Maurice Fadel

Modeling of multilevel converters

In this paper, the imbricated cells multilevel converters are studied and modeled from a control viewpoint. These converters make use of several switches connected in a series, which allows using switches with reduced voltage ratings; these low voltage switches have lower conduction losses and can switch at higher frequency. In addition to this feature common to all converters using series connected switches, the control signals of multilevel converters can be phase shifted to increase the apparent switching frequency and improve the dynamic performances of the whole converter. It is shown that a multilevel inverter leg, composed of p pairs of switches and p-1 capacitors, forms a multivariable nonlinear system that cannot be properly modeled by standard methods such as state-space averaging. The transient behavior of this system depends on the current harmonics and their phase shift with the different control signals. A specific model is detailed, studied, and used to illustrate the properties of these converters. In particular, the natural balancing of the voltage across the switches is demonstrated and the time constants involved in this process are determined.

Multicell converters: active control and observation of flying-capacitor voltages

The multicell converters introduced more than ten years ago make it possible to distribute the voltage constraints among series-connected switches and to improve the output waveforms (increased number of levels and apparent frequency). The balance of the constraints requires an appropriate distribution of the flying voltages. This paper presents some solutions for the active control of the voltages across the flying capacitors in the presence of rapid variation of the input voltage. The latter part of this paper is dedicated to the observation of these voltages using an original modeling of the converter.

Fault Diagnosis in Industrial Induction Machines Through Discrete Wavelet Transform

This paper deals with fault diagnosis of induction machines based on the discrete wavelet transform. By using the wavelet decomposition, the information on the health of a system can be extracted from a signal over a wide range of frequencies. This analysis is performed in both time and frequency domains. The Daubechies wavelet is selected for the analysis of the stator current. Wavelet components appear to be useful for detecting different electrical faults. In this paper, we will study the problem of broken rotor bars, end-ring segment, and loss of stator phase during operation.

A Predictive Control With Flying Capacitor Balancing of a Multicell Active Power Filter

Unlike traditional inverters, multicell inverters have the following advantages: lower switching frequency, high number of output levels, and less voltage constraints on the insulated-gate bipolar transistors. Significant performances are provided with this structure which is constituted with flying capacitors. This paper deals with a predictive and direct control applied to the multicell inverter for an original application of this converter: a three-phase active filter. To take advantage of the capabilities of the multicell converter in terms of redundant control states, a voltage control method of flying capacitor is added, based on the use of a switching table. Flying capacitor voltages are kept on a fixed interval, and precise voltage sensors are not necessary. The association of predictive control and voltage balancing increases considerably the bandwidth of the active filter.

Digital Predictive Current Control of a Three-Phase Four-Leg Inverter

While the classical control techniques for three-phase two-level four-leg inverters are based on pulsewidth modulation or 3-D space vector modulation, this paper presents a simple digital current control strategy without the modulation stage. The proposed controller uses the discrete nature of the four-leg inverter and filter to generate the switching states. Using a predictive cost function, the optimal switching state to be applied in the next sampling interval is selected. The proposed controller offers excellent reference tracking with less current harmonic distortion for balanced and unbalanced loading conditions. The feasibility of the proposed strategy is verified by digital implementation on a dSPACE DS1104-based rapid prototype platform.

Direct Control Strategy for a Four-Level Three-Phase Flying-Capacitor Inverter

A direct predictive control strategy is proposed for a three-phase four-level flying-capacitor (FC) inverter in this paper. The balancing of the FC voltages, a challenge in applications with small capacitors and low switching frequencies, is done without any modulation, simply using tables calculated offline. These allow the realization of fast-dynamics output currents with reduced dv/dt in the output voltages and reduced switching frequencies. Moreover, no interharmonics are created when operating at low switching frequencies and with reference currents containing multiple harmonic components, which is a key feature for active power filters. Simulations and experimental results are presented to demonstrate the excellent performance of the direct control strategy in comparison with a conventional pulsewidth-modulation control technique, mostly for operation at low switching frequencies.

Mono inverter dual parallel PMSM - structure and control strategy

This paper presents a dual parallel connected PMSM fed by a single power inverter. Both motors have to respect the synchronism even if they have different load torque. The rotor position of the two motors i.e. the load applied on each motor are consequently permanently compared. The motor with the highest load is set as the master one and is auto-piloted. The other one which has the same applied voltage has the same electric pulsation and so the same speed rotation. The change of the master choice is done whereas the load applied on the machine is changing so that oscillations appear during this change. The steady state is however rapidly attained and the synchronism stays always observed.

Sensorless control of PMSM based on extended kalman filter

This paper proposes a sensorless control system based on extended Kalman filter (EKF) for permanent magnet synchronous motors (PMSM). The EKF equations are built in rotor flux oriented synchronous coordinate, so it can easily be used for either non-salient or salient pole motors. Inertia and other mechanic parameters are not needed in this observer. Rotor speed and position can be estimated exactly and then a sensorless control system is built. The initial rotor position and the mechanic parameters are not needed in this system. By some compensation in observer equations, the observer can be always stable and has only one expected equilibrium point. So the motor can start up from any unknown initial positions.

A new approach to Predictive Torque Control with Dual Parallel PMSM system

An original approach to Predictive Torque Control “Split and Seek” (PTC SS) for Mono-Inverter Dual-Parallel Permanent Magnet Synchronous Machines (PMSM) system is presented. Only one cost function for both PMSM is defined to be minimized through the PTC approach. Unlike the Master-Slave classical control, solution of the cost function will depend on both PMSM references. The principle of this approach is to extend the possibilities of control by offering additional virtual vectors and to find the vector which minimizes the cost function. This process includes two steps: first one is searching for the angle and second one is searching for the magnitude. A model of the system is used to predict the behavior in the next sampling interval under these different virtual voltage vectors. After that, space vector modulation (SVM) technique will be applied to synthesize this vector. Simulations were built under Matlab/Simulink software to verify the applicability of this new approach. The obtained results verify the synchronism of two machines and the correct current tracking under different load and speed conditions. The performance improvement is highlighted from specific tests.

A Rotor Speed and Load Torque Observer for PMSM Based on Extended Kalman Filter

This paper proposed a state observer based on extended Kalman Alter (EKF) for the rotor speed and load torque observation of permanent magnet synchronous motor (PMSM). This observer can be used to estimate the precise rotor position and rotor speed in the servo systems with only optical encoder of limited accuracy. By using the observed rotor speed and position instead of the values got directly from the encoder, the speed and position control performances can be greatly improved. The observer can also give the load torque which can be used as the feedforward compensation of the speed PI controller. The compensation can greatly improve the speed control performance during load torque change. The extended Kalman filter is used to solve the nonlinear equation of the observer, considering the influence of the parameter errors and the noise in measurement. So it is very robust to the parameter errors.