Search

Given large-scale power networks with series compensation, the study of subsynchronous resonance (SSR) is a significant challenge, in practice, due to the model complexity and computation burden. To tackle these difficulties, this paper proposes a method to reduce a large-scale system to an equivalent model using a metric called damping sensitivity index. The proposed metric can quantitatively identify the boundaries of the equivalent model that ensure the accurate studies of SSR and reduce the computation burdens greatly. The effectiveness of the method is verified by its application to the SSR investigation of the modified IEEE New England 10-machine 39-bus system and 16-machine 68-bus system. The equivalent models obtained by the proposed method are compared with the original systems in terms of driving point impedances, electrical damping, and transient torques. These results obtained show that the equivalent models from the proposed method can reproduce the SSR dynamics of the original systems with a much shorter computation time. [ABSTRACT FROM PUBLISHER]

There are two critical issues in stabilizing subsynchronous resonance of practical power systems. One is to select an effective yet low-cost control scheme. The other is to optimize the controllers under all possible operating conditions and diversified system disturbances. To address these issues, this article proposes a combined control scheme and a coordinated control design method. The combined scheme is composed of a supplementary excitation damping controller and a voltage source converter based generator terminal subsynchronous damping controller deployed, respectively, on the rotor and stator sides of a generator to take full advantage of a supplementary excitation damping controller (very low cost) and generator terminal subsynchronous damping controller (fast response, flexibility in rating, and deployment). The coordinated control design is implemented through parameter optimization on the linearized system and performance verification with non-linear simulations. The former uses genetic algorithm and simulated annealing to solve the constrained non-linear optimization problem, while the latter inspects the dynamic control performance under either large or small disturbances. A practical system in northern China is taken for a case study. The results of both eigenvalue analysis and time-domain simulation have fully demonstrated the effectiveness of the optimally and coordinately designed subsynchronous resonance control system. [ABSTRACT FROM AUTHOR]

Supplementary excitation damping controller (SEDC) has been widely acknowledged as one of the effective measures to stabilize subsynchronous resonance (SSR). However, how to quantify its stabilizing ability is still an open issue raising widespread concerns. There are few in-depth studies or conclusions in this aspect yet. This paper presents a quantitative measure of SEDC's ability to damp SSR, namely stabilizing ability index (SAI). It is defined as the percentage margin of the effective gain relative to the critical stability gain (CSG). The CSG is the minimum gain of SEDC to guarantee SSR stability, while the effective gain is the control gain of SEDC actually functioning following system disturbances. A practical system is used to investigate the various factors determining the effective gain, the CSG and thus the SAI, based on eigenvalue analysis as well as time-domain simulation. The dominant factors identified include: the total equivalent series-compensation degree of system, the parameters and operating status of the generator, the response time and ceiling voltage of the exciter, and the severity of the disturbance. Why and how these factors affect the control capability of SEDC is examined and thus a practical method is offered for the assessment of SEDC's ability to stabilize SSR. [ABSTRACT FROM AUTHOR]

Highlights: [•] The new approach is based on the supplementary-excitation-signal-injection test. [•] It can identify frequencies and mechanic damping of all torsional modes concerned. [•] A solid theoretical foundation is established upon the dynamic shaft model. [•] A systematic test and identification procedure is developed. [•] The approach is applied in practical systems and validated through field test. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a generator terminal subsynchronous damping controller (GTSDC) for mitigating multimodal subsynchronous resonance (SSR) that may occur in series-compensated power systems. The proposed GTSDC system is composed of a digital controller and a power electronic inverter with current tracking control. It uses the shaft speed deviation of the generator turbine as feedback to modulate the dynamic current reference of the inverter through multimodal control paths. By exactly tracking the reference value, the power electronic inverter generates current at frequencies complementary to the torsional modes. Part of the current flows into the generator and creates damping torque on the shaft system to damp SSR. The relationship between the output current of GTSDC and the resulting electromagnetic torque is derived based on the complex torque coefficient method. Furthermore, a nonlinear optimization method is implemented to obtain the optimal parameters for all modal-control paths, thereby effectively enhancing the damping of all torsional modes under different operating conditions. The case study on a real series-compensated power system through eigenvalue analysis and electromagnetic simulations validates the effectiveness of the controller. [Copyright &y& Elsevier]

The Shangdu power plant has four 600-MW turbine-generators connected to the North-China Grid through two 500-kV transmissions, which are compensated with 45% fixed series capacitors. Extensive studies conducted on the system model indicate that the system suffers from multimodal subsynchronous resonance (SSR). To solve the problem, a countermeasure is developed by combining the supplementary excitation damping control (SEDC) and the torsional stress relay (TSR). In this paper, the characteristics of the SSR problem are investigated. Then the developed SEDC is presented. To validate the effectiveness of the proposed SEDC as well as the results of model studies, field tests were conducted under various operating conditions. The tests fully exposed the realistic threat of SSR in the system. Meanwhile, it is demonstrated that the developed SEDC can improve torsional damping significantly, and thus solve the multimodal SSR problem effectively. This is the first time in China that practical SEDCs have been developed and their ability to mitigate multimodal SSR has been verified in a real series-compensated system. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an intelligently optimized multimodal supplementary excitation damping control (OMSEDC) to depress subsynchronous resonance (SSR) that may occur in series-compensated power systems. In the proposed OMSEDC, each torsional mode is controlled through an independent feedback path in order to achieve better and multimodal damping. To make OMSEDC feasible and robust, the control parameters are optimized on a number of linearized system models over a set of carefully selected operating conditions. During system modeling, the time-delay of the firing control in the thyristor-based excitation system is taken into consideration for the first time, making OMSEDC practicable in real systems. The task of simultaneously tuning for stable control parameters considering multiple torsional modes and under different system conditions is formulated into a constrained nonlinear optimization problem, which is generally difficult for traditional methods. In this paper, the genetic and simulated annealing algorithm (GASA) is adapted and implemented to obtain the optimal parameters with high efficiency. A practical series-compensated system is employed to evaluate the effectiveness of OMSEDC. Both eigenvalue analysis and nonlinear electromagnetic simulations have demonstrated a satisfactory damping performance of the controller on multiple torsional modes and in different system conditions. [Copyright &y& Elsevier]