Environmental Engineering Reference
In-Depth Information
3.5 Control Strategy for Wind Energy Integration
into Power Network
In the WECS, as shown in Fig. 3.3 , the energy generated by a generator is firstly
transformed to a DC voltage by the machine side PWM inverter connecting the
machine to the DC link. Then, the grid side PWM inverter connecting the DC link
to the power grid transforms the DC to AC voltages, which is delivered to the power
grid. We can use the dual PWM inverters to transform the renewable energy to the
grid without any additional circuit. The machine side PWM inverter and the grid
side PWM inverter are independent. Both of them can be controlled separately. A
unit power ratio for the WECS can be realized using some control strategy.
It can be seen in Fig. 3.3 that the output of the DC-link voltage controller is the
d-axis reference current i d . For achieving the rectification or the inversion with unity
power factor, the component of the reactive current i q should be set to zero [ 24 ].
3.5.1 DC-Link Voltage Controller Design
Define the given DC-link voltage as u dc and its square as u ¼ u 2
dc , then the error
between the square of the DC-link and the square of the given DC-link voltage e 1 is:
e 1 ¼ u u
ð 3 : 21 Þ
Based on Eq. ( 3.20 ), the error e 1 can be expressed as:
p i L
e 1 ¼ u u ¼ 2
C E s i d þ 2
ð 3 : 22 Þ
C
To achieve fast error convergence and better tracking precision, a TSM man-
ifold was designed as follows [ 12 , 13 ]:
s 1 ¼ e 1 þ c 1 e q 1 = p 1
ð 3 : 23 Þ
1
where c 1 > 0, p 1 [ 0, q 1 [ 0, p 1 and q 1 are odd.
After the system states reach the TSM manifold s 1 = 0 in finite time, both e 1
and e 1 will converge to the original points along s 1 = 0 in finite time, i.e.,
e 1 ¼ e 1 ¼ 0
ð 3 : 24 Þ
Theorem 1 If the TSM manifold is chosen as Eq. ( 3.23 ), and the TSM control is
designed as follows, e 1 can converge to zero in finite time [ 25 ]:
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