In three-phase unbalanced systems, where the circulation of zero sequence current is necessary, f... more In three-phase unbalanced systems, where the circulation of zero sequence current is necessary, four-leg converters provide a neutral connection for single-phase or other unbalanced loads typically utilized in three-phase distribution systems. In addition, control of the magnitude and phase of the zero-sequence voltage and/or current are also achieved using four-leg power converters. However, even when four-leg converters have become very important in several fields as for instance, four-leg microgrids and aerospace applications, a comprehensive review of the converter topologies, control methods, modulation methods and output filters have not been hitherto published. In this paper, a comprehensive overview of the state-of-the-art of four-leg converters is presented, based on the selection of over 400 papers published in journals and conferences, identifying mature and incipient topologies, modulation strategies, control schemes and applications. Each topic presented in this work is thoroughly discussed and reviewed, analyzing characteristics, implementation issues, and reported advantages and disadvantages to provide a comprehensive overview of the current research and future challenges in four-leg converters. The most important applications of four-leg converters are also discussed in this work, including stand-alone power supply, uninterruptible power supplies, gridconnected 4-leg inverters, ground power units for aerospace applications, active filtering for power quality enhancement, cooperative control of 4-leg converters for micro-grid applications, among others. Finally, future work and conclusions are highlighted in this paper.
2021 6th IEEE Workshop on the Electronic Grid (eGRID), 2021
This paper proposes a secondary distributed control strategy to achieve the sharing of unbalanced... more This paper proposes a secondary distributed control strategy to achieve the sharing of unbalanced currents between 3-leg power converters, operating under droop control, in a three-phase three-wire isolated Microgrid (MG). To this end, a modified $Q$ - $E$ droop controller is used, where new control actions are defined to achieve the unbalanced currents sharing amongst the converters. These control actions are generated, in the secondary control level, by a consensus-based algorithm, where the consensus variables correspond to the single-phase reactive powers of the converters. This paper shows that sharing negative sequence current components amongst the power converters can be managed by achieving a consensus (per phase) of single-phase reactive powers. Extensive simulations demonstrate the excellent performance of the proposed controller.
2021 6th IEEE Workshop on the Electronic Grid (eGRID), 2021
This paper proposes a secondary distributed control strategy to achieve the sharing of unbalanced... more This paper proposes a secondary distributed control strategy to achieve the sharing of unbalanced currents between 3-leg power converters, operating under droop control, in a three-phase three-wire isolated Microgrid (MG). To this end, a modified $Q$ - $E$ droop controller is used, where new control actions are defined to achieve the unbalanced currents sharing amongst the converters. These control actions are generated, in the secondary control level, by a consensus-based algorithm, where the consensus variables correspond to the single-phase reactive powers of the converters. This paper shows that sharing negative sequence current components amongst the power converters can be managed by achieving a consensus (per phase) of single-phase reactive powers. Extensive simulations demonstrate the excellent performance of the proposed controller.
2021 6th IEEE Workshop on the Electronic Grid (eGRID), 2021
This paper proposes a secondary distributed control strategy to achieve the sharing of unbalanced... more This paper proposes a secondary distributed control strategy to achieve the sharing of unbalanced currents between 3-leg power converters, operating under droop control, in a three-phase three-wire isolated Microgrid (MG). To this end, a modified $Q$ - $E$ droop controller is used, where new control actions are defined to achieve the unbalanced currents sharing amongst the converters. These control actions are generated, in the secondary control level, by a consensus-based algorithm, where the consensus variables correspond to the single-phase reactive powers of the converters. This paper shows that sharing negative sequence current components amongst the power converters can be managed by achieving a consensus (per phase) of single-phase reactive powers. Extensive simulations demonstrate the excellent performance of the proposed controller.
2020 IEEE 21st Workshop on Control and Modeling for Power Electronics (COMPEL), 2020
This paper proposes a distributed control scheme for the economic dispatch of islanded AC microgr... more This paper proposes a distributed control scheme for the economic dispatch of islanded AC microgrids. The control goal is the economical power-sharing of distributed generators considering the marginal cost of active and reactive power. The controller is developed in a finite-time protocol over a droop-free strategy, without restoration needs for frequency. Simulations through the software PLECS are provided for validation purposes; they show adequate behaviour of the controllers under impact loads and plug & play operation.
