JPH06335295A - Method and apparatus for controlling variable-speed generator-motor - Google Patents

Abstract

PURPOSE:To prevent the influence of a system failure on a system protective system by estimating the phase of the secondary current of a generator-motor at the time of the opening of a breaker due to the system failure, based on the phase of the secondary current and a slip of the generatormotor at the time of the detection of the system failure. CONSTITUTION:If a failure of three-phase short circuit occurs in a system 8, a system failure detector 10 detects the system failure through the overvoltage of the secondary wiring circuit of a generator-motor 1, and outputs a detection signal to a control 't 4. The control device 4 outputs the slip value and the phase of secondary current of the generator-motor 1 to a phase operation unit 11 through a slip signal 4s and a phase signal 4p, respectively. The phase operation unit 11 carries out an operation to obtain the phase of the secondary current of the generator-motor 1 when a predetermined operation time of a breaker 7 passes, and outputs the result of the operation to an excitation selector 12. The excitation selector 12 compares the phase angle of the output phase signal 11p with 12 angles, and outputs direct current excitation corresponding to the closest angle to a switch 6. This enables continuous operation regardless of any system failure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method and device for a variable speed generator / motor system, and in particular, to excite the secondary winding of the generator / motor with direct current in the AC operation when a failure occurs in the system. The system protection system by shortening the recovery delay of the system voltage after opening the circuit breaker caused by the phase shift of the primary current of the generator motor due to The present invention relates to a variable speed generator / motor control method and device for preventing the influence on the variable speed generator / motor.

[0002]

2. Description of the Related Art Conventionally, for example, a variable speed pumped storage power generation system has been used as one of the variable speed generator / motor systems. FIG. 3 is a schematic diagram showing a configuration example of this type of variable speed pumped storage power generation system.

In FIG. 3, the variable speed pumped storage hydropower system supplies a variable AC exciting current to a generator motor 1 in which a rotor is provided with a three-phase winding so as to excite an AC, and a rotor coil of the generator motor 1 is supplied. Which controls the electric power converter 2 that drives the generator motor 1 during power generation, and the turbine / pump 3 that is a rotating machine that is driven by the generator motor 1 during pumping, the guide vanes of the turbine / pump 3, and the power converter 2. Controller 4
It consists of Further, as a device for responding to a system failure, the DC power source 5 is connected via a switch 6 which is an opening / closing means.
It is connected to the secondary winding (rotor winding) of the generator motor 1. Here, as the switch 6, for example, a thyristor,
A switching element such as GTO is used.

In such a variable speed pumped storage power generation system configuration, the primary winding (stator winding) of the generator motor 1 is connected to the system 8 via the breaker 7. The power converter 2 has its input side connected to the grid 8 via a transformer 9 and its output side connected to the secondary winding of the generator motor 1. Then, the power converter 2 is controlled by the control device 4 to convert the commercial frequency power to the variable frequency power and output the variable frequency power to the secondary winding of the generator motor 1, or conversely, the variable frequency power to the commercial frequency. The electric power is converted into the electric power and output to the grid 8 for bidirectional electric power conversion.

Further, the control device 4 takes in the rotational phase of the rotor of the generator motor 1 and the frequency of the system 8 by means of a detector, so that the magnetic field of the rotor is synchronized with the primary side system frequency. Output current, that is, the phase of the secondary current of the generator motor 1 is controlled. Then, an AC exciting current having a frequency corresponding to the slip between the system frequency and the rotor is passed through the secondary winding of the generator motor 1 to match the phases, thereby enabling the synchronous operation.

As described above, in the variable speed pumped storage power generation system, the speed of the rotor can be operated without being restricted by the synchronous speed, so that highly efficient operation can be performed and the input power during pumping can be adjusted. The feature is that it can greatly contribute to the adjustment of nighttime power.

In the variable speed pumped storage hydropower system, when a fault such as a three-phase ground fault or a three-phase short-circuit fault occurs near the system 8 to which the generator motor 1 is connected, a transient at the time of the fault occurs. Due to the current, an overvoltage is generated in the secondary winding of the generator motor 1, an unillustrated overvoltage protection device operates, and the system voltage drops. Therefore, the power converter 2 is temporarily stopped. And this power converter 2
Is stopped, the supply of the exciting current to the secondary winding of the generator motor 1 is stopped, so that the AC component of the transient current flowing in the primary side of the generator motor 1 becomes small, and the transient current becomes only the DC component. There is a possibility that the zero point will not be cut off, and the breaker 7 that cuts off the fault current may cause DC cutoff.

