Cascaded Voltage Control for Electric Springs With DC-Link Film Capacitors

For the conventional configuration of the single-phase electric springs, the electrolytic capacitor (E-cap) is required for buffering the double-line-frequency dc-link power. This demands large capacitance and constant average dc-link voltage for achieving sufficiently low-voltage ripples of the E-cap, which renders low efficiency and poor reliability of the ES. To address these issues, a cascaded voltage control scheme is proposed in this article. The proposed control scheme enables large fluctuations of the dc-link voltage so that the film capacitor (F-cap), which is of smaller capacitance and higher reliability, can be applied. In addition, the proposed control scheme can adaptively adjust the average dc-link voltage for achieving the minimum power loss of the ES. The quasi-steady-state and steady-state models of the electric-spring-based smart load are developed. The optimum average dc-link voltage for achieving the minimum power loss is analytically derived. The functionality and loss reduction capability of the proposed controller are verified through hardware experiments and simulations.