AN1913D Freescale Semiconductor / Motorola, AN1913D Datasheet - Page 14

• Manufacturer Part Number: AN1913D
• Description: 3-phase BLDC Motor Control with Sensorless Back-EMF ADC Zero Crossing Detection using DSP 56F80x
• Manufacturer: Freescale Semiconductor / Motorola

Control Technique
5.
5.1 Control Technique - General Overview
5.2 PWM Voltage Generation for BLDC
14
The divided phase voltages are connected to the AD convertor module on the DSP and are processed
in order to get the Back-EMF Zero Crossing signal. The Back-EMF Zero Crossing detection enables
position recognition, as explained in previous sections. The software selects one of the phases which
corresponds to the present commutation step.
A current shunt is used to measure the DC-Bus current. The obtained signal is rectified and amplified
(0-3.3V with 1.65V offset). The DSP A/D converter as well as Zero Crossing detection is
synchronized with the PWM signal. This synchronization avoids spikes when the IGBTs (or
MOSFETs) are switching and simplifies the electric circuit.
The A/D converter is also used to sense the DC-Bus Voltage and drive Temperature. The DC-Bus
voltage is divided down to a 3.3V signal level by a resistor network.
The six IGBTs (copack with built-in fly back diode) or MOSFETs and gate drivers create a compact
power stage. The drivers provide the level shifting that is required to drive high side bridge circuits
commonly used in motor drives. The PWM technique is applied to the control motor phase voltage.
The general overview of used control technique is shown in
following subsections:
The implementation of the control technique with all the software processes are shown in Flow Chart,
State diagrams and Data Flow. Refer to
A 3-phase voltage system (see
by 3-phase power stage with 6 IGBTs (MOSFET) power switches controlled by the DSP on-chip
PWM module (see
The PWM signals, with their current state, are shown in
Figure 5-2
off.
•
•
•
•
Control Technique
PWM voltage generation for BLDC
Back-EMF Zero Crossing sensing
Sensorless Commutation Control
Speed Control
shows that both the Bottom and Top power switches of the non-fed phase must be switched
Figure
BLDC control with BEMF Zero Crossing using ADC
Freescale Semiconductor, Inc.
For More Information On This Product,
5-1).
Figure
Go to: www.freescale.com
3-2.) needs to be created to run the BLDC motor. It is provided
Section
7.1,
Section
Figure 5-2
7.2, and
Figure
and
Section
Figure
4-1. It will be described in
7.3.
5-3.