Periodic Reporting for period 1 - MiDER (Microconverters for Distributed Energy Resources)
Reporting period: 2020-09-01 to 2022-08-31
The MiDER project was designed to provide guidelines for the optimal utilization of Wide-Bandgap technology in modern energy conversion systems for distributed energy resources (DERs). More specifically, the key direction was to re-design the power electronics for improved power density by disengaging from magnetic components. The technical objectives of the project were:
i) To develop a miniaturized and efficient multilevel converter (MMC) based on the Flying Capacitor (FC) topology with Gallium Nitride (GaN) devices and no magnetic components or electrolytic capacitors.
ii) To study the dynamic performance of the system and evaluate the effect of the miniaturization on the converter and power system stability.
The successful implementation of the project required a cross-sectorial knowledge on three disciplines: a) material science for the device characterization, b) power electronics which incorporate the circuit analysis, design, firmware development and c) control theory for securing optimal operation of the system during steady state and dynamic conditions. The project was conducted at Imperial College London in a duration of 24 months with a secondment in Ecole Polytechnique Fédérale de Lausanne that exceeded 2 months.
In line with the original project plan a 7-level 3-phase GaN multilevel inverter was developed for localized DERs. All the hardware and firmware components were assembled to evaluate a new concept for measuring the FCs with minimal footprint and cost. Further, the MiDER project had strong contribution to the fundamentals of power electronics as a new pulse width modulation (PWM) control was proposed for GaN-base inverters with improved natural balancing dynamic response.
The key conclusion of the project is that, in addition to the topology selection and device technology, the peripheral circuitry (measurement system, balancing circuit, isolation stage) pose equally important challenges in the effort for miniaturization of the converter
Alongside the technical advancements, the MiDER project was also targeting the personal development of the Researcher and his career progression. The Fellow participated in more than 10 training and career development activities that helped him prepare for his next professional step and to secure a tenure track assistant professor position in Greece.
Overall, the Marie Sklodowska Curie Individua Fellowship has been the key enabling factor for the scientific progression in the power electronics field as well as the career development of the Fellow.
i) To develop a miniaturized and efficient multilevel converter (MMC) based on the Flying Capacitor (FC) topology with Gallium Nitride (GaN) devices and no magnetic components or electrolytic capacitors.
ii) To study the dynamic performance of the system and evaluate the effect of the miniaturization on the converter and power system stability.
The successful implementation of the project required a cross-sectorial knowledge on three disciplines: a) material science for the device characterization, b) power electronics which incorporate the circuit analysis, design, firmware development and c) control theory for securing optimal operation of the system during steady state and dynamic conditions. The project was conducted at Imperial College London in a duration of 24 months with a secondment in Ecole Polytechnique Fédérale de Lausanne that exceeded 2 months.
In line with the original project plan a 7-level 3-phase GaN multilevel inverter was developed for localized DERs. All the hardware and firmware components were assembled to evaluate a new concept for measuring the FCs with minimal footprint and cost. Further, the MiDER project had strong contribution to the fundamentals of power electronics as a new pulse width modulation (PWM) control was proposed for GaN-base inverters with improved natural balancing dynamic response.
The key conclusion of the project is that, in addition to the topology selection and device technology, the peripheral circuitry (measurement system, balancing circuit, isolation stage) pose equally important challenges in the effort for miniaturization of the converter
Alongside the technical advancements, the MiDER project was also targeting the personal development of the Researcher and his career progression. The Fellow participated in more than 10 training and career development activities that helped him prepare for his next professional step and to secure a tenure track assistant professor position in Greece.
Overall, the Marie Sklodowska Curie Individua Fellowship has been the key enabling factor for the scientific progression in the power electronics field as well as the career development of the Fellow.
The MiDER project involved all the steps for the development of the GaN-based micro-converter, from circuit analysis to control and theoretical investigation for further miniaturization.
The first tasks that were undertaken at the beginning of project included a) the selection of the inverter topology, b) determination of the system parameters and c) sizing the active and passive components, such as the GaN devices and the ceramic capacitors based on the calculated voltage and current stress. Further, the PCB design was performed followed by the thermal analysis. Following the hardware construction, the researcher moved forward with the development of the firmware in an embedded microprocessor and exhaustive experimental validation.
In the meantime, detailed switching models of the prototype were developed in Matalab/Simulink to evaluate the control of the inverter, which includes the synchronization with the grid, the inner current controller, the pulse width modulation (PWM) and various active balancing algorithms. Particular emphasis was given to the development of a new PWM technique that ensures optimum dynamic response during active balancing.
During the secondment period, the Fellow investigated the potential and challenges of monolithic integration of the entire converter on a single chip, realizing that currently, the isolation requirements is the main limiting factor that hinders further miniaturization.
The Fellow has communicated the research through 2 industrial visits, 3 academic talks to universities, pitching to investors and other stakeholders and one invited lecture to a high school. The results of the project have been published in one paper in IEEE Transactions on Power electronics, while a second paper has been submitted for publication in IEEE Open Journal on Power electronics
Throughout the project, the Researcher took full advantage of the training opportunities that helped grow his knowledge, acquire new skills and develop his professional career. During the Fellowship, the Researcher secured a competitive position as an assistant professor in Greece.
