Multilevel converters are considered today as the state-of-the-art power-conversion systems for high-power and power-quality demanding applications. This paper presents a tutorial on this technology, covering the operating principle and the different power circuit topologies, modulation methods, technical issues and industry applications. Special attention is given to established technology already found in industry with more in-depth and self-contained information, while recent advances and state-of-the-art contributions are addressed with useful references. This paper serves as an introduction to the subject for the not-familiarized reader, as well as an update or reference for academics and practicing engineers working in the field of industrial and power electronics.

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Multilevel Converters: An Enabling Technology for High-Power Applications

Multilevel converters are considered today as the state-of-the-art power-conversion systems for high-power and power-quality demanding applications. This paper presents a tutorialonthistechnology,coveringtheoperatingprincipleand the different power circuit topologies, modulation methods, technical issues and industry applications. Special attention is given to established technology already found in industry with more in-depth and self-contained information, while recent advances and state-of-the-art contributions are addressed with useful references. This paper serves as an introduction to the subject for the not-familiarized reader, as well as an update or reference for academics and practicing engineers working in the field of industrial and power electronics.

Multilevel Converters: An Enabling Technology for High-Power Applications Multilevel converters generate voltage and current waveforms of improved quality, that can be used to power drives for trains and other vehicles, and many other applications.

The main objective of this two-part state-of-the-art paper called “Recent Advances in the Design, Modeling, and Control of Multiphase Machines” is to present latest contributions in the multiphase machines' field. The first part of this paper focuses on the recent progress in the design, modeling, and control, whereas the drive is in healthy operation. This second part presents relevant contributions in two not analyzed fields. The first is in relation with the use of the additional degrees of freedom of multiphase machines and the exploitation of their fault-tolerant capabilities without adding extra hardware. The second one analyzes multiphase generation, particularly in grid-connected wind energy conversion systems and stand-alone applications. Recent progresses are shown and open challenges and future research directions are discussed.

Recent Advances in the Design, Modeling, and Control of Multiphase Machines—Part II

The use of AC electrical machines in controlled electrical drive applications is reviewed. The major types of electrical machines are briefly summarized to set the context and establish the physical basis for the control techniques used. Machine properties, which are the key to successful control, can be obscured by the necessary mathematics required for machine analysis and control scheme derivations. The main focus of this paper is on control techniques which are being applied to make AC drives a rapidly growing area. Development of the control is discussed, with concentration on recent trends suitable for practical applications in the industry with good dynamic behavior. A particular feature is the increasing importance of speed or position sensorless techniques.

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Controlled AC Electrical Drives

Impedance-source networks cover the entire spectrum of electric power conversion applications (dc-dc, dc-ac, ac-dc, ac-ac) controlled and modulated by different modulation strategies to generate the desired dc or ac voltage and current at the output. A comprehensive review of various impedance-source-network-based power converters has been covered in a previous paper and main topologies were discussed from an application point of view. Now Part II provides a comprehensive review of the most popular control and modulation strategies for impedance-source network-based power converters/inverters. These methods are compared in terms of theoretical complexity and performance, when applied to the respective switching topologies. Further, this paper provides as a guide and quick reference for researchers and practicing engineers in deciding which control and modulation method to consider for an application in a given topology at a certain power level, switching frequency and demanded dynamic response.

Impedance-Source Networks for Electric Power Conversion Part II: Review of Control and Modulation Techniques

A pulsewidth modulation (PWM)-controlled active filter generates harmonics at the switching frequency and its multiples in the RF range, and the concentrated power spectrum may produce electromagnetic interference (EMI) problems. In this paper, the random PWM (RPWM) technique is applied in order to spread the noise spectrum over a wide range, thus, considerably reducing the amplitudes of these harmonics and the consequent EMI problems. To study the operation of active filters, the case of an ac/dc converter along with a power-factor corrector is considered as a nonlinear load and a series active filter, respectively. A line impedance stabilization network is used to study the RF noise emanating from the converter. A noise model to study the EMI emission is presented and used in this paper. Theoretical analysis of the RF noise power spectrum is carried out in order to demonstrate the advantages of the RPWM technique over conventional PWM. Experimental results confirm the validity of the theoretical calculations and simulation results, and demonstrate the effectiveness of applying the RPWM technique in reducing the RF noise level.

