FILTER DESIGN FOR MULTILEVEL CONVERTERS
1
Series-Parallel MultiLevel Cell with Filters
I chop
I LHV
LHV D
D
I LLV / 2 VHV
CHV
f
HV 0
VCHV
1 2 LHV CHV
I LV
D
D
1 D
1 D
1 D
1 D
LLV LLV
CLV VCLV
f sw 2
AC-equivalent circuit of Series-Parallel MultiLevel Cell
I LHV
LHV CHV VCHV
VHV
f
HV 0
1 2 LHV CHV
I LV np n p f sw
I LV
I LLV VHV ns .n p ns n p f sw
LLV / n p
CLV f 0LV
VCLV 1
2 LLV n p .CLV 3
Steady state, time domain : worst case ripples Pulsation on the Low Voltage side (2nd order filter)
LV ripple%
V
2 1 f VHV n p ns n p ns f sw 1 f 0LV 2 LLV n p .CLV V
LV pk ripple
LV 0
2
1 L n C LV p LV LV 2 ( n p ns )1.5 f sw Vripple% 2
Pulsation on the High Voltage side (2nd order filter)
I
HV ripple%
I 2 1 f I LVmax n p n p f sw 1 HV f0 2 LHV .CHV HV pk ripple
HV 0
2
1 LHV CHV HV 2 .n1p.5 f sw I ripple% 2
4
Ripples : from time domain to frequency domain
-20bB/dcd
200dB
+
-40dB/dcd
=
-60dB/dcd
fswitching B1≈ripple
Ripple requirement
100dB
f0
0dB
1kHz
10kHz
100kHz
1MHz
=>Conclusion : the ripple requirement allows increasing f0 when increasing fswitching
10MHz
5
EMC standards : frequency domain formulation
-20bB/dcd
200dB
+
-40dB/dcd
=
-60dB/dcd
fswitching B1≈ripple
100dB
0dB
Ripple requirement
f0
EN55022A
1kHz
10kHz
100kHz
1MHz
10MHz
6 =>Conclusion : salient point of EMC standards imposes decreasing f0 when increasing fswitching
EMC standards : frequency domain formulation fswitching
200dB
fswitching B1≈ripple
Ripple requirement 100dB
f0
EN55022A 7
Steady state : ripples and standards combined Required cut-off frequency vs switching frequency
4
2
1
3
2
1
4
3 8
Steady state : ripples and standards combined Required cut-off frequency vs switching frequency for MultiCell converters 10
Simplified EN55022A Filter for multiCell Chopper
5
nCell nCell nCell nCell
4
10
10
[email protected]
cutoff frequency [Hz]
10
=10 =2 =5 =1 = =15 =2 =12 = =1
3
2
10
3
10
4
10 switching frequency [Hz]
5
6
10 9
Steady state : ripples and standards combined
10
10
Required cut-off frequency • for ≠ standards, • for ≠ switching frequencies • for ≠ number of cells
4
3 Some standards
Simplified 5 HVDC Filter for multiCell Chopper; Pnom=100 10
cutoff frequency [Hz]
cutoff frequency [Hz]
Simplified EN55022A Filter for multiCell Chopper 5 10
10
10
4
3
180 EN55022A [dBuV] EN55022B [dBuV] HVDCA: P=100kW [dBuA] HVDCB: P=1kW [dBuA]
10
10
3
4
5
10 10 switching frequency [Hz]
10
maximum ripple [dBuX]
160
2
6
140
10
120
2
10
3
100
4
5
10 10 switching frequency [Hz]
10
6
80 60 40 20
10
10
10
4
3
2
10
0 3 10
10
4
5
10 10 switching frequency [Hz]
6
10
7
Simplified HVDC Filter for multiCell Chopper; Pnom=1k 5 10
cutoff frequency [Hz]
cutoff frequency [Hz]
Simplified EN55022B Filter for multiCell Chopper 5 10
3
4
5
