“RENEWABLE ENERGY UDC 620.92 BIOENERGY IN UKRAINE: CURRENT STATE AND DEVELOPMENT PROSPECTS. PART 1 Geletukha G.G., Ph.D. those. Sciences, Zheleznaya T.A., Ph.D. those. Sciences, Kucheruk P.P., ... "
RENEWABLE ENERGY
BIOENERGY IN UKRAINE: CURRENT STATE AND PROSPECTS
DEVELOPMENT. PART 1
Geletukha G.G., Ph.D. those. Sciences, Zheleznaya T.A., Ph.D. those. Sciences, Kucheruk P.P., Oleinik E.N.,
Triboy A.V.
Institute of Technical Thermophysics of the National Academy of Sciences of Ukraine, st. Zhelyabova, 2a, Kyiv, 03680, Ukraine
The paper covers the state of the art, the forecast for the development of bioenergy in the current state and the forecast for the development of bio- and outlook for bioenergy develop. We have assessed the energy potential in the EU. Assessed in the EU. Potential of biomass biomass, available for biomass potential, access-available for energy production in energy in Ukraine. Analyzed for energy production in Ukraine is assessed. Dynamics of the dynamics of change in the potential of bio-Ukraine. The dynamics of biomass potential over years is analyzed.
masi on rocks. dynamics of changes in biomass potential over the years.
Bible 14, table. 5, fig. 4.
Key words: biomass, biofuel, biogas, bioenergy, biomass potential, energy crops.
AIC – agro-industrial complex; AD – oil equivalent;
BM – biomass; agricultural – agriculture;
RES – renewable energy sources; dry t – tons of dry matter.
GFE – gross final energy consumption; Subscripts:
MSW – municipal solid waste; e – electric.
Development of bioenergy in the world of biomass. Its share in total consumption is consistently about 70%.
Renewable energy is the energy sector. The contribution of biomass to the gross final energy sector is dynamically developing in the world. The EU's consumption has already exceeded 8%, and by 2020, today the share of RES in the total primary supply should increase to 14% (Table 1). In some countries, energy in the world is about 13%, in leading countries the level of development of bioenergy and biomass is 10%, which corresponds to much higher than the European average. So, in lei 1300 million tons of oil equivalent per year.
In Finland, the share of biomass in the final energy of the European Union is successfully moving towards additional consumption of 28%, in Latvia - more than achieving the 2020 target for renewable
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The most appropriate energy potential is the distribution of the total area: willow - 25%, biomass in the country is about 20... scanthus - 15%, poplar - 10%, corn - 50%.
25 million tce/year. The main components of the proposed list of crops are one of the potential are agricultural waste - from the possible options selected for this production (straw, corn stalks, no assessment of the potential of biomass. In practice, sunflower stalks, etc.) - more than 11 million tons. t./ based on specific conditions, energy crops and other crops can be grown (according to 2013 data), for example, sugar crops - about 10 million tce/year (Table 3). sorghum.
At the same time, agricultural waste is the real part of the biomass potential, the mass in Ukraine fluctuates from year to year and depends, and data on energy crops reflect mainly the yield of the main crops. In 2013, when these crops were grown on free land, a record grain harvest in Ukraine over the past 20 years was collected.
It should be noted that this process of grain and leguminous crops (63 million tons) has been actively developing over the last few years. The potential assessment is conservative - it has reached its maximum value - almost no and includes the main types of biomass, having 28 million tons of fuel equivalent. (Fig. 4). On the contrary, 2003 was a year with a significant impact on the volume, potentially one of the poorest grain crops in the world. In practice, there are many sources of biomass (20 million tons), and the potential of biomass has fallen more - grain cleaning waste from elevators, tops to 18.5 million tons of fuel equivalent.
sugar beet, reed biomass and others. When assessing the potential, an extremely important question is the area of unused agricultural land, what share of waste/solid land in Ukraine is 3...4 million hectares of agricultural production residues, according to 2012 data - 3.5 million hectares (Table 4). can be used for energy needs Several possible cultivation scenarios without a negative impact on soil fertility.
energy crops on these lands are pre- Experts of the Bioenergy Association are shown in Table 5. The scenarios differ from each other, having carried out a corresponding study of the area of land allocated for them, they came to the conclusion that on average for the cultivation of energy crops - 1 million hectares it is possible to predict the use of hectares , 2 million hectares and 3 million hectares. For all scenarios, up to 30% of the theoretical potential of straw, the 4 most promising crops were selected - grain crops and up to 40% of the theoretical willow, miscanthus, poplar, corn and the following ISSN 0204-3602. Prom. Heat engineering, 2015, vol. 37, No. 2
RENEWABLE ENERGY
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* Conservative approach.
