A field test at a 500 MW solar-plus-storage plant in Qinghai, China, has reproduced wideband oscillation under controlled weak-grid conditions and then suppressed it. Sungrow's PV inverters identified grid strength within 40 milliseconds and stabilized voltage and frequency, and the test also validated grid-forming control in suppressing the oscillation.
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Sungrow, a China-based PV inverter and energy storage system provider, has reproduced and then suppressed wideband oscillation at a real-world 500 MW solar-plus-storage plant in Qinghai, China, in what the company describes as a world first. Sungrow and its industry partners conducted the field test using Sungrow PV inverters deployed across the site.
Wideband oscillation has become a growing concern as renewable penetration rises, and in severe cases it can cause renewable plants to disconnect from the grid or shut down. In 2014, oscillations at 250 to 350 Hz on Germany's BorWin1 offshore HVDC project damaged filter capacitors and led to a shutdown of approximately six months. In 2019, subsynchronous oscillation caused widespread disconnection at the Hornsea offshore wind farm in the UK, with a loss of approximately 3.2% of system load affecting around one million users.
Because the phenomenon is complex and hard to predict, reproducing it safely at a real-world plant has been difficult, and research has largely remained at the theoretical and simulation stage. For the Qinghai test, the team established weak-grid conditions and identified three contributing factors, namely power output, system short-circuit ratio (SCR) and control parameters, before reproducing a localized system oscillation under control.
The test then evaluated how Sungrow's PV inverters suppressed the oscillation under different grid conditions. Using the company's patented grid-strength adaptation technology, the inverters identified grid strength within 40 milliseconds, adjusted their control strategies and stabilized voltage and frequency. The test also validated grid-forming control, which Sungrow says enables stable operation across an SCR range of 1 to 40 and mitigates transient overvoltage.
"For renewable energy to become a truly stable and reliable source of power, it is essential to develop autonomous fault self-healing and grid-support capabilities," said Pan Nian'an, Chief Engineer and Chief Expert for Utility PV BU at Sungrow.
Sungrow is a PV inverter and energy storage system provider. The company has said it will continue research and development in grid technologies, focusing on wideband oscillation suppression, grid-forming control and multi-energy coordination.