three-phase DC AC DC
Downsizing of a transformer
Sinusoidal input current
Advantages
Increasing of power loss
Bulky electrolytic capacitor and input inductor
Disadvantages
Medium frequency transformer
Three-phase Isolated AC-DC converter
50 or 60 Hz
Rectifier
BulkyBulky
LC filter
Small
MC Obtains medium frequency ACfrom line frequency directly
Three-phase AC DCAC
Conventional circuit
Advantage:No electrolytic capacitor and small AC inductors compared to that of conventional circuit
Matrix converter
29Power Electronics Lab.
Experimental verifications
Operation waveforms
(Pout: 40kW)
Over 90%
Maximum efficiency 91.4 %
EfficiencyInput voltage (250V/div)
Input Current (200A/div)
Input current THD: 2.5%
100
0
Output Current (10A/div)
The sinusoidal input current is obtained with 2.5% THD.The efficiency is over 90% in products level.
30Power Electronics Lab.
Contents
1. Introduction-Importance of minimization of passive components
2. Approach I: Matrix converter-Circuit topology and features-Latest technologies: Three-phase to Single phase--Matrix converter in Market: general purpose drive/air conditioner/quick charger
3. Approach II: Active power decoupling for Single-phase converter-Principle-Integrated to PFC or Inverter-Integrated to Chopper
4. Approach III: Discontinuous Current Mode converter-Principle: Robustness for inductor -Single-phase inverter with DCM-Three-phase inverter with DCM
5. Approach IV: FRT capability of grid-tied inverter with minimized inductor-Mr. Nagai presents his projects
6. Conclusion
for reduction of Capacitor
31Power Electronics Lab.
Single-phase grid tied systems
Bucky electrolytic capacitors are connected to DC-linkto absorb power ripple of double frequency of power grid.
Constant power Grid powerAbsorbing power ripple
100 or 120Hz
Approach II: Active power decoupling
such as PCS for PV, On Board Charger for EV etc…
have mismatching between input and output power.
32Power Electronics Lab.
2min
2max2
1VVCE
Capacitor energy
small large
Capacitor voltage is actively oscillated instead of use of large capacitor.
Boost/buck chopper(*)
Small capacitor
(*)H. Hu, S. Harb, N. Kutkut, I. Batarseh, Z. J. Shen : “Power Decoupling Techniques for Micro-inverters in PV Systems — a Review,”Energy Conversion Congress and Exposition 2010, pp.3235-3240, pp. 12-16 (2010)
Principle of Active power decoupling
How to reduce the capacitor in DC-link
Film capacitors or ceramic capacitors will be used instead of electrolytic capacitors
Long life time will be achieved due to no electrolytic capacitor
33Power Electronics Lab.
Passive decoupling Active decoupling
ProsNo cooling system
No inductorSmall capacitance
Low rated voltage switches
ConsElectrolytic capacitors
are needed.High rated
voltage switchesLarge
capacitance
Comparison of these circuits in terms of efficiency and power density
Boost type Buck type
Circuit configuration of Basic active power decoupling
34Power Electronics Lab.
98
98.5
99
99.5
100
0 5000 10000 15000 200005 10 15 20Power density [kW/dm3]
098
98.5
99
99.5
100
SiC-MOSFET 20 kHz
1 kHz
Si-MOSFET 20 kHz
IGBT 15 kHz
SiC-MOSFET 30 kHz
fsw increases.
Pareto-front optimization: Relationship among efficiency, power density and switching frequency
Maximum parameterPower density
Passive18.8 kW/dm3
Active17.0 kW/dm3
EfficiencyPassive
99.9%Active
99.5%
Power density of conventional APD is 90% of that of passive topology.
Comparison of Basic active power decoupling circuits
Output power:6kW, Input :380VDC, Output:200Vac
Grid-tied inverter for PV
J. Itoh, T. Sakuraba, H. N. Le, K. Kusaka: "Requirements for Circuit Components of Single-Phase Inverter Applied with Power Decoupling Capability toward High Power Density", 18th European Conference on Power Electronics and Applications (EPE'16),. DS2a 0291, pp. (2016)
35Power Electronics Lab.
