Multiphase induction motor drives - a technology status review

The area of multiphase variable-speed motor drives in general and multiphase induction motor drives in particular has experienced a substantial growth since the beginning of this century. Research has been conducted worldwide and numerous interesting developments have been reported in the literature. An attempt is made to provide a detailed overview of the current state-of-the-art in this area. The elaborated aspects include advantages of multiphase induction machines, modelling of multiphase induction machines, basic vector control and direct torque control schemes and PWM control of multiphase voltage source inverters. The authors also provide a detailed survey of the control strategies for five-phase and asymmetrical six-phase induction motor drives, as well as an overview of the approaches to the design of fault tolerant strategies for post-fault drive operation, and a discussion of multiphase multi-motor drives with single inverter supply. Experimental results, collected from various multiphase induction motor drive laboratory rigs, are also included to facilitate the understanding of the drive operatio

Control of Cascaded Multilevel Inverters

A new type of multilevel inverter is introduced which is created by cascading two three-phase three-level inverters using the load connection, but requires only one dc voltage source. This new inverter can operate as a seven-level inverter and naturally splits the power conversion into a higher-voltage lower-frequency inverter and a lower-voltage higher-frequency inverter. This type of system presents particular advantages to Naval ship propulsion systems which rely on high power quality, survivable drives. New control methods are described involving both joint and separate control of the individual three-level inverters. Simulation results demonstrate the effectiveness of both controls. A laboratory set-up at the Naval Surface Warfare Center power electronics laboratory was used to validate the proposed joint-inverter control. Due to the effect of compounding levels in the cascaded inverter, a high number of levels are available resulting in a voltage THD of 9% (without filtering)

Control of Cascaded Multi-level Inverters

A new type of multi-level inverter is introduced which is created by cascading two three-phase three-level inverters using the load connection. This new inverter can operate as a nine-level inverter and naturally splits the power conversion into a higher voltage lower-frequency inverter and a lower-voltage higher frequency inverter. This type of system presents particular advantages to naval ship propulsion systems which rely on high power quality, survivable drives. New control methods are described involving both joint and separate control of the individual three-level inverters. Simulation results demonstrate the effectiveness of both controls. A laboratory set-up at the Naval Surface Warfare Center power electronics laboratory was used to validate the proposed joint-inverter control. Due to the effect of compounding levels in the cascaded inverter, a high number of levels are available resulting in a voltage THD of 9 % (without filtering)

Distributed Control of Hybrid Motor Drives

The hybrid inverter fed motor drive with two cascaded multilevel inverters is an attractive option for high performance high power applications such as naval ship propulsion systems due to a number of unique features. There is a natural split between a higher-voltage lower-frequency bulk inverter and a lower-voltage higher-frequency conditioning inverter in the cascaded system which matches the availability of semiconductor devices. Furthermore, the bulk inverter may be a commercial-off-the-shelf (COTS) motor drive meaning that only the conditioning inverter needs to be custom made. However, a drive involving a COTS bulk inverter would require a distributed conditioning inverter control which works completely independent of the bulk inverter control. In this paper, a set of distributed control methods are developed for the hybrid inverter drive with cascaded bulk and conditioning inverters, requiring only single dc source. Moreover, a solution to the practical problem of instant synchronization between the two inverters is presented. Laboratory measurements on a 3.7-kW induction motor drive validate the proposed control. Various practical considerations (such as low m-index performance and capacitor precharging options) are discussed and their solutions provided

Comparison of Hybrid Propulsion Drive Schemes

This paper provides a brief overview of a hybrid drives which have become popular in recent years. These drives combine two or more multilevel power inverters to obtain exceptional power quality which is necessary for Naval propulsion applications. Furthermore, for ship propulsion, where it may be difficult to obtain several isolated dc voltage sources, the inverter control can be set so that only one real dc power source is needed (or one per phase in the case of a series H-bridge type). Three types of hybrid drives considered and their advantages and limitations are described. Commonalities of the control of each hybrid drive type is discussed and three control schemes are applied to the various topologies in a set of simulation examples

A Novel Reduced Components Model Predictive Controlled Multilevel Inverter for Grid-Tied Applications

