THEORY EXAMINATION (SEM–VIII) 2016-17 POWER CONVERTER APPLICATIONS

Power Converter Applications – Section Wise Explanation

Section A – Basic Concepts of Power Electronics

Section A contains short questions that test the basic knowledge of power electronics devices and power conversion systems. Students are required to attempt all questions in this section. 

Power converters are electronic devices used to convert electrical energy from one form to another. These systems are widely used in renewable energy systems, industrial heating, power transmission, and electronic power supplies.

One basic concept in power electronics is the difference between power diodes and signal diodes. Power diodes are designed to handle high voltage and current levels, whereas signal diodes are used in low-power electronic circuits.

Another important device used in power electronics is the thyristor, which acts as a switching device in high-power applications. Thyristors can be turned off through special commutation techniques.

Commutation refers to the process of turning off a conducting thyristor so that current can be transferred to another device in the circuit.

Power systems also use different types of DC links in converter circuits to connect rectifiers and inverters.

Traditional linear power supplies have certain drawbacks such as low efficiency and large heat generation, which is why switching power converters are often preferred.

Modern power systems use technologies like FACTS (Flexible AC Transmission Systems) controllers to improve power flow control and stability in transmission lines.

Other concepts discussed in this section include harmonics, which are distortions in voltage or current waveforms caused by nonlinear loads.

Industrial applications such as induction heating also use power converters to generate high-frequency currents that produce heat in conductive materials.

Understanding these concepts helps engineers design efficient electrical power systems.

Questions for Section A

What is the difference between a power diode and a signal diode?

How can a thyristor be turned off?

What is commutation in power electronics?

What are the different types of DC links?

What are the drawbacks of linear power supplies?

Why are FACTS controllers needed in power transmission systems?

Explain the single line diagram and working of half wave transmission.

What causes voltage and current harmonics?

What are the advantages and disadvantages of pulverization?

Explain induction heating.

Section B – Power Converter Systems and Applications

Section B focuses on detailed explanations of power converter systems used in modern electrical power networks. Students must attempt any five questions from this section. 

One important topic in this section is the integration of renewable energy sources such as wind and small hydroelectric plants with the electrical grid. These renewable systems help reduce dependence on fossil fuels but require proper control systems to maintain stability in the power network.

Transmission lines also have power transfer limitations. Engineers analyze these limitations to determine the maximum power that can be transmitted safely through the line.

Another important topic is the grid interconnection of renewable energy systems. Connecting renewable sources to the utility grid can cause challenges such as voltage fluctuations, frequency instability, and power quality issues.

Power electronic devices such as Thyristor Controlled Series Capacitors (TCSC) and Static VAR Compensators (SVC) are used to control power flow and improve voltage stability in transmission lines.

Photovoltaic systems also require protective devices such as DC circuit breakers to prevent damage caused by faults or overloads.

Another important concept in power systems is reactive power control, which is essential for maintaining voltage levels and efficient power transmission.

Devices such as capacitor banks, synchronous condensers, and FACTS controllers are used to manage reactive power.

Excitation control of synchronous generators is also essential for maintaining system stability and controlling voltage levels.

Advanced devices such as Unified Power Flow Controllers (UPFC) provide flexible control over both voltage and power flow in transmission systems.

Questions for Section B

Explain the interconnection of wind and small hydro power plants with a block diagram.

What are the constraints and difficulties in renewable energy integration?

Calculate the maximum power transfer in a long transmission line.

What complications occur during grid interconnection of renewable energy sources?

Explain the working and characteristics of TSSC and SSVC.

How is a DC circuit breaker connected to a photovoltaic array?

What is reactive power control in power systems?

What devices are used for reactive power control?

Explain the need for excitation control in synchronous generators.

Explain the working principle of Unified Power Flow Controllers (UPFC).

Section C – Advanced Power Converter Applications

Section C contains advanced questions related to power electronic systems used in industrial and power supply applications. Students must attempt any two questions from this section. 

One important application discussed in this section is the inverter system. Inverters convert DC power into AC power and are widely used in renewable energy systems, backup power supplies, and industrial applications.

An inverter system includes several components such as a battery charger, battery bank, battery rack, and load management system. Proper design specifications for these components ensure reliable and efficient operation.

Another important system is the Uninterruptible Power Supply (UPS), which provides backup power during electrical outages.

UPS systems are commonly classified into two types:

Online UPS – continuously supplies power from the inverter and provides the highest level of protection.

Offline UPS – supplies power directly from the mains and switches to the battery during power failure.

Industrial heating applications also use high-frequency inverters to generate alternating current for heating metals through electromagnetic induction.

Another heating technique is dielectric heating, which uses high-frequency electric fields to heat insulating materials.

Comparing induction heating and dielectric heating helps engineers choose the appropriate technology for industrial processes.

Questions for Section C

What specifications should be considered when designing an inverter system?

Explain the components of an inverter such as battery charger and battery system.

Explain the working difference between online UPS and offline UPS.

What are high-frequency inverters used for induction heating?

Compare induction heating and dielectric heating.

Conclusion

The Power Converter Applications exam paper evaluates knowledge at three levels. Section A focuses on basic concepts of power electronics and power converters. Section B examines the applications of power converters in renewable energy integration and transmission systems. Section C explores advanced systems such as UPS, inverter design, and industrial heating applications. 

Understanding these concepts is important for engineers working in modern electrical power systems, renewable energy technologies, and industrial power applications.