JPH08322251A - Frequency converter for ac power - Google Patents

Abstract

PURPOSE: To easily convert the frequency of AC power by respectively connecting each output terminal of an AC power source to the input terminal of an AC load through switching elements and controlling the ignition of the switching elements in accordance with the required operating state of the AC load by means of a control circuit. CONSTITUTION: A frequency converter for AC power is provided with thyristors A1 -D2 which connect a single-phase DC power source to an AC load 10 and a control circuit 4 which controls the ignition of the thyristors A1 -D2 . When the ignition of thyristors A1 , A2 , D1 , and D2 is controlled, AC power from an AC power source is supplied to the load 10 without converting the frequency (f) of the power. When the ignition of thyristors B1 and C1 is alternately controlled, a half-wave component is supplied to the load 10 and converted into AC power having a frequency corresponding to f/2. When the control circuit 4b of a converter 1b controls the ignition of the thyristors A1 -D2 , the speed of an induction motor 2 can be switched between the full speed and a half full speed. Thus, the frequency of AC power can be converted easily.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC power frequency converter for converting AC power into AC power of different frequencies, and particularly to simplify speed control of an induction motor whose rotation speed depends on the frequency of the AC power. The present invention relates to an AC power frequency converter that can be implemented.

[0002]

2. Description of the Related Art The induction motor originally has a constant speed characteristic, and the constant speed changes in proportion to the frequency of the supplied AC power. Therefore, in order to control the speed of the induction motor, it is suitable to control the frequency of the AC power, and the inverter as the frequency control means is excellent in that the frequency can be changed continuously and in a wide range. However,
As is well known, the inverter is an indirect system in which AC power is once converted to DC by a forward converter and then converted to the AC power frequency required by an inverse converter, so the device cannot be complicated. Especially when the induction motor is used as an electric actuator for driving a butterfly valve,
A means that can more easily convert the frequency of AC power is desired. As an example of using an induction motor as the electric actuator, the effectiveness of speed control when an induction motor is used for a butterfly valve servo mechanism will be described below.

When the on / off control of the electric motor is carried out in order to carry out the control by the above-mentioned servo mechanism, the amount of driving the valve is taken into consideration even after the electric motor is turned off by the inertia of the electric motor and gears. ， It is necessary to set the point to control the motor off before the target point. The operating clearance, which is the difference between the off-control point of the electric motor and the target point, needs to be set larger as the control speed, that is, the speed of the electric motor, becomes larger, and the position control accuracy decreases. If the speed of the motor is slowed down, the control accuracy will be improved, but the control speed will be reduced. Also, if the operating clearance is set too small to stop beyond the target position, the motor reverses in an attempt to reach the target position again, causing cycling due to the forward / reverse switching operation around the target point. Will be lost. Therefore, the speed of the electric motor can be switched between the rated speed and a speed lower than the rated speed, and the speed is reduced when the target point is approached, whereby the control speed can be suppressed from being lowered and the control accuracy can be improved. For example, if it is possible to switch the speed to 1/2 of the rated speed, the inertia of the motor and gear will be 1/4,
The operating clearance can be reduced to about 1/4. If the required operating clearance (valve opening) for rated speed is ± 1.5 °, the operating clearance for 1/2 speed is ± 0.38.
This is all that is required, and practically sufficient position accuracy can be obtained. Particularly in butterfly valve control, the accuracy of the stop position when the valve is fully closed is extremely important. This means that when the valve is fully closed, the valve must be completely closed and the outflow of fluid must be completely stopped. This is because it is promoted and the life is shortened.

[0004]

When the induction motor is used as an electric actuator as described above, the control position accuracy can be improved by switching the rotation speed. However, the scale of the device would be too large to use an inverter for this speed switching. In addition to the valve servo mechanism described above, AC power frequency switching can often be effectively used for controlling electric actuators that may be slightly rougher than a servo motor, and a device that can easily convert AC power frequency from an inverter Realization of is awaited. It is an object of the present invention to provide an AC power frequency conversion device that can easily and directly convert the frequency of AC power.

