705 research outputs found
Modeling and Control of High-Voltage Direct-Current Transmission Systems: From Theory to Practice and Back
The problem of modeling and control of multi-terminal high-voltage
direct-current transmission systems is addressed in this paper, which contains
five main contributions. First, to propose a unified, physically motivated,
modeling framework - based on port-Hamiltonian representations - of the various
network topologies used in this application. Second, to prove that the system
can be globally asymptotically stabilized with a decentralized PI control, that
exploits its passivity properties. Close connections between the proposed PI
and the popular Akagi's PQ instantaneous power method are also established.
Third, to reveal the transient performance limitations of the proposed
controller that, interestingly, is shown to be intrinsic to PI passivity-based
control. Fourth, motivated by the latter, an outer-loop that overcomes the
aforementioned limitations is proposed. The performance limitation of the PI,
and its drastic improvement using outer-loop controls, are verified via
simulations on a three-terminals benchmark example. A final contribution is a
novel formulation of the power flow equations for the centralized references
calculation
Global Tracking Passivity--based PI Control of Bilinear Systems and its Application to the Boost and Modular Multilevel Converters
This paper deals with the problem of trajectory tracking of a class of
bilinear systems with time--varying measurable disturbance. A set of matrices
{A,B_i} has been identified, via a linear matrix inequality, for which it is
possible to ensure global tracking of (admissible, differentiable) trajectories
with a simple linear time--varying PI controller. Instrumental to establish the
result is the construction of an output signal with respect to which the
incremental model is passive. The result is applied to the boost and the
modular multilevel converter for which experimental results are given.Comment: 9 pages, 10 figure
Robust Passivity-Based Control of Boost Converters in DC Microgrids
This work deals with the design of a robust and decentralized passivity-based
control scheme for regulating the voltage of a DC microgrid through boost
converters. A Krasovskii-type storage function is proposed and a (local)
passivity property for DC microgrids comprising unknown 'ZIP' (constant
impedance 'Z', constant current 'I' and constant power 'P') loads is
established. More precisely, the input port-variable of the corresponding
passive map is equal to the first-time derivative of the control input. Then,
the integrated input port-variable is used to shape the closed loop storage
function such that it has a minimum at the desired equilibrium point.
Convergence to the desired equilibrium is theoretically analyzed and the
proposed control scheme is validated through experiments on a real DC
microgrid
Energy Shaping Control for Stabilization of Interconnected Voltage Source Converters in Weakly-Connected AC Microgrid Systems
With the ubiquitous installations of renewable energy resources such as solar and wind, for decentralized power applications across the United States, microgrids are being viewed as an avenue for achieving this goal. Various independent system operators and regional transmission operators such as Southwest Power Pool (SPP), Midcontinent System Operator (MISO), PJM Interconnection and Electric Reliability Council of Texas (ERCOT) manage the transmission and generation systems that host the distributed energy resources (DERs). Voltage source converters typically interconnect the DERs to the utility system and used in High voltage dc (HVDC) systems for transmitting power throughout the United States. A microgrid configuration is built at the 13.8kV 4.75MVA National Center for Reliable Energy Transmission (NCREPT) testing facility for performing grid-connected and islanded operation of interconnected voltage source converters. The interconnected voltage source converters consist of a variable voltage variable frequency (VVVF) drive, which powers a regenerative (REGEN) load bench acting as a distributed energy resource emulator. Due to the weak-grid interface in islanded mode testing, a voltage instability occurs on the VVVF dc link voltage causing the system to collapse. This dissertation presents a new stability theorem for stabilizing interconnected voltage source converters in microgrid systems with weak-grid interfaces. The new stability theorem is derived using the concepts of Dirac composition in Port-Hamiltonian systems, passivity in physical systems, eigenvalue analysis and robust analysis based on the edge theorem for parametric uncertainty. The novel stability theorem aims to prove that all members of the classes of voltage source converter-based microgrid systems can be stabilized using an energy-shaping control methodology. The proposed theorems and stability analysis justifies the development of the Modified Interconnection and Damping Assignment Passivity-Based Control (Modified IDA-PBC) method to be utilized in stabilizing the microgrid configuration at NCREPT for mitigating system instabilities. The system is simulated in MATLAB/SimulinkTM using the Simpower toolbox to observe the system’s performance of the designed controller in comparison to the decoupled proportional intergral controller. The simulation results verify that the Modified-IDA-PBC is a viable option for dc bus voltage control of interconnected voltage source converters in microgrid systems
Review on Control of DC Microgrids and Multiple Microgrid Clusters
This paper performs an extensive review on control schemes and architectures applied to dc microgrids (MGs). It covers multilayer hierarchical control schemes, coordinated control strategies, plug-and-play operations, stability and active damping aspects, as well as nonlinear control algorithms. Islanding detection, protection, and MG clusters control are also briefly summarized. All the mentioned issues are discussed with the goal of providing control design guidelines for dc MGs. The future research challenges, from the authors' point of view, are also provided in the final concluding part
- …