Viktor Valouch

Topologies and control of active filters for flicker compensation

The paper deals with the analysis of topologies and control strategies of active filters (AF) for voltage flicker compensation. The strategies based on parallel and series active filters, both working with the reactive power compensation (without an energy storage device) have been analyzed and compared. The basic operational characteristics for the parameters of a real distribution power system with an arc furnace and a static VAr compensator have been calculated to promote the installation of an active filter for the mitigation of the voltage fluctuation. The control strategies of the active filters have been analyzed in the frequency domain as well. Neither the parallel AF nor the series AF, both working with the reactive power compensation and without the static VAr compensator (SVC), do not represent an appropriate solution in the case of the study: the parallel AF would need a high power rating, while the series AF has a too narrow working area. The combined application of the current SVC and the AF is a beneficial solution, the series AF being preferred to the parallel one for a substantial reduction of the AF power rating.

An Analytical Modelling of Three-Phase Four-Switch PWM Rectifier Under Unbalanced Supply Conditions

A new description of the three-phase four-switch converter aimed at compensating reactive power in the general case of unbalanced source voltages is proposed. A mixed p-z approach based on integral transformations (the Laplace and modified Z-transform) is suggested for obtaining solution in a closed form. The analytical procedure is verified by experimental results to confirm the effectiveness of the proposed control scheme.

Optimal control of shunt active power filters in multibus industrial power systems for harmonic voltage mitigation

The bus voltage and branch current detection control strategies of the active power filters used in industrial multibus power systems for harmonic voltage mitigation are analyzed and compared in the paper. The effectiveness of both the methods with real control gains is assessed in terms of the harmonic bus voltage mitigation and of the demanded current spectrum injected by the active power filters.

Power Control of Grid-Connected Converters Under Unbalanced Voltage Conditions

This paper presents a grid current control technique on the power converter level. The submitted analysis deals with a control method of positive and negative current sequences in a grid-connected converter during voltage sags. The control method should assure the proper exchange of active and reactive powers without power ripple, the mitigation of harmonic distortion of grid currents, and should also enable the control of grid current peaks. A simple expression is determined, which allows estimation of maximum active and reactive powers exchanged between the grid and the converter without exceeding the admissible converter current. Some simulation and experimental results are reported to validate the theoretically predicted performance of the control strategy.

Analytical Modeling and Simulation of Four-Switch Hybrid Power Filter Working with Sixfold Switching Symmetry

Shunt active power filters are nowadays used for mitigation of harmonic currents from nonlinear loads. Current and voltage harmonics have negative effects on the operation of the electric power system. Thus, a great attention is focused on harmonic generation and control. Several standards have introduced limits on current harmonics injected into the power system and on voltage harmonics at the system busbars. The paper proposes a switching strategy for a four-switch converter as used in conventional six-switch converters. The voltage source converter is controlled by a unique space-vector modulation strategy proposed. Here is presented an analytical solution for a proposed active power filter topology, simulation, and experiments results proving the proposed strategy correctness and its characteristics.

Evaluation of IRP, FBD, SD, and generalized non-active power theories

Most of modern power equipments connected to the grid must be viewed as non-linear loads producing voltage and current harmonics, subharmonics, and quasi-periodic and stochastic disturbances even under normal operation conditions. An analysis and comparison of usage of different power theories for the parallel compensation of periodic and non-periodic disturbances is presented in the paper. Different reference voltage vectors and averaging time intervals are applied in the power theories.

Cooperative Control of Active Power Filters in Power Systems without Mutual Communication

The procedure for calculating controller parameters of the APFs implemented into a multibus industrial power system for harmonic voltage mitigation is presented. The node-voltage-detection control strategy is applied and the basic controller parameters are found under the condition that the demanded THD factors at the buses where the APFs are placed will be obtained. A cooperative control of several APFs without mutual communication is proposed, simulated, and experimentally verified. By tuning the controller gains without considering the power circuit parameters, all APFs used tend to share harmonic load currents approximately equally regardless of the operation modes of the nonlinear loads in different parts of the power system.

High frequency models of transistor voltage inverter-fed induction motor drives

The paper deals with equivalent multiblock circuits of the induction motor suitable for the analysis of parasitic high-frequency currents in the common and differential modes. Theoretical considerations are supplemented by several illustrative examples aimed at computational and experimental determination of a number of different quantities such as time responses of currents in both modes in a system consisting of the PWM inverter, long cable and induction motor. Discussed are also possibilities of evaluation of interferences in parallel telecommunication and signal lines produced by current pulses in the power feeding cable.

Synchronous phasors monitoring system application possibilities

The paper deals with some tasks of advanced methods to achieve security and reliability of transmission power systems. There are discussed advanced principles and techniques in monitoring systems. The paper main part is devoted to possible applications of PMUs (Phasor Measurement Unit) and their integration into WAMPaC systems (Wide Area Monitoring, Protection and Control). Significant transmission system states were analyzed in several case studies. PMUs utilization for voltage monitoring is demonstrated for three cases - standard system state, high-load state and islanding. Here the attention is paid to the possibilities of power system observability improvement using measuring chain error elimination. Other possible applications in transmission systems include ampacity determination of transmission corridors, the calculation of line electrical parameters using synchrophasor measurement, state estimation issues and power system stability. The power system model was established for methods and algorithms verification purposes. The appropriate algorithms and their parameters were found using simulation outputs to create the local automatics, e.g. Automatic Power System Stabilizer (PSS).

Harmonic voltage mitigation in power systems by using cooperative control of active power filters without mutual communication

The procedure for calculating controller parameters of the APFs implemented into a multibus industrial power system for harmonic voltage mitigation is presented. The node voltage detection control strategy is applied and the basic controller parameters are found under the condition that demanded THD factors at the buses where the APFs are placed will be obtained. A cooperative control of several APFs without mutual communication is proposed, simulated and experimentally verified. By tuning the controller gains without considering the power circuit parameters, all APFs used tend to share harmonic load currents approximately equally regardless the operation modes of the non-linear loads in different parts of the power system.