Armando Bellini

A Microcomputer-Based Optimal Control System to Reduce the Effects of the Parametric Variations and Speed Measurement Errors in Induction Motor Drives

A control methodology is presented for induction motor drives which makes it possible to reduce effectively the dependence of the stator flux and current both on the motor parametric variations and on the error on the motor angular speed measurement. To this aim, also the determination of the slip has been inserted in the closed-loop control system, and an optimization technique proper to bilinear systems has been applied. Then, a possible structure of the microcomputer-based controller is described, and the obtainable performances are examined by digital simulation.

Performances of a PLL based digital filter for double-conversion UPS

In uninterruptible power supplies (UPS) using an automatic bypass switch, to reduce the transients due to the switch commutations, it is convenient that the voltage waveforms produced by the inverter are synchronized with the grid ones. In three-phase UPS, the inverter controller employs, as reference signals, the components of the grid voltage phasor, referred to a fix reference frame, suitably multiplied by an amplitude correction factor. Generally, the reference signals are affected by harmonics and amplitude unbalances. Therefore, improper synchronization between the inverter outputs and the grid voltages can arise. To improve the synchronization, many solutions based on a phase locked loop (PLL) system have been proposed in literature. The paper proposes a different PLL structure employing a Steady-State Linear Kalman filter (SSLKF), based on a third-order linear and time-invariant observation model. Such filter is able to provide an accurate tracking of the grid voltage phasor also in critical operating conditions. The paper describes, at first, different PLL structures and then the proposed architecture based on a prediction-correction filter and its implementation on a DSP controller. Finally, a comparison, obtained by simulation, with traditional filters and some significant experimental results on a pre-production prototype are carried out.

MPPT algorithm for current balancing of partially shaded Photovoltaic modules

Among Renewable Energy Sources (RES), Photovoltaic (PV) sources represent an attractive solution because the solar energy is accessible everywhere; moreover, the price per watt of PV modules is going on decreasing. The output voltage furnished by a PV module is quite low; therefore, a series connection of different modules have to be employed in order to obtain a sufficient output dc voltage. In non-uniform irradiation conditions of a PV array, the traditional Maximum Power Point Tracking (MPPT) algorithms can converge to a relative maximum point; besides, the total power produced by the array can be lower than the sum of the maximum powers that could been produced by each module. To increase the power produced by partially shaded PV, is necessary to employ a power converter structure able to impose to each module of the PV array a different current value. The paper proposes a non-conventional MPPT algorithm able to maximize the photovoltaic energy supplied by partially shaded PV modules. To validate the algorithm, a comparison with a conventional architecture has been performed pointing out that the proposed configuration produces more power when the solar irradiation of the shaded module is greater than 20–30% of the other modules irradiation.

A digital filter for speed noise reduction in drives using an electromagnetic resolver

The measurement of the rotation speed is an important issue in closed-loop industrial drives. The motor speed is often calculated by a derivative operation of the position measure obtained by an electromagnetic resolver. As a consequence, especially at the lowest speeds, the noise overlapped to the measured speed is significant and a suitable filter becomes necessary. The paper presents a solution to such a problem based on the employment of a stationary Kalman filter, suitably inserted in a phase locked loop structure. The implementation in an industrial synchronous motor drive, using a 16-bit fixed point DSP, has confirmed the goodness of the proposed solution.

Implementation on a microcontroller of a space vector modulation technique for NPC inverters

The recent improvements in semiconductor technology made rather interesting the employment of the new high current-high voltage IGBTs in the inverters used in traction drives. At first, their utilization was limited to the drives for trams or regional trains, but now they are also becoming attractive for high-speed traction locomotives. For these applications, however, neutral point clamped (NPC) inverters must be used, to reduce the maximum drop voltage on the IGBTs. Authors have already been analyzed the problems connected to the development of modulation techniques useful for NPC inverter and, in a recent paper, they presented a first proposal of an interesting space vector modulation technique based on a six hexagons subdivision of the three-phase plane. The proposed technique preserves the advantages of the SVM used in traditional two-level inverters: to this aim, all the commutations can happen only between adjacent states so that, during each modulation interval, only three commutations occur. In present paper, the proposed approach is further improved, taking into consideration the problems connected to the movement from a hexagon to the next one, in such a way to preserve the previously mentioned adjacencies. Finally, the paper describes the procedure used for implementing the modulation procedure on a modern microcontroller.

Realization of a control device for a robotic manipulator based on nonlinear decoupling and sliding mode control

The realization of a control system for a robotic manipulator is described. The control scheme is subdivided into two hierarchical levels: the inner level performs the output decoupling of the joint dynamics: the outer one computes the desired accelerations. The decoupling, obtained by a simplified compensator and a sliding mode technique, is realized by means of analog circuits, while the tracking of the desired trajectories is performed by a digital computer. The description of measurements and tests is included. >

Resonant DC-DC converters for photovoltaic energy generation systems

Renewable energy generation systems, based on photovoltaic sources, currently represent the most suitable solution, for low power levels, to reduce the energy consumption produced by oil and gas. Moreover, they are becoming more and more attractive as the price per watt of the photovoltaic modules is decreasing. However, the conversion efficiency of commercial photovoltaic modules is still rather low so it is particularly important to be able to achieve, in every operating situation, the maximum possible energy. The paper focuses on double-stage, grid-connected, Photovoltaic conversion systems. In this frame, different structures of resonant DC-DC converters, which allows reduced switching losses, are analyzed accounting the specific behavior of Photovoltaic sources.

Robust PLL Algorithm for Three-Phase Grid-Connected Converters

Abstract The estimation of the grid angle is a key factor in the control of many power electronics applications using grid-connected three-phase converters. The knowledge of the grid angle is required for different goals such as the synchronization of the voltage or current waveforms produced by the converter to the utility grid, the power flow management and the reduction of the transients generated on grid failures or on the reconnection of the converter. Generally, the grid voltages are polluted with harmonics and affected by amplitude unbalances; thus, oscillation on the grid angle signal can lead to an improper synchronization between the converter outputs and the grid voltages. To improve the synchronization, the paper proposes a robust PLL structure employing a prediction-correction filter based on a second-order linear and time-invariant observation model. Such filter is able to provide an accurate tracking of the grid voltage angle also in critical operating conditions. The paper describes also the implementation on a low cost fixed-point DSP controller and a comparison, obtained by simulation, with traditional filters. Finally, some significant experimental results validate the performances of the proposed approach.

A Zero-Voltage transition full bridge DC-DC converter for photovoltaic applications

The paper focuses on a high efficiency Zero Voltage Transition (ZVT) DC-DC full-bridge converter using a high-frequency transformer. A novel structure with recovery of energy on load side is proposed. Such solution is particularly suitable for photovoltaic applications which require low losses and cannot recovery energy on source side. Moreover, a suitable architecture of snubber circuit that permits to improve significantly the efficiency is discussed. Analysis of its operating modes and a comparison of the conversion efficiencies with conventional ZVT-PWM converters are given. Design example of a 750 W 100 kHz DC-DC converter and different PSPICE simulation tests are provided.

On the Selection of the Commutating Instants in Induction Motor Drives

The main auxiliary phenomena are considered which arise in the drives using a frequency-controlled induction motor supplied by a three-phase bridge inverter as an actuator. Particularly, three quality indexes connected with these phenomena are taken into account and, for different drives, the commutating instants, which separately optimize the quality indexes, are determined. Lastly, a comparison among the optimum values of the quality indexes makes it possible to obtain simple variation laws of the commutating instants, which shows the overall behavior of the drive.