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Calculating current limit settings


andyf
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I have a Parker SM232A 3 phase brushless DC motor with:

Instantaneous current: 8.3 A peak

Continuous current: 2.8 A peak

 

Direct PWM driven by Power PMAC and 3U042 amplifier 4/8 A rms

 

If I follow the Power PMAC User's Guide for calculating maxdac and i2tset by hand I get the following:

 

maxdac = (8.3/13.01) * (32768 * .866) = 18103

i2tset = (2.8/13.01) * (32768 * .866) = 6107

 

However when setting this up using IDE motor setup it calculates:

 

maxdac = 20904

i2tset = 7052

 

It seems the values from motor setup seem to ignore the .866 required for 3-phase calculation. Please advise.

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Hi,

 

The System Setup software performs the correct calculations according to our Chief Engineer. Below is the calculation algorithm used in the software:

 


Motor[x].I2tSet 	Continuous current limit		
In these calculations assume:		
Ic = Safety.I2TProtection.ContCurrent	
Ii = Safety.I2TProtection.InstantaneousCurrent
t = Safety.I2TProtection.MaxTimeAllowed	
MaxADC = AmplifierInfo.MaxADC		
Switch (Control_Type)			
 	Case (PositionCtrl)		
 	Case (VelocityCtrl)		
 	 	Motor[x].I2tSet = 0	
 	 	Break;		
 	Case (TorqueCtrl)		
 	 	Motor[x].I2tSet = 32767 * Ic / Ii
 	 	Break;		
 	Case (CommutationCtrl)	
 	 	Motor[x].I2tSet = SQRT( (32768*32768*Ic[RMS]/(ABS(Motor[x].PwmSf)*Ii_forAmplifier[RMS]))^2 - Motor[x].IdCmd^2 )
 	 	Break;		
 	Case (CurrentLoopCtrl)	
 	 	Motor[x].I2tSet = SQRT( (32768*SQRT(2)*Ic* COS( 360*ABS(Motor[x].PhaseOffset)/2048 - 90 ) / MaxADC)^2 - Motor[x].IdCmd^2 )
 	 	Break;		
 	Case (DirectMicroSteppingCtrl)
	 	Motor[x].I2tSet = 32768*SQRT(2)*Ic* COS( 360*ABS(Motor[x].PhaseOffset)/2048 - 90 ) / MaxADC
	 	Break;		

Motor[x].I2tTrip 	Integrated current shutdown limit		
Switch (Control_Type)			
 	Case (PositionCtrl)		
 	Case (VelocityCtrl)		
 	 	Motor[x].I2tTrip = 0	
 	 	Break;		
 	Case (TorqueCtrl)		
 	Case (CommutationCtrl)	
 	Case (CurrentLoopCtrl)	
 	 	Motor[x].I2tTrip = ( Motor[x].MaxDac^2 + Motor[x].IdCmd^2 - Motor[x].I2tSet^2 ) * Safety.I2TProtection.MaxTimeAllowed                // Note: Based upon calculated values and not PMAC values
 	 	Break;		
 	Case (DirectMicroSteppingCtrl)
	 	Motor[x].I2tTrip = ( calcualtedMaxDac^2 - Motor[x].I2tSet^2 ) * Safety.I2TProtection.MaxTimeAllowed                // Note: Based upon calculated values and not PMAC values
	 	Break;		
Motor[x].IdCmd 	Desired magnetization (direct) current		 
Switch (Control_Type)				 
 	Case (PositionCtrl)			 
 	Case (VelocityCtrl)			 
 	Case (TorqueCtrl)			 
 	 	Motor[x].IdCmd = 0		 
 	 	Break;			 
 	Case (CommutationCtrl)		 
 	 	If (Motor Type = AC induction)	 
 	 		Motor[x].IdCmd =  (0.1 * 32768*32768*Ic[RMS])/(ABS(Motor[x].PwmSf)*AmplifierInfo.Ii[RMS])	 
 	 	Else			 
 	 		Motor[x].IdCmd = 0	 
 	 	Endif			 
 	 	Break;			 
 	Case (CurrentLoopCtrl)		 
 	 	If (Motor Type = AC induction)	 
 	 		Motor[x].IdCmd =  0.1 * 32768*SQRT(2)*Ic* COS( 360*ABS(Motor[x].PhaseOffset)/2048 - 90 ) / MaxADC	 
 	 	Else			 
 	 		Motor[x].IdCmd = 0	 
 	 	Endif			 
 	 	Break;			 
 	Case (DirectMicroSteppingCtrl)	 
	 	Motor[x].IdCmd =  0.5 * 32768*SQRT(2)*Ic* COS( 360*ABS(Motor[x].PhaseOffset)/2048 - 90 ) / MaxADC	 

Motor[x].MaxDac 	Instantaneous servo output limit			 
In these calculations assume:			 
MaxADC = AmplifierInfo.MaxADC			 
Switch (Control_Type)				 
 	Case (PositionCtrl)			 
 	Case (VelocityCtrl)			 
 	 	Switch(Output_Signal)	 
 	 	 	Case (DAC)	 
 	 	 	 	Motor[x].MaxDac = 32767	 
 	 	 	 	Break;	 
 	 	 	Case (Filtered_PWM)	 
 	 		 	Motor[x].MaxDac = 16384	 
 	 		 	Break;	 
 	 	Break;			 
 	Case (TorqueCtrl)			 
 	 	Switch(Output_Signal)	 
 	 	 	Case (DAC)	 
 	 	 	 	Motor[x].MaxDac = 32767 * MIN(MotorInfo.Ii, AmplifierInfo.Ii)/ AmplifierInfo.Ii	 
 	 	 	 	Break;	 
 	 	 	Case (Filtered_PWM)	 
 	 		 	Motor[x].MaxDac = 16384 * MIN(MotorInfo.Ii, AmplifierInfo.Ii)/ AmplifierInfo.Ii	 
 	 		 	Break;	 
 	 	Break;			 
 	Case (CommutationCtrl)		 
 	 	Motor[x].MaxDac = 32768*32768*MIN(MotorInfo.Ii[RMS], AmplifierInfo.Ii[RMS])/(ABS(Motor[x].PwmSf)*AmplifierInfo.Ii[RMS])	 
 	 	Break;			 
 	Case (CurrentLoopCtrl)		 
	 	Motor[x].MaxDac = 32768*SQRT(2)*MotorInfo.Ii* COS( 360*ABS(Motor[x].PhaseOffset)/2048 - 90 ) / MaxADC	 
	 	Break;			 
 	Case (DirectMicroSteppingCtrl)	 
	 	Motor[x].MaxDac = Motor_Max_Speed/60000*Elec._Cycles_per_Rev*2048*Sys.ServoPeriod/SlipGain*Sys.PhaseOverServoPeriod	 
	 	Break;			 

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