Contributions to Modulation and Control Algorithms for Multilevel Converters

Las actuales tendencias de la red eléctrica han lanzado a la industria a la búsqueda de sistemas de generación, distribución y consumo de energía eléctrica más eficientes. Generación distribuida, reducción de componentes pasivos, líneas DC de alta tensión son, entre otras, las posibles líneas de investigación que están actualmente siendo consideradas como el futuro de la red eléctrica. Sin embargo, nada de esto sería posible si no fuera por los avances alcanzados en el campo de la electrónica de potencia. El trabajo aquí presentado comienza con una breve introducción a la electrónica de potencia, concretamente a los convertidores de potencia conectados a red, sus estrategias de control más comunes y enfoques ante redes desbalanceadas. A continuación, las contribuciones del autor sobre el control y modulación de una topología particular de convertidores, conocidos como convertidores multinivel, se presentan como el principal contenido de este trabajo. Este tipo de convertidores mejoran la eficiencia y ciertas prestaciones, en comparación con convertidores más tradicionales, a costa de una mayor complejidad en el control al incrementar la cantidad de los componentes hardware. A pesar de que existen numerosas topologías de convertidores multinivel y algunas de ellas son brevemente expuestas en este trabajo, la mayoría de las aportaciones están enfocadas para convertidores del tipo diode-clamped converter. Adicionalmente, se incluye una aportación para convertidores del tipo multinivel modular, y otra para convertidores en cascada. Se espera que el contenido de la introducción de este trabajo, junto a las contribuciones particulares para convertidores multinivel sirva de inspiración para futuros investigadores del campo

Desarrollo de sistema electrónico de control de un variador de cinco fases para vehículo eléctrico CROSS RIDER

Se va a diseñar un sistema electrónico de control de un variador eléctrico de un vehículo eléctrico CROSS RIDER. Se partirá desde el centro de control del sistema y se llegará a la interfaz analógica dónde el motor irá acoplado. El centro de control se entenderá como el sistema de procesamiento de señales digitales (DSP) y la interfaz analógica se entenderá tanto como la toma de medidas del sistema (sensores del motor) como el envío de pulsos de potencia. Aunque el esquema básico de control es el expuesto en la Fig. 1, se requiere una amplia consideración de numerosos aspectos para alcanzar un sistema operativo y apto. Para empezar, el control se realizará según demanda del usuario a un nivel jerárquico mucho mayor, por lo que será el DSP el encargado de contextualizar esa demanda y traducirla para que se lleve a cabo tal actuación.Universidad de Sevilla. Máster en Ingeniería Industria

Voltage Balance for Five-Level DCC Based on Mixed-Integer Linear Programming

In power converters, the modulation stage commands the switching devices to drive the converter outputs to the voltage required by the inner controllers in order to achieve their objectives. However, in multilevel converters, the modulation may be in charge of an ad ditional goal since it also has to tackle with the capacitor voltage balancing issue. This paper formulates the modulation of multilevel three-phase power converters, specifically a five-level diode-clamped converter (DCC), as a mixed-integer linear optimization prob lem. In this paper, it is shown that the presented optimization problem can deal with the capacitor voltage balance at the same time that the number of commutations is minimized. The problem is solved offline and its solution is stored in a lookup table to be used during normal operation. Then, an online procedure to obtain the levels that modulate each phase from the lookup table is given. Comparisons with model predictive control, space-vector based algorithms and other modulation approaches are presented in simulations. Several experimental results are presented showing the feasibility of this approach with changes in the operating conditions

A simple modulation approach for interfacing three-level Neutral-Point-Clamped converters to the grid

Datos suplementarios: https://ars.els-cdn.com/content/image/1-s2.0-S0360544220309427-mmc1.mp4Multilevel converters are nowadays an enabling key in the integration of electric power into the grid as they introduce less distortion and, thus, they are more compliant with the grid standards, among other benefits. A well-known topology is the three-level Neutral-Point-Clamped whose control requires to deal with the capacitors voltage unbalance. This paper presents a modulation approach where the injection of a common component in the modulated voltage is studied in order to achieve such voltage balance. An optimization problem that, apart from the voltage balance, aims the lowest number of commutations and can be solved very efficiently with up to five computations of the cost function is formulated. The main advantages of the proposed modulation strategy are its simplicity and its flexibility, since it is also valid for unbalanced grid conditions and, with little added complexity, for low (and even zero) power factor conditions. Simulation results under unbalanced grid conditions are provided in order to show its validity under this scenario. The strategy is evaluated and compared with a space-vector-based approach in an experimental setup, yielding similar total harmonic current distortion, a 30% reduction in the number of commutations, and better voltage balance performance for lower power factor conditions.Ministerio de Economía y Competitividad DPI2016-75294-C2-1-RJunta de Andalucía (Consejería de Economía y Conocimiento), Programa Operativo FEDER Andalucía 2014-2020, US-1264655

