There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

The authors discuss high-voltage power conversion. Conventional series connection and three-level voltage source inverter techniques are reviewed and compared. A novel versatile multilevel commutation cell is introduced: it is shown that this topology is safer and more simple to control, and delivers purer output waveforms. The authors show how this technique can be applied to either choppers or voltage-source inverters and generalized to any number of switches.<<ETX>>

Multi-level conversion : high voltage choppers and voltage-source inverters

This paper presents a nonlinear control technique for a three-phase shunt active power filter (SAPF). The method provides compensation for reactive, unbalanced, and harmonic load current components. A proportional-integral (PI) control law is derived through linearization of the inherently nonlinear SAPF system model, so that the tasks of current control dynamics and dc capacitor voltage dynamics become decoupled. This decoupling allows us to control the SAPF output currents and the dc bus voltage independently of each other, thereby providing either one of these decoupled subsystems a dynamic response that significantly slower than that of the other. To overcome the drawbacks of the conventional method, a computational control delay compensation method, which delaylessly and accurately generates the SAPF reference currents, is proposed. The first step is to extract the SAPF reference currents from the sensed nonlinear load currents by applying the synchronous reference frame method, where a three-phase diode bridge rectifier with R-L load is taken as the nonlinear load, and then, the reference currents are modified, so that the delay will be compensated. The converter, which is controlled by the described control strategy, guarantees balanced overall supply currents, unity displacement power factor, and reduced harmonic load currents in the common coupling point. Various simulation and experimental results demonstrate the high performance of the nonlinear controller.

Correction to “Experimental Design of a Nonlinear Control Technique for Three-Phase Shunt Active Power Filter”

This paper attempts to improve the dynamic performance of a shunt-type active power filter. The predictive and adaptive properties of artificial neural networks (ANNs) are used for fast estimation of the compensating current. The dynamics of the dc-link voltage is utilized in a predictive controller to generate the first estimate followed by convergence of the algorithm by an adaptive ANN (adaline) based network. Weights in adaline are tuned to minimize the total harmonic distortion of the source current. Extensive simulations and experimentations confirm the validity of the proposed scheme for all kinds of load (balanced and unbalanced) for a three-phase three-wire system.

A Shunt Active Power Filter With Enhanced Performance Using ANN-Based Predictive and Adaptive Controllers

Since the beginning of railway electrification, power quality has been a main problem in railway networks because of their special characteristics. Many ways of power quality improvement have been investigated and applied to ac and dc traction systems through railway electrification history. This paper presents a perspective on power quality issues through railway electrification development and investigates the necessity of power quality and system requirements for appropriate power quality. Compensation strategies are classified and compared. This aims to provide a comprehensive perspective of the power quality issue in railway power/distribution networks for researchers and engineers working on railway electrification. Less than 100 research articles are referenced for researchers to obtain good background information.

Power Quality Issues in Railway Electrification: A Comprehensive Perspective

This paper proposes a combined system of a thyristor-controlled reactor (TCR) and a shunt hybrid power filter (SHPF) for harmonic and reactive power compensation. The SHPF is the combination of a small-rating active power filter (APF) and a fifth-harmonic-tuned LC passive filter. The tuned passive filter and the TCR form a shunt passive filter (SPF) to compensate reactive power. The small-rating APF is used to improve the filtering characteristics of SPF and to suppress the possibility of resonance between the SPF and line inductances. A proportional-integral controller was used, and a triggering alpha was extracted using a lookup table to control the TCR. A nonlinear control of APF was developed for current tracking and voltage regulation. The latter is based on a decoupled control strategy, which considers that the controlled system may be divided into an inner fast loop and an outer slow one. Thus, an exact linearization control was applied to the inner loop, and a nonlinear feedback control law was used for the outer voltage loop. Integral compensators were added in both current and voltage loops in order to eliminate the steady-state errors due to system parameter uncertainty. The simulation and experimental results are found to be quite satisfactory to mitigate harmonic distortions and reactive power compensation.

A Combination of Shunt Hybrid Power Filter and Thyristor-Controlled Reactor for Power Quality

This paper proposes a novel topology for a three-phase hybrid passive filter (HPF) to compensate for reactive power and harmonics. The HPF consists of a series passive filter and a thyristor-controlled-reactor-based variable-impedance shunt passive filter (SPF). A mutual-inductance design concept is used to reduce the series passive filter inductance rating. The special features of the proposed HPF system are as follows: 1) insensitivity to source-impedance variations; 2) no series or parallel resonance problems; 3) fast dynamic response; and 4) significant size reduction in an SPF capacitor. The performance of the proposed HPF system is validated by simulation, as well as by experimentation, under different load conditions. Experimental and simulation results show that the proposed system can effectively compensate all voltage and current harmonics and reactive power for large nonlinear loads.

A Hybrid Passive Filter Configuration for VAR Control and Harmonic Compensation

A comparative study of shunt hybrid and shunt active power filters for single-phase applications: Simulation and experimental validation

Multilevel inverters generate low harmonic waveforms at the output, which makes them suitable for high voltage energy conversion scheme to deliver efficient high power to the loads from renewable energy sources like photovoltaic systems which are penetrating to the electric grid nowadays, significantly. In this paper a single-phase hybrid multilevel inverter based on cascading full bridge and half bridge cells is introduced. Moreover the associated switching technique with multicarrier PWM is designed to generate five-level voltage at the output. As well, the designed switching technique allows the capacitors of the half bridge cell to have balanced voltage despite load changes. Furthermore, this study is extended to more cells using unequal DC sources to produce more voltage levels. Simulations have been performed on two and three cells to demonstrate the efficiency of the presented cascaded inverter with equal and unequal DC sources and switching technique.

Salem Rahmani

Papers

Correction to “Experimental Design of a Nonlinear Control Technique for Three-Phase Shunt Active Power Filter”

A Combination of Shunt Hybrid Power Filter and Thyristor-Controlled Reactor for Power Quality

A Hybrid Passive Filter Configuration for VAR Control and Harmonic Compensation

A comparative study of shunt hybrid and shunt active power filters for single-phase applications: Simulation and experimental validation

Cascaded multilevel inverter with multicarrier PWM technique and voltage balancing feature