JPS6260917B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a self-excited conversion device using a semiconductor element (hereinafter referred to as an element) having self-extinguishing ability, and in particular, the structure is improved to reduce voltage stress of the element and increase efficiency. This invention relates to a conversion device.

Self-excited conversion devices using thyristors are widely used as choppers and self-excited inverters. 1st
The figure shows a self-excited inverter circuit well known as a McMurray bed inverter, but since the thyristor itself does not have self-extinguishing ability, a commutation circuit is provided to turn off the thyristor.

In Fig. 1, 1 and 2 are DC power supply lines, 3 is a smoothing capacitor, 4 and 5 are thyristors, 6 and 7 are commutating reactors coupled to each other, 8 and 9 are commutating capacitors, 10 and 11 are feedback diodes, 12 is an AC power supply line, and 13 and 14 are snubber circuits. Although the operation of this circuit has been described in many books and need not be described in detail, the operation will be briefly described below in order to clarify the operational differences necessary to explain the present invention.

Thyristor 4 is on, AC feeder line 12
When the current I _L is flowing from the load toward the load (not shown), the electric charge of the commutating capacitor 8 is 0, and the commutating capacitor 9 is charged to the DC voltage E. Here, when the thyristor 5 is turned on, the commutation reactor 7
The voltage E of the commutation capacitor 9 is applied to the commutation reactor 7, and the voltage E is also induced in the commutation reactor 6 coupled to the commutation reactor 7. Since the voltage of the commutating capacitor 8 is 0 and the voltage of the commutating reactor 6 is E, the thyristor 4
A counter pressure E is applied to turn it off. The current I _L flowing through the commutation reactor 6 is transferred to the commutation reactor 7 at that moment. The electric charge of the commutating capacitor 9 flows from the DC power source to the load and commutating reactor 7 through the commutating capacitor 8, and the electric charge of the commutating capacitor 9 flows to the load and commutating reactor 7. As a result, when the voltage of the commutating capacitor 9 becomes E/2, the commutating reactor 6 The sum of the voltages generated at and 7 becomes E, and the reverse pressure applied to the thyristor 4 becomes 0. Further, as commutating capacitor 9 is discharged and commutating capacitor 8 is charged, a positive voltage is applied to thyristor 4. In this way, commutation is performed from thyristor 4 to 5, but in reality, the first closed loop of the thyristor, commutation reactor, and commutation capacitor, and the second closed loop of the commutation capacitor and smoothing capacitor 3 or a DC power supply (not shown) are The operation is slightly different because it includes stray inductance. This stray inductance creates an overlap period when thyristor 5 is turned on, during which both thyristors are turned on at the same time. If this overlap period is too long, commutation will no longer be possible, but if it is not over a certain amount, the current rises when the thyristor turns on (normally
di/dt) cannot be suppressed. In that sense, it is desirable to have a certain amount of stray inductance as shown in Figure 2a.
and b respectively show the current and voltage waveforms when the thyristor 4 is turned off. Time t ₁ when the current attenuates with a certain slope and reaches 0, and then the cap carrier in the thyristor discharges and the reverse recovery current reaches its maximum.
A counter pressure is applied to the thyristor. The slope di _R /dt when the reverse recovery current becomes 0 depends on the characteristics specific to the thyristor, but thyristor 4 has Ldi _R /dt
(Here, L is the inductance of the commutation reactor 6) is superimposed on the reverse pressure E, causing a surge reverse voltage v _ps
will occur. In order to suppress this voltage, the snubber circuit 13
is inserted. Similarly, the snubber 14 is also connected to the thyristor 5.
Inserted to suppress surge reverse voltage. The capacitor of this snubber circuit is approximately 0.5 to 0.1μF,
The resistance is about 10 to 100Ω.

To summarize the above, in the circuit shown in Figure 1, the thyristor snubber circuit is provided to absorb the overvoltage caused by the thyristor's reverse recovery current (usually on the order of 1/10 or less of the load current, which decreases as the stray inductance increases). The stray inductance of the circuit is effective in suppressing the di/dt of the thyristor.

