Cascaded sensorless BLDC control with a MSP430F5529 Launchpad in combination with a DRV8323 Boosterpack
This software provides a simple example of a cascaded speed control as a sensorless block commutation on an MSP430F5529 Launchpad in combination with a DRV8323 BoosterPack.
Other features include debugging via the serial interface (UartMonitor) and a decoupling of the DC link voltage.
The underlying current control as well as the sensorless calculations are generated with a frequency of max. 16kHz running. The DRV8323RS can be controlled with 6x, 3x or 1x PWM signals. According to the pin layout of the Launchpad it becomes clear that for the 6x or 3x PWM mode several different timer peripherals would be necessary. Unfortunately, there is no way to start different timers synchronized. Thus the 1x PWM method was used.
The ADC module offers the possibility to be started in hardware from one out of three timer modules. Sad to say, the Launchpad's routing in combination with the DRV BoosterPack does not allow you to use one of the three triggering timer modules. For this purpose, a timer interrupt is triggered at the reversal point of the PWM carrier signal and the ADC conversion is started in software!
Since the start of the ADC conversion is triggered in software, all calculations must be done so that the timer ISR can be triggered and called undisturbed: The ADC values are provided via DMA. From start sampling to calling the DMA ISR for motor control, nearly 22us pass. The calculations needed for motor control take almost 38us at a system frequency of 25MHz. Thus, about 60us pass, which represents the maximum value (62.5us at 16kHz PWM / ISR frequency) for the calculation time, so that the ISR / starting point of the ADC conversion is not called late / not correctly aligned.
The 1x PWM method is practicable. In a separate layout I would recommend to use one out of the three timer peripherals which allow you to start ADC sampling via hardware. In this way, the PWM frequency can be further increased because sufficient computation time is available, or the system frequency can be lowered.
Nonetheless, the MSP430 performs very well and can be used for simple motor control tasks with a suitable routing.
Set up an external serial to USB converter and select to correct COM port in the target config file to use the UART-monitor function descriped here: https://github.com/ben5en/MSP430_UartMonitor Everything set up, start the debug mode and go to the expressions tab. Type in "Status" and "TargetSpeed_pu". This way you can see and change the variables during runtime and start, stop / control the motor.
Source: some of the routines are based on routines of the "math blocks" found in the controlSuite for C2000 controllers.
