JPH05219759A - Inverter controller - Google Patents

Abstract

PURPOSE:To offer an inverter controller capable of using output capacity of an inverter at the maximum and safely by utilizing threshold performance of a switching element effectively. CONSTITUTION:A PWM control circuit 10 generates a PWM signal to drive a switching element 2 or 7, and output of a d.c. power supply 1 is converted into an a.c to drive an induction motor 8. Output current of an inverter detected by current detectors 11 and 12 is increased, and when it is in excess of current limit value, an operation circuit 15 turns a switch circuit OFF to limit the output current of the inverter. A voltage detection circuit 14 detects a d.c. input voltage of the inverter, and current limit value of the operation circuit 15 is changed in accordance with a d.c. input voltage. Current limit value of the switching element is changed in accordance with a d.c. input voltage value, so that capacity of the inverter can be increased while ensuring a safety operation region of the switching element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for a voltage type inverter that drives an induction motor or the like, and more particularly to an inverter control device that can maximize the output capacity of the inverter and safely.

[0002]

2. Description of the Related Art FIG. 3 is a diagram showing an example of a conventional inverter control device. In FIG. 3, 1 is a DC power source, 2 to 7 are switching elements, and a switching element 2 is provided.
Nos. 7 through 7 are equipped with flywheel diodes.
8 is an induction motor, 9 is a switch circuit, 10 is a PWM control circuit, 11 and 12 are current detectors, and 13 is a current monitoring circuit. In the figure, the PWM control circuit 10 is a PWM
Generate a signal to drive switching elements 2 to 7,
The output of the DC power supply 1 is converted into AC to drive the induction motor 8.

Since the PWM control circuit 10 controls the induction motor 8 smoothly with low torque ripple and high efficiency, a switching pattern (PWM pattern) in which the output of the inverter becomes an equivalent sine wave. Is generated and the switching elements 2 to 7 are driven. The current detectors 11 and 12 detect the output current of the inverter,
The detected current is input to the current monitoring circuit 13. The current monitoring circuit 13 monitors the output current of the inverter. When the output current of the inverter exceeds a specified limit value, the switch circuit 9 is turned off and the drive signals of the switching elements 2 to 7 are cut off.

The switching elements 2 to 7 made up of transistors and the like have the reverse bias SOA characteristics as shown in FIG. 2, for example. This figure is a diagram showing an example of a reverse bias SOA characteristic of a transistor, in which the horizontal axis represents the collector-emitter voltage and the vertical axis represents the collector current limit value. In order to operate the switching element safely, the switching element must be used within the range of this characteristic, and if it is used beyond the range shown in the figure, the element is very likely to be destroyed. . As is clear from FIG. 2, the reverse bias SOA characteristics are
It has a characteristic that the collector current limit value sharply decreases as the emitter-to-emitter voltage increases.

Therefore, in general, when the rating of the switching element is determined, the maximum value of the collector-emitter voltage is first assumed, and the collector current value corresponding to this voltage value is selected. In this case, the collector-emitter voltage is mainly determined by the DC input voltage value in the inverter.This DC input voltage value in the voltage source inverter is the power running operation by the regenerative energy of the electric motor during the regenerative operation. It is known to be much higher than time. Therefore, it is necessary to set the collector current limit value to a value corresponding to the DC input voltage value that allows for the amount of voltage increase during regenerative operation. In other words, the current limit value of the switching element is determined according to the assumed collector-emitter voltage, and the capacity of the inverter is determined according to the current limit value of the switching element.

By the way, since the current path of the voltage-type inverter having the converter constituted by the diode rectifier is unidirectional, continuous regenerative operation cannot be performed, and the regenerative operation state is temporarily set at a sudden change in setting. When the DC input voltage of the switching element is determined on the assumption of such a temporary voltage increase during regenerative operation, the collector current limit value of the switching element is significantly increased, as is clear from the characteristics of FIG. Will be reduced.

In the conventional inverter, the limit value in the current monitoring circuit 13 of FIG. 3 is set on the assumption of the temporary voltage increase during the regenerative operation as described above, and the inverter output current exceeds the above limit value. At this time, the switch circuit 9 is turned off to interrupt the drive signals of the switching elements 2 to 7. For this reason, the collector current limit value of the switching element has to be greatly reduced, and accordingly, the capacity of the inverter has to be significantly reduced.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks of the conventional device, and by effectively utilizing the limit performance of the switching element,
An object of the present invention is to provide an inverter control device that can maximize the output capacity of the inverter and safely.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and detects a DC power supply voltage of an inverter in a controller of a voltage source inverter which converts a DC voltage into an AC voltage. A voltage detector and output current limiting means for detecting the output current of the inverter and limiting the output current of the inverter to a predetermined value are provided. Then, by changing the predetermined value of the output current limiting means according to the DC power supply voltage detected by the voltage detector, the capacity of the inverter is increased while ensuring the safe operation area of the switching element. Further, the voltage source inverter can be applied to drive an induction motor.

[0010]

In the present invention, the current limit value of the switching element is not fixed to a constant value determined by the assumed maximum value of the DC input voltage, but is changed according to the DC input voltage. Therefore, in the region where the DC input voltage is low, the current limit value of the switching element can be increased, and the capacity of the inverter can be increased while ensuring the safe operation area of the element.

