AN2009 datasheet(10/39 Pages) STMICROELECTRONICS

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PWM MANAGEMENT FOR 3-PHASE BLDC MOTOR DRIVES USING THE ST7MC

4 PWM MANAGER IN VOLTAGE MODE AND CURRENT MODE

The PWM signal logically ANDed with the switch control signal is used to control the power ap-

plied to the motor. It can either control the voltage on the motor with a fixed PWM duty cycle

or the current by means of an integrated current control circuitry.

When the PWM signal controls the voltage, the motor is driven in voltage mode. When it is

controlling the current, the motor is driven in current mode.

Voltage mode allows you to control the speed easily by changing the motor reference voltage.

It does not give you fine control of the current but you can limit the current and consequently

the torque to a maximum value. The voltage control is done by the PWM duty cycle.

Current mode allows you to permanently control the torque by changing the motor reference

current, because torque is proportional to current. The current in the windings is regulated in

real time and there is a true DC current flowing through the DC Bus. Current mode also allows

the current for each of the 6 steps to be finely controlled as the current control is done during

the PWM cycle.

Depending on whether the motor is driven in current or voltage mode, the PWM signal does

not have the same origin as shown in Figure 7.

AN2009 Datasheet(PDF) 10 Page - STMicroelectronics