Óscar López Sánchez

University of Vigo | UVIGO · Department of Electronics Technology

Among six-phase motors, those featuring symmetrical winding arrangements with a single neutral point (S6N1) offer enhanced fault tolerance. However, a single neutral point lowers the dc-link utilization in the linear pulsewidth modulation (PWM) range. Most previous multiphase overmodulation (OVM) methods address this limitation by injecting just no...

Supplementary material of the paper: Comprehensive Comparative Assessment of Multiphase Overmodulation Techniques and Three-Phase Discontinuous PWM Methods Applied to Symmetrical Six-Phase Induction Motor Drives Under Overmodulation. * Description: simulation model including an implementation of MVDn, MVD6, CB6 and the DPWM methods for the overmod...

Multiphase motor drives based on cascaded Hbridge (CHB) voltage source inverters (VSIs) offer enhanced reliability by accommodating both motor and VSI faults. The VSI faults, the most prevalent type, can be addressed by bypassing damaged H-Bridges. However, operating the VSI in this condition without an appropriate postfault strategy can increase t...

This paper is accompanied by the Matlab script file "MXYFivePhases.m" with the code of proposed strategy for the five-phase case. Running this file has no particular requirements. It includes comments that explain the code. The script produces three image files: "MXY_cold.png", "MXY_warm.png" and "MIN.png".

Multiphase machines are a promising alternative for high-reliability applications. In these applications, overmodulation (OVM) is important since it allows attaining higher modulation indices by injecting, besides zero-sequence voltage harmonics, current-producing ones. In general, the existing techniques are able to limit to some extent the curren...

* Description: Simulation scripts including the offline optimization and the online implementation of the new overmodulation methods MCD_mu and MCD_ab_mu with minimum current distortion for A6N1, A6N2, S6N1 and S6N2 motor drives. For simplicity, a single modulation index M is considered for each case. Within each folder, run only the scripts contai...

Multiphase motor drives based on a cascaded H-bridge (CHB) voltage source inverter (VSI) are suitable for fault-tolerant applications because a damaged H-bridge can be safely bypassed without interrupting the drive operation. This bypass has the effect of an undesired dc-link voltage shortage that multiphase motors can effectively tolerate if appro...

Multiphase machines have significant benefits over their three-phase counterparts. One of them is the possibility of further exploiting the dc-link voltage by injecting non-torque-related voltage harmonics in the x-y planes. This allows reaching higher modulation indices in the overmodulation (OVM) region of pulse width modulation (PWM) while avoid...

This supplementary material is part of the paper: https://www.researchgate.net/publication/373555527_A_Carrier-Based_Overmodulation_Strategy_With_Minimum_Voltage_Distortion_for_Symmetrical_n-Phase_Induction_Motor_Drives . It contains the Simulink models of the proposed overmodulation technique for motors with phase numbers between 5 and 11.

Multiphase machines have significant benefits over three-phase machines. One of them is the possibility of further exploiting the dc-link voltage by injecting non-torque-related voltage harmonics in the x-y planes. This allows reaching higher modulation indices in the overmodulation region of pulse width modulation (PWM) without causing torque ripp...

This paper compares the most prominent overmodulation (OVM) techniques for five-phase induction motor drives with respect to the minimum current distortion (MCD) achievable. To attain a benchmark of the latter, two MCD OVM approaches are devised. Contrarily to previous strategies aimed at voltage distortion reduction/minimization, these MCD methods...

Simulation model including the implementation of the new overmodulation techniques: minimum current distortion with only x-y harmonics (MCDxy), minimum current distortion with alpha-beta and x-y harmonics (MCDabxy), and dual-mode (DM) methods. The look-up tables are the outcome of minimizing the cost functions in (12), with the following parameters...

Two common defects in induction machines (IMs) are eccentricity and interturn faults, which should be diagnosed to prevent performance degradation and further damage. A popular fault-detection approach is the current signature analysis (CSA), because of its simplicity and non-intrusiveness. Under closed-loop control, it is combined with analogous v...

