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This paper presents a novel concept of a circuit for voltage balance of three series-connected capacitors or batteries, as well as the research results. The problem is related to the control of voltage sharing on series capacitors, supercapacitors or battery banks in energy storage systems or direct current (DC)-link of four-level 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 selected transistors. This paper presents the basic concept of the converter, an analysis of control strategies and the simulation results for various cases of voltage balancing.

This paper presents a novel concept of the DC-AC system with the input voltage boost ability, seven-level output voltage modulation, and the input AC current reduction at the double frequency of the output voltage. The system integrates the NPC full-bridge inverter which is composed of four-level legs and an active input voltage balancer (AIVB). The DC-link is composed of three capacitors connected in a series. The source of the energy is connected directly to the middle capacitor while the upper and lower capacitors of the DC-link are charged by the AIVB. The operation of the AIVB leads to balancing of the DC-link voltage and a three-fold boosting of the input voltage. The AIVB utilizes a novel switched-capacitor (SC) topology and can be designed as a low-volume quasi-magneticless converter with a simple open-loop control. One of the proposed methods of the control of the AIVB allows for a double frequency reduction in the input current. The application of the AIVB allows for the use of a seven-level NPC full-bridge (FB) inverter with a simple classic carrier-based PWM which is not applicable in the typical DC-link configurations. This paper presents the converter’s concept, its operation, control methods, and the results of simulations and experiments.