Luis Arnedo

Synthesis and Integration of Future Electronic Power Distribution Systems

Future advanced electric power systems will have practically all loads interfaced to energy sources through power electronics equipment. Furthermore, all alternative, sustainable, and distributed energy sources, as well as energy storage systems, can be only connected to electric grid through power electronics converters. This will require new concepts for electronic control of all power flows in order to improve energy availability, power density, and overall energy and power efficiency in all electrical systems, from portable devices to cars, airplanes, ships, homes, data centers, and the power grid. Starting from the example of a computer power system, the paper contemplates possible future ac and dc electronic power system architectures, which fully decouple the dynamics between sources, distribution system, and loads by using separate source-, load-, and distribution-converters. Several ideas and possible methodologies for modeling, analysis, and system-level design of such systems, including power flow control, protection, stability, and subsystem interactions, are presented.

Polytopic black-box modeling of dc-dc converters

The objective of this work is to develop modular black-box converter models for system-level design and analysis that are valid in a wide variety of operating conditions. The approach used to address this problem is to divide the converter operating space into sub-spaces. For each sub-space, a linear local model is constructed from frequency response functions (FRFs) measured at the converter terminals. The FRFs are then post processed using system identification, the linear models obtained are valid as a local representation of the converter intrinsic dynamic at that operating condition. In the regions where two or more adjacent linear models overlap, an appropriate weighting is applied between them to produce an accurate approximation of the measured data. This new structure allows the characterization of converters with rich nonlinear dynamics, such as an unregulated dc-dc bus converter working near the boundary region between discontinuous and continuous conduction modes or a regulated flyback dc-dc converter. These two converters are effectively modeled with the proposed approach, and its models are presented in detail, providing an in-depth description of their implementation as well as their extensive experimental validation with laboratory prototypes.

System-Level Black-Box Dc-to-Dc Converter Models

This paper presents the application of black-box terminal characterization models (BBTC) for the simulation and analysis of distributed power electronics systems composed by commercial power electronics converters and filter modules. The models are shown to effectively predict the transient and steady state response of interconnected distributed power systems. They are also used to predict the small-signal stability between source and load converters. All simulation results are validated with experimental data.

Black-Box Terminal Characterization Models for the Analysis and Simulation of Distributed Power Electronic Systems

This paper presents the application of Black-box terminal characterization models for the simulation an analysis of distributed power electronics systems comprised by commercial power electronics and passive modules. The models predict the transient and steady state response of a cascade, parallel and distributed power system. Also are used to predict the stability condition between a source and a load converter. All simulation results are validated with experimental data.

80 kW hybrid solar inverter for standalone and grid connected applications

The aim of this work is the development of a solar photovoltaic generation system based on a standard power electronics cell for microgrid applications. The proposed system is capable of providing security of supply by delivering uninterrupted power to critical loads in standalone operation and transitioning seamlessly between stand alone and grid connected mode. To mitigate the effect of variability of the generation and load demand a state of the art 20kWh lithium-ion battery is used to balance the power flow in the system. This paper presents description of the hardware, proposed controls strategies and simulation models of the system.

An advanced high performance maximum power point tracking technique for photovoltaic systems

The key requirements for the control of the photovoltaic (PV) energy conversion systems are to achieve very fast yet quite accurate tracking of the maximum power point under rapidly changing environmental conditions and to obtain efficient unperturbed tracking operation under steady environmental conditions. In this work, a high-performance Maximum Power Point Tracking (MPPT) technique, based on existing Incremental Conductance method, is proposed to meet these challenging requirements. In the proposed MPPT technique, a new function for adaptive variable step-size is defined using the conductance of the PV arrays. Using this adaptive variable step-size, the proposed method can track the Maximum Power Point (MPP) in a very rapid manner, and hence, can achieve much faster dynamic response than the conventional MPPT methods. Further, an adaptive tolerance band is introduced to define the MPP condition. The proposed tolerance band is utilized to obtain highly accurate and oscillation free efficient MPPT operation under all the operating conditions; including low level insolation condition, under which the conventional methods fails to perform efficient operations. Analysis, simulation, and experimental results, carried out on a micro-grid based PV energy conversion system, are presented for the validation of the proposed technique.

