Power Electronics (EE-452)

Assignment # 05

Deadline: 17th

Dec 2015 5:00pm

Q1. In the 3-phase full –bridge Thyristor converter shown in Figure below

a) Draw the waveform of V1 for α = 30, 90 and 150 degree on Fig. 1. (Draw the waveforms on

separate graph for each α)

b) Assume R = 2Ω, VLL = 208 V at 60 Hz, and L is large enough for i1 to be virtually constant.

Find I1 for α=30°. What quadrant is the bridge operating in?

c) Find Pload and its direction of flow at α=30°.

d) Assume that α is varied from 30° to 150° momentarily and assume the load time constant is so

large that i1 stays unchanged during the period of this study. Find Pload and its direction of flow.

What quadrant is the bridge operating in?

e) Draw the phase-a current for α=30° on fig.2 and calculate: Ia1, Ia , DF,φ1, DPF, PF and THD.

Fig.1 ωt

V

Fig.2

Q2. In the single-phase rectifier, Vs = 120 V at 60 Hz, and Ls = 1 mH.

(a) Find the time expression for the dc-side current id shown in Fig.2.2

(b) Find the values of θb, θf, and Id, peak if Vd = 150 V.

Fig 2.1

Fig 2.2

Q2. Consider the balanced 3-Phase, 4-wire, 60-Hz system.

(a) Calculate the rms value of the neutral wire current IN, if the three

single-phase rectifiers as shown in the figure below.

(b) Draw the waveform of iN.

Q3. The core illustrated in Fig. below is 1 cm thick. All legs are 1 cm wide, except for the right-

hand side vertical leg, which is 0.5 cm wide. You may neglect non uniformities in the flux

distribution caused by turning corners.

(a) Determine the magnetic circuit model of this device, and label the values of all reluctances in

your model.

(b) Determine the inductance of the winding.

A second winding is added to the same core, as shown in Fig. (b).

(c) Modify your model of part (a) to include this winding.v1

(d) The electrical equations for this circuit may be written in the form

|𝑣1

𝑣2| = |

𝐿11 𝐿12

𝐿21 𝐿22|

𝑑

𝑑𝑡|

𝑖1

𝑖2|

Use superposition to determine analytical expressions and numerical values for L11, L12 and L22