JPH11289792A - Inverter device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inverter device which is able to drive an induction motor stably with respect to steep load fluctuations and restrain rotational speed from dropping for improved low-speed characteristics. SOLUTION: This inverter device is provided with a current filter 16 for outputting a current signal Ief following fluctuations in the first current of an induction motor 5 obtained by measuring DC input with a prescribed time constant, a sliding frequency output circuit 17 which outputs a sliding frequency fs which is proportional to the current signal Ief , an adding machine 18 adding the sliding frequency fs to command reference frequency fa to output command frequency (f). The inverter device adds a correction voltage Vd in proportion to the current signal Ief to command reference voltage of prescribed V/f ratio obtained by inputting the command frequency fs to turning a command voltage V, obtains a PMW signal by inputting the command frequency (f) and command voltage Va to control an inverter 4, and thus it is possible to perform satisfactory automatic torque boost control and sliding frequency compensation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter for controlling an induction motor at a variable speed, and more particularly to an inverter for improving the low-speed torque characteristic of an induction motor and improving its driving performance.

[0002]

2. Description of the Related Art FIG. 6 shows a conventional inverter device. 6, reference numeral 1 denotes an AC power supply, 2 denotes an AC / DC conversion circuit for converting AC output from the AC power supply 1 to DC, 3 denotes a smoothing capacitor connected in parallel to the output side of the AC / DC conversion circuit 2, and 4 denotes a smoothing capacitor. Is a DC / AC conversion circuit for converting the DC charged in the capacitor 3 into a new AC, and is hereinafter referred to as an inverter 4. 5 is Invar
An induction motor that receives AC power from the motor 4.

[0003] 6 is a frequency setting circuit for setting a frequency fe which is a reference of the rotation speed of the induction motor 5, 7 is a cushion circuit for outputting a command frequency f which smoothly follows the frequency fe set by the frequency setting circuit 6, 8 is a command reference voltage Va having a predetermined V / f ratio with respect to the input command frequency f.
A voltage frequency ratio circuit 9 for outputting a DC bus current idc connecting the smoothing capacitor 3 and the inverter 4;
Reference numeral 10 denotes a current detector which inputs a measured value of the measured DC bus current idc, detects a peak value thereof, and outputs a voltage proportional to the detected current.

[0004] Reference numeral 11 denotes a current value i of the induction motor 5 when there is no load.
A current value setting circuit for setting 0, an adder / subtractor 12 for detecting a current increase obtained by subtracting a current value set by the current value setting circuit 11 from an output of the current detector 10, 13 a current increase from the adder / subtractor 12 This is a correction voltage output circuit that outputs a correction voltage proportional to the minute, and its proportional constant is made to substantially match the primary resistance r1 of the induction motor 5. Reference numeral 14 denotes an adder that adds the correction voltage Vd output from the correction voltage output circuit 13 to the command reference voltage Va output from the voltage frequency ratio circuit 8 and outputs the result as a command voltage V.

A PWM generating circuit 15 generates a PWM signal based on the input of the command frequency f output from the cushion circuit 7 and the command voltage V output from the adder 14, and outputs the PWM signal to the inverter 4.

Next, the operation of the circuit will be described. In FIG. 6, when the frequency setting, that is, the speed setting is performed by the frequency setting circuit 6, the cushion circuit 7 receives the set frequency fe from the frequency setting circuit 6 so as not to abruptly change the current operating speed of the inverter device. Then, a command frequency f that smoothly follows the set frequency fe is output.
The voltage frequency ratio circuit 8 receives the command frequency f from the cushion circuit 7 and outputs a command reference voltage Va according to a predetermined voltage frequency ratio V / f.

On the other hand, the current detector 10 receives a measured value of the pulsating DC bus current idc, detects a peak value ip thereof, and, based on the detected peak value ip, determines a fundamental wave effective value of the primary current i of the induction motor. Calculate the value Ie.

