scholarly journals Enhanced dynamic performance of grid feeding distributed generation under variable grid inductance

Salman Harasis ◽  
Saher Albatran ◽  
Eyad Almaita ◽  
Khaled Alzaareer ◽  
Qusay Salem ◽  

<p>Controlling weak grid-connected systems is very challenging. In transient, frequency and voltage oscillations may lead to voltage and/or frequency stability problems and finally lead to system collapse. During steady-state operation and at the point of common coupling (PCC), voltage degradation and grid voltage background harmonics restrict the inverter's functionality, reduce the power flow capability and cause poor power quality. With weak grid connection, grid impedance variance will contaminate the voltage waveform by harmonics and augment the resonance, destabilizing the inverter operation. In this paper, complete mathematical modeling is carried out and state feedback-plus-integral control is implemented to support the stabilization of the system. The proposed controller is adopted to provide a smooth transient under sudden load change by controlling the injected grid current under different grid inductance values. Furthermore, the proposed control is used to reduce the order and size of the inverter output filter while maintaining system stability. The proposed control has been compared with the conventional proportional integral (PI) controller under different scenarios to validate its effectiveness and to strengthen its implementation as a simple controller for distributed generator applications.</p>

Energies ◽  
2019 ◽  
Vol 12 (5) ◽  
pp. 824 ◽  
Jinlian Liu ◽  
Zheng Xu ◽  
Liang Xiao

This paper aims to discover the general steady-state operation characteristics, as well as improving the dynamic performance, of the modular multilevel converter (MMC)-based unified power flow controller (UPFC). To achieve this, first, we established a detailed power flow model for MMC-based UPFC containing each critical part and made qualitative and graphical analyses combining 2-dimensional operation planes and 3-dimensional spatial curve surfaces comprehensively to derive general power flow principles and offer necessary references for regulating UPFC. Furthermore, to achieve better performance, we designed a feedforward control strategy for the shunt and series converters of UPFC, both comprising two feedforward control blocks with the introduction of necessary compensating branches, and analyzed the performance in complex and time domain, respectively. The proposed power flow principles and control strategies were validated by a (power systems computer aided design) PSCAD model of 220 kV double-end system; the results reveal the MMC-based UPFC can realize the power flow principles and improve the control speed, stability, and precision of the power flow regulations under various conditions.

2014 ◽  
Vol 25 (4) ◽  
pp. 128-135 ◽  
Othman Hasnaoui ◽  
Mehdi Allagui

The main causes of wind farms disconnection from the grid is the three-phase grid faults at the point common coupling (PCC) e.g. the voltage dip. The use of a Static Synchronous Compensator (STATCOM) which is from the family of Flexible AC Transmission System (FACTS) devices can be used effectively in a wind park based on FSIG to provide transient voltage and to improve wind system stability. Due to the asynchronous operation nature, system instability of wind farms based on FSIG (Fixed Speed Induction Generator) is largely caused by the reactive power absorption by FSIG because due to the large rotor slip during grid fault. STATCOM contributes to control the grid voltage at PCC and maintain wind farm connection to the grid during some severe conditions of grid faults and used for power flow control and for damping power system oscillations. The evaluation of this control strategy using (STATCOM) is investigated in terms of regulation reactive power and transient stability of the wind farm during grid disturbances.

Energies ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4441
Haoyu Li ◽  
Xuemei Zheng ◽  
Yanxue Yu

This paper presents a robust multi-input multi-output (MIMO) state-feedback control scheme for a photovoltaic (PV) inverter connected to a weak grid. For a weak grid, the point of common coupling (PCC) voltage is very sensitive to the power disturbances and it is dynamically coupled to the PLL dynamics. So far, most of the control methods do not take into accounts these couplings. Therefore, in this paper, the MIMO controller was designed taking into account the dynamics of the phase-locked loop (PLL) and coupling effects between PCC voltage and the active power to enhance the system’s robustness. As result, the robust performance of the PV inverter interfaced to a weak grid was yielded. In addition, the sensitivity of the system to PLL was eliminated, allowing the use of larger PLL bandwidth even in a very weak grid. Based on the eigenvalues analysis method, a comparative study between the proposed control method and the conventional vector control method was performed. The proposed method is verified with simulations in PLECS and real-time simulations in the RT Box. The results show that the proposed MIMO control method preserves the system stability robustness against any change of grid strength, generated power and PLL bandwidth.

