JPH06197540A - Power converter - Google Patents

Abstract

PURPOSE:To reduce the size, weight, and cost of a power converter and improve the responsiveness, protectivenss, and reliability of the converter by reducing the capacitance of a capacitor installed on the DC input side of a multilevel inverter circuit and, at the same time, the pulsation of the charging voltage of the capacitor. CONSTITUTION:In this converter provided with a multilevel inverter circuit 14, the pulsation of a positive and negative DC voltages against the centerpoint potential of a DC circuit on the DC input terminal side of the circuit 14 is reduced by providing at least one each of DC power source 15 and 16 connected for constituting the DC circuit between the center point and positive and negative input terminals of the DC circuit. In addition, the midpoint potential is earthed through an impedance element 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter for converting the power of an input AC power source into a DC power and converting it into AC power again by a multilevel inverter, and more particularly to downsizing the device and improving and protecting its operating performance. The present invention relates to a power conversion device with improved performance.

[0002]

2. Description of the Related Art As a conventional technique of a power conversion device according to the present invention, there is a multilevel inverter (for example, Japanese Patent Laid-Open No. 55-43996 bridge conversion circuit and its conversion method). There are various methods for this multi-level inverter circuit, but here
Annual Meeting of the Institute of Electrical Engineers of Japan, Paper No.91, Paper N
The problems of the prior art will be described with reference to a power converter using an inverter called a three-level inverter in O.92, Paper No. 94 and the like.

FIG. 6 shows a main circuit configuration of a power conversion device using a known three-level inverter. In this figure,
11 is a DC power supply, 12 and 13 are capacitors, 14 is a 3-level inverter circuit, and the 3-level inverter circuit 14 has DC input terminals P, O, N and AC output terminals U, V, W,
Each phase is a semiconductor switch S ₁ , S such as GTO or IGBT
It is composed of ₂ , S ₃ , and S ₄ .

Since the detailed operation of the three-level inverter circuit 14 is already known from the above-mentioned references and the like, description thereof will be omitted, but the DC voltage of the DC power supply 11 is divided by the capacitors 12 and 13 connected in series. Connected to the DC input terminals P, O, N of the 3-level inverter circuit 14
The DC power of 11 is converted into AC power by the three-level inverter circuit 14, and AC power of any frequency is output from the output terminals U, V, W. In this case the output terminals U, V, to obtain a 3-level voltage by the selection of the semiconductor switches _{S 1, S 2, S 3} , S 4 are the W, less harmonic components included in the AC power outputted, also DC The voltage is 1 / with capacitors 12 and 13
It is divided into two, and the semiconductor switches S ₁ , S ₂ ,
Since the charging voltage of the S _3, the S ₄ capacitor 12 or 13 is applied, the semiconductor switch _{S 1, S 2, S 3} , S 4 are than scheme using two semiconductor switches directly connected in series It has features such as improved voltage utilization.

In the power converter of FIG. 6, the characteristics as described above are known, but the charging voltage of the capacitors 12 and 13 is
There is a problem of pulsation due to an instantaneous change in the output current of the three-level inverter circuit 14. For details of this factor, refer to the 1992 National Conference of the Institute of Electrical Engineers of Japan, Industrial Application Division N
o.91 It is also explained in “Suppressing AC fluctuation of neutral point voltage of 3-level inverter”, etc., and charging voltage E _{d12 of} capacitors 12 and 13 is shown in FIG. 7 by PWM control of 3-level inverter circuit 14. It is stated that it pulsates as shown.

[0006] In FIG. 7, i _m is the output terminals U, V, W
The current waveform of the output current for one phase, E _d12 is the capacitor 12
Alternatively, the charging voltage of the capacitor 13, E _d, is a voltage corresponding to 1/2 of the DC voltage of the DC power supply 11, and the semiconductor switches S ₁ and S ₄ , S ₂ and S _{3 of} the three-level inverter circuit 14 operate symmetrically. If done, the charging voltage of the capacitors 12 and 13 is E _d
However, when PWM control is generally performed, the charging voltage is E
It becomes _d12 . According to the cited document, since the charging voltage E _d12 pulsates about 25% with respect to the charging voltage E _d , the semiconductor switches S ₁ , S ₂ , S ₃ , of the three-level inverter circuit 14 are
It is necessary to set S ₄ to a voltage rating corresponding to the above-mentioned charging voltage E _d12 , and the voltage utilization rate is greatly reduced.

