JP3362753B2 - Inverter-driven induction motor braking method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a braking method for an inverter drive (including a servo drive) which controls the speed of a three-phase induction motor by a PWM method.

[0002]

2. Description of the Related Art When an induction motor being driven by an inverter is braked, mechanical energy stored in an inertia moment of a rotor and a load as an induction generator is converted into electric energy and regenerated on a DC bus side of an inverter circuit. To be done. At this time, the regenerated electric energy raises the DC bus voltage as shown in FIG. 5 (a), leading to an overvoltage abnormality, and the protection circuit of the inverter device operates to enter the free-run state. If deceleration is attempted without this, the time required for deceleration becomes extremely long as shown in FIG. 5 (b). In order to prevent this, a resistor and a semiconductor switching element are installed between the DC buses as shown in FIG. 6, and when the voltage value detected by the DC voltage detection circuit exceeds the overvoltage level, the semiconductor switching element is turned on. Then, by supplying a regenerative current, the resistor consumes energy as heat,
The control is performed so as not to exceed the overvoltage level (conventional example 1).

Further, as a method of consuming the energy of the load in the rotor and not returning it to the inverter side, the DC braking in which a DC current is passed through the induction motor stator for braking, and the phase rotation direction of the applied voltage are changed. Reverse phase braking, which is the reverse, has been used for a long time (conventional example 2). On the other hand, JP-A-6-16
No. 5582 discloses an inverter device for quick stop control (conventional example 3). That is, in a voltage source inverter device that drives an induction motor, after starting deceleration of the induction motor, current value determination means for determining that the detected value of the inverter output current does not exceed a predetermined current limit value, and this detected value is When the current value determination means determines that the current value does not exceed the predetermined current limit value, the phase control means that stops the advance of the phase of the inverter output PWM voltage and the current value determination when the detected value does not exceed the predetermined current limit value. And an arm switching means for switching the inverter output arm to the return state when the means determines.
Further, after the deceleration of the induction motor is started, the speed judgment means for judging that the rotation speed of the induction motor has become equal to or lower than the predetermined rotation speed, and the speed judgment means for judging that the rotation speed of the induction motor has become equal to or lower than the predetermined rotation speed. If determined, it has a DC braking means for applying DC to the induction motor.

Further, Japanese Examined Patent Publication No. 63-20116 discloses a braking device when an induction motor driving an elevator by an inverter is under heavy load reduction, light load increase or deceleration (conventional example 4). That is, in these cases, the mechanical energy of the load is converted into electrical energy by the power generation action of the induction motor and returned to the DC side through the inverter, which causes an excessive increase in the DC side voltage as described above. Therefore, in order to prevent this regenerated power from being consumed inside the motor and returned to the inverter DC side, in the above case, the absolute value of the slip of the induction motor is r ₂ / (r ₁ + g ₀ Z
The output frequency of the inverter is controlled so that it becomes larger than the value determined by ² ) (however, the primary resistance value of the induction motor is r ₁ , the secondary resistance value is r ₂ , and the excitation conductance is g.
₀ , and the total inductance is Z). That is, by lowering the inverter output frequency below the frequency corresponding to this slip value, the motor input becomes positive, and regenerative power to the DC side can be suppressed.

[0005]

However, in the conventional example 1, the resistor for processing energy and the control circuit thereof are obstacles to miniaturization. Further, in the DC braking of Conventional Example 2, although the braking torque on the verge of stopping is large, the average braking torque is extremely small. Further, in the anti-phase braking, it is necessary to detect the time when the speed becomes zero by some method. The conventional example 3 is an inverter device that stops the progress of the phase of the inverter output PWM voltage when the current limit value is not exceeded and switches the inverter output arm to the return state. Furthermore, the rotation speed of the induction motor is predetermined. Since it is a device having a DC braking means when the rotation speed is less than or equal to, it is a rapid stopping means under the condition that the logical product of the limiting values that do not exceed the respective predetermined values of the DC bus voltage and the load current is taken, The control circuit is complicated and is not suitable for the purpose of downsizing the device.

In Conventional Example 4, a speed detector for obtaining the rotation speed of the electric motor is required, and the advantage of the induction motor that the structure is simple and robust is impaired. Therefore, an object of the present invention is to provide a braking method for an inverter-driven AC electric motor in which all the obstacles of these conventional examples are eliminated.

