Industrial and Technological Applications of Power Electronics Systems

The Special Issue "Industrial and Technological Applications of Power Electronics Systems" focuses on: - new strategies of control for electric machines, including sensorless control and fault diagnosis; - existing and emerging industrial applications of GaN and SiC-based converters; - modern methods for electromagnetic compatibility. The book covers topics such as control systems, fault diagnosis, converters, inverters, and electromagnetic interference in power electronics systems. The Special Issue includes 19 scientific papers by industry experts and worldwide professors in the area of electrical engineering

Data-driven model-based approaches to condition monitoring and improving power output of wind turbines

The development of the wind farm has grown dramatically in worldwide over the past 20 years. In order to satisfy the reliability requirement of the power grid, the wind farm should generate sufficient active power to make the frequency stable. Consequently, many methods have been proposed to achieve optimizing wind farm active power dispatch strategy. In previous research, it assumed that each wind turbine has the same health condition in the wind farm, hence the power dispatch for healthy and sub-healthy wind turbines are treated equally. It will accelerate the sub-healthy wind turbines damage, which may leads to decrease generating efficiency and increases operating cost of the wind farm. Thus, a novel wind farm active power dispatch strategy considering the health condition of wind turbines and wind turbine health condition estimation method are the proposed. A modelbased CM approach for wind turbines based on the extreme learning machine (ELM) algorithm and analytic hierarchy process (AHP) are used to estimate health condition of the wind turbine. Essentially, the aim of the proposed method is to make the healthy wind turbines generate power as much as possible and reduce fatigue loads on the sub-healthy wind turbines. Compared with previous methods, the proposed methods is able to dramatically reduce the fatigue loads on subhealthy wind turbines under the condition of satisfying network operator active power demand and maximize the operation efficiency of those healthy turbines. Subsequently, shunt active power filters (SAPFs) are used to improve power quality of the grid by mitigating harmonics injected from nonlinear loads, which is further to increase the reliability of the wind turbine system

