PELS DLs

This lecture provides an introduction to finite control set model predictive control (FCS-MPC), which is very popular in academia. Although only a one-step horizon is usually used, FCS-MPC performs particularly well when adopting long prediction horizons. To solve the underlying integer optimization problem, a tailored branch-and-bound method will be presented, which can be implemented on an FPGA with real-time guarantees. Application examples will be discussed, including converters with LC filters, which necessitate the use of long horizons. The lecture concludes with a critical assessment of FCS-MPC that identifies some of the obstacles to be addressed to make FCS-MPC a success not only in academia but also in industry.

The number of publications per year on predictive control doubles every three years. The strong interest in academia is reflected in industry with two recent product releases. Both use model predictive control for high-power variable speed drives, which improves efficiency, increases rated power and lowers the overall system cost. This lecture introduces the main predictive control methods available today in a concise yet intuitively accessible way. The lesser known methods are also discussed, providing a comprehensive introduction to the subject. The first two industrial success stories are presented in detail, and their commercial benefits are explained. The lecture concludes with a critical assessment of the state-of-the-art in predictive control and points out directions for future research.

Model predictive pulse pattern control (MP3C) fully exploits the performance potential of high-power converters by ensuring fast control at low switching frequencies with low harmonic distortions. The underlying research vision was to combine the benefits of deadbeat control with the optimal steady-state performance of optimized pulse patterns (OPPs). The MP3C principle can be applied to a wide range of applications, including medium-voltage (MV) drives, low-voltage traction converters, and modular multilevel converters used as STATCOM or railway interties. MP3C has recently been commercialized for a major MV drive. Extensive experimental results from the MV lab as well as results from a pilot installation will be shown and discussed.

Power electronics and static power converters play significant role in industrial applications, power generation and transmission, home appliance, transportation, etc., etc. Today, our life will be completely different without power electronics. Power electronics and power converters, particularly power semiconductors are progressing on daily bases. Designers of new generation of power converters are facing very strong demands to reduce the converter cost, size, weight and losses. To achieve these challenging objectives, new power semiconductors as well passive devices are a Must. However, each new generation of power semiconductor introduces new challenges and issues. Some of them make almost impossible to fully utilize full advantages of new power semiconductor devices. Two of the challenges are high di/dt and dv/dt, which in combination with parasitic inductance and capacitance of the power semiconductor and converter create issues of over-voltage, radiated and conducted EMI emission, stress of the load isolation, etc., etc. The above mentioned issues (di/dt and dv/dt) will make impossible to fully utilize all the benefits of future Wide Band Gap devices such as SiC and GaN. New devices packaging is a must. Where is the limit of new packages? Is it possible to solve all the issue with a new package and new power devices or something more is necessary? New system approach is a MUST! It is necessary to involve new topologies, such as multi-level, multi-cell and multi-level/cell converters.  In the first part of the seminar interleaved multi-cell (parallel) power converters will be discussed. The advantages of such a concept, such as switching frequency multiplication, the filter inductance and the dc bus capacitor reduction will be theoretical analyzed and practical examples given. Then, high current applications will be discussed with particular focus on di/dt and related over-voltage reduction. In the second part of the seminar interleaved multi-level (series) power converters will be discussed. The advantage such of such a concept, such as the filter inductance and devices voltage stress reduction will be theoretical analyzed and practical examples given. Then, medium/high voltage applications will be discussed with particular focus on dv/dt issue. Several case studies and design examples will be given as concluding part of the seminar. This seminar is aimed at power electronics engineers, professionals and graduate students who want to improve their knowledge and understanding of multi-level/cell power converters and their capabilities to push the limits of Si as  well as WBG devices.

The electric power system is going through an unprecedented transformation and related challenges in the implementation of smart grids. The smart grid is based on the flexible electrical power system that coordinates different energy resources and loads with the aim of delivering sustainable, economical and reliable electrical supply to the loads in an efficient manner.

