ABSTRACT
Multi-level transformerless inverters are widely used in grid-tied PV systems since they characterized by higher efficiency and lower cost. In this context, new topologies, modulation, and control schemes were presented to solve problems of a common-mode voltage and leakage current. This work proposes a transformerless five-level inverter with zero leakage current and ability to reduce the harmonic output content for a grid-tied single-phase PV system. The neutral of the grid links to a common on which the negative and the positive terminals of the DC-link are connected via parasitic capacitors that can eliminate the leakage current. The proposed topology, with its inherent circuit structure, leads to boost the overall efficiency. Simulation and experimental results show almost zero leakage current and a high-quality output when maintaining balanced capacitor voltages on the DC-link input. The experimental results show 1.07% THD and 96.3 % maximum efficiency when injecting a power of 1.1 kW that verify the performance of the proposed inverter with PV sources.
KEYWORDS:
1.
IGBT inverters
2.
Transformerless grid-connected
photovoltaic inverter
3. Solar PV
SOFTWARE: MATLAB/SIMULINK
CONCLUSION:
A new high-performance transformerless
5L-NPC inverter with its control strategy for a grid-tied PV system has been
presented. The major advantages of the presented system can be brief as
follows: 1. The topology of employing diode clamping MLI with suitable stray
capacitors makes the leakage current to flow through the system in a very low
value reaches zero. Furthermore, the system offers a connection between the
DC-link pass bar of a solar PV array with the grid neutral terminal that
results in zero leakage current. 2. The operation of the employed five-level
topology results in high performance for the harmonic distortion that allows
the reduction of filter components as compared with lower MLIs. 3. The proposed
5L-NPC topology eliminated the CM leakage current with 1.07% THD by using eight
power switches. The results confirmed the above-stated advantages, and the
proposed system offers approximately similar characteristics in reactive and
real power injections. Therefore, the proposed inverter topology and its
modulation scheme were a suitable and attractive solution for single-phase
grid-tied PV systems. Although the proposed 5L-NPC system achieved zero CM
leakage current with a very-low THD, the design is limited by eight switches
that are recommended to be reduced in future work. Moreover, the presented
system solved the balancing issue of the DC-link capacitors’ voltages that
required for proper operation by a modulation strategy inspired in [21], we
recommend easier algorithms to solve such issue.
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