25-08-2017, 09:32 PM
SINGLE PHASE AC VOLTAGE CONTROLLER
AIM :
To design and simulate a Single Phase AC Voltage Controller with R and RL load for given value of firing angle and to analyze the harmonics present in the output waveforms.
THEORY:
AC voltage controllers (ac line voltage controllers) are employed to vary the RMS value of the alternating voltage applied to a load circuit by introducing Thyristors between the load and a constant voltage ac source. The RMS value of alternating voltage applied to a load circuit is controlled by controlling the triggering angle of the Thyristors in the ac voltage controller circuits.
There are two different types of thyristor control used in practice to control the ac power flow
On-Off control
Phase control
1) ON-OFF CONTROL:
In On-Off control technique Thyristors are used as switches to connect the load circuit to the ac supply (source) for a few cycles of the input ac supply and then to disconnect it for few input cycles. The Thyristors thus act as a high speed contactor (or high speed ac switch).
2) PHASE CONTROL
In phase control the Thyristors are used as switches to connect the load circuit to the input ac supply, for a part of every input cycle. That is the ac supply voltage is chopped using Thyristors during a part of each input cycle.
By controlling the phase angle or the trigger angle ‘’ (delay angle), the output RMS voltage across the load can be controlled.
The trigger delay angle ‘’ is defined as the phase angle (the value of t) at which the thyristor turns on and the load current begins to flow.
APPLICATIONS OF AC VOLTAGE CONTROLLERS
Lighting / Illumination control in ac power circuits.
Induction heating.
Industrial heating & Domestic heating.
Transformer tap changing (on load transformer tap changing).
Speed control of induction motors (single phase and poly phase ac induction motor control).
Result :
Thus a Single Phase AC Voltage Controller with R and RL load for given value of firing angle was designed, simulated and the harmonics present in the output waveforms were analyzed.