Decoupled control of the active and reactive power in three-phase PWM rectifiers based on non-linear control strategies

Pulse-width modulated (PWM) current-source and voltage-source rectifiers (CSRs and VSRs) present several advantages as compared to thyristor line commutated and diode bridge rectifiers, respectively. Indeed, low supply current harmonic distortion and displacement power factor control including unity displacement power factor operation, can be obtained. However, the models of the CSRs and VSRs are nonlinear, which involves their analysis and certainly their control. This complexity is somehow avoided when using direct line current control and relatively high switching frequencies (>1 kHz). Unfortunately, this approach does not guarantees the stability of the rectifier, results in a dynamic that is load dependant and covers low to medium power level applications. This paper proposes the application of a nonlinear control strategy in combination with a high performance low switching frequency space vector modulation technique. The approach can be used in high power applications and allows the independent control of the two supply current components (active and reactive), which admits the converter to either generate or absorb reactive power according to a given set point while operates as an independent DC power supply. The paper includes a complete formulation of the system equations and a controller design procedure. Simulated results confirm the validity of theoretical considerations.