Slides of the keynote presentation "Fault Tolerance in Multiphase Electric Machine Drives" at IECMA 2022 || Video of the presentation: [https://rebrand.ly/w9gsocv] || Related journal papers: [https://rebrand.ly/m4u0qqt], [https://rebrand.ly/3cndlgy]

Multiphase machines are very convenient for applications with high reliability requirement. In this two-part survey, the state-of-the-art about fault tolerance in multiphase drives is reviewed. In Part 1, an overview including numerous fault types was presented, along with fundamental notions about multiphase drives. Here, in Part 2, the focus is p...

Multiphase drives offer enhanced fault-tolerant capability compared with conventional three-phase ones. Their phase redundancy makes them able to continue running in the event of faults (e.g., open/short-circuits) in certain phases. Moreover, their greater number of degrees of freedom permits improving diagnosis and performance not only under fault...

The space vector pulse width modulation (PWM) (SVPWM) techniques enhance the performance of multilevel multiphase inverters. With multilevel (three-phase) inverters and with (two-level) multiphase inverters, it is widely accepted that the typical SVPWM strategies have an equivalent carrier-based PWM (CBPWM) counterpart, which produces identical res...

Matlab functions of multidimensional space vector PWM (SVPWM) techniques.

Several proposals based on dc-current injection have been reported for estimating the stator winding resistance in induction machines, and recently extended for synchronous machines. Tracking this resistance can be very useful, e.g., for thermal monitoring or preserving control dynamics. In surface-mounted permanent-magnet synchronous machines (PMS...

This article presents a grid-side current controller for grid-tied inverters with LCL filter, including harmonic current elimination. The proposed controller only measures the grid current and voltage and it combines excellent dynamic characteristics with good robustness. Contrarily to previously proposed harmonic-current controllers, the presented...

Conventional resonant controllers (RCs) are commonly used in the current control of grid-tied converters with LCL filter due to their advantages, such as zero steady-state error at both fundamental sequences, easy design process, and straightforward implementation. Nevertheless, these traditional solutions do not permit to place the closed-loop pol...

Low-order current harmonics arise in ac drives due to nonlinearities, producing torque ripple and extra losses. In multiphase machines, which offer advantages over three-phase ones, the latter is aggravated because some harmonics map in low-impedance no-torque subspaces. A multiple-resonant-controller (MRC) structure, combining resonant controllers...

Traditionally, the current control of grid-tied converters with LCL filter is based on proportional-resonant or proportional-integral controllers, which often need an additional active damping method to achieve stability. These solutions do not permit to place the closed-loop poles in convenient locations when dealing with such high-order plants. T...

Dual three-phase machines are attractive due to advantages such as inherent fault tolerance. During postfault situation, the same magneto-motive force as in healthy operation should be maintained. Furthermore, it is also important to minimize the copper losses. Several strategies have been proposed to improve the postfault performance under open-ph...

Conventional resonant controllers (RCs) are commonly used in the current control of grid-tied converters with LCL filter due to their advantages, such as zero steady-state error at both fundamental sequences, easy design process, and straightforward implementation. Nevertheless, these traditional solutions do not permit to place the closed-loop pol...

This paper presents a grid-side current controller for grid-tied inverters with LCL filter, including harmonic current elimination. Contrarily to previously proposed harmonic-current controllers, the presented solution offers a generalized method that gives a consistent and stable performance irrespectively of the number of current harmonics to be...

Fault tolerance is an advantageous characteristic of multiphase machines when compared with three-phase ones. During open-phase fault, the current references need to be adapted to provide ripple-free torque. As a consequence of this modification, the post-fault phase currents might be larger than the rated current. Such situation leads to overheati...

