JPS6147079B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for an induction motor, and in particular, it can be used to start a single-phase induction motor, control the voltage of an induction motor, and control the voltage of a three-phase induction motor by detecting the phase difference between motor voltage and current. This invention relates to Y-Δ starting of induction motors, placking braking of three-phase induction motors, secondary impedance control of wound induction motors, etc.

In an induction motor, the phase difference between voltage and current changes in relation to the amount of slippage. The phase difference between voltage and current is large when the slippage is large, and becomes small when the slippage is small. Except for induction motors with capacitors connected, the current phase lags behind the voltage phase.

Additionally, when the supply voltage to the induction motor changes, the phase of the current also changes.

The present invention uses this principle to control the timing of adjusting the magnitude of the primary or secondary impedance of an induction motor. A variable impedance means is used to control the impedance, and this includes contacts for on/off control, non-contact relays, and devices that can continuously control the impedance.

Now, the phase difference between voltage and current also changes continuously as the magnitude of slippage increases. Therefore, the impedance of the variable impedance means can be continuously changed according to this phase difference. Therefore, if this variable impedance means is connected to the primary side of the induction motor, the voltage of the induction motor can be controlled. Furthermore, if it is connected to the secondary side, the magnitude of the output torque can be controlled, and in either case, the speed can be controlled.

When starting a single-phase induction motor, that is, disconnecting the starting capacitor from the power supply, or switching a three-phase induction motor from Y to Δ, or after reversing the phase rotation direction during placking braking, the rotation speed If the induction motor is disconnected from the power supply when the voltage has dropped sufficiently, there is no need to detect continuous changes in the phase difference between voltage and current. It is sufficient to detect only whether the phase difference has reached a certain value. To meet such requirements, it is desirable that the lead/lag relationship between the current phase, voltage, and phase be reversed at a certain level of slippage. Then, the operation of this device will be stable and highly reliable. However, as mentioned above, in many cases, the phase of the current lags behind the phase of the voltage, regardless of slippage. Therefore, a first detection means for detecting the phase of the current flowing into the induction motor and a second detection means for detecting the phase of the voltage supplied to the induction motor are provided. At this time, even if the voltage supplied to the induction motor changes and the phase of the current changes, the second detection means detects a high Compensation means is provided so that the phase of the detected voltage is delayed compared to when the voltage is applied. When the slippage is large, the output of the first detection means is delayed compared to the output of the second detection means that detects the phase of the voltage, and when the slippage becomes less than a certain value, the output of the first detection means becomes the output of the second detection means. so that it is either ahead of or in phase with the

Then, the variable impedance means is controlled by detecting the point in time when the phases of the outputs of the first detection means and the second detection means are reversed by the phase difference detection means. In other words, when starting a single-phase induction motor, when the phase difference detection means detects that the output of the second detection means is ahead in phase than the output of the first detection means, the variable impedance means is controlled to start the motor. If the output capacitor is connected in series with the auxiliary winding and in parallel with the main winding, and the phase difference detection means detects that the output of the second detection means is delayed in phase than the output of the first detection means. A variable impedance means is controlled to disconnect the starting capacitor from the power supply. When the present invention is applied to start a single-phase induction motor, the first detection means and the second detection means are adjusted so that the output of the phase difference detection means is inverted at a desirable time to disconnect the starting capacitor. When a three-phase induction motor is Y-Δ started, the phase difference detection means detects that the output of the second detection means is ahead of the output of the first detection means, and the variable impedance means is activated. The winding of the three-phase induction motor is connected to Y under control, and the output of the second detection means is
When the phase difference detection means detects that the phase lags behind the output of the first detection means, the variable impedance means is controlled to change the connection of the windings of the three-phase induction motor from Y to Δ. In this case, the first detection means and the second detection means are adjusted so that the output of the phase difference detection means is inverted at the desired timing for switching from Y to Δ. In order to perform anti-phase braking on a three-phase induction motor, when the motor is disconnected from the power supply when the rotational speed has sufficiently decreased after reversing the phase rotation, the output of the second detection means is higher than the output of the first detection means. When the phase difference detection means detects that the phase is ahead of the output of the first detection means, the variable impedance is controlled to reduce the impedance, and the output of the second detection means detects that the phase is behind the output of the first detection means. When the phase difference detection means detects the difference, the variable impedance is controlled to increase the impedance, and the three-phase induction motor is substantially disconnected from the power source.

