Active filtering of electric power has now become a mature technology for harmonic and reactive power compensation in two-wire (single phase), three-wire (three phase without neutral), and four-wire (three phase with neutral) AC power networks with nonlinear loads. This paper presents a comprehensive review of active filter (AF) configurations, control strategies, selection of components, other related economic and technical considerations, and their selection for specific applications. It is aimed at providing a broad perspective on the status of AF technology to researchers and application engineers dealing with power quality issues. A list of more than 200 research publications on the subject is also appended for a quick reference.

A review of active filters for power quality improvement

Fast Fourier Transform

There has been considerable interest in the development and applications of active filters because of the increasing concern over power quality, at both distribution and consumer levels, and the need to control reactive power and voltage stability at transmission levels. The existing approaches are classified and assessed to provide a framework of references for both researchers in this field and for generators, suppliers and consumers of electrical power who are, or may be, concerned about the problems associated with power quality and are considering installing active filters for their particular sets of problems.

Active power filters: a review

Power processing systems will be a key factor of future photovoltaic (PV) applications. They will play a central role in transferring, to the load and/or to the grid, the electric power produced by the high-efficiency PV cells of the next generation. In order to come up the expectations related to the use of solar energy for producing electrical energy, such systems must ensure high efficiency, modularity, and, particularly, high reliability. The goal of this paper is to provide an overview of the open problems related to PV power processing systems and to focus the attention of researchers and industries on present and future challenges in this field.

Reliability Issues in Photovoltaic Power Processing Systems

Multiloop control strategies have commonly been used to control power inverters of both the voltage-source and current-source topologies for power conversion applications including uninterruptible power supplies and utility interfaces for distributed power generation. However, these control strategies tend to be developed and comparatively evaluated for a particular application, with strategies for other applications presented as independent new developments. This paper presents a generalized analysis of different multiloop control approaches using alternative feedback control variables for several popularly adopted system configurations, highlighting similarities and identifying a generalized optimal control-variable selection criterion that is applicable across most multiloop-controlled inverter systems. The generality of the presented optimal variable selection criterion has been verified through the close similarities between the time-domain waveforms of the different inverter systems simulated in MATLAB Simulink and implemented experimentally in the laboratory.

Analysis of multiloop control strategies for LC/CL/LCL-filtered voltage-source and current-source inverters

A novel pulse-width-modulated (PWM) control technique for AC choppers is proposed that has the advantages of enabling linear control of the fundamental component of the output voltage and complete elimination of its harmonics up to a specified order Theoretical comparisons are made with other basic PWM techniques, and the computed performance indicates the superiority of the present method The carrier wave required for the new technique is easily determined as a modification of a basic triangular wave that enables these beneficial features to be obtained over the full range of chopper operation and can be implemented by the storage of relatively simple control equations An experiment has verified the feasibility of the method as applied to the control of a single-phase automatic voltage regulator In the experiment, the modified triangular carrier wave is used to generate the required PWM switching function Good agreement is obtained between the calculated and experimental results >

An improved PWM technique for AC choppers

A step-up/down AC voltage regulator is proposed, in which a tap-changing transformer and a pulsewidth modulation (PWM) AC chopper are combined. The proposed regulator can step up or down the output voltage to input voltage. Also, the proposed regulator restrains more harmonics of output voltage compared to the conventional PWM regulator. The input current flows continuously in the proposed regulator, while it flows discontinuously in the conventional PWM regulator. Through digital simulation, several characteristics are investigated theoretically and then compared with those of conventional schemes. Practical verification of the theoretical predictions is presented to confirm the capabilities of the proposed regulator.

Step-up/down AC voltage regulator using transformer with tap changer and PWM AC chopper

A BLDC motor with the characteristics of high speed and high power density has been more widely used in industrial areas. As for the design of the motor drive system, a simulation method has been used for the drive system, and the controller of the BLDC motor has become more complicated and precise. The torque characteristic of a BLDC motor is a very important factor in the design of the motor drive system, so it is necessary to predict the precise value of torque, which is determined by the back EMF waveform. The conventional simulation model of BLDC motor is obtained by approximation of real back EMF waveform to ideal trapezoidal waveform. But as the shapes of slot, skew and magnet of BLDC motor are various subject to design purposes, the real back EMF waveform is to some degree deviant from the ideal trapezoidal waveform. As a result, when using the ideal trapezoidal waveform, the error occurs. As a consequence, in order to lessen such an error, the model of the BLDC motor with a real back EMF waveform is needed instead of its approximation model. In this paper, for the reduction of error in simulation, a new simulation model of the BLDC motor with nearly real back EMF waveform is proposed and through the simulation, the validity of the proposed model is shown for a three-phase BLDC motor.

A new simulation model of BLDC motor with real back EMF waveform

Torque ripple generated in the commutation period is the main drawback of the brushless DC (BLDC) motor, which deteriorates its precision. Many methods to solve this problem have been studied. In many control methods, torque ripple reduction was considered at the point of current control, which means that if current can be controlled properly, the BLDC motor does not produce any torque ripple. In this paper, the authors propose that torque ripple in the commutation period of a BLDC motor is inevitable, even if the current control is successful. A torque model, considered with decaying phase back EMF, is introduced and the causes of commutation torque are analyzed. The influence of commutation time on torque ripple and the relationship between commutation time and speed are introduced. This paper deals with torque ripple reduction of a BLDC motor from the viewpoint of commutation time and gives a theoretical background to reduce it.

Analysis of torque ripple in BLDC motor with commutation time

Generally current controllers of three-phase PWM power converters have been implemented in the synchronous frame because the synchronous frame controller can eliminate steady state error and has fast transient response by decoupling control. However most of such controllers have been designed under balanced input voltage. Therefore such designed current controllers showed undesirable current control characteristics under unbalanced conditions because the current reference is distorted by the second order harmonic voltage due to negative sequence. In this paper, a current controller for a PWM power converter, considering unbalanced input voltage, is designed and verified by both simulation and experiment.

Gyu-Ha Choe

Papers

An improved PWM technique for AC choppers

Step-up/down AC voltage regulator using transformer with tap changer and PWM AC chopper

A new simulation model of BLDC motor with real back EMF waveform

Analysis of torque ripple in BLDC motor with commutation time

Design of current controller for 3-phase PWM converter with unbalanced input voltage