I. Introduction
Brushless dc current (BLDC) motors due to their high efficiency and also reliability, high speed range, and long life have gained increasing interest for variable speed applications [1]. However, in these types of motors, as one of the main disadvantages, the operational speed is largely limited due to the use of the constant magnetic field included in the rotor structure; in other words, because of the constant flux, this machine suffers from a limited constant-power operating range. Moreover, as discussed in more detail in [2], the permanent magnet (PM) employed in BLDC machine has several drawbacks including: increasing the total cost of the motor structure, limiting the top operational speed range, and demagnetizing the magnetic material due to environmental effects. Moreover, for high-speed applications, a simple and robust motor drive system with high energy efficiency and excellent operating performance is essential. Therefore, sensor less control is essential for high-speed BLDC motor drive. In this case, commutation error degrades the operating performance of high-speed PM BLDC sensor less drive significantly which requires complicated drive systems and control techniques [3], [4].