JPH05103418A - Low-voltage anomaly detection system - Google Patents

Abstract

PURPOSE:To shorten work stop time by stopping an inverter presuming low voltage anomaly only when a DC voltage obtained from a three-phase alternating current by full-wave rectification and smoothening with capacitors is lower than a chopper output DC voltage command value determined from an output voltage command value. CONSTITUTION:A three-phase alternating current is full-wave rectified 1, smoothened by an input side capacitor 2 and a DC current VDC1 is generated. The DC voltage VDC1 is turned ON/OFF by a chopper transistor 3 and turned into a DC voltage VDC2 through a DC reactor 5, and reversely converted 7 and then drives a motor 8. On the other hand, the DC voltage VDC2 is fed back to a DC voltage VDcr which was created by multiplying an output voltage command value Vref by 1.35 with a multiplier 10; then the voltage is processed by a PI controller 11, is PWM-converted 12, and the transistor 3 is turned ON/OFF. The three-phase power supply is interrupted and the voltage VDC1 of the capacitor 2 begins to drop, and a low voltage abnormal signal is output when it decreases below the DC VDcr. By doing this, stop of work due to instantaneous power interruption can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a chopper type PAM.
(Pulse amplitude modulation) Inverter low voltage abnormality detection method.

[0002]

2. Description of the Related Art FIG. 3 shows a low voltage detection circuit of a conventional chopper type PAM inverter. In FIG. 3, 1 is a diode bridge, 2 is a smoothing input side capacitor, 3 is a chopper transistor, 4 is a freewheel diode, 5
Is a DC reactor, 6 is a smoothing output side capacitor, 7 is an inverse conversion circuit composed of 6 switching elements, and 8
Is a motor, 9 is a comparator, 10 is a multiplier, 11 is a PI controller, and 12 is a PWM converter. The voltage of the input side capacitor 2 after the three-phase full-wave rectification of the input AC power supply voltage by the diode bridge 1 and the fixed low voltage detection voltage level, for example 210 V, are compared by the comparator 9, and the input side power source 2 When the voltage V _DC1 becomes lower than 210 V, the inverter judges that the low voltage is abnormal and stops the output of the inverter.

[0003]

The chopper voltage control of the chopper type PAM inverter will be described with reference to FIG. Here, the output voltage command value V _ref is a value when the three-phase AC voltage output from the inverter to the motor is measured by a rectifier voltmeter that calculates an average value and converts it into an effective value. PAM
For the inverter, the output voltage average value becomes 2/3 of the DC voltage V _DC2, the relationship between the DC voltage V _DC2 of the output side capacitor 6 and the output voltage command value V _ref (effective value) (1) become that way. V _DC2 = 1.35 × V _ref (1) First, the output voltage command V _ref is given, and the multiplier 10 gives the chopper voltage command V _DCr multiplied by 1.35. This V _DCr and the DC voltage V _DC2 of the output side capacitor 6
Is calculated by the PI controller 11, and the calculation result is P
The PWM signal is converted by the WM converter 12 and becomes the base signal of the chopper transistor 3. Output side capacitor 6
Since the DC voltage V _{DC2 of the above} is fed back and the DC voltage is controlled by the PI controller 11, the equation (2) is established. V _DCr = V _DC2 (2) Further, even if the input power supply voltage fluctuates, the DC voltage of the output side capacitor 6 can be kept constant by the feedback loop. Therefore, if the output voltage is set low and the motor is running, the inverter will operate according to the command while the condition of formula (3) is satisfied even if the DC voltage of the input side capacitor 2 drops due to an instantaneous power failure. It is possible to output the voltage of. V _DC1 ≧ 1.35 × V _ref (3) However, in the conventional technology, when the DC voltage V _DC1 of the input side capacitor 2 becomes lower than the low voltage level (210 V), the inverter outputs low voltage. It will stop as an abnormality. For this reason,
Even if an instantaneous power failure occurs, the inverter will continue to output while the commanded voltage is being output to the motor, and if there is a momentary power failure for a short period of time, the inverter will continue operation without stopping. could not. The present invention is
The purpose is to reduce the inverter stop time due to momentary power failure.

[0004]

In order to solve the above problems, the present invention provides a chopper type PAM inverter,
There is a means for comparing the DC voltage smoothed by a three-phase full-wave rectification of the input power source with a capacitor and the chopper output DC voltage command value obtained from the output voltage command, and the DC voltage smoothed by the capacitor is the chopper output DC voltage. When it is smaller than the voltage command value, the low voltage is abnormal.

[0005]

If the DC voltage V _DC1 after the three-phase full-wave rectification satisfies the condition of the expression (3), the output V _ref can be output by the chopper voltage control by the feedback loop. That is,
When the condition of Expression (3) is not satisfied, the comparator 9 outputs a low voltage abnormality.

[0006]

1 is a circuit diagram of an embodiment of the present invention. The output voltage command V _ref is multiplied by 1.35 by the multiplier 10 to obtain V
It becomes _DCr . This V _DCr and the voltage V of the output side capacitor 7
_{DC 2} is calculated by the PI controller 11. The calculation result is converted into a PWM signal by the PWM converter 12,
It becomes the base signal of the chopper transistor 3. The output voltage is controlled by this feedback loop. V _DCr multiplied by 1.35 by the multiplier 10 and the voltage V _DC1 of the input side capacitor 2 are compared by the comparator 9, and the comparator 9 outputs V _{DCr.
When DC1} becomes smaller than V _DCr , a low voltage abnormality signal is output. Fig. 2 shows a time chart of each voltage during an instantaneous power failure. When the input power source is 200V of three-phase AC, the DC voltage V _DC1 of the input side capacitor 2 is about 270V. Now, assuming that the output voltage to the motor is 50V, the DC voltage V _DC2 of the output side capacitor 6 is (1) by the chopper voltage control.
From the formula, it is about 67.5V. If an instantaneous power failure occurs at point A, V _DC1 will gradually decrease. But,
By the feedback loop control of the chopper voltage, V
_DC2 keeps 67.5V. In the conventional low voltage detection circuit, the inverter has stopped output due to a low voltage abnormality at point B, but in this method, the inverter can output up to point D. Further, for example, if the input power supply is restored at point C, the conventional method causes an abnormal stop, but in the present method, the operation can be continued without stopping.

[0007]

As described above, according to the present system,
By changing the low voltage detection level according to the output voltage command, when the motor is running at a low voltage, even if the voltage of the input side capacitor becomes low due to an instantaneous power failure, it will be abnormal compared to the conventional fixed low voltage detection level. Since the time until detection is long, there is an effect that the work stop time due to the inverter stop can be shortened.

[Brief description of drawings]

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

[Figure 2] Time chart of voltage at momentary power failure

FIG. 3 is a circuit diagram showing a conventional technique.

[Explanation of symbols]

 1 Diode Bridge 2 Input Side Capacitor 3 Chopper Transistor 4 Freewheel Diode 5 DC Reactor 6 Output Side Capacitor 7 Inverse Conversion Circuit 8 Motor 9 Comparator 10 Multiplier 11 PI Controller 12 PWM Converter

Claims (1)

[Claims] 1. A chopper type PAM inverter having means for comparing a DC voltage obtained by smoothing a three-phase full-wave rectification of an input power source with a capacitor with a chopper output DC voltage command value obtained from an output voltage command, A low voltage abnormality detection method for an inverter, wherein a low voltage abnormality is detected when the DC voltage smoothed by a capacitor is smaller than the chopper output DC voltage command value.