ABSTRACT:
The
three-phase synchronous reference frame phase-locked loop (SRF-PLL) is widely used
for synchronization applications in power systems. In this paper, a new control
strategy for three-phase grid-connected LCL inverters without a PLL is
presented. According to the new strategy, a current reference can be generated
by using the instantaneous power control scheme and the proposed
positive-sequence voltage detector. Through theoretical analysis, it is
indicated that a high-quality grid current can be produced by introducing the
new control strategy. In addition, a kind of independent control for reactive
power can be achieved under unbalanced and distorted grid conditions. Finally,
the excellent performance of the proposed control strategy is validated by means
of simulation and experimental results.
KEYWORDS:
1. Control
strategy
2. Grid-connected inverters
3. Instantaneous power control scheme
4. LCL filter
5. Positive-sequence voltage detector
SOFTWARE: MATLAB/SIMULINK
BLOCK
DIAGRAM:
Fig.
1. Block diagram of the control system with LCL filter.
EXPECTED SIMULATION RESULTS:
Fig.
2. Simulation results of the proposed control system. (a) Generated current
reference signals. (b) A-phase grid voltage and three-phase current. (c) Actual
active and reactive powers.
Fig.
3. Experimental results of the positive-sequence voltage detector under actual
grid operating conditions. (a) Utility voltage and the detected
positive-sequence signals. (b) Harmonic spectrum of the utility voltage. (c)
Harmonic spectrum of the detected positive-sequence signals.
Fig.
4. Experimental results of a step in the reactive power reference. (a) A-phase
grid voltage and three-phase current. (b) A-phase grid voltage and A-phase
current.
CONCLUSION:
A
new control structure for three-phase grid-connected voltage source inverters
(VSI) with an LCL-filter is proposed. By using the instantaneous power control
scheme and the proposed positive-sequence voltage detector, the current reference
can be indirectly generated, which avoids the complex PLL. The effectiveness of
the proposed system for three-phase grid-connected VSIs is demonstrated via simulation
results, which show a significant improvement in both the steady state and
transient behavior. The same behavior is experimentally verified. The fast
dynamic response to a reference step is not affected by the inclusion of
additional control loops. Good performance is guaranteed even under unbalanced
and distorted grid voltages.
REFERENCES:
[1]
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[2]
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[3]
F. Blaabjerg, R. Teodorescu, M. Liserre, and A. V. Timbus, “Overview of control
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[4]
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[5]
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