JPH08242594A - Power converter - Google Patents

Abstract

(57) [Abstract] [Purpose] It is an object of the present invention to provide a power conversion device capable of suppressing speed fluctuations and DC voltage fluctuations of electric motors caused by sudden changes in load. In a power conversion device that converts AC power obtained from an AC power supply into an arbitrary frequency and an arbitrary voltage to control the speed of an electric motor, an upper limit value of an electric motor torque reference is immediately set to zero when a sudden decrease in load is detected. As soon as a sudden increase is detected, the lower limit of the motor torque standard is set to zero,
Suppresses speed fluctuations of the electric motor that occur during sudden load changes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter for driving an electric motor at a variable speed, and more particularly to a control system for a power converter having a circuit for suppressing speed fluctuations and DC voltage fluctuations that occur during sudden load changes. Regarding

[0002]

2. Description of the Related Art A conventional power converter for controlling the speed of an electric motor has an arbitrary structure in which, as shown in FIG. 10, AC power obtained from an AC power supply 1 is connected in antiparallel with a thyristor element to form a bridge structure. The anti-parallel type thyristor converter 2 for converting into a DC voltage, the DC smoothing capacitor 3 for smoothing the output DC voltage of the anti-parallel type thyristor converter 2, and the DC voltage obtained from the DC smoothing capacitor 3 with any frequency. The reverse conversion device 4 converts the AC voltage into the electric motor 5, drives the electric motor 5, and transmits power to the load 6.

The control circuit of this converter includes a speed control unit 12 for calculating a torque reference of an electric motor from a speed feedback signal from a position / speed detector 11 for detecting the rotor position and speed of the electric motor and a speed reference of the electric motor. A torque limit 13 that gives an upper limit value and a lower limit value to the torque reference output from the speed control unit 12, an inverse conversion device output power calculation unit 14 that calculates the inverse conversion device output power from the speed feedback and the torque reference, and From the output voltage reference of the antiparallel thyristor converter, the voltage feedback signal from the voltage detector 15 that detects the voltage of the DC smoothing capacitor 3, and the output power signal output from the inverse converter output power calculation unit 14, the antiparallel type An anti-parallel type thyristor converter control unit 16 for outputting a thyristor converter control signal; Necessary to drive the electric motor 5 from the reference, the position feedback signal output from the position / speed detector 11, the current feedback from the current detector 17 provided at the output of the inverse converter, and the magnetic flux reference of the electric motor. A control circuit 18 for calculating a voltage and a frequency and outputting an inverse converter control signal for controlling the inverse converter 4, and a DC voltage feedback value exceeding an allowable range of the apparatus,
It is configured by a DC voltage fluctuation suppressing unit 19 that changes the upper limit value and the lower limit value of the torque limit to suppress the DC voltage fluctuation.

[0004]

However, in this control, since the control is delayed because the DC voltage fluctuation is suppressed after the fluctuation of the DC voltage, the sufficient effect may not be expected. Therefore, an object of the present invention is to provide a power conversion device that can detect a sudden load change quickly when a sudden load change occurs and can suppress a speed fluctuation and a DC voltage fluctuation of a motor caused by the sudden load change.

[0005]

To achieve the above object, in a power converter according to a first aspect of the present invention, AC power obtained from an AC power source is converted into an arbitrary frequency and an arbitrary voltage to control the speed of a motor. A power converter for performing, a current detection means provided on the output side of the power converter, a position / speed detection means for detecting the rotor position and speed of the electric motor, and a speed feedback signal from the position / speed detection means. A speed control means for calculating a torque reference of the electric motor based on a preset speed reference, a torque limiter for giving an upper limit value to the torque reference output from the speed control means, and a sudden load change detection for detecting a sudden load change. Means and the sudden load change signal from the sudden load change detecting means, the upper limit value of the torque limiter is set to zero when the load is suddenly decreased, and the torque limiter is increased when the load is suddenly increased. A sudden load change processing means for setting the lower limit value of the limiter to zero, a torque reference from the torque limiter, a position feedback signal output from the position / speed detecting means, a current feedback signal from the current detecting means, and the preset value Control means for calculating a voltage and a frequency necessary for driving the electric motor based on a magnetic flux reference of the electric motor and outputting a power converter control signal for controlling the power converter. .

According to another aspect of the power converter of the present invention, a power converter for converting the AC power obtained from the AC power source into an arbitrary frequency and an arbitrary voltage to control the speed of the motor, and an output side of the power converter. Current detection means provided in the, the position and speed detection means for detecting the rotor position and speed of the electric motor, by proportional integration based on the speed feedback signal from the position and speed detection means and a preset speed reference A speed control means for calculating a torque reference of the electric motor, a load sudden change detection means for detecting a sudden load change, and an integral of the speed control means at the time of a sudden load decrease or sudden load increase based on a sudden load change signal from the sudden load change detection means. Sudden load change processing means for making the value zero, the torque reference, the position feedback signal from the position / speed detection means, and the current from the current detection means Control means for calculating a voltage and a frequency necessary for driving the electric motor based on a feedback signal and a preset magnetic flux reference of the electric motor, and outputting a power converter control signal for controlling the power converter. Is provided.

