Grid-Forming Storage: Innovation to address challenges of renewable energy

By Kehua
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Currently, renewable energy sources, like wind and solar power, are playing an increasingly significant role in the power system. However, they are affected by natural environmental conditions, leading to randomness and volatility in their power generation. This variability poses challenges to maintaining balance and resource adequacy during peak demand periods, driving the rapid development of Battery Energy Storage Systems (BESS).

The unpredictable nature of renewable energy generation creates balancing issues for the system, especially during peak electricity demand. Traditional power systems rely on synchronous generators, which possess physical inertia and can sustain motion for several seconds (5-10 seconds) during sudden system oscillations. This inertia helps maintain system stability. However, traditional renewable power generators with a grid-following control algorithm do not provide inertia and are therefore unable to cope with system oscillations because of the below issues:

1. Phase-Locked Loop Loss: When the output power of the grid-following PCS increases, the phase-locked loop may struggle to maintain synchronization.

2. Insufficient Reactive Power Support: Grid-following PCS must detect voltage changes before generating reactive power, which limits the ability to provide instantaneous voltage support and may cause reactive power reversal during fault recovery.

Advantages of Grid-Forming PCS

To tackle the unstable operation of renewable energy units in weak grid scenarios, retrofitting existing units or adding grid-forming PCS offers a promising technological path. Countries are actively exploring the practical application of grid-forming functions and integrating them into power grids.

The key differences between grid-following and grid-forming PCS include:

1. Power Characteristics: Grid-forming PCS behave as a voltage source, with frequency changes determined by internal inertia and damping. Conversely, grid-following PCS act as a current source, with frequency governed by the phase-locked loop.

2. System Support Capability: Grid-forming PCS can provide voltage and frequency support respectively, demonstrating strong stability in weak grid conditions. In contrast, grid-following PCS rely on phase-locked loops for support, which can lead to broadband oscillation issues.

3. Virtual Synchronous Generator (VSG): By mimicking synchronous generator principles, grid-forming PCS offer functions such as primary frequency regulation, inertia response and damping response. They can quickly respond to sudden changes in grid voltage or frequency, providing essential active support to ensure stable power grid oscillations.

Exploration and Practice by Kehua

Kehua has conducted extensive research into grid-forming PCS and is the first company in the industry to have both completed full functional and technical verification of grid-forming technology and participated in setting group standards for this function in China. 

The Kehua PCS is a state-of-the-art solution designed to meet the evolving needs of the energy sector. For grid-following functions, Kehua is the first company in China to complete full verification of functional grid-forming and technical indicators, covering key functions such as inertia response, droop control and damping response. Relying on these functions, the Kehua PCS can provide active and effective support during power grid outages.

As a grid friendly product, the Kehua PCS can support not only active/re-active power control, but also the VSG function (optional), which can be widely used in different scenarios such as peak shaving, frequency regulation and renewable power consumption.

Designed for efficient space utilization, it maximizes energy storage capacity while simplifying installation with its integrated converter and transformer system. It also supports multi-machine parallel connections and black start capabilities, ensuring scalability and reliability during power outages.

Conclusion

The growing integration of renewable energy into traditional power systems presents both opportunities and challenges. The inherent randomness and volatility of renewable power generation necessitates innovative solutions. Grid-forming PCS offer a vital mechanism for enhancing voltage and frequency stability in the power grid, ensuring a more reliable and resilient energy system for the future.

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