JPH08308243A - Power converter - Google Patents

Abstract

PURPOSE: To increase the bouncing voltage suppressing function generated in a switching element without almost increasing the occurrence loss of the resistor of a snubber circuit. CONSTITUTION: An auxiliary diode 9 and an auxiliary capacitor 11 are connected in series between the positive side end of a positive side arm 2A and the negative side of a negative side arm 2B, and further an auxiliary resistor 10 is connected in parallel with the diode 9. At the time of switching off, a capacitor 8A and the capacitor 11 become in parallel to strengthen the bouncing voltage suppressing function. At the time of switching on, since the discharge of the capacitor 11 becomes only an overvoltage, the resistance loss due to this is small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter used in an electric vehicle or the like, and more particularly to a snubber circuit for protecting its switching element.

[0002]

2. Description of the Related Art FIG. 5 shows, for example, Japanese Patent Application Laid-Open No. 4-308474.
FIG. 1 is a circuit configuration diagram illustrating one phase of a conventional electric vehicle power conversion device (inverter device) described in Japanese Patent Laid-open Publication, particularly an element arm and each snubber circuit. In the figure, 1 is a filter capacitor serving as a DC power source, 2A is a positive arm, and is composed of a switching element 3A such as a GTO thyristor and a flywheel diode connected in antiparallel thereto. Similarly, the negative arm 2B is
Switching element 3B and flywheel diode 4B
It consists of and. The arms 2A and 2B are connected in series with each other, and further connected between the positive and negative terminals of the filter capacitor 1, and the connection point between the arms 2A and 2B is connected to an AC load terminal (not shown).

5A is a positive arm 2 in order to suppress a so-called spike voltage that generally occurs when switching is OFF.
A snubber circuit connected to A, which is composed of a diode 6A, a resistor 7A and a capacitor 8A which are connected as shown in the figure. Similarly, the snubber circuit 5B connected to the negative arm 2B is composed of a diode 6B, a resistor 7B and a capacitor 8B.

Next, the operation, mainly the operation of the snubber circuit will be described. First, from the state in which current flows from the positive terminal of the filter capacitor 1 to the load through the switching element 3A of the arm 2A, the switching element 3
Consider the operation when A turns off. By this OFF operation, the current until then flows into the capacitor 8A through the diode 6A, and the capacitor 8A is charged. The increase rate (dv) of the voltage V _AK across the switching element 3A at this time
/ Dt) is the capacitor 8A when the cutoff current is constant.
Proportional to the capacitance of.

This voltage V _AK also jumps up to a value V _DM higher than the DC voltage V _D of the filter capacitor 1 due to the wiring inductance between the filter capacitor 1 and the switching element 3A, and then the charged capacitor. The charge of 8 A is discharged by the resistor 7 A, and the voltage V _AK is attenuated to the voltage value V _D. Here, assuming that ΔV _DM = V _DM −V _D , ΔV _DM is equal to the capacitor 8 when the cutoff current is constant.
It is inversely proportional to the 1/2 power of the capacitance of A.

Next, the operation when the switching element 3A of the arm 2A is turned on while the current is flowing from the negative terminal of the filter capacitor 1 to the load through the flywheel diode 4B of the arm 2B will be described.
By the ON operation of the switching element 3A, the electric charge of the capacitor 8A, which has been charged by the voltage V _D until then, becomes the resistance 7A.
Through to discharge to 0V. At this time, a loss proportional to the electrostatic capacitance of the capacitor 8A occurs in the resistor 7A.

The switching element 3B of the arm 2B
Since the switching OFF and ON operations are the same as the switching operation of the switching element 3A of the arm 2A, the description thereof will be omitted.

[0008]

Since the snubber circuit of the conventional power converter is constructed as described above, the rate of increase (dv / dt) of the voltage V _AK is considered when the withstand voltage design of the switching element is considered. Within the allowable range of, the overvoltage component ΔV _DM can be suppressed to a low value by increasing the capacitance of the capacitors 8A and 8B, but in this case, conversely, the generated loss of the resistors 7A and 7B increases, and the device design It will be a disadvantage.

The present invention has been made in order to solve the above problems, and electric power which can effectively suppress the overvoltage component ΔV _DM without substantially increasing the generation loss of the resistance of the snubber circuit. The purpose is to obtain a conversion device.

[0010]

According to a first aspect of the power converter of the present invention, an auxiliary capacitor is connected between the positive side end of the positive side arm and the negative side end of the negative side arm.

A power conversion device according to a second aspect of the present invention is the power conversion device of the first aspect.
In addition, an auxiliary resistor is further inserted in series with the auxiliary capacitor.

A power conversion device according to a third aspect of the present invention is the power conversion device of the second aspect.
In addition, an auxiliary diode is connected in parallel with the auxiliary resistor.

