JPH0145837B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inverter device, and particularly to an inverter device that detects an inverter arm short circuit using a self-extinguishing element such as a gate turn-off thyristor (hereinafter referred to as GTO) or a power transistor at an early stage. The present invention relates to an inverter device that protects an inverter circuit.

Generally, short circuit protection is one of the important issues in GTO inverters, and this short circuit protection includes protection against arm short circuit and load short circuit.
In both arm short circuits and load short circuits, excessive current flows through the GTO that makes up the inverter, eventually leading to its destruction. Furthermore, a short circuit in the power supply may cause an accident to spread, and an inverter device is always provided with a protection circuit against such a short circuit accident.

A conventional inverter device has a configuration as shown in FIG. That is, AC power supplied from the AC receiving power source 1 is rectified into DC in the rectifier 2 . A smoothing capacitor 3 is connected in parallel to this rectifier 2. Further, a thyristor inverter 6 is connected to the smoothing capacitor 3 via a fast-acting fuse 8 . A smoothing capacitor 3 is connected to the (-) side of the thyristor inverter 6 via a parallel circuit of a current limiting reactor 4 and a freewheeling diode 5.
is connected. Further, a load 7 is connected to the thyristor inverter 6. As described above, a current limiting reactor is inserted into the circuit in order to suppress the rise of the main current when a conventional thyristor inverter is short-circuited. In the case of a thyristor, the switching speed is slower than that of a GTO, so the current limiting reactor and the fast-acting fuse 8, which blows at high speed, are used together.
In the event of a short circuit, protection can be provided by blowing the fuse.

FIG. 2 shows a conventional inverter device using a GTO. Components with the same reference numerals as in FIG. 1 are the same parts and have the same functions. In the figure, 9 is the GTO inverter circuit, 1
0 is a smooth reactor. In the GTO inverter device shown in FIG. 2, short circuit current is detected in the same manner as in the inverter device shown in FIG.
GTO can be protected. However, since GTO normally does not have a self-current limiting function, a current limiting reactor is essential to suppress the rate of increase in current in the event of a short circuit, and since it cannot be made small, there is a limit to its ability to handle the stored energy during steady state. It has the disadvantage that it is not suitable for high frequency switching operation.
In addition, from the point of view of protection coordination, fuses must be provided at both ends of the GTO, resulting in a large number of fuses and a disadvantage that maintenance is not easy.

FIG. 3 shows a conventional inverter device using another inverter arm short circuit detection method. This method uses the ON voltage of the short-circuit thyristor 11 to clamp the DC input terminal voltage of the GTO inverter and limit the current of the GTO arm. A diode 5 is connected in parallel to the reactor 4 to limit the current of the short-circuit thyristor 11 and to suppress transient voltage during steady operation. The fuse 8 is for protecting the thyristor 11. Since the thyristor 11 has a large surge current capacity, it is easy to adjust the fuse, and the value of the reactor 4 can be made small, so the circuit loss during steady state is small and high frequency operation is possible. However, this method has the disadvantage that a shorting thyristor 11 must be separately added to the circuit shown in FIG.

GTO has a self-extinguishing ability, so in order to make the inverter smaller and lighter, there is an advanced protection method in which short-circuit current is extinguished by the GTO itself, which makes up the inverter. In this case, as mentioned above,
For example, the GTO on the P side and the GTO on the N side can be used at the same time.
If some kind of short circuit occurs in the arm that turns ON, the current will gradually increase and destroy the GTO because it has no function to suppress the current.
Therefore, it is important to detect short-circuits in the inverter's arms and perform overcurrent detection at high speed before the GTO is destroyed. The short circuit current i _A is the power supply voltage E and the current limiting reactor inductance L.
Then, di _A /dt=E/T increases. Therefore, the short circuit current increases in proportion to the detection delay time, and the current that must be interrupted by the GTO increases accordingly. If the inductance L of the current limiting reactor is increased, the rate of increase in short-circuit current di _A /dt can be reduced, but increasing L has the drawback of being disadvantageous in terms of size and cost.