Integrated Control of Five-Level Diode-Clamped Rectifiers

This paper presents an approach for dealing with the control of five-level, diode-clamped rectifiers. The control of such converters is challenging since the voltage balancing among capacitors is not a trivial task. Some of the existing approaches that cope with this problem use specific modifications of one of the traditional modulation techniques such as using redundant vectors in SVM. The main feature of the proposed technique is that part of the modulation is considered in the system equations and, in this way, the voltage balance can be solved designing a specific controller for this problem. As a result, several levels are used within a switching period. Furthermore, it is shown that the proposed approach hardly affects the control of active and reactive powers and total dc-link voltage in such a way that the well-known direct power control (DPC) can be applied. As a consequence, the resultant modulation stage is simpler than other techniques based on, e.g., space vector modulation (SVM). The effectiveness and good performance of the system under the proposed control approach are validated by both simulation and experimental results.Ministerio de Economía y Competitividad y Unión Europea : DPI2016-75294-C2-1-

Feedforward Modulation Technique for More Accurate Operation of Modular Multilevel Converters

Modular multilevel converters have become the prominent topology for medium- and high-voltage applications. The performance of these converters highly depends on the accuracy of the used modulation approach, for which the capacitor voltage of submodules (SM) are usually assumed to be equal. This article exhibits that ignoring the capacitor voltage differences among SMs adversely affects the system performance. This becomes more obvious the larger the capacitor voltage differences are. Hence, this article proposes a more accurate feedforward modulation approach that takes into account either the instantaneous capacitor voltage value and the real output voltage in the modulation stage. As a result, in applications where larger SM voltage differences are expected, the current distortion and control performance are improved. Particularly, switching–saving approaches benefit from this method as it enables their operation with reduced switching losses without the downsides of increased distortion due to capacitor voltage differences. The proposed approach is analyzed and compared with the nearest-level modulation and with the level-shift PWM. Simulations and experimental validation are presented to confirm the effectiveness of the proposed technique.Ministerio de Ciencia, Innovación y Universidades PDI2019-105890RJ-100 y PID2019-109071RB-I00Comisión Europea H2020-821 381Junta de Andalucia P18-RT-134

Detection and supression of low-order harmonic in the grid current

[Resumen] La presencia de armónicos de bajo orden en la red eléctrica causa numerosas pérdidas económicas a la industria. Por ello, se están dedicando muchos esfuerzos en la búsqueda de soluciones para reducir su presencia en la red eléctrica. Una de esas soluciones es el algoritmo que se comenta en esta contribución. Consiste en la detección y posterior compensación de uno o varios armónicos presente en las corrientes de fase de forma simultánea. Para ello se plantea una etapa de detección, donde se extrae la componente del armónico o armónicos a compensar, y otra etapa de compensación, donde se utiliza un controlador para determinar una componente de referencia a introducir en las referencias de corriente. Este algoritmo ha sido testado experimentalmente y los resultados validan la capacidad del algoritmo para su uso con equipos reales.[Abstract] The low-order harmonic presence in the grid is the reason for many economical losses in the industry. Due to this, many efforts has been put in the search for approaches that solve such issue by suppressing them from the grid. This paper deals with one of these approaches. It consists in the detection and the consequent suppression of low-order harmonics by measu ring the grid current. To achieve so, a detection stage, where the considered harmonic to be compensated is extracted, is used along with a compensation stage, where a controller is considered such as to generate a harmonic sequence reference component that will afterwards be added to the final reference currents. This algorithm has been tested experimentally and the good results show its capability to be used for harmonic compensation.Ministerio de Economía y Empresa; DPI2013-41891-RMinisterio de Economía y Empresa; DPI2016-75294-C2-1-

A novel Controller for Grid-interfacing Solar Arrays through Five-level Diode-clamped Converters

This paper presents an approach to control a grid-connected, five-level, diode-clamped converter (DCC) with solar arrays directly connected to each capacitor of the dc-link, On one hand, the control of such converters is challenging as the voltage imbalance among the capacitor may affect the power controller. On the other hand, when dealing with solar arrays, the dc voltage is a key point considering that the efficiency of the array highly depends on it. This article presents a solution where both aims are fulfilled: the desired capacitor voltages, set by the maximum power point tracking (MPPT) algorithm, are reached at the same time that these values are taken into account in the power controller. This is an unusual approach for five-level DCC that avoids the use of DC-DC stages, therefore it makes the system more affordable and avoids extra losses. Thanks to the capacitor voltage controller, proper power extraction from each solar array is achieved. The theoretical presentation of this approach is shown along with simulation results that validates its effectiveness.MINECO-FEDE

A modulation algorithm for inter-phase balancing in CHB Converters

This paper presents a simple modulation algorithm which accomplishes the voltage balance across the capacitors of a Cascaded H-bridge (CHB) converter using zero voltage injection. CHB converters are widely used in renewable energy production, especially in solar plants due to their modularity. This advantage can also become a problem when the power generated by the solar cell or consumed by a load is not equal among the three phases, leading to an unbalanced situation. The inter-phase unbalance refers to the voltage differences among the capacitors of different phases, for which a well-known technique to solve it consists of injecting a zero sequence voltage according to the power distribution. A simple modulation algorithm, which uses it, is presented in this paper including a mathematical proof. The proposed algorithm has been tested by simulation with a five-level CHB converter. At the end of the paper, a modification is introduced to improve the converter efficiency