JP2001061280A - Serial multistage power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To balance the losses in freewheeling diodes connected in antiparallel with outside switching elements by making the capacities of the diodes larger than those of freewheeling diodes connected in antiparallel with internal switching elements. SOLUTION: The capacitances of substantial external freewheeling diodes are made larger than those of internal freewheeling diodes D2, D3, D6, and D7 by connecting freewheeling diodes D11, D14, D51, and D54 in antiparallel with transistors T1, T4, T5, and T8 which are external elements in addition to already existing external freewheeling diodes D1, D4, D5, and D8. Consequently, the capacitances of both external and internal freewheeling diodes are increased and, in addition, the unbalance between the losses in the external and internal freewheeling diodes can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a serial multiplex power converter, and more particularly to a freewheel diode.

[0002]

2. Description of the Related Art Conventionally, first, second, third and fourth switching elements are connected in series, and a connection point between the first and second switching elements and a connection point between the third and fourth switching elements. A series multiplexed power converter having a configuration in which a series circuit of clamping diodes is connected in anti-parallel between the switching elements and anti-parallel freewheeling diodes are connected to the respective switching elements is disclosed in Japanese Patent Application Laid-Open No. 2-262827. These are described in, for example, Japanese Unexamined Patent Publication No. Hei 2-131370 and Japanese Unexamined Patent Publication No. Hei 1-1198280.

[0003]

When the serial multiple power converter described in the above prior art is applied to an actual machine, it has been confirmed that a new problem occurs in that the loss of the freewheel diode becomes unbalanced. .

When an imbalance occurs in loss, for example,
If the cooling performance of the freewheel diode is made the same without any consideration, a difference in deterioration due to heat will occur, the life of the diodes will be unbalanced, and it will be necessary to replace parts twice. There's a problem. In a severe case, the temperature of the lossy freewheel diode rises, which may lead to destruction.

[0005] It is an object of the present invention to provide a series multiplexed power converter having no imbalance in loss of a freewheel diode.

[0006]

The above object is achieved by connecting first, second, third and fourth switching elements in series,
A series circuit of clamping diodes is connected in anti-parallel between the connection point of the first and second switching elements and the connection point of the third and fourth switching elements, and the freewheel is connected in anti-parallel to the respective switching elements. In a series multiple power converter having a configuration in which diodes are connected,
The capacitances of the freewheeling diodes connected in anti-parallel to the first and fourth switching elements are changed to the second and third switching elements.
This is achieved by increasing the capacity of the freewheeling diode connected in anti-parallel to the switching element.

[0007]

As will be described later, the loss of the freewheel diode connected in antiparallel to the first and fourth switching elements (outer switching elements) is opposite to the loss of the second and third switching elements (inner switching elements). It is larger than the loss of the freewheeling diode connected in parallel.
Since the capacity of the freewheeling diode connected in antiparallel to the outer switching element is made larger than the capacity of the freewheeling diode connected in antiparallel to the inner switching element, this loss imbalance can be eliminated.

[0008]

FIG. 1 shows an embodiment in which the present invention is applied to a series multiplex converter for an electric vehicle.

[0009] The AC of the AC overhead wire 1 is received by the pantograph 2, and the power is reduced by the transformer 3. The stepped-down AC is converted by the serial multiplex converter 4 into a DC that becomes a DC voltage command by executing pulse width modulation (PWM). The converted DC is input to an inverter 7 via voltage dividing capacitors (which also have a filter function) 5 and 6, and the inverter 7 converts the converted DC into a three-phase AC having a variable voltage and a variable frequency to drive an electric vehicle driving motor. Is driven. The inverter 7 may be a two-level inverter or a three-level (serial multiplex) like this converter. Further, a chopper that drives the drive motor as a DC motor may be used.

[0010] multi-series converter 4, transistors T ₁ through T ₄ is a switching element having a self-extinguishing function are connected in series, the freewheel diode D ₁ to D ₄ are connected in parallel to the respective transistors, and further And a circuit in which a series body of clamping diodes D ₁₂ and D ₁₃ is connected in anti-parallel between the connection points of the outer elements T ₁ and T ₄ and the inner elements T ₂ and T ₃ to constitute the U phase. The same applies to the V phase.