The first tasks that were undertaken at the beginning of project included a) the selection of the inverter topology, b) determination of the system parameters and c) sizing the active and passive components, such as the GaN devices and the ceramic capacitors based on the calculated voltage and current stress. Further, the PCB design was performed followed by the thermal analysis. Following the hardware construction, the researcher moved forward with the development of the firmware in an embedded microprocessor and exhaustive experimental validation.
In the meantime, detailed switching models of the prototype were developed in Matalab/Simulink to evaluate the control of the inverter, which includes the synchronization with the grid, the inner current controller, the pulse width modulation (PWM) and various active balancing algorithms. Particular emphasis was given to the development of a new PWM technique that ensures optimum dynamic response during active balancing.
During the secondment period, the Fellow investigated the potential and challenges of monolithic integration of the entire converter on a single chip, realizing that currently, the isolation requirements is the main limiting factor that hinders further miniaturization.
The Fellow has communicated the research through 2 industrial visits, 3 academic talks to universities, pitching to investors and other stakeholders and one invited lecture to a high school. The results of the project have been published in one paper in IEEE Transactions on Power electronics, while a second paper has been submitted for publication in IEEE Open Journal on Power electronics
Throughout the project, the Researcher took full advantage of the training opportunities that helped grow his knowledge, acquire new skills and develop his professional career. During the Fellowship, the Researcher secured a competitive position as an assistant professor in Greece.
The MiDER project contributed to the advancement of the research beyond the state-of-the-art in two directions:
1. Miniaturization of a GaN-Based multilevel inverter
It has been recognized that updating the transistor technology from Si to GaN and switching from conventional 2-level to multilevel topologies is not sufficient to achieve true miniaturization of the system. The main limiting factor is the measurement system that monitors the voltage of every stage of the inverter. This measurement network typically consists of several galvanically isolated sensors, that increase the overall footprint, weight, and cost of the system. During the MiDER project we designed and developed a new FC measurement system, based on precise sampling of the inverter switching node voltage, through a bidirectional clamping circuit. The deviation of FC voltages from their nominal values are extracted by solving a set of linear equations. With a single sensor per phase and no isolation requirements, our approach results in significantly lower cost, complexity, and circuit-size. The recorded performance renders the developed sensor an ideal solution for future MLIs based on wide-bandgap technology.
2. Dynamic response of a FC multi-stage inverter under natural balancing
Another major challenge of GaN-based FC inverters, particularly the ones with small-value ceramic capacitors, is related to the stringent requirements for precise and fast capacitor balancing. Conventional natural balancing techniques exhibit poor settling times, while active balancing normally requires one isolated sensor per FC which increases the overall system cost and footprint. In the MiDER project we have introduced a generalized pulse width modulation (PWM) strategy based on the phase-shift and carrier swapping principles for an arbitrary number of levels. We have provided an easy and intuitive method for the extraction of the PWM pattern, that leads to improved dynamic response during natural balancing and provides the right zero switching states for ac-side FC sensing in active balancing.
The conducted research has direct application and impact in the industrial world. The developed measurement system is expected to allow large scale utilization of GaN-based inverters in many practical applications with strict weight and size restrictions (e.g. aerospace, transportation). At the same time, the improved PWM strategy offers a unique solution to the balancing problem with fast and reliable voltage response, thus relaxing commercial inverters from additional balancing circuitry.
The utilization of the concepts that were generated during the MiDER project can result in more lightweight components thus, more efficient transportation, less fuel consumption and more reliable operation of the energy conversion system.
1. Miniaturization of a GaN-Based multilevel inverter
It has been recognized that updating the transistor technology from Si to GaN and switching from conventional 2-level to multilevel topologies is not sufficient to achieve true miniaturization of the system. The main limiting factor is the measurement system that monitors the voltage of every stage of the inverter. This measurement network typically consists of several galvanically isolated sensors, that increase the overall footprint, weight, and cost of the system. During the MiDER project we designed and developed a new FC measurement system, based on precise sampling of the inverter switching node voltage, through a bidirectional clamping circuit. The deviation of FC voltages from their nominal values are extracted by solving a set of linear equations. With a single sensor per phase and no isolation requirements, our approach results in significantly lower cost, complexity, and circuit-size. The recorded performance renders the developed sensor an ideal solution for future MLIs based on wide-bandgap technology.
2. Dynamic response of a FC multi-stage inverter under natural balancing
Another major challenge of GaN-based FC inverters, particularly the ones with small-value ceramic capacitors, is related to the stringent requirements for precise and fast capacitor balancing. Conventional natural balancing techniques exhibit poor settling times, while active balancing normally requires one isolated sensor per FC which increases the overall system cost and footprint. In the MiDER project we have introduced a generalized pulse width modulation (PWM) strategy based on the phase-shift and carrier swapping principles for an arbitrary number of levels. We have provided an easy and intuitive method for the extraction of the PWM pattern, that leads to improved dynamic response during natural balancing and provides the right zero switching states for ac-side FC sensing in active balancing.
The conducted research has direct application and impact in the industrial world. The developed measurement system is expected to allow large scale utilization of GaN-based inverters in many practical applications with strict weight and size restrictions (e.g. aerospace, transportation). At the same time, the improved PWM strategy offers a unique solution to the balancing problem with fast and reliable voltage response, thus relaxing commercial inverters from additional balancing circuitry.
The utilization of the concepts that were generated during the MiDER project can result in more lightweight components thus, more efficient transportation, less fuel consumption and more reliable operation of the energy conversion system.