Doubly-Fed Flywheel Inertia Control for Fast Grid Frequency Response
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Solution Overview
Problem
Current kinetic storage systems fail to provide both natural and synthetic inertial contributions effectively, leading to delayed responses to grid frequency changes due to high rolling friction losses and reliance on static converters, compromising thermal stability and response times.
Innovation Solution
A flywheel doubly-fed system with an asynchronous electric machine, a static converter, and electronic control means that allows for immediate natural inertial response and controlled synthetic inertial response, integrating both contributions to stabilize the electrical grid.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a static converter is used to control flywheel speed, then energy storage/delivery control is achieved, but response time to grid frequency changes is delayed due to measurement loop delays
Solution Approach 1:
The system segments the inertial response into two distinct components: natural inertial response (immediate, uncontrolled) and synthetic inertial response (delayed, controlled). This segmentation allows the system to provide immediate support through natural inertia while the static converter prepares the controlled response, effectively reducing the overall response time limitation.
Solution Approach 2:
The system performs preliminary action by having the natural inertial response activate immediately upon grid frequency change detection, before the static converter completes its measurement loops. This preliminary uncontrolled response provides immediate grid support, while the controlled synthetic response follows afterward.
2Use of energy by moving object
If the flywheel operates at high speeds (>10,000 rpm) to increase kinetic energy storage, then energy capacity increases, but rolling friction losses increase proportionally to the square of speed
Solution Approach 1:
The system changes the operational parameters by allowing the flywheel to operate at variable speeds rather than fixed high speeds. The static converter enables precise control of rotation speed, allowing the system to optimize the balance between kinetic energy storage (which requires higher speeds) and rolling friction losses (which increase with speed squared), adapting to different operational requirements.
3Ease of operation
If only synthetic inertia control is provided through static converter actions, then controlled response is achieved, but the system cannot provide immediate natural inertial response
Solution Approach 1:
The system merges two previously separate functions into one unified system: the natural inertial response (physical property of rotating mass) and the synthetic inertial response (controlled action through static converter). This combination allows the system to provide both immediate uncontrolled response and subsequent controlled response, eliminating the trade-off between the two.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system provides a fast, uncontrolled natural inertial response immediately followed by a controlled synthetic response, enhancing grid stability and reducing response times, overcoming the limitations of existing systems.
Implementation Method 1
an asynchronous electric machine that includes a rotor provided with an accessible rotor circuit and a stator provided with a stator circuit... the asynchronous electric machine is configured to absorb electrical energy from the electrical grid by converting the absorbed electrical energy into kinetic energy and by storing said kinetic energy by means of the flywheel and deliver electrical energy to the electrical grid by converting the kinetic energy stored by means of the flywheel into electrical energy
Implementation Method 2
a flywheel coupled to the rotor... for storing kinetic energy and for delivering the stored kinetic energy
Implementation Method 3
the asynchronous electric machine is configured to immediately provide an uncontrolled natural inertial response to said frequency variation
Data Source
Figure 1
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AI summary
The invention relates to a system (1) for supporting the stability of an electrical grid (2) by storing/releasing electrical energy from/ to said electrical grid (2), comprising: an asynchronous electric machine (11) including a rotor (111) provided with an accessible rotor circuit and a stator (112) provided with a stator circuit; a flywheel (12) coupled to the rotor (111); a static converter (13); and electronic control means (14). The stator circuit is connected to the electrical grid (2) to be fed by the latter. The static converter (13) is connected between the electrical grid (2) and the rotor circuit and is controllable to supply said rotor circuit with an electrical power supply with adjustable frequency and voltage. The asynchronous electric machine (11) is configured to: absorb electrical energy from the electrical grid (2) by converting the absorbed electrical energy into kinetic energy and storing said kinetic energy by means of the flywheel (12); and deliver electrical energy to the electrical grid (2) by converting the stored kinetic energy by means of the flywheel (12) into electrical energy and providing the latter to the electrical grid (2). The electronic control means (14) are configured to : receive measurement data indicative of a measured electrical grid frequency ( 2 ); determine, based on the received measurement data, ROCOF values indicative of a derivative of the measured frequency ( 2 ) of the electrical grid; and control the operation of the static converter ( 13 ) based on the determined ROCOF values. Furthermore, in case of a change in the frequency of the electrical grid ( 2 ), the asynchronous electric machine ( 11 ) i s configured to immediately provide an uncontrolled natural inertial response to said change in frequency by absorbing active power from the electrical grid ( 2 ) in case of an increase in frequency or by supplying active power to the electrical grid ( 2 ) in case of a reduction in frequency; and the electronic control means ( 14 ) are configured to determine a given ROCOF value relative to said change in frequency and, once said given ROCOF value has been determined, begin to control the operation of the static converter ( 13 ) such that the asynchronous electric machine ( 11 ) begins to supply a controlled synthetic inertial response wherein the active power absorbed/ supplied is modulated according to the given ROCOF value determined and the uncontrolled natural inertial response already provided.