Q: How to design a 3-phase inverter for motor drive applications?
Answer
3-phase inverter design: (6 MOSFETs or IGBTs in H-bridge configuration). Top: 3 high-side MOSFETs (VM supply). Bottom: 3 low-side MOSFETs (ground). Gate drives: use 3-phase gate driver IC (e.g. IR2136 DRV8301 L6388) which includes bootstrap capacitors for high-side. Key design points: (1) DC bus capacitor: 100 uF per amp of motor current + 100 nF ceramic for high-frequency decoupling. (2) Bulk capacitors should be close to the MOSFETs with short leads. (3) DC bus voltage: typically 1.4x motor RMS voltage (e.g. 24V motor -> 325V DC bus for full-wave rectification of 230V AC). (4) Bleeder resistor: 10-100 kOhm to discharge DC bus when powered off. (5) Current sensing: low-side shunt resistor (1-10 mOhm) per phase for FOC or single-shunt for BLDC 6-step. Use isolated OpAmps for current sensing. (6) Voltage sensing: resistor divider for DC bus voltage measurement. (7) Layout: keep power loops compact and wide copper pour for low inductance.
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