Wednesday, July 28, 2010

Power Converter Technology

Apart from power switching devices, the power-converter technology has also gone through significant developments in the recent past. Resonant converters specially the multi resonant converters are critical examples. High-phase-number converters is another area of development. (where the motors are no longer restricted to 3 phases).

Motor technology also went through a similar phase of developments, mainly after 1980. In 1985, the development of high energy permanent magnet, known as Nd-Fe-B (Nyoaliminium Iron Boron) resulted in a set of new motors such as brussless DC motors, switch reluctant motors, hybrid stepper motor, permanent magnet linear motor ...etc. The brussless DC motor is a good alternative to conventional (brushed) DC motors, it delivers the same performance without problems associated with a mechanical commutator.

Note: High energy permanent magnet materials especially Sm-Co (Samarian Cobolt) was in use prior to developing Nd-Fe-B but the high cost of Sm-Co and not allow its usage in industrial grade motors. It was used expensively in aerospace applications.

Unlike in the past, the selection of a motor today is conditioned by the power electronics availability too. We need to think of power electronic converters and the motor as a single unit and then make decisions. For an example a DC motor is expensive but its power electronic unit is cheap. The corresponding induction motor is cheap but its power electronic unit is expensive. Overall there is a cost different between the two options, so we have to make decision on the basis of the performance.

Control unit is implemented by microelectronic has several high-tech choices. This may be implemented using a micro-controller, a dedicated micro-controller, a hard-wired microelectronic unit, a PLC or similar other unit.

Analog controller are still using, but the can not process feedback messages and control accordingly.

With this type of control circuits it is possible to implements high performance control algorithms, such as vector control, field oriented control, high speed control all of which are related to electromagnetic state of the motor. Furthermore outer loop control for various dynamics requirements such as sliding motor controls, adaptive control, predictive control...etc are also implemented conventionally.

Beside all these, we find high performance PIC (Power Integrated Circuit), ASIC (Application Specific Integrated Circuits) ...etc, that ca greatly simplify the construction of the control and the power electronic unit both. For example, today we have complete PWM (Pulse Width Modulation) regulator in a single IC that can be replace the entire control unit in some systems. Compound driver IC can provide the complete solution of driving all six power switches in a three phase converter. There are numerous similar integrated circuits with more and more adding day by day. At the end of the day, system assembly will possibly involve only a withing up of a piece of control software with all hardware coming the right shape and form.

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