JPS609376A - Overcurrent detector of voltage type inverter - Google Patents

Abstract

PURPOSE:To prevent the detected error operation due to a snubber capacitor charging current by providing a circuit for simulating the charging current of a capacitor of a snubber circuit, and subtracting the output signal of the circuit by the output signal of an overcurrent detector. CONSTITUTION:A subtractor 25 is provided in a shortcircuiting current detector. The simulation waveform of a snubber charging current formed through a delay circuit 27 for inputting a gate signal of a GTO or a signal from a circuit 26 for generating a signal synchronized with the gate signal delaying the signal and delaying it, a monostable multivibrator 28 for outputting a suitable period pulse by the delayed signal and a waveform generator 29 having the integrating and discharging functions of the pulse signal, and a shortcircuit detection signal are subtracted by a subtractor 25, and a charging current of a snubber capacitor contained in the shortcircuit detection signal is removed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an overcurrent detection device for a voltage source inverter in a motor drive control device that operates an AC motor at variable speed, for example.

[Technical background of the invention]

Generally, as shown in Figure 1, a voltage source inverter consists of a rectifier 2 that rectifies an AC power supply 1, a main circuit filter capacitor 3 that completely smoothes the output voltage, and an inverter 4 that converts the smoothed DC voltage into an AC voltage. It has multiple configurations and drives an AC motor 5. Here, a diode is used as the rectifier 2, but a thyristor may also be used. In addition, GTO (dart tongue off-thigh transistors) are all used as the switching elements of the inverter 4, but if there is a circuit that can perform forced commutation, it may be a high-temperature transistor, or a natural GTR (cross-hat transistor) may be used.

FIG. 2 is a lecture diagram showing details of the main circuit filter capacitor 3, inverter 4, and AC motor 5 in FIG. Here, a coil 6 and a current detector (current transformer, etc.) 7 connected in series with the main circuit filter capacitor 3 have an inductance of 6D to suppress the discharge current of the main circuit filter capacitor 3 in the event of a short-circuit failure in the inverter 4. , and a detector for its current. A current detector (such as a current transformer) 8 connected in series with the inverter 4 detects the entire DC main circuit current flowing into the inverter 4 . (Current detectors 7, 8
can detect short circuit current, here it is not necessarily necessary to connect both. ) The details of the inverter 4 are GTO, which is a switching element that controls the inverter output voltage.
9 and a reactive power AC motor 5 connected in antiparallel to it.
anti-parallel diode 10 through which regenerative energy and circulating current flow, and d v /d t applied to those elements.
Snubber circuit (resistor 1) and diode 12 to suppress
(parallel connection and a series circuit with a capacitor 13).

FIG. 3 shows a conventionally used short circuit detection circuit. The current signal detected by the current detector 8 (current detector 7 may also be used) is compared with the level setter 22 by the comparator 23 throughout the current signal, and if it exceeds the set level, the signal is output from the protection sequence circuit 24. GTO9 r-1 with appropriate signal
- Perform protective actions such as block or dart full ignition. During normal operation, the snubber capacitor charging current also flows through the current detectors 7 and 8, so in order to prevent circuit malfunctions caused by this current, the detection level of the detection circuit must be increased, and the i4 pulse of that current must be increased. A filter circuit (integrator circuit) 21 having a time constant taking width into consideration is connected. For this reason, both are factors that delay the short circuit current detection time. Here, the snubber capacitor charging current during water flow operation will be explained with reference to FIGS. 4 and 5.

Fig. 4 shows one phase of the impark 4 shown in Fig. 2, and the subscripts on each of the upper and lower components are used to distinguish between the upper and lower parts.
U is attached to the upper phase component, and X is attached to the lower phase component. Also shown are a current i9U flowing through the GTO 9U, a current i1ox flowing through the parallel diode IOX, and a charging current 113X flowing through the snubber capacitor 13X.

