Thyristor and DC/AC Inverter - Coursework Example

Thyristor and DC/AC Inverter Name: Institution: Date: Thyristor and DC/AC Inverter The paper will highlight a clear description of the inverters and thyristors. It will discuss the various factors to consider while selecting an inverter depending on their sizes. It will also discuss the various states of a thyristor which must be considered in its functionality. The various states include; reverse blocking, forward blocking and forward conducting states. The paper will also discuss the operation of the thyristor, depending on the four semiconductor regions i.e. p-n-p-n regions. A power inverter can be described as a circuitry that converts direct (DC) current into alternating current (AC). It is important to understand that the inverter produces no power. The power has to be provided by a DC source. According to Lu, and Sharma (2008) it is important also to determine the design of the electronic device since it determines the input and output voltages. It also determines the overall power handling as well as the voltage frequency. Power inverters take different forms, they can either be entirely electronic, an arrangement of mechanical effects. In the application of the inverters knowledge on the input and output voltage is very important. The inverter requires a DC power source which is reliable and stable in supplying the required amount of current. This is determined by the amount of power required by a given system. Zhong, and Hornik, (2012) argued that while determining input voltage, it is important to consider, the purpose and the design of the inverter. The inverters are of different sizes depending on the intended purpose. For instance, a 12 VDC inverter is considered for smaller commercial inverters and consumers. They rely on 12 V rechargeable lead acid batteries. A 24, 36, and a 48 VDC is suitable for a home energy system. In photovoltaic solar panels, a bigger inverter ranging from 200 to 400 VDC is suitable. In vehicles, an inverter with 300-450 VDC is recommendable. Finally, high-voltage direct current systems will require hundreds of thousands of volts. Inverters also have output waveforms. They can produce a number of waves which include; modified sine waves, square waves, pulsed sine waves, and pulse width modulated waves. However, the most common and dominant waveforms are the sine wave and the modified sine waves as per the year 2017’s market. In the production of the household plug-in voltage from a DC source with low voltage, there are two basic designs. The first design is the one that uses switching boost converter and aid in the production of a high-voltage DC, and then converting it into AC. The other design is the one which will convert DC to AC at a level of a battery. This design is modified in such a way that it will apply line-frequency transformer in the creation of output voltage. According to Mohan, (2011) in output voltage, there is regulation of the AC output of the inverter such that it is equal to the grid line voltage. An inverter will also have an overall power rating which is given in kilowatts. These power units describe the amount of power available for the device that the inverter will be driving. A thyristor is a semiconductor device in the solid state; it consists of four alternating N layers and P-type materials. They are known for controlling a large amount of voltage and power using only a small device. For this reason, therefore, they have been highly applied in the control of electric current in a motor vehicle, e.g. in speed control and in other power transmissions requiring a high DC voltage. They can be used in a number of areas such as; inverter circuits, low-cost timer circuits, chopper circuits, oscillator circuits, speed control circuits, logic circuits, relay-replacement circuit, power-switching circuits, light dimming circuits, level detector circuits, phase control circuits among other applications. Tan, Wang, and Ji, 2007 postulated that these devices were first introduced in the market in the year 1956. However, the thyristor by then was not easily applicable in direct current since they were only relying on current reversals in order to turn them off. However, with improved devices that were later introduced in the market, it is easy to either be turned on or off by the use of control gate signals. Many people tend to confuse between a thyristor and a transistor. The two are different in that a thyristor is either on or off. Unlike a transistor, it can never be proportional; you either turn it off or on. On the other hand, a transistor has the ability to lie between the states of being on or off. Due to this reason, a transistor is suitable for analog amplifiers while a thyristor is suitable for a switch. There are three states that a thyristor will take in order for it to be effective, in their functionality. The first state is the reverse blocking mode. In this state, voltage is directed to the direction where a diode will block it. The other state is referred to as forward blocking mode. In this state, the voltage is directed towards a direction where the diode will have to conduct. The last state is the forward conducting mode. In this state, a thyristor unlike in the forward blocking mode has been activated to conduction. It is in this state that conduction will continue to a point where the forward current is below a holding current point. In order for one to understand how the thyristor operates and to be in a position to effectively utilize it is important to understand their theories and operation. According to Meyer, and Rufer, (2006) these devices are made of four regions which are semiconductors. These regions are the p-n-p-n. The cathode is made of the outer p while the cathode is made of the outer n. These regions are shown in the figure below Figure 1a Connecting a transistor to the cathode of the thyristor, the resulting device has a structure of n-p-n. Similarly, connecting a transistor on the anode, the resulting device will have a p-n-p structure. This is illustrated in the figure below . Figure 1b In the set up above, it can be observed that there is a positive feedback loop that has been formed within the thyristor. Here, the yielded current of the first transistor is fed to the input of the other. Similarly, the yield of the second transistor is fed to the input of the first transistor. Current will keep building up till a point where the two transistors are fully saturated. According to Nemati, (2007) the voltage will not flow when passed through the thyristor because none of the transistors are conducting. Consequently, the path across the