U. S. missile actuators employ REPM (rare earth permanent magnet) BLDCM (brushless D. C. motor). We are the first in China to propose square - wave REPM BLDCM for Chinese missile actuator.We found it necessary to desisn such square - wave motor with a method different from traditional ones. Traditionai methods for designing permanent - msanet BLDCM are based on sinusoidal gap magnetic density distribution and sinusoidal winding back EMF(electromotive force). They are not suitable for REPM square - wave motor which has square gap magnetic density distribution and trapezoidal winding back EMF. Table 1 gives for comparison the design formulas of inductive potential, armature current, electromagnetic torque, and no - load speed of REPM square - wave motor and of traditional permanent magnet BLDCM respectively. It is important to note that the elechromagnetic torque coefficient of REPM square - wave motor is about 5% higher than that of traditional BLDCM.We developed a prototroe of REPM square - wave motor. Its specifiations are: rated power = 30W, rated D. C. voltage = 48V, rated speed = 1000r/min. Its operation pattern is star - form three - phase six - state.Fig.1a shows test curves relating current I and efficiency n to output torque T respectively. Fig. 1b shows test curves relating input power P1 tal output power P2 to T respectively. The desisn error of rated torque is within 1. 7%. The prototype also achieves 17 500r/s2 starting acceleration and 0. 154 W/g power density and thus actuator performance is improved. All these indicate that our proposed design method is valid.
