Reviewer Doctor of Technical Sciences F.I.Kovalev
The principles of converting electrical energy: rectifying, inverting, converting frequency, etc. are described. The basic circuits of converters, methods of controlling them and regulating the main parameters are described, areas of rational use of various types of converters are shown. The features of design and operation are considered.
For engineers and technicians for the design and operation of electrical systems containing converting devices, as well as those involved in the testing and maintenance of converter technology.
Yu.K. Rozanov Power Electronics Fundamentals... - Moscow, Energoatomizdat publishing house, 1992. - 296 p.
Foreword
Introduction
Chapter one. The main elements of power electronics
1.1. Power semiconductor devices
1.1.1. Power diodes
1.1.2. Power transistors
1.1.3. Thyristors
1.1.4. Power semiconductor applications
1.2. Transformers and reactors
1.3. Capacitors
Chapter two. Rectifiers
2.1. General information
2.2. Basic rectification circuits
2.2.1. Single-phase full-wave midpoint circuit
2.2.2. Single-phase bridge circuit
2.2.3. Three-phase midpoint circuit
2.2.4. Three-phase bridge circuit
2.2.5. Multi-bridge circuits
2.2.6. Harmonic composition of rectified voltage and primary currents in rectification circuits
2.3. Switching and operating modes of rectifiers
2.3.1. Switching currents in rectification circuits
2.3.2. External characteristics of rectifiers
2.4. Energy characteristics of rectifiers and ways to improve them
2.4.1. Power factor and efficiency of rectifiers
2.4.2. Improving the power factor of controlled rectifiers
2.5. Features of rectifier operation for capacitive load and back-EMF
2.6. Smoothing filters
2.7. Rectifier operation from a source of comparable power
Chapter three. Inverters and frequency converters
3.1. Grid-Driven Inverters
3.1.1. Single Phase Midpoint Inverter
3.1.2. Three Phase Bridge Inverter
3.1.3. Power balance in grid-driven inverter
3.1.4. Main characteristics and modes of operation of grid-driven inverters
3.2. Standalone inverters
3.2.1. Current inverters
3.2.2. Voltage inverters
3.2.3. Thyristor voltage inverters
3.2.4. Resonant inverters
3.3. Frequency converters
3.3.1. Frequency converters with DC link
3.3.2. Direct coupled frequency converters
3.4. Regulation of the output voltage of autonomous inverters
3.4.1. General principles of regulation
3.4.2. Control devices for current inverters
3.4.3. Regulation of the output voltage by means of pulse width modulation (PWM)
3.4.4. Geometric stress addition
3.5. Ways to improve the shape of the output voltage of inverters and frequency converters
3.5.1. Influence of non-sinusoidal voltage on electricity consumers
3.5.2. Inverter output filters
3.5.3. Reduction of higher harmonics in the output voltage without the use of filters
Chapter four. Regulators-stabilizers and static contactors
4.1. AC Voltage Regulators
4.2. DC Regulators
4.2.1. Parametric stabilizers
4.2.2. Continuous stabilizers
4.2.3. Switching regulators
4.2.4. Development of pulse regulator structures
4.2.5. Thyristor-capacitor DC regulators with metered energy transfer to the load
4.2.6. Combined converters-regulators
4.3. Static contactors
4.3.1. Thyristoric AC Contactors
4.3.2. DC thyristor contactors
Chapter five. Converter control systems
5.1. General information
5.2. Block diagrams of control systems of converting devices
5.2.1. Control systems for rectifiers and dependent inverters
5.2.2. Direct coupled control systems for frequency converters
5.2.3. Stand-alone inverter control systems
5.2.4. Control systems for regulators-stabilizers
5.3. Microprocessor systems in converting technology
5.3.1. Typical generalized microprocessor structures
5.3.2. Examples of using microprocessor control systems
Chapter six. Application of power electronic devices
6.1. Areas of rational use
6.2. General technical requirements
6.3. Emergency protection
6.4. Operational control and diagnostics of technical condition
6.5. Providing parallel operation of converters
6.6. Electromagnetic interference
Bibliography
Bibliography
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FOREWORD
Power electronics is a constantly evolving and promising field of electrical engineering. Advances in modern power electronics have a great impact on the rate of technological progress in all advanced industrial societies. In this regard, there is a need for a wide range of scientific and technical workers in a clearer understanding of the foundations of modern power electronics.
