Low Cost MPPT Algorithms for PV Application: PV Pumping Case Study. M. A. Elgendy, B. Zahawi and D. J. Atkinson. Presented by:

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 motor 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 MPP 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

PV Array Current-Voltage Curves 1000 W/m 2 800 W/m 2 600 W/m 2 400 W/m 2 200 W/m 2 Maximum power line PV array current-voltage curves Mismatch between resistive load and PV Source; current voltage curves

PV Array Power-Voltage Curves PV array current-voltage curves Load line Maximum power line Mismatch between resistive load and PV Source; power voltage curves

MPPT Circuit I PV S L I L PV generator V PV C L C V L R L V PV I PV Duty Ratio DSP, interface, and driver circuits 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 470 F 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

Circuit Diagram II I 1080 Wp PV Array SS Selector Switch i PV v PV PWM i PV DSP Based v PV MPPT C L 470µF Step Down DC-DC Converter ai R a L a v a e b Motor-Pump Set B T e J T P Equivalent circuit of the PV pumping system setup

System Description 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

Voltage (V) Current (A) Directly Connected DC PV pumping system 220 200 180 160 140 120 100 80 60 40 20 0 Array/Motor Current Array/Motor Voltage ψ = 736 W/m 2, T C = 22.1 ºC 0 1 2 3 4 5 Time (sec) 7 6 5 4 3 2 1 0 Experimental results showing array/motor voltage and current waveforms

Speed (rad/sec) Flow Rate (l/min) Directly Connected DC PV pumping system 300 60 250 Motor Speed Flow Rate 50 200 40 150 30 100 ψ = 736 W/m 2, T C = 22.1 ºC 20 50 10 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 Time (sec) 0 Motor speed and flow rate waveforms

Directly Connected DC PV pumping system Influence of solar irradiance and cell temperature on MPP location

Directly Connected DC PV pumping system Influence of solar irradiance and cell temperature on the energy utilization

Directly Connected DC PV pumping system 62.7% Experimental system performance under slow changing irradiance

Directly Connected DC PV pumping system 51.3% 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

Constant Voltage MPPT Algorithm The system performance is affected by: V ref K P and K I Block Diagram of Constant Voltage MPPT Algorithm

Constant Voltage MPPT Algorithm Influence of solar irradiance and cell temperature on the energy utilization

Constant Voltage MPPT Algorithm ψ=8625w/m 2 and T C =28.6 C Experimental results showing array voltage, current, and power waveforms

Constant Voltage MPPT Algorithm 91.3% Experimental performance at nearly constant irradiance

Constant Voltage MPPT Algorithm 91.1% 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.

Perturb and Observe MPPT Algorithm Flowchart of P&O MPPT Algorithm

Perturb and Observe MPPT Algorithm Reference voltage control ipv v PV MPPT Control v ref - + PI Controller d PV System ipv v PV v PV Block diagram of MPPT with reference voltage control Direct duty ratio control ipv v PV MPPT Control d PV System ipv v PV Block diagram of MPPT with direct duty ratio control

Perturb and Observe MPPT Algorithm System performance is affected by: Step Size (Δd or ΔV ref ) Perturbation Frequency (f MPPT )

Power (W) Current (A) Voltge (V) P&O Algorithm Parameters 200 160 120 80 40 0 8 7 6 5 4 3 2 1 0 1000 800 =857.1W/m 2, T c =27.9 o C Measured Array Voltage Calculated MPP Voltage Measured Array Current Calculated MPP Current 600 V 400 ref =10V, f MPPT =1Hz 200 Measured Array Power Calculated Maximum Power 0 0 5 10 15 20 25 30 Time (sec) Three-level operation with reference voltage perturbation

Array Power (W) P&O Algorithm Parameters 1000 900 D C O A 800 700 =857.1W/m 2, T c =27.9 o C B 600 500 400 300 200 100 0 0 20 40 60 80 100 120 140 160 180 200 Array Voltage (V) Behavior with reference voltage perturbation in thee-level operation

Duty Ratio (%) Power (W) Current (A) Voltage (V) P&O Algorithm Parameters 200 160 120 80 40 0 8 6 4 2 0 1000 800 600 400 200 0 100 80 60 40 20 0 =946.3W/m 2, T c =43 o C d=5%, f MPPT =1Hz Measured Array Voltage Calculated MPP Voltage Measured Array Current Calculated MPP Current Measured Array Power Calculated Maximum Power Duty Ratio Optimum Duty Ratio 0 5 10 15 20 25 30 Time (sec) Three-level operation with direct duty ratio perturbation

Voltage(V) Voltage (V) Effect of P&O Algorithm Parameters 200 160 120 80 40 0 200 160 =973.2W/m 2, T c =42.5 o C d=2%, f MPPT =1Hz Measured Array Voltage Calculated MPP Voltage 120 80 =860.1W/m 2, T c =31.8 o C d=2%, f MPPT =10Hz 40 Measured Array Voltage Calculated MPP Voltage 0 0 5 10 15 20 25 30 Time (sec) The effect of algorithm parameters on the array voltage; P&O MPPT algorithm with direct duty ratio perturbation

