JP3247263B2 - Neutral point clamp type power converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a neutral point clamp type power converter in which a loss of a snubber circuit provided in a switching element constituting the neutral point clamp type power converter is reduced.

[0002]

2. Description of the Related Art In recent years, the switching frequency of a power converter such as an inverter or a converter using a high-speed switching element such as an IGBT has increased, and the snubber loss has continued to increase.

FIG. 5 shows a basic configuration of a main circuit of a neutral point clamp type power converter which generates a three-level output voltage which has been conventionally used. In FIG. 5, Vd1, Vd
d2 is a DC power supply connected between the DC positive bus P and the DC negative bus N and having a neutral point output terminal 0, and C1 and C2 are DC power supplies V
The smoothing capacitors SU1 to SU4 connected in parallel to d1 and Vd2, respectively, are connected in series between the DC positive bus P and the DC negative bus N, and are the first to fourth U-phase switching elements, similarly SV1 to SV4 and SW1 to SW1. SW4 is a V-phase and W-phase switching element.

[0004] DU1 to DU4 connected in antiparallel to U-phase switching elements SU1 to SU4, and DV1 to DV4 and W-phase switching element SW connected in antiparallel to V-phase switching elements SV1 to SV4, respectively.
DW1 to DW1 connected in anti-parallel to SW1 to SW4, respectively.
W4 is a freewheeling diode.

[0005] U-phase second and third switching element SU
2, DU5 and D3 connected in parallel to the series circuit of SU3 with opposite polarities and having a series connection point connected to the neutral point output terminal 0.
U6 is a U-phase clamp diode.

U-phase second and third switching elements SU
A series connection point of the SU2 and the SU3 is a U-phase AC terminal. Similarly, DV5 and DV6 are V-phase clamp diodes, and DW
5 and DW6 are W-phase clamp diodes.

[0007] The V-phase second and third switching elements S
The series connection point of V2 and SV3 becomes the V-phase AC terminal,
A series connection point of the second and third switching elements SW2 and SW3 of the phase becomes a W-phase AC terminal.

LOAD connected to the AC terminal is a three-phase load. The U-phase output voltage Vu of the neutral point clamp power converter configured as described above is controlled to the following three level values. That is, Vu = + Vd1 when the switching elements SU1 and SU2 are on, Vu = 0 when the switching elements SU2 and SU3 are on, and Vu = −Vd2 when the switching elements SU3 and SU4 are on. The V-phase output voltage Vv and the W-phase output voltage Vw are similarly controlled.

FIG. 4 is a detailed circuit configuration diagram in which a snubber circuit is provided in the neutral point clamp type power converter. (Only the U phase is shown in FIG. 5, but the V phase and the W phase have the same configuration, so the V phase and the W phase are omitted.) The first switching element SU1 is connected in parallel. First
Snubber capacitor SCU1 and snubber diode SDU
1 and a snubber circuit including a first snubber resistor SRU1 connected between the series connection point of the series circuit and the neutral point output terminal 0.

The second switching element SU2 includes a series circuit of a second snubber diode SDU2 and a snubber capacitor SCU2 connected in parallel, and a second snubber resistor SRU2 connected in parallel to the second snubber diode SDU2. A snubber circuit is provided.

A snubber composed of a series circuit of a third snubber capacitor SCU3 and a snubber diode SDU3 connected in parallel to the third switching element SU3 and a third snubber resistor SRU3 connected in parallel to the third snubber diode. A circuit is provided.

The fourth switching element SU4 includes a series circuit of a fourth snubber diode SDU4 and a snubber capacitor SCU4 connected in parallel, and a fourth snubber resistor SRU4 connected in parallel to the fourth snubber diode SDU4. A snubber circuit is provided.

Next, the operation of the snubber circuit of the neutral point clamp type power converter having the above-described configuration will be described. Now, when the switching elements SU1 and SU2 are turned on, the load current is flowing through the path of the DC power supply Vd1, the DC positive bus P, the switching elements SU1, SU2, and a load (not shown).

In this state, when the switching element SU1 is turned off, the energy of the wiring inductance (not shown) (between the DC power supply Vd1 and the switching element SU1) becomes
Snubber capacitor SCU1, snubber diode SDU
1. Flow through the switching element SU2 to charge the snubber capacitor SCU1.

