Spacevector Pwm Inverter.pdf

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P ROJECT #2 S PACE V ECTOR PWM I NVERTER
J IN -W OO J UNG , P H .D S TUDENT
E-mail: jung.103@osu.edu
Tel.: (614) 292-3633
A DVISOR : P ROF . A LI K EYHANI
D ATE : F EBRUARY 20, 2005
M ECHATRONIC S YSTEMS L ABORATORY
D EPARTMENT OF E LECTRICAL AND C OMPUTER E NGINEERING
T HE O HIO S TATE U NIVERSITY
1. Problem Description
In this simulation, we will study Space Vector Pulse Width Modulation (SVPWM) technique.
We will use the SEMIKRON® IGBT Flexible Power Converter for this purpose. The system
configuration is given below:
Fig. 1 Circuit model of three-phase PWM inverter with a center-taped grounded DC bus.
The system parameters for this converter are as follows:
IGBTs: SEMIKRON SKM 50 GB 123D, Max ratings: V CES = 600 V, I C = 80 A
DC- link voltage: V dc = 400 V
Fundamental frequency: f = 60 Hz
PWM (carrier) frequency: f z = 3 kHz
Modulation index: a = 0.6
Output filter: L f = 800 µH and C f = 400 µF
Load: L load = 2 mH and R load = 5 Ω
Using Matlab/Simulink, simulate the circuit model described in Fig. 1 and plot the
waveforms of V i (= [V iAB V iBC V iCA ]), I i (= [i iA i iB i iC ]), V L (= [V LAB V LBC V LCA ]), and I L (= [i LA
i LB i LC ]).
2
784947471.002.png
2. Space Vector PWM
2.1 Principle of Pulse Width Modulation (PWM)
Fig. 2 shows circuit model of a single-phase inverter with a center-taped grounded DC bus,
and Fig 3 illustrates principle of pulse width modulation.
Fig. 2 Circuit model of a single-phase inverter.
Fig. 3 Pulse width modulation.
As depicted in Fig. 3, the inverter output voltage is determined in the following:
When V control > V tri , V A0 = V dc /2
When V control < V tri , V A0 = −V dc /2
3
784947471.003.png 784947471.004.png
Also, the inverter output voltage has the following features:
PWM frequency is the same as the frequency of V tri
Amplitude is controlled by the peak value of V control
Fundamental frequency is controlled by the frequency of V control
Modulation index (m) is defined as:
v
peak
of
(
V
)
control
A
0
1
∴
m
=
=
,
v
V
/
2
tri
dc
where,
(V
)
:
fundamenta
l
frequecny
component
of
V
A0
1
A0
2.2 Principle of Space Vector PWM
The circuit model of a typical three-phase voltage source PWM inverter is shown in Fig. 4.
S 1 to S 6 are the six power switches that shape the output, which are controlled by the switching
variables a, a′, b, b′, c and c′. When an upper transistor is switched on, i.e., when a, b or c is 1,
the corresponding lower transistor is switched off, i.e., the corresponding a′, b′ or c′ is 0.
Therefore, the on and off states of the upper transistors S 1 , S 3 and S 5 can be used to determine the
output voltage.
Fig. 4 Three-phase voltage source PWM Inverter.
4
784947471.005.png 784947471.001.png
The relationship between the switching variable vector [a, b, c] t and the line-to-line voltage
vector [V ab V bc V ca ] t is given by (2.1) in the following:
V
1
−
1
0
a
⎡
⎤
⎡
⎤
⎡
⎤
ab
⎢
⎥
⎢
⎥
⎢
⎥
V
=
V
0
1
−
1
b
. (2.1)
⎢
⎥
⎢
⎥
⎢
⎥
bc
dc
⎢
⎥
V
⎢
−
1
0
1
⎥
⎢
c
⎥
⎣
⎦
⎣
⎦
⎣
⎦
ca
Also, the relationship between the switching variable vector [a, b, c] t and the phase voltage
vector [V a V b V c ] t can be expressed below.
⎡
V
⎤
2
−
1
−
1
a
⎡
⎤
⎡
⎤
an
V
⎢
⎥
⎢
⎥
⎢
⎥
dc
V
=
−
1
2
−
1
b
. (2.2)
⎢
⎥
⎢
⎥
⎢
⎥
bn
3
⎢
⎥
⎢
⎥
⎢
⎥
V
−
1
−
1
2
c
⎣
⎦
⎣
⎦
⎣
⎦
cn
As illustrated in Fig. 4, there are eight possible combinations of on and off patterns for the
three upper power switches. The on and off states of the lower power devices are opposite to the
upper one and so are easily determined once the states of the upper power transistors are
determined. According to equations (2.1) and (2.2), the eight switching vectors, output line to
neutral voltage (phase voltage), and output line-to-line voltages in terms of DC-link V dc , are
given in Table1 and Fig. 5 shows the eight inverter voltage vectors (V 0 to V 7 ).
Table 1. Switching vectors, phase voltages and output line to line voltages
5

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