单机等值系统调速器死区对频率振荡的影响

实际系统中多次发生一次调频过程不稳定导致的超低频频率振荡事件。调速器死区给系统带来非线性,进而影响系统的频率振荡行为。基于单机等值系统,采用描述函数法分析了无阶跃死区、有阶跃死区和滞环死区这3种死区对频率振荡的影响。在复平面上,给出了死区描述函数的负倒数随振幅变化的轨迹,以及调速器、原动机、发电机构成的开环传递函数随频率变化的曲线,两者相对位置关系决定系统的稳定性。负倒数随振幅变化特性曲线完全位于开环频率特性曲线左侧时,系统稳定。其他情况下2条曲线一般会相交,交点对应极限环,极限环稳定与否决定于交点的具体形态。同时分析了单机等值系统中调速器死区对频率振荡的影响,调速器无阶跃死区和有阶跃死区都不会减弱系统稳定性,但有滞环死区时可能导致原本稳定的系统出现稳定极限环引发的持续等幅振荡。时域仿真结果验证了上述结论。

Influence of Deadband of Governor on Frequency Oscillation in Single Machine Equivalent System

Ultra-low-frequency oscillations caused by the instability of primary frequency regulation process occurr in actual power systems. Governor deadband introduces nonlinearity to the system and affects frequency oscillation. The influence of non-step deadband, step deadband and hysterisis deadband on frequency oscillation are analyzed with the describing function method in the single-machine equivalent system. The locus of minus reciprocal of the describing function of deadband with oscillation amplitude, and the locus of open-loop transfer function with oscillation frequency are plotted on the complex plane. The relative location of the two loci determines the system stability. When the minus reciprocal locus entirely locates on the left of the open loop frequency characteristic locus, the system is stable. In other cases, the two loci intersect in general and the intersections correspond to limit cycles, and the stability is determined by the specific situation of the intersection. Furthermore, the influence of governor deadband on frequency oscillation in single machine equivalent system is analyzed. Non-step deadband and step deadband do not weaken the stability of the system, but hysterisis deadband may cause continuous oscillation due to stable limit cycle in a system which is initially stable without deadband. Results of time-domain simulations validate the conclusions.