ECE 477 Digital Systems Senior Design Project Spring 2006

Homework 12: Ethical and Environmental Impact Analysis

Due: Friday, April 14, at NOON

Team Code Name: ______H.E.A.D Gear______Group No. ___12___

Team Member Completing This Homework: ______Sriharsha Vangapaty______

E-mail Address of Report Author:

Evaluation:

Component/Criterion / Score / Multiplier / Points

Introduction and Summary

/ 0 1 2 3 4 5 6 7 8 9 10 / X 1
Ethical Impact Analysis / 0 1 2 3 4 5 6 7 8 9 10 / X 3
Environmental Impact Analysis / 0 1 2 3 4 5 6 7 8 9 10 / X 3
List of References / 0 1 2 3 4 5 6 7 8 9 10 / X 2
Technical Writing Style / 0 1 2 3 4 5 6 7 8 9 10 / X 1
Late Penalty
/ – 20
TOTAL

Comments:

1.0  Introduction

This project is to re-design the logic board of the Maximum Power Point Tracker (MPPT), which is currently in development by Purdue Solar Racing. A maximum power point tracker is a DC to DC converter which takes an input voltage from a solar cell array and converts it to the output voltage of a battery pack. For any solar cell array, there exists a point on its current versus voltage curve that produces the maximum power. The re-designed logic board will incorporate feedback control of the converter to obtain this maximum power point. Another feature of the logic board will be the CANbus interface that will allow for remote access of the data and diagnostics of the MPPT.

The design of the project also took into consideration various ethical issues. The ethical issues this report will focus on will be reliability, safety and durability issues. For reliability issues, the report discusses the testing procedures to ensure the robustness of the software. For safety issues, the report addresses the issue of protecting the user from high voltages, prevention of fires from high temperatures and handling potential software bugs. And finally, for the durability issues the report focuses on the packaging of the MPPT. The project has also focused on the environmental damages caused by manufacturing of the MPPT. A designated section in the report discusses about these damages and how to minimize the impact of these damages. There are potential environmental hazards while disposing the MPPT as well, and the report details out the steps to help prevent these damages.

2.0  Ethical Impact Analysis

The MPPT is small device inside a much larger device, the solar car; however it is a very critical part of the solar car since it is responsible for obtaining the maximum power from solar cells. Thus reliability of the device was one of the important factors during the design process. Along with reliability, safety and durability of the device were also given significant importance and thought during the design process. In this project’s scope reliability, durability and safety of the device, to a large extent, compliment each other. A product that is reliable will not fail too often, the reliability of this product is preserved or protected by the durability of the product and finally a product that does not fail often and durable is a safe product. An ethical team or corporation should always strive to produce or develop products with these three as the major factors in their design process.

2.1  Reliability Concerns

The major reliability concerns of the MPPT, aside from the physical components of the project, arise in the maximum power point tracking algorithm itself, since this algorithm is solely responsible for the precision of the maximum power point. A miscalculation of the maximum power point has several crucial effects on the project. A major effect would be the degradation of the efficiency of the converter. Another effect would be the difficulty in debugging the MPPT because of the incorrect power point the tracker will output, when it automatically shuts off because it crossed the 70W threshold. The critical part of the algorithm is the speed at which the algorithm runs, thus several tests were conducted before the speed of the algorithm was finalized. These tests were simple trial and error tests which helped us evaluate the power points from the I-V curve. While examining these power points, we looked to see if there was significant amount of difference between the power points so that we know that the filters had enough time to adjust to the new duty cycle. Thus we decreased the speed of the algorithm until a significant change in successive power points was detected. Also to test the current maximum power point, the algorithm obtains a power point to the left and right of the current maximum power point. These left and right power points are obtained by changing the duty cycle by a certain amount, and this amount was decided by running several tests and evaluating the data to make sure that the difference between the left and right points and the maximum power point was significant enough to make a valid comparison.

2.2  Safety Concerns

As mentioned above, the MPPT will be inside a larger device and will not have direct interaction with a human being. However, during the design process we took safety into consideration to further minimize any harm to the user.

One safety concern is the possibility of electrocuting the user due to the high voltage that is being used. There is an automatic shut down of the MPPT, but this feature is triggered only at a voltage of 70 volts or higher. However in case of an accident a voltage that is not close to 70 volts can also be very lethal, thus several steps have been taken to prevent this disaster. First the MPPT will be placed inside a fiberglass foam-core casing to prevent the users from having direct contact with the high voltages while it is powered on. Second, warning labels will be placed on the casing to alert the user about the potential dangers and finally the user will also be notified about the potential danger in the user documentation.

