Olav Bjarte Fosso | Norwegian University of Science and Technology (original) (raw)

Papers by Olav Bjarte Fosso

The chirp sweep is a go-to wide-band impedance measurement technique when speed and simplicity ar... more The chirp sweep is a go-to wide-band impedance measurement technique when speed and simplicity are of main concern. Additionally, the time-frequency trait of chirp scans provide unique benefits for systems exhibiting frequency couplings - a phenomenon often encountered in single-phase VSCs. Unfortunately, time domain interpretation of chirp responses are inaccurate if the VSC-based system exhibits weak damping, as the free response induced by the chirp cannot be safely neglected. We quantify this error for linear(ised) time-invariant and time-periodic systems, with impedance representations of scalar transfer functions and harmonic transfer functions, respectively. An observer termed the Multiple Chirp Reference Frame Filter is proposed which enables real-time estimation of the harmonic transfer functions and their corresponding chirp errors. By controlling the relative errors to negligible values, the chirp exhibits low rate around resonances and high rate elsewhere. An experimenta...

Journal of open source software, Oct 14, 2022

The electrical power distribution system is under constant development and multiple changes will ... more The electrical power distribution system is under constant development and multiple changes will occur in the upcoming years. Through the integration of new technology such as Renewable Energy Resources (RES) and flexible resources such as microgrids, battery energy storage systems, and electrical vehicles, the distribution system becomes more active where bidirectional power flow is possible. In an active distribution system, utilization and control of the different sources are possible. Additionally, the system becomes smarter through the integration of Information and Communication Technology (ICT) where intelligent monitoring, automated control, and communication are possible. These changes increase the complexity of the distribution network and new dependencies and interdependencies in the system arise with the modernization of the system.

This article describes a reference data set for a representative Norwegian radial, medium voltage... more This article describes a reference data set for a representative Norwegian radial, medium voltage (MV) electric power distribution system operated at 22 kV. The data set is developed in the Norwegian research centre CINELDI and will in brief be referred to as the CINELDI MV reference system. Data for a real Norwegian distribution system were provided by a distribution grid company. The data have been anonymized and processed to obtain a simplified but still realistic grid model with 124 nodes. The data set consists of the following three parts: 1. Grid data files: describe the base version of the reference system that represents the present-day state of the grid, including information about topology, electrical parameters, and existing load points. 2. Load data files: comprise load demand time series for a year with hourly resolution and scenarios for the possible long-term development of peak load. These data describe an extended version of the reference system with information abo...

IEEE Transactions on Power Electronics

Electric Power Systems Research

Power systems with high penetration of variable renewable generation are vulnerable to periods wi... more Power systems with high penetration of variable renewable generation are vulnerable to periods with low generation. An alternative to retain high dispatchable generation capacity is electric energy storage that enables utilization of surplus power, where the electric energy storage contributes to the security of supply. Such systems can be considered as energyconstrained, and the operation of the electric energy storage must balance operating cost minimization and the risk of scarcity. In this matter, operation dependent storage characteristics such as energy storage degradation are a complicating factor. This paper proposes a linear approximation of battery state-of-charge degradation and implements it in a stochastic dual dynamic programming based energy-management model in combination with cycling degradation. The implications of degradation modelling are studied for a small Norwegian microgrid with variable renewable power generation and limited dispatchable generation capacity as well as battery and hydrogen storage to balance supply and demand. Our results show that the proposed strategy can prolong the expected battery lifetime by more than four years compared to the naive stochastic strategy but may cause increased degradation for other system resources. It is also evident that a stochastic strategy is crucial to retain low risk of scarcity in energy-constrained systems.

IET Generation, Transmission & Distribution

2022 17th International Conference on Probabilistic Methods Applied to Power Systems (PMAPS)

2022 International Power Electronics Conference (IPEC-Himeji 2022- ECCE Asia)

2022 International Power Electronics Conference (IPEC-Himeji 2022- ECCE Asia)

2020 IEEE 21st Workshop on Control and Modeling for Power Electronics (COMPEL)

A Hilbert filter design is proposed with the intent of assembling a simple, yet frequency adaptiv... more A Hilbert filter design is proposed with the intent of assembling a simple, yet frequency adaptive single-phase grid synchronisation unit. The simplicity lies not with the filter itself, but with the linearity of the orthogonal system generator (OSG) and its absence of frequency feedbacks. This is a trait shared with many standard, frequency fixed OSGs - yet abandoned in the quest for fast and robust phase and frequency estimation. High modelling complexity of the synchronisation scheme severely hampers assessment of its interaction with controlling units, and the stability analysis of the converter. Although this article does not conclude on the superiority of any synchroniser, it presses the concern of establishing new performance evaluation criteria. For this reason, the dynamics of the Hilbert phase locked loop (PLL) are qualitatively explained, and compared to those of the frequency fixed and frequency adaptive second-order generalised integrator (SOGI) PLL. Simulation results indicate that by traditional perturbation tests - and for fast tuning of the SOGI - the PLL dominates the transient response for all synchronisers.