[0007] In the above references, but PWM control method of a three-level inverter circuit 14 for reducing the pulsation of the charging voltage E _d12 is proposed, transient output terminals U, V, W in the output current i _m is If such a fluctuation is made, the charging voltage E _d12 similarly pulsates greatly. That is, in the power conversion apparatus employing the three-level inverter circuit 14, for the purpose of accelerating the current control response of the load is large and transient variation of the output current i _m is generated from the application surface of the power converter. Therefore, the pulsation of the charging voltage E _d12 is inevitably generated. In order to reduce the pulsation of the charging voltage E _d12 thus inevitably generated, a method of increasing the electrostatic capacitances of the capacitors 12 and 13 is used. Since the pulsating voltage E _d12 and the electrostatic capacitance are in inverse proportion to each other, increasing the electrostatic capacitance reduces the pulsating voltage E _d12.
13 shape and price will increase significantly.

[0008]

[SUMMARY OF THE INVENTION Incidentally, in these power converter, size and weight reduction and cost reduction of the apparatus, speed control response characteristic of the output current i _m, improvement of reliability and protection of the device It is an important technical issue. However, the power conversion device using the multi-level (3 level) inverter using the conventional technique has not been able to sufficiently solve these problems in the following points. (1) In order to reduce the pulsation of the charging voltage E _d12 of the capacitors 12 and 13, it is necessary to increase the capacitance of the capacitors 12 and 13, and as a result, (a) the power conversion device becomes large-sized. To raise the price.

(B) When the electrostatic capacitance of the capacitors 12 and 13 increases, an excessive fault current flows when a DC short circuit fault of the three-level inverter circuit 14 occurs, and the semiconductor switches S ₁ , S ₂ , S ₃ , S ₄ etc. could not be sufficiently protected.

(2) Charging voltage E _d12 of the capacitors 12 and 13
Due to the pulsation of the semiconductor switches S ₁ , S ₂ , S ₃ , S ₄
Therefore, it is necessary to increase the voltage rating of the main circuit supplies, which lowers the voltage utilization rate and raises the price of the power conversion device.

(3) Due to the high DC voltage of the DC power supply 11 and the pulsation of the charging voltage E _d12 as described above, it is necessary to insulate the inside of the power conversion device at a high voltage level, which increases the insulation distance. As a result, the power conversion device becomes larger.

The present invention has been made in order to eliminate the above-mentioned drawbacks of the prior art. The capacitance of the capacitor is reduced by absorbing a part of the pulsating voltage of the charging voltage E _d12 to the DC power source side. Even if the pulsating voltage is reduced, it is an object of the present invention to provide a power conversion device that can realize a smaller and lighter device, a lower price, improved high-speed response, improved reliability, and improved protection.

[0013]

In order to achieve the above object, the present invention is constructed as follows.

According to a first aspect of the present invention, in a power converter having a multi-level inverter circuit, a DC power source connected for configuring a DC circuit on a DC input terminal side of the multi-level inverter circuit is the DC circuit. Midpoint,
At least one DC power supply having a bidirectional power supply function is provided between the positive and negative input terminals to reduce the pulsation of the positive and negative DC voltage with respect to the midpoint potential.

According to a second aspect of the present invention, in a power converter having a multi-level inverter circuit, a DC power source connected to the DC input terminal side of the multi-level inverter circuit is divided into at least two DC power sources. Is connected to the center point of the DC input terminal, and the connected middle point is grounded via an impedance element.

According to a third aspect of the present invention, in a power converter having a multilevel inverter circuit, the charging voltage of a capacitor connected to the DC input terminal side of the multilevel inverter circuit is set to the midpoint potential of the DC input terminal. On the other hand, a differential voltage detection and protection circuit is provided which detects the differential voltage separately on the positive side and the negative side and performs a protective operation when the differential voltage becomes a predetermined value or more.

[0017]

The invention corresponding to claim 1 reduces the pulsation by absorbing a part of the electric power for generating the pulsation of the charging voltage of the capacitor provided in the DC circuit into the DC power source having the bidirectional power source function. Act as you do.

In the invention corresponding to claim 2, since the neutral point of the DC voltage input to the three-level inverter circuit is impedance grounded, the ground potential of the power converter is divided into two DC power sources. It will be decided by the DC voltage. For this reason, the ground potential of the power converter is lowered, the insulation distance is reduced, and the power converter is downsized.

According to a third aspect of the present invention, when the difference voltage exceeds a predetermined value, a control command is generated according to the difference voltage to limit the output current of the multi-level inverter circuit or the power. The function of stopping the operation of the converter is applied to protect the power converter.

[0020]

FIG. 1 shows an embodiment corresponding to claim 1 and claim 2 of the present invention. The circuit elements having the same functions as those in FIG. 6 are designated by the same reference numerals.

