Control method for improving frequency stability of unit in isolated network system

Abstract

The invention discloses a control method for improving the frequency stability of a unit in an isolated network system. Based on the balance principle of the power supply and the power demand in the isolated network system, the flow of a steam turbine control valve is controlled, the load of the unit is regulated, the unbalance amount between the power supply load and the electrical load in the isolated network system is reduced, and the frequency stability control of the unit in the isolated network system is realized through an organic combination of three means of a frequency PID closed-loop regulating circuit which is controlled by the isolated network, a primary frequency modulation subsection control and the OPC action constant value setup differentiation of the unit. According to the control method for improving the frequency stability of the unit in the isolated network system, the isolated network frequency PID control circuit, the primary frequency modulation and the OPC constant value differential setup are fused, various working conditions are considered; when the frequency deviation is small, the isolated network frequency PID control circuit and the primary frequencymodulation will function at the same time; when the frequency deviation is large, different units will work respectively according to the frequency deviation through the OPC differential setup; the control method is more accurate, and a safe and stable operation of the isolated network system can be conveniently and rapidly maintained.

Description

technical field [0001] The invention relates to a control method for improving the frequency stability of a unit in an isolated grid system, and belongs to the technical field of frequency control of thermal power units. Background technique [0002] In recent years, with the rapid development of my country's economy, the power transmission scale of the interconnected grid has increased, the pace of grid construction has accelerated, and the interconnection between subsystems has become stronger and stronger. However, occasional accidents such as local grid failures, natural disasters, or human error cause the grid tie lines to be separated into isolated grids for operation, and the frequency of the grid fluctuates greatly. If the control strategy is inappropriate, it will cause the instability of the system frequency, and even the power grid collapse in severe cases, resulting in large-scale power outages in the regional network. [0003] Isolated grid operation is a speci...

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Problems solved by technology

[0005] (1) It is proposed that "the DEH load control loop increases the frequency control loop, that is, the professional PID frequency controller is used to adjust the power of the unit during grid-connected operation", but a large number of logical modifications to the DEH are required, and the conditions are basically not met; (2 ) proposed "primary frequency modulation control loop to control the stability of unit frequency", but its primary frequency modulation dead zone is generally set to ±2rpm, which is the boundary condition for the unit to start primary frequency modulation. The main parameters of the unit are unstable, which leads to poor frequency stability of the whole unit; (3) The primary frequency modulation function is generally set according to the 4%-6% speed unequal rate, and the slope is the same within the operating range. In the isolated grid system, the primary The speed adjustment range of frequency modulation is relatively large. When there is a large imbalance between the power supply load and the power consumption load, if the speed difference in the adjustment range is small, the steam turbine adjustment range will be large, and the main parameters of the unit will fluctuate greatly, even endangering the safe operation of the unit. , if the speed variation rate in the adjustment interval is large, the adjustment speed will be slow, and the frequency deviation will last for a long time, which is not conducive to the rapid stability of the frequency of the isolated grid

In addition, the patent CN201110034225 also mentioned the OPC action, the fixed value is 3090rpm, which is a conventional setting, that is, when the steam turbine speed reaches 3090rpm, the steam turbine control valve is closed to reduce the load of the unit and reduce the output power to the grid. However, if there are multiple units in the isolated grid Simultaneous actions are likely to aggravate network frequency oscillation

In addition, the primary frequency modulation control method mentioned in the above two documents, the OPC action and the use of PID frequency controller to adjust the power of the unit can not achieve the purpose of isolated network control well when applied alone

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