Back-up Power Generating Door Group 21 Kyle Rasmussen Michael Gan Allen Huang
Introduction • This project converts mechanical energy from opening a door into electrical energy for a backup power supply. This green energy solution makes use of an everyday occurrence to protect against intermittent power loss.
Features • Provides 120Vrms / 60Hz during intermittent power loss • Easily deployable on any door fixture • Senses power loss and automatically switches to backup power
Block Diagram Overview of Device Mechanical To Electrical Regulation And Storage dc to ac Conversion Recognition And Release
Overview • Mechanical: Transfers wide arc of door swing into spin on a mechanical shaft • Generator: Transforms rotation of shaft into electrical energy • Charge/storage: Stores energy created from the generator by charging it in a battery • Converter: Converts the DC power from the battery into AC power • Transfer Switch: Taps into the power from the battery to provide electrical control signals needed for the project to operate as well as controlling to flow of energy between each module • Detection: Detects power loss in the main power line and sends the appropriate signal to the transfer switch
Mechanical to Electrical: Introduction • This portion utilizes a series of gears to translate the swing of a door into rotational motion. • The rotational motion is fed to a generator to convert mechanical energy into electricity. • For our device to provide backup power for 15min., each door use must generate 22.5J from the generator.
Mechanical Overview • Capture motion from an opening and closing door • Convert Kinetic Energy into Electrical Energy • Provide enough energy to charge battery
Capture Design • Mountable with screws • Arms made from metal bars • Rotates with door for 1.05 rad/sec • Changed significantly from original design
Arm Kinematics Denavit-Hartenberg Parameters
Gear Train and Generator • Overall gear ratio of 1:128 • Hand picked gears from local hobby store • Placed on machined platforms • Generator acquired from power lab
Construction • Metal Grinder • Fashioned arms • Customized gears
Testing Generator Speed with Output Verified rated speed of generator Determined speed necessary for 14.88V into Buck Converter
Load Testing Generator Motor-Generator Configuration Measuring power output in response to different loads
Voltage Regulator • Protects battery from surging generator • Must handle voltage swings of +/- 2.5V • Limits charging current ripple to +/- 2% • Maintains charging voltage at 12V +/- 1%
Voltage Regulator • Buck Converter: Steps down voltage from generator • Hysteresis Controller: Feedback control of Buck Converter • MOSFET Driver: Steps up switching signal from Hysteresis Controller
Voltage RegulatorBuck Converter • Input voltage ranges from 13.63V to 16.13V. • Per specification of the battery, the maximum allowable output current was chosen to be 3.33A. • Assuming fswitch = 100kHz, solving for VL = L di/dt and Ic = Cdv/dt yields • L = 229uH • C = 122.1uF
Voltage RegulatorHysteresis Controller • Compares Buck Converter output (V-) to Vth • Voltage comparator outputs high if V- < Vth • Outputs low if V- > Vth
Voltage RegulatorHigh-Side Driver • Converts output of Hysteresis controller to 18.5V • Establishes Vgs > Vth for Buck Converter MOSFET.
Vin sweep from 12.4V to 17.38V Voltage RegulatorTesting Buck Converter
Voltage RegulatorTesting Buck Converter Snapshot of output during testing • Conclusions: • At the upper level of this sweep, the Buck Converter was still able to keep the output voltage within 1% of the nominal. • It is clear that the regulator could handle the 2.5V swing expected from the generator. • While the ripple voltage was higher than expected, this is mostly due to the switching frequency it was tested at.
Voltage Regulator • What went wrong? • An unsuccessful transfer of the regulator to the PCB board • On proto-board, Hysteresis not outputting • This can be fixed with simple debugging
Driver Signals • 12V provided by main lead acid battery • 15V provided by boost converter • 6V and 18V provided by external small batteries 6V 12 V 15 V 18 V
Boost Converter Materials Used • Power Inductor – Self wound • Schottky diode - MBR360 • Power MOSFET – IRF540 • PWM Chip - UC2843, High performance PWM controller • Capacitors –frequency adjustment and charging output • Resistors – voltage divider for feedback
Boosting Operation On State • Switch 1 is On, Switch 2 is Off • Inductor charges / current increases • Capacitor discharged across load • Output voltage decreases Off State • Switch 1 is Off, Switch 2 is On • Inductor discharges / current decreases • Capacitor gets charged • Output voltage increases S2 S1 S2 S1 www.coilgun.eclipse.co.uk/
Component Selection Calculations • Selection of R and C connected to the pins. Aiming for Freq = 100K. Looking at the graph for Timing Resistance vs. Frequency, R = 10K and C= 2nF. • Need to select voltage divider to bring to the feedback pin. Output is selected at 15V and internal comparator voltage is 2.5V. This means a voltage division of 1/6 is needed. 120K and 20K resistor is chosen http://focus.ti.com/docs/prod/folders/print/uc3843.html
Boost Converter Output • Average output voltage is 14.7V. Ripple occurs when MOSFET switches to discharge capacitor in order to lower output voltage.
