PWM Rectifier

Submitted by bssuperadmin on Sun, 07/27/2014 - 21:47

1.4.5 PWM Rectifier

The most interesting reduction technique of current harmonic is a PWM (active) rectifier (Fig. 1.3).


Two types of PWM converters, with a voltage source output (Fig. 1.4) and a current source output (Fig. 1.5) can be used.



First of them (fig-1.4) called a boost rectifier (increases the voltage) works with fixed DC voltage polarity.

And the second (fig-1.5), called a buck rectifier (reduces the voltage) operates with fixed DC current flow.


Fig-1.4: PWM boost rectifier




Fig-1.5 PWM buck rectifier






Among the main features of PWM rectifiers are:

  • bi-directional power flow,

  • nearly sinusoidal input current,

  • regulation of input power factor to unity, or leading.

  • Low harmonic distortion of line current (THD below 5%),


  • adjustment and stabilization of DC-link voltage (or current),

  • Reduced capacitor (or inductor) size due to the continuous current.


Furthermore, it can be properly operated under line voltage distortion and notching, and line voltage frequency variations. Similar to the PWM active filter, the PWM rectifier has a complex control structure; the efficiency is lower than the diode rectifier due to extra switching losses. A properly designed low-pass passive filter is needed in front of the PWM rectifier due to EMI concerns. But this technique is most impressive to advances in power semiconductor devices (enhanced speed and performance, and high ratings) and digital signal processes, which allow fast operation and cost reduction.

By using proper switching sequences and controlling the switching signal “unity power factor control” can be achieved with PWM rectifier Technology.



Related Items

Rectifiers, their advantages, and disadvantages

Power electronics in broader aspect actually controls the flow of power to make it suitable to be used by diverse type of instruments and appliances. The ability to control the flow of power is derived from using solid state switches along with their controllers.

Active PWM filter

An alternative to the passive filter is use of the active PWM filter (AF), which displays better dynamics and controls the harmonic and fundamental currents. Active filters are mainly divided into two different types..

Multi-pulse rectifier

1.4.3 Multi-pulse rectifier.

Mixing single and three phase diode rectifier

1.4.2 Mixing single and three phase diode rectifier

Traditional harmonic reduction technique

The traditional method of current harmonic reduction involves passive filters LC, parallel-connected to the grid. Filters are usually constructed as series-connected legs of capacitors and chokes [the number of legs depends on number of filtered harmonics (5th, 7th, 11th, 13th) ].