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For Medium Voltage DC (MVDC) power systems, we greatly extend the coverage of local-information-based fault protection (LIFP), an approach defined for independent distributed management of short-circuit line-to-line faults that does not rely on any high-speed ship-wide communications, to arc faults under varying load conditions. The method for LIFP was previously developed for systems where all loads...
We define an approach Local Information Based Fault Protection (LIFP) for robust protection against short-circuit faults that does not rely on microgrid-wide communications. Using a monopolar bus as an example, we show how each entity connected to the dc bus, including current-limiting power converters and non-load-breaking disconnect switches, can autonomously detect, identify, and appropriately...
Energy storage systems (ESSs) that are composed of batteries and supercapacitors are increasingly being used as receptors for regenerative braking energy (RBE) in railway applications. These ESSs can be installed on-board the rolling vehicle, or off-board wayside, or mixed on- and off-board. This paper presents a comparison of three different ESSs topologies applicable in trains powered by a dc feed...
Running megawatt-range ac microgrids at frequencies higher than the usual 50 or 60 Hz is feasible with readiness and maturation of advanced power system equipment, such as high speed generators and fast-response protection devices. Applications where weight and foot-print savings are vital would find it favorable and attractive. This paper examines the transient stability of such megawatt-range high...
The traditional method for the analysis of power quality (PQ) disturbances is fast Fourier transform (FFT) which suffers from spectral leakage phenomenon, and results in erroneous assessment in the presence of nonstationary PQ disturbances. Also, it cannot provide any time information as PQ indices are computed in the frequency domain only. Regarding the limitations of the FFT, in this paper Page...
Recent advances in the sensor and weapons systems being installed on US Navy ships and the electrification required to power them are now forcing the engineering community to re-evaluate the effectiveness of the tools and processes now in use. At the same time, over the last decade there have been significant changes in the way that software is architected and developed. User expectations for software...
Robust management of short-circuit faults in MVDC systems must rely on a combination of communication-dependent and communication-independent methods. In one approach, an MVDC system is designed to operate without breakers [1], so both methods rely on coordinated control of power converters and non-fault-breaking mechanical disconnect switches to effect the fault clearance process-fault detection...
In this paper, a tuned controller of variable reactors is developed to realize a reliable tieline reconnection of microgrids. It is very useful to solve the problem caused by synchronization issue during tieline reconnection, especially in absence of large-area communication network to cover all microgrids. The theoretical fundamental of this method is analyzed, based on which a set of tuning process...
Apparent resistance can be used by each power distribution element — supply converters and power circuit contactors — to identify and respond to faults in multi-terminal dc power systems. Each element can take appropriate independent action based on its own local measurements: Supply converters can go into current limiting or shut-down modes and (non-fault breaking) contactors can segment and/or reconfigure...
Traditional synchronizer cannot control multiple generators in distribution networks in coordination. In this paper, a real-time synchronization control (RTSC) is designed to keep all generators in different standalone distribution networks in synchronization at all times, which realizes a fast and reliable reconnection of disconnected power network. The frequency control and phase control in RTSC...
Surface wave propagation velocities on unshielded power cables are experimentally determined. The waves are launched using broadband monopole wave launchers. Gaussian pulse waveforms of duration 2 and 4 ns are used to perform the study. It is found that the velocity of propagation is about 2.8×108 m/s within the frequency range of 50–300 MHz. These results are of significance for future potential...
We show that an inverter coupled energy storage system can be used to provide a soft-restart for the zonal loads by first operating in a “protected ride-through” mode, then pre-energizing the loads, and finally transfer the loads bumplessly to the main generator. This method decreases by over 50% the inrush currents associated with restarting the loads. The inverter is controlled to achieve a voltage...
We present a fast and effective method for detecting and isolating faults in multi-terminal medium voltage dc shipboard power distribution systems. This new detection method permits coordination between the power supply converters and a set of bus segmentizing contactors without requiring fast communication between the elements. The power converters go into current-limiting mode as soon they recognize...
We describe a new method of operating MVDC power systems that is characterized by two aspects: 1) operation of main power sources in current-controlled mode, and voltage regulation via a (relatively) low-power voltage-source converter sourced from a small energy storage system (voltage regulator energy storage system or VRESS). In comparison to the bulk energy storage system, the VRESS is more agile...
Designers of shipboard power systems must consider many tradeoffs when selecting generators in the early-stage set-based design. This is not just an “equipment problem” based on physical design requirements such as limits of size and weight. The operating strategy for generators must be considered when evaluating the goodness of the design. To this end, this paper develops a design approach to impose...
The large-signal transient stability of generators running at frequencies higher than the usual 50 or 60 Hz was investigated as a function of system frequency in a micro-grid setting. A three phase bolted fault was taken as the mechanism for inciting potential instabilities. Simple rotor angle analysis leads one to believe that higher frequency power systems are inherently more unstable than lower...
This paper presents a method for driving an AC electric motor so that it emulates, at its drive shaft, the steady-state and transient loading and unloading dynamics of an aeroderivative twin-shaft gas turbine engine. This approach allows safe and robust testing of connected equipment, for example an electric generator, without having to install (or risk damage to) an actual gas turbine engine and...
Our investigation of variable speed operation of turbogenerators, including both single-shaft and twin-shaft variants, shows significant opportunities to improve part-load efficiency in those certain electrical power generation applications that permit variable speed operation. Efficiency improvement increases as load decreases and the improvement is larger for single-shaft engines than for twin-shaft...
We describe a process for using inverter-coupled local energy storage to softly-restart an industrial power network, and then bumplessly reclose the circuit breaker that has tripped the plant offline. The soft restart process eliminates a number of problems commonly associated with breaker reclosing such as large inrush currents, motor torque pulsations, and dipping of the line voltage feeding the...
We summarize the state of the art of Fault Current Limiters (FCL), focusing on devices in or near to field test status, and then, based on capabilities and characteristics of FCLs and smart grid, assign the various types to the most appropriate nodes in a smart grid.: 1) solid-state FCLs can be installed at microgrid and renewable energy resource feeders to replace circuit breaker and maintain protection...
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