JP2807284B2 - Snubber circuit - Google Patents

Description

The present invention relates to a snubber circuit of a power converter configured by connecting a plurality of power elements in series.

(Prior Art) A device for forming a power converter with a power element and performing power conversion is used in many fields.

In such a power converter, a snubber circuit is used to suppress the rate of voltage increase applied to the power element, and generally has a configuration as shown in FIG.
In FIG. 6, 1 is a gate turn-off thyristor (hereinafter referred to as GTO), 2 is a snubber capacitor, 3 is a snubber diode, and 4 is a snubber resistor. This snubber circuit is composed of a snubber capacitor 2 and a snubber diode 3.
It is provided to suppress the rate of voltage rise when O is turned off. That is, when GTO1 is on and GTO1 is turned off in a state where the voltage of snubber capacitor 2 is 0, the current flows to snubber capacitor 2 via current snubber diode 3 which has been flowing through GTO1. At this time, the voltage rise rate of GTO1 is suppressed by the voltage rise rate due to the charging of the snubber capacitor 2, so that no sharp voltage change occurs in GTO1. When GTO 1 is turned on, the charging energy of snubber capacitor 2 is consumed through snubber resistor 4. The power consumption of the resistor due to this operation is determined by the magnitude of the charging voltage of the snubber capacitor 2, the capacitance of the snubber capacitor 2, and the number of times the GTO1 is switched.

By the way, as a snubber circuit in which power consumption by a resistor is eliminated, there is, for example, U.S. Pat. No. 4,566,051 (1986). FIG. 7 shows an example of a circuit configuration of the voltage type inverter disclosed in the publication, showing an upper and lower arm for one phase of AC. In the figure, 1a and 1b are GTO, 2 is a snubber capacitor, 3 is a snubber diode, 5a and 5b are anti-parallel diodes, 6 is a diode, 7 is a capacitor, 8 is a DC power supply, 9 is a regenerative circuit, 10 is a reactor, 11 Is a positive DC terminal, 12 is a negative DC terminal, and 13 is an AC output terminal.

Here, the reactor 10 has an effect of suppressing a current change rate so that a sudden current does not flow when each of the GTO 1a and GTO 1b is switched on. The anti-parallel diodes 5a and 5b are connected in reverse direction and parallel to GTO1a and GTO1b so as to prevent reverse voltage from being generated in GTO1a and GTO1b.

In such a snubber circuit, a regular DC terminal
The potential of 11 is Vdc, the potential of the negative DC terminal 12 is 0, and the potential at point A is Vdc + Δe. Now, consider the state where GTO1a is on and GTO1b is off. When in this state GT
Since O1 is conducting, the potential of the AC output terminal 13 is equal to that of the positive DC terminal 11, the terminal voltage of GTO1a is 0, and the terminal voltage of GTO1b is Vdc.

When GTO1a is turned off and GTO1b is turned on from this state, the potential of the AC output terminal 13 gradually decreases and becomes equal to the potential of the negative DC terminal 12. At this time, the terminal voltage of GTO1a changes from O to V
Although the voltage rises to dc, the voltage rise rate is suppressed to a voltage change due to the charging of the snubber capacitor 2, and therefore, no rapid voltage rise occurs.

When the snubber capacitor 2 is charged and the potential at the point B becomes higher than the potential at the point A, a current flows to the capacitor 7 and the regenerative circuit 9 via the diode 6. When the current flowing through the reactor 10 becomes zero, all the current flowing from the AC output terminal 13 flows through the anti-parallel diode 5b. At this time, the terminal voltage of the snubber capacitor 2 becomes the terminal voltage of the capacitor 7, that is, Vdc + Δe.

Next, turn off GTO1b and turn on GTO1a.
The potential of 13 gradually rises and becomes equal to the positive DC terminal 11.
At this time, the terminal voltage of GTO1b rises from 0 to Vdc,
Since the rate of increase is suppressed by the voltage change due to the discharge of the capacitor 2, a rapid voltage increase does not occur. Further, since the voltage at the point B increases with the increase in the voltage of the AC output terminal 13, the energy of the snubber capacitor 2 flows through the diode 6 to the regenerative circuit 9. The energy stored in the snubber capacitor 2 is guided to the regenerative circuit 9, and its output is power-converted and then regenerated to the DC circuit of the inverter or another circuit.