Subsequently, a current value corresponding to the no-load current i0 is set by the current value setting circuit 11, and the primary current i of the induction motor output from the current detector 10 is output by the adder / subtractor 14.
The current value corresponding to the no-load current i0 set by the current value setting circuit 11 is subtracted from the fundamental wave effective value Ie to obtain a current increase Δi caused by an increase in the load on the induction motor 5. The correction voltage output circuit 13 calculates a product of the current increase Δi and the primary resistance value r1 of the induction motor 5 and outputs a correction voltage Vd. Then, in the adder 14, the voltage frequency ratio circuit 8
To the command reference voltage Va output from the
The command voltage V is obtained by adding the correction voltage Vd output from the control signal 3.

In the PWM generation circuit 15, the cushion circuit 7
And a command voltage V from the adder 14 to generate a PWM signal for turning on / off a switching element constituting the inverter 4.

[0010]

Since the conventional inverter device is configured as described above, when the induction motor 5 is driven by the AC output of the inverter 4, the DC current of the DC bus is detected by the current detector 10. Since the peak value ip of idc is detected and the effective value Ie of the primary current i of the induction motor obtained by the calculation is directly used for control, the follow-up to the current fluctuation at the time of load fluctuation becomes steep, and the inverter 4, the voltage fluctuation of the AC output is large, and the operation of the induction motor 5 may be unstable.

Further, since the slip frequency is not compensated, there is a problem that the slip S becomes large under heavy load, and the rotational speed of the induction motor 5 is greatly reduced. further,
There is a problem that the effective value Ie of the primary current i of the induction motor cannot be accurately calculated depending on the influence of noise.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is intended to reduce the induction motor even when the load of the induction motor fluctuates sharply or repeatedly. It is an object of the present invention to provide an inverter device that can drive stably and suppress a decrease in the number of revolutions when the load suddenly increases.

[0013] Further, it is an object of the present invention to obtain an inverter device capable of removing the influence of noise and improving the effective value calculation accuracy when calculating the effective value of the primary current of the induction motor by detecting the peak value of the DC bus current. Aim.

[0014]

According to a first aspect of the present invention, there is provided an inverter device comprising: a DC power supply; an inverter for converting a DC input from the DC power supply into an AC and outputting the AC to an induction motor; A control unit that outputs a PWM signal to the inverter unit and controls an AC output of the inverter unit. The control unit measures the DC input and outputs a current signal corresponding to a primary current of the induction motor. An output means, a command frequency generating means for generating a command frequency, and a command reference voltage having a predetermined V / f ratio obtained by inputting the command frequency, a correction voltage obtained from the current signal, and addition to the command reference voltage. Command voltage output means for outputting as a command voltage, and P
PWM for generating a WM signal and outputting to the inverter unit
In the inverter device having the generating means, the current signal output means includes a current filter for outputting a current signal that follows a primary current of the induction motor with a predetermined time constant, and the command voltage output means includes a current filter. Correction voltage calculation means for calculating a correction voltage proportional to a signal, wherein the command frequency generation means calculates a slip frequency proportional to the current signal; and a slip frequency calculation means for calculating a slip frequency proportional to the current signal. A command frequency correcting means for adding a frequency and outputting the command frequency is provided for performing automatic torque boost control and slip frequency compensation.

The inverter device according to a second aspect of the present invention is the inverter device according to the first aspect, wherein the inverter section includes a plurality of switching elements and a plurality of arms connected in parallel. A current signal output means is connected between a collective connection point of the plurality of arms connected in parallel in the inverter section and a negative electrode of the DC power supply section, and a pulsating DC current inputted to the inverter section. , A peak-hold means for holding the peak value of the current-proportional voltage measured by the current-detecting resistor, and a hold. Sampling means for sampling the peak value of the current value proportional voltage at a predetermined period, and a sampler of at least the maximum voltage value among a predetermined number of the sampled peak value samples. Current calculating means for calculating the primary current effective value of the induction motor based on the peak value samples excluding the above, and a current signal which follows the calculated primary current effective value of the induction motor with a predetermined time constant is output. And a current filter.

