Diode rectifiers are widely used in many applications, and therefore, there is a need for an accurate model to study the rectifiers. Because of the complexity and time consuming of the analytical model of rectifiers, the average value modeling has been introduced. This paper proposes a novel average value model (AVM) for the line-commutated rectifier bridge supplied with an unbalanced power source. The unbalance condition, here, refers to the asymmetry of the three-phase voltage magnitude and the three-phase impedance, which is possible due to the occurrence of asymmetry in the sources with winding such as power sources, generators, and transformers. According to the three-phase input current of the rectifier, one cycle is divided into some intervals, and the differential equation for each interval is provided. Then, utilizing these equations, the average value of the derivative of the load current is derived from which the average value of the load current and voltage can be calculated. The proposed AVM is then verified using simulation and experimental results for the diode rectifier bridge with the load of the brushless synchronous generator field winding. Besides, the model is investigated for different load and supply parameters.