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ECE 110 Lab Renewable Energy Battery Charger

ECE 110 Lab Renewable Energy Battery Charger. Group 21 Richard Schlude ECE 445 Senior Design 12/2/2011. Overview. This project set out to design and implement the power converter for a DC wind generator intended to charge the batteries used in the ECE 110 lab

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ECE 110 Lab Renewable Energy Battery Charger

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  1. ECE 110 Lab Renewable Energy Battery Charger Group 21 Richard Schlude ECE 445 Senior Design 12/2/2011

  2. Overview • This project set out to design and implement the power converter for a DC wind generator intended to charge the batteries used in the ECE 110 lab • The design implements a switching converter to control the current to the load with minimal power loss

  3. Design Features • Provides maximum 25W output (10V dc at 2.5A) • Operates over input range of 8V to 50V as governed by generator operation • Runs at 80-85% efficiency under nominal operation

  4. The Circuit Generator Input Driver Vcc Pulse GND Output

  5. Converter Circuit • The design consists of a buck-boost converter topology • Includes snubbing circuitry for increased efficiency • Circuit operates at 10kHz switching frequency

  6. Component Choices • The MTP 50N06 FET and the MBR360 Schottky Diode were decided upon to increase efficiency • FET RDSON=0.022Ω • Diode on-state voltage drop=0.74V at 3.0A • Output capacitors were added in series to reduce effective series resistance (ESR) losses.

  7. Gate Drive Circuit • Gate driver is IRS 21171 • Gate was driven with Vcc=15V and capacitor values of 1uF • Input square wave is 5V 28Ω

  8. Testing • Efficiency tests and output voltage ripple tests in addition to inductor current ripple tests were performed • Tests were performed first with a low loading to ensure proper voltage operation then tested at highest load (25W) to demonstrate full operation

  9. Efficiency Testing Procedure • For given load, input voltages were swept across expected range • Duty cycle of square wave gate signal to FET was adjusted using a function generator with 5V peak, f=10kHz

  10. Efficiency Test Results

  11. Efficiency Test Numerical Results

  12. Output Ripple Testing • Output ripple was first tested at low load and then at larger load. • At low load it was found to be 0.5%, as desired by initial specifications. • At high loading, the output ripple increased to 3.8%. This was not considered an issue since the load does not require very low ripple • 380mV/10V =3.8% ripple

  13. Looking Forward • Control must be implemented • PIC 16F887 was planned to be used to implement feedback control • Sense output voltage • Sense output current with use of 0.01Ω current sense resistor • Sense input voltage to indicate that charger can work given outdoor wind conditions

  14. Controller Operation Sense Battery Voltage (D=0%) V>8-10V? No Yes Increase Duty Cycle Increase Duty Cycle Sense Output Current Sense Output Current 2.7A>i>2.3A? .075A>i>.060A? No Yes No Charge for 1 Minute

  15. Control Considerations • Because of ripple on output current and input, proper filtering will be crucial • There must be some hysteresis within the control so that the duty cycle is not constantly varying • Because circuit was designed with PIC in mind, there should be no issues with the gate drive and switching frequency

  16. Future Hardware Considerations • Switch ringing, though reduced with the snubber, is still present • This can be reduced further using a Zener-diode clamper circuit • Also, tests must be done with the battery to observe converter response

  17. Successes/Challenges Successes: • Converter efficiency is good under nominal operation • Output ripple is good enough for non-sensitive load • Gate drive circuit operates at 5V input signal so that a microcontroller can be easily used for gate control Challenges: • Efficiency can improve at low input voltage operation • If battery turns out to be sensitive to ringing/ripple, more capacitors and improved noise reduction will be needed • PIC control was never implemented but is necessary looking forward

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