The inverter device according to a third aspect of the present invention is the inverter device according to the first or second aspect, wherein the current calculating means includes a predetermined number of peak value samples in the current value proportional voltage sampled at a predetermined cycle. Among them, the primary current effective value of the induction motor is calculated from the average voltage value of the peak value samples excluding at least the sample of the maximum voltage value.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 First Embodiment A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram showing a circuit configuration of the inverter device, and FIG. 2 is a block diagram showing a configuration of a current detector in the inverter device. FIG. 3 is a diagram showing a T-type equivalent circuit of the induction motor,
FIG. 4 shows the DC bus current of the inverter device, the primary currents Iu, Iv, Iw of the induction motor and the primary current amplitude Is.
FIG. 5 is a diagram showing a speed-torque characteristic curve with and without slip compensation control of the inverter device. In the figure, those denoted by the same reference numerals as those of the conventional example indicate the same or equivalent parts as those of the conventional example.

In FIG. 1, an AC / DC converter 2 for converting AC output from an AC power supply 1 to DC and a smoothing capacitor 3 connected in parallel to the output side of the AC / DC converter 2 constitute a DC power supply unit. Also, an inverter for converting the DC charged in the smoothing capacitor 3 into a new AC.
The inverter 4 is constituted by the inverter 4. In the inverter 4, two switching elements 4a are connected in series.
Three sets of arms (not shown) having the intermediate connection point as an output point are connected in parallel.

A pulsating DC bus 9A is connected between a negative electrode 3a of the smoothing capacitor 3 and a collective connection point 4b of three sets of arms (not shown) connected in parallel in the inverter 4. This is a current detection resistor for measuring the current idc. 10A, a current value proportional voltage measured as a voltage between its terminals is input by a current detection resistor 9A to detect a peak value ip thereof, and a primary current amplitude of the induction motor 5 is determined based on the detected peak value ip. This is a current detector that detects the value Is, converts it into a primary effective current value Ie, and outputs it. As shown in FIG. 2, the current detector 10A includes a peak hold circuit 10a, a sampling circuit 10b, and a voltage / current conversion operation circuit 10c.

Reference numeral 16 denotes a current filter for outputting a first-order delayed current signal Ief in response to the input of the primary current effective value Ie detected by the current detector 10A. The current detection resistor 9A, the current detector 10A and the current filter 16 constitute a current signal output unit.

Reference numeral 17 denotes a current signal Ie from the current filter 16.
f, and a slip frequency f proportional to the current signal Ief.
A slip frequency output circuit serving as a slip frequency calculation means for outputting s sets a coefficient k specific to the induction motor as a proportional constant thereof. Reference numeral 18 denotes a slip frequency output circuit 17 which outputs the command reference frequency fa output from the cushion circuit 7.
This is an adder as a slip frequency correction means for adding the slip frequency fs output from the controller, and outputs a command frequency f as a result of the addition. The frequency setting circuit 6, the cushion circuit 7, the slip frequency output circuit 17 and the adder 18 constitute a command frequency generating means.

A correction voltage output circuit 13 as a correction voltage calculation means receives the current signal Ief from the current filter 16 and outputs a correction voltage Vd proportional to the current signal Ief. It is made to substantially match the primary resistance r1 of the motor. The voltage frequency ratio circuit 8, the correction voltage output circuit 13 and the adder 14 constitute a command voltage output means.