On the other hand, in the gate turn-off thyristor (GTO) shown in FIG. 3, which is cited as an example of an element having self-extinguishing capability, the snubber circuit plays an extremely important role in this circuit. In Fig. 3, 21 and 22 are DC power supply lines 23
is a capacitor, 24 and 25 are GTO, 26 and 27
is a gate circuit, 28 and 29 are feedback diodes 30
31 and 32 are snubber circuits, and 33 is a stray inductance, respectively. In figure 3
When the GTO 24 is turned on and is supplying I _L to a load (not shown) via the AC power supply line 30, when a negative gate current is passed between the gate and cathode of the GTO 24 from the gate circuit 26, the GTO 24 is turned off. Since the load current I _L does not immediately become zero, the diode 29 becomes conductive, and the current continues to flow from the negative side of the DC power supply to the load. Then GTO2
Turn on 5. FIGS. 4a and 4b show the current and voltage waveforms, respectively, when the GTO 24 is turned off.

By generating voltage across the GTO,
Since the current is attenuated, the current in the stray inductance 33, whose waveform is completely different from that of the thyristor in Figure 2, is
Even if the GTO 24 is turned off, it cannot immediately become 0 or inverted, so it flows into the snubber circuit 31 of the GTO 24. The snubber circuit 31 includes a series circuit of a capacitor 311 and a diode 312, and a resistor 313 connected in parallel with the diode 312. When the capacitor 311 is charged by the current of the stray inductance 33 and the potential of the AC power supply line 30 becomes 0, the diode 2
9 conducts. After that, the voltage of the capacitor 311 increases until the current of the stray inductance 33 reaches 0 or reverses and reaches _-IL.The higher the voltage applied across the GTO 24, that is, the voltage of the capacitor 311, the higher the GTO must be used. Therefore, it is desirable that the capacitance of the capacitor 311 be as large as possible to reduce the voltage rise due to the stray inductance 33, but at the same time the loss increases. To show this quantitatively, let the size of the stray inductance 33 be L, the capacitance of the capacitor 311 be C, the current be I _L , the DC voltage be E, the frequency be f, then the capacitor voltage will be E+√I, and the loss will be 1/2 (LI ² + CE ² ) f.

Until now, transistors and GTOs have mainly been of small capacity, with small E and I, and because the devices are small, the stray inductance L has also been necessarily small (stray inductance is determined by the wiring length), and therefore the loss has been small. However, as GTOs and transistors become larger in capacity, for example, E = 500V, I = 500A, L = 5μ.
If H, C = 2μFf = 1000Hz, the snubber loss per element is 875W, which is a loss of over 2% when converted to a three-phase inverter. Also, since the voltage applied to the element is 1290V, if 1300V elements are used, two must be connected in series, which is uneconomical. One solution to this problem is to connect a snubber circuit 33, shown in dashed lines in FIG. 5, to both ends of the DC feed line that feeds the GTO and the diode stack. This makes it possible to reduce the voltage stress applied to the element and the circuit loss to some extent, but it is not sufficient and the number of components increases.

The purpose of the present invention is to reduce the voltage stress of semiconductor elements, increase efficiency, and downsize components and devices by adopting a structure suitable for self-excited conversion devices using semiconductor elements with large capacity self-extinguishing ability. The object of the present invention is to provide a conversion device that achieves the following.

The present invention achieves
One embodiment of this is shown in FIGS. 6 and 7.

FIG. 6 is a circuit diagram of a single-phase GTO inverter. Components that are the same as those in FIG. 3 are given the same numbers and their explanations will be omitted. 34 and 35 are GTOs, 38 and 39 are diodes, 40 is an AC feeder line, 21 ₁ , 21 ₂ , 2
2 ₁ and 22 ₂ are DC power supply lines. Also 20 ₁
is GTO24 and diode 29 or GTO34
refers to the first series circuit that connects the cathode side of the GTO and the cathode of the diode, such as diode 39,
₂₀₂ refers to a second series circuit in which the anode of the diode and the anode of the GTO are connected, such as diode 28 and GTO 25 or diode 38 and GTO 35. Here, the anode side and cathode side of GTO are
Anode or cathode direct case and fuse or dv/dt
This expression includes the case of inserting a protective reactor, etc.

