1

How to implement maximum power point tracking for low power solar charging

2

• Application definition and solution

• MPPT algorithm implementation

Agenda

3

Solar panel application definition

The solar problem

• I-V Characteristic

– High Impedance Source

– Non-ideal parameters affect curve

• Resistive losses

• Diode leakage

• Material properties

• Maximum Power Point

– Irradiance

• Affects short circuit current

– Temperature

• Shifts open circuit voltage

– Causes MPP to move

4

T

Input voltage (V)

0.00 5.00 10.00 15.00 20.00P

ow

er

(W)

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2.50

5.00

7.50

10.00

T

Input voltage (V)

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ow

er

(W)

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2.50

5.00

7.50

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Input voltage (V)

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ow

er

(W)

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2.50

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7.50

10.00

T

Input voltage (V)

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Po

we

r (W

)

0.00

2.50

5.00

7.50

10.00

T

Input voltage (V)

0.00 5.00 10.00 15.00 20.00

Cu

rre

nt (A

)0.00

250.00m

500.00m

750.00m

1.00

T

Input voltage (V)

0.00 5.00 10.00 15.00 20.00

Cu

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nt (A

)0.00

250.00m

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Input voltage (V)

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Cu

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1.00

The Solar Solution

• Maximum Power Point Tracking Algorithm

– Fractional Open Circuit Voltage (F.OCV)

• Fixed ratio of the instantaneous open-circuit

– Perturb & Observe (P&O)

• Manipulates load and monitors change in power

continuously

– Incremental Conductance (IC)

• Manipulates load and monitors change in

conductance

5

T

Input voltage (V)

0.00 5.00 10.00 15.00 20.00

Cu

rre

nt (A

)

0.00

250.00m

500.00m

750.00m

1.00

T

Input voltage (V)

0.00 5.00 10.00 15.00 20.00

Cu

rre

nt (A

)

0.00

250.00m

500.00m

750.00m

1.00

T

Input voltage (V)

0.00 5.00 10.00 15.00 20.00

Po

we

r (W

)

0.00

2.50

5.00

7.50

10.00

T

Input voltage (V)

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Po

we

r (W

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0.00

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7.50

10.00

Pk > Pk-1 Pk > Pk-1

1

2

1

2

K x VOC 1

1

2 ∆𝐏

∆𝐕 > 0

∆𝐏

∆𝐕 < 0

1

2

∆𝐏

∆𝐕 = 0

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MPPT Software Complexity Hardware Complexity Tracking Ability

F.OCV • Calculate K*VOC • Resistor divider

• Ratiometrically follows open circuit voltage

• Estimate of power point; good for single solar cell

• Partial shading affects estimate

Solution Comparisons • Algorithm/Controller Considerations

– Software

• Calculation | Measurement | Storage

• Processing | Power | Speed

– Hardware

• Sensing | Memory | Control

• Cost | Size | Speed | Efficiency

– Tracking Ability

• Accuracy | Adaptability | Timing

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MPPT Software Complexity Hardware Complexity Tracking Ability

IC • Calculate (I), (V) Slope and (P)

• Store Previous States

• (V) and (I) Sensors

• Controller (memory, multiplier)

• Can suffer from oscillation under certain conditions

• Step size determines tracking time

F.OCV • Calculate K*VOC • Resistor divider

• Ratiometrically follows open circuit voltage

• Estimate of power point; good for single solar cell

• Partial shading affects estimate

MPPT Software Complexity Hardware Complexity Tracking Ability

P&O • Calculate (P)

• Store Previous States

• (V) and (I) Sensors

• Multiplier

• Memory or State Machine

• Continuously tracks power

• Suffers from oscillation

• Step size determines tracking time

IC • Calculate (I), (V) Slope and (P)

• Store Previous States

• (V) and (I) Sensors

• Controller (memory, multiplier)

• Can suffer from oscillation under certain conditions

• Step size determines tracking time

F.OCV • Calculate K*VOC • Resistor divider

• Ratiometrically follows open circuit voltage

• Estimate of power point; good for single solar cell

• Partial shading affects estimate

The Solar Charging Solution – 3M Approach

• Basic Functions for a Solar Charger

→Monitor

• Key Charging and Input Parameters

→Manipulate

• Operating Point and Loading Conditions

→Maximize

• Input Power and Charging Current

7

8

MPPT Algorithm Implementation

Maximizing Charging Current

9

• Implementation

– Prioritize battery charging

– Adjust operating point to get max charge

• Assumptions

– Battery voltage constant

• CC Charge

– Low/constant System Load

• ISYS < ICHG << IINDPM Supplement Mode

• Goals

– Time

• Tracking within 5s

– Accuracy

• ±50mA of IMPP

• ± 300mV of VMPP

Algorithm Methodology

• Working Principle

– With given VBAT and ISYS charge current will move proportionally with input

power

• Neglect efficiency

• Neglect dynamic loading

– Based on P&O MPPT

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T

Input voltage (V)

0.00 5.00 10.00 15.00 20.00

Cu

rre

nt (

A)

0.00

250.00m

500.00m

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1.00

T

Input voltage (V)

0.00 5.00 10.00 15.00 20.00

Cu

rre

nt (

A)

0.00

250.00m

500.00m

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1.00T

Input voltage (V)

0.00 5.00 10.00 15.00 20.00

Po

we

r (W

)0.00

2.50

5.00

7.50

10.00

Ik < Ik-1

Ik > Ik-1

1

2

1

2

Algorithm Flow Diagram

• Core Blocks

– Device Initialization

• Setting Preconditions

• Is there power from the Panel?

