Patricio Salmerón Revuelta

Strategies of instantaneous compensation for three-phase four-wire circuits

When the voltage source is not balanced for three-phase four-wire circuits, instantaneous compensation for the instantaneous reactive power does not eliminate the neutral current on the source side. In facti when the zero-phase voltage of the source exists, none of the present compensation strategies can guarantee the instantaneous elimination of the neutral current in three-phase four-wire systems. Two approaches are distinguished in this paper for instantaneous compensation. The first eliminates the instantaneous reactive current, thus neutral current can still flow. The second eliminates the instantaneous pseudo-reactive current, so that the neutral current component is compensated. In the latter case, a new control strategy is designed to avoid instantaneous power flowing through the compensator. It provides flexibility in compensating for the neutral current in a three-phase four-wire system including the zero-sequence voltage. Finally, simulated and experimental results are obtained to confirm the theoretical properties and show the compensator performance.

Assessment on apparent power indices with hybrid active power filters

This paper presents a method for assessing the quality improvement of the electric power, when compensation equipment based on hybrid active power filters is applied. Power quality indicators that allow to separate the contribution to unbalance of each harmonic and interharmonic of voltages and currents are introduced, calculated with an enhanced procedure. To characterize the behavior of these indices, a hybrid series - active parallel - passive filter, SAPPF, is used for the compensation of a load in a system with unbalance and distortion. The results obtained with the practical cases have allowed to verify the validity of the proposed procedure, and to clarify the interpretation of the unbalance and harmonic distortion indices with this kind of compensation.

Instantaneous Reactive Power Theory

This chapter presents the fundamentals of the instantaneous reactive power theory for three-phase three/four-wire systems. The original formulation presents a description model of three-phase systems through the introduction of two power variables: the instantaneous real power and instantaneous imaginary power. The initial objective of the formulation was to serve as a basis for designing static compensators (active power filters) without energy storage elements. Following this, alternative formulations have been proposed, although they all have a clear nexus of inspiration in the original formulation. Here the basics of instantaneous reactive power theory are presented, as well as those derived formulations have greater acceptance, especially the modified formulation of instantaneous reactive power.

Series Active Power Filters

This chapter describes the most common control strategies applicable to active filters of series connection. The behavior of the active filter in steady state is analyzed. This allows a theoretical analysis of three different control strategies: detection of the source current, detection of the load voltage, and hybrid. The analysis is performed from the point of view of the distortion produced by the load and the distortion due to other nonlinearities than those produced by the load. In addition, the state model for a series active filter has been obtained. From system state equations, behavior for the three proposed strategies is analyzed, which allows to establish design rules for each of them. The theoretical analysis is contrasted with the results obtained using different simulation examples, which have allowed, from the point of view of harmonic elimination, to establish what is the strategy and the active filter topology most appropriate for each type of nonlinear load.

Combined Shunt and Series Active Power Filters

This chapter describes the main features that can be achieved with the use of combined series and shunt active power filters. It studies the different strategies to provide balanced, sinusoidal, and regulated voltages at the load terminals, as well as to obtain balanced sinusoidal supply currents in phase with the supply voltages. These targets allow us to define the structure and control calculations of a unified power quality conditioner (UPQC). The analysis of the state- space model will show the behavior of the conditioner to tune the components and control parameters. This analysis is contrasted with the results obtained in simulation and experimental cases. The power flow control and the voltage regulation in power systems with the unified power flow controller (UPFC) are also revised here. This can be combined with the tasks of the UPQC to design a universal active power line conditioner (UPLC). The control implementation and a practical case are developed to show its behavior.

Introduction to Power Quality from Power Conditioning

This chapter begins with an introduction to the concept of power quality, which has developed into a discipline that defines the reference parameters for assessing the suitability of the waveforms of voltage and current of an electrical system, so allowing compatible operation of all equipment that constitutes that system. Different standards set limits on the allowed disturbances of voltage and current source. Some disturbances that occur in an electrical network are due to the presence of nonlinear loads. A model based on the equivalent Norton of a load is presented, in order to develop a theoretical analysis of the system when this load type is present. Furthermore, an update of compensation equipment configurations most common in the technical literature is given, including active power filters. This equipment has proven effective in the dynamic compensation of nonlinear loads.

Shunt Active Power Filters

Progress in the technologies of electronic devices, and the DSP techniques has made possible the use of active power filter (APF) to correct the lack of electric power quality (EPQ). An APF uses a power converter to produce harmonics that cancel the load current harmonics, and in general, all the undesired components of the load current. The development and subsequent implementation of APFs have made it possible to compensate reactive power, unbalance currents, and harmonic currents, which results in a more generic term to designate them: active power line conditioners (APLC). Compensation strategies, simulation models, and practical developments are explained.

Hybrid Filters: Series Active Power Filters and Shunt Passive Filters

In this chapter, three control strategies for a combination of series active filters and parallel passive filters (SAPPF) are analyzed. These strategies are: control by source current detection, control by load voltage detection, and hybrid control. These strategies are analyzed in steady state. The theoretical analysis is made by considering two types of nonlinear loads with a dual distorting behavior: harmonic current source loads and harmonic voltage source loads. Additionally, a state space model for the hybrid filter configuration, SAPPF, is obtained. With this model, the behavior of the filter set is analyzed considering the three compensation strategies; and some design rules are established for each control strategy. The theoretical analysis has been contrasted with the results obtained with various simulation cases. An experimental prototype is designed to verify the behavior the hybrid filter.

Electrical Power Terms in the IEEE Std 1459 Framework

Apparent power is one of the magnitudes of more use and application in the field of electrical power. Its meaning in balanced three-phase systems is clear, however under conditions of imbalance and distortion there is no unanimous consensus. IEEE Standard 1459 attempts to resolve this issue with the proposal of a definition based on the effective voltage and current, and a partition of the effective apparent power that has three useful features: (a) the fundamental apparent power is conveniently separated from the nonfundamental apparent power, (b) provides a useful measure of harmonic “pollution” by the nonfundamental apparent power, and (c) provides a measure of the imbalance from the introduction of unbalanced fundamental apparent power. In this chapter the development of power terms in the most general conditions of asymmetry and distortion within the IEEE Std. 1459 is exposed.

Evaluation of the Distortion and Unbalance Emission Levels in Electric Networks

Electrical disturbances have important economic consequences for the consumer and the utilities, a fact which increases from the new electricity regulatory framework. Thus, Electric Power Quality, EPQ, has now become a priority within the field of electrical engineering. Power-quality deterioration is due to transient disturbances (voltage sags, voltage swells, impulses, etc.) and steady state disturbances (harmonic distortion, unbalance, and flicker). Among these are the so-called periodic disturbances such as distortion of the voltage and current waveforms, or unbalanced three-phase systems, [1-2]. This chapter is focused specif‐ ically on harmonic and unbalance phenomena.