You are here

Problem in BLDC PWM pulse

1 post / 0 new
Jose Jacob
Offline
Last seen: 1 year 1 month ago
Joined: 2021-02-23 11:57
Posts: 2
Problem in BLDC PWM pulse

Hello,

 

I am having issues in driving big motors with VESC BLDC firmware and IGBT.

 

There seems to be some problem in the PWM. In the PWM pulses for the low side IGBT’s, there is a weird pulse (which is unwanted) and causing problems especially in high duty cycle operation of the motor.

 

 

The captured PWM signals with back-emf’s and currents are shown in the figure below (waveforms are recorded using Logic Analyzer). The pulse causing the problem is highlighted in yellow.

 

I did many work-around to solve the problem but could not find a solution. I would really appreciate if anyone can give some idea to tackle this issue.

 

 

Figure explanation:

The first three waveforms are the phase currents, followed by three back-emf’s and PWM pulses

 

In the figure,

'High U' is the PWM pulse on high side of U phase

'Low U' is the PWM pulse on low side of U phase

'High V' is the PWM pulse on high side of V phase

'Low V' is the PWM pulse on low side of V phase

 

 

In the test the motor is running at no-load, duty cycle is 90% and switching frequency is around 20kHz

The IGBT module used: FAM65V05DF1

The BLDC motor used: T-Motor U15

 

Thanks in advance