On‐line preventive control for power system transient stability based on the energy function method

Abstract

For the purpose of maintaining the power system security, an integrated security monitoring and control (ISMAC) system, is being developed in which both preventive and emergency control have important roles. Static security control strategies which deal with the steady state after the contingency is cleared, have been studied by various researchers including the authors. However, the basic research on dynamic security control which deals with the transient state immediately after the contingency has occurred is seldom found. This paper presents a method of dynamic preventive control for the transient stability considering plural contingencies and coordinating in a flexible way the requirements of both security and economy. In the preventive control for transient stability, it is necessary to judge the transient behaviors properly and also to evaluate the security quantitatively for a postulated contingency. The authors define a security index which represents absorbing capacity of post‐fault kinetic energy based on the energy function method. The index has these advantages: it is possible to calculate values rapidly; and physical meanings are easily understood. The effectiveness of the proposed method is ascertained through numerical examples for model power systems.

An Optimal Generation Rescheduling Approach for Transient Stability Enhancement

“…To derive the formulas for evaluating gradient of the stability performance index with respect to , Lagrange multiplier vectors and are introduced to construct a new functional as follows [25]: (13) where , which emphasizes that at time , is a function of state variable . Considering (1) and (2), it is easy to see that the following holds true: (14) Using the formula of integration by parts, the following can be derived:…”

“…References [11] and [12] further enhanced the method of [9] and [10] for a set of postulated contingencies, where a set of power system equations and stability constraints for each contingency are incorporated into the overall optimization problem. In [13], the most severe contingency is recursively dealt with until all contingencies become stable. System security constraints have been gradually incorporated in studies of economic dispatch [14], [15], optimal power flow [16]- [20], and optimal operation [21].…”

Transient security dispatch for the concurrent optimization of plural postulated contingencies

“…The dot product is evaluated across the whole trajectory of the system and must be negative in order to guarantee the stability. This condition can be written for each th time step subsequent to the fault clearing time step (16) Bus voltages are constrained by the following bound for each time step: (17) Note that the bound is time variant in order to guarantee satisfactory voltage transient [15] with reguard to angle/voltage stability and protection system requirements.…”

“…In [16], the authors propose a preventive control technique which considers plural postulated contingencies collectively. After processing the most severe contingency, the security of the neglected contingencies is checked on the new generation schedule.…”

Transient stability preventive control for stable operating condition with desired CCT

“…Next, the values of real power and reactive power of all buses are calculated from the estimated bus voltages. Therefore, the generator bus current is calculated as in (10) where is the conjugate of the th generator bus voltage The voltage behind the transient reactance can be calculated as in (11) Finally, the estimated generator rotor angle is obtained as [15] Im Re (12) The rotor angels in the COA reference frame can be calculated by the results of (12).…”