Voltage Control of DC Microgrids: Robustness for Unknown ZIP-Loads

Abstract

In this letter we propose a new passivitybased control technique for Buck converter based DC microgrids comprising ZIP-loads, i.e., loads with the parallel combination of constant impedance (Z), current (I) and power (P). More precisely, we propose a novel passifying input and a storage function based on the mixed potential function introduced by Brayton and Moser, relaxing restrictive (sufficient) conditions on Z, P and the voltage reference, which are usually assumed to be satisfied in the literature. Consequently, we develop a new passivity-based controller that is robust with respect to uncertain ZIP-loads.

Passivity-Based Power Sharing and Voltage Regulation in DC Microgrids With Unactuated Buses

“…While centralized controllers can optimally coordinate the DGUs, they offer reduced scalability and flexibility and have a single point of failure [8]. On the other hand, decentralized controllers either only attempt to achieve voltage stability [9], [10], [11] or achieve load sharing at the cost of voltage regulation quality (e.g., the droop-based approaches in [3]).…”

“…Remark 3 (Regulating Current or Voltage): Without invalidating the stability analysis in the sequel, the regulator in (19) can be exchanged for simpler, purely linear current or voltage regulators (see [9], [10], [11]).…”

“…From the equation for i, it then follows that ẽd ≡ 0, which concludes this proof. Remark 10 (Compensating Nonpassive Loads): As demonstrated in [11], adding a term dependent on vk to the regulator output v s,k in (19) allows for damping to be added to the unactuated state v k . This, in turn, allows for regulation in the presence of nonpassive loads and can yield more favorable passivity indices when applying Theorem 10.…”

Robust Two-Layer Control of DC Microgrids With Fluctuating Constant Power Load Demand

“…Passivity theory was used in [13] and [14] to establish robust stability of the network equilibria to perturbations of the load demand. This work was extended in [15] to achieve global robust stability in the case of constant-impedance-current loads. It has been shown that the adoption of a more advanced technique can enlarge the region of attraction and provide stronger stability guarantees with respect to changes in the load demand.…”