Multi-Pulse Rectifier Solutions for Input Harmonics Mitigation

Adjustable speed AC drives are mainly made up of two power sections, i.e., a rectifier section and an inverter section. The AC source voltage is converted into a DC voltage by the rectifier circuit, and then the DC voltage is converted again into a PWM controlled variable voltage AC output by the inverter circuit. The six-diode bridge rectifier is most widely used as an AC-to-DC converter. This diode rectifier has a nonlinear (i.e. non-sinusoidal) load characteristic causing harmonic currents flow into the power source and results in line voltage distortion. Excessive harmonics in a power source raise many practical problems such as;

  • The rms current increase and input power factor reduction
  • Overheating of grid-connected motors, cables, transformers, and other distribution equipment
  • Resonating and harmonic heating of the power factor correction capacitors
  • Nuisance tripping of the thermal circuit breakers
  • Malfunction of PLCs, computers, and other harmonics sensitive equipment.

The Yaskawa E7,F7,G7, and P7-series drives above 30HP have a built-in DC link choke as a standard easily mitigating input current harmonics. In case of six-diode bridge rectifier, the input current Total Harmonic Distortion (THD) is approximately 40% at a full load condition. The harmonic currents can be further reduced to about 30% with the addition of input AC reactors in combination with a DC link choke. For further harmonics reduction, multipulse rectifier topologies are good practical solutions, which reduce input current harmonics to levels below 10%. This paper introduces general features and advantages of Yaskawa's multi-pulse solutions that include 12-pulse and 18-pulse rectifier topologies.

Learn More

What are your comments?

You cannot post comments until you have logged in. Login Here.

Comments

No one has commented on this page yet.

RSS feed for comments on this page | RSS feed for all comments