JPH11341882A - Controller for ac motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To permit an AC motor to be controlled until its speed reaches zero by inhibiting the operation of a trip detecting means over a prescribed time, when the detected DC intermediate voltage of a power converter drops to an undervoltage trip level, thereby preventing the interrupt of an output regardless of whether a load is heavy or light in the event of power failure. SOLUTION: If power failure occurs, a DC intermediate voltage detecting value Edc is reduced transiently due to delayed operation of a PI investigator 22 and reaches a trip level E2 or lower after prescribed time elapses. After a prescribed time has elapsed, undervoltage recovers to a higher value than the trip level E2 . If power supply voltage during power failure becomes lower than an instantaneous level E1 , the output of a voltage detector 20 changes from a high level into a low level. When it reaches the low level, a time counter 26 is started, the output reaches the high level during a prescribed time, and a switch 29 is released to inhibit a trip circuit 27 from operating. Thus output of an electric power converter 11 can be prevented from being interrupted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for continuing the operation of an AC motor during a momentary power failure without free-running (in which frequency control becomes impossible and speed control is not performed). The present invention relates to a control device for an AC motor.

[0002]

2. Description of the Related Art A variable frequency variable voltage power supply (VVVF) is
Since it enables high-precision speed control of AC motors such as induction motors and synchronous motors, it has been used in a wide range of industries. The variable frequency variable voltage power supply
Generally, AC power of a commercial frequency is once converted to DC power by a rectifier circuit, and then converted back to AC power of a variable frequency and a variable voltage by an inverter circuit.
By the way, as is well known, a commercial power supply suffers an instantaneous power failure due to various causes. Therefore, a variable frequency variable voltage power supply, that is, a power converter is required to take measures against an instantaneous power failure of a commercial frequency power supply.

When an instantaneous power failure occurs, the output of the power converter is generally cut off (tripped) by detecting a voltage drop. When the power converter trips,
The speed control of the AC motor by the variable frequency variable voltage power supply is not performed, and a so-called free-run state occurs.
However, as in the case of driving an AC motor for a spinning machine or the like, it may be necessary to prevent free-running of the motor even at the time of an instantaneous power failure, and to continue the operation to zero speed by using the operating energy.

FIG. 6 shows an example of such a conventional AC motor control device. During a momentary power failure occurs, detects that the power voltage by the voltage detector 20 drops below the instantaneous power failure level E _1, by closing the switch 25 acceleration calculator (HLR) to bypass the 24. Then, by operating the PI adjuster 22 so as to keep the DC intermediate voltage detection value _Edc constant, the frequency command value f ^** is immediately reduced, the motor is decelerated, and the motor is controlled to zero speed. I have. In FIG. 6, reference numeral 23 denotes a frequency command value f ^*.
Subtractor for calculating a deviation between the output of the PI controller 22 and the output of the PI controller 22, 27
Is a trip detection circuit; 28 is a voltage detector that compares the DC intermediate voltage detection value E _dc with an undervoltage trip level E ₂ ;
Reference numeral 9 denotes a switch that is turned off by the output of the voltage detector 20, and reference numeral 30 denotes a rectifier circuit.

[0005]

At a light load, assuming that the power supply is interrupted at time t _{1 as} shown in FIG. 7, the DC intermediate voltage E _dc fluctuates for a while immediately after that and then decreases after time t _7. , below the undervoltage trip level E ₂ at the time t _8. In this case, the decrease of the DC intermediate voltage E _dc is slow, and the constant DC intermediate voltage control by the PI controller 22 is possible. However, at the time of heavy load, as shown in FIG. 8, the DC intermediate voltage E _dc is below undervoltage trip level E ₂ at time t _9, the power converter to the output blocking. For this reason, the motor cannot be controlled to zero speed.

Accordingly, the present invention is to provide a control device for an AC motor capable of preventing the power converter from shutting down the output regardless of the load of the load and controlling the motor to zero speed when a power failure occurs. It is assumed that.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, an invention according to claim 1 is a power converter for supplying a variable frequency power to an AC motor for driving a load, and a DC intermediate between the power converter and the DC converter. Means for detecting a voltage; frequency command adjusting means for adjusting a frequency command value to the power converter so that the detected value of the DC intermediate voltage matches the command value; and A trip detection unit that shuts off the output of the power converter when the power supply drops, and a trip detection prohibition unit that prohibits the operation of the trip detection unit for a predetermined time when a power outage is detected.
It is provided with.

