Power Electronics and Power Systems

Power electronics is the engineering study of converting electrical power from one form to another. At a world-wide average rate of 12 billion kilowatts every hour of every day of every year, more than 80% of the power generated is being reprocessed or recycled through some form of power electronic systems. A lot of energy is wasted during this power conversion process due to low power conversion efficiency. It is estimated that the power wasted in desktop PCs sold in one year is equivalent to seventeen 500MW power plants! It is therefore very important to improve the efficiency of these power conversion systems. It is estimated that with the widespread use of efficient and cost-effective power electronics technology, the world could see a 35% reduction in energy consumption.

Research Showcase

New Cost-Effective Silicon Carbide High Voltage Switch Created

Researchers at North Carolina State University have created a high voltage and high frequency silicon carbide (SiC) power switch that could cost much less than similarly rated SiC power switches. The findings could lead to early applications in the power industry, especially in power converters like medium voltage drives, solid state transformers and high voltage transmissions and circuit breakers.

Electric Machines and Drives

The electric machine is an electromechanical energy conversion device that processes and delivers power to the load. The same electric machine can operate as a motor to convert electrical power to mechanical power or operate as a generator to convert mechanical power to electrical power. The electric machine in conjunction with the power electronic converter and the associated controller makes the motor drive. The power electronic converter is made of solid state devices and handles the flow of bulk power from the source to the motor input terminals. The advances in the power semiconductor technology over the past several decades enabled the development of compact, efficient and reliable DC and AC electric motor drives.

The controller is made of microcontroller or digital signal processor and associated small signal electronics. The function of the controller is to process the user commands and various sensor feedback signals to generate the gate switching signals for the power converter semiconductor switches following a motor control algorithm. The sensor signals include machine rotor position, phase currents, inverter bus voltage, and machine and inverter temperature outputs. Fault protection and diagnostics is also part of the motor controller algorithm.

Research in the area of electric machines and drives is focused on design optimization using 2D and 3D finite element analysis, and drives design at the systems level considering operating requirements and control opportunities. The research is multifaceted seeking innovations in machine configurations, motor control concepts, parameter identifications, and noise and vibration analysis. Motor drives are designed to make the system more efficient, fault tolerant, smoother in operation, smaller and matched to the applications. Modeling and design tools are developed to aid the machine design and drive development efforts. Particular research emphasis is on permanent magnet and reluctance type machines and drives.

Electric Vehicle Systems

Within a single century, personal transportation has progressed from the horse and buggy to nearly a billion private automobiles. It is projected that the need for personal mobility will grow even faster, as large numbers of people are lifted out of poverty in developing countries and demand transportation. Emissions from oil-burning automobiles clog our air and contribute to global warming. For all of these reasons, finding an alternative to oil for private transportation is imperative. Although several alternatives can propel a car, only one is readily available today: Electricity.

With the introduction of electric propulsion, a completely new drivetrain is introduced in the vehicle requiring multidisciplinary research into system components. The Electric vehicle system is comprised of electric motor, power electronics converters, and energy storage devices such as batteries. In addition, the overall system must be optimized to maximize overall system efficiency. Finally, to reduce the overall transportation emissions, the vehicle energy storage device should be recharged at times when the grid power production is most efficient and non-polluting.

NCSU research on electric vehicle systems focuses on extending the vehicle range by developing more efficient subsystems and including storage systems with higher energy and power densities. Another research topic focuses on development of fundamental and enabling technologies that will facilitate the electric power industry to actively manage and control large amount of plug-in vehicle charging. More info is at: http://www.atec.ncsu.edu/

Electronic Energy Systems Packaging

Electronic Energy Systems Packaging (including power electronics packaging) encompasses technologies focused on the physical implementation of power electronic and energy storage systems.

Electrical engineers develop circuits and schematics, but what is eventually delivered to a customer are electro-physical circuits concurrently designed and combined into a hardware system. These hardware systems must meet metrics, such as power, weight, and size densities; government and industry standards; and reliability.

Understandably, this research is broad-based and multidisciplinary with studies in electric, magnetic, thermal and mechanical components and circuits. The NCSU research focus is on high-frequency, high-density topologies that use ultrafast-switching power semiconductors, and the materials and fabrication processes to create such topologies.

