A hierarchical coordination approach for voltage regulation in a DER-rich grid edge ^*

The proliferation of solar PV in the distribution grid introduces challenges in maintaining grid voltages. Traditional voltage regulation methods which use electro-mechnical devices are insufficient in addressing the intermittency of PV generation, and result in loss of life of voltage regulation equipment such as load tap changers (LTCs). We propose the use of a hierachical voltage regulation strategy which leverages PV units alongside LTCs, to extend equipment life and improve grid voltages. The resulting mixed integer voltage regulation problem can be reformulated as a bi-level optimization with minimal data exchange between centralized LTC decisions over discrete variables, and distributed PV decisions over continuous setpoints. This minimal data exchange is extended to an intelligent coordination mechanism between the substation LTC and solar PV units, which restricts PV injections in order to maintain grid voltages. We validate our proposed method on a real utility distribution feeder with moderate PV penetration. Our proposed method is capable of (i) reducing the number of LTC tap changes; (ii) eliminating all voltage violations; (iii) effectively utilizing both real and reactive power capabilities of PV units without excessive curtailment; and (iv) reducing network losses.