Stochastic Frequency Control of Grid-Connected Microgrids

Abstract

Abstract-This paper proposes a stochastic control strategy, namely the unsynchronized Addictive Increase Multiplicative Decrease (AIMD) algorithm, to manage the power flow of interconnected microgrids (MGs). The proposed control aims at achieving a trade-off between the individual utility function of each MG while ensuring the stability of the grid. Both centralized and decentralized AIMD approaches are considered and compared. Extensive Monte Carlo simulations are performed on the IEEE 39-bus system, and show that the proposed control strategy is able to provide the sought trade-off.

Distributed model predictive control for energy management in a network of microgrids using the dual decomposition method

“…The first papers on this topic only addressed the problem of optimizing the decisions of single MGs, neglecting the existing interactions among different MGs. More recently, there is an increasing interest in investigating how the interactions among MGs may improve the operation of single MGs and, in general, affect the stability of the power grid . Due to the difficulty of predicting a future behavior of uncertain variables, most notably, the amount of energy that will be generated from renewable sources, most optimization strategies that have been proposed in the literature either focus on instantaneous, or greedy, optimization neglecting what will happen in a future horizon or have assumed that future forecasts of uncertain variables may be regarded as perfectly accurate …”

Decentralized Charging of Plug-In Electric Vehicles and Impact on Transmission System Dynamics

“…• A discussion on the non-obvious result that popular strategies based on locally measured grid frequency may not be appropriate for the control of PEV charging, as these approaches sometimes fail to predict stability of the network. The latter point may be regarded as a surprising result, given that, as discussed above, some works in the literature exploit small devices for supporting system frequency regulation, most notably electric vehicles [7], but also micro-grids [22], [23], or thermostatically controlled loads, such as refrigerators and airconditioners [24]. However, in such studies, the small devices do not originate the instability, which is what happens in the PEV charging problem investigated in this work.…”

“…Remark 2: In a practical implementation of this algorithm in a power grid, we assume that it would be too complicated, and anyway not fundamental, to change the charging rates of PEVs too often, and for this reason we assume that the occurrence of CEs only occurs every T p = 30 seconds, in accordance with [23].…”

Evaluation of the Impact of the Size of Storage Devices in Grid-Connected Microgrids

“…At the time of writing this paper, however, the transition from the conventional power grid to a population of interconnected, or grid-connected, MGs is still at an exploratory level, and the power community has just started investigating the possible challenges and consequences of such new topological schemes [5]- [8]. Previous work of the authors (e.g., see [9]- [12]) analyses the effects of a large population of grid-connected MGs, for instance in terms of the impact on the frequency of the power system.…”

“…Figure 1 shows the connections of the MG with the power system and the electricity market, where S is the state of charge of the storage device; P s is the power generated or absorbed by the storage device (where P s > 0 corresponds to charging); P g and P l are the generated active power and the power absorbed by local loads, respectively, of the MG; λ is the price of electricity; P out is the overall power exchanged with the outer power grid; and ω COI is the frequency of the center of inertia, that we consider here as a proxy to discuss the stability of the power system. This paper builds on previous work of the authors, namely, [9]- [12]. In particular, we use here the same models of the single elements that are required to simulate the interactions between the MGs: this includes the model of the power system; the model of the electricity market; and of the single MGs.…”