In the power converter according to claim 3, the thyristor elements connected in antiparallel form a bridge structure,
Anti-parallel type thyristor converter means for converting the AC power obtained from the AC power source into an arbitrary DC voltage, a DC smoothing capacitor for smoothing the output DC voltage of this anti-parallel type thyristor converter, and a DC voltage obtained from this DC smoothing capacitor To an arbitrary frequency and an inverse converter for converting to an arbitrary AC voltage, a power converter for controlling the speed of the electric motor, a current detecting means provided on the output side of the power converter, and the DC smoothing. Voltage detecting means for detecting the voltage of the capacitor; and an inverse for outputting an antiparallel thyristor converter control signal based on a preset output voltage reference of the antiparallel thyristor converter and a voltage feedback signal from the voltage detecting means. Parallel thyristor converter control means and position / speed detection for detecting rotor position and speed of the electric motor Stage, speed control means for calculating a torque reference of the electric motor based on a speed feedback signal from the position / speed detection means and a preset speed reference, and torque for inclining the torque reference from the speed control means. Rate means, a sudden load change detecting means for detecting a sudden load change, and when the sudden load change signal from the sudden load change detecting means indicates a sudden decrease in load, the inclination of the torque rate means is set large, otherwise the torque rate means. Based on the torque reference, the position feedback signal from the position / speed detecting means, the current feedback signal from the current detecting means, and the preset magnetic flux reference of the electric motor. Power converter control for controlling the power converter by calculating the voltage and frequency required to drive the electric motor. Characterized by comprising a control means for outputting a signal.

In the power converter according to claim 4, a thyristor element connected in anti-parallel has a bridge structure,
Anti-parallel type thyristor converter means for converting the AC power obtained from the AC power source into an arbitrary DC voltage, a DC smoothing capacitor for smoothing the output DC voltage of this anti-parallel type thyristor converter, and a DC voltage obtained from this DC smoothing capacitor To an arbitrary frequency and an inverse converter for converting to an arbitrary AC voltage, a power converter for controlling the speed of the electric motor, a current detecting means provided on the output side of the power converter, and the DC smoothing. Voltage detection means for detecting the voltage of the capacitor, position and speed detection means for detecting the rotor position and speed of the electric motor, and the speed feedback signal from the position and speed detection means and a preset speed reference based on the speed feedback signal. The speed control means for calculating the torque standard of the electric motor, the sudden load change detecting means for detecting the sudden load change, and the sudden load change detecting means Based on the sudden load change signal, the speed feedback signal and the torque reference, when the load sudden decrease and load sudden increase is not calculated and output the output power of the inverse converter based on the speed feedback signal and the torque reference, and output, Inverter output power calculation means for outputting a predetermined value when the load is suddenly decreased or suddenly increased, an output voltage reference of the antiparallel thyristor converter, a voltage feedback signal from the voltage detection means, and an inverse converter output power calculation means. An anti-parallel type thyristor converter control unit for outputting an anti-parallel type thyristor converter control signal based on an output power signal output from the output unit, a position feedback signal output from the torque reference and the position / speed detection unit, and the current detection. The current feedback signal from the means and the preset motor Characterized by comprising a control means for outputting a power converter control signal for controlling the power converter to calculate the voltage and frequency required to drive the motor based on the flux reference.

According to a fifth aspect of the power conversion device of the present invention, in the load sudden change detection means according to any one of the first to fourth aspects, the difference value between the current value and the previous value of the speed feedback signal from the position / speed detection means is determined. When the polarity of the speed feedback is positive, the load is sharply reduced when the absolute value of the difference value based on the torque is equal to or more than the second predetermined value, and when the polarity of the speed feedback is negative, the first predetermined value is set. When the absolute value of the torque-based difference value is equal to or less than the reverse polarity value of the value and is equal to or less than the second predetermined value, the load is rapidly increased.

According to a sixth aspect of the power conversion device of the present invention, in the sudden load change detecting means according to any one of the first to fourth aspects, the difference value between the current value and the previous value of the speed feedback signal from the position / speed detecting means is calculated. When the polarity of the speed feedback is positive, the load is applied when the absolute value of the difference between the current value of the speed feedback signal and the previous value when the filter processing is performed with the speed reference above the first predetermined value is less than the second predetermined value. When the speed feedback is negative and the polarity of speed feedback is negative,
When the absolute value of the difference value between the current value of the speed feedback signal and the previous value when the filter processing is performed on the basis of the reverse polarity value less than or equal to the predetermined value is less than the second predetermined value, the load is suddenly increased. Characterize.

[0011]

In the power converter according to the present invention, the load is reduced by immediately setting the upper limit value of the motor torque reference to zero when a sudden load decrease is detected, and immediately setting the lower limit value of the motor torque reference to zero when a sudden load increase is detected. It is possible to suppress fluctuations in the speed of the electric motor that occur during sudden changes.

In the electric power converter according to the second aspect of the present invention, the integrated value of the electric motor speed control unit is cleared to zero immediately after detecting the sudden load decrease or the sudden load increase, thereby suppressing the speed fluctuation of the electric motor which occurs when the load suddenly changes. be able to.

In the electric power converter according to the third aspect of the present invention, the gradient of the torque rate is set to a large value immediately after the sudden load decrease is detected, so that it is possible to suppress the DC voltage fluctuation that occurs when the load suddenly decreases.

In the power converter according to the present invention, when a sudden load decrease is detected, the inverse converter output power calculation means outputs a fixed negative power value as an output power signal to the antiparallel thyristor converter controller. By lowering the output DC voltage of the anti-parallel thyristor converter, it is possible to suppress the DC voltage fluctuation that occurs when the load suddenly decreases,
When a rapid load increase is detected, the inverse converter output power calculation means outputs a positive fixed power value as an output power signal to the antiparallel thyristor converter control unit to increase the output DC voltage of the antiparallel thyristor converter. By that,
It is possible to suppress the DC voltage fluctuation that occurs when the load suddenly increases.

