Munster found it difficult to get their hands on the ball and Robinson went close with a second penalty shot in the 15th minute.
Ben Sargent levelled the tie with a well-struck penalty goal in the 21st minute after Ulster flanker Dominic Gallagher was yellow carded for foul play spotted by a touch judge.
A second successful penalty from Robinson in the 35th minute brought Ulster back level at 6-6.
As the game turned in Munster's favour, the visitors took a quick tap penalty in the 38th minute. Ulster were caught cold when Munster winger Stephen Collins almost made the try-line, and the home side struggled to defend their whitewash.
Loosehead prop Jonathan Corscadden was pinged for hands in the ruck before Sargent slotted the penalty to take the visitors into a 9-6 half-time lead.
The first quarter of the second half was fairly scrappy, but then Ulster, who beat Leinster 8-6 at Donnybrook, suddenly brought Ravenhill to life with a lovely piece of individual skill from Corscadden.
The Malone clubman burst onto the ball on the Munster 22 and raced clear to score behind the posts. Robinson added the extras to take the Ulstermen into a 13-9 lead.
Three minutes later, flanker Gallagher charged down a clearance kick on the Munster ten-metre line and managed to gather the loose ball to sprint clear and score Ulster's second try.
Robinson converted to leave the final score at 20-9 and confirm the Niall Malone-coached home side as Interpro champions.
Congratulations to the players, management and backroom staff involved in the Ulster U-19 Clubs set-up.
ULSTER UNDER-19 CLUBS XV: Jonathan Milliken (Larne); Chris Leatherm (Banbridge), Patrick Robinson (Belfast Harlequins), Stuart Simpson (Londonderry YMCA), Craig Gilroy (Dungannon); Jonathan Pollock (Queen's University), Nicholas Andress (Instonians); Jonathan Corscadden (Malone), Logan McCallan (Ballynahinch), Lee McClure (Portadown), Connor Smyth (Coleraine), Stephen Leckey (Belfast Harlequins), Max Porter (Malone) (capt), Dominic Gallagher (Lisburn), Stephen Irvine (Banbridge).
Replacements: Gary Donegan (Enniskillen), Rory Sheard (Instonians), Jonathan Harris (Banbridge), Peter Starrett (Queen's University), Hazlit Brian (Enniskillen), Lee Murphy (Omagh), Chris Gillen (Ballyclare).
Head coach: Niall Malone
Assistant coach: Andy Ward
Conditioning coach: Paul Heasley
Manager: Chris Webster
Physio: Julia Webster