RU2428783C1 - Method of formation and control of high voltage of matrix cycloconverter of cascade type with high-frequency sine pulse-width modulation - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: there proposed is method of formation and control of high voltage of matrix cycloconverter of cascade type with high-frequency sine pulse-width modulation (PWM), each cascade (matrix) of which is built on completely controlled switches of IGBT-modules with two-sided conductivity as per bridge circuit. Method is implemented by introduction of natural drop of reactive (inductive) currents in phases of power supplies at their rectification and in phases of electric motor at switching of switches in mode of formation and control of output voltage by high-frequency bipolar PWM method. The proposed method has been implemented in software of prototype of matrix cycloconverter of cascade type with high-frequency sine PWM, which is intended to control high-voltage heavy-duty propulsion motor in electric propulsion systems of advanced heavy-tonnage vessels, e.g. ice navigation vessels and icebreakers of new generation.

EFFECT: increasing the efficiency and decreasing mass and dimensions parameters owing to excluding units with balancing capacitors at input terminals of cycloconverter at maintaining high quality parameters of electric power both on the side of supply mains and on the side of motor load.

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Description

1.1. The 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.

1.2. The prior art. A known method and device for controlling a frequency converter constructed according to the scheme of a 3-phase two-link low-frequency converter on IGWT modules, as on fully controllable keys with two-sided conductivity using the software method of high-frequency adaptive pulse-width modulation (PWM) for generating input and output currents and regulation output voltage, described, for example, in [1; 2].

In these sources of information as a method and device for compensating reactive (inductive) currents of the supply network, i.e. To maintain the continuity of the flow of currents in the circuits from the power sources to the phases of the electric motor when switching the keys both at the mains frequency and at the high PWM frequency, a method is used to connect the capacitor bank to the input terminals of the low frequency filter. Such a solution to the problem leads to additional energy losses, i.e. to reduce efficiency, as well as to increase the overall dimensions of the NPP.

In addition, the two-link low-frequency converter on IGWT modules with high-frequency PWM has a drawback due to the presence of two links in the conversion circuit, which also leads to additional power losses and to a reduction in efficiency.

Closer in the method of formation and regulation of the output voltage to the claimed method is a single-stage single-stage matrix array of low-frequency filters on IGWT modules with two-sided conductivity and high-frequency PWM, described in [3]. However, in [3], a method and device for protecting this circuit from emergency situations is patented, in which there is also a block with compensating capacitors connected to the input terminals.

The closest in technical essence to the claimed method is a method of forming a high voltage in the Converter according to the scheme of a single-link matrix cascade type NPC described in [4] (prototype).

In the specified converter, built on fully controlled keys of IGBT modules with two-sided conductivity, connected in each cascade by a 3-phase bridge circuit, the cascade principle of generating a high voltage at the output when powered from potentially isolated power sources using the software method of high-frequency sinusoidal PWM for its regulation. However, the keys of the bridge circuits in the specified converter operate in invert mode with an on-state duration of 120 ° el., And to maintain the continuity of the flow of currents in the circuits from voltage sources to the phases of the electric motor, the blocks necessary in this case with compensating capacitors are used.

1.3. A brief description of the drawings.

The invention is illustrated in the drawing (figure 1), which shows a block diagram of a three-phase matrix cascade type low-pass filter with a high-frequency sinusoidal PWM with an asynchronous motor winding connected to it.

Figure 2 shows the electrical circuit of one cascade (matrix) of the aforementioned NFC, built on fully managed keys of IGBT modules with two-sided conductivity in a three-phase bridge circuit. In the shown diagram of one cascade of a three-phase bridge, the following notation is used: 1 ... 6 - managed keys of IGBT modules; 7 ... 12 - snubber capacitors; 13 - driver devices; U _tm , i _2tm , R _tm , L _tm , where (m = a, b, c) is the voltage, currents and phase parameters of the secondary winding of the transformer (power source); i _i (i = 1 ... 6) - currents in the bridge keys; ~ U _d , i _d , е _d , R _d , L _d - output voltage and current, as well as the emf and phase parameters of the motor load.

Figure 3 presents the timing diagrams of the control signals during the formation of a high-frequency sinusoidal PWM for the keys of one cascade of the bridge circuit and the calculated curves of the phase current and voltage at the input and output terminals of the device according to the claimed method.

