RECTIFIERS AND INVERTERS

Rectification is  the process of conversion of alternating input  voltage  to direct output voltages. Converters are controlled  rectifiers which  convert constant ac voltage  to variable  de output  voltage. Since  the diode rectifiers are  uncontrolled rectifier because it gives fixed  output  voltages  only  whereas in controlled  rectifiers thyristors are used are  used to  control  the output voltage of converter by varying  the delay or firing  angle. These are phase controlled rectifiers which  are simple  less expensive and highly efficient. These are  also called ac de converters and are used extensively in industrial applications for example steel  rolling mills paper mills pining presses textile mills traction system magnet  power suppliers Hvdc  transmission  variable  speed  drives portable hand  tool  drives  electro  chemical and electrometallurgical processes etc.

The reverse  process of rectification is  know as inversion. An inverter converts fixed de voltage  to a variable ac voltage and variable frequency. Ups  induction heading , HVDC power  transmission    variable  frequency drives electric  vehicle drives and air  conditioning  are some  of important application of  inverter. An power  when main power is not available. When main  power is  restored a  rectifier is uded to supply DC power  to a higher  to recharge the batteries. Inverters convert  low  frequency main AC power is first rectified to provide DC power. The  inverter then  changes the Dc  power to high frequency AC power. With ?HVDC  power  transmission  AC power is rectified and high  voltage DC power is transmitted  to another location. At the receiving location an inverter n a static inverter plant  converts the power back to AC. A variable frequency drive controls the  operating speed of an AC motor. a an  inverter provides the controlled power. Inmost  cases the variable frequency drive includes a rectifier so the DC power for the   inverter can be provided from main AC power. Since an inverter is the key  component variable frequency driver are sometime called  inverter drives of just inverter. Adjustable speed motor  control  inverters are currently used to power the  traction motor  in some  electric locomotives and diesel electric locomotives as well as some battery electric vehicles and hybrid electric highway  vehicles. An air conditioner bearing the  inverter tag  uses a variable frequency  drive  to control  the speed  of the motor  and thus  the compressor.