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

[THA.1]

(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?

[GMA]

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

[THA.1]

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 · Accepted solution]

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

[THA.1]

Thank you for your answer !

Regards,

THA.1