Introduction to Rectifiers
- One of the first and most widely used application of power electronic devices have been in rectification. Rectification refers to the process of converting an AC voltage or current source to dc voltage and current.
- Rectifiers specially refer to power electronic converters where the electrical power flows from the ac side to the dc side. In many situations the same converter circuit may carry electrical power from the dc side to the ac side where upon they are referred to as inverters.
- The working principle and analysis of several commonly used rectifier circuits supplying different types of loads (resistive, inductive, capacitive, back emf type) can be studied. Points that are of interest are:
• Waveforms and characteristic values (average, RMS etc) of the rectified voltage and current.
• Influence of the load type on the rectified voltage and current.
• Harmonic content in the output.
• Voltage and current ratings of the power electronic devices used in the rectifier circuit.
• Reaction of the rectifier circuit upon the ac network, reactive power requirement, power factor, harmonics etc.
• Rectifier control aspects (for controlled rectifiers only)
- In the analysis, following simplifying assumptions will be made.
• The internal impedance of the ac source is zero.
• Power electronic devices used in the rectifier are ideal switches.
- The first assumption will be relaxed in a latter module. However, unless specified otherwise, the second assumption will remain in force.
- Rectifiers are used in a large variety of configurations and a method of classifying them into certain categories (based on common characteristics) will certainly help one to gain significant insight into their operation.
- Unfortunately, no consensus exists among experts regarding the criteria to be used for such classification.