Publications

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This paper presents simulation results of a control scheme for damping inter-area oscillations using high-voltage DC (HVDC) power modulation. The control system utilizes realtime synchrophasor feedback to construct a supplemental commanded power signal for the Pacific DC Intertie (PDCI) in the North American Western Interconnection (WI). A prototype of this controller has been implemented in hardware and, after multiple years of development, successfully tested in both open and closed-loop operation. This paper presents simulation results of the WI during multiple severe contingencies with the damping controller in both open and closed-loop. The primary results are that the controller adds significant damping to the controllable modes of the WI and that it does not adversely affect the system response in any of the simulated cases. Furthermore, the simulations show that a feedback signal composed of the frequency difference between points of measurement near the Washington-Oregon border and the California-Oregon border can be employed with similar results to a feedback signal constructed from measurements taken near the Washington-Oregon border and southern California. This is an important consideration because it allowed the control system to be designed without relying upon cross-system measurements, which would have introduced significant additional delay.

Distributed control compensation based on local and remote sensor feedback can improve small-signal stability in large distributed systems, such as electric power systems. Long distance remote measurements, however, are potentially subject to relatively long and uncertain network latencies. In this work, the issue of asymmetrical network latencies is considered for an active damping application in a two-area electric power system. The combined effects of latency and gain are evaluated in time domain simulation and in analysis using root-locus and the maximum singular value of the input sensitivity function. The results aid in quantifying the effects of network latencies and gain on system stability and disturbance rejection.

Lightly damped electromechanical oscillations are a source of concern in the western interconnect. Recent development of a reliable real-time wide-area measurement system (WaMS) has enabled the potential for large-scale damping control approaches for stabilizing critical oscillation modes. a recent research project has focused on the development of a prototype feedback modulation controller for the Pacific DC Intertie (PDCI) aimed at stabilizing such modes. The damping controller utilizes real-time WaMS signals to form a modulation command for the DC power on the PDCI. This paper summarizes results from the first actual-system closed-loop tests. Results demonstrate desirable performance and improved modal damping consistent with previous model studies.

This letter presents a new frequency control strategy that takes advantage of communications and fast responding resources such as photovoltaic generation, energy storage, wind generation, and demand response, termed collectively as converter interfaced generators (CIGs). The proposed approach uses an active monitoring of power imbalances to rapidly redispatch CIGs. This approach differs from previously proposed frequency control schemes in that it employs feed-forward control based on a measured power imbalance rather than relying on a frequency measurement. Time-domain simulations of the full Western Electricity Coordinating Council system are conducted to demonstrate the effectiveness of the proposed method, showing improved performance.

This paper proposes a method to modulate the power output of converter interfaced generators (CIGs) according to frequency variations. With the proposed approach, CIGs can successfully engage in the primary frequency regulation of a power system. The approach is a variation on the traditional droop-like proportional controller where the feedback signal is a global frequency measurement instead of a local one. Obtaining the global measurement requires transferring data using communications. This paper analyzes the performance of the proposed approach with respect to communications issues such as latencies and data dropouts. The approach implemented and tested in a simulation environment is compared against a method entirely based on local information. The results show that using global information in droop control provides benefits to the system as it improves its frequency regulation. The results also indicate that the proposed approach is robust to latencies and communication failures.

Power systems can be stabilized using distributed control methods with wide-area measurements for feedback. However, wide-area measurements are subject to time delays in communication, which can have undesirable effects on system performance. We present time-domain analysis results regarding the small-signal stability of a two-area power system with damping control subjected to asymmetric time delays in the feedback measurements. We consider two wide-area damping control implementations. The first is implemented with a High Voltage DC transmission line, and the second uses distributed Energy Storage devices. Numerical results show regions of stability for the closed-loop systems that depend on the time delays and the choice of the control gain. These results show that increasing the control gains cause the systems to be less robust to time delays, and, under certain conditions, increasing the time delays can have a stabilizing effect. Furthermore, we provide analysis of time simulations and eigenvalue plots that verify these stability regions and show how stability is affected as time delays increase.

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This paper proposes a method of enabling photovoltaic (PV) power plants to participate in primary frequency response by providing synthetic inertia (SI). This variation, referred to as communication enabled synthetic inertia (CE-SI), utilizes communication capabilities to provide global system frequency information to PV plants to emulate the inertial response of synchronous generators. The performance of CE-SI is analyzed with respect to the challenges associated with communication, such as latency and availability. Results indicate improvements in frequency response over SI using local frequency measurements when communication latency is sufficiently small.

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This paper describes the initial open-loop operation of a prototype control system aimed at mitigating inter-area oscillations through active DC power modulation. The control system uses real-time synchrophasor feedback to construct a commanded power signal added to the scheduled power on the Pacific DC Intertie (PDCI) within the western North American power system (wNAPS). The control strategy is based upon nearly a decade of simulation, linear analysis, and actual system tests. The control system must add damping to all modes which are controllable and 'do no harm' to the AC grid. Tests were conducted in which the damping controller injected live probing signals into the PDCI controls to change the power flow on the PDCI by up to ±125 MW. While the probing tests are taking place, the damping controller recorded what it would have done if it were providing active damping. The tests demonstrate that the dynamic response of the DC system is highly desirable with a response time of 11 ms which is well within the desired range. The tests also verify that the overall transfer functions are consistent with past studies and tests. Finally, the tests show that the prototype controller behaves as expected and will improve damping in closed-loop operation.

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This paper describes the design strategy and testing results of a control system to improve damping of inter-area oscillations in the western North American Power System (wNAPS) in order to maintain dynamic stability of the grid. Extensive simulation studies and actual test results on the wNAPS demonstrate significant improvements in damping of inter-area oscillations of most concern without reducing damping of peripheral oscillations. The design strategy of the control system features three novel attributes: (1) The feedback law for the control system is constructed using real-time measurements acquired from Phasor Measurement Units (PMUs) located throughout the power grid. (2) Control actuation is delivered by the modulation of real power flow through a High Voltage Direct Current (HVDC) transmission line. (3) A supervisory system, integrated into the control system is in charge of determining damping effectiveness, maintaining failsafe operation, and ensuring that no harm is done to the grid.

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To demonstrate and validate the performance of the wide-are a damping control system, the project plans to conduct closed-loop tests on the PDCI in summer/fall 2016. A test plan details the open and closed loop tests to be conducted on the P DCI using the wide-area damping control system. To ensure the appropriate level of preparedness, simulations were performed in order to predict and evaluate any possible unsafe operations before hardware experiments are attempted. This report contains the result s from these simulations using the power system dynamics software PSLF (Power System Load Flow, trademark of GE). The simulations use the WECC (Western Electricity Coordinating Council) 2016 light summer and heavy summer base cases.