Abstract
The grid-connected power generation of the household photovoltaic microgrid is situated at grid terminals, enabling loads to utilize electricity generated by photovoltaic cells, thereby significantly reducing transmission losses and optimizing energy utilization. This paper delves into the study of a household photovoltaic microgrid system, examining its structure, operation modes, control strategies, and seamless transition between grid-connected and islanded states. By leveraging energy storage control and genetic algorithms, a rational electricity plan for residential photovoltaic microgrids is formulated, showcasing its adaptability to smart grid development.
Keywords: Photovoltaic microgrid; Grid-connected and islanded operation; Seamless transition; Energy storage control; Genetic algorithm
1. Introduction
The advancement of renewable energy technologies, particularly photovoltaic power generation, has become a pivotal direction in global energy development. photovoltaic microgrids, characterized by their distributed nature and ability to operate both grid-connected and in islanded mode, provide a robust solution for improving power supply reliability and quality, especially in remote and rural areas. This paper presents a comprehensive study on the system of household photovoltaic microgrids, addressing its topology, design, control strategies, and operational characteristics.
2. Literature Review
Table 1. Overview of photovoltaic Microgrid Research Around the World
| Country | Key Characteristics | Objectives |
|---|---|---|
| Holland | 380 V, 50 Hz busbar and battery storage | Demonstrate automatic smooth switching between grid and island modes, ensure 24/7 operation, intelligent battery management |
| Germany | Microgrid installed in Mannheim | Gain societal acceptance of microgrids, achieve economic benefits |
| China | Started late but rapid development | Golden Sun Demonstration Project, “863” Project, and others |
3. System Design of Household photovoltaic Microgrid
3.1 Topology of Household photovoltaic Microgrid
The proposed household photovoltaic microgrid system includes a 3 kW photovoltaic panel, two sets of 12 V, 200 Ah batteries, a 3 kW grid-connected inverter, a 3 kW bidirectional inverter, and local AC loads. The system can operate in both grid-connected and islanded modes, providing high-quality power to loads and ensuring reliable operation.
Table 2. Major Components of Household Photovoltaic Microgrid
| Component | Specifications |
|---|---|
| Photovoltaic Panel | 3 kW |
| Battery | 12 V, 200 Ah (2 sets) |
| Grid-Connected Inverter | 3 kW |
| Bidirectional Inverter | 3 kW |
| Local AC Loads | As per design |
3.2 Bidirectional Inverter Capacity Selection
The bidirectional inverter serves two purposes: inverting DC power from batteries to AC for local loads during islanded operation and rectifying AC power from the grid for battery charging. Selected based on load requirements, the bidirectional inverter has a capacity of 3 kW, with a DC voltage level of 24 V and an AC voltage level of 220 V.
4. Control Strategies and Seamless Transition
4.1 Control Strategies
The photovoltaic microgrid employs peer-to-peer control, where distributed generation (DG) units operate independently based on local voltage and frequency measurements. Droop control is a commonly used method, enabling smooth transition between operation modes.
4.2 Seamless Transition Between Modes
When the grid fails, the photovoltaic microgrid seamlessly transitions to islanded mode, continuing to supply power to loads. This transition ensures continuous and reliable power supply without interruption. The bidirectional inverter provides voltage and frequency references during islanded operation, ensuring high-quality power.
Table 3. Modes of Operation and Transition
| Mode | Description | Conditions |
|---|---|---|
| Grid-Connected | Microgrid operates synchronized with grid | Grid is operational, normal power supply |
| Islanded | Microgrid operates independently of grid | Grid failure or maintenance, power supplied by DG units |
| Transition to Island | Grid-connected to islanded mode | Grid failure detected, smooth transition triggered |
| Transition to Grid | Islanded to grid-connected mode | Grid restored, conditions met for reconnection |
5. Islanding Detection and Anti-Islanding Measures
Islanding effect refers to the scenario where the photovoltaic microgrid continues to operate and supply power to loads after the grid disconnects due to fault or maintenance. To prevent non-planned islanding, anti-islanding measures are implemented.
Table 4. Anti-Islanding Measures
| Measure | Description |
|---|---|
| Real-time grid monitoring | Monitor grid voltage and frequency continuously |
| Passive detection methods | Use over/under voltage, over/under frequency detection |
| Active detection methods | Inject perturbations to detect islanding conditions |
| Communication-based methods | Use communication signals to detect grid status |
6. Case Study and Simulation Results
Taking a household in Tai’an, Shandong Province as an example, a rational electricity plan for the residential photovoltaic microgrid was formulated using energy storage level control and genetic algorithms. Simulation results demonstrated the effectiveness of the proposed topology and control strategies in ensuring high-quality power supply and seamless transition between modes.
7. Conclusion
This paper presents a comprehensive study on the system of household photovoltaic microgrids, addressing its topology, design, control strategies, and operational characteristics. The proposed photovoltaic microgrid system can operate in both grid-connected and islanded modes, providing high-quality power to loads and ensuring reliable operation. The seamless transition between modes, achieved through peer-to-peer control and anti-islanding measures, enhances the resilience and adaptability of the system.