Reduces the current duty caused by GTO's short circuit during short circuit,
Furthermore, in order to reduce the size of the current limiting reactor, it is desirable to shorten the short circuit current detection time as much as possible. The conventional method, in which the GTO itself interrupts the short-circuit current,
The current detection scheme is shown in FIG. A detection current transformer 14 is inserted into a circuit through which short-circuit current flows to detect short-circuit current. Many of the current inverters use pulse width modulation (hereinafter referred to as
(abbreviated as PWM) control. 3 is a smoothing capacitor, 4 is a current limiting reactor, 5 is a freewheeling diode, 9 is a GTO inverter, 14 is a current transformer,
12 is a detection signal amplification circuit, 13 is a protection sequence circuit, and a snubber circuit and a feedback diode DF are connected between the anode and cathode of each GTO. However, this method of detecting DC power is
In a GTO inverter that performs PWM (pulse width modulation) control, when reducing the output voltage to zero, all three phases must be operated in the same phase, but at this time, the snubber capacitors for the three phases are charged every time the DC section of the inverter is switched. The short circuit current detection level could not be set to a low value when operating margins were taken into consideration, as the currents flow simultaneously and reach a large value that significantly exceeds the controllable current of the GTO. Therefore, unless the dv/dt tolerance of the GTO is significantly improved and the characteristic impedance of the snubber charging circuit is increased to reduce the charging current, the DC power supply detection method is not suitable as a short circuit detection method for the GTO inverter. In particular, when a shunt resistor is used for detection, it is not appropriate in terms of circuit loss and noise tolerance as the inverter capacity increases. In particular, when the current transformer 14 is a shunt resistor, losses occur due to steady current, and when trying to reduce resistance losses,
This has the drawback that the detection signal becomes small and the detection signal must be amplified.

FIG. 5 shows a conventional detection method in which a current transformer 14 provided in the circuit of the smoothing capacitor 3 detects the current of the smoothing capacitor 3 that is discharged through the GTO in the event of a short circuit, and uses it as a short circuit signal. In this case as well, it is exactly the same as the conventional example shown in Figure 4, and the pulsed current that charges the snubber capacitor is superimposed on the main current flowing through the GTO, setting the detection level that takes advantage of the GTO's shearing ability. It has the disadvantage that it is difficult to

An object of the present invention is to provide an inverter device that can detect only a regular short-circuit current without being sensitive to pseudo-short-circuit currents.

In order to achieve the above object, the present invention provides an inverter circuit including a plurality of self-extinguishing elements as conversion elements, a group of snubber circuits connected in parallel to each self-extinguishing element, and a group of snubber circuits connected in parallel to each self-extinguishing element. a parallel circuit of a current limiting reactor and a freewheeling diode inserted and connected between the inverter circuit and the direct current power supply; In an inverter device comprising a filter capacitor connected in parallel with an inverter circuit, a capacitor or a series circuit of a capacitor and a resistor connected in parallel with the inverter circuit between the current limiting reactor and the inverter circuit; Current detection means detects the current flowing through the circuit connecting the series circuit, the parallel circuit of the inverter circuit, and the filter capacitor; and when the detection output of the current detection means exceeds the short-circuit setting level, The inverter device is provided with a control means for outputting a control signal for short circuit protection. Furthermore, the inverter circuit includes a plurality of self-extinguishing elements as conversion elements, a group of snubber circuits connected in parallel to each self-extinguishing element, a group of feedback diodes connected in parallel to each self-extinguishing element, and the inverter circuit. a parallel circuit of a current limiting reactor and a freewheeling diode inserted and connected between the current limiting reactor and the freewheeling diode, and a filter capacitor connected in parallel with the inverter circuit on the DC power supply side of the parallel circuit of the current limiting reactor and the freewheeling diode. In an inverter device equipped with
A capacitor or a series circuit of a capacitor and a resistor connected in parallel with the current limiting reactor, a current detection means for detecting the current of the current limiting reactor, and when the detection output of the current detection means exceeds the short circuit setting level. This inverter device is provided with a control means for outputting a control signal for short-circuit protection to the gate of each self-extinguishing element.

Examples of the present invention will be described below.

FIG. 6 shows an embodiment of the invention.

In the figure, a three-phase AC power source 1 is supplied to a rectifier 2 and converted into a DC power source. A current limiting reactor 4 is connected to the (+) side terminal of the rectifier 2 via a smoothing reactor 10. A resistor 15, an anode of GTO 1, an anode of GTO 3, and an anode of GTO 5 are connected to the other end of the current limiting reactor 4, respectively. The other end of the resistor 15 is connected to the (-) side terminal of the rectifier via a capacitor 16. This resistor 15 and capacitor 16 constitute a pulse current supply circuit 17. Furthermore, a diode 5 is inserted and connected between the terminals of the current limiting reactor 4 in the opposite direction. Further, a smoothing capacitor 3 is connected to the smoothing reactor 10, and the other end of the smoothing capacitor 3 is connected to the (-) side terminal of the rectifier 2.