By the way, in recent years, high performance and large capacity of power converters have been actively promoted. Therefore, in order to perform high-performance control on a power converter having a relatively small capacity, a method of increasing the switching frequency of the power element has been adopted. Because of this, the switching frequency cannot be increased too much.
In view of this, a configuration has been used in which a large-capacity converter can output three or more values of output voltage from the conventional two values. In order to configure a power converter capable of outputting three or more voltages, a method of multiplexing two or more inverters using a transformer or a reactor, and a method of connecting several inverters between a positive DC terminal and a negative DC terminal. There is a system that has such an intermediate potential and outputs from an AC output terminal in combination with a positive DC terminal, an intermediate potential, and a negative DC terminal. The former is described, for example, in Chapter 6 of Semiconductor Power Conversion Circuits (IEEJ, Technical Committee on Investigation of Semiconductor Power Conversion Systems), and the latter is described, for example, in the paper A New Neutral-Point-Clamped PWM Inverter (IEEE).
E TRANSACTION ON INDUSTRY APPLICATION.VOL.IA-17, N
o.5, SEPTEMBER / OCTOBER1981; AKIRA NABAE et al.) shows the circuit system and operation in detail.

FIG. 8 is an example of the latter circuit. In FIG. 8, 1a-
1d is GTO, 5a to 5d are antiparallel diodes, 6a and 6b are diodes, 7a and 7b are capacitors, 8 is a DC power supply, 11 is a positive DC terminal, 12 is a negative DC terminal, and 13 is an AC output terminal . The potential of the positive DC terminal 11 is Vdc, the potential of the negative DC terminal 12 is 0, and the potential at point A is Vdc / 2.

In the circuit shown in FIG. 8, when GTO1a and GTO1b are on and GTO1c and GTO1d are off, GTO1a and GTO1b are conductive and the terminal voltage is 0. Therefore, the potential of the AC output terminal 13 becomes positive DC terminal 11 Of the potential.

When GTO1b and GTO1c are on, GTO1a and GTO1d are off, and when the current flows from the AC output terminal 13 depending on the direction of the current, the current flows from the point A, and the diodes 6a and GT
If O1b is flowing, the current will flow from point A to diode 6
b and GTO1c, respectively, and the potential of the AC output terminal 13 becomes equal to the point A in each case.

When GTO1c and GTO1d are on and GTO1a and GTO1b are off, GTO1
Since the terminal voltage becomes 0 when c and GTO1d are conducting, the potential of the AC output terminal 13 becomes equal to the potential of the negative DC terminal 12.

Therefore, GTO1a, GTO1b, GT
By operating O1c and GTO1d as shown in FIG. 9, the potential of the AC output terminal 13 can be made closer to a sine wave.

(Problems to be Solved by the Invention) As described above, in the conventional large-capacity power converter, the GTO is widely used, and since the GTO has a large limitation on the rate of voltage change applied to the element, the snubber circuit is indispensable. Element. Even when a power element other than the GTO is used, it is necessary to use a snubber circuit in order to reduce the load on the power element.

However, in the case of a power converter having a configuration as shown in FIG. 8, a snubber circuit as shown in FIG. 7 cannot be formed. Therefore, for each GTO shown in FIG.
When a snubber circuit as shown in the figure is provided, the power consumption of the resistor constituting the snubber circuit is large, and as a result, the efficiency of the converter is reduced, or a cooling device for processing the power consumption consumed by the resistor is provided. And there is a problem that the converter becomes large.

The present invention does not use a snubber resistor for a plurality of power elements connected in series constituting a large-capacity power converter,
An object of the present invention is to provide a snubber circuit that can effectively absorb charging energy of a snubber capacitor and has low power consumption.

