JPS6031437Y2 - AC motor control method using thyristor inverter - Google Patents

Description

[Detailed description of the invention] The present invention relates to a control method for an AC motor using a thyrisk inverter, and is an improvement to eliminate the influence of pulsating torque proportional to the rotational speed of the AC motor at the resonance point of the mechanical system. .

In an AC motor controlled by a thyrisk inverter, pulsating torque with a frequency proportional to the rotational speed is generated.

On the other hand, mechanical systems always have a resonant frequency, and in the case of a fan in particular, the resonant frequency is relatively low. A phenomenon was observed in which the frequency of the pulsating torque and the resonance frequency of the mechanical system matched, causing the mechanical system to resonate.

Therefore, to deal with this problem, conventional techniques have taken measures such as increasing the strength of the mechanical system to withstand resonance, or devising the control circuit of the AC motor to reduce the pulsating torque.

However, in the former case, the mechanical system must be made more robust, and in the latter case, the control circuit must be made more complex, resulting in increased costs in both cases.

SUMMARY OF THE INVENTION In view of the above-mentioned prior art, it is an object of the present invention to provide a control system for an AC motor using a sirisk inverter that can eliminate the influence of resonance points of a mechanical system caused by pulsating torque with a simple circuit configuration.

The present invention, which is distantly related to such an object, provides a control method using two thyrisk inverters, in which the frequency characteristics of pulsating torque with respect to the rotational speed of an AC motor are different when two thyrisk inverters are used and when one thyrisk inverter is used. Focusing on the point that it is possible to make the frequency different between the The basis of the technical idea is that the system is operated using a single silice inverter.

Embodiments of the present invention will be described in detail below with reference to the drawings.

As shown in FIG. 1, a synchronous motor SM, which is a type of AC motor, is driven and controlled by two thyrisk inverters 1 and 2 via a transformer TF.

At this time, the thyristor inverters 1 and 2 are supplied with a direct current converted by a thyristor rectifier 3 connected to an alternating current power source (not shown).

Further, the transformer TF has two sets of primary windings and one set of secondary windings, and outputs the outputs of the thyrisk inverters 1 and 2 to be combined and supplied to the synchronous motor SM.

As a result, the frequency characteristics of pulsating torque when operating with the outputs of two sets of thyrisk inverters 1 and 2 combined are better than the frequency characteristics of pulsating torque when operating with the output of only one set of thyrisk inverters 2. It also has a steep rise characteristic.

This is shown in FIG.

In the figure, the horizontal axis represents the rotational speed of the synchronous electric motor M, and the vertical axis represents the frequency of the pulsating torque, with the solid line representing the case of two motors, and the dashed-dotted line representing the case of one motor.

At this time, the gate phase control device 4.5.6 controls the trigger timing and turn-off of the thyristor inverters 1, 2 and the thyristor rectifier 3, respectively.

A position detector ps and a rotational speed detector PC are respectively connected to the synchronous motor SM.

Of these, the position detector ps detects the relative position of the rotor and stator of the synchronous motor SM, and detects the relative position of the rotor and stator of the synchronous motor SM.
This is used to control the silice inverters 1 and 2.

Further, the rotational speed detector PG detects the rotational speed of the synchronous motor SM and sends the signal to the switching command circuit 7.

Upon receiving this signal, the switching command circuit 7 controls the gate phase control devices 4 and 6.

To further comment, while the rotational speed of the synchronous motor SM detected by the rotational speed detector PC is small, the synchronous motor SM is operated by the two Sirisk inverters 1 and 2, and the frequency of the pulsating torque with the characteristic shown by the solid line is the resonance frequency of the mechanical system. The gate phase control device 4 turns off the thyrisk inverter 1 at an appropriate point just before reaching the rotational speed N1 that coincides with fc, and the frequency of the pulsating torque having the characteristic shown by the dashed line coincides with the resonance frequency f0. The gate phase control device 4 is configured to turn on the thyrisk inverter 1 again at an appropriate point in time when the rotational speed N1 is exceeded before reaching the rotational speed N2.

That is, as shown in FIG.
An appropriate range before and after is operated using only the SIRIS inverter 2.

Note that when changing from one set to two sets of operation, the frequency of the pulsating torque is the resonance frequency f.

However, since this time is extremely short, there is no practical problem.

Here, when switching from an operation using two sets of Sylrisk inverters 1 and 2 to an operation using only Sylrisk inverter 2, and from an operation using only Sylrisk inverter 2 to an operation using two sets of Sylrisk inverters 1 and 2 again. The control mode when switching to the above will be explained in more detail.

In the former case, the gate phase control device 6 is first turned off to turn off the thyristor rectifier 3, and then the gate phase control device 4 is turned off.
is shut off, and then the gate phase control device 6 is used to turn on the silice rectifier 3.

In the latter case, after turning off the thyristor rectifier 3 in the same manner as above, the gate phase control device 4 is turned on,
Thereafter, the thyristor rectifier 3 may be turned on in the same manner as described above.

As described above, according to the present invention, it is possible to avoid the resonance point of the mechanical system and accelerate the AC motor by switching between the two sets of sirisk inverters, so there is no need to pay special consideration to the strength of the mechanical system. Furthermore, since the circuit configuration is simple, not only can costs be reduced, but also control reliability can be improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a characteristic diagram showing the frequency characteristics of rotational speed and pulsating torque. In the drawing, 1 and 2 are sirisk inverters, 7 is a switching command circuit, TF is a transformer, SM is a synchronous motor, PG is a speed detector, and fc is a resonance frequency.

Claims (1)

[Scope of utility model registration request] Driving and controlling an AC motor connected to the secondary winding of this transformer via a transformer having two sets of primary windings and one set of secondary windings connected to each of the two sets of thyrisk inverters. , the rotational speed of the AC motor when using either one of the silice inverters.
In a control method for an AC motor using a thyrisk inverter, in which the frequency characteristic of pulsating torque shows a steeper rise when both are used, the rotation speed detector detects the rotation speed of the AC motor; When the frequency of the pulsating torque reaches a rotational speed before matching the resonance frequency of the mechanical system in response to the signal from the detector, turn off any one of the sets of the silice inverters, and the rotational speed matches the resonance frequency. and a switching command circuit that turns off the thyrisk inverter again, which was turned off before the rotational speed reaches a rotational speed that exceeds the above and generates a pulsating torque having the same frequency as the resonance frequency when driven using a set of thyrisk inverters. A control method for an AC motor using a thyrisk inverter, which is characterized by the following.