According to the present invention, even when the DC intermediate voltage drops to the undervoltage trip level transiently due to the control delay of the frequency command adjusting means when a power failure occurs, the operation of the trip detecting means is maintained for a predetermined time. prohibited. Therefore, the AC motor can be controlled to zero speed without interrupting the output of the power converter.

According to a second aspect of the present invention, the control device for an AC motor according to the first aspect further comprises means for correcting the frequency command value according to the load amount when a power failure of the power supply is detected.

According to the present invention, by setting the frequency correction amount so that the frequency command value becomes smaller as the load becomes heavier, the frequency command value is corrected. Energy is regenerated to the DC circuit of the power converter to prevent the DC intermediate voltage from dropping to an undervoltage trip level. Thus, the AC motor can be controlled to zero speed without interrupting the output of the power converter.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a drive system of an AC motor to which the first embodiment of the present invention is applied, and FIG. 2 shows a control device of the AC motor according to the embodiment. This embodiment corresponds to the first embodiment of the present invention.

In FIG. 1, AC power from a commercial frequency power supply 10 is converted into AC power of a desired frequency by a power converter 11 and supplied to an AC motor (induction motor) 12. The load 13 is an industrial machine such as a spinning machine, and is driven by the electric motor 12. The power converter 11 includes a rectifier circuit 15, a smoothing capacitor 16, and an inverter 17.

In the control device shown in FIG. 2, a voltage detector 20 is a rectifier circuit 3 in the control device to which a power supply voltage is applied.
0 of the output voltage is compared with the instantaneous power failure level E _1. Here, unlike the rectifier circuit 15 of the main circuit, the rectifier circuit 30 does not include a smoothing capacitor, and the output voltage of the rectifier circuit 30 immediately decreases with a power outage. The voltage detector 20, when the power supply voltage is higher than the momentary power failure level E _1, which outputs a high level signal, the power supply voltage conversely outputs a low level signal falls below a momentary power failure level E ₁ It is.

On the other hand, the subtracter 21 outputs a deviation between the DC intermediate voltage detection value _Edc and the DC intermediate voltage command value _Edc ^* .
PI regulator 22 is a regulator by the proportional integral element, and outputs a frequency correction value f _c for the deviation to zero.
Subtractor 23 subtracts the frequency correction value f _c from the frequency command value f ^*, and provides the deviation acceleration calculator (HLR) 24. Acceleration / deceleration calculator 24 outputs frequency command value f ^** to the speed control system of power converter 11. This acceleration / deceleration calculator 24
Operates so that the output of the power converter 11 reaches the set frequency in a preset time.

The switch 25 is always off, and is turned on when the output of the voltage detector 20 changes from a high level to a low level. Thus, the acceleration / deceleration calculator 24
The operation is canceled by bypassing between the input and output of.
The time counter 26 is activated when the output of the voltage detector 20 goes low, and turns off the switch 29 for a set time (T ₁ in FIG. 3 described later). 6, both ends of the switch 29 are connected to the trip detection circuit 27 and the output side of the voltage detector 28. Here, the voltage detector 20, the time counter 26 and the switch 29 constitute trip detection inhibiting means.

Next, the operation of this embodiment will be described with reference to the timing chart of FIG. FIG.
(A), the voltage of the power supply voltage or a commercial frequency power source 10 (e.g., the effective value 200V) indicates, indicating that a power failure occurs at time t _1. FIG. 3B shows a DC intermediate voltage detection value E _dc of the main circuit (for example, 200 in normal times).
V × √2 ≒ 280 V), and the detected value E
_dc is transiently decreased by the operation delay of the PI regulator 22, between time t ₂ of t _3, undervoltage trip level E ₂
(For example, 230 V) or less. Then, time t ₃ thereafter, to recover the undervoltage trip level E ₂ or more.

