JPS61285075A - Inverter - Google Patents

Abstract

PURPOSE:To enable stable acceleration by resetting a voltage of an AC output to a voltage before correction when accelerating an AC motor, thereby preventing a load current from rapidly increasing. CONSTITUTION:A chopper controller 16 controls the conduction timing of the transistor of a chopper 4 so that the AC output of a DC/AC main converter 6 becomes the prescribed output voltage. When a set frequency is enhanced by a frequency setter 8, a gate circuit 26 is interrupted by the output of a comparator 25, and a correction signal from a correction signal generator 22 is interrupted. Thus, the voltage of the AC output of the converter 6 is reset to an output voltage before correction from the output voltage after the correction. A holding circuit 24 passes the output of the setter 8 after the prescribed delay time, and the circuit 26 becomes conductive. Accordingly, a control based on the output of the setter 8 is thereafter performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an inverter device for driving an AC motor such as an induction motor.

[Technical Background 1 of the Invention] Generally, when controlling an AC motor, such as an induction motor, at variable speed using an inverter device, the ratio of the output frequency (F) to the output voltage (V), so-called F/ By controlling the V ratio to be constant, the magnetic flux of the induction motor is kept constant to prevent saturation of the magnetic flux, and the output voltage is corrected so that the load current is minimized.

FIG. 3 shows an example of a conventional inverter device, which is of the chopper type RAM (pulse amplitude modulation) type. That is, 1 is an AC/DC converter consisting of a plurality of rectifying elements that converts AC power from an AC power supply 2 into DC power (DC output), and 3 converts the DC output from this AC/DC converter 1 into AC output. This is a DC/AC converter for

This DC/AC converter 3 includes a chopper 4 made of a transistor, which is a switching element that changes the output voltage by intermittent DC output from the AC/DC converter 1, and a smoothing capacitor 5 that smoothes the output from the chopper 4. and,
It is comprised of a DC/AC conversion main circuit 6 made up of a plurality of transistors, which are switching elements, that convert the DC output from the smoothing capacitor 5 into AC output. The AC output from this DC/AC conversion main circuit 6 is supplied to the induction motor 17. 8 is a frequency setter, and 9 is a frequency controller that receives a set frequency signal from the frequency setter 8. This frequency controller 9 outputs an output pulse based on a set frequency signal, and applies the output pulse to the transistor of the DC/AC converter main circuit 6 to control its conduction timing. The frequency of the AC output of 6 is controlled to be the frequency set by the frequency setter 8. Reference numeral 10 denotes a function generator to which the output pulses of the frequency controller 9 are applied, and this is an F/V generator as shown in FIG.
The ratio function output signal is output as a digital signal. The function output signal from the function generator 10 is applied to the positive (+) input terminal of the adder/subtractor 11. This adder/subtractor 11 adds and subtracts a function output signal applied to a positive input terminal and a correction signal applied to a negative (-) input terminal as described later, and outputs an addition/subtraction output signal. The output signal is converted into an analog signal via a D/A (digital-to-analog) converter 12. 13 is correct (
+) It is an adder/subtractor to which an analog signal from the D/A converter 12, that is, an added/subtracted output voltage is applied to its input terminal, and a transformer 14 serving as a load voltage detector is connected to its negative (-) input terminal.
and the DC/AC conversion main circuit 6 via the diode 15
The output voltage, that is, the load voltage is provided. This adder/subtractor 13 is configured to add and subtract an addition/subtraction output voltage applied to a positive input terminal and a load voltage applied to a negative input terminal, and output an addition/subtraction output signal. 16
is a chopper controller to which the addition/subtraction output signal from the adder/subtractor 13 is given; this outputs an output pulse according to the addition/subtraction output signal, and gives the output pulse to the transistor of the chopper 4 to control its conduction timing. By doing so, the output voltage of the DC/AC converter main circuit 6, that is, the load voltage is changed, thereby controlling the addition/subtraction signal of the adder/subtractor 13 to be zero. And the above frequency controller 9. Function generator 10. Adder/subtractor 11.0/A
Converter 12. Adder/subtractor 13. Transformer 14. diode 1
5 and the chopper controller 16 constitute a control circuit 17.

