180-DEGREE THREE PHASE INVERTER WITH SIMULATION

The inverters are used to convert DC power into AC power. There are several types of inverter available. Click on below link to know more about different types of inverter.

https://circuitdigest.com/tutorial/different-types-of-inverters

According to the mode of operation, three-phase inverters are classified into two types; 180-degree mode and 120-degree mode. Before going to classification, revise the circuit diagram of a three-phase inverter and it is as shown in below figure.

Circuit diagram of three-phase inverter:

As we can see in the circuit diagram, three phase star connected load is connected and output is measured at the load. One arm for each phase means we have a total of three arms. For switching purpose, we can use MOSFET or IGBT or any other power electronics switches according to the application.

When the upper switch of any phase is in conduction mode (ON), at that time positive half cycle of that phase appears in the output. When the lower switch of any phase is in conduction mode (ON), at that time negative half cycle of that phase appears in the output. In one arm two switches are available and these two switches never conduct at the same time. If this happens than DC source will short-circuit.

In the 180-degree mode of operation of the three-phase inverter, all switches conduct for 180-degree. In other words, MOSFET will ON for 180-degree and OFF for 180-degree of one cycle and the pulse width is 50% of the period.

Simulation in MATLAB/SIMULINK:

This is the simulation of three-phase inverter. The circuit diagram of 180-degree and 120-degree is same. The only difference is in the GATE pulse of switches. Here in this blog, we will discuss 180-degree inverter.

The gate pulse of 1 & 4, 3 & 6 and 5 & 2 are totally opposite in this mode of operation. When MOSFET-1 is ON at that same time MOSFET-4 is OFF.

Switching of MOSFET:

How to generate this gate pulse?

The screenshot of MATLAB for gate pulse generator is below image.

Gate pulse generator:

Vab = Va0 – Vb0

Vbc = Vb0 – Vc0

Vca = Vc0 – Va0

The peak value of phase voltage (Va0) is 2Vs/3 and the peak value of line voltage is Vs. where Vs is the DC supply voltage. The waveform of the 180 degrees is as shown in below figure. This is a book image. We will compare this image with simulation results at the end of this blog.

Waveform of 180-degree inverter:

How to set pulse width in the pulse generator. You have to create gate pulse only for MOSFET 1,3 and 5 and toggle it with the help of NOT gate and give it to MOSFET 6, 2 and 4. Now, the question is how to generate gate pulse for 1, 3 and 5. For that, we will use the PULSE GENERATOR. For 50Hz output signal, the time period is 20 msec and amplitude is 1 for all pulse generator. For 180-degree inverter mode, the pulse width is 50%.

Phase delay for one signal is 0 sec and this signal is for phase-A and MOSFET-1. It is clear in the above table that, there is 120-degree phase delay between these two signals. So, phase delay for phase B and MOSFET-3 is 120-degree or (2e-3)*2/3. Now for the third signal, the phase delay is 60-degree or (2e-3)*1/6 and this signal is for MOSFET-5.

By this way, we have three signals. For the other three signals we will use NOT gate and inverse this signals as shown in the above screenshot.                                      

Output waveform:

from above figure we can see that, for DC supply of Vs = 100V, the peak phase voltage Va0 is (2*100)/3=66.6V and the peak phase voltage Vab = 100V. This result is same as book waveform. If you need this simulation you can contact me or comment in this blog.

Thanks for reading.

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CLOSE LOOP INVERTER

Close loop inverter:

What is the difference between open loop and closed loop inverter?

* In Open loop inverter, the output is varying with respect to the input. Suppose, the source of the inverter is not the constant source and input of the inverter is not constant, its varying with respect to time. In this condition, if you have used an open loop inverter than the output of the inverter is also varying. This varying supply can damage the equipment. So, we need a constant output. In another word, the output voltage of inverter must remain constant when supply voltage varies.

* In close loop inverter, a controller is used to control the output voltage. In open loop inverter, the output voltage is not controlled. So, no need to use a controller. But in case of closed loop inverter, we need a controller which can control the output voltage at our reference voltage.

* Cost of open loop inverter is less compared to close loop inverter.

* Open loop inverter is easy to design. But close loop inverter is very difficult to design.

* Close loop inverter is used more in real life application.

How to make a closed loop inverter?

To make a closed loop inverter, we need an open loop inverter. Now we will apply control strategy to this inverter.

1) measure output voltage (Vact) of the inverter.

2) compare Vact to a reference voltage (Vref).

