JP3475729B2 - Inverter device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compensation function for an inverter device that drives an electric motor at an arbitrary frequency when the power supply voltage fluctuates.

[0002]

2. Description of the Related Art Conventionally, in an inverter device for driving an electric motor such as a compressor of an air conditioner at an arbitrary frequency, a DC voltage detecting means in the inverter device is disclosed in Japanese Patent Laid-Open No. 8-85332, for example. The input DC voltage is detected, and when the DC voltage fluctuates from the nominal voltage, the pulse width is reduced or expanded according to the degree of fluctuation with respect to the nominal voltage to maintain a predetermined frequency-voltage characteristic.

A device for avoiding troubles due to torque shortage and overcurrent abnormality due to fluctuations in the inverter output voltage due to fluctuations in the input voltage to the inverter device is disclosed, for example, in Japanese Patent Laid-Open No. 61-98163. As described above, in the arithmetic circuit that compensates the voltage signal according to the set frequency with the inverter DC input voltage, the output voltage is made inversely proportional to the input DC voltage to compensate the input DC voltage fluctuation. In addition, for example, JP-A-6-311787.
As disclosed in the official gazette, the correction circuit corrects the frequency control signal in order to obtain an output frequency with a rated V / F ratio according to the detection output of the power supply voltage detection circuit, and the output voltage is the rated V / F ratio. The voltage is determined by the / F ratio.

Each of the methods aims to realize an inverter device that can perform stable inverter operation in response to fluctuations in the input power supply voltage to the inverter device.

[0005]

However, in such an inverter device, even if the input DC voltage is higher than the nominal voltage, the inverter output voltage is lowered to the nominal voltage, and therefore the input voltage is high. In this case, it was impossible to effectively utilize the advantage of increasing the inverter output capacity and further reducing the current.

The present invention solves the above-mentioned conventional problems, and realizes stable driving even with respect to power supply voltage fluctuations and load fluctuations, and further realizes inverter efficiency increase and stable operation when the power supply voltage rises. The purpose is to do.

[0007]

In order to achieve this object, the inverter device of the present invention has an input voltage detecting means for detecting an input voltage, and an input voltage detected by the input voltage detecting means is a predetermined nominal value. When the voltage fluctuates, a control means having a function of realizing a predetermined output voltage and output frequency relationship by changing the pulse width according to the fluctuating input voltage is provided.

When the input voltage detected by the input voltage detecting means is higher than a predetermined nominal voltage,
The control means is provided to change the relationship between the predetermined output voltage and the output frequency and control so that the maximum value of the output voltage becomes the value of the input voltage.

Further, when the difference between the input voltage detected by the input voltage detecting means and the predetermined nominal voltage is a certain value or more, or when the difference is higher, the relationship between the predetermined output voltage and the output frequency is changed. However, a control means for controlling the maximum value of the output voltage to be the value of the input voltage is provided.

[0010]

With this configuration, when the input voltage detected by the input voltage detecting means changes from the predetermined nominal voltage, the inverter device changes the pulse width according to the changed input voltage. A predetermined output voltage and output frequency relationship is realized.

Further, when the detected input voltage is higher than the predetermined nominal voltage, the relationship between the predetermined output voltage and the output frequency is changed so that the maximum value of the output voltage becomes the value of the input voltage. Therefore, when the power supply voltage is high, it is possible to increase the torque of the inverter device, improve the efficiency, reduce the power supply, and thereby prevent the occurrence of overcurrent abnormality.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the inverter device according to the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of an inverter device according to the present invention. DC power supply 1 to smoothing capacitor 2
The control means 7 outputs a switching signal to the switching element 6 in consideration of the detected voltage information from the input voltage detection means 5 for detecting the DC voltage input via the input voltage and the information such as the set frequency supplied from the outside. . The switching element 6 switches the power supply from the DC power supply 1 on the basis of the switching signal to output an alternating current corresponding to the set frequency and drive the external electric motor 4.

FIG. 2 is an example of a frequency-voltage characteristic diagram of the inverter device without voltage correction. Generally, when the inverter device drives an electric motor, with respect to the output frequency,
The output voltage is changed by increasing the frequency as the frequency increases, like the straight line of the reference output voltage. On the other hand, when the input voltage of the inverter device becomes higher than the reference value, the output voltage from the inverter device increases in all frequency regions like a straight line when the power supply voltage is high. On the contrary, when the input voltage becomes lower than the reference value, the output voltage from the inverter device decreases in all frequency regions like a straight line when the power supply voltage is low. As a result, in the conventional inverter device, the power supply voltage fluctuates, and the output voltage deviates from the optimum voltage determined by the electric motor, resulting in a decrease in efficiency and an increase in current.

In order to solve the above problems, in the voltage correction in the conventional inverter device, the detected voltage information from the input voltage detecting means for detecting the DC voltage from the DC power supply and the predetermined nominal voltage are used. When the detected voltage is higher than the nominal voltage, the output pulse width of the inverter device is reduced, the output voltage is decreased, and the output voltage from the inverter device becomes equal to the value when the input voltage is the nominal voltage. To control. On the contrary, when the detected voltage is lower than the nominal voltage, the output pulse width of the inverter device is expanded to control the output voltage.

FIGS. 3A and 3B are characteristic diagrams showing an example of a method of adjusting the output pulse width. FIG. 3A shows a waveform of the inverter output voltage by pulse width modulation when the maximum output voltage VAC = 200V when the input voltage VDC is 280V and the nominal voltage is 280V. Figure 3
(B) shows that the input voltage VDC is 350 V and the nominal voltage is 280
7 shows a waveform of an inverter output voltage at the same output frequency in the case of V. Thus, even when the input voltage is high,
Since the correction is applied so that the output voltage VAC = 200V, the output voltage cannot be increased.

