Prioritized Backup Power System

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					Prioritized Backup Power System
               Texas Instruments Analog Design Contest Entry



Prepared by John Kruckenberg, Andrew Lippolis, Eric Schacht, and Chris Seeley

                          The Ohio State University
Executive Summary
This document presents a prototype design of a residential backup power system for seamless transition
among available backup power sources during residential power outages. The system provides a standard
way to interface with many different types of power sources so they can be used appropriately when
needed. In addition to the backup power transition, the system also relays power usage information to a
computer that has been wirelessly connected to receive the usage data. The system works in real homes
with the rated capacity of power circuits while complying with electrical safety standards.

Introduction

Society is becoming increasingly more dependent on electrical power, but concern about the pollution
from wasted energy is growing. Due to the current demand for energy management devices and the
simultaneous need to provide backup energy in the event of a power outage, a prioritized backup system
could allow modern and future energy sources to interface adaptively with current and future residential
electrical systems.

Design

The design of the prioritized backup power system was broken up into several categories and the team
followed a strict design model to ensure a structured and realizable finished product. The overall system
design consisted of hardware and software subsections to minimize system complexity, and to allow for a
more modular design approach. This approach led to better distribution of human resources and also
allowed for more system modularity, which allowed for better troubleshooting and upgradable
components.

Testing and Validation

The system was simulated in MATLAB/Simulink in order to test the various conditions that the system
would encounter during normal operation. Simulink’s graphical nature allowed for rapid prototyping
using hardware models for the system. The simulation environment helped identify potential system
issues before the physical system was constructed. The system met all of the performance, reliability and
safety requirements that were constituted in the original system framework.

Design Review

Many concerns and issues were discovered during the design and construction process. Noise issues, the
interaction of high and low voltage circuits, and the non-trivial nature of measuring the power of reactive
loads presented considerable design challenges for the group. A new system would include several
changes that would reduce signal noise, decrease power consumption, and isolate high and low voltage
equipment to maintain reliability, robustness, and safety.

The dynamic nature of the prioritized backup power system necessitated many independent electronic
components. Texas Instruments provided a powerful selection of well-engineered, robust, and easy to use
components that allowed for the construction of a remarkable and reliable system.




                                    Prioritized Backup Power System                                           i
Table of Contents
Executive Summary ....................................................................................................................................... i
List of Figures .............................................................................................................................................. iii
1. Introduction ............................................................................................................................................... 1
   1.1 Purpose................................................................................................................................................ 1
   1.2 Relevance ............................................................................................................................................ 1
   1.3 Problem Statement .............................................................................................................................. 2
   1.4 Scope ................................................................................................................................................... 2
2. Design ....................................................................................................................................................... 3
   2.1 Design Process Model......................................................................................................................... 3
   2.2 System Requirements.......................................................................................................................... 4
   2.3 System Design .................................................................................................................................... 4
   2.4 Hardware Design ................................................................................................................................ 6
   2.5 Software Design .................................................................................................................................. 9
3. Testing and Validation ............................................................................................................................ 10
   3.1 Software Simulation.......................................................................................................................... 10
   3.2 Hardware in the Loop ....................................................................................................................... 15
   3.3 System Calibration ............................................................................................................................ 15
   3.4 Validation of System Design ............................................................................................................ 16
       3.4.1 Performance ............................................................................................................................... 16
       3.4.2 Reliability ................................................................................................................................... 16
       3.4.3 Safety ......................................................................................................................................... 17
4. Design Review ........................................................................................................................................ 17
   4.1 Commentary on TI Products ............................................................................................................. 17
   4.2 TI Component Selection Review ...................................................................................................... 18
   4.3 Design Features that Should Change ................................................................................................ 19
   4.4 Design Features that Should Not Change ......................................................................................... 19
   4.5 Further Applications ......................................................................................................................... 20




