lOMoARcPSD|41168756

Contents

1. Introduction............................................................................................................................................. 4
1.1 Objectives.................................................................................................................................... 4
1.1.1 Features............................................................................................................................... 4
1.1.2 Benefits................................................................................................................................ 4
2 Design Overview.................................................................................................................................. 5
2.1 Block Descriptions........................................................................................................................ 6
2.1.1 H-Bridge............................................................................................................................... 6
2.1.2 Micro-controller................................................................................................................... 7
2.1.3 Buck and Boost Voltage Regulator....................................................................................... 7
2.1.4 Load Side Current and Voltage Sensors................................................................................ 7
2.1.5 Battery Side Current Sensor................................................................................................. 7
2.1.6 Switch.................................................................................................................................. 7
2.1.7 The Distance Sensor............................................................................................................. 8
2.1.8 LCD Screen........................................................................................................................... 8
3 Design Procedure and Details.............................................................................................................. 8
3.1 DC Motor Design.......................................................................................................................... 8
3.3 Mechanical Load Selection:......................................................................................................... 9
3.4 Output Converter Window of Operation Design........................................................................ 10
3.5 Output Converter Design........................................................................................................... 11
3.6 Control Design........................................................................................................................... 12
3.7 Power System Analysis.............................................................................................................. 16
3.8 Power Scaling Design................................................................................................................. 18
4 Costs and Labor................................................................................................................................. 19
5. Conclusion............................................................................................................................................. 20
5.1 Accomplishments...................................................................................................................... 20
5.2 Uncertainties............................................................................................................................. 21
5.3 Safety........................................................................................................................................ 21
5.4 IEEE code of Ethics.................................................................................................................... 21
5.4 Future work............................................................................................................................... 21

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1.Introduction
Lossless energy storage is what today’s Energy Companies are sought for. Battery technologies are improving
but have a limited useful lifetime, typically three to five years. In order to explore different types of energy
storage options, my teammate and I came across the idea of converting gravitational potential energy into
electrical energy.
This concept is known as the gravity battery. The idea utilizes a weight that acts as a gravitational
potential energy source when it is held at a height. When there is a demand, a control signal will be sent to
the device holding the weight and tell it to lower the weight, which in return will convert the gravitational
potential into kinetic energy that drives a machine that will act as a generator.
The reason for this alternative energy storage is that as long as the motor that provides the lift for the
weight as well as the generator that converts mechanical energy into electrical energy do not fail, the
physical weight will last for a long period of time. Therefore, this system will sustain an extensive period of
operation, unlike its counterpart, batteries, which will fail after couple thousands of charging cycles.
However, this technology does have its down side; it is a bulky mechanical device that requires an
adequate amount of space. How high can one lift the weight? And how heavy can the weight be without it
being posed as a safety hazard? How long is the return on investment if indeed such device is built?
Therefore, there is a feasibility problem that we have to address and try to point out the pros and cons of
this device.
At the end of this semester, we would like to demonstrate a working device that could harness green
energy sources from solar panels as well as wind turbines and store them effectively in terms of gravitational
energy.
A solution to that is a battery powered system that can store energy when the input power from
the source exceeds the load demand, and delivers energy when the input source is below the load
demand. Traditional chemical battery such as lead acid and lithium ion batteries have limited useful life
time and are susceptible environmental and performance factors like temperature, humidity, and depth
of charge.
In order to address the limitations of the traditional batteries, an alternative battery powered
supply system built using mechanical parts, DC motor and weights, will exploit the ruggedness and high
efficiency of electric machineries that can last for 15 to 20 years with proper maintenance [1].
In this project, a 100 times scaled down version of 1KW has been built and tested to examine
the feasibility and efficiency of this system.

1.1 Objective
s
1.1.1 Features
o Built in hysteresis control for state of charge
o up to 90% load converter efficiency and lower than 2% output voltage ripple load regulation
o Overcharge, discharge, and emergency shutdown protections
o Long useful life time
o Simple construction for minimal build of materials

1.1.2 Benefits
o Provide emergency back-up power supply when there is a power outage.
o Mechanical battery system provides an energy bank system that smooth out the output power
delivered to the load.

