JPS5927199B2 - Control device for control rod drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for a control rod drive device, and particularly to a control device for a control rod drive device suitable for a motor-driven control rod drive device.

The control rods of a nuclear reactor are driven by hydraulic pistons, magnetic jacks, or motors.

However, in cases where the power density of the reactor core is high, such as in fast reactors,
Even in light water reactors, when driving control rods at high output,
It is desirable that the unit of position control be as small as possible, and a method in which the rotational motion of the motor is converted into linear motion by a screw mechanism is preferred. This method of position control is based on numerical control (NC).
It is well known that it has been widely used in fields such as machine tools. However, the position control of the reactor control rods is particularly important for the safe operation of the reactor, and malfunctions cannot be tolerated.

Also, motors with brushes that require frequent maintenance are not suitable because of radiation problems.

By the way, as is generally known, step motors are suitable for such uses because they allow minute control of the rotation angle, do not require maintenance, and have a robust structure. However, a step motor is a type of synchronous motor, and a phenomenon called step-out (out of synchronization) may occur.

That is, if the load torque exceeds the escape torque of the motor, even if it is instantaneous, the synchronous relationship between the magnetic flux generated in the rotor and stator windings is lost, and the torque of the motor becomes almost zero.

Therefore, unless this is detected and protected in some way, the control rod will fall due to its own weight.

In fast reactors and pressurized water reactors, the fall of a control rod during reactor operation causes a sudden drop in reactor power (in some cases, the reactor shuts down), and in boiling water reactors, it causes a sudden drop in reactor power. A sudden increase in output occurs. The purpose of the present invention is to
An object of the present invention is to provide a control device for a control rod drive device that can prevent rapid fluctuations in reactor output due to step-out of a synchronous motor.

A feature of the present invention is that the rotational speed of the synchronous motor that rotates the screw rod and moves up and down the connecting member that engages with the control rod is slower than the speed determined by the frequency of the input pulse that drives the synchronous motor. A step-out detector detects step-out of the synchronous motor and a second step-out of the synchronous motor in which the rotational speed becomes faster than the speed determined by the input pulse frequency; and an electromagnetic brake that stops the synchronous motor and prevents the control rod from falling. and a control means for operating an electromagnetic brake to hold the control rod at the current position when the first step out or the second step out is detected.

The present invention will be explained in detail below using the drawings. FIG. 1 is a diagram schematically showing a control rod drive device used in a boiling water reactor to which the present invention is applied, in which the control rod 6 receives the rotational motion of a step motor 1 and transmits it to a screw 2, and a nut 3 that moves up and down. By moving, it operates together with the connecting rod 4. Note that 5 is a housing that accommodates the control rod drive unit, and 7 is a part of the reactor pressure vessel. Now, when a synchronous motor such as a step motor is used as a motor to drive a control rod having such a structure, the following four cases can be considered as phenomena when the motor steps out.

(1) When the control rod is being driven upward at a low speed, the rotor of the motor reaches zero speed after a minute period of time after step-out, and then reverses due to the weight of the control rod.

(2) When the control rod is being driven upward at high speed, the motor rotates in the positive direction for a period of time until the inertia energy of the rotating system is consumed (however, the speed is lower than the synchronous speed), and then the speed becomes zero. Then the reversal begins. (3) When the control rod is being driven downward at low speed, the rotor will continue to rotate at a speed faster than the synchronous speed after the control rod loses synchronization due to the addition of torque due to its own weight.

(4) When the control rod is being driven downward at high speed, the motor continues to rotate in the same direction after it loses synchronization, but it continues to rotate at a speed that balances the friction and viscous resistance of the rotor system and the torque due to the control rod's own weight. However, it may be faster or slower than the synchronous speed.

Since phenomena like the above four cases occur, for example, it is impossible to accurately determine whether or not synchronization has occurred by simply checking the correlation between changes in position signals and drive commands. It is possible. In other words, if we consider case (3) or (4) as the simplest example, based on the fact that a downward drive command is being output, whether or not the position signal indicates that it is descending. However, since the rotors rotate in the same direction and may be slower or faster than the synchronous speed, it is impossible to detect synchronization by this alone.

