Grid Connected Solar PV and Battery Energy Storage System with P&O MPPT

The integration of solar photovoltaic (PV) systems with battery energy storage and grid connectivity plays a crucial role in modern power systems. This blog explores a MATLAB/Simulink-based simulation model of a grid-connected solar PV system integrated with battery storage, focusing on the Perturb and Observe (P&O) MPPT algorithm for maximum power point tracking.

Overview of the System

The system comprises three main components:

• Solar PV Array

• Battery Energy Storage System (BESS)

• Single-Phase Grid

These are connected via a common DC bus, maintained at a constant 400V to ensure proper power flow and energy balance. Power flows in multiple directions:

• PV to Battery

• PV to Grid

• Battery to Grid

• Battery to DC Bus

Maintaining a stable DC bus voltage is essential to enable these power exchanges efficiently.

Solar PV Array Configuration

The solar array is configured with:

• 8 panels in series

• Each panel rated at 250W

• Open Circuit Voltage (Voc): 37.3V

• Short Circuit Current (Isc): 8.66A

• Voltage at Maximum Power Point (Vmpp): 30.67V

• Current at Maximum Power Point (Impp): 8.15A

The system’s behavior is analyzed under varying irradiance conditions (1000, 800, 600, and 400 W/m²) at 25°C. IV and PV characteristics confirm that the peak power point changes with irradiation, emphasizing the need for a maximum power point tracking (MPPT) algorithm.

Need for Maximum Power Point Tracking (MPPT)

Operating the PV system at its maximum power point ensures optimal power extraction. If the operating point is not aligned with the peak power point, a significant portion of energy goes unutilized. This mismatch makes the MPPT algorithm essential.

Perturb and Observe (P&O) MPPT Algorithm

The system uses a conventional Perturb & Observe (P&O) MPPT algorithm. The algorithm works by perturbing the operating voltage and observing the effect on power output. Based on the sign and magnitude of changes in voltage and power, the algorithm decides whether to increase or decrease the duty cycle of the DC-DC converter.

Four Key Conditions in P&O:

1. Voltage and Power both decreasing → Increase voltage

2. Voltage and Power both increasing → Increase voltage

3. Voltage increasing and Power decreasing → Decrease voltage

4. Voltage decreasing and Power increasing → Decrease voltage

These conditions help guide the operating point towards the maximum power point. The output of the P&O algorithm is a duty cycle, which is used in a PWM generator to control the converter.

Duty Cycle Management

The duty cycle is managed within predefined limits:

• Initial Duty Cycle

• Maximum Duty Cycle

• Minimum Duty Cycle

• Delta Duty Cycle (step size)

This ensures the system responds appropriately to irradiance and temperature changes without exceeding operational limits.

Battery Energy Storage System

The battery is rated at:

• Nominal Voltage: 240V

• Capacity: 40Ah

• Initial SOC: Configurable (e.g., 50%, 90%, 100%)

The battery charges when there is surplus PV power and discharges to supply the load or inject power into the grid during low PV generation (e.g., at night).

Bidirectional Converter for Battery

A bidirectional DC-DC converter is used to manage power flow between the battery and the DC bus. The converter is controlled using a voltage control strategy:

• The DC bus voltage is measured and compared to the 400V reference.

• The error is processed using a PI controller, generating the duty cycle.

• The PWM generator uses this duty cycle to control the converter.

Grid Integration via Inverter

The system uses a grid-tied inverter to synchronize and transfer power between the DC bus and the grid. This inverter operates bidirectionally:

• Sends power from PV/Battery to the grid

• Draws power from the grid to charge the battery or supply loads

PLL (Phase-Locked Loop) is used for synchronization, filtering harmonics, and generating the reference signals.

Control Strategy for Grid Inverter

A current control method is employed:

• Two states are considered: To Grid and From Grid

• A reference current is generated based on the desired power flow direction

  • Example: A negative reference current (e.g., -10A peak) means power is being drawn from the grid

These references are used to control the inverter current via appropriate modulation techniques.

Conclusion

This MATLAB/Simulink model illustrates the dynamic interaction between solar PV, battery storage, and grid connectivity. The use of the P&O MPPT algorithm ensures optimal solar energy extraction, while the battery and inverter control strategies enable flexible and intelligent power flow management. This system is a strong example of how renewable energy resources can be efficiently integrated into modern power systems.