EMPLOYER: Fire Wind and Rain Technologies [More Info]

PROJECT: A 4000-watt 60 Hertz, DC to AC sine wave inverter.

Project Description: Employed to complete an existing conceptual design, which was in the initial stages. The design consisted of a 4000-watt 60 Hertz, DC to AC sine wave inverter suitable for powering a single household from batteries or solar cells. As designed, the system was prone to self-destruction due to electrical spikes. The challenge was to stabilize the basic design, modify the design as needed to meet all power grid requirements, reduce the cost of the final design and provide better performance then the competition.

The final result was the production of prototypes that were installed at the independent testing center in Phoenix, AZ maintained by APS, (Arizona Public Service Utility Company). APS concluded that these units performed better then any other units tested.

Duties included:

• Examine power grid requirements and set target specifications for the design.
• Determine all changes to the existing conceptual design required to comply with the target specifications.
• Schedule and implement remaining work (Hardware and Software) required for completing the design.
• All embedded control software (Written in a mix of C and assembly). This included direct software generation of the stepped sine wave that drives the output stage with real-time amplitude and timing shifts to maintain output voltage and distortion within required specifications during load changes.
• After prototype testing, identify and implement improvements to optimize and enhance the design.

 

Accomplishments:

• Designed a new heat sink, which decreased the time involved in assembling the heat-sinked components by 1 manhour per unit while increasing the heat dissipation by a factor of two.
• The heat sink was part of an overall physical redesign, which decreased the overall assembly time by 3 manhours per unit.
• Reduced the size and cost of the spike protection circuit while increasing effectiveness to the point that a major source of failure was eliminated.
• Implemented a highly software driven (and thus inexpensive) method of generation of the output sine wave that used pre-computed sine tables and dynamically adjusted for real world load changes while using minimal processor time.
• Authored a software tool that automated the process of generating the sine wave tables using real world test data as input, thus compensating for any system non-linearity.