Alejandro Garces

Alejandro Garces
Universidad Tecnológica de Pereira | UTP · Faculty of Electrical Engineering, Electronics and Computer Systems

PhD

About

183
Publications
34,680
Reads
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1,937
Citations
Introduction
I am interested in mathematical optimization for the operation and control of power systems, including microgrids and active distribution networks.
Additional affiliations
January 2015 - present
Santo Tomás University
Position
  • Professor
Description
  • Smart Grids
January 2012 - present
Universidad Tecnológica de Pereira
Position
  • Professor
Description
  • Wind Energy, Mathematical Optimization, Power Systems Dynamics and Control
October 2008 - September 2012
Norwegian University of Science and Technology
Position
  • PhD Student
Education
September 2008 - September 2012
Norwegian University of Science and Technology
Field of study
  • Electrical Engineerig

Publications

Publications (183)
Article
Full-text available
This paper addresses the problem of determining the optimal location and operation of distribution static synchronous compensators (D-STATCOMs) in power distribution networks. Metaheuristic algorithms have been conventionally used to solve this mixed-integer nonlinear programming problem. In contrast, we propose a mixed-integer second-order cone pr...
Article
Full-text available
This paper deals with the power flow problem in bipolar direct current distribution networks with unbalanced constant power loads. The effect of the neutral wire is considered in two prominent cases: (i) when the system is solidly grounded at each load point and (ii) when the neutral terminal is only grounded at the substation bus. The problem is s...
Article
Power electronics converters are equipped with current controls that protect the converter from over-currents. This protection introduces non-differentiable equations into the power flow problem. The conventional Newton's method is not suitable in that conditions. This letter proposes a fixed-point iteration to overcome this difficulty. The techniq...
Article
Full-text available
Performance analysis is challenging in modern power distribution networks due to the increasing penetration of distributed energy resources (DERs) interfaced by voltage source converters (VSCs). Parameter uncertainty, black-box models of the components, and low inertia are some of the issues that must be addressed. The latter can represent high vul...
Article
Full-text available
The problem of the optimal siting and sizing of fixed-step capacitor banks is studied in this research from the standpoint of convex optimization. This problem is formulated through a mixed-integer nonlinear programming (MINLP) model, in which its binary/integer variables are related to the nodes where the capacitors will be installed. Simultaneous...
Book
Los sistemas eléctricos experimentan cambios importantes relacionados con su composición y la estructura, así como en las estrategias de control, protección y operación. Las micro-redes están encargadas de suministrar la energía al usuario final, y son objeto de valiosos estudios y publicaciones actuales, debido principalmente a que contribuyen con...
Article
This paper presents a sequential convex optimization model for operating an active distribution network in island mode when there is a lack of generation. The proposed model seeks to match the available generation with the load (minimizing the total unsupplied demand). Moreover, it considers generation capacity, bounds of voltage, and the effect of...
Article
This paper proposes an optimization model for the secondary control of islanded microgrids. It considers the action of the primary control and the references given by the tertiary control. The model is solved in each step, based on a linear approximation of the frequency-dependent power flow equations. The main objective of the model is to carry ou...
Article
This article presents an optimization model for tertiary control in three-phase unbalanced microgrids. This model considers 24h operation and includes renewable energy sources, energy storage devices, and grid code limitations. Power flow equations are simplified using a recently developed approximation based on Wirtinger’s calculus. The proposed m...
Article
This paper introduces a linear programming (LP)-based optimisation method of charging electric vehicles (EVs) in a decentralised fashion. It exploits the available photovoltaic (PV) power to charge EV batteries while maintaining the low-voltage (LV) network within its operational limits. A new energy-bound model is implemented in order to meet the...
Preprint
Full-text available
This article presents an optimization model for tertiary control in three-phase unbalanced microgrids. This model considers 24h operation and includes renewable energy sources, energy storage devices, and grid code limitations. Power flow equations are simplified using a recently developed approximation based on Wirtinger's calculus. The proposed m...