On the other hand, the (-) side terminal of the rectifier 2 is connected to the cathode of the GTO 1 via the GTO 2 which is connected in the forward direction. In addition, the cathode of GTO3 is
The (-) side terminal of the rectifier 2 is connected via the GTO 4 which is connected in the forward direction. Further, the cathode of the GTO 5 is connected to the (-) side terminal of the rectifier 2 via the GTO 6 which is connected in the forward direction. In addition, between the anode and cathode of each GTO, there is a snubber circuit consisting of a parallel circuit of a snubber diode DS and a snubber resistor RS connected in the forward direction, and a snubber capacitor CS connected to the parallel circuit. , and a feedback diode DF are connected respectively.

Also, the connection point of GTO1 and GTO2, and the connection point of GTO3
A three-phase induction motor 7, which is a load, is connected to a connection point between GTO 4 and GTO 4, and a connection point between GTO 5 and GTO 6.

Also, the (-) of the rectifier 2 between the smoothing capacitor 3 and the capacitor 16 of the pulse current supply circuit 17
A current transformer 14 is provided on the side line, and a detection signal amplification circuit 12 is connected to the current transformer 14 serving as current detection means. A protection sequence circuit 13 is connected to this detection signal amplification circuit 12 . The output from this protection sequence circuit 13 is configured to be supplied to the gates of each of the GTOs 1 to 6. That is, the detection signal amplification circuit 1
2 and the protection sequence circuit 13 are configured as control means, and output a control signal for short circuit protection to the gates of GTOs 1 to 6 when the detected current of the current transformer 14 exceeds the short circuit setting level. There is.

With this configuration, when the commercial three-phase AC power supply 1 is received, the pulsating current converted by the rectifier 2 is transferred to the smoothing reactor 10 and the smoothing capacitor 3.
GTO is smoothed by current limiting reactor 4.
It is applied to the inverter 9. Furthermore, the freewheeling diode 5 suppresses transient voltage during steady operation together with the current limiting reactor 4 connected in parallel, and performs a regenerative operation. Further, the snubber capacitors CS1 to CS6 are charged by a pulse current supply circuit 17 that supplies pulse current.

If the power supply of the GTO inverter 9 is short-circuited via the GTO due to an abnormality in the load or a malfunction of the GTO, the energy stored in the smoothing capacitor 3 will be rapidly discharged. GTO inverter 9
In order to operate normally, the power supply ripple must be above a certain level, and energy above a certain level must be stored, so the smoothing capacitor 3 needs to have a large capacity. . Inverters of tens of KVA to several tens of KVA usually have a capacity of millifarads (mF). Therefore, if a short circuit occurs in the GTO inverter 9, a large current will flow through the GTO, leading to its destruction.
For the same reason, the smoothing reactor 10 is also
The unit of henry (mH) is used.

Therefore, the short-circuit current is detected, and the gate signal of the GTO is operated based on the detection signal, and the short-circuit current is cut off by the self-extinguishing ability of the GTO, thereby protecting the GTO element itself and the circuit. As mentioned earlier, the GTO does not have a self-current limiting effect and its switching speed is faster than that of a thyristor, so the current limiting reactor 4 can suppress the increase in short circuit current and detect short circuit conditions accurately and quickly. However, the short-circuit current must be terminated before the GTO's breakdown current is reached.

This short circuit current i _A sets the terminal voltage of the smoothing capacitor 3 to E, and the inductance of the current limiting reactor 4 to L.
Then, di _A /dt=E/L increases. Therefore, the short circuit current increases in proportion to the detection delay time, and
The current that must be cut off by the GTO increases. If the inductance L of the current limiting reactor 4 is increased, the increase rate di _A /dt of the short circuit current can be limited to a low level, but increasing the inductance L does not result in miniaturization. Alternatively, it has the disadvantage of high cost. In order to reduce the current duty of the GTO and to reduce the inductance L, it is necessary to shorten the short circuit fault detection time as much as possible. By the way, the characteristics of GTO are the maximum current that can be used repeatedly, that is, the controllable anode current I TCM as shown in Figure 7a, and the maximum current that can be turned off for only one cycle, that is, the non-controllable anode current I _TCM as shown in Figure 7b. There is a maximum repeatable controllable current I _TCSM . In order to use the GTO capacity effectively and economically, the steady state current should be set to a value close to I _TCM shown in Figure 7 a, and Figure 7 c
The short circuit detection level is set between I _TCM and I _TCSM as shown in . Normally, it would be desirable to immediately detect when the I _TCM is exceeded and cut off the short-circuit current, but there are fluctuations in the power supply voltage, detection delay time, delay time of the detection circuit, protection sequence circuit, etc., and these delay times During this period, the short circuit current increases with a constant di _A /dt. Let td be _the detection delay time _, ts be the delay time of the protection sequence circuit, _etc. , and let E be _the power supply voltage. Inkutance L of current limiting reactor 4
Since the relationship is I _TCSM - I _TCM = E/L (t _d + t _s ), L=E (t _d + t _s )/I _TCSM - I _TCM .

