P-Q and P-V Control of Photovoltaic Generators in Distribution Systems

In this paper, simultaneous control of active power and volt/var is explored with photovoltaic (PV) generators in distribution systems. The PV active power output can be controlled in the load-following mode when sufficient solar power is available to supply a local load, or the maximum power point tracking (MPPT) mode when a local load is large or injection to the system is allowed. Two selected control approaches, P-Q control in the load-following mode and P-V control in the MPPT mode, are investigated in this paper. The P-Q control is implemented with a relatively simple approach, while the P-V control demands an extra MPPT logic, which is solved based on a power balance between the dc and ac sides in a two-stage PV configuration. The control algorithms are tested with the IEEE 13-bus distribution feeder with various system conditions like the presence of multiple PV generators, imbalance, harmonics, and faults. The MATLAB and SimPowerSystems simulation results clearly demonstrate the capability of the proposed control in maintaining the P/V bus as either a P-Q or P-V bus depending on different applications.