Closed loop control ZVS buck converter
That's the transient moment and it's normal to happen. At the time of the first turn on, the only load the source sees is the load plus the LC filter, which means you have a step function. By the time the rest of the circuit comes alive, the RLC network will respond with its natural response. In this case, you have ω = 47.67 kHz and Q = 83.9, which means that due to the very high Q the step response will show oscillations. But since this is a nonlinear circuit that ensures the current flow goes in one direction, only, the capacitor will charge with this peak voltage and then it discharges in the load. Since the RC time constant, 1.76 ms, is much greater than the switching frequency, 3.3 μs, the discharge is slow. All the loop can do at this point is to turn off the switching, since that is the fastest way the load can discharge (any switching eans current flowing from the source). Not lastly, you'd be better off using a comparator instead of an opamp, and your title (ZVS) has nothing to do with the circuit.