Roger A. Dougal

Design and Application of Surface Wave Sensors for Nonintrusive Power Line Fault Detection

This paper describes a novel conformal surface wave (CSW) launcher that can excite electromagnetic surface waves along unshielded power line cables nonintrusively. This CSW launcher can detect open circuit faults on power cables. Unlike conventional horn-type launchers, this CSW launcher is small, lightweight, and cost effective, and can be placed easily on a power cable. For a nonintrusive open fault detection, the error is <; 5% when the cable length is <; 10 m, which is comparable with other direct-connect fault-finding techniques. For a cable length of 15.14 m, 7.6% error is noted. Besides cable fault detection, the potential applications of the proposed launcher include broadband power line communication and high-frequency power transmission.

Coordinated Control of the Bus Tie Switches and Power Supply Converters for Fault Protection in DC Microgrids

For dc microgrids, coordinated operation of electronic power converters and mechanical contactors can rapidly isolate short circuit faults while maintaining continuity of power to loads. The entire process—rapidly limiting current, deenergizing the bus, reconfiguring the bus via segmentizers or bus ties, and reenergizing the network—can be accomplished in milliseconds, during which time diode-isolated load-side hold-up capacitors continue supplying power to critical loads. For a wide range of systems, reconfiguration can be accomplished in 8–10xa0ms, which is fast enough to comply with requirements of CBEMA and IEEE standards on power quality. Reconfiguration time depends on the power system dimensions, the number of sources connected to the system, the system nominal voltage, and the performance of segmentizers.

New Horizons in DC Shipboard Power Systems: New fault protection strategies are essential to the adoption of dc power systems.

In the last decade, the increased performance, improving efficiency, and decreasing cost of electronic power converters have spurred the rediscovery and proliferation of dc power distribution systems. These are increasingly of interest for ships, where a dc grid has significant benefits, yet significant challenges must also be overcome before these systems can be widely adopted.

Novel Dual-FCL Connection for Adding Distributed Generation to a Power Distribution Utility

A novel dual-connection of fault current limiters is described for use when connecting new distributed generation plants to the electric grid. The operation and control scheme of this connection are described and analysed. The proximate arrangement of the two current limiters has the advantage that they can share one cryogenic system. The dual connection limits fault currents sufficiently to avoid disturbing the original protection relay schemes of the utilities, and also improves synchronism between the new generator and the grid. These benefits are proven by simulations of a 36 MW, 4.16 kV gas turbine generator connected to an infinite grid. This dual-FCL connection reduces fault current contributions of the DG by 97% (from 41 to 1 kA), and maintains the circuit breakers within their duty limits when a three-phase fault occurs at a bus connected to the DG. Otherwise, when a three-phase fault occurs in the infinite system, this connection limits the fault current contribution of the DG from 4.8 to 0.4 kA, and frequency oscillations of the DG from 0.14 to 0.01 Hz. The power continuity in the local network is improved, as the voltage sag at the bus connected to the DG is reduced by 96% (from 851 to 32 V) during and after serious short-circuit faults.

A Coordinating Algorithm for Dispatching Regulation Services Between Slow and Fast Power Regulating Resources

This paper presents a novel coordinating algorithm for dispatching regulation services between slow and fast power regulating resources using a conventional power generator and a flywheel energy storage system as an example. The goal is to let the flywheel storage device follow the fast changes in the regulation signal and let the conventional generator compensate for the energy imbalance when the flywheel storage is nearly fully charged or discharged. A state-of-charge (SOC) band control algorithm is developed to maintain the storage device SOC within a desired range. Real system regulation signals were used to test the performance of the coordinating algorithm. The simulation results show that: 1) the HRR achieves the same fast response rate as that of the storage device, 2) the up and down movements of the generator are minimized, and 3) the SOC of the storage device is maintained within the desired range most of the time. Therefore, the proposed coordinating algorithm can provide the high quality regulation service while reducing maintenance-inducing strain on conventional generators.

