JPH0634583B2 - Inverter device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an improvement of an inverter device used for controlling and driving an AC electric motor such as an induction motor.

[Technical background of the invention]

Generally, when an AC motor, for example, an induction motor, is controlled at a variable speed by an inverter device, a ratio of an inverter output voltage V to an output frequency, that is, a so-called V / F ratio is made substantially constant as shown by a straight line A in FIG. The saturation of the magnetic flux is prevented by controlling the magnetic flux of the induction motor to be constant. Further, in order to prevent the low range of the induction motor output torque due to the lowering of the excitation voltage due to the drop of the primary winding impedance of the induction motor in the low frequency range, the output characteristics of the inverter device are taken into consideration as shown by the straight line B in FIG. It is also controlled. Then, these two control methods are very effective methods when the load of the induction motor is constant regardless of the rotation speed (so-called constant torque load characteristic).

On the other hand, when a load such as a fan, a blower, or a pump is driven by an induction motor, its load torque characteristic is often proportional to the square of the rotation speed (so-called square torque load characteristic), so that the curve C in FIG. By controlling the output voltage V of the inverter device in proportion to the square of the output frequency as shown in FIG. 1, it is often attempted to reduce the exciting current of the induction motor and the noise caused thereby.

Furthermore, the relationship between the output voltage V and the output frequency of the above-described inverter device is set in advance, and during operation of the inverter device, A of FIG. 1 is automatically set according to the type of load of the induction motor.
It is also practiced to select and control any one of the characteristics C to C.

[Problems of background technology]

However, even if the induction motor is controlled and driven according to the curve C that is generally said to be effective for the squared torque load characteristic, the voltage dependence characteristic of the exciting current of the induction motor has individual induction motors. Therefore, if the type of the induction motor, that is, the voltage dependence characteristic of the exciting current is different, the above-described sufficiently effective control cannot be performed with the uniform curve C, and as a result, the induction motor by the inverter device can be used. There is a problem that driving noise and vibration peculiar to driving are generated.

[Object of the Invention]

The present invention has been made to solve the above problems, and its object is to apply a voltage to an electric motor regardless of the load or the characteristics of an AC motor to be applied, regardless of the voltage dependence of the exciting current. An object of the present invention is to provide an inverter device capable of suppressing the operating noise and vibration peculiar to the driving as a minimum required value.

[Outline of Invention]

In order to achieve the above-mentioned object, an inverter device of the present invention comprises a DC converter for converting an AC voltage into a DC voltage, and a first DC converter.
And an inverter for converting the DC voltage from the DC converter into an AC voltage, a second switching element provided between the DC converter and the inverter, and a conduction timing of the first switching element. A frequency controller that controls the output frequency of the inverter to a predetermined value, and a voltage control that controls the conduction timing of the second switching element corresponding to the output frequency to control the output voltage of the inverter to a predetermined value. , A load current detector that detects the load current of the inverter, and a correction signal that gives a correction voltage signal to the voltage controller to minimize the load current based on the load current detected by the load current detector. And generating means.

That is, in the present invention, the load current of the AC electric motor, which is the load current of the inverter, is detected, and the output voltage of the inverter is automatically corrected and controlled so as to minimize it.

Example of Invention

An embodiment of the present invention shown in the drawings will be described below.
FIG. 2 is a block diagram showing a configuration example of the inverter device according to the present invention. In the figure, 1 is a DC exchanger for converting an AC voltage output from the commercial power supply 2 into a DC voltage, 3 is a first switching element such as a transistor, and an inverter for converting the DC voltage into an AC voltage. The output voltage is supplied to an induction motor 5 as an AC motor in which a fan 4 as a load is directly connected to the shaft. Also,
Reference numeral 6 is a second switching element such as a transistor provided on the positive potential line between the DC exchanger 1 and the inverter 3, and 7 is a smoothing capacitor.

On the other hand, reference numeral 8 is a frequency controller for controlling the conduction timing of the first switching element by its output pulse to control the output frequency of the inverter 3 to the frequency set by the frequency setter 9. A function generator 10 receives an output pulse from the frequency controller 8 and generates a function output having a V / F ratio that provides an output voltage corresponding to an output frequency based on the output pulse. Reference numeral 11 is an adder / subtractor that adds or subtracts the output signal of the function generator 10 and a correction voltage signal described later, and the output thereof is input to the D / A converter 12 and converted into an analog signal. Reference numeral 13 is a load voltage detector for detecting the load voltage which is the output voltage of the inverter 3, and
Reference numeral 4 denotes an output signal of the load voltage detector 13 output via the diode 15. An adder / subtractor for adding / subtracting the output signal of the D / A converter 12 and a chip controller 16 for inputting the output of the adder / subtractor 14 are provided for the second switching element 6 so that this deviation becomes zero. Is controlled to control the output voltage of the inverter 3. Here, the function generator 10, the D / A converter 12, and the chip controller 16 constitute a voltage controller.

