PLL-less control strategy of active front end converter with output impedance invariance

The paper presents the control strategy of the three-phase active front-end converter aimed to ensure its output impedance invariance during an input voltage variation. The proposed control strategy is based in abc reference frame. It was shown that under input voltage variation, the converter voltage loop transfer function becomes time-dependent, which leads to its output impedance variation and voltage ripples. But it is possible to eliminate this effect by adding the proposed input voltage-dependent correction term. PLL-less operation is achieved by redefining an output signal of the voltage-loop compensator and input currents template vector. To completely eliminate the need to use any type of the PLL, the three-phase input currents template vector is set to be equal to the input source phase voltages and the output signal of the voltage loop controller is redefined as transconductance, which connects converter ac-side phase currents and the product of the current template vector and the voltage loop controller output signal. A numerical analysis of the converter was implemented to estimate the converter dynamic properties working with the proposed control strategy and compare it with the classical abc reference frame strategy.