[0005]

In order to achieve the above object, the means adopted by the present invention is an AC power frequency converter for switching the frequency of the AC power supplied to the AC load according to the operating state of the AC load. In the device, a switching element connected between each output end of the AC power supply and each input end of the AC load, and each of the switching elements is connected to an arbitrary AC power depending on a state of operating the AC load. It is configured as an AC power frequency converter comprising: a control means for controlling ignition so as to supply a half-wave component of a cycle to the AC load in an alternating direction.

[0006]

According to the present invention, each output terminal of the AC power source and each input terminal of the AC load are connected by a switching element, and each switching element is connected in accordance with the state in which the AC load is operated by the control circuit. Control ignition. In this ignition control, each switching element is ignition-controlled so as to take out a half-wave component of AC power in an arbitrary cycle and supply it to an AC load in an alternating direction. For example, when the AC load is an induction motor and the frequency of the AC power supplied to the AC motor is switched to control the rotation speed, a switching element required to pass all half-wave components of the AC power as they are. When the ignition control is performed, the induction motor rotates at a speed corresponding to the frequency of the AC power, that is, full speed. When it is desired to rotate the induction motor at a speed of 1/2 of the full speed, for example, if the switching element is ignition-controlled so that only one half-wave component of the AC power is supplied to the induction motor in the alternating direction, Can obtain a speed equivalent to that of a state in which it is operated with AC power having a frequency half that of full speed. According to this configuration, since the AC power can be directly converted to a different frequency and supplied to the AC load, the frequency of the AC power can be converted more easily than the indirect configuration by the inverter. This is effective for speed control of electric actuators.

[0007]

Embodiments of the present invention will be described below with reference to the accompanying drawings for the understanding of the present invention. The following embodiments are examples embodying the present invention and do not limit the technical scope of the present invention. Here, FIG. 1 is a circuit diagram (a) showing a configuration of an AC power frequency converter according to a first embodiment of the present invention, and a circuit diagram (b) showing a configuration in which it is applied to speed control of a single-phase induction motor. ), FIG. 2 and FIG.
FIG. 4 is a timing chart of ignition control for explaining ignition control of the thyristor in the configuration of the first embodiment, and FIG. 4 is a circuit showing a configuration in which the AC power frequency converter according to the second embodiment is applied to speed control of a three-phase induction motor. 5 and 5 are ignition control timing charts for explaining the ignition control of the thyristor in the configuration of the second embodiment. In FIG. 1A, the AC power frequency conversion device 1a includes a single-phase AC power supply 3 and an AC load 10.
Thyristor (switching element) A ₁ connecting between
And to D _2, and is configured by including a control circuit 4a for ignition controlling each said thyristor A ₁ to D _2. The thyristors A _{1 to} D ₂ are output terminals u ₁ and v of the AC power supply 3.
₁ and the input ends u ₂ and v ₂ of the AC load 10 are arranged so that they can be connected to each other. The thyristor is not limited to this, and a power transistor, GTO, IGBT or the like may be used.

In the above structure, the thyristors A ₁ and A ₂ and the thyristors D ₁ and D, which are bidirectionally connected in antiparallel, are connected.
_{When 2} is synchronized with each half-wave component of the AC power shown in FIG. 2A and the ignition is controlled, the AC power frequency f from the AC power supply 3 is supplied to the AC load 10 as it is.
Next, the timing of the ignition control by the control circuit 4a when the AC power frequency f from the AC power supply 3 is converted to a frequency corresponding to f / 2 and supplied to the AC load 10 is shown in FIG.
As shown in (c). The thyristors A ₁ and D ₂ at the timing shown in FIG. 2B and the thyristors B ₁ and C _{1 at the} timing shown in FIG. When the ignition control is performed so as to be alternately turned on in synchronism with the cycle of 1), the half-wave component of the AC power is supplied to the AC load 10 in the alternating direction, and as shown in FIG. The frequency f of the AC power supply 3 is f
A state in which the AC power is converted into AC power having a frequency equivalent to / 2 is obtained.

