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Is max PWM modulation adjustment necessary for charging boot capacitor and how to do it?

THA.1
Associate II

(Environment)

MC_SDK 5.Y.3 + STM32CubeMX 6.3.0 with HAL + IAR EWARM 8.5

(Hardware)

custom board based on F446RE + custom power board(3-shunt) + Low Voltage BLDC motor with Encoder

(Control Mode)

Speed Control

(What I found)

In "parameters_conversion.h", there is defined MAX_MODULE as follows:

=================================================

/* MMI Table Motor 1 MAX_MODULATION_100_PER_CENT */

#define MAX_MODULE 32767

=================================================

If this 100% modulation is used, there might be some moments where low-side duty becomes close to zero (less than dead time). Then the boot capacitors might not be charged properly.

  • Is this value still good as is or need to be modified?
  • If modified, what would be the recommended value?
  • And can it directly modified in "parameters_conversion.h" or by workbench tools?

1 ACCEPTED SOLUTION

Accepted Solutions
GMA
ST Employee

Hello,

100% is not a default value, increasing the PWM frequency you will notice that Max Modulation Index will decrease.

The occurrence of having high side closed shouldn't happen during a long period (long enough have an impact on boot strap capacitor charge...), but if needed, you can change MAX_MODULE define.

Best regards.

GMA

If you agree with the answer, please accept it by clicking on 'Accept as solution'.
Best regards.
GMA

View solution in original post

4 REPLIES 4
GMA
ST Employee

Hello,

Thank you for your question.

May I propose you to have a look at this application note?

Considerations on bootstrap circuitry for gate drivers - Application note

On the other hand, investigations have to be done in order to cover all your points...

Best regards.

GMA

If you agree with the answer, please accept it by clicking on 'Accept as solution'.
Best regards.
GMA
THA.1
Associate II

Thank you for your reply.

I read that application note - I understood a few factors(dutycycle time, capacitance, etc) should be considered for proper operations.

MCSDK looks like using 100% modulation as default. Does ST recommend to appropriately change it(directly modifying #define MAX_MODULE 32767 in "parameters_conversion.h" while not supported at workbench tools)?

GMA
ST Employee

Hello,

100% is not a default value, increasing the PWM frequency you will notice that Max Modulation Index will decrease.

The occurrence of having high side closed shouldn't happen during a long period (long enough have an impact on boot strap capacitor charge...), but if needed, you can change MAX_MODULE define.

Best regards.

GMA

If you agree with the answer, please accept it by clicking on 'Accept as solution'.
Best regards.
GMA
THA.1
Associate II

Thank you for your answer !

Regards,

THA.1