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??

Drivers

Continuous source

Environment friendly

Low running cost

Low variability

Challenges

Low efficiency (19%)

High installation cost

only in day light

Market trend

Why solar power??

Drivers

Continuous source

Environment friendly

Low running cost

Low variability

Challenges

Low efficiency (19%)

High installation cost

only in day light

Market trend

Go green and save green with clean power!

Project Overview

Mission Statement:____________

-To operate the solar panel at its

maximum power point under variable

environmental conditions

-To operate a multi panel system at

maximum power point of each panel

-To achieve maximum power efficiency

Problem Targeted

Increased Efficiency______

Maximum

tracking

efficiency up to

more than 89.2%Market trends shifting to cater

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

To operate each of them at their

maximum power point

OUR VISION

ELECTRICITY FOR ALL

PROJECT OVERVIEW

DC-DC

converter

Panel A

Panel B

Charge

ControllerBJT

Excess power

delivered to load

Micro

controller

irradiance temperature

V pv

PWM

DAC

I base

V out

I out

V battery

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 Tcell

Measure V pv and dP / dV

Calculate co-efficients P1-

P4

dP / dV

= 0V optimum = V pv

Duty cycle calculated

dP / dV >

0

V pv = V pv + cV pv = V pv - c

YES

NO

YESNO

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 2nd order

low pass filter to get Vo.

-Vo = Vd * D

-Change D continuously to get

constant Vo.

Single input buck converter (contd.)

-Output current, IL, has a waveform as

shown.

-Output voltage is voltage across

capacitor = Vo + delta(Vo)

-Ripple in output current and output

voltage can be minimized by selecting

corner frequency of low pass filter,

fc << fs , which is our switching

frequency.

-fc = 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.