Sebastian Trip

An internal model approach to (optimal) frequency regulation in power grids with time-varying voltages

The power grid can be regarded as a large interconnected network of different subsystems, called control area’s. In order to guarantee reliable operation the frequency is tightly regulated around its nominal value, e.g. 50 Hz. Automatic regulation of the frequency in power grid is traditionally achieved by primary proportional control (droop-control) and a secondary PI-control on the generators, where economic considerations are largely neglected. Recently we proposed a novel distributed controller in [1] that controls power production such that the frequency is regulated in an economic efficient way. Main advantage of our approach, based on passivity properties of the system, is that it has the potential to deal with more complex models of dynamical networks and fairly rich classes of external perturbations.

An internal model approach to frequency regulation in inverter-based microgrids with time-varying voltages

This paper studies the problem of frequency regulation in inverter-based microgrids with time-varying voltages, described by a third-order model. Building upon our previous result on optimal frequency regulation in an ordinary power grid [1], we propose the design of internal-model-based controllers and analyze it within an incremental passivity framework. We believe that this framework is general enough to allow for more complex control scenarios in future extensions.

Optimal frequency regulation in nonlinear structure preserving power networks including turbine dynamics: An incremental passivity approach

This paper studies the problem of optimal frequency regulation in power networks, represented by a nonlinear structure preserving model, including turbine-governor dynamics. Exploiting an incremental passivity property of the power network, distributed controllers are proposed that regulate the frequency and minimize generation costs, requiring only frequency measurements.

Distributed Second Order Sliding Modes for Optimal Load Frequency Control

This paper proposes a Distributed Second Order Sliding Mode (D-SOSM) control strategy for Optimal Load Frequency Control (OLFC) in power networks, where besides frequency regulation also minimization of generation costs is achieved. Because of unknown load dynamics and possible network parameters uncertainties, the sliding mode control methodology is particularly appropriate for the considered control problem. This paper considers a power network partitioned into control areas, where each area is modelled by an equivalent generator including second-order turbine-governor dynamics. On a suitable designed sliding manifold, the controlled system exhibits an incremental passivity property that allows us to infer convergence to a zero steady state frequency deviation minimizing the generation costs.

Distributed MPC for controlling μ-CHPs in a network

This paper describes a dynamic price mechanism to coordinate electricity generation from micro Combined Heat and Power (μ-CHP) systems in a network of households. The control is done on household level in a completely distributed manner. Distributed Model Predictive control is applied to the network of households with μ-CHP installed. Each house has a unique demand pattern based on realistic data. Information from a few neighbors are taken into account in the local optimal control problems. Desired behavior for the network model in the distributed MPC approach is showed by simulation.

Distributed Optimal Load Frequency Control with Non-Passive Dynamics

Motivated by an increase of renewable energy sources, we propose a distributed optimal load frequency control scheme achieving frequency regulation and economic dispatch. Based on an energy function of the power network, we derive an incremental passivity property for a well-known nonlinear structure preserving network model, differentiating between generator and load buses. Exploiting this property, we design distributed controllers that adjust the power generation. Notably, we explicitly include the turbine-governor dynamics, where first-order and the widely used second-order dynamics are analyzed in a unifying way. Due to the non-passive nature of the second-order turbine-governor dynamics, incorporating them is challenging, and we develop a suitable dissipation inequality for the interconnected generator and turbine-governor. This allows us to include the generator side more realistically in the stability analysis of optimal load frequency control than was previously possible.

Optimal generation in structure-preserving power networks with second-order turbine-governor dynamics

Recently we have been exploring the role of passivity and the internal model principle in power network control in the presence of uncertainties due to unmeasured demand and supply. In this work we continue this line of research and extend our results to include more complex dynamics at the generation side. Namely, we study frequency stabilization by primary control and frequency regulation by optimal generation control, where we additionally incorporate second-order turbine-governor dynamics. The power network is represented by the structure-preserving Bergen-Hill model [1]. Distributed controllers that require local frequency measurements are proposed and are shown to minimize the generation costs. Asymptotic convergence is proven when the generators satisfy a local matrix condition. The effectiveness of proposed controllers is demonstrated in a case study.

Frequency Regulation in Power Grids by Optimal Load and Generation Control

This chapter studies the problem of frequency regulation in power grids in the presence of unknown and uncontrollable generation and demand. We propose distributed controllers such that frequency regulation is achieved, while maximising the ‘social welfare’, i.e. maximising the utility of consuming power minus the cost of producing power. The controllable generation and loads are modeled as the output of a first-order system, which includes a widely used model describing the turbine-governor dynamics. We formulate the problem of frequency regulation as an output agreement problem for distribution networks and address it using incremental passivity, enabling a systematic approach to study convergence to the steady state with zero frequency deviation. In order to achieve optimality, the distributed controllers are utilising a communication network to exchange relevant information. The academic case study provides evidence that the performance of the controllers is good.