JPS63220772A - Inverter - Google Patents

Abstract

PURPOSE:To shorten feedback working time, by providing the secondary winding of a current transformer with a tap, and by feeding back snubber energy to the DC power source of an inverter via the bridge circuit of a plurality of arms. CONSTITUTION:An inverter is built in a half-bridge form of the arm elements 1U-1X of self-arc-suppressing switching elements (GTO) which are alternately turned ON/OFF. Besides, reactors 2U-2X, snubbers 4U-4X, a diode circuit 5, a rectifier 6, and a diode rectification circuit 7 are arranged. In this case, the secondary winding terminals 6b-6c of the rectifier 6 are provided with an intermediate tap 6a, and a thyristor circuit 8 is set. Then, by changing the ratio of the secondary winding of the current transformer 6 to a primary winding according to the degree of the DC power voltage of the inverter, voltage lowering is compensated for, and so a working time in a feedback mode can be prevented from being made longer even if the power voltage is lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an inverter equipped with a snubber in which a means for returning the energy stored in the snubber to a DC power supply is improved.

[Conventional technology]

FIG. 6 is a circuit diagram showing a conventional inverter disclosed in Japanese Patent Application No. 59-18553, in which a self-extinguishing switching element is used as an arm element and is shown as a half bridge. In the figure, P+N is the positive and negative electrode of the DC power supply, IU, and 1X are the gate turn-or-thyristors (abbreviated as GTO), which are arm elements,
Its gate receives on and off signals so that it turns on and off alternately. 2U and 2X beam axles are connected in series and inserted between GTOI U and GTOlX. 3U and 3X are feedback diodes, and the feedback diode 3U is connected in anti-parallel to GTolU, and the feedback diode 3X is connected in anti-parallel to GTolX. Is snubber 4U a snubber condenser? 41U and a snubber diode 42U are connected in parallel to the GTOIU. The snubber 4X consists of a snubber capacitor 41X and a snubber diode 42X, and is connected in parallel to fi and GTOlX.
Ru. The 7th node side of the snubber diode 42U of the snubber 4U and the cathode side of the snubber diode 42X of the snubber 4X are connected via the diode circuit 5 and the primary winding of the current transformer 6. Further, this diode circuit 5 is inserted with its cathode side facing the anode side of the snubber diode 42U. Both ends 5a of the secondary winding of the current transformer 6,
5b are diodes 7a of the diode rectifier circuit T, respectively.
It is connected to the positive pole P of the DC power supply via p7b, and to the negative pole N of the DC power supply via diodes 7c and 7d.

Next, the operation of this device will be explained with reference to the time charts of FIGS. 7 and 8. In Figure 7, T
u and Tx are the gate on periods of GTOIU and 1X, respectively, Iw is the load current flowing to the load (L load in this example), Iu and Ix are the currents flowing to GTOiU and 1X, respectively, Iud and Ixd are the feedback diode 3U, respectively.
The current flowing through 3X, Vuc and Vxc are each snubber capacitor 41U.

41X voltage, In indicates the current flowing through the diode circuit 5 and current transformer 6. Further, FIG. 8 shows enlarged waveforms of the voltage and current of the primary winding of the current transformer 6 when the GTOiU is turned off, and Ver is the voltage of the primary winding of the current transformer 6.

Now, at time t1, for example, the GT that has been turned on until now
When OlU is turned off, the current Iu flowing through GTOIU is transferred to snubber 4U, and snubber capacitor 41U
begins to charge. At this time,.

The charge of the snubber capacitor 41X of the snubber 4X is the diode circuit 5 - current transformer 6 - snubber diode 42 U -1
, 1 through the AC output terminal U and the AC output terminal U, the discharge is completed at time t2, and the feedback diode 3X begins to conduct. During this time, the secondary output of the current transformer 60 is returned to the DC power source through the diodes 7a and 7d of the diode rectifier circuit 7, so a voltage proportional to the voltage of the DC power source is generated between the primary windings of the current transformer 6. Next, the energy of reactor 2U is transferred to reactor 2U - reactor 2X - snubber diode 42X - diode circuit 5 -
The current is fed back to the DC power source through the current transformer 6-snubber diode 42U path, and the current in the reactor 2U and current transformer 6 is attenuated. When the iron core of current transformer 6 undergoes magnetic saturation at time t8,
Although the voltage of the current transformer 6 momentarily generates an overvoltage of opposite polarity, the diode Tby7' is turned on and serves to clamp the voltage between the terminals 5a and 5b to the voltage of the DC power supply. This reverse voltage is generated by the snubber diode 42U - reactor 2U -
It works to increase the current in the loop of reactor 2X and snubber diode 42X, but because this loop voltage drop is small, the decay time of the current in reactor 2U and current transformer 6 is very long, so the voltage corresponding to this voltage drop increases. The time it takes for the current transformer 6 to be reset also becomes longer.