The waste potential of corn production must be addressed individually, taking into account grain and sunflower. At the level of taking into account existing non-energy specific agricultural enterprises for the use of straw and other waste or farming this issue of waste (for example, the use of ISSN 0204-3602. Industrial Heat Engineering, 2015, vol. 37, no. 2
RENEWABLE ENERGY
Rice. 4. Dynamics of biomass energy potential in Ukraine.
as organic fertilizer, bedding and the potential of biomass in the country and as feed for livestock). This is about 20...25 million tons of equivalent fuel per year. The main components of the potential are waste. Conclusions from agricultural production (straw, Renewable energy - the sector of energy corn stalks, sunflower stalks, etc.) genetics, which is dynamically developing in the world. By - more than 11 million tons of fuel equivalent / year (according to 2013 data) and today the share of renewable energy sources in the total supply of primary energy crops is about 10 million tons of fuel equivalent / energy in the world is about 13% , in year.
including biomass - 10%, which corresponds to For Ukraine, bioenergy is more than 1300 million tons of oil equivalent / year. Among the strategic directions of development, the European Union is successfully moving towards the renewable energy sector, achieving the 2020 goal of renewable energy, taking into account the country’s high dependence on immu energy - 20% of energy from renewable energy sources in imported energy carriers, primarily, final energy consumption. Over the past 10 years, this figure has increased from 8% to the mass available for energy production.
14 %. Contribution of biomass to the gross final energy consumption Unfortunately, the pace of bioenergy development in the EU has already exceeded 8%, and in Ukraine it still lags significantly behind. In 2020, it should increase to 14%. Most European. To date, the share of biomass has been achieved in the thermal mass sector in the total supply of primary energy in energy - biomass provides almost 16% of the country is only 1.2%, and in the gross total generation, which corresponds to the final energy consumption (according to the authors) in third place after natural gas and coal. – 1.78%.
UDC 621.039 NUCLEAR ENERGY PROS AND CONS Novozhentseva N.V. Scientific supervisor Rastorgueva Galina Sergeevna senior lecturer of the Department of Life Sciences Branch of the KSPU named after. V.P. Astafiev in Zheleznogorsk, Art. Lecturer, Bocharova E.V. IUBPiE SFU Siberian Federal University One of the important indicators of a country’s environmental and economic capabilities is the level of energy development. The development of the fuel and energy complex (FEC) currently cannot be imagined without nuclear energy. The birth of nuclear energy divided society into two camps, occupying directly opposite positions. Some see nuclear energy as an achievement of the human mind. Others consider it an evil that threatens the death of all life on our planet. At the end of the last century, the authority of the peaceful atom was greatly shaken by the accident at the Chernobyl nuclear power plant. Also, the events of the 21st century at the Fukushima-1 nuclear power plant that occurred on March 11, 2011 cast doubt on the further development of nuclear energy. But there is no denying the fact that nuclear energy, with the proper design of a nuclear reactor, has enormous potential for producing clean energy. Nuclear scientists today are still trying to learn a lesson from the tragedy. They are looking for ways to take reactor safety to the next level. On the other hand, in the face of the impending shortage of hydrocarbon resources, humanity has realized that nuclear energy has no worthy alternative. And now there is a revival of it all over the world. Recently, Russia has been striving not only to seriously strengthen its nuclear energy sector, but also to take a leading position in the international energy market. There are all the prerequisites for this. In particular, we carry out the full nuclear cycle: from the extraction and enrichment of nuclear fuel to its reprocessing and disposal after use. This is not the case in any other country in the world except France. And this advantage should be wisely used and developed to your advantage. The city of Zheleznogorsk, which is located 60 kilometers from Krasnoyarsk, has been directly connected with nuclear production throughout its history. The gas and chemical complex is a city-forming enterprise, most of the population is employed at the plant, the ADE-2 reactor provided the city with electricity and heat. Over the years of operation of the plant, a large amount of spent nuclear fuel has been accumulated. We live in close proximity to nuclear reactors, so I am interested in this topic, what will happen to the city, are there development prospects, what are they connected with. I want to have my own point of view on issues related to the development of nuclear energy based on the city of Zheleznogorsk. A point of view based on competent information, confirmed by facts and figures. The idea of participating in a conference on the topic “Nuclear Energy” was born as a continuation of my successful presentation back in 2011 at the city scientific and industrial complex in the “Nuclear Energy” section and participation in the All-Russian competition of research and design works “Energy of Future Generations”, which was held in April 2011 in St. Petersburg. This competition is held by the state corporation Rosatom and the all-Russian children's environmental movement Green Planet. At this competition, I met guys from different regions of Russia who are studying the development of nuclear energy. I wanted to understand this topic better and be able to convey this information to others, to be competent based on facts and figures. This