According to another aspect of the power converter of the present invention, the difference value between the current value of the speed feedback signal and the previous value is equal to or greater than the first predetermined value when the polarity of the speed feedback is positive, and the absolute value of the difference value based on the torque is absolute. When the value is less than or equal to the second predetermined value a, the load is suddenly decreased, and when the polarity of the speed feedback is negative, the reverse polarity value is less than or equal to the first predetermined value and the absolute value of the torque-based difference value is less than or equal to the second predetermined value. When, the load is detected as a sudden increase.

In the power converter according to the sixth aspect of the present invention, when the difference value between the current value of the speed feedback signal and the previous value is positive in the polarity of the speed feedback, the speed reference signal is equal to or higher than the first predetermined value and the speed reference is used as a filter. When the absolute value of the difference between the current value of the speed feedback signal and the previous value is less than or equal to the second predetermined value, the load is sharply decreased, and when the polarity of the speed feedback is negative, the load is less than the reverse polarity value of the first predetermined value. When the absolute value of the difference value between the current value of the speed feedback signal and the previous value when the speed-based filtering process is performed is less than or equal to the second predetermined value, it is detected as a sudden load increase.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of a first embodiment of the present invention. In the first embodiment, the AC power obtained from the AC power supply 1 is converted by the power converter 20 into an arbitrary frequency and an arbitrary AC voltage to drive the electric motor 5 and transmit power to the load 6.

Here, a cycloconverter, a voltage type inverter, a current type inverter or the like can be applied to the power converter 20. The control circuit of the power converter includes a speed control unit 12 that calculates a torque reference of the electric motor from a speed feedback signal from a position / speed detector 11 that detects the rotor position and speed of the electric motor and a speed reference of the electric motor, and A torque limit 13 that gives an upper limit value and a lower limit value to the torque reference output from the speed control unit 12, a position feedback signal output from the torque reference and the position / speed detector 11, and an output of the power converter are provided. A control circuit for calculating the voltage and frequency necessary for driving the electric motor 5 from the current feedback from the electric current detector 17 and the magnetic flux reference of the electric motor, and outputting an inverse converter control signal for controlling the power converter 20. 21 and the upper limit value and lower limit value of the torque limit based on the speed feedback signal and the torque reference output from the speed control unit 12. Composed of that sudden load change processing unit 22..

In the speed controller 12, proportional motor 23 and integrator 24 perform proportional-plus-integral (PI) control from the speed reference SP-R and the speed feedback SP-F to generate the torque reference T-R1, whereby the motor speed is changed. Controlled. The velocity feedback is obtained from the position velocity detector 11. The position / speed detector 11 comprises a resolver 25 for detecting the rotor position of the electric motor and a position / speed detector 26 for differentiating the rotor position feedback to calculate the speed.

The sudden load change processing unit 22 includes a sudden load change detection circuit 2
7 and the sudden load change processing circuit 28. In the sudden load change detection circuit 27, as shown in FIG. 2, the difference d-SP-F from the previous value of the speed feedback and the torque reference T which is the output of the speed control unit 12. -Detect the sudden increase and the sudden decrease of the load from the difference dTR from the previous value of R1. That is, as shown in FIG. 3, since the speed reference SP-R is increased, the speed feedback SP
If -F increases, torque standard T-R1 increases first,
Then the velocity feedback increases. On the other hand, if the load spikes, the speed feedback first decreases and then the torque reference increases to restore speed.
The same applies when the load suddenly decreases. Therefore, as shown in FIG. 2, when the absolute value of the difference dTR is smaller than the fixed value a and the difference d-SP-F is larger than the fixed value b, it is determined that a sudden load decrease is detected, and FLG-LOAD is set to " Set to 1 ”. Similarly, if the difference d-SP-F is smaller than the fixed value -b,
FLG-LOAD is set to "-1" when a sudden load increase is detected. If the above two types of conditions are not met, there is no sudden load change and FLG-LOAD is set to "0". Here, a and b are percentage threshold values for preventing erroneous detection of a sudden change in load, and a <b.

The sudden load change processing circuit 28 performs the following processing according to the value of the FLG-LOAD signal from the sudden load change detection circuit 27.

FLG-LOAD = -1 (rapid load increase): The lower limit value of the torque limit 13 is set to "0". FLG-LOAD = 0 (No sudden change in load): Returns the upper and lower limits of torque limit 13 to the normal state. FLG-LOAD = 1 (rapid load decrease): The upper limit of torque limit 13 is set to “0”.

Then, the torque reference T-R2 given upper and lower limits by the torque limit, the current feedback from the current detector 16 and the position feedback from the position / speed detector 11 provided at the output of the power converter 20. And the magnetic flux reference FLX-R are input to the control circuit 21 to output a power converter control signal to drive the electric motor 5 and the load 6 directly connected to the electric motor 5.