FIG. 5 shows current waveforms at various parts shown in FIG. 4, where a is the current flowing through the anti-parallel diode 16x and
The current circulating within the inverter 4 is the current that is used to reduce reactive power by the AC motor 5 and the main circuit filter capacitor 3. b is GTO when GTO9u is turned on at tl! With the current flowing through 91J, tl
-tz between main circuit filter capacitor 3-coil e- current detector & -GTO9U- anti-parallel diode l0X-
Short circuit current flowing in the path of main circuit capacitor 3, t2
is when the anti-parallel diode turns off, and between t2 and t3, the current flowing to the AC motor 5 and the main circuit filter capacitor 3 - coil 6 - current detector 8 - GTO 9, U - snubber diode 12X - snubber capacitor 13x - It is the sum of the snubber capacitor charging current flowing in the path of the main circuit filter capacitor 3, and after t3, the AC motor 5-
＼It is a flowing current. C is tlI-t3 of b waveform
This is the charging current of the snubber capacitor 13.0 flowing between the coil 6, the snubber capacitor 13x, and the pulse current determined by the voltage of the main circuit filter capacitor.

[Problems with background technology]

In particular, when all devices with low av/dtit characteristics such as GTO are used, the capacitance of the snubber capacitor is increased to lower the dv/dt(i) applied to the device.

For this reason, the snubber capacitor charging current is slightly reduced.

Peak value and pulse width increase. For example, when the main circuit filter capacitor voltage is 600 V, the snubber capacitor capacity is 4 μF, and the inductance of coil 6 is 10 μH, the Noyarsbeak value is about 30 OA and the pulse width is about 20 Ilsec, which are large values that cannot be ignored. becomes. Correspondingly, a delay in the detection time between the set value of the detection level setter 22 in FIG. 3 and the time difference between the filter 2 and the filter 2 becomes significant. On the other hand, GTO has a turn-off characteristic in which it will be destroyed if an off-state signal is applied when an anode current exceeding the turn-off capacity is flowing. Therefore, when detecting GTO inverter short-circuit fault current, there are stricter restrictions on the detection level and detection speed than with conventional thyristor circuits. If this problem is not resolved, the problem will arise that it will not be possible to coordinate the protection of Seiko.

[Purpose of the invention]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an overcurrent detection device for a voltage source inverter that eliminates detection malfunctions due to snubber capacitor charging current and enables faster detection.

[Key points of invention]

In order to achieve this object, the present invention provides a circuit for simulating the charging current of the capacitor of the snubber circuit, and subtracts the output signal of the circuit from the output signal of the overcurrent detection circuit. This is characterized in that the charging current of the snubber combiner contained in the Ia current signal is completely removed.

[Embodiments of the invention]

An embodiment of the present invention shown in FIGS. 6 and 7 will be described below. In FIG. 6, a subtraction circuit 25?1l-1 is added to the short-circuit current detection circuit of FIG.
A delay circuit 27 which inputs a signal from 6 and delays the signal, a monostable multi-circuit 28 which outputs all pulses for an appropriate period as well as the delayed signal, and a waveform generator having functions such as integrating and discharging the pulse signal. The signal waveforms of the simulation waveform of the snubber charging current created through the circuit 29 and the conventional short circuit detection signal (noise X removal filter 2) are different because the time constant is smaller. ) is configured to completely reduce the influence of the snubber charging current q.

Next, the filter protection operation of the present invention will be explained.

In Fig. 7, ■ is a filter 21 for removing all noise from the output signal of the current detector 8 that detects the main circuit DC current (unlike conventional filters, it is not for removing all the snubber current components, but for 1 μsec). This is the waveform (hereinafter referred to as va) that is passed through the □) which is used to remove all noise before and after the signal. (12-1,) is the output waveform of the monostable multicircuit 28 (hereinafter referred to as V), which rises with a delay of (12-1,) due to the delay circuit, and here falls in accordance with the peak time of the protruding part of V. It's set. ■ is the output waveform (hereinafter referred to as V) of the waveform generation circuit 29;
Here, a CR charging waveform and a CR discharging waveform are formed so that they disappear at time t4 when the protrusion of V ends.

■ is the output waveform of the subtraction circuit 25 (hereinafter referred to as V); v
The waveform is obtained by subtracting a and V.

