Multivariable Droop Control of Synchronous Current Converters in Weak Grids/Microgrids With Decoupled dq-Axes Currents

Weak grids/microgrids are gaining considerable attention due to the installation of renewable power generation resources in areas that are remote from load centers. This paper presents a multivariable-droop synchronous current converter control strategy for current management of weak grid/microgrid applications, and offers a systematic and straight-forward design approach using the loop shaping technique. The controller integrates current regulation, management, and limitation that are applicable to weak grids and microgrids (MGs). The multivariable synchronous current converter enables superior decoupling of d- and q-axis currents in weak grids and/or resistive grids where these control variables are highly coupled due to converter operation at large load-angles. Therefore, stable connection of weak (high impedance) resistive MGs to utility grids is feasible. The multivariable droop concept also realizes real power sharing by simultaneous drooping of both frequency and voltage amplitude, which enhances load sharing accuracy in resistive and/or weak grids. Similar to its predecessor, synchronous converters, the controller can eliminate phase-locked loop (PLL) and provides a unified controller, PLL, and load manager in one simple control methodology. This can facilitate grid auto-synchronization, which can improve the stability of voltage source converters in weak grid applications. Also, the controller can participate in the power system frequency, and voltage regulation and control. To evaluate the performance of the controller, several simulations are conducted under various typical scenarios and conditions.