Research On Control Strategy Of Power System Subsynchronous Oscillation

Short circuit fault, inappropriate circuit breaker operation, the introduction of the series compensation technology in power system can trigger strong coupling effect between mechanical equipment and electrical equipment, named subsynchronous oscillation(SSO), and the related physical quantity will produce sustained oscillation to be a damaged threat to the safe and stable operation of the power system. Especially, as our country is gradually establishing a large units, ultra-high voltage, large scale,long distance,AC/DC hybrid transmission,new smart grid,and the increasingly complex power grid structure and operation mode of diversity increased the instability of subsynchronous oscillation. On account of this background, this paper puts forward the control strategy to suppress subsynchronous oscillation in power system, Now summarized as follows:(1) Firstly, this paper attempt to make condensing steam turbine generator shaft system model be simplified to double rigid body model of shaft system only containing steam turbine and generator, by measuring the rotating angular displacement between the two rigid-body deviation to judge whether SSO is happened, and based on the accurate feedback linearization theory, the excitation and governor multi-index nonlinear coordinated controller is designed. Time domain simulation shows that when the system under short-circuit fault, power and pressure regulating disturbance, the proposed controller not only can well restrain shafting torsional vibration, reduce torsional vibration fatigue wear and tear, and can coordinate well dynamic and static performance of the generator, improve the operation stability of the system. (2) Then,to further refine steam-turbine generator shafting structure, this paper adopts a precise segmentation lumped mass spring model, and integrated two advantages,which are power regulation function of excitation regulator and providing positive damping properties to power system by accessing static synchronous series compensator (SSSC) to transmission lines. A19order state space model of shaft system, electromagnetic transient circuit, transmission system with SSSC is established in single machine infinite system.Based on linear optimal control algorithm(LOEC), the comprehensive linear optimal coordination controller integrated SSSC and excitation is derived. By analyzing the system eigenvalues, the controller for each mode of shafting torsional vibration has excellent inhibition effect. Time domain simulation of the first benchmark test model of IEEE sub-synchronous containing SSSC shows that, the results verify the effectiveness of suppressing the torque oscillation among each rigid body.(3) In consideration of similarity structure relation between reheat steam turbine generator set type valve opening control system model with piecewise lumped mass spring model, Based on the valve opening and excitation coordination control from the source to achieve inhibiting oscillation angle displacement deviation among mass. A advanced target holographic nonlinear feedback control (NCOHF) algorithm is applied, selecting the target angle displacement deviation among mass equations, the comprehensive coordination controller integrated excitation, high pressure valve and intermediate pressure valve is deduced, time domain simulation results show the effect of the inhibition of sub-synchronous oscillation is better than linear optimal controller.