This paper presents a method for estimating the positive and negative sequence grid voltage under unbalanced grid conditions using simple algebraic and trigonometric identities without dedicated grid voltage sensors in three phase grid connected boost rectifier converter system. The estimated voltages are then used to control the positive and negative sequence currents of the boost rectifier. The estimation method is based on the positive and negative sequence active and reactive power delivered by the converter to the grid. In addition to the estimation of the positive and negative sequence grid voltage, the proposed method also generates an estimate of the frequency information of the grid similar to a conventional PLL structure. Detailed theory and results confirm the feasibility of the proposed scheme.