[0011]

1 is a diagram showing an embodiment of the present invention. In FIG. 1, the same parts as those in FIG. 3 are designated by the same reference numerals, and in FIG. In addition to the above, the voltage detector 14 is added, the current monitoring circuit 13 is replaced by the arithmetic circuit 15, the switch circuit 9 is removed, and the output of the arithmetic circuit 15 is changed to the PWM control circuit 10. Has been entered in.

The PWM control circuit 10 shown in FIG. 1 generates a PWM signal to drive the switching elements 2 to 7, and converts the output of the DC power supply 1 into an AC current to induce the induction motor 8 as in the case shown in FIG. To drive. The current detectors 11 and 12 detect the output current of the inverter and input the detected current to the arithmetic circuit 13, as in the case shown in FIG. Further, the voltage detector 14 receives the DC input voltage, outputs a predetermined voltage according to the DC input voltage value, and inputs the detected voltage to the arithmetic circuit 15. The arithmetic circuit 15 is composed of an operational amplifier and the like, and compares the detected currents of the current detectors 11 and 12 with the specified current limit value shown in FIG.
The specified current limit value is changed according to the output of the voltage detection circuit 14 in the pattern shown in FIG.

Next, the operation of this embodiment shown in FIG. 1 will be described. The PWM control circuit 10 is similar to that shown in FIG.
In order to control the induction motor 8 smoothly with less torque ripple and with high efficiency, a drive signal of a switching pattern (PWM pattern) is generated so that the output of the inverter becomes an equivalent sine wave, and the switching element 2 or Drive 7 to obtain the desired inverter output. When driving,
The output current of the inverter is detected by the current detectors 11 and 12, and when the output current of the inverter increases, the arithmetic circuit 15 controls the output pulse width of the PWM control circuit 10,
The inverter output current value is limited to the value shown in FIG. At that time, the DC input voltage of the inverter is detected by the voltage detection circuit 14 and input to the arithmetic circuit 15. The arithmetic circuit 15 changes the limit value of the output current of the inverter according to the output of the voltage detector 14 in the pattern shown in FIG.

In the present embodiment, as described above, the current limit value in the arithmetic circuit 15 is changed according to the value of the DC input voltage of the inverter. When the input voltage rises, the current limit value can be lowered, and it is not necessary to select the current rating value of the switching element low in consideration of the temporary voltage rise. Therefore, the current limit value of the switching elements 2 to 7 can be set to the maximum value shown in FIG. 2, and the output capacity of the inverter can be maximized safely.

In the above embodiment, the arithmetic circuit 1
The example in which the drooping characteristic of No. 5 is the characteristic shown in FIG. 2 has been described, but the drooping characteristic in the arithmetic circuit 15 is similar to that in FIG.
Alternatively, the characteristic may be within the range of FIG. 2, and for example, a part or all of the curved portion may be approximated by a straight line, or a portion composed of a curved line and a straight line may be approximated by a single straight line. You can also Further, the characteristic shown in FIG. 2 is only one example, and the drooping characteristic in the arithmetic circuit 15 can be arbitrarily determined according to the switching element.

In the above embodiment, the arithmetic circuit 1
Although an example in which the output pulse width of the PWM control circuit 10 is narrowed by the output of No. 5 to limit the output current of the inverter is shown, the present invention is not limited to the above embodiment, and the inverter When the output current exceeds the current limit value shown in FIG. 2, the output of the arithmetic circuit 15 stops the output pulse of the PWM control circuit 10 to turn off the switching elements 2 to 7, or the PWM control circuit 10 is turned off. It is also possible to provide a switch circuit on the output side of and to cut off the control signal to the switching element.

Further, the arithmetic circuit 15 can be constructed by using a function generator composed of an operational amplifier.
When the inverter control device is composed of a processor such as a microcomputer, the function of the arithmetic circuit 15 can be realized by software. Furthermore, in the above embodiment, an example in which a transistor is used as a switching element has been shown, but the present invention is not limited to the one using a transistor as a switching element, and has a drooping characteristic as shown in FIG. It can also be applied to a control device of an inverter composed of other switching elements.

In the above embodiment, an example in which an induction motor is used as the load of the inverter is shown, and the case where the DC voltage rises during regeneration of the induction motor has been described.
The inverter load in the present invention is not limited to the above embodiment, and the present invention can be applied to cases other than the voltage increase during regeneration.

[0019]

As is clear from the above description,
In the present invention, since the current limit value of the switching element of the inverter is changed according to the DC input voltage value, it is possible to increase the capacity of the inverter while ensuring the safe operation area of the switching element,
An inverter having a large capacity can be configured with a switching element that is smaller than the conventional one, and the practical effect is great.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a reverse bias SOA characteristic.

FIG. 3 is a diagram showing a conventional inverter control device.

[Explanation of symbols]

 1 DC power supply 2, 3, 4, 5, 6, 7 Switching element 8 Induction motor 9 Switch circuit 10 PWM control circuit 11, 12 Current detector 13 Current monitoring circuit 14 Voltage detector 15 Arithmetic circuit

Claims (2)

[Claims] 1. A voltage source inverter control device for converting a DC voltage into an AC voltage, a voltage detection circuit for detecting a DC power supply voltage of the inverter, and an output current of the inverter being detected to limit the inverter output current to a predetermined value. The output current limiting means is provided, and according to the DC power supply voltage detected by the voltage detection circuit,
An inverter control device characterized in that a predetermined value of the output current limiting means is changed. 2. The inverter control device according to claim 1, wherein the induction motor is driven by a voltage source inverter.