what changes for HIGHER DC VOLTAGE AKST7MC starter KIT

Posted on May 17, 2011 at 10:18

Thank you Tanio for your reply,

but now i prefer to use an other power stage, instead of the IGBT's of the starter Kit. And there will be the next problem. The PWM signals i need for my new Power switches are inverted to the signals from the starter kit. And i don't know which changes are necessary for the special function register for these ports. I found that i have to change the settings of the MPOL register but i'm not sure. they refer to MPHST register and to the OP[5:0] bits, so i'm a bit unsure.

The simple way is to use seperate inverter circuits, but there is no space on my board.

I also don't knew how to change these register. The reset MPOL register value is 0011 1111 but when i tried to read them from the reseted MCU the value is 1111 1111.

Is it realy necessary to set the value bit by bit. I don't know much about port option.

And what does the complementary pwm mean in the st7 user's manual when they talk about the DTE bit whith Mosfet instead of IGBT's used.

I know it is a huge text but i hope anybody could help me.

Best regards.

yours sincerely Benn

Posted on May 17, 2011 at 10:18

Hello,

after the first tests with the Motor and AKST7MC kit iwas really satisfied how well it works. But the motor is made for DC BUS Voltage around 400 Vdc and the rectifier and the microcontroller will be deactivated around 240 Vac input voltage that is around 330 Vdc Voltage Bus. Can anybody help me i have to decide is it better to improve the starter kit easily or better to use a

different rectifier but which one?! It is not that easy.

I tried to change the capacitors on the dc link, but there is no information about type only max. DC Voltage an in some case the capacitance.

thank you for reply - i hope so

Benn

Posted on May 17, 2011 at 10:18

Hello,

looking at the power board schematic, these are the modifications you could try:

- the transils Z2, Z3, Z4 should be replaced with 3 transils of 150V each one;

- the bulk capacitors replaced with a pair of bigger voltage values;

- the capacitor C20 with a bigger voltage one;

- decrease the value of R20 in such a way the software protection is by-passed;

Please, take care that these modifications has been performed just in limited conditions, they are not fully tested: it is only my personal opinion on what you could change to solve your technical problem.

Your feedback would be appreciated...

Tanio

Posted on May 17, 2011 at 10:18

Hello Benn,

just for your understanding, let me explain the meaning of the two registers you are referring to:

- MPHST is the register that establishes which MTC output channels are currently active;

- MPOL register estbilishes which is the polarity of the active channel.

Please, refer to Table 76 on page 217 for more details.

In the next version of Control Panel (the GUI 2.0) it will be possible to manage also an external power board, taking care also of the polarity aspects.

Regarding your second question, as explained in the ST7 user's manual, here the purpose is to recirculate the current throught the MOSFET rather than its internal diode. To do that, it is necessary turn ON the MOS (that will work in reverse mode) while the other MOS of the same leg is active (PWM generating). To avoid cross conduction some dead-time has to be inserted by validating the DTE bit. That's called ''Synchronous rectification''.

Best regards,

Tanio