PEREC nductive load, when a<φ e The circuit can still work 事 The load current will be continuous just like the thyristors are short-circuit, and the thyristors can no longer control the magnitude of output voltage o The start-up transient will be the same as the transient When a rl load is connected to an ac source Start-up transient at ot =a (a<
Power Electron cs i 11 Inductive load, when Inductive load, when α < ϕ The circuit can still work. The circuit can still work. The load current will be The load current will be continuous just like the continuous just like the thyristors thyristors are short are short-circuit, circuit, and the and the thyristors thyristors can no longer control the longer control the magnitude of output voltage. magnitude of output voltage. The start The start-up transient will be up transient will be the same as the transient the same as the transient when a RL load is when a RL load is connected to an AC source connected to an AC source at ωt =α ( α < ϕ π ωt ωt ωt ωt α α+π O α θ O O O u1 iG1 iG2 i o ϕ iT1 iT2 Start -up transient up transient ϕ)
PEREC Harmonic analysis s There is no dc component and 100 even order harmonics in the curre 80 The current waveform is half- Fundamental wave symmetric 60 +p the higher the number of 40 harmonic ordinate the lower the harmonic content 20 中c=90° is when harmonics is the most severe 060120180 a(°) e the situation for the inductive load is similar to that for the Current harmonics resistive load except that the for the resistive load corresponding harmonic content is lower and is even lower as is Increasing 12
Harmonic analysis Harmonic analysis There is no DC component and There is no DC component and even order harmonics in the even order harmonics in the current. current. – The current waveform is half The current waveform is halfwave symmetric. wave symmetric. The higher the number of The higher the number of harmonic ordinate, the low harmonic ordinate, the low er the harmonic content. harmonic content. α = 90 ° is when harmonic is when harmonic s is the is the most severe. most severe. The situation for the inductive The situation for the inductive load is load is similar to that for the similar to that for the resistive load exce resistive load except tha t the corresponding harmonic content corresponding harmonic content is lower and is even lower as is lower and is even lower as ϕ is increasing. increasing. Power Electron cs i Current harm Current harm onics for the resistive load for the resistive load 0 6 0 120 180 Fundamental 3 5 7 α/( °) In/I* /% 20 40 60 80 100 12
PEREC 4.1.2 Three-phase Ac voltage controller 4 Classification of three-phase circuits VTNVI T Y connection Line-controlled A connection Branch-controlled A connection Neutral-point-controlled A connection
Power E l ect r o n cs i 13 4.1.2 Three-phase AC voltage controller phase AC voltage controller Classification of three Classification of three-phase circuits phase circuits Y connection Y connection Line-controlled controlled ∆ connection connection Branch-controlled controlled ∆ connection connection Neutral Neutral-point-controlled controlled ∆ connection connection
F3-phase 3-wire Y connection AC voltage controller VT n b 9 For a time instant, there are 2 possible conduction states Each phase has a thyristor conducting. Load voltages are the same as the source voltages There are only 2 thyristors conducting, each from a phase. The load voltages of the two conducting phases are half of the corresponding line to line voltage, while the load voltage of the other phase is 0
Power Electron cs i 14 3 -phase 3 phase 3 -wire Y connection wire Y connection AC voltage controller AC voltage controller n n ' a b c u a u b u c i a U a0' VT5 VT3 VT6 VT4 VT2 VT1 For a time instant, there ar For a time instant, there are 2 possible conduction states: e 2 possible conduction states: – Each phase has a Each phase has a thyristor thyristor conducting. Load voltages are the conducting. Load voltages are the same as the source voltages. same as the source voltages. – There are only 2 There are only 2 thyristors thyristors conducting, each from a phase. The conducting, each from a phase. The load voltages of the two conducting phases are half of the load voltages of the two conducting phases are half of the corresponding line to line voltage, while the load voltage of th corresponding line to line voltage, while the load voltage of the other phase is 0. other phase is 0