Switching common-mode voltage (CMV) generated by the pulse width modulation (PWM) of the inverter causes common-mode currents, which lead to motor bearing failures and electromagnetic interference problems in multiphase drives. Such switching CMV can be reduced by taking advantage of the switching states of multilevel multiphase inverters that prod...

Traditionally, the current control of grid-tied converters with LCL filter is based on proportional-resonant or proportional-integral controllers, which often need an additional active damping method to achieve stability. These solutions do not permit to place the closed-loop poles in convenient locations when dealing with such high-order plants. T...

Multiphase machines (MPMs) have become serious contenders in several applications, such as offshore wind energy and electric vehicles. Low-order current harmonics arise in actual drives due to converter and machine nonlinearities, thus producing losses and torque ripple. In comparison to three-phase machines, in MPMs this effect is aggravated becau...

Fault tolerance is an advantageous characteristic of multiphase machines when compared with three-phase ones. During open-phase fault, the current references need to be adapted to provide ripple-free torque. As a consequence of this modification, the post-fault phase currents might be larger than the rated current. Such situation leads to overheati...

Multiphase (MP) induction machines (IMs) provide important advantages over three-phase (3P) ones. Sensorless speed estimation makes it possible to obtain highperformance control and monitoring without the inconveniences of speed sensors. In 3P IMs, the speed estimation methods based on rotor slot harmonics (RSHs), normally on the principal RSHs (PS...

Dual three-phase machines are becoming increasingly popular due to advantages such as inherent fault tolerant capability and lower current per phase for a given power. As in three-phase machines, it is important to provide thermal protection, in order to prevent reduction of the lifetime. Proposals specifically targeted to dual three-phase machines...

Low-order odd current harmonics arise in practical multiphase drives due to machine and converter nonlinear behavior (e.g., deadtime and flux saturation). If the windings are distributed, some harmonics cause torque ripple, while others produce losses. The latter is aggravated by the small impedance in the no-torque subspaces. Current harmonics can...

Precise knowledge of the plant time constant L/R is essential to perform a thorough analysis and design of the current control loop in voltage source converters (VSCs). From the perspective of the current controller dynamics in the low frequency range, such plant time constant is also suitable for most cases in which an LCL filter is used. As the l...

Current controller performance is key in grid-connected power converters for renewable energy applications. In this context, a challenging scenario is arising in multi-MW wind turbines, where sampling and switching frequencies tend to be lower and lower as power ratings increase. This strongly affects achievable control time constant. With this per...

Rigorous analysis and design of the current control loop in voltage source converters (VSCs) requires an accurate modeling. The loop behavior can be significantly influenced by the VSC working conditions. To consider such effect, converter losses should be included in the model, which can be done by means of an equivalent series resistance. This pa...

Precise knowledge of the plant time constant is essential to perform a thorough analysis of the current control loop in voltage source converters (VSCs). As the loop behavior can be significantly influenced by the VSC working conditions, the effects associated to converter losses should be included in the model, through an equivalent series resista...

Current control in voltage source converters under balanced conditions is often performed by proportional-integral (PI) controllers in a single synchronous reference frame (SRF). The cross-coupling between its dq-axes is usually decoupled by a state-feedback (SF) decoupling technique, and less frequently by an alternative procedure based on complex...

This paper deepens on the transient response analysis of the so-called vector proportional-integral (VPI) controllers and compares them with the popular proportional-resonant (PR) controllers for grid-connected applications. The employed methodology is based on the study of the error signal roots: both reference tracking and disturbance rejection a...

Implementation of proportional-integral controllers in synchronous reference frame is a well-established current control solution for electric machines. Nevertheless, their gain selection is still regarded to be poorly reported, particularly in relation to the influence of the computation and modulation delay. To fill this gap, a design procedure t...

The use of multiphase motor drives is an increasingly important strategy nowadays. These multiphase machines are usually modeled by a reference frame transformation to avoid the cross-coupling of variables. This transformation decomposes the original n-dimensional vector space into orthogonal subspaces. Mapping the voltage and current harmonics int...

