Switching Frequency Optimization for a Solid State Transformer With Energy Storage Capabilities

Abstract

Abstract-This paper is focused on establishing a procedure for measuring the efficiency dependency on the switching frequency for a solid state transformer (SST), being one of the ports connected to an energy storage device (Lithium-Ion battery). Multiple contributions for measuring the efficiency/losses for different power converter structures for energy storage applications can be found in the literature. However, there are few references which consider the effects of the high frequency model of the battery in the complete system performance. This research will obtain a parametric high frequency model of the battery cells, based on a vector fitting method in frequency domain. This model will be used for the estimation of the overall system losses. It will be demonstrated that the contribution of the battery losses, as well as its behavior as a function of the switching frequency, can significantly affect the selection of the converter's switching frequency.

Impact of Wide-Bandgap Technology on Renewable Energy and Smart-Grid Power Conversion Applications Including Storage

“…It is interesting to see the reverse trend of the converter efficiency against battery efficiency, which resulted in the optimum operation point when taking the battery losses into consideration. As shown in Figure 15, the optimum operation point has been pushed from 22 to 30 kHz of the built TAB converter [18].…”

SoC Estimation in Li-ion Batteries Exploiting High-Frequency Model Properties

“…The parameters of the battery module have been estimated by a vector fitting method [17], [18]. On obtaining the proposed high frequency model, it has to be mentioned that the impedance spectrum of a battery is dependent on the actual SoC, the temperature and cycling [6], [19], [20].…”

“…This paper proposes the use of a hybrid technique based on the high-frequency model of the battery [16], [17], that is suitable for the calculation of the SoC and that is barely affected by the operating point of the battery. The underpinning idea is to use the harmonics delivered by the power converter needed for the battery interface.…”

Design Optimisation of a Current-Fed Solid-State Transformer for MV Grid-Connected Applications

“…Main objective functions are typically minimum losses [22][23][24][25] and or maximum power density (minimum volume) [26][27][28][29]. Other objectives include minimum dc-link capacitance [30] and minimum heatsink volume [31]. Typical optimisation parameters are flux density, current density, switching frequency, number of converter cells [22,25,26,[28][29][30][31] and types of semiconductor devices [23,27].…”