When the polarity of the load current is reversed at time t4, the load current flows through the path of the terminal [J IJ handle 2X-GTOlX.

[Problem that the invention seeks to solve]

Since the conventional inverter is configured as shown in Figure 2, during the return operation of the snubber energy, the energy of A. Mo-do returns due to
The operating time (ta-t2) at this time is determined by the primary voltage Ec of the current transformer 6, the inductance L of the reactors 2U and 2X, and the output current value I of the inverter.

It is obtained by tg-t2=mouse, and is influenced by the primary voltage Ec of the current transformer 6c. This II' [
'Since the voltage Ec is proportional to the DC 11 source voltage of the inverter, when operating the inverter with a low DC power supply voltage when the speed of the motor is low in applications such as driving a current-changing motor with an inverter, the feedback operation described above is necessary. Time (tg-t2
) became longer, and problems such as the inability to increase the switching frequency of the inverter occurred.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an inverter capable of high frequency switching in response to a drop in DC power supply voltage.

[Means for solving problems]

The inverter according to the present invention uses a single-phase bridge of diodes to incorporate a rectifier circuit that returns the stored energy of a snubber connected in parallel to a self-extinguishing switching element to a DC power source from a tap terminal provided on the secondary side of a current transformer. It consists of a mixed bridge circuit consisting of thyristors connected in series.

[For production]

In the inverter according to the present invention, when the DC power supply voltage is low, the conduction arm of the bridge circuit and the tap of the secondary winding of the current transformer are switched so that the voltage of the primary winding of the current transformer does not drop. .

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure is a circuit diagram showing an embodiment of the present invention, and the same components in FIG. 1 as in FIG. 6 are given the same reference numerals, and their explanation will be omitted. In FIG. 1, 5a, 5b, and 5c are terminals of the secondary winding of the current transformer 6, among which terminal 6
a is a midpoint tap.

7a, 7b, 7c, and 7d are diodes of a diode bridge circuit, the AC end of the diode bridge circuit is connected to the terminals 6a and 6b, and the DC end is connected to the terminals P and N of the DC power supply of the inverter on the N side. It is connected in the direction of conduction from the P side to the P side. 8a and 9b are thyristors of a thyristor circuit connected in series, the intermediate connection point of which is connected to the above-mentioned terminal 6C, and both ends thereof are connected to the terminals P and N of the DC power supply of the inverter in the direction of conduction from the N side to the P side. connected to.

Next, the operation will be explained. Since the operation on the primary winding side of the current transformer 6 is the same as that of the conventional one, the operation on the secondary winding side will be mainly explained with reference to FIGS. 2 and 3. Figure 2 shows the GTOIU when the DC power supply voltage of the inverter is low.
The figure shows the operating waveform of the current transformer 6 when the current transformer 6 is turned off, and the thyristors 8a+8b are controlled to be non-conductive. Time t
In the feedback mode from 1 to t8, a feedback current flows through the secondary winding of the current transformer 6 from the terminal 6b to the terminal 6a, and the diodes 7d and 7a of the diode bridge circuit become conductive.

Therefore, the DC voltage Ed of the inverter is applied between the terminals 6a and 6b of the secondary winding of the current transformer 6.

Here, if the turns ratio of the secondary winding (between 6C and 6b) and the primary winding of the current transformer 60 is n:l, then a voltage of 2Ed/n is applied to the primary winding end of the current transformer 6. occurs. During the period from time t2 to time t8, the primary winding current ID of the current transformer 6 is caused by the snubber diode 42.
It is attenuated in the path of U-Reactor 2U-Reactor 2X-Snubber diode 42X-Diode circuit 5-Current transformer 6, and if the inductance of reactors 2U and 2X is L, the time T28 from time t2 to t8 is as follows. Become.

Equal to the instantaneous value IO of the inverter's output current.