In this presentation, a plug and play type autonomous-microgrid system formation is proposed. Multiple distributed generating sources and loads interaction is considered pertaining to the stability of the micro-grid. The proposed method enables communication-less operation of each of the elements of the micro-grid system. It is also considered that the sources are of different power capacity as can be seen in a typical autonomous micro-grid system. Spatial Repetitive Controller (SRC) is proposed to control each of the distributed generating sources in a decentralized manner to stabilize the overall micro-grid system. The proposed system considers sudden change in load as well as other distributed generators conditions like a true plug and play operation. A novel signature frequency voltage injection method is proposed to identify the presence of special distributed generator and operation of backup distributed generators. The implemented control architecture also ensures stability of the micro-grid fundamental frequency even in the case of dynamic conditions unlike the traditional droop-control method. A detailed experimental study is carried out and the experimental results presented show the efficacy of the proposed system.

Renewable energy sources (RESs) have been receiving significant attention recently worldwide as a sustainable alternative type of energy supply in the energy mix. Inverters are being used to convert the dc voltage into ac voltage before being injected into the grid or isolated loads.

In this presentation, a novel current control technique is proposed to control both active and

reactive power flow from a renewable energy source feeding a micro-grid system through a single-phase parallel connected inverter. The parallel connected inverter ensures active and reactive power flow from the grid with low current THD even in the presence of non-linear load. A p-q theory-based approach is used to find the reference current of the parallel connected converter to ensure desired operating conditions at the grid terminal. The proposed current controller is simple to implement and gives superior performance over the conventional current controllers such as rotating frame PI controller or stationary frame Proportional Resonant (PR) controller. The stability of the proposed controller is ensured by direct Lyapunov method. A new technique based on the Spatial Repetitive Controller (SRC) is also proposed to improve the performance of the current controller by estimating the grid and other periodic disturbances. Detailed experimental results are presented to show the efficacy of the proposed current control scheme along with the proposed non-linear controller to control the active and reactive power flow in a single-phase micro-grid under different operating conditions.

Renewable energy sources (RESs) have been receiving significant attention recently worldwide as a sustainable alternative type of energy supply in the energy mix. Inverters are being used to convert the dc voltage into ac voltage before being injected into the grid or isolated loads.

In this presentation, a control strategy for a single-phase series connected inverter with the

micro-grid is proposed to interface AC loads not only to regulate the load voltage under voltage disturbances but also, to control the load power drawn from the micro-grid. The inverter compensating voltage works in such a way that, irrespective of any type of disturbances in the micro-grid voltage (such as sag, swell or harmonic distortions), the load voltage is maintained at its rated voltage level with low THD in voltage. The proposed control strategy also facilitates a specific amount of active power flow (from renewable energy source) to the load irrespective of the micro-grid voltage condition. The rest of the load power is supplied by the micro-grid. To facilitate this control strategy a Spatial Repetitive Controller (SRC) is proposed and implemented in micro-grid phase (q ) domain to make the controller independent of the micro-grid frequency. The proposed controller ensures dynamic stability of the system even if there is a sudden change in the micro-grid frequency. Detailed experimental results are presented to show the efficacy of the proposed series inverter system along with the controller under different operating conditions

Since the power converters used by renewable energy generation do not perform as conventional electromechanical generators, large-scale penetration of renewable energies processed by power converters can impact negatively to the overall performance of the power system. In addition to a review of the last requirements set by the grid codes for grid-connection of power converters, this lecture will offer a sound technical discussion about how the advanced functionalities provided by the power converter controllers should be transformed into ancillary and flexibility grid services, and how such services improve the operation of the distributed power system dominated by power electronics.

Power converters can take several roles when connected to an electrical grid, ranging from grid-following converters, which inject current into a given voltage source provided by the grid, to grid-forming converters, which are able to energize an electrical grid ‘from scratch’ and regulate its operation when other generators and loads are connected. Actually, this performance is quite similar to the one for the well-known synchronous generator. This lecture will present the operation principle and controllers of the grid-forming converters –sometimes also called virtual synchronous generators/machines, will analyse their performance and will make an overview of the most relevant implementation approaches exiting in the literature.Power converters can take several roles when connected to an electrical grid, ranging from grid-following converters, which inject current into a given voltage source provided by the grid, to grid-forming converters, which are able to energize an electrical grid ‘from scratch’ and regulate its operation when other generators and loads are connected. Actually, this performance is quite similar to the one for the well-known synchronous generator. This lecture will present the operation principle and controllers of the grid-forming converters –sometimes also called virtual synchronous generators/machines, will analyse their performance and will make an overview of the most relevant implementation approaches exiting in the literature.