[Configuration of the Invention] In order to achieve the above object, in the first invention, 2n + 1 (where n is an integer of 1 or more) power elements are connected in series between a positive DC terminal and an AC output terminal, In a power converter in which a positive arm and a negative arm are configured by connecting 2n + 1 (n: an integer of 1 or more) power elements in series between a negative DC terminal and an AC output terminal, the positive DC A forward diode and a snubber composed of a capacitor are connected from the anode terminal of the first power element connected to the terminal to the cathode terminal of the element, and a connection point between the diode and the capacitor of the snubber is connected to the positive DC terminal. A positive regenerative circuit is connected therebetween, and a capacitor and a snubber composed of a forward diode are connected from the anode terminal of the first power element connected to the negative DC terminal to the cathode terminal of the element. Snubber Daio A negative regenerative circuit is connected between the connection point of the capacitor and the capacitor and the negative DC terminal, and two power supply elements are respectively provided for the second and subsequent power elements of the positive arm and the negative arm. A set of elements, a capacitor is connected from the anode terminal to the cathode terminal of the power element on the positive side,
A first snubber is formed by connecting in the order of a forward diode, and a second snubber is formed by connecting a forward diode and a capacitor in this order from the anode terminal to the cathode terminal of the power element on the negative side. A regenerative circuit is connected to a connection point between the forward diode and the capacitor of the first snubber and a connection point between the forward diode and the capacitor of the second snubber.

(Operation) Therefore, in the snubber circuit having the configuration as in the first invention, 2n + 1 pieces are provided between the positive DC terminal and the AC output terminal and between the negative DC terminal and the AC output terminal ( (Where n is an integer equal to or greater than 1) in series, and when the first power element connected to the positive DC terminal and the negative DC terminal is turned off, the element and the positive DC Since the energy of the reactor provided between the terminal and the negative DC terminal flows through the regenerative circuit, excess energy existing in the reactor can be effectively utilized, and the second and subsequent positive and negative arms can be used. As with the first invention, when one set of power elements is turned on,
Since the energy stored in the capacitor of the second snubber flows through the regenerative circuit and is consumed, power loss can be reduced.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows one arm of an inverter as a configuration example of a snubber circuit according to the present invention. In FIG. 1, 1a to 1d are GTO, 2a to 2d are snubber capacitors, 3a to 3d
Are snubber diodes, 5a to 5d are antiparallel diodes, 6a to
6d is a diode, 7a and 7b are capacitors, 8 is a DC power supply, 9
a and 9b are regenerative circuits, 11 is a positive DC terminal, 12 is a negative current terminal,
13 is an AC output terminal. The potential of the positive DC terminal 11 is Vdc, the potential of the negative DC terminal 12 is 0, and the potential at the point A is Vdc / 2.
The regenerative circuits 9a and 9b are controlled so that the terminal voltage becomes sufficiently lower than the DC voltage Vdc.

Here, GTO1a to GTO1d are connected in series, and one end is connected to the positive DC terminal 11 connected to the DC power supply 8 and the other end is connected to the negative DC terminal 12 connected to the DC power supply 8, respectively. Capacitors 7a and 7b are connected in series between the positive DC terminal 11 and the negative DC terminal 12, and the voltage dividing point A is connected between GTO1a and GTO1b via a diode 6a and via a diode 6b. Between GTO1c and GTO1d. Furthermore, if GTO1a and GTO1b form a pair, an antiparallel diode 5a is connected between the anode and cathode terminals of GTO1a on the positive side, and a snubber capacitor is connected.
2a, connect a series circuit of forward direction snubber diode 3a,
Further, an anti-parallel diode 5b is connected between the anode terminal and the cathode terminal of the GTO 1b on the negative side, and a series circuit of a forward snubber diode 3b and a snubber capacitor 2b is connected. A connection point between the snubber capacitor 2a and the forward snubber diode 3b is connected to one end of the regenerative circuit 9a via a diode 6c having a polarity shown, and a connection point between the forward snubber diode 3b and the snubber capacitor 2b is connected. Regenerative circuit
It is connected to the other end of 9a.

The configuration when GTO1c and GTO1d are set as one set is the same as that described above, and the description is omitted here.