Optimisation of High Reliability Integrated Motor Drives

The development of integrated motor drives (IMDs) with high volumetric power density and reliability are crucial for the continued development and adoption of electric vehicles (EV). The development of the wide bandgap (WBG) devices, especially Silicon Carbide (SiC) MOSFETs, enables new possibilities for traction drive systems. However, to maximise the benefits of SiC, the IMD design process, including passive component selection, control and thermal management should be optimised. This thesis goes through the initial major design steps in SiC power system design, from SiC device analysis and modelling to circuit design and electrothermal simulation of an IMD system. A novel approach to discrete SiC MOSFET selection, using a method of calculating performance based on experimental data, is described. Dynamic behaviour of a family of 1200 V MOSFETs is studied at temperatures up to 175 °C using a double pulse test to show the combined effect of the differences in internal design between MOSFETs with different current ratings. It is observed that the 30 mΩ MOSFET had a 24 % higher switching loss than a 140 mΩ at a 30 A load current. The study then goes on to compare the effect of switching frequency, paralleling of MOSFETs and the device type used to demonstrate the inverter design with the lowest power losses, which will equate to low temperatures and high lifetime. The novel methodology can find the optimal choice of MOSFET from the family, and number required through paralleling, for a circuit when given the load current, temperature and switching. Understanding the device interdependencies in a single family is utilised to also predict the relative performance between SiC MOSFETs from different manufacturers. An axial-flux permanent magnet synchronous motor (PMSM) driven by a three-phase SiC inverter is simulated in PLECS using experimentally validated MOSFET models chosen by the device selection methodology. Electrothermal analysis shows the influence of switching frequency, temperature, MOSFETs paralleling and DC-link capacitance on voltage ripple, total harmonic distortion, efficiency and MOSFET loss and temperature profiles. With a 60 % decrease in THD and 50 % increase in maximum MOSFET junction temperature when switching frequency is increased from 10 to 100 kHz. The high-temperature stress on the semiconductors due to close proximity with the ma- chine stator means reliability is an important consideration that is yet to be fully investigated in IMD optimisations. This study uses a lifetime model specific to the transistor package TO-247 in reliability optimisation for IMD for the first time. It requires detailed MOSFET simulation outputs to provide a highly accurate lifetime for discrete SiC MOSFETs. Both single and multi-objective optimisations of the volume and lifetime of the three- phase inverter are presented. The single objective optimisation demonstrates the minimum volume and the corresponding switching frequency and lifetime when between three and six MOSFETs are paralleled at a temperature range between 50 and 150 °C. Design constraints were set limiting the feasible switching frequency range to between 13 kHz because of THD and 118 kHz because of efficiency limits, corresponding to required DC-link capacitors of 520 and 55 μF respectively. Increases in temperature were found to further limit the maximum switching frequency and therefore increase the minimum volume of the inverter. A Pareto front identifies a range of possible solutions for the volume and lifetime of an inverter with six paralleled MOSFETs through the multi-objective objective procedure. Further analysis of these possible solutions identified a single optimal solution for the system, using a DC-link capacitance of 190 μF at 45 kHz, giving a combined volume of the capacitor and MOSFETs of 440 cm3 and a lifetime of 12,000 hours. Finally, the electrothermal analysis of a dual inverter driving a symmetric six-phase PMSM is presented with the benefits of modular multi-phase systems in IMDs summarised. Effect on performance of lower per-phase current, interleaving strategies and fault tolerance are analysed and compared to equivalent three-phase systems, for 60 kW and 120 kW operation. A novel method for lifetime prediction of systems with paralleled MOSFETs or fault tolerance capabilities considering incremental damage is developed based on TO-247 lifetime calculations from PLECS simulation, and component-level reliability profiles using Monte Carlo analysis. The dual inverter is used to model the system and implements control schemes for both single-phase and single inverter failure while maintaining the 4000 rpm and 140 Nm speed and torque requirements. A twofold increase in B10 lifetime of is observed when the effect of paralleled SiC MOSFETs prevents immediate system failure in a three-phase inverter. A computational fluid dynamics (CFD) and 3D finite element thermal model are designed to study the inverter behaviour based on the thermal analysis of its shared cooling plate with a 300 mm diameter axial flux PMSM. Concentric layout designs minimise the variation of junction temperatures to 5 °C and the effect of the flow rate and temperature of the coolant in the PMSM cold plate is presented between 5 and 30 l/min. The multi-objective optimisation procedure used to compare the dual inverter demonstrated it outperformed the three-phase inverter with 15 % smaller required DC-link capacitance, higher efficiency and increased lifetime in part due to its fault-tolerant nature. The optimal dual inverter considering the design constraints consists of four 40 μF KEMET film capacitors operating with a switching frequency of 46 kHz giving an inverter volume of 300 cm3 and a lifetime of 16.3 years, assuming 1000 hours of operation annually

Power Quality

Electrical power is becoming one of the most dominant factors in our society. Power generation, transmission, distribution and usage are undergoing signifi cant changes that will aff ect the electrical quality and performance needs of our 21st century industry. One major aspect of electrical power is its quality and stability – or so called Power Quality. The view on Power Quality did change over the past few years. It seems that Power Quality is becoming a more important term in the academic world dealing with electrical power, and it is becoming more visible in all areas of commerce and industry, because of the ever increasing industry automation using sensitive electrical equipment on one hand and due to the dramatic change of our global electrical infrastructure on the other. For the past century, grid stability was maintained with a limited amount of major generators that have a large amount of rotational inertia. And the rate of change of phase angle is slow. Unfortunately, this does not work anymore with renewable energy sources adding their share to the grid like wind turbines or PV modules. Although the basic idea to use renewable energies is great and will be our path into the next century, it comes with a curse for the power grid as power fl ow stability will suff er. It is not only the source side that is about to change. We have also seen signifi cant changes on the load side as well. Industry is using machines and electrical products such as AC drives or PLCs that are sensitive to the slightest change of power quality, and we at home use more and more electrical products with switching power supplies or starting to plug in our electric cars to charge batt eries. In addition, many of us have begun installing our own distributed generation systems on our rooft ops using the latest solar panels. So we did look for a way to address this severe impact on our distribution network. To match supply and demand, we are about to create a new, intelligent and self-healing electric power infrastructure. The Smart Grid. The basic idea is to maintain the necessary balance between generators and loads on a grid. In other words, to make sure we have a good grid balance at all times. But the key question that you should ask yourself is: Does it also improve Power Quality? Probably not! Further on, the way how Power Quality is measured is going to be changed. Traditionally, each country had its own Power Quality standards and defi ned its own power quality instrument requirements. But more and more international harmonization efforts can be seen. Such as IEC 61000-4-30, which is an excellent standard that ensures that all compliant power quality instruments, regardless of manufacturer, will produce of measurement instruments so that they can also be used in volume applications and even directly embedded into sensitive loads. But work still has to be done. We still use Power Quality standards that have been writt en decades ago and don’t match today’s technology any more, such as fl icker standards that use parameters that have been defi ned by the behavior of 60-watt incandescent light bulbs, which are becoming extinct. Almost all experts are in agreement - although we will see an improvement in metering and control of the power fl ow, Power Quality will suff er. This book will give an overview of how power quality might impact our lives today and tomorrow, introduce new ways to monitor power quality and inform us about interesting possibilities to mitigate power quality problems. Regardless of any enhancements of the power grid, “Power Quality is just compatibility” like my good old friend and teacher Alex McEachern used to say. Power Quality will always remain an economic compromise between supply and load. The power available on the grid must be suffi ciently clean for the loads to operate correctly, and the loads must be suffi ciently strong to tolerate normal disturbances on the grid

