Types of Variable Frequency Drives: Complete Industrial Guide
Estimated reading time: 5 minutes
This guide explores the types of variable frequency drives (VFDs) available to industrial users and shows you how to match each drive family to real‑world applications.
Electric motors consume well over a third of all industrial electricity, yet many still run at full speed even when the process does not need it. Variable frequency drives solve this mismatch by letting you ramp motor speed and torque to demand. Because every facility, process and motor is different, engineers have developed several types of variable frequency drives—each optimized for a distinct operating envelope.
Understanding these drive classifications, their advantages and their limitations empowers you to select the ideal solution, reduce energy costs and boost reliability. This article reviews the main VFD categories, explains how each one works and offers product suggestions drawn from leading manufacturers.
AC vs DC – Core VFD Categories
Modern plants overwhelmingly choose AC VFDs because they pair with robust, brush‑free induction or synchronous motors and achieve high efficiency across the speed range. A voltage‑source inverter first rectifies the incoming AC, stores energy in a DC link, then recreates a variable‑frequency waveform for the motor. Consequently, AC drives cover horsepower ratings from sub‑fractional to hundreds, support 200 V–690 V supplies and integrate advanced control algorithms.
DC drives still serve legacy hoists, cranes and battery systems that demand full torque at zero speed with simple circuitry. They regulate armature voltage (or chop DC) to change speed. However, brushes, commutators and larger frame sizes raise maintenance costs. Unless your plant already owns a large DC motor, a retrofit to an AC motor plus closed‑loop vector VFD nearly always delivers better total cost of ownership.
Key takeaway: AC versions dominate most types of variable frequency drives, while DC units remain for niche, torque‑critical or mobile equipment.
Control Methods Inside Each Type Of Variable Frequency Drives (VFDs)
Control strategy defines another major branch of variable frequency drive varieties:
- V/Hz scalar control – simplest, low cost, ±3 % speed accuracy. Ideal for centrifugal fans or pumps.
- Sensorless vector – estimates motor flux to hold ±0.3 % speed and 180 % torque at 1 Hz without an encoder. Perfect for mixers or conveyors.
- Closed‑loop vector – adds an encoder, reaches ±0.01 % speed and 200 % torque at 0 rpm. Required for hoists and elevators.
- Direct Torque Control (DTC) – pioneered by ABB, calculates torque every 25 µs for sub‑2 ms response, often without feedback.
Because you can usually enable several modes in one chassis—such as on the Yaskawa GA800—it is wise to start in V/Hz for commissioning and switch to vector once process data is validated.
Power Topologies That Shape Performance
Most low‑voltage units fall into the PWM voltage‑source inverter class, yet other VFD categories exist:
- Voltage‑source inverter (VSI) – standard six‑pulse diode front end; add a brake resistor or active front end to handle regeneration.
- Current‑source inverter (CSI) – rugged, regeneration‑ready design for multi‑megawatt compressors but bulky at low powers.
- Matrix converter – AC‑to‑AC switching without DC capacitors. The Yaskawa U1000 offers <5 % THD and four‑quadrant operation in one cabinet.
Select a low‑harmonic or regenerative topology when IEEE 519 compliance or significant braking energy is a concern.
Application‑Specific Drive Types & Classes
Manufacturers bundle firmware and I/O to create drive types tuned for common industries:
- HVAC drives like Danfoss VLT or Eaton PowerXL focus on variable‑torque loads, built‑in PID and low noise.
- High‑torque industrial drives—ABB ACS880 or Lenze i500—offer 150 % overload for mixers, crushers and extruders.
- Crane and hoist drives integrate encoder feedback, brake logic and safe torque off for zero‑speed load holding.
- Servo‑grade VFDs merge motion control and field‑bus synchronisation for packaging, robotics and machine tools.
Review duty cycle, starting torque and safety codes before you decide which types of variable frequency drives align with your process.
Recommended Products & Helpful Links
Precision Electric stocks a complete range of AC variable frequency drives as well as essential accessories:
- VFD phase converters – run three‑phase motors on single‑phase supply.
- Input line reactors – cut harmonic current by up to 40 %.
- Output load reactors – protect motor insulation on long cable runs.
- Soft starters – ideal when speed control is unnecessary yet reduced inrush is desired.
For deeper troubleshooting, explore our cornerstone resources on overcurrent faults, VFD autotune and the comprehensive VFD programming guide.
Need low‑harmonic, regenerative or servo‑grade performance? Compare data sheets from ABB, Danfoss and Eaton to find the right fit.
Conclusion On Types of Variable Frequency Drives (VFDs)
Although one enclosure may look like another, the underlying types of variable frequency drives differ dramatically in topology, control method and duty rating. By matching these characteristics to your motor, load and power quality goals, you secure the best lifecycle value. When in doubt, contact Precision Electric for an unbiased comparison and turnkey commissioning support.
