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.