L.G.B. Rolim

Analysis and Software Implementation of a Robust Synchronizing PLL Circuit Based on the pq Theory

This paper presents the analysis and software implementation of a robust synchronizing circuit, i.e., phase-locked loop (PLL) circuit, designed for use in the controller of active power line conditioners. The basic problem consists of designing a PLL circuit that can track accurately and continuously the positive-sequence component at the fundamental frequency and its phase angle even when the system voltage of the bus, to which the active power line conditioner is connected, is distorted and/or unbalanced. The fundamentals of the PLL circuit are discussed. It is shown that the PLL can fail in tracking the system voltage during startup under some adverse conditions. Moreover, it is shown that oscillations caused by the presence of subharmonics can be very critical and can pull the stable point of operation synchronized to that subharmonic frequency. Oscillations at the reference input are also discussed, and the solution of this problem is presented. Finally, experimental and simulation results are shown and compared

A DQ Synchronous Reference Frame Current Control for Single-Phase Converters

This paper presents a current control using the dq synchronous reference frame for single-phase converters. This control method consists in transforming an orthogonal pair composed by the actual single-phase input current and a fictitious current, from a stationary to a rotating frame. The steady state current components in dq frame become DC instead of AC values so a zero error current control can be implemented. A single-phase PFC boost rectifier is used as an example application of this control. To validate the control method simulation and experimental results are presented

Torque ripple minimization in a switched reluctance drive by neuro-fuzzy compensation

A simple power electronic drive circuit and fault tolerance of converter are specific advantages of SRM drives, but excessive torque ripple has limited their use to special applications. It is well known that controlling the current shape adequately can minimize the torque ripple. This paper presents a new method for shaping the motor currents to minimize the torque ripple, using a neuro-fuzzy compensator. In the proposed method, a compensating signal is added to the output of a PI controller, in a current-regulated speed control loop. Numerical results are presented in this paper, with an analysis of the effects of changing the form of the membership function of the neuro-fuzzy compensator.

Proposition of an offline learning current modulation for torque-ripple reduction in switched reluctance motors: design and experimental evaluation

A new offline current modulation using a neuro-fuzzy compensation scheme for torque-ripple reduction in switched reluctance motors is presented. The main advantage of the proposed technique is that the torque signal is unnecessary. The compensating signal is learned prior to normal operation in a self-commissioning run, capturing the necessary current shape to reduce the torque ripple. Simulation results verify first the effects of speed and then load changes on the compensator performance. Implementation of the proposed technique in a laboratory prototype shows the feasibility and accuracy of the respective offline scheme.

Fuzzy logic control of a switched reluctance motor

This paper presents the use of fuzzy logic control (FLC) for switched reluctance motor (SRM) speed. The PLC performs a PI-like control strategy, giving the current reference variation based on speed error and its change. The performance of the drive system was evaluated through digital simulations through the toolbox Simulink of the Matlab program.

Flywheel Energy Storage System Description and Tests

This paper presents test results of a flywheel energy storage system (FESS) prototype. The bearing system is composed of a superconducting magnetic thrust bearing (SMB) and a permanent magnet bearing (PMB). The SMB was built with Nd-Fe-B magnet and YBCO superconducting blocks. The PMB has the function of positioning radially the switched reluctance machine (SRM) used as motor/generator and reduce the load over the SMB. The SRM drive is responsible to convert electrical into mechanical energy, and vice versa. The prototype still operates at low speeds, but the dynamical simulations of the SRM drive showed that the system can work at high speed, supplying the required energy during disturbances. In the tests performed with the FESS prototype, the system took or delivered energy from/to the grid when requested.

Development and Experimental Tests of a Simple Neurofuzzy Learning Sensorless Approach for Switched Reluctance Motors

Despite becoming competitive with ac and dc machines, the necessity for a shaft position transducer makes switched reluctance (SR) machines lose their low cost advantage, mainly as low power machines such as fans and pumps. Many techniques have been proposed for indirect rotor position detection for SR machines. However, their characteristics can be summed up as being based on a lookup table plus an interpolation algorithm, making them specific to a particular machine. For economic reasons and also dynamic performance, sensorless algorithms need a learning mechanism to allow them to adapt to a new SR machine or even adapt to changes in the SRM parameters. This paper presents a novel methodology for position sensor elimination for SR machines. Using the voltage from each conducting phase and the reference current signal as inputs, the rotor speed is first obtained as the output of a neurofuzzy learning system used as a “virtual” speed sensor. Then, the rotor position is determined by integrating the estimated value of speed. The effectiveness of the proposed sensorless technique was investigated through a series of real-time experiments on an SR drive system. The experimental results show that the suggested “virtual” speed sensor and corresponding rotor position can operate well in a sensorless SR speed control system.

Voltage sags compensation using a superconducting flywheel energy storage system

This paper presents a voltage sag compensator, which uses a flywheel energy storage system with superconducting magnetic axial thrust bearing (SMB) and a permanent magnet radial bearing (PMB). The SMB was built with Nd-Fe-B magnet and YBCO superconducting blocks, refrigerated with liquid Nitrogen. The magnets are assembled with magnetic flux shapers in order to increase the levitation force and the stiffness. The radial PMB is used to positioning the vertically arranged switched reluctance machine (SRM) used as motor/generator. Simulations of the power electronics and SRM show that the system can work up to 30,000 rpm supplying the required energy during disturbances.

Analysis and software implementation of a robust synchronizing circuit PLL circuit

This paper presents the analysis and software implementation of a robust synchronizing circuit - PLL circuit - designed for using in the controller of active power line conditioners. The basic problem consists in designing a PLL circuit that can track accurately and continuously the positive-sequence component at the fundamental frequency and its phase angle, even when the system voltage of the bus, to which the active power line conditioner is connected, is distorted and/or unbalanced. The fundaments of the PLL circuit are discussed. It is shown that the PLL can fail in tracking the system voltage during the startup, under some adverse conditions. Moreover, it is shown that oscillations caused by the presence of sub-harmonics can be very critical and can pull the stable point of operation synchronized to that sub-harmonic frequency. Oscillations at the reference input are also discussed, and the solution of this problem is presented. Finally, experimental and simulation results are shown and compared.

A new current control for the STATCOM based on secondary order generalized integrators

This paper presents a new current control for the STATCOM equipment (static synchronous compensator) based on secondary order generalized integrator (SOGI). This algorithm will become the STATCOM current control a very robust, fast and simple control strategy. These control characteristics are desirable, considering the new grid connection codes for renewable energy applications. The proposed control strategy is done at stationary reference frame, thus both the Clarke transformation and the instantaneous power theory are utilized. The SOGI algorithm is implemented in the main control and the PWM loop control, which have the objective of supplying the current references and supplying the states of the converter switches to apply the current that fulfil the requirement controls, respectively. In this work is presented the application of this algorithm in both control stages of the STATCOM. In order to verify its performance, computational simulations and experimental results will be shown.