Article
Full-text available
Short-Term Hydrothermal Scheduling (STHS) is a classic problem in power system operation where the aim is to decide the dispatch of both thermal and hydroelectric units. This problem is complex due to its non-linear non-convex nature, and the requirements for fast solving for daily operation. Technologies such as wind and solar generation introduce...
Article
Full-text available
This paper presents a model for stabilizing multi-terminal high voltage direct-current (MT-HVDC) networks with constant power terminals (CPTs) interfaced with power electronic converters. A hierarchical structure of hierarchical control is developed, which guarantees a stable operation under load variations. This structure includes a port-Hamiltoni...
Article
Widespread application of residential photovoltaic (PV) systems and electric vehicles (EVs) has led the distribution system operators (DSOs) to face new technical challenges such as overloading and significant voltage variations, especially on low voltage (LV) grids. This adverse effect may be mitigated by employing the aggregators as intermediary...
Article
Full-text available
This paper deals with an application of the nested convex programming to the optimal power flow (OPF) in multi-terminal high-voltage direct-current grids (MT-HVDC). The real-world optimization problem under consideration is non-convex. This fact implies some possible inconsistencies of the conventional numerical minimization algorithms (such as int...
Article
Full-text available
Phase balancing is a classical optimization problem in power distribution grids that involve phase swapping of the loads and generators to reduce power loss. The problem is a non-linear integer and, hence, it is usually solved using heuristic algorithms. This paper proposes a mathematical reformulation that transforms the phase-balancing problem in...
Article
Full-text available
The optimal placement and sizing of distributed generators is a classical problem in power distribution networks that is usually solved using heuristic algorithms due to its high complexity. This paper proposes a different approach based on a mixed-integer second-order cone programming (MI-SOCP) model that ensures the global optimum of the relaxed...
Chapter
This paper presents a sequential convex-optimization method for the optimal power flow in dc-grids under island operation. The proposed method is general for both high and low power applications. The former refers to multi-terminal high voltage direct current transmission and the latter include dc-distribution and dc-microgrids. Our analysis is bas...
Article
This paper proposes a general model for microgrids in the 0dq reference frame for stationary state and small dynamic variations. The proposed model considers the dynamics of the distribution lines, including mutual coupling and unbalanced loads, and the dynamics of the converters required to integrate renewable sources and energy storage devices (e...
Article
This paper presents a non-linear method based on sum-of-squares (SOS), to determine the stability of equilibrium points for the Buck, Boost, Buck-Boost and non-inverter Buck-Boost converters. These converters share a similar structure with a PI controller to regulate the output voltage. A quadratic Lyapunov function is proposed in all cases, and th...
Conference Paper
This paper addresses the problems of power flow and optimal power flow a nalysis c onsidering voltage-dependent load models from the convex point of view. First, Taylor series expansion method is employed for linearizing the power flow equations generating a set of affine h yperplanes. S econd, the sequential quadratic programming (SQP) approach is...
Conference Paper
This paper proposes a proportional-integral passivity-based controller (PI-PBC) for supporting voltage in linear loads integrated with Ćuk converters. An adaptive load estimator is also employed to avoid current measurements at the load point. This estimator permits an on-line estimation of the load conductance for maintaining the output voltage as...
Book
Full-text available
La potencia reactiva es un concepto abstracto y difícil de definir, especialmente en sistemas con alto desbalance y presencia de armónicos, se trata de una potencia circulante entre el campo magnético y el campo eléctrico, sin ser realmente generada o consumida. Sin embargo, este intercambio energético produce corrientes circulantes que, a su vez,...
Article
In this paper, the control problem of microgrids (MGs)operating in islanded mode is approached from a passivity-based control perspective. A control scheme is proposed that, relying only on local measurements for the power converters included in the network representation, achieves both voltage regulation and power balance in the network through th...
Article
Full-text available
This paper presents a passivity-based control method for a small hydro-power system that consists of a permanent magnet synchronous generator (PSMG) connected to the grid through a back-to-back converter. Nonlinear models of the hydraulic, mechanical, and electrical parts of the small hydro-power system are considered. Two approaches in the realm o...
