Problem with 12-pulse controlled rectifier (PSPICE)

Hello. I dont know if is the correct forum. My english es bad.

I have a problem with a 12-pulse controlled rectifier. The average voltage data did not coincide with theoretically calculated data. What is the error?

I get 934V with the theoretical calculations and 1080V with PSPICE.If I change the angle of shot (alpha) I get more and more different voltages. 

The code is:

*
.PARAM Vm = {400*SQRT(2/3)}
.PARAM f = 50
.PARAM p = {1/f}
.PARAM alpha = 30.1
.PARAM delay = {alpha/360/f}
.PARAM delay1 = {(alpha+330)/360/f}
*
Va a n SIN(0 {Vm} {f} 0 0 0)
Vb b n SIN(0 {Vm} {f} 0 0 -120)
Vc c n SIN(0 {Vm} {f} 0 0 120)
Xscr1 a g1 1 SCR
Xscr3 b g3 1 SCR
Xscr5 c g5 1 SCR
Xscr4 0 g4 a SCR
Xscr6 0 g6 b SCR
Xscr2 0 g2 c SCR
Vg1 g1 0 PULSE(0 1 {delay} 0 0 {p/2} {p})
Vg2 g2 0 PULSE(0 1 {delay+1*p/6} 0 0 {p/2} {p})
Vg3 g3 0 PULSE(0 1 {delay+2*p/6} 0 0 {p/2} {p})
Vg4 g4 0 PULSE(0 1 {delay+3*p/6} 0 0 {p/2} {p})
Vg5 g5 0 PULSE(0 1 {delay+4*p/6} 0 0 {p/2} {p})
Vg6 g6 0 PULSE(0 1 {delay+5*p/6} 0 0 {p/2} {p})

*
Va1 a1 n1 SIN(0 {Vm} {f} 0 0 30)
Vb1 b1 n1 SIN(0 {Vm} {f} 0 0 -90)
Vc1 c1 n1 SIN(0 {Vm} {f} 0 0 150)
Xscr1a a1 g1a 2  SCR
Xscr3a b1 g3a 2  SCR
Xscr5a c1 g5a 2  SCR
Xscr4a 1  g4a a1 SCR
Xscr6a 1  g6a b1 SCR
Xscr2a 1  g2a c1 SCR
Vg1a g1a 0 PULSE(0 1 {delay1} 0 0 {p/2} {p})
Vg2a g2a 0 PULSE(0 1 {delay1+1*p/6} 0 0 {p/2} {p})
Vg3a g3a 0 PULSE(0 1 {delay1+2*p/6} 0 0 {p/2} {p})
Vg4a g4a 0 PULSE(0 1 {delay1+3*p/6} 0 0 {p/2} {p})
Vg5a g5a 0 PULSE(0 1 {delay1+4*p/6} 0 0 {p/2} {p})
Vg6a g6a 0 PULSE(0 1 {delay1+5*p/6} 0 0 {p/2} {p})

*

L1 2 3 120mH IC=0
R1 3 0 12

.LIB ep3.lib
.TRAN 25us 200ms 180ms 25us UIC
.PROBE
.FOUR 50 30 I(R1)
.END

A greeting and thanks