On the other hand, 18 is a voltage correction circuit serving as voltage correction means, which will be described below. That is, 19 is a current transformer serving as a load current detector that detects the output current of the DC/AC conversion main circuit 6, that is, the load current, and the detected load current is A/D (analog-digital) converted via the diode 20. Vessel 21
The signal is supplied to the correction signal generator 22 and converted into a digital signal, and the digital signal is supplied to the correction signal generator 22.

The correction signal generator 22 outputs a correction signal to the negative input terminal of the adder/subtractor 11 so that the detected load current indicated by the digital signal is minimized.

[Problems with the front technology] According to the conventional inverter device as described above, the frequency of the AC output of the DC/AC conversion main circuit 6 is constantly operated at point B in FIG. 2, that is, the first output frequency F1. Then, the voltage of the AC output of the DC/AC conversion main circuit 6 is at the output frequency F1
Output at 8 points on straight line A in Figure 2, voltage Vt)
Instead, the motor is operated at a zero point (output voltage V1') corrected by the correction signal from the voltage correction circuit 18 so that the load current becomes minimum, that is, the output voltage becomes minimum. However, if the frequency setter 8 sets a second output frequency F2 that is higher than the current first output frequency F1, the frequency of the AC output of the DC/AC conversion main circuit 6 will change from the first output frequency F1. However, the voltage of the AC output increases as the frequency increases from the output voltage ■l' which is lower than the output voltage V1 corresponding to the first output frequency F1, so in order to obtain acceleration torque. The slip of the induction motor 7 becomes large, and the load current, which is the output current of the DC/AC conversion main circuit 6, increases rapidly as the output voltage starts to rise. The problem is that it becomes impossible to do so.

[Object of the Invention] The present invention has been made in view of the above circumstances, and its object is to provide a voltage correction means for correcting the voltage of the AC output of a DC/AC converter so as to minimize the load current.
To provide an inverter device capable of stably accelerating an AC motor by preventing a load current from rapidly increasing even when accelerating operation from a constant frequency operating state to a higher frequency operation is started.

[Summary of the Invention] The present invention provides a state detection circuit that outputs a detection signal when the frequency of the AC output of the DC/AC converter changes from a constant frequency state to a high frequency, and based on this detection signal, the DC/AC converter The present invention is characterized by a configuration in which the voltage of the AC output is returned to the output voltage before correction, and then the output frequency and output voltage are increased in accordance with the F/V ratio.

[Embodiment 1 of the Invention] Hereinafter, an embodiment of the present invention will be described with reference to FIG. 1. In FIG. 1, the same parts as in FIG. 3 are denoted by the same reference numerals.

Reference numeral 23 denotes an acceleration detection circuit as a state detection circuit, which includes a hold circuit 24 having delay characteristics and a comparison circuit 25. The hold circuit 24 is configured such that the set frequency signal from the frequency setter 8 is given to the input terminal, and when a high level signal is given to the control terminal, it enters a hold state and changes the setting given to the input terminal. It holds the frequency signal and outputs it as a hold frequency signal from the output terminal, and when a low level signal is given to the control terminal, it enters the hold release state after a slight delay and passes the set frequency signal given to the input terminal. It is designed to be output from the output terminal as a passing frequency signal. Further, the comparator circuit 25 is configured such that a set frequency signal from the frequency setter 8 is given to a first input terminal, and a hold frequency signal 9 suitable frequency signal from the hold circuit 24 is given to a second input terminal. A hold frequency signal in which the frequency indicated by the set frequency signal applied to the first input terminal is applied to the second input terminal.

