Integrative Power Electric and Electronic Systems

Power electronics is a key enabling technology for the emerging hydrogen economy, all-electric forms of transportation, high-performance computer power supplies, sustainable energy conversion, and other systems. Our interest concerns the innovative design of power electronic circuits and controls as well as the system integration. The systems that we have considered include the hybrid energy systems and distributed energy resources as described below in more detail.

Apart from power electronics technology itself, we also investigate the added value. This is for example of interest in the context of electricity markets.Prior to the introduction of electricity markets, the utility industry was largely vertically integrated with one and the same company being in charge of the three key tasks of electricity generation, transmission and distribution. With the deregulation and introduction of electricity markets, the responsibilities for these three tasks have been separated in many countries. In this context, the opportunities of enhanced controllability of power flow through power electronics based FACTS are beneficial.

Modeling and Simulation of
Heterogeneous Circuits

No one modeling and simulation methodology is bested suited for all types of circuits and therefore different methods do exist. Some circuits are diverse by itself and different waveform shapes are observed in different parts of the circuit. For this purpose we have investigated the use of locally varying methods. The results are promising.

Modeling and Simulation of
Next-Generation Distributed Energy Systems

The successful integration of distributed resources is vital for the nation's future prosperity. This success will heavily rely on the availability of efficient and accurate tools that allow the demonstration of the feasibility of this transformation and to perform key tasks such as research, planning, real time control and operation of next-generation energy systems. The proposed work will lead to the creation of the digital simulation technology that constitutes the basis for the development of such vital tools. A recent outcome of the research is a simulation algorithm that allows for time step changes without the need of changing the nodal admittance matrix.

Hybrid Energy Systems

In the search for higher efficiency, hybrid energy solutions have received increasing attention in recent years. A popular example is the hybrid car. We contribute to this field with the design of multilevel energy storage, which is a hybrid of diverse but complementary storage technologies. In particular, we presented the concept of Stochastic Energy Source Access Management (SESAM). In SESAM, stochastic renewable energy sources are coupled with multilevel storage to provide deterministic power output over diverse time scales

Integration of Distributed Energy Resources
and Hydrogen Economy

In June 2001, Business Week Online published a prediction from the Gas Research Institute saying that by the year 2030 distributed energy resources are expected to capture about 30 % of the energy market. Given the strategic importance of the energy systems for the security and economy of the United States, the successful integration of these distributed resources and of the hydrogen economy within the energy infrastructure is vital for the nation’s future prosperity. Our particular interest concerns in this context the creation of methods for the efficient power management, control, and network integration of environmentally benign resources and hydrogen systems. In 2005, our team was awarded the honorable mention award by the National Hydrogen Association for the “for the brilliant innovation, technical aptitude and superior originality in the design of a next-generation hydrogen power park”.

Analysis of Breaker Transient Recovery Voltages

When protective relays detect a fault on a high voltage transmission line, they send a signal to open the circuit breakers at each end of the line to isolate the fault. Because transmission lines are primarily inductive RLC circuits, currents cannot change instantaneously. As a result, a charge is trapped on the line when the breaker opens to clear the fault. This produces ringing of the voltage on the line side of the breaker at frequencies well above 60 Hz. Assuming there are other transmission lines feeding the substation besides the faulted line, the voltage on the bus side recovers to the system voltage. The transient recovery voltage (TRV) of the breaker is defined as the difference in potential between the line and bus side voltages after the breaker opens to clear the fault. Circuit breakers have a fault current rating, as well as a time-dependent TRV rating. Catastrophic failure can occur if the TRV from a fault exceeds the breaker capabilities. This can cost a utility hundreds of thousands of dollars per event to replace high voltage breakers.

IEC and ANSI standards specify the minimum acceptable TRV characteristics for circuit breaker manufacturers. These standards were created decades ago using a one-phase simplification of three-phase power systems. Frequency dependence and mutual coupling of transmission lines were neglected due to computational limits at the time. Recent investigations suggest that the made simplifications are not of sufficient accuracy. A breaker that meets the IEC and ANSI standards for TRV may still be prone to catastrophic failure from a simple three-phase fault. We study this breaker TRV problem in greater detail. We use models of realistic power systems in an electromagnetic transients simulator to compare present TRV characteristics to the IEC and ANSI standards. We analyze the results and intend to determine which system parameters have the greatest impact on TRV.