– MPPT Initialization

• Setting Limits to the Algorithm

• Redefining Parameters

– MPP Tracker

• Manipulate the operating point

• Monitor outputs

• Maximize charging current

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Core Sub-Blocks

• Device Initialization

– Unclamped Power Point

• IINDPM

• Charge Current

• FORCE_VINDPM

– Power Good

• Heavily shaded?

• Damaged?

• Power Not Good

– Default Hi-Z

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Core Sub-Blocks

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• MPPT Initialization

– Hi-Z mode for VOC

– 65%VOC

• Definable

• Optimize

– Tracking Time

– IV Curve

• Start Condition

– ICHGMAX

• Compare to instant ICHG

• Update

Core Sub-Blocks

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• MPP Tracker

– ADC Read

• Burst Mode

• Multiple reads = Precision

– Charge Current > ICHGMAX?

• Current increasing/decreasing

• Update Max Charge

– Increment VINDPM

• Step Size

– Optional: Stop after decrease

• Improves speed of algorithm

– Sample Interval

• Sunlight variance

bq25895

+

-

Test Conditions

• Model (Simulated Panel)

– Standard 4-Component Model

• Outdoor (Real Panel)

– SolarLand Model #: SLP005-06U

– Polycrystalline

– 5W, 6V, 10.5V VOC, 0.67A ISC

– 3.1V VBAT, 6Ah capacity

• Testing Conditions

– 4.5V – VMPP+1

– Stop after Max Power

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High Irradiance Model: 1A Short Circuit Current

• High Irradiance Test

• Results

– Charge current = Max

Stop Tracking

– Similar ICHG readings

• Near VMPP

• Could affect reading

• Select Midpoint as Max

– VMPP(Real) - VMPP(Selected) = 100mV

– PMPP(Real) - PMPP(Selected) = 70mW

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1.00

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9.00

0.50

0.75

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1.25

1.50

1.75

2.00

2.25

2.50

4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0

Po

wer

(W)

Cu

rren

t (A

) Voltage (V)

MPPT Model Test - 10VOC, 1A ISC, 3.8VBAT

ADC Charge Current

Real Charge Current

Panel Power

Panel Power

Real MPP

Selected MPP

Low Irradiance Model: 0.5A Short Circuit Current

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• Low Irradiance Test

• Results

– Similar behavior to 1A ISC

– Power has sharp corner

• Non-ideal Solar Model

– VMPP(Real) - VMPP(Selected) = 300mV

– PMPP(Real) - PMPP(Selected) = 40mW

1.00

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4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5

Po

wer

(W)

Cu

rren

t (A

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Voltage (V)

MPPT Model Test - 10VOC, 0.5A ISC, 3.8VBAT

ADC Charge Current

Real Charge Current

Panel Power

Panel Power

Real MPP

Selected MPP

Input Current Input Voltage Charge Current

Test Results - Model

• Results

– Sweeps/Tracks in 6.4s

• Faster if 65-90%VOC

– Near VOC, sharp corner in

power

• No effect on tracking

– Customizable hold time

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Bounded track time ~3.5s

Input Power

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

5.00

0.50

0.60

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1.00

1.10

1.20

4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5

Po

wer

(W)

Cu

rren

t (A

)

Voltage (V)

MPPT Outdoor Test - 9.5VOC, 0.65A ISC, 3.1VBAT, 6Ah

Test Results – Outdoor: Real Panel

• Results

– PMPP(Selected) = PMPP(Real)

– Sunlight can change in seconds

• Affects Temperature

• Shifts Power curve

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Input Power

ADC Charge Current

Input Current

Real MPP

Selected MPP

• Measure Solar Panel Open-Circuit Voltage with 100mV

resolution, Charging Current with 50mA resolution, and

Battery Voltage with 20mV resolution

• Adjust Solar Panel Power Point through VINDPM

• Optimized Input Power Conversion for Maximum Charge

• Operate with High Voltage Solar Panels up to 14V

• Provide Reverse Current Protection to the Solar Panel

• TIDA-01556 Tools Folder

• Design Guide

• Design Files: Software

• Device Datasheets: ‒ bq25895

‒ MSP430FR4133

bq25895 I2C Controlled Single Cell 5-A Charger with Power Management for MPPT with Solar Input

• Integrated 7-Bit ADC to Monitor Input Voltage, Battery

Voltage, and Charge Current

• Adjustable Input Voltage Power Management threshold

with 100 mV Resolution

• High Charge Efficiency with 93% @ 2 A and 91% @ 3 A

• Wide Input Voltage Operating Range from 3.9 V to 14 V

• Integrated Reverse Blocking at Input

Features Benefits

Tools & Resources

• Smart Shared Bikes

• IP Cameras

• Portable Speakers

Applications

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Conclusion / Summary

• Solar Power Tracking

– Max Power moves with Sunlight and Temperature

• Algorithms: F.OCV | P&O | IC

• Trackers: Software | Hardware | Accuracy

– 3M: Monitor | Manipulate | Maximize

• Simple MPPT Implementation

– Max ICHG PMPP

• P&O approach

• Reflected PIN

• TIDA-01556: I2C Controlled Single Cell 5-A Charger

with Power Management for MPPT with Solar Input

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