Efficient Harmonic Filter Allocation in an Industrial Distribution System

In order to properly suppress the harmonic current in a power system, the harmonic similarity metric is developed in this paper and used to establish an efficient strategy for harmonic filter placement. To validate the strategy, an industrial distribution system is analyzed under two harmonic current injection scenarios. It is demonstrated that the proposed strategy has a robust ability to successfully determine the most efficient and effective location for placing a harmonic filter bank based upon the desired objectives. The two harmonic current injection scenarios serve to validate the proposed strategy regardless of the power distribution level at which harmonic current is injected.

Latency-Based Approach to the Simulation of Large Power Electronics Systems

We define a new hybrid simulation scheme that combines latency insertion with nodal and state-space methods. The conditions for stability and multirate time stepping of the hybrid method are defined. Further, we show how to define appropriate flow variable injections so that the hybrid method can be extended to applications involving either multiple technical domains or hardware in the simulation loop. The hybrid method permits significant increases of simulation speed while contributing less than 1% to RMS simulation error.

Novel Unity-Gain Frequency Tracking Control of Series–Series Resonant Converter to Improve Efficiency and Receiver Positioning Flexibility in Wireless Charging of Portable Electronics

Currently available wireless charging technology for portable electronics demonstrates several shortcomings. For the consumers, the two major shortcomings are limited receiver positioning flexibility and lower efficiency compared to hard-connected charging. For the industry, the major disadvantages are higher cost and complexity in design and control. To overcome these shortcomings and disadvantages, this paper presents a novel control method for unity-gain frequency tracking (UGFT) under coupling coefficient (k) variation in a resonant converter containing a symmetrically implemented series-series (SS) resonant tank. An SS resonant converter employing the UGFT control provides several desirable features: the need for digital communication between the transmitter and the receiver to achieve leakage inductance compensation is eliminated, the design is robust against coupling (k) and load (Q) variations, the SS resonant converter can operate most of the time at the frequency of highest efficiency (unity-gain frequency fO), and the downstream regulator commonly employed in a wireless charging system may be eliminated. Furthermore, in this paper, frequency-domain characteristics of SS resonant tank are explained in detail to illustrate various desirable characteristics. Detailed design criteria for SS resonant tanks are provided to achieve these characteristics. Throughout the analysis, various simulation results are provided to complement the discussion. The proposed UGFT control method is validated through experimental results.

Soft-Synchronization of Generators Using Controllable Inductive Fault Current Limiters

We describe a method for soft-synchronization of generators by controlling an inductive fault current limiter located between the generator and the grid. Our method limits the peak shaft torque and the frequency oscillations that normally occur following mistimed closure of the bus tie switch. The method improves the success rate of generator close-in, especially during emergencies or when operating with low transient-stability margin, with low inertia and, therefore, it lengthens the life of turbogenerators. This method introduces no adverse effects during an ideal (correctly timed) generator-synchronization process. We prove the success of the technique by using transient time-domain analysis and describe the control and an approach to analyze the soft-synchronization process that can be generally applied to either an infinite power system or to a limited-capacity system. After the generator is synchronized to a grid and operates stably, the transient-stability margin between the generator and the grid is not affected by this method. This soft-synchronization method has been validated by simulations with the increased critical margin of the rotor-angle difference and the improved faulty synchronization process with limited power impulse and frequency oscillation.

Tieline reconnection of microgrids using controllable variable reactors

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 of variable reactors controller are derived. The feasibility and effectiveness of this tieline reconnection method with tuned controller is analyzed and verified by simulations. This method can greatly improve the transient stability of non-conventional grid, which consists of multiple microgrids and require an ability of frequent reliable reconnections, and limit system oscillation to less than 50%. The tieline reconnection controller can be easily integrated with power flow control into existing variable reactor devices at low cost. And the tuning process of the controller is simple and suitable for industrial applications.