Flywheel Energy Storage System

The goal of this project is to develop math models, that with certain inputs will calculate needed dimensions and values for both the electrical and mechanical aspects of a stator for a high speed flywheel.

Background
One of the problems a potential lunar mission faces is energy generation and storage. While both solar and nuclear power generation are options, they do have drawbacks. Generating electricity using solar power would not be possible during the approximately 14-day lunar night, and nuclear power generation would have to decrease during the lunar day due to heat. As a result of these drawbacks, an efficient method of storing energy would be needed to ensure the success of any planned lunar mission. The University of Idaho has put forward the idea of using a FES system (FESS) to accomplish this. FES is advantageous due to its high energy density and low maintenance compared to other methods of energy storage.

The previous years, a low speed FESS was manufactured, but now the research team has started to focus on developing a high speed FES. The goal is to store 100x more energy than the low speed version. Whether this is still feasible or not, is still being determined due to a plethora of aspects, such as material property constraints within the flywheel, how quickly it can be accelerated, and numerous other factors. The purpose behind this senior project is to develop math models that will calculate various stator perimeters for both the electrical and mechanical aspects. Once the research team is able to determine the constrains for the flywheel, these will but plugged into our models to produce the required stator.

Stator
Determining the UIFESS stator parameters and dimensions is the task for this senior design project. There are two main aspects to the stator design, electrical and mechanical.

Mechanical Aspect of Stator Design
The mechanical engineers on the Lunar Flywheel team were tasked with solving the fatigue and heat transfer issues seen by the stator when under operation.

Fatigue Cyclical Loading Modeling
While the FESS is operational, it will be accelerated and decelerated over a set period of time by a specified torque. This torque will be full fully reversed when either accelerating or decelerating the flywheel, causing fatigue, torsional load on the stator.

Heat Transfer Model
Also, while the FESS is operational, thermal heat will be produced by the stator coil windings. The coil wires for the windings, have a small resistance and once a current is passed through them to create the torque required to rotate the flywheel, heat will be produced. Removing this heat is imparative to keeping the efficiency of the FRRM as high as possible, and reducing the temperature of the coils increases their life expectancy.

Problem Statement
From previous Capstone design teams, a low speed FESS was designed and built. The research group has moved forward with the intent to produce a high speed flywheel. While parameters for the high speed rotor are being determined, the senior design team is tasked with producing math models, that once the rotor parameters are found, the stator dimensions can be calculated quickly using inputs from the rotor dimensions.

Specifications
High Priority: Target Velocity: 25,000 - 30,000 RPM Time to Reach Target: 1 day Minimum Allowable Air Gap: 1 mm Math models can easily be adjusted

Medium Priority: Energy Efficiency: 70% During Acceleration Maximum Coil Temperature: 100 C Maximum Velocity Overshoot: 10 rad/s Maximum Settling Time: 1 s Maximum Rise Time: 10 s

Design Development
As stated, the Lunar Flywheel team was responsible for developing math models that would calculate the parameters for the electrical and mechanical aspects of the stator.

Testing
Simulations performed in MATLAB indicated the current control algorithm would perform to an acceptable level, though with a moderate degree of overshoot and some ripple in the steady state response due to the constant voltage switching. Another key factor which needed to be tested for was the how quickly the current in a coil could be changed, in order to ensure that the current could be changed quickly enough to achieve the desired state before the rotor had moved on. Simulations indicated that even at the ideal speed of 2500 RPM the current could be changed quickly enough to avoid issues.

Team Bios
The 'Fly Rollers' team contributed to this project from Fall 2016 - Spring 2017 and was responsible developing math models to calculate the desired stator parameters. The team consisted of the following members: