JPS6137868B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for a synchronous motor equipped with a frequency conversion device, and in particular, to stably switch the power supply and switch from the field voltage regulator to the automatic voltage regulator while accelerating the synchronous motor. The present invention relates to a control device for a synchronous motor suitable for controlling a synchronous motor.

Generally, as a method for starting a synchronous motor, a starting method using a static frequency converter is conventionally known.

This starting method divides the speed control range of the synchronous motor at startup into an intermittent current start control range, constant current acceleration control range, and constant speed control range, and sequentially controls the synchronous motor in each control range as follows. This is what we do.

That is, first, in the current intermittent startup control region, a current is passed intermittently during initial startup to start the synchronous motor. Next, in the constant current acceleration control region, the armature current of the synchronous motor is caused to flow continuously to accelerate the synchronous motor. In the constant speed control region, when the rotational speed of the synchronous motor approaches the synchronous speed, the frequency difference, voltage difference, and phase difference between the AC power supply and the AC side terminal voltage of the synchronous motor are controlled within a certain tolerance range, and the motor stops. This is to perform synchronous parallel connection from the frequency converter to the AC power source.

A control device using a static frequency converter that performs such control is herein collectively referred to as a synchronous motor control device.

By the way, the acceleration torque of a synchronous motor is the difference between the torque generated by the armature current and the field magnetic flux caused by the excitation current flowing through the field winding, and the reaction torque at the rotation speed, and is the difference between the torque generated by the armature current and the field magnetic flux due to the excitation current flowing through the field winding, and the reaction torque at the rotation speed. It is well known that in order to do this, it is necessary to apply a field current to the synchronous motor, and that changing the field current changes the acceleration torque.

Furthermore, due to the starting characteristics of a synchronous motor that is started by a static frequency converter and the limitations of the functions of the static frequency converter, it is generally started in a constant excitation state using a field voltage regulator during initial startup. It is.

However, in continuous operation after the synchronous motor is connected to an AC power source, an automatic voltage regulator must be used to keep the voltage of the synchronous motor constant despite load fluctuations and system fluctuations. For this purpose, it is necessary to switch the field circuit from being excited by the field voltage regulator to being excited by the automatic voltage regulator during the acceleration period by the static frequency converter of the synchronous motor.

Furthermore, at the beginning of startup, the synchronous motor voltage is low and its terminal voltage cannot be used as an excitation power source.
Using an AC power source such as an in-house power source as an excitation power source,
After parallel connection, it is necessary to switch the power supply so that the excitation power is taken from the terminal of the synchronous motor. Furthermore, if the power supply is switched after the synchronous motor is connected in parallel, fluctuations of the AC power supply will occur, which is not desirable, so it is necessary to switch the power supply during the acceleration period by the static frequency converter.

However, when constant current acceleration control is performed using a static frequency converter with constant excitation, the terminal voltage of the synchronous motor becomes a voltage proportional to the rotation speed of the synchronous motor. Therefore, when switching from constant excitation by the field voltage regulator to the automatic voltage regulator in the constant current acceleration control region, there is a deviation between the set value of the automatic voltage regulator and the synchronous motor terminal voltage, so the field This causes the terminal voltage of the synchronous motor to vary, resulting in transient fluctuations in the armature current. Furthermore, a similar phenomenon occurs when the power source is switched, and the armature current of the synchronous motor fluctuates greatly.

For this reason, in conventional synchronous motor control devices, the variation in the armature current exceeds the output current tolerance of the static frequency converter, and as a result, the overcurrent protection circuit of the static frequency converter is activated. There was a problem that led to a system trip.

The present invention eliminates the above-mentioned problems, and even if the power supply is switched and the field voltage regulator is switched from the field voltage regulator to the automatic voltage regulator while the synchronous motor is being accelerated by the static frequency converter, the transient of the static frequency converter It is an object of the present invention to provide a control device for a synchronous motor that can perform stable control by suppressing the maximum value of output current.

In order to achieve this objective, the present invention temporarily limits the output current of the static frequency converter in the constant speed control region, and during that time, switches the excitation power supply and switches from the field voltage regulator to the automatic voltage regulator. It is characterized in that it performs the following.

Hereinafter, the present invention will be explained with reference to embodiments of the drawings.

FIG. 1 is a block diagram of a control device for a synchronous motor showing an embodiment of the present invention, and 1 is a synchronous motor.

This synchronous motor 1 is equipped with a position detector (not shown) that detects the relative electrical position of the stator and rotor, and a rotational speed detection device (not shown) that detects the rotational speed.

The armature of the synchronous motor 1 is connected to an AC power supply bus 3 via a breaker 2 . Furthermore, a blade breaker 4, a static frequency converter 5, and a blade breaker 6 are connected in series between the armature of the synchronous motor 1 and the AC power supply bus 3. As the frequency conversion device, for example, a forward converter having bridge-connected thyristors and an inverse converter having bridge-connected thyristors connected in series is used.

Signals from the position detector and rotation speed detection device of the synchronous motor 1 are applied to a control signal converter 7. The control signal converter 7 converts a signal from the position detector and a signal corresponding to the rotational speed from the rotational speed detection device into control signals.

The control signal from this control signal converter 7 is applied to a speed control device 8. This speed control device 8 is
A thyristor gate control signal is given to the static frequency converter 5 to control the armature current flowing through the armature of the synchronous motor 1. Also,
The driving power for this speed control device 8 is obtained from the AC power supply bus 3 through a disconnector 6 .

The field circuit of the synchronous motor 1 includes a special commutation circuit 20 and a special commutation pulse generator 21, and the field winding 9 includes a field shunter, a disconnector 10, and a DC converter 11.
It is connected to an alternating current power source 12 such as an in-house power source through a shield disconnector 17 in series, and is further connected to a terminal of the synchronous motor 1 through a shield disconnector 18 and an excitation power transformer 19 in series. .

The DC converter 11 is, for example, a bridge-connected thyristor, and controls the DC current flowing through the field winding 9 by controlling its gate. The field voltage applied to the field winding 9 is also applied to the field voltage adjustment device 13. This field voltage adjustment device 13 receives the set output and field voltage of the constant excitation setting device 14, and controls the field voltage when the control mode of the synchronous motor 1 is in the current intermittent start control region and the constant current acceleration control region. The DC converter 11 is controlled so that the voltage on the line 9 is constant.

On the other hand, 15 is an automatic voltage regulator to which the armature voltage of the synchronous motor 1 is input. This automatic voltage regulator 15 compares the terminal voltage of the synchronous motor 1 with the set output of the voltage setter 16, and uses the output to adjust the DC voltage so that the terminal voltage of the synchronous motor 1 becomes equal to the set voltage. It controls the converter 11.

In addition, the shield breakers 17 and 18 are for switching the excitation power source, and when switching the excitation power source, a pulse is generated from the special commutation pulse generator 21 so as not to cut off the excitation current, and this pulse is used to generate a special pulse. The commutation circuit 20 is made conductive and the field current is bypassed through this circuit, and the mustard cutters 17 and 18 are switched.

Furthermore, 22 is an output current limiting control device which operates when the control mode is in the constant speed control region and outputs a limit signal to limit the output current value of the static frequency converter.

Fig. 2 shows the operation control form of the synchronous motor 1 and the time changes of various quantities, where a is the rotational speed N
, b is the terminal voltage V and the field voltage I _f
c shows the time change of the output current I _M of the static frequency converter 5. Also,
d shows the operation control form of the synchronous motor 1, where A is the current intermittent start control area, B is the constant current acceleration control area, C is the constant speed control area, and D is the synchronous motor 1 connected to the AC power source 3. This is a parallel control area.

When starting the synchronous motor 1, first, the shield breakers 4, 6, 17 and the field shield cutter 10 are closed.

As a result, AC power is supplied to the static frequency converter 5 via the AC power supply bus 3 and the mustard disconnector 6 . This alternating current power is converted to a predetermined frequency by a static frequency converter 5, and power is supplied to the synchronous motor 1 from the output side thereof via a shingle breaker 4.

On the other hand, the DC converter 11 is connected to the field voltage regulator 1
3, whereby the field winding 9 is controlled by
The synchronous motor 1 is excited to a set value set in the constant excitation setting device 14, and starts in a constant excitation state.

That is, the armature of the synchronous motor 1 is supplied with the intermittent rectangular wave output current I _M shown in FIG. 2c from the static frequency converter 5, and as shown in FIG. Start rotating gradually. Eventually, when the rotational speed N of the synchronous motor 1 reaches _n1 , the current intermittent start control region A is switched to the constant current acceleration control region B, and the output current I _M of the static frequency converter is controlled to a continuous output of a constant value. The rotational speed N is the acceleration torque of the difference between the torque generated by the output current I _M and the field current I _f and the reaction torque at that rotational speed.
will rise. When the rotational speed N of the synchronous motor 1 reaches _n2 , it switches to the uniform speed control region C, and uniform speed control of the synchronous motor 1 is started by an automatic synchronizer (not shown).

At this time, the output limit control device 22 operates,
The output of the static frequency converter 5 is limited, the output current I _M is narrowed down to a certain value, and once it reaches a certain value, the excitation power source for the synchronous motor 1 is switched from within the station etc. using switching control. AC power supply 12
By utilizing the special commutation pulse generator 21, the special commutation circuit 20 is made conductive and the field current I _f is commutated to the special commutation circuit, turning off the shield breaker 17 and turning on the shield breaker 18. Then, the power source is switched to the AC power source from the terminal power source of the synchronous motor 1. At the same time, the field control is switched from the field voltage regulator 13 to the automatic voltage regulator 15.

