ABSTRACT:
We
propose a vector current control derived from direct power control (VCC-DPC)
for a three-phase voltage source inverter (VSI) in the synchronous rotating
frame through instantaneous real and reactive powers. The proposed VCC-DPC method
has the same control structure as the conventional VCC except for the
coordinate transformation, since we obtain the d–q axes currents model of VSI
without using Park transformation and
the PLL system. Consequently, the proposed method has the same property as the
conventional VCC if the PLL extracts the phase angle of the grid voltage
correctly. However, with the consideration of the slow dynamics of the PLL, the
proposed method has an enhanced dynamical performance feature compared with the
conventional VCC. Moreover, it has another benefit that the reduction of the
computational burden could be expected since
there is no Park transformation and the PLL in the controller implementation.
We can guarantee that the closed-loop system with the proposed method is
exponentially stable in the operating range.
Finally, both simulation and experimental results using a 15-kW-inverter system
match the theoretical expectations closely.
KEYWORDS:
1. Voltage
source inverter
2. Vector
current controller
3. Instantaneous
real and reactive powers
4. Exponentially
stable
SOFTWARE:
MATLAB/SIMULINK
Fig.
1. Block diagram of (a) the standard VCC with PLL; (b) the proposed method
without PLL.
EXPERIMENTAL RESULTS:
Fig.
2. Performance of the inverter when the reference of id is changed from 5 A to
10 A at 1:51 s. (a) grid voltage, (b) id, (c) iq. (red-solid line: conventional
method; blue-dashed line: proposed method).
Fig.
3. Performance of the inverter when the inverter is connected at 0:51 s and the
reference of id is changed to 5 A. (a) grid voltage, (b) real power, (c)
reactive power, (d) id, (e) iq, (red-solid line: conventional VCC method; green-solid
line: conventional VCC method with faster PLL; blue-dashed line: proposed
method)
CONCLUSION:
In
this paper, we have introduced a VCC-DPC for three phase VSI with instantaneous
real and reactive powers. We obtained the d–q axes currents model of VSI
without using Park transformation and the PLL. For fair comparison, we designed
a PI controller with feed forward. Thus, the proposed method has the same
control structure as the conventional VCC except for the coordinate
transformation and PLL. Moreover, the proposed VCC-DPC will reduce the
computational burden since there is no Park transformation and as well as the PLL.
Simulation results show that the proposed method has the same properties as the
conventional VCC when the PLL extracts the correct phase angle of the grid
voltage. However, in the case where the slow dynamics of the PLL is activated, the proposed method has improved dynamical
performance in comparison with the
conventional VCC. We have also tested the performance of the proposed method
with a 15-kW inverter system. Experimental results show that the proposed
method has a robust property for the parameter uncertainness as well. This work
is an initial start for the VCC-DPC through the DPC model. In the future, we
will design a compensator for the harmonics or unbalanced issues based on this
concept.
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