In the present invention, from the capacitor 23 to the GTO
The AC feeder lines 30 and 40 pass through the circuit and connect to the DC feeder line 2.
1 ₂ and 22 _2. As shown in the figure, feeder lines through which currents of equal magnitude and opposite directions flow are arranged close to each other. Assuming that the current flows in the direction of the arrow in the figure, the DC feeder lines 21 ₁ and 22 ₁ and the DC feeder line 22 ₂ and the AC feeder lines 30 and 40 are placed close to each other, and an additional DC current is applied in case the GTOs 25 and 34 are turned on. It is assumed that the power supply line ₂₁₂ and the AC power supply lines 30 and 40 are placed close to each other. A specific structural diagram is shown in FIG. In Figure 7, GTO24, 25, 34, 3
5 and diodes 28, 29, 38, 39 are arranged in upper and lower two stages as stacks 43 ₁ and 43 ₂ which are pressure-welded through a cooling fin 41 and an insulator 42 as shown in the figure, and the capacitor 23 is connected to these stacks 43 ₁
and ₄₃₂ . stack 43
The DC power supply lines from ₁ , 43 _{and 2} to the capacitor 23 are partially different in connection order from the DC power supply lines shown in FIG. 6, so they are distinguished by different symbols.

In FIG. 7, DC feed lines 21 ₃ and 22 ₃ , 2 leading to GTO or diode and capacitor 23
1 ₄ and 22 ₄ are arranged close to each other with AC feed lines 30 and 40 sandwiched between them, and furthermore, the AC feed line 40 is close to the DC feed lines 21 ₃ and 22 ₃ up to the vicinity of one AC feed line 30. and then connect it to a load (not shown).

In the above configuration, if the GTOs 24 and 35 are electrically connected and current flows as shown in the arrow as shown in Fig. 6, then in Fig. The currents in close proximity between the feed lines are opposite, the magnetic fields created by these feed lines cancel each other out, and the inductance is reduced by 1/4.
- sharply reduced to 1/10. As a result, in the example cited earlier, by applying the present invention, L can be reduced to 1 μH.
The voltage applied to the element is 854V (66%),
It was found that the snubber loss was 375V (43%), a significant improvement.

When two sets of the first series circuit and the second series circuit are used, a single-phase inverter shown in FIG. 6 is constructed, but when three sets each are used, a three-phase inverter is constructed. In this case, there will be three AC power supply lines, but these power supply lines should not be connected directly from the stack to the load, but must be concentrated in one place while being close to part of the DC power supply line. . However, the purpose is not to reduce the inductance of the AC power supply line itself, but to reduce the inductance of the DC power supply line. Also, in a multi-stage conversion device configured by using multiple sets of these single-phase or three-phase inverters as unit inverters, the AC feeder line for each single-phase or three-phase unit inverter may be connected close to a part of the DC feeder line. However, in many cases, the load will be connected to a transformer, concentrating it in one place.

FIGS. 8 and 9 show other embodiments of the present invention.
the cathode of the diode of the first series circuit;
The difference from FIG. 6 is that the reactors 51 and 52 with midpoints are inserted instead of being directly connected to the anodes of the diodes in the series circuit.

For example, this reactor with a center point causes a sudden voltage change in GTO25 at the moment GTO24 turns on.
This is to prevent dv/dt from being applied, and power is supplied to the load from the midpoint. In such a case, the DC power supply line 21 ₃ connected to the stack in FIG.
₂₂₃ and the AC feeder lines 30 and 40, and the DC feeder lines ₂₁₄ and ₂₂₄ and the AC feeder line 40, it is difficult to make them close to each other, so a line connecting the midpoint reactors 51 and 52 from the stack is used. 30 ₁ and 3
0 ₂ or 40 ₁ and 40 ₂ are placed close to the DC power supply line. Also, instead of the reactor with center point in Fig. 8,
Reactor 53 and diode 54 as shown in the figure
When inserting a protection circuit consisting of the capacitor 23 in series with the capacitor 23 or a part of the DC power supply line, take measures such as placing the connecting wires between the diode 54 and the capacitor 23 close to each other or twisting them together as shown in Fig. 11. to prevent an increase in inductance. The same applies when inserting a fuse.

In the converter described above, the capacitor 23 is a part of the DC power supply and is connected to a DC supply source (not shown), and power is supplied to the load provided on the AC side through the converter. Recently, attempts have been made to connect such a converter to an AC system and use it as a phase-leading/phase-lag reactive power generator, but the DC circuit does not have a DC supply source and the capacitor 23 is connected. (aside from protection circuits), the losses of the converter are supplied from the AC system. It is obvious that the structure of the converting device of the present invention can be applied to this case as well.

