ABSTRACT:
In this paper, an alternative control
method is proposed to improve the harmonic suppression efficiency of the
activepower filter in a distorted and an unbalanced power system to compensate
for the perturbations caused by the unbalanced nonlinear loads. The proposed
method uses a self-tuning filter (STF) to process the grid voltage in order to
provide a uniform reference voltage to obtain the correct angular position of
the phase locked loop. Moreover, the required compensation currents are
obtained by implementing another STF in the transformed set of currents in order
to separate the fundamental and the harmonic currents. This allows the
calculation of a precise reference current for the unbalanced, the non-linear
and the variable load conditions. The proposed control method gives an adequate
compensating current reference even for a nonidealvoltage and unbalanced
current conditions. The real-time control of the filter under the distorted and
the unbalanced power system is developed in an RT-LAB real-time platform. The
results obtained in the software-in-the-loop configuration are presented to
verify the effectiveness of the proposed control technique.
SOFTWARE:
MATLAB/SIMULINK
Fig.
1 Block diagram of the APF and the proposed control method
Fig.
2 Voltage and the current waveforms
a
Ideal grid voltage
b
Non-ideal (distorted and unbalanced) grid voltage
c
Load currents under the ideal grid voltage
d
Load currents under the non-ideal grid voltage
Fig.
3 Compensation of the grid current harmonics by using the conventional dq
method
a
Under the ideal voltage
b
Under the non-ideal voltage, and by using the conventional pq method
c
Under the ideal voltage
d
Under the non-ideal voltage
Fig.
4 Compensation of the grid current harmonics
a By
using the STF-based pq theory under the ideal voltage
b By
using the STF-based pq theory under the ideal voltage
c By
using the proposed method under the ideal voltage
d By
using the proposed method under the non-ideal voltage
In this paper, the design of a control
method that generates thecorrect reference current signal in order to satisfy
the requirements of a harmonic suppression and a reactive power compensation,
for the unbalanced non-linear load combinations under the case of the non-ideal
grid voltageconditions have been discussed. An alternate method is proposed
where two STF are applied to manage the distorted and the unbalanced voltage
and current. In the proposed method, the distorted and the unbalanced voltages are
first processed by using the STF to determine the correct angular positions.
Then, a second STF is used toextract the balanced load current waveforms. This
methodeliminates the need for additional low-pass or high-pass filtering when
extracting the harmonic components from the fundamental. A step-by-step
performance study, in a real-time environment, shows that the proposed control technique
is able to generate the proper compensating reference current during the steady
state and the dynamic load change conditions under the distorted and the unbalanced
grid voltage conditions.
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