Optimal Control of Power Quality in Microgrids Using Particle Swarm Optimisation

Driven by environmental protection, economic factors, conservation of energy resources, and technical challenges, the microgrid has emerged as an innovative small-scale power generation network. Microgrids consist of a cluster of Distributed Generation units that encompass a portion of an electric power distribution system and may rely on different energy sources. Functionally, the microgrid is required to provide adequate levels and quality of power to meet load demands. The issue of power quality is significant as it directly affects the characteristics of the microgrid’s operation. This problem can be defined as an occurrence of short to long periods of inadequate or unstable power outputs by the microgrid. In a stand-alone operation mode, the system voltage and frequency must be established by the microgrid, otherwise the system will collapse due to the variety in the microgrid component characteristics. The harmonic distortion of the output power waveforms is also a serious problem that often occurs because of the high speed operation of the converter switches. The long transient period is a critical issue that is usually caused by changing the operation mode or the load demand. Power sharing among the Distributed Generation units is also an important matter for sharing the load appropriately, particularly given that some renewable energy resources are not available continuously. In a utility connected microgrid, the reliable power quality mainly depends on the regulation of both active and reactive power, because the microgrid’s behaviour is mostly dominated by the bulk power system. Therefore, an optimal power control strategy is proposed in this thesis to improve the quality of the power supply in a microgrid scenario. This controller comprises an inner current control loop and an outer power control loop based on a synchronous reference frame and conventional PI regulators. The power control loop can operate in two modes: voltage-frequency power control mode and active-reactive power control mode. Particle Swarm Optimisation is an intelligent searching algorithm that is applied here for real-time self-tuning of the power control parameters. The voltage-frequency power controller is proposed for an inverter-based Distributed Generation unit in an autonomous operation mode. The results show satisfactory system voltage and frequency, high dynamic response, and an acceptable harmonic distortion level. The active-reactive power controller is adopted for an inverter-based Distributed Generation unit in a utility operation mode. This controller provides excellent regulation of the active and reactive power, in particular when load power has to be shared equally between the microgrid and utility. The voltage-frequency and active-reactive power control modes are used for a microgrid configured from two DG units in an autonomous operation mode. The proposed control strategy maintains the system voltage and frequency within acceptable limits, and injects sustained output power from one DG unit during a load change. The reliability of the system’s operation is investigated through developing a small-signal dynamic model for the microgrid. The results prove that the system was stable for the given operating point and under the proposed power controller. Consequently, this research reveals that the microgrid can successfully operate as a controllable power generation unit to support the utility, thus reducing the dependency on the bulk power system and increasing the market penetration of the micro-sources

