JP2755601B2 - Power converter - Google Patents

Description

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

(Prior Art) A power converter is configured using a power semiconductor device,
Devices for power conversion are used in many fields. A snubber circuit used for suppressing a voltage change rate of a semiconductor device is generally as shown in FIG. 4th
In the figure, 1 is a gate turn-off thyristor (hereinafter GT)
2 is a diode, 3 is a resistor, and 4 is a capacitor. This snubber circuit is provided to suppress the rate of voltage rise when the GTO is turned off. That is, when GTO1 is on and the voltage of capacitor 4 is zero, GTO1
Is turned off, a charging current flows through the capacitor 4 via the diode 2, so that a rapid voltage change does not occur in GTO1. When GTO1 turns on, the charging energy of the capacitor 4 is consumed through the resistor 3. The power consumption of the resistor due to this operation is determined by the magnitude of the charging voltage, the capacity of the capacitor, and the number of times of switching.

A snubber circuit that eliminates power consumption due to resistance, for example,
JCBENDIEN etal “RECOVERY CIRCUIT FOR SNUBBER ENE
RGY IN POWER ELECTRONIC APPLICATIONS WITH HIGH SWI
TCHING FREQUENCIES "16th Annual IEEE PESC 1985, p165
It is described in. FIG. 5 shows an example of a circuit configuration of a voltage type inverter, showing upper and lower arms for one phase of AC. In the figure, 5 is a positive DC terminal, 6 is a negative DC terminal, 7 is an AC terminal, 8 is an anode reactor, 9 and 10 are GTO, 11, 12 are feedback diodes, 13, 15 are diodes, 14, 16 Is a capacitor, and 17 is a regenerative circuit. Anode reactor 8 is GTO
At the time of switching on the switches 9 and 10, the current change is suppressed so that no sudden current flows. Positive DC terminal 5
Is given to the point A in the figure. Now, consider a state in which GTO9 is on and GTO10 is off and current is flowing from the AC terminal. At this time, the potential of the AC terminal is equal to the potential of the DC terminal 5 on the positive side. When GTO 9 is turned off and GTO 10 is turned on from this state, the current flowing from the AC terminal 7 is the current flowing through the feedback diode 12, the anode reactor 8, the diode 13, the capacitor
14 would be supplied by the current. Capacitor
When the potential at the point B becomes higher than the potential at the point A, the capacitor 16 and the regenerative circuit 17
Current flows through When the current flowing through the anode reactor 8 becomes zero, all the current flowing from the AC terminal flows through the feedback diode 12. At this time, capacitor 14
Are charged at the same voltage as the capacitor 16. Next, GT
When O10 is turned off and GTO9 is turned on, the current flowing from the AC terminal current is gradually transferred from the feedback diode to the anode reactor 8, GTO9, and the potential of the AC terminal becomes equal to the potential of the DC terminal on the positive side. At this time, the capacitor
The charge charged in 14 flows through the diode 15 to the capacitor 16 and the regenerative circuit 17. The energy stored in the capacitor 14 is guided to the regenerative circuit 17, and its output is power-converted and then regenerated to the DC circuit of the inverter or another circuit.

(Problems to be Solved by the Invention) In recent years, power converters have also been increasing in capacity, and power semiconductor devices have also been used in GTO and capacitive thyristors (SI).
High-speed switching devices such as thyristors and IGBTs are being applied. When a plurality of such high-speed switching devices are connected in series to one arm to realize a high-voltage converter, a snubber circuit as shown in FIG. 5 cannot be realized. Further, in the circuit shown in FIG. 4, when switching is performed at a high frequency, the power consumption of the resistor is large, and the efficiency of the conversion device is reduced.
The size of the cooling device for processing the resistance and the power consumption consumed by the resistance increases, and the size of the device increases.

The present invention has been made in consideration of the above points, and has as its object to implement a snubber circuit suitable for a power converter in which power semiconductor devices are connected in series.

[Configuration of the invention]

(Means for Solving the Problems) In the present invention, two power elements connected in series are set as one set, and a diode-capacitor snubber having a capacitor on the anode side and a negative side for each set are provided on the positive side power element. A diode-capacitor snubber having a capacitor on the cathode side is connected to the power element, and a regenerative circuit is connected between the connection points of each diode and capacitor.

(Operation) In such a configuration, when the arm is turned off, the capacitor connected to each device is charged via a diode, the rate of voltage rise can be suppressed, and when the arm is turned on, a regenerative circuit is used. The energy charged in the capacitor flows into the input terminal of the.

(Embodiment) FIG. 1 is a block diagram showing one embodiment of the present invention, and shows one arm when applied to an inverter. 5 is a positive DC terminal, 6 is a negative DC terminal, 7 is an AC terminal, 34 and 35 are anode reactors, 36, 37, 22 to 29 are diodes, 40 and 4
1,30-33 are capacitors, 38,39 are regenerative circuits, 18-19 are GTO
It is.