0
0.1
0.2
0.3
0.4
0.5
0.6
1000 2000 3000 4000 5000 60000
0.1
0.2
0.3
0.4
0.5
Vol
ume
[dm
3 ]
0.6
2 3 4 5Rated power [kW]
1 6
CSPI=3 ̊ C/dm3
(Natural cooling)
50 kHz40 kHz
50 kHz
40 kHz
40 kHz35 kHz
30 kHz
35 kHz
30 kHz25 kHz
Switching frequency : 20 kHz
Boost type vs. Buck type
Boost type
Buck type
Minimum volume point is calculated in each rated power.
Buck type < Boost type Buck type > Boost type
Best topology depends on rated power. In high power, boost type is superior
36Power Electronics Lab.
0
20
40
60
80
100
120
従来 SiC‐MOSFET
(100
%=
0.32
dm
3 )
Total volume of APD components is compared to electrolytic cap.
1.1 times larger than that of passive topology
Volume analysis
Boost inductor is dominated by 30% of total volume even though SiC device is used in APD.
Buffer capacitor becomes1/3 of Elec. cap
37Power Electronics Lab.
Buffer circuitI
V
0
Active clamp snubber in indirect matrix converter is used for APD operation
Current source rectifier Voltage source inverter
Small capacitor
SC
Points of the proposed circuit
Only requiring a small capacitor and no additional a boost inductor
The buffer switch (Sc) achieves the zero current switching The efficiency improvement and size reduction are achieved by matrix converter technology
Proposed circuit I: APD with indirect matrix converter
Y. Ohnuma and J. Itoh, "Space vector modulation for a single phase to three phase converter using an active buffer," The 2010 International Power Electronics Conference - ECCE ASIA -, Sapporo, 2010, pp. 574-580.
APD is integrated to PFC
38Power Electronics Lab.
Input current is controlled by switch Sc and zero vectors of inverter
Separating three parts
Operation principle
Load current becomes current source for DC side
Inverter becomes single-switch which is operated by zero vectors
Switch Sc controls buffer capacitor voltage
Operation condition: vc> vIN
Charging : Inverter regenerates the power from load.
Discharge: Sc is turned ON
Inverter & outputBuffer circuit
Idc
vCvIN
Input &Rectifier
Equivalent circuit
In equivalent circuit,
Inverter & outputBuffer circuit
Input &Rectifier
39Power Electronics Lab.
C:50F only
Conventional circuit
(THD 49.8%)
Operation waveforms at 1 kW
Output current can not keep sinusoidal waveform
C:50F + SW
APD circuit with IMC
Output current THD 5.1%
Input current THD 3.9%
Sinusoidaloutput current waveform although the DC capacitor is only 50uF
40Power Electronics Lab.
THD of input and output currents
The minimum value
Output current THD 6.7%
Input current THD 3.3%
Input power factor
Input power factor of over 99 %
although diode rectifier is used
99%
Experimental verifications
41Power Electronics Lab.
Feature of proposed circuit
The power pulsation is absorbed by the capacitor
Small
Capacitance value is reduced by controlling the voltage variation
Small ac filter because proposed converter is current source type.
Capacitor voltage variation is not influence to the ripple of input and output
ab
IN ac
APD circuit in ChopperCurrent source inverter
Proposed inverter achieves MPPT, grid connection and power decoupling capability
Small
Proposed circuit II: APD integrated to chopper
Additional components are minimized for APD
Ref: Y.Ohnuma, K.Orikawa, J. Itoh: "A Single-phase Current Source PV Inverter with Power Decoupling Capability using an Active Buffer ", IEEE Energy Conversion Congress and Expo 2013, pp. 3094-3101 (2013)
42Power Electronics Lab.
Mode1
Mode4
Input power is directly transferred to ac side
Short circuit mode to keep input inductor current
Proposed converter is operated as boost chopper
APD circuit current pass does not appear in these modes
Operation principle I: chopper mode
43Power Electronics Lab.
Mode3
Buffer capacitor is discharged by connecting in series to input voltage.
Mode2
Buffer capacitor is chargedby connecting in parallel to input voltage
Buffering power is controlled by mode 2 and 3
Operation principle II: Energy management mode
Buffer voltage is independently controlled.
44Power Electronics Lab.
