JPH05168286A - Regeneratively braking method for inverter at power interruption - Google Patents

Abstract

PURPOSE:To smoothly and rapidly decelerate a motor by smoothly regeneratively braking an induction motor at the time of power interruption of a voltage type inverter with the motor as a load. CONSTITUTION:An inverter is set to an output interruption state for a predetermined period from the time of power interruption when a power source of the inverter is interrupted, and a negative slip frequency is provided while an output frequency of the inverter after a predetermined period is elapsed is being reduced at a predetermined time gradient responsive to decelerating characteristics of a motor from an initial value according to a predetermined relation with an output frequency and an output voltage at the time of occurring a power interruption as variables. And, its output voltage is increased from zero at a predetermined time gradient, and if the output voltage reaches a predetermined value of a predetermined proportional relation to the output frequency, it is then reduced together with the output frequency according to the proportional relation, or an output current constant control period for a predetermined period from the time point of end of the output interruption state is provided, thereby providing a smoothly regenerative braking of the motor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a regenerative braking method for a PWM type voltage source inverter which uses an induction motor as a load when the power source is interrupted.

[0002]

2. Description of the Related Art As a conventional regenerative braking method of this kind,
When the power supply of the inverter is interrupted, the output of the inverter is continuously cut off to put the load induction motor in a free run state to decelerate, and braking control by regenerative power from the motor is not performed, but the deceleration pattern. Is known as shown in the operation waveform diagram of FIG. FIG. 4A is an operation waveform diagram of the rotation speed N of the electric motor driven by the inverter with respect to time (t).
It is shown that the electric motor decelerates in a free run state from ₀ to the power recovery time t ₄ . The amount of decrease in the rotational speed at time t ₄ from the rotational speed N _u before the power failure occurs as shown in the drawing is small. 4B is an operation waveform diagram of the DC intermediate voltage V _dc of the inverter corresponding to the power failure and the power recovery of the power source at the time t ₀ and the time t ₄ . 7 shows a pattern of changes in V _dc with respect to a value V _s when the power supply voltage is normal.

[0003]

However, according to the conventional method of decelerating the load induction motor by the free run as described above, the required stop time of the electric motor becomes long, and if the electric motor is operating at a high speed. If this is the case, there is a risk of maintenance due to the high-speed free-run state and the occurrence of malfunctions in the mechanical system. In view of this, the present invention provides
It is an object of the present invention to provide a braking method capable of smoothly and promptly decelerating the electric motor of the load induction motor regardless of the operating state of the load induction motor when a power failure occurs.

[0004]

In order to achieve the above object, an inverter regenerative braking method at the time of power failure of the present invention comprises:
If a power failure occurs in the AC power supply during operation of the PWM voltage source inverter using the induction motor as a load, the inverter
Whether the power is in a state of regenerating electric power from the electric motor is determined from an increase / decrease change in the DC intermediate voltage, and if it is in the regenerative state, the state is continued to decelerate the electric motor, and if If it is not in the regenerative state, the inverter is temporarily cut off for a predetermined period after the power failure occurs, and the output frequency of the inverter output after the predetermined period elapses is output at the time of the power failure. While decreasing the output voltage at a predetermined time gradient corresponding to the deceleration characteristic of the electric motor from an initial value in accordance with a predetermined functional relationship in which the frequency and the output voltage are variables, and increasing the output voltage from zero at a predetermined time gradient. When the output voltage reaches a value that is in a predetermined proportional relationship with the output frequency, the output voltage may be decreased together with the output frequency according to the proportional relationship, or If the power regeneration state is not as described above at the time of the power failure, the inverter is temporarily turned off for a predetermined first period from the time of the power failure, and the inverter output after the predetermined period has elapsed. The output frequency has an initial value according to a predetermined functional relationship in which the output frequency and the output voltage at the time of occurrence of the power outage are variables, and the output voltage is controlled to control the output voltage over a predetermined second period. The output current of the inverter is controlled to be constant, and the output frequency of the inverter is reduced with a predetermined time gradient corresponding to the deceleration characteristic of the electric motor with the value at the end point as a starting point at the end of the second period. After that, the output voltage of the motor is reduced in a predetermined proportional relationship with the output frequency so as to brake the electric motor, and the output disconnection state of the inverter is terminated. Regarding the predetermined functional relationship regarding the frequency initial value in the output frequency control, the initial value is not stepwise reduced by a predetermined value from the output frequency at the time of occurrence of the power failure, and the reduced predetermined value is appropriate. A value obtained by multiplying the ratio of the output voltage at the time of occurrence of the power failure to the maximum value of the output voltage of the inverter from the set first frequency set value by the second frequency set value appropriately set. And the second frequency setting value is selected to be smaller than the first frequency setting value.

