Encoder speed overflow (SpinTAC Position Converter)

Felix,

I think the issue is the scaling in your system. Converting from electrical angle to speed uses the system scaling including the sample time. By changing the pwm frequency, this will change the sample time of the speed conversion algorithm. The easy thing to try would be to increase the value for USER_IQ_FULL_SCALE_FREQ_Hz. You can also post your user.h file and I can try to find the source of the problem.

Hi Adam,

USER_IQ_FULL_SCALE_FREQ_Hz is currently set to 1310.0, which is (according to the excel spreadsheet delivered with motorware) the maximum allowed value for the hardware. Is it save to increase it significantly beyond that value or do I risk to damage something?

This is my user_j1.h:

//! \brief CURRENTS AND VOLTAGES
// **************************************************************************
#define USER_IQ_FULL_SCALE_FREQ_Hz        (1310.0)  // value given by the excel spreadsheet

#define USER_IQ_FULL_SCALE_VOLTAGE_V      (24.0)  // 24.0 Set to Vbus
#define USER_ADC_FULL_SCALE_VOLTAGE_V     (44.30) // BOOSTXL-DRV8305EVM = 44.30 V
#define USER_IQ_FULL_SCALE_CURRENT_A      (24.0)  // BOOSTXL-DRV8305EVM = 24.0 A
#define USER_ADC_FULL_SCALE_CURRENT_A     (47.14) // BOOSTXL-DRV8305EVM = 47.14 A
#define USER_NUM_CURRENT_SENSORS          (3)
#define USER_NUM_VOLTAGE_SENSORS          (3)

#define   I_A_offset    (1.004728198)
#define   I_B_offset    (1.005483985)
#define   I_C_offset    (1.006817698)

#define   V_A_offset    (0.4910094738)
#define   V_B_offset    (0.4885113835)
#define   V_C_offset    (0.4871017337)

//! \brief CLOCKS & TIMERS
// **************************************************************************
#define USER_PWM_FREQ_kHz         (30.0)
#define USER_MAX_VS_MAG_PU        (0.5)

//! \brief DECIMATION
// **************************************************************************
#define USER_NUM_PWM_TICKS_PER_ISR_TICK        (1)
#define USER_NUM_ISR_TICKS_PER_CTRL_TICK       (1)
#define USER_NUM_CTRL_TICKS_PER_CURRENT_TICK   (1)
#define USER_NUM_CTRL_TICKS_PER_EST_TICK       (1)
#define USER_NUM_CTRL_TICKS_PER_SPEED_TICK    (15)
#define USER_NUM_CTRL_TICKS_PER_TRAJ_TICK     (15)

//! \brief LIMITS
// **************************************************************************
#define USER_MAX_NEGATIVE_ID_REF_CURRENT_A   (-0.5 * USER_MOTOR_MAX_CURRENT)
#define USER_R_OVER_L_EST_FREQ_Hz            (300)
#define USER_ZEROSPEEDLIMIT                  (1.0 / USER_IQ_FULL_SCALE_FREQ_Hz)
#define USER_FORCE_ANGLE_FREQ_Hz             (2.0 * USER_ZEROSPEEDLIMIT * USER_IQ_FULL_SCALE_FREQ_Hz)

//! \brief POLES
// **************************************************************************
#define USER_VOLTAGE_FILTER_POLE_Hz  (344.62)   // BOOSTXL-DRV8305 = 344.62 Hz


//! \brief USER MOTOR & ID SETTINGS
// **************************************************************************

#define USER_SYSTEM_BANDWIDTH      (100.0) // tuned in lab 13a

#define USER_MOTOR_TYPE                 MOTOR_Type_Pm
#define USER_MOTOR_NUM_POLE_PAIRS       (12)
#define USER_MOTOR_Rr                   (0.0)
#define USER_MOTOR_Rs                   (0.2319251)
#define USER_MOTOR_Ls_d                 (0.0001494264)
#define USER_MOTOR_Ls_q                 (0.0001494264)
#define USER_MOTOR_RATED_FLUX           (0.009320291)
#define USER_MOTOR_MAGNETIZING_CURRENT  (NULL)
#define USER_MOTOR_RES_EST_CURRENT      (1.0)
#define USER_MOTOR_IND_EST_CURRENT      (-1.0)
#define USER_MOTOR_MAX_CURRENT          (9.0)
#define USER_MOTOR_FLUX_EST_FREQ_Hz     (120.0) // Given by excel spreadsheet. Default 20.
#define USER_MOTOR_MAX_SPEED_KRPM       (6.0)

#define USER_MOTOR_ENCODER_LINESi       (500.0)
#define USER_SYSTEM_INERTIA             (0.02391791343688965)  // determined with lab12a
#define USER_SYSTEM_FRICTION            (0.042265355587005615)  // determined with lab12a

you are running the entire control system at 30 KHz, which is overflowing the interrupt I'm sure.

