JPH04255497A - Voltage type inverter - Google Patents

Abstract

PURPOSE:To provide a voltage type inverter of a DC line current detecting system which can prevent the occurrence of a fault even when a driving motor is restarted in a zero-frequency state while the motor rotates. CONSTITUTION:A means which outputs a full-phase 'off' signal to an inverter device for an arbitrary period at arbitrary time is provided. When a motor is restarted in a zero-frequency state while a motor rotates at a low speed, the output of the inverter device becomes a zero-vector output and a circulating current flows due to short circuit, but an overcurrent can be detected, since the circulating current is made to flow to the current detector 5 of a DC line by means of the full-phase 'off' signal.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage source inverter that is less likely to fail even when started at zero frequency while a drive motor is rotating.

0002

2. Description of the Related Art FIG. 4 shows an example of the configuration of a three-phase voltage source inverter. 1 is an input AC power source, which is converted into a DC power source by a rectifier 2 and a smoothing capacitor 3. 4 is an inverter circuit, with diodes 4DU, 4DV, 4DW, 4D
X, 4DY, 4DZ and transistors 4TU, 4TV,
U, V, W with 4TW, 4TX, 4TY, 4TZ,
This circuit is composed of X, Y, and Z phases, and reconverts the DC power that has been converted by the rectifier 2 and smoothing capacitor 3 into an AC power source with variable voltage and variable frequency. 5 is a current detector for overcurrent protection of the inverter circuit 4; 6 is a circuit for driving and controlling the inverter circuit 4; and 7 is a current detector for the inverter circuit 4.
This is an electric motor that serves as a load.

[0003] The motor 7 being driven is connected to an inverter circuit 4.
When disconnected from the output of the motor 4, the motor 4 continues to rotate due to inertia and generates an induced voltage due to residual voltage. In addition, since the inverter circuit 4 generally performs constant V/f control, it outputs a low voltage when outputting a low frequency, so the PWM output is almost always a zero voltage output,
In other words, the output is a zero vector (all upper arms are on, all lower arms are off, or vice versa).

When the inverter circuit 4 is started from zero frequency while the motor 7 is generating an induced voltage due to residual voltage, the inverter output is almost zero vector, so the induced voltage generated by the motor 7 is is short-circuited by the inverter circuit 4, and a large current flows. As shown by the arrow in FIG. 4, for example, if the induced voltage of the motor 7 is positive in the W phase and negative in the other phases, all the upper arms are on and all the lower arms are off. If the inverter circuit 4 outputs a zero vector, the induced voltage will be short-circuited between the W-phase diode 4DW and the U- and V-phase transistors 4TU and 4TV, and a large current will flow.

If the starting frequency is high, the switching of the three phases will be faster, and the time that the current flows concentrated in one phase will be shorter, which will reduce the influence. However, if the starting frequency is 0.
It must be set considerably higher than 5 to 3 Hz.

FIG. 5 shows examples of current waveforms in various parts when the electric motor 7 is rotating and started at zero frequency. FIG. 5(a) shows an example of an induced voltage waveform of a motor. At this time, if the inverter circuit 4 outputs a zero vector as shown in FIG. 5(b), then FIGS. 5(c) and (d)
As shown in FIG. 2, a short-circuit current of the induced voltage flows through the W-phase and V-phase transistors 4TW and 4TV according to the polarity of the induced voltage. The value of the flowing current depends on the magnitude of the induced voltage and the electrical characteristics of the motor 7, but generally a current that is three to four times the current rating of the transistor flows. Although such usage is generally prohibited, depending on how it is used, it may occasionally occur, and as a result, inverters of the type that have a current detector only on the DC line, as shown in Figure 4, , equipment was destroyed because no current passed through the DC line.

Of course, if two or more current detectors are provided on the AC output side, overcurrent can be detected and this problem will not occur, but the cost will be very high, so it is not suitable for general-purpose products. Cannot be hired.

[0008]

[Problems to be Solved by the Invention] As mentioned above, in the conventional type of inverter that has a current detector only on the DC line, when the drive motor starts at zero frequency while rotating, the induced voltage is output as a zero vector. There was a problem in that the current detector of the DC line could not detect the return current generated due to the short circuit. Furthermore, if two or more current detectors are provided on the AC output side, overcurrent can be detected and this problem will not occur, but the cost will be very high, so it cannot be adopted for general-purpose products.

SUMMARY OF THE INVENTION Therefore, the present invention is intended to solve the above-mentioned problems of the voltage source inverter using the DC line current detection method. The purpose is to provide inverters. [Structure of the invention]

0010

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an inverter section that has a switching element and reconverts DC power from a DC power source into AC power, and an inverter section that controls the switching element. In an inverter device that operates a motor connected to an inverter part at variable speed under arbitrary operating conditions, the voltage type is equipped with an output means for outputting a signal of all phases off at an arbitrary time and for an arbitrary period. It provides an inverter.

