JPS5821505B2 - Forced commutation type converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention comprises a main bridge circuit consisting of a main controllable electric valve;
A forced commutation type conversion device in which a non-controllable electric valve is commonly connected to an auxiliary bridge circuit on the AC side, and a commutation auxiliary circuit including a commutation capacitor is connected between the DC side terminals of the same polarity of both bridge circuits. Regarding.

This type of forced commutation type converter can be used even in a control angle range that is advanced in phase with respect to the AC power supply voltage by connecting an AC power supply to the AC side of the main bridge circuit and connecting a DC load to the DC side of the main bridge circuit. Can be used as an operable rectifier.

Moreover, if this type of forced commutation type converter is connected in antiparallel on the DC side and connected to an AC load, it becomes a cycloconverter.

Alternatively, it can be used as a current source inverter by connecting an AC load such as an AC motor to the AC side of the main bridge circuit and connecting a DC voltage source to the DC side via a smoothing reactor.

In this type of forced commutation type converter, abnormal voltage is likely to occur due to the influence of the inductance of the power supply or load connected to the AC side of the main bridge circuit.

This is because the energy of those inductances is transferred to the commutation capacitor during the commutation process, causing the commutation capacitor to be overcharged.

Such overcharging of the commutating capacitor is extremely inconvenient in large-capacity converting devices because it requires components within the converting device to withstand voltages higher than necessary.

Therefore, some means is required to suppress overcharging of the commutating capacitor.

An object of the present invention is to provide an overvoltage absorbing means suitable for the forced conversion type inverter as mentioned at the beginning.

In other words, the purpose is to absorb overvoltage using the simplest possible means without reducing the efficiency of the converter.

According to the invention, this object is achieved by connecting an overvoltage absorbing capacitor between the DC side terminals of the auxiliary bridge circuit so that the energy stored in this capacitor is regenerated to the power supply.

This allows overvoltage to be absorbed with almost no power loss, and since the auxiliary bridge circuit is used as a part of the overvoltage absorption device, the advantage is that the device can be made smaller and costs can be reduced accordingly. is obtained.

Hereinafter, the present invention will be explained in more detail with reference to the drawings.

The figure shows an embodiment of the present invention configured as a forced commutation type rectifier that can be operated at a control angle that is advanced in phase with respect to the AC power supply voltage.

The AC side of the main syris bridge 1 consisting of the main syrisks U to Z is connected to 3 via a power transformer (not shown), for example.
It is connected to a phase alternating current power source, and a load (not shown) is connected to the direct current side.

A diode bridge 2 consisting of a diode Du''Dv is commonly connected to the main silis bridge 1 on the alternating current side.

A commutating capacitor CP is connected between the positive DC terminals of both bridges.
A series circuit of a rectifier reactor LP and a diode DP is connected, and an inverting thyristor TP is connected in parallel to the series circuit of a commutating capacitor Cp and a commutating reactor LP.

A commutating capacitor CN is connected between the negative polarity DC terminals of both bridges.
A series circuit of a commutating reactor LN and a diode DN is connected, and an inverting thyristor TN is connected in parallel to the series circuit of a commutating capacitor CN and a commutating reactor LN.

The series circuit of commutating capacitor CP and commutating reactor LP is connected via auxiliary charging cyrisk Qp and braking resistor rp, and the series circuit of commutating capacitor CN and commutating reactor LN is connected to auxiliary charging cyrisk QN and braking resistor. rN
It is possible to connect between both DC terminals of the diode bridge 2 through the respective DC terminals of the diode bridge 2.

An overvoltage absorbing capacitor CF is connected between both DC terminals of the diode bridge.

The DC input side of a separately excited inverter 3 constituted by three-phase bridge-connected SYRISC is connected between both ends of the capacitor CF via a smoothing reactor LP.

The AC output side of the separately excited inverter 3 is connected to a three-phase AC power supply to which the main thyristor 1 is connected via an auxiliary transformer Tr, but this connection is omitted in the figure.

The auxiliary transformer Tr may be combined into one secondary two-winding transformer that is common to the power transformer to which the main silis bridge 1 is connected.

The commutating capacitor Cp is common to the main thyristors UW, and the commutating capacitor CN is common to the main thyristors X=Z.

For example, when main thyristor W is to be turned off and main thyristor U is to be turned on in a state where the main thyristors W and Y are passing load current, first the inverting thyristor TP is turned on and charged to the polarity shown. The commutating capacitor cP is reversely charged.