IEEE Transactions on Power Delivery, 2022

2021 IEEE 12th Energy Conversion Congress & Exposition - Asia (ECCE-Asia), 2021

This paper proposes an efficient methodology for distribution network loss minimization and volta... more This paper proposes an efficient methodology for distribution network loss minimization and voltage stability improvement with optimal Distributed Generation (DG) placement and operation. A sensitivity-based technique is developed for finding the best location for DGs. Subsequently, with an objective to minimize the network power losses and improve its voltage profile, optimal size and power factor for the DGs are obtained by solving non-linear Optimal Power Flows (OPFs). When applied to standard distribution test systems such as IEEE 69 bus and Indian 85 bus networks, the proposed technique shows its effectiveness with significant reduction in network losses for all test cases. Use of free and open source software for the development and application of the methodology provide a cost-effective solution to the utilities.

Electric Power Systems Research, 2021

This paper studies the electricity price formation in a competitive market when introducing gener... more This paper studies the electricity price formation in a competitive market when introducing generation from variable renewable energy technologies with zero marginal cost and electric energy storage systems. A power system is analyzed with a stochastic optimization model combining multi-period optimal power flow with stochastic dynamic programming. The results illustrate how variable renewable energy, in this case solar photovoltaic generation, displaces some of the expensive thermal generation and reduces the price. Electric energy storage will reduce the price variations caused by the variable renewable generation and demand as the time with price cap and zero price is reduced. In systems with only variable renewable generation and energy storage, the price will be set by the probability of scarcity similar to the price formation in hydro power dominated systems. The price will indicated the future cost of scarcity as a stochastic expectation value. This paper assumes that the demand is inflexible. However, the resulting electricity prices will remunerate provision of flexibility, which in turn will contribute to securing the supply and reducing the price volatility.

2018 International Conference on Smart Energy Systems and Technologies (SEST), 2018

Phasor estimation has many application areas and has therefore attracted significant research foc... more Phasor estimation has many application areas and has therefore attracted significant research focus. Classical phasor estimation proposed many years ago, considers the phasor to be time independent which means constant amplitude and phase. However, the dynamic phasor concept introduced recently, improves the accuracy of the phasor estimation under a nonstationary signal as is typically the case of low frequency oscillations (LFO). However, more accurate estimates lead to higher computation time. To achieve both low computation time and more accurate estimates, an adaptive phasor estimation concept based on both static and dynamic phasors is proposed in this paper. A new method based on the Adaptive Prony algorithm is presented, in which the Static Prony is employed under steady state conditions and the Dynamic Prony under dynamic conditions. To switch between these two algorithms, a Cumulative Summation of the Phasor Estimation Error (CSPEE) is used. Simulation results show the applicability of the proposed method to achieve the most accurate estimates at the lowest computation time. Total Vector Error (TVE) and Floating Point Operation (FLOP) are used to evaluate the proposed method.

2020 IEEE 4th Conference on Energy Internet and Energy System Integration (EI2), 2020

Power systems, especially distribution systems, are undergoing the most drastic overhauls with th... more Power systems, especially distribution systems, are undergoing the most drastic overhauls with the growing integration of renewable energy and digitalization. One of the most efficient technological solutions to address the challenges the distribution system faces today, is the formation of microgrids. With heterogeneous driving forces from policy, regulation, system operation, infrastructure developer, aggregator, and end-user, how microgrid will evolve and develop in the future distribution system remains an open question and deserve closer scrutiny. In this paper, a brief state of the art of current microgrid design is introduced considering knowledge and experience from both practitioner and academia. Based on a simple foresight method, three foreseeable scenarios for the future distribution system are depicted. Aspects related to its use cases, energy management system features, and market models will be discussed for each possible scenario. This will shed light onthe future research and development of microgrid applications.

2021 IEEE/IAS Industrial and Commercial Power System Asia (I&CPS Asia), 2021

Lifetime is an important indicator of system reliability. With the paradigm power system evolves ... more Lifetime is an important indicator of system reliability. With the paradigm power system evolves into a power electronics based power system, lifetime modelling method for power electronics needs to be revisited and perspective for modelling power electronics lifetime for system planning and operation usage is worth looking at. In this paper, the existent methods for modelling lifetime for power electronic system are reviewed and classified. The purpose of the paper is to give a brief overview of different modeling methods for power electronics lifetime, and to introduce how this lifetime information can be used for the system level reliability for the power electronics based power system taking the example of the microgrid application. New concept of system level reliability management based on lifetime model is envisaged.

