Читать книгу Smart Solar PV Inverters with Advanced Grid Support Functionalities - Rajiv K. Varma - Страница 33

Unbalance in power supply voltages results in unsymmetrical phase currents which can be potentially damaging to voltage‐sensitive equipment, transformers, and motors [46]. Unbalanced currents can cause torque pulsations, mechanical stresses, higher losses, and overheating of windings that can reduce their lifecycle. Grid codes typically specify that voltage unbalances [47] must be constrained within 2% of the PCC voltage.

Voltage unbalance issues are experienced with PV systems connected to single‐phase distribution systems [48, 49]. Small PV and wind DERs (up to 10 kW) are typically connected to single‐phase low‐voltage networks. Many a times the combination of PV system and interconnected loads do not appear as balanced systems across the three phases at the substation. This unbalance causes neutral voltage to rise and phase voltage to increase in one or two phases. Ideally, phase balancing should be performed at the time of installation; however, it may not be possible to do so due to the extensive effort involved. Phase balancing is usually undertaken if a power quality complaint is received [18]. In Ontario, several cases of PV inverter shutdowns have been reported due to voltage unbalance in the feeders.