View attachment 127436 Hi all I am busy designing and building a grid tie inverter, I like challenges!
At the moment I am working on the unfolder or inverse rectifier that connects the unipolar output of the SMPS to the bipolar grid, it is an H bridge that switches at twice the supply frequency and here in the UK with our 240Vrms grid means it deals with about 350Vpeak on both the grid and DC sides. Like all things it works nicely when you are looking at it BUT when you turn your back POP goes another mosfet!
Although the switching speed is low the timing around zero cross of the grid is critical as having the wrong half of the H-bridge conducting tries to short out the grid with only one outcome (smelly electronics) but timing is difficult to ensure given the gate drive has to be (advisable) galvanically isolated from the control logic.
It turned out however the problem was an occasional glitch in one of the gate drives causing a large shoot through by turning on both mosfets on the same side of the bridge simultaneously, the glitch grew and shrank with temperature and was caused by both lower bridge legs sharing the same driver chip.
Really what I am trying to say it is not always the obvious reason that causes a fault
I hope everybody knows what an Hbridge is, if not https://en.wikipedia.org/wiki/H_bridge
I enclose the offending glitch, red trace is mosfet gate driveView attachment 127435
At the moment I am working on the unfolder or inverse rectifier that connects the unipolar output of the SMPS to the bipolar grid, it is an H bridge that switches at twice the supply frequency and here in the UK with our 240Vrms grid means it deals with about 350Vpeak on both the grid and DC sides. Like all things it works nicely when you are looking at it BUT when you turn your back POP goes another mosfet!
Although the switching speed is low the timing around zero cross of the grid is critical as having the wrong half of the H-bridge conducting tries to short out the grid with only one outcome (smelly electronics) but timing is difficult to ensure given the gate drive has to be (advisable) galvanically isolated from the control logic.
It turned out however the problem was an occasional glitch in one of the gate drives causing a large shoot through by turning on both mosfets on the same side of the bridge simultaneously, the glitch grew and shrank with temperature and was caused by both lower bridge legs sharing the same driver chip.
Really what I am trying to say it is not always the obvious reason that causes a fault
I hope everybody knows what an Hbridge is, if not https://en.wikipedia.org/wiki/H_bridge
I enclose the offending glitch, red trace is mosfet gate driveView attachment 127435