topic Re: Problems with theta calculation in PMSM Vector Control function in Other NXP Products

Problems with theta calculation in PMSM Vector Control function

peterdufault — Fri, 27 Jun 2014 14:56:36 GMT

I'm still working with something based on AN3206. I'm trying to figure out what's wrong with my commutation, and I started reading back the theta from the eTPU. It doesn't make any sense to me.

I have a 4000 count encoder and a motor with two pole pairs. According to the function description theta = (2 * encoder)/4000, so theta should advance twice for each cycle. However, it isn't even synchronized with the zero position of the encoder. See the attached plot.

In etpu_pmsmvc.c scale is set to scale = motor_pole_pairs * 0x1000000 / qd_pc_per_rev; .

Since there was not a "get theta" function I added one like this:

fract24_t fs_etpu_pmsmvc_get_theta(uint8_t channel)

{

uint32_t *pba;

pba = fs_etpu_data_ram(channel) + (0x4000 >> 2);

return (fract24_t)(*(pba + ((FS_ETPU_PMSMVC_THETA_OFFSET) >> 2)));

}

Any ideas?

Re: Problems with theta calculation in PMSM Vector Control function

peterdufault — Fri, 27 Jun 2014 15:51:32 GMT

Well, whatever I'm getting back with that fs_etpu_pmsmvc_get_theta() function it isn't theta. Even if I stop the motor rotation I get the same -1 to 1 ramp. I've asked Freescale for the eTPU code that is being generated by the eTPU function selector so I can figure out what's going on.

Re: Problems with theta calculation in PMSM Vector Control function

peterdufault — Fri, 27 Jun 2014 16:04:42 GMT

Never mind. I had used the PMWmaster channel instead of the PMSMVC_channel and happened to get back that thing that went from -1 to 1. Now that I've fixed it I get what I expect.