On the other hand, Fig. 3 shows the operating waveform of the current transformer 6 when the GTOlU is turned off when the DC power supply voltage of the inverter is high.9 A gate signal is applied to the thyristor circuits 8a and 9b to make them conductive. . In the feedback mode from time t1 to t8, a feedback current flows through the secondary winding of the current transformer 6 via the diode 7d and the thyristor 8a, and the inverter's DC power supply is connected between the secondary winding terminals 6C and 6b. A voltage Ed is applied, and a voltage Ed,/n is generated at the end of the primary winding. At this time, time T2B is as follows.

As described above, by switching the ratio between the secondary winding and the primary winding of the current transformer 6 according to the magnitude of the DC power supply voltage of the inverter, the voltage drop at the end of the primary winding is compensated for. In order to be
(11, (As is clear from Equation 21, the operating time T28 in the feedback mode depends on the power supply voltage. In the above embodiment, the secondary winding of the current transformer 6 is provided with an intermediate tap, but the fourth As shown in the figure, multiple sets of taps may be provided on the secondary winding of the current transformer 6. 8C and 8d are thyristors connected in series to the secondary winding terminals of the current transformer 6. 6d.Here, assuming that the taps of the secondary winding of the current transformer 6 are wound equally, when the DC power supply voltage of the inverter is low, the thyristor circuits 83 to 8d Thyristors 8C and 8d are turned off, and when thyristors 8a and 8b are turned on, the primary winding In this case, when the thyristors 8C and 8d are turned on and the thyristors 8a and 8b are turned off, the primary winding is also tapped.In the above embodiment, the current transformer 60 secondary winding is equally divided and tapped. Although an example has been shown, the taps of the secondary winding may be divided unequally, and the division ratio in that case is selected according to the variation range of the DC power supply voltage.

Further, in the above embodiment, the diode circuit 5 is connected in series with the primary winding of the current transformer 6, but instead of this, a self-extinguishing switching element 9 such as a GTO is used as shown in FIG. In this case, the self-extinguishing switching element 9 is turned off at the time ta when the feedback operation ends (see Figures 2 and 3), and the K current switch is connected. 6 reset operation is current transformer 6 2
On the next winding side, it is faster because it is done via the diodes 7c and 7b, or the thyristor 8b and the diode 7b.

〔Effect of the invention〕

As described above, according to the present invention, a tap is provided in the secondary winding of the current transformer 6, and the direct current of the inverter is transmitted through a bridge circuit of multiple arms consisting of diodes and thyristors. Since the inverter is configured to feed back the snubber energy to the source, even if there is a fluctuation in the voltage of the DC power source, the time required for feeding back the snubber energy of the inverter can be shortened and a stable feeding operation can be achieved.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an inverter according to an embodiment of the present invention, FIGS. 2 and 3 are time charts of signals at various parts of the circuit diagram, and FIGS. 4 and 5 are diagrams showing other inverters according to the present invention. FIG. 6 is a circuit diagram showing an example of a conventional inverter, and FIGS. 7 and 8 are time charts of signals at various parts of the circuit diagram. lU, lX are gate turn-or-thyristors, 2U. 2X is a reactor, 4U and 4X are snubbers, 5 is a diode circuit, 6 is a current transformer, 7 is a diode rectifier circuit, 8 is a thyristor rectifier circuit, and 9 is a self-extinguishing switching element. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Patent applicant Mitsubishi Electric Corporation No. 10 j+iz t3 Figure 5 Figure 6

Claims (1)

[Claims] A self-extinguishing switching element is used as an arm element, a reactor is connected in series to at least each of the positive and negative side arm elements, and each of the arm elements is provided with a snubber consisting of a series body of a snubber capacitor and a snubber diode, A diode or a feedback self-extinguishing switching element and the primary side of the current transformer are connected in series between the snubber diodes and the snubber capacitor of both snubbers, and this series connection body is connected between the snubber diodes and the snubber capacitors. An inverter equipped with a rectifier circuit that is inserted so as to form a closed circuit in which current circulates with the positive and negative side reactors, and that feeds back the energy stored in the snubbers from the secondary side of the current transformer to the DC power source. In this case, the rectifier circuit is constituted by a mixed bridge circuit consisting of a single-phase bridge in the diode section and a thyristor connected in series, and when the DC power supply voltage is low on the secondary side of the current transformer, the rectifier circuit is A tap is provided to feed back through the diode section, and when the DC power supply voltage is high, to feed back through the diode section and thyristor of the rectifier circuit, thereby compensating for a drop in the primary side voltage of the current transformer. An inverter featuring: