JPH0648909B2 - Inverter device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a restart operation of an inverter device, and in particular, even if a period during which normal power conversion cannot be continued occurs due to a momentary power failure of input power, power recovery is performed. It is intended to provide an improved inverter device which can be continuously operated again later.

[Background of the Invention]

Regarding the restart method when the input power of the inverter device is momentarily interrupted, the frequency and phase of the terminal voltage of the AC motor connected to the inverter device have been detected for a long time, and the frequency and phase must be matched. , It has been proposed to control the power conversion operation in the inverter device. However, PWM (Pulse Width) which has developed especially in recent years
In a modulation-controlled inverter device, the distortion component of the output current is very large, and it is difficult to accurately detect the current phase supplied to the AC motor. In particular, an output current detection circuit, a waveform shaping circuit, a low-pass filter circuit, etc. are required, which makes the control device expensive and complicated.

On the other hand, there is also proposed a so-called soft start method in which the output voltage of the inverter device is simply lowered at the time of restart. However, since the back electromotive force due to the residual magnetism is generated while the induction motor, which is connected to the inverter device during the power failure period, continues to operate (rotate) due to inertia, a switching element that constitutes the inverter part of the inverter device is generated. When a firing signal is applied to the switching element, the switching element becomes conductive due to the back electromotive force, a closed loop passing through the winding of the induction motor and the switching element is formed, and a large current flows, which may destroy the switching element.
In particular, such a tendency is caused by PAM (Pulse Amplitude Modula).
It appears strongly in the controlled inverter device. Further, in recent PWM control inverter devices, there is a tendency to increase the number of pulses in one cycle for the purpose of improving the output waveform. When such ignition control is performed, each ignition pulse of a soft start is generated. Even if the pulse width is narrowed, the switching element conducted by the first ignition pulse is given the next ignition pulse again before the output current disappears due to the back electromotive force and the induction component of the induction motor. Eventually, the switching element continues to be in a conductive state and is destroyed.

Alternatively, when an induction motor is connected to the inverter device, it may be possible to short-circuit the terminals of the induction motor to consume the counter electromotive force and then restart it when a power failure occurs. In order to consume the electromotive force, it is necessary to prepare a resistor having a large capacity, and the rotation of the induction motor is greatly reduced, so that it is difficult to obtain smooth driving characteristics.

[Object of the Invention]

Therefore, the present invention provides an improved inverter device capable of reliably performing the restart operation of the inverter device even when the back electromotive force of the AC motor connected as a load is generated.

[Outline of Invention]

That is, the present invention controls the conduction and non-conduction of an inverter unit having a plurality of switching elements that receives DC power, converts the DC power into AC power, and supplies the AC power to an AC motor. In response to the ignition pattern generating means for generating the ignition pattern signal and the abnormal state in which normal power conversion cannot be performed in the inverter section is returned to the normal state, the restart command signal of the inverter section is set to the point. In an inverter device having an operation command circuit for outputting to an arc pattern generation means, the non-output of the ignition pattern signal, in response to the restart command signal, of the call pattern signal generated from the ignition pattern generation means. When the period is an asynchronous operation in which the output voltage phase of the inverter unit and the voltage phase of the back electromotive force due to the residual magnetism of the AC motor are not synchronized The delay time of the extinction of the output current of the inverter section that occurs in the above is longer than the delay time.