When the frequency is higher than the frequency indicated by the passing frequency signal, a high level output signal is output from the output terminal as a detection signal. The hold frequency signal 9 suitable frequency signal from the hold circuit 24 is given to the frequency controller 9, and the frequency controller 9 outputs pulses based on the hold frequency signal 1 suitable frequency signal. Output. Reference numeral 26 denotes gate means, such as a gate circuit consisting of a transfer gate circuit (analog switch), which is interposed between the negative input terminal of the adder/subtractor 11 and the output terminal of the correction signal generator 22. This gate circuit 26 has its gate terminal supplied with the output signal from the comparator circuit 25, and when the output signal is at a low level, it becomes conductive and allows the correction signal from the correction signal generator 22 to pass through. When it is at level, it becomes non-conductive and cuts off the correction signal. Reference numeral 27 denotes a voltage determination circuit, which has an input terminal supplied with an addition/subtraction signal from the adder/subtractor 13, and outputs a high-level output signal from an output terminal when the addition/subtraction signal becomes zero. It has become. 28 is a logic circuit consisting of an exclusive OR circuit, the first input terminal of which is supplied with the output signal of the comparison circuit 25, and the second input terminal of which is supplied with the output signal of the voltage determination circuit 27. The output signal from the output terminal is applied to the control terminal of the hold circuit 24.

Next, the operation of this embodiment will be explained with reference to FIG. 2.

Assume now that the frequency setter 8 is outputting a set frequency signal indicating the first frequency F1, and at this time the hold circuit 24
is in the hold release state, the frequencies indicated by the set frequency signal and the passing frequency signal of the hold circuit 24 are the same, which is the first frequency F1, so the output signal of the comparator circuit 25 is at a low level, and the gate circuit 26 is at a low level. It becomes conductive and allows the correction signal from the correction signal generator 22 to pass through and is applied to the negative input terminal of the adder/subtractor 11. Further, since the frequency controller 9 is given a passing frequency signal indicating the first frequency F+ from the hold circuit 24, the frequency controller 9 outputs an output pulse corresponding to this, and the DC/AC converter main circuit 6
The frequency of the AC output of the DC/AC conversion main circuit 6 becomes the first frequency F1. Further, the function generator 10 outputs a function output signal indicating the output voltage ■1 corresponding to the first frequency Fl, and therefore the adder/subtractor 11 is corrected by the correction signal from the correction signal generator 22. The addition/subtraction output signal indicating the output voltage V1' is outputted, and the chopper controller 16 controls the conduction timing of the transistor of the chopper 4 so that the voltage of the AC output of the DC/AC exchange main circuit 6 becomes the output voltage V1'. do. In this way, when the induction motor 7 enters the operating state at the first frequency F1 which is a constant frequency, the addition/subtraction calculation output signal of the adder/subtractor 13 becomes zero, so the voltage determination circuit 2
The output signal of logic circuit 2 becomes high level, and therefore the output signal of logic circuit 2 becomes high level.
8, when only one of the two input signals becomes high level, the output signal becomes high level,
The hold circuit 24 enters a hold state, holds a set frequency signal indicating the first frequency Fl, and outputs this as a hold frequency signal. The hold frequency signal indicating this first frequency F1 is transmitted to the frequency controller 9 and the comparison circuit 2.
5, the induction motor 17 continues to operate at the output frequency F1 and the output voltage 1/.

After that, the frequency setter 8 sets the first frequency F.
5 to the second frequency F2, the second frequency F2 indicated by the set frequency signal of the frequency setter 8 becomes higher than the first frequency F1 indicated by the hold frequency signal of the hold circuit 24, and the comparison The output signal of the circuit 25 becomes high level, and therefore the gate circuit 26 becomes non-conductive and cuts off the correction signal from the correction signal generator 22.

