Speed control for multi-three phase synchronous electrical motors in fault condition

The growth of electrification transportation systems is an opportunity for delving into new feasible solutions for more reliable and fault tolerant arrangements. So far, many investigations distant from the market have been carried out. Most of the works are looking at new control strategies adding extra components increasing manufacturing efforts and costs. Considering a nine phase synchronous multi-three phase electrical motor with disconnected neutral points, this manuscript compares the common speed reference configuration (where all the drives are configured in speed mode) and the torque follower configuration (where one drive is in speed mode and all the others are in torque mode). Furthermore, a post-fault operation in open-circuit condition is proposed. Analytical equations and experimental validation in nominal and fault condition are given by means of Matlab/Simulink simulations and by experimental on a 22kW test rig

Distributed speed control for multi-three-phase motors with enhanced power sharing capabilities

This thesis describes the last three years work and the results achieved after several stages of design and experimental validation. The main result is the development of a novel sharing current controller for multi-three-phase electrical machines. The proposed regulator, called "speed-drooped" or simply "droop" controller, allows the current transient triggered by a step change within the rotating reference frame to be controlled. Since multi-three-phase systems appear to be very good candidates for future Integrated Modular Motor Drives and next transportation system challenges, the work has been set up with modularity and redundancy for next future motor drives. During the preliminary stages, the mathematical models of the droop controller have been derived and validated on a multi-drive rig with two three-phase induction motors on the same shaft at the University of Nottingham. After, while developing a new general purpose control platform for power electronics able to control up to three three-phase systems, the Vector Space Decomposition for de-coupling the mutual interactions within multi-three-phase electric motors has been studied. Thanks to it, the inductance matrix of a triple-star two poles synchronous generator at the University of Trieste, Italy, has been diagonalised. Finally, the proposed current controller has been experimentally validated on a nine-phase synchronous generator and compared with the state of the art current sharing techniques. Furthermore, a post-fault compensation strategy has been formulated and validated by means of simulation work. If compared to the state-of-the-art current sharing techniques, the "droop" regulator capability of controlling current sharing transients while keeping constant speed of the shaft has been proven and successfully demonstrated by means of Matlab/Simulink simulations and experiments on both rigs

Distributed speed control for multi-three-phase motors with enhanced power sharing capabilities

This thesis describes the last three years work and the results achieved after several stages of design and experimental validation. The main result is the development of a novel sharing current controller for multi-three-phase electrical machines. The proposed regulator, called "speed-drooped" or simply "droop" controller, allows the current transient triggered by a step change within the rotating reference frame to be controlled. Since multi-three-phase systems appear to be very good candidates for future Integrated Modular Motor Drives and next transportation system challenges, the work has been set up with modularity and redundancy for next future motor drives. During the preliminary stages, the mathematical models of the droop controller have been derived and validated on a multi-drive rig with two three-phase induction motors on the same shaft at the University of Nottingham. After, while developing a new general purpose control platform for power electronics able to control up to three three-phase systems, the Vector Space Decomposition for de-coupling the mutual interactions within multi-three-phase electric motors has been studied. Thanks to it, the inductance matrix of a triple-star two poles synchronous generator at the University of Trieste, Italy, has been diagonalised. Finally, the proposed current controller has been experimentally validated on a nine-phase synchronous generator and compared with the state of the art current sharing techniques. Furthermore, a post-fault compensation strategy has been formulated and validated by means of simulation work. If compared to the state-of-the-art current sharing techniques, the "droop" regulator capability of controlling current sharing transients while keeping constant speed of the shaft has been proven and successfully demonstrated by means of Matlab/Simulink simulations and experiments on both rigs

Distributed speed control for multi-three phase electrical motors with improved power sharing capability

This paper proposes a distributed speed control with improved power sharing capability for multi-three phase synchronous machines. This control technique allows the speed to be precisely regulated during power sharing transients among different drives. The proposed regulator is able to control the time constant of the current within the dq0 reference frame to a step input variation. If compared to current set-point step variations, the proposed droop controller minimises device’s stress, torque ripple, and thus mechanical vibrations. Furthermore, since distributed, it shows improved fault tolerance and reliability. The design procedure and the power sharing dynamic have been presented and analysed by means of Matlab/Simulink and validated in a 22kW experimental rig, showing good agreement with the expected performances

Enhanced power sharing transient with droop controllers for multithree-phase synchronous electrical machines