[0011]

[Function] According to the voltage source inverter of the present invention configured as described above, it is possible to output a signal that turns off all phases at any time and for any period. The current that could not be detected by the line current detector is regenerated to the DC line side during the period when all phases are off, and can be detected by the DC line current detector. That is, the present invention solves the problem that in an inexpensive DC line current detection type voltage source inverter, when the drive motor is rotating and starts at zero frequency, there is a current that does not flow to the current detector. is possible.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. However, the same parts as in the prior art are given the same reference numerals as those in FIG. 4, and the explanation thereof will be omitted.

In FIGS. 1 and 2, 8 is an inverter control circuit, and conventionally, PWM signals U* to Z*, which are output from this circuit, are applied to the inverter circuit 4 through a base amplifier. In this embodiment, P of the inverter control circuit 8
An AND circuit 9 for turning off all phases is inserted between the WM outputs U* to Z* and the base amplifier. The other end of the all-phase OFF AND circuit 9 is connected to the output of an OR circuit 10 , one end of the input of the OR circuit 10 is connected to the inverter control circuit 8 , and the other end is connected to the one-shot circuit 11 . The input of the one-shot circuit 11 is connected to the output of the oscillator 12.

According to this embodiment configured as described above,
Since the all-phase OFF AND circuit 9 is AND logic,
When the input level of the other end (common end) of the all-phase OFF AND circuit 9 is high level, the PWM output U* ~ Z* of the inverter control circuit 8 is directly transmitted to the base amplifier, and when it is low level, the all-phase OFF output is output. transmits the signal to the bass amplifier. In other words, the inverter control circuit 8 at the input of the OR circuit 10
When the level of one end connected to is high level, the PWM output U* ~ Z* of the inverter control circuit 8 is transmitted to the base amplifier as it is, and when the level is low level, it is connected to the other end of the input of the OR circuit 10. , one-shot circuit 1
Depending on the signal 1, the PWM outputs U* to Z* or an all-phase off signal are output.

The one-shot circuit 11 is triggered by the output of the oscillator 12, that is, it outputs a pulse having a time width determined by the time constant of the one-shot circuit 11 in the oscillation period of the oscillator 12.

Next, FIG. 3 shows the electric motor 7 according to this embodiment.
An example of the current waveform of each part when started at zero frequency while rotating is shown. FIG. 3(a) shows an example of an induced voltage waveform of the electric motor 7. At this time, the inverter circuit 4 inserts and outputs the all-phase off output according to this embodiment into the zero vector as shown in FIG. As shown in Fig. 3(c) and (d), the short-circuit current of the induced voltage flows through the W-phase and V-phase transistors 4TW and 4TV according to the polarity of the induced voltage, only during normal PWM output. flows. At the time of all-phase OFF output, the freewheeling mode in the inverter circuit 4 disappears, and the inverter circuit 4 becomes a mere rectifier circuit. That is, as shown by the arrow in FIG. 2, the current flows back through the DC current detector 5 and charges the smoothing capacitor 3. The flowing current value depends on the magnitude of the induced voltage and
Although it depends on the electrical characteristics of the motor 7, a current three to four times the current rating of the transistor generally flows, and a current having a waveform as shown in FIG. 3(e) flows only in the all-phase off mode.

As described above, by inserting the all-phase off mode, the inverter section when started at zero frequency while the drive motor is rotating can be used with an inexpensive configuration consisting of only a DC line current detector. An abnormal large return current was detected, and the equipment was fully protected.

Furthermore, the all-phase off output and the example vector inserted in this example have the same zero voltage when viewed between the drive motor terminals (between the inverter output terminals), so there is no change in the output waveform. .

As another embodiment of the present invention, in the above embodiment, the all-phase output OFF signal is inserted even at a vector other than the zero vector, but if the input of the OR circuit (between the terminals connected to the inverter control circuit) is The same effect can be obtained by making use of the fact that it can be prohibited by controlling and inserting it only at the time of zero vector output, or only for a certain period of time after the motor orbits when the return current flows.

[0020]

As described above, according to the present invention, even with an inexpensive type of inverter that has a current detector only on the DC line, the motor can be started at zero frequency while the motor is rotating. It is now possible to detect the return current generated by a short circuit due to the zero vector output of the induced voltage using a DC line current detector, and it is possible to provide a robust inverter that will not break even in such a mode.

[Brief explanation of the drawing]

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

FIG. 2 is a diagram showing the operation of the circuit shown in FIG. 1;

FIG. 3 is a diagram showing current waveforms at various parts of the circuit shown in FIG. 1;

FIG. 4 is a diagram showing a circuit configuration of a conventional voltage source inverter.

FIG. 5 is a diagram showing current waveforms at various parts of the circuit shown in FIG. 4;

[Explanation of symbols]

1 Input AC power supply 2 Rectifier 3 Smoothing capacitor 4 Inverter circuit 7 Electric motor 8 Inverter control circuit 9 AND circuit for all phase off 10 OR circuit 11 One-shot circuit 12 Oscillator

Claims (1)

[Claims] 1. An inverter section having a switching element and reconverting DC power from a DC power source into AC power;
In an inverter device comprising a control means for controlling the switching element and operating a motor connected to an inverter section at variable speed under arbitrary operating conditions, an output that outputs a signal to turn off all phases at an arbitrary time and for an arbitrary period. A voltage source inverter characterized by comprising means.