JP2002345260A - Power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain size, weight and cost reductions, and response, protection and reliability improvements in a device by reducing the electrostatic capacity of capacitors 12, 13 provided on the DC input side of a multi-level inverter circuit 14 and relieving the pulsation of the charging voltage. SOLUTION: In a power converter having the multi-level inverter circuit 14, as a DC power supply connected to constitute a DC circuit on the DC input terminal side of the multi-level inverter circuit 14, at least DC power supplies 15, 16 having a two-way power supply function respectively are provided each between the midpoint of the DC circuit and positive and negative input terminals, thus relieving the pulsation of positive and negative DC voltages relative to midpoint potential. The midpoint potential is grounded 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 supply into DC power and converting it into AC power again using a multi-level inverter. The present invention relates to a power conversion device with improved performance.

[0002]

2. Description of the Related Art As a prior art of a power converter according to the present invention, a multi-level inverter (for example, Japanese Patent Laid-Open No.
996 bridge conversion circuit and its conversion method). There are various types of this multi-level inverter circuit.
91, Article No. 92, paper no. 94 and 3
The problems of the prior art will be described with reference to a power converter using an inverter called a level inverter. FIG. 5 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 three-level inverter circuit, and the three-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 such as GTO or IGBT
₁ , S ₂ , S ₃ , and S ₄ . The detailed operation of the three-level inverter circuit 14 is already known in the above cited documents and the like, and therefore the description is omitted. However, the DC voltage of the DC power supply 11 is divided by the series-connected capacitors 12 and 13 to obtain a three-level voltage. Inverter circuit 1
4 is connected to the DC input terminals P, O, and N, and the DC power of the DC power supply 11 is converted into AC power by the three-level inverter circuit 14, and AC power of an arbitrary frequency is output from the output terminals U, V, and W. . At this time, since three-level voltages are obtained at the output terminals U, V, and W by selecting the semiconductor switches S ₁ , S ₂ , S ₃ , and S ₄ , the output AC power contains less harmonic components, The voltage is between capacitors 12 and 1
3 and is divided into 1/2 by the semiconductor switches S ₁ ,
Since the charging voltage of the capacitor 12 or 13 is applied to S ₂ , S ₃ , and S ₄ , the semiconductor switches S ₁ , S 4
₂ , S ₃ and S ₄ are characterized in that the voltage utilization is improved as compared with a system in which two semiconductor switches are directly connected in series.

In the power converter shown in FIG. 5, the above-mentioned characteristics are known, but there is a problem that the charging voltage of the capacitors 12 and 13 pulsates due to an instantaneous change in the output current of the three-level inverter circuit 14. I do. The details of this factor are described in the above-mentioned 1992 National Institute of Electrical and Industrial Engineers Industrial Application Section National Convention No. 91 "Method of suppressing AC fluctuation of neutral point voltage of three-level inverter", etc., and charging voltage _{Ed12 of} capacitors 12, 13 is controlled by PWM control of three-level inverter circuit 14, as shown in FIG. Pulsation is stated. In FIG. 6, _{i m} is the output terminal U, V, 1 phase of the output current of the current waveform of the W, E
_d12 is the charging voltage of the capacitor 12 or the capacitor 13, _{E d} is a voltage corresponding to 1/2 of the DC voltage of the DC power supply 11, the semiconductor switch _{S 1} of the three-level inverter circuit 14 and _S 4, _{S 2} and _{S 3} Although but a charge voltage E _d of the capacitor 12 and 13 is performed symmetrical operation, the charging voltage generally performs PWM control E
_d12 . According to the cited document, the charging voltage E
_d12 in order to pulsating about 25% with respect to the charging voltage _{E d,} the semiconductor switch _S 1 of the three-level inverter circuit _{14, S 2, S 3,} S 4 are the charging voltage E
_It is necessary to set a voltage rating corresponding to _d12 , and the voltage utilization rate is greatly reduced.

In the cited document, the charging voltage E_d12of
P of the three-level inverter circuit 14 for reducing pulsation
Although a WM control method has been proposed, output terminals U, V, W
And the output current i_mIs the same when
Charge voltage E_d12Will pulsate greatly.
That is, a power conversion device employing a three-level inverter circuit 14
Is intended to speed up the current control response of the load.
Many, the output current i _mThe transient fluctuation of
It arises from the application side of the installation. Therefore, the charging voltage E _d12
Pulsation also occurs inevitably. Inevitably occur like this
Charging voltage E_{d 12}In order to reduce the pulsation of
A method has been taken to increase the capacitance of the capacitors 12 and 13
I have. The pulsating voltage E_d12Is inversely proportional to capacitance
When the capacitance is increased, the pulsation voltage E
_d12Is smaller, but the outer shape of capacitors 12 and 13
And prices will increase significantly.