FIG. 3C shows a frequency command value f ^* before adjustment ^.
And the frequency command value f ^** after the adjustment. Although prior to modulation of the frequency command value f ^* is constant, for constant control of the DC intermediate voltage E _dc by PI controller 22, the frequency command value f ^** At time t ₁ after, gradually decreases with time, Time t ₅
It becomes zero at. That is, by lowering the frequency command value f ^** , the AC motor 12 is decelerated, and its energy is regenerated by the inverter 17 of FIG. 1 so that the DC intermediate voltage _Edc is maintained constant. Incidentally, at time t _5, the speed of the AC motor 12 becomes zero.

[0018] FIG. 3 (d) shows the output of the voltage detector 20, the output is a power failure at time t _1,
When the power supply voltage falls below the instantaneous power failure level E ₁ (for example, 100 V), the power supply voltage changes from a high level to a low level. FIG.
(E) shows the output of the time counter 26, and the time t ₁
Between the set time T ₁ of the up t _4, the output becomes a high level, to prohibit the operation of the trip detection circuit 27 by opening the switch 29.

FIG. 3F shows an acceleration / deceleration calculator (HLR) 2
The state of _No. 4 is shown. At time t1, the switch 25 changes from the OFF state to the ON state, and the operation of the acceleration / deceleration calculator 24 is canceled. That is, HLR cancellation is turned on. Figure 3 (g), the DC undervoltage indicates an alarm, to turn on the alarm when trip time t ₆ after the power converter 11. Here, as is the alarm lighting circuit not shown in FIG. 2, for lighting the alarm to the DC intermediate voltage E _dc undervoltage trip level E ₂ period other than the setting time T ₁ a time period of less May be configured. Note that the voltage detector 20 and the time counter 26
There is a slight time delay before the output of the switch 25 and the state of the switch 25 are reversed. It is assumed that this delay is negligible.

At a point before time t _{1 in} FIG.
The power converter 11 is operating normally, and the DC intermediate voltage detection value _Edc does not decrease, and the DC intermediate voltage command value _Edc ^*
Matches. Therefore, the frequency command value f ^* is not subject to correction by the frequency correction value f _c. At this time, switch 2
Reference numeral 5 denotes an off state, and the acceleration / deceleration calculator 24 outputs a frequency command value f ^** .

When a power failure occurs at time t ₁ , FIG.
As shown in (b), the DC intermediate voltage detection value _Edc starts to decrease. As a result, the DC intermediate voltage detection value E _dc and the command value E _dc
^* Deviation between occurs, PI regulator 22 operates to the deviation to zero, it outputs the frequency correction value f _c. This frequency correction value f _c, decreases the frequency command value f ^**. In other words, the kinetic energy of the AC motor 12 is reduced by decreasing the frequency command value f ^**.
7 to operate to maintain the DC intermediate voltage _Edc constant.

[0022] However, in practice due to the operation delay in the PI controller 22, immediately can not be maintained DC intermediate voltage E _dc constant is maintained constant at a later time than the time t _4. Further, after time t ₁ , the output of the time counter 26 is at the high level during the set time T ₁ , so that the operation of the trip detection circuit 27 is prohibited during this time, and the output cutoff of the power converter 11 is prevented. At the same time, the DC undervoltage alarm remains off. At the same time, the time t ₁ thereafter switch 25 is turned on, the operation of the acceleration and deceleration calculator 24 is canceled.

If the set time T ₁ of the time counter 26 is set long enough to include the period from the time t ₂ to the time t ₃ , the output cutoff of the power converter 11 immediately after the occurrence of the power failure is prevented. The set time T ₁ is determined from the response characteristics of the control system. At time t ₄ after the set time T ₁ is completed, while maintaining higher than the DC intermediate voltage E _dc undervoltage trip level E _2, will reduce the frequency command value f ^**, at time t _5, The frequency command value f ^** becomes zero.

As described above, in the present embodiment, the AC motor 12 is controlled to zero speed without interrupting the output of the power converter 11. When the AC motor 12 is stopped at time t _5, the DC intermediate voltage E _dc Since energy is eliminated regenerated is gradually reduced in a subsequent time t _6, it reaches the undervoltage trip level E ₂ again. Therefore, this time t ₆ after, DC undervoltage alarm is turned on.

