Analysis of dependency current harmonics on load and filter parameters for asymmetrical network models

Abstract

The paper presents the operation of three-phase magneto conjugate LCL-filters used in inverter systems of solar power plants. The purpose of their usage is maintaining the coefficient of load current harmonics within the limits imposed by electric power quality standards. As opposed to widespread LC-filters, the LCL-filters enable using of an inverter system for operation in reverse mode at night to charge the batteries of solar power plants. In its turn, the structural design of filter inductances in the form of a three-leg magnetic system that generates magnetic coupling between inductances of different phases ensures the reduction of filter dimensions and its cost. Filter’s transfer characteristic was generated and on its basis plotted were dependencies between the current harmonics coefficient and the load, as well as network power coefficient and filter parameters. Analysis of these dependencies demonstrated the availability of composite resonance of currents in the circle, with the greatest resonant currents (and at the same time harmonics coefficients) being observed at light network loads. Considerable restriction of the current harmonics coefficient may be achieved by regulating the filter capacity depending on inductances and power coefficients.