robert lasseter - Academia.edu (original) (raw)

Papers by robert lasseter

Hawaii International Conference on System Sciences, Jan 6, 2003

This paper presents a new advanced model of an electric power system with distributed energy sour... more This paper presents a new advanced model of an electric power system with distributed energy sources forming a microgrid (µGrid). The µGrid is a radial or networked low voltage distribution system with distributed sources. Each source is interfaced to the system via converters. The DC bus of the converter may have energy storage capability via large capacitors or batteries. The µGrid load consists of both single and three phase loads resulting in unbalanced operating conditions. The µGrid circuits may be three-wire, four-wire or five-wire. The grounding of the system may be single point or multipoint. The analysis of this system requires a new approach. This paper presents a new method for modeling and analysis of this system. The approach consists of two steps: (a) modeling each component of the system via a set of quadratic equations no matter how complex the nonlinearities of the model are and (b) a Newton's method for the solution of the overall network equations. The method is extremely efficient and robust. The proposed method can accommodate various control modes of micro-sources. Examples of these controls are given in the paper.

PESC `92 Record. 23rd Annual IEEE Power Electronics Specialists Conference

The classical analysis is often applicable, but can, as demonstrated here and in [1,5], fail for ... more The classical analysis is often applicable, but can, as demonstrated here and in [1,5], fail for certain circuit parameters and operating conditions. Under these conditions, both the voltage and the current waveforms become greatly distorted with large harmonic components. This distortion is associated with a resonance phenomenon in which the natural frequencies of the circuit, from when the reactor is fully on to when it is fully off, span an odd harmonic. This harmonic distortion can lead to instabilities as switching times suddenly

2014 IEEE Energy Conversion Congress and Exposition (ECCE), 2014

ABSTRACT This paper investigates an electric vehicle (EV) charging station that uses a CERTS micr... more ABSTRACT This paper investigates an electric vehicle (EV) charging station that uses a CERTS microgrid in a hybrid architecture that incorporates both ac and dc power buses. A dynamic model is developed that incorporates a CERTS ac microgrid and a parallel configuration of multiple electric vehicle batteries with droop-controlled dc/dc chargers that are connected to the dc bus of a single CERTS ac microsource. Components of the hybrid microgrid model are validated using a combination of experimental results and PLECS simulations. The small-signal stability of the dc bus dynamics is investigated. Simulations and experimental results are used to demonstrate that the hybrid CERTS microgrid can successfully accommodate diverse ac and dc load transients, including islanding and grid reconnection.

2012 IEEE Power and Energy Conference at Illinois, 2012

Frequency droop algorithms used by CERTS Microgrid inverters adjust power by changing the output ... more Frequency droop algorithms used by CERTS Microgrid inverters adjust power by changing the output frequency. This concept assumes that the interconnecting impedance is primarily inductive, but it can be shown that the reactance-to-resistance (X/R) ratio significantly affects the dynamic response and the rate at which steady-state behavior is restored following transient events. The concept of active resistance is introduced as a means to accelerate the rate of convergence to steady state following a transient without the dissipative losses associated with additional line resistance. With active resistance, the damping of the system is shown to significantly increase and the stable operating region is expanded.

2010 IEEE Energy Conversion Congress and Exposition, 2010

Abstract Microgrids can employ a variety of sources that work together to supply local power and ... more Abstract Microgrids can employ a variety of sources that work together to supply local power and offer significant system efficiency gains from combined heat and power (CHP). Energy storage elements offer the flexibility to supply power even when intermittent sources are ...

2014 Power and Energy Conference at Illinois (PECI), 2014

A second-life battery is an electric vehicle battery pack that has reached an end-of-life conditi... more A second-life battery is an electric vehicle battery pack that has reached an end-of-life condition for its vehicular use, yet retains enough performance to be re-purposed for another application. One promising application of a second-life battery is stationary energy storage within a CERTS microgrid. This paper investigates the modeling of multiple paralleled traction battery packs within a CERTS microgrid, examining the impacts of elevated internal pack impedance on microgrid system operation. Impedance spectroscopy and hybrid-pulse power characterization are used to model vehicular Li-ion cells under a range of conditions that include second-life aging. The ac bus dynamics of the microgrid model are validated experimentally. Second-life battery models are incorporated into two CERTS microgrid architectures and system-level effects of changing the battery impedance are explored. Simulation results indicate that the modeled EV second-life batteries deliver promising performance characteristics in both CERTS microgrid architectures that were investigated.

