State-of-charge estimation and charge equalization for electric agricultural machinery using Square-Root Central Difference Kalman Filter

Accurate State-of-Charge (SOC) estimation and reasonable charge equalization for power batteries is important for prolonging their lifetime. In the application of electric agricultural machinery, the SOC estimation of Ni-MH power batteries was implemented by the Square-Root Central Difference Kalman Filter (CDKF) approach in this paper. To provide charge equalization for all the battery strings in the test module, a relay matrix module was used for the power converter and the equalization method was based on the estimated SOC of the battery strings. The test results confirm that the SOC obtained from the Square-Root CDKF method can converge to the true biases much quicker in comparison with the EKF method. The experimental data illustrate that the battery strings are balanced well at the end of the charge equalization mode.