L. Vaccaro

A Rogowski coil for high voltage applications

The design of a large bandwidth Rogowski probe for very high voltage applications is considered, based on the analysis of stray capacitance and shielding issues. The Rogowski is interfaced to the measuring instrument through a high CMRR instrumentation amplifier. The focus is on electric field rejection rather than insulation, that is ensured with optical or radio link. Target application is the current measurement on high voltage electric railway and power transmission and distribution lines.

A New Cascaded Multilevel Converter Based on NPC Cells

A new converter topology, which is based on the modular use of modified Neutral Point Clamped cells and suitable to supply high-power medium-voltage ac motors, is presented. The proposed structure allows a remarkable reduction of the dc-link voltage capacitors and/or of the dc-link voltage ripple, with respect to the more conventional topology, owing to the implementation of a new devised control strategy. The new structure uses only two additional controllable switch-diode couples for each basic NPC cell, with a small increment in cost and complexity of the converter system. No impact on both the load and line side is created, to the exclusion of the improvement of the load voltage waveform.

A new balancing technique with power losses minimization in diode-clamped multilevel converters

A new PWM technique, capable of achieving a correct dc-link capacitor voltages balance in Diode- Clamped Multilevel inverters, within the limits defined by the theory, is presented. This result is obtained while decreasing the switching power losses when compared to techniques based on the use of redundant switching vectors. The combined use of such a technique and of additional chopper stages permits the correct operation of the converter in all operating conditions, maximizing the energy efficiency and decreasing the cost of the additional passive and active components. A detailed explanation of the new devised PWM technique and the main results, including the evaluation of the converter efficiency in the most significant operating points, are reported.

A Novel approach for DC-link voltage ripple reduction in cascaded multilevel converters

A new cascaded multilevel converter structure is proposed, which allows a remarkable reduction of the DC-link voltage ripples, owing to the implementation of a new devised control strategy. The new topology uses only an additional controllable switch-diode couple for each basic H-bridge cell, with a small increment in cost and complexity of the converter system. Several results are presented, which confirm the validity of the proposed approach

FPGA implementation of a sensorless PMSM drive control algorithm based on algebraic method

In this paper, a new algorithm for position and speed estimation in permanent magnet synchronous motors is presented, which is based on the high frequency permanent motor model and on high frequency signal injection, using an algebraic approach and aimed to low speed range applications. High frequency injection allows, by means of simple mathematical relationships, the estimation of motor characteristic inductances. The machine inductances are characterized by a certain degree of position dependent magnetic saliency, as a function of the shaft position, in particular the mutual inductance value, which is proportional to the error between the true angle and an estimated angle value. The angle error is utilized as error signal, in a phase locked loop technique, in order to track the motor position and speed. The proposed solution has been implemented in a low cost FPGA platform.

Energy efficiency improvement in ac/dc/ac diode-clamped multilevel conversion systems

An analysis of the efficiency of AC/DC/AC diode-clamped multilevel converters is presented, where commanded and suitable variations of the DC-link voltages are proposed in order to decrease the energy losses. The study is carried out also aiming at the correct DC-link capacitor voltage balance, obtained with additional chopper stages together with a new PWM technique, considering both inverter and line-side converter behaviour in different working points. The minimum losses and the correct operation of the system are then obtained by combining the optimal operating conditions of the converters. A detailed explanation of the efficiencies evaluation and the main results are reported.

Design of a pulse generator for wideband applications

The final application is an E-field reference generator with a discrete spectrum extended above 3 GHz. This work presents a series of circuit solutions for the generation of pulses with rise time in the range of 50-250 ps and significant amplitude (above 0.5 V). The pulse generator is designed for a 50 ohm load, which will be replaced by the antenna set (short dipole or horn antenna) for E-field generation; it is driven by a high slew rate square wave local oscillator or possibly by an external generator.

Optimal operation mode for Modular Multilevel Converter based HVDC

In this paper an analytical study on the Modular Multilevel Converter architecture applied to HVDC is presented. The influence of the circulating injected currents on the converter performance is the main object of this analysis. In particular, the influence of the second and fourth harmonics circulating injected current on the capacitor voltage ripple in a general working point are object of investigation. The main four working points, inverter, rectifier, inductive and capacitive, are studied in detail.

A sensorless PMSM drive with inductance estimation based on FPGA

A new algorithm for position and speed estimation in permanent magnet synchronous motors is presented, which is based on the high frequency signal injection and uses an algebraic approach. Motor inductances are estimated by simple mathematical relationships and motor position and speed are tracked using a phase locked loop technique. The estimated machine inductances values are utilized, in real time mode, as parameters, in the field oriented control of the permanent magnet synchronous motor for an improved robustness. A sensorless drive, based on the algorithm presented, has been tested on a low cost field programmable gate array (FPGA) platform. A simple communication protocol, between host PC and FPGA board, has been designed and implemented, for algorithm parameters real time update and state observation.

Effects of the 2 nd order harmonic leg current in a MMC converter

In this paper an exhaustive analysis of the utilization of the second harmonic component of the circulating currents in a modular multilevel converter for HVDC application is presented, with the aim of highlighting the effects on the maximum arm energy ripple, i.e. capacitors voltage ripple, and on semiconductor losses. Simulation results are presented and design remarks are indicated.