Method for DC-bus capacitance minimization of hybrid clamped converter
View Patent ↗The present invention provides a method for DC-bus capacitance minimization of hybrid clamped converter (HCC), which includes: obtaining the system parameters of the HCC during operation; determining the reference wave; determining the duty ratio of each switch according to the reference wave; determining the total neutral point current of the system; the fundamental component of the upper and lower DC-bus capacitor voltage of the system; determining the maximum voltage fluctuation of the upper and lower DC-bus capacitors; determining the minimum DC-bus capacitance value that satisfies the requirements of system capacitor voltage fluctuation by traversing the capacitance value. The present invention not only reduces the design complexity and cost of the high-power HCC system, but also improves the power density and reliability of the converter.
1 . A method for DC-bus capacitance minimization of hybrid clamped converter (HCC), comprising following steps:
step 1 : obtaining a DC-bus voltage V dc , a reference wave frequency f ac , a carrier frequency f c , a modulation ratio m a , a power factor cos φ, a load impedance Z, and a limit ΔV limit of a system capacitor voltage fluctuation when the HCC is operating;
step 2 : determining a reference wave
V
ref_x
′
:
V
ref
-
x
′
=
V
ref
-
x
+
V
com
=
{
V
ref
-
a
+
V
com
=
m
a
2
sin
(
2
π
f
ac
t
)
+
0.5
+
V
com
V
ref
-
b
+
V
com
=
m
a
2
sin
(
2
π
f
ac
t
-
2
π
3
)
+
0.5
+
V
com
V
ref
-
c
+
V
com
=
m
a
2
sin
(
2
π
f
ac
t
-
4
π
3
)
+
0.5
+
V
com
wherein, V ref_x takes V ref_a , V ref_b , V ref_c , V ref_a , V ref_b , and V ref_c denote a reference wave of a-phase, b-phase, and c-phase, respectively; V com denotes a common-mode voltage;
step 3 : determining a switch duty ratio D Nx of the HCC according to the reference wave
V
ref_x
′
:
D
Nx
=
f
(
V
ref
-
x
′
)
=
{
2
V
ref
-
x
′
0
≤
V
ref
-
x
′
≤
1
/
3
2
/
3
1
/
3
≤
V
ref
-
x
′
≤
2
/
3
2
(
1
-
V
ref
-
x
′
)
2
/
3
≤
V
ref
-
x
′
≤
1
step 4 : determining a total neutral point current i N of a system according to the switch duty ratio D Nx and a load current i ox :
i
N
=
D
Na
·
i
o
a
+
D
Nb
·
i
o
b
+
D
Nc
·
i
o
c
wherein D Nx denotes a switch duty ratio of a-phase, b-phase or c-phase; D Na denotes the switch duty ratio of a-phase; D Nb denotes the switch duty ratio of b-phase; D Nc denotes the switch duty ratio of the c-phase; i ox denotes the load current of a-phase, b-phase or c-phase; i oa denotes the load current of a-phase; i ob denotes the load current of b-phase; i oc denotes the load current of c-phase;
step 5 : determining a fundamental component V cap of capacitors voltage of upper and lower DC-bus of the system according to the total neutral point current i N of the system:
V
cap
=
∫
0
t
i
N
dt
C
d
1
wherein C d1 denotes a value of a DC-bus capacitance to be determined, DC-bus capacitors are divided into three DC-bus capacitors: an upper DC-bus capacitor, a middle DC-bus capacitor, and a lower DC-bus capacitor, and capacitance values of the three DC-bus capacitors are equal;
step 6 : determining a maximum voltage fluctuation ΔV cd1/cd3_max of upper and lower DC-bus capacitors according to V cap :
Δ
V
cd
1
/
cd
3
_
max
=
Δ
V
cd
1
/
cd
3
_
f
_
max
+
Δ
V
cd
1
/
cd
3
_
h
_
max
=
max
(
V
cap
)
-
min
(
V
cap
)
2
+
3
Δ
V
cd
2
_
max
wherein ΔV cd1/cd3_f_max is the fundamental component of the maximum voltage fluctuation of the upper and lower DC-bus capacitors; ΔV cd1/cd3_h_max is a harmonic component of the maximum voltage fluctuation of the upper and lower DC-bus capacitors; max(V cap ) is a maximum value of the fundamental component of voltage of the upper and lower DC-bus capacitors, and min(V cap ) is a minimum value of the fundamental component of voltage of the upper and lower DC-bus capacitors; ΔV cd2_max is a maximum voltage fluctuation of the middle DC-bus capacitor; and
step 7 : traversing the value C d1 from 0 to C max , a step length of the traversing is M 1 , repeating steps 1 - 6 to obtain a corresponding ΔV cd1/cd3_max of different capacitance values, and when the ΔV cd1/cd3_max is less than or equal to V limit for a first time, outputting a corresponding capacitance value, that is, a minimum DC-bus capacitance value satisfying a requirement of the system capacitor voltage fluctuation.
2 . The method for DC-bus capacitance minimization of HCC according to claim 1 , wherein in step 1 , a range of V limit is 0-100% of a rated operating value of a capacitor voltage, and the rated operating value of the capacitor voltage is ⅓ of the DC-bus voltage.
3 . The method for DC-bus capacitance minimization of HCC according to claim 1 , wherein in step 2 ,
V
com
=
0.25
·
m
a
2
·
sin
(
2
·
3
f
ac
π
t
)
.
4 . The method for DC-bus capacitance minimization of HCC according to claim 1 , wherein in step 4 , the load current i ox satisfies
{
i
oa
=
I
sin
(
2
π
f
ac
t
-
φ
)
i
ob
=
I
sin
(
2
π
f
ac
t
-
φ
-
2
π
3
)
i
ob
=
I
sin
(
2
π
f
ac
t
-
φ
-
4
π
3
)
,
wherein I denotes a maximum load current amplitude,
I
=
1
2
·
m
a
·
V
dc
Z
.
5 . The method for DC-bus capacitance minimization of HCC according to claim 1 , wherein in step 6 ,
Δ
V
cd
2
-
max
=
3
3
-
2
12
·
I
·
T
c
C
d
1
,
wherein T c is a reciprocal of the carrier frequency f c .
6 . The method for DC-bus capacitance minimization of HCC according to claim 1 , the maximum voltage fluctuation of the upper and lower DC-bus capacitors as a main reference for the DC-bus capacitance minimization.
7 . The method for DC-bus capacitance minimization of HCC according to claim 1 , wherein in step 7 , C max is 0.001 mF to 100 mF, and the step length M 1 is 0.0001 mF to 5 mF.
8 . The method for DC-bus capacitance minimization of HCC according to claim 1 , wherein the method is applicable to a wide output voltage current frequency 1-1000 Hz condition and a wide carrier frequency 500-10000 Hz condition.