| 摘要 |
PURPOSE:To obtain a commutation timing which corresponds with the rotational position of rotor highly accurately by temporarily shortening the modulation interval of PWM signal, which governs the accuracy of commutation timing, during a specific interval close to a cross point with a terminal voltage reference determining the timing of a conduction signal. CONSTITUTION:A waveform synthesizing circuit 32 recognizes zero-cross of terminal voltage Vu, Vv, Vw of each winding 15u-15w of a brushless motor 15 or the vicinity of cross point of voltage reference thus recognizing a specific interval and delivering a pulsating specific interval signal Si to a modulation period selecting circuit (MC) 33. The MC 33 has constant voltage V1, V2 sources one of which is set by means of a manual switch 34. A set constant voltage signal is synchronized with input of the specific interval signal Si and delivered, as a modulation period selection signal Sp, to a pulse width modulation circuit (PC) 35. The PC 35 controls the modulation period of the PWM signal P1 to be longer, during a specific interval, than that during other interval. |