Next, the operation of the snubber circuit configured as described above will be described.

Now, it is assumed in FIG. 1 that the upper arm, that is, GTO1a, GTO1b is in the ON state, and the GTO1c, GTO1d of the lower arm is in the OFF state. At this time, since GTO1a and GTO1b are conducting, the potential of the AC output terminal 13 is equal to the potential of the positive DC terminal 11, and the terminal voltages of GTO1a and GTO1b are 0, G
The terminal voltages of TO1c and GTO1d are each Vdc / 2. Also,
The terminal voltages of the snubber capacitors 5a and 5b are 0, respectively, and the terminal voltages of the snubber capacitors 5c and 5d are Vdc / 2.

When GTO1a is turned off and GTO1c is turned on from this state, GTO1
The terminal voltage of a gradually increases. At this time, the voltage rise rate of the GTO 1a is suppressed to a voltage change due to the charging of the snubber capacitor 2a, so that a rapid voltage rise does not occur. Also, GT
When O1c is turned on, a circulating current flows through the GTO 1c, the diode 3d, the regenerative circuit 9b, the diode 6d, and the snubber capacitor 2c, so that all the energy of the snubber capacitor 2c is guided to the regenerative circuit 9b. And the AC output terminal 13
Becomes equal to the point A, the terminal voltage of the snubber capacitor 2a becomes Vcd / 2, and the terminal voltage of the snubber capacitor 2c becomes 0.

Next, when GTO1b is turned off and GTO1d is turned on from this state,
The terminal voltage of GTO1b gradually increases. At this time, the voltage rise rate of the GTO 1b is suppressed to a voltage change due to the charging of the snubber capacitor 2b, so that a sharp decrease in the voltage does not occur. When GTO1d is turned on, a circulating current flows through GTOd, snubber capacitor 2d, regenerative circuit 9b, diode 6d, and snubber diode 3c, so that all energy of snubber capacitor 2d is guided to regenerative circuit 9d. Then, the potential of the AC output terminal 13 becomes equal to that of the negative DC terminal 12, the terminal voltage of the snubber capacitor 2b becomes Vdc / 2, and the terminal voltage of the snubber capacitor 2d becomes 0.

In the other switching modes, the same operation is performed, and the voltage rise rate when the GTO is off is suppressed by charging the corresponding snubber capacitor. When the GTO is on, all the energy of the snubber capacitor is guided to the regenerative circuit 9a or 9b.

As described above, in this embodiment, the charging energy of the capacitor can be effectively guided to the regenerative circuit by the snubber circuit including the series-connected GTO diode and the capacitor.

 Next, another embodiment of the present invention will be described.

FIG. 2 shows a configuration example in which four sets are connected in series when the number of series is two. In FIG. 2, 8a to 8d
Is a DC power supply, and the other components correspond to the corresponding symbols in FIG. 1, and therefore description thereof is omitted here.

As for the operation of the main circuit, when GTO1a to GTO1d are on and the other GTOs are off, the potential of the AC output terminal 13 becomes equal to that of the positive DC terminal 11. GTO1b ~ GTO1e on, other GTO
Is off, the potential of the AC output terminal 13 becomes equal to the point A.

When GTO1c to GTO1f are on and the other GTOs are off, the potential of the AC output terminal 13 becomes equal to the point B.

When GTO1d to GTO1g are on and the other GTOs are off, the potential of the AC output terminal 13 becomes equal to the point C.

When GTO1e to GTO1h are on and the other GTOs are off, the potential of the AC output terminal 13 becomes equal to that of the negative DC terminal 12.

Regarding the regenerative operation, the voltage rise rate of the GTO is suppressed by the snubber capacitor when the GTO is turned off, and the energy of the snubber capacitor is guided to the regenerative circuit when the GTO is turned on, as in the above embodiment.