2017 6th International Conference on Clean Electrical Power (ICCEP), 2017

This paper presents an analytical method developed to explain the mechanism of harmonic transfer ... more This paper presents an analytical method developed to explain the mechanism of harmonic transfer between the ac and dc sides of a single-phase inverter in a PV microgrid. The model explains how the feed-forward of the current from the ac side of the PV-inverter into the control system, causes even harmonics on the dc voltage. It further shows how the controller's feedback of the dc bus voltage carrying even harmonics results in odd harmonics on the ac side of the PV-inverter. This harmonic propagation model is verified with a simulation of the PV microgrid system. The results of this simulation study provides consistency by proving that odd harmonics on the ac voltage causes even harmonics on the dc bus, and that even harmonics on the dc bus again causes more odd harmonics on ac voltage.

2021 IEEE Madrid PowerTech, 2021

A new sensitivity-based approach is formulated in this paper for the optimal placement and sizing... more A new sensitivity-based approach is formulated in this paper for the optimal placement and sizing of Distributed Generation (DG) units in a practical Distribution Network (DN). The objective is to minimize the network power losses and improve its voltage stability with a user specified number of DG units. The proposed technique is simulated on an 88-bus DN present in a remote island of Norway. Results show that with optimal placement and sizing of DG units, significant reduction in network power losses and subsequent improvement in bus voltage stability is obtained. The simulations are carried out with free and open source software for their applicability by the power utilities.

The chirp sweep is a go-to wide-band impedance measurement technique when speed and simplicity ar... more The chirp sweep is a go-to wide-band impedance measurement technique when speed and simplicity are of main concern. Additionally, the time-frequency trait of chirp scans provide unique benefits for systems exhibiting frequency couplings - a phenomenon often encountered in single-phase VSCs. Unfortunately, time domain interpretation of chirp responses are inaccurate if the VSC-based system exhibits weak damping, as the free response induced by the chirp cannot be safely neglected. We quantify this error for linear(ised) time-invariant and time-periodic systems, with impedance representations of scalar transfer functions and harmonic transfer functions, respectively. An observer termed the Multiple Chirp Reference Frame Filter is proposed which enables real-time estimation of the harmonic transfer functions and their corresponding chirp errors. By controlling the relative errors to negligible values, the chirp exhibits low rate around resonances and high rate elsewhere. An experimenta...

Journal of open source software, Oct 14, 2022

The electrical power distribution system is under constant development and multiple changes will ... more The electrical power distribution system is under constant development and multiple changes will occur in the upcoming years. Through the integration of new technology such as Renewable Energy Resources (RES) and flexible resources such as microgrids, battery energy storage systems, and electrical vehicles, the distribution system becomes more active where bidirectional power flow is possible. In an active distribution system, utilization and control of the different sources are possible. Additionally, the system becomes smarter through the integration of Information and Communication Technology (ICT) where intelligent monitoring, automated control, and communication are possible. These changes increase the complexity of the distribution network and new dependencies and interdependencies in the system arise with the modernization of the system.

This article describes a reference data set for a representative Norwegian radial, medium voltage... more This article describes a reference data set for a representative Norwegian radial, medium voltage (MV) electric power distribution system operated at 22 kV. The data set is developed in the Norwegian research centre CINELDI and will in brief be referred to as the CINELDI MV reference system. Data for a real Norwegian distribution system were provided by a distribution grid company. The data have been anonymized and processed to obtain a simplified but still realistic grid model with 124 nodes. The data set consists of the following three parts: 1. Grid data files: describe the base version of the reference system that represents the present-day state of the grid, including information about topology, electrical parameters, and existing load points. 2. Load data files: comprise load demand time series for a year with hourly resolution and scenarios for the possible long-term development of peak load. These data describe an extended version of the reference system with information abo...

