In today's era of large-scale integration of new energy sources such as photovoltaics and wind power, instantaneous drops in grid voltage (such as lightning strikes and short circuit faults) may cause passive disconnection of inverters, triggering chain reactions and even large-scale power outages. Low voltage ride through (LVRT) technology, as the core capability of grid connected inverters, enables equipment to maintain grid connected operation during voltage drops and respond quickly after the grid is restored, becoming an invisible defense line to maintain the coordinated stability of new energy and the grid. Its technological maturity directly affects the safety of high proportion renewable energy grids.
1 The core logic of LVRT: from "passive protection" to "active support"
The "off grid protection" of traditional inverters has fatal flaws. When the voltage of the power grid drops below 80% of the rated value, the old-fashioned inverter will trigger overcurrent protection, cutting off the connection with the power grid within 0.1 seconds, causing the output of new energy to disappear instantly. In 2019, a wind farm in Europe experienced a voltage drop due to lightning strikes, causing 300 inverters without LVRT to collectively disconnect from the grid, resulting in frequency fluctuations in the regional power grid exceeding 0.5Hz and almost triggering the start-up of backup power sources.
The new generation LVRT technology achieves dual functions of "fault ride through" and "voltage support". When a voltage drop is detected (such as dropping to 20% of the rated value), the inverter responds by activating the crowbar circuit to consume excess energy on the DC side and avoid IGBT (Insulated Gate Bipolar Transistor) overvoltage damage; At the same time, adjust the current output and inject reactive current (with an amplitude of up to 1.5 times the rated current) into the grid to help the grid voltage quickly recover. The actual test of a photovoltaic power station in China shows that the inverter equipped with LVRT can maintain grid connected operation for 150ms when the voltage drops to 0% (three-phase short circuit), and restore normal output within 0.5 seconds after the fault is cleared.
2 Technological Evolution: From 'Compliance' to 'Performance Optimization'
Hardware upgrade supports extreme working conditions. The power module of the inverter adopts high-voltage resistant IGBT (blocking voltage 1700V), which increases the overvoltage margin by 40% compared to traditional 1200V devices; The DC side is equipped with a supercapacitor energy storage unit, which can absorb energy fluctuations within 200ms and prevent the DC bus voltage from getting out of control. A certain brand of 100kW inverter successfully withstood the extreme working condition of voltage dropping from 100% to 0% and then recovering during LVRT testing. The module temperature remained stable within 85 ℃ without any damage.
Software algorithms improve response speed. The LVRT algorithm based on Model Predictive Control (MPC) increases the sampling frequency to 10kHz, which is 5 times faster than traditional PI control. It can identify voltage drops and adjust output current within 5ms. The "grid impedance sensing" technology developed by a German inverter manufacturer can real-time determine the cause of voltage drops (faults or load changes) and adjust reactive power injection strategies accordingly: injecting more reactive power during faults (lagging at a power factor of 0.9) and injecting less reactive power during load changes (leading at a power factor of 0.9), reducing grid recovery time by 30%.
3 Standards and Scenarios: The Technological Game of Global Adaptation
The differentiation of LVRT standards in different countries tests product compatibility. Chinese GB/T 19964 requires photovoltaic inverters to remain connected to the grid for 2 seconds when the voltage drops to 20%; The EU EN 50530 stipulates that when the voltage drops to 0%, it must be supported for 150ms; the US UL 1741 SA emphasizes the active power recovery rate under low voltage (restored to 90% within 2 seconds after fault clearance). In order to meet the global market, a certain enterprise has developed a "programmable LVRT curve", which allows users to configure 20 different standard crossing features through software. The product has achieved barrier free applications in more than 100 countries around the world.
Adaptive verification of complex power grid scenarios. In weak power grids (such as remote distribution networks), voltage drops may be accompanied by harmonic distortion, and inverters need to have anti harmonic capabilities (total harmonic distortion rate THD<5%); In a multi inverter cluster scenario, it is necessary to avoid current oscillations during the LVRT process. A wind farm used "cluster coordinated control" to control the current deviation of 50 inverters within 5%, avoiding secondary faults. These practices demonstrate that LVRT technology has evolved from simply meeting standards to a system level solution that adapts to complex power grid environments.
As the proportion of new energy exceeds 40%, LVRT technology will shift from an "optional configuration" to a "mandatory requirement". The LVRT capability of the next generation inverters will be extended to "high voltage ride through (HVRT)" and "frequency ride through" to achieve full scenario response to grid anomalies. This technological transition from "passive adaptation" to "active support" makes grid connected inverters not only energy conversion devices, but also "intelligent regulators" for maintaining grid stability, providing core support for building new power systems.