JP2000060108A - Capacitor group circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce wiring inductance and save overvoltage suppressing circuit such as a snubber circuit by installing film capacitor for absorbing high frequency current ripples, due to switching and an electrolytic capacitor group for suppressing ripples caused by the fundamental frequency. SOLUTION: Overvoltage caused by a wiring inductance Ls and high frequency current ripple caused by switching are absorbed by a film capacitor Cc. Ripples (current ripples) of a DC voltage caused by a fundamental frequency is absorbed by an electrolytic capacitor group Cd. When switching elements Sa-Sf are shorted and broken, stored energy of film capacitor Cc flows into the broken switching elements Sa-Sf. Since this energy is small, spread expansion of the accidence can be prevented. In the case of large storage energy of the electrolytic capacitor group Cd, a current is blocked by a fuse Fs so that fire spread or the like is prevented. As a result, a wiring inductance is reduced and an overvoltage suppressing circuit can be omitted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitor group circuit connected to a predetermined connected switching element group such as an inverter.

[0002]

2. Description of the Related Art An example of a circuit configuration in which a capacitor group circuit is connected to a switching element group in which a plurality of GTOs, IGBTs and the like are connected in a predetermined manner is an inverter, an example of which is shown below with reference to FIG. In the figure, (1) is a three-phase inverter (hereinafter, referred to as an inverter), (Ca) is a DC capacitor, and (Fs) is a fuse.

The inverter (1) has three arm portions (1) in which switching elements (Sa) and (Sb), (Sc) and (Sd), and (Se) and (Sf) are connected in series.
a) (1b) and (1c) are connected in parallel. A positive / negative pulse train having a predetermined width and a predetermined cycle is generated by an ON / OFF switching operation from a DC voltage, converted into an AC voltage having a predetermined frequency, and outputted to a load (not shown). ). The DC capacitor (Ca) is a series connection of a plurality of electrolytic capacitors, which are connected in parallel to the inverter input and charged by the DC power supply to smooth DC voltage ripples, absorb switching ripples (current ripples), and store energy. Aim. The fuse (Fs) is inserted in series between the inverter (1) and the electrolytic capacitor (Ca).

At this time, a floating inductance (wiring inductance) (Ls) is inevitably generated due to the wiring between the inverter (1) and the DC capacitor (Ca). When the wiring inductance (Ls) is large, the current energy stored therein becomes an excessively large voltage (voltage jump = spike voltage) due to forcible current interruption when the switching element is turned off, and the switching elements (Sa) to (S)
f) threatens the safe operation and, in the worst case, leads to device destruction. Therefore, it is desirable to connect the inverter (1) and the DC capacitor (Ca) with the shortest distance using a copper bar wiring or the like, and to reduce the wiring inductance (Ls) as much as possible.

[0005] However, the switching element (Sa) ~
In the case where (Sf) is short-circuited and broken due to malfunction or the like, the flow of energy from the DC capacitor (Ca) is prevented, and the DC capacitor (Ca) and the switching elements (Sa) to (Sf) are used to prevent the spread of accidents such as fire spread. Must be inserted with a protective fuse (Fs). Thereby, the DC capacitor (Ca) and the switching elements (Sa) to (S)
f) and the wiring inductance (Ls)
Increase.

Furthermore, it is difficult to manufacture an electrolytic capacitor constituting a DC capacitor (Ca) having a withstand voltage of about 500 V or more due to restrictions on electrical characteristics and the like. In the case of an inverter having a rated voltage of a DC circuit exceeding about 500 V, It is necessary to connect an electrolytic capacitor corresponding to the DC voltage in series with a copper bar wiring or the like. The number of series is several to 10 or more series in a GTO inverter or the like whose rated DC voltage reaches several thousand volts. In order to make these electrolytic capacitors in series, it is difficult to shorten the wiring layout. The increase of the floating wiring inductance (Ls) due to the above cannot be avoided.

Therefore, conventionally, an overvoltage suppression circuit such as a snubber circuit (2) composed of a capacitor (Cb), a diode (D), a resistor (R), etc. for suppressing an overvoltage is added, and the wiring inductance (Ls ) Was absorbed by the capacitor (Cb) and consumed by the resistor (R).

[0008]

As described above, if a snubber circuit (2) is added in order to prevent an overvoltage at the time of current interruption, the energy of the overvoltage is eventually consumed as heat. Loss occurs, causing a reduction in the conversion efficiency of the inverter (1), and the installation of the snubber circuit (2) causes a problem that the wiring structure becomes complicated and costs increase.

In order to avoid an increase in the wiring inductance (Ls) by avoiding a large number of electrolytic capacitors constituting the DC capacitor (Ca) in series, a film capacitor capable of producing a high withstand voltage product is used instead of the electrolytic capacitor. good. However, when current flows in and out of the capacitor due to current ripple caused by the fundamental frequency (commercial frequency) and the voltage fluctuates, the voltage fluctuation of the film capacitor is smaller than that of the electrolytic capacitor because the capacitance, that is, the energy density is small. Largely, it is difficult to suppress the voltage ripple (voltage fluctuation) of the DC circuit caused by the fundamental frequency (commercial frequency) only with the film capacitor. Further, increasing the number of parallel circuits to increase the capacitance and store energy equivalent to that of an electrolytic capacitor requires an enormous number of parallel circuits.

An object of the present invention is to provide a capacitor group circuit in which wiring inductance is reduced and an overvoltage suppression circuit such as a snubber circuit is omitted.