The configuration shown in FIG. 1 (a) is applied to the speed of the induction motor.
When applied to control, its configuration is shown in Fig. 1 (b).
To change. As shown in the figure, the induction motor 2
The AC power frequency conversion device 1b in the case of a current load is
Cyris connected in anti-parallel for all connection lines
Type A₁~ D₂Is provided. Basic for frequency conversion
The configuration shown in Fig. 1 (a) may be used, but if the AC load is
In the case of an electric motor, the frequency is converted so that
When switching from high speed to low speed,
Until it slows down,
It operates as an electric machine and sends current back to the power supply side for regenerative braking.
Bidirectional connection in each connection line because operation is performed
Is required. With the configuration shown in FIG.
Operate machine 2 at full speed proportional to frequency f of AC power supply 3
State and the frequency f of the AC power supply 3 to a frequency equivalent to f / 2
Convert and switch to the state of operating at half the full speed
The control operation to obtain will be described below with reference to FIG.
It Fig. 2 (a) shows the output waveform of the AC power supply 3, which is a single-phase positive
It is output as a chord wave. Driving the induction motor 2 at full speed
When the control circuit 4b is used, the thyristor A ₁,
A₂, D₁, D₂Each half of the AC power frequency
By controlling ignition in synchronization with the cycle, AC power supply 3
The AC power frequency f from is supplied to the induction motor 2 as it is.
The induction motor 2 is supplied with
Drive at high speed.

Next, when the induction motor 2 is operated at half the total speed, thyristors A ₁ , A ₂ and D ₁ , D ₂ connected in antiparallel as shown in FIG. 2B are used. , And thyristors B ₁ , B ₂ and C ₁ , C ₂ connected in anti-parallel as shown in FIG. 2 (c) alternate in synchronism with the cycle of one half-wave component of AC power (hatched portion). The ignition is controlled so that it is turned on. As a result, the induction motor 2 is supplied with the half-wave component of the alternating-current power in the alternating direction.
As shown in (d), the induction motor 2 is operated at a frequency corresponding to 1/2 of the AC power frequency f, and the rotation speed is 1/2.
Becomes As described above, the thyristor A is controlled by the control circuit 4b.
_By controlling the ignition of each of _{1 to} D _2, the speed of the induction motor 2 can be controlled to be switched between the full speed and ½ of the full speed. The AC waveform shown in FIG. 2 (d) includes harmonics and has a main component of f / 2 and (3/2) f, but the drive torque due to f / 2 is significantly larger. When the full speed operation is switched to the half speed operation, the induction motor 2 is switched to the half speed by f / 2. The above control is switching between full speed and half speed, but it is also possible to convert the AC power frequency applied to the induction motor 2 so that the speed becomes half speed or less. For example, as shown in FIGS. 3B and 3C, thyristors A ₁ and A ₂ and D ₁ and D ₂ ,
The thyristors B ₁ , B ₂ and C ₁ , C ₂ are connected to the AC power supply 3
If alternating current ignition frequency is controlled so that the half-wave component on one side of the alternating-current power frequency f is taken out every other cycle, the induction motor 2
Can be operated at 1/4 speed of full speed. That is,
AC power frequency f from the AC power supply 3 shown in FIG.
Is converted into a frequency corresponding to f / 4 of the AC power frequency f and applied to the induction motor 2 as shown in FIG.

Next, a configuration in which the present invention is applied to frequency conversion of three-phase AC power will be described below as a second embodiment. In FIG. 4, the AC power frequency converter 5 according to the second embodiment has output terminals u ₁ , v ₁ , w ₁ of a three-phase AC power supply 7 and an input terminal u _{2 of} a three-phase induction motor (AC load) 6. , V ₂ , w ₂
And thyristors A _{1 to} I for bidirectional connection between
₂ and a control circuit 8 for controlling firing of each of the thyristors A _{1 to} I ₂ . With the above configuration, in order to switch the three-phase induction motor 6 between full-speed operation and half-speed operation, the frequency f of the AC power applied to the three-phase induction motor 6 is equivalent to f during full-speed operation and f / 2 during half-speed operation. A state in which the thyristors A _{1 to} I ₂ are ignited by the control circuit 8 so as to have a frequency will be described with reference to FIG. At full speed operation, thyristors A ₁ , A ₂ , E ₁ , E ₂ , I ₁ ,
I ₂ is ignition controlled. In this ignition control state, u ₁ -u ₂ , v ₁ -v ₂ , and w ₁ -w ₂ between the output end of the three-phase AC power supply 7 and the input end of the three-phase induction motor 6 are respectively connected. Thyristors A ₁ , A ₂ , E ₁ , connected in anti-parallel,
E _2, I _1, because it is connected bidirectionally by I _2, when it was synchronized with the period of each half-wave of the three-phase AC power frequency controlling ignition, three-phase AC power source shown in FIG. 5 (a) The three-phase AC power from 7 is supplied to the three-phase induction motor 6 as it is, and the three-phase induction motor 6 is operated at a full speed proportional to the three-phase AC power frequency f.

