RU2227362C2 - Valve inverter - Google Patents

Abstract

FIELD: electrical engineering; inverters and computerized dc and ac drives. SUBSTANCE: valve inverter has power valve unit whose output is connected to load and control circuits of valves, to control device whose respective inputs are connected to regulation unit and to protective gear units; ac transformers installed in inverter phases with common-point resistors connected to their secondary windings; m-phase device for inverter output current module separation that incorporates single-phase precision rectifiers built around operational amplifiers; and adder. Inputs of rectifiers are connected to respective resistors and to their common point and outputs, to adder inputs; output of the latter is connected to respective inputs of regulation and protective gear units. EFFECT: simplified design, enhanced reliability, measurement accuracy, and precision of regulation. 2 cl, 4 dwg

Description

The invention relates to electrical engineering, in particular to the field of converter technology and automated electric drive.

Known valve semiconductor converter, which is the basis of the electric drive [1] and containing: power thyristor unit, a pulse-phase control system (SIFU), a control unit consisting of current and speed controllers of the motor; current sensor, thyristor conductivity sensor, logic device for separate control of thyristor sets, protection unit. The disadvantage of this regulation system is the difficulty in that it requires the use of current sensors and thyristor conductivity sensors, which are complex devices. Moreover, to regulate the current, a current sensor is used at the output of the converter connected to the shunt, and for the current protection device, information on the full current of the converter is required, which is carried out either using AC transformers installed in the phases of the converter, or using current reed relays or other devices. Thus, here the current regulator, the current protection device and the separate logic control device are controlled respectively from the three types of special devices (sensors) indicated above.

The closest in technical essence to the claimed solution and taken as a prototype is a thyristor converter, which is the basis of the electric drive EPU 1 manufactured by Cheboksary Electric Appliance OJSC [2].

The thyristor converter of the electric drive EPU 1 has the structure shown in figure 1, and contains: power thyristor unit 1, the load in the form of a DC motor 2, a pulse-phase control system (SIFU) 3, control unit 4, protection unit 5, unit 6 separate control (switching unit), AC transformers 7-9, resistors 10-12, a diode bridge rectifier 13 and a thyristor conductivity sensor 14. The disadvantage of the prototype is that the diode bridge rectifier 13 makes a significant error in the selection of information on the current of the converter, especially at low current values. The error is due to the significant value of the voltage drop across the rectifier bridge diodes, which is about 2-3 V. In this case, the reversing converters (as opposed to the non-reversing ones) use an additional switching unit 6, which is connected to the thyristor conductivity sensor 14. This sensor is a rather complex electronic device [2]. These features complicate the valve converter as a whole, reduce its reliability and accuracy of current regulation, especially when the ambient temperature changes and in the region of small current values.

The technical result of the proposed solution is to simplify the valve Converter, increasing its reliability and accuracy of current regulation. The technical result is achieved in that in a valve converter containing a power valve unit, the output of which is connected to the load, the control circuits of the valves are connected to a control device, the corresponding inputs of which are connected to the control unit and the protection unit, and AC transformers are installed in the converter phases, to the secondary windings of which are connected resistors having a common point, an m-phase device for isolating the rectified current module of the converter, containing precision single-phase output rectifiers based on operational amplifiers and an adder, while the inputs of the rectifiers are connected to the corresponding resistors and their common point, and the outputs to the inputs of the adder, the output of which is connected to the corresponding inputs of the control and protection unit; a switching unit has also been introduced, the input of which is connected to the output of the adder of the m-phase device for isolating the converter's rectified current module, and the output to the control device.

A distinctive feature of the invention is that the simplification, improving the reliability and accuracy of measuring and regulating the current of the converter is achieved by creating a multifunctional m-phase device for isolating the rectified current module of the converter, consisting of precision single-phase rectifiers and an adder, respectively connected to each other by current transformers, resistors and their common point and connected to the inputs of the blocks of regulation and protection. Moreover, in electric drive systems with reverse and engine braking, the m-phase module isolation device is also connected to a switching unit, which, for example, performs the function of a separate control unit in reverse thyristor converters.

Thus, the simplification, improving the reliability and accuracy of current regulation consists in creating and introducing into the converter a multifunctional device with its corresponding connections to the control unit, protection and switching.

Figure 2 shows a diagram of the inventive valve Converter, where the following notation:

1 - power valve block of the converter. As the converter can be a converter of alternating voltage to direct (figa) or alternating voltage to alternating (figb);

2 - load, for example, a DC motor (figa) or alternating current (figb);

3 - control device, for example, a pulse-phase control system (SIFU);

4 - control unit, for example, containing current and speed controllers;

5 - protection unit [2], including the maximum current and time current;

6 - switching unit. For example, in reverse thyristor converters it is a logic block for separate control of thyristor sets [2]. In AC converters (thyristor regulators) for an electric drive, this is a phase sequence change unit or a device for dynamic engine braking;

7-9 - AC transformers;

10-12 - resistors;

13 - m-phase device for isolating the rectified current module of the converter;

15-17 - precision single-phase rectifiers, made on the basis of an operational amplifier, measuring the module of the input signal, including in the millivolt range;

18 - adder.

