Direct angle control and energy-shaping techniques for grid-connected converters

Abstract

In this paper, a framework for designing three-phase grid-connected converter control strategies is investigated. The crucial aspect is augmenting an integrator for the DC-link voltage measurement, and assigning it to the (virtual) angle of the instantaneous modulation vector. Exact model-matching with the synchronous machine is thus realized, with equivalent inertia and damping rendered by the DC-side circuit elements. The implementation does not require inner tracking loops and naturally provides frequency support. By further exploiting the flexibility of the inverter, additional features such as a synchronizing torque, a voltage controller and a power set-point tracking mechanism are designed via two energy-shaping techniques. One energy function is used to implement a grid-feeding control scheme, akin to a phase-locked-loop design, while the other is used to implement a grid-forming control scheme, which recovers active-power droop. The results are first formally derived, and then evaluated experimentally on a front-to-front experimental setup.