Next, during half-speed operation, the one-side half-wave component (positive side in the figure) of each phase of the three-phase AC power is the three-phase induction motor 6
Thyristor A
₁ ~I ₂ is ignited controlled at the timing shown in Figure 5 (b). By the ignition control shown in FIG. 5 (b), the half-wave component (hatched portion) of each phase of the three-phase AC power output from the three-phase AC power supply 7 shown in FIG. 5 (a) is shown in FIG. 5 (c). As shown, each phase winding of the three-phase induction motor 6 is supplied in an alternating direction, and the three-phase induction motor 6 is driven at an AC power frequency corresponding to f / 2. Therefore, the three-phase induction motor 6 has half the full speed.
It is operated at the rotation speed of. In the first and second embodiment configurations, two thyristors connected in antiparallel are
It is possible to replace it with a bidirectional switching element such as two triacs, but when the AC load is an inductive load as in the above-mentioned embodiments, there is a high possibility that false ignition will occur. As shown in the above configuration, it is desirable to connect unidirectional switching elements in anti-parallel and individually control ignition. When controlling the opening of the butterfly valve using the present invention, full speed operation is performed until the valve reaches a predetermined opening close to full closure, and a signal for detecting that the predetermined opening is reached is input. At that time, the half-speed control or the speed control at a lower speed can be switched to improve the stop accuracy at the time of fully closing.

[0013]

As described above, according to the present invention, a state in which each output terminal of the AC power source and each input terminal of the AC load are connected by switching elements and the control circuit operates the AC load In accordance with the above, each switching element is controlled to fire. In this ignition control, each switching element is ignition-controlled so as to take out a half-wave component of AC power in an arbitrary cycle and supply it to an AC load in an alternating direction. For example,
When the AC load is an induction motor and the frequency of the AC power supplied to the AC motor is switched to control the rotation speed, a switching element is required to pass all half-wave components of the AC power as they are. When the arc control is performed, the induction motor rotates at a speed corresponding to the frequency of the AC power, that is, full speed. When it is desired to rotate the induction motor at a speed of 1/2 of the full speed, for example, if the switching element is ignition-controlled so that only one half-wave component of the AC power is supplied to the induction motor in the alternating direction, Is 1/2 of full speed
It is possible to obtain a speed equivalent to that when operated with AC power of the frequency. According to this configuration, AC power can be directly converted into different frequencies and supplied to the AC load.
Compared to an indirect configuration using an inverter, the frequency of AC power can be converted more easily, which is effective for speed control of electric actuators.

[Brief description of drawings]

FIG. 1 is a circuit diagram (b) showing a basic configuration (a) of an AC power frequency conversion device according to a first embodiment of the present invention and a configuration in which the basic configuration is applied to speed control of an induction motor.

FIG. 2 is a timing chart illustrating ignition control of the configuration of the first embodiment.

FIG. 3 is a timing chart illustrating firing control of the configuration of the first embodiment.

FIG. 4 is a circuit diagram showing a configuration in which an AC power frequency conversion device according to a second embodiment is applied to speed control of a three-phase induction motor.

FIG. 5 is a timing chart illustrating ignition control of the configuration of the second embodiment.

[Explanation of symbols]

1a, 1b, 5 ... AC power frequency converter 2 ... induction motor (AC load) 3 ... AC power source 4a, 4b, 8 ... control circuit 6 ... three-phase induction motor (AC load) 7 ... three-phase AC power supply A ₁ ~ I ₂ thyristor (switching element)

Claims (1)

[Claims] 1. An AC power frequency converter for switching the frequency of AC power supplied to an AC load in accordance with the operating state of the AC load, between an output terminal of an AC power supply and an input of an AC load. The switching elements connected to each other and the switching elements are ignited so that a half-wave component of an arbitrary cycle of AC power is supplied to the AC load in an alternating direction according to the state of operating the AC load. An AC power frequency conversion device, comprising: a control unit for controlling.