JPS6327936B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reactive power control device that improves the power reception rate at a power receiving end of a private substation or the like.

Generally, when a private substation receives power from the power company's power transmission system, it aims to reduce power charges by improving the power factor at the power receiving point, that is, by bringing the received power factor pf closer to pf = 1.0.

Conventionally, a reactive power control device as shown in FIG. 1 has been proposed and implemented for the purpose of improving the power factor at the power receiving end. That is, Fig. 1 shows a control system in which a synchronous motor SM is connected in parallel with a load L to the secondary side of the power receiving transformer RT, and the field current of this synchronous motor SM is controlled to improve the power receiving ratio. , a received reactive power detector RPD 1 formed by connecting a voltage transformer PT ₁ and a current transformer CT ₁ is provided in the primary power transmission system of the receiving transformer RT, and this received reactive power detector RPD ₁ is provided.
A setting device S is provided to determine the control setting value based on the detected value of RPD ₁ , and on the other hand, the reactive power output of the synchronous machine SM using the excitation control method using the thyristor SCR in the secondary power distribution system of the power receiving transformer RT is detected. A reactive power detector RPD ₂ of the synchronous motor SM is provided by connecting a voltage transformer PT ₂ and a current transformer CT ₂ to
The reactive power output detected by the reactive power detector RPD ₂ and the control setting value set by the setting device S are supplied to the reactive power regulator RPR, and the obtained signal is used to control the excitation current of the synchronous motor SM. The power is supplied to the gate terminal of the thyristor SCR to operate the synchronous motor SM, and the power factor is controlled so that the power factor at the receiving point in the secondary power distribution system of the receiving transformer RT is always close to 1, thereby improving the power factor. It is composed of

However, when a reactive power control device with such a configuration is applied to a system where the load fluctuates rapidly over a short period of time, such as connecting rolling equipment at a steel mill, the setter S operates frequently and the machine of the setter is This not only shortens the life of the reactive power control system, but also causes the control operation to be unable to follow frequent fluctuations in reactive power due to the delayed response of the reactive power control system, resulting in a hunting phenomenon.

SUMMARY OF THE INVENTION An object of the present invention is to provide a received reactive power control device that can achieve stable control without causing any hunting or equipment damage in a system with severe load fluctuations.

In order to achieve the above object, the present invention provides a receiving reactive power control device that maintains a high receiving point power factor by controlling the reactive power of a synchronous machine connected to a power distribution system. a first reactive power detector for detecting reactive power; a second reactive power detector for detecting reactive power of a synchronous machine; an integrating circuit for integrating a detection value of the first reactive power detector; Specify the first and second sample-hold circuits that repeatedly sample and hold the integrated value of the circuit and the detected value of the second reactive power detector at a predetermined cycle, and the timing of the sample operation at a predetermined cycle in both sample-hold circuits. control means for generating a pulse that specifies the timing for resetting the integrating circuit to be performed after the completion of the sampling operation together with a pulse for resetting the sample, an adding means for calculating the sum of the output values of both sample and hold circuits, and setting an output value of the adding means. The present invention is characterized in that it is equipped with a reactive power regulator that performs excitation control of the synchronous machine so that the detected value of the second reactive power detector matches this value.

Next, the received reactive power control device according to the present invention will be described in detail with reference to the accompanying drawings, using a synchronous motor as an example to be controlled.

In FIG. 2, reference numeral 10 indicates a receiving transformer, and a receiving reactive power detector 16 is connected to the primary power transmission system of the receiving transformer 10 via a voltage transformer 12 and a current transformer 14. There is. In addition, a synchronous motor 18 is included in the secondary electrical system of the power receiving transformer 10.
and other loads 20 are connected, and a reactive power detector 26 for the output of the synchronous motor is connected to the output conductor of the synchronous motor 18 via a voltage transformer 22 and a current transformer 24. Further, an excitation coil 30 is connected to the excitation power supply system of the synchronous motor 18 via an excitation current control thyristor 28 .