Article
This paper presents a model for the small signal analysis in island microgrids, that includes the effect of time constants and droop controls as the effect of the frequency in the parameters of the grid. It is demonstrated that high values of the time constant and/or the droop constant could lead to unstable operation. However, the microgrid is rob...
Conference Paper
Full-text available
This paper deals with an application of the nested convex programming to the optimal power flow (OPF) in multi-terminal high-voltage direct-current grids (MT-HVDC). The real-world optimization problem under consideration is non-convex. This fact implies some possible inconsistencies of the conventional numerical minimization algorithms (such as int...
Article
Full-text available
A bilinear PI control based on passivity theory for the adequate integration of distributed energy resources (DERs) in ac microgrids is presented in this paper. DERs are integrated into the grid by voltage source converters (VSC), the most common and suitable technology for this type of application. The proposed control guarantees asymptotically st...
Article
Full-text available
This study addresses the power-flow-analysis problem for direct-current (DC) grids from a numerical perspective. Classical and emerging algorithms for power flow solutions in DC networks such as Gauss-Seidel, successive approximations, Newton-Raphson, and Taylor-based methods are reviewed herein in detail by providing their mathematical derivations...
Chapter
Phase balancing is an optimization problem which can reduce power losses in modern power distribution grids. The problem consists on phase swapping of the loads at the feeder level in order to reduce the unbalance of the grid. Despite being a classic problem, it is still relevant since unbalance is a common phenomena in power distribution grids and...
Book
La optimización convexa tiene una fundamentación teórica sólida y un rango de aplicación amplio. Por tanto, estudiaremos primero el aspecto teórico antes de adentrarnos en sus aplicaciones. En general, los modelos de optimización convexa incluyen a los problemas de PL y algunos de PNL. Sin embargo, otros tipos de problemas pueden ser solucionados m...
Book
Los sistemas eléctricos actuales están experimentando cambios importantes relacionados con su estructura y su forma de operación. De manera similar a aquello que ocurre en los sistemas de potencia, los sistemas de distribución a media y baja tensión, encargados de suministrar la energía al usuario final, son objeto de análisis debido a que tienen p...
Article
Full-text available
This paper presents the modeling and control of a small hydro-power plant (SHP) for a DC microgrid based on passivity theory. The SHP is made up of a turbine, a permanent magnet synchronous generator (PMSG), a voltage source converter and a DC microgrid. The electrical, mechanical and hydraulic dynamics in the mathematical model of the SHP are cons...
Article
Full-text available
This paper addresses the problem of control design for hydro-turbine governing systems with surge tanks from the perspective of standard passivity-based control. The dynamic model of a synchronous machine is considered in conjunction with a model of the hydro-turbine to generate an eleventh-order nonlinear set of differential equations. A Euler-Lag...
Article
This paper proposes to modify the classic control of voltage source converters for photovoltaic generation and battery energy storage systems, using model predictive control for the outer-loop and the conventional vector oriented control for the inner loop, in order to improve the voltage profiles in weak distribution networks. The proposed approac...
Article
This paper presents a unified Hamiltonian formulation for controlling distributed energy resources (DERs) in ac single-phase microgrids (SP-MGs) via proportional-integral passivity-based control (PI-PBC), and interconnection and damping assignment passivity-based control (IDA-PBC). The proposed Hamiltonian formulation allows us to consider both pul...
Conference Paper
Full-text available
This paper presents the control of the active and reactive power of a superconducting magnetic energy storage (SMES) system for compensating fluctuations of a power system with high penetration of wind energy during extreme scenarios of wind gusts. The wind energy conversion system (WECS) is a Type-A turbine with squirrel cage induction generator (...
Article
Full-text available
This paper proposes an interconnection and damping assignment passivity-based control (IDA-PBC) for multimachine power systems including hydro-turbine governing systems (HTGS) with surge tank. The main objective is to stabilize the rotor speed and regulate the terminal voltage of each synchronous machine in a power system. The proposed control is d...