Example of Invention

An embodiment of the present invention will be described in detail below. In FIG. 1, reference numeral 1 is a converter section connected to a three-phase AC power supply R, ST, and supplies rectified and converted DC power to an inverter section 2. The inverter unit 2 is composed of a plurality of transistors or switching elements such as thyristors, converts DC power into AC power, and supplies the AC power to the induction motor 4, for example. Reference numerals 3 and 5 are smoothing capacitors and current detectors provided in the DC power supply circuit. 6 is a speed setting volume for setting the output frequency of the inverter device, 7 is a ramp circuit for moderately changing the output frequency command signal of the speed setting volume 6 according to the acceleration / deceleration characteristics of the induction motor 4, and 8 is a lamp. A voltage-frequency converter that outputs an output voltage command signal and an output frequency command signal that correspond to the output voltage and output frequency ratio required in accordance with the output frequency command signal from the circuit 7, and 9 is a signal from the voltage-frequency converter 8. It is a firing pattern generator that receives and receives the firing pattern of the switching elements that form the inverter unit 2, and is generally composed of a triangular wave generation circuit, a sine wave generation circuit, and an arithmetic circuit. That is, the oscillation frequency of the triangular wave generated by the triangular wave generation circuit is adjusted by the output frequency command signal, and the oscillation cycle of the sine wave generation circuit is adjusted by the output frequency command signal. The oscillation amplitude is adjusted. further,
The output signals of both generation circuits are combined by the arithmetic circuit to obtain the necessary ignition command signal for PWM control. The ignition command signal is further amplified by the drive circuit 10 and given to each switching element of the inverter section.
Reference numeral 11 denotes an overcurrent detection signal, which receives a current signal corresponding to the DC supply current from the current detector 5 and issues an abnormal signal to the drive circuit 10 when the inverter device is overloaded or in another abnormal state, It works to stop the operation of the inverter device.

Such a configuration is already known, and this embodiment is further characterized by the following configuration. Reference numeral 12 is an operation command circuit, which is an operation command circuit that monitors the AC input voltage supplied to the converter unit and detects a power failure, and 13 is a restart that receives a restart command signal from the operation command circuit and becomes longer as the output period increases. Restart pattern generator that outputs pattern signal,
14 is an AN of the restart pattern signal of the restart pattern generator 13 and the ignition pattern signal of the ignition pattern generator 9.
AND circuit for outputting D signal to drive circuit 10, 15
Is a restart compensating circuit for compensating the output frequency of the AC power supplied from the inverter device at the time of restart in accordance with the rotation speed of the induction motor 4 which decreases during a power failure.

More specifically, the operation command circuit 12 includes three-phase AC power supplies R, S. Rectifier circuit 121 for receiving the output voltage of T to obtain a voltage signal, power failure detection circuit 122 that detects that the voltage signal has stopped and outputs an operation stop command signal, restarts by detecting that the voltage signal has recovered again A power recovery detection circuit 123 that outputs a command signal, a timer comparison circuit 124 that is set by an operation stop command signal and reset by a restart command signal, and an AND circuit 125. That is, the timer comparison circuit 124 measures the power failure time with the timer unit 124a, and compares with the comparison unit 124b whether or not the measurement result is within a predetermined restartable operation time range,
If it is within the range, a restart command signal is output to the restart pattern generator 13 through the AND circuit 125. Conversely, if it is outside the range, the restart operation is not performed, or the start operation of the inverter device is stopped after the induction motor 4 is stopped. It issues a command signal required to be executed. Restart compensation circuit 15 is G
The D ² setting volume 16 is provided, and the output frequency command signal is output from the prediction circuit 151 that predicts the change in the operating speed of the induction motor during the power failure period to the set speed set by the speed setting volume from the prediction speed of the prediction circuit 151.
Second ramp circuit 15 that recovers according to the acceleration characteristics of
2 is provided. That is, the prediction circuit 151 in the restart compensation circuit 15 is provided with a pattern generator corresponding to the operating speed that changes due to the inertial operation of the induction motor 4 when the horizontal axis represents the power failure time t and the vertical axis represents the operating speed v. Therefore, when the restart command signal is input from the operation command circuit 12, the timer signal (a signal corresponding to the power failure time) output from the timer comparison circuit 124b is input, and it is predicted that the timer signal has changed according to the power failure time. The operating speed signal corresponding to the operating speed is output to the second ramp circuit 152. The restart pattern generator 13 includes a ramp circuit 131, a triangular wave generation circuit 132, and an arithmetic circuit 133. The arithmetic circuit 133 causes the output signals of both circuits 131 and 132 to be matched, and the triangular wave generation circuit is generated from the output signal of the ramp circuit 131. When the output signal of 132 is small, the high level signal H, the ramp circuit 13
When the output signal of the triangular wave generating circuit 132 is larger than the output signal of 1, the pulse-shaped restart pattern signal of the low level signal L is generated. The restart pattern signal is input to the AND circuit 14 and is output to the drive circuit 10 only during the AND period with the firing pattern signal from the firing pattern generator 9.