Controllers of grid-connected power converters impact significantly on the performance of the electrical grid, giving rise to phenomena, such as the sub-synchronous interactions, which should be properly studied to ensure a stable operation in the power system. Stability analysis at the system level, when such a system is dominated by grid-connected power converters, is still a challenging study among power converter designers. This lecture shows how to elaborate power converter models compatible with power system models, and how power systems analysis techniques should be used and adapted to properly tune the power converter controllers according to given operational requirements.  

Grid synchronization and current/voltage control of grid-connected power converters are two essential low-level areas that should be perfectly dominated to design modern grid applications, such as renewable energy generators, energy storage systems, microgrids and HVdc links. This lecture not only will offer a detailed review of the most popular techniques used in the synchronization and control of power converters, but it will provide valuable insights about their actual implementation, pointing out their pros and cons, and evaluating their performance under real grid operating conditions, e.g. connection to weak grids and response in front of gird faults, distortion and unbalances.

This presentation covers control algorithms for active filter (AF). A three-phase insulated gate bipolar transistor (IGBT) based current controlled voltage source inverter (CC-VSI) with a DC bus capacitor can be used as an AF. There are many control algorithms for the AF such as reactive power control, active power control, power-balance control, direct and quadrature (d-q) model-based control systems, etc. It is noted that most existing feedforward control methods of the AF system result in switching notches (sharp-rising ripples) in the supply current during transitions of the stepped waveshape nonlinear load current. Through laboratory experimentation, it is demonstrated that the direct current control method, which works on the principle of feedback, eliminates switching notches in supply currents and locks sinusoidally shaped three-phase supply currents in-phase with the supply voltages. Use of wide bandgap (WBG) devices will also be discussed as WBG devices offer significant potential to miniaturize AF hardware.

In this lecture a broad review of vehicles for farming operation will be given starting from tillage to crop harvesting. Vehicle that have significant use of power electronics will be covered such as Exact Emerge Planter for seeding operation. This presentation will cover how power electronics supports crop-care system to exactly apply prescription such as fertilizers, pesticides, fungicide, etc. Idea is to create awareness that power electronics professionals could enable increased productivity so that by 2050 over 9.5 billion could have food, shelter, and an efficient transportation system. This talk will also cover how vehicle electrification enables many functions, forms, and features in off- and on-highway vehicles that were not cost- and space-effective possible without SiC and GaN devices.

Abstract: - This presentation will cover publicly known information on the 200 kW 1050 VDC silicon carbide (SiC) inverter technology development project in John Deere. The SiC inverter converts vehicle engine power into electrical power needed for the permanent-magnet-motor based electric powertrain used in heavy-duty construction and mining vehicles. The presentation will cover design, development, and test verification of WBG technology deployed in the successful realization of a power-dense (43 kW/Liter) high-temperature (suitable for 115°C coolant) high-efficiency (> 98% over entre range of coolant) SiC dual-inverter.

Power electronics are becoming ubiquitous in the power grid, driven largely by renewable energy. In addition to being the grid interface for PV and wind turbines, power electronics also enable new grid infrastructures and energy storage that are necessary for supporting large-scale renewable development. With many countries pledging to carbon neutrality in less than 30 years, the grid will be increasingly dominated by renewables and inevitably evolve into a converter-based power system that is in sharp contrast to today’s grid based on synchronous generators. This talk gives a general overview of power electronics applications in power systems, discusses fundamental differences between converters and machines in the context of system stability, and sheds some lights on possible ways to design and control a converter-based power system.

Development of converter-based power systems requires new stability theories and design tools. Fast controls of converters introduce high-frequency dynamics and create the potential for instability in the EMT frequency range that is not considered in traditional power system stability studies. Existing stability theories and methods based on fundamental-frequency (rms-value) models are not applicable in the EMT frequency range, and EMT simulation models, being time variant and highly nonlinear, are not suitable for general stability studies. Small-signal sequence impedance theory has been developed to address these challenges and provides a general framework for frequency-domain stability studies of converter-based power systems. This talk gives an overview of the theory and its applications.

