Regional Coordination for under Frequency Load Shedding

Frequency deviation can be used as an indicator of imbalance between supply and demand. When generation is insufficient, it can cause frequency decline in a power system operation. Implementing under frequency load shedding (UFLS) is one of the common methods to overcome this problem. This paper proposes a novel approach for adaptive load shedding. The concept is an extension of shared and targeted load shedding using reserve margin. The optimal system configuration is then selected from those candidates to fulfill operational objectives. Operational constraints related to system parameters, threshold frequency, total of load shed and control area including line capacity are considered. An example using four sub-areas connected to an external system shows that the proposed regional coordination as an adaptive UFLS is feasible.

Synchronization Stability of Interconnected Microgrids with Fully Inverter-based Distributed Energy Resources

In this paper,the synchronization stability challenges of same-rated frequency interconnected microgrids(IMGs)with fully inverter-based generation units are studied.In this type of weak power grid with low X/R ratios and low line impedances,no strong source with a high-inertia rating exists with which other generation units can be synchronized.Two IMGs controlled using a pinning consensus-based control architecture are considered.The inrush power flow at the beginning of the interconnection process is modeled and analyzed.This power flow is affected by the voltage/phase/frequency difference of the IMG points of common coupling.A small-signal model of the IMGs is obtained that includes a synchronization control unit,and small-signal stability is analyzed based on sensitivity analysis of the most important control and operational parameters.In addition,the transient stability of a nonlinear model of the IMGs under study as implemented in Sim Power Systems/MATLAB is investigated.Stable synchronization is more challenging than the synchronization of multi-area strong power grids and grid-connected MGs.However,synchronization can still be performed by selecting more limited ranges for the control gains and threshold values of the synchronization algorithm.Nevertheless,different disturbances such as high load conditions can cause synchronization instability.

Autonomous Dual Active Power-frequency Control in Power System with Small-scale Photovoltaic Power Generation

Active power control of the photovoltaic(PV)power generation system is a promising solution to regulate frequency fluctuation in a power system with high penetration of renewable energy.This paper proposes an autonomous active power control of a small-scale PV system for supporting the inertial response of synchronous generators and power-frequency control.In the proposed control approach,an effective grid frequency regulation scheme is realized using slow-and fast-frequency responses.A low-pass filter based frequency measurement is used for slow-frequency response,while direct frequency measurement is used for fast-frequency response.The designed dual droop characteristic-based control is shaped to achieve a smooth transition between slow-and fast-frequency responses.The performance of the proposed control approach is demonstrated for serious disturbance scenarios,i.e.,considerable power-load imbalance and generation trip.In the powerload imbalance test scenario,the proposed control approach works properly within the normal frequency deviation region even when the frequency deviation exceeds that region occasionally.In the generation trip test,the frequency deviation is mitigated quickly,and the employed droop control is smoothly transferred from the slow-to fast-frequency responses.

Dynamic Improvement of DC Microgrids Using a Dual Approach Based on Virtual Inertia

In this paper,inspired by the concept of virtual inertia in alternating current(AC)systems,a virtual impedance controller is proposed for the dynamic improvement of direct current microgrids(DCMGs).A simple and inexpensive method for injecting inertia into the system is used to adjust the output power of each distributed generation unit without using additional equipment.The proposed controller consists of two components:a virtual capacitor and a virtual inductor.These virtual components can change the rate of change of the DC bus voltage and also improve the transient response.A small-signal analysis is carried out to verify the impact of the proposed control strategy.Numerical simulation studies validate the effectiveness of the proposed solution for increasing the inertia of DCMGs.