Add in this HW decimation tick to run the interrupt, current, and estimator at 30 / 2 = 15 KHz

and the speed, position at 15 / 15 = 1 KHz

Hi Chris,

when I set USER_NUM_PWM_TICKS_PER_ISR_TICK to 2, the overflow already occurs at 2.5 krpm instead of 5 krpm. So it has the same effect as setting PWM frequency to 15 kHz instead.

I tracked it down, using the different levels of decimation rates and at each level, halving the frequency also halved the maximum speed before the overflow. In the end it seems like the maximum possible speed is directly proportional to the frequency of the the speed controller. Examples:

#define USER_PWM_FREQ_kHz                   (30.0)
#define USER_NUM_PWM_TICKS_PER_ISR_TICK        (1)
#define USER_NUM_ISR_TICKS_PER_CTRL_TICK       (1)
#define USER_NUM_CTRL_TICKS_PER_CURRENT_TICK   (1)
#define USER_NUM_CTRL_TICKS_PER_EST_TICK       (1)
#define USER_NUM_CTRL_TICKS_PER_SPEED_TICK    (15)

--> overflow at 5 krpm

#define USER_PWM_FREQ_kHz                   (30.0)
#define USER_NUM_PWM_TICKS_PER_ISR_TICK        (1)
#define USER_NUM_ISR_TICKS_PER_CTRL_TICK       (1)
#define USER_NUM_CTRL_TICKS_PER_CURRENT_TICK   (1)
#define USER_NUM_CTRL_TICKS_PER_EST_TICK       (1)
#define USER_NUM_CTRL_TICKS_PER_SPEED_TICK    (30)

--> overflow at 2.5 krpm

#define USER_PWM_FREQ_kHz                   (30.0)
#define USER_NUM_PWM_TICKS_PER_ISR_TICK        (1)
#define USER_NUM_ISR_TICKS_PER_CTRL_TICK       (1)
#define USER_NUM_CTRL_TICKS_PER_CURRENT_TICK   (1)
#define USER_NUM_CTRL_TICKS_PER_EST_TICK       (1)
#define USER_NUM_CTRL_TICKS_PER_SPEED_TICK    (10)

--> motor reaches maximum speed of around 6 krpm without overflow.

I just tried to increase USER_IQ_FULL_SCALE_FREQ_Hz, as Adam suggested, but I immediately get USER_ErrorCode_voltageFilterPole_Hz_Low.

are you sure this is a 24 pole motor? do you have a link to any documentation on it?
Any information on max RPM, or KV?

have you tried running proj_lab05a or 5b and see if you can reach > 6 KRPM?
I suppose this comments means that you did?
"When only doing torque control, It works well even after the overflow occurs, so I guess the electrical angle is still measured correctly and it is probably only an issue with the conversion from angle to speed."

How do you know the overflow is occurring? You're still running proj_lab12 so you can see the speed from the encoder but running with just an IqRef_A command?


Your USER_IQ_FULL_SCALE_FREQ_HZ is already at the maximum for the HW, don't increase. This should allow Speeds up to 6550 RPM before an overflow. So hopefully your motor is rated for < 6 KRPM.

As for the decimation I would use the default values to start:
#define USER_PWM_FREQ_kHz (45.0)

#define USER_NUM_PWM_TICKS_PER_ISR_TICK (3)

#define USER_NUM_ISR_TICKS_PER_CTRL_TICK (1)

#define USER_NUM_CTRL_TICKS_PER_CURRENT_TICK (1)

#define USER_NUM_CTRL_TICKS_PER_EST_TICK (1)

#define USER_NUM_CTRL_TICKS_PER_SPEED_TICK (15)

#define USER_NUM_CTRL_TICKS_PER_TRAJ_TICK (15)

The motor we are using is a T Motor Antigravity 4004 KV300 (see here for details: www.rctigermotor.com/.../288.html). They don't explicitly mention a max RPM, but if I understand it correctly, it should be 7200 rpm (given KV=300, max I = 9A, max P = 216W). We won't need the full speed, though, so it is no problem for us if we have to stay below 6000 rpm.

I set PWM frequency and decimation as you suggested. Overflow is now occuring at 2500 rpm.

I just realized, I did not explicitly mention this in the question, not sure if this was clear: Only measurement from the encoder (SpeedQEP_krpm) is affected by the overflow, FAST estimation (Speed_krpm) is working correctly.

For torque control, I indeed use a modified version of lab12b (removed the velocity controller and set IqRef directly). I also see the overflow when using the original 12b, though.
I also tried it with lab05a and 05b now. Even after increasing USER_MOTOR_MAX_SPEED_KRPM to 7, the motor won't spin faster than approx. 6 krpm with any of these labs.