Replacing a battery pack with a battery emulator (BE) in a Power Hardware-in-the-Loop Simulation (HILS) setup facilitates the testing of new prototype hardware but stability and high fidelity are not a priori ensured. Due to the large output capacitance that devices implementing BEs usually have, their dynamic response differs compared to a real battery which operates like a voltage source with a series resistance. This problem becomes particularly intense when the hardware under test (HUT) also has a large input capacitance. The intuitive solution proposed is to connect a series resistor between the BE and the HUT to replicate the battery series resistance. This paper describes the conditions that this resistor needs to follow in order to ensure stability. It is also shown that the limited bandwidth of the power device used to implement the BE is possible to bring the emulation into stability even if those conditions are violated. Finally, examples are given on how a low sampling frequency in the feedback loop cause oscillations. Simulations and experiments are used to demonstrate all the findings.
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