A Precise and Efficient Frequency Estimation Method for Single-Phase Grid With DC Offset

The frequency component of the grid voltage plays a crucial role in ensuring the stable operation of power electronic grid-connected systems. When the grid voltage contains a DC offset disturbance, the parameter estimation methods in the literature suffer from estimation errors, and a filter is always required to counteract its impact. In this paper, a nonlinear algebraic transformation method is proposed to eliminate the influence of the DC offset completely. By applying the nonlinear algebraic transformation to four consecutive sampling points, a first-order linear regression model of voltage is constructed for a single-phase grid affected by DC offset. This model inherently eliminates the offset’s impact on the model parameters. A parameter estimator is then developed for the linear regression model, and the frequency can be directly derived from the parameters of this model. Rigorous theoretical analyses confirm the stability and convergence of the proposed parameter estimator. Meanwhile, the results demonstrate that the proposed parameter estimator can globally track the frequency variations in single-phase grids with DC offset. Experimental results further confirm the efficacy of the proposed nonlinear algebraic transformation method.