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FOC concept in Motor Drive.

Rahul Sharma
Expert 2725 points

Dear Team,

I know the concept of FOC and have gone through the TI motor control seminar videos. There i come to know that the Angle of the output voltage vector is determined by relative 'on' time between the two adjacent voltage states and the magnitude of that voltage vector is determined by the relative 'on' time between the two adjacent vectors and the null vector. Hence there is "Angle" which defines the speed(frequency) and the magnitude of the vector which defines the torque.

 


I have two doubts- 

1) In current controlled project (lab5a), when i am commanding the Iq_ref value then what actually i am commanding? Is it the only magnitude of that vector?

2) Whenever i set the variable "USER_IQ_FULL_SCALE_FREQ_Hz = 146.7 (for max target speed = 2000 rpm)", and after enabling "Run_Identity_flag" and “Flag_enableSys”, then what exactly happens? a constant pattern of PWM signals is generated to provide 146.7 Hz Sine wave frequency? or it is being varied by the Iq_ref variable?

If i simplify my question then how both frequency and the magnitude of voltage vector depends on Iq_ref parameter?

Thanks.

  • 0
    TI__Guru** 114905 points
    Hi Rahul,

    Your post is being moved to the InstaSPIN forum for better support.
  • 0 in reply to Rick Duncan
    TI__Expert 8565 points
    Hi Rahul,

    1. the current vector consists of Iq and Id. in lab 5a you can control both current values but only Iq is generating torque since it is perpendicular to the rotor flux.

    2. USER_IQ_FULL_SCALE_FREQ_Hz is needed to scale the fixed point numbers for the electrical frequency of the motor. It is needed to prevent overflows in the numbers. It is not generating a fixed pwm pattern, actually I think you will not see differences in operation when you change this value.

    If you give controller a Iq_ref it will place the voltage vector in the machine to achieve this Iq current. When Iq is present the machine will generate torque and accelerates so the frequency of the voltage vector also needs to increase to remain Iq perpendicular to the rotor flux.

    Does this help?
  • 0 in reply to Simon Jagla
    Expert 2725 points
    Hi Simon,
    I got the point.
    That means if i am giving the Iq_ref then the torque will produced first and frequency of the voltage vector will always adjust itself to make the Iq perpendicular to rotor flux. If it so, then thanks for the clarification.