What Is Torque Control in VFDs and How It Improves Motor Efficiency

Modern Variable Frequency Drives (VFDs) do far more than just control speed — they also precisely manage motor torque. Torque control is a powerful feature that ensures consistent performance, optimised energy use, and enhanced protection across industrial applications. Understanding how torque control in VFDs works is essential if you want to achieve maximum efficiency, smoother operation, and longer equipment life.

In this guide, we’ll explain what torque control is, how it works within modern inverter drives, and how it improves overall motor efficiency and process reliability. We’ll also show how to integrate this with your system design using our free tools like the VFD Sizing Calculator and Braking Resistor Calculator.

Understanding Torque in Electric Motors

Torque is the rotational force that causes a motor shaft to turn. It’s measured in Newton-metres (Nm) and directly determines how much mechanical work the motor can perform. The relationship between torque, speed, and power is given by the formula:

Power (kW) = (Torque × Speed) ÷ 9550

For example, a 4 kW motor running at 1,500 rpm produces approximately 25.5 Nm of torque. Managing that torque effectively is what enables the motor to deliver the required load performance while maintaining efficiency.

What Is Torque Control in a VFD?

Torque control is a VFD operating mode that regulates the torque output of a motor rather than its speed. Instead of simply setting a target frequency (Hz), the inverter adjusts voltage and current in real time to achieve a precise torque value. This is especially useful in processes where constant torque or tension is critical, such as:

✅ Winding and unwinding machines
✅ Conveyors and extruders
✅ Lifts, hoists, and cranes
✅ Printing and textile machinery
✅ Pumping systems requiring controlled torque ramp-up

By controlling torque directly, the VFD ensures the motor operates within optimal efficiency and mechanical limits, regardless of speed variations or load disturbances.

How Torque Control Works in Modern VFDs

Torque control uses sophisticated feedback algorithms within the inverter. Depending on the model, this may involve either open-loop (sensorless) or closed-loop (feedback-based) control.

1. Open-Loop Torque Control (Sensorless Vector Control)

Sensorless vector control uses internal motor models and voltage/current measurements to estimate rotor flux and torque. It does not require an encoder but still delivers precise torque regulation down to low speeds. Many modern drives, such as the Invertek Optidrive E3 or Danfoss VLT Micro Drive FC-51, include this capability as standard.

2. Closed-Loop Torque Control (Field-Oriented Control)

Closed-loop torque control, also called Field-Oriented Control (FOC) or vector control with feedback, uses a shaft encoder or resolver to provide real-time rotor position data. This enables the VFD to regulate magnetic flux and torque with extreme precision — ideal for high-performance motion control, hoisting, and servo-like applications.

High-end inverters such as the ABB ACS880 and Allen Bradley PowerFlex 525 use this technology to deliver smooth torque even at 0 Hz (zero speed).

Key Benefits of Torque Control in VFDs

Implementing torque control offers significant benefits across both mechanical and electrical performance areas:

⚙️ Improved Energy Efficiency: The motor only produces as much torque as needed, reducing wasted current and improving overall efficiency.
⚙️ Smoother Starting and Stopping: Controlled torque ramping eliminates mechanical shock and reduces stress on couplings, gearboxes, and belts.
⚙️ Enhanced Process Accuracy: Maintains constant tension or pressure in variable load applications such as winding or extrusion.
⚙️ Reduced Maintenance Costs: Lower mechanical stress translates to longer motor and bearing life.
⚙️ Protection from Overloads: Built-in current limiting prevents excessive torque that can damage mechanical systems.

When to Use Torque Control vs Speed Control

Torque control is not always necessary — it depends on your process requirements. Here’s a simple comparison:

Application Type	Recommended Mode
Centrifugal pumps and fans	Speed Control (Variable Torque)
Conveyors, mixers, compressors	Torque Control (Constant Torque)
Hoists, cranes, lifts	Closed-Loop Torque Control
Winders, extruders	Sensorless Vector Torque Control

For most constant torque applications, enabling torque mode ensures precise control during load fluctuations and startup.

Using Torque Control for Energy Savings

Many engineers focus on speed reduction for energy savings, but torque control can offer even greater efficiency improvements. By dynamically limiting torque to actual load demand, the VFD automatically reduces current draw and reactive power — leading to lower energy costs.

In variable torque systems like fans and pumps, this aligns perfectly with the affinity laws — reducing torque and speed yields a cubic reduction in power consumption. For example, reducing torque by 20% can cut power use by nearly 50%.

