JPH0333197Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a variable speed AC induction motor that is configured based on an AC induction motor having a structure similar to a general-purpose "squirrel cage" type AC induction motor and is capable of increasing and decelerating in multiple stages.

The electric motor used as a drive source for a compressor for a refrigeration system with a large load fluctuation range is preferably of a variable speed structure capable of changing speed over a wide range, and is preferably a low-cost electric motor from the standpoint of versatility.

Therefore, recently, AC induction motors have been put into practical use in which the speed can be changed using a control device so that the output can be adjusted to suit the load.A representative example of this is a static frequency converter. One example is a transmission method that uses

To obtain this frequency output, it is necessary to convert alternating current to direct current and then back to alternating current, which necessitates two conversions, making the equipment complex and increasing costs unavoidable. There was a problem in that the power loss increased due to this, and the significance of the variable speed structure was lost.

In order to address these problems, the present applicant has attempted to provide a variable speed motor based on an AC induction motor that is economically advantageous, has extremely low power loss, and can be made at low cost. Hasaki has made several proposals, including Japanese Patent Application Laid-Open No. 56-103989, but to explain the outline of the structure, the number of stator windings of an AC induction motor is A plurality of bidirectionally controlled rectifiers corresponding to the By coupling with an electric motor, it is possible to easily perform continuous speed changes and reduce loss on the power side.The stepping circuit is driven by a frequency oscillator that can change the frequency steplessly. The turn-on direction of the trigger output sent to the gate terminal of the bidirectionally controlled rectifying element is made to follow or reverse the direction of rotation of the motor, and the turn-on period is made faster so that the rotation speed is higher than or equal to or lower than the rated speed. It is rotatable.

However, this stepless variable speed device has some practical problems that need to be improved.
In order to continuously change the motor rotation speed, if the oscillation frequency of the frequency oscillator is changed steplessly, the motor rotation speed will suddenly change at a certain period determined by the difference between the power supply frequency and this oscillation frequency. This means that it will decline.

For example, one example is shown in Figure 5, but 2
When a pole single-phase induction motor is controlled by the stepless variable speed device in a speed range below the rated speed (3600 rpm), control for changing the turn-on period of the bidirectional control rectifying element is performed. When the variable resistance was changed steplessly, the rotation speed suddenly decreased to about 2,500 r.p.m. in the process of operating from one notch to the right to the next two notches to the right after passing the middle notch.
It has been experimentally revealed that rotational speeds higher than pm cannot be stably obtained.

The reason for this is that a triax is interposed in the power line, and a bidirectionally controlled rectifier element, such as a stator winding, is connected in series with the triax, so when one triax is turned on, The triaxes that were previously turned on and then given an off command do not turn off at the same time, but remain on for a while.
This acts as a brake, leading to a sudden drop in rotational speed.

As described above, the control method proposed earlier has some points that require some improvement in practical terms, and the present invention has been devised here in order to solve such problems. The purpose of this is to prevent a sudden drop in speed even temporarily and to accurately control the rotational speed to the set rotational speed, thereby achieving stability and reliability of control.

To this end, the present invention is particularly directed to an AC induction motor having stator windings in the stator whose number is an integral multiple of the product of the number of power supply phases and the number of poles, and a winding end of each of the stator windings connected to a power supply connection terminal. A bidirectional control rectifier is inserted in each wiring, and a trigger is driven by a variable frequency oscillator to sequentially output an output to the gate terminal of each bidirectional control rectifier. A stepping circuit that rotates the rotor above or below the rated rotational speed by shifting the turn-on direction toward or against the rotational direction of the rotor of the AC induction motor and increasing the turn-on period. A variable speed AC induction motor is configured, and the variable frequency oscillator is capable of switching oscillation to a plurality of frequencies having different values within a frequency range below the power supply frequency and which do not cause a sudden speed reduction to the AC induction motor. The induction motor is formed in an oscillator, and the timing is set until the bidirectional control rectifier element that was previously turned on is completely turned off, and at the same time, the induction motor By controlling the rotation in multiple stages, it became possible to accurately control the speed according to the set value, and the desired objective was achieved.