FIG. 3 shows an example of a configuration in which two sets are connected in series for the case where the number of series is three, and the same symbols are given to the same components as those in FIG. In this case, the third
One set of GT connected to the positive DC terminal 11 side as shown in the figure
In the O series circuit, an anti-parallel diode 5a, a series circuit of a snubber diode 3a and a snubber capacitor 2a are connected between the anode and the cathode of the GTO 1a, and the anode side of the GTO 1a is connected to a regenerative circuit 9a via a diode 6e having the illustrated polarity. And snubber diode 3a and snubber capacitor 2a
Is connected to the regenerative circuit 9a. Also, the other two GTs
The configuration of O1b and GTO1c is the same as the case where the two shown in FIG. Another GTO series circuit connected to the negative DC terminal 12 is configured in the same manner as described above.

In this way, even when the number of series is odd, the operation of the main circuit is the same as that of the embodiment of FIG. 2, and the description thereof is omitted here.

Further, FIG. 4 shows that two sets are connected in series for the case where the number of GTOs is three, and the reactors 10a and 10a are connected to the positive DC terminal 11 and the negative DC terminal 12 derived from one DC power supply 8, respectively. Shows a configuration example connected via 10b,
The same components as those in FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted. In the embodiment shown in FIG. 4, the voltage change rate is limited by a snubber capacitor, and the current change rate is limited by a reactor.

 Next, the operation of the embodiment shown in FIG. 4 will be described.

Now, in FIG. 4, it is assumed that the positive arm, that is, GT01a to GT01c is on, and the negative arm GT01d to GT01f is off. At this time, since GT01a to GT01c are conducting, the potential of the AC output terminal 13 is equal to the potential of the positive DC terminal 11, and the terminal voltages of GT01a to GT01c are 0,
The terminal voltages of d to GT01f are respectively Vdc / 3. The terminal voltages of the snubber capacitors 2a to 2c are each 0, and the terminal voltages of the snubber capacitors 2d to 2f are each Vdc / 3.

When GT01a to GT01c are turned off and GT01d to GT01f are turned on from this state, the current flowing through the reactor 10a flows through the snubber diode 3a, the snubber capacitors 2a and 2b, the snubber diodes 3b and 3c, and the snubber capacitor 2c, and The snubber capacitors 2a to 2c are charged. At this time, the terminal voltages of GT01a to GT01c increase, but the rate of voltage increase is suppressed to the voltage change due to the charging of snubber capacitors 2a to 2c, respectively, so that a sharp voltage increase does not occur in GT0. When the charging voltage of each of the snubber capacitors 2a to 2c exceeds Vdc / 3, the load current starts flowing through the negative arm GT01d to GT01f, and the current of the reactor 10a is the reactor 10a, the snubber diode 3a, the diode 6a, and the regenerative circuit. Decreases by circulating 9a. At this time, when GT01d and GT01e are turned on, GT01d and GT01e, snubber capacitor 2e, regenerative circuit 9c,
A circulating current flows through the diode 6c and the snubber capacitor 2d, and the energy of the snubber capacitors 2d and 2e is regenerated.
It is led to. Also, when GT01f turns on, GT0
A circulating current flows through 1f, reactor 10b, regenerative circuit 9d, diode 6d, and snubber capacitor 2f, and the energy of snubber capacitor 2f is guided to regenerative circuit 9d.

From this state, turn off GT01d to GT01f of the negative arm and turn on GT01a to GT01c of the positive arm to turn on reactor 10b.
The current flowing to the snubber capacitor 2d, the snubber diodes 3b and 3e, the snubber capacitors 2e and 2f, the snubber diode
The current flows through 3f to charge the negative-side snubber capacitors 2d to 2f.
At this time, the terminal voltages of GT01d to GT01f increase, but the rate of voltage increase is suppressed to the voltage change due to the charging of snubber capacitors 2d to 2f, respectively, so that abrupt voltage increase does not occur in GT0. When the charging voltage of snubber capacitors 2d to 2f exceeds Vdc / 3, the load current is
Current flows through the reactor 10b, the reactor 10b, the snubber diode 3f, the diode 6d, the regenerative circuit 9
circulates through d and decreases. At this time, GT01b, GT01c
Is turned on, a circulating current flows through GT01b, GT01c, snubber capacitor 2c diode 6d, regenerative circuit 9b and snubber capacitor 2b, and the energy of snubber capacitors 2b and 2c is guided to regenerative circuit 9b. When GT01a is turned on, a circulating current flows through GT01a, reactor 10a, regenerative circuit 9a, diode 6a, and snubber capacitor 2a, and the energy of snubber capacitor 2a is guided to regenerative circuit 9a.

