Methods for Realizing Power Balance in an Interleaved Configuration of LLC Resonant Converters. Heiko Figge, , IBM Technology Symposium

Transcription

1 Methods for Realizing Power Balance in an Interleaved Configuration of LLC Resonant Converters Heiko Figge, ,

2 Outline Why going for LLC? Why going for interleaved LLC? The balancing issue of interleaved LLC Solutions to the balancing issue Measurement results 2

3 Why going for LLC? LLC topic addresses the PSU DC-DC converter stage 1ɸ AC in AC/DC PSU DC-DC VR VR Fans Server Loads Server Rack 3

4 Efficiency in % Why going for LLC? 80plus Efficiency levels for 12V output units (high line) Titanium Platinum Gold Silver Bronze Load in % 4

5 Why going for LLC? Titanium efficiency-level goal (96% peak efficiency) LLC has demonstrated best-in-class efficiency in case of 54V 2-3kW output (96%+ rectifiers) best-in-class efficiency in case of 12V <1kW output (96% peak efficiency rectifiers) high robustness against abnormal operating conditions, e.g. short-circuit capability of linear ramp-up 5

6 Outline Why going for LLC? Why going for interleaved LLC? The balancing issue of interleaved LLC Solutions to the balancing issue Measurement results 6

7 Why going for interleaved LLC? Principal schematic of LLC DC-DC converter Kirchhoff's current law V bulk S 1 i r C s L s n:1:1 D 2 i Cout i out I out i out I out S 2 L m i m C out + V out R L D 1 7

8 Why going for interleaved LLC? not interleaved I out i Cout i o (t) t interleaved I out i o _ A io _ B ( t) ( t) 8 t

9 Why going for interleaved LLC? Example: V out = 12V and P out = 3000W I out = 250A RMS ripple current taken by output capacitor C out not interleaved: I Cout = 154A rms interleaved: I Cout = 31A rms Interleaving reduces output current ripple by factor 5 9

10 Outline Why going for LLC? Why going for interleaved LLC? The balancing issue of interleaved LLC Solutions to the balancing issue Measurement results 10

11 The balancing issue of interleaved LLC Interleaved LLC in a typical front-end structure i out_a LLC Rail A I out PFC Stage V bulk C bulk i out_b C out V out LLC Rail B 1Ф AC in DC link DC out 11

12 The balancing issue of interleaved LLC Interleaved LLC may result in unbalanced power distribution power per LLC rail / % 100% 80% 60% 40% 20% 0% Rail B Rail A typical operating area sw. frequency of both LLC rails is pinned together normalized switching frequency (f s /f 0 ) 12 LLC has passive components L s, C s, L m assumed tolerance here: ±2% graph based on worst-case assumption graph data based on time-domain simulation

13 Outline Why going for LLC? Why going for interleaved LLC? The balancing issue of interleaved LLC Solutions to the balancing issue Measurement results 13

14 Power balancing by input voltage control bulk voltages / V Solutions to the balancing issue Rail A ΔV bulk 13V normalized switching frequency (f s /f 0 ) 14 Rail B graph shows balanced condition assumed tolerance here ±5% graph based on worst-case assumption graph data based on time-domain simulation

15 Solutions to the balancing issue Interleaved LLC in a Split-Bulk structure PFC Rail A PFC Rail B V bulk_a V bulk_b C bulk_a C bulk_b LLC Rail A LLC Rail B i out_a i out_b I out C out V out 1Ф AC in DC link DC out 15

16 Solutions to the balancing issue Interleaved LLC in a Two-Bulk structure i out_a PFC Stage (e.g. Vienna- Rectifier) V bulk_a V bulk_b C bulk_a C bulk_b LLC Rail A LLC Rail B i out_b I out C out V out 3Ф AC in DC link DC out 16

17 Outline Why going for LLC? Why going for interleaved LLC? The balancing issue of interleaved LLC Solutions to the balancing issue Measurement results 17

18 Eff[%] Measurement Results Efficiency status of current P1 lab unit (incl. Bridgeless PFC) 96 12V, 3000W 1.6 kw/l (26W/in 3 ) Full digital control 92 P1 status Titanium V AC Load [%] 18

19 Measurement Results Waveforms measured on current P1 lab unit ~V bulk_a (20V/div) ~V bulk_b (20V/div) 100% load (I out = 245A) i r_a (10A/div) i r_b (10A/div) 19 t (4ms/div)

20 Measurement Results Waveforms measured on current P1 lab unit ~V bulk_a (20V/div) ~V bulk_b (20V/div) 30% load (I out = 73A) i r_a (10A/div) i r_b (10A/div) 20 t (4ms/div)

21 Summary LLC resonant converter enables Titanium-Efficiency designs High-Power units benefit from interleaving technology In case of LLC, interleaving reduces the current ripple flowing in the output filter capacitor by factor 5 Power Balancing by the separate bulk voltages control method overcomes the balancing issue in a quite reliable way Complete DVT of P1 lab unit is in process 21

22 Smarter. Greener. Together. Heiko Figge Coesterweg 45 Soest, Germany