UM0723 Datasheet, PDF (21/48 Pages) STMicroelectronics – 1 kW three-phase motor control demonstration board

UM0723
Figure 12. Three-shunt configuration
Board description
+5 V
Smart SD
COMPARATOR ₊
–
10 CP+
OPOUT 7
VCC
OPAMP ₊
–
VREF
9 OP+
6 OP–
L6390
+3.3 V
R3 (R52, R78, R97)
(R53, R75, R99)
R2 (R54, R76, R100)
Shunt
resistor
R (R46, R66, R92)
r (R48, R72, R94)
GND
AM00474
For previously mentioned FOC configurations it is necessary to set the proper gain by
applying the W10 jumper and by applying the W11 jumper to the dash marked position.
Six-step (block commutation) current reading configuration
In case of six-step (also called block commutation) current control, only two of the motor
phases conduct current at the same time. Therefore, it is possible to use only one shunt
resistor placed on the DC link to measure the motor phase current. Moreover, as the current
is always flowing on the shunt resistor in the same direction, only positive current must be
measured, and in this case, the amplifying network needs to be properly designed. The
details of single-shunt current sensing reading configuration are shown in Figure 13. In this
configuration, the current sampling is done only when the value on the shunt resistor is
positive. The only positive value read on the shunt resistor allows the setting of a higher gain
for the op amp than the one set in the three-shunt reading mode.
The op amp is used in follower mode with the gain of the op amp set by resistor r and R:
Equation 5
G = ^R------+-----^r-
r
It is possible to calculate the voltage on the output of the op amp, OP OUT V_OUT, as the sum
of a bias, V_BIAS, and a signal, V_SIGN, component equal to:
Equation 6
V_OUT = V_SIGN + V_BIAS
Doc ID 15870 Rev 4
21/48