FIGS. 12 and 13 are examples in which the idea of the present invention is applied to a chopper. In FIG. 12, 60 is a DC power supply, 61, 62, 64 ₁ , 64 ₂ , 65 are DC power supply lines, and 63 is a reactor.

When the GTO 24 is on, a current flows from the DC power supply 60 in the direction of the arrow. When the GTO 24 is turned off, the current in the reactor 63 circulates through the load and the diode 29 (not shown). From the point of view of GTO voltage stress and snubber loss, DC power supply 6
0. The smaller the stray inductance of the closed loop of the DC power supply lines 61, 62, GTO 24, and diode 29, the better. If the DC feed lines 64 ₁ and ₆₅ come out from both terminals of the diode 29 as shown in FIG. Avoid placing it close to either 61 or 62. If the DC feed line 65 is not connected to the point A near the cathode of the diode but to the point B near the DC power supply 60, the DC feed line ₆₄₁ is close to or closer to the DC feed lines 61 and 62. Stray inductance is reduced by connecting to the reactor 63 from point B while performing alignment. FIG. 13 shows the case of a boost chopper, in which the DC power supply lines 64 and 65 leading to the second series circuit ₂₀₂ and the capacitor 66 are placed close together or twisted together, and the connection between the DC power supply 60 and the series circuit of the reactor 63 is Perform near the anode and cathode sides of GTO25.

As explained above, by considering the wiring route, the present invention can simultaneously realize a significant reduction in the voltage stress and circuit loss of a semiconductor element having a self-extinguishing element, and furthermore, it is possible to significantly reduce the voltage stress and circuit loss caused by the The overall size of the device has been reduced by reducing the number of sections and parts, and its industrial value is extremely high.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of the conventional device, Fig. 2 is a waveform diagram to explain the operation of Fig. 1, Fig. 3 is another circuit diagram of the conventional device, and Fig. 4 explains the operation of Fig. 3. FIG. 5 is yet another circuit diagram of the conventional device; FIG. 6 is a circuit diagram showing an embodiment of the present invention; FIG. 7 is a configuration diagram showing a specific example of FIG. 6; FIG. 8 is a circuit diagram showing another embodiment of the present invention, FIG. 9 is a configuration diagram of the eighth embodiment, and FIGS. 10 to 13 are circuit diagrams showing other embodiments of the present invention. be. 3, 23, 66... DC circuit capacitor,
8, 9... Commutation capacitor, 4, 5... Thyristor, 24, 25, 34, 35... GTO, 10,
11, 28, 29, 38, 39, 54... Diode, 6, 7... Commutation reactor, 13, 14,
33... Snubber circuit, 26, 27... GTO gate circuit, 20 ₁ ... First series circuit, 20 ₂ ...
...Second series circuit, 60...DC power supply, 63...
Reactor, 41... Fin, 42... Insulator.

Claims (1)

[Scope of Claims] 1. A set of arms consists of at least two series-connected semiconductor elements having self-extinguishing ability and respective snubber circuits connected in antiparallel to these elements, and In a conversion device, at least two sets of DC power supplies are connected in parallel to ignite the semiconductor elements in a predetermined order to obtain alternating current at a frequency higher than the commercial frequency through the series connection points of the arms. A conversion device characterized in that positive and negative DC power supply lines from the to the arm are arranged close to each other so that the current directions are opposite, and an AC power supply line that supplies power to an AC load is arranged close to the DC power supply line. 2. A first set of arms consisting of a semiconductor element and a diode equipped with a snubber circuit having a self-extinguishing ability in which a pair of arms are connected in series with at least the cathode side in common.
a second series circuit consisting of a semiconductor element including diodes connected in series with the anode side in common and a snubber circuit having self-extinguishing ability;
It consists of a reactor with an intermediate tap connected between the series connection points of the first and second series circuits, and at least two sets of these arms are connected in parallel to a DC power supply to connect the semiconductor elements in a predetermined order. In a converter that is ignited to obtain an alternating current of a frequency higher than the commercial frequency through an intermediate tap of the reactor, the positive and negative direct current feed lines from the direct current power source to the arm are connected so that the current directions are opposite. and an AC feeder line from the arm to the reactor of the arm is placed close to the DC feeder line.