Abstract
Large frequency deviation degrades the operation performance of the boiler and its auxiliaries. It affects the output of thermal power units. A significant change in power generation leads to a great frequency deviation. An extended frequency response model for long-term frequency stability assessment is constructed to consider the effects of frequency deviations on boiler auxiliaries. The static power-frequency characteristic of the thermal power unit within an extensive frequency variation range is analyzed. It reveals that the active power output of the generating unit is not monotonically increasing with frequency dropping. An inflection point is observed on the static power-frequency characteristic curve when considering boiler auxiliary frequency characteristics. In the range of greater frequency deviation, the output power decreases rapidly with frequency declination, and an unstable equilibrium point (UEP) of frequency stability is identified. A quantitative index is proposed for frequency stability assessment based on UEP. The stability characteristic and the frequency stability quantitative index based on UEP are analyzed. The frequency dynamic behaviors of the extended model are demonstrated to analyze frequency stability characteristics within an extensive frequency variation range by a single machine system and the IEEE 39-bus system with considering boilers and its auxiliaries.
Highlights
Frequency is one of the most significant variables indicating the security and stability of the power system
This paper mainly considers the auxiliaries equipped with the traditional induction motor
If the frequency characteristic of the auxiliaries is considered, the performance of boiler feedwater pumps is affected by large frequency deviations
Summary
Frequency is one of the most significant variables indicating the security and stability of the power system. 1) an extended single machine frequency response model is constructed to analyze the static power-frequency characteristic to the thermal power unit and long-term frequency stability within an extensive frequency variation range. THE STRUCTURE OF THE EXTENDED FREQUENCY RESPONSE MODEL The conventional single machine frequency response model simulates frequency dynamic behaviors of the power system with small disturbance It considers the speed-governor, the steam turbine, the generator inertia swing equation, and some nonlinear constraints. 3) The extended model does not consider frequency stability control measures and only considers the effects of frequency deviation on the output of boiler auxiliaries in the response process. The auxiliaries sense the frequency change and regulate feedwater and fuel to maintain boiler steam pressure stable. The feedwater flow is the intermediate constraint variable in the extended frequency response model
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