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A decoupled model predictive control (MPC) power balancing strategy for a coupled inductor-based flying capacitor DC–DC converter (FCDC) is a proposed to solve the power imbalance caused by the parameter differences in the coupled inductor. The decoupled mathematical model of coupled inductor FCDC is firstly derived by analyzing the converter operation state under various modes. On this basis, the control relationship between inductor current and flying capacitor (FC) voltage is redefined and an MPC power balance strategy based on the inductor current with single-step optimization is proposed. The proposed MPC strategy not only achieves decoupled power balancing control but also solves multi-objective dynamic optimization control of the inductor current and FC voltage, greatly reducing the computation load. A detailed theoretical analysis of the proposed strategy is presented and the balancing performance is effectively verified through the experiments. [ABSTRACT FROM AUTHOR]

This letter presents a fast open circuit diagnostic method for modular multilevel DC/DC converter (MMDDC), which is applied in super capacitor energy storage system. The proposed method is derived based on the analysis of submodule output characteristics under both normal and fault conditions. For MMDDC, different types of open circuit fault are reflected by the output voltage of submodule in certain operating modes, thus a simple and effective diagnostic method by the aid of a hardware circuit and a fast fault location algorithm is proposed. The hardware circuit is responsible for detecting submodule output voltage and its output result is transmitted to a processor to accomplish the final fault diagnosis along with drive signals. The proposed approach avoids complex mathematical operations and minimizes fault diagnostic time; moreover, it can achieve fault diagnosis under a wide super capacitor operating voltage range. Finally, the proposed diagnostic method is verified experimentally based on a laboratory-scale MMDDC energy storage prototype. [ABSTRACT FROM AUTHOR]

• The proposed converter solves the over- current issue of MMDDC in charge mode. • The boost function of impedance source helps to reduce the number of sub-modules. • The reduction of sub-modules can reduce the total voltage on energy storage side. • The working current on energy storage side is continuous. • Shoot through operation can increase the sub-module control degree. This paper proposes a novel impedance source modular DC/DC converter for the energy storage system (ESS), which overcomes the drawbacks of traditional modular multilevel DC/DC converter (MMDDC), such as discontinuous current on energy storage side, easy over-current in charge mode, large number of sub-modules etc. A new quasi-Z source (qZS) sub-module is constructed by combining bi-directional quasi Z source and half bridge converter. The bi-directional qZS can make the input voltage of half bridge sub-module controllable, and then solve the over-current issue of the traditional MMDDC in charge mode. Meanwhile, the boosting function of the impedance source can help to reduce the number of sub-modules when the system is applied to the medium and high voltage occasions, simplifying the system structure and improving system efficiency. More importantly, the bi-directional qZS can make the current on energy storage side continuous, improving the lifetime of energy storage device. Detailed analysis about the operation principle and characteristics of the proposed converter are presented in the paper, and the study of control strategy design for the proposed converter is also carried out. At last, the effectiveness of the proposed converter and control strategy is verified by experimental results. [ABSTRACT FROM AUTHOR]