Classical Control of a Neutral Leg - Control of Power Inverters in Renewable Energy and Smart Grid Integration - page 195

0.1 100

0.05 50

0 0

−0.05 −50

−0.1 −100

0 0.02 0.04 0.06 0.08 0.1 0.08 0.085 0.09 0.095 0.1

Time [s] Time [s]

(a) Shift of the neutral point (b) Filtered inductor voltage

2 0.4

i N i L

1 0.2

0 0

−1 −0.2

−2 −0.4

0.099 0.0992 0.0994 0.0996 0.0998 0.1 0.08 0.085 0.09 0.095 0.1

Time [s] Time [s]

(c) Inductor and neutral currents (d) Filtered capacitor current

Figure 11.9 Simulation results when i N = 0

0 V although there are some pulses left after filtered by the hold filter; the current flowing
through the inductor is nearly a triangle wave with an amplitude of about 1 25 A; the current

i c is very small although there are some spikes, which are not shown in the figure because of
the filtering effect of the hold filter F ( s ). The average of the inductor current is 0, which is the
same as the neutral current.

.

11.5.2 With a 50 Hz Neutral Current
When the buck converter has a single-phase load R 5mH

and works at 50 Hz, the peak amplitude of the output voltage is about 360 V. This offers a
neutral current of about 68 A peak. The simulation results are shown in Figure 11.10. The

= 5 in series with an inductor L =

0.1 300

0.05 150

0 0

−0.05 −150

−0.1 −300

0 0.02 0.04 0.06 0.08 0.1 0 0.02 0.04 0.06 0.08 0.1

Time [s] Time [s]

(a) Shift of the neutral point (b) Filtered inductor voltage

120 0.5

i N i L

80

0.25

40

0

0

−0.25

−40

−80 −0.5

0 0.02 0.04 0.06 0.08 0.1 0 0.02 0.04 0.06 0.08 0.1

Time [s] Time [s]

(c) Inductor and neutral currents (d) Filtered capacitor current

Figure 11.10 Simulation results when the main component of the neutral current is 68 A, 50 Hz