Liquid cooling

Transcription

1 SKiiPPACK no. 3 4 [ 1- exp (-t/ τ )] + [( P + P )/P ] R [ 1- exp (-t/ τ )] Z tha tot3 = R ν ν tot1 tot tot3 thaa-3 aa 3 ν= Liquid cooling The following table contain the characteritic R ν and τ ν for thermal calculation according to the 4-time-contant-model for SKiiPPACK on a tandard water-cooled heatink S with mutual water inlet/outlet, 50/50 % water-glycol-mixture at a coolant temperature of 50 C. Since the temperature T of the internal temperature enor of the SKiiP i alo available here a a reference point for the heatink temperature T h, the following definition are valid: R thw tot : tationary thermal reitance a a reult of the temperature difference between temperature enor (T ) and coolant (T w ), with reference to the total power diipation P tot of the aembly. R thw = R tot Z thw tot : Z 4 ν= 1 ν tranient thermal impedance a a reult of the temperature difference between temperature enor (T ) and coolant (T w ),with reference to the total power diipation P tot of the aembly. 4 thw tot = R ν τ ν ) ν= 1 [ 1- exp (-t/ ] Coolant by-pa l/min R 1 thermal characteritic (4-contant-model) R R 3 R 4 ΣR τ 1 τ τ 3 τ 4 -fold SKiiPPACK fold SKiiPPACK

2 4-fold SKiiPPACK Calculation of thermal tacking i baically made the ame way a with air cooling. 3.4 Power deign MOSFET, IGBT or SKiiP power circuit are deigned in printed circuit board technology, or by mean of cable or maive copper or aluminum bar, depending on the current and voltage to be witched. Apart from the general pecification to be met, for example with regard to creepage and triking ditance or current denity, the hort witching time within the nano to microecond range demand a ophiticated power deign, which alo live up to the requirement of highfrequencie Paraitic inductance and capacitance To analye the effect of paraitic inductance and capacitance of converter, it will be ufficient to examine one commutation circuit. Figure 3.3 how the commutation circuit of an IGBT-inverter with paraitic element, coniting of DC-link voltage v d (correpond to commutation voltage v K ) and two IGBT witche with driver and invere diode. Commutation voltage i impreed by the DC-link capacitance C d. The impreed current i L flow out of the commutation circuit. 165

3 i K L 11 C 11 L 61 L 71 Driver ± V Dr L 1 T1 D1 R Gon R Goff C 31 C 41 C 1 L 31 E`1 C d V d (V K ) L 41 L 51 i L E 1 C 1 L 6 L 7 Driver ± V Dr L T D R Gon R Goff C 3 C 4 C L 3 E` L 4 L 5 L 1 E Figure 3.3 Commutation circuit with paraitic element The effect of paraitic element / counter-meaure Total commutation inductance In the commutation circuit with T1 and D, the amount of L 11, L 61, L 31, L 41, L 7, L 5 and L 1 i effective a total commutation inductance. In analogy, the amount of L 11, L 71, L 51, L 6, L 3, L 4 and L 1 i effective in the commutation circuit with D1 and T. During active turn-on of T1 or T, repectively, the total commutation inductance become effective a turn-on relief, which will reduce turn-on power diipation in T1 or T (ee chapter 3.8). However, during active turn-off of T1 and T a well a during revere-recovery-di/dt of D1 and D, witching overvoltage are generated in the tranitor and diode due to high di/dt caued by the commutation inductance. Thi will increae turn-off power diipation and voltage tre of the power emiconductor. Thi effect i epecially critical with regard to hort-circuit and overload (ee chapter 3.6). Moreover, together with paraitic capacitance unwelcome high frequency ocillation may be generated. Therefore, it i of major importance to minimize inductance in the commutation circuit of hardwitching converter. Except for L 11 and L 1, all inductance are generated in the module, which may not be influenced by the uer. In thi repect, it i up to the manufacturer of power 166