As described above, according to the present invention, a control device as described above or similar to the above-mentioned control device can be constructed by detecting the phase difference between the voltage and current of the induction motor. Since this is different from controlling by capturing current or voltage values, stable operation can be achieved even if the voltage applied to the motor fluctuates considerably.

1, 2, and 3 show a starting device for a single-phase induction motor with dual voltage specifications, for example, switching between 100V and 200V, showing an embodiment of the present invention. This example will be explained below. 1 is a single-phase AC power supply, and 2 is a single-phase induction motor. A starting capacitor 4 and a triax 5 as variable impedance means are connected in series to an auxiliary winding 3 of a motor 2, and connected in parallel to a main winding 6. Then, the main winding 6 is connected to the power source 1. The first detection means 7 is a current transformer CT
It consists of a resistor R ₁ and a diode D ₁ . Current transformer
The CT detects the current flowing through the main winding 6. Resistor R ₁ is for converting current into voltage, and diode D ₁ is for rectification. The second detection means 8 sandwiches the transformer T and is constructed as follows.
That is, the primary side of the transformer T is connected to a single-phase AC power source 1 to which a single-phase induction motor 2 is connected. The secondary side of the transformer T is a resistor R ₃ and a Zener diode ZD ₁
and Zener diode ZD ₂ are connected in series.
Furthermore, a differentiator circuit consisting of a series circuit of a capacitor C ₁ and a resistor R ₄ is connected between the terminals of the Zener diode ZD ₂ . In addition, a surge killer SK is connected to the primary side of the transformer T to absorb noise. Now, when the supply voltage of single-phase AC power supply 1 is 200V,
Assuming that _{the voltage waveform obtained through the transformer T 1 is as shown by V 1 in FIG .}
It's quite late, and as the startup progresses,
As shown by I′ ₁ , the delay becomes very small. Further, in the second detection means 8, the voltage waveform _V1 input via the transformer T is processed as follows. First, considering the case where there is no Zener diode ZD ₂ and capacitor C ₁ , the voltage at point A in FIG. 1 is equal to the input voltage V ₁ as shown by VA ₁ in FIG.
rises to the Zener voltage VZd ₁ of the Zener diode ZD ₁ with a delay. Therefore, this Zener diode
By appropriately selecting the Zener voltage VZd ₁ of ZD ₁ , it is possible to obtain a voltage waveform delayed at a constant rate with respect to the power supply voltage. Therefore, by selecting the Zener voltage Vzd ₁ of the Zener diode ZD ₁ ,
The delay of voltage waveform VA ₁ is set between the delays of current waveforms I ₁ and I′ ₁ . The voltage at point A is a Zener diode
By adding ZD ₂ , it is further processed,
As shown by VA′ ₁ , the Zener voltage of the Zener diode ZD ₂ is regulated to be less than Vzd ₂ . Finally, when the voltage waveform at point A is added to the differential circuit, at point B,
An output signal with a voltage waveform indicated by Vp ₁ in FIG. 2 is obtained. Therefore, the phase of the current detected by the first detecting means 7 and the phase of the voltage detected by the second detecting means 8 are compared by a phase difference detecting means indicated by 9, which will be explained next, and the output of the second detecting means 8 is When the output of the second detecting means 8 lags behind the output of the first detecting means 7, the triac 5 is kept conductive.
becomes non-conductive. That is, the phase difference detection means 9 is composed of the following. First, the voltage induced in the secondary winding of the transformer T is full-wave rectified by the full-wave rectifier circuit REC. Connect a resistor R ₆ and a capacitor C ₂ in series to the DC output side of the rectifier circuit REC. Transistors Q ₂ and Q ₃ form a Schmitt circuit, the base of transistor Q ₂ is connected to the other terminal of capacitor C ₂ via Zener diode ZD ₃ , and the emitter is connected to the other terminal of capacitor C ₂ . .
Connect the collector terminal of transistor _Q3 to the gate terminal of triac 5. In this circuit, if the voltage across the capacitor _C2 is higher than the Zener voltage of the Zener diode _ZD3 , the transistor _Q2 is conductive and the transistor _Q3 is non-conductive. When the transistor _Q3 is non-conductive, the triac 5 is non-conductive, so the starting capacitor 4 is disconnected from the power supply 1. Therefore, the first detection means 7
When the output of the second detection means 8 becomes earlier in phase than the output of the second detection means 8, the charging voltage of the capacitor _C2 may be made higher than the Zener voltage of the Zener diode _ZD3 . Conversely, when the output of the first detection means 7 is delayed in phase than the output of the second detection means 8, that is, at the beginning of startup, the transistor _Q3 must be rendered conductive. Then, tryack 5
connects the continuity state and the starting capacitor 4 connects to the power supply 1.
It will be connected to. To do this, the charging voltage of the capacitor C ₂ should be prevented from reaching the Zener voltage of the Zener diode ZD ₃ . Therefore,
In this embodiment, a thyristor THY is connected in parallel to the capacitor _C2 , and when the output of the first detection means 7 is delayed in phase than the output of the second detection means 8, the thyristor THY is made conductive and the phase is reversed. Then make the thyristor THY non-conductive. Therefore, the output of the first detection means 7 is connected to the transistor Q ₁
The output of the second detection means 8 is applied between the collector and emitter of the transistor _Q1 . In other words, the output of the first detection means 7 is applied to the transistor _Q1 before the output of the second detection means 8.
When the transistor _Q1 becomes conductive, no gate signal is applied to the thyristor THY. Conversely, the output of the first detection means 7 is higher than the output of the second detection means 8.
If the output of the second detection means 8 is delayed, the transistor _Q1 becomes non-conductive at the stage when the output of the second detection means 8 is input, and the gate signal is applied to the thyristor THY.

