Power Electronics

IPM Speeds Motor Drive Design

An intelligent motor drive power module, the PI-IPM from International Rectifier Inc., contains all peripherals needed to control an IGBT-based inverter, including voltage, temperature, and current output sensing, completely interfaced with a 40MIPS DSP (photo, right). The module also contains an isolated port for incremental encoder inputs or synchronous serial port communication, making it a complete user-programmable solution connected to the system through a serial link cable. The module has two subsystems: the power output module (“EMP”) and the embedded control/logic board (“EDB”), as shown in the figure, below.

Connections between the EMP and EDB are through single in-line connectors on the EDB with mating pins on the EMP. This allows upgrading by merely plugging in a different EDB. Software upgrades are possible, but don't require hardware changes due to the DSP's ability to be reprogrammed through the serial or JTAG ports.

The EMP module contains a 3-phase, six IGBT bridge with HEXFRED® diodes in a standard inverter configuration. IGBTs are the NPT 1200V-50A, Generation V, and HEXFRED. Generation V devices don't need a negative gate voltage for complete turn-off, and their tail effect is greatly reduced from prior versions. Sensing resistors in the three output phases provide precise motor current sensing and short-circuit protection.

The module's package is mechanically compatible with the EconoPack outline. The mechanical configuration of the EDB allows it to fit into the same space as the standard Econo II package.

Module packaging uses DBC (direct-bond copper) over an allumina (Al2O3) substrate with a 300-mg copper foil on both sides. IGBTs and diode dice are directly soldered and bonded with a 15-mils aluminum wire for power and signal connections. The components in the device are then covered by a silicone gel for mechanical protection and electrical isolation.

The EDB contains all control and driving functions with dual functions of mechanical cover and intelligent interface. A Texas Instruments DSP, the TMS320LF2406A, provides interface functionality. Compared to previous DSPs, it has added features, including faster speed, more I/0 pins, boot ROM, CAN interface, and a faster A/D converter.

The EDB includes a flyback power supply with three 15V outputs with 1.5kV (min.) isolation from each other, plus single 5V and 3.3V outputs. The 5V supplies all low-voltage electronics, and the 3.3V linear regulator powers the DSP and some analog and logic interfaces to it. The flyback supply has its own undervoltage lockout to prevent all circuits from operating when the supply voltage is too low (minimum recommended supply voltage is 12V).

An IR2213 gate driver provides 2A sink and 2A source maximum gate driving current in a SO16W package. IGBTs used in the module don't need a negative gate drive voltage for complete turn-off. The dc bus and input voltage feedback continuously checks the voltage of the two supply lines: Vin and dc bus. Vin is the only external power supply needed for all electronics in the EDB.

International Rectifier Inc., El Segundo, Calif.
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