[0007]

The braking method for an induction motor according to the present invention utilizes the characteristics of the induction motor to determine the total amount of regenerative energy in which the mechanical energy of the load and the rotor during braking is regenerated as electric energy. The loss is consumed as a loss in the electric motor and is not regenerated to the driving inverter side, thereby preventing a rise in the DC bus voltage of the inverter. That is, when a deceleration command is received when shifting to deceleration, first the output frequency is once reduced to a predetermined frequency, and then the output frequency is increased at a predetermined increase rate while detecting and monitoring the DC bus current or DC bus voltage. When it is detected that the regeneration of energy from the electric motor to the inverter has started from the direction of the DC bus current or the rise of the DC bus voltage, the output frequency is decreased at a predetermined decrease rate, and during deceleration, it is always A means for decelerating the electric motor is used by suppressing the regeneration to the inverter by consuming all the regenerative energy in the electric motor.

[0008]

The operation of the present invention will be described with reference to FIG. FIG. 2 is a known induction motor characteristic diagram, in which torque T against slip s of the motor, output P _out , loss W in the motor, and input P _in
And the line current I. Slip on the horizontal axis s =
The left side of 0 represents the electric motor side, and the right side represents the regenerative side. The present invention utilizes the characteristics of the regenerative side region as an induction generator during braking. That is, when decelerating while reducing the output frequency by the inverter, the operation region is the regeneration side region in the figure. On the regeneration side, the electric motor serves as a generator and the mechanical output _Pout has a (-) sign. In the figure, in the section from the point of slip s = 0 to the operating point a, the remaining input P _{in obtained} by subtracting the loss W (mainly copper loss) in the motor from the mechanical energy P _out returned from the load and the motor rotor. Also indicates the (-) sign and is regenerated to the inverter side as electric energy.
In the area where the absolute value of slip is larger than the operating point a (direction from the right), the loss W in the motor becomes larger than the regenerative energy, and energy is no longer regenerated to the inverter. P _in is supplied to the electric machine consumption. The present invention controls the output frequency and the output voltage while monitoring the DC bus voltage or the DC bus current when decelerating the motor, so that the slip is maintained near the operating point a and the regenerative energy is stored in the motor. It is intended to prevent the voltage rise of the DC bus and the troubles associated with it, without being consumed and returned to the inverter side.
It is possible to eliminate or miniaturize the resistor and control circuit for regenerative energy processing as described in the conventional example.

[0009]

Embodiments of the present invention will now be described with reference to the drawings.
Explain. FIG. 1 shows an inverter-driven induction motor of the present invention.
Control inverter to which one embodiment of the above braking method is applied
2 is a circuit configuration diagram of FIG. The motor used in the examples is
Rated voltage 200V, 60Hz, 4 poles, 3.7kW induction
Moment of inertia of load J_L Is the inertia of the motor rotor
Moment J _M 9 times the size of the V / f constant control
Driven and the DC bus voltage of the inverter is at the rated operation
At 280V, and the overvoltage detection level is 400V. Three-phase
The converter 1 converts the input from the power supply into direct current, and
Output of variable voltage and variable frequency by induction motor 3.
Is given to 4. The motor 4 has a moment of inertia J_L Have
The load 9 is connected. Main circuit capacitor 5 is direct current
The voltage detector 10 connected between the bus bars detects the DC bus voltage.
It is for. The current detector 6 is for detecting the DC bus current,
The output devices 7 and 8 are for detecting the output current (= motor line current).
It The control circuit 11 outputs the voltage value of the DC bus from the voltage detector 10.
, And the DC bus current obtained from the current detectors 6 and 7.
Value and output current value, and output frequency value
And the output voltage value are calculated, and are output via the drive circuit 12.
By PWM controlling each power element of the inverter 3
Performs speed control of the induction motor during deceleration.

