• Energy Research

Advantages of operating wind turbine generators at variable speed are well known. Various approaches have been proposed to extract maximum power from the turbines by operating them at the optimum tip-speed ratio. Often, they feature a three-phase controlled rectifier d-c link followed by a three-phase inverter type of power converter topology to deliver constant frequency a-c output power from a variable speed generator coupled to the turbine. However, in stand-alone power supply applications for remote sites, where the power level is a few kW or less, this approach is economically unjustifiable. This paper presents a single switch power electronic converter to regulate the power output of a permanent magnet alternator driven turbine feeding a battery, featuring minimal additional costs suitable for low power applications. Power converter operation and a control strategy to maintain optimum tip-speed ratio are discussed in the paper. Computer simulations of the complete system verifying the proposed concepts are presented.

Advantages of operating wind turbine generators at variable speed are well known. Various approaches have been proposed to extract maximum power from the turbines by operating them at the optimum tip-speed ratio. Often, they feature a three-phase controlled rectifier d-c link followed by a three-phase inverter type of power converter topology to deliver constant frequency a-c output power from a variable speed generator coupled to the turbine. However, in stand-alone power supply applications for remote sites, where the power level is a few kW or less, this approach is economically unjustifiable. This paper presents a single switch power electronic converter to regulate the power output of a permanent magnet alternator driven turbine feeding a battery, featuring minimal additional costs suitable for low power applications. Power converter operation and a control strategy to maintain optimum tip-speed ratio are discussed in the paper. Computer simulations of the complete system verifying the proposed concepts are presented.

Electrical energy conversion systems and power supply systems form an integral component of electrical and electronic systems used in residential, commercial, aerospace, transportation, and manufacturing applications. Practicing electrical engineers are often called to solve electrical energy and power-related problems. Therefore, an effective course that provides graduating electrical engineers with an energy-oriented perspective is highly desirable in today's workplace. This paper documents a course that provides students with problem solving experience in electrical systems and electronic circuits. The paper presents the pedagogical premise, course objectives, and details of lesson and lab activities, student projects, and experiences.

Electrical energy conversion systems and power supply systems form an integral component of electrical and electronic systems used in residential, commercial, aerospace, transportation, and manufacturing applications. Practicing electrical engineers are often called to solve electrical energy and power-related problems. Therefore, an effective course that provides graduating electrical engineers with an energy-oriented perspective is highly desirable in today's workplace. This paper documents a course that provides students with problem solving experience in electrical systems and electronic circuits. The paper presents the pedagogical premise, course objectives, and details of lesson and lab activities, student projects, and experiences.

Extension of electrical service to large rural populations in developing nations is a key requirement to realize human development goals set forth by international agencies. This paper presents the case for distributed generation in the form of microgrids, which should be the preferred path towards rural electrification in developing communities and a vital complement to expensive centralized grid expansion. The technical features of frequency and voltage control for distributed generation devices in a microgrid are discussed along with a presentation of their stability attributes. Computer simulation results and experimental results from a laboratory scale microgrid are also presented.

Extension of electrical service to large rural populations in developing nations is a key requirement to realize human development goals set forth by international agencies. This paper presents the case for distributed generation in the form of microgrids, which should be the preferred path towards rural electrification in developing communities and a vital complement to expensive centralized grid expansion. The technical features of frequency and voltage control for distributed generation devices in a microgrid are discussed along with a presentation of their stability attributes. Computer simulation results and experimental results from a laboratory scale microgrid are also presented.

This paper discusses the issues related to the operation of a microgrid being called to feed reliable electric power to sensitive electrical loads. Challenges and solutions involved in terms maintaining adequate voltage quality and load tracking capabilities are discussed in the paper.

This paper discusses the issues related to the operation of a microgrid being called to feed reliable electric power to sensitive electrical loads. Challenges and solutions involved in terms maintaining adequate voltage quality and load tracking capabilities are discussed in the paper.

This paper investigates the impact of input voltage unbalance and sags on stresses in the dc-bus choke inductor and dc-bus electrolytic capacitors of adjustable-speed drives (ASDs). These stresses are primarily attributable to the rectifier's transition into single-phase operation, giving rise to low-order harmonic voltages (120 Hz, 240 Hz, etc.) that are applied to the dc-link filter components. These harmonics elevate the ac-flux densities in the dc choke core material significantly above values experienced during normal balanced-excitation conditions, causing additional core losses and potential magnetic saturation of the core. It is shown that the effects of voltage unbalances and sags on the dc-link capacitor lifetime will be the same when either line inductors or a dc-link choke inductor are used if the dc choke-inductance value is twice the value of the line inductance. Simulations and experimental tests are used to verify the accuracy of predictions provided by closed-form analysis and simulation for a 5-hp or 3730-W ASD system.

This paper investigates the impact of input voltage unbalance and sags on stresses in the dc-bus choke inductor and dc-bus electrolytic capacitors of adjustable-speed drives (ASDs). These stresses are primarily attributable to the rectifier's transition into single-phase operation, giving rise to low-order harmonic voltages (120 Hz, 240 Hz, etc.) that are applied to the dc-link filter components. These harmonics elevate the ac-flux densities in the dc choke core material significantly above values experienced during normal balanced-excitation conditions, causing additional core losses and potential magnetic saturation of the core. It is shown that the effects of voltage unbalances and sags on the dc-link capacitor lifetime will be the same when either line inductors or a dc-link choke inductor are used if the dc choke-inductance value is twice the value of the line inductance. Simulations and experimental tests are used to verify the accuracy of predictions provided by closed-form analysis and simulation for a 5-hp or 3730-W ASD system.