This paper presents a droop-based distributed control strategy for multithree-phase machines that provides augmented controllability during power sharing transients. The proposed strategy is able to mitigate the mutual interactions among different sets of windings without controlling any subspace variable, also offering a modular and redundant design. On the contrary, in a centralized configuration, subspaces would be controlled using the vector space decomposition, but fault tolerance and reliability levels required by the stricter regulations and policies expected in future transportation systems would not be satisfied. The proposed method is analytically compared against the state-of-the-art power sharing technique and equivalent models and control design procedures have been derived and considered in the comparison. Uncontrolled power sharing transients and their effects on mutual couplings among isolated sets of windings have been compared against the proposed regulated ones. Experimental results on a 22-kW nine-phase multithree-phase synchronous machine rig validate the design procedures showing good agreement with the expected performances

Response to Discussion of “A modular speed-drooped system for high reliability integrated modular motor drives”

The authors appreciate the interest shown in our paper. In the paper under discussion [1], a distributed speed control strategy suitable for multi-three-phase machines with enhanced power sharing capability is presented. The focus of the manuscript is on the power sharing transient controllability achieved by using a sharing regulator based on the droop controller, which was introduced for the first time by Fingas and Lehn [2]. In [1], the authors added the outermost loop in charge of restoring the drooped output speed. The overall control strategy and the design procedure of each loop - current, sharing, and speed - is presented and validated by means of experimental results. Two off-the-shelf three-phase induction machines coupled on the same shaft and controlled by a custom inverter were loaded by a third off-the-shelf three- phase induction machine

A modular speed-drooped system for high reliability integrated modular motor drives

Future transportation challenges include a considerable reduction in pollutant emissions at a time when significant increase in demand is predicted. One of the enabling solutions is the electrification of transport systems as this should lead to improved operability, fuel savings, emission reduction, and maintenance. While state-of-the-art technology has demonstrable benefits there needs to be considerable advancement to meet future transportation affordability and emission targets. Primarily, electrical drives need an improved power density, an increased reliability, and a reduced specific cost. For this reason, integrated modular motor drives (IMMDs) present an attractive solution. Modularity leads to redundancy and easier integration. This paper presents a novel speed-drooped control system applied to motors fed by modular paralleled converters. This control technique allows precise speed regulation and power sharing among different segments showing improved fault tolerance and reliability. The design procedure and the power sharing dynamic have been presented and analyzed by means of MATLAB/Simulink and validated in a 3-kW experimental rig, showing good agreement with the expected performance

A Digital Internal Model Current Controller for Salient Machines

The performance of anisotropic electrical machines is strongly dependent on the current loop characteristics. The problems for achieving robustness and fast response, without overshoot and oscillations, are mainly related to different values and behaviour of the direct and quadrature inductances (Ld, Lq), as well as to high output frequencies. In this paper, a novel current controller structure based on Internal Model Control (IMC) method is presented, taking into account the magnetic anisotropy (Ld != Lq). The model of salient machines is derived directly in the discrete domain and used to obtain a model-based controller. The controller derivation does not rely on transport-delay approximations, which enables improved decoupling of axes dynamics and the closed-loop robustness for very high output frequencies. The presented controller enables enhanced response for higher current loop bandwidth and output frequencies than the state-of-the-art methods. The experimental verification is performed on a 3-phase synchronous machine, using a standard industrial 3-phase inverter

Distributed current control for multi-three phase synchronous machines in fault conditions

Among challenges and requirements of on-going electrification process and future transportation systems there is demand for arrangements with both increased fault tolerance and reliability. Next aerospace, power-train and automotive systems exploiting new technologies are delving for new features and functionalities. Multi-three phase arrangements are one of these novel approaches where future implementation of aforementioned applications will benefit from. This paper presents and analyses distributed current control design for asymmetrical split-phase schemes composed by symmetrical three phase sections with even number of phases. The proposed design within the dq0 reference frame in nominal, open and short circuit condition of one three-phase system is compared with the vector space decomposition technique and further validated by mean of Matlab/Simulink ~R simulations

uCube: control platform for power electronics

This paper presents a versatile tool for development, control and testing of power electronics converters. In the last decade, many different expensive off-the-shelf tools for rapid prototyping and testing have been developed and commercialised by few market players. Recently, the increasing diffusion of low cost, Do It Yourself targeted development tools gained market shares previously controlled by conventional players. This trend has been driven by the fact that, despite their lower performances, many of these low cost systems are powerful enough to develop simple power electronics systems for learning and teaching purposes. This paper describes a control platform developed within the University of Nottingham, targeting at the market and application segment in between the expensive off-the-shelf control boards and the low cost emerging systems. The platform is based on the Microzed evaluation board, equipped with the Xilinx Zynq System-on-Chip. Its flexibility, features and performances will be addressed and examples of how they are being experimentally validated on different rigs will be provided