4 module, to keep on working on the minimization of internal inductance by improving module aembly technologie (ee chapter 1.4). SEMIKRON dataheet indicate the internal inductance becoming effective at the module output terminal (Example: SKM100GB13D: L CE = max. 30 nh). In the cae of ingle witch module (1 IGBT/MOSFET + 1 invere diode), the connection of both module ha to be made a low-inductive a poible in an converter phae. Low-inductance DC-link power bubar are of pecial importance. Thi goe for the connection bubar of the capacitor battery itelf a well a for connection of the power module to the DClink. In thi repect, laminated bubar ytem (tightly paralleled plate ytem) adapted to the pecific inverter layout have gained general acceptance in practice, achieving bubar inductance up to nh. Some example of thi are hown in Figure The effect of the remaining inductance L 11 +L 1 on the power emiconductor can till be reduced by connecting C-, RC- or RCD-circuit directly to the DC-link terminal of the power module. In mot cae, a imple C-circuit with film capacitor within the range of µf i connected. Inductance of emitter or ource The element L 31 or L 3 of the emitter/ ource inductance are effective in the power circuit a well a in the driver circuit of the tranitor. Due to the fat di/dt of the tranitor current, voltage will be induced which will have the effect of invere feedback in the driver circuit (emitter/ource invere feedback). Thi, however, will decelerate the charging proce of the gate-emitter-capacitance during turn-on and the dicharging of the gate-emitter-capacitance during turn-off, reulting in increaed witching time and witching loe. The invere feedback effect of the emitter may be utilized for limitation of the collector current di/dt in the cae of hort-circuit near the module. To minimize the inductance L 31 and L 3, power module are equipped with eparate emitter control terminal. If everal BOTTOM driver tage of a converter are upplied by a common operating voltage with negative DC-link reference, the paraitic inductance between the ground connector of the driver and the negative potential of the DC-link may caue unwelcome ocillation in the ground loop. Thi problem can be olved by HF-tabilization of the driver operating voltage near to the output tage or eparate upply voltage potential of the BOTTOM driver tage in high-power inverter. Inductance L 1 and L Inductance L 1 or L, repectively, deignate the inductance of the upply line between driver and tranitor. Apart from increaing the impedance of the driver circuit, they may caue unwelcome ocillation with the input capacitance of the tranitor. Thi may be remedied by a hort, low-inductance connection between driver and tranitor. Capacitance The capacitance C xx in Figure 3.3 tand for the intrinic capacitance in the power emiconductor (voltage-dependent, non-linear) and cannot be influenced by the uer. They indicate the minimum value of the commutation capacitance C K and, principally, effect a reduction of power diipation during turn-off (ee chapter 0 and 3.8). 167

5 Additional power diipation are generated during active turn-on due to the recharge proce of the commutation capacitance; thee have to be conidered in many high-frequency MOSFETapplication ( khz...). C 11 and C 1 caue an invere dv/dt-feedback to the gate (Miller effect, ee Figure 3.35). In combination with the inductance near the witche, the intrinic component capacitance may caue unwelcome ocillation EMI/main feedback Procee in the converter Procee in a converter ytem will alway produce unwelcome interference due to the witching operation of the power emiconductor on the one hand (Figure 3.4) and welcome energy tranmiion with the correponding ignal proceing on the other hand. Procee in the Converter Power Converion (Main Function) Noie Propagation (paraitic) Information Proceing (neceary) Reaction to Main and Load EMC Energy Tranmiion between Main and Load Noie Source of Power Converion Noie Source of Information Proceing Control of Power Converion - High Power - Middle Power - Small Power - Small Power - DC-Parameter, Fundamental Harmonic - Higher Harmonic - Higher Frequencie - Higher Frequencie High-Energy-Procee Low-Energy-Procee Figure 3.4 Energy procee in converter [99] Thee procee can be divided up into high-energy-procee, which may caue interference in the main and the load within a frequency range between fundamental frequency and about 10 khz, and low-energy-procee above 10 khz up to about 30 MHz, where noie radiation and, conequently, non-conducted current flow will tart to be propagated. The frequencie mentioned originate more or le from poible meauring procedure, and not from phyical effect. In the low-frequency range, thee effect are called converter main feedback, which are 168

6 traditionally characterized by dicrete harmonic current ocillation up to about khz. Above 10 khz thee ocillation are called radio interference voltage, which are indicated in db/µv and are deignated a interference voltage due to elective meaurement. For the interim frequency range, within which modern power emiconductor are witched, the firt attempt are currently being made to introduce meauring procedure a well a limit rating. Dicuion on thee diturbing ide-effect are contradictory, ince the ame phyical procee are decribed under different apect. The difference between deignation uch a zero current, leakage current or aymmetrical interference voltage i only given by variou frequency range claification and by the frequency dependency of all witching parameter. Since thi frequency dependency i continuou jut a the tranition to radio interference, the frequency tranition range are inevitably very broad Caue of interference current All interference i caued by the witching operation mode of power emiconductor. Caue of interference may be explained by the equivalent commutation circuit in Figure 3.5. Network 1 i dm L K Module Network i cm1 S 1 C K V K i L i dm i cm L K S C K Baeplate i cm Z ch Z N1 Z N1 Z N Z N Heatink Z hg GROUND Figure 3.5 Equivalent commutation circuit with noie propagation path [99] In the cae of inductive commutation witch S 1 will witch to the conducting witch S. In a hard witching proce (L K = L Kmin, C K = C Kmin ) firtly the current will be commutated with a di/dt given by the emiconductor characteritic of witch 1. Commutation i finalized by the revere-recovery-di/dt of witch, which determine voltage commutation and, conequently, dv/dt together with the current-carrying inductance and the effective capacitance C K. The effective capacitance comprie all capacitance C which are effective toward the neutral potential. Together with the impedance of the commutation voltage connection to the neutral potential parallel impedance of the commutation capacitance will become effective. At the 169