Therefore, in order to prevent such a phenomenon, when the power converter 2 is stopped, the secondary winding of the generator motor 1 is switched by another means using the DC power source 5 through the switch 6. Is excited by direct current to secure the alternating current component of the transient current. In the secondary winding of the generator motor 1 having the three-phase winding, how to connect the p, n of the DC power supply to the u, v, w terminals depends on the AC just before the failure. The DC power supply 5 is connected so that it is close to the phase when it is excited.

However, if the secondary winding of the generator motor 1 is DC-excited at the time of the above failure, the following problems will occur. That is, when the power converter 2 is stopped at the time of system failure, the
By applying a direct current to the next winding, the generator motor 1
The transient current on the secondary side can be converted into alternating current, but since the rotor of the generator motor 1 rotates with a certain slip,
As time passes, the AC component phase of this transient current and the phase of the system 8 do not always match, and they shift.

When the failure point occurs on one of the two lines, the voltage must be restored as soon as the circuit breaker of the failure line is opened. The phase shift becomes large depending on the timing, and the output of the generator motor 1 acts in the direction of suppressing the system voltage, so that the voltage recovery after opening the breaker 7 may be slow. Especially, the larger the slip, the more remarkable this phenomenon appears.

Normally, the AC operation at the time of failure is operated when the power converter 2 is stopped after the occurrence of the system failure, and the failure point is removed by the circuit breaker 7, and the operation is stopped when the system voltage is restored. After the control is stopped and the AC operation is stopped, the power converter 2 is restarted to return to the normal operation.

However, as described above, if the phase shift at the time when the circuit breaker 7 is opened is large, the recovery of the system voltage after the circuit breaker 7 is opened is delayed, so that the stop of AC operation is delayed, and thus the failure point is Even though it has been removed, a large current will flow unnecessarily from the generator motor 1. This may cause the system protection system (system protection relay) near the generator motor 1 to malfunction.

[0013]

As described above, in the control of the conventional variable speed generator-motor system, when a failure such as a three-phase ground fault or a three-phase short circuit occurs in the system, the power converter is stopped. In the AC operation, which is a means for avoiding DC interruption that may occur with the occurrence of DC power, a phase shift from the system of the primary current of the generator motor occurs due to the DC excitation of the secondary winding of the generator motor. Therefore, there is a problem that the recovery of the system voltage after opening the breaker is delayed and the AC operation after opening the breaker affects the system protection system.

An object of the present invention is to eliminate the phase shift between the primary current of the generator motor and the system due to the direct current excitation of the secondary winding of the generator motor in the AC operation when a failure occurs in the system. Highly reliable, which can shorten the recovery delay of the system voltage after the breaker is opened to quickly stop AC conversion and prevent the influence on the system protection system by the AC operation after the breaker is opened. A variable speed generator motor control method and apparatus are provided.

[0015]

In order to achieve the above object, first, in the invention described in claim 1, an AC excitation type generator-motor in which a primary winding is connected to a system through a circuit breaker. And a variable speed constituted by a power converter having an input side connected to the grid and an output side connected to the secondary winding of the generator motor, for exciting the generator motor with variable alternating current, and a rotating machine connected to the generator motor. In the control method of the generator motor system, when a system failure occurs, the phase of the secondary current of the generator motor and the slip of the generator motor at the time when the system failure is detected are determined when the breaker is opened due to the system failure. The predictive calculation of the phase of the secondary current of the generator motor is performed, and the secondary winding of the generator motor is DC-excited so as to be closest to the phase.