[0005]

In general, regenerative braking of an induction motor is possible by regenerating the AC excitation input of the motor with a negative slip frequency and regenerating the rotational energy of the motor as electric power to the power source side. Therefore, when the drive power source of the motor is a voltage source inverter, the output AC frequency is controlled to be smaller than the frequency corresponding to the actual rotation speed of the motor, and the input DC power source side of the inverter is controlled. The regenerative braking can be performed by absorbing the regenerative electric power of.
Further, during the regenerative braking as described above, in order to ensure the normal operation of the inverter, it is necessary that the main circuit voltage and the control voltage thereof, that is, the DC intermediate voltage thereof be ensured to be a predetermined value or more in the required braking range. Therefore, at the time of regenerative braking by the inverter at the time of the AC power failure, the negative power is compensated for by the regenerative power from the electric motor, and a uniform braking is performed by performing uniform power regeneration. It is necessary to control the value of the slip frequency.

In accordance with the above, according to the present invention, the output frequency of the inverter is controlled to be smaller than the frequency corresponding to the actual rotation speed of the induction motor and is controlled to be reduced with a predetermined time gradient corresponding to the deceleration characteristic of the motor. The output voltage is also controlled in conjunction with the output frequency to absorb the regenerative power, and further, in order to avoid a sudden decrease in the DC intermediate voltage immediately after the power failure occurs, the inverter is operated for a predetermined period from the power failure occurrence time. Shut off the output of the
The inverter is operated for a predetermined period after the release of the output cutoff.
The output current of the motor is controlled at a constant level to facilitate the transition to deceleration by the frequency reduction control.

By the way, the inverter to be reduced and controlled as described above.
The time characteristics of the output frequency f _i are based on the following relational expressions (1) and (2). f _i = (f _i0 −Δf) − (f _im / T) · t (1) Δf = f _s1 − (V _i0 / V _im ) · f _s2 ……………… ( 2) Here, the time t is not zero at the frequency reduction control start time point after the release of the inverter output cutoff, f _i0 is the f _i value at the time of the power failure, f _im is the maximum value of f _i ,
f _s1 and f _s2 are appropriately set first and second frequency set values, V _i0 is the inverter output voltage at the time of the power failure, and V _im is the maximum value of the inverter output voltage. , T is the deceleration setting time. Further, Δf is a predetermined reduction value that should be stepwise subtracted from the f _i0 in order to determine the initial frequency value at the start of the frequency reduction control,
It is selected such that f _s1 > f _s2 . Therefore, the Δf is the V
It becomes smaller as _i0 increases. Note that the frequency reduction control according to the above equation (1) is continuous control with respect to time t,
In addition, a small frequency change (f _im / T).
Even in the step-like control in which Δt is formed and the average time gradient thereof is negative f _im / T, the same braking result can be obtained by proper selection of Δt.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will now be described with reference to FIGS. 1 and 2 which are various operation waveform diagrams showing a braking control pattern of a voltage source inverter having a load on an induction motor when a power failure occurs in the motor. A description will be given according to each figure in FIG. First, (a) in FIG.
Is an operation waveform diagram of the rotation speed N of the electric motor with respect to time t. Times t ₀ and t ₄ respectively indicate a power failure and a power recovery of the power source, and a time t ₁ is an inverter from the time t _0. −
Indicates the end point of output control. N _s is a control command value for the rotation speed N between times t ₁ and t _4, and corresponds to the output frequency f _i of the inverter according to the above relational expressions (1) and (2). , ΔN _s is a rotation speed reduction predetermined value corresponding to the frequency reduction predetermined value Δf according to the relational expression (2), N _u is the rotation speed during steady operation before the occurrence of the power failure, and N _d1 is This is the value of the decelerated rotation speed at time t ₄ . As shown in the figure, the electric motor is brought into a free run state between the time points t ₀ and t ₁ and slightly decelerated, and the actual rotational speed N is lower than the command value N _s between the time points t ₁ and t _4. When it becomes large, the electric motor is subjected to AC excitation having a negative slip frequency, the electric power is regenerated according to the slip frequency, and the electric motor is decelerated. It should be noted that the above-described rotation speed N in the power recovery state after time t ₄
And illustrated the change pattern with its command value N _s is shows an example thereof, the magnitude relation of the both have reversed the motor is gradually restored to the rotational speed N _u of accelerated enters the power running state said.

