The University of Texas at El Paso
College of Engineering
Department of Electrical Engineering
A little about our project, the design idea was orignally developed for the purpose of assisting those who are not close to power sources. Our overall project was the joint effort of two teams. One team was responsible for the hardware and the other was responsible for the software. This project construction was basically broken down into three modules: The Cuk Converter Module, The Inverter Module and the Filtering/Sensing Module. More is explained on these matter in later sections of the web page.
The objective of our team is to implement the inverter’s control, protection and communications interface.
Electrical Ingenuity designed the control, protection and communications interface for an inverter. Certain standards and regulations had to be met for acceptable completion of the project. Our team decided to use a digital signal processor (DSP) chip to perform the functions mentioned above, but later changed to a micro-controller, whic proved to be more efficient for our purpose. Programming was done using Dynamic C, which is a C language specific for the JACKRABBIT. The team set up a series of tasks and deadlines which were met accordingly. Progress was measured by first making sure deadlines were met, then once the prototype was built, it was measured with a series of tests to ensure its functionality. The inverter was about 91% efficient.
METHOD OF COMPLETITION
Each member took on responsiblities for this portion of the project and then integrated with the corresponding person fron the hardware responsible team. Finally, all the modules were integrated for the completion of the project. The following is a breakdown of this process:
CUK CONVERTER MODULE Vanessa Melendez - Ivan Hernandez
INVERTER MODULE Angie Rodriguez - Vasilios Vlahos
FILTERING/SENSING MODULE Juanpablo Gonzalez - Casey Cook
This project was completed using a Jackrabbit Micro-controller. This micro-controller is developed by Z-World and utilizes a Rabbit 2000 processor. Again, the programming was done in Dynamic C. The software was included in the Jackrabbit Development board. This programming is very user friendly, which made the programming process much easier.
In order to implement the controls for the Cuk converter, it was necessary to generate a series of pulses using a Sawtooth Pulse Width Modulation scheme. The duty cycle of the signals (defined as the ratio of the on duration to the switching time period) was required to be adjusted in order to achieve the necessary output voltage. The signals were generated within a software program using the jackrabbit microcontroller by comparing a control voltage with a constant peak repetitive waveform (sawtooth). The
program reads the DC control voltage from an analog input on the microcontroller. The voltage read is then compared with the sawtooth signal generated and the duty cycle is calculated. After that, the PWM signal with the required duty cycle is generated and sent to the switch from an analog output on the microcontroller. The process is then repeated reading again the control voltage and creating continuously the required PWM signal in a closed feedback loop system. Also, a PI controller was implemented in
hardware to provide the control voltage which was used to create the PWM signals.
The software for this module was incorportating the comparision of a sine wave and a triangular wave. Once the comparision is done, the signal is generated and it basically works on a "on"/"off" timing state, where the timing depends on where exactly the triangular wave is compared to the sine wave. This was developed on following a bi-polar sinsusoidal PWM switching scheme. The following picture illustrates the pwm scheme used.
In the program, this comparision was incorporated with delays on the "on" and "off" timings for the pulse. They were incorporated with the use of loops that cause the continual changing of the duty cycle. The duty cycle ranged from 3% to 98% and along with this, an inverses of this signal was generated. This was not a true inverse, but a shorten pulse. The pulse was shorten to prevent shorting of the circuitry. These signals were tested and incorporated with the the inverter module.
The filtering portion was done in hardware by the other team and had no software involved. But software was incorporated for the sensing. Sensing was done for temperature, voltage and current. What was done is that external sensors were to be used to send signals to the micro-controller and then these signal were checked within code. For all three sensing parts, the basic ideology behind it was to read the signal--> check if it was within set limits-->
if within limits continue checking
if not within limits, glitch checker increase
-->if glitch checker count=10, shutoff
The shutoff sequence is illustrated in the following chart.
Some of the issues that might be considered in the future in order to improve upon this project are the need for a feed back to the PI Controller and common mode leg .
The project was completed with support for CVI POWER. Through several months of work as two team we completed the project as one team. The project finished up to a 90% completition due to the lack of parts, complete integration and other minor details. Each module was independtly also approximately 90% complete, but even though this was so, the project prototype was 91% efficient. Electrical Ingenuity would like to thank CVI POWER, whose team teamwork and support was greatly appreciated...Good job guys!!