The following notation is used in the presented diagrams and curves: U _ta , U _tb , U _tc - voltage of the phases of the secondary winding of the transformer; U _on - reference high-frequency sawtooth voltage; U _y - voltage control duty cycle sinusoidal PWM; J ₁ , J ₂ , J ₃ - resolution functions of the PWM of the shoulders of the bridge; K ₁ , K ₂ ... K ₆ - the state function of the shoulders of the bridge; i _dA , i _dB , i _dC , U _dA , U _dB , U _dC - the calculated phase currents and voltages at the output of the LPC according to the scheme of figure 1 (on the terminals of the motor).

1.4. Disclosure of invention

The claimed method is implemented in a device matrix cascade type NPC with a high-frequency sinusoidal PWM, which provides an increase in efficiency compared to the prototype [4] and a decrease in its overall dimensions due to the exclusion of blocks with compensating capacitors while maintaining high parameters of the quality of electricity both from the supply network and from the electric motor.

The indicated technical result is achieved by introducing a natural decrease in reactive (inductive) currents in the phases of the power sources when they are switched in the bridge circuits (matrices) of each stage in the rectification mode and in the phases of the electric motor when the keys are switched in the mode of generating and regulating the output voltage by the high-frequency sinusoidal bipolar PWM method.

Cascade type high-frequency matrix array device. a sinusoidal PWM that implements the claimed method consists of a t-phase power unit 1 and a microprocessor control system (SU) 2 with a control panel 3 (figure 1). Each m-phase (A; B; C) of the power unit 1 contains n-cascades of bridge circuits 4 (matrices). The inputs of the bridge circuits 4 by means of contactors 5 are connected to (m × n) potentially decoupled three-phase power supplies (secondary windings of transformers) 6 with a low voltage level, half of which is connected by a "star" and the other: half by a "triangle", which contributes to improvement of parameters, quality of electricity from the supply network. In addition, the inputs of the bridge circuits 4 are connected to voltage sensors 7, the outputs of which are in turn connected to the control system 2.

The outputs of the n-stages of the bridge circuits 4 of each phase are interconnected in series according to one another and are connected on the one hand through phase current sensors 8 to the phases of the electric motor 9, and on the other hand are connected to a common point. Each stage of the power unit 1 is built on IGVT modules 1 ... 6 (Fig.2) with keys, two-sided conductivity, shunted by snubber capacitors 7 ... 12 and connected by a three-phase bridge circuit.

The method of forming and regulating the high voltage matrix cascade type LPC with a high-frequency sinusoidal PWM is implemented as follows.

The signal from the control panel 3 SU 2 (figure 1) enables the contactors 5 and thereby supply power from (m × n) the secondary windings of the transformers 6 to the inputs of the bridge circuits 4 of each n-th cascade.

The control signals received from the SU 2 to the driver device 13 IGVT modules 1 ... 6 (figure 2), enable and disable the keys on the shoulders of the bridge circuits 4 in the rectification mode with a control angle α = 0 with a duration of allowed opening of the keys (120 ° + γ) email. for both half-waves of the output voltage ~ U _d . The signals from the voltage sensors 7, entering the control system 2, provide synchronization of the control signals of the keys of the bridge circuits 4 in frequency and phase with the emf (е _2tm ) secondary windings of transformers 6.

The output voltages ~ U _{d of the} n-stages of the bridge circuits 4 in each m-phase (A; B; C) are summed up when they are turned on simultaneously, which ensures the required high voltage level in the sinusoidal PWM mode. Next, the sum of the voltages ~ U _d from the n-stages of the bridge circuits 4 of each m-phase enters through the phase current sensors 8 to the phases of the electric motor 9 (Fig. 1).

For the purpose of software implementation of the rectification mode of each bridge circuit (Fig. 2), PWM key resolution functions are introduced, which are synchronized in frequency and phase τ with the emf. e _2tm (m = a, b, c) of the power source. In this case, the instantaneous values of the PWM resolution functions J _i (i = 1, 2, ... 6) are determined by the following conditions (for one of the bridge groups) (Fig. 3):

The initial conditions J ₁ = J ₂ = J ₃ = 0

The increase in the duration of the resolution of the on state of the keys relative to the generally accepted in [3; 4] duration of 120 ° el. at the angle of commutation, (overlap) γ leads to the creation of a regime of natural decline of reactive (inductive) currents i _2tm , where m = a, b, c (Fig. 2), when they are switched in the bridge circuit. In this case, the duration of the switching angle γ at the beginning of each switching is calculated according to the functional dependence:

where: X _γ = inductive resistance (reduced) of the phase of the power source (secondary winding of the transformer);

i _d - current instantaneous value of the output current (phase current of the electric motor) at the time of switching;

E _2t - phase emf (actual value) of the power source (secondary winding of the transformer).