This talk reviews the development of small-signal sequence impedance models for wind turbines and the use of such models in wind energy system stability studies. Both type-III and type-IV turbines are covered, with their impedance models given in a similar analytical form to highlight key factors that dominate the impedance. The mechanisms and root causes for each type of turbines to develop instability with different types of transmission systems (long overhead lines, series-compensated lines, cables, and HVDC converter) in the subsynchronous, supersynchronous, and high frequency range are explained based on theoretical analyses and field measurements. Practical solutions to each type of instability problems are also reviewed.

This talk reviews the development of small-signal sequence impedance models for HVDC converters and the use of such models in HVDC transmission system stability studies. The focus is on VSC-HVDC based on MMC, but classical HVDC based on LCC is also considered. The developed impedance models include the effects of second harmonics in MMC and all characteristic harmonics in LCC. Impedance-based stability analysis is used to explain the modes and root causes of possible instability at both ac and dc terminals of each HVDC converter. Several case studies from an offshore wind farm with HVDC transmission are presented to demonstrate the behavior of system instability and possible solutions.

Battery energy storage systems (BESS) are the main infrastructures in the microgrids to ensure power balance and stable operation, as well as in the utility grid to enhance flexibility and stability. Bi-directional DC-DC converters are the key elements in BESS, which interface batteries and DC bus for power transfer. In this lecture, a comprehensive review for isolated bi-directional DC-DC converters is presented. The requirements of BESS on isolated bidirectional DC-DC converters with high efficiency and high power density are introduced. Two major solutions of isolated bidirectional DC-DC converters, CLLC resonance converter and dual-active-bridge (DAB) converter, are investigated and compared, including modeling methods, control strategies and design considerations with the use of SiC and GaN devices. This lecture points out that both CLLC and DAB converters have their own advantages and good application prospects in future large-scale energy storage systems. Moreover, a modular multi-port CLLC converter based on high frequency AC bus sharing is proposed to integrate multiple battery stacks, which features high efficiency, high reliability and good scalability.

Hybrid AC/DC microgrids with DC and AC sources/loads are considered to be the most likely future microgrid structures, since DC subgrid features high efficiency and free of harmonics/reactive power, and AC subgrid is easy to connect conventional utility grid. A panoramic overview of hybrid AC/DC microgrids is given in this lecture through the review of ongoing projects. The operation control and power management strategies of hybrid AC/DC microgrids based on the inter support between AC subgrid and DC subgrid are discussed. High penetration integration of renewable generation brings some challenges into hybrid AC/DC microgrids, hence, this lecture focuses on the coordination control between renewable generation and energy storage. Moreover, as a future trend, the conceptual framework of networked microgrid clusters is introduced to further enhance system operation flexibility. Smart multi-functional services of AC/DC interfacing converters are presented in terms of resilience control, active stabilization, power quality improvement and cost-efficiency optimization.

In the future smart grid, it is a significant trend to integrate large capacity renewable energy into medium voltage (MV) DC grids. The high power conversion techniques for wind generation, photovoltaic generation and hydrogen energy system integrated into MVDC grids are reviewed and compared in this lecture, including the system configurations, AC-DC and DC-DC converter designs, control strategies and fault protection. Novel solutions of DC grid-connected photovoltaic generation system are presented, providing new ways to integrate solar energy to DC grids with high efficiency and high power density. As the key element of high power isolated DC-DC converters, high frequency transformers with high withstand voltage are studied in terms of multi-physics modeling, magnetic integration, insulation design, thermal design and multi-objective optimization.

Power loss modelling of magnetic components becomes increasingly important in the design of power electronics converters, especially in the case of higher switching frequencies enabled by emerging wide-bandgap devices where the magnetic component loss can be significant. There are clear challenges in both the core loss and winding loss estimation. For the core loss, under PWM (rectangular) excitation with dc-bias and non-50% duty cycle, the conventional Steinmetz Equation or Improved Steinmetz Equation are not accurate anymore. For winding (copper) loss, the increased skin and proximity effect and random winding patterns make the conventional modelling methods very difficult to work. This lecture will introduce a ‘Triple Pulse Test’ (TPT) method, which can be used to predict the losses of magnetic components through a number of tests with three pulses and a loss map. The proposed TPT is analogous to the common ‘Double Pulse Test’ for characterising the losses of power electronics devices and converters. How to further build a user-friendly datasheet for magnetic components based on the TPT will be discussed. Several examples of inductors, transformers with various magnetic material will be given to demonstrate the proposed method. 