In the present invention, the received reactive power detector 1
6 and the reactive power detector 26 to improve the power factor at the power receiving point.
is provided to integrate the received reactive power at predetermined time intervals, calculate a control set value while sampling and holding this integrated value, and perform reactive power feedback control of the synchronous motor based on this set value. That is.

That is, as shown in FIG. 3, the set value calculator 32 includes an integrating circuit 34 that inputs the output of the received reactive power detector 16 and integrates it, and an integral circuit 34 that inputs the output of this integrating circuit 34 and integrates the output. a sample-and-hold circuit 36 that stores the output of the reactive power detector 26, a sample-and-hold circuit 40 that inputs the output of the reactive power detector 26 via the filter 38 and stores it, and controls based on the stored contents of both the sample-and-hold circuits 36 and 40. It is comprised of an addition delay circuit 42 that forms a set value, and a logic circuit 44 that instructs the operation of each of the circuits 34, 36, 40, and 42.

Note that the logic circuit 44 includes AND elements AD ₁ and AD ₂
, monostable elements MS ₁ , MS ₂ , and NOR elements NR _{1 to 5}
and time-limiting elements TD _{1 and} TD ₂ , which sample and hold the time t ₁ for integrating the reactive power detected by the received reactive power detector ₁₄ and the integral value. and a time _t2 for calculating a control setting value to be supplied to the reactive power feedback control system from this sampled and held integral value, and furthermore, at each time interval, an AND element,
It is configured to operate a NOR element, a monostable element, etc. to generate a logic pulse, and instruct the operation of the integration circuit 34 and sample-and-hold circuits 36 and 40.
In this way, the control setting value calculated by the addition delay circuit 42 is supplied to the reactive power regulator 46 together with the reactive power detection value of the synchronous motor output to generate a signal that can keep the power factor of the load close to 1 at all times. Furthermore, by supplying this signal to the gate terminal of the thyristor 28 connected to the excitation power supply system of the synchronous motor 18, the excitation current can be adjusted to improve the power factor of the load.

Next, with respect to the control device of the present invention having the above-described configuration, the operation of the set value calculator 32, which is a main part thereof, will be explained below with reference to the time chart shown in FIG.

First, when starting a control operation, the logic circuit 4
A logic signal “1” is supplied to the input terminal p of the fourth
Figure 1]. By inputting this logic signal “1”, AND
The element AD ₁ operates and outputs a logic signal "1" [Fig. 4 2], and this output signal is input to the NOR elements NR ₁ and NR ₄ and the monostable element MS ₁ , respectively.
NR ₂ and AND element AD ₂ each have a logic signal “1”
is output to energize the time limit element TD ₂ for a predetermined time t ₂ and at the same time, the monostable element MS ₁ operates. As a result, the monostable element MS ₁ outputs a logic pulse "1", thereby activating the sample and hold circuits 36 and 40 (FIG. 4, 3). Next, when the monostable element MS ₁ outputs a logic pulse "0", the NOR element NR ₅ outputs a logic signal "1" to operate the monostable element MS ₂ (FIG. 4). As a result, the monostable element MS ₂
The integrating circuit 34 is reset by outputting a logic pulse "1" (FIG. 4, 6).

Then, after a predetermined time t ₂ has elapsed, the NOR element
Due to the output signal "0" of _NR3 , the AND element _AD1 becomes inactive and outputs a logic signal "0" [Fig. 4 2],
This output signal is generated by the NOR element NR ₁ ,
input into NR ₄ and monostable element MS ₁ , respectively,
The NOR elements NR ₁ and NR ₄ each output a logic signal "1" to energize the time limit element TD ₁ for a predetermined time t ₁ and to put the integrating circuit 34 into operation. Note that in this case, the monostable element MS ₁ becomes inactive. In this way, when the integrating circuit 34 is in the operating state for the predetermined time _t1 , the detected value ΔQ of the received reactive power detector 26 [the fourth
FIG. 5] is input to the integrating circuit 34 and integrated [FIG. 4, 6].

