DC-current injection with minimum torque ripple in interior permanent-magnet synchronous motors

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 (PMSMs), it is possible to inject a dc component in the d -axis, without perturbing the torque. However, it has been claimed that, for synchronous machines with saliency, it is not possible to avoid the torque ripple due to such injection. This letter proposes optimum reference currents to impose dc current in three-phase interior PMSMs while minimizing to practically zero its associated torque ripple. Namely, the dc signal is injected in combination with a suitable second-order harmonic so that the stator current space vector follows the constant-torque locus, while the fundamental is set according to the maximum-torque-per-ampere strategy. Experimental results validate the theory.Agencia Estatal de Investigación | Ref. DPI2016-75832-

Enhanced resonant current controller for grid-connected converters with LCL filter

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 poles of the system in convenient locations when dealing with a fourth-order plant model such as the LCL filter plus the computation delay. Therefore, the reference tracking and the disturbance rejection are deficient in terms of transient behavior and depend on the LCL filter. Furthermore, an additional active damping method usually has to be designed in order to ensure stability. This paper presents an enhanced current RC with stable and fast response, negligible overshoot, good disturbance rejection, and low controller effort for grid-tied converters with LCL filter. The developed solution uses a direct discrete-time pole-placement strategy from the classical control theory (using transfer functions), involving two extra filters, to enhance the performance of the RC. In this manner, the complexity of state-space methods from modern control theory is avoided. Simulation and experimental results are provided to verify the effectiveness of the proposed control scheme.Ministerio de Ciencia e InnovaciónAgencia Estatal de Investigación | Ref. DPI2016-75832-RMinisterio de Economía y Competitividad | Ref. BES-2013-06314

Generalized multifrequency current controller for grid-connected converters with LCL filter

This paper 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 solution offers a generalized method that gives a consistent (with minimal variation in the reference-tracking dynamics) and stable performance irrespectively of the number of current harmonics to be canceled and of the resonant frequency of the LCL filter (provided that it is lower than the Nyquist frequency). The response to reference commands is completely damped and fast. The response speed is set in accordance with the low-pass characteristic of the LCL filter so as to limit the control effort. Concerning the disturbance rejection, the controller offers an infinite impedance to any disturbances (such as grid voltage harmonics) at a set of arbitrarily specified frequencies. This allows the designer to eliminate all the undesired current harmonics with a simple design process. In addition, the performance of the presented controller is evaluated in terms of a fundamental tradeoff that exists between robustness to variations in the grid impedance and the number of frequency components rejected. Finally, simulation and experimental results that validate the proposal are presented.Ministerio de Ciencia e InnovaciónEuropean CommissionAgencia Estatal de Investigación | Ref. DPI2016-75832-RMinisterio de Educación, Cultura y Deporte | Ref. FPU14/0068

Space-vector PWM with common-mode voltage elimination for multiphase drives

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 produce zero CMV. Specific space-vector PWM (SVPWM) techniques with CMV elimination, which only use zero CMV states, have been proposed for three-level five-phase drives, and for open-end winding five-, six-, and seven-phase drives, but such methods cannot be extended to a higher number of levels or phases. This paper presents a general (for any number of levels and phases) SVPMW with CMV elimination. The proposed technique can be applied to most multilevel topologies, has low computational complexity and is suitable for low-cost hardware implementations. The new algorithm is implemented in a low-cost field-programmable gate array and it is successfully tested in the laboratory using a five-level five-phase motor drive.Ministerio de Ciencia e InnovaciónEuropean CommissionMinisterio de Economía y Competitividad | Ref. DPI2012-31283Ministerio de Economía y Competitividad | Ref. DPI2015-6541

Melloras na monitorización térmica e na tolerancia a faltas en accionamentos eléctricos polifásicos