At the beginning of the start of the single-phase induction motor 2, when the phase of the output of the second detection means 8 is ahead of the phase of the output of the first detection means 7, the second detection means is activated before the transistor _Q1 becomes conductive. At the output of 7, the thyristor THY becomes conductive and the voltage of the capacitor _C2 does not rise to the Zener voltage of the Zener diode _ZD3 . Transistor Q ₂ is therefore non-conductive and transistor Q ₃ is conductive. Triac 5 therefore remains conductive. In this state, when the single-phase induction motor 2 accelerates and the phase of the output of the second detection means 8 lags behind the phase of the output of the first detection means 7, the transistor Q ₁ is activated before the output of the second detection means 8 is output.
becomes conductive depending on the output of the first detection means 7, and therefore the thyristor THY becomes non-conductive.
Therefore, transistor Q ₂ becomes conductive and transistor Q ₃ becomes non-conductive. As a result, the triax 5 becomes non-conducting and the single-phase induction motor 2 enters the operating state.

The transistor _Q4 turns on when the Zener diode _ZD3 becomes conductive, and even if for some reason the phase of the second detection means 8 leads the phase of the output of the first detection means 7, the triac 5 does not become conductive again. Do it like this. Note that R ₅ , R ₇ to R ₁₂ are resistors, and D ₂ and D ₃ are diodes.

