Lecture Notes on Photovoltaic System | ECEN 4517, Study notes of Electrical and Electronics Engineering

Download Lecture Notes on Photovoltaic System | ECEN 4517 and more Study notes Electrical and Electronics Engineering in PDF only on Docsity! ECEN 4517 1 Lecture 2 ECEN 4517/5517 Experiment 1: Photovoltaic System Characterize the SQ-85 PV panels, and find numerical values of model parameters for use now and later in semester Test the inverter provided Charge the battery from the panel, using the Direct Energy Transfer method Hope for sun! Experiment 1 to be performed this week, weather permitting If weather is poor, then do Exp. 2 (pulse-width modulator) this week instead, and do Exp. 1 next week Final reports for both Exp. 1 and Exp. 2 due at beginning of lab on Feb. 3-5 ECEN 4517 2 Lab reports • One report per group. Include names of every group member on first page of report. • Report all data from every step of procedure and calculations. Adequately document each step. • Discuss every step of procedure and calculations – Interpret the data – It is your job to convince the grader that you understand what is going on with every step – Regurgitating the data, with no discussion or interpretation, will not yield very many points – Concise is good ECEN 4517 5 Apparent path of sun through sky Baseline Rd. is 40˚N Times are not corrected for location of Boulder in Mountain Time Zone Net panel irradiation depends on cos( ) with = angle between panel direction and direction to sun So take your data quickly 8 Laboratory facilities: mobile PV cart PV panel 85 Wpk 17.2 V at 4.95 A Shell SQ-85P C on ne ct or s + – PV panel + – Battery + – Isolated dc-dc converters + – 12V + – 12V + – 5V Inverter 60 Hz 300 W 120 Vrms 6 outlet ac power strip Alarm Battery low voltage Voltmeter Battery voltage Battery charger Battery 12 V deep-discharge 56 A-hr Off cart: on stationary workbench 9 Deep-Discharge Lead-Acid Batteries Theory and modeling of batteries Don t overcharge: this causes outgassing and can quickly ruin the battery Don t discharge below 50% SOC: this reduces battery life Battery state of charge (SOC) vs. terminal voltage 100% SOC 12.80 volts or greater 75% SOC 12.55 volts 50% SOC 12.20 volts 25% SOC 11.75 volts 0% SOC 10.50 volts┠56 Ampere-hour Power Electronics Laboratory How a pulse-width modulator works Sawtooth wave generator + – vsaw(t) vc(t) comparator δ(t) PWM waveform analog input vsaw(t)VM 0 δ(t) t TsdTs vc(t) 0 2Ts Power Electronics Laboratory Equation of pulse-width modulator vsaw(t)VM 0 δ(t) t TsdTs vc(t) 0 2Ts For a linear sawtooth waveform: d(t) = vc(t) VM for 0 ≤ vc(t) ≤ VM So d(t) is a linear function of vc(t). Sawtooth (Ramp) Oscillator UC1525A Oscillator Schematic VREF Rr Syne “ “as as ~~ | a 274K 3 (as as - Ramp tak aK z To PWM 2k aw | an poz | Olt Wu nw . 400 Sage “a Blanking Spt A) To Output & — | I 23k ~ 4 WAN ee et “\ az sm anal L fas Sak = 250k 3% J go 4) => Clock Power Electronics Laboratory Power Electronics Lab Error Amplifier with Load 9 + _ 1 2 v1 v2 i9 Z(s)gm(v2 - v1) ))(( 129 vvsZgv m −= The differential voltage gain is: gmZ(s) With large Z(s), the differential voltage gain is large. The data sheet specifies a low-frequency differential voltage gain of at least 1000 (60 dB). Power Electronics Lab Connect to produce adjustable D 1 2 9 to PWM comparator gm vcomp internal Z(s) Vref pin 16 external pot vin The error amplifier is connected as a unity-gain stage: vcomp = vin The duty cycle D can be adjusted by the external pot. Power Electronics Lab Outputs of the UC3515A Output of PWM comparator Flip-flop output Q Flip-flop output Q Output A Output B DTs Ts output A output B 11 14 VC 13 output of PWM comparator flip-flop output Q flip-flop output Q Frequency of the outputs is one half the oscillator frequency. Duty cycle cannot be greater than 50%. Such outputs are needed in some types of switching converters such as “push-pull.” Outputs A and B can be OR-ed to restore the PWM pulses at the oscillator frequency.