Three-Phase Current Measurement0 pages

Beyond Bits

Motor Control Edition

Three-Phase Current Measurement
Freescale dedicated MCUs make it easy
Overview

Figure 1: Three-Phase Inverter Topology

Advanced motor control algorithms
such as field-oriented control (FOC)
and direct torque control (DTC) require
sensing of motor phase currents. To
reduce the number of sensors and
overall cost of the solution, the phase
currents can be measured by means of
low-cost shunt resistors with a simple
interface between the shunt resistors
and MCU inputs. The phase current is
measurable only at a certain instant and
thus the current sensing based on the
shunt resistors requires support from
the MCU. Freescale dedicated motor
control devices provide exceptional
hardware support, allowing the user to
solve specific application needs.

T1

Rdc

T5

T2

Vdc

T3
T4

T6

R1

R2

R3

Ph. B
Ph. A

Ph. C

Figure 2: Current Sensing
PWM1-T1
PWM2-T2
PWM1-T1

PWM3-T3
PWM4-T4
PWM5-T5

PWM2-T2

PWM6-T6
ISA

Dead
Time

ISB

ISC
Isense_A

Isense_A

Time to Current
Stabilization

Isense_B

ADC Current Sensing
Conversion Duration

Isense_C

Critical PWM
Pulse Width

time
PWM
Reload

Current
Sampling

PWM
Reload

Current
Sampling

PWM
Reload

Current
Sampling