C99 Captain reported encountering severe turbulence and while trying to descend; the trim control section of the Captain's control yoke broke off and resulted in a precautionary landing.

Narrative

During a flight from ZZZ1 to ZZZ I encountered multiple spells of severe turbulence which resulted in damage to the flight yoke [and] trim system. The turbulence was caused by imbedded thunderstorms located along the route; mostly encountered during the descent/arrival phase of the flight. During some of the more severe spells; I was unable to maintain aircraft attitude and altitude; with deviations +/-300 ft. and uncommanded 1000 FPM descent/climbs. Multiple attempts to change heading and altitude were made to escape the turbulence; and did not subside until leveling off at 3;000 ft. on the arrival. Once established on the approach; I crossed the final approach fix and pushed the nose over to descend. During this motion; the trim control section of the Captain's yoke broke off; exposing wires with one being disconnected. At that moment; the nose continued to pitch down; and the main trim became unusable. I turned off the main trim and activated the standby trim. I [requested priority handling] with Tower out of an abundance of caution over a potential trim runway with the exposed wires. I did not have time to troubleshoot; as I was established on the ILS approach in past the FAF. Landed without incident. Upon landing; I tested the main trim system and it did function normally; although the Captain side was still unusable. System malfunction was noticed on approach past the FAF. Severe turbulence due to embedded buildup of thunderstorms resulting in aggressive movements of the flight controls. In addition; this aircraft was not equipped with NEXRAD and the onboard radar did not show any returns of potential hazards. ATC notified of moderate precipitation in all directions; but vectored through the worst part anyways. I had no way of seeing the storms from my position in the cockpit and had to rely on poor vectors. Upgraded transponder with ADS-B In capabilities would have allowed me to use NEXRAD on the GTN 750 to make vector requests around the buildup. Also; the current radar installed in our aircraft is useless; no echo returns observed despite it being right in front of me. Other aircraft that were equipped with capable radar were requesting vectors around the cells; but I was at the mercy of ATC.