The case where the power supply voltage is 200V has been described above, and next, the circuit operation when the power supply voltage is switched to 100V will be described.
FIG. 3 shows the vector relationship between the voltage and current at the beginning of starting the single-phase induction motor 2. That is, V ₁ , I ₁ are
These are the voltage and current vectors when 200V is supplied. As is clear from FIG. 3, the phase difference θ ₂ when feeding 100V is larger than the phase difference θ ₁ when feeding 200V. Therefore, even if the phase difference between the voltage and current changes due to a change in the power supply voltage, this control device can similarly detect the degree of recovery of the current phase according to the starting state of the single-phase induction motor. It must be equipped with the necessary functions. Therefore, in this control device, a Zener diode ZD ₁ is provided in the second detection means 8 as a compensation means for the phase difference so that the phase difference between the voltage and current at the beginning of startup remains almost constant even if the power supply voltage fluctuates. . That is, when 100V is supplied to the single-phase induction motor 2, a voltage waveform _V2 shown in FIG. 2 is obtained on the secondary side of the single-phase induction motor 2 via the transformer T. At this time, the output of the first detection means 7 is the current when 200V is supplied, as shown by _I2 at the beginning of the start.
I'm even further behind than ₁ . Further, as the starting progresses, the delay of the current I ₂ becomes smaller as shown by the current I' ₂ . However, this current _I'2 lags behind the current _I'1 . In the second detection means 8, the voltage waveform _V2 input via the transformer T is processed as follows. First, if we consider the case where there is no Zener diode ZD ₂ and capacitor C ₁ , the voltage at point A in Figure 1 is equal to the input voltage V ₂ as shown by VA ₂ in Figure 2.
rises to the Zener voltage Vzd ₁ of the Zener diode ZD ₁ with a delay. Naturally, the input voltage V ₂ rises to 200V
Since the input voltage V is less than ₁ when powered by
The time it takes to reach the Zener voltage Vzd ₁ is longer than when 200V is being supplied. Therefore, the rise of the voltage VA ₂ at point A is delayed from the rise of the voltage VA ₁ when 200V is supplied.
By adding a Zener diode ZD ₂ , the voltage at point A can be changed to the Zener voltage as shown by VA′ ₂ .
Regulated to VZD ₂ or less. Finally, when the voltage at point A is applied to the differential circuit, at point B, Vp ₂ in Figure 2
An output signal with the waveform shown is obtained. That is, at this stage, the phase difference θ' ₂ between the output I ₂ of the first detection means 7 and the output Vp ₂ of the second detection means 8 is equal to the output I ₁ of the first detection means 7 obtained when 200V is supplied. The phase difference θ' with the output Vp ₁ of the second detection means 8 is approximately equal to ₁ . Therefore, based on the output signals of both detection means 7 and 8, even when 100V power is supplied,
The auxiliary winding 3 of the single-phase induction motor 2 can be disconnected by controlling the triax 5 in the same way as when 200V power is supplied.

Furthermore, an example of another embodiment will be explained with reference to FIG. In this embodiment, the parts denoted by the same reference numerals as in FIG. 1 have the same functions, so a description thereof will be omitted.
Transistor Q ₅ is connected in parallel to capacitor C ₂ . That is, when the output of the first detection means 7 lags behind the output of the second detection means 8, the output of the second detection means 8 is applied to the base of the transistor _Q5 , and the transistor _Q5 becomes conductive. Therefore, when transistor _Q5 conducts, the capacitor
The voltage of _C2 does not rise to the Zener voltage of Zener diode _ZD3 , and as a result, transistor _Q2 becomes non-conductive, transistor _Q3 becomes conductive, and triac 5
will maintain a conductive state. Also, transistor Q ₆ operates similarly to transistor Q ₃ , so that
The base of this is connected to the collector of transistor _Q2 . The collector of this transistor Q ₆ is connected via the diode D ₄ to the base of the transistor Q ₁ . That is, this transistor
The circuit consisting of Q ₆ and the diode D ₄ always keeps the transistor Q ₁ conductive when the triax 5 is non-conducting, so that for some reason the phase of the second detection means 8 may lead the phase of the output of the first detection means 7. This is to prevent the triac 5 from becoming conductive again even if it happens. Note that R ₁₃ is a main winding constructed by dividing the resistors 6 ₁ and 6 ₂ into two. Further, since other circuit operations can be easily inferred based on the previously described embodiments, details will be omitted.

