IGBT并联使用技术

nullParalleling IGBT ModulesParalleling IGBT ModulesWorst case: All contacts shortedWorst case: All contacts shortedDifferent IGBT modules with different Switching speeds ton and toff Gate thershold voltages VGE(th) Gate charge characteristic VGE = f(QG) and „Miller Capacity“ Cres Transfer characteristic IC = f(VGE)Hard Connected Gate with Common ResistorHard Connected Gate with Common ResistorHard connected Gates All IGBTs have different gate threshold voltages  VGE(th) IGBT1, with the lowest VGE(th) turns on first. The gate voltage is clamped to the Miller-Plateau. Therefore IGBT’s with higher VGE(th) can not turn on. They turn on only after t1. The IGBT1 with low VGE(th) takes all the current and switching losses during turn on. On going process by negative thermal coefficient of VGE(th) Introduction of Gate ResistorsIntroduction of Gate ResistorsSeparated by gate resistors The gate voltage of each IGBT can rise independent from the other one. Note: The gate resistors must be tolerated < 1 %VGE 1With individual gate resistors all IGBTs are independent from each otherVGE 2VGE nIntroduction of Gate ResistorsIntroduction of Gate ResistorsSeparated by gate resistors All IGBTs still have different gate threshold voltages VGE(th) But: The gate voltage of each IGBT can rise independently from the other ones. The Miller-Plateau will be reached after a short time t1. Only small differences in current sharing and switching losses between paralleled IGBTs. Worst case: All contacts shortedWorst case: All contacts shortedTaking stray inductances into regard Due to hard connected gates and varying transfer characteristics, all IGBTs have different switching times and speeds; dix/dt varies in each leg The circuit also has different stray inductances; Lx Therewith vx = Lx x dix/dt varies in each leg (e.g.: 1000 A/µs x 10 nH = 10 V) Nearly unlimited equalising currents i flow also via the thin connecting wires Additionally: Oscillations between parasitic capacitances (semiconductors) and -inductances are not damped. Introduction of Auxiliary Emitter ResistorsIntroduction of Auxiliary Emitter ResistorsThe introduction of REx (≈ 10 % of RGx) leads to Limitation of equalising currents i ≤ 10 A Damping of oscillations V1V2VnRE1RE2REnIntroduction of Auxiliary Emitter ResistorsIntroduction of Auxiliary Emitter ResistorsThe introduction of REx leads also to a negative feedback: The equalising current i leads to a voltage drop VREx at the Emitter resistors REx VRE1VRE2fast IGBTslow IGBTIntroduction of Auxiliary Emitter ResistorsIntroduction of Auxiliary Emitter ResistorsThe introduction of REx leads also to a negative feedback: The voltage drop VRE1 reduces the gate voltage of the fast IGBT and decreases therewith its switching speed. The voltage drop VRE2 increases the gate voltage of the slow IGBT and makes it faster. During switch off: vice versa. fast IGBTslow IGBTVRE1VRE2Additional proposalsAdditional proposalsThe introduction of Z-Diodes prevents over voltages at the gate contacts. Therefore these clamping diodes must be placed very close to the module connectors Additional proposalsAdditional proposalsThe introduction of Shottky-Diodes parallel to REx helps to balance the emitter voltage during short circuit case. Dimensioning ≈ 100V, 1A. Auxiliary Printed Circuit BoardAuxiliary Printed Circuit BoardPCB for paralleling IGBT directly at the module connectors Same track length on the board Short, twisted pair wires from the main driver to the auxiliary PCB at the IGBT moduleAdditional Parallel BoardAdditional Parallel BoardPCB for paralleling IGBT close to the module connectors Same track length on the board Short, twisted pair wires from the board to the modules (≤ 5 cm)Additional Parallel BoardAdditional Parallel Board