3) difference between output voltage and the reference voltage is called an error and this error is given to the controller (PI, PID)

4) the output of the controller is the modulation index.

5) The modulation index changes with respect to actual output. This modulation index is multiplied with sine wave signal.

6) this sine wave signal is compared with a triangular signal and according to that gate pulse for IGBT is generated. This method is known as the SPWM technique to control the output.

If you need this simulation, comment your mail ID.

For simulation of closed loop inverter:

https://youtu.be/oAAlrNxoGmE

For simulation of open loop inverter:

https://youtu.be/YOrpGGn4mbY

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SINGLE PHASE INVERTER WITH SIMULATION (MATLAB)

Single phase inverter:

Single phase inverters are used in low power applications like home, office etc. This type of inverter is not use in industries to run heavy load.

There are two types of supplies from utility company; one is single phase supply and other is three phase supply. This type of inverters is use where single-phase utility supply is available. The combination of inverter and battery are used for backup power. In solar power plants, solar energy is generated by PV panels. This power is unregulated DC power. So, this power is not useful, we cannot directly use this power for our home appliances because, this equipment is made for AC supply. So, it requires pure AC supply which is directly not available from PV panels. In this case, the inverters are plays an important role and it is used to convert unregulated DC power in to regulated AC power. This is the main function of inverter.

Operation of single phase inverter:

                In single phase inverter, four IGBTs are used for switching. For upper half cycle of sine wave two IGBT (1&4) will operate and for lower half cycle remaining two IGBT (2&3) will operate. By this way, we can get AC waveform across the load. Now, we need gate pulse to ON and OFF IGBT. As we seen, IGBT 1 & 4 operate at same time. So, same gate pulse is required for this both IGBT. Similarly, IGBT 2 & 3 operate at same time. IGBT 1 & 4 operates simultaneously, both switches cannot operate at same time. So, pain 1-4 and 2-3 has exactly opposite gate pulse. This is how we can get square wave AC output. But our appliances are not suitable with this supply. So, we need to convert this square wave output into the pure sine wave output. For that we will use LC filter or LLC filter.

  

Simulation of single-phase inverter in MATLAB:

Open loop single-phase inverter:

                In MATLAB, IGBT/diode is used for switching purpose. The pulse generator is used to generate gate pulse for all IGBT. [A] is gate pulse for IGBT 1-4. [B] is gate pulse for IGBT 2-3. Connect all components as shown in below picture and for more info watch video.

circuit diagram (simulation in MATLAB):

 Waveform without filter:

Waveform with filter:

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SINGLE PHASE OPEN LOOP INVERTER

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INTRODUCTION OF FACTS DEVICES

FACTS (Flexible AC Transmission System)

Introduction:

FACTS devices are used in AC transmission system. These devices are used to improve the stability and controllability of the transmission network. The FACTS is a static device, which is based on the power electronics. The power transfer capacity is fixed for any transmission network. If we transfer power beyond this limit, equipment may get damage. We can increase power transfer capacity by changing the layout of the power system but this is not a feasible way. So, in the actual power system, we use FACTS devices to increase power transfer capacity.

In simple word, FACTS is a variable impedance device like inductors and capacitors. In an ideal transmission system, the active power is equal to the apparent power. It means that the Power factor is unity. The power factor is defined as the ratio of the active power to the apparent power. This is the main role of FACTS devices, it is trying to keep power factor as near as possible to unity.

The active power is known as true power and it is useful for work in the system. The reactive power is not useful for the load. The reactive power is caused by the energy storage equipment. If we want to achieve the maximum power transfer capacity, we have to reduce the amount of reactive power. The reactive power reduces the power transfer capacity. The techniques used to reduce reactive power is known as the compensation technique.

In order to improve the efficiency of the power system, the compensation technique is supplying the inductive and reactive power to the power system. By these techniques, we can improve the quality of power, stability, voltage regulation, power factor.

Classification:

According to the type of connection; series compensation, shunt compensation.

Series compensation:

This type of compensation technique, FACTS devices are connected in series with the power system network. By series compensation, we can improve the stability and dynamic response of the system. Generally, the capacitors are connected in series with the transmission network. The amount of compensation is controlled by power electronics switches. For better control, more than one capacitor (capacitor bank) is connected.

