Guido Cavraro

Distributed Reactive Power Feedback Control for Voltage Regulation and Loss Minimization

We consider the problem of exploiting the microgenerators dispersed in the power distribution network in order to provide distributed reactive power compensation for power losses minimization and voltage regulation. In the proposed strategy, microgenerators are smart agents that can measure their phasorial voltage, share these data with the other agents on a cyber layer, and adjust the amount of reactive power injected into the grid, according to a feedback control law that descends from duality-based methods applied to the optimal reactive power flow problem. Convergence to the configuration of minimum losses and feasible voltages is proved analytically for both a synchronous and an asynchronous version of the algorithm, where agents update their state independently one from the other. Simulations are provided in order to illustrate the performance and the robustness of the algorithm, and the innovative feedback nature of such strategy is discussed.

Data-driven approach for distribution network topology detection

This paper proposes a data-driven approach to detect the switching actions and topology transitions in distribution networks. It is based on the real time analysis of time-series voltages measurements. The analysis approach draws on data from high-precision phasor measurement units (μPMUs or synchrophasors) for distribution networks. The key fact is that time-series measurement data taken from the distribution network has specific patterns representing state transitions such as topology changes. The proposed algorithm is based on comparison of actual voltage measurements with a library of signatures derived from the possible topologies simulation. The IEEE 33-bus model is used for the algorithm validation.

A distributed control strategy for optimal reactive power flow with power and voltage constraints

We consider the problem of exploiting the microgenerators connected to the power distribution network to provide distributed reactive power compensation for power losses minimization and voltage support. The proposed strategy relies on the fact that all the intelligent agents, located at the microgenerator buses, can measure their voltage, communicate data with other agents on a cyber-layer, and adjust the amount of reactive power injected into the grid according to a feedback control law that descends from duality-based methods applied to the optimal reactive power flow problem. We provide numerical simulations to verify the effectiveness of the proposed algorithm and we discuss its innovative feedback nature.

Topology detection in microgrids with micro-synchrophasors

Network topology in distribution networks is often unknown, because most switches are not equipped with measurement devices and communication links. However, knowledge about the actual topology is critical for safe and reliable grid operation. This paper proposes a voting-based topology detection method based on micro-synchrophasor measurements. The minimal difference between measured and calculated voltage angle or voltage magnitude, respectively, indicates the actual topology. Micro-synchrophasors or micro-Phasor Measurement Units (μPMU) are high-precision devices that can measure voltage angle differences on the order of ten millidegrees. This accuracy is important for distribution networks due to the smaller angle differences as compared to transmission networks. For this paper, a microgrid test bed is implemented in MATLAB with simulated measurements from μPMUs as well as SCADA measurement devices. The results show that topologies can be detected with high accuracy. Additionally, topology detection by voltage angle shows better results than detection by voltage magnitude.

A distributed control algorithm for the minimization of the power generation cost in smart micro-grid

We consider the problem of minimizing the power generation cost by exploiting the distributed renewable energy sources(DRES) located in the power distribution network. The proposed strategy requires that the intelligent agents, located at the microgenerator buses, measure their voltage and then adjust the amount of injected power, according to a feedback control law that is indeed a projected gradient descent strategy. Simulations are provided in order to illustrate the algorithm behavior.

Distribution network topology detection with time-series measurements

This paper proposes a novel approach to detecting the topology of distribution networks based on the analysis of time series measurements. The analysis approach draws on data from high-precision phasor measurement units (PMUs or synchrophasors) for distribution systems. A key fact is that time-series data taken from a dynamic system show specific patterns regarding state transitions such as opening or closing switches, as a kind of signature from each topology change. The algorithm proposed here is based on the comparison of the actual signature of a recent state transition against a library of signatures derived from topology simulations. The IEEE 33-bus model is used for initial algorithm validation.

A linear dynamic model for microgrid voltages in presence of distributed generation

We consider the scenario of a low voltage microgrid populated by a number of distributed microgenerators. We focus on the problem of obtaining a dynamic model that describes the input-output relation between complex power commands sent to the microgenerator inverters and the voltage measurements across the network. Such a model is intended as a necessary tool in the design of distributed and centralized control algorithms for the provision of ancillary services in the power distribution grid. Because this model is to be used for the design of such algorithms, we look for an analytical derivation instead of a simulative tool. The proposed model is linear and explicitly contains the network parameters and topology. Simulation shows how the proposed model approximates well the behavior of the original nonlinear system.

A distributed control strategy for optimal reactive power flow with power constraints

We consider the problem of exploiting the microgenerators dispersed in the power distribution network in order to provide distributed reactive power compensation for power losses minimization. The proposed strategy requires that all the intelligent agents, located at the microgenerator buses, measure their voltage and share these data with the other agents on a cyber layer, then actuate the physical layer by adjusting the amount of reactive power injected into the grid, according to a feedback control law that descends from duality-based methods applied to the optimal reactive power flow problem subject to power constraints. Convergence of the algorithm is proved analytically for both a synchronous and an asynchronous version of the algorithm, where agents update their state independently one from the other. Simulations are provided in order to illustrate the algorithm behavior, and the innovative feedback nature of such strategy is discussed.

A Distributed Feedback Control Approach to the Optimal Reactive Power Flow Problem

We consider the problem of exploiting the microgenerators connected to the low voltage or medium voltage grid in order to provide distributed reactive power compensation in the power distribution network, solving the optimal reactive power flow problem for the minimization of power distribution losses subject to voltage constraints. The proposed strategy requires that all the intelligent agents, located at the generator buses, measure their voltage and share these data with the other agents via a communication infrastructure. The agents then adjust the amount of reactive power injected into the grid according to a policy which is a specialization of duality-based methods for constrained convex optimization. Convergence of the algorithm to the configuration of minimum losses and feasible voltages is proved analytically. Simulations are provided in order to demonstrate the algorithm behavior, and the innovative feedback nature of such strategy is discussed.

A master/slave control of distributed energy resources in low-voltage microgrids

The paper deals with the control of low-voltage microgrids with master/slave architecture. Distributed energy resources (DERs) are interfaced to the grid by means of conventional inverters (slave units), and a microgrid master controller (master unit) governs the interaction between the utility and the microgrid at the point of common coupling with the main grid. The power sharing among the available resources is achieved by the power-based control, a technique which allows to pursue both local (DER level) and global (microgrid level) optimization goals. The paper overviews and analyzes the control algorithm and focuses on how the considered approach can be employed to attain effective modes of operation in microgrids. Simulation results supporting the proposed approach are finally provided.