The output of the transformer 3 is connected between the connection points of the inner elements (between the transistors T ₂ and T ₃ and between the transistors T ₆ and T ₇ ). In addition, the voltage dividing capacitor 5
Positive side and the cathode of the transistor T _5, the collector and the freewheel diode D ₁ of the T _6, D ₅ of are respectively connected,
The negative side of the voltage dividing capacitor 6 is connected to the emitter sides of the transistors T ₄ and T ₈ and the anode sides of the freewheel diodes D ₄ and D ₈ , respectively. Also, the voltage dividing capacitors 5, 6
(Referred to as a neutral point) is connected to a connection point between the clamping diodes D ₁₂ and D _{13 and} a connection point between D ₅₂ and D ₅₃ .

Although the self-extinguishing type switching element is a transistor in this embodiment, the principle of the present invention described below does not change even with a GTO thyristor, an IGBT and a capacitance thyristor.

In addition to the basic configuration of the series multiplex converter described above, in the present embodiment, the transistors T ₁ ,
To T ₄ , T ₅ , and T _{8, in addition} to the existing outer free wheel diodes D ₁ , D ₄ , D ₅ , and D ₈ , anti-parallel free wheel diodes D ₁₁ , D ₁₄ , D ₅₁ , and D ₅₄ are connected. Thus, the capacitance of the substantial outer freewheel diode is made larger than the capacitance of the inner freewheel diodes D ₂ , D ₃ , D ₆ , and D ₇ . In the circuit shown in FIG. 1, these freewheeling diodes are connected in series to the clamping diode. However, as long as they are connected at electrically equivalent positions, for example, the existing outer freewheeling diode can be used. It may be connected in parallel on the side.

Next, the principle of this embodiment will be described with reference to FIGS.

FIGS. 2 and 3 are diagrams showing one phase of the operation mode of the serial multiplex converter. FIG. 2 shows that the voltage at the connection point of the transistors T ₂ and T ₃ (AC side voltage) is 0 and E
FIG. 3 shows that the AC side voltage is E /
A mode changing between 2 and E is shown.

By having these modes, the serial multiplex converter converts AC into DC or converts DC into AC.

First, FIG. 2 will be described. Transistor T
_When the neutral point voltage is output to the load 10 through the clamping diode D ₅ and the transistor T ₂ by turning on ₂ , a current flows in the direction shown in the figure. Then the current flowing thereto until the load 10 by turning off the transistor T ₂ flows in the freewheel diode D _3, D _4.
By repeating this, a voltage of E / 2,0 is output to the load. At this time, on-off signals of T ₁ through T ₄ are, T ₁ is always off, T ₃ is always on, T ₂ and T _4, via a non-lap time T _D for preventing a short circuit, off → Repeat on, on → off.

Here, the freewheel diode D ₃ ,
When the D ₄ is switched to the mode from the mode of in freewheeling, but switches to turn on the T ₂ from the off, E / 2 is applied to the free wheel diode D ₄ by the operation. In this case, the freewheeling diode D _4, as was the under current conduction from the anode to the cathode direction, is canceled by E / 2 under power, current flows in the opposite direction once decreases gradually. This phenomenon is called a diode recovery phenomenon, and causes a recovery loss in the diode.

At this time, the freewheel diode D ₃ is
D ₄ flows the same load current and is, transistor T
For always on signal is applied to ₃ in this mode, since the reverse current in the freewheeling diode D ₃ is conductive the transistor T ₃ when the flow-like, recovery phenomenon occurring in the free wheel diode D ₄ is generated I know you don't.

The same applies to the freewheel diodes D ₁ and D _{2, with} reference to FIG.

When the transistor T ₃ is turned on,
Through the load 10, through the transistor T ₃ -T _6, the current shown in FIG flows toward the neutral point voltage. By then T ₃ off, which until the current flowing in the load 10, flows through the freewheeling diode D _1, D _2. By this repetition, voltages of E / 2 and E are output to the load 10.

