Grid voltage ride-through refers to the critical capability of power electronic devices (especially inverters) to maintain stable grid connection and continuous operation during temporary voltage deviations, including Low Voltage Ride-Through (LVRT) and High Voltage Ride-Through (HVRT). For NMS (Networked/Modular Smart) inverters—key components in renewable energy systems (solar, wind) and microgrids—this adaptability directly determines grid stability, power supply reliability, and compliance with grid codes.
LVRT specifically requires inverters to remain connected when the grid voltage drops to a specified threshold (e.g., 0-90% of nominal voltage) for a defined duration (typically 0.1-3 seconds), while HVRT addresses overvoltage scenarios (110-150% of nominal voltage). Unlike traditional inverters, NMS inverters integrate modular design, real-time communication, and adaptive control, enabling enhanced ride-through performance through distributed processing and coordinated regulation.
NMS inverters adopt a parallel modular structure, where each power module operates independently yet communicates synchronously. During voltage sags/swells:
Fault isolation: Faulty modules are quickly disconnected without affecting the entire system, ensuring partial power output retention.
Capacity redundancy: Spare modules automatically compensate for reduced output of affected units, maintaining total power stability.
Distributed control: Each module executes local ride-through algorithms (e.g., voltage feedforward control, current limiting) while coordinating via a central controller, reducing response latency to <20ms.
Example: In a 1MW NMS inverter system with 20×50kW modules, a 30% voltage sag triggers 3 modules to enter current-limiting mode. The central controller redistributes the load to the remaining 17 modules, preserving 85% of rated output without grid disconnection.
Voltage-oriented control (VOC): Adjusts d/q-axis current in real time to suppress voltage fluctuations, ensuring grid-side power quality meets IEEE 1547 standards.
Model Predictive Control (MPC): Predicts voltage changes using a grid model, pre-emptively adjusting inverter output to mitigate the impact of voltage deviations.
Fault Ride-Through (FRT) logic: Integrates LVRT/HVRT curves specified by grid operators (e.g., China’s GB/T 38941, EU’s EN 50530), automatically switching to ride-through mode when voltage exceeds thresholds.
Fast-response IGBT modules: With switching frequencies up to 20kHz, enabling rapid current regulation during transient voltage events.
Energy storage integration: Built-in supercapacitor or battery modules absorb surplus energy during HVRT or supply supplementary power during LVRT, stabilizing DC-link voltage.
Grid monitoring sensors: High-precision voltage/current transducers (sampling rate ≥1kHz) detect voltage deviations within milliseconds, triggering control actions.
Global grid codes mandate strict LVRT/HVRT performance for inverters:
LVRT: For example, the German BDEW standard requires inverters to remain connected when voltage drops to 0% for 0.15 seconds, 15% for 0.5 seconds, and gradually recover above 90% within 3 seconds.
HVRT: The US FERC Order 827 requires inverters to withstand 110% nominal voltage for 5 seconds and 120% for 0.5 seconds without tripping.
NMS inverters achieve compliance through:
Pre-programmed ride-through curves calibrated to regional grid codes.
Real-time communication with grid management systems (GMS) to receive voltage regulation commands.
Self-testing and calibration functions to ensure consistent performance over time.
Solar PV systems: NMS inverters maintain grid connection during cloud-induced voltage sags, avoiding power curtailment and maximizing energy yield.
Wind farms: Mitigate voltage fluctuations caused by wind speed variations, ensuring stable power injection into the grid.
In islanded or grid-connected microgrids, NMS inverters coordinate with other distributed energy resources (DERs) to:
Support LVRT during load surges (e.g., industrial motor startup).
Enable HVRT during regenerative braking of electric vehicles (EVs) or sudden load shedding.
For data centers, hospitals, and industrial facilities requiring uninterrupted power:
LVRT capability prevents inverter tripping during grid faults, avoiding blackouts.
HVRT protects sensitive equipment from overvoltage damage, ensuring operational continuity.
Extreme voltage events: Ultra-low (≤10%) or ultra-high (≥130%) voltage deviations may exceed the inverter’s current-limiting capacity, requiring enhanced hardware ruggedness.
Grid synchronization: Maintaining phase lock loop (PLL) stability during severe voltage distortions (e.g., harmonics, unbalance) remains a technical bottleneck.
Cost optimization: Integrating advanced control and energy storage increases hardware costs, requiring trade-offs between performance and affordability.
AI-driven adaptive control: Machine learning algorithms will optimize ride-through parameters based on historical grid data, improving response accuracy.
Wide-bandgap (WBG) semiconductors: Silicon carbide (SiC) and gallium nitride (GaN) modules will replace IGBTs, reducing switching losses and enhancing high-temperature performance.
Grid-forming inverters: NMS inverters will evolve to provide voltage and frequency support, enabling LVRT/HVRT in weak grids or islanded operation.
The LVRT/HVRT adaptability of NMS inverters is a cornerstone of modern power system stability, especially as renewable energy penetration increases. Through modular design, advanced control strategies, and compliance with grid codes, NMS inverters not only ensure uninterrupted operation during voltage deviations but also enhance the resilience and flexibility of the power grid. Future developments in power electronics and artificial intelligence will further elevate their performance, making them indispensable for the transition to a low-carbon, distributed energy system.
