| UNDER the concept of Global Energy Interconnection and Clean Development,the scale of grid interconnection is constantly expanding and the proportion of clean energy is keeping increasing,which is believed to be the future trend of the power grid.As a result,the grid damping is being reduced,accompanied by the Low-Frequency Oscillation easier to occur.The suppression of LFO is traditionally related to the Power System Stabilizers,namely PSS.However,the PSS is absolutely effective for Local Modes but for Interarea Modes.Additionally,it is hard to set the PSS parameters in the multi-machine systems.Fortunately,the Battery Energy Storage which may offer power at any time can balance the unbalanced power in the system in time.It can be installed at the generator or under the tie line,which is very beneficial for suppressing oscillations of Local Modes or Interarea Modes.For that reason,it is of practical significance to study how to control Energy Storage Devices to suppress LFO more effectively and where to install them so that they can produce a better effect.Firstly,the principle of suppressing LFO by Energy Storage Devices is detailedly analyzed based on the Heffron-Phillips model of Single-Machine Infinity-Bus system in this paper.The changes of curves of synchronous torque coefficient and damping torque coefficient are compared when the power deviation and rotational speed deviation are input separately.Then the Battery Energy Storage based on the control strategy of Power Oscillation Damping,namely POD,is linearized at the equilibrium point,and we get two system state matrixes which consider the installed energy storage of single-machine system and multi-machine system.After that,the eigenvalue analysis method is used to calculate the electromechanical modes,damping ratio,eigenvector,and eigenvalue sensitivity,which are the theoretical basis for the quantitative analysis of energy storage site selection and damping controller parameter optimization.In order to optimize the damping controller parameters to achieve a better effect of suppressing LFO,I adopt three ways to improve the basic Firefly Algorithm which is also called FA,and obtain GWFA which means a improved Firefly Algorithm based on Gaussian-decreasing-inertia-Weight.First,introduce Gaussian-decreasing-inertia-Weight into the position-updated-formula to enhance the algorithm's global search ability in the early stage and local search ability in the final stage.Second,change the maximum attractiveness constant into a function of iterative number to speed up the convergence of the algorithm.Third,introduce the compression factor into the final position-updated-formula to achieve a better result between the convergence speed and population diversity.After all these steps,an appropriate fitness function is designed,which is related to the real parts of eigenvalues and damping ratios of all electromechanical modes.Then the different effects of suppressing LFO of different groups of controller parameters which are set by the Residue method,FA and GWFA,are compared by simulations.The results show that the controller parameters set by GWFA can get the best results.Finally,the problem of location of Battery Energy Storage in suppressing LFO in multi-machine systems is studied.In the four-machine two-area system,two different working conditions are set,and the optimal installation position is obtained by the eigenvalue sensitivity method and the eigenvector method respectively.It is found that the optimal installation positions obtained by the two methods are occasionally different.In order to verify the accuracy,the LFO suppression effects of different installation positions are compared by setting three kinds of fault under the simulation model of four-machine two-area system on MATLAB/Simulink platform.It turns out that the installation position of Battery Energy Storage determinated by eigenvalue sensitivity is correct. |
PDF Full Text Request