Real-World Example: Conveyor System with Constant Torque Load

Consider a 5.5 kW conveyor motor running under constant torque conditions. When driven by a fixed-speed starter, it consumes full power even during light loading. By switching to a VFD operating in torque control mode, the drive automatically adjusts voltage and current to match actual torque demand. The result: smoother acceleration, less belt wear, and energy savings of up to 25%.

To correctly size the drive for such applications, use our VFD Sizing Calculator to ensure the inverter’s torque capacity aligns with the load characteristics.

Torque Boost and Torque Limits

Most VFDs allow fine-tuning of torque parameters via settings such as “Torque Boost” or “Torque Limit.”

Torque Boost: Adds extra voltage at low frequencies to overcome motor resistance — ideal for starting high-inertia loads.
Torque Limit: Caps the maximum torque output to prevent mechanical overload or slippage in belt-driven systems.

Drives like the Delta MS300 or Invertek Optidrive E3 provide easy parameter access for both settings, allowing custom tuning to your process needs.

Monitoring and Feedback for Torque Control

Accurate torque regulation requires precise feedback of motor current, voltage, and sometimes rotor position. Many modern drives offer built-in torque monitoring via Modbus, Ethernet/IP, or Profinet, making it easy to visualise real-time torque and load data on your HMI or SCADA system.

Pairing this with our VFD Cable Sizing Calculator ensures your wiring supports the necessary current levels for accurate torque feedback and protection.

Braking and Regeneration Under Torque Control

When a system decelerates or reverses, it can generate torque in the opposite direction — acting as a generator. In such cases, a braking resistor or regenerative unit is needed to safely dissipate or return the energy to the grid.

To size this correctly, use our Braking Resistor Calculator. Many ABB ACS355 and Allen Bradley PowerFlex 4M drives include built-in braking chopper connections, making integration straightforward.

Torque Control in Sensorless Vector Drives

Sensorless vector drives calculate torque by measuring stator voltage and current and estimating rotor flux. This enables precise control even without a feedback encoder, offering a cost-effective solution for 90% of industrial applications.

Drives with advanced sensorless vector algorithms can maintain full torque down to 1 Hz, providing smooth low-speed performance for conveyors, mixers, and tension control systems.

Torque Control in Field-Oriented (FOC) Drives

For ultra-precise applications such as hoists, robotics, and position-critical systems, Field-Oriented Control provides near-servo performance. The drive decomposes motor current into two components — magnetising and torque-producing — allowing independent control of both. This ensures full torque at zero speed, perfect for lifts or presses requiring holding torque without motion.

The ABB ACS880 and Allen Bradley PowerFlex 755 series are prime examples, offering fully closed-loop torque control for the most demanding industrial uses.

Practical Tips for Setting Up Torque Control

🔧 Enter accurate motor nameplate data — voltage, current, power factor, and frequency.
🔧 Perform motor auto-tuning to calibrate the inverter’s internal model.
🔧 Set acceleration/deceleration times appropriate for load inertia.
🔧 Enable torque limit parameters to prevent mechanical stress.
🔧 Monitor torque via the drive display or communication network.

Following these steps ensures stable operation and high efficiency right from commissioning.

Common Applications Benefiting from Torque Control

🏗️ Hoists and cranes — precise lifting force with no rollback
🧵 Textile winders — constant yarn tension
🚚 Conveyors — smooth start/stop without belt slip
🌀 Pumps — controlled acceleration to avoid pressure surges
🪓 Crushers — steady torque despite load fluctuations

Improving Efficiency with Correctly Sized Drives

Torque control is most effective when paired with a correctly sized inverter. Undersized drives may not provide sufficient current for torque response, while oversized units can cause unnecessary cost and harmonics. Use the VFD Sizing Calculator to match the inverter’s continuous current and overload capacity to your motor rating and load profile.

Conclusion: Unlock Maximum Motor Efficiency with Torque Control

Torque control transforms how VFDs manage motor power — delivering smooth performance, lower energy use, and longer system life. By understanding how to implement and tune torque mode, you can achieve more consistent production, fewer breakdowns, and measurable efficiency gains.

Combine this with Drive Outlet Megastore’s range of professional tools to optimise every stage of your setup:

Explore our full selection of advanced inverter drives from industry-leading brands like ABB, Allen Bradley, Danfoss, Invertek, and Delta — all available at unbeatable prices and fast UK delivery.

At Drive Outlet Megastore, we help engineers and maintenance professionals find the perfect VFD solution for every application. Visit our store or contact our expert team for free technical advice today.