Variable-Angle Phase-Shifted PWM for Multilevel Three-Cell Cascaded H-bridge Converters

Multilevel cascaded H-bridge converters have become a mature technology for applications where high-power medium ac voltages are required. Normal operation of multilevel cascaded H-bridge converters assumes that all power cells have the same dc voltage, and each power cell generates the same voltage averaged over a sampling period using a conventional phase-shifted pulse width modulation (PWM) technique. However, this modulation method does not achieve good results under unbalanced operation per H-bridge in the power converter, which may happen in grid-connected applications such as photovoltaic or battery energy storage systems. In the paper, a simplified mathematical analysis of the phase-shifted PWM technique is presented. In addition, a modification of this conventional modulation method using variable shift angles between the power cells is introduced. This modification leads to the elimination of harmonic distortion of low-order harmonics due to the switching (triangular carrier frequency and its multiples) even under unbalanced operational conditions. The analysis is particularized for a three-cell cascaded H-bridge converter, and experimental results are presented to demonstrate the good performance of the proposed modulation method

Extended State Observer-Based Sliding-Mode Control for Three-Phase Power Converters

This paper proposes an extended state observer (ESO) based second-order sliding-mode (SOSM) control for three-phase two-level grid-connected power converters. The proposed control technique forces the input currents to track the desired values, which can indirectly regulate the output voltage while achieving a user-defined power factor. The presented approach has two control loops. A current control loop based on an SOSM and a dc-link voltage regulation loop which consists of an ESO plus SOSM. In this work, the load connected to the dc-link capacitor is considered as an external disturbance. An ESO is used to asymptotically reject this external disturbance. Therefore, its design is considered in the control law derivation to achieve a high performance. Theoretical analysis is given to show the closed-loop behavior of the proposed controller and experimental results are presented to validate the control algorithm under a real power converter prototyp

Integral Sliding-Mode Control-Based Direct Power Control for Three-Level NPC Converters

Three-level neutral-point-clamped (NPC) converter is widely used in energy conversion systems due to its good properties for high-power systems presenting output waveforms with reduced harmonic distortion. To obtain better system performance, an integral sliding-mode control (ISMC)-based direct power control (DPC) strategy is proposed for NPC converters. The controller achieves three objectives. First, an extended state observer (ESO)-based ISMC strategy, to enforce the active and reactive power to their reference values, is applied in the power tracking loop. ESO is used to reduce the influence of parameter uncertainties. Next, in the voltage regulation loop, a radial basis function neural network (RBFNN)-based adaptive ISMC strategy is applied to regulate the DC-link voltage. RBFNN is used to estimate the load variation, which is considered as a disturbance, to improve the system disturbance rejection ability. An adaptive law is used in the controller to reduce the chattering of reference active power which can reduce the current harmonic distortion. Finally, a proportional-integral (PI) control strategy is applied in the voltage balancing loop to achieve voltage balance between two DC-link capacitors. Experimental results show the effectiveness and superiority of the proposed control strategy for the NPC power converter compared with PI-based DPC strategy.National Natural Science Foundation of China 61525303National Natural Science Foundation of China 41772377National Natural Science Foundation of China 61673130Laboratorio Estatal Clave de Robótica y Sistema (HIT) SKLRS201806

A High-Gain Observer-Based Adaptive Super-Twisting Algorithm for DC-Link Voltage Control of NPC Converters

Acting as an interface between the grid and many energy systems, the active front-end (AFE) has been widely used in a large variety of industrial applications. In this paper, in order to ensure the fast dynamic performance and good disturbance rejection ability of the AFE, a high-gain observer (HGO) plus adaptive super-twisting algorithm (STA) for the three-level neutral-point-clamped (NPC) converter is proposed. Comparing with the conventional PI control strategy, the proposed controller implements the adaptive STA in the voltage regulator to provide a faster transient response. The gains of the adaptive STA keep varying according to the rules being reduced in steady state but increasing in transient conditions. Therefore, the chattering phenomenon is mitigated and the dynamic response is guaranteed. Additionally, to undermine the impact of external disturbances on the dc-link voltage, a high-efficiency HGO is designed in the voltage regulation loop to reject it. Experimental results based on a three-level NPC prototype are given and compared with the conventional PI method to validate the fast dynamic performance and high disturbance rejection ability of the proposed approach.National Key R&D Program of China SQ2019YFB130028National Natural Science Foundation of China 61525303National Natural Science Foundation of China 41772377National Natural Science Foundation of China 61673130Self-Planned Task of State Key Laboratory of Robotics and System (HIT) SKLRS201806BMinisterio de Economía y Competitividad TEC2016-78430-RJunta de Andalucía P18-RT-1340Fondo de Investigación Nacional de Qatar NPRP 9-310-2-13