At this time, the on / off signals of the transistors T _{1 to} T ₄ are such that T ₄ is always off, T ₂ is always on, and T ₁
And T ₃ is turned on from off via a non-lap time T _D for preventing a short circuit, repeat from ON to OFF.

Here, the freewheel diode D ₁ ,
When D ₂ is switched to the mode from the mode of in freewheeling switches to turn on the transistor T ₃ from the off, but this operation, E / 2 is applied to the free wheel diode D _1. In this case, the freewheeling diode D _1, as was the under current conduction from the anode to the cathode direction, is canceled by E / 2 on the power supply, current flows in the opposite direction once decreases gradually. Recovery loss occurs in this case the free wheel diode D _1. At this time, the free wheel diode D ₂ is similar to the load current and the D ₃ is flowing, the transistor T
Because it is always ON signal in this mode ₂ is added, the current in the opposite direction to the free wheel diode D ₂ is conducting is T ₂ when the flow-like, recovery phenomenon occurring in the free wheel diode D ₁ does not occur I understand.

From the above, it can be seen that the recovery phenomenon occurs in the outer freewheel diodes D ₁ and D _4, but not in the inner freewheel diodes D ₂ and D ₃ .

Next, the losses of the outer freewheeling diodes D ₁ and D ₄ and the inner freewheeling diodes D ₂ and D ₃ will be compared using FIG.

FIG. 4 shows an example of a diode forward voltage and a recovery loss.

The switching frequency of the inner transistors T ₂ and T ₃ is now ₃ kHz, the conduction width in the freewheel mode is 50% duty, and the AC average value of the diode current is 3 kHz.
Assuming 00A, the breakdown of the loss is as follows.

Forward loss = 300 A × 1.25 V × 0.5 (duty) × 0.5 (AC half-wave) = 94 W Recovery loss = 0.25 J × 3000 (switching frequency) × 0.5 (AC half-wave) ) = 375 W From the above, the loss of the outer freewheeling diodes D ₁ and D ₄ with recovery loss is 369 W, and the inner freewheeling diodes D ₂ and D ₃ without recovery loss are:
94W, which shows that there is a large imbalance between the two.

In order to correct the imbalance of the loss occurring in the outer and inner freewheeling diodes, the following means can be considered. (1) Make the capacity of the outer freewheeling diode larger than the capacity of the inner freewheeling diode. (2) A plurality of outer freewheeling diodes are connected in parallel, so that the number is larger than the number of parallel diodes of the inner freewheeling diode. (3) The cooling performance of the cooling fins of the outer freewheeling diode is made higher than that of the inner freewheeling diode.

The embodiment shown in FIG. 1 realizes the above (2) based on the above idea (1).

According to the present embodiment, by making the capacitance of the outer freewheeling diode larger than that of the inner freewheeling diode, there is an effect that the imbalance occurring between the inner side and the outer side can be reduced.

FIG. 5 is a specific configuration diagram of the main circuit of the converter shown in FIG. 1, showing one phase thereof. Transistors T _{1 to} T ₄ , freewheel diodes D _{1 to} D ₄
In the following, an embodiment will be described in which a semiconductor switch module is used in which the semiconductor switch modules are housed in the same package.

The minimum components constituting the series multiplex converter circuit are the semiconductor switch modules TD _{1 to} TD ₄ and the diode modules DM ₅ and DM ₆ . In addition, diode modules DM ₁₁ and DM ₄₁ for increasing capacity are connected in parallel with the semiconductor switching modules TD ₁ and TD ₄ .

[0034] positioned in the semiconductor switch modules TD ₁ ~TD ₄ straight as shown in four series, diode modules DM _5, DM ₆ the circuit the configuration, the semiconductor switch modules TD ₂ from miniaturization of the wiring member, It is placed next to the TD _3. By arranging the diode module DM _11, DM ₄₁ across diode modules DM _5, DM _6, can constitute a good converter circuit space efficient.
That is, since the cooling member is attached to the back side of the module, it is possible to reduce waste of the cooling area.