According to the first embodiment constructed as described above, the following operational effects can be obtained. For example, when the load 6 suddenly decreases, the speed feedback SP-F first increases. The speed increase at this time occurs because the load torque before the sudden load decrease is replaced by the acceleration torque of the electric motor due to the actual decrease in the load. Therefore, it is necessary to prevent the torque on the positive side from being output as soon as a sudden decrease in load is detected. Therefore, as soon as the sudden load change detection circuit 27 detects a sudden load decrease, the sudden load change processing circuit 2
By setting the upper limit value of the torque limit to "0" in 8, it is possible to prevent the acceleration torque from being generated and prevent the electric motor from becoming overspeed.
The case of a sudden increase in load is similar to the case of a sudden decrease in load, and the above processing makes it possible to suppress speed fluctuations during a sudden change in load.

Next, a second embodiment of the present invention will be described. FIG. 4 is a block diagram showing a schematic configuration of the second embodiment of the present invention. The second embodiment is different from the first embodiment only in the detection method of the sudden load change detection circuit 27,
Since the other parts are the same as those in the first embodiment, only the part of the sudden load change detection circuit 27 will be described here.

The details of the sudden load change detection circuit 27 are shown in FIG. That is, the difference d-SP-F from the previous value of the speed feedback SP-F and the difference d-SP-R from the previous value after filtering the speed reference SP-R are calculated. The filter time constant of the filtering process applied to the speed reference SP-R is set to be equal to or longer than the speed response time of the motor.

As shown in FIG. 6, when the speed feedback SP-F increases due to the increase of the speed reference SP-R, the speed feedback SP-F and the filtered speed reference SP-R1 are Similar waveform, and difference d-SP
-R will increase and then speed feedback SP-F will increase. On the other hand, if the load changes suddenly, the speed reference SP
-R is unchanged but speed feedback
Only SP-F changes suddenly. A method of detecting the sudden load change timing by utilizing this phenomenon is shown in the flowchart of FIG. That is, if the absolute value of the difference d-SP-R is smaller than the fixed value a and the difference d-SP-F is smaller than the fixed value -b, it is assumed that a load surge is detected and FLG-LOAD = -1. To do. The absolute value of the difference d-SP-R is smaller than the fixed value a, and the difference d-
If SP-F is larger than the fixed value b, FLG-LOAD = 1 is set, assuming that a sudden load decrease has been detected. In cases other than the above, set FLG-LOAD = 0 with no sudden change in load. Here, a and b are percentage threshold values for preventing erroneous detection of a sudden change in load.
= Substantially 0 and a <b.

Therefore, according to the second embodiment constructed as described above, the same operational effect as that of the first embodiment can be obtained. Next, a third embodiment of the present invention will be described.

FIG. 7 is a block diagram showing a schematic configuration of the third embodiment of the present invention. In the third embodiment, the AC power obtained from the AC power supply 1 is converted by the power converter 20 into an arbitrary frequency and an arbitrary AC voltage to drive the electric motor 5 and transmit power to the load 6.

Here, a cycloconverter, a voltage type inverter, a current type inverter or the like can be applied to the power converter 20. The control circuit of the power converter includes a speed control unit 31 that calculates a torque reference of an electric motor from a speed feedback signal from a position / speed detector 11 that detects the rotor position and speed of the electric motor and a speed reference of the electric motor, and Necessary to drive the electric motor 5 from the torque reference, the position feedback signal output from the position / speed detector 11, the current feedback from the current detector 17 provided at the output of the power converter, and the magnetic flux reference of the electric motor. Of the speed control unit 31 from the control circuit 32 that calculates a proper voltage and frequency and outputs the power converter control signal that controls the power converter 20, and the speed feedback signal and the torque reference that is the output of the speed control unit 31. Load sudden change processing unit 3 that controls the integral value
And 3.

In the third embodiment, in the first and second embodiments, the sudden load change processing unit controls the upper limit value and the lower limit value of the torque limit, while the integral value of the speed control unit 31 is changed. It is designed to be controlled.

The output of the proportionalizer 34 of the speed control unit 31 becomes a negative value immediately after, for example, a sudden load decrease. On the other hand, in the integrator 35, if the value integrated before the occurrence of the sudden load decrease is positive, integration in the negative direction is started with this value as the initial value, and the output of the integrator 35 is instantaneously output. It cannot be negative.

Therefore, in the third embodiment, the integral value of the speed control integrator 35 is cleared to zero as soon as the sudden load change is detected. According to the third embodiment configured as described above, the same effects as those of the first and second embodiments can be obtained.

Next, a fourth embodiment of the present invention will be described. FIG. 8 is a block diagram showing a schematic configuration of the fourth exemplary embodiment of the present invention. In the fourth embodiment, the AC power obtained from the AC power supply 1 is connected in antiparallel to the thyristor elements to form a bridge structure, and the antiparallel thyristor converter 2 for converting the AC power into an arbitrary DC voltage and the antiparallel thyristor converter 2 are described. DC smoothing capacitor 3 for smoothing the output DC voltage of No. 3, and an inverse converter 4 for converting the DC voltage obtained from the DC smoothing capacitor 3 into an arbitrary frequency and an arbitrary AC voltage. Power is transmitted to 6.

The control circuit of this electric power conversion system includes a position / speed detector 1 for detecting the rotor position and speed of the electric motor.
1, a speed control unit 12 which calculates a torque reference of an electric motor from a speed feedback signal from the electric motor 1 and a speed reference of the electric motor; a torque rate 41 which gives an inclination to the torque reference output from the speed control unit 12; and the antiparallel thyristor. The output voltage reference of the converter, the voltage feedback signal from the voltage detector 16 which detects the voltage of the DC smoothing capacitor 3, and the antiparallel thyristor converter control unit 42 which outputs the antiparallel thyristor converter control signal, and the torque reference. A voltage required to drive the electric motor 5 based on the position feedback signal output from the position / speed detector 11, the current feedback from the current detector 17 provided at the output of the power converter, and the magnetic flux reference of the electric motor. A control for calculating the frequency and outputting an inverse converter control signal for controlling the inverse converter 4 described above. A circuit 43, and a sudden load change processing unit 44 which controls the inclination of the torque rate and a torque reference which is the output of the speed feedback signal and a speed control unit 12.