Next, FIG. 1B shows the DC intermediate voltage V _dc of the inverter corresponding to the state change at each time.
FIG. 7 is a time-dependent operation waveform diagram showing the change pattern of the voltage V _dc with respect to the value V _s when the power supply voltage is normal. Achieve adequate reduction of the voltage V avoiding a significant reduction of _dc and the rotational speed N by performing moderate power regeneration deviation forms a negative appropriate amount of a double amount N and N _s of the as shown be able to. Further, FIG. 1C shows a detection signal L of the power failure.
A change pattern in which V becomes an ON state in which the signal level becomes H when the power supply voltage is detected at time t ₀ , and an OFF state in which the signal level becomes L when the power recovery is detected at time t ₄ Is.

Next, both (a) and (b) of FIG. 2 correspond to both of (a) and (b) of FIG. ₁ , respectively, which correspond to time t ₁ and time t ₄ respectively. set from t ₁ to time t ₂ after a predetermined time, the viz in the predetermined period inverter - said in a predetermined period after the output unblocking of data inverter -
2C is an operation waveform diagram when the output current constant control of the data is performed, and FIG. 2C is the same as FIG. 1C. N _d2 is the value of the decelerated rotation speed at time t ₄ . Further, in the constant output current control of the inverter, the initial value of the output frequency command value at the control start time point at time t ₁ is set to the value (f _i0 −Δ) in the relational expression (1).
f), and thereafter, a predetermined output current control is performed while maintaining the ratio of the output voltage to the output frequency at a predetermined value, and smoothing the transition to deceleration by the frequency reduction control by stabilizing the regenerative power. At the same time, the DC intermediate voltage is stabilized.

[0011] FIG. 3 is the inverter between times t ₁ and t ₄ of FIG. 1 (a) - is an operation waveform diagram showing a control pattern of the motor output voltage V _i, after a predetermined time has elapsed from the time t ₁ the time t ₃ of the provided shows the case where the voltage controlled as a command value V _iS with respect to the voltage V _i to illustrate the command value V _is2 shown solid in dotted lines. Times t ₁ and t as shown
_{During the} period of ₃ , the command value V _is2 uniformly increases from zero in time. Incidentally illustrated one-dot chain line is inverted according to the command value V _IS is the relationship (1) - is indicative of the command value V _is1 that assumed as being proportional to the data output frequency f _i,
The voltage V _i is controlled in accordance with the command value V _is1 after the time t ₃ which gives a time point when the both command values V _is1 and V _is2 become equal. _Further , the stepwise change amount ΔN _s / K of the command value V _is1 at time t ₁ corresponds to the sudden change command value Δf of the output frequency f _i according to the relational expression (2), and the K is a proportional constant. Is. As shown in FIGS. 1 to 3, by appropriately setting the command values for the output frequency and the output voltage, smooth regenerative braking of the load induction motor by the inverter after the power failure is achieved.

[0012]

According to the present invention, when a power failure occurs in the AC power supply during the operation of the PWM type voltage source inverter using the induction motor as a load, the inverter is operated for a predetermined period from the time of the power failure. -Turn off the output once,
The output frequency of the inverter output after the lapse of the predetermined period is determined according to a predetermined functional relationship in which the output frequency and the output voltage at the time of occurrence of the power outage are variables, and the output frequency is suddenly reduced in a stepwise manner from the output frequency at the time of the outage. From the initial value at a predetermined time gradient corresponding to the deceleration characteristic of the electric motor, and the output voltage is increased from zero at a predetermined time gradient, and the output voltage has a predetermined proportional relationship with the output frequency. When a certain value is reached, the output frequency is then reduced according to the proportional relationship, or the output voltage is given the initial value for the output control after the output disconnection state of the inverter. By controlling the constant output current of the inverter, which is controlled together with the control over a predetermined period, the operation state before the occurrence of the power failure can be determined. Nevertheless, regenerative braking of the load induction motor by the inverter can be performed to achieve smooth and quick deceleration, and there is a risk of maintenance due to the occurrence of a high speed free run state of the motor and a malfunction to the mechanical system. Can be avoided.

