Sizing of Hybrid Energy Storage Systems for Inertial and Primary Frequency Control

Abstract

The exponential rise of renewable energy sources and microgrids brings about the challenge of guaranteeing frequency stability in low-inertia grids through the use of energy storage systems. This paper reviews the frequency response of an ac power system, highlighting its different time scales and control actions. Moreover, it pinpoints main distinctions among high-inertia interconnected systems relying on synchronous machines and low-inertia systems with high penetration of converter-interfaced generation. Grounded on these concepts and with a set of assumptions, it derives algebraic equations to rate an energy storage system providing inertial and primary control. The equations are independent of the energy storage technology, robust to system nonlinearities, and rely on parameters that are typically defined by system operators, industry standards, or network codes. Using these results, the authors provide a step-by-step procedure to size the main components of a converter-interfaced hybrid energy storage system. Finally, a case study of a wind-powered oil and gas platform in the North Sea demonstrates with numerical examples how the proposed methodology 1) can be applied in a practical problem and 2) allows the system designer to take advantage of different technologies and set specific requirements for each storage device and converter according to the type of frequency control provided.

Allocation of spinning reserves for autonomous grids subject to frequency stability constraints and short-term solar power variations

“…The natural and controlled damping of the system is represented by coefficient B. Applying Newton's second law of motion to this simplified model, and multiplying both sides by the angular speed ω, therefore gives the following equation [29]:…”

“…1, which is also known as the Swing Equation, represents the power balance that is required to maintain this system at its rated angular speed ω s . The frequency deviation f = ω−ωs ωs can, after this equation has been normalized by ω s and by the total apparent power of the generators S n , be estimated by [29]:…”

“…Note that the FCR strategy (proportional control) cannot restore frequency to its rated value. Achieving the zero steady-state error ( f = 0) therefore requires p G and p L to be matched by generator re-dispatching, through integral control [37,29]. This requires additional spinning reserves, which are referred to as frequency restoration reserves (FRR) [35].…”

Optimised operation of low-emission offshore oil and gas platform integrated energy systems

“…Electrical stability of oil and gas installations with wind power supply has been studied both for isolated systems [14,15,16] and for systems with cable link to shore [17,18], with conclusions indicating that such systems can perform well with appropriate energy management and electrical system controls [19]. In systems with large energy supply and demand variability, energy storage may be needed both for energy balancing and for electrical stability [20]. A challenge with high shares of converter interfaced load and generation is that it gives volatile electrical systems with low inertia, requiring new types of control [21,22].…”

Understanding the Effects of Exponentially Decaying DC Currents on the Dual dq Control of Power Converters in Systems with High X/R

“…1. It illustrates a case study used by [4] of an O&G platform in the North Sea isolated from the continental electrical grid. This power intensive industrial process is fed by two 35 MW gas-powered generators.…”