In the speed controller 12, proportional motor 23 and integrator 24 perform proportional-plus-integral (PI) control from the speed reference SP-R and the speed feedback SP-F to generate the torque reference T-R1, whereby the motor speed is changed. Controlled. The velocity feedback is obtained from the position velocity detector 11. The position / speed detector 11 comprises a resolver 25 for detecting the rotor position of the electric motor and a position / speed detector 26 for differentiating the rotor position feedback to calculate the speed.

The sudden load change processing unit 44 is used for the sudden load change detection circuit 4.
5 and the sudden load change processing circuit 46. In the sudden load change detection circuit 45, as shown in FIG. 6 also shown in the second embodiment,
Difference between the previous value of speed feedback d-SP-F and the previous value of the torque reference T-R1 output from the speed control unit 12
Detect sudden load increase / decrease from dTR.

The sudden load change processing circuit 46 performs the following processing according to the value of the FLG-LOAD signal from the sudden load change detection circuit 45.

FLG-LOAD = -1 (rapid load increase): The gradient of the torque rate 41 is returned to "0". FLG-LOAD = 0 (no sudden change in load): The slope of the torque rate 41 is returned to “0”. FLG-LOAD = 1 (a sharp decrease in load): The slope of the torque rate 41 is set large. For example, when considering a mill of a rolling mill, a sudden load increase occurs when the material is bitten by the mill, and a sudden load decrease occurs when the material exits the mill. Immediately after the mill bites the material,
Since the speed of the mill needs to be quickly returned to the specified speed, the gradient of the torque rate should be '0'. Also at this time,
Since the speed is decreasing, the kinetic energy of the motor is also temporarily decreasing, and considering the safety of the entire device, it is shifting to the safe direction, so the torque reference is set to quickly return to the predetermined speed. There is no problem if given in steps.

On the other hand, immediately after the material is removed from the mill, there is no need to load the mill, so there is no need to quickly return the mill speed to a predetermined speed. Further, at this time, the speed increases, so the kinetic energy of the electric motor also temporarily increases, and if this kinetic energy is regenerated at once, the DC voltage may become an overvoltage.

From the above, the inclination of the torque rate 41 is set large only when a sudden load decrease is detected. Since this setting method depends on the type of load and the operating condition of the motor, it is possible to respond flexibly according to these conditions.Here, as a typical example, the rolling mill The case was explained.

The torque reference T-R3, which is the output of the torque rate 41, and the current feedback from the current detector 17 provided at the output of the inverse converter 4 and the position / speed detector 1
The position feedback from 1 and the magnetic flux reference FLX-R are input to the control circuit 43, which outputs an inverse converter control signal to drive the electric motor 5 and the load 6 directly connected to the electric motor 5.

According to the fourth embodiment constructed as above, the following operational effects can be obtained. For example, when the load 6 suddenly decreases, the speed feedback SP-F first increases. The speed increase at this time occurs because the load torque before the sudden load decrease is replaced by the acceleration torque of the electric motor due to the actual decrease in the load. When the motor speed increases, the speed control unit 12 rapidly reduces the torque reference T-R1 from the positive polarity to the negative polarity in an attempt to return the motor speed to the speed reference. This means that the electric motor 5 suddenly changes from the power running state to the regenerative state when the load suddenly decreases.
Since the electric motor 5 is in the regenerative state, the regenerative energy charges the DC smoothing capacitor 3.

At this time, there is no problem if the antiparallel thyristor converter 2 can immediately shift from the power running operation to the regenerative operation, but in the antiparallel thyristor converter 2, there is a dead time before the power running operation to the regenerative operation. Will always occur, so the migration will take time.

The torque reference T- which is the output of the speed control unit 12
R1 suddenly changes from positive to negative, but torque rate 4
Since the rate of change of the torque reference is limited by 1, the regenerative energy of the electric motor 5 gently charges the DC smoothing capacitor 3, so that a DC overvoltage can be prevented.

Even in the case of a sudden increase in load, in the case of a load in which the inclination of the torque rate 41 can be set large, the same effect as in the case of sudden decrease in load can be obtained. From the above, according to the present embodiment, it is possible to suppress the DC voltage fluctuation that occurs when the load changes suddenly.

Next, a fifth embodiment of the present invention will be described. FIG. 5 is a block diagram showing a schematic configuration of the fifth embodiment of the present invention. In the fifth embodiment, the AC power obtained from the AC power supply 1 is connected in antiparallel to the thyristor elements to form a bridge structure, and the antiparallel thyristor converter 2 for converting the AC power into an arbitrary DC voltage and the antiparallel thyristor converter 2 are provided. DC smoothing capacitor 3 for smoothing the output DC voltage of No. 3, and an inverse converter 4 for converting the DC voltage obtained from the DC smoothing capacitor 3 into an arbitrary frequency and an arbitrary AC voltage. Power is transmitted to 6.