is the first. And secondly, Krasnoyarsk is located in close proximity to the closed nuclear city of Zheleznogorsk, as already mentioned. Now there are pressing issues related to city development and radioactive waste. These two questions are interrelated. On the one hand, spent nuclear fuel can be considered waste, and on the other hand, it can be considered a raw material for the production of MOX fuel. Accordingly, the attitude towards the city and prospects for development will also be different. Back in 2011, my work covered the topics of creating MOX fuel from spent spent nuclear fuel, and these were just projects. To date, the first tablets of processed uranium and plutonium dioxide have already been created. Today's leaders of nuclear energy, the French, having 2nd generation technology at their best plant UP-3, assessed the presentation of the Mining and Chemical Combine as 4th generation. A significant difference between this generation is the absence of liquid radioactive waste. Third, while conducting a survey, I saw that my peers are very little informed about the development and prospects of this industry. Our generation needs to know whether there is a future for nuclear energy, what the production of MOX fuel is, does the world need nuclear energy and how dangerous is it? My specialty is directly related to the topic of my work, because I am a future economist, and the main task of the economy as a whole is the maximum possible conservation of exhaustible resources. In addition, nuclear energy now provides the cheapest electricity. If in conventional, thermal, fossil fuel-based energy, about 60% of the tariff is the cost of natural resources and fuel (in this fuel there is a large share of natural resource rent, rather than wages), then the cost of the natural component in nuclear energy is 15%, a large part of which is the labor component. Fuel reserves for all organic energy will only last for decades, while for nuclear energy - for millennia. The cost of electricity production at nuclear power plants is 1.5-2 times cheaper compared to thermal stations. Today I want to have my own point of view on issues related to the development of nuclear energy in the current socio-economic situation based on the advanced city of Zheleznogorsk. The desire to answer these questions for myself prompted me to undertake this research. 2
“133 Electrical engineering and power engineering UDC 62-83: 621.314.632 BBK 31.291 G.P. OKHOTKIN, E.S. ROMANOV COMPARATIVE ANALYSIS OF POWER CIRCUITS OF PULSE...»
Electrical engineering and power engineering
UDC 62-83: 621.314.632
G.P. OKHOTKIN, E.S. ROMANOVA
COMPARATIVE ANALYSIS OF POWER CIRCUITS
PULSE CONVERTERS
FOR DC ELECTRIC DRIVE
Key words: pulse converter, transistor pulse converter, pulse DC voltage converter, transistor DC electric drive.
A comparative analysis of power circuits of pulse converters for DC electric drives and their static characteristics was carried out. The given advantages and disadvantages of the circuits allow you to reasonably select an electric drive circuit.
G.P. OKHOTKIN, E.S. ROMANOVA
COMPARATIVE ANALYSIS OF POWER CIRCUITS
OF PULSED CONVERTERS FOR DC MOTOR
Key words: pulse converter, transistor pulse converter, DC pulse converter, transistor DC motor.Was made a comparative analysis of the power circuits of pulse converters for DC motor and its static characteristics. Adducting advantages and disadvantages of schemes admit reasonably choose the electric circuit.
Construction of an optimal control system for a pulsed-DC voltage converter (PPDC) is possible only if the valve control signal is generated by the control system based on complete information about the state of the controlled object. The state of the control object - a DC motor - is characterized by two variables: armature current and angular speed of rotation.
Current and speed sensors are used to monitor motor state variables. Modern transistor DC electric drives are built according to a slave coordinate control scheme with an internal current loop and an external speed loop. There are irreversible and reversible electric drives.
Irreversible electric drives, in turn, can have a braking circuit or can be built without a braking circuit. In the latter case, braking is carried out by coasting, i.e. under the influence of static load.
First, let's consider the functional diagram of a transistor irreversible electric drive without a braking circuit (Fig. 1, a). It consists of an automaton K; TV matching transformer; rectifier B, built according to a bridge circuit; capacitive filter C; regulating transistor VT; reverse diode VD; external reactor Lp; independent excitation direct current motor (DCM) M; DT current sensor; SU control systems; tachogenerator BR.
The regulating transistor VT and the reverse diode VD represent the simplest circuit of a DC-to-DC valve converter (VC) (DC-DC converter). Timing diagrams of the operation of the DC-DC converter in the steady-state operating mode of the electric drive (ED) are presented in Fig. 1, b and c.
Let's consider the operation of a DC-DC converter in continuous current mode (CNT).
After turning on the control transistor VT at time t = nT (Fig. 1, b), under the influence of the input voltage Up of the DC-DC converter in the armature winding of the DPT, the current increases exponentially in the circuit: terminal plus power source - transistor VT - reactor Lp - armature winding DPT – current sensor DT – minus terminal of the power source.
The back-EMF E of the motor rotating at an angular velocity is directed counter to Up. The duration of the open state t0 of the control transistor VT is determined by the control circuit as a function of feedback signals for the current Uot and speed Uos. IN.
134 Bulletin of Chuvash University. 2012. No. 3 moment of time t = nT + t0 the control system turns off the regulating transistor VT.
