Hysteresis Droop Controller with One Sample Delay for DC-DC Converters in DC Microgrids

Droop control is a common control strategy used in DC microgrids to manage power distribution among parallel Distributed Energy Resource (DER) converters. With droop control, the static dc bus voltage varies in a specified range according to load conditions. In order to maintain the dynamic dc bus voltage in the same range during load changes, droop-controlled DER converters usually have either large output capacitance or high voltage loop bandwidth. The latter enables the adoption of small output capacitance that improves the dc bus behaviour also during bus faults. However, with traditional control techniques, for example, the single-sampled PID controllers, the voltage loop bandwidth is limited by the control delay, including the computation time and the modulation delay. From this point of view, oversampled hysteresis control is appealing, because it reduces the modulation delay by removing the modulator. Also, the hysteretic nature allows nonlinear switching actions during transient, which further speeds up the dynamic response. Consequently, small output capacitance can be used without concerns of overvoltage and undervoltage. Moreover, hysteresis control is typically implemented on Field Programmable Gate Arrays (FPGAs). Differently, this paper focuses on the less-expensive Digital Signal Processors (DSPs) implementation. The influence of additional computation time introduced by DSP on the converter's stability is also analyzed. Simulations and experiments are carried out to verify the performance of the DSP-implemented hysteresis droop controller.