In addition, if it is acceptable to take a sufficiently long time to detect step-out, it is possible to consider a method such as letting the control rod fall under its own weight to the stop position and making a determination based on the difference in time required. It is not appropriate to apply it to a position control system due to safety concerns.

The device of the present invention is characterized in that step-out can be reliably detected in any of the four cases described above, and that the device is extremely simple.

FIG. 2 is a diagram showing an embodiment of the apparatus of the present invention, which will be described in detail below. In FIG. 2, reference numeral 20 denotes a step motor drive circuit, which rotates the step motor 1 in a direction corresponding to a forward rotation or reverse rotation command from a terminal 51 or 52 in accordance with a pulse from a rotation pulse input terminal 50.

Since the details of this circuit can be applied to, for example, the circuit described in Japanese Utility Model Publication No. 52-962, detailed explanation will be omitted here. Reference numeral 21 denotes a position detector, which outputs signals having a phase relationship depending on the direction of rotation to lines 54 and 55 when the motor rotates by a certain angle.

In general, there are two types of position detectors: one that outputs a digital signal and one that outputs an analog signal. In the latter case, the analog output may be converted into a digital signal using a well-known circuit.

22 to 25 are AND gates, 26 is an OR gate, and 27 is a counter that receives pulses from the motor drive circuit 50. When the signal at the reset terminal 28 becomes "BI", the counted value is cleared.

29 is a reset flip-flop (hereinafter referred to as R-SF).
), 30 and 31 are JK flip-flops (abbreviated as F), 30 and 31 are JK flip-flops (
(also called JKFF), 32 is Orgate,
Reference numeral 7 denotes an electromagnetic brake, which is directly connected to the rotating shaft of the motor 1 as shown in Fig. 1, and generates a brake torque when the output force of the OR gate 32 reaches 1'' and when the motor power is cut off. .

The operation of the apparatus of the present invention constructed in this way will be explained in detail with reference to FIGS. 3 and 4.

Assume that a forward rotation command signal ``1'' for the motor is now applied to the terminal 51 in Fig. 2, and a pulse as shown in Fig. 3A is applied to the terminal 50, so that the motor 1 is rotating. do.

At this time, the counter 27 counts the rotation pulses, and the terminal 28
If no clear signal is given to n=5, for example
lines 56 and 57 every 4th or 5th pulse.
Outputs signal “1” to

(Fig. 3, opening and c) However, if the motor 1 is now following the pulse normally and has not stepped out, the detector 21 that detects the rotor position of the motor will detect the In order to output a position signal, the n-bit terminal 57 of the counter
No signal is output. In other words, the position detector 21 uses a well-known shaft encoder, and when the rotation direction is positive (reverse), the outputs of the terminals 54 and 55 lead the output signals of the terminals 55 and 54 by about 900 in phase. Outputs the signal that is present.

However, the phase angle does not need to be specified to 900, and it is sufficient if there is simply a difference that allows the direction of rotation to be determined. Therefore, the output of the EOR gate 34 is as shown in FIG.
The output will also look like this. For this reason, the counter 27
, a clear signal is always given while five pulses are input, and at the time T2 position shown by the dotted line in Figure 3 C, no pulse is output, and counting starts again from O. It will become.

However, if the motor loses synchronization and the rotational speed becomes slower than the speed determined by the frequency of the input pulses, the position detector signal will no longer be output at time T3 or T4 in FIG. 3, so the counter 27 will receive five pulses. line 57 when
111 will be output to the flip-flop 29.
The output Q becomes ゛pi.

In other words, the phenomenon of step-out itself, in which the motor does not rotate in response to a given pulse, is detected.

Next, a step-out phenomenon in which the motor rotates faster than the speed determined by the frequency of the input pulse due to an external force will be explained with reference to FIG.