FIG. 6 shows an embodiment of an actual arrangement for increasing the capacity of both the outer freewheeling diode and the inner freewheeling diode and reducing the imbalance between the losses.

The circuit is such that a freewheel diode is further connected in anti-parallel to the circuit shown in FIG.

[0037] Connect the respective diode module in reverse parallel to the semiconductor switch modules TD ₁ ~TD _4, extra only the outer free wheel diodes, connecting the diode modules DM _12, DM ₄₂ in antiparallel transistors TD _1, TD ₄ Things.

With this configuration, in addition to the effect of reducing the loss imbalance, there is also an effect that the capacity shortage of the freewheel diode can be eliminated.

In the embodiment shown in FIGS. 5 and 6, the number of parallel freewheeling diodes is one and two. However, the object can be achieved even if the number of paralleling is further increased. Can be.

FIG. 7 shows a flat semiconductor element (GT) in which a semiconductor pellet is sandwiched between disk-shaped copper posts on both sides and pressed.
An example in which the present invention is applied to an O thyristor) will be described. GTO
This is an example in which freewheel diodes D ₁₁ and D ₄₁ are connected in parallel to thyristors G ₁ and G ₄ in antiparallel. Of course, even if the capacitances of D ₁ and D ₄ are larger than D ₂ and D ₃ without adding the freewheel diodes D ₁₁ and D ₄₁ , the purpose of reducing the loss imbalance can be achieved.

FIG. 8 shows an example of an arrangement of switching elements and diodes to be pressed when forming a converter circuit using the flat semiconductor element shown in FIG.

When a flat semiconductor element such as a GTO thyristor is used, one phase of the converter must be arranged in a line because of the special nature of the pressure contact and the cooling method.
As shown in the figure, between the GTO thyristor G ₁ and the clamping diode D ₅ ,
_2, during the D _3, insert a respective insulator 11 between the clamping diode D ₆ and GTO thyristors G _4, free wheel diodes D _1, D ₄ of as newly shown outside diode D _11, D By arranging ₄₁ , one phase can be arranged in one line. Then, if pressure contact is made from both sides with a specified pressure, a circuit can be formed in the capacity.

FIG. 9 shows an example in which the present invention is applied to a flat semiconductor element (a reverse conducting GTO thyristor or the like) in which a switching element and an antiparallel diode are integrated on the same semiconductor pellet. Freewheel diodes D ₁₁ and D ₄₁ are connected in anti-parallel to the reverse conducting GTO thyristors GD ₁ and GD ₄ . Of course, without adding D ₁₁ and D ₄₁ , the capacity of GD ₁ and GD _4
2, purpose even as larger than GD ₃ can be achieved.

FIG. 10 shows an example of the arrangement of switching elements and diodes which are pressed together when forming the converter circuit using the flat semiconductor element shown in FIG. It can be seen that the circuit can be easily configured by arranging in this manner and press-contacting with the specified pressure from both sides.

When a flat semiconductor device is applied, the object can be achieved by changing the capacity of a cooling fin for cooling the device.

FIG. 11 shows the embodiment shown in FIG. 7 in which the freewheeling diodes D ₁₁ and D ₄₁ for increasing the capacity are not added.
This is a case where the capacities of the cooling fins of the outer freewheel diodes D ₁ and D ₄ and the inner freewheel diodes D ₂ and D ₃ are changed. Fins F ₁ on both sides in the free wheel diode D _1, the provided fins F _2, whereas the free wheel diode D ₄ fins F ₁₁ on both sides, and enhance cooling by providing a fin F _12, freewheeling Diode D
₂ has fin F ₆ on one side and freewheel diode D
It is single-sided cooling provided with fins F ₇ on one side to the _3.

Even when the fins are connected to both sides without cooling on one side, the cooling performance of the fins of the outer freewheel diodes D ₁ and D ₄ is controlled by the inner free wheel diodes D ₂ and D ₂ .
Similarly the object can be achieved by increasing the cooling performance of the fin of D _3.

