Jaime Prieto

Compensation in nonsinusoidal, unbalanced three-phase four-wire systems with active power-line conditioner

For three-phase four-wire circuits, two compensation criteria have been established: one based on the instantaneous value concept and the other on the average value concept. Thus, according to the instantaneous value concept the non instantaneous power current is reduced, without altering the instantaneous active power. According to the average value concept, the nonactive average-current is reduced, without altering the average power. When the zero-sequence voltage component exists, both compensation types would not enable the zero-sequence (neutral) source current elimination. Then, two approaches are marked in this paper. The first one is for eliminating the non instantaneous power current or the nonactive average-current but the neutral current can still flow. The second one for eliminating the modified non instantaneous power current or the modified nonactive average-current, thus the neutral current component is compensated. According to recent recommendations in this work three-phase systems are considered as four-conductor systems. Experimental results are obtained to confirm the theoretical properties and to show the compensator performance.

New Distortion and Unbalance Indices Based on Power Quality Analyzer Measurements

Voltage and current waveform distortion are more prevalent on power systems today related to nonlinear loads. The proliferation of loads of this kind and their interaction with the power supply system is increasing the need to use power monitoring equipment to evaluate electric power quality. Measurements show that waveform harmonics and unbalance are variable over time due to changes in load conditions and in the system configuration. Thus, the electrical engineer has a large amount of data available from each phase, acquired using commercial Analyzers. Therefore, it is necessary to find ways to characterize this group of recorded data, to allow proper evaluation of the situation. Two indices, which can be calculated with these measurements, are proposed in this work: a three-phase total demand distortion index and a total unbalance index. In addition, this paper proposes an easy way to characterize the time-varying data to simplify their representation. The exposed procedures are applied to the data registered from an electrical power system, to show the performance of the proposed methods.

A series-parallel configuration of active power filters for VAr and harmonic compensation

A new design method for the control implementation of a combined series-shunt active power filter (load compensation active conditioner, LCAC) for electrical power quality improvement is proposed. This active conditioner allows to cancel source voltage harmonics, to symmetrize the supply voltage, and to eliminate current harmonics and reactive/unbalanced load currents. The study of the higher harmonics passive filtering behaviour has permitted an enhancement of the compensating performance of the active conditioner. Practical case results are presented to support the performance of the new control design.

A unified power quality conditioner for wide load range: Practical design and experimental results

This paper presents the obtained experimental results with a single-phase experimental prototype of a load compensation active conditioner, sLCAC. The sLCAC is composed by a series-parallel combination of active power filters, to provide a global conditioning of a load against harmonic distortion: to isolate the load voltage vL from the harmonics in the supply voltage vS, as well as to regulate it to the nominal value; and also to enhance the supply current iS, compensating the harmonic and reactive components of the load current iL. Experimental prototype results with two different types of load are presented to support the performance of the proposed design.

Practical implementation of a three-phase active power line conditioner with ANNs technology

In this paper, a new method to control an active power line conditioner (APLC) using neural networks is presented. Actually, there is an increase of voltage and current harmonics in power systems, caused by nonlinear loads. The APLCs are used to compensate the generated harmonics and to correct the load power factor. The proposed control design is a pulse width modulation control (PWM) with two blocks that include neural networks. Adaptive networks estimate the reference compensation currents. On the other hand, a multilayer feedforward network (trained by a backpropagation algorithm) works as hysteresis band comparator. An experimental prototype was built to check the proposed control performance. The practical results confirm the possibility and usefulness of controlling an APLC by means of artificial neural networks.

Practical application of the instantaneous power theory in the compensation of four-wire three-phase systems

For three-phase four-wire circuits, two compensation criteria are possible: one based on the instantaneous value concept and the other on the average value concept. Thus, according to the first method the noninstantaneous power current is reduced, without altering the instantaneous active power (time-instantaneous compensation, TIC). On the other one, according to the second method the nonactive current is reduced, without altering the average power (time-average compensation, TAC). When the zero-sequence voltage component exists, both compensation types, would not enable the zero-sequence (neutral) source current elimination. Then, two approaches are marked in this paper. The first one, is for eliminating the noninstantaneous power current or eliminating nonactive current component but neutral current can still flow. The second one for eliminating the modified noninstantaneous power current or the modified nonactive current, thus the neutral current components is compensated. Experimental results are obtained to confirm the theoretical properties and show the compensator performance.

Load compensation active conditioner for power quality

This paper presents the obtained experimental results with a single-phase experimental prototype of a load compensation active conditioner, sLCAC. The sLCAC is composed by a series-parallel combination of active power filters, to provide a global conditioning of the load against harmonic distortion: to isolate the load voltage vL from the harmonics of the supply voltage vS, as well as to regulate it to the rated value; and also to enhance the supply current iS, compensating the harmonic and reactive components of the load current iL. The control and components design of the LCAC allows to apply it to different types of load, with an efficient and robust behavior. Experimental prototype results are presented, applied to two types of non-linear loads with distorted supply voltage. The analysis of these results show the validity of the proposed design for the development of active conditioners with a wide load range in highly distorted environments

Power quality evaluation indices in three-phase networks

The large use of nonlinear and time-varying single- phase and three-phase loads produces current waveform distortion. Their interactions with the power supply system has made that the industrial electrical consumer systematically need measure equipment to evaluate the electric power quality. The measurements show that the harmonics of the waveforms and the unbalance are variable along with the time due to the changes in the load conditions and in the system configuration. Thus, due to the use of commercial analysers, the electrical users dispose of a great quantity of data from such of the three phases of the supply. Therefore, it is necessary to find a way to characterize this great group of registered data. In this work two indices are proposed: a three-phase total demand distortion index and a total unbalance index. Besides, this paper proposes an easy way to characterize, statistically, the groups of data to simplify their representation. The study carried out is applied to the data registered in an electrical power system.

Comparative analysis of compensation strategies for series APF based on the electric power dual formulation

Different electrical power formulations have been developed to improve the quality of electrical power. These developments have served to establish different strategies for the control of active power filters (APF). However, most strategies have been applied to APF of parallel connection. These type of compensators are only effective in compensating loads of the harmonic current source type (HCS). In the case of loads called harmonic voltage source (HVS) a series APF is required. The strategies proposed for parallel APFs must be reformulated so that they can be applied to the series APF topologies. In this paper, different compensation strategies based on the dual electrical power formulations are proposed for APF of series connection. A simulation platform designed for this purpose has allowed the evaluation of each strategy under different load conditions. The results obtained let to establish a comparative analysis for different load condition.

Different Approaches Assesment in Active Power Filter Compensation

In this paper, the five main formulations of the instantaneous reactive power theory have been chosen to study a nonlinear load compensation. They are p-q original theory, d-q transformation, modified or cross product formulation, p-q-r reference frame and vectorial theory. The obtention of the compensation current according to each formulation has been established. Next, the behavior of an active power filter (APF) implemented with those different control algorithms have been studied. The APF control strategies have been implemented in an experimental platform constituted by a 20 kVA power inverter and a 400 MHz digital signal processing (DSP) controller board. Results got from an unbalanced and non-sinusoidal three-phase four-wire system have been compared. The final analysis shows that, in general, the five theories present a different behavior, depending on the supply voltage, respect to the distortion. However, all of them widely decrease the waveforms distortion. Moreover, a more general compensation objective is possible. It obtains balanced and sinusoidal source current in any conditions of supply voltage