The controllability of capacitor voltages in multilevel converters is essential to enable their use in practice. This includes the voltage control of the dc-link capacitors and the flying capacitors (FC). When the number of voltage levels of NPC converters is four or higher, or simplified multilevel topologies with reduced number of devices are used, the capacitor voltage control becomes particularly challenging. This lecture will introduce a new ‘Redundant Level Modulation’, when combined with optimal zero-sequence injection, has superior capability to balance the dc-link capacitor voltages and control the flying capacitor voltages through software, without the need of additional hardware. This enables conventional NPC converters with four or higher number of levels or simplified topologies to operate independently as a single rectifier or inverter (or with a passive front end) over the full power factor and modulation index range. This lecture will also review various multilevel topologies and existing control methods to introduce the new advanced modulation method. Several exemplar multilevel converters using the proposed method and how new wide-bandgap devices can further facilitate the adoption of the proposed method will be shown. 

The power rating of large off-shore wind turbines is getting higher and higher, reaching 14MW. Medium-voltage power conversion is generally favoured for large wind turbines in terms of higher power density, reduced current level, associated losses, cable twisting, etc. This lecture will first review existing power conversion (drive train) solutions for large wind turbines and then propose three multi-level modular high power converter topologies together with corresponding generator configurations for large wind turbines. A configuration with a 10-kV generator, a modular power converter, and a multi-winding step-up transformer will be presented in detail with experimental results, which has clear application potential for 10MW+ wind turbines. The proposed converter has fault-tolerant capability, which is essential given the high maintenance/repair cost for wind power applications. The lecture will also talk about how to reduce the amount of capacitance required in the system given the capacitors have the highest failure rates among the converter components. Furthermore, converter topology options for future 20MW wind turbines will also be presented and discussed.

This lecture will first provide an overview of the performance of state-of-the-art SiC devices and converters. While the opportunities in achieving higher-density, higher-efficiency and higher-frequency are clear, there are also significant design challenges relating to high speed (dv/dt), high voltage and high temperature operation. For example, in SiC motor drives, the high switching speed and high switching frequency can cause increased level of motor over-voltage, insulation and bearing degradation. These challenges will be analysed and several solutions aiming to fully exploit the superior characteristics of SiC devices will be given, through new topologies, new modulation and control, soft-switching, filtering, etc. Several design examples such as a 500kW high-density power converter based on SiC MOSFETs, high temperature converters with 180°C SiC BJTs and high voltage 10kV SiC converters for solid state transformer applications will be given to demonstrate the opportunities, design challenges and the proposed solutions.

The increasing demand for more efficient, flexible and reliable loads, storage systems and renewable energy sources has promoted energy conversion systems extensively in industrial, commercial and residential low voltage networks. However, these converters generate reactive power as well as network disturbances, in particular waveform distortion in a broad range of frequencies.   The main aim of this lecture is to review and analyse:  ·  Standards and recommended practices·  Needs for revision of IEEE and IEC standards, e.g. IEC 61000-3-2 &12, IEC 61000-3-16, IEC-61000-4-7&30, IEC 61000-2-2, IEEE 519, IEEE 1547·   Quality aspects of industrial, commercial and residential grids;·  Power quality metering and monitoring systems

Due to an increasing number of modern power electronics converters (such as solar inverters, wind turbines, electrical vehicle chargers, storage converters and variable speed motor drive systems) low frequency distortion (harmonics, interharmonics within 0-9 kHz) and higher frequency distortion (9-150 kHz) as well as different other disturbances and interactions have been reported in distribution networks around the world. These issues are e.g.:   ·   generation of higher frequency distortion (switching frequency emission) and fast transients  ·   creation of new or shift in existing resonant frequencies in grids   ·   strong interactions between grid and power converters, reducing harmonic instability, reliability and power quality of the grids ·   modelling, measurement and analysis of potential problems