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I. Store excess energy into the mechanical system when the input power from the source
(e.g. solar panel) is higher than the demand of the load.
II. Deliver needed power from the mechanical system to the load when the power from
the source is lower than the power drawn from the load
III. No need to sell the excess energy to the grid.
o Long shelf life and almost no energy loss due to self-discharge in comparison to a typical battery.
For example, Lithium-ion battery self-discharge 20% per month when fully charged [2].
o Can be discharged from full capacity without reduction in battery life cycle in comparison to
regular batteries. For example, a typical lithium Ion battery life cycle for a 100% depth of
discharge is 300 to 500 cycles [3].

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o Resistant to ambient temperature variation without reduction in battery shelf life and life cycle.
For example, for a typical lead acid battery, an hour at 35 C is equivalent in battery life to two
hours at 25 C [4].

2 Design Overview
In our initial design, we are only operating this battery system as a back-up power supply when the
there is a power outage. However, we thought that the old design does not fully utilizes the input source
like a solar panel when there is insolation, and there is a power demand.

To solve that issue, we thought that we can use the gravity battery as a power supply interface for
the unstable input source, solar panel, to provide nearly constant power to the load. This means that the
battery can be used during the day when there is insolation as well as an emergency back-up power
supply.

Therefore, one power bus line is needed to deliver energy to the load from the source or battery.
Similarly, this same bus line is used for charging or discharging the battery. This means that the terminal
voltage of the battery has to stay the same during charge and discharge mode.

Figure 1. High Level Block Diagram.

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2.1 Block Descriptions

2.1.1 H-Bridge
The essential storage component of the gravity battery is using DC-machine to “charge”
or “discharge” the battery by running it in motor or generator mode, respectively. The
terminal voltage of the dc machine is dependent on the direction of the angular rotation of
its output shaft. Since the angular rotation of the DC machine is reversed for running in
generator mode than that of the motor mode, we need a rectifying device that can reverse
the polarity change at the DC machine terminal.

The solution that we come up with after consulting to Professor Krein is using an H-
Bridge, which allows bi-directional current flow capability.

The working principle of the H-Bridge is shown below in Figure 2:

Figure 2. H-Bridge Operation.

When switch pair {1,1, 2,2} is on, the positive terminal of the DC machine draws input
current from the power bus and is running in the motor mode to lift the mechanical weight
up. On the other hand, when the switch pair {1,2, 2,1} is on, the machine is running in
reverse direction, so the current will flow out of the negative terminal to the bus line as the
weigh drops. This scheme allows us to use one power bus line to charge and discharge from
the battery.
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2.1.2 Micro-controller
In here we are using a general purposed micro-controller, Beagle Bone, to receive the
signals from the input side current and voltage sensors, the motor side current sensor, and
the distance sensor. The micro-controller will take the input from these signals and
determine the state of charge of the system. If everything works within the limit, the micro-
controller will output the state of charge to the LCD screen as well as calculating the energy
flow of the system.

2.1.3 Buck and Boost Voltage Regulator

We are using a voltage regulator to output a constant output voltage to simulate a
constant power output load condition.

2.1.4 Load Side Current and Voltage Sensors

They are powered by the 3.3V power supply from the Beagle Bone for this project only.
In reality, you would want to power all the sensors and controller using a rechargeable
battery to make sure that they are on always and proper controls signal can be sent out.
These two sensors are used to determine the output power delivered to the load by
multiply them together. The voltage sensor is also used to determine the power line
voltage, which is needed to control the charge and discharge mode.

2.1.5 Battery Side Current Sensor

This sensor is to monitor the input current into the motor when running in charge mode
and the reverse current when the machine is running in generator mode. Then we can
calculate the amount power delivered from the battery and evaluate its efficiency by
comparing how far the weight has dropped vs how much electrical power is been delivered.
ℎ 𝑖𝑖 𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖 = ∆ (1)
ℎ 𝑖𝑖 𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖 = 𝑖𝑖
∫ ()( ) 𝑖𝑖 (2)
𝑖
The displacement of the weight can be obtained0 from
the height sensor. The
instantaneous power output from the DC machine can be calculated using the battery side
current sensor and the power line bus voltage sensor at the load side. Using micro-
controller, we can calculate these values.
If we are only concerning the efficiency of generator after one discharge, the period can
be determined by examining the duration of the discharge state.

