Tracking maximum power point of a multi panel solar system Presenters: Annum Malik Asad Najeeb Joveria Baig Sohaib Iqbal
Presentation at a glance… Introduction Project Overview PV panel characteristics Block diagram and flow of project DC-DC convertor Charge controller Q & A session
Introduction Need for alternative sources: a. Fossil fuel depletion b. Fossil fuel pollution c. Increase in energy demand d. Gap in supply and demand
Why solar power?? Challenges Drivers Low efficiency (19%) Continuous source High installation cost Environment friendly only in day light Low running cost Market trend Low variability
Why solar power?? Challenges Low efficiency (19%) High installation cost Drivers only in day light Continuous source Market trend Environment friendly Low running cost Low variability
Go green and save green with clean power!
Project Overview Mission Statement: ____________ Increased Efficiency ______ -T o operate the solar panel at its maximum power point under variable environmental conditions -T o operate a multi panel system at maximum power point of each panel -T o achieve maximum power efficiency Maximum tracking efficiency up to more than 89.2% Market trends shifting to cater Problem Targeted demand_______________________ _ Market moving towards Cleaner energy
PV array characteristics Power maxima varies with irradiance and temperature MPPT algorithm needed to track this maxima in varying conditions T o operate each of them at their maximum power point
OUR VISION ELECTRICITY FOR ALL
PROJECT OVERVIEW V out DC-DC Charge BJT converter Controller I out Panel A PWM I base DAC Panel B Micro V pv controller V battery irradiance temperature Excess power delivered to load
Case 1: Not on maximum power point 1. MPPT algorithm detects system is not on MPP. 2. It calculates the optimum voltage the panel should be on. 3. PWM signal is generated to alter the duty cycle, ensuring constant V out . 4. I base is calculated using V optimum . I out is hence changed. ( B * I base ) 5. Characteristic resistance changes ( V out / I out ). 6. The load-line hence shifts, and the solar panel starts operating at MPP.
Case 2: Change in irradiance or temperature 1. Microcontroller detects the change 2. New optimum voltage is calculated. 3. I base calculated accordingly 4. Duty cycle of the PWM wave is altered to ensure V out remains constant. 5. I base changes I out . Hence the load line shifts to intersect with MPP.
Case 3: Battery is not fully charged i.e. variable load resistance 1. V battery is measured by the micro controller. 2. A PWM is generated to ensure V out = V battery . 3. I base is altered to ensure the load line continues to intersect with the MPP. 4. As the battery charges, V battery changes dynamically, hence PWM is continuously altered. 5. I base is also changed dynamically ensuring MPP is maintained.
Measure G now and T now Calculate T cell Calculate co-efficients P1- P4 Measure V pv and dP / dV dP / dV YES V optimum = V pv = 0 NO Duty cycle calculated NO dP / dV > YES 0 V pv = V pv - c V pv = V pv + c
Equations
Single input buck converter -Dealing with continuous conduction mode. -Input signal from Vd from solar panel -Use PWM duty cycle, D, generated from microcontroller for switching. -Essentially passing through a 2 nd order low pass filter to get Vo. -Vo = Vd * D -Change D continuously to get constant Vo.
Single input buck converter (contd.) -Output current, I L , has a waveform as shown. -Output voltage is voltage across capacitor = V o + delta(V o ) -Ripple in output current and output voltage can be minimized by selecting corner frequency of low pass filter, f c << f s , which is our switching frequency. -f c = 1 / (2*pi *sqrt(RC))
TWO INPUT BUCK CONVERTER Traditional two input buck converter
A BETTER DESIGN Cost reduced and power circuit simplified
TWO FAULTY APPROCHES Connecting the two sources in parallel and PWM used to transfer power to the load (based on the time sharing concept). Disadvantage : power cannot be delivered to the load simultaneously. Connecting the sources in series with bypass paths incase one of the input is not connected. Disadvantage: huge variations when only one source is connected.
INNOVATIVE DOUBLE INPUT PWM DC-DC CONVERTER
ADVANTAGES Both sources can transfer power individually as well as simultaneously. No variations And the magnitude of the input dc voltage can be higher or lower than the one with regulated output.
CIRCUIT OPERATION MODE1 (SHI: ON/SLO: OFF): VHI will charge the inductor and the capacitor as well as provide current to the load.
MODE2 (SHI: OFF/SLO: ON): In this mode VLO will charge the inductor and the capacitor will provide the current to the load
MODE3 (SHI: OFF/SLO: OFF): Both the voltage sources are disconnected from the circuit and thus the energy stored in the inductor and capacitor will be released to provide the required current to the load.
MODE4 (SHI: ON/SLO: ON): The input voltages VOL and VHI are connected in series to charge the inductor. The capacitor provides the current to the load.
OUTPUT WAVEFORMS
CHARGE CONTROLLER Regulates the rate at which current is added or drawn from the battery. Prevents over charging, over voltage and complete discharging (by disconnecting the load) Life of the battery is increased and it is protected from getting damaged. “12 volts” solar panels emit around 16 to 20 volts so charge controllers are vital.
TYPES OF CHARGE CONTROLLERS SERIES CONTROLLERS: disables further current flow when batteries are fully charged. SHUNT CONTROLLERS: diverts excess current to drive the shunt load such as a water heater. Simple charge controllers stop charging a battery when they exceed a set high voltage level, and re-enable charging when battery voltage drops back below that level.
PWM CONTROLLERS Good quality controllers use PWM to charge. On reaching the regulation voltage (14.1V), a PWM algorithm reduces the charging current and continues charging slow enough to prevent the battery overcharging instead of stopping charging and so are 30 % more efficient.
3 STAGES OF A SINGLE CHARGE CYCLE BULK PHASE: voltage of the battery gradually rises to a bulk level while drawing maximum current (14.4 to 14.6 volts). ABSORPTION PHASE: voltage is maintained at the bulk level for some specific time while the current tapers off gradually as the battery charges up. FLOAT LEVEL: After the absorption time passes, the voltage is lowered to a lower level i.e. the float level (13.4 to 13.7 volts) during which a small maintenance current flows until the next cycle.
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