Next, the operation of this embodiment will be described with reference to the flow chart of FIG. Hereinafter, the S number in the text indicates the step number of the operation. First, with the start of the program, the coefficient k ₁ for changing the rate of decrease when decreasing the output frequency is set to "1" as an initial value,
Coefficient k ₂ used for addition when increasing the rate of fall
Is set to "0" as an initial value (S1). Next, when a deceleration command is input while the electric motor 4 is rotating at a constant speed at a power supply frequency of 60 Hz (S2), the control circuit 11 first applies a base block to each power element of the inverter 3 to cut off the inverter output (S3). ). Fixed time (0.3m here)
After the elapse of s), the output frequency is set to 5 Hz which is the DC braking start frequency, and at the same time, the V / f setting of the inverter 3 is rated at 2
The output is lowered to 50V / 60Hz, which is a quarter of 00V / 60Hz (S4). That is, the output voltage is (50V / 60
Hz) × 5 Hz≈4.16V. The time for the base block to start at the start of deceleration is set according to the decrease in the residual voltage of the motor. The V / f set value shown in step S4 is a value that makes the inverter output current as large as possible within the range allowable by the inverter during deceleration, and is determined by calculation or actual measurement. As a method of limiting the inverter output current, constant current control is performed so as to keep the output current constant at the rated current, and another method of controlling the output voltage (V / f setting) so that the current is constant is also effective. is there. Next, vdc> 310V and (vdc-vdcn)> 2V
If the condition of (vdc is a DC bus voltage, vdcn is a DC bus voltage 10 ms before) is not satisfied (S5), the output frequency is increased at a preset increase rate (1 Hz / 10 ms) (S6, S7). ). If this condition is satisfied in step S5, DC braking is immediately applied (S
19). Then, when the output bus frequency rises and the DC bus voltage rises due to regenerative energy and the above condition is satisfied (S7), the actual slip of the motor is the operating point a in FIG.
It is determined that the output frequency has passed to the left side of the operating point a (operating point detection), and the output frequency is set to a preset rate of decrease (60 Hz /
It is lowered for 1.5 s) to decelerate the electric motor (S8). In step S7 described above, in consideration of the transient voltage change and noise when the frequency drops, the condition that the DC bus voltage rises to 310 V or higher is introduced as a logical product condition, and when both are satisfied, the frequency It started to drop. The rate of decrease may be determined by calculating, for example, by multiplying the rate of increase of the DC bus voltage by a predetermined coefficient, and thus the rate of decrease can be automatically determined according to the load.

If during this deceleration, energy is regenerated
If the DC bus voltage rises, the DC bus voltage rises.
Depending on the rate, speed up the decrease in frequency temporarily. That is,
So that the rotation speed is at or above the operating point a.
While slowing down. Here, according to the method described above
Frequency is not sufficiently reduced to stop energy regeneration.
If it does not, the DC bus voltage vdc is 350
V (S9), vdc-vdc2> 2V (vdcn
If 2 is the DC bus voltage before 1 ms) (S10), output
The power frequency is further reduced by 2 Hz (S
11). If the DC bus voltage vdc is 350 V or less,
In addition, it is 310 V or more, and vdc-vdc
If n> 1V (S11), the rate of decrease is [k₁ = {(V
dc-vdcn) / 4V} + k₂ ] Of output frequency
The decrease is accelerated (S13). k₁ Changes the rate of decline
It is a coefficient to make it go to S8 again through the following process.
When it returns, the output frequency will decrease faster. k₂ Is further
It is a coefficient to accelerate the decrease of the output frequency.
If regeneration does not resolve at the rate of decrease due to ₂ To
(K₂ +4) to increase the falling rate, and output frequency
The number decreases repeatedly. DC bus voltage vdc is 310V or more
Underneath, and if vdc-vdcn is 1 V or less (S
12), k in the next step S14₁ The initial value is "1"
And k₂To the initial value "0". Furthermore, 10
At a frequency of Hz or higher or a DC bus voltage of 310 V or higher
When vdc-vdcn <1V (S15),
Since the frequency has dropped excessively due to the above frequency drop
k₁ = 0 (S16) Stop the frequency reduction and
Wait for the rotating speed of the machine to decrease, then restart the DC bus
When the voltage starts to rise, the frequency is restarted. to this
The inverter frequency to match the actual deceleration speed of the motor.
Therefore, it is possible to lower the value.

As described above, the output frequency is 10 Hz.
Return to step S8 and repeat the operation until the value is lowered to
(S17). On the other hand, regenerative energy is load and rotor
Equivalent to the rotational energy of (J _L + J_M ) Ω² (Ω
Is the rotational angular velocity of the electric motor). Therefore the frequency
When the number is low, regenerative energy decreases, so deceleration
Even then, the DC bus voltage begins to drop. Therefore,
In this embodiment, after the output frequency starts decreasing due to deceleration,
When the inverter output frequency falls below 10 Hz (S1
7), time required from the start of output frequency reduction (S8)
The average fall rate is calculated from the drop rate and
It is trying to decelerate (S18). DC output frequency
DC control when the braking start frequency is reduced to 5 Hz
Motion (S20), stop the motor (S21),
End the operation.