To explain in more detail the signal processing process of Example by Figure 2, reference numeral P ₁ is shows an example of a firing pattern signal points generated by the ignition pattern generator 9, and this firing pattern signal P ₁ The restart pattern signal P ₂ whose output period Q becomes longer as soon as it is output from the restart pattern generator 13 is input to the AND circuit 14. Eventually, the signal P ₂ is input from the AND circuit 14 to the drive circuit 10 and the inverter device is operated only while both signals P ₁ and P ₂ are being input. At this time, when it is considered that the operation phase due to the inertial operation of the induction motor at the start of the restart operation and the AC output phase of the inverter device are maximized (relatively 180 ° in electrical angle) to start the asynchronous operation, Even if the drive signal of the switching element of the section disappears, the disappearance delay time Q of the output current is as shown in FIG. 3 due to the relationship between the back electromotive force of the induction motor 4 and the time constant.
₂ occurs, the non-output period Q ₁ of the restart pattern signal P ₂ must be set to be longer than the extinction delay time Q ₂ .
Of course, the extinction delay time Q ₂ will decrease as the induction motor 4 is pulled in synchronously.

Now, the operation of the inverter device thus configured will be briefly described. For example, when the operation start switch S ₀ is pressed, the operation command circuit 12 closes the contact S ₁ . This starts the operation of the inverter device. If a power failure occurs during the operation of the inverter device, the power failure detection circuit 122 detects this and sets the timer comparison circuit 124. At the same time, the operation command circuit 12 opens the contact S ₁ by the operation stop command signal. If necessary, the input signal of the drive circuit 10 is cut off and the induction motor 4 is put into the free-run state. In such a state, when the power recovery detection circuit 123 detects the power recovery and the restart command signal is issued, the timer comparison circuit 124 is reset and determines whether the power failure time is within the restartable range. When it is determined that the restart is possible, the operation command circuit 12 outputs the power failure time data to the restart compensation circuit 15 together with the restart command signal. The operation command circuit 12 also closes the contact S ₂ and outputs a restart command signal to the restart pattern generator 13. As a result, the restart compensation circuit 15 causes the voltage-frequency converter 8 to output an output frequency command signal that slowly recovers from the operating speed predicted to have decreased due to the inertial operation of the induction motor 4 to the target speed set by the speed setting volume 6. Output. As a result, as already described in detail with reference to FIGS. 2 and 3, the inverter device supplies intermittent AC power to the induction motor 4 in which the output current does not grow enough to destroy the switching element. Therefore, the induction motor 4 is gradually pulled into normal operation and restarted.

I haven't explained in detail, but GD ² setting volume 16
Is for setting the magnitude of the moment of inertia of the load machine connected to the induction motor 4, and is for adjusting the multiplier (inclination of the graph shown in the figure) in the prediction circuit 151. If the induction motor 4 is equipped with a speed generator, a ramp circuit can be provided so that the output frequency command signal can be restored to the target speed based on the measurement result. It is also possible to measure the inertial operation speed from the back electromotive force voltage between the terminals of the induction motor 4 and use the measurement result. Simply, the operation start speed at the time of restart is set to a certain value in advance. It can also be placed.