[0005]

[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, a power conversion device using a multi-level (three-level) inverter using the conventional technology cannot sufficiently solve these problems in the following points. (1) In order to reduce the pulsation of the charging voltage _Ed12 of the capacitors 12 and 13, it is necessary to increase the capacitance of the capacitors 12 and 13. As a result, (a) the power converter becomes large , Higher prices. (B) When the capacitance of the capacitors 12 and 13 increases,
When a DC short-circuit fault or the like of the three-level inverter circuit 14 occurs, an excessive fault current flows, and the semiconductor switches S ₁ , S ₂ , S ₃ , S _{4 and the} like cannot be sufficiently protected. (2) for the pulsation of the charging voltage _{E d12} of the capacitor 12 and 13, the semiconductor switches _{S 1, S 2, S 3} , S
_It is necessary to increase the voltage rating of main circuit products such as ₄ ,
The voltage utilization rate has decreased, and the price of the power converter has been increased.

(3) If the DC voltage of the DC power supply 11 is high,
Charging voltage E as described above_d12 Due to the pulsation of electricity
The insulation inside the converter must also be at a high voltage level.
And the insulation distance increases, and the power converter becomes larger.
You. The present invention is intended to eliminate the disadvantages of the prior art described above.
The charging voltage E_d12Part of the pulsating voltage of
Is absorbed by the DC power supply,
The pulsating voltage can be reduced even if the electric capacity is reduced, and the device is small and light.
Quantitative and low cost, improved high-speed response, reliability and protection
To provide a power converter capable of realizing improvement.
aimed to.

[0007]

In order to achieve the above object, the present invention is configured as follows. As an invention with respect to claim 1, in a power conversion device having a three-level inverter circuit, a DC power supply connected for the configuration of a DC circuit on the DC input terminal side of the three-level inverter circuit is connected to a midpoint of the DC circuit and the A bi-directional power supply function and a midpoint that allow DC current to flow in both directions from the AC input side to the output side or from the output side to the AC input side in parallel with two sets of capacitors provided between the positive and negative input terminals, respectively. At least one DC power supply having a voltage control function of controlling a pulsation of a DC voltage with respect to the potential is provided, and at least one DC power supply is provided. Reduce the pulsation of DC voltage. According to a first aspect of the present invention, the pulsation is reduced by absorbing a part of the electric power for generating the pulsation of the charging voltage of the capacitor provided in the DC circuit by the DC power supply having the bidirectional power supply function. Works.

[0008]

FIG. 1 shows an embodiment corresponding to claim 1 of the present invention. Circuit elements having the same functions as those in FIG. 5 are denoted by the same reference numerals. In FIG. 1, 15 and 16 are divided DC power supplies, 17 is an impedance element, 1
8 is a ground pole. In this figure, DC power supplies 15 and 1
Numeral 6 is connected to capacitors 12 and 13, respectively, and three terminals P, O and N of DC power supplies 15 and 16 connected in series are connected to a DC input terminal of a three-level inverter circuit 14, and DC power of DC power supplies 15 and 16 is connected. To the three-level inverter circuit 1
The power is converted to AC power by 4 and the power is supplied to the load from the output terminals U, V, W. Output terminals U, V, the output current _{i m} to be supplied to the load or to vary transiently by W, pulsation of the charging voltage _{E d12} of 3-level inverter circuit 14 of the PWM control method is a factor the capacitor 12 and 13 Even if an attempt is made to generate the DC power, the DC power supplies 15 and 16 are made bidirectional power supplies capable of supplying and absorbing power, so that a part of the current pulsating the charging voltage _Ed12 of the capacitor 12 or the capacitor 13 is supplied to the DC power supply 15. Alternatively, by compensating with the DC power supply 16, the pulsation of the charging voltage can be reduced.

A DC power supply having a bidirectional power supply function as described above.
An example of the source 14 or 15 is shown in FIG. In FIG. 2, 1
9 is an input AC power supply, 20 is a bidirectional rectifier circuit, TH₁When
TH ₂Is a thyristor. 2 bidirectional rectifier circuit 2
0 is thyristor TH₁And TH₂Antiparallel consisting of
Because it is composed of a connected three-phase full-wave rectifier circuit,
It has a power conversion function and directly converts AC power from the input AC power supply 19.
It can also be converted to current power and output.
The power can be regenerated to the input AC power supply 19. Therefore, FIG.
A DC power supply having a bidirectional power supply function as shown in FIG.
Of the DC power supplies 15 and 16
And the charging voltage E of the capacitor 12 or 13_d12Pulse
Voltage controller for DC power supplies 15 and 16
Depending on the charging voltage E_d12Pulsation is suppressed,
Make the capacitance of the capacitors 12 and 13 relatively small
Can be DC power supplies 15 and 16
The midpoint where the sensors 12 and 13 are connected in series is shown in FIG.
And the terminal O at the middle point is connected to the impedance element 17.
To the ground electrode 18 via As shown in FIG.
Terminal P or terminal N
Earth potential is half that of the case without impedance grounding.
Minutes. For this reason, the ground potential of the entire power converter is low.
The insulation distance is reduced, and the power converter can be downsized.
You. In addition, when the potential of the power converter becomes lower,
Protection is also important in terms of personal safety in
Improve in width.