As a result, the adder/subtractor 11 outputs an addition/subtraction output signal indicating the output voltage V1 before correction, and the adder/subtractor 13
outputs an addition/subtraction calculation output signal indicating (VI Vt'). That is, the value indicated by the addition/subtraction output signal from the adder/subtractor 13 is other than zero, and the output signal from the voltage determination circuit 27 is at a low level. In this case, the comparison circuit 25
When the output signal of the voltage determination circuit 27 becomes high level as described above, for a short time until the output signal of the voltage determination circuit 27 becomes low level, the logic circuit 28 outputs the output signal for a short time when both input signals become high level. However, even if the output signal of the logic circuit 28 goes low for a short period of time, the hold circuit 24 does not immediately go into the hold release state, but there is a slight delay time. The circuit 24 has the frequency F! of Ml. A hold frequency signal indicating this will continue to be output. Then, before the delay time of the hold circuit 24 elapses, the output signal of the voltage determination circuit 27 becomes low level, and the logic circuit 28 outputs an output signal because only one of the two input signals becomes high level again. The signal becomes high level, and the hold circuit 24 continues to be in the hold state. Thereafter, when the voltage of the AC output of the DC/AC conversion main circuit 6 rises to the pre-correction output voltage V1, the addition/subtraction output signal of the adder/subtractor 13 becomes zero, the output signal of the voltage determination circuit 27 becomes high level, and the logic circuit 28 sets the output signal to low level because both input signals are high level. As a result, the hold circuit 24 enters the hold release state after a slight delay time, passes the set frequency signal indicating the second frequency F2, and outputs it as a pass frequency signal. As a result, the frequencies indicated by the set frequency signal and the passing frequency signal applied to the comparator circuit 25 both become the second frequency F2, and the output signal of the comparator circuit 25 becomes a low level.
- The circuit 26 becomes conductive and allows the correction signal from the correction signal generator 22 to pass and is applied to the negative input terminal of the adder/subtractor 11. Further, since the pass frequency indicating the second frequency F2 from the hold circuit 24 is given to the frequency controller 9, the DC/AC conversion main circuit 6 is controlled so that the frequency of its AC output becomes the second frequency F2. Along with
Since the function generator 10 also outputs a function output signal based on the F/V ratio shown in FIG. 2, the adder/subtractor 13 outputs an addition/subtraction output signal corrected by the correction signal.
The chopper 4 is controlled so that the voltage of the AC output of the DC/AC conversion main circuit 6 corresponds to the second frequency F2 and is corrected so that the load current is minimized.

As described above, according to this embodiment, when accelerating the induction motor R7 from the first frequency F1 to the second frequency F2 higher than this, the voltage of the AC output of the DC/AC conversion main circuit 6 is adjusted to the corrected voltage. The output voltage V1' is returned to the output voltage v1 before correction, and then the first frequency F1 is accelerated to the second frequency F2 based on the F/■ ratio. The load current does not increase suddenly, and stable accelerated operation is possible.

Although the above embodiment is a case in which the present invention is applied to a chopper type PAM type inverter device, the present invention is not limited to this, and may be applied to, for example, a phase control type PAM type or PWM (pulse width modulation) inverter device.
The present invention can be similarly applied to an inverter device of this type.

However, it goes without saying that the present invention is not limited to the embodiments described above and shown in the drawings, but can be implemented with appropriate modifications within the scope of the invention.

[Effects of the Invention] As explained above, the present invention provides an inverter device that corrects the voltage of the AC output in order to minimize the load current, and when accelerating the AC motor, the voltage of the AC output is changed to the voltage before correction. Therefore, it is possible to prevent the load current from increasing suddenly and achieve the excellent effect of enabling stable accelerated operation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a characteristic diagram showing the F/V ratio of a DC/AC converter, and FIG. 3 is a block diagram showing a conventional example. In the drawings, 1 is an AC/DC converter, 3 is a DC/AC converter, and 7 is an AC/DC converter.
is an induction motor (AC electric TL), 8 is a frequency setting device, 1
7 is a control circuit, 18 is a voltage correction circuit (voltage correction means),
Reference numeral 23 indicates an acceleration detection circuit (state detection circuit), and 26 indicates a gate circuit (gate means). Agent: Patent attorney Kensuke Norichika (and 1 other person) Figure 2 Figure 3

Claims (1)

[Claims] 1. A DC/AC converter consisting of a plurality of switching elements for converting DC power into AC output, and controlling the conduction timing of the switching elements of this DC/AC converter to control the frequency of the AC output of the DC/AC converter. and a control circuit for controlling the voltage, a voltage correction means for detecting the load current of the DC/AC converter and applying a correction signal to the control circuit so as to minimize the load current, and a frequency of the AC output of the DC/AC converter. a state detection circuit that detects and outputs a detection signal when the frequency becomes higher than a constant frequency state, and a voltage correction means that corrects the voltage of the AC output of the DC/AC converter based on the detection signal from the state detection circuit. An inverter device comprising gate means for restoring the previous voltage.