In the embodiment shown in FIG. 4, two sets of GTOs are connected in series when the number of GTOs is three, and the positive DC terminal 11 and the negative DC terminal derived from one DC power source 8 are connected. In the configuration connected to the terminal 12 via the reactors 10a and 10b respectively to suppress the voltage change rate and the current change rate applied to each GTO1a to GTO1f, the snubber capacitors 2a to 2f and the reactors 10a, The energy of 10b can be effectively utilized and guided to the regenerative circuits 9a to 9b.

Fig. 5 shows the case where the number of series GTOs is five.
FIG. 4 shows a configuration example in which the sets are connected in series and connected to the positive DC terminal 11 and the negative DC terminal 12 derived from one DC power supply 8 via the reactors 10a and 10b, respectively. Parts corresponding to the components shown are given the same symbols. The operation of the main circuit is the same as that of FIG. 5, and the description thereof will be omitted.

[Effects of the Invention] As described above, according to the present invention, the charging energy of the snubber capacitor is reduced without using a snubber resistor for a plurality of serially connected power conversion elements constituting a large-capacity power converter. , A snubber circuit with low power consumption that can effectively absorb the noise can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a snubber circuit according to the present invention, FIGS. 2 to 5 are circuit diagrams showing other different embodiments of the present invention, and FIG. 6 is a conventional snubber circuit. 7, FIG. 7 is a block diagram of a conventional snubber circuit including a regenerative circuit, FIG. 8 is a circuit diagram showing a configuration example of an inverter capable of ternary output to an AC output terminal, and FIG. 9 is a circuit diagram of FIG. It is a time chart for demonstrating an effect | action. 1a-1h …… GTO, 2a-2h …… Snubber capacitors, 3a-3h
…… Snubber diode, 5a-5h …… Anti-parallel diode,
6a to 6j: Diode, 7, 7a, 7b: Capacitor, 8, 8a
~ 8d ... DC power supply, 9a ~ 9f ... Regeneration circuit, 10a, 10b ...
Reactor, 11… positive DC terminal, 12… negative DC terminal, 13… AC output terminal.

Claims (2)

(57) [Claims] (1) A 2n + terminal is provided between a positive DC terminal and an AC output terminal.
One (but n: 1 or more) power elements are connected in series, and 2n + 1 (but n: 1 or more) power elements are connected in series between the negative DC terminal and the AC output terminal. In the power converter configured as a positive arm and a negative arm
A forward diode and a snubber comprising a capacitor are connected from the anode terminal of the first power element connected to the positive side DC terminal to the cathode terminal of the element, and a connection point between the diode and the capacitor of the snubber is connected to the A positive-side regenerative circuit is connected between the positive-side DC terminal and a capacitor and a forward diode are connected from the anode terminal of the first power element connected to the negative-side DC terminal to the cathode terminal of the element. A snubber is connected, a negative regenerative circuit is connected between the connection point between the diode and the capacitor of the snubber and the negative DC terminal.
For each of the subsequent power elements, a pair of two power elements is formed, and a first snubber is connected by connecting a capacitor and a forward diode in this order from the anode terminal to the cathode terminal of the power element on the positive side. A forward diode and a capacitor are connected in order from the anode terminal to the cathode terminal of the power element on the negative side to form a second snubber;
A snubber circuit, wherein a regenerative circuit is connected to each of the connection point between the capacitor of the first snubber and the forward diode and the connection point between the forward diode and the capacitor of the second snubber. 2. A 2n + 1 (where n is an integer not less than 1) power element connected in series between a positive DC terminal and an AC output terminal and between a negative DC terminal and an AC output terminal. 2. The snubber circuit according to claim 1, wherein a reactor is provided between each of the first power elements and the positive DC terminal and the negative DC terminal.