The present embodiment can shorten the deceleration time of the electric motor while preventing the regeneration of energy to the inverter by the above braking method. FIG. 4 is a graph showing changes in the DC bus voltage, the inverter output frequency, and the motor rotation speed when the inverter-driven induction motor according to this embodiment is decelerated, and it can be seen that deceleration and stop can be smoothly performed in a short time. The method of decelerating the motor based on the judgment of the rise and the rate of rise of the DC bus voltage has been described above, but the same applies when the DC bus current is detected and the energy regeneration is judged by its direction and magnitude. . In this embodiment, the output voltage is adjusted by lowering the V / f setting during deceleration. However, in the case of current limitation,
If the output current is limited when the output current becomes large, the peak portion of the current is suppressed and the current waveform is distorted. On the other hand, when the output current reaches the current limit value, the output voltage is lowered to suppress the output current within the current limit value, whereby the distortion of the current waveform can be eliminated.

In the embodiment, when the operating point was found, the frequency was raised at a constant rate. However, the rate may be changed according to the magnitude of the DC bus current, or the frequency may be changed stepwise. The operating point search time can be shortened by using the method of determining whether to raise or lower the frequency by changing the DC bus current value or DC bus voltage value at that time. In the embodiment, DC braking is applied at an inverter output of 5 Hz or less, but this frequency may be changed depending on the system. In addition, a method of setting the V / f setting or the current limit value smaller than the value during deceleration can be considered in order to suppress the influence of torque fluctuation and the like until the operating point is determined. Even if the output current of the inverter is above the rated current, if it is below the overcurrent, it can be output until the time integrated value of the current exceeds a certain value (overload level). Therefore, in order to increase the braking torque during deceleration, it is effective to raise the current limit value above the rated value within the range where protection does not work.

[0015]

As described above, according to the present invention, the inverter output frequency is first lowered to a predetermined low frequency together with the deceleration command, and then the output frequency is raised to start the flow of regenerative energy from the electric motor side to the inverter. The operating point is searched by monitoring the rise of the DC bus voltage or the direction of the DC bus current, and the output frequency is lowered while keeping this operating point to decelerate the motor. Since regeneration can be eliminated and DC bus voltage rise can be prevented, resistors and control circuits for processing this energy can be removed or downsized, and a braking torque higher than DC braking can be achieved in the high-speed range. Therefore, the time required for deceleration can be shortened.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an inverter circuit to which an embodiment of a braking method for an inverter-driven induction motor of the present invention is applied.

FIG. 2 is a known induction motor characteristic diagram.

FIG. 3 is a flowchart showing an operation of an embodiment of a braking method for an inverter-driven induction motor of the present invention.

FIG. 4 is a diagram showing changes in the motor rotation speed, the DC bus voltage of the inverter, and the output frequency during deceleration of the induction motor to which the embodiment of the present invention is applied.

5 (a) and 5 (b) are views corresponding to FIG. 4 when the conventional braking method is used.

FIG. 6 is a circuit configuration diagram of an induction motor drive inverter having a conventional braking circuit with a resistor connected to a DC bus.

[Explanation of symbols]

1 converter 3 inverter 4 electric motor 5 Main circuit capacitor 6 DC bus current detector 7,8 Output current detector 9 load 10 DC bus voltage detector 11 Control circuit 12 drive circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Takayuki Yamakawa No. 2-1, Shiroishi Kurosaki, Yawatanishi-ku, Kitakyushu, Fukuoka Prefecture Yasukawa Electric Co., Ltd. (72) Toshihiro Sawa No. 2 Shiroishi, Kurosaki, Hachimanishi-ku, Kitakyushu, Fukuoka Yasukawa Electric Co., Ltd. (56) Reference JP-A-6-165547 (JP, A) JP-A-5-103485 (JP, A) JP-A-5-168286 (JP, A) JP-A-7-7981 ( (58) Fields surveyed (Int.Cl. ⁷ , DB name) H02P 3/18 101 H02P 5/41 302

Claims (15)

