Reference-Input-Based Imaginary Axis Current Estimation Method for DQ Control Strategy in Single-Phase PWM Converters

For $dq$ control strategies in single-phase pulse width modulation (PWM) converters, the $\beta-\mathbf{axis}$ current must be created by imaginary axis current estimation (IACE) methods. The estimated error of the $\beta-\mathbf{axis}$ current during the transient process causes $d-q$ axis current loops to be incompletely decoupled, thereby affecting the dynamic performance of the current loop. The second-order generalized integrator (SOGI) method suffers from slow dynamic response. The fictive-axis emulation (FAE) method provides fast dynamic response but it is sensitive to circuit parameters. A reference-input (RI)-based IACE method is proposed to overcome the above shortcomings. According to the characteristic that the $\beta-\mathbf{axis}$ current loop has no transient process, the $\beta-\mathbf{axis}$ current is estimated by the $d-q$ axis reference inputs. This is equivalent to introducing the $\beta-\mathbf{axis}$ reference input as a feedforward term into the $d-q$ axis current loop, so the parameter sensitivity problem is solved, and the parameter tuning is not needed. The proposed method can maintain good steady-state performance and significantly improve the dynamic performance of the current loop. Furthermore, it is straightforward and can be easily implemented in digital controllers. Comprehensive hardware-in-the-loop (HIL) experimental comparisons with the SOGI and FAE methods have been conducted to verify the correctness and effectiveness of the proposed RI-based IACE method.