Sims have always been able to get a raise during work - it's one of those random events, like "x has a horrible day today. From chasing down criminals to filling in paperwork, x is really stressed out!" or "x caught a criminal red-handed today. The boss was so happy, they promoted x on the spot!".
Now, what really intrigues me is about the performance bar filling up again - what do you mean? Is the sim at Level 10 of their career?