In FIG. 1, 15 and 16 are divided DC power supplies, 17 is an impedance unit, and 18 is a ground electrode. In this figure, DC power supplies 15 and 16 are connected to capacitors 12 and 13, respectively, and three terminals P, O and N of the DC power supplies 15 and 16 connected in series are connected to a DC input terminal of a three-level inverter circuit 14, The DC power of the DC power supplies 15 and 16 is converted into AC power by the three-level inverter circuit 14, and the output terminals U,
Power is supplied to the load from V and W.

The output terminal U, V, the output current i _m to be supplied to the load or to vary transiently by W, the capacitor 12 is PWM control method of a three-level inverter circuit 14 is a factor
Even if the pulsation of the charging voltage E _d12 of 13 or 13 is about to occur, the charging voltage E _d12 of the capacitor 12 or the capacitor 13 is _{pulsated by} setting the DC power supplies 15 and 16 as bidirectional power sources capable of supplying and absorbing electric power. DC power supply 15
Alternatively, the pulsation of the charging voltage can be reduced by compensating with the DC power supply 16.

FIG. 2 shows an example of the DC power supply 14 or 15 having the bidirectional power supply function described above. In FIG. 2, 19 is an input AC power supply, 20 is a bidirectional rectification circuit, and TH ₁ and TH ₂ are thyristors. The bidirectional rectifier circuit 20 shown in FIG. 2 is composed of an antiparallel three-phase full-wave rectifier circuit composed of thyristors TH ₁ and TH ₂ , and therefore has a reversible power conversion function and the input AC power supply 19 has a The AC power can be converted to DC power and output, and the DC power can be regenerated to the input AC power supply 19.

Therefore, by providing a DC power supply having a bidirectional power supply function as shown in FIG. 2 to the DC power supplies 15 and 16 of FIG. 1, respectively, the charging voltage E of the capacitor 12 or 13 is charged.
_When the pulsation of _d12 occurs, the pulsation of the charging voltage E _d12 is suppressed by the voltage control function of the DC power supplies 15 and 16,
The capacitance of the capacitors 12 and 13 can be made relatively small. In addition, DC power supplies 15 and 16, capacitors 12 and 13
1 are connected in series as shown in FIG. 1, and the terminal O at this middle point is connected to the ground electrode via the impedance element 17.
Connect to 18. By grounding the terminal O with impedance as shown in FIG. 1, the ground potential of the terminal P or the terminal N becomes half as compared with the case without impedance grounding. Therefore, the ground potential of the entire power conversion device is lowered, the insulation distance is reduced, and the power conversion device can be downsized. Further, when the ground potential of the power conversion device becomes low, the protection performance is significantly improved in terms of personal safety in driving operations and periodic inspections.

FIG. 3 shows a circuit configuration example of a bidirectional power supply applicable as another embodiment of the present invention. In FIG. 3, 21
Is a PWM control converter, D ₁ is a diode, and T ₁ is a self-turn-off device. Since the PWM control converter 21 can easily switch the power control direction at high speed as is well known,
When the DC power supplies 15 and 16 of FIG. 1 have the configuration of FIG. 3, it is more effective than the configuration of FIG.

FIG. 4 shows an example of the circuit configuration of the bidirectional power source, as described above. In FIG. 4, 19 is an input AC power supply, 22 is an input transformer, 23 is a circulating current source converter, and TH ₁ and TH ₂
Is a thyristor, and X ₁ and X ₂ are DC reactors. The circulating current source converter 23 is also provided with a three-phase full-wave rectifier circuit composed of thyristors TH ₁ and TH ₂ on the secondary side two windings of the transformer 22, respectively, and the circulating current is supplied via the DC reactors X ₁ and X _2. Because of the flow system, the current control can be performed at high speed similarly to the PWM control converter 21 of FIG. 3, and the same effect as the configuration of FIG. 3 can be obtained.

FIG. 5 is a circuit diagram showing an embodiment corresponding to claim 3 of the present invention. In this figure, circuit elements having the same functions as those in FIG. 1 are designated by the same reference numerals, and 24 is a differential voltage detection protection circuit. The differential voltage detection protection circuit 24 is a capacitor
It has a function of detecting a difference voltage between the charging voltages E _d12 of 12 and 13 and performing a protection operation on the power conversion device when the value of the difference voltage exceeds a predetermined value. As the protection operation, the output terminal U, V, may be a function of limiting the output current i _m of from W, may be a function of stopping the operation of the power converter, it is not particularly limited.

The power converter can protect the excessive pulsation of the charging voltage E _d12 of the capacitors 12 and 13 by the action of the differential voltage detection protection circuit 24. Further, the semiconductor switches S ₁ and S ₂ or S ₃ and S of the three-level inverter circuit 14
_{Even if} the DC short circuit ₄ occurs, the differential voltage between the capacitors 12 and 13 becomes too large, so that detection and protection can be performed at high speed. As a result, the configuration of FIG. 5 can significantly improve the protection of the power conversion device.