Experimental verifications
Input voltage:70VDCOutput voltage:100Vac,50HzOutput power: 400WBuffer capacitance: 50uF
Operation waveforms
Constant input current is obtained with 9.33% of input ripple.Sinusoidal output current is obtained with 4.2% of THD.
Maximum efficiency 94.9%Output power factor 99.9%
45Power Electronics Lab.
Eff
icie
ncy
[%]
Maximum power density of 1.8 times is obtained
Volume of buffer capacitor becomes 1/10 due to use of ceramic capacitor
Comparison of power density
Vol
ume
[cm
3 ]
Volume analysis
Heat sink will be smaller if SiC device applied to proposed circuit.
Conventional circuit = boost chopper +VSI
46Power Electronics Lab.
iin vbuf
Cbuf
Lboost
1
234
vdc
Cdc
iL
Vin
Lin
Cin
DCM is used for discharge of buffer capacitor Cbuf
Cbuf:Charge mode
Cbuf:Discharge mode
Average current of iL keeps constantBecause DC input current iin should be
constant direction, constant value
※Current source:Single-phase VSI
Proposed circuit III: APD integrated to chopper with DCM
Boost inductor is shared to APD operation.
Buffer voltage becomes higher than DC-link voltage = boost type
J. Itoh, T. Sakuraba, H. N. Le, K. Kusaka: "Requirements for Circuit Components of Single-Phase Inverter Applied with Power Decoupling Capability toward High Power Density", 18th European Conference on Power Electronics and Applications (EPE'16),.DS2a 0291, pp. (2016)
47Power Electronics Lab.
Without APD operation With APD
Buffer capacitor voltage oscillates at 100 Hz.
100 Hz components in input current is suppressed by 96.8%.
output power: 600 W
Operation waveform
iin iL
48Power Electronics Lab.
1 2 3 43
0 597.5
98.5
99.5
99
98
fsw
1 kHz
DC-DC converter with power decoupling capability
However total loss becomes 1.5 times higherProposed circuit achieves 1.1 times higher power density
Volume comparison
BCM will be applied to improve the efficiency because conduction loss is dominated in total loss
49Power Electronics Lab.
Cbuf:Charging mode
Cbuf:Discharging modeCurrent source:Single-phase VSI
Proposed circuit IV: APD integrated to chopper with DCM
Boost inductor is shared to APD operation.
Buffer voltage becomes lower than DC-link voltage = buck type
-Only one switch from input voltage to DC-link-Low voltage devices applied to APD
Low conduction loss
Same concept to proposed circuit III
J. Itoh, T. Sakuraba, H. Watanabe, N. Takaoka: "DC to Single-phase AC Grid-Connected Inverter using Back Type Active Power Decoupling Circuit without additional magnetic component", Energy Conversion Congress Exposition 2017, pp. 1765-1772 (2017)
50Power Electronics Lab.
Without APD operation With APD
Buffer capacitor voltage oscillates at 100 Hz.
100 Hz components in input current is suppressed by 90.2 %.
Operation waveforms
51Power Electronics Lab.
Efficiency is larger than 94% in region over 10% of rated power
Max. efficiency is 96.0% at 600 W output
Efficiency
Maximum:96.0%
52Power Electronics Lab.
Pareto-front curve of power density and efficiency
Max. power densityConventional buck
type active buffer method4.7 kW/dm3 (98.2%)
Proposed circuit achieves;
1.26 times higher power density is obtained
Proposed DCM active buffer method7.2 kW/dm3 (98.6%)
Passive method5.7 kW/dm3 (98.8%)
Volume of capacitors is reduced by 42.7 %.
Comparison of each DC-DC converter with APD
53Power Electronics Lab.
Neutral point voltage control in T-type inverter is used as APD capability
DCM is applied to ac current control
Proposed circuit V: APD integrated to T-type inverter with DCM
A. Omomo, K. Kusaka , J. Itoh, H. N. Le, N.Takaoka: "T-type NPC Inverter with Active Power Decoupling Method using Discontinuous Current Mode for Micro-Inverter", 7th International Conference on Renewable Energy Research and Applications (ICRERA 2018), (2018)
54Power Electronics Lab.
Operation principle
Neutral point current is controlled for APD
Output current is sum of APD current and reactive current
Reactive current
g g pSum of APD and reactive current become zero
at around 0 and of grid voltage phase.
