JPH06315300A - Power system stabilizing equipment - Google Patents

Abstract

PURPOSE:To improve the stability of a power system, by deriving the q-axis current of a synchronous machine from its terminal voltage and its output current, and by making the q-axis current a stablized signal. CONSTITUTION:The terminal voltage and output current of a synchronous machine 1 obtained respectively from a voltage transformer 2 and a current transformer 3 are converted by a transducer 41 for a power into the effective power, reactive power and terminal voltage of the synchronous machine 1, and these are inputted to a q-axis current transducer 42. In the q-axis current transducer 42, first, effective and reactive currents are calculated, and then, the q-axis current of the synchronous machine 1 is calculated. In a stabilizing circuit 43, the output signals of the transducer 42 are converted from their stationary values into their deviation signals, and after their delaying, leading, and gain compensations, an automatic voltage regulator 5 is controlled by their stabilized signals. Thereby, the stability of a power system is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power system stabilizer (hereinafter referred to as PSS) added to an automatic voltage regulator (hereinafter referred to as AVR) of a synchronous machine.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional power system stabilizing device. The PSS has the function of improving stability by adding a braking force to the power fluctuations that the synchronous machine connected to the grid has with the grid. It is a device that has come to be applied well. The following three types of PSS control signals (which are called stabilizing signals) are currently in practical use. (1) Rotor speed deviation signal (abbreviated as Δω signal) of synchronous machine (2) Power deviation signal (abbreviated as ΔP) (3) Frequency deviation signal (abbreviated as Δf) Braking force is rotor speed deviation Δω (steady) Change from value)
Since the torque component is proportional to, when the Δω signal is used, the excitation control may be performed so as to generate a torque proportional to this. When the ΔP signal is used, the fact that the equivalence as shown in equation (1) is established between the ΔP signal and the Δω signal is used from the equation of motion of the synchronous machine.

[Equation 1] Δω = (ΔP _m −ΔP) / (MS + D) (1) Δω = rotor speed deviation of the synchronous machine (PU) ΔP _m = change of mechanical input / output (PU) ΔP = electric input / output (Power) Change (PU) M = Unit Inertia Constant (SEC) D = Inherent Braking Torque Coefficient (PU) To be precise, this relationship should be used to control to generate a torque in phase with Δω. , Mechanical input / output ΔP _m
Since it is difficult to detect with a high degree of accuracy, this is considered to be approximately 0 and is controlled only by the power signal.

Generally, the stabilization circuit 10 of the PSS is provided with an incomplete differentiation circuit called a signal reset circuit 11, and a stabilization signal detected by some method usually first passes through this circuit. The transfer function of this circuit is (2)
Shown by the formula,

[Equation 2] Its role is to change the stabilization signal into a signal corresponding to the change from the steady value. The frequency component of power fluctuation (usually 0.5 to 2).
Hz) is passed through well, but the time constant Tsr is appropriately selected so as to exclude slow frequency components below that. The signal passed through the signal reset circuit 11 passes through the phase compensation and gain compensation circuit 12, and finally passes through the limiter circuit 13
It becomes an input signal to VR.

[0004]

In the method using the conventional .DELTA.P signal which is generally widely used, there is no problem when the change of the mechanical input is relatively slow and small compared with the frequency of the power fluctuation, but the change does not occur. When occurs relatively quickly and significantly, the PSS output produces a signal that is not directly related to power swings, which causes the AVR output to swing significantly. As a result, the terminal voltage of the synchronous machine is greatly changed, and excessive reactive power flows in and out, which is not preferable in terms of hardware and stability. An example of such a change in the mechanical torque is seen when the pump is started and when the pump is started.
In order to prevent this by the conventional method, there are only two methods: to reduce the time constant Tsr of the signal reset circuit 11 or to lower the limit value of the limiter circuit 13. However, any of the methods has an influence on the power fluctuation which is originally a problem, and weakens the braking effect.

On the other hand, when the Δω signal is used as the stabilization signal, the rotation speed is constant with almost no deviation from the frequency of the system even if there is a change in the mechanical torque due to load demand. Even if there is a torque change, it does not increase or decrease the voltage of the synchronous machine, but it requires a device for detecting the number of rotations in the synchronous machine body, which complicates the structure of the synchronous machine body and reduces maintainability. was there. Further, the Δf signal uses the frequency of the terminal voltage of the synchronous machine, and shows a movement equivalent to the Δω signal with respect to the change in the rotation speed of the synchronous machine, but does not have an equivalent movement with respect to the change on the load side. Therefore, good results could not be expected. The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a power system stabilizing device that does not greatly fluctuate the AVR output even when the mechanical torque varies with load demand.

[0006]

In order to achieve the above object, a power system stabilizing device of the present invention uses a power transducer for detecting terminal voltage, active power, and reactive power, and a synchronous machine q-axis current from its output. The q-axis current transducer that outputs the signal and a stabilizing circuit that uses the q-axis current of the synchronous machine as a stabilizing signal and performs appropriate phase lead compensation and gain compensation.

With the above structure, the terminal voltage output of the power transducer connected to the output terminal of the synchronous machine, the active power output,
The stability of the power system can be improved by calculating the q-axis current of the synchronous machine by the q-axis current transducer using the reactive power output and using the q-axis current as the stabilization signal. Here, supplementing the physical meanings of the synchronous machine q-axis current and the stabilization signal, the synchronous machine q-axis current i _q in the one machine-to-infinity system is given by equation (3), which is linearly approximated ( Equation (4) is obtained, and equation (5) is obtained when ω is a constant oscillation frequency.

