Comparative Study of P&O vs. INC MPPT for Solar PV

Publication Details

  • Article: “A Comparative Study of Perturb and Observe (P&O) and Incremental Conductance (INC) PV MPPT Techniques at Different Radiation and Temperature Conditions.”

  • Source: Engineering and Technology Journal, Vol. 40, No. 02, 2022.

  • Authors: Marwan E. Ahmad, Ali H. Numan, Dhari Y. Mahmood (University of Technology-Iraq).

Highlights

  • The main challenge for PV panels is extracting maximum power under varying solar radiation and temperature.

  • This study performs a comparative MATLAB/Simulink analysis of two common MPPT algorithms: Perturb & Observe (P&O) and Incremental Conductance (INC).

  • A boost converter is used to step-up PV voltage via duty-cycle $D$ control.

  • P&O works acceptably under Standard Test Conditions (STC) but suffers from oscillations in dynamic environments.

  • INC shows faster convergence, higher accuracy, and reduced oscillation during irradiance/temperature changes.

Global Context & Motivation

  • Growing global electricity demand and reliance on fossil fuels highlight the need for renewable energy like solar PV.

  • PV's low efficiency and strong dependence on irradiance (GG) and temperature (TT) cause shifts in I-V & P-V characteristics, necessitating Maximum Power Point Tracking (MPPT).

Solar-Cell / PV-Array Fundamentals

  • PV cells generate low voltage, typically aggregated in series/parallel. The single-diode model describes cell behavior.

  • The study utilized a 17 kW array (2 series × 28 parallel SunPower SPR-305-WHT panels).

  • Characteristic curves show that lower irradiance shifts the MPP downward and leftward, while higher temperature lowers $V_{oc}$.

Maximum Power Point Tracking (MPPT) – Generalities

  • A PV array has a unique Maximum Power Point (MPP) that non-linearly depends on solar irradiance and cell temperature.

  • MPPT controllers adjust the converter's duty-cycle to keep the PV operating at its MPP.

Perturb & Observe (P&O) Algorithm

  • Core Idea: Periodically perturb voltage (or current) and observe the change in power (ΔP\Delta P).

    • If \Delta P/\Delta V > 0, increase $V$; if \Delta P/\Delta V < 0, decrease $V$.

  • Pros: Simple, low computational burden, no explicit PV parameters needed.

  • Cons: Inevitable oscillations around MPP, potential for incorrect tracking under rapid changes, step-size trade-off.

Incremental Conductance (INC) Algorithm

  • Mathematical Basis: At MPP, $dP/dV = 0 \Rightarrow dI/dV = -I/V$.

  • Implementation: Compares incremental conductance ΔI/ΔV\Delta I/\Delta V to instantaneous conductance −I/V-I/V to adjust voltage.

  • Pros (over P&O): Faster and more accurate MPP localization, smaller steady-state oscillations, better at distinguishing environmental changes.

  • Cons: Slightly higher computational and sensing complexity.

Boost Converter Fundamentals

  • A boost converter is a DC–DC converter used to step-up voltage, matching the PV output to the load.

  • Key components: inductor, switch (MOSFET/IGBT), diode, capacitor, load.

  • Continuous-Conduction-Mode (CCM) voltage gain: M<em>v=V</em>o/Vs=1/(1−D)M<em>v = V</em>o/V_s = 1/(1-D).

  • Design equations are provided for minimum inductor (L<em>minL<em>{min}) and output capacitor (C</em>minC</em>{min}) sizing.

Simulation Configuration (MATLAB/Simulink)

  • The simulation used a PV array (17 kW), boost converter, and switchable MPPT block (P&O/INC) with a resistive load.

  • Scenarios assessed:

    1. Scenario I – STC: G=1000 W/m2,T=25∘CG=1000\text{ W/m}^2, T=25^{\circ}\text{C}.

    2. Scenario II – Dynamic/Partial-Shading: Step changes in irradiance and temperature over 2 seconds.

Results Synopsis
Scenario I – STC

  • P&O: Rapid initial convergence but persistent oscillatory duty-cycle and power ripple.

  • INC: Slightly slower initial lock, but significantly reduced duty-cycle ripple leading to a smoother $P_{PV}$ plateau and superior stability.

Scenario II – Dynamic Conditions

  • P&O: Struggles with irradiance changes, increased oscillations, and slower MPP re-establishment.

  • INC: Tracks new MPP swiftly with minimal overshoot, maintaining higher average power and smoother duty-cycle adjustments.

Practical, Ethical & System-Level Implications

  • Higher MPPT efficacy increases energy yield, reduces Levelised Cost of Electricity (LCOE), and lowers carbon footprint.

  • Reduced oscillations prolong converter lifespan and improve micro-grid stability, especially under partial shading.

Conclusions

  • Both P&O and INC find the MPP.

  • P&O: Better for steady conditions, but poor with rapid environmental changes due to oscillation and sluggishness.

  • INC: Superior overall due to faster convergence, lower steady-state error, and robustness against irradiance/temperature swings.

  • Recommendation: INC (or enhanced variants) is recommended for real-world PV installations with variable environmental conditions.

Key Equations Reference List

  • Key equations for PV-cell current, PV power derivative, MPP condition, boost