The indicated dependence of the switching angle γ as a function of the current value of the current i _d (phase current of the electric motor 9) is provided by the program of work of the control system 2 based on the information received from the phase current sensors 8 (Fig. 1).

In addition, SU 2 continuously forms known [1; 2] programmatically signals (direct and inverse) high, with sinusoidal PWM variable duty cycle (Figure 3) based on the comparison reference voltage U _op sawtooth control voltage and U _y sinusoidal.

When the signals of the sinusoidal PWM coincide with the resolution functions, the PWM J _{i of the} previous rectification mode, control signals are generated to turn the keys on and off at the shoulders of the bridge circuits, performing bipolar (positive or negative) connection of the “rectified” voltages ~ U _d (Fig. 2) simultaneously from each cascade of 3-phase power supplies 6 to the corresponding phases of the electric motor 9 (figure 1).

For software implementation of the state of the keys in the shoulders of the bridge circuit (figure 2), the state functions of the shoulders K _{i are used} , where: i = 1, 2, 3, 4, 5, 6. If the shoulder of the bridge is open, then K _i = 7. If the shoulder of the bridge is closed, then K _i = 0 (figure 3). With a bipolar PWM for the shoulders of the opposite group of the bridge, their inverse state is true:

где

Where

When the bridge circuit operates in a sinusoidal bipolar PWM mode, the values of the functions K _{i are} determined by the following conditions:

K ₁ = K ₂ = K ₃ = K ₄ = K ₅ = K ₆ = 0,

Thus, due to the introduction of a natural decrease in reactive (inductive) currents in the phases of the secondary windings of transformers when they are switched in n-cascades of bridge circuits of each m-phase of the LPC and in the phases of the electric motor when switching keys at a bipolar PWM frequency, continuity of the flow of currents from power sources is ensured to the phases of the electric motor. This eliminates the need for blocks with compensating capacitors at the input terminals of each stage of the matrix LPC.

1.5. The implementation of the invention.

The claimed method of forming and regulating the high voltage of a cascade type matrix low-frequency converter with a high-frequency sinusoidal PWM and its software are implemented in a prototype device according to the scheme of Fig. 1 without blocks with compensating capacitors. The mentioned prototype is designed to regulate a high-voltage propeller motor in the electric propulsion system of promising large-tonnage vessels, for example, ice navigation vessels and a new generation of icebreakers.

Figure 3 shows the timing diagrams of the control signals during the formation of a high-frequency sinusoidal bipolar PWM for one cascade of the NPC bridge circuit and the phase current and voltage curves at its input and output terminals, calculated on the basis of a mathematical model of the system consisting of a 1000 kW synchronous generator - matrix LPC - an asynchronous electric motor with a power of 800 kW at a supply frequency of 50 Hz, an output frequency of 17 Hz and a PWM frequency of 1200 Hz.

Literature

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

2. The method of frequency conversion. Shreiner R.T., Krivovyaz V.K. and other RF Patent No. RU 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. Matrix cascade frequency converter of СIMR-МХ1S type on IGВТ-modules with high-frequency PWM and with energy recovery for a high-voltage AC electric drive with power up to 6.0 MVA. - Prospectus of the company "Yaskawa Electric Corporation" (Japan), 2007

Claims (1)

1. The method of forming and regulating the high voltage of the cascade type direct matrix frequency converter with a high-frequency sinusoidal PWM, which contains n cascades of 3-phase bridge circuits in the m-phase power section on IGBT modules with double-sided conductivity keys shunted with snubber capacitors, the outputs of bridge circuits are connected in series according to, and the inputs are connected to (m × n) potentially decoupled 3-phase power supplies (secondary windings of transformers), using in a microprocess a known control system known programming method for generating control signals by high-frequency sinusoidal pulse width modulation (PWM) with adjustable duty cycle to control the moment of turning on and off the keys of these n stages of bridge circuits, characterized in that the control signals at the power frequency provide a rectification mode with a control angle α = 0 and with the duration of the permission for the included state of the keys (120 ° + γ) e. for both positive and negative half-waves of the output voltage, and at a high frequency sinusoidal PWM, in coincidence with the previous mode, bipolar (positive or negative) phases of 3-phase power supplies of each n-th stage are simultaneously connected to the corresponding phases of the electric motor, where γ - the angle of natural current decline in the phases of the power sources at the time of the beginning of each switching is calculated by the formula

X _γ - inductive resistance (reduced) of the phase of the power source (secondary winding of the transformer);
i _d is the current instantaneous value of the motor current;
E _2t - phase emf (effective value) of the power source (secondary winding of the transformer).

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