Testing the boost converter Line Regulation • Varied input voltage and fixed load • Measure of how well the boost converter handles various input voltages Load Regulation • Fixed input voltage and varied load • Measure of how well the boost converter maintains 15V
Line Regulation Tables 2.67% 32.77% 33.09% 33.29%
Load Regulation vs. Load • Load Regulation is better for higher loads • Ideally you want 0% load regulation • Why almost 24% load regulation at 3Ω?
Analysis of Load / Line Regulation Discrepancies Recommendations Increase duty cycle of the switch that drives the MOSFET Gives inductor more time to charge and less time to discharge • Line Regulation in 30%s, Load Regulation in the 10%s to 20%s • Discontinuous mode operation - current in inductor to drop to 0A between switching cycles • Inductor discharges into capacitor prematurely
DC/AC ConverterObjectives Ideally, • Transform 12Vdc from a battery into 12Vac • Voltage waveform at 60Hz • Smooth signal and eliminate harmonics with a filter
DC/AC ConverterGeneralOverview • Voltage Sourced Inverter (VSI) • Full Bridge Orientation • Switches are Power MOSFETs with reverse-parallel diodes
DC/AC ConverterSwitching: Overview Opposite switching signals to each leg • Switching signals generated by astable multivibrator • Voltages stepped up through MOSFET drivers
DC/AC ConverterSwitching: Generation Astable Multivibrator • Incorporates LM555 timer • Thresholds established through voltage division • Capacitor voltage triggers state changes • Conceptual circuit • Provide calculations in appendix to refer to • Conceptual waveforms • Or real if they are available
DC/AC ConverterSwitching: Generation • To realize a 60Hz square wave with 50% duty • C = 11.32 μF • RA = 120Ω • RB = 1KΩ
DC/AC ConverterSwitching: Drivers • 4V to 15V conversion • Establish VGS ≥ VTH • Two High-side: • LMD18400N (inv. & non) • Two Low-side: • MIC4427 (non) • MIC4426 (inv.)
DC/AC ConverterSwitches: Drivers Signal to Switch 1,1 Signal to Switch 1,2 Signal to Switch 2,2 Signal to Switch 2,1
DC/AC ConverterInverter Output • Leg one • Leg two • Signal across load Signal 1: Inverter output voltage Signal 2: 555 output voltage
DC/AC ConverterInverter Output Measured over 3Ω load • Signal 1: Voltage out of Inverter • Signal 2: Current out of Inverter
DC/AC ConverterInverter Output As the power drawn from the battery increases, so does the power loss over the inverter. However, for the range of loads tested, the losses turn out to be relatively proportional, and the overall efficiency of the inverter remains around 2/3.
DC/AC ConverterInverter Output Factors in Power Loss Pg 473 of Krein Need datasheet of MOS
DC/AC ConverterOutput Filtering • Originally attempted to use LCR series resonant filter • Balanced Q with L • Given Q = 3.4 • L = 7.633mH • C = 921.8 μF
DC/AC ConverterOutput Filtration 1 2 3 • 7.1ohm load (Vrms = 7.87) • 3.55 ohm load (Vrms = 4.96) • 1.1 ohm load (Vrms = 2.56)
DC/AC ConverterOutput Filtration What went wrong? • Not Core Saturation: • Inductors within volt-sec and amp-turn limits • ESR: • Inductor had an ESR of 0.69Ω • Increased power output meant greater voltage drop • Additional Inductance • Transformer introduced unaccounted for inductance • Filter ceases to be resonant (XL> XC)