Microgrids are small-scale power networks where distributed generation and inverter interfaced power sources are common. These networks are faced with more significant control challenges; a smaller system can less effectively dampen and distribute power disturbances or fluctuations, and the system frequency is less robust without synchronous generators to provide rotational inertia. In this paper we will develop optimal control algorithms to control the voltage and frequency in an islanded inverter-based microgrid. The voltages and frequency of this system are controlled using decentralized ℋ∞ control. The decentralized controllers operate using only local data, making the control methodolgy scalable. In addition, the studied controllers can be tuned to achieve the desired transient behavior. For voltage and frequency control of microgrids, transient performance is still an area of weakness. The proposed control scheme extends optimal control to the field of microgrid control and can improve the state of microgrid technology.

This paper identifies how the topology of a microgrid, particularly with respect to localized power injections, can affect the overall stability of the system. Microgrids are smaller-scale power networks that can disconnect from, and operate independently to, the main grid if necessary; accordingly, distributed and local generation is much more common in these systems. Of these local power sources, a significant proportion interface with the microgrid via inverters, and therefore lack physical inertia. This absence of physical inertia exacerbates the control challenge in a microgrid. These issues motivate the question of how to best control distributed generators to realize grid-wide improvements to power quality. We outline how the placement of controlled distributed generators can result in varying degrees of improved transient behavior, following disturbances to a microgrid. In this resulting simulations and analysis, we find that when the power sources in a microgrid are of varying capacity or rating, then the network topology can have a significant effect on transient performance deterioration. Notably, we find that if even a single a lower rated power source is ‘near’ or adjacent to a grid disturbance, then the microgrid may experience severe harmonic disturbances. In addition, we show that if such sources are controlled with a decentralized optimal controller, rather than a typical droop mechanism, then the overall microgrid performance is significantly improved.

The goal of this paper is to control the dynamics of an islanded microgrid, a small-scale power system with distributed generation. An islanded microgrid is disconnected from the larger, main grid, and must maintain voltage and frequency standards using only local generation. As a result, islanded microgrids are more vulnerable to fluctuations in power supply and demand; this is especially relevant for intermittent renewable sources like wind turbines. The system is stabilized with static-output-feedback ℋ∞ γ-suboptimal control. This is a multiple-input multiple-output (MIMO) controller in which the measured data is used as the direct input to a static gain matrix, whose output is in turn used to control the closed-loop system. In order to judge the performance of the decentralized controllers, the micgorid is controlled first in a centralized manner, where each controller has access to all measured state variables. Decentralized controllers are then synthesized by casting the problem as a convex program, where each controller only has access to locally measured variables. Control performance is compared with respect to a switched-on wind turbine, where we see that the decentralized controller effectively mitigates the system disturbance due to the renewable intermittency.

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