2.1.6 Switch
The switch here is built using a schokky diode that is used to block any reverse current
back from the source with the gravity battery is in discharge mode. The reason for choosing
a schokky diode is that it has fast recovery time and less power loss due to low forward
voltage [5]. A lower forward voltage means that less power will be dissipated through the
diode, and thus a higher efficiency.
The specification of the diode is that it has to block 12 V max and is able to carry 6 A
max current.
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Based on this specification, a Vishay VS-MBR1045PBF schottky diode with 45 V reverse

blocking voltage, 10 A average rectified current, and .570 V forward maximum voltage [6].

2.1.7 The Distance Sensor

The distance sensor is used to measure how far the weight is off the ground, and it can
be used to estimate the capacity of the battery. If we define the ground to be the zero
potential and the mount the distance sensor at the top of the structure, the capacity can be
calculated in Equation (3).
−
%100 𝑖𝑖 𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖 = ∗ 100 (3)
𝑖 𝑖 𝑖𝑖

Hmeasured= Measured distance from the sensor

Hmax= Maximum height that weight can be lifted up from the ground.

2.1.8 LCD Screen

The monitor that is used for this project is just the computer that is communicating with
the micro-controller.

3 Design Procedure and Details

3.1 DC Motor Design
From the purpose of our project, we would like the discharging cycle to be around 15 to 20 seconds
𝑖
from a 1.6 meter drop. This means that we need a motor will linear velocity around .1 , which translate
𝑖
to around 40 RPM with a one inched spindle radius. Therefore we chose to use a 1LPV4A Dayton DC
motor with 62:1 gear Ratio as shown in Table 1.

Table 1. 1LPV4A Dayton Name Plate Rating

Rated Voltage [V] Rated Speed Rated Current [A] Rated Torque Gear Ratio
[RPM] [NM]

12 41 2.1 2.9 62:1

With a rated speed of 41 RPM at one inched spindle radius, using the equations below, we can obtain a
rough estimate of the discharging time.

𝑖𝑖𝑖𝑖𝑖𝑖 𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖 𝑖𝑖 ℎ = 𝑖𝑖𝑖 ∗ 2

𝑖𝑖𝑖𝑖𝑖𝑖 (4)
∗𝑖 ∗
60

Using Equation (4).

𝑖
Linear Velocity of the Spindle= .11
𝑖
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3.5 Output Converter Design

We see that the input range of the converter needs to meet from 7 volt to 12 voltage. We also know
that the converter works most efficiently when the input voltage is relative close to its output voltage.
This means that we that output voltage needs to be match the output voltage of the generator. Since
the output voltage of the DC machine varies as its load changes, we need to make sure that at different
load conditions, the output voltage regulator needs to match that condition. Therefore, the output
voltage must regulate between 7 and 10 volt.

The solution that we come up with is using a buck and boost controller with diodes and transistors rated
at six amperes. The reason is that for the buck and boost topology, the average inductor current is the
sum of the average input and output current. The worst case output current is when the output voltage
is 10 V at .5 A, and the lowest input voltage is at 5 volt. Assume average input power equals to output
power, this means that the input current will be one ampere. Thus, the average current that the
inductor needs to handle is 1.5 A. Since the worst current peak current that the inductor can experience
is twice as that of the average inductor current. So the inductor, MOSFE switch, and diodes need to
handle at least 3 Amperes. For a good design, the current rating of these components should be twice as
high as that of the worst case current. Thus, the device current rating that we chose is at six amperes,
which is summarized in Table 2.