According to a fourth aspect of the present invention, there is provided a power conversion device, wherein a node between a diode and a capacitor of a snubber circuit of a positive side arm and a negative side end of the negative side arm, and a positive side end of the positive side arm and the positive side arm. Auxiliary capacitors are connected between the negative arm snubber circuit and the connection point between the diode and the capacitor.

[0014]

In the power conversion device according to the first aspect, the capacitor of the snubber circuit and the auxiliary capacitor function in parallel during the switching OFF operation, so that the function of suppressing the jump-up voltage generated in the switching element increases. During the switching ON operation, the auxiliary capacitor is discharged only by the overvoltage, and the resistance loss becomes small.

In the power converter according to claim 2,
The auxiliary resistor suppresses the oscillating component of the current flowing through the auxiliary capacitor.

In the power converter according to claim 3,
During the switching OFF operation, the auxiliary diode short-circuits the auxiliary resistor, so that the function of suppressing the jump-up voltage by the auxiliary capacitor is fully exerted.

In the power converter according to claim 4,
During the switching OFF operation, the capacitor in the snubber circuit and both auxiliary capacitors function in parallel, so that the jump-up voltage suppressing function generated in the switching element is increased.

[0018]

【Example】

Example 1. 1 is a circuit configuration diagram of a power converter according to a first embodiment of the present invention. In the figure, 1 to 8B are the same as the conventional ones, and the individual explanations are omitted. Reference numerals 9, 10, and 11 are wirings shown in the drawing, which are connected between the positive and negative terminals of the filter capacitor 1, that is, between the positive side end of the arm 2A and the negative side end of the arm 2B. It is a capacitor.

Next, the operation will be described with reference to the timing charts of FIGS. First, the operation when the switching element 3A is turned off from the state where the current is flowing from the positive terminal of the filter capacitor 1 through the switching element 3A of the arm 2A to the load will be described with reference to the drawings. In FIG. 2, at time t ₁ , the switching element 3A
Starts OFF operation. At the same time, current flows through the diode 6A and into the capacitor 8A,
The place where A is charged is the same as the conventional one.

The voltage of the capacitor 8A (V (8
A))), that is, the voltage corresponding to V _AK here is
When the DC voltage V _D is exceeded (time t ₂ ), the auxiliary diode 9
Is energized, the filter capacitor 1 and the switching element 3
The energy stored in the wiring inductance with A flows into not only the capacitor 8A but also the auxiliary capacitor 11 through the auxiliary diode 9, so that the overvoltage component ΔV _DM is the electrostatic capacitance between the capacitor 8A and the auxiliary capacitor 11. This is inversely proportional to the 1/2 power of the sum of the above, and this overvoltage component ΔV _DM is effectively suppressed.

When the commutation of the switching element 3A is completed at time t ₃ , the part of the electric charge charged in the auxiliary capacitor 11 which exceeds the DC voltage V _D is discharged through the auxiliary resistor 10.

Next, the operation when the switching element 3A of the arm 2A is turned on in the state where the current flows from the negative terminal of the filter capacitor 1 to the load through the flywheel diode 4B of the arm 2B according to FIG. explain. In FIG. 3, at time t ₄ , the switching element 3A
When is turned on, the electric charge stored in the capacitor 8A is discharged through the resistor 7A as in the conventional case. on the other hand,
The charge stored in the auxiliary capacitor 11 is stored in the auxiliary resistor 10
However, this discharge ends at t ₅ at the end of commutation, and the voltage of the auxiliary capacitor 11 (indicated as V (11) in FIG. 3) rises again and is charged to the DC voltage V _D. (Time t ₆ ). That is, the auxiliary capacitor 11
Is maintained at approximately the DC voltage V _D , the auxiliary capacitor 11 only repeats charging and discharging for the overvoltage during commutation, and the loss generated in the auxiliary resistor 10 through which the current flows is extremely small.

In other words, the present invention relates to the capacitor 8A.
Since the auxiliary capacitor 11 is newly provided instead of increasing the electrostatic capacity of itself, the overvoltage component ΔV _DM can be effectively suppressed with almost no increase in resistance loss.

Since the auxiliary resistor 10 in FIG. 1 suppresses the discharge current at the time of commutation and the subsequent resonance with the filter capacitor 1 described above, the current capacity of the auxiliary capacitor 11 and the filter capacitor 1 is set low. can do. Further, by providing the auxiliary diode 9,
The insertion of the auxiliary resistor 10 prevents the overvoltage suppressing effect from being hindered.

