Background

Currently, renewable energy sources, like wind and solar power, are playing an increasingly significant role in the power system. However, these energy sources 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). However, these energy sources 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). 

Randomness and Volatility of Renewable Energy Generation

The unpredictability 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 grid-following control algorithms do not provide inertial and, therefore, unable to copewith  system oscillations because of the below issues:

1. Phase-Locked Loop Lock 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 behaves 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, a PV and ESS expert with 36 years of experience in the power electronics industry, has conducted extensive research into grid-forming PCS. Kehua is the first enterprise in the industry to complete full functional and technical verification of grid-forming technology and has 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 the full function of grid-forming and technical indicator verification, with key functions such as inertia response, droop control and damping response. Relying on these functions, Kehua PCS can provide active and effective support during power grid shocks.

As grid grid-friendly product, Kehua PCS can support not only active/reactive power control but also VSG function(optional), which can be widely used for different scenarios like peak shaving, frequency regulation, renewable power consumption and so on.

Designed for efficient space utilization, the Kehua PCS 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.

In November 2024, Kehua successfully completed the world's largest grid-forming standalone energy storage project—a 300 MW/1200 MWh project in China. This project holds demonstrative significance in the country and represents a successful attempt at grid construction in the independent energy storage sector. 

Conclusion

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

About Kehua

Based on 36 years of experience in power electronic technology, Kehua has diversified solutions and rich project experience in the fields of photovoltaic, energy storage, micro-grids and integrated energy services. By the end of 2023, Kehua´s PV installation has exceeded 46GW and its energy storage installation has exceeded 15.2GW/8.2GWh globally. Presently, Kehua has become the world's third largest PCS supplier (S&P), a Tier 1 energy storage supplier and a Top 10 solar inverter manufacturer (BloombergNEF). As a reliable PV and ESS expert, Kehua is dedicated to enabling a zero-carbon lifestyle for individuals worldwide.