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

Efficient FPSoC Prototyping of FCS-MPC for Three-Phase Voltage Source Inverters

This work describes an efficient implementation in terms of computation time and resource usage in a Field-Programmable System-On-Chip (FPSoC) of a Finite Control Set Model Predictive Control (FCS-MPC) algorithm. As an example, the FCS-MPC implementation is used for the current reference tracking of a two-level three-phase power converter. The proposed solution is an enabler for using both complex control algorithms and digital controllers for high switching frequency semiconductor technologies. An original HW/SW (hardware and software) system architecture for an FPSoC is designed to take advantage of a modern operating system, while removing time uncertainty in real-time software tasks, and exploiting dedicated FPGA fabric for the most complex computations. In addition, two different architectures for the FPGA-implemented functionality are proposed and compared in order to study the area-speed trade-off. Experimental results show the feasibility of the proposed implementation, which achieves a speed hundreds of times faster than the conventional Digital Signal Processor (DSP)-based control platform.Ministerio de Economía y Competitividad TEC2016-78430-RFondo Nacional de Investigación de Qatar NPRP 9-310-2-13

Real-Time Selective Harmonic Mitigation Technique for Power Converters Based on the Exchange Market Algorithm

Hand-in-hand with the smart-grid paradigm development, power converters used in high-power applications are facing important challenges related to efficiency and power quality. To overcome these issues, the pre-programmed Pulse-Width Modulation (PWM) methods have been extensively applied to reduce the harmonic distortion with very low power switching losses for high-power converters. Among the pre-programmed PWM techniques, Selective Harmonic Elimination (SHE) has been the prevailing solution, but recently, Selective Harmonic Mitigation (SHM) stands as a superior alternative to provide further control of the harmonic spectrum with similar losses. However, the large computational burden required by the SHM method to find a solution confines it as an off-line application, where the switching set valid solutions are pre-computed and stored in a memory. In this paper, for the first time, a real-time implementation of SHM using an off-the-shelf mid-range microcontroller is presented and tested. The Exchange Market Algorithm (EMA), initially focused on optimizing financial transactions, is considered and executed to achieve the SHM targets. The performance of the EMA-based SHM is presented showing experimental results considering a reduced number of switching angles applied to a specific three-level converter, but the method can be extrapolated to any other three-level converter topology.Ministerio de Ciencia e Innovación de España TEC2016-78430-RJunta de Andalucía P18-RT-1340Fondo Nacional de Investigación de Qatar NPRP 9-310-2-13