                                                       Prioritized Backup Power System                                                                           ii
List of Figures
Figure 1: Distribution of Residential Energy Usage in the United States..................................................... 1
Figure 2: V Model for Verification and Validation ...................................................................................... 3
Figure 3: Subsystem Communication ........................................................................................................... 4
Figure 4: Overall Design Flow Diagram....................................................................................................... 5
Figure 5: Completed System and Locations of Components ........................................................................ 6
Figure 6: TI Low Side Driver Relay Switching Circuit ................................................................................ 7
Figure 7: Primary Load Monitoring and Control Circuit Board ................................................................... 8
Figure 8: Op-Amp Rectifying and Filtering Circuit ..................................................................................... 9
Figure 9: System Simulation Model Top Level .......................................................................................... 11
Figure 10: Circuit Breaker Box Subsystem Model ..................................................................................... 11
Figure 11: Controller Subsystem Model ..................................................................................................... 12
Figure 12: Simulation Data Showing Chattering from Controller .............................................................. 13
Figure 13: Simulation Data Showing Delayed Switch Condition to Prevent Chatter ................................ 14
Figure 14: Hardware in the Loop Testing ................................................................................................... 15
Figure 15: Calibration Curve for Resistive Loads ...................................................................................... 16
Figure 16: LM317 Regulator ...................................................................................................................... 18
Figure 17: UCC37324 MOSFET drivers .................................................................................................... 18
Figure 18: eZ430-RF2500 Wireless Development Tool ............................................................................. 19
Figure 19: OPA2344 Op-Amp .................................................................................................................... 19




                                                  Prioritized Backup Power System                                                                iii
1. Introduction
1.1 Purpose
The purpose of the Prioritized Backup Power System is to distribute a limited supply of energy to the
most important circuits at the expense of the least important ones. In order to do so, a priority must be
assigned to each circuit by the user. This document presents a prototype design for assigning priorities to
circuits while seamlessly transitioning among available power sources in the case of power shortages.
Power shortages can occur if power from the electrical grid is not available and a backup source is used.
The same concept can be used to encourage reductions of energy use.

We built a system based on three principles of success in energy management that we have observed:

    1. Consumers will buy more efficient products if they are priced reasonably
    2. Consumers will use less energy if they get feedback and learn how to reduce consumption
    3. Energy management is successful when features of the system are increased rather than limited

1.2 Relevance
Society is becoming increasingly more dependent on electrical power, but concern about the pollution
from wasted energy is growing. New growing technologies such as green energy generation, smart power
grids, and alternative energy vehicles are beginning to find their ways into the homes of consumers,
which presents opportunities to use these new technologies along with existing ones to provide the
convenience of backup electrical power when it could not otherwise be available.

It is notable that the power consumption of home loads may not be related to its importance in a power
outage. For many consumers, powering the refrigerator, freezer, and communication mediums such as the
telephone and internet devices may be very important, while the air conditioning, plasma TV, and water
heating are less important. Automatically powering only necessary devices allows a home to run longer
with a backup power source, or even use a backup source that is not powerful enough to run the entire
house.




                      Figure 1: Distribution of Residential Energy Usage in the United States



                                      Prioritized Backup Power System                                Page 1
New technologies are becoming commercially available, offering opportunities to provide backup power
to a residence through an intelligent distribution box. While the following technologies are not typically
used to provide backup power, the priority backup design can make use of the potential they offer:

    1.   Electric vehicles
    2.   Engine-powered vehicles
    3.   Solar power
    4.   Wind power
    5.   Sterling engines
    6.   Portable generators
    7.   High capacity battery backup systems

Existing technologies are growing around the market of home energy management, but there are
significant differences and advances in our design that are not seen elsewhere. Existing systems are all
device-oriented. Systems like the X-10 hardware and Google Smarter Power allow monitoring or
switching of individual components, but this process is remarkably tedious and difficult to troubleshoot.
The priority backup system is centralized for ease of use and simple, reliable operation.

Due to the current demand for energy management devices and the simultaneous need to provide backup
energy in the event of a power outage, this design could be the solution that meets customers’ needs. The
ability to meet multiple consumer needs makes this product a relevant one for today’s society and culture.

1.3 Problem Statement
Power outages are inconvenient and expensive, especially in modern society. However, extensive
electrical outages are still occurring in recent years and in developed cities despite an over-developed
sense of security that people may have. Examples of extensive power outages in Columbus, OH in recent
years are the week-long outage due to Hurricane Ike in autumn 2008 and the Northeast Blackout in 2003.
Power outages are disastrous and difficult to mitigate without very expensive backup power systems.

1.4 Scope
The proposal is limited to a prioritized backup system and its common protocol for power and energy.
The system is implemented as an information-based circuit switching system and a wireless interface to
an automobile. While proposed as possible, the system does not include generating backup power or
managing power use other than switching entire house circuits on or off based on optimization criteria.
The proposal does not include managing other potential power sources such as solar cells.




