TMS320F28027: Trying to increase PID response on a load change

Hello everyone!

I want to change analog pwm uc... on tms320... I have a buck converter which need to regulate output current (not voltage!), so output capacitor is almost absent. I`m using LEM as a sensor. There is a load frequency of 500 Hz for example (can be changed since 0 till 5 KHz) commutating short circuit and R=5 Ohm.

Earlier there was an analog regulator, and it was faster. Magnitude of current overshoot was less in 3 times at least. I`m trying some way to increase tms320 speed. In a SLUA708 for ucd3138 there is a 2.2 "Firmware Implementation of PI Controller" and looks like there is an opportunity to change gains depending on error. F_pwm=50kHz (T=20us). I wrote some coarse code for trying in
interrupt void cpu_timer2_isr(void) - 5 us since start of a period every cycle:

diff = Adc_Vout1 - Vout_Ref_wInj;

if(diff > 900000)//about 1 A magnitude
{//
  CpuTimer2.InterruptCount++;
  Pgain = 4000;
  Igain = 1;
  CpuTimer2Regs.TCR.bit.TIE = 0;//stop timer2
  if(CpuTimer2.InterruptCount > 5 && flag_trip == 0)//new gain should be not more than 5 times during short cirquit
  {
    Pgain = 2500;//
    Igain = 80;
    CpuTimer2.InterruptCount = 0;
    flag_trip = 1;
  }
}

if(diff <= 900000)//if error less than 1 A, we use small gain
{
  flag_trip = 0;
  Pgain = 2500;
  Igain = 80;
  CpuTimer2.InterruptCount = 0;
}

That works much worse than just 2500 or 4000 because of oscillations. You ask: why don`t you use Pgain = 4000 since the beginning! I`ll say that there are oscillations too. There is a such a dependence: big gain - oscillations and unstable system, small gain - big overshoot. This is ususal and logical.

Can anyone give me some fragment of working source code (I can`t find for ucd3138 PWR026 PFC EVM source code)? Is there any sence in such an approach for tms320?  Would anyone offer some approach for such a load mode? Maybe it`s impossible to get the same result as for analog controller, but  I want to reach it as close as possible.

Will be very appreciate for any help!