In this paper, we investigate the control of inverterbased resources (IBRs) for optimal voltage unbalance attenuation
(OVUA). This problem is formulated as an optimization program under a tailored dq-frame, which minimizes the negativesequence voltage at the point of common coupling (PCC) subject
to the current, active power, synchronization stability, and feasibility constraints. The program is inherently nonconvex and
intractable. So, to guarantee the optimality, a rigorous optimality analysis is performed by leveraging analytical optimization.
The analysis is divided into two cases: full mitigation of VU and
partial attenuation of VU. For the former case, we directly solve
the original program since the resultant VU is immediately deducible. For the latter one, directly solving the problem becomes
very hard. Thus, we reformulate the program into an equivalent
but more tractable form under certain conditions, by which the
analytical optimum can be derived. It is found that the optimum
trajectory has three stages (O1–O3), depending on two critical
boundary conditions (C1 and C2). We implement the optimum
with a photovoltaic (PV)-storage system by developing an OVUA
controller. The proposed approach is demonstrated by dynamic
simulations under different VU conditions and is compared with
several existing practices. Finally, we discuss the extension of the
proposed solution in a multi-IBR system.