                                    Prioritized Backup Power System                                 Page 2
2. Design
2.1 Design Process Model
In order to follow a consistent design process through the design and testing stages of development, the
                                              V-model.
Prioritized Backup Power team followed the V model. Advantages of this model include collaboration
                 mbers,
among team members, a reduction of project risks, and assured validation of design goals. A diagram
representing the steps of the V model is shown below in Figure 2.




                               Figure 2: V Model for Verification and Validation

                   model
The steps of the V-model are described below:

SYSTEM REQUIREMENTS – The necessary specifications of the designed system are determined and a
plan to test these requirements is written for future validation.

                         level                                          low-level
SYSTEM DESIGN – The high-level design is determined without considering low level subsystem details.

DETAILED HARDWARE DESIGN – Hardware is designed in detail such that it can be constructed.

                                                                                  implem
DETAILED SOFTWARE DESIGN – Software is designed in detail so that it is ready for implementation.

                                                                                validation.
IMPLEMENTATION – The hardware and software are combined in a working system for validation

SOFTWARE SIMULATION – Software is tested in computer simulation in order to validate functionality
of basic logical functions.

                           ware
HARDWARE in the LOOP – Hardware is added to the controller simulation with some functions still
emulated in software.

SYSTEM CALIBRATION – Using actual hardware, sensor readings are calibrated such that measured
values are correct for accurate use.

                           calibrated
SYSTEM VALIDATION – Entire calibrated system is tested to ensure that system requirements are met.



                                    Prioritized Backup Power System                                 Page 3
2.2 System Requirements
As a solution to the problem statement, technical specifications have been determined to be requirements
for the system design. These include performance, reliability and safety considerations.

2.3 System Design
The prioritized backup power system detects power loss, engages a backup power circuit, and manages
the power used. To produce the system, an MSP430, a standard breaker box, a set of power relays,
current sensors, and a voltage sensor were used. Communication between various backup sources, the
residential circuit breaker box, and a user’s PC occurs as described below.

             Backup Power Sources Home Electrical Loads                 PC User Interface




                                    Figure 3: Subsystem Communication

The MSP430 series of microcontrollers meets the demand for: a high number of I/O channels, built in
LCD drivers, high frequency sampling, and an on-chip comparator. The system monitors system voltage
and currents on sources and circuits. The controller then reacts to power loss by disconnecting the grid
and connecting and/or enabling available backup power sources. In addition to automatically connecting
the backup source, the controller monitors and switches load circuits to maintain functionality for
important loads while using a power-limited or capacity-limited backup source.




                                   Prioritized Backup Power System                                Page 4
                                    Figure 4: Overall Design Flow Diagram

After switching the system to operate on a backup power source, the system must determine which, if
any, circuits need to be turned off to avoid overloading the backup source. The system defaults all
circuits to the off state and turns the backup source on when the grid power is lost. When the source is
available it iteratively adds the circuits according to available power and energy. The process of using the
backup source and turning prioritized circuits on and off is summarized in Figure 4 which shows the flow
diagram for load changing.




                                    Prioritized Backup Power System                                  Page 5
The total system constructed includes three circuit boards to house all the hardware for monitoring and
controlling the system. To power the control system, two power supplies for 120 volts AC to 12 volts DC
                                       and
connect to each AC source separately and the 12 volts is connected in parallel to the primary circuit
board. The grid power is switched by a large external relay shown in the breaker box. The backup
                                                                                          compact design.
source relay is integrated into the main control and monitoring board allowing for a very c




                                   :
                           Figure 5: Completed System and Locations of Components

2.4 Hardware Design
The load switching of the power system is very important to overall functionality. The hardware must be
             ,
quick, robust, and compact. For these reasons, TI low side drivers were used to switch mechanical relays
that would in turn, switch the AC loads directly. This design allows complete isolation electrically for the


                                    Prioritized Backup Power System                                  Page 6
                                                  large
microcontroller as well as robust operation. The large current carrying capability of the low side drivers
enables them to drive the coils of mechanical relays using an extremely small signal from the
microcontroller. The low side driver’s wide range of output current at 12 volts allows a very versatile
  stem
system driving anything from the grid’s 100A relay to the load’s 15A relays.

Figure 6 shows a small portion of the main control board where the low side drivers are used to control
two load relays.