Applications are in new integrated power systems from chip to ship including land-based smart grid power systems; electric vehicle converters and drives; high performance power supplies for aerospace, telecom and DC distribution systems; and ultrafast fault protectors using the latest in SiC and GaN semiconductors.

Those interested in this area would find it advantageous to have had primary study in power electronics and physics with strong interests in heat transfer, materials or structural mechanics.

Power Electronics

Power electronics is the technology associated with the efficient conversion, control and conditioning of electric power by static means from its available input form into the desired electrical output form.

Power electronic converters can be found wherever there is a need to modify the electrical energy form (i.e. modify its voltage, current or frequency.) With “classical” electronics, electrical currents and voltage are used to carry information, whereas with power electronics, they carry power. Some examples of uses for power electronic systems are DC/DC converters used in many mobile devices, such as cell phones or PDAs, and AC/DC converters in computers and televisions. Large scale power electronics are used to control hundreds of megawatt of power flow across our nation.

Research in this area includes power electronics applications to control large scale power transmission and distribution as well as the integration of distributed and renewable energy sources into the grid. NCSU also has a strong program on the emerging applications of wide bandgap semiconductor devices that offer high oeprating temperatures, higher efficiency and higher power density.

Power Management ICs

Power management ICs are used to manage the accurate power flow in portable and handheld devices, such as cell phone power amplifiers and LED display, CPU, DRAM, Graphics, High Speed I/O and USB. In addition, under-voltage or other fault conditions are monitored to prevent damage to the system. The soft-start feature reduces stress on power supply components and increase product reliability. Implementation is typically done using analog integrated circuits but there is a strong trend to move towards digital or mixed signal implementation.

Power Semiconductor Devices

Power semiconductor devices are semiconductor devices used as switches or rectifiers in power electronic circuits (switch mode power supplies for example). They are also called power devices or when used in integrated circuits, called power ICs.

Some common power devices are the power diode, thyristor, power MOSFET and IGBT (insulated gate bipolar transistor). A power diode or MOSFET, for example, operates on similar principles as its low-power counterpart, but is able to carry a larger amount of current and typically is able to support a larger reverse-bias voltage in the off-state.

Research needs in this area include on one hand to increase the maximum power handling capability of the power devices, on the other hand include the need to increase the speed they can switch. Power semiconductor is also the key in determining the power conversion efficiency. NCSU’s research concentration is on power devices that use wide bandgap semiconductor materials (e.g. SiC and GaN).

Research projects are focused on the analysis of power device structures using numerical simulations and the development of analytical models based on semiconductor transport physics. Students are encouraged to validate the theoretical analysis using electrical characterization of commercially available devices and by the fabrication of novel device structures. The impact of improvements in power device characteristics on specific applications allows an understanding of trade-offs between on-state characteristics, reverse blocking capability, and switching performance.

Power Systems

Electric power systems are comprised of components that produce electrical energy and transmit this energy to consumers. A modern electric power system has mainly six main components: 1) power plants which generate electric power, 2) transformers which raise or lower the voltages as needed, 3) transmission lines to carry power, 4) substations at which the voltage is stepped down for carrying power over the distribution lines, 5) distribution lines, and 6) distribution transformers which lower the voltage to the level needed for the consumer equipment. The production and transmission of electricity is relatively efficient and inexpensive, although unlike other forms of energy, electricity is not easily stored, and thus, must be produced based on the demand.

NCSU research on electric power systems concentrates on the study of emerging technologies such as power electronics, energy storage, renewable and distributed energy sources on the electric power system operation, control and protection. The research is coordinated through two major centers:

  • Future Renewable Electric Energy Delivery and Management Systems Center (FREEDM) focuses on development of a smart-grid that will enable anybody to integrate new renewable energy technologies into the power grid for a secure and sustainable future. Research involves development or adoption of new power electronics, communication, and control technologies to demonstrate and prototype such a system. More info is at: http://www.freedm.ncsu.edu/
  • Advanced Transportation Energy Center (ATEC) focuses on development of fundamental and enabling technologies that will facilitate the electric power industry to actively manage and control large amount of plug-in hybrid vehicle (PHEV) and plug-in electric vehicle (PEV). More info is at: http://www.atec.ncsu.edu/

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