As soon as the charging polarity of the commutating capacitor cP starts to return to the original polarity after this inversion charging is completed, the load current flowing through the main thyristor W is commutated to the road via the commutating capacitor cp.

As a result, the commutating capacitor cP is charged with the polarity shown by the load current.

When the commutating capacitor CP is charged until a forward voltage is applied to the main thyristor U, if a firing pulse is given to the main thyristor U, the main thyristor U becomes conductive and the current flows through the commutating capacitor CP. The load current commutated to this main thyristor U.

During this commutation type period, the inductance of the power supply and the energy stored in the commutation reactor are delivered to the commutation capacitor CP.

Therefore, when the load current is large, the commutating capacitor voltage after the commutating period ends becomes excessive.

However, according to the invention, the diode bridge 2
Because a capacitor cF is connected between the DC side terminals of It will be done.

The energy stored in the capacitor CF is regenerated to the power source by the separately excited inverter 3.

As described above, according to the present invention, it is possible to efficiently suppress the overvoltage of the commutating capacitor, and the size and cost of the device can be reduced by using the diode bridge 2 as a part of the device necessary for this purpose. be able to.

Furthermore, in the illustrated embodiment, in order to avoid insufficient voltage of the commutating capacitor during no-load or light-load conditions, a supplementary charging circuit consisting of supplementary charging cyrisk Qp +Qw and braking resistors rp and rN is provided.

In this case, the diode bridge 2 also serves as a voltage source for this supplementary charging circuit.

That is, in the illustrated embodiment, the diode bridge 2 is commonly used as a part of each of the commutation auxiliary circuit, the auxiliary charging circuit, and the overvoltage absorption circuit.

The supplementary charging thyristor may be ignited after the corresponding main thyristor and reversal thyristor are extinguished.

The diode D P pDN is provided to prevent a short circuit of the power supply when the auxiliary charging thyristor is ignited.

When the illustrated forced commutation type converter is used as a current source inverter for controlling the speed of an AC motor, the motor is connected to the AC side of the main bridge 1.

The DC side of the main bridge 1 is connected to a rectifier via a smoothing reactor.

The transformer T is also connected to the AC power source of the rectifier.

In this case, the auxiliary charging circuit may be omitted.

[Brief explanation of the drawing]

The figure is a circuit connection diagram showing one embodiment of the present invention. 1... Main bridge circuit (main silis bridge), 2... Auxiliary bridge circuit (diode bridge), 3... Separately excited inverter, CP, CN.
... Commutation capacitor, LP, LN ... Commutation reactor, TP, TN ... Thyristor N Qp for inversion, QN ... Thyristor for supplementary charging,
rp, rN...braking resistance, Dp, DN...
... Diode for reverse current prevention, CF ... Capacitor for overvoltage absorption, LF ... Smoothing actuator, Tr ... ... Transformer.

Claims (1)

[Claims] 1. A main bridge circuit consisting of main controllable electric valves and an auxiliary bridge circuit consisting of non-controllable electric valves are commonly connected on the AC side, and a transfer is made between the DC side terminals of the same polarity of both bridge circuits. In a forced commutation type converter in which a commutation auxiliary circuit including a current capacitor is connected, an overvoltage absorbing capacitor is connected between the DC terminals of the auxiliary bridge circuit, and the energy accumulated in this capacitor is transferred by a power converter. A forced commutation type conversion device characterized by regenerating power to the power source. 2. In claim 1, each commutation auxiliary circuit is characterized by comprising a series circuit of a commutation capacitor and a commutation reactor, and an auxiliary controllable valve connected in parallel to this series circuit. Forced commutation type converter. 3. In claim 2, an auxiliary electric valve for preventing reverse flow is connected in series in a line connecting the series circuit in each commutation auxiliary circuit and the corresponding DC side terminal of the main bridge circuit, and A forced commutation type conversion characterized in that a connection point between the series circuit and its auxiliary electric valve is connected to a DC terminal on the opposite side of the auxiliary bridge circuit via an auxiliary electric valve for auxiliary charging and a braking resistor. Device. 4. In any one of claims 1 to 3, the power converter has a DC side connected between both ends of the overvoltage absorbing capacitor via a reactor, and an AC side connected to a transformer. A forced commutation type converter characterized in that it is a separately excited type converter connected to an alternating current power source through an AC power source.