4.1.1 Single-phase AC voltage controller Resistive load lo R at l 4 The phase shift range (operation range of phase delay angle) at 0≤a<π 7The phase shift range The phase shift range (operation range of phase (operation range of phase delay angle): delay angle): 0 ≤ α ≤ π Resistive load Resistive load Power Electron cs i u1 u o R io VT1 VT2 O u1 u o io uVT ω t O ωt O ωt O ωt 4.1.1 Single -phase AC voltage controller phase AC voltage controller 7