Example 2. FIG. 4 is a circuit configuration diagram of a power converter according to a second embodiment of the present invention. In this example,
Diode 6A and capacitor 8A of positive side snubber circuit 5A
An auxiliary capacitor 12A is connected between the connection point between the positive arm 2A and the negative side end of the negative side arm 2B, and the positive side end of the positive side arm 2A and the capacitor 8B and the diode 6B of the negative side snubber circuit 5B.
The auxiliary capacitor 12B is connected between the connection point and the connection point.

Also in this case, the operation is the same as that of the first embodiment, and the overvoltage component ΔV _DM is effectively suppressed without increasing the resistance loss. Here, the resistors 7A and 7B not only limit the discharge current of the capacitors 8A and 8B, but also have the function of limiting the discharge current of the auxiliary capacitors 12A and 12B. Further, the diodes 6A and 6B are turned off.
The current has a function of charging not only the capacitors 8A and 8B but also the auxiliary capacitors 12A and 12B and blocking discharge of these.

Embodiment 3 FIG. Although the pair of arms on the positive and negative sides have been described in the above embodiments, the present invention is not limited to a power conversion device between a direct current and a single-phase alternating current, but may be a direct current and a three-phase alternating current.
The present invention can be applied to a power converter between equal-phase and multi-phase alternating current.

[0028]

As described above, in the power converter according to the first aspect of the present invention, since the auxiliary capacitor is connected between the positive side end of the positive side arm and the negative side end of the negative side arm, almost no resistance loss occurs. The jump-up voltage suppressing function is increased without increasing it.

Further, in the power converter according to claim 2,
Since the auxiliary resistor is inserted in series with the auxiliary capacitor, the vibration component of the current flowing through the auxiliary capacitor is suppressed.

Further, in the power converter according to claim 3,
Since the auxiliary diode is connected in parallel with the auxiliary resistor, the jump-up voltage suppressing function of the auxiliary capacitor is fully exerted.

Further, in the power converter according to claim 4,
Connection between the diode-capacitor connection point of the positive arm and the negative end of the negative arm, and between the positive end of the positive arm and the snubber circuit diode capacitor of the negative arm. Since the auxiliary capacitors are respectively connected between the point and the point, the jump-up voltage suppressing function is increased with almost no increase in resistance loss.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing a main part of a power conversion device according to a first embodiment of the present invention.

FIG. 2 is a timing chart showing an operation when switching is off in the circuit of FIG.

FIG. 3 is a timing chart showing an operation when switching is turned on in the circuit of FIG.

FIG. 4 is a circuit configuration diagram showing a main part of a power conversion device according to a second embodiment of the present invention.

FIG. 5 is a circuit configuration diagram showing a main part of a conventional power conversion device.

[Explanation of symbols]

1 filter capacitor, 2A positive arm, 2B negative arm, 3A, 3B switching element, 4A, 4B
Flywheel diode, 5A, 5B snubber circuit, 6A, 6B diode, 7A, 7B resistor, 8
A, 8B capacitors, 9 auxiliary diodes, 10 auxiliary resistors, 11 auxiliary capacitors, 12A, 12B auxiliary capacitors.

Claims (4)

[Claims] 1. An arm composed of a switching element and a flywheel diode antiparallel-connected to the switching element is provided on the positive and negative sides and connected in series to each other to be connected to a DC positive and negative terminal, and between the positive and negative arms. A power conversion device for connecting a connection point to an AC terminal, wherein a snubber circuit including a capacitor and a diode connected in series with each other and a resistor connected in parallel with the diode is provided at both ends of each arm. In the power converter, an auxiliary capacitor is connected between the positive side end of the positive side arm and the negative side end of the negative side arm so as to reinforce the jumping voltage suppressing function generated in the switching element by the snubber circuit. A power conversion device characterized in that 2. The power converter according to claim 1, wherein an auxiliary resistor is inserted in series with the auxiliary capacitor to suppress an oscillating component of a current flowing through the auxiliary capacitor. 3. The power converter according to claim 2, wherein an auxiliary diode is connected in parallel with the auxiliary resistor to increase the effect of suppressing the jumping voltage generated in the switching element. 4. An arm composed of a switching element and a flywheel diode antiparallel-connected to the switching element is provided on the positive and negative sides and connected in series to each other to be connected to a DC positive and negative terminal, and between the positive and negative side arms. A power conversion device for connecting a connection point to an AC terminal, wherein a snubber circuit including a capacitor and a diode connected in series with each other and a resistor connected in parallel with the diode is provided at both ends of each arm. In the power converter, between the connection point between the diode and the capacitor of the snubber circuit of the positive side arm and the negative side end of the negative side arm, and the snubber circuit of the positive side end of the positive side arm and the negative side arm. Auxiliary capacitors are connected between the diode-capacitor connection point and the snubber circuit switching element. Power conversion device is characterized in that so as to reinforce the bouncing up voltage suppression function of live.