Article
This paper presents a nonlinear stability analysis for DC-microgrids in both, interconnected and island operation with primary control. The proposed analysis is based on the fact that the dynamical model of the grid is a gradient system generated by a strongly convex function. The stability analysis is thus reduced to a series of convex optimizatio...
Article
Introducción: La detección temprana de la infección por Helicobacter pylori (HP) ha cobrado mayor relevancia, siendo el test de aliento con urea carbono-14 (C-14) uno de los métodos de diagnóstico no invasivos; sin embargo, no ha sido comprobada su utilidad en la población ecuatoriana. Objetivo: Evaluar la sensibilidad y especificidad del test de a...
Article
This paper proposes a direct power control (DPC) for a high-voltage direct-current system using voltage source converters (VSC-HVDC) by applying passivity-based control theory. This system allows doing an efficient and reliable integration of electrical network from renewable energy sources. The DPC model permits instantaneous control of the active...
Conference Paper
Full-text available
Short term hydrothermal dispatch is a classic problem in power systems operation. This problem is usually solved by heuristic algorithms that are unsuitable for real time operation. This paper presents a quadratic convex approximation that guarantees a global optimum with fast convergence. Our approximation is based on the semidefinite properties o...
Article
The power flow equations in DC microgrids are nonlinear due to the presence of constant power terminals. In this context, a rigorous demonstration of the convergence and uniqueness of the solution for Newton’s method is required. This problem is particularly important in islanded microgrids, where the power flow method determines the equilibrium po...
Data
The Poster of: "A Quadratic Convex Approximation for the Short-Term Hydrothermal Dispatch", Presented at IEEE PowerTech 2019, Milan, Italy
Article
This paper proposes a direct power control for electrical energy storage systems (EESS) in ac microgrids. This strategy allows managing instantaneous active and reactive power without using a conventional inner-loop current regulator and without a phase-locked loop, increasing the reliability of the system while reducing investment costs. PI passiv...
Article
This paper proposes a logarithmic transformation of voltages (LTVM) for the power flow in DC grids. This problem is non-linear due to the presence of constant power loads (CPLs), which also introduce a negative resistance effect that can create numerical instability for conventional algorithms. The proposed methodology is applied to dc-microgrids,...
Conference Paper
This paper proposes a passive PI control for applications of photovoltaic (PV) systems integrated with boost DC–DC converters. The proposed controller guarantees asymptotically stability in closed–loop for the boost DC–DC converter using Lyapunov theory. In addition, the proposed controller is robust to parametric uncertainties and unmodeled dynami...
Conference Paper
Full-text available
The proportional-resonant control (PR-control) is a simple and efficient control, which has the ability to eliminate error in linear time varying signals. This type of control is typically used in applications such as the integration of solar panels, energy storage and electric vehicles among others. Despite having non-linear dynamics, the analysis...
Conference Paper
This paper addresses the economic-environmental dispatch problem for thermal plants on a Multi-terminal HVDC power grid. A multi-objective optimization approach is used for modeling the compromise between fuel costs and the greenhouse gas emissions by the thermal plants. The grid topology is also considered by proposing a convex reformulation of th...
Article
Full-text available
This paper investigates the existence of an equilibrium point in multiterminal HVDC (MT-HVDC) grids, assesses its uniqueness and defines conditions to ensure its stability. An offshore MT-HVDC system including two wind farms is selected as application test case. At first, a generalized dynamic model of the network is proposed, using hypergraph theo...
Article
Low-frequency oscillations can occur in hydropower systems under in the new context of power system and the classical controller for hydro-turbine governing systems need to be enhanced with the purpose of improving its stability. We propose a controller based on passivity theory with the aim of damping oscillations in a power system. Passivity-base...
Article
In this paper, we address the optimal power flow problem in dc grids (OPF-DC). Our approach is based on sequential quadratic programming which solves the problem associated with non-convexity of the model. We propose two different linearizations and compare them to a non-linear algorithm. The first model is a Newton-based linearization which takes...
