RU2475930C1 - Device for protection of matrix cascade frequency converter - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: device for protection of a matrix cascade frequency converter that contains (in every m-phase of the power part) n cascades (matrixes) of bridge circuits on IGBT-modules (the outputs of each cascade bridge circuits, via contactors, are connected to (mxn) potentially loose 3-phase power supplies, a microprocessor control system (CS) generating controlling opto-signals for the driver devices performing the bridge circuit cascades keys switching on/off and current protection; the protection device consists of (m×n) units with balancing capacitor, each of them connected (via a 3-phase rectifier), to the said bridge circuits inputs; introduced into each unit circuit are a current sensor and a threshold element (varistor) placed in series with the balancing capacitor bypassed with a dummy burden resistor; the current sensors outputs are summed in pairs and connected (via the signal converters boards) to the CS that ensures (relying on a signal from the current sensor) snowballing processes of switching off the keys of IGBT-modules of the other cascades in the same or other phases and contactors switching off at the inputs of each cascade bridge circuits.

EFFECT: triggering reliability enhancement combined with the implementation process simplification.

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Description

1. Field of technology.

The present invention relates to the field of semiconductor converting technology, in particular to direct frequency converters (NFC) for regulating high-voltage AC electric motors of high power.

2. The prior art.

A control device for a 3-phase two-link LPC based on fully controllable keys of IGBT modules with two-sided conductivity using the software method of high-frequency adaptive pulse-width modulation (PWM), described, for example, in [1; 2].

In the specified frequency converter as a device for compensating reactive (inductive) currents of the supply network when switching keys at a PWM frequency, incl. in emergency situations with switching errors, the method of connecting a capacitor bank to the input terminals of the low frequency drive is used. Such a solution to the problem leads to additional energy losses, i.e. to a decrease in efficiency in normal NPP modes, as well as to an increase in overall dimensions.

Closest to the technical solution to the claimed device is a method and device for protecting a single-stage matrix low-frequency converter on the managed keys of IGBT modules with two-sided conductivity and high-frequency PWM, described in [3] (prototype). In this NPC, a rather complex algorithmic method of protection is used, which includes the stage of detecting a switching error, and then implementing the protection itself, which requires appropriate programming.

However, this protection method is itself susceptible to errors and programming failures. In addition, in the protection device there is a unit with a compensating capacitor, which is connected to the input terminals by means of a 3-phase rectifier and, therefore, is continuously under the rectified voltage of the supply network, which leads to a decrease in the efficiency in normal operating conditions of the low frequency drive.

3. A brief description of the drawings.

The invention is illustrated in the drawing (figure 1), which shows a block diagram of a known matrix 4-stage frequency converter (MFC) with a high-frequency sinusoidal PWM [4] and the proposed device for its protection.

In the presented block diagram of figure 1, the following notation is used:

1 - power unit 2 - microprocessor control system (SU); 3 - fiber optic communication line; 4 - cascade (matrix) of the IED; 5 - vacuum contactor; 6 - potentially isolated power sources (secondary windings of the transformer); 7 - block protection device; 8 - adder; 9 - optical converter board; 10 - opto-signal converter board; 11 - board reverse conversion of optical signals; 12 - contactor control device; U _sa , U _sb , U _sc - supply voltage.

Each cascade (matrix) of the IEDC under consideration is built on fully controllable keys of IGBT modules with two-sided conductivity according to the bridge circuit. Figure 2 shows the electrical circuit of one cascade (matrix) of the said MFC and the circuit of one block of the protection device.

In the presented scheme (figure 2) of one cascade, the following notation is used:

4.1 - keys of IGBT modules with two-sided conductivity; 4.2 - driver device boards; 7.1 - 3-phase rectifier; 7.2 - current sensor; 7.3 - threshold element (varistor); 7.4 - compensating capacitor; 7.5 - ballast resistor; U _tm , i _2tm , L _tm , where (m = a, b, c) are the voltages, currents and intrinsic inductances of the phases of the secondary winding of the transformer (power source); ΔU _ta , ΔU _tb , ΔU _tc - overvoltage in the phases of the power source; ~ U _d , i _d , R _d , L _d - output voltages, current and equivalent load parameters of one stage.

Figure 3 shows the appearance of the protection device with two blocks located on a common board installed in the prototype MCPC.

4. Disclosure of the invention.

The proposed device protection matrix cascade frequency converter in comparison with the prototype [3] is characterized by a simpler process for implementing protection, in particular, it does not have the stage of detecting switching errors, and thereby increase the reliability of protection.

The specified technical result is achieved due to the rejection of the algorithmic method of protection while simultaneously introducing into each block with a compensating capacitor present in the prototype [3] a current sensor and a threshold element (varistor) with a non-linear current-voltage characteristic.

The proposed protection device m-phase (A; B; C) matrix n-cascade frequency converter (figure 1), consisting of a power unit 1, a microprocessor control system (SU) 2 and fiber optic communication lines (FOCL) 3, includes n × m blocks 7, the input terminals of each of which are connected to the input power terminals of one of the n × m stages 4.

The structure of each block of the protection device 7 includes (Fig. 2) a 3-phase rectifier 7.1, the output of which through a current sensor 7.2 and a threshold element (varistor) 7.3 is connected to a compensating capacitor 7.4, shunted by a ballast resistor 7.5.