When the snubber capacitor SCU1 absorbs the energy of the wiring inductance, the load current flows through the neutral point output terminal 0, the clamp diode DU5, the switching element SU2, and the load.

Since the snubber capacitor SCU1 was originally charged by the DC power supply Vd1, when the energy of the wiring inductance is charged, the snubber capacitor SCU1 is charged to the voltage of Vd1 or more. The charged energy is discharged through the snubber resistor SRU1 and stopped when the voltage of the snubber capacitor SCU1 becomes Vd1. That is, the snubber capacitor SC
The voltage of U1 repeats charging and discharging only for the energy of the wiring inductance. The above is the so-called DC
It has a clamp type snubber circuit configuration.

On the other hand, the snubber circuit operation of the switching element SU2 has a complete discharge type snubber circuit configuration. When the switching element SU2 is turned off, the energy of the wiring inductance (between the neutral point output terminal 0 and the switching element SU2) is charged. When the absorption of the energy of the wiring inductance is completed, the load current flows back through the freewheeling diodes DU4 and DU3.

Since the energy of the wiring inductance is absorbed, the voltage of the snubber capacitor SCU2 becomes equal to the power supply voltage Vd.
Rise to 2 or more. All the energy is consumed through the snubber resistor SRU2 when the next switching element SU2 is turned on.

As described above, the snubber circuit of the complete discharge type results in greatly increased snubber loss as compared with the DC clamp type snubber circuit. Similarly, the snubber circuit of the switching element SU4 operates as a DC clamp type snubber circuit. However, the snubber circuit of the switching element SU3 operates as a complete discharge type snubber circuit similarly to the snubber circuit of the SU2. The loss increases.

[0020]

In the conventional neutral point clamp type power converter described above, the loss of the snubber circuit of the second switching element and the third switching element becomes very large. Since the increase in the snubber loss cannot be ignored with the increase of the switching frequency in the future, it is very important to reduce the loss of the snubber circuit.

Accordingly, an object of the present invention is to provide a neutral-point-clamped power converter that reduces the loss of a snubber circuit of a second switching element and a third switching element that constitute a neutral-point-clamped power converter. It is to provide a converter.

[0022]

In order to achieve the above object, the present invention provides a DC power supply connected between a DC positive and negative bus and having a neutral point output terminal, and a DC power supply connected in series between the DC positive and negative buses. The series circuit of the first to fourth switching elements, the first to fourth freewheeling diodes respectively connected in anti-parallel to the switching elements, and the second and third switching elements have opposite polarities. Neutral point connected in parallel and having a series connection point formed of a series circuit of a pair of clamp diodes connected to the neutral point output terminal, wherein the series connection point of the second and third switching elements is an AC terminal. In a clamp converter, a first snubber capacitor and a snubber diode connected in parallel to the first switching element are provided.
And a snubber circuit including a first snubber resistor connected between a series connection point of the series circuit and the neutral point output terminal, and a series connection point of the first and second switching elements. An anode is connected, and a cathode is connected to the neutral point output terminal via a second snubber capacitor.
A snubber diode consisting of a second snubber diode, a snubber circuit comprising a second snubber resistor connected between a series connection point of the second snubber diode and the snubber capacitor and the DC positive bus, and a third snubber diode. A third snubber diode having a cathode connected to the series connection point and an anode connected to the neutral point output terminal via a third snubber capacitor; and a third snubber diode and a snubber capacitor. A snubber circuit consisting of a third snubber resistor connected between the series connection point of the DC negative bus and a series circuit of a fourth snubber diode and a snubber capacitor connected in parallel to the fourth switching element; A snubber circuit including a fourth snubber resistor connected between a series connection point of the series circuit and the neutral point output terminal; a neutral point output terminal and the second and third switches; It is characterized in that provided with the snubber circuit of the fifth snubber resistor and snubber capacitor connected in series between the connection point device.

[0023]

According to the present invention having the above-described structure, the second snubber capacitor SCU2 that has absorbed the energy of the wiring inductance transfers the absorbed energy to the second snubber capacitor SCU2, the second snubber resistor SRU2, and the DC current. Discharge occurs in the path of the power supply Vd1 and the second snubber capacitor SCU2, and stops when the voltage of the second snubber capacitor SCU2 becomes equal to the voltage of the DC power supply Vd1. As described above, the second snubber capacitor SCU2 does not consume all of its charging energy by the second snubber resistor, so that the snubber loss is reduced.