Power electronics currently has a fairly deeply developed theoretical foundations, however, the author did not set himself the task of even a partial presentation, since numerous monographs and textbooks are devoted to these issues. The content of this book and the method of its presentation are designed primarily for engineers and technicians who are not specialists in the field of power electronics, but are associated with the use and operation of electronic devices and devices and who want to get an idea of \u200b\u200bthe basic principles of operation of electronic devices, their circuitry and general provisions for development and operation. In addition, most of the sections of the book can also be used by students of various technical educational institutions in the study of disciplines, the curriculum of which includes issues of power electronics.
Power electronics is called the field of science and technology, which solves the problem of creating power electronic devices, as well as the problem of obtaining significant electrical energy, controlling powerful electrical processes and converting electrical energy into a sufficiently large energy of another type when using these devices as the main tool.
Below are considered power electronics devices based on semiconductor devices. It is these devices that are most widely used.
The solar cells discussed above have been used to generate electrical energy for a long time. At present, the share of this energy in the total electricity volume is small. However, many scientists, including the Nobel Prize laureate academician Zh.I. Alferov, consider solar cells to be very promising sources of electrical energy that do not disturb the energy balance on Earth.
The control of powerful electrical processes is precisely the problem in solving which power semiconductor devices are already very widely used, and the intensity of their use is rapidly increasing. This is due to the advantages of power semiconductor devices, the main of which are high speed, low drop in the open state and low drop in the closed state (which provides low power losses), high reliability, significant current and voltage load capacity, small size and weight, ease of use. control, organic unity with semiconductor devices of informative electronics, which facilitates the integration of high-current and low-current elements.
In many countries, intensive research and development work on power electronics has been launched, and thanks to this, power semiconductor devices, as well as electronic devices based on them, are constantly being improved. This enables a rapid expansion of the field of application of power electronics, which in turn stimulates research and development. Here we can talk about positive feedback on the scale of the whole field of human activity. The result is the rapid penetration of power electronics into a wide variety of technical fields.
The proliferation of power electronics devices began especially rapidly after the development of power field-effect transistors and IGBTs.
This was preceded by a rather long period when the main power semiconductor device was an unlocked thyristor, created in the 50s of the last century. Non-latching thyristors have played an outstanding role in the development of power electronics and are widely used today. But the impossibility of switching off by means of control pulses often complicates their application. For decades, developers of power devices had to come to terms with this drawback, using in some cases rather complex nodes of power circuits to turn off thyristors.
The widespread use of thyristors led to the popularity of the term "thyristor technology" that emerged at that time, which was used in the same sense as the term "power electronics".
Power bipolar transistors developed during this period found their field of application, but did not radically change the situation in power electronics.
Only with the advent of power field-effect transistors and 10 W in the hands of engineers were fully controllable electronic switches, approaching in their properties to ideal. This greatly facilitated the solution of a wide variety of tasks for controlling powerful electrical processes. The presence of sufficiently sophisticated electronic keys makes it possible not only to instantly connect the load to a DC or AC source and disconnect it, but also to generate very large current signals or practically any required form for it.
The most common typical power electronics devices are:
contactless switching devices alternating and direct current (interrupters) designed to turn on or off the load in the alternating or direct current circuit and, sometimes, to regulate the load power;
rectifiersconverting the variable in one polarity (unidirectional);
invertersconverting constant to variable;
frequency convertersconverting a variable of one frequency to a variable of another frequency;
dC converters (converters), converting a constant of one quantity into a constant of another quantity;
phase convertersconverting an alternating one with one number of phases into an alternating one with a different number of phases (usually single-phase is converted to three-phase or three-phase - to single-phase);
compensators (power factor correctors) designed to compensate for reactive power in the AC supply network and to compensate for distortions of the current and voltage waveform.
