Convert PID parameters to Q15 format
First at all the maximum representables values of the Q15 format are -1 and 0.9999. So you might have a problem with your Ki.
The most common solution for converting a double to a Q15 is to multiply it with 2^15.
I am usually using this macro:
#define Q15(x)(s16) ((x&lt;0.0) ? (s16)(32768*(x) - 0.5):(s16)(32768*(x) + 0.5))

But because of your Ki is not working with the Q15 format you should use another Q-format. eg: Q6 or Q7.
For further information you could check wikipedia.