Phase Controlled Rectifiers in Power Electronics And Drives : Practice MCQ Questions & Answers with Explanations

A single-phase fully controlled rectifier uses four thyristors in a full-bridge configuration to convert AC input into controlled DC output. The firing angle α determines the output voltage level, ranging from maximum positive DC at α = 0° down to zero at α = 180°.

The average output voltage of a single-phase half-wave controlled rectifier is (V_{o(avg)} = \frac{V_m}{2\pi}(1 + \cos\alpha)). With (V_m = 400) V and (\alpha = 60°): (V_{o(avg)} = \frac{400}{2\pi}(1 + \cos 60°) = \frac{400}{2\pi} \times 1.5 = \frac{300}{\pi}).

A TUF close to unity is desirable as it indicates the transformer is being used efficiently. A higher pulse number reduces DC ripple and harmonics, improving smoothing and commutation. Statement b is incorrect — the PIV to no-load DC output voltage ratio should be kept low, not high, to prevent diode breakdown.