Hereinafter, one embodiment of the present invention will be described based on the accompanying drawings.

The illustrated example is an AC induction motor, for example, a single-phase induction motor, and a predetermined number of bidirectional control rectifier elements 6a, 7a...
and an ignition device formed from gate circuits 11-6a, 11-7a..., a stepping circuit 12, and a variable frequency oscillator 13.As shown in FIG. The stator has coils 1a to 1f as windings and coils 2a to 2f as auxiliary windings, and the illustrated example shows a two-pole structure with two coils, Both coil groups must have the same number, and must have an integral multiple of the product of the number of poles and the number of power supply phases.

Coils 1a to 1f and coils 2a to 2f are arranged alternately and wound around the stator, and for both coil groups 1a to 1f and 2a to 2f, the winding starts between adjacent coils of the same type. The ends of the windings are directly connected to each other as shown in the first figure,
Two loop-shaped closed circuits are formed in the stator.

Note that it is necessary to provide a positional relationship between the coils 1a to 1f and the coils 2a to 2f such that the phase angle between the coils 1a and 2a is 90 degrees, and in the example shown in Figure 1, the coils Since the number is 12, the spatial relationship is 90°.

On the other hand, as the bidirectional control rectifying element, for example, a triax is used, and the coils 1a to 1f and the coil 2
Triaxes 6a to 6f, 7a to 7f, 8a to 8 in multiples (24 pieces) for the total number of a to 2f (12 pieces)
f, 9a to 9f are arranged at appropriate locations on the electric motor frame, and triaxes 6a to 6f and 7
a to 7f are branch-connected to respective winding start and winding end direct connection parts 3a to 3f in the loop-shaped closed circuit on the main winding side, while triaxes 8a to 8f
and 9a to 9f are each winding start/winding end direct connection portion 4a in the loop-shaped closed circuit on the auxiliary winding side.
~4f, respectively.

And the triaxes 7a to 7f and 9a to
Connect the non-connection side terminals of 9f to one pole of the single-phase AC power supply 5, for example, the ground pole, and connect the triax 6.
The load side terminals of the capacitor 10 have the unconnected side terminals of a to 6f connected all at once to the other pole of the power source 5, such as the ungrounded electrode, and the unconnected side terminals of the triaxes 8a to 8f connected to the ungrounded electrode. Connect all at once.

Next, the ignition device was set up to correspond to each triax, as outlined in Figures 2 and 3.
It consists of 24 gate circuits 11-6a, 11-9f, a stepping circuit 12, and a variable frequency oscillator 13, the structure and function of which will be described later.

The operating principle of the embodiment of the present invention having the structure described above will be explained below. By applying a trigger pulse to the gates G ₁ and G' ₁ of the triaxes 6a and 7d to operate both triaxes 6a and 7d, the main winding is activated. When the wires are energized, current flows in the same direction in the coils 1a to 1c, and current flows in the coils 1d to 1f in the opposite direction to the previous three coils, so that magnetic poles are formed in the stator.

Similarly, the gates G ₇ of triaxes 8a and 9d,
When the auxiliary windings are energized by simultaneously applying a trigger pulse to G' ₇ and activating both triaxes 8a and 9d, currents in the same direction flow through the coils 2a to 2c, and this current flows through the coils 2d to 2f. A current flows in the opposite direction, and two magnetic poles are also formed by the auxiliary winding.

Thus, there is a phase angle difference of 90° between the magnetic pole formed by the main winding and the magnetic pole formed by the auxiliary winding, and a current with an advanced phase angle of 90° flows through the auxiliary winding via the capacitor 10. Therefore, the combination of the magnetic fields formed by the two windings, the main winding and the auxiliary winding, naturally becomes a rotating magnetic field, which causes the rotor to rotate.

