Manuele Bertoluzzo

Development of Electric Propulsion Systems for Light Electric Vehicles

This paper presents two light electric vehicles (LEVs) with a electric propulsion system developed at an academic laboratory. One LEV is an electric city scooter powered by a lithium-ion battery pack and propelled by a wheel motor drive. The other LEV is an electric bicycle powered by a fuel cell system with the assistance of a supercapacitor bank. Power and energy design of the electric propulsion systems of the two LEVs as well as characterization of the energetic devices are illustrated.

Direct torque control of an induction motor using a single current sensor

A novel scheme for the direct torque control (DTC) of an induction motor (IM) is proposed, which uses a single sensor of current inserted in the inverter dc link. The rationale behind the proposal is to develop a low-cost but high performance IM drive. The scheme exploits a simple and robust algorithm to reconstruct the stator currents needed to estimate the motor flux and torque. The algorithm operates in two stages: first, it predicts the stator currents from a model of the motor and then adjusts the prediction on the basis of the sensed dc-link current. Experimental results are given to demonstrate the ability of the scheme in reproducing the performance of a traditional DTC IM drive.

Design and Experimentation of WPT Charger for Electric City Car

Wireless power transfer systems (WPTSs) with inductive coupling are advantageously used to charge the battery pack of electric vehicles. They basically consist of coil coupling, power supply circuitry connected to the transmitting side of the coil coupling, and power-conditioning circuitry connected to the receiving side of the coil coupling. This paper presents the design and implementation of a wireless power transfer (WPT) battery charger for an electric city car. A short overview on the working principles of a series-series resonant WPTS is given before describing in detail the design procedure of the power circuitry needed for its operation, i.e., an alternating-current-direct-current converter cascaded by a high-frequency inverter in the transmitting section and a diode rectifier cascaded by a chopper in the receiving section. The coil coupling with spiral coils is designed with the help of a finite-element-method code. A prototype of the WPT battery charger is built up according to the design results, and experiments that validate the design procedure are carried out.

Performance analysis of a high-bandwidth torque disturbance compensator

Recent availability of encoder with millions of counts per revolution makes it possible to enlarge the bandwidth of the torque disturbance observer (TDO) equipping a servo drive. As a consequence, the TDO dynamics are no more decoupled from those of current and the behavior of the torque disturbance compensator (TDC) is influenced by the current dynamics as well as by the discrete-time implementation of TDO. The purpose of this paper is to analyze the TDC performance under the above-mentioned circumstances. The main outcome is the underdamped or even unstable behavior of TDC. Another outcome is the limited range of values allowable for the parameter mismatch to preserve stability. The conditions on the TDO bandwidth and the parameter mismatch for TDC to be stable and to be damped are provided. Experimental tests are given, which substantiate the theoretical findings.

Control schemes for steer-by-wire systems

Steer-by-wire (SbW) systems are candidate to replace the conventional steering equipment in the new generation of vehicles. The task of a SbW system is twofold: turning the steered wheels by tracking the handwheel rotation and providing the driver with a feeling of the steering effort. In this paper, the design of the control scheme for SbW systems is faced. Two schemes are considered: one is derived from the model of conventional steering equipment whilst the other one exploits the features of a SbW system to cope with the interaction of the steered wheels to the road surface. Implementation of the control schemes on a test vehicle is described and experimental results are given.

Lumped Track Layout Design for Dynamic Wireless Charging of Electric Vehicles

Dynamic wireless charging (DWC) of electric vehicles (EVs) is an emerging technology that could lead to the breakthrough of EVs. The technology is based on the inductive coupling between an electrified track deployed under the road surface and a pickup coil fitted in EV. This paper refers to a lumped track made of DD coils and is concerned with the design of the track layout, namely coil dimension in the motion direction and track coil distance for a given energy requirement. This paper starts by comparing the coupling characteristics of DD coils with different dimensions by a finite-element method (FEM) analysis. Afterward, an analytical procedure is developed to establish the track coil distance able to transfer to a moving EV the propulsion energy required per unit of traveled space. The procedure utilizes the DD-coil coupling characteristics to calculate the power and, from it, the energy transferred from the track coils to the pickup coil along the track. Instrumental in the calculation is the definition of a parameter, denoted as track flux coverage, which gives the ratio between the dimension of the track coils in the motion direction and the coil distance; such a parameter corresponds to the percentage of road populated with track coils so that it is a cost index of the DWC system implementation. Effects of a lateral displacement of the EV motion from the line joining the track coil centers are also analyzed. Design findings are checked against the results obtained with a computer-assisted analysis.

