Current H Repetitive Control - Control of Power Inverters in Renewable Energy and Smart Grid Integration - page 88

3.4.2.2 With a Resistive Load

In this experiment, a balanced resistive local load was connected to the inverter ( R A = R B =

). The grid output current reference I d was set at 2 A (after connecting the inverter
to the grid) and the reactive power was set at 0 Var ( I q

R C = 12

0). The output current i a , the
reference current i ref , the current tracking error e i and the spectrum of the grid output current
i a are shown in the right column of Figure 3.7. The controller again demonstrated very good
harmonics rejection and tracking performance. The current THD is slightly higher because
the current injected into the grid is lower than that in the previous experiment.

=

3.4.2.3 With an Unbalanced Load

In this experiment, an unbalanced resistive local load was connected to the system ( R A = 12 ,

). The grid current reference I d was set at 2 A (after connecting the
inverter to the grid) and the reactive power was set at 0 Var ( I q

R B =∞ and R C = 12

0). The output current i a ,
the reference current i ref , the current tracking error e i and the spectrum of the grid output
current i a are shown in the left column of Figure 3.8. Because of the available neutral line, the
imbalance of the load did not affect the performance of the system.

=

3.4.2.4 With a Non-linear Load
In this experiment, a non-linear load (a three-phase uncontrolled rectifier loaded with an LC fil-
ter L

= 150 μ H, C = 1000 μ F and a resistor R = 20 ) was connected to the inverter. The grid

5 5

i ref i a i ref i a

2.5 2.5

0 0

−2.5 −2.5

−5 −5

1.5 1.5

e i e i

1 1

0.5 0.5

0 0

−0.5 −0.5

−1 −1

−1.5 −1.5

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08

Time [s] Time [s]

(a) Grid current i a , its reference i ref and the current tracking error e i

5 15

THD of i a =1.55% THD of i a =4.91%

4

10

3

2

5

1

0 0

0 5 10 15 20 25 30 0 5 10 15 20 25 30

Harmonics order Harmonics order

(b) Spectra of the grid current i a

Figure 3.8 Experimental results in the grid-connected mode: with unbalanced local loads (left column)
and with a non-linear local load (right column)