Essentially, power electronics devices convert powerful electrical signals. For this reason, power electronics is also referred to as converter technology.
Power electronics devices, both standard and specialized, are used in all areas of technology and in almost any fairly complex scientific equipment.
As an illustration, we indicate some objects in which power electronics devices perform important functions:
Electric drive (regulation of speed and torque, etc.);
Plants for electrolysis (non-ferrous metallurgy, chemical industry);
Electrical equipment for the transmission of electricity over long distances using direct current;
Electrometallurgical equipment (electromagnetic stirring of metal, etc.);
Electrothermal installations (induction heating, etc.);
Electrical equipment for battery charging;
Computers;
Electrical equipment of cars and tractors;
Electrical equipment of aircraft and spacecraft;
Radio communication devices;
Equipment for TV broadcasting;
Devices for electric lighting (power supply of fluorescent lamps, etc.);
Medical electrical equipment (ultrasound therapy and surgery, etc.);
Power tool;
Consumer electronics devices.
The development of power electronics also changes the very approaches to solving technical problems. For example, the creation of power field-effect transistors and IGBTs significantly contributes to the expansion of the field of application of inductor motors, which in a number of areas are replacing collector motors.
A significant factor that has a beneficial effect on the spread of power electronics devices is the success of informative electronics and, in particular, microprocessor technology. To control powerful electrical processes, more and more complex algorithms are used, which can be rationally implemented only with the use of sufficiently advanced informative electronics devices.
The effective combination of advances in power and power electronics produces truly outstanding results.
Existing devices for converting electrical energy into other types of energy with the direct use of semiconductor devices do not yet have a high output power. However, encouraging results were obtained here.
Semiconductor lasers convert electrical energy into coherent energy in the ultraviolet, visible and infrared ranges. These lasers were proposed in 1959, and were first implemented on the basis of gallium arsenide (GaAs) in 1962. Semiconductor lasers are distinguished by high efficiency (above 10%) and long service life. They are used, for example, in infrared floodlights.
Super-bright white LEDs, which appeared in the 90s of the last century, are already used in a number of cases for lighting instead of incandescent lamps. LEDs are significantly more economical and have a significantly longer lifespan. The range of applications for LED luminaires is expected to expand rapidly.
In this article, we'll talk about power electronics. What is power electronics, what is it based on, what are the advantages, and what are its prospects? Let us dwell on the components of power electronics, consider briefly what they are, how they differ from each other, and for what applications are these or those types of semiconductor switches convenient. Here are examples of power electronics devices used in everyday life, at work and at home.
In recent years, power electronics devices have made a major technological breakthrough in energy conservation. Power semiconductor devices, due to their flexible controllability, enable efficient conversion of electricity. The weight and size indicators and efficiency achieved today have already brought the converting devices to a qualitatively new level.
Many industries use soft starters, speed controllers, uninterruptible power supplies, operating on a modern semiconductor base, and showing high efficiency. These are all power electronics.
Controlling the flow of electrical energy in power electronics is carried out using semiconductor switches, which replace mechanical switches, and which can be controlled according to the required algorithm in order to obtain the required average power and precise action of the working body of one or another equipment.
So, power electronics is used in transport, in the mining industry, in the field of communications, in many industries, and not a single powerful household appliance can do today without power electronic units included in its design.
The main building blocks of power electronics are precisely the semiconductor key components that are capable of opening and closing a circuit at different speeds, up to megahertz. In the on state, the resistance of the key is units and fractions of an ohm, and in the off state - megaohms.
Key management does not require a lot of power, and the losses on the key arising during the switching process, with a well-designed driver, do not exceed one percent. For this reason, the efficiency of power electronics is high compared to the losing ground of iron transformers and mechanical switches such as conventional relays.