Time shearing to achieve both control at the same time
Fundamental frequency of neutral point current is the same to grid frequency
55Power Electronics Lab.
Without power decoupling
vout 100 V/div
iout 2 A/div
Iin 1 A/div
With power decoupling
fluctuated
vout 100 V/div
iout 2 A/div
Iin 1 A/div
Harmonic analysis of input current
100 Hz
Time 4 ms/div
Time 4 ms/div
0 A
0 A
0 V
0 A
0 A
0 V
THDiout
3.13%
THDiout
3.19%
Operation waveforms
2nd order harmonics in DC input current is reduced by 77%
56Power Electronics Lab.
Contents
1. Introduction-Importance of minimization of passive components
2. Approach I: Matrix converter-Circuit topology and features-Latest technologies: Three-phase to Single phase--Matrix converter in Market: general purpose drive/air conditioner/quick charger
3. Approach II: Active power decoupling for Single-phase converter-Principle-Integrated to PFC or Inverter-Integrated to Chopper
4. Approach III: Discontinuous Current Mode converter for Reduction of indcutor-Principle: Robustness for inductor -Single-phase inverter with DCM-Three-phase inverter with DCM
5. Approach IV: FRT capability of grid-tied inverter with minimized inductor-Mr. Nagai presents his projects
6. Conclusion
57Power Electronics Lab.
Motivation to use DCM
Problems: Inductor is bulky and expensiveAdvantages of DCM are;1)Use of small inductance with
small volumePeak current becomes double average current in boundary condition Example: 1/10 of inductance, : double peak current then, amount of energy 2/5
Volume is reduced by 60%
3)Small RMS current in light load under same average current 2)Low inductor loss due to optimum design
DCM is suitable for high power
density converters
58Power Electronics Lab.
Disadvantages:-Inductance-dependent-Difficult to design cut-off frequency DCM Regeneration/-Powering transition control has not been realized.
Advantages:-Inductance-independent-Easy to design cut-off frequency-DCM Regeneration/Powering transitioncontrol is realized.
Problem and solution
Pervious duty value is used instead of induction value for nonlinear compensation.
Conventional method Proposed method
Nonlinear characteristic is compensated by inverse model of Transfer function
H. N. Le, K. Orikawa, J. Itoh: "Circuit-Parameter-Independent Nonlinearity Compensation for Boost Converter Operated in Discontinuous Current Mode",IEEE Transactions on Industrial Electronics, Vol. 64, No. 2, pp. 1157-1166 (2017)
59Power Electronics Lab.
CCM/DCM Regeneration/Powering Transition CCM/DCM Syn. Switching:
obtains maximum efficiency of 99.0% and Eff. over 98.7% at all load
Parameters
Experimental verifications
Powering and Regeneration
Current command responseSame current response is obtainedwith both CCM and DCM
60Power Electronics Lab.
Single-phase Grid-Tied Inverter
small
5ms/div
Iout
[A]
Current Command
DistortionCurrent Detection Value
Applying DCM to Single-phase inverter
Mixed PWM using both CCM andDCM is used to suppress the peak current
-Input current distortion becomes higher because loop gain from command to current is different to each modulation.-Modulation mode should be changed smoothly
H. N. Le, J. Itoh: "Inductance-Independent Nonlinearity Compensation for Single-Phase Grid-Tied Inverter Operating in Both Continuous and Discontinuous Current Mode", IEEE Transactions on Power Electronics, Vol. 34, No. 5, pp. 4904-4919 (2019)
61Power Electronics Lab.
Relationship between duties in DCM and CCM
Conventional Method-Use L to calculate IBCM
-Use IBCM to detect mode
Focusing point in conventional method
Focusing point in proposed method
DCMIICCMII
Vf
VVV
LI
BCMinBCMin
outsw
inoutinBCM
:,:
2
)(1
Proposed Method-Use relationship between DutyDCM and DutyCCM to detect mode
Mode detection between CCM and DCM
Inductance detection
Calculation of DutyDCM and DutyCCM
does not require L.Inductance-independent mode detection
62Power Electronics Lab.
