Dissertation to receive a master degree "M.Sc" in the field of power electrical engineering
High voltage trend
Abstract
Inverters can produce single-phase and three-phase ac voltages from a constant or variable dc voltage. There are various methods to control the output voltage of the inverter, which is introduced in this thesis from an inverter system with solar panel input. The boost is converted into the set voltage. Then this DC voltage is converted into alternating voltage using a three-level inverter with SVM control. The use of a three-level inverter reduces the switching frequency and reduces the losses. To check the accuracy of the operation, the system is simulated in the simulink environment of matlab software. Chapter One: Introduction
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Direct current to alternating current converters are known as inverters. The task of an inverter is to convert a direct input voltage into an alternating and symmetrical output voltage current with the desired amplitude and frequency. The output voltage can have a fixed or variable value at a fixed or variable frequency. The output voltage can be obtained by changing the direct input voltage and keeping the inverter gain constant. On the other hand, if the direct input voltage is constant and cannot be controlled, a variable output voltage can be obtained by changing the gain of the inverter. This operation is usually done by controlling the width modulation (pwm) internally. The efficiency of the inverter can be defined as the ratio of the output alternating voltage to the direct input voltage.
The waveform of the output voltage in the inverter should be sinusoidal in ideal inverters, however, in scientific inverters these waveforms are non-sinusoidal and have a series of specific harmonics. In medium power and low power applications, square or almost square voltages may be acceptable, but in high power applications, sine waves with very low distortion are needed. By having fast power semiconductor parts, it is possible to significantly reduce output voltage harmonics by using switching methods.]14 [
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Inverters are widely used in industry (such as AC motor drives with variable speed, induction heating, auxiliary power supplies and uninterruptible power supplies) The input of the inverter may be a battery, cell Coal, solar cell or any other direct source. The output of single phase inverters is usually equal to (1) 120 volts at 60 Hz frequency, (2) 220 volts at 50 Hz frequency and (3) 115 volts at 400 Hz frequency. (2) 120/208 V at 60 Hz frequency and (3) 115/200 V at 400 Hz frequency).]11[
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Inverters can be divided into two general categories: 1) single-phase inverters and 2) three-phase inverters
Each category can be used depending on the type of application depending on the type of application. controlled switching on and off (such as BJTs, MOSFETs, IGBTs, MCTs, SITs and GTOs) or thyristors with forced commutation. These inverters usually use PWM control signals to generate alternating output voltage. If the input voltage of the inverter is constant, the inverter is called a voltage-fed inverter, and if the input current is kept constant, it is called a voltage-fed inverter, and if If the input current is kept constant, it is called a current-fed inverter, and if the input is controllable, it is called a variable dc connection inverter. [11]
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You can see the general and simple scheme of a single-phase full-bridge inverter in the figure below
Table 1-1: Switching table in the single-phase full-bridge inverter
Figure 1-1: General and simple scheme of a single-phase full-bridge inverter
As you can see in the table above, all keys and The voltage output signal will be + and when the and keys are turned on, the voltage output signal will be - and when the and keys or the and keys are turned on, the output voltage will be zero.
Figure 1-2: Output waveform of voltage and current of single phase full bridge inverter
The figure below shows the voltage and output current waveforms of single phase full bridge inverter with IGBT.
Figure 1-3: General scheme of a single-phase full-bridge inverter and output voltage and current waveform
The inverter waveform is usually close to a square waveform. In order to bring this waveform closer to a sinusoidal state, we can connect several inverters together and make a multi-level inverter. Figure 4-1 is a simple view of a multi-level inverter. Figure 4-1: A simple representation of a multilevel inverter
Inverters have no moving parts and are used in a wide variety of applications, from computer power supplies to large bulk transportation equipment. Inverters are usually used to provide AC current from DC sources such as solar panels or batteries.
Inverter is a high power electronic oscillator. The reason for this name is that this device performs the reverse operation of a common AC to DC power converter. In fact, an inverter or AC drive is a device that can be used to control the speed of a three-phase AC motor without reducing the power and torque of the motor. Inverters are made in different capacities, for example, a 20 HP inverter should be used for a 20 horsepower motor.
In terms of input, inverters are divided into two groups, single phase and three phase. Of course, the output of all of them is three phase. For inverters with more than 3 horsepower, only three-phase input is used.
Some low-power inverters have a warning not to use them to turn on ordinary fluorescent lamps. The reason for this warning is that the power correction capacitor is connected in parallel with the lamp. By removing the capacitor, the problem will be solved.]13[
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Decreasing the energy consumption and therefore reducing the cost of electricity, reducing the starting current and thus prolonging the life of the motor, the possibility of changing the motor speed, the possibility of changing the direction of the motor movement, having protection against overload, the possibility of the motor working in conditions where the input voltage is variable, the possibility of remote control, creating a speed greater than the rated speed of the motor, planning the movement.
The inverter intelligently adjusts the amount of load It detects the input to the motor and gives current to the motor according to the same load, and this current is often less than the rated current of the motor. It is an electronic device that can be used to change the speed of three-phase motors.]15[
Its other uses can be mentioned as follows:
**Motor speed regulator (remote control)
**Easily changing the direction of rotation without the need for a contactor
**Turning the motor on and off without the need to disconnect and connect the main power
**Reducing mechanical shocks and As a result of increasing the useful life of the mechanical part
**Protecting the engine against voltage increase and preventing engine damage
Soft start of the engine without any impact on the mechanical parts such as couplings, clutches, belts, chains and so on. and as a result, it will increase the useful life of the engine and other mechanical parts
protecting the engine against overload; In this case, if the motor load exceeds the normal permissible value, the inverter will turn off the motor and show the user an overload message.
Preventing the motor from heating up and eventually burning out in applications where the motor is continuously turning left and right or turning off. During start-up, this current reaches 60 amps, and if an inverter is used, this current reaches a maximum of 12.
The motor current is automatically reduced when the motor load is reduced. This capability will increase the useful life of the motor in addition to reducing the cost of electricity. (2.2kw) in the sense that a three-phase motor can be started in a normal way with household electricity.