Application of Random PWM Technique for Reducing the Conducted Electromagnetic Emissions in Active Filters

In this paper, a flux search controller is proposed to improve the efficiency of direct torque control of a six-phase induction machine. The proposed flux search controller is based on adaptive gradient descent of motor flux value with fast response and easy implementation. A proper loss model of six-phase induction motor in conjunction with the proposed method has been presented. Stator frequency variation with respect to flux reduction is considered as a new aspect of fast flux search control. Reduction of the flux in the search control technique leads to an increase in stator frequency, and an error in core loss calculation occurs if the frequency variation is ignored. The proposed search controller greatly improves efficiency by reducing core loss as well as harmonics loss. The approach not only is easy to implement and adaptive with regard to parameter variations but also requires no additional hardware for practical implementation. The simulation and experimental results presented in this paper verify the effectiveness of the proposed method in improving efficiency of direct torque control of six-phase induction motor drive.

Efficiency Improvement in DTC of Six-Phase Induction Machine by Adaptive Gradient Descent of Flux

In this paper, a flux search controller is proposed to increase the efficiency of a direct torque-controlled induction motor in full load range. The value of the flux reference is determined through a minimization algorithm. The amplitude of stator current is used as the objective function since it is shown that samples of the stator current have better statistical properties than input power. In addition, the stator current has more sensitivity to the flux variation than input power. These two properties allow implementing an adaptive algorithm to determine the proper flux step without waste of time. The minimum allowable value of the flux step has been determined based on this process to prevent the divergence problem. This adaptive algorithm set a large flux step for transient state to speed up the convergence process and a small flux step for steady state to minimize the flux ripple. Simulation and experimental results presented in this paper confirm the fast dynamic of the proposed method.

A Fast Flux Search Controller for DTC-Based Induction Motor Drives

In this paper, sliding-mode control (SMC) is applied to a z-source converter to control output dc voltage of impedance network The converter is assumed working in continuous conduction mode (CCM) First a comprehensive review of the literature for z-source inverter (ZSI) and use of sliding mode control in switched converters are performed The procedure of SMC design used in ZSI is presented The simulations for the application of SMC in z-source inverter are made and the results are illustrated The results verify the effectiveness and robustness of the controller

Sliding-mode control of z-source inverter

The limited value of the insolated-gate bipolar transistors (IGBTs) blocking voltage is an important issue for applying these devices to the high-voltage power converters. An effective solution is to use a series configuration of these devices in order to achieve higher voltage ratings in addition to save the interesting features such as fast rising time. To reach this goal, acceptable equal voltage sharing for the IGBTs are provided by the series stacking schemes in the normal operation. However, a considerable difference in their voltage level will be occurred in the short-circuit condition. Although the IGBT can withstand the short-circuit current in a defined time, the occurred high voltage stress for the IGBT is fatal in such condition. To solve the mentioned problem, this paper proposes a short-circuit protection system suitable for the series stacked IGBTs. Using this proposal, the safe voltage level for IGBTs as well as the adequate time for the performance of the detection and elimination of the short-circuit fault will be provided. Each IGBT can have a different short-circuit current in the active region since the proposed scheme makes the IGBTs independent in terms of the current in the series structure. An external resistor added to the IGBTs emitter improves the equality of the IGBTs short-circuit currents and consequently their voltage sharing. This resistor controls the system short-circuit current by changing the operating point of IGBTs in active region in the short-circuit fault. The experimental and simulation results show that the safe condition is provided for the IGBTs under the short-circuit fault.

Shahriyar Kaboli

Papers

Application of Random PWM Technique for Reducing the Conducted Electromagnetic Emissions in Active Filters

Efficiency Improvement in DTC of Six-Phase Induction Machine by Adaptive Gradient Descent of Flux

A Fast Flux Search Controller for DTC-Based Induction Motor Drives

Sliding-mode control of z-source inverter

A Series Stacked IGBT Switch With Robustness Against Short-Circuit Fault for Pulsed Power Applications