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THREE PHASE CONTROLLED RECTIFIERS

    • 2.3

      Control strategies

      • 2.3.1

        Introduction

The control of PWM converter can be considered as a dual problem with vector control of an induction motor IM (see figure and table below).

DPC

DTC

Direct Power Control

Direct Torque Control

Control of PWM rectifier

IM control

VOC

FOC

Voltage Oriented Control

Field Oriented Control

Figure 2.7 : PWM rectifier and IM control duality

Control of PWM rectifier Speed control loop of vector drive

IM control dc link voltage

Reference angle between stator current and rotor flux

Reference angle of line voltage

Table 2.2 : PWM rectifier and IM control duality [9]

We can classify the PWM rectifier method in two categories : voltage based and virtual flux based control (See following Figure 2.8).

Figure 2.8 : Control strategies [9]

All these control strategies can achieve the same main goals, such as high power factor and near sinusoidal input current waveforms.

The Voltage Oriented Control (VOC) guarantees high dynamic and static performance via an internal current control loop. But the quality depends mainly on the current control strategy.

The Direct Power Control (DPC) is based on the instantaneous active and reactive power control loop. There are no internal current control loop and no PWM modulator block. The switching state are determined with a switching table based on the instantaneous errors between the commanded and estimated values of active and reactive power.

The Virtual Flux Based Control (VF) correspond to a direct analogy of IM control.

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