COMPUTER SIMULATION MODEL OF AUTONOMOUS VOLTAGE INVERTER OF ELECTRIC LOCOMOTIVE SERIES "O'ZBEKISTON"

ABSTRACT

Creation of a computer simulation model that allows to reproduce electromagnetic processes in a traction electric drive and in an autonomous voltage inverter (AVI), as well as the processing functions of the obtained simulation results, adequate to the real conditions of use on electric rolling stock of converters with various control algorithms in traction and regenerative braking modes. The computer simulation model is designed to reproduce electromagnetic processes in the traction electric drive and AVI when determining the energy characteristics and studying the AVI of an electric locomotive of the “O'zbekiston” series.

АННОТАЦИЯ

Создание компьютерной имитационной модели позволяющей воспроизводить электромагнитные процессы в тяговом электроприводе и в автономном инверторе напряжения (АИН), а также функции обработки полученных результатов моделирования, адекватные реальным условиям применения на электрическом подвижном составе преобразователей с различными алгоритмами управления в режимах тяги и рекуперативного торможения. Компьютерная имитационная модель, предназначена для воспроизведения электромагнитных процессов в тяговом электроприводе и АИН при определении энергетических характеристик и исследования АИН   электровоза серии «O’zbekiston».

Keywords: asynchronous traction motor, and autonomous inverter, “O'zbekiston” series electric locomotive, computer simulation model.

Ключевые слова: асинхронный тяговый электродвигатель, автономный инвертор, электровоз серии «O’zbekiston», компьютерная имитационная модель.

Investigation of an autonomous voltage inverter of the electric locomotive of the series "O'zbekiston"

The operational fleet of the depot of the railways of Uzbekistan is mainly made up of electric locomotives of the old generation of the VL80s series. The well-established mainline electric locomotive VL80s is gradually becoming technically obsolete. In 2003 The Chuzhou Electric Locomotive Plant in China purchased single-section electric locomotives of the “O'zbekiston” series (Fig. 1), which was intended for operation on electrified sections of the alternating current of the railways of Uzbekistan [5].

Figure 1. Single-section electric locomotive of the “O'zbekiston” series

Autonomous inverter is a converter that converts a single-phase direct current into a multi-phase alternating current, the frequency of which is determined by the control system, and the value and the shape of the output voltage depends on the nature and parameters of the load. Unlike a dependent inverter, the frequency of which is determined by the mains frequency, an independent inverter receives an alternating current of any frequency at the output, and the voltage smoothly changes from zero to the maximum allowable value.

A characteristic feature of an autonomous voltage inverter is that it receives power from a voltage source; capacitor large capacity. The second feature of the AVI is the use of fully controlled valves shunted with reverse current diodes as switches. AVI generates a rectangular voltage in the load, and form current is determined by the nature of the load. AVI is widely used in converter technology, it is otherwise called a universal power conversion module. On its basis, AC voltage regulators, direct frequency converters, active voltage and current filters, reactive power compensators are made.

Depending on the number of switching currents, inverters with one- and two-stage switching are distinguished. With single-stage switching, the load current immediately passes to the thyristor entering into operation, with two-stage switching, the load first switches to the auxiliary chain and then to the main. When using single-operation thyristors, the circuits are supplemented with special forced switching nodes. In autonomous inverters based on thyristors, complete switching with current switching from one branch of the circuit to another is performed in several stages. First, there is a decrease in the forward current in one of the thyristors to zero, then a delay in the application of forward voltage on it until the blocking ability is fully restored, and then an increase in the forward current in the second thyristor.  

Figure 2. Three-phase autonomous voltage inverter

The power section contains GTO thyristors of an autonomous voltage inverter. It contains six thyristor switches VT1–VT6 with six reverse current diodes VD1–VD6, forming a ­bridge circuit and connected in parallel to the power source. A simplified diagram of a three-phase bridge AVI using GTO thyristors is shown in fig. 2.

