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.
Highlights
Photovoltaic (PV) power as renewable energy is more and more popular recently, but the power fluctuations harm the quality and stabilization of the grid voltage and frequency
Several articles have published recently with different control strategies for grid integrated PV systems such as a modified sine-cosine optimized (MSCO) [1], fuzzy space vector PWM [2], and intelligent fuzzy [3], these algorithms merged with the particle swarm optimization (PSO) to get maximum power extraction from a PV with a high convergence velocity
SIMULATION RESULTS A grid-tied MLI inverter needs to handle both reactive and active power based on standards such as EN 50438, where an inverter needs to operate at power factor (PF) in the range (0.95 lag - 0.95 lead) [44]
Summary
Photovoltaic (PV) power as renewable energy is more and more popular recently, but the power fluctuations harm the quality and stabilization of the grid voltage and frequency. In PV grid-tied inverter systems, high-frequency commonmode (CM) voltages need to be avoided due to its causes of the charging/discharging current to flow through the inverter to ground This leakage current will lead to an increase in losses, current harmonics, safety issues, and interference problems of electromagnetic effects [14]–[18]. This work develops a system that includes a 5L-NPC inverter with a control strategy maintaining the desired voltages balancing for the input DC-link of a transformerless grid-tied single-phase PV system. It allows zero leakage current and the ability to reduce the harmonic content of the output. This work solves the unbalancing problem by developing a modulation strategy [21] that controlling the DC-link capacitor voltages to follow a required reference value and creates the required AC output voltage despite the dynamic capacitor voltage values
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