As is clear from the above description, the present invention includes a first detection means for detecting the phase of the current flowing into the induction motor, a second detection means for detecting the phase of the supplied voltage, and a comparison of the outputs of both detection means. However, when the induction motor is equipped with a phase difference detection means for controlling the variable impedance means connected to the induction motor, it is possible to reliably detect changes in the phase of the current even when the power supply voltage changes and the current delay becomes large. In order to delay the detection of the voltage phase by the amount of current delay corresponding to the change in the power supply voltage, the second detection means is configured to output an output when the power supply voltage rises to a predetermined voltage value. It is. Therefore, according to the present invention, even if the supplied voltage is changed in an induction motor with different voltage specifications, the induction motor can be continuously controlled without changing the circuit of the control device or adjusting the circuit conditions. I can go.

In the above description, a triac is used as the variable impedance means, but of course this can also be constructed from thyristors or transistors connected in antiparallel, or other relay circuits.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the control device of the present invention, Fig. 2 is a time chart, Fig. 3 is a vector diagram showing the relationship between voltage and current, and Fig. 4 is a circuit diagram showing another embodiment. It is. 2... Induction motor, 3... Auxiliary winding, 4... Capacitor, 5... Triax showing an example of variable impedance means, 7... First detection means, 8...
...Second detection means, 9...Phase difference detection means.

Claims (1)

[Claims] 1. A variable impedance means for controlling the primary or secondary side impedance of the induction motor, a first detection means for detecting the current phase of the current flowing into the induction motor, and a variable impedance means for controlling the primary or secondary side impedance of the induction motor; a second detection means for detecting a voltage phase when a predetermined constant value is reached; and a phase difference detection means for comparing a phase difference between the output of the first detection means and the output of the second detection means. A control device for an induction motor, characterized in that the variable impedance means is controlled by the output of the phase difference detection means. 2. A capacitor-started single-phase induction motor is used as the induction motor, and the variable impedance means is connected in series with the auxiliary winding and the starting capacitor of the capacitor-started single-phase induction motor and in parallel with the main winding. When the phase difference detection means outputs an output indicating that the output of the second detection means is ahead of the output of the first detection means, the impedance of the variable impedance means is reduced, and the impedance of the second detection means is reduced. When the phase difference detection means outputs an output indicating that the output lags behind the output of the first detection means, the impedance of the variable impedance means is increased. A control device for an induction motor according to scope 1. 3. A three-phase induction motor is used as the induction motor, the variable impedance means is provided on the primary side of the three-phase induction motor, and the output of the second detection means is ahead of the output of the first detection means. When the phase difference detection means outputs an output indicating that the variable impedance means has a smaller impedance, the output indicating that the output of the second detection means lags behind the output of the first detection means is outputted. 2. The control device for an induction motor according to claim 1, wherein the impedance of the variable impedance means is increased when the phase difference detection means is outputting the signal. 4. A three-phase induction motor is used as the induction motor, and the variable impedance means that can change the connection of the three-phase induction motor to Y and Δ is provided, and the output of the second detection means is determined by the output of the first detection means. When the phase difference detection means outputs an output indicating that the second detection means is advancing, the variable impedance means is controlled to connect the three-phase induction motor to Y, and the output of the second detection means A patent claim characterized in that when the phase difference detection means outputs an output indicating that the output is behind the output of the detection means, the variable impedance means is controlled to connect the three-phase induction motor to Δ. A control device for an induction motor according to item 1. 5. A wound three-phase induction motor is provided as the electric motor, and the variable impedance means is connected to the secondary side of the wound three-phase induction motor, and the output of the second detection means is higher than the output of the first detection means. When the phase difference detection means outputs an output indicating that the phase difference is progressing, the impedance of the variable impedance means is increased, and the output of the second detection means lags behind the output of the first detection means. 2. The control device for an induction motor according to claim 1, wherein the impedance of the variable impedance means is made small when the phase difference detection means outputs an output indicating .