L. Qi

Applying a STATCOM for stability improvement to an existing wind farm with fixed-speed induction generators

Wind farms are becoming important distributed renewable energy resources. However, voltage stability issues with wind farms employing fixed-speed induction generators may require such systems to be augmented with dynamic compensation devices, such as STATCOM units. In preparation for deployment of a 10 MVA STATCOM at an existing wind farm in the Bonneville Power Administration (BPA) system, the STATCOM controller is to be tested through hardware-in-the-loop simulation with a real-time digital simulator, which will model both the BPA system and wind farm with high fidelity, transient models. This paper presents groundwork conducted in preparation for the dynamic testing of the controller, including studies of the stability improvement facilitated by the introduction of the STATCOM into the BPA system. The enhancement of voltage stability and induction generator stability by the STATCOM is studied analytically by power-voltage and torque-slip relationships of a simple wind power system, as well as through simulation studies with the real-time simulation to be used for testing of the controller. Simulation results from both approaches are compared and illustrate the potential benefit of the STATCOM in preventing voltage collapse caused by serious network changes, such as opening a line, as well as improvement of the Fault Ride Through capability of the wind power system.

Investigating the Impact of Pulsed Power Charging Demands on Shipboard Power Quality

The impact of pulsed power loads on shipboard power systems need to be properly determined to prevent pulsed loads from causing unacceptable power quality deviations, interference with other loads and degradation of overall system performance. This paper uses a high fidelity modeling and simulation approach to investigate the impact of real and reactive power, pulse ramp rate, pulse duration and frequency of occurrence of the pulsed power load. For this purpose, a notional shipboard power system, modeled in a real-time digital simulator, is used. Most pulsed loads on shipboard systems are not fed directly from the prime power system but via an energy storage system. This energy storage system in turn is interfaced with the shipboard prime power system typically through an electronic front-end charging circuit. In order to evaluate the impact of pulsed loads, existing power quality standards (related to voltage transients, harmonic distortions, and frequency variations) are applied.

Prony analysis for power system transient harmonics

Proliferation of nonlinear loads in power systems has increased harmonic pollution and deteriorated power quality. Not required to have prior knowledge of existing harmonics, Prony analysis detects frequencies, magnitudes, phases, and especially damping factors of exponential decaying or growing transient harmonics. In this paper, Prony analysis is implemented to supervise power system transient harmonics, or time-varying harmonics. Further, to improve power quality when transient harmonics appear, the dominant harmonics identified from Prony analysis are used as the harmonic reference for harmonic selective active filters. Simulation results of two test systems during transformer energizing and induction motor starting confirm the effectiveness of the Prony analysis in supervising and canceling power system transient harmonics.

A Novel Hierarchical Section Protection Based on the Solid State Transformer for the Future Renewable Electric Energy Delivery and Management (FREEDM) System

The effectiveness of a protection scheme in any power grid is essential to the reliability of the supply. One of the main goals of the FREEDM systems is to increase supply reliability to end users. However, traditional protection methods, including over current, sequential components, and wide differential area protection, are not suitable for this system for several reasons that will be explained in the paper. A new protection strategy is presented in this paper. This protection scheme takes advantage not only of the system configuration but mostly of the solid state transformer capability and design to minimize any circuit and communication that are needed for a successful protection strategy. A real time digital simulator (RTDS) is used to model a sample FREEDM system in order to verify the proposed protection scheme. Hardware-in-the-loop (HIL) testing was performed to verify the proposed protection scheme.

Evaluating dynamic performance of modern electric drives via power-hardware-in-the-loop simulation

Hardware in the loop (HIL) simulation, especially power HIL (PHIL) simulation, is a promising tool for motor drive design and prototyping. It inherits both the flexibility of simulation and the authenticity of hardware itself, which therefore allow an actual motor drive design to be thoroughly scrutinized under almost any conceivable condition. In this paper, a unique 5 MW PHIL simulation facility which is in its last stage of commissioning in the Center for Advanced Power Systems (CAPS) is introduced. An illustrative PHIL simulation example based on a similar but downscaled 50 kW test bed is performed. Interesting results very well demonstrates how a PHIL simulation on a motor drive system can expose the hidden problems that are difficult to be identified by other testing methods.

Testing of a controller for an ETO-based STATCOM through controller hardware-in-the-loop simulation

The testing of a controller for a proposed 10 MVA STATCOM through hardware-in-the-loop experimentation is described in this paper. The electrical environment into which the STATCOM is to be inserted, including a significant portion of the utility network and a nearby wind farm are simulated using a large-scale digital real time electromagnetic transients simulator. The STATCOM controller is interfaced to the simulation, providing firing pulses to the simulated STATCOM and receiving feedback of system voltages and currents. Notional wind speed data is used to simulate realistic behavior of the wind farm. This paper presents preliminary results of the ongoing testing of the controller under the most realistic system conditions.

Implementation and validation of a Five-Level STATCOM Model in the RTDS small time-step environment

In this paper, the implementation issues of a five-level STATCOM model in RTDS small time-step environment are studied. The five-level STATCOM is modeled by two small time-step VSC models and connected by a three-phase cross card Bergeron transmission line. With appropriate transmission line parameters, little voltage and current distortion is found on voltages and currents along the transmission line. The effectiveness of the STATCOM model is verified by comparing the simulation results of a test system modeled on RTDS to the results of the model from Matlab/Simulink/SimPowerSystems. The sensitivity study of the power loss provides valuable information on the actual and artificial power loss of the STATCOM model. In addition, harmonics analysis further validates the STATCOM model. From the power loss and the comparative study, the effectiveness of the STATCOM model is verified for use in a Control-Hardware-In-Loop (CHIL) testing of the STATCOMs controller.

Analysis of stability issues during reconfiguration of shipboard power systems

Stability, an important aspect of reliability, should be maintained during reconfiguration operations in shipboard power systems (SPS). This paper discusses the effects of characteristics of SPS and dynamic phenomena on its stability during reconfiguration actions. Results derived from these investigations were used as the basis for developing a SPS modeling method and a SPS stability assessment method.

Study of Power Loss of Small Time-Step VSC Model in RTDS

In this paper, the power loss of power electronic switches modeled as RTDS small time-step voltage source converter (VSC) is studied. The reduction of time step size and resistance at OFF state can decrease the artificial switching loss in the RTDS small time-step VSC models. Higher noise levels in the RTDS simulations indicate more power loss in the RTDS simulations than in equivalent PSIM simulations. The sensitivity of the power loss and the total harmonic distortion (THD) to parameters, including switch model parameters and interface transformer model parameters are studied. With appropriately selected component model parameters, the power loss of the modeled switches can be reduced.

Hardware-in-the-Loop Experiments on the Use of Propulsion Motors to Reduce Pulse-Load System Disturbances

Pulse power loads are assuming increased importance in the development of all-electric naval surface combatants. One possible means for countering the potentially destabilizing effect of pulse loads is by manipulating the power of the propulsion motors to smooth out the variations in system power caused by the pulse loads. Hardware-in-the-loop experiments were conducted with the 2.5 MW motor-dynamometer system at the Center for Advanced Power Systems at Florida State University to test this possibility. RMS variations in system power were successfully reduced and several avenues for controller development were suggested by the results.