Solar PV systemMPP Tracking techniques

Presented by: Piyush Agarwal CE16M107Rakesh Kumar Yadav CE16M109

Why Solar power ??• Limited conventional natural

resource like coal, petroleum & natural gas• Greenhouse gas levels are

increasing drastically. • Global warming and ozone layer

depletion• Little maintenance required

India China Germany United States Japan Others0

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India; 1954

China; 8206

Germany; 755

United States; 5074

Japan; 1223

Others; 14522

CO2 emission in million tons

Factors affecting PV generation• PV cell can convert 12%-19% sunlight energy into electricity• Dirt and shadow losses is around 8%• Module losses around 50%• System losses (cables and inverter) of around 5 %• Module losses around 50%• Overall efficiency is around 16%

Modeling of photovoltaic cell

The power output can be calculated as P=V*I.Voltage at the maximum power point can be calculated as

PV cell characteristics

Block Diagram of a typical photovoltaic system

Boost converterWhen a direct connection is carried out between the source and the load, the output of the PV module is irregularly shifted away from the maximum power point. It is necessary to overcome this problem, so we have added one adaptation circuit between the source and the load. And a MPPT controller circuit with a DC-DC converter circuit is used as an adaptive circuit.

Functions• Blocking Diodes-facilitates the array generated power to flow only

towards the power conditioner• the charge -discharge controller is responsible for

preventing overcharging or over discharging of the battery bank• battery bank is required to store electricity generated by the solar

energy to use during sunless time.• MPPT is used to maximize the power output.• Inverter is used to convert dc power to ac power to be supplied in the

grid and for local loads.

MPPT• An algorithm used for extracting maximum available power from PV

module under certain conditions. • Voltage at which PV module can produce maximum power is called

'maximum power point‘.• MPP changes with temperature and intensity of light, so tracking is

required.• MPPT gives triggering signal to the DC-DC boost controller .

Perturbation & Observation Algorithm

• the module voltage is periodically given a perturbation and the corresponding output power is compared with that at the previous perturbing cycle.

• With the perturbation, power can either be increased or decreased.

• Simplest method of power tracking

• Sampled voltage and current value is used to calculate power.

P&O Disadvantages1. During rapidly changing irradiation, it is possible for the

classic P & O algorithm to get confused and track the MPP inthe wrong direction

2. At steady state, the operating point oscillates around the MPP voltage giving rise to the waste of some amount of available energy.

3. Poor efficiency at low irradiation.4. Small step size increase efficiency but reduces speed.5. Perturbation size must be sufficient to prevent system to be affected by

measurement noise

P&O Disadvantages1. Changing irradiation

Starting from an operating point A, if atmospheric conditions stay approximately constant, If the irradiance increases and shifts the power curve from P1 to P2 within one sampling period, the operating point will move from A to C.

P&O Disadvantages2. Oscillations about MPP

Oscillation-

Case 1

P&O Disadvantages2. Oscillations about MPP

Case 2

Improved P&O• Variable step size should be implemented to increase efficiency and speed simultaneously.• When the system starts up and environment varies, constant step size is used to firstly to make

the working point close to the MPP stably, then oscillations near MPP and misjudgements during environmental varies would be solved by variable step P&O method.

• The principle of constant voltage method is based on the near linear relationship Vm = K*Voc

where K is between 0.71-0.78, determined by PV system parameters.

• The smaller dp/dv is , the nearer working point is to the MPP. • If dp/dv < 0, the operating point is to the right of MPP and vice versa.• The steps are not equal on the left and right sides of MPP where their powers are equal, the left

step is larger than the right. • b and a (b>a) are step proportionality coefficients on left and right sides of MPP

Improved P&O

Simulation result

1000 w/m2

1200 w/m2

1200 w/m2

1000 w/m2

Fixed Step

Variable Step

Inferences-• Startup time reduces• improve the speed of system response

when the irradiance changes suddenly

Incremental Conductance MethodSearches for the voltage operating point at which the conductance is equal to the incremental conductance . Once MPPT is reached, it stops oscillating

Improved InCnd

• The direction of perturbation embedded in the variable step-size Vstep itself, therefore the flowchart of the variable step-size INC algorithm is more concise than the fixed step-size one.

• The acceleration factor β , should be a small positive number near to zero.

• A change in indicates a change in atmosphericconditions.

Inferences• Automatically adjusts the step

size according to the operating point of the PV array.

• When the operating point is far from the MPP of the PV array, the step size is great and the operating point of the PV array approaches quickly to the MPP and vice versa.

Improved InCnd

ComparisonP & O Incremental Conductance

Cannot track MPP in fast varying environmental conditions

It can track MPP in fast varying environmental conditions.

Oscillates about the MPP which results in power loss.

Once it has reached the MPP and it stops perturbing the operating point.

Simple to implement Increased hardware and software complexity

Less computation is required and hence is fast

Increased computation times which slows down sampling rate

References

• Comparison of Photovoltaic Array Maximum Power Point TrackingTechniquesTrishan Esram; Patrick L. Chapman IEEE Transactions on Energy ConversionYear: 2007, Volume: 22, Issue: 2

• A variable step-size P&O method in the application of MPPT control for a PV system XuYang Zhang; HuaGuang Zhang; HanQing Zhang; PengQiao Zhang; Feng Wang; Hong Jia; DeYu Song 2016 IEEE Advanced Information Management, Communicates, Electronic and Automation Control Conference (IMCEC)Year: 2016

• Analysis and Improvement of Maximum Power Point Tracking AlgorithmBased on Incremental Conductance Method for Photovoltaic Array Bangyin Liu; Shanxu Duan; Fei Liu; Pengwei Xu 2007 7th International Conference on Power Electronics and Drive SystemsYear: 2007

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