SU1688359A1 - Autonomous current inverter - Google Patents

Description

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(21) 4605450/07 (22) 11/14/88 (46) 10.30.91. Bulle # 40

(71) Electrotechnical Research Institute of Production Association KhEMZ

(72) V.A.Reznikov, V.V. Zhenov and A.S. Ivashchenko

(53) 621.314.572 (088.8)

(56) USSR Copyright Certificate No. 748742, cl. H 02 M 7/515, 1978.

For Japan No. 58-22944, CL. H 02 M 7/515, 1983. (54) AUTONOMOUS CURRENT INVERTER

(57) The invention relates to converter technology, more specifically to autonomous current inverters in frequency converters for drives with a short-circuited asynchronous motor of small and medium power for various industries. The purpose of the invention is to increase reliability, simplification due to circuit design. The device contains a three-phase bridge rectifier 1 connected to the network, and the output through electronic switches 2, 3 - to the inverter input of the frequency converter, the output of which is connected to the asynchronous machine 10, parallel to the input of the current inverter is a thyristor voltage inverter driven by the network 11, moreover, the current inverter at the input is shunted by series-connected electronic switch 12 and diode 14. 1 sludge.

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The invention relates to converter technology, and more specifically to autonomous current inverters in frequency converters for drives with a short-circuited asynchronous motor of small and medium power for various industries.

The aim of the invention is to increase reliability by simplifying the circuit design.

The goal is achieved by the fact that the inverter containing a DC power source, which is connected to the DC terminals of the inverter's main thyristor by the output terminals through the electronic switches, is outputted via electronic keys to the DC-based inverters. A driver connected to the mains and connected in parallel with the terminals of the input of the current inverter of the thyristor voltage inverter driven by the network.

The drawing shows the scheme of the proposed autonomous current inverter.

The device contains a three-phase bridge rectifier 1, made on diodes and connected to a three-phase AC network with a frequency of 50 Hz. The output terminals of the rectifier 1 are connected via electronic keys 2,3 to the terminals of the inverter of the main thyristors 4-9 of the current inverter, connected to an asynchronous machine; parallel to the output terminals of the current inverter is a voltage inverter 11, driven by a network, made on a three-phase bridge circuit on thyristors and connected to a three-phase supply network of alternating voltage the current inverter is shunted by the serially connected electronic switch 12 and diode 13, in addition, the electronic switch 12 is also shunted by diode 14. The control unit 15 controls the thyristors 4–9 current inverters, controls the keys 2, 3, 12 and controls the thyristors of the inverter 11, for example network driven.

A current meter 16 (shunt) and a high-frequency zero-current sensor 17 are installed between the connection output of the cathode group of the thyristors 5, 7, 9 of the current inverter and the common connection point of the electronic switches 3, 12 of the cathode of the diode 14 and the anode group of the thyristors of the voltage inverter 11.

The thyristors of the inverter 11 of the voltage driven by the network are continuously triggered by pulses with a duration of 120 °, at times corresponding to the inverter mode of operation of the voltage inverter. The angle corresponding to the inverter mode is set to 150 °. In this case, the output voltage of the inverter 11 voltage in accordance with the formula is equal to

Ud 1.35Un cos a,

silt - line voltage;

and - thyristor control angle. With 1) „380 V and a 150 ° Ud 1.35-380 cos150 ° 446.3 V.

As electronic switches 2, 3, 12 (as shown in Fig. 1), transistors are used (for example, a 2M2-40-7 transistor module with parameters: I 40 A. U 70 ° C). Instead of transistors 2, 3, 12 can be

lockable thyristors are used.

The control unit 15 includes a system for controlling the current and frequency of the converter. The rate of change of frequency is determined by the intensity adjuster,

connected to the input of the master oscillator, the output of which is connected to a counting ring defining the order of the control signals to the thyristors of the current inverter. According to the motor current, the control signal is generated, which is compared in the comparators circuit. The control system contains logical device key management logic.

The device works as follows.

