I'm designing a three-phase inverter and have been looking up information online with respect to grounding, which led me to a somewhat misapprehension.
In my system I firstly planned on separating the ground of microcontrollers (PWM, digital signals etc..) and sensors (analog signals such as current/voltage measurements) from the power ground, which is the one in the 400 V DC LINK of the three-phase legs. I intend to do that with optocouplers and hall sensors.
However, I'm still confused as to why there's a need to isolate these grounds. Can I not simply be careful with pcb routing not to create dangerous return paths and I'm good to go? Is there really a specific need to isolate grounds that PCB routing cannot solve?
For instance, this design from ST uses a shared ground for both MCU and power transistors : https://www.st.com/resource/en/data_brief/steval-esc001v1.pdf