A Direct Torque Control Scheme for Induction Motor Drives Using the Current Model Flux Estimation

The paper deals with a direct torque control (DTC) scheme for Induction Motor (IM) drives where flux and torque of the motor are estimated by the IM current model instead of by the voltage model. The scheme is intended to enable operation of the DTC IM drives at zero speed. As a return, its implementation requires the knowledge of speed, rotor time constant and inductive parameters of the motor. In the paper the performance of the proposed scheme is studied for a drive equipped with an incremental encoder and commanded with a constant flux. Using the position information delivered by the encoder, a suitable representation of the current model is formulated that makes the drive operation feasible at true zero speed. Operating with a constant flux command, the variations in the rotor time constant dominate over the other parameters; their effect on the drive behavior is analyzed in steady state founding that the motor flux and torque are deviated from the references of a quantity, which is a function of the torque reference. Experimental results are given to substantiate both the capabilities of the scheme of developing the full torque at a standstill and the theoretical findings on the drive behavior under rotor time constant mismatch.

An assessment of the inverter switching characteristics in DTC induction motor drives

The switching characteristics of an inverter feeding an induction motor controlled with the direct torque control (DTC) technique are assessed in steady state. At first, the application share of the inverter voltage vectors for the stator flux covering half a sextant is defined and predicted. The prediction indicates that, under operation at fixed inverter dc link voltage and stator flux magnitude, the application share depends only on the supply frequency of the motor and, to a small extent, on the load. Afterwards, the inverter transitions and the corresponding phase commutations within a stator flux sextant are analyzed. The outcome of the analysis permits to compute the commutations of the inverter phases in one turn of the stator flux and, from them, the inverter switching frequency is obtained. Its value is influenced by the sampling interval and the control delay arising from the microprocessor implementation of DTC. For given sampling interval and control delay, it is shown that the inverter switching frequency depends on the same quantities as the application share of the inverter voltage vectors. A comparison with the switching characteristics of an inverter controlled with the space vector modulation technique is carried out. At last, the paper discusses the sensitivity of the switching frequency of an inverter for DTC to the following quantities: inverter dc link voltage, sampling interval and control delay. Throughout the paper simulation and experimental results are given to confirm the theoretical findings.

Neural network technique for the joint time-frequency analysis of distorted signal

Nonstationary distorted signals need to be analyzed in both the time and frequency domains to determine their characteristics. In this paper, a technique based on a neural network (NN) is presented which has the merit of providing such an analysis in real time. After arranging a suitable NN, the algorithm utilized to carry out the analysis is illustrated. Then, expressions assessing the dynamic behavior and the steady-state accuracy of the technique are derived. From the expressions, the influence of the NN parameters on the technique performance is readily recognized. As an example, the technique is applied to the analysis of the time evolution of the current harmonics absorbed by a diode rectifier and the results are compared with those obtained by the short-time Fourier transform.

Torque Ripple-Free Operation of PM BLDC Drives With Petal-Wave Current Supply

Further to the vector analysis in the stationary plane of the behavior of a permanent-magnet brushless dc (PM BLDC) drive, this paper proposes a method of synthesizing the current supply of the motor that ensures torque ripple-free operation of the drive. The synthesis is carried out analytically by the vector approach, and the resulting current vector is then expressed in motor phase coordinates. It comes out that the current vector has a petal-shape trajectory in the stationary plane. The operation of the drive with such a current supply is extensively examined; in particular, the torque capability for an rms value of the phase currents equal to the rated one, the requirements for the voltages to be applied across the motor terminals, and the base speed in correspondence to the supply voltage saturation are determined. At last, experimental traces obtained from an in-wheel PM BLDC drive used for the traction of light electric vehicles are included to corroborate the theoretical findings.