Traditionally, digital signal processor (DSP) control algorithms for three-phase power converters are designed in rotating or stationary reference frames. These approaches require the use of rotation matrices and employ linear controllers such as proportional integral (PI) and proportional resonant. This chapter presents an alternative control solution developed in the natural reference frame and applied to a three-phase unity power factor rectifier (UPFR). This solution requires no transformation matrices, and by harnessing all computation capabilities of the modern DSPs, nonlinear techniques, such as sliding-mode control (SMC) [1, 2] and Kalman filter (KF) [3], can be employed. The main features, along with the advantages and the limitations, of this approach will be discussed in detail throughout the chapter.