10 10 switching frequency [Hz]
10
6
10
10
10
4
3
2
10
3
4
5
10 10 switching frequency [Hz]
10
10
6
Influence of the discrete nature of the spectrum (mainly for choppers…)
10
10
10
HVDC Filter for multiCell Chopper; Pnom=100kW
5
nCell = 1 nCell = 2 nCell = 3 nCell = 4 nCell = 5 nCell = 6 nCell = 7 nCell = 8 nCell = 9 nCell =10 nCell =11 nCell =12 randomcheck
4
3
2
10
3
10
4
10
5
10
6
switching frequency [Hz] random check for EN550222B: swF=120kHz; nCell =1; duty =0.51 180 EN55022B vHdBuV(duty) envdBuV envdBuVFB
160
maximum ripple [dBuV]
cutoff frequency [Hz]
10
140 120 100 80 60 40 20 0 4 10
5
10 switching frequency [Hz]
10
6
11
Steady state : ripples and standards combined
10
10
5
HVDC Filter for multiCell Chopper; Pnom=100kW 5 10
EN55022A Filter for multiCell Chopper
Accounting for the discrete nature of the spectrum (mainly for choppers…)
4
3 Some standards
cutoff frequency [Hz]
cutoff frequency [Hz]
10
10
10
4
3
180 EN55022A [dBuV] EN55022B [dBuV] HVDCA: P=100kW [dBuA] HVDCB: P=1kW [dBuA]
10
10
3
4
5
10 10 switching frequency [Hz]
10
maximum ripple [dBuX]
160
2
6
140
10
120
2
10
3
100
4
5
10 10 switching frequency [Hz]
10
6
80 60 40 20
10
10
10
5
EN55022B Filter for multiCell Chopper
0 3 10
4
3
2
10
10
4
5
10 10 switching frequency [Hz]
6
10
HVDC Filter for multiCell Chopper; Pnom=1kW 5 10
7
cutoff frequency [Hz]
cutoff frequency [Hz]
10
3
4
5
10 10 switching frequency [Hz]
10
6
10
10
10
4
3
2
10
3
4
5
10 10 switching frequency [Hz]
12
10
6
Step response, average model : full load => no load Worst Case :
D 100%; I
( t 0 ) LHV
I LVmax Voltage overshoots
I LVmax
LHV 0.ILV
VHV
I L( tLV0 ) I LVmax
CHV VCHV
0
LLV / n p 0.VHV
CLV VCLV
Best response of the control to limit overshoot on LV side : impose D=0 13
Step response, state plane analysis full load => no load High Voltage Side
Low Voltage Side
VCHV
VCLV
Worst Case
VHV
VHV
I LHV 0
I LVmax
LHV CHV
LHV CHV
I LLV 0
I LVmax
LLV CLV
LLV CLV 14
Full load => no load : dynamic requirement HV side
Limit the voltage overshoot on the High Voltage Side
I LV . HV Vovrsht %
LHV CHV
VHV
HV LHV VHV .Vovrsht % ........... ............... CHV I LV max 15
Step response, average model : no load => full load
D 100%; I
Worst Case :
( t 0 ) LHV
0 Voltage dips
I LVmax
LHV I L( tLV0 ) 0 VHV
CHV VCHV
0
LLV / n p
CLV VCLV Best response of the control to limit voltage dip on LV side : maintain D=100% 16
Step response, state plane analysis no load => full load High Voltage Side
Low Voltage Side
VCHV
VCLV
VHV
VHV Worst Case
I LHV 0
I LVmax
LHV CHV
LHV CHV
I LLV 0
I LVmax
LLV n p CLV
LLV n p CLV 17
No load => Full load : dynamic requirement LV side
Limit the voltage dip on the Low Voltage Side
I LV . LV Vdip
LLV n pCLV VHV
........... ...............