                                   e
                              Figure 6: TI Low Side Driver Relay Switching Circuit

In order to power the correct number of circuits, each individual circuit needs to be monitored constantly.
                                       on
Even when the system is still running o grid power, the circuits need to be monitored in order to
maintain average power consumption information. The average power consumption information will be a
                                          priority
key factor in determining when specific priority circuits need to be switched off to maintain backup
power. Storage of power consumption information is dependent on how much system memory is
available on the microcontroller. It may also be beneficial to keep several averages for each circuit. For
instance, a separate average for the past minute, 10 minutes and hour may provide for better priority
switching information.

Along with gathering continuous power draw information about individual circuits, the monitoring
system will also gather transient power draw data from each circuit. In backup mode the priority backup


                                     Prioritized Backup Power System                                 Page 7
system will not be connected to the main power grid. Since the backup source may not instantaneously
turn on, transient power draw information would be a valuable resource for maintaining system stability
in switching events or startup. The transient data also provides a safety measure for the management of
startup currents in the circuit. When devices are turned on, their transient power draw is generally much
greater than the continuous load on the circuit. Therefore, storing and maintaining data from peak
consumption is crucial to the management of the system.

The constructed monitor circuit includes a voltage measurement of both the grid voltage and the backup
voltage as well as a current measurement for each load. Using this monitoring the system has a
measurement of the voltage on either the grid source or the backup source and then according to which
source is connected to the system the power for each circuit and the entire system is calculated. The
voltage is measured using two transformers that scale the voltages of the sources to 5 volts and then uses
a high resistance voltage divider to scale the 5 volts to 2.5 volts. The current of each load is measured by
a Parallex current transformer (sensor). Figure 7 shows the primary circuit board holding the
microcontroller, control relays, low side drivers, current transformers, and microcontroller power supply
capacitors and voltage regulator. Figure 8 shows the schematic for the signal conditioning of voltage and
current measurements. This circuit uses op-amp circuits to rectify the AC signals and then low pass filter
the signals. An additional circuit board was constructed to hold signal conditioning circuitry before
connecting the signals to the analog inputs of the MSP430 microcontroller.




                          Figure 7: Primary Load Monitoring and Control Circuit Board




                                     Prioritized Backup Power System                                 Page 8
                               Figure 8: Op-Amp Rectifying and Filtering Circuit

Beyond monitoring the power consumption at the breaker box, the backup source also needs to be
monitored. In order to shut off certain prioritized circuits at correct intervals, the backup source needs to
be polled for available power and energy. The remaining fuel or state of charge needs to be measured on
the backup sources in order to give the priority backup system adequate sustainability information. The
expected run time of the backup source will depend on the remaining fuel or state of charge and also by
fluctuations in fuel or discharge efficiency. Since there are numerous devices that could be used as
backup sources, power meters with built in wireless capabilities would have to be created for all unique
systems. Hybrid cars usually supply the necessary information needed for monitoring, while other
sources, such as gas generators, would need to be retrofitted with a tank measuring device that had built in
wireless capabilities. The source power supply is a valuable resource in detecting faults in the backup
system. For instance, if the total sum of the power being consumed by the individual priority circuits
deviates from the power being supplied by the backup source, the user will be notified that there is a
system malfunction that needs to be corrected.

The priority backup system maintains the following rules in order to keep the highest priority circuits
powered.

    1. If a higher priority circuit consumes more power than the backup source can handle, then allow
       lower priority circuits that do not consume more power to operate.
    2. Allow highest priority circuits to remain on while the backup source can maintain them. As the
       backup source is unable to provide enough power for lower priority circuits, then shut them off.
    3. When the backup source is switched on, keep all circuits off. Decide which priority circuits can
       be turned on. Turn on the highest transient producing circuit first, and then sequentially turn on
       the next highest transient producing circuit until all maintainable priority circuits are on.

2.5 Software Design
In order to design several subsystems quickly and efficiently, the team chose to use multiple TI eZ430-
RF2500 microcontrollers. The use of multiple microcontrollers allowed the division of work among


                                     Prioritized Backup Power System                                  Page 9
multiple team members. This approach was very practical due to the clear divisions among identifiable
projects and due to the low cost and feasibility of purchasing multiple eZ430 kits for development.
Examples of divided tasks are:

    •   Wireless communication
    •   Serial communication
    •   Analog interpretation of sensor data
    •   Control logic
    •   Digital output switching

These projects were divided and solved individually before being combined into a single system for
development.

