I recently took a PG test for an application with local LE organization. This test was different than anything else I have read about on this website. There was no stim test, and rather than giving me a long speech about how accurate the polygraph is, the examiner actually told me that there can be false positives when people are nervous or unsure about the test. He then read me the 15 questions he was going to ask me. The first two were my name and whether I intended to tell the truth. All the remaining questions were relevant. There was not a single probable lie or directed lie question. After the first run he asked me if I thought of anything else I needed to tell him and when I said no, he repeated the same 15 questions, in the same order. That was it. No post test interrogation either.

Lest anyone asks, this definitely was a polygraph: two pneumo tubes, blood pressure cuff, and two sensors on my fingers. However, there was also a microphone on the desk.

What kind of test was this and how are you supposed to increase your chances of passing when there aren't any control questions?

This technique seems to be a home-brewed variation on the relevant/irrelevant "test." The polygrapher was likely looking for significant reactions to any of the relevant questions. A number of applicants for employment with small police departments have reported encountering a similar polygraph technique, where a list of relevant questions is read, each beginning "Did you lie about..." followed by a relevant topic from a pre-polygraph questionnaire.

I have seen a Screening Test, that comprises approximately 15 questions
Approx 12 Relevants and a couple of Controls.
Its was usually used as a screening test. One or two charts.
Not very popular as the efficacy thereof is low.
I think it was first devised and used in the security industries prior to EPPA