Hello @Lars
As per my understanding, you are trying to control a 3-phase inverter using “TMS320F280049” microcontroller and want to sample three phase voltage waveforms for closed loop control.
The “TMS320F280049c” microcontroller has 3 ADC modules. They are: “ADCa”, “ADCb” and “ADCc”. Each ADC module has 16 SOCs (Start Of Sequence) which trigger the start of conversion of an analog signal applied on a particular pin. Further, you can individually control the trigger source of each SOC and also the “channel” corresponding to it. (Here,”channel” refers to any of the ADC pins available on the microcontroller. Example: “ADCINA4”)
Refer to the technical reference manual of “TMS320F28004c” by Texas Instruments for a more detailed explanation:
You can configure the “ADCs” in many ways as given in the above Technical Reference manual, but I am summarising two of them, which might prove useful for your case.
1) Basic Synchronous Operation:
In this operation, three SOCs, each on “ADCa”, “ADCb” and “ADCc” are configured for same trigger source and “ACQPS” (Acquisition period) value. Whenever the trigger is recieved, all the three ADCs will simultaneously sample. In this way, all the ADC modules works in synchronism. You can select the trigger source as “CPU timer” interrupt or “SOC signal” generated by any of the “ePWM” module. As an example, you can assign the "SOC0" to "ADCINA1", "ADCINB1" and "ADCINC1" and configure the trigger signal for "SOC0" to be one of the ePWM sources.
2) Using only one ADC module:
Here, only one ADC module is used to sample all the analog signals. As an example, consider that you want to sample phase voltages ”Va”, “Vb” and “Vc”. Let the ADC pins measuring these signals be: “ADCINA1”, “ADCINA2” and “ADCINA3” and let us select their start of conversion (SOC) as “SOC0”, “SOC1” and “SOC2” respectively. In this case, all the “SOCs” should have the same trigger source. Here, in your case, the most suitable trigger source will be the instance when any of the “ePWM” counter resets to its “zero” count in every period.
Conclusions:
If you're dealing with a fast control loop that demands a minimal sampling time period, it's advisable to choose the first approach. This method will simultaneously convert the three-phase voltage present on the pins "ADCINA1," "ADCINA2," and "ADCINA3," and then store the results in the respective "ADCRESULTS" registers. This method can sample all the voltages in less number of clock cycles.
If your control loop does not require a small time step and you can tolerate the delay from sampling the three-phase signals consecutively, the first method is a suitable choice. Its primary advantage over other methods is its simplicity and ease of understanding.
To summarise the things from the Technical Reference Manual,
Which ever method you chose, it is advisable to operate all the ADC modules synchronously. To make sure synchronous operation, all ADCs on the device must operate in lockstep. This is accomplished by writing configurations to all ADCs that cause the sampling and conversion phases of all ADCs to be exactly aligned. The easiest way to accomplish this is to write identical values to the SOC configurations for each ADC for trigger select and “ACQPS”.
I hope it helps !