U _s - the driving signal that determines the output parameter, for example, the speed of the engine 2;

U _оc - feedback signal, for example, by engine speed;

I _n - load current;

i _A , i _B , i _C are the currents in the phases of the converter made, for example, according to a three-phase bridge rectification circuit.

Figure 3 shows the operation diagram of the device 13, where U ₁₈ is the output voltage of the adder 18. In the proposed device, the power valve unit 1 is connected to the load 2, for example, with an electric motor, the control circuits of unit 1 are connected to the control device 3, the corresponding inputs which are connected to the control unit 4 and the protection unit 5; the power inputs of the valve unit 1 through the transformers 7-9 AC are connected to the mains, the secondary windings of the current transformers are shunted by resistors 10-12 having a common point, while the resistors 10-12 are connected to the inputs of the m-phase device 13 for selecting the rectified current module, consisting of precision single-phase rectifiers 15-17 and the adder 18, the inputs of which are connected to the outputs of the rectifiers 15-17 and the common point, and the output to the control unit 4 and the protection unit 5. The converter can be used for reversing and (or) braking the engine. For this, a switching unit 6 is introduced into it, the input of which is connected to the output of the adder 18 of the m-phase device 13 for isolating the converter rectified current module, and the output to the control device 3.

The device operates as follows.

Embodiment 1. Here, the non-reversible valve converter of FIG. 2a and 2b without block 6, which corresponds to claim 1 of the claims.

With a setpoint signal U _of the block at the output 4 there is control signal that is supplied to the unit 3 by determining an angle adjusting power block valves 1. Also drive signal to block 4 enters the main feedback signal U _oc, for example, engine speed 2. isolation a signal proportional to the rectified current I _{n of the} converter, an m-phase device 13 for isolating the rectified current module is introduced. On resistors 10-12 we obtain voltage drops proportional to the phase currents i _A , i _B , i _C , which are proportional to the load current I _n . Data voltage drops (up to 100 mW) are fed to the inputs of precision rectifiers 15-17, which together with the adder 18 emit a signal proportional to the value of I _n . The signal from output 18 is used as a current feedback signal at the inputs of blocks 4 and 5. In this case, in block 4, this signal is used for the current limiting unit, in block 5, for overcurrent and time-current protection.

Precision single-phase rectifiers, made on the basis of operational amplifiers, make it possible to measure signals with a high degree of accuracy, including the millivolt range. This provides a sharp decrease in voltage at the outputs of current transformers 7-9, and therefore reduces their dimensions, because the latter are determined by the relation

where W ₂ - the number of turns of the secondary winding of current transformers;

Q is the cross section of the magnetic circuit of the current transformer;

In _m - induction;

E ₂ - secondary emf in the winding W2, equal to the voltage drop across the resistors 10-12;

K is the coefficient.

From (1) it follows that the dimensions of transformers 7-9 can be reduced by reducing the product (W ₂ Q) by reducing E ₂ .

In this device, transformers 7-9 control the currents of all phases of the converter, including during emergency conditions (interphase short-circuit and earth fault).

In Fig.2b, the same control structure is used as in Fig.2a for an AC voltage converter, which is widely used in thyristor starters for AC motors.

Option 2. This option applies to the reversible DC / DC converter of FIG. 2a with block 6, as well as to the AC reverse converter of FIG. 2b with switching the alternation of two phases and (or) a device of dynamic engine braking, which corresponds to paragraph. 2 claims.

The difference between the options lies in the functional purpose of the converters, which is determined by the structure of the power unit 1 and the introduction to the control part of the regulation system of the switching unit 6. This unit in a reversible DC-DC converter (Fig. 2a) performs the function of a separate control unit and functions depending on the output signal of unit 13. In the prototype (Fig. 1), a complex block of the thyristor conductivity sensor was used for these purposes. The ability to use the current signal from the output of the adder 18 to control the conductivity of the converter valves is due to the high sensitivity of the unit 13, which greatly simplifies the device unit as a whole.

In a reversible AC converter (for example, in a thyristor starter), block 6 performs the function of controlling the switching of thyristors when changing the phase sequence during reversal and (or) dynamic braking of the motor. Thus, the device 13 in both versions of the converters is the same, unified and multifunctional, namely: it serves the current control channel, current protection and in the reversing converters - the switching unit.

Sources of information

1. Perelmuter V.M., Sidorenko V.A. Control systems for thyristor electric drives of direct current. - M .: Energoatomizdat, 1988, p. 67-90.

2. Electric drives the unified three-phase EPU1M series. Industrial catalog 08.41.11-99, UDC 62-83: 621.9.06 (085), GRNTI 45.41.33, pp. 7-12.

Claims (2)

1. A valve converter containing a power valve block, the output of which is connected to the load, and the control circuit is connected to a control device, the corresponding inputs of which are connected to the control unit and the protection unit, AC transformers installed in the converter phases, the secondary windings of which are connected to resistors, having a common point, characterized in that an m-phase device for isolating the rectified current module of the converter is introduced into it, including precision single-phase rectifiers based on operational amplifiers and the adder, while the inputs of the rectifiers are connected to the corresponding resistors and their common point, and the outputs to the inputs of the adder, the output of which is connected to the corresponding inputs of the control and protection units. 2. The device according to claim 1, characterized in that the switching unit is additionally introduced, the input of which is connected to the output of the adder of the m-phase device for isolating the converter rectified current module, and the output to the control device.

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