I have been working on a microinverter with a high frequency transformer followed by a cycloconverter. However I have found, there are several high voltage surges occurring across the secondary of the transformer what might be the possible reason for this?
Leakage reactance of the transformer, self reactance ,forced commutation of cyclo converter switch, can anyone give a possible explanation?
Hi. You may want to check the current waveform in the primary of the transformer. As the device that excites the primary moves from overdrive to cutoff, the current in the primary suddenly drops and a large peak of fem with reverse polarity appears in the primary. If this is not properly handled (e.g. via clamp circuit, proper damping) it may find its way to close the circuit and produce an extra current spike which will be reflected as a narrow voltage spike in the secondary of the transformer. Poor transformer design or component choice exacerbate the problem. Farnell has a set of application notes on TOPSwitch devices covering many of the tricky aspects that may help you better understand your problem. Try this: http://www.farnell.com/datasheets/307754.pdf
Dear Sabah,
I assume by "Cycloconverter" you refer to a matrix-converter.
These may induce high voltage spikes as a consequence of mistuned commutation timing sequences. In case your sequence is incorrect, you'll interrupt an inductive current which in turn triggers those high voltage spikes.
If you correct the sequence and/or introduce a proper clamping circuit to the switching matrix, your problem should find a solution.
Hi Sabah,
You may also check if you have used any "diverting circuit" - just to dissipate or utilize the stored energy in transformer winding inductance. If not use some sort of clamp circuit (as suggested by Claro).
@Claro Antonio Noda sorry for the delay in response.I know its really late.I am stuck with some driver problems for some time.I was trying to use IR2125 for driving the cyclo switches and it hasnt released any pulses yet.Your suggestions really helped me but i am yet to try on hardware.Thank U
Hello sir, it may be because of the air gap the transformer might working as a coupled inductor. The energy is trapped in the air gap and the release of this energy is responsible for the spikes.
Could you please post a schematic, and some waveforms from the oscilloscope?
Voltage spikes might be produced due to inductive effect (Ldi/dt) of transformer coils. Therefore it is important to see the load current as well; if there is discontinuity in it or not.