2000 IEEE 31st Annual Power Electronics Specialists Conference. Conference Proceedings (Cat. No.00CH37018), 2000

This paper develops a scheme to control a parallel connected, multiterminal DC power distribution... more This paper develops a scheme to control a parallel connected, multiterminal DC power distribution system without the need of central control unit for fast communication. The described scheme utilizes superconductors on the DC bus and incorporates UPS properties with the ability to supply large passive loads than conventional UPSs. A five terminal, mesh connected study system is used to demonstrate the basic characteristics of DC power distribution system such as the ability to ride through an AC system outage. In this paper, a simulation model of the study system is developed and the simulation results show that the proposed DC power distribution system has a high power quality performance.

PESC '91 Record 22nd Annual IEEE Power Electronics Specialists Conference

Tools are developed to study the harmonic interactions of a single-phase, fine commutated convert... more Tools are developed to study the harmonic interactions of a single-phase, fine commutated converter with power systems. It is shown that the classical method of analysis is incorrect when dealing with systems close to resonance points. For example, the operation of such a converter with the rest of the power system can have two solutions and/or no solutions for regions which the classical method predicts both existence and uniqueness of solutions

2011 IEEE Energy Conversion Congress and Exposition, 2011

Microgrids are highly compatible with photovoltaic (PV) sources because of their ability to inter... more Microgrids are highly compatible with photovoltaic (PV) sources because of their ability to internally aggregate and balance multiple PV sources without imposing restrictions on the penetration of such intermittent power sources. There are two major types of inverter control configurations that are used in photovoltaic inverters to provide an interface to a CERTS microgrid. These control configurations exhibit important duality characteristics, and both are capable of tracking maximum input power while abiding by the CERTS droop algorithms. This paper investigates and demonstrates the comparative performance characteristics of these two major controller types: 1) a grid-forming droop-style controller similar to those used for controlling distributed generators; and 2) a current-regulated grid-follower controller. It is shown that only the grid-forming controller allows a PV source to operate alone in an islanded CERTS microgrid, but the grid-follower controller enjoys some inherent advantages with regard to faster dynamic response.

Physical Review Letters, 1974

IEEE Transactions on Power Systems, 1986

The reliability assessment [1, 2] of power distribution systems requires the development of model... more The reliability assessment [1, 2] of power distribution systems requires the development of modeling and computa¬ tional techniques that reflect the operational behavior of these systems and their effect on the consumers. One important procedure in distribution systems is the use of local generating facilities which A) in normal conditions can supply the load which cannot be supplied because of limitations in the generated power, i.e., peak shaving; B) under outage conditions can supply the load which cannot be supplied because of capacity limitations in the remaining circuits after the outage has occurred. The local generating plants of a distribution system can be connected anywhere in the system and can be considered as either parallel redundant (objectives A and B) or stand-by redundant (objective B). The paper describes models and computational techniques that have been developed to trans¬ late the conceptual ideas of local generation into practical analysis which evaluates the five reliability indices for each load-point of interest (Expected Failure Rate X, Average Outage Time r, Expected Annual Outage Time U, Average Load Disconnected L, Average Energy not Supplied E). The ability of a generating station to contribute to local generation depends upon the station staffing arrangements and its resultant operating times. Three-shift stations and automatically controlled generating units (gas turbines) are assumed to be continuously on call. Oneand two-shift stations, however, are assumed to be operable only during their specified shift times. The generating plants are divided into three groups accord¬ ing to their switching time, this being defined as the time required by each station to supply its full output. This includes the run-up time of the units and the time for closing all the breakers. Two switching times can be specified: one for simulating the fast start-up stations (gas turbines, hydro¬

IEEE Transactions on Power Electronics, 1987

... 4, OCTOBER 1987 A Hybrid Converter for HV DC Applications KWA-SUR TAM, MEMBER, IEEE, AND ROBE... more ... 4, OCTOBER 1987 A Hybrid Converter for HV DC Applications KWA-SUR TAM, MEMBER, IEEE, AND ROBERT H. LASSETER, MEMBER, IEEE ... KS Tam is with the Department of Electrical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061. ...

