Edson H. Watanabe

New concepts of instantaneous active and reactive powers in electrical systems with generic loads

Conventional active and reactive power theory, valid for the steady-state analysis is reviewed. The instantaneous power theory, introduced by H. Akagi et al. (1983, 1984) is also presented. This instantaneous theory is valid for steady and transient states and for generic voltage and current waveforms. Some examples explaining the physical meaning of the new concepts are presented. By using the concepts of symmetrical components together with the new theory, the powers in an unbalanced system are analyzed, including the zero-sequence instantaneous power. An example showing how this theory can be used to design and control an active power filter is presented. Some simulation results are presented and discussed. >

New control algorithms for series and shunt three-phase four-wire active power filters

This paper presents the general equations that relate the new concepts of instantaneous active and reactive power theory and the well known theory of Symmetrical Components, for the case of 3-phase 4-wire systems, where zero sequence components and harmonics may be present in both voltages and currents. Based on these equations, new control algorithms for 3-phase 4-wire shunt and series active filters for unbalanced power systems are proposed and validated through simulations. The control algorithms presented here are very important for active power filter design and also for FACTS technology reactive power compensators. >

Rotor Voltage Dynamics in the Doubly Fed Induction Generator During Grid Faults

This paper presents a new control strategy for the rotor-side converter (RSC) of wind turbines (WTs) based on doubly fed induction generators (DFIG) that intends to improve its low-voltage ride through capability. The main objective of this work is to design an algorithm that would enable the system to control the initial overcurrents that appear in the generator during voltage sags, which can damage the RSC, without tripping it. As a difference with classical solutions, based on the installation of crowbar circuits, this operation mode permits to keep the inverter connected to the generator, something that would permit the injection of power to the grid during the fault, as the new grid codes demand. A theoretical study of the dynamical behavior of the rotor voltage is also developed, in order to show that the voltage at the rotor terminals required for the control strategy implementation remains under controllable limits. In order to validate the proposed control system simulation, results have been collected using PSCAD/EMTDC and experimental tests have been carried out in a scaled prototype.

Simplified Modeling of a DFIG for Transient Studies in Wind Power Applications

Improving the fault ride-through (FRT) capability of doubly fed induction generators (DFIGs) in wind power applications is a very important challenge for the wind power industry. The mathematical models of such generators enable us to analyze their response under generic conditions. However, their mathematical complexity does not contribute to simplifying the analysis of the system under transient conditions and hence does not help in finding straightforward solutions for enhancing their FRT. This paper presents a simplified model of the DFIG, which has been extracted from the classical fifth-order model, which can accurately estimate the behavior of the system while significantly reducing its complexity. In this paper, the mathematical deduction of this model will be presented, and simulations and experimental results will be shown to demonstrate the accuracy and reliability of the proposed algorithm.

Comparisons Between the p--q and p--q--r Theories in Three-Phase Four-Wire Systems

This paper presents a comparative analysis between results from applications of the p-q and the p-q-r theories in shunt active power filters for three-phase four-wire systems, discussing aspects related to the influence of the system voltage in the control methods that calculate the compensating currents. It is shown that in some cases, a preprocessing of the system voltage is required if the goal is to achieve sinusoidal compensated currents. On the other hand, when the goal is to compensate zero-sequence current, the need of energy storage elements in the active filter is discussed. In this case, if zero-sequence components are present simultaneously in the system voltage and load current, they produce zero-sequence power flow, and the control methods based on both theories must contain additional calculations to allow the elimination of energy storage elements in the active filter. A control strategy based on the p-q theory is proposed to eliminate the neutral current without the need of energy storage elements, with the advantage of avoiding the extra transformation from alphabeta0 to pqr coordinates that is needed in the p-q-r theory. Simulation results are presented for the purpose of comparing the performance of both control methods.

Going the Distance

The transmission of bulk power over long distances is a very current topic in the worldwide energy sector. An excellent example is the transmission system of Madeira River Hydropower Generation Project in Brazil, which includes two 2,400-km transmission lines, designed to transmit 3,150 MW through each HVDC link. In fact, long transmission trunks enable the use of natural resources that are far from major load centers as well as provide the interconnection of large power systems.

Analysis of the dynamic and steady-state performance of Cockcroft-Walton cascade rectifiers

A detailed analysis, based on digital simulation, of the Cockcroft-Walton rectifier, including transient and steady-state voltages and currents on any component, was performed. It is shown that the numerical solution of the system may be effectively implemented by coupling the modified nodal approach formulation of the circuit equations with companion models and piecewise linear approximations of nonlinear elements. Good agreement between simulated and experimental results confirmed the validity of the proposed model/program. In the transient analysis it was shown that the start-up time of a Cockcroft-Walton rectifier is directly related to the number of stages, increasing as the number of stages increases. The output voltage regulation characteristics are worse for a larger number of stages. A study of the influence of an inductance in series with the voltage source showed that it may be chosen in such a way as to increase the output average voltage and improve its regulation. The analysis of this rectifier fed by a square-wave voltage source showed that, in this case, the output voltage regulation is improved. However, the output voltage overshoots and input current peaks are increased.<<ETX>>

Instantaneous p-q power Theory for compensating nonsinusoidal systems

This paper presents a tutorial about compensation of nonsinusoidal systems based on the instantaneous active and reactive power theory or the p-q theory. The history related to this theory is presented and then the definitions of real, imaginary and zero-sequence powers are introduced. The physical meanings of each of these powers are explained and some basic compensation examples are shown considering different active power conditioners. It is shown that this theory can be very practical for understanding problems due to nonsinusoidal voltages or currents. It is especially interesting for the design of power conditioners for three-wire or four-wire three-phase system with or without distortions in voltages and currents.

SSR and Power Oscillation Damping Using Gate-Controlled Series Capacitors (GCSC)

The subsynchronous resonance (SSR) phenomenon may occur when a steam turbine-generator is connected to a long transmission line with series compensation. The main purpose of this work is to verify the capability of the gate-controlled series capacitor (GCSC) to mitigate SSR. For this study the GCSC was tested in conjunction with the IEEE First Benchmark Model. The actual possibility of controlling SSR was verified by digital simulation using the alternative transients program/electromagnetic transients program. As a result it was shown that GCSC can damp SSR even without a specific control. It was also shown that, using a simple controller, SSR as well as electromechanical oscillation can be damped.

GTO controlled series capacitors: multi-module and multi-pulse arrangements

This paper describes the GTO controlled series capacitor-G4CSC, an equipment for controlled series compensation of transmission systems. The principles of operation of the GCSC are reviewed and harmonic analysis is performed, showing how much of voltage harmonics are produced by the GCSC. Novel configurations using multi-module and multi-pulse GCSCs are proposed in order to reduce the voltage harmonics. Digital simulations using the EMTP are presented to validate the proposed configurations.