Isaac Soares de Freitas

Fault tolerant control of five-phase AC motor drive

This paper investigates the voltage and current control of a five-phase induction motor drive under fault conditions. The control strategies allow for continuous and disturbance free-operation of the drive without any additional hardware connections at the occurrence of complete loss of one or two legs of the inverter or motor phases. The control presented here is oriented to open loop torque control strategies (e.g., Volts/Hz control), but can be very useful for direct torque control or even field oriented control strategies. A complete analysis of voltage and current controls are presented. Experimental and simulation results demonstrate the validity of the proposed systems.

Reduced-Switch-Count Six-Leg Converters for Three-Phase-to-Three-Phase/Four-Wire Applications

Two reduced-switch-count ac/ac dc-link six-leg converters are investigated in this paper. The proposed topologies allow for three-phase-to-three-phase power conversion to supply a three-phase four-wire load without any capacitor dc-link-midpoint connection. The converters provide bidirectional power flow and power-factor control. Pulsewidth modulation techniques are derived by using the concept of local and general apportioning factors. The overall control strategy for providing dc-link voltage and power-factor control is presented. A control strategy to obtain the maximum utilization of the dc-link voltage is also proposed. In addition, several relevant characteristics of the converter are addressed, such as voltage analysis, distorted and unbalanced voltages operation, shared-leg currents, power rating, and total harmonic distortion. The proposed converters are compared to six-leg converters that use the capacitor dc-link-midpoint connection and also to the full-bridge seven-leg converter. Experimental and simulated results are presented

A Carrier-Based PWM Technique for Capacitor Voltage Balancing of Single-Phase Three-Level Neutral-Point-Clamped Converters

In this paper is presented a PWM technique for single-phase neutral-point-clamped converters for capacitors voltage balancing. The technique is based on the injection of a common mode voltage signal into the sinusoidal modulating signals of the conventional carrier-based pulse width modulation. Although several strategies have been reported for such a problem by using the voltage signal injection, the proposed method is very simple with easy implementation. It is presented a set of equations to demonstrate how the injected voltage signal introduces a dc component on the neutral-point current, which can be controlled in order to allow the capacitors voltages balancing. Selected results have been used demonstrate the effectiveness of the proposed strategy.

Three-Phase-to-Three-Phase AC/AC DC-Link Five-Leg Converters Based on Three- and Two-Level Legs

The five-leg back-to-back converter shares a leg between the grid and load sides. In the conventional five-leg converter, all legs are of same type, i.e., either two- or three-level legs. This paper presents topologies of five-leg converters based on the combination of two- and three-level legs. The proposed configurations permit one to obtain intermediary characteristics between the five-leg converter with all three-level legs and that with all two-level legs. The choice of the number of two- and three-level legs and how combine them are shown in order to obtain some characteristics of the grid- and load-side converter voltages. The modeling of the system and the pulsewidth-modulation strategy based on carrier-based and space-vector approaches is presented. Analysis of the total harmonic distortion and power switches losses are also addressed to characterize the configurations. Experimental and simulated results show the system feasibility.

An integration algorithm for induction motor stator flux estimation with DC offset compensation

This paper presents an integration algorithm for induction motor stator flux estimation. The proposed algorithm is able to solve the problems associated with pure integrators and operates over a wide speed range. The estimated and the actual stator flux are indirectly compared by using the estimated electromagnetic torque and the measured load torque.

AC-DC-AC nine-phase machine drive system based on H-bridges and three-leg converters

This paper presents an ac-dc-ac reversible nine-phase machine drive system. The grid side converter is composed of Y-connected single-phase bridges. As the machine is composed of three three-phase groups, a three-leg converters are connected separately to each group. The topology does not make use of input isolation transformers and reduces the power processed by converter switches when compared to that of conventional two-level converter. Moreover, harmonic distortion in voltages generated by the grid side converter is reduced when compared to conventional two-level converter. The model and the control strategy have been developed. Simulation and experimental results are also presented.

A stationary stator reference frame control of DFIG under unbalanced voltage conditions

In this paper a control strategy of a wind turbine based on Doubly-Fed Induction Generator (DFIG) supply with unbalanced grid voltage is presented. In the proposed control strategy, the rotor side converter (RSC) is able to keep sinusoidal stator and rotor currents and also remove the pulsations in either stator active power or stator reactive power (this case eliminates the oscillation in electromagnetic torque). Unlike the other reported techniques, rotor currents scheme has been implemented in the stationary stator reference frame. These currents are regulated by a synchronous controller (similar to resonant type) without any positive or negative component decomposition. Simulation results are presented.

Applied control strategy in a micro system interconnected between a renewable energy source and a single-phase electric power

In this paper is presented a synchronous reference frame control strategy applied to a single-phase microgrid system connected to a renewable energy power source. The control strategy aims to regulate active power flow and to optimize the power factor at the point of common coupling (PCC). The whole control system is carried out on the synchronous reference frame of the PCC voltage. On this frame the direct current is responsible for active power regulation while the quadrature one regulates power factor. The direct current is used to regulate the dc-link voltage of the single-phase converter, consequently keeping the active power balance on the system. Experimental results are presented to demonstrate the system feasibility and effectiveness.

Fault tolerant high performance drive system using six-phase induction machine

In this paper is presented a fault tolerant drive system based on Six-Phase Induction Machine (SPIM) with both Direct Torque Control - DTC and Indirect Field Oriented Control-IFOC strategies. The system is mainly comprised by a six phase Voltage Source Inverter (VSI) and a Six-phase Induction Machine (SPIM). Simulation and experimental results are addressed to support the conclusions.

A PWM Strategy with Reduced Bearing Currents for Five-Phase Motors

The problem of bearing currents in ac motor drive systems can be mitigated by proper selection of the PWM strategy. In this paper, a modulation strategy to reduce the bearing currents in five-phase electric machines is studied.