In the above embodiment, the restart pattern generator 1 is used as means for temporarily expanding the non-output period of the firing pattern signal.
Although 3 is prepared, the present invention can be implemented by providing means for generating an ignition pattern signal which is effective only at the time of restarting. For example, a firing pattern generator 9
The triangular wave generating circuit and the sine wave generating circuit of 1 may be configured as follows. That is, the triangular wave generation circuit is configured so that the repetition cycle of the triangular wave is lengthened at the time of restart and returns to the normal repetition cycle as the restart operation progresses. A similar restart operation can be performed by clipping with a value and devising such that it returns to a sine wave when the restart operation is completed. This will be further briefly described with reference to FIG. 4. (a) is the output waveform of each generation circuit at the start of restart, (b) is the output waveform at the completion of restart, and c is the triangular wave generation circuit. , D is the output waveform of the sine wave generating circuit, and e is the firing pattern signal obtained by combining the former two signals.

In the above embodiment, an example in which the present invention is implemented by hard logic has been described, but in recent years, a large number of computer controlled inverter devices have been proposed. Therefore, in this case, in addition to the normal control program, a pattern generation program (pattern table) that obtains the pattern output as already described in FIG. 2 is prepared, and this pattern generation program The main program can be configured so that a required ignition signal of the switching element can be obtained from a normal ignition control program. In this case, when restarting is performed several times in succession, some kind of alarm may be output as a power supply abnormality or an operation abnormality.

Although the restart operation due to a power failure is described in the above embodiment, this can also be used for the restart operation when the AC conversion is interrupted due to a temporary electric circuit abnormality, commutation failure, or the like. In the embodiment, voltage-type PWM
Although the present invention has been described as an inverter device that performs control, the present invention can be applied to a current type inverter device or a PWM control type or cycloconverter type inverter device.

〔The invention's effect〕

As is apparent from the above description, in the present invention, the non-output period of the firing pattern signal is synchronized with the output voltage phase of the inverter and the voltage phase of the counter electromotive force due to the residual magnetism of the AC motor connected to the output of the inverter. The output period of the ignition pattern signal is gradually lengthened so that it will be longer than the extinction delay time of the inverter output current that occurs during asynchronous operation at the time of restarting, and based on this ignition pattern signal, the inverter device Since the restart operation is performed, it is possible to prevent a closed loop due to the back electromotive force from being generated through the switching element that constitutes the inverter section, and the restart operation can be performed safely and reliably without breaking the switching element. Is something that can be done.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining one embodiment of the present invention, FIGS. 2 and 3 are time charts for explaining the operation of the embodiment, and FIG. 4 is another embodiment of the present invention. 5 is a waveform diagram for explaining FIG. 2 ...... inverter, 9 ...... firing pattern generator, 12 ...... operation command circuit, 13 ...... restarting pattern generator, _{P 1} ...... firing pattern signal, _{Q 1} ...... non-output period, _{Q 2} ...... The disappearance delay time.

Claims (2)

[Claims] 1. An inverter unit comprising a plurality of switching elements for inputting DC power, converting the DC power into AC power and supplying the AC power to an AC motor, and controlling conduction and non-conduction of each of the switching elements. Firing pattern generating means for generating a firing pattern signal, and a restart command signal for the inverter unit in response to the fact that an abnormal state in which normal power conversion cannot be performed in the inverter unit has returned to the normal state. An operation command circuit for outputting to the arc pattern generating means is provided, wherein the ignition pattern generating means is responsive to the restart command signal, and is shorter than the steady-state ignition pattern signal output period at the initial stage of the response, and thereafter. The firing pattern signal is output so that the output period gradually becomes longer, whereby the non-output period of the firing pattern signal is changed from the output voltage phase of the inverter unit to the front. The inverter device is characterized in that the residual voltage phase of the AC motor is set to be equal to or longer than the extinction delay time of the output current of the inverter section that occurs during asynchronous operation in which the AC motor is not synchronized. 2. The ignition pattern generating means outputs a steady-state ignition pattern signal, and a steady ignition pattern generating means, which is responsive to the restart command signal, and which is in a steady state at an initial stage of the response. A restart pattern generating means for outputting a restart pattern signal that is shorter than the ignition pattern signal output period and then gradually increases in output period, and a logical product of the output of the ignition pattern generating means and the output of the restart pattern generating means. Claim 1 characterized in that it is provided with means for taking the firing pattern signal.
Inverter device according to the item.