MATLAB Simulation of 15 kW OFF Grid PV Battery System
PV Array Specifications
The system begins with a PV array, which is the primary energy source for the off-grid system. The array comprises individual panels with the following specifications:
Panel Power Rating: 193 W
Voltage: 28.94 V
Current: 6.68 A
The array uses a total of 3 strings, with each string containing 26 panels in series, making it capable of producing a total power of 15.08 kW at standard conditions of 1000 W/m².
The voltage from the PV array is stepped down via a BU converter to match the battery voltage.
BU Converter and Battery Configuration
The voltage from the PV array (750 V) is converted to the battery voltage (54 V) using a BU converter. The system uses a 42 x 12 battery configuration to achieve the required voltage, with a total of 12 batteries connected in series. The rated capacity of the battery is 200 Ah.
The BU converter plays a crucial role in extracting the maximum power from the PV array, optimizing the energy storage in the battery. Additionally, a charger controller is used to adjust the duty cycle for controlling the BU converter based on real-time PV voltage and current.
Circuit Breaker and Power Management
A circuit breaker is incorporated into the system to ensure safety and efficiency. It operates based on two main conditions:
If the PV power is less than 300 W.
If the PV voltage falls below 50 V.
Under these conditions, the PV system disconnects from the battery. During the daytime, when the PV array is generating power, it charges the battery and supplies the load. At night, the PV system disconnects, and the battery solely powers both DC and AC loads.
DC Load Management
The system supports various DC loads such as LED lights, gate lights, and downlights. These loads are powered directly from the battery, which stores the energy generated by the PV system during the day.
Inverter and AC Load Management
For AC load applications, the system uses an inverter that converts DC power to AC power. The inverter is controlled by a sophisticated control system to ensure stable power delivery to AC devices such as refrigerators, air conditioners, water pumps, televisions, and other appliances. The inverter's current and voltage are carefully monitored to maintain efficiency and stability in the system.
Control System and Load Monitoring
The inverter control system uses a feedback loop where the load voltage is converted into an alpha-beta format, and then into the dq reference voltage. This reference voltage is used to generate the required reference current, which is compared with the actual inverter current. The inverter's performance is continuously adjusted to meet the load requirements.
Additionally, the system includes measurement blocks that continuously monitor the following parameters:
PV Measurements: Voltage, current, and power generated by the PV array.
Battery Measurements: Voltage, current, and power levels of the battery.
AC and DC Load Measurements: Voltage, current, and power consumption of connected loads.
The system simulates real-time conditions by varying irradiation levels, which affect the performance of the PV array and, consequently, the battery's charging and discharging cycles.
Real-Time Simulation and System Dynamics
The system is designed to simulate real-time scenarios where the irradiation levels change dynamically, affecting the power generated by the PV array. As the irradiation increases, the PV system starts generating power, and the battery switches to charging mode. When irradiation decreases, the battery switches to discharging mode to supply power to the AC and DC loads.
This real-time simulation provides valuable insights into the system's efficiency and how it adapts to fluctuating solar radiation levels. It also helps to understand the interplay between the PV array, battery storage, and the loads in off-grid applications.
Conclusion
This MATLAB simulation of a 15 kW off-grid PV battery system offers a comprehensive view of how solar energy can be used effectively in off-grid environments. The integration of a PV array, battery storage, BU converter, and inverter ensures a reliable and efficient energy supply to both DC and AC loads. The system's dynamic simulation, based on varying irradiation levels, showcases the adaptability and potential of solar energy in off-grid applications.
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