[0011]

SUMMARY OF THE INVENTION The present invention provides a high-voltage film capacitor which is connected in parallel close to a predetermined connected switching element group and absorbs high-frequency current ripple due to switching, and a fuse connected to the switching element group. And a series of electrolytic capacitors that are connected in parallel via the first capacitor and suppress pulsation caused by the fundamental frequency.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a capacitor group circuit according to the present invention will be described below with reference to FIG. In the figure, (1) is an inverter, (Cc) is a film capacitor, and (Cd) is an electrolytic capacitor group. The inverter (1) has the switching elements (Sa) and (S
b), three arms (1a), (1b), and (1b) each connected in series with (Sc) and (Sd), and (Se) and (Sf).
c) is a three-phase inverter connected in parallel to convert and output DC voltage to AC voltage.

Since the film capacitor (Cc) can be manufactured with a high withstand voltage and does not need to be connected in series, it is connected in parallel near the inverter (1), and is connected close to the inverter (1) and has a wiring inductance (Ls). Can be reduced. Further, since the film capacitor (Cc) has a long life and does not require replacement, it is not necessary to mount the film capacitor (Cc) on the premise of replacement. Therefore, there is no mechanical restriction on the mounting, and a wiring structure can be obtained in which the distance between the switching elements (Sa) to (Sf) is shortened as much as possible and the switching elements (Sa) to (Sf) are brought close to each other to reduce the wiring inductance (L). As a result, the overvoltage (spike voltage) of the switching elements (Sa) to (Sf) when the current is interrupted is reduced, and an overvoltage suppression circuit such as a snubber circuit that generates power loss becomes unnecessary, and the conversion efficiency of the inverter (1) is reduced. Is improved.

In terms of volume ratio, the film capacitor (Cc) has a larger current ripple resistance than the electrolytic capacitor, has a capacitance of, for example, 100 μF or more, and has a high frequency by the switching elements (Sa) to (Sf). Is absorbed by the film capacitor (Cc).
When the capacitance of the film capacitor (Cc) is several μF or less, spike voltage can be suppressed, but current ripple due to switching cannot be absorbed.

The electrolytic capacitor group (Cd) is connected in parallel to the inverter (1) via a fuse (Fs), has a capacitance of, for example, 1000 μF or more, and suppresses pulsation of DC voltage (voltage ripple caused by the fundamental frequency). Suppress.
In addition, since the electrolytic capacitor needs to be replaced as needed every 5 to 10 years, it is installed at a slight distance from the switching elements (Sa) to (Sf) via the fuse (Fs), and is easily removed and replaced. The mechanism arrangement giving priority to the property can be performed.

According to the above configuration, first, the overvoltage due to the wiring inductance (Ls) and the high-frequency current ripple due to switching are absorbed by the film capacitor (Cc), and the pulsation (current ripple) due to the fundamental frequency of the DC voltage is eliminated by the electrolytic capacitor. Absorbed in group (Cd). Further, when the switching elements (Sa) to (Sf) are short-circuit broken, the energy stored in the film capacitor (Cc) flows into the broken switching elements (Sa) to (Sf). However, the stored energy of the film capacitor (Cc) is several thousand to several tens of thousands μF or more.
Since the energy is sufficiently small in proportion to the capacitance in comparison with the stored energy of d), the energy flowing from the film capacitor (Cc) into the switching elements (Sa) to (Sf) is small, and the spread of the accident can be prevented.

On the other hand, in the case of the electrolytic capacitor group (Cd) having a large stored energy, the current is blocked by the fuse (Fs), so that it is possible to prevent the spread of accidents such as fire spread. At this time, even if the fuse (Fs) is inserted, since the overvoltage due to the wiring inductance (Ls) is suppressed by the film capacitor (Cc), no trouble occurs. Further, since the shape of the fuse does not need to be low-inductance wiring, there is no limitation on the shape, size and the like.

In the above embodiment, a three-phase inverter has been described as a switching element group. However, the present invention is not limited to this. For example, a circuit in which a capacitor group circuit is connected to another switching element group connected in a predetermined manner, for example, It is also applicable to single-phase inverters, chopper circuits, and the like.

[0019]

According to the present invention, a high-breakdown-voltage film capacitor is connected in parallel close to a predetermined connected switching element group to absorb current ripple due to switching, and the switching element group is connected via a fuse. Since the pulsation of the DC voltage is suppressed by connecting the electrolytic capacitors in parallel, the wiring inductance is reduced, and an overvoltage suppression circuit such as a snubber circuit is not required, thereby improving the conversion efficiency of the inverter. In addition, since the film capacitor has a long service life and does not require replacement, there is no need to mount it as a prerequisite for replacement, and there are fewer mechanical restrictions, improving the degree of freedom in mechanical design, and enabling mounting with reduced wiring inductance. This eliminates the need for a snubber circuit and the like, and similarly improves the conversion efficiency of the inverter. Also, the electrolytic capacitors that need to be replaced can be installed at a slight distance from the switching elements via fuses, increasing the degree of freedom in placement, making it easy to remove, and enabling a mechanism arrangement that prioritizes replacement workability. Become.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a capacitor group circuit according to the present invention.

FIG. 2 is a circuit diagram showing an example of a conventional capacitor group circuit.

[Explanation of symbols]

 1 switching element group Cc film capacitor Cd electrolytic capacitor group

Claims (1)

[Claims] 1. A high-voltage film capacitor that is connected in parallel close to a predetermined connected switching element group and absorbs high-frequency current ripple due to switching, and connected in parallel to the switching element group via a fuse. A capacitor group circuit comprising: a group of electrolytic capacitors for suppressing pulsation due to frequency.