Prior to the description of the operation of the circuits shown in FIGS. 1 and 2, the basis of the present invention will be described with reference to FIG. In the equivalent circuit of the induction motor 5 shown in FIG.
1 is E1 = V− (r1 + jωL1) · Ie (3) where, if the primary current effective value is Ie, jω = 2πf r1: primary resistance of the induction motor 5 L1: primary leakage inductance of the induction motor 5 Here, in the equation (3), the primary leakage inductance L1 is smaller than the primary resistance r1 and is neglected because it is small. E1 = V−r1 · Ie = V−Vd (4) where Vd = r1 · Ie: drop voltage . In the equation (4), the command reference voltage Va is approximately approximated so that the primary induced voltage E1 becomes equal to the command voltage V.
Automatic torque boost control corrects the voltage drop Vd proportional to the primary current effective value Ie.

The actual rotation frequency fm of the induction motor 5
Decreases by the slip frequency fs. In Equation (5), the slip frequency fs corresponding to the command reference frequency fa in proportion to the primary current effective value Ie is approximately compensated so that the actual rotation frequency fm of the induction motor 5 becomes equal to the command frequency f. This is slip frequency compensation control.

The present invention provides the above automatic torque boost control,
In the slip frequency compensation control, instead of directly using the primary current effective value Ie, a steep change in the primary current effective value Ie obtained by passing through the primary delay current filter 16 is smoothly performed with a predetermined time constant. Using the following current signal Ief, the correction voltage Vd (= r1 · Ief:
Voltage drop) and slip frequency fs (fs = k · Ie)
f) is calculated and used, so that the induction motor 5 is controlled so as to smoothly follow with a predetermined time constant even when the current fluctuates sharply due to a load fluctuation, and the induction motor 5 is driven by the slip S. 5, the reduction in the number of rotations is suppressed, and the low-speed torque characteristics are further improved.

Next, the operation of the circuits shown in FIGS. 1 and 2 will be described. First, the pulsating DC bus current idc is measured by the current detecting resistor 9A shown in FIG.
A receives the measured value of the DC bus current idc, detects the peak value ip, and detects the detected peak value ip.
, The primary effective current value Ie of the induction motor 5 is detected and output.

That is, as is clear from FIG. 4, the pulsating DC bus current i measured by the current detecting resistor 9A
The peak value ip of dc is the primary current amplitude value Is of the induction motor.
Therefore, the peak value ip of the DC bus current idc is detected and held by the peak hold circuit 10a shown in FIG. Next, the sampling circuit 10b
Sampling at every predetermined sampling period to obtain a sampling value. Next, the voltage-current conversion operation circuit 10
At c, an average value of the sampling values excluding at least the maximum value of the plurality of sampling values is obtained, and the primary current effective value Ie is obtained based on the average value.

Next, the primary current effective value Ie output from the current detector 10A is input to the filter 16, and a current signal that smoothly follows a steep change of the primary current in the induction motor 5 with a predetermined time constant. Outputs Ief.

Next, the slip frequency output circuit 17 multiplies the input current signal Ief by k to output a slip frequency fs. Then, the adder 18 adds the slip frequency fs output from the slip frequency output circuit 17 to the command reference frequency fa output from the cushion circuit 7 to obtain the command frequency f.

Next, the command frequency f is input to the voltage frequency ratio circuit 8, and a command reference voltage Va having a predetermined V / f ratio is output. On the other hand, in the correction voltage output circuit 13, the current signal Ie
The correction voltage Vd is calculated and output from the product of f and the proportional constant r1. Next, the adder 14 adds the command reference voltage Va input from the voltage frequency ratio circuit 8 to the correction voltage output circuit 13.
, The command voltage V is obtained by adding the correction voltage Vd input from the control circuit.

Next, a PWM signal is generated in the PWM generation circuit 15 based on the input of the command frequency f and the command voltage V, and is output to the inverter 4. With this PWM signal,
By turning on / off the switching element 4b constituting the inverter 4, the induction motor 5
To supply an output voltage and an output frequency corresponding to the command frequency V and the command frequency f to drive the induction motor 5.

