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MATLAB Simulation of a 15 kW Off-Grid PV Battery System

Writer's picture: LMS RSLMS RS

MATLAB Simulation of a 15 kW Off-Grid PV Battery System

1. Overview of the PV Array and System Components

The heart of the off-grid system is the photovoltaic (PV) array. Each panel in this system has a power rating of 193 watts, with a voltage of 28.94 V and a current of 6.68 A. The system comprises 3 strings, each with 26 panels in series, making it a robust array capable of generating substantial power.

Under standard conditions of 1000 W/m² solar radiation, the array is designed to produce approximately 15.08 kW of power at 72.4 V. This energy is crucial for powering the connected battery storage system and supplying loads.

2. Battery Storage and Power Conversion

The energy generated by the PV array is stored in a battery system. In this simulation, a 42-battery configuration is used, with each battery rated at 12 V. These batteries are connected in series to achieve a combined voltage of 54 V. The battery has a rated capacity of 200 Ah, providing significant storage capacity.

To connect the PV array to the battery, a BU converter is employed. This converter steps down the voltage from the PV array, which is 750 V, to the battery’s voltage of 54 V. The BU converter also ensures efficient power extraction from the PV system by maintaining optimal performance as energy is transferred to the battery.

3. Control Logic and System Operation

The system's control logic is central to its operation. A charger controller regulates the charging process by continuously monitoring the PV voltage and current. Based on these measurements, the controller generates the necessary duty cycle to control the BU converter, ensuring efficient energy transfer to the battery.

The system also includes a circuit breaker that automatically disconnects the PV array when the power output falls below 300 W or when the PV voltage drops below 50 V. This feature protects the system and ensures stable operation.

During the day, the PV array is connected to the battery, providing charging and powering DC loads. At night, when solar energy is unavailable, the PV array is disconnected, and the battery continues to supply both AC and DC loads.

4. Powering AC and DC Loads

The system is designed to power both AC and DC loads, making it versatile for various applications. DC loads, such as LED lights and other small appliances, are powered directly from the battery. The DC energy is then converted to AC using an inverter, which supplies power to typical household appliances, including refrigerators, washing machines, air conditioners, and more.

The inverter in the system is a single-phase inverter, designed to convert DC energy into AC energy at a 60 Hz frequency. It works in coordination with a control system that adjusts the inverter's operation based on the load demands and energy availability.

5. Real-Time Simulation and Performance Monitoring

One of the key features of this simulation is its ability to replicate real-time changes in solar radiation and their effects on system performance. The irradiation levels are varied from 0 to 1000 W/m², simulating real-world conditions.

The simulation continuously monitors various system parameters, including PV voltage, PV current, battery voltage, battery current, AC load voltage, and DC load voltage. These values are measured and adjusted in real time, providing insights into how the system responds to changes in solar radiation and power demand.

6. Dynamic Charging and Discharging Cycle

As solar radiation fluctuates throughout the day, the battery alternates between charging and discharging modes. In the morning, when solar power is minimal or absent, the battery supplies energy to the DC and AC loads. As the sun rises and the PV system starts generating power, the battery switches to charging mode, storing excess energy for later use.

During the day, when the PV array generates more power than the loads require, the excess energy is used to charge the battery. As solar radiation decreases in the evening, the battery once again takes over to supply the system, ensuring uninterrupted power for the loads.

7. Conclusion: A Reliable Off-Grid Power System

This MATLAB simulation provides a detailed view of how a 15 kW off-grid PV battery system can efficiently manage power generation, storage, and distribution to meet the needs of both AC and DC loads. By integrating solar energy with a battery storage solution, this system ensures reliable power delivery, regardless of time of day or fluctuating weather conditions.

The dynamic nature of the system, where power from the PV array is continually adjusted based on radiation levels, demonstrates the importance of real-time monitoring and control in off-grid systems. This simulation can be a valuable tool for designing, optimizing, and analyzing renewable energy systems in off-grid applications.

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