Conference Paper
This paper presents a global tracking passivity–based proportional–integral (PI) control for output voltage regulation of a dc-dc Buck converter. The proposed controller is based on passivity formulation since dc-dc Buck converter has a passive structure in open-loop. Additionally, the controller takes advantage of the PI actions to design a contro...
Article
A mathematical optimization approach for the optimal operation focused on the economic dispatch for dc microgrid with high penetration of distributed generators and energy storage systems (ESS) via semidefinite programming (SDP) is proposed in this paper. The SDP allows transforming the nonlinear and non-convex characteristics of the economic dispa...
Article
This paper presents a general form of designing passivity–based controllers for electrical energy storage systems (EESS) in three–phase microgrids (TP–MGs) under time–domain reference frame. The control strategy proposed in this paper use the Clark’s transformation known as αβ reference frame, avoiding to use phase–locked loop (PLL) systems, which...
Preprint
This paper presents a non-linear stability analysis for dc-microgrids in both, interconnected mode and island operation with primary control. The proposed analysis is based on the fact that the dynamical model of the grid is a gradient system generated by a strongly convex function. The stability analysis is thus reduced to a series of convex optim...
Article
This paper proposes a methodology to control the active and reactive power of a superconducting magnetic energy storage (SMES) system to alleviate subsynchronous oscillations (SSO) in power systems with series compensated transmission lines. Primary frequency and voltage control are employed to calculate the active and reactive power reference valu...
Article
Full-text available
This paper presents a generalized model for small signal stability in dc microgrids considering electric vehicles. The proposed model considers four type of terminals, namely: constant power, constant voltage, constant current and constant impedance. A Newton-Raphson methodology is used to calculate the operation point of the microgrid and a sensit...
Article
Contexto: la enfermedad inflamatoria intestinal (EII) es un proceso inflamatorio crónico del intestino con sus dos variedades, la colitis ulcerativa (CU) y la enfermedad de Crohn (EC). El objetivo del tratamiento es la remisión clínica y endoscópica de la enfermedad, sin embargo, la calidad de vida que esta influye en el manejo y evolución de la en...
Article
Full-text available
En este artículo se presenta el diseño y la aplicación de la teoría de control basada en pasividad para la integración de recursos energéticos distribuidos (REDs) a través de convertidores controlados por voltaje en redes monofásicas de corriente alterna. La representación Hamiltoniana de estos sistemas facilita el desarrollo de controladores pasiv...
Conference Paper
Full-text available
This paper presents an asymptotically stable global controller design for distributed energy integration in electrical distribution networks using a three-phase voltage source converter (VSC). An invariant Park’s transformation is used to obtain the mathematical representation of the VSC in dq0 reference frame. To design of the proposed controller,...
Conference Paper
This paper addresses the problem of optimal location and sizing of distributed generators (DGs) in direct-current (dc) power grids by using a mixed-integer nonlinear programming (MINLP) formulation. The reduction of the power losses in all branches of the network are considered as the objective function; while the restrictions are the power balance...
Conference Paper
This paper presents a general control design for photovoltaic systems integrated with Direct–Current power grids by using an unidirectional boost converter. Passivity–based control (PBC) theory is used as a control technique since the dynamical model of the boost converter has an intrinsically port–Hamiltonian structure, where PBC theory is based u...
Conference Paper
This paper presents an exact feedback linearization control strategy to operate superconducting magnetic energy storage (SMES) systems connected to an electric distribution network through a pulse–width–modulated current source converter (PWM–CSC). To model this system an average model is employed by using dq reference frame. The dynamical model of...
Article
This express brief presents the stability analysis of single-phase microgrids (SP-MG) operating under master–slave connection with constant power terminals. The SP-MG is composed of linear elements, nonlinear loads, and distributed generators modeled as PQ constant terminals interconnected through power electronic converters. Lyapunov’s direct meth...
Article
This express brief shows a convex quadratic approximation for the optimal power flow (OPF) in direct-current microgrids () via Taylor’s series expansion. This approach can be used for solving OPF problems on radial and meshed s with multiple constant power terminals, allowing to cover a wide range of configurations. Two test s with 10 and 21 nodes...