The use of multiphase AC electric machines together with multiphase power converters has been recognize as a viable approach to obtain higher power ranges without increase the current per phase. The greater degrees of freedom of a multiphase machine compared with a three-phase one can be exploited in different manners. Regarding three-phase machines, several strategies have been proposed for thermal monitoring based on dc-signal injection. However, due to such injection, a certain torque ripple is produced. In this dissertation, the additional degrees of freedom available in multiphase drives for condition monitoring are exploited to develop an algorithm based on dc-signal injection that enables the drive to estimate online the stator winding temperature avoiding the production of torque ripple. On the other hand, the greater degrees of freedom can also be used to increase the fault tolerant capability of the motor drive. This characteristic is crucial in applications that require a high degree of reliability, such aerospace of marine applications. In this maner, as far as the post-fault control strategies is concerned, the existing ones do not minimize the stator winding losses in the whole torque operation range (TOR). Thus, another objective of this thesis is to develop optimized post-fault strategies that improve the performance of the previous ones in this regard. In addition to the stator winding losses, the converter ones also play an important role in the whole drive. Therefore, it is also of interest to compare the different post-fault methods in terms of converter losses, which has not been taken into account in the past in this context in spite of its importance.El uso de las máquinas polifásicas de corriente alterna junto con los convertidores de potencia polifásicas es reconocido como una alternativa viable para obtener rangos de potencia más elevados sin incrementar la corriente por fase. El mayor número de grados de libertad de una máquina polifásica comparado con los de una trifásica puede ser explotado de diversas formas. En cuanto a estimación de temperatura en máquinas trifásicas, existen varias propuestas basadas en inyección de señal continua. Sin embargo, debido a la inyección, se produce un cierto rizado de par. En esta tesis, los grados de libertad adicionales disponibles en accionamentos polifásicos son explotados para la realización de una monitorizacióin térmica de la máquina basada en inyección de una componente continua, y evitando la generación de rizado de par. Por otro lado, el mayor número de grados de libertad también puede ser utilizado para aumentar la capacidad ante a tolerancia a faltas de accionamientos eléctricos. Esta característica es crucial para aplicaciones que requieren un alto grado de fiabilidad, como aeroespacial y marinas. En esta línea, varios autores han propuesto estrategias de control en situación de falta. Sin embargo, ninguna de ellas consigue minimizar las pérdidas del devanado estatórico de la máquina en todo el rango de operación. Por esto, otro objetivo de esta tesis es desarrollar técnicas de generación de referencias optimizadas que mejoren el comportamiento de las ya publicadas. Además de las pérdidas estatóricas, las pérdidas en el convertidor juegan un papel importante en el conjunto global del accionamiento. Por esto, es interesante comparar las diferentes estrategias en términos de pérdidas del convertidor, que todavía no ha sido realizado a pesar de su importancia.O uso das máquinas polifásicas de corrente alterna xunto cos convertedores de potencia polifásicos é recoñecido como unha alternativa viable para obter rangos de potencia máis elevados sen incrementar a corrente por fase. O maior número de graos de liberdade dunha máquina polifásica comparado cos dunha máquina trifásica pode ser explotado de diversos xeitos. En canto a estimación de temperatura en máquinas trifásicas, existen varias propostas basadas en inxección dunha sinal continua. Sen embargo, debido a dita inxección, prodúcese un certo rizado de par. Nesta tese, o grados de liberdade adicionais dispoñibles en accionamentos polifásicos son explotados para a realización dunha monitorización térmica da máquina basada en inxección dunha compoñente continua, e evitando a xeración de rizado de par. Por outro lado, o maior número de grados de liberdade tamén pode ser utilizado para aumentar a capacidade ante a tolerancia a faltas do accionamento eléctrico. Esta característica é crucial para aplicacións que requiren un alto grao de fiabilidade, como aeroespacial e mariñas. Nesta liña, varios autores propuxeron estratexias de control en situación de falta. Sen embargo, ningunha delas consigure minimizar as perdas no bobinado estatórico da máquina en todo o rango de operación. Por esto, outro obxetivo desta tese é desenvolver técnicas de xeración de referencia optimizadas que melloren o comportamento das xa publicadas. Ademais das perdas estatóricas, as perdas no convertidor xogan un papel importante no conxunto global. Por eso, é interesante comparar as diferentes estratexias en termos de perdas no convertidor, que aínda non foi realizado, a pesar da súa importancia

Carrier-Based PWM equivalent to multilevel multiphase space vector PWM techniques

The space vector pulsewidth modulation (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 pulsewidth modulation (CBPWM) counterpart, which produces identical results. However, the conclusions reached in the articles that show these cannot be applied, nor even extended, to SVPWM techniques with more than two levels and three phases. This article shows that the most widely accepted multilevel multiphase SVPWM techniques have a fully equivalent CBPWM counterpart, which consists of a phase disposition pulsewidth modulation with an appropriate zero-sequence injection scheme. Closed-form expressions to calculate the zero sequences are provided. The proposed modulation techniques are simulated and then implemented in a field- programmable gate array, showing that the equivalent CBPWM techniques produce identical results as the original SVPWM ones, but with a significant reduction of hardware requirements. The proposed methodology can be generalized to other multilevel multiphase SVPWM techniques.European CommissionEuropean Regional Development Fund | Ref. DPI2016-75832Ministerio de Ciencia e Innovación (España