FIG. 3 is applicable as another embodiment of the present invention.
1 shows a circuit configuration example of a simple bidirectional power supply. In FIG. 3, 2
1 is a PWM control converter and D₁Is a diode, T
₁Denotes a self-extinguishing element. PWM control converter 21
Can easily switch the power control direction at a high speed as is well known.
Therefore, the DC power supplies 15 and 16 in FIG.
Then, it is more effective than adopting the configuration of FIG.
You. FIG. 4 shows a circuit configuration example of a bidirectional power supply as described above.
You. In FIG. 4, 19 is an input AC power supply, and 22 is an input
Compressor, 23 is a circulating current type converter, TH₁And TH
₂Is a thyristor, X₁And X₂Is a DC reactor
is there. Circulating current type converter 23 is also on the secondary side of transformer 22
Thyristor TH for each of two windings₁And TH₂ Composed of
DC reactor X₁When
X₂Since the circulating current flows through the
Current control at high speed as in the PWM control converter 21 of FIG.
Thus, the same effect as the configuration of FIG. 3 can be obtained.

Although the three-level inverter circuit 14 has been cited as a multi-level inverter, even in a multi-level inverter in which a DC voltage is divided into four by a capacitor, the midpoint of the DC power supply may be grounded by an impedance element.
Alternatively, a configuration of two DC power supplies or a DC power supply for each individual capacitor may be employed, and the present invention does not limit the configuration. In addition, the present invention can be implemented by making various design changes without departing from the scope of the present invention.

[0012]

As described above, according to the present invention, it is possible to provide a power conversion device having 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 can be obtained. (A) It is possible to prevent the power converter from becoming large and expensive. (B) An excessive fault current does not flow even if a DC short-circuit fault of the three-level inverter circuit occurs. This facilitates accident protection of the semiconductor switch. (2) Since the pulsation of the charging voltage of the capacitor can be reduced,
Since it is not necessary to increase the voltage rating of the main circuit components such as the semiconductor switch more than necessary, the voltage utilization rate is improved, and the price of the power converter can be prevented from being increased.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment corresponding to claim 1 of a power conversion device of the present invention.

FIG. 2 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 supply used for the DC power supplies 15 and 16 of the embodiment.

FIG. 3 is a main circuit configuration diagram showing an example in which a PWM control converter is applied as a bidirectional power supply used for the DC power supplies 15 and 16 of the 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 supply used for the DC power supplies 15 and 16 of the embodiment.

FIG. 5 is a main circuit configuration diagram showing a conventional power conversion device using a three-level inverter.

FIG. 6 is a waveform diagram showing an example of pulsation of a capacitor charging voltage of a conventional power converter.

[Explanation of symbols]

11, DC power supply, 12, 13, capacitor, 14.3 level inverter circuit, 15,
16 DC power supply comprising bidirectional power supply, 17 impedance element, 18 ground electrode, 19
Input AC power supply, 20 ··· bidirectional rectifier circuit, 21 ··· PWM control converter, 22
..Input transformer, 23..Circulating current type converter,
24 ..Difference voltage detection protection circuit, S ₁ , S ₂ ,
S ₃ , S ₄ ··· semiconductor switch, P, O, N ··· DC input terminal, 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} · · diodes, _{T 1} · · self-turn-off devices, X
₁ , X ₂ DC reactor.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H006 AA03 AA05 AA07 CA01 CA03 CA07 CB01 CB08 CC03 CC06 CC08 DA04 FA01 FA02 5H007 AA04 AA06 AA08 CA05 CB02 CB05 CC04 CC06 CC12 CC14 EA02 FA01 FA03 FA12 FA13 FA17

Claims (1)

[Claims] In a power converter having a three-level inverter circuit, a DC power supply connected for the construction of a DC circuit on the DC input terminal side of the three-level inverter circuit is connected to a midpoint of the DC circuit and its positive and negative inputs. A bidirectional power supply function that allows a DC current to flow in both directions, from the AC input side to the output side or from the output side to the AC input side, in parallel with two sets of capacitors provided between the terminals. A DC power supply having at least one DC power supply having a voltage control function for controlling pulsation of the DC voltage is provided, and a positive / negative DC voltage with respect to a midpoint potential that fluctuates at a frequency three times the output frequency of the three-level inverter circuit is provided. A power converter characterized by reducing pulsation of the power.