This paper presents an improved single-phase Multilevel Inverter (MLI) which is conceptualized to reduce power switches along with separate DC voltage sources. Compared with recent modular topologies, the proposed MLI employs a reduced number of components. The proposed inverter consists of a combination of two circuits, i.e., the level generation and polarity generation parts. The level generation part is used to synthesize different output voltage levels, while the polarity inversion is performed by a~conventional H-bridge circuit. The performance of the proposed topology has been studied using s single-phase seven-level inverter, which utilizes seven power switches and three independent DC voltage sources. Model Predictive Control (MPC) is applied to inject a sinusoidal current into the utility grid which exhibits low Total Harmonic Distortion (THD). Tests, including a~change in grid current amplitude as well as operation under variation in Power Factor (PF), have been performed to validate the good performance obtained using MPC. The effectiveness of the proposed seven-level inverter has been verified theoretically using MATLAB Simulink. In addition, Real-Time (RT) validation using the dSPACE-CP1103 has been performed to confirm the system performance and system operation using digital platforms. Simulation and RT results show improved THD at 1.23% of injected current

Improved space vector modulation with reduced switching vectors for multi-phase matrix converter

Multi-phase converter inherits numerous advantages, namely superior fault tolerance, lower per-leg power rating and higher degree of freedom in control. With these advantages, this thesis proposes an improved space vector modulation (SVM) technique to enhance the ac-to-ac power conversion capability of the multi-phase matrix converter. The work is set to achieve two objectives. First is to improve the SVM of a three-to-seven phase single end matrix converter by reducing number of space vector combinations. Second is to use the active vector of the SVM to eliminate the common-mode voltage due to the heterogeneous switching combination of a dual three-to-five phase matrix converter. In the first part, the proposed technique utilizes only 129 out of 2,187 possible active space vectors. With the reduction, the SVM switching sequence is greatly simplified and the execution time is shortened. Despite this, no significant degradation in the output and the input waveform quality is observed from the MATLAB/Simulink simulation and the hardware prototype. The results show that the output voltage can reach up to 76.93% of the input voltage, which is the maximum physical limit of a three-to-seven phase matrix converter. In addition, the total harmonics distortion (THD) for the output voltage is measured to be below 5% over the operating frequency range of 0.1 Hz to 300 Hz. For the second part, the common-mode voltage elimination is based on the cancellation of the resultant vectors (that causes the common-mode to be formed), using a specially derived active vectors of the dual matrix converter. The elimination strategy is coupled with the ability to control the input power factor to unity. The proposed concept is verified by the MATLAB/Simulink simulation and is validated using a 5 kW three-to-five phase matrix converter prototype. The SVM switching algorithm itself is implemented on a dSPACE-1006 digital signal processor platform. The results prove that the common-mode voltage is successfully eliminated from the five-phase induction motor winding. Furthermore, the output phase voltage is boosted up to 150% of the input voltage in linear modulation range

A Novel Design Optimization of a Fault-Tolerant AC Permanent Magnet Machine-Drive System

In this dissertation, fault-tolerant capabilities of permanent magnet (PM) machines were investigated. The 12-slot 10-pole PM machines with V-type and spoke-type PM layouts were selected as candidate topologies for fault-tolerant PM machine design optimization problems. The combination of 12-slot and 10-pole configuration for PM machines requires a fractional-slot concentrated winding (FSCW) layout, which can lead to especially significant PM losses in such machines. Thus, a hybrid method to compute the PM losses was investigated, which combines computationally efficient finite-element analysis (CE-FEA) with a new analytical formulation for PM eddy-current loss computation in sine-wave current regulated synchronous PM machines. These algorithms were applied to two FSCW PM machines with different circumferential and axial PM block segmentation arrangements. The accuracy of this method was validated by results from 2D and 3D time-stepping FEA. The CE-FEA approach has the capabilities of calculating torque profiles, induced voltage waveforms, d and q-axes inductances, torque angle for maximum torque per ampere load condition, and stator core losses. The implementation techniques for such a method are presented. A combined design optimization method employing design of experiments (DOE) and differential evolution (DE) algorithms was developed. The DOE approaches were used to perform a sensitivity study from which significant independent design variables were selected for the DE design optimization procedure. Two optimization objectives are concurrently considered for minimizing material cost and power losses. The optimization results enabled the systematic comparison of four PM motor topologies: two different V-shape, flat bar-type and spoke-type, respectively. A study of the relative merits of each topology was determined. An automated design optimization method using the CE-FEA and DE algorithms was utilized in the case study of a 12-slot 10-pole PM machine with V-type PM layout. An engineering decision process based on the Pareto-optimal front for two objectives, material cost and losses, is presented together with discussions on the tradeoffs between cost and performance. One optimal design was finally selected and prototyped. A set of experimental tests, including open circuit tests at various speeds and on-load tests under various load and speed conditions, were performed successfully, which validated the findings of this work

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 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.Ministerio de Ciencia y Tecnología DPI2001-3089Ministerio de Eduación y Ciencia d TEC2006-0386