as MOSFET, IGBT etc, a capacitor and two fly-wheel
diodes (D1 and D2), which form the H semi-bridge structure.
R and L are resistance and inductance of coil respectively.
The operation states of the three-level semi-bridge
PWM switching power amplifier are divided into four
states: i.e., charge state, discharge state and two persistence
states, which are shown in Fig. 2, respectively.