2021 6th IEEE Workshop on the Electronic Grid (eGRID), 2021
This paper proposes a secondary distributed control strategy to achieve the sharing of unbalanced... more This paper proposes a secondary distributed control strategy to achieve the sharing of unbalanced currents between 3-leg power converters, operating under droop control, in a three-phase three-wire isolated Microgrid (MG). To this end, a modified $Q$ - $E$ droop controller is used, where new control actions are defined to achieve the unbalanced currents sharing amongst the converters. These control actions are generated, in the secondary control level, by a consensus-based algorithm, where the consensus variables correspond to the single-phase reactive powers of the converters. This paper shows that sharing negative sequence current components amongst the power converters can be managed by achieving a consensus (per phase) of single-phase reactive powers. Extensive simulations demonstrate the excellent performance of the proposed controller.
2020 IEEE 21st Workshop on Control and Modeling for Power Electronics (COMPEL), 2020
The rise of new dc technologies is pushing the development of highly efficient dc-dc converters, ... more The rise of new dc technologies is pushing the development of highly efficient dc-dc converters, especially at high voltage and high step ratio. Modular multilevel converters (MMCs) are an attractive alternative because they can manage medium and high dc voltages with standard semiconductor devices with high efficiency if they employ soft-switching techniques. However, the latest soft-switching techniques have been proposed for fixed voltage range, limiting their operation. This paper proposes a soft-switching modulation for the high step ratio Modular Multilevel dc-dc Converter in extended voltage range. The proposal achieves zero-current switching and regulates the voltage balance among the floating cell capacitors, while using a simple control scheme to regulate the output voltage. The theoretical analysis has been verified with full-scale simulations, demonstrating excellent dynamic response and reduced rms current. Index Terms-dc-dc conversion, modular multilevel converter, high step ratio conversion, triangular current mode, trapezoidal current mode.
2020 IEEE 21st Workshop on Control and Modeling for Power Electronics (COMPEL), 2020
This paper proposes a distributed control scheme for the economic dispatch of islanded AC microgr... more This paper proposes a distributed control scheme for the economic dispatch of islanded AC microgrids. The control goal is the economical power-sharing of distributed generators considering the marginal cost of active and reactive power. The controller is developed in a finite-time protocol over a droop-free strategy, without restoration needs for frequency. Simulations through the software PLECS are provided for validation purposes; they show adequate behaviour of the controllers under impact loads and plug & play operation.
2020 IEEE 21st Workshop on Control and Modeling for Power Electronics (COMPEL), 2020
The rise of new dc technologies is pushing the development of highly efficient dc-dc converters, ... more The rise of new dc technologies is pushing the development of highly efficient dc-dc converters, especially at high voltage and high step ratio. Modular multilevel converters (MMCs) are an attractive alternative because they can manage medium and high dc voltages with standard semiconductor devices with high efficiency if they employ soft-switching techniques. However, the latest soft-switching techniques have been proposed for fixed voltage range, limiting their operation. This paper proposes a soft-switching modulation for the high step ratio Modular Multilevel dc-dc Converter in extended voltage range. The proposal achieves zero-current switching and regulates the voltage balance among the floating cell capacitors, while using a simple control scheme to regulate the output voltage. The theoretical analysis has been verified with full-scale simulations, demonstrating excellent dynamic response and reduced rms current. Index Terms-dc-dc conversion, modular multilevel converter, high step ratio conversion, triangular current mode, trapezoidal current mode.
2021 IEEE Green Technologies Conference (GreenTech), 2021
This paper proposes a consensus-based distributed control scheme, augmented by the conservative p... more This paper proposes a consensus-based distributed control scheme, augmented by the conservative power theory for compensating imbalance and harmonics at the Common Connection Point (PCC). The consensus algorithm allows to achieve effective coordination among the grid-following converters; whereas the conservative power theory is used to compute the unwanted currents and powers at the connection point that should be compensated via the remaining volt-ampere (VA) capacity of each converter. The mathematical formulation of the proposal, along with its validation through simulations, using a three phase – four wire microgrid, is provided.
2021 IEEE Green Technologies Conference (GreenTech), 2021
This paper proposes a consensus-based distributed control scheme, augmented by the conservative p... more This paper proposes a consensus-based distributed control scheme, augmented by the conservative power theory for compensating imbalance and harmonics at the Common Connection Point (PCC). The consensus algorithm allows to achieve effective coordination among the grid-following converters; whereas the conservative power theory is used to compute the unwanted currents and powers at the connection point that should be compensated via the remaining volt-ampere (VA) capacity of each converter. The mathematical formulation of the proposal, along with its validation through simulations, using a three phase – four wire microgrid, is provided.
