Part Number: TMS320F28P650DK Tool/software: "Should the Current Loop Bandwidth (wccD/wccQ) in FCL Be Fixed Based on Sampling Frequency or Adapted Dynamically Based on Motor Speed?" I'm working on a motor control project " tida_010936_ganhfmd" using TI's Fast Current Loop (FCL) with a BLDC motor. In the reference code, the current loop bandwidth ( wccD and wccQ ) is defined as a fixed value based on the sampling frequency: This makes the current loop bandwidth constant, tied to the PWM frequency rather than motor speed. For example, with a 20 kHz PWM frequency, the calculated current loop bandwidth is: #define SAMPLING_FREQ (ISR_FREQUENCY * 1000) #define CUR_LOOP_BANDWIDTH (2.0F * PI * SAMPLING_FREQ / 40) #define ISR_FREQUENCY (PWM_FREQUENCY) #define PWM_FREQUENCY 20 // 20 kHz 2 π* 20000/40 = 3141.59 rad/s However, motor dynamics (such as back-EMF, inductive reactance, and motor time constant) change with speed. Therefore, I would expect the optimal gain crossover frequency to scale with the motor electrical frequency (which depends on motor speed) rather than remain constant. Now, My Questions: Should the current loop bandwidth ( wccD and wccQ ) be dynamically adjusted based on motor electrical frequency instead of being fixed? If yes, would it be better to set the gain crossover frequency to around 10% to 20% of the motor electrical frequency for consistent phase margin and bandwidth across different speeds? Would this approach provide better stability and consistent phase margin across different speeds? 4. Are there any recommended guidelines or trade-offs when setting the target crossover frequency based on motor electrical frequency in FCL? The issue I'm facing is my motor is not smooth at some speeds when running closed loop speed control and in one particular direction. I tried changing phase sequence, WccD & WccQ values and PID values, but the issue persists. I want to confirm whether this dynamic tuning approach is more suitable for maintaining consistent current loop response across varying motor speeds. Any insights or recommendations would be greatly appreciated! Thanks & Regards Raghu
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