Interlink Converter with Linear Quadratic Regulator Based Current Control for Hybrid AC/DC Microgrid

Abstract

A hybrid alternate current/direct current (AC/DC) microgrid consists of an AC subgrid and a DC subgrid, and the subgrids are connected through the interlink bidirectional AC/DC converter. In the stand-alone operation mode, it is desirable that the interlink bidirectional AC/DC converter manages proportional power sharing between the subgrids by transferring power from the under-loaded subgrid to the over-loaded one. In terms of system security, the interlink bidirectional AC/DC converter takes an important role, so proper control strategies need to be established. In addition, it is assumed that a battery energy storage system is installed in one subgrid, and the coordinated control of interlink bidirectional AC/DC converter and battery energy storage system converter is required so that the power sharing scheme between subgrids becomes more efficient. For the purpose of designing a tracking controller for the power sharing by interlink bidirectional AC/DC converter in a hybrid AC/DC microgrid, a droop control method generates a power reference for interlink bidirectional AC/DC converter based on the deviation of the system frequency and voltages first and then interlink bidirectional AC/DC converter needs to transfer the power reference to the over-loaded subgrid. For efficiency of this power transferring, a linear quadratic regulator with exponential weighting for the current regulation of interlink bidirectional AC/DC converter is designed in such a way that the resulting microgrid can operate robustly against various uncertainties and the power sharing is carried out quickly. Simulation results show that the proposed interlink bidirectional AC/DC converter control strategy provides robust and efficient power sharing scheme between the subgrids without deteriorating the secure system operation.

A Robust Suboptimal Current Control of an Interlink Converter for a Hybrid AC/DC Microgrid

“…However, comparing the current output in Figure 13a,b, the LQR method shows increasing circulating current at t = 13 s. Meanwhile, the proposed method shows a consistent performance. This result is unexpected since, in [17], the LQR method demonstrated a good resulting current under a high load perturbation. However, in that case, the filter parameters are known by the controller.…”

“…Next, the proposed control performance is compared to the existing current control, LQR method [17]. Similar to the the previous simulations, unknown filter parameters are used in the hybrid AC/DC microgrid.…”

“…Several studies have designed a model-based IC current control [12,17]. In those controllers, the filter connected through the IC, as shown in Figure 1, plays an important role in modeling the IC.…”

“…However, to the best of our knowledge, there is no significant work done on robust control of interlink converter using an LMI-based approach. In our previous work [17], LQR for current control of the IC is devised. In comparison with the PI control, the LQR-based current control shows superior performance in high loading condition.…”

An Optimal Current Control of Interlink Converter Using an Explicit Model Predictive Control

“…Robust current control for the IC is investigated by [3]. Some literatures [4][5][6][7] show interest in the optimal control method for the IC controller. For example, an adaptive hysteresis control method is designed by [4] such that the switching loss of the traditional hysteresis is reduced.…”