电路分析基础第3章 (1).ppt

****************************************以网孔电流作为电路的独立变量uS1i1i3uS2R1R2R3ba+–+–uS3-+i2im2im1abim2im1-i1+i2+i3=0u1+u2=0-u2+u3=0u1=-uS1+R1i1=-uS1+R1im1u2=R2i2+uS2=R2(im1-im2)+uS2u3=R3i3+uS3=R3im2+uS3§3-4网孔电流法(只对平面网络适用）各支路列VCR网孔列KVL结点列KCL整理得:(R1+R2)im1–R2im2=uS1-uS2-R2im1+(R2+R3)im2=uS2-uS3R11im1+R12im2=uS11R21im1+R22im2=uS22uS1i1i3uS2R1R2R3ba+–+–uS3-+i2im2im1-i1+i2+i3=0u1+u2=0-u2+u3=0u1=-uS1+R1i1=-us1+R1im1u2=R2i2+uS2=R2(im1-im2)+uS2u3=R3i3+uS3=R3im2+uS3i1=im1i2=im1－im2i3=im2由节点a由网孔1、2由网孔电流与支路电流的关系写出各支路电压各电压源电压与网孔电流一致，取负号，反之取正号。R11im1+R12im2=us11R21im1+R22im2=uS22R11=R1+R2自阻网孔1所有电阻之和R22=R2+R3网孔2所有电阻之和自阻总是正R12=R21=R2互阻网孔1、2的公共电阻两网孔电流通过公共电阻的参考方向相同时，互阻为正两网孔电流通过公共电阻的参考方向相反时，互阻为负两网孔电流间没有公共电阻时，互阻为零网孔电流的方向均为顺时针，则互阻总为负uS11=uS1-uS2网孔1的总电压源电压uS22=uS2-uS3网孔2的总电压源电压uS1i1i3uS2R1R2R3ba+–+–uS3-+i2im2im1R11im1+R12im2+R13im3+---+R1mimm=us11R21im1+R22im2+R23im3+---+R2mimm=uS22------------------------Rm1im1+Rm2im2+Rm3im3+---+Rmmimm=uSmm推广:举例:用网孔法求各支路电流。解：(1)设选网孔电流(顺时针)(2)列网孔电流方程(R1+R2)I1－R2I2=US1－US2－R2I1＋(R2+R3)I2－R3I3=US2－R3I2＋(R3+R4)I3=－US4I1I3I2+_US2+_US1IaIbIcR1R2R3+_US4R4Id即:80I1-20I2=40-20I1+60I2-40I3=10-40I2+80I3=40(3)求解回路电流方程，得I1=0.786,I2=1.143,I3=1.071(4)求各支路电流： Ia=I1,Ib=I2-I1,Ic=I2-I3,Id=-I3(5)校核：选一新回路。60Ia-40Id=50+40即90=90返回R11i11+R12i12+…+R1Li1L=uS11R21i11+R22i12+…+R2Li1L=uS22……RL1i11+RL2i12+…+RLLi1L=uSLL回路法:自阻、互阻、电压源的讨论同网孔法§3-5回路电流法(loopcurrentmethod)以一组独立回路电流为电路变量求解电路n个结点b条支路回路电流数L=b-n+1由L个