Many control theory based approaches have been proposed to provide QoS assurance in increasingly complex software systems. These approaches generally use single model based, fixed or adaptive control techniques for QoS management of such systems. With varying system dynamics and unpredictable environmental changes, however, it is difficult to design a single model or controller to achieve the desired QoS performance across all the operating regions of these systems. In this paper, we propose a multi-model framework to capture the multi-model nature of software systems and implement self-managing control systems for them. A reference-model and extendable class library are introduced to implement such self-managing control systems. The proposed approach is also validated and compared to fixed and adaptive control schemes through a range of experiments.