5a shows the relationship between the speed N and the torque T in the induction motor 5 of the conventional inverter device, and 5a shows the relationship between the speed N and the torque T in the inverter device shown in the first embodiment. As compared with the conventional inverter device without the slip compensation control shown in 5b, the inverter device of the first embodiment in which the slip compensation control shown in 5a is performed has a rise in the torque T near zero of the slip S. Are steep, indicating the effects of good automatic torque boost control and slip frequency compensation control.

As described above, the inverter device shown in the first embodiment uses the primary current effective value Ie of the induction motor 5 detected by the current detector 10A directly in the calculation of the correction voltage Vd for correcting the command voltage V. The current signal Ief obtained without using the primary current effective value Ie through the current filter 16 having the primary delay
Is used, the current fluctuation can smoothly follow the load fluctuation of the induction motor 5, the voltage fluctuation is relatively small, and the induction motor 5 can be driven stably.

The correction voltage V is calculated using the current signal Ief.
d, and the command voltage V is corrected. Similarly, the slip frequency fs is calculated using the current signal Ief, and the command frequency f is corrected by the obtained slip frequency fs. Good slip frequency compensation control is performed, the command voltage V and the command frequency f are stably controlled, the induction motor 5 can be driven stably, and a decrease in the rotation speed of the induction motor 5 due to the slip S is suppressed. The low-speed torque characteristics can be improved.

Further, in the inverter device shown in the first embodiment, a current detecting resistor 9A is provided between the negative electrode 3a of the DC power supply and the collective connection point 4b of each arm constituting the inverter 4. Since the DC bus current idc was measured by connection, the current detector 10A inputs the measured value of the DC bus current idc and calculates the primary current effective value Ie of the induction motor 5 from the average value of the tower v-ring value. Therefore, the influence of the noise on the calculation accuracy of the primary current effective value Ie can be removed.

In the voltage-current conversion operation circuit 10c in the current detector 10A shown in FIG. 2, an average value of the sampling values obtained by sampling, excluding at least the maximum value, is used. Although an example is shown, by using a sampling value indicating an intermediate value of a plurality of consecutive sampling values in the order of larger values or in the order of smaller values,
The influence of the noise on the calculation accuracy of the primary current effective value Ie can be removed.

Further, in the inverter device shown in the first embodiment, the current detector 10A, the current filter 16, and the like in the control section are constituted by H / W. However, the inverter is not necessarily constituted by H / W. The same effect can be obtained by replacing the function in the process up to calculating the command voltage V and the command frequency f of the inverter 4 with a function obtained by executing a predetermined program using a microprocessor.

[0038]

According to the first aspect of the invention, a current signal that follows the primary current of the induction motor with a predetermined time constant and is obtained by measuring the DC bus current is calculated, and this current signal is used to calculate the current signal. , A slip frequency and a correction voltage, and calculates the command frequency by adding the slip frequency to a command reference frequency input separately.
/ F ratio by adding the correction voltage to the command reference voltage to obtain a command voltage.
Since the inverter is controlled by generating the M signal, slip frequency compensation can be performed together with good automatic torque boost control, voltage fluctuation is relatively small with respect to load fluctuation of the induction motor, and the induction motor is stabilized. In addition to being able to be driven, there is an effect that a reduction in rotation speed due to slippage can be suppressed and a low-speed torque characteristic can be improved.

According to the second aspect of the present invention, a pulsating DC bus current is generated by connecting a current detecting resistor between a negative electrode of a DC power supply and a collective connection point of each arm constituting an inverter. Is measured, the peak value is detected from the measured value, sampling is performed, and the primary current effective value of the induction motor is calculated from the sampling value obtained by removing at least the maximum value among a plurality of sampling values obtained by sampling. Therefore, there is an effect that an effect that can reduce the influence of noise on the calculation accuracy of the primary current effective value can be obtained.

According to the third aspect of the present invention, the primary current effective value of the induction motor is calculated from the average value of the sampling values excluding at least the maximum value among the plurality of sampling values obtained by sampling. The effect of noise on the calculation accuracy of the primary current effective value can be further reduced, and there is an effect that a more accurate primary current effective value can be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of an inverter device according to a first embodiment of the present invention.

