Question

2. Figure 2 shows a 6-pulse thyristor rectifier feeding a DC static load an operating at steady-state. The ac input power supply is a symmetric set of three-phase voltages forming a direct sequence, having rms line-to-line voltage of Vuns equal to 415 V and angular frequency ω equal to 100π rad/s. The load is sufficiently inductive to smooth out the load current i(t), i.e. i 1, where I is a constant. a. Derive the mathematical expression of the average DC output voltage, as a function of the firing angle, α Note: for the solution, remember that: sin(a)-sin(B)-2 cos[(α + β)/2) sin(α-β)/2] Calculate the amplitude and phase angle, referred to the correspondin phase voltage, of the fundamental component of the ac current for a firing angle a T/6 (30 degrees) and a load current / - 20 A. b. i(t) P iL(t) i (t) v(t) Fig. 2. Schematic of a 6-pulse thyristor rectifier feeding a static load. c. Explain inverter-mode operations of the rectifier and, using the attached graph paper, indicate the waveform of the load voltagev(t) for a firing angle α = 2/3m (120 degrees). d. Propose a closed-loop control for the voltage across the load, clearly indicating the function of each block diagram, the measured quantities (if any) and the control quantities.

Answer 1

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