6.5 Single Phase Full Wave Ac Voltage Controller (Ac Regulator) or Rms Voltage Controller with Resistive Load Single phase full wave ac voltage controller circuit using two SCRs or a single triac is generally used in most of the ac control applications. The ac power flow to the load can be controlled in both the half cycles by varying the trigger The RMS value of load voltage can be varied by varying the trigger angle The input supply current is alternating in the case of a full wave ac voltage controller and due to the symmetrical nature of the input supply current waveform there is no dc component of input supply current i.e., the average value of the input supply current is zero. A single phase full wave ac voltage controller with a resistive load is shown in the figure below. It is possible to control the ac power flow to the load in both the half cycles by adjusting the trigger Hence the full wave ac voltage controller is also referred to as to a bi-directional controller. Fig 6.7: Single full wave ac voltage controller (Bi-directional Controller) using SCRs The thyristor is forward biased during the positive half cycle of the input supply T1 voltage. The thyristor is triggered at a delay angle of Considering T1 the ON thyristor as an ideal closed switch the input supply voltage appears across the load T1 resistor and the output voltage during to The load current flows RL vO vS through the ON thyristor and through the load resistor in the downward direction T1 RL during the conduction time of from to T1 At , when the input voltage falls to zero the thyristor current (which is flowing through the load resistor ) falls to zero and hence naturally turns off . No current flows RL T1 in the circuit during to The thyristor is forward biased during the negative cycle of input supply and when T2 thyristor is triggered at a delay the output voltage follows the negative T2 halfcycle of input from to When is ON, the load current flows in the T2 reverse direction (upward direction) through during to The time T2 interval (spacing) between the gate trigger pulses of and is kept at or 1800. At T1 T2 2 the input supply voltage falls to zero and hence the load current also falls to zero and thyristor turn off naturally. T2 Instead of using two SCR’s in parallel, a Triac can be used for full wave ac voltage control.
6.5 Single Phase Full Wave Ac Voltage Controller (Ac Regulator) or Rms Voltage Controller with Resistive Load Single phase full wave ac voltage controller circuit using two SCRs or a single triac is generally used in most of the ac control applications. The ac power flow to the load can be controlled in both the half cycles by varying the trigger The RMS value of load voltage can be varied by varying the trigger angle The input supply current is alternating in the case of a full wave ac voltage controller and due to the symmetrical nature of the input supply current waveform there is no dc component of input supply current i.e., the average value of the input supply current is zero. A single phase full wave ac voltage controller with a resistive load is shown in the figure below. It is possible to control the ac power flow to the load in both the half cycles by adjusting the trigger Hence the full wave ac voltage controller is also referred to as to a bi-directional controller. Fig 6.7: Single full wave ac voltage controller (Bi-directional Controller) using SCRs The thyristor T1 is forward biased during the positive half cycle of the input supply voltage. The thyristor T1 is triggered at a delay angle of Considering the ON thyristor T1 as an ideal closed switch the input supply voltage appears across the load resistor RL and the output voltage vO vS during to The load current flows through the ON thyristor T1 and through the load resistor RL in the downward direction during the conduction time of T1 from to At , when the input voltage falls to zero the thyristor current (which is flowing through the load resistor RL ) falls to zero and hence T1 naturally turns off . No current flows in the circuit during to The thyristor T2 is forward biased during the negative cycle of input supply and when thyristor T2 is triggered at a delay the output voltage follows the negative halfcycle of input from to When T2 is ON, the load current flows in the reverse direction (upward direction) through T2 during to The time interval (spacing) between the gate trigger pulses of T1 and T2 is kept at or 1800. At 2 the input supply voltage falls to zero and hence the load current also falls to zero and thyristor T2 turn off naturally. Instead of using two SCR’s in parallel, a Triac can be used for full wave ac voltage control.
U8_L50-Single-Phase-Full-Wave-Ac-Voltage-Controller.docx