In this case, under the influence of the self-induction EMF arising on the inductance coil of the armature circuit, the reverse diode VD opens, and the armature current begins to decrease exponentially in the circuit: reactor Lp - armature winding DPT - current sensor DT - diode VD - reactor Lp. At time t = (n + 1)T, the control circuit again opens the regulating transistor VT, and the armature current begins to increase exponentially. Next, the process of regulating the current and voltage of the DPT armature circuit continues by cyclically switching the regulating transistor VT with a high frequency.
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It is more convenient to carry out a comparative analysis of the characteristics of various systems when their parameters are expressed in relative units. To do this, we introduce relative values: 0 = t0 /T – relative duration of the open state of the control transistor; = Ud / Up – relative average value of the converter output voltage; = Eя/Uп – relative back-EMF of the motor;
I = RяEя / Up – relative average armature current, taking Ub = Up, Tb = T as base variables – base voltages and time.
Then the relative average value of the armature voltage from (1) is expressed as = 0. (3) Dependence of the relative average value of the output voltage of the converter on the relative duration of the open state of the control transistor 0, i.e. = f(0) is called the control characteristic of the DC-DC converter. The adjustment characteristic of the converter (3) is located in the first quadrant of the coordinate plane (0,) and is a straight line (more precisely, a straight line segment 0 1) passing through the origin of coordinates. Consequently, in the simplest DCDC converter only unipolar modulation (0 0 1) is possible, which leads to regulation of the average voltage in relative units in the range 0 1.
By changing the voltage of the armature circuit, the speed of the DC motor is controlled. To obtain the regulating characteristics of the DC motor, equation (2) is presented in relative units in the form = – I, (4) where the back-EMF of the motor is proportional to the angular velocity Eя = K, at = const, i.e.
The control characteristic = f()|I = const DC motor according to (4) is a family of parallel lines located in the first and fourth quadrants of the coordinate plane (,), depending on the armature current I. Taking into account the fact that the irreversible electric drive in question is able to operate with a load characterized only by the reactive moment of resistance, the adjustment characteristic of the DC motor (4) is located only in the first quadrant of the coordinate plane (,).
From the control characteristics (3), (4) we obtain the equation for the control characteristics of the DC-DC converter – DPT (VP-DPT) system in the form = 0 – I. (5) Adjustment characteristics = f(0)|I = const by ( 5) have the form of parallel lines located only in the first quadrant of the coordinate plane (0,). From the characteristics (5) it follows that the speed of the DPT () is regulated by changing the duration of the open state of the control transistor 0 at a given load I.
The electromechanical characteristic of the VP-DC system is the dependence of the relative average voltage of the armature circuit on the relative average armature current I, i.e. = (I)| = const at a given motor speed. These characteristics are a family of parallel straight lines with a constant angle of inclination to the abscissa axis, located in the first quadrant of the coordinate plane (I,). The angle of inclination is determined by the active resistance of the armature chain.
In the intermittent current (IDC) mode, the armature current drops to zero during the discrete interval. Timing diagrams presented in Fig. 1, c differ from the RNT time diagrams by the presence of a dead-current pause interval tп. During the dead pause interval, the voltage of the armature circuit corresponds to the value of Ei, therefore the average value of the voltage of the armature circuit is determined by the relation 1 nT t0 1 (n1)T Up Up Ud U p dt T Eya dt T t0 T tp, (6) T nT (n 1) T tп where tп is the duration of the dead-time interval.
136 Bulletin of Chuvash University. 2012. No. 3 Passing in equation (6) to relative units, taking into account (4) we obtain the equation for the control characteristic of the VP-DC system in the form = 0 + p – I, (7) where p = tp /T is the relative duration of the no-current interval pauses.
It is not possible to obtain expressions for determining n explicitly. Therefore, the construction of the control characteristics of the VP-DPT system in the RPT is carried out using its electromechanical characteristics. In this regard, the regulating characteristics of the VP-DC system at intermittent currents become nonlinear.
The electromechanical characteristics of the VP-DC system in the intermittent current mode are also nonlinear. They are a family of curved lines starting from the ideal no-load point and ending at the intermittent current boundary at the points where the continuous current characteristics begin.
The electromechanical characteristics in intermittent current mode have low rigidity compared to the characteristics of continuous current.
The nonlinearity of the static characteristics of the VP-DC system in the RPT reduces the control accuracy and stability of the electric drive. Therefore, measures must be provided to either eliminate intermittent currents or linearize the control characteristics.
The advantages of the scheme under consideration include the extremely small number of elements of the power part of the converter.
The disadvantages of such a system are: the absence of regenerative engine braking modes, which negatively affects the dynamic properties of the electric drive; the presence of nonlinear sections of mechanical characteristics that have low rigidity; the presence of nonlinear sections of control characteristics; increased additional losses in the motor when operating in intermittent current mode.
