(2)半桥差动 Z1=(1+δ)Z,Z2=(1-δ)Z,Z3=Z4=Z -δ M0= 2 us Z us uo（2）半桥差动 123 4 (1 ) , (1 ) , 2 O S Z ZZ ZZ Z Z u u δ δ δ = + =− = = − = us