Similarly, the third snubber capacitor SCU3, which has absorbed the energy of the wiring inductance, transfers the absorbed energy to the third snubber capacitor SCU3, the DC power supply Vd2, the third snubber resistor SRU3, and the third snubber capacitor SCU3. Discharge occurs in the path, and when the voltage of the third snubber capacitor SCU3 becomes equal to the voltage of the DC power supply Vd2, the discharge stops. Therefore, the third snubber capacitor S
The CU 3 also does not consume all of its charging energy with the third snubber resistor, so that the snubber loss is reduced.

As described above, the snubber circuit provided in the second and third switching elements of the present invention operates in the same manner as the DC clamp type snubber circuit, so that the snubber loss can be greatly reduced.

Also, snubber capacitors SCU2, SCU3
The very short surge voltage that cannot be removed by the above can be absorbed by the snubber circuit comprising the fifth snubber resistor and capacitor series circuit. The fifth snubber capacitor is 1/5 to 1/1 of the snubber capacitors SCU2 and SCU3.
It is about 0, which is a discharge type, but the loss is very small.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the embodiment of FIG. 1 in which the same parts as those of FIG. Where U
Since the phases, V-phase and W-phase have the same configuration, only the U-phase will be described below.

The present invention relates to DC power supplies Vd1 and Vd2 connected between DC positive and negative buses P and N and having a neutral point output terminal 0.
First to fourth switching elements SU1 to SU4 connected in series between the DC positive and negative buses P and N, and first to fourth freewheels connected in antiparallel to the switching elements SU1 to SU4, respectively. -Ring diode DU1
DU4 and the second and third switching elements SU2, S
The second switching element SU2 comprises a series circuit of a pair of clamp diodes DU5 and DU6 which are connected in parallel with the series circuit of U3 in reverse polarity and whose series connection point is connected to the neutral point output terminal. , SU3 having a series connection point as an AC terminal, a neutral point clamp type converter having a first switching element SU1 and a fourth switching element S
The snubber circuit provided in U4 is the same as the conventional snubber circuit shown in FIG. 4, and therefore the description thereof is omitted here, and the snubber circuits provided in the second and third switching elements will be described.

The snubber circuit provided in the second switching element includes first and second switching elements SU1 and SU2.
A second snubber diode SDU2 having an anode connected to the series connection point of the second and a cathode connected to a neutral point output terminal via a second snubber capacitor SCU2; and a second snubber diode SDU2. And a second connection point connected between the DC positive bus P and the series connection point of the
The snubber resistor SRU2 of FIG.

Further, the snubber circuit provided in the third switching element SU3 includes a third fourth switching element SU3.
A third snubber diode SDU3 in which a cathode is connected to the series connection point of the third and SU4 and an anode is connected to the neutral point output terminal 0 via the third snubber capacitor SCU3.
, And a third snubber resistor SRU3 connected between the series connection point of the third snubber diode SDU3 and the snubber capacitor SCU3 and the DC negative bus N.

A snubber circuit in which a fifth snubber resistor SRU5 and a snubber capacitor SCU5 are connected in series is connected between the neutral point output terminal O and the connection point between the second and third switching elements.

In the neutral point clamp type power converter of the present invention configured as described above, as shown in FIG. 2, the switching element SU1 is turned off, and the load current is reduced to the wiring inductances l2, l1, the clamp diode DU5. When the switching element SU2 is turned off while the switching element SU2 is flowing in the path of the load, the wiring inductance l
The current flowing in 1 is a clamp diode DU5, a snubber diode SDU2, and a snubber capacitor SCU2.
The energy flows through the path of the wiring inductance l1, and the energy of the wiring inductance l1 is stored in the snubber capacitor SCU2.

On the other hand, the current flowing through the wiring inductance l2 is reduced by the snubber capacitors SCU3 and snubber diode SCU3.
SDU3, freewheeling diode DU3, flows on the path of the load, and the energy of the wiring inductance l2 is stored in the snubber capacitor SCU3.

After all the energy of the wiring inductance l2 is stored in the snubber capacitor SCU3, the load current flows back through the freewheeling diodes DU4 and DU3.

