The Method To Measure Phase Currents With An 1Shunt Resistance - Renesas RA6T2 Application Note

Sensorless vector control for permanent magnetic
synchronous motor - 1shunt current detection

3.1.7 The method to measure phase currents with an 1shunt resistance

In the chapter, the method to measure phase currents using in this software is explained.
3.1.7.1 The timing of measure phase currents
Figure 3-3 The wave form of PWM (in case of duty pattern W>V>U)
In this program, Triangle-wave PWM mode 3 is used to generate PWM wave with dead time by GPT unit.
Figure 3-3 The wave form of PWM (in case of duty pattern W>V>U) shows the wave form of PWM in case of
duty pattern W>V>U.
At the point A in the figure, only W phase upper arm is ON as shown in the red rectangle in right side. In
that case, the current which flows in the 1shunt resistance is same as current flows in W phase.
At the point B in the figure, only U phase low arm is ON as shown in the blue rectangle. In that case, the
current which flows in the 1shunt resistance is same as current flows in U phase.
The remained V phase current can be calculated with these phase currents by the first theory of Kirchhoff.
Therefore, the three phase currents can be measured with measurement of point A and B.
The case which is shown in Table 3-6 Relation between Duty pattern and phase current is the duty pattern
W>V>U. Six duty pattern will be performed with each phase PWM output. The currents which be measured
in point A and B changes according to duty pattern, so it is necessary to assign calculated currents to each
phase. The assignment is possible, because each phase relations can be known at each PWM duty
calculation.
Table 3-6 Relation between Duty pattern and phase current
R01AN6840EJ0100 Rev.1.00
May 23, 2023
Duty pattern Point A
W > V > U Iw
W > U > V Iw
V > W > U Iv
V > U > W Iv
U > W > V Iu
U > V > W Iu
For Renesas Flexible Motor Control Series
Point B
-Iu
-Iv
-Iu
-Iw
-Iv
-Iw
Page 38 of 73