This paper presents a dynamic average model of the Quasi-Z-Source Inverter (QZSI), based on the short term average values over one PWM-period, and the analysis of the possible switching states that can occur in the QZSI. The model is considerably descriptive since the modeling has been performed by analyzing the physical and functional relations with only little mathematical complexity. Another advantage of the proposed model is that the load current only acts as a disturbance input, and is not directly linked with the model structure itself. This allows a separate examination of either command input or disturbance response and makes the model independent of the given load. The model has been tested successfully in conjunction with an adequate cascade control loop design and a QZSI-prototype in hardware.