JPH1028397A - Control method for inverter device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of vibration, heating, etc., due to flowing of a large higher harmonic current, in the case of controlling an induction motor with a relation V/F=fixed by PWM controlling an inverter device. SOLUTION: In a microcomputer, based on an output frequency command input from an input device 9 and information from a DC voltage detection circuit 7, a DC voltage control circuit 8 and a transistor module control circuit 5 are controlled, a transistor module 3, by maintaining a relation in which V/F=fixed, is PMW controlled, an induction motor 4 is efficiently driven. In order to realize this relation V/F=fixed, a rectifier circuit output voltage of a DC voltage variable rectifier circuit 2 is controlled, so as to generate output voltage of minimum value during the time from Fmim to F1, and increase the output voltage by a fixed ratio during the time from F1 to Fmax. On the other hand, driving of the transistor module 3 is controlled, so as to increase a PWM modulation factor by fixed ratio during the time from Fmin to F1 and fix the modulation factor during the time from F1 to Fmax.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling an inverter for driving an induction motor.

[0002]

2. Description of the Related Art Induction motors have been used in many fields due to their simple and robust structure and recent advances in control technology. Among conventional control methods for an induction motor, an inverter device for driving an induction motor using a PWM control method and a control method thereof will be described with reference to FIGS.

In FIG. 4, 1 is an AC power supply, 2 'is a rectifier circuit, 3 is a transistor module, 4 is an induction motor,
Reference numeral 5 denotes a transistor module control circuit, and reference numeral 6 denotes a microcomputer. In this device, a doubling rectifier circuit is shown as the rectifier circuit 2 'on the assumption that the AC power supply voltage is 100V.

Here, the DC output voltage of the rectifier circuit 2 'varies somewhat due to power supply voltage fluctuations or load fluctuations, but is almost uniquely determined by the voltage of the AC power supply 1. The voltage (FIG. 5B) is about 2√2 times the AC power supply voltage.

On the other hand, to efficiently drive the induction motor 4 at a variable frequency and a variable voltage, the transistor module 3
Is constant, ie, V /
It is well known that it is effective to control so that F = constant. (FIG. 5A) The microcomputer 6 calculates the PWM modulation degree for each output frequency and controls the transistor module 3 via the transistor module control circuit 5.

[0006] Here, as shown in FIG.
Since the DC output voltage of ′ is almost constant, it is necessary to change the PWM modulation ratio in proportion to the transistor module output frequency in order to realize V / F = constant control as shown in FIG. FIG. 5C shows the relationship between the PWM modulation degree and the transistor module output frequency.

[0007]

Generally, in a PWM control type inverter device, the higher the DC voltage and the lower the modulation rate, the larger the ratio of the carrier frequency voltage component to the fundamental wave voltage component, and the distortion is large. It is known.

[0008] This will be described with reference to FIG.
The M control is schematically illustrated, and the hatched portion of the pulse width indicates a dead time of about 12 μsec for preventing the elements between the power supplies from being simultaneously fired and the power supply from being short-circuited when the inverter device commutates. It is time. Therefore, this period is a time that does not contribute to the PWM modulation degree.

FIG. 6A shows that V / F = constant control is performed, and the voltage is kept high and constant at Va irrespective of the pulse width regardless of whether the frequency is high or low. Therefore, when the frequency is high, the pulse is narrow, and when the frequency is low, the pulse becomes narrow and high, and the ratio of the carrier frequency voltage component to the fundamental voltage component increases, resulting in large distortion. Things.

For this reason, when controlling the induction motor with V / F = constant, the modulation is very small in the low frequency region where the output voltage is small, and the output voltage distortion is very large. As a result, in a low frequency range, a large harmonic current flows through the induction motor, and there is a problem that vibration, heat generation, and the like increase.

From the relationship between the ratio between the fundamental wave component and the carrier frequency voltage component, the output voltage distortion is minimized when the modulation factor is 1. In the conventional method, however, FIG. As is apparent, there is only one secondary frequency at which the modulation factor is 1, and at other frequencies, a voltage distortion larger than an ideal state occurs, a large harmonic current flows through the induction motor, and vibration,
The fever was large.

When the induction motor having large vibration and heat generation is used as a driving source of the compressor of the air conditioner,
Operational efficiency could not be improved due to the adverse effect on the characteristics of the compressor.

Accordingly, the present invention relates to a method of controlling an inverter device for driving an induction motor of a PWM control system, comprising:
When the induction motor is controlled with F = constant, a large harmonic current flows through the induction motor to prevent generation of vibration, heat, and the like, and has high operating efficiency suitable for a drive source such as a compressor of an air conditioner. It is an object of the present invention to provide a method for controlling an inverter device for driving an induction motor.