Table 2 Main Output Voltage Regulator Components

Type of Components Description

MBRD360 Schokky Diode 6 A peak Repetitive current

FDS5351 N-Channel MOSFET 60 V, 6.1 A, 35 mΩ Rdson

LM5118 Buck-Boost Controller [9] 3 to 75 voltage input voltage

Output Capacitance >133 uF (from data sheet calculation) [9]

Inductor 16 uH

Thermal dissipation calculation −

𝑖𝑖 𝑖 𝑖𝑖 = [10] (10)
Ø

Where PDMAX is the power dissipation, TJMAX=maximum allowable junction temperature, Ta= ambient
Temperature, and Øja=junction to ambient thermal resistance.

To calculate the maximum the device can dissipate without a heat sink, Equation (10) can be used.
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We can just use the regular power equation 𝑖 = 𝑖2 ∗ or 𝑖 = 𝑖 ∗ 𝑖𝑖𝑖𝑖𝑖 𝑖𝑖𝑖 to approximate the
actual power dissipation with the maximum current that is allowed the circuit. We used 3 A as the
maximum current for the worst case conduction power loss

Table 3 Power Dissipation Verification for Diode and MOSFET

Description Maximum Power Dissipation for Worst Case conduction Power

the device [W] Loss [W]

MBRD360 Schokky Diode 1.875 1.35

Øja=80 K/W, TJMAX=175,

Vforward=.45 @125 C [11]

FDS5351 N-Channel MOSFET 2.5 W .315

Øja=50 K/W, TJMAX=150, 35 mΩ

Rdson [12]

As seen for table 3 above, the worst case conduction power loss for the diode and MOSFET are under
the maximum power dissipation requirements.

3.6 Control Design

States:

Idle:

Used to select discharge or charge based on the bus voltage.

Stays in this state when Vbus is in between 6.5 V and 11 V and charge or discharge is not
triggered.

Discharge:

Used to operate the electric machine as a generator.

Stays in this state when height is less than 1.5 m, bus voltage is less than 11 V, and the
emergency button is not pushed.

Charge:

Use to operate the electric machine as a motor

Stay in this state when height is greater than 0.3 m, bus voltage is greater than 6.5 V, and
emergency button is not pushed.
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Discharge Idle:

Used to remove jitter, discussed below, for discharging.

Stay in this state when bus voltage is less than 11 V, and reset button (emergency button) is not
pushed.

Charge Idle:

Used to remove jitter, discussed below, for charging.

Stay in this state when bus voltage is greater than 6.5 V, and reset button (emergency button) is
not bushed.

Figure 4. State Transition Diagram (last line indicates the output of each state. All lines above are the
input conditions).

Design parameter:

For this demo, few conditions are imposed. First, the voltage from the DC machine will not exceed 12V.
Second, the current will not exceed 2.1 A. The state diagram shown above in Figure 4 uses the bus line
voltage and the height of the weight as input variables for the state machine. The voltage hysteresis
boundaries are between 6.5V to 11V. The upper boundary of the hysteresis is chosen in order to stay
within the voltage rating of the electric machine, 12V. The height sensor is used to indicate the energy
stored in the system, as well as over and under charge protection.
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E = mgh (11)

Where E is the potential energy in the system, m is the mass used to store energy, g is the gravitational
acceleration, and h is the height of the mass.

The over-charge protection will prevent the weight from hitting the top of the stand. The over-discharge
protection is mainly used to turn off the electric machine when the mass hits the ground. If the electric
machine is not turned off after hitting the ground, it will draw power from the source to lift the weight
in the opposite direction. This switch of direction is not detectable by the program, and it is also
undesirable. The height is measured from the top of stand to the mass. This means that the overcharge-
protection is 0.3 m or 100% charged. 1.5 m is used for undercharge protection or 0% charged. The
electric machine with no load is rated at 0.1 m/s to lift the weight. When the weight is added, the
electric machine will operate at a lower operating speed. Therefore, the height sensor only needs to
response at a speed of 0.1 second for a smooth transition.