On the other hand, 17 is a load current detector that detects a load current that is the output current of the inverter 3, and 18 is the load current detector 17 that is output via a diode 19 and converted into a digital signal by an A / D converter 20. In the correction signal generator which receives the output signal of (1), the correction voltage signal is given to the adder / subtractor 11 of the voltage controller so that the load current is minimized.

Next, the operation of the inverter device will be described. First, the AC voltage of the commercial power supply 2 is converted into a DC voltage by the DC converter 1. The converted DC voltage is interrupted by the second switching element 6 and smoothed by the smoothing capacitor 7, and is controlled to a DC voltage of a magnitude corresponding to the AC output voltage of the inverter 3. This DC voltage is converted by the inverter 3 into an AC voltage corresponding to the frequency set by the frequency setting unit 9 and supplied to the induction motor 5.

On the other hand, the frequency signal set by the frequency setter 9 is converted into a pulse by the frequency controller 8 and given to the inverter 3 as its control signal. When the inverter 3 is composed of a three-phase bridge, an AC voltage having a frequency ⅙ of the frequency of the input pulse appears as the output voltage of the inverter 3. The output pulse of the frequency controller 8 is converted into an analog signal via the function generator 10, the adder / subtractor 11 and the D / A converter 12. In this case, when the output of the correction signal generator 18 is zero, the function generator 10 changes the frequency of the input pulse so that the output signal of the D / A converter 12 has a V-relationship shown by a straight line B in FIG. The function conversion is performed to a digital signal that gives In that case, since the output voltage of the inverter 3 is rectified by the diode 15 detected by the transformer 13 and input to the adder / subtractor 14, the output of the D / A converter 12 (command value of the controller) And the deviation is added / subtracted
4 is input to the chip controller 16. Then, the chip controller 16 controls the second switching element 6 so that this deviation becomes zero, so that the relationship between the output voltage of the inverter 3 and the frequency is automatically as shown by the straight line B in FIG. Controlled by.

Now, if the correction signal generator 18 to which the output signal of the load current detector 17 for detecting the load current of the inverter 3 is added, outputs a (+) correction value signal, For the output, the value obtained by subtracting the correction value of the correction signal generator 18 from the value of the output signal of the function generator 10 is D / A.
Since it is input to the converter 12, the output voltage of the inverter 3 is changed from the voltage value of V-relation shown by the curve B in FIG.
The voltage value becomes lower by the correction value of 8. (In FIG. 1, the output voltage is changed from V ₁ to V _2. ) FIG. 3 shows a change in current flowing through the induction motor 5 in this case. In the figure, I ₁ is an inverter 3
Load current of the induction motor 5 when the output voltage V ₁ shown in Figure 1, likewise I ₂ output voltage of the inverter 3 is V ₂
In this case, the load current of the induction motor 5 is shown. When the induction motor 5 is driving a load having a square torque load characteristic such as the fan 4, the load current I ₂ is smaller than I ₁ if the output voltage V ₂ is an appropriate value. The reason can be easily understood by dividing the load current into the execution current and the exciting current. In FIG. 3, I ₀₁ , I ₀₂ and IL ₁ , IL ₂ are shown as the exciting current and effective current of the load currents I ₁ and I ₂ , respectively. That is, when the output voltage of the inverter 3 changes from V ₁ to V ₂ , the exciting current of the induction motor 5 greatly decreases from I ₀₁ to I ₀₂ due to the non-linear characteristic of the magnetic material as shown in FIG. On the other hand, the effective current increases from IL ₁ to IL ₂ in inverse proportion to the decrease in voltage, but the combined load current decreases from I ₁ to I ₂ . This load current is detected by the load current detector 17
Is detected by the diode 19 and becomes a DC signal.
It is converted into a digital value by the / D converter 20 and input to the correction signal generator 18. The correction signal generator 18 stores the load current I ₁ before outputting the correction voltage signal and compares the magnitude with the load current I ₂ after outputting the correction voltage signal. Since I ₁ > I ₂ in the above example, the correction signal generator 18 outputs a larger correction signal. as a result,
The output voltage of the inverter 3 is V ₃ as shown in FIG. 1, and the load current I ₃ is shown in the same figure (I ₁ <I _{2 in} the case of FIG. 3).
As shown in, it becomes larger than I ₂ . This is I
_As shown in FIG. 4, the amount of decrease in the exciting current I ₀₃ of No. 3 becomes smaller, and as can be seen from FIG. ₃ , the increase in the effective current IL ₃ cannot be ignored and, on the contrary, the load current increases. Next, the correction signal generator 1 compares the load current I ₃ with the load current I ₂ before it, detects that I ₂ <I ₃ , and sets the magnitude of the correction voltage signal to V ₂ . Change to the correction signal value. Here, if the change amount of the correction signal value is reduced, the inverter 3 set by the frequency setter 9 is set.
It can be easily understood that the output voltage of the inverter 3 that minimizes the load current of the induction motor 5 at the output frequency ₁ of ₁ can be detected.