The switching duration of the thyristor switches and, consequently, the frequency of the output voltage is determined by the control system. In the interval of one period of the output voltage, the thyristors of the anode and cathode groups can be switched once and repeatedly. With a single switching, the thyristors can be open for 120°, 150° or 180°. The simplest way to control the thyristor switches VT1-VT6 of the inverter, ensuring the invariance of the structure of the power circuit, is the method with α=180°. The simplest ways to control thyristors, in which the structure of the inverter power circuit changes, are methods with α=120° and α=150°. With these control methods, branches are formed in the output stage circuit that close only through the reverse bridge diodes. The structure of the output circuit of such an inverter will depend on the direction of the current in these branches. In turn, the moment of current change in one or another branch of the circuit depends on the nature of the load. Therefore the form output voltage at α=120° will also depend on the nature of the load. At α=120° the structure of the power circuit remains unchanged if cosφ_n ≤ 0.55. Form load voltage in this case is similar to the shape at α=180°. A common disadvantage of these methods is the need to use controlled valves. The load of the three-phase AI is switched on either according to the scheme stars . The effective value of the phase voltage when the load is connected by a star is determined by the formula

                                                                    (1)

Where U_P - power supply voltage.

Accordingly, the effective value of the line voltage is equal to

.                                                                  (2)

Form The current of the output circuit depends on the nature of the load. With an active-inductive load, it is a broken curve consisting of four exponentials in a section equal to half the period. The effective value of the load current is determined by integrating the characteristic sections of the current curve [6].

When the load is connected by a star, the effective value of the current is [6]:

,                                       (3)

where coefficient  is inversely proportional to the time constant, and the parameter  . Expression (3) is valid for the time interval

 .

The required shape of the load current, including the sinusoidal one, can be obtained by repeatedly turning on and off the controlled valves at the interval of one period. In this case, the effective value of the voltage on the load changes smoothly.

To regulate the output voltage using an inverter, the most widely used is pulse-width modulation (PWM) with the formation of an envelope in the form of a rectangle, trapezoid or sinusoid. Rectangular modulation is otherwise called pulse-width control (PWC). Pulse-width regulation of the voltage at the output of the inverter at the fundamental frequency is carried out by changing the relative duration of the load on in chain power source. SHIRT finds application when two power thyristors of the same group are locked in a pause between pulses. Then, with open thyristors VT1, VT2, VT3, VT1 and VT3 are locked to create a pause in the voltage at the load. The single switching algorithm is able to create a pause in the output voltage of the inverter at any values of the time constant

                                                                           (3)

With the group switching algorithm, a pause is created in the voltage at the load if, by the time the two thyristors of the group are turned off, the current changes sign. This phenomenon can occur at small values of load time constants. If the value is large and by the moment under consideration the current does not change sign, then it will not be possible to form a pause in the output voltage. With PWM at the fundamental frequency, the harmonic composition of the output voltage and current deteriorates sharply in the region of low voltages and frequencies. To eliminate this undesirable phenomenon, pulse-width regulation at the carrier frequency is used. The greatest reduction in the content of higher harmonics is achieved with pulse-width modulation according to a sinusoidal law. In this case, a triangular-shaped reference voltage is formed in the control circuit, which is compared with a sinusoidal modulating curve. The duration of the output voltage pulse is determined by the intersection points of these curves [4].

Сomputer model AIN with an asynchronous traction electric motor of the electric locomotive of the “O'zbekiston” series

System traction electric drive electric locomotive series "O'zbekiston" implementing function by axis regulation consists of from two-level offline inverters voltage and asynchronous traction motor (ATD). nutrition AI carried out from intermediate link permanent current, containing filter capacitors.

IN models vector systems automatic management given rotation speed n ^* and load moment 𝑇 𝑚 applied to the shaft engine, may be chosen with help block manual switching, to use or permanent meaning, or step function.