Another safety concern is the possibility of fire due to overheating of any of the physical components of the MPPT. This problem is addressed by having a temperature sensor that triggers the on-board fan and allows the MPPT to cool off. The last safety concern would be software bugs, which can have unpredictable effects. An example of one such effect can be a latch caused by software which will cause the tracker to read in incorrect input values. This bug can have several effects one of which will be a miscalculation of the power point. Another one can be that the temperature sensor will not trigger the fan when it should because it is reading in incorrect temperature. One more effect would be loading in an incorrect CAN address through the SPI which will disable any communication between that tracker and the rest of the car. This can be very dangerous as there can be times when the chase vehicle, using the telemetry system, would like to shut off the tracker but in this case it would not be able to do so, thus causing the tracker to overcharge the battery on the power board which can lead to a fire. This concern was addressed by thoroughly testing the software of the MPPT and eliminating every bug we detected. Also we followed a strict coding procedure where we took care of every possible case when the software had to make a decision. This will eliminate the possibility of any latches being created by the software.

2.3  Durability

The durability of any product is very critical as this shows the integrity of the company that produced or developed the product. Thus, a significant amount of time was spent on packaging considerations of the MPPT. In the end, a fiberglass foam core casing was chosen for the MPPT. This will help keep the MPPT and power board intact and reduce the amount of the shock from the car, especially when it travels over uneven surfaces. This casing, as mentioned earlier, will also act as a safety tool by preventing the user from having direct contact with the high voltages of the MPPT.

3.0  Environmental Impact Analysis

The commercial production of the MPPT will also have an impact on the environment. Hence an ethical team and company should be well aware of the potential hazards to the environment involved in the production and disposal of their device.

3.1  Manufacture

The MPPT utilizes a double sided printed circuit board and the manufacturing of the printed circuit board creates waste which is an environmental hazard. A double sided printed circuit board is usually manufactured by producing patterns of conductive material on a non conductive substrate by subtractive process. The subtractive process involves cleaning and surface preparation of the base, electroless copperplating, pattern printing and masking, electroplating and etching. In the manufacturing process there are also potential air emissions which include sulfuric, hydrochloric, phosphoric and several other acids. Solid wastes are also produced through the process of manufacturing; these wastes can include scrap board materials, plating and hydroxide sludges, and inks [1]. Also the lead used in soldering the electrical components on MPPT board can present additional hazards, but there are lead-free solders under development that can be used in the future [3].

Board designers and manufacturers can minimize the effects of the hazards and waste by following certain procedures such as minimizing chemical dragout, minimizing the amount of water used for ringing and by recovering and reusing and recycling of copper [3]. Another design consideration to minimize environmental hazard can be the use of surface mount technologies (SMT) rather than the plated through-hole technology that is currently being used on the MPPT board. However the switch to SMT from through-hole technology is not possible for the MPPT board due to the design of the connector on the power board. The power board connector’s design requires through-hole technology to provide a stable connection to the MPPT board. The chances of the MPPT board disconnecting from the power board increase drastically if SMT was used rather than through-hole technology.

One more way of minimizing the hazardous effects on the environment is by reducing the amount of lead, cadmium, mercury, hexavalent chromium, polybrominated biphenyl (PBB) and polybrominated diphenyl ether (PBDE) flame retardants and asking the manufacturers to comply with RoHS Directive [1] [7].

3.2  Normal Use

During the normal use of the MPPT, very minimal environmental hazards are present. The main reason for this is because the MPPT does not use any rechargeable batteries and it does not have any components which can emit hazardous material.

3.3  Disposal/Recycling

In general printed circuit boards are difficult waste material to process since the printed circuit board is useless once it is removed from the electrical component in which they were installed. Printed circuit board consists mostly of materials that are hazardous partly because they fail TCLP for metals [4]. Usually printed circuit boards are part of “special” waste stream where they are segregated and handled separately from other non-hazardous solid streams. If printed circuit boards are not handled as waste materials they must be processed by a disposal option, which is very expensive and not efficient since some of the options do not include destruction of waste circuit boards, in which case the company producing the circuit boards is liable for handling and disposal of the waste material [2].

The printed circuit board can be recycled to recover materials such as silver, lead, copper and gold which can lower the overall cost of production. Reduction of hazardous waste and recycling of printed circuit boards allows a company to meet the requirements of waste reduction under RCRA, 40 CFR 262 and Executive Order (EO) 13148, and comply with EO 13101 [5] [6]. The benefits from such disposal process will also eliminate potential hazardous waste, reduce liability associated with improper handling and disposal procedures and the company can increase their awareness by publicizing such recycling efforts at their facilities [2].

4.0  Summary

This report consists of ethical and environmental impact analysis of the Maximum Power Point Tracker. The ethical impact analysis has been broken down to three sub categories, reliability, safety and durability concerns. The Reliability Concerns section discussed about the tests conducted to ensure the robustness of the MPPT algorithm, which is the brain of the entire project. The Safety Concerns section discussed the procedures taken to address safety concerns such as protecting the user from high voltages, protecting board from high temperatures and fires and finally the dangers caused by software bugs. The Durability section discussed about the packaging of the MPPT and how it protects the MPPT from physical damages.

The environmental impact analysis has been broken down into three categories as well and these categories address how the problem of the environmental hazards will be handled in the manufacture, use and disposal stage of the project. The Manufacture section discussed about the environmental hazards from manufacturing a printed circuit board and the steps to minimize these hazards. The Normal Use section discussed about the environmental hazards present during the use of the device and the Disposal/Recycling section instructed on the proper procedures to dispose the MPPT.