(57) [Claims] 1. A method of braking an induction motor driven by an inverter by controlling an inverter output frequency, wherein when a deceleration command is received when shifting to deceleration, the output frequency is first lowered to a predetermined frequency and then While detecting and monitoring the DC bus current or DC bus voltage, increase the output frequency at a predetermined rate of increase.From the direction in which the DC bus current flows or the DC bus voltage rises, energy is regenerated from the motor to the inverter. When it is detected that the motor has begun to break, the output frequency is reduced at a specified rate of decrease and the motor is decelerated while suppressing regeneration to the inverter side by constantly consuming all regenerative energy in the motor during deceleration. And a method for braking an induction motor driven by an inverter. 2. The braking method for an inverter-driven induction motor according to claim 1, wherein the V / f setting of the inverter is reduced during the period from the start of deceleration to the end of deceleration so that the output current does not become overcurrent or overload. 3. The braking method for an inverter-driven induction motor according to claim 1, wherein during the period from the start of deceleration to the end of deceleration, constant current control is performed by keeping the output current of the inverter constant so as not to cause overcurrent or overload. . 4. The braking method for an inverter-driven induction motor according to claim 1, wherein the predetermined frequency which is once lowered is within a range of 90% or less of an operating frequency before deceleration is started. 5. The DC braking start frequency is set to the predetermined frequency which is once lowered, and the DC braking is immediately applied if the DC bus voltage rises or the direction of the DC bus current is a direction in which energy is regenerated when the frequency is lowered. Claims 1 to 3
The method for braking an inverter-driven induction motor according to any one of 1. 6. In order to determine the maximum frequency at which energy is not regenerated to the inverter, when the output frequency once lowered is raised, it depends on the magnitude of the DC bus current or the rate of change of the DC bus voltage. The method of braking an inverter-driven induction motor according to claim 1, wherein an increase rate of the output frequency is determined. 7. A method of determining the maximum frequency at which energy is not regenerated to the inverter, the purpose estimated from the direction and magnitude of the DC bus current or the rate of change of the DC bus voltage at the once lowered predetermined frequency. 2. The braking method for an inverter-driven induction motor according to claim 1, wherein the output frequency is stepwise shifted to the frequency of, and the frequency is similarly shifted to the next frequency to determine the target maximum frequency. 8. The braking method for an inverter-driven induction motor according to claim 1, 6 or 7, wherein the current limit value is smaller than the rated current value during the period when the output frequency is increased. 9. A regenerative energy and a motor loss are calculated by reducing the output frequency by calculating the decrease rate without energy regeneration to the inverter from the direction and magnitude of the DC bus current or the increase rate of the DC bus voltage. The method of braking an inverter-driven induction motor according to claim 1, wherein deceleration is performed while maintaining a balanced state. 10. The method according to claim 1, wherein when the regeneration of energy to the inverter is detected during deceleration, the output frequency is temporarily reduced according to the magnitude of the DC bus current or the increase rate of the DC bus voltage. Inverter-driven induction motor braking method. 11. The frequency drop is temporarily stopped when the DC bus voltage that rises during deceleration or the direction of the DC bus current changes to the direction of supplying energy, and after the frequency drop is stopped, The braking method for an inverter-driven induction motor according to claim 1, 2, 3 or 10, wherein the frequency is restarted when the DC bus voltage starts to rise or the direction of the DC bus current becomes a direction in which energy is regenerated. 12. When decelerating from a constant speed operation to an arbitrary frequency, the output frequency is switched to an arrival target frequency by deceleration at an arbitrary time interval during deceleration, and at that frequency, energy is supplied to the electric motor in the direction of the DC bus current. If the DC bus voltage does not rise during any sampling time, it is determined that the target frequency has been reached and the deceleration is completed and steady operation is started. The braking method for an inverter-driven induction motor according to claim 1, wherein deceleration is continued by returning to the frequency before switching the frequency. 13. A deceleration restart voltage level is set between the DC bus voltage level before the start of deceleration and the overvoltage detection level,
When it is determined that the rotation speed of the motor has decreased due to deceleration and the regenerative energy has decreased, and the DC bus voltage has fallen below the deceleration restart level, the average fall rate is calculated from the time required from the deceleration start to the determination and the frequency difference between them. The braking method for an inverter-driven induction motor according to any one of claims 1 to 12, wherein the braking operation is performed and deceleration is performed based on the descending rate. 14. A deceleration restart voltage level is set between a DC bus voltage level before deceleration start and an overvoltage detection level,
13. The deceleration reduces the rotation speed of the electric motor to reduce regenerative energy, and when it is determined that the DC bus voltage has dropped below the deceleration restart level, deceleration is performed at a preset rate of decrease in frequency. A method for braking an inverter-driven induction motor according to item. 15. The inverter has overcurrent and overload protection, and the current limit level is set higher than a rated value within a range in which the overcurrent and overload protection does not function only during deceleration, and the protection is also provided. 15. The braking method for an inverter-driven induction motor according to claim 1, wherein the current limit level is varied according to the current value detected by the current detector or the integrated value of the current.