thyristor is incomplete. The transistor TR2 will be turned ‘on’ when some current is passed via gate electrode. When the TR2 is turned on, its collector falls to the emitter’s voltage. This will lead to the current flowing via the base of TR1 turning the transistor on. The emitter of TR1 will also fall on the voltage. Again, the current will have to flow to the TR2’s emitter and turn it on. This state will have to be maintained. If this state is maintained, the thyristor will be turned on if some trigger impulse is applied. They will not be turned off not unless the voltage supply is removed. It is also important to understand the Gate Turn-Off Thyristor Concept (GTO). The gate of the thyristor is not only used to turn it on but also turning it off. It is turned either on or off through introduction of a pulse, that triggers it. They are very helpful, particularly, in areas such as; variable speed motor drives, inverters, high power among other similar areas. They are more advantageous in relation to the standard forms since they are in a position to overcome a number of the disadvantages of the standard forms. This is the reason in most conversion units of DC to AC and DC to DC the GTO are used. The first GTO entered the market in the year 1973. The difference between the two is that the standard one can be switched on and off using the gate while the GTO can only be turned on using the gate but not off. Failures have been recorded in the AC-DC-AC system. These faults have affected different industries due to mechanical breakdown of the machines. Among the failures that have been realized over time include; power switch failure, gate drive pulse failure, and DC link capacitor fault (open or short circuit). In the reduction of the low order harmonics in the AC-DC-AC system, one requires having a rigid DC link voltage. Electrolytic capacitors are supplied for this purpose. The main reason why one should opt for capacitors is that they will iron out all ripples in a voltage. The ripples arise from the refinement of AC voltage. According to Dedié, Brommer, and Scharnholz, (2009) the inverters are likely to be degraded in case the capacitors are in fault. This will, as a result, affect the motor’s performance. Ripples will occur on the DC link as a result of capacitor open circuit. Noting that the DC current’s composition is defined by the electrolytic capacitor that is linked with a DC link is very important in the identification of failures in the system. A motor’s torque is highly affected by the occurrence of low-order harmonics. The problem of capacitor open circuit is also associated with the direction in which the power flows. In an AC-DC-AC inverter, the DC current will be determined by the kind of load which has been attached as well as the switching algorithm put in place for the electronic switches. This system is complex since it is composed of both AC and DC, with the AC categorized into two; the low and the high-frequency AC. In operation, the DC component has to allow the AC components to pass. This explains the elementary capacitive reactance property. The capacitor blocks the AC components in a case of line inductance. This will result to split up of the AC current into two; the high-frequency AC and the low-frequency AC. The high-frequency AC will get its way through the capacitor. The current will be positive if the system is operating normally and if the power is flowing from the source towards the load. In case the capacitor is removed, no component will be there to compensate the line inductance. Any change in the system will, therefore, be opposed by the line inductance. This will generally affect the behavior of the circuit. In conclusion, a thyristor is a solid-state device which is a semiconductor. These electronic devices are used in the regulation and control of a large amount of voltage even in small machines. They have been used in different industries with their applications majorly realized in the following fields, inverter circuits, low-cost timer circuits, chopper circuits, oscillator circuits, speed control circuits, logic circuits, relay-replacement circuit, power-switching circuits, light dimming circuits, level detector circuits, and phase control circuits. There are a number of thyristors which include; the gate turn-off switch (GTO), silicon rectified controlled rectifier (SCR), unijunction transistor (UJT), programmable unijunction transistor (PUT), and silicon controlled switch (SCS). In the paper, GTO has been examined. It is used to turn the thyristor on and off. The GTO is useful since they are able to overcome some disadvantages that are associated to the standard thyristors (Meyer, Kowal, & De Doncker, 2005). They are commonly used in variable speed motor drives, inverters, and high power among other similar areas. In the AC-DC-AC system, some failures and faults are likely to occur. The common faults in this system include; power switch failure, gate drive pulse failure, and DC link capacitor fault (open or short circuit). There are different output waveforms that are produced by the inverters. Theses waveforms include; modified sine waves, square waves, pulsed sine waves, and pulse width modulated waves. However, the common waveform is the market is the sine wave and the modified sine waves. Bibliography Dedié, P., Brommer, V. and Scharnholz, S., 2009. ICCOS countercurrent-thyristor high-power opening switch for currents up to 28 kA. IEEE Transactions on Magnetics, 45(1), pp.536-539. Lu, B. and Sharma, S., 2008, October. A literature review of IGBT fault diagnostic and protection methods for power inverters. In Industry Applications Society Annual Meeting, 2008. IAS'08. IEEE (pp. 1-8). IEEE. Meyer, C., Kowal, M. and De Doncker, R.W., 2005, October. Circuit breaker concepts for future high-power DC-applications. In Industry Applications Conference, 2005. Fourtieth IAS Annual Meeting. Conference Record of the 2005 (Vol. 2, pp. 860-866). IEEE. Meyer, J.M. and Rufer, A., 2006. A DC hybrid circuit breaker with ultra-fast contact opening and integrated gate-commutated thyristors (IGCTs). IEEE Transactions on Power Delivery, 21(2), pp.646-651. Mohan, N., 2011. Power electronics: a first course. Wiley. Nemati, T.R., A High-Speed High-Density Embedded Memory Technology for Nano-scale CMOS, 2007. In Hot Chips. Tan, G.H., Wang, J.Z. and Ji, Y.C., 2007. Soft-switching flyback inverter with enhanced power decoupling for photovoltaic applications. IET Electric Power Applications, 1(2), pp.264-274. Zhong, Q.C. and Hornik, T., 2012. Control of power inverters in renewable energy and smart grid integration (Vol. 97). John Wiley & Sons. Read More