As described above, since the energy of the wiring inductance is absorbed by the snubber capacitors SCU2 and SCU3, no overvoltage is applied to the switching element SU2. The snubber capacitor SCU2 which has absorbed the energy of the wiring inductance l1 is connected to the snubber resistor SRU2, the DC power supply Vd
1. Discharge is performed on the path of the snubber capacitor SCU2, and ends when the voltage becomes equal to the voltage of the DC power supply Vd1.

That is, only the energy of the wiring inductance l1 is discharged. Therefore, unlike the conventional snubber circuit, the snubber loss is extremely reduced because not all of the electric charge of the snubber capacitor is consumed by the snubber resistor.

Similarly, the energy of snubber capacitor SCU3 that has absorbed the energy of wiring inductance l2 is discharged to DC power supply Vd2 via snubber resistor SRU3, and the discharge ends when the voltage of snubber capacitor SCU3 becomes equal to Vd2. . This snubber capacitor SCU3
Is also discharged by the energy of the wiring inductance l2. Therefore, unlike the conventional snubber circuit, the snubber loss is extremely reduced because not all of the electric charge of the snubber capacitor is consumed by the snubber resistor.

Next, the operation of the fifth snubber resistor and the snubber capacitor will be described with reference to FIG. The snubber capacitor SCU2 is charged with the voltage of Vd1, and the snubber capacitor SCU3 is charged with the voltage of Vd2.

When the snubber diodes SDU2 and SDU3 are simultaneously turned on when absorbing the energy of the wiring inductances l1 and l2, Vd1 is applied to the switching element SU2.
A voltage of + Vd2 is applied. Since the wiring inductance l1 is originally a very small value, the time when the snubber diode SD2 is off is very short, but the voltage of Vd1 + Vd2 is still applied.

Therefore, during the time when the snubber diode SDU2 is turned off by absorbing the energy of the wiring inductance l1 (for example, 200 to 300 .mu.s), the energy of the wiring inductance l2 flows to the load through the fifth snubber resistor and the snubber capacitor and the snubber capacitor SCU5. The voltage is discharged to zero whenever the switching elements SU2 and SU3 are turned off (this is well-known from the operation of the neutral point clamp type inverter, and is omitted here).
That is, the snubber capacitor SCU5 and the snubber resistor SRU
5 is the voltage V of the snubber capacitor SCU3.
While less than d2, the snubber capacitor SCU2 absorbs the energy of the wiring inductance l1 and the snubber diode
It is only necessary to turn off the SDU2. Thereafter, the energy of the relatively large wiring inductance l2 may be absorbed by the snubber capacitor SCU3.

Next, referring to FIG. 3, the load current is
Switching element SU3, clamp diode DU6
The operation when the switching element SU3 is turned off in a state where the current flows through the path of the wiring inductance l3 and the wiring inductance l2 will be described.

In the state described above, the switching element S
When U3 is turned off, the current flowing through the wiring inductance l3 becomes the snubber capacitor SCU3 and the snubber diode.
SDU3, clamp diode DU6, and wiring inductance l3 flow, and the energy of wiring inductance l3 is stored in snubber capacitor SCU3.

On the other hand, the current flowing through the wiring inductance l2 is changed by a load, a freewheeling diode DU.
2, snubber diode SDU2, snubber capacitor SC
U2, flows on the path of the wiring inductance l2, and transfers the energy of the wiring inductance l2 to the snubber capacitor SCU2.
To store.

After all the energy of the wiring inductance l2 has been stored in the snubber capacitor SCU2, the load current flows back through the freewheeling diodes DU2 and DU1.

As described above, the wiring inductances l 2, l
3 is absorbed by snubber capacitors SCU2 and SCU3, so that no overvoltage is applied to switching element SU3.

The snubber capacitor SCU2 that has absorbed the energy of the wiring inductance l2 becomes a snubber resistor SRU.
2. Discharge occurs in the path of DC power supply Vd1 and snubber capacitor SCU2, and ends when the voltage becomes equal to the voltage of DC power supply Vd1.

That is, only the energy of the wiring inductance 11 is discharged. Therefore, unlike the conventional snubber circuit, the snubber loss is extremely reduced because not all of the electric charge of the snubber capacitor is consumed by the snubber resistor.