Design Logic:

In order to account for the voltage hysteresis, at least 2 states are needed, one for charging and one for
discharging. When bus voltage is greater than or equal to 11 V, the state will change to charging. Once
bus voltage is 11 V the system will keep charging until voltage decrease to 6.5V. This means that if
voltage does not fall below 6.5V, the system will keep charging, even above 100%. In order to fix this
issue, a height sensor is added for over-charge protection. Since height sensor have errors, another state
is added to fix the edge case. At the edge case, the brake will turn on and off to lift the weight along the
boundary causing repetitively switching. Once the over-charge protection is triggered, the state changes
to Charge Idle to turn on the brake. While in Charge Idle state, the system will wait for the bus voltage to
drop below 6.5V to change back to Idle state. Thus, the repeatedly switching effect is eliminated. In the
case of the height sensor failure, an emergency button is added to activate the brake. Moreover, a reset
button is also added in case the system brake before it’s fully charged, or discharged. The same logic
applies to Discharging state and Discharging Idle state. The Idle state is added for easy transition
between charge and discharge.

Design parameter:

As stated above, the voltage sensor is needed to control the system. There are four design parameters
taking into consideration when designing the voltage sensor. First of all, the power consumption of the
voltage sensor should be low to reduce power lost. Secondly, the upper voltage boundary of the sensor
output must be with in the BeagleBone Black ADC limit, 1.8 V. Third, the voltage sensor should have low
error of 0.2V, which is 3% error based on the lower hysteresis boundary, 6.5 V. Lastly, the error should be
less than 0.2 V with data acquisition frequency of 10 Hz.

The follow formula is derived to find the desirable voltage divider ratio.
𝑖𝑖𝑖𝑖 𝑖 𝑖𝑖 𝑖1 (12)
=
𝑖 𝑖𝑖𝑖𝑖 𝑖𝑖 1+𝑖2
+

𝑖𝑖𝑖𝑖 𝑖 𝑖𝑖 is the maximum adc voltage, 1.8V. 𝑖𝑖𝑖𝑖𝑖𝑖𝑖 is the maximum expected bus line voltage, 12 V.
Using Equation (12) and parameter stated, the resistor ratio is calculated to be 0.15. To allow a higher
bus line voltage, and the availability of resistor values, a 1/11 resistor ratio is used. This allows a
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maximum bus line voltage measurement of 19.8 V. A zener diode is used as a voltage regulator, to
output a maximum sensor reading of 1.8 V. The higher voltage boundary, and the zener diode are both
designed to protect the ADC. The circuit is shown in Figure B3 in Appendix B.

When the voltage sensor is tested separately, the output is very constant with constant reading up to 3
digits after the decimal. When the entire system is tested as a whole, the voltage started to oscillate
with error greater than 0.2 V. This is due to the EMI from the electric machine on top of the stand, and
the buck-boost voltage regulator at the output side of the system.

Final Design:

To reduce EMI, the PCB board is placed far away from the electric machine. The 0.1 μF is added to the
circuit as shown in Figure (B3) (Right side) in Appendix B. The capacitor can filter out some of the high
frequency noises. This will help to reduce the voltage sensor oscillation.

Figure A9 and Table A4 in Appendix A, shows a linear relation between the Fluke Digital Multi Meter,
Fluke DMM, measurement and the BeagleBone Black ADC measurement. It also shows the oscillation in
the voltage sensor. The oscillation is within the error of 0.2 V

Height Sensor:

Design parameter:

The height sensor is used for overcharge and over discharge protection. 0.3 m and 1.5 m are used for
maximum charge, and minimum charge respectively. Due to the 1.6 m height of our physical device, the
sensor chosen must have very low error, around 0.05 m. It must be able to operate in the range defined,
between 0.3 m and 1.5 m. The operating frequency must be greater than the 10 Hz for data acquisition
rate.

Height Sensor Selection:

If the BealeBone Black is programed in the lower level programing language assembly, it will be able to
read the pulse output of height sensor. The control program for this design is written in python;
therefore analog sonar range sensor, LV-MaxSonar-EZ2 Range Finder is chosen as an alternative. The
maximum output for this voltage sensor is the same as Vin [17]. It has a minimum measurement of
0.1524 m, a maximum measurement of 6.45 meters, and 2.54 cm of error [17]. All these parameter are
within the allowed range of the design parameter.
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3.3V input is used with 2-1k ohms resistor for voltage divider at the output. This will ensure the output
voltage fall in the range of 0 to 1.8 V, 0 to 1.65 to be exact. The zener diodes is used to regulator the
voltage to 1.8V for additional protection. The circuit is shown in Figure B4 in Appendix B.

