P. C. Cortizo

Speed control of permanent magnet motors using sliding mode observers for induced EMF position and speed estimation

This paper presents a speed control system for a permanent magnet synchronous motor (PMSM) in which the sliding mode technique is used to estimate the induced EMF, rotor position and speed. The electrical dynamic equations of PMSM are modified to obtain the sliding mode observer model and then the variables are estimated by using only measured stator currents and voltages. Firstly, the observer of the induced EMF is implemented using analog devices. Taking the output signals of this observer, the estimated speed and position variables are numerically calculated. Information on the induced EMF is used for the implementation of feedforward action in the current loop. Speed and position information are used for speed loop control and variable transformations, respectively. Simulation results of these observers are presented. Experimental results confirm the good performance of the closed loop speed control using the proposed observer.

Comparative analysis of power LEDs dimming methods

Light emitting diodes (LEDs) have many features that make them very attractive for use in lighting. The main features that stand out is its small size compared to incandescent and fluorescent lamps. Also, they have high luminous efficiency, long lifetime and are resistant to shocks and vibrations, which contributes to increasing their reliability. This paper presents a current source for Power LEDs. As the luminous intensity of LEDs is directly related to the direct current flowing through them, this source must have characteristics of current source. Two methods of dimming LEDs are analyzed: continuous variation of current and pulse width modulation (PWM). These methods are implemented, tested and compared. A current loop to control the current through the LEDs is designed to keep the current in the LEDs always constant, so that the luminous flux emitted by them does not change.

Electronic Ballast for High Pressure Sodium Lamps without Acoustic Resonance via Controlled Harmonic Injection Synthesized with PWM

This paper presents a study and analysis of a electronic ballast for high pressure sodium lamps followed by simulation and experimental results. The acoustic resonance control technique consists in the injection of current harmonics fed to the lamp, which are synthesized by the full bridge inverter via PWM through an LC filter. The controlled harmonic spectrum of current supplied has been used in order to avoid acoustic resonance. Another interesting feature of this approach is the reduction of the crest factor of the lamp current. Acoustic resonance happens when the inverter is operating in high frequency, which has certain advantages as the use of smaller and less costly passive elements, although the switching losses increase and acoustic resonance may occur. The use of currents with harmonics is a way of avoiding the excitation of this resonance due to the frequency spread. The LC filter design is also presented, which allows the desired harmonics to pass with controlled amplitudes, while filtering undesired high frequency components. Furthermore, simulation and experimental results of the proposed electronic ballast are presented to verify the analytical discussions and the design specifications

Sliding mode control for current distribution in DC-to-DC converters connected in parallel

This paper presents a novel control scheme for current distribution in parallel connected DC-to-DC converters. It uses a sliding-mode controller (SMC) to achieve both output current equalization and output voltage regulation. The controller improves the dynamic performance of a parallel buck converter: the output voltage is robust against load disturbances and the output currents are very well equalized. An analysis and design of the sliding mode controller is developed. Simulation and experimental results are presented, showing a good dynamic performance of the control scheme proposed.

Passivity-based control of PFC boost converter with high-level programming

This paper presents a procedure for high-level programming of a microcontroller using passivity-based control implemented in PFC (Power Factor Correction) boost converters. This is a non-conventional approach, where libraries are used to directly interface with the Texass DSP 2812. Initially, the block diagrams that contain the control equations are constructed. Then, the codes are generated automatically. The advantages provided by the proposed method are: economy of development cycle time, easy understanding of the control process and programming, standardization and concurrent simulation. The other contribution of the paper refers to the development of a regulated source with high power factor and low THD using a boost converter controlled via passivity-based method. The approach based on passivity has been studied recently due to clear advantages in view of disturbances in the operation conditions of the system. The purpose of this technique is to improve the converter efficiency in applications of low and medium power, and improve the quality of the energy in the grid. Finally, in a new and satisfactory way, this nonlinear control technique has been validated experimentally for boost converters.

PLL-based repetitive control applied to the single-phase power factor correction using boost converter

The low frequency ripple in single-phase power factor correction (PFC) boost converters dramatically limits the bandwidth in standard control strategies, deteriorating the overall system performance. This paper presents the study and the implementation of a Phase-Locked Loop (PLL)-based repetitive controller in order to improve the dynamics and the input current distortion in a PFC boost converter. The repetitive control applied to the PFC presents a straightforward implementation with satisfactory results when compared to other techniques, as described in the paper. Experimental results validate this claim.

Acoustic Resonance Rejection via Voltage Modulation Method for HPS Lamps

A voltage modulation method in order to prevent acoustic resonance (AR) in HPS lamps is presented. Two voltage modulation techniques via PWM inverter are proposed. The first one injects harmonic components in the lamp voltage reference. The second one consist of high frequency voltage modulated by a low frequency waveform. These techniques allow the control of crest factor other than rejecting the AR.

Sliding mode controller for parallel connected inverters

This paper presents a control scheme for output voltage regulation and output current sharing in parallel connected inverters using sliding mode control. The theoretical analysis and design of the sliding mode controller are presented. Simulation results are also presented which show the behavior of the system under load disturbances, considering parametric differences between inverters.

Power system stabilizer for comunicationless parallel connected inverters

In this paper, small-signal stability issues of low-voltage parallel-connected voltage source inverters without control interconnections are addressed by means of dynamic analysis and experimentations. The studies performed showed that the parallel system damping is severely reduced when the traditional droop method is employed and the cabling is long. This paper proposes the application of the PSS (Power System Stabilizer) action to the control of parallel inverters in order to increase the stability range concerning the connection impedance composition R/X. It is shown that the PSS action can significantly improve the system damping. Experimental results for two 1kVA inverters in parallel sharing a common load are presented and corroborate the presented ideas.

Application of modular multilevel converter for HVDC transmission with selective harmonics

The modular multilevel converter (MMC) is based on the cascaded interconnection of half-bridge switching sub-modules. It features modular characteristics that allow its expandability while providing high quality voltage and current output waveforms and removing the need for bulky passive filters. This paper proposes a control technique and two modulation techniques for the modular multilevel converter. For the first time a multiple cuts ellipsoidal algorithm is used in order to find the switching angles for the selective harmonic elimination (SHE PWM).