According to the second aspect of the present invention, an AC excitation type generator / motor in which the primary winding is connected to the system via a circuit breaker, and an input side in the system and an output side in the generator / motor are connected. A failure detecting a system failure in a controller of a variable speed generator-motor system, which is composed of a power converter that is connected to a secondary winding and that excites the generator motor with variable AC, and a rotating machine that is connected to the generator motor. Detection means,
From the secondary current phase of the generator motor and the slip of the generator motor at the time when the failure is detected by the failure detecting means, the power generation at the time of opening the breaker due to the system failure based on the preset operation time of the breaker. Phase calculation means for predicting and calculating the phase of the secondary current of the electric motor, DC power supply for exciting the secondary winding of the generator motor by direct current, and power generation by the DC power supply so as to be closest to the phase calculated by the phase calculation means. And an excitation control means for controlling DC excitation of the secondary winding of the electric motor.

Here, in particular, as the excitation control means,
Excitation phase selecting means for selecting the direction of the direct current flowing through each coil of the secondary winding of the generator motor so as to be closest to the phase calculated by the phase calculating means, and the DC power supply and the secondary winding of the generator motor. And an opening / closing means for controlling DC excitation of the secondary winding of the generator motor by turning on / off by a selection signal from the excitation phase selecting means.

[0018]

Therefore, in the variable speed generator motor control method and apparatus of the present invention, when a fault such as a three-phase ground fault or a three-phase short circuit occurs in the system, the fault detecting means detects the fault in the system. Then, the slip value of the rotor of the generator motor and the phase angle of the secondary current at this time are taken into the phase calculating means, and the phase calculating means uses the slip value and the phase angle to preset the operating time of the breaker. Based on, the phase of the secondary current of the generator motor during the opening operation of the breaker is predicted and calculated.

On the other hand, when the exciting coil of the three-phase winding, which is the secondary winding of the generator motor, is DC-excited, 12 phases can be obtained every 30 degrees depending on how the current is passed.
Then, the excitation control means performs DC excitation of the secondary winding of the generator motor so that the phase calculated by the phase calculation means is the phase closest to this phase angle.

As a result, the phase shift between the system voltage when the circuit breaker is opened and the primary current of the generator motor can be suppressed to a small level, and the system voltage can be recovered faster after the circuit breaker is opened.
The alternating current operation will be stopped immediately.

[0021]

First, the concept of the present invention will be described. As described above, in the variable speed generator motor system using the AC excitation type generator motor, when a system failure occurs,
The power converter that performs AC excitation cannot operate normally.
For this reason, the power converter may be suspended,
At this time, the AC component of the transient current flowing through the primary side of the generator motor may be lost, and the breaker may perform DC interruption. Therefore, as a countermeasure against this, an AC component is generated on the primary side of the generator motor by temporarily exciting the secondary winding of the generator motor with DC.

In the present invention, in such an AC operation, by optimizing the DC excitation method of the secondary winding of the generator motor with respect to the phase, the AC operation is performed when the breaker is opened due to a system failure. By suppressing the effect of phase shift due to operation,
The influence on the system protection system is avoided, and the smooth continuous operation of the variable speed generator-motor system after the occurrence of the system failure is enabled.

An embodiment of the present invention based on the above concept will be described below in detail with reference to the drawings.
FIG. 1 is a schematic diagram showing a configuration example of a variable speed pumped storage hydropower system to which the present invention is applied. The same parts as those in FIG. 3 are denoted by the same reference numerals and the description thereof will be omitted, and only different parts will be described here. .

That is, in the variable speed pumped storage hydropower system of this embodiment, as shown in FIG. 1, a system fault detector 10, a phase calculator 11, and an excitation phase selector 12 are added to the system of FIG. It is configured. This excitation phase selector 1
2 and the switch 6 constitute an excitation control means.

Here, the system failure detector 10 detects a failure such as a three-phase ground fault or a three-phase short circuit of the system 8 due to an overvoltage in the secondary winding circuit of the generator motor 1. .

Further, the phase calculator 11 detects the phase signal 4p of the secondary current of the generator motor 1 from the controller 4 and the generator motor 1 at the time when the system failure detector 10 detects the failure.
The slip signal 4s is input to the circuit breaker 7 due to a system failure based on the preset operation time of the circuit breaker 7.
The phase of the secondary current of the generator motor 1 at the time of opening the is predicted and calculated, and the phase signal 11p is output.

Further, the excitation phase selector 12 receives the phase signal 11p from the phase calculator 11 and controls the direct current flowing through each coil of the secondary winding of the generator motor 1 so as to be closest to this phase. The direction is selected and the selection signal 12c is output to the switch 6 as its on / off control signal.

