RU2523042C2 - Method of bidirectional switch control in three-level semiconductor rectifier - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: rectangular voltage pulse is generated, with middles of generated rectangular pulses synchronised with phase voltage of power supply network by moments of voltage transition over zero, effective value of first harmonic of rectifier phase current is measured, angle δ is calculated by expression

, where ω is circular frequency of phase voltage of power supply network; L is phase inductance of rectifier; I₁ is effective value of first harmonic in input phase current of rectifier; U₁ is effective value of first harmonic in phase voltage of power supply network, generated rectangular pulses are phase-shifted back by δ angle, then fed to control inputs of bidirectional switches of three-phase three-level semiconductor rectifier.

EFFECT: possible formation of unity rate for rectifier phase current shift against first harmonic voltage upon change of given current value.

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Description

The invention relates to electrical engineering and can be used to control a rectifier with a capacitive filter at the output when creating electromechanical systems, for example, when creating AC electric drives.

A known method of controlling bidirectional switches of a three-phase three-level semiconductor rectifier with a capacitive voltage divider (USSR author's certificate No. 1460761, bull. No. 7 02/23/1989), which consists in the fact that they form a reference voltage that exceeds the voltage drop on the thyristor, positive values of each measured voltage between the anode and cathode of the thyristor, the formation of a reference signal is carried out by summing all the selected positive values, compare the measured voltage I have a reference voltage, and the generated control pulse is fed to the thyristor control electrode, the voltage on which is greater than the reference voltage.

A significant disadvantage of this method is the formation of the input current of the rectifier non-sinusoidal shape, which significantly reduces the input power factor of a three-phase three-level rectifier.

. Передние фронты импульсов синхронизируют с фазными напряжениями питающей сети в моменты перехода напряжений через ноль, сформированные импульсы подают на управляющие входы двунаправленных ключей трехфазного трехуровневого полупроводникового выпрямителя (далее выпрямителя).In addition, a method is known for controlling bidirectional keys of a three-phase three-level semiconductor rectifier (Mehl, E. LM, and Barbi, I. "Designe Oriented Analysis of a High Power Factor and Low Cost Three-Phase Rectifier", Proceeding of the 27 ^th IEEE Power Electronics Specialists Conference, Baveno, Italy, June 23-27, Vol.1, PP. 165-171, 1996.), which is the prototype of the invention, in which rectangular voltage pulses of duration $$\frac{\pi }{}$$$$\frac{}{6}$$

. The leading edges of the pulses are synchronized with the phase voltages of the supply network at the moments when the voltage passes through zero, the generated pulses are fed to the control inputs of the bidirectional keys of a three-phase three-level semiconductor rectifier (hereinafter rectifier).

A significant drawback of this method is the tight binding of the leading edges of the voltage pulses to the moments of phase voltage transitions through zero and, as a result, the inability to form a unit phase shift coefficient of the rectifier relative to the voltage at the first harmonic when changing the magnitude of this current.

The objective of the invention is to provide a control method that allows you to generate a unit phase shift coefficient of the rectifier current relative to the voltage at the first harmonic when changing the value of this current.

, середины импульсов синхронизируют с фазными напряжениями питающей сети по моментам перехода напряжений через ноль, измеряют действующее значение первой гармоники фазного тока выпрямителя, вычисляют значение угла 6 согласно выражениюThe solution to this problem is achieved by the fact that in the known method of controlling bidirectional keys of a three-phase three-level semiconductor rectifier with a capacitive voltage divider, rectangular voltage pulses of a duration equal to $$\frac{\mathrm{<figure-callout\; id="6"\; label="\pi "\; filenames="00000010.png"\; state="\{\{state\}\}">\pi </figure-callout>}}{6}$$

, the midpoints of the pulses are synchronized with the phase voltages of the supply network at the moments of voltage transitions through zero, the effective value of the first harmonic of the phase current of the rectifier is measured, the value of the angle 6 is calculated according to the expression

where: ω is the angular frequency of the phase voltage of the supply network;

L is the phase inductance of the rectifier;

I ₁ - the effective value of the first harmonic of the current input phase of the rectifier;

U ₁ - the effective value of the first harmonic of the phase voltage of the supply network.

The generated rectangular pulses are phase shifted in the direction of lag by an angle δ relative to their midpoints, and then fed to the control inputs of the bidirectional keys.

Figure 1 shows the structural diagram of a control system that implements the proposed method for controlling bidirectional keys in a three-phase three-level semiconductor rectifier capacitive voltage divider; figure 2 - diagrams explaining the control method; figure 3 is a vector diagram of the currents and voltages acting in the input phase of the rectifier.

The device (figure 1) contains a three-phase supply network of sinusoidal voltages 1, 2, 3. The first phase of the supply network is connected to the input of the phase reactor 4, the second and third phases of the supply network are connected to the inputs of the phase inductors 5 and 6, respectively. The outputs of the phase chokes 4, 5, 6 are connected to the inputs 7, 8 and 9 of a three-phase three-level rectifier (TTV) 10, forming the input phase of the rectifier. A current sensor 11 is included in one of the input phases of the rectifier. At the same time, the phases of the supply network are connected to the inputs of the pulse generator 12. The output of the current sensor 11 is connected to the input of the calculation unit 5-13, the output of block 13 is connected to the first input of the shift unit 14, the second, third, and the fourth inputs of which are connected to the pulse generator 12. The outputs of block 14 are connected to the control inputs of the bidirectional switches 15, 16, 17. Each bi-directional switch is connected to the input phase of the rectifier by one output, and by the other output to the common point 18 of the output capacitors 19, 20 connected in series. Parallel to the output capacitors, a load (H) 21 is connected, which is also connected to the output of the rectifier.

