Enhancement of Frequency Response Capability of Grid Connected Photovoltaics

As the penetration levels of Photovoltaic Generators (PVG) progresses in the utility scale distribution networks, the effective inertia due to the constant power factor ’Negative Loading’ is also reduced. One important regulation featured in the ’Network Codes’ of the ENTSO-E is the requirement of frequency response by the renewable energy sources. This is generally provided by the Photovoltaic Generators (PVG) at the sub-transmission levels. However, when the grid size is small, the dominating system is substantially a low or a medium voltage network. Due to the rising number of the PVGs in such networks, the voltage is not constant at the PCC, acerbated with a significant value of impedance as seen by the source. Therefore, rooftop PVGs also must cater to the frequency response services. These services are provided, generally with the help of a negative drooping of the active power. However, the droop control is a proportional controller, which can have detrimental small signal stability effects, and hence, for the grid connected operation of the PVG, a P-D control or an inertial control, which mimics the swing equation of the synchronous generator, is deployed for harnessing inertial response from the PVG in case of over frequencies. The efficacy of the controller has been tested for different frequency conditions, and it is observed that the PVG, even under weak grid conditions, can deliver frequency response, enhanced by an inertial support.