IEEE Transactions on Power Delivery, 1990

Harmonics that arise from the interaction of thyristor controlled reactors (TCRs) and power syste... more Harmonics that arise from the interaction of thyristor controlled reactors (TCRs) and power systems can sometimes cause stability problems. The stability problems are hard to analyze since the harmonics are affected by the power system. The classical method for calculating harmonics is to calculate the harmonic current assuming an infinite bus at the high side of the TCR transformer. This current is then used as a harmonic current source on the ac system. The basic problem with this method is that many of the interactions between the ac system and the TCR are neglected. In this paper two methods for studying the neglected interactions are described. The first uses state variables to analyze the circuit containing the TCR. The resulting equations are linear differential equations with periodic coefficients. This formulation allows the study of stability, periodic operation, and resonance which can not be achieved by other methods. The second method uses a Fourier matrix description of the TCR. In this model the coupling between the different harmonics due to the switching is clearly shown.

IEEE Transactions on Power Delivery, 2014

Microgrids are highly compatible with photovoltaic (PV) sources because of their ability to inter... more Microgrids are highly compatible with photovoltaic (PV) sources because of their ability to internally aggregate and balance multiple renewable sources. Traditional grid-connected PV inverter control configurations are basically current sourced and cannot easily control ac voltage or frequency. The PV inverter using the Consortium for Electric Reliability Technology Solutions (CERTS) concepts can control ac voltage and frequency but have a major problem with load transients. During a load transient, the PV microsource becomes overloaded with the possibility of collapsing the dc bus voltage resulting in an ac voltage drop. This paper presents a PV inverter control strategy which enables PV to behave as a voltage source and is capable of maintaining dc bus voltage stability during load transient. With this PV inverter control configuration, it is shown that the PV microsource can operate as a voltage source in the CERTS microgrid.

Electric Power Systems Research, 2012

Ever increasing electrical energy demand is forcing power serving entities around the world to us... more Ever increasing electrical energy demand is forcing power serving entities around the world to use various demand management programs to help in stressful times of the electric power grid. Demand management programs aim to control electrical energy demand among customers and create load relief for electric utilities. Recently demand management contracts have been designed in which incentives are offered to customers who willingly sign up for load interruption. In recent years much technological advancement has been made in distributed generation, and the cost of using this option can bring about extra flexibility into existing demand management schemes. This paper explores the use of distributed generation technology within the existing demand management ideas. More specifically, it compares economic aspects of using demand management contracts with the use of distributed generation. A key observation of this paper is that there may be cases where it is more beneficial to use distributed generation rather than demand management contracts.

Hawaii International Conference on System Sciences, Jan 6, 2003

This paper presents a new advanced model of an electric power system with distributed energy sour... more This paper presents a new advanced model of an electric power system with distributed energy sources forming a microgrid (µGrid). The µGrid is a radial or networked low voltage distribution system with distributed sources. Each source is interfaced to the system via converters. The DC bus of the converter may have energy storage capability via large capacitors or batteries. The µGrid load consists of both single and three phase loads resulting in unbalanced operating conditions. The µGrid circuits may be three-wire, four-wire or five-wire. The grounding of the system may be single point or multipoint. The analysis of this system requires a new approach. This paper presents a new method for modeling and analysis of this system. The approach consists of two steps: (a) modeling each component of the system via a set of quadratic equations no matter how complex the nonlinearities of the model are and (b) a Newton's method for the solution of the overall network equations. The method is extremely efficient and robust. The proposed method can accommodate various control modes of micro-sources. Examples of these controls are given in the paper.

PESC `92 Record. 23rd Annual IEEE Power Electronics Specialists Conference

The classical analysis is often applicable, but can, as demonstrated here and in [1,5], fail for ... more The classical analysis is often applicable, but can, as demonstrated here and in [1,5], fail for certain circuit parameters and operating conditions. Under these conditions, both the voltage and the current waveforms become greatly distorted with large harmonic components. This distortion is associated with a resonance phenomenon in which the natural frequencies of the circuit, from when the reactor is fully on to when it is fully off, span an odd harmonic. This harmonic distortion can lead to instabilities as switching times suddenly

2014 IEEE Energy Conversion Congress and Exposition (ECCE), 2014

ABSTRACT This paper investigates an electric vehicle (EV) charging station that uses a CERTS micr... more ABSTRACT This paper investigates an electric vehicle (EV) charging station that uses a CERTS microgrid in a hybrid architecture that incorporates both ac and dc power buses. A dynamic model is developed that incorporates a CERTS ac microgrid and a parallel configuration of multiple electric vehicle batteries with droop-controlled dc/dc chargers that are connected to the dc bus of a single CERTS ac microsource. Components of the hybrid microgrid model are validated using a combination of experimental results and PLECS simulations. The small-signal stability of the dc bus dynamics is investigated. Simulations and experimental results are used to demonstrate that the hybrid CERTS microgrid can successfully accommodate diverse ac and dc load transients, including islanding and grid reconnection.