IEEE Transactions on Power Electronics

Electric Power Systems Research

Power systems with high penetration of variable renewable generation are vulnerable to periods wi... more Power systems with high penetration of variable renewable generation are vulnerable to periods with low generation. An alternative to retain high dispatchable generation capacity is electric energy storage that enables utilization of surplus power, where the electric energy storage contributes to the security of supply. Such systems can be considered as energyconstrained, and the operation of the electric energy storage must balance operating cost minimization and the risk of scarcity. In this matter, operation dependent storage characteristics such as energy storage degradation are a complicating factor. This paper proposes a linear approximation of battery state-of-charge degradation and implements it in a stochastic dual dynamic programming based energy-management model in combination with cycling degradation. The implications of degradation modelling are studied for a small Norwegian microgrid with variable renewable power generation and limited dispatchable generation capacity as well as battery and hydrogen storage to balance supply and demand. Our results show that the proposed strategy can prolong the expected battery lifetime by more than four years compared to the naive stochastic strategy but may cause increased degradation for other system resources. It is also evident that a stochastic strategy is crucial to retain low risk of scarcity in energy-constrained systems.

IET Generation, Transmission & Distribution

2022 17th International Conference on Probabilistic Methods Applied to Power Systems (PMAPS)

2022 International Power Electronics Conference (IPEC-Himeji 2022- ECCE Asia)

2022 International Power Electronics Conference (IPEC-Himeji 2022- ECCE Asia)

2020 IEEE 21st Workshop on Control and Modeling for Power Electronics (COMPEL)

A Hilbert filter design is proposed with the intent of assembling a simple, yet frequency adaptiv... more A Hilbert filter design is proposed with the intent of assembling a simple, yet frequency adaptive single-phase grid synchronisation unit. The simplicity lies not with the filter itself, but with the linearity of the orthogonal system generator (OSG) and its absence of frequency feedbacks. This is a trait shared with many standard, frequency fixed OSGs - yet abandoned in the quest for fast and robust phase and frequency estimation. High modelling complexity of the synchronisation scheme severely hampers assessment of its interaction with controlling units, and the stability analysis of the converter. Although this article does not conclude on the superiority of any synchroniser, it presses the concern of establishing new performance evaluation criteria. For this reason, the dynamics of the Hilbert phase locked loop (PLL) are qualitatively explained, and compared to those of the frequency fixed and frequency adaptive second-order generalised integrator (SOGI) PLL. Simulation results indicate that by traditional perturbation tests - and for fast tuning of the SOGI - the PLL dominates the transient response for all synchronisers.

IEEE Transactions on Power Delivery, 2022

2021 IEEE 12th Energy Conversion Congress & Exposition - Asia (ECCE-Asia), 2021

This paper proposes an efficient methodology for distribution network loss minimization and volta... more This paper proposes an efficient methodology for distribution network loss minimization and voltage stability improvement with optimal Distributed Generation (DG) placement and operation. A sensitivity-based technique is developed for finding the best location for DGs. Subsequently, with an objective to minimize the network power losses and improve its voltage profile, optimal size and power factor for the DGs are obtained by solving non-linear Optimal Power Flows (OPFs). When applied to standard distribution test systems such as IEEE 69 bus and Indian 85 bus networks, the proposed technique shows its effectiveness with significant reduction in network losses for all test cases. Use of free and open source software for the development and application of the methodology provide a cost-effective solution to the utilities.

Electric Power Systems Research, 2021

This paper studies the electricity price formation in a competitive market when introducing gener... more This paper studies the electricity price formation in a competitive market when introducing generation from variable renewable energy technologies with zero marginal cost and electric energy storage systems. A power system is analyzed with a stochastic optimization model combining multi-period optimal power flow with stochastic dynamic programming. The results illustrate how variable renewable energy, in this case solar photovoltaic generation, displaces some of the expensive thermal generation and reduces the price. Electric energy storage will reduce the price variations caused by the variable renewable generation and demand as the time with price cap and zero price is reduced. In systems with only variable renewable generation and energy storage, the price will be set by the probability of scarcity similar to the price formation in hydro power dominated systems. The price will indicated the future cost of scarcity as a stochastic expectation value. This paper assumes that the demand is inflexible. However, the resulting electricity prices will remunerate provision of flexibility, which in turn will contribute to securing the supply and reducing the price volatility.

2018 International Conference on Smart Energy Systems and Technologies (SEST), 2018

Phasor estimation has many application areas and has therefore attracted significant research foc... more Phasor estimation has many application areas and has therefore attracted significant research focus. Classical phasor estimation proposed many years ago, considers the phasor to be time independent which means constant amplitude and phase. However, the dynamic phasor concept introduced recently, improves the accuracy of the phasor estimation under a nonstationary signal as is typically the case of low frequency oscillations (LFO). However, more accurate estimates lead to higher computation time. To achieve both low computation time and more accurate estimates, an adaptive phasor estimation concept based on both static and dynamic phasors is proposed in this paper. A new method based on the Adaptive Prony algorithm is presented, in which the Static Prony is employed under steady state conditions and the Dynamic Prony under dynamic conditions. To switch between these two algorithms, a Cumulative Summation of the Phasor Estimation Error (CSPEE) is used. Simulation results show the applicability of the proposed method to achieve the most accurate estimates at the lowest computation time. Total Vector Error (TVE) and Floating Point Operation (FLOP) are used to evaluate the proposed method.

