JPS63268465A - Power converter - Google Patents

Abstract

PURPOSE:To prevent the breakdown of an element by connecting a first capacitor having a small capacity between positive and negative terminals at the interconnection terminals of a converter and an inverter and connecting a second capacitor having a large capacity through an impedance element. CONSTITUTION:A power converter is composed of a transformer TR connected to a current collector PAN, a converter CONV through a reactor L1, a capacitor CO for smoothing and an inverter INV, and drives an induction motor IM as load. A capacitor C1 is connected between the positive and negative terminals of the DC output terminals of the converter CONV and a capacitor C2 between the positive and negative terminals of the DC input terminals of the inverter INV respectively while resistors R1, R2 are interposed at that time. The capacity of the capacitors C1, C2 is made smaller than the capacitor CO. Accordingly, the voltage fluctuation of pulse-shaped high frequency is inhibited by the capacitors C1, C2 having small capacity, and the voltage fluctuation of low frequency is suppressed by the capacitor CO having large capacity.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a DC output terminal of a converter formed by bridge-connecting controlled rectifying elements in which diodes are connected in antiparallel to each other, and a DC output terminal of an inverter. The present invention relates to a power conversion device in which input terminals are interconnected and a capacitor is connected between the positive and negative terminals of these interconnection terminals.

(Prior Art) FIG. 5 shows the configuration of the main circuit of a conventional power converter of this type used in electric railways. In the figure, one end of the primary winding of the transformer TR is connected to the current collector PAN, the other end is grounded via a wheel, etc., and the secondary winding of the transformer TR is connected via a reactor L1. converter C0
The AC input end of NV is connected. This converter C
A capacitor CO, which is generally called a smoothing capacitor, is connected to the 0NV DC output terminal, and a DC input terminal of the inverter INV is also connected thereto. An induction motor IM as a load is connected to the AC output terminal of this inverter INV. Here, converter C0NV
is 4 in which diodes D1 to D4 are connected in antiparallel, respectively.
GTO thyristors T1 to T4 are connected in a single-phase bridge, and the inverter INV is connected to diodes D11 to T4.
D16 is a three-phase bridge connection of six GTO thyristors T11 to T16, each connected in antiparallel.

With the above configuration, the single-phase AC taken in from the current collector PAN is transformed by the transformer TR, and is transferred to the converter C0NV via the reactor L1 that can suppress short-circuit current.
is input. GTO thyristors T1 to T4 of converter C0NV are PWM (pulse width modulation) controlled by a control circuit (not shown) so that the voltage across capacitor CO is constant, thereby converting single-phase alternating current to constant voltage direct current. and is input to the inverter INV. The GTO thyristors Tll to T16 of the inverter INV are also PWM-controlled by a control circuit (not shown), converting direct current into three-phase alternating current with variable voltage and variable frequency, and controlling the induction motor IM with variable speed in addition to the induction motor IM. do.

This power conversion device connects GTO thyristors T1 to T4 to P
Switching using WM signals has the advantage of increasing the input power factor and enabling control with fewer harmonics, but since it is targeted at electric railways, a single-phase converter C0NV is used. The input voltage and input current are shown in Figure 6 (
It changes as shown in a) and (b). In addition, the power output from the converter C0NV, that is, the DC input power seen from the capacitor CO, is as shown in the same figure (c).
The power supplied from the inverter INV to the induction motor IM, that is, the DC output power seen from the capacitor CO, changes at a frequency twice the AC frequency with a pulsation rate of approximately 100%, as shown in Figure (d). Changes to The capacitor CO is the deviation between these DC input power and DC output power,
That is, it can be said that the electric power shown in the shaded area in FIG. 3(c) is stored to compensate for the lack of DC output. Generally, if the converter uses three-phase AC power, the area of the shaded area will be smaller, so a smoothing capacitor with a smaller capacity can be used, but since electric railways can only obtain single-phase AC power, the capacitor CO Therefore, we had no choice but to use one with a large capacity.

On the other hand, this capacitor Co plays another important role in addition to smoothing the DC power.

This will be explained below.

