Fig. 9.

Fourth Mode (a) State-1 (b)State-2 (c)Current flow graph

(a) State-1 (t0 < t < t1): From the battery, as shown in Fig. 9(a) L_a gets charged and S_a is ON, S_b is OFF, so current goes through S_a and C_b gets discharged, and at t = t1, the state 1 analysis is completed, making the S_b turn ON.

(b) State-2 (t1 < t < t2): In Fig. 9(b), from the battery L_a gets discharged and S_b is ON, and now the current passes through it, making the charging of C_b and the completion of the steady-state analysis of mode 4 at t = t2. The steady-state analysis of mode 4 is shown in Fig. 9(c).