What is 6-pulse VFD?

6-pulse vfd The most common rectifier circuit in three-phase pwm drives, 6-pulse vfd uses six-pulse diode rectifier. A 6-pulse rectifier is the most robust and cost effective solution in the vfd industry as of today, even though input current contains some amount of low order harmonics.

What is pulse in Drive?

In this paper, a new transmission principle, named “pulse drive,” is proposed for potentially realizing a highly compact, high-efficiency, infinitely variable transmission, such as that used in switching electrical power supply systems, by transmitting the driving power intermittently through periodic vibration control …

What is the difference between 6-pulse and 12-pulse rectifier?

A 3-phase, full-wave rectifier is a 6-pulse device. The phase angle between successive secondary voltages is 120 deg. In a 12-pulse converter, the phase-shifting transformer converts the 3-phase input to 6-phase voltages, which when rectified, produce 12 ripples in the dc output voltage.

What is meant by 12-pulse?

A 12-pulse rectifier uses two 6-pulse rectifiers in parallel (12 diodes) to feed a common DC bus. A transformer with one primary and two secondary windings creates a 30 degree phase shift between the two current waveforms, which eliminates the 5th and 7th harmonics and reduces current THD to between 10 and 15 percent.

What is the working principle of VFD?

VFDs manipulate the frequency of their output by rectifying an incoming AC current into DC, and then using voltage pulse-width modulation to recreate an AC current and voltage output waveform. However, this frequency conversion process causes 2% to 3% loss as heat in the VFD — caloric energy that must be dissipated.

What does a VFD do?

A variable frequency drive controls the speed of an AC motor by varying the frequency supplied to the motor.

What is harmonics in VFD?

Harmonics are defined from the Fourier series that defines any periodic wave shape. Typically a three-phase, six-pulse VFD will draw nonlinear current that introduces the fifth and seventh harmonics on top of the fundamental frequency. The symptoms of the VFD related harmonics are evident as a distorted line voltage.

What are the advantages of 12 pulse converter?

The advantages of Twelve pulse converter are obvious. The ripple content of the ac voltage superimposing the mean value of the dc voltage is reduced greatly. The value of g increases (0.988) effectively improving the power factor.

Which frequency is a harmonic of 60 Hz?

120 Hz
a 60 Hz system is 2*60 or 120 Hz. At 50Hz, the second harmonic is 2* 50 or 100Hz. 300Hz is the 5th harmonic in a 60 Hz system, or the 6th harmonic in a 50 Hz system.

What causes harmonics in VFD?

Harmonics are caused by the first stage of a VFD (the rectifier). The distortion of input current feeding this rectifier on a standard (6-pulse) VFD ranges between 70-100%. AC line reactors (see Figure 8) and DC link chokes (reactors) will make the current drawn from the power line more sinusoidal (see Figure 9).

How can we reduce harmonics?

Five Ways to Reduce Harmonics in Circuits and Power Distribution Systems

1. K-Rated Transformers. ANSI Standard C57.
2. Measuring K-Factor. In any system containing harmonics, the K-factor can be measured with a power quality analyzer (see Figure 1).
3. Circuit Load.
4. Harmonic Mitigating Transformers.
5. Delta-Wye Wiring.
6. Zigzag Windings.

What’s the difference between 6 pulse and 12 pulse VFDs?

Unlike standard 6-pulse VFDs, which contain six diodes, 12-pulse VFDs contain two separate, parallel 6-pulse bridges in the input converter of the VFD. These additional pulses smooth out the waveform, making it more sinusoidal and generating less harmonic distortion to be distributed through your power system and ultimately returned to the utility.

Why are there six pulses in a DC drive?

This isn’t useful in a DC drive, but works fine for AC variable frequency drive (VFD). Standard industrial drives – both AC and DC – use six rectifier devices to form a three-phase full-wave bridge. This type of converter is called a “six-pulse” design, because it draws current in six distinct pulses from the AC line.

What causes the frequency of a VFD drive?

These levels are also induced by source impedance, that being the line supply and distortions within it. VFD also employs a DC bus line reactor to help with harmonic distortions. This allows distances between the motor and drive of 1000 plus feet without aid.

When does a six pulse converter draw current?

This type of converter is called a “six-pulse” design, because it draws current in six distinct pulses from the AC line. They do NOT draw current continuously, but (in the case of a VFD) only when the incoming line voltage exceeds the drive’s DC bus voltage, or in the case of a DC drive, only when the SCR in the converter is gated on.