Low Cost MPPT Algorithms for PV Application: PV Pumping ... · PDF fileLow Cost MPPT...

31 Jan 2012NEWCASTLE UNIVERSITY

Power Electronics, Drives and Machines Research Group

Low Cost MPPT Algorithms for PV Application: PV

Pumping Case Study

M. A. Elgendy, B. Zahawi and D. J. Atkinson

Presented by:

Bashar Zahawi

E-mail: bashar.zahawi@ncl.ac.uk

Outline

Maximum power point tracking

Experimental system description

Directly Connected PV Pumping Systems

PV Pumping systems with MPPT

Constant Voltage MPPT Algorithm

Perturb and Observe (P&O) MPPT Algorithm

Incremental Conductance (INC) MPPT Algorithm

Conclusions

Introduction

Water pumping is probably one of the most

important applications of PV systems

Particularly in rural areas with no grid supply

Low power pumps ranging from 200W to 2kW

Most commonly used motor is the PM brushed dc

Induction motors used for bore-hole and deep-well

pumping

The dc motor/pump set is connected directly to the

PV array in most commercial systems

Maximum Power Point Tracking

A PV array or generator will have one point on its

current/voltage characteristic that corresponds to

maximum power output

This is referred to as the maximum power point or MPP

Directly connected systems do not operate at the

Significant amounts of available energy are wasted

A pump controller (dc-dc converter) is required to

better match the PV generator to the motor/pump set

This is referred to as MPPT

1000 W/m2

400 W/m2

800 W/m2

600 W/m2

200 W/m2Maximum power line

PV array current-voltage curves

Mismatch between resistive load and PV Source; current–voltage curves

PV Array Current-Voltage Curves

Load line

Maximum power line

PV array current-voltage curves

Mismatch between resistive load and PV Source; power–voltage curves

PV Array Power-Voltage Curves

MPPT Circuit

Duty Ratio

IPVVPV

DSP, interface, and driver circuits

generator CL

IPV IL

Circuit diagram for PV system with MPPT control

MPPT Algorithms

Mapping or Model Based algorithms

A model of the system is developed to “map” the operating

characteristics and identify the MPP

Simple models are not very effective

More complex models require significant computational

resources and are site specific

Not suitable for commercial applications

Constant voltage algorithm

Hill climbing algorithms

Hill Climbing MPPT

Outline of Presentation

Experimental investigation of the performance of

Maximum power point tracking algorithms for

pumping applications

Constant Voltage Algorithm

Perturb and Observe (P&O) Algorithm

Incremental Conductance (INC) Algorithm

In each case, system performance is investigated

and the energy utilisation efficiency calculated

Experimental Set Up

Experimental investigation of the performance of

Maximum power point tracking algorithms for

pumping applications

Constant Voltage Algorithm

Perturb and Observe (P&O) Algorithm

Incremental Conductance (INC) Algorithm

In each case, system performance is investigated

and the energy utilisation efficiency calculated

Experimental Set Up

1080-Wp PV array facing south at a tilt angle of 54

w.r.t. the horizontal

Two parallel branches of 3 series connected 180-Wp solar

modules

Weather station installed at the same roof

Weather parameters were recorded at a 1 sec sampling rate

Solar irradiance was measured by a radiation sensor fixed

on a surface inclined at the same tilt angle

10-stage centrifugal surface pump driven by a

brushed PM dc motor

Experimental Set Up

Step-down dc-dc converter

470F link capacitance and 10kHz PWM frequency

Texas Instruments DSP based eZdsp kit used for

control and data acquisition

DSP used to provide flexibility

In a commercial product, a low cost microcontroller would

be more than adequate

Array installed on the roof of the New and

Renewable Energy Centre (NaREC) in

Northumberland.

