This paper presents a novel concept and research results of a circuit for voltage balance of three series-connected capacitors or batteries. The problem is associated with control of voltage sharing on series capacitor, supercapacitor or battery banks in energy storage systems or DC-link of four-level NPC (Neutral Point Clamped) inverters. The proposed circuit is a switched-capacitor (SC) resonant converter composed of a single capacitor and seven transistor switches. Control of the converter makes it possible to transfer energy between any capacitors, by switching of selected transistors. This paper presents the basic concept of the converter, analysis of control strategies and simulation results for various cases of voltage balancing.