Mauricio Aredes

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. >

Analysis and Software Implementation of a Robust Synchronizing PLL Circuit Based on the pq Theory

This paper presents the analysis and software implementation of a robust synchronizing circuit, i.e., phase-locked loop (PLL) circuit, designed for use in the controller of active power line conditioners. The basic problem consists of designing a PLL circuit that can track accurately and continuously the positive-sequence component at the fundamental frequency and its phase angle even when the system voltage of the bus, to which the active power line conditioner is connected, is distorted and/or unbalanced. The fundamentals of the PLL circuit are discussed. It is shown that the PLL can fail in tracking the system voltage during startup under some adverse conditions. Moreover, it is shown that oscillations caused by the presence of subharmonics can be very critical and can pull the stable point of operation synchronized to that subharmonic frequency. Oscillations at the reference input are also discussed, and the solution of this problem is presented. Finally, experimental and simulation results are shown and compared

A DQ Synchronous Reference Frame Current Control for Single-Phase Converters

This paper presents a current control using the dq synchronous reference frame for single-phase converters. This control method consists in transforming an orthogonal pair composed by the actual single-phase input current and a fictitious current, from a stationary to a rotating frame. The steady state current components in dq frame become DC instead of AC values so a zero error current control can be implemented. A single-phase PFC boost rectifier is used as an example application of this control. To validate the control method simulation and experimental results are presented

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.

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.

Compensation of nonperiodic currents using the instantaneous power theory

This paper presents a discussion about the use of the instantaneous active and reactive power theory (p-q theory) for the compensation of nonperiodic currents in three-phase circuits. First, the concept behind the term nonperiodic is discussed. A summary of the basic points of the instantaneous power theory is presented and them some examples of nonperiodic currents and their identification and compensation by active filters are presented. This paper shows that it is not possible to have at the same time a perfect compensation, where the source currents are purely sinusoidal and the power flowing in the circuit is constant. The user has to decide which condition has higher priority and adapt the compensation characteristics of the active filter.

Multi-pulse STATCOM operation under unbalanced voltages

This work presents a study about static synchronous compensators (STATCOM) operating in electrical systems where the voltages are unbalanced and contain negative sequence components. In balanced systems the STATCOM has a very good performance, allowing compensation of capacitive or inductive reactive power with a fast transient response. However, when there are negative sequence components, the STATCOM has its performance diminished. An analytical analysis, using the instantaneous power theory and the switching functions technique, and simulations of a STATCOM quasi 48-pulses using the electromagnetics transients program (ATP-EMTP) show how STATCOM is affected by negative sequence components and how its performance is degraded. A proposal to improve the STATCOM performance under negative sequence unbalance is shown.

An Improved iUPQC Controller to Provide Additional Grid-Voltage Regulation as a STATCOM

This paper presents an improved controller for the dual topology of the unified power quality conditioner (iUPQC) extending its applicability in power-quality compensation, as well as in microgrid applications. By using this controller, beyond the conventional UPQC power quality features, including voltage sag/swell compensation, the iUPQC will also provide reactive power support to regulate not only the load-bus voltage but also the voltage at the grid-side bus. In other words, the iUPQC will work as a static synchronous compensator (STATCOM) at the grid side, while providing also the conventional UPQC compensations at the load or microgrid side. Experimental results are provided to verify the new functionality of the equipment.