2012 IEEE Power and Energy Conference at Illinois, 2012

Frequency droop algorithms used by CERTS Microgrid inverters adjust power by changing the output ... more Frequency droop algorithms used by CERTS Microgrid inverters adjust power by changing the output frequency. This concept assumes that the interconnecting impedance is primarily inductive, but it can be shown that the reactance-to-resistance (X/R) ratio significantly affects the dynamic response and the rate at which steady-state behavior is restored following transient events. The concept of active resistance is introduced as a means to accelerate the rate of convergence to steady state following a transient without the dissipative losses associated with additional line resistance. With active resistance, the damping of the system is shown to significantly increase and the stable operating region is expanded.

2010 IEEE Energy Conversion Congress and Exposition, 2010

Abstract Microgrids can employ a variety of sources that work together to supply local power and ... more Abstract Microgrids can employ a variety of sources that work together to supply local power and offer significant system efficiency gains from combined heat and power (CHP). Energy storage elements offer the flexibility to supply power even when intermittent sources are ...

2014 Power and Energy Conference at Illinois (PECI), 2014

A second-life battery is an electric vehicle battery pack that has reached an end-of-life conditi... more A second-life battery is an electric vehicle battery pack that has reached an end-of-life condition for its vehicular use, yet retains enough performance to be re-purposed for another application. One promising application of a second-life battery is stationary energy storage within a CERTS microgrid. This paper investigates the modeling of multiple paralleled traction battery packs within a CERTS microgrid, examining the impacts of elevated internal pack impedance on microgrid system operation. Impedance spectroscopy and hybrid-pulse power characterization are used to model vehicular Li-ion cells under a range of conditions that include second-life aging. The ac bus dynamics of the microgrid model are validated experimentally. Second-life battery models are incorporated into two CERTS microgrid architectures and system-level effects of changing the battery impedance are explored. Simulation results indicate that the modeled EV second-life batteries deliver promising performance characteristics in both CERTS microgrid architectures that were investigated.

2000 IEEE 31st Annual Power Electronics Specialists Conference. Conference Proceedings (Cat. No.00CH37018), 2000

This paper develops a scheme to control a parallel connected, multiterminal DC power distribution... more This paper develops a scheme to control a parallel connected, multiterminal DC power distribution system without the need of central control unit for fast communication. The described scheme utilizes superconductors on the DC bus and incorporates UPS properties with the ability to supply large passive loads than conventional UPSs. A five terminal, mesh connected study system is used to demonstrate the basic characteristics of DC power distribution system such as the ability to ride through an AC system outage. In this paper, a simulation model of the study system is developed and the simulation results show that the proposed DC power distribution system has a high power quality performance.

PESC '91 Record 22nd Annual IEEE Power Electronics Specialists Conference

Tools are developed to study the harmonic interactions of a single-phase, fine commutated convert... more Tools are developed to study the harmonic interactions of a single-phase, fine commutated converter with power systems. It is shown that the classical method of analysis is incorrect when dealing with systems close to resonance points. For example, the operation of such a converter with the rest of the power system can have two solutions and/or no solutions for regions which the classical method predicts both existence and uniqueness of solutions

2011 IEEE Energy Conversion Congress and Exposition, 2011

Microgrids are highly compatible with photovoltaic (PV) sources because of their ability to inter... more Microgrids are highly compatible with photovoltaic (PV) sources because of their ability to internally aggregate and balance multiple PV sources without imposing restrictions on the penetration of such intermittent power sources. There are two major types of inverter control configurations that are used in photovoltaic inverters to provide an interface to a CERTS microgrid. These control configurations exhibit important duality characteristics, and both are capable of tracking maximum input power while abiding by the CERTS droop algorithms. This paper investigates and demonstrates the comparative performance characteristics of these two major controller types: 1) a grid-forming droop-style controller similar to those used for controlling distributed generators; and 2) a current-regulated grid-follower controller. It is shown that only the grid-forming controller allows a PV source to operate alone in an islanded CERTS microgrid, but the grid-follower controller enjoys some inherent advantages with regard to faster dynamic response.