Connect the main winding side triax from 6a, 7d to 6
b, 7e, then 6c, 7f... 6f, 7c, then 6a, 7d, and at the same time, the auxiliary winding side tri-attack is activated from 8a, 9d to 8b, 9.
e, then 8c, 9f... 8f, 9c again 8
When ignition is performed in sequence from a to 9d, the rotating magnetic field formed by the phase difference between the currents supplied to the main winding and the auxiliary winding is further rotated in the direction of ignition. become.

That is, if the direction of ignition is the same as the rotating magnetic field, the rotational speed will be the sum of the synchronous rotational speed inherent to the induction motor and the ignition speed.

When firing in the opposite direction, the rotational speed is naturally subtracted by the firing speed.

It is therefore possible to increase or decrease the speed of the motor rotor by changing the speed as well as the direction for sequential firing.

The above operation examples can be summarized as general operation conditions as follows.

The coils 1a and 1d equally arranged in accordance with the number of poles are selected as a group in the loop-shaped closed circuit on the main winding side, and the winding start, winding end direct connection parts 3a,
3d, so that both poles of the AC power supply 5 are alternately conducted, a trigger pulse is applied to the corresponding triaxes 6a and 7d, and at the same time, a trigger pulse is applied equally to the auxiliary winding side loop-shaped closed circuit corresponding to the number of poles. For the arranged and selected coils 1a and 1d
The coils 2a and 2d having a phase angle relationship of 90° are selected as a group, and the corresponding triaxes 8a are connected to the winding start and winding end direct connection portions 4a and 4d so that both poles of the AC power source 5 are alternately electrically connected. ,9d
While applying a trigger pulse to the motor rotor, the trigger pulse is stepped sequentially and at variable pulse speeds to triacs corresponding to adjacent coil groups in the direction of rotation of the motor rotor or in the opposite direction. It is.

Therefore, in order to sequentially turn the firing of the triax, as shown in Fig. 3, the frequency corresponding to the required rotation speed, that is, f = | PN / 120 - f ₀ | However, P ; Number of poles, N; Required rotational speed, f ₀ ; The stepping circuit 12 is driven by pulses oscillated from the oscillator 13, which is capable of oscillating at the frequency of the AC power supply, and each gate is The circuits _11-6a to _11-9f may be connected sequentially.

The direction of this stepping is 1-2-3-4-5
-6-1 (speed increase direction) can also be shifted to 1-6
-5-4-3-2-1 (deceleration direction) is also possible.

Note that one terminal of the stepping circuit 12 has 4
The respective terminals of the gate circuits associated with the triax corresponding to four gate circuits, that is, two selected coils of the main winding and two selected coils of the auxiliary winding, are connected simultaneously, and the gate circuits are connected at the same time. The opposite terminals of the circuits 11-6a to 11-9f are all connected in common to the terminal _T0 .

On the other hand, since the gate circuits 11-6a to 11-9f have different potentials between the stepping circuit 12 and the respective gates of each triac, they must be insulated from each other. Therefore, a photocoupler 14 is used as shown in FIG. are doing.

Each capacitor provided in the circuit shown in Figure 1
In _C1 ..., when the firing of a triax is transferred to the next one, the triax through which current was flowing up to that point must be forcibly extinguished, so
This is a capacitor used for forced commutation.

The variable frequency oscillator 13, which is an element that transmits a variable speed command, is connected to NAND circuits _14-1 and 14- as shown in FIG.
₂ , _14-3 , and switching elements _15-1 , 15
_-2 ...15- _o , time constant capacitor _C1 , and frequency setting resistors _R1 , _R2 , connected to the switching elements _15-1 , _15-2 ...15- _o , respectively.
... _Ro , and has a structure that allows frequency switching and oscillation in multiple stages as shown below.

That is, due to the potential difference between the input and output of the NAND circuits _14-1 to _14-3 , the capacitor C ₁ and the resistors R ₁ to R _o
Current flows through one of the capacitors
Charging of _C1 progresses and the voltage decreases.

When this happens, the voltage across the resistor also decreases, and the first NAND circuit _14-1 is inverted.

This operation continues to be repeated, resulting in oscillation.

