View Schematics and PCB Layout on
We want to build an open source micro-inverter.
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Transparency and Trust: Open sourcing fosters transparency, providing users and developers with complete visibility into how the microinverter works. This builds trust within the community and ensures that the technology operates as advertised.
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Collaborative Development: The open-source model encourages collaboration from a diverse group of developers, engineers, and enthusiasts. This collective effort often leads to innovative solutions, enhanced functionality, and improved performance.
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Rapid Iteration and Improvement: With a broader community involved, improvements and bug fixes can happen at a faster pace. Developers can quickly identify and rectify issues, leading to a more robust and reliable microinverter.
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Customization and Adaptability: Open sourcing allows users to modify the microinverter to suit their specific needs. Whether it's adapting the hardware for different solar panel configurations or modifying the software for specific energy management, users have the freedom to customize.
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Cost-Effectiveness and Affordability: By making the designs and software open source, the overall cost of development can be reduced. Individuals and organizations can access the project without expensive licensing fees, making renewable energy solutions more accessible to a wider audience.
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Knowledge Sharing and Learning Opportunities: Open-source projects serve as valuable learning resources for students, researchers, and professionals looking to understand the technology, its design principles, and best practices in renewable energy.
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Global Impact and Adoption: Open sourcing allows for widespread adoption and deployment, especially in regions where cost and accessibility are significant factors. It facilitates the dissemination of renewable energy technology to areas that need it most.
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Alignment with Ethical and Environmental Values: Open-source projects align with values of openness, collaboration, and sustainability. By promoting transparency and knowledge sharing, it contributes to a sustainable and ethical approach to technology development and use.
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Long-Term Sustainability and Maintenance: With a diverse community contributing to the project, the microinverter is likely to remain relevant and actively maintained over the long term, ensuring its sustainability and continued development.
Comparison of micro-inverters with rated output power between 350VA and 400VA:
| Model | HM-3501 | HM-4001 | IQ7A2 | EVT3003 | TSOL-M8004 |
|---|---|---|---|---|---|
| Manufacturer | Hoymiles | Hoymiles | Enphase | Envertech | TSUN |
| Number of solar panels | 1 | 1 | 1 | 1 | 2 |
| Recommended input power (W) | 280-470+ | 320-540+ | 295-460 | 180-420+ | 2 |
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33 | 34 | 38 (18) | 24 | 33 |
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48 | 48 | 43 (58) | 45 | 48 |
| Start-up voltage (V) | 22 | 22 | 22 | - | - |
| Operating volage range (V) | 16-60 | 16-60 | 16-58 | 18-54 | 16-60 |
| Maximum input current (A) | 11.5 | 12 | 12 | 12 | 11.5 |
| Maximum input short circuit current (A) | 15 | 15 | 20 | 15 | 15 |
| Rated output power (VA) | 350 | 400 | 349 | 300 | 600 |
| Peak efficiency (%) | 96.7 | 96.7 | 97.7 | 95.4 | 96.7 |
| CEC weighted efficiency (%) | 96.5 | 96.5 | 97.0 | 95.0 | 96.5 |
Subject to further modifications, the micro-inverter should have the following specifications:
- Efficiency > 90%
- Operating range: 16V - 58V
- Input power from solar panel: 350W - 550W
- Power: 400VA with possibility of software limitation.
- Power factor ≈ 1
- Total Harmonic Distortion (THD) < 5%.
- Electrical isolation between solar module and grid voltage
- Temperature range: -40 °C to 60 °C
- Interfaces:
- WIFI with SunSpec Modbus
- Powerline Communication (PLC)
Optional features:
- Adjustable Power Factor
The following table shows a comparison of different solar modules and their technical data, which were adopted as a guide for designing the microinverter.
| Model | WS350M5 | Meyer Burger White6 | JAM72S-30-550-MR7 |
|---|---|---|---|
| Manufacturer | Wattstunde | Meyer Burger White | JA Solar |
| Power (Wp) | 350 | 400 | 550 |
| Short Circuit Current (A) | 9.68 | 10.9 | 14.00 |
| Open Circuit Voltage (V) | 46.7 | 44.6 | 49.9 |
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38.1 | 38.6 | 41.96 |
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9.19 | 10.4 | 13.11 |
The technical implementation of the micro-inverter will be continuously revised and iteratively improved during the course of the project. Comments and suggestions for improvement are welcome here!
During basic research, we first came across the application note 8. The design is based on 2 power stages, namely an interleaved isolated DC-DC boost converter and a DC-AC converter. The application note provides a detailed description of the operation and component selection. We apoted and extended several things from the design, especially the DC-AC converter. It is worth mentioning that the capacity of the DC bus is of such low capacitance that it can be implemented as film capacitors, which avoids the eventual lifetime issues with electrolytic capacitors.
For the DC-DC converter we used the application note 9 as guide to integrate a LLC resonant converter into our design. The application note describes the implementation of a 250W grid-connected LLC converter micro-inverter. The design of the resonant corverter consinsts of a switchwing bridge, a LLC tank, a transformer and a rectifier.
The circuit design of the micro inverter was simulated in LTspice. All LTspice simulations are stored in the simulation folder. Since the entire circuit design is quickly complex and time-consuming to simulate, the individual building blocks of the circuit were first built and simulated individually. Please mind, that in the current state of the project there are a bunch of LTspice simulations since we discussed a lot of topologies.
The design process of the LLC resonant converter is documented in a interactive jupyter notebook.
See CONTRIBUTING.