Question

Design a circuit that converts a sinusoidal wave with 480Vrms at 60Hz into a three-phase set of voltages with 400 Vrms (Phase voltage) at 50 Hz. Suppose that this circuit is loaded with a Y-connected RL- series load with R=50Ω and 50 mH per phase. Make sure that the output THD is less than 5%. Verify your results with simulations. Estimate the power output with simulations in simulink.

Answer 1

The circuit converts AC voltage to DC and then inverts it to three phase @50Hz with a six step inverter:

Switches have a 50% duty cycle and a period of 50Hz,

Opposite switches:

SW1 SW4

SW2 SW5

SW3 SW6

Each switch triggers T/6 after the previous one, thus, the sequence is:

S1-S2-S3-S4-S5-S6

With a 3.33ms delay from each other.

Control signal of the switches, S4,S5 and S6 are complements of S1,S2,S3

To calculate the THD:

Voltage components for every harmonic:

for n=1,5,7

Impedance magnitude:

n	Vn,L-N	Zn	In	Irms
1	432.15	25.44	16.99	12.01
5	86.43	81.09	1.07	0.75
7	61.74	111.82	0.55	0.39

THD: