3.相量表示 C U=UZO 120° UB=U∠-1200 120° 120° UC=U∠120° UB (v=0) 20211/27 62021/1/27 6 3. 相量表示 ( 0) 120 120 0 o C o B o A = =  = − =  • • • ψ U U U U U U A • U C • U B • U 120° 120° 120°