Experimental System

1080 WpPV Array

DSP Based MPPT

PWMiPV

vPVvPV

CL470µF

Step Down DC-DC Converter

Motor-Pump Set

SelectorSwitch

Equivalent circuit of the PV pumping system setup

Circuit Diagram

Mismatch between motor-pump load and PV generator when pump is

connected directly to PV array; current-voltage curves

System Description

Mismatch between motor-pump load and PV generator when pump is

connected directly to PV array; power-voltage curves

0 1 2 3 4 5

Time (sec)

Voltage (

Array/Motor Current

Array/Motor Voltage

ψ = 736 W/m2, TC = 22.1 ºC

Experimental results showing array/motor voltage and current waveforms

Directly Connected DC PV pumping system

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Time (sec)

Speed (

Motor Speed Flow Rate

ψ = 736 W/m2, TC = 22.1 ºC

Motor speed and flow rate waveforms

Influence of solar irradiance and cell temperature on MPP location

Influence of solar irradiance and cell temperature on the energy utilization

Experimental system performance under slow changing irradiance

Experimental system performance under rapidly changing irradiance

Outline

• Introduction

• System Description

• Directly Connected PV Pumping Systems

• PV Pumping systems with MPPT

– Constant Voltage MPPT Algorithm

– Perturb and Observe (P&O) MPPT Algorithm

– Incremental Conductance (INC) MPPT Algorithm

• Conclusions

Block Diagram of Constant Voltage MPPT Algorithm

• The system performance is affected by:

– Vref

– KP and KI

Influence of solar irradiance and cell temperature on the energy utilization

ψ=8625W/m2 and TC=28.6˚C

Experimental results showing array voltage, current, and power waveforms

Experimental performance at nearly constant irradiance

Experimental performance at rapidly changing irradiance

Conclusions I

Directly connected PV pumping systems eliminate

the use of power electronics converters but suffer

from low energy utilization efficiency.

Simple constant voltage MPPT algorithm offers

significantly higher energy utilization efficiencies

(about 91%).

For more significant improvements in energy

utilization, more efficient MPPT control algorithms

that take into account the effects of insolation and

temperature variations on the MPP voltage would be

required.

Outline

• Introduction

• Conclusions

Perturb and Observe MPPT Algorithm

Flowchart of P&O MPPT Algorithm

Reference voltage control

Direct duty ratio control

Controller

System

Control

PVi PVi

System

Control

PVvPVv

PVi PVi

Block diagram of MPPT with reference voltage control

Block diagram of MPPT with direct duty ratio control

System performance is affected by:

Step Size (Δd or ΔVref)

Perturbation Frequency (fMPPT)

012345678

0 5 10 15 20 25 300

Time (sec)

=10V, fMPPT

Voltge (

=857.1W/m2, T

c=27.9

Measured Array Current

Calculated MPP Current

Measured Array Power

Calculated Maximum Power

Measured Array Voltage

Calculated MPP Voltage

Three-level operation with reference voltage perturbation

P&O Algorithm Parameters

0 20 40 60 80 100 120 140 160 180 2000

Array Voltage (V)

=857.1W/m2, Tc=27.9oC

Behavior with reference voltage perturbation in thee-level operation

Voltage (

=946.3W/m2, T

0200400600800

0 5 10 15 20 25 300

Time (sec)

Ratio (

d=5%, fMPPT

Measured Array Current

Calculated MPP Current

Measured Array Power

Calculated Maximum Power

Duty Ratio

Optimum Duty Ratio

Three-level operation with direct duty ratio perturbation

=973.2W/m2, T

c=42.5

d=2%, fMPPT

0 5 10 15 20 25 300

Time (sec)

=860.1W/m2, T

c=31.8

d=2%, fMPPT

The effect of algorithm parameters on the array voltage; P&O MPPT

algorithm with direct duty ratio perturbation

Effect of P&O Algorithm Parameters

=760.3W/m2, T

ref=2V, f

MPPT=1Hz

0 5 10 15 20 25 300

=938.6W/m2, T

c=27.6

=2V, fMPPT

Time (sec)

Experimental results showing the effect of algorithm parameters on the

array voltage; P&O MPPT algorithm with reference voltage perturbation

=889.1W/m2, T

c=41.3

d=5%, fMPPT

0 1 2 3 4 5 6 755

Time (sec)

Confusion due to system

dynamics

Confusion due to branch

disconnection

Experimental results showing the system responses to a PV array

branch disconnection (Δd=5%, fMPPT=4Hz)

Energy Utilization with P&O Algorithm

=2V, fMPPT

0 200 400 600 800 1000 1200012345678

Time (sec)