                Example of series compensation:

                                Thyristor Controlled Switched Capacitor (TCSC)

                                Static Synchronous Series Compensator (SSSC)

                                Fixed Series Capacitor (FSC)

                                Thyristor Switched Series Capacitor (TSSC)

                                Thyristor Switched Series Reactor (TSSR)

Shunt compensation:

in this type of compensation technique, FACTS devices are connected in parallel or shunt with the transmission network. In this technique, the current is injected into the system from the FACTS devices and by this way the reactive component is reduced. This technique is used to improve voltage regulation and reduce losses of the power system. There are two types of shunt compensation; shunt capacitive compensation and shunt inductive compensation. The shunt capacitive compensation technique is used to improve the power factor. The shunt inductive compensation technique is used to charging the transmission line in low load condition or no-load condition.

                Example of Shunt compensation:

                                STATic Synchronous COMpensator (STATCOM)

                                Static VAR Compensator (SVC)

                                                Thyristor Controlled Reactor (TCR)

                                                Thyristor Switched Reactor (TSR)

                                                Thyristor Switched Capacitor (TSC)

In the next article, we will discuss briefly on all types of compensation device.

Please review this article, at the bottom of this page.                                      

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INVERTER

What is the function of Inverter?

There are two types of electrical energy; AC power and DC power. In our regular life, generally we use AC power for our household equipment and in office also we need AC power. But we cannot store electrical energy in the form of AC. We can store only DC power. For that, we use a battery. The batteries are run on very low voltage. The battery cannot be used to run household appliances. Power generated from a diesel generator or power supplied by the utility is AC power and most of all appliances are also designed to run on AC power.

Now you think what is the function of the inverter in office or home. The inverter is used to supply back up power when utility fails to supply power or during maintenance. The inverter takes DC power from the battery and converts it into AC power. This is the main function of an inverter.

Types of inverter:

(A) According to the output characteristic (shape of AC wave they produce), inverters are classified into three types.

                1) The square wave inverter

                2) The modified sine wave inverter or quasi-sine wave inverter

                3) The pure sine wave inverter

        The output waveform of this inverter is a square wave. This type of inverter is not used because the shape of the output waveform is not suitable for most running appliances. Construction of square wave inverter is easy and cheap in cost. but square wave inverters are obsolete from the market because of fewer applications.

        In this type of inverter, the output waveform is not a pure sine wave and not a square wave. The shape of the output power is similar to the staircase. This shape is useful for appliances like television, radio etc. but not useful for sensitive devices like a battery charger, variable speed motor and heaters. In this waveform some amount of noise is present. It is cheap compared to pure sine wave inverter. So, it depends on the application, if you require inverter for selected household application only then go for this inverter otherwise go for pure sine wave inverter.

        This is the best inverter for all type of applications and efficient for all nature of the load. Generally, if cost is not considerable than always use pure sine wave inverter. The shape of output power is a pure sine wave. This shape is the same as utility power. Filters are used to getting a pure sine wave. The pure sine wave inverters are the costliest inverter compared to all another inverter.

(B) The output of the inverter is AC power and there are two types of AC power; single phase and three phase. According to output power inverter can classify into two types;

                1) single phase inverter

                2) three phase inverter

        This is depending on the utility connection. For a small load, single phase connection is provided and for large load three phase connection is provided. Generally, for domestic load single phase connection is used and for industrial load three phase connection is used.

(C) According to a source of input;

                1) current source inverter (CSI)

                2) voltage source inverter (VSI)

        In CSI, the input is a current source. This type of inverters is widely used in the medium voltage industrial application, where high-quality current waveform are compulsory. But CSIs are not popular.

        In VSI, the input is a voltage source. This type of inverter is widely used in all applications because it is more efficient and have higher reliability and faster dynamic response. VSI is capable of running motors without de-rating.

Applications:

1) An uninterrupted power supply (UPS) supplies AC power with the help of inverter and battery combination.

2) Speed control of electric motor: An inverter is designed to produce a variable output voltage and by controlling the output voltage of the inverter, we can control the speed of an electric motor.

3) In the compressor of refrigerator and air-conditioner: In the simple inverter, single speed compressor switches on and off periodically. But in inverter compressor, VFD (variable frequency drive) is used to control the speed of compressor motor and according to this control of cooling is done.

4) Solar: Output of solar PV panels is DC. So, we have to convert it to AC for that inverters are used.

5) HVDC transmission line: For bulk power transmission, HVDC transmission line has more advantages than HVAC transmission line. In this transmission network, power is generated in AC and convert in DC with the help of rectifier and transmit this DC power for long distance. At receiving end power is converted into AC with the help inverter.

Simulation of simple three-phase inverter:

https://articleelectrical.blogspot.com/2018/11/simulation-of-three-phase-inverter.html

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