Design and analysis of a novel two phase BLDC machine avoiding demagnetization

In the family of brushless permanent magnet (PM) machines, 3-phase drive systems are the most commonly employed and are well-known for their high performance. But two-phase machines require less number of hall sensors to detect rotor position and have light weight. Over recent years, the performance comparison of two-phase and three-phase machines has also been investigated for low cost purpose in many applications as discussed in [1-2]. In PM machines, permanent magnets are the prime source of flux distribution. Normally, all conventional PM machines operate in both magnetization process and demagnetization process. During the demagnetization phenomena, the magnets lose its magnetism due to some internal and external demagnetizing fields which may fail the operation of the machine in certain fault conditions. The permanent magnets in PM machines are almost never operated at maximum energy product BH
max
because of possible irreversible demagnetization with increasing temperature and opposing fields. To ensure the healthy operation of PM machines, it becomes necessary to operate the permanent magnets away from the coercivity in all normal and abnormal conditions. Traditionally, thick magnets are used to avoid the demagnetization of magnets which contribute a significant high cost of PM machines. The risks of irreversible demagnetization and rotor configurations to protect the magnets from demagnetization are presented in [3-4].