This paper proposes a distributed predictive secondary control strategy to share imbalance in thr... more This paper proposes a distributed predictive secondary control strategy to share imbalance in three-phase, three-wire isolated AC Microgrids. The control is based on a novel approach where the imbalance sharing among distributed generators is controlled through the control of single-phase reactive power. The main characteristic of the proposed methodology is the inclusion of an objective function and dynamic models as constraints in the formulation. The controller relies on local measurements and information from neighboring distributed generators, and it performs the desired control action based on a constrained cost function minimization. The proposed distributed model predictive control scheme has several advantages over solutions based on virtual impedance loops or based on the inclusion of extra power converters for managing single-phase reactive power among distributed generators. In fact, with the proposed technique the sharing of imbalance is performed directly in terms of single-phase reactive power and without the need for adding extra power converters into the microgrid. Contrary to almost all reported works in this area, the proposed approach enables the control of various microgrid parameters within predefined bands, providing a more flexible control system. Extensive simulation and Hardware in the Loop studies verify the performance of the proposed control scheme. Moreover, the controller’s scalability and a comparison study, in terms of performance, with the virtual impedance approach were carried out.
This paper proposes a distributed predictive secondary control strategy to share imbalance in thr... more This paper proposes a distributed predictive secondary control strategy to share imbalance in three-phase, three-wire isolated AC Microgrids. The control is based on a novel approach where the imbalance sharing among distributed generators is controlled through the control of single-phase reactive power. The main characteristic of the proposed methodology is the inclusion of an objective function and dynamic models as constraints in the formulation. The controller relies on local measurements and information from neighboring distributed generators, and it performs the desired control action based on a constrained cost function minimization. The proposed distributed model predictive control scheme has several advantages over solutions based on virtual impedance loops or based on the inclusion of extra power converters for managing single-phase reactive power among distributed generators. In fact, with the proposed technique the sharing of imbalance is performed directly in terms of single-phase reactive power and without the need for adding extra power converters into the microgrid. Contrary to almost all reported works in this area, the proposed approach enables the control of various microgrid parameters within predefined bands, providing a more flexible control system. Extensive simulation and Hardware in the Loop studies verify the performance of the proposed control scheme. Moreover, the controller’s scalability and a comparison study, in terms of performance, with the virtual impedance approach were carried out.
In three-phase unbalanced systems, where the circulation of zero sequence current is necessary, f... more In three-phase unbalanced systems, where the circulation of zero sequence current is necessary, four-leg converters provide a neutral connection for single-phase or other unbalanced loads typically utilized in three-phase distribution systems. In addition, control of the magnitude and phase of the zero-sequence voltage and/or current are also achieved using four-leg power converters. However, even when four-leg converters have become very important in several fields as for instance, four-leg microgrids and aerospace applications, a comprehensive review of the converter topologies, control methods, modulation methods and output filters have not been hitherto published. In this paper, a comprehensive overview of the state-of-the-art of four-leg converters is presented, based on the selection of over 400 papers published in journals and conferences, identifying mature and incipient topologies, modulation strategies, control schemes and applications. Each topic presented in this work is thoroughly discussed and reviewed, analyzing characteristics, implementation issues, and reported advantages and disadvantages to provide a comprehensive overview of the current research and future challenges in four-leg converters. The most important applications of four-leg converters are also discussed in this work, including stand-alone power supply, uninterruptible power supplies, gridconnected 4-leg inverters, ground power units for aerospace applications, active filtering for power quality enhancement, cooperative control of 4-leg converters for micro-grid applications, among others. Finally, future work and conclusions are highlighted in this paper.
2021 6th IEEE Workshop on the Electronic Grid (eGRID), 2021
This paper proposes a secondary distributed control strategy to achieve the sharing of unbalanced... more This paper proposes a secondary distributed control strategy to achieve the sharing of unbalanced currents between 3-leg power converters, operating under droop control, in a three-phase three-wire isolated Microgrid (MG). To this end, a modified $Q$ - $E$ droop controller is used, where new control actions are defined to achieve the unbalanced currents sharing amongst the converters. These control actions are generated, in the secondary control level, by a consensus-based algorithm, where the consensus variables correspond to the single-phase reactive powers of the converters. This paper shows that sharing negative sequence current components amongst the power converters can be managed by achieving a consensus (per phase) of single-phase reactive powers. Extensive simulations demonstrate the excellent performance of the proposed controller.