On computer models exit ATD connected to mechanical load, which imitates action wheeled couples locomotive, characterized moment inertia, coefficient friction And torsional moment resistance.

Principled scheme power chains with two-level autonomous inverter voltage. Every AI consists of from three power GTO modules that form a three-phase voltage by algorithm sinusoidal PWM.

System automatic management AI implements algorithm control ATD "current corridor", in which the inverter sets itself source current.

A functional diagram of the vector automatic control system with the implementation of the "current corridor" control algorithm is shown in fig. 3.

A dual-loop control system that implements the "current corridor" control algorithm was developed using the demonstrative file power_acdrive.slx. The external contour of the control system ensures the stabilization of the given rotational speed of the ATD. The internal contour of the control system forms a "current corridor" [2].

Figure 3. functional scheme vector systems management ATD

The signal of the actual engine speed n comes from the speed sensor to the input of the comparison element, where it is subtracted from the given signal n. Further, the mismatch signal is processed by PI controllers to generate a torque signal Te, which enters the input of the iqs calculator unit. Then the signal iqs is fed to the input of the coordinate transducer, the inputs of which are also supplied with the signals of the calculator ids and the signal of the calculator θe, thus forming a three-phase system of currents of a fixed coordinate system. Further, inside the block of the hysteresis current controller, the given signals of the three-phase current are compared with the actual signals of the three-phase current of the ATD stator winding, then the mismatch signals are sent to the blocks of relay elements that implement the “current corridor” algorithm when controlling the AVI [1].

Virtual laboratory installation shown in fig. 4.

The simulation is carried out for each value of the load resistance, and the ratio between its active and reactive components must remain unchanged.

The time diagrams of the currents and voltages of the AVI, observed on the oscilloscope screen, are shown in fig. 5 and with the spectral composition of the load current are shown in fig. 6 [3].

Figure 4. Virtual model of a three-phase AVI electric locomotive of the “O'zbekiston” series

Figure 5. Oscillograms of currents and voltages of a three-phase autonomous inverter

Figure 6. Spectral composition of the load current

Conclusion

A simulation computer model of the AVI with ATD of an AC electric locomotive of the “O'zbekiston” series has been developed, which makes it possible to study electromagnetic processes in power circuits. A dual-loop control system has been developed that implements the “current corridor” control algorithm and was developed using the demonstrative file power_acdrive.slx. The external contour of the control system ensures the stabilization of the given rotational speed of the ATD.

References:

1. Dyakonov V.P. MATLAB 6.5 SP1/7 + Simulink 5/6. Basics of application. / V. P. Dyakonov. // M.: SOLON-Press 2005. - 800s. (Series "Professional Library").
2. German-Galkin, S. G. Computer simulation of semiconductor systems in MATLAB 6.0: tutorial / S. G. German-Galkin., // - St. Petersburg: Crown 2001- 320 p.
3. Nazirkhonov T. M. Analysis of the spectral composition of the input current and voltage 4q-s of the converter of the electric locomotive of alternating current of the O'Z-ELR series using a computer simulation model / T.M. Nazirkhonov, A.Ya. Yakushev, I.P. Vikulov // Bulletin of scientific research results. – 2020. – no. 3. - S. 41-63.
4. Plaks, A.V. Control systems for electric rolling stock / M.: Route, 2005 - 224 p.
5. Vikulov I. P. Comparative analysis of the technical characteristics of electric locomotives of the O'Z-ELR and O'zbekiston series / I. P. Vikulov, T. M. Nazirkhonov // Izv. Petersburg. University of Communications. - St. Petersburg: PGUPS, 2019. - T. 16. Issue. 1. - S. 68-76.
6. Yakushev A. Ya. Determination of the main parameters of an asynchronous traction motor / A. Ya. Yakushev, T.M. Nazirkhonov, I.P. Vikulov, K.V. Markov // Izv. Petersburg. University of Communications. - St. Petersburg: PGUPS, 2019. - T. 16. - Issue. 4. - S. 592-601.