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THREE PHASE CONTROLLED RECTIFIERS

  • Solution requires a fast microprocessor and A/D converters.

      • 2.3.3

        Voltage and Virtual Flux Oriented Control

Figure 2.10 : VOC block scheme [9]

The Voltage Oriented Control (VOC) and Virtual Flux Oriented Control (VFOC) are close to Field Oriented Control for induction motor. The method is based on the transformation between

stationary coordinates

and synchronous rotating coordinates dq. This strategy guarantees :

  • Fast transient response

  • High static performance via internal current control loop.

Consequently, the performance depends on the quality of the current control loop.

We can find several strategies that can be applied for current control. A widely used scheme for high performance current control is the dq synchronous controller, where the regulated current are DC quantities. This eliminates steady state errors.

VOC and VFOC provide some advantages compared to DPC.

  • Low sampling frequency for good performance

microcontroller)

  • Fixed switching frequency (easier design of input filter)

(cheaper

A/D

converters

and

Furthermore, VFOC provides improved rectifier control under non ideal line voltage condition (because ac voltage sensorless operation is much less noisy thanks to the natural low pass behavior of the integrator used in the flux estimator).

Both methods also have some disadvantages :

  • Coupling occurs between active and reactive components and some decoupling solution is

required.

  • Coordinate transformation and PI controllers are required.

13

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