Next, the operation of the variable speed pumped storage hydropower system of the present embodiment configured as described above will be described. In FIG. 1, when a failure such as a three-phase ground fault or a three-phase short-circuit occurs in the system 8 now, the system failure detector 10 detects that the
A system fault is detected by the overvoltage of the secondary winding circuit, and a detection signal is output to the control device 4. Then, the control device 4 outputs the slip value and the phase of the secondary current of the generator motor 1 at the time when the detection signal is received to the phase calculator 11 as a slip signal 4s and a phase signal 4p, respectively. As a result, in the phase calculator 11, the phase of the secondary current of the generator motor 1 at the time when the preset operation time of the circuit breaker 7 has elapsed according to the slip value of the slip signal 4s and the phase of the phase signal 4p. The calculated value is output to the excitation selector 12 as the phase signal 11p.

On the other hand, the phase angle of the magnetic field obtained when a direct current is applied to the secondary winding, that is, the three-phase winding provided on the rotor of the generator motor 1 depends on how the DC power source 5 is connected. The phase angle can be obtained and the angle is 0
The angle is 30 degrees, 30 degrees, 60 degrees, ... 330 degrees, and the angle is every 30 degrees.

In the excitation phase selector 12, the phase angle of the phase signal 11p obtained from the phase calculator 11 is compared with these 12 kinds of angles, and the closest angle is selected. Then, the selection signal 12c is output to the switch 6 so as to establish the DC excitation connection corresponding to this angle.

The switch 6 is a switch for connecting the secondary winding of the generator motor 1 and the DC power supply 5, and is a switch for the generator motor 1.
A switch Pu and a switch Nu (not shown) are connected to the U phase of the next winding, one of the switches Pu is connected to the plus of the DC power supply 5, and one of the switches Nu is connected to the minus of the DC power supply 5. That is, either the switch Pu or the switch Nu is selected and turned on depending on the direction of the direct current flowing in the U phase. The same applies to the V phase and the W phase, and there are a total of 6 switches.

Therefore, when the secondary winding of the generator motor 1 is DC-excited, three or two of the six switches are used.
Turn on the pieces. That is, the ON / OFF of the switch is controlled by the selection signal 12c from the excitation phase selector 12, the secondary winding of the generator motor 1 is DC-excited, and the phase angle of the phase signal 11p obtained by the phase calculator 11 is determined. A phase angle close to is obtained by DC excitation.

FIG. 2 is a diagram showing the concept of phase angle prediction when the circuit breaker is open.
The waveform of the next current is shown. In FIG. 2, the vertical axis represents the intensity of current and the horizontal axis represents time and phase angle. Further, T ₁ is a system failure occurrence time, T ₂ is an opening time of the breaker 7, θ ₁ and θ ₂ are phase angles of the secondary current of the generator motor 1 at respective times, and T _CBO is an operation of the breaker 7. It's time.

The frequency f _{I2 of the} current waveform is the product of the system frequency f _K and the slip S, and the phase is the generator motor 1
Are controlled by the control device 4 so that the phase difference angle is determined by the active power and the reactive power required for the above. The part indicated by the dotted line in the waveform is the locus of the secondary current of the generator motor 1 to be followed when no system failure has occurred. Therefore, if the relationship between the phase angle and time obtained from this waveform is satisfied when the circuit breaker 7 is opened, the phase shift with the system 8 does not occur.

That is, the phase calculator 11 obtains the phase θ ₂ when the breaker 7 is opened by performing the following calculation. When the angular velocity of the secondary current of the generator motor 1 is ω, θ ₁ = ωT ₁ + θi (θi is an initial phase angle) θ ₂ = ω (T ₁ + T _CBO ) + θi = θ ₁ + ωT _CBO ω = 2πSf _K , Θ ₂ = θ ₁ + 2πSf _K T _CBO Therefore, if the operating time T _CBO of the circuit breaker 7 is determined in advance, the phase angle θ _{1 of the} secondary current of the generator motor 1 and the slip of the generator motor 1 at the time of failure occur. From S, the phase angle θ _{2 of the} secondary current of the generator motor 1 is obtained. Note that f _K
Is set to 50 HZ or 60 HZ (system frequency variation is small and can be ignored).

