4 Rules to Run Multiple Motors on One VFD Safely

In field applications, driving multiple motors with a single variable frequency drive (VFD) is a common yet problematic design. Many engineers encounter faults such as overcurrent, overload, or IGBT damage during commissioning, often stemming from improper selection or parameter configuration.
This guide combines practical engineering experience to comprehensively cover the key operational aspects of Single VFD control multiple motors across four dimensions: selection principles, parameter configuration, motor protection, and start/stop operations. It empowers you to build a safe, stable, and efficient multi-motor control system.

flowchart showing multiple motors on one VFD setup — from power calculation, parameter setting, protection, to sequential start-stop process

VFD Selection Principles: Correct Configuration for Multiple Motors on One VFD

When designing a VFD multi-motor application, selection is the most critical step.
If one VFD drives multiple motors, it must satisfy these two principles:

  • VFD power rating ≥ Sum of all motor power ratings.
  • VFD rated current ≥ sum of rated currents for all motors.

For example, with three motors rated at 5kW, 7.5kW, and 11kW, the selected VFD must have a power rating ≥ 23.5kW and a total rated current exceeding the combined motor currents.
For stable operation, moderately oversize the VFD by one rating level to prevent overload or IGBT overheating during prolonged operation.

Key Points for VFD Parameter Settings (Multi-Motor System)

When configuring VFD parameters for a multi-motor system, strictly adhere to the following logic:

  1. Motor rated power parameter: Enter the sum of all motor powers.
  2. Motor rated current parameter: Set to the total rated current of all motors.
  3. Motor rated voltage: Typically 380V or 400V.
  4. Rated frequency: Set to 50Hz as per motor nameplate.
  5. Control mode (V/F Control Mode):
    • For VFD fan or VFD pump loads, select V/F squared mode (Variable Torque Load);
    • For constant torque loads like mixers or conveyors, set to Linear V/F (Constant Torque Load);
    • Vector Control mode is prohibited, as inconsistent feedback signals during multi-motor operation cause oscillations and overcurrent.
  6. Acceleration/Deceleration Time:
    • If VFD overcurrent fault occurs during startup, extend acceleration time;
    • If a VFD overvoltage trip occurs during shutdown, extend the deceleration time.
  7. Overload Protection Settings: Set the VFD overload protection parameter to 150% of the total rated current to prevent overly lenient protection from causing IGBT protection failure.
  8. Torque Boost: Appropriately amplify to ensure smooth startup without stalling at low frequencies.

Motor Protection in Multi-Motor Setup

In VFD multiple motors configurations, a single VFD cannot provide individual protection for each motor. Therefore, external protection circuits must be added:

  1. Each motor should be equipped with:
    • Circuit breaker (Short Circuit Protection)
    • AC contactor (Contactor)
    • Thermal overload relay (Thermal Overload Relay) (Thermal Overload Relay)
  2. When any motor experiences overload, short circuit, or stalled rotation, the faulty circuit can be isolated independently without affecting other motors’ operation.
  3. If long cables exist in the system, consider implementing a VFD overvoltage solution for long cables or adding an output reactor to protect motor insulation.

Multi-Motor Starting and Stopping Procedure

In the VFD multi-motor starting procedure (low frequency) scenario, incorrect start/stop methods are the primary cause of VFD trips.

Correct operation is as follows:

  1. Startup Process:
    • First run the VFD no-load at 2–5Hz;
    • Then sequentially connect motors, starting one at a time;
    • After all motors are running, gradually increase to the target frequency.
    • This method effectively prevents overcurrent alarms caused by excessive locked rotor current.
  2. Stopping Procedure:
    • Gradually reduce the operating frequency to 2–5Hz;
    • Stop motors sequentially one by one;
    • Finally, shut down the VFD main unit to prevent energy backfeed causing DC bus overvoltage.

This staged start/stop strategy significantly reduces the risk of VFD overload trips and IGBT damage.

Conclusion – VFD Multi-Motor Application Best Practices

In summary, implementing Multiple Motors on One VFD requires mastering four key principles:

  • Proper selection: Total power and current sum is the primary consideration;
  • Accurate Parameters: Strictly configure settings for multi-motor loads;
  • Comprehensive Protection: Independently configure short-circuit and thermal protection;
  • Smooth Start/Stop: Implement low-frequency staged start-up and sequential shutdown.

By following these methods, you can safely achieve system control for One VFD multiple motors, enhancing operational stability while extending the service life of both motors and inverters.