An Estimation Method of High-Order LC Circuits in Power Electronic Converters

This article proposes a parameter estimation method for high-order LC circuits conducted during the power-OFF of power electronic converters. It is based on a battery-powered compact signal injection unit and a circuit modeling method to estimate the LC circuit parameters. The proposed method aims for LC component condition monitoring in applications with routine-based maintenance or frequent ON/OFF operation (e.g., wind power, photo-voltaic (PV), and traction systems). Compared with LCR meters and impedance analyzers, the proposed method has a significantly lower implementation cost and does not require disassembly of components. Moreover, it is a converterlevel method in which the signal injection unit only needs to connect the converter inputs or outputs. Compared with power-ONLC parameter estimation methods, the proposed one is noninvasive without adding any hardware or software algorithm that may introduce new risks to converter operation. This method can handle the converters with high-order LC structures (e.g., second- to fourth-order) in converter power- OFF state, which has not been achieved by existing power- OFF solutions. Therefore, the proposed method is promising for the specific applications of interest mentioned previously. The parameter estimation algorithm and signal injection unit design are presented. The experimental results indicate that the estimation errors of the second-order equivalent circuit, third-order equivalent circuit, and fourth-order equivalent circuit are lower than 1.6%, 2.5%, and 3%, respectively. The estimated LC parameters can be further used as inputs for operation optimization or condition monitoring of the converters.