FIG. 2 is a circuit block diagram of a current detector in the inverter device shown in FIG.

FIG. 3 is a diagram showing a T-type equivalent circuit of the induction motor.

FIG. 4 is a waveform diagram showing a detection current of the inverter device and a primary current amplitude value Is of the induction motor.

FIG. 5 is a diagram showing a speed-torque characteristic curve with and without slip compensation control of the inverter device.

FIG. 6 is a circuit block diagram of a conventional inverter device.

[Explanation of symbols]

1 AC power supply, 2 AC / DC conversion circuit, 3 Smoothing capacitor, 4 DC / AC conversion circuit, 5 induction motor, 6 Speed setting device, 7 Cushion circuit, 8 Voltage frequency ratio circuit, 9A current detection resistor, 10A current detector , 1
3 Correction voltage output circuit, 14 adder, 15 PWM generation circuit, 16 current filter, 17 slip frequency output circuit, 18 adder.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masato Koyama 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Inside Mitsubishi Electric Corporation (72) Inventor Sumio Sumoto 1-1-1 Imajuku Higashi, Nishi-ku, Fukuoka City, Fukuoka Prefecture No. Fukuishi Semicon Engineering Co., Ltd. (72) Inventor Masaki Sakai 1-1-1, Imajuku Higashi, Nishi-ku, Fukuoka City, Fukuoka Prefecture Fukuishi Semicon Engineering Co., Ltd.

Claims (3)

[Claims] 1. A DC power supply unit, an inverter unit for converting a DC input from the DC power supply unit into AC and outputting the AC to an induction motor, outputting a PWM signal to the inverter unit, and outputting an AC output of the inverter unit. A control unit for controlling, the control unit measures the DC input and outputs a current signal according to a primary current of the induction motor, and a command frequency generating means for generating a command frequency, Command voltage output means for obtaining a command reference voltage having a predetermined V / f ratio by inputting the command frequency, obtaining a correction voltage from the current signal, adding the corrected voltage to the command reference voltage, and outputting the same as a command voltage; By inputting the command frequency and the command voltage, P
PWM for generating a WM signal and outputting to the inverter unit
In the inverter device having the generating means, the current signal output means includes a current filter which outputs a current signal which follows a primary current of the induction motor with a predetermined time constant. A correction voltage calculating means for calculating a correction voltage proportional to the signal; wherein the command frequency generating means calculates a slip frequency proportional to the current signal; and a slip frequency calculating means for calculating a slip frequency based on a separately input command reference frequency. An inverter device comprising command frequency correcting means for adding a frequency and outputting the command frequency as a command frequency, and performing automatic torque boost control and slip frequency compensation. 2. The inverter device according to claim 1, wherein the inverter unit includes a plurality of switching elements and includes a plurality of arms connected in parallel, and the current signal output unit includes a plurality of switching elements. A current detecting device connected between the collective connection point of the plurality of arms connected in parallel and the negative electrode of the DC power supply unit for measuring a pulsating DC current input to the inverter unit as a current value proportional voltage. A resistor; peak-hold means for holding the peak value of the current proportional voltage measured by the current detecting resistor; and a peak value of the held current proportional voltage. Sampling means for sampling at a predetermined period, and a peak value sample obtained by removing at least a sample of a maximum voltage value from among a predetermined number of the sampled peak value samples. An inverter comprising: a current calculating means for calculating a primary current effective value of the induction motor; and a current filter for outputting a current signal which follows the calculated primary current effective value of the induction motor with a predetermined time constant. apparatus. 3. The inverter device according to claim 2, wherein the current calculating means removes at least a sample of a maximum voltage value from a predetermined number of peak value samples in a current value proportional voltage sampled at a predetermined cycle. And calculating an effective primary current value of the induction motor from the average voltage value of the peak value samples.