DC-link voltage stabilization and source THD improvement using d-axis current injection in reduced DC-link capacitor system

This paper proposes an active damping control method to reduce the voltage fluctuation caused by using the reduced DC-link film capacitors instead of the conventional electrolytic capacitors. The motor drive system with the reduced DC-link capacitor has the problem of an unstable DC-link voltage. The ripple of the capacitor voltage is caused by the resonance of both the large input line filter and the reduced DC-link capacitor. To solve this problem, the active damping control method using the d-axis current injection is proposed in this paper. The virtual damping impedance is applied to the equivalent circuit of the system to suppress the voltage ripple of the DC-link. The damping impedance is generated by injecting the DC and AC components into the d-axis current. The relationship between the injected d-axis current and the damping impedance is analyzed through the equational analysis. The proposed method can decrease the DC-link capacitor voltage oscillation and minimize the torque ripple because the injection current is not q-axis but d-axis. The simulation results are presented to prove the validity of the proposed method.