[Equation 3] The Δi _q signal is a signal whose phase is delayed by 90 degrees from the Δω signal, but can be handled in the same manner as Δω by increasing the phase lead compensation. Moreover, the q-axis current transducer, the effective power output of a power transducer, reactive power output, from the synchronous machine terminal voltage output, calculates the effective current i _p and reactive current i _Q, from the q-axis synchronous reactance X _q, (6 ) Is used to output i _q .

[Equation 4] Here, the equation of the above-mentioned synchronous machine q-axis current i _q is obtained from the following equation from the synchronous machine vector diagram of FIG.

[Equation 5] Here, ~: represents a complex number, and ~ * represents a complex complex number. j: complex symbol P _g: active power Q _g: reactive power i _d: synchronous machine d-axis current E _q: q-axis synchronous reactance behind voltage X _q: q-axis synchronous reactance i _p: active current i _q: reactive current e _t : Synchronous machine terminal voltage

[0007]

Embodiments will be described below with reference to the drawings. Figure 1
FIG. 1 is a configuration diagram of an embodiment of a power system stabilizing device according to the present invention. In FIG. 1, 1 is a synchronous machine, 2 is a voltage transformer (PT), 3 is a current transformer (CT), and has a configuration in which an electric quantity is taken into the power system stabilizing device 4 via each of the transformers. is doing. An automatic voltage regulator (AVR) 5 is connected to the gate of the thyristor 6, and the thyristor has a connection structure for exciting the exciting winding 8 through the exciting transformer 7. 41 is a power transducer, 42 is q
The axis current transducer 43 is a stabilizing circuit. Therefore, to explain the overall operation, the synchronous machine terminal voltage and output current obtained from PT2 and CT3 are converted into active power, reactive power and synchronous machine terminal voltage by the power transducer 41, which are q-axis current transducers. 42
Entered in. The q-axis current transducer 42 first calculates the active current and the reactive current by dividing the active power and the reactive power by the synchronous machine terminal voltage using a divider, and then inputs the active power, the active current, the reactive current and the set value. was the q-axis synchronous reactance X _q, divider, multiplier, and calculates the synchronous machine q-axis current i _q indicated by using the square root unit (6). In the stabilization circuit 43, the signal is a deviation signal (Δi
_(q signal), and delay, lead compensation and gain compensation are applied to control AVR5 as an output signal of PSS4. A
The VR 5 controls the thyristor rectifier 6 using the exciting transformer 7 as a power source based on the synchronous machine terminal voltage and the output signal of the PSS 4 to control the current flowing through the exciting winding 8 of the synchronous machine 1.

When power fluctuation occurs for some reason, the q-axis current of the synchronous machine 1 detected by the q-axis transducer 42 is detected as a signal whose phase is 90 degrees delayed from the fluctuation of the rotation speed. The stabilizing circuit 43 adds phase lead compensation to the synchronous machine q-axis current signal in consideration of the control delay of the AVR 5 including the synchronous machine 1 and the phase delay of the synchronous machine q-axis current detection signal with respect to the fluctuation signal of the rotation speed. Furthermore, appropriate gain compensation is added. Then, the increase / decrease control of the field current of the synchronous machine 1 is performed through the AVR 5. As described above, since the q-axis current signal of the synchronous machine is equivalent to the rotation speed signal by adding the phase lead compensation, the power fluctuation can be quickly suppressed by the control similar to the PSS by the Δω signal. According to the above-described embodiment, the Δi _q signal, which is a control signal equivalent to the Δω signal, is obtained without installing the rotation speed detector, only by electrical input by the PT and CT that are normally installed in the power plant. be able to. Further, by using the Δi _q signal as the control signal, it is possible to suppress the power fluctuation of the synchronous machine without unnecessarily increasing or decreasing the AVR output even when the ramp-shaped mechanical torque changes with the demand of the load. You can Although the detection of the q-axis current of the synchronous machine of the present invention can be easily realized by using a digital computer, it can also be realized by using a multiplier, a divider and a square root even in an analog circuit. . The point is that it is realized by detecting the Δi _q signal based on the terminal voltage and output current of the synchronous machine.

[0009]

As described above, according to the present invention, the stabilizing control signal Δi can be obtained only by an electric input signal having good maintainability without adding a rotation speed detecting device to the main body of the synchronous machine. _q signal can be obtained. Further, even when the ramp-shaped mechanical torque changes due to additional demand, the synchronous machine output can be stabilized without increasing or decreasing the terminal voltage of the synchronous machine.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of a power system stabilizing device according to the present invention.

FIG. 2 is a vector diagram for calculating a q-axis current.

FIG. 3 is a diagram showing a conventional stabilizing circuit.

Claims (1)

[Claims] 1. A power system stabilizing device, wherein an output from a stabilizing circuit is input to an automatic voltage adjusting device, and excitation is adjusted to stabilize the synchronous machine. In the power system stabilizing apparatus, the synchronous machine is calculated from the terminal voltage and the output current of the synchronous machine. The q-axis current transducer for deriving the q-axis current and the stabilization circuit for inputting the q-axis current to generate a stabilization signal.