When the input fets are on the output 'diode' (fets in your case) should be off, hence good to get the phasing of the gate drive correct. I suggest you put zeners or TVS's across the fets at 90% of Vds to protect them,ДЄs the sources are tied together you can link the gates as well so only two windings are needed to drive the two sets of fets.ДЄlso the dot notation on the main Tx needs to change if you want pos in and pos out, at the moment pos in gives neg out (the tops). This is because there will be quite a bit of dead time at light loads where all fets need to be off, else there will be a lot of circulating current which you will not want. The commonest and most robust way is to generate your gate drive signals is on to a gate drive transformer (+/- 15V say) and have sufficient isolated output windings to drive your fets, making sure the phasing is correct, thus you can turn the i/p and output sides on and off alternately (not at the same time), you may not need to modulate the drive away from 50:50 if you seek a 1 to 1 conversion - but at light loads the fet drive will need to be reduced. My question is, how can I implement a simple way to drive the 4 MOSFETs in the bidirectional sequence described above? Circuit operation is repeated When transistor Q3 is turned off and transistor Q2 is turned on again.' During a second time interval, the switching states of transistors Q2 and Q3 are reversed, driving current out through the input terminals via inductance L1, and charging the input capacitor C2a. At the 1st interval, transistor Q3 is off and transistor Q2 is on.

Transistor Q1 and transistor Q4 are held on this period transistors Q2 and Q3 switch alternately at high frequency. Finally, when AC is negative and load current is out of phase with load voltage. Circuit operation is repeated when transistor Q2 is turned off and Q3 is turned on again. During a second time interval, the switching states of transistors Q2 and Q3 are reversed. For the 1st time interval of this high frequency alternation, transistor Q2 is off and transistor Q3 is on. During this period transistors Q2 and Q3 switch alternately at high frequency. Transistor Q1 and transistor Q4 are held on. Once this occurs, the energy transfer capacitors discharge, driving current out through the input terminals.ДЄt negative AC and when load current is in phase With load voltage. During a second time interval of the high frequency alternation, the switching states of transistors Q1 and Q4 are reversed. During this interval diode D1 is forward biased and the energy transfer capacitors C1a and C1b charge through the choke inductor L2. During this period transistors Q1 and Q4 switch alternately at high frequency, for a 1st time interval of this high frequency alternation, transistor Q4 is off and transistor Q1 is on. For a period during which input AC is positive and load current is in OUT of phase with load voltage, Transistor Q2 and transistor Q3 are held on. Circuit operation is repeated When transistor O1 is turned off and transistor O4 is turned on again. Once this occurs, the energy transfer capacitors C1a and C1b discharge, driving current through the output load via inductance L2, and charging the output capacitor C2b. During this interval diode D4 is forward biased and the energy transfer capacitors C1a and C1b charge through the choke inductor L1.

For a 1st time interval of this high frequency alternation, transistor Q1 is off and transistor Q4 is on. During this period transistors Q1 and Q4 switch alternately at high frequency in response to a high frequency control signal from the controller. Transistor Q2 and transistor Q3 are held on and therefore, in conjunction with diode D2 and diode D3, provide bi-directional current paths. 'For a period during which input AC is positive and load current is in phase with load voltage. I found a solution for driving the MOSFETS in a patient by Simon Greenwood, and it had described a sequence as follows: I input 80v AC 50Hz and I'd like to obtain AC voltages ranging from 0v to 80v at 50Hz, feeding and restrictive inductive load whilst being able to obtain an output current of up to 1A RMS. I am essentially building a solid state 'electronic' variac(variable autotransformer).

The isolated cuk converter waveforms