Hello! I have been working on a BLDC Motor Controller for some time and have been struggling to debug an issue with my current sense. I am sampling the current drained through the low side of my system during the low period using center-aligned PWM and offset, synchronized timers. Using a system to buffer data on-board I sampled the following current readings and discovered that I am losing a huge amount of the signal on the low side (it occasionally happens on the high side but only on the downwards part of the sinusoid). If anyone has an ideas as to what the problem may be, it would be greatly appreciated! Thank you.

 

You'll need to post more information about your circuit, etc. Hard to tell from a single set of samples.

 

I will do my best to clarify. This is the electrical system for a brushless motor where the MOSFETs are driven by my microcontroller (STM32F405).

I have a shunt resistor in between the drain of the low fets to ground. This creates a small voltage across the shunt which I pass through a gain stage. This gain stage then feeds into the 12-bit ADC on-board the micro. Please let me know if there is any additional information you believe would help with solving this issue. Thank you.

 

Apologies, I forgot to mention that my control method is Field oriented control (FOC). I am also using a DRV8312 for driving the motor in case there may be some issues related to the controller.

 

I have a shunt resistor in between the drain of the low fets to ground. This creates a small voltage across the shunt which I pass through a gain stage.

Circuit unclear. One resistor per drain? A single resistor from just one drain to ground? .....?
The drain voltage of the low-side FETs should rise to near the positive rail, so why is the voltage small?
What over-current arrangement are you using with the driver IC?

 

Hi Alec, there is one resistor per drain. The system has inductance which is why the voltage varies across the shunt. High frequency switching allows for this to occur. I know for a fact I am not over-current on the system given the bounds shown in my original diagram!