SU752617A1 - Method of frequency control for electric power station - Google Patents

Description

(54) METHOD FOR REGULATING FREQUENCY AT POWER PLANTS

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The invention relates to the field of frequency regulation in the power system and can be used in hydroelectric power plants,

There is a method of controlling the frequency at power plants by changing the active power of a station as a function of the current frequency value measured on station tires i - | Q

The disadvantage of this method is that when it is used on hydropower stations with long pipelines, it is necessary to select such settings of stabilizing devices that significantly slow down the process of frequency control in the system.

There is a method of controlling the frequency at a hydroelectric power station, in which the signal of the current frequency deviation of the station from the setpoint is measured, and converted into a control signal for the active station using a device that implements the specified control law 2} .25

This method also has a disadvantage when it is used on hydropower stations with long pipelines, where the hydraulic impact phenomenon is strongly pronounced, as well as at stations where group regulation is frequent.

Pieces are carried out using digital control machines. The phenomenon of water hammer as well as the control resolution discreteness caused by the use of digital control machines causes a delay in the station frequency control loop. This makes it difficult to ensure the stability of the control system and makes it necessary to apply such adjustments to the stabilizing devices of the frequency regulator, which greatly slow down the frequency control process. A slowdown in the process of frequency regulation leads to a delayed input of generating power in case of load surges, which, with small reserves of generating power in the system, may contribute to the occurrence of accidents like avalanche frequency.

The aim of the invention is to improve the reliability of the power system by increasing the frequency control speed.

This goal is achieved by the fact that, when measuring the frequency deviation of a station of a given setpoint and generating a control signal of active power, in each control cycle the mechanical

.moment station, then form the signal estimates of the frequency deviation and the deviation of the active power. An estimate of the frequency deviation is formed by summing the frequency deviations remembered from the previous cycle, the deviations of the active power and measured in the current cycle of the mechanical torque and frequency deviations, and the deviations of the active power are estimated by summing the frequency deviations of the active power and the frequency deviation measured in the current cycle. All terms are taken with coefficients determined by the power system parameters, then the frequency deviation value is predicted by summing the obtained estimates and the mechanical moment of the station, taken with coefficients depending on the pipeline time constant and the control update period. Depending on the received signal, the active power of the station is controlled.

The use of the frequency prediction makes it possible to compensate for the lag in the frequency control loop at the station and thereby increase the stability range of the control system in the plane of the tuning coefficients of the frequency regulator. As a result, it is possible to choose tuning factors that significantly reduce the time required to adjust the frequency. The system frequency is predicted using an automatically tuned model of the power system.

The variables of the model of the power system in which the regulated station operates are described by the following system of equations

. R

a (f-S);

- DS +

 nb lr t

..

: f-s), where S is the power system frequency rating h

. - estimation of the unbalance of the active power of the power system; f is the frequency measured at the station;

Tj. - equivalent constant inertia of the rotors of the power generators; D - self-leveling coefficient

power systems; - constant coefficients.

a,, a. The power system model equations additionally include terms proportional to the mismatch between the measured frequency at the station and the frequency estimate in the power system that adjust the model. This reduces errors that occur when assessing the state of the power system. The power system frequency is predicted based on current estimates of the frequency and unbalance of the active power of the power system. In the proposed method, the equations presented are implemented in finite-difference form.

The drawing shows a functional (concept that implements the proposed method of frequency control at the station

The functional diagram contains a frequency sensor 1, a frequency setting device 2, a device for measuring mechanical torque, a digital computing device (UBVJI 4, and a digital-to-analog converter (D / A) 5).

The outputs of the frequency sensor 1, the setpoint setting device 2 and the mechanical moment measurement device 3 are connected to the corresponding inputs of the DVC 4. The output of the DVR 4 is connected via the DAC 5 to the station's active power control device.

The process of calculating and issuing a new value of the active power control signal is carried out periodically. At each cycle of operation of the device, frequency sensor 1, setpoint setting device 2, and device 3 for measuring the mechanical moment are first polled. The measured signals are fed to the corresponding inputs of DVC 4. At the DVR, the current values of the estimated deviations of the frequency DZ of the unbalance of the active power of the power system are initially calculated. For this purpose, the following expressions are successively calculated: fi fi-fo)

AS, ASi -. - R, 5., -DAS. -d5) . P "& V, cA (ufi - usj where the f-signal from the frequency sensor;

- signal from the setpoint device;

-signal from the device for measuring the mechanical moment;

-index corresponding to the values of the variables at the current time;

i -1

an index corresponding to the values of the variables on the previous cycle of the computing device; A, .O are constant. coefficients ..

The calculated values of d5 are stored in the memory of the digital computing device so that they can be used in the next cycle of the computing device. At initial start-up, the D5 device is assumed to be zero. If, as a result of unaccounted factors or inaccurate setting of the initial values of the DZ, there is a mismatch between the current estimate of the frequency deviation obtained in the DCC and the frequency deviation in the power system, then the indicated mismatch is used to correct the estimates obtained. As a result of this, the evaluation error is reduced to:

Claims (1)

Claim A method of controlling the frequency at a power plant, by measuring the deviation of the station frequency from a given set point and generating an active power control signal, characterized in that, in order to increase the reliability of the power system, the station mechanical moment is additionally measured in each regulation cycle, and then frequency deviation estimation signals are generated and active power deviations, moreover, the frequency deviation estimate is formed by summing the frequency deviation estimates stored from the previous cycle from the lap of the active power and the measured mechanical moment and frequency deviation in the current cycle, and the estimate of the active power deviation is formed by summing the estimates of the frequency deviation, active power deviation and the frequency deviation measured in the current cycle that are memorized from the previous cycle, all terms are taken with coefficients determined by the parameters of the power system , then predict the value of the frequency deviation by summing the obtained estimates and the mechanical moment of the station, taken with coefficients that depend and from the time constant of the pipeline and the period of updating the control action and depending on the received signal, the active power of the station is controlled.