Large magnets with superconductive windings could serve to perform a power system function analogous to pumped storage hydro. A conventional Graetz bridge converter as used in dc transmission provides an ideal interface between the three-phase power system and the superconductive magnet or inductor. Such Inductor-Converter or I-C units, when properly controlled, provide significant power system benefits. Power reversibility is achievable within a few cycles without switching. Power system electromechanical oscillations can be damped effectively. Computer studies reveal that this damping capability may be useful even with smaller inductor sizes when energy storage in large amounts is not the primary objective. In sizes greater than 1,000 MWh, economic studies show promise.

Superconductive energy storage inductor-converter units for power systems

In this paper, the direct method of stability analysis using energy functions is applied for single and multi-machine AC/DC power systems. The system loads including the terminal characteristics of the DC link are represented as constant current type loads, and their effects on the generators at the internal nodes are obtained as additional bus power injections using the method of distribution factors, thus avoiding transfer conductance terms. Using the center of angle formulation, a modified form of the energy-function method is used for the swing equations and the DC link dynamical equations to compute the critical clearing time for a given fault. Numerical results of critical clearing time for a single and multi-machine system using the energy-function method agree well with the step-by-step method.

Transient Stability Analysis of Multi-Machine AC/DC Power Systems Via Energy-Function Method

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.

https://ieeexplore.ieee.org/ielaam/59/8496918/8353481-aam.pdf

Interarea Oscillation Damping Control Using High-Voltage DC Transmission: A Survey

This paper presents DC modeling improvements and extensions to include three terminal systems for AC/DC system studies that have been developed and implemented in a large scale stability program. Particular emphasis will be on the representation of DC transmission controls and their effects on dynamic system performance.

The dynamics of AC/DC systems with controlled multiterminal HVDC transmission

Hybrid AC/HVDC (AC-HVDC) grids have evolved to become huge cyber-physical systems that are vulnerable to cyber attacks because of the wide attack surface and increasing dependence on intelligent electronic devices, computing resources and communication networks. This paper, for the first time, studies the impact of cyber attacks on HVDC transmission oscillation damping control.Three kinds of cyber attack models are considered: timing attack, replay attack and false data injection attack. Followed by a brief introduction of the HVDC model and conventional oscillation damping control method, the design of three attack models is described in the paper. These attacks are tested on a modified IEEE New England 39-Bus AC-HVDC system. Simulation results have shown that all three kinds of attacks are capable of driving the AC-HVDC system into large oscillations or even unstable conditions.

Impact of Cyber Attacks on High Voltage DC Transmission Damping Control

An evaluation is made of the effectiveness of a dynamically responsive dc line in improving the steady-state and transient stability of a power system. A control system, incorporated into the Edison Electric Institute (EEI) 700-kW model, is described. Studies also reported compare the performance of a simple system consisting of two ac transmission lines with the same system when one of the ac lines is replaced by an equivalent dc line.

Thomas Hillesland

Papers

Power System Stability Considerations with Dynamically Responsive DC Transmission Lines