8,070 research outputs found
Control and Limit Enforcements for VSC Multi-Terminal HVDC in Newton Power Flow
This paper proposes a novel method to automatically enforce controls and
limits for Voltage Source Converter (VSC) based multi-terminal HVDC in the
Newton power flow iteration process. A general VSC MT-HVDC model with primary
PQ or PV control and secondary voltage control is formulated. Both the
dependent and independent variables are included in the propose formulation so
that the algebraic variables of the VSC MT-HVDC are adjusted simultaneously.
The proposed method also maintains the number of equations and the dimension of
the Jacobian matrix unchanged so that, when a limit is reached and a control is
released, the Jacobian needs no re-factorization. Simulations on the IEEE
14-bus and Polish 9241-bus systems are performed to demonstrate the
effectiveness of the method.Comment: IEEE PES General Meeting 201
A Pseudospectral Approach to High Index DAE Optimal Control Problems
Historically, solving optimal control problems with high index differential
algebraic equations (DAEs) has been considered extremely hard. Computational
experience with Runge-Kutta (RK) methods confirms the difficulties. High index
DAE problems occur quite naturally in many practical engineering applications.
Over the last two decades, a vast number of real-world problems have been
solved routinely using pseudospectral (PS) optimal control techniques. In view
of this, we solve a "provably hard," index-three problem using the PS method
implemented in DIDO, a state-of-the-art MATLAB optimal control toolbox. In
contrast to RK-type solution techniques, no laborious index-reduction process
was used to generate the PS solution. The PS solution is independently verified
and validated using standard industry practices. It turns out that proper PS
methods can indeed be used to "directly" solve high index DAE optimal control
problems. In view of this, it is proposed that a new theory of difficulty for
DAEs be put forth.Comment: 14 pages, 9 figure
Sum-Rate Maximization in Two-Way AF MIMO Relaying: Polynomial Time Solutions to a Class of DC Programming Problems
Sum-rate maximization in two-way amplify-and-forward (AF) multiple-input
multiple-output (MIMO) relaying belongs to the class of difference-of-convex
functions (DC) programming problems. DC programming problems occur as well in
other signal processing applications and are typically solved using different
modifications of the branch-and-bound method. This method, however, does not
have any polynomial time complexity guarantees. In this paper, we show that a
class of DC programming problems, to which the sum-rate maximization in two-way
MIMO relaying belongs, can be solved very efficiently in polynomial time, and
develop two algorithms. The objective function of the problem is represented as
a product of quadratic ratios and parameterized so that its convex part (versus
the concave part) contains only one (or two) optimization variables. One of the
algorithms is called POlynomial-Time DC (POTDC) and is based on semi-definite
programming (SDP) relaxation, linearization, and an iterative search over a
single parameter. The other algorithm is called RAte-maximization via
Generalized EigenvectorS (RAGES) and is based on the generalized eigenvectors
method and an iterative search over two (or one, in its approximate version)
optimization variables. We also derive an upper-bound for the optimal values of
the corresponding optimization problem and show by simulations that this
upper-bound can be achieved by both algorithms. The proposed methods for
maximizing the sum-rate in the two-way AF MIMO relaying system are shown to be
superior to other state-of-the-art algorithms.Comment: 35 pages, 10 figures, Submitted to the IEEE Trans. Signal Processing
in Nov. 201
A power consensus algorithm for DC microgrids
A novel power consensus algorithm for DC microgrids is proposed and analyzed.
DC microgrids are networks composed of DC sources, loads, and interconnecting
lines. They are represented by differential-algebraic equations connected over
an undirected weighted graph that models the electrical circuit. A second graph
represents the communication network over which the source nodes exchange
information about the instantaneous powers, which is used to adjust the
injected current accordingly. This give rise to a nonlinear consensus-like
system of differential-algebraic equations that is analyzed via Lyapunov
functions inspired by the physics of the system. We establish convergence to
the set of equilibria consisting of weighted consensus power vectors as well as
preservation of the weighted geometric mean of the source voltages. The results
apply to networks with constant impedance, constant current and constant power
loads.Comment: Abridged version submitted to the 20th IFAC World Congress, Toulouse,
Franc
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