[Brief description of drawings]

FIG. 1 is an operation waveform diagram of regenerative braking at power failure of an inverter showing a first embodiment of the present invention.

FIG. 2 is an operation waveform diagram of regenerative braking at the time of power failure of the inverter showing the second embodiment of the present invention.

FIG. 3 is an operation waveform diagram of an inverter output voltage corresponding to FIG.

FIG. 4 is an operation waveform diagram of braking during power failure of an inverter showing an embodiment of the prior art.

[Explanation of symbols]

LV Power failure detection signal N Induction motor speed N _d1 Induction motor speed at power recovery N _d2 Induction motor speed at power recovery N _s Induction motor speed command value N _u Induction at power failure motor speed .DELTA.N _s rotational speed of the stepwise reduction predetermined value V _i inverter - motor output voltage V _IS inverters - command value t ₀ power outage occurrence time t ₁ inverter of motor output voltage - motor load drops control end time t ₂ inverter - data output current constant control end time t ₃ inverter - motor output voltage uniform increase control end time t ₄ power power recovery time

Claims (3)

[Claims] 1. When a power failure occurs in the AC power supply during operation of a PWM type voltage source inverter using an induction motor as a load, it is determined whether the inverter is in a state of regenerating electric power from the motor. Judging from the increase / decrease change in the DC intermediate voltage, if in the regenerative state, continue that state to continue decelerating the motor, and if not in the regenerative state, continue for a predetermined period from the time of occurrence of the power outage. An initial value according to a predetermined functional relationship in which the output frequency of the inverter output after the lapse of the predetermined period is set to the output frequency and the output voltage at the time of occurrence of the power outage as variables. To a predetermined time gradient corresponding to the deceleration characteristic of the electric motor, and its output voltage is increased from zero to a predetermined time gradient, and the output voltage is The predetermined hereafter Once you reach a certain value proportional the ratio of the power supply during a power failure, characterized in that to achieve the braking of the motor is reduced with the output frequency according to the relation inverter - motor regenerative braking method. 2. When a power failure occurs in the AC power supply during the operation of a PWM type voltage source inverter using an induction motor as a load, it is determined whether the inverter is in a state of regenerating electric power from the motor. Judging from the increase / decrease change in the DC intermediate voltage, if in the regenerative state, continue the state to continue decelerating the electric motor, and if not in the regenerative state, the predetermined first from the time of occurrence of the power outage. The output of the inverter is temporarily cut off for a period of, and the output frequency of the output of the inverter after the predetermined period has a predetermined functional relationship with the output frequency and the output voltage at the time of occurrence of the power outage as variables. The output voltage of the inverter is controlled to be constant over a predetermined second period by controlling the output voltage of the inverter and the end of the second period. Starting from the value at the point, the output frequency of the inverter is reduced with a predetermined time gradient corresponding to the deceleration characteristic of the electric motor, and the output voltage is reduced together with the output frequency in a predetermined proportional relationship. An inverter regenerative braking method at the time of power failure, which is characterized by braking an electric motor. 3. The inverter regenerative braking method at the time of power failure in accordance with claim 1 or claim 2, wherein a predetermined functional relationship relating to an initial frequency value in output frequency control of the inverter after the output disconnection state is completed. With respect to the above, the initial value is stepwise reduced by a predetermined value from the output frequency at the time of occurrence of the power outage, and the predetermined reduction value is set from the appropriately set first frequency set value to the inverter frequency. The value obtained by multiplying the ratio of the output voltage at the time of occurrence of the power failure to the maximum value of the output voltage of the power supply by the second frequency set value set appropriately, and the second frequency set value. Is smaller than the first frequency setting value. An inverter regenerative braking method at the time of power failure.