This paper presents a novel average voltage estimation model of a Voltage Source Inverter (VSI) for Permanent Magnet Synchronous Generator (PMSG) drive systems which when included in a complete electromechanical system model results in significantly reduced simulation times. Sinusoidal Pulse Width Modulation (PWM) control techniques are implemented with the proposed model enabling effective control of generator current, power, electromagnetic torque and DC link voltage control. A detailed back to back VSI switching model for a fractional horsepower PMSG is used as a benchmark against which the results of the average voltage model are compared. Both models have been implemented in the PORTUNUS simulation package and verified against an experimental back to back converter module connected to a variable speed PMSG. The results show good agreement between both simulation models and experimental data with the average voltage estimation model accurately reproducing generator currents over the linear and over-modulation regions, with the advantage of reducing simulation times by up to a factor of 10 compared to the switching model. The simulation results show the capability of the proposed average voltage estimation model over a wide range of speed and can be used to study and analyze the performances of variable speed PMSG energy conversion system.