[0014]

According to a first aspect of the present invention, there is provided a method for controlling an inverter device, comprising the steps of:
A part for converting an alternating current into a direct current in an inverter device for controlling an induction motor by converting the voltage into a variable voltage of alternating current and controlling the ratio of the alternating current output voltage to the alternating current output frequency to be constant (V / F = constant). A function that can change the DC voltage, a function that can change the AC output voltage according to the modulation degree by adopting the PWM method in the part that converts DC into AC, and a function that fixes the DC voltage to a minimum value in a low frequency range. PW
A control function of obtaining a V / F = constant characteristic by changing the modulation rate of M, and a control function of fixing the PWM modulation rate and changing the DC voltage to obtain a V / F = constant characteristic in a high frequency range. This is achieved by providing:

In this way, a PWM modulation degree equal to or higher than that of the conventional system can be secured in almost all output frequency ranges as compared with the conventional system. Further, even in the output frequency range in the worst case, a PWM modulation degree equal to or higher than that of the conventional method can be secured. As a result, in most output frequency ranges, voltage distortion applied to the induction motor can be made smaller than in the conventional method, and vibration, heat generation, and the like of the induction motor can be reduced.

According to a second aspect of the present invention, there is provided a method of controlling an inverter device, wherein AC power is converted into AC power having a variable frequency and a variable voltage, and the relationship between the AC output voltage and the AC output frequency is constant (V / F). = Constant), in which the induction motor is controlled so that the DC voltage can be varied in the part that converts AC to DC, and the PWM output voltage is adopted in the part that converts DC back to AC using the PWM method. And the DC / DC voltage is fixed to a minimum value and the PWM modulation rate is changed in a low frequency range to change the V / F
= Control function to obtain constant characteristics and high frequency range:
The PWM modulation rate is fixed at 1 and the DC voltage is changed to
/ F = control function for obtaining constant characteristics.

In this manner, a PWM modulation factor of 1 that minimizes the output voltage distortion can be ensured in the widest output frequency range. As a result, vibration, heat generation, and the like of the induction motor can be minimized in the widest output frequency range.

According to a third aspect of the present invention, a control method of an inverter device is achieved by applying the induction motor according to the first or second aspect to a compressor of an air conditioner.

Thus, the operation efficiency can be improved by removing the vibration, heat generation, and the like that have adversely affected the operation characteristics of the compressor.

[0020]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment of an inverter device to which the control method according to claim 1 of the present invention is applied.

In the figure, 1 is an AC power supply, 2 is a DC voltage variable rectifier circuit, 3 is a transistor module, 4 is an induction motor, 5 is a transistor module control circuit, 6 is a microcomputer, 7 is a DC voltage detection circuit, and 8 is DC The voltage control circuit 9 is an input device. Therefore, the rectifier circuit 2 'of FIG.
Instead, a DC voltage variable rectifier circuit 2 is used. Here, the voltage of the AC power supply 1 is similar to that of the conventional example shown in FIG.
100V is assumed.

On the other hand, the DC voltage variable rectifier circuit 2 is a circuit usually called an "active filter" and has two purposes of reducing harmonic distortion of the AC power supply current and varying the output DC voltage. Here, the minimum value of the output voltage of the DC voltage variable rectifier circuit 2 satisfies minimizing the power supply current harmonic distortion, and is about √2 times the AC power supply voltage plus about 10 V.

Although the maximum value of the DC voltage variable rectifier circuit 2 has a relationship with the withstand voltage of the parts used, it is possible to output 2√2 times or more of the AC power supply voltage without any problem. That is, the output voltage of the DC voltage variable rectifier circuit 2 can be freely set between about 0.5 and 1.3 times the output voltage of the rectifier circuit 2 'in FIG.

The microcomputer 6 controls the DC voltage control circuit 8 and the transistor module control circuit 5 based on the output frequency command input from the input device 9 and the information from the DC voltage detection circuit 7, and controls the transistor module 3 to PWM.
The induction motor 4 is driven under the control.

The relationship between the transistor module output frequency and the transistor module output voltage is shown in FIG.
As shown in FIG. 5A, the induction motor is driven efficiently while maintaining the same V / F = constant relationship as in the conventional method shown in FIG.

In order to realize the relation of V / F = constant, the output voltage of the rectifier circuit of the DC voltage variable rectifier circuit 2 is minimized between Fmim and F1, as shown in FIG. Value (approximately 0.5 of the output voltage in the conventional method)
Times). The output voltage is controlled so as to increase at a constant rate between F1 and Fmax.

This is because, as shown in FIG.
/ F = constant control, the voltage Vc can be set high and variably in the high frequency range, and the voltage is kept constant at Vb in the low frequency range. This also means that the fundamental voltage component is sufficiently ensured and distortion can be reduced.