The control circuit of this converter includes a speed control section 12 for calculating a torque reference of the electric motor from a speed feedback signal from a position / speed detector 11 for detecting the rotor position and speed of the electric motor and a speed reference of the electric motor. , A load sudden change detection circuit 45 that detects a sudden load increase and a sudden load decrease from the speed feedback signal and the torque reference that is the output of the speed control unit 12, and the output of the sudden load change detection circuit 45, the speed feedback, and the torque reference are input, When the output of the sudden load change detection circuit 45 is a sudden change of the load, a predetermined value is output, and when the output of the sudden load change detection circuit 45 is not a sudden change of the load, the inverse converter output power is calculated and output from the speed feedback and the torque reference. Of the output voltage calculation section 51, the output voltage reference of the antiparallel thyristor converter, and the DC smoothing capacitor 3 An anti-parallel type thyristor converter control section 16 for outputting an anti-parallel type thyristor converter control signal from the voltage feedback signal from the voltage detector 15 for detecting the pressure and the output power signal output from the inverse converter output power calculation section 51. The motor 5 is driven from the torque reference, the position feedback signal output from the position / speed detector 11, the current feedback from the current detector 17 provided at the output of the inverse converter, and the magnetic flux reference of the motor. A control circuit 1 for calculating the voltage and frequency required for the output and outputting an inverse converter control signal for controlling the inverse converter 4.
8 and.

In the speed control unit 12, the proportional speed 23 (integrator) and the integrator 24 perform proportional-plus-integral (PI) control from the speed reference SP-R and the speed feedback SP-F to generate the torque reference T-R1, and thereby the motor speed is changed. Controlled. The velocity feedback is obtained from the position velocity detector 11. The position / speed detector 11 comprises a resolver 25 for detecting the rotor position of the electric motor and a position / speed detector 26 for differentiating the rotor position feedback to calculate the speed.

In the sudden load change detection circuit 45, as shown in FIG. 6, the difference d-SP-F from the previous value of the speed feedback and
A sudden load increase and a sudden load decrease are detected from the difference dTR from the previous value of the torque reference T-R1 which is the output of the speed control unit 12, and FLG-LOAD is passed to the inverse converter output power calculation unit 51 as a result.

The inverse converter output power calculation unit 51 calculates the output power POWER by multiplying the speed feedback SP-F and the torque reference T-R1 when no sudden load change occurs, and the thyristor converter control unit. It is output to 16.

The antiparallel thyristor converter device 2 is
Generally, a dead time is generated when switching between the power running operation and the regenerative operation, resulting in extremely poor voltage response. When a sudden load change occurs, the electric motor 5 often switches from the power running state to the regenerative state, so it is necessary to promptly notify the thyristor converter control unit 16 of this change. Therefore, when the load changes suddenly, the output power POWER
The following processing is performed without waiting for the calculation of.

FLG-LOAD = -1 (rapid increase in load): 10% of the maximum output power of the antiparallel thyristor converter is POWER
Output as FLG-LOAD = 1 (rapid load decrease): Outputs -10% of the maximum output power of the anti-parallel thyristor converter as POWER.

In the inverse converter output power calculation unit 51, after the above processing, the speed feedback SP-F and the torque reference T-R1
If the absolute value of the result is larger than the fixed output power (10%) set when the load changes suddenly, the subsequent output power POWER will be calculated by the speed feedback SP-F and the torque reference T-R1. The result of multiplication is output.

The thyristor converter control unit 16 controls the voltage reference VR and the voltage feedback from the voltage detector 15 for detecting the voltage of the DC smoothing capacitor 3 and the output power POWER output from the inverse converter output power calculation unit 51. A thyristor converter control signal for controlling the voltage of the anti-parallel type thyristor converter is output. That is, proportional-integral control is performed by the output voltage reference VR and the voltage feedback signal VF, and the output power signal PO
By adding WER, voltage control is performed quickly.

According to the fourth embodiment constructed as above, the following operational effects can be obtained. For example, when the load 6 suddenly decreases, the speed feedback SP-F first increases. The speed increase at this time occurs because the load torque before the sudden load decrease is replaced by the acceleration torque of the electric motor due to the actual decrease in the load. When the motor speed increases, the speed control unit 12 rapidly reduces the torque reference T-R1 from the positive polarity to the negative polarity in an attempt to return the motor speed to the speed reference. This means that the electric motor 5 suddenly changes from the power running state to the regenerative state when the load suddenly decreases.
Since the electric motor 5 is in the regenerative state, the regenerative energy charges the DC smoothing capacitor 3.

At this time, there is no problem if the anti-parallel thyristor converter 2 can immediately shift from the power running operation to the regenerative operation. However, in the anti-parallel thyristor converter 2, there is a dead time before shifting from the power running operation to the regenerative operation. Will always occur, so the migration will take time. In order to minimize this dead time, the inverse converter output power calculation unit 51 immediately outputs the output power POWER to the anti-parallel thyristor converter 2 regardless of the output power calculation as soon as a sudden load decrease is detected.
It is set to -10% of the maximum output power of, and output to the thyristor converter control unit 16. As a result, the output of the thyristor converter control unit 16 quickly transitions from the power running state to the regenerative state, so that it is possible to prevent a DC overvoltage.

In the case of sudden increase in load, the same effect as in the case of sudden decrease in load can be obtained. From the above, according to the present embodiment, it is possible to suppress the DC voltage fluctuation that occurs when the load changes suddenly.