When the integration of the integration circuit 34 is performed for a predetermined time _t1 ,
The time-limiting element TD ₂ is activated again for a predetermined time, and during this time the sample and hold circuits 36 and 40 operate, and the sample and hold circuit 36 calculates the integral value 1/t ₁ of the received reactive power detection value ΔQ obtained by the integration circuit 34. ∫ΔQ _dt
The sample and hold circuit 40 samples and holds the reactive power detection value Q of the synchronous motor 18. Next, the integral value 1/t ₁ ∫ΔQ sampled and held in the sample and hold circuits 36 and 40 and the detected value Q are input to the addition delay circuit 42 to obtain the control set value Q+1/t ₁ ∫ΔQ.
is calculated [Fig. 4, 7].

As is clear from the above, even when the received reactive power changes significantly due to severe load fluctuations, it can be periodically integrated and sampled and held at predetermined time intervals, and control is performed based on the sampled and held integrated values. Since the set value is calculated, stable control can be achieved regardless of response delays of the control system. In addition, in the above embodiment, the time-limiting elements TD ₁ , which constitute the logic circuit 44
Regarding the settling times t ₁ and t ₂ of TD ₂ , it is preferable to set the operating time t ₁ of the integrating circuit 34 to be longer than the operating time t ₂ of the sample and hold circuits 36 and 40.

Therefore, the received reactive power control device according to the present invention integrates the detected value ΔQ _o (n represents the period) of the received reactive power at a period with a predetermined time interval t ₁ , t ₂ in the integrating circuit. The integral value (1/t ₁ ∫ΔQ _o ) is determined, and then, in the integral calculation circuit, the control set value Q _o =Q _o-1 +1/t ₁ ∫ΔQ _o is determined based on the integral value and the reactive power output of the synchronous motor. Therefore, in a synchronous motor, while the integral operation based on the detected value of the received reactive power is performed, the excitation control that improves the load power factor based on the control setting value one cycle before affects the load fluctuation. This means that the process will be carried out smoothly without any problems.

Although the preferred embodiments of the present invention have been described above, it goes without saying that various design changes can be made without departing from the spirit of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of a conventional received reactive power control device, FIG. 2 is a system diagram showing the basic configuration of a received reactive power control device according to the present invention, and FIG. 3 is a block diagram showing the main configuration of the device of the present invention. The wiring diagram, Figures 4 1 to 7, shows the operation of each component of the circuit shown in Figure 3.
is the received reactive power control command signal, and 2 is the logic circuit's control command signal.
The output of AND element AD ₁ , 3 is the output of monostable element MS ₁ of the logic circuit, 4 is the output of monostable element MS ₂ of the logic circuit, 5 is the detected value of the received reactive power detector 26, 6
is the output of the integration circuit 34 and 7 is the output of the integration calculation circuit 4
FIG. 2 is a waveform diagram of each output of FIG. 10...Power receiving transformer, 12...Voltage transformer, 1
4...Current transformer, 16...Receiving reactive power detector, 18...Synchronous motor, 20...Load, 22...
...Voltage organizer, 24...Current transformer, 26......
Reactive power detector, 28...thyristor, 30...
Excitation coil, 32...Set value calculator, 34...Integrator circuit, 36...Sample hold circuit, 38...
...Filter, 40...Sample hold circuit, 4
2... Addition delay circuit, 44... Logic circuit, 46...
…Reactive power regulator.

Claims (1)

[Scope of Claims] 1. In a receiving reactive power control device that maintains a high power factor at a receiving point by controlling the reactive power of a synchronous machine connected to a power distribution system, there is provided a first step for detecting reactive power at a receiving point. a first reactive power detector, a second reactive power detector that detects the reactive power of the synchronous machine, an integrating circuit that integrates the detected value of the first reactive power detector, and a second reactive power detector that detects the reactive power of the synchronous machine; The sample operation is completed with the first and second sample hold circuits that repeatedly sample and hold the detected values of the two reactive power detectors at a predetermined cycle, and a pulse that specifies the timing of the sample operation at a predetermined cycle in both sample hold circuits. A control means for generating a pulse that specifies the timing of resetting the integrating circuit to be performed later; an addition means for calculating the sum of the output values of both sample and hold circuits; A receiving reactive power control device comprising: a reactive power regulator that performs excitation control of a synchronous machine so that the detection values of the reactive power detectors match.