As described above, the present inverter device includes the DC exchanger 1 for converting an AC voltage into a DC voltage, and the inverter 3 for converting the DC voltage into an AC voltage, which includes the first switching element.
And the second switching element 6 provided between the DC converter 1 and the inverter 3 and the conduction timing of the first switching element to control the output frequency of the inverter 3 by the frequency setting device 9. A frequency controller 8 for controlling to a set value, and a function generator 10 for controlling the conduction timing of the second switching element 6 corresponding to the output frequency to control the output voltage of the inverter 3 to a predetermined value.
A voltage controller including a chip controller 16, a load current detector 17 for detecting a load current of the inverter 3, and a correction voltage signal based on the load current so as to minimize the load current. And the correction signal generator 18 for the

Therefore, the output voltage of the inverter 3 is automatically corrected and controlled so that the load current of the induction motor 5, which is the load current of the inverter 3, is minimized, so that the voltage applied to the induction motor 5 is set to the required minimum value. It becomes possible to do. Therefore, even if the type of the induction motor 5 is different and the voltage dependence characteristic of the exciting current is different for each induction motor, the induction motor 5 is effectively controlled and driven, that is, uniform characteristics (A, B in FIG. 1,
It is possible to perform optimal control operation for each induction motor that cannot be obtained in C), suppress the operation noise and vibration peculiar to the induction motor drive by the inverter device, and improve the operation efficiency. it can.

In the above embodiment, the correction signal generator 18 is
Although both output signals have a function of operating with digital values, this can be easily realized even by using a microcomputer or the like. FIG. 5 is a flow chart showing the operation when the microcomputer is used. In the figure, the microcomputer reads the load current I _n of the induction motor 5 from the output of the A / D converter 20, compares it with the load current I _n-1 read previously,
The correction voltage signal ΔV or −ΔV is output based on the result. In this case, if there is no change in load current (if below a value sufficient for practical change in correction voltage signal values I _n -I _n-1 value ΔV for a digital control) correction voltage signal Do not output. The control effect wait time is the time until the effect appears as a change in the load current of the induction motor 5 after the correction voltage signal ΔV is output, the stability of the system including the inverter device, the induction motor 5 and the fan 4, and the like. It is a waiting time control that is determined in consideration of the above.

Further, in the above embodiment, the relationship between the output voltage V and the output frequency of the inverter device when the correction signal generator 18 does not function has been described by taking the straight line B of FIG. 1 as an example, but the present invention is not limited to this. Alternatively, the same effect can be obtained by using an arbitrary relational line such as the curve C.

Furthermore, when the correction signal generator 18 is realized by a microcomputer as described above, it is possible to include and control all of the above-mentioned controllers of the inverter device depending on its capability.

Furthermore, although the DC converter 1 and the switching element (transistor) 6 are used to obtain the DC voltage in the above embodiment, a thyristor is used as a constituent element of the DC converter 1 without using the switching element 6, and Controller 16
The same effect can be obtained even if is replaced with a thyristor phase controller.

〔The invention's effect〕

As described above, according to the present invention, the output voltage of the inverter is automatically corrected and controlled so that the load current of the AC motor, which is the load current of the inverter, is automatically minimized. Even if the characteristics of
It is possible to provide an extremely highly reliable inverter device capable of suppressing the operating noise and vibration peculiar to its drive to a minimum by setting the voltage applied to the electric motor to the required minimum value regardless of the voltage dependence of the exciting current.

[Brief description of drawings]

FIG. 1 is a diagram showing the output voltage and output frequency of the inverter device, FIG. 2 is a block diagram showing an embodiment of the present invention, and FIG.
FIG. 4 and FIG. 4 are characteristic charts for explaining the operation of the present invention, and FIG. 5 is a flow chart showing another embodiment of the present invention. 1 ... DC exchanger, 3 ... Inverter, 5 ... Induction motor, 6 ... Switching element, 8 ... Frequency controller, 1
0 ... Function generator, 11, 14 ... Adder / subtractor, 12 ...
D / A converter, 13 ... Load voltage detector, 16 ... Chip controller, 17 ... Load current detector, 18 ... Correction signal generator, 20 ... A / D converter.

Claims (1)

[Claims] 1. A DC converter for converting an AC voltage into a DC voltage; an inverter for converting a DC voltage from the DC converter into an AC voltage; and an inverter for converting the DC voltage from the DC converter into an AC voltage. A second switching element provided between the first switching element and a frequency controller that controls the conduction timing of the first switching element to control the output frequency of the inverter to a predetermined value; and a frequency controller that corresponds to the output frequency. A voltage controller that controls the conduction timing of the second switching element to control the output voltage of the inverter to a predetermined value, a load current detector that detects the load current of the inverter, and a load current detector. Correction signal generating means for giving a correction voltage signal to the voltage controller so as to minimize the load current based on the detected load current. An inverter device characterized in that