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Voltage Sags in Photovoltaic Systems

Category: Distributed Generation, PQ Theory

Understand the impact of voltage sags in photovoltaic systems and the result of such an event.


Photovoltaic (PV) generation is electrically in parallel with the utility supply, and thus lowers the steady-state system impedance. The ideal result is a reduction in locally caused voltage sags as the PV system supplies power to high-current loads.


The actual result can be an increase in voltage sag severity, due to the design of typical PV inverters. The reasons for this unfortunate result are presented here, along with a real-world example.


A PV system consists of several components, including the panels themselves, interlocks and switches, and in particular, a DC->AC inverter (see Figure 1). The raw PV output is DC; the inverter converts this to a 60 Hz sinusoidal voltage waveform.


Because the inverter output is connected in parallel to the distribution transformer secondary, the amplitude and phase of the inverter output must be carefully controlled and adjusted to match the utility voltage. The inverter must target an amplitude slightly higher than the utility voltage to supply positive power to any attached loads (or loads upstream)...


This white paper includes:

  • Simple Distributed Generation Model
  • PV Inverter
  • Real-World Example

Download White Paper Here