CCS/TMS320F28379D: Absolute position sensing

Hridya I

Part Number: TMS320F28379D

Tool/software: Code Composer Studio

Hi,

I am planning to do PMSM control for electric vehicle application using 28379D DSP. This is not specific to the controller but control of PMSM itself.

What I understand is that the incremental encoder can give the relative position and not absolute position and every time during the start-up of motor an initial rotor alignment is needed. This means that the vehicle itself has to move for the initial alignment.

Then comes the relevance of absolute encoder that can give the absolute position during start itself. But I see that they communicate with the controller through different communication protocols and QEI can't be really used for that.

1, Is my understanding correct?

2. If yes, could anyone suggest some absolute encoder makes/ part number?

Thanks

Hridya

over 4 years ago

0 ChrisClearman over 4 years ago

TI__Guru** 118000 points

1. yes, your understanding is correct. during initialization you need to move the motor into an electrical alignment and then read the index signal to get a mechanical location on the encoder. You then make that your zero point by subtracting that index from read values. We do this in all the examples with incremental encoders.

2. most traction motors use a resolver as an absolute encoder. This is an analog approach. Many servo drives & robotics use digital absolute encoders with different communication techniques (Biss-C, EnDAT, etc.). We have examples of many of these in our www.ti.com/c2000drives solutions. You can also look at our EV page for solutions www.ti.com/c2000ev

0 Hridya I over 4 years ago in reply to ChrisClearman

Intellectual 400 points

Thanks Chris.

I see that there are a lot of linear hall sensor ICs available for getting absolute position. Can I use directly the 2 sine waves produced by them and take tan inverse to get the abs. angle?

Or should I pass through some MCU and then to SPI/SSI/EnDAT to take into my controller?

0 ChrisClearman over 4 years ago in reply to Hridya I

TI__Guru** 118000 points

I haven't seen those used on a typical motor for a traction inverter. The encoder/resolver will need to mechanically link to the rotor shaft.

For a resolver you generate the stimulus and then read the signals. This can be done with a standalone resolver chip (which then usually talks over SPI to a controller), a small MCU just doing the resolver function (talking over SPI), or integrated into the main larger digital controller using ADC + PWM.

0 Hridya I over 4 years ago in reply to ChrisClearman

Intellectual 400 points

ok. Do you have any recommendations on the absolute encoder that can be used for traction application that talks through SPI/ Analog signals?

0 ChrisClearman over 4 years ago in reply to Hridya I

TI__Guru** 118000 points

these are often custom made for a specific motor.

we are using one from

https://www.minebeamitsumi.com/english/strengths/column/resolver/

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CCS/TMS320F28379D: Absolute position sensing