Now let's consider a non-reversible electric drive circuit with regenerative engine braking (Fig. 2, a). The functional diagram of an irreversible half-bridge DC-DC converter circuit consists of two simple valve converter circuits (the first is built on transistor VT2 and diode VD1, and the second is built on VT1 and VD2), where the second VP circuit is connected counter-parallel to the motor. This VP switching circuit ensures that a reverse (bipolar) current flows in the motor armature, so let’s call it a current-reversible converter. IPPN, in contrast to the scheme shown in Fig. 1, a, is equipped with an energy reset unit DC to prevent overvoltages on capacitor C in braking modes of engine operation.
The first simplest VP circuit, made on transistor VT2 and diode VD1, serves to regulate the average voltage at the motor armature and is therefore called the VP accelerating kit. The second set of VP, made on transistor VT1 and diode VD2, serves for regenerative braking of the DPT and can be called a brake set of VP. There is joint and separate management of VP sets.
With separate control of VP sets, the timing diagrams of the operation of the DC-DC converter under consideration in the motor mode of operation of the DC motor completely coincide with the timing diagrams of the operation of the circuit presented in Fig. 1, a.
The static characteristics of the VP-DC system in the continuous current mode are linear, and in the intermittent current mode they are nonlinear. The transition to the generator mode of braking the electric drive by the circuit is carried out after the armature current drops to zero.
One of the disadvantages of separate control of VP sets is the nonlinearity of static characteristics in the intermittent current mode. Joint control of VP sets makes it possible to eliminate the dead-time interval and linearize the static characteristics of the VP-DC system. Therefore, in the future we will dwell in more detail on the consideration of joint management of VP sets.
Electrical engineering and power engineering Time diagrams of the operation of the VP in the DC armature current mode with a positive average value (iа 0, Iа 0) are shown in Fig. 2, b. The formation of current and voltage curves in this mode is carried out by a VP accelerating kit, the operation of which is described in detail above (Fig. 1, b). The mode is characterized by the fact that during the entire discrete interval the instantaneous and average armature current is greater than zero, i.e. iа 0 and Iа 0. The average armature current Iа and the back-EMF Eа of the motor are directed in the opposite direction, so machine M operates in motor mode.
The operation of the valve converter in the AC armature current mode with a positive average value (Iа 0) is illustrated by the timing diagrams presented in Fig. 2, c. When jointly controlling the VP sets at possible dead-time intervals, the VP brake set generates a current in the motor armature that coincides in direction with the back-EMF Eya. To do this, unlocking pulses are supplied to the transistors of the sets in antiphase, i.e. when transistor VT2 is open, transistor VT1 is closed and vice versa.
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As a result, an alternating current flows in the motor armature, providing generator braking of the motor in the interval tt + td. In this case, the dead-time interval disappears, the average armature current and the motor torque utilization factor decrease. Despite the presence of a negative instantaneous armature current in the interval tt + td, the average value of the armature current in the discrete interval of the converter is greater than zero, i.e. Iа 0. Under the influence of the average armature current of positive polarity, directed counter-EMF Ea, an electromagnetic torque is created in the motor and its shaft rotates.
138 Bulletin of Chuvash University. 2012. No. 3 When the control system reduces the duration t0 of the open state of transistor VT2, the interval tc of the armature current decaying to zero decreases, the intervals tt and td increase, and the average value of the armature current Iya decreases. When the average value of the armature current reaches zero value Iа = 0, the machine M goes into the so-called ideal idle operating mode. The alternating current flowing in the armature windings heats them and does not create torque in the machine.
A further decrease in the duration t0 of the open state of transistor VT2 leads to a change in the sign of the average armature current Iа 0 and the transfer of machine M into the regenerative braking mode, consisting of intervals of dynamic tt and regenerative braking td. The alternating current with a negative average value flowing in the armature windings creates a braking torque in the rotating machine, and the engine begins to brake. The intensity of DPT braking is determined by the value of the average armature current.
During regenerative braking of the engine, the accumulated kinetic energy is converted by the machine into electrical energy, which is transmitted through the power buses to the power source and accumulates on the capacitive filter C. This can lead to an increase in the supply voltage Up. To limit the supply voltage Up in braking modes of operation of the electric drive, a reset unit is introduced, containing a semiconductor switch, a ballast resistor, a key control circuit and a voltage control circuit on the capacitive filter C. When the voltage on the capacitive filter exceeds 5-10% of the nominal value, the DC starts dumping excess energy into the ballast resistor by switching the switch with a high frequency.
In this case, the capacitor C is discharged to the ballast resistor and the voltage Up is reduced to the nominal value.
Thus, in the pulsating armature current generated by the valve converter, four modes can be distinguished: positive direct current, when the instantaneous and average armature current is greater than zero (iI 0, II 0); alternating current with positive Iya, when the instantaneous current is alternating and the average value of the armature current is greater than zero (~iа, Iа 0); alternating current with negative Iа (~iа, Iа 0); negative direct current (iа 0, Iа 0). Moreover, when a direct or alternating current flows in machine M with Iа 0, it operates in motor mode, and when an alternating or direct current flows with Iа 0, it switches to a regenerative braking mode, consisting of intervals of dynamic and regenerative braking.