Therefore, the period of this repetition is the capacitor C ₁
It can be changed by changing the resistance value that can change the charging speed, that is, the charging current.The larger the resistance value, the longer the period and the lower the oscillation frequency.Conversely, the smaller the resistance value, the lower the oscillation frequency. The oscillation frequency becomes higher.

Therefore, as frequency setting resistors, several types of resistors R ₁ to _{R o} with different resistance values are connected in parallel via switching elements 15-1 _to 15- _o , and the resistance value is increased depending on the command signal. The switching is performed from the smallest to the largest, or conversely from the smallest to the largest.

Thus, in the former case, the output oscillation frequency changes stepwise on the increasing side, and in the latter case, it changes stepwise on the decreasing side.

In this case, the resistance values of the resistors R ₁ to _{R o} are selected so as to avoid a speed range that causes a sudden speed reduction in the target induction motor.

For example, if a single-phase induction motor whose speed is being controlled is the drive source for a compressor in an air conditioner, it detects the room temperature and converts it into several types of signals depending on the difference between the room temperature and the set temperature. When the temperature difference is large, the electric motor is rotated at high speed by connecting the resistor _R1 with the smaller resistance value, and the rotational speed is decreased by sequentially switching the resistance value to the larger one according to the temperature difference. If the load is large and the temperature difference becomes large, the resistance value may be gradually changed to smaller resistance values.

By performing stepwise control of the oscillation frequency in an increasing or decreasing manner in this manner, it is possible to eliminate the sudden speed drop phenomenon described above.

The embodiment described above is a single-phase AC induction motor, but in addition to this, a three-phase AC induction motor can also be used to change the speed in stages using similar means. The stepping circuit 12 is constructed by connecting the wires in a star pattern and inserting bidirectional control rectifying elements in the wiring from each winding to the neutral point.
The direction and period of turn-on may be changed depending on the situation, and such an example is naturally included in the present invention.

As is clear from the above explanation, the present invention has the following features:
The stator windings of an AC induction motor are sequentially energized, and the turn-on direction is the same as or opposite to the rotor, and the speed can be changed by changing the turn-on period, Since the structure is simple and the control system is simple, costs can be kept low.

Furthermore, the oscillation frequency of the frequency oscillator 13, which determines the speed of energization, is not continuously variable, but is controlled in multi-step changes to avoid the rotation speed range that causes a sudden speed reduction in the AC induction motor. Therefore, it is possible to eliminate the drawbacks of the continuously variable system, such as the speed suddenly decreasing at a certain oscillation frequency, and improve reliability due to the certainty of speed control.

[Brief explanation of the drawing]

Figure 1 is an expanded circuit diagram of one example of the present invention, Figure 2 is a developed circuit diagram of one example of the present invention;
Figure 3 and Figure 3 are the gate circuit diagram and stepping circuit diagram of the ignition device in the speed change control system, and Figure 4.
This figure is a schematic circuit diagram of the variable frequency oscillator in FIG. 3, and FIG. 5 is a speed control characteristic diagram of the AC induction motor. 1a, 2a... stator winding, 6a, 7a... bidirectional control rectifier, 12... stepping circuit,
13...Variable frequency oscillator.

Claims (1)

[Scope of utility model registration request] Stator winding 1 with an integral multiple of the product of the number of power supply phases and the number of poles
a, 2a... as a stator, and each of the stator windings 1a, 2a of this AC induction motor.
Bidirectional control rectifying elements 6a, 7a... are respectively interposed in each wiring connecting the winding ends of... to the power supply connection terminals.
Then, a trigger output is sequentially generated by the variable frequency oscillator 13 to the gate terminal of each of the two-way control rectifying elements 6a, 7a, etc., and the turn-on direction generated in this order is determined by the rotation of the AC induction motor. the variable frequency oscillator; 13 is formed into a multi-stage frequency oscillator capable of switching and oscillating at a plurality of frequencies with different values within a frequency range below the power supply frequency and which do not cause a sudden speed reduction in the induction motor. AC induction motor.