JPH04289773A - Smoothing capacitor unit - Google Patents

Abstract

PURPOSE:To provide a smoothing capacitor unit wherein ripple currents flowing through respective capacitors can be averaged. CONSTITUTION:In a smoothing capacitor unit comprising capacitors 3a-3d connected sequentially in series between positive/negative terminals 7a, 8a on one end and positive/negative terminals 7b/8b on the other end, the capacitor 3a connected with the negative terminal 8a on one end is connected, at the other end, with the positive terminal 7b on the other end through a lead 9 whereas the capacitor 3d connected with the negative terminal 8b on the other end is connected, at the other end, with the positive terminal 7a on one end through a lead 10.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a smoothing capacitor unit used for smoothing direct current in a PWM-controlled voltage source inverter or the like.

0002

2 shows the main circuit configuration of a PWM-controlled voltage source inverter, in which 1 is an AC power source, 2 is a rectifier, 3 is a smoothing capacitor unit, 4 is a PWM-controlled inverter, 5 is the load. Smoothing capacitor unit 3
is formed by connecting a plurality of capacitors 3a to 3d in parallel due to the shape of the container to be mounted (for example, a cylindrical container, etc.), and in order to suppress the inductance of the circuit, a plurality of two sets of terminals 7a,
The terminals 7a and 8a are connected to the positive and negative output terminals of the rectifier 4, respectively, and the terminals 7b and 8b are connected to the positive and negative input terminals of the inverter 4, respectively.

[0003]The rectifier 2 is connected to the AC power source 1 as shown in FIG. 3(a).
The three-phase alternating current shown in is rectified and converted to direct current. Since this direct current pulsates as shown in FIG. The inverter 4 switches the DC smoothed by the smoothing capacitor unit 3 to supply AC of variable voltage and variable frequency to the load 5 . FIG. 3(d) shows the output voltage waveform of the inverter 4.

0004

[Problem to be solved by the invention] The switching element of the inverter 4 that outputs alternating current of variable voltage and variable frequency by PWM control is turned on and off at several KHz to several tens of KHz.
Therefore, a high-frequency pulse current (shown in (c) of FIG. 3) flows through the smoothing capacitor unit 3, and the smoothing capacitor unit 3 receives this pulse current and the rectifier 2.
A ripple current (shown in (e) of FIG. 3) that is a composite of the pulsating currents from the oscillating currents flows.

For this reason, among the capacitors 3a to 3d,
Ripple current concentrates on the end capacitors 3a and 3d near the terminals 7a and 8a and the terminals 7b and 8b, and the temperature rise becomes higher than that of the other capacitors 3b and 3c, causing variations in the lifespan of the capacitors and increasing the size of the capacitors. If this is avoided, there is a problem that the capacitor unit 3 will have to be replaced more frequently, resulting in higher costs.

The present invention has been made to solve this problem, and an object of the present invention is to provide a smoothing capacitor unit that can equalize the ripple current flowing through each capacitor constituting the smoothing capacitor unit. .

[0007]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a smoothing capacitor unit consisting of capacitors sequentially connected in parallel between positive and negative terminals on one end and positive and negative terminals on the other end. The other end of the end capacitor connected to the negative terminal on the side is connected to the positive terminal on the other end side through a lead, and the other end of the end capacitor connected to the negative terminal on the other end side is connected through another lead. and is connected to the positive terminal on the one end side.

[0008]

[Operation] In the present invention, since the wiring length of each capacitor is equal when viewed from the positive and negative terminals on one end and the positive and negative terminals on the other end,
Ripple current flowing from the terminal is equally divided into each capacitor.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, a lead 9 extends from one end (positive end) of the capacitor 3d to the terminal 7a. 10 is a lead, which is one end of the capacitor 3a (
It extends parallel to the lead 9 from the positive electrode side end) to the terminal 7b. The other end of the capacitor 3a is connected to a terminal 8a, and the other end of the capacitor 3d is connected to a terminal 8b. The other configurations are the same as those in FIG. In addition, leads 9 and 10
are the same length.

In this configuration, each capacitor 3a to
Since the wiring lengths seen from terminals 7a, 8a and terminals 7b, 8b of 3d are equal, the ripple current is equally divided into each capacitor 3a to 3d.

Note that the negative end of the capacitor 3a is connected to the lead 9.
It is also possible to connect the capacitor 3d to the terminal 8b with the lead 10, and connect the negative end of the capacitor 3d to the terminal 8a with the lead 10.

[0013]

[Effects of the Invention] As explained above, according to the present invention, by equally dividing the ripple current flowing from the terminal to each capacitor, it is possible to reduce the variation in life caused by the variation in temperature rise of each capacitor. , it is possible to extend the lifespan and improve the reliability compared to the conventional method without increasing the size.

[Brief explanation of the drawing]

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

FIG. 2 is a circuit diagram of a voltage source inverter using a conventional smoothing capacitor unit.

FIG. 3 is a waveform diagram of each part of the voltage source inverter.

[Explanation of symbols]

2 Rectifier 3 Smoothing capacitor units 3a to 3d
Capacitor 4 Inverse converter 7a-8b Terminals 9, 10 Lead

Claims (1)

[Claims] Claim 1: In a smoothing capacitor unit consisting of capacitors connected in parallel in sequence between positive and negative terminals on one end and positive and negative terminals on the other end, the other end of the end capacitor connected to the negative terminal on one end is a lead. and the other end of the capacitor connected to the negative terminal of the other end is connected to the positive terminal of the one end via a lead. Smoothing capacitor unit.