single resistor software MC9S12ZV

[zhouqicheng]

After debugging with the official single resistor software MC9S12ZV, it was found that the peak value of the bus current was relatively high, and there was only one 470uf capacitor on the demo board. Increasing the capacitor significantly improved the performance. Is this a common feature of single resistor schemes? Is it still a hardware issue, and does this chip not support floating-point operations? When performing floating-point operations, did an error occur during the previous compilation? Is the error option incorrect?

[RadekS]

Hi zhouqicheng,

The DC bus voltage and current ripples are natural to all kinds of inverter driving, not only to a single shunt scheme. The ripples depend on switching frequency and mainly on currents.
The AN5327 software use the "double switching PWM" technique that allows the current measurement even in specific situations when standard center aligned PWM has two PWM edges come close to each other. For more detail, please look at chapter 3.3.2 Phase currents reconstructions in AN5327. From this point of view, this is robust technique, but the we pay by double amount switching during the same time in compare with standard PWM. This might slightly affect switching looses and DC bus noise parameters.
However, the value of DC bus ripples mainly depends on the currents. From you pictures is obvious that 30A is quite high current and you need external DC bus capacitor. So, this is expected behaviour and DC bus capacitor capacity is application specific.
Some more details may be found also in https://www.nxp.com/webapp/Download?colCode=AN5207

Regarding floating-point operations)
The S12Z MCUs do not contain the hardware floating-point unit (FPU). Therefore all floating-point operations must be calculated by CPU and it takes really long time - It cannot be used for motor control tasks where we need specific timing.
Even significatnt part of fixed-point arithmetic operations in AMMCLib are written and optimized in assembler code to keep the execution time in limit. So, you may create S12Z project with FP support, but this doesn't make sense for motor control due to missing CPU performance - therefore this option is not supported from NXP side. In short, S12Z = fixed point arythmetic, no FP.

I hope it helps you.

Best regards

RadekS