With the initial setting of the frequency converter equal to zero, the electronic switches 2, 3, 12 are open. When submitting the task

the current inverter current signals to turn on the transistors 2, 3 and 12 and let the signals to turn on the thyristors 4 and 7 are given. When turning on the transistors 2 and 3, the current 1and is indicated by the arrow

the directions in FIG. 1, under the influence of voltage, rectifier 1 is increasing. When exceeding the value of a given current, the value of which can be regulated by the installation in the control unit 15,

A control signal is issued to turn off transistors 2 and 3, and transistor 12 remains on. With the opening of the transistors 2 and 3, the current 1H under the influence of the emf self-induction windings a and b of the stator

induction motor 10 begins to flow along the circuit: thyristor 7 is transistor 12 and diode 13 is thyristor 4, i.e. shunting of windings a, b of the stator of the motor occurs through the listed elements. When the current value decreases, n in relation to the setpoint set by the control system of the unit 15, the signal for turning on the transistors 2 and 3 is issued again. At the set time of the thyristors

4 and 7 of the current inverter, determined by the given frequency of the converter, the continuity of the specified load current is provided by switching the transistors 2, 3 and the operation of transistor 12. This ensures a low level of current ripple in the load. When forming the operation of thyristors 4 and 9 and the need to turn off the operation of thyristor 7, the control system of unit 15 releases control signals from transistors 2, 3, 12 and removal of control signals from thyristors 4, 7 of the current inverter. When transistors 2, 3 and 12 are disconnected, the current n under the influence of the electromotive force of the inverter 11 of the voltage driven by the network decreases and flows as shown in FIG. 1 dotted line, i.e. forced quenching of current in the windings a and b of the motor stator into the network occurs due to the output voltage of the inverter voltage, driven by the network. When the current drops to zero, the thyristors 4, 7 are closed by the current inverter. The control system of the unit 15, receiving a signal from the high-frequency sensor 17 of the zero current about the absence of current in the load, processes it and, after a pause in time of 0.3-0.5 ms, turns on the transistors 2, 3, 12 and applies control signals to thyristors 4, 9 current inverter, i.e. the inclusion in the work on the flow of current in the winding a and C. When transistors 2, 3 are turned on under the influence of the voltage of the rectifier 1, the current increases. When the set current is exceeded, the keys 2, 3 are turned off and the current begins to fall through the switched on thyristors 4, 9 - transistor 12 and diode 13, i.e. the process of maintaining a given current and a further transition to the operation of the other phases of the current inverter is the same as described.

The necessary pause in the current inverter current in time is 0.3-0.5 ms, as described, between switching the operation of other phases is necessary for the accurate closing of the working thyristors after the open state (the time for restoring the closed state of the thyristor, as is known, is 30 100µs).

The principal feature in maintaining a given current is that the formation of electromagnetic processes, the rise and fall of the current in the switching circuits occur by a variable factor, i.e. the current rise is forced when the transistors 2 and 3 are turned on, and the decrease is slow due to the current inverter shunting the transistor 12. The shunting transistor 12 when the load current decreases significantly

reduce the switching frequency of the transistor. -m; 2, 3, while maintaining the current and facilitating their r-chbotu, in addition to this, it was possible to improve the energy performance when the electricity consumption from the network.

For this frequency converter, the normal operating mode is both power consumption mode and power recovery to the network, which contributes to

0 also improve energy performance,

In the inverter of the current frequency converter and in the inverter of the voltage driven by the network, conventional thyristors and optocoupler thyristors, for example, TO2 40-9 (with 40 A, 900 V) can be used. When using optocoupler thyristors that have the potential isolation of control electrodes from the power

0 thyristor circuit; schematic solution of thyristor control of current inverter and voltage inverter, driven by the network, is simplified, since no pulsed transformer nodes are required

5 when using conventional thyristors and carrying out potential isolation between low-voltage control circuits and high-voltage circuits of the power section. Pause in the absence of current in the engine

Claims (1)

0 (0.3-0.5 ms) does not affect the speed control characteristics, while the time does not change the speed, since the time of the absence of current is very small relative to the constant time of the engine flywheel and load. Claims of the invention A stand-alone current inverter comprising a series-connected input bridge rectifier and an output 0 the current inverter, as well as the inverter, driven by a network, the inputs of which are connected to the input terminals of the inverter, and the cathodes of the cathode group of the thyristors are connected to the cathode output of the rectifier, 5 anodes of anode group - with anode output of a rectifier, characterized in that, in order to increase reliability, it is equipped with three key elements, two diodes, a current meter and a high0 frequency zero current sensor, and a key element is included in the circuit of each output terminal of the rectifier the current inverter input is shunted by a series-connected diode and a third key 5, an element that is shunted by a reverse diode, and between the connection point of the transistor and the cathodes of the cathode group of the output inverter thyristors are connected in series to the current meter and high-frequency zero current sensor.