System inertia plays a vital role in controlling the angular stability of the system during a disturbance. Due to increased penetration of power electronic interfaced sources, such as Solar Photovoltaic (SPV) source, the overall system inertia reduces and varies depending on their operating conditions. In this paper, an approach for online inertia estimation in the power system network with SPV sources is proposed, using the synchronized measurements from Phasor Measurement Units (PMUs). An equivalent swing equation is used to emulate the network dynamics. A relationship between the inertia constant and the roots of this equation is determined. In order to numerically obtain the roots, the Estimation of Signal Parameter via Rotational Invariance Techniques (ESPRIT) method is first used to find the modes present in the frequency signal. A new formulation is proposed to extract an equivalent mode from all the obtained modes. Also, to avoid phase step error, Rate Of Change Of Frequency (ROCOF) is estimated from the equivalent mode of the frequency signal. Results obtained for the 39 bus New England system for various test cases, using Real-Time Digital Simulator (RTDS), prove the efficacy and superiority of the proposed approach over the existing approaches in the literature.

Online Estimation of System Inertia in a Power Network Utilizing Synchrophasor Measurements

Design, Modelling, and Analysis of Novel Solar PV System using MATLAB

The proposed method is effective in increasing the damping of the system at the frequencies of interest, also in the case of system parameter uncertainties and at various connection points of the compensator. First, the analysis of the im-pact of active and reactive power injection into the power system will be carried out using a simple two-machine system model. A control strategy that optimizes active and reactive power injection at various connection points of the STATCOM will be derived using the simpliﬁed model. Small-signal analysis of the dynamic performance of the proposed control strategy will be carried out. The effectiveness of the proposed control method to provide power oscillation damping irrespective of the connection point of the device and in the presence of system parameter uncertainties will be veriﬁed through simulation and experimental results.

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An Adaptive Power Oscillation Damping Controller by STATCOM With Energy Storage

This paper presents photovoltaic (PV) system control as distributed static compensator (DSTATCOM), termed as PV-DSTATCOM, operated with active current control (ACC) and feed-forward control loop (FFCL). Besides active power injection into the utility grid, the proposed PV system autonomously transforms into a DSTATCOM to provide various ancillary services including source current harmonic suppression, load reactive current compensation, zero sequences component mitigation, and power factor correction. Since PV-DSTATCOM operates with ACC, it precisely extracts the fundamental in-phase and quadrature components of current. It introduces high-gain at the third-order harmonic and thereby alleviates stationary errors in the current control loop of PV inverter. The proposed ACC+FFCL structure is computationally efficient and unconditionally stable. Practically, FFCL addresses the challenges emerged due to nonlinearity introduced by the PV unit and ensure a rapid power balance between the PV unit and electric grid. Further, a simplified perturb and observe based maximum power point tracker has been employed to evacuate the maximum power from the PV array. The proficiency of the developed ACC+FFCL structure is investigated through a comprehensive set of transient studies using MATLAB/Simulink software. Finally, a laboratory setup has been developed using the dSPACE-1104 platform and experimental results are recorded with detailed comparative evaluation.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-gtd.2019.1487

Photovoltaic system operation as DSTATCOM for power quality improvement employing active current control

This paper presents a novel fast frequency response and power oscillation damping control by large-scale PV plants controlled as STATCOM, termed PV-STATCOM, to simultaneously enhance frequency regulation and small signal stability of power systems. Frequency deviations typically occur together with power oscillations in large power systems. The proposed controller comprises: first, power oscillation damping controller based on reactive power modulation and second, fast frequency response controller based on real power modulation, both of which are applied to the plant level controller of PV-STATCOMs. The proposed composite control is shown to successfully reduce frequency deviations, damp power oscillations, and provide voltage regulation both during over-frequency and under-frequency events. The proposed smart inverter control makes effective utilization of the PV inverter capacity and available solar power. For large power flows, the proposed control is shown to be superior than the conventional droop control recommended by North American Electric Reliability Corporation for generating plants. MATLAB/Simulink-based simulations are conducted on two-area power system using generic PV plant dynamic models developed by Western Electricity Coordinating Council, for a wide range of system operating conditions. Such grid support functionality is expected to bring new revenue making opportunities for PV solar farms.

Simultaneous Fast Frequency Control and Power Oscillation Damping by Utilizing PV Solar System as PV-STATCOM

This IEEE Working Group paper presents a review of selected journal papers published on control of STATCOM – a Flexible AC Transmission System (FACTS) device, during the period 2016-2017. This review includes STATCOM controls utilized in different applications such as voltage control, stability improvement, mitigation of subsynchronous resonance (SSR), integration of renewable energy systems, energy storage systems, and coordination with HVDC systems. Journal papers have been searched through different search engines such as, IEEE Xplore, SCOPUS and others. This review includes papers published during 2016 to October 2017 (until the submission of this Review paper). The total journal papers found in this search were 260, of which only 75 were found through IEEE Xplore, while the remaining 170 were discovered from other non-IEEE search engines. Due to the page limitation, a total of 60 papers are included in this Bibliography. The bibliographic citations of the remaining papers will be provided on the website of this IEEE Working Group. The objective of this Working Group paper is to disseminate information and thereby educate the power and energy systems community worldwide about the controls of STATCOMs for providing various grid benefits.

Control of STATCOMs – A Review

This paper presents a novel reactive power-based frequency support service through large-scale PV plants. Frequency is conventionally controlled through real power, which may not be always available from PV solar systems. In addition, PV power may need to be curtailed during high power production periods (e.g. noontime) for frequency support. On the other hand, reactive power is always available, which provides the PV plants with the opportunity of being controlled as a STATCOM, known as PV-STATCOM both during night and day. Although less effective, reactive power can also influence the system frequency through modulation of voltages at the terminals of loads. This paper investigates the feasibility, challenges and effectiveness of Reactive power-based Frequency Controller (RFC) added to PV-STATCOMs. The proposed controller aims to enhance the stability of the "frequency regulation mode" of the system. The design of RFC through small signal residue-based technique and time domain simulations are performed in Matlab to demonstrate the benefits of the proposed control in a two-area power system. This novel control of PV solar farms as PV-STATCOM can effectively complement the frequency support from other generators in the power grid, on a 24/7 basis.

Mohammad Akbari

Papers

Simultaneous Fast Frequency Control and Power Oscillation Damping by Utilizing PV Solar System as PV-STATCOM

Control of STATCOMs – A Review

A Novel Reactive Power based Frequency Control by PV-STATCOMs during Day and Night