Three-Phase brushless DC motors (BLDC) have become increasingly popular in many fields including industrial controls and remote-control hobby toys. They offer many advantages over their brushed counterparts such as smaller size, longer service life, and increased efficiency; however, one drawback is that commutation must be handled electrically using a controller…
Three-Phase brushless DC motors (BLDC) have become increasingly popular in many fields including industrial controls and remote-control hobby toys. They offer many advantages over their brushed counterparts such as smaller size, longer service life, and increased efficiency; however, one drawback is that commutation must be handled electrically using a controller rather than by a mechanical commutator. Rotor position must be estimated in order to accurately commutate the motor, this is calculated either by sensors (sensored) or by measuring the generated Back-Electromotive Force (sensorless). There are two primary methods of brushless DC motor commutation, trapezoidal and sinusoidal. Both methods have advantages and disadvantages, as well as unique sets of rotor position estimation strategies. This paper will discuss in detail the development of a novel motor control algorithm that employs one method of sensorless trapezoidal control of BLDC motors where the BEMF is integrated after a zero-crossing event, the various challenges associated with direct BEMF measurement, and demonstrate a practical implementation of the new algorithm. Using a robust, high frequency sampling scheme and on-the-fly detection strategies, this new algorithm overcomes many of the shortcomings of similar control algorithms currently available on the market. As a result, this new algorithm provides even more robust control over BLDC motors, increased efficiency, and improved dynamic performance compared to its counterparts while simultaneously requiring little to no additional hardware in practical implementations. Topics investigated include BLDC motors, sensored and sensorless rotor estimation, PWM strategies, terminal voltage sensing, third harmonic voltage sensing and integration, sample timing, switching noise, and current recirculation.
Leonard Hayflick studied the processes by which cells age during the twentieth and twenty-first centuries in the United States. In 1961 at the Wistar Institute in the US, Hayflick researched a phenomenon later called the Hayflick Limit, or the claim that normal human cells can only divide forty to sixty…
Leonard Hayflick studied the processes by which cells age during the twentieth and twenty-first centuries in the United States. In 1961 at the Wistar Institute in the US, Hayflick researched a phenomenon later called the Hayflick Limit, or the claim that normal human cells can only divide forty to sixty times before they cannot divide any further. Researchers later found that the cause of the Hayflick Limit is the shortening of telomeres, or portions of DNA at the ends of chromosomes that slowly degrade as cells replicate. Hayflick used his research on normal embryonic cells to develop a vaccine for polio, and from HayflickÕs published directions, scientists developed vaccines for rubella, rabies, adenovirus, measles, chickenpox and shingles.
Although best known for his work with the fruit fly, for which he earned a Nobel Prize and the title "The Father of Genetics," Thomas Hunt Morgan's contributions to biology reach far beyond genetics. His research explored questions in embryology, regeneration, evolution, and heredity, using a variety of approaches.