Transient Overload Conditions Research Articles

Effect of Prime Mover's Characteristics on the Survivability of a Synchronous Generator-Based Distributed Energy Resource During Transient Overload Conditions

Recently, prime-mover stalling phenomenon was observed in a synchronous generator-based distributed energy resource (DER) for large step load changes during experimental testing at the Consortium for Electric Reliability Technology Solutions Microgrid. It is found to highly impact the generator's survivability during transient overload conditions. The stalling occurs in synchronous generator-based DER because of a sustained imbalance between electrical load demand and mechanical power available from the prime mover, thus depleting the generator's stored kinetic energy. In particular, mechanical power capability of the prime mover and stored kinetic energy in the rotating mass are the causal factors. This article evaluates two different types of prime movers—reciprocating engine and combustion gas turbine—for the DER survivability. The characteristics of these two commonly used prime movers are investigated during transient overload conditions by simulation case studies using PSCAD/EMTDC software.

Survivability of Synchronous Generator-Based Distributed Energy Resources for Transient Overload Conditions in a Microgrid

A synchronous generator-based distributed energy resource (DER) is commonly employed in microgrids due to its low cost and simple controls. However, there are many challenges to the DER operation when it is sized for supplying the critical loads alone in a microgrid. In particular, the DER would experience an overload condition during the microgrid transition from grid-connection to islanded operation, when the noncritical loads are also supplied momentarily. Therefore, it is very important to have a clear understanding on the survivability of a synchronous generator-based DER for transient overload conditions. Recently, experimental tests on survivability of the DER were carried out in the Consortium for Electric Reliability Technology Solutions Microgrid Testbed at American Electric Power. In this paper, an in-depth analysis of the synchronous generator-based DER operation during transient overload conditions is presented. The key relationships governing the system dynamic behavior of synchronous generator-based DER are analyzed to design the load shedding scheme for its survivability. Several case studies are illustrated to demonstrate the validity of the proposed load shedding method.

Discriminatory processor sharing queues with stationary ergodic service times and the performance of TCP in overload

In a recent paper, Bonald and Roberts (2001) [6] studied non-persistent TCP connections in transient overload conditions, under the assumption that all connections have the same round-trip times. In this paper our goal is to develop theoretical tools that will enable us to relax this assumption and obtain explicit expressions for the rate of growth of the number of connections at the system, the rate at which TCP connections leave the system, as well as the time needed for the completion of a connection. To that end, we model the system as a discriminatory processor sharing (DPS) system which we analyze under very mild assumptions on the probability distributions related to different classes of arrivals: we only assume that the arrival rates of connections exist, and that the amount of information transmitted during a connection of a given type forms a stationary ergodic sequence. We then proceed to obtain explicit expressions for the growth rate of the number of connections at the DPS system for several specific probability distributions. We check through simulations the applicability of our queueing results for modeling TCP connections sharing a bottleneck.

Transient Capability of Superconducting Devices on Electric Power Systems

Superconducting devices operating within a power system are expected to go through transient overload conditions during which the superconducting coil has to carry currents above the rated values. Designing the coil to remain superconducting through any possible fault scenario can be cost prohibitive, necessitating operation beyond the critical current for short periods. In order to set operating limits and design adequate protection systems for superconducting devices connected to a power system, the region of safe operation of these devices has to be described with general capability curves. Existing standards that define limits for these over-current situations are based on copper winding experience that do not apply to devices with superconducting components because of the highly nonlinear interaction between magnetic fields, operating temperature, and current density in the superconductor, and the rapidly varying material properties at cryogenic temperatures. In this paper, the behavior of superconducting coils during over-currents is discussed and a simplified capability curve is described to help standardize device capabilities. These curves are necessary to aid power system designers in appropriately designing the system and associated protection systems.

Quality-of-Control Management in Overloaded Real-Time Systems

Transient overload conditions may cause unpredictable performance degradations in computer controlled systems if not properly handled. To prevent such problems, a common technique adopted in periodic task systems is to reduce the workload by enlarging activation periods. In a digital controller, however, the variation applied on the task period also affects the control law, which needs to be recomputed for the new activation rate. If computing a new control law requires too much time to be performed at runtime, a set of controllers has to be designed offline for different rates and the system has to switch to the proper controller in the presence of an overload condition. In this paper, we present a method for reducing the number of controllers to be designed offline, while still guaranteeing a given control performance. The proposed approach has been integrated with the elastic scheduling theory to promptly react to overload conditions. The effectiveness of the proposed approach has been verified through extensive simulation experiments performed on an inverted pendulum. In addition, the method has been implemented on a real inverted pendulum. Experimental results and implementation issues are reported and discussed

COSMIC: A real-time event-based middleware for the CAN-bus

The paper describes the event model and the architecture of the COSMIC (COoperating SMart devICes) middleware. Based on the assumption of tiny smart sensors and actuators, COSMIC supports a distributed system of cooperating autonomous devices. COSMIC considers quality of service requirements in the event model and provides an application interface which allows to express the respective temporal and reliability attributes on a high, application related abstraction level. According to the need in most real-time systems, COSMIC supports event channels with different timeliness and reliability classes. Hard real-time event channels are considered to meet all temporal requirements under the specified fault assumptions. The resource requirements for this type of channel are statically assigned by an appropriate reservation scheme. Soft real-time event channels are scheduled by their deadlines, but they are not guaranteed under transient overload conditions. Non-real-time event channels are used for events without any specified timeliness requirements in a best-effort manner. The paper finally presents the layered COSMIC architecture to map the different channel classes to the CAN-Bus.

IGBT Package Design for High Power Aircraft Electronic Systems

This paper will discuss the design of semiconductor packages having integrated air cooled heatsinks for use in high power electronic systems. It will demonstrate how simple models of the heat transfer from the heatsink fins, which are based on empirical correlations, may be utilized in combination with either simple analytical models or two-dimensional finite difference (FD) models of the heat conduction from the semiconductor die through the multilayer package structure to the base of the fins. These models allow the rapid evaluation of performance under both steady-state and transient overload conditions, and can be used to rapidly explore a wide range of design options before selecting candidate layouts for more detailed evaluation using 3D analysis tools. Wind tunnel experiments, which will also be reported, have been carried out to verify the modeling results for different semiconductor device layouts. These trials demonstrate excellent agreement between the models and experimental results.