King Air C90 pilot reported they were fast on their approach on short final and porpoised the landing resulting in a prop strike.

Narrative

I was the PIC for a part 135 flight. We were scheduled to leave at XA01 and the forecast conditions were for a broken ceiling at 3500 feet with a temporary condition of Broken at 2000 with 4 miles of visibility around our arrival. I elected to file an alternate even though it was not required so I used ZZZ1 which had legal alternate filing weather. I updated my numbers for icing the morning of the flight but anticipated being above it by changing my filed altitude from 240 to 280. Flight proceeded uneventfully when we got close enough to the airport they were advertising GPS approaches to [runway] XX so I asked for direct ZZZZZ [Intersection] (IAF) while still approximately 70 miles away and received it. About half way there ATC said they were having better results with XX so I was cleared direct to ZZZZZ1 [Intersection]. As we were getting near ZZZZZ1 [Intersection]; ATC switched back to XY and gave me vectors to the East. We were then cleared to ZZZZZ2 [Intersection] after doing a 270 degree turn for spacing. We got established to ZZZZZ2 [Intersection] after clarifying I wanted Z RWY XX not Y (we already had Z in the box). I armed approach mode but set 6300 for my next step down as Garmin will not descend in VNAV until the final approach fix (ZZZZZ3 [Intersection]) is active. I descended to 6300 and as I approached ZZZZZ3 [Intersection] set the missed approach altitude 7000. At ZZZZZ3 [Intersection]; the aircraft did not begin descending so I turned off the autopilot and initiated a descent. Once I captured the glide path I coupled again and went back on the autopilot. I broke out at approximately 500-600 feet and turned off the autopilot. I was high according to the VASI and tried to capture it since I was visual at this point ( VASI is not coincident with the glide path). This caused me to pick up some unintended speed and by the time I was over the numbers I was approximately 10 kts over Vref and when I flared I ballooned up more than I anticipated and used poor technique to execute a bad landing due to not being in a good flaring attitude; which caused approximately 3 porpoises before I added some power and then landed when the porpoises stopped. Winds were 320/8 so I didn't consider them to be a large factor. I taxied in and shut down the airplane . I did not realize we had a prop strike till the walk around.