Experimental system performance under slow changing irradiance; P&O

algorithm with reference voltage perturbation (ΔV=2V and fMPPT=5Hz)

oltage (

=5V, fMPPT

0 200 400 600 800 1000 12000

Time (sec)

Experimental system performance under rapidly changing irradiance;

P&O algorithm with reference voltage perturbation

0 200 400 600 800 1000 12000

Time (sec)

d=2%, fMPPT

200 400 600 800 1000150

Experimental system performance under slow changing irradiance;

direct duty ratio perturbation

oltage (

d=2%, fMPPT

0 200 400 600 800 1000 12000

Time (sec)

Conclusions II

The P&O MPPT algorithm is a simple algorithm that

does not require previous knowledge of the PV

generator characteristics or the measurement of

solar intensity and cell temperature.

Two approaches for implementing the P&O

algorithm have been investigated; reference voltage

perturbation and direct duty ratio perturbation.

Conclusions II

With reference voltage perturbation, the system has a faster

transient response to irradiance and temperature

transients.

However, stability is lost if the MPPT algorithm is operated at

high perturbation rates or if low pass filters are used to reject

noise from the array current and voltage feedback signals.

Conclusions II

• Direct duty ratio control offers better stability characteristics

and higher energy utilization efficiency at a slower transient

response and worse performance at rapidly changing

irradiance.

• Noise has significant impact on the algorithm

performance, especially with low step sizes where

the system response to noise is comparable to that

of MPPT perturbations.

Outline

• Introduction

• Conclusions

0 50 100 150 200 250 3000

Voltage (V)

1000 W/m2, 60C

Power-Voltage Curve of a PV Generator

Incremental Conductance MPPT Algorithm

0 50 100 150 200 250 3000

Voltage (V)

1000 W/m2, 60C

Power-Voltage Curve of a PV Generator

Reference voltage for the array output voltage

Converter duty ratio

Controller

System

Control

PVi PVi

System

Control

PVvPVv

PVi PVi

Block diagram of MPPT with reference voltage control

Block diagram of MPPT with direct duty ratio control

The system performance is affected by:

Step Size (Δd or ΔVref)

Perturbation Frequency (fMPPT)

Three-level operation with reference voltage perturbation

INC Algorithm Parameters

Three-level operation with direct duty ratio perturbation

The effect of algorithm parameters on the array voltage; INC MPPT

algorithm with direct duty ratio perturbation

The effect of algorithm parameters on the array voltage; INC MPPT

algorithm with reference voltage perturbation

The effect of noise on the decision of the INC algorithm; reference

voltage perturbation

Experimental results showing the system responses to a PV array

branch disconnection (Δd=2%, fMPPT=10Hz)

Energy Utilization with INC Algorithm

reference voltage perturbation (ΔV=2V and fMPPT=5Hz)

97.6% ΔVref=5V and fMPPT=5Hz

reference voltage perturbation

94.9% ΔVref=5V and fMPPT=5Hz

98.5% Δd=2% and fMPPT=10Hz

96.8% Δd=2% and fMPPT=10Hz

The INC algorithm is less confused by noise and system

dynamics compared to the P&O algorithm. However, contrary

to general perceptions, it was found to exhibit worse confusion

than the P&O algorithm in rapidly changing weather

conditions.

Both algorithms offer high energy utilization

efficiencies of up to 99% depending on weather

conditions. The efficiency is marginally lower for

rapidly changing irradiance due to the energy loss

during the confusion and recovery periods.

Conclusions III

M. A. Elgendy, B. Zahawi and D. J. Atkinson,

“Comparison of Directly Connected and Constant

Voltage Controlled Photovoltaic Pumping Systems,”

IEEE Transactions on Sustainable Energy, Vol. 1, No.

3, pp. 184-192, Oct. 2010

M. A. Elgendy, B. Zahawi and D. J. Atkinson,

“Assessment of Perturb and Observe MPPT

Algorithm Implementation Techniques for PV

Pumping Applications,” IEEE Transactions on

Sustainable Energy, Vol. 3, No. 1, pp. 21-33, Jan. 2012

More Details

Thank you

Bashar Zahawi

E-mail: bashar.zahawi@ncl.ac.uk

Low Cost MPPT Algorithms for PV Application: PV Pumping ... · PDF fileLow Cost MPPT...

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