Enhanced Performance Bidirectional Quasi-Z-Source Inverter Controller

A novel direct control of high performance bidirectional quasi-Z-source inverter (HPB-QZSI), with optimized controllable shoot-through insertion, to improve the voltage gain, efficiency and to reduce total harmonic distortion is investigated. The main drawback of the conventional control techniques for direct current to alternating current (DC-AC) conversion is drawn from the multistage energy conversion structure, which implies complicated control, protection algorithms and reduced reliability due to the increased number of switching devices. Theoretically, the original Z-source, Quasi-Z-source, and embedded Z-source all have unlimited voltage gain. Practically, however, a high voltage gain (>2 or 3), will result in a high voltage stress imposed on the switches. Every additional shoot-through state increases the commutation time of the semiconductor switches, thereby increasing the switching losses in the system. Hence, minimization of the commutation time by optimal placing of the shoot-through state in the switching time period is necessary to reduce the switching loss. To overcome this problem, a combination of high performance bidirectional quasi-Z-source inverter with a sawtooth carrier based sinusoidal pulse width modulation (SPWM) in simple operation condition for maximum boost control with 3rd harmonic injection is proposed. This is achieved by voltage-fed quasi-Z-source inverter with continuous input current, implemented at the converter input side which can boost the input voltage by utilizing the extra switching state with the help of shoot-through state insertion technique. This thesis presents novel control concepts for such a structure, focusing mainly on the control of a shoot-through insertion. The work considers the derivation and application of direct controllers for this application and scrutinizes the technical advantages and potential application issues of these methodologies. Based on the circuit analysis, a small signal model of the HPB-QZSI is derived, which indicates that the circuit is prone to oscillate when there is disturbance on the direct current (DC) input voltage. Therefore, a closed-loop control of shoot-through duty cycle is designed to obtain the desired DC bus voltage. The DC-link boost control and alternating current (AC) side output control are presented to reduce the impacts of disturbances on loads. The proposed strategy gives a significantly high voltage gain compared to the conventional pulse width modulation (PWM) techniques, since all the zero states are converted into shoot-through states. The simulated results verify the validity and superiority of the proposed control strategies

Design Synthesis and Optimization of Permanent Magnet Synchronous Machines Based on Computationally-Efficient Finite Element Analysis

In this dissertation, a model-based multi-objective optimal design of permanent magnet ac machines, supplied by sine-wave current regulated drives, is developed and implemented. The design procedure uses an efficient electromagnetic finite element-based solver to accurately model nonlinear material properties and complex geometric shapes associated with magnetic circuit design. Application of an electromagnetic finite element-based solver allows for accurate computation in intricate performance parameters and characteristics. The first contribution of this dissertation is the development of a rapid computational method that allows accurate and efficient exploration of large multi-dimensional design spaces in search of optimum design(s). The computationally efficient finite element-based approach developed in this work provides a framework of tools that allow rapid analysis of synchronous electric machines operating under steady-state conditions. In the developed modeling approach, major steady-state performance parameters such as, winding flux linkages and voltages, average, cogging and ripple torques, stator core flux densities, core losses, efficiencies and saturated machine winding inductances, are calculated with minimum computational effort. In addition, the method includes means for rapid estimation of distributed stator forces and three-dimensional effects of stator and/or rotor skew on the performance of the machine. The second contribution of this dissertation is the development of the design synthesis and optimization method based on a differential evolution algorithm. The approach relies on the developed finite element-based modeling method for electromagnetic analysis and is able to tackle large-scale multi-objective design problems using modest computational resources. Overall, computational time savings of up to two orders of magnitude are achievable, when compared to current and prevalent state-of-the-art methods. These computational savings allow one to expand the optimization problem to achieve more complex and comprehensive design objectives. The method is used in the design process of several interior permanent magnet industrial motors. The presented case studies demonstrate that the developed finite element-based approach practically eliminates the need for using less accurate analytical and lumped parameter equivalent circuit models for electric machine design optimization. The design process and experimental validation of the case-study machines are detailed in the dissertation

Advanced Statistical Modeling, Forecasting, and Fault Detection in Renewable Energy Systems

Fault detection, control, and forecasting have a vital role in renewable energy systems (Photovoltaics (PV) and wind turbines (WTs)) to improve their productivity, ef?ciency, and safety, and to avoid expensive maintenance. For instance, the main crucial and challenging issue in solar and wind energy production is the volatility of intermittent power generation due mainly to weather conditions. This fact usually limits the integration of PV systems and WTs into the power grid. Hence, accurately forecasting power generation in PV and WTs is of great importance for daily/hourly efficient management of power grid production, delivery, and storage, as well as for decision-making on the energy market. Also, accurate and prompt fault detection and diagnosis strategies are required to improve efficiencies of renewable energy systems, avoid the high cost of maintenance, and reduce risks of fire hazards, which could affect both personnel and installed equipment. This book intends to provide the reader with advanced statistical modeling, forecasting, and fault detection techniques in renewable energy systems