The average value of the armature circuit voltage in the direct current mode is determined by (1), and in the alternating current mode as nT t 0 1 (n1)T 1 Up Up Ud U p dt U p dt T t0 T td, (8) T nT T ( n1)T t d or in relative values = 0 + d, (9) where d = t d /T is the relative duration of the open state of diode VD2.
The DC-DC converter circuit provides unipolar modulation (0 0 1), and therefore the control characteristic is located in the first quadrant of the coordinate plane and has a linear dependence in all current modes. The external characteristic of the DC-DC converter is located in the first and second quadrants of the coordinate plane, since the converter ensures the flow of reverse armature current and also has a linear dependence.
The advantages of the circuit include: the linearity of the static characteristics of the VP-DC system, which is achieved in the circuit by excluding the intermittent current mode; high speed of the electric drive, which is achieved by providing generator braking of the machine.
Electrical engineering and power engineering The disadvantages include: a relatively large number of elements of the power part of the converter, leading to a more complex control circuit; reduction in the utilization rate of the machine in AC armature mode.
Next, we will consider the main reversible circuits of transistor DC electric drives, which can be implemented using one Up or two constant voltage sources Up1 and Up2. First, let's look at two reversible circuits of transistor DC electric drives with two DC voltage sources. The first functional diagram of the electric drive, shown in Fig. 3, is made using a reversing half-bridge circuit of a DC-DC converter, consisting of two transistors VT1, VT2 and diodes VD1, VD2. The reversible circuit is formed by the back-to-back connection at the output of two sets of non-reversible VPs, made according to the simplest circuit. The regulating transistor VT1 and diode VD2, which represent the first set of VPs, form an adjustable average voltage of positive polarity in the armature circuit of the motor for the direction of rotation “Forward”, and transistor VT2 and diode VD1 (the second set of VPs) - of negative polarity for the direction of rotation “Backward” .
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expressed in relative units, is located in the first and fourth quadrants of the coordinate plane (0,) and passes through the zero value of the relative average stress = 0 at 0 = 1/2. This means that the DC-DC converter carries out bipolar modulation, transferring energy from the machine M to the input voltage source Up2 at 0 0 1/2, and vice versa - from the source Up1 to the machine at 1/2 0 1.
From the adjustment characteristics (11) and (4) we obtain the equation for the adjustment characteristics of the VP-DPT system in the form = 20 – 1 – I. (12) The adjustment characteristics = f(0)|I = const according to (12) have the form of parallel straight lines, located in the first and fourth quadrants of the coordinate plane (0,) and pass through the zero value of the relative average voltage = 0 at 0 = 1/2 and I = 0. From characteristics (12) it follows that the speed of the DC transformer () is regulated by changing the duration of the open state regulating transistor 0 at a given load I.
Electromechanical characteristics of the VP-DC system = (I)| = const, created by the first set of VPs and the machine, are a family of parallel straight lines with a constant angle of inclination to the abscissa axis, located in the first and fourth quadrants of the coordinate plane (I,), since the circuit of the first set of VPs reverses only the average voltage of the armature circuit, and the average armature current does not change polarity. The electromechanical characteristics of the VP-DPT system, created by the second set of VP and the machine, are located in the third and second quadrants of the coordinate plane (I,). Therefore, in general, the electromechanical characteristics of the VP-DC system will be located in all four quadrants.
With separate control of VP sets for the direction of engine rotation “Forward”, transistor VT2 is constantly closed, and therefore the operation of the converter is possible in intermittent current mode. In this case, the armature current in the discrete interval drops to zero. In this case, the control and electromechanical characteristics of the VP-DC system become nonlinear.
With the joint control of VP sets, an alternating armature current is generated, the dead-time interval is eliminated, which linearizes the static characteristics of the VP-DC system. This also provides regenerative braking of the machine, which significantly increases the speed of the electric drive.
The second functional diagram of a reversible half-bridge circuit with zero gates of a DC-DC converter is shown in Fig. 4, a. The reversible circuit is formed by the back-to-back connection at the output of two sets of non-reversible VPs VT1, VT3 and VT2, VT4, made according to the simplest circuit and different from the circuit in Fig. 1, but using transistors VT3 and VT4 instead of zero gates. Zero valves reduce motor armature current ripple in contrast to the previous circuit shown in Fig. 3. Diodes VD1 and VD2 protect transistors VT1 and VT2 from overvoltages when transistors VT3 and VT4 are turned off.
Here, joint and separate control of VP sets is possible. The timing diagrams of the converter operation with separate control of sets in continuous and intermittent current modes are similar to Fig. 1, b, c. In the mode of intermittent armature current, the regulating and electromechanical characteristics of the VP-DPT system become nonlinear.
