The increasing number of megawatt-scale photovoltaic (PV) power plants and other large inverter-based power stations that are being added to the power system are leading to changes in the way the power grid is operated. In response to these changes, new grid code requirements establish that inverter based power stations should not only remain connected to the grid during faulty conditions but, also provide dynamic support. This feature is referred in the literature to as momentary cessation operation. The few published studies about momentary cessation operation for PV power plants have not shed much light on the impact of these systems on the overall power system stability problem. As an attempt to address this issue, this paper proposes a control scheme for PV inverters that improves the transient stability of a synchronous generator connected to the grid. It is shown through the paper that the proposed control scheme makes the PV inverter’s dc link capacitors absorb some of the kinetic energy stored in the synchronous machine during momentary cessation. Besides that, the proposed solution is also able to improve voltage stability through the injection of reactive power. Experimental and simulation results are presented in order to demonstrate the effectiveness of the proposed control scheme.
- Photovoltaic generation
- Synchronous machine
- Transient stability
- Voltage stability
Figure 1. Three-Phase Diagram Of A Utility-Scale Hybrid Power System.
EXPECTED SIMULATION RESULTS:
Figure 2. Experimental Results Showing The Performance Of The Proposed Control. Results Obtained For: (A) No Control Scheme Implemented; (B) Inverter With The Proposed Control Scheme And No Reactive Power Support; And (C) Inverter With The Proposed Control Scheme And Reactive Power Support.
Figure 3. Comparative Responses Of The Hybrid System Subjected To A 2lg Fault. (A) Sm Active Power Output. (B) Pv System Active Power Output. (C) Sm Reactive Power Output. (D) Pv System Reactive Power Output.
Figure 4. Comparative Responses Of The Hybrid System Subjected To A 2lg Fault. (A) Pcc Voltage. (B) Dc Link Voltage. (C) Pv Unit’s Inverter Current Output. (D) Sm Rotor Angle.
In this work, a control scheme for PV inverters is proposed to act during faults that could compromise the transient and voltage stability of a hybrid power system. The analysis demonstrated that the proposed control scheme can act while the PV system is in MC operation, supporting the grid to recover stability during and after a disturbance on the transmission grid. The proposed control scheme makes the SM kinetic energy to be absorbed into the dc link capacitors to ensure transient stability. Besides that, it also enables the injection of reactive power into the grid to support voltage stability. Experimental and simulation results have shown that the proposed control scheme can reduce the rotor angle oscillations within the first few cycles of the fault, effectively ensuring the SM’s transient stability. It has also shown improvements in the grid voltages during the fault period and a very fast post-fault voltage recovery in comparison with other FRT control schemes.
 M. Milligan, B. Frew, B. Kirby, M. Schuerger, K. Clark, D. Lew, P. Denholm, B. Zavadil, M. O’Malley, and B. Tsuchida, “Alternatives no more: Wind and solar power are mainstays of a clean, reliable, affordable grid,” IEEE Power Energy Mag., vol. 13, no. 6, pp. 78_87, Nov. 2015.
 N. W. Miller, “Keeping it together: Transient stability in a world of wind and solar generation,” IEEE Power Energy Mag., vol. 13, no. 6, pp. 31_39, Nov. 2015.
 IEEE Standard for Interconnecting Distributed Resources With Electric Power Systems, IEEE Standard 1547-2003, Jul. 2003.
 W. Weisheng, C. Yongning, W. Zhen, L. Yan, W. Ruiming, N. Miller, and S. Baozhuang, “On the road to wind power: China’s experience at managing disturbances with high penetrations of wind generation,” IEEE Power Energy Mag., vol. 14, no. 6, pp. 24_34, Nov. 2016.
 IEEE Standard for Interconnection and Interoperability of Distributed Energy Resources With Associated Electric Power Systems Interfaces, IEEE Standard 1547-2018, Apr. 2018.