Here, the time (t2-tl) differs depending on the magnitude of the load current, and the time becomes longer as the load iQ current increases, so strictly speaking, the delay time of the delay circuit must be changed using the full load current as a variable. However, when the load 'α current is small, the peak value of V (snubber charging current + load '11 (
Since the current) also becomes smaller, if the delay time is set at the full rated current, the effect of the present invention can be maintained sufficiently even if there is a slight deviation. Therefore, the latter fixed delay time method is used here. Also, the time (14-12) is the snubber
Since this is the nominal pulse width of the charging current, it is determined for each individual device, and this setting only needs to be set once in the monostable multi-circuit or waveform generation circuit. Therefore, v
,! :v is matched by the input resistance of the a d subtraction circuit, so that the protruding part of va and vd take the same value, and va and V
By subtracting , the waveform of shive can be formed. In addition, the waveform of v4 can be made into various waveforms using a waveform generation circuit, such as a charge/discharge waveform using a capacitor and a resistor or a capacitor, a resistor and an inductance, a triangular waveform using an integrating circuit, and a nonlinear characteristic of semiconductors. A digital staircase wave or the like can be considered. In addition, as a simple circuit, a waveform generation circuit is not provided and only a monostable multi-circuit is used to calculate the time during the pulse (
It is also possible to perform this by using a rectangular wave up to tzt4).

What is important here is to make the protrusion waveform of VA and the simulation signal as similar as possible, but as long as the middle of the pulse matches, the effect of the present invention will be sufficient. The first priority is to match the width.

As described above, by performing all short circuit detection using the signal ve which has been compensated for V, the noise removal filter that slows down the short circuit detection speed is able to remove the pulse of the noise signal that should be removed compared to the conventional one. Since only a narrow space other than the snubber charging flow is required, the number of hours can be reduced. Further, the setting value of the short circuit detection level setting device 22 can also be set near the maximum load current.

As a result of these factors, the detection speed in the event of a short-circuit fault is further improved, so that the increase in short-circuit current from the time the fault occurs until the protection circuit operates is reduced, and protection coordination with the elements is improved.

〔Effect of the invention〕

As explained above, the present invention solves the problem of snubber light flow that adversely affects short-circuit detection using control circuit signals. By doing this, the circuit is configured to subtract this simulation signal from the conventional overcurrent detection signal, and the overcurrent detection speed in the event of a failure is faster than that of the conventional circuit, which has the effect of completely improving the protection coordination of the elements. .

[Brief explanation of the drawing]

Figure 1 does not show a general voltage source inverter;
The figure is a block diagram showing the inverter section and main circuit filter capacitor section in Figure 1, Figure 3 is a block diagram showing a conventional overcurrent detection circuit, and Figure 4 is a block diagram showing one phase of the inverter section in Figure 2. Figure 5 is a waveform diagram showing the waveforms of each part of Figure 4.
FIG. 6 is a configuration diagram showing one embodiment of the present invention, and FIG.
FIG. 3 is a waveform diagram showing waveforms of various parts in the figure. 9...GTollo...Anti-parallel diode, 1 no.
・Snubber resistor, 12... Snubber/<-diode, 1
3... Snubber capacitor, 8... Current detector, 2
No. Noise removal filter circuit, 26. Button signal or r-to signal synchronization signal generation circuit, 27. Delay circuit, 28. Monostable multi circuit, 29. Waveform generation circuit. Applicant's representative Patent attorney Takehiko Suzue Figure 1 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1t2t4

Claims (2)

[Claims] (1) In a voltage source inverter device that has an inverter section that converts the DC voltage into AC voltage via a filter capacitor in the main circuit after rectifying the AC power supply, there is a switching element that controls the output voltage waveform of the inverter, and a switching element that is inversely parallel to this. In a voltage source inverter comprising an anti-parallel diode connected to the elements, and a snubber circuit connected in parallel with those elements to control dv/dt'z applied to those elements, A circuit for simulating the charging current of the snubber capacitor in the circuit is set up using the snubber capacitor obtained in the simulation from the output signal of the current detector that picks up the DC current of the voltage source inverter or the filter capacitor current. An overcurrent detection device for a voltage source inverter, characterized in that it obtains a signal with all charging current removed. (2) The circuit for simulating the charging current of the snubber capacitor has a plurality of delay circuits and waveform generation circuits that manually generate a dart signal of the control circuit or a signal synchronized with the dart signal. Range 1
An overcurrent detection device for a voltage source inverter as described in .