Advanced techniques for integration of energy storage and photovoltaic generator in renewable energy systems

In renewable energy systems, the highly intermittent nature of energy sources with the unpredicted nature of load and grid availability make it a great challenge to operate and transition a system seamlessly under large number of modes while still being able to follow the command of the supervisory control. In this work, an advanced control technique is proposed to integrate energy storage elements with intermittent renewable sources that can achieve seamless transitions while implementing the key protections and ability to follow external commands. The proposed control technique is based on instantaneous power balance theory and dynamic power limiter of the energy source, which is implemented in fast local controller and it does not require any exclusive determination of modes. Therefore, under rapid change of source, load, and grid conditions, the proposed system can respond more quickly and make transitions with increased reliability. Furthermore, the conventional techniques for Maximum Power Point Tracking (MPPT) fail to perform efficiently under low insolation level condition and they do not offer accurate yet oscillation free operation at MPP. In this work, an adaptive tolerance band is proposed to achieve highly accurate fluctuation free MPPT under all the operating conditions, and hence, to improve the performance of the integrated system. Simulation and experimental results are presented to validate the proposed techniques.

Hybrid damping of grid-tie inverter output harmonics for resonance rejection & wind park stability under high penetration

Grid-tie inverters are usually connected to Pad-Mount Transformers (PMT) through passive filters. Most grid-tie inverter manufacturers design these passive filters to eliminate high frequency current ripples and switching harmonics generated by the switching actions of inverters. Under high wind power penetration output power filters are susceptible to create severe resonance due to their interaction with the grid voltage harmonics and transmission line impedances. This resonance generates high harmonics which are not only not in compliance with the IEEE 519 power quality requirement, but also are very harmful to power system components. This paper proposes a hybrid damping approach which combines the passive damping of the filter with a physical resistor and an active damping of the inverter output harmonics with grid voltage harmonics feed-forward. The approach takes into account the passive filters interaction with the grid through impedance analysis under high wind power penetration. Simulations and field tests are shown to demonstrate the validity of the proposed approach.

An integral method combining V/Hz and vector control of permanent magnet motor

This paper presents an original method for sensorless speed control of Permanent Magnet Motors (PMM). The proposed method is robust to parameter variations, does not require a starting sequence and shows good performance at low and high speeds operation. The benefits mentioned above are achieved by combining features of volts per hertz and vector control methods. The proposed method uses the q axis current regulator to estimate the angular speed of the PMM instead of providing the q axis voltage command for the inverter as is done in traditional motor control methods. The q axis voltage inverter command is calculated from q axis and d axis current references and motor parameters similar to V/Hz control method. An observer performs the estimation of q and d axis rotor fluxes, from measured and reference currents and voltages. The observer estimates are crucial for flux and consequently voltage estimation and robust operation of the method. In addition, the d axis current regulator performance is enhanced, with a feed-forward voltage signal calculated from motor parameters. The analysis presented in this paper, shows that error in the alignment with rotor flux position is proportional to the estimated rotor flux in q axis which was consequently used for rotor angle alignment.

System level wind turbine controls with seamless transitions between standalone and grid connected mode

The aim of this work is the development of a system-level wind turbine control strategy that allows wind turbines to operate in grid-connected or off-grid mode and transition seamlessly between these modes of operation. Conventional wind turbines with a front-end inverter are designed to work as a grid tie system meaning that the inverter needs the grid voltage to synchronize and the inverter becomes a current source. As opposed to current practice, this paper proposes a wind turbine control strategy designed to work as a controlled voltage source emulating the behavior of large synchronous generators. This mode of operation will allow wind turbines to transition seamlessly from grid-connected to off-grid mode of operation. Furthermore, because of its power sharing features it will allow wind turbines to operate in remote areas without causing power quality or instability issues. The turbine will also be able to interface with microgrid systems or form a microgrid. This paper presents an overview of the proposed control strategies and simulation results demonstrating the feasibility of this approach.