[0059]

According to the present invention, it is possible to suppress the speed fluctuation and the DC voltage fluctuation of the electric motor when the load changes suddenly.
In the power converter according to claim 1 of the present invention, the load is reduced by immediately setting the upper limit value of the motor torque reference to zero upon detecting a sudden load decrease, and immediately setting the lower limit value of the motor torque reference to zero upon detecting a sudden load increase. It is possible to suppress speed fluctuations and DC voltage fluctuations of the electric motor that occur during sudden changes.

In the electric power converter according to the second aspect of the present invention, as soon as a sudden load decrease or sudden load increase is detected, the integral value of the electric motor speed control section is cleared to zero, so that the speed fluctuation of the electric motor occurring at the sudden change of the load. Further, it is possible to suppress the DC voltage fluctuation.

In the electric power converter according to the third aspect of the present invention, the slope of the torque rate is set to a large value immediately after the sudden load decrease is detected, so that the speed fluctuation and the DC voltage fluctuation of the electric motor which occur during the sudden load decrease are suppressed. be able to.

In the power converter according to the fourth aspect of the present invention, when the load sudden decrease is detected, the inverse converter output power calculating means uses the negative fixed power value as the output power signal to perform the antiparallel thyristor converter control. Output voltage to the reverse parallel thyristor converter to lower the output DC voltage, it is possible to suppress the speed fluctuations and DC voltage fluctuations of the motor that occur when the load suddenly decreases. The output power calculation means outputs a fixed power value of positive polarity as an output power signal to the antiparallel thyristor converter control unit to increase the output DC voltage of the antiparallel thyristor converter, thereby increasing the load It is possible to suppress speed fluctuations and DC voltage fluctuations.

According to a fifth aspect of the present invention, in the power converter according to any one of the first to fourth aspects, the load sudden change detection circuit of the power converter is provided with a difference value between the current value and the previous value of the speed feedback signal. When the polarity of the speed feedback is positive, the load is sharply reduced when the absolute value of the difference value of the torque reference is equal to or larger than the predetermined value b and is equal to or smaller than the predetermined value a. When the absolute value of the difference value of is less than or equal to the predetermined value a, it is detected as a sudden load increase, and the speed fluctuation and DC voltage fluctuation of the electric motor that occur when the load suddenly increases are suppressed.

According to a sixth aspect of the present invention, there is provided a power converter according to any one of the first to fourth aspects, in which the load sudden change detection circuit is provided with a difference value between a current value and a previous value of the speed feedback signal. When the polarity of the speed feedback is positive, the load is sharply reduced when the absolute value of the difference between the current value of the speed feedback signal and the previous value when the filter processing is performed with the speed b as a reference value is equal to or less than the predetermined value a. When the polarity of the speed feedback is negative, it is detected as a sudden increase in load when the absolute value of the difference between the current value of the speed feedback signal and the previous value when the filter processing is performed with the speed equal to or less than the predetermined value -b is less than or equal to the predetermined value a. By doing so, fluctuations in the speed of the electric motor and fluctuations in the DC voltage that occur when the load suddenly increases are suppressed.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a power conversion device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing details of the sudden load change detection circuit according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a detection principle of the sudden load change detection circuit according to the first embodiment of the present invention.

FIG. 4 is a block diagram showing a schematic configuration of a power conversion device according to a second embodiment of the present invention.

FIG. 5 is a diagram showing details of a sudden load change detection circuit according to a second embodiment of the present invention.

FIG. 6 is a diagram showing a detection principle of a sudden load change detection circuit according to a second embodiment of the present invention.

FIG. 7 is a block diagram showing a schematic configuration of a power conversion device according to a third embodiment of the present invention.

FIG. 8 is a block diagram showing a schematic configuration of a power conversion device according to a fourth embodiment of the present invention.

FIG. 9 is a block diagram showing a schematic configuration of a power conversion device according to a fifth embodiment of the present invention.

FIG. 10 is a block diagram showing a schematic configuration of a control system of a conventional power conversion device.

[Explanation of symbols]

 1 ... AC power supply 2 ... Anti-parallel type thyristor converter 3 ... DC smoothing capacitor 4 ... Inverse converter 5 ... Electric motor 6 ... Load 11 ... Position speed detector 12, 31 ... Speed control unit 13 ... Torque limit 14, 51 ... Inverse converter output power calculation unit 16, 42 ... Thyristor converter control unit 18, 21, 32, 43 ... Control circuit 20 ... Power converters 22, 33, 44 ... Load sudden change processing unit 23, 34 ... Proportional circuit 24, 35 ... Integrator circuit 27, 36, 45 ... Load sudden change detection circuit 28, 37, 46. ..Sudden load change processing circuit 41 ... Torque rate

Claims (6)