Final Design:

To reduce noise induced by the EMI, the height sensor wires are now placed far away from the electric
machine, and the buck-boost converter. The height sensor has to be mounted on the bottom side of the
top stand. This means wire or WIFI module is needed to communicate with the BeagleBone Black. WIFI
module and height sensor both require a power supply. If it uses the power supply on the BeagleBone
Black, wires will be required. Otherwise a new power supply circuit can be built to supply power. Due to
limited time to build an efficient voltage regulators, the wiring meth is chosen. The wire length of 1 m is
used. The length of the wire could induce additional noise to the sensor output. In order to fix this issue,
the wires are twisted to decrease current loop area and reject common-mode noise.

The Charge Brake 2 in Table A5 in Appendix A, shows the error is greater than what is shown in the
requirement, and the data sheet, and the output do oscillate. The error greater than 0.05 m only occurs
in one of 8 experiments. This is a small amount of chance, which can safely be ignored. The data also
points out the over charge and discharge do occur. This is reasonable taken into account for the sensor
error.

3.7 Power System Analysis:

This demo uses DC power supply and outputs a DC voltage. With proper design the output voltage and
current ripple are very low. The load for the buck-boost converter is a resistor. Therefore the output
current will also be DC. The experimental result of the buck boost converter shows a very low voltage
ripple. These ripples can safely be ignored. The following equations are used to calculate the energy of a
DC system:

∆ =�∗∆ (13)

𝑖 = �∗ � (14)

𝑖 𝑖 = 𝑖𝑖−1 + ∆ 𝑖 (15)

Where ∆ is the change in energy over a period, P is the average power output, ∆ change is time, 𝑖𝑖−1
is the total energy before new charging or discharging cycle, and Ei is the current overall energy
consumption.

In order to perform the above calculation current sensors are needed. The program will be able to show,
the total energy consumed by the electric machine and output load. It can also be used to calculate the
energy used to charge the battery, and the total energy output during discharging.
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At the end of each cycle, the calculated energies: total energy, charging energy, and discharging energy
will be updated. The program will also display the operation time, and refresh rate in seconds.

Current sensor:

Design Requirements:

The current sensor must have a low power consumption to reduce power lost. The accuracy of the
sensor must be height enough to detect -2.1 A to 2.1 A. This is to take into account for the operation of
the electric machine. During discharging the polarity of the current is consider to be positive. During
charging the polarity of the current is consider to be negative. The current sensor has to be able to read
0 A, because the electric machine will only operate in Charge and Discharge states. During other state
the current flow will ideally be 0, but the build in control for the H-Bridge do consume some power.
Since the current only goes from -2.1 to 2.1, which is 0 to 2.1 for the differential amplifier, the current
sensor should have a lower error of 60 mA.

Current Sensor Selection:

MAX9929 has an input range of -0.1 V to 28 V, a gain of 50, error of 50 mV, it is able to detect the
polarity of the system [18]. The following equation and the gain of the system can be used to find the
current sensing resistor.

𝑖𝑖𝑖𝑖 = 𝑖 ∗ ∗ 𝑖𝑖𝑖𝑖 (16)

To protect the ADC of BeagleBone Black, and meet the low power consumption, a current sensing
resistor of 0.010 ohms is calculated from Equation (6). This current sensing resistor will consumes a
maximum power of 0.0441 W, and a voltage drops of 0.021 V. These values are calculated based on 2.1
A of current. This resistor value allows a current measurement up to 3.6 A. The buck-boost converters
usually have a current spike during turn-on and turn-off of the MOSFET. The source interface of our
circuit should have lower the current spike on the bust line. To add an additional protection, a 1.8 V
Zener diode is used as voltage regulator to limit the ADC voltage to 1.8 V. Circuit diagram is show in
Figure B5 in Appendix B

Verification:

The experimental result in Table A6 in Appendix A, shows the current sensor error on the load side is
within the requirement. The current sensor on the electric machine side has errors within the
reasonable range. During charging, the motor side current sensor reading oscillates. This is due to the
high current ripple of the electric machine. The ADC output oscillates around ± 0.1 A around the
desired measurement. This is good for a time domain reading for energy calculation.
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3.8 Power Scaling Design

In order to build a viable commercial size gravity battery, a 1KWh power supply is needed. The reason for
choosing a 1 kw power supply is that the average US house hold consumption is 903 kWh per month,
which translates to roughly 1KW [13] This means that we need to need to store 1KWh energy in terms of
potential energy and extract it out in case of a power outage.