That is, when the above two switching controls are performed in the constant speed control region C, the field current _If increases or decreases, and the power balance state between the synchronous motor 1 and the static frequency converter 5 is temporarily lost. As a result, the output current I _M of the static frequency converter fluctuates as shown in FIG. 2c. Therefore, if the above two switching controls are performed without limiting the output of the static frequency converter 5, the output current of the static frequency converter 5 will change as shown by the broken line in FIG. 2c. When I _M exceeds the output current I _ML , the overcurrent protection circuit (not shown) of the static frequency converter 5 operates, resulting in a system trip.

However, in the case of this embodiment, the output of the static frequency converter 5 is limited by the output limit control device 22 to reduce the output current I _M to a certain value, so the solid line in FIG. As shown, even if the armature current I _M fluctuates, it does not exceed the allowable output current value I _ML of the static frequency converter 5. Moreover, the output current I _M of the static frequency converter 5 is
In Figure 2, the period for limiting is shown as being longer to make the explanation easier to understand.
In reality, the time is only several hundred milliseconds, so it has almost no effect on uniform speed control.

Next, when the power supply switching and the switching from the field voltage regulator 13 to the automatic voltage regulator 15 are completed, the output limit control device 22 is turned off, and the output limit of the static frequency converter 5 is removed. , the output current I _M can be changed freely. Thereafter, the static frequency converter output current I _M of the synchronous motor 1 is controlled by the automatic synchronizer (not shown) and the speed control device 8 operating in the constant speed control region C, and the frequency and phase are controlled. be exposed. Further, voltage control is performed by an automatic voltage regulator 15 using a signal from an automatic synchronizer (not shown) to control the field current I _f of the synchronous motor 1.
This is done under the control of As a result, when the frequency, voltage, and phase difference fall within allowable ranges, the shield breaker 2 is turned on, and at the same time the shield circuit breakers 4 and 6 are tripped. As a result, power is supplied to the synchronous motor 1 via the shield and disconnector 2 to complete the startup, and thereafter the motor is operated using the power from the AC power supply bus 3.

In this way, when starting the synchronous motor 1, the output current of the static frequency converter 5 is temporarily changed to the output current limiting control device 2 in the uniform speed control region C.
2, active limit control is performed, during which the excitation power source is switched and control is switched from the field voltage regulator 13 to the automatic voltage regulator 15, after which the limit control is released and normal speed control is performed. By doing this, the maximum value of the transient current that occurs when switching the control device or power supply is reduced, and the synchronous motor 1 is smoothly operated without system tripping and without fluctuation of the AC power supply bus 3 after switching on. You will be able to start it. Furthermore, at this time, the static frequency converter 5
The allowable output current value can be determined only by the general variation of the armature current, and there is no need to take into account an extra output current value, making it possible to manufacture an inexpensive static frequency converter 5. .

In the above embodiment, in order to temporarily limit the output current I _M of the static frequency converter 5,
Although an output current limiting control device 22 was provided,
Instead, similar results can be obtained by providing a circuit capable of similar control in other devices such as the control signal converter 7, speed control device 8, static frequency converter 5, automatic synchronization device, etc. Needless to say.

As described above, according to the present invention, a device that can temporarily limit the output of a static frequency converter is provided, and during speed equalization control, after limiting the output of the static frequency converter, power supply switching and field Since the voltage regulator is replaced with an automatic voltage regulator, a synchronous motor control device that can be started smoothly without system tripping can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a control device for a synchronous motor showing an embodiment of the present invention, and FIG. 2 is a diagram showing the operational control form of the synchronous motor and changes in various quantities over time to explain its operation. The a is the rotational speed N of the synchronous motor
and time t, part b is a relationship diagram between the terminal voltage V and field current I _f of the synchronous motor and time t,
Part c is a diagram of the relationship between the output current I _M of the static frequency converter and time t, and part d is a diagram illustrating the mode of operation control. 1...Synchronous motor, 2, 4, 6, 17, 18...
...Shield disconnector, 3...AC power supply bus, 5...Static frequency converter, 7...Control signal converter, 8...
Speed control device, 9...Field winding, 10...Field shield and disconnector, 11...DC converter, 12...AC power supply, 13...Field voltage adjustment device, 14...Constant excitation setting equipment, 15... automatic voltage regulator, 16... voltage setting device, 19... excitation power supply transformer, 20... special commutation circuit, 21... special commutation pulse generator,
22... Output current limit control device, N, n ₁ , n ₂ ,...
...Synchronous motor rotation speed, V...Synchronous motor terminal voltage, I _f ...Field current, I _M ...Static frequency converter output current, I _ML ...Static frequency converter output current permissible limit, t... …time.

Claims (1)

[Claims] 1. While accelerating the synchronous motor using a frequency converter, switch the excitation power source of the synchronous motor in the uniform speed control region and switch the excitation control from excitation control by the field voltage regulator to excitation control by the automatic voltage regulator. In the control device for the synchronous motor, a device is provided to temporarily limit the output of the frequency converter in the uniform speed control region, and the power supply switching and the excitation control are performed while the output of the frequency converter is limited. A control device for a synchronous motor, characterized in that it performs switching.