An Improved Passivity-Based Direct Power Control Strategy for AC/DC Converter Under Unbalanced and Distorted Grid Conditions

AC/DC power converter is the momentous interface of the power router, which is responsible for maintaining the dc bus voltage stability. However, under unbalanced and distorted grid voltage conditions, there are voltage ripples in the dc bus, and grid currents will also be severely distorted. Accordingly, this article proposes an improved passivity-based direct power control (IPBDPC) strategy based on extended reactive power theory in the
$\alpha \beta$
-axis, which can effectively suppress dc voltage ripples and current harmonics of power converter. Meanwhile, with the proposed IPBDPC, the fundamental grid voltages and those orthogonal components are injected into the improved passivity model, so that the controller can further reduce the THD of the grid current when unbalanced and distorted grid conditions coexist. Compared with the traditional modified direct power control, the IPBDPC strategy has a simple structure and strong robustness, does not require complex positive and negative sequence separation, and power compensation value calculation. Moreover, the sequence impedance model of IPBDPC is constructed based on the harmonic linearization method to verify the robustness of the control system against parameters uncertainty. The simulation and experimental results based on a three-phase three-level converter system further demonstrated the effectiveness of the proposed control strategy.