When jointly controlling the VP sets, an alternating current is generated in the motor armature circuit, eliminating the dead-time interval and ensuring the linearity of the static characteristics of the VP-DC system.
A controlled zero valve, implemented on transistors VT3 and VT4, allows you to speed up the process of the armature current decaying to zero. So, when transistor VT3 or VT4 is turned on, the motor armature current in the circuit drops slowly, and when transistors VT3 (VT4) are turned off, the armature current quickly drops through open diodes VD1 or.
Electrical engineering and power engineering VD2 under the influence of power sources Up1 or Up2. This increases the speed of the electric drive compared to the circuit shown in Fig. 1, a.
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b Fig. 4 A reversible circuit of a transistor DC electric drive with one constant voltage source based on an IPPN bridge circuit is shown in Fig. 4, b. The reversible VP circuit, which changes not only the direction of the current, but also the polarity of the armature voltage of the electric motor, makes it possible to provide regenerative braking of the machine and reverse speed. The bridge circuit of a pulsed-DC voltage converter (Fig. 4, b) consists of two racks. The first rack is formed by a circuit connected in series with transistors VT1 and VT3 in relation to the power source, and the second - by transistors VT2 and VT4. A DC electric motor is included in the diagonal of the bridge formed by transistor switches.
The VP is powered from a constant voltage source Up, shunted by a capacitor C and a reset unit US.
There are many methods for switching bridge circuit transistors, which are both further developments of the switching methods described above, as well as new ones. Some of them provide both joint and separate control of sets of valves that form two non-reversible circuits.
142 Bulletin of the Chuvash University. 2012. No. 3 with back-to-back connection at the output. The bridge circuit provides regenerative braking of the machine and increases the speed of the drive.
To ensure linear static characteristics of the VP-DC system, it is necessary to switch the transistors of the bridge circuit in such a way that alternating current flows in the motor armature. Any deviation from this condition leads to the appearance of nonlinearity in the static characteristics of the VP-DC system.
When VP is formed at the output of unipolar rectangular voltage pulses, armature current ripples and additional power losses are reduced, and the reliability of the valve converter and the drive as a whole is increased. Therefore, the bridge circuit of the valve converter, despite the large number of elements of the power section, is widely used in reversible DC electric drives.
Literature
1. Glazenko T.A. Semiconductor converters in DC electric drives. L.: Energy, 1973.
2. Zinoviev G.S. Fundamentals of power electronics: textbook. allowance. Novosibirsk: NSTU Publishing House, 2003.
OKHOTKIN GRIGORY PETROVICH – Doctor of Technical Sciences, Professor, Dean of the Faculty of Radio Engineering and Electronics, Chuvash State University, Russia, Cheboksary ( [email protected]).
OKHOTKIN GRIGORY PETROVICH – doctor of technical sciences, professor, dean of Radio Engineering and Electronics Faculty, Chuvash State University, Russia, Cheboksary.
ROMANOVA EVGENIYA SERGEEVNA – Master's student of the Department of Industrial Electronics, Chuvash State University, Russia, Cheboksary ( [email protected]).
ROMANOVA EVGENIA SERGEEVNA – master’s program student of Industrial Electronics Chair, Chuvash State University, Russia, Cheboksary.
UDC 62-83: 621.314.632 BBK 31.291 G.P. OKHOTKIN, E.S. ROMANOVA
ANALYSIS OF KEY SWITCHING LAWS
BRIDGE DIAGRAM OF PULSE CONVERTER
Key words: pulsed DC voltage converter, bridge circuit of a pulsed converter, laws of switching switches.An analysis of the laws of switching switches of pulse converters is given. It has been established that the most effective is alternate asymmetric switching of transistors. To prevent through currents in the power circuit, it is proposed to form non-overlapping key control pulses.
G.P. OKHOTKIN, E.S. ROMANOVA
ANALYSIS OF KEY SWITCHING LAWS
FOR BRIDGE CIRCUIT OF PULSE CONVERTER
Key words: pulse converter of DC voltage, the bridge circuit of pulse converter, the laws of switching keys.The laws analysis of keys switching of pulse converters is given. It is established, that the most effective is serial asymmetrical switching of transistors. To prevent cross-cutting currents in the power scheme, it is offered to form some not blocked impulses of keys control.
When building a high-quality reversible DC electric drive, the bridge circuit of a pulse converter is widely used (Fig. 1, a). A bridge circuit, made on four transistors with freewheeling diodes, allows you to create a reversible (four-quadrant) pulsed constant voltage converter (PPDC) with a high frequency and various switching laws of the power circuit, which has high energy performance, good performance.
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In order to study the amplification of the incident light, it is necessary to somehow reverse the population of the levels. Those. make sure that a larger energy value corresponds to a larger number of atoms. In this case, they say that a set of atoms has an inverse (reverse) population of levels.
