Felipe Wilches-Bernal

Small signal stability of the western North American power grid with high penetrations of renewable generation

The goal of this effort was to assess the effect of high penetration solar deployment on the small signal stability of the western North American power system (wNAPS). Small signal stability is concerned with the system response to small disturbances, where the system is operating in a linear region. The study area consisted of the region governed by the Western Electricity Coordinating Council (WECC). General Electrics Positive Sequence Load Flow software (PSLF®) was employed to simulate the power system. A resistive brake insertion was employed to stimulate the system. The data was then analyzed in MATLAB1® using subspace methods (Eigensystem Realization Algorithm). Two different WECC base cases were analyzed: 2022 light spring and 2016 heavy summer. Each base case was also modified to increase the percentage of wind and solar. In order to keep power flows the same, the modified cases replaced conventional generation with renewable generation. The replacements were performed on a regional basis so that solar and wind were placed in suitable locations. The main finding was that increased renewable penetration increases the frequency of inter-area modes, with minimal impact on damping. The slight increase in mode frequency was consistent with the loss of inertia as conventional generation is replaced with wind and solar. Then, distributed control of renewable generation was assessed as a potential mitigation, along with an analysis of the impact of communications latency on the distributed control algorithms.

Power system controllability through nontraditional generation

Power system electromechanical oscillation dynamics can be described using second-order consensus dynamics. The synchronizing torques that hold the machines together are determined by the Laplacian matrix of the consensus dynamics. This paper develops a framework to investigate the effect of connecting nontraditional generation (NTG), in the form of active and reactive current injection, on the consensus dynamics of a 2-machine power system. The damping of inter-area oscillations power systems control problem is investigated for the linear model of a two-area test power system using reactive as well as active current injection. The control design is based on solving a LQR control problem. Results show that it is possible to control the power system dynamics through the use of nontraditional current injection. The relative effectiveness of the active and reactive components of the current injection is investigated, and the impact of the location of the injection is studied.

Effects of communication latency and availability on synthetic inertia

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.

Small-signal analysis of power system swing modes as affected by wind turbine-generators

The power electronic grid interface of converter-based energy systems such as wind turbine-generators (WTGs) is modifying the dynamics governing power systems. For a fundamental understanding of the impact of power electronic interface on the electromechanical modes, that is, the synchronizing and damping torque on synchronous machines, this paper provides a small-signal analysis about the impact of WTGs on the local mode of a single-machine infinite-bus (SMIB) system. The main contribution is the incorporation of the WTG voltage control into the modal decomposition diagram of Heffron-Phillips and deMello-Concordia. Sensitivity coefficients are developed for the WTG voltage control loop and their impact on the real and imaginary parts of the local mode is illustrated with an example.

Interarea Oscillation Damping Control Using High Voltage DC Transmission: a Survey

High-voltage direct current (HVDC) transmission lines are increasingly being installed in power systems around the world, and this trend is expected to continue with advancements in power electronics technology. These advancements are also bringing multiterminal direct current (MTDC) systems closer to practical application. In addition, the continued deployment of phasor measurement units makes dynamic information about a large power system readily available for highly controllable components, such as HVDC lines. All these trends have increased the appeal of modulating HVDC lines and MTDC systems to provide grid services in addition to bulk power transfers. This paper provides a literature survey of HVDC and MTDC damping controllers for interarea oscillations in large interconnected power systems. The literature shows a progression from theoretical research to practical applications. There are already practical implementations of HVDC modulation for lines in point-to-point configuration, although the modulation of MTDC systems is still in the research stage. As a conclusion, this paper identifies and summarizes open questions that remain to be tackled by researchers and engineers.

Impact of communication latencies and availability on droop-implemented primary frequency regulation

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 system frequency control using Type-4 wind turbine generators

System frequency response can be negatively impacted by significant penetration of wind generation. This paper studies the effects of integrating Type-4 full converter wind turbine generators (WTG) on the frequency response of a test system. A controller that enables frequency response in a Type-4 WTG is then proposed to restore and improve the frequency regulation of the system. The design and performance of the proposed controller are demonstrated using linear analysis and nonlinear simulation. The results are then compared with those for Type-3 DFAG frequency regulation technology.

Time-domain analysis of power system stability with damping control and asymmetric feedback delays

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.

Open-loop testing results for the pacific DC intertie wide area damping controller

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.

Impact of wind generation power electronic interface on power system inter-area oscillations

The dynamics governing power systems are being modified by the continued increase in the installation of wind turbine-generators (WTGs). This paper presents a small-signal analysis on the impact of the power electronic interface of large quantities of wind generation have on the inter-area oscillation of a two-area system. In particular the sensitivity of this inter-area mode with respect to: (i) increased wind penetration, (ii) loading conditions in the face of wind integration, and (iii) the active and reactive power control parameters of a WTG are presented in this paper. The results show that wind integration increases the damping of this oscillation for most of the cases except when implemented in the area that is importing power.