Power electronic devices are devices in which the effective current is greater than or equal to 10 amperes. In this case, the key semiconductor elements can be: bipolar transistors, field-effect transistors, IGBT transistors, thyristors, triacs, lockable thyristors, and lockable thyristors with integrated control.
Low control power also allows you to create power microcircuits in which several blocks are combined at once: the key itself, the control circuit and the control circuit, these are the so-called intelligent circuits.
These electronic building blocks are used both in high-power industrial installations and in household electrical appliances. An induction oven for a couple of megawatts or a home steamer for a couple of kilowatts - both have semiconductor power switches that simply operate at different powers.
Thus, power thyristors operate in converters with a capacity of more than 1 MVA, in circuits of DC electric drives and high-voltage AC drives, are used in reactive power compensation installations, in induction melting installations.
The lockable thyristors are controlled more flexibly, they are used to control compressors, fans, pumps with a capacity of hundreds of kVA, and the potential switching power exceeds 3 MVA. allow the implementation of converters with a capacity of up to MVA units for various purposes, both for controlling motors and for ensuring uninterrupted power supply and switching high currents in many static installations.
MOSFETs have excellent controllability at frequencies of hundreds of kilohertz, which greatly expands their range of applicability compared to IGBTs.
Triacs are optimal for starting and controlling AC motors, they are capable of operating at frequencies up to 50 kHz, and for control they require less energy than IGBT transistors.
Today, IGBT transistors have a maximum switching voltage of 3500 volts, and potentially 7000 volts. These components can replace bipolar transistors in the coming years, and they will be used on equipment up to MVA units. For low-power converters, MOSFETs will remain more acceptable, and for more than 3 MVA - lockable thyristors.
According to analysts, most of the power semiconductors in the future will be modular, with two to six key elements located in one package. The use of modules allows you to reduce weight, reduce the size and cost of the equipment in which they will be used.
For IGBT transistors, the progress will be an increase in currents up to 2 kA at a voltage of up to 3.5 kV and an increase in operating frequencies up to 70 kHz with simplified control circuits. One module can contain not only keys and a rectifier, but also a driver and active protection circuits.
Transistors, diodes, thyristors produced in recent years have already significantly improved their parameters, such as current, voltage, speed, and progress does not stand still.
For a better conversion of alternating current into direct current, controlled rectifiers are used, which allow smoothly changing the rectified voltage in the range from zero to nominal.
Today, in the excitation systems of DC electric drives, thyristors are mainly used in synchronous motors. Dual thyristors - triacs, have only one gate electrode for two connected anti-parallel thyristors, which makes control even easier.
To carry out the reverse process, the conversion of direct voltage to alternating voltage is used. Independent semiconductor switch inverters give the output frequency, shape and amplitude determined by the electronic circuit, not the network. Inverters are made on the basis of various types of key elements, but for high powers, more than 1 MVA, again, IGBT-based inverters come out on top.
Unlike thyristors, IGBTs provide the ability to more widely and more accurately shape the current and voltage at the output. Low-power car inverters use field-effect transistors in their work, which, at powers of up to 3 kW, do an excellent job of converting the direct current of a 12-volt battery, first into direct current, through a high-frequency pulse converter operating at a frequency from 50 kHz to hundreds of kilohertz, then - in alternating 50 or 60 Hz.
To convert a current of one frequency into a current of another frequency, they are used. Previously, this was done exclusively on the basis of thyristors, which did not have full controllability; it was necessary to design complex forced-locking circuits for thyristors.
The use of switches such as field-effect MOSFETs and IGBT transistors facilitates the design and implementation of frequency converters, and it can be predicted that in the future, thyristors, especially in low-power devices, will be abandoned in favor of transistors.
For reversing electric drives, thyristors are still used; it is enough to have two sets of thyristor converters to provide two different directions of current without the need for switching. This is how modern contactless reversing starters work.
We hope that our short article was useful for you, and now you know what power electronics is, what elements of power electronics are used in power electronic devices, and how great the potential of power electronics is for our future.
