Explanation:

A single-phase half wave voltage controller is a device that controls the average value of the output voltage of a single-phase AC supply. This is done by adjusting the conduction angle of the SCR (Silicon Controlled Rectifier).

The half wave voltage controller can be implemented using two types of configurations - parallel and anti-parallel.

Parallel Configuration:
In this configuration, one SCR is connected in parallel with one diode. The SCR and diode are connected in series with the load. The working of this configuration is as follows:

1. During the positive half-cycle of the AC supply, the diode conducts and the SCR is reverse-biased. The load voltage is equal to the input voltage.

2. At a particular point in the positive half-cycle, the gate signal is applied to the SCR. This causes the SCR to turn on and conduct. The load voltage is now equal to the voltage drop across the SCR.

3. As the input voltage decreases to zero, the SCR turns off and the load voltage becomes zero.

4. During the negative half-cycle of the AC supply, both the SCR and diode are reverse-biased. The load voltage is zero.

Anti-parallel Configuration:
In this configuration, one SCR is connected in anti-parallel with one diode. The SCR and diode are connected in series with the load. The working of this configuration is as follows:

1. During the positive half-cycle of the AC supply, the diode conducts and the SCR is reverse-biased. The load voltage is equal to the input voltage.

2. At a particular point in the positive half-cycle, the gate signal is applied to the SCR. This causes the SCR to turn on and conduct. The load voltage is now equal to the voltage drop across the SCR.

3. As the input voltage decreases to zero, the SCR turns off and the load voltage becomes zero.

4. During the negative half-cycle of the AC supply, the diode is reverse-biased and the SCR is forward-biased. The load voltage is equal to the input voltage.

The anti-parallel configuration is preferred over the parallel configuration as it provides better protection against reverse voltage and reverse current.