Measurement and simulation of current total harmonic distortion on three-level single phase transformerless photovoltaic inverter
Daut IsmailM. IrwantoTunku Mansur Tunku Muhamad NizarAli RosnazriGomes NairYusoff Mohd IrwanFitra Muhammad
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Single phase
THD analyzer
Harmonic
Phase distortion
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In recent years, the photovoltaic (PV) transformerless inverters are becoming more and more popular, and a variety of inverter topologies have been proposed. With a review of the state-of-the-art transformerless inverter topologies and the related pulsewidth modulation (PWM) method, this paper proposes a family of transformerless inverter topologies with asymmetric phase-legs. PWM modulation and inverter operating modes are then detailed, experiment results demonstrate the validity of proposed inverter topology.
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With the rapid development of advanced power electronics technology and photovoltaic power systems, transformerless photovoltaic (TPV) inverters have been widely used due to the advantages in weight, size, efficiency and so on. However, there exists common-mode leakage current in TPV inverters, which should be satisfied the DIN VDE0126-1-1 standard. A novel H6 topology (H6-N) with dedicated modulation strategy for the TPV inverter is proposed to make the TPV inverter generate smaller common-mode leakage current comparing with the existed TPV inverter topologies and achieve low total harmonic distortion (THD) of output current. The common-mode voltage (CMV), common-mode leakage current and power losses of the single-phase TPV inverters with H6-N, H5 and HERIC topologies are compared respectively via simulation analysis. Finally, a universal prototype of TPV inverter using H6-N topology is built and tested to validate the effectiveness of the presented topology.
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This paper presents a solar-powered Partial Resonant Inverter (PRI) interfaced with an asymmetrical cascaded nine-level inverter. The DC input of the proposed system is obtained using Solar Photovoltaic (SPV) panel. The input DC sources fed to the asymmetrical cascaded nine-level inverter are in the ratio of 1:3. The step modulated nine-level inverter works with a precalculated switching angle for a fixed modulation of 0.7. Compared to the conventional 50 Hz inverter and the multi-output transformer design, the proposed system is more compact because of the high-frequency AC link. The PRI ensures Zero Voltage Switching (ZVS) and reduces the switching losses. The proposed scheme has been validated in the MATLAB/ SIMULINK environment and an experimental prototype is built in the laboratory. Based on the investigations the Selective Harmonic Elimination (SHE) method gives superior performance when compared to the Optimal Harmonic Stepped Modulation (OHSM) method. From the results and comparative analysis, the proposed system uses fewer switches to obtain the nine-level output, uses the PRI setup with the multioutput transformer to make the design compact and improves the power quality of the system.
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This paper presents a new pulse-width modulation that allows the three-phase Z-source inverter photovoltaic system operate without transformer and assuring very low leakage currents. Furthermore, a proper switching pattern is chosen in order to assure a reduced number of commutations, leading to reduced switching losses in the inverter. Experimental results of the three-phase Z-source inverter connected to a RL load are obtained to validate the theoretical models.
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This paper proposes an integrated common and differential mode filter with passive damping for single-phase grid-connected transformerless photovoltaic (PV) microinverters, employing the full-bridge voltage source inverter (VSI) topology with continuous unipolar modulation. This strategy achieves low current distortion, low leakage current and high efficiency. A design procedure for the proposed filter is presented including the passive damping components. The effectiveness of the proposed solution is confirmed by simulation and experimental results. Additionally, discussions about safety standards, analysis of leakage current production mechanism and some common mode (CM) filter implementations found in the literature are presented.
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Photovoltaic (PV) ac module becomes a trend for its great flexibility and high system-level energy harnessing. Non-isolated two-stage PV ac module with non-isolated high boost ratio dc-dc converter and transformerless inverter can be an option for high efficiency design. This paper starts with review of state-of-the-art transformerless inverters, and proposes a novel high efficiency and high reliability transformerlees inverter, which prevents from phase-leg shoot through, eliminates the PWM dead-time, minimizes leakage current, avoids body diode conduction for main devices, and effectively utilizes magnetic components. Modulation method and common mode leakage current issue are then described. Experiment results of a 250W (380Vdc, 240Vac) hardware prototype are shown to demonstrate the merits of proposed transformerless inverter.
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This letter proposes a hybrid multicarrier pulse width modulation (H-MCPWM) technique to reduce leakage current in a transformerless cascaded multilevel inverter for photovoltaic (PV) systems. The transformerless PV inverter topology has the advantages of simple structure, low weight and provides higher efficiency. However, the topology makes a path for leakage current to flow through parasitic capacitance formed between the PV module and the ground. A modulation technique has significant impact to reduce the leakage current without adding any extra component. The proposed H-MCPWM technique ensures low leakage current in the transformerless PV inverter system with simplicity in implementation of the modulation technique using lesser number of carriers. Experimental prototype developed in the laboratory demonstrates the performance of the proposed modulation technique in reducing the leakage current.
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Three-phase Z-source inverters are an interesting solution for connecting transformerless photovoltaic systems to the grid, due to its boost characteristic. Nevertheless, the traditional topology and its pulse-width modulation techniques generate undesired leakage currents in transformerless systems. Moreover, a recent study showed that, under certain conditions, the Z-source inverter presents stability issues. Therefore, this paper proposes a modified Z-source inverter topology and a particular pulse-width modulation that allow the three-phase Z-source inverter transformerless photovoltaic system to operate always in the stability range with very low leakage currents. A comparative study between the proposed system and the traditional dc-dc boost converter cascaded with a voltage source inverter is carried out, in order to highlight the major features of both solutions. Furthermore, simulation results of the three-phase proposed Z-source inverter topology connected to a RL load are obtained to validate the theoretical models.
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