What I have heard is BLDC is workhorse in industry even laptop fans they work on BLDC but why they are called DC motor as eventually they use inverter to get ac as input? Can I directly give AC supply to BLDC motor without inverter? Is BLDC a misnomer or does it has some significance ?
BLDC motors, or brushless Direct current motors, are, as the name suggests, motors which have no brushes and are powered from DC.
You are correct, they use a style of inverter to convert from DC to a waveform which switches to activate the windings of the motor as required. However, this is not an AC motor, as an AC motor is tuned to operate at a speed to use the fluctuations of the supplied AC. The BLDC unit is designed to operate from DC which is switched as required by the motor. AC motors tend to be large, steady state, single speed style of motors powered by mains electricity. BLDCs are a lot better at handling different speeds (in very general terms).
An AC motor is defined from the AC supply. The "inverter" of the DC motor is defined from the motor.
All motors are basically AC motors in principle: they rely on varying a magnetic field in a circular fashion to produce forces that turn the shaft. That ‘varying magnetic field’ is what the inverter (or, commutator) is controlling when it converts DC to coil drive voltages for a BLDC.
So you’re basically correct: a 3-phase induction motor is remarkably similar to a BLDC without its inverter. As it is, if you feed a 3-phase waveform of appropriate voltage to the BLDC coils, it will spin too.
They differ in that the induction motor has a rotor designed to generate back-emf to make the attracting field, while the BLDC uses permanent magnets or a field coil.
Here’s the thing. The 3-phase AC induction motor runs at or near a fixed speed set by the line frequency. In contrast, a BLDC with an inverter can use variable frequency and thus can vary its RPM over a wide range. This makes BLDC more suitable for transport and other uses that need a wide range of speeds.
The other advantage of BLDC is using DC power. This is more compatible with batteries, and also with large vehicle systems like electric train grids where power is recovered from regenerative braking.