On the other hand, when the transistor module 3 is driven, as shown in FIG.
Increases from F1 to Fmax at a fixed rate, and from F1 to Fmax
Is controlled to be constant during the period.

Next, this control will be described with reference to the flowchart shown in FIG. The microcomputer 6 determines in step 31
A frequency command from the input device 9 is read, and a step 32 is executed.
Then, the DC voltage control circuit 8 is controlled so that the rectifier circuit output voltage is based on the relationship shown in FIG. Next, at step 33, the DC voltage which is the output voltage of the DC voltage variable rectifier circuit 2 is read from the DC voltage detection circuit 7.

Here, in step 34, it is determined whether or not the DC voltage has the target value as shown in FIG. 2B. If the DC voltage has not reached the target value, the process returns to step 32 and returns to step 32. The control value to the voltage control circuit 8 is changed, and control is performed so that the target DC voltage is obtained.

When the DC voltage has reached the target value in the relationship shown in FIG. 2B, in step 35, the PWM modulation factor is determined based on the relationship shown in FIG. Control.

Thus, the relationship between the output frequency and the output voltage of the transistor module 3 is controlled so as to satisfy the relationship shown in FIG. These controls are performed so as to comprehensively achieve the relationship shown in FIG.

"Relationship between transistor module output frequency and PWM modulation degree" in this embodiment of the present invention (FIG. 2)
Comparing (C)) with the relationship of the conventional method (FIG. 5 (C)), the embodiment of the present invention can secure a larger PWM modulation degree at most output frequencies.
Even at the worst output frequency, P
The WM modulation degree can be secured.

As a result, at most output frequencies, the voltage distortion applied to the induction motor can be made smaller than in the conventional system, and as a result, the vibration and heat generation of the induction motor can be reduced.

Next, an embodiment of a control method according to claim 2 of the present invention will be described. The circuit configuration of the second embodiment, the relationship between the transistor module output frequency and each parameter, and the operation flowchart of the microcomputer are the same as those of the first embodiment, and are shown in FIGS. 1, 2 and 3, respectively.

In the control method according to claim 2 of the present invention, the PWM modulation degree a between F1 and Fmax in FIG.
There is a feature in that.

By setting the PWM modulation a to 1 between F1 and Fmax, the voltage distortion included in the transistor module output voltage during this period is minimized. As a result, vibration, heat generation, and the like of the induction motor can be significantly reduced as compared with the conventional method.

[0038]

As described above, the control method of the inverter device of the present invention can secure a PWM modulation degree equal to or higher than that of the conventional system in almost all output frequency ranges as compared with the conventional system. Further, even in the output frequency range in the worst case, a PWM modulation degree equal to or higher than that of the conventional method can be secured.

In the widest output frequency range,
By securing the PWM modulation degree 1 that minimizes the output voltage distortion, vibration, heat generation, and the like of the induction motor can be minimized in the widest output frequency range.

As a result, in most output frequency ranges, the voltage distortion applied to the induction motor can be made smaller than in the conventional system, and the vibration, heat generation, etc. of the induction motor can be reduced.

Further, by applying this control method to an induction motor for driving a compressor, it is possible to eliminate vibrations, heat generation, etc., which have adversely affected the characteristics of the compressor, thereby improving the operation efficiency. It is.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment to which a control method of the present invention is applied.

FIG. 2 is a diagram showing the relationship between the transistor module output frequency of the present invention and each parameter.

FIG. 3 is a flowchart showing a control operation of the present invention.

FIG. 4 is a configuration diagram showing an embodiment to which a conventional control method is applied.

FIG. 5 is a diagram showing a relationship between a conventional transistor module output frequency and each parameter.

FIG. 6 is a schematic diagram of PWM control.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 AC power supply 2 DC voltage variable rectifier circuit 2 'Rectifier circuit 3 Transistor module 4 Induction motor 5 Transistor module control circuit 6 Microcomputer 7 DC voltage detection circuit 8 DC voltage control circuit 9 Input device

Claims (3)

[Claims] An AC motor is converted into AC power having a variable frequency and a variable voltage, and the induction motor is controlled such that the ratio between the AC output voltage and the AC output frequency becomes constant (V / F = constant). In the inverter device, the DC voltage is made variable in a portion for converting AC into DC, and the PWM output system is adopted in a portion for converting DC into AC again, and the AC output voltage is made variable by the degree of modulation. V / F = constant characteristic is obtained by fixing the DC voltage to the minimum value and changing the PWM modulation rate, and in the high frequency range, the PWM modulation rate is fixed and the DC voltage is changed to change V / F = constant in the high frequency range. A method for controlling an inverter device, characterized by obtaining characteristics. 2. The method according to claim 1, wherein the modulation rate is set to 1 in a frequency range in which the PWM modulation rate is fixed. 3. The method according to claim 1, wherein the induction motor is for driving a compressor of the air conditioner.