The Essential Role and the Continuous Evolution of Modulation Techniques for Voltage-Source Inverters in the Past, Present, and Future Power Electronics

The cost reduction of power-electronic devices, the increase in their reliability, efficiency, and power capability, and lower development times, together with more demanding application requirements, has driven the development of several new inverter topologies recently introduced in the industry, particularly medium-voltage converters. New more complex inverter topologies and new application fields come along with additional control challenges, such as voltage imbalances, power-quality issues, higher efficiency needs, and fault-tolerant operation, which necessarily requires the parallel development of modulation schemes. Therefore, recently, there have been significant advances in the field of modulation of dc/ac converters, which conceptually has been dominated during the last several decades almost exclusively by classic pulse-width modulation (PWM) methods. This paper aims to concentrate and discuss the latest developments on this exciting technology, to provide insight on where the state-of-the-art stands today, and analyze the trends and challenges driving its future

A Multi-stack Power-to-Hydrogen Load Control Framework for the Power Factor-Constrained Integration in Volatile Peak Shaving Conditions

Large-scale power-to-hydrogen (P2H) systems formed by multi-stack are potentially powerful peak-shaving resources of power systems. However, due to the research gap in connecting the grid-side performance with the inherent operation control, the continuous operation of P2H loads is limited by the PF assessment under volatile conditions when integrating into the grid. This paper first fills the gap in proposing the analytical models of active and reactive power of P2H loads with a typical power converter interface topology. On this basis, the all-condition PF characteristics of multi-stack P2H loads are captured as functions of unified current and temperature control variables. Then, a PF-constrained multi-timescale control framework is constructed to evaluate flexibility, PF, production, and security comprehensively. A two-level nexus, including a model-based hour-ahead robust model predictive controller and a rule-based real-time increment correction algorithm, is proposed to guarantee the control accuracy and tractability. Case studies verify an intrinsic control tradeoff between PF and production, resulting in an unequal-split allocation strategy compared to the traditional production-oriented control. The significance of the extended PF and security dimensions is verified to improve the flexibility. Furthermore, five typical operating modes respectively corresponding to low, medium, and high load levels at the cluster level are concluded for industrial application

Rectifier power converter for marine applications with compensating capacitor and boost converter stage

Environmental concerns and new emissions regulations, as well as increasing power needs for marine electrical grids, are pushing the development of more efficient power converters for shipboard power systems (SPS). The priorities for SPS design are reliability and power density especially in harsh operating conditions. Safety, space, and weight are of paramount importance requirements on a ship. One factor affecting the design of SPS is the high inductive impedance presented by ac generators, which requires high voltage ratios to compensate for. Therefore, ac-dc converters, sitting as they do between ac generators and the dc bus of the SPS, are identified as a point of potential development to improve the form factor and efficiency of SPS. A novel series capacitor compensation technique is proposed and applied to an ac-dc boost rectifier. Time-averaged equations are derived and compared to simulated waveforms generated using MATLAB/Simulink. Total harmonic distortion (THD) and power factor (PF) are calculated and measured. THD is found to be the limiting factor in designing the proposed compensator. The circuit is simulated in one and three phases, and several input-to-output voltage ratios are compared. To verify the practicality of the compensation method, a single-phase 1 kW rated prototype is implemented and practical results are presented and compared with the simulated waveforms. It is found that the compensation method can control THD to acceptable levels for a large range of inductive impedances, suggesting that this solution should be further developed and investigated for application in SPS.Environmental concerns and new emissions regulations, as well as increasing power needs for marine electrical grids, are pushing the development of more efficient power converters for shipboard power systems (SPS). The priorities for SPS design are reliability and power density especially in harsh operating conditions. Safety, space, and weight are of paramount importance requirements on a ship. One factor affecting the design of SPS is the high inductive impedance presented by ac generators, which requires high voltage ratios to compensate for. Therefore, ac-dc converters, sitting as they do between ac generators and the dc bus of the SPS, are identified as a point of potential development to improve the form factor and efficiency of SPS. A novel series capacitor compensation technique is proposed and applied to an ac-dc boost rectifier. Time-averaged equations are derived and compared to simulated waveforms generated using MATLAB/Simulink. Total harmonic distortion (THD) and power factor (PF) are calculated and measured. THD is found to be the limiting factor in designing the proposed compensator. The circuit is simulated in one and three phases, and several input-to-output voltage ratios are compared. To verify the practicality of the compensation method, a single-phase 1 kW rated prototype is implemented and practical results are presented and compared with the simulated waveforms. It is found that the compensation method can control THD to acceptable levels for a large range of inductive impedances, suggesting that this solution should be further developed and investigated for application in SPS

Multilevel Converters: An Enabling Technology for High-Power Applications

| Multilevel converters are considered today as the state-of-the-art power-conversion systems for high-power and power-quality demanding applications. This paper presents a tutorial on this technology, covering the operating principle and the different power circuit topologies, modulation methods, technical issues and industry applications. Special attention is given to established technology already found in industry with more in-depth and self-contained information, while recent advances and state-of-the-art contributions are addressed with useful references. This paper serves as an introduction to the subject for the not-familiarized reader, as well as an update or reference for academics and practicing engineers working in the field of industrial and power electronics.Ministerio de Ciencia y Tecnología DPI2001-3089Ministerio de Eduación y Ciencia d TEC2006-0386

Stability enhancement of HVAC grids using HVDC links.