Physical Review Letters, 1974

IEEE Transactions on Power Systems, 1986

The reliability assessment [1, 2] of power distribution systems requires the development of model... more The reliability assessment [1, 2] of power distribution systems requires the development of modeling and computa¬ tional techniques that reflect the operational behavior of these systems and their effect on the consumers. One important procedure in distribution systems is the use of local generating facilities which A) in normal conditions can supply the load which cannot be supplied because of limitations in the generated power, i.e., peak shaving; B) under outage conditions can supply the load which cannot be supplied because of capacity limitations in the remaining circuits after the outage has occurred. The local generating plants of a distribution system can be connected anywhere in the system and can be considered as either parallel redundant (objectives A and B) or stand-by redundant (objective B). The paper describes models and computational techniques that have been developed to trans¬ late the conceptual ideas of local generation into practical analysis which evaluates the five reliability indices for each load-point of interest (Expected Failure Rate X, Average Outage Time r, Expected Annual Outage Time U, Average Load Disconnected L, Average Energy not Supplied E). The ability of a generating station to contribute to local generation depends upon the station staffing arrangements and its resultant operating times. Three-shift stations and automatically controlled generating units (gas turbines) are assumed to be continuously on call. Oneand two-shift stations, however, are assumed to be operable only during their specified shift times. The generating plants are divided into three groups accord¬ ing to their switching time, this being defined as the time required by each station to supply its full output. This includes the run-up time of the units and the time for closing all the breakers. Two switching times can be specified: one for simulating the fast start-up stations (gas turbines, hydro¬

IEEE Transactions on Power Electronics, 1987

... 4, OCTOBER 1987 A Hybrid Converter for HV DC Applications KWA-SUR TAM, MEMBER, IEEE, AND ROBE... more ... 4, OCTOBER 1987 A Hybrid Converter for HV DC Applications KWA-SUR TAM, MEMBER, IEEE, AND ROBERT H. LASSETER, MEMBER, IEEE ... KS Tam is with the Department of Electrical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061. ...

IEEE Transactions on Power Delivery, 1990

Harmonics that arise from the interaction of thyristor controlled reactors (TCRs) and power syste... more Harmonics that arise from the interaction of thyristor controlled reactors (TCRs) and power systems can sometimes cause stability problems. The stability problems are hard to analyze since the harmonics are affected by the power system. The classical method for calculating harmonics is to calculate the harmonic current assuming an infinite bus at the high side of the TCR transformer. This current is then used as a harmonic current source on the ac system. The basic problem with this method is that many of the interactions between the ac system and the TCR are neglected. In this paper two methods for studying the neglected interactions are described. The first uses state variables to analyze the circuit containing the TCR. The resulting equations are linear differential equations with periodic coefficients. This formulation allows the study of stability, periodic operation, and resonance which can not be achieved by other methods. The second method uses a Fourier matrix description of the TCR. In this model the coupling between the different harmonics due to the switching is clearly shown.

IEEE Transactions on Power Delivery, 2014

Microgrids are highly compatible with photovoltaic (PV) sources because of their ability to inter... more Microgrids are highly compatible with photovoltaic (PV) sources because of their ability to internally aggregate and balance multiple renewable sources. Traditional grid-connected PV inverter control configurations are basically current sourced and cannot easily control ac voltage or frequency. The PV inverter using the Consortium for Electric Reliability Technology Solutions (CERTS) concepts can control ac voltage and frequency but have a major problem with load transients. During a load transient, the PV microsource becomes overloaded with the possibility of collapsing the dc bus voltage resulting in an ac voltage drop. This paper presents a PV inverter control strategy which enables PV to behave as a voltage source and is capable of maintaining dc bus voltage stability during load transient. With this PV inverter control configuration, it is shown that the PV microsource can operate as a voltage source in the CERTS microgrid.

Electric Power Systems Research, 2012

Ever increasing electrical energy demand is forcing power serving entities around the world to us... more Ever increasing electrical energy demand is forcing power serving entities around the world to use various demand management programs to help in stressful times of the electric power grid. Demand management programs aim to control electrical energy demand among customers and create load relief for electric utilities. Recently demand management contracts have been designed in which incentives are offered to customers who willingly sign up for load interruption. In recent years much technological advancement has been made in distributed generation, and the cost of using this option can bring about extra flexibility into existing demand management schemes. This paper explores the use of distributed generation technology within the existing demand management ideas. More specifically, it compares economic aspects of using demand management contracts with the use of distributed generation. A key observation of this paper is that there may be cases where it is more beneficial to use distributed generation rather than demand management contracts.