Characteristics of proposed control:① Does not use inductance value to calculate DDCM&DCCM
➁ Use relationship between duties to detect mode
①
➁
Control block diagram of proposed modulation
Inductance-Independent CCM/DCM control is achieved
Pervious duty value is used instead of induction value for nonlinear compensation.
63Power Electronics Lab.
vDCDC link Voltage 350 VvgGrid Voltage 200 VrmsPnNominal Power 4 kW
TdeadtimeDead Time 500 ns25 kHz
1 kHz
fgGrid Frequency 50 Hz
fswSwitching Frequency 100 kHz
fsamp
fc
Sampling Frequency
Crossover Frequency
60oPMPhase Margin
SymbolDescription Value
LgGrid Inductance
LInverter-side Inductance
LfGrid-side Inductance
RdDamping Resistance
CFilter Capacitance
nCapacitance Ratio
LCL Filter Design Case IICase I
2000 H00160 H160 H580 H10 H10 H10 H16 F16 F4 F
1.51.50.516 16 16
Case III
2000 H160 H
10 H16 F
1.58
Experimental and simulation verification
vdcCf
Lg
vg
iout ig
SW1 SW2
SW2 SW1
L Lg
Lf
Lf
LInverter side Grid side
(260,80,60)mm
%Z=1.8% %Z=0.5%
64Power Electronics Lab.
Operation in normal grid
Conventional controller, %ZL=1.8% Conventional controller, %ZL=0.5%
Proposed controller, %ZL=1.8% Proposed controller, %ZL=0.5%
Proposed controller reduces the zero-crossing current distortion
65Power Electronics Lab.
Operation in weak grid for case II & III
3700
3800
3900
4000
4100
4200
4300
-400 -300 -200 -100 0 100 200Real Axis [s]
Imag
inat
ion
Axi
s [s
]
Design Case II
Design Case III
n = 0.5
n = 1.0
n = 1.5
n = 2.0n = 2.5
n = 3.0
Rd increases
Lg = 2000 HL = 160 HLf = 10 HC = 16 F
Proposed controller, %ZL=0.5% R=16 ohm
Proposed controller, %ZL=0.5% R=8 ohm
Pole trajectory
Filter design using pole trajectory enables
achieve desired stabilitywith lowest damping loss
66Power Electronics Lab.
Zero-crossing distortion occurs in output currentas same to single-phase inverter because DCM appears by dead-time
Inverter Output Current
Without dead time With dead time
Continuous Current Mode
Discontinuous Current Mode
Applying DCM to Three-phase inverter
Vdc
LUp Vp
Un Vn
Wp
Wn
L
L
DCM employs whole period to reduce distortionH. N. Le, J. Itoh: "Discontinuous Current Mode Control for Minimization of Three-phase Grid-Tied Inverters in Photovoltaic System", IEEJ Journal of Industry Applications, Vol. 8, No. 1, pp. 90-97 (2019)
67Power Electronics Lab.
How to apply proposed DCM to three-phase
Considering interval 0o~60o
Proposed method splits control of iu and iw
into 2 intervals:(i) D1 and D2 control iu
(ii) D3 and D4 control iw
Desired current waveform
Time sharing control
Each phase current is individually controlled.
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Operation of proposed DCM control(700W prototype)
u-phase voltage and INV currents Grid voltage and grid voltage
Magnified waveform
DCM operation is achieved in whole period.
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Step response & Current THD characteristic
Step response Current THD characteristic
Gir
d C
urre
nt T
HD
ig[%
]
Quick, stable step response, and Current THD below 5% are obtained at rated load Good control performance
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Efficiency Charactrarits Comparison
Maximum efficiency of 97.8%
synchronous switching Compared to asynchronous switching, synchronous switching reduces loss by 33.3% at rated load
1.3% up
(Loss -33.3%)
71Power Electronics Lab.
Contents
1. Introduction-Importance of minimization of passive components
2. Approach I: Matrix converter-Circuit topology and features-Latest technologies: Three-phase to Single phase--Matrix converter in Market: general purpose drive/air conditioner/quick charger
3. Approach II: Active power decoupling for Single-phase converter-Principle-Integrated to PFC or Inverter-Integrated to Chopper
4. Approach III: Discontinuous Current Mode converter-Principle: Robustness for inductor -Single-phase inverter with DCM-Three-phase inverter with DCM
5. Approach IV: FRT capability of grid-tied inverter with minimized inductor-Mr. Nagai presents his projects
6. Conclusion
72Power Electronics Lab.