Voltage (V) Voltage (V) P&O Algorithm Parameters 200 160 120 80 40 0 200 160 =760.3W/m 2, T c =26 o C V ref =2V, f MPPT =1Hz Measured Array Voltage Calculated MPP Voltage 120 80 =938.6W/m 2, T c =27.6 o C V ref =2V, f MPPT =10Hz 40 Measured Array Voltage Calculated MPP Voltage 0 0 5 10 15 20 25 30 Time (sec) Experimental results showing the effect of algorithm parameters on the array voltage; P&O MPPT algorithm with reference voltage perturbation

Duty Ratio (%) Array Current (A) Array Voltage (V) P&O Algorithm Parameters 160 140 120 100 =889.1W/m 2, T c =41.3 o C 8 6 d=5%, f MPPT =4Hz 4 2 95 85 75 65 Confusion due to branch disconnection Confusion due to system dynamics 55 0 1 2 3 4 5 6 7 Time (sec) Experimental results showing the system responses to a PV array branch disconnection (Δd=5%, fmppt=4hz)

Array Current (A) Array Voltage (V) Solar Irradiance (W/m 2 ) Energy Utilization with P&O Algorithm 1200 1000 800 600 400 200 0 200 160 120 80 40 V ref =2V, f MPPT =5Hz 0 8 7 6 5 4 3 2 1 0 0 200 400 600 800 1000 1200 Time (sec) 97.2% Experimental system performance under slow changing irradiance; P&O algorithm with reference voltage perturbation (ΔV=2V and f MPPT =5Hz)

Array Current (A) Array Voltage (V) Solar Irradiance (W/m 2 ) Energy Utilization with P&O Algorithm 1200 1000 800 600 400 200 0 200 160 120 80 40 0 10 V ref =5V, f MPPT =5Hz 97% 5 0 0 200 400 600 800 1000 1200 Time (sec) Experimental system performance under rapidly changing irradiance; P&O algorithm with reference voltage perturbation

Array Current (A) Array Voltage (V) Solar Irradiance (W/m 2 ) Energy Utilization with P&O Algorithm 1200 1000 800 600 400 200 0 200 150 100 50 0 8 6 4 2 170 160 150 200 400 600 800 1000 d=2%, f MPPT =10Hz 99% 0 0 200 400 600 800 1000 1200 Time (sec) Experimental system performance under slow changing irradiance; direct duty ratio perturbation

Array Current (A) Array Voltage (V) Solar Irradiance (W/m 2 ) Energy Utilization with P&O Algorithm 1200 1000 800 600 400 200 0 200 150 100 50 0 8 6 4 2 d=2%, f MPPT =10Hz 97.9% 0 0 200 400 600 800 1000 1200 Time (sec) Experimental system performance under rapidly changing irradiance; direct duty ratio perturbation

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.

Power (W) Incremental Conductance MPPT Algorithm 1000 1000 W/m2, 60C 800 600 400 dp dv 0 dp dv 0 200 dp dv 0 0 0 50 100 150 200 250 300 Voltage (V) Power-Voltage Curve of a PV Generator

Power (W) Incremental Conductance MPPT Algorithm 1000 1000 W/m2, 60C 800 600 di dv I V dp 0 dv di dv dp 0 dv I V 400 200 di dp I 0 dv V 0 0 50 100 150 200 250 300 Voltage (V) Power-Voltage Curve of a PV Generator

Incremental Conductance MPPT Algorithm Reference voltage for the array output voltage ipv v PV MPPT Control v ref - + PI Controller d PV System ipv v PV v PV Block diagram of MPPT with reference voltage control Converter duty ratio ipv v PV MPPT Control d PV System ipv v PV Block diagram of MPPT with direct duty ratio control

Incremental Conductance MPPT Algorithm The system performance is affected by: Step Size (Δd or ΔV ref ) Perturbation Frequency (f MPPT )

INC Algorithm Parameters Three-level operation with reference voltage perturbation

INC Algorithm Parameters Three-level operation with direct duty ratio perturbation

INC Algorithm Parameters The effect of algorithm parameters on the array voltage; INC MPPT algorithm with direct duty ratio perturbation

INC Algorithm Parameters The effect of algorithm parameters on the array voltage; INC MPPT algorithm with reference voltage perturbation

INC Algorithm Parameters The effect of noise on the decision of the INC algorithm; reference voltage perturbation

INC Algorithm Parameters Experimental results showing the system responses to a PV array branch disconnection (Δd=2%, f MPPT =10Hz)

Energy Utilization with INC Algorithm ΔV ref =5V and f MPPT =5Hz 97.6% Experimental system performance under slow changing irradiance; reference voltage perturbation (ΔV=2V and f MPPT =5Hz)

Energy Utilization with INC Algorithm ΔV ref =5V and f MPPT =5Hz 94.9% Experimental system performance under rapidly changing irradiance; reference voltage perturbation

Energy Utilization with INC Algorithm Δd=2% and f MPPT =10Hz 98.5% Experimental system performance under slow changing irradiance; direct duty ratio perturbation

Energy Utilization with INC Algorithm Δd=2% and f MPPT =10Hz 96.8% Experimental system performance under rapidly changing irradiance; direct duty ratio perturbation

Conclusions III 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.

More Details 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

Thank you Bashar Zahawi E-mail: bashar.zahawi@ncl.ac.uk