To begin the process, the first MSP430 was connected to a computer that ran a simple priority switching
program. The program sent serial data to the first microcontroller, which in turn transmitted this data
wirelessly to the second microcontroller in the breaker box. The data sent was a simple string of
characters that was then degenerated into single characters on the micro inside the breaker box. These
characters would be used as priority switching information. The data included remaining battery power,
and which priority each breaker in the box was. This way, intelligent switching algorithms could be
implemented to turn off certain breakers depending on the backup and priority information.

Not only did the IAR-Kickstart application provide rapid development and debugging solutions, it was
easy to use and the cost was included in the purchase of the microcontroller. It would be hard to find
another solution that contained the same level of ease, low cost, and flexibility that the MSP430 provided.

The IAR programming suite made it easy to jump in and start coding for the MSP430. Even though none
of the group members had much experience programming a microcontroller before the project, the
flexibility of being able to code in assembly, C, or C++, contributed greatly in the ability to rapidly
develop and modify the functions of the microcontroller in the breaker system. Another nice feature in
the IAR software was the debug mode. Since it was easy to execute code until a certain line and also
check values of variables mid execution, it was much easier to find errors and correct coding issues.


3. Testing and Validation
3.1 Software Simulation
Software simulation was done in MATLAB/Simulink to offer an environment where various conditions
and control could be tested quickly. The software being designed in Simulink provided the first layout of
the system due to the graphical nature of Simulink. In addition, the system theory of operating various
loads on an automatic basis was tested with a simplified controller. The Simulink model created showed
all aspects of the system in a visual environment. Figure 9 shows the model from the top level. Beneath
the surface of each sub-system the components are modeled. The breaker box sub-system is shown in
Figure 10 and the controller is shown in Figure 11.




                                    Prioritized Backup Power System                                Page 10
Figure 9: System Simulation Model Top Level




Figure 10: Circuit Breaker Box Subsystem Model



                                      Prioritized Backup Power System   Page 11
Figure 11: Controller Subsystem Model

In order to increase software modeling speed the model was created only with basic load dynamics and a
simple conceptual state flow controller. This simplification allowed a very rapid calculation speed, with
minimal error.

The software environment helped identify chattering issues in development and final software could then
be written to prevent chattering. Figure 12 shows the chattering seen before adding a delay after the
switching process. Figure 13 shows after the chattering was removed with software modifications.




                                        Prioritized Backup Power System                           Page 12
Figure 12: Simulation Data Showing Chattering from Controller




                                       Prioritized Backup Power System   Page 13
Figure 13: Simulation Data Showing Delayed Switch Condition to Prevent Chatter




                                       Prioritized Backup Power System           Page 14
3.2 Hardware in the Loop
The most expensive component of our backup power system would be the backup power source. In order
to test the system’s functionality when operating with a backup storage system or alternate energy source,
tests were performed in the form of Hardware in the Loop. This strategy allowed the team to test our
existing software with our control system while simulating hardware that is not yet available. The three
test modes for the system’s Hardware in the Loop operation were:

    1. Simulated depleting energy source
    2. Alternate energy source, non-depleting
    3. Alternate energy source with intermittent availability (user-generated)

Figure 14 shows the power measurement (in ADC bits, not calibrated) of the four load circuits as the
user-generated power availability changes. This test demonstrates the functionality of the system. The
system is turning individual loads on and off by priority, so the measured load power is fluctuating.




Figure 14: Hardware in the Loop Testing

3.3 System Calibration
In order to interpret the power consumption of the four load circuits, the ADC output codes need to be
converted to power consumption in watts. This was done by comparing the ADC data to a Kill A Watt™


                                          Prioritized Backup Power System                         Page 15
power meter. The calibration curve for several resistive loads is shown below. As expected, the transfer
curve is quite linear. After the calibration data was taken, the conversion formula was used in the data
acquisition program in order to display the power consumption information in watts.


                                          Calibration curve for power measurement
                                250
                                                                         y = -5E-05x2 + 0.287x + 8.916
                                                                                   R² = 0.991
                                200
    Power measurement (Watts)




                                150


                                100


                                50


                                  0
                                      0      100   200     300     400       500       600       700     800   900
                                                            Analog input value (ADC bits)


Figure 15: Calibration Curve for Resistive Loads

3.4 Validation of System Design
The system was proven to meet the system requirements of performance, reliability and safety
considerations. Performance goals were met for switching to backup power, turning off loads according to
power availability and priority, and recording and displaying data. In addition, the system was packaged
in a reliable and safe package as shown below.