Now, considering an inverter with (t _d + d _s ) of about 20 μs, E of 400 V, and +KVA, and assuming that the I _TCSM of the GTO used is 180 Å and the I _TCM is 60 Å, as shown in Figure 7,
The current that increases during (t _d + t _s ) = 20 μs is (I _TCSM −
The L required to keep the voltage down to I _TCM ) = 120A is L = 400 x 20/120≒67 (μH).

However, in the three-phase inverter shown in Fig. 6,
During synchronous operation where the output voltage is reduced to zero using PWM control,
Snubber capacitor C _S1 , C _S3 , C _S5 or C _S2 ,
_{GTO1 ,}
A charging current flows simultaneously every time GTO 3, 5 or GTO 2, 4, 6 switches. In FIG. 6, if the pulse current supply circuit 17 for charging the snubber capacitor is not provided, as shown in FIG. Charging current appears. The peak value of the current I _{d0 nax} is about 10 KVA
In this inverter, from the dv/dt tolerance of the GTO used, C _S is 0.5 μF, the power supply voltage is 400 V, and L is the value mentioned above.
If it is 67μH, From the formula, it is approximately 120A. That is, since a current larger than controllable current I _TCM :60A appears, the short circuit detection level is the peak value I _{d0 nax} shown in Figure 7d.
_The detection level must _be set at _a higher value as shown in FIG. During steady state when there is no pulse current supply circuit 17, the current transformer 14
An example of a detected waveform appearing in FIG. 8A is shown in FIG. 8A, and an example of a detected waveform by the current transformer 14 in a steady state when a pulse current supply circuit is added is shown in FIG. 8B. Both A and B in Figure 8 are in steady operation.
This is an example of one chopping waveform under PWM control. In the case of Figure 8A, which does not have a pulse current supply circuit, there is a charging current for charging one snubber capacitor C _S and a forward current at the beginning of the current flow, as shown at point h of the d waveform in Figure 8A. During phase mode switching, in other words, during delayed power factor operation caused by the load inductance L, a pseudo short circuit occurs,
The pulsed current also appears superimposed on the load current. This phase advance mode switching is
This is a case where a load current is already flowing through the anti-parallel connected feedback diode DF1 at the time when the off-gate signal of GTO1 is applied. Next is the anti-arm GTO
When 2 is fired, a current flows from the power supply in a direction that cancels the current in the feedback diode DF1. The recovery current of this feedback diode DF and the charging current of the snubber capacitor C _S1 appear at _IL . The same thing is done for the other arms.

In the case shown in FIG. 8A without the pulse current supply circuit 17, the detection margin time is several μs as shown by T ₀ in FIG. Even if you think about it, it is difficult to detect. When the pulse current supply circuit 17 is added, the detected current waveform becomes as shown in FIG. 8B, and a pseudo short circuit does not occur due to the charging of the snubber capacitors for three phases in the current of the current limiting reactor 4, as shown in FIG. 8B. As shown in (c), the detection level can be set low, making full use of the GTO's ability during steady operation, and in the event of a short-circuit accident, the short-circuit accident can be detected in an extremely short detection time, and the detection signal can be amplified by the amplifier circuit 12 or It is possible to carry out protection operations such as performing V conversion, etc., suppressing the firing signal of the GTO of the short circuit arm with the protection sequence circuit 13, and energizing the arc extinguishing pulse to cut off the short circuit current with the GTO. . In FIGS. 8A and 8B, e indicates the short circuit current, T ₀ and T ₁ indicate the detection margin time, and t ₀ and t ₁ indicate the time required to detect the short circuit, respectively.

In this embodiment, the pulse current supply circuit 17 is configured by a series circuit of the resistor 15 and the capacitor 16, but it can also be configured by only the capacitor 16.

