US 11,121,642 B2 · Simplified space vector modulation method for multi-level converter

Abstract

The disclosure discloses a simplified space vector modulation method for multi-lever converters, and relates to the field of space vector modulation methods for multilevel converters, which solves problems that a redundant on-off state is greatly increased along with increase of a number of levels in a traditional SVM technology, and SVM is difficult to realize due to calculation of the redundant on-off state and selection of a proper on-off state. The method includes the following steps of: step 1: establishing a vector expression; step 2: establishing a reference vector trajectory model; step 3: respectively representing reference signals and level signals by coordinate components of a reference vector and a basic vector and corresponding component sums; step 4: constructing a star-connected multilevel converter; step 5: sampling a phase voltage reference vector trajectory model of the star-connected multilevel converter, and synthesizing the reference vector.

A simplified space vector modulation method for a multi-level converter, comprising the following steps of:

step 1:
an expression of a basic vector Vαβ(vα,vβ) corresponding to a phase voltage in a traditional Cartesian coordinate system (referred to as an α-β coordinate system) being:
[
v
α
v
β
]
=
[
1
3
⁢
(
2
⁢
v
a
-
v
b
-
v
c
)
3
3
⁢
(
v
b
-
v
c
)
⁢
]
,
wherein vα and vβ represent coordinate components corresponding to the basic vector Vαβ, va, vb and vc respectively represent levels corresponding to three phase voltages of the multi-level converter, (va,vb,vc) is called a switching state corresponding to the basic vector Vαβ, and for an n-level converter, wherein n is an integer and equals to two or greater, va, vb, vc∈[(n−1), (n−2), . . . , 2, 1, 0];
and
a reference vector Vrαβ(vrα,vrβ) calculated according to phase voltage reference signals in the α-β coordinate system being:
[
v
r
⁢
⁢
α
v
r
⁢
⁢
β
]
=
3
3
⁢
m
⁡
(
n
-
1
)
⁡
[
cos
⁢
⁢
ω
⁢
⁢
t
sin
⁢
⁢
ω
⁢
⁢
t
]
;
wherein vrα and vrβ represent coordinate components corresponding to the reference vector Vrαβ;
step 2:
rotating a coordinate axis of an α-β plane counterclockwise by 45 degrees and compressing an axial proportion to obtain an α′-β′ coordinate system, and establishing a reference vector trajectory model;
a basic vector V′(v′α,v′β) in the coordinate system α′-β′ being:
[
v
α
′
v
β
′
]
=
[
1
0
-
1
-
1
1
0
]
⁡
[
v
a
v
b
v
c
]
=
[
v
a
-
v
c
⁢
-
v
a
+
v
b
]
,
wherein v′α and v′β represent coordinate components corresponding to the basic vector V′;
a reference vector V′r(v′rα,v′rβ) calculated according to phase voltage reference signals in the α′-β′ coordinate system being:
[
v
r
⁢
⁢
α
′
v
r
⁢
⁢
β
′
]
=
m
⁡
(
n
-
1
)
2
⁡
[
3
⁢
⁢
cos
⁢
⁢
ω
⁢
⁢
t
+
sin
⁢
⁢
ω
⁢
⁢
t
⁢
-
3
⁢
⁢
cos
⁢
⁢
ω
⁢
⁢
t
+
sin
⁢
⁢
ω
⁢
⁢
t
]
,
wherein v′rα and v′rβ represent coordinate components corresponding to the reference vector V′r;
the reference vector trajectory model in the α′-β′ coordinate system being:
(
v
r
⁢
⁢
α
′
+
v
r
⁢
⁢
β
′
m
⁡
(
n
-
1
)
)
2
+
(
v
r
⁢
⁢
α
′
-
v
r
⁢
⁢
β
′
3
⁢
m
⁡
(
n
-
1
)
)
2
=
1
;
m
=
3
⁢
U
r
(
n
-
1
)
⁢
E
;
wherein Ur represents a phase voltage amplitude expected to be outputted by the multi-level converter, which is also called a reference voltage amplitude, and E represents a direct current voltage corresponding to a unit level;
step 3:
in the α′-β′ coordinate system, respectively representing line voltage reference signals −urca, −urab and urbc by the coordinate components v′rα and v′rβ of the reference vector V′r and the sum of the two components v′rα+v′rβ, and respectively representing line voltage level signals −vca, −vab and vbc by the coordinate components v′α and v′β of the basic vector V′ and the sum of the two coordinate components v′α+v′β:
{
v
r
⁢
⁢
α
′
=
u
ra
-
u
rc
=
-
u
rca
⁢
v
r
⁢
⁢
β
′
=
-
u
ra
+
u
rb
=
-
u
rab
⁢
v
r
⁢
⁢
α
′
+
v
r
⁢
⁢
β
′
=
u
rb
-
u
rc
=
u
rbc
,
wherein urab, urbc and urca respectively the represent reference signals of the three line voltages;
[
v
α
′
⁢
v
β
′
⁢
v
α
′
+
v
β
′
]
==
[
v
a
-
v
c
⁢
-
v
a
+
v
b
v
b
-
v
c
⁢
]
=
[
-
v
ca
-
v
ab
v
bc
⁢
]
,
wherein vab, vbc and vca respectively represent levels corresponding to the three line voltages, vab, vbc, vca∈[±n, ±(n−1), . . . , ±2, ±1, 0], and each line voltage outputs 2n+1 levels;
step 4:
constructing a new star-connected multi-level converter, so that line voltage reference signals of the new star-connected multi-level converter are the same as line voltage reference signals of a controlled delta-connected multi-level converter;
step 5:
sampling a phase voltage reference vector trajectory model of the constructed star-connected multi-level converter, calculating three basic vectors closest to the sampled reference vector V′r, using the three basic vectors as equivalent basic vectors, the three equivalent basic vectors forming a sector triangle, and synthesizing the reference vector by using the three equivalent basic vectors;
step 6:
calculating duty cycles of the equivalent basic vectors which synthesize the sampled reference vector by using the volt-second balance principle:
when the reference vector is located in Sector-I:
{
t
1
=
T
S
⁡
(
1
+
v
α
′
-
v
r
⁢
⁢
α
′
)
⁢
t
2
=
T
S
⁡
(
1
+
v
β
′
-
v
r
⁢
⁢
β
′
)
⁢
t
3
=
T
S
⁡
(
v
r
⁢
⁢
α
′
+
v
r
⁢
⁢
β
′
-
v
α
′
-
v
β
′
-
1
)
,
wherein t1, t2 and t3 respectively represent duty cycles of vectors V′1, V′2 and V′3, and TS represents the sampling period;
when the reference vector is located in Sector-II:
{
t
0
=
T
S
⁡
(
1
+
v
α
′
+
v
β
′
-
v
r
⁢
⁢
α
′
-
v
r
⁢
⁢
β
′
)
t
1
=
T
S
⁡
(
v
r
⁢
⁢
α
′
-
v
α
′
)
⁢
t
3
=
T
S
⁡
(
v
r
⁢
⁢
β
′
-
v
β
′
)
⁢
,
wherein t0, t1 and t3 respectively represent duty cycles of vectors V′0, V′1 and V′3;
and
step 7:
using the components of the equivalent basic vector of the phase voltage reference vector of the star-connected multi-level converter and the sum of the two components as switching states for controlling a line voltage of the delta-connected multi-level converter.

536 more elements

Simplified space vector modulation method for multi-level converter

Life of this patent

Simplified space vector modulation method for multi-level converter

Life of this patent

Abstract

Claims7