Current overshoot suppression during Fault Ride-throughfor Three-phase Grid-tied Inverter with Low Inductance
Proposed method: Current overshoot is suppressed with the high-speed update of the inverter output voltage.
Occurrence of current overshoot with low inductance=>Update delay of inverter output at voltage drop and recovery
Abstracts
Satoshi Nagai, Jun-ichi ItohNagaoka University of Technology, Japan
The current overshoot is suppressed to less than 150% in the low inductance (%Z = 0.38%) with the proposed method.
73Power Electronics Lab.
Background
Minimization of system volume with high switching frequency
The inductor achieves small size by reducing the inductance.
Low inductance
Problem
Application
Solar cell*1
Power conditioning system
DCAC
grid
*1 https://biblion.jp/articles/ADTUP*2 S. Nagai, H. N. Le, T. Nagano, K. Orikawa, and J. Itoh, “Minimization of Interconnected Inductor for Single-Phase Inverter with High-Performance
Disturbance Observer”, the 2016 8th International Power Electronics and Motion Control Conference - ECCE Asia, No.Wb8-06 , (2016)
Downsizing of inductor
High switching frequency
Applying SiC or GaN devices to grid-tied inverter
Reduction ofdisturbance suppression performance*2
74Power Electronics Lab.
100
Voltagedrop Voltage
recovery
0 s 1.0 s0
Less than150 ms
20% of rated power/ s
20
5.0 s
FRT requirements
Grid-tied inverters stop at grid disturbanceContinuous operation is necessary without disconnection from grid
Decision of FRT / Disconnection (E. ON code) Output recovery requirements (E. ON code)
(FRT:Fault Ride Through)
Period of voltage sag less than 150 ms: FRT is necessary*3.
FRT requirements
Black out
Current overshoot rate at voltage recovery : Less than 150%*4
*3: Grid Code: High and Extra High Voltage, E.ON Netz GmbH Tech. Rep., 2006, Status:1*4: RPI-M20A, Delta Electronics, Inc., Taipei, Taiwan, 2014. [Online]. Available: http://www.deltaww.com/fileCenter/Products/Download/05/05 01/RPI-M20A_TechData_20141126.pdf
75Power Electronics Lab.
Requirement of grid-tied inverter
Continuing operationduring grid fault
FRT operation with low inductanceInverter operation stopsdue to over current protection.
Purpose
Minimization of inductorSuppression of current overshoot
Voltage sag
Overshoot occurs
Volt. drop Volt. recovery
Volt. sag
Problem for FRT with low inductance
Overshoot occurs
76Power Electronics Lab.
acvt
L
acL
vi t
L
acvt
L ac
L
vi t
L
Principal of current overshoot at voltage sag
The inductor voltage vL is increased due to an update delay of the inverter output voltage vinv at the voltage drop and recovery.
Inductor voltage vL: Large => Occurrence of inductor current overshoot
The current overshoot increases with the low inductance. The update delay should be reduced to suppress the current overshoot.
Conventional FRT: Large update delay of output voltage t
77Power Electronics Lab.
Conventional FRT control (Command change)
Reactive current control*3
=>Adjustment of reactive currenttoward voltage drop level
Command limiter*5
=>Suppression of maximumcurrent during voltage sag Reactive current injection (E.ON code)*3
Current command limiter*5*5: Y. Yang, F. Blaabjerg and H. Wang, "Low-Voltage Ride-Through of Single-Phase TransformerlessPhotovoltaic Inverters," in IEEE Transactions on Industry Applications, vol. 50, no. 3, pp. 1942-1952, 2014.
Impossible to update inverter output with high-speed at voltage drop and recovery
The current overshoot is increased by applying the low inductance.
Rea
ctiv
e cu
rren
t[%
]
78Power Electronics Lab.
Conventional FRT control (high-speed control)
Current control with 1 MHz-PLL and dead-beat control*6
*6: Y. Hanashima and T. Yokoyama, "FRT capability of 100kHz single phase utility interactive inverter with FPGA based hardware controller," 2012 15th International Power Electronics and Motion Control Conference (EPE/PEMC), Novi Sad, 2012, pp. LS8b.1-1-LS8b.1-8.
