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Grid Connected and standalone mode operation of PV with battery system

Grid Connected and standalone mode operation of PV with battery system

Introduction to the PV with Battery System

We'll look at the operation of a PV system with a battery in both grid-connected and standalone modes. When the grid is unavailable, the PV system with the battery should supply AC and DC loads. When the grid is available, it will connect to the PV system and battery, and based on PV system parameters (such as PV current, power, or battery state of charge), we will decide whether to send power to the grid or draw power from it to supply the AC and DC loads.



Simulink Model Overview

We have developed a Simulink model for both the standalone PV system with a battery and the grid-connected PV system with a battery. This model includes:

  • PV Panel: Controlled using incremental conductance MPPT to extract maximum power.

  • Boost Converter: Connects to the DC bus.

  • DC Load: Connected to the DC bus.

  • Battery and Bi-directional DC-DC Converter: Connects to the DC bus, controlled by a voltage controller to maintain the DC bus voltage at 400V.

  • Single-Phase Inverter: Connects to the DC bus with an LCL filter and supplies AC load.

  • Control Logic for Grid-Connected and Standalone Modes: Allows the inverter to operate in both modes.

PV System Control

  • Incremental Conductance MPPT: Controls the PV panel to maximize power output.

  • Voltage Controller: Maintains the output voltage of the bi-directional DC-DC converter.

Inverter Control

The inverter has two control modes:

  1. Grid-Connected Mode: The control logic manages the inverter when connected to the grid.

  2. Standalone Mode: The control logic manages the inverter when operating independently from the grid.

Switching Between Modes

We have implemented a control logic to switch between grid-connected and standalone modes:

  • Standalone Mode: When the grid is unavailable, the system supplies power to AC and DC loads from the PV and battery.

  • Grid-Connected Mode: When the grid is available, the system can either draw power from or supply power to the grid, depending on the PV system parameters.

Islanded Mode Control

In islanded mode, we measure inverter voltage and convert it into a dq form, generating reference values compared with actual quantities. A PI controller processes these values to generate control voltages, which are then converted back to abc form for modulation.

Simulation Results

We simulate the model in three scenarios:

  1. Standalone Mode: The system operates independently from the grid, supplying power to AC and DC loads from the PV and battery.

  2. Grid-Connected Mode: The system connects to the grid, with power flowing based on the PV system parameters.

  3. Mode Transition: The system switches between grid-connected and standalone modes.

Standalone Mode Results

During standalone mode, the grid voltage and current are zero, indicating no power from the grid. The PV and battery continuously supply power to the AC and DC loads.

Grid-Connected Mode Results

In grid-connected mode, the system supplies power to the AC and DC loads, with the grid voltage and current indicating power flow to and from the grid.

Mode Transition Results

During the transition from grid-connected to standalone mode, the system continues to supply power to the loads with minimal deviation. After a brief adjustment period, the system stabilizes and continues to operate effectively.

Conclusion

We have successfully demonstrated the operation of a PV with battery system in both grid-connected and standalone modes using a Simulink model. The system efficiently supplies power to AC and DC loads, with seamless transitions between modes

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