2021 6th IEEE Workshop on the Electronic Grid (eGRID), 2021
This paper proposes a secondary distributed control strategy to achieve the sharing of unbalanced... more This paper proposes a secondary distributed control strategy to achieve the sharing of unbalanced currents between 3-leg power converters, operating under droop control, in a three-phase three-wire isolated Microgrid (MG). To this end, a modified $Q$ - $E$ droop controller is used, where new control actions are defined to achieve the unbalanced currents sharing amongst the converters. These control actions are generated, in the secondary control level, by a consensus-based algorithm, where the consensus variables correspond to the single-phase reactive powers of the converters. This paper shows that sharing negative sequence current components amongst the power converters can be managed by achieving a consensus (per phase) of single-phase reactive powers. Extensive simulations demonstrate the excellent performance of the proposed controller.
2021 6th IEEE Workshop on the Electronic Grid (eGRID), 2021
This paper proposes a secondary distributed control strategy to achieve the sharing of unbalanced... more This paper proposes a secondary distributed control strategy to achieve the sharing of unbalanced currents between 3-leg power converters, operating under droop control, in a three-phase three-wire isolated Microgrid (MG). To this end, a modified $Q$ - $E$ droop controller is used, where new control actions are defined to achieve the unbalanced currents sharing amongst the converters. These control actions are generated, in the secondary control level, by a consensus-based algorithm, where the consensus variables correspond to the single-phase reactive powers of the converters. This paper shows that sharing negative sequence current components amongst the power converters can be managed by achieving a consensus (per phase) of single-phase reactive powers. Extensive simulations demonstrate the excellent performance of the proposed controller.
2020 IEEE 21st Workshop on Control and Modeling for Power Electronics (COMPEL), 2020
This paper proposes a distributed control scheme for the economic dispatch of islanded AC microgr... more This paper proposes a distributed control scheme for the economic dispatch of islanded AC microgrids. The control goal is the economical power-sharing of distributed generators considering the marginal cost of active and reactive power. The controller is developed in a finite-time protocol over a droop-free strategy, without restoration needs for frequency. Simulations through the software PLECS are provided for validation purposes; they show adequate behaviour of the controllers under impact loads and plug & play operation.
2021 6th IEEE Workshop on the Electronic Grid (eGRID), 2021
This paper proposes a secondary distributed control strategy to achieve the sharing of unbalanced... more This paper proposes a secondary distributed control strategy to achieve the sharing of unbalanced currents between 3-leg power converters, operating under droop control, in a three-phase three-wire isolated Microgrid (MG). To this end, a modified $Q$ - $E$ droop controller is used, where new control actions are defined to achieve the unbalanced currents sharing amongst the converters. These control actions are generated, in the secondary control level, by a consensus-based algorithm, where the consensus variables correspond to the single-phase reactive powers of the converters. This paper shows that sharing negative sequence current components amongst the power converters can be managed by achieving a consensus (per phase) of single-phase reactive powers. Extensive simulations demonstrate the excellent performance of the proposed controller.
2020 IEEE 21st Workshop on Control and Modeling for Power Electronics (COMPEL), 2020
The rise of new dc technologies is pushing the development of highly efficient dc-dc converters, ... more The rise of new dc technologies is pushing the development of highly efficient dc-dc converters, especially at high voltage and high step ratio. Modular multilevel converters (MMCs) are an attractive alternative because they can manage medium and high dc voltages with standard semiconductor devices with high efficiency if they employ soft-switching techniques. However, the latest soft-switching techniques have been proposed for fixed voltage range, limiting their operation. This paper proposes a soft-switching modulation for the high step ratio Modular Multilevel dc-dc Converter in extended voltage range. The proposal achieves zero-current switching and regulates the voltage balance among the floating cell capacitors, while using a simple control scheme to regulate the output voltage. The theoretical analysis has been verified with full-scale simulations, demonstrating excellent dynamic response and reduced rms current. Index Terms-dc-dc conversion, modular multilevel converter, high step ratio conversion, triangular current mode, trapezoidal current mode.
2020 IEEE 21st Workshop on Control and Modeling for Power Electronics (COMPEL), 2020
This paper proposes a distributed control scheme for the economic dispatch of islanded AC microgr... more This paper proposes a distributed control scheme for the economic dispatch of islanded AC microgrids. The control goal is the economical power-sharing of distributed generators considering the marginal cost of active and reactive power. The controller is developed in a finite-time protocol over a droop-free strategy, without restoration needs for frequency. Simulations through the software PLECS are provided for validation purposes; they show adequate behaviour of the controllers under impact loads and plug & play operation.