, середины которых синхронизируют с фазными напряжениями питающей сети по моментам перехода напряжений через ноль. Полученные импульсы с блока 12 поступают на второй, третий и четвертый входы блока сдвига импульсов 14. С помощью датчика тока 11 измеряют величину действующего значения первой гармоники тока входной фазы выпрямителя, полученное значение передают в блок вычисления угла δ 13. Вычисляют значение угла 5 и полученное значение передают в блок сдвига 14. В блоке сдвига 14 импульсы сдвигают по фазе в сторону отставания на угол δ (фиг.2, а, б). Импульсы, сдвинутые по фазе в сторону отставания на угол δ по отношению к фазному напряжению 1 питающей сети, подают на управляющий вход двунаправленного ключа 15. Импульсы, сдвинутые по фазе в сторону отставания на угол δ по отношению к фазным напряжениям 2, 3 питающей сети, подают на управляющие входы двунаправленных ключей 16 и 17 соответственно. Двунаправленные ключи переключают согласно импульсам и формируют на входах 7, 8 и 9 относительно общей точки 18 напряжения: u_7-18, u_8-18, u_9-18 (фиг.2, в, г, д). Соответственно, между нулем питающей сети и общей точкой 18 формируют напряжение (фиг.2, е) согласно выражению:The method of controlling bidirectional keys of a three-phase three-level semiconductor rectifier is as follows. In the pulse generator 12 form a rectangular voltage pulses of duration $$\frac{\pi }{}$$$$\frac{}{6}$$

, the midpoints of which synchronize with the phase voltages of the supply network at the moments of voltage transitions through zero. The received pulses from block 12 are fed to the second, third and fourth inputs of the pulse shift unit 14. Using the current sensor 11, the value of the effective value of the first harmonic of the current of the input phase of the rectifier is measured, the obtained value is transferred to the block for calculating the angle δ 13. The angle 5 is calculated and the obtained the value is transmitted to the shear unit 14. In the shear unit 14, the pulses are phase shifted in the direction of the lag angle δ (Fig. 2, a, b). The pulses are phase-shifted in the direction of the delay by an angle δ with respect to the phase voltage 1 of the supply network, and are fed to the control input of the bi-directional switch 15. The pulses are phase-shifted in the direction of the delay by an angle of δ relative to the phase voltages 2, 3 of the supply network served on the control inputs of bidirectional keys 16 and 17, respectively. Bidirectional keys are switched according to the pulses and formed at the inputs 7, 8 and 9 relative to the common voltage point 18: u _7-18 , u _8-18 , u _9-18 (Fig.2, c, d, d). Accordingly, between the zero of the supply network and the common point 18, a voltage is generated (FIG. 2, e) according to the expression:

At the inputs 7, 8 and 9 relative to zero of the supply network form voltage u ₇₀ , u ₈₀ , u ₉₀ according to the expressions:

u ₇₀ = u _7-18 -u _0-18 ;

u ₈₀ = u _8-18 -u _0-18 ;

u ₉₀ = u _9-18 -u _0-18 ;

the first harmonics of which are obtained shifted in phase in the direction of the lag relative to the phase voltages of the supply network by an angle δ (in Fig. 2, g only voltage u _{70 is} shown).

Thus, the voltage shift u ₇₀ , u ₈₀ , u ₉₀ relative to the phase voltage of the supply network by an angle δ is a condition that ensures the formation of a unit shear coefficient of the first harmonic of the rectifier phase current.

We show this by analyzing the vector diagram of figure 3. From the vector diagram it can be seen that in order to form a unit phase shift coefficient of the rectifier current relative to the voltage at the first harmonic, when the magnitude of this current changes, it is necessary to change the angle δ according to the following expression

Thus, the proposed method allows you to generate a unit phase shift coefficient of the rectifier current relative to the voltage at the first harmonic when changing the value of this current, unlike the prototype, where the angle between the phase voltages of the supply network and the first harmonic of the voltages u ₇₀ , u ₈₀ , u _{90 is} constant and not varies from the magnitude of the current input phase rectifier.

Claims (1)

A method for controlling bidirectional switches in a three-phase three-level semiconductor rectifier with a capacitive voltage divider, which consists in the formation of rectangular voltage pulses of duration

which are fed to the control inputs of bidirectional keys of a three-phase three-level rectifier, characterized in that the midpoints of these rectangular pulses are synchronized with the phase voltages of the supply network at the moments of voltage transition through zero, the effective value of the first harmonic of the rectifier phase current is measured, the angle value δ is calculated according to the expression

,
where: ω is the circular frequency of the phase voltage of the supply network;
L is the phase inductance of the rectifier;
I ₁ - the effective value of the first harmonic of the current input phase of the rectifier;
U ₁ - the effective value of the first harmonic of the phase voltage of the supply network,
the formed rectangular voltage pulses are phase shifted in the direction of lag by an angle δ, and then fed to the control inputs of bidirectional keys.

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