The solution that we come up is use an AC motor that can deliver output power at the shaft at
1KW. Thus, we chose to use a commercial AC motor with following characteristics as the basis for the
power scaling calculation.

Table 4 Motor Name Plate Rating [14]

Rated Speed [RPM] Rated Torque [NM] Rated Output Power [W]

3000 2.9 1

We also need to store energy by drilling wells. So, we chose five wells, each of 100 m deep with average
charge time of 20 minutes. With 88% efficiency for AC Synchronous machine and 90% efficient
converter, we need a 1.43 KW solar panels [15]. An average solar panel outputs 200 w, therefore to
meet 1.4kw input power, we need roughly eight solar panels [16].

To calculate the weight and gear ratio, we need to look at the following equations:

𝑖𝑖 𝑖𝑖𝑖
𝑖 =
20 𝑖 𝑖𝑖𝑖𝑖𝑖𝑖 ∗
60

𝑖
𝑖 =
𝑖𝑖𝑖𝑖𝑖𝑖𝑖
𝑖

60
𝑖𝑖𝑖𝑖𝑖𝑖𝑖 𝑖𝑖𝑖 = 𝑖
∗ 2∗𝑖

𝑖 𝑖𝑖𝑖 𝑖𝑖𝑖𝑖𝑖
𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖 = (17)
𝑖𝑖𝑖𝑖𝑖𝑖𝑖 𝑖𝑖𝑖

Dwell= Depth of each Well

By using equation 17, we calculate the gear Ratio to be around 575

𝑖𝑖 = 𝑖𝑖 ∗
𝑖𝑖𝑖𝑖Ratio (18)
𝑖𝑖
𝑖 =
∗
 lOMoARcPSD|41168756

Ta= Rated Torque [NM]

Tb=Output Torque after gearings

Rspinde= Spindle radius.

By using equation 1, the required mass needed=1228.13 kg (1.35 tons)

We can see that as the final system needs wells that are 100 meters deep and needs to lift around 1.35
tons of weight. This means that this system needs to be very stable, and the cables needs to be strong
enough to handle 1.35 tons of weights.

4 Costs and Table 5 Part Cost

Labor

Part Number Description Quantity Unit Cost (s) Sub Total (S)
S7076-ND PinHead 1 1.23 1.23
MAX9929FAUA+-ND Current Sensing Amplifier 2 1.46 2.92
ED2580-ND Terminal Block 2 0.42 0.84
LM5118MH/NOPB Buck/Boost Controller 1 6.08 6.08
TLE5206-2 H-Bridge Driver 1 7.19 7.19
MMSZ4678T1G 1.8 V Zener Diode 4 0.029 0.116
MC0125W120611M 1 M ohms resistor 1 0.009 0.009
ERJ-8ENF18822V 18.2 k ohms resistor 1 0.006 0.006
ERA-8AEB3322V 33.2 k ohms resistor 1 0.123 0.123
RC1206FR-07100KL 100 k ohms resistor 3 0.004 0.012
RC1206R-0710RL 10 ohms resistor 1 0.004 0.004
MC0125W120611K 1 k ohms resistor 5 0.003 0.015
0.018 ohms current sense
PRL1632-R018-F-T5 resistor 1 0.068 0.068
MC1206B105K500CT 1 uF capacitor 1 0.031 0.031
12065E104MAT2A 0.1 uF capacitor 6 0.03 0.18
C3216X5R1E476M160AC 47 uF capacitor 5 0.9 4.5
C3216X7R1E335K160AC 3.3 uF capacitor 6 0.329 1.974
MC1206B224K500CT 0.22 uF capacitor 2 0.024 0.048
UPW1H181MPD1TD 180 uF capacitor 2 0.152 0.304
UPW1H151MPD1TD 150 uF capacitor 1 0.151 0.151
MC1206B561K500CT 560 pF capacitor 1 0.011 0.011
0.010 ohms current sense
588-LVK12R010DER resistor 2 0.24 0.48
R470B63V 470 uF capacitor 1 0.49 0.49
EEU-FR1E332 3300 uF capacitor 1 1.81 1.81
 lOMoARcPSD|41168756

