Analysis and Design of an Active Series Resonant Voltage Balancer for High Peak Current Supercapacitor Modules in Mobile Robot Applications

Abstract

Mobile robot platforms are increasingly deployed in modern industrial environments, and ensuring their efficient operation has become an important aspect of system design. Their highly dynamic power profile, characterized by regenerative braking, fast acceleration, and frequent cycling, creates significant challenges for providing a stable and efficient energy storage. To meet these demands, modern mobile robot applications tend to integrate supercapacitor energy storage systems, either standalone or as part of a hybrid energy-storage system (HESS). The supercapacitor modules are often implemented in different series and parallel configurations of cells to meet the application requirements. However, cell-to-cell variations in capacitance, equivalent series resistance (ESR), and aging behavior in the module lead to voltage imbalance, reducing usable energy and further accelerating degradation. Thus, to prevent these effects and maintain uniform cell utilization over time, an efficient voltage-balancing device is required. This article proposes an active resonant voltage balancer (ARVB) as a solution to balance voltages between series supercapacitor cells within a module of an HESS for a mobile robot. Compared to other active balancing methods, the advantages of the ARVB solution are high efficiency, high power capability, and low complexity, making it a suitable choice for this application. The guidelines are provided for the design optimization of the ARVB, based on the specified worst-case voltage imbalance in the supercapacitor module. The selected design is implemented and experimentally verified on an equivalent supercapacitor module for a single ARVB fundamental block. The benefit of using ARVB in the supercapacitor module is demonstrated by the increased total energy stored in the module at the end of the CC charging cycle. It shows an increase in stored energy up to 34% at a charging current of $I_{\text{ch}}=3\;[\text{A}]$, compared to the supercapacitor module without ARVB. Two energy efficiency metrics were evaluated in this work. The charging energy utilization efficiency was evaluated with respect to the ideal balancing case and represents the achievable improvement in usable stored energy after charging enabled by the balancing system. A maximum charging energy utilization efficiency of 85.5% was obtained at a charging current of $I_{\text{ch}}=3\;[\text{A}]$. In addition, the balancing energy efficiency was evaluated during idle-state equalization, typically used in the literature. The maximum efficiency of 95.7% is obtained for the initial voltage difference $\Delta u_{12}=150\;[\text{mV}]$.