Although the 3-level inverter circuit 14 is cited as the multi-level inverter, even in the multi-level inverter in which the DC voltage is divided into four by the capacitor, the midpoint of the DC power supply may be grounded by an impedance element, or 2 The configuration may be one DC power source or a DC power source for each individual capacitor, and the present invention does not limit the configuration. In addition, various design changes can be made without departing from the scope of the present invention.

[0030]

As described above, according to the present invention, it is possible to provide a power conversion device that achieves the following effects. (1) The pulsation of the charging voltage can be reduced without increasing the capacitance of the capacitor. As a result, the following effects are obtained. (A) It is possible to prevent the power conversion device from becoming large and expensive. (B) An excessive fault current does not flow even if a DC short circuit fault occurs in the three-level inverter circuit. Therefore, accident protection of the semiconductor switch is facilitated.

(2) Since the pulsation of the charging voltage of the capacitor can be reduced, it is not necessary to raise the voltage rating of the main circuit article such as the semiconductor switch more than necessary, so that the voltage utilization rate is improved and the power conversion device Higher prices can be prevented.

(3) Since the ground voltage of the power converter is lower than that of the prior art, the midpoint of the DC voltage is grounded through the impedance element, so that the insulation distance inside the power converter can be reduced. Therefore, the power converter can be downsized, and the maintainability can be improved. (4) By providing the differential voltage detection protection circuit, it is possible to significantly improve the protection of the power conversion device such as highly reliable DC short circuit protection. (5) Even if the control response of the power converter is fast, the pulsation of the charging voltage can be reduced, so that a high-performance power converter can be provided.

[Brief description of drawings]

FIG. 1 is a power conversion device according to the present invention.
The block diagram of the Example corresponding to.

FIG. 2 is a main circuit configuration diagram showing an example in which a reversible converter using a thyristor is applied as a bidirectional power source used for the DC power sources 15 and 16 of the above embodiment.

FIG. 3 is a main circuit configuration diagram showing an example of a case where a PWM control converter is applied as a bidirectional power source used for the DC power sources 15 and 16 of the above embodiment.

FIG. 4 is a main circuit configuration diagram showing an example of a case where a reversible converter using a thyristor is applied as a bidirectional power source used for the DC power sources 15 and 16 of the above embodiment.

FIG. 5 is a configuration diagram of an embodiment corresponding to claim 3 of the power converter of the present invention.

FIG. 6 is a main circuit configuration diagram showing a power conversion device using a conventional three-level inverter.

FIG. 7 is a waveform diagram showing a pulsating example of a capacitor charging voltage of a conventional power conversion device.

[Explanation of symbols]

11 ... DC power supply, 12, 13 ... Capacitor,
14 ... 3-level inverter circuit, 15, 16 ... DC power supply composed of bidirectional power supply, 17 ... Impedance element, 18
… Grounding electrode, 19… Input AC power supply, 20…
Bidirectional rectifier circuit, 21 ... PWM control converter, 22
… Input transformer, 23… Circulating current type converter, 24
... differential voltage detection protection _{circuit, S 1, S 2, S} 3, S 4 ... semiconductor switches, P, O, N ... DC input terminals, U,
V, W ... AC output terminal, i _m ... output current,
E _d ... DC voltage, E _d12 ... Charging voltage,
TH ₁ , TH ₂ ... Thyristor, D ₁ ... Diode,
T ₁ ... Self-extinguishing element, X ₁ , X ₂ ... DC reactor.

Claims (3)

[Claims] 1. A power converter having a multi-level inverter circuit, wherein a DC power supply connected for the configuration of a DC circuit on the DC input terminal side of the multi-level inverter circuit is provided.
At least one DC power supply having a bidirectional power supply function is provided between the midpoint of the DC circuit and its positive and negative input terminals to reduce the pulsation of the positive and negative DC voltage with respect to the midpoint potential. Converter. 2. A power converter having a multi-level inverter circuit, wherein a DC power source connected to a DC input terminal side of the multi-level inverter circuit is divided into at least two, and a midpoint of the DC power source and the DC input. A power conversion device characterized in that a terminal midpoint is connected and the connected midpoint is grounded via an impedance element. 3. A power converter having a multi-level inverter circuit, wherein the charging voltage of a capacitor connected to the DC input terminal side of the multi-level inverter circuit is set to the positive side with respect to the midpoint potential of the DC input terminal. A power conversion device comprising: a differential voltage detection and protection circuit that detects a differential voltage separately on the negative side and performs a protection operation when the differential voltage exceeds a predetermined value.