According to this embodiment, after the power failure is detected by the voltage detector 20, the set time T by the time counter 26 is set.
_Since the operation of the trip detection circuit 27 is prohibited during the period of _1, the DC intermediate voltage E
If _{the dc} becomes undervoltage trip level E ₂ less transiently also without interrupting the output of the power converter 11, the AC motor 12 is controlled to zero speed.

Next, a second embodiment of the present invention will be described with reference to FIGS. The same components as those in the embodiment shown in FIG. 2 are denoted by the same reference numerals, and the detailed description will be omitted. This embodiment corresponds to the second embodiment of the present invention.

First, referring to FIG.
0 is a frequency correction value f _d set in advance according to the load amount.
Is output. Specifically, as the load becomes heavier, and is configured to output a larger correction value f _d. When a power failure occurs, the output of the voltage detector 20 causes the switch 41 on the output side of the frequency correction calculator 40 to switch to the switch 25.
Turned with the frequency correction value f _d is given by the shown polarity to the subtracter 42.

Therefore, the frequency command value f ^* is
In addition to the subtraction of the frequency correction value f _c , the frequency correction value f _d is further subtracted by the subtractor 42 to become the frequency command value f ^** . The operations of the time counter 26, the trip detection circuit 27, the switch 29 and the like are the same as those in the embodiment shown in FIG.

Next, the operation of this embodiment will be described with reference to FIG. When a power failure occurs at time t _1, the output of the voltage detector 20 becomes low level, and turns on the switch 25 to cancel the operation of the acceleration and deceleration calculator (HLR) 24. At the same time, the switch 41 is turned on is started to correct the frequency command value by subtracting the frequency correction value f _d, the frequency command value f ^** gradually decreases toward zero speed.

[0030] Thus, energy regenerating increases, the DC intermediate voltage detection value without E _dc drops to undervoltage trip level E _2, the AC motor 12 is controlled to zero speed. Therefore, according to this embodiment, even when a power failure occurs during a heavy load, the frequency command value f ^** rapidly decreases, and the output of the power converter 11 is not interrupted. Can control up to speed.

The frequency correction value _fd is supposed to be increased as the load becomes heavier. However, there is a risk of tripping when the load is heavy, so that the frequency correction value fd is set only when the load amount is equal to or more than a predetermined value. The arithmetic unit 40 may be operated. Further, the frequency correction value f _d may be a constant value corresponding to an assumed heavy load.

[0032]

As described above, according to the present invention, when a power failure occurs, it is possible to prevent the power converter from shutting off the output regardless of the load, and to control the motor to zero speed. A control device for an AC motor can be provided. Therefore, the operation can be continued without causing the spinning AC motor or the like to coast free at the moment of an instantaneous power failure.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration example of a system that drives an AC motor by a power converter.

FIG. 2 is a block diagram illustrating a configuration of a first exemplary embodiment of the present invention.

FIG. 3 is a timing chart showing the operation of the device of FIG. 2;

FIG. 4 is a block diagram showing a configuration of a second embodiment of the present invention.

FIG. 5 is a timing chart showing the operation of the device of FIG.

FIG. 6 is a block diagram showing a configuration of a conventional technique.

FIG. 7 is a timing chart showing an operation at a light load in FIG. 6;

FIG. 8 is a timing chart showing an operation at a heavy load in FIG. 6;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Commercial frequency power supply 11 Power converter 12 AC motor 13 Load 15, 30 Rectifier circuit 16 Smoothing capacitor 17 Inverter 20, 28 Voltage detector 21, 23, 42 Subtractor 22 PI adjuster 24 Acceleration / deceleration calculator (HLR) 25, 29, 41 switch 26 time counter 27 trip detection circuit 40 frequency correction calculator

Claims (2)

[Claims] 1. A power converter for supplying variable frequency power to an AC motor for driving a load, means for detecting a DC intermediate voltage of the power converter, and a DC intermediate voltage detection value matching a command value. Frequency command adjusting means for adjusting a frequency command value to the power converter; trip detecting means for shutting off the output of the power converter when the DC intermediate voltage drops to an undervoltage trip level; And a trip detection inhibiting means for inhibiting the operation of the trip detecting means for a predetermined time when the power failure is detected. 2. The control device for an AC motor according to claim 1, further comprising means for correcting the frequency command value according to a load amount when a power failure of the power supply is detected.