Dead-beat control:Output current follows in one sampling period.(100 kHz sampling)
1 MHz-PLL: Multi rate sampling(6.7 kHz to 1 MHz)
Achieving high-speed tracking to current command=>It is impossible to suppress the current overshoot in less than
the sampling period (10 s).
79Power Electronics Lab.
Proposed current overshoot reduction during FRT
Current overshoot reduction with high-speed update of inverter output at voltage drop and recovery
At voltage drop At voltage recovery
Current overshoot is reduced=> Counter voltage vector
(Achieving by gate-block operation)
Output vector: Same as grid voltage => Current slope becomes zero
The current overshoot is suppressed with the proposed vector at voltage drop and recovery.
Voltage vectorbefore voltage drop
=>Then, the high-speed voltage sag detection is necessary.
80Power Electronics Lab.
High-speed voltage sag detection method
Voltage sag is detected by HPF and comparator.
(x = a, b, c)
Voltage drop and recovery signals are generated in FPGA.
Threshold:
Signal for the proposed operation is generated by HPF output overshoot at grid voltage drop and recovery.
Grid voltage
MU
X2
5 times for HPF maximum output during rated operation
81Power Electronics Lab.
Inductance is designed with proposed FRT operation.
LL Ii 1_
tL
VIi ac
LL
tL
Vi acL 2_
_
acbd
L th L
VL t
I I
Inductor current overshoot rate is less than 150% for rated inductor current peak at voltage recovery.
Rated current peak Transient current
+
Inductor currentovershoot
Minimized inductance design
Inductance L is designed to0.48 mH (%Z = 0.38%)
Grid voltage peak: 163 V
Rated current peak: 4.0 A
Inductance design to meet FRT requirements
u(t): unit step function
82Power Electronics Lab.
Pout
fcry
L
tdelay
Experimental conditions
Verification in maximum-current-overshoot condition
Experimental condition
Voltage sag: down to 0 V
Using programmable power source:Voltage drop and recovery occur at voltage peak.
400 V
Line to line:200 Vrms
Occurrence of phase detection failure
Voltage drop Voltage recovery
Gridvoltage
Outputcurrent
Phaseinformation
ProgrammableAC power source
83Power Electronics Lab.
Comparison of current overshoot at voltage drop
The current overshoot at the voltage drop is reduced to 230%.
Comparison between conventional and proposed FRT method
With only reactive current control
With prop. method
84Power Electronics Lab.
0
0
Inductor current 5 A/div
Grid voltage100 V/div
a phase
b phase
b phase
a phase Maximum current4.91 A (123%)
c phase
c phase
250 s/div
Voltage recovery with prop. method (a phase peak)
With counter voltage vector (gate-block) => Current overshoot due to command tracking
With Prop. method
The current overshoot with prop. method is reduced to 46%.
85Power Electronics Lab.
Conclusion of FRT
Current overshoot suppression during Fault Ride-throughfor Three-phase Grid-tied Inverter with Low Inductance
The FRT operation was achieved with the proposed method without disconnection from grid.
Inverter side inductance: 0.38%Current overshoot rate: Less than 150%
Verification of asymmetrical voltage sag operation
Future work
Considering current overshoot suppression at voltage drop and recovery with low inductance
The proposed method achieved the high-speed update of the inverter output voltage.
86Power Electronics Lab.
Conclusion
1. Introduction-minimization of passive components is important more and more to obtain
high power density2. Matrix converter is one of candidate to eliminate DC cap.
Products in market: general purpose drive/air conditioner/quick charger3. Active power decoupling is effective for Single-phase converter
It is important to integrate APD to PFC, inverter, or chopper to realize high power density
4. Discontinuous Current Mode converter is good way to minimize inductors.Inductance-Independent CCM/DCM control is achieved for single-phase and three-phase inverters
5. FRT capability of grid-tied inverter becomes important when minimized inductoris used.High speed gate block method is one of solution to meet FRT standard.
87Power Electronics Lab.
Thank you for your kind attention
Thousand of Japanese sake bottles are waiting for youwhen you visit Japan.