M.C. Di Piazza

A technique for power supply harmonic impedance estimation using a controlled voltage disturbance

A method for power system impedance estimation is presented. The method employs a power converter to inject a voltage transient onto the supply system. As the technique employs controlled power electronic devices it may be used as a stand alone piece of a portable measurement equipment, or it may be embedded into the functions of an active shunt filter for improved harmonic control. The impedance is estimated through correlation of the measured voltage and current transients. Simulations and experimental results demonstrate the measurement technique is highly accurate and effective.

An Improved Active Common-Mode Voltage Compensation Device for Induction Motor Drives

This paper presents a new device for the compensation of common-mode (CM) disturbance in induction motor drives, based on the active cancellation approach. The detailed design and the experimental implementation issues of the new active compensation device for a 380-V/50-Hz pulsewidth-modulation (PWM) induction motor drive are discussed. Starting from the idea of the active common-noise canceller, the proposed active compensation device is suitably improved in order to overcome the limitations of similar previously proposed circuits. In fact, it can be successfully used within a drive system with a rated voltage of 380 V or higher by employing an improved active circuit with a dedicated dc power supply derived from the ac power supply line. In addition, the design follows the criteria of compactness and minimum cost. The performance of the realized active compensation device is verified through experimental measurements of the CM voltage, the CM current, and the motor shaft voltage. The effectiveness of the proposed solution is demonstrated by experimental results.

Real time simulation of renewable sources by model-based control of DC/DC converters

This paper presents a DC/DC buck converter circuit for real-time laboratory simulation of renewable sources. The DC/DC converter, suitably driven, can accurately describe the current-voltage characteristic of a photovoltaic (PV) array and of a fuel cell (FC). In perspective its hardware structure, if the source modelling is correctly known and implemented, can reproduce any renewable source with rated data compatible with those of the DC/DC converter. The I-V laws of the PV and the FC have been obtained by an appropriate modelling of the considered renewable sources. Particular care has been given to the design of the converter control, to ensure the desired stability and dynamics. It has been verified in numerical simulation and experimentally that the designed DC/DC buck converter is able to reproduce the electrical characteristics of the experimental generator both in steady state and transient conditions, due to either load or parameters variations. The effectiveness of the proposed circuit is verified by laboratory experiments, obtained by implementing the converter control on a low cost DSP board.

Analytical Versus Neural Real-Time Simulation of a Photovoltaic Generator Based on a DC–DC Converter

This paper presents a simulator of a PV (photovoltaic) field where the current-voltage characteristic is obtained either with a fully analytical model or with a numerical model based on a Growing Neural Gas (GNG) Network. The power stage is obtained with a DC-DC buck converter driven by the current-voltage-irradiance-temperature relation of the PV array. The improvements introduced here, respect to previous works, are the following: 1) the mathematical model is given as a continuous surface in the irradiance domain, 2) a relation between temperature and irradiance is obtained by a LSR (Leasr Square Regression) method, 3) the thermal constant of the PV field is introduced, 4) a lower number of neurons is used, 5) a better learning of the data is achieved, 6) an experimental prototype of higher rating has been devised and constructed. For both the approaches a more performing control technique of the converter has been used. Finally a PV simulator prototype is experimentally tested.

Estimation of load impedance in a power system

This paper describes a novel technique for measuring power system impedance back to source. The technique employs a power electronic converter which injects a voltage transient onto the network via an inductor. The resulting current is correlated with the disturbance voltage to determine the impedance. Simulation results indicate that this technique works effectively for various simple network topologies. As the technique employs controlled power electronic devices it may either be used as a stand alone piece of measurement equipment, or it may be embedded into the functions of an active shunt filter for improved harmonic control.

An Optimized Feedback Common Mode Active Filter for Vehicular Induction Motor Drives

This paper proposes a common mode (CM) electromagnetic interference active filter devised for application in automotive induction motor drives. The active filter is based on a feedback scheme and it is realized using linear amplifiers. It performs the compensation of the CM voltage at the motor input, allowing an increase of the drive reliability and a reduction of the harmonic content of leakage high-frequency CM currents that affect the vehicle electromagnetic compatibility. A size-optimized layout is proposed and the influence of the power linear amplifier performance on the CM voltage compensation is discussed. General guidelines for the active filter design are given and its experimental implementation is presented. Finally, the filter performance is assessed by simulations and experimental tests.

Power-Loss Evaluation in CM Active EMI Filters for Bearing Current Suppression

This paper is focused on the analysis of the power losses in a common-mode (CM) active electromagnetic-interference filter for induction-motor drives. The studied filter works according to a feedforward voltage-sensing-voltage-compensating scheme; it performs the compensation of the CM voltage at the motor terminals. In this way, the shaft voltage is dramatically reduced and the resulting bearing currents are practically eliminated. The contributions to the total power losses associated to the active filter are assessed with reference to medium-power induction-motor drives with different rated powers and switching frequencies. The single terms of power losses due to each part of the active filter are accounted for, and their dependence on the motor-drive size is addressed. Furthermore, the influence of the active-filter losses on the drive efficiency is evaluated.

Estimation of power supply harmonic impedance using a controlled voltage disturbance

A novel method for power system impedance estimation is presented. The method employs a power converter to inject a voltage transient onto the supply system. The impedance is estimated through correlation of the measured voltage and current transients. Simulations and experimental results demonstrate the effectiveness of this measurement technique.

Generalized classification of PV modules by simplified single-diode models

This paper proposes a theoretical study supporting the use of simplified single-diode photovoltaic (PV) models to accurately reproduce the behaviour of PV generators. In particular, a newly defined parameter is introduced, which allows to classify PV modules according to the possibility to neglect either the series- or the shunt resistance in the circuit model. On such a basis, equations allowing to identify the nonneglected resistance and the other unknown model parameters, are derived. The resolution of such equations is non-iterative, therefore, the proposed approach is suitable for on-line parameter identification, for example for supporting a maximum power point tracking circuit. The accuracy of the proposed method is assessed by practical cases of PV model parameter extraction.

Design of Grid-Side Electromagnetic Interference Filters in AC Motor Drives With Motor-Side Common Mode Active Compensation

The aim of this paper is to analyze how the introduction of a motor-side common mode (CM) active filter, in a power drive system, influences the CM disturbance propagation. A circuit model of the whole drive, including the active filter, is used as an investigation tool. The accuracy of all simulated results is validated by experimental measurements. Both the electromagnetic interference (EMI) toward the grid and the internal CM disturbance propagation are analyzed. These phenomena are compared when the power drive system is operated both with and without the active filter at the inverter output. An additional effect of the motor-side CM active filter is a slight reduction of EMI toward the grid at lower frequencies. This condition allows a reduction in the size of the power grid CM EMI filter necessary to achieve electromagnetic compatibility requirements compliance for the drive.