Transient stability analysis of inverter interfaced distributed generators in a microgrid system

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Transient stability analysis of inverter interfaced distributed generators in a microgrid system

  1. 1. <ul><ul><li>Transient Stability Analysis of Inverter-Interfaced Distributed Generators in a Microgrid System </li></ul></ul><ul><ul><li>F. Andrade, J. Cusidó, L. Romeral </li></ul></ul><ul><ul><li>Motion Control & Industrial Applications Center, MCIA </li></ul></ul><ul><ul><li>Universitat Politècnica de Catalunya. </li></ul></ul><ul><ul><li>CTM Centre Tecnològic </li></ul></ul><ul><ul><li>Intelligent Microgrids integrate different energy resources, especially renewable source, to provide dependable, efficient operations, while works connected to the grid or islanding mode. </li></ul></ul><ul><ul><li>It can be ensured an uninterrupted reliable flow of power, economic and environmental benefits while minimizing energy loss through transmission over long distances. </li></ul></ul><ul><ul><li>The use of intelligent power interfaces between the renewable source and the grid is required. </li></ul></ul><ul><ul><li>Each generator has a power DC renewable source, a DC/AC inverter, a low pass filter and it is managed by two control loops </li></ul></ul><ul><ul><li>The study shows: </li></ul></ul><ul><ul><li>a mathematic model of a Microgrid system in stand-alone based in parallel connected inverters </li></ul></ul><ul><ul><li>works with no-lineal tool and computer simulations, phase-plane trajectory analysis and method of Lyapunov for evaluate the limits of the small signal models. </li></ul></ul>Fig 2: Methodologies applied for bearing diagnosis. Electric Utility Fig 1: Connected Microgrid system based in power electronic interfaces. Microgrid <ul><ul><li>The PQ controller: </li></ul></ul><ul><ul><li>The power angle between both generators: </li></ul></ul><ul><ul><li>Working in the time domain: </li></ul></ul><ul><ul><li>The PQ power: </li></ul></ul><ul><ul><li>The whole model: </li></ul></ul><ul><ul><li>Equilibrium points </li></ul></ul>Fig 3: the equilibrium point X0 the range of the variable X5 <ul><ul><li>The equilibrium point X0=[0.0019 320.1 320.1 239.7 239.6] </li></ul></ul>MATHEMATICAL MODEL INTRODUCTION Variable Value Unit Operating Voltage range 218,5 – 241,5 Vrms Operating Frequency range 49 - 51 Hz Freq. droop coefficient (K p1 = K p2 ) 1,33e-4 rad.s -1 /W Voltage droop coefficient (K v1 = K v2 ) 0.0015 V/VAR Cutoff frequency filter 5 Hz
  2. 2. <ul><ul><li>In this paper, a nonlinear state-space model of a Microgrid is presented. The model includes the most important dynamics. The no-linear model can find the equilibrium points. The model has been analyzed by means of both studies, first, a study of small signal stability by mean of linearization and root locus plot and transient stability by mean of Lyapunov function. </li></ul></ul><ul><ul><li>The studies of small signal could be done for adjustment the controller and improve the transient response and the steady-state error. Using that Lyapunov function the region of asymptotic stability, the size of the disturbed and his duration time could be determined. These tools will allow the design of Microgrid systems with loads, generators and storage systems assuring the global stability of the system. </li></ul></ul><ul><ul><li>Using the Jacobian matrix of f(X) at the equilibrium point. </li></ul></ul>Fig 4: Root locus for 1.3e-4< Kp <7.8e-4 <ul><ul><li>An analysis of the equilibrium point and small-signal stability </li></ul></ul><ul><ul><li>Transient Stability Analysis of Inverter-Interfaced Distributed Generators in a Microgrid System </li></ul></ul><ul><ul><li>F. Andrade, J. Cusidó, L. Romeral </li></ul></ul><ul><ul><li>Motion Control & Industrial Applications Center, MCIA </li></ul></ul><ul><ul><li>Universitat Politècnica de Catalunya. </li></ul></ul><ul><ul><li>CTM Centre Tecnològic </li></ul></ul><ul><ul><li>Stability of Lyapunov </li></ul></ul><ul><ul><li>Considering only the first generator; it has been considerate variations in the angle, active power and frequency. It was negligence variation in the voltage. The second generator is an infinite bus with fixed frequency and voltage </li></ul></ul>Where Fig 6: phase portrait in Z1 –Z2. (x=Z1 y=Z2) <ul><ul><li>Simulations result </li></ul></ul>Fig 5: Function f(Z 1 ) <ul><ul><li>the region of asymptotic stability is obtained as </li></ul></ul>Fig 7: Active Power dispatch by each DGs when it is increase the Kp Fig 8: two large disturbances in the Microgrid. STABILITY OF THE SYSTEM CONCLUSIONS

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