[Claims] 1. A power converter for converting AC power obtained from an AC power supply into an arbitrary frequency and an arbitrary voltage to control the speed of an electric motor, and a current detecting means provided on the output side of the power converter. Position speed detecting means for detecting a rotor position and speed of the electric motor, and speed control means for calculating a torque reference of the electric motor based on a speed feedback signal from the position speed detecting means and a preset speed reference. A torque limiter for giving an upper limit value to the torque reference output from the speed control means, a sudden load change detection means for detecting a sudden load change, and a sudden load decrease based on a sudden load change signal from the sudden load change detection means. From the torque limiter, a sudden load change processing unit that sets the upper limit value of the torque limiter to zero and sets the lower limit value of the torque limiter to zero when the load suddenly increases. Voltage required to drive the electric motor based on the torque reference, the position feedback signal output from the position / speed detection means, the current feedback signal from the current detection means, and the preset magnetic flux reference of the electric motor. And a control means for calculating a frequency and outputting a power converter control signal for controlling the power converter. 2. A power converter for converting AC power obtained from an AC power supply into an arbitrary frequency and an arbitrary voltage to control the speed of an electric motor, and a current detection means provided on the output side of the power converter. A position / speed detecting means for detecting a rotor position and a speed of the electric motor; and a torque reference of the electric motor by proportional integration based on a speed feedback signal from the position / speed detecting means and a preset speed reference. Speed control means, load sudden change detection means for detecting a sudden load change, and load sudden change processing for making the integral value of the speed control means zero when there is a sudden load decrease or sudden load increase based on a sudden load change signal from the sudden load change detection means. Means, the torque reference, the position feedback signal from the position / speed detection means, and the current feedback signal from the current detection means are set in advance. And a control means for calculating a voltage and a frequency required to drive the electric motor based on the magnetic flux reference of the electric motor and outputting a power converter control signal for controlling the power converter. Power converter. 3. An anti-parallel type thyristor converter means for converting an AC power obtained from an AC power source into an arbitrary DC voltage and an output of the anti-parallel type thyristor converter, wherein the thyristor elements are connected in anti-parallel in a bridge configuration. A DC smoothing capacitor that smoothes the DC voltage and an inverse converter that converts the DC voltage obtained from this DC smoothing capacitor into any frequency and any AC voltage, and a power converter that controls the speed of the motor, From the current detection means provided on the output side of the power converter, the voltage detection means for detecting the voltage of the DC smoothing capacitor, the preset output voltage reference of the antiparallel thyristor converter and the voltage detection means. Anti-parallel thyristor converter that outputs an anti-parallel thyristor converter control signal based on the voltage feedback signal of the Controller, a position / speed detector for detecting the rotor position and speed of the electric motor, and a torque reference for the electric motor based on a speed feedback signal from the position / speed detector and a preset speed reference. Speed control means, a torque rate means for inclining the torque reference from the speed control means, a sudden load change detection means for detecting a sudden load change, and a sudden load change signal from the sudden load change detection means indicating a sudden load decrease. A sudden load change processing means for setting the inclination of the torque rate means to a large value and otherwise setting the inclination of the torque rate means to zero, the torque reference, the position feedback signal from the position / speed detection means, and the current detection. Driving the electric motor based on a current feedback signal from the means and a preset magnetic flux reference of the electric motor. Power conversion device is characterized in that and a control means for outputting a power converter control signal for controlling the power converter to calculate the voltage and frequency required. 4. An anti-parallel type thyristor converter means for converting an AC power obtained from an AC power source into an arbitrary DC voltage and an output of the anti-parallel type thyristor converter, wherein the thyristor elements are connected in anti-parallel in a bridge configuration. A DC smoothing capacitor that smoothes the DC voltage and an inverse converter that converts the DC voltage obtained from this DC smoothing capacitor into any frequency and any AC voltage, and a power converter that controls the speed of the motor, Current detection means provided on the output side of the power converter, voltage detection means for detecting the voltage of the DC smoothing capacitor, position / speed detection means for detecting the rotor position and speed of the electric motor, and the position / speed Speed control means for calculating the torque reference of the electric motor based on the speed feedback signal from the detection means and a preset speed reference A load sudden change detection means for detecting a sudden load change, a load sudden change signal from the load sudden change detection means, the speed feedback signal and the torque reference, based on the speed feedback signal and the torque reference, the speed feedback signal and the An inverse converter output power calculation means for calculating and outputting the output power of the inverse converter based on a torque reference, and outputting a predetermined value in the case of sudden load decrease and sudden load increase, and output of the antiparallel thyristor converter An anti-parallel thyristor converter control unit that outputs an anti-parallel thyristor converter control signal based on a voltage reference signal, a voltage feedback signal from the voltage detection unit, and an output power signal output from the inverse conversion device output power calculation unit, The torque reference and the position feedback signal output from the position / speed detection means, and A power converter control signal for controlling the power converter by calculating the voltage and frequency required to drive the electric motor based on the current feedback signal from the flow detecting means and a preset magnetic flux reference of the electric motor. And a control means for outputting the electric power. 5. The load abrupt change detection means is a torque reference when the difference between the current value and the previous value of the speed feedback signal from the position / speed detection means is a first predetermined value or more when the polarity of the speed feedback is positive. When the absolute value of the difference value is less than or equal to the second predetermined value, the load is suddenly decreased, and when the polarity of the speed feedback is negative, the absolute value of the torque reference difference value is less than or equal to the reverse polarity value of the first predetermined value. The load is rapidly increased when it is equal to or less than a second predetermined value.
5. The power conversion device according to any one of 4 to 4. 6. The load abrupt change detection means, when the difference between the current value of the speed feedback signal from the position / speed detection means and the previous value is positive in the polarity of the speed feedback, the speed reference is equal to or more than a first predetermined value. When the absolute value of the difference between the current value of the speed feedback signal and the previous value when the filter processing is performed is less than or equal to the second predetermined value, the load is sharply reduced, and when the polarity of the speed feedback is negative, the first predetermined value is set. When the absolute value of the difference value between the current value of the speed feedback signal and the previous value when the filter processing is performed on the basis of the reverse polarity value of the speed reference signal or less, the load is rapidly increased. The power conversion device according to claim 1.