Question

A three-phase six-step inverter delivers power to a resistive load from a 450 V
dc source. For a star-connected load of 10 ? per phase, determine:
(i) rms value of load current
(ii) rms value of IGBT current
(iii) Load power.

Answer 1

Answer :

E_dc=450V

R_Load=10ohm Per Phase

when the load is a balance resistive load  the phase to neutral Voltages in three phase are V_AN = 1/3 E_dc =1/3*450=150V

V_BN = -2/3 E_dc=-2/3*450=-300V

V_CN = 1/3 E_dc=1/3*450=150V

where V_AN ,V_BN, V_CN are the phase to Neutral voltages of A,B,C phases.

now the resistance per phase is 10 ohms

so per phase current is for I_AN=V_AN/R=150/10=15A

I_BN=V_BN/R=-300/10=-30A

I_CN=V_CN/R=150/10=15A

as 2 IGBTs are conducted at a time are in series so rms value of IGBT Current is 15A

in star connected system Line current is sames as the phase current so

rms value of load current =15A

per phase voltage is 150V so line voltage is 1.732*150=260V

so load power is V*I=260*15=3900watts