3.4.1 Performance
The system measured and controlled loads based on original design. The system had limitations
measurements, which limits further testing and performance as explained further in the Lessons Learned
section.

3.4.2 Reliability
The constructed system performed the same results with various loads. The system continued to perform
without failure throughout testing aside from hand construction requiring initial troubleshooting to
diagnose loose or faulty connections. The system reliability could be improved as explained in the
Lessons Learned section.




                                                         Prioritized Backup Power System                             Page 16
3.4.3 Safety
The system was capable of maintaining all original circuit protection in the form of panel box breakers.
In addition the system was capable of housing the properly sized components and wiring to safely and
efficiently perform the design functions.


4. Design Review
The system constructed performed well in a prototype setting. Selected components served reliably in
functionality and versatility. However, during the design and construction process many aspects of the
design were revisited and further changes would be made for a new system. It was known prior to
construction that signal noise is a risk or concern. In addition, household voltage next to low power
electronics poses a danger to both the components and the assembly of the system due to the large
potential difference. The risks prove real in noise primarily, but were never experienced for household
power next to low power. Another considerable concern seen in two parts relates to the current
measuring. Converting an AC current measurement to a DC voltage signal is not trivial. The two parts
proving difficult were rectifying the signal and measuring the power factor. Rectifying the signal was
accomplished with reliable accuracy, but had a very small range of measurement. The second part
proving difficult was the power factor or real versus imaginary loads on the system. Measuring power
factor accurately on the system is important to final accuracy, but would require more hardware and more
processing then currently implemented.

A much less concerning, but further understood fact of the system relates to hardware and circuitry
construction. In keeping the scope of the project within well achievable goals a totally integrated system
was never considered, but was understood to usually prove most accurate, reliable, and easily
manufactured. The modular approach chosen allowed the team to function independently and the system
boards and components to be removed and tested separately. The space freedom also allowed reliable
construction under this simple proof of concept system and modular approach. However, the separation
of components and wiring involved introduces noise and additional connections to troubleshoot.

Any new system built would begin to integrate the components together on smaller boards and with
greater precision. This would move towards a more manufacturable design with less signal noise, power
consumption and greater reliability. Lastly a considerable amount of effort would be made in further
design to keep household power from the low power electronics, even in an integrated system.

4.1 Commentary on TI Products
The use of TI parts during the design and implementation of the project had advantages and
disadvantages. A major advantage of using the TI eZ430-RF2500 was the ease of plug and play with
Windows XP and Windows 7 RC1. The software and hardware were so easy to use that it only took 15
minutes to get a sample demo running on the controller with a good representation of its functions. The
EZ430 microcontrollers have a large amount of potential to make rapid prototyping projects possible, but
there are some features that should be adopted to make their use easier. The incompatibility of the
software on Windows Vista was a prohibitive problem among the team members. Having a group of
demonstration programs to use with the microcontroller was very useful in creating the code for the
microcontrollers in the priority circuit box. However, more commenting of the distributed code would
have been helpful. Development would be much more appealing with walkthrough programs to clarify


                                    Prioritized Backup Power System                               Page 17
the code’s functions1. To quickly gather information, it is important to have a streamlined support site
with easy access to information. As more information is available, this interface should be improved to
reduce clutter. While the IAR workbench software provided the necessary functions, additional features
would reduce development time and organization:

    •   Standard libraries for tasks such as converting strings to integers and sleeping
    •   Saving versions of the workspace with different names for improved version tracking
    •   Autocomplete of function names and argument lists

Hardware support from TI was fantastic. Free samples from TI were a great resource in the completion of
the project. The rapid delivery time and wide selection of samples allowed for the proper component
selection in the sub-circuits. The datasheets for the samples were easy to access from the web and
included all the necessary information for using the components.

4.2 TI Component Selection Review
The prioritized backup power system consists of power, switching, control, and analog sensor processing
systems. These functions rely heavily on selecting the best components, and Texas Instruments provided
the well-engineered components we needed for rapid prototyping of the powerful and reliable system.

