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

Transcription

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

2 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

3 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

4 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

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

6 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

7 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

8 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

9 Hill Climbing MPPT

10 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

11 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

12 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

13 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.

14 Experimental System

15 Experimental System

16 Experimental System

17 Experimental System

18 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

19 System Description Mismatch between motor-pump load and PV generator when pump is connected directly to PV array; current-voltage curves

20 System Description Mismatch between motor-pump load and PV generator when pump is connected directly to PV array; power-voltage curves

21 Voltage (V) Current (A) Directly Connected DC PV pumping system Array/Motor Current Array/Motor Voltage ψ = 736 W/m 2, T C = 22.1 ºC Time (sec) Experimental results showing array/motor voltage and current waveforms

22 Speed (rad/sec) Flow Rate (l/min) Directly Connected DC PV pumping system Motor Speed Flow Rate ψ = 736 W/m 2, T C = 22.1 ºC Time (sec) 0 Motor speed and flow rate waveforms

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

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

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

26 Directly Connected DC PV pumping system 51.3% Experimental system performance under rapidly changing irradiance

27 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

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

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

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

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

32 Constant Voltage MPPT Algorithm 91.1% Experimental performance at rapidly changing irradiance

33 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.

34 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

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

36 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

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

38 Power (W) Current (A) Voltge (V) P&O Algorithm Parameters =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 Time (sec) Three-level operation with reference voltage perturbation

39 Array Power (W) P&O Algorithm Parameters D C O A =857.1W/m 2, T c =27.9 o C B Array Voltage (V) Behavior with reference voltage perturbation in thee-level operation

40 Duty Ratio (%) Power (W) Current (A) Voltage (V) P&O Algorithm Parameters =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 Time (sec) Three-level operation with direct duty ratio perturbation

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

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

43 Duty Ratio (%) Array Current (A) Array Voltage (V) P&O Algorithm Parameters =889.1W/m 2, T c =41.3 o C 8 6 d=5%, f MPPT =4Hz Confusion due to branch disconnection Confusion due to system dynamics Time (sec) Experimental results showing the system responses to a PV array branch disconnection (Δd=5%, fmppt=4hz)

44 Array Current (A) Array Voltage (V) Solar Irradiance (W/m 2 ) Energy Utilization with P&O Algorithm V ref =2V, f MPPT =5Hz Time (sec) 97.2% Experimental system performance under slow changing irradiance; P&O algorithm with reference voltage perturbation (ΔV=2V and f MPPT =5Hz)

45 Array Current (A) Array Voltage (V) Solar Irradiance (W/m 2 ) Energy Utilization with P&O Algorithm V ref =5V, f MPPT =5Hz 97% Time (sec) Experimental system performance under rapidly changing irradiance; P&O algorithm with reference voltage perturbation

46 Array Current (A) Array Voltage (V) Solar Irradiance (W/m 2 ) Energy Utilization with P&O Algorithm d=2%, f MPPT =10Hz 99% Time (sec) Experimental system performance under slow changing irradiance; direct duty ratio perturbation

47 Array Current (A) Array Voltage (V) Solar Irradiance (W/m 2 ) Energy Utilization with P&O Algorithm d=2%, f MPPT =10Hz 97.9% Time (sec) Experimental system performance under rapidly changing irradiance; direct duty ratio perturbation

48 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.

49 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.

50 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.

51 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

52 Power (W) Incremental Conductance MPPT Algorithm W/m2, 60C dp dv 0 dp dv dp dv Voltage (V) Power-Voltage Curve of a PV Generator

53 Power (W) Incremental Conductance MPPT Algorithm W/m2, 60C di dv I V dp 0 dv di dv dp 0 dv I V di dp I 0 dv V Voltage (V) Power-Voltage Curve of a PV Generator

54 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

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

56 INC Algorithm Parameters Three-level operation with reference voltage perturbation

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

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

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

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

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

62 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)

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

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

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

66 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.

67 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 , Oct 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 , Jan. 2012

68 Thank you Bashar Zahawi