Now, let us consider a state in FIG. 1 in which the upper arm, that is, the GTOs 18 and 19 are on, the GTOs 20 and 21 on the lower arm are off, and the current of the AC terminal is constant in the flowing direction. It is assumed that the regenerative circuits 38 and 39 are controlled so that the voltages of the capacitors 40 and 41 always become Δe. At this time, since the upper arm is on and the lower arm is off, the potential of the positive DC terminal 5 is V _dc , the voltage of the capacitors 30 and 31 is O, and the voltage of the capacitors 32 and 33 is V _dc / 2. Is hanged. The current from the AC terminal flows through the anode reactor 34 and the GTOs 18 and 19. Next, turn off the upper arm, that is, GTO18,19, and lower arm,
Turn on GTO20,21. The current flowing from the AC terminal 7 is supplied from the current flowing through the anode reactor 34, the capacitor 30, the diodes 26, 27, and the capacitor 31, and the current flowing through the anode reactor 35 and the feedback diodes 25, 24. The energy of the anode reactor is charged to the capacitors 30 and 31 and eventually the anode reactor 34
Current becomes zero, and all the current at the AC terminal flows through the anode reactor 35 and the feedback diodes 25 and 24. Then, the AC terminal voltage becomes zero (the potential of the negative AC terminal voltage). At this time, if the sum of the voltages of the capacitors 30 and 31 is larger than V _dc + Δe, the AC terminal 7 and the capacitor 3
1. A mode in which current flows through the capacitor 40 and the regenerative circuit 38, the diode 36, the capacitor 30, and the anode reactor 34, and the voltage of the capacitors 30, 31 is (V _dc + Δe)
/ 2. At this time, since current flows through the regeneration circuit 38 and the positive DC terminal, power regeneration is performed. Since the regenerative circuit 38 is not a main part of the present invention, a description thereof will be omitted.
It is assumed that the input voltage Δe is controlled to be kept constant.

Next, consider the case where the lower arm, that is, GTO20,21 is turned off, and the upper arm, GTO18,19, is turned on. AC terminal 7
The current flowing out of the anode reactor 35, the current passing through the feedback diodes 25 and 24, and the anode reactor 3
4. Supplied from the current passing through the GTOs 18 and 19, the potential of the AC terminal 7 gradually increases. At this time, since the GTOs 18 and 19 are on, the energy of the capacitors 30 and 31 becomes
The operation moves to the capacitor 40 and the regeneration circuit 38. That is, the diode 36, the capacitor 30, the GTO 18, 19, the capacitor 31,
A current flows in the order of the capacitor 40 and the regenerative circuit 38. Eventually, all the current flowing from the AC terminal 7 is supplied from the anode reactor 34 and the GTOs 18 and 19. A current flows through the regenerative circuit until the voltage of each of the capacitors 30 and 31 becomes Δe / 2. The energy stored in the capacitor of the upper arm is guided to the regenerative circuit 38 every time the GTO is switched. The energy stored in the capacitor of the lower arm is guided to the regenerative circuit 39 by the same operation.

(Effect) As described above, in the present embodiment, one set of series-connected
The energy stored in the capacitor can be effectively led to the regenerative circuit by the snubber circuit using the GTO diode and capacitor. In this embodiment, the same effect can be obtained when a plurality of GTOs are connected in series as shown in FIG. However, each element in FIG. 2 corresponds to the element of the same number in FIG.

FIG. 3 is a block diagram showing another embodiment of the present invention.
Reference numerals 2 and 43 are resistors, and the other elements correspond to the elements having the same numbers shown in FIG. In the first embodiment, the voltage of the capacitors 30, 31 was Δe / 2 even when the upper arm was on.
When the upper arm is turned off under such conditions, a voltage of Δe is applied to the GTO in a step-like manner at the time of off, and in some cases,
GTO could be adversely affected. In this embodiment, since the energy of the capacitor is discharged through the resistor 42 while the GTOs 18 and 19 are on, when the upper arm is turned off, a more stable operation is performed without applying severe stress to the GTO. can get.

In the embodiment, the regenerative circuits 38 and 39 are provided. However, the regenerative circuits 38 and 39 may be replaced with resistors, and snubber energy may be consumed collectively.

〔The invention's effect〕

As described above, in the present invention, a converter configured by connecting a plurality of power elements in series can improve the efficiency by an effective snubber circuit, and can reduce the size of the device by modularizing the regenerative circuit. Becomes

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIGS.
FIG. 4 is a block diagram showing another embodiment of the present invention, FIG. 4 is a block diagram of a conventional snubber circuit, and FIG. 5 is a block diagram of a conventional snubber circuit including a regenerative circuit. 1,9,10,18,19,20,21… Gate turn-off thyristor (GT
O) 2,13,15,26,27,28,29,36,37… Diode 3,42,43… Resistance 4,14,16,30,31,32,33,40,41… Capacitor 5… Positive Side DC terminal 6… Negative side DC terminal 8,34,35… Anode reactor 11,12,22,23,24,25… Feedback diode 17,38,39… Regeneration circuit

Claims (1)

(57) [Claims] 1. A power converter comprising a plurality of power elements connected in series per arm on one side, wherein two power elements connected in series form one set, and each set includes a power From the anode terminal of the element to the capacitor,
A first voltage change rate suppressing snubber circuit connected in series in the order of an anode terminal and a cathode terminal of a diode, and a second snubber circuit connected in series in the order of an anode terminal of the diode, a cathode terminal, and a capacitor from the anode terminal of the negative power element.
And a connection point between the diode and the capacitor of the second voltage change rate suppression snubber circuit from a connection point between the capacitor and the diode of the first voltage change rate suppression snubber circuit. And a regenerative circuit.