Manuel Guerreiro

A Speed Controller for a Two-Winding Induction Motor Based on Diametrical Inversion

The objective is to control the speed of a single- or two-phase induction motor using diametrical inversion (DI) of the stator voltages. DI is a particular reversal of the sequence phases characterized by replacement of the voltage phasor by another that is diametrically opposed to it and rotating in the opposite direction. Every DI is provoked by a change in the sign of the simplest switching function (speed error) of a sliding mode. These changes cause jumps of 180° of the stator voltage phasor and successive discontinuities of its angular velocity. The main and auxiliary windings are always connected, the speed-error sign decides the rotating field direction, and so, the actual rotor velocity can be reduced (braked) or increased (accelerated). The motor is fed by a rectifier associated with a three-phase inverter. The common point of the windings is connected to the inverters middle leg, which is switched at high frequency with a duty cycle of 50%. The core of the drive command is a 16-b dsPIC device, which receives the speed-error sign and generates the appropriate pulsewidth modulated signals to the three-phase inverter. Matlab/Simulink simulation and experimental results showed a good performance of the speed controller based on the DI.

A Sensolrless Speed Control System for an Electric Vehicle without Mechanical Differential Gear

Two DC motors drive the two independent rear wheel of an electric vehicle with electric differential. The speed estimation of each wheel drive is based on the voltage equation which requires the voltage and armature current measures and a previous knowledge of the machine parameters. The current limitation and the speed control of the DC motors are determined by the result of a logical function, thus PI controllers are unnecessary. The overall control strategy is guaranteed by a single microcontroller, PIC18F452

Anti-slip wheel controller drive for EV using speed and torque observers

A wheel slip controller of an electric vehicle with two independent rear wheel drives is presented. The vehicle dynamic model and the proposed torque controller for the DC motors are also presented. The speed and torque observer solution proportionate the necessary external torque estimation to the anti-slip wheel controller. The wheel slip is based on the comparison of the real vehicle velocity and the estimated velocity given by the speed observer.

A Sensorless PMDC Motor Speed Controller with a Logical Overcurrent Protection

A method to control the speed or the torque of a permanent-magnet direct current motor is presented. The rotor speed and the external torque estimation are simultaneously provided by appropriate observers. The sensorless control scheme is based on current measurement and switching states of power devices. The observers performances are dependent on the accurate machine parameters knowledge. Sliding mode control approach was adopted for drive control, providing the suitable switching states to the chopper power devices. Despite the predictable chattering, a convenient first order switching function was considered enough to define the sliding surface and to correspond with the desired control specifications and drive performance. The experimental implementation was supported on a single dsPIC and the controller includes a logic overcurrent protection.

A Transformer Differential Relay Based on a Multiple Park Transformation

Discrimination between an internal fault and a magnetizing inrush current has been recognized as a power transformer protection problem, since can cause malfunction of a differential relay. To overcome this problem the paper proposes a new approach for transformer differential protection. This approach is based on the Park transformation of the differential currents. Using this technique each harmonic that must be used for the protection will be converted in a dc component. So, one of the advantages of this approach is that the proposed algorithm does not require a very high computational effort. The evaluation of this technique is performed by a Matlab/Simulink-based simulator. From the obtained results it is possible to verify that the relay can correctly discriminates magnetic inrush from an internal fault.

Three-phase multilevel inverter based on LeBlanc transformer

A new power conversion structure for a three-phase multilevel inverter is proposed in this paper. This structure uses a LeBlanc transformer and three single-phase voltage source inverters. The power converter topology has two single-phase outputs that connect to the LeBlanc transformer. This transformer allows deriving two-phase voltage to a three-phase source. This multilevel power conversion structure allows obtaining a five-level three-phase inverter. To control the proposed converter a sliding mode controller with a vectorial modulator was used. Simulation results of the proposed converter structure with their control system are presented. From the obtained results it possible to confirm the voltage multilevel waveforms and the effectiveness of the proposed control system technique.

Dynamic voltage restorer using a multilevel converter with a novel cell structure

Voltage sags and swells have a severe impact on sensitive loads. To overcome this problem Dynamic Voltage Restores (DVR) are often used. The DVR is very attractive due to its potential for fast dynamic response to sags disturbances. In this paper, a new multilevel power converter structure for the DVR is proposed. This structure uses three single phase inverters and one three-phase inverter. In this way, a power converter with a five level output voltage is obtained. To control the proposed multilevel power converter a sliding mode controller is used. This control system presents important characteristics such as fast dynamic response and robustness to external perturbations. Several computer simulation results are presented in order to verify the proposed DVR structure.

Power electronics didactic modules for direct current machine control

Several didactic modules for an electric machinery laboratory are presented. The modules are dedicated for DC machinery control and get their characteristic curves. The didactic modules have a front panel with power and signal connectors and can be configurable for any DC motor type. The three-phase bridge inverter proposed is one of the most popular topologies and is commercially available in power package modules. The control techniques and power drives were designed to satisfy static and dynamic performance of DC machines. Each power section is internally self-protected against misconnections and short-circuits. Isolated output signals of current and voltage measurements are also provided, adding versatility for use either in didactic or research applications. The implementation of such modules allowed experimental confirmation of the expected performance.

Unity power factor isolated three-phase buck-boost rectifier based on scott transformer

In this paper it is proposed a unity power factor isolated three-phase rectifier with buck-boost characteristics. This rectifier is based on the scott transformer and only uses two single-phase buck-boost rectifiers. In this way only two switches are used. To achieve sinusoidal input current and high power factor, a fast and robust pulse with sliding mode modulation of the input current is proposed. An output voltage compensator is also used to establish the amplitude of the reference currents. Several results are presented in order to show the effectiveness of the proposed rectifier.

A phasor speed control of a single or two phase induction motor

This paper is focused on the speed control of a single or two phase induction motor using a diametrical inversion (DI) of the stator voltages. The changes in the speed error sign are responsible for each DI which inverts the stator voltage phasor and its angular velocity. The main and the auxiliary windings are always connected and thus the speed error sign allows to determinate the rotating field direction. The motor is fed by a rectifier associated with a three-phase inverter. The core of the drive command its a 16-bit dsPIC device, which receives the speed error sign and generate the appropriate PWM reference voltages signs to the three-phase inverter. Simulation and experimental results allow assume a good performance.