In converter C0NV and inverter INV, which are composed of GTO thyristors, GTs connected in series are
O thyristors, for example, T1 and T2, T11 and T12, turn on and off alternately, but since these are not ideal switches, there may be a delay in turning on and off.
Due to this delay, a momentary reverse current may flow through the diode. Furthermore, an instantaneous reverse current may flow not only due to a time delay between on and off, but also during commutation. For example, in a commutation mode in which GTO thyristor T1 is turned on and current flows through diode D2, a reverse voltage is applied to diode D2 at the same time as GTO thyristor T1 is turned on, and this diode D2
Ideally, it should also be turned off. However, in reality, GTO
Since the diode D2 does not turn off at the same time as the thyristor T1 turns on, but turns off after a short period of time, a pulsed reverse current flows through the diode D2 during this time. This pulsed reverse current causes the DC voltage to fluctuate rapidly, causing large voltage fluctuations (dV/d t ) in the voltages applied to other GTO thyristors.
This may cause the TO thyristor to malfunction. The generation of such pulsed current and the accompanying voltage fluctuation are caused by each G
This occurs every time the TO thyristor is switched.
In order to alleviate these problems, the capacitor CO of the DC circuit has become indispensable.

Thus, a capacitor CO of a large capacity is used as a capacitor CO in a conventional power conversion device, and this plays the dual role of suppressing low frequency DC voltage fluctuations and suppressing high frequency DC voltage fluctuations.

(Problems to be Solved by the Invention) Although the above-mentioned capacitor °CO prevents the GTO thyristor from malfunctioning due to pulsed reverse current, it is susceptible to various surge voltages such as lightning surges. Malfunctions of the GTO thyristors due to noise cannot be suppressed, and in some cases, these GTO thyristors may be erroneously fired. If the positive terminal side and negative terminal side of the DC circuit are short-circuited due to this erroneous ignition, the erroneous ignition GT
Through the O thyristor, the charge on the capacitor CO is rapidly discharged. In this case, if the capacitance of capacitor CO is large, a current with a large peak value will flow for a long time, and GT
O thyristor cannot withstand this and this GTO
There was a risk of destroying the thyristor. Therefore, if an attempt was made to use a GTO thyristor that could withstand this discharge current, there was a problem in that the device would become larger than necessary.

The present invention was made in order to solve the above problems, and even if the capacitance of the capacitor connected between the converter and inverter is increased so as not to impair the operation of the converter and inverter, the control rectifier It is an object of the present invention to provide a power conversion device that can reliably prevent this control rectifier element from being destroyed due to overcurrent during erroneous ignition.

[Structure of the invention]

(Means for Solving the Problems) The present invention provides a system in which the DC output end of a converter formed by bridge-connecting control rectifying elements in which diodes are connected in antiparallel to each other and the DC input end of an inverter are connected together. , and is characterized in that a first capacitor with a small capacitance is connected between the positive and negative terminals of these interconnecting ends, and a second capacitor with a large capacitance is connected via an impedance element. be.

(Function) In this invention, considering the two roles of a capacitor in a DC circuit, the first capacitor with a small capacity directly connected to the converter and inverter suppresses high frequency voltage fluctuations caused by pulsed current. By suppressing low-frequency voltage fluctuations by a second capacitor with a large capacity connected via an impedance element, and by having the impedance element limit the discharge current of this second capacitor, malfunctions of the converter and inverter can be prevented. In addition to preventing accidental firing, G
Limit the current in the TO thyristor to prevent damage to it.

(Embodiment) FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention, and the same reference numerals as in FIG. 5 indicate the same elements. Then, a capacitor C1 is connected between the positive and negative terminals of the DC output terminal of the converter C0NV, and a capacitor C2 is connected between the positive and negative terminals of the DC input terminal of the inverter INV.
are connected respectively, and a resistor R1 is connected between the positive terminal of the capacitor CO and the positive terminal of the converter C0NV.
The difference from FIG. 5 is that a resistor R2 is connected between the positive terminal of the capacitor Co and the positive terminal of the inverter INV. Here, the capacitor CO is shown in Figure 6 (
A capacitor with a large capacity is used to store the power shown in the shaded area in c), but capacitors C1 and C2 have a much smaller capacity than the capacitor CO. Further, the resistors R1 and R2 are of a value sufficient to suppress the peak value of the discharge current from the capacitor CO to a value below the allowable value of the GTO thyristor.

The operation of this embodiment configured as described in Section 2 will be explained below, focusing in particular on the points that are different from the conventional apparatus.

First, capacitor C1 absorbs high-frequency pulse-like voltage fluctuations that occur during the switching operation of converter C0NV. Further, the capacitor C2 absorbs high frequency pulse-like voltage fluctuations that occur during the switching operation of the inverter INV. On the other hand, capacitor CO absorbs low frequency power fluctuations due to the influence of power supply voltage.

