The E.Lu (Undervoltage) error signals a voltage drop in the DC bus below the critical limit, and to prevent emergency stops in unstable grids, the automatic restart function must be activated. When the supply voltage at terminals R, S, T decreases, the intermediate DC link capacitors discharge. If this level drops below the hardware threshold (for example, about 350 V for three-phase 380 V grids), the microprocessor immediately blocks the output IGBT switches to prevent damage to the power modules due to excessive current.
By default, Veichi frequency inverters block operation after sudden voltage sags. This factory setting is a basic safety measure. It prevents uncontrolled, spontaneous startup of industrial equipment (such as machine tools, saws, or conveyors) after power restoration, which could lead to personnel injury. However, for many technological processes, such as water supply, ventilation, or the operation of remote pumping stations where operator presence is not expected, such blocking is a critical drawback that stops the entire system until the service team arrives.
To solve this problem, modern automation systems use special automatic restart algorithms. If you want to select equipment resistant to voltage fluctuations, pay attention to the devices represented by this specific category of our catalog. They feature flexible tools for configuring protection against grid emergency modes.
Configuring Auto-Restart: Step-by-Step Algorithm
To activate automatic restart after a power outage, set parameter F07.06 to 2 (or another number of attempts), and set the waiting interval F07.07 to 0.00 seconds for an instant start. This will allow the system to automatically resume operation as soon as the DC bus voltage returns to the nominal range.
The process of configuring the auto-restart parameters on the Veichi control panel is performed according to the following algorithm:
Switch the frequency inverter to stop mode (the RUN indicator should not be lit). Configuration of many system parameters is blocked while the motor is rotating.Press the PRG key to enter the main programming menu.Use the up/down arrows to find the F07 parameter group, which is responsible for auxiliary functions and protection modes, and press ENTER.Find parameter F07.06. This parameter determines the number of allowed automatic restart attempts after an E.Lu undervoltage error occurs. The default value is 0 (function disabled). Change its value to 2 (or more, depending on your system requirements) and press ENTER to save.Go to parameter F07.07. It determines the delay time before each restart attempt. Set the value to 0.00 seconds for the fastest possible recovery, or set a small delay (for example, 2.0-5.0 seconds) to allow transient processes in the grid to fully stabilize. Press ENTER to confirm.Press the PRG key several times to exit the programming menu and return to operation mode.Parameter CodeParameter NameSetting RangeFactory ValueRecommended ValueF07.06Number of auto-restart attempts0 - 10 attempts0 (Disabled)2 (or more)F07.07Auto-restart delay time0.00 - 100.00 s0.50 s0.00 s (or as needed)
Please note that if the number of restart attempts exceeds the limit set in parameter F07.06 and the voltage still does not stabilize, the frequency inverter will lock out completely and display a persistent E.Lu error, which will require a manual reset (via the RESET button or an external digital input).
Optimizing Operation in Unstable Grids: Parameter Group P9
Configuring the parameters of the special P9 group allows adapting the frequency inverter to operate in "dirty" power grid conditions, preventing false protection trips without a complete shutdown of the equipment. A "dirty" grid refers to power lines with high levels of harmonic distortion, constant short-term voltage sags due to the startup of powerful neighboring consumers, or unstable operation of generator sets.
To increase the resilience of the Veichi inverter to such disturbances, the P9 parameter group is used (in some firmware versions, it is duplicated or linked to advanced protection settings). The main parameters of this group allow changing the undervoltage protection trip threshold and configuring input signal filtering:
Undervoltage detection threshold: allows lowering the minimum allowable voltage on the DC bus at which the VFD still continues to operate without triggering an E.Lu error. This is critical for facilities where the voltage is consistently low (for example, 340 V instead of 380 V).Error filtering time: determines the duration of a voltage sag that the device can ignore. If the sag lasts less than the set time (for example, 0.1-0.2 seconds), the system continues to operate using the energy stored in the capacitors without stopping the motor.Voltage compensation function: automatically adjusts the PWM modulation index to maintain a stable output voltage on the motor during supply voltage fluctuations.Group P9 ParameterFunctional PurposeImpact on System OperationF07.02Undervoltage protection levelLowers the E.Lu error trip threshold for operation in sagged gridsF07.03Undervoltage detection delay timePrevents shutdown during microsecond impulse sagsF07.05Dynamic DC bus compensationStabilizes motor output torque during power fluctuationsComparative Analysis of Veichi VFD Operating Modes
The choice between standard blocking and automatic restart depends on the safety requirements of the specific facility: for conveyors, safety is the priority, whereas for pumping stations, continuity of operation is key. Each mode has its advantages and limitations, which must be considered when designing automation systems.
Below is a comparative table of the three main behavior strategies of the frequency inverter during unstable power supply:
Comparison CriterionFactory Settings (Blocking)Activated Auto-Restart (F07.06=2, F07.07=0.00)Optimized Mode (Group P9)Behavior during voltage sagInstant stop, trip to E.Lu faultStop, and automatic start after grid recoveryContinued operation without stopping during short sagsPersonnel safetyMaximum (spontaneous start is excluded)Medium (warning measures required)High (equipment does not stop unnecessarily)Impact on motor lifespanNone (motor is simply de-energized)Minimal (start occurs along a set ramp)Minimal (stable torque due to compensation)Application areaMachine tools, hoists, hand toolsPumps, fans, smoke exhausters, compressorsCritical process lines with sensitive processesPractical Recommendations for Safe Operation
Before implementing auto-restart, be sure to install warning signs on the equipment and ensure that a sudden motor start does not threaten the lives of maintenance personnel. Since the motor can start at any moment after power is restored, the work area must be completely protected from accidental access by unauthorized persons.
To ensure high stability and safety, it is recommended to adhere to the following rules:
Use light and sound alarms that warn of voltage application and imminent drive startup.Integrate the frequency inverter with the overall safety system (for example, via safety relays or industrial controllers) to block auto-restart when protective guards are open.Regularly check the condition of the intermediate DC link capacitors, as their wear reduces the device's ability to smooth out micro-sags in voltage.Choose high-quality power equipment. If you need an efficient frequency inverter, this specific category of our online store offers a wide range of Veichi models adapted to difficult operating conditions.
The correct combination of auto-restart settings (F07.06, F07.07) and noise immunity parameters (group F10) allows creating a fully autonomous system that effectively counters the instability of local power grids, minimizing production downtime while maintaining a high level of safety.
The E.Lu error indicates undervoltage in the DC link of the inverter. It occurs when the input supply voltage drops below the critical threshold set by the manufacturer. This is a protective mechanism that prevents damage to the IGBT power transistors.
This is done for safety reasons to prevent uncontrolled startup of connected equipment after power is restored. A sudden start of mechanisms could injure maintenance personnel or damage mechanical components of the system. Special parameter configuration is required for automatic startup.
The number of auto-restart attempts is set in parameter F07.06. By default, it is set to 0, which completely disables this function. To activate it, set a value from 1 to 10 attempts, depending on the requirements of your technological process.
Parameter F07.07 determines the delay time before each automatic restart attempt after the error clears. If set to 0.00 seconds, the device will attempt to start instantly after the voltage stabilizes. Increasing this time allows transient processes in the grid to fully complete before starting the motor.
The parameters of the P9 group allow configuring the device's sensitivity to voltage fluctuations and setting the filtering time for short-term sags. Thanks to this, the VFD can continue operating during microsecond power disturbances without tripping into the E.Lu fault mode. This significantly increases system stability under low power quality conditions.
