Invariant-set design of robust switched trackers for bidirectional power converters in hybrid microgrids

Abstract

The small-signal stability of a hybrid (DC/AC) microgrid is highly affected by the direction and amount of power flow through the interlinking converter (IC). This article proposes an invariant-set design of non-droop tracker (to follow the desired time-varying reference) for controlling the power flow in hybrid microgrids in both inversion and rectification modes. The proposed tracker provides fast response, zero steady state error, and robustness against system uncertainty. Since the invariant-set is difficult to calculate, it is approximated using a bounding ellipsoid (being a linear function, and the problem reduces to convex optimization, easy to solve). A novel linear matrix inequality-based theorem is established to obtain the optimal trackers. The hybrid microgrid has been modelled and linearized in the two modes of operation. In Mode I, the interlink converter acts as an inverter, transferring power from the DC side to the AC side. During Mode II, the interlink converter acts as a rectifier, transferring the AC power to the DC side. The suggested trackers' performance has been compared to that of the H∞ trackers in various operational scenarios. The results show that the proposed controller is much faster and has much less overshoot than the H∞ controller. Moreover, the proposed technique can be considered a platform for hybrid microgrid systems since it is easy, straightforward to be implemented, and computationally inexpensive compared to other corresponding techniques in the literature.

Keywords

• Bidirectional power flow
• H∞ control
• Interlink Converter
• Invariant Sets
• Microgrids