M. Sc. Eng. University of KwaZulu-Natal, Pietermaritzburg 2016.Eskom is facing challenging times where the national power grid is placed under extreme pressure, therefore, the long existing poorly damped low frequency inter area oscillations affects the stability constraints thus reducing the power transfer capacity. Consequently new power stations are being built in remote locations to reduce the short fall of generation capacity and the HVDC technology has become appealing to transport large amount of power over long distance. This research aims to prove that stability enhancement of parallel AC systems can be achieved with the use of HVDC schemes. The HVDC system has the rapid ability to control the transmitted power during transient disturbances and this power system control has a significant effect on the dynamic performance of the system after a disturbance therefore the dynamic performance is related to the small signal stability, where the rotor oscillations are minimised and the system is brought back to steady state after an event or disturbance.The fundamentals of small signal stability in terms of observability, controllability, residues, network sensitivities and mode shape are explained together with a dominant oscillation path definition for HVDC links location selection. The key importance in controlling the power of the HVDC link to affect stability requires that the oscillation is observable and controllable. Simulation results on a simple four-generator, twoarea test system are presented, with a view to benchmark the results and develop a fundamental understanding of how using HVDC links for power transfer can stabilise the grid. The eigenvalue analysis of the system indicates the frequency of oscillations in the system and the generator’s participation factors, together with the controllability and observability of the inter area mode (mode of interest). There are a number of test simulations results from a LCCHVDC system (First Cigrê benchmark model) integrated into a test network where the influence on the small signal stability is analysed. Various literature has been reviewed which supports the basic principles, promoting the benefits of using HVDC systems to enhance stability of a parallel AC system (Hybrid) and then integrating supplementary control. This research investigates the use of the HVDC system to enhance the small signal stability with supplementary control which is termed predictive control. Power Oscillation Damping (POD) control through LCC HVDC links is studied to ensure secure operation of power systems. The Power oscillating damper is expressed as a transfer function whereas the MPC (Model Predictive Controller) is expressed as cost functions of a feedback signal which is a measured quantity. Two feedback signals are selected and their effectiveness with regard to their contribution to the damping of the system is investigated. The controller feedback signals are real power and voltage difference across the AC tie lines. Bode plots, root locus plots and time domain simulation results show the comparison between the different selected controller inputs and supplementary controls. The voltage angle difference is most effective as it is more sensitive to changes in the system and assists the controller in bringing the system to steady state in a shorter period of time when compared to the controller input that uses real power across the AC tie line. The controllers with the HVDC integrated, do improve the damping of the system and it is related to shorter mode decay time, the MPC however has been investigated to reduce the change of loading levels of the AC tie lines following a change in system operating conditions. Simulation responses from the research show that this method is more promising and does not require prior knowledge of the possible contingencies due to its ability to handle complex multi variable systems with constraints, by using cost function algorithms to perform predictions of future plant behaviour and calculating the suitable corrective control actions needed to take the predicted output as close as possible to the target value which is the steady state. This research however demonstrates the fundamental principle which proves that the HVDC together with supplementary control can enhance stability of a parallel AC system

Asset management strategies for power electronic converters in transmission networks: Application to HVdc and FACTS devices

The urgency for an increased capacity boost bounded by enhanced reliability and sustainability through operating cost reduction has become the major objective of electric utilities worldwide. Power electronics have contributed to this goal for decades by providing additional flexibility and controllability to the power systems. Among power electronic based assets, high-voltage dc (HVdc) transmission systems and flexible ac transmission systems (FACTS) controllers have played a substantial role on sustainable grid infrastructure. Recent advancements in power semiconductor devices, in particular in voltage source converter based technology, have facilitated the widespread application of HVdc systems and FACTS devices in transmission networks. Converters with larger power ratings and higher number of switches have been increasingly deployed for bulk power transfer and large scale renewable integration—increasing the need of managing power converter assets optimally and in an efficient way. To this end, this paper reviews the state-of-the-art of asset management strategies in the power industry and indicates the research challenges associated with the management of high power converter assets. Emphasis is made on the following aspects: condition monitoring, maintenance policies, and ageing and failure mechanisms. Within this context, the use of a physics-of-failure based assessment for the life-cycle management of power converter assets is introduced and discussed

An Overview of Applications of the Modular Multilevel Matrix Converter

The modular multilevel matrix converter is a relatively new power converter topology suitable for high-power alternating current (AC)-to-AC applications. Several publications in the literature have highlighted the converter capabilities, such as full modularity, fault-redundancy, control flexibility and input/output power quality. However, the topology and control of this converter are relatively complex to realise, considering that the converter has a large number of power-cells and floating capacitors. To the best of the authors’ knowledge, there are no review papers where the applications of the modular multilevel matrix converter are discussed. Hence, this paper aims to provide a comprehensive review of the state-of-the-art of the modular multilevel matrix converter, focusing on implementation issues and applications. Guidelines to dimensioning the key components of this converter are described and compared to other modular multilevel topologies, highlighting the versatility and controllability of the converter in high-power applications. Additionally, the most popular applications for the modular multilevel matrix converter, such as wind turbines, grid connection and motor drives, are discussed based on analyses of simulation and experimental results. Finally, future trends and new opportunities for the use of the modular multilevel matrix converter in high-power AC-to-AC applications are identified.Agencia Nacional de Investigación y Desarrollo/[Fondecyt 11191163]/ANID/ChileAgencia Nacional de Investigación y Desarrollo/[Fondecyt 1180879]/ANID/ChileAgencia Nacional de Investigación y Desarrollo/[Fondecyt 11190852]/ANID/ChileAgencia Nacional de Investigación y Desarrollo/[ANID Basal FB0008]/ANID/ChileAgencia Nacional de Investigación y Desarrollo/[Fondef ID19I10370]/ANID/ChileUniversidad de Santiago/[Dicyt 091813DD]//ChileUCR::Vicerrectoría de Docencia::Ingeniería::Facultad de Ingeniería::Escuela de Ingeniería Eléctric