FIG. 4 is an example of a frequency-voltage characteristic diagram of an inverter device by conventional voltage correction. In the correction when the input voltage is high, the inverter output voltage is controlled so as to be the same as in the case of the nominal voltage power supply by the operation of the pulse width as described above. However, in this case, since the maximum output voltage is controlled so that the nominal voltage becomes the maximum value, the advantages such as increased output torque, decreased current, and increased efficiency cannot be realized when the input voltage is high. There was a problem.

FIG. 5 is an example of a frequency-voltage characteristic diagram of the inverter device 3 by voltage correction according to the present invention. In the inverter device 3 of the present invention, the control unit 7 compares the detected voltage from the DC voltage from the DC power supply 1 with the detected voltage from the input voltage detection unit 5 and a predetermined nominal voltage. When the input voltage is higher than the nominal voltage, the relationship between the predetermined output voltage and the output frequency when the input voltage is the nominal voltage is changed, and voltage correction is added so that the maximum value of the output voltage becomes the value of the input voltage. As shown in this figure, by changing the frequency at which the output voltage becomes the maximum value and the base frequency to a large value, the straight line between the output voltage and the output frequency is extended, and the maximum value of the output voltage becomes the value of the input voltage. Voltage correction is added so that As a result, output torque can be increased, current can be decreased, and efficiency can be increased.

FIG. 6 is a frequency-voltage characteristic diagram of an example of voltage correction of the inverter device according to the present invention. When the power supply voltage deviates from the nominal voltage, the output voltage is corrected by changing the pulse width as described above, but the inverter device of the present invention limits the correction amount. By providing the width of the correction maximum value as shown in the figure, it is possible to protect the inverter device when an abnormal voltage is detected or when a failure occurs in the voltage detection means.

FIG. 7 is a flow chart of an example of voltage correction of the inverter device according to the present invention. In the inverter device of the present invention, first, in step S1, the DC voltage VDC from the DC power supply 1 is detected, and in step S2,
Compare the value VDC with the nominal voltage, and if it is greater than the nominal voltage,
Moreover, when the output frequency is higher than the base frequency, the voltage frequency straight line (VF straight line) is extended in step S4 and correction is performed so that the maximum voltage becomes the input voltage. On the other hand, V
If DC is smaller than the nominal voltage, correction is made in step S5 so that the voltage frequency straight line (VF straight line) is the same as at the nominal voltage. Finally, in step S6, the correction amount is compared with a predetermined correction maximum value. If the correction amount is larger than the correction maximum value, the maximum value is limited in step S7. By the above, the correction of the output voltage is achieved.

The control means 7 of the present invention may be realized by a dedicated hardware circuit or software using a microcomputer.

[0022]

As described above, in the inverter device according to the present invention, when the input voltage detecting means for detecting the input voltage and the input voltage detected by the input voltage detecting means fluctuate from a predetermined nominal voltage, A predetermined output voltage and output frequency relationship is realized by changing the pulse width according to the fluctuating input voltage, and when the input voltage is higher than the predetermined nominal voltage, the predetermined output voltage and output frequency relationship is By changing and controlling so that the maximum value of the output voltage becomes the value of the input voltage, and further limiting the maximum value to the amount to be corrected, the control means reduces the efficiency even when the power supply voltage changes,
When the power supply voltage is high without causing an increase in current, the torque of the inverter device is increased, the efficiency is improved, the current is reduced, and the occurrence of overcurrent abnormality is prevented.

[Brief description of drawings]

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

FIG. 2 is a frequency-voltage characteristic diagram of an inverter device without voltage correction.

FIG. 3 is a characteristic diagram of an example showing a method for adjusting an output pulse width of an inverter device according to the present invention.

FIG. 4 is a frequency-voltage characteristic diagram of an inverter device using conventional voltage correction.

FIG. 5 is a frequency-voltage characteristic diagram by voltage correction of the inverter device according to the present invention.

FIG. 6 is a frequency-voltage characteristic diagram of an example of voltage correction of the inverter device according to the present invention.

FIG. 7 is a flowchart of an example of voltage correction of the inverter device according to the present invention.

[Explanation of symbols]

1 DC power supply 2 Smoothing capacitor 3 Inverter device 4 electric motor 5 Input voltage detection means 6 switching elements 7 Control means

Continuation of the front page (56) Reference JP-A-6-311787 (JP, A) JP-A-7-172155 (JP, A) JP-A-6-169503 (JP, A) (58) Fields investigated (Int .Cl. ⁷ , DB name) H02P 5/41 H02M 7/48 H02P 5/402

Claims (2)

(57) [Claims] 1. In an inverter device for driving a motor at a variable speed by pulse width modulation in a predetermined output voltage and output frequency relationship, input voltage detection means for detecting an input voltage of the inverter device, and the output voltage and output frequency. And a control unit that realizes the relationship, wherein the control unit changes the pulse width according to the changed input voltage when the input voltage detected by the input voltage detection unit is lower than a predetermined nominal voltage. By this, a predetermined output voltage and output frequency relationship is realized, and when the input voltage detected by the input voltage detecting means is higher than a predetermined nominal voltage, the predetermined output voltage and output frequency relationship is changed. An inverter device having a function of controlling the maximum value of the output voltage to be the value of the input voltage. 2. The control means has a function of setting a predetermined upper limit value to the amount of pulse width to be changed when the input voltage detected by the input voltage detection means fluctuates from a predetermined nominal voltage. The inverter device according to claim 1, which has.