Here, the operating time T _CBO of the circuit breaker 7 is
An estimated time as described above, the actual operating time of the breaker 7 to be used depend upon configuration of the size and system protective system fault point and fault current, somewhat against the operating time of the breaker 7 T _CBO Although there is a difference of, it can be ignored in practice. Further, the slip S of the generator motor 1 is assumed not to change in a short time after the breaker 7 is opened after the occurrence of a failure.

As described above, in the present embodiment, the AC excitation type generator-motor 1 whose primary winding is connected to the system 8 via the circuit breaker 7 and the input side to the system 8 via the transformer 9. A power converter 2 that is connected and has its output side connected to the secondary winding of the generator motor 1 to excite the generator motor 1 with a variable alternating current.
In the controller of the variable speed pumped storage power generation system including the controller 4 and the water turbine / pump 4 which is a rotating machine connected to the generator motor 1, a failure such as a three-phase ground fault or a three-phase short circuit of the system 8 occurs. And a phase signal 4p of the secondary current of the generator motor 1 from the control device 4 and a slip signal 4s of the generator motor 1 at the time when the failure is detected by the system failure detector 10. A phase calculator for inputting and predicting the phase of the secondary current of the generator motor 1 at the time of opening the breaker 7 due to a system failure based on the preset operation time of the breaker 7 and outputting a phase signal 11p 11, a DC power source 5 for DC-exciting the secondary winding of the generator motor 1, and a phase signal 11p from the phase calculator 11 to input the 2 of the generator motor 1 so as to be closest to this phase.
The direction of the direct current flowing through each coil of the secondary winding is selected, and the selection signal 12c is selected and the secondary winding of the generator motor 1 and the direct current power source 5 are selected.
And an excitation phase selector 12 which outputs an ON / OFF control signal to a switch 6 for connecting
When the system failure occurs, the phase of the secondary current of the generator motor 1 at the time of detecting the system failure and the slip of the generator motor 1 are used to determine the 2 of the generator motor 1 at the time of opening the breaker 7 due to the system failure. The phase of the next current is predicted and calculated, and the secondary winding of the generator motor 1 is DC-excited so as to be closest to this phase.

Therefore, in the alternating operation as described above performed when a failure occurs in the system 8, the secondary winding (three-phase winding of the rotor) of the generator motor 1 is brought close to the secondary current phase when a failure occurs. Since a phase is selected so as to be close to the voltage phase of the system 8 when the circuit breaker 7 is opened, and the direct current is excited, the alternating current that the generator motor 1 supplies is the voltage of the system 8 and its phase difference. Becomes smaller, and the voltage recovery is not suppressed by the alternating current, so that the system voltage can be quickly raised.

Since the system voltage is quickly recovered, the control device 4 immediately stops the alternating current operation, so that no unnecessary current flows and the system protection system is not affected. Further, the generator motor 1 can be quickly returned to the normal operation, and if the system sway after the system failure has occurred after the recovery, it can contribute to the stabilization immediately.

As a result, it becomes possible to smoothly continue the operation of the variable speed pumped storage hydropower system after a system failure occurs. The present invention is not limited to the above embodiment, but can be implemented in the same manner as described below.

(A) In the above embodiment, the case where the DC power source 5 is used for DC exciting the secondary winding of the generator motor 1 for the AC operation is described, but the present invention is not limited to this, and for example, the DC power source. Instead of 5, it is also possible to use a charged capacitor (for example, a smoothing capacitor provided between the inverter and the converter configuring the power converter 2) or a storage battery.

(B) In the above embodiment, the system fault detector 1
0 has described the case of detecting a failure such as a three-phase ground fault or a three-phase short circuit of the system 8 due to an overvoltage in the secondary winding circuit of the generator motor 1, but the present invention is not limited to this. As a method of detecting the failure of, for example, the voltage of the grid 8
There are a method of detecting a change in the current and a method of receiving an operation signal from a protection relay arranged in the system 8.

(C) In the above embodiment, the case where the present invention is applied to the variable speed pumped storage power generation system has been described, but the present invention is not limited to this, and the present invention is applicable to a variable speed phase shifter system, a variable speed flywheel power generation system, and a variable speed flywheel power generation system. The present invention can be similarly applied to all other variable speed generator-motor systems such as a shift frequency power conversion system.

