Modelling and Identification of the Common and Differential Mode LCL Filter Parameters in Grid-Tied Voltage Source Inverters

A method is introduced to estimate the parameters of differential and common mode filters in three-phase grid-tied voltage source inverter (VSI) systems. To do so, first an exact equivalent circuit for the VSI systems along with differential and common mode filters is presented. To estimate the parameters and eliminate the dependence on the time derivatives of quantities that appear in the dynamic system expressions, transformations through linear-time invariant filters are applied to eliminate the derivatives of signals and to make the expressions independent of the grid voltage source. Doing so converts the differential equations of the system to linear algebraic equations in the parameters of the differential and common mode filters to be estimated. The inverter-side currents of the three phases are measured to quantify the common and differential mode currents while the pulse width modulation (PWM) reference signals available through the VSI controller outputs combined with measurements of the DC link voltage are exploited to assess the common and differential mode voltages for the estimation process. The effectiveness of the proposed method is verified through simulations of a three-phase 5kVA grid-tied voltage-source-inverter system with and without the presence of voltage source harmonics. The tolerance effects of the filter components employed in different phases on the estimation accuracy are also investigated.