It has been previously suggested to use multiple reference frame (MRF) structures, based on proportional-integral controllers in synchronous reference frames (SRFs), to suppress current harmonics caused by nonlinearities in multiphase drives. However, the rotational transformations are computationally demanding. In Part 1, the three-phase strategy...

Low-order odd harmonics arise in practical multiphase drives because of the machine and converter nonlinear behavior (e.g., deadtime and saturation). If the windings are distributed, some of the harmonics cause torque ripple, while others cause losses. The latter is aggravated by the small impedance in the no-torque subspaces. The harmonics can be...

The multi-motor drive concept is based on the use of the additional degrees of freedom available in multiphase motors to independently control a group of series-connected machines fed from a single voltage source inverter. To achieve this independent control, the motors should have a perfectly sinusoidal distribution of the stator windings. However...

Current control performance is key in some ac power conversion applications, such as renewable energies and motor drives. This paper presents a method for accurate assessment of dq-PI current controllers dynamics. The proposed methodology is based on linear control for multivariable systems. First, the plant and controller matrices are modeled incl...

Implementation of proportional-integral controllers in synchronous reference frame is a well-established current control solution for electric machines. Nevertheless, their gain selection is still regarded to be poorly reported, particularly in relation to the influence of the computation and the modulation delay. To fill this gap, a design procedu...

Low-order odd harmonics are particularly problematic in multiphase drives, due to the small impedance in the no-torque subspaces. The harmonics can be compensated by proportional-integral controllers in multiple synchronous reference frames (SRFs). In three-phase systems, the computational burden of such scheme is often avoided by implementing inst...

Proportional-integral (PI) controllers in a single synchronous reference frame (SRF) are popular for current control in voltage source converters. The most common technique to decouple the cross-coupling between its axes is to add/subtract at the output of the PI controller in each axis the current of the orthogonal axis, multiplied by the plant re...

Optimization of the current control loop in voltage source converters (VSCs) requires an accurate modeling. The VSC behavior can be significantly influenced by its working conditions. To consider such effect, converter losses should be included in the model, which can be done by means of an equivalent series resistance. This paper proposes a method...

The increasing number of distributed power generation systems (DPGSs) is changing the traditional organization of the electrical network. An important part of these DPGSs is based on renewable energy sources. In order to guarantee an efficient integration of renewable-based generation units, grid codes must be fulfilled. Their most demanding requir...

Multiphase drives are advantageous when high overall system reliability and the reduction in the total power per phase are required. The control strategies for these applications require a good knowledge of the machine parameters to ensure a high quality of the dynamic and steady-state drive performance. Multiphase machines are still not common in...

Multiphase induction machines (IMs) are gaining increasing interest in industry due to their numerous advantages over the conventional three-phase ones. A lot of different parameter estimation methods have been developed for three-phase IMs, but the existing literature regarding specific identification techniques for multiphase IMs is almost nonexi...

Corrections to the above titled paper (ibid., vol. 25, no. 7, pp. 1692-1712, Jul. 2010) are presented here.

The torque and flux of sinusoidally distributed multiphase machines can be controlled by using only two stator d-q components. Thus, in these machines there exist additional degrees of freedom, which in multimotor drive systems are used to independently control a group of series-connected multiphase machines. Series connected machines share stator...

Multilevel multiphase inverters are a promising practical solution for high-power applications. In applications where high switching frequency cannot be accommodated due to the increased switching losses associated to the pulse-width modulation techniques, the space vector control modulation technique is a feasible alternative. The space vector con...

Grid codes force generation units based on renewable sources to act similarly to conventional power plants: when a fault is detected, they must remain connected and support the grid. To fulfill these requirements, the transient response of the current controllers is critical. This paper applies a recently proposed methodology which assesses and opt...