Domenico Casadei

Theoretical and experimental investigation on the stability of matrix converters

Matrix converters perform a direct coupling between two ac sources without the need for energy storage components. This characteristic, together with the presence of L-C input filters and the feedforward compensation of the input voltage variations, may determine unstable operation as the power delivered to the load exceeds a limit value. In this paper, a theoretical analysis of the stability of matrix converters is presented with the aim of predicting possible critical operating conditions. It is verified that all of the system parameters affect more or less the stability, including the delay introduced by the digital controller and the power losses. The theoretical analysis is supported by numerical simulations and experimental results carried out on a matrix converter prototype.

Theoretical and experimental analysis for the RMS current ripple minimization in induction motor drives controlled by SVM technique

In this paper, an analytical approach useful for predicting the current ripple in induction motor drives controlled by space-vector modulation (SVM) technique is presented. The analysis is applied to determine the optimal modulation technique that minimizes the rms value of the current ripple. The minimization procedure is based on the analysis of the locus described by the current ripple in the /spl alpha/--/spl beta/ reference frame. As a result, a simple equation has been obtained, which allows the online calculation of the optimal SVM switching pattern. It has been verified that it is possible to obtain a current ripple lower than that of symmetric modulation, and with a reduced number of commutations. Experimental results are provided to confirm the theoretical approach.

Common- and differential-mode HF current components in AC motors supplied by voltage source inverters

In this paper, an inverter-fed ac motor drive is analyzed in order to investigate the conducted electromagnetic interferences at both the input and output sides of the inverter. HF lumped equivalent circuits for the inverter and the motor stator windings are proposed. The overall circuit model allows time- and frequency-domain analysis to be performed with standard circuit simulators. The proposed model can also predict common- and differential-mode HF current components. The equivalent circuit is verified by experimental tests carried out on a prototype of ac motor drive.

Flux signature analysis: An alternative method for the fault diagnosis of induction machines

Intensive research efforts have been focused on the signature analysis (SA) to detect electrical and mechanical faults of induction machines. Different signals can be used: voltage, current, flux and power. In the case of current signals (CSA), the interpretation of one-phase current spectrum or the three-phase current space vector spectrum provides direct information on the presence of abnormal conditions. With proper operative condition, a similar interpretation can be obtained by using flux sensor (FSA). In this paper, it is proved that a simple external leakage flux sensor is more efficient than the classical motor current signature analysis (MCSA) to detect both stator and rotor faults in induction machines.

Simulation of a doubly-fed induction machine for wind turbine generator fault analysis

For modern large wind farms, it is more and more interesting to design an efficient diagnostics system oriented to wind turbine generators based on doubly-fed induction machine (DFIM). In this paper, a complete system will be analyzed by suitable simulations to deeply study fault influence and to identify the best diagnostic procedure to perform predictive maintenance. All the research efforts have been developed on different signature analysis (XSA) in order to detect or to predict electrical and mechanical faults in wound-rotor induction machines. They will be applied on wind turbine generators and their effectiveness will be studied.

A novel modulation strategy for matrix converters with reduced switching frequency based on output current sensing

The performance of matrix converters is strictly related to the modulation strategy adopted to control the state of the switches. In this paper a novel modulation strategy, based on the measurement of the output currents, is presented and discussed. The proposed strategy allows sinusoidal input and output currents to be obtained, like the well-known space vector modulation or Alesina-Venturini Modulation. However, compared to those modulation strategies, it requires a lower number of switch commutations for cycle period, thus leading to a sensible reduction of the converter switching losses and of the effects related to the switching dead time. Furthermore, the maximum voltage transfer ratio can be preserved. The modulation strategy is theoretically derived using the duty-cycle space vector theory that represents a systematic approach towards the modulation problem for matrix converters. Simulation results are also given.

Power balancing of a multilevel converter with two insulated supplies for three-phase six-wire loads

A multilevel converter topology feeding three-phase open-end winding loads is considered in this paper. The scheme is based on two insulated DC supplies, each one feeding a standard two-level, three-phase inverter. A three-phase, six wires load is connected across the output terminals. A new modulation technique able to regulate the sharing of the output power between the two DC sources within each switching cycle is presented. The performance of the whole system has been verified by numerical simulations

Power quality improvement and uninterruptible power supply using a power conditioning system with energy storage capability

A power conditioning system with energy storage capability is proposed as a viable solution for improving the quality and the reliability of the electric energy supply. Several tasks can be performed at the same time, such as reactive power compensation, current harmonic reduction, and smoothing of pulsating loads. Moreover, the power conditioning system can operate as an uninterruptible power supply during short time interruptions of the grid supply. The proposed system is a flexible structure that can be coupled to several energy storage devices like batteries, flywheels, supercapacitors, superconductive magnetic energy storage systems. In order to show the power conditioning system performance, experimental tests have been carried out using a flywheel as storage device. The effectiveness of the proposed control system has been successfully verified in several operating conditions of the grid supply and of the load.