The other design is the one which will convert DC to AC at a level of a battery. This design is modified in such a way that it will apply line-frequency transformer in the creation of output voltage. According to Mohan, (2011) in output voltage, there is regulation of the AC output of the inverter such that it is equal to the grid line voltage. An inverter will also have an overall power rating which is given in kilowatts. These power units describe the amount of power available for the device that the inverter will be driving.

A thyristor is a semiconductor device in the solid state; it consists of four alternating N layers and P-type materials. They are known for controlling a large amount of voltage and power using only a small device. For this reason, therefore, they have been highly applied in the control of electric current in a motor vehicle, e.g. in speed control and in other power transmissions requiring a high DC voltage. They can be used in a number of areas such as; inverter circuits, low-cost timer circuits, chopper circuits, oscillator circuits, speed control circuits, logic circuits, relay-replacement circuit, power-switching circuits, light dimming circuits, level detector circuits, phase control circuits among other applications.

Tan, Wang, and Ji, 2007 postulated that these devices were first introduced in the market in the year 1956. However, the thyristor by then was not easily applicable in direct current since they were only relying on current reversals in order to turn them off. However, with improved devices that were later introduced in the market, it is easy to either be turned on or off by the use of control gate signals. Many people tend to confuse between a thyristor and a transistor. The two are different in that a thyristor is either on or off.

Unlike a transistor, it can never be proportional; you either turn it off or on. On the other hand, a transistor has the ability to lie between the states of being on or off. Due to this reason, a transistor is suitable for analog amplifiers while a thyristor is suitable for a switch. There are three states that a thyristor will take in order for it to be effective, in their functionality. The first state is the reverse blocking mode. In this state, voltage is directed to the direction where a diode will block it.

The other state is referred to as forward blocking mode. In this state, the voltage is directed towards a direction where the diode will have to conduct. The last state is the forward conducting mode. In this state, a thyristor unlike in the forward blocking mode has been activated to conduction. It is in this state that conduction will continue to a point where the forward current is below a holding current point. In order for one to understand how the thyristor operates and to be in a position to effectively utilize it is important to understand their theories and operation.

According to Meyer, and Rufer, (2006) these devices are made of four regions which are semiconductors. These regions are the p-n-p-n. The cathode is made of the outer p while the cathode is made of the outer n. These regions are shown in the figure below Figure 1a Connecting a transistor to the cathode of the thyristor, the resulting device has a structure of n-p-n. Similarly, connecting a transistor on the anode, the resulting device will have a p-n-p structure. This is illustrated in the figure below .

Figure 1b In the set up above, it can be observed that there is a positive feedback loop that has been formed within the thyristor. Here, the yielded current of the first transistor is fed to the input of the other. Similarly, the yield of the second transistor is fed to the input of the first transistor. Current will keep building up till a point where the two transistors are fully saturated. According to Nemati, (2007) the voltage will not flow when passed through the thyristor because none of the transistors are conducting.

Consequently, the path across the thyristor is incomplete.

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