Similarly, the energy of snubber capacitor SCU3 that has absorbed the energy of wiring inductance l3 is discharged to DC power supply Vd2 via snubber resistor SRU3, and the discharge ends when the voltage of snubber capacitor SCU3 becomes equal to Vd2. . This snubber capacitor SCU3
Is also discharged by the energy of the wiring inductance l3. Therefore, unlike the conventional snubber circuit, the snubber loss is extremely reduced because not all of the electric charge of the snubber capacitor is consumed by the snubber resistor. Also in this case, the snubber resistor SRU5 and the snubber capacitor SCU5
Is exactly the same as the operation shown in FIG. 2, and a detailed description thereof will be omitted.

The neutral point clamp type power converter of the present invention can be used as either an inverter for converting DC to AC or a converter for converting AC to DC.

[0050]

As described above, according to the present invention, the neutral point clamp type electric power which can greatly reduce the snubber loss by simply changing the connection without adding any new parts to the conventional one. A converter can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a neutral point clamp type power converter showing one embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation of the present invention.

FIG. 3 is a diagram for explaining the operation of the present invention.

FIG. 4 is a configuration diagram of a conventional neutral point clamp type power converter.

FIG. 5 is a basic configuration diagram of a neutral point clamp type power converter.

[Explanation of symbols]

Vd1, Vd2 DC power supply C1, C2 Smoothing capacitor SU1, SV1, SW1 First switching element SU2, SV2, SW2 Second switching element SU3, SV3, SW3 Third switching element SU4, SV4, SW4 ... Fourth switching element DU1, DV1, DW1... First freewheeling diode DU2, DV2, DW2... Second freewheeling diode DU3, DV3, DW3. -Wheeling diodes DU4, DV4, DW4 ... fourth freewheeling diodes SCU1, SCV1, SCW1 ... first snubber capacitors SCU2, SCV2, SCW2 ... second snubber capacitors SCU3, SCV3. SCW3: Third snubber capacitor SCU4, SCV4, SCW4 Fourth snubber capacitor SCU5, SCV5, SCW5 ... fifth snubber capacitor SDU1, SDV1, SDW1 ... first snubber diode -
Do SDU2, SDV2, SDW2 ... second snubber
Do SDU3, SDV3, SDW3 ... third snubber
Do SDU4, SDV4, SDW4 ... 4th snubber
De SRU1, SRV1, SRW1 ... first snubber resistor SRU2, SRV2, SRW2 ... second snubber resistor SRU3, SRV3, SRW3 ... third snubber resistor SRU4, SRV4, SRW4 ... fourth snubber resistor SRU5, SRV5, SRW5 ... Fifth snubber resistor DU5, DV5, DW5 ... Clamp diode DU6, DV6, DW6 ... Clamp diode

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-276760 (JP, A) JP-A-6-62582 (JP, A) JP-A-6-165524 (JP, A) JP-A-6-165524 253545 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H02M 7/48 H02H 7/12

Claims (1)

(57) [Claims] 1. A DC power supply having a neutral point output terminal connected between a DC positive and negative bus, a first to a fourth switching element connected in series between the DC positive and negative buses, and a switching element opposite to the DC power supply. First to fourth connected in parallel
And a pair of clamp diodes connected in parallel to the series circuit of the second and third switching elements with opposite polarities and having a series connection point connected to the neutral point output terminal. A neutral point clamp converter having a series connection point of the second and third switching elements as an AC terminal, wherein a first snubber capacitor and a snubber diode connected in parallel to the first switching element are provided. And a snubber circuit comprising a first snubber resistor connected between a series connection point of the series circuit and the series connection point of the series circuit and the neutral point output terminal; and a series connection point of the first and second switching elements. Ano
A second snubber diode, a cathode connected to the neutral point output terminal via a second snubber capacitor, and a series connection point of the second snubber diode and the snubber capacitor. A snubber circuit including a second snubber resistor connected between the DC positive buses, and a cathode connected to a series connection point of the third and fourth switching elements.
A third snubber diode having an anode connected to the neutral point output terminal via a third snubber capacitor; and a series connection point of the third snubber diode and the snubber capacitor. A snubber circuit comprising a third snubber resistor connected between the DC negative buses, a series circuit of a fourth snubber diode and a snubber capacitor connected in parallel to the fourth switching element, and a series connection of the series circuit A snubber circuit including a fourth snubber resistor connected between a point and the neutral point output terminal; and a fifth snubber circuit between the neutral point output terminal and the connection point between the second and third switching elements. Neutral point clamp type power converter provided with a snubber circuit in which a snubber resistor and a snubber capacitor are connected in series.