2020 IEEE 21st Workshop on Control and Modeling for Power Electronics (COMPEL), 2020
The rise of new dc technologies is pushing the development of highly efficient dc-dc converters, ... more The rise of new dc technologies is pushing the development of highly efficient dc-dc converters, especially at high voltage and high step ratio. Modular multilevel converters (MMCs) are an attractive alternative because they can manage medium and high dc voltages with standard semiconductor devices with high efficiency if they employ soft-switching techniques. However, the latest soft-switching techniques have been proposed for fixed voltage range, limiting their operation. This paper proposes a soft-switching modulation for the high step ratio Modular Multilevel dc-dc Converter in extended voltage range. The proposal achieves zero-current switching and regulates the voltage balance among the floating cell capacitors, while using a simple control scheme to regulate the output voltage. The theoretical analysis has been verified with full-scale simulations, demonstrating excellent dynamic response and reduced rms current. Index Terms-dc-dc conversion, modular multilevel converter, high step ratio conversion, triangular current mode, trapezoidal current mode.
2021 IEEE Green Technologies Conference (GreenTech), 2021
This paper proposes a consensus-based distributed control scheme, augmented by the conservative p... more This paper proposes a consensus-based distributed control scheme, augmented by the conservative power theory for compensating imbalance and harmonics at the Common Connection Point (PCC). The consensus algorithm allows to achieve effective coordination among the grid-following converters; whereas the conservative power theory is used to compute the unwanted currents and powers at the connection point that should be compensated via the remaining volt-ampere (VA) capacity of each converter. The mathematical formulation of the proposal, along with its validation through simulations, using a three phase – four wire microgrid, is provided.
2021 IEEE Green Technologies Conference (GreenTech), 2021
This paper proposes a consensus-based distributed control scheme, augmented by the conservative p... more This paper proposes a consensus-based distributed control scheme, augmented by the conservative power theory for compensating imbalance and harmonics at the Common Connection Point (PCC). The consensus algorithm allows to achieve effective coordination among the grid-following converters; whereas the conservative power theory is used to compute the unwanted currents and powers at the connection point that should be compensated via the remaining volt-ampere (VA) capacity of each converter. The mathematical formulation of the proposal, along with its validation through simulations, using a three phase – four wire microgrid, is provided.
This paper proposes a distributed predictive secondary control strategy to share imbalance in thr... more This paper proposes a distributed predictive secondary control strategy to share imbalance in three-phase, three-wire isolated AC Microgrids. The control is based on a novel approach where the imbalance sharing among distributed generators is controlled through the control of single-phase reactive power. The main characteristic of the proposed methodology is the inclusion of an objective function and dynamic models as constraints in the formulation. The controller relies on local measurements and information from neighboring distributed generators, and it performs the desired control action based on a constrained cost function minimization. The proposed distributed model predictive control scheme has several advantages over solutions based on virtual impedance loops or based on the inclusion of extra power converters for managing single-phase reactive power among distributed generators. In fact, with the proposed technique the sharing of imbalance is performed directly in terms of single-phase reactive power and without the need for adding extra power converters into the microgrid. Contrary to almost all reported works in this area, the proposed approach enables the control of various microgrid parameters within predefined bands, providing a more flexible control system. Extensive simulation and Hardware in the Loop studies verify the performance of the proposed control scheme. Moreover, the controller’s scalability and a comparison study, in terms of performance, with the virtual impedance approach were carried out.
This paper proposes a distributed predictive secondary control strategy to share imbalance in thr... more This paper proposes a distributed predictive secondary control strategy to share imbalance in three-phase, three-wire isolated AC Microgrids. The control is based on a novel approach where the imbalance sharing among distributed generators is controlled through the control of single-phase reactive power. The main characteristic of the proposed methodology is the inclusion of an objective function and dynamic models as constraints in the formulation. The controller relies on local measurements and information from neighboring distributed generators, and it performs the desired control action based on a constrained cost function minimization. The proposed distributed model predictive control scheme has several advantages over solutions based on virtual impedance loops or based on the inclusion of extra power converters for managing single-phase reactive power among distributed generators. In fact, with the proposed technique the sharing of imbalance is performed directly in terms of single-phase reactive power and without the need for adding extra power converters into the microgrid. Contrary to almost all reported works in this area, the proposed approach enables the control of various microgrid parameters within predefined bands, providing a more flexible control system. Extensive simulation and Hardware in the Loop studies verify the performance of the proposed control scheme. Moreover, the controller’s scalability and a comparison study, in terms of performance, with the virtual impedance approach were carried out.
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Papers by Claudio Burgos