STUDY OF A SINGLE PHASE GRID CONNECTED PV INVERTER PERFORMANCE UNDER A WEAK GRID CONDITIONS FOR CAMBODIA

Abstract

A single-phase grid connected PV inverter performance under a weak grid condition is the integrated practice of renewable energy sources as hydro, wind, biomass, thermal energy and solar PV with the grid power or power penetration at point of common coupling (PCC). Study objects shall be analyzed PV inverter performance, a weak grid characteristics, the distorted grid and harmonic effects with correction and reliability. Nowadays, Cambodia does not yet comprise full electric power in utility needs for production chances and daily lives, but electric energies shall reach the households in 2020 by the royal government policy with renewable energy generation. Components of solar energy system comprise solar panels, charge controllers, batteries and PV inverters and PV inverters are used to convert DC to AC energies, more addition, as Off-grid or On-grid. PV inverters are being used currently as single-phase and three-phase types and particularly, the internal inverters comprise three types of output filters as L, LC and LCL categories. A weak grid system has internal impedance of grids which shall fluctuate from distribution generations (DG) and could lead voltage deviation (ΔV) at inverter terminals and the inverter instability. The low voltage fluctuation of Cambodia is not below -10% and over +6% of nominal voltage magnitudes, and system frequency fluctuation (Δf) is not above 50.5Hz and below 47.5Hz, otherwise, the max THD values are not allowed over 5% of nominal operation system. The distorted grid systems shall occur at the distribution generation points and enhance power harmonic in a grid or otherwise, PV irradiations decrease due to low power operation, then PV inverters may generate more undesirable harmonics. This study presents a simulated modeling and control of a single-phase grid connected PV inverter performance under a weak grid condition. The control of a weak grid system is penetrated power to PV inverter at the point of common coupling (PCC), and before the power injections take place, the both-side power systems are controlled judiciously power transparency. A single-phase grid connected PV inverter under a weak grid condition is verified experimental applications of ideal grid system according to the results, the grid systems locate in simple operation conditions with corrections and reliabilities. The distorted grid voltage system is certified power systems stand in good operation conditions with correction and reliability, but THD current values spread up to 8.88% which harmonic effects could attract extremely grid system, therefore, power systems shall be disconnected immediately or the systems shall be allowed to transfer power. A weak grid system with impedance values (XL) is modified the max PCC voltage increased to 221.77V, but the grid systems considered as normal operation network and THD current amplitudes expand higher than average values (<1%) which effects could absorb unsmooth current flow pathway and ripple current waveforms in the grids. More addition, a weak grid system is connected with XL and R components reflected the max PCC voltage magnitudes grow up to 238.11V of basic voltage about 8% expansion according to power regulation of low voltage fluctuation in Cambodia passed by EAC, this grid system shall be disconnected automatically by protection equipment and the max PCC current decrement is a round 2A of total current 23A because of impedance value growth in a weak grid, whereas, THD current rates increase higher than average values (<1%) which effects could absorb unsmooth current flow pathway and distorted-ripple current waveforms in the grids. Overall conclusions of the inverter efficiency are fair good of the whole grid systems. The system is modeled and simulated in Laboratory and a distance, conductor sizes, length are calculated properly and results compare with appropriate data which have be installed already in households or other working places.

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