Published Date: 12.10.2017
Do you know the basics of power electronics?
We can see overwhelming progress in this matter towards the development of commercial thyristors or silicon rectifiers (SCRs) from General Electric Co. Power electronics concept
Power electronics - one of the modern topics of electrical engineering, which has recently achieved great success and has influenced human life in almost all areas. We ourselves use so many power electronic applications in our daily life without even realizing it. Now the question arises: "What is power electronics?"
We can define power electronics as an item that is a hybrid of energy, analog electronics, semiconductor devices and control systems. We base the foundations of each subject and apply it in a combined form to obtain a regulated form of electrical energy. Electrical energy by itself is not applicable until it is converted into a tangible form of energy such as movement, light, sound, heat, etc. To regulate these forms of energy, an effective way is to regulate the electrical energy itself. and these forms the content of subjective power electronics.
We can see overwhelming progress in this matter towards the development of commercial thyristors or silicon rectifiers (SCRs) from General Electric Co. in 1958. Prior to this, control over electrical energy was carried out mainly with the use of thyratrons and mercury arc rectifiers, which operate on the principle of physical phenomena in gases and vapors. After SCR, there have been many powerful electronic devices such as GTO, IGBT, SIT, MCT, TRIAC, DIAC, IEGT, IGCT and so on. These devices are rated for several hundred volts and amperes, as opposed to signal level devices that operate at several volts and amperes.
To accomplish the purpose of power electronics, the devices operate like nothing more than a switch. All power electronics act like a switch and have two modes, i.e. ON and OFF. For example, the BJT (Bipolar Junction Transistor) has three areas of operation in the cut-off characteristics of the output characteristics, active and saturated. In analog electronics, where the BJT is to act as an amplifier, the circuit is designed to bias it into the active region of operation. However, in power electronics, the BJT will operate in the cutoff region when it is off and in the saturation region when it is on. Now that the devices are supposed to work as a switch, they must follow the basic characteristic of the switch, that is, when the switch is on, it has zero voltage drop across it and transfers full current through it, and when it is OFF, it has a full voltage drop across it. it and zero current flowing through it.
Now, since V or I is zero in both modes, the switch power is always zero as well. This characteristic is easily visualized in a mechanical switch, and the same must be observed in a power electronic switch. However, there is almost always a leakage current through the devices when it is in the OFF state, i.e. Ileakage ≠ 0, and there is always a voltage drop in the ON state, that is, Von ≠ 0. However, the value of Von or Ileakage is very less and therefore the power through the device is also very small, in the order of a few millivolts. This power is dissipated in the device and therefore proper heat evacuation from the device is important. In addition to these state and OFF state losses, there are also switching losses in power electronic devices. This happens mainly when the switch is switched from one mode to another, and V and I are changed through the device. In power electronics, both losses are important parameters of any device and are necessary to determine its voltage and current ratings.
Power electronics alone are not as useful in practical applications and therefore require circuit design along with other supporting components. These supporting components are like the decision part that controls the power electronic switches to achieve the desired result. This includes a firing circuit and a feedback loop. The block diagram below shows a simple power electronic system.
The control unit receives the output signals from the sensors and compares them with the references and accordingly introduces the input signal to the firing circuit. The firing circuit is basically a pulse generating circuit that provides a pulse output in such a way as to control the power electronic switches in the main circuit unit. The end result is that the load receives the required electrical power and therefore delivers the desired result. A typical example of the above system would be speed control of motors.
There are basically five types of power electronic circuits, each with a different purpose:
- Rectifiers - Converts Fixed AC to AC DC
- Choppers - Converts DC to AC DC
- Inverters - convert DC to AC with variable amplitude and variable frequency
- AC voltage controllers - converts fixed AC to AC at the same input frequency
- Cycloconverters - Converts Fixed AC to Variable Frequency AC
There is a common misconception regarding the term transformer. A converter is basically any circuit that converts electricity from one form to another. Therefore, all of the five listed are types of transducers.