Next, when the GTO thyristor of converter C0NV accidentally fires and shorts the positive and negative sides of the DC circuit, these G
Although the discharge current of the capacitor C1 flows through the TO thyristor, the discharge current of the capacitor CO, which has a large capacity, is limited to a permissible value or less by the resistor R1. Also, inverter IN
When the GTO thyristors of V are erroneously fired and the positive and negative sides of the DC circuit are short-circuited, the discharge current of capacitor C2 flows through these GTO thyristors, but the discharge current of capacitor CO with a large capacity is reduced by resistor R2. Restricted to below permissible value.

Thus, according to this embodiment, malfunctions of the converter and inverter can be suppressed, and even if the GTO thyristor should accidentally fire, the current of the GTO thyristor can be limited and damage to the GTO thyristor can be prevented.

FIG. 2 shows the configuration of a second embodiment of the present invention.
Reactor L11 is used instead of resistor R1 in FIG.
A reactor L12 is connected in place of the resistor R2. According to this configuration, it is possible to perform the same operation as the embodiment shown in FIG. 1, and also to reduce power loss during steady state.

FIG. 3 shows the configuration of a third embodiment of the present invention.
The capacitor C2 and resistor R2' in FIG. 1 are removed, and the positive terminal of the DC input end of the inverter INV is connected to the positive terminal of the DC output end of the converter C0NV. With this configuration, all high-frequency voltage fluctuations due to switching operations of converter C0NV and inverter INV are absorbed by capacitor C1, and the number of circuit components can be reduced compared to the above embodiment. .

FIG. 4 shows the configuration of a fourth embodiment of the present invention, in which a reactor L11 is connected in place of the resistor R2 in FIG. In this way, not only can the same operation as shown in FIG. 3 be performed, but also the steady loss in the resistor can be reduced.

In each of the above embodiments, a power conversion device using a GTO thyristor has been described, but the present invention is not limited to this, and it is possible to use other controlled rectifying elements such as a transistor instead of the J'GTO thyristor. It can also be applied to devices that have

Further, in the above embodiments, the capacitor CO is connected via a resistor or an axle, but these impedance cables may be connected in series or in parallel if necessary.

Furthermore, although the above embodiment has been described with reference to a single-phase manual converter, the present invention can also be applied to a three-phase input converter.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the first capacitor with a small capacitance directly connected to the converter and the inverter suppresses high frequency voltage fluctuations caused by pulsed current, while the first capacitor is connected via an impedance element. A second capacitor with a large capacitance is used to suppress low frequency voltage fluctuations, and an impedance element is used to suppress low frequency voltage fluctuations.
Release of the capacitor! By limiting the current m, malfunctions of the converter and inverter can be prevented, and even if erroneous firing occurs, the current of the control rectifying element can be limited to prevent t and ii.

[Brief explanation of the drawing]

1 to 4 are circuit diagrams showing the configuration of an embodiment of the present invention, FIG. 5 is a circuit diagram showing the configuration of a conventional power conversion device, and FIGS. FIG. 3 is a waveform diagram for explaining the operation of the conversion device. C0NV...Converter, INV...Inverter,
Co, C1, C2... Capacitor. T1-T4, T1
1-T16...GTO thyristor, D1-D4, Dl
l~D16...Diode. Applicant's representative Sato - Weaning 1 Diagram 2 Diagram 3 Concave 4 Closure 5 Koiroki 6 Mouth

Claims (1)

[Claims] 1. A DC output end of a converter formed by bridge-connecting controlled rectifying elements each having diodes connected in antiparallel;
A first capacitor with a small capacitance is connected between the positive and negative terminals of these interconnection terminals, and a second capacitor with a large capacitance is connected via an impedance element. A power conversion device characterized by connecting a capacitor. 2. Using a GTO thyristor as the controlled rectifier,
2. The power conversion device according to claim 1, wherein the converter is a single-phase bridge-connected GTO thyristor, and the inverter is a three-phase bridge-connected GTO thyristor. 3. The power conversion device according to claim 1 or 2, wherein one or both of a resistor and a reactor is used as the impedance element. 4. The first capacitor is separately connected to the output end of the converter and the input end of the inverter, and the second capacitor is connected to the output end of the converter and the inverter, respectively, through the separate impedance element. The power conversion device according to any one of claims 1 to 3, wherein the power conversion device is connected to an input terminal of the power conversion device. 5. The first capacitor is a single capacitor that is commonly connected to the output terminal of the converter and the input terminal of the inverter. The power conversion device described.