2P2Z for PID control

PID controller is just a particular case of 2P2Z controller, just A1= -1  and A2 =0. Few examples from Ti  put A1 = 1  to go from PID to 2P2Z  instead of -1 !!!!!!!!!!!!! see  code bellow ( line : CNTL_2P2Z_CoefStruct1.a1 = _IQ26(1.0); // A1 = 1   )

please any idea  why ? 

Thank you

Hamid

/ ADC feedback connections

ADCDRV_1ch_Rlt1 = &Adc_Vout1;

ADCDRV_1ch_Rlt2 = &Adc_Vout2;

//2P2Z connections for the Voltage Loop - Ch1

CNTL_2P2Z_Ref1 = &Vout1SetSlewed; // Slewed Voltage command

CNTL_2P2Z_Out1 = &Duty1A; // Duty command

CNTL_2P2Z_Fdbk1 = &Adc_Vout1; // O/P Voltage feedback

CNTL_2P2Z_Coef1 = &CNTL_2P2Z_CoefStruct1.b2; // point to first coeff.

// Coefficients for the Voltage Loop - PID coefficients & Clamping (Q26)

Dmax1 = _IQ24(0.8);

Pgain1 = _IQ26(0.001953);

Igain1 = _IQ26(0.003);

Dgain1 = _IQ26(0.0);

// Coefficient init - Coeeficient values in Q26

CNTL_2P2Z_CoefStruct1.b2 = Dgain1; // B2

CNTL_2P2Z_CoefStruct1.b1 = (Igain1-Pgain1-Dgain1-Dgain1); // B1

CNTL_2P2Z_CoefStruct1.b0 = (Pgain1 + Igain1 + Dgain1); // B0

CNTL_2P2Z_CoefStruct1.a2 = 0.0; // A2 = 0

CNTL_2P2Z_CoefStruct1.a1 = _IQ26(1.0); // A1 = 1

CNTL_2P2Z_CoefStruct1.max = Dmax1; //Clamp Hi

CNTL_2P2Z_CoefStruct1.min = _IQ24(0.0); //Clamp Min

//2P2Z connections for the Voltage Loop - Ch2

CNTL_2P2Z_Ref2 = &Vout2SetSlewed; // Slewed Voltage command

CNTL_2P2Z_Out2 = &Iref2; // Peak current reference command

CNTL_2P2Z_Fdbk2 = &Adc_Vout2; // O/P Voltage feedback

CNTL_2P2Z_Coef2 = &CNTL_2P2Z_CoefStruct2.b2; // point to first coeff.

// Coefficients for the Voltage Loop - PID coefficients & Clamping (Q26)

Dmax2 = _IQ24(0.8);

Pgain2 = _IQ26(0.001953);

Igain2 = _IQ26(0.003);

Dgain2 = _IQ26(0.0);

// Coefficient init - Coeeficient values in Q26