2018 ◽  
Vol 2 (1) ◽  
Ali Abdulazeez ◽  
Bassam Mohammed ◽  
Bilal Nasir ◽  
Mohammed Yasen

Power System Stabilizer (PSS) is one of the most used controllers in the local generations, primarily it aimed to suppress local mode of oscillations. On the other hand, the Unified Power Flow Controllers (UPFC) the most versatile member of flexible alternating current transmission system devices to simultaneously control real and reactive power flows on transmission lines, as well as regulate selected bus voltage. Each of these controllers, on their own, can show satisfactory performance to enhance power system stability. However, when they utilized together, their dynamic performance can degrade due to controller interaction, that should be strategically optimized. In this paper, the coordinated design of pss's and upfc is realized to damp inter-area oscillations in  two-area power system using particle swarm optimization (PSO) method. The simulated cases in Matlab environment show that the interaction of pss's and upfc can be optimized, so the inter-area oscillations can be effectively mitigated following after fault, the simulation results of the uncoordinated design are also presented.

2016 ◽  
Vol 4 (2) ◽  
pp. 256-264 ◽  
Xinshou TIAN ◽  
Gengyin LI ◽  
Yongning CHI ◽  
Weisheng WANG ◽  
Haiyan TANG ◽  

2011 ◽  
Vol 121-126 ◽  
pp. 1744-1748
Xiang Yang Jin ◽  
Tie Feng Zhang ◽  
Li Li Zhao ◽  
He Teng Wang ◽  
Xiang Yi Guan

To determine the efficiency, load-bearing capacity and fatigue life of beveloid gears with intersecting axes, we design a mechanical gear test bed with closed power flow. To test the quality of its structure and predict its overall performance, we establish a three-dimensional solid model for various components based on the design parameters and adopt the technology of virtual prototyping simulation to conduct kinematics simulation on it. Then observe and verify the interactive kinematic situation of each component. Moreover, the finite element method is also utilized to carry out structural mechanics and dynamics analysis on some key components. The results indicate that the test bed can achieve the desired functionality, and the static and dynamic performance of some key components can also satisfy us.

2014 ◽  
Vol 986-987 ◽  
pp. 1286-1290
Jin Li ◽  
Ya Min Pi ◽  
Hui Yuan Yang

In this paper, the series converters of Distributed Power Flow Controller are the main object of study. Its mechanism of suppressing power system oscillations is studied by theoretical analysis and formula derivation, which relies on a single-machine infinite-bus power system, installed the series converters. Then based on the mechanism, adopting the classic PI control and the damping controller, designed the transient stability control loop for the series converters. Finally, simulations performed by PSCAD/EMTDC, the results show that DPFC device can effectively suppress oscillation and improve system stability.

2015 ◽  
Vol 740 ◽  
pp. 438-441 ◽  
Wei Zheng ◽  
Fang Yang ◽  
Zheng Dao Liu

The power flow calculation is study the steady-state operation of the power system as basic electrical calculations. It is given the power system network topology, device parameters and determines system health boundary conditions, draw a detailed operating status of the power system through numerical simulation methods, such as voltage amplitude and phase angle on the bus system the power distribution and the power loss. Flow calculation is the power system operation, planning and safety, reliability analysis, is fundamental to the system voltage regulation, network reconfiguration and reactive power optimization must call the function, so the trend has very important significance to calculate the power system.

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