When the motor is not out of step, the output of the n-1 bit of the counter 27 always becomes "1" before the position signal arrives twice, so the flip-flops 30 and 31 are cleared thereby, and the output of the flip-flop 31 is cleared. Qi) Ge1
It will never be 7.

However, when the motor steps out of synchronization and rotates faster than the synchronous speed, the output of the n-1 bit of the counter 27 does not reach "1" from time t1 to T4, as shown by the opening in FIG. The signal 21 is output twice in the time T2 and t3 as shown in C, 2, and this becomes the output of the AND gate 24. This pulse is sent to the JK flip-flop 30.
The output Q of the flip-flop 30 changes to "11" at time T2, and then becomes 11 at time T3.Thus, motor step-out is detected. .

Now, as is clear from the above explanation, the number n of bits of the counter 27 needs to be determined depending on the resolution of the position detector. For example, when five rotation pulses are given as in the embodiment, one position pulse is given. If it is output, it is set as n-5.

If this is set to 5 or more, synchronization may not be detected even if the rotation is slower than the synchronous speed, and if it is set to 5 or less, a synchronization signal will be output even during normal operation.

After detecting synchronization in this manner, the electromagnetic brake 7 is activated to hold the control rod at its current position to ensure safety.

The brake 7 is excited by the same power source (not shown) and is in a released state when the motor is rotating normally or when it is outputting holding torque under DC excitation, but the power source is cut off for some reason. When this occurs, brake torque is automatically generated to prevent the control rod from falling due to its own weight.

As described above, in the embodiment shown in FIG. 2, when the motor loses its torque due to loss of synchronization or the power supply is cut off, the brake is automatically activated to hold the strut rod at its current position. be able to.

In the embodiment shown in FIG. 2, a case has been described in which a JK flip-flop is used to detect step-out when rotating at a synchronous speed or higher, but a counter may also be used.
Furthermore, although the above explanation has been made regarding the case where a step motor is used, it is not limited to this, and it goes without saying that the present invention can also be applied to electric motors such as reluctance motors in which rotation is given by pulse commands. Nor.

According to the present invention, it is possible to detect both a step-out in which the synchronous motor rotates slower than the synchronous speed determined by the input pulse frequency and a step-out in which the synchronous motor rotates faster than its synchronous speed. It is possible to reliably prevent control rods from falling due to step-out.

Therefore, it is possible to avoid sudden fluctuations in the reactor output due to the out-of-step of the synchronous motor, and the safety of the reactor can be significantly improved.

[Brief explanation of drawings]

FIG. 1 is a control rod drive device to which the present invention is applied, FIG. 2 is an embodiment of the present invention, and FIGS. 3 and 4 are explanatory diagrams of the operation of the embodiment shown in FIG. 20...Step motor drive circuit, 21...
...Position detector, 22-25...AND gate, 26...OR gate, 27...Counter, 28...Reset terminal, 29. ...
...Set reset flip-flop, 30-31...
...J-K flip-flop, 32...OR gate, 34...EOR gate, 50...
...Rotation pulse input terminal, 51...Forward rotation command input terminal, 52...Reverse rotation command input terminal, 53.
... Reset input terminal, 54 ... Advance signal output terminal, 55 ... Delay signal output terminal.

Claims (1)

[Claims] 1. A control device for a control rod drive device that includes a synchronous motor, a screw rod connected to the synchronous motor and arranged in the vertical direction, and a connecting member that has a nut member that meshes with the screw rod and engages with the control rod. an electromagnetic brake that stops the synchronous motor and prevents the control rod from falling; and an electromagnetic brake that stops the synchronous motor and prevents the control rod from falling; a step-out detector for detecting a first step-out and a second step-out of the synchronous motor in which the rotational speed becomes faster than a speed determined by the frequency of the input pulse; A control device for a control rod drive device, comprising: control means for operating the electromagnetic brake to hold the control rod at the current position when the control rod is detected.