Overspeed Protection Control Research Articles

A Control Scheme with the Variable-Speed Pitch System for Wind Turbines during a Zero-Voltage Ride Through

Zero-voltage ride through (ZVRT) is the extreme case of low-voltage ride through (LVRT), which represents the optimal grid-connection capability of wind turbines (WTs). Enforcing ZVRT will improve the dynamic performance of WTs and therefore significantly enhance the resiliency of renewable-rich grids. A control scheme that includes a pitch system is an essential control aspect of WTs riding through voltage dips; however, the existing control scheme with a pitch system for LVRT cannot distinguish between a ZVRT status and a power-loss condition, and, consequently, does not meet the ZVRT requirements. A system-level control scheme with a pitch system for ZVRT that includes pitch system modeling, control logic, control circuits, and overspeed protection control (OPC) is proposed in this paper for the first time in ZVRT research. Additionally, the field data are shared, a fault analysis of an overspeed accident caused by a voltage dip that describes the operating status at the WT-collapse moment is presented, and some existing WT design flaws are revealed and corrected by the fault analysis. Finally, the pitching performance during a ZVRT, which significantly affects the ZVRT performance of the WT, is obtained from laboratory and field tests. The results validate the effectiveness of the proposed holistic control scheme.

A Simulation-Based Procedure to Determine Optimum Range of Settings of Fast Valving Action of Steam Turbines to Enhance Frequency Stability

Fast Valving (FV) mechanism of steam turbines is considered to be one of the most effective actions for enhancing the security of a power system subsequent to disturbances. It plays a significant role in mitigating the impact of severe disturbances by instantly decreasing steam turbine power, thus ensuring the power system stability. There is a direct relationship between the settings of Over-Speed Protection Control (OPC) unit of steam turbines and the control functions of FV. This paper proposes a generalized simulation-based procedure to determine the optimum intermediate valve actuation timings of the FV control action. A coal-fired thermal power plant has been used as the case study and the accuracy of the settings made using the proposed approach has been demonstrated using actually happened contingencies in a real power system. Finally, it is concluded that the proper selection of actuation timings of intermediate valves for FV scheme has a significant effect on enhancing frequency stability under transient conditions.

Impact of Overspeed Protection Control on Stability for Islanded Power System

Islanded power system can be formed by unexpected electric equipment failure or initiative breaking off of a main system avoiding a whole collapse. Unbalanced power between generation and load may cause an overspeed of the units and trigger the action of Overspeed Protection Controller (OPC) which is mainly designed for a load rejection condition. The mathematic model was built to simulate the islanded system stability with the effect of OPC. The simulation reproduced the power and frequency oscillation as the accidents. The results show a great impact of OPC on the stability of an islanded system. Modified OPC logic was proposed to avoid the oscillation and increase the stability.

Variable structure servomechanism design and applications to overspeed protection control

A new class of variable structure feedback systems capable of rejecting a persistent disturbance is developed. This type of system which is called the VS servo is structurally similar to linear multivariable servomechanisms. Its behavior on the switching manifold and its internal stability and output regulation properties are examined using the theory of variable structure systems and sliding modes and existing results on high gain feedback. The concepts of the VS servo are particularly well suited for the study of ‘emergency’ control system design. The design of the VS servo is applied to the problem of overspeed protection control for large steam turbines. This study leads to an understanding of the generic difficulty associated with the application of overspeed protection control to large coal fired power plants and provides a feedback control structure with considerable promise for such applications. In addition, the paper serves as a useful illustration of the flexibility and potential applicability of variable structure designs. The effect of actuator parasitic dynamics is considered.

An Application of a Variable Structure Servomechanism Design to Turbine Overspeed Protection Control

The concepts of variable structure systems and sliding mode are particularly well suited for the study of ‘emergency’ control system design. In this paper, recent results pertaining to the design of variable structure servomechanisms are applied to the problem of overspeed protection control for large steam turbines. The study leads to an understanding of the generic difficulty associated with the application of overspeed protection control to large coal fired power plants and provides a feedback control structure with considerable promise for such applications. In addition, the paper serves as a useful illustration of the flexibility and potential applicability of variable structure designs. The effect of actuator parasitic dynamics are considered.