Voltage H Repetitive Control with a Frequency-adaptive Mechanism - Control of Power Inverters in Renewable Energy and Smart Grid Integration - page 114

and R B =∞ . The grid voltage was taken directly as the voltage reference without filtering

so that the inverter was synchronised and ready to be connected to the utility grid. This is
equivalent to setting the grid current references to be 0.

5.4.1.1 With a Resistive Load

The results are shown in the left column of Figure 5.7. The reference voltage was tracked
well. The recorded local voltage THD was 1 . 05% and the local load current THD was 1 . 06%.

30 30

u ref u A u ref u A

15 15

0 0

−15 −15

−30 −30

4 4

e u e u

2 2

0 0

−2 −2

−4 −4

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) Local load voltage u A , its reference u ref and voltage tracking error e u

4 4

i A i A

2 2

0 0

−2 −2

−4 −4

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]

(b) Local load current i A

5 5

THD of u A =1.05% THD of u A =3.34%

4 4

3 3

2 2

1 1

0 0

5

THD of i A =1.06% THD of i A =75.68%

60

4

3

40

2

20

1

0 0

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

Harmonics order Harmonics order

(c) Spectra of local load voltage u A and current i A

Figure 5.7 Stand-alone mode: with a resistive load (left column) and with a non-linear load (right
column)