The outputs of the current sensors 7.2 of each block 7 in pairs by means of an adder 8 are combined into one common channel connected to the board of the optical converter 9, which in turn is connected via the FOCL 3 channels to microprocessor control system 2. The latter is connected via the FOCL 3 channels through the optical signal converter boards 10 connected to driver device boards 4.2, which have the function of their own protection of keys of IGBT modules 4.1 from currents (i _2ta ; i _2tb ; i _2tc during overloads and short circuits (short circuit).

In addition, SU 2 (Fig. 1) is connected via fiber optic channels 3 to the inverse optical signal conversion board 11, the output of which is connected to the control device 12 of the contactors 5.

The proposed protection device works as follows: If during normal operation in one of the cascades 4 (figure 2) of any phase of the MFC, an emergency occurs for one of the following reasons:

- due to the operation of the personal protection of a driver device 4.2 to disconnect the keys of the IGBT module 4.1 from overload currents or short circuit in the input or output circuit;

- due to a break in the circuits of the formation or sewerage of the control electric or optical signals to turn on the keys of IGBT modules 4.1;

- due to a software error in the key switching algorithm of the IGBT modules 4.1,

then the power circuit of this cascade 4 is open at least in one phase.

As a result, due to an _open circuit of the input currents (i _2ta ; i _2tb ; i _2tc ), the inductances (L _ta ; L _tb ; L _tc ) of the power source (secondary winding of the transformer) 6 cause an overvoltage surge (ΔU _ta ; ΔU _tb ; ΔU _tc ). When exceeding the voltage level determined by the threshold element (varistor) 7.3, the input currents (i _2ta ; i _2tb ; i _2tc ) are closed by the circuit: 3-phase rectifier 7.1 - current sensor 7.2 - threshold element 7.3 - compensating capacitor 7.4 - ballast resistor 7.5 .

The resulting electrical signal at the output of the current sensor 7.2 is fed to the optical converter board 9, which generates an optical signal and passes it through the fiber optic link 3 to microprocessor control system 2. The latter, in accordance with the program of its operation, interrupts the supply of control optical signals to the driver device cards 4.2 of the remaining stages in this and in two other phases, by turning off the keys of all IGBT modules 4.1 of the MKHR. In addition, SU 2 (Fig. 1) generates opto-signals for switching off the contactors 5, which are fed via fiber optic channels 3 to the boards for the inverse conversion of opto-signals 11 into electrical signals that act on the control devices 12 of the contactors 5 of each stage 4 in each phase (A; B ;FROM).

Thus, after an emergency occurs in one of the cascades 4 of any phase, for at least one of the above reasons, the input circuit of the 3-phase power supply is open and the reactive energy of the power supply 6 is automatically compensated by the proposed protection device 7, causing avalanche-like processes to turn off the IGBT keys -module 4.1 of the remaining stages in this and other phases and disconnection of the contactors 5 at the inputs of the bridge circuits of each stage 4 in all phases (A; B; C) of the MFC. Moreover, on the compensating capacitor 7.4 in the initial state, due to the presence of the threshold element 7.3, there is no voltage, which contributes to an increase in the efficiency in normal operation of the MFC compared to the prototype low-frequency filter [3].

5. The implementation of the invention.

The proposed protection device is designed and manufactured in the form of a separate board with two blocks according to the scheme of figure 2 for installation in a prototype matrix cascade frequency converter, designed to power a high-voltage AC propeller.

Figure 3 shows the appearance of the protection device with two blocks located on a common board installed in the cabinet of the prototype matrix 4-stage frequency converter type NPCH-4,5-100UHL4 according to the scheme of figure 1 with a capacity of 1.0 MW.

Literature

1. Device and method for controlling a reversible converter of AC energy into AC energy. Shreiner R.T., Efimov A.A. and others. Patent RU No. 2265947 C2, class. Н02М 5/27 from 07/09/2002.

2. The method of frequency conversion. Shreiner R.T., Krivovyaz V.K. and others. Patent RU No. 2269860 C2, class. Н02М 5/16 from 09.16.2003.

3. Method and apparatus for protecting PWM cycloconverter. Sawa Toshihiro, ... Patent Yap. No. EP 1154552, class Н02М 5/27 dated 11/14/2001.

4. The device for forming and regulating the voltage of the matrix direct frequency converter with a high-frequency sinusoidal PWM. Skvortsov B.A., Vasin I.M. and other Application No. 201029681/07 of 07.15.2010. (Decision of the Federal Service of ROSPATENT on the grant of a patent for an invention No.2012929681 / 07 (042187) dated 02.02.2011).

Claims (1)

A protection device for a matrix cascade frequency converter containing in each m phase of the power part of n-cascades (matrices) of bridge circuits on IGBT modules with keys of double-sided conductivity, and the inputs of the bridge circuits of each cascade through contactors are connected to (m × n) potentially decoupled 3 phase power supplies (secondary windings of transformers), a microprocessor control system (CS) that generates control optical signals for driver devices that enable, turn off and current protect keys connected cascades of bridge circuits, consisting of (m × n) blocks with a compensating capacitor, each of which is connected to the inputs of these bridge circuits through a 3-phase rectifier, characterized in that a current sensor and a threshold element (varistor) are introduced into the circuit of each block connected in series with a compensating capacitor shunted by a ballast resistor, the outputs of the current sensors are summed up in pairs and connected to the microprocessor control system through the boards of the signal converters, which in case of emergency tion in one stage provides a signal from detector current avalanche process off IGBT-modules keys other stages in this and other phases and at the inputs of switching off the contactor bridge circuits of each stage.

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