2020 IEEE 4th Conference on Energy Internet and Energy System Integration (EI2), 2020

Power systems, especially distribution systems, are undergoing the most drastic overhauls with th... more Power systems, especially distribution systems, are undergoing the most drastic overhauls with the growing integration of renewable energy and digitalization. One of the most efficient technological solutions to address the challenges the distribution system faces today, is the formation of microgrids. With heterogeneous driving forces from policy, regulation, system operation, infrastructure developer, aggregator, and end-user, how microgrid will evolve and develop in the future distribution system remains an open question and deserve closer scrutiny. In this paper, a brief state of the art of current microgrid design is introduced considering knowledge and experience from both practitioner and academia. Based on a simple foresight method, three foreseeable scenarios for the future distribution system are depicted. Aspects related to its use cases, energy management system features, and market models will be discussed for each possible scenario. This will shed light onthe future research and development of microgrid applications.

2021 IEEE/IAS Industrial and Commercial Power System Asia (I&CPS Asia), 2021

Lifetime is an important indicator of system reliability. With the paradigm power system evolves ... more Lifetime is an important indicator of system reliability. With the paradigm power system evolves into a power electronics based power system, lifetime modelling method for power electronics needs to be revisited and perspective for modelling power electronics lifetime for system planning and operation usage is worth looking at. In this paper, the existent methods for modelling lifetime for power electronic system are reviewed and classified. The purpose of the paper is to give a brief overview of different modeling methods for power electronics lifetime, and to introduce how this lifetime information can be used for the system level reliability for the power electronics based power system taking the example of the microgrid application. New concept of system level reliability management based on lifetime model is envisaged.

2017 6th International Conference on Clean Electrical Power (ICCEP), 2017

This paper presents an analytical method developed to explain the mechanism of harmonic transfer ... more This paper presents an analytical method developed to explain the mechanism of harmonic transfer between the ac and dc sides of a single-phase inverter in a PV microgrid. The model explains how the feed-forward of the current from the ac side of the PV-inverter into the control system, causes even harmonics on the dc voltage. It further shows how the controller's feedback of the dc bus voltage carrying even harmonics results in odd harmonics on the ac side of the PV-inverter. This harmonic propagation model is verified with a simulation of the PV microgrid system. The results of this simulation study provides consistency by proving that odd harmonics on the ac voltage causes even harmonics on the dc bus, and that even harmonics on the dc bus again causes more odd harmonics on ac voltage.

2021 IEEE Madrid PowerTech, 2021

A new sensitivity-based approach is formulated in this paper for the optimal placement and sizing... more A new sensitivity-based approach is formulated in this paper for the optimal placement and sizing of Distributed Generation (DG) units in a practical Distribution Network (DN). The objective is to minimize the network power losses and improve its voltage stability with a user specified number of DG units. The proposed technique is simulated on an 88-bus DN present in a remote island of Norway. Results show that with optimal placement and sizing of DG units, significant reduction in network power losses and subsequent improvement in bus voltage stability is obtained. The simulations are carried out with free and open source software for their applicability by the power utilities.

—The Empirical Mode Decomposition (EMD) is a signal analysis method that separates multi-componen... more —The Empirical Mode Decomposition (EMD) is a signal analysis method that separates multi-component signals into single oscillatory modes called intrinsic mode functions (IMFs), each of which can generally be associated to a physical meaning of the process from which the signal is obtained. When the phenomena of mode mixing occur, as a result of the EMD sifting process, the IMFs can lose their physical meaning hindering the interpretation of the results of the analysis. In the paper, One or Two frequencies? The Empirical Mode Decomposition Answers, Gabriel Rilling and Patrick Flandrin [3] presented a rigorous mathematical analysis that explains how EMD behaves in the case of a composite two-tones signal and the amplitude and frequency ratios by which EMD will perform a good separation of tones. However, the authors did not propose a solution for separating the neighboring tones that will naturally remain mixed after an EMD. In this paper, based on the findings by Rilling and Flandrin, a method that can separate neighbouring spectral components, that will naturally remain within a single IMF, is presented. This method is based on reversing the conditions by which mode mixing occurs and that were presented in the map by Rilling and Flandrin in the above mentioned paper. Numerical experiments with signals containing closely spaced spectral components shows the effective separation of modes that EMD can perform after this principle is applied. The results verify also the regimes presented in the theoretical analysis by Rilling and Flandrin.