Control of switch-mode converters Current Programmed Mode control - PDF document

[9-1] Mor M. Peretz, Switch-Mode Power Supplies Control of switch-mode converters Current Programmed Mode control CPM Mor M. Peretz, Switch-Mode Power Supplies [9-2] Problem of voltage mode control V o d   dB dB - 40 dec dB - 20 dec Second order transfer function = complex compensator 1

[9-3] Mor M. Peretz, Switch-Mode Power Supplies Additional feedback System order reduction System order is reduced for each state variable (inner loop) feedback Mor M. Peretz, Switch-Mode Power Supplies [9-4] Current feedback loop I o L i o V o v o S V in C R L D N d D AMP V MOD  V v e e i o  1 For ‘strong’ feedback v N   e LG 1 v 0 ε 1  i v o e N 2

[9-5] Mor M. Peretz, Switch-Mode Power Supplies System representation in CPM v e N v o v e R L N 1  π C o R 2 L Mor M. Peretz, Switch-Mode Power Supplies [9-6] Design of the feedback loops V o V e Instrumentation I limit L V e BW of the inner loop must be well above the outer loop BW 3

[9-7] Mor M. Peretz, Switch-Mode Power Supplies Design of the feedback loops V  Mor M. Peretz, Switch-Mode Power Supplies [9-8] The advantages of current feedback v o v v o e v  db 20 e dec  db 40  db dec 40 dec  20 db dec Same power stage Typical power stage (outer loop) with VM CM 4

[9-9] Mor M. Peretz, Switch-Mode Power Supplies Average current mode Z Z inv fv Z fi V ref Mor M. Peretz, Switch-Mode Power Supplies [9-10] Peak current mode I L I c t T S Cycle-by-cycle protection 5

[9-11] Mor M. Peretz, Switch-Mode Power Supplies PCM and ACM • Current feedbacks - reduce the order of system • The difference is in BW of the current feedback loop • Increase the output impedance Mor M. Peretz, Switch-Mode Power Supplies [9-12] Sub-harmonic oscillations I L V e D<0.5  I 2 <  I 1  I 1  I 2 t T S I L V e  I D>0.5  I 2 >  I 1 1  I 2 t 6

[9-13] Mor M. Peretz, Switch-Mode Power Supplies Stability analysis of Sub-harmonic oscillations       I t I m t 0 L on L on 1       I T I t m t L s L on off 2        I T I m t m t 0 L s L on off 1 2      I T I Steady-state: 0 L s L  m t m t on off 1 2 t D m   on on 2 t m D off off 1 Mor M. Peretz, Switch-Mode Power Supplies [9-14] Stability analysis of Sub-harmonic oscillations                I D d T I i m D d T 0 0 L s L L s 1       DC I DT I m DT : 0 L s L s 1       AC I dT i m dT : 0 L s L s 1     i m dT 0 L s 1    i T m dT L s s 2     m D           i T i i  on   2  0 0   L s L L m D     off 1 7

[9-15] Mor M. Peretz, Switch-Mode Power Supplies Stability analysis of Sub-harmonic oscillations   D        on  i T i 0   L s L D   off     2 D D           i T i T  on  i  on  2 0     L s L s L D D     off off n     D D              i nT i n T  on  i  on  1 0     L s L s L D D     off off  D   on 0, 1 D  n     off D        i nT Stable when D  0.5    on  i nT i 0 L s on   L s L  D D    on off  , 1 D  off Mor M. Peretz, Switch-Mode Power Supplies [9-16] Slope compensation i C m r i L m 2 m 1 t DT s T s       I t I t I L r c       I t I I t L c r 8

[9-17] Mor M. Peretz, Switch-Mode Power Supplies Slope compensation i C    I I t m r     c r    i m m dT 0 L r s 1 i L m 2     m 1    i T m m dT L r s 2 t    m m DT s T s       i T i r  2  0 L s L  m m   n    r m m 1           i nT i r i n 0  2  0 L s L  L m m   r 1     0, 1     i nT L s    , 1  m m   r r 1 1  m m m m m          r r 2 2 2 0.5  m m D m m m m   r on r r 1 1 2 m m D m off 2 2 2 Mor M. Peretz, Switch-Mode Power Supplies [9-18] 9

[9-19] Mor M. Peretz, Switch-Mode Power Supplies Mor M. Peretz, Switch-Mode Power Supplies [5-20] 10