Variable-angre Modulation for Modular Power Converters

Tesis no disponible por acuerdo de confidencialidad.El trabajo desarrollado y que se presenta en este documento es el resultado de la investigación desarrollada como parte del grupo de electrónica de potencia en la Universidad de Sevilla durante los últimos tres años. Dicha investigación se enmarca en el campo de los convertidores de potencia basados de tipo modular. Durante las últimas décadas, esta técnica se ha vuelto muy popular ya que ha dado solución a los problemas que la sociedad y la industria necesitaba permitiendo construir una nueva generación de convertidores de potencia. Sin embargo, esta técnica presenta algunos problemas cuando los convertidores son operados bajo unas condiciones desbalanceadas o asimétricas. Como consecuencia, el rendimiento y las buenas propiedades que estos convertidores presentan se ven deterioradas. Por lo tanto, el principal objetivo de este documento es dar solución a estos problemas para esta familia de convertidores de potencia. Como ocurren en la mayoría de los circuitos electrónicos, existe una analogía entre tensiones y corrientes. Esto está presente desde las leyes de Kirchoff (leyes de tensiones y corrientes) a las propiedades de los elementos electrónicos como pueden ser condensadores y bobinas, los cuales presentan una, más que clara, simetría. Así pues, problemas similares pueden ser encontrados cuando se construye un convertidor de potencia modular, ya sea en serie o en paralelo. Los convertidores serie presentan dicho problema en su tensión de salida mientras que los convertidores conectados en paralelo sufren el problema en su corriente de salida. Así que este documento puede ser dividido en dos partes bien diferenciadas. El capítulo 1 introduce al lector en el actual escenario energético. Además, este trata de explicar la razón de introducir los convertidores modulares en el escenario actual ilustrándolo con algunos ejemplos de aplicación real. Desde el capítulo 2 hasta el capítulo 9 el trabajo se centra en los problemas encontrados en los convertidores modulares en serie, en particular, en los problemas presentes en la tensión de salida para el convertidor cascada. Para ello, se ha desarrollado un modelo matemático basado en las series de Fourier que ha demostrado ser muy preciso. Se ha desarrollado varias técnicas de modulación para el convertidor cascada solucionando el problema de la distorsión generada en la tensión de salida el cual se localiza en el primer armónico de la portadora y sus múltiplos. Este problema se ha resuelto en el mayor rango posible en términos del número de celdas usado. Por otro lado, ante la imposibilidad de encontrar solución analítica cuando se considera más de un armónico simultáneamente, se han usado técnicas numéricas y algoritmos de búsqueda para encontrar la solución más apropiada teniendo en cuenta múltiples factores. La técnica propuesta no solo se puede usar para el convertidor cascada, sino que es fácilmente extensible a otros convertidores multinivel presentes en el mercado. Por otro lado, desde el capítulo 10 hasta el capítulo 12 este documento trata de afrontar los problemas encontrados en los convertidores modulares conectados en paralelo. Como se ha comentado, estos problemas se encuentran en la corriente de salida. Este fenómeno se estudia en profundidad para el caso del convertidor dc-dc de tres celdas para la aplicación fotovoltaica. Usando la misma filosofía y metodología, se puede controlar a voluntad el contenido armónico de la corriente total de salida. Esto afecta de manera directa a la vida útil del condensador pudiéndose extender la vida útil del mismo tal y como se ha demostrado a lo largo de la tesis. Esto se ha desarrollado para un convertidor tipo elevador de tres celdas para la aplicación de fotovoltaica. Sin embargo, como se ha visto a lo largo del desarrollo, es un procedimiento totalmente general y solo es necesario tener en cuenta la topología del convertidor para el cálculo de los coeficientes de Fourier. Por lo tanto, de nuevo nos encontramos ante un procedimiento totalmente extensible y compatible con otras aplicaciones

Adaptive phase-shifted PWM for multilevel cascaded H-bridge converters with large number of power cells

Article number 7915210Cascaded H-bridge multilevel converters are usually applied for high-power systems with independent dc sources. It can be used as PV inverter or to operate independent battery stacks. In these cases, as each dc source can be working at different operational points, conventional modulators lead to high distorted output waveforms degrading the converter performance. In this paper, a modulation method as a modified version of conventional phase-shifted PWM is presented when the CHB converter has a large number of power cells. This method is an extension of a previous technique only suitable for CHB converters with three power cells per phase. Simulation results show the good performance of the proposal with higher number of cells.Qatar National Research Fund NPRP9-310-2-134Junta de Andalucía P11- TIC-7070Ministerio de Educación y Ciencia de España TEC2016-78430-RMinisterio de Educación y Ciencia de España 115142

Common DC-Link Capacitor Harmonic Current Minimization for Cascaded Converters by Optimized Phase-Shift Modulation

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).This paper investigates the influence of a constant carrier phase shift on the DC-link capacitor harmonic current of cascaded converters used in fuel-cell and mild-hybrid electric vehicles. In these applications, a DC-DC converter can be adopted between the battery and the motor drive inverter in a cascaded structure, where the two converters share the same DC-link. Since the DC-link capacitor of such a system represents a critical component, the optimization of the converter operation to limit the current stress and extend the lifetime of the capacitor is an primary objective. This paper proposes the use of a carrier phase shift between the modulations of the two converters in order to minimize the harmonic current of the DC-link capacitor. By harmonic analysis, an optimal carrier phase shift can be derived depending on the converter configuration. Analytical results are presented and validated by hardware-in-the-loop experiments. The findings show that the pulse width modulation carrier phase shift between the interleaved boost converter and the voltage source motor drive inverter has a significant influence on the DC-link capacitor current and thus on its lifetime. A case study with two-cell and three-cell interleaved boost converters shows a possible DC-link capacitor lifetime extension of up to 390%