[0044]

As described above, according to the present invention, when a system failure occurs, the system is determined from the phase of the secondary current of the generator motor and the slip of the generator motor at the time when the system failure is detected. The phase of the secondary current of the generator / motor at the time of opening the breaker due to a failure is predicted and calculated, and the secondary winding of the generator / motor is DC-excited so that the phase is closest to the phase. In the AC operation when the power generation occurs, the recovery delay of the system voltage after opening the breaker caused by the phase shift between the primary current of the generator motor and the system due to the DC excitation of the secondary winding of the generator motor is shortened. Thus, it is possible to provide an extremely reliable variable-speed generator-motor control method and device capable of quickly stopping the alternating current and preventing the influence on the system protection system due to the alternating current operation after the breaker is opened.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an embodiment of a variable speed pumped storage power generation system to which the present invention is applied.

FIG. 2 is a view showing the concept of phase angle prediction when the breaker is opened in the same embodiment.

FIG. 3 is a schematic diagram showing a configuration example of a conventional variable speed pumped storage hydropower system.

[Explanation of symbols]

1 ... Generator motor, 2 ... Power converter, 3 ... Water turbine / pump,
4 ... Control device, 5 ... DC power supply, 6 ... Switch, 7 ... Breaker, 8 ... System, 9 ... Transformer, 10 ... System failure detector,
11 ... Phase calculator, 12 ... Excitation phase selector.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuyuki Abe 1-3-1, Uchiyuki-cho, Chiyoda-ku, Tokyo Within Tokyo Electric Power Company (72) Ryoji Sugawara 6-15-1, Ginza, Chuo-ku, Tokyo Power supply development Co., Ltd. (72) Inventor Takayoshi Sano 6-15-1, Ginza, Chuo-ku, Tokyo Power supply development Co., Ltd. (72) Inventor Kazuo Hachiya 6-15-1, Ginza, Chuo-ku, Tokyo Power supply opening (72) Inventor Hideyuki Nakano 1 Toshiba Town, Fuchu City, Tokyo Fuchu Factory Ltd. (72) Inventor Kenji Kudo 1-1-1, Shibaura, Minato-ku, Tokyo Toshiba Head Office Co., Ltd.

Claims (3)

[Claims] 1. An alternating current excitation type generator motor whose primary winding is connected to a system via a circuit breaker; an input side is connected to the system and an output side is connected to a secondary winding of the generator motor. In a method for controlling a variable-speed generator-motor system that includes a power converter that excites the generator-motor with variable AC excitation, and a rotating machine that is connected to the generator-motor, when a failure of the system occurs, the system From the phase of the secondary current of the generator motor at the time of detecting a failure and the slip of the generator motor, the phase of the secondary current of the generator motor at the time of opening the breaker due to the system failure is predicted and calculated. A method of controlling a variable speed generator-motor, characterized in that the secondary winding of the generator-motor is DC-excited so as to be closest to the phase. 2. An alternating current excitation type generator motor whose primary winding is connected to a system via a circuit breaker; an input side is connected to the system and an output side is connected to a secondary winding of the generator motor. A power converter that excites the generator motor with variable alternating current, and a controller of a variable speed generator motor system that includes a rotating machine that is coupled to the generator motor, and a failure detection unit that detects a failure of the system, From the phase of the secondary current of the generator motor and the slip of the generator motor at the time when the failure is detected by the failure detection means, the breaker due to the system failure is set based on a preset operation time of the breaker. , A phase calculation means for predicting and calculating the phase of the secondary current of the generator motor at the time of opening, a DC power supply for exciting the secondary winding of the generator motor by DC, and the phase calculation means. A variable speed generator-motor control device comprising: excitation control means for controlling the DC excitation of the secondary winding of the generator motor by the DC power source so that the phase becomes closest to the calculated phase. . 3. The excitation control means selects the direction of a direct current flowing through each coil of the secondary winding of the generator motor so as to be closest to the phase calculated by the phase calculation means. Direct current excitation of the secondary winding of the generator motor is provided between the selector and the DC power supply and the secondary winding of the generator motor, and is turned on / off by a selection signal from the excitation phase selector. 3. The variable speed generator-motor control device according to claim 2, further comprising an opening / closing means for controlling the.