AC Drive vs VFD: What is the Difference and How to Choose?

If you've searched for a drive for your motor and found terms like "AC drive", "VFD", "variable speed drive", and "inverter drive" all being used interchangeably — you're not confused, the industry actually uses all of them to mean the same thing. This guide breaks down what these devices are, how they work, the real benefits they deliver on the shop floor, which brands to trust in India, and exactly how to pick the right one for your application.

AC Drive = VFD — Same Device, Many Names

Before anything else, let's settle the terminology debate that confuses most engineers and procurement managers.

AC Drive is the broader commercial term used widely in India and Asia-Pacific. It emphasises that the device drives an AC motor.

VFD stands for Variable Frequency Drive — the technically accurate name. The core function of the device is to vary the frequency of the AC power supplied to the motor, which controls the motor's speed. This is the term most commonly used by engineers and in technical documentation.

Variable Speed Drive (VSD) is the European standard term, commonly used with Schneider Electric and Siemens documentation. Inverter drive is the Japanese term, popularised by Mitsubishi and Yaskawa, referring to the internal DC-to-AC inversion stage.

How an AC Drive / VFD Works

An AC induction motor runs at a speed determined by the supply frequency and the number of pole pairs. On a standard Indian power supply (415V, 50 Hz), a 4-pole motor runs at approximately 1440–1480 RPM. If you need to run the motor at 720 RPM or 2800 RPM, a VFD is the answer.

The VFD achieves variable speed control through a three-stage power conversion process:

The control unit (DSP or microprocessor) adjusts the IGBT switching pattern in real-time based on speed commands from an operator panel, analog signal (4–20 mA or 0–10 V), fieldbus (Modbus, PROFIBUS, EtherNet/IP), or PLC output.

Key Benefits of Using a VFD

Engineering teams often add a VFD as an afterthought for speed control. But the return on investment comes from multiple directions simultaneously:

Top AC Drive / VFD Brands Available in India

India has strong distribution networks for the following brands. Each has a distinct positioning in the market:

Why Delta VFDs are popular in India

Delta Electronics has built one of the strongest after-sales and spare parts networks in India over the past decade. The VFD-E series (0.4 kW to 15 kW) is the go-to choice for OEM machine builders in Pune, Ahmedabad, and Ludhiana because of competitive pricing, reliable availability, and Indian-language service support. The VFD-C2000 series covers up to 280 kW for heavy industrial use.

Schneider Altivar — when to specify it

Schneider's Altivar 310 and 320 series are specified most frequently in government infrastructure projects (water treatment, sewage pumping), commercial HVAC, and any project where a global brand warranty and local Schneider service engineers are required. The Altivar Process series handles large centrifugal pumps and includes advanced PID, flow measurement integration, and pipe protection algorithms.

Siemens SINAMICS — for integrated automation

If your plant runs SIMATIC S7 PLCs and TIA Portal, specifying SINAMICS G120 or V20 gives you native PROFINET integration, standardised parameterisation through TIA Portal, and a single-vendor support chain. The premium over Delta is typically 2–3× but the engineering time saved on commissioning complex multi-drive systems can justify it.

Price Ranges in India (2025)

VFD prices vary significantly by brand, power rating, and features. Below are approximate market prices for a standard 3-phase general purpose VFD from authorised distributors (inclusive of GST):

How to Choose the Right VFD for Your Application

Use this checklist before placing an order. Getting any of these wrong can lead to nuisance tripping, premature failure, or under-performance:

• Match the motor kW rating — never underrate Always select a VFD with a current (ampere) rating equal to or greater than the motor's full-load current. A 7.5 kW motor may draw up to 16 A FLC — confirm this from the motor nameplate, not just kW.
• Confirm input voltage and phases Indian industrial supply is typically 3-phase 415V ±10%, 50 Hz. For single-phase 230V supply (small workshops), confirm the VFD model explicitly supports single-phase input. Not all do.
• Identify your load type: constant torque or variable torque Pumps and fans are variable torque (torque reduces at lower speeds — lighter duty). Conveyors, extruders, and compressors are constant torque (full torque required even at low speeds). Choose the correct overload rating (110% vs 150% for 60 seconds).
• Plan the control interface How will the VFD receive its speed command? Keypad only, analog 4–20 mA from a PLC, digital inputs for run/stop/jog, or fieldbus (Modbus RTU, PROFIBUS, EtherNet/IP)? Pick a model with the required I/O count.
• Cable distance: motor to VFD Long cable runs (above 30–50 metres) can cause high dV/dt stress on motor windings. Use an output dV/dt filter or motor choke, or specify an inverter-duty motor rated for VFD use. Confirm with your motor OEM.
• Enclosure rating and installation environment Standard VFDs are IP20 (panel installation). For dusty, wet, or outdoor locations, choose IP54 or IP65 rated units — or install in a suitable panel. Never install a standard VFD exposed to direct moisture or conductive dust.
• Derating at high altitude or high ambient temperature VFDs are typically rated at 40°C ambient and up to 1000 m altitude. Above these values, the VFD must be derated (run at lower current). Consult the brand's derating curves if your installation is in hilly terrain or a very hot plant room.

Frequently Asked Questions