Construction Design And Parameter Coordination Of Multi-band PSS

Under some special cases, low frequency oscillation may occur in the power system, when the system negative damping offsets the positive damping contributed by generators and excitation system. As the most mature technology, power system stabilizer (PSS) is widely used to inhibit low frequency oscillation. It introduces a supplementary signal to act on the generator field voltage through the excitation system, then produces a large enough positive damping torque. So far many researchers do a lot of study on the methods of PSS construction and parameters design.With the rapid growth of the scale of the modern power system, the number of the oscillation modes in the system is also increasing. From the economic point of view, a PSS is desired to improve more than one mode damping performance simultaneously. For the conventional single band PSS, a wider compensation band can be acquired by adjust time constants of the lead-lag stages, to affect more modes. But because of the limitation of the single band characteristics, while the damping performances of some modes are better, that of some other modes may be worse.In order to improve the PSS selectivity of oscillation modes, the multi-band PSS (MBPSS) is proposed. But the construction of the conventional MBPSS is complex, and the number of the compensation bands is fixed. So the flexibility of MBPSS application is limited. A novel power-input MBPSS is proposed in this paper. The frequency characters of the PSS are analyzed, and the method of selecting time constants is decided.Taking account the random factors in power system operation, the probabilistic theory is introduced to estimate whether the system is stable. Based on the sixth-order machine representation and GMR/PMT technique, probabilistic sensitivity analysis is used to determine the number of the PSS band and the installation location. According to the PSS parameter design method, parameters are coordinated by using the nonlinear programming technique.In a testing 8-machine system, all the nodal injections and voltage are regarded as random variables. With the 720 operating conditions of the system as samples, the probabilistic environment is made. According to the proposed method, the constructions of PSSs are determined, and PSSs is installed at the suitable location. Then the selected parameters are optimized. Without PSS, all of the seven electro-mechanical oscillation modes of the system are not robust sable under multioperating condition. When the PSSs have been equipped, the damping and stability performances of all modes are greatly improved, and all the probabilistic indices of modes satisfied robust stable need. At the same time, it is proved that the PSS can be applied as a single-band PSS to increase only one mode damping ratio, or a MBPSS which can improve more than two mode damping performance.