LLV n p CLV
LV VHV .Vdip
I LVmax 18
Calculation of the components High Voltage side
Low Voltage side
nCell n p HV I pk ripple HV Rip I % ripple% I LV max 1 f 0 2 LHV .CHV
1.5 f 0 min nCell f sw Rip % 2
;
nCell n p .ns LV V pk ripple LV Rip % Vripple% VHV 1 f 0 2 L n .C LV p LV
gabmax f salient, nCell . f sw
Valid for uncoupled AND coupled magnetic components
. max f salient, nCell . f sw 3 2VHV . f sw
19
Calculation of the components High Voltage side
Low Voltage side
HV LHV VHV .Vovrsht % CHV I LVmax 1 LHV .CHV 2 . f 0HV
HV VHV .Vovrsht % LHV 2 . f HV I 0 LVmax I LVmax C HV HV 2 . f 0HVVHV .Vovrsht %
LV LLV n p VHV .Vdip % CLV I LVmax 1 L n .C LV p LV 2 . f 0LV
LV VHV .Vdip % LLV n p 2 . f 0LV I LVmax I LVmax C LV LV 2 . f 0LVVHV .Vdip %
Valid for uncoupled AND coupled magnetic components
20
Calculation of the components Example #1 : 2-level converter => from 10 to 150kHz, the tendancy is an increase of passive components MultiCell -2 Chopper with: nS=1; VHV=800; ILVmax=250; IHVmax=125; relativeOutRipple=0.01; VHVovershoot=0.1; VLVdip=0.05;standardHV=HVDCA;standardLV=EN55022A 10 LHV CHV LLV CLV
-3
L and C values [H or F]
10
10
-4
10
3
10
4
10 switching frequency [Hz]
5
10
6
21
Calculation of the components Example #2 : series 2-cell converter => the HV filter is unchanged, LLV and CLV are reduced if fsw > 80kHz MultiCell -2 Chopper with: nS=2; VHV=800; ILVmax=250; IHVmax=125; relativeOutRipple=0.01; VHVovershoot=0.1; VLVdip=0.05;standardHV=HVDCA;standardLV=EN55022A 10 LHV @nS=1 CHV @nS=1 LLV/
[email protected]=1 CLV @nS=1 LHV @nS=2 CHV @nS=2 LLV/
[email protected]=2 CLV @nS=2 -3
L and C values [H or F]
10
10
-4
10
3
10
4
10 switching frequency [Hz]
5
10
6
22
Calculation of the components Example #3 : parallel 2-cell converter => all passive components are reduced if fsw > 80kHz MultiCell -2 Chopper with: nS=1; VHV=800; ILVmax=250; IHVmax=125; relativeOutRipple=0.01; VHVovershoot=0.1; VLVdip=0.05;standardHV=HVDCA;standardLV=EN55022A 10 LHV @nP=1 CHV @nP=1 LLV/
[email protected]=1 CLV @nP=1 LHV @nP=2 CHV @nP=2 LLV/
[email protected]=2 CLV @nP=2 -3
L and C values [H or F]
10
10
-4
10
3
10
4
10 switching frequency [Hz]
5
10
6
23
Calculation of the components Example #4 : parallel multiCell converter => with 10 // cells, all passive components start decreasing at fsw > 15kHz MultiCell -2 Chopper with: nS=1; VHV=800; ILVmax=250; IHVmax=125; relativeOutRipple=0.01; VHVovershoot=0.1; VLVdip=0.05;standardHV=HVDCA;standardLV=EN55022A 10 LHV @nP=1 CHV @nP=1 LLV/
[email protected]=1 CLV @nP=1 LHV @nP=2 CHV @nP=2 LLV/
[email protected]=2 CLV @nP=2 -3
L and C values [H or F]
10
10
-4
10
3
10
4
10 switching frequency [Hz]
5
10
6
24
Combined requirements High Voltage side
Low Voltage side
LHV
LLV Current design Current design Candidates for volume reduction
0
CHV
Candidates for volume reduction
0
CLV
For the same amount of energy, magnetic components are (2 to 10 times??) bigger, heavier and more expensive than capacitor => Reducing the inductances and increasing the capacitance leaves room for25 optimization… (and increasing the inductance must not be rejected a priori!)