Another embodiment of the invention is shown in FIG. This embodiment differs from the embodiment illustrated in FIG.
The pulse current supply circuit 17 is configured to be connected in parallel to the current limiting reactor 4, and the current flowing through the current limiting reactor 4 is detected by the current transformer 14. The circuit operation and effects are the same as the embodiment shown in FIG. That is, pulse current supply circuit 1
During normal operation, the capacitor 16 of 7 is charged with a voltage that is negligible compared to the voltage of the smoothing capacitor (filter capacitor) 3. Therefore, when the inverter circuit 9 is switched, the charging current of the snubber capacitor and the feedback diode are A pulse current similar to the recovery current is generated. In the inverter pseudo short circuit state, this pulse current is supplied from the smoothing capacitor 3 via the pulse current supply circuit 17. Therefore, if the current of the current limiting reactor 4 is detected, it will hardly be affected by the pseudo short circuit, and a true short circuit current can be detected at high speed, similar to the embodiment shown in FIG. Further, in this case, since the pulse current supply circuit 17 acts as a bypass circuit for the current limiting reactor 4, the polarity of charging the snubber capacitor is the same as in the embodiment shown in FIG. According to this embodiment, the GTO inverter can be protected against short-circuit accidents by using the GTO that constitutes the inverter main circuit.
Moreover, the current limiting reactor can be small. moreover,
As a short-circuit accident detection method, the level of short-circuit current can be detected well, and the detection speed is extremely high, ranging from several μs to more than ten μs. Since the current limiting reactor can be made sufficiently small, the circulating current is also reduced, and the diode current connected in parallel to the current limiting reactor is also reduced.
An inexpensive, small-capacity one will suffice.

Therefore, the inverter according to this embodiment is small, inexpensive, and has low loss. There are dozens of explanations
This was done when the KVA power supply voltage was 400V or 800V, but the same short circuit fault detection can be done regardless of the capacity or voltage. The effect is particularly noticeable when the capacity is large.

As explained above, according to the present invention, it is possible to detect only the regular short circuit current without being sensitive to the pseudo short circuit current, so it is possible to lower the short circuit setting level, and to shorten the regular short circuit. It is possible to protect the self-extinguishing element group by detecting it in time.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a conventional thyristor inverter device, Figure 2 is a circuit diagram of a conventional GTO inverter device, and Figure 3 is a circuit diagram of a conventional GTO inverter device.
A circuit diagram of a GTO inverter device, Fig. 4 is a circuit diagram of a GTO inverter device using a conventional current limiting reactor, Fig. 5 is a circuit diagram with the current detection point changed when detecting a short circuit in Fig. 4, and Fig. 6 is a circuit diagram of a GTO inverter device using a conventional current limiting reactor. The figure is a circuit diagram showing an embodiment of the present invention, FIGS. 7 and 8 A and B are characteristic diagrams of the embodiment illustrated in FIG. 6, and FIG. 9 is a circuit diagram showing another embodiment of the present invention. . 3... Smoothing capacitor, 4... Current limiting reactor, 9... GTO inverter circuit, 14... Current transformer.

Claims (1)

[Claims] 1. An inverter circuit having a plurality of self-extinguishing elements as conversion elements, a group of snubber circuits connected in parallel to each self-extinguishing element, and a group of feedback diodes connected in parallel to each self-extinguishing element. a parallel circuit of a current limiting reactor and a freewheeling diode inserted and connected between the inverter circuit and the DC power supply, and a parallel circuit of the current limiting reactor and the freewheeling diode connected in parallel with the inverter circuit on the DC power supply side of the parallel circuit of the current limiting reactor and the freewheeling diode. In an inverter device comprising a filter capacitor connected thereto, a capacitor or a series circuit of a capacitor and a resistor connected in parallel with the inverter circuit between the current limiting reactor and the inverter circuit, and a capacitor connected in parallel with the inverter circuit; A current detection means for detecting the current flowing through the circuit connecting the parallel circuit of the circuit and the filter capacitor, and a short-circuit protection device installed at the gate of each self-extinguishing element when the detection output of the current detection means exceeds the short-circuit setting level. An inverter device comprising a control means for outputting a control signal. 2. An inverter circuit having a plurality of self-extinguishing elements as conversion elements, a group of snubber circuits connected in parallel to each self-extinguishing element, a group of feedback diodes connected in parallel to each self-extinguishing element, and the inverter circuit. A parallel circuit of a current limiting reactor and a freewheeling diode inserted and connected between the current limiting reactor and the freewheeling diode, and a filter capacitor connected in parallel with the inverter circuit on the direct current power source side of the parallel circuit of the current limiting reactor and the freewheeling diode. In an inverter device equipped with a capacitor or a series circuit of a capacitor and a resistor connected in parallel with the current limiting reactor, a current detection means for detecting the current of the current limiting reactor, and a detection output of the current detection means are short-circuited. An inverter device comprising: control means for outputting a control signal for short-circuit protection to the gate of each self-extinguishing element when a set level is exceeded.