FIG. 12 shows cooling fins F ₁₃ and F ₁₄ of the outer reverse conducting GTO thyristors GD ₁ and GD ₄ without adding the free wheel diodes D ₁₁ and D ₄₁ for increasing the capacity in the embodiment shown in FIG. , F ₂₀ , F ₂₁ , and cooling fins F ₁₆ , of the inner reverse conducting GTO thyristors GD ₂ , GD ₃
Constituted by three F _17, F ₁₈ is an example of achieving the object by possible to save the number of fins.

As described above, the cooling performance of the fins of the outer reverse conducting GTO thyristors GD ₁ , GD ₄ is improved by
The purpose can be similarly achieved by making the cooling capacity of the fins of the thyristors GD ₂ and GD ₃ larger than that of the fins.

According to the above-described embodiment, the loss imbalance can be reduced without increasing the capacity and the number of freewheel diodes.

By the way, in the embodiments described so far,
Everything was about converters. This is because this tendency is remarkable during electric vehicle power running (when the converter is performing AC / DC conversion).

However, even with a three-level converter (serial multiplex inverter) that converts a direct current into a three-level alternating current to energize the induction motor, the regenerative operation is performed. Not a little balance occurs. For this reason, the capacity of the outside freewheel diode of the three-level inverter may be increased as described above. That is, the present invention can be applied to a serial multiplex power converter.

In the main circuit configuration of the serial multiplex converter and the serial multiplex inverter, it is essential to increase the capacity or cooling of the outer freewheeling diode on the converter side, but the inverter is not necessarily required.

Further, although the above-described embodiment is directed to an electric vehicle control device, the present invention is not limited to this, and is applicable to any device using a serial multiplex converter or an inverter. For example, it goes without saying that a converter for controlling a rolling mill or an inverter main circuit can be used.

[0055]

According to the present invention, a diode having an appropriate capacity without waste is applied to both of the outer freewheel diode and the inner freewheel diode with respect to the loss imbalance of both diodes, and furthermore, an appropriate cooling is achieved. A series multiplex power converter capable of giving performance can be configured, and is economically excellent.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of the present invention.

FIG. 2 is a diagram illustrating the principle of the present invention.

FIG. 3 is a diagram illustrating the principle of the present invention.

FIG. 4 is a diagram illustrating the principle of the present invention.

FIG. 5 is a layout view of a modular switch element to which the present invention is applied.

FIG. 6 is a diagram showing another embodiment of the present invention.

FIG. 7 is a circuit diagram in which the present invention is applied to a pressure contact type semiconductor device.

FIG. 8 is a diagram showing an arrangement of press-contact type semiconductor elements.

FIG. 9 is a circuit diagram in which the present invention is applied to a reverse conducting pressure welding type semiconductor element.

FIG. 10 is a diagram showing an arrangement of a reverse conducting press-contact type semiconductor element.

FIG. 11 is a diagram showing another embodiment of the present invention.

FIG. 12 is a diagram showing another embodiment of the present invention.

[Explanation of symbols]

T ₁ through T ₈ ... _{transistors, D 12, D 13, D} 52, D 53 ... clamping _{diodes, D 1 ~D 4, D 5} ~D 8 ... freewheeling _{diode, D 11, D 14, D} 51, D ₅₄ … Freewheel diode for capacity increase.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hideharu Saito 1070 Ma, Katsuta-shi, Ibaraki Pref. Mito Plant, Hitachi, Ltd. (72) Inventor Hiroshi Itana 832 Horiguchi, Katsuta-shi, Ibaraki 2 Hitachi Systems Mito Engineering Co., Ltd.

Claims (1)

[Claims] Claims 1. An alternating current of an overhead contact line is received by a pantograph.
A step-down transformer and a series-multiplexed (three-level) power converter for converting the stepped-down AC into DC are provided with a two-level variable voltage on the DC side of the series-multiplexed power converter via a voltage dividing capacitor. A series multiplex power converter, wherein a two-level inverter for converting into a three-phase AC having a variable frequency is connected, and an electric vehicle driving motor is connected to the AC side of the inverter.