The ratio of the number of atoms at levels and is equal to:
In the case of population inversion. It follows that the exponent must be greater than zero - . But . Therefore, for the exponent to be greater than zero, the temperature must be negative - .
Therefore, a state with an inverted population of levels is sometimes called a state with a negative temperature. But this expression is conditional, because the very concept of temperature is applicable to equilibrium states, and a state with an inverted population is a nonequilibrium state.
In the case of population inversion, light passing through the substance will be amplified. Formally, this corresponds to the fact that in Bouguer’s law the absorption coefficient will be negative. Those. a set of atoms with an inverted population of levels can be considered as a medium with a negative absorption coefficient.
So, to amplify light by a substance, we need to create an inverse population of the levels of this substance. Let's see how this is done using the example of a ruby laser.
Ruby is an aluminum oxide in which some aluminum atoms are replaced by chromium atoms. This ruby is irradiated with a wide spectrum of electromagnetic wave frequencies. In this case, chromium ions go into an excited state (see Fig. 4). Aluminum ions do not play a significant role in this matter.
The energy state represents a whole band due to the interaction of ions with the crystal lattice. From the level, two paths are possible for chromium ions.
1. Return to the original state with energy with the emission of a photon.
2. Transition to a metastable state with energy through thermal interaction with ions of the aluminum crystal lattice.
The lifetime at the level, as usual, is equal to the lifetime in the excited state - . The spontaneous transition to a level is indicated by an arrow, and the transition to a metastable level is indicated by an arrow.
Calculations and experiment show that the transition probability is much greater than the transition probability. In addition, the transition from a metastable state with energy to the ground state is prohibited by selection rules (selection rules are not absolutely strict, they only indicate a greater or lesser probability of the transition).
Therefore, the lifetime at the metastable level is one hundred thousand times greater than the lifetime at the level.
Thus, with a sufficiently large number of chromium atoms, an inverse population of the level can occur - the number of atoms at the level will exceed the number of atoms at the level, i.e. we may get what we want.
A spontaneous transition from a level to the main level is indicated by an arrow. The photon arising during this transition can cause stimulated emission of the next photon, which is indicated by an arrow. This one is another one, etc. Those. a cascade of photons is formed.
Let us now consider the technical structure of a ruby laser.
It is a rod with a diameter of the order and a length of . The ends of the rod are strictly parallel to each other and carefully polished. One end is an ideal mirror, the second is a translucent mirror that transmits about the incident energy.
Several turns of a pumping lamp - a xenon lamp operating in pulsed mode - are installed around the ruby rod.
So, stimulated photons were formed in the body of the rod. Those photons, the direction of propagation of which makes small angles with the axis of the rod, will repeatedly pass the rod and cause stimulated emission of metastable chromium atoms. The secondary photons will have the same direction as the primary ones, i.e. along the axis of the rod. Photons from the other direction will not develop a significant cascade and will leave the game. If the beam intensity is sufficient, part of it comes out.
Ruby lasers operate in pulsed mode with a repetition rate of several pulses per minute. In addition, a large amount of heat is released inside them, so they have to be intensively cooled.
Let us now consider the operation of a gas laser, in particular a helium-neon laser.
It consists of a quartz tube containing a mixture of helium and neon gases. Helium is under pressure, and neon is under pressure, with approximately 10 times more helium atoms than neon atoms. The main emitting atoms here are neon atoms, and helium atoms play a supporting role in creating the inverse population of neon atoms.
Energy pumping in this laser is carried out using the energy of a glow discharge. In this case, helium atoms are excited and go into an excited state (see Fig. 5). This state for helium atoms is metastable, i.e. reverse optical transition is prohibited by selection rules. Therefore, helium atoms can go into an unexcited state, transferring energy to neon atoms during collisions. As a result, neon atoms enter an excited state, which is close to the state for helium. Neon atoms are excited both by the glow discharge energy and by collisions with helium atoms.
In addition, the level is unloaded by selecting the dimensions of the tube so that the neon atoms, being at the level, would transfer energy to them upon collisions with the walls, moving to the main level.
As a result of these processes, the level population for neon is inverted. It is possible to move from level to level.
The main structural element of this laser is a quartz gas-discharge tube with a diameter of about . It contains electrodes to create an electrical discharge. At the ends of the tube there are plane-parallel mirrors, one of which, the front one, is translucent. Conditions for amplification arise only for those photons that are emitted parallel to the laser axis.
The operating frequency of the laser is the transition. The selection rules allow about thirty transitions. To highlight one frequency, mirrors are made multilayer, tuned to reflect only one specific wave. Lasers emitting waves with a wavelength of . But the most intense transition is with wavelength , i.e. in the infrared region of the spectrum.
Gas lasers operate in continuous mode and do not require intensive cooling.
Distinctive features of laser radiation are:
1. Temporal and spatial coherence.
2. Strict monochromaticity.
3. Great power
4. Narrowness of the laser beam.
Lecture 15. (2 hours)