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In this article, when the cascaded H-bridge topology is used in the asymmetrical multilevel hybrid energy storage system (AM-HESS), the asymmetry of the energy storage components’ types and voltages makes it difficult for traditional modulation methods to realize an independent power control of each energy storage unit. Thus, these methods cannot be directly applied to the realization of the complex working modes of AM-HESS. To this end, an AM-HESS hybrid level shifted pulsewidth modulation (PWM) (HLS-PWM) technique is proposed. According to the directions of supercapacities’ (SCs’) output power and the total output power of the energy storage system, the HLS-PWM is divided into the two fundamental modes—the same (MP) and opposite (MN) modes. Subsequently, the SC charge and discharge control under both the unit power factor and the nonunit power factor is analyzed for the two modes. Furthermore, five operation modes and the power control method of AM-HESS are implemented through the charge and discharge control of the SC. Finally, simulation and experimental results verify that the proposed HLS-PWM can realize an efficient power control of the AM-HESS. [ABSTRACT FROM AUTHOR]

This article proposes a fault-tolerant control method for the battery-supercapacitor (SC) hybrid energy storage system (HESS) based on the cascaded multilevel converter during active dc-side failure (ADCF). When ADCF occurs, the magnitude of the output voltage will be seriously affected because of the decline of the dc-side voltage. Consequently, the system cannot operate normally. To tackle this problem, an auxiliary power loop, which uses the dual-frequency phase-shifted carrier pulsewidth modulation to transfer power between different energy storage units, is added into the HESS. The topology of the HESS and the principle of power transfer during failure operation are introduced. The requirement to the numbers of different types of cells: discharging, charging, and standby, is analyzed mathematically. The SC capacity and the control system designs are given. Finally, the simulation results obtained from MATLAB/Simulink as well as experiments based on a prototype are presented to verify the effectiveness of the HESS and the fault-tolerant control. [ABSTRACT FROM AUTHOR]