Mihaita Linca

On the cascade control system tuning for shunt active filters based on modulus optimum criterion

This paper focuses on the control system for the output current and voltage across the DC capacitor of a three-phase shunt active filter. A classical PI-PI cascade control solution is taken into consideration. The design of both inner current loop and outer voltage loop is based on Modulus– Optimum criterion. It is pointed out that this tuning approach provides a good phase margin. In order to finalize the voltage controller tuning, the passband of the unity feedback system is imposed. Simulations were performed under Matlab-Simulink environment and the results are presented to show the effectiveness of such tuning technique. Moreover, the experimental results agree with the simulated waveforms of the current supply.

Conservative power theory implementation in shunt active power filtering

This paper analyzes the current decomposition, in three-phase, three-wire systems, based on the Conservative Power Theory (CPT), and the application of these components in the active filtering. The CPT current decomposition gives the active component of the current, the reactive component, which can be compensated or not and the void current. It does not give the asymmetry current component, separately. For this reason, the active shunt compensators based on the CPT have the capability of compensating only parts of the non-active current, as needed. The reactive component can be compensated or not, but the void current, which contains the harmonic content, is normally compensated. A problem of the CPT, latter resolved, is the asymmetry current component which was not included in the first definitions. The aim of this paper is to analyze the performance of an experimental active compensator based on the early CPT definitions and a comparative study with the performances of the same compensator based on the improved CPT definitions.

Orthogonal reference frame based methods in three-wire active power line conditioners: Practical evaluation under unbalanced load and nonideal voltage conditions

This paper is concerned with the practical implementation of some orthogonal reference frame based methods in the control of a shunt three-phase three wire active power line conditioner in order to compensate unbalanced nonlinear loads under nonideal voltage conditions. The first two developments are based on the components of voltage and current space vectors in the orthogonal stationary reference frame associated with the p-q theory of the instantaneous reactive power. They allow obtaining either unity power factor or perfect harmonic cancellation after compensation. Other two developments are based on the current components in the orthogonal rotating reference frame d-q with axis d in the direction of the voltage vector, which is specific of the id-iq method. This time, the compensation target is the total compensation through the perfect harmonic cancellation. The control algorithms were first modelized and tested by simulation under Matlab/Simulink. Then, experimental tests were conducted on a dSPACE platform based on DS1103 controller board for modern rapid prototyping. The compensating performance, in terms of harmonic distortion factor, unbalance factor, global power factor and displacement power factor, are analyzed for each situation. All the results prove that the desired compensation goals can be achieved through the conceived algorithms and the proposed practical implementation.

The synchronous fundamental dq frame theory implementation and adaptation for the active filtering

The synchronous fundamental dq frame is a time domain method derived from the space vector transformations of three phase systems. While these methods had been extensively used for the analysis of three phase circuits this particular method is suitable for the active filtering. This is because it obtains the non-sinusoidal current fundamental which can be used for the compensating current computation. The compensation result of this method is a sinusoidal grid current, not in phase with the grid voltage, so only the distortion component of the current is compensated, the reactive component has to be compensated by an external circuit, or absorbed from the power grid. In order to compensate the reactive current this method can be adapted to compute not only the load current fundamental, but also the active component of the load current fundamental. Another adaptation of this method is the unity power factor compensation, which implies that the compensated current has the same shape and phase with the grid voltage, so the active power is transported not only on the voltage fundamental, but also on the voltage harmonics. The implementation of this method and its adaptations on an active filtering system are the objectives of this paper.

Study of energetic performances of a power static converter with current-source and parallel resonance inverter for induction heating applications

This paper analyses the energetic performances of an induction heating system for a pipe rolling machine, based on a single-phase current inverter. The study was based both on the real system experimental measurements, as well as on the equivalent Simulink model of the system. The obtained simulation results performed on the measured experimental conditions confirmed the validity of the virtual system. At the same time, the system structure was adopted for a given inductor corresponding to the rolling plant, and for a set of typical pipes. For each pipe, the compensating capacitor value was chosen according to the working frequency corresponding to the thickness of the processed pipe, the resonance frequency of the reactive circuit being equal to the working frequency. The aim of the paper was the performance analysis of the system as well as the power quality analysis at the grid side and at the load side of the system.

Energy-Efficient Inverter-Fed Induction Motor Driving System

This paper deals with energy optimal control of variable induction motor drive which operates at constant mechanical power. At given steady-state operation point, the optimum efficiency is achieved by adapting the voltage- frequency correlation so that the active power absorbed by the motor is minimal. But, the minimum active power depends on the modulation strategy of the voltage inverter. In this paper, the search of optimum active power was achieved for pulse trains modulation strategy which simply allows developping high torques at low shaft speeds with respect to V/radicf control. The analysis reveals the energy efficiency improvement through the new optimal control. It is quantified on 2.6 kW motor drive how much energy optimal control can improve the system efficiency compared with constant V/radicf control. Several numerical results followed by some experimental verifications show that an efficiency improvement is obtainable by this optimal control.

Limitations of LCL filter for three-phase shunt active power filters in active traction substations

The main goal of this paper is to underline the limitations of LCL interface filter used in three-phase shunt active power filter for active traction substations. Starting from the two main functions that should be fulfilled by the interface filter, i.e. let them unchanged the current harmonics that must be compensated and stop harmonics due to inverter switching, it is shown that they can not be met and that the only viable solution is to achieve a compromise between the two. The analysis carried out is based on the transfer functions of currents and creates the premises to elaborate the design algorithm to achieve the most appropriate compromise between the two requirements.

Virtual instrumentation for no-load testing of induction motor

The main objective of this paper is to solve a practical and current problem, by taking advantage of the virtual instrumentation in testing electrical machines. The abilities of virtual instrumentation are used to data acquisition, measurement and analyze the values of no-load testings parameters for three-phase induction motor. The virtual measurement system bench is designed and consist from two principal components: the hardware components (six LEM transducers for measuring three voltages and three currents; elements for signal conditioning and power transducers; USB multifunction Input / Output module; a personal computer) and the software components (operating system for the computer; drivers for the acquisition and manipulation of data; virtual instrument for calculation and graphical presentation of results). The LabVIEW graphical programming environment is used for designing virtual instrument. This virtual measurement system bench is an easy to use device which can be used in engineering education laboratories from universities or in electrical machines testing workbenches; it is capable of data acquisition, storage or memorization on different media, visualization of different graphs or analysis on-line or off-line of the results obtained. The virtual measurement system described in the paper can work independently (in the Simulation mode or Real time Acquisition mode) or integrated as part of a future complex virtual system for measurement and analysis in the domain of electrical machines testing workbenches.

The performances of an active filtering and regenerative system for DC railway traction substations

This paper presents the performances of filtration and regeneration system for DC traction substations equipped with 12 pulse series rectifier, that allows connection of the system directly to the secondary of the traction transformer. Modeling of the whole system and vehicle - DC line assembly was done in Matlab-Simulink, and on this basis, were determined the performances, both as filtering and in regeneration mode.

Transient Response Analysis of Shunt Active Power Compensators under Asymmetric Voltage

This paper analyzes the dynamic response of a shunt active compensator, in three-phase, three-wire systems, based on the dSpace DS1103 control board and using the Conservative Power Theory for the compensating current computation, in non-sinusoidal and unbalanced conditions. The active filtering system was investigated both by simulation and experiment, the virtual filtering system being equivalent to the experimental one. The load under test was a balanced full-wave rectifier supplied from an unbalanced voltage source. The voltage unbalance was obtained by inserting a resistor between the grid and load on one phase, the absorbed current creating voltage unbalance, and also important voltage distortion.