In the signal processing, active signal filters are commonly used to filter out the zero-average high-frequency components of a signal. In the power system, the power filters are used to filter and control the harmonics in voltages and current waveforms in the concept of power quality. In this paper, we introduce energy filters to filter and control the undesirable frequency components of power flow waveforms in the concept of energy quality. In contrast to the power filters, a family of general energy filters (GEFs) using energy storage is proposed, which virtually work as low-pass filters of power flow and can smooth, track, and process the power flow, as the power filters do with the current and voltage waveforms. In order to illustrate the GEF, the mainstream electrical energy storage (EES) systems are briefly reviewed and classified, and a general model of the EES is developed accordingly. Then, the series, parallel, and series-parallel GEF in the first and second order are proposed, and the focuses are laid on their topologies and controls. Time-domain demonstrations of the GEF based on different implementations are presented on RTDS. Bode plots of the proposed GEF are also obtained through simulations. Finally, key factors in designing GEF for practical applications are briefly discussed.