SER2915L-153KL 15 uH inductor 1 6.12 6.12

B1045 Schottky diode 1 0.05 0.05
MBRD360T4GOSCT-ND Schokky Diode 2 0.72 1.44
FDS5351CT-ND N MOSFET 2 1.46 2.92
3590S-2-103L-ND 10 K Potentiometer 1 13.03 13.03
1LPV4 Gearmotor 1 193.25 193.25
Total 245.402

Table 6 Labor Cost

Name Hourly Rage ($) Hours (hr) Total ($)
Xainxi Li 40.00 150 15,000
Fansheng Shi 40.00 150 15,000
Total 30,000

Table 7 Total Cost

Parts Cost Labor Cost Total Cost

$245.40 $30,000 $30,245.40

5.Conclusion
5.1 Accomplishments
In this project, we have built a miniature system that can work discharge around two to three watts for
20 seconds. In addition to that, we have implemented over-charge, over-discharge, and emergency
shutdown measures. Lastly, we have used three sensors, two current and one voltage sensor, to
monitor the energy flow of the system.

The overall efficiency that we have calculated using 25 Lbs. at 1.6 m height is summarized in the Table 5
below using Table A2 from Appendix A and maximum potential energy Mgh of 183 J.

Table 5 Overall Efficiency

Parameters Efficiency [%]

Charging Efficiency 46

Discharge Efficiency 28

Power Electronics Efficiency 90

Overall Efficiency 11.6

 lOMoARcPSD|41168756

5.2 Uncertainties
We have not be able to obtain a 10 W output as one of the objectives, but instead, we were only able to
output around two to three watts in generation mode. In addition, the efficiency of the overall system is
not as good as we have hoped. The possible power losses in the system can associated with the .91 Ω
armature winding resistance (Appendix A Table A3), mechanical loss, and kinetic energy loss.

We can see that from Table 5, the discharge efficiency is relatively low, which means that a major
portion of energy loss is the final kinetic energy when the weight hits the ground.

5.3 Safety

The commercial size battery will use a 1 KW Synchronous Electric Machine, a 100 m well for charging
and discharging, and 1228.12 kg weight to store energy. The wells must be properly sealed, the area
must be fenced, and display proper danger warning signs to prevent accidental injury.

5.4 IEEE code of Ethics

5. To improve the understanding of technology; its appropriate application, and potential consequences
[19].

Our project will improve the public understanding of electric machine. The gravity battery will
demonstrate power generation process of electric machine.

9. To avoid injuring others, their property [19].

To avoid injuring others during testing, we have a responsibility to ensure the weight of gravity battery is
not lifted in a crowed area. The weight used must be within the tolerances of the mechanical structure,
and structure limited of the building. Proper warning is given to avoid potential electrical shock during
generating process.

5.4 Future work

On a real device, some of the parameter defined in the designing state transition diagram do not apply.
The input current for the buck-boost and the electric machine need to lift the weight can exceed the
rated current. During this state, there needs to be an additional control to brake. Also during discharging
state, the input voltage also needs to be monitored, because the input voltage can be higher than the
discharging voltage of the electric machine. When such event occurs, the electric machine will start to
draw power from the input source to increase its velocity in order to match the voltage on the bus line.
Once eclectic machine output voltage matches the bus line voltage, the diode will block the input. If the
input voltage does not change, the electric machine will speed up and slow down. To avoid such
condition, a high efficient boost converter can be added to ensure the output from the DC machine is at
least 1 V above the input source voltage. Therefore, an additional boost converter needs to be
implemented as one of the future work.