replacement scheme used in ac voltage regulator using TRIAC.
An ac voltage controller is used to vary the rms value of the alternating voltage applied to the load circuit by inserting the thyristor between the load and the constant voltage source. the rms value of the alternating voltage applied to the load circuit is controlled by controlling the trigger angle of the thyristor in the ac voltage control circuit.
In short, the ac voltage controller is a type of thyristor power converter used to convert a fixed voltage, the supply of fixed frequency ac inputs to obtain variable voltage output.
There are two types of thyristor controls used in practice to control the ac power flow
- On-off control
- Phase control
These are the two ac output voltage control techniques.
In the on-off control technique, the thyristor is used as a switch to connect the load circuit to an ac supply (source) for multiple input ac cycles and then disconnect it for multiple input cycles. thyristors thus act as high speed contractors (or high speed ac switches).
In the thyristor control phase is used as a switch to connect the load circuit to the ac input supply, for part of each input cycle. it is an ac supply voltage that is chopped up using a thyristor during part of each input cycle.
The thyristor switch is turned on for part of every half cycle, so the input supply voltage appears across the load and then switched off for the rest of the half of the input cycle to disconnect the ac from the load.
By controlling the phase angle or the trigger angle (snooze angle), the output rms voltage across the load can be controlled.
Ac thyristor voltage controller using ac path shift or ac phase shift. the thyristor in the ac voltage controller is the mutated line (the ignited phase) because the input supply is ac. when the ac voltage of the input reverses and becomes negative for half the negative cycle the current flowing through the thyristor conductor decreases and drops to zero. so that on the thyristor is naturally dead, when the device current goes down to zero.
Thyristor phase controls are relatively inexpensive, thyristor level converters are slower than fast-switch thyristor-level inverters typically used.For applications up to 400Hz, if the triac is available to meet the voltage and current rating of a particular application, triac is more commonly used.
Due to ac path change or natural turnover, no extra circuit or component turnover and circuit for ac voltage controller is very simple.
Because of the nature of the output waveform, analysis, the expression derivation for performance parameters is not simple, especially for controlling the phase ac voltage controlled by the load rl. but anyway most of the practical load is of type rl and hence the rl load should be considered in the analysis and design of the ac voltage control circuit.