Reliable and safe power: Adjustable voltage regulator (TI LM317)
The LM317 adjustable voltage regulator provides a simple and versatile power
source over a wide range of 1.25 to 37 V outputs. Built-in safety and reliability
features of this component were vital to the system’s success:

    •   Ease of use for rapid prototyping designs
    •   Internal short circuit current limiting and thermal overload protection
                                                                                     Figure 16: LM317
    •   0.01 % load regulation per volt, 0.1 % line regulation per volt              Regulator

Load switching: Power MOSFET Drivers (TI UCC37324P)
                   To amplify logic level signals for high-power operations such as switching large
                   relays and contactors, we chose TI low-side power MOSFET drivers. The TI chips
                   had features that fit the load switching applications perfectly:

                          •    High power, very versatile chips in a development-friendly package
Figure 17:                •    Fast 15-20 ns switching time
UCC37324                  •    Low power, low heat dissipation
MOSFET drivers




1
 Example “Learning” section reduces the learning curve for programming the device:
http://arduino.cc/en/Tutorial/HomePage


                                     Prioritized Backup Power System                                Page 18
Control supervisor: Wireless Development Tool (TI eZ430-RF2500)

The prioritized backup power system requires a powerful supervisory
controller with access to analog, digital, serial, and wireless interfaces. In
addition, the controller must be easy to access, program, and debug in
order to aid rapid prototype development. Critical eZ430vfeatures are:

    •   Simple USB programming and debugging interface
    •   Built-in CC2500 2.4 GHz wireless adapter for safe and reliable           Figure 18: eZ430-RF2500
        use with high voltage power distribution box                             Wireless Development Tool

    •   Fast 16-MIPS performance
    •   Ultra-low power consumption, stays alive with capacitor charge

Analog sensor processing: Rail-To-Rail Operational Amplifier (TI OPA2344)

                               Oscillating signal measurements and complex power calculations are best
                               made real-time using analog op-amp designs. The OPA2344 excels due to:

                                  • Rail-to-rail input and output, very significant in logic level signals
                                  • Low power usage, as with the eZ430 controller
                               Compact, easy to use package: 2 op-amps on 8-DIP component.
Figure 19: OPA2344 Op-Amp


4.3 Design Features that Should Change
The system that was built is for proof of concept therefore further design or implementation of the system
includes many changes or upgrades. These changes include expansion, better accuracy, better reliability,
and more measurement.

The following changes would be made in future work:
   1. Add many more communicating devices. For example the backup source needs to communicate
        information that is currently user input, such as power and energy available.
   2. Shield and encase the sensors and analog signal wires to prevent signal noise.
   3. Design system around production type components such as surface mount board and chips to
        greatly improve robustness, reliability, and construction of the circuitry.
   4. Reduce power consumption of additional circuitry used to operate the system such as using
        normally closed relays so that during normal grid operation there is a minimal power loss.
   5. Add separate location for main and backup source breakers to distinguish source protection from
        load protection devices. This would result in clarity for installer, technician, and user.

4.4 Design Features that Should Not Change
The system shows exemplary performance in a prototype environment, therefore many original system
design aspects would not change.

The following aspects would not change in future work:




                                      Prioritized Backup Power System                                  Page 19
    1. The TI MSP430 provides a versatile low power microcontroller; this would not change as it best
       meets the system needs. However, larger systems would require a different model with more I/O
       and additional memory.
    2. The TI low side drivers carry the current for operating devices operated by the controller,
       therefore these would remain the same.
    3. Current measurements would remain transformer based sensors, which prevents heating of the
       element changing calibration under loads.
    4. The system would still be implemented inside or at the main breaker box of an electrical system.
       This proves to be the best place to centralize and control such as versatile system for power
       outage control and home automation.

4.5 Further Applications
The original concept of a backup power system, which prioritizes and controls the loads allows for many
further ideas and concepts to be explored. The team discussed many different features that could add on
to the backup system or operate from the designed hardware.

The following applications or additions to the system were considered:

    1. Automating the home could be implemented. This could provide light changing during vacation,
       and shut off non-essential rooms or loads at night, etc. This addition would simply require
       computer software on the remote access for setting the priority.

    2. The system could provide remote access to home power. This would require a new system and
       software that would communicate with the breaker box controller.

    3. Adding frequency and source syncing could allow alternative energies such as wind, solar, and
       batteries to be controlled and used by the system.

    4. The system could provide security for the home by implementing new sensors that would turn
       loads on and off based on sensing around the home.




                                   Prioritized Backup Power System                              Page 20

				
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